2023-11-03_GENERAL DOCUMENTS - C1981019

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reclamation parcels. The reference areas are the sagebrush reference area and the mountain shrub reference area. Success standards are based on weighted average of the pre-mining vegetation communities in each reclamation block(as shown on Map 3 and 4 in Colowyo's PAP). Permit Page 4.15-18 states that the"...herbaceous cover of the revegetated area will be considered adequate for final bond release if it is not less than 90% of the herbaceous cover as determined from the reference areas with 90% statistical confidence utilizing a standard student's statistical t-test comparison of the means." All reclamation parcels contained in SL-22 being requested for Phase II bond release were sampled in 2022 in accordance with the vegetation monitoring plan, detailed in Volume 1, Section 4.15 in the Colowyo PAP. Sample adequacy was determined using the Cochran formula. Both the sampling plan and the sample adequacy determination are acceptable to the Division. Results for vegetation cover for each reclamation parcel is summarized below. Sedimentolog The Division reviewed the sedimentology evaluation provided in the SL-22 application. As per Rule 4.15.1(2)(b), vegetation cover shall be capable of stabilizing the soil surface to achieve erosion control equal to or greater than pre-mining levels. To demonstrate this, Colowyo provided estimation on soil loss based upon post-mining site specific data using the Revised Universal Soil Loss Equation (RUSLE). Results from the RUSLE were then compared to baseline data from associated slopes to the reclamation blocks being requested for Phase H bond release. For SL-22, there was a total of 2 slopes, Slope A and Slope B (as labeled and shown in the application), associated with the SL-22 reclamation blocks that were evaluated. Results of this demonstration as well as vegetative cover results are summarized below. Phase II Bond Release Parcel Result Summary—Cover Herbaceous cover: 28.3% Herbaceous cover standard (90%): 16.4% The 2022 sample data successfully exceeds 90% of the herbaceous cover standard. Phase 11 Bond Release Parcel Result Summary— Sedimentology Post-Mining—Slope A: 0.137 tons/acre/year Pre-Mining— Slope A: 0.252 tons/acre/year The 2022 sedimentology evaluation data shows post-mining condition sediment loss to be less than pre-mining conditions. Post-Mining—Slope B: 0.060 tons/acre/year Pre-Mining— Slope B: 0.092 tons/acre/year The 2022 sedimentology evaluation data shows post-mining condition sediment loss to be less than pre-mining conditions. Proposed Decision and Findings of Compliance November 3,2023 Partial Phase 11 Bond Release SL-22 Page 7