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• A 12 -inch LCRS pipe and gravel layer; • An 8-ounce/square yard separator geotextile; and • A 12 -inch thick protective cover soil layer. The slope liner system consists of: • Prepared subgrade; • A 24 -inch thick low permeability soil (maximum permeability of 1 x 10-7 cm/sec) or GCL; • A 60 mil HDPE liner (single sided textured, textured side down); • A geocomposite drainage net (geonet); and • A 12 -inch thick protective cover soil layer. Recognizing the likelihood of leachate accumulation in the leachate sumps a double composite liner system is proposed for these areas. In fact, in light of the critical nature of the sump design, the leachate extraction system installed in the sumps will also incorporate a conservative design, with multiple sump locations and dual extraction ports, so that the system is 100% redundant. 3.2 Leachate Volume As summarized in the site JTD, modeling of potential leachate generation within the landfill expansion was completed using the United States Army Corps of Engineers HELP3 (Hydrologic Evaluation of Landfill Performance, Version 3.06). The HELP simulations conservatively ignored placement of intermediate cover soils, and assumed that a one -foot thick LCRS drainage layer would be placed at a 2% gradient with LCRS collection pipe placed on 200 -foot centers. Calculated peak daily leachate generation was 4,073 gallons/acre or approximately 0.0045 cubic feet per second (cfs). The peak daily head on the liner system was calculated to be approximately 1.6 inches. Since the largest tributary area within the planned new liner system is approximately 23 acres, the peak daily flow through leachate collector pipes to the leachate sumps is only about 0.10 cfs. Since the maximum capacity of the proposed 6 -inch diameter mainline LCRS pipe placed at a two percent slope is 1.03 cfs, a factor of safety of over 10 is calculated. 3.3 Leachate Chemistry The Austin Road Landfill has no LCRS, so no comment can be made regarding leachate chemistry beyond the expectation that it should improve over time. In contrast, the Forward Landfill is a mature landfill with an active LCRS and relatively benign leachate chemistry has been reported (Appendix A). This benign leachate chemistry is likely to be the result of Forward's history of operation which has included waste reduction, waste stream restrictions and a rigorous load check program. Given the fact that these clearly successful programs have been in place for a number of years at Forward and the fact that the future combined facility will be operated in the same fashion, this leachate chemistry -6- C:U000-049\Fo`wnrd Composite Liner V3.doc\09119102 Geologic Associates