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WIPE :FltllAepq/,run1 <br /> Mr. Theodore I. Wittmayer, Attorney at Law September 28, 1992 <br /> Stone Brothers and Associates Page 3 <br /> a borehole and sampling is the north side. It is reasonable, however, to assume that the <br /> maximum lateral extent on the north side of the tank would be no greater than five to ten feet <br /> beyond the former location which is equivalent to the approximate distance from the former tank <br /> location to the "clean" boundary between borings B-6 and B-7. <br /> Based on the above evaluation, the lateral extent of hydrocarbon impact related to the IIformer <br /> tank location has been established. The vertical extent, however, has not been establiled due <br /> to the presence of total petroleum hydrocarbons as gasoline (TPH-G) in the deepest sample from <br /> boring B-6 taken at a depth of 50 feet. Although this TPH-G concentration is relatively low, <br /> the San Joaquin County Environmental Health Division (EHD) could require additional <br /> characterization of the hydrocarbon depth extent based on the lack of "clean" samples at the <br /> bottom of B-6. WESTON's experience with the County is that typically the County has not been <br /> convinced the depth extent of hydrocarbons has been determined until two samples in sequence <br /> have shown nondetectable results. <br /> An additional issue in Area 1 is the alleged presence of "solvents" in the soil. This issue has <br /> been raised by EAI based on evidence such as odor and interpretation of chemical analyses. The <br /> source of these solvents was claimed to be a break in a below-grade sewer line located near the <br /> south side of the auto shop and it was EAI's contention that chemical compounds in boring B-6 <br /> were actually solvents derived from the sewer line leak. Previous investigations have indicated <br /> that some hydrocarbon compounds are present at shallow depths in the soil near the sewer break. <br /> However, it has been WESTON's opinion throughout the history of the site characterization, <br /> based on interpretation of analytical results and spacial association, that the hydrocarbon <br /> compounds present in boring B-6 are most likely related to the former gasoline tank and not to <br /> solvents leaking from the sewer line. <br /> The recent Phase IV work adds additional substantiation to this interpretation. Borings -7 and <br /> B-8, recently installed near the sewer line and sampled by EAI, showed virtually no hydr carbon <br /> presence to the boring total depth of 30 feet below grade. Since these borings are located <br /> between the sewer line break and boring B-6 which has shown elevated concentrations of <br /> hydrocarbons, the results demonstrate that the minor hydrocarbon presence found near the sewer <br /> lines is not linked to the hydrocarbon presence in boring B-6. WESTON's conclusion with <br /> regard to B-6 continues to be that the elevated hydrocarbon levels found in that boring are <br /> related to leaks or spills from the former underground storage tank location, not to a break in <br /> the sewer line. <br /> Area 2 Issues <br /> EAI installed soil borings B-9 and B-10 in the vicinity of the former location of Fuel Island <br /> No. 2. Soil samples from boring B-10 contained no significant hydrocarbon presence while the <br /> RMSW-rMVR:.WP <br />