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r ' 61 10 January 1998 AGE-NC Project No 95-0142 Page 4 of 5 r _ Both water samples were found to lack detectable concentrations of nitrogen, a vital nutrient to ' support a microfauna for bioremediation Under the present circumstances, natural attenuation by bioremediation is not likely to occur 3 3 ANALYTICAL RESULTS OF PURGED WATER SAMPLES IDetectable concentrations of TPH-g were present in the sample colIec#ed from the barrel of purge water stored on-site BTE&X compounds were detected at concentrations as high as 23 ppb(xylene) ' The laboratory report (MAI Laboratory I D No 84184), chain-of-custody and QA/QC report are included in Appendix B ' 4.0. SUMMARY 1 CONCLUSIONS ' Based upon data collected from the site, AGE concludes • Ground water flow direction vanes from northeast to southeast, but is generally eastward in _ the vicinity of the hydrocarbon release(TK 1-90),therefore well MW-5 represents the down- gradient well at the site ' 0 With ground water well above the slotted intervals of ground water monitoring wells MW-1 through MW-3, these wells may not have been adequate to characterize the dissolved-phase hydrocarbon plume The well-placed screen intervals of wells MW-4,MW-5 and vapor wells ' VW-1 through WV4 were adequate to characterize the dissolved-phase hydrocarbon plume t • Detectable concentrations of hydrocarbons were present in both down gradient wells MW-4 ' and MW-5 The concentration of TPH-g and benzene in MW-5 appears to be declining slightly over the last four monitoring quarters, while the concentrations in MW-4 appear to be fluctuating between low concentrations and undetectable concentrations, suggesting that ithe well is at the margin of the dissolved hydrocarbon plume • The highest concentration of dissolved petroleum hydrocarbons remains in the area of the documented release(vapor well VW-1), located immediately adjacent to the former TK1-90 UST Concentrations of TPH-g and BTE&X in the ground water samples collected from vapor wells VW-2 and VW-4 have remained similar to the concentrations in samples also ' collected during the previous quarter, while hydrocarbon concentrations decreased-in the sample collected from VW-3 I I } • The dissolved hydrocarbon plume margins are not well delineated north,west and southwest of VW-4 or south of VW-1. The estimated dissolved hydrocarbon plume is depicted in Figure 4 r Advanced Geo£nvironmental,lnc. 1 ,