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FIELD PROCEDURES <br /> Alton Geoscience monitored and sampled ground water Monitoring Wells AW-1,AW-2,and <br /> AW-4 through AW-8 on July 20, 1992, and AW-3 and AW-9 on July 21, 1992. Alton <br /> Geoscience ground water monitoring and sampling protocol is presented in Appendix A. <br /> ' Ground water field survey forms including field measurements and observations are <br /> presented in Appendix B. <br /> Ground water samples were analyzed for total petroleum hydrocarbons as diesel and <br /> gasoline (TPH-D and TPH-G); and BTEX at Sequoia Analytical Laboratory, Concord, <br /> California. Official laboratory reports and chain of custody records are included in <br /> Appendix C. <br /> DISCUSSION OF RESULTS <br /> Laboratory results for this and previous ground water monitoring and sampling events are <br /> summarized in Table 1. A ground water elevation contour map for the July 1992 event is <br /> shown in Figure 3. Results of this event are summarized as follows: <br /> • to Average depth ground g p gr water was 10.91 feet, with an average hydraulic gradient <br /> of 0.012 foot per <br /> foot. The <br /> ground watergradient <br /> direction and magnitude have <br /> remained relatively consistent to the northeast since 1990. <br /> • TPH-G and BTEX were not detected at or above reported detection limits in any <br /> of the wells except benzene in AW-9 (0.74 ppb). <br /> • TPH-D was present only in AW-3 and AW-8 (870 ppb and 63 ppb). <br /> • The presence of TPH-D in AW-8 is not considered related to the former Mobil Bulk <br /> Plant. <br /> • It appears that concentrations of hydrocarbons in AW-3 and AW-9 may have <br /> decreased in response to interim remediation. <br /> ALTON GEOSCIENCE <br /> Stephan Rosen Peter C. , R.G. 89 <br /> Senior Geologist Associate, No hem California Operations <br /> i <br /> 2 <br />