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t ' 22 June 2001 AGE-NC Prod ect No 97-0333 Page 5 of 10 i2 4 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 westem 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 Stanislaus 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 5 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 3 Depth to ground water was measured at approximately 16 feet bsg during a 31 January 2001 ground water monitoring event at the site, ground water flow direction was inferred towards the north at a gradient of 0 001 i 3,0 SCOPE OF WORK ' Based on threegr ound water sampling events and data collected during the CPT investigation, fuel component-impacted ground water appears to have migrated at least 60 feet north of the site (P-10) and vertically to depths of at least 140 feet bsg(P-S), furthermore, a municipal drinking water wells is located approximately 1,500 feet south of the site and a second municipal water well is located Advanced GeAnvironmental,(no.