Foreword This 2009 Site History and Environmental Monitoring Report for the Sheffield Low-Level Radioactive Disposal Site was developed by the Illinois Emergency Management Agency (IEMA), Bureau of Environmental Safety (BES) to provide information to anyone interested in this closed low-level radioactive waste (LLRW) disposal site. This report provides historical background on the Sheffield LLRW site and its operation including the context of the time that it operated, design flaws, remedies, key regulatory issues, and the site’s past and current performance. IEMA published this report in an effort to communicate background information on the site, the current conditions and hopefully answer questions that residents and the general public may have about the Sheffield LLRW site. IEMA’s continuing objective at the closed Sheffield LLRW site is to ensure that the radionuclides entombed there are isolated from people and the environment, in accordance with regulatory requirements, until the radionuclides become stable through radioactive decay. Questions regarding the Sheffield LLW site or this report should be directed to: Gary McCandless, P. E. Chief, Bureau of Environmental Safety Illinois Emergency Management Agency 1035 Outer Park Drive Springfield, IL 62704 Phone: 217-785-9954 Fax: 217-524-6417 Copies of this report may be obtained from IEMA BES or by downloading it from http://www.state.il.us/iema/publications/publications.asp. TABLE OF CONTENTS Page Foreword i A Brief History of the Sheffield LLW Disposal Facility 1 Agreed Order aka the Sheffield Settlement Agreement 8 Tritium Migration 10 Summary of Hydrologic and Geologic Studies at the LLW site 11 The Environmental Monitoring Program at the Sheffield LLW site 14 Ambient Gamma Exposure 16 Surface Waters 17 i Trout Lake 20 Off-site Public and Private Wells 21 Onsite Groundwater Monitoring Wells 22 Discovering the Migration Pathways at the LLW site 24 The Northeast Pathway 27 The Southeast Pathway 28 Conclusion 30 References 32 APPENDIX A A-1 Sheffield Low-Level Radioactive Waste Licensing Chronology A-1 Timeline of Selected Sheffield LLRWDF Events A-3 List of Maps Map 1 Location of the Sheffield LLW Disposal Facility 1 Map 2 Areas where tritium was found at and near the Sheffield LLW 12 Disposal Facility Map 3 Watershed & Drainage Areas – Upper Mississippi Watershed 17 and Area Drainage map with states overlay Map 4 Close-up of the Illinois State Water Survey Map, Major 18 Watersheds of Illinois Map 5 Projected flow paths of tritium migration to groundwater in 23 relation to trenches Table of Contents, continued List of Maps, continued Map 6 Chronology of the discovery of tritium in groundwater wells at 24 and near the Sheffield LLW Disposal Facility Map 7 Monitoring Wells by Unit and Monitoring Frequency (Fold-out) 26 Map 8 2004 H3 Concentrations in the NEP Monitoring Wells 27 Colorization of various tritium concentrations in the Northeast Pathway Map 9 Comparison of the 1967-1988 extension of the Southeast 29 Pathway with data from 2004 List of Photos & Slides Photo 1 Aerial view of the Sheffield LLW Disposal Facility with feature 2 overlays Photo 2 Low-level radioactive waste awaits disposal at the Sheffield site 2 Photo 3 Burial of LLW at the Sheffield LLW Disposal Facility 3 Photo 4 State Inspector standing in flooded swale at the base of a 5 disposal trench at the Sheffield LLW Disposal Facility ii Photo 5 Collapse holes exposed in trench surfaces after the snow 6 melted in spring 1979 Photo 6 View towards the Old Chem Site from stop Trenches 1, 2, and 7 3, winter 2005 Photo 7 Location of tunnel constructed to facilitate USGS investigation 25 of the of the Sheffield LLW Disposal site Photo 9 View from Trout Lake towards the Sheffield LLW Disposal 31 Facility, winter 2005 List of Drawings (DWG) DWG 1 Location of wells, borings, trenches, and tunnel at Sheffield 3 LLW Disposal Facility DWG 2 End view of a typical trench 5 Table of Contents, continued List of Tables Table 1 Maximum values estimated in the Sheffield inventory 4 Table 2 Regulatory Limits in Water for Selected Radionuclides 8 Table 3 Surface Water Monitoring Locations 19 Table 4 Drinking Water Sources Near the Sheffield LLW site 21 List of Data Graphs Graph 1 Convergence of tritium levels at G-1-D, G-1-S, and Trout Lake D 14 Graph 2 Ambient Gamma Exposures, Mean of exposure rates at and near 16 the Sheffield LLW site Graph 3 Tritium In Trout Lake Water Samples 20 Graph 4 Tritium In the NE Pathway Monitoring Wells 28 Graph 5 Tritium concentrations in USGS Well 561 30 iii Site History and Environmental Monitoring Report for the Sheffield LLRW Disposal Site 1 A Brief History of the Sheffield LLRW Disposal Facility The Sheffield Low-Level Radioactive Waste Disposal Facility (Sheffield site) is located approximately three miles southwest of the town of Sheffield in rural Bureau County, Illinois; the white star on the map below marks the approximate location. Map 1 – Location of the Sheffield LLRW Disposal Facility (IEMA, 2005) The Sheffield LLRW disposal facility operated from 1967 through 1978. During that time, about 3.2 million cubic feet of LLRW was buried in 21 earthen trenches. Since the 1980s, the Sheffield site has included both the “20-acre LLRW Disposal Site” and the surrounding 170-acre buffer zone shown in green on Photo 1 (p. 2). Trout Lake, a 31-acre strip mining lake that is fed by natural springs, is along the northeastern boundary of the buffer zone. Two hazardous chemical waste (HCW) disposal areas are located to the north and northwest of the 20.5-acre low-level radioactive waste disposal area and are separated from it by at least 150 feet. Site History and Environmental Monitoring Report for the Sheffield LLRW Disposal Site 2 Photo 1 - Aerial view of the Sheffield LLRW Disposal Facility with feature overlays (IEMA, 1999) These HCW areas were used for the disposal of non-radioactive waste. The first HCW site accepted waste from 1968 to 1974 and the second from 1974 to 1983. Photo 2 - Low-level radioactive waste awaits disposal at the Sheffield site (IEMA, 1970s) In accordance with accepted practice at the time, low-level radioactive waste was packaged and placed in unlined disposal trenches. The configuration of these Site History and Environmental Monitoring Report for the Sheffield LLRW Disposal Site 3 Photo 3 - Burial of LLRW at the Sheffield LLRW Disposal Facility (IEMA, date unknown) trenches is shown on Drawing 1 below (USGS, 1985). Drawing 1 Location of wells, borings, trenches, and tunnel at Sheffield LLRW disposal site (after A precise inventory of lowFoster and Erickson, 1980, in ISGS Contract/- level radioactive waste buried in each trench was not kept Grant Report 1985-1) by the site operator, but has been estimated in three separate studies (NUS, 1979; Dragonette et al, 1979; MacKenzie et al, 1985). The estimated inventory of important radionuclides is listed in Table 1, Maximum Values Estimated in the Sheffield Inventory. Site History and Environmental Monitoring Report for the Sheffield LLRW Disposal Site 4 Table 1 – Maximum Values Estimated in the Sheffield Inventory Important Radionuclides with half-lives greater than five years, as estimated by three studies Radionuclide Curies Half-life (Years) H-3 (Tritium) 5,990 12.35 C-14 (Carbon) 450 5,730 I-129 (Iodine) 0.01 15,700,000 Sr-90 (Strontium) 3,690 29.12 Cs-137 (Cesium) 15,500 30 Co-60 (Cobalt) 20,000 5.27 Pu-238 (Plutonium) 7.5 87.74 Pu-239, Pu-240, Pu-241 4,870 24,065; 6,550; 14.4 Am-241 (Americium) 137.5 43.2 (IEMA, 2009) All trenches were located in the unsaturated zone on the higher ground in areas where water levels fluctuate least and are located 2 to 10 feet above the water table, except Trench 18 which was partly below the water table (USGS, 1984, p.35). However, the original trench design, depicted below in DWG 2, did not function as well as expected. See Appendix A for a chronology and timeline of regulatory events that led to improvement of the trench performance. DWG 2 - End view of a typical trench (USGS, 1984) A key problem with the original trench design was that water accumulated between the trench caps, as shown in Photo 4 where of the State inspector is standing in a swale. It is probable that the soil covering the waste in the trenches was not adequately compacted and that coupled with seepage into the trenches resulted in cap subsidence. Vertical collapse holes in the vicinity of Site History and Environmental Monitoring Report for the Sheffield LLRW Disposal Site 5 Photo 4 - State inspector standing in flooded swale at the base of a disposal trench at the Sheffield LLRW Disposal Facility (IEMA, date unknown) the trenches occurred on the Sheffield site during spring months, as shown on the photos below. Although the site contractor filled these on a routine basis, the collapse holes provided a pathway for rapid movement of surface water into the Site History and Environmental Monitoring Report for the Sheffield LLRW Disposal Site 6 Photo 5 - (USGS, 1984) shallow aquifer through waste-disposal trenches (USGS, 1986, p. 15). Precipitation falling on open trenches moistened trench walls, lowered the cohesive strength of the silt layers exposed there, and resulted in occasional slumps while the trenches were being filled with waste. Holes occasionally formed in the trench caps when voids developed below the cap, resulting in collapse of the cap material into the void. Collapse holes were repaired by filing the holes with silty-clay that was Site History and Environmental Monitoring Report for the Sheffield LLRW Disposal Site 7 compacted by running heavy equipment over the fill (Kahle and Rowlands, 1981, in USGS 83-4125, 1984, p.