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SryJamGer?DOD ICnr CUAIfMA)' ~ P0J1J0/BOA/I RPIPOJP x H)'J/r9/A8J! Rl</0>AOIi9A El'AIAOI)rzA 1 3 <br />The majorin• of the vegetation prior to mining in all three areas was Alkali Sagebrush, with minor <br />• areas of Sagebmsh-Grass. The C factor for premising conditions was determined using a weighted <br />average. <br />2.5 SUPPORT PRACTICE FACTOR (PI <br />The P factor represents practices designed to convo] erosion. For the existing reclaimed conditions, a <br />P factor of 0.8 was used to account for the rough soil conditions from disking along contour and seed <br />drilling. For the premising conditions, a P factor of 7.0 was used. <br />3.0 RESULTS AND CONCLUSIONS <br />Calculation spreadsheets shoyadng all inputs and results are included in Attachment 1, Calculation <br />Spreadsheets. Table 2 summarizes the calculation results. <br />u <br />TABLE 2 <br />Sediment Yield Calculation Results <br />Area Annual Sediment Yield <br />tons/acre/year <br />Mart Pit Reclaimed IPre 1986 Reclamation) 0.63 <br />Mart Pit Preminin IAlkali Sa ebrush and Sa ebrush-Grass) 1.05 <br />720 Pit Reclaimed 11995 Reclamation) 0.54 <br />720 Pit Preminin IAlkali Sagebrush and Sa ebrush-Grassi 1.12 <br />Pit 1 Reclaimed 11996 Reclamation) 0.83 <br />Pit 1 Preminin IAlkali Sa ebrush antl Sa ebrush-Grassi 2.39 <br />As indicated br Table 2. calculated sediment yields for the reclaimed conditions are significandy less <br />(35 to GO percent of premising cields) than for the premising conditions for all three of the major <br />mine disturbance areas. This reduction is a reflection of a number of factors including: <br />• Overall reduction of slope gradients in significant portions of the 720 Pit and Pit ] <br />• Reductions in effective hydraulic slope lengths in the 720 Pit and Pit 1 through the use of <br />closed contour furrows <br />• Reductions in surface erosion. mnoff, and sediment vansport potential through surface <br />roughening <br />• Increases in effecvye vegetative cover due to reductions in sagebrush densities (ie: sagebrush <br />provides canopy cover but limits ground corer since antibiotic effects hinder establishment <br />and groy~nh of grass and forb species direcdy under sagebrush plants) <br />The significant reductions in calculated sediment cields provide reasonable evidence of effective <br />hydrologic reclamation consistent y~tith the applicable regulators provisions of Rule 3.03.1(3)(b). <br />• <br />Afwngamrp lI ounn ' HO. Bar %%4078 Steombool SynngJ. CO 804 %% ` (970J 8%J-6?GO <br />u ~u vr-,.u~.,..-e..,n,... <br />