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Mr.Steven Meeks Environmental <br /> Resources <br /> 28 August 2006 Management <br /> Page 2 <br /> In view of that, ERM evaluated the following applicable technologies: <br /> • Dual Pumping - Uses independent pumps to extract water and <br /> product from well; <br /> • Dual-Phase or High Vacuum or Multi-Phase Pumping (Multi-Phase <br /> Pumping) - Uses a downwell extraction tube with application of high <br /> vacuum to remove all fluids (vapor, water, and product) from an <br /> extraction well; and <br /> • Vacuum-Enhanced Skimming -Uses a downwell skimmer with low <br /> vacuum to enhance product mobility and recovery. <br /> Rationale and details of the proposed system are provided below. <br /> PROPOSED SYSTEM DESCRIPTION <br /> Free-phase product skimming technology typically involves the recovery <br /> of only free-phase product from an extraction well. The removal of <br /> product from the extraction well creates a gradient that induces <br /> additional product to migrate to the well. Free-phase product skimming <br /> was used at monitoring well MW-06A in 1995 (Table 1). Since the <br /> product thicknesses have been relatively thin at the site, passive <br /> skimmers with hydrophobic-oileophilic selective membranes would be <br /> installed. Passive skimmers actively remove product from the well and <br /> store it within a downhole recovery canister. The accumulated product <br /> would be manually removed from the skimmer periodically. <br /> In addition, UPRR proposes to enhance free-phase product skimming <br /> using low vacuum soil vapor extraction (SVE) at the skimming wells. <br /> Low vacuum SVE imparts pressure gradient to product in the formation <br /> and can significantly increase the efficiency of skimming systems, <br /> reducing the overall remedial time frame. Under vacuum-enhanced <br /> skimming, product mobilizes relatively readily, since the pore space <br /> above the water table is less saturated with water. SVE also promotes <br /> increased in-situ aerobic biodegradation of dissolved-phase product <br /> within capillary fringe soils. <br /> Application of higher vacuums within a well may produce large <br /> amounts of free-phase product, provided that there are large thicknesses <br /> of product present. However, ground water upwelling decreases the <br /> accessible free-phase product saturated formation especially when <br />