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,1,C_ }} ,,.... VvATC '1 A S S O C I A T E S I N C A subsurface investigation was conducted on October 17 and 18, 1989 by WaterWork Corp. Six soil borings (SB-1, SB-2, MW1, MW2, MW3, and MW4) were drilled at the subject site to depths ranging from 16 to 36 feet below grade. Four of these borings were completed as two-inch diameter groundwater monitoring wells (MW1 through MW4). 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 petroleum hydrocarbons to the subsurface. TPHd was detected in all borings with the exception of MW1, at depths varying from 10 to 15 feet below grade. Groundwater was initially encountered at approximately 11.5 feet below grade. Hydrocarbon constituents were detected in groundwater =� samples from monitoring wells MW3 and MW4 subsequent to development(Table 3). A more detailed description of work performed prior to 1991 is included in WaterWork Corp./RESNA Industries Inc. (RESNA) December 5, 1990 "Preliminary Report - Assessment of 1` Potential Soil and Groundwater Contamination". On February 28, 1992, the 5,000-gallon diesel UST was removed from the site by Falcon Energy j Associates. RESNA was present in an advisory capacity. A soil sample collected from beneath the center of the tank indicated that TPHd at a concentration of 340 parts per million (ppm)was present r- at 18 feet bgs. Free petroleum product was noted floating on groundwater within the excavation. 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 MW4). TPHd was detected at 55 parts per billion(ppb) in well MW3 during the second quarter of 1993. RESNA has periodically bailed floating free product from well MW4. Free product is stored on-site in DOT approved drums pending appropriate disposal. A summary of free product removal is presented on Table 2. �a On August 3, 4, and 5, 1993, RESNA drilled and sampled a total often soil borings (SB-3 through -s SB-10, MW5, and MW6) at the project site to approximately 15-20 feet bgs. Two of the borings (MW5 and MW6) 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) using the Hydropunch technology. The boring/well locations are shown on Figure - 2. Discrete groundwater samples were collected from the four soil borings (SB-3, SB-7, SB-8 and SB-9) nearest MW4. I,:f w:\Wordpro162574162574.021Reportslwcll_install.doc 2