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' 11 June 2001 AGE-NC Project No. 96-0232 ' Page 4 of 11 ' 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 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 Deep Water Channel, located approximately 3,000 feet west of the property. 2.5. GROUND WATER DEPTH AND FLOW DIRECTION The estimated depth to ground water at the site is approximately 40 feet below surface grade(bsg) based on information from Lines of Equal Depth of Water Wells Spring 1999, published by the San Joaquin County Flood Control District and Water Conservation District(SJCFCD).Based on review of a regional ground water elevation map published by the SJCFCD, the prevailing ground water ' flow direction in central Stockton is generally toward the northeast, although flow directions may be both locally and seasonably variable. Based on data collected during the February 2001 ground water monitoring event, first observed ground water was approximately 38 feet bsg; the ground water flow direction was towards the northeast at a calculated gradient of 0.005. Ground water flow direction at the site was inferred towards the northeast from thirteen consecutive quarterly ground water monitoring events between September 1997 and February 2001. Advanced GeoEnvironmental,Inc. 1