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• Ozone Microsparge System Pilot Test Status Report, Former Unocal Service Station No 0187, Stockton,CA April 28,2003 • On December 8, 2000, the last sampling event before the test, TPHg concentrations in well NP-2-22 were reported to be 520 ppb On the August 12, 2002 quarterly monitoring event, TPHg concentrations in NP-2-22 decreased to below the reporting limit and remained below the reporting limit for the remainder of the test period,as shown on Graph 4 • Baseline TPHg concentration in well NP-2-60 was 12,000 ppb on December 8, 2000 Between December 19, 2000 and February 6, 2003, TPHg concentrations fluctuated between 20,000 ppb and less than the reporting limit, as shown on Graph 5 On February 6, 2003, TPHg concentrations in well NP-2-60 were 2,600 ppb,which is below the baseline concentration • In well NP-2-116,TPHg concentrations remained near the baseline concentrations during the duration of the test period • Baseline TPHg concentration in well U-3 was 12,300 ppb After approximately six months of system operation, the TPHg concentration decreased to non-detect TPHg concentrations in well U-3 were below the reporting limit during the remainder of the test period except on sax occasions,as shown on Graph 7 • TPHg concentrations in well U-10 decreased from 383 ppb at the test baseline to be at or slightly above the reporting limit, as shown on Graph 8 • Benzene Concentration Trends • As shown on Graph 1, benzene concentration in well NP-1-22 decreased from 740 ppb (baseline) to less than the reporting limit • As shown on Graph 2, benzene concentration in well NP-1-65 decreased from 2,000 ppb(baseline)to 120 ppb • As shown on Graph 3, benzene concentrations in well NP-1-111decreased from 4 8 (baseline) to below the reporting limit on February 6,2003 • At the test baseline, the benzene concentration in well NP-2-22 was 14 ppb Between the beginning of the pilot test and the installation of additional sparge points,benzene concentrations remained at or near the baseline concentration Following the installation of additional sparge points, benzene concentrations decreased to below the reporting limits, as shown on Graph 4 • Baseline benzene concentration in well NP-2-60 was 4,300 ppb on December 12, 2000 For the duration of the test period, benzene concentrations remained at or near the baseline concentration, as shown on Graph 5 • In well NP-2-116, benzene concentrations remained near the baseline concentrations during the duration of the test period, as shown on Graph 6 24004211-2 5