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Dewatering Evaluation Report <br />Varra Grevel Operation <br />Greeley, Colorado <br />Page 5 <br />in Attachment A. Simulations were run as steady state because dewatering in the area has <br />occurred over an estimated 20-year period. <br />A head distribution map generated by the model shows that the gravel quarry is a <br />groundwater sink for the majority of the model area south of the Cache la Poudre River, <br />which is a constant head boundary. The analytical model clearly shows that the hydraulic <br />barrier created by the Cache la Poudre River mitigates any aquifer stresses (north of the <br />river) created by dewatering on the south side of the river. As expected, the ari?al extent <br />of drawdown associated with dewatering operations was greatest in the southern portion <br />of mining operations and extended to approximately 600 feet south of the most southern <br />mine face (estimated at 0.10 feet of drawdown). The TWO-DAN analytical model <br />simulations correlated well with hand calculations, which also indicated an effective radius <br />of influence of 600 feet. The predicted groundwater inflow to the mine was 5,322 gallons <br />per minute with seepage from the Poudre River and adjacent pond contributing 47 percent <br />of the total water pumped from the mine to the river. The measured groundwater flow into <br />the mine was estimated at 4500 to 5000 gallons in February 2004. The rated capacity of <br />the discharge pump used at the Varra mine is 6,000 gallons per minute. The model <br />calculated saturated thickness in the vicinity of the Carbaugh well was 19 feet. Hand <br />calculations estimated the saturated thickness at 16.77 feet and the measured thickness <br />was on the order of 15 feet. Based on available data it appears the between two and four <br />feet of drawdown in the vicinity of the Carbaugh well is related to aquifer stresses other <br />than mine dewatering. An aerial photograph with model simulated head distribution is <br />presented in Attachment A. The model generated head distribution map is presented in <br />Attachment A as well. It should be noted that an additional line sink was added to <br />represent additional dewatering for mining that will occur to the north and northwest of <br />current mine operations. The analytical model did not indicate any additional drawdown in <br />the vicinity of the Carbaugh well. <br />Specific capacity calculations were used to estimate the drawdown that would be expected <br />at the Carbaugh well based on current conditions. According to construction details and <br />water level information provided to the author, the water column in the Carbaugh well is <br />