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44 -' <br /> 1 <br /> DURAY SILVER MINES <br /> The storage volume to prevent discharge is calculated as the volume of the main pit above the <br /> water table. The water table lies greater than 5 feet below the surrounding surface. This <br /> scenario assumes that the pump is not working and the pit has filled to equilibrium level. The <br /> area of lower pit that will have the 5 feet of available height is calculated below: <br /> The following areas were calculated using a scaled map image from 2011 in Survcadd which <br /> was used in the SWMP Map. <br /> Project: SWB-7 By: B Langenfeld Date: 04/05/12 15:34:20 <br /> Location: Revenue Mine <br /> 1. Runoff Curve Number (CN) <br /> Cover description CN Soil Group Area(Acre) <br /> Mined Land, Disturbed (Poor) 87 C 14.431 <br /> CN (weighted): 87.0 <br /> Total Area: 14.431 Acre <br /> 2. Runoff <br /> Return Period: 10-Year <br /> Rainfall, P: 2.60 in <br /> Runoff, Q: 1.3952 in <br /> Runoff Volume: 1.6778 Acre-Ft <br /> The available storage volume of Pond 2 is a minimum of 2.02 acre feet therefore the pond is <br /> adequately sized. <br /> Runoff Curve Numbers CN for Watershed Area Draining to Mine Pond 3 6.995 acres <br /> Description Hydrologic Soil Group Area (acres) CN <br /> Disturbed Land Group C Soils 6.955 87 <br /> An area of 6.955 acres will drain to the discharge point for Pond 3 for the worst case <br /> disturbance of this site. <br /> Stormwater Management Plan 14 1 P a g e <br />