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' Historical Background • DEN'S AUTO REPAIR ' 308 South El Dorado Street, Stockton, California ' The site is located at 308 South El Dorado Street in Stockton, California in a commercial/industnal area of south Stockton at the southeast corner of the intersection of South El Dorado Street and East Lafayette Street A single structure is located on the property and is currently occupied by an auto repair facility (Figure 2) ' REGIONAL GEOLOGIC/HYDROGEOLOGIC SETTING ' The site is located in an area of low topographic relief According to Geologic Map of California, published in 1966 by the California Department of Conservation Division of Mines and Geology, the site area is shown to be within the Great Valley Geomorphic Province of California a large, elongate,northwest-trending structural trough This province is subdivided into two major divisions, designated the Sacramento and San Joaquin Valleys,which have been filled to the present elevation with thick sequences of sediment These sediments range in age from Jurassic to Recent, and create ' a nearly flat-lying alluvial plain that extends from the Tehachapi Mountains in the south to the Klammath Mountains in the north The western and eastern boundaries of this province are comprised of the California Coast Range and the Sierra Nevada, respectively Based on data collected in February 2002, the average depth to ground water at the site is approximately 25 feet below surface grade (bsg) The ground water in February 2002 was inferred to be flowing toward the north-northeast under a gradient of 0 008 ft/ft UNDERGROUND STORAGE TANK REMOVAL On 25 and 26 May 1995, four underground storage tanks (USTs) and their associated piping were removed from the site by Valley Environmental Solutions (VES) of Stockton, California One 8,000-gallon leaded gasoline UST,one 7,000-gallon unleaded gasoline UST, and one 5,000-gallon unleaded gasoline UST were removed from a large excavation north of the repair facility building, a single 500-gallon waste oil UST was removed from an excavation located on the south side of the building(Figure 2) Upon removal of the USTs, soil samples were collected from beneath each UST, the piping areas, and the excavated soil Total petroleum hydrocarbons quantified as gasoline(TPH-g)was detected in the soil samples at concentrations up to 9,100 part per million(ppm)in sample TK3-N,collected from the northern boundary of the property I Advanced GeoEnvironmental,inc �,