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N <br /> A second assessment of the site was conducted by Woodward-Clyde Consultants (WCC) <br /> in August, 1988 The details of this investigation are presented in the WCC report titled <br /> `Subsurface Assessment Report, Thrifty Oil Service Station 171, Stockton, California, <br /> dated October 6, 1988 The investigation consisted of advancing three exploratory <br /> bonngs at the site Each boring was converted to maintain 4-inch diameter PVC <br /> groundwater monitoring well to depths of about 50 to 60 feet Soil sample MW2 at 36 <br /> feet bgs indicated the only significant TPH and benzene, toluene, ethylbenzene and xylene <br /> (BTEX) concentrations (2,200 mg/kg TPH and less than detectable to 235 mg/kg BTEX) <br /> In November 1992, Thrifty conducted an additional assessment that included installation <br /> of four groundwater monitoring wells (NMR, MW4, MWS, and MW6) at the site <br /> Because the water table had dropped about 30 feet since installation of the original wells, <br /> these deeper wells were required to monitor the groundwater quality These wells were <br /> installed to 90 feet below grade and are constructed of 2-inch diameter PVC Also, as <br /> part of the investigation, two vapor wells (VW 1 and VW2) were installed near the former <br /> tank pit Results of the investigation showed that soils near the western boundary of the <br /> site contained significant hydrocarbon concentrations Groundwater in each of the deep <br /> wells had high contamination levels Results of the investigation are presented in Thrifty's <br /> Site Assessment Report dated January 17, 1988 <br /> In November 1994, Thrifty removed the former tanks and replaced them with the new <br /> tanks in the northeast corner of the site These construction activities resulted in the loss <br /> of wells MW 1, VW 1, and VW2 which were located in close proximity to the former <br /> tanks Also, well MW3R was damaged during installation of the new tanks Thrifty <br /> addressed replacement of these wells in the current scope of work During site <br /> reconstruction, some of the contaminated soil that was encountered during excavation was <br /> reportedly placed in the former tank cavity as fill material <br /> Page 2 <br />