Laserfiche WebLink
Runoff Curve Numbers(CN) for Watershed Area (Mining Phase f) <br />Description Hydrolog[c Soil Group Area (acres) CN <br />Streets and Roads: Dirt Group C Soils 2.00 87 <br />Pasture or Rangeland: Good (50-75% ground Group C Soils 30.00 74 <br />cover; not heavily grazed) <br />Total Area and Average CN 32.00 74.81 <br />Hydrologic Soil Group <br />Group A Soils: High infiltration (low moot?). Sand, loamy sand, or sandy loam. Infiltration m[e> 0.3 inch/hr when wet. <br />Group B Soils: Moderate iofiltation (modemte runott). Silt loam or loam. Infiltration mte 0.15 to 0.3 inch/hr whrn wet. <br />Group C Sons: Low infiltmtion (moderate to high mnott). Sandy clay loam. Infiltration rate 0.05 m 0.15 inct/hr when we <br />Group D Soils: Very low infiltration (high ruuoft). Clay loam, silty clay loam, sandy clay, silty clay, or clay. Infiltration <br />' mte 0 to 0.05 inch/hr when wet. <br />The storage volume of the pond is calculated as the extraction azea above the water table. The <br />water table lies approximately 6 feet below the surrounding surface. This allows for a more <br />than sufficient storage volume for all mining azeas. <br />Stormwater/Sediment Pond Desien <br />Design Event 100-yr 24-hr Event <br />Design Precipitation (inches) 2.60 <br />Watershed Area (acre) 32.00 <br />Watershed Average CN 74.81 <br />Calculated S 3.37 <br />Calculated Runoff Volume (Q) 0.70 <br />Calculated Runoff Volume (acre-ft) 1.87 <br />Ponding Percentage <br />5.0% <br />Actual Ruuoff (acre-ft) 1.78 <br />Since very little area lies outside the pit and with the ability to store 6 feet of inflow per acre, it <br />is easily seen that the ponds will have sufficient storage. All water trapped fmm the storm <br />event will be allowed to evaporate or seep out of the pond within a 24-hour period. <br />Topsoil and Overburden Stripping <br />Topsoil will be stripped and stockpiled as the isolation berm prior to the commencement of <br />mining in a particular mining azea. After stripping, the topsoil stockpile will be seeded <br />promptly in order to minimize soil loss for any stockpiles which are in place for more than one <br />year. There will be an abundance of topsoil due to the reduction in surface azea caused by the <br />formation of a lake within the permit area. This excess topsoil will be used for extra growth <br />11/7/2005 Page D-3 <br />