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1 <br /> ' 3.0 CONCLUSIONS AND RECOMMENDATIONS <br /> 1 Following the 90-day OS pilot test, well GWX-1 showed TPHg, BTEX and naphthalene concentrations <br /> that either are or are near historic lows. These decreases in contaminant concentration support that the <br /> i OS System was effective in delivering ozone to the aquifer system beneath the Site. It is our opinion <br /> that the result for well GWX-1 is most similar to what would reasonably be expected with a full-scale <br /> OS system using new, appropriately screened sparge wells. Of the onsite monitoring wells situated <br /> 1 within the source area, GWX-1 is the only one screened across the more recent groundwater surface. <br /> The lower effects of the OS System observed at wells MW-1 and MW-3 is likely attributable to those <br /> i wells being constructed for a groundwater surface that was approximately 25 feet deeper than the <br /> present surface, and thus completed with screen intervals beginning approximately 20 feet beneath the <br /> current groundwater surface. Even still, the decreasing trend in well MW-3 appears promising. <br /> 1 <br /> The supplemental sampling supports that the use of ozone will not result in by-products that would <br /> 1 adversely affect groundwater quality. Despite no significant increases of DO reported for any of the <br /> monitored wells, we believe this is due to the remaining contamination consuming the available <br /> 1 oxygen and we expect that with continued sparging, DO levels will increase. Based on the above <br /> results, we conclude that this pilot test has shown OS to be an effective method of groundwater <br /> remediation for the Site and recommend the installation of a full-scale OS system. <br /> 1 We continue to support our recommendation that each of the existing SVE wells with the exception of <br /> 1 VX-1 be appropriately destroyed. We would also now recommend the destruction of the five air-sparge <br /> wells as their construction material is not suitable to withstand a full-scale exposure to ozone. <br /> 1 Quarterly groundwater monitoring is scheduled to continue for the Site. Sample collection for the <br /> Second Quarter—2009 was completed on June 22. The Second Quarter—2009 groundwater monitoring <br /> 1 report is scheduled to be submitted to the CVRWQCB and the San Joaquin County Environmental <br /> Health Department(SJCEHD)by July 30,2009. <br /> 1 <br /> 1 <br /> 1 <br /> i <br /> 1 <br /> Project No.S9183-06-02 -9- July 2,2009 <br /> 1 <br />