PB98-963139 EPA 541-R98-151 March 1999 EPA Supei fund Explanation of Significant Difference for the Record of Decision: Tri-County Landfill/ Waste Management Illinois South Elgin, IL 4/23/1998 ------- UNITED STATES ENVIRONMENTAL PROTECTION AGENCY \ REGIONS 8 77 WEST JACKSON BOULEVARD CHICAGO, IL 60604-3590 REPLY TO THE ATTENTION OF EXPLANATION OF SIGNIFICANT DIFFERENCES TRI-COUNTY-ELGIN LANDFILLS SUPERFUND SITE KANE COUNTY, ILLINOIS I. INTRODUCTION The Tri-County/Elgin Landfill Superfund Site (TCLF) encompasses both the Tri-County and Elgin Landfills. The site is located in northeastern Illinois on the east side of Kane County near the triple junction of Kane, Cook, and DuPage Counties. The Tri-County Landfill, an inactive landfill of approximately 46 acres, and the 20-acre Elgin Landfill, are located 2/3 of a mile southeast of the Village of South Elgin. The land to the west of the site is occupied by the Woodland Landfill, an active sanitary landfill which has accepted municipal and selected special wastes since 1976. Response actions at the site are being taken under the authority of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) as amended by the Superfund Amendments and Reauthorization Act (SARA) and the National Contingency Plan (NCP). The lead and support regulatory agencies for the TCLF site are the United States Environmental Protection Agency (EPA) and the Illinois Environmental Protection Agency (ffiPA), respectively. Section 117(c) of CERCLA and Section 300.43 5(cK2)(i) of the NCP establish procedures for explaining, documenting, and informing the public of significant changes to the remedy that occur after the Record of Decision (ROD) is signed. Significant changes to a component of a remedy generally are incremental changes to the management approach selected for the site (e.g., a change in timing, cost, materials, etc.). Significant changes do not fundamentally alter the overall approach intended by the remedy. When such changes are necessary, EPA publishes an Explanation of Significant Differences (ESD). Generally, an ESD is prompted when significant new information becomes available during or after the public comment period for the ROD. In the case of the TCLF site, this information was developed during the Remedial Design (RD) process. The RD was conducted by two potentially responsible parties (PRP) under an Administrative Order on Consent. The purpose of this ESD is to explain why the design for the- landfill cap component of the remedy differs from that set forth in the ROD and to address the cost differentials associated with the change. This Explanation of Significant Differences and supporting documents are a part of the Administrative Record file which is available for viewing at the Gail Borden Public Library, Elgin, Illinois, and the EPA Regional Offices at 77 West Jackson Boulevard in Chicago, Illinois, during normal business hours. Notice of availability of this ESD and supporting documents will be Ftocyclad/RacycUble • Printed with VeoetaWe Oil Baaod Inks on 50% Recycled Paper (2O% Postconsumer) ------- published in a local newspaper of general circulation. The public is encouraged to review the updated Administrative Record to better understand EPA's rationale for modifying the selected remedy. H. BACKGROUND The Tri-County Landfill property was part of a gravel mining operation prior to the 1940s. Disposal of industrial, commercial, and household waste began in April 1968 and continued until December 1976, under a series of disposal permits and owners/operators. The existing landfill cover was installed in early 1981. The Elgin Landfill property was also the site of a sand and gravel mining business that was operated until the late 1950s. Waste disposal operations began in 1961 with the landfill accepting a variety of residential and commercial wastes, as well as construction and demolition refuse. The property has recently been used for disposal of construction and landscaping material. Several commercial enterprises operate out of buildings on top of the landfill. Immediately to the north of the site is a State of Illinois conservation area. Northwest is agricultural land and wetland, and to the south are undeveloped upland and wetland areas. The Site was placed on the National Priorities List (NPL) of Superfund sites in March 1989. EPA conducted a Remedial Investigation and Feasibility Study (RTFS) from 1988 to 1992 to define the nature and extent of contamination and evaluate alternatives for Site cleanup. The RI identified contamination in soil, sediment, and ground water, and determined that a primary pathway for the contaminants to migrate off-site is through rain and snowmelt infiltrating through the inadequate landfill cover, leaching contaminants from the landfilled materials, and transporting them to ground water and surface water by surface and subsurface flow. On September 30, 1992, EPA signed a Record of Decision (ROD) selecting a remedy for the Site with the concurrence of the Illinois Environmental Protection Agency (IEPA). The major components of the 1992 ROD include: excavation and consolidation under the landfill cap of contaminated sediments that exceed background levels; construction of a landfill cap in compliance with Title 35, section 807.305, Illinois Solid and Special Waste Management Regulations, and RCRA Subtitle D cover requirements, as applicable. These regulations require a low permeability clay barrier layer a minimum of 24 inches thick, with a minimum of eight inches of topsoil as a vegetated erosion layer; collection, treatment, and disposal of leachate and contaminated groundwater at the landfill perimeter, with natural attenuation of off-site, low-level ground water contamination, to ultimately comply with drinking water or health-based standards for all ground water outside of the waste boundaries; active collection and treatment of landfill gases; comprehensive monitoring program to ensure the effectiveness of the remedy; institutional controls to limit land and groundwater use; provisions for contingency measures to address new information or previously unknown problems, and flexibility on type and timing of the ground water response component; and remedy cost estimate of $12,624,000. ------- EPA entered into an Administrative Order on Consent (AOC) for RD on February 2, 1994, with Waste Management of Illinois, Inc. (WMI) and Browning-Ferris Industries of Illinois, Inc. (BFI). In order to ensure that the final remedy would meet the performance standards in the ROD and the statutory requirement for long-term effectiveness of the remedy, the AOC established functional design specifications for each remedy component set forth in the ROD. With regards to the landfill cap, the ROD specified low permeability as the qualitative performance standard for the clay barrier layer. This performance standard relates to the rate at which water will infiltrate through the barrier layer, potentially leaching contaminants from the underlying waste and transporting them to ground water. The AOC implemented the ROD requirement by establishing the following design specifications and associated performance standards for the landfill cap: 1) a two-foot thick clay barrier layer, buried below maximum frost depth, with a hydraulic conductivity (infiltration rate) of not more than 1 x 10"7 cm/sec and 2) a one-foot thick drainage layer, with a hydraulic conductivity of not less than 1 x 10~3 cm/sec. The AOC also provided some design flexibility to meet these performance standards, allowing for use of alternative materials for the barrier layer. In a 1996 ESD, EPA deferred implementation of the ground water component of the remedy to allow for a monitoring period to determine how effective the other remedy components alone would be in reducing migration of ground water contamination from the landfill. EPA's decision to issue the ESD was primarily based on the results of a pre-design investigation (PDI), where EPA used a computer-aided infiltration model to study the rate of water infiltration through the landfill surface. Infiltration rates through the current, inadequately capped, landfill surface ranged from 3 to 56 inches per year. The model predicted a reduced infiltration rate of 0.85 inches per year, assuming the landfill was covered by a cap designed to maintain the low permeability of the barrier layer over the life of the remedy. A design analysis predicted that the reduced leachate generation alone could result in a 60 to 80 percent reduction in off-site contaminant concentrations within the first five years of remedy operation. EPA issued the 1996 ESD because it believed that the landfill cap, if designed and constructed pursuant to the terms of the 1994 AOC for RD, would significantly reduce the migration of contaminants into the ground water. EPA will make future decisions on ground water response actions based on long-term ground water monitoring results. On September 30, 1997, EPA approved the final Remedial Design submitted by WMI and BFI. The RD included a landfill cap with different design specifications than those set forth in the ROD or AOC. The RD specifies the use of synthetic materials for the cap, namely, a 40 mil geomembrane for the barrier layer, a geonet drainage layer, a geotextile to protect the drainage layer, and approximately 18 inches of soil cover. The following discussion explains EPA's rationale for approving the modified landfill cap design and explains the associated cost differences. ffl. BASIS FOR AND DESCRIPTION OF SIGNIFICANT DIFFERENCES EPA has determined that the modified landfill cap design, as approved in the RD, is the best approach for this site in meeting the performance standards in the ROD and AOC for low permeability of the barrier layer. The changes will more effectively satisfy the evaluation criteria ------- in the NCP for long-term effectiveness and permanence, short-term effectiveness, and implementability of the remedy. The reduced infiltration rates may also result in a lowering of the water levels within, the waste mass, allowing more contaminants to be removed by the gas collection system. The ROD required the construction of a low-permeability clay barrier layer a minimum of 24 inches thick, covered with a layer of topsoil at least 8 inches thick. The AOC required the barrier layer to be buried below the maximum frost depth in Kane County. The purpose of the frost depth requirement was to protect the barrier layer from-the damaging effects of freeze-thaw cycles, which are known to cause significant, permanent increases in hydraulic conductivity in compacted clay covers. Research has demonstrated that the hydraulic conductivity of an unprotected clay layer can increase by one to three orders of magnitude within three to five freeze-thaw cycles. The resulting barrier layer would then fail to meet the low-permeability performance standard specified in the ROD over the life of the remedy. The AOC also required the construction of a one-foot thick drainage layer directly above the clay barrier layer. The purpose of the drainage layer is to minimize the thickness of standing water (the "hydraulic head") in the saturated soil over the barrier layer, in order to eliminate as much infiltration of precipitation as possible from reaching the waste and leaching additional contaminants to ground water. Because the barrier layer requires a very thick layer of soil cover to protect it from freezing, this increases the thickness of the hydraulic head. Without a lateral outlet for the water through the drainage layer, the hydraulic head would create a steady downward pressure on the barrier layer and contribute to increased infiltration. The design options in the AOC for the barrier layer were either to 1) add a frost-protective soil layer approximately 42 inches thick over the 24-inch barrier layer; or 2) use alternative barrier materials that are not subject to frost damage, and therefore do not require a thick protective layer. The former approach would require trucking in over 600,000 cubic yards of soil, or approximately 15,000 truck trips. With regard to short-term effectiveness, this could be unnecessarily disruptive to the local area. In addition, because the waste goes right up to the property boundaries, the cover would not meet maximum side slope requirements without extending well into a highway right-of-way and conservation areas. This would pose implementability problems. Accordingly, EPA determined that it was appropriate to substitute an alternative material - a 40 mil low density polyethylene (LDPE) geomembrane - in place of the clay layer. Geomembranes are not subject to frost damage and therefore need not be buried below maximum frost depth. In addition, they have lower permeability than clay and require fewer truck trips to deliver the materials. The end result is a lower overall thickness for the cap system. EPA also determined that a "geonet" synthetic drainage layer should be substituted for a sand or gravel drainage layer because of its superior performance, comparable cost, and compatibility with the geomembrane. As a result of information gathered after the issuance of the ROD and the modifications to the landfill cap design, EPA has adjusted its original ROD cost estimate and is presenting a revised ------- cost estimate based on the RD. The estimated present worth of the ROD remedy in 1992 was $12,624,000. The ROD calls for a ground water treatment and discharge system as pan of the remedy, but certain costs for this component were omitted from the ROD estimate. Through this ESD, EPA is correcting the 1992 ROD estimate and setting forth a revised estimate of $14,309,500* The 1992 ROD cost estimate also did not include a figure for retaining commercial uses at the Site. Several commercial enterprises currently operate out of buildings on the landfill and immediately adjacent to the waste boundaries. The ROD states that the impacts to these businesses shall be considered during the design process. EPA determined that there is no risk- related basis for requiring the businesses to relocate, and that the remedy can be designed to accommodate the existing buildings and commercial activities. Under several different cost estimating scenarios (primarily associated with differing quantities or unit costs for materials), the cost of retaining commercial use appears to be between 1.7 and 2 million dollars. While the ROD does not require that commercial uses of the site be retained, the ROD gives EPA the discretion to accommodate such uses. Accordingly, EPA approved the RD, which provides for the retention of the existing business at the Site. EPA has estimated that the modified remedy set forth in the RD, including a figure for retention of commercial uses, will cost approximately $16,650,000. EPA developed this estimate using currently available unit costs for materials and services. This estimate does not include a figure for the groundwater component of the remedy, as that has been deferred by the 1996 ESD. Because of the reduction in leachate generation and contaminant concentrations that will be achieved through the synthetic cap, it is very likely that EPA would not require the construction of the ground water component of the remedy after the period of observation. By comparison, the cost of the remedy set forth in the 1992 ROD, using currently available unit costs for materials and services, would be approximately $18,600,000. This estimate includes figures for the ground water component and retention of commercial use at the Site. The approved modifications to the remedy, through this ESD, are as follows: 1 Appendix E of the FS estimated the costs for all components of the selected remedy to be approximately $9,544,000 for capital costs and $310,000 for annual operation and maintenance (O&M) over 30 years. In preparing this ESD, EPA found that, through an oversight, the ROD omitted costs for the ground water treatment and discharge systems. Appendix E estimated the combined capital costs for those systems at approximately $910,000, and the annual O&M costs at $64,400. Taking these additional costs into account results in a corrected 1992 ROD cost estimate of $14,309,500. ------- Cap profile: Eight inches of topsoil 24 inches of low-permeability clay Cost estimate for entire remedy: -in 1992: $14,309,500 -in 1998: $18,600,000 Cap profile: Six inches of topsoil 12 inches general soil fill (protective layer) Geotextile to protect the drainage layer Geonet drainage layer 40 mil LLDPE geomembrane 6-inch bedding layer for the geomembrane Cost estimate for entire remedy: $16,650,000 IV. SIGNIFICANCE OF THE CHANGE The significance of a change in the remedy determines how EPA must document and communicate that change to the public. EPA has determined in this case that the change is significant, but not fundamental. The landfill cap design in the final RD was modified in order to ensure the long-term effectiveness and performance of the remedy, and improve short-term effectiveness and implementability. The cost of the remedy changed as a result of the modifications, and EPA estimates the cost of the remedy to be $16,650,000. All other remedy components remain unchanged. The fundamental objectives of the remedy also remains the same: to contain contamination within the vertical boundaries of the landfill, prevent direct contact with waste materials, and prevent infiltration of precipitation from carrying contamination to ground water. The changes to the remedy will allow these objectives to be met more efficiently and effectively, from both a cost and technical perspective. V. SUPPORT AGENCY COMMENTS The Illinois Environmental Protection Agency (IEPA) supports the change. VL AFFIRMATION OF STATUTORY DETERMINATIONS The statutory determinations in the ROD are reaffirmed, in light of the changes made in this ESD. U.S. EPA has determined that the revised landfill cap profile, in conjunction with the other remedy components, is protective of human health and the environment, complies with applicable or relevant and appropriate requirements (ARARs), and meets the objectives of the remedy. William E. Muno, Director Superfund Division Date ------- AR. U.S. ENVIRONMENTAL PROTECTION AGENCY REMEDIAL ACTION ADMINISTRATIVE RECORD FOR TRI-COUNTY/ELGIN LANDFILLS SITE ELGIN, KANE COUNTY, ILLINOIS UPDATE #3 MARCH 26, 1998 NO. DATE 1 09/30/92 AUTHOR U.S. EPA RECIPIENT Public TITLE/DESCRIPTION PAGES Record of Decision for 136 Tri-County/Elgin Land- fills Site 2 02/02/94 U.S. EPA Respondents 3 08/00/95 4 03/00/96 5 04/00/96 6 06/25/96 7 07/00/96 U.S. EPA/ NRMRL U.S. EPA U.S. DOI/ Bureau of Reclamation and U.S. EPA/ NRMRL Montgomery Watson U.S. EPA U.S. EPA Public Bartz, L., Earth Tech Ballard, W. U.S. EPA Administrative Order 80 on Consent re: Predesign and Remedial Design for the Tri-County/ Elgin Landfills Site Project Summary: Effect 161 of Freeze-Thaw on the Hydraulic Conductivity of Barrier Materials: Laboratory and Field Evaluation (EPA/600/ SR-95/118) Report: Freeze-Thaw 128 Cycling and Cold Temp- erature Effects on Geomembrane Sheets and Seams (U.S. DOI Report: R-96-03) Remedial Design Work 118 Plan for the Tri-County/ Elgin Landfills Site Explanation of Signifi- 8 cant Differences for the Tri-County/Elgin Land- fills Site FAX Transmission 4 Forwarding 30% and 60% Remedial Design Final Cover Detail Drawings ------- HO. DATE 8 11/12/96 AUTHOR Ballard, W., U.S. EPA RECIPIENT Leibrock, M., Haste Manage- ment , Inc./ Midwest Tri-County/Elgin AR Update #3 Page 2 TITLE/DESCRIPTION PAGES Letter re: U.S. EPA's 2 Comments on WMI'S Responses to U.S. EPA 30% Design Comments for the Tri-County/Elgin Landfill Site 11/21/96 U.S. EPA File 60% Design Meeting Submittals 10 11/25/96 11 11/25/96 12 11/26/96 13 12/09/96 14 12/12/96 Benson, C.; University of Wisconsin/ Madison Moses, D. and D. Taylor; U.S. Army Corps of Engineers/ Omaha District Ballard, W., U.S. EPA Leibrock, M., Waste Manage- ment , Inc./ Midwest Leibrock, M., Waste Manage- ment , Inc. Ballard, W., U.S. EPA Ballard, W., U.S. EPA Leibrock, M., Waste Manage- ment, Inc./ Ballard, W., U.S. EPA Ballard, 'W. , U.S. EPA Memorandum re: Clay Barriers Used in Liners and Covers FAX Transmission Forwarding Attached Journal Article: Effects of Freezing on Hydraulic Conductivity of Compacted Clay (Kim, W., et al; Journal of Geotechnical Engineering/July 1992) Letter re: U.S. EPA's Disapproval of Design for the Tri-County/ Elgin Landfills Site Letter re: Notification of Dispute Resolution Letter re: Resubmittal of 60% Remedial Design w/Montgomery Watson's Attachments and Plan Set 97 15 12/16/96 Ballard, W., U.S. EPA Leibrock, M., Waste Manage- ment , Inc./ Midwest Letter re-. U.S. EPA's Disapproval of the Re-Submitted 60% Design for the Tri-County/ Elgin Landfills Site ------- NO. DATS 16 12/18/96 ADTHOR Moses, D., U.S. Army Corps of Engineers/ Omaha District RECIPIENT Ballard, W., U.S. EPA Tri-County/Klgin AR Update #3 Page 3 TITLB/DB3CRIPTION PAGHS FAX Transmission: 6 Supporting the Need for Frost Protection and Drainage Layer 17 12/23/96 18 12/31/96 Leibrock, M., Was te Manage- ment, Inc. Ballard, W., U.S. EPA Ballard, W.,. U.S. EPA Leibrock, M., Waste Manage- 19 01/01/97 Benson, C. ,- University of Wisconsin/ Madison Letter re: Re-Submittal of 60% Design Drawings w/Drawings and Calcula- tions Submitted Under Separate Cover Letter re: U.S. EPA's Written Response to Notice of Dispute w/ Attached (1) Excerpts from May 1991 U.S. EPA Seminar Publication: Design and Construction Of RCRA/CERCLA Final Covers/ (2) Excerpts from July 1989 U.S. EPA Technical Guidance Document: Final Covers on Hazardous Waste Land- fills and Surface Impoundments; (3) August 1991 U.S. EPA Project Summary: Factors Controlling Minimum Soil Liner Thickness; and (4) Excerpts from the March 12, 1992 Scope of Work, August 1993 Pre-Design Report, March 1994 RD/RA Work Plan and November 1994 30t Remedial Design for the Hunts Disposal Land- fill (WI) Site Report: A Review of Alternative Landfill Cover Demonstrations (Executive Summary and Conclusions) [Environ- mental Geotechnics Report No. 97-1) 13 23 ------- NO. DATE 20 01/07/97 21 01/08/97 22 01/09/97 AUTHOR Ballard, W., U.S. EPA U.S. EPA Moses, D., U.S. Army Corps of Engineers/ Omaha District RECIPIENT Leibrock, M., Waste Manage- ment , Inc./ Midwest File Leibrock, M., Waste Manage- ment , Inc. Tri-County/Blgin AR Update #3 Page 4 TITLE/DESCRIPTION PAGES Letter re: U.S. EPA's Clarification of State- ments Made in U.S. EPA's December 31, 1996 Written Response to Notice of Dispute Agenda and Handout Material from the January 8, 1997 Dispute Resolution Meeting re: the Tri-County/Elgin Landfills Site FAX Transmission Forwarding Examples of Synthetic Cap Profiles 10 23 01/15/97 24 01/27/97 25 01/30/97 26 02/04/97 Leibrock, M., Waste Manage- ment , Inc. Ballard, W., U.S. EPA • Leibrock, M., Waste Manage- ment , Inc./ Midwest Honegger, S., Lathrop & Gage/ M. Flowers, Waste Manage- ment , Inc. Ballard, W., U.S. EPA Leibrock, M., Waste Manage- ment , Inc./ Midwest Ballard, W., U.S. EPA Kallos, C., U.S. EPA Letter re: WMI's Response to U.S. EPA's December 31, 1996 Written Response to Notice of Dispute Letter re: U.S. EPA's Surreply to WMI's • January 15, 1997 Letter Letter re: WMI's Response to U.S. EPA's Proposal to Consider an Alternative Design Cover Letter re: Response to U.S. EPA's January 29, 1997 Letter Concerning the Administrative Record for Dispute for the Tri-County/Elgin Landfills Site 11 ------- HO. DATS 27 02/05/97 28 02/14/97 AUTHOR Kallos, C., U.S. EPA Mayka, J., U.S. EPA RECIPIENT M. Flowers, Waste Manage- ment , Inc./ S. Honegger, Lathrop & Gage Leibrock, M., Haste Manage- ment , Inc./ Midwest Tri-County/Elgin AR Update #3 Pag* 5 TITLE/DESCRIPTION PAGES Letter re: Disputed 5 Issues and the Alterna- tive Cap Design for the Tri-County/Elgin Land- fills Site Letter re: U.S. EPA's 4 Written Notification of Resolution of Dispute Concerning the Predesign and Remedial Design for the Tri-County/Elgin Landfills Site 29 09/00/97 30 09/00/97 31 09/23/97 32 09/30/97 Montgomery Watson U.S. EPA Montgomery Watson Leibrock, M., Waste Manage- ment , Inc. Ballard, W., U.S. EPA U.S. EPA Ballard, W., U.S. EPA Leibrock, M., Waste Manage- ment , Inc./ Midwest Final (100%) Remedial 100 Design Report: Volume 1 of 2 (Text, Tables and Figures) [Revised August 1997 Report] Final (100%) Remedial 440 Design Report: Volume 2 of 2 (Appendices A-K) [Revised August 1997 Report] Letter re: Modifications 7 to the Final Remedial Design for the Tri-County/ Elgin Landfills Site w/ Attached Revised Pages Letter re: U.S. EPA's 2 Approval with Modifica- tions and Exception for the Final Remedial Design for the Tri-County/Elgin Landfills Site 33 10/01/97 Ballard, W., U.S. EPA Leibrock, M., Waste Manage- ment , Inc./ Midwest Letter re: Revision to September 30, 1997 Remedial Design Approval Letter 34 01/15/98 Ballard, W., U.S. EPA Leibrock, M., Waste Manage- ment , Inc./ Midwest Letter re: Cost Esti- mates for the Remedial Action at the Tri-County/ Elgin Landfills Site w/ Attached Tables 12 ------- NO. DATS 35 02/16/98 36 03/24/98 AUTHOR Prattke, M., Waste Manage- ment and M. Miller, Browning Ferris Industries Ballard, W., U.S. EPA RECIPIENT Ballard, W., U.S. EPA File Tri-County/Klgin AR Update #3 Page 6 TITLB/DB8CRIPTIOH PAGRS Letter re: WM/BFI's 59 Responses to U.S. EPA's Review of Cost Estimates for the Tri-County/Elgin Landfills Site w/ Attachments Memorandum re: Cost 21 Estimates for Remedial Action at the Tri-County/ Elgin Landfills Site ------- U.S. ENVIRONMENTAL PROTECTION AGENCY REMEDIAL ACTION ADMINISTRATIVE RECORD FOR TRI-COUNTY/ELGIN LANDFILLS SITE ELGIN, KANE COUNTY, ILLINOIS UPDATE #4 APRIL 23, 1998 NO. DATE 1 02/00/97 AUTHOR Melchior, S. RECIPIENT TITLE/DESCRIPTION PAGES 12/00/97 Chamberlain, E., et al. U.S. Army Corps of Engineers Journal Article: In-Situ Studies on the Perform- ance of Landfill Caps (Compacted Soil Liners, Geomembranes, Geosyn- thetic Clay Liners, Capillary Barriers) [Proceedings of the International Containment Technology Conference, February 1997] Report: Frost Resistance of Cover and Liner Materials for Landfills and Hazardous Waste Sites (Special Report 97-29) 32 01/15/98 03/30/98 Muno, W., U.S. EPA Ballard, W., U.S. EPA Pingel, B., St. Charles Resident Potentially Responsible Parties Letter re: U.S. EPA's Response to Citizen's Concerns About Property Which is Part of the Tri-County/Elgin Landfills Site Cover Letter with Draft Explanation of Signifi- cant Differences and the Administrative Record Index for Update #3 for the Tri-County/Elgin Landfills Site Attached 13 04/14/98 Mayka, J. and W. Carney; U.S. EPA U.S. EPA/ Superfund RPMs Memorandum re: Findings and Recommendations of the Working Group Reviewing Landfill Cover Requirements and Decision Making by Region 5 Superfund Program 25 ------- NO. DATE 6 04/14/98 7 04/23/98 8 04/23/98 AUTHOR Miller, M., Browning- Ferris Industries of Illinois Ballard, W., U.S. EPA RECIPIENT Ballard, W., U.S. EPA File U.S. EPA Public Tri-County/Elgin AR Update #4 Pag* 2 TITLE/DESCRIPTION PAGES Letter from BFILL on the 5 Draft Explanation of Significant Differences for the Tri-County/Elgin Landfills Site Memorandum: U.S. EPA's 4 Response to Input on the Draft Explanation of Significant Differences for the Tri-County/Elgin Landfills Site Explanation of Signifi- 14 cant Differences for the Tri-County/Elgin Landfills Site ------- |