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West Elk Mine <br />• If subsidence impacts do occur along a stream channel such as Dry Fork, mitigation <br />measures will be implemented to limit and control the interruption of flows, as described in <br />Section 2.05.6(6)(f)(iv)(A-D). In addition, the Minnesota Creek augmentation plan will <br />protect downstream water users from potential loss of streamflows due to mining activities. <br />• The only reservoir located near the permit area is Minnesota Reservoir. The longwall panel <br />layout has been designed to keep the reservoir outside of even the most conservative angle <br />of draw. Therefore, no subsidence effects will be seen at the reservoir. <br />• The most likely water quality impacts to surface water as a result of subsidence is the <br />increase in stream erosion rates. However, the projected changes in stream channel slopes <br />are estimated to result in changes in sediment load of less than five percent. <br />• Mine water discharges are anticipated to continue to follow historic patterns. Even with the <br />encountering of the BEM and 14HG fault inflows, the salinity loading to the North Fork has <br />been within the projected value assigned to the mine in the CHIA. <br />• Groundwater quantity effects due to mining involves the caved/fractured zone intercepting a <br />water bearing unit overlying the coal seam. Due to the lenticular nature of the sandstones in <br />the Mesaverde Formation, this phenomenon typically results in initial inflows of 10 to 15 <br />gpm and the flow tapering off to a trickle within a couple of weeks. The nature of the <br />groundwater occurrence has also led to a lack of water supply wells in the permit area. <br />• The BEM and 14HG faults are exceptions in that they contained large volumes of water, <br />which resulted in very high initial inflow rates and sustained flows. Analyses by MCC and <br />its consultants has shown the residence time of these waters to be on the order of 10,000 <br />years. The fault inflows have been decreed in water court as non-tributary water; therefore, <br />the interception of the water has not adversely impacted any groundwater users in the area. <br />Groundwater quality effects can occur as a result of fractures allowing water to migrate <br />between geologic units. The practical significance of this phenomenon in the permit area is <br />minuscule due to the scarcity of water in the formation and the lack of water supply wells in <br />the vicinity. <br />Surface Water Quantity Effects <br />As discussed in Section 2.04.7, surface water resources have been studied extensively by MCC <br />since 1970. Map 34 and Exhibit 71 shows the existing hydrologic monitoring network. The surface <br />water monitoring network at West Elk Mine consists of the following: <br />1. Streamflow and/or water quality monitorhig stations on the North Fork upstream (USGS) and <br />dotivnstream of the mine, Sylvester Gulch, Gribble Gulch, Upper and Lower Minnesota <br />Creek, Lich Creep, Dry Fork (Upper, Middle, and Lower), Horse Gulch, East Gulch east of <br />Horse Gulch, Deep Creek and Box Canyon. No stations were placed on Raven Creek as a result <br />. of a subsidence protection zone stipulated in the Lease and EA. <br />2.05-186 Revised June 2005 PRI Q January 2006. dlarch 2006; Rev. May 2006 PRIG. Non. 2006 TR107; Sep. 2007 PR12; Feb 2008 PRI2