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N 09 April 2002 AGE-NC Project No. 97-0301 IJ Page 4 of 14 the northeast, east and southeast of the former UST area. i -� 2.4. REGIONAL GEOLOGIC SETTING According to a 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 is subdivided into two major divisions designated the Sacramento and San Joaquin Valleys, which f . have been filled to the present elevation with thick sequences of sediment ranging in age from -J Jurassic to present day, 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. t. _ Based on a 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 described as being 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 JHS soils generally formed from mixed rock sources. 2.5 . GROUND WATER DEPTH AND GRADIENT The estimated depth to ground water at the site is approximately 30 feet bsg based on information from Lines ofEqual Depth of Water Wells Spring 1999, published by the San Joaquin CountyFlood Control District and Water Conservation District (SJCFCD). Based on review of a regional ground water elevation map also published by the SJCFCD, the prevailing ground water flow direction in south Stockton is generally toward the northeast, although flow directions may be both locally and seasonably variable. =i Based on ground water monitoring data collected at the site on 20 December 2001 , depth to ground _ water was recorded at approximately 30 feet bsg and ground water flow direction was inferred to be i toward the northeast at a gradient of 0.001 ft/ft. i_ 3.0. SCOPE OF WORK AGE proposes to drill and install nine (9) wells screened through Vadose Zone (located between surface grade and 30 feet bsg) and/or the First Water Zone (located between 30 and 55 feet bsg): one 6-inch diameter ground water extraction well (EW4 ) will be screened between 25 feet and 55 feet LAdvanced GeoEnvironmental, Inc.