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1 1.0 INTRODUCTION In July 1995, Thomas ONeill of Valley Motors retained Upgradient Environmental Consultants to assess the vertical extent of gasoline contamination beneath the Valley Motors property located at 800 ' East Main Street in Stockton, California Valley Motors operates a wholesale used car dealership and is owned by Mr Andrew Hyduke Gasoline contamination had been discovered during the removal of two underground storage tanks (UST's) in 1990 and was subsequently investigated by William Hunter I & Associates The soil bonngs that were drilled during that investigation provided data on the lateral extent of soil contamination, but were terminated at shallow depths before reaching the base of the -- contamination or the top of the saturated zone San Joaquin County Public Health Services, Environmental Health Division (PIJSIEHD), the lead regulatory agency, therefore requested further work to determine whether groundwater has been impacted by gasoline Upgradient investigated this question in September 1995,the purpose of this report is to present our findings I 20BACKGROUND 2.1 Site Location and Description The site is located several blocks east of downtowri 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 Soil samples were collected from beneath the tanks during their removal, and petroleum hydrocarbons were detected However, the laboratory results were subsequently ruled invalid by PHS/EHD and further investigation was requested Unfortunately, Mr Hyduke experienced serious health problems and two years passed before any additional work was performed William Hunter & Associates conducted a soil investigation in 1994 and drilled 5 bonngs (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 I � 1