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3.2.2 Time of Circulation Within Cell <br /> tA graph of circulation times versus radial distance from the UVB system has been prepared for <br /> several porosities (Figure 7) Circulation time is defined as the time required for a unit volume <br /> of water to move from the upper, outflow zone of the well through the radius of interest from the <br /> UVB system, and back into the lower, inflow zone of the well The midpoint axis of interest for <br /> former Exxon RS 7-3942 site is expressed in terms of the percentage of the stagnation point <br />' distance S in the direction parallel to the natural gradient Similarly, the midpoint axis of interest <br /> for the site is expressed in terms of the percentage of(B,+Bb)/4 in the direction perpendicular to <br /> the natural gradient The travel times to reach the radius of interest are approximately one-half <br />' the circulation times as defined <br /> Based on Figure 7, the maximum time to complete one pore volume flush of the circulation <br />' through some radial distance from the UVB well is 40-68 days for the given range of effective <br /> porosity <br />' 3.23 Volatile Organics Removal <br /> The stripping efficiency of the UVB stripping reactor is based on the air-to-water ratio, residence <br />' time in the stripping zone, and the movement of air and water in the stripping zone The <br /> residence time is increased by circulating currents within the stnppmg zone The air and water <br /> pathways are directed in a countercurrent motion to enhance mixing and increase residence time <br /> The UVB well will draw in approximately 200 m3/h of air, and the pump will be set for a flow <br /> rate of 2m3/h (Q) into the stripping reactor These flow rates (200 m3/hr to 2 m#/hr) produce an <br /> air to water ratio of 100 1, and a corresponding stripping efficiency ranging from 90-99 percent, <br /> rfudging from previous applications of the system <br /> Based on an aquifer flow rate Q) of 0 20 m3/h through the capture zone cross-section (see <br /> rFigure 5), and an internal combined flow rate (Q) of 2 m3/h, the UVB system will be able to <br /> recirculate 90 percent of the influent water through the stripping zone more than once <br /> rAssuming complete mixing, 10 percent of the effluent that moves downstream will have passed <br /> through the circulation cell once, while the remaining 90 percent of the effluent will have passed <br /> rthrough the circulation cell at least twice <br /> r <br /> r <br />' WP61 73942 WP1096 7X 5 6 <br />