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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 Mr Andrew Hyduke Investigation of the extent of hydrocarbon contamination beneath the Valley Motors property was begun in 1990 following the removal of two underground storage tanks (UST's) and related equipment Further investigation took place in late 1995, and documented the existence of groundwater contamination beneath the site San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD), the lead regulatory agency, therefore requested further drilling to determine the lateral extent of groundwater contamination A work plan to drill up to six additional borings, including as many as three within the public right-of-way, was submitted by Upgradient Environmental Consultants in May 1996 The work plan was approved by PHS/EHD, and dnlling took place in early July This report presents the results of the investigation 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 Iot 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 1