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RWQCB. New monitoring wells installed on site and the locations of nearby wells will be plotted on the new, detailed topographic map. Pacific Gas and Electric Company (PG&E) provides electrical power and natural gas. Electrical power is delivered through overhead lines, natural gas through underground pipelines. Wastewater is disposed on site to septic tanks and a leach field on the east side of the property, terminating in two sumps near the southeast corner. These features are shown on Figure 3 and in more detail in Section III illustrations in this work plan. There are currently no known underground or aboveground storage tanks (USTs or ASTs) on the site. Only one rectangular building was shown on the property in the USGS 1987 7.5-minute Stockton West quadrangle. From the 2012 aerial view site vicinity map (Figure 2), the 50,000- square-foot warehouse includes an annex on the northeast side, and a 1500-square-foot office building is located at the northeast corner of the property. The railroad spur on the west side of the property shown on the topographic quadrangle is evident in the latest aerial view. C. GEOLOGY/HYDROGEOLOGY 1. Regional Geology and Hydrogeology The following geological description is excerpted directly from the Eastern San Joaquin Groundwater Basin Groundwater Management Plan prepared by the San Joaquin County Department of Public Works(2004). San Joaquin County is situated within the Central Valley, a 400-mile long, 50 mile wide northwestward trending, asymmetrical structural trough. The Sierra Nevada Ranges, east of the Central Valley, is comprised of pre-Tertiary igneous and metamorphic rocks. The Coastal Ranges, to the west, is comprised of pre-Tertiary and Tertiary semi-consolidated to consolidated marine sedimentary rocks. The geologic formations within San Joaquin County vary in origination in geologic times ranging from Recent to Pre-Cretaceous. Six to 10 miles of sediment have been deposited within the Central Valley and include both marine and continental gravels,sands, silts and clays. During the middle Cretaceous(-100 million years ago), parts of the Central Valley were inundated by the Pacific Ocean resulting in deposition of marine deposits. Marine conditions persisted through the middle Tertiary period after which time sedimentation changed from marine to continental. The material source for the continental deposits are the Coastal Ranges and Sierra Nevada which are composed primarily of granite, related plutonic rocks, and metasedimentary and metavolcanic rocks from Late Jurassic to Ordovician age (Bertoldi, et al, 1991). The Central Valley has one natural surface water outlet,the Carquinez Strait located east of San Francisco Bay(USGS). Geologic formations within the Central Valley and San Joaquin County are generally grouped as either east-side or west-side formations based on their location relative to the San Joaquin River, and the source of the sedimentary material of which they are composed. Generally, Eastside formation material originates in the Sierra Nevada and Westside formation material originates in the Coastal Ranges. The most important fresh