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1 29 March 2004 i AGE-NC Project No. 97-0327 Page 2of12 ' The site presently consists of two 12,000-gallon gasoline/diesel USTs, one mini-market building, one carwash building and fuel dispensing islands under a canopied structure. The site is currently connected to the City of Stockton sanitary sewer system,which is located along ' the easement in the west section of the property along Oro Avenue. It is AGE's understanding that no septic tank has been utilized on the property since 1966. 2.2. REGIONAL GEOLOGIC/HYDROGEOLOGIC SETTING The property is situated within the Great Valley Geomorphic Province of California, a large, elongate, north-northwest trending, asymmetric structural trough. The Great Valley Province has t been filled with thick sequences of sediment ranging in age from Jurassic to Recent,creating a nearly flat-lying alluvial plain, extending from the Tehachapi Mountains 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. Rocks composing the basement complex of the province have not been completely defined but are believed to be metamorphic and igneous in origin. The northern and southern portions of the Great Valley Province have been ' . designated the Sacramento and San Joaquin Valleys, respectively. Based on the 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 Jackson-Hallenbeck-Stockton (JHS) association. The JHS soils are located within basins, and ' generally consist of moderate to poorly drained fine textured,soils. The soils are generally derived from both marine and non-marine sediment, and are generally formed in alluvium derived from mixed rock sources. ' The Modesto,Riverbank,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 2,500 feet north of the site. ' Based on regional information from Lines Of Equal Depth To Ground Water and Lines of Equal Elevation Of Ground Water, published by the San Joaquin County Flood Control and Water Conservation District between 1971 and present, the depth to ground water at the:property has. generally fluctuated between 50 and 80 feet bsg;regional ground water flow direction has generally been oriented towards the northeast.