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4.6.3 Protection of the Hvdrologic Balance <br />9.6.3.1 Surface Water • <br />9.6.3.1.1 Process Facility Area <br />Overland flow from undisturbed areas above the process facility <br />area will be routed through the facilities and collected in Sedi- <br />ment Pond A. Calculations and on site observations during heavy <br />rainfall substantiate that the flows from the undisturbed areas <br />will be small. Diversion channels were considered to divert <br />upstream undisturbed flows around the surface facilities. However, <br />the steep slope gradients and geot:echnical considerations indicated <br />the hydrologic balance would have the greatest amount of protection <br />by oversizing Pond A by 35 percent to accommodate the undisturbed <br />flows (Figure 9.3-6). <br />The process facility area will bE~ graded and contoured to drain to <br />Pond A. Final contours will drain all runoff and other drainage <br />that occur in the process area into sediment control Pond A. Pond • <br />A is located downstream of the preparation facilities as shown in <br />Figure 4.2-3. <br />Sediment Pond A will be dry most of the time. Excess surface <br />runoff collected during storms will be recycled for subsequent use <br />in the hydraulic mining process. Discharges from Pond A will be <br />very infrequent (only flows in excess of the 10-year, 29-hour <br />event) but will comply with State and Federal effluent regulations. <br />An NPDES discharge permit has been obtained from the Colorado <br />Department of Health. <br />Pond A is designed to store the runoff from the 10-year, 29-hour <br />storm. Cross sections and details are shown in Figure 9.3-6. The <br />pond has an emergency spillway designed to pass the discharge from <br />a 25-year, 29-hour storm, with adequate freeboard. The pond does <br />NCIG - Coal Ridge #1 4-78 ABC/1145/910509 • <br />