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k p V In the Tracy area, groundwater occurs in the Recent alluvium, both above and below the aereally extensive Corcoran Clay. Water below the Corcoran Clay is generally of good quality and is ' widely used for agriculture, industry, and drinking water. Above the Corcoran Clay,water quality varies,with high mineral concentrations noted in several areas. (26) Groundwater occurs approximately 8 feet below ground surface (bgs) at the Cox & Cox site, and generally flows to the north and northwest in the vicinity of the site. Materials in the unsaturated zone beneath the site consist of sands and clays. (3) 3.2.2 Groundwater Targets. There are 10 municipal drinking water wells maintained by the City of Tracy within 4 miles of the site. These wells are part of a blended system composed of 30 percent groundwater and 70 percent treated surface water from the Delta Mendota Canal under the Central Valley Water Project. The City of Tracy serves approximately 40,507 people with municipal drinking water from this blended system. The active drinking water well nearest the site is less than 0.5 mile southwest of the Cox& Cox site. (27) One private drinking water well, less than 0.25 mile from the site on the Tracy Joint Union High School campus, was closed in December 1979 due to gasoline contamination. A new private well was reportedly installed in its stead in February 1980, but it is used for agricultural purposes only. This private well has been out of service since 1985 due to a collapsed well casing. (28,29, 30,31, 32) In December 1979, gasoline was reportedly detected in the Lincoln Park and Fine wells, two , municipal drinking water wells located approximately 0.5 to 1 mile from the site (33). These wells were not in use after 1982 because of contamination from an irrigation conduit, and were apparently destroyed in 1986. A new Lincoln Park municipal drinking water well was constructed in August 1989, 1,500 feet away from the former Lincoln Park municipal drinldng water well site. (34) This new municipal well is part of the total blended system and is located 0.5 mile from the Cox & Cox site (27). 3.23 Groundwater Pathway Conclusion. Depth to groundwater beneath the site is approximately 8 feet bgs. Geologic materials in the unsaturated zone beneath the site consist of sands and clays. (3) Ten municipal drinking water wells are within 4 miles of the site and serve approximately 40,507 people with drinking water from a blended system. The nearest active drinidng water well is less than 0.5 mile southwest of the site. (27) 3.3 Surface Water Pathway Surface water runoff from the site flows into the city's storm drain system along East Eleventh Street. According to the Department of Public Works, stormwater runoff from the site ultimately discharges into the Sugar Cut Slough. Sugar Cut Slough is greater than 2 miles from the site. (35) The site is outside of a 500-year floodplain (36). x y' 3.4 Soil Exposure and Air Pathway 3.4.1 Physical Conditions. The Cox & Cox site is located in a commercial area. The ground surface in the southern half of the site is paved, while the northern half is gravelled. A fence surrounds the perimeter of the site, except for the south side that borders Eleventh Street. However, this side of the site is occupied by a business. A former underground storage tank area onsite underwent excavation and is now surrounded by a 6-foot-high chain-link fence. (5) F PA Cox&Cox-BB-9/93 7 Pdded on W%recyded aper. m