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Ozone Microsparge System Pilot Test Status Report,Former Unocal Service Station No.0187, Stockton,CA November 19,2003 • Between March and September 2003,TPHg concentrations in well NP-1-i 11 has remained below the reporting limit with the exception of one occasion of detectable concentration, as shown on Graph 3. • 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 until the April 22, 2003 event. During the April 22, 2003 event, TPHg concentration of 170 ppb were detected in well NP-2-22. Between May and September 2003, three occasions of detectable concentrations of TPHg were reported in N-2-22. • 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. Between February and September 2003, TPHg concentrations fluctuated between 2,600 and 59 ppb. On September 18, 2003, TPHg concentrations were reported to be 550,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. Between February and . September 2003, TPHg concentrations fluctuated between 530 and less than the reporting limit, 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 concentrations in well NP-1-22 decreased from 740 ppb (baseline)to at or slightly above the reporting limit of 0.05 ppb. • As shown on Graph 2, benzene concentrations in well NP-1-65 decreased from 2,000 ppb (baseline)to 23 ppb. • As shown on Graph 3, benzene concentrations in well NP-1-11Idecreased from 4.8 (baseline) to below the reporting limit. • At the test baseline, the benzene concentrations in well NP-2-22 was 1.4 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 concentrations in well NP-2-60 was 4,300 ppb on December 12, 2000. For the majority of the test period,benzene concentrations remained at or near the baseline concentration, as shown on Graph 5. 240042.11-3 5