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SECTION 2 Site Setting and Background This section summarizes the site setting and background for the Disco site. This summary is f not intended to provide a definitive description of what is known about this site,but is included to provide the reader with a brief synopsis of the site as it is currently understood by Del Monte,C112M HILL,PHS/EHD,and the Central Valley Regional Water Quality Control Board (CVRWQCB). 2.1 Site Setting The Disco site is located near the intersection of Myrtle Street and Filbert Street in Stockton, California (Figure 2-1). The site is a former underground storage tank(UST)site that consisted of three 10,000 gallon gasoline tanks that were removed in 1985. Currently the site is vacant,unpaved,and fenced.Access to the site is limited to Del Monte employees. 2.2 Site Background The Disco site is currently owned by Del Monte.Parmaceast owned the site from mid-1960s until 1976,and operated the USTs that were associated with a former gasoline station. Del Monte purchased the property from Parmaceast in 1976,and never operated or used the F USTs. In October 19851,Del Monte removed the USTs under the supervision of PHS/EHD. The tanks contained water at the time of removal, and soil beneath the tanks contained gasoline constituents. Soil beneath the tanks was excavated and was aerated on site to reduce the levels of volatile hydrocarbons below 1,000 mg/Kg.The aerated soil was backfilled into the excavation (Exceltech,1985). In 1991,under the direction of the PHS/EHD,Del Monte conducted a soil and groundwater investigation in the vicinity of the Disco site that included a soil-gas survey,seven soil borings and eight monitoring wells. The results indicated gasoline constituents in soil at depths between 55 and 75 feet below ground surface(bgs),and in groundwater. The site is underlain by unconsolidated alluvial sediments. The soil types include clay,silt, sand,and gravel.The predominant soil types are interbedded sandy clay and silty sand. The current depth to groundwater is approximately 44 feet bgs.Historic water levels in this area of Stockton were as low as 100 to 105 ft bgs between 1972 and 1977,as shown on the hydrograph of a nearby water well (State Well No.: 01N,07E,07F,01M) (Figure 2-2).Water levels from 1991 through 1998 from monitoring well MW-DIS-2 are also plotted on this hydrograph,indicating that the levels measured in well 01N,07E,07F,01M are representative of water levels beneath the Disco site.This well is located approximately 4,000 feet south- southwest of the site at the Diamond Walnut Facility located at 1050 South Diamond Street at Charter Way. Since 1991,groundwater levels beneath the site have risen approximately 33 feet(from 77 feet bgs to 44 feet bgs),and the direction of groundwater flow has changed directions by SFOICPT REPORT_1 AOC1003670036 2.1 I