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i <br /> Ms. Vicki McCartney Project No. 8800401A.0201 <br /> October 26, 2004 <br /> Page 10 <br /> DPE <br /> DPE involves removing soil vapor and groundwater from beneath the site via an <br /> �. extraction well utilizing a high vacuum liquid ring blower. The extracted groundwater <br /> would be disposed of utilizing existing sewer facilities and the extracted soil vapor is ! <br /> - treated before release to the atmosphere using a.thermal oxidizer. Based on the extent of <br /> groundwater and possible soil impact on-site, and the high vacuum applied by the DPE <br /> system, a majority of the subsurface impact could be removed in a reasonable period of <br /> time. Groundwater monitoring would continue for up to one year following completion <br /> of DPE activities to confirm mass reduction. <br /> Cost: $408,000.00 <br /> Time Frame: 4 years <br /> Advantages: ➢ Removal' of soil vapor can reduce residual and potential source <br /> ' hydrocarbon concentrations. <br /> ➢ Removal of hydrocarbon impacted groundwater can reduce dissolved <br /> hydrocarbon concentrations. <br /> >f <br /> ➢ Groundwater extraction can provide hydraulic control inhibiting further <br /> downgradient migration hydrocarbon plume. <br /> Disadvantages: ➢ Initial installation and operation costs for the DPE system could be high. <br /> ➢ Some disruption of station activities in order to install and operate the <br /> extraction system. <br /> l ➢ This method is slightly less protective -of the environmental as <br /> j hydrocarbon impacted groundwater is transported above ground, <br /> increasing risk of release to the environment. <br /> The rationale for selecting the preferred remedial alternative for restoring and <br /> protecting impacted or threatened waters. <br /> t Shaw recommends ozone microsparge as the remedial alternative for its effectiveness <br /> and relatively rapid remedial action against the constituents of concern at the site. This <br /> l option is preferred because it has the possibility to expedite site closure, and is lower in <br /> cost compared to long-term groundwater monitoring or DPE. <br /> 1 , <br /> I `V <br /> �i <br /> i t N:IsaeDP120041Pr1188018800401A.4ad.doc Shaw Environmental,Inc. <br /> L <br />