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12 January 1998 • AGE-NC-95-0103 , Page 4 of 7 1 - - 3 3 IN-SITU AIR SPARGING- Slightly elevated concentrations of dissolved oxygen were detected in monitoring wells MW-1 and - ' MW-4,as well as in observation well ASO-2 Dissolved oxygen concentrations in the remaining wells showed no significant changes The greatest changes of dissolved oxygen content were observed in monitoring wells closer to the sparging wells Since the initiation of in-situ air sparging began at the site in April 1997, the average dissolved oxygen concentrations for wells ASO-1, MW-1 and ASO-2 were 102 6%, 78% and 44 5%, respectively Wells MW-2 and MW-4 have had average dissolved oxygen concentrations of 112% and 12 7% While the more distal down-gradient wells MW-6, MW-3 and MW-5 have had average ' dissolved oxygen concentrations of 5 5%,6 1% and 8 3%, respectively The dissolved oxygen data is summarized on Table 4 _ _ Sparging rates were measured at approximately 10 scfm during each monitoring event A pressure of approximately 15 psi was maintained for the air sparging flow rate -34 SOIL VAPOR EXTRACTION The SVE unit operated at varying rates during the current quarter Extraction flow rates were calculated to range from 150 to 160 scfm Typically, the operation averaged 150 scfm dur ng the _ period Operation of the unit was attempted at 200 scfm, the maximum operational rate of the unit, however the unit would automatically shut off, possibly due to lower oxygen levels than required for pre-heater combustion, or possibly due to a higher than tolerable vacuum load on the vacuum ® generator(blower) � - An induced vacuum (negative pressure)of approximately 28 to 30 inches of water was measured in the piping between the blower and extraction wells The radius of measurable vacuum at the outlying well-heads was noted to range from 0 07 inches of water at well MW-2 at approximately 90 feet from VW-1 to 30 inches of water at ASO-3 at VE-1 ' Two sets of extracted soilas samples mples were analyzed for TPH-g, BTE&X and methyl-tert-butyl ether(MTBE) and other oxygenated fuel additives tertiary butyl alcohol (TBA), di-isopropyl ether (DIPE),ethyl,tertiary butyl ether(ETBE)and tertiary amyl methyl ether(TAME)in accordance with EPA-methods 8015m and 8020 and 8260m TPH-g was detected in the 22 October 1997 sample collected from influent vapor concentration of 890 arts $r billion p stream at a __ _ p P (ppb,reported as micrograms per liter) B TE&X were detected ' at concentrations as high as 28 ppb (xylene) However, BTE&X confirmation by EPA method 8260 Advanced CeoEnvironmental,Inc