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12 February 1999 <br /> • AGE-NC Project No. 95-0109 <br /> Page 3 of 4 <br /> 3.2. MICROBIOLOGICAL ACTIVITY IN GROUND WATER <br /> Concentrations of dissolved oxygen increased in all wells measured at the site since the September <br /> 1998 monitoring event. Dissolved oxygen concentrations were similar to those observed during the <br /> June 1998 monitoring event, following addition of hydrogen peroxide to monitoring wells. <br /> 3.3. PETROLEUM HYDROCARBON-IMPACTED GROUND WATER <br /> During the December 1998 monitoring event, petroleum hydrocarbons were detected in ground <br /> water samples from four of the seven wells sampled. TPH-g concentrations ranged from below <br /> laboratory method detection limits to 3,400 parts per billion(ppb; reported as micrograms per liter). <br /> Benzene, ethylbenzene and xylenes were detected at concentrations as high as 13 ppb, 170 ppb and <br /> 130 ppb,respectively.Toluene was not detected The highest concentrations were detected in samples <br /> collected from MW-8 and MW-9. The results of analysis by EPA Method 602 for the December <br /> 1998 monitoring event are presented on Table 3. Historical analytical results by EPA Method 602 <br /> are presented in Table 4. <br /> • Oxygenated compounds were not detected in the samples collected during the December 1998 <br /> sampling event. 1,2-Dichloroethane (1,2-DCA) was detected in MW-7, MW-9, and MW-14 at <br /> concentrations ranging from 36 ppb to 59 ppb. Seven additional analytes, detected by EPA Method <br /> 8260,are noted in Table 5. The laboratory report(MAI Laboratory I. D.Nos. 00784 through 00790) <br /> and chain-of-custody forms are included in Appendix B. <br /> 4.0. DISCUSSION AND CONCLUSIONS <br /> Based upon data collected from the site, AGE finds: <br /> • Ground water elevation increased at the site during the fourth quarter of 1998. Ground water <br /> flow direction continues to be toward the south-southwest at the site. A ground water around <br /> was observed near MW-9. Recharge may be occuring north of MW-9 on the former Lincoln <br /> School property. <br /> • Hydrocarbon concentrations decreased or remained stable in all wells sampled during the <br /> fourth quarter of 1998. <br /> • Oxygenates were not detected during the December 1998 monitoring event. <br /> • Concentrations of dissolved oxygen had increased by the June 1998 monitoring event, <br /> following the additions of hydrogen peroxide, compared to previously obtained data. <br /> Advanced GeoEnviron mental,Inc. <br />