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SOUTHFIELD MINE LOADOUT <br />PHASE 2 BOND RELEASE <br />PRE AND POST MINE SEDIMENT ANALISIS <br />1.0 INTRODUCTION <br />As part of phase 2 bond release for the Southfield Mine Loadout, MWH has conducted a sediment <br />yield analysis to determine if the sediment yield from the existing post mine conditions is comparable <br />or better than pre mine conditions. The Loadout area was reclaimed and seeded during 1997 and <br />reseeded again March, 1999. The following is the methodology and assumptions used in the analysis. <br />2.0 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) were: <br />A= RKLSCP <br />Where: R= 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 />2.1 Rainfall Factor a) <br />The R factor is an excerption of the erosivity of rainfall and runoff at a particular location. An <br />average annual R factor is needed when computing long term erosion. MW used the same R factor <br />used in the existing Permit document which was determined using the following equation: <br />Rannuar = 27P2,62.2 for a Type II storm <br />P2,6 = 2 year, 6 hour precipitation in inches <br />= 0.8 inches <br />R= 27 x (0.8)22 = 16.4 <br />2.2 Soil Erodibility(K) <br />The K factor representes the susceptibility of the soil material to erosion, transportility of the sediment, and <br />the amount of runoff given aparticulare rainfall input, as measured under started conditions. For this <br />analysis MW used the K value from the existing permit document. <br />K = 0.32 (Soil Type- Kim - Cascajo complex) <br />2.3 Length Slope Factor (LS) <br />The LS factor accounts for the effects of a hillslope length (L) and a hillslopes - gradenent (S). The <br />equation for determining the LS factor is: <br />