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Project No 014-95262 Page No 3 an aeration pond (>500,000 gal capacity) After pre-treatment is complete, wastewater is transferred via pipeline to a city-owned sanitary sewer located along Argonaut Street Considerable additional site-specific background information is included in Krazan's Phase I Environmental Site Assessment for the Safeway site dated October 3, 1995 i 5.0 GEOLOGIC AND HYDROLOGIC SETTING The subject site lies near the northern end of the San Joaquin Valley portion of the Great Valley Geomorphic Province The Great Valley is bordered to the north by the Cascade and Klamath ranges, to a the west by the Coast Ranges, the East by the Sierra Nevada, and to the south by Transverse Ranges The valley is characterized by a thick sequence of sediments derived from erosion of the adjacent Sierra Nevada to the east and the Coast Range to the west These sedimentary rocks are mainly Cretaceous in age The depth of the sediments vary from a thin veneer at the edges of the valley to depths in excess of 50,000 feet near the western edge of the valley In the vicinity of the site, these sediments are over 15,000 feet deep Near-surface sediments are predominantly fine-grained and were deposited during flood stages of major rivers and streams The San Joaquin Valley has historically been a province of relatively low seismic activity The nearest active faults to the site are the Foothills Fault system located near the base of the Sierra Nevada and the Coast Ranges Sierran Block Boundary Zone located along the base of the Coast Ranges There are no known active fault traces in the project vicinity The Stockton Fault Zone is located less than one mile from the project site There is no history of activity for this fault zone and it is known only through ' vertical offsets in deeper geologic formations observed in petroleum exploration and production wells According to Soil Survey maps published by the Soil Conservation Service (SCS), the soils at the subject site consist predominantly of the Jacktone clay This urut is slowly permeable and contains a hardpan at depths of 20 to 40 inches Previous subsurface borehole data at the site show the upper soil profile (to approximately 26 feet bgs) to be dominated by low permeability silty and clayey units More permeable clean to silty sands interbedded with low permeability units were noted below a depth of 26 feet bgs Review of the San Joaquin County Flood Control and Water Conservation District (WCD) map entitled "Ground Water Elevations, Spring 1993" shows a groundwater elevation contour of-20 feet in the vicinity of the subject property Review of the 7 5 minute Stockton West, California topographic quadrangle map, photorevised 1987, indicates an elevations of 7 feet above mean sea level (amsl) near the KRAZAN&ASSOCIATES, INC Offices Serwng the Western United States 95262 Ps2