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' S E C 0 R ' Request for No Further Action Chevron Station 9-2396 December 16,2004 Page 2 ' numerous folds, flanked by normal and reverse faults, throughout the Central Valley Depositional setting for the Valley has ranged from predominantly marine to fluvial In origin ' The Cretaceous ushered in seas that lasted until the Pleistocene Pleistocene through to Present day has seen continual uplift of the Coast Range, causing the Inland sea to withdraw Following evacuation of the marine environment, freshwater swamps and lakes ' formed and those were eventually replaced by the current system of rivers, deltas, and alluvial fans 2 2 Stratigraphy The Valley fill is a broad clastic wedge that thickens to the west and south' (Figure 2) Ordovician to Jurassic units consist of granite, granodionte, dlorlte, and metasedimentary shale and sandstone This Includes the Sierra Nevada batholith and the crystalline basement underlying the valley fill Cretaceous and Tertiary strata Include grains derived from marine and continental sources in laterally continuous, thick packages of rhythmically Interbedded mudstone, siltstone, conglomerate, sandstone, and limestone Quaternary to Recent units are solely continental in origin, consisting of lake deposits and alluvium derived from the Sierra Nevada and Coast Ranges Valley fill is comprised of nonmarine well-sorted sands of the Sierra Nevada that interfinger with the nonmarine poorly sorted clays and silts of the Coast Ranges 1 2 3 Hydrogeology The majority of the groundwater reservoir consists of Pliocene and Pleistocene continental deposits, Pliocene marine deposits, and Quaternary alluvium The groundwater regime consists of a single heterogeneous body of interbedded fluvial and lacustrine deposits with 1 discrete lenses of gravel, sand, silt, and clay that act mainly as a single semi-confined hydrostratigraphic unit These vertically and horizontally scattered lenses provide Increasing confinement with depth Groundwater in the San Joaquin Valley consists of good ' quality water that is capped by water of poorer quality and underlain by a body of saline water Overall, groundwater 1s rich in bicarbonates throughout the Central Valley4 However, in the San Joaquin Valley, sulfate predominates on the southwest side of the ' Valley and chloride predominates on the northwest side of the Valley In the early part of the 20th Century, the groundwater flow system of the Central Valley was ' In a state of dynamic equilibriums Recharge to the aquifer occurred via rain and snowmelt in the mountains at the Valley margins, moved downward and laterally Into the aquifer, and then moved upward to discharge at rivers in the valley axis Therefore, with the exception ' of the extreme southern portion of the San Joaquin Valley, which Is a closed groundwater basin, groundwater flow In the Central Valley ultimately discharges at the San Joaquin- Sacramento River Delta With the construction of hundreds of thousands of wells over 4 Bertoldi G 1,Johnston, R H and Evenson, K D, 1991, Groundwater m the Central Valley California—A Summary Report Professional Paper 1401-A United States Geological Survey, Regional Aquifer System Analysis Program 5 Bertoldi, G L, 1991, Overview of Phase I Regional Aquifer System Analysis, Central Valley, California Aquifers of the Far ' West,American Water Resources Association, p 15-26 ' 1 IChevron1923961Reports\FINAL_NFAR_REPORT doc