GENERAL44240 - Laserfiche WebLink

Home Browse Search

-ao- the inflow in the Somerset mine workings below Hubbard Creek. There is strong evidence that the U. S. Steel Somerset Mine may already be depleting flow in Hubbard Creek. (See Exhibit E9-3361 "Water Sources in the Somerset Mine" within the Somerset Mine Permit Application). However, this impact is mitigated in part since Somerset discharges excess flows into Bear Creek and Blue Ribbon discharges the inflows back into Hubbard Creek. The Mt. Gunnison application 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 the Mt. Gunnison Mine permit review because this area lies outside of the current, 5-year permit area. The Division stipulated that site-specific monitoring data concerning subsidence and its hydrologic effects be taken into account in the design of any protection plan. Three perennial streams cross the southern portion of the Mt. Gunnison life-of-mine area; Lick Creek, South Prong, and Horse Creek. Subsidence effects could be significant along these stream courses as well, unless the Mt. Gunnison Mine develops and institutes a subsidence protection plans for these drainages as well as Dry Fork. Depletion of Seeps and Springs Underground mining, even in the absence of subsidence, could cause flow from intermittent and perennial springs to be depleted, or even to go completely dry. The significance of this effect depends upon the use of the spring water and its contribution to flow in receiving streams. Underground mining at the Mt. Gunnison Mine has a high potential for affecting springs located in Sylvester Gulch. However, flow from these springs is already diverted into the Tony Bear Pipeline for use in the Bear mining operation, and does not reach the North Fork of the Gunnison River. The Mt. Gunnison permit application identified numerous springs in or adjacent to the area to be mined. The application 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 stream flow for the Mt. Gunnison life-of-mine area during the dry part of the year. In a worst-case scenario, where all of the springs dry up, 6.2 percent of the low flow runoff could be lost. In reality, it is probable that not all the springs would be affected and, therefore, reduction of surface flow, although significant, would be less than the worst-case scenario. A loss of spring flow may not entirely be lost to the hydrologic system. It may temporarily become a part of the ground water system and eventually reemerge at the surface. It is difficult to predict where this water may reemerge. It could reemerge downstream in the same drainage within the Minnesota Creek system, or it could reemerge along the North Fork of the