Laserfiche WebLink
Section 6 <br />Sunday Mine <br />i? <br />S is related to the soil and cover conditions of the watershed through the Curve <br />Number (CN). CN has a range of 0 to 100, and S is related to CN by: <br />S _ 1000 -10 <br />CN <br />According to the US Department of Agriculture (USDA) TR 55 report (USDA 1986), <br />the CN for bare soil of hydrologic soil group of "D" is 94. For P equal to 3.0 inches <br />and CN equal to 94, S equals 0.64 and Q equals 2.35 inches. Therefore, CDM used 2.35 <br />inches as the design runoff for the berm design calculations. <br />The total runoff volume was divided by available catchment area within the surface <br />facilities area to calculate the minimum required berm elevations of Basins 2 through <br />5. The calculated minimum berm elevation is 1.5 feet, which includes 1-foot of <br />freeboard, for Basins 2 through 5. Existing berms enclose Basins 2 through 5. <br />However, CDM recommends increasing the height of the existing berms, where they <br />are less than 1.5-feet high, to the calculated minimum elevation. Details for this <br />calculation are included in Appendix B. CDM also recommends connecting any <br />breached areas along the berms. In addition, existing berms enclosing Basins 3 and 4 <br />should be extended to contain the 100-year, 24-hour event within the basin boundary <br />(refer to Exhibit E-1). <br />The total runoff volume of Basin 6 was calculated to evaluate the sizing of the <br />proposed catchment basin. Assuming that the proposed catchment basin is 45 feet <br />wide and 150 feet long with 1.5:1 (H:V) bank slope, the minimum required depth of <br />the catchment basin is approximately 4.0 feet. Therefore, CDM recommends <br />modifying the existing catchment area to a depth of 5.0 feet, which includes 1-foot of <br />freeboard, a width of 45 feet, and a length of 150 feet, to contain the 100-year, 24-hour <br />storm event (refer to Exhibits E-1 and E-2). Details for this calculation are included in <br />Appendix B. <br />The total runoff volume of Basin 7 was also calculated to evaluate the sizing of the <br />proposed catchment basin. Assuming that the proposed catchment basin is 60 feet <br />wide and 400 feet long with 1.5:1 (H:V) bank slope, the minimum required depth of <br />the catchment basin is approximately 3.5 feet. Therefore, CDM recommends <br />modifying the existing catchment area to a depth of 4.5 feet, which includes 1-foot of <br />freeboard, a width of 60 feet, and a length of 400 feet, to contain the 100-year, 24-hour <br />storm event (refer to Exhibits E-1 and E-2). Details for this calculation are included in <br />Appendix B. <br />6.5 Conclusions and Recommendations <br />CDM proposed additional control structures to route offsite surface flow around the <br />surface mine area and contain the 100-year, 24-hr storm event within the onsite berms <br />and catchment. CDM recommends the following for Sunday Mine storm water <br />drainage control: <br /> <br />6-4 <br />• <br />ON649W - DenisonWask Order 1 - Sunday Minas Dreiroge StudA]ReporWinet ReporWinal Sunday Mines Drairo9e ReporL052208.doc