5541Golder Associates Inc.400 Commercial StreetManchester, NH USA 03-101-1113Telephone (603) 668-0880Fax (603) 668-1199

REMEDIAL INVESTIGATION REPORTOPERABLE UNIT 2

SALTVILLE WASTE DISPOSAL SITESALTVILLE, VIRGINIA

Prepared for:

Olin CorporationLower River Road

Charleston, TN 37310

Prepared by:

Golder Associates Inc.400 Commercial StreetManchester, NH 03101

December 1994 Project No. 883-6174

ftR3Qi'372OFFICES IN AUSTRAIIA CANADA f^FPMAMV HI lNfiAr?V ITAIV c;\A/pnPM I iMircn i/iM^norv/i i IMITCH CTATCC

REMEDIAL INVESTIGATION REPORTSALTVILLE WASTE DISPOSAL SITE

SALTVILLE, VIRGINIA

TABLE OF CONTENTS

Volume 1 of 6

Executive Summary

Volume 2 of 6

Remedial Investigation Report

Volume 3 of 6

Appendix A - Record of DecisionAppendix B - Consent DecreeAppendix C - Borehole/Monitoring Well Logs

Volume 4 of 6

Appendix D - Packer Test DataAppendix E - Electro-Piezocone ReportAppendix F - Cone Penetrometer DataAppendix G - Rising Head Tests

Volume 5 of 6

Appendix H - Water Level DataAppendix I - FPM Theory DocumentationAppendix J - Analytical Testing Data ReportsAppendix K - 1989 Hydrology DataAppendix L - 1990 Hydrology DataAppendix M - 1991 Hydrology Data

Volume 6 of 6

Appendix N - Site Seismic ConsiderationsAppendix O - Probablistic Simulation DataAppendix P - Dike Stability Laboratory testing and ResultsAppendix Q - Geohydrologic Study of the Former

Chlorine Plant SiteAppendix R - Allison Gap Road Project Investigation Report for

VDOTAppendix S - ABB-ES Risk AssessmentAppendix T - * Site Water BalanceAppendix U - Precipitation vs TimeAppendix V - Responses to CommentsAppendix W •- Olin Report on Former Chlorine Plant Site, River Bottom

Excavation and Site Capping 1982-1983, Saltville, VAA R 3 G I 3 7 3

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TABLE OF CONTENTS

Table of Contents [

SECTION PAGE

1.0 INTRODUCTION 1-21.1 Purpose 1-31.2 Site Background 1_3

1.2.1 Site Description 1-31.2.2 Demography 1-31.2.3 Surface Features 1-31.2.4 Site History 1-51.2.5 Previous Investigations . 1-8

1.3 Report Organization 1-10

2.0 STUDY AREA INVESTIGATIONS 2-12.1 Data Needs and Objectives 2-12.2 Base Map Preparation and Historical Drawings Review 2-32.3 Hydrologic Investigations 2-3

2.3.1 Precipitation Monitoring Stations 2-42.3.1.1 TVA Rain Gauge 2-42.3.1.2 On-site Continuous Recording Rain Gauge 2-5

2.4 Surface Water Monitoring Stations 2-52.4.1 North Fork Holston River Stage and Discharge 2-62.4.2 Pond 5 Decant Inlet 2-62.4.3 Pond 5 Decant Outlet 2-72.4.4 Swale 3 Discharge 2-8

2.5 Geologic Investigations 2-92.5.1 Field Reconnaissance and Literature Review 2-92.5.2 Geotechnical Subsurface Investigation 2-10

2.6 Hydrogeologic Investigations 2-122.6.1 General Description 2-122.6.2 Exploratory Boreholes 2-122.6.3 Pressure Packer Testing 2-142.6.4 Slug Testing 2-172.6.5 Electropiezocone Penetrometer Testing 2-17

2.7 Contaminant Source Investigations 2-18

3.0 DIKE AND ASAW STABILITY 3-13.1 Project Considerations 3-1

3.1.1 Site Description 3-13.1.2 Site History Review 3-13.1.3 Project Description 3-23.1.4 Dike Construction 3-3

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TABLE OF CONTENTS (cont'd)

SECTION PAGE

3.2 Field Investigations 3-43.3 Subsurface Conditions 3-6

3.3.1 Pond 5 Dike Stability Investigation 3-63.3.2 Pond 5 Subsurface Investigation 3-103.3.3 Laboratory Testing Program 3-13

3.3.3.1 Dike 5 Laboratory Testing Program 3-133.3.3.2 Pond 5 Laboratory Testing Program 3-16

3.4 Stability Analysis Of The Pond 5 Dike 3-183.4.1 General 3-183.4.2 Slope/Dike Geometry 3-193.4.3 Material Properties 3-193.4.4 Conclusions Regarding Pond 5 Dike Stability 3-21

3.5 Investigation Of Pond 5 Waste 3-223.5.1 Deposition and Historical Observations 3-223.5.2 Field Observations 3-22

3.6 Summary of Cone Penetrometer Exploration of Pond 5 3-243.7 Results of Cone Penetrometer Investigation 3-253.8 ASAW Compressibility and Estimated Settlement Behavior 3-283.9 Liquefaction Potential 3-293.10 Conclusions - Pond 5 Ammonia Soda Ash Waste , 3-31

4.0 GEOLOGY . 4-14,1 Regional Geology 4-14.2 Site Geology 4-2

4.2.1 Site Stratigraphy 4-24.2.1.1 Price Formation 4-24.2.1.2 Maccrady Formation 4-34.2.1.3 Little Valley Formation 4-44.2.1.4 Hillsdale Limestone Formation 4-44.2.1.5 Ste. Genevieve and Gasper Formations 4-5

4.2.2 Fill Materials 4-54.2.2.1 Ammonia Soda Ash Waste 4-54.2.2.2 Slaker Waste . 4-54.2.2.3 Starter Dike 4-6

4.2.3 Natural Soils 4-64.2.3.1 Alluvium . 4-74.2.3.2 Colluvial Soils 4-74.2.3.3 Residual Soils 4-7

4.2.4 Structural Features 4-7

5.0 HYDROGEOLOGY 5-15.1 General 5-15.2 Regional Hydrogeology 5-15.3 Site Hydrogeology 5-2

5.3.1 FCPS Hydrogeology 5-3

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TABLE OF CONTENTS (cont'd)

SECTION PAGE

5.3.2 Bedrock Hydrogeology 5.55.3.2.1 Bedrock Hydrostratigraphic Units 5-55.3.2.2 Bedrock Hydraulic Conductivity 5-75.3.2.3 Potentiometric Level Fluctuations 5-105.3.2.4 Bedrock Hydraulic Gradients and Flow Directions 5-125.3.2.5 Bedrock Vertical Gradients 5-145.3.2.6 Bedrock Groundwater Flow Velocities 5-17

5.3.3 Pond Fill Hydrogeology 5-185.3.3.1 Pond Fill Composition 5-185.3.3.2 Pond Fill Hydraulic Conductivity 5-195.3.3.3 Potentiometric Level Fluctuations 5-235.3.3.4 Pond Fill Hydraulic Gradients and Flow Directions 5-245.3.3.5 Pond Fill Vertical Hydraulic Gradients 5-265.3.3.6 Pond Fill Groundwater Flow Velocities 5-26

5.4 Numerical Modeling Of Groundwater Flow 5-275.4.1 General 5-275.4.2 Numerical Model Code 5-285.4.3 Model Calibration ' 5-295.4.4 Modeling Results 5-305.4.5 Modeling Conclusions 5-31

5.5 Site Conceptual Groundwater Flow Model 5-325.5.1 Groundwater Flow Between Bedrock and Pond Fill 5-325.5.2 Groundwater Recharge and Discharge Areas 5-335.5.3 Site Groundwater Level Fluctuations 5-345.5.4 Discussion and Conclusions 5-35

6.0 HYDROLOGY 6-16.1 Regional Hydrology 6-16.2 Site Hydrology for Pond 5 6-2

6.2.1 Pond 5 Sub-watershed 6-26.2.2 Precipitation 6-56.2.3 Evaporation and Evapotranspiration 6-76.2.4 Storm Water Runoff 6-8

, 6.2.4.1 Flow in Swales and Western Diversion Ditches 6-86.2.4.2 Pond 5 Decant Structure Inlet and Outlet 6-106.2.4.3 North Fork Holston River 6-11

6.3 Site Hydrology for Pond 6 6-126.3.1 Pond 6 Sub-watershed 6-126.3.2 Precipitation 6-136.3.3 Evaporation and Evapotranspiration 6-136.3.4 Storm Water Runoff 6-13

6.4 Site Hydrology for FCPS 6-146.4.1 FCPS Sub-watershed 6-146.4.2 Precipitation 6-156.4.3 Evaporation and Evapotranspiration 6-156.4.4 Storm Water Runoff 6-15

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TABLE OF CONTENTS (cont'd)

SECTION PAGE

6.5 Water Balance for the Pond 5 Sub-watershed 6-156.6 Site Conceptual Hydrologic Flow Model 6-18

6.6.1 Flow Through the Little Mountain Sub-Watershed 6-186.6.2 Flow Through Pond 5 6-196.6.3 Flow Through Pond 6 6-236.6.4 Flow Through the FCPS Sub-watershed 6-24

6.7 Daily Water Balance for Pond 5 6-256.7.1 Excerpts from the Draft OU-3 RI: RIVER and PONDS Models 6-276.7.2 Interpretation of PONDS Results 6-35

7.0 NATURE AND EXTENT OF CONTAMINATION 7-17.1 Source of Mercury 7-17.2 Remedial Investigation Sampling Program 7-27.3 Extent of Mercury in Soils and Pond Wastes 7-3

7.3.1 Former Chlorine Plant Site Soils 7-37.3.2 Waste Ponds 5 and 6 ASAW 7-47.3.3 Allison Gap Road Bridge Soils 7-67.3.4 Other Constituents of Potential Concern in Soils 7-7

7.4 Extent of Mercury in Groundwater 7-87.4.1 Former Chlorine Plant Site Groundwater 7-87.4.2 Pond 5 and 6 Groundwater 7-97.4.3 Other Constituents of Potential Concern in Groundwater 7-10

7.5 Pond 5 and 6 Outfalls 7-117.5.1 Mercury Analyses 7-117.5.2 Other Constituents of Potential Concern 7-12

7.6 Surface Water and Sediment 7-137.7 Air 7-13

8.0 MERCURY FATE AND TRANSPORT 8-18.1 Contaminant Migration Pathways 8-1

8.1.1 Seepage from the FCPS 8-28.1.2 Pathways from Ponds 5 and 6 8-4

8.1.2.1 Seepage through the Pond 5 and 6 Dikes 8-58.1.2.2 Pond 5 and 6 Outfall Discharges 8-6

8.2 Mercury Form and Persistence 8-118.2.1 Air 8-118.2.2 Water and Sediment 8-118.2.3 Fish 8-12

9.0 HUMAN HEALTH RISK ASSESSMENT 9-1

10.0 SUMMARY AND CONCLUSIONS 10-110.1 Summary 10-1

10.1.1 Investigations 10-110.1.2 Nature and Extent of Contamination 10-110.1.3 Fate and Transport 10-210.1.4 Risk Assessment 10-3

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TABLE OF CONTENTS (cont'd)

SECTION PAGE

10.2 Conclusions 10-410.2.1 Data Limitations and Recommendations for Future Work 10-410.2.2 Remedial Action Objectives 10-5

REFERENCES 11-1

At end of eachCorresponding Section

LIST OF TABLES

Table 2-1 Pond 5 Decant Structure Inlet Stage-Discharge Rating Table for Standard90-Degree V-Notch Weir

Table 2-2 Pond 5 Decant Structure Outlet Stage-Discharge Rating TableTable 2-3 Swale 3, Stage Discharge Rating Table for 0.75 Feet H-Flume

Table 3-1 Dike Material Properties for Deterministic AnalysisTable 3-2 Dike Material Properties for Probabilistic AnalysisTable 3-3 Critical Surface Factors of Safety

Table 5-1 Pressure Packer TestingTable 5-2 Rising Head Test ResultsTable 5-3 Permeability Values Previous ResultsTable 5-4 Table of Horizontal GradientsTable 5-5A Vertical Gradients in Bedrock, Based on 1990 "High" Water LevelsTable 5-5B Vertical Gradients in Bedrock, Based on 1990 "Low" Water LevelsTable 5-6 Table of Groundwater Flow Velocities for Base of Fill/Top of RockTable 5-7 Table of Horizontal GradientsTable 5-8 Vertical Gradients in Pond 5 FillTable 5-9 Table of Groundwater Flow VelocitiesTable 5-10 Measured and Modelled Water Levels at Calibration NodesTable 5-11 Aquifer Parameters PermeabilityTable 5-12 Net Water BudgetTable 5-13A Vertical Gradients Between Rock and Fill Based on 1990 "High"Table 5-13B Vertical Gradients Between Rock and Fill Based on 1990 "Low"

Table 6-1 TemperatureTable 6-2 Precipitation SummaryTable 6-3 Comparison of Precipitation Gauge ResultsTable 6-4 Comparison of Precipitation Gauge ResultsTable 6-5 Swale Flow SummaryTable 6-6 Monthly Water Balance Calculations

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TABLE OF CONTENTS (cont'd)

LIST OF TABLES (Cont'd)

Table 7-1A Summary of Mercury Concentrations in Soil Borings FCPS (Harza, 1976)Table 7-1B Soil Sample Results Former Chlorine Plant Site (Olin, 1982)Table 7-2 Mercury Concentrations in Pond Material (Harza, 1980)Table 7-3 Summary of Metals Concentrations Pond 5 and Pond 6 ASAW April 1990Table 7-4 Summary of VOC Concentrations OU-2 Sampling Locations April 1990Table 7-5 Summary of Mercury Concentrations in Groundwater FCPSTable 7-6 Sumary of Metals Concentrations OU-2 Groundwater April 1990Table 7-7 Pond 5 Outfall Metals Concentrations 1990 and 1991 MonitoringTable 7-8 Pond 6 Outfall Metals Concentrations 1990 and 1991 Monitoring

LIST OF FIGURES

Figure 1-1 Site Location MapFigure 1-2 Holston River-Cherokee Reservoir SystemFigure 1-3 Map of Prior Remedial ActionsFigure 1-4 Pond 5 Planview with Decant StructureFigure 1-5 Detail and Section of Decant Structure

Figure 2-1 Surface Water Monitoring StationsFigure 2-2 Site Plan with Boring and Profile LocationsFigure 2-3 Conceptual Hydrogeologic Systems

Figure 3-1 Geotechnical Borehole, Piezometer, Monitoring Well, and ConePenetrometer Location Plan

Figure 3-2 Sections of Impoundments Constructed by Upstream MethodFigure 3-3 Inferred Section - Dike 2Figure 3-4 Photo of Dike 2 Breach View from DownstreamFigure 3-5 Photo of Dike 2 Failure View from UpstreamFigure 3-6 Photo of Early Dike 5 ConstructionFigure 3-7 Photo of Starter Dike ConstructionFigure 3-8 Photo of Dike 2 and River Reroute OperationsFigure 3-9 Photo of Pond 5 OperationFigure 3-10 Cross Sections 1-1', 3-3', and 5-5Figure 3-11 Ammonia Soda Ash Waste Thickness (Isopach)Figure 3-12 Settlement vs ASAW Thickness (P-5, ST-1)Figure 3-13 Settlement vs ASAW Thickness (P-8, ST-3)

Figure 4-1 Site Geologic Map with Geologic Survey LinesFigure 4-2 Geologic SectionFigure 4-3 Lineament Traces from Aerial Photo Interpretation at 1:12000 ScaleFigure 4-4 Local Scale Aerial Photo Lineament Azimuth Rose DiagramFigure 4-5 Local Scale Aerial Photo Azimuth Rose Diagram of Lineament Greater than

1000 feet

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TABLE OF CONTENTS (cont'd)

LIST OF FIGURES (Cont'd)

Figure 4-6 Stereogram of Joint Orientations Displayed by Rock Type of Joint Locationfrom Oriented Rock Core

Figure 4-7 Interpretive Subsurface Profiles A-A1 and B-B1Figure 4-8 Interpretive Subsurface Profiles C-C and D-D'Figure 4-9 Interpretive Subsurface Profiles E-E' and CompositeFigure 4-10 Geologic Section and Generalized Geologic Map

Figure 5-1 Hydrogeologic Units Along Extended Section CFigure 5-2A Comparison of Daily Water Level and Precipitation Data March-April 1991Figure 5-2B Comparison of Daily Water Level and Precipitation Data March-April 1991Figure 5-3A Potentiometric Surface Base of Fill/Top of Bedrock Based on 1990 "Low"

Water LevelsFigure 5-3B Potentiometric Surface Base of Fill/Top of Bedrock Based on 1990 "High"

Water LevelsFigure 5-4A Comparison of Daily Water Level and Precipitation Data December 1990Figure 5-4B Comparison of Daily Water Level and Precipitation Data December 1990Figure 5-5A Phreatic Surface in Fill Based on 1990 "Low" Water LevelsFigure 5-5B Phreatic Surface in Fill Based on 1990 "High" Water LevelsFigure 5-6 Finite Element Mesh, Materials, and Boundary ConditionsFigure 5-7 Pond 5 Materials and Calibration PointsFigure 5-8 Relative Permeability ValuesFigure 5-9 Flow Net, Entire MeshFigure 5-10 • Simulated Potentiometric Head Pond 5Figure 5-11 Simulated Flow Lines Pond 5Figure 5-12 Simulated Pond 5 Darcy Velocity VectorsFigure 5-13 Exploration Location Plan with Mercury Concentrations

Figure 6-1 Schematic Diagram of Pond 5 Water BalanceFigure 6F5.5.2 Model of Runoff, Baseflow, SS, and Chloride for North Fork Holston

RiverFigure 6F5.7.1 , Pond 5 Conceptual ModelFigure 6F5.7.2Figure 6F5.7.3A Pond 5 Outlet Flows 1982 and 1983Figure 6F5.7.3B Pond 5 Outlet Flows 1984 and 1985Figure 6F5.7.3C Pond 5 Outlet Flows 1986 and 1987Figure 6F5.7.3D Pond 5 Outlet Flows 1988 and 1989Figure 6F5.7.3E Pond 5 Outlet Flows 1990 and 1991

Figure 7-1 Well Location Plan at Former Chlorine PlantFigure 7-2 Borehole Location Plan with Polygons for Estimation of Mercury

ConcentrationsFigure 7-3 Potentiometric Surface and Flow Direction Based on November 6-8, 1979

Water LevelsFigure 7A Locations of Cross Sections, Olin Waste Pond No. 5Figure 7-5 Section A-A' through Waste Pond No. 5Figure 7-6 Section B-B1 through Waste Pond No. 5

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TABLE OF CONTENTS (Cont'd)

LIST OF FIGURES (Cont'd)

Figure 7-7 Section C-C through Waste Pond No. 5Figure 7-8 Section D-D' through Waste Pond No. 5Figure 7-9 Sections E-E' and F-F' through Waste Pond No. 5Figure 7-10 Site Plan of Waste Pond 6 with Borehole Sampling Locations and Analytical

ResultsFigure 7-11 Site Plan of Waste Pond 5 with Borehole Sampling Locations and Analytical

ResultsFigure 7-12 Exploration Location Plan With Mercury Concentrations at Monitoring Well

Locations

Figure 8-1 Graph of Pond 5 Discharge, TDS, Hg and Precipitation vs. Time for HighFlow/Precipitation Month

Figure 8-2 Graph of Pond 5 Discharge, TDS, Hg and Precipitation vs. Time for HighFlow/Precipitation Month

Figure 8-3 Pond 5 Discharge vs Mercury Concentration 1980-1991

LIST OF APPENDICES

Appendix A Record of DecisionAppendix B Consent DecreeAppendix C Borehole/Monitoring Well LogsAppendix D Packer Test DataAppendix E Electro-Piezocone ReportAppendix F Cone Penetrometer DataAppendix G Rising Head TestsAppendix H Water Level DataAppendix I FPM Theory DocumentationAppendix J Analytical Testing Data ReportsAppendix K 1989 Hydrology DataAppendix L 1990 Hydrology DataAppendix M 1991 Hydrology DataAppendix N Site Seismic ConsiderationsAppendix O Probabilistic SimulationAppendix P Dike Stability Laboratory Testing and ResultsAppendix Q Previous Investigation ReportsAppendix R Allison Gap Road Project Investigation for VDOTAppendix S ABB-ES Risk AssessmentAppendix T Site Water BalanceAppendix U Precipitation vs TimeAppendix V Responses to Comments

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1.0 INTRODUCTIONOlin Corporation (Olin), under a Consent Decree entered into with the United States

| Environmental Protection Agency (EPA) on September 15,1988, has conducted a Remedial| Investigation and Feasibility Study (RI/FS), for the Olin Saltville Waste Disposal Site in the

| town of Saltville, Virginia. The studies and interim remedial measures ordered by the| Consent Decree and undertaken by Olin were outlined in a Record of Decision (First| ROD) dated June 30, 1987. The First ROD identified mercury as the contaminant ofconcern and a preferred Remedial Alternative consisting of:

Upgrading surface water runon controls by means of ditches, berms, anddownchutes around Pond 5;

Treating Waste Pond 5 outfall using either sulfide precipitation techniquesor carbon adsorption;

Additional Studies;

Installation of a groundwater monitoring system at the conclusion ofstudies; and

Operation and maintenance of a treatment facility and continued samplingand analysis of the North Fork of the Holston River (NFHR) upgradientand downgradient of Pond 5 outfall.

The RI/FS studies have been conducted in accordance with the National Contingency Plan(NCP), Comprehensive Environmental Response, Compensation and Liability Act(CERCLA), and the Superfund Amendments and Reauthorization Act (SARA). TheVirginia/West Virginia Remedial Response Section of the EPA Third District is overseeingthe project studies and remediation. To facilitate project efficiency, the Preferred

Remedial Alternative identified by the First ROD was divided into three Operable Units.The Operable Units consist of:

• Operable Unit 1 (OU-1) - Design and Construction of Interim RemedialMeasures;

• Operable Unit 2 (OU-2) - Groundwater and Source Area Studies; and

Operable Unit 3 (OU-3) - Biological Assessment of the NFHR.

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This Remedial Investigation Report presents the findings and conclusions of the OU-2studies. Where appropriate, reference is made to the findings of other operable unit

studies that impact the findings or support the conclusions of the OU-2 RI Report. TheOU-2 studies were conducted in accordance with the Work Plan, Operable Unite 2 and

3, Groundwater and Bioassessment Studies (Olin, 1989), approved by EPA on September22,1989.

1.1 Purpose

| The purpose of the OU-2 RI studies has been to develop supplemental site data regarding| hydrogeology and source characteristics that were not available to EPA at the time of| preparation of their Record of Decision (First ROD), dated June 30,1987. These data were

required by EPA to supplement the limited information that formed the basis for theselection of preferred interim remedial measures subsequently ordered by the Consent

Decree. The planned OU-2 Feasibility Studies, in progress, review previously identifiedremedial alternatives and identify new potential remedial alternatives in view of the

increased knowledge of the site conditions, mechanics and site risks-to human health andthe environment.

The objectives of the studies performed for the OU-2 RI Report were to:

1. Determine the Extent of Source Contamination.

2. Characterize Site Hydrogeologic Conditions.

3. Assess Dike Stability.

4. Conduct a Baseline Risk Assessment consisting of:• Identification of contaminants of concern;• Toxicity assessment;• Exposure assessment; and• Risk characterization.

5. Identify Potential Remedial Technologies and Remedial Alternatives.

The remainder of Section 1 of this report provides background information regarding theSaltville Waste Disposal Site, describes existing concerns, presents the organization of thereport/and gives an overview of past studies conducted at the site. Finally, an overviewof the Remedial Investigation Report organization is given.

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1.2 Site BackgroundThis section describes the Olin Saltville Facility and its history. Past investigations andremedial activities are summarized. This section also traces the involvement of theCommonwealth of Virginia and EPA in the study and remediation of the site.

1.2.1 Site DescriptionThe Olin Saltville Facility consists of a former soda ash manufacturing plant, a former

chlorine plant site (FCPS) and several ammonia soda ash waste (ASAW) settling ponds.Pond 5 and Pond 6, were operated concurrently with the former chlorine plant and are

considered in this study. The facility lies between the town of Saltville and thecommunity of Allison Gap in western Smyth County, Virginia, extending partly into

Washington County, Virginia. Saltville is located approximately 12 miles north ofInterstate Highway 81. Map coordinates for the site are latitude 36 degrees 53 minutes

north and longitude 81 degrees 47 minutes west.

The site is located in the North Fork Holston River (NFHR plain. It is bounded to thenorth by Little Mountain and to the south by a ridge formed by the Greendale Syncline(see Figure 1-1). The NFHR flows to the south and is located along the southern border

of the site at river mile (NFHRM) 80.8 to 82.4. The confluence of the NFHR with theSouth Fork Holston River in Tennessee forms the Holston River. The Holston River flows

into Cherokee Reservoir in Tennessee. Figure 1-2 is a schematic of the Holston-Cherokeesystem.

1.2.2 Demography

ABB Environmental Services, Inc. conducted human population studies for the vicinityof the Saltville site. The study reveals that there are three residential clusters in the

vicinity of the site (see Figure 1-1). Approximately 40 residential dwellings are located tothe south of Pond 5 on Henrytown Road. To the northeast of Ponds 5 and 6 in

Perryville, there are approximately 46 residential dwellings. The third area is on thenorthern side of the site and has five homes.

1.2.3 Surface FeaturesThe topography of the site area is rugged, lying within the Appalachian Valley and RidgePhysiographic Province of western Virginia. The surface features of the site and

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surrounding area reflect the local geologic conditions. The NFHR in Smyth andWashington Counties has incised its channel into soft shales and siltstones. More

competent rock forms the ridges to the north and south of the site.

The site includes two drained settling ponds impounded by steep dikes along the river.The dikes are approximately 35 and 100 feet high for Ponds 6 and 5, respectively. Thesurfaces of the ponds are relatively level and support a moderate growth of grasses.Pond 5 covers approximately 75 acres. It is one and three quarters miles long and onequarter mile wide. Pond 6 covers approximately 50 acres. Pond 6 is three quarter miles

long and slightly less than one quarter mile wide.

The Pond 5 Decant Structure was constructed in the southwest corner of the pond at thetime the pond was built. It was designed to control the water elevation within Pond 5

and to drain excess water to the NFHR as the Solvay process wastes settled.

The decant structure consists of a vertical concrete shaft of square cross section. The baseelevation is just above the modern river bed. The top elevation is approximately equalto the elevation of the top of the dike separating the pond from the river. The north side

| is the inlet side of the shaft and is open. Guide slots were cast into the concrete on either| side of the inlet face for the positioning of stoplogs (long concrete blocks placed in the

| inlet slots) that controlled the pond water elevation during pond operation.

The top of the shaft was open when originally constructed. At present, the top and theopen side from the top to the current elevation of the ASAW are covered with steel grate.

No stop logs are currently in place at the pond surface. A 90 degree, sharp crestedV-notch weir and Steven's recorder are placed such that surface water flowing over thesurface of the ASAW in front of the decant structure flows over the weir and into thedecant structure shaft.

| At some distance below the current pond surface, the shaft bends to the north and| follows the slope of the inboard side of the dike to the base of the pond. At the base of

the structure, the shaft is connected to a five-foot diameter concrete culvert which flowson a shallow grade to the outlet just above the current normal flow elevation of theNFHR. Staff gauges, floats, and Steven's recorders for measurement of outfall discharge

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have been installed within four feet of the outlet of the concrete culvert. A

non-conventional, sharp crested, compound weir made from steel plate has been placedacross the mouth of the culvert and is the final component of monitoring equipment atthe decant structure outlet.

Approximately eight feet into the culvert, thick deposits of white precipitate fill the culvert

to almost one half of its total diameter. These deposits restrict entrance and visual| inspection of the flow path of water through the culvert to the decant structure shaft.

| Manned access of the shaft and the culvert was not performed as part of this| investigation. Figure 1-4 is a plan view of Pond 5 showing the location of the decant

structure. Figure 1-5 shows a schematic cross section of the decant structure derived fromlimited historical plans available.

A similar decant structure exists at Pond 6 and extends to the base of the pond. Thedecant structure for Pond 6 is located in the southeast section of Pond 6.

A diversion ditch was installed around the western perimeter of Pond 5 in 1982-1983 to

divert the majority of surface water flowing onto the pond from Little Mountain. AnEastern Diversion Ditch around the eastern portion of Pond 5 was constructed in 1991

as part of the Operable Unit 1 Interim Remedial Measures. The Eastern Diversion Ditchcollects the remaining surface water flow from Little Mountain. A high, chain-link fencebounds Ponds 5 and 6 on three sides. The river and a steep bank restrict access on theremaining side.

The Former Chlorine Plant Site (FCPS) is located approximately one half mile upstreamand east of the ponds. The FCPS has been remediated by installation of a clay cap andvegetative cover. As shown in Figure 1-3, the FCPS covers approximately one acre.

Rip-rap, consisting of small boulders, was installed along the river bank adjacent to theFCPS following the site remediation to prevent river bank erosion.

1.2.4 Site HistoryDuring the period from 1895 to 1972, the site was used by Olin Corporation and itspredecessors (Mathieson Chemical Corporation and Mathieson Alkali Works) as thelocation for various chemical manufacturing operations. A soda ash plant was

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constructed in 1894 and began operations in 1895. Settling ponds were constructed toreceive slurried waste solids from soda ash manufacturing by the Solvay process.

Mathieson Chemical Company constructed a mercury cell chlor-alkali plant in 1950. Theplant produced chlorine gas and sodium hydroxide by passing brine, obtained by solutionmining salt deposits in the area, between electrodes. The cathode used in this processwas mercury and is considered the source of mercury in the pond wastes. The electricalcurrent passing through the brine caused the formation of chlorine gas at the anode. Atthe same time, a sodium amalgam was formed at the cathode. This amalgam was passedinto a decomposing tower where the sodium was separated by reacting with water toform sodium hydroxide. Some of the mercury was lost in the production of chlorine andsodium hydroxide. The mercury was solubilized and passed into Pond 5 in thewastewaters. In addition, some mercury was lost to washdown waters and was

discharged to the NFHR or conveyed to Pond 5. In 1954, Olin Corporation merged withMathieson Chemical Corporation.

| Pond 6 began operation in 1964 and was used to settle ASAW. Based on current| knowledge of the mercury cell plant operation, it is possible that the weak brine purge| water from the chlorine plant may have been used to help slurry the ASAW for pumping| from the Solvay process plant to Pond 6. However, mercury-contaminated wastewatercontinued to be discharged into Pond 5.

In 1969, after work by Swedish scientists discovered that inorganic mercury dischargesto natural waters were detrimental due to methylation, the U.S. Army and Federal Water

Pollution Control Authority began to limit mercury discharges to navigable waters byrequiring permits. In order to control discharge to the river, Olin redirected most of theprocess and washdown wastewater to Pond 5.

The process and washdown wastewater was conveyed to the eastern end of Pond 5separate from the ASAW slurry. The wastewater was discharged onto the surface of

Pond 5 near the eastern edge. It was directed around the northern perimeter by bermsbuilt with slaker waste and ASAW at the edge of the pond on the dike surface. Theeastern end of Pond 5, from approximately the line formed by the old Pond 2 dike to theeastern edge, was operated "dry" (i.e., ASAW slurry was not deposited in this area). This

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observation is based on review of aerial photographs dated 1953,1963, and 1969 (USEPA,1983) and 1960 (Va. Highway Dept. Photograph). The intent was to allow the wastewater

,sto percolate into the pond, adsorbing mercury onto the fine, alkaline particles of theASAW.

After Olin shut down the Saltville plant in 1972, it began demolition activities of the FCPS.The demolition of the process equipment was completed in June 1973. Process mercurywas removed from the equipment and shipped to Olin plants in Georgia and Alabamafor re-use. The equipment was cleaned with wash water which was allowed to percolate

| into the soils at the chlorine plant site. The process equipment was then shipped to other| sites for re-use or placed in the easternmost end of Pond 6 along with building demolition

| debris and covered with clean fill.

| Following closure of the plant, a program of site security and maintenance was| implemented by Olin to limit site trespass and ensure that remaining structures such as

v. I the pond dikes and site fences remained intact and functional. These activities were• ^ .

| expanded to include site monitoring of outfall discharge water and groundwater as

| monitoring wells were installed for studies of various site areas. Following construction| of the FCPS site cap, the maintenance program has been expanded to include mowing| of the grass growing on the FCPS cap and annual inspection and removal of woody| brush along the FCPS river bank.

Environmental studies of the site began in conjunction with heightened concern aboutmercury discharges nationwide. An investigation of the plant site arid nearby NFHR byOlin, the Commonwealth of Virginia, and local agencies during the late 1960's revealedmercury contamination of the site and in the NFHR. As a result of mercury

concentrations found in fish, both Virginia and Tennessee placed a ban on fishing in theNFHR in 1970. Both bans were later modified (Tennessee's in 1972, Virginia's in 1974) to

permit fishing on a catch and throw-back basis.

Since 1970, fish and sediment sampling in the NFHR has been conducted every year.Oak Ridge National Laboratory (ORNL) conducted a study of the site in 1975 (ORNL,1980). Mercury concentrations in the downstream sediments near the site areapproximately 3-9 mg/kg and decrease downstream of the site to less than 0.5 mg/kg at

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NFHR Mile 8 (Olin, 1987). Mercury concentrations in edible fish tissues exceeded the FDArecommended action level prior to 1984. In November 1984, FDA changed the action level

from 1 mg/kg total mercury to 1 mg/kg methylmercury in edible tissues.

In 1978, a Task Force was formed which included the Virginia State Water Control Board(SWCB), Virginia Attorney General's Office, Tennessee and Virginia State Departmentsof Health, the Tennessee Valley Authority, and the USEPA. The Task Force required Olin

to conduct studies to identify the sources of mercury contamination, and negotiatedcleanup measures with Olin Corporation to reduce mercury input to the NFHR. InNovember 1982, the Virginia SWCB, acting on behalf of the Task Force, issued a SpecialOrder to Olin calling for river sediment removal and partial run-on diversion aroundPond 5. Under the Order, Olin diverted a 1,300 foot section of the NFHR and dredged

| 1,000 feet of the exposed river bed. The excavated sediment was processed through a 1| inch screen. Material smaller than 1 inch effective diameter was completely enclosed in| a 110 mil reinforced hypalon liner. This entire system sits atop a 16 oz. non-woven| geotextile fabric over a 6-inch thick levelling course of sand and was covered with another| 16 oz. nonwoven geotextile protective pad and 6 inches of sand. The material larger than| 1 inch effective diameter was placed adjacent to the southeast side of the hypalon| enclosed material. Both sets of processed material were covered with 2 feet of compacted| clay, 6 inches of select fill, and 6 inches of topsoil and then seeded. The NFHR cleanup

was completed in 1983. Rip-rap was placed along the river's edge. In addition, Olin| placed rip-rap along the riverbanks further downstream to stop erosion. Appendix W| presents the details of the river dredging and FCPS capping operations. A westernupland diversion ditch was installed around Pond 5 to reduce surface water run-on to

the pond. Figure 1-3 indicates the areas addressed by these remedial actions.

1.2.5 Previous InvestigationsA number of significant investigations have been conducted at the Olin Saltville site.Many of the studies were conducted prior to the First ROD and formed the basis for theremediation and further studies required by the Consent Decree. A substantial numberof additional documents are included in the administrative record and are reviewed inthe OU-2 Previous Data Summary, the pertinent previous investigations and reports areas follows:

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Harza Engineering, October 1976, "Investigation of Mercury Occurrence, FormerChlorine Plant Site, Saltville, Virginia", (included as Appendix D in Olin, 1989).

Harza Engineering, November 1976, "Olin Corporation, Saltville Works, Stabilityof Waste Ponds No. 5 & 6"

Dames and Moore, April 1977, "Investigation of Ground Water and Surface WaterConditions Related to Quality of Water in the North Fork of the Holston Rivernear Saltville, Virginia".

Dames and Moore, July 1978, Draft Report, "Mercury and TDS in the North Forkof the Holston River in the Vicinity of Saltville, VA".

Harza Engineering, June 1979, "Waste Pond No. 5, Stability Review, Saltville,Virginia".

Harza Engineering, March 1980, "Investigation of Mercury Occurrence at WastePond No. 5, Saltville, Virginia".

Dames and Moore, August 1980, "Chlor-Alkalj/Soda Ash Waste Ponds, TotalDissolved Solids and Mercury Assessment, North Fork of the Holston River,Saltville, Virginia".

•-±i\ Law Engineering, August 1981, Final Draft, "Geophysical Report, Muck PondNumber 5, Saltville, Virginia".

Wehran Engineering, September 1981, "Waste Pond No. 5, Cap Feasibility Studyand Storm Water Diversion Design".

U.S. Environmental Protection Agency, 1981, "Remedial Actions at HazardousWaste Sites: Survey and Case Studies", Section 2, Site A, Olin Corporation,Saltville, Virginia, EPA/430/9-81-05.

GCA, August 1986, "Saltville Waste Disposal Site Risk Assessment".

GCA, August, 1986, "Saltville Waste Disposal Site Feasibility Study".

Law Environmental, May 1987, "Report of Diversion Ditch Failure & ReportEvaluation, Muck Pond No. 5, Saltville, Virginia, Project No. ED 6439".

USEPA, June 1987, Record of Decision, Remedial Alternative Selection, SeeAppendix A.

US District Court for the Western District of Virginia/EPA, September, 1988,Consent Decree, See Appendix B.

The reports identified below comprise the studies that have been compiled into this RIReport:

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ABB Environmental Services, Inc, 1993, "Risk Assessment for Saltville WasteDisposal Site, Saltville, Virginia, Final Report".

Golder Associates Inc., October 1989, "Geotechnical Report for East DiversionDitch, Olin Saltville Site".

Golder Associates Inc., April 1989, "Conceptual Hydrogeologic Report, Olin SaitvilleSite, Saltville, Virginia.

Golder Associates Inc., August 1990, "Final Report on Swale Investigation andCutoff Wall Feasibility Study, Saltville, Virginia".

Golder Associates Inc., August 1990, "Final Report on Pond 5 Dike Stability andPond 5 Waste Characterization".

Golder Associates Inc., September 1991, "Hydrogeologic Investigation Report, OlinSaltville Site, Saltville, Virginia".

Harza Engineering Company, 1976, "Investigation of Mercury Occurrence, FormerChlorine Plant Site, Saltville, Virginia".

Hiltgen, K.D., 1982, "Geohydrologic Study, Former Chlor-Alkali Plant Site, Saltville,Virginia".

:Woodward-Clyde Consultants, 1993, Draft "Operable Unit 3 Remedial InvestigationReport, Saltville Waste Disposal Site, Saltville, Virginia".

These studies have been reviewed and the information incorporated into or appendedto this report as appropriate.

1.3 Report OrganizationThe USEPA document "Guidance for Conducting Remedial Investigations and FeasibilityStudies Under CERCLA" (October 1988) provides a basic outline for the organization ofa Remedial Investigation Report. The report format includes:

Section 1.0 - Introduction

Section 2.0 - Study Area Investigation

Section 3.0 - Physical Characteristics of the Study Area

Section 4.0 - Nature and Extent of Contamination

Section 5.0 - Contaminant Fate and Transport

Section 6.0 - Baseline Risk Assessment

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Section 7.0 - Summary and Conclusions

In order to better describe the complex Physical Characteristics of the Study Area, Section3 was divided into four separate sections addressing:

• Dike and ASAW Stability;

• Geology;

• Hydrogeology; and

• Hydrology.

The Dike and ASAW Stability was an important component of the Work Plan (Olin, 1989)for this site. In order to better understand the waste in Pond 5 and to assess dike

stability (considered important for the feasibility study) this section was included. Thethree remaining sections on geology, hydrogeology and hydrology are usually groupedunder Physical Characteristics but were broken out for this report in view of the size ofthe site and the detailed nature of each site characteristic. The remainder of the reportfollows the guidance document format.

The following sections of this report are organized as follows:

Section 2.0, Study Area Investigation, presents the data needs and objectives of the RI

and describes the scope of the exploration, monitoring, sampling and analytical programs,including the geologic, hydrogeologic and hydrologic investigations, and ecological

investigations.

Section 3.0, Dike and ASAW Stability, presents the results of stability analyses for thePond 5 Dike and engineering characterization of the Pond 5 wastes.

Section 4.0, Geology, provides and overview of regional and site geologic conditions

including stratigraphy and structure.

Section 5.0, Hydrogeology, presents regional and site hydrogeologic conditions includingresults of a numerical groundwater modeling effort.

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Section 6.0, Hydrology, provides a discussion of regional and site hydrologic conditionsincluding a site water balance and conceptual flow model.

Section 7.0, Nature and Extent of Contamination, presents the results of site

characterization regarding the areal and vertical distribution of mercury in the WastePonds, FCPS, natural soils, groundwater and surface water, native soils, and air.

Section 8.0, Mercury Fate and Transport, discusses potential routes of migration,

persistence and migration, and factors affecting each.

Section 9.0, Baseline Risk Assessment, reviews the risk to public health including

| exposure and toxicity assessments and risk characterization.

Section 10.0, Summary and Conclusions, summarizes the geology, hydrogeology andhydrology at the Olin Saltville Facility, chemical investigations, contaminant fate and

| transport, risks to public health, preliminary remedial technologies and alternatives, andpresents the conclusions of the RI.

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2.0 STUDY AREA INVESTIGATIONS

The RI/FS Work Plan for the Saltville Waste Disposal Site Operable Units 2 and 3(Groundwater and Bioassessment) (Olin, 1989) was designed to address deficiencies in the

existing data identified by the First ROD and to describe a plan to collect and analyzethose data required. These OU-2 data gaps and the field activities conducted to collectthe needed data are described below.

2.1 Data Needs and Objectives

Preparation of the RI/FS Work Plan involved an extensive review of available informationon the Saltville Site. Although many studies had been conducted, data regarding the

| hydrogeologic conditions at the site were limited. The GCA Risk Assessment (1986)| considered the available data on the FCPS to sufficiently characterize the site. The 1986

| Risk Assessment further considered the FCPS remediated and to "not contribute| significantly to the mercury flux into the NFHR." Based upon the long record of| monitoring available and the non-detectable, to very low concentrations of mercury in| Pond 6 outfall discharge water, Pond 6 was also considered to not contribute significantly

| to the mercury flux into the NFHR. The extent of mercury in Pond 6 was unknown at| the time and the occasional discharges from Pond 6 which contained low levels of

| mercury were attributed to the presence of demolition debris from the Chlorine Plant| structures along the eastern end of Pond 6.

| There were, however, significant questions regarding possible seepage losses through the| Pond 5 dike and potential losses of Pond 5 water to underlying bedrock groundwatersystems. It was further considered that given these data gaps, the risks to human health

| and the environment resulting from Pond 5 could not be evaluated thoroughly at the

time of preparation of the First ROD. Consequently, additional remedial alternativesmight present themselves given an increased understanding in site characterization.

As described in Section 1.0, the general objectives of the RI/FS are to determine the extent

of source contamination, characterize site hydrogeologic conditions, assess dike stability,and identify potential remedial technologies and remedial alternatives. To achieve theseobjectives, it was necessary to understand, to the extent practical, the following:

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• Source characterization;

• The geologic conditions of the Olin Saltville Facility and the surroundingarea;

• The hydrogeology of the porids and surrounding areas includinggroundwater recharge and discharge relationships;

• The water balance for the site and environs;

• Nature and extent of contamination; and,

• Potential impact of identified routes of exposure.

| Because the GCA Risk Assessment and Feasibility Study (1986) considered mercury to be| the contaminant of concern and Pond 5 to be the only significant source of mercury flux| to the NFHR, the RI field studies and monitoring, outlined in the June 1989 RI Work Plan,| concentrated primarily on Pond 5. At the time the Work Plan was developed, it was| recognized that because of the strike of the geologic formations at the site, the overall| geology would be reasonably constant over the length of the site. Review of literature| and available topographic and geologic maps indicated that the structural geologic trends| were the same for both ponds and for the FCPS. Accordingly, exploratory drilling in

| Pond 6 was not included in the field program beyond the cone penetrometer testing at| one location. For the purpose of monitoring, three well clusters (MW-8, MW-9 and MW-| 10) were included in the program to identify possible migration of mercury through the| groundwater from the demolition debris at the eastern end of Pond 6. The presence of| mercury in the Pond 6 solids was not suspected because of a long record of non-detect| to very low mercury concentrations in Pond 6 discharge waters. However, a sampling| program to screen Pond 6 solids for mercury was included in the RI Work Plan.

I| Based on similar pond construction, similar geologic structure and lithology, and| comparable watersheds and hydrology, the hydrogeology of Pond 6 was considered toj function the same as Pond 5. As such, the RI Work Plan concentrated monitoring of| surface water flow, and discharge rates at the Pond 5 watershed.

I| The FCPS, the subject of several previous characterization studies, was not considered a| significant source of mercury in flux into the NFHR (GCA, 1986), and was considered to| be substantially remediated. Further characterization was therefore not included in the

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| planned RI activities beyond reviewing available data and ongoing sampling of| monitoring wells.

| Data needs identified in the RI Work Plan were addressed as outlined below.

2.2 Base Map Preparation and Historical Drawings Review

To facilitate site characterization and provide accurate base maps from which to preparedesign drawings for remediations required under Operable Unit 1, a detailed topographic

plan of the site was photogrammetrically prepared by the Tennessee Valley Authority(TVA). Subsequent surface mapping and surveys of exploratory boreholes werereferenced to this TVA plan and the TVA grid.

Construction drawings from the design of the Pond 5 and Pond 6 structures werereviewed to gain further insight into the potential for seepage through the dikes. Thedrawings were also used to assess the condition and type of existing dike core drains.

These documents, together with historical photographs of the Pond 5 dike construction,were useful in assessing the strength parameters and seepage characteristics of the

various components of the dikes.

2.3 Hydrologic Investigations

New surface water flow monitoring locations were installed. Additional surface waterdischarge measurements were undertaken to fill known data gaps from the existing

| surface water monitoring program, concentrating on Pond 5. Additional monitoringstations were installed to attempt to quantify surface flows into the Pond 5 system fromLittle Mountain, and to correlate measurements of flow into the Pond 5 Decant Structureat the elevation of the current pond surface with those flowing out of the DecantStructure at the outfall into the NFHR. Existing and additional monitoring stations arediscussed below.

A satisfactory hydrologic flow model that adequately accounted for observed flows fromthe Pond 5 system was not previously attained. Accordingly, existing and additionalsurface water data were used to develop a conceptual model of hydrologic flow throughthe Pond 5 sub-watershed. Development of the conceptual model and supporting waterbalance analyses are presented in Section 6.

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Over two years of continuous data have been collected under the expanded surface water 'monitoring program. Locations of the monitoring stations are shown in Figure 2-1.Concurrent precipitation and stage data within the Pond 5 sub-watershed have beencollected, with precipitation data beginning at the:

• Saltville Waste Water Treatment Plant (WWTP) on May 1,1989;

• Pond 5 Trailer on January 1,1990;

and continuous stage data within the Pond 5 sub-watershed beginning at the:

• Decant Outlet on May 18, 1989;

• Decant Inlet on June 2,1989; and

• Swale 3 Flume on January 1,1990.

The source data from on-site monitoring stations are recorded on strip chart recorders.

2.3.1 Precipitation Monitoring Stations

TVA Station 318A rain gauge is installed at the Saltville WWTP. Daily precipitationmeasurements have been obtained for the period from January, 1989 to September 17,1991. Data are reported as daily rainfall totals. More detailed data collection was desiredto measure precipitation falling directly onto Pond 5. Data was needed to assist incorrelating both precipitation duration and magnitude with observed surface andgroundwater flows on the site. Accordingly, a continuous recording rain gauge wasinstalled at the Pond 5 site trailer. Establishment of a precipitation gauge on-site alsoenabled evaluation of local variability in storm duration and magnitude. Continuousprecipitation measurements began on January 1, 1990 and are reported here throughSeptember 17,1991.

2.3.1.1 TVA Rain GaugeThe rain gauge at the Saltville WWTP is operated by TVA. It is located south and eastof the Robertson Branch Bridge along the NFHR. The rain gauge has a record length of40 years. The rain gauge is read at approximately 8:00 a.m. each day. Measurements

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reflect precipitation that has fallen during the preceding 24 hours. Precipitation data from

the rain gauge are transmitted via the Saltville Olin office on a monthly basis.

2.3.1.2 On-site Continuous Recording Rain GaugeGolder installed a continuous recording tipping bucket precipitation gauge on a small riselocated approximately 75 feet northeast of the Pond 5 site trailer at the east end of Pond

5. The gauge records rainfall in increments of 0.01 inches on a strip chart recorder. Thepaper in the recorder is changed and the gauge inspected once a week.

The total precipitation occurring on each day is expected to vary somewhat from thatrecorded by the daily TVA gauge at the WWTP (approximately one half mile away). Ingeneral, however, weekly and monthly total rainfall quantities from the two gauges were

found to agree closely.

2.4 Surface Water Monitoring StationsA major component of a water balance is surface water flow. A number of surface waterflows were monitored as part of this investigation including the following:

• The North Fork of the Holston River;

• The Pond 5 decant inlet;

• The Pond 5 decant outlet; and,

• The Swale 3 discharge.

The surface water monitoring was undertaken as part of the hydrogeologic study toidentify the processes and quantify the amounts of water flowing into and out of Pond5. Field observations and evaluation of the monitoring data were combined to formulate

a conceptual model of flow through the pond sub-watershed. The conceptual model wasthen used to develop monthly and daily water balance calculations (Sections 6.3,6.4, and

6.5 and Appendix T). The conceptual model was used to formulate boundary conditionsfor a computer model of the local groundwater system (Section 5.4).

The following sections describe the monitoring locations, the monitoringmethods/instrumentation and the frequency of data collection.

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2.4.1 North Fork Holston River Stage and Discharge

The NFHR is the receiving body for surface water discharge from the site. The NFHR isalso considered to be the principal zone of groundwater discharge. River flow and stage

level information for the NFHR was obtained from an existing monitoring station andfrom two staff gauges installed for this investigation.

The existing surface water monitoring station was the U.S. Geological Survey (USGS)

stream gauge (USGS Station 3488) located on the NFHR approximately three milesupstream from the site. The gauge has a 70 year length of record. A stage-dischargerelationship developed by the USGS is used to convert stage records to discharge values.The USGS gauging data are transmitted to Golder on a quarterly basis. Data obtainedfrom USGS Station 3488 were used to identify peak stage and discharge for various largestorm events, and to confirm the correlation between river stage. The data were used todetermine the elevation at which the Pond 5 Decant Structure Outlet is flooded by the

river. The USGS data were also used to correlate peak precipitation events, river stagepeaks, and peak discharges at Swale 3 and the Pond 5 Decant Structure outlet. Thisevaluation was used in the development of the conceptual model for the daily waterbalance (Section 6.4).

The two staff gauges (Stations 1 and 2) were placed in the NFHR above and below Pond5 (Figure 2-1). The purpose of the two staff gauges was to measure change in dischargebetween the three stations along the NFHR. Gauge height and discharge were measuredon several occasions in late May, 1989. Three stream flow measurements were made atthe upstream gauge (Station 1) and six measurements were made at the downstreamgauge (Station 2). On May 28 and May 30, 1989, measurements were made at bothstations.

2.4.2 Pond 5 Decant InletTo record the runoff from the surface of the Pond 5 ASAW, a conventional 90 degreeV-notch weir was installed at the inlet of the Pond 5 decant structure. The decantstructure consists of a decant tower constructed with a series of removable stoplogs for

control of the level of water in the pond. The metal, sharp crested weir was positionedso that water collecting on the surface of the ASAW in the pond passes over the weirbefore entering the decant structure and being discharged.

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A Steven's recorder, with a stilling well and float, was attached to the structureimmediately adjacent to the weir to continuously measure and record the depth of runoff

flow from the pond. A small staff gauge was attached along the entrance to the weir toverify the stage recorded by the float in the stilling well when charts were changed and

the gauge inspected. This Steven's recorder became operational on June 2, 1989. Thedischarge associated with the continuous stage recorder is provided by the dischargeformula for a sharp crested 90 degree V-notch weir (Bureau of Reclamation, 1984) as:

Q = 2.5 X h25

where: Q = discharge (cfs)and h = water level (feet).

This relationship has been tabulated and is presented as Table 2-1.

2.4.3 Pond 5 Decant OutletThe compound weir at the Pond 5 Outlet is a non-conventional design. The

sharp-crested weir, cut into plate steel, is attached across the outlet of the culvert leadingfrom the Pond 5 Decant structure. The outlet discharges into the NFHR.

The compound weir at the Pond 5 Outlet was fitted with a Steven's continuous chartrecorder. The recorder was attached to a float in a stilling well to measure and recordstage in the outlet culvert. The Steven's recorder became operational on May 18,1989.The rating curve for the compound weir was established by Olin and was used tocalculate discharge at the outlet from the continuous record of stage provided by theSteven's recorder. The rating table is presented as Table 2-2.

A differential level survey of major components of the outlet monitoring system wasconducted on December 12, 1990. The discharge weir crest, the Olin staff gauge, thelower stream Golder staff gauge in the NFHR, and several local reference points were

included to check survey error. The survey error was found to be less than 0.015 feet.The survey also indicated that when the river stage rises to 4.55 feet on the upstream staffgauge, the river begins to flood the Pond 5 Decant Outlet culvert (assuming a horizontalwater surface profile). As a result, the recent Steven's recorder values above

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approximately 0.95 feet are influenced by river flooding and are not indicative of actualdischarge from the Pond 5 Decant Outlet. This elevation is just above the transition zoneof flow across the compound weir.

The survey results are consistent with the record of storms occurring on January 30,1990,on February 10, 1990, and on May 28, 1991. The initiation of inundation andsimultaneous manual readings of both the river and Olin culvert staff gauges were

recorded for these storms. A 0.2-foot difference between the river elevation predicted bythe horizontal survey and the actual flood elevation on the river staff gauge is attributed

to a non-uniform water surface between the river staff gauge and the culvert staff gauge.

Measurements of readings provided by both the Olin and Golder staff gauges in thedischarge culvert were also made at the time of the survey. The water levels providedby the two staff gauges differed by only 0.015 feet.

2.4.4 Swale 3 Discharge

The location of Swale 3 is illustrated in Figure 2-1. Water flows continuously in the upperportion of Swale 3, in part due to an old cistern, which brings shallow groundwater to

the suiface whereupon it enters the swale channel. The flow is a source of inflow toPond 5 and provides an indication of the probable magnitude of subsurface flow in theadjacent swales.

A 0.75-foot H-flume, a stilling well, float and Steven's recorder were installed in Swale 3.The discharge in the swale is monitored by continuously recording the depth of flow

through the flume. Depth of flow is converted to discharge by a rating table providedby the flume manufacturer, and is presented in Table 2-3. The monitoring station was

constructed upstream of a contact with an upper sandstone unit (overlying a massivesiltstone series) of the Price Formation. Downstream from this point, much of the surfaceflow disappears underground (see Section 6.2.4.1). The Steven's recorder became

operational on January 1,1990.

A staff gauge was also placed in an energy dissipating structure at the outlet of Swale 3.The purpose of this staff gauge was to assist in estimating discharge during site visits.

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The source data from on-site monitoring stations are recorded on strip chart recorders.

The original data have been reviewed for consistency with manual observations takeneach week when the recorder chart paper was replaced. Minor scale corrections havebeen made, and periods when the gauges were malfunctioning, frozen, or swamped byhigh flows have been noted. The resulting data have been summarized in tabular form,

chronologically listing daily precipitation and both the measured stage and computeddischarge for each stream flow station. When tabulating the continuous flow data, care

was taken to represent each flow peak and inflection point in the hydrograph record, sothat subsequent graphical presentations are accurate representations of the hydrographs.

These summary data are presented for 1989 as Appendix K, for 1990 as Appendix L, andfor 1991 as Appendix M. Also included in each appendix for each month of the year aregraphical representations of the data: daily hydrographs (rainfall) and continuousdischarge hydrographs (flow).

23 Geologic Investigations

25.1 Field Reconnaissance and Literature Review| The areas surrounding Ponds 5 and 6, and the FCPS were the subject of geologic

reconnaissance and mapping. The purpose of the mapping was to delineate the arealextent of lithologic units around the site, measure the orientation of geologic structuresand discontinuities in the area, and provide a correlation of observed stratigraphy withthat reported in the literature and with the geology found in the exploratory drillingprogram.

The mapping was conducted in three phases consisting of: .

1. Review of available geologic literature of the area to develop typicalstratigraphic sections for locally occurring rock formations/units;

2. Reduction of existing topographic maps, development of cross sections,review of available aerial photographs, and performance of a fracture traceanalysis to identify local and regional geologic trends; and

3. Field verification of identified trends, and detailed mapping of identifiedrock units, particularly the occurrence and variations in formation/memberthickness, orientation, weathering, cementation, and mineralogy.

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Concurrent with the subsurface explorations, a geotechnical reconnaissance of the| northern pond margins, southern slopes of Little Mountain, and the environs east, west,| and south of the Ponds and FCPS was made to map visible rock outcrops, identify the

lithologies of exposed rock outcrops, and measure the orientation and geometry ofobservable geologic structures.

A review of pertinent literature, including papers by Butts (1940), Cooper (1966), and Ross(1965), provided background data regarding regional geologic structures, formation namesand lithologies. Of these papers, Cooper's work contained the most reliable informationregarding the geologic conditions at the Olin Saltville Facility, and formation occurrenceat Allison Gap and along Little Mountain.

Aerial photographs of the site were provided by Olin. The photographs comprised blackand white stereo pairs of the project site at a scale of 1:12,000, taken on March 11,1988,and were relatively free of summer foliage that would obscure subtle lineaments. Thephotos were analyzed with a Dietzgen stereo viewer and lineaments traced on mylar

overlays of the photographs. In addition to lineaments, obvious alluvium, solution

features, streams, and Ponds 5 and 6 were plotted on the mylars for reference.

Information obtained from the field mapping, literature review and aerial photographinterpretation was used to develop rose diagrams and stereographic plots of lineament,joint, fracture and bedding orientations for geologic structure analysis. Geologic mapsand stratigraphic cross-sections were also developed. This information is presented in

Section 4.0.

25.2 Geotechnical Subsurface Investigation| A subsurface investigation was conducted at the site and included twelve borings within

| the swales along the Pond 5 perimeter, eastern Pond 6 margin, between Pond 6 and the| NFHR, and along the southern portion of Little Mountain; fifteen borings within the| Pond 5 dike; fourteen borings for preliminary siting of an outfall effluent treatment plant;

and fourteen borings for development of geotechnical design criteria for the Eastern

Diversion Ditch. The locations of these borings are provided in Figure 2-2. Borehole logsfor these investigations are provided in Appendix C.

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Boreholes were advanced in soils with 8-inch outside diameter (O.D.) continuous flighthollow stem auger equipment. Drilling in bedrock was accomplished using NQ or HQdiamond coring bits and wireline drilling equipment. Soil samples were obtained at 5foot intervals using a 2—inch O.D. split spoon. Samples were driven with a 140 Ib.

hammer falling through a height of 30 inches. Sampling was conducted in accordancewith ASTM Standard Penetration Test Method D-1586. Continuous core samples ofbedrock were retrieved from the diamond coreholes. Some core loss was experienced inzones of highly weathered or highly fractured rock.

| Cone penetrometer testing (discussed in Section 2.6.5) was conducted in Pond 5 and Pond| 6 to characterize the mechanical properties of the ASAW. Past geotechnical studies of| Pond 6 include two stability investigations of the pond dike and ammonia soda ash waste| conducted by Harza in 1971 and 1976. These reports are presented in Appendix I of the| Previous Data Summary Report (1992). One cross section through Pond 6 was analyzed| for the stability of the waste and dike during the Harza investigation in 1976. Three| boreholes were drilled along a cross section in Pond 6 to determine the composition of| the waste and to determine the depths and thicknesses of natural materials.

I| The borehole logs reveal the composition of Pond 6 to be the same as Pond 5, consisting| of gray-white, ammonium soda ash waste (ASAW). The depth of the waste and dike| ranged from about 15 feet to about 60 feet. Alluvium and cemented alluvium were| encountered at the base of Pond 6 (as they were in Pond 5 during this RI), as well as,| weathered limestone. The depth of the limestone ranged from 18 feet to 60 feet below| ground surface.

| The calculated factors of safety for the stability analysis of the Pond 6 dike and waste| were higher than for the taller Pond 5 dike. The critical failure surface, as with Pond 5,| was a surficial surface within the slaker waste.

I| Because the FCPS was the subject of two previous hydrogeologic investigations, no| further investigative work, beyond continued monitoring of groundwater, were| conducted at the FCPS during this RI.

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2.6 Hydrogeologic Investigations2.6.1 General Description

The hydrogeologic field investigation was conducted in accordance with the Work Plan(Odin, 1989). The Scope of Work was developed based upon the conceptualhydrogeologic model presented in a Golder report entitled "Conceptual HydrogeologicReport" dated April 1989 (OU-2, Milestone Report No. 1).

The conceptual hydrogeologic model, consisted of shallow and deep flow systems. Theconceptual model is presented schematically in Figure 2-3. This model was formulatedduring the initial stages of the RI/FS studies. It was based on field observations of surfacewater flow, surface discharge of groundwater, geology and stratigraphy and initialrecords of decant structure flow. The model also served as a guide for development ofthe field investigation program. Boreholes and piezometers were located to assess thevalidity of the conceptual model and to provide information for refinement of the modelto the level of detail needed for the RI/FS.

The hydrogeologic field investigation included exploratory drilling, monitoring well andpiezometer installation, in-situ pressure packer testing and slug testing, and monitoringwell and electropiezocone penetrometer testing (ECPT). A summary of these efforts isprovided below.

2.6.2 Exploratory Boreholes

A total of 76 boreholes were drilled on site between October 1988 and April 1989. Thelocations are shown in Figure 2-2. The boreholes completed during the period fromOctober 19, 1988 through December 12, 1988 were drilled by National FoundationEngineering (NFE) of Baltimore, Maryland. The boreholes completed during the periodfrom January 4,1989 through April 2,1989 were drilled by Law Engineering of Nashville,Tennessee and Highland Drilling Company of Oak Ridge, Tennessee.

Boreholes were numbered in accordance with the tasks assigned by Olin (TP-treatmentplant, ED-East Diversion Ditch, D-dike stability, SW-swale, CO-cutoff wall, CP-conepenetrometer). Boreholes were located to cover the areas and ranges of material typesexpected to be encountered for each task.

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Boreholes were advanced through soil and fill materials with 6-inch and 8-inch O.D.continuous flight hollow stem augers (HSA). Samples were obtained at 5 foot intervals

by driving a 2-inch O.D. split-spoon sampler with a 140 pound hammer free fallingthrough 30 inches (ASTM D-1586), from which Standard Penetration Resistance (SPR)

values were obtained. Relatively undisturbed samples were obtained using 3-inch O.D.thin wall Shelby tube, piston, and Osterberg sampling devices. The collected samples

were subjected to laboratory tests to establish index properties, compressibility, hydraulicconductivity, shear strength, specific gravity, and unit weight.

Boreholes were advanced through coarse starter dike boulders by Highland Drilling usingair-rotary methods to facilitate placement of casing into bedrock. Following casing

installation, bedrock was drilled with 2-inch O.D. NQ-sized or 2.5-inch O.D. HQ-sizeddiamond coring equipment.

Piezometers and monitoring wells were installed in the boreholes immediately after they

were drilled, between December 1988 and March 1989. The majority of the piezometerand monitoring well boreholes were part of the geotechnical investigation. Additional

boreholes were added, or the geotechnical boreholes deepened, to accommodateinstallation of piezometers and monitoring wells.

Piezometers and monitoring wells were assigned the prefixes "P" and "MW", respectively.They were located to comply with the well installation rationale outlined in the Work

Plan (Appendix C). As a result of the installation of a piezometer or monitoring well ina geotechnical borehole, some boreholes have two names: a geotechnical task name and

a piezometer or monitoring well name. For example, borehole D-13, drilled as part of thedike stability investigation, is the borehole in which piezometers P-14 (S,D) were installed.

For this report, the location reference will be the well or piezometer name (e.g., P-14(S,D)). A cross reference between hydrogeologic and geotechnical borehole, names is

presented in Appendix C.

The majority of piezometers and monitoring wells were installed in pairs or clusters ofthree. Pairs were installed in the same borehole (S = shallow, D = deep), while clusterswere installed in 2 adjacent boreholes (shallow (S) in one borehole; intermediate (I) anddeep (D) in an adjacent borehole). The screened well/piezometer.intervals were isolated

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with bentonite to preclude communication of groundwater between the well screens. Thepurpose of the multiple well/piezometer installations was to allow observation of vertical

groundwater gradients at the well locations.

The shallow piezometers and wells were constructed within soil or fill overburdenmaterials. Intermediate and deep piezometers and wells were constructed in the bedrockzones below soil overburden and upper weathered and fractured rock materials. Welland piezometer screen intervals were selected in identifiable zones of differing materials:(i.e., bedrock, ASAW, or alluvium). Some pairs were constructed in more than onematerial type to identify vertical gradients. The majority of piezometers and wells weredrilled with hollow stem augers. All of the piezometers and monitoring wells, with the

exception of P-10(D) (drilled by National Foundation Engineering of Baltimore, Maryland), "were installed by Law Engineering of Nashville, Tennessee.

The piezometer and well cluster boreholes containing intermediate and deep installations

(P-12, P-15, MW-3, MW-5, and MW-7) were installed in drillholes advanced throughcasings set by air rotary methods. The casings were set by drilling 5 feet into bedrock,setting 6 1/4-inch ID steel pipe casing (1/4 inch wall thickness) into position, and grouting

the casing' into place with cement-bentonite grout. The purpose of the casing is to

segregate the pond materials from the bedrock and prevent shallow contamination fromentering the bedrock.

Logs of the subsurface explorations conducted for this investigation, together withmonitoring well installation details, are presented in Appendix C. Borehole logsdeveloped for past site investigations are also presented chronologically from the mostrecent explorations.

2.6.3 Pressure Packer Testing

Pressure packer testing was conducted in several boreholes to determine the permeabilityof encountered rock units. Boreholes MW-1, SW-5, and P-3 were tested because theywere drilled deeper into bedrock. They provided a thick section of rock for testing, ratherthan a thin potentially fractured upper rock zone. The testing was performed usingmethod E-18, outlined in the Bureau of Reclamation Earth Manual. The test apparatusconsisted of two Bimbar rubber inflatable glands separating a 10 foot long test section of

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perforated pipe. Test sections were overlapped by approximately 6 inches to include the

entire cored length of the borehole. The very top and bottom of the cored sections werenot tested due to the position and length of the packer glands. The following describes

the general test procedures.

The double packer assembly was lowered to the desired depth using steel piping andclamped off at the top of the borehole. Once the packer tool was positioned to straddlethe interval of interest, both packers were inflated simultaneously using compressed

nitrogen to at least 300 psi. In cases where the fluid uptake was comparatively high, thepackers were inflated to their maximum rated pressure of 450 psi. After allowing several

minutes for the packers to set against the sides of the borehole, a water injection line wasplumbed into the top of the packer tool assembly which was connected to a utility pump

and a potable water supply. A flow meter and valve'assembly was installed in-linebetween the packer tubing and water supply to monitor flow rates during injection. A

pressure gauge was also fitted to the top of the packer tubing just above the waterinjection port.

The maximum injection pressure (P) was calculated, prior to the commencement of

testing, from the overburden pressure (Op) (determined from height of rock column and

material density). In turn, the pressure was corrected for rock quality (P = Op xcorrection factor). The rock quality correction factors used were 0.5 for poor rock, 0.7 formoderate, and 1.0 for good. Testing was initiated by filling the packer assembly withwater and adjusting the injection rate until the desired pressure was reached. Pressuretesting was accomplished as a series of injection "steps". Injection pressures wereincreased in 2 or 3 stages until P was reached, and then stepped back down towards the

initial test pressure. For example, a pressure testing sequence might utilize injectionpressures of 0.5P, 0.75P, P, 0.75P, and finally 0.5P. Injection pressures and flow rates wereheld as constant as possible throughout each individual testing stage. Several readingsof both pressure and flow were recorded for each injection step. Once testing wascompleted on a given interval, the packers were deflated, the injection manifolddecoupled from the packer tool, and the entire assembly positioned for the next test

interval.

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Prior to the analysis of the raw data, a plot of flow rate (Q) versus injection pressure (P)was constructed for each test interval. The mean injection pressure and flow rate for

each stage of a given test were plotted, and a straight line fitted to the data. If theinjection rate changes linearly with each progressive increase in injection pressure, then

one may be reasonably certain that the injection procedure did not result in a significantdisturbance of the rock mass. Under there conditions, any step in a given test sequence

may be used to derive an estimate of hydraulic conductivity. In general, a pressure stepusing a median value of P was used to evaluate each test.

The selected injection step for each packer test interval was analyzed to determinehydraulic conductivity using the following equation:

K = Q InflVrt ; for L > lOr (1)2«(L)H

where: K = hydraulic conductivityQ = constant flow rateL = length of test intervalH = injection head (from P)r = radius of borehole

The raw field data and calculations for each packer test are provided in Appendix D.

The 3 coreholes tested were drilled into the Price Formation quartzose sandstones.Measured permeabilities (hydraulic conductivity) ranged from 9 x 10-3 cm/sec to less thanl.Ox 10-8 cm/sec (no flow). The screen lengths and depths of the piezometers andmonitoring wells installed in the boreholes were selected based upon the results of the

packer testing, where available. The results of the packer testing correlated well with theobservation of fracture indices in recovered rock cores. As such, fracture indices wereused to optimize the locations of monitoring well and piezometer screens in boreholes notpacker tested.

Originally, boreholes P-2 and MW-1 were scheduled to include only 1 piezometer or well.In borehole P-2, however, 2 piezometer screens were installed in shallow and deepintervals exhibiting the highest measured permeabilities that were vertically farthest apart.Borehole MW-1 exhibited artesian flow below a depth of 27 feet below ground surface.

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Two monitoring wells were installed in the borehole to monitor the observed shallow(non-artesian) and deep flow zones.

2.6.4 Slug TestingRising head tests were performed in 13 wells completed in the bedrock immediately

following development. Wells were purged using a Waterra Hand Pump capable of amaximum withdrawal rate of about 0.5 gpm. The static water level in each well was

recorded prior to the commencement of testing. Head recovery following purging wasmonitored using an electronic water level meter. All recovery tests were analyzed using

the procedure described by Hvorslev (1951).

The Hvorslev analysis (Hvorslev, 1951) requires the plotting of the head ratio (percentageof head yet to recover) on the vertical scale of semi-log paper versus time on the linearhorizontal scale. The plotted data should produce a straight line between 90 percent and50 percent recovery. Early and late time data may result in a curved plot due to wellborestorage, skin, or boundary effects.

The required data point from the graph of the Hvorslev analysis is the projected time for

the 37 percent head ratio (or 63 percent recovery). This point (T) can be extrapolatedfrom the straight line portion of the curve. Once T has been established, a hydraulic

conductivity estimate can be obtained from the equation:

Kh = InfL/R r (2)2LT

where: Kh = horizontal hydraulic conductivity incm/sec

r • = drill rod inside diameter in cmR = borehole diameter in cmL = test interval length in cmT = time of 37 percent head ratio recovery in seconds

2.6.5 Electropiezocone Penetrometer Testing

Cone penetrometer testing of dike fills and pond materials was conducted to develop acontinuous sampling of material strengths and stiffnesses through these stratified units.

It also measured consolidation parameters, permeability, and in-situ pore pressures. Cone

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penetration tests were performed by Applied Research Associates (ARA) of SouthRoyalton, Vermont, at the locations shown in Figures 2-2 and 3-1.

Cone penetrometer testing consisted of advancing a 60 degree cone, with an end-area of10 square centimeters, into the ASAW and underlying soil at a uniform rate ofapproximately 2 centimeters per second. The tip resistance required to advance the cone

through the ASAW and soil was recorded and a plot of tip resistance versus depthdeveloped. Following normalization of these data relative to overburden depth andpressures, soil strength parameters can be inferred.

Pore pressure transducers, located behind the cone tip, recorded the pressure of waterin the soil pores as the tip was advanced. Pore pressure dissipation tests were conducted

to observe the rates at which excess pore pressures caused by advancing the conedissipated. Analysis of the pressure dissipation data yielded horizontal consolidationcoefficients and permeabilities. Detailed methodology and plots of normalized data are

presented in Appendix E.

A discussion of the permeability and piezometric data derived from the cone testing ispresented in Section 3.7 and a tabulation of these hydrogeologic data is presented inAppendix F.

2.7 Contaminant Source Investigationsfc

Prior to the commencement of the remedial investigation, several studies had beenconducted regarding the source of mercury in the FCPS, the NFHR, and Pond 5. Asnoted in Section 1.2.4, Site History, free mercury within the river was removed duringFCPS and NFHR remedial activities. These activities included dredging of the river,placement of the mercury contaminated dredge spoils on the FCPS with encapsulationof the 1-inch minus fractions in a hypalon liner and by capping of the FCPS with 2 feetof clay and 1-foot of vegetative cover soil. Harza (1980) conducted an investigation ofmercury occurrence at Pond 5. The study concluded that the majority of mercury waslocated in the upper 17 feet to 20 feet of ASAW. Most of the mercury present was alongthe northern edge of Pond 5 and at a location on the eastern edge of the pond.

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Because of the inclusion of some of the demolition debris from the FCPS in the eastern| end of Pond 6, this RI included sampling of the Pond 6 wastes to assess distribution ofmercury within the ASAW. The waste sampling program completed for this study

involved hand-augering approximately 30 boreholes in and around Pond 6. Inaccordance with the Sampling and Analytical Plan (SAP), waste samples were taken from

| the surface to 1 foot, from 1 foot to 4 feet, and from 8 feet to 10 feet depth intervals andthe deepest sample obtainable not in native soils beneath Pond 6. The samples were

analyzed for total mercury. In addition, one sample from Pond 6 and two from Pond 5were analyzed for TCL metals and organics to screen the site for other contaminants. The

groundwater contaminant investigation involved the collection of four quarterly samplesfrom selected monitoring wells. The results of this study together with the findings ofthe Harza investigation are presented in Section 7.3 of this report.

Golder Associates

TABLE 2 - 1POND 5 DECANT STRUCTURE INLETSTAGE-DISCHARGE RATING TABLE FOSTANDARD 90-DEGREE V-NOTCH WE

(Source: Water Measurement Manual)

Stage(ft)0.020.040.060.080.100.130.150.170.190.210.230.250.270.290.310.330.350.380.400.420.440.460.48 .0.500.520.540.560.580.600.630.650.670.690.710.730.75

Q(gpm)0.080.421.152.354.106.449.4313.1417.5922.8528.9435.9143.7952.6362.4573.2985.1898.15112.24127.46143.86161.45180.27200.33221.68244.32268.30293.62320.32348.41377.93408.89441.31475.23510.65547.60

Stage(ft)0.770.790.810.830.850.880.900.920.940.960.981.001.021.041.061.081.101.131.151.171.191.211.231.251.271.291.311.331.351.381.401.421.441.461.481.50

Q(gpm)586.10626.17667.84711.12756.02802.58850.81900.73952.361005.711060.801117.661176.301236.741298.991363.081429.011496.821566.501638.091711.601787.041864.431943.782025.122108.452193.802281.172370.592462.072555.632651.272749.022848.892950.893055.04

A R 3 G U 1 8

TABLE 2-2POND 5 DECANT STRUCTURE OUTLETSTAGE-DISCHARGE RATING TABLE

(Provided by Olin for a Compound Weir w/19.2 degree V-Notch)

Stage(ft)0.020.040.060.080.100.130.150.170.190.21

• 0.230.250.270.290.310.330.350.380.400.420.44

. 0.460.480.500.520.540.560.580.600.620.650.670.690.710.730.75

Q(gpm)

0.010.070.190.380.661.051.542.152.893.764.775.927.248.7110.3512.2014.2016.3018.7021.2024.0027.0030.1033.5037.1040.9045.0049.3053.8058.5063.5068.8074.3080.0086.1095.30

Stage(ft)0.770.790.810.830.850.880.900.920.940.960.981.001.021.041.061.081.101.131.151.171.191.211.231.251.271.291.311.331.351.381.401.421.441.461.481.50

Q(gpm)113.50136.80164.00194.30227.40263.00300.90341.00383,00427.00472.00519.00568.00618.00669.00722.00776.00831.00887.00944.001003.001062.001122.001184.001246.001309.001373.001437.001503.001569.001636.001703.001772.001841.001910.001980.00

TABLE 2-3SWALE 3

STAGE-DISCHARGE RATING TABLE FO0.75 FEET H-FLUME

(Source: Water Measurement Manual)

Stage(ft)

00.010.020.030.040.050.060.070.080.090.100.110.120.130.140.150.160.170.180.19

' 0.200.210.220.230.240.250.260.270.280.290.300.310.320.330.340.350.360.37

Q(gpm)

00.000.280.560.971.462.082.713.614.515.636.818.069.4410.8312.5014.2416.0418.0620.2122.5024.9327.5030.1432.9935.9739.1742.4345.9049.5853.4057.4361.4665.5670.0074.9379.4484.38

Stage' (ft)

0.380.390.400.410.420.430.440.450.460.470.480.490.500.510.520.530.540.550.560.570.580.590.600.610.620.630.640.650.660.670.680.690.700.710.720.730.740.75

Q(gpm)89.3194.72 .100.56106.39112.22118.06124.31130.63137.36144.10151.25158.40166.04174.17182.22190.28198.82207.36216.32225.28234.72244. 17254.03263.89274.24285.00295.76306.53317.78329.44341.11352.78364.86377.36390.00403.06416.04429.51

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3.0 DIKE STABILITY AND ASAW CHARACTERIZATIONThe purpose of the geotechnical dike and ASAW studies was two-fold:

• To analyze the deterministic and probabilistic stability of the Pond 5 dikeunder current drained and possible future flooded (refilled) conditions forstatic and earthquake loading; and

• To develop material strength, settlement properties, and subsurfacegeometry of the contents of Pond 5 for evaluation of remediationalternatives.

3.1 Project Considerations3.1.1 Site Description

| The study area consists of Ponds 5 and 6, which were operated for containment ofammonia soda ash wastes (ASAW), and the FCPS. The dikes containing the ponds wereconstructed with rockfill cores (starter dikes) and built up with accumulations of slakerwaste made up primarily of spent coke and roasted limestone wastes.

The ponds occupy the former NFHR alluvial plain between Little Mountain to the north,

and the river. The site is relatively flat, with the exception of the dike slopes rangingfrom 1/2H:1V (horizontal to vertical) to 2H:1V, consisting of the dike crests and toes, andwaste pond surfaces. At its highest elevation, Pond 5 dike crest is at elevation 1,768 feet(MSL), approximately 15 feet above the level of ASAW in Pond 5, and 100 feet above theNFHR. Some fracture/drainage tracts cross the surface of the ponds, trending fromswales in the southern flank of Little Mountain to the pond decant structure. Vegetation

| on the site is moderate and consists predominantly of weeds and grasses, brush, andsome young trees with trunk diameters of 6 inches or less.

3.1.2 Site History ReviewOlin began operations in Saltville in 1894 with the construction of a soda ash

manufacturing facility. The facility used salt, solution-mined at Saltville, and limestonemined in the area as raw materials for producing soda ash by the Solvay process. Thefacility generated large volumes of solid waste, consisting of inert solids (predominantlycalcium carbonate), and wastewaters comprising chloride brines. These solid and liquidwastes were discharged as a slurry into large settling ponds with decanted liquid wastesdischarged to the NFHR. A total of 6 waste ponds were constructed at the facility

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between 1894 and 1965 to provide soda ash waste storage. Only Ponds 5 and 6 were inoperation while the chlorine plant was in service. Pond 5 began operation in 1925. Pond6 began operation in 1964. Plant operations ceased in 1972. The stoplogs in the decantstructures in Ponds 5 and 6 were removed to drain the waste ponds in August 1978.

3.1.3 Project DescriptionAs part of the RI studies the stability of the Pond 5 dike under static and earthquake

(pseudo-static) scenarios was reviewed. Past site investigation (e.g., Harza., 1976), basedon a single set of input values for each dike component material, have indicated that the

dike is stable. Harza recommended rip-rapping the toe of the dike slope in some areasfor stabilization. Placement of the recommended rip-rap was completed in 1981.However, as the materials in the dike are not homogeneous, it was necessary to examinethe stability under various loading and dike strength conditions. Golder Associates

performed further studies on the dike stability problem under various loading conditions.The variability of the strength of dike materials and probability of various magnitudes ofearthquake events that could potentially affect the Saltville, Virginia area wereincorporated into the OU-2 RI studies. The analyses were developed for present drainedconditions and a scenario in which the pond would be allowed to refill with water to

elevation 1,758 feet. r

Another task of the OU-2 studies involved characterizing the ammonia soda ash wasteswithin Pond 5 and establish the depth to pond invert. In-situ and laboratory testing on

the wastes was performed to develop design parameters and estimate consolidationbehavior of the ASAW under potential future loading conditions.

The potential loading conditions reviewed included construction of a clay or geosyntheticcap over the pond and possible flooding of the pond. The clay cap envisaged consistedof up to 10 feet to 15 feet of clay compacted on the surface of the pond. Surcharges onthe ASAW surface associated with this remediation scenario range from approximately

1,200 psf to 1,800 psf. Construction of a geosynthetic cap envisaged placement of agrading fill course to create a crown for drainage, and installation of a membrane and

cover, and involved a surcharge on the order of 300 psf to 500 psf on the ASAW surface.Controlled flooding was not considered a detrimental load to the ASAW in the long termas it would induce saturation and reduce effective stress through buoyant soil conditions.

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Additional loading to the dike would occur, but would be roughly equivalent to pastloads experienced by the dike during pond operation.

3.1.4 Dike Construction

The Pond 5 dike was constructed from 1925 to 1927 and increased in height during thepond's use as the primary ASAW waste disposal facility until circa 1965. Pond 5 wasdeveloped following the failure of the dike of Pond No. 2 on December 24,1924.From review of construction drawings for Pond 5 and Pond 2 dikes provided by Olin,

significant differences in construction methods and design are apparent (pond locationsare shown in Figure 3-1). The Pond 2 dike was constructed by the upstream construction

method. Consecutive berms, were added to raise dike levels as the pond level rose. Eachberm was constructed partly on existing dike and partly on pond waste materials. Aschematic of upstream dike construction methods similar to those probably used for Dike2 is presented in Figure 3-2. The Pond 2 dike was raised rapidly, owing to the slendernature of the impoundment and facility production rates between 1917 and 1924. Dike

crest elevations rose as tabulated on Figure 3-3. Prior to the failure of the dike,eyewitness accounts of cracks parallel to the dike axis, forming in the ASAW behind the

dike, have been recorded. A review of post-failure photographs indicated the presenceof large blocks of the dike across the NFHR (Figures 3-4 and 3-5). The photographic

evidence, and limited back analyses of the failure suggest that the failure occurred alongthe base of the dike foundation and was of a translational nature. A minor earthquake

(having a magnitude less than 4 on the Richter Scale) was recorded for the region onDecember 25,1924. Foreshocks from this event, combined with deformation or creep, the'formation of cracks in the dike and ASAW and attendant high pore pressures at depth,and potential weak earthy shale foundation conditions, may have led to the failure.

In response to the failure, the Pond 5 dike was constructed by the downstream| construction method. Dike plans show the dike incorporated in its design a large rockfill| core (starter dike), cutoff trench, a drain system comprising vitrified clay pipes draining| the starter dike to the NFHR, and an upstream low permeability soil facing on the starter| dike, probably to limit seepage through the rockfill starter dike. The pipe drains are now| filled with a white precipitate and no flow has been observed from these pipes.

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Pond 5 was developed within the broad alluvial plain containing Palmerville. The NFHRwas re-routed to its present location along the north escarpment of the Sinkhole Knobs.The channel in the vicinity of the east end of the dike was blasted into bedrock. Thewaste rock from the channel excavation was used for construction of the rockfill starterdike (Figures 3-6 and 3-7). The dike was constructed of slaker waste over the rockfillstarter dike, with slaker waste delivered to the dike by railcars and deposited withclamshell buckets (Figure 3-8). A photograph of Pond 5 in operation circa 1947 is

presented as Figure 3-9.

3.2 Field InvestigationsSubsurface Explorations

A total of fourteen boreholes were drilled for the dike stability study. Boreholescompleted during the period of October 19,1988 through December 12,1988 were drilledby National Foundation Engineering (NFE) of Baltimore, Maryland. Boreholes completedduring the period of January 4, 1989 through April 2, 1989 were drilled by LawEngineering Company of Nashville, Tennessee and Highland Drilling Company of OakRidge, Tennessee.

In addition to the drilling program, cone penetrometer testing (CPT) of dike fills andpond materials was conducted to develop a continuous subsurface profile. CPT measuredmaterial strength and in-situ pore pressures, and provided data to calculate ASAWconsolidation parameters and permeability. Cone penetration tests were performed byApplied Research Associates (ARA) of South Royalton, Vermont. The locations of thesubsurface explorations are shown in Figure 3-1.

Boreholes and cone penetrometer holes were numbered in accordance with the tasksassigned by Olin (D=dike stability and CP=cone penetrometer). Borehole locations wereselected to cover the areas and ranges of material types expected to be encountered foreach task.

Boreholes were advanced through soil and fill materials with 6-inch and 8-inch O.D.continuous flight hollow stem augers (HSA). Split-spoon samples (18-inch) were takenat five foot intervals using a 140 pound hammer free falling through 30 inches (ASTMD-1586), from which Standard Penetration Resistance N-values were obtained. Relatively

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undisturbed samples of ASAW and stratified ASAW/slaker units were obtained using3-inch O.D. thin wall Shelby tube, piston, and Osterberg sampling devices. The collectedsamples were subjected to laboratory testing to establish index properties, compressibility,shear strength, specific gravity, and unit weight.

Drilling through coarse boulder starter dike material was performed by Highland Drillingusing air-rotary methods to facilitate placement of casing into bedrock. In some caseswhere casing was not installed, wash drilling or coring methods were used to advance

borings through starter dike boulders.

Drilling in bedrock was performed using 2-inch inside diameter (I.D.) NQ-sized or3.98-inch O.D. HQ-sized diamond coring equipment. Rock core diameter was generally

dictated by well and piezometer installation requirements. In some cases, availability ofcoring equipment was also a factor.

Piezometers and monitoring wells were installed in boreholes between December, 1988and March, 1989. The majority of the piezometer and monitoring Well boreholes weredrilled as part of the geotechnical investigations. Additional boreholes were added, orexisting boreholes deepened, to accommodate installation of piezometers and monitoring

wells. All of the piezometers and monitoring wells, with the exception of P-10(D) (drilledby National Foundation Engineering in December, 1988) were installed by LawEngineering. Well installation logs are presented as Appendix C.

As a result of the installation of piezometers and monitoring wells in many of thegeotechnical boreholes, some boreholes have been assigned two names; a geotechnicalname and a piezometer or monitoring well name. A cross reference betweenhydrogeologic and geotechnical borehole names is presented in Appendix C.

Borehole logs for the dike and ASAW investigations are presented in Appendix C.Relevant borehole logs developed for past site investigations are also presentedchronologically beginning with the most recent explorations and ending with the 1924borings drilled for the river re-routing project.

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Cone penetration testing consisted of advancing a 60 degree cone with an end area of 10

square centimeters into the ASAW and soil at a uniform rate of approximately 2centimeters per second (4 feet per minute). The tip resistance required to advance thecone through the material was recorded and a plot of tip resistance versus depthdeveloped. Following normalization of these data relative to overburden depth andpressures, soil/ASAW strength parameters were calculated.

A pore pressure transducer, located behind the cone tip, recorded soil/ASAW porewater

pressures as the tip was advanced. Pore pressure dissipation tests were conducted toobserve the rates at which excess pore pressures were dissipated. Analyses of thepressure dissipation data yielded consolidation coefficients and horizontal permeabilities(hydraulic conductivities).

Detailed methodology and plots of normalized data are presented in ARA's final report,presented as Appendix E. Discussions of the cone penetration test results, andcomparison of the results with laboratory data and observed materials behavior, arepresented in the following paragraphs.

3.3 Subsurface Conditions

3.3.1 Pond 5 Dike Stability InvestigationAs noted previously, a total of 14 boreholes were drilled for the dike stabilityinvestigation. Of these, 9 boreholes were aligned along 3 different sections, Sections 1-1,3-3, and 5-5, to explore conditions within the dike (see Figure 3-1). The data from theseboreholes were used to define the composition of Dike 5. Sections developed from thedata are presented in Figure 3-10.

A total of 6 different materials were encountered in the 6 dike boreholes (D-4, D-5, D-6,D-7, D-8, D-9, D-ll, D-12, and D-13) and consisted of:

1. A stratified mixture of ASAW and slaker waste;

2. Slaker waste;

3. ASAW;

4. Starter dike rockfill;

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5. Residual or alluvial soil and fill consisting of residual soil or alluvium; and

6. Bedrock.

The following paragraphs describe these materials in detail regarding the extent,thickness, and physical properties of each unit.

Stratified ASAW and Slaker Waste

Stratified layers of ASAW and slaker waste were encountered at the ground surface atboreholes D-6, D-7, D-12, and D-13. The thickness of this material ranged from 37.0 feetin borehole D-7 to 86.0 feet in borehole D-13. The ASAW and slaker waste unit isgenerally located within the uppermost bench of Dike 5, upstream (pond side) and above

the starter dike. Typical thicknesses of stratified ASAW and slaker waste strata are 0.1 to3.0 inches. The materials can be recognized by texture and color. The ASAW is a white,

fine grained silt-like material; the slaker waste has the appearance of a medium to finegrained silty gray to gray-brown sand.

Standard Penetration Test (SPT) N-values in the slaker/ASAW unit ranged from 1 to over

100 blows per foot, and averaged 21 blows per foot. The wide range and variability ofSPT values reflects the heterogeneity of the dike materials in general, and suggests a highdegree of vertical variability of strength in this unit.

Moisture contents within the unit ranged from 31.5 to 210.0 percent, and averaged 81.8percent. A moisture content profile through the dike at D-6 indicates extreme changesin moisture content, on the order of 100 percent. Moisture contents greater than 100percent most likely indicate an increased concentration of ASAW in the mixtures.

The alternating layers of ASAW and slaker waste were clearly visible after roadway cutsin the uppermost portion of Dike 5 were made at boreholes D-7 and D-12. The cuts were

made to facilitate access to these boreholes and maintain site access along the existingroadway. Hollow stem auger drilling and split barrel sampling of this material proceededwithout incident, though the slaker waste was slightly cemented at many elevations andlocations. Ten relatively undisturbed samples of the slaker/ASAW were obtained forsubsequent laboratory testing. Sieve analyses performed on this material resulted in aUnified Soil Classification System (USCS) classification of SM, or a sand-silt mixture.

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Slaker Waste

The slaker waste is typically light to dark gray in color, composed predominantly ofmedium to fine sand sized particles, with little to some silt. The slaker waste exhibits

cementation probably due to the 'pozzolanic properties of its roasted limestonecomponent. Moisture contents in the slaker waste ranged from 30.5 to 37.5 percent, and

averaged 34.0 percent. The slaker waste reacted violently with a 10 percent solution ofHC1, indicating a high carbonate or hydroxide content.

Slaker waste was encountered at or just below the ground surface at boreholes D-4, D-5,D-9, and D-ll. The thickness of the slaker waste ranged from 4.0 feet at D-ll to greaterthan 40.0 feet at D-5. The slaker waste unit is generally located on the downstream faceof Dike 5 below (south of) the uppermost access road. The surface of the slaker waste;

where intact, has a relatively smooth plaster-like finish. One eyewitness account creditsthe smooth surface finish to manual placement and trowelling of the slaker waste.Isolated areas of the downstream face of the dike have vertical or near vertical faceswhich measure up to 6 feet in height. Strong cementation of surface and many

subsurface layers of the slaker waste were noted during sampling and drilling. Theselayers were evidenced from drilling response (i.e., increased sampling resistance) andduring visual inspection of the downstream face. A high degree of vertical variability wasinferred from these observations, though horizontal variability may be as great due to thenature of placement (individual railcars and clamshell buckets). SPT values ranged from6 to 65 blows per foot, and averaged 21 blows per foot, indicative of a compact (mediumdense) material.

Upon inspection of sloughed areas of the downstream face and eroded areas of the toeof the dike, thin layers of ASAW were noted. This ASAW was notably drier than theASAW at the top of the dike. This observation suggests possibility of continuous ASAWlayers from the starter dike through to the downstream face of Dike 5.

Starter DikeStarter dike rockfill was encountered in boreholes D-4, D-7, D-8, D-9, and D-ll at depthsranging from 2.5 feet to 37.0 feet below ground surface. Penetration into the starter dikewith hollow stem augers or air rotary techniques was characterized by violent drill rigresponse including sudden grinding and chattering of drill bits. Significant time and

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effort was required to advance the boreholes through the starter dike with augers. Theair rotary technique had difficulty with borehole cave-ins during and after drilling, as wellas casing placement. Standard Penetration Test (SPT) N-values ranged from 0 to greater

than 100 blows per foot, and averaged 50 blows per foot. The "0" N-value occurred inborehole D-7 at a depth of 55.0 feet, probably in an interstitial rockfill void resulting from

the augers removing fines that existed between two large boulders within the dike.

The thickness of the starter dike ranged from 20.0 feet in D-ll to 50.5 feet in D-8, andaveraged 33.7 feet. The samples recovered, representing interstitial material, ranged fromsilty clay to angular fine gravels. Moisture contents of recovered samples ranged from4.3 to 23.0 percent, and averaged 14.0 percent. Photographs taken during constructionof the starter dike reveal a wide range and variety of grain sizes, from fines to boulders(see Figures 3-6 and 3-7). For the purpose of analysis, the rockfill was assigned aninternal friction angle of 50 degrees and was assumed to be cohesionless.

Fill, Residuum, and Alluvium

This unit consists of soils encountered, predominantly, beneath the starter dike or abovebedrock. In many cases the nature of deposition (occurrence) was difficult to distinguishfrom retrieved samples, and was likely masked by construction disturbance or reworkingduring dike construction.

Encountered soils which could not be placed in any distinct material category wereconsidered to be fill. This "fill" could represent several materials. These include a portionof the starter dike upstream earth blanket, residual soils, or alluvium that were disturbedor regraded to facilitate starter dike construction, or a portion of the starter dike itself.

Fills were encountered in boreholes D-4 (beneath the starter dike), D-6 (beneath ASAWand slaker waste and above bedrock), D-7 and D-9 (beneath the starter dike), D-12 andD-13 (beneath ASAW and slaker waste and above bedrock), at depths ranging from 43.0

to 94.0 feet below ground surface.

Fill thicknesses ranged from 4.3 to 27.5 feet in boreholes D-6 and D-13, respectively, andaveraged 13.3 feet. SPT N-values ranged from 16 to greater than 100 blows per foot, and

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averaged 40 blows per foot. Moisture contents in the fills ranged from 12.0 to 41.3

percent, and averaged 25.8 percent.

The only distinguishable occurrence of alluvium was encountered in borehole D-9 from53.8 to 59.4 feet below ground surface. The encountered material was a mixture of gravel,

sand, and clayey silt, and is situated directly above the bedrock. An SPT value of 25blows per foot was recorded. Laboratory testing was not performed on this sample.

Approximately 5 feet of identifiable residual soil was encountered in borehole D-13. Tripletube coring was implemented to obtain as much of the soil/rock fragments as possible,with limited results. The material retrieved consisted of clayey silt and sand with a fewrock fragments, representing a weathered earthy shale member of the Little Valley "

Formation.

BedrockDark gray to red-brown fossiliferous limestones, sandstones, and sandy siltstones of the

Little Valley Formation were encountered beneath Dike 5 in all the boreholes exceptborehole D-4, which was terminated in fill materials. A detailed discussion of thisformation and other geologic formations and structures encountered during thesubsurface investigation at the Saltville site is presented in Section 4.0.

3.3.2 Pond 5 Subsurface Investigation

A total of 5 boreholes were drilled for the Pond 5 subsurface investigation; P-4, P-5, P-7,P-8, and P-9. Six materials were encountered in these boreholes and consisted of:

Fill;Ammonia Soda Ash Waste (ASAW);Residual Soil;Alluvium;Cemented Alluvium; and,Bedrock.

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FillThe fill that was encountered in boreholes P-4, P-8, and P-9 consisted of crushed gravel

placed for an access roadway onto Pond 5. Boreholes P-5 and P-7 were drilled adjacentto the access road, and thus did not encounter the fill.

The fill consisted of the dark gray and brown angular fine gravel and coarse to fine sandwith little silt fines, or the "crusher run" stone which was obtained from Kendrick Quarryin Meadowview, Virginia. Eight to twelve inches of crusher run stone were placed overa woven geotextile to construct an access roadway section for approximately 3,600 linearfeet on the surfaces of Ponds 5 and 6 and the top of Dikes 5 and 6.

Ammonia Soda Ash WasteASAW was encountered at the ground surface or beneath the constructed access roads

on Pond 5. The ASAW thickness ranged from 51.0 feet at P-9 to 66.0 feet at P-5. AnASAW thickness plan, incorporating boreholes that encountered Pond 5 ASAW during

this investigation, as well as boreholes which were drilled for previous investigations, ispresented as Figure 3-11.

Moisture contents ranged from 63.9 to 358.0 percent, and averaged 188.4 percent. The

ASAW is typically white to light gray in color. ASAW is composed predominantly of finegrained (silt sized) particles with fine sand lenses and occasional cemented laminationswhere calcium has precipitated within the ASAW. SPT values in the ASAW ranged from0 to 13 blows per foot and averaged 3 blows per foot, indicating a very soft to firmconsistency. The ASAW generally did not react with a 10 percent HC1 solution, unlesssome calcium precipitate was present in the sample.

Drilling proceeded rapidly through the ASAW until the bit was advanced to the watertable. Once the augers penetrated the groundwater surface, ASAW ran into the augers,

requiring cleaning of the auger annulus prior to sampling. Obtaining thinwall samplesof the ASAW was difficult due to the materials sensitivity. As such, Piston and Osterbergsamplers frequently had to be employed. Eleven relatively undisturbed thin wall sampleswere taken from the Pond 5 boreholes for laboratory testing.

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During the investigation, subsurface cracks caused by settlement of the ASAW were

observed just below the pond surface. Due to the orientation of the major fractures(NW-SE and aligning with the off-site swales), Golder believes that these features aremaintained by erosion resulting from surface and near surface runoff.

Residual SoilResidual soils were encountered in boreholes P-7 and P-9 at depths of 56.9 and 56.0 feetbelow ground surface, respectively. Thicknesses of the residual soils measured 30.4 and13.8 feet. SPR values ranged from 10 to greater than 100 blows per foot and averaged 65blows per foot. Moisture contents of 12.6 and 22.8 percent were measured on recovered

samples.

The residual soils consisted of brown silt and fine sand grading to a orange-brown siltyclay in P-7, or a light to dark brown and red clayey silt in P-9.

AlluviumDeposits left by the NFHR, which ran along the east, west, and northern perimeters ofPond 5 prior to the river channel relocation in 1925, were encountered in borehole P-5between the depths of 66.0 to 72.5 feet.

The alluvium consisted of light to dark brown rounded sands and gravels with little siltyclay. P-5 may have been located within the old river channel. SPT N-values of 41 andgreater than 100 blows per foot were recorded in the alluvium, and a moisture contentof 28.2 percent was measured.

Cemented AlluviumCemented alluvium was encountered in boreholes P-4 and P-8 at depths of 59.6 and 56.6feet below ground surface, respectively. Due to the strong cementation, the alluvium hadto be cored with conventional diamond rock coring techniques.

Within the cemented alluvium in P-4, and beneath the cemented alluvium in P-8, cleansubrounded gravels were encountered. Both P-4 and P-8 were terminated within thislayer.

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It is likely that the cemented alluvium was created by mixing of pond slimes and alluvium

and precipitation of calcium carbonates and calcium sulfates (from the ASAW and thepond waters) in the alluvium during early operation of the pond.

Bedrock

Slightly to highly weathered light gray to dark gray sandy and silty limestones, siltstones,

and shales of the Little Valley and Maccrady Formations were encountered beneath Pond5 materials. A detailed discussion of these formations is presented in Section 4.2.1.

Groundwater

Groundwater was encountered in the boreholes at the elevations indicated on theborehole logs. A plan with phreatic surface contours developed for Pond 5 is presented

in Figures 5-5A and 5-5B. Water levels in boreholes drilled in the dike were significantly| lower than those measured in boreholes drilled in Pond 5 waste, as can be noted in

| Figure 3-10 (the flooded conditions in this figure represent an assumed worst case| scenario of high water levels). The lower water levels within the dike indicate that the

dike and pond bottoms are sealed relatively well against seepage through and under the| dike, and that the rockfill starter dike, former river channel, and pipe drains beneath the

dike, combined with the slaker waste's higher permeability relative to the ASAW,effectively drain the dike section. Discussion of Pond 5 hydrogeology and hydrology arepresented in Sections 5.0 and 6.0, respectively.

3.3.3 Laboratory Testing Program

Laboratory testing was performed on selected samples to characterize physical properties,compressibility, and shear strengths of the Dike 5 and Pond 5 materials, and provide a

basis for comparison with collected piezocone test data. The following sections discussthe engineering properties and laboratory testing programs for the dike and pond waste

materials separately. Laboratory test plots and a tabulation of test results are presentedin Appendix P.

3.3.3.1 Dike 5 Laboratory Testing Program

The laboratory strength testing program for the stability analysis concentrated on theslaker waste/ASAW mix and slaker waste materials, which make up the majority of Dike5. The other materials encountered in Dike 5 above the bedrock (the starter dike rockfill,

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fill, and alluvium) were tested for index properties. Due to the size of boulders (see

Figures 3-6 and 3-7) located in the starter dike, representative samples could not beobtained using conventional drilling techniques.

Slaker Waste/Ammonia Soda Ash WasteGeneral Description and Index Properties

The slaker waste/ASAW is typically white to gray in color, and stratified. It is foundtypically above the crest of the starter dike and beyond the upstream face. Moisture

contents ranged from 31.5 to 210.0 percent, and averaged 81.8 percent, as notedpreviously.

In its present state, the slaker waste/ASAW is loose to very dense. In some layers the

slaker waste is cemented. Atterberg limits testing on this material show it to benon-plastic. The thickness of alternating layers of slaker waste/ASAW range from 0.25inches to several inches and varies with depth and location. The stratification of thismaterial was observed on a much larger scale when portions of Dike 5 adjacent to theuppermost access road were cut with a bulldozer to facilitate access to borehole locationsD-7 and D-12. These visual observations indicated the variability of the material wasgreater vertically than laterally. Mechanical analyses performed on selected samples

resulted in a USCS classification of SM, which is a silty sand or a sand-silt mixture.Determination of the actual grain size distribution below the 200 screen mesh using ahydrometer was not always possible, because the ASAW reacted with the dispersingagent (sodium hexametaphosphate) in the hydrometer jar and jelled.

Total unit weights ranged from 48.7 to 110.1 pounds per cubic foot (pcf), and averaged81.0 pcf. Specific gravities of solids ranged from 2.29 to 2.64.

CompressibilityA consolidation test, performed on a stratified sample of slaker waste/ASAW (classifiedas a sand-silt mixture (SM) according to USCS) from borehole D-13, at a depth of 16.5 to18.5 feet yielded the following parameters:

Pc' (preconsolidation pressure) = 2900 psfC (compression ratio) = 0.15Cc (compression index) = 0.64e0 (initial void ratio) = 3.25

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Dividing the preconsolidation pressure (Pc') by a calculated effective vertical pressure (P0')

of 1500 psf, results in an overconsolidation ratio (OCR) of 1.9. The high compressionindex (Cc) and high initial void ratio (ej correlate to highly plastic fine grained soils. Thephysical property test results, however, indicate that the slaker waste/ASAW is a

non-plastic, sand-silt mixture. The chemical composition of the slaker waste is probablythe reason for this disparity.

Measurements of shear strength and related deformations (stress-strain relationships)

were evaluated by triaxial shear testing. The objective of the triaxial shear test is to obtainthe deformability and shear strength parameters of cohesion and angle of internal friction

(c and phi).

Two types of triaxial shear tests were performed for the stability analysis:

1. Unconsolidated - Undrained test (UU)

2. Consolidated - Undrained test (CU) with pore pressure measurements.

The UU test is applicable for conditions where the engineering loading is assumed to

occur so rapidly that the induced pore water pressure cannot dissipate during the loadingperiod.

The CU test is applicable for conditions where soils have fully consolidated. Afterallowing the sample to consolidate, loads are imposed on the sample without allowingdrainage from the sample to occur. The pore pressures developed during shear are

measured to permit calculation of effective (drained) stress conditions.

A total of 6 CU and 3 UU triaxial tests were performed on undisturbed samples obtainedfrom the dike boreholes. The CU tests were staged tests; that is, a sample was subjectedto two or three different confining pressures, allowed to consolidate at each pressure,then sheared. The staged tests allow development of a failure envelope for a singlesample, from which c and phi (or c' and phi') can be measured directly.

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A summary of the CU triaxial shear test with pore pressure measurement effectivestrength results are as follows:

c1 (range) =145-990 psf, phi' (range) = 35° - 43°c' (average) = 495 psf, phi' (average) = 39°

A summary of the UU triaxial shear test undrained results are as follows:

cu (range) = 780 - 1,700 psf, phi = 0°cu (average) = 1,370 psf

Individual test results are presented in the Soil Laboratory Testing Summary, AppendixP.

The sample effective stress condition (normally consolidated (NC) or overconsolidated(OC) can be inferred from the shape of the stress path (P-Q) curve during shear. Reviewof the P-Q curves from CU triaxial testing exhibited overconsolidated (OC) behavior,which confirm the consolidation test results from borehole D-13.

3.3.3.2 Pond 5 Laboratory Testing ProgramThe laboratory testing program for the Pond 5 subsurface investigation concentrated on

the ASAW, which is the major constituent of the pond. Mixed ASAW/slaker waste wasfound predominantly in the uppermost portion of the dike.

Ammonia Soda Ash Waste

General Description and Index PropertiesThe ASAW is typically white to light gray in color, and has a homogeneous to slightlystratified structure. Individual grains are not distinguishable by sight but occasional finesand and calcium precipitate laminations were noted within the ASAW.

In its existing condition, the ASAW is firm to very soft and has moisture contents rangingfrom 63.9 to 358.0 percent, and averaging 188.4 percent. Atterberg limits testing onvarious ASAW samples yielded a variety of results: non-plastic (NP), low plasticity silts(ML), high plasticity silts (MH), and high plasticity clays (CH). Total unit weights rangedfrom 77.2 pcf to 86.3 pcf, and averaged 82.0 pcf.

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Mechanical sieve analyses, in conjunction with the Atterberg limits results, yielded USCS

classifications of SM, ML, MH, and CH for the ASAW. As with the slaker waste/ASAWdiscussed in Section 4.2.2, determination of the actual grain size distribution for thefraction finer than the 200 sieve was not always possible, as the ASAW reacted with thedispersing agent in the hydrometer cylinder and jelled. Specific gravities of solids rangedfrom 2.08 to 2.34 for 7 tested samples.

Compressibility

Consolidation tests were conducted on the following three ASAW samples:

USCSBorehole Sample Classification Depth (ft)

P-5 ST-1 MH 11.5-13.5

P-8 ST-3 CH 46.5-48.5

P-9 ST-1 ML 16.5 - 18.5

yielding the following results:

P ' P 'rc 1 oBorehole Sample (psf) (psf) C C_, ^ OCR

P-5 ST-1 1200 710 0.12 0.68 4.63 1.7

P-8 ST-3 2500 2230 0.13 0.32 1.44 1.1

P-9 ST-1 1000- 1500 0.12 0.28 1.30 0.7-4000 2.7

Thus, the ASAW is a slightly overconsolidated plastic, fine grained material. Plots of theindividual consolidation tests are presented in Appendix P.

These parameters correlate moderately well with published values for cohesive finegrained soils.

Shear StrengthBoth UU (1 test) and CU (4 tests) triaxial shear strength tests were performed on thinwalled tube samples of ASAW for the Pond 5 waste characterization.

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The CU triaxial shear tests with pore pressure measurements yielded the followingresults:

c' (range) =0-175 psf, phi' (range) = 34° - 47°

c' (average) = 88 psf phi1 (average) = 38°

The UU triaxial shear test yielded the following results:

c = 350 psf, phi = 0°

Plots of the CU and UU tests are presented in Appendix P.

3.4 Stability Analysis Of The Pond 5 Dike

3.4.1 GeneralEvaluation of the stability of the Pond 5 Dike involved review of past studies performedon the site and attendant subsurface and laboratory information, review of regional

seismic activity, review of construction design drawings, photographs and records, andcompilation of data regarding geometry, subsurface conditions, and laboratory testing

performed for this study. From the review of these data, three cross sections, 1-1,3-3, and5-5, were developed at the locations shown in Figure 3-1. The sections were located tocomplement 2 sections (regarded as sections 2-2 and 4-4 for the purpose of this study)analyzed by HARZA in 1976 and 1979.

The cross sections, shown in Figure 3-10, have idealized material boundaries developedfrom past and recent subsurface information and construction drawings developed in1925.

Following development of the three sections, material properties were assigned to thevarious dike components and the sections analyzed for static and earthquake(pseudo-static) loading under drained (existing) conditions and flooded conditions withthe pond filled to elevation 1,758 feet (MSL). The analyses identified mathematical criticalsurfaces having lowest factors of safety for 3 common modes of failure.

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After identification of the mathematical critical surfaces, a series of analyses wereconducted for the critical surfaces by varying the dike material strength properties and

under several earthquake accelerations. By combining the probability of failure underdifferent earthquake loads with the probability of those earthquake loads occurring, the

probability of failure (P[F]) was determined. The following sections discuss the analysesin detail.

3.4.2 Slope/Dike GeometryThree cross sections along the Pond 5 Dike were developed for this study. The sections

represent the range of outboard slope and internal rockfill starter dike conditionsencountered and documented in construction and past site investigation records. The

sections illustrated in Figure 3-10, were located as shown in Figure 3-1 and were selectedfor the following reasons:

Section 1-1 reflects conditions near the transition from the former Pond 2

Dike, where the outboard edge of the dike toe consists of a rock knob(remnant of the channel excavation), the lower portion of the dike slopecomprises a veneer of slaker waste over rockfill at a slope of 1.5H:1V, and

upper slopes, with the exception of one steep 1H:1V pitch, generally onthe order of 2.5H:1V and are relatively shallow;

Section 3-3 represents the thickest portion of the dike with lower slopescomprising slaker waste and the rockfill starter dike located beneath thetoe of the upper dike slopes; upper and lower dike slopes consist of slakerwastes and have overall slopes of 1H:1V and 1.75H:1V, respectively; and,

Section 5-5 represents the downstream portion of the dike having a morecentrally located rockfill starter dike and steep lower slopes (0.5H:1V)

reflecting erosion of the dike toe and ravelling of the dike face.

3.4.3 Material PropertiesThe dike materials in the idealized sections were divided into 6 units consisting of:rockfill, slaker waste, a stratified mixture of slaker waste and ASAW, ASAW, reworkedalluvium (fill) and alluvium, and bedrock.

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Material properties for each of these units were selected for application in deterministic

stability analyses from laboratory test data, field measurements (SPT and conepenetrometer tests), and the literature, and are presented in Table 3-1. Static andpseudo-static slope stability analyses of the 3 dike sections were applied to identify critical

circular, non-circular, and block translational surfaces possessing low safety factors againstfailure.

Table 3-1 presents the values developed for individual samples obtained from specific

locations within the dike. These values were appropriate for static and pseudo-staticanalyses. However, for analysis of probability of failure, the potential variability of thedike materials, due to stratification and questionable continuity of individual stratumthickness and lateral extent, was addressed by assigning average strength values over the 'area of concern (i.e., over the arclength or length of the critical surfaces through the dikeand foundation materials). A coupled probability distribution function for the variablesof internal friction angle (phi) and cohesion (c) was developed for the analysis based onlaboratory data, field data, field observations, and engineering judgement. The meanvalues for the strength variables and their standard deviation are presented in Table 3-2.

Material densities, averaged over the volume of interest (including the failure surfaces)were assumed constant and maintained as fixed variables as presented in Table 3-2.

Stability Analysis

The stability of the Pond 5 dike was analyzed for the possible loading conditions andvarious earthquake accelerations on cross-sections 1-1, 3-3, and 5-5. The analysesconsisted of mathematically modeling the behavior of the sections with 2 computerprograms simulating the dike slopes with modified Bishop's Analyses and SarmaAnalyses. PCSTABL5M, a computer program developed at Purdue University, was usedto identify mathematical critical surfaces for circular and non-circular failure modes.CSLOPE, a computer program developed by Golder Associates, was used to perform the

Sarma Analyses and Monte Carlo Analyses for variation of strength parameters anddetermination of probability of failure. A detailed discussion of the probability analysis

is presented in Appendix O.

Both programs were used to analyze the sections under simulated earthquake loading bypseudo-static - analysis. For design purposes, a maximum credible earthquake of

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magnitude 6 was used for analysis, with a corresponding bodywave acceleration of 0.25g.A detailed discussion of the site seismic considerations, the probability of seismic eventoccurrence, and a tabulation of significant seismic events is presented in Appendix N.

Table 3-3 presents computed factors of safety on presumed critical surfaces for the 3failure modes and 2 loading conditions under static conditions and 4 accelerations varying

from 0.05 g. to 0.45 g. (The latter is much greater than the maximum credible earthquake).

The maximum computed probabilities of failure for the sections and failure modesanalyzed under drained and flooded conditions are 0.23 percent and 0.45 percent,

respectively. These probabilities are considered to be very low. The probabilistic analysesare in agreement with the deterministic static and pseudo-static analyses.

3.4.4 Conclusions Regarding Pond 5 Dike StabilityThe slope stability analyses conducted on the 3 dike sections presented in this report

indicate that the dike is stable against large scale slope failure under current drainedpond conditions. The analyses also indicated that the dike would be stable under flooded

conditions and maximum credible earthquake loading.

Visual observation of the dike, and review of minor (small) critical surfaces identified bythe computer simulations, suggest that the dikes are stable to slopes of approximately

1.75H:1V to 1.5H:1V depending on the dike material; (i.e., ratio of slaker waste to ASAWand degree of induration of the slaker waste). Significant accumulation of sloughed orravelled dike material was noted along the toe of dike. This indicates the face of the dikeis susceptible to erosion and mechanical weathering. Some adjustments to oversteepening(probably caused by erosion of the toe by the NFHR) have occurred in the past. Visualobservation of the dike's condition 65 years after its construction including 47 years of

operation, lends credence to the favorable findings of the stability analyses.

The probabilistic analyses allowed input of uncertainty of dike material strengthparameters and assessment of the probability of adverse seismic conditions occurring in

the future. The results of the probabilistic analyses further corroborate the findings of thedeterministic analyses. The highest calculated probability of failure, for a 30 year periodunder existing conditions, is 0.23 percent. This probability is very low. The increase of

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probability of failure by refilling the pond suggests that this scenario is less attractive thanmaintaining drained conditions, even though the probability of failure (0.45 percent)

under refilled pond conditions is still very low. The probability of failure for the refilledpond assumes a condition of water ponding within Pond 5 and hydraulic connectionbetween the ponded water and the dike foundation. Under these conditions, thepressure head developed in the foundation is significantly higher than one that would

develop under ponding over a clay liner or membrane without the hydraulic connection.

The calculated stability of the dike is very good. There is limited ravelling of the dikeslope faces and erosion at the dike toes by the NFHR. Ravelling and minor sloughingcould be mitigated by vegetating the slopes and regrading/dressing the slopes to flatter

slope angles. Erosion of the toe could be mitigated by placement of rip-rap or othererosion protection along the toe of the dike.

3.5 Investigation Of Pond 5 Waste

3.5.1 Deposition and Historical ObservationsASAW was slurried through pipes to Pond 5 from 1927 until Pond 6 became operational

following the completion of Dike 6 (circa 1965). Upon discharge, the slurry was directedalong Dike 5 with small diversion berms. By placing the slurry in this manner, coarsercomponents of the waste settled out first, close to the dike, while fines were transportedtoward the center portion of the pond and gradually settled out of suspension. Excesswater was decanted off the surface of the impoundment and discharged to the NFHR bya decant structure located in the southwestern portion of Pond 5.

Stoplogs in the decant structure were removed in August 1978, and Pond 5 was permittedto drain under relatively rapid drawdown conditions. The draining of the pond resultedin the formation of large vertical crevices on the pond surface, reportedly as deep as 30feet. The metastable crevices eventually collapsed and became smaller in width,

appearing as depressions or drainage tracts on the pond surface.

3-5.2 Field Observations

Upon initiation of the field investigation at the site in October 1988, a brief sitereconnaissance was conducted. Much of the pond surface could not support muchweight (it was not uncommon for a person to sink up to one foot into the ASAW). As

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a result, it was necessary to construct suitable access for mechanized equipment thatwould perform the pond field investigation. A system of access roads, comprising awoven slit film geotextile and approximately 8 to 12 inches of "crusher run" stone, wasconstructed to provide drill rig access on the pond. These roads were capable of

supporting fully loaded tandem axle dump trucks and the cone penetrometer truck, eachweighing about 15 tons.

As mentioned previously in Section 3.3.2, the Pond 5 ASAW was easily drilled with hollowstem auger equipment. However, when boreholes were completed, a significant

additional grout volume, in excess of the calculated borehole volume (>20 percent), wasrequired to backfill most boreholes. This extra grout take may have occurred as a result

of densification of ASAW immediately adjacent to the borehole due to the density of thegrout, creation of a flow path for grout at the interface of the ASAW and materials

directly beneath it, or filling of ASAW fracture voids adjacent to the borehole. Thethickness of ASAW encountered during this investigation ranged up to 66.0 feet atborehole P-5. However, previous investigations yielded 67.7 feet of ASAW at M-4, 70.0feet at M-18, and 76.5 feet at M-6. Figure 3-11 presents an ASAW thickness plan

incorporating Pond 5 borehole data developed for this and previous investigations.

During the field investigation, small sub-horizontal cylindrical-shaped voids wereobserved at or just below the pond surface. Upon further observation, the voids werefound to exist across the central portion of Pond 5 on both sides of the newly constructedaccess roads (which facilitated access from the west). In general, these voids trendednorth to south and appear to run between the swales north of the site and the decantstructure at the southwest portion of Pond 5.

The fractures that exist across much of Pond 5 appear to be consolidation features.Discussions with Olin personnel indicate that when the ponds were drained in 1978, the

fractures were very pronounced. This suggests that the fractures formed under water(some are visible under water in historical air photos) as the ASAW solids consolidated

under their own weight. During one hydrometer test in the Golder soils laboratory, acrack, similar to those described in the pond, developed in the test liter jar under 1-footwater. The crack was approximately 1/4 inch wide and 1.5 inches deep, and formed ina settled sample having a diameter of 2.4 inches. This corroborates the hypothesis that

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the fractures are consolidation rather than desiccation or erosion features. Many major

fractures trend from the swales to the decant structure, suggesting that these features actas a conduit for subsurface water flow and are maintained by solutioning/erosion causedby such water movement.

Old Dike 2 was encountered in CP-7 and CP-8 during the piezocone investigation. Therelative thicknesses and elevations in which the dike was encountered appear to verifythe upstream construction technique for Dike 2 and the dike geometry presented in the

1925 drawing from which Figure 3-3 was developed. Golder feels that CP-7 wasterminated on top of the starter dike of Dike 2, based on cone tip resistance and

comparison of the 1925 Dike 2 blueprint, and that CP-8 encountered only a 5-foot thicksection of dike at elevation + 1,730 feet.

3.6 Summary of Cone Penetrometer Exploration of Pond 5

A piezo-seismic electric cone penetration (P/S-ECPT) and dilatometer (DMT) testingprogram was performed around the perimeter of Pond 5, through the southeast cornerof Dike 6, and within Pond 5 and 6 materials. The testing was conducted by AppliedResearch Associates, Inc. (ARA) of South Royalton, Vermont between December 10,1988and January 17,1989, and consisted of a total of 28 piezo-ECPTs, 4 DMPs and 2 seismicECPTs. Of these, 12 ECPTs and 1 S-ECPT were completed with the limits of Pond 5. Acopy of ARA's final report is presented as Appendix E.

The purpose of P/S-ECPT and DMT field program was to obtain a continuous subsurface

profile of various strength parameters of the pond materials. The cone penetration testwas conducted by hydraulically advancing a 10.0 cm2 60 degree conical probe into thesubsoils at a constant rate of 4.0 feet per minute (2.0 cm/sec). Tip resistance (qj, sleevefriction (f,.), and dynamic pore water pressures were measured continuously duringpenetration. The acquisition of these data, along with the seismic data allow correlationto static pore pressures (u0), horizontal coefficients of permeability (Kh), horizontalcoefficients of consolidation (Ch), angles of internal friction (phi), undrained shearstrengths (Su), and overconsolidation ratios (OCR).

Cone penetrometer test locations were selected to encounter a variety of anticipatedsurface and subsurface features, including:

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• deep crevices or voids;• Dike 2 materials;

• Pond 2 materials; and• Dike 5 materials beneath Pond 5 ASAW.

The Marchetti Dilatometer Tests (DMT) were conducted to estimate lateral earth pressures

and soil compressibilities. The dilatometer consists of a flat-plate penetrometer which isinstrumented with a flexible, circular diaphragm mounted on the face of the blade. Thedilatometer is hydraulically pushed at a different location from the ECPT location to

predetermined depths below ground surface. For this program, DMT was performed at2-foot intervals below ground surface. At each predetermined depth, the diaphragm is

expanded a fixed volume with compressed gas. The pressure required to inflate thediaphragm was used to derive overconsolidation ratios (OCR's) and static pore pressures

(u0). Upon measurement of the appropriate pressures, the diaphragm is deflated priorto advancing the dilatometer.

Materials above the water table were analyzed assuming zero cohesion and materialstrength derived from friction (drained conditions).

Materials below the water table were analyzed using undrained conditions, where friction(phi) is zero and all shear strength is derived from interparticle cohesion. Undrainedshear strengths were estimated with an empirical relationship, and an analytical model.

3.7 Results of Cone Penetrometer Investigation

The following observations can be drawn from the results of the P/S-ECPT and DMTtesting of the Pond 5 materials:

1. Based upon the tip resistance values, the undrained shear strength of theASAW increases slightly with depth, suggesting the material at the base ofthe pond is drained and has consolidated. No voids were identified bythe core data.

2. Of the 12 ECPTs across Pond 5, the static pore pressure in 7 of these(CP-2, 3, 4, 5, 8, 12, and 20) decrease at the base of the pond. Thisindicates that, at these locations, groundwater is draining from the base ofthe ASAW into the underlying alluvium.

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3. Based on the Marchetti and Crapps classification system and the DMTresults from DMT-5 (CP-5), the ASAW in Pond 5 has properties similar toa soft silty clay or clayey silt. This classification suggests highcompressibility and low density.

4. Empirical relationships for the DMT data in CP-5 were used to determinethe coefficient of lateral earth pressure at rest (K,,) and theoverconsolidation ratio (OCR). The results are as follows:

K0 (range) = 0.5 - 2.0K0 = 1.0 - 2.0 from 5 to 15 feet BGS

(EL 1733 to 1723)K0 = 1.0 from 20 to 55 feet BGS

(El. 1718 to 1683)

OCR (range) = 2.5 to 5.5

OCR = 4.5 to 5.5 from G.S. to 25 feet BGS(El. 1738 to 1713)

OCR = 2.5 to 3.0 from 25 to 45 feet BGS(El. 1713 to 1693)

OCR = 3.5 to 4.0 from 45 to 55 feet BGS(El. 1693 to 1683)

5. The S-ECPT performed downhole velocity surveys in CP-5 obtained thefollowing:

a. The speed of the compressive wave averaged about 2,030 feel/sec,which corresponds to silty clay/clayey silt velocities.

b. Shear wave speeds ranged from 260 feet/sec from ground surfaceto 45 feet BGS to 520 feet/sec from 45 feet BGS to the bottom ofPond 5; correlating the findings of measured strength and densitynear the base of the ASAW within the pond.

6. Horizontal coefficients of consolidation (CH) were calculated at 50 percentof excess pore water pressure dissipation (Pso)- Typical CH values in theASAW ranged from 0.21 to 1.95 cm7sec.

Horizontal coefficients of permeability (KH) were estimated using CH, theunit weight of water, and several variables. The range of estimated KH isfrom 2.5 x 10* to 2.5 x 10'5 cm/sec, and appears to decrease with depth.

7. The undrained shear strengths (Su) developed from the cone penetrometerdata using empirical correlations typically ranged from 3 to 10 psi.

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Comparison of P/S-ECPT and Laboratory Testing ResultsA comparison of in-situ and calculated results of the electric cone penetrometer testing

program with laboratory ASAW results is made herein. Applicability of results topublished data is discussed.

The coefficient of lateral earth pressure at rest (KJ expresses the ratio of effectivehorizontal stresses to effective vertical stresses. The calculated and in-situ measurement

Ko values are:

KO Typical KO In-SituCalculated Values Measured Values0.41 to 0.57 1.0 to 2.0

The calculated K0 values were obtained from the empirically derived relationship of KQ

and phi1:

K0 = 1 - sin (phi1)

This relationship was originally derived for soils from a series of consolidation tests whichwere instrumented with strain gauges to measure lateral forces resulting from inducednormal forces.

The in-situ KO values were obtained from actual DMT readings in the ASAW. Thesein-situ values suggest that the ASAW is overconsolidated (from unloading or erosion)within Pond 5.

The calculated K0 values do not correlate well with the in-situ values. This is not

surprising, however, as DMT measurements are very reliable and more representative ofactual stress conditions. In addition, the ASAW is a chemical waste, and the empiricalrelationship of K0 and phi1 was derived from normally consolidated clays (Ladd, et. al.,1977).

Overconsolidation ratios (OCR's) were calculated from the DMT data in CP-5 andlaboratory data.

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OCR OCRfrom Lab Data from DMT Data

1.7 2.5 to 5.5

These calculations indicate that the ASAW is slightly (lab) to very (DMT) overconsolidated.Mechanisms which may have resulted in an overconsolidated stress condition within

Pond 5 include: larger seasonal changes in pond groundwater elevations since 1978;desiccation due to surface drying; change in ASAW structure due to secondary

compression; pH and temperature fluctuations; salt concentration fluctuations; chemicalchanges due to precipitation; cementation; and, ion exchange.

Values of the coefficient of horizontal consolidation, CH, ranged from 0.21 to 1.95 cm2/sec.

The relationship between CH and Cv has been investigated for normally consolidatedclays and ratios of CH to Cv often range from 1.0 to 4.0. The range of coefficients of.consolidation, however, are 2 to 4 orders of magnitude greater than typical clays values

and are indicative of non-plastic silt behavior.

Values for the horizontal coefficients of permeability, kH, were estimated from CH. The*~~ . -kH values typically ranged from 2.5 x 10"" cm/sec to 2.5 x ra5 cm/sec. As the ASAW is

homogeneous to slightly stratified, the corresponding values for ky should be relativelysimilar (that is, within an order of magnitude). This range of permeability values isrepresentative of silts; mixtures of sand, silt, and clay; clayey silts; and, silty clays.

The undrained shear strengths of the ASAW typically ranged from 3.0 to 10.0 psi, or 430to 1440 psf, and increased slightly with depth. An unconsolidated, undrained (UU)triaxial shear strength test on P-9, ST-1 yielded a shear strength of 360psf.

3.8 ASAW Compressibility and Estimated Settlement Behavior

Two compression indices were selected from the laboratory data as being representativeof the range of compressibility likely within the stratified ASAW. From these indices, thebulk unit weight of the ASAW and existing groundwater conditions, settlement of thePond 5 surface was estimated for surcharge loads ranging from 250 psf to 2000 psf.

Total settlements will include primary and secondary consolidation components, and areestimated to range from approximately 2.5 feet to 3.5 feet for a 2000 psf surcharge over

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60 feet of ASAW. For the same thickness of ASAW, a surcharge of 500 psf yields anestimated range of total primary consolidation from 0.5 feet to 1 foot.

Figures 3-12 and 3-13 present families of curves of primary consolidation settlement versusthickness of underlying ASAW for loads ranging from 250 psf to 2,000 psf. The primaryconsolidation values can be increased by up to 1.3 feet to estimate total settlementsincluding secondary consolidation effects.

3.9 Liquefaction PotentialUnder cyclic (dynamic) loading conditions, such as those generated during an earthquake,

saturated cohesionless soils can undergo liquefaction. During repeated cycles of loadingand unloading, progressively increasing magnitudes of excess soil porewater pressures

can build up to a magnitude equal to the confining (overburden) stress thereby reducingthe effective stress to zero. At this point, a granular soil will lose its strength and

essentially flow like a liquid, hence the term liquefaction. This phenomenon is most likelyto occur in loose, clean uniformly graded sands under shallow groundwater conditions.Even if the induced cyclic porewater pressures do not build up to the confining stress,the resultant reduction in effective stress, from which a cohesionless material develops its

strength, can cause significant strains to develop, even in dense, dilative sands. Thisphenomenon is called cyclic mobility and is also referred to as a liquefactionphenomenon. In such cases a complete loss of strength is not observed; however, thedeformation developed may still be greater than can be tolerated for a given structurebearing on the soil. In this sense, failure can be said to have occurred.

The potential for liquefaction of a soil decreases as the density or fines content of the soil

increases. Soils with plasticity are less likely to liquefy or experience significant cyclicmobility.

Several methods exist for the evaluation of liquefaction potential. The most frequently

used methods involve empirical correlations developed over the years by Professor H.Bolton Seed and others at the University of California at Berkeley (Seed, 1979; Seed et. al.,1983). These include methods based on established correlations between actualperformance of soil deposits under earthquake loading and various in-situ characteristics

of the deposit. Standard Penetration Test (SPT) and Cone Penetration Test (CPT) data

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are the most common. The methods also include analyses based on laboratory cyclicloading tests to determine the relationship between the cyclic stress ratio to induceliquefaction and the number of applied loading cycles. (There are numerous definitions

for induced liquefaction which all relate to degrees of deformation.) The field stress ratiois then calculated and compared with the laboratory cyclic shear strength ratio for theequivalent number of cycles associated with the design earthquake. If the field stressratio is less than the laboratory value, for the same number of cycles, then liquefaction

is unlikely to occur.

While the two basic methods appear to be quite different, they involve the same basicapproach and differ only in the manner in which the liquefaction characteristics of thesoil deposit are defined.

It is significant that the bulk of the literature dealing with the phenomenon of liquefactionhas developed correlations for clean, loose sands. The majority of data found in theliterature are recorded for sites in California and Japan where liquefaction of sand subsoilshas been widely observed as a result of seismic activity. Little data are found in theliterature for cohesive soils exhibiting plasticity (e.g., clays, silty clays and clayey silts),

iperhaps because the reaction to cyclic loading in these materials is less pronounced andcauses less damage to structures. It is also possible that the potential reaction to seismicevents is strain due to cyclic mobility, and the resultant damage to structures is less.

The ASAW stored in the waste ponds at Olin contains significant (on the order of 50percent to 80 percent) fines, and as such, does not behave as a cohesionless material.Review of the literature indicates that tailings slimes (fine grained soils with someplasticity) have higher cyclic shear strength ratios than clean sands (Garga and McKay,1984; Poulos et. al, 1985). As noted above, shear resistance for cyclic mobility isestablished using various degrees of induced strain, for a given number of loading cycles,as the "failure criterion" (e.g., 5 percent double amplitude strain); higher cyclic resistancewould be measured for a higher allowable strain criterion. If a structure can withstandsignificant strains, as flexible membrane cap systems have shown in landfill applications,the cyclic shear strength ratio can be further increased.

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The factor of safety (FS) of a material against cyclic mobility (or other liquefaction effects)can be defined as the ratio of the cyclic shear strength to the cyclic stress induced by a

design seismic event. From the literature, the cyclic shear strength of the ASAW can beestimated at about 0.30 for a 5 percent double amplitude strain criterion. Based upon site

data and a design earthquake of magnitude 6, (having a peak acceleration of 0.25 g), aprofile of cyclic shear stress was developed for a typical Pond 5 section (at CP-4). The

factors of safety against liquefaction effects were generally in excess of 1.0, with theexception of a band of ASAW starting at the water table and extending to 15 feet below

the water table. Safety factors for this portion of the section were on the order of 0.95,indicating a potential for cyclic mobility. If the cyclic shear strength is increased to allow

for more than 5 percent strain, the likelihood of liquefaction effects (beyond somesettlements at the surface of the pond) is significantly reduced.

It should be noted that current geotechnical knowledge of liquefaction potential is forclean sands at low density. Consequently, exact quantification of the liquefaction

potential of the ASAW in Pond 5 is not possible at this time. Estimates can be made forbehavior of materials such as ASAW, however correlations drawn from the current

documented soil liquefaction behavior for natural sands and tailings are not appropriatesince they exhibit markedly different behavior from slightly plastic to plastic silty or

clayey soils.

Based on judgement, structure considerations, and the applicability of the empiricalmethod used to the specific site conditions, cyclic mobility of the ASAW is possible under

earthquake conditions, probably resulting in localized settlements (if the surface of theASAW; however, full liquefaction under these conditions is not likely. Given the natureof currently proposed remediation plans presently under consideration (i.e., capping thePond 5 surface, and maintaining drained pond conditions) adverse effects to a flexible capstructure beyond the localized settlements noted above are not anticipated.

3.10 Conclusions - Pond 5 Ammonia Soda Ash Waste

Based on the field and laboratory data and the analyses discussed previously, thefollowing conclusions are drawn.

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December 1994________________3-32____________________883-6174

The ASAW within Pond 5 behaves similarly to a very soft to firm, sensitive, slightlyoverconsolidated, silty clay to clayey silt. Similarly, settlement behavior is anticipated toparallel that of silty clay. The conceptual alternatives of capping the pond surface witha thick (15 foot) clay cover or a lighter cap (e.g., a base course and geosyntheticmembrane) present a wide range of estimated settlement behavior. Total settlements ofthe pond surface ranging from 2.5 to 3.5 feet (for an ASAW depth of 60 feet) are

anticipated for the heavier cap surcharge of approximately 2000 psf. Settlements will varywith the thickness of ASAW below the surcharge and will decrease proportionally with

decreases in ASAW thickness at the pond margins.

Under cyclic loading (earthquake) conditions, the ASAW is not likely to liquefy due to itsplasticity. Some loss of strength (cyclic mobility) may occur, but the effect of the lowerstrength would only be minor local settlements in the pond surface. Such settlements

should prove tolerable to structures designed to withstand the total settlements estimatedunder surcharges.

The similarity of behavior of the ASAW and naturally occurring clayey soils indicates thatthe material has consolidated and increased in strength since the pond was drained in1978. The ASAW possesses a relatively high drained shear strength which should increaseas the ASAW continues to consolidate.

Remedial alternatives, as noted above, will have to take into account the sensitivity of theASAW to loading. Alternatives with high surcharge loads should be evaluated weighingthe necessity for possible staged construction to allow ASAW consolidation and increasein shear strength. Similarly, final design of alternatives with high loads should includeverification of dike stability against temporary construction loads.

Golder Associates q R 3 L1 i 4 '0 5

TABLE 3-1

Diie Material Properties for Deterministic Analyses

• """. /: ' ;.. .,:'; /;"•>: Internal '•.•?;.;; • .-. ''..•".*.,, ' •'•• •'' •- .••:'•"'' •• .Friction- '..,'"•. "..Material Angle (phi)

Slaker WasteSlaker Waste/ ASAASAWRock FiUAlluvium/FillBedrock

353642503260

Cohesion(psi)

900175000

5,000

" '• ' I . .' ' ' ':":••

Unit Weight;(pcf)

1028570130115155

Golder Associates

Gi 456

TABLE 3-2

Dike Material Properties for Probablistic Analyses

Internal .Friction

Material Angle (phi)

Slaker WasteSlaker Waste/ AS AASAWRock FillAlluvium/FillBedrock

383735503460

StandardDeviation(degrees)

2.43.03.03.01.80.0

Cohesion(psf)

1,0004001500

1755,000

StandardDeviation

(psf)

305180910.01070.0

Unit Weight(pcf)

1028570130115155

Golder Associates AR3QU57

TABLE 3-3

Critical Surface Factors of Safety

:;::;:; V/-:Honz6ntal'' :?;-;:;;.-5; Acceleration/(Probability of ah)

O.Og (static)O.OSg (66.9%)0.15g(24.6%)0.25g (6.4%)

0.35g (1.5%)0.45g (0.6%)

Section.... • Existing

3.543.162.602.18

1.871.64

1-1 '. ;Flooded

3.543.162.602.18

1.871.64

Section 3-3Existing Flooded

2.312.091.731.46

Maximum

1.251.09

2.211.991.651.39

SectionExisting

2.372.101.701.42

5-5Flooded

2.372.101.701.42

Credible Earthquake

1.191.03

1.211.05

1.211.05

Golder Associates ,,. . . ,A R o u m 5 8

UNSCANNED ITEM(S)

ONE OR MORE OF THE FOLLOWING ITEMS MAY BE ASSOCIATEDWITH THIS DOCUMENT:

PHOTOGRAPHSDRAWINGS

OVERSIZED MAPSROLLED MAPS

PLEASE CONTACT THE CERCLA RECORDS CENTER TO VIEW THEITEM(S)

SUBSEQUENT DIKES CONSTRUCTED POOLFROM BORROW MATERIALS ORCOARSE PORTION OF WASTEMATERIAL————'-

STARTER DIKE——* ORIGINAL GROUND SURFACE———' L——ASAW

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PERIPHERAL DISCHARGE LINE ——— v POOL

COARSE FRACTIONOF WASTE —————

STARTER DIKE——» ORJGINAL GROUND SURFACE ———' <———FINE FRACTIONOF WASTE

B) Embankment built from coarsefraction of waste as part of hydraulic deposition process

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December 1994_________________4-1_____________________883-6174

4.0 GEOLOGY

4.1 Regional GeologyThe regional geology of the Saltville area is relatively complex, comprising synclinal

folding and thrust faulting of the northeast striking formations. The primary geologicstructures in the region are the Greendale Syncline and the Saltville Thrust Fault.Between Ponds 5 and 6 and the town of Saltville, the southeastern limb of the syncline

is overturned and the syncline recumbent. South of the syncline, the Mississippianformations form the footwall of the Saltville Thrust Fault, which has thrust older

Cambrian shales, limestones and dolomites over the Mississippian formations exposed inthe study area. A geologic map of the site is presented in Figure 4-1.

The northwestern limb of the syncline includes the watershed surrounding the project

and Devonian shales in Poor Valley, north of Little Mountain. From the ridge of LittleMountain to the limestone bluffs along the south bank of the NFHR, the formation bedsstrike approximately North 60 degrees East, and dip to the southeast approximately 30degrees.

Drainages on the slopes of Little Mountain, and the NFHR have preferentially incised oreroded the softer rock types within the study area. Along several stretches, the river hasfollowed the approximate strike of the dipping beds, which is also the strike of acomplementary joint set dipping to the northwest. Within Pond 5, the old river channel

followed the strike of the dipping beds at the foot of Little Mountain along the northernPond 5 margin. The old river channels along the base of the old Pond 2 dike and

adjacent to the area of historic Henrytown followed courses parallel to fracture systemsaligned with Henrytown Road (which bisects the Sinkhole Knobs from Saltville to theriver), and the drainage swales along Little Mountain, respectively (see Figures 4-2 and2-2).

The river alignment east and west of the site follows the orientation of these three

fracture systems for the most part. The river appears to have incised its channelpreferentially into the Maccrady and Little Valley Formations based upon their degree offracture (or increased fracture in response to tectonic activity) and lower relative intactrock strengths. Some block sliding of rock strata, in response to past undercutting of thedip slope of Little Mountain, was noted along the northern margin of Pond 5. The

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headscarp of the blocks formed along complementary joint sets with strikes parallel to thestrike of the dipping strata and dips of approximately 60 degrees northwest. Because of

these block movements, some of the rock outcrops along the Western Diversion Ditch andnorthern Pond 5 margin yield rock -strata orientations (strike and dip data) not in

agreement with those measured at adjacent intact rock outcrops on Little Mountain.

4.2 Site Geology

The site geologic map and stratigraphic section developed from field measurements arepresented as Figures 4-1 and 4—2, respectively. The results of the fracture trace analyses

are presented as Figures 4-3, 4-4, 4-5, and 4-6. The locations of the geologic sectionsmeasured are, presented in Figure 4-1. Interpretive subsurface profiles trending

perpendicular to the general strike of the formation bedding are presented in Figures 4-7,4-8, and 4—9. A composite profile, combined from the five profiles and geologic mapping

of outcrops is presented in Figure 4-9 and illustrates the degree of coverage afforded bythe subsurface exploration program.

4.2.1 Site StratigraphyThe stratigraphy of the Greendale Syncline pertinent to this study consists of 6 formationsof Mississippian Age, ranging from Kinderhookian to Chesterian stage. These formationsare of marine depositional origin. Evaporites (salt, gypsum and anhydrite) found in the

upper plastic shale member of Maccrady Formation, have been the basis of the chemicaland gypsum (plaster) industries in Saltville. The following sections describe theformations in detail. A detailed geologic section is presented as Figure 4-2.

4.2.1.1 Price FormationThe southern slopes of Little Mountain along State Route 611 consist predominantly ofgreenish gray quartzose sandstones of the Price Formation. The upper contact with theoverlying Maccrady Formation forms the knobs between swales along State Route 611 (SR611) up to the western end of Pond 5. At this point the contact is obscured by cover tonearly the end of Pond 6. The lower contact of the Price Formation, where it grades intothe Parrot Formation, has been mapped by others along the northern slopes of Little

Mountain.

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The majority of the Price Formation comprises medium to thinly bedded, greenish-gray,quartzose strong sandstones. The upper 40 feet of the formation is interbedded with thin

coal laminations and several thin coal beds. Many of these contain casts of plantstructures. Plant fossils, some slightly pyritized, have been noted in the upper Price

Formation. A thick (70-foot) zone of very thinly-bedded, intercalated sandstones andsandy siltstones was mapped at Allison Gap. This zone is expressed in the localtopography as the shallow slopes half way up the southern flank of Little Mountain, and

the sharp bend in Robertson Creek in Allison Gap. In both locations, these intercalatedsiltstones and sandstones have been differentially eroded. The upper Price contact has

been arbitrarily delineated at the base of a zone of brown to red siltstone and sandstonevariegated with green "blotches" (Cooper, 1966).

4.2.1.2 Maccrady Formation

The Maccrady Formation has been the focus of most of the geologic studies of theSaltville-Broadford area for over two hundred years. The Maccrady was subdivided into

three distinct members by Cooper (1966) based upon areal occurrence and economicinterest. The three members consist of lower sandstone-siltstone member, a middle

dolomitic member, and an upper plastic shale member. The upper plastic shale memberhas been the most significant in economic terms because this member contains evaporitesmined by U.S. Gypsum in Plasterco and Locust Cove, and by Olin in brine wells located

in Saltville.

The thickness of the formation varies greatly over the short distance from Saltville toAllison Gap. This variation in thickness has been attributed to deformation of the

formation during folding of the syncline which concentrated the plastic shale member,for the most part, in the recumbent southeastern limb of the Greendale Syncline (figure4-10). The thickness of the plastic shale member is about 30 feet at Allison Gap (Cooper,1966 and Ross, 1965), and on the order of 1500 feet in brine wells and exploratoryboreholes in Saltville less than a mile away. Cooper (1966) observed that the salt depositsin the Maccrady Formation were not in the form of bedded and intercalated shales andevaporites. Rather, the salt bearing portions of the formation comprised a tectonic brecciawith a characteristic salmon-red color caused by dissemination of red to maroon plasticshales within the salt matrix. Evaporite occurrence in the plastic shale member on thenorthwestern limb of the syncline is generally rare and discontinuous if present.

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At Allison Gap and along the base of Little Mountain, the Maccrady Formation is about135 feet thick. The formation consists of about 30 feet of an upper member of red, grayand green shales often showing signs of localized plastic deformation; 20 to 30 feet ofearthy shales, limestone, and dolostone of the middle member; and 80 to 90 feet ofintercalated sandstones and siltstones of the lower member.

4.2.1.3 Little Valley Formation

The Little Valley Formation underlies the majority of the site and crops out on the knobsimmediately east of Pond 5, east of Allison Gap Road, northwest of the Dotson Wheel

manufacturing plant and west and south of Pond 6. The formation consists of slightlyto heavily weathered calcareous shales, sandstones and siltstones, intercalated withlimestone and dolostone beds. The formation generally weathers to a yellowish-gray tobrown color. Fossil fragments including crinoid columnals, brachiopods, corals andbryozoans can be found in highly weathered earthy shales exposed on the site and westof Pond 6. Cooper (1966) states that the lower part of the Little Valley Formation islithologically transitional with the upper Maccrady plastic shales and contains evaporites.

This upper zone, however, is not present on the northwestern limb of the syncline andaccording to Cooper (1966) is "...known only from well cuttings and cores in the

Saltville-Plasterco sector".

4.2.1.4 Hillsdale Limestone FormationThe lower contact of the Hillsdale Limestone Formation consists of a black chertylimestone, overlain by black fossiliferous shale. The overall thickness of the formation inthe Greendale Syncline is approximately 250 feet. The Hillsdale is transitional into anoverlying gray fossiliferous limestone formation.

As mapped byCooper (1966), the Hillsdale crops out in the NFHR at the roadway bridgeadjacent to the FCPS, and along the southern bank of the river (Figure 4-10). GolderAssociates has arbitrarily drawn the upper contact of the Hillsdale at the top of a 25-footthick sequence of thinly laminated, intercalated, sandy limestones and calcareoussiltstones overlying a 2-foot thick coal bed exposed in the 1925 channel excavation acrossthe river from Pond 5. Above this point, the lithology changes to a dark gray to black,strong, medium bedded limestone.

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4.2.1.5 Ste. Genevieve and Gasper Formations

The upper elevations of the Sinkhole Knobs and pastureland across the river from thePond 5 dike are formed by limestone members of the Ste. Genevieve Formation. At thehigher elevations, outcrops are of slightly to moderately weathered, medium tothickly-bedded, dark gray, weathering to light gray limestone with crinoid fossils. Theoutcrops exhibit the effects of chemical weathering and minor solutioning. Some solutionfeatures have been noted along the axis of the Greendale Syncline in the Ste. Genevieve

Formation. Farther west, within an area adjacent to the synclinal axis, the Ste. Genevievetransitions into the Gasper formation.

4.2.2 Fill MaterialsFill materials placed at the site generally fall into four categories: natural soil placed for

construction of the pond dikes; slaker waste placed in conjunction with pond dikeconstruction; ammonia soda ash waste deposited in the ponds; and, demolition debris,

from the razing of the FCPS, which was placed along the west side of the dike separatingPonds 5 and 6.

4.2.2.1 Ammonia Soda Ash Waste

Ammonia Soda Ash Waste (ASAW) is a by-product of the Solvay process, and iscomposed of inert solids (predominantly calcium carbonate) and chloride brines. Thewaste was hydraulically deposited into Pond 5 from the Soda Ash plant site through steelpipes, located along the southern perimeter of Pond 5.

The ASAW is typically white to gray in color, and composed predominantly of silt-sizedparticles with fine sandy lenses and occasional cemented veins; The thickness of theASAW ranges from 50 to 70 feet under most of Pond 5 and covers an area ofapproximately 75 acres in Pond 5, as shown in Figures 3-12 and 3-13.

4.2.2.2 Slaker Waste

Slaker waste, a by-product of the limestone calcining/slaking process, was deposited onthe top of and on the downstream face of Dike 5 to build up the dike above the starter

dike materials. Slaker waste was emplaced using railroad cars and rail-mounted clambucket loaders.

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The slaker waste is typically light to dark gray in color, and is composed ofpredominantly medium to fine sand sized particles with little to some silt-sized particles.The waste exhibits a progressive cementation of grains over time. The thickness of the

slacker waste ranges from 2 feet to 50 feet on the downstream face of Dike 5, and isinterlayered with ASAW within the dike to depths of as much as 70 feet below the dike

surface.

4.2.2.3 Starter DikeFollowing the failure of Dike 2 in 1924, the NFHR was rechanneled to permit constructionof a new dike. The core of the new dike (the starter dike) was constructed from blasted

rock, generated by the new river channel excavation. The rockfill starter dike within Dike5 connects the intact portion of Dike 2 along the NFHR on the east and the hillside at the

northwest corner of Pond 5.

The materials encountered within the rockfill starter dike during the geotechnical• investigation were typically a mixture of large boulders with interstitial material consisting

of gravel, sand, and clayey silt The gravels probably represent fragments of larger rocksbroken off during augering and sampling. The sands and clayey silts represent materials

which have filled the voids between the large boulders of the dike. Based on designdrawings, the width of the rockfill starter dike along its crest ranged from 15 feet where

it rested on the remnant of a blasted rock knob, to 50 feet along the rest of the dike.

The design indicated a low permeability facing, composed of crushed shales, was placedon the upstream face of the rockfill starter dike (shown on old drawings), probably tolimit seepage through the starter dike. This upstream low permeability layer, and a

system of clay pipe drains within the rockfill starter dike are evidence of a relativelysophisticated dike design for the period.

4.2.3 Natural Soils

Boreholes advanced through the ponds and along State Route 611 encountered a mantleof alluvium, colluvium or residual soils above bedrock. For the purposes of the OU-2

studies, the mechanical and hydrogeologic characteristics of the soil were studied.Agronomic soil descriptions are presented in the OU-3 RI Report.

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4.2.3.1 Alluvium

In the pond areas, alluvial soils comprise the surface materials onto which dike and pondfills were placed. These soils consist of sand, gravel, silt, river sediment, and flood plaindeposits. In boreholes MW-6, P-4 and P-8, the encountered alluvium was cemented by

the ASAW and had developed a "crust" about 2 feet thick resembling a sandstone matrixconglomerate containing limestone, quartzite, sandstone, gravels, cinder, and brick

fragments. Below the cemented crust, diamond coring equipment encountereduncemented alluvial gravels.

4.2.3.2 Colluvial SoilsColluvium was encountered on the slopes of Little Mountain and approached a depthof 4 feet to 5 feet in borehole MW-1. The colluvium consisted of sandy silts and siltysands with varying amounts of coarse sand to fine gravel-sized sandstone and siltstone

fragments.

4.2.3.3 Residual SoilsThe Maccrady and Little Valley Formations contain siltstone and shale members that, in

some areas, are highly weathered and have altered to residual soils. Outcrops containingresidual Maccrady Formation soils are located along State Route 611 adjacent to thenortheastern corner of Pond 5 and near the western tip of Pond 6. These soils comprisea maroon to orange-tan silty cla'y having medium plasticity. Some of the siltstones andshales of the Maccrady Formation reportedly alter to illite/chlorite rich clays (Ross, 1965).

Outcrops of residual Little Valley Formation were noted adjacent to the jobsite trailernorth of an old concrete pad, and west of the Pond 6 terminus gate in a newly cut bankadjacent to a meadow. The soils consist of olive-brown to tan sandy silts and containbrachiopod and bryozoan casts. Cooper (1966) described this member of the Little ValleyFormation as an "earthy shale largely leached of original lime".

4.2.4 Structural FeaturesStatistical plots (rose diagrams) of the occurrence and orientation of observed lineamentswere developed for a total of 378 lineaments and for 116 lineaments having lengths over

1,000 feet. Both plots indicate strong lineation in the strike and dip directions of theformations, as well as lineations trending parallel to Henrytown road (N65°W).

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A polar stereographic plot of joint orientations measured at outcrops and core orientedto the strike and dip measured at adjacent outcrops, indicates a strong trend of jointsparallel to the predominant strike of the bedding and concentrations of dips in the 30 to60 degree range to the northwest and southeast. Due to the vertical orientation of thecore, axis subvertical orthogonal joints were seldom noted in the cores examined.

In general, the Rock Quality Designation (R.Q.D.) of the recovered core is lowest, and thefracture frequency index highest, within the upper 50 feet of the bedrock (about 60 feet

below ground surface). At depths greater than 60 feet below ground surface, the R.Q.D.typically ranges from approximately 85 percent to 100 percent, and the fracture frequencyindex is generally less than 5 fractures per foot. In contrast, the upper 50 feet of thebedrock at P-2 is characterized by an R.Q.D. which ranges from 0 percent to 100 percent

(less than 10 percent for the upper 30 feet of bedrock), and a fracture frequency indexwhich ranges from less than 5 to over 25 fractures per foot.

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JOB NO. 883-6174DRAWN LASCHECKED

SCALE N/ADATE 07/18/89DWG NO VA01-224

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JOB NO. 883-6174DRAWN CSCCHECKED

SCALE AS SHOWNDATE 3/23/89DWG. NO. VA01-252

GEOLOGIC SECTION ANDGENERALIZED GEOLOGIC MAP

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5.0 HYDROGEOLOGY5.1 GeneralAn extensive hydrogeologic investigation of the facility was conducted to better definegroundwater behavior at the site; to refine and verify the conceptual hydrogeologicmodel; and to develop a preliminary numerical groundwater flow model. Data collectedduring the investigation included in-situ and laboratory estimates of permeability, long

term monitoring of hydraulic heads in bedrock and the pond fills, and correlation ofhydraulic test results with information derived from the geologic and geotechnicalinvestigations of site subsurface conditions.

A total of 71 groundwater monitoring points were installed throughout the Pond 5 areaas part of the hydrogeologic investigation (Figure 3-1). The groundwater monitoringpoints include wells and piezometers completed by Golder in late 1988 and early 1989("MW" and T" series), borings completed by Harza in 1976 and 1980 ("B" and "M" seriesrespectively), and borings completed by Wehran Engineering in 1981 ("W" series).

Slug tests were completed in some of the wells and piezometers. Pressure packer testswere performed on discrete intervals in some of the geotechnical borings. The tests wereconducted prior to installation of long term groundwater monitoring equipment. Cone

penetrdmeters were advanced in portions of the fill in which in-situ permeability andhydraulic head measurements were made.

The location of all groundwater monitoring points are presented in Figure 3-1. A detailedsummary of well and piezometer construction depths, surveyed elevations, and lithologiesof the screened intervals is presented in Appendix C. In addition, boring and rock corelogs for all completed holes are also presented in Appendix C with the exception of 2unidentified borings (designated #11 and #20) for which no logs are available.

*

5.2 Regional Hydrogeology

The repetitive sequence of the various lithologies in the Valley and Ridge Provincecombined with the occurrence of strike and dip-oriented streams result in thecompartmentalization of groundwater flow into adjacent, but discretely isolated shallowflow regimes (Seaver et al, 1988). In most areas, groundwater flow is from the ridges tothe adjacent valleys, generally across the prevailing strike direction. Groundwater is

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typically discharged directly into local streams upon entering the valleys, or in some cases

may be intercepted by a high permeability horizon and directed along strike (Seaver etal., 1988).

The most productive units are generally soluble carbonate strata, especially whenassociated with thick deposits of regolith, as the regolith often serves as an important

storage reservoir throughout most of the region (Seaver et al, 1988). When a sufficientthickness of regolith is present, water that might ordinarily be lost as runoff may be

stored and then slowly discharged to the underlying aquifers. Sandstones in the Valleyand Ridge typically possess intermediate porosity and permeability, while clastic shales

and siltstones are generally the least productive units within the region. Shales andsiltstones often serve as confining aquitards between more productive fractured units,although shales may act as aquifers locally when they are hard and brittle enough tomaintain open fractures (Seaver et al., 1988).

The Paleozoic units of the Valley and Ridge are characterized by low primary porosityand permeability. Secondary porosity and permeability features are associated with

fracturing and dissolution. These are typically concentrated in the upper portion of thebedrock, and are-important in the storage and transmission of groundwater throughout

the region (Seaver et al., 1988). The frequency and distribution of fracture and dissolutioninduced secondary porosity and permeability are principally responsible for the

occurrence and flow of groundwater within the major Paleozoic aquifers of the province.

5.3 Site Hydrogeology| As discussed in Section 1.2, the focus of the field hydrogeologic investigations was the| Pond 5 environs, and the eastern and southeastern margin of Pond 6. The FCPS was the| subject of two previous hydrogeologic studies in 1976 and 1982. The site hydrogeologic| conditions have been grouped into categories of the FCPS, the bedrock hydrogeology and

| the Ponds 5 and 6 hydrogeology. The RI and previous studies have indicated that the| hydrogeologic conditions are similar for the FCPS, Pond 5, and Pond 6 based on the:

I| • continuity of geology along strike and dip beneath both ponds;I| • similar hydrogeologic controls provided by the underlying alluvium,I bedrock lithologies and structural geology;

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| • similar adjacent recharge mechanisms, runon and interflow in shallowj fractured bedrock/colluvium; andI| • similar dike construction and pond solids properties, including aj developed network of vertical consolidation fractures extending the lengthj of the ponds, trending toward the decant structure and apparentlyj collecting flow from the area of the swales along the north side of thej pond.

5.3.1 FCPS HydrogeologyAs noted above, the FCPS has been the subject of two previous hydrogeologicinvestigations. The studies, conducted by Harza in 1976 and Olin in 1982, werecompleted following demolition and removal of the chlorine plant equipment and prior

to encapsulation of sediments removed from the NFHR and capping of the FCPS.

Review of the reports indicates that the geologic formations identified as underlying thesite were incorrect. However, the lithologic descriptions of collected bedrock samples fit

the upper Little Valley Formation as described in the measured geologic section presentedin Figure 4-2. These upper units underlie the Hillsdale Limestone Formation which is

exposed in the adjacent NFHR. They comprise slightly to moderately weathered,laminated to thinly laminated gray to greenish gray intercalated calcareous siltstone andsilty and sandy limestones with some fossiliferous beds (generally in earthy shales leachedof original lime) (Cooper, 1966).

During the course of the geologic mapping for the RI, several units were noted in theLittle Valley Formation that were relatively soft and would be difficult to sample duringdrilling. These units comprised soft earthy shales and siltstones. During the course ofdrilling beneath the Pond 5 dike it was recognized that occasionally the coring equipmentwould pass from a competent sandstone or limestone into a softer brown unit. In theseunits, the recirculation water would turn brown and there was no recovered core.During drilling of borehole D-3, the upper contact of rock was recognized in a split spoonsample as highly weathered earthy shale and a carbide HQ bit and coring equipment wasused to recover the weak rock material. Even using such equipment, recovery waslimited.

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Review of the Harza and Hiltgen boring logs raises questions with regard to the accuracywith which the upper rock contact was identified at the FCPS. The logs frequently cite

that alluvium was cored and that boulders of sandstone were encountered "generallywith a soft silty and sandy clay matrix" (reference Exhibit 4, Section A-A1) or recorded

"boulders, fine grained red and white sandstone. Driller reports 4 soft zones betweenboulders, each 5 to 9 inches thick, between 12.5 to 15.75 ft" (reference field log for Harzaboring C-ll). These logs also show that core runs up to 5 feet long were made inalluvium. It is unusual that as many full 5-foot runs could be made in alluvium withoutcored pieces from boulders or pieces of gravel blocking the core barrel as would

customarily happen when coring boulders. Also, the upper rock contact is not identifiedin Harza borings C-9 and C-10. However, as shown in Exhibit 7 of the Harza report, the

identified alluvium extends at least 10 feet below the level of the NFHR. The NFHRchannel adjacent to the plant site has exposed bedrock of the Hillsdale Limestone

Formation, and was so mapped by Cooper in 1966.

Because of the inconsistencies in the Harza and Hiltgen logs, and observed conditionsnoted during mapping and drilling downstrike at the Pond 5 dike, the alluvium noted

| in the previous investigations is probably soft bedrock comprising the intercalated| lithologies described in Section 4 and by Cooper(1966). The elevation of bedrock beneath| the FCPS would therefore be greater than the elevation of bedrock in the adjacent NFHR| channel. This stands to reason because the river would have preferentially eroded its] channel in such alluvium rather than the Hillsdale Limestone in its current channel. The| probable higher elevation of bedrock than noted in the logs is further supported by the| presence of an adjacent resistant bedrock knob across RTE 634 from the FCPS which has

| been excavated for recent (and past) roadway construction. Based on the more recent RI| geologic and hydrologic data, a revised interpretation of the previous boring logs suggests| that the bedrock surface should be about 4 feet to 8 feet higher than is shown on the| previous report cross sections, at about the location where the start of diamond coring| was required.

I| Groundwater flow occurs at the FCPS in the fill/alluvium and bedrock underlying the site.| Flow in the bedrock is probably confined to individual rock units (i.e., individual beds of| sandstone/siltstone or limestone) and along the upper weathered rock contact in residual| soU/colluvium. Although Harza considered that some flow of groundwater in bedrock

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| (trace amounts) occurs, current study results suggests that movement of groundwater| upsection through lithologies of high permeability contrast (i.e., from a sandy limestone| upsection through an earthy shale weathered to clay) is unlikely. Thus, the shortest and| most preferential groundwater path, possessing the highest permeability, is through the[ alluvium/fill beneath the site to the NFHR. Discharge of deep groundwater, probably| unaffected by the site, is to the NFHR upstream of the FCPS or to Robertson Branch| Creek where flow along strike within individual beds can discharge.

I| 5.3.2 Bedrock Hydrogeology

The following sections present a description of the findings of the hydrogeologicinvestigation with regard to the hydraulic properties and flow within the bedrock

underlying the site.

| 5.3.2.1 Bedrock Hydrostratigraphic UnitsThe principal bedrock flow regimes beneath the facility were delineated based upon thefindings of the geologic and geotechnical investigation as described previously in Section2.6. In general, hydrostratigraphic divisions have been made based upon detaileddescriptions of bedrock lithology, fracture frequency and orientation, and overall geologicstructure.

The site is underlain by a sequence of Devonian and Mississippian age sandstones,siltstones, shales, and limestones. These rocks have been subjected to bothsyndepositional and postdepositional deformation, resulting in the formation of asyncline. Regionally this structure has been dissected by a thrust fault which has resultedin the overturn of the southeastern limb of the syncline. Many of the shale units(particularly the Maccrady) exhibit drastic variations in thickness due to both subsidenceduring deposition, and plastic deformation during folding. Numerous lineaments areevident in the sandstone and limestone units. The lineaments control the direction ofsurface water flow and may also act as conduits between the surface water andgroundwater flow systems. Additional localized fracturing of the shallow bedrock maybe due in part to previous blasting activities which were used to remove part of a knobformerly located at the southeast corner of Pond 5 prior to rerouting the North Fork ofthe Holston River.

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The geologic units were grouped into a series of hydrostratigraphic flow regimes to reflect'lithologies which are believed to possess similar flow and hydraulic characteristics. Thesedelineations have been made based upon lithologic type, fracture frequency andorientation, and overall geologic structure. In general, the interpreted hydrostratigraphic

divisions consist of alternating zones of shales, interbedded sandstones, limestones, andsiltstones with smaller amounts of interbedded shale, which do not typically coincide with

formational contacts. The delineated hydrostratigraphic divisions in the bedrock areshown in Figure 5-1.

Presented below, from youngest to oldest, are detailed descriptions of each of theinterpreted hydrogeologic units:

Unit 1 Ste. Genevieve and Hillsdale Limestone - Approximately 750 feet of fossiliferousgray limestone exposed in the core of the Greendale Syncline. These units underlie the

| Sinkhole Knobs. Bedding dips from 30° SE on the upright limb, to 60° NW on theoverturned limb.

Unit 2 Hillsdale Limestone Formation and Little Valley Formation Shale - Approximately65 feet of thinly laminated, fossiliferous, calcareous shale with intercalated siltstone. This

unit underlies the current channel of the North Fork of the Holston River, adjacent toPond 5, and is exposed along the banks.

Unit 3 Little Valley Formation sandstone, siltstone, limestone, and shale - Approximately300 feet thick, this unit consists of 50 feet of predominantly sandstone and siltstone,underlain by 80 feet of gray to yellow weathered shale and siltstone, from which originallime has been leached (Cooper, 1966), and 185 feet of sandstones dolostones andlimestone.

Unit 4 Maccrady Shale - Approximately 20 feet of the upper red plastic shale member ofthe formation. This unit probably forms a partial barrier to flow trending E-W beneath

the base of the pond.

Unit 5 Maccrady limestone, siltstone, sandstone, and dolostone that forms the majorityof Maccrady Formation - Approximately 100 feet thick, with intercalated shale.

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Unit 6 Maccrady and Price Formation shale and sandstone - Approximately 10 feet of

shale, underlain by 8 feet of dense sandstone, and another 8 feet of shale. This unitconfines the lower artesian portion of MW-1, and can be seen as a resistant outcrop onthe lower slopes of Little Mountain.

Unit 7 Price and Parrot Formation sandstone - Approximately 270 feet of thin to medium

bedded sandstone with some intercalated siltstone. This unit crops out on the slopes ofLittle Mountain from approximately 200 feet north of Pond 5, to the break in slope on the

north side of the ridge.t

Unit 8 Undifferentiated Devonian shale - Of undetermined thickness, this unit crops outon the north side of Little Mountain. The top of this unit forms the base of the modeledsection.

5.3.2.2 Bedrock Hydraulic Conductivity

Determinations of hydraulic conductivity in the bedrock were obtained from theperformance of rising and falling head slug tests in several of the site wells, and from

pressure packer tests of discrete intervals in 2 borings, prior to the installation ofgroundwater monitoring equipment. There are several different sources of these data

which are described below:

Golder, 1989 - Pressure packer testing in boring MW-1 and P-2 in units 6and 7 (see Section 2.6.3, Table 5-1, and Appendix D);

Golder, 1989 - Variable head tests in 13 bedrock monitoring wells locatedin and around Pond 5 (see Table 5-2 and Appendix G); and

Harza, 1976 - Rising and falling head tests in 7 bedrock borings at theFormer Chlorine Plant Site (see Table 5-3).

Table 5-2 presents the results of variable head tests performed in both the bedrock andfill within the Pond 5 area. A description of the lithology tested for each well is alsoincluded in this table. The raw data and calculations for each of the Pond 5 area wellstested by Golder are presented in Appendix G. Table 5-3 presents the results of thevariable head tests performed by Harza (1976) at the FCPS, along with a description of

each lithology tested.

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Presented in Table 5-1 is a summary of the results of the packer testing conducted inboreholes MW-1 and P-2.

The results of variable head tests performed in the uppermost portions of the bedrock

were compared to the results from wells which were screened well within the rock strata.Test results for wells MW-1S, MW-2, MW-3I, MW-5I, MW-8D, MW-9D, and MW-10D weregrouped together for comparison purposes since the top of the sand pack for each of

these wells is generally within the upper 10 feet of the bedrock. Similarly, test results forwells MW-1D, MW-3D, MW-4, MW-5D, and MW-7D were used to represent the

magnitude of hydraulic conductivities at depth, as the top of the completed intervals foreach of these wells were generally located at least 30 feet into bedrock. The geometric

| mean of hydraulic conductivity for the upper bedrock wells was calculated as 2.1 x 10"5cm/sec. In contrast, the geometric mean of hydraulic conductivity for the deep bedrock

| wells was estimated at 3.4 x 10"6 cm/sec. Thus, this comparison suggests thatpermeabilities within the upper portions of the bedrock are approximately one order ofmagnitude higher than those at depth. This may be due in part to a reduction in fractureaperture width and frequency with depth.

Comparisons were also made between the results of pressure packer tests performed inborehole P-2 (CO-3) and the rock core log (provided in Appendix C) for each test interval.

In general, the Rock Quality Designation (R.Q.D.) of the recovered core is lowest, and thefracture frequency index highest, within the upper 50 feet of the bedrock (or within about

60 feet below ground surface). At depths greater than 60 feet below ground surface, theR.Q.D. typically ranges from approximately 85 percent to 100 percent, and the fracturefrequency index is generally less than 5 fractures per foot. In contrast, the upper 50 feetof the bedrock at P-2 is characterized by an R.Q.D. which ranges from 0 percent to 100percent (less than 10 percent for the upper 30 feet of bedrock), and a fracture frequencyindex which ranges from less than 5 to over 25 fractures per foot.

Pressure packer tests conducted in the upper 47 feet of the bedrock were grouped for| comparison purposes. The geometric mean of hydraulic conductivity was 1.7 x 10"4cm/sec. A geometric mean of hydraulic conductivity was also calculated for the pressurepacker tests performed in the lower 60 feet of borehole P-2. The geometric mean of

| hydraulic conductivity for this lower interval was estimated at 5.3 x 10"5 cm/sec. These

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results suggest that the upper portions of the bedrock possess hydraulic conductivities'

which are close to one order of magnitude higher (on average) than deeper horizons.The variable head tests suggested the same conditions.

It should be noted that a hydraulic conductivity value could not be calculated for a

packer test conducted near the bottom of borehole P-2, since no flow was observedduring testing. Additionally, a pressure packer test conducted from 87.11 ft to 97.11 ftbelow ground surface resulted in a hydraulic conductivity estimate of 9 x 10-3 cm/sec,

which is inconsistent with observations made in the borehole record. This test result may| be somewhat elevated due to packer bypass through subvertical fractures which areknown to exist beneath this portion of the site (see Section 4.0). Bypass around thepackers due to improper inflation is considered unlikely, because an inflation pressure of,

approximately 450 psi was used during this test, which greatly exceeds the maximuminjection test pressure of 60 psi. Therefore, the estimated mean hydraulic conductivity

of the lower portion of the borehole is probably somewhat lower than the viable testresults would indicate.

Hydraulic conductivity estimates derived from pressure packer tests were compared toresults obtained from rising head tests where both types of tests were performed on the

| same interval within the same borehole. Comparisons between rising head test and| packer test results in borehole MW-1D indicated values of hydraulic conductivity of 2 x| 10"6 cm/sec and 1 x 10"3 cm/sec, respectively. The disparity in the comparison of the

results obtained from the two types of testing methods may be explained by one or more

of the following factors:

1. Due to the high yield of artesian well MW-1D, which was flowing at a rateof about 0.5 gpm prior to testing, water could not be withdrawn at a highenough rate to create sufficient drawdown to complete an accurate slugtest. This may have resulted in a misleading estimate of permeability.

2. Bypass may have occurred around the packers in the test of MW-1D,resulting in an elevated value of hydraulic conductivity. This bypass mayhave taken place through vertical fractures adjacent to the borehole, orthrough a damaged section of the borehole. Improper packer inflation isnot considered likely, as the test inflation pressures used were well inexcess of test injection pressures.

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The bedrock flow system appears to be strongly controlled by fractures and partingsoriented in the direction of the bedding, which dip approximately 30 degrees across the

site. Thus, because of the dip of the bedrock strata beneath the site relative to theorientation of boreholes and test wells, the hydraulic conductivity values may or may notrepresent actual maximum values of horizontal permeability. However, if the degree ofinterconnection between fracture sets is significant, this may offset these differences in

orientation, such that discrepancies between measured and actual horizontal hydraulicconductivity may be slight.

Overall, the distribution of hydraulic conductivity values in the bedrock, both areally andwith depth, suggest a high degree of heterogeneity throughout the bedrock flow system.

In general, hydraulic conductivity values appear to be higher in the upper portions of thebedrock where fracture distribution and frequency and weathering are most prevalent.

The magnitude of permeability within any given stratum is likely controlled to a greatdegree by secondary porosity and permeability characteristics affiliated with fracturing,weathering, and dissolution. These findings are consistent with existing knowledge ofthe hydrogeology of this region (see Section 5.2).

5.3.2.3 Potentiometric Level Fluctuations

The complete water level database for all wells, piezometers, and borings is presented inAppendix H. Hydrographs based on monthly monitoring data collected in 1990 are also

provided in Appendix H.

Daily water level measurements were initiated in select wells in late 1990, and continuedinto 1991. Collection of these data allowed for the comparison of daily water levelfluctuations to daily precipitation events. This information was then used to assess therelative importance of precipitation as a recharge mechanism for the various hydrologicunits at the site.

Figures 5-2A and 5-2B present sample comparisons of daily water level response inbedrock well P-7D (screened in the bedrock beneath the pond), to plots of daily andcumulative precipitation for the months of March and April 1991, respectively. As Figure5-2A illustrates, individual precipitation events do not necessarily result in direct

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correlations in water level response, however, longer term precipitation trends correlateto general water level trends.

A significant rise in groundwater elevation occurs in late March and early April. This is

considered to be the result of large precipitation events over the time period immediatelypreceding the increase in water level within the bedrock and much higher runoff and

infiltration due to reduced seasonal evapotranspiration. Figure 5-2B compares thecumulative precipitation during March and April 1991, to daily water levels recorded over

the same period. The data suggest that larger and more rapid increases in water levelelevations take place only after a period of continued significant rainfall. Similarly, water

levels began to decline within a few days following the onset of a dry period lastinglonger than several days. Similar responses were observed in other wells completedwithin both the bedrock and ASAW. (Fluctuations within the ASAW are discussed ingreater detail in Section 5.3.2.3.)

Wells completed within the bedrock do not appear to be dramatically affected by isolatedprecipitation events. The level of response observed within the groundwater system

seems to be more dependent upon duration and frequency of events. Some time lag isevident in water level responses in some of the site wells, relative to the advent of

precipitation. This time lag is generally on the order of a few days. On other occasions,there is little measurable response in groundwater elevation due to isolated or shortduration precipitation events. Rainfall from short but intense precipitation events may

| travel rapidly overland as runoff or through the fracture system in the pond solids, and

ultimately to the decant structure. Thus, short, isolated events may not leave enoughwater in residence to result in substantial amounts of infiltration. In contrast, longduration events, or those of high frequency within a limited time period, provide enoughwater over a sufficient period of time to result in infiltration, and thus groundwater level

| response. Therefore, reaction to direct precipitation onto the pond appears to be reflected| in the bedrock well water levels only when the precipitation occurs in long duration, or| high frequency. This reaction is likely due to pressure coupling between the pond and| bedrock groundwater systems during wet antecedent conditions.

Although most of the bedrock wells and piezometers exhibit very similar overall patternsover the year, some well hydrograph records vary somewhat from the average case (see

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Appendix I). For example, piezometers P-l and P-2, and well cluster MW-1S,D, show very

large variations in water levels over the course of the year 1990. All of these wells arelocated within the swales on the side of Little Mountain. Vertical fracture systems exist

on this side of the mountain and form the swales. Dilated and weathered bedding jointsare present in the near surface rock These likely provide viable conduits for the

interception and subsequent deep infiltration of surficial runoff. Rapid response toprecipitation events supports the concept of this area acting as a significant recharge zone

for the bedrock. In contrast, bedrock piezometer P-13D, located along the dike on thenorth side of the NFHR, exhibits one of the smallest variations in water level over thecourse of 1990. In this case, downward infiltration of water is likely inhibited bysomewhat less permeable and less fractured material associated with the dikeconstruction.

As discussed previously, open sub-vertical fractures and dilated bedding joints in the rock

above and below State Route 611 at the base of Little Mountain have been observed toaccept the majority of the runoff from the mountain except in heavy rainfall events.Water flowing into these fractures is believed to recharge the shallow bedrock and wastein the pond where it flows in the buried alluvial and pond fill deposits (see Section 6.2).

Discharge of this shallow flow system into the pond has been observed in Swale 5, andwas the reason for constructing a catch basin between the swale and Western DiversionDitch. When the capacity of these vertical fractures is exceeded, water flows overlandinto the Western Diversion Ditch where it is eventually transferred to the NFHR. Thislimits the total volume of runoff available to supply recharge to the shallow bedrocksystem under the pond.

5.3.2.4 Bedrock Hydraulic Gradients and Flow DirectionsThe 1990 water level data were examined to determine the periods where overall waterlevels in the bedrock were at their highest and lowest points. Water level elevations werelowest during December 1990 and highest during February 1990. Interpolated

potentiometric surface maps of the upper bedrock were constructed for both of theseperiods, and are presented as Figures 5-3A and 5—3B, respectively. Section lines were

constructed at right angles to the equipotential lines at various locations across the siteto obtain estimates of horizontal hydraulic gradients during both the high and low water

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surface periods. The locations of these section lines are shown in Figures 5-3A and 5-3B.

Table 5-4 presents calculated horizontal hydraulic gradients during December and

February 1990. Gradients were calculated by dividing the change in hydraulic head bythe distance over which the change occurred. The gradients are representative of those

changes which occur in an idealized horizontal plane across the site. Actual overall flowdirections and magnitudes are 3-dimensional in nature, but the data may only beassimilated by performing analyses in idealized horizontal and vertical planes. Calculatedgradients are based upon the assumption of isotropic conditions, as the magnitude,direction, and distribution of any anisotropy is not known.

The horizontal hydraulic gradients within the upper bedrock vary from 0.020 ft/ft to 0.308

ft/ft during December 1990 (Table 5-4). Gradients are highest in the southeastern portionof the site near the dike and the NFHR, and lowest in the west-central area of the site

beneath the fractured portion of the pond. In addition, it is anticipated that gradients inthe bedrock on the side slope of Little Mountain are quite high as this is an area of

recharge and steep topographic gradients. However, data are not available which wouldallow quantification of the gradients in this area.

Horizontal hydraulic gradients during February 1990 ranged from 0.029 ft/ft to 0.286 ft/ftacross the site (Table 5-4). Again, gradients were highest in the southeastern portion ofthe site near the river, and lowest in the west-central part of the site beneath the pond.Overall gradients were slightly higher in most areas during this period when the bedrockpotentiometric surface was at its highest yearly level, as compared to the period whenwater levels were at their lowest point.

Examination of groundwater potentiometric surfaces during high and low water level

periods in the upper bedrock suggests that overall groundwater flow is generally in asoutherly direction (Figures 5-3A and 5-3B). Flow generally takes place from LittleMountain north of the site, across the site to the NFHR in the south. Interpolation ofgroundwater contours suggests that the river acts as an area of groundwater dischargeand that Little Mountain and direct precipitation likely serve as the principal areas forrecharge to the shallow bedrock portion of the flow system.

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Flow to the NFHR appears to occur beneath the base of the dike located along thenorthern flank of the river. The data do not suggest any clear influence of the old riverchannel or the decant structure on the direction of groundwater flow within the shallow

bedrock over the bulk of the site; however, this may be due to the level of resolution ofavailable groundwater monitoring points. The bedrock knobs located in the southeastern

portion of Pond 5 appear to act as localized zones of recharge to the shallow bedrocksystem. Groundwater appears to be preferentially directed around these knobs within

the shallow bedrock. Groundwater moving between and around the bedrock knobsappears to be discharging toward a common area of somewhat higher permeability

(possibly toward a bedrock lineament feature). There is no apparent significant differencein the inferred direction of groundwater flow between periods of high and lowgroundwater levels.

5.3.2.5 Bedrock Vertical Gradients

Comparisons of shallow and deep bedrock well and piezometer data were made for boththe high and low water level conditions to assess the vertical gradients within the

bedrock flow system. In general, clustered bedrock wells or piezometers were used forcomparison. Table 5-5A presents the bedrock well pair data used to assess vertical

gradients during February 1990 when overall groundwater elevations were at theirhighest level during the year. Similarly, Table 5-5B presents those well pair data used to

determine vertical gradients during that portion of 1990 when overall water levels werelowest (December). Gradients were calculated by dividing the change in hydraulic headbetween appropriate wells in a given cluster, by the distance between the centers of thescreened intervals of each well pair.

Vertical Gradients, December 1990Data from the low water level period in December 1990 was examined for 7 wells clusters.Three clusters exhibited upward vertical gradients and four exhibited downward verticalgradients. However, three of the clusters which exhibited downward gradients and oneof the clusters that exhibit upward vertical gradients had gradients which were very closeto zero in magnitude (and have been noted as such in Table 5-5B). This suggests more

or less horizontal flow in these areas (Table 5-5B). Well clusters located near the NFHR(MW-3LD, MW-5LD, MW-7LD, P-12LD, and P-15S,I,D) suggest either no vertical gradientor a slight downward gradient in the area adjacent to the river. One cluster (MW-5S,I,D)

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is characterized by a strong downward vertical gradient from the shallow to intermediatedepth bedrock flow system, with essentially no gradient between the intermediate anddeep wells. This suggests that vertical flow is preferentially toward the intermediate

portion of the bedrock system monitored. Vertical gradients as monitored in well clustersnear the NFHR do not exhibit distinct upward flow as might be expected in a zone ofgroundwater discharge. However, groundwater elevations during both low and highwater table periods (Figures 5-3A and 5-3B, respectively) suggest discharge to the river,which is consistent with the regional hydrogeology discussed in Section 5.2. Bedrock wellclusters completed in the dike area do not likely possess sufficient vertical separation toreflect pronounced upward gradients at this distance from the river.

The two well clusters (MW-1S,D and P-2S,D), which are located near the base of LittleMountain, both exhibit upward vertical gradients, suggesting discharge of groundwaterfrom the deeper bedrock to the upper bedrock. These upward gradients are due to the

presence of a relatively unf ractured sandstone bed. Beneath this layer, artesian conditionshave been measured. The layer is considered to be continuous by virtue of the fact that

artesian conditions were noted in MW-1 and P-l which are located in Swales 2 and 4,respectively.

Vertical Gradients, February 1990Similar comparisons of vertical gradients were made in the same well clusters as discussedabove when the overall bedrock potentiometric surface was at its highest level. Table5-5A presents the results of the vertical gradient analysis for each well cluster studied.Of the seven well clusters examined, four exhibited upward vertical gradients, and threedemonstrated downward vertical gradients. Vertical gradients were generally more

pronounced during the high water level period than the low period described previously.

Well clusters located along the dike near the NFHR (MW-3LD, MW-5I,D, MW-7LD,P-12LD, and P-15S,I,D) possessed moderate to small upward vertical gradients or small

downward gradients. Once again, a significant downward vertical gradient did existbetween piezometers P-15S and P-15I, and a very slight downward gradient was apparentbetween P-15I and P-15D. This suggests that vertical flow near this cluster waspreferentially toward the intermediate bedrock zone, perhaps around a zone of greaterfracture intensity. The higher potentiometric heads present during February 1990 resulted

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in a more pronounced tendency for upward gradients near the river, reinforcing the '

hypothesis that the river serves as a zone of groundwater discharge for the shallowbedrock portion of the system.

The 2 clusters monitored near the base of Little Mountain, MW-1S,D and P-2S,D, showedupward and downward vertical gradients, respectively. Well MW-1D has consistently

demonstrated artesian heads which likely explains why gradients at this location aregenerally upward. A high pressure zone must exist at depth which may be fed by

recharge from Little Mountain. This high pressure zone, in turn, likely supplies aconstant source of water to the upper bedrock portion of the flow system.

Examinations of precipitation data (see Section 6.2) indicate that precipitation during

February was moderate (4.83 inches). Precipitation for the preceding month of Januarywas also moderate at 4.61 inches. More precipitation was measured during the months

of May, July, October, and December, although water levels for most bedrock wells werehighest in February (a few wells were slightly higher in other months).

It should be noted that the months preceding the 4 wetter months had only smallamounts of precipitation, and that evapotranspiration is generally higher in most of thesemonths than it is in February. The fact that water levels are generally highest inFebruary, is influenced by 2 major factors. First, examinations of daily precipitation data

indicate that monthly water level measurements were often recorded at times when theprecipitation at the time of collection was disproportionately low or high relative to themonthly precipitation as a whole (i.e. the water level for December occurred at thebeginning of the month whereas the precipitation for December all occurred at the end

of the month). Thus, monthly water levels do not necessarily reflect the distribution ofprecipitation within a given month, rather, they reflect the time immediately precedingwater level collection. Second, some wells do not exhibit the same overall seasonalpatterns as the majority of wells, suggesting the degree of vertical and horizontal fractureinterconnection at any given location to the flow system may vary. Therefore, althoughhigh and low water level conditions were selected based upon the behavior of themajority of the site wells and piezometers, different amounts of precipitation at differenttimes of year seem to cause some wells to exhibit their highest (or lowest) responses atsomewhat different times. The mechanism for this response is not clearly understood,

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however, this phenomenon has some impact on the evaluation of vertical gradientswithin the bedrock system. For example, examinations of water levels in cluster MW-7LDindicate that like most of the site wells MW-7I has the highest water level duringFebruary 1990. However, MW-7D has a much greater response during August. Althoughthe precipitation during August was actually less than it was in February, the precedingmonth of July had the second largest amount of precipitation.

Thus, vertical gradients calculated during overall high or low periods cannot necessarilybe assumed to represent gradients during times when all wells have their highest orlowest water levels. In fact, such a comparison is not possible since gradients would have

to be calculated based upon water elevations taken during different times of the year inthe same well cluster. This does not mean that the gradient determinations made for thesite wells are without use. Rather, the combination of varying precipitation intensitiesand durations relative to water level elevation and vertical gradients, provide useful

insight into the character of the site flow system. In general, the vertical gradientscalculated from data obtained during February and December are reflective of existingvertical flow conditions during the seasonal extremes in water level, since the majority ofwells exhibit consistent results during these time periods. The implications of water levelfluctuations in response to precipitation events is discussed in greater detail in Sections5.3.2.3 and 5.3.3.3.

5.3.2.6 Bedrock Groundwater Flow VelocitiesGroundwater seepage velocities were calculated for the bedrock along the section lines

shown in Figures 5-3A and 5—3B, low and high water level periods respectively.Groundwater seepage velocity is dependent upon the hydraulic conductivity of the

medium, the horizontal hydraulic gradient, and the effective porosity. The seepagevelocity can be described by the equation (Freeze and Cherry, 1974):

y=__K_dh_ne(dl)

where: Vs = seepage velocityK = hydraulic conductivitydh = change in hydraulic headdl = distance over which dh occursne = effective porosity

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Of the required parameters, the effective porosity is the most poorly known. Maximum

and minimum values of effective porosity were selected from a range of values forfractured rock, and used in calculations of seepage velocity for the bedrock system.

Minimum and maximum values of 1 percent and 10 percent, respectively, were obtainedfrom Freeze and Cherry (1974). One pressure packer test was conducted in theuppermost portion of the bedrock in borehole P-2. The resultant hydraulic conductivity

value of 4 x 10"5 cm/sec, was used in all subsequent calculations of seepage velocity sincethis was the most appropriate estimate of this parameter available. Using the above

referenced parameters, the idealized horizontal hydraulic gradient from each respectivesection line was used to calculate a seepage velocity for each designated location across

the site. Estimates of seepage velocity across the section lines depicted in Figures 5-3Aand 5-3B for the low (December) and high (February) water level periods are presented

in Table 5-6.

Seepage velocities ranged from 0.33 ft/day up to 3.2 ft/day for effective porosities of 1percent, and 0.033 ft/day to 0.32 ft/day for porosities of 10 percent during February 1990(high groundwater level) (Table 5-6). The highest seepage velocities were in areas where

the horizontal hydraulic gradient was highest, since the same permeability and porosityestimates were used in all calculations. As would be expected, seepage velocities were

highest for the minimum estimated value of effective porosity.

Similar calculations were performed for the December 1990 low groundwater period.Seepage velocities ranged from 0.23 ft/day up to 3.5 ft/day for an effective porosity of 1percent, and from 0.023 ft/day up to 0.35 ft/day for effective porosities of 10 percent (Table5-6). As before, the magnitude of seepage velocity across the site varied in accordance

with the horizontal hydraulic gradient.

5.3.3 Pond Fill Hydrogeology5.3.3.1 Pond Fill Composition

The character of the fill in Pond 5 is described in detail in Section 3.2.2. Stratificationwithin the ASAW is approximately horizontal, due to its method of deposition. Thecomponents of the fill cannot necessarily be defined as distinct hydrogeologic units,although variations in ASAW structure and composition may serve to create zones of

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variable flow behavior in some cases. Presented below is a brief description of the various'

components within the Pond 5 fill:

Ammonia Soda Ash Waste

Silt to sand sized material was deposited within Pond 5 as a slurry. The contentand coarseness of sand size particles are highly variable; however, the sand iscontained in a very fine grained matrix. Saturated samples of the ASAWlaboratory tests tended to develop cracks. Laboratory testing of saturated samplesof ASAW by Golder found water contents ranging from less than 100'percent togreater than 200 percent of the sample dry weight.

Starter Dike

Coarse grained material, consisting of blasted rock and excavated surface material,was laid down to divert the NFHR and initiate construction of the Pond 5.

Dike

Primarily, slaker waste was placed over the starter dike to raise the dike, confinethe pond and regulate seepage through the dike. An upstream weathered shaleblanket, worked to a soil/clay consistency was placed over the upstream face ofthe starter dike to inhibit seepage through the starter dike.

Fill, Natural Ground, and Residual Soil

These materials consist of sand, gravel, silt, and clay sized particles and can bedifficult to distinguish from one another in borings due to similar lithology.

5.3.3.2 Pond Fill Hydraulic ConductivityEstimates of hydraulic conductivity within the pond fill were obtained from theperformance of rising and falling head tests in several site wells, cone penetrometerstudies in the ASAW, and laboratory permeability estimates from materials extracted fromboreholes W-2 and W-3. There are several different sources of these data which aredescribed below:

Golder, 1989 - Variable head tests in 5 of the fill monitoring wells located in Pond5 (see Table 5-2 and Appendix G).

ARA, 1989 - Cone penetrometer tests in the ASAW in Pond 5 (see Section 2.6.5,and Appendices E and F).

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Wehran, 1981 - In-situ and laboratory permeability tests of borings W-2 and W-3in ASAW (see Table 5-3).

Harza, 1976 - Rising and falling head tests in 10 borings completed in the fill andalluvium at the FCPS (see Table 5-3).

Presented in the following sections are descriptions of the methods and results from thepermeability testing of the Pond 5 fill.

Variable Head TestsRising head tests were performed in 4 wells completed in the fill by Golder, immediately

following development. A falling head test was performed in one well (MW-5S) becausethere was insufficient water present to perform a rising head test. All rising and falling

head tests were completed and analyzed using the procedures described in Section 2.6.

In addition to the variable head tests performed by Golder, similar tests were conductedby Wehran (1981) in wells W-2 and W-3, and by Harza (1976) around the FCPS. Table5-2 presents the results of all variable head tests performed by Golder in the fill.

| Hydraulic conductivities from these tests ranged from 5.1 x 10'7 cm/sec in the ASAW| (MW-7S), to 5.4 x 10"4 cm/sec in the cemented alluvium (MW-6). A description of the type

of fill tested is provided in Table 5-2 for each well. The raw data and calculations for allvariable head tests are presented in Appendix G.

Table 5-3 presents the results of the rising head tests performed by Wehran Engineering(1981) in borings W-2 and W-3, along with the results of tests conducted by Harza (1976)in wells at the FCPS. Both variable head tests performed in the ASAW by Wehran

| yielded values of 1 x 10'5 cm/sec. Tests performed by Harza in the fill and alluvium| ranged from less than 1.6 x 10'5 cm/sec (C-12), to 1.4 x 10'2 cm/sec (C-4). A great deal of

heterogeneity was exhibited by the FCPS wells tested by Harza.

Cone Penetrometer TestsCone penetrometer test estimates of hydraulic conductivity were performed by ARA in1989 at 14 of 26 penetrometer test locations. Testing was accomplished in each hole atseveral different depths. The details of cone penetrometer testing are discussed in Section

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2.6.5. Appendices F and I present the raw data and results of testing at each depth foreach location where permeability was estimated.

Cone penetrometer test results indicate fairly good agreement between values of

hydraulic conductivity at different depths within a given hole. Except in a few cases,permeability estimates generally varied by less than one order of magnitude with depth,at any particular location. Examinations of cone penetrometer plots of cone tip pressure(ARA, 1989) reveal sharp spikes suggesting the existence of more resistant, coarse grainedor cemented layers within the ASAW, generally less than 2 feet in thickness. Thepermeabilities of these layers may not be reflected in the cone penetrometer data due tothe larger spacing (5 feet) between pore pressure dissipation tests. At refusal, the cone

penetrometer indicated very low permeabilities at the base of pond/top of bedrockinterface.

Laboratory Tests

Laboratory tests were performed on ASAW samples collected by Wehran Engineering(1981) from boreholes W-2 and W-3. The results of the triaxial testing indicated vertical

| and horizontal hydraulic conductivity values of 6.2 x 10"7 cm/sec and 2.5 x 10"7 cm/sec,respectively for samples collected from W-2 (Wehran, 1981). A vertical hydraulic

| conductivity was determined for a sample from boring W-3, and estimated at 5.6 x 10'7cm/sec (Wehran, 1981). These values are about 2 orders of magnitude lower thanestimates for the same holes derived by in-situ permeability testing. Wehran (1981) statedthat the in-situ permeability tests are probably more indicative of true horizontalhydraulic conductivity than the laboratory tests. One possible explanation for this maybe that solutioned openings and fractures within the ASAW cannot be adequatelypreserved in laboratory samples, thus apparent permeabilities are lower. In general,in-situ estimates of permeability are regarded as more reliable than laboratory tests, wherethe natural structure of samples may be disturbed, and where secondary porosity andpermeability features usually cannot be adequately preserved. It should be noted,however, that a 1/4-inch wide crack formed in ASAW, under 1+ foot of water, duringhydrometer analysis testing in the laboratory. This suggests that the fracture features inthe ASAW may extend below the water table within the ponds.

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Discussion of Results

Permeability tests were conducted in the soil fill, slaker waste, ASAW, alluvium, residualsoils, and bedrock. With the exception of the soil fill and alluvium, there are not enoughestimates of permeability in other materials, and in particular the fractured ASAW, todraw comparisons of overall hydraulic properties between the various components ofPond 5. In general however, the alluvium at the base of the pond seems to possess thehighest overall intact material permeability. Estimates of permeability from the four tests

conducted range from 5.4 x 10"4 cm/sec (MW-6) up to 1 x 10'2 cm/sec (C-ll), with anoverall geometric mean of 2.4 x 10"3 cm/sec. Hydraulic conductivities within the fill exhibit

a great deal of heterogeneity in this portion of the pond, and range from 5.1 x 10~* cm/sec(MW-3S) to 1.4 x 10'2 cm/sec (O-4), with an overall geometric mean of 2.4 x 10"4 cm/sec.

In general, it is anticipated that the pond fill and ASAW possess highly variable hydraulicproperties, owing to the irregular size and distribution of fractures. These features havebeen observed some times to collapse, and at other times to open at the pond surface, asa result of surface water flow, changing levels of moisture and the response of therelatively weak pond material to consolidation and erosion. Thus, the distribution andintensity of secondary porosity and permeability features appears to vary from location

to location. Therefore, specific conclusions regarding the hydraulic properties of theASAW, as compared to the alluvium for example, are difficult. The hydraulics of the

ASAW are believed to be somewhat similar to karstic limestones, except that the structureof the ASAW is much more varied and is less predictable owing to its lack of strength andstructural control compared to limestone.

5.3.3.3 Potentiometric Level FluctuationsThe complete water level database for air wells, piezometers, and borings is presented inAppendix H. Hydrographs developed using monthly monitoring data collected in 1990,are also provided in Appendix H.

The majority of high water levels were recorded in February while the lowest wererecorded in December of 1990. In general, most wells exhibit a pattern over the yearwhich indicates water levels are higher in earlier months, with a gradual decline in thewater table taking place towards the end of the year. These findings are consistent withwater levels recorded from wells and piezometers completed in the bedrock. As stated

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previously in Section 5.3.1.3, the highest and lowest overall water level elevations do notnecessarily correspond to months in which the precipitation was highest or lowest.

Hydrographs of daily water levels, recorded in select wells during December 1990, werecompared to daily precipitation data recorded at the wastewater treatment plant. Figures

5—4A and 5-4B present comparisons of water level fluctuations recorded in well clusterP-8S,D to precipitation data compiled over the same period. Figure 5—4A presents a

comparison of daily water level data collected from P-8D (completed in the alluvium), anddaily precipitation recorded during December 1990. As this figure shows, there is noimmediate response in the groundwater table to the initial precipitation events. However,as precipitation continues for a sufficient time period, water levels within P-8D graduallybegin to rise. Similarly, examination of cumulative precipitation data during the monthof December indicates that water levels do not respond to small amounts of cumulativeprecipitation as shown in comparisons to daily water levels in P-8S in Figure 5-4B. Aresponse is seen only after periods of prolonged rainfall. Variability in water levelresponse between wells to precipitation may be explained by variations in fractureintensity and distribution around each screened interval.

In addition, some of the disparity seen between highest and lowest water level responsein a particular well, relative to the amount of rainfall recorded in those months, may bedue to the timing of monthly water level collection. For example, although there was amoderate amount of precipitation during December 1990, a majority of the wells exhibittheir lowest water levels during this time. However, the preceding month of November,had the lowest monthly rainfall during the year. Water levels in all wells were recordedbetween December 11 and 12, while the bulk of precipitation fell during the latter half ofthe month, after the monthly readings were taken (see Figures 5-4A and 5-4B). Therefore,the water table elevations recorded at this time reflect the dry period immediatelypreceding the monthly collection of water levels. Care must therefore be exercised whendrawing comparisons between overall monthly precipitation volumes and a singlemonthly water level reading.

Although a great deal of infiltration can rapidly proceed downward through the pondby way of cracks and fractures, the lack of response observed in pond wells andpiezometers following isolated storm events indicates that very little of this water must

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actually infiltrate immediately to significant depths, or into the matrix of the pond. Thereis some evidence that the fill material may have a substantial storage capacity and that

matrix permeability may be very low (see Section 6.2). Indeed, flows at the decant outletseldom exhibit immediate changes in response to individual short term precipitation

events. This may indicate that a great deal of the runoff and precipitation falling directlyon the pond may not directly affect water levels unless enough water is built-up withinfractures to permeate the fill and minor fracture systems. Sufficient volumes of water

within the fractures may have to be established by sustained precipitation in order toprovide adequate impetus for the flow of water into minor fractures and the matrix ofthe fill, thus resulting in a measurable water table response. Short term rainfall eventsare likely only to load major fractures radiating outward from the decant structure, with

enough water to promote flow at the outfall.

5.3.3.4 Pond Fill Hydraulic Gradients and Flow DirectionsExamination of water level data collected during 1990 indicates that the months of highest

and lowest overall groundwater elevations in the Pond 5 wells were February andDecember, respectively. Phreatic surface maps of the low and high water table periodswere constructed for the pond and are presented as Figures 5-5A and 5-5B, respectively.Horizontal hydraulic gradients were calculated along each of the section lines shown inFigures 5-5A and 5-5B, using the methods and assumptions described in Section 5.3.1.4.Table 5-7 presents the results of horizontal hydraulic gradient analyses for the low andhigh water table periods.

The horizontal hydraulic gradients within the Pond 5 area vary from 0.011 ft/ft to 0.103ft/ft during December 1990, and from 0.012 ft/ft to 0.143 ft/ft during February 1990.Horizontal gradients are highest near the dike on the flanks of the NFHR, and lowest inthe central portion of the site around the most fractured portion of the pond, during boththe low and high water table periods of 1990 (Figures 5-5A and 5-5B).

Examinations of groundwater phreatic surface contours during the high and low waterlevel periods in the pond suggest that the overall groundwater flow is toward the south,from Little Mountain to the NFHR. This observation is consistent with findings from thestudy of the shallow bedrock portion of the system. Interpolated groundwater contourssuggest that the NFHR acts as an area of groundwater discharge. Runoff infiltrating into

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the vertical fractures located near State Route 611 at the base of Little Mountain, likelysupplies recharge to the Pond 5 flow system. Groundwater may also be discharged intothe Pond 5 waste from the mountain itself by way of orthogonal fracture sets.

The intensely fractured area in the west-central portion of the pond seems to act as agroundwater sink, diverting much of the flow in the pond toward the decant outletstructure located in the dike at the southwestern margin of the site (Figures 5-5A and5-5B). Groundwater discharge through or at the base of the dike is also implied by thedistribution of hydraulic heads during both the high and low water table periods. Water

level elevations in the dike are frequently high enough to promote flow over the top ofthe upstream blanket and through the starter dike drain, allowing enhanced seepage.

No obvious effects of the old stream channel are evident in the water level data, however,

groundwater monitoring points may not provide enough resolution to distinguish theseeffects. Additionally, the effects of the decant structure and the highly fractured and

dissected zone in the central portion of the pond, may be sufficient to mask influence ofthe old river channel. Groundwater within the pond flow system appears to flow aroundthe bedrock knobs located in the southeastern portion of the site.

A seismic refraction survey of Pond 5 conducted by Law Engineering (1981) revealed no

hard layers within 30 feet of the surface of the pond, and indicated that the water tablewas from 15 to 25 feet below the surface of the pond during the study. In addition, thisinvestigation did not indicate the presence of cracks or voids greater than 6 inches innominal size within the ASAW. There was also no apparent evidence of cracks or largevoids within the ASAW during the cone penetrometer study. This information iscontradictory to field observations made during investigation of the site. Many cracks

and fissures have been observed which extend to unknown depths below the surface ofthe pond. The cracks' possess aperture widths of several inches to almost one foot, andare most intense near the decant structure, from which they radiate outward into thepond trending generally toward the swale discharges on Little Mountain. Severalobservers uncovered fractures which existed just below the pond surface, but possessed

little surficial expression. These observations, taken in conjunction with interpretationsof the Pond 5 hydraulic head data, suggest that flow within the pond is controlled bycracks within the ASAW, which generally divert flow toward the decant outlet structure,

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where it is ultimately discharged to the NFHR. The majority of flow in the pond may,'however, occur within the more permeable alluvial deposits near the base of the pond,with overlying cracks and fractures acting to direct the downward and lateral migrationof groundwater in the direction of the site decant structure. The conceptual flow within

the pond will be discussed in greater detail in Section 5.4.

| 5.3.3.5 Fond Fill Vertical Hydraulic GradientsComparisons were made between hydraulic heads recorded in wells within several

clusters, for both the low and high water table period. The method employed in theanalysis of vertical hydraulic gradients within the pond fill was consistent with theprocedure described in Section 5.3.1.5. The results of the vertical gradient analyses of

wells in the fill are presented in Table 5-8 for the low and high water table periods.

Both of the two clusters suitable for vertical gradient analysis exhibited downward verticalgradients during the high and low water table periods (Table 5-8). Gradients were of

significant magnitude in all cases, particularly at cluster P-8S,D. Well cluster P-4S,D couldnot be used in the final vertical gradient analysis. The integrity of both wells has been

compromised by movement in the ASAW that has resulted in bending of the riser pipes.

| 5.3.3.6 Pond Fill Groundwater Flow VelocitiesGroundwater seepage velocities were calculated for the low and the high water tableperiods along the section lines depicted in Figures 5-5A and 5-5B, respectively.Calculations were performed in accordance with the procedure described in Section5,3.1.6. The effective porosity of the fill material within Pond 5 is not well known. It isdifficult to quantify this parameter in material dissected by randomly distributed cracksand fractures which have been enlarged by solutioning or erosion. Additionally, thereis strong evidence to suggest that the system of fractures within the pond is dynamic,with frequent changes occurring as the result of consolidation and low material strength.However, examinations of geotechnical laboratory data suggest that the effective porositymay be as high as 50 percent. Abo, the morphology of the fill suggests that the pondflow system may behave similarly to karstic limestone, owing to its irregular pattern ofcontrolling fractures in a low permeability matrix. Freeze and Cherry (1974) report thatthe typical range of porosity for such material varies between 5 percent and 50 percent.

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Therefore, minimum and maximum porosity values of 5 percent and 50 percent,respectively, have been assumed for seepage velocity calculations.

A geometric mean of hydraulic conductivity of 1.69 x 10'5 cm/sec, was calculated from

appropriate permeability test results conducted within pond related materials. This valuewas used in all seepage velocity calculations. As a result, the magnitude of the seepagevelocity from section to section changes in accordance with the horizontal hydraulicgradient. Thus, velocities are highest in areas where horizontal gradients are highest,such as the portion of Pond 5 nearest the dike, and lower in areas of lower gradients,such as the central portion of the pond.

Presented in Table 5-9 are the results of the seepage velocity analyses for the fill, for boththe December, 1990, low and February, 1990, high water level measurements. Seepagevelocities for the low water table period of 1990 ranged from 0.11 ft/day to 0.99 ft/day, foreffective porosities of 5 percent, and 0.011 ft/day to 0.099 ft/day for porosities of 50 percent

(Table 5-9). Velocities for February 1990, ranged from 0.11 ft/day to 1.4 ft/day, for effectiveporosities of 5 percent, and from 0.011 ft/day to 0.14 ft/day for porosities of 50 percent(Table 5-9).

5.4 Numerical Modeling Of Groundwater Flow5.4.1 General

A numerical groundwater flow model was developed to aid in the understanding of thesignificant influences of groundwater flow patterns and to refine the site conceptualhydrogeologic model. It was not the intent of the model to quantify flow volumes. Theprocess of developing a groundwater flow model requires the modeler to examine andevaluate carefully the available site hydrogeologic data as site specific information (e.g.,hydraulic conductivity data, potentiometric head data, etc.) must be incorporated into themodel. During the model development process it may become apparent to the modelerthat initial assumptions concerning the conceptual hydrogeologic model may not be valid.Therefore, the process of developing a groundwater flow model may result in therefinement of the initial conceptual model based on the rigorous review of the site dataduring its incorporation into the model.

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As discussed in Section 4.0, the geometry of the site geologic structures displays a strong

trend of bedrock strata striking approximately north 60 degrees east and dipping 30degrees southeast along the northwest limb of the Greendale Syncline. The southernslopes of Little Mountain are formed by the surfaces of dipping beds of the Price-ParrotFormation sandstone. Rock outcrops in the vicinity of the site indicate that thisorientation of bedding is consistent from Little Mountain to beyond the southern bank

of the NFHR. A set of subvertical joints trends in the dip direction. The principaldirection of hydraulic conductivity (maximum permeability) is expected to be downdip

in a southeasterly direction.

Accordingly, a cross-section was constructed along section C-C, trending parallel to theprobable direction of greatest flow. The mesh extends approximately one-half mile to thenorth and south of Pond 5, and to a maximum depth of 3,000 feet below the pond, toreduce boundary effects. It is bounded at the base by the contact with Devonian shale,the south by overturned beds of the Greendale Syncline and a probable wedge of densebrine groundwater associated with the Maccrady Formation evaporites, and on the north*by recharge areas on the slopes of Little Mountain. The mesh, hydrogeologic unit

(material) boundaries, and boundary conditions are illustrated in Figure 5-6.

The complex geometry of the site, dipping bedrock, and sub-horizontal alluvium andr

pond materials, necessitated selection of an appropriate model which afforded flexibility

in reflecting the geometry of the known hydrogeologic units. Based upon thisrequirement, Flow through Porous Media (FPM) program, a finite element,two-dimensional vertical slice model which is part of the Golder Groundwater Package(GGWP), was selected for simulation of site hydrogeology.

5.4.2 Numerical Model CodeFPM was developed by Golder Associates in the 1970's and later modified for use on PCbased systems in the 1980's. The User's Manual for FPM is presented as Appendix I.

The mesh was designed with 859 nodes and 895 elements, as shown in Figure 5-6. Thebase and southern end of the mesh were assumed to have No Flow boundary conditions.The upper edge of the model was designated as a phreatic (water table) surface, with theexception of constant head nodes at the NFHR, a spring on Little Mountain, and at the

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extreme north end of the mesh. Constant flow, simulating average effective daily rainfall,was applied to line segments between phreatic nodes to account for infiltration ofprecipitation.

The mesh was divided into hydrogeologic units to represent the geohydrologiccharacteristics of the pond materials, alluvium, and various mapped geologic formations.Figure 5—7 shows the material boundaries in the immediate vicinity of the Pond.

Initial permeability values for materials were selected from the range of measured valuesfor available units and from published ranges for similar materials for the remainingunits. Figure 5-8 presents the ranges of values of hydraulic conductivity typically foundfor sedimentary rock formations, together with values used for the final calibration.

5.4.3 Model Calibration

Following development of the mesh, initial estimates of the hydraulic conductivity valuesfor the various units were entered into the model. Model output was compared tomeasured water levels in 11 wells and piezometers within 200 feet of the cross section,and to the estimated elevation of the phreatic surface. The locations of the calibrationpoints are. shown in Figure 5-7. The calibration process involved adjustment of the

permeability values and the location of the material boundaries to optimize the fitbetween simulated and measured heads at the calibration points. The objective functionused to calibrate the model was the least square statistic of the deviation between theobserved and modeled potentiometric head values, as shown in Table 5-10. Maximum andminimum observed heads were derived from historical water level data recorded during1989 when calibration was performed.

A constant Surface Distributed Inflow, corresponding to 13.1 inches per year, was appliedto the phreatic surface. This infiltration rate approximates an estimate derived from theUSEPA HELP model for the southwestern region of Virginia.

Initial calibration of the model used the original material boundaries with stratigraphicunits extending to the base of the section as presented in Figure 5-1. This achieved areasonably good fit to measured heads, but required an excessive volume of inflow tomaintain constant head conditions at the spring on Little Mountain.

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Review of the model balance indicated that significant flow was lost through the lowerportions of the model (e.g. deep bedrock). This situation was not considered valid.Information collected during the site investigation (i.e. packer testing) and publishedregional information indicates that the hydraulic conductivity decreases with depth.Therefore, there should be a corresponding decrease in the volume of groundwater flow

with depth.

To more accurately simulate field conditions a ninth bedrock unit (Unit 9) was added tothe model. This unit was used to simulate the decreased values of hydraulic conductivitywith depth. This final calibration achieved good correlation between measured andmodeled heads and a net water balance approximating an overall infiltration rate of 14.3inches per year. The final calibration process included the adjustment of the hydraulic

conductivity values used for various units (within ranges appropriate for each unit) andthe addition of five constant head nodes around the peak of Little Mountain. Theconstant head nodes were required to more accurately simulate the groundwater recharge

| from Little Mountain, and although the node representing the spring on Little Mountain

| acted as an inflow point, the important aspect of surface water occurring at the spring| node in the model was simulated. The purpose of the model was to verify the conceptual

| model rather than quantify flows. A water balance, discussed in Section 6, was utilized| to estimate flows and seepage losses through the dike. Similarly, since the Pond's outfall| was not modelled, the volumes of flow discharging at the NFHR constant head nodes| should not be construed as seepage quantities passing through and under the dike.

Parameters used for the final calibration are presented in Table 5-11. Table 5-10 presentsthe range of water levels measured in 11 wells and piezometers (during 1989) within 200feet of the modeled section, and the corresponding simulated water levels. Table 5-12presents the net water budget for the final calibration. Figure 5-9 illustrates the location

of the phreatic surface relative to ground surface for the model mesh. Little informationbeyond the presence of springs is available for calibrating the model on the slopes of

Little Mountain.

5.4.4 Modeling ResultsThe simulated steady state conditions, including the phreatic surface potentiometric head

contours, and flow lines from the final calibration run, are presented in Figure 5-9. The

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area of Pond 5 is enlarged in Figures 5-10, 5-11, and 5-12 to present the results of the

simulation regarding potentiometric head contours, flow lines, and Darcy velocity vectors,respectively, in detail.

The Darcy velocity vectors presented on Figure 5-12 indicate that the vertical gradientsin the bedrock beneath the Pond change from upward in the north to downward in thesouth. This change in gradient is induced by the presence of Unit 4, representing the

Maccrady Formation shale. This unit acts as a partial barrier to flow in the bedrockbeneath the Pond. As a result, groundwater is forced upward into the alluvium on thenorth side of the barrier and re-enters the bedrock on the south side. In Figure 5-11, flowlines running parallel to the alluvium indicate that groundwater flow does not, for themost part, cross the alluvium layer to flow from bedrock to the ASAW, or vice versa. The

exception to this is groundwater passing between the -10 and -20 flow lines, which entersthe north end of the pond as subsurface recharge, flows along the alluvium layer, and

passes through bedrock for a short distance beneath the dike before discharging to theNFHR.

The majority of flow is within the alluvium. It is important to note that the flow vectors

depicted in Figure 5-12 indicate that a significant portion of flow occurs within thealluvium. This is attributed to the fact that this material has a maximum hydraulicconductivity (i.e. high hydraulic conductivity parallel to bedding) significantly higher thanoverlying ASAW. In addition, the orientation of the maximum hydraulic conductivity isessentially horizontal (i.e. along horizontal bedding planes) and is therefore coincidentwith the direction of greatest hydraulic gradient. This is in contrast to the underlyingbedrock units where the maximum hydraulic conductivity of these bedrock units isparallel to the bedding planes, that dip at an angle approximately 30° to the horizontal.

5.45 Modeling ConclusionsThe simulated flow patterns largely support the interpretations of the hydrogeologypreviously presented. Essential elements of this simulated flow are:

1. Most groundwater discharges to the NFHR from the Pond and bedrockflow systems;

2. Flow beneath the pond is concentrated in the alluvium layer except in thearea of the dike where flow is concentrated in the shallow bedrock;

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3. The volume of groundwater that flows from the ASAW into the bedrockis relatively low in comparison to volume of flow from the bedrock toNFHR and other flow paths;

4. Hydraulic communication between the bedrock and pond solids is oflimited significance; and

5. Recharge to the Pond and bedrock flow systems originate principally fromLittle Mountain and direct precipitation.

The model was successfully calibrated for steady state conditions, to the degree that themodeled and measured heads were within an average of 1.8 feet of each other at eachof the eleven monitoring points.

5.5 Site Conceptual Groundwater Flow Model5.5.1 Groundwater Flow Between Bedrock and Pond Fill

Tables 5-ISA and 5-13B present the analyses of vertical gradients between the shallowbedrock and fill for the high and low water level periods, respectively. Of the 13 wellclusters examined, 4 exhibit upward vertical gradients during February 1990, and 9downward vertical gradients (Table 5-16A). Similarly, 3 upward vertical gradients and 10

downward vertical gradients were delineated during the low water level period inDecember 1990 (Table 5-16B).

There are no obvious patterns to the distribution of vertical gradients within the Pond 5

portion of the facility. The presence of predominantly downward vertical gradients doesnot necessarily imply that vertical flow occurs from the pond into the bedrock, as

gradients may appear downward between the two flow systems for the followingreasons:

1. Bedrock wells, particularly beneath the pond, may not be deep enough toreflect the true hydraulic interaction between the bedrock and fill.Down-ward vertical gradients may be more reflective of preferential flowtoward a more permeable horizon near the base of the pond/top ofbedrock, rather than towards the deep bedrock flow system itself.

2. Some perching of water may occur within portions of the pond due to thedistribution and extent of pond fracture networks, and the lowpermeability of portions of the pond matrix. The pond fill is suspected tobe heterogeneous.

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Hydraulic communication between the bedrock and pond fill is not believed to be

significant because:

1. Bedrock wells fail to respond dramatically to short term precipitationevents. If the vertical fractures within the pond conducted water rapidlydownward and good hydraulic connection existed between the rock andfill, a more pronounced reaction to individual precipitation events wouldbe expected. The absence of a clear response in both the bedrock and fillto isolated storm events suggests that the residence time of rainfall andrunoff within the pond is rather short. This in turn implies that thepreferential direction of flow is laterally towards the dike and decant outletstructure, not downward.

2. Most of the water levels between the bedrock and pond fill have severalfeet of separation, even during dry periods, suggesting (along with otherinformation provided) that the pond and bedrock behave more asindependent flow systems than as an integrated, well connected regime.

3. A permeability contrast exists between the shallow bedrock, deep bedrock,and pond alluvium. Geometric means of hydraulic conductivity indicate

| that the deep bedrock permeability is on the order of 5 x 10"5 cm/sec, the| shallow bedrock 2 x 10"4 cm/sec, and the alluvium 3 x 10"3 cm/sec (see

Sections 5.3.1.2 and 5.3.2.2). This would indicate that preferential flowwould be within the alluvial sediments at the base of the pond, ratherthan downward into the deeper bedrock which possesses permeabilitiesthat average two orders of magnitude lower.

4. Examination of groundwater chemistry data indicates that concentrationsof mercury in the shallow bedrock are well below those observed in thePond 5 outflow. If significant flow through the bottom of the pond wasoccurring, higher concentrations, similar to those observed in outfalldischarge, should be observed in the sampled groundwater. This suggeststhat significant downward migration of mercury into the bedrock flowregime has not occurred (see Section 5.5). Therefore, suitable migrationpathways, and/or downward driving forces, apparently do not existbetween the pond and bedrock.

5.5.2 Groundwater Recharge and Discharge AreasRecharge to the shallow bedrock portion of the flow system is believed to be principallycontrolled by water infiltrating downward through the subvertical cracks and fractureslocated at the base of Little Mountain, above and below State Route 611. Recharge to thedeep bedrock may take place from the deep bedrock portion of the system within LittleMountain itself. Deep wells completed in the mountain swales (particularly MW-1D)suggest a steady upward flow of deep, artesian groundwater into the bedrock flow

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system. However, a lack of vertical pathways between the artesian portions of the systemand the upper bedrock may limit the extent of this contribution.

Some recharge to the uppermost fractured and weathered portions of the bedrock mayoccur from the pond during sustained, long term precipitation events. However, thereis strong evidence suggesting that deep infiltration does not take place.

Recharge to the fine matrix of ASAW in the pond flow system is believed to occur when

direct precipitation and runoff from Little Mountain are sustained long enough todevelop both sufficient head and residence time within the pond fracture network. Thisenhances the infiltration of water into minor fracture systems and the overall pond matrixresulting in an increase in pond water levels. Recharge is also contributed to the pondfrom the rock fractures located at the base of Little Mountain.

The groundwater discharge from the pond and bedrock flow systems is believed to bethe NFHR. This is consistent with the existing knowledge of the flow systems of this

region (see Section 5.2), Discharge to the river is suggested by interpreted groundwatercontours of both systems, which imply gradients towards the river. Flow to the riveroccurs as outflow from the decant outlet structure, particularly from the pond flowsystem. Flow in the upper bedrock is also likely directed preferentially toward the decantstructure and dike by overlying higher permeability alluvial material and pond fracture

networks which extend at depth toward the base of the pond. Discharge to the river alsoseems to occur as seepage through the dike itself. The less permeable upstream blanketalong the starter dike, contained within the Pond 5 dike, seems to have caused somemounding. Water levels within the pond rise to elevations which can allow flow over thetop of the blanket and into the starter dike and dike drain system. Groundwater flowin the upper fractured bedrock may also be discharged to the river as seepage beneaththe dike.

5.5.3 Site Groundwater Level FluctuationsDue to the presence of an areally extensive fracture network throughout the pond fill,water from runoff and direct precipitation from short duration rainfall events does notreside long enough within the pond to promote significant infiltration. Rather, water isconducted rapidly through the fracture network to the decant outlet structure to the

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NFHR. However, sustained periods of precipitation allow build-up of water within thefracture network to allow the flow of water into the pond matrix and shallow bedrock.The result is a commensurate rise in the phreatic and potentiometric surfaces.

Similarly, water flowing into the vertical fractures located at the base of Little Mountainlikely does not contribute substantially to the deep bedrock flow system in response to

limited precipitation events. In this case, water is probably directed through fractures intothe pond margins. The water then flows in preferential directions controlled by the fillfracture network and the distribution of overlying alluvium, to the decant structure ordike. If rainfall is sustained for long periods, some flow will be contributed to the deep

bedrock flow system potentially resulting in an increase in bedrock water levels.

In general, water levels are highest in the fill and bedrock following periods of sustained

precipitation. Water levels are the lowest during protracted dry spells. The variabilityin the responses of some of the site wells and piezometers is likely caused by variations

in vertical and horizontal fracture frequency in the area surrounding screened intervals.This undoubtedly influences the degree of interconnection between the monitored zoneand the overall hydrologic and hydrogeologic flow systems.

5.5.4 Discussion and ConclusionsThe findings of the hydrogeologic investigation of the site may be summarized by thefollowing conclusions:

Permeability and flow characteristics within the pond and bedrock areprincipally controlled by secondary porosity and permeability featuresassociated with the distribution, frequency, persistence, and aperture widthof fractures, joints and lineaments.

The fracture network within the pond fill is dynamic, with old fracturessometimes closing, and others opening as a result of ongoingconsolidation, erosion and the low strength of the fill materials.

The pond fill material is very heterogeneous with respect to hydraulicconductivity. In addition, site data suggest there is a distinct contrast inthe hydraulic conductivity of the alluvium, upper bedrock, and lowerbedrock, with permeability decreasing with increasing depth.

Water level fluctuations within the fill and bedrock are principallycontrolled by the duration and intensity of precipitation events. Shortduration precipitation events do not seem to contribute substantially to

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water level fluctuation as runoff and direct rainfall are believed to berapidly conducted out of the pond system by existing fracture networksto the decant structure.

• Overall groundwater flow in both the pond fill and bedrock is toward thesouth to the NFHR.

• Recharge to the pond and bedrock systems ultimately originates fromLittle Mountain as runoff, deep groundwater flow, and recharge fromdirect precipitation on the pond. Seasonal variation in the effects ofprecipitation attributable to variation in evapotranspiration have beennoted. When precipitation events are of sufficient duration and intensity,recharge to the bedrock is noted.

• Groundwater discharge from the fill and bedrock is to the NFHR by wayof flow from the decant structure, and as minor seepage above and belowand, to a limited extent, through the starter dike. Alluvial depositsaffiliated with the old river channel, near the base of the pond, inconjunction with pond fracture networks, act as controlling pathways forthe flow of groundwater.

• There are no apparent data to support high flow quantities from the baseof the pond to the bedrock. There is a definite interconnection betweenthe ASAW and the bedrock, but this interconnection is poor due todeposits of precipitate (e.g., cemented alluvium) and the pond sealintegrity and is not as preferred a flowpath as the ASAW fractures to theoutfall. The upper bedrock comprising a fractured and weathered zoneis considered the lower limit of the pond system, and the pond systemdrains to the NFHR.

• There does not appear to have been significant mercury migration fromthe pond fill into the shallow bedrock based on the results of thegroundwater sampling.

Based upon the site investigations and review of hydrologic and hydrogeologic data,

water enters the Pond 5 system by:

• Precipitation;

• Surface water run-on where no diversion ditch has been constructed (asof November 1991, the Eastern Diversion Ditch now intercepts thisrun-on);

• Shallow subsurface interflow into the Pond from a fractured rock zonealong the toe of Little Mountain; and

* Upward groundwater flow toward the base of the pond from the bedrockflow system.

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Water exits Pond 5 by way of:

Flow from the pond decant structure consisting of subsurface pond flowand intermittent surface discharge at the decant structure inlet;

Evapotranspiration;

Minor seepage through shallow fractured bedrock, the Pond 5 dike oralong the gravel river bed of the former North Fork Holston River channel,into the NFHR; and

Minor downward flow to shallow bedrock and the NFHR.

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