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o v_i <br />2.3 Minintt Hydrology <br />• The objective of these studies <br />surface water runoff from the <br />groundwater impact to serve as <br />operation. <br />is to provide an evaluation of the <br />mine area and potential for <br />a basis for final design and <br />2.3.1 Surface Water Hydrologic Controls <br />Surface runoff areas have been subdivided into disturbed and <br />undisturbed areas, see Figures 2.2-1 and 2.3-4. Runoff from <br />disturbed areas will be routed into or through appropriate <br />sedimentation controls that will insure compliance with all <br />applicable effluent limitations when discharged into the ephemeral <br />drainage of Munger Creek or into East Salt Creek. Runoff from the <br />undisturbed areas will be diverted around the disturbances and <br />routed to a natural channel. The design of sedimentation ponds is <br />addressed in Section 2.3.4. <br />The project area was divided into eight watersheds which are shown <br />on Figure 2.3-4. The individual watershed areas range in size from <br />18 acres to 4,800 acres. Hydrologic parameters of each are given in <br />Table 4.5-11. Rainfall values for a 10 year 24 hour precipitation <br />event and runoff rates were established according to Technical <br />Manual No. 1, a Manual for Estimating Flood Characteristics of <br />Natural Flow Streams in Colorado and the publication Peak Flows in <br />• Colorado. The Munger Canyon site is not located near a gauged <br />stream of reference in the manual; therefore, regression equations <br />were derived from the manual. Eight drainage areas shown in Figure <br />2.3-4 with potential effect on disturbed areas associated with the <br />Munger Canyon project, received the most attention and were <br />evaluated as to degree of impact. The size of the culverts needed <br />to pass flow under the roads, around the mine bench and around the <br />waste rock disposal area were based on calculations made on these <br />drainage areas, see Section 4.5.3.3.2. The overall hydrologic <br />regime of Munger Canyon is addressed in Section 4.5. <br />UNDISTURBfiD FLOW - MINE BENCH AREA <br />Runoff from watershed A, 1.3 sgmi, will be carried around the mine <br />bench area in a permanent diversion to be constructed in the valley <br />to the northeast, see Figure 2.2-14. This diversion which is <br />designed to pass the flow from a 100 year 24 hour precipitation <br />event, see Table 4.5-11, will be constructed between the fill <br />associated with the mine bench and the existing ground to the <br />northeast. The gradient of this diversion adjacent to the bench is <br />2.5X. Figure 2.3-2 is the indicated section and gives the hydraulic <br />data used for its design. The gradient in the outslope area is 30X <br />and Figure 2.3-3 shows its section and hydraulic data. <br />The side slopes of the diversion will be revegetated to minimize <br />erosion. That portion of the channel carrying water will be lined <br />with rock for sediment control purposes. A stilling basin will be <br />constructed to reduce the flow velocity before it merges with the <br />original channel. <br />Q~N-o~, <br />