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i 12 July 2001 AGE-NC Project No 98-0432 Page 4 of 10 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 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 Delhi- Ventas-Tinnin(DVT) association The DVT soils are located within dunes, alluvial fans and stream terraces along the Stamslaus River, and generally consist of well drained coarse textured soils The soils are generally derived from both marine and non-marine sediment, and are generally formed in alluvium derived from granitic and mixed rock sources 2 4 GROUND WATER DEPTH AND GRADIENT The estimated depth to ground water at the site is between 15 and 20 feet below surface grade (bsg) based on information from Lines of Equal Depth of Water Wells Spring 1998, 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 Manteca is generally toward the north, although flow directions may be both locally and seasonably variable Ground water is considered to be of beneficial use and is used for domestic, industrial and commercial purposes Depth to ground water was measured at approximately 16 feet bsg during the May ground water extraction pilot test, during the last monitoring event ground water flow direction was inferred towards the northwest at a gradient of 0 003 3.0. SCOPE OF WORK Based on ground water sampling events and data collected during the site assessment investigations, • fuel component-impacted ground water appears to have migrated at least 100 feet north of the gasoline USTs formerly located on the site and vertically to depths of at least 50 feet bsg Advanced GeoEnvfronmental,ine