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17 August 1998 <br /> AGE-NC Project No 95-0103 <br /> ' Page 4 of 7 <br /> ' 1,100 parts per billion(ppb,reported as micrograms per liter), 9,000 ppb, 30,000 ppb and 500 ppb, <br /> respectively <br /> Benzene was detected in wells MW-l. MW-3 and MW-4 at concentrations of 24 ppb, 170 ppb and <br /> 2,700 ppb,respectively Benzene was not detected in wells MW-2,NNW-5,MW-6 and MW-7 Other <br /> BTE&X compounds were detected in wells MW-1, MW-3, MW-4 and MW-5 at concentrations as <br /> high as 4,800 ppb Ethylbenzene and xylenes were detected in well MW-4 at concentrations of 850 <br /> ppb and 3,900 ppb,respectively Petroleum hydrocarbons were not detected in the samples collected <br /> from wells MW-2, MW-6, and the eastern most well MW-7 <br /> MTBE was detected in the samples collected from well MW-I at a concentration of 38 ppb, DIPE <br /> ' was detected in samples collected from wells MW-3 and MW-5 at concentrations of 26 ppb and 46 <br /> ppb,respectively, TBA was detected in the samples collected from wells MW-1 at a concent]ation <br /> of 29 ppb ETBE or TAME were not detected in samples collected from the site <br /> ' The analytical results of current and previous samples are summarized in Table 2 and Table 3 The <br /> laboratory report(MAI sample ID Numbers 91469 through 91475) and chain-of-custody forms are <br /> included in Appendix B <br /> ' 34 IN-SITU AIR SPARGING <br /> Elevated concentrations of dissolved oxygen were detected in monitoring wells MW-1 and MW-4, <br /> and well ASO-2 Dissolved oxygen concentrations in the remaining wells showed only slight <br /> changes The greatest changes of dissolved oxygen content were observed in monitoring wells closer <br /> ' to the sparging wells/points <br /> Since the initiation of in-situ air sparging began at the site in April 1997, the average dissolved <br /> ' oxygen concentrations for wells ASO-1, MW-I and ASO-2 were 94%, 72%and 45%, respectively <br /> Wells MW-2 and MW-4 have had average dissolved oxygen concentrations of 13%and 7%, while <br /> the more distal down-gradient wells MW-6,MW-3 and MW-5 have had average dissolved oxygen <br /> ' concentrations of 5%,3 6% and 4 3%, respectively The dissolved oxygen data is summarized on <br /> Table 4 Sparging rates were measured at approximately 10 scfm during each monitoring event A <br /> minimum pressure of 15 psi was maintained for the air sparging flow rate <br /> 3 5. SOIL VAPOR EXTRACTION <br /> ' The SVE unit operated at varying rates during this quarter Extraction flow rates were calculated to <br /> range from 180 to 190 scfm Typically, the operation averaged 180 scfm during the period An <br /> Advanced GeoEnvironmental,Inc <br />