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` Ozone Microsparge System Pilot Test Status Report, Former Unocal Service Station No 0187, Stockton,CA <br /> Apnl 28, 2003 <br /> • Baseline benzene concentration in well U-3 was 515 ppb After approximately six months of system <br /> operation, the benzene concentration decreased to non-detect Benzene concentrations in well U-3 <br /> were less than the reporting limit during the remainder of the test period except on four occasions, as <br /> shown on Graph 7 <br /> • Benzene concentrations in well U-10 decreased from 57 9 ppb at the test baseline to beat or near the <br /> reporting limit, as shown on Graph S <br /> Discussion of Results <br /> A summary of the results of the ozone microsparge pilot test is as follows <br /> • Sample results from wells NP-1-22,NP-1-65,NP-1-111, NP-2-22, U-3,and U-10 indicate that ozone <br /> microsparge treatment has been effective at decreasing petroleum hydrocarbon concentrations in <br /> groundwater near these wells <br /> • Hydrocarbon concentrations in well NP-2-60 and NP-2-116 have remained at baseline concentrations <br /> CONCLUSIONS AND RECOMMENDATIONS <br /> The ozone microsparging system has been effective in reducing dissolved hydrocarbon concentrations in <br /> . the groundwater at this site GR recommends that operation of the treatment system be continued and <br /> further groundwater sampling performed to confirm the system's effectiveness GR also recommends an <br /> additional system status report be prepared at the end of the third quarter 2003 <br /> i <br /> 24004211-2 6 <br />