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' Ms Mary Meays Page 3 September 11, 1997 All analyses were performed by Inchcape Testing Services (San Jose, California), ' with the exception of the plate counts, which were sent to Aquatic Biological Sciences of South Burlington,Vermont Laboratory data sheets and Chain-of- Custody forms associated with the December 1996 and May 1997 sampling ' events are included in Attachment C TPH as diesel and gasoline and BTEX compounds were detected in ground water ' samples collected from Former Tank Sites#1 and #2 at concentrations similar to those associated with recent sampling rounds These detections are summarized below and in Tables 1 and 2, respectively ' As discussed in previous correspondence, naturally-occurring microbes will degrade petroleum contaminants by utilizing nutrients present in the ' subterranean environment During biodegradation, microbes transform available nutrients into forms useful for energy and cell reproduction through the transfer of electrons Through this process, microbes utilize the electron ' acceptors (1 e , dissolved oxygen (DO), sulfate, and nitrate) to produce metabolites (i e , manganese (IV), iron (III), methane, and carbon dioxide) ORC socks were installed in eight wells to increase DO levels in ground water and ' thus enhance biodegradation of TPH Water quality parameters are presented in Tables 3 and 4 for the former tank sites #1 and #2, respectively As summarized below, these results indicate that the ORC sock installation is affecting water conditions as expected ' Former Tank Site #1 TPH and BTEX detections in ground water samples collected from the Former ' Tank Site #1 during the last two monitoring rounds are comparable to those associated with historical sampling events TPH(g) was only detected in the MW-4 and MW-5 samples, the highest detections were associated with MW-5 ' TPH(d) was detected at low concentrations in all of the wells, the highest detections were associated with MW-5 BTEX compounds were generally not detected during these last two sampling rounds The one exception,benzene, ' was detected in both of the MW-5 samples at concentrations comparable to previous sampling events Historical trend analysis indicates that TPH and ' BTEX concentrations have decreased significantly over time As presented in Table 3, the water quality measurements do not exhibit notable trends at this time, as evidenced by comparison of post-ORC to baseline (10/96) ' conditions The dramatic increase in heterotrophic plate count in the samples collected from MW-4 and MW-5 indicates that the presence of the ORC socks ' appears to be enhancing microbial activity Former Tank Site #2 TPH and BTEX detections in ground water samples collected from the Former Tank Site#2 during the last two monitoring events are comparable to those 1