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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 strean-flows 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 1976. Map 34 and Exhibit 71 shows the existing hydrologic monitoring network and Exhibit <br /> 71A shows the recommended added monitoring. The surface water monitoring network at West <br /> Elk Mine consists of the following: <br /> 1. Streamflow and/or water quality monitoring stations on the North Fork upstream (USGS) and <br /> downstream of the mine, Sylvester Gulch,Upper and Lower Minnesota Creek, Lick Creek,Dry <br /> Fork (Upper, Middle, and Lower), Horse Gulch, East Gulch east of Horse Gulch, Upper Deep <br /> Creek, Lower Deep Creek, Lower Prong Creek, South Fork of South Prong Creek, and the <br /> North Fork of South Prong Creek. <br /> 1.05-186 Rev.06/05-PRIG,01/06-PRIO,03/06-PRIO,05/06-PRIO,11/06-TR107,09/07-PR12,02/08-PR72;08/16-TR139,08/18 PR15 <br />