2011-03-21_PERMIT FILE - C2009087 ‎(5)‎

• Permit No: C2009087
• IBM Index Class Name: Permit File
• Doc Date: 3/21/2011
• Doc Name: Sump Design Report
• Section_Exhibit Name: Exhibit 2.05.3-E2 Appendix 2.05.3-E2.E
• Media Type: D
• Archive: No

Peabody Sage Creek Mine — Sump Design Report
• Provide a non - clogging dewatering device or conduit spillway to remove water storage
resulting from inflow in accordance with Rule 4.05.6(3)(b).
• Provide a spillway system for either a combination of principal and emergency spillway,
or a single spillway configured as required by Rule 4.05.9(2)(a), capable of passing
runoff from the 25 -year, 24 -hour storm event in accordance with rule4.05.9(2)(c)(ii).
• If a combination of principal and emergency spillways are designed and constructed
then there shall be no out -flow through the emergency spillway during passage of runoff
from the 10 -year, 24 -hour storm event in accordance with Rule 4.05.9(2)(b).
The sumps are upstream of Pond 002 (Wadge Impoundment). The sumps serve as pre -
settling basins to pre -treat the sediment loading from the South Surface Facilities Area, with
the exception of the Portal Area. The sumps will not be permitted under the Colorado Water
Quality Control Division's (WQCD) Colorado Discharge Permit System (CDPS) and,
consequently, there are no effluent limitations (e.g., settleable solids concentrations) for the
discharge. Pond 002 is the permitted CDPS structure for the drainage network designed for
the South Surface Facilities Area. Since there will be no effluent limitations that apply to
discharges from the sumps, Rules 4.05.2(7) and Rule 4.05.6(3)(b) are not applicable.
4.0 SEDCAD Demonstration
The hydrology and sedimentology of the watershed were analyzed using the SEDCAD4
computer program (Schwab, 1998). Model methodology and assumptions are presented in
Exhibit 2.05.3 -E2, Drainage and Sediment Control Plan. Appendix 2.05.3- E2.E.1 and
2, contain the SEDCAD modeling demonstrations for the 10 -year, 24 -hour and the 25 -year,
24 -hour storm events, respectively.
Inputs include precipitation (inches), watershed area (acres), time of concentration (hours),
runoff curve number, representative particle size distribution of soils in the area,
sedimentology information, spillway dimensions, etc. The drainage area for the watersheds,
as well as, slope lengths and distances for time of concentration estimates were measured
from a permit topographic map (see Map 2.05.3 M4).
The Upper Sump design assumed that there is a constant inflow surge of surge water that
goes to PECOCO Pond and subsequently to the Upper Sump from the Portal Area. The
design assumed an inflow rate of 80 gallons per minute (0.35 acre -feet per day). This results
in a permanent pool elevation that is 0.3 feet above the invert elevation of the principal
spillway and results in constant flow. The Lower Sump design included the constant flow
from the Upper Sump as well as the influx of perennial spoil spring inflow. Seneca Coal
Company has a spoil spring monitoring site in the near vicinity of the Lower Sump;
measurements for site SSSPG7 indicate a mean discharge of 60 gpm. These inflows were
accounted for in the Lower Sump design. The 25 -year, 24 -hour event demonstration was
designed using a conservative emergency spillway assumption — the sumps are 100 % full to
the emergency spillway invert elevation (e.g., principal spillways are inoperable).
Precipitation and Storm Type: The precipitation amounts for the design storms were
obtained from Frequency atlas of the Western United States — Volume H — Colorado
(National Oceanic Atmospheric Administration [NOAA], 1973). A standard soil
Conservation Service (SCS) Type II storm was utilized for each analysis.
TRO 1 -10 2.05.3 -E2.E2 2/11