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Section 2 <br />Drainage Contra/Design <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 U.S. Department of Agriculture (USDA) TR 55 report (USDA 1986), <br />the major factors that determine the CN include the hydrologic soil group (HSG), <br />cover type, treatment, hydrologic condition, and antecedent runoff condition (ARC). <br />HSG of the Van 4 Mine area was determined based on USDA, Natural Resources <br />Conservation Service (NRCS) soil map (refer Appendix C). The soil type of the mine <br />area is classified as "Monogram Loam", which has a moderately high rate of water <br />transmission (0.20-0.60 in/hr). Therefore, based on the soil type and soil drainage <br />class, the mine area was classified as HSG "B". <br />The CN for newly graded areas, average ARC, and HSG of "B" is 86. For P equal to <br />3.0 inches and CN equal to 86, S equals 1.63 and Q equals 1.66 inches. Therefore, CDM <br />used 1.66 inches as the design runoff for the berm design calculation. <br />The total runoff volume from Basin 2 was calculated by multiplying the basin area by <br />the design runoff (1.66 inches). Then the calculated total runoff volume was divided <br />by available retention area within the surface facilities area to calculate the minimum <br />required berm elevation of Basin 2. The calculated minimum berm elevation is 1.5 <br />feet, which includes 1-foot of freeboard. Details for these calculations are shown in <br />Table 2-4. <br />As noted on Exhibits A and B, an existing berm encloses Basin 2. CDM recommends <br />that Denison complete a field inspection to confirm that the existing berm satisfies the <br />design criteria (e.g., minimum berm height is greater than or equal to 1.5 feet) and <br />encloses the retention area illustrated in Exhibits A and B. If the existing berm does <br />not meet the above criteria, Denison will modify the berm to satisfy the configuration <br />as illustrated in Exhibits A and B. <br />The total runoff volume from Basin 3 was also calculated by multiplying the basin <br />area by the design runoff (1.66 inches). Then the calculated total runoff volume was <br />divided by available flat retention area along the toe of the DRA to calculate the <br />minimum required berm elevation of Basin 3. The calculated minimum berm <br />elevation is 1.5 feet, which includes 1-foot of freeboard. Details for these calculations <br />are shown in Table 2-4. <br />As noted on Exhibits A and B, an existing berm (or water bar) encloses Basin 3. CDM <br />recommends Denison complete a field inspection to confirm that the existing berm <br />satisfies the design criteria (e.g., minimum berm height is greater than or equal to 1.5 <br />feet) and encloses the retention area illustrated in Exhibits A and B. If the existing <br />berm does not meet the above criteria, Denison will modify the berm to satisfy the <br />configuration as illustrated in Exhibits A and B. <br />Fs <br />2-4 <br />T:t84986Denison Mines\Task Order 1 - Sunday Mines Drainage SludoVan 4 Mine Drainage Study\ReportVan4 Mine Drainage Report_final.d=