Laserfiche WebLink
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 Division's calculation was based on data in the permit application package for climate, soil types <br />and control/practice factors; slope measurements from the existing topography maps submitted <br />annually by SPL; and vegetation monitoring data from the SL7 application for the Phase II bond <br />release and Extended Reference areas. Several slopes in the reclamation area were individually <br />modeled and then averaged and compared to a weighted average of the extended reference areas. <br />The definition for the RUSLE variables are presented below in Table 5: <br />Z able J. RUJLL Variables and their <br />Variable Definition 11 <br />R Climatic erosivity factor due to precipitation <br />K Soil crodibility under a standard condition <br />LS Slope length and steepness factor <br />C Cover management/ land use <br />Only the "C" factor varies <br />between the pre -mining and the <br />post -mining calculations; all <br />other variables are constant for <br />pre -and post -mining. The C <br />factor takes into account land <br />use, vegetative canopy cover, <br />effective cover and grass type. <br />The pre -mining calculation utilized baseline vegetation cover values from the permit application. <br />Table 6. The Division's RUSLE Calculations for Disturbed Areas <br />Area* <br />A <br />R <br />K <br />LS <br />C <br />P <br />YPM11 <br />0.028362 <br />30 <br />0.32 <br />0.984789873 <br />0.003 <br />1 <br />YPM4 <br />0.100375 <br />30 <br />0.32 <br />3.485259632 <br />0.003 <br />1 <br />YPM4-1 <br />0.050055 <br />30 <br />0.32 <br />1.738037222 <br />0.003 <br />1 <br />YPM4-2 <br />0.064747 <br />30 <br />0.32 <br />2.248170942 <br />0.003 <br />1 <br />YPM3-2A <br />0.052765 <br />30 <br />0.32 <br />1.832112897 <br />0.003 <br />1 <br />Average <br />0.059261 <br />Tons/acre/year <br />Tons/acre/year <br />weighted <br />*indicates area within named drainage watershed <br />Table 7. The Divisions RUSLE Calculations for Reference Areas <br />Area <br />A I <br />R <br />K <br />LS <br />C <br />P <br />% Area <br />Weighted <br />Aspen <br />0.119627 <br />30 <br />0.24 <br />16.61 <br />0.001 <br />1 <br />0.244 <br />0.029189 <br />Steep Mnt. Brush <br />0.1433 <br />30 <br />0.2 <br />3.98 <br />0.006 <br />1 <br />0.24 <br />0.034392 <br />Mnt. Brush <br />0.602464 <br />30 <br />0.32 <br />20.92 <br />0.003 <br />1 <br />0.489 <br />0.294605 <br />Sagebrush <br />0.460269 <br />30 <br />0.37 <br />41.51 <br />0.003 <br />1 <br />0.027 <br />0.012427 <br />Tons/acre/year <br />weighted <br />0.370613 <br />The calculations, presented in Tables 6 and 7, indicate that sediment delivery from the mined areas is <br />approximately 0.31 tons /acre/year less than that of the adjacent unmined areas. This is reasonable as <br />the reclaimed areas consist of densely rooted grasses and forbs and exhibit less bare soil than the <br />brush and shrub system. <br />Permit Number C-1994-082 Page 13 of 23 <br />