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Vegetation Cover <br /> The Colowyo Mine uses two reference areas for the comparison of success of their SL-19 <br /> reclamation parcels. The reference areas are the sagebrush reference area and the mountain shrub <br /> reference area. Success standards are based on weighted average of the pre-mining vegetation <br /> communities in each reclamation block(as shown on Map 3 and 4 in Colowyo's PAP). <br /> Permit Page 4.15-18 states that the"...herbaceous cover of the revegetated area will be considered <br /> adequate for final bond release if it is not less than 90% of the herbaceous cover as determined from <br /> the reference areas with 90% statistical confidence utilizing a standard student's statistical t-test <br /> comparison of the means." <br /> All reclamation parcels contained in SL-19 being requested for Phase II bond release were sampled <br /> in 2019 in accordance with the vegetation monitoring plan, detailed in Volume 1, Section 4.15 in <br /> the Colowyo PAP. Sample adequacy was determined using the Cochran formula. Both the <br /> sampling plan and the sample adequacy determination are acceptable to the Division. Results for <br /> vegetation cover for each reclamation parcel is summarized below. <br /> SedimentoloQU <br /> The Division reviewed the sedimentology evaluation provided in the SL-19 application. As per <br /> Rule 4.15.1(2)(b),vegetation cover shall be capable of stabilizing the soil surface to achieve erosion <br /> control equal to pre-mining levels. To demonstrate this, Colowyo provided estimation on soil loss <br /> based upon post-mining site specific data using the Revised Universal Soil Loss Equation <br /> (RUSLE). Results from the RUSLE were then compared to baseline data from associated slopes to <br /> the reclamation blocks being requested for Phase II bond release. For SL-19,there was a total of 3 <br /> slopes associated with the SL-19 reclamation blocks that were evaluated. Slopes 1 and 2 are located <br /> in West Pit and Slope 3 is located in the East Pit as shown in Section III of the SL-19 application. <br /> Results of this demonstration as well as vegetative cover results are summarized below. <br /> Phase II Bond Release Parcel Result Summary—Cover <br /> Herbaceous cover: 39.78% <br /> Herbaceous cover standard(90%): 15.95% <br /> The 2019 sample data successfully exceeds 90% of the herbaceous cover standard. <br /> Phase II Bond Release Parcel Result Summary—Sedimentologyy <br /> Post-Mining—Slope 1: 0.047 tons/acre/year <br /> Pre-Mining—Slope 1: 0.488 tons/acre/year <br /> The 2019 sedimentology evaluation data shows post-mining condition sediment loss to be <br /> less than pre-mining conditions. <br /> Post-Mining—Slope 2: 0.015 tons/acre/year <br /> Proposed Decision and Findings of Compliance October 26,2020 <br /> Partial Phase II Bond Release SL-19 Page 7 <br />