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Ozone Microsparge System Pilot Test Status Report, Former Unocal Service Station#2859,Stockton,CA June 6,2003 System Operation The system cycles ozone/air injection between eight specially designed micro-sparge points The schedule was initially set to cycle through each point 18 tunes per day, for nine minutes per point per cycle There is an eight minute rest period between cycles This schedule was vaned over the course of the test as part of the system evaluation process to provide more treatment to selected areas Groundwater Sampling System effectiveness was monitored by collecting groundwater samples from groundwater monitoring wells MW-2, MW-10, MW-11 and piezometer well NP-1 Wells MW-2, MW-10,MW-11, and NP-1 are located adjacent to the eastern property boundary of the site (Figure 2) Well MW-2 is screened from 20 to M feet bgs Wells MW-10 and MW-11 are screened from 50 to 60 feet bgs Well NP-1 is screened from 85 to 90 feet bgs The screened intervals of wells MW-2, MW-10, MW-11 and NP-1 are all within the zone of influence of one or more sparge points Well MW-2 has been sampled as part of the ongoing quarterly groundwater monitoring program since June 6, 1988 Wells MW-10 and NP-1 have been sampled as part of the ongoing quarterly monitoring program since February 1, 1999 Well MW-11 has been sampled as part of the ongoing quarterly monitoring program since June 6, 2001 For the current pilot test, the wells were sampled prior to system start-up and groundwater grab sampling was performed on a monthly basis thereafter All samples were analyzed for TPHg by EPA method 8015, and for benzene, toluene, ethylbenzene, and xylenes (BTEX), and MtBE by EPA method 8020 Graphs of analytical results and depth to water data from groundwater sampling during prior to and the test period are included in Appendix A Laboratory results and groundwater monitoring data from ongoing quarterly groundwater monitoring and sampling program were also used for system evaluation (Appendix B) Groundwater Sampling Results Monitoring wells used in evaluating the system effectiveness were MW-2, MW-10, MW-11 and nested piezometer well NP-1 The primary constituents of concern at this site are TPHg and benzene The following pilot test discussion and evaluation is based on groundwater sampling data collected, from August 9 and 10, 2002 through March 21, 2003 Sample results taken before the system startup were used as a baseline for evaluating treatment effectiveness TPHg Concentrations i • TPHg concentrations in MW-2 decreased from 45,000 ppb prior to system startup (baseline) to 940 ppb, as shown on Graph I • On August 9, 2002, the TPHg concentration in well MW-10 was 93,000 ppb (baseline) Within two months of operation, TPHg concentrations increased to 120,000 ppb (10/21/02 sampling event) Following the initial increase, TPHg concentrations decreased to 19,000 pbb, as shown on Graph 2 • In well MW-11, TPHg concentrations decreased from 23,000 ppb (baseline) to 8,800 ppb, as shown on Graph 3 240072 06 4