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West Elk Mine The probable surface and groundwater hydrologic consequences presented herein assume implementation of the West Elk Mine mining plans as shown on Map 51 and Map 52. These mining plans are subject to refinement during detailed mine plan prepazations by MCC. However, for purposes of discussing anticipated hydrologic consequences, these plans (Map 51 and Map 52) reasonably represent what will occur. The PHCs anticipated within the current permit and South of Divide permit revision azea aze presented as follows: 1. Surface Water Quantity Effects. 2. Surface Water Quality Effects. 3. Groundwater Quantity Effects. 4. Groundwater Quality Effects. While a complete discussion of the PHCs for the permit azea is wntained in the following sections of this document, a brief synopsis of the key PHCs is beneficial due to the length of the full discussion. A concise summary of the primary PHCs for the permit azea is as follows: • The probability of a surface crack encountering a surface water resource (i.e., stream, spring, or stock pond) is small, mostly due to the infrequent occurrence of surface cracks above the longwall panels. This is consistant with mining at West Elk where this has never happened. • If a surface crack does encounter a surface water resource, the impact to the water balance would be insignificant and likely temporary. The volume of a crack would fill rapidly with water and carry with it sediment to begin the sealing and healing processes. • If subsidence impacts do occur along a stream channel such as Dry Fork, mitigation measures will be implemented to limit and control the interruption of flows. In addition, the Minnesota Creek augmentation plan will protect downstream water users from potential loss of streamflows due to mining activities. • The only reservoir located neaz the permit area is Minnesota Reservoir. The longwall panel layout has been designed to keep the reservoir outside of even the most conservative angle of draw. Therefore, no subsidence effects will be seen at the reservoir. • The most likely water quality impacts to surface water as a result of subsidence is the increase in stream erosion rates. However, the projected changes in stream channel slopes aze estimated to result in changes in sediment load of less than five percent. • Mine water discharges are anticipated to continue to follow historic patterns. Even with the encountering of the BEM and 14HG fault inflows, the salinity loading to the North Fork has been within the projected value assigned to the mine in the CHIA. • Groundwater quantity effects due to mining involves the caved/fractured zone intercepting a water bearing unit overlying the coal seam. Due to the lenticular nature of the sandstones in 2.05-I55 Revised November 1004 PRIO