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------- <br /> A S S O C I A T E S I N C <br /> A subsurface investigation was conducted on October 17 and 18, 1989 by WaterWork Corp. Six soil <br /> borings (SB-1, SB-2, MW-1, MW-2, MW-3, and MW4) were drilled at the subject site to depths <br /> ranging from 16 to 36 feet below grade. Four of these borings were completed as two-inch diameter <br /> groundwater monitoring wells (MW-1 through MW4). Soil boring locations are shown on Figure 2. <br /> �===� Soil samples collected during drilling activities were analyzed for the presence of benzene, toluene, <br /> ethylbenzene, and xylenes (BTE3� and TPHd. Field observations and laboratory analyses of soils <br /> collected from the soil borings (Table 1) indicated that soil had been impacted by the release of <br /> petroleum hydrocarbons to the subsurface. TPHd was detected in all borings with the exception of <br /> MW-1, at depths varying from 10 to 15 feet below grade. Groundwater was initially encountered at <br /> approximately 11.5 feet below grade. Hydrocarbon constituents were detected in groundwater <br /> samples from monitoring wells MW-3 and MW4 subsequent to development(Table 3). <br /> A more detailed description of work performed prior to 1991 is included in WaterWork Corp./RESNA <br /> Industries Inc. (RESNA) December 5, 1990 'Preliminary Report -Assessment of Potential Soil and <br /> Groundwater Contamination". <br /> On February 28, 1992, the 5,000-gallon diesel UST was removed from the site by Falcon Energy <br /> Associates. RESNA was present in an advisory capacity. A soil sample collected from beneath the <br /> center of the tank indicated that TPHd at a concentration of 340 ppm was present at 18 feet below <br /> ground surface. Free petroleum product was noted floating on groundwater within the excavation. <br /> During the first quarter of 1992, RESNA was retained by the City of Stockton to conduct quarterly <br /> groundwater monitoring and sampling of the site monitoring wells (MW-1 through MW-4). TPHd <br /> t_==� was detected at 55 parts per billion (ppb) in well MW-3 during the second quarter of 1993. RESNA <br /> has periodically bailed floating free product from well MW4. Free product is stored on-site in DOT <br /> approved drums pending appropriate disposal. A summary of free product removal is presented on <br /> Table 2. <br /> ..f <br /> On August 3, 4, and 5, 1993, RESNA drilled and sampled a total of ten soil borings (SB-3 through <br /> SB-10, MW-5, and MW-6) at the project site to approximately 15-20 feet below grade. Two of the <br /> borings (MW-5 and MW-6) were advanced an additional 15 feet and converted to groundwater <br /> monitoring wells. Discrete groundwater samples were also collected from four of the soil borings (SB- <br /> 3, SB-7, SB-8, and SB-9) using the Hydropunch technology. The boring/well locations are shown on <br /> Figure 2. Discrete groundwater samples were collected from the four soil borings (SB-3, SB-7, SB-8 <br /> and SB-9)nearest MW-4. <br /> w:162574162574.021mNAslsup_sub_inv.doc 2 <br /> :j <br />