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in each well except BM-10. The sample from BM-10 was broken during transportation to the laboratory. Ferrous iron is generated by microorganisms which convert ferric iron to ferrous iron during the metabolization of hydrocarbons. ' Normally ferrous iron is not present in groundwater and its presence is an indication of natural bioremediation. Although the ferrous iron levels are slight apparently some bioremediation is occurring. Nitrates and Sulfates are normally present in groundwater and microorganisms use these chemicals when metabolizing hydrocarbons. The highest level found for nitrates was 12 mg/L in BM-11 . All the other levels were around 2 mg/L. The depression over the site is an indication of natural bioremediation. The highest ' sulfate level was 63 in well BM-4. It appears that bioremediation 1s taking place selectively especially in the western portion of the site. Dissolved oxygen is used by microorganisms during aerobic metabolization. Usually the core of the hydrocarbon plume have very low levels. This is the case although we do not have wells upgradient which presumably would have higher levels of oxygen. Water can contain about 8 to 9 mg/L of oxygen if there is no bioremediation taking place. The fact that well BM-11 has a higher level is probably indicative of fresh non-plume water mixing with the lower plume water farther away from the main plume. See Figures 2 through 5. CONCLUSIONS The next quarterly monitoring will take place in January, 1997. We expect to install the vapor extraction/thermal oxidization system this quarter. The site where the Thermal Oxidizer is in use has been closed and we are negotiating with PG&E to install i a natural gas line to operate the burner. 1 Yours truly, ohn Cussen ,o�� Reg. Environmental Assessor #1979 N0,66M RG #6506 aF I Incl . 1 Water Analysis q P 1 Chain of Custody �OFCRIVIP OR 9 Sampling reports. r 1 Plots. cc: Mr. Roger Liston, Darpetro, Inc. Mr. G.L. Boggs, RWQCB Page 2 w