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dliy O'1VJ • 20 October 1997 AGE-NC Project No. 95-0109 Page 3 of 5 3.2. MICROBIOLOGICAL ACTIVITY IN GROUND WATER Microbiological plate counts decreased in the ground water sample collected from MW-9 during the third quarter of 1997. General plate counts increased in MW-14, but selective degraders decreased. Nutrient concentrations generally decreased in MW-14 and MW-9, however, specific nutrients showed an increase during the past quarter. Nitrate was detected in MW-9 and MW-14 at concentrations of 0.1 ppm and 2.8 ppm, respectively. Nitrite was detected in MW-9 and MW-14 at concentrations of <0.1 ppm and 7.0 ppm, respectively. Absolute numbers of both plate counts and nutrients remain below optimum levels. Total nitrogen concentrations of 10 parts per million (ppm) to 20 ppm are preferred, and concentrations as high as 100 ppm are acceptable for maximum biodegradation. These data indicate that site conditions are less than optimal to promote biologic breakdown of the hydrocarbon contaminants. Chemical and microbiological data for ground water are summarized on Table 2 and Table 3. The laboratory report (A. Keith Kaufman - 24 September 1997) and chain-of-custody form are included in Appendix B. 3.3. PETROLEUM HYDROCARBON-IMPACTED GROUND WATER During the September 1997 sampling event, petroleum hydrocarbons were detected in ground water samples from five of the seven wells sampled. TPH-g concentrations ranged from below laboratory method detection limits to 8,600 parts per billion (ppb; reported as micrograms per liter). BTE&X were detected at concentrations as high as 260 ppb benzene (MW-14), 180 ppb toluene (MW-14), 550 ppb ethylbenzene (MW-9), and 440 ppb xylenes (MW-14). TPH-g and BTE&X were not detected in samples collected from MW-6 or MW-12 during the September 1997 sampling. Hydrocarbon concentrations decreased in four of the wells sampled, increased in one well (MW-9) and remained non-detect in two wells sampled. Charts I - 6 (Appendix C) illustrate benzene concentration verses time for monitoring wells MW-6, MW-8, MW-9, MW-10, MW-14 and EW-1. Oxygenated compounds, including MTBE, were not detected in the samples collected during the September 1997 sampling event. 1,2-Dichloroethane was detected in MW-8 and MW-9 at concentrations of 2.4 ppb and 160 ppb, respectively. Isopropylbenzene was detected in MW-8 and MW-9 at concentrations of 8.5 ppb and 140 ppb, respectively. 1,2,4-Trimethylbenzene was detected in MW-8, MW-9 and MW-14 at concentrations of 73 ppb, 760 ppb and 110 ppb, respectively. 1,3,5- Trimethylbenzene was detected in MW-8,MW-9 and MW-14 at concentrations of 6.8 ppb, 200 ppb and 20 ppb, respectively. Vinyl Acetate was detected in MW-8 at a concentration of 3.0 ppb. Other analytes included in EPA method 8260 were not detected. Analytical results of ground water samples are summarized on Tables 4 and 5. The laboratory report P Advanced GeoEnvironmental,Inc.