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1 <br /> tFIRST QUARTER,1998 <br /> GROUNDWATER MONITORING REPORT <br /> USA STATION#65-LODI <br />' FEBRUARY, 1998 <br /> 5.1 Groundwater Flow and Gradient <br /> Groundwater data collected at the site on January ry16 1998 indicate that the depths to <br /> groundwater ranged from 41 15 to 43 72-feet bgs The groundwater elevations ranged from <br /> 3 80 to 5 84-feet below MSL Groundwater elevations have risen since the fourth quarter <br /> monitoring event <br />' The direction of groundwater flow has been calculated to be to the south southeast with an <br /> average hydraulic gradient of approximately 0 0035-ft/ft across the site Histonc field data <br /> suggests that the groundwater generally flows southerly, with minor fluctuations to the east <br /> and/or west, as shown on Figures 4 and 5 <br /> 5.2 Results of Groundwater Laboratory Analyses <br /> The January 16, I998 analytical reports indicated that TPH G, benzene and MTBE were non- <br /> detect (ND) at the method detection ]unit in all wells sampled, except for MW-4, where it was <br /> reported at 1,500, 0 87 and 5 2 micrograms per liter(99/1), respectively Groundwater analytical <br /> data are summarized in Table 2, and shown on Figure 6 Laboratory reports with COC <br />' documentation are included in Appendix B <br /> Monitoring well MW-4 continues to have sporadic elevated concentrations of TPH G and <br />' benzene The chromatographic signature in Appendix B for samples from MW4 indicate an <br /> older weathered gasoline The high groundwater levels during the winter months appear to have <br /> re-solubilized degraded petroleum hydrocarbon compounds, which have been in the capillary <br />' fringe or vadose zone The limited lateral extent of impacted groundwater is demonstrated by the <br /> lack of TPH in the downgradient wells The relationship between TPH G and benzene <br /> concentrations and groundwater elevations in MW4 are shown on Figure 7 <br /> 6.0 CONCLUSIONS <br />' HGconcentrations <br /> TP remain low with the exception of sporadic seasonal concentrations in MW- <br /> 4 Wells downgradient from MW-4 continue to be ND for TPH and BTEX compounds With the <br /> replacement of the USTs and Ines and the removal of most of the impacted soil during the site <br /> retrofit, potential risks associated with this service station have been significantly reduced This <br /> site should be considered for no further action as s a Iow risk site There does not appear to be any <br /> indication of plume migration <br /> 5 <br />