2020-03-24_PERMIT FILE - C1981019A (5)

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RULE 2 PERMITS Runoff, Q = (P-0.2S)2 P+0.8S Curve Number, CN = 1000 10+S, and Initial abstration, la = 0.2S, Where S is the maximum potential difference between P, Precipitation, and Q, Runoff, in inches, at the time of a storm's beginning. Estimating composite Curve Numbers of 67 and 63 for the premining and postmining conditions respectively results in maximum potential differences of 4.93 inches for the premining condition and 5.87 inches for the postmining or reclaimed condition. Utilizing these relationships results in an estimated mean annual runoff or 0.35" and 0.24" for the premining and reclaimed postmining conditions, respectively. These relationships are tabulated below. Item Pre-Mining Post-Mining Curve Number CN 67 63 Runoff, Q, in inches 0.35 0.24 Potential difference, S, in inches 4.93 5.87 Initial abstraction, 1 a, in inches 0.99 1.17 During the life of the mine, it is anticipated that a total of 2298 acres will be eventually disturbed in Streeter Gulch and other areas tributary to Goodspring Creek. Another 1512 acres will be disturbed in areas which are included in the Taylor Creek-Wilson Creek drainage basins. Mean annual runoff from these reclaimed areas are estimated to be as follows: Drainage Basin Premining Postmining Difference Good Spring Creek 79 ac. ft. 55 ac. ft. -24 ac. ft. Taylor Creek 40 ac. ft. 28 ac. ft. -12 ac. ft The hydrologic consequences of mining on the various drainage basins downstream of the Colowyo Mine site are summarized below: Drainage & Premining Postmining Difference Post/Pre Location AF AF AF Good Spring Creek at Axial 1,479 1,455 -24 98.38 Taylor Creek at Mouth 110 98 -12 89.09 Wilson Creek Near Axial 1,372 1,360 -12 99.13 Milk Creek Rule 2 Permits 2.04-33 Revision Date: 12/20/19 Revision No.: TR-135