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r September 18, 1996 Page 2 the site, and one fiberglass waste-oil UST (1,000-gallon) located behind the former ' service station building Both generations of facilities have been removed from the site The site is bounded to the east by a Unocal service station, to the west by a residence, to the south by a restaurant and ARCO AWPM Mini-Mart, and to the north by medical offices Geology /Hydrogeology The site is located in the northern part of the San Joaquin Valley and is underlain by approximately 3,000 feet of alluvial gravel, sand, slit, and clay Groundwater in these alluvial deposits is unconfined to semlconfined (GTI, March 1994) Significant ground- water extraction for irrigation and public water supply has reduced groundwater eleva- tions in-Stockton to approximately-30 to -40 feet mean sea level (MSL) Subsurface investigations indicate that the site is underlain by interbedded clayey silts, and silty clays with sand lenses to the total depth explored (70 feet below ground surface [bgs]) Historically, depth to groundwater has ranged from 35 36 feet bgs (Well MW-8, February 7, 1989) to 58 01 feet bgs (Well MW-10, October 26, 1992) Quarterly groundwater momtonng data from November 1988 to present indicate that groundwater beneath the site consistently flows in a northeasterly direction at an approximate gradient of D 002 to 0 003 feet per feet The nearest surface water to the site is Yosemite Lake located at the east end of Smith Canal, approximately 3,500 feet west,of the site, and the deep water channel of the San Joaquin River located approximately 4,500 feet south of the site The site lies at an ' approximate elevation of 13 feet above MSL, topography in the vicinity is essentially flat Regional groundwater flow paths merge toward central and western Stockton due to extensive pumping of water wells in this area (EA Engineering, Science and Technology, Inc [EA], January 1989) ' A well survey (EA, 1988) was performed for the site using data from the California State Department of Water Resources (DWR) Using these data, seven water wells were identified within 1/2 mile of the site The closest well is a domestic well located at 919 Center Street approximately 1,700 feet south (upgradient) of the Chevron station Stockrton community water supplies were also surveyed as part of defining the physical characteristics of the site Stockton receives its drinking water supply�from the surface water of New Hogan Reservoir and groundwater at various locations throughout the City and San Joaquin County Based on a list of active water-supply wells provided by California Water Services, there are three additional groundwater-supply wells located between a 1/2- to 1-mile radius of the site These wells are located at Ellis Street East, Conimerce and Wyandotte, and East Poplar between San Joaquin and Hunter A list of private and municipal wells and available well construction detail information is presented in Table 1 320133713 CLO SURE1