Laserfiche WebLink
<br />Tab 12 -Coal Resource Reco ery Plan <br />26. As noted in the comments for Tab 6 above, there aze some azeas of landslides which will <br />potentially affect the plan, but aze not discussed or recognized in the permit application <br />at this time. These azeas should be delineated, and the mining plan should address how <br />potentially unstable azeas and active landslide areas will be affected/mitigated during the <br />mining operations, specifically: <br />a. A potentially unstable area on the west upper slopes and gulch of the Pond 11 <br />drainage could impact road or ditch construction. The 1999 pit could cause slope <br />failure problems at the head of this drainage. <br />The following items aze also of concern, but need not be addressed as adequacy concerns <br />for the first permit term: <br />b. The "neck pit" will be developed throu a significant landslide/colluvial deposit <br />which could adversely affect pit stability, and future topsoil stockpile <br />locations. <br />c. Mining in the southern part of the area could affect stability of the existing active <br />landslide complex above the road adjacent to Sage Creek in section 19, as well as <br />affect future topsoil stockpile locations. There aze several other landslide deposits <br />which could affect or be affected by mining in this southern pit area as well. <br />Tab 13 -Facilities <br />27. Table 13-1, Curve Number Table for Yoast, lists some curve number assignments with <br />which the Division disagrees. Documentation for the Division's estimated curve numbers <br />is the Soil Conservation Service's Technical Release SS (TR-55). They are as follows: <br />a. Rock Outcrop is assigned a 93. Impervious azeas should be assigned a 98. <br />b. Paved Roads aze assigned a range of 89 - 93. Since pavement u impervious, it <br />should be 98. <br />c. Topsoil Salvage areas are assigned a range of 85-94. If the topsoil is stripped, <br />there would no longger be B through D soil types. What would remain would be <br />subsoil, which is a D e soil. Therefore, the value should simply be 94. This <br />same to 'c would apply to Spoil, Graded Spoil, and Pit azeas, which were also <br />assigned the same range. <br />Please revise the curve number assignments accordingly, or submit additional information <br />to support SCCs assignments. <br />28. Page 7 gives the precipitation amounts for the 10-, 25-, and 100-year precipitation events. <br />The values given are averages of precipitation from Ma to October, which would exclude <br />snow melt Page 58 of Tab 17 states that the runoff from an average year's snow pack <br />could produce ten times the runoff from summer or frontal storms. Given that statement, <br />the Ihvision believes it would be prudent for SCC to consider runoff from snow melt in <br />design calculations for sediment control structures. Also, in accordance with the <br />definition of precipitation event (Rule 1.04(94), the value used should include water <br />emanatingg from snow cover as snow melt in a limited period of time. Please revise page <br />7 of Tab 13 and all of the sediment control structure designs using precipitation amounts <br />based on annual averages. Annual averages for the 10-, 25-, and 100-year storms in the <br />Yoast Mine vicinity are 1.7, 2.1, and 2.5, respectively. <br />M. Ntavilla and G. Wendt (i January 23, 1995 <br />