2011-02-10_PERMIT FILE - C1981012A ‎(3)‎

• Permit No: C1981012A
• IBM Index Class Name: Permit File
• Doc Date: 2/10/2011
• Section_Exhibit Name: Section 2.05 Operation and Reclamation Plan
• Media Type: D
• Archive: Yes

• Ditch 27 will direct runoff from Warehouse 1 to Containment Area 2. The total drainage area is
2.9 acres. A total of 0.28 acre -feet of storage is required to handle the 10 -year 24 -hour event and
0.38 acre -feet of storage is required to handle a 25 -year 24 -hour event. The three -year sediment
volume is 0.02 acre -feet. Ditch 28 will direct disturbed runoff from a 15.45 -acre disturbed area
to Containment Area 1. A total of 1.51 acre -feet of storage is required to handle a 10 -year
24 -hour event and 2.01 acre -feet for a 25 -year 24 -hour event. The three -year sediment storage
volume is 0.07 acre -feet. Containment Area 1 also controls drainage from the non -coal waste
disposal area.
Ditch 29 collects runoff from 67.2 acres of undisturbed runoff and directs this runoff to the
laydown area without impacting any disturbed area. Culvert C -27 has been installed at the east
end of the laydown area to handle peak flows from Drainage Basins CC and DD as shown on
Map 13A— Drainage Basins.
Ditches 39a and 39aa are proposed to route stormwater around the cut slope of the substation and
rock dust system to maintain the integrity of the slope. At the time of construction, the slope
material characteristics will be evaluated to determine if a drop structure is necessary to carry the
cut slope runoff. The details of the cut slope are included as Figure 2d.
The proposed DWDA stormwater management above, around and on the waste pile was
evaluated for a 100 year, 24 -hour storm event. The results indicate that the management system
already in place for the site will safely pass the storm with the recommendation that the berms
and ditches are field verified to be constructed as designed. The stormwater routing near the
DWDA is shown on Figure 2e. The runoff above (North) is diverted through Ditch D -11
• through culvert C -30, ditch D -1, culvert C -26, and ditch D -32 to the river. This is shown in
Figure 2e. Exhibit 39 Sediment Design Specification – Development Waste Disposal Area
demonstrates that the existing ditches are appropriately sized to carry divert the stormwater
above the DWDA.
The DWDA runoff is routed through a small catchment into culvert C -13 and to pond 007. The
engineering evaluation of the DWDA is included as Exhibit 39 Sediment Design Specification
– Development Waste Disposal Area. The catchment area is 4.09 acres and is isolated from
other catchments by existing diversion ditches and grade breaks. The 100 year, 24 -hour storm
precipitation is 4.2 inches. The model predicts the peak runoff to be 12.76 inches with 4.2 inches
of runoff. The required ditch size to convey that flow is a trapezoidal channel of bottom width
3.0 ft, height of 1.5 ft, side slopes of 1:1 and a minimum slope of 1 %. Existing ditches are of this
recommended size and shape. The minimum pipe diameter needed to convey the 100 year, 24-
hour peak flow to pond 007 is 24 inches. The existing culvert is 24 inches. The pipe installation
should have a minimum of 1.2 feet of material from the top of the pipe to the top of the bank (i.e.
the lowest point on any top of berm/top of bank around the DWDA shall be no less than 1.2 feet
above the top of the 24 inch outlet pipe.
An erosion estimate was done for the proposed DWDA and as a result, a small sediment basin of
250 cubic yards is recommended if no cover management is practiced on the DWDA. The
sediment basin should be installed at the inlet to the culvert, the entire volume of which is below
the pipe invert. The sediment basin will require regular maintenance.
Culverts C -21 through C -25 direct undisturbed runoff south of the fan and substation to the
• Purgatorie River. Sizing data is provided in Exhibit 19— Sediment Design Specifications.
TR 53 Page 2.05A0 Revised 1 -3 -2011