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C 4 0 CONCLUSIONS AND RECOMMENDATIONS Dissolved phase petroleum hydrocarbons were reported in groundwater collected from wells MW-14A, VM-1, and VM-2 located within the immediate vicinity of the former UST excavation Results from September/October 2005 sampling show decreasing concentrations of TPH/g, TPH/d, and BTEX since the last sampling event in June 2005 in wells VM-2 and MW-14A and slightly increasing levels for these constituents in well VM-1 The sample from well VM-1 also contained 24 micrograms per liter (Ng/L) tert-butanol (TBA) for the first time A comparison with contours from the second quarter show that the TPH/g plume has generally shifted slightly to the south (Figure 5) Groundwater flow direction has shifted slightly In the northerly direction and now flows northeast Minor amounts of benzene and toluene (0 75 pg/L and 0 86 pg/L, respectively) were detected in well MW-11 for the first time since 1997 Toluene (1 2 pg/L) was detected in well MW-12 In June 2005, but was not detected this quarter However, TPH/d (76 pg/L) was detected in well MW-12 for the first time since 2003 No detectable amounts of hydrocarbon constituents were reported in downgradient wells MW-24 and MW-13, except for 1 1 pg/L 1,2—dichloroethane (1,2-DCA) in well MW-13 Petroleum constituents were not reported above detection limits in any of the other wells sampled DO levels In impacted wells MW14A, VM-1, and VM-2 are lower than remaining wells with no detectable contaminants Low or negative ORP levels and higher ferrous iron concentrations in impacted wells indicate natural biodegradation is currently less active As air sparging occurs, higher DO and ORP, and lower ferrous iron concentrations in impacted wells are expected as bioactivity Increases SECOR recommends continued monitoring on a quarterly basis to provide further data to support cleanup efforts at the Site The next groundwater monitoring and sampling event is scheduled for December 2005 after system start-up and will provide a comparison of analytical data to conditions prior to system operation i 11CALTRANSIStockton-Shop 101GW Monitonngl3rd Qtr 2005103'05 0M&M, Final doc November 29 2005 Protect No 940T 43148 00 7 SECOR International Incorporated