CORRESPONDENCE_2003-2004 - Laserfiche WebLink

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The design effort associated with this extension will include evaluation of. A. Slope,bench intervals, and any soils placed for cover enhancement. B. Performance of synthetic liner materials when subject to refuse surcharge and resulting differential settlements, including consideration of: • Overfill of side slope liner to final grade • Depths of existing refuse under side slope liner, and settlement that may be expected. C. Slope stability,using: • Dr. Abrahamson's Seismic Criteria, 04/13/02, in Appendix F,ROWD. • Slope stability criteria and methodologies in Appendix F,ROWD. • Existing refuse fill,proposed liner/cover profiles, and refuse overfills. Preventing the natural venting of LFG by installing an impermeable HDPE barrier poses the risk of increasing LFG pressure beneath the HDPE, causing the membrane to lift off the surface("balloon"). While the County recognizes the importance of providing a barrier and drain layer between the existing refuse on Module "I" and the refuse placement made possible by the installation of Module 1,perhaps this barrier need not include an impermeable membrane. 2. Final Closure of Crest of Module"I" The flat areas (slope less than 6:1) of Module"I"will receive final closure cap. The County intends to evaluate the use of an evapo-transporative(ET) cover for closure; however, the investigation of on-site soils for use in a prescriptive closure cap will be investigated concurrently with investigation of an ET cover unless it is clear that an ET cover will be successful. It is understood at this time that the success of an ET cover can be demonstrated to the satisfaction of RWQCB staff by computer modeling. The investigation of ET cover will include: A. Meeting with RWQCB staff to clarify procedures and acceptance criteria for ET cover. Computer modeling will include the use of UNST-H Version 3 (or higher)in modeling. B. Investigation of on-site borrow sources for the evapor-transporative(ET) cover, in particular, the soil in the area of Module 2 and the stockpile placed during the excavation of Module 1. This investigation will include: • Historical Meteorological Data, including daily data for critical(wetter than normal) years. • ASTM D422—Grain Size • ASTM D4318—Atterberg Limits to make a preliminary determination of the suitability of select on-site sources Foothill Sanitary Landfill Site Improvement 2 Department of Public WorkstSolid Waste Revised March 12,2004 County of San Joaquin