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-.,,.. Lithologic analyses of overburden at the Erlna mine described in Section 2.2.2.2 found no material that was either acid-forming, toxic-forming, or would form condi- tions detrimental to biota or usr_s of water. This conclusion is confirmed by the analysis of revegetation success on. raw spoils as well as the water quality and fish and wildlife portions of the environmental resources description. Continued monitoring of the surface and ground water, as rlescriherl in Sections L' and VI, will constitute a warning system if undetected detrimental overburden chemicals have come in contact with water. V. HYDROLOGIC l3ALANCF.; SURFACE [•JATER (2.04.5, 2.04.7, 2.05.3(4), 2.05.6(3), 9.05 A11 runoff from disturbed areas at the mine site is routed through sedimentation ponds in order to reduce degradation ol` wafer quality in Trout and Oak Creeks. The applicant requested, however, that certain small areas be exempted from this require- ment. These are areas of minor disturbance on the frinrles of mining activity or adjacent to buildings at the mine site that comprise small acreages and/or are located on drainage divides. Alternative sediment control will be provided by contour furrowing, revegetation and strawbale filters (p. 4.6-56 of the permit appli- cation). In order that the pz'oposed sedimentation control plan be incompliance with Section 4.05.2(3) of the Colorado permanent regulatory program, the Division hereby grants an exemption from the requirements of 4.05.2(1) for the following areas: Area ~ Acreage Location clap West Ridge 14.5 Ex. 4.6-17 West Ri dqe 9.5 Ex. a.6-.17 Center Ridge 2.1 Ex. 4. u'-23 Tipple Area 0.3 Ex. 4.6-22 Moffat Area 25 Ex. 4.G-2 The exemption :s being yranterl in accordance with S,~ction 9.05.2(3) based on the finding that 1) rho construction of sediment ponds i, either impractical or unfeasible, or 2) the area of disturbance is r,ma11 such that a!te nr~~tive sediment control measures are adequate to meet effluent limitations. Peak flows For all water control structures, with the erception of those in the [Jest Ridge area, were generated using the [•JASFfF'O subroutine of the DEPOSITS model re- searched by the University of kentud:y. These flows were checked using the Soil Conservation Service publication TP.-55, L/rhnn Rydrolorry for Small [•Jatersheds, and found to be acceptable. Precipitation estimates r~•cre verified using NOAA infor- mation. The Curve Numbers (GV) were rcvicwerl, and, although questionably low, were sufficiently justified (Volume 77, Section 4.6 of the permit application). Sedi- ment storage calculations based on the Universal Soils 7,oss Equation were checked and found to be acceptable. Using the 10-year, 24-hour inflow hydrograph, sediment inflow, pond capacity and outflow hydrograph, the DEPOSITS model generated, among other output, the peat, stage of runoff and the detention time of flow in the pond.