2008-04-02_REVISION - C1981044 (5)

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constituents a~°e likely to be present in discharge effluent, and did not include all of the constituents fir which there are instream standards in the Williams Fork River. It is unlikely, however, that the effluent would have contained these other constituents in significant amounts; therefore, it is reasonable to conclude that operations in the bond release area ~~re in compliance with the instream standards. Future exceedances of instream standards in the Williams Fork River or Yampa River are unlikely after final bond release Hof the entire permit area based on the mass-balance calculations, unless reactivated mine operations cause changes in water quality (see Table 5 in the hydrology evaluation memorandum). The mass-balance calculations in Table 5 are consistent with the conclusions of the Division's Yampa River Cumulative Hydrologic Impact Assessment. Compliance with Material Damage Suspect Levels CDRMS 1988 Guideline). The Division's guideline issued in 1988 specifies 1,000 umhos/cm as the maximum conductivity in northwest Colorado that would generally indicate irrigation water is potentially impaired. Crop irrigation is one potential use of Williams Fork River water downstream from the Eagle Mine complex. As previously mentioned, the permittee monitors water in the Williams Fork River at a site upstream from the Eagle mines (WF- 1) and a site downstream from the mines (WF-2). Comparison of the upstream and downstream data indicate operations at the Eagle Mines currently do not cause the 1,000 umhos/cm material damage suspect level to be exceeded. Mine water discharging to the Williams Forlc River, whether from a portal or coal seam, is not likely to cause an exceedance oi' the suspect level in the future because of the dilutional capacity of the Williams Forl<; River, as shown in the analysis summarized in Table 5 in the hydrology evaluation memorandum. In a year having precipitation near the historical average, mine water seepage would not cause a detectable increase in TDS or other constituents in the analysis. In a ciry year, concentrations of several constituents would be increased by mine water, but the increases would not be enough to cause an exceedance of the instream standards, including the Division's 1,000 mmhos/cm threshold for indicating material damage to alluvial valley floors. Prevention off impacts to surface water that adversely impact the postmining land use within the permit area (CDRMS regulation 4.05.1(2)). Surface water features in the permit area are the Williams Fork and Yampa Rivers. The postmining land uses of rangeland/wilcilife, pastureland, and cropland can be expected to use surface water for watering of wildlife and livestock. Mining and reclamation operations in the bond release area have not impaired surface water for these uses. The concentration of total dissolved solids of suriEace waters in the area are well below 5,000 mg/1, ause-suitability benchmark for wildlife and livestock. The long-term outlook is for this water quality to continue. Prevention oiF material damage to the hydrologic balance outside the permit area (CDRMS regulation 4.05.1(1)). Mining and reclamation at the Eagle Mines have not caused significant impacts to the hydrologic balance outside the permit area, and are not likely to cause significant impacts in the future.