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TO: George Patterson <br />P.O. Box 459 <br />115 East Main <br />Florence, CO 81226 <br />FROM: Thomas E. Leidich <br />MWH <br />DATE <br />REFERENCE: <br />March 9, 2010 <br />SUBJECT: Kerr Coal Mine Tipple Phase 3 Bond Release Pre And Post Mine Sediment <br />Analysis <br />1.0 INTRODUCTION <br />As part of the final bond release for the Kerr Coal Mine Tipple Area, MWH has conducted a sediment <br />yield analysis to determine if the sediment yield from the existing post-mine conditions is comparable or <br />better than pre-mine conditions. The Tipple Area was reclaimed and seeded in 1999. The following is <br />the methodology and assumptions used in the analysis. <br />2.0 METHODOLOGY AND ASSUMPTIONS <br />The sediment yields for both pre- and post-mine conditions were determined using the Revised <br />° Universal Soil Loss Equation (RUSLE). <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 (R) <br />The R factor is an excerption of the erosivity of rainfall and runoff at a particular location. An average <br />annual R factor is needed when computing long-term erosion. MWH used the same R factor that was <br />determined in the existing permit with the following equation: