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List of Attachments Attachment 1 Seismic Characterization 1. INTRODUCTION The Corral Hollow Landfill (Landfill) is a closed Class III landfill located in Northern California on the eastern edge of the Central Valley (37.6691 N, -121.4590 V). The Landfill is located approximately 5 miles southwest of Tracy, California on the eastern margin of the Diablo Range Mountains. This report presents the results of a stability analysis carried out to verify the stability of the soil and geosynthetic cover that has been designed to cover waste that is currently residing outside the permitted waste footprint. 1.1 Project Understanding San Joaquin County has enlisted the services of Shaw Environmental, Inc. to design a final landfill cap extension to cover waste that was discovered outside the currently closed and capped landfill. The existing landfill cap consists of a soil foundation layer, a one foot low permeability soil layer, and an approximately one foot vegetative soil layer. Expansion of the final cover to incorporate the waste currently residing outside the existing closure area will utilize a soil and geosynthetic lined cover. The cap extension design utilizes an impermeable geomembrane overlain by a geocomposite drainage net, an earthfill layer, and a vegetation layer. The maximum slope for the geosynthetic lined portion of the cover will be 3:1 ( :V), with the maximum height of the 3:1 slopes being approximately eight feet. The maximum height of the 3:1 slopes will be on the north side of the landfill access road between approximate stations 5+50 and 10+50, reference Figure 1. It is anticipated that the 3:1 geosynthetic lined slopes will pose the most significant risk for soil veneer failure and will therefore be the focus of this stability report. 2. DESIGN CRITERIA AND METHODOLOGY ' 2.1 Design Criteria Stability analyses have been performed for both static and seismic conditions. Because the Landfill is a Class III facility, the seismic slope stability has been performed using ground motions corresponding to the maximum probable earthquake (MPE) as required by Title 27 of the California Code of Regulations (Title 27 CCR). Shaw Environmental, Inc. (Shaw) developed the MPE and corresponding ground motions based on a site- specific seismic characterization, reference Attachment 1. ' 2.1.1 Static Design Criteria Title 27 of CCR does not specify a minimum factor of safety requirement for slope ' stability under static conditions. However, traditional geotechnical practice typically requires a static factor of safety of 1.5 for the stability of permanent slopes. Accordingly, Slope Stability Analysis Corral Hollow Landfill—Rev 2 5/20/2012 2