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3.2 Geologic Setting and Hydrogeology The LNC site is located in the Great Valley Province in the northern San Joaquin Valley of California, a broad structural trough located between the Coast Ranges on the west and the Sierra Nevada on the east(Figures 1 and 2). The Site is located on the low alluvial fan and plain deposits of the Mokelumne River and other streams that drain the uplands and foothills of the Sierra Nevada to the east. The Site and vicinity are underlain by at least 2,000 feet of Miocene to Holocene age unconsolidated sediments. These sediments include approximately 100 feet of Holocene Younger Alluvium and Pleistocene Older Alluvium(consisting of an interbedded mixture of unconsolidated gravel, sand, silt, and clay of Sierran origin), approximately 100 feet of the Pleistocene-age Turlock Lake Formation (consisting of a heterogeneous mixture of poorly consolidated,poorly sorted gravel, sand, silt, and clay of Sierran origin), and approximately 200 feet of the Pliocene-age Laguna Formation (consisting of poorly consolidated bedded sands, silts and clays of Sierran origin). Beneath the Laguna Formation are over 1,000 feet of the Pliocene- age Mehrten Formation(consisting of poor to moderately consolidated beds of black sands and brown clays of volcanic origin) and the Valley Springs Formation(consisting of poor to moderately consolidated beds of light colored sand, ash, and clays of volcanic origin) (Page, 1986). 3.2.1 Regional Hydrogeology Groundwater within the City of Lodi area occurs primarily within a leaky-aquifer system of Younger and Older Quaternary Alluvium and within the underlying Turlock Lake, and the Laguna Formations (Piper and others, 1931; Page, 1986). Gravel and sand intervals in the Quaternary alluvium yield significant quantities of high quality groundwater to wells completed in these intervals. The Turlock Formation also yields significant quantities of groundwater if the wells are completed within buried stream channel lenses of coarse-grained sediments. Sand intervals located within the Laguna and Mehrten Formations may also yield significant M ain\D:AEnvironmentaI\LN CV\10152007.wpd 9