2001-12-11_PERMIT FILE - C1982056A (4)

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-11- I For Pond A, flow will be conveyed dowr. the haul road embankment from the 60-inch RCF emergency spillwa}-. It ui11 be conveyed down the embankment in ' a riprap lined channel which is shown in cross-section on LRCIdE Figure 4, Sedimentation Pont A, Emergency Spillway Channel. An adequate energy dis- sipator should be installed at the toe of the slope. I REQllIRED SEDIAfENTATION VOLUMES I 30CFR816.46 (b) provides two methods for computing required sedimentation I volume_=. The first i_= the product of 0.1 acre-feet per acre and the total number of disturbed acres during the mining and reclamation activities. For I the 10 pond sites, this method was used to determine an approximation of the sedimentation veiume. For those sites which required greater than 20 feet or greater Chan 20 acre-feet to contain the sum of the required sedimentation I volume and the 10-year inflow flood, the required sedimentation volume was computed using the alternate technique. The alternate technique utilizes the Universal Soil Loss Equation (USLE), gully erosion rates, and sediment del- ivery ratios. The total of eroded material which would accumulate from three years of average erosion was converted to a sediment volume using appropriate sediment densit~~ data. Tae form of the USLE used in this analysis is A = R(K) (LS) (VM), which is the more applicable form of the equation for surface coal mining and reclamation activities. It is described in an art- icle titled "Rigliway Erosion Control Systems- an Evaluation Based on the Uni- versal Soil Loss Equation" which was published in Soil Erosion: Prediction and Control, published and copywrited in 1976 by the Soil Conservation Society of America. The VD1 factor accounts for the effects of all erosion control measures which may be applied to an}' given site, including planting vegetation, ~ physical changes, and application of chemicals. The factors R, K, and LS are defined in Technical Release Number 51, published by the Soil Conservation Service in 1977. Erosion control measures which will be undertaken as part of the mining and reclamation plans are more fully described in Section 780.21 of the application. The most critical year from the point of view of generation of sediment was determined for each site. For this analysis, a \'M factor ranging from i.0 for all disturbed areas with no ground cover, to a • value of 0.05 for all areas permanently seeded after 12 months was used. The Permit Renewal No. 3 Exhibit 8q 1/15/00 Page 13 of 22