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a 1.0 INTRODUCTION Valley Motors operates a wholesale used car dealership at 800 East Main Street in Stockton, California and is owned by Mr Andrew Hyduke Investigation of the extent of hydrocarbon contamination beneath the Valley Motors property has been directed by San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD and performed in phases The first phase was conducted by Hunter & Associates in 1994 and documented the presence of contaminated soil In the second and third phases, Upgradient Environmental demonstrated that groundwater had been impacted The purposes of the present phase are to 1) identify the contamination source(s), 2) complete the delineation of soil and groundwater contamination, and 3) identify potential receptors of contaminated groundwater 2.0 BACKGROUND 2.1 Site Location and Description The site is located several blocks east of downtown Stockton and several blocks north of Mormon Slough (Figure 1) It occupies an L-shaped parcel of land at the corner of Main and Grant Streets The area is zoned commercial and light industrial Small businesses and a vacant lot are located to the north, across Main Street, and a paint company is located to the west, across Grant Street The topography in the area is flat 2.2 Previous Work It is our understanding that two UST's were removed from the site by Siebold Corporation in 1990 The tanks were located beneath the sidewalk along Grant Street (Figure 2) They were reportedly used to store gasoline, although no fuel dispensers were present when the tanks were removed However, the tanks had not been in use since Mr Hyduke acquired the property about 1987 William Hunter & Associates conducted a soil investigation in 1994 and drilled 5 borings (Figure 2) Forty soil samples were collected for analysis, but only 4 of these contained hydrocarbons at concentrations above detectable limits The hydrocarbons were reported by FGL Laboratory to be within the compositional range of Stoddard Solvent, although specific carbon ranges were not reported The maximum depth at which hydrocarbons were detected was approximately 25 feet, which is approximately 10 feet above the historically highest recorded groundwater level in the site area(35 feet in 1983) Upgradient Environmental installed groundwater monitoring well VM-1 in September 1995 Contaminated soil was detected at a depth of 25 feet, and groundwater samples collected in September and October were also contaminated Gasoline, diesel, BTEX, and several chlorinated hydrocarbons were detected in the groundwater In February 1996, Upgradient collected eight samples from the soil that had been excavated during the UST removal in 1990 This soil was stockpiled at the south end of the site With the approval of 3