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T <br />K=- <br />S <br />Where: T = Transmissivity (ft'/day/ft) <br />S = Saturated Thickness (ft) <br />Transmissivity was estimated based on pump test data from alluvial wells in the area. <br />An average specific capacity of 7.5 gpm/ft was determined. From this, an estimate <br />was made of the transmissivity based on the U.S. Department of the Interior's <br />Groundwater Manual (1981). The value of transmissivity detemvned was 32,000 <br />gpd/fc. <br />The drawdown in the surrounding water levels as a result of the dewatering <br />operation will increase as the transmissiviry increases. Thus an average transmissivity <br />of 50,000 gpd/ft was used in the model as a conservative estimate. The average <br />saturated thiclmess was determined to be 20 feet based on maps developed by the <br />L1SGS. <br />The bedrock elevations were digitized based on contour maps developed by the <br />LJSGS in 2000. A linear interpolation scheme was used to deternune the bedrock <br />elevations for input into the MODFLOW model. <br />The alluvium was assumed to be homogeneous and isotropic. This assumption is <br />necessary due to the fact that actual geologic sampling throughout the area was not <br />available. The model, when calibrated to current water level data, accounts for <br />differences in strata throughout the alluvium. <br />• Steady-state conditions were assumed in order to avoid bringing in a level of <br />complexity to the model that is not necessary for the purposes of this analysis. <br />Additionally, the groundwater flow in the area is highly variant and dependant upon <br />seasonal precipitation, local infiltration resulting from imgation, and the intemuttent <br />pumping of nearby wells. <br />• The influences of the surrounding wells on groundwater flow were not explicitly <br />modeled. Most of the surrounding wells are small capacity domestic wells that are <br />unlikely to have any significant impact on the results of the modeling. Any influence <br />of these wells was taken into account in the cakbration of the model. <br />The surrounding lakes were modeled as areas of relatively high hydraulic <br />conductivity in order to obtain an estimate of the decline in water elevation in the <br />lakes as a result of the mining operation. The hydraulic conductivity assigned to the <br />lakes was 20,000 ft/day. <br />Lafarge West, Inc. -4- Applegate Group, Inc. <br />Duckworth Pit Groundwater Study March, 2004 <br />