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SECOND QUARTER, 1999 GROUNDWATER MONITORING REPORT USA STATION#110 - STOCKTON JUNE, 1999 Groundwater elevation contours constructed from the April 30, 1999 measurements indicate groundwater is flowing to the northeast at a hydraulic gradient of approximately 0 001-feet/feet A review of the historical field data suggests that the groundwater generally flows to the northeast with minor fluctuations to the north and south, as shown on Figures 4 and 5 3.2 Results of Groundwater Laboratory Analyses r TPH G was non-detect (ND) at the method detection Limit of 50 micrograms per liter (µg/1) in all wells except MW-1, wluch contained 380 µg/1 Benzene was ND at the method detection hnut of 0 5 µg11 m allwells except MW-1, which contained 10 µg/1 Groundwater analytical results are summarized in Table 2, and shown on Figure 6 Copies of laboratory reports with COC documentation are included in Appendix B 3.3 Conclusions Groundwater elevations have risen since the last quarterly measurements and are now at an all time high for tlus site TPH G concentrations have continued to decline in all wells with only TPHG present in.MW-1, the shallow side gradient well closest to the abandoned Chevron site across Farmington Avenue It is our opinion that the impacted groundwater plume continues to be minimal in size and is stable In November, 1997, the UST's and piping were replaced No obvious holes were observed during the retrofit m the tanks or Imes Downgradient well g shave been consistently ND at the method detection limit, which define a "zero-line" closure With the UST and line treplacement the potential risk at this site has been significantly reduced There does not appear to be any indication of plume migration after monitoring the groundwater for six years This site Ishould be considered for no further action as a low risk site 3