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• i~«iniiiiiiiiiiu • <br />RECEIVED <br />MINING PLAN EXHI9IT D {coot) <br />JUL 2 5 1998 <br />nraision of Minerals 8 Geology <br />Surface Drainage Plan -Initial 10 Year Operation <br />For the initial 10 years of the operation, removal of all gravel products will reach a maximum of <br />only 50,000 tons per year and the disturbed area will be no greater than 29.2 acres, as shown on <br />Figure 4, enclosed in this section. <br />The ] 0 yeaz design has a disturbed area of 29.2 acres. Overburden and\or topsoil will be stockpiled <br />on the western and northern sides of the disturbed area. Ditches immediately above the piles will <br />be used to prevent any undisturbed runoff from the upland area to the west from entering the site. <br />A sediment collection sump will be dug at the low point of the pit azea to collect all runoff from the <br />100 year - 24 hour event. Since no discharge will occur from the site for this storm event, no <br />NPDES permit will be required. Using the TR-55 charts for runoff at a curve number of 79 and a <br />precipitation of 2.2 inches, the runoff produced is 0.64 inches. Therefore: <br />Total Runoff Volume = 0.64 inches x 1 ftl12 inches x 29.2 acres = 1.55 acre-feet. <br />The pond is also designed to handle the 3 year sediment volume from the disturbed area. This <br />volume is calculated using the recently revised universal soil loss equation RUSLE. For this <br />equation, the erosion loss in tons per acre per year (A) is calculated as follows: <br />A=RxKx(LxS)xCxPxSDL <br />where: <br />A =soil loss in tons/year per acre <br />R =rainfall factor (from standard chart of area) <br />K =soil erodibility factor (function of site specific soil from SCS soil data) <br />26 <br />