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Water quality in the main stem of Jubb Creek is dominated by calcium -sodium anions and <br />chloride -sulfate -bicarbonate cations. TDS concentrations exceeded the USEPA secondary <br />drinking water standards, but manganese concentrations did not. Total recoverable iron <br />standards did not exceed the USEPA aquatic life standard. TDS concentrations increase in the <br />downstream direction. <br />The Division has determined that alluvial valley floors (AVFs) exists within the area of the <br />Collom permit expansion area, as well as the adjacent area. These can be found within the <br />watersheds of Collom Gulch, Little Collom Gulch and Morgan Gulch. Per Rule 4.24.2, surface <br />coal mining and reclamation operations at Colowyo must preserve the essential hydrologic <br />functions of AVFs outside the permit area and (if necessary) will reestablish the essential <br />hydrologic functions of AVFs within the affected area, throughout the mining and reclamation <br />process. At this time, CCC does not intend to disturb any AVFs with in the permit boundary, nor <br />is it anticipated that mining and reclamation activities for Collom will impact hydrologic <br />functions outside of the boundary. <br />Ponds at the Colowyo Mine are designed, constructed, and maintained to hold and passively treat <br />the volume from a 10 -year, 24-hour precipitation event. Discharges from ponds are monitored to <br />detect exceedances of limitations listed in the Colorado Discharge Permit System (CDPS) <br />permit. In addition to the use of sediment ponds, the Division proposes to grant small area <br />exemptions (SAES) for some locations on the Collom site, which shall be outside of the sediment <br />control system of ditches and ponds. Some of the proposed SAES in the Collom area drain areas <br />larger than the Division usually considers appropriate for SAES (largest of 7.66 acres). To <br />determine if runoff from these areas will meet effluent standards, CCC used the grass filter <br />routine in SEDCAD, and the results showed that the native vegetation should be effective <br />enough that CCC will be in compliance with Rules 4.05.2 and 4.05.5. It should be noted that any <br />water pumped from pits and discharged with surface water runoff must be discharged through <br />sediment ponds, not through SAES. <br />Additional information related to surface water at the Colowyo Mine: <br />• Precipitation averages 18 inches annually on the Colowyo property, and runoff is limited. <br />Flows in the smaller drainages are mainly in response to snow melt or intense <br />thunderstorm events. <br />• Previous studies by Tetra Tech and by Cedar Creek Associates have identified 33 seeps <br />and springs within the Collom Gulch, Little Collom Gulch, and Jubb Creek drainages. <br />• The Wilson Reservoir, from which water is drawn for mining activities, is not within the <br />Permit area. The pumping station at the reservoir and the pipeline from the pumping <br />station to the mine are included in the Permit. <br />PR -04, Colowyo Coal Mine C1981-019 22 August 2016 <br />