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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. 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 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 approximately 15,000 feet deep. The San Joaquin Valley has historically been a province of relatively low seismic activity. The nearest faults to the site are Foothills Fault system located near the base of the Sierra Nevada and the Coast rRanges Sierran Block Boundary Zone located along the base of the Coast Ranges. There are no known active fault traces in the project vicinity. 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 unit is slowly permeable and contains a 1 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 subject property. Comparison of the two elevations indicates that groundwater in the vicinity of the project site would be approximately 27 feet below existing grade. According to subsurface investigative reports reviewed for the project site, groundwater was reported to be approximately 30 feet below grade as of June 1994. KRAZAN&ASSOCIATES, INC. Offices Serving the Western United States 95262.WP