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Appendix B - Site Background Information Former FISCO WAREHOUSE (Howard Lenz Property) 1648 Shaw Road, Stockton, California The site is located in a commercial area of low topographic relief in east Stockton, California, at an approximate elevation of 25 feet above/Wean sea level (MSL). The site is bounded on the north and east by the Stockton Diverting Canal, on the west by State Highway 99, and on the south by Shaw Road. Golden West Irrigation, an agricultural irrigation supply and distributing facility, presently occupies the property. REGIONAL GEOLOGIC/HYDROGEOLOGIC SETTING The property is situated within the Great Valley Geomorphic Province of California, a large, elongate, northwest-trending, asymmetric structural trough. The Great Valley Province has been filled with thick sequences of sediment ranging in age from Jurassic to Recent,creating 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. Rocks composing the basement complex of the province have not been completely defined but are believed to be of metamorphic and igneous origins. The northern and southern portions of the Great Valley Province have been designated the Sacramento and San Joaquin Valleys, respectively. The Modesto, Riverbank, and Turlock Lake Formations and overlying Recent alluvium are the principal source of domestic ground water in the 13,500-square-mile San Joaquin Valley Ground Water Basin (Basin 5-22). This basin is drained primarily by the San Joaquin River. The nearest surface water feature in the vicinity of the property is the Stockton Diverting Canal, located approximately 300 feet north of the site. The canal could be the cause of the significant fluctuation in ground water flow direction and elevation at the site. UNDERGROUND STORAGE TANK REMOVAL Two 550-gallon underground storage tanks(USTs)were removed from the site on 03 October 1986 by Stockton Service Station Equipment Company. According to correspondence from the San Joaquin County-Environmental Health Department(EHD),both USTs were reportedlyused to store gasoline.Upon removal of the USTs,one soil sample was collected from the floor of the excavation. The sample was analyzed by California Water Labs, Inc., a state-certified analytical laboratory, for total petroleum hydrocarbons quantified as diesel (TPH-d),benzene, toluene, and xylenes. TPH-d and xylenes were detected in the soil sample at concentrations of 3,000 milligrams per kilogram(mg/kg)and 0.188 mg/kg,respectively.Benzene and toluene were not detected above the analytical method reporting limit of 0.010 mg/kg.Based upon results of the soil sample analysis,the EHD required assessment of the lateral and vertical extents of hydrocarbon-impacted soil and/or Advanced GcoEnvironmental,Inc