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3.6 2008 DUAL-PHASE EXTRACTION (DPE) PILOT TESTING <br /> During April 2008, three DPE wells (MW-37, MW-38, and MW-39) and two observation <br /> wells (P-1 and P-2) were installed for pilot testing purposes. During May 2008, DPE <br /> pilot testing was performed. The pilot test results demonstrate that DPE is technically <br /> feasible at this site. However, based on the groundwater production rate and <br /> drawdown profile, a DPE system would require several closely spaced extraction wells <br /> for adequate coverage in each source area. This well array would result in significant <br /> groundwater production and require handling, treatment, and disposal (CRA, <br /> September 30, 2008). CRA prepared a remedial action plan (RAP) proposing DPE <br /> system installation(CRA,December 15,2008). <br /> 3.7 2009 AIR SPARGE (AS)/SVE PILOT TESTING <br /> In CRA's February 13, 2009 report, we recommended evaluating AS/SVE as a remedial <br /> option. During April 2009, CRA conducted an AS/SVE pilot test. CRA concluded that <br /> AS/SVE would be technically feasible and preferable to DPE (CRA, October 30, 2009). <br /> CRA prepared a revised RAP proposing AS/SVE system installation (CRA, <br /> January 19,2010). <br /> 4.0 DISTRIBUTION OF COCs <br /> 4.1 HYDROCARBON DISTRIBUTION IN SOIL <br /> Hydrocarbon-impacted soil is present on site, with maximum concentrations of <br /> 4,400 milligrams per kilogram (mg/kg) TPHd, 4,100 mg/kg total petroleum <br /> hydrocarbons as gasoline (TPHg), and 2.7 mg/kg benzene detected in vadose-zone soils <br /> near the loading rack. Up to 1,500 mg/kg TPHg was also detected in the source area <br /> near Tank 14. As previously presented in the investigation reports submitted by <br /> Groundwater Technology, 1986; Law Engineering, 1988; Harding Lawson Associates, <br /> 1993; Pacific Environmental Group, 1994 and 1995; and TOXICHEM Management <br /> System, 2000 and 2001; off-site subsurface investigations have adequately defined the <br /> horizontal extent of these soil impacts. The vertical extent of impacted soil extends to <br /> groundwater. Available soil analytical data are presented on Table 4, and soil sampling <br /> locations are shown on Figure 2. <br /> 241729(33) 7 CONESTOGA-ROVERS&ASSOCIATES <br />