FINAL REPORT

FIVE-YEAR REVIEW REPORT

Special Five-Year Review Report

for

Denver Radium Site

S.W.Shattuck Chemical Operable Unit #8

City and County of DenverState of Colorado

Submitted by:

SC&A, Inc.1625 17th Street, Suite 323

Denver, CO 80202

Submitted to:

Mr. Clint BurklinEastern Research Group

P.O. Box 20101600 Perimeter Park DriveMorrisville, NC 27560-2010

In response to:EPA Contract Number 68-D7-0001

November 12, 1999

Max H. Dodson, Assistant Regional Administrator, Office of Environmental Protection & Remediation

FINAL REPORT

FIVE-YEAR REVIEW REPORT

Submitted by:

SC&A, Inc.1625 17th Street, Suite 323

Denver, CO 80202

Submitted to:

Mr. Clint BurklinEastern Research Group

P.O. Box 20101600 Perimeter Park Drive

Morrisville, NC 27560-2010

In response to:

EPA Contract Number 68-D7-0001

November 12, 1999

EPA F i v e - Y e a r Review S i g n a t u r e CoverKey Review I n f o r m a t i o n

Site name: Denver Radium/Shattuck Chemical site OV#8 EPA ID: COD980716955Region: 8 State: CO C i t y / C o u n t y : City and County of Denver

N P L status: FinalR e m e d i a t i o n s ta tu s ( u n d e r cons truc t i on, o p e r a t i n g , c o m p l e t e ) : Under constructionM u l t i p l e O U ' s * ( h i g h l i g h t ) : NC o n s t r u c t i o n c o m p l e t i o n date: Not officially accepted as complete at the time of this reviewF u n d / P R P / F e d e r a l f a c i l i t yl e a d : PRP Lead agency: S.W.Shattuck Chemical Company

Has site been put i n t o reuse? (highlight): Y $|

Who c onduc t ed the review (EPA R e g i o n , S t a t e , F e d e r a l ag ency): Joint HQ/EPA Region 8A u t h o r name: SC&A, Inc. A u t h o r title: Subcontractor to Eastern Research GroupA u t h o r affiliation: EPA Contract Number 68-D7-0001Review p e r i o d : 10 June -12 November 99 D a t e ( s ) of s i te i n s p e c t i o n : 21 June 1999H i g h l i g h t : S t a t u t o r yP o l i c y P o l i c y T y p e (name):1. Pre-SARA2. Ongo ing3. Removal o n l y4. Regional Discretion

Review number (1, 2, etc.)1 = first review, etc.First detailed review for OU#8

Triggering act ion event: 5th anniversary of the actual RA onsite construction startT r i g g e r action date: 31 March 1993Due da t e: 31 March 1998

Table of Contents

I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-1I.A Who Conducted the Five-Year Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-2I.B Purpose of the Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-3I.C Other Review Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-4

II Site Chronology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-1

III. Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-1III.A Physical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-1III.B Land and Resource Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-2III.C History of Contamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-2III.D Initial Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-3III.E Contamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-4

III.E.1 Shattuck Property . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-4III.E.2 Railroad Rights-of-Way . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-5III.E.3 Vicinity Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-6III.E.4 Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-7III.E.5 Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-7III.E.6 Groundwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-8

III.F Summary of Site Risks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-10III.G Human Health Risks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-11

III.G.1 Principal Threats Posed by the Site . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-11III.G.2 Radon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-12III.G.3 Gamma Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-12

IV. Remedial Actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV-1IV.A Remedy Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV-1

IV.A.1 Groundwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV-2IV.B Remedy Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV-3IV.C System Operations/Operation and Maintenance (O&M) . . . . . . . . . . . . . . . . . . . . . . . . . IV-5IV.D Progress Since the Last Five-Year Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV-6

V. Five-Year Review Findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V-1V.A Team Members . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V-1V.B Community Activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V-3V.C Technical Exchanges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V-3V.D Site Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V-4V.E Risk Information Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V-4V.F Risk Recalculation/Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V-10V.G Data Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V-11

Table of Contents(Continued)

VI. Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VI-1VI.A Changes in Conditions External to the Remedy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VI-1

VI.A.1 Land Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VI-1VI.A.2 Contaminants and Pathways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VI-1VI.A.3 Hydrologic/Hydrogeologic Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VI-2

VI.B Implementation of the Remedy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VI-2VI.B.1 Health and Safety Plan/Contingency Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VI-2VI.B.2 Institutional Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VI-3VI.B.3 Remedy Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VI-3VI.B.4 Adequacy of System Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VI-3VI.B.5 Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VI-4VI.B.6 Indicators of Potential Failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VI-4VI.B.7 O&M Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VI-4

VII. Deficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VII-1VII.A Lack of Institutional Control of Plume Outside Site Boundary . . . . . . . . . . . . . . . . . . . . VII-1VII.B Vulnerabillity of Cover/Monolith Design to Long-term Degradation . . . . . . . . . . . . . . . . VII-1VII.C Monolith-Monitoring Plan Deficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VII-2VII.D Plume-Monitoring Plan Deficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VII-3VII.E Site Characterization and Modeling Deficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VII-5VII.F Risk Assessment Deficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VII-6VII.G Specific Design Technical Issues That Need to Be Re-evaluated . . . . . . . . . . . . . . . . . . VII-6

VIII. Recommendations and Required Actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VIII-1VIII.A Institutional Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VIII-1VIII.B Performance Assessment Modeling of Cover/Monolith Design Long-Term

Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VIII-2VIII.C Monolith-Monitoring Plan Upgrade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VIII-4VIII.D Plume-Monitoring Plan Upgrade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VIII-5VIII.E Development of a More Sophisticated Groundwater and Contaminant

Transport Model to Assess Natural Attenuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VIII-8VIII.F Development of Sufficient Site Characterization Data to Define Plume and

Support Risk Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VIII-9VIII.G Conduct Risk Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VIII-11VIII.H Specific Design Technical Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VIII-12

IX Protectiveness Statement(s) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IX-1

VIII. Next Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . X-1

XI. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . XI-1

Tables

Table 1: Contents of the Five-Year Review Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-2Table 2: Chronology of Site Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-2Table 3: Current Annual O&M Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV-5Table 4: Actions Taken Since the Last Five-Year Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV-6Table 5: Summary of Soil Concentrations Remaining After Clean-up . . . . . . . . . . . . . . . . . . . . . . . . . . . V-8Table 6: Identified Deficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VII-1Table 7: Recommendations and Required Actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VIII-1

Appendices

Appendix A Expert Panel ReviewAppendix B Scoping Analysis Report on Site Risks

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I. Introduction

The purpose of this Work Assignment was to prepare an EPA technical report required by theSuperfund five-year review requirements. This report was prepared independently by SC&A, Inc.(SC&A), under subcontract to Eastern Research Group (ERG). Tim Fields, Administrator for the EPAOffice of Solid Waste and Emergency Response (OSWER), is the decision-maker to whom the reportis directed. This review is one of the major milestones leading toward a Fall 1999 decision to completethe high-level review of the original Region 8 and State of Colorado remedy for the Shattuck site.

The Shattuck site - Operable Unit VIII - is one of the 65 Denver area properties involving operatingbusinesses that required various levels of cleanup, such as excavation and removal of contaminated soilto a permanent disposal site, removal of floors to excavate underlying wastes, and installation ofventilation systems to reduce levels of radon. Cleanup actions at Shattuck included onsite stabilizationby cement/flyash solidification, followed by capping with a low-permeability composite clay barrier.About 56,000 cubic yards of contaminated soils have been treated and placed on site in a monolithform. The total final volume of the monolith is about 70,000 cubic yards.

This review considered only the Shattuck site and offsite contamination attributed to the Shattuck site.The resulting Five-Year Review report describes actions required to achieve protectiveness andincludes other recommendations for the implementation and maintenance of the remedy andcoordination with authorities.

The Five-Year Review report was written after the collection and evaluation of site information anddocuments the results of the review. It summarizes the adequacy of the implementation of the remedyand changes to applicable or relevant and appropriate requirements (ARARs) and other risk-relatedfactors. It identifies deficiencies, recommendations, and required actions. The report also provides thebackground information necessary to understand the review analysis and discusses the findings of eachreview activity.

Although the report is directed to the EPA/OSWER Assistant Administrator, it is also of interest to theother principal stakeholders and the general public. Therefore, the report was written to be understoodby someone unfamiliar with the site. The report presents all of the information needed to understand thepast activities at the site and the current status of all remedial actions.

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The following table summarizes the major components of this report.

Table 1: Contents of the Five-Year Review Report

Report Section Discussion

I. Introduction Synopsis of who conducted the review, when, and for what site: the purpose of the

review; whether the review is required by statute or as a matter of policy; whether it isthe first or a subsequent review of the site; and what action triggered the review.

II. Site Chronology Dates of major events such as the initial discovery of contamination, NPL listing,decision and enforcement documents, start and completion of remedial actions,construction completion, and prior five-year reviews.

III. Background Description of the site and threats, including discussions of relevant physical

characteristics, land and resource use, contaminants, and initial response. IV. Remedial Actions Description of the remedial action objectives and the remedy, remedy implementation,

O&M requirements, and O&M activities to date.

V. Five-Year ReviewFindings

Description of the results of each of the review tasks: ARARs review, any riskrecalculation or new risk assessment, and review of documents and analytical data.

VI. Assessment Discussion of the conclusions reached, including whether conditions external to theremedy have changed since the remedy was selected, whether the remedy has beenimplemented in accordance with decision documents, and whether any risk or ARARs

information has changed.

VIII. Deficiencies List of any deficiencies.

VIII. Recommendations

and Required

Actions

List of any recommendations, including required actions to achieve protectiveness,

parties responsible for implementation, agencies with oversight authority, and theschedule for completion.

I.A WHO CONDUCTED THE FIVE-YEAR REVIEW

SC&A furnished the personnel, services, materials, and equipment to assist EPA with the Five-YearReview report in accordance with the draft OSWER Directive 9355.7-03B-P, March 1999,Comprehensive Five-Year Review Guidance.

In planning the review, SC&A established a review team, comprising the following technical experts:

C Construction Representative/Geotechnical Engineer, who reviewed composite clay cover

design and construction

C Process Engineer, who reviewed groundwater/leachate collection and treatment

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C Civil Engineer, who reviewed stabilized/solidified monolithic waste form and general siteconditions

• Hydrogeologist, who reviewed aquifer characterization

• Geochemist, who reviewed fate and transport of radiological contaminants

• Risk Assessor, who reviewed risk assessment

In Section V, the peer review team members are identified and their backgrounds are briefly described.

While the review was conducted independently, SC&A coordinated with the EPA and the ColoradoDepartment of Public Health and Environment (CDPHE) in order to facilitate access to files andconfirm the accuracy of data inputs.

The Five-Year Review report includes a peer review record. Individual peer review members’comments are presented in Appendix A.

SC&A was also given the task of deciding whether a recalculation of risk or a risk assessment scopinganalysis was needed. SC&A determined that a scoping analysis was indeed needed and it is presentedin Appendix B.

Monitoring and sampling data and the documentation of operation and maintenance (O&M) were alsoexamined.

I.B PURPOSE OF THE REVIEW

The purpose of a five-year review is to determine whether the remedy at a site is protective of humanhealth and the environment. The five-year review does not reconsider decisions made during theselection of the remedy, but evaluates the implementation and performance of the selected remedy. Thereview includes recommendations to ensure that the future remedy will be protective and to address anydeficiencies identified during the review process.

Specific to the situation at Shattuck, the Record of Decision (ROD) specified that, in all likelihood,groundwater monitoring would be the only activity implemented during the long-term remedial actionperiod. The ROD component for groundwater was thus considered a No Action or No Further ActionROD. Rather than to verify the performance of a groundwater

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restoration or containment remedy, the purpose of the required groundwater monitoring was to ensurethat ROD assumptions regarding no action for groundwater were correct. The ROD presumed that theaquifer could not be used. However, statutory five-year reviews are still required in cases wherehazardous substances, pollutants, or contaminants remain above levels that allow for unlimited use andunrestricted exposure.

I-C OTHER REVIEW CHARACTERISTICS

This is the first Five-Year Review for the Shattuck site since the remedy was fully implemented. Twoearlier reviews occurred (9/12/94, 11/20/98) prior to and at the completion of the remedy. Thetriggering action for this statutory review is as follows.

The EPA, through its Technical Assistance Grant Program, has granted funds for residents in Superfundsite areas to review EPA studies and cleanup work and to communicate their findings to the community.A local community group, the Overland Neighborhood Environmental Watch Group, has received aTechnical Assistance Grant (TAG) from EPA to conduct a review of the Shattuck site. TAG recipientsoften suggest improvement to the plans for remediation and monitoring. In this case, an interest groupfrom the community organized itself to challenge the findings in the first five-year review and filed a casein the U.S. District Court. The trial date has been postponed until 30 November 1999 to givealternative dispute resolution initiatives an opportunity to work.

Tim Fields, Administrator for the EPA Office of Solid Waste and Emergency Response (OSWER),met the Mayor of Denver on March 11, 1999. During that visit, the City and County of Denverreassured Mr. Fields that it would be making a commitment to work with the EPA and participate inthe four-part review process for this site. Theresa Donahue, Manager of Environmental Health for thecity, joined the Mayor in expressing an interest in going forward under a spirit of cooperation. On April23, 1999, Mr. Fields completed his personal initiative to meet with the principals of the stakeholderswhen he visited with Jane Norton, Director of the Colorado Department of Public Health and theEnvironment. He gained her commitment to participate in this review. The other parts of the ongoingreview include a facilitated process with the principals (convened by the Keystone Center) to addressoutstanding issues, the National Ombudsman report, and the work product from this Five-YearReview. Mr. Fields was committed to moving forward with these reviews and accomplishing majormilestones along the way leading to a Fall 1999 decision to complete his high-level review of theoriginal Region 8 and State of Colorado remedy for the Shattuck site.

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II. Site Chronology

The Shattuck property has been the location of several minerals-processing operations since the early1900s. These operations included the extraction of molybdenum and vanadium from ores, processing of“radium slimes” for the production of radium salts and uranium compounds, recovery of rhenium as abyproduct of molybdenum production, and processing of depleted uranium. As a result of theseactivities, the primary site contaminants are radium, thorium, uranium, molybdenum, arsenic, selenium,and some organic compounds. Shattuck’s operations ceased in 1984.

EPA selected an onsite Stabilization and Solidification remedy for this Operable Unit (OU) in a Recordof Decision (ROD) dated January 1992. The objectives of this remedy were to prevent (1) radiationexposure due to inhalation of radon gas and its daughter products, (2) radiation exposure due toinhalation and ingestion of long-lived radionuclides, and (3) direct exposure to gamma radiation. Theremedy was also ostensibly intended to prevent further groundwater degradation and allowcontamination in the groundwater to attenuate over time.

The selected remedy included demolition of existing facilities on the Shattuck property, stabilization andonsite disposal of an estimated 50,000 cubic yards of contaminated soil, and capping the treated soil.

The Shattuck Chemical Company, Inc. was identified as a potentially responsible party and theremedial action proceeded under a Unilateral Administrative Order dated August 1992. An Operationand Maintenance Plan and an Institutional Control Plan were developed to ensure the protectivenessand permanence of the selected remedy.

Table 2 lists all important site events and relevant dates in the site chronology. The identified events areillustrative, not comprehensive.

In response to questions from the City and County of Denver and public concern, EPA formed anindependent peer review board to provide input to the Five-Year Review. The peer review boardconsisted of independent professionals who reviewed the remedy at OU VIII, including ARARs andtechnical issues, and it made recommendations. The board’s report is incorporated into this Five-YearReview as Appendix A.

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Table 2: Chronology of Site Events

EVENT DATE

Initial discovery of problem or contamination 1979

NPL listing September 1983Surface Impoundment Closure 1987

Superfund State Contract or Agreement signature May 1988Baseline Risk Assessment September 1991RI/FS complete September 1991

Pre-NPL responses October 1991ROD signature January 1992

Enforcement documents (UAO) August 1992Remedial Design start April 1994Previous Five-Year Reviews September 1994, November 1998

Remedial Design complete June 1996Construction date (start) monolith July 1996

Actual RA start September 1996Oily Soils Shipped Offsite 1997Storm Sewer Remediation Activity February-March 1997, March-May 1999

Construction completion date monolith September 1998Final Close Out Report February 1999

ROD Amendments or ESDs None

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III. Background

III.A PHYSICAL CHARACTERISTICS

The S. W. Shattuck Chemical Company plant processed minerals for more than six decades(1918-1984). Also called the Denver Radium site, it is located in southwest Denver, northeast of theintersection of Evans Avenue and Santa Fe Drive. The site includes the 5.9-acre S.W. ShattuckChemical Company, Inc. (“Shattuck”) property located at the 1805 South Bannock Street, the4.3-acre railroad rights-of-way located to the west of the Shattuck property, and nearby (“vicinity”)properties located within the area bounded by South Santa Fe drive (U.S. Highway 85), SouthBroadway, Jewell Avenue, and New Mexico Avenue.

The facilities located on the Shattuck property at the time of the ROD included six permanent buildings,miscellaneous storage sheds, underground storage facilities, above-ground storage tanks, processequipment and piping, and asphalt and concrete paving.

South Santa Fe Drive borders the site west of the railroad rights-of-way. Overland Park Golf Courselies west of South Santa Fe Drive. The South Platte River forms the western boundary of the golfcourse.

Land use in most of the area, with the exception of the Overland Park Golf Course, is typical urbandevelopment, ranging from industrial to residential. The Shattuck property is located in an area of thecity designated as commercial/industrial. Land use within two blocks south and east of the Shattuckproperty is predominantly industrial, although some residential use exists. The industrial/commercial areaextends from the Shattuck property north for several blocks following the railroad lines.

Residential areas are located three blocks east of the Shattuck property (east of South Broadway), andsouth of the golf course and west of South Santa Fe Drive (approximately 600 feet southwest of theShattuck property). Water for domestic use is supplied to the area by the Denver Water Department.

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III.B LAND AND RESOURCE USE

The site is located within the drainage basin of the South Platte River, which is located approximately3,000 feet west of the site. A shallow unconfined aquifer exists below the site. The shallow aquifer isperched on bedrock and merges with the alluvial aquifer beneath the floodplain of the South PlatteRiver. The groundwater is not currently used as a drinking water source, however, at least two localresidents water their lawns with water obtained from shallow wells.

Studies of potential future use are currently being conducted by another contractor. At present, the areasurrounding the site is mixed use - light industrial, recreational, and domestic housing.

III.C HISTORY OF CONTAMINATION

The Shattuck property has been the location of several mineral-processing operations, including theprocessing of tungsten ores, carnotite ores (for uranium and vanadium), radium slimes, molydbenuinores, and depleted uranium. The contamination of the site is due to the historical use for those mineralprocessing operations. Approximate time frames for some of the processing activities at the site are:

1920s- Treatment of molybdenum ores and extraction of ferric vanadate fromvanadium and uranium ores or byproducts

1930s- Processing of radium slimes for recovery of radium, as well as production ofradium salts, uranium compounds, and other rare mineral products fromcarnotite ores

1940s- Processing of uranium compounds and molybdenum

1950s- Processing of uranium ores

1960s- Unknown

1970-80s- Processing of uranium compounds, molybdenum and rhemium

From 1969 to 1984, the operations at the facility consisted primarily of processing molybdenite for therecovery of molybdenum compounds, with recovery of rhenium as a by-product. In addition, a smallbatch operation for the production of uranium products from depleted uranium

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existed. Operations at the Shattuck facility ceased in 1984. The Shattuck property is currently fenced,and access is restricted by Shattuck.

The railroad rights-of-way include two rail lines which have been operating since the late 19th century.In addition, a rail spur onto the Shattuck property was in place by 1915. The two rail lines are utilizedas main lines through the Front Range and handle a total of about twenty to thirty general freight andcoal trains per day. The east rail line is located on property owned by the Atchison, Topeka & SantaFe Railway Company, and the western line is owned by the Denver & Rio Grande Western RailroadCompany.

III.D INITIAL RESPONSE

The United States Bureau of Mines, in cooperation with private industry, established the NationalRadium Institute (NRI), which successfully developed radium processing in the Denver area. In 1979,EPA noted a reference to the NRI in a 1916 United States Bureau of Mines Report. Subsequent fieldresearch revealed the presence of 31 radioactive sites within the City and County of Denver. Afteridentifying these properties, the Radiation Control Division of the CDPHE notified affected propertyowners of the presence of radiological contamination. Pursuant to a cooperative agreement with EPA,CDPHE initiated engineering assessments of the majority of the identified properties. In October 1981,the Denver Radium Site was placed on the Superfund Interim Priorities List. The Site was included onthe National Priorities List on September 8, 1983.

CDPHE began a remedial investigation in November 1988. Since 1979, CDPHE, the EPA, andShattuck have conducted various studies of the site media, which have included soil and groundwatersampling. The remedial investigation evaluated the existing data and included collection of additionaldata to characterize the nature and extent of contamination.

During the remedial investigation, additional radiological contamination was discovered to the east andnorth of the property at 1805 South Bannock Street. EPA evaluated the extent of this contamination.These areas are referred to as the “vicinity properties” in the Record of Decision and the supportingdocumentation. In August 1989, EPA conducted an emergency removal action at one of the vicinityproperties, which involved installation of an active radon reduction system in order to reduceexcessively high levels of radon present at a commercial property.

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A subsurface impoundment, utilized as an evaporation pond when the 1805 South Bannock facility wasin operation, was excavated and closed in 1987, pursuant to a consent decree between CDPHE andthe S.W. Shattuck Chemical Company, Inc.

III.E CONTAMINATION

Radiologically contaminated soils were identified on the Shattuck property, the railroad rights-of-way,and the vicinity properties. Areas were considered contaminated with radium-226 when radium-226concentrations in soil exceed 5 pCi/g above background in the top 15 cm of soil or 15 pCi/g abovebackground in any layer below the top 15 cm. Contaminated soil on the Shattuck property, prior to theremediation specified in the ROD, covered approximately 230,000 square feet. The estimated volumeof contaminated soil on this property is 38,500 cubic yards.

Radioactive soil contamination covered approximately 34,000 of the 186,000 square foot railroadrights-of-way. The volume of contaminated materials on the railroad rights-of-way was estimated to begreater than 4,500 cubic yards. The volume of contaminated soil on the vicinity properties wasestimated to be 6,000 cubic yards.

These estimates were based primarily on radium-226 contamination. Additional metals’ contaminationincluding radioactive lead-210, thorium-230, and uranium, as well as non-radioactive metals such aslead and arsenic, was also identified in site soils. The majority of the additional contaminants wereco-located with the radium-226 contamination.

III.E.1 Shattuck Property

Discussion of the pre-remedy Shattuck property condition is divided into three areas: (1) the buildingsand process areas that were located in the center of the property; (2) the open space areas to the northand south; and (3) the closed evaporation pond which was located in the north open area of theproperty.

Buildings and Process Area

The soils throughout most of the buildings and process area were contaminated. The highest measuredone-meter gamma radiation exposure rate in this area was 2,800 micro-roentgens/hour near thesoutheast corner of Building 6. Subsurface radiation data indicated contamination

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depths ranging from one to nine feet, with an average depth of about 40 inches and an averageequivalent radium-226 concentration of about 90 pCi/g.

Open Space Areas

The open areas of the Shattuck property to the north and south of the buildings and process areagenerally exhibited contamination throughout the area, with the exception of the southern area near theperimeter of the property, the area near the southwest corner of Building 6, and the areas east andsouth of the closed evaporation pond. Depth of contamination for these areas ranged from 0.5 to over14.5 feet, with an average depth of about 39 inches and an average equivalent radium concentration ofabout 69 pCi/g.

The CERCLA action addressed the underlying soils of the surface impoundment (evaporation pond)that was closed under RCRA. The RCRA closure had removed the pond waste materials and the linermaterials, but left the underlying soils to the CERCLA action.

Direct gamma radiation measurements on the asphalt surface of the closed pond indicated no surfacecontamination in this area. Soil immediately beneath the asphalt cover exhibited backgroundconcentrations of radioactive contaminants. However, radium-226 contamination was found from about6 feet to about 7.5 feet below the surface over the western two thirds of the former pond area.Thorium-230 contamination was also found in this area.

III.E.2 Railroad Rights-of-Way

The 4,500 cubic yard estimate of contaminated soil on the railroad rights-of-way included nearly the fulllength of the area between the east rail line and the Shattuck property, as well as some limited areas tothe west of the rail line. The estimated depth of contamination was 0.5 to 2.5 feet along the southernportion and 5 feet from the northern portion.

Although the soil directly beneath the rail line was not sampled, the data for the surrounding areaindicated that radium contamination beneath the line is likely. The highest radium equivalent valuemeasured in the railroad rights-of-way was 570 pCi/g.

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III.E.3 Vicinity Properties

EPA performed the assessment of the vicinity properties after surface gamma scans indicated the presence of radioactivity on properties in the vicinity of the Shattuck property. The estimated volume ofthese materials was 6,000 cubic yards. The following is a summary of the primary deposits found on thevicinity properties:

C The 1860 South Bannock Street property. Radium-contaminated soils were locatedbeneath the floor slab of a building, the concrete driveway and parking area, andbeneath an asphalt-covered area extending beyond the property to the north and south.The deposit was approximately 2,700 cubic yards and extended to a depth of overeight feet. In August 1989, an emergency removal action was conducted at thisproperty because of the very high levels of radon gas and decay products measuredwithin the building. The removal action involved radon mitigation measures, includingsealing slab joints and installing a vent system. Contaminated source materials were notremoved.

C The area adjacent to the west side of South Bannock Street from approximately 1700to 1830 South Bannock. The contaminated area consisted of uncovered soil, as well asasphalt, concrete, driveways, and parking areas. The deposit included approximately1,300 cubic yards of material contaminated with radium to a depth of over three feet.

C The 1822 South Bannock Street property. Soil contaminated with radium existed in thefill material beneath the concrete floor slab of a building and adjacent to the east side ofthe building. The deposit included approximately 250 cubic yards of material andextends to a depth of approximately 2.5 feet.

C The 1788 South Acoma Street residential property. Soil contaminated with radium waslimited to exterior soils and ranges to two feet, with an estimated volume of 220 cubicyards.

C In addition, 1,100 cubic yards of soils contaminated with radium were estimated toexist beneath South Bannock Street. This estimate was based on adjacentinvestigations; investigation into the street was not performed because of the presenceof numerous utility lines.

The remedial investigation did not attempt to estimate the extent of possible uranium and thorium-230contamination for the railroad and vicinity properties. Based on the data from the Shattuck property atthe time of the ROD, it was believed that the total amount of radiologically contaminated soils requiringremediation could possibly be higher than estimated because of

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radiological constituents other than radium-226 or lead-210. However, it was believed that additionalmaterials would not influence the remedy selected in the Record of Decision.

III.E.4 Facilities

The following buildings and tanks have been completely removed.

Buildings

Based on procedures outlined in the Nuclear Regulatory Commission (NRC) Guide 1.86, radioactivecontamination was identified in five of the six permanent buildings on the Shattuck property. The volumeof the radiologically contaminated material associated with the buildings was estimated to beapproximately 2,095 cubic yards. This estimate included 100 percent of three of the buildings and thefloor slabs of two of the buildings. At least one building was contaminated with depleted uranium.

The contamination of the buildings was associated with radioactive constituents which had beenprocessed on the site. Radium-226 and uranium were identified in building-material samples. Based onvisual inspection, radiologically contaminated building materials were also suspected to contain relativelyabundant concentrations of asbestos in two of the contaminated buildings, with minor amounts in a thirdbuilding.

Tanks

Direct radiation measurements showed elevated levels of total alpha activity for five tanks, indicatingthat these tanks were contaminated by the processing operations at the site. The averages of the totalalpha activity on the five tanks were greater than the NRC Regulatory Guide 1.86 average. However,no maximum measurements exceeded the NRC maximum. The radioactive contamination associatedwith the tanks was at relatively low levels, and it was expected that the tanks could be adequatelydecontaminated.

III.E.5 Air

The following describes the historical air monitoring results during the completed remediation activities.

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Atmospheric contaminants of concern at the site consisted primarily of radon, a radioactive gasproduced by the decay of radium-226 and airborne thorium-230 particles associated with soilcontamination.

Air investigations included indoor and outdoor measurements for radioactive contaminants and organicvapors. Of the six buildings on the Shattuck property, three exhibited concentrations of radon gas andits decay products in excess of the EPA guideline of 0.02 working levels (WL), a measurement unitassociated with radon gas. Given the gamma radiation levels associated with two additional buildings, itwas expected that these additional two buildings may also have periodically exceeded the EPAguideline.

Monitoring of the outdoor air detected low atmospheric concentrations of radioactive contaminants.Measurements of alpha activity and thoriurn-230 concentrations were in the 10-14 to 10-15 microcuriesper milliliter range or lower. Air monitors attached to workers performing the remedial investigationindicated up to 10-12 microcuries alpha activity per milliliter for activities disturbing the soils.

At a vicinity property, an emergency removal was performed to mitigate very high radon concentrations(up to 4 - 6 working levels). The removal action reduced radon levels; however, gamma radiation stillposes a potential risk. Measurements of radon at other vicinity properties where soils contaminatedwith radium were identified did not exceed the EPA guideline of 0.02 working levels.

Indoor and outdoor measurements of organic vapors were less than the detection limit of approximatelyone part per million benzene equivalent.

III.E.6 Groundwater

Data from the supplemental monitoring system installed during the remedial investigation was used inconjunction with data from monitoring performed by the Shattuck Chemical Company to characterizegroundwater flow and quality for the site. Potentiometric surface maps were prepared during theremedial investigation and indicated that contaminated groundwater from the site flows in a west tonorthwest direction from the site and is contained beneath the Overland Park Golf Course. The golfcourse obtains its water from ponds supplied from the South Platte River. At the time of the ROD, EPAbelieved that there was no current use of alluvial groundwater affected by the site. Groundwater leveldata also indicated that contaminated

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groundwater from the site did not flow beneath the residential area located to the south of OverlandPark Golf Course. Currently, water for domestic use is supplied to the area by the Denver WaterDepartment. However, there is a historical usage pattern.

The aquifer immediately below the site flows into a larger aquifer associated with the South Platte River.EPA estimated the groundwater velocity to be 0.51 feet/day beneath the site. At this rate, groundwaterwould take an estimated 2.7 years to reach the eastern edge of Overland Park Golf Course. Beneaththe golf course, the hydraulic gradient increases dramatically as the shallow aquifer beneath the sitedrops into the valley that was carved by the South Platte River during the Pleistocene era. The valley isnow filled with alluvial sand and gravel. The velocity of the groundwater increases through this section,with the total elapsed time for groundwater to travel from the site to the South Platte River estimated tobe slightly more than three years.

Isolated occurrences if gross alpha and beta radioactivity have been detected in the alluvial aquifer. Theprimary radioactive contaminant in the groundwater is uranium, which has been detected in excess ofthe range of proposed standards. The offsite alluvial aquifer downgradient from the site continues toexhibit significant concentrations of radioactivity which were estimated by EPA to diminish tobackground levels as the aquifer is diluted by the system underlying the Platte River.

Volatile organic compounds were detected in concentrations above MCLs in an upgradient well, onsitewells, and downgradient offsite wells. Data from the upgradient well provide strong evidence thatsignificant offsite sources of volatile organic compounds, specifically 1,1,1-trichloroethane, haveaffected groundwater. Soil boring data indicate that onsite sources of tetrachloroethene and associateddegradation products may impact groundwater quality as well. The semi-volatile compounds phenol,benzoic acid, and phthalates were detected in onsite wells.

The metals arsenic, cadmium, and selenium were measured in levels exceeding MCLs, and very highconcentrations of molybdenum were observed in onsite and offsite well samples.

Data submitted by the City and County of Denver, and confirmed by CDPHE, indicate thatgroundwater associated with the site was infiltrating a storm sewer located along South Santa Fe Drive.The storm sewer discharges into the South Platte River just south of Louisiana Avenue. Data forsamples obtained from manhole 23A and the storm sewer outfall showed elevated levels of ammonia,molybdenum, copper, and uranium. Remediation work was conducted on the storm sewer in duringFebruary through April 1997 and March through May 1999.

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At the time of CDPHE sampling, the manhole upgradient (south) of manhole 23A was dry, indicatingthe water sampled in manhole 23A was infiltrating the storm sewer at the point between the manholes.Contours on the potentiometric surface measured in 1989 indicate the portion of the storm sewer intowhich groundwater is infiltrating is located downgradient of the site.

Data for well SHB-3 show elevated levels of ammonia, molybdenum, copper, and uranium. TheSHB-3 data are generally higher than the data for the manhole, indicating that some dilution occursbetween SHB-3 and the storm sewer.

III.F SUMMARY OF SITE RISKS

A baseline risk assessment was conducted as part of the remedial investigation/feasibility study tocharacterize the current or potential threat to human health and the environment that may be posed bythe contamination on the site.

The principal health threat posed by the site is the carcinogenic risk related to soils contaminated withradium-226. Risk estimates were calculated based on the concentration of contamination found on thesite. The potential pathways of exposure evaluated in the baseline risk assessment include futureresidential or occupational use of the site. This type of land use was selected based on the past andpresent use of the site and surrounding area and the site’s location within a large metropolitan area.Exposure durations were evaluated in conjunction with the contamination levels identified at the site toestimate the baseline risks. The following potential exposure pathways were considered:

C Inhalation of radon, particulate, and organic compoundsC Direct exposure to gamma radiationC Ingestion of contaminated soilC Ingestion of groundwaterC Ingestion of garden produce grown in contaminated soil

In risk analysis, carcinogenic risk is presented in the form of a probability (i.e., the increased chance ofcontracting cancer over a lifetime attributable to the site). As required by the NCP, the risk range ofone in ten thousand to one in one million (10-4 to 10-6) is used as the range to indicate whether the siteposes an unacceptable risk. For non-carcinogenic compounds, hazard quotients are calculated bycomparing a reference dose (Rfd), which is a dose for which there is a potential for adverse healtheffects, to the estimated potential dose for a given pathway of

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exposure. The hazard quotients for a potential pathway of exposure are summed to obtain a hazard

index. A hazard index greater than one poses an unacceptable risk.

III.G HUMAN HEALTH RISKS

The following discussion reflects the historical site condition at the time of the 1991 Risk Assessment.

III.G.1 Principal Threats Posed by the Site (Pre-Remedy)

The two major contaminants of concern for radiological exposure at the site were radon gas and

gamma radiation, both of which are attributable to the radium-contaminated soil located on the site.

Radon gas, a decay product of radium, was migrating from contaminated soil into the atmosphere. The

risk associated with radon gas results from inhalation of its short-lived decay products which can

expose the internal tissue of the lungs to bursts of energy if they decay within the lungs.

Prolonged inhalation of air with a high concentration of radon decay products has been conclusively

shown to increase the risk of contracting lung cancer in uranium miners. When radon gas emanates from

soil contaminated with radium, dispersion into the air generally dilutes the radon. In open spaces, such

dispersion usually reduces radon concentrations to low enough levels that outdoor risks of radon

exposure are insignificant. However, radon decay products can accumulate to unacceptable

concentrations in buildings built over radium contamination, because structures tend to trap radon gas.

The radioactive decay of radium and its decay products also results in the emission of highly penetrating

gamma radiation. Gamma radiation is continuously emitted from radiologically-contaminated soil.

Gamma radiation is omitted in all directions from a source, and exposure is dependent on proximity to

the source and whether physical materials shield the source. Gamma radiation emitted by unshielded

radium-containing soil penetrates the soil to give anyone standing over a contaminated area a radiation

dose over the whole body. The greater the duration and intensity of this exposure, the larger the dose,

and hence the greater the risk of adverse health effects.

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III.G.2 Radon Conditions (Pre-Remedy)

Seasonally corrected interior radon concentrations of 0.12 working levels were observed on the

historic Shattuck property. These concentrations correspond to a 5 x 10-2 lifetime cancer risk to a

future resident for a 30-year exposure, or a 1 x 10-1 lifetime cancer risk to a future worker with a

20-year exposure.

Dispersion modeling was used to estimate the offsite radon concentrations attributable to the site. The

results indicate that the contribution of the Shattuck property to offsite radon concentrations was

negligible, with levels estimated to be 0.0002 working levels for the 1800 block of South Acoma

(modeled as the nearest residential area) and 0.008 working levels immediately north of the Shattuck

property (modeled as the nearest offsite worker location).

III.G.3 Gamma Radiation (Pre-Remedy)

The projected lifetime cancer risk from gamma radiation to an individual working 75 percent indoors

and 25 percent outdoors on the Shattuck property for 20 years was 1 x 103 . The lifetime cancer risk

from gamma radiation exposure for a future residential scenario on the Shattuck property was 5.6 x

10-3, based on a 30-year exposure and the average one-meter gamma radiation measurements in the

vicinity of the process buildings. The risks calculated for radon inhalation and gamma radiation were

independent of each other. Hence the total risk potentially posed by radium-contaminated soil was the

sum of the radon and gamma risks.

The risks represented herein were the calculated risks attributable to the historic site. For comparison,

the background gamma risks, based on gamma measurements taken at the Overland Park Golf Course

were calculated as 1.2 x 10-3 for the future onsite residential scenario and 1.9 x 10-4 for the future onsite

worker scenario. A background risk for indoor radon was not calculated. Indoor levels for radon can

vary widely, depending on soil compensation and the physical characteristics of a building.

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IV. Remedial Actions

IV.A REMEDY SELECTION

EPA selected an onsite stabilization and solidification remedy for OU VIII in a Record of Decision

(ROD) dated January 1992. The objectives of this remedy were to prevent:

• Radiation exposure due to inhalation of radon gas and its daughter products• Radiation exposure due to inhalation and ingestion of long-lived radionuclides• Direct exposure to gamma radiation

The remedy was also designed to prevent further groundwater degradation and allow contamination in

the groundwater to attenuate over time.

The Decision Summary for the Record of Decision provides a performance criteria standard of 1,000

years for the remedy as a whole. This standard is based on 40 CFR 192 Subpart A, which states that

the design should be for 1,000 years to the extent reasonably achievable, and, in any case, for at least

200 years. This is a functional requirement not a system component. A system component is a physical

part of the disposal facility, and each component may be designed to perform a number of functions.

Monolith construction effectively diluted the contaminated soil by 30 percent; thus a degraded monolith

source was effected that would no longer be comparable to the original open-site condition prior to

onsite disposal. As such, even if the monolith begins to degrade, contaminants will not be released at

the same rate as they would have been from the pre-remedy onsite soils because (1) they are diluted,

(2) the reactive surface area is considerably reduced, and (3) the chemical form of at least some of the

contaminants will have been changed by chemical reactions involving the soil and monolith materials.

However, pilot-study leaching tests show that leachates from the monolith often exceed several

groundwater standards, notably with respect to heavy metals.

TCLP tests were used to determine potential leachate composition for the monolith. Specifically, the

tests showed that the leachably metal content for molybdenum was consistently leached at higher

concentrations than the groundwater ARAR limits; cobalt, chromium, and vanadium, leached at

concentrations close to or just above the groundwater regulatory limit of 50 µg/L in some samples.

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IV.A.1 Groundwater

For groundwater, the remediation requirement is to prevent the ingestion of groundwater with

contaminants in excess of ARARs, TBCs, or health-based concentrations if no ARARs exist.

Attenuation will improve the groundwater quality after the remedy is complete. Stabilization of the

contamination will reduce the mobility of contaminants and reduce the release to the groundwater.

Specific performance standards, used to ensure that the requirements for the groundwater are met, are:

• Groundwater monitoring will be performed to assess the effectiveness of stabilizationsuch that any release to groundwater from the disposal unit will not cause thegroundwater to exceed ARARs and TBCs.

• Groundwater monitoring will also be performed to monitor the existing plume ofcontamination. Design of a network of wells to monitor post-remediation groundwaterquality was developed during remedial design. When monitoring indicates that ARARsare being maintained for the contaminated plume, the frequency of the plume monitoringmay be reduced or discontinued. However, monitoring of groundwater near thedisposal unit will continue.

• Further groundwater remediation may be required if monitoring shows that attenuationof the contamination will not achieve ARARs.

• Corrective action as required to comply with the Clean Water Act and ColoradoWater Quality Control regulations (5 CCR 1002-2 Sections 3.1, 3.8, and 6.1 et. sec.)will be undertaken to address the contaminated groundwater infiltrating the storm sewerwest of the site. The means of compliance were to be determined during remedialdesign.

• 5 CCR 1002-8 section 3.12.0, Classifications and Water Quality Standards forGround Water, is an applicable requirement for groundwater at the site. The regulationsets an interim narrative standard that requires that groundwater be maintained at theless restrictive of: (1) existing ambient quality as of October 30, 1991, or (2) thatquality which meets the most stringent criteria set forth in Tables 1 through 4 of “TheBasic Standards for Ground Water.” The regulation provides that for contaminatedgroundwater, the intent is not to limit remediation. This requirement will be met bycontrolling the source of contaminants and attenuation of the groundwater to thecontaminant-specific levels set forth in Table 3 of Appendix A of the ROD.

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• All other ARARs identified in EPA’s ROD for groundwater must also be met.

For concerns related to monitoring design and performance, see Section VII.

IV.B REMEDY IMPLEMENTATION

The Remedial Action at OU VIII was substantially completed in September 1998. Remedial actionoperations at OU VIII include the following:

• Demolition of radium-contaminated buildings

• Excavation of radium-contaminated soil from vicinity properties, Bannock Street, thestorm sewer located east of Santa Fe Drive, and the Shattuck Chemical property

• Onsite stabilization/solidification of the radium-contaminated soil into a disposal cell

• Capping of the stabilized material

• Installation of monitoring wells to evaluate the effectiveness of the remedy

The remedial action at OU VIII was conducted in two phases, beginning September 1992, and wassubstantially complete in September 1998. During Phase I, approximately 67,345 tons of buildingdebris were disposed of off site and 8,700 cubic yards of soil were excavated from the vicinityproperties. During this phase, approximately 200 cubic yards of asbestos-containing material wereremoved and disposed of under appropriate regulations. Approximately 400 cubic yards ofradiologically contaminated material were excavated from beneath Bannock Street.Stabilization/solidification of the radiologically contaminated material began in July 1996 and wascompleted in November 1997.

Approximately 65,000 loose cubic yards of radiologically contaminated soil excavated from ShattuckChemical and the vicinity properties were stabilized/solidified onsite in a disposal cell. Capping of thestabilized material was completed in June 1998. The Draft Construction Completion Report wassubmitted on September 29, 1998.

A waste form (i.e., monolith) was constructed on site consisting of compacted layers of contaminatedsoil, cement, fly ash, and water. In the pilot treatability study, the soils were to be mixed at a ratio of70:20:10 (soils: cement: fly ash), compacted to an ASTM standard value, and

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a moisture content to maintain a 0.4 ratio of water to cement. The study results indicate that, at least inthe near-term, structural strength of the concrete meets the requirements of the EPA in terms ofcompressibility and permeability. Toxicity Characteristic Leaching Procedure (TCLP) results wereconsistently close to or just below the groundwater ARAR limits for cobalt, chromium and vanadium,and higher concentrations than the groundwater ARAR limits for molybdenum.

These tests confirm the near-term acceptability of the waste form, but do not address its long-termperformance as a part of the remedial system.

The monolith is covered with a surface barrier or cap, which in some form or another has beendesigned and used throughout the Western United States at Uranium Mill Tailing Remedial Action(UMTRA) sites. The cover ultimately used is a variant of those typically applied for UMTRA; however,the UMTRA caps in use may not have been in place a sufficient amount of time to adequately evaluatetheir efficiency and long-term performance. The Department of Energy (DOE) is currently conductinglong-term surveillance of UMTRA caps under an alternative cap study. Already, concern has beenraised about the UMTRA-type caps’ long-term performance related to the clay barrier in and regionsand vegetation invasion (Hakonson, 1997).

During the excavation of radiologically contaminated soils, oil-impacted soils were also found onsite.The materials were below the action levels established in the ROD. Approximately 2,000 cubic yardsof oil-impacted soil were excavated during Phase II activities from the Shattuck Chemical Propertylocated at 1805 South Bannock Street. This material was covered and transported by truck toConservation Services Inc. (CSI) in Bennet, Colorado. Bioremediation was used for oil-impacted soilsthat extended beneath the completed portion of the monolith. A plan addressing the remaining soilscontaminated with oil at OU VIII was submitted in August 1998. The bioventing system was approvedby EPA and was installed in September 1998.

In 1997, the storm sewer along Santa Fe Boulevard west of the site was remediated. The remediationconsisted of using InSituForm to install a lining within the existing sewer lines, manholes, and inlet boxes.The sewer remediation effort was conducted in 1997 in accordance with the EPA-approved design.Based on water quality sampling and water level data obtained in 1998, EPA determined that anadditional section of the sewer located to the north of the section previously determined to be locatedbelow the shallow groundwater table, also needed to be remediated. This additional section of thestorm sewer line was remediated using the

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InSituForm process in 1999. EPA has requested additional water quality sampling of the storm sewerand a decision is pending.

IV.C SYSTEM OPERATIONS/OPERATION AND MAINTENANCE

The System Operations/O&M requirements are not identified in a single document. Components maybe found in the monolith-monitoring plan, the plume-monitoring plan, and the bioremediation plan.

Security arrangements discussed in this report are based on visual observations during the July 1999site visit and oral discussions with a Shattuck representative. Site-security arrangements that aretemporarily in place and consist of a 24-hour, round-the-clock guard and a controlled access systemconsisting of a fence and a locked gate. The bioremediation system has operated since 1998 withoutincident. The existing monolith- and plume-monitoring wells are being sampled quarterly. Annualizedcosts for the site security arrangements, the bioremediation system, and the monolith- andplume-monitoring system are presented in Table 3. The site engineer has indicated that the securityarrangements will most likely be discontinued in the near future and therefore costs associated with sitesecurity are not included in Table 3. Apparently, site groundskeeping activities will be maintained andare presented in Table 3.

Table 3: Current Annual O&M Costs

O&M ITEMDates

ESTIMATED ANNUALIZED COSTSFROM TO

Grounds Keeping 1/99 12/99 $10,000

Bioremediation 1/99 12/99 $15,000

Monolith and plume monitoring 1/99 12/99 $220,000

Additional costs have been incurred to replace the protective fencing around the site. The fence on thewestern side of the site was taken down by a Regional Transportation Department construction crewduring an adjacent construction activity.

In addition, considerable debate is going on with regard to the adequacy of the existing monolith-andplume-monitoring programs. Potential expansion of these programs is under consideration. Expansioncould take the form of geoprobes, additional wells, additional constituents to be monitored for,additional surface water and soil sampling, as well as additional testing and

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monitoring of the monolith itself (coring to evaluate the monolith’s intactness, evaluating the capstatistically, setting benchmarks for settlement evaluation, etc.). These activities would require significantcapital cost outlays and could also significantly increase the upcoming and future annualized O&Mcosts.

IV.D PROGRESS SINCE THE LAST FIVE-YEAR REVIEW

Table 4 itemizes the actions taken since the last Five-Year Review. At the time of the last five-yearreview, the remedial action for OU VIII had just been completed. This included the excavation andstabilization of the contaminated soil and select vicinity properties, the construction of the cap, andinstallation of the bioremediation system. Since then, the Operation and Maintenance Plan wasdeveloped and implemented, and Shattuck initiated sampling under the plume-monitoring andmonolith-monitoring plans.

Table 4: Actions Taken Since the Last Five-Year Review

RECOMMENDATIONS/REQUIRED ACTIONS

PARTYRESPONSIBLE

ACTIONS TAKEN DATE OFACTION

Excavation & stabilization Shattuck completed 1998

Construction of cap Shattuck completed 1998

Bioremedition system Shattuck completed 1998

Monolith Shattuck completed 1998

Sewer System Shattuck completed 1998

Plume-monitoring plan Shattuck developed & implemented 1998

Monolith-monitoring plan Shattuck developed & implemented 1998

Bioremediation Shattuck developed & implemented 1998

The current monolith-monitoring program consists of 10 monitoring wells; five wells on the western sideof the monolith and five wells on the eastern side of the monolith.

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VI. Five-Year Review Findings

V.A TEAM MEMBERS

This section briefly describes the technical experts who served on the Peer Review Team.

Mr. John Darabaris managed the Peer Review Panel. He is a geologic engineer with extensiveexperience in EPA-OSW RCRA Corrective Action and Permitting Actions, and ComprehensiveEnvironmental Response Compensation Liability Act (CERCLA) Environmental Restorations. He hasserved in lead roles on prior peer reviews.

Mr. Phillip Rogers was the process engineering representative on the Peer Review Panel. Mr. Rogersis a professional engineer with more than 23 years of experience. His experience includes thedevelopment of complex conceptual and numerical models that capture processes such as preferentialflow in the vadose zone, the effects of tank waste chemistry on radioisotope mobility, alternative endstate configurations, and infiltration. He has extensive experience with CERCLA and RCRA projects,including hazardous and municipal waste landfills, mine waste, mixed wastes, and petroleumcontamination at Air Force bases. Mr. Rogers also managed and was the principal author of thehydrogeologic impact sections and sensitivity analysis appendix of the Retrieval Performance EvaluationMethodology for the AX Tank Farm (U.S. DOE, DOE/RL-98-72, April 1999). For that report, hesuccessfully managed and implemented the detailed evaluation of the hydrogeologic impacts of retrievaland closure of high-level radioactive waste tanks at DOE’s Hanford Site.

Dr. Allen Hatheway was the Construction/geotechnical engineering representative on the PeerReview Panel. Dr. Hatheway has more than 38 years of professional experience in environmentalmanagement and geotechnical options; exploration program design; hazardous and special wastemanagement facility siting, design and permitting; site and waste characterization and remedialengineering for uncontrolled sites; seismic risk assessment; hazards mitigation; rock engineering andunderground construction; critical facility siting; and expert testimony.

Dr. John W. Goode was the Risk Assessment Specialist on the Peer Review Panel. Dr. Goode has aPh.D. in toxicology. He has 26 years of management, technical, and business-related experience in abroad range of environment, health, and safety areas. Dr. Goode currently represents EPA as the leadinspector in determining compliance of the major nuclear waste sites

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in the United States that will eventually ship waste to the Waste Isolation Pilot Project outside ofCarlsbad, N.M. Dr. Goode has managed or participated as a senior investigator in major riskassessment and exposure information projects. For example, he has managed a screening level humanhealth-risk assessment for direct and indirect exposure to combustion emissions for chemical agentincinerators located at the Tooele Army Depot in Utah. Dr. Goode has also managed a risk assessmentof the closure of the 2101-M pond at Hanford. He validated analytical data generated by U.S. Testing,and provided a risk-assessment model to the Washington Department of Ecology.

Dr. Steven Schaffer was the aquatic biologist on the Peer Review Team. Dr. Schaffer has a Ph.D. inBiology/Environmental Health Science from New York University. Dr. Schaffer is a senior scientistresponsible for a wide variety of ecological, health, and regulatory activities and has lead responsibilitiesfor SC&A’s chemical risk-assessment business. He managed a project that produced theEnvironmental Impact Statement and Regulatory Analysis in support of NRC’s decommissioningstandards. He is also responsible for SC&A’s technical training business, which offers seminars in riskassessment, environmental chemistry, and quality control to industry and government. Dr. Schaffer hasalso performed several studies for the EPA concerning the risks and hazards of both chemical andradiological contaminants.

Mr. David Back was the Hydrogeologist on the Peer Review Team. Mr. Back has over 14 years ofexperience reviewing and evaluating hazardous and nuclear waste disposal technologies; performinggroundwater contamination assessments; developing and implementing remedial measures andevaluating remedial effectiveness; conducting aquifer tests, geophysical surveys, tracer tests, and soiland water sampling; performing numerical and analytical simulations of groundwater flow andcontaminant transport; and implementing quality-assurance and quality-control procedures. Mr. Backhas been the lead author of several EPA/DOE/NRC joint guidance documents developed to facilitatethe selection and application of groundwater models at Federal facilities, EPA sites, and potential low-level waste sites.

Dr. Wendy Harrison was the geochemist expert on the Peer Review Panel. Dr. Harrison is aprofessor at Colorado School of Mines with more than twenty years of experience, and hasparticipated in numerous peer review panels.

Dr. Charles Shackelford was the civil engineer on the Peer Review Panel. Dr. Shackelford is aprofessor of Civil Engineering at Colorado State University with more than 20 years of experience. Hehas participated on numerous expert panels, specializing in closure design issues.

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V.B COMMUNITY ACTIVITIES

Members of the Peer Review Panel attended four Shattuck dialogue meetings. The first meeting washeld on May 21, 1999, at which time the scope of work was discussed. In a meeting on July 7, 1999,several administrative actions were discussed and it was agreed that another contractor would addressa report on development options for the Shattuck site in future meetings. Relative to this workassignment, the Peer Review Panel members were identified and resumes made available. A meeting onJuly 23-24 discussed decision criteria for use by the EPA/OSWER Administrator and plans for anin-depth discussion of perspectives on costs and benefits at the upcoming August meeting. The City ofDenver presented alternatives that address its criteria. A proposed work plan for the remainder of thedialogue was also presented. Progress to date was discussed as was the desired future course of thedialogue in relation to the other Shattuck review tracks. With respect to this review, a need to conducta scoping analysis of the site’s risk assessment was identified. This analysis had been identified in theoriginal work plan as a “to be-determined” item. All members of the Peer Review Panel attended thedialogue meeting on September 9, 1999. The purpose of this meeting was to receive updates from themajor dialogue initiatives. These updates included the redevelopment study, a re-mining feasibility study,the work of the environmental response team, and the expert panel study conducted as part of thisassignment.

V.C TECHNICAL EXCHANGES

No formal interviews were scheduled during this peer review. However, all Panel members haddiscussions with various members of the dialogue, representatives of EPA Region VIII, the City ofDenver personnel, and Shattuck site personnel as necessary. This included attendance by some of thePanel in the monthly Shattuck technical meetings with EPA, the State, the City of Denver, ShattuckChemical Company, and stakeholder technical staff. Mr. Darabaris attended the majority of themeetings, with participation by Mr. Back, Mr. Rogers, Dr. Goode, Dr. Hatheway, Dr. Shackelford,and Dr. Harrison as needed.

As part of the Technical Exchange process, and to ensure the technical accuracy of the review, eachPanel member met with interested parties to discuss their individual findings. In preparation for thesemeetings, the interested parties had a rough draft of the initial findings, concerns, and assessments ofeach Panel member as presented in Appendix A. Furthermore, the Working Draft of the Five-YearReview itself was made available for comments from interested parties. Comments were forwardedunder an October 15, 1999 deadline. Panel members

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reviewed the comments and revisions were made to the Five-Year Review as deemed appropriate toensure technical accuracy and clarity.

V.D SITE INSPECTION

Expert Panel members Darabaris, Rogers, Schackelford, Hatheway, and Harrison participated in a siteinspection on July 6, 1999. Jim Hanley of the EPA and Paul Rosasco of EMSI also accompanied themembers of the Peer Review Panel on the site Visit.

The Shattuck Site now consists of a fenced rectangular property on which solid waste is disposed in alandfill that occupies the majority of the surface area. The surface of the unit was covered with riprapconsisting of large, irregularly shaped rock. The surface topography appeared uneven, with randomlyscattered highs and lows, possibly due to the size of the rock and the method of placement. Plate 2 ofthe Construction Completions Report shows the top the of monolith to be crowned with an overallslope of one percent to the northwest. There appeared to be a “drain” consisting of coarse gravel orrock around the perimeter of the cap. This drain is designed to capture runoff from the cap and divert itto a sump. The cap design and waste monolith characteristics would seem to indicate very littleinfiltration through the unit.

A system of groundwater monitoring wells could be observed near the landfill. The system appeared tobe limited to one row of upgradient wells on the east side of the landfill and one row of downgradientwells on the west side. The wells were located very close to the toe of the landfill cap.

There did not appear to be a reliable system to determine settlement. Based on an inspectionperformed on behalf of EPA in June 1999, Morrison-Knudsen concluded that there is no indication ofan imminent or ongoing threat to the monolith and cover system from potential impacts due tosettlement, subsidence, slope movement, or erosion. Expert Panel members also inspected the site andagreed with the Morrison-Knudsen inspection report. However, visual observation of the cap surface isnot conclusive. Excessive settlement could occur and not be detected or, conversely, false indicationsof settlement could be interpreted from the uneven rock surface.

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V.E RISK INFORMATION REVIEW

The 1991 baseline risk assessment for the Shattuck site meets the EPA guidelines that were in place atthe time the risk assessment was conducted. In recent years, new guidelines for Exposure Assessment(1992), Carcinogenic Risk (1996), Reproductive Toxicity Risk (1996), and Ecological Risk (1998)have been issued. The newer guidelines do not change the overall approach of the risk-assessmentprocess but continue EPA’s risk-development process initiated in the early 1980s. The newerguidelines have increased the emphasis on exposure characterization and provide better guidance forassessing ecological exposure to chemicals and human exposure to radiological agents. These twoareas are important in evaluating the applicability of the 1991 risk assessment to the current sitecircumstances.

The primary agencies with regulatory authority for the cleanup of sites contaminated with radioactivityinclude the EPA, the Nuclear Regulatory Commission (NRC), the Department of Energy (DOE), andthe State of Colorado. National and international scientific advisory organizations providerecommendations related to radiation protection and radioactive waste management but have no regula-tory authority. EPA’s authority to protect public health and the environment from adverse effects ofradiation exposure is derived from several statutes, including the Atomic Energy Act, the Clean Air Act,the Uranium Mill Tailings Radiation Control Act (UMTRCA), the Nuclear Waste Policy Act, andCERCLA. EPA’s major responsibilities with regard to radiation include the development of Federalguidance and standards, assessment of new technologies, and surveillance of radiation in theenvironment. EPA also has lead responsibility in the Federal government for advising all Federalagencies on radiation standards.

The State of Colorado has its own authority and regulations for managing radioactive material andwaste. State regulations are potential ARARs.

The following were reviewed to determine changes in ARARs that could affect the Shattuck site.

• 10 CFR Part 20, Standards for Protection Against Radiation

• 10 CFR Part 61, Licensing Requirements for Land Disposal of Radioactive Waste

• 40 CFR Part 190, Environmental Radiation Protection Standards for Nuclear Power

Operations

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• 40 CFR Part 191, Environmental Standards for the Management and Disposal ofSpent Nuclear Fuel, High-Level and Transuranic Radioactive Waste

• 40 CFR Part 61, National Emission Standards for Hazardous Air Pollutants

• 40 CFR Part 141, Interim Primary Drinking Water Regulations

• 40 CFR Part 142 National Primary Drinking Water Regulations- Radionuclides

• 40 CFR Part 192, Health and Environmental Protection Standards for Uranium andThorium Mill Tailings

• 40 CFR Part 300, National Contingency Plan (NCP) and Supporting Guidance

• 10 CFR Part 834, Radiation Protection of the Public and the Environment

• 40 CFR Part 311, Worker Protection

• 40 CFR Part 440, Ore Mining and Dressing Point Source Category

• 40 CFR Part 58, Ambient Air Quality Surveillance

• Colorado Department of Public Health and Environment 6 CCR 1007-2, RegulationsPertaining to Solid Waste Disposal Sites and Facilities

• Colorado Department of Public Health and Environment 7 CCR 261, Identification andListing of Hazardous Waste

• Colorado Department of Public Health and Environment, Water Quality ControlCommission Regulation No. 41, The Basic Standards for Groundwater

• Colorado Department of Public Health and Environment, Air Quality ControlCommission Regulation No. 8, Control of Hazardous Air Pollutants

• Colorado Department of Public Health and Environment, Radiation ServicesCommission, Part 1 General Provisions

• Colorado Department of Public Health and Environment, Radiation ServicesCommission, Part 3 Licensing of Radioactive Material

• Colorado Department of Public Health and Environment, Radiation ServicesCommission, Part 4 Standards for Protection Against Radiation General Provisions

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• Colorado Department of Public Health and Environment, Radiation ServicesCommission, Part 14 Licensing Requirements for Land Disposal of Low LevelRadioactive Waste

• Federal Guidance Report No. 13, Part I - Interim Version, Health Risks fromLow-Level Environmental Exposure to Radionuclides, EPA 402-R-97-014, Office ofRadiation and Indoor Air, January 1998

• Risk-Based Concentration Table, USEPA Region III

• Selecting Exposure Routes and Contaminants of Concern by Risk-Based Screen,EPA/903/R-93-001, January 1993

• OSWER Memorandum No. 9200.4-23, Clarification of the Role of Applicable, orRelevant and Appropriate Requirements in Establishing Preliminary Remediation Goalsunder CERCLA

• OSWER Memorandum No. 9200.4-18, Establishment of Cleanup Levels forCERCLA Sites with Radioactive Contamination

• Regulatory Guide 8.36, Radiation Dose to the Embryo/Fetus, NRC, July 1992

• Effects of Ionizing Radiation on Terrestrial Plants and Animals: A Workshop Report,ORNL/TM-13141, Oak Ridge National Laboratory, December 1995

• The Health Physics and Radiological Health Handbook, Scinta, Inc., 1992, (BernardShleien, ed.)

• Environmental Protection Agency, Risk Assessment Guidance for Superfund, Vol. I,Human Health Evaluation Manual (Part A), Office of Emergency and RemedialResponse. EPA/540/1-89/002, 1998

• Environmental Protection Agency, Uses of Soil Cleanup Criteria in 40 CFR 192 asRemediation Goals for CERCLA Sites, OSWER Directive No. 9200.4-25, February12, 1998

It was determined that there were no ARAR changes that materially affected the site. Since the soil wasremoved and concentrated in the landfill and the current groundwater usage is minimal, the site remedywould not be affected by small changes in ARAR concentration levels. However, there are concernsthat the goals of the original remedial design were not stringent enough and could have fallen short of theARAR requirements in place at the time of the remedy.

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The Construction Completion Report states that the soil cleanup levels were based on ARARsdeveloped at the time of the ROD, 1992. The levels for Ra-226, Th-230 and gamma radiation werebased upon the uranium mill tailings standard 40 CFR 192. This standard does not specify levels foruranium, so DOE Order 5480.1 was used.

Since the time of the ROD, EPA issued two OSWER Memoranda concerning residual levels ofradioactivity left onsite after remediation. An August 22, 1997, OSWER Memorandum (OSWER No.9200.4-18) states that the maximum concentrations of residual contaminants (including radionuclides)should not exceed the 10-4 cancer risk. This limit is based on a site-specific risk assessment anddepends on the site-specific radionuclides and exposure pathways. A February 12, 1998, OSWERMemorandum (OSWER No. 9200.4-25) further clarifies the use of the soil cleanup criteria in 40 CFRPart 192 as remediation goals for CERCLA Sites. This memorandum specifically addresses subsurfacesoils and states that the subsurface criterion for radium (15 pCi/g) is only potentially relevant andappropriate if the distribution of subsurface contamination is similar to the 24 UMTRCA Title I sites.

A cursory review of the soil concentrations remaining after cleanup supports the finding that the site maynot meet the new EPA cleanup criteria in OSWER No. 9200.4-18, and that the doses may be wellabove acceptable levels. Table 5 illustrates this point.

Table 5: Summary of Soil Concentrations Remaining After Cleanup

RADIONUCLIDESOIL RISK

CONVERSION (perpCi/g)1

SITE SOIL CONCENTRATIONSAFTER CLEANUP RISK LEVEL

Mean U-95% Mean U-95%

Ra-226 5.6x10-5 5 7.6 2.8x10-4 4.3x10-4

Total Uranium 3.6x10-7 14 20 5.0x10-6 7.2x10-4

Th-230 1.6x10-5 9 13 1.4x10-4 2.1x10-4

TOTAL 4.2x10-4 6.4x10-4

1 Taken from Radiation Site Cleanup Regulations: Technical Support Document for the Development of

Radionuclide Cleanup Levels for Soils, EPA, September 1994, using the commercial industrial exposurewithout the groundwater pathway.

2Calculated from Table 5 of the Construction Completion Report Vol 1, Shattuck Chemical Company, Inc.,

February 8, 1999. Radium-226 background of 1.5 pCi/g subtracted from mean and U-95% concentrations.

(pCi/g)2

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The table shows that the average subsurface soil concentration remaining onsite could exceed theEPA’s suggested limit by as much as a factor of 6.4. This table was developed using soil riskconversions based upon generic and standardized usage and exposure factors, and chemical equilibriumconstants assuming surface soil exposures. It has been our experience that many regulatory agencies,including EPA, assume that subsurface soils can be brought to the surface by human activity therebycreating surface soil exposure scenarios.

If the EPA assumes that the residual contamination remains buried, then OSWER No. 4200.4-25provides specific guidance. It states that, if the subsurface contamination exists at a level between 5pCi/g to 15 pCi/g averaged over 100 m2, then conditions at the site are not sufficiently similar to anUMTRCA site to consider the subsurface contamination standard in 40 CFR Part 192 a relevant orappropriate requirement. The EPA recommends that in this situation the 5 pCi/g surface standard mightbe used as a cleanup goal provided a site-specific risk assessment demonstrates that this level isprotective. In addition, when parent radionuclides of radium exist in the soil (Thorium 230 and 232),EPA recommends that the soil should be cleaned to 5 pCi/g concentration for the parent radionuclidestoo. This prevents future buildup of radium to levels greater than the 5 pCi/g standard.

Again we find that the residual levels of radionuclides in subsurface soils are not relevant andappropriate according to this newer directive. Table 5 shows that the average subsurface values forradium, thorium and uranium are all between 5 and 15 pCi/g. This means that the 15 pCi/g subsurfacecriterion in 40 CFR Part 192 should not be used as a cleanup goal because it is not relevant andappropriate for this site. Table 5 also shows that the residual levels of Ra-226 and Th-230 are abovethe 5 pCi/g health based criterion in the UMTRCA standard.

To determine the safe levels for the radionuclides in the residual subsurface soils at the site, a sitespecific risk assessment needs to be performed. Risks for subsurface soils could be higher or lowerthan those shown in Table 5. The direct shine dose contribution from Ra-226 and Th-230 wouldessentially decrease to zero because of the shielding from the soil above, but other exposuremechanisms would become more important. For subsurface exposures, one needs to consider radonmigration into dwellings and groundwater contamination from uranium.

Radon in dwellings and subsequent inhalation is one of the critical exposure pathways the EPA soughtto mitigate in the UMTRCA regulation. Indoor radon standards under 40 CFR 192(b)(1) and 192.41(b) are potentially relevant and appropriate requirements. Radon gas is a daughter product of thecontaminants of concern. Migration through soil is highly variable and can range

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from a few centimeters to many meters. The average travel distance was about 5 meters. The distanceradon travels is dependent on whether the soil media is highly compacted which inhibits movement orcontains cracks and conduits that promote migration. It is possible that radon from the subsurface soilsand the monolith could travel to nearby buildings through spaces in the soils and conduits created byunderground utilities.

Since uranium can readily move into groundwater, the subsurface soils could become an easy sourcefor groundwater uranium contamination. This is because the contamination is only a short distanceabove the water table.

V.F RISK RECALCULATION/ASSESSMENT

The 1991 risk assessment evaluated the level of risk for the underlying aquifer, and found the waterunacceptable for drinking. Of the radioactive contaminants, uranium was the most significant, with acalculated lifetime risk of 6.7 x 10-3 based on drinking two liters of water per day for 30 years. Asstated above, this finding (based on 1991 RA) is a cause for concern since uranium has a long half-life(U-234 = 240,000 yrs., U-238 = 4,400,000,000 yrs.) and would not be expected to lose appreciableactivity in the proposed 200-year time period.

The 1991 risk assessment information did not address future risk which is a concern at the Shattuck siteand surrounding area since hazardous contaminants have been left in place and complete remediation ofgroundwater may not occur for decades in the future.

The Panel’s main concern is the long-term risk potential of the groundwater. There has been use of thegroundwater in the past, and without strict institutional controls, there may be use of the groundwaterbefore the present risk level has been reduced. A recent M-K sampling report since completion of themonolith still shows constituents, such as molybdenum, above trigger levels. The passive nature of theremedial alternative for groundwater that essentially relies solely on dilution for the long-livedradionuclides places an even greater importance on extensive groundwater monitoring. Unless acredible understanding of the groundwater flow and contaminant processes can be developed the trueenvironmental impacts may remain unknown. Performance criteria, especially for the groundwaterplume, should be developed and monitored. The goal of these criteria should demonstrate that MCLsfor all groundwater constituents will be achieved in the regulatory timeframe. Without this information,the Panel is not convinced that the groundwater will achieve necessary standards required by CFR 40192 within the 100-year timeframe.

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Additional onsite and offsite data is necessary before conducting a risk assessment of the currentsituation at the Shattuck site and surrounding areas. Increasing the number of samples and locations ofsamples will increase the precision and accuracy of results. More data must be obtained to demonstratethat the site meets the criteria given in 40 CFR 192.

V.G DATA REVIEW

The Panel concluded that too few samples of media had been taken since remediation to conduct anacceptable risk assessment of the current situation. Quarterly groundwater sampling has beenconducted and is the major source of new data. The 1991 baseline risk assessment concluded that thegroundwater was a major source of risk, and the ROD concluded that natural flushing was the choicefor remediation of the aquifer. Many more data points are necessary to address issues raised by thePanel before a meaningful risk assessment of the current situation at Shattuck can be conducted.

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VI. Assessment

VI.A CHANGES IN CONDITIONS EXTERNAL TO THE REMEDY

VI.A.1 Land Use

Land use at the site itself has not changed since the ROD. However, the review has found that theoriginal remedy did not adequately address potential groundwater usage. The reasonably expected landuse within the site boundaries is restricted by deed. It is also important to recognize that the land use ofthe surrounding areas is not restricted by any formal legal means and is, in fact, mixed residential andindustrial. Also, the aquifer is considered a potential source of drinking water as a Class II aquifer underthe “Guidelines for Groundwater Classification under the EPA Groundwater Protection Strategy, FinalReport, November 1986,” issued by the EPA’s Office of Groundwater Protection.

Given the longevity of the remedy, it is possible that land use downgradient of the site may change withrespect to groundwater and surface-water use.

VI.A.2 Contaminants and Pathways

Currently, the monolith provides an improved waste-management form from the pre-remediationcircumstances. In the near term, there is no evidence that the monolith is not performing as expected(i.e., stabilizing the site contaminant source term). The review has identified significant design issues thatquestion the ability of the site to confirm long-term performance of the monolith. From an exposurepoint of view, the monolith represents a new contaminant source because it changes the externalexposure geometry and provides a concentrated source for radon emanation.

Based on the preliminary findings presented in Section V, Table 5, the remaining soils and aquifermaterials within the plume could have sufficient metals' loading to act as a source. Data are insufficient toassess the magnitude of this source.

Although there are no currently known downgradient groundwater users, there are groundwater usersin the area. Furthermore, while the State of Colorado has not formally classified the Upper Terraceaquifers, the State’s position is that aquifers not designated as being of limited beneficial use must beconsidered as having potential beneficial use to the public. The underlying Denver

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formation aquifer is classified as a Class I aquifer by the State, equivalent to the Class I aquiferdesignation found in the 1986 CERCLA Guidance. In addition, surface water is currently being usedfor recreation (Platte River). There is also an unnamed pond downgradient of the site that may bereceiving groundwater recharge from the contaminant plume. Water from this pond may be used forirrigation. The Remedial Investigation Report and the Baseline Risk Assessment removed fromconsideration the groundwater exposure pathway for human and ecological risk. This review finds thatthe decision to eliminate the groundwater pathway was based on insufficient data and not supported byregulatory concerns. Likewise, this review finds that the surface-water exposure pathway waseliminated based on minimal data and regulatory support.

VI.A.3 Hydrologic/Hydrogeologic Conditions

There is no evidence that the hydrologic/hydrogeologic site conditions have changed. However, theseconditions may not have been characterized in sufficient detail. The site hydrogeologic conditionspresented in the remedial assessment and remedial investigation are not a complete depiction of theactual site conditions.

The review finds that the groundwater plume condition does not meet CERCLA 121(d) standards.The site characterization program does not define site hydrogeologic conditions sufficiently to supportnatural monitored attentuation. Site geology (upper aquifer soils and underlying bedrock) may exhibit agreat deal more variability and channeling characteristics than the simplistic model presented in sitedocuments. There are significant questions regarding the adequacy of the definition of the plumecharacteristics (lateral extent, vertical extent, fate and transport characteristics).

VI.B IMPLEMENTATION OF THE REMEDY

VI.B.1 Health and Safety Plan/Contingency Plan

The project’s health and safety requirements, equipment, and procedures required of all contractorsand subcontractors at the Shattuck site are described in section 01020 of the Construction CompletionReport, February 1999.

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VI.B.2 Institutional Controls

An institutional controls program has been developed and implemented to control access to thestabilized materials. Security measures such as fencing and surveillance are in place. Groundwatermonitoring is in place ostensibly to monitor the effectiveness of the stabilized material so that anygroundwater loading from the disposal unit will not cause the groundwater to exceed ARARs. Theexisting plume of contamination will be monitored. An air monitoring plan was in place to monitorvolatile and semi-volatile and particulate (PM10) and total suspended particulate (TSP) constituentsduring the construction phase. Currently, no continuous air monitoring is taking place under the existingsite institutional control program. However, at the end of the cap construction, a gamma flux and radonemission measurement program was conducted as part of the construction completion and will becontinued on an annual basis.

This review finds it questionable whether the institutional controls required to restrict the use ofcontaminated groundwater can ever be implemented.

VI.B.3 Remedy Performance

Currently, the monolith provides an improved waste management form from the pre-remediationcircumstances. In the near term, there is no evidence that the monolith is not performing as expected(i.e., stabilizing the site contaminant source term). However, there are a number of technical findingsthat raise doubt about the site’s ability to confirm long-term performance of the monolith and controlover the contaminated groundwater.

Limited recent-sampling data indicated that contaminants may still be present in soil and groundwaterand, if not controlled, may cause harm to humans, the environment, and ecological organisms.

VI.B.4 Adequacy of System Operations

The systems operations requirements appear adequate for the site and are being properly implemented.The security breaches during construction appear to have been eliminated.

However, as noted above, although there is apparently no groundwater exposure today, the reviewfinds that no institutional controls are in place to prevent offsite groundwater access. Also, the reviewfinds that the surface water was also poorly characterized. Only one surface-

VI-4

water sample from a runoff catchment basin was analyzed. For this sample, only gamma activity,indicating Ra-226 and/or elevated natural uranium, was determined; other constituents, such as metalsand organic compounds, were not determined. Thus, the characterization of the surface-water qualitywas incomplete.

VI.B.5 Optimization

The determination of the extent of groundwater contamination and the movement of the contaminantplume was incomplete. Thus, the effectiveness of the remedy in protecting human health andenvironmental quality cannot be fully assessed at this time with respect to the groundwatercontamination exposure path. Likewise, analyses of soil metals were perfunctory and sparse. Thus, thereview finds that data are insufficient to confirm whether all the metal-contaminated soil was removed,or whether metals loading into the aquifer materials occurred. Inadequate information exists todetermine if metal-contaminated soils remain, although apparently radioactive materials were removedproperly and adequately to the target levels established at the time of the remedy.

Many more data points are desirable to characterize the plume and to make a meaningful assessment ofthe current situation at Shattuck. There is not a long enough history of “clean” sampling results forsampling to be reduced. Increased sampling of groundwater and offsite soil is necessary because, asmentioned, site soils and groundwater that exceeded general EPA guidance for radioactive cleanup mayhave been left in place.

VI.B.6 Indicators of Potential Failure

There is no history of frequent equipment breakdowns or changes in the scope of system operationsthat indicate potential problems.

VI.B.7 O&M Costs

At the present level of operations, there are no potential problems. However, an increase in necessaryoffsite institutional controls would increase cost in the near term. The City and County of Denver hasthe authority to control use of groundwater downgradient from the Shattuck site or anywhere within theservice area of the Denver Water Board. Accordingly, an offsite institutional control can beimplemented by Denver by enacting an ordinance. The City and County of Denver has indicated thatthey have no intention to enact such an ordinance. Nor, for

VI-5

that matter, is it clear that the PRP ever approached the City and County to enact such an ordinance.

From a review of the Shattuck documents, it appears that the PRG was set for achieving a risk of 1 x10-4 (industrial). Future risk assessment and performance standards of the Shattuck site should evaluatea more conservative goal. The latter may be more appropriate for the following reasons:

• The surrounding site area presently includes recreational and residential activities.

• Trying to predict the future of land use over the next 200 years for Shattuck and the

surrounding area is difficult. However, there is justification for believing that Denver willcontinue to grow and will have several times its present population in 200 years.

• The contaminants include long half-life radioactive contaminants (up to 1010 years forU-238), which guarantees that they will retain much of their activity throughout the200-year period and beyond.

• Shattuck is a unique situation because it is the only radiation waste repository set in amajor metropolitan area in the United States

• Security at present does not go beyond the site boundaries, and the EPA has gone onrecord (FR 1/11/95) as limiting credible maintenance of the site to 100 years.

• Actions at Superfund sites should be based on estimates in the high-end of theintake/dose distribution.

The EPA has generally assumed that cleanups to ARARs are satisfactory because the residual risk willbe in the 104 to 106 range. However, the Agency has clarified that cleanups of radionuclides aregoverned by the risk range for all carcinogens established in the NCP when ARARs are not availableor are not sufficiently protective. That is, cleanup should generally achieve a level of risk within the 10-4

to 10-6 range based on the reasonable maximum exposure for an individual. The Peer Review Panel isconcerned as to whether the original goal of 1 x 10-4 for the Shattuck cleanup is appropriate given thesurrounding site circumstances.

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VII. Deficiencies

Table 6 details shortcomings in current site operations, noting which inadequacies currently prevent theremedy from being protective.

Table 6: Identified Deficiencies

DEFICIENCIESCURRENTLY AFFECTSPROTECIVENESS (Y/N)

Lack of institutional control of plume outside site boundary Y

Vulnerability of cover/monolith design to long-term degradation Y

Monolith-monitoring plan deficiencies Y

Plume-monitoring plan deficiencies Y

Site characterization and modeline deficiencies Y

Risk assessment deficiencies Y

Specific design technical issues that need to be re-evaluated Y

A brief discussion of each deficiency follows.

VII.A LACK OF INSTITUTIONAL CONTROL OF PLUME OUTSIDE SITE BOUNDARY

This review finds that the offsite impact of the degraded groundwater plume has not been covered byany formal institutional control. Shattuck does not consider itself responsible for ensuring offsite landuse, and the State/City governments have not provided definitive assurances of institutional controls forthe life of the remedy specified in the ROD (200 years).

VII.B VULNERABILITY OF COVER/MONOLITH DESIGN TO LONG-TERM

DEGRADATION

The remedial design is ostensibly based on UMTRA design concepts. However, this review finds thatthe remedial design does not include performance assessment modeling that is typically used to confirmlong-term performance capability. Furthermore, there is great concern that the limited performanceanalysis that was done (i.e., reduction factor analysis presented in Appendix F of the Remedial Design)does not accurately reflect the anticipated chemical and

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hydrologic performance (i.e., more uniform flow based on a higher incidence of microfractures; ratherthan dilution, water passing down the column will acquire more contamination until it reaches the baseof the monolith). Specifically, the approach used to calculate the “Reduction Factors” in Appendix F isbased on a uniform mixing type approach that is known to be nonconservative when compared againstmethods that better represent groundwater flow and contaminant transport and predict dilution ratesbased on vertical and transverse dispersion.

Also, it has been reported that some “high quality concretes made with sulfate-resisting cements havedeteriorated prematurely in the field” (Kalousek et al., 1972). Given the required long service life of themonolith and lack of supporting data, it is concluded that the sulfate resistance of the monolith isuncertain. The monolith mixture is described as 70 percent soil and rubble, 20 percent Type I/II cementand 10 percent Class C fly ash. The uncertainty in monolith sulfate resistance stems from (1) thepresence of sulfates and potential chlorides, (2) the potential for water to come into contact with themonolith, and (3) the lack of available chemical documentation on the fly ash combined with the type offly ash used. Most Class F fly ashes improve sulfate resistance of Type II cements and are generallymore efficient in improving sulfate resistance (Klieger and LaMond, 1994). This variability hasprompted investigators to recommend that Class C fly ashes be individually evaluated if intended forsulfate resistance. Chemical variability in fly ash would not be uncommon from ashes from one source.In this case, it is not known how many sources of fly ash were used for the monolith nor were chemicalanalyses made available. Guidelines for the use of fly ashes for the improvement of sulfate resistancehave been published by several sources. Dunstan 1980 proposes a fly ash “sulfate resistance factor R”and has documented the “drastic” reduction of sulfate resistance due to use of inappropriate fly ashes.Such fly ashes (i.e., those that would not improve sulfate resistance or potentially reduce sulfateresistance) would generally be characterized as being high in calcium oxide content and comparably lowin ferric oxide content. Finally, there are no available data on the sulfate resistance of monolith samplesas could have been determined by laboratory testing. Several laboratory (and field) tests are in standarduse, such as ASTM C 1012, which involves the expansion of mortar specimens in a 5 percent sodiumsulfate solution or the Bureau of Reclamation Procedure 4908, Methods A, B, or C.

VII.C MONOLITH-MONITORING PLAN DEFICIENCIES

The review finds the current monolith monitoring plan deficient. The monolith-monitoring plan (MMP)outlines the approach that was used to place monitoring wells to detect leaks from the monolith. Acomputer code (i.e., MEMO) was used in a stochastic framework to predict how

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much of the monolith area would be effectively covered in terms of leak detection by potentialmonitoring wells. One of the key parameters for this analysis is the transverse dispersivity (i.e., theamount that the plume spreads perpendicular to groundwater flow). The MMP cites a 1985 EPAguidance document indicating that transverse dispersivity can be estimated as 0.33 times the longitudinaldispersivity. In the case of the monolith, the longitudinal dispersivity is estimated to be 10 percent of thetravel distance from the monolith to the site boundary or 35 ft. Therefore, a transverse dispersion of 12ft was assumed (0.33 times the longitudinal dispersivity).

The greater the transverse dispersivity the more likely the plume will intersect a monitoring well. Thevalue for transverse dispersivity cited in the 1985 EPA document was developed prior to the famoustracer tests performed at the Borden test site that indicated considerably lower transverse dispersivityvalues. More recently, Dr. Len Gelhar, a professor at MIT with considerable knowledge ofcontaminant transport, has estimated transverse dispersivities in the alluvial aquifer system in the vicinityof Yucca Mountain Nevada to be approximately 10 percent of the longitudinal dispersivity. This systemis similar to the one at the Denver Radium site. This would result in a transverse dispersivity of 3.5 ft.The MEMO modeling results indicate that with a transverse dispersivity of 6 ft, the monitoring wellswould effectively cover 86 percent of the monolith area. Therefore, we know that this coverage wouldbe reduced if a value of 3.5 were to be used for transverse dispersivity. Furthermore, the transversedispersivity could be even smaller if preferential pathways exist beneath the monolith.

MEMO should be rerun with smaller, more representative transverse dispersivities. Based on theMEMO results, additional monitoring wells should be placed to offset those that currently exist in orderto provide at least a 95 percent confidence that any leaks will be detected. Since the groundwater isestimated to be moving at 0.5 ft/yr and the mean distance is approximately 350 ft, it could take up totwo years for the contaminants to move from the monolith to the site boundary. These relatively lowvelocities would suggest that only every other well would need to be sampled annually.

VII.D PLUME-MONITORING PLAN DEFICIENCIES

The review finds the Plume-Monitoring Plan deficient and far too limited in scope. As noted in theROD, the second objective of groundwater monitoring is to monitor the currently existing plume ofcontamination. An implicit argument in the RI, however, was that plume monitoring does not have to beparticularly intensive because concentrations are low once the plume is diluted within the alluvial aquiferand the river. This assertion cannot be supported without a

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properly designed monitoring program. The actual concentrations in the alluvial aquifer will remainunknown since the downgradient concentrations currently being observed may be on the plume fringesrather than on the centerline.

With respect to monitoring under a monitored natural attenuation remedy, OSWER Directive 9200.4states (p.22) that the monitoring program should be designed to accomplish the following:

• Demonstrate that natural attenuation is occurring according to expectations;

• Detect changes in environmental conditions (e.g., hydrogeologic, geochemical,microbiological, or other changes) that may reduce the efficacy of any of the naturalattenuation processes;

• Identify any potentially toxic and/or mobile transformation products;

• Verify that the plume(s) is not expanding (either downgradient, laterally or vertically);

• Verify no unacceptable impact to downgradient receptors;

• Detect new releases of contaminants to the environment that could impact the effectivenessof the natural attenuation remedy;

• Demonstrate the efficacy of institutional controls that were put in place to protect potentialreceptors; and

• Verify attainment of remediation objectives.

To address these issues, the groundwater monitoring program needs to be comprehensive. It isimportant to note that the OSWER Directive, in discussing the monitored natural attenuation alternativefor metals/radionuclides, only briefly mentions dilution as a mechanism to be relied upon to lowercontaminant concentrations in the groundwater. Only processes such as sorption and oxidation thatactually remove the contaminant from solution are discussed.

The passive nature of the remedial alternative for groundwater, which essentially relies solely on dilutionfor the long-lived radionuclides, makes extensive groundwater monitoring even more important. Unlessa credible understanding of the groundwater flow and contaminant processes can be developed, notonly will the true environmental impacts remain unknown, but a poor precedent will be set for futuremonitored natural attenuation remedies.

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VII.E SITE CHARACTERIZATION AND MODELING DEFICIENCIES

This review finds that the site characterization program does not sufficiently define site hydrogeologicconditions to support a passive groundwater remediation strategy. Site geology (upper aquifer soils andunderlying bedrock) may exhibit a great deal more variability and channeling characteristics than thesimplistic model presented in site documents. There are significant questions regarding the adequacy ofthe definition of the plume's characteristics (lateral extent, vertical extent, fate and transportcharacteristics). If one assumes that “institutional control” is plausible and allows for a passive naturalremediation process, EPA standards (40CFR192, Groundwater Standards for Remedial Actions atInactive Uranium Processing Sites, Final Rule) call for a demonstration that the natural remedy can meetgroundwater standards within a 100-year timeframe. Specifically,

for aquifers where compliance with the groundwater standards can be projected to occurnaturally within a period of less than 100 years, and where the groundwater is not now used fora public water system and is not now projected to be so used within this period, this rulepermits extension of the remedial period to that time, provided institutional control and anadequate verification plan which assures satisfaction of beneficial uses is established andmaintained throughout this extended remedial period,

andIf the Secretary determines that sole reliance on active remedial procedures is not appropriateand that cleanup of the groundwater can be more reasonably accomplished in full or in partthrough natural flushing, then the period for remedial procedures may be extended. Such anextended period may extend to a term not to exceed 100 years if: (A) The concentration limitsestablished under this subpart are projected to be satisfied at the end of this extended period,(B) Institutional control, having a high degree of permanence and which will effectively protectpublic health and the environment and satisfy beneficial uses of groundwater during theextended period and which is enforceable by the administrative or judicial branches ofgovernment entities, is instituted and maintained, as part of the remedial action, at theprocessing site and wherever contamination by listed constituents from residual radioactivematerials is found in groundwater, or is projected to be found, and (C) The groundwater is notcurrently and is not now projected to become a source for a public water system subject toprovisions of the Safe Drinking Water Act during the extended period.

This review finds that an expanded site hydrogeologic investigation is necessary to adequately define:(1) variability of hydrogeologic regimes, (2) fate and transport characteristics,

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(3) background, and (4) plume extent. After this investigation, a sufficiently rigorous and sophisticatedmodel could be developed to assess the ability of natural remediation processes to achieve remediationgoals within the specified maximum regulatory time period (100 years).

There are questions as to whether the remaining soils and aquifer materials within the plume havesufficient metals loading to act as a source. This review also finds that insufficient data exist to assess themagnitude of this source. Because the groundwater contaminant plume cannot be remediated“instantly,” there is a period of time where two possibilities arise: (1) the groundwater remains abovestandards despite the completion of the remedial action, but comes into compliance over somenon-established time period; and (2) the groundwater does not meet standards over any reasonableshort term because remaining soil and aquifer material release contaminants previously taken up(adsorbed, precipitated, exchanged, etc.). The re-introduction of contaminants could be caused by thechanged water quality resulting from site remediation. Improved contaminant transport models can beused to estimate a duration for plume remediation.

VII.F RISK ASSESSMENT DEFICIENCIES

The review finds that the remedy did not consider either a groundwater or a surface-water receptor.While land use on the site is restricted by deed, there are no apparent offsite legal land-use restrictionsthat would prevent Shattuck’s neighbors from using the groundwater and surface water. Therefore, asupplemental risk assessment should be performed that includes both groundwater and surface-waterreceptor scenarios. This supplemental risk assessment should consider maximum groundwatercontaminant levels with the understanding that the limited plume-monitoring system may not be sufficientto capture maximum contaminant concentrations. Also, appropriate release models and realistictime-variant infiltration rates through the cap and monolith are required.

Also, no ecological risk assessment has been done for the site. It is now standard practice to completesuch assessments.

VII.G SPECIFIC DESIGN TECHNICAL ISSUES THAT NEED TO BE RE-EVALUATED

Although the remedy has been implemented in accordance with the gist of the decision documents, thisreview finds that several technical issues apparently were overlooked in the

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original design. Since these design-related technical issues may affect the performance of the remedyover the 200-yr design life, these technical issues need to be addressed. They are:

• Water balance analysis• Potential for shrinkage cracking of GCL• Confirmation of hydraulic conductivity of RS/CL slope• Settlement

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VIII. Recommendations and Required Actions

Table 7 specifies the required and suggested improvements to current site operations. It notes theparties responsible for actions, milestone dates, and the agencies with oversight authority.

Table 7: Recommendations and Required Actions

RECOMMENDATIONS/REQUIRED ACTIONS

Institutional Controls

Performance Assessment Modeling of Cover/Monolith Design Long-term

Performance

Monolith-Monitoring Plan Upgrade

Plume-Monitoring Plan Upgrade

Development of a More Sophisticated Groundwater and ContaminantTransport Model to Assess Natural Attenuation

Develop Sufficient Site Characterization Data to Define Plume and SupportRisk Assessment

Conduct Risk Assessment

Specific Design Technical Issues

The following is a brief discussion addressing all deficiencies that currently affect protectiveness.

VIII.A INSTITUTIONAL CONTROLS

Protective fencing is currently around the site. However, the western portion was taken down by RTDduring their construction of the light rail line on the adjacent property and subsequently replaced byShattuck. It is important to note that Shattuck does not consider itself responsible for maintaining thesite fence and access control. The Record of Decision specifies that the owner will acquire deedrestrictions necessary to allow institutional protection of all site development. However, nothing seemsto be in place to prevent any vicinity property owners from developing groundwater resources in thetime frame it would take to remediate the contaminant plume.

Institutional control agreements should be enacted to control surface and groundwater usage. If thelatter is not feasible, the site remedy should be re-evaluated to address groundwater and surface waterin a pro-active manner, through both more definitive site characterization and possibly more aggressiveremediation strategies.

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VIII.B PERFORMANCE ASSESSMENT MODELING OF COVER/MONOLITHDESIGN LONG-TERM PERFORMANCE

From about 1918 to 1984, the site was used to receive and treat molybdenum ore, carnotite ore,vanadium ore, uranium ore, and radium salts. Other ores may have been received and treated inaddition to those documented. Much of the contaminated soils incorporated into the monolith isassumed to consist of ore and ore waste. These ores and ore-related wastes commonly contain varioussalts, including those of sulfate. The presence of sulfates and perhaps chloride salts in the ore calls intoquestion the long-term acceptability of the waste form. Constructed on site, the waste form (i.e.,monolith) consists of compacted layers of contaminated soil, cement, fly ash, and water. In the pilottreatability study, the soils were to be mixed at a ratio of 70:20:10 (soils: cement: fly ash), compacted toan ASTM standard value, and a moisture content to maintain a 0.4 ratio of water to cement. The studyresults indicate that, at least in the near-term, structural strength of the concrete meets the requirementsof the EPA in terms of compressibility and permeability. Toxicity Characteristic Leaching Procedure(TCLP) results were consistently close to or just below the groundwater ARAR limits for cobalt,chromium and vanadium, and higher concentrations than the groundwater ARAR limits formolybdenum. These tests confirm the near-term acceptability of the waste form, but do not address itslong-term performance as a part of the remedial system.

A review of concrete longevity in Service Life of Concrete (Clifton and Knab, 1989) and ConcreteLongevity Overview (Chang and Hasan, 1990) provide a basis for the concern over the long-termperformance of the monolith. Among the most common and destructive factors affecting concrete aresulfates in soil, groundwater, or seawater. The degradation caused by sulfate varies from minor surfaceerosion to complete loss of structural strength leading to total structural failure of the concrete (Changand Hasan, 1990). The most commonly found sulfate salts in soils are sodium sulfate, calcium sulfate,and magnesium sulfate. They are found in rocks as well as mineral deposits. Another destructive factorin concrete is the presence of chloride ions. Chloride ions are common in nature, and they exist in soil inthe form of chloride salts such as calcium chloride, magnesium chloride, and sodium chloride. They arefound in igneous rocks and sedimentary rocks. Particularly high levels of chloride ions are found inevaporates. In arid regions, the soil usually contains high chloride concentrations due to a highevaporation rate. Chlorides such as magnesium chloride and aluminum chloride react with time to formunstable and water-soluble compounds. Chang and Hasan, in a 1990 report, note that the presence ofchloride ions in concrete reduces its resistance to attack by sulfates in soils.

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While much of the research has focused on the external effects of sulfates in soil and groundwater, thesame deleterious effects are expected when sulfate-rich aggregates are used because all aggregates are,to a certain extent, chemically reactive with the cement paste. Aggregates (in this case the contaminatedsoil and other material) must conform to certain standards for optimum engineering use. They must beclean, hard, strong, durable particles free from deleterious coatings that could affect hydration andbonding of the cement paste. They must not be easily split and should have high resistance to the effectsof weathering.

Suitable aggregates do not contain deleterious substances that react chemically (e.g., sulfates andchlorides) to produce significant volume changes or harmful byproducts, or that interfere with ordinaryhydration of cement.

Given the history of the site, the waste quite possibly contains various sulfates and chloride compoundsthat would interfere with cement reactions. The only available data on sulfate content of the wastemixed into the monolith is related to testing samples used in the Pilot Scale Treat ability Study (EarthSciences Consultants, 1993). Three test feed materials were developed: 1) one with averageradioactivity (sulfate concentration of 1,440 mg/kg), 2) one with elevated radioactivity (sulfateconcentration of 2,390 mg/kg), and 3) one with elevated radioactivity containing building rubble (sulfateconcentration 4,400 mg/kg). Sulfate concentration data in adjacent soil and groundwater were notreviewed. Various organizations such as the Bureau of Reclamation (Concrete Manual, 1975) and thePortland Cement Association (Kosmatka and Panarese, 1988 and Guide to Durable Concrete, 1992)have developed guidance for the identification of the potential severity of sulfate attack and appropriateprecautionary measures but, this guidance is intended for use in concrete construction under ordinaryservice life conditions and may not necessarily be appropriate for long-term service life, such asrequired for hazardous waste containment (Klieger and LaMond, 1994). Never-the-less, if one appliesthe guidance (Guide to Durable Concrete, 1992) to the limited data, then a cement formulation that is atleast moderately resistant to sulfate attack would be required based on the “average soil” sulfateconcentration of 1,440 mg/kg. This does not consider the potential cumulative sulfate attack from theother external sources (i.e., groundwater and leaching from adjacent soil).

The pilot treatability study did not directly address these issues. The Shattuck site may be a very severeenvironment for long-term cement stabilization of the waste because of the various sulfates andchlorides in the site waste. As noted by Clifton and Knab (1989), “a site with a very severeenvironment is, undoubtedly, unfit for storing LLW in concrete vaults.” They go on to

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note that following design recommendations should result in a concrete with acceptable durability formany years, possibly for the 60- to 100-year design life of typical concrete structures. There is no basis(at the time of the report in 1989) for predicting the service life of a concrete exposed to a sulfateenvironment, especially in the case of a concrete with a design life of hundreds of years.

Also, the record of groundwater levels is relatively short compared to the period over which levels mustbe predicted; thus, there is not enough information to say with certainty that groundwater levels willremain below the base of the monolith, and the potential impact of changes in groundwater levels shouldbe evaluated via performance assessments.

Calculating the contaminant mass flux that is released from the monolith to the underlying vadose zonerequires the development of assumptions concerning (1) how waste is released for the waste form (i.e.,the monolith) and (2) the time-variant infiltration rate through the cap and monolith. Appendix F,“Groundwater Evaluation,” from the Shattuck RI design report includes a calculation of a so-called“reduction factor” that is used to demonstrate the effectiveness of the design with respect tocontaminant concentrations in the groundwater at the downgradient boundary. Essentially, thisapproach calculates a potential dilution rate rather than a release rate.

A more standard approach to calculating the mass flux of contaminants to the groundwater isrecommended. This approach, called the congruent dissolution release model, has been used by severalperformance assessments (PAs) and environmental impact statements (EISs) involving the disposal ofradioactive waste. The congruent dissolution release approach, combined with realistic time-variantestimates of infiltration rates through the cap, is recommended for reassessment of the Shattuck Site.Recent analyses involving the disposal of radioactive waste that have adopted the assumptionsassociated with congruent contaminant release include the Retrieval Performance EvaluationMethodology for the AX Tank Farm (DOE 1999), Performance Assessment of Grouted Double-ShellTank Waste Disposal at Hanford (Kincaid et al. 1995), and Tank Waste Remedial System, HanfordSite, Richland Washington, Final Environmental Impact Statement (DOE 1996).

VIII.C MONOLITH-MONITORING PLAN UPGRADE

Several monitoring wells surround the monolith, and these wells can be used to assess the elevation ofthe water table relative to the base of the monolith and to make periodic analyses of contaminants ofconcern. In a conservative sense, such monitoring may be adequate.

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Unfortunately, by the time any radionuclides and metals such as molybdenum and arsenic are detected,the chemical stability of the monolith will have been compromised. That is, there is no forewarning ofincipient chemical failure of the monolith. A more aggressive monitoring plan would be to expand the listof chemical constituents being analyzed to include sodium, potassium, magnesium, silicon, aluminum,and possibly other elements that might serve as a fingerprint for this particular fly-ash-cement-soilmixture.

This review finds that the site monitoring plan is not clear as to what constitutes a significant releasefrom the monolith and what actions are triggered by such releases. The monolith monitoring plan states,“A review of currently available chemical data suggests that the most reliable indicators of contaminantmigration from the monolith are likely to be molybdenum and uranium.” A Morrison-Knudsen (MK)sampling report dated May 7, 1999, indicates that MK compared the averages of the contaminantconcentrations in the upgradient wells with those in the downgradient wells and concluded that “At a95% level of statistical confidence, no difference was found in the average concentrations for radium orthorium. However, average uranium concentrations exhibit a significant difference between upgradientand downgradient wells at the 95 percent level of confidence.”

The report also concludes that, in general, molybdenum concentrations in the terrace wells are greaterthan the ARAR, while concentrations in alluvial wells are at or below the ARAR. This last conclusionimplies that as long as ARARs will be met in the downgradient monitoring wells, no further action isrequired. This is exactly why a remedial alternative based solely on dilution becomes so untenable. Itcould be argued that since dilution alone was good enough for the remediation of residual levels ofcontaminants currently in the groundwater, why not rely on it for releases from the monolith itself. Itshould be kept in mind that CERCLA statute 121D2B requires that the ARARs (e.g., MCL) be met atthe site boundary.

Trigger levels and remedial alternatives should be developed for addressing potential releases from themonolith, and the number of wells and the spacing of the wells should be re-evaluated per commentsmade regarding the MEMO program in Section VII.

VIII.D PLUME-MONITORING PLAN UPGRADE

The ROD specified that one of the objectives of the groundwater monitoring is to monitor the currentlyexisting plume of contamination. The ROD goes on to indicate that a network of wells will beestablished to monitor post remediation groundwater quality. We find that the current

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network of wells is insufficient to define the currently existing plume of contamination. Incorrespondence with the EPA, the USGS recommends that additional monitoring wells be installed andsupplementary constituents be analyzed. The USGS bases its recommendations on a general lack ofsite characterization data. It finds that the existing information is insufficient to define critical aspects ofthe contaminant migration, including vertical and horizontal extent of the contaminant plume, temporaltrends in the behavior of the plume, presence of preferential pathways, and the effect that the SouthPlatte River has on migration rates and directions.

The two basic objectives of the groundwater monitoring program are to (1) provide sufficientinformation from which both downgradient concentrations in groundwater can be established andoverall mass-loading rates to the river can be estimated, and (2) assess the degree to whichcontaminants are confined to the monolith and to detect any statistically significant releases prior tocontaminants migrating off site.

In augmenting the existing monitoring well network, the USGS recognized the need to identify the plumecenterline as well as the transient behavior of the plume. In so doing, the Survey incorporates threecross sections of wells perpendicular to groundwater flow. Clearly, additional data are needed; thequestion is, how can data needs be balanced against the overall objectives and the practicality ofperforming long-term monitoring of numerous wells.

In correspondence with the USGS, EPA posed the question of whether geoprobe sampling could bean alternative to several wells in a row and whether it could be used to define the plume and preciselylocate monitoring wells, thereby reducing the number of wells. In response to this suggestion, the USGSindicated that data from exploratory drilling would provide only a “snapshot” of the distribution ofcontaminants, which probably changes over an annual cycle and with year-to-year variations inrecharge of precipitation. Although the points the Survey makes are true, there are a number ofadvantages to collecting hydropunch samples in order to optimize the locations of future monitoringwells. These advantages including the following:

• Concentrations are far more representative of actual pore-water values, as they are not

integrated over the entire screened interval

• Hydropunch samples provide a much better three-dimensional view of the plume

morphology

• Hydropunch samples facilitate the identification of preferential pathways

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As the USGS notes, the concentrations will change with time; however, it is likely that the overall shapeof the plume will remain relatively constant. Therefore, defining the plume reasonably well byhydropunch sampling would facilitate the optimization of the monitoring well placement.

We recommend that a downgradient geoprobe investigation should be conducted in order to establishthe general three-dimensional shape of the plume.

Once the morphology of the plume is established, a numerical modeling study should be performed inorder to optimize the placement of the monitoring wells. Factors that need to be considered includeplume dispersion, contaminant velocity, nature of the source release (e.g., pulse or continuous),presence of preferential pathways and sampling frequency. A number of computer programs aredesigned specifically for this purpose.

Since metals/radionuclide speciation and mobility are very dependent on the presence or absence ofoxygen, dissolved oxygen and Eh should be measured in the monitoring wells.

Once the extent of the existing plume is determined, an assessment should be made as to whether amonitoring well should be placed on the other side of the South Platte River.

The presence of dissolved uranium (in some cases in exceedance of the ARARs) and othercontaminants in monitoring wells USE 1 through 5 will make it difficult to ascertain whether releasesfrom the monolith have occurred. The problem is further exacerbated by the means outlined in theMonitoring Plan for determining whether a release has occurred. The MP directs that statisticalcomparisons be made to determine whether there are significant differences in chemical concentrationsbetween downgradient and upgradient monitoring wells. This method could mask releases ifconcentrations in the upgradient monitoring wells rise with time.

As noted, the high uranium concentrations in the upgradient wells suggests that water quality in thesewells may be impacted by wastes still remaining in place (i.e., beneath Bannock Street). Furthermore,at least two mechanisms exist that could lead to a reversal in groundwater gradients and could place theexisting background wells directly downgradient from the source. First, future recharge through themonolith could create a groundwater mound, in which case flow from the monolith would be in a radialdirection. Second, a rise in the water table could intersect the monolith, which would, in turn, act as ahydraulic barrier and potentially reverse the groundwater gradients.

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We recommend that a hydropunch investigation be performed to establish background locations.Additional background wells should be installed. Trends should be assessed statistically, not onlyagainst the background wells, but also against the downgradient wells through time.

VIII.E DEVELOPMENT OF A MORE SOPHISTICATED GROUNDWATER AND

CONTAMINANT TRANSPORT MODEL TO ASSESS NATURAL ATTENUATION

The Remedial Investigation presents a very simplistic approach to predicting the amount of dilution ingroundwater downgradient from the monolith. This type of analysis is more suited to a scoping typeexercise than in support of a full blown risk assessment.

The analysis performed with regard to the large dilution rates attributed to the South Platte River andcited in the Remedial Investigation should be presented. However, metals do not always stay in solutionand can precipitate as stream sediment. For example, in studies of molybdenum geochemistry in thestream system draining the Climax area of Colorado, Kaback and Runnels (1980) found that themolybdenum was precipitating out of solution. Furthermore, even if molybdenum stays in solution ittends to accumulate in vegetation and if present in excessive amounts can cause problems for grazinganimals (Dye and O’Hara, 1959).

We recommend that a numerical model of the groundwater flow system be constructed in order toobtain more reliable estimates of dilution, and groundwater flow rates and directions.

Stream sediment from the South Platte River should be sampled. Contaminant concentrations inadditional monitoring wells placed close to the river could be used to select sampling locations andanalytes. The actual origin of any contaminants detected may be difficult to establish. However, ifcontaminants are not detected, it would eliminate the sediment as an exposure route. The potentialeffects of bioaccumulation of metals in plant and animal tissue needs to be investigated as part of anEcological and Human Food Chain Risk Assessment.

The contaminant transport model depends on two fundamental sets of data - hydrogeology andwater-aquifer chemical reaction (chemistry of attenuation). In the case of the Shattuck site, neither thehydrogeology nor the nature of the chemical reactions within the aquifer has been adequatelycharacterized. Thus, the contaminant transport model is vastly oversimplified and, as such, is a poorbasis for eliminating the groundwater exposure path from the risk assessment. The groundwaterexposure path cannot be eliminated based on current information about the contaminant plume.

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Multiple problems underlie the hydrologic model for the Shattuck site. Uncertainties in the sitehydrogeologic and transport model include (1) incomplete knowledge of quality of infiltrating surfacewater, including any source that might result from monolith leaching; (2) extent of groundwaterinteraction with Platte River flow system; (3) seasonal changes in surface water groundwaterinteractions in the area including the Overland Golf Course holding ponds, (4) lack of any sensitivityanalyses on variables including dispersivity, flow rate, hydraulic conductivity; (5) assumption of ahomogeneous aquifer with no allowance for channeling; (6) lack of control points in several key areas;(7) poor understanding of bedrock-alluvial hydrologic interactions; (8) no allowance for contaminantattenuation; (9) no evaluation of the effect of a catastrophic hydrologic event (dam failure, 200-yearstorm etc.) on plume behavior; (10) lack of prediction of effect of groundwater use on hydrology andcontaminant plume; and (11) lack of a consistent set of chemical analyses and a manageable data basefor monitoring wells.

Only one surface water sample from a runoff catchment basin was analyzed. For this sample, onlygamma activity, indicating Ra-226, and/or elevated natural uranium was determined; other constituents,such as metals and organic compounds, were not determined. Thus, the characterization of the surfacewater quality was incomplete. Exposure risk from surface water cannot be eliminated if the data basefor assessing the water quality is so small.

VIII.F DEVELOPMENT OF SUFFICIENT SITE CHARACTERIZATION DATA TODEFINE PLUME AND SUPPORT RISK ASSESSMENT

The Remedial Investigations Report shows that 76 soils (combining surface and subsurface) wereanalyzed, but only 14 of these were analyzed for a set of metals, including Al, Sb, As, Ba, Be, Cd, Ca,Cr, Co, Cu, Fe, Pb, Mg, Mn, Hg, Ni, K, Se, Ag, Na, Th, V, Zn. No tungsten analyses were included(see above). Surprisingly, only one soil was analyzed for molybdenum (Mo), and the balance wereanalyzed only for As and Se consistently, and Hg, Ag, V, Cr, Cu, Pb, Cd on occasion. It is unclearwhy As and Se were selected for such detailed analysis, and why molybdenum was ignored given theplant's history of processing molybdenum ore. An inventory of the data presented in the RemedialInvestigations Report shows that 55 samples were used to characterize the radioactive materials, 69samples were used to characterize the distribution of arsenic and selenium, 29 samples were used tocharacterize a heavy metal suite including Hg, Ag, V, Cr, Cu, Pb, Cd, and one sample was analyzed formolybdenum. Molybdenum was subsequently eliminated as a metal of concern for the soil exposurepathway. Exposure risk from soil exposure cannot be eliminated if the data base for assessing the soilquality is so small.

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The derivation of the list of toxic metals in the Baseline Risk Assessment eliminates copper, cadmium,rhenium, and silver. Given that maximum soil copper concentrations are almost 300 times abovebackground and average copper concentrations are 100 times above background, why was coppereliminated from the Risk Assessment?

Inadequate data have been provided to demonstrate that particular metals or organic compounds areoriginating from the site. Verbal and written reports that the copper and chromium in groundwateroriginate from other offsite industrial activities cannot be confirmed from current data. Given theadmitted gaps in the site's own waste management history, a more specific identification of otherpotential contributions to the site groundwater degradation should be conducted.

The Construction Completion Report shows that soil quality was monitored by gamma radiation, withsamples taken to confirm that Ra-226 was below 15 pCi/g. However, as discussed, monitoring for onlya limited suite of metals took place; thus, the data are inadequate for determining both the original extentof non-radioactive metals contamination as well as the post-remediation distribution of metals.

Although in a gross sense it is true that removing radium contaminated soils would also likely removeother metals, this cannot be stated with certainty (nor do the site documents make such a case).Recognize first, metals in the soils probably did not originate from similar sources: ores of molybdenumand uranium, for example, are geochemically completely different. Second, we are not sure to whatdegree mine-site enrichment occurred for the ores. Assuming that metal waste was deposited onto thesoils over an extended period (tens of years) then it is likely that normal geochemical processes,including aging, surface water infiltration, and natural attention will have dispersed the metals through thesoil in a chromatographic-like pattern (as a simple analogy). As such, it is a gross oversimplification toconsider that the limited monitoring will provide 100 percent certainty that all metals have beenremoved. An uncertainty remains with respect to the quality of the remaining soil.

Finally, no deep soil samples were analyzed, nor were any samples recovered from below the watertable (i.e., soil and aquifer materials from within the contaminant plume). This is a critical piece ofinformation for assessing the potential of the aquifer itself to act as a source by releasing previouslyadsorbed/precipitated metals back to the water. Achieving the groundwater remediation goal dependson the natural attenuation of contaminants; that is, contaminated water will deposit metals onto theaquifer materials, thereby removing contaminants from the water.

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However, the chemical processes involved in attenuation are all reversible, to a greater or lesser extent.Much of the adsorptive capacity of an aquifer is determined by a combination of water pH and Eh andaquifer mineralogy - notably its clay mineral type and content, the presence of organic material, and thepresence of iron and manganese hydroxides. If water pH and Eh change, previously adsorbed metalscan be released (see technical notes below).

Aquifer mineralogy is unknown beyond simple visual observations, no attempt has been made todetermine total metals loading within the aquifer, and no attempt has been made to determine thepartitioning of any metals among the different mineral fractions. Without such data, it is premature toeliminate the aquifer as a source during risk assessment and it is premature to assume that the aquiferhas the capacity to attenuate all contaminants effectively over a 100-year period.

Attenuation of a contaminant involves multiple processes, including dilution by simple physical mixingand dispersion and removal from the water by several types of chemical reactions, including adsorption,ion-exchange, solid phase precipitation, and co-precipitation. Because of aquifer heterogeneity withrespect to organic matter content and proportions of minerals with significant adsorption andion-exchange capacities, the normal procedure is to determine an empirical attenuation factor or Kd fora given site. To expect attenuation to be a simple process that has a linear dependence on time is a vastoversimplification.

A pro-active approach is recommended; that is, the better our understanding of the complexities of thegroundwater-soil aquifer geochemistry, the higher confidence we will be able to place in the naturalattenuation remedy and the less vulnerable to unanticipated plume behavior impacts.

VIII.G CONDUCT RISK ASSESSMENT

The EPA, DOE, DOD, and NRC have developed a multi-agency approach to performing the finalradiation survey to prove that the cleanup criteria at radiation sites are met (see the Multi-AgencyRadiation Survey and Site Investigation Manual (MARSSIM), NUREG -1575, EPA 402-R-97-016,December 1997).

Also, EPA has developed new cleanup levels for radionuclides in soil for Superfund sites. An August22, 1997, OSWER Memorandum (OSWER No. 9200.4-18) states that the maximum radiation doselimit for humans at Superfund sites should be 15 mrem/yr effective dose equivalent (EDE) from allradionuclides and exposure pathways. This limit is based on a site-

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specific dose assessment and is dependent on the site-specific radionuclides and exposure pathways.

A cursory review of the soil concentrations remaining after cleanup indicates that the site does not meetthe new EPA cleanup criteria, and that the doses could be well above acceptable levels.

There were also some changes in MCLs between the time of the risk assessment and the time of thefinal remedial design. However, these changes were taken into account before the implementation of thefinal design. Since 1996, the guideline for arsenic has changed, but the change in magnitude was of noconsequence to the RA or remedial design.

A current risk assessment would be appropriate given the design life of the remedy (200 to 1,000 yrs),the potential for recreational use near groundwater discharge points along the Platte River, potentialfuture groundwater use, and the potential for additional surface-water use from nearby ponds.However, at present, data are insufficient to support a credible risk assessment. The necessary stepsinclude a better definition of the aquifer, expansion of monitoring data, collecting additional ecologicaldata, reviewing appropriate conceptual models, calculating contaminant concentrations in groundwater,and calculating risk. An updated assessment should include the following:

• An ecological risk assessment• A residential groundwater user scenario• A recreational surface water user• A release from the monolith under conditions that could include fracturing and degradation

of the cap

VIII.H SPECIFIC DESIGN TECHNICAL ISSUES

Relatively recent studies concerning water balance modeling indicate that commonly used water-balance models, such as the HELP model which was used in the design of the cover system, have atendency to overpredict overland flow and, thus, underpredict percolation through the cover system,particularly in semi-arid or arid sites subject to snow cover and snow melt (e.g., Khire et al. 1997).This overprediction in overland flow has been attributed, in part, to the inability of the models toaccurately reflect the thermal conditions in the soil. This finding is of particular concern for the Shattucksite due to the semi-arid nature of the climate and the large snowfalls that often occur in the spring (i.e.,March and April). These snowfalls commonly occur over relatively short durations (24-48 hrs), and arefollowed by a warming period that results in rapid

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melting (personal observation). In this case, the ground may not be frozen, resulting in a large pulse ofinfiltration into the cover system, even though the annual precipitation may be low.

We recommend that a more extensive water-balance analysis be performed to account for the potentialsnowmelt problem, possibly using two or more models with reference to the cited publication.

Recent comments by Shattuck (Shattuck Response Document, October 15, 1999) define the Shattuckfinal cover as “Resistant-Armored” and, as such, it is stated that the cover “...acts as a one-way” valvein that water can get in but cannot be removed by surface runoff or evapotranspiration.” Maximizationof both surface runoff and evapotranspiration would result in minimization of infiltration of water into theunderlying monolith, and subsequent leaching of potentially harmful chemical constituents, into theunderlying groundwater. Thus, the above stated inability of the cover system to provide for surfacerunoff or evapotranspiration of water supports the contention that the cover system is inadequate tosustain the long-term performance of the selected remedy. Furthermore, Shattuck consultants confirmthat “All the models require significant tweaking to accurately present armored final covers.” andsupports the review comment in that a much more site-specific modeling be conducted.

A key component in the overall performance of the cover system is the GCL. Research has establishedthat GCLs can maintain their integrity throughout a reasonable magnitude of differential settlement, aswell as environmental factors such as wet/dry cycles and freeze/thaw cycles. However, some evidenceindicates that divalent (e.g., calcium) for monovalent (e.g. sodium) ion exchange within the bentonitecomponent of the GCL can lead to cracking of the GCL, resulting in poor performance and even failureof the GCL.

For example, James et al. (1997) investigated the cause of leakage through GCLs that were used in acover system for brick arches to protect water reservoirs. The exchange complex of the bentonite in theGCL was initially dominated by sodium with a cation exchange capacity (CEC) of 90.2 meq/100 g.After leakage was observed in the field, tests on exhumed specimens of the GCL indicated that theCa2+ concentrations on the exchange complex increased substantially, whereas Na+ concentrations onthe exchange complex decreased substantially. Based on these data and other tests, James et al. (1997)concluded that calcium from the foundation soil and overlying cover soils had migrated into the GCLand displaced the sodium from the exchange complex, which resulted in subsequent shrinkage andcracking of the bentonite. Similar results

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also have been reported elsewhere (Aboveground Tank Update 1992, and Dobras and Elzea 1993).

We recommend that specimens of the GCL in the cover system be exhumed and examined forshrinkage and cracking, tested for exchangeable cations and CEC, and tested for hydraulicconductivity. The results of these tests should be compared to the results of the same tests performedon unexposed specimens of the same GCL. Of course, any place where specimens have been exhumedmust be retrofitted to a satisfactory condition. As an alternative to exhumation of intact GCL specimens,complete chemical analyses of all of the materials (riprap, sand, gravel, recompacted soil/clay liner, etc.)used in the cover system should be performed to evaluate the potential for an adverse ion-exchangeeffect on the GCL. As a minimum, these chemical analyses should include, where appropriate, solublesalts, exchangeable cations, CEC, soil pH, and soil electrical conductance. All of these tests should beperformed using unexposed materials, since the materials at the site have undoubtedly already beenexposed to some washing from precipitation.

Recent comments provided by Shattuck (Shattuck Response Document, October 15, 1999) regardingthe potential for cation exchange in the bentonite of the GCL and the subsequent increase in hydraulicconductivity do not address the washing of soluble salts from the overlying gravel and riprap into theunderlying clay that may have occurred during the first wetting event after placement of these materials.Also, the theoretical analyses performed to evaluate the potential for cation exchange do not considerany site-specific data regarding chemical concentrations of pore waters, and no mention is made of thepotential for cation exchange resulting from the soluble salts in the pore water of the underlying RS/CL(i.e., as opposed to the underlying monolith). Finally, the value of 25 percent for the porosity of thebentonite in the GCL used in the Shattuck Response Document’s theoretical analysis may besignificantly in error. For example, Petrov and Rowe (1997) present data that indicate the porosity ofGCLs can range from 50 to 80 percent depending on hydration and applied stress conditions. The onlyway to alleviate the concern with respect to the long-term performance of the GCL is to perform teststhat use site-specific materials and conditions as recommended.

The review team perceived two major issues related to the performance and integrity of therecompacted soil/clay layer (RS/CL) used in cover system. First, the RS/CL is relatively thin (15 cm).Benson and Daniel (1994) have shown from case histories that the hydraulic conductivity of compactedclay liners decreases as the thickness of the liner increases from 15 cm (6 in) to 90 cm (36 in), withunacceptably high (> 10-7 cm/s) hydraulic conductivities for the thinner liners.

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This effect of thickness on hydraulic conductivity is usually attributed to continuity of cracks resultingfrom desiccation and lack of proper construction quality control. Second, the hydraulic conductivity ofthe RS/CL was based on only laboratory tests using small-scale specimens. However, standardpractice for evaluating the hydraulic conductivity of compacted clay barriers requires either fieldhydraulic conductivity tests performed on test pads (Daniel 1990) and/or laboratory tests performed onlarge-scale specimens ($ 30 cm) (Benson et al. 1994) recovered from test pads due to the potentialeffect of scale on the hydraulic conductivity of the compacted clay. Thus, there is concern about theoverall integrity of the RS/CL in the cover system.

We recommend that the hydraulic conductivity and the associated performance of the RS/CLcomponent of the cover system be re-evaluated.

Recent Shattuck comments (Shattuck Response Document, October 15, 1999) neglect the importanceof the 6-inch RS/CL layer on the overall performance of the cover system. For example, it is stated thatthe permeability of the 6-inch thick portion of the RS/CL is considered to be “...of secondary value”,yet the permeability of this soil was measured in the laboratory, and we assume the measured value wasused in the HELP analysis for the water balance calculations. Also, Shattuck data supports theobservation that the hydraulic conductivity of 6-inch (15-cm) compacted clay barriers tend to rangefrom about 10-6 cm/s to as high as about 10-4 cm/s, depending on the quality of construction. Thus, theactual field hydraulic conductivity for the 6-inch RS/CL layer may be as much as 10 to 1000 timeshigher than previously assumed on the basis of the laboratory measured hydraulic conductivity values.Also, the 6-inch RS/CL layer is subjected to a greater potential for infiltration and subsequent leachingof underlying contaminants since the 6-inch layer is on a flatter slope and covers a greater surface area.Thus, prudence dictates that the primary focus of the evaluation be placed on the 6-inch thick RS/CL,not the thicker and steeper side slopes, particularly with respect to the long-term (200+ years)performance of the selected remedy.

Last, given the magnitude of the project and the potential for detrimental environmental consequencesresulting from cracking of the monolith over the design life of 200 years, the Review Team recommendsthat a system of settlement markers be installed to monitor the actual settlement of the monolith.

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IX. Protectiveness Statement(s)

Clearly, the site remedy has significantly improved the overall protectiveness of human health and theenvironment over the short term. However, there are technical findings that raise doubt about thelong-term effectiveness and permanency of the site remedy and the concomitant ability of the site tomeet the optimization and institutional control requirements inherent within the remedy.

The review finds that the offsite impact of the degraded groundwater plume has not been covered byany formal institutional control. Shattuck does not consider itself responsible for ensuring offsite landuse, and the state/city governments have not provided definitive assurances of institutional controls forthe life of the remedy specified in the ROD (200 years).

Also, the review finds that the public’s goals were not adequately assessed and reflected in the RODand the remedy. While some of the stakeholders may be comfortable with long-term restrictions anddiminishment of resource usage, the community does not share this sentiment, and the community’sviews deserve attention.

We recommend re-evaluating the site remediation concept to ensure that community land-use goals areunderstood and protected. The re-evaluation should be supported by more rigorous performanceassessment modeling relative to monolith integrity over the long term. We also recommend that thegroundwater pathway be considered a viable pathway and that a risk assessment be completedaccordingly to allow for accurate assessment and evaluation of the overall site remediation strategy.This will require a sufficient database of site characterization information (hydrogeology, ecology, soiland groundwater samples, etc.).

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X. Next Review

This Five-Year Review recommends that the remedy be re-evaluated and that additional responseactions be considered. Based on the information available, the review finds that it is unclear whether theremedy will meet cleanup levels for contaminants of concern within the specified 100-year periodidentified as the maximum allotted time for material flushing to achieve clean-up criteria. Thus, thereviewers believe that the remedy must be re-evaluated because the plume and its impact on thegroundwater and surface pathways have not been sufficiently addressed.

This report documents findings of inadequacies and inefficiencies in current site operations and designpresentations. In particular, it identifies deficiencies that currently prevent the remedy from beingconsidered protective in the future. These deficiencies include changes needed to ensure the propermanagement of the remedy. They are documented in Section VII, indicating which need to becorrected to achieve protectiveness.

Based on these findings, it is recommended that after additional data become available that address theissues raised in this review, another review be conducted.

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XI. References

The references cited in the text are given in Appendix A.

APPENDIX A

EXPERT PANEL REVIEW

Table of Contents 1. Introduction 1-1 2. Approach 2-1 3. Expert Panel Comments 3-1 4. Documents Reviewed 4-1

i

1. Introduction The peer review summary report is presented herein and includes all materials considered by the Peer Review Panel. Information about the peer reviewers themselves is also presented in this section. Section 2 contains information about the conduct and approach of the peer review, along with an explanation of the "charge" questions submitted to the Peer Review Panel. Included Section 3 of this report are the panel's written comments, as well as materials received from the peer reviewers in support of their response to the "charge" question. The peer process review has been designed to provide the foundation for the five-year review. More information about the documents considered and reviewed as part of the expert panel review is presented in Section 4: "Documents Reviewed." The expert panel reviewed the major documents in the administrative record for the Shattuck record of decision (ROD) in accordance with the Agency's Peer Review Handbook (EPA 100-B-98-001), January 1998. Section 4 includes a bibliography of all documents reviewed by one or more members of the panel. The peer review process is one type of peer involvement through which EPA augments its capabilities by inviting experts from outside EPA to become involved in discerning whether EPA has met two important criteria: (1) whether the remedy is based upon the best current knowledge from science, engineering, and other domains of technical expertise; and (2) whether the remedy decision is supported by the technical documents prepared for the administrative record. Sanford Cohen & Associates (SC&A) met all the responsibilities of the "peer review leader" as that role is defined in the handbook. In this role, SC&A received periodic input during the peer review process from representatives of the community stakeholders to ensure that the charge questions in this document fully express their concerns. As peer review leader, SC&A took no further technical direction from EPA Region 8 after this assignment was accepted and the work plan was written. Selection of the external peer reviewers, facilitation of review meetings, preparation of the peer review report, and presentation of the review findings were completely under the control of the SC&A Peer Review Team Leader, John Darabaris, with no influence or control from EPA Region 8. Mr. Darabaris is a geologic engineer with significant experience in EPA-ORIA assignments (WIPP) and EPA-OSW RCRA Corrective Action and Permitting Actions. He also has significant CERCLA Environmental Restoration experience relative to the DOE complex and has served in lead roles on prior peer reviews. Mr. Darabaris was assisted by a Peer Review Panel of multidisciplinary experts. The areas of technical expertise on the Peer Review Team included:

• Construction Representative/Geotechnical Engineer to focus on general site conditions

• Process Engineer to focus on groundwater/leachate collection and treatment

• Civil Engineer to focus on the stabilized/solidified monolithic waste form and composite clay cover design and construction

1-1

• Hydrogeologist to focus on the adequacy of aquifer characterization and remediation approach

• Geochemist to assess the fate and transport of radiological contaminants and hazardous

waste contaminants

• Risk Assessor to evaluate the baseline risk assessment and assess the impact of changes of ARAR since the ROD and Remedy Implementation, as well as conduct additional scoping analyses as deemed necessary

The following staff were selected by SC&A as subject matter experts. Dr. Alien Hatheway was designated as the Construction/Geotechnical Engineering Representative on the Peer Review Panel. Dr. Hatheway has over 38 years of professional experience in environmental management and geotechnical options; exploration program design; hazardous and special waste management facility siting, design and permitting; site and waste characterization and remedial engineering for uncontrolled sites; seismic risk assessment; hazards mitigation; rock engineering and underground construction; critical facility siting; and expert testimony. In addition to university teaching, research, and consulting, he served in senior technical management positions in respected geotechnical consulting firms for 12 years. Mr. Phillip Rogers was the Process Engineer on the Peer Review Panel. Mr. Rogers is a Professional Engineer with over 23 years of experience. This includes the development of complex conceptual and numerical models that capture various processes such as preferential flow in the vadose zone, the effects of tank waste chemistry on radioisotope mobility, alternative end state configurations, and infiltration. He has extensive experience with Comprehensive Environmental Response Compensation Liability Act (CERCLA) and Resource Conservation and Recovery Act (RCRA) projects including hazardous and municipal waste landfills, mine waste, mixed wastes, and petroleum contamination at Air Force bases. Mr. Rogers managed and was the principal author of the hydrogeologic impact sections and sensitivity analysis appendix of the Retrieval Performance Evaluation Methodology for the AX Tank Farm (U.S. DOE, DOE/RL-98-72, April 1999). For this report, he successfully managed and implemented the detailed evaluation of the hydrogeologic impacts of retrieval and closure of high-level radioactive waste tanks at DOE's Hanford Site. Dr. John W. Goode was designated as the Risk Assessment Specialist of the Peer Review Panel. Dr. Goode has a Ph.D. in toxicology. He has 26 years of management, technical, and business-related experience in a broad range of environment, health, and safety areas. As an EPA contractor, Dr. Goode is the lead inspector in determining the compliance of the major nuclear waste sites in the United States that will eventually ship waste to the Waste Isolation Pilot Project near Carlsbad, New Mexico Dr. Goode has managed or participated as a senior investigator in major risk assessment and exposure information projects, including management of a screening-level human health risk assessment for direct and indirect exposure to combustor emissions for chemical agent incinerators located at the Tooele Army Depot in Utah. Dr. Goode has also managed a risk assessment on the closure of the 2101-M pond at Hanford. He validated analytical data generated by U.S. Testing and provided a risk assessment model suitable for submittal to the Washington Department of Ecology.

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Dr. Steven Schaffer was designated as the Aquatic Biologist for the Peer Review Team. Dr. Schaffer has a Ph. D. in Biology/Environmental Health Science from New York University. Dr. Schaffer is a senior scientist responsible for a wide variety of ecological, health, and regulatory activities, and has lead responsibilities for SC&A's chemical risk assessment business. He managed a project that produced the Environmental Impact Statement and Regulatory Analysis in support of NRC's decommissioning standards. He is also responsible for SC&A's technical training business, which offers seminars to industry and government concerning risk assessment, environmental chemistry, and quality control. Dr. Schaffer also performed several studies for the EPA concerning the risks and hazards of both chemical and radiological agents in waste. Dr. Charles Shackelford was designated as the Civil Engineer on the Peer Review Panel. Dr. Shackelford is a professor of Civil Engineering at Colorado State University with more than 20 years of experience. He has participated in numerous expert panels, specializing in closure design issues. Mr. Dave Back was designated as the hydrogeologist for the Peer Review Team. Mr. Back has over 14 years of experience reviewing and evaluating hazardous and nuclear waste disposal technologies; performing groundwater contamination assessments; developing and implementing remedial measures and evaluating remedial effectiveness; conducting aquifer tests, geophysical surveys, tracer tests, and soil and water sampling; performing numerical and analytical simulations of groundwater flow and contaminant transport; and implementing quality assurance and quality control procedures. Mr. Back has been the lead author of several EPA/DOE/NRC joint guidance documents developed to facilitate the selection and application of groundwater models at Federal facilities, EPA sites, and low-level waste sites. Dr. Wendy Harrison was designated as the Geochemist, providing fate and transport expertise for the Peer Review Panel. Dr. Harrison, a professor at Colorado School of Mines with over 20 years of experience, has participated in numerous peer review panels.

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2. Approach Table 2.1 identifies the key documents that were initially forwarded by the EPA and Colorado Department of Public Health (CDPH) for peer review and the panel members responsible for reviewing those documents. All panel members were given access to all documents. Many additional document reviews were conducted as necessary, based on a review of EPA and CDPH files. The Peer Review Panel was given complete cooperation and full access to these files. A complete bibliography of documents reviewed by panel members is presented in Section 4.

Table 2.1 Initial Documents Forwarded by EPA for Peer Review J.

Darabaris J.

Goode S.

Schaffer D.

Back W.

Harrison P.

Rogers A.

Hatheway C.

Shackelford ROD √ √ √ √ √ √ √ √ ATDSR √ √ √ √ √ RI √ √ √ √ √ √ √ √ Hydrogeology (1)

√ √ √ √ √

Hydrogeology (2)

√ √ √ √ √

Five-year Guidance

√ √ √

Peer Review Guidance

√ √ √ √ √ √ √ √

Risk Assessment

√ √ √

Modeling √ √ √ √ MK Sampling Report

√ √ √ √ √ √

TCLP √ √ √ √ √ Construction Report

√ √ √ √ √

In addition, several of the panel members (Mr. Darabaris, Mr. Rogers, Dr. Shackelford, Dr. Hatheway, and Dr. Harrison) participated in tours of the site. The peer review process started when the EPA requested the SC&A Peer Review Team to answer the three key questions for the technical assessment to be conducted during the five-year review. To answer these questions, the Peer Review Panel followed several steps. The process included a review of applicable or relevant and appropriate requirements (ARARs) and the factors used to develop site-specific, risk-based levels. Through the document review, the peer reviewers were able to determine the full scope of the remedy, its goals, and its current status. Since construction is complete, pertinent documents were reviewed to determine the following:

• Remedial action objectives and cleanup levels specified in the ROD and other decision documents

• The remedial actions and their design

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• Any changes to the assumptions underlying cleanup levels (e.g., ARARs, contaminant characteristics, and potential exposure)

• The status of the implementation of the remedy and O&M • The status of the implementation and enforcement of institutional controls

• The effectiveness of the remedy in meeting remedial action objectives

Each reviewer was asked to focus his review towards answering the three key questions. Question A: Have conditions external to the remedy changed since the remedy was selected? To determine whether conditions external to the remedy have changed, the following five sub-questions were posed. Although the five questions are inter-related, each question was treated as essentially independent. An affirmative answer to any sub-question was considered an affirmative answer to Charge Question A and led to a recommendation for additional work, as noted in the right-hand column of Table 2.2. A negative answer indicated that no additional action is necessary on that specific question.

Table 2.2 Five Questions to Determine if Conditions External to the Remedy Have Changed

Question If Yes, Question 1: Has land use or expected land use on or near the site changed? (e.g., industrial to residential, commercial to residential) Question 2: Have any human health or ecological exposure pathways changed or been newly identified? (e.g., dermal contact where none previously existed, new populations or species identified onsite or near the site) Question 3: Are there new contaminants or contaminant sources? Question 4: Are there unanticipated toxic byproducts to the remedy not previously addressed by the ROD? (e.g., byproducts not evaluated at the time of remedy selection)

The SC&A Peer Review Team will request that the risk assessor perform a risk evaluation (risk recalculation or new risk assessment). Depending on the results of the risk evaluation, additional response actions may be needed.

Question 5: Have hydrologic/hydrogeologic site conditions changed? (e.g., changes in anticipated direction or rate of groundwater flow)

Check impact on remedy. May require changes to groundwater monitoring remedy or additional response actions.

Question B: Has the remedy been implemented in accordance with decision documents? In answering Question B, the SC&A Peer Review Team evaluated the ability of the remedy to achieve the goals stated in the ROD and other decision documents. In this way, the remedial action objectives were evaluated.

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Shattuck is a fully operational and functional remedial action site that includes groundwater monitoring components that require more than five years to complete. The time frame is particularly relevant at Shattuck since groundwater and surface water restoration apparently depends on allowing a passive remedy (i.e., natural attenuation) to occur. The greater than five year time frame may also apply to the bioremediation remedy for the oily soils encountered at the site. The SC&A Peer Review Team first determined the scope of the action by reviewing the Construction Completion Report. The SC&A reviewers also examined other documents, including the ROD and follow-up reports (such as the plume and monolith monitoring plans), to better understand the scope and technical detail of the remedial action. Following this initial review, the remedial action was assessed through the review of additional documents, as appropriate. The assessment included the following:

• Review of documents - such as the Construction Completion Report, along with decision documents such as the ROD and ESDs

• Confirmation that measures are in place and effective - the access (e.g., fencing and/or

security guards) and institutional controls needed at this stage of the remediation are in place and effective, and other actions (e.g., removals) necessary to ensure that immediate threats have been addressed are complete

• Confirmation that the remedial action continues to be operating and functioning as

designed - the remedial action is performing as expected in achieving cleanup goals • Evaluation of system operations - operating procedures, as implemented, will maintain

the effectiveness of response actions, at least to the extent that protectiveness is assured • Identification of opportunities for optimization - opportunities to improve the

performance and/or reduce the costs of monitoring, sampling, and treatment systems • Check for early indicators of potential remedy failure - problems that could lead to

remedy failure or that show that protectiveness is at risk unless changes are made; for instance, telltale geochemical signatures of decomposition of the stabilized, solidified waste form, or unusual radon gas emission from the cap

Question C: Has any risk information changed since the remedy was selected? To determine if any risk information has changed, the SC&A Peer Review Team identified and evaluated any changes in promulgated standards or toxicity factors and other contaminant characteristics used to calculate risk. In answering Question C, the panel also examined the cleanup levels and other requirements to assess whether they were still protective of human health and the environment. Cleanup levels are based on ARARs (levels based on promulgated standards) or on calculated risk (site-specific risk-based levels). The SC&A Peer Review Team identified and reviewed changes in

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ARARs, and in the case of site-specific risk-based levels, changes in contaminant characteristics or other factors used to set these levels. Standards and data relevant to ecological receptors as well as to human health were reviewed. When a more stringent ARAR or more stringent risk information was found, the review team evaluated whether a risk should be recalculated to determine whether the risk posed by the current cleanup level remains acceptable. Although some ARARs were "frozen" at the time of ROD signature, new or changed ARARs were examined to determine if they call into question the protectiveness of the remedy. New or revised chemical-specific requirements, such as Federal or State drinking water maximum contaminant levels (MCLs), were also reviewed. In addition, the panel reviewed changes in action and location-specific requirements related to the protection of human health and the environment. For instance, changes in State requirements for landfill construction, new requirements for the protection of habitat, and State requirements prohibiting construction of landfills in flood plains without specific controls to prevent flooding, were reviewed. However, only those ARARs that addressed the risk posed to human health or the environment needed to be reviewed because only they relate to the protectiveness of the remedy. In summary, the SC&A Peer Review Team identified the following:

• Changes in the Federal and State laws and regulations used in the remedy decision process

• Federal and State laws and regulations promulgated since the signing of the ROD that

are applicable or relevant and appropriate

• Changes "to be considered" in cases where the protectiveness of the original remedial decision may be affected

Where changes were identified, the review team determined whether the new requirement was more stringent, and if so, whether the existing remedial action met the new requirement. If the remedial action was not able to meet the new requirement, a scoping risk recalculation was conducted to determine the risk associated with the levels that are actually achievable. If this risk fell within the appropriate risk range, existing cleanup levels were considered protective. If risks were not acceptable, the remedial action was not considered protective. In the case of soils, risks associated with site cleanup levels were also calculated based on site-specific, risk-based levels for chemicals where standards were not protective. The SC&A Peer Review Team drew upon a useful resource in checking changes in toxicity — EPA's Integrated Risk Information System (IRIS). In addition, non-cancer and cancer toxicity data were found on the EPA's Risk Assessment Guidance for Superfund web page under the "Document and Components Download Area" currently located at http://www.epa.gov/oerrpage/superfund/programs/ risk/rsk_sf1.htm.

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3. Expert Panel Comments This section presents the expert panel responses to questions in the five-year review. Responses are provided in the following order: Mr. John Darabaris, Dr. Charles Shackelford, Mr. Dave Back, Dr. Steven Schaffer, Dr. John Goode, Mr. Phillip Rogers, Dr. Wendy Harrison, and Dr. Alien Hatheway. No effort was made to achieve a consensus among the panel members. Each expert has presented his or her comments on an individual basis. Apart from formatting and standard editorial review, the comments of the individual experts on the panel are presented in an unvarnished fashion. Overview Several panel members expressed similar opinions regardless of their particular discipline or background. These opinions form the basis for an overview of the panel's findings, as follows:

Summary of Expert Panel's Confidences in the Remedy Concept 1) No conclusive evidence of current settlement problems and concomitant monolith

degradation. 2) Principal immediate threat (radionuclides-air pathway) has been effectively addressed in

the near term by the improved waste configuration (i.e., monolith) from pre-remedy situation. 3) Site's potential as a continuing groundwater source term (in the near term) has been mitigated

with respect to the improved waste management situation (monolith) in contrast to the pre-remedy situation.

4) Risk assessment and basic design of the monolith nominally met protocols existing at the time. 5) Potential for natural disaster impacting monolith's performance has been adequately addressed

in the design. 6) Quality control/quality assurance of the monolith's construction was adequate and effective. 7) No conclusive evidence of RCRA management issues. 8) Design of the monolith site and wording of the deed minimize the potential for inadvertent

intrusion of the monolith itself. 9) Current public contact with the groundwater and surface water is minimal.

Summary of Expert Panel's Findings Concerning the Remedy Concept 1) Viability of institutional control (lack of control outside site boundary and lack of a buffer

zone).

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2) Applicability of "Limited Use" aquifer definition to the site groundwater (does not qualify). 3) Ability to demonstrate and meet dilution/attenuation goals consistent with current EPA

policies. 4) Vulnerability of cover/monolith design to long-term degradation. 5) Lack of performance assessment modeling detail to support contention that long-term design

criterion are met. 6) Lack of survey benchmarks to evaluate settlement. (Note: no conclusive signs of current

settlement.) 7) Monolith Monitoring Plan deficiencies (well locations, sampling suite) and undefined criteria

for predicting release. 8) Plume Monitoring Plan deficiencies in regard to downgradient site characterization and

establishment of upgradient background concentrations. 9) Groundwater flow model and site geology assumptions are too simplistic. 10) Contaminant transport model is poorly defined; lack of sophisticated analysis of key water-soil

rock reactions and their impact on contaminant transport model. 11) Insufficient site characterization data; limited suite of constituents addressed in pre-remedy

site characterization and post-remedy monitoring. 12) Baseline Risk Assessment and remedy dismiss groundwater and surface water pathways

without adequate justification; scoping analysis shows that adding groundwater pathway places remedy's overall risk profile on the borderline.

13) Uncertainty as to whether site meets new EPA cleanup guidelines for residual radionuclide

levels left in soil after cleanup. (Compare final status survey to MARSSIM approach.) 14) Cleanup should reflect a land use scenario consistent with existing site area circumstances and

NCP Policy Criteria and UMTRCA Siting Criteria. Particular significance should be attached to opinions shared by many panel members because of the diverse technical expertise that these opinions represent.

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Exper t Panel Comment s for 5-Year ReviewS h a t t u c k Chemica l S i t e

Denver, C o l o r a d oMr. J o h n Darabaris , P.E., C.P.A.Peer Review T e a m L e a d e r( 0 8 / 2 5 / 9 9 )

Q U E S T I O N S U B - Q U E S T I O N • A N S W E R - & R E C O M M E N D A T I O N SA - H a v e c o n d i t i o n sexternal to the remedychanged since the remedywas s e l e c t e d ?

1) Has land use ore xp e c t ed land use onor near the sitechanged?

Land use has not changed since the ROD.Expec t ed land use w i th in the s i te boundariesis restricted by deed. Land use of thesurrounding areas is not re s tr i c t ed by anyformal legal means and is mixed res identialand i n d u s t r i a l .

I s s u e :T h e Uranium M i l l T a i l i n g s R a d i a t i o n Control A c t ( U M T R C A ) h a sextens ive criteria for what is necessary for a long-term p r o t e c t i v esite. Both s i t i n g criteria and d e s i g n cri teria are p r o v i d e d for inU M T R C A and the equivalent state regulations. Of direct relevanceto S h a t t u c k are Cr i t e r i on 1A and 1C of the C o l o r a d o Rule s andR e g u l a t i o n s Per ta in ing to Radiat ion Contro l:

Criterion 1A. The general goal... in s i t i n g and de s ign deci s ionsis permanent i so lat ion of t a i l i n g s and associated contaminants byminimizing disturbance and d i s p e r s i o n by natural f orc e s , and todo so without ongoing maintenance. ...The f o l l o w i n g sitefeatures ... must be considered in s e l e c t ing among alternativet a i l i n g s d i s p o s a l sites or j u d g i n g the adequacy of ex i s t ingt a i l i n g s sites:(1) Remoteness from p o p u l a t e d areas;(2) H y d r o l o g i c and other natural conditions as they contribute tocontinued immobil izat ion and i s o l a t i o n of contaminants f romground-water sources; and(3) P o t e n t i a l f or m i n i m i z i n g erosion, di s turbance, and d i s p e r s i o nby natural f o r c e s over the long-term. (Exc erp t f r om A p p e n d i xA, Part 18, C o l o r a d o Rul e s and R e g u l a t i o n s Pertaining toR a d i a t i o n C o n t r o l ) and these s i t i n g criteria requirements a p p e a rto d i r e c t l y o p p o s e l o ca t ing a radioact ive waste d i s p o s a l m o n o l i t hin an urban area given its p o t e n t i a l for intense human ac t i v i ty .Criterion 1C. In the s e l e c t i o n o f d i s p o s a l s i t e s , primarye m p h a s i s must be given to i s o l a t i o n of t a i l i n g s or wastes, amatter having long-term i m p a c t s , as o p p o s e d to c o n s i d e r a t i o non ly of short-term convenience or b e n e f i t s , such asminimiza t i on of t r a n s p o r t a t i o n or land a cqu i s i t i on costs. W h i l ei s o l a t i o n of t a i l i n g s w i l l be a f u n c t i o n of bo th s i t e andengineering de s ign, overr id ing cons iderat ion must be givento s i t i n g f e a t u r e s given the l o n g - t e r m nature o f the t a i l i n g shazards. ( E x c e r p t f r om A p p e n d i x A, Part 18 , C o l o r a d o Rulesand R e g u l a t i o n s Perta ining to Radiat ion Control).________

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Mr. J o h n Darabaris (con t inued)( 0 8 / 2 5 / 9 9 )

S U B - Q U E S T I O NA - H a v e c o n d i t i o n sexternal to the remedychanged since the remedywas se lected? ( C o n t i n u e d )

1) Has land use ore x p e c t e d land use onor near the s i techanged? (Cont inued)

I s s u e : ( C o n t i n u e d )The crux of the issue is r e l a t e d to the d e f i n i t i o n s of "opt imization"and " i n s t i t u t i o n a l contro l s" as they per ta in to environmental s t a t u t e s ,EPA regulat ions, and implementat ion guidance. T h e s e twoc o n c e p t s have been e x p l i c i t l y embraced by rad ia t i on p r o t e c t i o ns t a n d a r d - s e t t i n g bod i e s and are f u n d a m e n t a l to many EPAregu la t i on s d e a l i n g wi th rad ia t i on pro t e c t i on. It i s not i m m e d i a t e l yapparent whether the " ins t i tut ional control" concept is embod i edeither e x p l i c i t l y or i m p l i c i t l y in the ROD.The concept of " o p t i m i z a t i o n " was f o r m a l l y a d o p t e d as part of therad ia t i on p r o t e c t i o n framework i n I C R P 6 0 ' . I n e s t a b l i s h i n g i t srad ia t i on pro t e c t i on framework, th e ICRP d e f i n e s three t y p e s o fexposure: o c cupa t i ona l , m e d i c a l , and p u b l i c exposure. Thed i s t i n c t i o n is made because the radia t ion pro t e c t i on s tandard s andt y p e s o f c o n t r o l s o f t e n d i f f e r f o r t h e d i f f e r e n t t y p e s o f exposure. I na d d i t i o n , the recommended s tandard s and t y p e s of contro l srecommended by the ICRP differ d e p e n d i n g on whether they a p p l yto o n g o i n g or p lanned pract i ce s which are causing or w i l l causeexpo sure s , or to intervention aimed at reduc ing exposures . Theconcept of in t ervent ion is g e n e r a l l y a p p l i e d to po s t-acc idents i t u a t i o n s and exposure s to e l evated l e v e l s of n a t u r a l l y occurringradioactivity.N o t w i t h s t a n d i n g the t y p e of exposure , or whether the e xpo sure i sf r o m an e x i s t i n g or p lanned prac t i c e , an a c c id en t , or naturalr a d i o a c t i v i t y , the ICRP has a d o p t e d , as part of i t s sys tem ofr a d i o l o g i c a l p r o t e c t i o n , the concept o f op t imiza t ion. The system ofr a d i o l o g i c a l p r o t e c t i o n recommended by the ICRP for p r o p o s e d andc o n t i n u i n g prac t i c e s i s based on the f o l l o w i n g general p r i n c i p l e s 2 :

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Mr. J o h n Darabaris ( c o n t i n u e d )( 0 8 / 2 5 / 9 9 )

Q U E S T I O N S U B - Q U E S T I O N • A N S W E R ; ; I S S U E S & R E C O M M E N D A T I O N SA - H a v e c o n d i t i o n sexternal to the remedychanged since the remedywas s e l e c t e d ? ( C o n t i n u e d )

1) Has land use ore xp e c t ed land use onor near the sitechanged? ( C o n t i n u e d )

I s s u e : ( C o n t i n u e d )1. The j u s t i f i c a t i o n o f a prac t i c e: No p r a c t i c e i n v o l v i n g exposure s

to radiat ion should be adop t ed unle s s it produces s i g n i f i c a n tb e n e f i t to the expo s ed i n d i v i d u a l s or to society.

2. The o p t i m i z a t i o n of pro t e c t i on: The magni tude or the i n d i v i d u a ldoses , the number of p e o p l e e x p o s e d , and the l i k e l i h o o d ofincurring expo sure s should be kept as low as is reasonablyachievable , economic and social f a c t o r s b e ing taken intoaccount.

3. I n d i v i d u a l dose and risk l i m i t s : The exposure of i n d i v i d u a l sresul t ing from the combination of all the relevant practicesshou ld be sub j e c t to dose l i m i t s , or to some control of risk in thecase of p o t e n t i a l exposures.

The system of radiological protection recommended by the ICRPfor intervention is based on the f o l l o w i n g general pr inc ip l e s :1. The proposed intervention should do more good than harm.2. The form, scale, and duration of intervention should be

op t imized so that the net b ene f i t in reduction of the radiationdetriment, minus the detriment associated with the intervention,should be o p t i m i z e d .

I t e m s No. 2 for both c o n t i n u i n g p r a c t i c e s and for interventione s t a b l i s h the d e f i n i t i o n and s cope of " o p t i m i z a t i o n " as they a p p l y tor a d i a t i o n pro t e c t i on . T h e s e d e f i n i t i o n s e s t a b l i s h t h e ba s e l ine f r o mwhich we evaluate and compare other s tandards of environmentalp r o t e c t i o n . F o r e x a m p l e , C E R C L A / S A R A a n d i t s i m p l e m e n t i n gr egu la t i on s a d o p t nine evaluat ion criteria for s e l e c t i n g a remedy foran environmental i n s u l t . Several of these nine criteria deal witho p t i m i z a t i o n issues, t h o u g h the term "optimization" is not e x p l i c i t l yused to de scr ibe the d e c i s i on-making process . The same c o n c e p t sare embodied in the seven recommendations set f o r t h in EPAF e d e r a l Radia t i on P r o t e c t i o n Guidanc e f or Exposure o f th e GeneralP u b l i c (59 FR 66414, December 23, 1994).______________

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Mr. J o h n Darabaris (cont inued)( 0 8 / 2 5 / 9 9 )

• A N S W E R -A - H a v e c o n d i t i o n sexternal to the remedychanged since the remedywas s e l e c t ed? ( C o n t i n u e d )

1) Has land use ore x p e c t e d land use onor near the s i t echanged? (Cont inued)

I s s u e : ( C o n t i n u e d )The concept of " i n s t i t u t i o n a l control" does not have the samep e d i g r e e as does the concept of op t imiza t i on . It made it s debutmore as a regulatory concept p e r ta in ing to l ow-l eve l rad ioac t ivewaste management than as a f u n d a m e n t a l rad ia t i on p r o t e c t i o np r i n c i p l e . The concept o f " i n s t i t u t i o n a l control" was f o r m a l l yincorporated into l o w - l e v e l rad ioac t ive waste management in 10CFR Part 61.7, and was c r a f t e d and incorporated into NRCr egu la t i on s over concern that persons might occupy a l i c e n s e d low-l eve l radioact ive waste d i s p o s a l s i t e in the f u t u r e and engage innormal pur su i t s without knowing that they were receiving radia t i onexposure. T h e s e "normal" pur su i t s are d e f i n e d to i n c l u d eexcavating some of the waste when b u i l d i n g a home on the site andusing the site for agr i cu l tura l purpos e s . T h e s e persons are referredto as "inadvertent intruders." Prot e c t i on of such intruders caninvolve two p r i n c i p a l control s: in s t i tu t i ona l control over the s i t ea f t e r operations terminate, and d i s p o s i n g of the waste in a mannerthat prov ide s some form of in truder barrier.A second, more d i f f i c u l t element of " i n s t i t u t i o n a l control" is thecontrol of d egraded groundwater resources and the o f f s i t e p l u m ethat may s eparate f r om contaminated sites. T h i s e lement ofi n s t i t u t i o n a l control was recognized by EPA Region 8.

"The i m p o r t a n c e of i n s t i t u t i o n a l c on tro l s in t h i s remedy isgreat... The remedy re l i e s on p r e v e n t i n g i n g e s t i o n ofcontaminated ground water by the use of in s t i t u t i ona l controls...It must be noted that EPA has no mechanism to prevent theuse of water if a user wants to use it, and no mechani sm toprevent d r i l l i n g in the area d o w n g r a d i e n t o f the site." (Noemphas i s was a d d e d ) (memo f r o m Darcy C a m p b e l l ,H y d r o g e o l o g i s t , t o Rebecca T h o m a s , Remedial P r o j e c tManager , Denver Radium S i t e , da t ed May 27, 1992).______

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Mr. J o h n Darabaris (con t inued)( 0 8 / 2 5 / 9 9 )

Q U E S T I O N S U B - Q U E S T I O N : : A N S W E R ; : : ;I S S U E S & R E C O M M E N D A T I O N S

A - H a v e c o n d i t i o n sexternal to the remedychanged since the remedywas s e l e c t e d ? ( C o n t i n u e d )

1) Has land use ore x p e c t e d land use onor near the s i t echanged? ( C o n t i n u e d )

I s s u e : ( C o n t i n u e d )Both of these c onc ep t s ( " i n s t i t u t i o n a l control" and " o p t i m i z a t i o n " )are incorporated into the l i c e n s i n g requirements for land d i s p o s a l ofradioact ive wastes as set f o r t h in 10 CFR Part 61. S p e c i f i c a l l y ,higher a c t i v i t y / l o n g - l i v e d waste, which could pose a threat a f t e r aperiod o f i n s t i t u t i o n a l control f o l l o w i n g the t e rminat ion o fop era t i on s , is required to be emp la c ed in d i s p o s a l units that ares p e c i f i c a l l y des igned against an inadvertent intruder. Other lowera c t i v i t y / s h o r t e r l iv ed waste can be d i s p o s e d of in waste d i s p o s a lunits that do not contain intruder barriers. However , the t y p e andquanti ty of radioactive material contained in these wastes arel imi t ed such that, a f t e r a per iod of insti tutional control , therad ioac t iv i ty has decayed to a point that it no longer represents anunaccep tab l e hazard to an inadvertent intruder.The concept of ins t i tut ional control represents an a t t empt to dealwith the long lasting hazards of many environmental contaminants.We have a r e spon s i b i l i ty to do all that is reasonable (note that thisincorporates the op t imiza t i on c onc ep t) to protect the p u b l i c f r om thepo t en t ia l harmful e f f e c t s o f the contaminants for their hazardousl i f e . Other statutes and regula t ions e m p l o y d i f f e r e n t s trategie s f ord e a l i n g with thi s issue. For e xampl e , C E R C L A evaluation criteriaaddre s s both long-term e f f e c t i v e n e s s and short-term e f f e c t i v e n e s s .S p e c i f i c a l l y , 40 CFR 300 p r o v i d e s for the following:_________

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Mr. J o h n Darabaris (con t inued)( 0 8 / 2 5 / 9 9 )

I S S U E S & R E C O M M E N D A T I O N SA - H a v e c ond i t i on sexternal to the remedychanged since the remedywas s e l e c t e d ? ( C o n t i n u e d )

1) Has land use ore x p e c t e d land use onor near the s i t echanged? ( C o n t i n u e d )

I s s u e : ( C o n t i n u e d )S e c t i o n 3 0 0 . 4 0 3 ( e ) ( i i i ) ( A ) ( O v e r a l l Pro t e c t iv ene s s o f H u m a n H e a l t hand the Env ironment) s ta t e s that a l t e r n a t i v e s s h a l l be assessed todetermine whether they can a d e q u a t e l y protec t human h e a l t h andthe environment, in both the short- and long-term, f r o munacc ep tab l e risks po s ed by hazardous substances present at the siteby e l i m i n a t i n g , r educ ing , or c o n t r o l l i n g expo sure l e v e l s e s t a b l i s h e ddur ing d e v e l o p m e n t o f r emed ia t i on goa l s . Overall p r o t e c t i o n o fhuman hea l th and the environment draws upon the assessment ofother criteria, e s p e c i a l l y long-term e f f e c t i v e n e s s and permanence,short-term e f f e c t i v e n e s s , and c o m p l i a n c e with A R A R s .S e c t i o n 3 0 0 . 4 3 0 ( e ) ( i i i ) ( C ) (Long-term E f f e c t i v e n e s s andPermanence) s tate s that a l t ernat ive s shal l be assessed for the long-term e f f e c t i v e n e s s and permanence they a f f o r d , a long with thedegree of certainty that the a l t ernat ive w i l l prove s u c c e s s f u l .F a c t o r s that sha l l be cons idered , as a p p r o p r i a t e , inc lude thef o l l o w i n g : ( 1 ) M a g n i t u d e o f r e s idual risk remaining f r o m untreatedwaste or treatment r e s i d u a l s remaining at the conclus ion of theremedial ac t ivi t i e s . The characteri s t i c s of the r e s i d u a l s should becons idered to the degree that they remain hazardous, t a k i n g intoaccount the ir volume, t o x i c i t y , m o b i l i t y , and p r o p e n s i t y tobioaccumulate.S e c t i o n 3 0 0 . 4 3 0 ( e ) ( i i i ) ( E ) ( S h o r t - t e r m E f f e c t i v e n e s s ) s p e c i f i e s thatthe short-term impac t s of a l t ernat ive s s h a l l be assessed c o n s i d e r i n gthe f o l l o w i n g : (1) Shor t- t e rm risks that migh t be po s ed to thec o m m u n i t y d u r i n g i m p l e m e n t a t i o n o f an a l t e r n a t i v e ; (2) P o t e n t i a li m p a c t s on workers during the r emed ia l action and the r e l i a b i l i t y ofpro t e c t i v e measures; (3) Pot en t ia l environmental impac t s o f theremedia l action and the e f f e c t i v e n e s s and r e l i a b i l i t y of p r o t e c t i v emeasures; and (4) T i m e un t i l p r o t e c t i o n is achieved._________

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Mr. J o h n Darabaris ( c o n t i n u e d )( 0 8 / 2 5 / 9 9 )

Q U E S T I O N S U B - Q U E S T I O N - A N S W E R : I S S U E S & R E C O M M E N D A T I O N SA - H a v e c o n d i t i o n sexternal to the remedychanged since the remedywas s e l ec t ed? (Continued)

1) Has land use ore x p e c t e d land use onor near the sitechanged? ( C o n t i n u e d )

I s s u e : ( C o n t i n u e d )C l e a r l y the s i t e remedy has achieved a s i g n i f i c a n t short termimprovement in the overal l pro t e c t iv ene s s of human h e a l t h and theenvironment. However, there is concern about the long-terme f f e c t i v e n e s s and permanency of the site remedy and theconcomitant ab i l i ty of the s i t e to meet the o p t i m i z a t i o n andi n s t i t u t i o n a l control requirements inherent w i t h i n the remedy.Recommenda t i on:Re-evaluate the site remediation concept to ensure long-termprotec t ivene s s g o a l s are met.I s s u e : The o f f s i t e impact o f the degraded groundwater p l u m e hasnot been covered by any formal i n s t i t u t i o n a l control. Shat tu ck doesnot consider i t s e l f r e spons ib l e for ensuring o f f s i t e land use and theS t a t e / C i t y governments have not provided d e f i n i t i v e assurances thatthey can assure in s t i t u t i ona l controls for the life of the remedys p e c i f i e d in the ROD (200 years).Recommendation: Consider the groundwater pathway a viablepathway and comple t e a risk assessment accordingly to al low foraccurate assessment and evaluation of the overall site remediationstrategy.Issue: The public's land use goals were not adequate ly assessed andr e f l e c t e d in the ROD and the remedy. W h i l e the site i t s e l f may becomfor tab l e with long-term restrictions and diminishment ofresource usage, community sent iment is to the contrary anddeserves attention.Recommenda t i on: Re-evaluate the s i te r emed ia t i on concept toensure community land use g o a l s are under s tood and protec ted.___

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Mr. J o h n Darabaris (cont inued)( 0 8 / 2 5 / 9 9 )

A - H a v e condi t ionsexternal to the remedychanged since the remedywas selected?( C o n t i n u e d )

2) Part 1 - H a v e anyhuman h e a l t hpa thways changed orbeen newlyi d e n t i f i e d ?

Yes. Original ba s e l in e risk assessmentd i smi s s ed the groundwater and s u r f a c e waterpa thways . EPA 4 0 C F R 192 does not p r o v i d ea basis for long-term dismissal of thesepathways.

I s s u e A2.1: 4 0 C F R Part 192 - Groundwater S t a n d a r d s for RemedialA c t i o n s o f I n a c t i v e Uranium Proce s s ing S i t e s d e f i n e s a l i m i t e d u s egroundwater as a "groundwater that is not a current or p o t e n t i a lsource of drinking water because of (1) the concentration of totald i s s o l v e d s o l i d s is in excess of 10,000 mg/1; or (2) w i d e s p r e a d ,ambient concentration not due to ac t iv i t i e s invo lv ing re s idualrad ioac t iv e m a t e r i a l s f r o m a de s ignat ed pro c e s s ing s i te e x i s t s thatcannot be cleaned up using treatment me thod s reasonably e m p l o y e din p u b l i c water systems; or (3) the quanti ty of water reasonablyavai lab l e for su s ta ined continuous use is l e s s than 150 g a l l o n s perday." The u p p e r a q u i f e r below the S h a t t u c k site does not meet thed e f i n i t i o n of " l imi ted use groundwater."T h i s in t erpre ta t ion is f u r t h e r s u p p o r t e d by a May 27, 1992, internalmemo between EPA Region VIII H y d r o g e o l o g i s t Darcy C a m p b e l lt o EPA Region VIII Remedial P r o j e c t Manager, Rebecca T h o m a s :2. In some of the supporting documents I was given for the site, thestatement is made that the alluvium and the Denver formationwould not be considered aquifers based on EPA groundwaterclassification, due to low yield. This is incorrect, since these unitsare used in the Denver area to provide drinking water, and the Stateof Colorado is currently trying to classify the alluvial aquifer as adrinking water source. We should be careful about saying theaquifers are not drinking water sources, when they are currentlyused in some areas of Denver now and may be in the future, andwill likely be classified by the State as drinking water sources.R e c o m m e n d a t i o n A2.1: G r o u n d w a t e r pa thway must be consideredas a v iab l e pa thway in site risk asses sment and r emed ia t i on s t r a t e g y .

2) Part 2 - H a v e anye c o l o g i c a l exposurep a t h w a y s changed orbeen newlyi d e n t i f i e d ?

Unknown I s s u e A2.2: No e c o l o g i c a l risk asses sment has been done for thesi te. It is now s tandard prac t i c e to c o m p l e t e such assessments.Furthermore , the si te is near the S o u t h P l a t t e River, which ist y p i c a l l y d e v e l o p e d within th e m e t r o p o l i t a n area f or recreationalp u r p o s e s . There i s al so a g o l f course nearby ( O v e r l a n d ) withs u r f a c e water bod i e s ( p o n d s ) and i r r i g a t i o n usage.R e c o m m e n d a t i o n A2.2: C o m p l e t e an e c o l o g i c a l risk a s s e s sment .

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Mr. J o h n Darabaris ( c o n t i n u e d )( 0 8 / 2 5 / 9 9 )

Q U E S T I O N S U B - Q U E S T I O N - A N S W E R ' I S S U E S & R E C O M M E N D A T I O N SA - H a v e c o n d i t i o n sexternal to the remedychanged since the remedywas s e l e c t e d ?( C o n t i n u e d )

3) Part 1 - Are there newcontaminants?

T h e r e is p r o b a b l y not a new contaminant.However , given t h e s i t e ' s i n a b i l i t y t o prov ided e t a i l e d waste management prac t i c e s for thel i fe of the f a c i l i t y , there i s a p o t e n t i a l thatprior contaminants may have been missedd u r i n g the earlier exercise. T h i s que s t ioncannot be d e f i n i t i v e l y answered at t h i s time.

I s s u e A3.1: The ROD l i s t s "unknown" for the site prac t i c e s in the1960s, and because of that and the u n e x p e c t e d occurrences of "oi lywastes" and the RCRA closure of the evapora t i on pond , there isconcern whether the site wastes are RCRA under the "derived rule."Recommendat i on A3.1: A n o t h e r contractor ( A g u i r r e ) i s e v a l u a t i n gthe waste charac t er i za t i on issue. Aquirre ' s assessment s hou ld ber e f l e c t e d in the f i n a l dec i s ion.

C u r r e n t l y , the monol i th provide s animproved waste management form f rom theprior ( p r e - r e m e d i a t i o n ) circumstances. Inthe near term, there is no evidence that themonolith is not per forming as expected (i.e.,s t a b i l i z i n g the site contaminant source term,subs tantial improvement in the air pathway).There are concerns regarding the ab i l i ty ofthe site documents to conf irm long-termperformance of the monoli th.

I s s u e A3.2.1: The p u b l i c has expres sed concerns regarding sur fac ee xpr e s s i on s that could ind i ca t e s e t t l emen t . T h e s e s ur fa c eexpre s s i on s do not nece s sari ly indicate mono l i th p e r f o r m a n c eprob l ems . Given the cons truc t ion pract ice s and l i m i t s in ob ta in ing"smooth" f inal grade, the areas that have been pointed to aspo t en t ia l example s of "settlement" could j u s t as easi ly be expectedd i f f e r e n t i a l s in f ina l grade, given the cover material andconstruction technique. Regrettably, the site did not e s tab l i shsurvey benchmarks that could be d e f i n i t i v e l y measured forse t t lement.Recommendation A3.2.1: E s t a b l i s h survey benchmark point s aspart of an expanded monol i th monitoring plan. ___ ____

A - Have c ond i t i on sexternal to the remedychanged since the remedywas s e l e c t ed?( C o n t i n u e d )

3) Part 2 - Are there newcontaminant sources?

I s s u e A3.2.2: Current monol i th monitoring w e l l s t i g h t l y abut theunit. There is concern that the capture zone is not adequate. Also ,the mono l i th monitoring program is l imited to a suite of cons t i tuent sthat f o cu s e s on i d e n t i f y i n g contaminant release and is not c a p a b l e ofd e t e c t i n g t r e n d s in concrete d e g r a d a t i o n that could prec ede (andp r e d i c t ) p o t e n t i a l c o n s t i t u e n t r e l ea s e prior to occurrence.Recommenda t i on A3.2.2: Revise m o n o l i t h monitoring p l a n toa l l o w f or a d d i t i o n a l o f f - s i t e w e l l s t o ensure adequate capture radiusand expand suite of s a m p l e a n a l y s i s to incorporate cementc o n s t i t u e n t s to prov ide advance warning of p o t e n t i a l d e g r a d a t i o n .

A - H a v e c ond i t i on sexternal to the remedychanged since the remedywas s e l e c t ed?(Cont inued)

4) Are thereunant i c i pa t edb y p r o d u c t s to theremedy notprev iou s ly addressedby the ROD?

Yes, s i te s o i l s may have been left in p l a c ethat exceeded general EPA guidance forrad ioac t iv e c l e a n u p .

I s s u e : S i t e remediation s t ra t egy c a l l e d for a remediation c u t - o f f inexcess of the 15 mrem standard c a l l e d for under an A u g u s t 22, 1997O S W E R memorandum ( O S W E R N o . 9200.4-18).R e c o m m e n d a t i o n : Per form s i t e - s p e c i f i c dose assessment based ons i t e - s p e c i f i c radionucl ide s and exposure pathways to ensure that ther emed ia t i on program meets overall national cont ingency p l a n goa l s(i.e., risk of 10-" to IP' 6).________________________

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Mr. J o h n Darabaris ( c o n t i n u e d )( 0 8 / 2 5 / 9 9 )

x I S S U E S :A- H a v e condi t ionsexternal to the remedychanged since the remedywas s e l e c t ed?( C o n t i n u e d )

5 ) H a v e h y d r o l o g i c /hydrogeo logic sitec o n d i t i o n s changed?

Y e s , t h e s i t e h y d r o g e o l o g i c c o n d i t i o n spresented in the RA, RI, and remedialdec i s i on may not accurate ly d e p i c t the actualsite c ondi t i on s . A l s o , th e groundwater p l u m ec o n d i t i o n a p p a r e n t l y does not meetC E R C L A 1 2 1 ( d ) standards.

I s s u e : The s i t e charac t er iza t ion program does no t s u f f i c i e n t l y d e f i n esite hydrogeo l og i c conditions to support a passive groundwaterr emed ia t i on s trat egy. S i t e g e o l o g y ( u p p e r a q u i f e r s o i l s a n du n d e r l y i n g bedrock) may exh ib i t a great deal more v a r i a b i l i t y andchanne l ing characteris t ic s than the s i m p l i s t i c model pre s ented in sitedocuments. There are s i gn i f i can t questions regarding the adequacyo f t h e d e f i n i t i o n o f t h e p l u m e ' s characteris t ic s ( l a t e r a l e x t en t ,vertical extent, f a t e and transport charac ter i s t i c s). If one assumes" in s t i tu t i ona l control" is p l a u s i b l e and a l l o w s for a pa s s iv e naturalremediation process, EPA standards ( 4 0 C F R 1 9 2 , GroundwaterS t a n d a r d s for Remedia l A c t i o n s at Inac t ive Uranium Proc e s s ingS i t e s ; F i n a l Rul e) cal l f or a demonstrat ion that the natural remedycan meet groundwater s tandards w i th in a 100-year t ime f rame .S p e c i f i c a l l y ,"for a q u i f e r s where compl iance with the groundwater s tandard s canbe p r o j e c t e d to occur n a t u r a l l y w i th in a per iod of l e s s than 100years, and where the groundwater is not now used for a p u b l i c watersystem and is not now p r o j e c t e d to be so used wi th in t h i s p e r i o d ,t h i s rule permit s extension of the r emed ia l per iod to that time,p r o v i d e d i n s t i t u t i o n a l control and an adequate v e r i f i c a t i o n p l a nwhich assures sa t i s fa c t i on of b en e f i c i a l uses is e s tab l i shed andmaintained throughout th i s e x t ended remedia l p er i od ,"and

5-13

Mr. J o h n Darabaris ( c o n t i n u e d )( 0 8 / 2 5 / 9 9 )

Q U E S T I O N S U B - Q U E S T I O N x A N S W E R - I S S U E S & R E C O M M E N D A T I O N SA - H a v e c o n d i t i o n sexternal to the remedychanged since the remedywas s e l e c t e d ?( C o n t i n u e d )

5 ) H a v e h y d r o l o g i c /hydrogeo logi c sitec o n d i t i o n s changed?( C o n t i n u e d )

( C o n t i n u e d )"(2)(I) If t h e S e c r e t a r y determines that s o l e rel iance on activeremedial proc edure s is not a p p r o p r i a t e and that c l e a n u p of thegroundwater can be more reasonably a c c o m p l i s h e d in full or in partthrough natural f l u s h i n g , then the per iod for remedial pro c edur e smay be e x t ended . S u c h an ex t ended p er i od may extend to a termnot to exceed 100 years if: (A) The concentration l i m i t s e s t a b l i s h e dunder this subpart are p r o j e c t e d to be s a t i s f i e d at the end of thisex t ended p e r i o d , (B) I n s t i t u t i o n a l contro l , having a h igh degree ofpermanence and which wi l l e f f e c t i v e l y protec t p u b l i c h e a l t h and theenvironment and s a t i s f y b e n e f i c i a l uses of groundwater during theextended period and which is en f or c eab l e by the administrative orj u d i c i a l branches of government ent i t i e s , is ins t i tu t ed andmaintained, as part of the remedial action, at the proce s s ing site andwherever contamination by l i s t ed const i tuents f r om residualradioact ive materials is f ound in groundwater, or is p r o j e c t e d to bef o u n d , and (C) The groundwater is not currently and is not nowp r o j e c t e d to become a source for a pub l i c water system subjec t toprovisions of the Safe Drinking Water Act during the extendedperiod."Recommendat i on: Conduct an expanded site h y d r o g e o l o g i ci n v e s t i g a t i o n that can adequa t e ly d e f i n e : (1) var iab i l i ty o fh y d r o g e o l o g i c regimes, (2) f a t e and transport characteri s t i c s , (3)background, and (4) p l u m e extent. T h i s inve s t iga t i on should a l l owa s u f f i c i e n t l y rigorous and s o p h i s t i c a t e d model to be d e v e l o p e d toassess the a b i l i t y of natural r emed ia t i on progre s s to achieveremediat ion g o a l s w i t h i n the s p e c i f i e d maximum regula tory extentof time (100 years).___________________________

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Mr. J o h n Darabaris ( c o n t i n u e d )( 0 8 / 2 5 / 9 9 )

B - Has the remedy beenimpl ement ed in accordancewith dec i s i on documents?

N A In the near term, the m o n o l i t h is p robab lyp e r f o r m i n g in accordance with remedialgoa l s . However , i n s u f f i c i e n t i n f o r m a t i o n i spresented t o c on f i rm t h e m o n o l i t h ' s l ong-term per f o rmanc e .

I s s u e : The remedial d e s i gn i s o s t e n s i b l y based on UMTRA de s ignconcepts. However, the remedial design does not i n c l u d e thep e r f o r m a n c e assessment m o d e l i n g that i s t y p i c a l l y used to assesslong-term p er f ormanc e c a p a b i l i t y at c omparab l e (NRC l e a d ) s i t e s .Furthermore , there is s trong concern that the l imi t ed p e r f o rmanc ea n a l y s i s that was done (i.e., r educ t i on f a c t o r analys i s pre sented inA p p e n d i x F of the Remedial D e s i g n ) does not accurate ly r e f l e c t thean t i c ipa t ed chemical and h y d r o l o g i c p e r f o r m a n c e (i.e., moreuniform f l o w based on a h igher inc idence of mi c ro f ra c tur e s ; ratherthan d i l u t i o n , water p a s s i n g down the column wil l acquire morec on tamina t i on u n t i l it reaches the base of the mono l i th).Recommendat ion: Conduct p e r f o rmanc e m o d e l i n g in accordancewith accepted de s ign prac t i c e s for units with long-term de s igncriterion.

C - Has any riski n f o r m a t i o n changed sincethe remedy was s e l e c t e d ?

N / A Changes have occurred in s p e c i f i ccons t i tuent s and overal l EPA gu idance withregard to rad ioac t ive s i te c l eanup s t a n d a r d s .The original base l ine risk assessment s p e c i f i cpathways that based on current s t a n d a r d s ,s h o u l d have been addressed._________

I s s u e : I n s u f f i c i e n t site characterization i n f o r m a t i o n i s a v a i l a b l e top e r f o r m a thorough risk assessment for al l relevant pathways.R e c o m m e n d a t i o n : Acquire a p p r o p r i a t e level o f site in format ionand conduct a full human heal th and e c o l o g i c a l risk assessment.

1. ICRP Publ i ca t i on 60, "1990 Recommendat ions of the I n t e r n a t i o n a l C o m m i s s i o n on R a d i o l o g i c a l Pro t e c t i on ," p u b l i s h e d for the I n t e r n a t i o n a l Commis s i on on R a d i o l o g i c a lP r o t e c t i o n , Pergamon Press , 1991.2. T h e s e d e f i n i t i o n s have been p a r a p h r a s e d f rom I C R P - 6 0 . See I C R P - 6 0 for the exact d e f i n i t i o n s and q u a l i f i c a t i o n s .

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Mr. J o h n Darabaris (con t inued)( 0 8 / 2 5 / 9 9 )

References40 CFR Part 192 - Groundwater S t a n d a r d s for Remedial A c t i o n s of Inac t ive Uranium Proce s s ing S i t e s .40 CFR Part 300 - Oil and Hazardou s Subs tance s P o l l u t i o n Cont ingency Plan.C o l o r a d o Rules and Regulat ions Pertaining to Radiat ion C o n t r o l , A p p e n d i x A, Part 18.Internal memorandum between EPA Region VIII H y d r o g e o l o g i s t Darcy C a m p b e l l t o EPA Region VIII Remedial P r o j e c t Manager, Rebecca T h o m a s ,May 27, 1992.U.S. Environmental Protection Agency. Memo from Darcy C a m p b e l l , H y d r o g e o l o g i s t , to Rebecca Thomas, Remedial P r o j e c t Manager, DenverRadium S i t e , May 27, 1992.

3-16

Expert Panel Comment s for 5-Year ReviewS h a t t u c k Chemical S i t e

Denver, C o l o r a d oDr. Charles S h a c k e l f o r d( 0 8 / 1 7 / 9 9 )

'•M(§^ji^i^^^M^'f.A - H a v e c o n d i t i o n sexternal to the remedychanged since the remedywas s e l e c t e d ?

; ; ; : : : r ; : : : v s u B - i 3 U E S T i Q N : ; : . ; ; ; : :1) Has land use or

expec ted land use onor near the sitechanged?

2) H a v e any humanh e a l t h or e c o l og i ca lexposure pa thwayschanged or beennewly i d e n t i f i e d ?

3) Are there newcontaminants orcontaminant sources?

4) Are thereu n a n t i c i p a t e dbyproduc t s to theremedy not p r e v i o u s l yaddre s s ed by theROD?

5 ) H a v e h y d r o l o g i c /h y d r o g e o l o g i c s i t econdi t ions changed?

: p : L ; ^ ; : ; : ' l ; : ; : A H ^The reviewer has not read or seenany informat ion that indicates thatland use near the site has changeds u b s t a n t i a l l y since the c o m p l e t i o nof the remedial de s ign (RD).However , it is not p o s s i b l e at th i stime to determine the e x p e c t e d landuse over the duration of the 200-year de s ign l i f e .The reviewer has not read or seenany i n f o r m a t i o n that ind i ca t e s thatany human h e a l t h or e c o l o g i c a lexposure pa thways have changed orbeen newly i d e n t i f i e d since thec o m p l e t i o n of the remedial de s ign(RD).The reviewer has not read or seenany informat ion that indica t e s thatany new con taminant s orcontaminant sources have beeni d e n t i f i e d .T h i s ques t ion i s o u t s i d e thee x p e r t i s e of t h i s reviewer.

The reviewer has not read or seenany i n f o r m a t i o n that i n d i c a t e s thath y d r o l o g i c /h y d r o g e o l o g i c s i t e c o n d i t i o n s havechanged since the c o m p l e t i o n of ther e m e d i a l d e s i g n (RD).

;:p:i;if ::̂ ii ; ! ; ; : : : . ' . ; • - - . ; ; ; ; ; ; ; ; ; ; ; ; ; : ; ^I s s u e : N o n e .Recommendation: None.

I s s u e : None .Recommenda t i on: N o n e .

I s s u e : N o n e .R e c o m m e n d a t i o n : None .

I s s u e : N AR e c o m m e n d a t i o n : N A

I s s u e : N o n e .R e c o m m e n d a t i o n : N o n e .

3-17

Dr. Charl e s S h a c k e l f o r d (cont inued)( 0 8 / 1 7 / 9 9 )

Q U E S T I O N S U B - Q U E S T I O N • I S S U E S v & i R E G O M M E N D A T I O N S vB - Has the remedy beeni m p l e m e n t e d in accordancewith dec i s ion document s?

N A A l t h o u g h the remedy has beeni m p l e m e n t e d in accordance with theg i s t o f the d e c i s i on document s ,several t e chn i ca l issues a p p a r e n t l ywere overlooked in the o r ig ina ldes ign. S i n c e these t e chnica l issuesmay have a bearing on thep e r f o r m a n c e of the remedy over the200-yr d e s i g n l i f e , these technicalissues s h ou ld be addre s s ed .

I s s u e B . I : Cover S y s t e m / S n o w m e l t :R e l a t i v e l y recent s t u d i e s concerning water balance m o d e l i n g have ind i ca t edthat commonly used water balance m o d e l s , such as the HELP mode l thatwas used in the d e s i g n of the cover system, have a t endency to overpred i c toverland f l o w and, t h e r e f o r e , u n d e r p r e d i c t p e r c o l a t i o n through the coversystem p a r t i c u l a r l y in semi-arid or arid s i tes that are s u b j e c t to snow coverand snow melt (e.g., K h i r e et al. 1997). T h i s overpredi c t ion in overlandf l o w has been a t t r i b u t e d , in part , to the i n a b i l i t y of the mode l s to accurate lyr e f l e c t the thermal c o n d i t i o n s in the s o i l . T h i s f i n d i n g i s o f p a r t i c u l a rconcern in the present scenario due to the semi-arid nature of the c l imateand the large s n o w f a l l s that o f t e n occur in the S p r i n g (e.g., March andApril). T h e s e s n o w f a l l s commonly occur over r e l a t i v e l y short durations(24-48 hrs) f o l l o w e d by a warming period that re sul t s in rapid mel t ing(personal observation). In this case, the ground may not be frozen re su l t ingin a large pu l s e of i n f i l t r a t i o n into the cover system, even though the annualprec ip i ta t ion may be low.Recommendation B.I: A more extensive water balance analysis should bep e r f o r m e d to account for the potent ial snowmelt prob l em, p o s s i b l y usingtwo or more m o d e l s with reference to the cited publ icat ion.

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Dr. Charles S h a c k e l f o r d (continued)( 0 8 / 1 7 / 9 9 )

^ S U B - Q U E S T I O N ; ; .B - Has the remedy beenimplemented in accordancewith dec i s ion documents?( C o n t i n u e d )

N / A I s s u e B.2: Cover S y s t e m / G C L : A key component in the overa l lp e r f o rmanc e of the cover system is the G C L . Research has e s t a b l i s h e d thatG C L s can maintain their i n t e g r i t y with re spec t to a reasonable m a g n i t u d e ofd i f f e r e n t i a l s e t t l e m e n t as we l l as environmental f a c t o r s such as w e t / d r ycyc l e s and f r e e z e / t h a w cycles . However , some evidence i n d i c a t e s thatd i v a l e n t (e.g., ca l c ium) for monovalent (e.g., s o d i u m ) ion exchange wi thinthe bentoni t e component of the GCL can lead to cracking of the GCLr e s u l t i n g in poor p e r f o r m a n c e and even f a i l u r e of the G C L .For e x a m p l e , J a m e s et al. ( 1 9 9 7 ) i n v e s t i g a t e d the cause of l eakage throughG C L s that were used in a cover system for brick arches to protec t waterreservoirs. The exchange c o m p l e x of the bentoni t e in the GCL i n i t i a l l y wasdominated by sodium with a cation exchange c a p a c i t y ( C E C ) of 90.2meq/100 g. A f t e r l eakage was observed in the f i e l d , t e s t s on exhumedspe c imen s of the GCL indicated that the Ca2+ concentrations on theexchange complex increased s u b s t a n t i a l l y whereas Na + c oncentrat ions onthe exchange c o m p l e x decreased s u b s t a n t i a l l y . Based on this data and othert e s t s , J a m e s et al. ( 1 9 9 7 ) concluded that calcium from the f o u n d a t i o n soiland overlying cover so i l s had migrated into the GCL and d i s p l a c e d thesodium f r o m the exchange c o m p l e x r e s u l t i n g in subsequent shrinkage andcracking of the bentoni t e . S i m i l a r r e su l t s a l so have been reported elsewhere(Aboveground Tank Update 1992, and Dobras and Elzea 1993).Recommenda t i on B.2: S p e c i m e n s of the GCL in the cover system can beexhumed and examined for shrinkage and cracking, te s t ed for exchangeabl ecat ions and C E C , and t e s t ed for h y d r a u l i c c o n d u c t i v i t y . The r e s u l t s o f the s et e s t s should be compared against the r e s u l t s of the same t e s t s p e r f o r m e d onunexpo s ed s p e c i m e n s of the same G C L . Of course, any p l a c e wheres p e c i m e n s have been exhumed must be r e t r o f i t t e d to a s a t i s f a c t o r ycond i t i on . As an al t ernat ive to e xhumat ion of in tac t GCL s p e c i m e n s ,c o m p l e t e chemical ana ly s i s o f a l l o f th e m a t e r i a l s ( r i p rap, sand, gravel ,recompacted s o i l / c l a y liner, etc.) used in the cover system should bep e r f o r m e d to evaluate the p o t e n t i a l for an adverse ion exchange e f f e c t on theGCL. As a minimum, these chemical analy s e s shou ld i n c l u d e , wherea p p r o p r i a t e , s o l u b l e s a l t s , e x c h a n g e a b l e ca t i ons , C E C , soil p H , a n d soi le l e c t r i c a l conductance. All o f these t e s t s s hou ld be p e r f o r m e d u s ingu n e x p o s e d mater ia l s since the mat er ia l s at the s i t e have u n d o u b t e d l y a l r e a d ybeen e x p o s e d to some washing f rom precipitation.________________

5-19

Dr. Char l e s S h a c k e l f o r d ( c o n t i n u e d )( 0 8 / 1 7 / 9 9 )

Q U E S T I O N S U B - Q U E S T I O N • A N S W E R : : I S S U E S £ R E C O M M E N D A T I O N SB - Has the remedy beeni m p l e m e n t e d in accordancewith d e c i s i o n documents?( C o n t i n u e d )

N / A I s s u e B . 3 : Cover S y s t e m / R e c o m p a c t e d S o i l / C l a y Layer ( R S / C L ) : T h ereviewer p er c e iv e s two m a j o r issues re la t ed to the p e r f o r m a n c e and i n t e g r i t yof the recompacted s o i l / c l a y layer (RS/CL) used in the cover system. F i r s t ,the RS/CL is r e l a t i v e l y t h i n (15 cm). Benson and Daniel ( 1 9 9 4 ) have shownon the basis of data f rom case h i s t o r i e s that the hydrau l i c c o n d u c t i v i t y ofcompacted clay liners decreases as the t h i c k n e s s of the liner increases f rom15 cm (6 in) to 90 cm (36 in), with u n a c c e p t a b l y high (> 10~7 cm/s)h y d r a u l i c c o n d u c t i v i t i e s f or the thinner liners. T h i s e f f e c t o f thicknes s onhydrau l i c c o n d u c t i v i t y g e n e r a l l y i s a t tr ibuted to c o n t i n u i t y of cracksre su l t ing f r o m d e s i c ca t i on and lack of p r o p e r construct ion q u a l i t y contro l .Second, the hydraulic conduct ivi ty of the R S / C L was based on onlylaboratory tes t s using s m a l l - s c a l e specimens. However, standard pract i cefor evaluat ing the hydraul ic conductivity of compacted clay barriers requireseither f i e l d hydraul i c conduct ivi ty tes t s p er f ormed on test pad s (Daniel1990) and/or laboratory tests performed on large-scale specimens (> 30 cm)(Benson et al. 1994) recovered from test pad s due to the p o t e n t i a l e f f e c t ofscale on the hydraulic c onduc t iv i ty of the compacted clay. Thus , there is aconcern about the overall integri ty of the RS/CL in the cover system.Recommendation B.3: The hydraulic conductivity and the associatedper f ormance of the RS/CL component of the cover system should be re-evaluated. One recommendation would be to excavate to the d e p t h of theRS/CL at several locat ions across the cover to determine if any de s i c ca t i onhas occurred since c o m p l e t i o n of construction. Another recommendation isto construct a test pad on the s i t e us ing the same RS/CL and the samecons truc t ion equipment and m e t h o d s as used in the original cover systemf o l l o w e d by either f i e l d h y d r a u l i c c o n d u c t i v i t y t e s t i n g on the test pad a n d / o rl a r g e- s ca l e laboratory hydrau l i c c o n d u c t i v i t y t e s t i n g on spec imens recoveredf r o m the test pad._________________________________

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Dr. Charle s S h a c k e l f o r d (con t inued)( 0 8 / 1 7 / 9 9 )

B - Has the remedy beeni m p l e m e n t e d in accordancewith decis ion documents?( C o n t i n u e d )

N / A I s s u e B.4: Cover S y s t e m / S t a b i l i t y : T h e s l o p e s t a b i l i t y ana ly s e s a p p a r e n t l ywere p e r f o r m e d us ing a Mohr-Coulomb f a i l u r e e n v e l o p e that cons i s t ed ofboth cohesion and f r i c t i o n . However , the mechanism for the cohesion wasnot i d e n t i f i e d . The reviewer s u s p e c t s that the cohesion derived f r o m theshear s trength t e s t s was due e i ther (a) to unsaturated nature of the spec imensduring shear r e s u l t i n g in an apparen t cohesion, or (b) f rom e x t r a p o l a t i o n ofthe test r e su l t s using a s tra ight- l ine f a i l u r e e n v e l o p e when, in r e a l i t y , thef a i l u r e enve l op e was curved. In the case of (a), the apparen t cohesions hou ld not be used in the analyse s since i n f i l t r a t i o n into the cover wouldreduce or c o m p l e t e l y d e s t r oy th i s component of strength. In the case of (b),use of a linear f a i l u r e envelope may result in too high a strength at the lowc o n f i n i n g s tres ses t y p i c a l l y associated with cover sys tems and, t h e r e f o r e ,unconservative f a c t o r s o f s a f e t y . In a d d i t i o n , p u b l i s h e d re su l t s have shownthat t h e drained, e f f e c t i v e stress f r i c t i o n angle s f o r f u l l y hydrated G C L s m a ybe as low as 10° and, as a result, the GCL t y p i c a l l y represents the weak linkin the cover system (e.g., Shan and Daniel 1 9 9 1 ) .Recommendat i on B.4: A l t h o u g h the reviewer does not f e e l that the f a c t o r smentioned above are nec e s sar i ly critical given the r e l a t i v e l y h igh f a c t o r s ofs a f e t y a s soc ia t ed with the cover system in the or ig ina l remedial de s ign, thereviewer nonethe l e s s recommends that the s t a b i l i t y of the cover system bere-evaluated to inc lude an assessment of the above fac tor s .I s s u e B.5: M o n o l i t h / S e t t l e m e n tS e t t l e m e n t Markers: W h i l e the reviewer has not checked the or ig inalc a l c u l a t i o n s o f t h e s e t t l e m e n t analys i s f o r t h e m o n o l i t h , t h e r e v i e w e r ' si m p r e s s i o n i s that th e s e t t l ement a n a l y s i s f o l l o w s s tandard g eo t e chn i ca lengineer ing pract ice u s ing t h e m o d i f i e d Schmertmann analys i s . A l t h o u g hthis a n a l y s i s i n d i c a t e s s m a l l s e t t l e m e n t s (< 1.0 in) are e xp e c t ed for them o n o l i t h , the a n a l y s i s contains several a s s u m p t i o n s and the reviewer couldnot f i n d any mention for the p o t e n t i a l f or d i f f e r e n t i a l s e t t l e m e n t s that c ou ldresult in cracking o f th e r e l a t i v e l y s t i f f , unre in for c ed mono l i th .R e c o m m e n d a t i o n B.5: Given the m a g n i t u d e of the p r o j e c t and thep o t e n t i a l f or detr imental environmental consequences r e s u l t i n g f romcracking of the monol i th over the d e s i g n life of 200 years, the reviewerrecommends that a sys tem of s e t t l e m e n t markers be i n s t a l l e d to moni tor theactual s e t t l e m e n t o f the monol i th .

5-21

Dr. Char l e s S h a c k e l f o r d ( c o n t i n u e d )( 0 8 / 1 7 / 9 9 )

Q U E S T I O N S U B - Q U E S T I O N • A N S W E RB - Has the r emedy beeni m p l e m e n t e d in accordancewith dec i s ion documents?( C o n t i n u e d )

I s s u e B.6: G r o u n d w a t e r / A t t e n u a t i o n M e c h a n i s m s :The groundwater r emedia t ion is based on source control and a t t enua t i on ofp o l l u t a n t s . However , other than the r educ t i on ( d i l u t i o n ) f a c t o r s de s cr ibed inA p p e n d i x F of the remedial d e s i g n , the reviewer f o u n d no mention of otherattenuation mechanisms, such as radioactive decay, adsorp t ion,p r e c i p i t a t i o n , etc. A l s o , a l t h o u g h the r educ t i on f a c t o r s (RF) ca l cu la t ed inA p p e n d i x F are considered large ( 1 1 7 . 9 for mono l i t h and cover withoutRS/CL and GCL component s , and 235 for m o n o l i t h and cover asconstructed with the RS/CL and GCL componen t s) , the reviewer f o u n d noevidence that these reduct ion f a c t o r s were evaluated with re spec t to theA R A R s . For e x a m p l e , a large RF of 1000 may reduce a contaminantconcentration from 1000 mg/L to 1 mg/L, but the re su l t ing concentration of1 mg/L may still exceed the relevant standard concentration based on theARARs.Recommendat ion B.6: The role of attenuation with respect to thegroundwater remedy should be re-evaluated inc luding consideration of theattenuation mechanisms and the relevance of the RFs to the ARARs.I s s u e B.7: G r o u n d w a t e r / F u t u r e Use:In terms of protec t ion of groundwater, the remedy is based on the pre c ep tthat the groundwater is not currently being used and, th er e f or e , groundwaterprotec t ion can be based on (a) source control and (b) attenuation. However,the reviewer could f i n d no mention of the expec ted f u tur e use of ground-water over the full 200-yr de s ign l i f e - o f the remedy. The reviewer believesthat groundwat er resources in the western US, i n c l u d i n g Denver, w i l lbecome more c r i t i c a l into the next m i l l e n i u m as d e v e l o p m e n t of the Denverarea increases.R e c o m m e n d a t i o n B.7: The entire groundwater remedy needs to be re-eva lua t ed with respect to the p o t e n t i a l f u t u r e use of the groundwater. Fore x a m p l e , can the ex i s t ing groundwater be treated to a usable s tandard and, ifso, at what cost?___________________________

3-22

Dr. Charle s S h a c k e l f o r d (con t inued)( 0 8 / 1 7 / 9 9 )

B - Has the remedy beeni m p l e m e n t e d in accordancewith decision documents?( C o n t i n u e d )

I s s u e B.8: M o n i t o r i n g / M o n o l i t h :The current monol i th mon i t o r ing program cons i s t s of 10 monitoring w e l l s , 5w e l l s on the western s ide of the m o n o l i t h and 5 w e l l s on the eastern s ide ofthe mono l i th . In reviewing the monol i th monitoring program, the reviewercou ld f i n d no ra t i ona l e for the number and s p a c i n g of these w e l l s . In f a c t ,the w e l l s are l o ca t ed so c lo se to the m o n o l i t h that the reviewer doub t s thecapture zone of the w e l l s is much greater than the c o l l e c t i v e diameters of thew e l l s . T h u s , there is a concern that s i g n i f i c a n t contamination could e scapethe m o n o l i t h without be ing d e t e c t e d by the monol i th moni tor ing w e l l s .In a d d i t i o n , the current monitoring program does not i n c l u d e m a j o r chemicalcon s t i tu en t s that would r e f l e c t d e g r a d a t i o n o f th e m o n o l i t h . In p a r t i c u l a r ,the r e v i e w e r ' s experience i s that l e a c h i n g of f ly ash t y p i c a l l y r e s u l t s ins i g n i f i c a n t concentrations of aluminum and boron. In th i s case, d egrada t i onof the s o l i d i f i e d monoli th might be r e f l e c t e d in e l eva t ed aluminum andboron concentrations.Recommendation B.8: Given the confinement of the property line withre spec t to the perimeter of the mono l i th , it is u n l i k e l y that any we l l systemother than a continuous system of w e l l s around the c ircumference of themono l i th would prov ide an adequate capture zone. T h i s scenario isunreasonable and not prac t i ca l . T h u s , some al t ernat ive measure, such asconstruction of a low-permeabi l i ty, vertical c u t o f f wall around the perimeterof the m o n o l i t h should be cons idered.I s s u e B.9: M o n i t o r i n g / G r o u n d w a t e r :The number and l o ca t i on o f mon i t o r ing w e l l s f or the groundwat er o u t s i d ethe immed ia t e v i c i n i t y of the remedy seem to be too sparse to p r o v i d e as u f f i c i e n t assessment of the p o t e n t i a l impact of the remedy on surroundinggroundwater.R e c o m m e n d a t i o n B.9: A re-assessment of the groundwater monitoringprogram to i n c l u d e an eva lua t i on of (a) the number and l o ca t i on s of w e l l s ,(b) the paramet er s to be monitored (see I s s u e B.8), and (c) the i m p a c t of thesurrounding contaminant sources on the overa l l groundwater qual i ty shouldbe p e r f o r m e d .

C - Has any riski n f o r m a t i o n changed sincethe r emedy was s e l e c t e d ?

The reviewer is not q u a l i f i e d toassess risk.

I s s u e : N AR e c o m m e n d a t i o n : N A

Refer enc e s

3-23

Dr. Charles S h a c k e l f o r d (continued)( 0 8 / 1 7 / 9 9 )Aboveground Tank Update ( 1 9 9 2 ) . S o d i u m bentonite l iner f o u n d degraded at New York site. February, p. 1.Benson, C. H. and Daniel , D. E. ( 1 9 9 4 ) . Minimum thicknes s of compacted soil l iners: II. A n a l y s i s and case histories. Journal of GeotechnicalEngineering, A S C E , Reston, VA, V o l . 120, No. 1, 153-172.Benson, C. H., H a r d i a n t o , F. S., and Motan, E. S. (1994). Representative specimen size for hydraul i c c onduc t iv i ty assessment of compacted soil liners.Hydraulic Conductivity and Waste Contaminant Transport in Soil, ASTM STP 1142, D. E. Daniel and S. J. Trautwein, Eds., ASTM, WestConshohoken, PA, p. 3-29.Daniel , D. E. ( 1 9 9 0 ) . Summary review of construction qual i ty control for earthen liners. Waste Containment Systems: Construction, Regulation, andPerformance, R. Bonaparte, Ed., A S C E , Reston, VA, p. 175-189.Dobras, T. N. and Elzea, J. M. ( 1 9 9 3 ) . In-situ soda ash treatment for contaminated geosynthet ic clay liners. Geosynthetics '93, IFAI, St. Paul, MN, p.1145-1159.James , A. N., F u l l e r t o n , D., and Drake, R. (1997). F i e l d performance of GCL under ion exchange conditions. Journal of Geotechnical andGeoenvironmental Engineering, A S C E , Reston, VA, V o l . 123, No. 10, 897-901.Khire, M. V., Benson, C. H., and Bosscher, P. J. (1997). Water balance m o d e l i n g of earthen f ina l covers, Journal of Geotechnical andGeoenvironmental Engineering, A S C E , Reston, VA, V o l . 123, No. 8, 744-754.Shan, H . - Y . and Daniel, D. E. ( 1 9 9 1 ) . Resul t s of laboratory t e s t s on g e o t e x t i l e / b e n t o n i t e material. Geosynthetics '91, IFAI, St. Paul , MN, p. 517-535.

3-24

Mr. Dave Back( 0 8 / 2 9 / 9 9 )

Expert Panel Comment s for 5-Year ReviewS h a t t u c k Chemical S i t e

Denver, C o l o r a d o

i Q l l J E S T I D N ; • • A N S W E R : : : 1 S S I J E S : ; & : : R E C O M M E N D A T I O N S : :A - H a v e c ondi t i on sexternal to the remedychanged since the remedywas s e l e c t e d ?

1) Has land use ore xp e c t ed land use onor near the sitechanged?

Not evaluat ed by t h i s reviewer. I s s u e :R e c o m m e n d a t i o n : N o comments.

2) H a v e any humanh e a l t h or e c o l og i ca lexposure pa thwayschanged or beennewly i d e n t i f i e d ?

See issue and re commendat ionsdi s cus s ion.

I s s u e : D i l u t i o n c a l c u l a t i o n s ar e t oo s i m p l i s t i cThe Remedial I n v e s t i g a t i o n pre s en t s a very s i m p l i s t i c a p p r o a c h (i.e.,P L U M E 2 D M o d e l ) to p r e d i c t i n g the amount of d i l u t i o n in groundwater downgradient f rom the m o n o l i t h . T h i s t y p e of ana ly s i s i s moresuited to a s c o p i n g t y p e exercise than to s u p p o r t i n g a f u l l - b l o w n riskassessment.The analys i s , which was c i t ed in the Remedial I n v e s t i g a t i o n , p e r f o r m e dthe large d i l u t i o n rates a t t r i bu t ed to the S o u t h P l a t t e River needs to bepre s en t ed . It should be kept in mind, however, that m e t a l s do notalways stay in s o l u t i o n and can p r e c i p i t a t e as stream sediment. Fore x a m p l e , in s t u d i e s of mo lybdenum geochemis try in the stream systemdraining the Cl imax area of C o l o r a d o , Kaback and Runnel s ( 1 9 8 0 )f o u n d that the m o l y b d e n u m was p r e c i p i t a t i n g out of s o lu t ion.Furthermore, even if m o l y b d e n u m stays in s o lu t i on , it t end s toaccumulate in vegetation and, if present in excessive amounts, cancause prob l ems f o r graz ing an imal s (Dye a n d O ' H a r a , 1 9 5 9 ) .R e c o m m e n d a t i o n sA numerical model of the groundwater f l o w system shou ld beconstructed in order to obtain more r e l i a b l e e s t i m a t e s of d i l u t i o n , andgroundwater f l o w rates and direc t ions .S a m p l i n g r e su l t s f r o m the e x p a n d e d m o n i t o r i n g w e l l network shou ld beused to d e s i g n a stream s a m p l i n g program. Stream sediment f r o m theS o u t h P l a t t e River s hou ld b e s a m p l e d . T h e p o t e n t i a l e f f e c t s o fb i o a c c u m u l a t i o n of me ta l s in p l a n t and animal t i s s u e need to bei n v e s t i g a t e d as part of an E c o l o g i c a l and H u m a n F o o d Chain RiskA s s e s s m e n t .

3-25

Mr. Dave Back (cont inued)( 0 8 / 2 9 / 9 9 )

Q U E S T I O N S U B - Q U E S T I O N : : i S S U E S - : & ; ; R E ; C : O l V l : I V I E N D A T I Q N S :A - H a v e c o n d i t i o n sexternal to the remedychanged since the remedywas s e l e c t e d ?( C o n t i n u e d )

3) Are there newcontaminant s orcontaminant sources?

Not eva lua t ed by th i s reviewer. I s s u e :R e c o m m e n d a t i o n : N o comments.

4) Are thereunantic ipatedb y p r o d u c t s to theremedy not p r e v i o u s l yaddre s s ed by theROD?

Not eva lua t ed by th i s reviewer. I s s u e :Recommendation: No comment.

5 ) H a v e h y d r o l o g i c /h y d r o g e o l o g i c s i tecondit ions changed?

Not evaluated by th i s reviewer. I s s u e :Recommendat ion: No comments

B - Has the remedy beenimplemented in accordancewith decis ion documents?

See issue and recommendationdiscussion.

Issue Bl: Lack of Downgradient S i t e Characterization DataIn correspondence with the EPA, the USGS recommends thata d d i t i o n a l monitoring w e l l s be i n s t a l l e d and s u p p l e m e n t a r y const i tuentsbe analyzed. The USGS bases its recommendations on a general lackof site characterization data, f i n d i n g that the e x i s t i n g in format ion isi n s u f f i c i e n t to d e f i n e critical a spe c t s of the contaminant migrationincluding: vertical and horizontal extent of the contaminant p lume;temporal trends in the behavior of the p lume; presence of pr e f e r en t ia lpathways; and the e f f e c t that the S o u t h Pla t t e River has on migrationrates and directions.The two basic o b j e c t i v e s of the groundwater m o n i t o r i n g program are to( 1 ) p r o v i d e s u f f i c i e n t i n f o r m a t i o n f r o m which both d o w n g r a d i e n tconcentrations in groundwater can be e s t a b l i s h e d and overa l l mass-l o a d i n g rates to the river can be e s t i m a t e d ; and (2) assess the degree towhich contaminants are c on f ined to the monol i th and to de t ec t anys t a t i s t i c a l l y s i g n i f i c a n t releases prior t o contaminants m i g r a t i n g o f f site.I n augment ing t h e e x i s t i n g monitoring wel l network, t h e U S G Srecognized the need to i d e n t i f y the p l u m e c en t er l ine as we l l as thetransient behavior of the p l u m e . In d o i n g so, the Survey incorporate sthree cros s- sec t ions o f w e l l s p e r p e n d i c u l a r t o groundwater f l o w .C l e a r l y , there is a need for a d d i t i o n a l data; the que s t ion is how to bestbalance the data needs against the overa l l o b j e c t i v e s and the p r a c t i c a l i t yof p e r f o r m i n g long-term m o n i t o r i n g of numerous wells._________

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Mr. Dave Back ( c o n t i n u e d )( 0 8 / 2 9 / 9 9 )

- A N S W E R : ; I S S U E S ^B - Has the remedy beeni m p l e m e n t e d in accordancewith dec i s ion documents?(Cont inued)

N A See issue and recommendationdiscuss ion.

I s s u e B l : Lack o f D o w n g r a d i e n t S i t e C h a r a c t e r i z a t i o n Data( C o n t i n u e d )In c orr e spondenc e t o th e USGS, EPA asked whether g eoprob es a m p l i n g could be an alternative to several w e l l s in a row and whetherit could be used to d e f i n e the p l u m e and p r e c i s e l y l o ca t e mon i t o r ingw e l l s , thereby r educ ing the number of w e l l s . In response to th i ss u g g e s t i o n , t h e U S G S i n d i c a t e d that data f r o m e x p l o r a t o r y d r i l l i n gwould provide only a "snapshot" of the d i s t r ibu t ion of contaminantswhich p r o b a b l y changes over an annual cycle and year-to-yearvariations in recharge of p r e c i p i t a t i o n . A l t h o u g h the Survey p o i n t s aretrue, there are a number of advantages to c o l l e c t i n g hydropunchs a m p l e s in order to op t imize the locat ions of f u t u r e moni t or ing w e l l s ,inc luding: 1) concentrations are far more r e p r e s e n t a t i v e of actual pore-water values, as they are not in t egrated over the entire screenedin t e rva l ; 2) s a m p l e s prov ide a much better three-d imens ional view oft h e p lume m o r p h o l o g y ; 3) s a m p l e s f a c i l i t a t e t h e i d e n t i f i c a t i o n o fp r e f e r e n t i a l pathways . As th e USGS notes, t h e concentrations w i l lchange with t ime; however, it is l i k e l y that the overall shape of theplume will probably remain re la t iv e ly constant. T h e r e f o r e , betterd e f i n i n g the p l u m e by hydropunch s a m p l i n g would f a c i l i t a t e th eo p t i m i z a t i o n of monitoring well p lacement .It i s a l so d i f f i c u l t t o ascertain e x a c t l y how th e USGS determined i t sp r o p o s e d we l l spac ings . I d e a l l y , characteri s t i c s such as p l u m ed i s p e r s i o n , contaminant v e l o c i t y , nature of the source re l ease (e.g.,p u l s e or cont inuous), presence o f p r e f e r e n t i a l p a t h w a y s and s a m p l i n gf r equency would be considered. The current lack of site data, however,would p r e c l u d e a p a r t i c u l a r l y quant i ta t iv e a n a l y s i s . T h e r e f o r e ,empirical i n f o r m a t i o n gained f rom h y d r o p u n c h s a m p l i n g s hou ldf a c i l i t a t e t h e o p t i m a l s p a c i n g o f a d d i t i o n a l moni t or ing w e l l s .An i m p l i c i t argument in the RI is that m o n i t o r i n g does not have to bep a r t i c u l a r l y in t en s iv e because c o n c e n t r a t i o n s are so low, once thep l u m e i s d i l u t e d w i t h i n the a l l u v i a l a q u i f e r and the river. T h i s assertioni s d i f f i cu l t t o s u p p o r t without a p r o p e r l y d e s i g n e d m o n i t o r i n g programsince the actual c onc en tra t i on s in the a l l u v i a l a q u i f e r w i l l remainunknown. The d o w n g r a d i e n t c onc en t ra t i on s curren t ly be ing observedmay be on the p l u m e f r i n g e s rather than on the centerline._______

3-27

Mr. Dave Back ( c o n t i n u e d )( 0 8 / 2 9 / 9 9 )

Q U E S T I O N S U B - Q U E S T I O N j I S S U E S & v R E e Q M M E N D A T U J N S : ;B - Has the remedy beeni m p l e m e n t e d in accordancewith d e c i s i on documents?( C o n t i n u e d )

I s s u e B l : Lack o f D o w n g r a d i e n t S i t e C h a r a c t e r i z a t i o n Data( C o n t i n u e d )W i t h respect to moni tor ing under a monitored natural a t t enuat ionremedy, O S W E R Directive 9200.4 s ta t e s ( p . 2 2 ) that the moni tor ingprogram s h o u l d be d e s i gned to a c c o m p l i s h the f o l l o w i n g :• Demonstrate that natural attenuation is occurring according to

expectations;• Detect changes in environmental conditions (e.g., hydrogeologic,

geochemical, microbiological, or other changes) that may reducethe efficacy of any of the natural attenuation processes;

• Identify any potentially toxic and/or mobile transformationproducts;

• Verify that theplume(s) is not expanding (either downgradient,laterally or vertically)',

• Verify no unacceptable impact to downgradient receptors;• Detect new releases of contaminants to the environment that could

impact the effectiveness of the natural attenuation remedy;• Demonstrate the efficacy of institutional controls that -were put in

place to protect potential receptors; and• Verify attainment of remediation objectives.

To addre s s these issues, the groundwater moni tor ing program needs tobe comprehensive. T h e r e f o r e , the items l i s t ed above should be expl i c i tdata q u a l i t y o b j e c t i v e s o f t h e p l u m e - m o n i t o r i n g p l a n .The pa s s iv e nature of the remedial a l t ernat ive for groundwater thate s s e n t i a l l y r e l i e s s o l e l y on d i l u t i o n f or th e l ong- l iv ed r a d i o n u c l i d e sp l a c e s an even greater importance on extensive groundwatermoni tor ing. U n l e s s a c r e d i b l e under s tanding o f the groundwater f l o wand contaminant proce s s e s can be d e v e l o p e d , not only wi l l the trueenvironmental i m p a c t s remain unknown._________________

3-28

Mr. Dave Back (cont inued)( 0 8 / 2 9 / 9 9 )

^ A N S W E R :B - Has the remedy beenimpl ement ed in accordancewith dec i s i on documents?( C o n t i n u e d )

I s s u e Bl: Lack o f Downgrad i en t S i t e C h a r a c t e r i z a t i o n Data( C o n t i n u e d )Recommenda t i on Bl:To a c c o m p l i s h the second goal of the groundwater monitoring p l a n(i.e., maintain the current ly e x i s t ing p l u m e of contanimat ion), thef o l l o w i n g a c t i v i t i e s should be undertaken:1) A downgradient geoprobe i n v e s t i g a t i o n shou ld be conducted inorder to e s t a b l i s h the general three-dimens ional shape of the p lume .2) Once the m o r p h o l o g y of the p l u m e is e s t a b l i s h e d , a numericalmode l ing s tudy should be p e r f o r m e d in order to o p t i m i z e the p la c ementof the monitoring w e l l s . F a c t o r s that need to be considered inc lude:p l u m e d i s p e r s i o n , contaminant ve loc i ty , nature of the source re lease(e.g., pu l s e or continuous), presence of p r e f e r e n t i a l pathways, ands a m p l i n g f r equency. A number of computer programs that ared e s i g n e d s p e c i f i c a l l y f o r th i s purpo s e .3) Since m e t a l s / r a d i o n u c l i d e s p e c i a t i o n and m o b i l i t y are verydependent on the presence or absence of oxygen, d i s s o lv ed oxygen andEh shou ld be measured in the moni tor ing w e l l s .4) D e p e n d i n g on the s a m p l i n g r e su l t s o f the e x p a n d e d p l u m e wel lnetwork, a moni tor ing well may need to be p l a c e d on the o ther s i d e ofthe S o u t h P l a t t e River.

5-29

Mr. Dave Back ( c o n t i n u e d )( 0 8 / 2 9 / 9 9 )

Q U E S T I O N S U B - Q U E S T I O N ^ A N S W E R - & R E C O M l V I E N D A T r O N SI s s u e B 2 : I n s u f f i c i e n t M o n o l i t h M o n i t o r i n gT h e M o n o l i t h M o n i t o r i n g P l a n ( M M P ) o u t l i n e s t h e a p p r o a c h that w a sused to p l a c e moni tor ing w e l l s to de t e c t l eaks f r o m the m o n o l i t h . Acomputer code (i.e., M E M O ) was used in a s to chas t i c framework top r e d i c t how much of the m o n o l i t h area would be e f f e c t i v e l y covered interms of leak d e t e c t i o n by p o t e n t i a l moni tor ing w e l l s . One of the keyparameters for th i s a n a l y s i s i s the transverse d i s p e r s i v i t y (i.e., theamount that the p l u m e spr ead s p e r p e n d i c u l a r to groundwater f l o w ) .The MMP ci te s a 1985 EPA guidance document that i n d i c a t e s thattransverse d i s p e r s i v i t y can be e s t imated as 0.33 times the l o n g i t u d i n a ld i s p e r s i v i t y . In the case of the monol i th the l o n g i t u d i n a l d i s p e r s i v i t y ises t imated at 10% of the travel di s tance f rom the monol i th to the siteboundary or 35 ft. T h e r e f o r e , a transverse d i s p e r s i o n of 12 ft wasassumed (0.33 times the l o n g i t u d i n a l dispersivity).____________

3-30

Mr. Dave Back (cont inued)( 0 8 / 2 9 / 9 9 )

B - Has the remedy beeni m p l e m e n t e d hi accordancewith decision documents?( C o n t i n u e d )

I s s u e B 2 : I n s u f f i c i e n t M o n o l i t h M o n i t o r i n g( C o n t i n u e d )The greater the transverse d i s p e r s i v i t y , the more l i k e l y the p lume w i l lintersect a moni tor ing w e l l . The value for transverse d i s p e r s i v i t y citedhi the 1985 EPA document was d e v e l o p e d pr i or to the f a m o u s tracerte s t s p e r f o r m e d at the Borden test s i te that i n d i c a t e d cons iderably lowertransverse d i s p e r s i v i t y values. More recent ly, Dr. Len G e l h a r , ap r o f e s s o r at MIT who has c on s id erab l e knowledge of contaminanttranspor t , has e s t imat ed transverse d i s p e r s i v i t i e s in the a l l u v i a l aqu i f e rsystem in the v i c i n i t y of Yucca Mounta in , N e v a d a , at a p p r o x i m a t e l y10% of the l o n g i t u d i n a l d i s p e r s i v i t y . T h i s sy s t em is s imilar to the one atthe Denver Radium site. T h i s would result in a transverse d i s p e r s i v i t yof 3.5 ft The MEMO m o d e l i n g re sul t s indicate that with a transversed i s p e r s i v i t y o f 6 f t . th e monitoring w e l l s e f f e c t i v e l y cover86% of the monol i th area. T h e r e f o r e , we know that th i s coveragewould be reduced if a value of 3.5 were to be used for transversed i s p e r s i v i t y . Furthermore , the transverse d i s p e r s i v i t y could be evens m a l l e r i f p r e f e r e n t i a l pathways exi s t beneath the monol i th .R e c o m m e n d a t i o n B2:1) M E M O should be rerun with s m a l l e r , more repre s entat ivetransverse d i sper s iv i t i e s .2) Based on the MEMO r e s u l t s a d d i t i o n a l moni tor ing w e l l s s h o u l d bep l a c e d o f f s e t to those that current ly exist to p r o v i d e at ieast a 95%c o n f i d e n c e that any leaks w i l l be d e t e c t e d . S i n c e the groundwater ismoving at 0.5 ft/yr and the mean d i s t anc e is a p p r o x i m a t e l y 350 ft, itcould take up to two years for the contaminant s to move f r o m themono l i th to the s i t e boundary. T h e r e f o r e , o n l y every other w e l l wouldneed to be s a m p l e d on an annual basis.__________________

3-31

Mr. Dave Back (con t inued)( 0 8 / 2 9 / 9 9 )

Q U E S T I O N S U B - Q U E S T I O N • A N S W E R I S S U E S & R E e O M J V l E N D A T l O N SB - Has the remedy beeni m p l e m e n t e d in accordancewith d e c i s i o n document s?( C o n t i n u e d )

I s s u e B 3 : U p g r a d i e n t Background C o n c e n t r a t i o n s A r e P o o r l yE s t a b l i s h e dThe presence of d i s s o l v e d uranium (in some cases over the ARARs)and other contaminant s in moni tor ing w e l l s USE 1 through 5 castsdoubt on their u t i l i t y as background w e l l s . The p r o b l e m is f u r t h e rexacerbated by the means o u t l i n e d in the M o n i t o r i n g Plan forde t ermining whether a re l ea s e has occurred. The MMP direc t s thats t a t i s t i c a l compari sons w i l l be made to determine whether there ares i g n i f i c a n t d i f f e r e n c e s in chemical concentrat ions betweendowngrad i en t and u p g r a d i e n t mon i t o r ing w e l l s . T h i s method couldmask release s if concentrations in the upgrad i en t moni tor ing w e l l s risewith time.As noted above, the high uranium concentrations in the upgradientw e l l s suggest that true background has not been e s tab l i shed .Furthermore, at least two mechanisms exist that could lead to a reversalin groundwater gradients and could p l a c e the ex i s t ing background w e l l sd i r e c t ly downgradient from the source. F i r s t , the low permeab i l i tyunits of the monoli th may allow water to c o l l e c t within the monoli thi t s e l f . T h i s monol i th water may be continuously discharged at a slowrate to the aqui f er . During time per iods over which there is l i t t l enatural recharge (i.e., summer), the water d i s charg ing f rom them o n o l i t h to the groundwater could create a mound beneath themonoli th. T h i s e f f e c t i s c ommonly re f err ed to as the "bathtub e f f e c t "and can lead to radial f l o w f r o m the m o n o l i t h . S e c o n d , a rise hi thewater t a b l e could intersect the m o n o l i t h which w o u l d , in turn, act as ah y d r a u l i c barrier and p o t e n t i a l l y reverse the ground-water gradient s .R e c o m m e n d a t i o n B3:1) P e r f o r m a h y d r o p u n c h i n v e s t i g a t i o n to e s t a b l i s h backgroundloca t i on s .2 ) I n s t a l l a d d i t i o n a l background w e l l s .3) S t a t i s t i c a l l y assess t r end s not o n l y against the background w e l l s butal so agains t the d o w n g r a d i e n t w e l l s through time.____________

3-32

Mr. Dave Back (con t inued)( 0 8 / 2 9 / 9 9 )

^ S U B - Q U E S T I O N : -B - Has the remedy beenimpl ement ed in accordancewith dec i s ion documents?( C o n t i n u e d )

I s s u e B4: C r i t e r i a Are Not C l e a r f or E s t a b l i s h i n g a ReleaseT h e r e does not a p p e a r to be clear guidance as to for what c on s t i tu t e s as i g n i f i c a n t release f r o m the m o n o l i t h and what actions are t r i g g e r e d bysuch releases. The M o n o l i t h Monitoring Plan states that a review ofcurrently available chemical data suggests that the most reliableindicators of contaminant migration from the monolith are likely to bemolybdenum and uranium. A M o r r i s o n - K n u d s e n (MK) s a m p l i n greport dated May 7, 1999 indicate s that MK compared the averages ofthe contaminant concentrations in the u p g r a d i e n t w e l l s with those in thedowngradient w e l l s and conc luded that at a 95% level of statisticalconfidence, no difference was found in the average concentrations forradium or thorium. However, average uranium concentrations exhibita significant difference between upgradient and downgradient wells asthe 95% level of confidence.The report a l so c onc lude s that , in general , m o l y b d e n u m concentrationsin the terrace w e l l s are greater than the A R A R , w h i l e c oncentra t ions ina l l u v i a l w e l l s are at or below the ARAR. T h i s la s t conclus ion i m p l i e sthat as l ong as A R A R s w i l l be met in the downgradi en t moni tor ingw e l l s , no f u r t h e r action is required. T h i s is e x a c t l y why a remedialalternative based s o l e l y on d i l u t i o n becomes so untenable . It could beargued that since d i l u t i o n alone was good enough for the remediat iono f r e s i d u a l l e v e l s o f c o n t a m i n a n t s c u r r e n t l y in th e g r o u n d w a t e r , whynot re ly on it for re l ease s f r o m the m o n o l i t h i t s e l f . It s h o u l d be kept inmind that C E R C L A s ta tu t e 121D2B requires that the ARARs (e.g.,MCL) be met at the s i t e boundary.Recommenda t i on B4:1) T r i g g e r l e v e l s and r emed ia l a l t e r n a t i v e s need to be d e v e l o p e d fora d d r e s s i n g p o t e n t i a l r e l ea s e s f r o m the monolith.______________

3-33

Mr. Dave Back (cont inued)( 0 8 / 2 9 / 9 9 )

Q U E S T I O N S U B - Q U E S T I O N A N S W E R - & R E C O M M E N D A T I O N SB - Has the remedy beeni m p l e m e n t e d in accordancewith d e c i s i on documents?( C o n t i n u e d )

I s s u e B 5 : A n a l y s i s f o r P r e d i c t i n g S o u r c e T e r m ReleaseC o n c e n t r a t i o n s I s Overly O p t i m i s t i cA p p e n d i x F of the Remedial Design c a l c u l a t e s a r educ t i on f a c t o r to theconcentrat ions of contaminant s i f any water i n f i l t r a t e s t hrough them o n o l i t h . T h i s a p p r o a c h assumes un i f orm mixing and may lead tononconservative r e su l t s when compared against d i l u t i o n e s t imate sp r e d i c t e d by d i sp er s i on-ba s ed mode l s .R e c o m m e n d a t i o n B5:1) It is a very s t r a i g h t f o r w a r d process to numeri ca l ly model themonol i th under various a s sumpt ion s (e.g., recharge rates) to assess howmuch d i l u t i o n wil l p o t e n t i a l l y occur.

B - Has the remedy beenimplemented in accordancewith decis ion documents?( C o n t i n u e d )

Issue B6: Lack of Any Source Term Release C a l c u l a t i o n s ofR a d i o n u c l i d e s f r o m the Concrete.The long-term behavior of concrete d e p e n d s upon numerous fac tor s .The s e f a c t o r s can be grouped broadly as chemical attack, phys i ca lstress, and microbial action. Degradation caused by chemical attackincludes the e f f e c t s o f s u l f a t e attack, calcium hydroxide leaching,alkali-aggregate reaction, and salt c ry s ta l l i za t i on . Degradation causedby physical stress includes the e f f e c t s of freeze-thaw cycles, wet-drycycles , and osmotic pressure. Degrada t i on caused by microbial actioni n c l u d e s th e e f f e c t s o f s u l f u r - o x i d i z i n g and n i t r i f y i n g bac t er ia andh e t e r o t r o p h i c organisms. It was not apparent that any a n a l y s i s has beenp e r f o r m e d to de t ermine the rate of concrete d e g r a d a t i o n of them o n o l i t h in the f u t u r e .Recommendat i on B6:An analys i s s h ou ld be p e r f o r m e d that assesses the f u t u r e d e g r a d a t i o n ofthe concrete and the f u t u r e re lease of r a d i o n u c l i d e s . A few computercodes have been d e v e l o p e d to p r o v i d e i n s i g h t into r e l a t i v e l y c ompl exgeochemistry for use s p e c i f i c a l l y to p r e d i c t concrete d e g r a d a t i o n andsubsequent release of m e t a l s / r a d i o n u c l i d e s . Most notable are BLT-EC( M a c K i n n o n e t a l , 1 9 9 5 ) a n d 4 S I G H T ( N a t i o n a l I n s t i t u t e o f S t a n d a r d sand T e c h n o l o g y , unpublished).______________________

3-34

Mr. Dave Back (con t inued)( 0 8 / 2 9 / 9 9 )

^ l l ^ p P S S i lC - Has any riskin format ion changed sincethe remedy was s e l e c t e d ?

i ; ? i : : ' £ ^ ^N / A

i^i:i^;liiiEffiii§ :ii^Not eva lua t ed by t h i s reviewer.

BH^B:£-^^^• • • - -.-.•.•.•.•.-.•.•.•...•.•.•.•.•.•.•. . . ,.-.;. .;. . . . . . . . . ; . . ; . ; . .-. ...... .- -. ...... ... ... . ... ..... . -.-.. -.. -.. ..-.. - .. ................. ........... ..... ...... .;............ ... . . . . . . . . . . . . . . . . . .•-• • ' •••••-••• ••••'••• • -•-•-•---•-•- - -.--. ...•.•..:•:•...•:•......:.... ,.,.;.. ....... ...-: . : .-.-. ::•:::•:•:::•:•::::::•; •-•-• ;-• • • :-• -.•.-.•.•.•.-.-.--•. -:.•,;,•.-.•. . . .;. .-... ....;.. .... .;..-............. ...... ...... ...........I s s u e :Recommendat ion: No comments.

Reference sEPA, A p r i l 1999, Directive 9200.4 Use of Monitored Natura l Attenuat ion at S u p e r f u n d , RCRA Corrective Act i on , and Underground Storage TankS i t e s , ( 1 7 p . ) .Kaback, D.S., and Runnel l s , D.D., 1980, Geochemis try of molybdenum in some stream sediments and waters: Geochimica et Cosmochimica Acta, v.44, p. 447-456.Dye,W.B., and O'Hara, J.L., 1959, M o l y b d o s i s : N e v a d a Agri cu l tura l Experimental S t a t i o n B u l l e t i n 208, 32 p .MacKinnon, R.J., T.M. S u l l i v a n , S.A. Simonson, and C.J. Suen, "BET-EC (Breach, Eeach, T r a n s p o r t , and Equil ibrium C h e m i s t r y ) , a Fini t e -El ementMode l f o r A d d r e s s i n g th e Release o f Radionuc l id e s F r o m Low-Eevel Was t e Dispo sa l U n i t s , U.S. N u c l e a r Regulatory Commis s ion, N U R E G / C R -6305, August 1995.

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Expert Panel Comments for 5-Year ReviewS h a t t u c k Chemical S i t e

Denver, C o l o r a d oDr. Steven S c h a f f e r( 0 8 / 2 2 / 9 9 )

S U B - Q U E S T I O N I S S U E S & R E C O M M E N D A T I O N SA - H a v e c o n d i t i o n sexternal to the remedychanged since the remedywas s e l e c t ed?

5) Has land use ore x p e c t e d land use onor near the sitechanged?

No. S e e m s to have remained commercial -indu s t r ia l .

I s s u e : N o n e .Recommendation: None.

6) Have any humanhealth or ecologicalexposure pathwayschanged or beennewly i d e n t i f i e d ?

Possible . C a n ' t determine f rom dataprovided. J u d g i n g from the information inthe RI report and the ATSDR H e a l t hConsul tat ion, a survey of water we l l s in thearea showed that no one was ut i l iz ing thegroundwater down gradient from the site.Based on this survey, everyone agreed thatno groundwater exposures were occurring,and groundwater c leanup was assumed to beunnecessary.

Issue: It is p o s s i b l e that new w e l l s have been i n s t a l l e d , and oldunused w e l l s have been reactivated in this ten year period.Recommendation: The survey is ten years old and needs to beupdated to conf irm the original assumption. Withou t this updatedsurvey, there is no d e f i n i t i v e proof that groundwater exposurepathway is not now occurring.

3-36

S U B - Q U E S T I O NA - H a v e condi t ionsexternal to the remedychanged since the remedywas s e l e c t ed?( C o n t i n u e d )

7) Are there newcontaminants orcontaminant sources?

Poss ib l e . F r o m an exposure po in t of view,the monolith represents a new contaminantsource because it changes the externalexposure geometry and prov id e s aconcentrated source for radon emanation.

8) Are thereunantic ipatedb y p r o d u c t s to theremedy not p r e v i o u s l yaddres s ed by theROD?

N o .

9) H a v e hydro l o g i c /h y d r o g e o l o g i c si tec ondi t i on s changed?

N o .

I s s u e : There is no p o s t - c l o s u r e moni tor ing program except forgroundwater. There is no way now or for fu tur e f i v e year reviewsto d e t ermine if exposures are occurring for the f o l l o w i n gpathways:

• radon emanation from the surface of the monolith intothe open airradon emanation f r o m the s u r f a c e of the monol i th be lowgrade and subsurface travel into b u i l d i n g s and d w e l l i n g ssurface water r u n o f f into storm sewers and neighboringland sur face s .

Monitor ing these pa thways i s c r i t i ca l for d e t e rmining the l o n gterm prot e c t ivene s s of the remedy.Recommenda t i on: A p o s t - c l o s u r e moni tor ing program needs tobe d e v e l o p e d for the above pa thways so that the EPA candetermine for fu ture f i v e year reviews if the remedy is acting asdes igned. The monitoring program should include yearly radonemanation measurements at the top of the m o n o l i t h and at thef enc e l ine . T h i s w i l l show if the m o n o l i t h i s s tar t ing to d egradeand will al low exposure estimates for p e o p l e l iv ing and workingnear the monol i th. The program should i n c l u d e yearly radonmoni tor ing in nearby basements. T h i s w i l l show if sub sur faceradon migration is causing unheal thy exposures. Y e a r l y radium,thorium and uranium measurements in storm sewer sediment andneighbor ing surface soil w i l l h e l p de termine i f s ur fa c e waterr u n o f f is occurring. Once this program is d e v e l o p e d it should bereviewed to determine if appropr ia t e techniques are used formeasurement s en s i t iv i ty , q u a n t i f y i n g spac ia l and temporalv a r i a b i l i t y , and assuring data quality._________________I s s u e : N o n e .Recommendation: None.

I s s u e : N o n e .Recommenda t i on: N o n e .

3-37

Dr. Steven S c h a f f e r (con t inued)( 0 8 / 2 2 / 9 9 )

Q U E S T I O N S U B - Q U E S T I O N . A N S W E R : -B - Has the remedy beeni m p l e m e n t e d in accordancewith dec i s ion documents?

N A New EPA guidance may show that theremedy f a i l e d to meet c l e a n u p goal s . TheEPA, DOE, DOD and NRC have d e v e l o p e da m u l t i - a g e n c y approach to p e r f o r m i n g thef i n a l radiat ion survey to prove that the clean-up criteria at rad ia t i on s i t e s are met (Mult i -A g e n c y R a d i a t i o n Survey and S i t e I n v e s t i -ga t i on Manual ( M A R S S I M ) , N U R E G -1575,EPA 402-R-97-016, December, 1997).

I s s u e : It is unclear f r o m the documents I reviewed that anapproach s imilar to (or as good as) thi s new survey guidance wasf o l l o w e d to prove that the re s idual r a d i o a c t i v i t y in soil meets theARARS. If an i n f e r i o r survey a p p r o a c h was taken, then thep o s s i b i l i t y e x i s t s that the remedy has not achieved its goal s .Recommendat ion: The actual f i n a l survey approach should becompared to the approach f o u n d in the new gu idance to d e t e rmineif it is adequate.

3-38

Dr. Steven S c h a f f e r (con t inued)( 0 8 / 2 2 / 9 9 )

A N S W E R ; ; !C - Has any riski n f o r m a t i o n changed sincethe remedy was s e l e c t ed?

N / A Y e s . T h e Cons t ru c t i on C o m p l e t i o n Reports tates that the soil c l e a n u p l e v e l s were basedon ARARs d e v e l o p e d at the time of theROD, 1992. The l e v e l s for Ra-226, T h - 2 3 0and gamma radiat ion were based upon theuranium m i l l t a i l i n g s s tandard 40 CFR 192.T h i s s tandard does no t s p e c i f y l ev e l s f o ruranium so the DOE order 5480.1 was used.

I s s u e : S i n c e the time of the ROD, EPA issued two O S W E RMemoranda concerning re s idual l ev e l s o f r a d i o a c t i v i t y l e f t onsitea f t e r remediation. An A u g u s t 22, 1997, O S W E R Memorandum( O S W E R No. 9200.4-18) s ta t e s that the maximum concentrat ionsof r e s idual rad i oa c t iv i ty s h o u l d not exceed t h e l O " 4 cancer risk.A c c o r d i n g to EPA the dose l e v e l s a p p r o x i m a t i n g t h i s risk l i m i t forhumans at S u p e r f u n d s i t e s should be l e s s than 15 mrem/yre f f e c t i v e dose equivalent (EDE) f r o m all radionuc l ide s andexposure pathways. T h i s l i m i t i s based on a s i t e - s p e c i f i c do s eassessment and d e p e n d s on the s i t e - s p e c i f i c r a d i o n u c l i d e s andexposure pathways. A February 12, 1998, O S W E R Memorandum( O S W E R No. 9200.4-25) fur th er c l a r i f i e s the use of the soilcleanup criteria in 40 CFR Part 192 as remediation goal s forC E R C L A S i t e s . T h i s memorandum s p e c i f i c a l l y addr e s s e ssub sur face s o i l s and s ta t e s that the sub sur fac e criterion for radium(15 p C i / g ) i s only h e a l t h p r o t e c t i v e and p o t e n t i a l l y relevant anda p p r o p r i a t e i f the d i s t r i b u t i o n of s ub sur fa c e contamination issimilar to the 24 U M T R C A Title I sites.A cursory review of the soil concentrations r emaining a f t e rc l e a n u p s u p p o r t s the f i n d i n g that the s i t e may not meet the newEPA c l e a n u p criteria in O S W E R No. 4200.4-18, and that thedose s may be w e l l above a c c e p t a b l e l e v e l s . The t a b l e on thef o l l o w i n g page i l l u s t r a t e s th i s po in t .The tab l e shows that , even a f t e r the remedy and with radiumbackground l e v e l s e x c l u d e d , the average so i l concentrat ionbeneath t h e mono l i th could exceed t h e E P A ' s s u g g e s t e d l i m i t b yas much as a f a c t o r of 2.3. T h i s t a b l e was d e v e l o p e d u s ing so i ldose conversions based upon generic and s t andard i z ed usage andexposure f a c t o r s , and chemical equi l ibr ium constants a s sumings u r f a c e soil exposures . It has been our experience that manyr e g u l a t o r y agenc i e s , i n c l u d i n g EPA, assume that s u b s u r f a c e s o i l scan be brought to the s u r f a c e by human a c t i v i t y thereby creatings u r f a c e soil expo sure scenarios.

3-39

Dr. Steven S c h a f f e r (cont inued)( 0 8 / 2 2 / 9 9 )

Q U E S T I O N S t I B - Q U E S T I 0 N A N S W E R I S S U E S & R E C O M M E N D A T I O N SC - Has any riski n f o r m a t i o n changed sincethe remedy was s e l e c t ed?( C o n t i n u e d )

If t h e EPA assumes that t h e re s idual c o n t a m i n a t i o n remainsbur i ed , then O S W E R N o . 4200.4-25 p r o v i d e s s p e c i f i c guidance.It s tates that , if the s u b s u r f a c e contaminat ion exi s t s at a levelbetween 5 p C i / g to 15 p C i / g averaged over 100 m 2, thenc o n d i t i o n s at the s i te are not s u f f i c i e n t l y s i m i l a r to an UMTRCAsite to cons ider the sub sur fac e contaminat ion s tandard in 40 CFRPart 192 a relevant or a p p r o p r i a t e requirement. The EPArecommends that in th i s s i tua t i on the 5 p C i / g s ur fa c e standard beused p r o v i d e d a site s p e c i f i c risk assessment demons tra t e s that th i slevel is protect ive. In a d d i t i o n , when parent r a d i o n u c l i d e s ofradium exist in the soil (Thor ium 230 and 232 and p o s s i b l yUranium 234 and 238), EPA recommends that the soil should be .cleaned to 5 p C i / g concentration for the parent rad i onuc l i d e s too.T h i s prevents f u t u r e b u i l d u p of radium to unsa f e l ev e l s .Again we f i n d that the residual l eve l s of rad ionuc l ide s insubsurface s o i l s are not health protective according to thi s newerdirective. The table on the f o l l o w i n g page shows that the averagesubsurface values for radium, thorium and uranium are allbetween 5 and 15 p C i / g . T h i s means that the 15 p C i / g subsurfacecriterion in 40 CFR Part 192 should not be used as a c l e a n u p goalbecause it is not h e a l t h p r o t e c t i v e for t h i s site. The t a b l e belowshows that the r e s i d u a l l e v e l s of Ra-226 and T h - 2 3 0 are above the5 p C i / g h e a l t h based criterion in the U M T R C A s tandard.Recommenda t i on: To de t ermine th e s a f e l e v e l s f o r th er a d i o n u c l i d e s in the r e s idual s ub sur fa c e s o i l s at the s i t e , a s i t es p e c i f i c risk asses sment needs to be p e r f o r m e d . Doses forsub sur fac e s o i l s could be h igh er or lower than those shown intab l e . The direct shine dose contribution f r o m Ra-226 and T h - 2 3 0would e s s e n t i a l l y decrease to zero because of the s h i e l d i n g f r o mthe soil above, but other expo sure mechanisms would becomemore important . For s u b s u r f a c e exposure s , one needs to cons iderradon migration into d w e l l i n g s and groundwater contaminationf r o m uranium._____________________________

3-40

Dr. S t e v e n S c h a f f e r (cont inued)( 0 8 / 2 2 / 9 9 )

C - Has any riskin format i on changed sincethe remedy was s e l e c t ed?( C o n t i n u e d )

Radon in d w e l l i n g s and subsequent inhalat ion is one of the c r i t i c a lexposure pathways the EPA sought to mi t igat e in the UMTRCAregulat ion. Radon gas is a d a u g h t e r produc t of the contaminantsof concern. A recent s tudy showed that the d i s tance radonmigrate s through soil is h i g h l y var iab l e and can range f r o m a fewle s s than a meter to many meters. The average travel d i s tanc e wasabout 5 meters. The d i s t anc e radon trave l s is d ependent onwhether the soil media is h i g h l y compac t ed which inhib i t smovement or contains cracks, f r a c t u r e s and c ondu i t s that promotemigration. It i s p o s s i b l e that radon f rom the s u b sur fa c e s o i l s andthe mono l i t h could travel to nearby b u i l d i n g s through spaces inthe s o i l s and c ondu i t s created by underground u t i l i t i e s .S i n c e uranium can r ead i ly move into groundwater, the sub sur fa c eso i l s could become an easy source for groundwater uraniumcontaminat ion. T h i s is because the c on tamina t i on is only a shortd i s t a n c e above the water table.____________________

S u m m a r y o f S o i l C o n c e n t r a t i o n s R e m a i n i n g A f t e r C l e a n u p

;:;:R ;AMi3^ic;]LIiDE;;=' • - - " - - ' .:?::....... . ' : : . ' . V . . V . - : - • • ' • ' • ' • ' • '

Ra-226T o t a l UraniumTh-230

T O T A L

:^^son^M^;:-M^.^•f^ONV^R^N^::

(mrem per p C i / g ) !

30.04

1

'-^M^^&'s^^; ; l ; S ; : : < S o i S f e E N ^ A T r o ^ s l : : : l ; : : i ;• : : : A F T 1 S R C L E A N U P ( p C i / g ) : : 2 : ; ; ;

Mean5149

U-95%7.62013

: ;::;:S:AiNGAtlMEC^i^E 7 : s :l:;:;^;;;;;p.osE;:EQup^^EN^;;;;;:ii:• : : : : : ; ; : ; . ; : ; ; . : : . ; : . ( m rem) . . • / V : : : . • : • ' . . • - : : : • ' - ' : •

Mean15

0.569

25

U-95%23

0.781337

1 Taken f r o m Radiation Site Cleanup Regulations: Technical Support Document for the Development of Radionuclide Cleanup Levels for Soils, EPA, S e p t e m b e r 1994, us ingthe commercial i n d u s t r i a l e xpo sure w i thou t the groundwater p a t h w a y .2 C a l c u l a t e d f r o m T a b l e 5 of the Construction Completion Report Vol 1, S h a t t u c k C h e m i c a l C o m p a n y , Inc., F e b r u a r y 8, 1999. Radium-226 background of 1.5 p C i / gsubtrac ted f r o m mean and U-95% c o n c e n t r a t i o n s .

3-41

Dr. Steven S c h a f f e r ( con t inued)( 0 8 / 2 2 / 9 9 )

Reference sBaseline Risk Asse s sment f o r Denver Radium S i t e Operable Unit VIII: C o l o r a d o Department o f H e a l t h : S e p t e m b e r 1991 .Denver Radium S i t e Cons truc t ion C o m p l e t i o n Report , Vol. 1&3, The S h a t t u c k Chemical Company, February 8, 1999.H e a l t h Consu l ta t i on for the Denver Radium S i t e , ATSDR, A p r i l 8 , 1999.Letter s f r om D.T. C h a f m and J.K. Otton o f the USGS to J. H a n l e y EPA Region VIII. March 24 ,1999 and May 24, 1999.RI Report for the Denver Radium S i t e OU VIII, CDH, S e p t e m b e r 1991.

3-42

Dr. J o h n G o o d e( 0 8 / 1 7 / 9 9 )

Exper t Panel Comment s for 5-Year ReviewS h a t t u c k Chemical S i t e

Denver, C o l o r a d o

A - H a v e condi t i onsexternal to the remedychanged since the remedywas s e l e c t ed?

1) Has land use ore x p e c t e d land use onor near the sitechanged?

The reviewer has not read or seen anyin f ormat i on that land use near the s i t e haschanged.

I s s u e : The 200-year de s ign l i f e makes p r e d i c t i o n o f f u t u r e landu s e d i f f i c u l t .Recommendat i on: S h o u l d prepare for most sensi t ive use;re s ident ial and recreational with e c o l o g i c a l organisms.

2) Have any humanheal th or e co log i ca lexposure pa thwayschanged or beennewly i d e n t i f i e d ?

The reviewer has not read or seen anyin format ion that any human h e a l t h ore co l og i ca l exposure pathways changed orwere newly i d e n t i f i e d .

I s s u e : The e c o l og i ca l pa thway a l o n g with some other minorpathways were not c o m p l e t e l y reviewed prior to the r emedia ldes ign.Recommendat ion: S h o u l d more t h o r o u g h l y review thesepathways a f t e r a d d i t i o n a l s a m p l i n g data have been p r o d u c e d .

3) Are there newcontaminant s orcontaminant sources?

The reviewer has not read or seen anyi n f o r m a t i o n that there are new contaminantsor contaminant sources.

I s s u e : The m o n o l i t h could become a source for f u r t h e rcontaminat ion of the groundwater.Recommendat ion: S h o u l d review remedial d e s ign to ensurem o n o l i t h i n t e g r i t y for the 200-year period and beyond.

4) Are thereu n a n t i c i p a t e db y p r o d u c t s to theremedy not p r e v i o u s l yaddre s s ed by theROD?

One unant i c ipa t ed byproduc t would be them o n o l i t h becoming a point source forgroundwater contaminat ion.

I s s u e : N o n e .Recommendat ion: As above.

5 ) H a v e h y d r o l o g i c /h y d r o g e o l o g i c s i t ec ond i t i on s changed?

The reviewer has not read or seen anyi n f o r m a t i o n that h y d r o l o g i c / h y d r o g e o l o g i csite c o n d i t i o n s have changed.

I s s u e : T h e r e i s ev idence that the h y d r o g e o l o g i c c ond i t i on s wereno t f u l l y character ized and t h i s i n c l u d e s t h e P l u m eCharac t er iza t i on (Emerald Environmental R e p o r t ) ( U . S .G e o l o g i c a l S u r v e y ) . Because of th i s , the general d i s t r i b u t i o n ofcontaminant c onc en tra t i on s in groundwater may not bec o m p l e t e l y characterized.R e c o m m e n d a t i o n : S h o u l d implement a m o n i t o r i n g program toh e l p ensure that contaminant concentrations are at a c c e p t a b l el ev e l s .

3-43

Dr. J o h n G o o d e ( c o n t i n u e d )( 0 8 / 1 7 / 9 9 )

Q U E S T I O N S U B - Q U E S T I O N - A N S W E R ; : I S S U E S : & R E C O M M E N D A T I O N SB - Has the remedy beeni m p l e m e n t e d in accordancewith dec i s ion documents?

N A In general the remedy has been i m p l e m e n t e din accordance with the de c i s i on documents.The ROD se l e c t ed the r emed ia t i on ofcontaminated mater ia l s l o ca t ed on theS h a t t u c k p r o p e r t y t o u s e s t a b i l i z a t i o n . T h i swas to i n c l u d e : (1) remedial action asrequired to addre s s the contaminated ground-water which i n f i l t r a t e s the storm sewerlocated west of the s i t e ; and (2)impl emen ta t i on of monitoring, in s t i t u t i ona lcontrols , and operation and maintenance.

I s s u e : S i n c e the nature and extent of the contamination togroundwater may not have been c o m p l e t e l y charac t e r i z ed , it is notcertain that this phase of the r e m e d i a t i o n has been p r o p e r l yi m p l e m e n t e d .R e c o m m e n d a t i o n : The groundwater monitoring program s h o u l dbe reviewed for e f f e c t i v e n e s s and expanded if necessary and thenused to addre s s whether active groundwater restoration measuresare warranted.

C - Has any riskinformation changed sincethe remedy was s e l ec t ed?

N / A T h e r e were some changes in M C L s betweenthe risk assessment and the time of the f inalremedial des ign. However, these changeswere taken into account prior to theimpl ementa t i on of the f i n a l de s ign. S i n c e1996, there has been a change in theg u i d e l i n e for arsenic, but the change inmagni tude was of no consequence to the RAor remedial d e s ign.

1991 Risk Asse s sment ReviewAs part of the Remedial Inve s t iga t i on and F e a s i b i l i t y S t u d y , abaseline risk assessment was conducted. The site contained mixedwaste that included radiation, metal s , and v o l a t i l e organiccompounds. Risks were determined for an onsite worker, onsiteresident, onsite trespasser, o f f s i t e worker, and o f f s i t e resident.Moni t o r ing data f rom each medium were evaluated to determinethe contaminants of greatest concern. Chemica l s were selectedaccording to the ir quant i ty and prevalence at the s i te , intrinsict o x i c o l o g i c a l p r o p e r t i e s , and p h y s i c a l and chemical p r o p e r t i e s .Eleven me ta l s , f o u r v o l a t i l e organic c o m p o u n d s , three semi-v o l a t i l e organic c ompounds and six i s o t o p e s were s e l e c t e d asc on taminant s of concern which were i n c l u d e d in the b a s e l i n e riskassessment.S e v e r a l chemical migrat ion pathways for contaminant re lease swere reviewed i n c l u d i n g groundwater , s ur fa c e water, s o i l , and air.The p a t h w a y s through the air and soil were determined to have themost p o t e n t i a l for contaminant migration. The reason for noti n c l u d i n g groundwater and s u r f a c e water pa thways was based onlack of r e c ep tor s . A t o x i c i t y assessment was then conductedwhere an e s t ima t e of the r e l a t i o n s h i p between the extent ofexposure to a contaminant and the increased l i k e l i h o o d a n d / o rseverity of adverse e f f e c t s to e x p o s e d i n d i v i d u a l s was made.___

3-44

Dr. John Goode (continued)( 0 8 / 1 7 / 9 9 )

; : ; A N S W E R ^C - Has any riski n f o r m a t i o n changed sincethe remedy was s e l e c t ed?( C o n t i n u e d )

1991 Risk A s s e s s m e n t Review( C o n t i n u e d )Risk characterization i d e n t i f i e d f o u r receptor groups i n c l u d i n gcurrent onsite workers, f u t u r e onsi te r e s i d e n t s , t r e s p a s s i n gch i ldr en , and current o f f s i t e r e s i d en t s . The s i te risks as soc iatedwith each re c ep tor group were determined.N o n r a d i o a c t i v e chemicals were evaluat ed . M o l y b d e n u mpresented the greatest noncarcinogenic hazard of th i s group, whi l earsenic and v o l a t i l e organic c ompound s presented cancer risks ofconcern.The most impor tant source of risk i d e n t i f i e d in the risk assessmentwas with the r a d i o l o g i c group of compounds. The greatest riskf r o m the site was whole body gamma exposure. Radon wasanother important source of ons i t e r a d i o l o g i c a l risk, but the o f f s i t eradon concentrat ions are c o m p a t i b l e with background radonvalues.U n c e r t a i n t i e s in the risk assessment inc luded measurement error,random var iab i l i ty , s a m p l i n g error, use o f p r o f e s s i o n a l j u d g m e n t ,m o d e l i n g uncer ta in t i e s , and u n c e r t a i n t i e s o f backgroundconc en tra t i on s .The 1991 risk assessment approa ch is d e t a i l e d and meets the EPAg u i d e l i n e s that were in p l a c e at the t ime the RA was c onduc t ed .T h e r e are now newer g u i d e l i n e s for Expo sure Ass e s smen t ( 1 9 9 2 ) ,Carcinogenic Risk ( 1 9 9 6 ) , R e p r o d u c t i v e T o x i c i t y Risk ( 1 9 9 6 ) ,and E c o l o g i c a l Risk ( 1 9 9 8 ) . The newer g u i d e l i n e s do not changethe overa l l a p p r o a c h of the RA but are a cont inuation of the EPA'sRA deve l opment proces s ini t ia t ed in the early 1980s. The newergu id e l in e s have an increase in f o c u s on exposure characterizationand p r o v i d e b e t t e r gu idanc e to a s s e s s i n g e c o l o g i c a l expo sure toc h e m i c a l s and human exposure to r a d i o l o g i c a l agents . T h e s e twoareas are a matter of concern with the 1 9 9 1 risk a s s e s sment

3-45

Dr. J o h n G o o d e ( c o n t i n u e d )( 0 8 / 1 7 / 9 9 )

Q U E S T I O N S U B - Q U E S T I O N • A N S W E R :C - Has any riski n f o r m a t i o n changed sincethe remedy was s e l e c t e d ?( C o n t i n u e d )

1991 Risk A s s e s s m e n t Review ( C o n t i n u e d )The g u i d e l i n e s do not addre s s f u t u r e risk which is a concern at theS h a t t u c k s i t e and the surrounding area since hazardouscontaminants have been left in p l a c e and c o m p l e t e r emed ia t i on ofgroundwater may not occur for de cade s in the f u tur e .Exposure AssessmentT h e Risk Ass e s smen t Guidanc e f o r S u p e r f u n d ( " R A G S " ) i ncharacterizing exposure d i s cu s s e s three basic land use categories:re s ident ia l; c o m m e r c i a l / i n d u s t r i a l ; and recreational. Based onactivities in the area, R A G S also a l lows for more than a s ing l eland use. T h i s is a j u d g m e n t issue. In determining future land use,RAGS states "Because re s ident ial land use is most o f t e nassociated with the greatest exposures, it is generally the mostconservative choice to make when dec id ing what type of alternateland use may occur in the future." It fur ther states to assumefuture residential land use, if it seems pos s ib le , based on theevaluation of the available information. For e xampl e , "if the siteis currently industrial but is located near residential areas in anurban area, future residential land use may be a reasonablepossibility."The N a t i o n a l C o n t i n g e n c y P l a n (40 CFR 300) e s t ab l i s h e s thatc l e a n u p s of r a d i o n u c l i d e s are governed by the risk range forcarcinogens at l e v e l s in the 10~" to 10"6 range. The l i m i t s of thisrange are g enera l ly used as guidance to de t ermine pre l iminaryremediation c l eanup goa l s ( P R G s ) between commercial andr e s i d e n t i a l / r e c r e a t i o n a l sites. It s hou ld be noted that the EPA doesnot consider 1 x 10"4 or 1 x 10"6 as "discrete lines."U p o n review of the S h a t t u c k document s , it a p p e a r s that the PRGwas set for a ch i ev ing a risk of 1 x 10"4 ( i n d u s t r i a l ) . T h a t may notbe s u f f i c i e n t l y p ro t e c t i v e . The reasons for th i s are:

3-46

Dr. J o h n G o o d e (cont inued)( 0 8 / 1 7 / 9 9 )

I - A N S W E R : ; I S S U E S & R E C O M M E N D A T I O N SC - Has any riskin format ion changed sincethe remedy was s e l e c t ed?( C o n t i n u e d )

1991 Risk A s s e s s m e n t Review( C o n t i n u e d )

1. The site area p r e s e n t l y inc lude s recreational and r e s i d e n t i a lac t ivi t i e s , and these should have been r e f l e c t e d in the c l e a n u pgoal.2. T r y i n g to p r e d i c t the f u t u r e of land use over the next 200years i s d i f f i c u l t . However , there i s j u s t i f i c a t i o n for b e l i e v i n gthat Denver w i l l continue to grow and wi l l be m u l t i p l e s of itspresent p o p u l a t i o n in 200 years.3. The long h a l f - l i f e of the radioactive contaminants (up to10E10 years for U - 2 3 8 ) guarantees that the r a d i o n u c l i d econtaminants w i l l s t i l l have much of th e i r a c t i v i t y throughoutthe 200-year period and beyond.4. T h i s is the on ly r a d i a t i o n waste r epo s i t o ry set in a m a j o rm e t r o p o l i t a n area in the U.S. and as such is unique.5. S e c u r i t y at present does not go beyond the s i t e boundarie s ,and the EPA has gone on record (FR 1 / 1 1 / 9 5 ) as l i m i t i n gc r e d i b l e maint enance to 100 years.

T h i s l a s t point pr e s en t s a current issue for the s i t e . 40 CFR 192a l l o w s for natural restoration as a viable a l t ernat ive in s i t u a t i o n swhere groundwater use and e c o l o g i c a l c o n s i d e r a t i o n s are nota f f e c t e d , a n d c l e a n u p w i l l occur w i t h i n a r ea sonab l e t ime . T h i sreasonable time to restore the a q u i f e r us ing p a s s i v e r e s t ora t ion isd e f i n e d as 100 years. At that t ime, the a q u i f e r is to be returned tobackground l e v e l s o r d r i n k i n g water s t a n d a r d s ( A C L s ) . I f t h eres torat ion c a n ' t b e a c c o m p l i s h e d i n t h i s p er i od ( 1 0 0 years), thencorrective action is to be taken. Because of the r a d i o l o g i c a lc o n t a m i n a t i o n , it is p r o b a b l e that t h i s a q u i f e r can not be restoredto d r i n k i n g water s t a n d a r d s w i t h i n 100 years. __ ^^^

3-47

Dr. J o h n G o o d e ( c o n t i n u e d )( 0 8 / 1 7 / 9 9 )

^ Q U E S T I O N ; ; / S l I B - Q l f E S T i O N v ^ A N S W E R : :C - Has any riski n f o r m a t i o n changed sincethe remedy was s e l e c t ed?( C o n t i n u e d )

1991 Risk A s s e s s m e n t Review( C o n t i n u e d )Pathways

The 1991 pr e l iminary risk assessment did not c o m p l e t e l yevaluate p o t e n t i a l human h e a l t h risk associated with e i ther thegroundwater pa thway or sur fa c e water exposure. The r a t i o n a l e ford i s m i s s i n g the s ur fa c e water p a t h w a y was (pg. 16) "Groundwaterm o d e l i n g and a n a l y t i c a l data indicate that site groundwatercontaminants are not expected to s i g n i f i c a n t l y contribute tosur face water contamination levels."The e co log i ca l pa thway was d i smi s s ed because "due to a lgalgrowth and a not iceable surface sheen on the retention pond... p o t e n t i a l exposures to either human or ecological receptors isconsidered to be unlikely..." (p. 17). The groundwater pathwaywas di smi s s ed with the rationale that there are no currentdowngradient users ( p g . 17).The 1991 risk assessment did evaluate the level of risk for theu n d e r l y i n g a q u i f e r which showed it to be unacceptable as drinkingwater. For rad i oac t iv e contaminants, uranium was the mosts i g n i f i c a n t contributor, with a ca l cu la t ed l i f e t i m e risk of 6.7 x 10"3

based on drinking two l i t e r s of water per day for 30 years. T h i s isd i s t u r b i n g since uranium has a l o n g h a l f - l i f e (U-234 = 240,000yrs, U-238 = 4,400,000,000 yrs) and would be e xp e c t ed to lo s ea p p r e c i a b l e a c t i v i t y in the p r o p o s e d 200-year time p e r i o d .

In a d d i t i o n , the a n a l y t i c a l da ta summarized in the 1991 riskassessment ( T a b l e 1 ) i n d i c a t e s non-carcinogenic tox i c e f f e c t s w i thseveral c on taminant s e x c e ed ing current ARAR leve l s .C a l c u l a t i o n s f o r non-radioac t ive groundwater contaminantsi n d i c a t e that arsenic is the carcinogen of highest concern, with al i f e t i m e risk of 2.7 x 10-4, whi l e the non-carcinogeniccontaminant s , m o l y b d e n u m and antimony, were of concern withhazard indices of 160 and 5 respectively.______________

3-48

Dr. J o h n G o o d e (con t inued)( 0 8 / 1 7 / 9 9 )

C - Has any riski n f o r m a t i o n changed sincethe remedy was s e l e c t e d ?( C o n t i n u e d )

1991 Risk A s s e s s m e n t Review( C o n t i n u e d )The uncer ta int i e s section of the 1991 Preliminary RiskA s s e s s m e n t does not c o m p l e t e l y addre s s other minor pathwaysre la t ed to the groundwater and sur face water. A l t h o u g h theinges t ion pathway is the ma jor pa thway of concern wi th thegroundwater, a d d r e s s i n g only thi s f u t u r e use for the groundwatermay be viewed as i n d i c a t i n g that the groundwater s i tuat ion isa c c e p t a b l e , as l ong as d r i n k i n g the water is p r e c l u d e d . Based oncurrent data, any f u t u r e use has to be viewed as u n a c c e p t a b l e . Fore x a m p l e , use of groundwater for irrigation would o f f e r a pa thwayfor r a d i o l o g i c a l as we l l as other contaminants to p l a n t s andanimals and other e c o l o g i c a l organisms, as we l l as an entry to thef o o d chain for humans. Such use may al so d e p o s i t thecontaminant s in soil and present a pathway for a d d i t i o n a l humanexposure through the i n h a l a t i o n ( d u s t ) and inge s t i on pathways.Cons idera t i on should al so be given to c o n d i t i o n s that mightaero so l ize some contaminants if the groundwater is sprayed towater lawns, or used in f o u n t a i n s , etc.The 1991 risk assessment did evaluate the inge s t i on of gardenv e g e t a b l e s grown in c o n t a m i n a t e d s o i l which e x i s t e d on aresidential vicinity property. T h i s resulted in a ca l cu la t ed risk of 6x 10~6 for a one-year consumption of home grown v e g e t a b l e s and1.9 x 10"4 for t h i r t y years of consumpt ion. T h i s pa thway is ofconcern not o n l y for contaminated so i l but a l s o for a scenariowhere the a q u i f e r or area s u r f a c e water is used for i r r i g a t i o n . T h i spa thway warrants f u r t h e r s tudy.S i n c e t h e r a d i o l o g i c a l c on taminan t s w i l l b i o a c c u m u l a t e in a n i m a l sand p l a n t s , these pa thways , a l t h o u g h s m a l l , must be c a r e f u l l ycons idered when d e c i d i n g on f u t u r e uses for the groundwater.

3-49

Dr. J o h n G o o d e ( c o n t i n u e d )( 0 8 / 1 7 / 9 9 )

Q U E S T I O N S U B - Q U E S T I O N I S S U E S & R E C O i a i V l E I S T J A T I O N SC - Has any riski n f o r m a t i o n changed sincethe remedy was s e l e c t e d ?( C o n t i n u e d )

1991 Risk Ass e s smen t Review( C o n t i n u e d )There is a concern that the s u r f a c e water and e c o l o g i c a l p a t h w a y swere not evaluated f u l l y . The 1991 risk assessment s ta t e s"Contact with the water in the retention pond could adverselyimpac t e i ther human or e c o l o g i c a l receptors." A l s o , it is notunders tood why rul ing out the retention pond also ruled out anye co l og i ca l assessment. T h i s is p a r t i c u l a r l y important since theretention pond may be recharged by the groundwater, whichwould present a p o t e n t i a l hazard upon reaching the surface.However, there was l i t t l e if any consideration given to thispathway. Due to area recreational and residential act ivi t ie s , thep o s s i b l e recharge of surface water, and the c loseness of the P l a t t eRiver, a more comprehensive e co log i ca l evaluation should bemade.An Oak Ridge Laboratory workshop on eco logical risk concludedthat protec t ion of humans genera l ly means protect ion to p l a n t s andanimals except where human access is restricted for pro t e c t ion,where unique exposure pathways exist and/ or where endangeredspe c i e s are present. At leas t two of these c o n d i t i o n s exist at thepresent site. The Oak Ridge Laboratory workshop a l s orecommended a 0.1 r a d / d a y l i m i t for a n i m a l s and p l a n t s .A current risk assessment would be a p p r o p r i a t e given the de s ignlife of the remedy (200 to 1,000 yrs), the po t en t ia l for recreationaluse near groundwater d i s charge po in t s a long the P l a t t e River,p o t e n t i a l f u t u r e groundwater use, and the p o t e n t i a l for a d d i t i o n a lsur fac e water use f r o m nearby pond s . However , there is nots u f f i c i e n t data at present to c ompl e t e a c r e d i b l e risk assessment.The s t e p s necessary i n c l u d e a better d e f i n i t i o n o f the a q u i f e r ,expans ion o f monitoring data, c o l l e c t i n g a d d i t i o n a l e c o l o g i c a ldata, reviewing a p p r o p r i a t e c oncep tua l m o d e l s , c a l c u l a t i n gcontaminant concentrations in groundwater, and c a l c u l a t i n g risk.The assessment should i n c l u d e the following:____________

3-50

Dr. John Goode (continued)( 0 8 / 1 7 / 9 9 )

S U B - Q U E S T I O N I S S U E S & R E G I O 3 V O ^ I E ^ ^ D A T K ) N SC - Has any riskin f ormat i on changed sincethe remedy was s e l e c t ed?( C o n t i n u e d )

1991 Risk A s s e s s m e n t Review( C o n t i n u e d )

An eco log i ca l risk assessmentA r e s i d e n t i a l groundwater user scenarioA recreational sur fa c e water userA release f r o m the m o n o l i t h under c ond i t i on s that couldinclude f r a c t u r i n g and d e g r a d a t i o n of the cap.

Background DataA minor concern with the 1991 risk assessment was itspresentation of contaminants detected at the site s e lec ted forinc lu s i on in the risk assessment process. A p p e n d i x A of the 1991Risk Ass e s smen t report contains t ab l e s that i l l u s t r a t e the f a c t o r sused in the s e l ec t ion process. The r epor t s s tate s that eleven metalswere s e l e c t e d as p o t e n t i a l inorganic chemica l s of concern becauseof e l evated l e v e l s on site (i.e., above background l e v e l s obtainedf r o m the nearby g o l f course). A p p e n d i x A contains apparenterrors which increase the background l e v e l s for most of thecontaminants . The f o o t n o t e i m p l i e s that where the contaminant swere not de t e c t ed , the value was set at one-half the sampleq u a n t i t a t i o n l i m i t (SQL). In the m a j o r i t y o f cases where t h i soccurred, the value was set at the S Q L . In T a b l e A-3 there areseveral reported values for s i t e s a m p l e s that are below the S Q L s .The s e t t i n g of background values for c o p p e r , iron, arsenic andvanadium, which were analyzed for but not d e t e c t e d , a p p e a r s tohave no r e l a t i o n s h i p to t h e i r S Q L s even t h o u g h the f o o t n o t e to thetab l e s tate s they do . In T a b l e s A-4, V o l a t i l e Organic S a m p l e d inS o i l s ; T a b l e A - 5 , V o l a t i l e Organic S a m p l e d i n Groundwat er;T a b l e A-6, S e m i - V o l a t i l e Organic C h e m i c a l s S a m p l e d i n S o i l ; a n dT a b l e A-7, S e m i - V o l a t i l e Organic C h e m i c a l s S a m p l e d inGroundwater , all the background values are l i s t e d as ana lyzed forbut not d e t e c t e d .

3-51

Dr. J o h n G o o d e ( c o n t i n u e d )( 0 8 / 1 7 / 9 9 )

Q U E S T I O N S U B - Q U E S T I O NC - Has any riski n f o r m a t i o n changed sincethe remedy was s e l e c t e d ?( C o n t i n u e d )

1991 Risk A s s e s s m e n t Review ( C o n t i n u e d )The as sociated numerical value is s tated to be one-ha l f the s a m p l equant i ta t ion l i m i t . In most cases the SQL is used. In other cases,such as D i - n - b u t y l p h t h a l a t e , the background given is s tated at one-h a l f SQL and is l i s t e d at 850, the SQL is 165 and the average andmaximum re sul t given for site s a m p l e s i s 59, below the SQL. Inother words, the SQL is incorrect ly used as the surrogate forbackground for many of the contaminants which do not exist inthe background.R A G S encourages the use of SQL for sett ing values for non-detec ted chemicals at a site where there is reason to believe thatthe chemical is present. In th i s way, the risks that would be posedif the chemical is present at the SQL can be compared with risksposed by other chemicals at the site. T h i s approach is used inorder to be conservative in the es t imation of risk. But s e t t ing allthe background values at SQL for all non-detects is not conserva-tive where risk is concerned, as many contaminants may bee l iminat ed as concerns and/or, at l eas t , have values diminished byhigh background values. The approach also assumes there is abackground for every chemical at every po in t in the country.Current and f u t u r e risk e v a l u a t i o nIt should be s tated that there is no i n f o r m a t i o n in the documentsreviewed showing that any current o f f - s i t e risks to human h e a l t hexi s t . However , the contaminant s are s t i l l pr e s en t and, if notc o n t r o l l e d , s t i l l have the p o t e n t i a l for causing harm to humans, theenvironment, and e c o l og i ca l organisms.A review was undertaken to see if a d d i t i o n a l i n f o r m a t i o n wasa v a i l a b l e since the 1991 Risk A s s e s s m e n t that would a l l ow thereviewer to p r o v i d e an e s t imate of current r a d i o l o g i c a l risk. T h i si n c l u d e d a review of moni t or ing and other i n f o r m a t i o n that has

3-52

Dr. J o h n G o o d e ( c o n t i n u e d )( 0 8 / 1 7 / 9 9 )

S S B B - - Q U E S T I O N : : ; • • A N S W E R " I S S U E S & R E C O M M E N D A T I O N SC - Has any riskinformat ion changed sincethe remedy was s e l e c t ed?( C o n t i n u e d )

1991 Risk Asse s sment Review( C o n t i n u e d )been documented since that p er i od . A d d i t i o n a l i n f o r m a t i o n woulda l l o w us to decrease some of the unc er ta in t i e s documented in the1991 assessment.The 1991 risk assessment i n f o r m a t i o n did not addre s s f u t u r e riskwhich is a concern at the S h a t t u c k s i t e and surrounding area sincehazardous contaminants have been left in p l a c e and c o m p l e t eremediation of groundwater may not occur for decade s to come.

The main concern is the long-term risk po t en t ia l of thegroundwater. There has been use of the groundwater in the pastand without s trict i n s t i t u t i o n a l c on tro l s , there may be use of thegroundwater b e f o r e its present risk level has been reduced . Therecent M-K s a m p l i n g report since c o m p l e t i o n of the m o n o l i t h s t i l lshows con s t i tu en t s , such as mo lybdenum, above t r i g g e r l ev e l s .The pas s ive nature of the remedial al ternative for groundwater thate s s e n t i a l l y r e l i e s s o l e l y on d i l u t i o n f or the l o n g - l i v e dradionuc l ide s , p la c e s an even greater importance on extensivegroundwater monitoring. U n l e s s a c r ed i b l e under s t and ing of thegroundwater f l o w and contaminant proce s s e s can be d e v e l o p e d ,the true environmental i m p a c t s may remain unknown.P e r f o r m a n c e c r i t e r i a , e s p e c i a l l y f o r t h e groundwater p l u m e ,should be d e v e l o p e d and monitored. The goal of these cr i t er iashould d emons t ra t e t h e M C L s f o r a l l groundwater c o n s t i t u e n t sw i l l be achieved in the r egu la t o ry t i m e f r a m e . W i t h o u t t h i si n f o r m a t i o n , the Panel is not convinced that the groundwater w i l lachieve necessary groundwater s t a n d a r d s required by CFR 40 192with in the 100-year timeframe.___________ ______

Dr. J o h n G o o d e ( c o n t i n u e d )( 0 8 / 1 7 / 9 9 )

Q U E S T I O N S U B - Q U E S T I O N • / A N S W E R ;C - Has any riskinformation changed sincethe remedy was s e l e c t e d ?( C o n t i n u e d )

1991 Risk A s s e s s m e n t Review( C o n t i n u e d )The EPA has g e n e r a l l y assumed that c l eanups to ARARS ares a t i s f a c t o r y because the r e s idua l risk w i l l be in the 10~4 to 10"6

range. However , EPA has c l a r i f i e d that c l e a n u p s of r a d i o n u c l i d e sare governed by this risk range for all carcinogens e s t a b l i s h e d inthe NCP when A R A R s are not available or are not s u f f i c i e n t l ypro t e c t ive . EPA i n c l u d e s all r a d i o l o g i c c omponen t s ascarcinogens. T h a t is, c l eanup shou ld g enera l ly achieve a l eve l ofrisk within the 10~4 to 10~6 range based on the reasonablemaximum exposure for an individual . However, the u p p e rboundary of the risk range is not a discrete line at 1 x 10"4,al though EPA genera l ly uses 1 x 10"4 in making risk managementdecisions. A s p e c i f i c risk estimate around 10"4 may be consideredacceptable if j u s t i f i e d based on s i t e - s p e c i f i c conditions. However,because of the recreational and re s ident ia l activities in theShattuck area, a lower risk level may be more appropriate.____

3-54

Exper t Panel Comment s for 5-Year ReviewS h a t t u c k Chemical S i t e

Denver, C o l o r a d oMr. Phil Rogers( 0 8 / 2 3 / 9 9 )

A - H a v e c o n d i t i o n sexternal to the remedychanged since the remedywas s e l e c t ed?

1) Has land use ore x p e c t e d land use onor near the sitechanged?

T h i s reviewer has not seen any i n f o r m a t i o nthat would i n d i c a t e pre sent land use haschanged. H o w e v e r , f u t u r e e xp e c t ed land useis reasonably expec t ed to change withrespec t to groundwater and sur fa c e wateruse. Given the l o n g e v i t y of the remedy, it isnot unreasonable that land use downgradientof the site may change and that change couldenta i l renewed groundwater use.

I s s u e : The remedy did not cons ider e i ther a groundwater ors ur fa c e water receptor . Land use on the site is res tricted by d e e d ,and there are no apparen t o f f s i t e l egal land use re s tr ic t ions .R e c o m m e n d a t i o n : Per form a s u p p l e m e n t a l risk assessment thati n c l u d e s both groundwater and sur fac e water receptor scenarios.T h i s s u p p l e m e n t a l risk assessment shou ld consider maximumgroundwater contaminant l e v e l s with the u n d e r s t a n d i n g that thel i m i t e d p l u m e moni t or ing system may not be s u f f i c i e n t to cap turemaximum contaminant concentrations.

2) H a v e any humanh e a l t h or e co l og i ca lexposure pa thwayschanged or beennewly i d e n t i f i e d ?

T h i s reviewer has not seen any i n f o r m a t i o nthat would i n d i c a t e present human hea l th ore c o l o g i c a l exposure pathways have changed.However, f u t u r e p o t e n t i a l groundwaterreceptors and c u r r e n t / f u t u r e s u r f a c e waterr e c e p t o r s have been i d e n t i f i e d . T h e r e are nocurrently known downgradi en t groundwaterusers. T h e r e are groundwater users in thearea and given the e x p e c t e d l o n g e v i t y of theremedy, it is not unreasonable to assume af u t u r e downgrad i en t groundwater receptor.S u r f a c e water i s currently being used forrecreation ( S o u t h P l a t t e River). T h e r e i s anunnamed pond d o w n g r a d i e n t of the s i t e thatmay be r e c e iv ing groundwater recharge f r o mt h e contaminant p l u m e . W a t e r f r o m t h i spond may be used for i r r i g a t i o n . ^^

I s s u e : The remedy did not s u f f i c i e n t l y consider either thep o t e n t i a l groundwater or sur fa c e water pathways. T h e s e p o t e n t i a lf u t u r e p a t h w a y s could be viable given the uncertainty in 1) f u t u r eland use and 2) the long-term p e r f o r m a n c e of the remedy (seeI s s u e s under Ques t ion B).Recommendat ion: Per f orm a s u p p l e m e n t a l risk assessment thatin c lude s both groundwater and s u r f a c e water r e c ep tor scenarios.T h i s s u p p l e m e n t a l risk assessment should consider maximumgroundwater contaminant l e v e l s , with the u n d e r s t a n d i n g that thel i m i t e d p l u m e monitoring system may not be s u f f i c i e n t to capturemaximum contaminant concentrations. A l s o , a p p r o p r i a t e releasem o d e l s and r e a l i s t i c time-variant i n f i l t r a t i o n rates through the capand m o n o l i t h are required.

3) Are there newcontaminants orcontaminant sources?

The reviewer has not seen da ta ori n f o r m a t i o n that would ind i ca t e that there arenew contaminants or sources.

I s s u e : N o t a p p l i c a b l e .R e c o m m e n d a t i o n : N o t a p p l i c a b l e .

3-55

Mr. Phil Rogers (con t inued)( 0 8 / 2 3 / 9 9 )

^ . Q U E S T I O N ; ; V A N S W E R ; : I S S U E S & R E C O M M E N D A T I O N SA - H a v e c o n d i t i o n sexternal to the remedychanged since the remedywas s e l e c t ed?( C o n t i n u e d )

4) Are thereunant i c ipa t edbyproduc t s to theremedy not p r e v i o u s l yaddre s s ed by theROD?

The reviewer has not seen data ori n f o r m a t i o n that would i n d i c a t e that there arenew contaminants or sources.

I s s u e : N o t a p p l i c a b l e .Recommendat i on: N o t a p p l i c a b l e .

5 ) H a v e h y d r o l o g i c /h y d r o g e o l o g i c sitecondi t ions changed?

There are i n s u f f i c i e n t data and i n f o r m a t i o nto addre s s th i s subquestion.

I s s u e : The reviewer notes that the h y d r o g e o l o g i c data andin f ormat i on downgradient of the site are p o t e n t i a l l y i n s u f f i c i e n t toaddress this subquestion.Recommendat ion: I m p l e m e n t t h e U S G S p r o p o s e d enhancementsto the groundwater monitoring system.

B - Has the remedy beeni m p l e m e n t e d in accordancewith deci s ion documents?

N A The reviewer has not seen data orinformation that would indicate that theremedy has met the long-term per formancerequirements of C E R C L A .

I s s u e : U n c e r t a i n t y on the L o n g - T e r m P e r f o r m a n c e of theRemedyThe remedy did not s u f f i c i e n t l y consider either the po t en t ia l fu turegroundwater or surface water pathways. T h e s e po t en t ia l fu tur epathways could be viable given the uncertainty in 1) fu ture landuse and 2) the long-term performance of the remedy. Severalpoint s concerning the long-term performance of the remedy arediscussed in the f o l l o w i n g .The m a j o r components and f e a t u r e s of the remediation are 1) thebase of the waste is currently p l a c e d a d i s t anc e of at least f o u r f e e tabove the groundwater l e v e l , 2) the waste f orm is a mono l i thc on s i s t ing of cement, contaminat ed s o i l , and fly ash, and 3) them o n o l i t h is covered by a l o w - p e r m e a b i l i t y sur fac e barrier (cap)c o n s i s t i n g o f a r i p r a p layer, f i l t e r drainage layer, g e o syn th e t i c c layl i n e r , and a r e compac t ed clay layer. The required long-termp e r f o r m a n c e of the system as a whole is compromised if any oneof these f e a t u r e s f a i l s to f u n c t i o n as d e s i gned or if s ite condi t i onschange such that any f e a t u r e is no longer e f fec t ive.________

3-56

Mr. Phil Rogers ( c o n t i n u e d )( 0 8 / 2 3 / 9 9 )

B - Has the remedy beeni m p l e m e n t e d in accordancewith d e c i s i on documents?( C o n t i n u e d )

I s s u e : U n c e r t a i n t y on the L o n g - T e r m P e r f o r m a n c e o f theRemedy ( c o n t i n u e d )T h i s is not to say that a ca ta s t r oph i c f a i l u r e would be e x p e c t e d tooccur. S y s t e m p e r f o r m a n c e d e g r a d a t i o n would be e x p e c t e d to bein the form of a gradual increase in the rate of contaminant releaseto the vadose zone or groundwater, d e p e n d i n g on f u t u r egroundwater l e v e l s . T h i s t y p e o f system d e g r a d a t i o n could bevery d i f f i c u l t to detec t and c o n f i r m , e s p e c i a l l y given theuncertainty in background contaminat i on l e v e l s and the presentmonitor ing system.The Decision Summary for the Record of Deci s ion prov id e s ap e r f o r m a n c e criteria s tandard of 1,000 years for the remedy as awhole based on 40 CFR 192 S u b p a r t A, which s ta t e s the de s ignshould be for 1,000 years to the extent reasonably achievable , and,in any case, for at leas t 200 years. T h e r e are a d d i t i o n a lrequirements set f o r t h by the U.S. N u c l e a r RegulatoryCommiss ion (NRC). The NRC did not s p e c i f y a p e r f o r m a n c eper i od f o r t h e overall engineering f a c i l i t y . The NRC, however, d ids tate in one of the p e r f o rmanc e o b j e c t i v e s that the d e s i g n of aLLW d i s p o s a l f a c i l i t y must p r o v i d e p r o t e c t i o n t o i n d i v i d u a l s f r ominadver t en t in tru s i on as expre s s ed in 10 CFR 6 1 . 7 ( b ) ( 5 ) where it iss tated that as a "Concept" any component serving as an intruderbarrier should have an e f f e c t i v e life of 500 years.T h i s is a f u n c t i o n a l requirement not a system component . Asystem component i s a p h y s i c a l part of the d i s p o s a l f a c i l i t y , andeach component may be d e s i gned to p e r f o r m a number off u n c t i o n s .

3-57

Mr. Phil Rogers (cont inued)( 0 8 / 2 3 / 9 9 )

Q U E S T I O N S U E t Q U E S T I O N : : : A N S W E K :

B - Has the remedy beenimplemented in accordancewith d e c i s i on documents?( C o n t i n u e d )

I s s u e : U n c e r t a i n t y on the L o n g - T e r m P e r f o r m a n c e o f theRemedy ( c o n t i n u e d )1.0 Ground-water Contact with the MonolithThe groundwater level record is r e l a t i v e l y short compared to theper i od over which it must be p r e d i c t e d ; thus, there is not enoughinformat ion to say with cer tainty that groundwater l e v e l s w i l lremain below the base of the m o n o l i t h . The remedy does notincorporate an under-drain or l eachate c o l l e c t i o n system.T h e r e f o r e , if groundwater l eve l s would rise to or above the base ofthe monolith, the water would be expected to have a de l e t er iousleaching e f f e c t . Leaching is the most l i k e l y process to causeconcrete degradat ion in the waste repo s i tory environment (Changand Hasan , 1990). As Chang and H a s a n point out, mostremediations have requirements that concrete structures be placedabove the groundwater table. However, it is d i f f i c u l t to ensurethat the water tab l e wi l l not change over such a long period oftime as is required for radioactive waste d i s p o s a l .2.0 Monolith LongevityFrom about 1918 to 1984, the site was used to receive and treatmo lybdenum ore, carnoti te ore, vanadium ore, uranium ore, andradium s a l t s . Other ores may have been received and treated ina d d i t i o n to tho s e documented . Much of the c on taminat ed soilin corpora t ed into the mono l i th is assumed to consist of ore and orewaste. T h e s e ores and ore-related wastes c ommonly containvarious s a l t s in c lud ing those o f s u l f a t e . The presence o f s u l f a t e sand p e r h a p s ch l or id e s a l t s in the ore c a l l s into question the long-term a c c e p t a b i l i t y of the waste form. The waste form (i.e.,m o n o l i t h ) has been cons truc t ed on s i te c on s i s t ing of compactedlayers of contaminated s o i l , cement, fly ash, and water. In thep i l o t t r e a t a b i l i t y s t u d y , the s o i l s were to be mixed at a ratio of70:20:10 ( s o i l s : cement: f ly ash), compacted to an ASTM standard

3-58

Mr. Phi l Rogers (cont inued)( 0 8 / 2 3 / 9 9 )

B - Has the remedy beeni m p l e m e n t e d in accordancewith d e c i s i on documents?( C o n t i n u e d )

I s s u e : U n c e r t a i n t y on the L o n g - T e r m P e r f o r m a n c e o f theRemedy ( c o n t i n u e d )value, and a moisture content to maintain a 0.4 ratio of water tocement. The s t u d y r e s u l t s ind i ca t e that, at least in the near-term,structural s t r eng th of the concrete met the requirements of theEPA in terms of c o m p r e s s i b i l i t y , p e r m e a b i l i t y , and T o x i c i t yCharac t er i s t i c Leaching Procedure.T h e s e t e s t s c o n f i r m the near-term a c c e p t a b i l i t y of the waste f ormbut do not addre s s its long-term p e r f o r m a n c e as a part of theremedial system.A review of concrete l o n g e v i t y in Service Life of Concrete( C l i f t o n and Knab, 1989) and Concrete Longevity Overview(Chang and H a s a n , 1 9 9 0 ) p r o v i d e a basis for the concern over thelong-term p e r f o r m a n c e of the m o n o l i t h . A m o n g the mostcommon and des truc t ive f a c t o r s a f f e c t i n g concrete are s u l f a t e s ins o i l , groundwater, or seawater. The d egrada t i on caused by s u l f a t eattack varies f r o m minor sur fac e erosion to c o m p l e t e l o s s ofstructural s t r ength l e a d i n g to to ta l s truc tural f a i l u r e o f the concrete( C h a n g and H a s a n , 1990). The most commonly f o u n d s u l f a t es a l t s in s o i l s are sodium s u l f a t e , ca l c ium s u l f a t e , and magnesiums u l f a t e . T h e y are f ound in rocks as w e l l as mineral d e p o s i t s .A n o t h e r d e s t ru c t i v e f a c t o r in concrete is the pre s ence of c h l o r i d eions. C h l o r i d e ions are common in nature and they exist in so i l inthe f o r m s of ch l o r id e s a l t s such as ca l c ium c h l o r i d e , magnesiumc h l o r i d e , and sodium ch l or id e . T h e y are f o u n d in igneous rocksand s ed imen tary rocks. P a r t i c u l a r l y high l e v e l s of c h l o r i d e ionsare f o u n d in evapora t e s . In arid regions , the soil u s u a l l y containshigh ch lor id e concentrat ions due to h i g h evapora t ion rate.C h l o r i d e s such as magnesium c h l o r i d e and a l u m i n u m c h l o r i d ereact w i th l ime to f o rm un s tab l e and water s o l u b l e c ompound s .C h a n g and H a s a n , ( 1 9 9 0 ) r epor t tha t the pre sence o f c h l o r i d e ionsin concrete reduce s its r e s i s tance to a t t a c k by s u l f a t e s in s o i l s .

3-59

Mr. P h i l Rogers ( c o n t i n u e d )( 0 8 / 2 3 / 9 9 )

Q U E S T I O N S U B - Q U E S T I O N :; ANSWER;B - Has the remedy beeni m p l e m e n t e d in accordancewi th de c i s i on document s?( C o n t i n u e d )

I s s u e : U n c e r t a i n t y on the L o n g - T e r m P e r f o r m a n c e o f theRemedy ( c o n t i n u e d )The source of s u l f a t e s associated with s u l f a t e attack may be e i therexternal or internal to the monol i th . External sources i n c l u d es u l f a t e s that or ig inate f r o m groundwater or that leach f roma d j a c e n t soi l . In th i s case, the a t tack progre s s e s f r o m the s ur fa c eof the m o n o l i t h (e.g., s id e s and bo t t om) and progre s s e s into theinterior. I n t e r n a l sources i n c l u d e the waste, minerals in otheraggrega t e s such as the ruble (th i s may be u n l i k e l y but there arel i t t l e ava i lab l e data to make a determination), s u l f a t e s d i s s o l v e d inthe mix water, and admixtures (e.g., fly ash). Data are avai lab l eon s u l f a t e concentrations in the groundwater, however, theavailable data relative to po t ent ia l s u l f a t e sources in the adjacentsoil and waste that was mixed into the monol i th are apparen t lyscarce. The only avai lable data on s u l f a t e content of the wastemixed into the monolith is related to t e s t ing s ampl e s used in thePilot S c a l e Treat a b i l i t y S t u d y (Earth Science s C o n s u l t a n t s , 1993).Three test f e e d materials were d e v e l o p e d : 1) one with averagerad ioac t iv i ty ( s u l f a t e concentration of 1,440 m g / k g ) , 2) one withe l eva t ed radioac t iv i ty ( s u l f a t e concentration of 2,390 m g / k g ) , and3) one with elevated radioact ivi ty containing b u i l d i n g rubble( s u l f a t e concentration 4,400 m g / k g ) . S u l f a t e concentration data ina d j a c e n t s o i l and groundwater were not reviewed. Var i ou so r g a n i z a t i o n s such as the Bureau of Rec lamat ion (ConcreteM a n u a l , 1 9 7 5 ) and the Port land Cement A s s o c i a t i o n ( K o s m a t k aand Panarese, 1988 and G u i d e to Durable Concre t e , 1 9 9 2 ) haved e v e l o p e d gu idance f o r t h e i d e n t i f i c a t i o n o f t h e p o t e n t i a l severityof s u l f a t e a t tack and a p p r o p r i a t e precaut ionary measures but, th i sgu idanc e is i n t e n d e d for use in concrete construction underordinary service life c ond i t i on s and may not n e c e s s a r i l y bea p p r o p r i a t e f or l ong- t e rm service l i f e , such as required forhazardous waste containment ( K l i e g e r and L a M o n d . 1994 ).N e v e r - t h e - l e s s , i f one a p p l i e s the guidance ( G u i d e to DurableConcrete, 1 9 9 2 ) to the l i m i t e d data, then a cement f o r m u l a t i o n thatis at l ea s t m o d e r a t e l y r e s i s tant to s u l f a t e attack would be requiredbased on the "average soil" s u l f a t e concentration of 1,440 m g / k g .

3-60

Mr. Phil Rogers (continued)( 0 8 / 2 3 / 9 9 )

S S U B l Q U E S T I O I f i • • A N S W E R ^ : I S S U E S : & - R E G O M M E N l D A T I O N S ^B - Has the remedy beenimplemented in accordancewith decis ion documents?( C o n t i n u e d )

I s s u e : U n c e r t a i n t y on the L o n g - T e r m P e r f o r m a n c e o f theRemedy ( c o n t i n u e d )T h i s does not consider the po t en t ia l cumulative s u l f a t e attack f r o mthe other external sources (i.e., groundwater and l each ing f r o ma d j a c e n t s o i l ) . The ROD requires that the base of the monol i th beat l ea s t f o u r f e e t above the groundwater l eve l . S u l f a t e in thegroundwater could come in contact with the m o n o l i t h via thec a p i l l a r y f r i n g e which could extend to the base of the m o n o l i t hf r o m time to time d e p e n d i n g on grain size in the beneath them o n o l i t h and groundwater l eve l . The groundwater l e v e l s could bemonitored with add i t i ona l monitoring w e l l s and neutron l o g g i n g .If the guidance were a p p l i e d to the s u l f a t e concentration of 4,400m g / k g observed in the Pi lo t S c a l e T r e a t a b i l i t y S t u d y then a cementf o r m u l a t i o n to resist "severe" s u l f a t e attack would be required.W h i l e much of the research has f o c u s e d on the external e f f e c t s ofs u l f a t e s in soi l and groundwater, the same d e l e t e r i o u s e f f e c t s aree x p e c t e d when s u l f a t e - r i c h aggregat e s are used because, allaggregates are, to a certain extent, chemically reactive with thecement pas t e . A g g r e g a t e s (in thi s case the contaminated soil andother m a t e r i a l ) must c on f orm to certain s t andard s for op t imume n g i n e e r i n g use. T h e y must be clean, hard, s trong, durab l ep a r t i c l e s f r e e f r om d e l e t e r i o u s coa t ings that c ou ld a f f e c t h y d r a t i o nand b o n d i n g of the cement pa s t e . T h e y must not be e a s i l y s p l i t ,and shou ld have h igh re s i s tance to the e f f e c t s of weathering.S u i t a b l e aggregate s do not contain d e l e t e r i o u s subs tances thatreact c h e m i c a l l y (e.g., s u l f a t e s and c h l o r i d e s ) to p r o d u c es i g n i f i c a n t vo lume changes or h a r m f u l b y p r o d u c t s , or thati n t e r f e r e with ordinary hydrat ion of cement. ___

3-61

Mr. Phil Rogers (con t inued)( 0 8 / 2 3 / 9 9 )

Q U E S T I O N S U B - Q U E S T I O N A N S W E R ; : I S S U E S & R E C O M M E N D A T I O N SB - Has the remedy beeni m p l e m e n t e d in accordancewith d e c i s i o n document s?( C o n t i n u e d )

I s s u e : U n c e r t a i n t y on the L o n g - T e r m P e r f o r m a n c e o f theRemedy ( c o n t i n u e d )Given the hi s tory of the site, it is reasonable to expec t the waste tocontain various s u l f a t e s and c h l o r i d e c o m p o u n d s that wou ldi n t e r f e r e with cement reactions. A summary of these p o t e n t i a lin t er f er ence s f r om Chang and H a s a n ( 1 9 9 0 ) f o l l o w s .T h e r e are three p r i n c i p a l chemical reactions that lead to concretede ter iorat ion. One involves sodium s u l f a t e and t r i ca l c iumaluminate, the compound r e spon s i b l e for the cementi t iouspropert ie s and the hydration of cement. The reaction re sul t s in thef ormat ion of a mineral c a l l e d et tringite. Et tr ingi t e , which isin s o lub l e in water, has cons iderably more volume than thecombined reactants. The expanded volume of e t t r ingi t e generatesenormous internal expansive stresses. Over time, as moree t t r ing i t e is generated by the interaction, internal expansivestresses build within the concrete composite. Eventual ly, ifinternal stresses exceed the structural s trength of the concrete, thestructure either c o l l a p s e s or d i s in t egra t e s . The format ion ofe t t r ing i t e has been f ound to be the princ ipal cause of mostconcrete d e t e r i ora t i on when exposed to s u l f a t e s .A n o t h e r reaction involves the conversion of the ca l c iumh y d r o x i d e in cement into gyp sum (ca l c ium s u l f a t e ) . G y p s u m is amaterial that has l i t t l e structural s t r eng th and is a l e a c h a b l ecompound. G y p s u m also has more volume than the combinedreactants. T h e d e l e t e r i o u s e f f e c t i m m e d i a t e l y f o l l o w i n g g y p s u mformat ion is the expansive s tress generated by the increasedvolume. As the l e a c h i n g proce s s progre s s e s , the internal pressured i s s i p a t e s , and d e g r a d a t i o n mechanisms change f rom structuralstrain to l o s s of s truc tural mat er ia l . As gyp sum leaches f r o m theconcrete c o m p o s i t e , it l eaves behind a porous and weakerstructure s u b j e c t to other f o r m s of deterioration.__________

3-62

Mr. Phil Rogers (con t inued)( 0 8 / 2 3 / 9 9 )

B - Has the remedy beeni m p l e m e n t e d in accordancewith d e c i s i on documents?( C o n t i n u e d )

I s s u e : U n c e r t a i n t y on the L o n g - T e r m P e r f o r m a n c e of theRemedy ( c o n t i n u e d )The third reaction invo lve s magnesium s u l f a t e and the calc iumhydrox id e in cement and is considered one of the more severelyde l e t e r i ou s reactions. Magne s ium s u l f a t e reacts with calciumhydroxide to form magnesium hydroxide, a substance that ish i g h l y s o l u b l e in water. T h i s reaction can lead to the rap idd i s s o l u t i o n of ca l c ium h y d r o x i d e in the cement structure and candes troy the s tructural i n t e g r i t y of concrete in a very short period oftime.It does not seem that these issues were d i r e c t l y addre s s ed in thep i l o t t r e a t a b i l i t y s tudy (Earth Science C o n s u l t a n t s , 1993). T h i ss i t e may represent a very severe environment for long-termcement s t a b i l i z a t i o n of the waste because of the various s u l f a t e sand ch l or id e s present in the s i te waste. If so then, as noted byC l i f t o n and K n a b , 1989 "a s i te with a very severe environment is,u n d o u b t e d l y , u n f i t for s tor ing LLW in concrete vaults." T h e y goon to note that f o l l o w i n g de s ign r e commendat ions shou ld result ina concrete with a c c e p t a b l e d u r a b i l i t y for many years, p o s s i b l y forthe 60 to 100 year d e s i g n life of t y p i c a l concrete structures. T h e r eis no basis (at the time of the report in 1 9 8 9 ) for p r e d i c t i n g theservice l i fe of a concrete e xpo s ed to a s u l f a t e environment,e s p e c i a l l y in the case of a concrete with a d e s i g n l i f e of hundredsof years.A model d e v e l o p e d by Berner ( 1 9 9 0 ) s i m u l a t e s the cement matrixd e g r a d a t i o n a f t e r d i s s o l u t i o n and removal o f s o l u b l e mater ia l ssuch as a l k a l i sa l t s . The model is grounded in e m p i r i c a lobservations that concrete a l t era t i on s e q u e n t i a l l y removes excessa l k a l i s , p o r t l a n d i t e , and tobermori t e or c a l c i u m - s i l i c a t e - h y d r a t e( C S H ) . Decreased s t r e n g t h a t t e n d s removal o f por t land i t e .____

•"i f ^J - O J

Mr. Phi l Rogers ( c o n t i n u e d )( 0 8 / 2 3 / 9 9 )

S U B - Q U E S T I O N " A N S W E R - : - :B - Has the remedy beenimpl ement ed in accordancewith decision documents?( C o n t i n u e d )

I s s u e : U n c e r t a i n t y on the L o n g - T e r m P e r f o r m a n c e o f theRemedy ( c o n t i n u e d )A critical amount of f l o w must occur be fore this degradat iont h r e s h o l d is crossed. A volume equivalent to 100 pore volumeshas been taken as the c r i t i ca l f l o w volume, based on value s forcommon c o m p o s i t i o n s of ordinary p o r t l a n d cement concrete(Berner 1990). A l s o f o l l o w i n g Berner, the model tracks theamount of f l o w as pore volumes, reasoning that f l o w occurs onlythrough pores and that a l t e ra t i on is t h e r e f o r e l imi t ed to the s o l i d sthat surround the pores. The model does not e x p l i c i t l y account forthe s trength of the concrete but instead makes the conservativeas sumpt ion that phys i ca l f a i l u r e occurs s u d d e n l y at the onset ofchemical attack on concrete, that is, at a p p r o x i m a t e l y 100 porevolumes. As a re sul t , ini t ia l poros i ty of the hardened concrete is akey parameter for de termining concrete.The initial p e r m e a b i l i t y of hardened cement is d i r e c t ly re lated tothe connecting poros i ty that permits f l o w to occur. Initialpermeab i l i ty of ordinary por t land cement is a strong func t i on ofthe watencement ratio of the mix. H i g h e r water contents producehigher poro s i ty and p e r m e a b i l i t y . The range in poro s i ty m o d e l e d(5 to 40 p e r c e n t ) can create an order or magni tude spread inp r e d i c t e d p e r f o r m a n c e l i f e .Data s u p p o r t i n g Berner ' s concrete d egrada t i on model comep r i m a r i l y f r o m two sources: the international r e p o s i t o r y l i t e ra tur eand j o u r n a l s on concrete construction ( f o r e x a m p l e , dams orb r i d g e s ) . The in t ernat ional l i t era ture on r e p o s i t o r i e s contains bothmodel s and empirical s tudie s c on f i rming that alteration ofconcrete w i l l result in decreased p o r o s i t i e s and p e r m e a b i l i t i e s inc l o s ed systems. Experience f or dams c o n f i r m s t h i s c onc lu s i onand c o n f i r m s the d i f f u s i o n - d r i v e n concrete a l t e r a t i o n rates used inthe mode l . The general concrete l i t e ra tur e c o n f i r m s the values ofinitial permeabil i ty and poro s i ty of hardened concrete used in themode l .

3-64

Mr. Phi l Rogers (cont inued)( 0 8 / 2 3 / 9 9 )

S U B - Q U E S T I O N : ANSWER;B - Has the remedy beeni m p l e m e n t e d in accordancewith dec i s ion documents?( C o n t i n u e d )

I s s u e : U n c e r t a i n t y on the L o n g - T e r m P e r f o r m a n c e o f theRemedy ( c o n t i n u e d )It may be p o s s i b l e to p a r t i a l l y or f u l l y m i t i g a t e for s u l f a t e .A p p l i c a b l e to the S h a t t u c k s i te , three mi t iga t i on s could becons idered: use of s u l f a t e - r e s i s t a n t cement (i.e., Port land cementT y p e V), u s e o f admixtures (i.e., Por t land cement T y p e II with ap o z z o l a n such as fly ash), and 3) good drainage. Of the two t y p e so f s u l f a t e - r e s i s t a n t cement Port land T y p e II ha s t r i ca l c i umaluminate content <8% and Por t land T y p e V has tr i ca l c iumaluminate content < 5%. Chang and H a s a n , 1990 ind i ca t e that theT y p e II with pozzo lan admixture can achieve the same leve l ofs u l f a t e resi s tance as the T y p e V. U n f o r t u n a t e l y , long-termd u r a b i l i t y t e s t s on the s u l f a t e resi s tance of concrete containingpozzo lan (e.g., f ly ash) have not been repor t ed ( C l i f t o n and Knab,1989). A l s o , as mentioned above, Chang and H a s a n , 1990 reportthat the presence of chloride ions in concrete reduces its resistanceto attack by s u l f a t e s in s o i l s , or in t h i s case s u l f a t e s in the waste.It has been reported that some "high qua l i ty concretes made withs u l f a t e - r e s i s t i n g cements have de t er iorated pr emature ly in thef i e l d " ( K a l o u s e k e t al., 1972). Given the required long service l i f eof the m o n o l i t h and lack of s u p p o r t i n g data, it is conc luded thatthe s u l f a t e r e s i s tance o f the m o n o l i t h i s uncertain. The m o n o l i t hmix tur e is de s cr ibed as 70% soil and rubble , 20% T y p e I/IIcement and 10% C l a s s C fly ash. The uncertainty in m o n o l i t hs u l f a t e res i s tance stems f r o m 1) the presence o f s u l f a t e s andp o t e n t i a l l y c h l o r i d e s a s d i s cu s s ed above, 2) the p o t e n t i a l for waterto come into contact with the mono l i th , and 3) the lack ofa v a i l a b l e chemical documentat ion on the fly ash combined withthe t y p e o f f ly a sh used. Most C l a s s F f ly ashes improve s u l f a t eresistance of T y p e II cements and according to ( K l i e g e r andL a M o n d , 1994) are g e n e r a l l y more e f f i c i e n t in i m p r o v i n g s u l f a t er e s i s tance than C l a s s C. More i m p o r t a n t l y , h i g h c a l c i u m C l a s s Cfly ashes are var iab l e , o f t e n poor , and may reduce s u l f a t ere s i s tanc e ( K l i e g e r a n d L a M o n d , 1994). T h i s v a r i a b i l i t y has___

5-65

Mr. Phil Rogers (con t inued)( 0 8 / 2 3 / 9 9 )

Q U E S T I O N S U B - Q U E S T I O N • A N S W E R : I S S U E S & R E C O M M E N D A T I O N SB - Has the remedy beeni m p l e m e n t e d in accordancewith dec i s ion document s?( C o n t i n u e d )

I s s u e : U n c e r t a i n t y on the L o n g - T e r m P e r f o r m a n c e o f th eRemedy ( c o n t i n u e d )p r o m p t e d inve s t igator s to recommend that C l a s s C fly ashes bei n d i v i d u a l l y evaluat ed i f i n t e n d e d f o r s u l f a t e resi s tance ( H a r b o e ,no d a t e ) C h e m i c a l v a r i a b i l i t y in fly ash would not be uncommonfrom ashes f r o m one source. In this case, it is not known howmany sources of fly ash were used for the m o n o l i t h nor werechemical analyses made avai lable . G u i d e l i n e s for the use o f f lyashes for the improvement of s u l f a t e res i s tance have beenp u b l i s h e d by several sources. Dunstan 1980 propo s e s a fly ash" s u l f a t e resistance f a c t o r R" and has documented the "drastic"reduction of s u l f a t e resistance due to use of inappropr ia t e f lyashes. Such fly ashes (i.e., those that would not improve s u l f a t eresistance or p o t e n t i a l l y reduce s u l f a t e resistance) would genera l lybe characterized as being high in calcium oxide (CaO) content andcomparably low in f e rr i c oxide ( F e 2 O 3 ) content. F i n a l l y , there areno avai lab l e data on the s u l f a t e resistance of the monoli th sample sas could have been determined by laboratory testing. Severallaboratory (and f i e l d ) te s t s are in standard use such as ASTM C1012 which involves the expans ion of mortar specimens in a 5%sodium s u l f a t e s o l u t i o n or the Bureau of Reclamat ion Procedure4908, M e t h o d s A, B, or C.3.0 Surface Barrier and Release MechanismThe m o n o l i t h is covered with a sur fa c e barrier or cap, which insome f o r m or another has been d e s i g n e d and used throughout theWes t a t Uranium M i l l T a i l i n g Remedia l A c t i o n ( U M T R A ) sites.The cover u l t i m a t e l y used i s a variant of those t y p i c a l l y a p p l i e dfor UMTRA; however, the UMTRA caps in use may not havebeen in p l a c e a s u f f i c i e n t amount of t ime to a d e q u a t e l y evaluatetheir e f f i c i e n c y and long-term per formance . A l r e a d y , concern hasbeen raised about the U M T R A - t y p e cap s ' long-term per formancerelated to the c lay barrier in arid regions and vege ta t i on invasion( H a k o n s o n , 1997).___________________________

3-66

Mr. Phil Rogers (con t inued)( 0 8 / 2 3 / 9 9 )

I S S U E S & R E C O M M E M ) A T I O N S :B - Has the remedy beeni m p l e m e n t e d in accordancewith dec i s ion documents?( C o n t i n u e d )

I s s u e : U n c e r t a i n t y on the L o n g - T e r m P e r f o r m a n c e o f theRemedy ( c o n t i n u e d )Vege ta t i on , i n c l u d i n g several d e ep-roo t ed s p e c i e s , has invadedsome d i s p o s a l c e l l s . T h e s e invas ions may create a p a t h w a y forwater to i n f i l t r a t e the waste. A near-term remedy has been forDOE to i n i t i a t e a herbic ide spraying program.3 a. I n f i l t r a t i o n Rate T h r o u g h the Cap. A f i n i t e v o lume of waterw i l l i n f i l t r a t e t hough th e cap, d i s s o l v e contaminants wi thin th em o n o l i t h , and transport these d i s s o l v e d contaminants into thevadose zone and u n d e r l y i n g uncon fmed aqui f er . In the near-term,it is b e l i ev ed , based on review of the data and i n f o r m a t i o n , that thei n f i l t r a t i o n rate w i l l be i n s i g n i f i c a n t . Given the long h a l f - l i f e o fsome of the contaminants, cons iderat ion must be given to long-term p e r f o r m a n c e of the cap and m o n o l i t h . The cap cons truc t edfor the S h a t t u c k s i t e i s minimal compared to caps p lanned formany o f D O E ' s radioac t ive waste sites. Withou t ex t ens ivemaintenance, it is uncertain that the S h a t t u c k cap w i l l p e r f o r ms a t i s f a c t o r i l y for the minimum 200-year period and d o u b t f u l that itw i l l p e r f o r m s a t i s f a c t o r i l y for 500 years.E v a l u a t i o n s of cap p e r f o r m a n c e , some of which are ana logou s tothe S h a t t u c k site c ondi t i ons , are ava i lab l e f r om the l i t erature. Thework at DOE's H a n f o r d S i t e in eastern W a s h i n g t o n i s c i ted in thef o l l o w i n g because o f s i m i l a r i t i e s in c l i m a t i c c o n d i t i o n s and waste.The e v a l u a t i o n s in th e TWRS EIS (DOE, 1 9 9 6 ) represent th elower bound for i n f i l t r a t i o n rate through a cap. The cap assumedfor the T W R S EIS eva lua t i on i s c a l l e d a H a n f o r d Barrier and i s asystem that has been engineered for l o n g e v i t y and minimumi n f i l t r a t i o n . H a n f o r d is in an arid c l imate not much d i f f e r e n t thanthe F r o n t Range, so the H a n f o r d - a s s u m e d i n f i l t r a t i o n rates area p p l i c a b l e to the Denver area for the same t y p e of cap. TheH a n f o r d Barrier i s a m u l t i - l a y e r engineered s u r f a c e cap withd e s i g n li fe of 1,000 years and a t h i c k n e s s of a p p r o x i m a t e l y 15 f e e t

3-67

Mr. P h i l Rogers (con t inued)( 0 8 / 2 3 / 9 9 )

Q U E S T I O N S t f B - Q U E S T J O N • A N S W E R - I S S t l E S & J R E C O M M E N D A T I O N SB - Has the remedy beeni m p l e m e n t e d in accordancewith d e c i s i o n documents?( C o n t i n u e d )

I s s u e : U n c e r t a i n t y on the L o n g - T e r m P e r f o r m a n c e o f theRemedy ( c o n t i n u e d )( B H I 1996). T h e d e s i g n s p e c i f i c a t i o n s o f t h e H a n f o r d Barrier f a rexceed those used for the cap at the S h a t t u c k site.The Department of Energy (DOE) e s t imate s that i n f i l t r a t i o nthrough the H a n f o r d Barrier w i l l be an average of 0.05 cm/yearfor the i n i t i a l 1,000-year per iod a f t e r the cap was constructed.F o l l o w i n g that ini t ial p e r i o d , the H a n f o r d Barrier per formance is

.degraded such that i n f i l t r a t i o n rate is assumed to increase to 0.1cm/year for thousands o f years (DOE, 1996, A p p e n d i x F, pg. F-44). A more recent s tudy assumed the i n f i l t r a t i o n rate wouldincrease to 0.03 cm/year a f t e r the init ial 1,000-year period (DOE1999).Another cap that is being considered for radioactive waste closureact ivi t ie s is an Enhanced RCRA S u b t i t l e C Barrier. The EnhancedRCRA S u b t i t l e C Barrier is also a multi-layer engineered surfacecap with de s ign life of 500 years and a thickness of a p p r o x i m a t e l y5.6 f e e t (DOE 1999). DOE es t imate s that i n f i l t r a t i o n through theEnhanced RCRA S u b t i t l e C Barrier w i l l be an average of 0.1cm/year for the i n i t i a l 500-year p e r i o d a f t e r the cap wascons tructed. F o l l o w i n g that i n i t i a l p e r i o d , t h e Enhanced RCRAS u b t i t l e C Barrier p e r f o r m a n c e i s degraded such that i n f i l t r a t i o nrate is assumed to increase to 0.3 cm/year for t h ou sand s of years(DOE, 1999). The d e s i g n s p e c i f i c a t i o n s of the Enhanced RCRAS u b t i t l e C Barrier far exceed those used for the cap at the S h a t t u c ksite.

3-68

Mr. Phi l Rogers ( c o n t i n u e d )( 0 8 / 2 3 / 9 9 )

^ A N S W E R S I S S U E S & R E C O M M E N D M I O N SB - Has the remedy beenimpl emen t ed in accordancewith dec i s ion documents?( C o n t i n u e d )

I s s u e : U n c e r t a i n t y on the L o n g - T e r m P e r f o r m a n c e o f theRemedy ( c o n t i n u e d )3b W a s t e Release Mechani sms . C a l c u l a t i n g the contaminant massf l u x that is r e l ea s ed f rom the monol i th to the u n d e r l y i n g vadosezone requires the deve lopment of a s sumpt i on s concerning 1) howwaste is released f rom the waste form (i.e., the m o n o l i t h ) and 2)the time-variant i n f i l t r a t i o n rate through the cap and monol i th .A p p e n d i x F "Groundwater Evaluat ion" f r o m the S h a t t u c k RIde s ign report inc lude s a ca l cu la t i on of a s o- ca l l ed "reductionfac tor" that is used to demonstrate the e f f e c t i v e n e s s of the d e s i g nwith respect to contaminant concentrat ions in the groundwater atthe downgradi en t boundary. It is not clear if the reduct ion f a c t o rapproach is conservative; it is, however, unique.A more s tandard approach to c a l c u l a t i n g the mass f l u x ofcontaminants to the groundwater is recommended. T h i s approach ,c a l l e d the congruent d i s s o l u t i o n re l ease m o d e l , has been used inseveral p e r f o r m a n c e assessments ( P A s ) a n d environmental impactstatements (EISs) involving the d i s p o s a l o f radioactive waste. Thecongruent d i s s o l u t i o n contaminant re l ease a p p r o a c h , combinedwith r e a l i s t i c time-variant e s t imates o f i n f i l t r a t i o n rates throughthe cap, i s recommended for reassessment of the S h a t t u c k S i t e .Recent analys e s i n v o l v i n g the d i s p o s a l o f rad i oa c t iv e waste thathave a d o p t e d the a s s u m p t i o n s a s soc ia ted with congruentcontaminant release in c lude the 1) Retrieval PerformanceEvaluation Methodology for the AX Tank Farm (DOE 1 9 9 9 ) , 2)Performance Assessment of Grouted Double-Shell Tank WasteDisposal at Hanford ( K i n c a i d et al. 1 9 9 5 ) , and 3) Tank WasteRemedial System, Hanford Site, Richland Washington, FinalEnvironmental Impact Statement (DOE 1996). The congruentrelease model is best d e s c r i b ed by e x a m p l e which is p r o v i d e d inthe f o l l o w i n g excerpt f r o m DOE 1996:_______________

3-69

Mr. Phil Rogers ( c o n t i n u e d )( 0 8 / 2 3 / 9 9 )

l|l;||;^iE^MNl:!;:: ::':i| ;C - Has any riski n f o r m a t i o n changed sincethe remedy was s e l e c t e d ?

11 ; l : S u | ^ i E S T i ( 9 i l l l l :N / A

:ii!!!ll3^The reviewer has not seen da ta ori n f o r m a t i o n that would i n d i c a t e that riskin format i on has changed since the remedywas s e l e c t e d .

i i^SI^IS^ii^BSSi^Si^SlII s s u e : N o t a p p l i c a b l e .Recommenda t i on: N o t a p p l i c a b l e .

ReferencesBHI 1996. Focu s ed F e a s i b i l i t y S t u d y of Engineered Barriers for Was t e Management Uni t s in the 200 Areas. Bechtel H a n f o r d , Inc. Richland, WA.1996.Chang and Hasan, 1990. Wal la c e Chang and Nausherwan Hasan. Concrete Longevity Overview. Prepared for E G & G I d a h o , Inc. D O E / L L W - 1 0 5 .I d a h o F a l l s , I D . Sep t ember 1990.C l i f t o n and Knab, 1989. J. R. C l i f t o n and L. I. Knab. Service Life of Concrete. Prepared for the U.S. Nucl ear Regulatory Commission and theNational I n s t i t u t e of S t a n d a r d s and T e c h n o l o g y . NUREG/CR-5466;NISTIR 89-4086. Washington, DC. November 1989.Concrete Laboratory Report No. C-828. Effect of Cement Type on the Resistance of Concrete to Sulfate Attack, U.S. Department of the Inter iorBureau of Reclamation, Division of Engineering Laboratories, Denver, CO, November 1958.Concrete Laboratory Report No. C-931. Mortar Bar Expansion Tests for Chemical Reactivity Between Sulfate Bearing Rocks in Aggregate andPortland Cements, U.S. Department of the I n t e r i o r Bureau of Reclamation, Divi s ion of Engineer ing Laboratorie s , Denver, CO, February 1960.Concrete Manual , 1975. Concrete Manual. Bureau of Rec lamat ion, Denver, CO. 1975.DePuy, G.W. Chemical Resistance of Concrete, ASTM STP 169.Dikeou, J.T.. Fly Ash Increases Resistance of Concrete to Sulfate Attack, U.S. Department of the Interior, Division of Research, Denver, CO.DOE 1999. Retrieval Performance Evaluation Methodology for the AX Tank Farm. DOE/RL-98-72. U. S. Department of Energy. Rich land , WA.A p r i l 1999.

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Mr. Phil Rogers ( c o n t i n u e d )( 0 8 / 2 3 / 9 9 )

Q U E S T I O N S U B - Q U E S T I O N • A N S W E R : I S S U E S & R E C O M M E N D A T I O N SB - Has the remedy beeni m p l e m e n t e d in accordancewith d e c i s i o n documents?( C o n t i n u e d )

I s s u e : U n c e r t a i n t y on the L o n g - T e r m P e r f o r m a n c e o f th eRemedy ( c o n t i n u e d )

The durat ion of the release is based on a congruentd i s s o l u t i o n m o d e l . I n t h i s m o d e l , a l l c o n s t i t u e n t s i n t h ewaste inventory are assumed to be re leased in p r o p o r t i o nto the most abundant material in the waste inventory,ni tra t e , and at the rate of nitrate d i s s o l u t i o n . T h u s , thedurat ion of release for each source area is based on thes o l u b i l i t y of nitrate, which is assumed to be 360g r a m s / l i t e r ( g / L ) ( S e r n e - W o o d 1990), volumetric waterf l u x (area of source t imes 5.0 cm/year (1.36"4 m / d a y[2.0 i n . / y e a r ] ) ) , and the initial mass of nitrate in theinventory.

It should be noted that the source term d e v e l o p e d under th i sa l t e rna t iv e is overly conservative for many of the contaminant smode l ed because s o l u b i l i t y contro l s in groundwater of neutral pH(7.0 to 8.0) and r e l a t i v e l y o x i d i z i n g condi t i on s (EH of 300 to 400mv SHE) would cause the contaminants to be leached at a rate les sthan ni tra t e ( N O 3

M ) , or because the contaminants would bei n s o l u b l e under these c ond i t i on s . A s i m p l e e x a m p l e of thecongruent d i s s o l u t i o n mode l f o l l o w s .

Given t h e f o l l o w i n g data:Source area of 100 m2 (=1,080 ft2);I n f i l t r a t i o n of 5.0 cm/year (1.36E-04 m / d a y )into the waste; and

• S o l u b i l i t y of n i t ra t e = 360 g/L (3.6E+08 g / m 3 ) ,The v o l u m e t r i c f l u x into the waste is 1,000,000, cm2 • 5.0c m / y e a r = 5,000,000 cmVyear. The time required tod i s s o l v e the inventory is 7.2E+08 g / ( 0 . 3 6 0 g / c m 3 •5.0E+06 cmVyear) = 400 years. In th i s e x a m p l e , the rateof release for nitrate and t e chne t ium is 7.20E+08/400 =1.8E+06 g / y e a r and 3.6E+04/400 = 90 g / y e a r ,respectively._____________________________

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Mr. Phil Rogers (con t inued)( 0 8 / 2 3 / 9 9 )

K o s m a t k a and Panarese, 1988. Kosmatka , S. H. and W. C. Panarese. Design and Control of Concrete Mixtures. PCA Engineering B u l l e t i n , 13 t h ed.,Port land Cement Assoc ia t ion. S k o k i e , IL. 1988.von F a y , Kurt F., and Jame s S. Pierce. Sulfate Resistance of Concretes with Various Fly Ashes, Research and Laboratory Servi c e s Divis ion, Bureauof Reclamation, Denver, CO.

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Mr. Phil Rogers ( c o n t i n u e d )( 0 8 / 2 3 / 9 9 )

DOE 1996. Tank Waste Remedial System, Hanford Site, Richland, Washington, Final Environmental Impact Statement. D O E / E I S - 0 1 8 9 . U. S.Department of Energy. Richland, WA. 1996.Dunstan, 1980. Dunstan, E. R. A Possible Method for Identifying Fly Ashes That Will Improve the Sulfate Resistance of Concretes. AmericanS o c i e t y for T e s t i n g and Mater ia l s . P h i l a . PA. 1980.Earth Sci enc e s C o n s u l t a n t s , Inc . P i l o t - S c a l e T r e a t a b i l i t y S t u d y . Denver Radium S i t e Operable Uni t V I I I . P r o j e c t N o . 886s. J u l y 1993.F e a s i b i l i t y S t u d y , 1991. Feasibility Study for Denver Radium Site Operable Unit VIII, C o l o r a d o Department of H e a l t h , S e p t e m b e r 1991.Guide to Durable Concrete, 1992. Guide to Durable Concrete. ACI Manual of Concrete Practice s , Part 1. ACI 201.2R-77. American ConcreteI n s t i t u t e . Detroi t , MI. 1992.Hakonson, 1997. T. E. Hakonson. Capping as an Alternative for Landfill Closures-Perspectives and Approaches. P u b l i s h e d in Conf er enc eProceed ings o f L a n d f i l l C a p p i n g in the S e m i - A r i d W e s t : Problems, Per spe c t iv e s , and S o l u t i o n s . I d a h o F a l l s , ID. 1997.Harboe , no date. Harboe , E. L o n g - T i m e S t u d i e s and F i e l d Experiences with S u l f a t e Attack .K a l o u s e k et. al. K a l o u s e k , G.L. L. C. Porter, and E. J. Benton. Concrete for Long-Time Service in Sulfate Environment. V o l . 2, pp. 79-89. Cementand Concrete Research. Pergamon Press, I n c . 1972.K a l o u s e k et. al. K a l o u s e k , G.L. L. C. Porter, and E. M. Harboe . Past, Present, and Potential Developments of Sulfate-Resisting Concretes, Journalof T e s t i n g and Evaluation, V o l . 4, No. 5, American S o c i e t y for T e s t i n g and M a t e r i a l s , P h i l a d e l p h i a , PA, 1976.Kinca id e t a l . 1995. K i n c a i d , C . T . , J . W . S h a d e , G.A. W h y a t t , M.G. P i e p h o , K . Rhoads, J . A . V o o g d , J . H . W e s t s i k , J r . , M.D. F r e s h l e y , K . A .Blanchard, and E.G. Lauzon. Performance Assessment of Grouted Double-Shell Tank Waste Disposal at Hanford. W H C - S D - W M - E E - 0 0 4 , Rev. 1.W e s t i n g h o u s e H a n f o r d Company. Richland, WA. May 1995.K l i e g e r and L a M o n d , 1994. K l i e g e r , P. and J. L a M o n d , Edi tor s . Significance of Tests and Properties of Concrete and Concrete Making Materials.S T P 169C. American S o c i e t y f o r T e s t i n g a n d M a t e r i a l s . 1994.

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Dr. W e n d y H a r r i s o n( 0 8 / 1 7 / 9 9 )

E x p e r t Panel Comment s for 5-Year ReviewS h a t t u c k C h e m i c a l S i t e

Denver, C o l o r a d o

Q U E S T I O N S U B - Q U E S T I O N ; • ; A N S W E R : ^A - H a v e c o n d i t i o n sexternal to the remedychanged since theremedy was s e l e c t ed?

1) Has land use orexpec t ed land use onor near the s i techanged?

A p p a r e n t l y not: new RTD l igh t railcons truc t ion is in the vic ini ty of the si te butt h i s should not impact the pro t e c t ed site, norshould RTD be l i k e l y to access thecontaminant p l u m e . As noted be low,inadequate soil charac t er iza t ion with respectto heavy m e t a l s might be a concern to RTD:RTD should be aware of the p o t e n t i a l formetal-rich soil to be present in their landuse corridor and should consider makingtheir own baseline assessment of soilquality.

I s s u e : The Record of Deci s ion requires pro t e c t iv e f e n c i n g around thesite. Damage to th i s observed in July 1999 shou ld be repaired.I n s t i t u t i o n a l contro l s shou ld mandate i m m e d i a t e f e n c e repair asa p p a r e n t l y the observed damage had l e f t the s i t e a c c e s s i b l e for severalweeks. The Record of Deci s ion s p e c i f i e s that owner wi l l acquire deedre s tr i c t ions necessary to a l l o w inst i tut ional pro t e c t i on of all s i ted e v e l o p m e n t . However , nothing seems to be in p l a c e to prevent anyv i c i n i t y p r o p e r t y owners f r o m d e v e l o p i n g groundwater resources in thet ime- frame it would take to remediate the contaminant p lume . Fore xampl e , vicinity p r o p e r t y owner F l a n a g a n Cement, whose land isad jac en t to the north site boundary, could (in theory) install agroundwater well that would intersect the p lume or withdraw water thatcould cause a reversal in hydraulic gradient s u f f i c i e n t to change thegeometry of the plume. As noted below, the Remedial I n v e s t i g a t i o nReport did not assess the e f f e c t of po t en t ia l groundwater removal onplume and hydraulic gradients (required by MARRSSIM andC E R C L A ) .Recommendation: I n s t i t u t i o n a l controls should be adequate toprevent an unant i c ipat ed change in land use of site and should alsoaddress v i c in i ty p r o p e r t y that could intersect groundwater exposurepathway.

2) H a v e any humanh e a l t h or e c o l o g i c a lexpo sure p a t h w a y schanged or beennewly i d e n t i f i e d ?

The Remedia l I n v e s t i g a t i o n Report and theBase l ine Risk Asse s sment removed thegroundwater expo sure pa thway for humanand e co log i ca l risk. The d e c i s i on toel iminate the groundwater pa thway wasbased on hydrologic and contaminanttransport m o d e l i n g that was too s i m p l i s t i cand involved a s s u m p t i o n s that would not bea c c e p t a b l e today. T h e r e is an unknownp o t e n t i a l for e c o l o g i c a l risk in the Pla t t eRiver and in the Overland G o l f Courseh o l d i n g p o n d s . T h e sur fac e water exposurepa thway was e l i m i n a t e d based on minimaldata. See comments below.

I s s u e s :

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Dr. Wendy Harrison (continued)( 0 8 / 1 7 / 9 9 )

S U B - Q U E S T I O N ^ A N S W E R ; : ; I S S U E S & R E C O M M E N D A T I O N SA - H a v e c o n d i t i o n sexternal to the remedychanged since theremedy was s e l e c t e d ?( C o n t i n u e d )

3) Are there newc on taminant s orcontaminant sources?

It is unknown whether or not the r emainings o i l s and a q u i f e r mater ial s within the p l u m ecould have s u f f i c i e n t m e t a l s l o a d i n g to actas a source. A l s o , i n s u f f i c i e n t data exist toassess the magnitude of t h i s source.Because the groundwater contaminantp l u m e cannot be remediated "instantly",there is a per iod of t ime where twop o s s i b i l i t i e s arise: (1) th e groundwaterremains above s tandards d e s p i t e thec ompl e t i on of the remedial action, but oversome non-e s tab l i shed t ime per iod comesinto c o m p l i a n c e ; and (2) the groundwaterdoes not meet s tandards over anyreasonable short term because remainingsoil and a q u i f e r material releasecontaminants p r e v i o u s l y taken up( a d s o r b e d , p r e c i p i t a t e d , e x changed , etc.).The re-introduction of contaminants couldbe caused by the changed water qualityr e s u l t i n g f r o m s i te r emed ia t i on . I m p r o v e dcontaminant transport m o d e l s can be usedto e s t i m a t e a durat ion for p l u m eremediat ion. See a d j a c e n t comments.

I s s u e : S o i l a n d A q u i f e r C h a r a c t e r i z a t i o nThe basic t e c h n i c a l issue i s as f o l l o w s : s e l e c t i o n and i m p l e m e n t a t i o nof a remedy requires that the extent of c on taminat i on be we l l known.If the characterization o f the initial s tate o f c on taminat i on i si n c o m p l e t e , then uncertainty surrounds the e f f e c t i v e n e s s o f ther emedia t i on . W h e r e a s none of the f o l l o w i n g p o i n t s may be a concern, 1cannot conc lude f r o m the do cumenta t i on a v a i l a b l e at t h i s t ime that anyparty has t h o r o u g h l y i d e n t i f i e d :(1) a l l the heavy m e t a l s o r i g i n a t i n g from the s i t e;(2) the extent to which other operations have provided metals andorganic c ompound s to the contamination attributed to S h a t t u c kChemica l Co.;(3) whether all the me ta l - con taminat ed soil was incorporated into them o n o l i t h ; and,(4) whether the groundwater contaminant p l u m e has d e p o s i t e d me ta l sonto the aqu i f er mat er ia l s ( n o t a b l y c lay s , organic mat er ia l , and ironh y d r o x i d e s ) as a result of natural at t enuat ion over the many year per iodd u r i n g which the p l u m e must have ex i s t ed.I am concerned about the p er s i s t en t report s that p r o c e s s i n g a c t i v i t i e sat the S h a t t u c k s i t e are not known for a per iod of time in the 1950s.G e o c h e m i s t s assess e l ement behavior by a s s o c ia t i on; thus, if oneelement is i d e n t i f i e d as pr e s en t , others l i k e l y a s s o c ia t ed with it wouldb e s o u g h t . An e x a m p l e i s the as soc iat ion of cadmium wi th zinc. Whati s th e p o s s i b i l i t y that u n i d e n t i f i e d c on taminant s remain? A d d i t i o n a l l y ,k n o w l e d g e of the sources of ores be ing proce s s ed would p r o v i d ei n s i g h t into p o s s i b l e contaminants. F o r e x a m p l e , t h e C l i m a xm o l y b d e n u m d e p o s i t a l s o produc ed large quant i t i e s o f tungs t en andantimony. Were q u a l i t y control a n a l y s e s of ore concentrates receivedat the S h a t t u c k site examined to ascertain that the l i s t of c o n t a m i n a n t swas comprehensive?______________________________

3-75

Dr. W e n d y Harri son (con t inued)( 0 8 / 1 7 / 9 9 )

Q U E S T I O N S U B - Q U E S T I O N A N S W E R :A - H a v e condi t ionsexternal to the remedychanged since theremedy was s e l e c t e d ?( C o n t i n u e d )

3) Are there newcontaminants orcontaminant sources?( C o n t i n u e d )

I s s u e : S o i l a n d A q u i f e r C h a r a c t e r i z a t i o n ( c o n t i n u e d )I f u r t h e r que s t ion the s e l e c t i o n of the l i s t of non-radioact ive e l ement s ofconcern and whether or not the d i s t r i b u t i o n of these m e t a l s wast h o r o u g h l y reported. The f o l l o w i n g data i l l u s t r a t e how much morecomprehensive the documentat ion of radioac t ive contaminants wasrelative to the metal s . Documentat ion of organic contaminants was theleast d e t a i l e d .The Remedial I n v e s t i g a t i o n s Report shows that 76 s o i l s (combiningsur fac e and sub sur fa c e) were analyzed, of which only 14 were analyzedfor a set of metals including: AI, Sb, As, Ba, Be, C d , . C a , Cr, Co, Cu,F e , P b , M g , M n , H g , N i , K , S e , A g , N a , T h , V , Z n . N o tungstenanalyses were included (see above). S u r p r i s i n g l y , only one soil wasanalyzed for molybdenum (Mo), and the balance were analyzed onlyfor As and Se consis tently, and Hg, Ag, V, Cr, Cu, Pb, Cd on occasion.It is unclear why As and Se were selected for such d e t a i l e d ana ly s i s ,and why molybdenum was ignored given the plant' s h i s tory ofproc e s s ing mo lybdenum ore. An inventory of the data presented inthe Remedial I n v e s t i g a t i o n s Report shows that 55 sampl e s were used tocharacterize the radioact ive mater ia l s , 69 s ampl e s were used tocharacterize the d i s t r i b u t i o n of arsenic and selenium, 29 s a m p l e s wereused to characterize a heavy metal suite i n c l u d i n g Hg, Ag, V, Cr, Cu,Pb, Cd, and 1 s a m p l e was analyzed for molybdenum. M o l y b d e n u mwas s ub s equen t ly e l i m i n a t e d as a metal of concern for the soil exposurepathway. E x p o s u r e risk f r o m soil e x p o s u r e cannot be e l i m i n a t e d i fthe d a t a base for as se s s ing the soil q u a l i t y is so s m a l l .The derivation of the l i s t of toxic me ta l s in Base l ine Risk Ass e s smente l iminate s c o p p e r , cadmium, rhenium, and s i lver . G i v e n thatmax imum soi l c o p p e r c onc en t ra t i on s are a l m o s t 300 t ime s abovebackground and average c o p p e r c o n c e n t r a t i o n s are 100 t imesabove b a c k g r o u n d , why was c o p p e r e l i m i n a t e d f r o m the RiskA s s e s s m e n t ?R e c o m m e n d a t i o n : Reassess extent of so i l contamination with re spectto heavy m e t a l s w i th an adequate number of samples.__________

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Dr. W e n d y H a r r i s o n (con t inued)( 0 8 / 1 7 / 9 9 )

S U B - Q U E S T I O N ; : ; J A N S W E R - : I S S U E S & R E C O M M E N D A T I O N SA - H a v e c ond i t i on sexternal to the remedychanged since theremedy was se lec ted?( C o n t i n u e d )

3) Are there newcontaminants orcontaminant sources?( C o n t i n u e d )

I s s u e : S o i l a n d A q u i f e r C h a r a c t e r i z a t i o n ( c o n t i n u e d )I n a d e q u a t e d a t a have been p r o v i d e d to d emons t ra t e that p a r t i c u l a rm e t a l s or organic c ompound s are o r i g i n a t i n g f r o m site. For e x a m p l e ,the groundwater sample s reported by Harding-Lawson show evidencethat the l , l , l , T r i c h l o r o e t h a n e does not originate f rom the site. Verbaland written repor t s that the c o p p e r and chromium in groundwateror ig ina t e f r o m other o f f - s i t e i n d u s t r i a l a c t i v i t i e s cannot be c o n f i r m e df r o m the current da ta s e t .The Cons truc t ion C o m p l e t i o n Report shows that soil q u a l i t y wasmonitored by gamma rad ia t i on , with s a m p l e s taken to c o n f i r m that Ra-226 was below 15 p C i / g . However, no monitoring of soil qual i ty formetals contamination took p l a c e ; thus, inadequate data exist tode t ermine both the or ig ina l extent o f non-radioact ive m e t a l scontaminat ion as wel l as the p o s t - r e m e d i a t i o n d i s t r i b u t i o n of me ta l s .F i n a l l y , no d e e p soil s a m p l e s were a n a l y z e d , nor were any s a m p l e srecovered f rom below the water t a b l e , i.e., soil and a q u i f e r m a t e r i a l sf r o m within the contaminant p l u m e . T h i s is a critical piece ofi n f o r m a t i o n for a s s e s s ing the p o t e n t i a l of the a q u i f e r i t s e l f to act as asource by r e l e a s i n g p r e v i o u s l y a d s o r b e d / p r e c i p i t a t e d m e t a l s back to thewater. The groundwater r emedia t i on goal d e p e n d s on the naturala t t e n u a t i o n o f c o n t a m i n a n t s ; that i s , c ontaminated water w i l l d e p o s i tm e t a l s onto th e a q u i f e r m a t e r i a l s , thereby removing c on taminant s f r omthe water. However, the chemical proce s s e s involved in a t t e n u a t i o n areall r ever s ib l e , to a greater or l e s s e r extent. Much of the a d s o r p t i v ec a p a c i t y of an a q u i f e r is d e t e r m i n e d by a c o m b i n a t i o n of water pH andEh and a q u i f e r minera l ogy - n o t a b l e its c lay mineral t y p e and con t en t ,the presence of organic mater ia l , and the presence of iron andmanganese h y d r o x i d e s . If water pH and Eh change, p r e v i o u s l yadsorbed m e t a l s can be r e l ea s ed (see t e chn i ca l notes b e l ow). A q u i f e rm i n e r a l o g y is unknown beyond s i m p l e visual observations, no a t t e m p thas been made to d e t e r m i n e t o ta l m e t a l s l o a d i n g w i t h i n the a q u i f e r , andno a t t e m p t has been made to d e t e r m i n e the p a r t i t i o n i n g of any m e t a l samong th e d i f f e r e n t mineral fractions._________________

3-77

Dr. W e n d y Harr i s on ( c o n t i n u e d )( 0 8 / 1 7 / 9 9 )

S U B - Q U E S T I O N • A N S W E R ^ I S S U E S & R E C O M M E N D A T I O N SA - Have c o n d i t i o n sexternal to the remedychanged since theremedy was s e l e c t ed?( C o n t i n u e d )

3) Are there newcontaminant s orcontaminant sources?( C o n t i n u e d )

I s s u e : S o i l a n d A q u i f e r C h a r a c t e r i z a t i o n ( c o n t i n u e d )W i t h o u t such d a t a , it is p r e m a t u r e to e l i m i n a t e the a q u i f e r as asource d u r i n g risk as se s sment and it is p r e m a t u r e to assume thatthe a q u i f e r has the c a p a c i t y to a t t e n u a t e al l c o n t a m i n a n t se f f e c t i v e l y over a 100-year per iod .Recommenda t i on s : Determine a q u i f e r material and d e e p soilc on tamina t i on using a sequential extract ional pro toco l that wi l l a l l o we x i s t ing me ta l s l o a d i n g and r a d i o n u c l i d e l o a d i n g to be measured.T e c h n i c a l N o t e s on A t t e n u a t i o n through W a t e r - S o i l / R o c kReactionsAttenua t i on of a contaminant involves m u l t i p l e processes inc ludingd i l u t i o n by s i m p l e phys i ca l mixing and d i s p e r s i o n , and removal fromthe water by several type s of chemical reaction i n c l u d i n g adsorp t ion,ion-exchange, s o l id phase p r e c i p i t a t i o n , and co-prec ip i ta t ion. Becauseof aqui fer heterogeneity with respect to organic matter content andpropor t i on s of minerals that have s ign i f i can t adsorpt ion and ionexchange capac i t i e s , a normal treatment is to determine an empiricala t t enua t i on f a c t o r or Kd for a given site. To expec t attenuation to be as i m p l e proc e s s that has a l in ear d e p e n d e n c e on t ime is a vasto v e r s i m p l i f i c a t i o n , and some e x a m p l e s are p r o v i d e d herein to i l l u s t r a t ethe point._________________________________

3-78

Dr. W e n d y Harr i s on (con t inued)( 0 8 / 1 7 / 9 9 )

• A N S W E R ; : ;A - H a v e condit ionsexternal to the remedychanged since theremedy was s e l e c t e d ?( C o n t i n u e d )

3) Are there newcontaminant s orcontaminant sources?( C o n t i n u e d )

Recommenda t i on s:T e c h n i c a l N o t e s o n A t t e n u a t i o n t hrough W a t e r - S o i l / R o c kReactions ( c o n t i n u e d )A d s o r p t i o n i s pH d e p e n d e n tT h e f i g u r e below (Langmuir , 1 9 9 7 ) shows p H - d e p e n d e n t a d s o r p t i o nisotherms for several chemical c o n s t i t u e n t s re levant to the S h a t t u c ksite. N o t i c e that s e l en ium, vanadium, chromium, and arsenic anionsare s t r o n g l y adsorbed at low pH (acid water) and are released at highpH (alka l ine water), whereas the reverse is true for cat ions of severalmetals. One important p i e c e of chemical i n f o r m a t i o n is thus theaqueous s p e c i a t i o n of the water: in what form are the d i s s o l v e d spec i e spresent? N o t i c e al so , that a small change in pH can have a large e f f e c ton the quanti ty of metal adsorbed. For e x a m p l e at pH 5, cadmium isnot adsorbed on iron hydrox id e , at pH 6, 50% is ad sorbed , and at pH 7,100% is adsorbed. A l t h o u g h a q u i f e r pH may not vary by 2 pH unit s , af r a c t i o n of a pH unit change could be e x p e c t e d to a l t e r the d i s s o l v e dcadmium load by several percent, p o s s i b l y r e su l t ing in non-compliancewith s t andard s . F i n a l l y , notice that each metal has a unique a d s o r p t i o ncurve and pH space; for e x a m p l e , at pH 6, 100% of lead and c o p p e r areadsorbed , whereas 50% cadmium, 30% zinc and <10% Ni areadsorbed . In the case of the S h a t t u c k site, where m u l t i p l e d i f f e r e n tmetal s may be present in the groundwater, t h i s t y p e of a n a l y s i s ise s s ent ial in order to p r e d i c t the movement of the various c o n s t i t u e n t s oft h e contaminant p lume . T h i s p a r t i c u l a r e x a m p l e i l l u s t r a t e s c l e a r l y thatd i f f e r e n t contaminants w i l l be at tenuated at d i f f e r e n t rates and l e v e l s .Furthermore , some remedial ac t ions , i n c l u d i n g b i o r e m e d i a t i o n o forganic c ompound s may reduce groundwater pH and thus m o b i l i z ep r e v i o u s l y adsorbed metals.________________________

3-79

Dr. W e n d y Harr i s on ( c o n t i n u e d )( 0 8 / 1 7 / 9 9 )

Q U E S T I O N S U B - Q U E S T I O N • A N S W E R - : :A - H a v e c o n d i t i o n sexternal to the remedychanged since theremedy was s e l e c t e d ?( C o n t i n u e d )

3) Are there newcon taminant s orcontaminant sources?( C o n t i n u e d )

A d s o r p t i o n / i o n exchange i s m i n e r a l - t y p e d e p e n d e n tIon exchange and a d s o r p t i o n reactions o f t e n depend s t rong ly on t o ta la v a i l a b l e s u r f a c e area. I n d i v i d u a l mineral phase s that have thec a p a b i l i t y of a d s o r p t i o n a n d / o r ion exchange have w i d e l y varyingsur fac e areas. For e x a m p l e , clay mineral t y p e has a p r o f o u n d i n f l u e n c eon total s u r f a c e area and thus ion exchange capac i ty . S u r f a c e areas fork a o l i n i t e , i l l i t e , and m o n t m o r i l l o n i t e , a l l commonly f o u n d in FrontRange s o i l s and sedimentary rocks, have t y p i c a l s u r f a c e areas of 10-30mVgm, 80-100 m 2 / g m , and 500-1000 mVgm, r e sp e c t iv e ly (Grim,1953; Moore and Reynolds , 1997). T h u s , in a s imp l e s i tuat ion whereattenuation might be con tro l l ed by ion exchange on clay mineralsurface, knowledge of the total clay content and the propor t ions of thed i f f e r e n t clay type s present would be needed to predict the uptake oftrace metals. C l e a r l y , very small quantities of smect i te-group clayminerals would dominate the total surface area and exchange capaci tyof the soil. No such analyses have ever been made for the S h a t t u c k siteso i l s and aqui fer materials.Contaminants have a pr e f e r enc e for certain "modes-of-occurrence"Because most s o i l s and a q u i f e r mater ial s are m u l t i - m i n e r a l mix ture s ,a t t e n u a t i o n occurs through m u l t i p l e mechanisms, and it is w e l ldocumented that d i f f e r e n t m e t a l s have a p r e f e r e n c e f or d i f f e r e n tre s idence s w i th in the s o i l . In a s i m p l e m o d e l , a normal soil i scomprised of organic debris, carbonates, s u l f a t e s , iron and manganeseh y d r o x i d e s , and s i l i c a t e minerals. Any given trace metal may havep r e f e r e n c e for as soc iat ion with one of these f r a c t i o n s .For e x a m p l e , arsenic and uranium have a strong p r e f e r e n c e fora d s o r p t i o n on iron h y d r o x i d e whereas c o p p e r and molybdenum have ap r e f e r e n c e for b i n d i n g to organic mater ia l . S o i l analys i s thus involvesdeterminat ion of the f r a c t i o n s and the me ta l s a s soc iated with eachf r a c t i o n : such a n a l y s i s involves a set of s equent ial chemicalex t rac t i on s , each removing a more res i s tant, l e s s s o l u b l e por t i on of thesoil (e.g., Chao , 1984). In the case of the S h a t t u c k site, where the___

3-80

Dr. W e n d y Harr i s on ( c o n t i n u e d )( 0 8 / 1 7 / 9 9 )

A - H a v e c ond i t i on sexternal to the remedychanged since theremedy was s e l e c t ed?( C o n t i n u e d )

3) Are there newcontaminants orcontaminant sources?( C o n t i n u e d )

A d s o r p t i o n / i o n exchange i s minera l- type d e p e n d e n t ( c o n t i n u e d )T h i s would serve two purposes: (1) attenuation mechanisms would bedetermined and (2) the p o t e n t i a l for the a q u i f e r to act as a source couldbe assessed.R e c o m m e n d a t i o n : Ful ly i m p l e m e n t a contaminant transport modelwith Kds de termined using g u i d e l i n e s e s t a b l i s h e d in EPA-402-R-99-004A&B.

4) Are thereunant i c ipa t edb y p r o d u c t s to theremedy notprev iou s ly addre s s edby the ROD?

The remedy s e l e c t e d requires that them o n o l i t h s hou ld remain above the watert a b l e . U n d e r such c o n d i t i o n s , m u l t i p l ei n v e s t i g a t i o n s have shown p o z z o l a n i ccements to be c h e m i c a l l y s t a b l e forex tended p e r i o d s o f t ime (see, f or e x a m p l e ,Massazza, 1998). I n s u f f i c i e n t s i t e data havebeen gathered to assess whether the watert a b l e could rise over the 200-year timeframe for which the remedy is e xp e c t ed tobe protec t ive . See a d j a c e n t comments onh y d r o l o g i c mode l ing . Remedial Des ign andP i l o t S t u d y report s document labora toryl e a c h i n g behavior of monol i th a d e q u a t e l yand accurately. Maintenance of m o n o l i t habove water t a b l e is a cri t i cal a spec t of theremedy.One que s t i on surrounds the i n j e c t i o n of theb i o r e m e d i a t i o n oxygen compound a d j a c e n tto the western boundary of the mono l i th:verbal c ommunica t i on s u g g e s t s that waterq u a l i t y in the s e w e l l s has d e c l i n e d withre spe c t to m e t a l s and radioac t ive e l emen t s .No da ta were p r o v i d e d for i n s p e c t i o n tod e t e rmine if t h i s is the case.

Issue: Chemica l S t a b i l i t y o f M o n o l i t hAbove the water t a b l e , the m o n o l i t h is p r o b a b l y s t a b l e for an extendedper iod of time. Reaction rates in the absence of water are extremelyslow. Even if the monol i th becomes cracked, its chemical s tab i l i ty willnot be s i g n i f i c a n t l y degraded unle s s cracking is pervasive and f ra c tur e sare of a size that wil l a l l ow water storage. Large, f r e e l y drainingfrac tur e s w i l l not permit water storage and consequent chemicalreaction. Water stored in f rac ture s for several days w i l l react with themono l i th cement and cause hydrat ion d e c o m p o s i t i o n p r o d u c t s . W h i l ep i l o t mono l i th l e a c h i n g t e s t s create a f l u i d of pH 11 or greater, smallquant i t i e s o f t h i s s o lu t i on within f ra c tur e s w o u l d : (1) evaporate andd e p o s i t mineral s such as g y p s u m , chalcedony, iron and manganeseo x i d e s , and ca l c i t e in the unsaturated zone,1 or (2) p e r c o l a t e downwardsinto the water t a b l e and be d i l u t e d or absorbed onto u n d e r l y i n g soilmater ia l s . The l a t t e r scenario was not a d e q u a t e l y addre s s ed in theRemedial Des ign document ( A p p e n d i x F) and must be asses sed u s i n greaction p a t h and reaction t ranspor t m o d e l s .M o n o l i t h c o n s t r u c t i o n e f f e c t i v e l y d i l u t e d t h e contaminated so i l b y30%: thus a d egraded m o n o l i t h source would no longer be c omparab l ewith soil that was removed for d i s p o s a l . If the mono l i th begins tod e g r a d e , contaminant s w i l l not be re l eased at the same rate as theywould have been f r o m soi l because (1) they are d i l u t e d , (2) the react ives u r f a c e area wi l l be c o n s i d e r a b l y r educ ed , and (3) the chemical form ofat l ea s t some of the c on taminant s w i l l have been changed by chemicalreactions involving the so i l and m o n o l i t h mater ia l s . P i l o t s t udyleaching t e s t s show that l e a c h a t e s f r o m the m o n o l i t h o f t e n exceedseveral groundwater s t a n d a r d s , n o t a b l y wi th re spec t to heavy meta l s .

D o c u m e n t e d in a l k a l i n e , arid c l i m a t e s o i l s .

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Q U E S T I O N ^ A N S W E R : ; : : I S S U E S : : & : R E C O M I V I E N I > A T I Q N S : : : :A - H a v e c ond i t i on sexternal to the remedychanged since theremedy was s e l e c t e d ?( C o n t i n u e d )

4) Are thereu n a n t i c i p a t e db y p r o d u c t s to theremedy notp r e v i o u s l y addre s s edby the ROD?( C o n t i n u e d )

I s s u e : C h e m i c a l S t a b i l i t y o f M o n o l i t h ( c o n t i n u e d )An analy s i s o f t h e l eachate impact t o groundwater q u a l i t y ( A p p e n d i x F;Remedial Des ign R e p o r t ) determined that no s t andard s would bee x c e e d e d ; however, the c a l c u l a t i o n of the reduc t ion f a c t o r (that i s , thee f f e c t i v e c o m p o s i t i o n of the m o n o l i t h l eachate when it reaches thea l l u v i a l a q u i f e r ) is based s o l e l y on an a n a l y s i s of p h y s i c a l m i x i n g of theleachate with i n f i l t r a t i n g sur fac e water and with groundwater.T h i s approach c o m p l e t e l y ignores any chemical interac t ions which w i l loccur. The chemistry of water mix ing is well understood (e.g.,Runne l l s , 1969). The various geochemical reactions are complex andcannot be p r e d i c t e d without computer s imulat ion 2 : for e xampl e ,mixing two waters one of pH 11 ( l ea cha t e) and one of pH 7(groundwater) in equal proport ions does not produce a pH 9 so lut ion,nor does mixing two solutions both saturated with respect to calc i t eneces sari ly result in the so lut ion remaining saturated with calc i t e (e.g.Drever, 1988). A c o m p l e t e discussion of the geochemical interactionsamong leachate, groundwater and so i l -aqui f er minerals is beyond thescope of th i s review; however, my recommendation is that a q u a l i f i e dgeochemist with e xper t i s e in chemical m o d e l i n g techniques be retainedto f u l l y evaluate the risk a s soc ia t ed with l eachate inf i l trat ion.______

2 M o d e l s such as E Q 3 / 6 can be used for t h i s c a l c u l a t i o n ; W o l e r y , 1983, W o l e r y and Daveler, 1992.3-82

Dr. W e n d y Harr i s on (con t inued)( 0 8 / 1 7 / 9 9 )

SUB-^QUESTIOM S A N S W E R - i I S S U E S ; & ; ; R E G Q M M E N D A T I O N S : sA - Have condi t ionsexternal to the remedychanged since theremedy was s e l e c t ed?( C o n t i n u e d )

4) Are thereu n a n t i c i p a t e db y p r o d u c t s to theremedy notpr ev i ou s ly addr e s s edby the ROD?( C o n t i n u e d )

I s s u e : C h e m i c a l S t a b i l i t y o f M o n o l i t h ( c o n t i n u e d )There are two scenarios for monol i th monitoring, the f i r s t of which isin p l a c e at this time. Several monitoring w e l l s surround the monol i th,and these w e l l s can be used to assess the e l e v a t i o n of the water tab l er e la t iv e to the base of the m o n o l i t h and to make p e r i o d i c analy s e s forcontaminant s of concern. In a conservative sense, such moni tor ingmay be adequate. U n f o r t u n a t e l y , by the time any r a d i o n u c l i d e s , andmetal s such as mo lybdenum and arsenic are d e t e c t e d , the chemicals t a b i l i t y of the m o n o l i t h w i l l have been compromi s ed . T h a t i s , there i sno f o r e w a r n i n g of inc ip i ent chemical f a i l u r e of the monoli th. A moreaggress ive monitoring p l a n would be to expand the l i s t of chemicalcon s t i tu en t s being analyzed to in c lud e sodium, p o t a s s i u m , magnesium,s i l i c o n , aluminum, and p o s s i b l y other e lements that might serve as af ingerpr in t f or this par t i cu lar f ly ash-cement-soil mixture. W h i l e thereis an a d d i t i o n a l f i n a n c i a l burden as soc iated with a larger ana ly t i ca lprogram, t h i s would be sma l l in terms of the f o r e w a r n i n g of m o n o l i t hf a i l u r e and the resultant o p p o r t u n i t y to assess remedial actions aso p p o s e d to having to take emergency action once the m o n o l i t h haddegraded.Recommendat ion: I m p l e m e n t a more comprehensive monitoring andm o d e l i n g i n v e s t i g a t i o n (see a l so comments by others in th i s review).

5 ) H a v e h y d r o l o g i c /h y d r o g e o l o g i c s i t ec o n d i t i o n s changed?

No; however, the s e c o n d i t i o n s have notbeen characterized in d e t a i l . See t e c h n i c a lcomments in issues and recommendations.

I s s u e : C o n t a m i n a n t T r a n s p o r t M o d e lThe B a s e l i n e Risk A s s e s s m e n t e l iminat ed the groundwater e xpo sur epathway because of: (1) lack o f groundwater use and (2) r e s u l t s f r o m acontaminant transport mode l that showed no p o s s i b i l i t y ofcontaminant s reaching e i t h e r the P l a t t e River or the Overland G o l fCourse irrigation water h o l d i n g p o n d s . As a r e su l t , e c o l og i ca l andenvironmental risk was al so e l i m i n a t e d . As noted above, a l t h o u g hthere is a p p a r e n t l y lack of groundwater expo sure t o d a y , there are noi n s t i t u t i o n a l c on tro l s in p l a c e to prevent o f f - s i t e groundwater access inthe f u tur e . The contaminant transport model d e p e n d s on twof u n d a m e n t a l sets o f data: h y d r o g e o l o g y and wa t e r-aqu i f e r chemicalr eac t i on ( c h e m i s t r y o f a t t e n u a t i o n ) . I n t h e case o f t h e S h a t t u c k s i t e ,nei ther the h y d r o g e o l o g y nor the nature of the chemical reac t ionswi th in the a q u i f e r have been a d e q u a t e l y characterized.__________

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S U B - Q U E S T I O N I S S U E S & R E C O M M E N D A T I O N SA - H a v e c o n d i t i o n sexternal to the remedychanged since theremedy was s e l e c t e d ?( C o n t i n u e d )

5 ) H a v e h y d r o l o g i c /h y d r o g e o l o g i c sitecondi t i ons changed?( C o n t i n u e d )

I s s u e : C o n t a m i n a n t T r a n s p o r t M o d e l ( c o n t i n u e d )T h u s , t h e c o n t a m i n a n t t r a n s p o r t model i s v a s t l y o v e r s i m p l i f i e dand, as such, is a poor f o u n d a t i o n f r o m which to e l i m i n a t e theg r o u n d w a t e r e xpo sur e p a t h f r o m the risk assessment. Thegroundwater exposure p a t h cannot be e l iminated based on currentinformation about the contaminant p lume .M u l t i p l e prob l ems u n d e r l i e th e h y d r o l o g i c model f or th e S h a t t u c k site.Most of these have been o u t l i n e d in a series of l e t t er s exchangedbetween the EPA and the USGS. My review of the content of thesel e t t er s is provided below. However, in essence, uncertainties in the sitehydrogeo log i c and transport model include (1) i n c o m p l e t e knowl edgeof quality of i n f i l t r a t i n g surface water, inc luding any source that mightresult f r om mono l i t h l each ing; (2) extent of groundwater interactionwith P l a t t e River f l o w sys tem; (3) seasonal changes in sur fac e water -groundwater interactions in the area inc luding the Overland G o l fCourse h o l d i n g p o n d s ; (4) lack of any sensitivity analyses on variablesinc luding d i s p e r s i v i t y , f l o w rate, hydraulic conduct ivi ty; (5)assumption of a homogeneous aquifer with no al lowance forchannel ing; (6) lack of control p o i n t s in several key areas; (7) pooru n d e r s t a n d i n g o f b e d r o c k - a l l u v i a l h y d r o l o g i c i n t e r a c t i o n s ; (8) noa l l o w a n c e for contaminant a t t e n u a t i o n ; (9) no evaluat ion of ac a t a s t r o p h i c h y d r o l o g i c event (dam f a i l u r e , 200-year storm, etc.) onp l u m e behavior; (10) lack of p r e d i c t i o n of e f f e c t o f groundwater use onh y d r o l o g y and contaminant p l u m e ; and (11) lack of a consi s tent set ofchemical analyse s and a manageable data base for moni tor ing we l l s .T h i s l a t t e r is so serious that I s p e c i f i c a l l y a d d r e s s it in therecommendations section below.Only one sur fac e water s a m p l e f r o m a r u n o f f catchment basin wasanalyzed. For this s a m p l e , only gamma a c t i v i t y , i n d i c a t i n g Ra-226a n d / o r elevated U-nat., was d e t e r m i n e d , and other c o n s t i t u e n t s such asmetals and organic c o m p o u n d s were not de t ermined . T h u s , thecharacterization of the s u r f a c e water q u a l i t y was incomplete.______

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S U B - . Q U E S T I O NA - H a v e c o n d i t i o n sexternal to the remedychanged since theremedy was s e l e c t ed?( C o n t i n u e d )

5 ) H a v e h y d r o l o g i c /h y d r o g e o l o g i c s i t ec o n d i t i o n s changed?( C o n t i n u e d )

Issue: Con taminant T r a n s p o r t M o d e l( c o n t i n u e d )R e c o m m e n d a t i o n s :USGS made recommendations t o EPA regard ing (1) assessment o fs p a t i a l d i s t r i bu t i on of contaminant p l u m e , (2) assessment ofcontaminants which could originate u p g r a d i e n t o f the S h a t t u c k s i t e , (3)assessment of i n f l u e n c e of groundwater on water qual i ty in irr iga t ionwater s torage p o n d s , and (4) assessment of interac t ion of p l u m e withS o u t h P l a t t e . All f o u r items are needed to de t ermine p u b l i c h ea l th risk;the second is needed to correctly i d e n t i f y contaminant sources andr e s p o n s i b l e part ie s . T h e overall o b j e c t i v e o f t h e U S G S monitoring p l a nis sound: only l i m i t e d m o d i f i c a t i o n s to the number and lo ca t i on of themonitoring w e l l s could be made without c o m p r o m i s i n g thee f f e c t i v e n e s s of the p l a n in achieving the s tated goal s .Three new transverse transec t s , p e r p e n d i c u l a r to f l o w , with ana p p r o x i m a t e l y E-W orientation, p o s i t i o n e d to intersect e x i s t i n gmoni tor ing w e l l s where p o s s i b l e (to minimize co s t), have beenrecommended. H y d r o l o g i c c o m p l e x i t i e s o f recharge, d i s c h a r g e , andmixed f l o w r eg imes , as we l l as the c o m p l e t e l y unknown extent ofh e t e r o g e n e i t y , j u s t i f y t h e p r o p o s e d m o n i t o r i n g w e l l network.______

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Q U E S T I O N S U B - Q U E S T I O N ; ? I S S U E S : & : : R E C O M M E N D A T i O N S : ; :A - H a v e c o n d i t i o n sexternal to the remedychanged since theremedy was s e l e c t e d ?( C o n t i n u e d )

5 ) H a v e h y d r o l o g i c /h y d r o g e o l o g i c sitec ondi t i on s changed?( C o n t i n u e d )

Recommenda t i on s : ( c o n t i n u e d )Recommended a d d i t i o n s to the p r o p o s e d ground-water cons t i tuent l i s tf o r moni t or ing th e m o n o l i t h have l e s s importance t o m o n o l i t h s t a b i l i t y(see above) and are more relevant to u n d e r s t a n d i n g the g e o ch emi s t ry oft h e mono l im-aqui f er-groundwat er system. A l t h o u g h t h e L J S G Sind i ca t e s a d d i t i o n a l chemical data would be used to a l l ow for watert y p e c l a s s i f i c a t i o n , a greater b e n e f i t would come from the a b i l i t y tolook at aqui f er-groundwater reactions, no tab ly to p r e d i c t those thatmight favor contaminant attenuation, such as the p r e c i p i t a t i o n of ironor manganese hydrox id e s which act as scavengers of many metals . Ialso concur with the sugge s t ion in the EPA's accompanying l e t t er thate levat ion of water table re lat ive to base of mono l i t h is an adequatemethod to assess monolith teachability risk; however, in the event thatthe mono l i t h would breach the water table, background data ona l k a l i n i t y , s i l i ca , a l k a l i s , s u l f a t e , etc. would be invaluable ine s t ab l i s h ing basel ine water quali ty. Incremental cost for several eas i lyanalyzed elements is small re lat ive to the insight gained into long-termbehavior of monolith-groundwater system.I concur with th e USGS's stated op inion that i t ha s i n s u f f i c i e n ti n f o r m a t i o n to evaluate ex trac table hydrocarbons and v o l a t i l e organicc ompounds . T h e s e are not c l ear ly re lated to the p l u m e and require as eparat e m o n i t o r i n g approach. W h i l e a b ioremedia t ion program is inp l a c e , no data have been p r o v i d e d to show progre s s in this treatment.I also concur with the USGS recommendation to analyze total uraniumas o p p o s e d to separate i s o t o p e s of r a d i o n u c l i d e s , and the e l imination ofradium i s o t o p e analyse s , as w e l l as its ob s ervat ion that the radioact ivee l ement s re lated to the S h a t t u c k s i t e a p p e a r to have been e f f e c t i v e l ya d d r e s s e d . A su i tab l e ana ly t i ca l p r o t o c o l for t o ta l uranium w i l l have tobe e s t a b l i s h e d .

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S S U B - Q U E S T l f Q N TISSUES : ; &: : : l lE;GOlt iHE;IVl>ATIQNS •;A - H a v e condit ionsexternal to the remedychanged since theremedy was s e l e c t e d ?( C o n t i n u e d )

5 ) H a v e h y d r o l o g i c /h y d r o g e o l o g i c si tec ond i t i on s changed?( C o n t i n u e d )

R e c o m m e n d a t i o n s : ( c o n t i n u e d )A l t h o u g h some concern has arisen r egard ing the extent of a d d i t i o n a lmoni tor ing sugge s t ed by the USGS, it appear s that it s p r o p o s a l isreasonable given the questions that need to be answered. T h e r e is noex i s t ing data base that would a l l o w groundwater- sur face waterinteraction in the Overland h o l d i n g p o n d s or in the S o u t h P l a t t e to bea s s e s s ed; there is no w e l l - d e f i n e d analysi s of the contaminant p l u m eand the extent to which some of its chemical c omponen t s might becontributed from locations upgradient of the Shat tuck S i t e ; there are nodata regarding the presence (or absence) of groundwater channe l ing;and e x i s t i n g water qual i ty data are of l i m i t e d value in p r e d i c t i n gcontaminant p l u m e behavior because of the very l i m i t e d number ofchemical c on s t i tu en t s analyzed .Rede t ermine groundwat er e xpo sur e and e n v i r o n m e n t a l risk basedon a more accurate and c o m p l e t e h y d r o l o g i c model and s u f f i c i e n tminera l og i c and chemical data to implement a more accuratecontaminant transport mode l . S p e c i f i c a l l y , r e - ca l cu la t e th econtaminant transport model using:(1) an improved hydro log i c data base acquired in part throughi m p l e m e n t i n g t h e m a j o r i t y o f t h e U S G S recommendat ion s;(2) mineralogy and m e t a l s l o a d i n g of the a q u i f e r and over lying s o i l sde t e rmined w i th a s equent ia l ex tract ion pro to co l to a l l o w metal mode-of-occurrence to be e s t a b l i s h e d ;( 3 ) K d values f o r t h e a q u i f e r d e t ermined u s i n g a p p r o p r i a t ee x p e r i m e n t s ; and(4) a p o t e n t i a l m o n o l i t h l eachate .Kd values s h o u l d c on form wi th EPA 402-R-99-004A&B which c l e a r l ystate that l i t e r a t u r e measurements of Kd are only s u i t a b l e in a s c o p i n gs tudy and for all other cases experimental de t erminat ions are required.

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Dr. W e n d y H a r r i s o n ( c o n t i n u e d )( 0 8 / 1 7 / 9 9 )

A - Have c ond i t i on sexternal to the remedychanged since theremedy was s e l e c t e d ?( C o n t i n u e d )

5 ) H a v e h y d r o l o g i c /h y d r o g e o l o g i c si tecondi t i on s changed?( C o n t i n u e d )

D e v e l o p a c o m p l e t e and c omprehen s iv e d a t a base for water q u a l i t yparame t er s . T h i s w i l l make p l u m e behavior and groundwaterr emed ia t i on much easier to f o l l o w . Curren t ly , data are scattered amongd i f f e r e n t contractors, government agencies, and the owner. M u l t i p l ereport s have to be read in order to review his toric and current data. In acomprehens ive data base, all parameters measured on a s i n g l e waters a m p l e shou ld be archived by s a m p l e : that i s , keep m e t a l s , pH, Eh,a l k a l i n i t y , etc., together. The s eparat ion of me ta l s concentrat ions in onetab l e f rom pH and a lka l in i ty in an a p p e n d i x tab le (the current s tate ofindiv idual data s e t s) makes the data d i f f i c u l t to interpret f r om ageochemical point of view. Both f i l t e r e d and u n f i l t e r e d sampl e s shouldbe analyzed and the data base annotated ac cord ing ly: human hea l thand groundwater chemistry have d i f f e r e n t needs in terms of f i l t r a t i o n .The current s tate of the groundwater qua l i ty data could at best bedescribed as di sorganized. The most recent reports of s ampl ing byMorri son-Knudson seem to be headed in the right direction and wouldprovide a starting point from an organizational point of view.Evalua t e worst-case scenarios for p u b l i c awareness and education.W o r k i n g f rom the s t r ength of improved h y d r o l o g i c and contaminantt ran spor t mode l s , several worst-case scenarios could be evaluated thatwould p r o v i d e area r e s i d e n t s wi th a d d i t i o n a l background into why them o n o l i t h is the most e f f e c t i v e remedy for thi s site:(1) Construct a worst-case scenario that r e su l t s in mono l i th in t e r s e c t ingwater tab l e ; evaluate th e interaction o f m o n o l i t h l eachate (pH 11) withgroundwater;(2) Evaluate recharge c ond i t i on s necessary for water t a b l e to rise tointersect m o n o l i t h ; then e s t a b l i s h what c l i m a t i c c o n d i t i o n s could lead tot h i s scenario;(3) The m o n o l i t h covering was d e s i g n e d to be p r o t e c t i v e of them o n o l i t h in event o f f a i l u r e o f C h a t f i e l d Reservoir dam: i f t h i sh a p p e n s , what would the water t a b l e look l ik e?(4) If water t a b l e in t er s e c t s m o n o l i t h , what are geochemicalconsequences and over how many years would the m o n o l i t h degrade tothe p o i n t of r e l ea s ing con taminant s of concern?_____________

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iiill^isi^B - Has the remedy beenimplemented inaccordance withde c i s i on documents?

C - Has any riski n f o r m a t i o n changedsince the remedy wass e l e c t e d ?

:;:S;;:;:;::;SU]B-QUEs|i[^|^S::::N / A

N / A

l l i i l l;!^Yes, with the notable except ion of theinadequate air monitoring during sitec on s t ruc t i on a c t i v i t i e s . However , since thes u r f a c e , a ir-exposed d u s t , d ir t , and otherdebri s is now removed, fur th e r action seemsirrelevant, unle s s workers and r e s i d en t swere expo s ed dur ing construct ion. Anassessment shou ld be made of the p o t e n t i a lcon s t ruc t i on-re la t ed exposure.

Not a d d r e s s e d by t h i s reviewer.

l i l l i i i l i f l ^I s s u e s :Overal l , the monol i th appears to be protec t ive of human health throughsur fa c e exposure p a t h s for an extended period of time. No analy s i s ofthe long-term s t a b i l i t y of the mono l i t h has been made for the s p e c i f i cs i te condit ions. On the basis of general s c i e n t i f i c and engineer ingk n o w l e d g e of pozzo lan i c cements, it is reasonable to expect that them o n o l i t h w i l l be c h e m i c a l l y s t a b l e as l ong as it remains above thewater tab l e and does not crack so e x t en s iv e ly that it acquires thecapac i ty to store i n f i l t r a t i n g s ur fa c e water. The on-site exposure riskf r om sur fa c e and shal low organic, inorganic, and radioac t ivecontamination has been e f f e c t i v e l y removed.V i c i n i t y workers and r e s id en t s have been pro t e c t ed f r o m the radiat ionhazard; however, i n s u f f i c i e n t data have been gathered to assess whetherv i c i n i t y workers and r e s i d en t s have been a d e q u a t e l y pro t e c t ed fromremaining s o i l s , sur fac e water, i n c l u d i n g the P l a t t e River, andgroundwater exposure. Based on the original d e s c r ip t i on of the so i land groundwater contamination, the s e l e c t ed r emed ia t i on me thod , aswell as the monitoring p lan appear s u f f i c i e n t ; however, the original s i t echaracterization, the d e t erminat ion of the extent of groundwatercontamination, and the movement of the contaminant p l u m e wereinadequate . T h u s , the e f f e c t i v e n e s s o f the remedy in p r o t e c t i n g humanh e a l t h and environmental q u a l i t y cannot be assessed with re spec t to thegroundwater c on tamina t i on exposure pa th . Likewi s e , soil m e t a l sa n a l y s e s were p e r f u n c t o r y and sparse , thus there is i n s u f f i c i e n t da ta toassess whether or not all the metal contaminated so i l was removed, orwhether meta l s l o a d i n g on to the a q u i f e r m a t e r i a l s occurred. I n a d e q u a t einformation exists to determine if metal-contaminated s o i l s remain,a l t h o u g h a p p a r e n t l y removal of r a d i o a c t i v e m a t e r i a l s was donep r o p e r l y and a d e q u a t e l y .R e c o m m e n d a t i o n : A s s e s s groundwater expo sure risk. A s s e s se f f e c t i v e n e s s o f so i l removal for heavy meta l s contaminat ion.I s s u e :R e c o m m e n d a t i o n :

3-89

Dr. Wendy Harrison (continued)( 0 8 / 1 7 / 9 9 )

A d s o r p t i o n of various metal cations andoxyanions (each at a trace concentration of 5 xl O ' 7 M ) , b y f err ihydri t e ( S f e ( I I I ) = 1 0 ' 3 M ) , a s af u n c t i o n of pH at an ionic s t r e n g t h of 0.1 mol/kg.T h e r e are 2 x 10' 4 M of reactive sites on theo x y h y d r o x i d e . The dashed curves have beenc a l c u l a t e d . The p l o t s are a f t e r W. S t u m m ,Chemistry of the solid-water interface, C o p y r i g h t© 1992 by J o h n W i l e y & Sons, Inc. Reprintedby permission of J o h n W i l e y & Sons, Inc.

F i g u r e 1. A d s o r p t i o n of Various Metal C a t i o n s and Oxyanions by F e r r i h y d r i t e

3-90

Dr. W e n d y Harr i s on (con t inued)( 0 8 / 1 7 / 9 9 )

Reference sChao, T.T., 1984, Use of part ia l d i s s o l u t i o n techniques in geochemical e xp l ora t i on: Journ. Geochemical E x p l o r . , 20, p. 101-135.Drever, J.I. The Geochemis try of Natura l Water s , 2 n d Edi t i on. P r e n t i c e - H a l l , 43 7p.Grim, R.E., 1953, Clay M i n e r a l o g y , M c G r a w - H i l l .Langmuir, D.W., 1996, Aqueous Environmental Geochemi s try, Prentice Hall , New J e r s e y , 589p .Massazza, F, 1998, Pozzolana and Pozzolanic Cements: Chap t e r 10 in H e w l e t t , P.C. (ed.), Lea's Chemis try of Cement and Concrete, J o h n W i l e y andS o n s , N e w York, 1053p.Moore D. M. and Reynolds, R.C. Jr, 1997, X-ray d i f f r a c t i o n and the id en t i f i ca t i on and analysis of clay minerals, second edition, Oxford UniversityPress, 378p.Runnel l s , D.D., 1969, Diagenes i s , chemical sediments , and the mixing of natural waters: J. Sed. Pe tro l . , v. 39, p. 1188-1202.U.S. Environmental Pro t e c t i on A g e n c y , The Kd M o d e l , M e t h o d s o f Measurement and A p p l i c a t i o n o f Chemical Reaction C o d e s , V o l u m e I. EPA-402-R-99-004A.U.S. Environmental Pro t e c t i on Agency, Review of Geochemi s t ry and A v a i l a b l e Kd V a l u e s for Cadmium, Cesium, Chromium, L e a d , P l u t o n i u m ,Radon, S t r o n t i u m , Thor ium, T r i t i u m ( 3 H ) , a n d Uranium, Volume I I . EPA-402-R-99-004B.W o l e r y T . J . , 1 9 8 3 , E Q 3 N R . A computer program f o r geochemical aqueous s p e c i a t i o n - s o l u b i l i t y ca l cu la t i on s : U s e r ' s guide a n d documentation.Lawrence Livermore N a t i o n a l Laboratory Report , U C R L - 5 3 4 1 4 , 189 pp.W o l e r y TJ. and Daveler S.A., 1992, EQ6 a computer program for reaction path m o d e l i n g o f aqueous geochemical systems: theoret ical manual,u s e r ' s gu id e , a n d re lated documentation. Lawrence Livermore N a t i o n a l Laboratory Report , U C R L - M A - 1 1 0 6 6 2 P T I V , 3 3 8 p p .

3-91

Dr. A l i e n H a t h e w a y( 0 8 / 2 0 / 9 9 )

Expert Panel Comment s for 5-Year ReviewS h a t t u c k Chemica l S i t e

Denver, C o l o r a d o

Q U E S T I O N S U B - Q U E S T I O N A N S W E R ; : • : I S S U E S & RECOM M E N T A T I O N S ; ;A - H a v e condi t i onsexternal to the remedychanged since the remedywas s e l e c t e d ?

Yes; C E R C L A s i t e and wastecharacter izat ion was i n s u f f i c i e n t to s u p p o r tthe s e l e c t ed r emed ia l de s ign. CERCLA si teand waste charac t er izat ion did not p r o v i d e ana p p r o p r i a t e level of accuracy r e l a t i n g toc o n d i t i o n s a f f e c t i n g f a t e and transport o fcontaminat ion below the m o n o l i t h f o o t p r i n tand l i k e l y to be entering the site s u b sur fa c eand p a s s i n g below the site.

I s s u e : C E R C L A - R e l a t e d I s s u e s :• S t a t i s t i c a l l y d e f i n e d changes in pH of site groundwater were

not reviewed in terms of p o t e n t i a l re l ease of heavy m e t a l s forcontaminant migration.

• S e l e n i u m is not characterized in terms of its m o l e c u l a r naturenor is it a s s igned an h i s t or i c proces s origin. S e l e n i u m ,th er e f or e , becomes an i n o p e r a b l e c a n d i d a t e for beingaddres sed in the F i n a l Clo sur e Plan.

• S i t e g e o l o g i c characterization does not appr e c ia t e the typ i ca lvariat ions of grain-size and a l luv ia l s edimentary character thatcan and do d e f i n e various contaminant pathways in the Plar t eRiver alluvium.

• Rhenium and molybdenum residues are not characterizedchemica l ly and therefore cannot be accommodated indeve lopment of groundwater monitoring programs nor inClosure S y s t e m design. Not all such wastes could have beenremoved by excavation.

Seismic Parametric I m p a c t s• Relative to p u b l i c concern for s e i s m i c a l l y induced d e f o r m a t i o n

or in s tab i l i ty of the monol i th or its f o u n d a t i o n when sub j e c t edto a Denver-Area Maximum C r e d i b l e Event, th i s MCE shouldbe Richter Local M a g n i t u d e of about 7.0 (based on per sonalexperience). Furthermore, the typical inter-tonguing of thethree t y p e s o f Denver F o r m a t i o n soil unit s (c lay s t one s ,s i l t s t o n e s , and s a n d s t o n e ) , are e l o n g a t e d in the general WNW-E S E .

• C o n s i d e r i n g the nature of s i te g e o l o g y , domina t ed by gravelabove 10 f e e t and by conso l ida t ed Denver Formationc lays t one s , s i l t s t o n e s , and sands tone s , and the squat and broadin t e r l o ck ing monol i th of hard igneous rocks, the onlyconceivable form of s e i s m i c a l l y induced ground d e f o r m a t i o nwould be that of l i q u e f a c t i o n . Even l i q u e f a c t i o n l i e s o u t s i d e ofthe only po s s i b l e e f f e c t , due to the re la t ive ly coarse nature ofthe f o u n d a t i o n s o i l s , a long with the c o n s o l i d a t i n g e f f e c t s o f th em o n o l i t h . T h i s r e s u l t s in a continual drying out of the s o i l sb e low the f o o t p r i n t and lack of nearby s l o p e f a c e s that mighto therwi s e p r o v i d e a cause for instability._____________

3-92

Dr. A l i e n Hatheway (cont inued)( 0 8 / 2 0 / 9 9 )

A - Have condi t i onsexternal to the remedychanged since the remedywas selected?( C o n t i n u e d )

P o t e n t i a l Dynamic I m p a c t o f P a s s i n g Rai lroad T r a i n s• The p o t e n t i a l issue here is that of s u p p o s e d dynamic

compac t i on f r o m vibrations o f pa s s ing railroad trains. Thenature of such is repet i t ive compressional p u l s i n g downwardthrough the rail embankment, which is s l i g h t l y lower than thevi s i b l e m o n o l i t h base and which th i s Panel Member b e l i eve sw i l l exert only a minimal load on any p o r t i o n of the m o n o l i t hf o u n d a t i o n s o i l s and then only for a few meters into the s o i l sbelow the western rim of the m o n o l i t h f o u n d a t i o n .

• The s e f or c e s w i l l fall , in magnitude, below those capable ofs t r e s s ing the s o i l s beyond any form of e l a s t i c l i m i t andt h e r e f o r e should not be capab l e of e f f e c t i n g any changes intheir current or long-term e l a s t i c p r o p e r t i e s . It f o l l o w s ,t h e r e f o r e , that ongoing railroad s tre s s ing w i l l not be f e l t by them o n o l i t h so i l s . In any event, the presence and l o c a t i o n of suchstress could not bring about a n y t h i n g but p o s i t i v e condi t i onsa f f e c t i n g m o n o l i t h s t a b i l i t y or the hydrau l i c p r o p e r t i e s o f them o n o l i t h f o u n d a t i o n s o i l s .

Recommenda t i on s : The e x i s t i n g mono l i t h should be consideredc a p a b l e o f a d d r e s s i n g th e long-term p r o t e c t i v e d e s i g n c r i t e r ia , i fand only if a P e r f o r m a n c e M o n i t o r i n g Program is dev i s ed toaddre s s recognized da ta g a p s r e l a t i n g to accessory site and sitearea c on tamina t i on , and to f u r t h e r r e f i n e the PMP so as to raise thes i t e containment m o n o l i t h .

1) Has land use orexpected land use onor near the s i t echanged?

No changes were d e t e c t e d at present due tourban deve lopment considerations that maya f f e c t in s t i tu t i onal c on tro l s f or the 200-year p e r f o r m a n c e d e s i g n l i f e .

I s s u e : C o a l - T a r D y e M a n u f a c t u r i n g P l a n t ; W e s t e r n ChemicalM a n u f a c t u r i n g Co. (1887 t i t l e ) ; General Chemical Company 1890t i t l e ; A l l i e d Chemical C o m p a n y Chemica l waste remnants f r o mthe above ac t iv i ty were i d e n t i f i e d in the Source area wi l l bev i r t u a l l y s t a b l e in p l a c e but s u b j e c t to d i s s o l u t i o n and contaminantt ransport o f f s i t e , t o a d j a c e n t g o l f course.R e c o m m e n d a t i o n : Recommend recovery and a n a l y s i s of suchrecords and f a c t o r i n g relevant i n f o r m a t i o n into M o n o l i t hP e r f o r m a n c e M o n i t o r i n g Program.

3-93

Dr. A l i e n Hatheway (continued)( 0 8 / 2 0 / 9 9 )

Q U E S T I O N ^ ^ S U B - Q U E S T I O N : : ;A - Have conditionsexternal to the remedychanged since the remedywas s e l e c t e d ?( C o n t i n u e d )

2) H a v e any humanh e a l t h or e c o l o g i c a lexpo sure p a t h w a y schanged or been newlyi d e n t i f i e d ?

Yes, see response to Question A - l . Issue: Y e s , see response to Question A - l .R e c o m m e n d a t i o n :

3) Are there newcontaminants orcontaminant sources?

Yes.N e w l y deduced location of coal-tar dyemanufac t ory at 1271 Bayaud Stre e t .L i k e l y presence of abandonedm u n i c i p a l / i n d u s t r i a l waste dump on eastf r inge of g o l f course.

I s s u e A3.1: Presence of coal-tar d er iva t iv e s such as anthracineand b enzo(a)pyrene , carcinogenic hazardous coal-tar r e s i d u a l snow known as present and detected on the site. See items inE P A / V I I I S i t e I n f o r m a t i o n Document Control Syst em.Recommendat ion A3.1: C o m p i l a t i o n of d e t a i l e d site history andhistoric site operational summary, neither of which have ever beenc o m p l e t e d .I s s u e A3.2: General presence of numerous mixedm u n i c i p a l / i n d u s t r i a l waste d i s p o s a l dumps in Denver area.Recommendat ion A3.2: H a t h e w a y had 1987 personalcommunication with the late Eugene Waggoner, a Woodward-C l y d e f o u n d e r , and post-1946 Denver g e o l o g i c consultant. Suchsites may number more than 30, and all should be regarded asmixed munic ipal and industrial. The po t en t ia l for any nearbyunrevealed m u n i c i p a l / i n d u s t r i a l d u m p should be assessed.

4) Are there u n a n t i c i p a t e dbyproduc t s to theremedy not p r e v i o u s l yaddre s s ed by theROD?

Yes, see re sponse to Quest ion A-3. I s s u e : See re sponse to Quest ion A-3.Recommendation: See response to Question A-3.

3-94

Dr. A l i e n H a t h e w a y (con t inued)( 0 8 / 2 0 / 9 9 )

s A N S W E R sA - Have c o n d i t i o n sexternal to the remedychanged since the remedywas s e l e c t ed?( C o n t i n u e d )

5 ) H a v e h y d r o l o g i c /h y d r o g e o l o g i c sitecondit ions changed?

Y e s , due to f l a w e d site and wastecharacterization e f f o r t u t i l i z e d at the t ime ofthe RI and carried on into the RemedialDesign.

I s s u e : The Surface Impoundment o c cupi e s the extreme northerntwenty percent o f the mono l i th . The impoundment containedabout 1.2 m of pond precipitate in March 1984, and this materialwas treated and removed for d i s p o s a l e l sewhere.The author f e e l s that the i m p a c t s o f the d e t e c t ed p o n d - l e a k eventand of p o t e n t i a l pre-1984 impoundment l eakage, e s p e c i a l l y inview of its gravel-on-30 mil PVC liner, were not s u f f i c i e n t l yevaluated to p r e c l u d e the presence of remaining on-sitecontamination.Recommendat i on s: Add provis ions for gaining accurate sitecondi t i ons to the p r o p o s e d M o n o l i t h Performance M o n i t o r i n gProgram.

B - Has the remedy beeni m p l e m e n t e d in accordancewith dec i s ion documents?

N A T h i s a p p e a r s to be the case. I s s u e : No adverse comments.Recommendat ion: N o n e .

C - Has any riski n f o r m a t i o n changed sincethe remedy was s e l e c t ed?

N / A Reviewer b e l i eve s that e s s e n t i a l , f u n d a m e n t a le x i s t i n g g e o l o g i c , h y d r o l o g i c andgeo t e chni ca l data used in risk f o r m u l a t i o n ares i g n i f i c a n t l y d i f f e r e n t f r om r e a l i t y .

I s s u e : Reviewer b e l i eve s that s i te risk assessments w i l l not beaccurate enough for their intended use unt i l an e x p a n d e d site andwaste character izat ion program is c o m p l e t e d . Risk a n a l y s i sshou ld then be r e- ca l cu la t ed on the basis of e xpanded s i te andwaste characterization.R e c o m m e n d a t i o n : S i t e e x p l o r a t i o n shou ld be executed inaccordance w i th an e x p a n d e d s i t e and waste charac t e r i za t i onprogram. Risk analy s i s must be re-calculated on the basis ofnecessary as soc iated s i t e and waste characterization.________

3-95

4. Documents Reviewed The following four sections provide examples of the type of documents considered for review as part of the five-year review process supported by the expert panel report. The document review comprised four categories, each addressing a different aspect of the implementation of the remedy. The categories are the remedy decision, remedy implementation, operation and maintenance (O&M), and legal documentation. The exhibits and text below were used as a guide by the Peer Review Panel. Remedy Decision Remedy decision documents establish the basis upon which the remedy was selected or modified. The documents in the table below identify the background and goals of the remedy and any changes in laws and regulations that affect the remedy. Other sources of remedy decision information were the Remedial Investigation/Feasibility Study (RI/FS), toxicological and chemical characteristics databases, transcripts of public meetings, and "to be considered" (TBCs). TBCs include guidelines and proposed rules that suggest whether the remedy is protective or is likely to be considered not protective in the future. For instance, a proposed rule may suggest that cleanup levels are likely to change in the future.

Exhibit 4-1 Document Purpose of Document Use During Five-Year Review

Decision Documents - RODs - ROD Amendments - Explanations of Significant Differences - Action Memoranda

- Records of remedial decisions or other actions, and significant changes from the original remedy

- Goals of the remedy - Background information on the site - Basis for action - Cleanup levels and applicable or relevant and appropriate requirements (ARARs) - Community concerns and preferences

Federal Laws and Regulations - Statutory and regulatory requirements that may be ARARs

- Changes in ARARs established in the ROD which provide a basis for cleanup levels/protectiveness of the remedy. Only ARARs that are related to protectiveness need be reviewed. For example, standards set under the National Historic Preservation Act are not relevant to protectiveness. - Pertinent laws and regulations promulgated since the signing of the ROD that may be ARARs are also reviewed.

State Laws and Regulations - Statutory and regulatory requirements that may be ARARs

- State laws and regulations have the same standing under the National Contingency Plan (NCP) as Federal laws and regulations and should be reviewed in the same manner. The State typically performs this component of the review.

4-1

Remedy Implementation Remedy implementation documents were reviewed to obtain information about design assumptions, design plans or modifications, and documentation of completed construction and site completion. Design reports and plans and specifications were other documents providing further information.

Exhibit 4-2 Document Purpose of Document Use During Five-Year Review

Remedial Action Reports (and Interim Remedial Action Reports)

- Documents that show for a single operable unit whether all construction activities are complete, the remedy is operational and functional, and cleanup levels have been achieved - Interim Remedial Action Reports are used for long-term remedial actions where cleanup levels have not yet been achieved

- Detailed history and status of remedial actions

Remedial Drawings (As-Builts) - Documents changes/ modifications to the original design that occurred during the construction

- Documentation of completed action and/or implemented remedy

Close Out Reports (Preliminary and Final) - Documents that all physical construction for all operable units at a site is complete

- Background information and the status of the remedial actions at the site

Health and Safety Plan, Contingency Plan/Emergency Response Plan

- Establishes policies and procedures for protecting the health and safety of personnel during operations - Establishes procedures to minimize risks associated with potential site emergencies

- Confirmation of compliance - Site access restrictions and protective clothing requirements for site inspection

4-2

Operation and Maintenance O&M documents were evaluated to assess the ongoing requirements for the implementation of the remedy. They provide the structure for O&M at the site and confirm whether the O&M is proceeding as planned. Other types of O&M data reviewed included permit compliance data such as the air sampling results, facilities' operation data such as treatment train, operational records, gas monitoring and leachate collection data, and current sampling data. These data demonstrate the proper O&M of the remedy.

Exhibit 4-3

Document Purpose of Document Use During Five-Year Review O&M Manual - Contains technical

information necessary to operate and maintain the remedy

- Purpose and function of the equipment and systems that constitute the overall facility

O&M Reports - Documents O&M activities, data, and costs

- To check whether O&M is proceeding as planned

Discharge Permits and Deviations - Notes contaminant levels for the discharge permits - Notes contaminant levels for deviations

- To check whether the remedy is operating within design parameters

Monitoring Information/Records (information could include air sampling, groundwater monitoring, survey/settlement monument records, and gas generation records)

- Records monitoring data and other information

- To check whether contaminant levels are within established criteria

4-3

Legal Documentation Legal documentation pertinent to the site was reviewed to evaluate who is responsible for conducting remedial actions, implementing institutional and access controls, and performing elements of the five-year reviews. Examples of the types of documents under this category and the purpose for their review are presented below.

Exhibit 4-4 Document Purpose of Document Use During Five-Year Review

Enforcement Documents - Consent Decrees - Unilateral Administrative Orders - Administrative Orders on Consent

- Commitments/agreements regarding implementation and operation of the remedy, and conduct of studies

- Responsibilities of the PRP for conducting remedial activities at various stages at the site - When these documents are used to enforce the performance of O&M, they may contain O&M requirements and may incorporate O&M documents, such as the O&M Manual

Institutional Controls - Deed notices, easements, other conditions, covenants or restrictions on deeds, and groundwater and land use restriction documents

- Means to restrict the use of a parcel or an associated resource, such as groundwater

- Status of institutional controls

Superfund State Contracts and Cooperative Agreements

- State assurances to conduct O&M - State authorities responsible for O&M - Specific O&M requirements - Agreements with Indian tribes

- O&M implementation and reporting requirements - Roles of different agencies

Interagency Agreements and Federal Facility Agreements

- Responsibilities of other agencies

- O&M guidelines and rules in effect (sometimes other agencies adopt their own guidelines and rules, which must be consistent with those established by EPA)

Bibliography Exhibit 4-5 lists the actual documents reviewed by one or more members of the Expert Panel. The majority of the documents were site-specific and were obtained from the administrative record files for Shattuck that are available at EPA Region VIII and the Colorado Department of Public Health (CDPH). The panel members had available to them all the files housed within the EPA Region VIII and CDPH offices. The panel focused on those documents and correspondence deemed most relevant. In addition, relevant statutory citations are provided in Exhibit 4-5. Source material not related to the Shattuck site, such as technical studies and reports that panel members drew upon to assist them in their assessments, are also listed in the exhibit. The panel's goal was to access and review all information germane to assessing the remedy's effectiveness. However, there is no all-encompassing document or road map that captures all the essential details of the Shattuck Site Remedy. Therefore, the panel made efforts to confirm with EPA Region VIII and CDPH its assumptions regarding the most current and accurate data sources.

4-4

Exhibit 4-5. Documents Reviewed 10 CFR Part 20, Standards for Protection Against Radiation. 10 CFR Part 61, Licensing Requirements for Land Disposal of Radioactive Waste. 40 CFR Part 190, Environmental Radiation Protection Standards for Nuclear Power Operations. 40 CFR Part 191, Environmental Standards for the Management and Disposal of Spent Nuclear Fuel, High-Level and Transuranic Radioactive Waste. 40 CFR Part 61, National Emission Standards for Hazardous Air Pollutants. 40 CFR Part 141, Interim Primary Drinking Water Regulations. 40 CFR Part 142, National Primary Drinking Water Regulations - Radionuclides. 40 CFR Part 192, Health and Environmental Protection Standards for Uranium and Thorium Mill Tailings. 40 CFR Part 300, National Contingency Plan (NCP) and Supporting Guidance. 10 CFR Part 834, Radiation Protection of the Public and the Environment. 40 CFR Part 311, Worker Protection. 40 CFR Part 440, Ore Mining and Dressing Point Source Category. 40 CFR Part 58, Ambient Air Quality Surveillance. Aboveground Tank Update (February 1992). Sodium bentonite liner found degraded at New York site. p. 1. Agency for Toxic Substances and Disease Registry (April 8, 1999). U.S. Department for Health and Human Services Health-Consultation Report for Operable Unit 8, Denver Radium Site. Air Monitoring Data, October 1996 to October 1997. Baseline Risk Assessment for Denver Radium Site Operable Unit VIII: Colorado Department of Health: September 1991. Bechtel Hanford, Inc., Focused Feasibility Study of Engineered Barriers for Waste Management Units in the 200 Areas. Richland, Washington, 1996. Benson, C. H. and Daniel, D. E. (1994). Minimum thickness of compacted soil liners: II. Analysis and case histories. Journal of Geotechnical Engineering, ASCE, Reston, VA, Vol. 120, No. 1, 153-172.

4-5

Benson, C. H., Hardianto, F. S., and Motan, E. S. (1994). Representative specimen size for hydraulic conductivity assessment of compacted soil liners. Hydraulic Conductivity and Waste Contaminant Transport in Soil, ASTM STP 1142, D. E. Daniel and S. J. Trautwein, Eds., ASTM, West Conshohoken, PA, p. 3-29. BHI 1996. Focused Feasibility Study of Engineered Barriers for Waste Management Units in the 200 Areas. Bechtel Hanford, Inc., Richland, WA. 1996. Chang, W. and N. Hasan (1990). Concrete Longevity Overview. Prepared for EG&G Idaho, Inc. DOE/LLW-105. Idaho Falls, ID. September 1990. Chao, T. T. (1984). Use of partial dissolution techniques in geochemical exploration: Journ. Geochemical Explor., 20, p. 101-135. City and County of Denver, Department of Environmental Health, Considerations for the Shattuck Site (Denver Radium Site OU VIII). Prepared for U.S. Environmental Protection Agency, Office of Solid Waste and Emergency Response, August 30, 1999. Clifton, J. R., and L. I. Knab (1989). Service Life of Concrete. Prepared for the U.S. Nuclear Regulatory Commission and the National Institute of Standards and Technology. NUREG/CR-5466; NISTIR 89-4086. Washington, DC. November 1989. Colorado Department of Public Health and Environment 6 CCR 1007-2 Regulations Pertaining to Solid Waste Disposal Sites and Facilities. Colorado Department of Public Health and Environment, 7 CCR 261 Identification and Listing of Hazardous Waste. Colorado Department of Public Health and Environment, Water Quality Control Commission Regulation No. 41, The Basic Standards for Groundwater. Colorado Department of Public Health and Environment, Air Quality Control Commission Regulation No. 8, Control of Hazardous Air Pollutants. Colorado Department of Public Health and Environment, Radiation Services Commission Part 1, General Provisions. Colorado Department of Public Health and Environment, Radiation Services Commission Part 3, Licensing of Radioactive Material. Colorado Department of Public Health and Environment, Radiation Services Commission Part 4, Standards for Protection Against Radiation, General Provisions. Colorado Department of Public Health and Environment, Radiation Services Commission Part 14, Licensing Requirements for Land Disposal of Low Level Radioactive Waste. Colorado Rules and Regulations Pertaining to Radiation Control, Appendix A, Part 18.

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Concrete Laboratory Report No. C-828. Effect of Cement Type on the Resistance of Concrete to Sulfate Attack, U.S. Department of the Interior Bureau of Reclamation, Division of Engineering Laboratories, Denver, CO, November 1958. Concrete Laboratory Report No. C-931. Mortar Bar Expansion Tests for Chemical Reactivity Between Sulfate Bearing Rocks in Aggregate and Portland Cements, U.S. Department of the Interior Bureau of Reclamation, Division of Engineering Laboratories, Denver, CO, February 1960. Concrete Manual, 1975. Concrete Manual. Bureau of Reclamation, Denver, CO. 1975. Daniel, D. E. (1990). Summary review of construction quality control for earthen liners. Waste Containment Systems: Construction, Regulation, and Performance, R. Bonaparte, Ed., ASCE, Reston, VA, p. 175-189. Decision Summary for the Record of Decision - Denver Radium Site, Operable Unit VIII. Denver Radium Site Construction Completion Report, Vols. 1, 2, & 3, The Shattuck Chemical Company, February 8, 1999. DePuy, G. W. Chemical Resistance of Concrete, ASTM STP 169. Dikeou, J. T.. Fly Ash Increases Resistance of Concrete to Sulfate Attack, U.S. Department of the Interior, Division of Research, Denver, CO. Dobras, T. N. and Elzea, J. M. (1993). In-situ soda ash treatment for contaminated geosynthetic clay liners. Geosynthetics ' 93, IFAI, St. Paul, MN, p. 1145-1159. DOE 1999. Retrieval Performance Evaluation Methodology for the AX Tank Farm. DOE/RL-98-72. U.S. Department of Energy. Richland, WA. April 1999. DOE 1996. Tank Waste Remedial System, Hanford Site, Richland, Washington, Final Environmental Impact Statement. DOE/EIS-0189. U.S. Department of Energy. Richland, WA. 1996. Draft Final-Plume Monitoring Plan, Groundwater Monitoring Program; Remedial Design/Remedial Action: Denver Radium Site, Operable Unit VIII (December 5, 1997). Prepared by Harding Lawson Associates, Project No. 389232. Drever, J. I. (1988). The Geochemistry of Natural Waters, 2nd Edition. Prentice-Hall, 437p. Dunstan, 1980. Dunstan, E. R. A Possible Method for Identifying Fly Ashes That Will Improve the Sulfate Resistance of Concretes. American Society for Testing and Materials. Phila. PA. 1980. Dye, W. B., and O'Hara, J. L. (1959). Molybdosis: Nevada Agricultural Experimental Station Bulletin 208, 32 p. Earth Sciences Consultants, Inc. Pilot-Scale Treatability Study. Denver Radium Site Operable Unit VIII. Project No. 886s. July 1993.

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Facsimile letter from Robert H. Oliver, Shattuck Chemical Company, to Rebecca J. Thomas, U.S. Environmental Protection Agency, Region VIII, and Lawrence J. Bruskin, Colorado Department of Public Health and Environment, February 27, 1997. Facsimile letter from Robert H. Oliver to Lawrence J. Bruskin, Colorado Department of Public Health and Environment, November 1,1996. Feasibility Study, 1991. Feasibility Study for Denver Radium Site Operable Unit VIII, Colorado Department of Health, September 1991. Final Closure Plan: Bannock Street RCRA Facilities, Denver, Colorado, May 1984, EPA ID No. COD 007057417. Final Remedial Investigation Report for Denver Radium Site Operable Unit VIII (September 1991). Colorado Department of Health. Final Review of Reports and Information of the Denver Radium Site Operable Unit VIII Hydrogeology and Groundwater Contamination Plume (March 1998). Emerald Environment LLC and Realistic Environmental Solutions. Grim, R. E. (1953). Clay Mineralogy, McGraw- Hill. Groundwater Quality Data for Overland Storage LOG: July 25, 1996. Guide to Durable Concrete, 1992. Guide to Durable Concrete. ACI Manual of Concrete Practices, Part 1. ACI 201.2R-77. American Concrete Institute. Detroit, MI. 1992. Guros, F., Trip Report by Frank Guros, Morrison Knudsen, June 25.1999, Settlement. Hakonson, T. E. (1997). Capping as an Alternative for Landfill Closures-Perspectives and Approaches. Published in Conference Proceedings of Landfill Capping in the Semi-Arid West: Problems, Perspectives, and Solutions. Idaho Falls, ID. Historic American Engineering Report #CO-71. From Robert H. Oliver, Shattuck Chemical Company to Mr. Gregory D. Kendrick, Chief History Branch, Division of National Preservation Programs, National Park Service (RMR-PR), June 16, 1993. Harboe, no date. Harboe, E. Long-Time Studies and Field Experiences with Sulfate Attack. Health Consultation for the Denver Radium Site, ATSDR, April 8, 1999. James, A. N., Fullerton, D., and Drake, R. (1997). Field performance of GCL under ion exchange conditions. Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Reston, VA, Vol. 123, No. 10,897-901. Kaback, D. S., and Runnells, D. D. (1980). Geochemistry of molybdenum in some stream sediments and waters: Geochimica et Cosmochimica Acta, v. 44, p. 447-456.

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Kalousek et. al. Kalousek, G. L. L. C. Porter, and E. J. Benton. Concrete for Long-Time Service in Sulfate Environment. Vol. 2, pp. 79-89. Cement and Concrete Research. Pergamon Press, Inc. 1972. Kalousek et. al. Kalousek, G. L. L. C. Porter, and E. M. Harboe. Past, Present, and Potential Developments of Sulfate-Resisting Concretes, Journal of Testing and Evaluation, Vol. 4, No. 5, American Society for Testing and Materials, Philadelphia, PA, 1976. Khire, M. V., Benson, C. H., and Bosscher, P. J. (1997). Water balance modeling of earthen final covers, Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Reston, VA, Vol. 123, No. 8, 744-754. Kincaid, C. T., J. W. Shade, G. A. Whyatt, M. G. Piepho, K. Rhoads, J. A. Voogd, J. H. Westsik, Jr., M. D. Freshley, K. A. Blanchard, and B. G. Lauzon. (May 1995). Performance Assessment of Grouted Double-Shell Tank Waste Disposal at Hanford. WHC-SD-WM-EE-004, Rev. 1. Westinghouse Hanford Company. Richland, Washington. Klieger and LaMond, 1994. Klieger, P. and J. LaMond, Editors. Significance of Tests and Properties of Concrete and Concrete Making Materials. STP 169C. American Society for Testing and Materials. 1994. Kosmatka and Panarese, 1988. Kosmatka, S. H. and W. C. Panarese. Design and Control of Concrete Mixtures. PCA Engineering Bulletin, 13th ed., Portland Cement Association. Skokie, IL. 1988. Langmuir, D. W., 1996, Aqueous Environmental Geochemistry, Prentice Hall, New Jersey, 589p. Letter from M. Lammering, Environmental Protection Agency Region VIII, to J. Hanley, Environmental Protection Agency Region VIII, dated Nov. 10, 1999 Subject: Review Comments - SC&A's Working Draft Five-Year Review Report, Chapter V. Letter from J. Faught, John Faught & Associates, to T. Fields, US Environmental Protection Agency OSWER, dated October 27, 1999. Subject: Operable Unit VIII Denver Radium Site Comments from Commentors of the Five-Year Review Report. Memo from P. Osborne, US Environmental Protection Agency Region VIII, to J. Hanley et. al.,. U.S. Environmental Protection Agency Region VIII, dated October 19, 1999. Subject: Comments on Five-Year Review Report. Letter from Maureen Dudley of the City and County of Denver Department of Environmental Health, dated October 18, 1999. Subject: Correction of October 12, 1999 Letter. Letter from John D. Faught to Timothy J. Fields, Jr., U.S. Environmental Protection Agency, Office of Solid Waste and Emergency Response, regarding Operable Unit VIII, Denver Radium Site, 5-Year Review Plan, dated October 15, 1999. City and County of Denver Department of Environmental Health, Comments on the Working Draft Five Year Review Report, received October 14, 1999.

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Letter from M.. Lammering and R. Graham, US Environmental Protection Agency Region VIII, to J. Hanley, US Environmental Protection Agency Region VIII, dated October 13, 1999. Subject: Review Comments on the Five-Year Review Report. Letter from Maureen Dudley of the City and County of Denver, Department of Environmental Health, dated October 12, 1999. Subject: Denver Radium Site Operable Unit VIII (S.W. Shattuck Chemical Co.) Impact on the South Platte River. Overland Neighborhood Environmental Watch Five-Year Review Report Comments prepared by L. Goodbee and submitted October 11, 1999. Letter to J. Darabaris, SC&A, Inc., from J. Student, City and County of Denver, Department of Public Health and Environment, dated October 5,1999. Subject: Denver Radium Site Operable Unit VIII (S. W. Shattuck Chemical Co.) - Denver's Soil and Groundwater Investigation of Mexico Avenue. Letter to J. Student, City and County of Denver, Department of Environmental Health, from P. Osborne, US Environmental Protection Agency Region VIII, dated September 27, 1999. Subject: Review of the Subsurface Investigation of Mexico Avenue from Acoma Street to Bannock Street from the City and County of Denver - May 25, 1999. Letter from Theresa M. Donahue, Manager, Denver Department of Environmental Health, to Timothy Fields, Assistant Administrator, U.S. Environmental Protection Agency, Office of Solid Waste and Emergency Response, regarding successful resolution of the remedy at the Shattuck Chemical Company Site, dated August 31, 1999. Letter from James Hanley, U.S. Environmental Protection Agency Region VIII, to Tim Fields, U.S. Environmental Protection Agency Headquarters, Office of Solid Waste and Emergency Response: Response to stakeholders' comments on independent reviews, July 7, 1999. Letter from Shattuck Chemical to Jim Hanley, U.S. Environmental Protection Agency: Uses of recommendations, July 6, 1999. Letter from Daniel Chafin/James Otton, U.S. Geological Survey, to James Hanley, U.S. Environmental Protection Agency: U.S.G.S. Site Characterization Recommendations, May 24, 1999. Letter from Theresa Donahue, City of Denver Department of Environmental Air to Tom Sheckles, U.S. Environmental Protection Agency: Concerns with remedy, April 30, 1999. Letter from James Hanley, U.S. Environmental Protection Agency, to Earl Cassidy, U.S. Geological Survey: U.S.G.S. Site Characterization Recommendations, April 16, 1999. Letter from David Chafin, James Otton, U.S. Geological Survey, to James Hanley, U.S. Environmental Protection Agency: U S.G.S. Site Characterization Recommendations, March 24, 1999.

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Letter from Robert H. Oliver, Shattuck Chemical Company, to James Hanley, U.S. Environmental Protection Agency Region VIII: Bioremediation System, October 26, 1998. Letter from Larry Bruskin, Colorado Department of Public Health and Environment, to Karen Hancock, Emerald Environmental, LLC: Oily soils, October 26, 1998. Letter from Robert T. Jelinek, Engineering Management Support, Inc., to Robert H. Oliver, c/o John D. Faught & Associates: Proposed bioremediation system, August 10, 1998. Letter from Patrick B. Brown, Quanterra, to Paul Rosasco, Engineering Management Support, Inc.: Transmitting results of May 26, 1998 sampling, June 22, 1998. Letter to D. Vodehnal, U.S. Environmental Protection Agency Region VIII and H. Roitman, Colorado Department of Public Health and Environment, from S. Fonte of the City and County of Denver, Department of Environmental Health. Dated May 29, 1998. Subject: Denver Radium Site, Operable Unit VIII, Storm Sewer Remedy. Letter from J. Kahrnak, Environmental Protection Agency-ORIA to Frank Cardile, Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission. Subject: Review Comments on the Radiological Criteria for License Termination: Uranium Recovery Facilities (Federal Register Vol. 62. No. 139), November 28, 1997. Letter from Robert H. Oliver, Shattuck Chemical Company, to Rebecca J. Thomas, U.S. Environmental Protection Agency, Region VIII, and Lawrence J. Bruskin, Colorado Department of Public Health and Environment: Stop work order, January 31, 1997. Letter from Robert H. Oliver, Shattuck Chemical Company, to Rebecca J. Thomas, U.S. Environmental Protection Agency, Region VIII, and Lawrence J. Bruskin, Colorado Department of Public Health and Environment: Stop work order, January 28, 1997. Letter from Harry Roof, Western Ash Company, to Clay Abbott, Colorado/Wyoming Railroad: Transmitting test results from Accu-Lars, Research, Inc. on the fly ash, January 26, 1994. Letter from Keith E. Wier, Ryan-Murphy Incorporated, to Shawn Sullivan, Assistant City Attorney of Denver: Vitrification/treatability study, November 1995. Letters from Lawrence Bruskin, Colorado Department of Public Health and Environment, to Rebecca Thomas, U.S. Environmental Protection Agency, Region VIII: December 7, 1992; Material placement and cover issues, May 7, 1997; Comments on revised cover design, July 9, 1997. Letters from Robert H. Oliver, Shattuck Chemical Company, to Rebecca J. Thomas, U.S. Environmental Protection Agency, Region VIII: Phase II - Final remedial design cover system comments, August 19, 1996; Response to comments, Phase II - Final remedial design, December 18, 1996; Monolith cover system design, March 19, 1997; Final cover design revisions, June 18, 1997; Soil screening, July 25, 1997; Revised cover design comments, August 18, 1997; Modification of clay specification, September 15, 1997; Clay specification modifications, October 13, 1997; Revised cover

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design, October 22, 1997; CAP material analysis, October 23, 1997; Modification in lift placement in rows 23 and 24, November 5, 1997; RIPRAP materials, (Dr. T. P. Pasteur's petrographic exam), November 18, 1997; Revised clay layer and liner specifications, December 5, 1997; Slope stability analysis, February 5, 1998; Oil-impacted soils - bioremediation proposal, March 10, 1998; Procedure for performing gamma and radon surveys, March 22, 1998; RIP/RAP, March 27, 1998; Air monitoring data, April 24 1998; Lab report, oily soils, April 30, 1998; Soil borings, June 24,1998. Letters from Rebecca J. Thomas, U.S. Environmental Protection Agency, Region VIII, to Robert H. Oliver, Shattuck Chemical Company: Radon background determination cover system demonstration, May 20, 1993; Phase II - Remedial Action, January 29, 1997; National placement and cover design, May 8, 1997; Oil contaminated soils, May 11, 1997; Cover specification modifications, June 24, 1997; Cover design, July 11, 1997; Cover design, October 3, 1997. Letters from Larry Bruskin, Colorado Department of Public Health and Environment, to Robert H. Oliver, Shattuck Chemical Company: Oil impacted soils, March 25, 1997; Proposed spec. change for placement RSCL, August 8, 1997; Strength tests on borrow source material, September 4, 1997; Bioremediation proposal, March 16, 1998; Comments on bioremediation system, August 20, 1998. Letter from Robert H. Oliver, Shattuck Chemical Company, to Lawrence J. Bruskin, Colorado Department of Public Health and Environment: Oil impacted soil, November 1, 1996; Oil impacted soil, April 4, 1997; Oil impacted soil, May 29, 1997; Monolith topslope reconfiguration, August 15, 1997. Letter from Karen J. Hancock, Emerald Environmental, LLC, to Larry Bruskin, Colorado Department of Public Health and Environment: Oil impacted soils, October 2, 1998, May 3, 1998. Letter from Larry Bruskin, Colorado Department of Public Health and Environment, to Karen Hancock, Emerald Environmental, LLC: Oil impacted soil, April 8, 1998. MacKinnon, R. J., T. M. Sullivan, S. A. Simonson, and C. J. Suen (August 1995). "BLT-EC (Breach, Leach, Transport, and Equilibrium Chemistry), a Finite-Element Model for Addressing the Release of Radionuclides From Low-Level Waste Disposal Units," U.S. Nuclear Regulatory Commission, NUREG/CR-6305. Massazza, F. (1998). Pozzolana and Pozzolanic Cements: Chapter 10 in Hewlett, P.C. (ed.), Lea's Chemistry of Cement and Concrete, John Wiley and Sons, New York, 1053p. Material Safety Data Sheets for the flyash used in the Monolith (May 29, 1996). Memorandum from John D. Faught to the Shattuck Dialogue Members regarding Denver August 16, 1999 Rebuttal Comments, dated August 31, 1999. Memorandum from Frank Guros, Morrison Knudsen Corporation, to Susan Ford: Ability of Claymax Zoor to tolerate differential settlement, June 28, 1999. Memorandum from Susan Ford, Morrison Knudsen Corporation, to Rebecca Thomas, U.S. Environmental Protection Agency, Region VIII: Bi-weekly reports, May 15, 1998.

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Memorandum from Susan Ford, Morrison Knudsen Corporation, to Rebecca Thomas, U.S. Environmental Protection Agency, Region VIII, August 12, 1998. Memorandum from Edward R. Bates, U.S. Environmental Protection Agency, National Risk Management Research Laboratory, to Rebecca Thomas: meeting and site visit notes regarding final stages of soil treatment (solidification/stabilization), October 9, 1997. Memorandum from Darcy Campbell, Hydrogeologist, U.S. Environmental Protection Agency, to Rebecca Thomas, Remedial Project Manager, Denver Radium Site, dated May 27, 1992. Monolith Monitoring Plan (April 16, 1998). Prepared by Harding Lawson. Moore D. M. and Reynolds, R. C. Jr. (1997). X-ray diffraction and the identification and analysis of clay minerals, second edition, Oxford University Press, 378p. Morrison Knudsen Summary Report - Construction Activities, Bi-weekly reports from April 28, 1997 to May 9, 1997. Morrison Knudsen, Transmittal to J. Hanley U.S. Environmental Protection Agency, January 1999 Data Report. Oak Ridge National Laboratory (December 1995). Effects of Ionizing Radiation on Terrestrial Plants and Animals: A Workshop Report, ORNL/TM 13141. Oil Impacted Soils Correspondence (1996). Several documents dealing with specific technical issues. Operable Unit VIII, Denver Radium Site; Photos of Monolith Construction Activities - July 1999. OSWER Memorandum No. 9200.4-23 Clarification of the Role of Applicable, or Relevant and Appropriate Requirements in Establishing Preliminary Remediation Goals under CERCLA. OSWER Memorandum No. 9200.4-18 Establishment of Cleanup Levels for CERCLA Sites with Radioactive Contamination. Phase II Final Remedial Design, S.W. Shattuck Chemical Company, Project No. 886S, June 6, 1996. Pilot-Scale Treatability Study, Denver Radium Site Operable Unit VIII (July 1993), Appendix D, Volumes 2, 3, 4, & 5. Prepared by Earth Sciences Consultants, Inc., Project No. 886S. Pilot-Scale Treatability Study for The Denver Radium Operable Unit VIII-Operations Plan (December 1992). Prepared by Earth Sciences Consultants, Inc. Plume Monitoring Plan, Groundwater Monitoring Program, Remedial Design/Storage LOG: RS 217, April 16, 1993.

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Remedial Design, Final Design Correspondence (1988). Several documents dealing with specific technical issues. Remedial Design, 90% Design Correspondence - Several documents dealing with specific technical issues, 1988 - open-ended. Response to Comments, Phase II, Final Design, Cover System, December 18, 1996. Response to Comments, Phase II, Final Design, Cover System, November 1, 1996. Response to Draft Comments, Prefmal Remedial Design Reports, Denver Radium Site, Operable Unit VIII, S. W. Shattuck Chemical Company, March 1996. RI Report for the Denver Radium Site OU VIII, CDH, September 1991. RIRAP Source Material, March 27, 1998. Risk Assessment Guidance for Superfund 1989 and Additional Technical Directives. Runnells, D. D. (1969). Diagenesis, chemical sediments, and the mixing of natural waters: J. Sed. Petrol., v. 39, p. 1188-1202. Shan, H.-Y. and Daniel, D. E. (1991). Results of laboratory tests on geotextile/bentonite material. Geosynthetics ' 91, IFAI, St. Paul, MN, p. 517-535. U.S. Department of Energy (April 1999). Retrieval Performance Evaluation Methodology for the AX Tank Farm. DOE/RL-98-72. Richland, WA. U.S. Department of Energy (1996). Tank Waste Remedial System, Hanford Site, Richland Washington, Final Environmental Impact Statement. DOE/EIS-0189. Richland, WA. U.S. Environmental Protection Agency (January 1993). Selecting Exposure Routes and Contaminants of Concern by Risk-Based Screen, EPA/903/R-93-001. U.S. Environmental Protection Agency (1999). Understanding Variation in Partition Coefficient, Kd, Values, Vol. 1 & 2, EPA 402-R-99-004A&B. U.S. Environmental Protection Agency (April 1999). Directive 9200.4 (17p.), Use of Monitored Natural Attenuation at Superfund, RCRA Corrective Action, and Underground Storage Tank Sites. U.S. Environmental Protection Agency (March 1999). Draft Comprehensive Five-Year Review Guidance, OSWER Directive 9355.7-03B-P. PB99-963214. U.S. Environmental Protection Agency, 40 CFR Part 192, Groundwater Standards for Remedial Actions at Inactive Uranium Processing Sites; Final Rule, p. 2854.

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U.S. Environmental Protection Agency, Office of Ground-Water Protection, Office of Water, Guidelines For Ground-Water Classification Under The EPA Ground-Water Protection Strategy, Final Draft, November 1986. U.S. Environmental Protection Agency, Office of Radiation and Indoor Air (January 1998). Federal Guidance Report No. 13, Part I-Interim Version, Health Risks from Low-Level Environmental Exposure to Radionuclides, EPA 402-R-97-014. U.S. Environmental Protection Agency, Office of Radiation and Indoor Air (July 22,1996.), Reassessment of Radium and Thorium Soil Concentrations and Annual Dose Rates. U.S. Environmental Protection Agency (January 1998). Peer Review Handbook; prepared by Peer Review Advisory Group/U.S. Environmental Protection Agency's Science Policy Council, EPA100-B-98-001. U.S. Environmental Protection Agency Region VIII, Superfund Records Center, Site Information Document Control Systems, Denver Radium Site Index. U.S. Environmental Protection Agency Region III, Risk-Based Concentration Table. U.S. Nuclear Regulatory Commission (1992). Regulatory Guide 8.36, Radiation Dose to the Embryo/Fetus, July 1992. U.S. Nuclear Regulatory Commission. Various studies dealing with long-term design objectives for concrete. Various Treatability Reports Correspondence - 1992 to 1994. von Fay, Kurt F., and James S. Pierce; Sulfate Resistance of Concretes with Various Fly Ashes, Research and Laboratory Services Division, Bureau of Reclamation, Denver, CO. Wolery TJ. (1983). EQ3NR. A computer program for geochemical aqueous speciation-solubility calculations: User's guide and documentation. Lawrence Livermore National Laboratory Report, UCRL-53414, 189 pp. Wolery TJ. and Daveler S. A. (1992). EQ6, a computer program for reaction path modeling of aqueous geochemical systems: theoretical manual, user's guide, and related documentation. Lawrence Livermore National Laboratory Report, UCRL-MA-110662 PT IV, 338 pp.

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APPENDIX B

SCOPING ANALYSIS REPORT ON SITE RISKS

Appendix B

SCOPING ANALYSIS REPORT ON SITE RISKS

Submitted by:

SC&A, Inc. 1625 17th Street, Suite 323

Denver, CO 80202

Submitted to:

Mr. Clint Burklin Eastern Research Group

P.O. Box 2010 1600 Perimeter Park Drive

Morrisville, NC 27560-2010

In response to:

EPA Contract Number 68-D7-0001

November 11, 1999

Introduction The Shattuck Site is one of the 65 Denver area properties where operating businesses required different levels of cleanup, such as excavation and removal of contaminated soil to a permanent disposal site; removal of floors to excavate underlying wastes, followed by replacement of floors; or installation of ventilation systems to vent high levels of radon. Cleanup actions at Shattuck included on-site stabilization by cement/flyash solidification followed by capping with a low-permeability composite clay barrier. About 70,000 yards of contaminated soils have been treated and placed on site. This report was prepared on an independent basis by SC&A, Inc. (SC&A), under subcontract to ERG to support a five-year review process. The purpose of the five-year review is to determine whether the remedy at a site is protective of human health and the environment. The purpose of this report is to support the response to one of the main questions to be answered in the five-year report, "Has any risk information changed since the remedy was selected?" The approach was to review any new risk-based site information since the 1991 Risk Assessment was conducted. This included a review of monitoring and other information documented since that period. A number of key contaminants and risk factors were then selected for study. The study included a review of changes in maximum contaminant levels, revised protectiveness standards in health-based and chemical-specific ARARs, and any new toxicological information about the contaminants selected. The new information and data were then compared with the earlier information/data to assess the change in hazard potential at the site. The comparison was made by using tables similar to the standard table formats presented in "Risk Assessment Guidance for Superfund: Volume I, Human Health Evaluation Manual (Part D), January 1998." Review of 1991 Risk Assessment As part of the Remedial Investigation and Feasibility Study for Shattuck, a baseline risk assessment was conducted in 1991. The study determined that the site contained mixed waste, including radiation, metals, and volatile organic compounds. Risk scenarios were established for an on-site worker, on-site resident, on-site trespasser, off-site worker, and off-site resident. Monitoring data for soil, groundwater, and air were evaluated to determine the contaminants of greatest concern. Chemicals were selected based on their quantity and prevalence at the site, intrinsic toxicological properties, and physical and chemical properties. Eleven metals, four volatile organic compounds, three semi-volatile organic compounds, and six isotopes were identified as contaminants of concern. Several migration pathways for contaminant releases were reviewed including groundwater, surface water, soil, and air. The air and soil pathways were determined to have the most potential for contaminant migration. The groundwater and surface water pathways were thought to be of less concern because of the lack of receptors. A toxicity assessment was then conducted which estimated the relationship between the extent of exposure to a contaminant and the increased likelihood and/or severity of adverse effects on exposed individuals. Risk characterization identified four receptor groups, including current on-site workers, future on-site residents, trespassing children, and current off-site residents. The risks for each receptor group were determined.

1

An evaluation of nonradioactive chemicals revealed that, in this group, molybdenum presented the greatest noncarcinogenic hazard, while arsenic and volatile organic compounds presented the greatest cancer risks. The most important source of risk identified in the risk assessment was the radiologic group of compounds. The greatest risk from the site was whole body gamma exposure. Radon was another important source of on-site radiological risk, but the off-site radon concentrations were determined to be compatible with background radon values. Uncertainties in the risk assessment included measurement error, random variability, sampling error, the use of professional judgment, modeling uncertainties, and uncertainties in background concentrations. The 1991 baseline risk assessment for the Shattuck site is detailed and meets the EPA guidelines that were in place at the time the risk assessment was conducted. There are now newer guidelines for Exposure Assessment (1992), Carcinogenic Risk (1996), Reproductive Toxicity Risk (1996), and Ecological Risk (1998). The newer guidelines do not change the overall approach of the risk assessment process but are a continuation of the EPA's risk development process initiated in the early 1980s. The newer guidelines give increased emphasis to exposure characterization and provide better guidance for assessing ecological exposure to chemicals and human exposure to radiological agents. These two areas are important when evaluating the 1991 risk assessment and assessing the current situation at the site. The guidelines do not address future risk which is a concern at the Shattuck site and the surrounding area since hazardous contaminants have been left in place and complete remediation of groundwater may not occur for decades in the future. Current Risk Assessment Needs There is no information in the documents reviewed that definitively establishes any current off-site risks to human health. However, contaminants are still present in soil and groundwater and, if not controlled, they may cause harm to humans, the environment, and ecological organisms. Overall, the monolith appears able to protect human health from surface exposure paths for an extended period of time. The on-site exposure risks from surface and shallow organic, inorganic, and radioactive contamination have been effectively removed. Workers and residents in the vicinity have been protected from a radiation hazard; however, additional data are needed to assess whether vicinity workers and residents have been adequately protected from remaining soils, surface water, including the Platte River, and groundwater exposure. Because the extent of groundwater contamination and the movement of the contaminant plume was inadequately determined, the effectiveness of the remedy in protecting human health and environmental quality cannot be assessed for the groundwater contamination exposure path. Likewise, analyses of soil metals were perfunctory and sparse. Thus, although removal of radioactive materials was apparently done properly and adequately, data are insufficient to assess whether or not all the soil contaminated with metals was removed, or whether metals loading into the aquifer materials occurred.

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A current risk assessment would be appropriate given the length of the design life of the remedy (200 to 1,000 years). The potential for recreational use near groundwater discharge points along the Platte River, potential future groundwater use, and the future use of surface water from the downgradient pond are additional reasons for updating the assessment. A review was undertaken to see if monitoring data and other information that became available after the 1991 risk assessment would permit an estimate of current radiological risk. Additional information might reduce some of the uncertainties documented in the 1991 baseline risk assessment. Finally, any information would be used in assessing proposed remediation scenarios. However, the new data were insufficient for a credible assessment. Information needs include a better definition of the aquifer, expansion of monitoring data, collecting additional ecological data, reviewing appropriate conceptual models, calculating contaminant concentrations in groundwater, and calculating risk. Any future risk assessment should include the following:

• An ecological risk assessment • A residential groundwater user scenario • A recreational surface water user scenario • A scenario involving a release from the monolith under conditions that could include

fracturing and degradation of the cap Current State of Risk Assessment Data Support After review, it was concluded that there are too few samples of media taken since remediation to conduct an acceptable risk assessment of the current situation. Quarterly groundwater sampling events are the major source of new data. The 1991 baseline risk assessment concluded that the groundwater was a major source of risk, and the ROD concluded that natural flushing was the choice for mediation of the aquifer. As such, there is a need for current onsite and offsite data before a credible risk assessment on the present situation can be conducted. A groundwater sampling program has been recently established and an expansion is under review. There are no hard and fast guidelines for determining the appropriate number of samples, but greater precision is necessary before a meaningful risk assessment can be conducted. More precision can be achieved by taking more samples. The appropriate number of samples to be employed in characterizing the Shattuck site is the least number of samples required to generate a sufficiently precise estimate of the true means of the concentration of the contaminants at the site and/or the minimal number of samples needed to demonstrate that the upper limit of the confidence interval for the mean for the contaminant of concern is less than the applicable regulatory threshold. The analytical data summarized in the 1991 risk assessment indicated noncarcinogenic toxic effects with several contaminants exceeding current ARAR levels. Calculations for nonradioactive groundwater contaminants indicated that arsenic is the carcinogen of highest concern, with a lifetime risk of 2.7 x 10E-4, while the contaminants molybdenum and antimony are the greatest noncarcinogenic concerns, with hazard indices of 160 and 5, respectively. However, the derivation of the list of toxic metals in the Baseline Risk Assessment eliminated copper, cadmium, rhenium, and silver. Given that maximum soil copper concentrations are almost 300 times above background and average copper concentrations are 100 times above background, it is not clear why copper was eliminated from the risk assessment. It is also unclear why molybdenum was eliminated as a metal of

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concern given the plant's history of processing molybdenum ore. A current risk assessment should reevaluate these compounds as chemicals of concern. Data were inadequate to demonstrate whether metals and organic compounds are originating from the site. For example, it has been indicated that many of the semi-volatiles do not originate from Shattuck, but this cannot be confirmed. Likewise, verbal and written reports that the copper and chromium in groundwater originate from other off-site industrial activities cannot be confirmed from the current data set. Regardless, the contaminants are present and further effort is warranted to determine if they are chemicals of concern. If a definite origin cannot be determined, then the compounds should be included in a current assessment. The Construction Completion Report shows that soil quality was monitored by gamma radiation, with samples taken to confirm that Ra-226 was below 15 pCi/g. However, no additional monitoring of the soil for metals contamination was performed. These data should be obtained to determine both the original extent of contamination by nonradioactive metals, as well as the post-remediation distribution of metals. General chemistry data are also needed for a current assessment since metals and groundwater are involved. Each metal has a unique adsorption curve and pH space; for example, at pH 6, 100% of lead and copper are adsorbed, whereas 50% cadmium, 30% zinc, and <10% Ni are adsorbed. In the case of the Shattuck site, where many different metals may be present in the groundwater, this type of analysis is essential in order to predict the movement of the various constituents of the contaminant plume. This particular example illustrates clearly that different contaminants will be attenuated at different rates and levels. Furthermore, some remedial actions, including bioremediation of organic compounds, may reduce groundwater pH and thus mobilize previously adsorbed metals. Of foremost importance is the implementation of an adequate groundwater monitoring program. An implicit argument in the Remedial Investigation is that monitoring does not have to be particularly intensive because contaminant concentrations are very low once the plume is diluted within the alluvial aquifer and the river. This assertion is difficult to support without a properly designed monitoring program since the actual concentrations in the alluvial aquifer remain unknown. Downgradient concentrations currently being observed may be on the plume fringes rather than on the centerline. As previously noted, although groundwater exposure apparently does not appear to present a danger today, there are no institutional controls in place to prevent off-site groundwater access in the future. The present contaminant transport model depends on two fundamental sets of data: hydrogeology and water-aquifer chemical reaction (chemistry of attenuation). In the case of the Shattuck site, neither the hydrogeology nor the nature of the chemical reactions within the aquifer have been completely characterized. Thus, the contaminant transport model is vastly oversimplified and, as such, is a poor foundation from which to eliminate the groundwater exposure path from the risk assessment. The groundwater exposure path should not be eliminated based on current information about the contaminant plume. The Remedial Investigation presents a very simplistic approach to predicting the amount of dilution in groundwater downgradient from the monolith.

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The analysis in the Remedial Investigation of the large dilution rates attributed to the South Platte River needs to be reevaluated. Metals do not always stay in solution and can precipitate as stream sediment. The surface water was also poorly characterized. Only one surface water sample from a runoff catchment basin was analyzed. For this sample, only gamma activity, indicating Ra-226, and/or elevated U-nat. was determined, and other constituents such as metals and organic compounds were not determined. Thus, the characterization of the surface water quality was incomplete. Exposure risk from surface water cannot be eliminated if the data base for assessing the water quality is so small. A numerical model of the groundwater flow system should be constructed in order to obtain more reliable estimates of dilution and groundwater flow rates and directions. Off-site characterization of groundwater and surface water should be determined prior to a new risk assessment. The background levels for contaminants should be reviewed. The baseline risk assessment states that 11 metals were selected as inorganic chemicals of potential concern because of elevated levels on the site (i.e., above background levels obtained from the nearby golf course). The use of the golf course as a credible source of background levels should be evaluated because of the possibility that dusts and contaminated water originating from the Shattuck site may have deposited contaminants on the golf course soil. Also, the presence of dissolved uranium (in some cases, over the ARARs) and other contaminants in monitoring wells USE 1 through 5 casts doubt on their value as background wells. The high uranium concentrations in the upgradient wells suggest that true background has not been established. Furthermore, at least two mechanisms exist that could lead to a reversal in groundwater gradients and could place the existing background wells directly downgradient from the source. First, a future recharge through the monolith could create a groundwater mound, in which case, flow from the monolith would be in a radial direction. Second, a rise in the water table could intersect the monolith which would, in turn, act as a hydraulic barrier and potentially reverse the groundwater gradients. Clearly, additional data are needed. The question is how to best balance the data needs against the overall objectives and the practicality of performing long-term monitoring of numerous wells. The objective is to establish a reasonable maximum exposure that an individual may experience. When determining background levels when human health is the concern, the lower confidence level of the mean should be used since this would tend to maximize the risk and assure that human health and/or environmental organisms are not exposed to polluted areas. When applying this conservatism to background issues, the concern appears to be that an area may occasionally be designated as polluted when it is not. The concern for human health must override any concern that a high background sample may be mistakenly identified. A minor concern with the 1991 risk assessment was its selection of which contaminants detected at the site should be included in the risk assessment process. Appendix A of the risk assessment report, which contains tables illustrating the factors in the selection process, contains apparent errors that

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increase the background levels of most of the contaminants. The footnote to the tables implies that when the contaminants were not detected, their reported values were set at one-half the sample quantitation limit (SQL). However, in the majority of these cases, the value was set at the SQL. In Table A-3, several reported values for site samples are below the SQLs, and the setting of background values for copper, iron, arsenic, and vanadium, which were analyzed for but not detected, appears to have no relationship to their SQLs even though the footnote to the table states that they do. All the background values are listed as analyzed for but not detected in Table A-4, Volatile Organic Sampled in Soils; Table A-5, Volatile Organic Sampled in Groundwater; Table A-6, Semi-Volatile Organic Chemicals Sampled in Soil; and Table A-7, Semi-Volatile Organic Chemicals Sampled in Groundwater. The associated background numerical value should have been one-half the sample quantitation limit, but in most cases, the SQL is used. In other words, the SQL is used as the surrogate for background for many of the contaminants that do not exist in the background. In other cases, values for contaminants are reported that are below the SQL. For example, Din-butylphthalate has a background value stated at one-half SQL but is listed at 850, the SQL is 165, and the average and maximum value given for site samples is 59, which is below the SQL. The Risk Assessment Guidance for Superfund (RAGS) encourages the use of the SQL for setting values for nondetected chemicals at a site where there is reason to believe that the chemical is present. In this way, the risks that would be posed if the chemical is present at the SQL can be compared with risks posed by other chemicals at the site. This approach is used in order to be conservative in the estimation of risk. But setting all background values at their SQL for non-detects is not conservative where risk is concerned, as many contaminants may be eliminated as concerns, or, at least, have their site contaminant values diminished by artificially high background values. The approach also assumes there is a background for every chemical at every point in the country. This approach should be reconsidered in a current assessment of background for the Shattuck area. Exposure Assessment RAGS, in characterizing exposure, discusses three basic land use categories: residential commercial/ industrial and recreational. Based on activities in an area, RAGS also allows for more than a single land use. This is a judgment issue. In determining future land use, RAGS states, "Because residential land use is most often associated with the greatest exposures, it is generally the most conservative choice to make when deciding what type of alternate land use may occur in the future." It further states, "Assume future residential land use if it seems possible based on the evaluation of the available information. For example, if the site is currently industrial but is located near residential areas in an urban area, future residential land use may be a reasonable possibility." The National Contingency Plan (40 CFR 300) establishes that cleanups of radionuclides are governed by the risk range for carcinogens at levels in the 10E-4 to 10E-6 range. The limits of this range are generally used as a guidance to determine preliminary cleanup goals (PRGs) between commercial and residential/recreational sites. The EPA does not consider these discrete lines at 1 x 10E-4 or 1 x 10E-6. Review of the Shattuck documents reveals that the PRG was set for achieving a risk of 1 x 10E-4 (industrial). A current risk assessment of the Shattuck site should evaluate whether a more conservative goal is needed for the following reasons:

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1. The site area presently includes recreational and residential activities. 2. Trying to predict the future of land use over the next 200 years for Shattuck and the

surrounding area is difficult. However, there is justification for believing that Denver will continue to grow and will have multiples of its present population in 200 years.

3. The contaminants include long half-life radioactive contaminants (up to 10E10 years

for U-238) which guarantees that they will retain much of their activity throughout the 200-year period and beyond.

4. The Shattuck site is unique because it is the only radiation waste repository set in a

major metropolitan area in the United States.

5. Security at present does not go beyond the site boundaries, and the EPA has gone on record (FR 1/11/95) as limiting credible maintenance of the site to 100 years.

6. Actions at Superfund sites should be based on estimates in the high end of the

intake/dose distribution.

RAGS defines the reasonable maximum exposure (RME) expected to occur under both current and future land-use conditions. The RME is defined as the highest exposure that is reasonably expected to occur for an exposure pathway at a site. It is intended to account for both uncertainty in the contaminant concentration and variability in the exposure parameters. In this way, the use of the maximum values is defensible. It is also reasonable to assume that the values used are below the upper confidence limits of the mean sample values. Pathways The uncertainties section of the 1991 Risk Assessment does not sufficiently address minor pathways related to the groundwater and surface water. Although the ingestion pathway is the major pathway of concern with the groundwater, future uses of the groundwater are unacceptable as long as drinking it is prohibited. Based on current data, any future use of groundwater has to be viewed as unacceptable at this time. For example, use of groundwater for irrigation would offer a pathway for radiological and other contaminants to reach plants and animals and other ecological organisms as well as to enter the food chain for humans. Such use would deposit the contaminants in soil and present a pathway for additional human exposure through the inhalation (dust) and ingestion pathways. Consideration should also be given to conditions that result in volatilising some contaminants if the groundwater is sprayed to water lawns, used in fountains, etc. The Remediation Investigation did not sufficiently consider either the potential future groundwater or surface water pathways. The rationale for dismissing the surface water as a pathway was that groundwater contaminants were not expected to contribute significantly to surface water contaminant levels. The ecological pathway was dismissed due to algal growth and a noticeable surface sheen on the retention pond. The investigation concluded that exposures to either human or ecological receptors

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were unlikely. The groundwater pathway was dismissed based on the rationale that there were no current downgradient users. However, the 1991 risk assessment states, "Contact with the water in the retention pond could adversely impact either human or ecological receptors." These potential future pathways could be viable given the uncertainty in (1) future land use and (2) the long-term performance of the remedy. It is unclear why ruling out the retention pond made an ecological assessment unnecessary. The retention pond may be recharged by the groundwater which may result in a potential risk to humans when that groundwater reaches the surface. However, little if any consideration was given to this pathway. Due to recreational and residential activities in the area, the possible recharge of surface water, and the closeness of the Platte River, a more comprehensive ecological evaluation should be part of any future risk assessment. Effects manifest themselves differently in different ecosystems, depending on the magnitude of the disturbance and the nature of habitat receiving the disturbance. The 1991 assessment did not consider these factors. The 1991 risk assessment did evaluate the level of risk for the underlying aquifer and found the aquifer unacceptable as drinking water. Of the radioactive contaminants, uranium was the most significant contributor, with a calculated lifetime risk of 6.7 x 10E-3 based on drinking two liters of water per day for 30 years. As stated above, this is a cause for concern since uranium has a long half-life (U-234= 240,000 years, U-238= 4,400,000,000 years) and would not decay significantly in the proposed 200-year time period. The 1991 risk assessment also evaluated the ingestion of garden vegetables grown in contaminated soil on a residential property in the vicinity. This resulted in a calculated risk of 6 x 10E-6 for a one-year consumption of home-grown vegetables and 1.9 x 10E-4 for thirty years of consumption. However, as discussed above, this pathway is of concern for contaminated soil and if the aquifer or area surface water is used for irrigation without further study. An Oak Ridge Laboratory workshop on ecological risk concluded that protection of humans generally means protection of plants and animals except where human access is restricted for protection, where unique exposure pathways exist, and/or where endangered species are present. At least two of these conditions exist at the present site. This workshop also recommended a 0.1 rad/day limit for animals and plants. It is necessary in defining the scope and design of an ecological assessment at the Shattuck site to determine the full spatial extent of the contamination through sampling and measurement. The sampling plan should be designed broadly enough to find the "edge of the plume," the farthest extent of the contamination in soils or other environmental media. Off-site information needs to be better defined for the area surrounding the Shattuck site. Attention should be paid to the "daughter contaminants" that will increase in the environment as parent radionuclides diminish. The future persistent and continued release of radionuclides to potentially exposed organisms should be estimated. Studies should be considered that would assess long-term population effects, not only because of the increase in concentration of the "daughter" radionuclides but also because of the potential bioaccumulation potential of these compounds.

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Before conducting another risk assessment of the Shattuck area and determining the actual or potential effects of the contaminants on wildlife species, habitats, or special environments, it will be necessary to study or research the species and habitats in the area. An ecological risk assessment should help define the extent of the contamination. The risk assessment should also determine if there are significant effects other than toxicity. The extent of delineation of exposed habitats should be determined by the potential for exposure of concern, not by arbitrary distances or boundaries that lack biological justification. Habitats in the vicinity of Shattuck including the pond and the Platte River should be selected based on:

• Direct or indirect exposure to the site's contaminants due to transport from the source Before conducting another risk assessment of the Shattuck area and determinating the actual or potential effects of the contaminants on wildlife species, habitats, or special environments, it will be necessary to study or research the species and habitats in the area. An ecological risk assessment should help define the extent of the contamination. The risk assessment should also determine if there are significant effects other than toxicity. The extent of delineation of exposed habitats should be determined by the potential for exposure of concern, not by arbitrary distances or boundaries that lack biological justification. Habitats in the vicinity of Shattuck including the pond and the Platte River should be selected based on:

• Direct or indirect exposure to the site's contaminants due to transport from the source • Physical disruption of the habitat due to the site's design or operation, or chemical

disruption of ecosystem processes due to the contaminants' interference with natural biochemical, physiological, and behavioral processes

Stream sediment from the South Platte River should be sampled. The potential effects of bioaccumulation of metals in plant and animal tissue need to be investigated as part of an Ecological and Human Food Chain Risk Assessment. Because radionuclide contamination is present in the soil, the food chain should be investigated by collecting a few earthworms or small rodents and measuring for radionuclides and other contaminants. Therefore, a current supplemental risk assessment that includes both groundwater and surface water receptor scenarios should be conducted. However, this risk assessment should await data that address the issues raised by the expert panel. Current Risk The EPA has generally assumed that cleanups to ARARS are satisfactory because the residual risk will be in the 10E-4 to 10E-6 range. However, the EPA has clarified that cleanups of radionuclides are governed by this risk range established in the NCP for all carcinogens when ARARs are not available or are not sufficiently protective. The EPA includes all radiologic components as carcinogens. That is, cleanup should generally achieve a level of risk within the 10E-4 to 10E-6 range based on the reasonable maximum exposure for an individual. A specific risk estimate around 10E-4

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may be considered acceptable if justified by on site-specific conditions. However, for the reasons stated above, the 1 x 10E-4 risk level does not seem justified for the Shattuck area. The EPA has a consistent methodology for assessing cancer risks and determining PRGs at CERCLA sites no matter the type of contamination. Cancer risks for radionuclides are evaluated by using the slope factor approach identified in EPA's methodology. Slope factors were developed by the EPA for radionuclides in the Health Effects Assessment Summary Tables (HEAST). Cleanup levels for radioactive contamination at CERCLA sites should be established as they would for any chemical that poses an unacceptable risk, and the risks are to be characterized in standard EPA risk language consistent with CERCLA Guidance. Cancer risk from both radiological and nonradiological contaminants are to be summed to provide risk estimates for persons exposed to both types of carcinogenic contaminants. The 1991 risk assessment information did not address future risk which is a concern at the Shattuck site and surrounding area since hazardous contaminants have been left in place and complete remediation of groundwater may not occur for decades in the future. The Panel's main concern is the long-term risk potential of the groundwater. There has been use of the groundwater in the past and without strict institutional controls, there may be use of the groundwater in the future before the present risk level had been reduced by natural processes. The recent M-K sampling report (post-completion of the monolith) still shows constituents, such as molybdenum, above trigger levels. The passive nature of the remedial alternative for groundwater that essentially relies solely on dilution for the long-lived radionuclides places an even greater importance on extensive groundwater monitoring. Unless a credible understanding of the groundwater flow and contaminant processes can be developed, the true environmental impacts may remain unknown. Performance criteria, especially for the groundwater plume, should be developed and monitored. The goal of these criteria should demonstrate that MCLs for all groundwater constituents will be achieved in the regulatory timeframe. Without this information, the Panel is not convinced that the groundwater will achieve necessary standards required by CFR 40 192 within the 100-year timeframe.

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MEMORANDUM 20 December 1999

In accordance with national policy, the Five-Year Review Report for the Shattuck Superfund

Site has been evaluated by the site team and management from the Office of Environmental Protection& Remediation (8EPR), Office of Communications & Public Involvement (8OCPI), Office of RegionalCounsel (8ORC), and Office of Enforcement, Compliance, and Environmental Justice (8ECEJ). Sincethis is a joint HQ/R8 effort, the Five-Year Review Report has also been reviewed by the staff from theOERR Region 3/8 Center, OSRE, and OGC.

I recommend that EPA accept the final Five-Year Review Report and that you indicate thatwith your signature on the attached cover page which will be filed with the body of the Report.

Attachments

1. Five Year Review Report Summary2. Report cover page for signature and return

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION 8

999 18TH STREET - SUITE 500 DENVER, CO 80202-2466

Denver Radium Site

(Shattuck Chemical) Operable Unit #8

Five-Year Review

(Denver, Colorado)

I. Introduction

Authority Statement. Purpose. EPA Region 8 conducted this review pursuant to CERCLA section 121(c), NCP section 300.400(f)(4)(ii), OSWER Directive 9355.7-03B-P and EPA Peer Review Handbook (EPA 100-B-98-001). It is a part of the statutory review and covers only Operable Unit #8 of the Denver Radium Site. The sitewide review is being prepared separately and will be issued early next year (2000). The purpose of a five-year review is to ensure that remedial action remains protective of public health and the environment and is functioning as designed. This document will become a part of the administrative record. This review is applicable to a site at which response is ongoing. II. Incorporation by Reference

EPA Region 8 conducted this five-year review of this operable unit of the Denver Radium Superfund Site to evaluate whether the response actions taken at the site are protective of human health and the environment. SC&A (subcontractor) under the prime contractor (ERG) prepared a report, Five-Year Review, 12 November 1999, for EPA HQ and Region 8, and it is hereby incorporated by reference in this concurrence memo. The report discusses the location, history, remedial objectives, summary of selected remedy, site inspection notes, findings or deficiencies, and recommendations for resolution. III. Deficiencies Identified in the SC&A Report

The ability of the monolith/cover design to meet the long term performance criteria specified in the Record of Decision (ROD) is not demonstrated and reviewers have identified potential deficiencies in the design that raise doubt whether the said performance criteria can be met. EPA HQ and Region 8 technical staff agree with this finding without dissenting opinion. The following list of deficiencies was also identified in the report. The Site team has found that although some of these deficiencies may cause some additional technical concerns with the remedy, most do not rise to the same level of significance as those for the monolith and cover system. The combination of these deficiencies influenced our determination about how protective the remedy is.

Lack of institutional control of plume outside site boundary Plume-monitoring plan deficiencies Site characterization and modeling deficiencies Risk assessment deficiencies Specific design technical issues that need to be re-evaluated

IV. Recommendations

The SC&A Report recommended a number of additional sampling and analytical activities, as well as potential design upgrades. These recommendations were an attempt to provide resolution to the deficiency finding. However, SC&A believes that “after the fact” design retrofits in this particular case are inherently difficult to successfully enact and may still not provide reasonable assurance of long-term effectiveness. Measures to address these deficiencies need to be evaluated in the alternatives analysis during reconsideration of the remedy. V. Statement on Protectiveness For Operable Unit #8

The remedial action at OU 8 is currently protective of human health and the environment; however the long-term protectiveness provided by the monolith/cover design cannot be reasonably assured. The review has been future oriented in keeping with the long term compliance requirements specified in the ROD. Given the high degrees of uncertainty in the future site and surrounding site conditions, the SC&A Report takes a very conservative approach in its review of specific issues such as risk, remedy performance and potential land use. VI. Other Comments

This report included background concentrations of metals and radionuclides which are normally excluded from contaminant concentrations derived from the Site before an EPA risk assessment following Superfund Program guidance (RAGS) is calculated. Although the upgradient wells show elevated levels of uranium, their validity as a true indication of the naturally-occurring uranium in groundwater should not be discounted. The report illustrates how difficult it is to determine groundwater uranium background concentrations in this geographical region.

This report made scoping calculations with the maximum concentration values instead of the 95% Upper Confidence Limit (UCL) on the arithmetic average. The impact of these technical deviations from Program guidance on statistical significance was not evaluated in this report. It is likely that the impact may have overstated the actual risks, but since the monitoring wells may not be sampling the actual centroid of the contaminant plume, the results of this overly conservative approach cannot be discounted completely.

This report assumes that 5 pCi/g of Ra-226 in residual soils left beneath the monolith poses

unacceptable risk levels and that EPA draws an un-equivocal risk management threshold level at 1x10-4. OSWER Directive No. 9200.4-15 (Feb 12, 1998) states that the 5/15 pCi/g standards are based upon totally acceptable risk levels which “... correspond to the same risk level as that associated with a 15 mrem/year EDE...” (OSWER Directive 9200.4-18, Aug. 20, 1997). Furthermore, OSWER Directive No. 9355.0-30 (April 22, 1991) clearly states that the “.. upper boundary of the risk

management range is not a discrete line at 1x10-4, although EPA uses 1x10-4 in making risk management decisions...”. The impact of these technical deviations from Program guidance on risk-based soil standards was not evaluated in this report and it is likely that the impact may have overstated the actual risks. Reconsideration of the original remedy deals only with the monolith and leaves the groundwater remedy decision for further investigation. Therefore, the other comments in this section have no technical bearing on reconsideration of the monolith and will be resolved during further investigation of the groundwater remedy. VII. Next Five-Year Review

This Five-Year Review recommends that the monolith remedy should be re-evaluated and that additional characterization of the groundwater should be considered. Based upon that new information, the groundwater component of the remedy may need to be re-evaluated. If that response action is selected, although there would no longer be a statutory requirement for another five-year review for the stabilized/solidified soils (i.e. Monolith), future five-year reviews will continue to be needed to evaluate the protectiveness of the groundwater component to the remedy.