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• Mountain Coal Company West Elk Mine Exhibit 67 Windy Gap Process Discussion The following information has been compiled using da[a that is consistent with the 8.2 million tons per year (TPY) production rate expected at the West Elk Mine (WEM) through the permit term ending August, 2001. Although WEM has not yet reached the maximum production level, the following calculations represent the depletion to the North Fork of the Gunnison River (North Fork) at this maximum production rate. • Recen[ changes to the depletion calcula[ion include [he addi[ional sedimen[ ponds proposed to be constructed in [he Sylvester Gulch Facilities Area and for the Refuse Pile Expansion Area, and for a mine water treatment pond at Lone Pine Gulch. MCC's water usage has also been updated to account for water usage in 1996, water returned from the Waste Water Treatment Plant in 1996 and for upcoming construction projects. However, the amount of water contributed through mine inflows has not been updated due to the unusual nature of the inflows encountered in 1996 and 1997. A calcula[ion based on the inflows that occurred in 1996, shows that MCC returned more water to the North Fork than was used from the river. Therefore, the following revised estimate continues to be conservative. As MCC continues to evaluate the mine intlow situation and develop plans to more effectively handle the inflows, the annual water depletion estimate will be updated again. Depletions from the North Fork by WEM can be attributed to stream flow diversions under WEM's existing water rights. Return flows to the North Fork from WEM can be attributed to treated water from both the Waste Water Treatment Plant (WWTP) and water circulated through the mine. Other contribu[ions include treated water from non-alluvial groundwater in the mine workings. Depletions WEM pumps water from the North Fork into a 10 acre-foot storage pond. Water may also be pumped from the North Fork directly to the water treatment plant or into the mine and/or WEM's new 1.2 million gallon raw water storage tank. WEM also utilizes water storage rights contained in three sedimentation ponds on the WEM site and a right to water produced in the mine. At a production rate of 8,200,000 TPY, WEM's likely maximum water requirement is estimated at approximately 150 acre-feet per year and the very conservative maximum water requirement is approximately 300 acre-feet per year. Dust Suppression • Water use for underground dust suppression is estimated at 2% of production tonnage. Based upon an annual coal production of 8,200,000 TPY, approximately 134.6 acre-feet of water per year is depleted as a result of dust Exhibit 67-1 Rrvisrd Sept. f 995 TRT7; RrvisrC Apr. (997 TIP79