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A S S O C I A T E S I N C (ppm)total petroleum hydrocarbons as diesel (TPHd). Results of soil sample analysis are summarized in Table 1. As a result of this investigation, PHS/EHD required further assessment of the extent of contamination at the subject site. A subsurface investigation was conducted on October 17 and 18, 1989 by WaterWork Corp. Six soil == borings (SB-1, SB-2, MW-1, MW-2, MW-3, and MW4) were drilled at the subject site to depths . ranging from 16 to 36 feet bgs. Four of these borings were completed as two-inch diameter groundwater monitoring wells(MW-1 through MW-4). Soil boring locations are shown on Figure 2. Soil samples collected during drilling activities were analyzed for the presence of benzene, toluene, ethylbenzene, and xylenes (BTEX) and TPHd. Field observations and laboratory analyses of soils =< collected from the soil borings (Table 1) indicated that soil had been impacted by the release of ace. TPHd was detected in all borings with the exception of petroleum hydrocarbons to the subsurf MW-1, at depths varying from 10 to 15 feet bgs. Groundwater was initially encountered at approximately 11.5 feet bgs. Hydrocarbon constituents were detected in groundwater samples from f_J monitoring wells MW-3 and MW-4 subsequent to development(Table 2). j A more detailed description of work performed prior to 1991 is included in WaterWork Corp./RESNA Industries Inc.'s (RESNA's) 'Preliminaty Report - Assessment of Potential Soil and Groundwater Contamination"dated December 5, 1990. On February 28, 1992, the 5,000-gallon diesel UST was removed from the site by Falcon Energy Associates. RESNA was present in an advisory capacity. A soil sample collected from beneath the r center of the tank indicated that TPHd at a concentration of 340 ppm was present at 18 bgs. Free r petroleum product was noted floating on groundwater within the excavation. k== During the first quarter of 1992, RESNA was retained by the City of Stockton to conduct quarterly groundwater monitoring and sampling of the site monitoring wells (MW-1 through MW-4). TPHd was detected at 55 parts per billion (ppb) in well MW-3 during the second quarter of 1993. RESNA periodically bailed floating free product from well MW-4. A summary of free product removal is presented in Table 3. In August 1993, RESNA drilled and sampled a total of ten soil borings (SB-3 through SB-10, MW-5, and MW-6)at the project site to depths of approximately 15 to 20 feet bgs. Two of the borings(MW- 5 and MW-6) were advanced an additional 15 feet and converted to groundwater monitoring wells, Discrete groundwater samples were also collected from four of the soil borings (SB-3, SB-7, SB-8, and SB-9)nearest MW-4. TPHd was reported at levels ranging from less than 1.0 ppm to 720 ppm in soil samples collected across the site. No TPHd was detected in borings SB-7 or MW-5. Results of laboratory analysis of soil samples are summarized in Table 1. Soil samples collected from depths greater than 11 feet bgs were within the saturated zone. Analytical results of those samples were more indicative of groundwater contamination rather than soil w:162574.021reportslolosure-smith.doe 2 rI,J