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In accordance with Rule 3.03.1(3)(b) and with Section III.A.7.a. of the Division's 1995 Guideline <br /> Regarding Selected Coal Mine Bond Release Issues, Trapper submitted two evaluations to demonstrate <br /> that runoff from each bond release block will result in equivalent or lesser sediment contribution as <br /> compared to baseline conditions and similar undisturbed lands. <br /> Trapper's bond release application compares pre and postmining sediment yields by calculating <br /> expected sediment yields for both conditions. Trapper used the USLE(Universal Soil Loss Equation), <br /> and SEDCAD 4 for Windows calculation methods. The USLE calculates expected average annual <br /> soil loss per acre of land (rate of erosion), based on slope, rainfall pattern, soil type and vegetation <br /> type. SEDCAD 4 calculates the expected settleable solids concentration in runoff from a precipitation <br /> event. Trapper's two sets of pre-mining and post-mining sediment control demonstration models <br /> comprise Appendix 3 (SEDCAD 4), and Section 1.4 (USLE), of the bond release application. <br /> LISLE Comparison: Only the "C" factor and the Curve Number varies between the pre-mining and <br /> the post-mining calculations; all other variables are constant for pre-and post-mining. The C factor <br /> takes into account land use, vegetative canopy cover, effective cover and grass type. The Curve <br /> Number represents vegetation. The pre-mining calculation utilized baseline vegetation cover values <br /> from the permit application (Table 2.3-13 and 4.4-2). The post-mining calculation uses vegetation <br /> cover data for the disturbed area collected in 2023. <br /> The variables used in the calculations are reasonable for making the comparison. The comparison <br /> therefore is technically valid. A chief cause of soil loss is transport of solids in suspension. The <br /> comparison indicates the total drainage area does not yield more suspended solids than pre-mining <br /> conditions. <br /> The USLE is an empirical formula approximating <br /> expected sediment yield from a parcel of land. It <br /> is reasonable to hypothesize that the USLE is <br /> useful for discriminating between two <br /> significantly different yield rates. However, it is <br /> not useful for discriminating between two yield - <br /> rates of similar magnitude. For the bond release <br /> parcels in SL24, Trapper calculated a premining , <br /> sediment yield rate of 2.74 tons per acre per year " <br /> and a postmining rate of 1.34 tons per acre per year. `�� <br /> 5 <br /> The difference between these two calculated rates ++'' <br /> illustrates that the postmining rate is less than the <br /> premining rate. This conclusion is only valid if <br /> Trapper used reasonable variables in the USLE <br /> calculations. The variables employed in the <br /> USLE equation, and their definitions are <br /> presented in the Tables 3 and 4 below. The <br /> Division finds Trapper's selected USLE variables <br /> reasonable. The variables are similar to those <br /> found acceptable by the Division for Trapper's Photo 3: Recently repaired reconstructed <br /> previous bond releases. The lands in SL24 are drainage MF3 in parcel LA18, with check dam in <br /> similar to lands in previous bond releases. upper right. <br /> Permit Number C1981010 <br /> SL24 Page 11 of 16 <br />