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SUBJECT: Amended Record of Decision (ROD) for Mid

Superfund Site

America Tanning Company

FROM: Michael I Sanderson .Director, Superfund Division

Dennis Grams, P.E. Regional Administrator

Attached is an Mended operated as a hideCompany Superfimd Site. During ated8 wastewater stream which contaminated thetanning facility. The tanning operat .8 ., . mium jhe U.S. Environmentalonsite treatment system and Decision jn 1991 which called for the solidificationProtection Agency (EPA) issued * ^ soil capping. The EPAof contaminated sludges, sediments _ J . (rd) in 1993. Data obtained during the subsequently went on to complete a Renje 8 t > revealed that the clay-linedRD and a Potentially Responsewhen they were disturbed. Air impoundment areas on-site wereSere to be remediated as originally

heptane >eve,s of hydrogen su.hde gas wouM be leased

during the solidification process.

remedy which is outlined in the amendment t ... . re

MEMORANDUM

SUBJECT: Amended Record of Decision (ROD) for Mid-America Tanning CompanySuperfund Site

FROM: Michael J. SandersonDirector, Superfund Division

TO: Dennis Grams, P.E.Regional Administrator

Attached is an amended Record of Decision (ROD) for the Mid-America Tanning Company Superfund Site. During the 1970s and 80s, Mid-America Tanning operated as a hide tanning facility. The tanning operations generated a wastewater stream which contaminated the On-site treatment system and surrounding soils with chromium. The U.S. Environmental Protection Agency (EPA) issued a Record of Decision in 1991 which called for the solidification of contaminated sludges, sediments and soils on-site followed by soil capping. The EPA subsequently went on to complete a Remedial Design (RD) in 1993. Data obtained during the RD and a Potentially Responsible Party-lead Removal in 1994, revealed that the clay-lined impoundment areas on-site were releasing hydrogen sulfide gas when they were disturbed. Air sampling and modeling data indicated that if the site were to be remediated as originally recommended in the ROD, that unacceptable levels of hydrogen sulfide gas would be released during the solidification process.

In response to this concern, the EPA evaluated the remedy and identified an alternative remedy which is outlined in the amendment to the ROD. The amended remedy is equally as protective of human health and the environment and will also reduce the potential for hydrogen sulfide gas emissions. In addition, the amendment to the ROD addresses some areas of the site which were not included in the original remedy, but which will need to be remediated. These areas include the wet well area, aeration basin, final clarifier, filter press building and miscellaneous soils and debris.

The EPA held a public comment period to allow the community to comment on the proposed plan. In addition, the EPA offered to hold a public availability session to address comments on the proposed plan. No comments were received regarding the proposed ROD amendment nor were there any requests to hold a public availability session.

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In summary, the amended remedy addresses the health and safety concern raised by the presence and potential for hydrogen sulfide emissions, addresses all areas of the site requiring remediation, is equally as protective of human health and the environment, and will provide a more cost-effective remedy for the site.

Please let me know if you have any questions or would like additional clarification.

Attachment

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DECLARATIONRECORD OF DECISION AMENDMENT FOR THE

MID-AMERICA TANNING COMPANY SUPERFUND SITE WOODBURY COUNTY, IOWA

JULY 1996

SITE NAME AND LOCATION

Mid-America Tanning Company Superfund Site Woodbuiy County, Iowa

INTRODUCTION

The United States Environmental Protection Agency (EPA) is amending the Record of Decision (ROD) for the Mid-America Tanning Company Superfund Site. On September 24, 1991, a ROD was issued for the Mid-America Tanning Company Site located in Woodbuiy County, Iowa. The ROD presented the remedy selected by the EPA for this site, which called for in-situ immobilization of the densely-contaminated sediments in the east and west aeration lagoons and the northeast field in conjunction with the placement of soil-clay caps over the less densely-contaminated source areas. Impoundment waters were to be treated as necessary and either discharged to the nearby oxbow lake or transported off site to a Publicly Owned Treatment Works (POTW). As a result of information which has been developed subsequent to the issuance of the ROD, the EPA has determined that fundamental changes to the remedy were necessary. The amendment to the ROD describes and summarizes the basis for these changes as well as documenting changes in the remedy at the site.

The EPA is the lead agency for the site, and the Iowa Department of Natural Resources (IDNR) has been designated the support agency. The amendment to the ROD is being issued by the EPA with concurrence by the state of Iowa.

The ROD amendment together with the original ROD presents the selected remedial action for the site. This action was chosen in accordance with the Comprehensive Environmental Response, Compensation and Liability Act of 1980 (CERCLA), as amended by the Superfund Amendments and Reauthorization Act of 1986 (SARA), and the National Contingency Plan (NCP). Section 117(c) of CERCLA provides that after the adoption of a final remedial action plan, if any remedial action is taken, or if any enforcement action under section 106 or 122 is entered into, and such action, settlement or decree differs in any fundamental respect from such final plans, the lead agency shall publish an amendment to the ROD with the reasons such changes were made. The ROD amendment will explain these changes to the remedy. In accordance with the NCP, 40 C.F.R. 300.825 (a)(c)(21), this

amendment and the information supporting these decisions are part of the administrative record file and are available for public review and comment. The administrative record file is available for review at the the Sergeant Bluff City Hall, Sergeant Bluff, Iowa and the EPA Region VH Office, Kansas City, Kansas.

DESCRIPTION OF THE AMENDED SELECTED REMEDY

The major components of the selected remedy, as amended, include:

• Contaminated soils in the northeast Held will be consolidated and/or excavated and consolidated with the Polishing Basin sediments and covered with a soil/clay cap or geosynthetic cap such as high-density polyethylene (HDPE) that achieves the same level of performance;

• Sediments in the polishing basin and east and west aeration lagoons will be dewatered. The dewatered sediments will then be covered with a clay/soil cover or comparable geosynthetic cap;

• On-site treatment and discharge of impoundment water to the nearby oxbow lake;

• Excavation of the burial trench material followed by on-site stabilization and consolidation with the northeast field soils prior to capping;

• Excavation of the contaminated soil areas, other than the northeast field, and consolidation of this material with the aeration lagoon sediments and/or polishing basin sediments prior to capping;

• Removal of the sediments in the wet well, aeration basin, and final clarifier and consolidation of this material with the sediments in the aeration lagoons prior to capping. The emptied basins will be decontaminated with high-pressure steam and backfilled with clean soil;

• The filter press building along with other miscellaneous contaminated debris will be decontaminated by washing these items with a high-pressure steam cleaner. Wash water will be treated on-site and discharged to the oxbow lake. Floor scrapings and building residue will be disposed of in accordance with the Resource Conservation and Recovery Act (RCRA); and

• Land use restrictions in the form of deed restrictions will be instituted to limit future use of the property.

STATUTORY DETERMINATIONS

The selected remedy as amended remains protective of human health and the environment, complies with federal and state requirements that were identified in the ROD as applicable or relevant and appropriate to this remedial action and is cost effective. In addition, the remedy, as revised, utilizes permanent solutions and alternative treatment technologies to the maximum extent practicable for this site. These changes to the remedy will increase protectiveness of human health and environment, both short term and long term.

Dennis Grams, P.E. DateRegional Administrator Environmental Protection Agency Region VII

Attachment:

Decision SummaryResponsiveness Summary-Attachment A

t

AMENDMENT TO THE

RECORD OF DECISION FOR THE

MID-AMERICA TANNING COMPANY SUPERFUND SITE

WOODBURY COUNTY, IOWA

Prepared by:

U.S. Environmental Protection Agency

Region VII

Kansas City, Kansas

July 1996

Amended Record of Decision

Decision Summary

Contents

l. Introduction........................................................................ ......... . 1

n. Community Relations....................................................................... 2m. Reasons for Issuing the ROD Amendment..................................... 2

IV. Description of the New Alternatives............................................... 3

V. Evaluation of Alternatives............................................................... 5

VI. Statutory Determinations................................................................ 13

Responsiveness Summary............................................................... Attachment A

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DECISION SUMMARYRECORD OF DECISION AMENDMENT for the

MID-AMERICA TANNING COMPANY SUPERFUND SITE WOODBURY COUNTY, IOWA

L INTRODUCTION

The Mid-America Tanning (MAI) Company Superfund Site is located in Woodbury County, Iowa, approximately seven miles south of Sioux City and four miles south of the town of Sergeant Bluff. The MAT site occupies 98.7 acres of land in an industrial area known as the Port Neal Industrial District. The site is bordered on the north by Kind & Knox, a gelatin manufacturer, on the east by a Chicago and Northwestern railroad right-of-way, and on the west and south by agricultural land and public-use hunting grounds. The nearest stretch of the Missouri River is approximately l.S miles to the southwest.

The MAT Site operated as a hide tanning processor under several different ownerships from 1970 until 1989. The tanning process included fleshing,, brine curing and trimming of hides as well as brine and chrome tanning. The tanning operations generated a wastewater stream that contained dirt, brine, flesh, detergents, hair, sulfides, ammonia, lime, grease and chromium. During a period of the operation, contaminated sludges were buried in trenches and land fanned on the site. The Environmental Protection Agency (EPA) completed an Remedial Investigation/Feasibility Study (RI/FS) in July 1991 and issued a Record of Decision (ROD) in September 1991. The selected remedy in the ROD consisted of in-situ immobilization of the densely-contaminated sediments in the east and west aeration lagoons and the northeast field, placement of a soil-clay cap over the less densely-contaminated source areas, and treatment and discharge of contaminated impoundment waters. The EPA completed a Remedial Design (RD) in 1993, and in 1994 the Foxley Cattle Company was ordered to conduct a removal action at the site. Foxley complied with the Order and completed the removal action in May 1995. While conducting the RD and subsequent removal action, EPA determined that the sediments found in the clay-lined impoundment areas were generating hydrogen sulfide gas at concentrations posing significant health risks. Air sampling and modeling indicated that unacceptable levels of hydrogen sulfide gas would be released during the solidification process. In response to this concern, EPA is amending the remediation to minimize disruption of the waste and the release of hydrogen sulfide gas. The ROD amendment recommends dewatering the impoundment areas using a system of wick drains and then applying an improved cap to the area. In addition, the ROD amendment addresses the need to remediate the sediments in the wet well area, aeration basin and final clarifier. These sediments will be consolidated with the aeration lagoon sludges and/or polishing basin sediments and capped. The ROD amendment also provides for decontamination of the filter press building and other debris on site.

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U. COMMUNITY RELATIONS

The EPA is issuing this ROD Amendment to meet the public participation provisions mandated under Section 117(a) of the Comprehensive Environmental Response,Compensation, and Liability Act (CERCLA), as amended by the Superfund Amendments and Reauthorization Act (SARA) of 1986, and Section 300.435 (c)(2)(II) of the National Oil and Hazardous Substances Pollution Contingency Plan (NCP).

The proposed plan for this ROD amendment was made available to the public in the administrative record file located at the Sioux City Public Library, 529 Pierce Street, Sioux City, Iowa and the EPA Region VII Office, Kansas City, Kansas. A public notice was published in the Sinnx ri«y Journal announcing the commencement and length of the public comment period and the availability of the administrative record file. The EPA offered to hold a public meeting to discuss the ROD Amendment if requested; however, no requests were received. Comments received during the public comment period are addressed in the Responsiveness Summary. The EPA received no comments to the proposed plan for this ROD Amendment.

m. REASON FOR ISSUING THE ROD AMENDMENT

During the Remedial Design and subsequent Removal Actions at the site, the EPA determined that the sediments found in the clay-lined impoundments were generating hydrogen sulfide gas at concentrations posing significant health risks. Air sampling indicated that the levels of hydrogen sulfide gas released would significantly increase when the impoundment sediments were disturbed.

The selected remedy in the ROD for the impoundment sediments is in-situ stabilization followed by a 2-foot soil cap. In-situ solidification requires disturbing the impoundment sediments with a large-scale auger. Based on air sampling and modeling, the levels of hydrogen sulfide released during the mixing of impoundment sediments with solidification agents are projected to exceed worker permissible exposure limits as defined by the National Institute for Occupational Safety and Health (NIOSH) and the Occupational Safety and Health Administration (OSHA). Air dispersion modeling also indicates a reasonable likelihood that hydrogen sulfide emissions at the site perimeter would exceed the permissible exposure levels for hydrogen sulfide established by the Agency for Toxic Substances and Disease Registry (ATSDR).

An alternate remedy of dewatering the sediments would substantially reduce the disturbance of the impoundment sediments. Therefore, significantly less hydrogen sulfide gas

emissions would be generated as compared to implementation of the in-situ solidification. A geosynthetic cap or an improved clay Cap would be placed over the dewatered sediments

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forming an infiltration barrier that can resist leaching from deformations caused by settling and drying, thereby, potentially reducing long-term cap maintenance costs.

IV. DESCRIPTION OF THE NEW ALTERNATIVES

The original remedy for remediation of the contaminated soil, sediment and impoundment water included the following major components:

• Treatment followed by discharge or off-site disposal of impoundment waters;

• In-situ stabilization/solidification of contaminated sediments and soils in the east aeration lagoon, west aeration lagoon, and northeast Held, followed by a 2-foot soil cap;

• Soil/clay capping of the polishing basin sediments and miscellaneous contaminated surface soils;

• Stabilization/solidification of contaminated sludges removed from burial trenches followed by either onsite or off-site disposal;

• Semi-annual monitoring and maintenance of soil/clay caps and immobilized materials; and

• Annual long-term ground water monitoring.

The amended remedy will be as protective of human health and the environment, be more implementable and decrease the cost of the remedial action. The changes include the replacement of the in-situ solidification of impoundment sediments and northeast field soils with innovative dewatering technology followed by an improved cover design; inclusion of additional site contaminated areas at the site into the remedy; and documentation of the final decisions on waste disposal options identified in the original ROD. The amended remedy will fully meet the remedial action objectives identified in the Feasibility Study identified as prevention of direct contact and contaminant migration to the ground water.

The major changes in the amended remedy include:

• Contaminated noitheast field soils would not undergo in-situ stabilization, but rather would be consolidated and/or excavated and consolidated with the Polishing Basin sediments and covered with an improved soil/clay cap meeting specified performance criteria or geosynthetic cap such as high-density

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polyethylene (HDPE) that would achieve similar performance criteria. Depth of the contamination in the northeast Held ranges from 1 to 1.5 feet, and a redesigned cap will continue to provide an implementable, cost-effective, and equally protective

remedy. Contamination from this area may also be excavated and consolidation with the Polishing Basin sediments. This would be equally protective and may be even more cost-effective.

• Sediments in the east and west aeration lagoons would not undergo stabilization/solidification. Instead, the impoundment areas would be dewatered and capped. The impoundment covers would be redesigned to incorporate an improved soil/clay cap meeting the performance criteria or comparable geosynthetic cap such as high-density polyethylene. Post-ROD sampling indicated the presence of hydrogen sulfide gas production from the impoundment sediments. Air sampling and modeling indicates that dangerous levels of hydrogen sulfide gas would be emitted should the impoundment sediments be disturbed which would occur under the original remedy. This change will provide a more cost effective remedy that greatly reduces the potential for releases of hydrogen sulfide gas, thereby reducing the health risk to on-site workers and the nearby public. The amended remedy is also protective due to the improved cover design.

• Contaminated soil areas, other than the northeast field, will be excavated and consolidated with the aeration lagoon sediments and/or polishing basin sediments prior to capping. The original remedy had these areas capped in place; however, by consolidating these soils, the costs associated with cap construction will be significantly reduced while maintaining equal protection to the public health and the environment.

The following are the areas where the original remedy contained options:

• The original remedy indicated that impoundment waters were to be treated as necessary and either discharged to the nearby oxbow lake or transported off site to a POTW. All impoundment water will be treated on-site if necessary and discharged to the nearby oxbow lake. The EPA has determined that on-site treatment would be most cost-effective due to the quantity of water potentially needing to be treated. This is not a change from the original remedy and just serves to document EPA’s preference for treating the water on-site.

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• The original remedy indicated that contaminated sludges excavated from the burial trenches were to be stabilized and disposed of either on-site or off-site. Based on preliminary calculations, on-site stabilization and consolidation with the northeast field soils followed by capping will be the most cost-effective way to remedy this area of the site. This is not a change from the original remedy and just serves to document EPA’s preference for treating the burial trench material on-site.

The following are the areas that the original remedy did not address.

• The original remedy did not address the sediments remaining in the wet well, aeration basin, and final clarifier. This ROD amendment addresses the removal of the contaminated material and consolidation of it with the sediments in the aeration lagoons and/or polishing basin. These sediments would then be capped. The emptied basins will be decontaminated with high-pressure steam and backfilled with clean soil. These actions will further reduce the risk of direct contact to site contaminants and the potential threat of contaminant releases to the environment.

• The original remedy did not address the decontamination of the filter press building and miscellaneous contaminated debris. This ROD amendment addresses decontamination of these areas by washing with a high-pressure steam cleaner. Wash water will be treated on-site and discharged to the oxbow lake. Floor scrapings and building residue will be disposed of in accordance with the Resource Conservation and Recovery Act (RCRA). These actions will provide additional protection of human health and the environment.

V. EVALUATION OF ALTERNATIVES

The NCP sets forth nine evaluation criteria which serve as a basis for comparing the remedial alternatives for final actions. The nine criteria are divided into three categories: Threshold Criteria, Primary Balancing Criteria, and Modifying Criteria. If any remedial alternatives identified during the Feasibility Study do not meet the Threshold Criteria (Criteria 1 and 2), EPA will not consider them as possible final remedies. If the alternatives satisfy the Threshold Criteria, they then are evaluated against the next rive criteria, called the Primary Balancing Criteria. These criteria are used to compare the remedial alternatives against each other in terms of effectiveness, implementability, and cost. The final two criteria, state acceptance and community acceptance, are called Modifying Criteria. The alternatives are compared against the Modifying Criteria after the state and community have reviewed and commented on die Proposed Plan and the other alternatives considered by EPA.

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The following is a discussion of the nine criteria used by EPA for remedy selection.

A. Threshold Criteria:

1. Overall Protection of Human Health and the Environment

The EPA assesses the degree to which the alternatives would eliminate, reduce, or control threats to public health and the environment through removal, containment, and/or institutional controls. An alternative is

normally considered to be protective of human health if the excess cancer risk is reduced to less than 1 in 1,000,000 (10-6) and risks do not pose non-carcinogenic health risks {Hazardous Index (HI) < 1}.

Based on the results of the risk assessment performed at MAT, current and/or future contact to sediment in the east and west aeration lagoons, the polishing basin, and the soils in the northeast field, pose a potential human health risk. The original remedy reduced the threat of exposure of the contaminants by in-situ stabilization and capping of the soils and sediments and the removal and discharge of contaminated impoundment waters. The amended remedy would adequately protect human health because it addresses the principal threat of exposure by treating and discharging impoundment waters and by capping the associated contaminants and preventing direct contact. The amended remedy would also reduce the likelihood of all exposure of ecological receptors to the contaminated areas. The amended remedy also provides greater protection as compared to the original remedy by reducing the likelihood of hydrogen sulfide gas emissions at levels above worker threshold standards during the remedial action. In this case, the amended remedy is more protective. The amended remedy also includes an improved capping system which will help ensure and minimize contaminant migration into the groundwater in the future. Institutional controls in the form of deed restrictions limiting building of structures on site will supplement the containment measures and help to ensure that exposures in these areas will not increase to the extent that the carcinogenic risks would be unacceptable.

2. Compliance with all Applicable or Relevant and Appropriate State And Federal Environmental Regulations

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%The amended remedy will comply with all federal and state applicable or relevant and appropriate requirements (ARARs). Applicable requirements are those state or federal requirements legally applicable to the release or remedial action contemplated that specifically address a hazardous substance, pollutant, contaminant, remedial action, location, or other circumstance found at the site. If it is determined that a requirement is not applicable, it may still be relevant and appropriate to the circumstances of the release. Requirements are relevant and appropriate if they address problems or situations sufficiently similar to the circumstances of the release or remedial action contemplated, and are well-suited to the site.

The majority of the ARARs which applied for the originally selected alternative also apply to the amended alternative. The chemical-specific ARARs that are relevant and appropriate at the site include Ambient Water Quality Criteria (AWQC) and National Pollution Discharge Elimination System (NPDES) standards. As with the original remedy, the amended remedy involves removal of surface water in the polishing basin and east and west aeration lagoons followed by treatment and discharge to an on-site surface water (oxbow lake). Soils and sediments will be capped in place. Capping includes provisions for drainage and runoff control. The substantive requirements include AWQC, effluent limitations and monitoring requirements and will be met by the amended remedy.

The state of Iowa promulgated regulations pursuant to Iowa Code Section 455E.5 will apply to cleanup actions at the site where significant amounts of soil contamination are present and groundwater contamination is Occurring. These regulations, set forth in 567 LAC 133, are applicable since groundwater contamination has been observed at the site. As with the original ROD, groundwater contamination and long term monitoring will be addressed in a separate action.

The federal and state action-specific ARARs include all OSHA, all Hazardous Materials Transportation Act (HMTA) regulations, and the Clean Water Act (CWA) regulations applicable to discharge to POTWs. The RCRA regulations would only be considered applicable for the trench material because of the TCLP test results. Trench materials will be treated through ih-situ stabilization prior to consolidation and capping. The RCRA regulations are not relevant and appropriate to the chromium contaminated soils and sediments since they do not fail TCLP.

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In addition, RCRA regulations may be considered as relevant and appropriate for materials which may be generated such as floor scrapings. Floor scrapings which might be generated as part of the decontamination process will be tested. Based on the results of these tests, the materials will either be consolidated with the soils and sediments and capped or consolidated with the trench materials prior to in-situ stabilization and capping.

B. Primary Balancing Criteria

1. Long-Term Effectiveness and Permanence

Long-term effectiveness and permanence refers to the ability of a remedy to maintain reliable protection of human health and the environment over time once clean up goals have been met. Institutional controls, including local zoning regulations which limit the uses of the property and deed restrictions prohibiting the construction of buildings or other structures on the capped areas of the site, would prevent damage or deterioration of the capped areas and exposure of the contaminants present at the site. These restrictions will apply to this property regardless of any subsequent change in ownership, thereby offering long-term effectiveness and permanence of the selected amended remedy.

Evidence indicates that the levels of contamination in several areas of the site potentially pose a current and/or future risk to human health or the environment. The implementation of the amended remedy will result in a reduction in the risk in all areas where contamination was found to pose a risk through direct contact or inhalation. The amended remedy provides more protection by including additional areas in the remediation.

The amended alternative includes treatment of contaminants and engineering controls. Surface waters will be treated if necessary prior to discharge. Although contaminated soils and sediments will be left in place and capped, potential for direct exposure will significantly be reduced. Mobility of the contaminants will be reduced through dewatering and an improved capping system. The improved cap will limit the ability of surface water runoff to cause contaminants to migrate into the groundwater. Both the original remedy and the amended remedy rely on groundwater monitoring to ensure that the remedy continues to provide effective long-term protection of human health and

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the environment. The improved cap contained in the amended remedy will be constructed and maintained in a manner that provides long term effectiveness and permanence. Groundwater will be monitored to ensure that the remedy is operating as designed.

2. Reduction of Toxicity, Mobility, or Volume Through Treatment

Section 121(b) of CERCLA states that remedial actions involving treatment which permanently and significantly reduce the volume, mobility or toxicity of the hazardous materials, are to be preferred over those not involving such treatment. This evaluation criteria relates to the ability of a remedial alternative to control or eliminate risks caused by the mobility, toxicity or volume of hazardous wastes.

The amended alternative will reduce the toxicity of the surface waters of the polishing basin and east and west aeration lagoons by treating these waters prior to discharge. Neither the original nor the amended remedy reduce the toxicity of the hazardous constituents in the contaminated soils and sediments.

The original remedy employed in-situ stabilization to reduce the mobility of the contaminants. The amended alternative will employ capping and engineering controls to reduce the mobility of the hazardous constituents. The amended remedy will reduce mobility of the contaminants through the use of the clay-lined impoundment system. An improved cap will further reduce the likelihood of infiltration of surface water causing the contaminants to migrate.

The original remedy’s use of in-situ stabilization would have increased the volume of material significantly. The amended alternative is an improvement in that the volume of contamination will actually be decreased through the dewatering of the polishing basin and impoundment areas.

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3. Short-Term Effectiveness

Short-term effectiveness evaluates the length of time needed to implement each segment of the alternatives. The EPA considers the risks that a particular activity may pose to site workers, nearby residents, or the local environment. Short-term effectiveness involves the period of time needed to achieve protection and considers any adverse impacts on human health and the environment that may be posed during the construction and implementation period until clean up goals are achieved.

The amended remedy requires less disturbance of the contaminated sediments in the impoundment areas, thereby, reducing their agitation and potential for release of emissions of hydrogen sulfide gas which may affect on-site workers and nearby residents. The previously selected remedy anticipated the use of a large-scale auger which would have significantly disturbed the sediments and resulted in releases of high levels of hydrogen sulfide gas into the air. Based on air sampling and modeling, the levels of hydrogen sulfide released during the action of mixing impoundment sediments with solidification agents as specified in the original ROD would exceed worker permissible exposure limits as defined by NIOSH and OSHA. In addition, air dispersion modeling indicates that when conducting the original ROD there would be a reasonable likelihood that hydrogen sulfide emissions at the site perimeter would exceed the permissible exposure levels for hydrogen sulfide established by ATSDR.

4. Implementability

The EPA considers how difficult the alternative is to construct and operate, how other government agencies and EPA will coordinate monitoring programs and the availability of goods and services and personnel needed to implement and manage the alternative. Implementability addresses the technical and administrative feasibility of a remedy, including the availability of materials and services needed to implement the chosen solution.

Given the potential for releases of high levels of hydrogen sulfide gas into the atmosphere, the original remedy is no longer as readily implementable. Higher levels of worker protection would be necessary. This would increase the time necessary to implement the remedy and add

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an additional risk factor which must be accounted for in completing the effoit. The amended remedy is readily implementable in that dewatering the impoundment areas can be implemented more easily than dewatering followed by solidification. In addition, the amended remedy minimizes the disturbance of the areas lowering the threat of hydrogen sulfide gas releases. Therefore, special provisions for dealing with these releases can be eliminated. Because of the increased concern over the releases of hydrogen sulfide gas, the original remedy would have taken longer to complete; however, the amended remedy should be able to be completed in the original time frame (44 weeks).

5. Cost

The HPA considers capital costs, operation and maintenance costs, and present worth, which is the cost of the activities that will take place until the remedial action is completed. Capital costs apply to activities such as construction, land and site development, and disposal of waste materials. Annual operation and maintenance costs are spent on activities such as on-going operation of equipment, insurance and periodic site reviews.

The CERCLA requires that the EPA select a cost-effective alternative that protects human health and the environment and meets other requirements of the law. The EPA has determined that the selected remedy is as protective and in some cases more protective of human health and is more

cost effective to implement. The estimated capital cost for the original remedy was $4,621,300 and Operation & Maintenance cost for 30 years of $21,000 per year. Costs are estimated to have increased through inflation to approximately $5,574,000 using today’s pricing data for the same remedy. The original remedy’s cost estimate did not include the cost for remediating the wet well, aeration basin, final clarifier, filter press building or miscellaneous contaminated soils nor did it include dewatering and treatment of the total volume of water now contained in the impoundment areas. The potential for hydrogen sulfide emission would also increase the cost of implementing the original remedy in that a higher level of worker protection would be needed during construction activities. This higher level of protection would cause work to proceed at a slower pace increasing the overall time needed to complete the remediation. The increased time on-site would increase the labor costs

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associated with the construction causing the overall costs to be even higher than the estimate above.

The preliminary cost estimate to implement the amended remedy is $2,661,593 depending on the amount of consolidation of the contamination that is possible. This estimate also includes remediation of all areas identified in the original remedy plus the wet well, aeration basin, final clarifier, filter press building and miscellaneous contaminated soils. This estimate prices out the remediation of the northeast field as a separate containment cell, but does assume that a moderate amount of consolidation of the contaminated areas is possible. When these factors are taken into consideration, the cost to implement the amended remedy is significantly less than the cost to implement the original remedy. In addition, if a geosynthetic cap is utilized, Operation & Maintenance (O&M) costs could be reduced since there are minimal costs associated with long term maintenance of synthetic caps. Overall, the amended remedy is seen to be a more cost effective remedy providing equivalent or greater protection to human health and the environment.

C. Modifying Criteria:

1. State Acceptance

The state of Iowa, through the Iowa Department of Natural Resources (IDNR), is supportive of the amended remedy for this site and prefers this remedy to the originally selected remedy.

2. Community Acceptance

The EPA held a public comment period to allow the community to comment on the preferred alternative as set forth in the proposed plan and supported by the administrative record. In addition, the EPA notified the public regarding its willingness to conduct a public availability session on the proposed plan. The EPA did not receive any comments regarding the proposed ROD Amendment at the site nor requests to conduct a public meeting.

In comparing the original remedy with the amended remedy, the EPA has determined that the original and amended remedy meet the threshold criteria, overall protection of human

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.health and the environment, and compliance with state and federal requirements.

The amended remedy presents the better balance of tradeoffs, with respect to the primary balancing criteria, in particular with respect to implementability and cost. In addition, the amended remedy continues to be protective of human health and reduces mobility of the contamination by providing an improved capping system. For the modifying criteria of state and community acceptance, the amended alternative is preferred. In the tradeoff and balancing of all nine criteria, the amended remedy is EPA’s preferred remedy.

VL STATUTORY DETERMINATIONS

The EPA has determined, and the state of Iowa concurs, that the selected amended remedy herein satisfies the statutory requirements specified in CERCLA Section 121 which state that the selected remedy must protect human health and the environment and comply with applicable or relevant and appropriate federal and state requirements. In addition, the remedy, as amended, utilizes permanent solutions and alternative treatment technologies to the maximum extent practicable for this site. These changes to the remedy will increase protectiveness of human health and environment, both short term and long term.

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ATTACHMENT A

RESPONSIVENESS SUMMARY RECORD OF DECISION AMENDMENT

MID-AMERICA TANNING COMPANY SUPERFUND SITE

In accordance with CERCLA Section 117, a public comment period was held from May 13, 1996 to June 11, 1996, to receive comments from interested parties on the EPA’s proposed plan for the Record of Decision Amendment for the Mid America Tanning Company Superfimd Site, Sergeant Bluff, Iowa. The EPA received no written comments on the proposed plan.

The EPA offered to hold a public meeting if requested. No requests for a public meeting were received.