2012-06-08_PERMIT FILE - C2009087A ‎(12)‎

• Permit No: C2009087A
• IBM Index Class Name: Permit File
• Doc Date: 6/8/2012
• Doc Name: DRAINAGE AND SEDIMENT CONTROL PLAN
• Section_Exhibit Name: Exhibit 2.05.3-E2 Drainage and Sediment Control Plan
• Media Type: D
• Archive: Yes

Peabody Sage Creek Mine — Drainage and Sediment Control Plan
2.1.4. Watershed Area
The watershed areas were determined by direct measurement from Map 2.05.3 M4,
Drainage and Sediment Control Plan (operations) or Map 2.05.4 M1, Postmine
Topography.
2.1.5. Time of Concentration
The time of concentration (T j was calculated using the NRCS upland method (SCS, 1986) —
the method is included as a sub - routine built into the SEDCAD4 model. The hydraulic
lengths, drainage heights and associated slopes were measured directly from the drainage
and sediment control plan watershed maps. The calculated T, value for each structure is
presented in the SEDCAD4 results. Maximum overland flow was generally assumed to be
no more than 400 feet.
2.1.6. Muskingum Routing Parameters
The Muskingum Routing parameters K and X were also calculated using the NRCS upland
method (SCS, 1986). The hydraulic lengths, drainage heights and associated slopes were
measured directly from the drainage and sediment control plan maps. The calculated K and
X values for routing between each structure are found in the SEDCAD4 results.
2.1.7. Curve Number
The runoff curve number (CN) is a factor relating the amount of rainfall to the amount of
runoff for a given area. The CN value is dependent upon the infiltration characteristics of
the soil types and the type and amount of vegetation. Curve number values used in the plan
were taken from the approved Seneca II Mine permit; the values were originally described in
Technical Release No. 55 (SCS, 1986).
The undisturbed lands in the Little Grassy Creek watershed located to the south of the South
Surface Facilities and Portal Area, as well as, a portion of the PM -5 watershed utilized an
area - weighted CN value based on undisturbed area soil and vegetation information taken
from Exhibits 9 and 10, respectively, of the Seneca II Mine permit. Consequently, the CN
values for the undisturbed areas in the model demonstration are an average representative of
numerous soil series and vegetative community characteristics.
The curve number values on Table 2.05.3 -E2 -1, Curve Number Values, were utilized in
the design of both channels for mine operations and the permanent postmine conditions.
2.2 Sedimentation Calculations
The SEDCAD4 model calculates storm event sediment yield using the Revised Universal
Soil Loss Equation (RUSLE). Input parameters used in the sedimentation analysis are
described in the following sections.
TRO 1 -10 2.05.3 -E2.7 12/10