ARCHIVED REPORTS_FEASIBILITY STUDY AND CORRECTIVE ACTION PLAN

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supplemented with a soil vapor treatment (oxidizer or carbon adsorption) system. The treated vapor is discharged to atmosphere under the authorization of a permit to operate issued by the air pollution control district. Extracted groundwater is treated by an oil/water separator and carbon adsorption and discharged to the local sanitary sewer, storm drain, or land with the appropriate authorization, or off-hauled to a disposal facility. 5.3.1.2 FEASIBILITY During May 2008, CRA conducted a DPE pilot test to investigate feasible soil and groundwater remediation methods for the three source areas. DPE testing utilized various existing wells and the newly installed wells MW-37, MW-38, and MW-39. The results of the DPE test are summarized below: • The total vapor-phase mass removed from the extraction wells are as follows: 265 pounds of TPHg, 1.48 pounds of benzene, 0.43 pounds of toluene, 0.606 pounds of ethylbenzene, 1.51 pounds of total xylenes, and 0.218 pounds of MTBE. The majority of this mass was removed from well MW-37 because of the higher vapor concentrations and longer operational time. • The theoretical vacuum radius of influence is estimated to be only as much as 12.8 feet. • The pumping data suggest groundwater production between 3 and 4 gallons per minute (gpm). Groundwater production may be sourcing from the silty sand horizon,rather than the silts and clays,present below 20 fbg in wells P-1,MW-37, and MW-38. • Drawdown was more significant in P-1 when the electric pump was used for dewatering well MW-37. The water column in well MW-37 was dewatered to approximately 20 fbg. Approximately 2.5 feet of drawdown (to approximately 12.5 fbg) was observed in P-1, which is located approximately 18.5 feet from the extraction well MW-37. The drawdown profile is steep and deep. • The pilot test results demonstrate that DPE is technically feasible at this site. However, based on the groundwater production rate and drawdown profile, a DPE system will require several closely spaced extraction wells for adequate coverage in each source area. The DPE pilot test also showed that the groundwater yield was approximately 4 gpm per well and a steep groundwater drawdown profile. Based on the DPE radius of 241729(33) 13 CONESTOGA-ROVERS&ASSOCIATES