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i <br /> f <br /> THIRD QUARTER,1997 i <br /> GROUNDWATER MONITORING REPORT <br /> USA STATION#165-LODI <br /> AUGUST!1997 <br /> Concentrations of TPH G for this sampling event ranged from 70 micrograms per liter(µg/1) in <br /> MW-2 to 16,000 µg/I in S-1 . TPH G was non-detect (ND) at the method detection limit in wells <br /> MW-1, MW-4, MW-5, MW-6, and MW-7. Benzene was detected in four monitoring wells <br /> (MW-3, MW-8, S-1, and S-2) at concentrations ranging from 30 µg/1 inMW-3 to 1,600 pg/l in <br /> S-1. Benzene was ND in wells MW-1, MW-2, MW-4, MW-5, MW-6, and MW-7. MTBE was <br /> ND in all wells. Analytical results are summarized in Table 2, and shown on Figure 5.' Copies of <br /> laboratory�reports and COC documentation are included in Appendix B. g <br /> The dissolved hydrocarbon concentrations in MW-4 have decreased to values similar to historical <br /> r* data. MW-3 continues to have sporadic elevated concentrations of TPH G and benzene. The <br /> chromatographic signature in Appendix B for groundwater in MW-3 indicates an older weathered <br /> gasoline as do the low benzene level compared to xylene and the lack of MTBE. The high <br /> L� groundwater levels during the winter months appears to have resolubilized degraded petroleum <br /> L� hydrocarbon compounds, which had been in the capillary fringe or vadose zone. The limited i <br /> lateral extent of impacted groundwater is demonstrated by the lack of TPH in the downgradient <br /> wells. <br /> _. There does not appear to be any indication of plume migration. At this time; GHH recommends <br /> that monitoring be continued. <br /> 4 1 <br /> k <br /> 5 I bL <br /> 5 <br /> } <br />