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PENDIX BRISK BASEDCORRECTIVEACTION TIER 1 AND TEER 2 ANALYSIS SITE CLOSURE EVALUATION REPORT Former Beacon Station No 695 900 South Cherokee Lane Lodi, California Delta Project No D093-915 Page 12 As of March 1996, hydrocarbons remain in three areas subsequent to remedial action 1) SB-I, SB-2, SB-3, and SB-6 reported hydrocarbons Just above the water table, 2) unpacted soil existed in an isolated area around 34 5 feet in SB-5, and 3) SB-6 had intermittent impacts by hydrocarbons between 24 5 and 66 5 feet. Horizontally, it is estimated these impacts encompass an area of approximately 6,600 square feet The statistical representative concentration samples from the collective source area are: benzene 0.97 milligrams per kilogram (mg/kg), toluene 4 4 mg/kg, ethylbenzene 9 4 mg/kg, and total xylenes 74 mg/kg, as presented in Table 11 and Appendix J Noticeably, these concentrations are well below the maximum concentrations found in SB-6 at 24 5 feet Although the BTEX levels are high in this sample, the occurrence is isolated (1 of 41 samples), and thus are not representative The same forces (i e , capillary, diffuses, etc ) that may have limited the effectiveness of SVE in this area should additionally limit mugration of these constituents 7 1 2 Ground Water In June 1991, free product was detected in MW-8 During that sampling event, 1 51Lg/L of benzene was detected in downgradient well MW-20 located 300 feet downgradient In 1992, free product was no longer detected at the site and the furthest impacted downgradient monitoring well was MW-1, approximately 35 feet downgradient During the last monitoring event on March 29, 1996, the maximum benzene concentration was detected in MW-10 at 73 µg/L The only monitoring wells that contained detectable levels of benzene over the last year were MW-8, MW-10, and RW-2 with highest benzene concentrations of 73, 22, and 3 5 Ag/L, respectively, and which encompass an area of approximately 250 square feet Table 12 summarizes the analytical data for monitoring wells MW-8, MW-10, and RW-2 over the last year Appendix J includes the statement calculation for characterizing the source distribution The statistically calculated UCLs are shown in Table 13 for BTEX, to ensure stringent protection of ground water the maxunum concentration will be measured against the Risk Based Screening Levels (RBSL) and Site Specific Target Levels (SSTLs) for ground water RPT001 915