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-40- above the affected areas. Related changes in local piezometric surfaces could result in the modification of springs. and seeps. Waters, having entered the subsurface strata could reemerge downstream in the same drainages or migrate towards the underground workings. In some cases this water may reemerge as a discharge from the portal or as springs along the subcrop or outcrop. Possible Effec>is of Subsidence upon Minnesota Creek Drainage in future permit terms if mining does occur. Over the life of the mine, subsidence from Mt. Gunnison's underground mining operations could affect surface water hydrology in the North Fork of the~Gunnison and the Minnesota Creek watersheds. Subsidence effects would reduce the surface flow from an affected watershed in several ways: 1) by increasing infiltration which would, in turn decrease runoff, 2) by lowering the piezometric surface and causing springs to dry up, and 3) by direct infiltration from streams and their alluvium, or terraces. In areas not covered by soils, subsidence fractures would directly divert runoff into the ground water system. .. In such an area, numerous open fractures could significantly reduce surface runoff. In areas covered with soils (which would not maintain an open fracture), any reduction in runoff would be less severe. Subsidence fractures would increase deep percolation of soil water, but the infiltration characteristics of the soil would still control the amount of runoff. Infiltration might still increase slightly, because deep percolation might more rapidly deplete soil moisture and decrease antecedent moisture. A lowering of the piezometric surface might cause intermittant and perennial springs to go completely dry. Exhibit 2.8.1.U identifies numerous springs in or adjacent to the area to be mined. The application (2-253-6) indicates that springs contribute 11 percent of the flow in Lower Dry Fork, 4 percent of the flow in Lick Creek, 12.6 percent of the flow in South Prong, and 0.9 percent of the flow in Horse Creek. Excluding the Sylvester Gulch data, springs could contribute 6.2 percent of the low flow runoff. In reality, it is probable that not all the springs would be affected and, therefore, reduction of surface flow would be less than the worst case scenario. Subsidence could reduce stream flow by directly diverting surface flow and alluvial ground water into the bedrock ground water system. This effect is undesirable both because of the hydrologic effects and the mine operation problems it could produce. The applicant has proposed a subsidence protection plan for the Dry fork of Minnesota Creek to protect streamflow. The adequacy of this protection plan was not assessed as a part of this permit review. The Division prefers that ",.}