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<br />Memo to Wallace Erickson 6 Mav 3. 2001 <br />distance from the edge of the pit to the Robinson Well, conservatively specified to be 960 feet or <br />292.6 meters, is the appropriate input parameter to Neuman's solution. <br />•: Time t is the period over which the dewatering pumps will be operating. In general, the longer the <br />pumps operate, the greater the magnitude of the drawdown will be at some radial distance r. <br />However, the magnitude of drawdown will stabilize at some point once a stable pumping rate <br />establishes at the dewatering pit. The Applicant has proposed a seasonal operation where <br />dewatering will be intermittent, and the pit will be allowed to refill with water during periods of <br />nonuse. DMG has selected a dewatering time period x180 days or 15,552,000 seconds for input to <br />the model. <br />With the above listed input parameters, rrB and n may now be calculated: <br />1 <br />- = 0.06 <br />rr a <br />_ rZ _ 292.6; ~ 4096 <br />~ b' 4.572 <br />Using these calculated values, the magnitude of the unconfined well function W(uA,uB, r~ is selected from <br />the graph attached to this memo. Given the large value of rj that has been derived for the Line Camp Pit <br />water table drawdown model, DMG has conservatively selected W(u,r,ue, r1J = 0.03. <br />Now all of the input parameters to Neuman's solution have been determined and the predicted <br />drawdown at the Robinson Well is given by the following calculation. <br />s <br />0.003 5 nr <br />ha - h = drawdowt: _ ~ W(uB, r~) = sec ~ x 0.03 = 0.65meters = 2.1 feet <br />4~rT 4 x 3.14 x 0.0000129 m <br />sec <br />Based on rigorous and exhaustive parametric sensitivity analysis of the Line Camp Pit drawdown <br />prediction, DMG believes that 2.1 feet is a conservative value for drawdown at the Robinson Well, i.e., <br />that the actual drawdown is likely to be less [Ilan 2.1 feet. The result of all of the analyses are not <br />included with this memo for reasons of space and because the calculations were done by hand on scratch <br />paper and are not available in electronic format. The hand calculation sheets will be preserved in the <br />Line Camp Pit reclamation permit file. In addition to the conservative nature of the predicted 2.1 foot <br />drawdown, there are physical processes at work in the pit area that may serve to further limit drawdown <br />in the Robinson Well that may be caused by dewatering the pit. These processes will be discussed <br />below. First, an evaluation of the effect of limited drawdown in the Robinson Well on the well's yield <br />will be provided. <br />