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BACKGROUND INFORMATION • Proposed EL DORADO APARTMENTS 2424 & 2450 South El Dorado Street, Stockton, California 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 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 I • 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 Old River,approximately 2 5 miles west of the property I PREVIOUS SITE ASSESSMENT Previous site assessments on the property include • February 2002 - A geotechnical investigation was conducted at the site by Raney Geotechnical Inc (RGI) During the course of the investigation, soil samples collected from Itwo borings (B4 and B5) were noted as having a"gasoline odor" • May 2002 - One soil boring (B-5)was advanced near the former UST area by Construction Testing & Engineering, Inc (CTE) to determine the nature and extent of soil possibly impacted by petroleum hydrocarbons Soil samples collected from soil boring B-5 contained concentrations of total petroleum hydrocarbons quantified as gasoline (TPH-g), diesel I (TPH-d)and/or motor oil(TPH-mo) The highest detected concentrations were found in soil samples collected at depths of 10 and 15 feet below surface grade (bsg), respectively, • however,additional laboratory analysis of the 15-foot sample from boring B-5 did not detect Ivolatile organic compounds (including benzene, toluene, ethylbenzene and total xylenes I