2020-07-06_GENERAL DOCUMENTS - C1994082

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calculated 2016 cover standard was 44.9%. The results of vegetation monitoring conducted on the bond release area, compared with reverence area monitoring result indicate SPL successfully established vegetation supporting the approved postmining land use. Successful revegetation for the parameter of cover was demonstrated in both 2015 and 2016. Suspended Solids Demonstration The operator submitted pond discharge sample data for all of the ponds receiving discharge from the proposed release area, as well as receiving stream sample data from monitoring points upstream and downstream of the pond outfalls. The pond outfall data indicate that total suspended solids (TSS) contributions do not exceed the limits set forth by the Colorado Department of Public Health and Environment. Monitoring data of the upstream and downstream receiving stream sites indicate that TSS is reduced from the upstream site at the downstream site. The sediment ponds receiving runoff from the proposed release area (Ponds 010, 011, 012, 013, and 014) have all been proposed as permanent ponds; the operator demonstrated that the quantity and quality of impounded water were appropriate for their intended use. Final approval is dependent on approval from the Colorado Department of Water Resources where water rights are concerned. In addition to the pond effluent sample data submitted by SPL, the Division requested annual sediment level data from Seneca Property LLC (Table 4), for the ponds receiving run off from the proposed release area. The data show that sediment levels in the ponds have stabilized since revegetation activities began in 2006. None of the ponds have required cleaning since Pond 010 was dredged in 2002 and Pond 011 in 2003. Table 4: Sediment Data Provided by Seneca Coal Company The Division also independently completed a Revised Universal Soil Loss Equation (RUSLE) calculation comparing the reclaimed areas to the adjacent unmined areas. The RUSLE calculates expected average annual soil loss per acre of land (rate of erosion), based on slope, rainfall pattern, soil type and vegetation type from the equation A=RKLSCP; where A (average annual soil loss) represents the product of the six variables defined below. The RUSLE is an empirical formula approximating expected sediment yield from a parcel of land. It is reasonable to hypothesize that the RUSLE is useful for discriminating between two significantly different yield rates. However, it is not useful for discriminating between two yield rates of similar magnitude. Permit Number C-1994-082 Page 12 of 23 Sediment Trends Pond Id ac ft gained/lost by year Year 2009 2010 2011 2012 2013 2014 2015 atershed area 010 00 -0.2 -0.2 0 0.3 -1.4 0 940.4 ac 011 00 00 00 0 -0.1 0.1 0 141.3 ac 012 00 -0.4 1 -0.1 -0.4 1 -0.1 1 0 1 0 136.8 ac 013 0.1 -0.1 0.1 -0.2 -0.2 0 0 34 ac 014 3.0 -0.1 0.1 0 0 0.5 0 154.3 ac The Division also independently completed a Revised Universal Soil Loss Equation (RUSLE) calculation comparing the reclaimed areas to the adjacent unmined areas. The RUSLE calculates expected average annual soil loss per acre of land (rate of erosion), based on slope, rainfall pattern, soil type and vegetation type from the equation A=RKLSCP; where A (average annual soil loss) represents the product of the six variables defined below. The RUSLE is an empirical formula approximating expected sediment yield from a parcel of land. It is reasonable to hypothesize that the RUSLE is useful for discriminating between two significantly different yield rates. However, it is not useful for discriminating between two yield rates of similar magnitude. Permit Number C-1994-082 Page 12 of 23