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18 June 1997 AGE-NC Project No. 95-0109 Page 3 of 6 3.0. FINDINGS 3.1. GROUND WATER GRADIENT AND DIRECTION The depth to ground water ranged from 54.1 feet below surface grade (bsg) at the north end of the site to 57.2 feet bsg south of the site. The data indicates an average decrease in ground water elevation of 1.65 feet since March 1997. Ground water elevations are summarized on Table 1. Ground water elevation contours, based upon data collected on 1 I June 1997, are depicted in Figure 3. The flow direction is towards the south and, as in previous monitoring events, the gradient steepens towards the south end of the site. The gradient also appears to be steeper north of the site during the June monitoring event. 3.2. MICROBIOLOGICAL ACTIVITY IN GROUND WATER Microbiological plate counts from ground water samples collected during the second quarter of 1997 showed a decrease in MW-14. Plate counts were fairly stable in MW-9. Nutrient concentrations generally increased in MW-14 and decreased in MW-9 during the past quarter. Absolute numbers of both plate counts and nutrients remain below optimum. 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. Chemical and microbiological data for ground water are summarized on Table 2 and Table 3. The laboratory report(A. Keith Kaufman-26 June 1997) and chain-of-custody form are included in Appendix B. 3.3. PETROLEUM HYDROCARBON-IMPACTED GROUND WATER During the June 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 7,400 parts per billion (ppb; reported as micrograms per liter). BTE&X were detected at concentrations as high as 400 ppb benzene (MW-14), 290 ppb toluene (MW-14), 190 ppb ethyl benzene (MW-9), and 1,300 ppb xylenes (MW-14). TPH-g and BTE&X were not detected in samples collected from MW-6 or MW-12 during the June 1997 sampling. Hydrocarbon concentrations increased in five of the wells sampled and remained non-detect in two wells sampled. Charts 1 - 6 (Appendix D) illustrate benzene concentrations verses time for monitoring wells MW-6, MW-8, MW-9, MW-10, MW-14 and EW-1. • MTBE was detected in the samples collected from MW-9 and MW-14 at concentrations of 5.2 ppb and 7.7 ppb, respectively. However, the laboratory noted that the detected constituent does not Advanced GeoEnviron mental,Inc.