2010-05-07_PERMIT FILE - C2009087A ‎(28)‎

• Permit No: C2009087A
• IBM Index Class Name: Permit File
• Doc Date: 5/7/2010
• 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
2.1.5 Time of Concentration
The time of concentration (Tc) was calculated suing 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 Tc 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 watershed 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 11 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.
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The following curve number values were utilized in the design of both channels for mine operations
and the permanent postmine conditions.
TABLE 2.05.3 -E2 -1
Curve Number Values
Land Condition
Ground Cover Type
Hydrologic
Condition
Hydrologic
Soil Group
Curve
Number
Undisturbed
Mixed Brush
Fair 30 - 70 %)
n/a
70
Mesic Drainage
Fair 30 - 70 %)
C
81
Sagebrush
Fair (30 — 70 %)
C
63
Disturbed
Topsoil Stripped
Bare
B
86
Spoil
Bare
C
89
Haul Road/Facility
Area
Bare
D
91
Reclaimed (reve etated 2 — 5 s )
Herbaceous
Fair (30% - 70% )
B
71
Reclaimed (ready for bond release
Herbaceous
Good ( >70 %)
B
62
Notes: 1) Undisturbed land condition information is an "average" of soil and vegetation information presented
in the Seneca II Mine permit; the CN value of 70 is from the Seneca II Mine permit SEDCAD modeling
demonstrations.
2.05.3 -E2.7