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In the West Pit, all runoff from the reclaimed areas is conveyed to the West Pit Pond via <br />the permanent ditches West Pit Coal Road Ditch and East Taylor Pond Ditch. Runoff <br />passes through the West Pit Pond before being released to the East Fork of Taylor <br />Creek. As in the case of the East Pit, the permanent ditches have been designed to <br />convey the 100-yr/24 hr or 10-yr, 24-hr storm runoff flow as applicable under Section <br />4.05.4 or 4.05.3. The West Pit Pond will be removed once sediment control release has <br />been approved. <br />Certain stock ponds will remain in place after bond release to support the approved <br />post-mining land use as described in Section 2.05.05. These are generally less than 1 <br />acre-foot in capacity. The locations of these are presented on Exhibit 1, Phase III Bond <br />Release. <br />4.2 Surface Water Impacts <br />Performance of the surface hydrologic system in concert with the successfully <br />revegetated surface is addressed via modeling and via examination of offsite receiving <br />stream data where available. <br />With regard to runoff water quality, the modeled comparison was done by employing the <br />RUSLE (Revised Universal Soil Loss Equation) to estimate sediment yield from the <br />reclaimed lands as compared to the premining condition. The results for the reclaimed <br />lands that are the subject of this Phase III bond release application were presented in a <br />series of Phase II bond release applications dated September 25, 1987, August 15, <br />2001 and June 1, 2010. The estimated sediment yield from the reclaimed lands using <br />this method was in all cases below the comparable estimated sediment yield for the <br />premining condition. <br />With regard to surface water quantity, the modeled comparison is best described in <br />Volume 1, Section 2.04.7, Hydrology Information of the original application. That <br />discussion concludes that the volume of runoff from the reclaimed lands will be similar <br />to the premining condition, largely because the surficial soils and reclaimed vegetative <br />cover are the same or similar. The reclaimed lands may present a lesser runoff volume <br />to the extent that they tend to be more gently graded than the premining condition, with <br />reclaimed slopes kept flatter than 3(hz):1(vt). The point is also made that the total area <br />mined is a small fraction of the total watershed, less than 10%. The 967.4 acres of <br />reclaimed lands that are the subject of this application are a subset of that, and amount <br />to about 4% of the total tributary watershed at the point where the mine runoff meets the <br />offsite receiving streams. The Volume 1 Hydrology discussion concludes that the <br />Colowyo Mine was expected to have no significant impact on the hydrologic balance, <br />and in particular have no measurable quality and quantity changes to the Yampa River. <br />Offsite monitoring stations above and below the areas in the East Pit that are the <br />subject of this bond release application support that conclusion, at least in the <br />immediate vicinity of the mine. These upstream and downstream stations are NUGSC <br />(New Upper Good Spring Creek) and LGSC( Lower Good Spring Creek), respectively. <br />The reach of the creek between the two is about 4.25 miles. Runoff from the reclaimed <br />Phase 111 Bond Release Application 13