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REMHDIATION CONFlRMATION SAMPLING RESULTS <br /> AND CLOSURE RECOMMENDATION REPORT <br /> (March 1994 Revision) <br /> 909 West Hammer Lane Stoddon Califomla <br /> i <br /> 5 0 GROUNDWATER MONITORING <br /> 5.1 Groundwater Levels <br /> On June 21, 1993, Aegis personnel collected depth-to-groundwater measurements in <br /> wells MW-1, MW-2, MW-5, MW-6, and MW-8, prior to purging and sampling Wells <br /> MW-3, MWA and MW-7 could not be located Since September 1992, the average <br /> groundwater elevation has increased 5 28 feet in those wells monitored during the <br /> September 1992 and July 1993 monitoring event (MW-1, MW-2, MW-6, and MW-8) On <br /> Ithe basis of the June 21, 1993, measurements, groundwater is estimated to flow to the <br /> south-southeast at an average gradient of 0 001 ft/ft Figure 5 is a potentiometric surface <br /> map of the shallow water-bearing zone on June 21, 1993 Historically, the gradient has <br /> been typically northeast or east <br /> Groundwater levels since 1991 are summarized in Table 2 and shown on Figure 6 All <br /> groundwater elevation measurements were conducted according to the Aegis SOP <br /> included in Appendix A <br /> 5.2 Groundwater Sampling and Analysis <br /> i <br /> On June 21 , 1993, Aegis personnel collected groundwater samples from the five <br /> accessible wells at the site The samples were collected according to the Aegis SOP <br /> included in Appendix A, and submitted under chain-of-custody to Pace Incorporated of <br /> Novato, California, a state-certified analytical laboratory The samples were analyzed for <br /> a) TPH-G by modified EPA Method 8015, and, <br /> b) BTEX by modified EPA Method 8020 <br /> Laboratory analytical reports did not indicate petroleum hydrocarbons in any of the five <br /> wells sampled on June 21, 1993 The recent and historical analytical results are <br /> summarized in Table 3 The analytical reports and chain-of-custody form are included <br /> in Appendix C Figure 7 shows the well locations and sampling results <br /> 6.0 CONCLUSIONS <br /> The data collected from the confirmation borings demonstrated that soil vapor extraction <br />' has reduced petroleum hydrocarbon concentrations in the soil Although petroleum <br /> hydrocarbon constituents were present from 16 to 36 feet below grade in SB-9, no <br /> benzene was detected This indicates the success of vapor extraction in removing the <br /> more volatile and mobile hydrocarbon compounds <br /> i <br /> 1 93 005C QMR 5 <br />