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JD -7 Mine – Drainage Design Plan 18 <br />number of 80, 71, or 62 corresponding to an herbaceous mix of grass, weeds, and minor brush, in poor, fair, or <br />good condition or 86 for newly graded area (Table 9). These curve numbers also reflect the reclamation <br />practices for the operating mine. Reclamation of the OPMW will occur in a phased approach. <br />Recontouring and revegetation will be ongoing as the waste rock pile grows. The surface will be contoured <br />by tracking, furrowing, and seeding. Heavy equipment will be used to pock the surface for water retention <br />to promote more successful vegetation establishment. <br />For sub - basins containing more than one soil or cover type, weighted average curve numbers were <br />calculated based on the relative areas of each CN. The spatial distribution of curve numbers across the JD- <br />7 Mine area for the current condition is shown in Figure 6. <br />Site curve numbers are listed in Table 9 and the area - weighted average curve numbers for each modeled <br />sub -basin are provided in Attachment 2. <br />Table 8. Runoff Curve Numbers for Arid and Semi -Arid Rangelands <br />(Table 2 -2d of TR -55 [NRCS, 1986]) <br />Cover Description <br />Curve Numbers for <br />Hydrologic Soil Grou <br />Cover Type <br />nditi og (2) <br />Coondition <br />A <br />B <br />C <br />D <br />Herbaceous - mixture of grass, weeds, and low - growing brush, <br />with brush the minor element <br />Poor <br />80 <br />87 <br />93 <br />Fair <br />71 <br />81 <br />89 <br />Good <br />62 <br />74 <br />85 <br />Oak - aspen— mountain brush mixture of oak brush, aspen, <br />mountain mahogany, bitter brush, maple, and other brush <br />Poor <br />66 <br />74 <br />79 <br />Fair <br />48 <br />57 <br />63 <br />Good <br />30 <br />41 <br />48 <br />Pinyon-juniper—pinyon, juniper, or both; grass understory <br />Poor <br />75 <br />85 <br />89 <br />Fair <br />58 <br />73 <br />80 <br />Good <br />41 <br />61 <br />71 <br />Sagebrush with grass understory <br />Poor <br />67 <br />80 <br />85 <br />Fair <br />51 <br />63 <br />70 <br />Good <br />35 <br />47 <br />55 <br />Desert shrub —major plants include saltbush, greasewood, <br />creosote bush, blackbrush, bursage, palo verde, mesquite, and <br />cactus <br />Poor <br />63 <br />77 <br />85 <br />88 <br />Fair <br />55 <br />72 <br />81 <br />86 <br />Good <br />49 <br />68 <br />79 <br />84 <br />Gravel Road <br />76 <br />85 <br />89 <br />91 <br />Notes- <br />( 1) Based on average runoff condition, and la, = 0.2S. <br />(2) Poor- <30% ground cover (litter, grass, and brush overstory). <br />Fair. 30 to 70% ground cover. <br />Good. > 70% ground cover. <br />(3) Source for gravel road CN is Table 2 -2a of TR -55 (NRCS 1986) <br />4149A.140207 Whetstone Associates <br />