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• 1.0 INTRODUCTION Upgradient Environmental Consultants (Upgradient) assumed the responsibility for assessment and monitoring of groundwater contamination at the Gillies Trucking facility in Stockton, California in September, 1994 Upgradient submitted Quarterly Reports in October 1994, January 1995, August 1995, and September, 1995, describing the progress of the investigation through the third quarter of 1995 The purpose of this report is to present the results of groundwater monitoring activities during the fourth quarter of 1995 2.0 BACKGROUND INFORMATION 2.1 Site Location and Description The project site is located at 3961 Newton Road, in an industrial area on the northeast outskirts of Stockton near U 'S Highway 99 The location of the site is shown in Figure 1, and the site facilities are shown in Figure 2 Originally agncultural property, the site was developed as a commercial truck terminal in 1973 The property occupies an area of about 3 5 acres Topography in the area is generally flat, although the project site is elevated several feet above the adjacent parcels There is a maintenance building and office fronting Newton Road, with a large, unpaved storage yard/parking lot in the rear A diesel and gasoline fueling facility, consisting of two underground storage tanks (UST's), was formerly present on the east side of the storage yard (Figure 2) This facility was removed in 1989 and replaced with an above-ground fueling facility, which is located to the south of the abandoned facility 2.2 Previous Work Soil samples collected during the UST removal in 1989 contained petroleum hydrocarbons in the gasoline and diesel ranges, prompting assessment of the extent of soil contamination Contarrunated soil was excavated to a depth of 35 feet by SEMCO in July, 1990, but residual hydrocarbons were detected in all eight soil samples collected from the floor and sidewalls of-the excavation Clean soil was excavated from the south end of the property and placed into the open excavation the contaminated soil was then treated with bacteria and stored at the south end of the property It was later sampled and approved for disposal by San Joaquin County Public Health Service, Environmental Health Division (PHS/EHD) The soil was then spread out and the area was graded Further assessment of the extent of contamination was requested by PHS/EHD The firm of Richesm & Associates of Danville, California was retained in November, 1990 to perform further subsurface investigation Two bonngs were drilled, one was completed as a groundwater monitoring well, and soil and water samples were collected for analysis Hydrocarbons were detected to the bottom of the soil bonng (70 feet) and to a depth of 85 feet in the monitoring well, and both gasoline and diesel were detected in the groundwater sample from the well It is our