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SECOND QUARTER 1996 <br /> GROUNDWATER MONITORING REPORT <br /> USA STATION#110 - STOCKTON <br /> MAY, 1996 <br /> ' Groundwater elevation contours constructed from the April 26, 1996, gauging activities indicate <br /> groundwater is flowing to the northeast at a hydraulic gradient of approximately 0 0038-feet/feet <br /> A review of the histoncal field data suggests that the groundwater generally flows to the northeast <br /> ' with minor fluctuations to the north and south, as shown on Figures 4 and 5 <br /> 3.2 Results of Groundwater Laboratory Analyses <br /> ' TPH G was detected only in monitoringwells MW-2-P and MW-3-P at 1,000 and 140 <br /> micrograms per liter(µg/1),respectively TPH G was non-detect at the method detection limit in <br /> all other monitoring wells TPH D and organic lead were also non-detect at the method detection <br /> limits in all the wells sampled during this quarter Analytical results are summarized in Table 3 <br /> and shown on Figure 6 Copies of laboratory reports and COC documentation are provided in <br /> Appendix B <br /> 3.3 Conclusions <br /> A review of the groundwater monitoring results suggests that TPH impacted groundwater is not <br /> present in the off-site wells The wells with detectable hydrocarbon concentrations are MW-2-P <br /> and MW-3-P, which are in close proximity to the on-site underground fuel tanks and dispenser <br /> islands These wells are also located on the upgradient side of the site If the source of TPH <br /> ' compounds is on-site, the impacted groundwater does not appear to have migrated significantly <br /> from the source <br /> Groundwater has recharged approximately 2-feet since the previous monitoring event on January <br /> 18, 1996 Groundwater is currently at its highest elevation since the beginning of monitoring <br /> activities The slight increase in TPH G 1n MW-2-P may be due to this groundwater elevation <br /> increase <br /> It is our opinion that the impacted groundwater appears to be stable Downgradment wells have <br /> ' been consistently non-detect at the method detection limit, which defines a "zero-line" closure <br /> These findings indicate closure as a low risk site may be warranted <br /> 1 <br /> 3 <br />