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-48- <br />ground water systems. Due to the increased flow retention and <br />ground water recharge in perennial stream valleys, there is a <br />greater potential for stream depletions by mining adjacent to or <br />under these stream valleys. The mine could generate depletions by <br />increasing mine inflows in the area. These mine inflows could be <br />induced either through the mine workings encountering existing <br />faults or fractures or strata recharged by the stream, or through <br />the mine producing subsidence fractures which extend to the stream <br />valley bottom or to rock strata recharged by the stream. <br />The Somerset operation will undermine a perennial stream, and one <br />mining operation, Blue Ribbon will be mining adjacent to a <br />perennial drainage tributary to the North Fork of the Gunnison. <br />Both the Blue Ribbon and the Somerset mines have surface facilities <br />and underground mine workings located in the Hubbard Creek <br />Drainage. The combined mining operations of the Blue Ribbon and <br />Somerset mines may impact the quality of surface water flowing in <br />Hubbard Creek and in the irrigation ditches supplied by Hubbard <br />Creek. The quantity of flow may be depleted through the dewatering <br />of faults, fractures and rock strata which are in direct or in <br />indirect communication with the alluvium or stream bottom of <br />Hubbard Creek. <br />The Somerset Mine has mined beneath Hubbard Creek. Inspection of <br />the underground workings by CMLRD hydrologists showed this portion <br />of the mine to be making significant amounts of water. At the <br />present time it is uncertain whether or not surface flows are being <br />depleted. However, there is a greater concentration of inflows and <br />increased discharges associated with the inflow in the Somerset <br />mine workings below Hubbard Creek. <br />The Mt. Gunnison application proposed a subsidence protection plan <br />for the Dry Fork of Minnesota Creek to protect streamflow. The <br />adequacy of this protection plan was not assessed as a part of the <br />Mt. Gunnison Mine permit review (this area lies outside of the <br />current five year permit area). The Division stipulated that <br />site-specific monitoring data concerning subsidence and its <br />hydrologic effects be taken into account in the design of any <br />protection plan. <br />Three perennial streams cross the southern portion of the Mt. <br />Gunnison life-of-mine area: Lick Creek, South Prong, and Horse <br />Creek. Subsidence effects could be significant along these stream <br />courses as well, unless WECC develops and institutes subsidence <br />protection plans for these drainages as well as Dry Fork. <br />Depletion of Seeps and Springs <br />Underground mining, even in the absence of subsidence, could cause <br />flow from intermittent and perennial springs to be depleted, or <br />even to go completely dry. The significance of this effect depends <br />upon the use of the spring water and its contribution to flow in <br />receiving streams. <br />