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• KERR COAL COMPANY -PARTIAL BOND RELEASE <br />HYDROLOGIC RECLAMATION EVALUATION <br />1.0 INTRODUCTION <br />As part of Phase II partial bond release application for the 720 Pit and Pit 7 reclaimed areas, <br />1\4ontgomen~ \X~atson (\7\X--~ conducted a sediment yield analysis to determine if calculated sediment <br />yields for the reclaimed areas are comparable to or better than calculated sediment yields for <br />premising conditions. l7ajor mine disturbance areas include; the Marr Pit area, which was reclaimed <br />and seeded prior to 7986; the 720 Pit area, which was reclaimed and seeded in 7995: and the Pit ] <br />area, which was reclaimed and seeded in 7996. The folloudng sections summarize the methodology <br />and assumptions used in the analysis and ana]vsis results and conclusions. <br />2.0 METHODOLOGY AND ASSUMPTIONS <br />Sediment vields for the major mine disturbance areas were determined for both premising and <br />reclaimed conditions using acma] vegetative cover data (reference area data for premising and <br />disturbed area data for reclaimed) and the Revised Universal Soi] Loss Equation (RUBLE): <br />A=RKLSCP <br />\V}tere: A=Average annual soil loss in tons/acre/}m <br />• R= Rainfall factor R <br />K= soil erodibilin• factor <br />L5= Length/slope factor <br />C= Coyer management factor <br />P= Suppon practice factor <br />RUBLE was used in preference to SEDCAD+ because RUBLE focuses specifically on sediment <br />vields, where SEDCAD focuses on watershed hydraulics. In fact, SEDCAD+ uses an older and <br />slighdy less accurate version of RUBLE to calculate sediment yields. <br />2.1 RAINFALL FACTOR IR) <br />The R factor is an expression of the erosivin of rainfall and runoff at a particular location. An <br />average annual R factor is needed when computing long-term erosion. M\X% used the same R factor <br />used in the existing Pemvt document u-hick was determined using the folloudng equation: <br />:~ <br />R„n~,,,,t = 29Pz.h for a Type I] storrn <br />Pao = 2-tear, 6-hour precipitation in inches = 0.8 inches <br /> <br />2.2 SOIL ERODIBILITY IKI <br />• The K factor reflects the susceptibilin of the soil material to erosion, the potential for sedvnem <br />vanspon_ and the amount and rate of runoff given a particular rainfall input, as measured under <br />standard conditions. For this analysis, ;\1\\% used the K value from the evsting permit document. <br />,1]nm¢gmrri A otwrr ' P.O. Bax 774018 StromGmt SpnnE ~~ CO 8041%' (970f 8i9-6?G0 <br />Y )'i. -.. iii lY.i Arv ivv... l-~mry~ Mxanu <br />%iv.., <br />