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HYDROLOGIC DOCUMENTATION <br />SMALL AREA EXEMPTION <br />SOUTH MINE FAN INSTALLATION <br />1.0 Fan Ins[allation Sediment Fence <br />The following calculations demons[nte the amount of sediment fence rurface area required to <br />adequately handle the runoff from the south Ean ins[allation area. <br />Runoff peak dixharge calculations were performed utilizing the SEDCAD+ computer model <br />consistent with the methodology previously discussed in this Exhibit. The sediment fence was <br />designed [o handle the peak discharge from a 10-year, 24-hour storm event. <br />1.1 Hydrology Inputs <br />The CN numbers used were obtained from Procedures for Determining Peak Flows in Colorado <br />and Technical Release No. 55. Based on soil type and vegetation cover, curve numbers were <br />determined for the following condition. <br />Undisturbed <br />Soil Type: B <br />Ground Cover: > 3096, Fair <br />Cover Type: Pinyon -Juniper <br />• <br />CN: 58 <br />Revegetated <br />Soil Type: B <br />Ground Cover: > 30 %, Fair <br />Cover Type: Herbaceous <br />CN: 71 <br />All other hydrology inputs are shown on the attached SEDCAD+ computer printouts <br />1.2 Hydrology Results <br />Peak Discharge: 0.27 ds <br />1.3 Sediment Fence Requirements <br />Sediment Fence Permiuivi[y: 15 gal/min/ft' or 0.033 cfs/ft' <br />Required Surface Area: 0.27 cfs / 0.033 cfs/ft= ~ 8 ft' <br />2.0 Cut Material Stockpile Catchment Ditch <br />The following alcvlations demonstrate that the proposed cathment ditch is adequate to control <br />• drainage and sedimentation from the cut material stockpile uea. <br />~: <br />CLVe07RISAPP <br />vo/+~ ~~ Revised -November 1993 <br />