2000-04-10 – Remedial Investigation Report – West Lake Landfill Operable Unit 1

2000-04-10-remedial-investigation-report-west-lake-landfill-operable-unit-1

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Remedial Investigation Report

West Lake Landfill
Operable Unit 1

Prepared For:
West Lake OU-1 Respondents Group
Prepared By:
Engineering Management Support, Inc. 12335 West 53rd Avenue, Suite 201 Arvada, Colorado 80002
April 10, 2000 Table of Contents
1.0 INTRODUCTION 1
1.1 Purpose and Scope of the Remedial Investigation Report 1
1.2 Report Organization 1
2.0 SUMMARY OF PREVIOUS INVESTIGATIONS 4
2.1 Pre-RI Reports 4
2.2 Operable Unit-1 RI/FS Work Plans 5
2.3 Operable Unit-1 Investigative Reports 5
2.4 Operable Unit-2 Plans and Reports 6
2.5 Landfill Reports 7
2.6 Ford Property Reports 7
3.0 SITE BACKGROUND 8
3.1 Landfill Description and Location 8
3.2 Summary of Landfill Operations 9
3.2.1 Radiological Area 1 10
3.2.2 Radiological Area 2 10
3.2.3 Inactive Landfill Operations 10
3.2.4 Current Active Landfill Operations 11
3.3 Activities Adjacent To The Landfill 11
4.0 SITE INVESTIGATION ACTIVITIES 12
4.1 Site Reconnaissance 12
4.1.1 Summary of Methods and Procedures Used 12
4.1.2 Deviations from Work Plan 13
4.1.3 Summary of Results 13
4.1.4 Data Quality Issues 14
4.1.5 Outstanding Issues or Items 14
4.2 Threatened or Endangered Species Assessment 14
4.2.1 Summary of Methods and Procedures Used 15
4.2.2 Deviations from Work Plan 15
4.2.3 Summary of Results 15
4.2.4 Data Quality Issues 16
4.2.5 Outstanding Issues or Items 16
ii 4.3 Overland Gamma Survey 16
4.3.1 Summary of Methods and Procedures Used 17
4.3.2 Deviations from Work Plan 17
4.3.3 Summary of Results 17
4.3.4 Data Quality Issues 18
4.3.5 Outstanding Issues or Items 18
4.4 Surface and Subsurface Soil and Perched Water Investigations 19
4.4.1 Purpose and Scope of Investigation 19
4.4.2 Summary of Methods and Procedures Used 20
4.4.2.1 Surface Geophysical and Landfill Vapor Surveys 21
4.4.2.2 Soil Boring Drilling 21
4.4.2.3 Soil Sample Collection and Chemical Analyses 23
4.4.2.4 Perched Water Sample Collection and Analyses 26
4.4.2.5 Down-Hole Radiological Logging 27
4.4.2.6 Soil Boring Abandonment 27
4.4.2.7 Geotechnical Sampling and Testing 28
4.4.3 Deviations from Work Plan 29
4.4.4 Summary of Results 30
4.4.4.1 Landfill Setting 31
4.4.4.2 Radiological Constituents 31
4.4.4.3 Non-radiological Constituents 33
4.4.4.4 Perched Water 35
4.4.4.5 Geotechnical Testing 36
4.4.5 Data Quality 39
4.4.6 Outstanding Issues or Items 41
4.5 Groundwater Investigation 41
4.5.1 Purpose and Scope of Investigation 41
4.5.2 Summary of Methods and Procedures Used 42
4.5.2.1 Monitoring Well Installation 42
4.5.2.2 Monitoring Well Development 43
4.5.2.3 Groundwater Level Measurement 43
4.5.2.4 Well Slug Testing 43
4.5.2.5 Groundwater Sample Collection 44
4.5.3 Deviations from Work Plan 45
4.5.4 Summary of Results 46
4.5.5 Data Quality Issues 47
4.5.6 Outstanding Issues or Items 48
4.6 Surface Water and Sediment Investigation 48
4.6.1 Purpose and Scope of Investigation 49
4.6.2 Summary of Methods and Procedures Used 50
4.6.2.1 Rainwater Runoff Sampling 50
4.6.2.2 Erosional Sediment Sampling 51
4.6.2.3 Surface Water and Leachate Sampling 51
4.6.3 Deviations from Work Plan 52
4.6.4 Summary of Results 52
iii
4.6.5 Data Quality Issues 54
4.6.6 Outstanding Issues or Items 55
4.7 Radon, Landfill Gas, and Fugitive Dust Investigations 55
4.7.1 Purpose and Scope of Investigations 55
4.7.2 Summary of Methods and Procedures Used 56
4.7.2.1 Radon Sampling 57
4.7.2.2 Soil Vapor Sampling 57
4.7.2.3 Soil Sampling for Non-Radiological Compound Vapor Discharge 58
4.7.2.4 Fugitive Dust Sampling 58
4.7.3 Deviations from Work Plan 58
4.7.4 Summary of Results 58
4.7.5 Data Quality Issues 60
4.7.6 Outstanding Issues Or Items 60
5.0 PHYSICAL CHARACTERISTICS OF THE STUDY AREA 61
5.1 Climate 61
5.1.1 Temperature 61
5.1.2 Precipitation 61
5.1.3 Wind Distribution 62
5.2 Land Use 62
5.3 Surface Features 63
5.3.1 Topography 63
5.3.2 Surface Soils 64
5.3.3 Surface Water 65
5.3.3.1 Area 1 Drainage 65
5.3.3.2 Area 2 Drainage 65
5.3.3.3 Off-Site Surface Water 66
5.4 Biota 67
5.4.1 Plant Communities 67
5.4.1.1 Area 1 Plant Communities 67
5.4.1.2 Area 2 Plant Communities 68
5.4.1.3 Plant Communities in Other Areas at or Near the landfill 68
5.4.2 Threatened and Endangered Species 69
5.4.3 Area Wildlife 70
5.5 Subsurface Features 70
5.5.1 Geology 71
5.5.1.1 Bedrock Geology 71
5.5.1.2 Unconsolidated Materials 75
5.5.2 Landfill Deposits 75
5.6 Hydrogeology 76
5.6.1 Regional Hydrogeology 77
5.6.2 Landfill Hydrogeology 78
5.6.2.1 Groundwater Occurrence 78
iv
5.6.2.2 Groundwater Levels and Elevations 79
5.6.2.3 Hydraulic Gradient 79
5.6.2.4 Hydraulic Conductivity and Porosity 81
5.6.2.5 Groundwater Flow Directions, Velocity and Flux 82
5.6.3 Water Supply Wells in the Vicinity of the Landfill 84
6.0 NATURE AND EXTENT OF RADIOLOGICALLY IMPACTED MATERIALS 85
6.1 Procedures Used to Characterize Radiologically Impacted Materials 85
6.2 Background Levels of Radionuclides 86
6.3 Use of Numerical Standards and Reference Levels 87
6.4 Radiologically Impacted Materials in Area 1 90
6.4.1 Radiologically Impacted Materials at the Surface in Area 1 90
6.4.2 Radiologically Impacted Materials in the Subsurface of Area 1 91
6.4.3 Correlation of Radionuclide Occurrences in Area 1 93
6.5 Radiologically Impacted Materials in Area 2 93
6.5.1 Radiologically Impacted Materials at the Surface of Area 2 94
6.5.2 Radiologically Impacted Materials in the Subsurface of Area 2 95
6.5.3 Correlation of Radionuclide Occurrences in Area 2 99
6.6 Radiological Occurrences in the Northeastern Portion of Area 2 99
6.7 Distribution of Radiologically Impacted Materials in Areas 1 and 2 99
6.8 Radiologically Impacted Materials at the Ford Property 100
6.9 Summary of Radiologically Impacted Material Occurrences 102
7.0 CONTAMINANT EXTENT, FATE AND TRANSPORT 103
7.1 Extent of Contamination and Potential Contaminant Migration 103
7.1.1 Airborne transport 103
7.1.1.1 Radon Gas 103
7.1.1.2 Fugitive Dust 106
7.1.2 Surface Water Transport 107
7.1.2.1 Rainwater Runoff Transport 108
7.1.2.2 Surface Water Samples 110
7.1.3 Sediment Transport 111
7.1.3.1 Sediment Transport in Surface Drainage Channels 112
7.1.3.2 Sediment Transport From Area 2 Slope Erosion 116
7.1.4 Groundwater 118
7.1.4.1 Migration of Radionuclides into Perched Groundwater or the Leachate Seep 118
7.1.4.2 Existing Radionuclide Levels in Groundwater 119
7.1.4.3 Future Leaching to Groundwater and Subsequent Off-site Transport 121
7.2 Contaminant Fate and Persistence 122
7.2.1 Radioactive Decay 122
v
7.2.2 Changes in Radionuclide Concentrations 123
7.2.3 Other Fate and Transport Processes 125
7.2.3.1 Leaching and Sorption 125
7.2.3.2 Volatilization 128
8.0 NON-RADIOLOGICAL CHEMICAL OCCURENCES IN AREAS 1 AND 2 129
8.1 Non-Radiological Constituents Detected in Soil Samples 129
8.1.1 Trace Metals Detected in Soil Samples 130
8.1.1.1 Trace Metals in Area 1 Soil Samples 130
8.1.1.2 Trace Metals in Area 2 Soil Samples 131
8.1.2 Total Petroleum Hydrocarbons Detected in Soil Samples 132
8.1.2.1 Petroleum Hydrocarbons in Area 1 Soil Samples 132
8.1.2.2 Petroleum Hydrocarbons in Area 2 Soil Samples 132
8.1.3 Volatile Organic Compounds Detected in Soil Samples 133
8.1.4 Semi-Volatile Organic Compounds in Soil Samples 134
8.1.5 Pesticides and Poly-Chlorinated Biphenyls in Soil Samples 135
8.2 Non-Radiological Constituents Detected in Erosional Sediments 135
8.3 Non-Radiological Constituents Detected in Rainwater Runoff Samples 136
8.4 Non-Radiological Constituents Detected in Surface Water Samples 137
8.5 Non-Radiological Constituents in Perched Water and Area 2 Seep 137
8.6 Non-Radiological Constituents Detected in Groundwater Samples 138
9.0 BASELINE RISK ASSESSMENT 142
9.1 Human Health Evaluation 142
9.1.1 Chemicals of Potential Concern 143
9.1.2 Exposure Assessment 143
9.1.3 Toxicity Assessment 144
9.1.4 Risk Characterization 144
9.1.5 Uncertainty Assessment 145
9.2 Ecological Evaluation 145
10.0 SUMMARY AND CONCLUSIONS 147
10.1 Summary of Site Conditions 147
10.1.1 Surface Setting 147
10.1.2 Subsurface Setting 148
10.2 Radiologically Impacted Materials 150
10.3 Potential Migration Pathways 151
10.3.1 Airborne Transport 152
10.3.2 Rainwater Runoff Transport 152
10.3.3 Soil Erosion and Sediment Transport 152
10.3.4 Leaching to Groundwater and Groundwater Transport 153
vi
10.4 Baseline Risk Assessment 154
11.0 REFERENCES 156
Tables Figures
APPENDICES Appendix A : Baseline Risk Assessment Appendix B : Radiological and Non-Radiological Analytical Results for Soil
Samples Appendix C : Radiological and Non-Radiological Analytical Results for Groundwater Samples Appendix D : Radiological and Non-Radiological Analytical Results for Surface Water Samples Appendix E : Radiological and Non-Radiological Analytical Results for Sediment Samples
vii List of Tables
Table 4-1: Summary of Site Investigation Activities and Investigative Data Reports Table 4-2: Summary of Geotechnical Testing Results Table 4-3: Summary of RI Depth to Water Level Measurements Table 4-4: Summary of RI Groundwater Elevation Measurements Table 4-5: Summary of Groundwater Monitoring Wells Sampled as Part of the RI Table 4-6: Monitoring Well Construction Summary Table 4-7: Soil Vapor Methane Concentrations, Radiological Areas 1 and 2
Table 5-1: Summary of Plant Species Present in or Near Areas 1 and 2 Table 5-2: Summary of Water Level Measurements from Well Clusters Table 5-3: Summary of Alluvial Aquifer Hydraulic Conductivity Values
Table 6-1: Summary of Radionuclide Occurrence Above Reference Levels in Area 1 Surface Samples
Table 6-2: Summary of Radionuclide Occurrence Above Reference Levels in Area 1 Subsurface Samples
Table 6-3: Summary of Radionuclide Occurrence Above Reference Levels in Area 2 Surface Samples
Table 6-4: Summary of Radionuclide Occurrence Above Reference Levels in Area 2 Subsurface Samples
Table 6-5: Summary of Background Radionuclide Levels at the West Lake Landfill
Table 6-6: Background Gamma and Radionuclide Concentrations in Surface Soil Samples in the State of Missouri
Table 6-7: Summary of Area 1 Downhole Gamma Log Results
Table 6-8: Summary of Estimated Thicknesses of Subsurface Radiologically Impacted Materials in Area 1
Table 6-9: Summary of Area 2 Downhole Gamma Log Results
Table 6-10: Summary of Estimated Thicknesses of Subsurface Radiologically Impacted Materials in Area 2
Table 6-11: Summary of Elevated Downhole Gamma Levels, Soil Samples Above Reference Levels and Boring Log Descriptions
Table 6-12: Summary of Estimated Areal Extent and Volume of Radiologically Impacted Materials
Table 6-13: February 2000 Analytical Results for Surface Soil Samples from the Buffer Zone and Crossroads Properties
Table 7-1: Radon Flux Measurement Results
Table 7-2: Surface Soil Radionuclide Analytical Results at the Fugitive Dust Sampling Locations
Table 7-3: Fugitive Dust Analytical Results
Table 7-4: Comparison of 1995, 1996 and 1997 Radium-226 Results in Groundwater Samples
viii List of Tables (cont.)
Table 8-1: Priority Pollutant Metals Summary for Soil Samples Table 8-2: Total Petroleum Hydrocarbons Summary for Soil Samples Table 8-3: Volatile Organic Compounds Summary for Soil Samples Table 8-4: Semi-Volatile Organic Compounds Summary for Soil Samples Table 8-5: Pesticides and Polychlorinated Biphenyls Summary for Soil Samples Table 8-6: Priority Pollutant Metals Summary for Groundwater Samples Table 8-7: Total Petroleum Hydrocarbons Summary for Groundwater Samples Table 8-8: Volatile Organic Compounds Summary for Groundwater Samples Table 8-9: Semi-Volatile Organic Compounds Summary for Groundwater Samples Table 8-10: Pesticides and Polychlorinated Biphenyls Summary for Groundwater
Samples
Table 9-1: Chemicals of Potential Concern for Human Health Risk Assessment Table 9-2: Summary of Calculated Risks for Current and Future Potential Receptors Table 9-3: Uncertainties Associated with Estimated Human Health Risks for OU-1 Table 9-4: Summary of Estimated Ecological Risks for Operable Unit 1
ix List of Figures
Figure 3-1: Site Vicinity Map Figure 3-2: Site Location Map Figure 3-3: Site Ownership Map in the Vicinity of Area 1 and Area 2 Figure 3-4: Landfill and Surrounding Area Zoning Figure 3-5: Areas of Landfill Operations Figure 3-6: Existing Buffer Zone on the West Side of Area 2
Figure 4-1: Surface Drainage Patterns at the West Lake Landfill Figure 4-2: Areas of Hydrophyllic Vegetation in Area 1 Figure 4-3: Areas of Hydrophyllic Vegetation in Area 2 Figure 4-4: Overland Gamma Survey Results Compared to a 10 µR/hr Background Value Figure 4-5: Overland Gamma Survey Results Compared to a 12.5 µR/hr Background
Value Figure 4-6: Overland Gamma Survey Results Compared to a 15 µR/hr Background Value Figure 4-7: Overland Gamma Survey Results Compared to 17.5 µR/hr Background Value Figure 4-8: Overland Gamma Survey Results Compared to 20 µR/hr Background Value Figure 4-9: Area 1 and 2 Soil Boring Locations Figure 4-10: Occurrences of Perched Water and Leachate Seepage in Areas 1 and 2 Figure 4-11: Locations of Groundwater Monitoring Level Wells Figure 4-12: Locations of Groundwater Quality Monitoring Wells Figure 4-13: Surface Water, Rainwater/Runoff, and Sediment Sample Locations Figure 4-14: Radon Flux Measurements Locations Figure 4-15: Methane Gas Measurement Locations in Area 1 Figure 4-16: Methane Gas Measurement Locations in Area 2 Figure 4-17: Fugitive Dust Monitoring Locations in Area 1 Figure 4-18: Fugitive Dust Monitoring Locations in Area 2
Figure 5-1: Normal Monthly Precipitation for St. Louis Lambert International Airport Figure 5-2: Generalized Stratigraphic Column for the St. Louis Area Figure 5-3: Cross Section 1A – 1A’ Figure 5-4: Cross Section 2A – 2A’ Figure 5-5: Alluvial Aquifer Water Table Map – October, 1995 Figure 5-6: Alluvial Aquifer Water Table Map – January, 1996 Figure 5-7: Alluvial Aquifer Water Table Map – April, 1996 Figure 5-8: Alluvial Aquifer Water Table Map – July, 1996 Figure 5-9: Water Wells in the Vicinity of the West Lake Landfill
Figure 6-1: Approximate Extent of Radionuclide Impacted Materials at the Landfill Surface Figure 6-2: Approximate Extent of Radionuclide Impacted Materials in the Subsurface at the Landfill
x List of Figures (cont.)
Figure 6-3: Approximate Extent of Radionuclide Impacted Materials at the Surface in Area 1 Figure 6-4: Approximate Extent of Radionuclide Impacted Materials in the Subsurface in Area 1 Figure 6-5: Approximate Extent of Radionuclide Impacted Materials at the Surface in Area 2 Figure 6-6: Approximate Extent of Radionuclide Impacted Materials in the Subsurface in Area 2 Figure 6-7: Approximate Extent of Radionuclide Impacted Materials in Surface Soil in the Buffer Zone and Crossroads Properties Figure 6-8: Occurrences of Radionuclide Impacted Materials in Subsurface Soil in the Buffer Zone and Crossroads Properties Figure 6-9: Current Condition of Buffer Zone and Crossroad Properties (Former Ford Property) Figure 6-10: February 2000 Sampling Locations, Buffer Zone and Crossroad Properties
Figure 7-1: Conceptual Model of Potential Migration Pathways Figure 7-2: Uranium-238 Radioactive Decay Series Figure 7-3: Uranium-235 Radioactive Decay Series Figure 7-4: Thorium-232 Radioactive Decay Series
xi
1.0 INTRODUCTION
This Remedial Investigation (RI) report has been prepared by Engineering Management Support Inc. (EMSI) on behalf of Cotter Corporation (N.S.L.), Bridgeton Landfill, LLC (formerly known as Laidlaw Waste Systems [Bridgeton], Inc.), Rock Road Industries, Inc., and the United Sates Department of Energy (the “Respondents”). The RI Report has been prepared as part of the Remedial Investigation/Feasibility Study (RI/FS) for Operable Unit (OU) -1 at the West Lake Landfill located in Bridgeton, Missouri. OU-1 addresses conditions associated with two areas of radiological impacted materials present at the West Lake Landfill, Radiological Area 1 (Area 1) and Radiological Area 2 (Area 2). Investigations and evaluations of the occurrences of non-radioactive constituents in other parts of the landfill are being performed by Bridgeton Landfill, LLC under a separate operable unit (OU-2) RI/FS.
The RI report for OU-1 at the West Lake Landfill has been prepared in accordance with the requirements of Administrative Order on Consent (AOC) between the U.S. Environmental Protection Agency (EPA) and the Respondents for OU-1. Specifically, this report presents the information required by Section 4.4.3 of the Remedial Investigation/ Feasibility Study (RI/FS) Statement of Work (SOW) to the AOC.
1.1 Purpose and Scope of the Remedial Investigation Report
The purpose of the RI report is to present the results of the various site characterization activities. As required by Section 4.4.3 of the SOW of the AOC, the RI report should summarize the results of the field activities conducted to characterize the following:

Conditions at the site;


The sources of contaminants;


The nature and extent of contaminants and associated impacts; and


The fate and transport of the contaminants.

Each of these requirements is addressed in later sections of this report.
1.2 Report Organization
The remainder of this report is organized as follows:
RI Report West Lake Landfill OU-1 April 10, 2000 Page 1

Section 2 presents a summary of previous investigations;


Section 3 presents a general description of the West Lake Landfill, its location and the characteristics of surface and subsurface features at the landfill;


Section 4 describes the various investigations performed as part of the Remedial Investigation;


Section 5 describes the physical characteristics of the West Lake Landfill;


Section 6 describes the nature, occurrence and distribution of the sources of contamination associated with OU-1 including affected media, location, types of contamination, physical state of contaminants, contaminant concentrations and quantity of contaminants and affected media;


Section 7 presents an evaluation of the fate and transport of the radiological contaminants including potential migration pathways and a description of the extent of migration, if any, along each pathway;


Section 8 presents a summary of the non-radiological contaminants detected in Radiological Areas 1 and 2 and the various environmental media in the vicinity of these areas;


Section 9 presents a summary of the results of the Baseline Risk Assessment which is included as Appendix A to the RI report;


Section 10 presents a summary of the site conditions, a revised conceptual model of the occurrence of radiologically impacted materials and potential pathways through which radionuclides could migrate from Areas 1 and 2, and the estimated risks associated with occurrences of radionuclides onsite and potential offsite migration.


Section 11 lists the various references used in completing this report.

The appendices that have been prepared as part of the RI report include the following:
Appendix A: Baseline Risk Assessment (prepared by Auxier & Associates)
Appendix B: Summary of soil sample radiological and non-radiological analytical results
Appendix C: Summary of groundwater sample radiological and non-radiological analytical results
RI Report West Lake Landfill OU-1 April 10, 2000 Page 2
Appendix D: Summary of surface water samples radiological and non- radiological analytical results
Appendix E: Summary of sediment sample radiological and non-radiological analytical results
RI Report West Lake Landfill OU-1 April 10, 2000 Page 3
2.0 SUMMARY OF PREVIOUS INVESTIGATIONS
Numerous reports on the conditions at the West Lake Landfill have previously been prepared. These include the following:

Pre-RI reports,


OU-1 RI/FS Work Plan and related documents,


Investigation reports prepared as part of the OU-1 RI/FS,


Work plan documents and site characterization reports prepared for OU-2,


Reports prepared as part of the landfill development and operations, and


Investigative reports associated with the buffer zone and Crossroad properties (formerly referred to as the Ford property) located immediately to the northwest of Area 2.

The specific reports that have previously been prepared and that were considered during the preparation of this RI are listed below.
2.1 Pre-RI Reports
The following reports were prepared prior to the initiation of the RI/FS activities for OU-1:

Report of Site Visit – West Lake Landfill, St. Louis County, Missouri (Radiation Management Corporation, 1981)


Radiological Survey of the West Lake Landfill, St. Louis County, Missouri (Radiation Management Corporation, 1982)


Radioactive Material in the West Lake Landfill, Summary Report (U.S. Nuclear Regulatory Agency, 1988)


Letter from Rodney Bloese to Joseph Homsy re: West Lake Landfill CERCLA dated December 12, 1989, (Foth & Van Dyke, 1989) (contains information on local water wells)


Preliminary Health Assessment, West Lake Landfill, Bridgeton, St. Louis County, Missouri (Missouri Department of Health, 1991)

RI Report West Lake Landfill OU-1 April 10, 2000 Page 4
2.2 Operable Unit-1 RI/FS Work Plans
The following planning documents were previously prepared as part of the RI/FS for OU-1:

RI/FS Work Plan for the West Lake Site, Bridgeton, Missouri, August 15, 1994 (McLaren/Hart, 1994),


Amended Sampling and Analysis Plan, West Lake Landfill Operable Unit 1, February 29, 1997 (EMSI, 1997a),


Responses to EPA’s Comments on the Amended Sampling and Analysis Plan for Operable Unit 1, West Lake Landfill (EMSI, 1997e), and


Draft Investigation Derived Waste Management and Interim Remedial Measures Plan, West Lake Landfill Operable Unit 1, September 1997 (EMSI, 1997d).

The RI/FS Work Plan was approved by EPA in September 1994 (EPA, 1994). The ASAP, although not formally approved, was submitted to EPA for review and comment and EPA’s comments (EPA, 1997a and 1997b) and appropriate responses or modifications to the draft ASAP were provided to EPA (EMSI, 1997e). EPA subsequently provided verbal authorization to proceed with the ASAP activities. EPA provided comments on the Draft Investigation Derived Waste Management and Interim Remedial Measures Plan and responses to those comments and necessary modifications to the draft plan are still under development.
In addition, minor modifications to some of these plans were made and approved by EPA and/or their oversight contractor during the course of the field investigations. Many of these changes were documented in letters prepared by McLaren/Hart. Some of these changes were formally approved in letters from EPA. Where appropriate, these specific letters are referenced as part of the discussions of the various investigative activities contained in Section 4 of this RI report.
2.3 Operable Unit-1 Investigative Reports
The following investigative documents were previously prepared as part of the RI/FS for OU-1:
• Overland Gamma Survey Report, West Lake Landfill Radiological Areas 1 & 2, April 30, 1996 (McLaren/Hart, 1996a);
RI Report West Lake Landfill OU-1 April 10, 2000 Page 5

Site Reconnaissance Report, West Lake Landfill Radiological Areas 1 & 2, May 16, 1996 (McLaren/Hart, 1996b);


Threatened or Endangered Species Assessment Report, West Lake Landfill Radiological Areas 1 & 2, May 17, 1996 (McLaren/Hart, 1996c);


Radon Gas, Landfill Gas and Fugitive Dust Report, West Lake Landfill Areas 1 & 2, November 22, 1996 (McLaren/Hart, 1996d);


Rainwater Runoff, Erosional Sediment, Surface Water, and Leachate Sampling Data Report, West Lake Landfill Areas 1 & 2, November 22, 1996 (McLaren/Hart, 1996e);


Split Soil and Groundwater Sampling Data Summary Report, West Lake Landfill Areas 1 & 2, November 22, 1996 (McLaren/Hart, 1996f);


Groundwater Conditions Report, West Lake Landfill Areas 1 & 2, November 26, 1996 (McLaren/Hart, 1996g),


Soil Boring/Surface Soil Investigation Report, West Lake Landfill Areas 1 & 2, November 26, 1996 (McLaren/Hart, 1996h),


Interim Investigation Results Technical Memorandum, West Lake Landfill Operable Unit 1, January 28, 1997 (EMSI, 1997a),


Site Characterization Summary Report, West Lake Landfill Operable Unit 1, August 1997 (EMSI, 1997c),

2.4 Operable Unit-2 Plans and Reports
The following investigative documents were previously prepared as part of the RI/FS for OU-2:

Remedial Investigation/Feasibility Study Work Plan (Golder Associates, 1995a)


Draft Hydrogeological Characterization Report for the Bridgeton Active Sanitary Landfill, Bridgeton, Missouri, September 1995 (Golder Associates, 1995b)

RI Report West Lake Landfill OU-1 April 10, 2000 Page 6

Physical Characterization Technical Memorandum for the West Lake Landfill Operable Unit 2, Bridgeton, Missouri, November 1996 (Golder Associates, 1996a)


West Lake Landfill, Operable Unit 2 RI/FS, Site Characterization Summary Report, December 1997 (Water Management Consultants, 1997)

2.5 Landfill Reports
The following reports were prepared in support of the ongoing landfill operations at the West Lake Landfill:

Environmental Investigation and Health Impact Assessment, Bridgeton Sanitary Landfill, October 1993 (Golder Associates, 1993)


Radiological Survey of West Lake Landfill Bridgeton, Missouri, June 4, 1996 (Golder Associates, 1996b)

2.6 Ford Property Reports
In addition to the studies of the Ford property (now the buffer zone and Crossroad property) discussed in the OU-1 investigative reports, the following reports have been prepared specifically for the Ford property located to the northwest and adjacent to Radiological Area 2:

Phase II Investigation Report (Dames & Moore, 1990)


Phase III Radiological Site Assessment, Earth City Industrial Park (Dames & Moore, 1991)

All of the above reports were reviewed during the preparation of this document. Information, data and interpretations from each report were incorporated as applicable. It should be noted that the discussion of the nature and extent of contamination presented in Sections 6 and 7 of this report is based primarily upon the data and results obtained as part of the OU-1 field investigations and laboratory analyses. Chemical and radiological results obtained as part of other investigations of the landfill, principally the pre-RI investigations and the OU-2 investigations, were evaluated and considered as part of the assessment of the nature and extent of contamination associated with Areas 1 and 2 for OU-1. These non OU-1 data were used to assess the representativeness of the OU-1 results. However, the non-OU-1 data generally were not tabulated or integrated into the statistical or other evaluations of the OU-1 data that form the principal basis for the evaluation of the nature and extent of contamination for OU-1.
RI Report West Lake Landfill OU-1 April 10, 2000 Page 7
3.0 SITE BACKGROUND
This section presents a brief description of the West Lake Landfill including its location, an overview of past and current landfill operations, and a discussion of activities occurring adjacent to the landfill.
3.1 Landfill Description and Location
The West Lake Landfill is located within the western portion of the St. Louis metropolitan area on the east side of the Missouri River. The landfill is situated approximately one mile north of the intersection of Interstate 70 and Interstate 270 within the city limits of the City of Bridgeton in northwestern St. Louis County.
The West Lake Landfill is an approximately 200-acre parcel containing multiple facilities. The primary facility, the Bridgeton Landfill (formerly known as the Laidlaw Landfill and before that as the West Lake Landfill) has an address of 13570 St. Charles Rock Road, St. Louis County, Missouri (Figure 3-2). St. Charles Rock Road (State Highway 180) borders the landfill on the north. Taussig Road and agricultural land lie to the southeast of the landfill. Old St. Charles Rock Road, along with undeveloped land, borders the southern and western portions of the landfill (Figure 3-2).
The West Lake Landfill includes an active solid waste landfill, an inactive demolition landfill, and an inactive sanitary landfill. In addition, included within the boundaries of the site as defined in the OU-2 Work Plan, are concrete and asphalt batch plants, an automobile repair shop and a former telephone switching station although these operations are not the subject of the RI/FS. Current surface ownership of the landfill property in the vicinity of Areas 1 and 2 is depicted on Figure 3-3.
A 6-foot high chain-link fence with a 3-strand barbed wire canopy encloses the entire landfill. The main access gate is located on the northeastern perimeter off of St. Charles Rock Road. An additional gate is located on the southwestern perimeter to provide access to the borrow area located across Old St. Charles Rock Road. A third gate provides access to the automobile repair shop.
The Earth City industrial park lies to the west and adjacent to the West Lake Landfill across Old St. Charles Rock Road. Previously undeveloped property now or formerly owned by Ford Financial Services Group (Ford property) lies immediately to the northwest of the landfill (Figures 3-2 and 3-3). Property to the north of the landfill, across St. Charles Rock Road, is moderately developed with commercial, retail and manufacturing operations. Zoning for the landfill and surrounding area is depicted on Figure 3-4.
RI Report West Lake Landfill OU-1 April 10, 2000 Page 8
A deed restriction was recorded in May 1997 against the entire landfill area prohibiting residential use and groundwater use. An additional deed restriction was recorded in January 1998 restricting construction of buildings and underground utilities and pipes within Areas 1 and 2. These deed restrictions cannot be terminated without the written approval of the current owners, MDNR and EPA.
3.2 Summary of Landfill Operations
The West Lake Landfill is comprised of approximately 200 acres. Limestone was quarried from the landfill area from 1939 to 1988. Beginning in the early 1950s or perhaps the late 1940s, portions of the quarried areas and adjacent areas were used for landfilling municipal refuse, industrial solid wastes and construction demolition debris. It has been alleged, but never substantiated, that liquid wastes were also placed in the landfill. These activities were not subject to State permitting, and the portion of the landfill where these activities occurred has been termed the “unregulated landfill”. In 1974, a State landfill permit was obtained and landfilling began in the portion of the property described below as the North Quarry Pit. Landfilling continued in this area until 1985 when the landfill underwent expansion to the southeast in the area described below as the South Quarry Pit. Landfill activities conducted in 1974 and afterwards within the quarry area were subject to a permit from the Missouri Department of Natural Resources (MDNR) and hence this area is referred to as the “regulated landfill”.
The landfill can be divided into the following six distinct areas (Figure 3-5):

Radiological Area 1 within and adjacent to the North Quarry Pit inactive sanitary landfill


Radiological Area 2 within the inactive demolition landfill


Inactive demolition landfill (excluding Area 2)


Inactive sanitary landfill


North Quarry Pit inactive sanitary landfill (excluding Area 1), and


South Quarry Pit landfill (the active sanitary landfill).

These six areas are briefly discussed below. There also is a surface water retention pond, abandoned leachate lagoons and an active leachate retention pond associated with the sanitary landfill operations. The focus of OU-1 is Radiological Areas 1 and 2 and the nearby Ford property which is adjacent to Area 2 (Figure 3-6).
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3.2.1 Radiological Area 1
Radiological Area 1 is located immediately to the southeast of the landfill entrance. This area was part of the unregulated landfill operations conducted up through 1974. Based on the drilling logs obtained as part of the RI/FS investigations for OU-1, the waste materials within Area 1 consist of municipal refuse (sanitary wastes) with an average thickness of approximately 36 feet.
Area 1 consists of approximately 10 acres that may have been impacted by radiological materials (Fig 3-5). There is an asphalt entrance road and parking area located on the northwestern border of Area 1 near the landfill office building. The remaining portions of Area 1 are mainly covered with grass. An underground diesel tank is located beneath the asphalt-paved area in the western portion of Area 1. The tank is no longer in use but has not been removed because it is within the boundaries of Area 1.
3.2.2 Radiological Area 2
Radiological Area 2 is located in the northwestern part of the landfill. This area was also part of the unregulated landfill operations conducted up through 1974. Based on the drilling logs obtained as part of the RI/FS investigations for OU-1, the waste materials within Area 2 consist of construction and demolition debris and municipal refuse with an average thickness of approximately 30 feet.
Area 2 consists of approximately 30 acres that may have been impacted by radiological materials (Fig 3-5). Large portions of this area are covered with grasses, native bushes and trees while other portions are unvegetated and covered with soil, gravel, concrete rubble and miscellaneous debris consisting of concrete pipe, metal and automobile parts, discarded building materials, and other non-perishable materials. Scattered throughout Area 2 are a number of small depressions, some of which seasonally contain ponded water and phreatophytes such as cattails. The northern and western portions of Area 2 are bounded by the landfill berm, the slopes of which are covered with a dense growth of trees, vines and bushes.
3.2.3 Inactive Landfill Operations
In addition to Radiological Areas 1 and 2, an inactive demolition landfill and an inactive sanitary landfill area are located in the north central part of the landfill property. The inactive demolition landfill is located on the southeast side of Radiological Area 2, between Area 2 and the landfill entrance road. The inactive sanitary landfill is located to the southwest of the inactive demolition landfill. As with the landfill operations conducted in Areas 1 and 2, the operations performed in these areas were also part of the unregulated landfill operations conducted up through 1974. Wastes disposed of in these
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areas are believed to consist of sanitary wastes, a variety of other solid wastes and demolition wastes.
3.2.4 Current Active Landfill Operations
The north quarry pit and the south quarry pit are associated with current landfilling operations. Landfilling activities conducted in these areas are subject to a permit issued by MDNR in 1974. Extensive information is available regarding the operations conducted and the nature and configuration of the waste materials disposed of in these areas (McLaren/Hart, 1994). Disposal activities at the north quarry pit were previously completed and this area is currently inactive. Disposal activities are currently being conducted at the south quarry pit.
3.3 Activities Adjacent To The Landfill
The property located to the west of Area 2 (the buffer zone and Crossroad properties formerly referred to as the Ford property) was recently developed as an industrial park. The subdivision plat for the Crossroad property, known as Crossroads Industrial Park, currently reflects a 1.785-acre buffer created adjacent to the Area 2 slope. The buffer zone includes the area of radiologically impacted surface soils as identified in the “Phase III Radiological Assessment” performed by Dames & Moore for Ford Financial Services Group (Ford) in 1991. The boundary of the current buffer zone is shown on Figure 3-6. The Respondents and Ford are currently engaged in discussions that would result in transfer of the buffer zone ownership to one or more of the Respondents.
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4.0 SITE INVESTIGATION ACTIVITIES
This section of the RI report describes and summarizes the results of the various site investigation activities performed in conjunction with the development of the RI/FS for OU-1. More detailed descriptions of the RI field investigations can be found in the various reports listed in Section 2 of this document and referenced in the following discussions. Table 4-1 presents a summary of the various investigative activities and the associated reports prepared by McLaren/Hart or EMSI.
4.1 Site Reconnaissance
McLaren/Hart completed a site reconnaissance to identify site features that may have changed since preparation of the Work Plan and to identify site conditions that may affect the remedial investigations and ultimately the development of remedial alternatives. McLaren/Hart prepared a report titled Site Reconnaissance Report – West Lake Landfill Radiological Areas 1 & 2 dated May 16, 1996 (McLaren/Hart, 1996 b), which was previously submitted to EPA.
4.1.1 Summary of Methods and Procedures Used
The site reconnaissance was completed on October 18, 1994, prior to the start of any of the sampling activities. Activities completed as part of the site reconnaissance included the following:

Identification of any changed conditions that would affect the completion of the field activities;


Identification of any planned or new residential or commercial construction;


Examination of the soil cover and adjacent slopes in Areas 1 and 2 for evidence of potential hazardous chemicals;


Evaluation of runoff and sedimentation patterns in and around Areas 1 and 2;


Evaluation and selection of potential staff gauge locations and surface water sampling points;


Inspection of all existing monitoring wells and evaluation of their suitability for water level measurements and groundwater sampling; and


Inspection of the site for evidence of habitat for threatened or endangered species.

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A more detailed description of the specific activities completed as part of the site reconnaissance effort as well as the methods used can be found in the Site Reconnaissance Report – West Lake Landfill Radiological Areas 1 & 2 dated May 16, 1996 (McLaren/Hart, 1996b).
4.1.2 Deviations from Work Plan
The RI/FS Work Plan did not specifically address procedures for site reconnaissance; therefore, no deviations from the Work Plan exist.
4.1.3 Summary of Results
Results of the site reconnaissance effort were previously presented in the Site Reconnaissance Report – West Lake Landfill Radiological Areas 1 & 2 dated May 16, 1996 (McLaren/Hart, 1996 b). A general summary of results of the site reconnaissance effort and the conclusions reached by McLaren/Hart are as follows:

No changed conditions were identified by McLaren/Hart;


No planned or new residential or commercial construction was identified by McLaren/Hart at the time the site reconnaissance was conducted (It should be noted that although not anticipated in 1994 at the time of McLaren/Hart’s site reconnaissance, substantial new commercial building construction has occurred to the south and west of the landfill in the last twelve to eighteen months);


No evidence of potential hazardous chemicals in Areas 1 and 2 was identified by McLaren/Hart;


McLaren/Hart identified four locations from which runoff from Area 1 occurs. This runoff flows into the perimeter drainage ditch and ultimately into a closed topographic depression (the North Surface Water Body) near the northern portion of Area 2 (Figure 4-1);


McLaren/Hart identified five locations from which runoff from Area 2 occurs. This runoff flows either to the North Surface Water Body, onto the Ford Property farmers field or out along the access road to Area 2 in the vicinity of the demolition landfill and the roll-off bin storage area;


McLaren/Hart identified potential locations for the staff gauges and surface water sampling points within the North Surface Water Body and the flood control channel located along the western portion of the landfill. These locations were

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presented to EPA in McLaren/Hart’s March 30, 1995 letter (McLaren/Hart,
1995b) and were approved by EPA on May 5, 1995 (EPA, 1995a);

McLaren/Hart inventoried all existing monitoring wells which could be located at the landfill, noted those wells with problems such as crushed or broken casings, re-surveyed the well locations and collar elevations, re-developed the existing wells and evaluated the suitability of the existing wells for use in water level measurements and groundwater sampling;


McLaren/Hart located a number of cased soil borings used by Radiation
Management Corporation during its investigations conducted in 1981; and


McLaren/Hart performed an inspection of the landfill area for evidence of
threatened or endangered species habitat (discussed below).

A more detailed description of the results of the site reconnaissance effort can be found in the Site Reconnaissance Report – West Lake Landfill Radiological Areas 1 & 2 dated May 16, 1996 (McLaren/Hart, 1996 b).
4.1.4 Data Quality Issues
McLaren/Hart identified no data quality issues in its report. EMSI also did not identify any data quality issues associated with the site reconnaissance effort.
4.1.5 Outstanding Issues or Items
McLaren/Hart did not identify any outstanding issues in its report for this activity. EMSI also did not identify any outstanding issues during our review of this activity.
4.2 Threatened or Endangered Species Assessment
McLaren/Hart completed an assessment of the potential for the presence of threatened or endangered species occurrences at the landfill. The purpose of this assessment was to identify and characterize the dominant plant communities and to assess the site for the presence of threatened or endangered species.
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4.2.1 Summary of Methods and Procedures Used
The methods used by McLaren/Hart to complete this investigation included the following:

Qualitative identification of dominant plant communities in Areas 1 and 2;


Submission of a written request to the U.S. Fish and Wildlife Survey to investigate whether any listed or proposed species have been determined to be present in the area of the landfill; and


Completion of a detailed field survey to investigate whether the Western Fox Snake, a Missouri State-listed endangered species, was present at the site.

A more detailed description of the specific activities completed as part of the threatened or endangered species assessment as well as the methods used can be found in the Threatened or Endangered Species Assessment Report – West Lake Landfill Radiological Areas 1 & 2 dated May 17, 1996 (McLaren/Hart, 1996c).
4.2.2 Deviations from Work Plan
The RI/FS Work Plan did not specifically address procedures for the Threatened and Endangered Assessment; therefore, no deviations from the Work Plan exist.
4.2.3 Summary of Results
Following the completion of the threatened or endangered species assessment, McLaren/Hart concluded that:

Four dominant plant communities exist at the landfill, including a forested community, an old field community, a maintained field community, and a wetland type vegetated community (plant species that may be found in wetlands);


Six small isolated areas in Area 1 (Figure 4-2) and ten small isolated areas in Area 2 (Figure 4-3) contain plant species that may be found in wetlands (wetland type vegetated community). These areas were located in small surface depressions in the surface of the landfill and are an artifact of landfill construction and settlement and the placement of perimeter berms which obstruct surface water flow, restrict off site flow of rainwater runoff, and lead to water ponding on the landfill surface cover;

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Given that the small isolated depressions within Areas 1 and 2 are generally less than one-tenth of an acre in size (actual size varies from 0.01 to 0.36 acres), they do not contain water except after a rainwater event, they do not appear capable of functioning together as a wetland complex and they are artifacts of landfill construction and subsequent subsidence, McLaren/Hart concluded that no further assessment of these areas was necessary or appropriate to determine whether any of these areas exhibit other necessary characteristics of a wetland; and


Review of the US Fish & Wildlife Service and Missouri Department of Conservation databases along with the results of the field inspection did not indicate that any threatened or endangered species (including the Western Fox Snake) were present in the vicinity of the landfill; therefore, no further assessment activities were necessary.

A more detailed description of the results of the threatened or endangered species assessment can be found in the Threatened or Endangered Species Assessment Report – West Lake Landfill Radiological Areas 1 & 2 dated May 17, 1996 (McLaren/Hart, 1996c).
4.2.4 Data Quality Issues
McLaren/Hart identified no data quality issues in its report. EMSI also did not identify any data quality issues associated with the threatened or endangered species assessment.
4.2.5 Outstanding Issues or Items
McLaren/Hart identified no outstanding issues in its report nor were any identified by EMSI during our review of this activity.
4.3 Overland Gamma Survey
The purpose of the overland gamma survey was to delineate the approximate areal extent of Radiological Areas 1 and 2 and to identify areas of elevated gamma readings (“radiologically affected areas”) for investigation during subsequent field activities. Information from the overland gamma survey was subsequently used in finalizing the locations of those soil borings and monitoring well installations that would be located in radiologically affected areas. McLaren/Hart prepared a report for this activity titled Overland Gamma Survey Report – West Lake Landfill Radiological Areas 1 & 2 dated April 30, 1996 (McLaren/Hart, 1996a).
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4.3.1 Summary of Methods and Procedures Used
The overland gamma survey was completed by collecting near-continuous readings on an approximately 30 foot transect spacing. Readings were collected using a 2-inch by 2-inch sodium iodide detector. Measurements were also taken at eight potential background locations. The resulting data (56,736 readings) were evaluated and computer-processed by McLaren/Hart to depict the areal distributions of the resultant gamma readings based upon different assumed background levels.
4.3.2 Deviations from Work Plan
The main deviation from the RI/FS Work Plan was the change in the sampling density resulting from implementation of a near continuous readout procedure used for the overland gamma survey. Measurements were obtained at approximately every 1 to 2 seconds at a walking speed of approximately 2 feet per second as opposed to the collection of discrete measurement points proposed in the Work Plan. As a result, the sampling grid utilized during the field work changed from an approximate 30 by 30-foot grid to a 1 to 4-foot by 30-foot grid. Use of the continuous readout system also increased the number of measurement points from approximately 5,000 to over 50,000 measurements. EPA’s oversight contractor approved this change in the field prior to onset of the field work.
In addition to the change in grid spacing, the following deviations to the overland gamma survey were also implemented after approval by EPA or its oversight contractor:

The number of background sampling locations was increased from two to eight sites; and


A hand-held Geiger Mueller counter was used to initially locate areas of elevated gamma readings.

4.3.3 Summary of Results
The results of the overland gamma survey are described in detail in the Overland Gamma Survey Report – West Lake Landfill Radiological Areas 1 & 2 (McLaren Hart, 1996a). Significant findings reached by McLaren/Hart include the following:
• Evaluation and comparison of the results from the eight background locations indicated a wide range of background values;
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A single “site specific” background value could not be derived because of the wide variation in background values. McLaren/Hart suggested a range between 10 and 20 micro-Rems per hour (µR/hr);


The size of the areas defined, as two times background is dependent upon the assumed background value. McLaren/Hart prepared five different figures depicting the areas with gamma readings twice the background level based upon background values of 10, 12.5, 15, 17.5 and 20 µR/hr (Figures 4-4 through 4-8);


McLaren/Hart concluded that the 17.5 and 20 µR/hr values are the most
representative of background conditions based upon the generally known
locations of the radiological materials at the landfill; and


Based upon the overland gamma survey, McLaren/Hart identified locations to advance soil borings to collect vertical profiles of the radiologically impacted materials.

4.3.4 Data Quality Issues
McLaren/Hart identified no data quality issues in its report. EMSI also did not identify any data quality issues during review of this activity.
4.3.5 Outstanding Issues or Items
McLaren/Hart identified no outstanding issues in its report. EMSI did not identify any data quality issues during our review of this activity. If used alone without the use of other site data, the inability to derive a single background number could result in uncertainties in deriving representative material volumes during the preparation of the FS. However, when the overland gamma results are used in conjunction with the results of the soil boring, down-hole gamma logging and soil sampling and analysis results, it is EMSI’s opinion that representative and generally reliable estimates of the approximate volumes of impacted materials can be developed. These estimates are presented in Section 6 of this RI report.
It should be noted that the Overland Gamma Survey by itself may not completely define the areal extent of radiologically impacted areas. Information obtained from the Overland Gamma Survey should be used in conjunction with other information such as soil sample analyses and downhole gamma log results to assess areas potentially impacted by radonuclides.
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4.4 Surface and Subsurface Soil and Perched Water Investigations
This section describes the surface and subsurface soil investigation activities including surface geophysical investigations, landfill gas surveys, borehole drilling, soil sample collection and chemical analyses, down-hole gamma logging, soil boring abandonment, and geotechnical sampling and testing. Also included in this section is a discussion of occurrences and sampling of perched water encountered during the soil-boring program.
4.4.1 Purpose and Scope of Investigation
The surface and subsurface soil and perched water investigation activities were completed to characterize the distribution and extent of radioactive and hazardous non.radioactive constituents within the landfill mass, including the various cover soils and potential perched water occurrences in Areas 1 and 2. McLaren/Hart completed or supervised all initial field activities and prepared a summary report titled Soil Boring/Surface Soil Investigation Report (McLaren/Hart, 1996h).
McLaren/Hart’s investigation of the landfill soils and perched water included the following:

Pre-screening of each soil boring location within the landfill for potential large metal obstacles and methane concentrations;


Drilling of 20 borings in Area 1 and 40 borings in Area 2, including pre-drilling of all planned monitoring wells to be completed through areas underlain by landfill refuse. In addition, five hand borings were drilled and sampled in a closed topographic depression within Area 2;


Collection of soil samples from all of the soil borings, generally at five-foot depth intervals, and performance of radiological and chemical analyses on selected soil samples from the various soil borings;


Collection of samples from four background locations potentially representative of daily cover materials and performance of radiological and chemical analyses;


Down-hole radiological logging of all of the newly drilled soil borings and of all existing monitoring wells and cased soil borings remaining from the prior site investigation (RMC, 1982) that could be located;


Collection of selected perched water samples encountered during the soil boring activities; and

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• Collection and laboratory testing for selected geotechnical properties of four soil samples obtained from the landfill slope at the northern edge of Area 2 above the former Ford Property.
Supplemental surface and subsurface soil investigation activities were conducted by EMSI as requested by EPA to assess the lateral extent of constituents in the southwestern portion of Area 1 and to further evaluate the lateral extent of surface and near subsurface constituents on the Ford Property. The supplemental activities were described in a letter to EPA (EMSI, 1997e), which responded to EPA’s comments on the ASAP (EPA, 1997b), and included the following:

Drilling of four borings in the southwestern portion of Area 1. The locations for these borings were developed using the same methodology as was used for selecting the random boring locations for the previous field investigation. Additional grids were added in the southwest corner of the of the existing grid system for Area 1. Surface samples were collected at each boring location and downhole geophysical logging was performed in each borehole. As elevated gamma levels were not encountered during the geophysical logging, no subsurface samples were collected. Radiological analyses were performed on the surface soil samples and the boring locations were surveyed.


Additional surface and near surface samples were collected at eight locations on the Ford property. Surface samples were collected at a depth interval between 0 to 3 inches below ground surface (bgs) at each location. A hand auger was also advanced at each location and samples were collected from the hand auger boring at depth intervals of 3 to 6 inches, 6 to 12 inches, 1 to 2 feet, 2 to 3 feet, 3 to 4 feet, and 4 to 5 feet bgs. The surface sample and the sample from 1 to 2 feet from each location were analyzed for radionuclides. As the results of these analyses along with the results of the previous analyses performed by McLaren/Hart indicated that vertical extent of radionuclide occurrences did not extend below a depth of approximately six inches, the samples collected at the other depths were not analyzed.

4.4.2 Summary of Methods and Procedures Used
The methods and procedures used included: surface geophysical surveying; landfill vapor sample collection and field analysis; auger and mud rotary drilling and soil boring advancement; soil sample collection, chemical analysis of soil samples; perched water sample collection and chemical analysis; down-hole radiological logging; and soil-boring abandonment. Summary information on each activity is provided below. Detailed descriptions of each field activity and laboratory analysis conducted by McLaren/Hart are contained in the Soil Boring/Surface Soil Investigation Report (McLaren/Hart, 1996 h). Detailed descriptions of the supplemental field and laboratory activities conducted by
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EMSI can be found in the letter from EMSI to EPA dated April 29, 1997 (EMSI, 1997e) and the Site Characterization Summary Report (SCSR) for OU-1 (EMSI, 1997c).
4.4.2.1 Surface Geophysical and Landfill Vapor Surveys
Surface geophysical surveying consisted of completing a non-intrusive total magnetic surface survey at each planned boring location within Areas 1 and 2 as proposed in the RI/FS Work Plan. The objective was to identify the spot within 30 feet of each proposed location within Areas 1 and 2 with the lowest potential for buried ferromagnetic debris. Final borings were then advanced at the selected locations. Geotechnology of St. Louis, Missouri using a GEM GSM-19 magnetometer/gradiometer, completed the surface geophysical survey.
Soil vapor samples were collected at depths of 5 and 10 feet at each proposed boring location in Areas 1 and 2 and analyzed for methane gas to determine the potential hazard posed by possible landfill gases at each proposed boring location. This activity and associated methodology was first described in the RI/FS Work Plan and the associated Sampling and Analysis Plan. GEO Environmental Testing under the supervision of McLaren/Hart completed the work. Further details related to the surface geophysical and landfill vapor surveys are presented in the Soil Boring/Surface Soil Investigation Report (McLaren/Hart, 1996h) and the Radon Gas, Landfill Gas and Fugitive Dust Report (McLaren/Hart, 1996d).
4.4.2.2 Soil Boring Drilling
The EPA approved RI/FS Work Plan called for a total of 50 soil borings to be drilled as part of the OU-1 field investigation. These fifty borings included 18 borings in Area 1 and 32 borings in Area 2. As part of the evaluation of the Overland Gamma Survey results (McLaren/Hart, 1996a), McLaren/Hart proposed minor modifications in the soil boring locations resulting in a total of 18 borings in Area 1 and 33 borings in Area 2 for a total of 51 soil borings. EPA subsequently approved these boring locations in its letter dated July 21, 1995 (EPA, 1995b).
A total of 20 soil boring locations were ultimately drilled by McLaren/Hart in Area 1 and 40 soil boring locations plus five hand-auger borings were drilled in Area 2 (Figure 4-9). These borings include two additional borings in Area 1 and seven additional borings in Area 2 beyond the number proposed in the Overland Gamma Survey report and subsequently approved by EPA. The additional borings were the result of encountering shallow perched water within the body of the landfill debris. To avoid creating a conduit for leachate migration, any boring that encountered perched water was abandoned prior to reaching total depth and a new boring was drilled outside of the area of perched water. In addition, at several locations, multiple borings were drilled due to encountering auger refusal at shallow depths within the landfill or to loss of the boring
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due to caving of the borehole walls or flowing sands encountered in the alluvial materials beneath the landfill deposits.
During the field investigation, 52 borings were actually drilled at or near the 51 locations proposed in the Overland Gamma Survey Report (McLaren/Hart, 1996a) as approved by EPA. An additional boring, WL-205, was drilled adjacent to boring WL-204 located on the Ford property. This additional boring was drilled as part of the pre-drilling of monitoring wells and as a result of occurrences of caving sands in alluvial materials encountered in boring WL-204 that prevented completion of boring WL-204 to the full depth originally intended.
The locations of six of the Area 2 borings, WL-212, WL-216, WL-217, WL-234, WL-235 and WL-236 were moved a significant distance (50 to 200 feet) during the field investigation. Boring WL-212 was moved approximately 50 feet to the southeast in response to field conditions. Boring WL-216 was originally located outside of Area 2 and was re-located to be within the boundary of Area 2. Boring WL-217, scheduled for installation of a monitoring well, was also originally located outside of the boundaries of Area 2. WL-217 was subsequently relocated to within the boundaries of Area 2. The remaining three of these borings (WL-234, WL-235 and WL-236) were moved back away from the edge of slope in the southwestern portion of the landfill for safety reasons.
In addition to the 51 soil boring locations proposed in the Overland Gamma Survey Report (McLaren/Hart, 1996a) and additional boring WL-205, two contingent borings (WL-118 and WL-119) were drilled in Area 1 and six additional soil borings were drilled in Area 2 (WL-228, WL-229, WL-237, WL-238, WL-240 and WL-241). The majority of these additional borings (WL-118 and 119 and WL-237, 238, 240, and 241) were drilled in response to the discovery of perched water in other borings. Two of these borings (WL-228 and 229) were drilled in conjunction with the installation of monitoring wells, the locations of which were re-located in response to field conditions necessitating acquisition of subsurface information at the new locations of these wells. As a result, a total of 60 soil borings were drilled as part of the OU-1 RI field investigations.
In addition to the eight contingent soil borings, five additional hand-auger borings were advanced to depths of one to two feet in and around the closed topographic depression and the northern landfill berm in the northeastern portion of Area 2. These five hand-auger borings were recommended in the Overland Gamma Survey Report (McLaren/Hart, 1996a).
Three different drilling methods were utilized during the soil boring activities. Borings in areas underlain by landfill debris were advanced to the bedrock contact using a 24-inch diameter truck mounted auger. Borings in areas not expected to be underlain by landfill debris (i.e. the Ford property) were advanced with a hollow-stem auger drill rig. Contingency soil borings located in the closed topographic depression in the northern portion of Area 2 were manually advanced with a hand-auger. All of the drill
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rig advanced soil borings were drilled using the procedures proposed in the RI/FS Work Plan.
Organic vapor, explosive gas and radiological measurements were obtained in the field during the advancement of each soil boring using a photo-ionization detector (PID), an oxygen/combustible gas indicator, and a Geiger/Mueller instrument, respectively. Field measurements were generally made at 5-foot intervals during drilling and when visual changes in the drill cuttings were observed.
Detailed lithologic logs were prepared for each machine-advanced boring. The lithologic logs include descriptions of the soil and bedrock materials encountered and classification based on the Unified Soil Classification System. The soil boring logs along with additional details regarding the drilling procedures are presented in McLaren/Hart’s Soil Boring/Surface Soil Investigation Report (McLaren/Hart, 1996a).
EMSI advanced an additional four soil borings on May 13 and May 14, 1997 according to the procedures contained in the approved ASAP. All four borings were advanced using hollow-stem auger until alluvial materials were encountered. Each boring was then logged using gamma-gamma and natural gamma tools. Soil samples were collected at the surface and submitted for radiological analysis. Subsurface samples were not submitted because neither clearly identifiable soil layers nor elevated downhole gamma readings were encountered in any of these four borings.
As part of the ASAP activities, eight hand-auger borings were drilled by EMSI to depths of 5-feet on the Ford property. Samples were obtained from these hand-auger borings from depth intervals of 0 to 3 inches, 3 to 6 inches, 6 to12 inches, 1 to 2 feet, 2 to 3 feet, 3 to 4 feet, and 4 to 5 feet below ground surface.
4.4.2.3 Soil Sampl