ARCHIVED REPORTS XR0001724 - Laserfiche WebLink

Home Browse Search

19 July 1996 AGE-NC-95-0109 Page 4of6 3.3. GROUND WATER GRADIENT AND DIRECTION The depth to ground water ranges from 54.8 feet below surface grade (bsg) at the north end of the site to 56.8 feet bsg south of the site. The data indicates an average drop of ground water elevation of 0.45 feet since March 1996. Ground water elevations are summarized on Table 5. ' Ground water elevation contours, based upon data collected on 17 June 1996, 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. I ' 3.4. PETROLEUM HYDROCARBON-IMPACTED GROUND WATER In April 1996, TPH-g was detected in MW-14 at a concentration of 2,800 ,ugll (micrograms per liter or parts per billion: ppb); BTE&X were detected in MW-14 at concentrations ranging from 19 ppb (ethyl benzene) to 350 ppb (xylenes). Only xylene was detected in EW-i at a concentration of 0.85 ppb in April 1996. In May 1996, TPH-g was detected in MW-14 at a concentration of 1,700 ppb. BTE&X were detected at concentrations ranging froze. 9.2 ppb (ethyl benzene) to 120 ppb (xylenes). Petroleum hydrocarbons were not detected in the sample from EW-I during the May monitoring. During the June 1996 sampling, petroleum hydrocarbons were detected in ground water samples from six of the ten wells sampled. TPH-g concentrations ranged from below detection limits to 11,000 ppb (MW-9); detectable BTE&X concentrations ranged up to 430 ppb (ethylbenzene, MW- 9). TPH-g and BTE&X were not detected in samples fro3n MW-6, MW-10, MW-12 and MW-13 during the June 1996 sampling. Between March and .lune 1996, TPH-g concentrations increased in six of the ten wells sampled and remained below detection limits in four wells sampled. Benzene concentrations increased in one well, decreased in two wells and remained undetectable in the remaining seven wells. Charts 8 - 13 (Appendix E) illustrate benzene concentrations verses time for monitoring wells MW-6, MW-8, MW-9, MW-10, MW-14 and EW-1. EDB was detected in the sample from MW-14 at a concentration of 1.0 ppb. 1,2-Dichloroethane was detected in samples from EW-1, MW-8, MW-9, MW-13 and MW-14 at concentrations of 1.2 ppb, 1.8 ppb, 47 ppb, 1.5 ppb and 240 ppb, respectively. This is a concentration increase in four of seven wells compared to the previous monitoring results. Chloroethane, tetrachloroethene and other volatile halocarbons were not detected in any of the water samples analyzed. Analytical results of ground water samples are summarized on Tables 6 and 7. The laboratory report (MAI Laboratory I. D. Nos. 64509, 64510, 65386, 63587 and 66164 through 66173) and chain-of-custody forms are included in Appendix D. I