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r <br /> -- (1.12 ft/day)(2 )(70 ft. )(0.35) x (7.5 gallon/ft3) = 21982 <br /> gallon/day = 15 GPM. If the pumping well is further down-- <br /> gradient, the required pumping rate is reduced <br /> Proportionately. This analyses assumes no loss of <br /> transmissivity due to drainage in the unconfined aquifer. <br /> Case 3. <br /> Since contaminant travel of only about 100 feet has occurred <br /> a maximum average groundwater velocity (ignoring <br /> retardation) can be calculated and an hydraulic conductivity <br /> } back-calculated. <br /> E'k Therefore 100 ft/365 days = 0.27 9t/day = Ki/9 <br /> or K = 19.2 ft/day = 143.8 gpd/ft <br /> This lower conductivity value may be characteristic of the <br /> upper portion of the aquifer where most of the contamination <br /> Is concentrated. A pumping rate necessary to capture a <br /> plume down-gradient 70 ft, is calculated using the lower K <br /> value above and is: <br /> Vn = 0.27 ft/day = VP = 0/2 rh© <br /> or for r = 70 ft., 4 = 3.6 gpm <br /> The two calculated rates (15 and 3.6 gpm) probably reflect <br /> the range of pumping rates necessary to hydraulically, <br /> control contaminant migration. Based an. uncertainties': <br /> .'inherent in these types of calculations it is,'x�ccmmanded <br /> t, a <br /> t -the dumping rate be determined'::from field° 6bservat1ons <br /> duirig longer term operating conditions. <br /> For an assumed pumping rate of 10 gpm the well drawdown over <br /> one year can be estimated ,form the MW2 test at 3,5 gpm. <br /> Drawdown = (10_) [(drawdown at 240 min, ) +(M x 3,33)] <br /> 3.5 <br /> Where M = slope of semilog straight line <br /> 3:33 = number of log cycles between 240 and 525,000 minutes <br /> {1 yr. ) <br /> = 2.86 [1.77 +0.3331 <br /> 6.01 ft. <br /> Assuming no drainage from the unconfined aquifer. <br /> Applying a safety factor of 20$ this suggests a pump setting <br /> depth of at least 26 feet. <br /> Adjustments to setting depth will be made based on net <br /> Positive suction head requirements__of_--the-_pump--and- <br /> ------well/aquifer the ----- --- --- -- <br /> conditions._ - -- <br /> 1 <br />