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affects of dewatering significantly during the growing season. In addition, calculations were <br />made assuming the entire pit area would be exposed and dewatered continuously. In reality, <br />with phased mining and concurrent reclamation, it is anticipated that only a fraction of the total <br />pit area will be dewatered at any one time, and for only two months each year. The reduced <br />dewatered pit azea and dewatering duration, and recharge from the rivers and irrigation, are <br />expected to reduce the affects of dewatering. Therefore, the calculation is considered to be a <br />worst-case estimate. <br />The approach that was used to estimate the extent of drawdown from dewatering is referred to as <br />"flow to a drainage trench from a line source" and is referenced in Powers (] 992). Results were <br />checked with additional approaches as presented in Freeze and Cherry (1979). Results indicate <br />that drawdown from pit dewatering will extend approximately 1,800 feet from the pit boundary. <br />The saturated thickness of the alluvial aquifer during dewatering is illustrated in Figure 1. <br /> Two Rivers Drawdown <br /> 2s <br />v <br /> m 2 0 <br /> <br />7 m <br />LL <br />N ~ 15 <br /> <br />~ 10 <br /> Y <br />> !~ <br />~ L s <br />'a ~ <br /> 0 <br /> 0 1,000 2,000 3,000 4,000 5,000 <br /> Distance from Pit (feet) <br />Figure 1. Proposed Two Rivers Mine Dewaterieg Drawdowe <br />References <br />Barnett, Adrienne and Ellefsen, Karl J. 2000. Assessment of the Alluvial Sediments in the Big <br />Thompson River Valley, Colorado. U.S. Geological Survey Digital Data Series DDS-66. <br />Fetter, C.W. 1994. Applied Hydrogeology. 3rd Edition. <br />Freeze, Allen R. and Cherry, John A. 1979. Groundwater. Prentice Hall. <br />Poweres, J. Patrick. 1992. Construction Dewatering, New Methods and Applications. John <br />Wiley and Sons, New York, N.Y. 2°d Edition. <br />4 <br />