Laserfiche WebLink
Peabody Sage Creek Mine — Drainage and Sediment Control Plan <br />TABLE 2.05.3 -E2 -1 <br />Curve Number Values <br />Land Condition <br />Ground Cover <br />Type <br />Hydrologic <br />Condition <br />Hydrologic <br />Soil Group <br />Curve <br />Number <br />Undisturbed <br />Mixed Brush <br />Fair (30 -70 %) <br />n/a <br />70 <br />D <br />Mesic Drainage <br />Fair (30 -70 %) <br />C <br />81 <br />Sagebrush <br />Fair (30 -70 %) <br />C <br />63 <br />Disturbed <br />Topsoil Stripped <br />Bare <br />B <br />86 <br />Spoil <br />Bare <br />C <br />89 <br />Haul Road/ <br />Facility Area Bare D 91 <br />Reclaimed (revegetated 2 -5 yrs) <br />Herbaceous <br />Fair (30 -70 %) <br />B <br />71 <br />Reclaimed (ready for bond release) <br />Herbaceous <br />Good (.70 %) <br />B <br />62 <br />Notes: 1) Undisturbed land condition information is an "average" of soil and vegetation <br />information presented in the Seneca I1 Mine permit; the CN value of 70 is from the Seneca I1 <br />Mine permit SEDCAD modeling demonstrations. <br />2.2.1 Rainfall Factor <br />The Rainfall Factor, or Rainfall Erosivity Index, (R) is a measurement of the amount of <br />erosion caused by the rainfall event. It is directly proportional to the total storm energy <br />times the maximum 30- minute intensity. Historically, SCC used an R- factor of 30 for <br />sedimentology evaluations at its Seneca II, Yoast and II -W operations — this value is suitable <br />for bare or disturbed lands that are easily eroded. Consequently, the design evaluations for <br />Pond 002, as well as, the South Surface Facilities and Portal Area sumps used an R- factor <br />value of 30. <br />A postmine landscape held or approved for bond release is characterized as being well - <br />vegetated and generates significantly less erosion than disturbed lands. Consequently, the <br />postmine demonstrations utilized an R- factor of 10, which is representative of conditions in <br />northwest Colorado (Renard, et al, 1997). <br />2.2.2 Soil Erodibility Factor <br />The soil Erodibility factors (K) are based on historic soil survey information taken from Tab <br />9, Soil Baseline Study, of the Seneca II Mine permit (Nyenhuis, 1994). The undisturbed <br />lands modeled in the Pond 002 demonstration utilized and area- weighted value. <br />Consequently, the K values for the undisturbed area are an average representative of <br />numerous soil series characteristics. The following table presents the K factor values used <br />for the sedimentology demonstrations. <br />TABLE 2.05.3 -E2 -2 <br />Soil Erodibility Factor Values <br />Soil Characteristic <br />Hydrologic Soil Group <br />K factor <br />Undisturbed <br />B <br />0.19 <br />Topsoil Stripped <br />C <br />0.29 <br />Parking Lot/Facilities Area <br />D <br />0.36 <br />Reclaimed <br />B <br />0.24 <br />TRO1 -10 <br />2.05.3 -E2.8 <br />12/10 <br />