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(GCL) or geomembrane materials and geotextile materials. The analyses <br />considered a variety of material interfaces that may exist in any planned cover <br />configuration. Based on the results of the analyses, a suite of acceptable shear <br />strengths for geosynthetic liner material interfaces was identified. While the GCL <br />may be used in place of a compacted clay layer, its internal shear strength when <br />hydrated is relatively low, and an additional 40 -mil HDPE geomembrane layer <br />could be required if a GCL is employed in the cover design. A VFPE <br />geomembrane is proposed for the barrier layer of the Forward Landfill final <br />cover. The seismic stability analyses of the proposed refuse configuration <br />indicate that seismic displacements under'Maximum Credible Earthquake (MCE) <br />loads will be negligible. <br />The slope stability analyses also assessed the integrity of the final cover system <br />under both static and seismic loads. The analyses indicate that the interface <br />between the geomembrane and the overlying vegetative soil layer will be the <br />critical surface, but that a factor.ot.safety,of .:1-5,can..be.achieved sa long as,a <br />drainage layer is placed between the geomembrane and the overlying soils. The <br />seismic stability analyses also indicate that the earth -induced displacement of the <br />landfill cover will be negligiblQ under MCE loads. <br />3.6.1 DRAINAGE CONTROL SYSTEM DESIGN <br />The primary function of the Forward Landfill drainage control system is to collect <br />and convey storm water in a controlled manner to minimize erosion and <br />infiltration of storm water into the refuse prism. The following sections describe <br />the site hydrology and existing and proposed drainage control features. <br />3.6.1.1 HYDROLOGY <br />A hydrology study for the proposed conditions at the site was conducted in <br />accordance with 27 CCR, Section 20365. The objective of the hydrology study <br />was to calculate storm water run-off for sizing and location information for the <br />site's storm drain facilities at closure. <br />The Rational Method hydrology utilizing guidelines set forth in the San Joaquin <br />County hydrology manual was used to calculate peak discharge rates for a 24 - <br />Forward Landfill PCPCMP 3-8 <br />L:\Allied\2000.193\Reports\FinaIPCPCMP:FL-sec3: 8/20/01 BRYAN A. STIRRAT S. ASSOCIATES <br />