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<br />I <br />• <br />C? <br />J <br />In order to achieve the above goals, which are a reasonable and practical basis for judging successful <br />reclamation, Trapper Mine proposes an effective cover standard designed such that soil loss due to rill <br />and sheet erosion will not exceed four tons per acre per year. This is an acceptable soil loss erosion rate <br />below what has occurred on premine areas and is the basis for our proposed technical standard for <br />cover. The majority of the topsoils being used for reclamation at Trapper Mine have a T value <br />(maximum soil loss permissible under Soil Conservation Service Criteria on an annual basis) of five tons <br />per acre per year. Additionally, the proposed limit is less than the weighted average T value of 4.33 <br />Tons/A/Yr, Table 4.4-5. The proposed limit is conservative and site specific to Trapper Mine. <br />Trapper won't propose a historic standard for herbaceous cover. The data is extremely variable and the <br />resulting lower confidence limits are too low to provide an acceptable level for erosion control, the <br />primary purpose for cover, Table 4.4-4. <br />The proposed effective standards for range sites A, B, and C were calculated using the USLE. The <br />calculation and resulting numeric cover standards are shown on Table 4.4-1. <br />Effective cover to meet the standards will utilize a combination of herbaceous cover and litter cover. A <br />historic average percent litter factor was calculated from 1979 and 1985 cover data, Table 4.4-2. To <br />obtain the level of herbaceous cover required by the standard, the historic average percent litter factor is <br />multiplied times the needed effective cover and the result is subtracted from total effective cover <br />required by the standard. For example, let us say 50% effective cover is necessary to result in not <br />exceeding 4 tons/A/yr, the calculation would then proceed as follows: <br />(50% effective cover)(.372 avg % litter factor) Table 4.4-2 = 18.6% litter <br />(50% effective cover - 18.6% litter) = 31.4% herbaceous cover. <br />Thus, in this case the effective cover reclamation standard would be no less than 31% actual herbaceous <br />cover and no more than 19% actual litter cover. Actual litter cover may exceed 19% but only 19% actual <br />litter cover could be used to meet the standard. <br />Based upon an analysis of potential soil erosion, Table 4.4-1, the proposed effective cover standards will <br />not result in excessive postmine soil erosion. <br />4-102 <br />Revision: i Q - 41 <br />Approved: 7 //% f8