2018-09-04_REVISION - C1980007 (11)

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49 permit area. Mining activities will not have a significant effect on snowmelt runoff. Overland runoff passes over disturbed areas within the permit area to one of the eight sedimentation ponds, mentioned previously in this section. This water may be discharged to the North Fork or stored when water rights are in priority. During Water Year 1982, MCC’s conditional right to withdraw water from the North Fork was deemed absolute. When this water right is in priority, water can be pumped from the intake point to the 10 acre-foot freshwater pond. This water right is expected to be out of priority from July to September. Average withdrawals from the North Fork of the Gunnison are not expected to exceed 400,000 gallons per day (gpd) and are likely to be on the order of 200,000 gpd. The freshwater pond is filled during spring runoff and kept full until water rights are out of priority. The water is either treated to meet potable and sanitary water requirements, used and then treated as sanitary waste water, or is withdrawn for dust suppression in the mine and becomes mine water. The potential effects of MCC’s water diversion on North Fork flows have been projected for flow rates and flow volumes. With the existing pump capacity, 450 gallons per minute (gpm), the diversion would result in a measurable change in flow during low flows having return periods of about 200 years or greater, and would be less than 5 percent. During extreme low flow periods, MCC's water rights would be out of priority and diversion would not be undertaken. Although subsidence fractures that develop over and next to mine workings have the potential to dewater streams and ponds, Section 2.05.6(6) of the permit application explains that dewatering is unlikely to occur because subsidence cracks that develop at the surface will not extend deep enough to intersect fractures propagating upward from the caved and fractured zones. Also, the stratigraphic sequence in stream valleys is resistant to fracturing due to the presence of interbedded fine- grained units. These beds would more likely undergo ductile deformation (bed bending), rather than brittle deformation (bed fracturing). Stream flows and local channel elevations will continue to be monitored in the permit area, as set forth in the permit application. Subsidence magnitudes of stock ponds will also be monitored. Specific measures MCC will employ for assessing and protecting the Minnesota Creek water supply are described in Exhibit 58 of the permit application titled, "Protection of Minnesota Creek Water Supply." Possible subsidence impacts to streams and ponds are discussed in the following Subsidence Control section. Underground mine workings will come within 800 ft. of the Monument Dam and Minnesota Reservoir. MCC explains in Section 2.05.6(6) of the permit application that the reservoir is unlikely to be affected by mining because the dam and reservoir are outside the predicted angle of