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Semi-Annual Groundwater Monitoring and Quarterly Remediation Progress Report-First Quarter 2013 April 30, 2013 Project#52.75118.2390 Page 4 (SP-1 through SP-10, screened in the A-Zone). On February 27, 2012, the OS system was shut-down due to the ozone conveyance tubing becoming cracked and brittle over time. ATC requested permission to keep the system off-line indefinitely, citing the lack of dissolved-phase petroleum hydrocarbons in the A-Zone. ATC's request was approved in a SJCEHD letter dated February 28, 2012. The OS system did not operate during the current reporting period. Cumulatively, the OS system has operated for 53,021 hours and has injected a total of approximately 477.2 lbs of ozone. 4.0 Discussion / Conclusion 4.1 A-ZONE During the First Quarter of 2013, all wells screened in the A-Zone were sampled; MW-1, MW-3, MW-4, MW-8, MW-9, MW-10, MW-12, and MW-13. A groundwater concentration map for the A-Zone is provided as Figure 7. Dissolved GRO Distribution GRO has historically been detected in MW-1, MW-3, MW-4, MW-8, MW-10, MW-12 and MW-13, with the highest concentration reported at 180,000 pg/L in MW-3 in 2001. GRO was not detected above the laboratory PQL in any A-Zone well during the First Quarter 2013. According to the sampling results provided by CRA for the former Shell service station, TPPH (equivalent to GRO)was present in three of the off-site wells S-1, S-2, and S-10 at concentrations up to 3,900 pg/L (S-2). Dissolved BTEX Distribution BTEX constituents have historically been detected in MW-1 through MW-3, with the highest concentration of benzene reported at 470 pg/L in MW-3 in 2001. BTEX was not detected above laboratory PQLs in any A-Zone well during the First Quarter 2013. According to the sampling results provided by CRA for the former Shell service station, benzene was present in one off-site well S-10 at concentrations of 700 pg/L. Dissolved MTBE Distribution MTBE has historically been detected in MW-1, MW-3, MW-4, MW-9, MW-12, and MW-13, with the highest concentration reported at 200,000 pg/L in MW-3 in 2001. MTBE was not detected above laboratory PQL in any A-Zone well during the First Quarter 2013. According to the sampling results provided by CRA for the former Shell service station, MTBE was detected in one A-Zone monitoring well S-10 at a concentration of 6.8 pg/L. Dissolved TBA Distribution TBA has historically been detected in MW-1, MW-3, MW-9, MW-12, and MW-13, with the highest concentrations reported at 240,000 pg/L in MW-3 in 2002. During First Quarter 2013, TBA was detected above the laboratory PQL in one A-Zone well MW-3 at a concentration of 26 pg/L, a decrease from recent detections. According to the sampling results provided by CRA for the former Shell service station, TBA was not detected in the one A-Zone monitoring well analyzed for the presence of TBA (S-10) during the First Quarter 2013.