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constituents near well MW-35 (RETEC, January 14, 2005). Eleven direct push borings <br /> (SB-9 through SB-19) were installed and depth-discrete groundwater samples were <br /> collected near well MW-35. Based on the groundwater analytical data,well MW-36 was <br /> installed. <br /> 2004-2005 Oxygen Injection Pilot Testing: During 2004, the feasibility of performing an <br /> oxygen injection pilot test was evaluated (RETEC, November 24, 2004). During 2005, <br /> several oxygen injection wells and down-gradient monitoring points were installed <br /> along the southern property boundary near wells MW-20, MW-21, and MW-22. As <br /> discussed in RETEC's February 6, 2006 report, the pilot testing was cancelled because <br /> the total petroleum hydrocarbons as gasoline concentrations were not low enough to be <br /> sufficiently reduced by oxygen injection. Alternatively, a temporary pumping system <br /> was proposed. <br /> 2006-Current Temporary GWE Operations: A temporary GWE system began operating <br /> on April 10, 2006. The GWE system pumps groundwater from well MW-1 using a top <br /> loading submersible pneumatic pump. Groundwater is stored in an on-site baker tank <br /> and vacuum trucks transport the water to Shell's Martinez refinery for recycling. <br /> 2007 and 2008 Subsurface Investigation: During December 2007, Conestoga-Rovers & <br /> Associates (CRA) installed seven vapor wells (V-1, V-2, V-4, V-5, V-6, V-8, and V-10) <br /> and three soil borings (V-7, SB-20, and SB-21) to assess the potential for vapor intrusion <br /> into indoor air at the commercial buildings and to assess soil impacts within the <br /> unsaturated zone(CRA,September 26,2008). <br /> During March 2008, CRA destroyed down-gradient well MW-27 to facilitate off-site <br /> construction(CRA,May 13,2008). <br /> During March and April 2008, CRA installed six soil borings (SB-22 through SB-27) to <br /> further assess soil and groundwater beneath and down gradient of the site (CRA, <br /> September 26,2008). <br /> 2008 Dual-Phase Extraction (DPE) Pilot Testing: During April 2008, three DPE wells <br /> (MW-37, MW-38, and MW-39) and two observation wells (P-1 and P-2) were installed <br /> for pilot testing purposes. During May 2008, DPE pilot testing was performed. The <br /> pilot test results demonstrate that DPE is technically feasible at this site. However, <br /> based on the groundwater production rate and drawdown profile,a DPE system would <br /> require several closely spaced extraction wells for adequate coverage in each source <br /> area. This well array would result in significant groundwater production and require <br /> 241729(33) A-3 CONESTOGA-ROVERS&ASSOCIATES <br />