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<br /> <br /> <br /> <br /> <br /> <br /> <br />1 <br />11 <br />1 <br /> <br />1 <br /> <br /> <br />1 <br /> <br />r <br />[1 <br />MODEL INPUTS <br />Darcy's Equation (and in turn, the Dupuit Equation) requires the following inputs relating to aquifer <br />characteristics: <br />a Hydraulic conductivity, K <br />Previously reported hydraulic conductivity values for the Arkansas River quaternary <br />alluvium ranged from 2,000 to 12,000 gpd/ftz, in addition to an estimate of transmissivity, <br />which is related to hydraulic conductivity by saturated thickness, reported as 40,000 gpd/ft. <br />In their 1998 report, Gilmer Geophysics, Inc. reported hydraulic conductivities for the <br />outwash aquifer at 400 to 2,000 feet per day (300 gpd/ftz to 1500 gpd/ftz), which <br />correspond to transmissivities of 6,000 gpd/ft to 30,000 gpd/ft, respectively. These values <br />were derived for the report "...based on an interpretation of sieve analyses of the sands, and <br />gravels, percolation tests, and water production rates measured during the drilling of two <br />monitoring wells." (Gilmer Geophysics, 1998) From the value range reported by Gilmer <br />Geophysics, Inc., an average hydraulic conductivity of 1,200 ft/day was selected for use in <br />the model. Because the hydraulic conductivity is one of the primary factors for determining <br />the effects to ground water flow from the operation a sensitivity analysis was performed on <br />this parameter to better gauge the effects of this assumption. <br />• Drawdown at the well, S <br />This parameter defines the expected drawdown at various locations along the alluvial <br />aquifer, notably well no. 186110, as influenced by each of the three hypothetical pit wells. <br />In the case of well no. 186110 these values were calculated based on average distances of <br />518 feet, 509 feet, and 837 feet (west to east) from the hypothetical well locations. <br />• Pumping rate, Q <br />The pumping rate in each conceptualized well location was assumed to be equal to the <br />maximum pumping rate specified for the site. This is a very conservative estimate as in <br />reality a cumulative maximum of 4,100 gpm will be discharged at any given time for the <br />whole site. Thus, the model essentially uses a total discharge of 12,300 gpm from the entire <br />site. This excess should more than account for the unmodeled effects of the impermeable <br />boundary conditions imparted by the surrounding rock formations. <br />• Average saturated thickness, H <br />For the average saturated thickness of the outwash alluvial aquifer, a value of 20 feet was <br />used feet from the surface as reported in all investigatory reports of the site's hydrogeology. <br />SIMULATION OF IMPACTS OF THE DEWATERING OPERATION <br />Through the implementation of the above assumptions and the conceptualization of the dewatering <br />operation, the net anticipated drawdown at various points throughout the outwash aquifer on the <br />north side of the Arkansas River was determined. Although discussed below, impacts to the south <br />of the Arkansas River were not explicitly modeled because the conceptualization requires violation <br />of the boundary condition that mandates drawdown at the river is negligible due to the constant <br />head source. <br />Parkdale Aggregate Mine I Parkdale Mine Analytical Ground Water Model <br />