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-40- <br />only drive sixteen (16) main entries (Mains) beneath Dry Fork and Lick Creek. <br />WECC will, if development and engineering constraints allow, locate these main <br />entries such that at least 300 feet of overburden will separate the Mains and <br />the valley floor. In the vicinity of Dry Fork and Lick Creek, except for the <br />Mains, a zero (0) extraction area is proposed to remain unmined until <br />collection and analysis of subsidence data is completed. The area of limited <br />extraction will be established using the following criteria: <br />(1) The valley width will be established at the first break in slope. <br />(2) One hundred (100) feet will be added to the measured valley width on each <br />side. <br />(3) A 20.5 degree angle of draw will be extended downward from the outside <br />edges of the valley width plus 100 feet line. <br />(4) Aline drawn vertically to the surface from where the angle of draw <br />reaches the F seam will define the proposed area of zero extraction in <br />the vicinity of Dry Fork and Lick Creek. <br />Subsidence could modify the surface water hydraulics of the drainage through <br />impacts to the locations of discharges or through damage to the structural <br />integrity of impoundments. Regardless of the source of mine inflows, these <br />will probably be discharged from only one location at a mine. In another <br />• situation, water whicfi supplies springs in the Minnesota Creek drainage could <br />be intercepted by subsidence fractures passed through more permeable abandoned <br />mine workings and discharge into springs directly tributary to the North Fork <br />of the Gunnison River. The baseflow in Minnesota Creek would be decreased <br />while the flow in the North Fork of the Gunnison above Paonia would be <br />increased. Although subsidence might logically increase infiltration rates in <br />an undermined watershed, and therefore decrease runoff, the Division is <br />unaware of any literature documenting that this affect actually occurs. <br />However, all active mines examine the affected areas annually and report on <br />the magnitude of surface subsidence cracks, when encountered. <br />Geomorphic impacts from subsidence could Include a change in channel and <br />watershed morphology or a modification in erosion rates. Reconfigurations in <br />channel and watershed geometry could be a consequence of extensive surface <br />subsidence cracking. Erosion rates would subsequently be impacted by changes <br />in watershed geometry, changes 1n streamflow or through subsidence <br />fracture-induced channellzation. While all of these impacts are possible, <br />they are not probable. <br />Withdrawal of Water from the North Fork of the Gunnison River for Mine Use <br />Streamflows may also be diminished through the withdrawal of water from the <br />stream or the alluvium of the stream for use in the mining operations. <br />The Western Slope Carbon Hawk's Nest Mine. located on the north slope of the <br />basin above Somerset, utilizes its surface water rights and rights to mine <br />• inflow water (Appendix XIII, Volume 3 of the Hawk's Nest permit application) <br />to meet the water requirements for mining operations, wash plant operations <br />and domestic use. Water rights held by Western Slope Carbon are adequate to <br />