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Colowyo, C1981-019, PR3 adequacy 10 <br />February 25, 2011 <br />wildlife. The Division will not make further comments about CCC's wildlife mitigation plan <br />until Colowyo has had a chance to review this letter and make appropriate changes to PR-3. <br />Rule 2.05.6(3)(a) Protection of the Hydrologic Balance <br />1. The application contains limited permit text narrative with regard to impacts to registered <br />ground water users due to pit dewatering and development and is deficient with regard to <br />impacts to ground water users (see discussion above under Rule 2.04.7(3)). Please expand the <br />permit text narrative under the section discussing probable hydrologic consequences to ground <br />water quantity, with particular emphasis on discussion of impacts to wells owned by others. <br />2. Discussion is also limited with regard to the potential for development of a spoil aquifer and <br />potential long-term discharge of the spoil aquifer to the surface water system. Proposed text <br />narrative provides an analysis indicating that development of a spoil spring, if it occurs, would <br />take 100 years or more to develop to the point where it would discharge to the surface water <br />system. The Division believes a spoil aquifer will develop over time within the confines of the <br />backfilled Collom Lite pit, based on past experience in northwestern Colorado. Long-term <br />discharge of degraded spoil water could therefore impact areas downstream. Alluvial valley <br />floors, as defined by the Coal Rules, are located downstream of the permit area in Collom <br />Gulch. Please expand the permit text narrative regarding the potential for spoil water discharge <br />and impacts to downstream areas. <br />3. As mentioned previously, the plan for control of surface water drainage through the disturbed <br />area is deficient at this time due to uncertainty of the proposed mine plan and the long-term <br />presence of the temporary spoil pile in the center of the disturbed area. The application does <br />not adequately present how surface water will be handled over the life of the operation (Rule <br />2.05.6(3)(b)(i)). <br />Rule 2.05.6(3)(b) Hydrologic Controls <br />The applicant has presented a plan for monitoring surface and ground water in accordance with <br />Rule 2.05.6(3)(b)(iv). Any deficiencies with regard to the plan are noted under Rule 4.05.13 <br />below. <br />1. Please add to Section 2.05.6(3)(b)(iii) a calculation of annual seepage of spoil water into the <br />downdip pitwalls of both pits, using the Darcy equation for flow through a porous medium. <br />The equation is Q = KA(h/1), where Q is volume of flow per unit time, K is hydraulic <br />conductivity, and h/1 is the hydraulic gradient (USGS Ground Water Manual, 1977, page 20). <br />Please use in the calculations a hydraulic gradient of 0.1 ft/ft, based on a representative 6- <br />degree bedding plane dip in the area (hydraulic gradient = tangent of 6 degrees = 0.1). <br />2. Please revise the prediction of spoil spring discharges to the surface (Section 2.05.6(3)(b(iii)) to <br />reflect the requested calculations of annual pitwall seepage.