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• Ozone Microsparge System Pilot Test Status Report,Former Unocal Service Station No. 0187,Stockton,CA November 19,2003 Groundwater Sampling System effectiveness was monitored by collecting groundwater samples from nested piezometer wells NP-1 and NP-2 and groundwater monitoring wells U-3 and U-10 (Figure 2). Each of the piezometer well contains three 1-inch diameter wells screened at three different depths. Both medium and deep screen intervals in well NP-1 are within the zone of influence of one or more sparge points. The shallow screen interval in well NP-1 is approximately 5 feet above the level of the shallow sparge points. The shallow, medium, and deep screen intervals in well NP-2 are also within the zone of influence of one or more sparge points. The screened interval in well U-3 is within the zone of influence of one or more sparge points. The screened interval in well U-10 is within the zone of influence of sparge point SP-SA. Well U-10 and the deep screen interval in well NP-2 are screened at approximately the. same depth interval. Well depths, screen intervals, and screen lengths for ozone sparge wells and monitoring wells are included in Appendix A Wells NP-1 and NP-2 have been sampled as part of the ongoing quarterly groundwater monitoring program since February 5, 1999. Well U-3 has been sampled as part of the ongoing quarterly monitoring program since August 19, 1994. Well U-10 has been sampled as part of the ongoing quarterly monitoring program since May 31, 2000. For the current pilot test, the wells were sampled prior to beginning operation of the system; and the grab sampling was performed monthly. All samples were analyzed for TPHg by EPA method 8015, and for benzene, toluene, ethylbenzene, and xylenes(BTEX), and MtBE by EPA method 8020. Graphical representations of the sampling during the test period are included in Appendix B. Sample results from the ongoing quarterly groundwater monitoring and sampling program were also used for system evaluation(Appendix Q. Groundwater Sampling Results Wells used in evaluating the system effectiveness were wells NP-1-22,NP-1-65,NP-1-111,NP-2-22,NP- 2-60, NP-1-116, U-3, and U-10. These wells are near sparge points and screened at approximately the same depths. The primary constituents of concern at this site are TPHg and benzene. The following discussion is based on groundwater sampling data collected over the course of the test, from November 11, 2000 through September 18,2003 (Table 1). The sample results taken before the system startup were used as the baseline for evaluating treatment effectiveness. Sampling results were generally positive,with significant decreases in petroleum concentrations in many areas. Historical groundwater chemical analytical data prior to November 11, 2000 is included in Appendix C. Laboratory analytical reports and chains-of-custody for the monthly sampling are included as Appendix D. TPHg Concentration Trends • Between Marchand September 2003, TPHg concentrations in well NP-1-22 remained below the reporting limit with the exception of four occasions of detectable concentrations, as shown on Graph 1. • TPHg concentrations in NP-1-65 decreased from 33,000 at test baseline to 1,100 ppb, as shown • on Graph 2. 240042.11-3 4