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FOURTH QUARTER 1996 <br /> GROUNDWATER MONITORING REPORT <br />' USA STATION#110 - STOCKTON <br /> NOVEMBER, 1996 <br />' Groundwater elevation contours constructed from the October 30, 1996 gauging activities <br /> indicate groundwater is flowing to the east northeast at a hydraulic gradient of approximately <br /> 0 0013-feet/feet. A review of the historical field data suggests that the groundwater generally <br />' flows to the northeast with nunor fluctuations to the north and south, as shown on Figures 4 and <br /> 5 <br />' 3.2 Results of Groundwater Laboratory Analyses <br /> TPH G and benzene were detected only in monitoring well MW-2-P at 1,300 and 160 micrograms <br />' per liter (ag/l),respectively TPH G was non-detect at the method detection limit in all other <br /> monitoring wells TPH D, MTBE and total lead were also non-detect at the method detection <br /> limits in all the wells sampled Analytical results are summarized in Table 2 and shown on Figure <br />' 6 Copies of laboratory reports and COC documentation are provided in 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 only well with detectable hydrocarbon concentrations is MW-2- <br /> P which is in close proximity to the on-site underground fuel tanks and dispenser islands This <br /> well is located on the upgradient side of the site If the source of TPH compounds is on-site, the <br />' impacted groundwater does not appear to have migrated significantly from the source <br /> It is our opinion that the impacted groundwater plume is minimal in size and appears to be stable <br /> Downgradient wells have been consistently non-detect at the method detection limit, which define <br /> a "zero-line" closure. These findings suggest that closure as a low risk site may be warranted <br /> ,r <br /> r i <br /> I <br /> 3 <br /> t <br />