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10 May 1999 ... AGE-NC Project No. 95-0103 Page 4 of 6 MTBE was detected in the samples collected from wells MW-1 and MW-4 at concentrations of 2.3 — and 7.5 /ig/l; sample MW-4 was not analyzed by EPA Method 8260 to confirm the MTBE. DIPE was detected in samples collected from wells MW-3, MW-5 and vapor well VE-6 at concentrations of 74µg/1, 47 µg/l and 54,ug/l, respectively. ETBE, TBA and TAME were not detected in samples collected from the site. The analytical results of current and previous samples are summarized in Table 2 and Table 3. The laboratory report (MAI sample ID Numbers 08263 through 08270), quality assurance and quality control (QA/QC) data and chain-of-custody form are included in Appendix B. 3.3. IN-SITU AIR SPARGING Elevated concentrations of dissolved oxygen were detected in the ground water samples from monitoring wells MW-1 and MW-4, and the ASO wells as compared to off site wells representing background dissolved oxygen concentrations. Over the last quarter of IAS injection, the dissolved oxygen concentrations for wells and MW4,were — once measure to be as high as 92.8%and 111.2%,respectively. The more distal dwarf-gradient wells MW-2,MW-6,MW-3,MW-5 and MW-7 had lower dissolved oxygen concentrations of 1.2%, 1.9%, 2.5%, 18.2% and 8.7%, 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. 3.4. 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 180 scfm during the period. An induced vacuum (negative pressure) of 40 to 45 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-I to MW-3, with a transmitted vacuum force (potential) of 0.27 inches of water. TPH-g and BTEX were not detected in the three soil vapor samples collected from the site. The laboratory report (MAI Lab ID No. 04535 and 09613 and 09614), Quality Assurance and Quality Control (QA/QC) reports and chain-of-custody form are included in Appendix C. Advanced GeoEnNironmenNI,Inc.