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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 />