2010-07-21_PERMIT FILE - C1982056A (4)

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NORTH MINING DISTRICT (PR99 -05 and PR06 -07) Is The mine inflow predictions were generated using a different methodology than was used for the EMD. The discussion and calculations are presented in Section 2.05 of this application. The methodology used a mirror - well technique, which should be adequate for predicting inflows into the mine. NMD (Panels 17 -Right through 25- Ri2ht, PR03 -06 and PR06 -07) - The mine inflow predictions were generated using a different methodology than was used for the EMD. The discussion and calculations are presented in Section 2.05.6(3) of this application. The methodology used a mirror -well technique, which should be adequate for predicting inflows into the mine. WESTERN MINING DISTRICT (WMD, Panels 12 -Left through 17 -Left, PR06 -07, TR08 -64, PR09 -08) Because it falls within the Twentymile Park Basin, the geology of the WMD is similar to the previously permitted areas. The Twentymile Park synclinal axis, oriented NE -SW, is the northern boundary of the WMD, the area is bounded on the east by one of the primary faults (orient NNW to SSE), the western boundary is the Tow Creek Anticline and Hayden Syncline, and the SMD lies along the southern limit of the area. General surface geology and coal seam structure for all mine areas are shown on Maps 5, and 6 (Confidential), respectively. With the exception of the primary fault that extends through the eastern portion of the WMD, the WMD sedimentary strata are not disturbed by any significant faults. The structural and lithologic characteristics of the permit area are depicted on Geologic Cross Sections B -B' and E -E' (both east -west, and Maps 8 and 9A, Confidential). Under PR06 -06, only limited main and sub -main development will occur. Given the limited area that will be developed, groundwater inflows are expected to be minimal. Prior to actual mining of this area, inflow modeling will be completed and incorporated into the PAP. (2) The use of approved modeling techniques may be included as part of the permit application, but the same surface and ground water information ma by a required for each site as when models are not used. RESPONSE Modeling of geologic conditions has been utilized to predict subsidence potential; the results of the modeling are set forth in Exhibit 7, Subsidence Predictions. Overburden stratigraphy, uniaxial compressive strength and tensile strength, angle of draw, caving, and flexure characteristics have been modeled using methods described in the Subsidence Engineer's Handbook (NCB Mining Department, 1975). Modeling of surface water conditions has been utilized as set forth in Exhibit 8, Sediment Control Plan. Characteristics of surface runoff, peak flow, reservoir routing, sediment yield, and theoretical detention time have been modeled using the techniques described in "Procedures for Determining Peak Flows in Colorado" (USDA, SCS 1977) and "Applied Hydrology and Sedimentology For Disturbed Areas" (Barfield, Warner and Haan 1981). These techniques have been incorporated into the DEPOSITS model, which has been utilized in the design of treatment facilities for the underground mine. Finally, streamflow and water quality in streams draining the general area has been modeled using the WATBAL model, for the purposes of the assessment of probable hydrologic consequences of mining on surface water, required by Rule 2.05.6(3). Modeling of ground water conditions has been utilized in this application, specifically under Rule 2.05.6(3) and in Exhibit 9, Aquifer Test Data. Dewatering, drawdown and solute transport characteristics have been modeled using the analytical methods described in "Ground Water Hydraulics" (Lohman 1979), "Selected Handheld Calculator Codes for the Evaluation of the Cumulative Hydrologic Impacts of Mining" USDI. Office of Surface Mining 1981, and the finite- difference GRWATER computer model described in "Ground Water Hydrology and Hydraulic" (McWhorter and Sunada 1977). PR09 -08 2.04 -11 04/10/09