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The internal stability of the interface and side slope lining system was also considered. The GCL, HDPE geomembrane, and GDN will be placed on a maximum 2:1 slope. A protective operations soil layer will be placed against the slope as WMU FU-03 filling operations progress (i.e., the operations layer will not be "hung"on the side slope). To minimize interface liner loads, it was assumed that the operations layer would be placed up to a maximum height of 10 feet above the refuse fill level using a wheel loader2. Minimal equipment loads will, therefore, be applied to the slope. To maintain the stability of the slope lining system, the anchor trench is required only to support its own weight. The anchor trench for the side slope lining system was therefore designed to resist self-weight (dead) loads only. 3.1 Seismic Hazard Analysis Because the Forward Landfill is located in a seismically active area, stability analyses for final grade conditions must consider seismically induced forces on the refuse fill and slope. The Title 27 regulations require that landfills that accept designated waste be designed to withstand the maximum credible earthquake(MCE). The Forward Landfill, which is located in the Central Valley of California, has a history of low seismic activity. It is not located in an area of rapid geologic change. The surface projection of the Tracy- Stockton Fault Zone passes through the City of Stockton, 6.5 miles northwest of the site. This fault zone is the closest known to the landfill site and does not show evidence of Holocene displacement.No special containment structures are therefore needed for the landfill to preclude failure due to such events. A seismic hazard analysis (GeoSyntec, 2001)was performed for the Forward Landfill on the basis of information provided in recent relevant studies of known active and potentially active faults and earthquake zones in California. Significant active and potentially active faults and seismic source zones within 100 miles(160 km)of the project site are listed in the analysis. Also listed are the strong ground shaking duration (DS) and Peak Horizontal Ground Acceleration (PHGA) estimates for the MPE and MCE. Both estimates are for a hypothetical bedrock outcrop at the geometric center of the Forward landfill site. The seismic hazard analysis indicates that the M,,, 6.4 MPE event on the Great Valley blind thrust system at a distance of 21mi (34 km) induces the highest bedrock MPE PHGA at the site. The analysis further indicates that the M,,, 6.7 MCE event on the Great Valley blind thrust system at a distance of 21 miles(34 km) induces the highest bedrock MCE PHGA at the site. The MPE and MCE on the San Andreas fault system are characterized by the same Mµ,7.9 event at a distance of 70 miles (112 km). This large-magnitude distant event induces the longest duration of strong ground shaking at the site. Given a relatively small difference in the estimated bedrock PHGA and the relatively large difference in estimated DS, the M,y 7.9 event on the San Andreas fault system may be the most damaging earthquake for the Forward Landfill. Therefore, the M„.7.9 event on the San Andreas fault system should be considered for evaluation of both MPE and MCE design ground motions at the Forward Landfill along with the appropriate M,,,event on the Great Valley blind thrust system. 2 Based on information provided by Butch 5tefani(Site Manager at the Forward,Inc.Landfill),the protective operations layer will be placed on the WMU FU-03 51ope using a Caterpillar 966F Series Wheel Loader with a 4.5 cy bucket. FORWARD LANDFILL WMU F-03 AND F-WEST DESIGN REPORT 3-2