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Page 1 <br />Section 3.03.1 <br />SOUTHFIELD MINE FACILITY AND RDA <br />PHASE II BOND RELEASE <br />RECLAIMED AND NON -MINED LANDS SEDIMENT ANALYSIS <br />INTRODUCTION <br />As part of Phase II bond release for the Southfield Mine Facility and RDA, a sediment yield analysis <br />was developed to determine if the sediment yield from the existing reclaimed condition is <br />comparable or better than the non -mined condition. The Facility area was reclaimed and seeded in <br />2003. The RDA was reclaimed progressively over the life of the mine and seeded in various phases <br />beginning in 1983 through the final seeding in 2003. <br />Rule 3.03.1(3) (b) requires that "No more than sixty (60) percent of the bond shall be released so long <br />as the lands to which the release would be applicable are contributing suspended solids to streamflow <br />or runoff outside the permit area in excess of premining levels as determined by baseline data or in <br />excess of levels determined on adjacent nonmined areas; until soil productivity for prime farmlands <br />has returned to equivalent levels of yield as nonmined land of the same soil type on the surrounding <br />area under equivalent management practices as determined from the soil survey performed under <br />2.04.12 and 2.06.6 and the success determination methodology of 4.25.5(3)(a); or, on alluvial valley <br />floors, until the essential hydrologic functions and agricultural productivity have been reestablished." <br />The following is the methodology and assumptions used in this analysis to demonstrate that the <br />reclaimed area does not contribute excess suspended solids to streamflow as compared to a similar <br />non -mined area. <br />METHODOLOGY AND ASSUMPTIONS <br />The sediment yield for both pre and post mine conditions were determined using the Revised <br />Universal Soil Loss Equation (RUSLE): <br />A=RKLSCP <br />Where: A= Average annual soil loss in tons/acre/yr <br />R= Rainfall factor R <br />K= soil erodibility <br />LS= Length/slope factor <br />C= Cover management <br />P= Support practice <br />Rainfall Energy Factor (R) <br />The R factor is a representation of rainfall energy at a particular location. An average annual R factor <br />is needed when computing long-term erosion. The R factor used in this sediment calculation is the <br />same as the R factor used in the approved Southfield permit application, which was determined using <br />the following equation: <br />R,,,.., = 27P2,6 2 2 for a Type II storm <br />P2.6 = 2 year, 6 hour precipitation in inches <br />= 1.2 inches <br />