ARCHIVED REPORTS_FEASIBILITY STUDY AND CORRECTIVE ACTION PLAN

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quarter 2000,well MW-13 was added to the GWE system. During April 2001,the system was shut down due to more stringent NPDES permit requirements. During October 2003, the GWE system was restarted, and discharge to the sanitary sewer began. The pumping wells were MW-10, MW-15, and MW-16. The system operated intermittently until March 9, 2005 and has not discharged to the sanitary sewer since that time. A detailed description of GWE operations is presented in The RETEC Group,Inc.'s (RETEC's) January 30,2004 report. 3.3 1996 TO 2001 SOIL VAPOR EXTRACTION(SVE) OPERATIONS SVE began on April 16, 1996 and operated intermittently until May 23, 2001. The SVE system consisted of a Thermtech VAC-250 thermal oxidizer unit that was connected to wells MW-1, MW-11, MW-15, MW-16, MW-17, MW-23, and MW-24. The system was shut down due to high water levels and the lack of available vadose screen for SVE (RETEC,November 1,2004). 3.4 2004 TO 2005 OXYGEN INJECTION PILOT TESTING During 2004, the feasibility of performing an oxygen injection pilot test was evaluated (RETEC, November 24, 2004). During 2005, several oxygen injection wells and down-gradient monitoring points were installed along the southern property boundary near wells MW-20, MW-21, and MW-22. As discussed in RETEC's February 6, 2006 report, the pilot testing was cancelled because the total petroleum hydrocarbons as gasoline concentrations were not low enough to be sufficiently reduced by oxygen injection. Alternatively,a temporary pumping system was proposed. 3.5 2006 TO CURRENT TEMPORARY GWE OPERATIONS A temporary GWE system began operating on April 10, 2006. The GWE system pumps groundwater from well MW-1 using a top loading submersible pneumatic pump. Groundwater is stored in anon-site baker tank, and vacuum trucks transport the water to Shell's Martinez refinery for recycling. 241729(33) 6 CONESTOGA-ROVERS&ASSOCIATES