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and fine materials that eventually clog the well screen and reduce capacity4. <br /> Accordingly, it is recommended that a safety factor of 1.5 to 2 be applied, which <br /> corresponds to 21 to 28 injection wells to accommodate 40 gpm. <br /> As previously discussed, remediation is targeting the three source areas and DPE <br /> requires sustained dewatering for effective vapor extraction of saturated soils. Three <br /> criteria are identified in conceptualizing DPE with re-injection relative to the three <br /> source areas: <br /> • The design strategically calls for re-injection into the center of the contaminant <br /> plume in order to have higher discharge limits. <br /> • Re-injection cannot occur in the extraction area as it will inhibit dewatering of <br /> saturated soils and prevent effective vapor extraction. <br /> Extraction must occur down-gradient of the injection area to prevent migration <br /> of contaminants as a result of re-injection. <br /> These three design criteria either minimize the area that DPE can target at any given <br /> time or require additional extraction and injection wells to accommodate full-scale <br /> operation. Lastly, it may not be feasible to install this many extraction and injection <br /> wells with associated piping at this facility due to the constraints of the existing <br /> equipment and structures. <br /> Similar to land disposal, greenhouse gas emissions are lower for the re-injection option <br /> since wastewater treatment plant capacity is not being consumed. However, all the <br /> other elements remain the same. Additional extraction and injection wells would <br /> increase the carbon footprint relative the land disposal option. The electrical usage, <br /> travel and transport to maintain operation, and waste disposal (carbon) are still <br /> considered excessive and not environmentally sustainable. For the reasons discussed, <br /> re-injection of treated groundwater is not a viable option. <br /> 5.3.1.3 RECOMMENDATION <br /> DPE requires the disposal of treated groundwater. CRA has evaluated three different <br /> means of disposal: sanitary sewer discharge, land disposal, and re-injection. Each <br /> disposal option presented technical issues that ruled out its viability. Since DPE is not <br /> viable,a life-cycle cost estimate was not prepared. <br /> 4 Driscoll,F.G.,1986. Groundwater and Wells,Johnson Division,St.Paul,Minnesota pp. 218,771-772 <br /> 241729(33) 16 CONESTOGA-ROVERS&ASSOCIATES <br />