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Additionally, until subsidence data are obtained, MCC has redesigned the mine plan to exclude most mining beneath Dry Fork and Lick Creek. Instead of the previous plan to utilize 50 percent extraction beneath the stream areas, MCC will only drive sixteen (16) main entries (Mains) beneath Dry Fork and Lick Creek. MCC will, if development and engineering constraints allow, locate these main entries such that at least 300 feet of overburden will separate the Mains and the valley floor. In the vicinity of Dry Fork and Lick Creek, except for the Mains, a zero (0) extraction area is proposed to remain unmined until collection and analysis of subsidence data is completed. The area of limited extraction will be established using the following criteria: (t) The valley width will be established at the First break in slope; (2) One hundred (100) feet will be added to the measured valley width on each side; (3) A 20.5 degree angle of draw will be extended downward from the outside edges of the valley width plus 100 feet line; and (4) Aline drawn vertically to the surface from where [he angle of draw reaches the F seam will define [he proposed area of zero extraction in the vicinity of Dry Fork and Lick Creek. ' Subsidence could modify the surface water hydraulics of the drainage through impacts to the locations of discharges or through damage to the structural integrity of impoundments. Regardless of the source of mine inflows, these will probably be discharged from only one location a[ a mine. In another situation, water which supplies springs in the Minnesota Creek drainage could be intercepted by subsidence fractures passed through more permeable abandoned mine workings and discharge into springs directly tributary to the North Fork of the Gunnison River. The baseflow in Minnesota Creek would be decreased while the flow in the North Fork of the Gunnison above Paonia would be increased. Although subsidence might logically increase infiltration rates in an updetmined watershed, and therefore decrease runoff, the Division is unaware of any literature documenting that this affect actually occurs. However, all active mines examine the affected areas annually and report on the magnitude of surface subsidence cracks, when encountered. - Geomorphic impacts from subsidence could include a change in channel and watershed morphology or a modification in erosion rates. - Reconfigurations in channel and watershed geometry could be a consequence of extensive surface subsidence cracking. Erosion rates would subsequently be impacted by changes in watershed geometry, changes in streamflow or through subsidence fracture-induced channelization. While all of these impacts are possible, they are not probable. Withdrawal of Water from the North Fork of the Gunnison River for Mine Use Streamflows may also be diminished through the withdrawal of water from the stream or the alluvium of the sveam for use in the mining operations. The Western Slope Carbon Hawk's Nest Mine, located on [he north slope of [he basin above Somerset, utilized its surface water rights and rights to mine inflow water to meet the water requirements for mining operations, wash plant operations and domestic use. Water rights held by Western Slope Carbon were adequate [o cover the consumptive use in their mine operations (pages 2.04-29 to -33 of the Hawk's Nest permit application). Western Slope Carbon estimated that the Hawk's Nes[ Mine would consume 215 acre-feet of water per year, which amounts to 0.07 percent of the mean annual yield of the North Fork of the Gunnison River. The site is reclaimed, and is not using any water as of 1997. For the MCC West Elk Mine, the worst-case scenario would be if the 150 acre-feet per year of water used for spraying the coal and for the potable water supply were entirely removed from the basin. On the average, this would amount to approximately 12.5 acre-feet of water each month. It appears that the months of August and September will be the critical months for removal of water from the watershed. In reality, most of the water used for potable water will be returned to the North Fork of [he Gunnison River. Consequently, MCC's main concern will be the water lost due to spraying activities. MCC will store water diverted from the North Fork in a storage pond on the mine site. The total estimated worst-case depletion (l50 acre-feet per year) would amount to only 0.05 percent of the mean annual yield of the North Fork. (See materials submitted by ARCO Coal Company, December 15, 1981, in • 18