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�itc� ess�c��t flop munaan ftma 6 off 0 <br /> i well search. The I�ockeford eater tower well is located approximately 600 <br />! fleet northeast of, and cross-gradient to, the subject site. <br /> Well No. 39035 could not be positively identified in the field, however, it was <br /> plotted as close to the subject site as would be possible based on the driller <br /> log description and the fact that the well must be located in Section 36 off <br /> 44N/R7E. <br /> An estimation off the time it would flake the benzene identified in <br /> groundwater at the site to travel to the closest supply cvell (i.e. the dockeford <br /> Water Tower Well) is calculated as follows: <br /> The dry sandy silt which was identified) between 87 and 900 feet bgs is used <br /> here as the representative soil medium for the lateral fate and transport of <br /> Benzene in groundwater. The following hydrogeologic characteristics are <br /> listed as ffollows: <br /> Hydraulic conductivity o a=LO gpd/ft 0=0A3 ft/day (i.e. silt to silty sand, <br /> Preeze and Cherry 1979) <br /> Effective porosity - n=0.�6 (i.e. silt to fine sant), Handbook off Ground V'dater <br /> ®evelopment by Roscoe Bloss company, 9990, page 7, Table 9.2) <br /> . HVdrauRc gradient o i=0.0T ffoot/ffoot to the west based upon water levels as <br /> measured during Rlovember and December in water supply wells 43088, <br /> 151154, and 270805 (See f ouire 2 ffor lnVdraulic grmad6ent). Grote: the wWer <br /> levels reported do not necessarily reflect a gone off effective draw-down <br /> during pumping, however, 0.01 ffoot/foot is a typical regional groundwater <br /> gradient. <br /> Since V= seepage velocity, them <br /> V = Ki/n = 0.9 3 (0.01)/0.16 <br /> = 0.000 feet/day = 125 days/foot <br /> Since the Lockeford Water Tower well is 600 feet from the site, then <br /> 600 feet X 125 days/foot = 75,000 days <br /> = 205 '/s years <br /> It will take approximately 205 '/s years for the 4.3 ppb benzene identified in <br /> groundwater to reach the nearest supply well. <br /> jThis is a very conservative estimate as no other factors, which would inhibit <br /> migration or cause attenuation of the contaminant, have been taken into <br />