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QO&gccat hchnxs Inc Page 5 George's Service Feasibility Study Project No 425 2 April 28,2004 2.6 Dual Phase Extraction i I Dual Phase Extraction (DPE) is a process that extracts air and water from the subsurface aquifer and unsaturated zone under very high vacuum (up to 24 inches Hg) By depressing groundwater, volatile organic compounds (VOCs) are also removed from the smear zone r Both the saturated and unsaturated zones are screened, a stinger (long tube) is positioned near the bottom of the well so that both groundwater and vapor are brought to the surface by a vacuum applied to the stingier Once above ground surface the two phases are separated ' and treated Dual phase extraction is essentially a combination of SVE and Pump and Treat technologies DPE is not a viable option for the reasons discussed in Sections 2 2 and 2 5 above 2.7 Soil Excavation Excavation simply involves the digging and removal of contaminated soil from the site Excavations are simple and cost effective at sites that have heavy contamination in the vadose zone located in a spatially small area At the George's site, most of the contamination is located between 7 and 28 feet bgs and spread over a large area An excavation would require the removal of approximately seven feet of clean overburden so that approximately 20-feet of contaminated soil could be excavated Dewatering of the excavation would be required at great expense Sands will likely flow into the excavation from under the clay-sand layer, destabilizing the outer edge of the excavation area, and it would complicate the excavation of the last eight feet of ' contaminated soil A large portion of the plume is beneath Durham Ferry Road and the site is underlain by ' multiple utilities including a fiber optic line 2.8 In Situ Chemical Treatment In situ remedial systems are processes that treat the groundwater in place rather then removing it to the surface and treating it above ground The chemical treatment typically involves redox reactions that chemically convert hazardous contaminants to non-hazardous or less toxic compounds that are more stable, less mobile, or inert Redox reactions involve the transfer of electrons from one compound to another I Advanced Oxidation Processes AOPs Advanced oxidation processes (AOPs) are processes that create and use a highly reactive radical that effectively oxidize MTBE and other organic compounds by chemical reaction The most prominently used radical is the hydroxyl radical, designated as OH The OH ion ' will capture a hydrogen atom from a molecule of contaminant, which then causes the contaminant molecule to become unstable and breakdown further The end products of this breakdown process are reported to be bicarbonate, water and small amounts of mineral acid from any halogen, nitrogen or sulfur present in the groundwater i