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i i . Site Background Information ' K& S GAS & GROCERY 701 East Charter Way, Stockton, California ' The site is located in arelatively flat,commercial area of Stockton,California on the northeast corner of Charter Way and Stanislaus Street(Figure 1) The site is presently utilized as a fueling facility and ' convenience store One 20,000-gallon fuel underground storage tank(UST) is presently located on the western portion of the property ' REGIONAL GEOLOGIC SETTING ' According to Geologic Map of California, published in 1966 by the California Department of Conservation Division of Mines and Geology, the site area is within the Great Valley Geomorphic Province(GVGP)of California a large,elongate,northwest-trending structural trough The GVGP Iis subdivided into two mayor divisions, designated the Sacramento and San Joaquin Valleys,which have been filled to the present elevation with thick sequences of sediment ranging in age from Jurassic to Recent, creating a nearly flat-lying alluvial plain that extends from the Tehachapi IMountains in the south to the Klamath Mountains in the north The western and eastern boundaries of this province are comprised of the California Coast Range and the Sierra Nevada, respectively I. Based on General Soil Map from the San Joaquin County Soil Survey, published by the United States Department of Agriculture Soil Conservation Service in 1992, the site area is within the Jacktone-Ho I lenbeck-Stockton (JHS) association JHS soils are located on basin rims and within basins,and generally consist of somewhat poorly-drained and moderately well-drained,fine-textured soils that are moderately deep and deep to a cemented hardpan The JHS soils generally formed in ' alluvium derived from mixed rock sources ' UNDERGROUND STORAGE TANK REMOVAL On 13 February 1998, two 12,000-gallon USTs and one 1,000-gallon UST were removed from the ' site Petroleum hydrocarbons were detected in soil samples collected from below the two 12,000-gallon USTs at concentrations as high as 1,400 milligrams per kilogram(mg/kg) Petroleum hydrocarbons were not detected beneath the 1,000-gallon UST I PREVIOUS SUBSURFACE INVESTIGATIONS On 19 June 1997,four soil probe borings were advanced at the site near the two 12,000-gallon USTs Three borings were advanced to a vertical depth of 20 feet below surface grade (bsg), due to the presence of hydrocarbon odor, one boring (B2) was advanced to a vertical depth of 45 feet bsg TPH-g was detected at depths of 30 feet and 40 feet bsg at concentrations of 460 mg/kg and 1,000 mg/kg, respectively, beneath the south ends of the USTs Petroleum hydrocarbons were not I Advanced GeoEnvironmental,Inc