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1.0 INTRODUCTION Valley Motors operates a wholesale used car dealership at 800 East Main Street in Stockton, California and is owned by Mrs 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) 2.0 BACKGROUND 2.1 Site Location and Descriphon 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 comer 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 about 1987,when Mr Hyduke acquired the property 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 Upgradient Environmental installed groundwater momt6nng 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 July 1996, three soil bonngs were drilled and two were converted to monitoring wells Contaminated soil was encountered in two of these, and one or more hydrocarbon contaminants were detected in water samples from all three, as well as 1n the previously drilled well (VM-1) The resulting data helped to partially define the limits of soil contamination, but the limits of groundwater contamination were not reached A soil vapor survey was conducted in March 1998,' in order to better define the extent of near- surface soil contamination This survey was followed by the dnlling of two new soil borings to 2