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l� Interim Remedial Action Test Report,Former Unocal#0187,Stockton,CA August 15,2001 tubing was run through Schedule 40 PVC conveyance piping for added protection The process flow diagram is presented as Figure 5 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 times per day, for nine minutes per point per cycle There is an eight minute rest period between cycles This schedule was varied over the course of the test as part of the system evaluation process to provide more treatment to some areas The system is designed for continuous operation, other than the rest periods between cycles Generally the system has run as planned during the test However, there was some down time, generally as a result of loose wires caused by system vibration, and some instances of tubing failure Groundwater Sampling The effectiveness of the system was monitored by collecting groundwater samples from nested piezometer wells NP-1 and NP-2 Each of these contains three 1-inch diameter wells screened at three different depths Well NP-1 is near the former UST location at the southeast corner of the site, in the treatment area The medium and deep screen intervals in well NP-1 are both within the zone of influence of one or more sparge points The shallow screen interval in well NP-1 is approximately 40 feet above the level of the shallow sparge points Well NP-2 is located down gradient from the treatment area, across California Street,approximately 75 feet from the sparge points Wells NP-1 and NP-2 have been sampled as part of the ongoing quarterly groundwater monitoring program since February 5, 1999 For the current test,the wells were sampled on December 8,2001,prior to beginning operation of the system, the sampling was performed weekly for the first three months of the test and every two weeks since then Groundwater chemical analytical data through July 17, 2001 are included in this report (Table 1) All samples were analyzed for TPHg by EPA method 8015, and for benzene, toluene, ethylbenzene, and xylenes (BTEX), and MtBE by EPA method 8020 Sample results from the ongoing quarterly groundwater monitoring and sampling program were also used for system evaluation(Table 2) Sample results for on-site wells U-1, U-2, and U-3 are discussed below Graphical representations of the historical sampling results, as well as sampling during the test period are included in Appendices C and D, respectively Groundwater Sampling Results 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 December 8, 2000 through July 17, 2001 The sample results taken before the system startup were used as the baseline for evaluating treatment effectiveness Historical quarterly sampling data from wells U-1, U-2, and U-3 were also used for this evaluation Sampling results were generally positive, with significant decreases in petroleum concentrations in many areas 24004209-1 7