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31 January 2013 <br />AGE-NC Project No. 02-0926 <br />Page 13 of 21 <br />groundwater, could be extremely excessive. Independently groundwater extraction is not <br />a feasible remedial alternative at the site based on its inability to treat the residual <br />smear/saturated zone soils at the site. In order for groundwater to be considered as a <br />remedial alternative it would have to be coupled with a form of in-situ soil treatment. <br />9.1.3. Duration <br />Based on AGE's experience, groundwater extraction systems typically require several <br />years in order to remove a bulk of the contaminants dissolved within groundwater. Based <br />upon the groundwater plume size and the general lithology beneath the site, it appears <br />that a 24 to 36-month period would be required to effectively remediate impacted <br />groundwater at the site. <br />9.1.4. Cost <br />Costs for installation of a "pump and treat" groundwater remediation system typically <br />ranges from $80,000 to $100,000, including the installation of large-diameter extraction <br />wells. The approximate cost to operate, sustain, monitor and sample a groundwater <br />extraction remediation system could vary from $50,000.00 to $75,000.00 per year. <br />9.2. DUAL PHASE EXTRACTION <br />Dual phase extraction (DPE) or high vacuum groundwater extraction is a technology that <br />simultaneously recovers adsorbed hydrocarbons from the vadose zone and the saturated <br />zone subsurface by locally extracting groundwater and lowering the groundwater level to <br />expose soil strata to a high vacuum. <br />9.2.1. Principles <br />Recovery of hydrocarbons from the saturated subsurface is often difficult due to the fact <br />that hydrocarbons can exist in the vapor-, dissolved- and liquid-phase. Liquid-phase <br />hydrocarbons both dissolve into groundwater , and adsorb and/or vaporize into pore <br />spaces between sediment grains. Dissolved phase hydrocarbons also vaporize into pore <br />spaces until equilibrium is established between the liquid, dissolved, and vapor phases. <br />Remediation methods effective in treating one phase may not be efficient for the <br />remediation of other hydrocarbon phases. <br />High-vacuum (vacuum pump capable of producing 25 to 30 inches of mercury) DPE <br />Advanced GeoEnvironmental, Inc.