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UM, <br /> ` _ - y <br /> x. <br /> The steady state downgradiGnt (rd) capture radius was calculated using <br /> the methods of Keely and Tsang (1983). The Following equations were <br /> used: <br /> V. Ki/n = .45 ft/day <br /> VV - Q/2nrbn <br /> rd � Q/2nTi <br /> rI rrd <br /> where: <br /> V,, is the natural groundwater velocity, <br /> VP is the pumping induced groundwater velocity <br /> Q is the pumping rate <br /> rr is the downgradient radius of capture <br /> rl is the width of the capture zone perpendicular to the <br /> - gradient <br /> The extent of the capture zone and the total plume recovery time were <br /> calculated for two recovery.;scenarios, (.i) a .single recovery well <br /> near the downgradient edge of the propertypumping at three gallons <br /> per,:minutem­(gpm), and (2) ...two recovery , wells. located near the <br /> downgradient boundary of the property each producing 3 gpm. <br /> Scenarios with more than two recovery wells were not considered due <br /> to the situ size, which would result in unacceptable interference <br /> affects between wells. <br /> Both of the recovery scenarios provide capture zones capable of <br /> w encompassing the entire site and extending downgradient (off-site3-a <br /> distance of at least 46 feet at 3 gpm and approximateI;y 90 feet for <br /> the twc well scenario. The primary difference in the two approaches <br /> is the time required to re-over the on-site .contamination. Due to <br /> the substantially greater pumping induced velocities at .higher rates <br /> the two well approach approximately halves the total recovery time. <br /> It is estimated that the total recovery time will be approximately <br /> one-two years. However, the plume ,Ywcovery time is sensitive to a. <br /> number cf factors which are difficult to predict. The recovery time <br /> •- :nay be reduced depending upon the affect of upgradient injection of� <br /> treated water and the affect of the soil vapor extraction systai,1 <br /> (VES). Injection was not considered in the recovery time estimate <br /> w due to the present uncertainty associated with obtaining Waste <br /> Discharge Requirements, but it would greatly increase groundwater <br /> flow velocities toward the recovery well(s). Additionally, the VES <br /> will have a significant impact on the dissolved hydrocarbon phases <br /> within the saturated zone; however, quantification of this effect is <br /> -------�=-----x`---•----------diff_icult...---------------------------- ------------------ --- -- -- --------._-- ------=- <br /> „ " Based upon the. limited d estimated size of the plume.- <br /> t, the site ' 'the <br /> j lack. :of free­;product,'; the :degredad chemical signature of the <br /> dissolved product ,and the'R relatively log: levels,czf:,total dissolved <br /> Weber Point..Propertl - 475 - <br /> . H26R6PT91.TL",. 10 - - - <br />