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\n0, Site Background Information ARROYO'S SMOG SHOP 3012 East Waterloo Road, Stockton, California The subject property, located at 3012 East Waterloo Road in an unincorporated portion San Joaquin County, California, is situated in an area of mixed commercial/residential and light industrial use. Historical site usage research performed by AGE has indicated that the property was utilized as a gasoline service station for approximately 40 years. REGIONAL GEOLOGIC/HYDROGEOLOGIC SETTING The site is situated within the southern portion of the Great Valley Geomorphic Province of California, a large, elongate, northwest trending, asymmetric structural trough. The northern and southern portions of the Province have been designated the Sacramento and San Joaquin Valleys, respectively. The Province is bordered by the Coast Ranges to the west, the Klamath Mountains and Cascade Range to the north, and the Sierra Nevada to the east. The Great Valley has been filled with sediments derived from both marine and continental sources.Thickness of the sedimentary fill ranges from thin veneers along the valley edges to more than 20,000 feet in the south central portion of the valley. The sedimentary formations range in age from Jurassic to Recent, with the older deposits being primarily marine in origin and the younger deposits being primarily continental. Continental-derived sediments were primarily deposited in lacustrine, fluvial, and alluvial environments with sediment sources being the mountain ranges surrounding the valley(Olmsted and Davis, 1961). The site itself is located on unconsolidated and semi-consolidated alluvium, lake, playa and terrace deposits of Quaternary age (California Division of Mines and Geology, 1977). Rocks composing the basement complex of the Province have not been completely defined but are believed to be metamorphic and igneous in origin. The Modesto, Riverbank and Turlock Lake Formations and overlying Recent alluvium are the principal sources of domestic groundwater in the 13,500-square mile San Joaquin Valley Groundwater Basin (Basin 5-22). The nearest surface water feature to the site is the Stockton Diverting Canal, located approximately 1,600 feet northeast of the site. Based upon groundwater maps prepared by the San Joaquin County Flood Control and Water Conservation District and well information obtained from nearby sites,groundwaterflow direction is variable nearthe site. Depth to water is currently estimated to occur between 55 and 65 feet below surface grade (bsg). However, this may vary greatly due to local recharge and discharge patterns.