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19. The Operator contends that over time the uranium concentrations in the mine <br />pool will eventually decrease to background concentrations. <br />20. The Division does not agree that it is certain that the reducing trend will <br />continue. However, the Division calculated that if the trend continues, it may take seventeen <br />years for the mine pool to attain uranium concentrations of 0.03 mg/L. <br />21. At the hearing, the Operator asserted that the contaminated mine pool water is <br />contained and isolated. The Operator based this conclusion in part on the low-permeability <br />rock containing the mine pool and that the groundwater inflow rates averaged about 190 <br />gallons per minute when the mine was dewatered. However, the Operator in its April 19, <br />2010 EPP considered the mine pool a possible conduit for uranium into Ralston Creek. <br />22. In the EPP, the Operator addressed the hydrogeology of the mine and <br />unweathered bedrock stating, "[t]he mine voids ... provide a permanent hydraulic <br />connection throughout the rock mass in the mine area. Although there is not a strong <br />hydraulic connection between the flooded mine voids and the Ralston Creek alluvium ... a <br />weak hydraulic connection is adequate to dominate the flow regime." The Operator <br />continues with "the flowpath between the mine voids to the creek is shorter than the average <br />flowpath that previously existed between bedrock and the creek." EPP p. 8-40. The <br />Operator states that "the hydraulic connection between the mine and the creek is not strong . <br />.." EPP p. 8-41. In the EPP the Operator does not state that the mine pool is isolated and <br />contained. Rather, the Operator says "[a]lthough the flooded mine workings are not a <br />primary source of chemical loading to the alluvium adjacent to Ralston Creek, they may be a <br />minor source." EPP p. 9-4. <br />23. The exact amount of uranium contribution to Ralston Creek from the mine <br />pool is unknown. However, the Operator states that "[i]ncreases in sulfate and uranium <br />concentrations in alluvial groundwater that were observed in Fall 2008 and Spring 2009, <br />suggest that the flooded mine could contribute 0.8 to 8% of the alluvial flow." April 16 <br />Memo, p. 2 fn. 1. At the July 2010 hearing, the Operator explained that the calculation was a <br />worst case evaluation of the maximum upper limit of possible contribution from the mine <br />pool. <br />24. The Division disputes the Operator's assessment at the hearing that the mine <br />pool is contained and isolated. The Division cited data showing that at times the ground <br />water inflow to the mine was as high as 600 gallons per minute (Figure 8-9 from Division's <br />power point presentation). The EPP provides data regarding the groundwater inflow to the <br />mine from 1973-1999. In the EPP, the Operator describes how the inflow rates varied <br />greatly depending on the location and types of mining operations. EPP p. 8-21. The sources <br />of water inflow during mining included "infiltration of groundwater through porous bedrock; <br />infiltration of groundwater along faults, fractures, pegmatites and other permeable structures; <br />and recharge by precipitation and surface water through bedrock in the upper levels of the <br />mine." EPP p. 8-23. <br />Cotter Corp. <br />Schwartzwalder Mine 4 <br />M-1977-300 <br />MV-2010-018