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01 March 1999 AGE-NC Project No. 95-0103 Page 5 of 8 3.3. IN-SITU AIR SPARGING Elevated concentrations of dissolved oxygen were detected in monitoring wells MW-1 and MW-4, and the ASO wells, on-site as compared to off site wells representing background dissolved oxygen concentrations. Over the last quarter of IAS injection,the dissolved oxygen concentrations for wells ASO-1, MW-1, ASO-2 and ASO-3, were once measure to be 51.5%, 77.1%, 46.6% and 70.2%, respectively. Over the last quarter well MW-4 had a high dissolved oxygen concentrations of 88%. The more distal _ down-gradient wells MW-2, MW-6, MW-3, MW-5 and MW-7 had high dissolved oxygen concentrations of 4.2%, 4.3%, 3.1%, 28% and 8.9%, respectively. The dissolved oxygen data is summarized on Table 4. Sparging rates were measured at approximately 10 scfm during each monitoring event.A minimum pressure of 12 psi was maintained for the air sparging flow rate. 3.5. SOIL VAPOR EXTRACTION The SVE unit operated at varying rates during this quarter. Extraction flow rates were calculated to range from 180 to 185 scfm. Typically, the operation averaged I80 scfm during the period. An induced vacuum (negative pressure) of 40 inches of water was measured in the piping between the blower and extraction wells. The radius of a measurable vacuum at the outlying wellheads was noted to extend 90 feet from VW-1 to MW-3, with a transmitted vacuum force (potential) of 0.27 inches of water. TPH-g was detected in one sample collected on 30 December 1998 from the influent vapor stream at a concentration of 100 4g11. This sample was collected with well VE-6 in the soil gas/vapor network. BTEX compounds were detected in the soil gas/vapor samples. The analytical results of soil-vapor samples are summarized on Table 5. The laboratory report (MAI Lab ID No. 01151 and 01152), Quality Assurance and Quality Control (QA/QC) reports and chain-of-custody forms are included in Appendix B. 3.6. MASS OF RECOVERED HYDROCARBONS The hydrocarbon mass removed during the operating period was calculated using the following equation: M= C•Q•t where: M=cumulative mass recovered (kg) Advanced GeuEnvirunmental,Inc.