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r THIRD QUARTER 1996 GROUNDWATER MONITORING REPORT USA STATION#110-STOCKTON AUGUST, 1996 Groundwater elevation contours constructed from the July 19, 1996 gauging activities indicate groundwater is flowing to the northeast at a hydraulic gradient of approximately 0 0013-feet/feet A review of the histoncal 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 rTPH G was detected only in monitoring wells MW-2-P and MW-3-P at 190 and 130 micrograms per liter(µg/1), respectively TPH G was non-detect at the method detection limit in all other monitoring wells TPH D, MTBE and total lead were also non-detect at the method detection limits in all the wells sampled during this quarter Analytical results are summarized in Table 2 and shown on Figure 6 Copies of laboratory reports and COC documentation are provided in Appendix B 3.3 Conclusions rA review of the groundwater monitoring results suggests that TPH impacted groundwater is not present in the off-site wells The wells with detectable hydrocarbon concentrations are MW-2-P and MW-3-P, which are in close proximity to the on-site underground fuel tanks and dispenser islands These wells are also located on the upgradient side of the site If the source of TPH compounds is on-site, the impacted groundwater does not appear to have migrated significantly from the source Groundwater has recharged approximately 0 5 to 1-foot since the previous monitoring event on ' April 26, 1996 Groundwater is currently at its highest elevation since the beginning of monitoring activities ' It is our opinion that the impacted groundwater plume appears to be stable Downgradient wells have been consistently non-detect at the method detection limit, which defines a "zero-hne" closure These findings indicate closure as a low risk site may be warranted r VI 1Q f � J r 'A-) r r 3 1