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SUBSURFACE ,' ,i The geologic conditions of the site were investigated by Kleinfelder in 1985 during development of the landfill. The results of the investigations are summarized below. The landfill is located near the northeastern edge of the San Joaquin Valley, part of the Great Valley geomorphic province. The Great Valley is a structural trough between the Sierra Nevada and Coast Ranges. The valley is a deep, asymmetric structural trough filled with sediments derived from adjacent mountain ranges. The landfill is located in an area underlain by volcanic flows and sediments of Miocene and Pliocene age. These deposits have been eroded since their deposition and weathered to form the present day low, rolling hill topography. 2.2 Site Geology The northern portion of the landfill property is underlain by consolidated alluvial deposits of the Laguna formation. The Laguna Formation consists of consolidated gravels, sandstone, and siltstone. The southern portion, including proposed Module 1, is underlain by the Mehrten Formation (slightly older than the Laguna Formation). The Mehrten Formation in the vicinity of proposed Module 1 generally consists of cemented silt and clay with layers of fine sandstone that are several feet thick. The Laguna and Mehrten Formations are overlain by residual soil or recent alluvial deposits except where exposed by landfilling activities. 2.3 Groundwater Conditions The oldest significant fresh water bearing formation in the vicinity of the site is generally considered to be the Mehrten Formation. Many of the deeper sands of the Mehrten Formation are relatively permeable and furnish water of good quality to deep wells. Groundwater is primarily recharged by percolation from the surface that originates in the foothills of the adjacent Sierra Nevada. ®\\SACRFPI\COMMON\sacDP\2002\PRJ\PJ8\83\835608.2bz.doc EMCs®w® ' Inc. Rev. 0, 07/31/02 2-1