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r
<br /> rTHIRD AND FOURTH QUARTER, 1999
<br /> GROUNDWATER MONITORING REPORT
<br /> r USA STATION#110- STOCKTON
<br /> DECEMBER, 1999
<br />' The groundwater elevations ranged from 30 80 to 31 00-feet below mean sea level on July 7,
<br /> 1999, and 33 20 to 33 43-feet below mean sea level on October 21, 1999 Groundwater
<br /> elevations dropped an average of 2 27-feet between the third and fourth quarter gauging events
<br /> iGroundwater elevation contours constructed from the July 7, 1999 measurements indicate
<br /> groundwater was flowing to the east-northeast at a hydraulic gradient of approximately 0 0005-
<br /> feet/feet at the time of the thud quarter gauging event Measurements taken on October 21, 1999
<br /> indicate that during the fourth quarter gauging event the groundwater was flowing to the
<br /> northeast in a more northerly direction A review of the historical field data suggests that the
<br /> groundwater generally flows to the northeast with minor fluctuations to the north and south, as
<br /> shown on Figures 4, 5 and 6
<br /> 3.2 Results of Groundwater Laboratory Analysis
<br /> For the July 7, 1999 sampling event, MW-1-P, MW-4-P, MW-5-P, MW-6-P, and MW-2 reported
<br /> non-detect (ND) at the method detection limits for all petroleum compounds analyzed TPH G
<br /> was reported in MW-1, MW-2-P and MW-3-P at 750, 970 and 340 micrograms per liter(µg/1),
<br /> respectively Benzene was reported in MW-1 and MW-2-P at 0 71 and 51 µg/l, respectively
<br /> MW-1 also reported toluene, ethylbenzene, xylenes, and MTBE at 19, 19, 3 1, and 64 µg/1,
<br /> respectively NfW-2-1? reported toluene, ethylbenzene, xylenes, and MTBE at 8 2, 2 9, 5 8, and
<br /> 7 6 µg/l, respectively for the July 7, 1999 sampling event MTBE was also detected in MW-3-P
<br /> rat 28 µg/1
<br /> For the October 21, 1999 sampling event, MW-1-P, MW-4-P and MW-6-P reported ND for all
<br /> petroleum compounds MW-5-P reported TPH G at 100 µg/1 and xylene at 1 3 µg/1 for the
<br /> fourth quarter samphng TPH G was report at 64µg/1 in MW-2, and 260, 920 and 230 µg/l,
<br /> respectively in MW-1, MW-2-P and MW-3-P MW-1 also reported toluene, xylenes and MTBE
<br /> at 5 6, 1 0 and 81 ug/l, respectively, but was ND for ethylbenzene Toluene, ethylbenzene,
<br /> xylenes, and MTBE were reported in MW-2-P at 10, 0 99, 3 4, and 12 µg/1, respectively MTBE
<br /> ' was also detected in MW-3-P at 22 µg/1 Benzene was only detected m one well, MW-2-P at i I
<br /> ,ug/l
<br /> ' Groundwater analytical results are summarized nn Table 2, and shown on Figures 7 and 8 Copies
<br /> of laboratory reports with COC documentation are included in Appendix B
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<br /> 3
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