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12 October 1999 • AGE-NC Project No 98-0497 Page 2 of 7 2 2 UNDERGROUND STORAGE TANK REMOVAL On 29 September 1998, two 12,000-gallon diesel USTs (Tank No 1 and Tank No 2), two fuel ' dispensers and all associated product piping were removed from the site Laboratory analysis of soil samples collected beneath the former UST areas detected total petroleum hydrocarbons quantified as diesel (TPH-d)at concentrations up to 5,100 mg/kg (milligrams per kilogram) Analytical results of soil samples collected during tank removal activities are summarized in Table 1 23 REGIONAL GEOLOGIC 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,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 in 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 sources 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 Mormon Slough, approximately 1,000 feet north of the property 2 4 GROUND WATER DEPTH AND FLOW DIRECTION 10Based on review of the Lines of Equal Depth to Groundwater, Fall 1997 map published by the San Joaquin County Flood Control District and Water Conservation District(FCD&WCD),the estimated ' depth to ground water at the site is between 65 and 70 feet below surface grade (bsg) Review of the AdvancedGeoEniron mental,Inc