2009-11-13_PERMIT FILE - C1982056A ‎(5)‎

• Permit No: C1982056A
• IBM Index Class Name: Permit File
• Doc Date: 11/13/2009
• Doc Name: COAL REFUSE DISPOSAL AREA EXPANSION
• Section_Exhibit Name: Exhibit 08EE Coal Refuse Disposal Area Expansion Drainage Designs
• Media Type: D
• Archive: Yes

September 2009 Foidel Creek Mine * Refuse Disposal Area Expansion — Surface Water Control Plan * Page 6
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TABLE 3
20MM Yard Ex ansion Culvert Desi ns
Culvert
Peak Flow
Maximum
Design
Multiples
(cfs)
Headwater (ft)
Diameter
36 -inch
48 -inch
(inches)
RDA -lc -1
84.0
3.0
96
7
4
RDA -lb -1
94.0
3.0
108
9
5
RDA -3 -1
29.0
3.0
36
Install minimum 36 inch
RDA -5a -1
104.0
3.5
96
7
4
RDA -5 -1
104.0
3.5
96
7
4
RDA -7 -1
12.5
3.0
21
Install minimum 24 -inch
RDA -7 -2
83.5
3.5
84
6
3
RDA -1 -1
105.3
3.5
96
7
4
Note: 1) the peak flow value used for sizing culvert RDA -7 -2 is a combination of peak flows from
channels RDA -7 and existing ditches D- 3A/3B.
2) the peak flow value used for sizing culvert RDA -1 -1 is a combination of peak flows from
channels RDA -lb and RDA -6.
5.0 Underdrain Design
Previous refuse disposal area investigations (CTL Thompson, 1992) report that the refuse disposal
• area does not classify as a valley fill according to Regulations of the Colorado Mined Land
Reclamation Board for Coal Mining (1.04(148)), and is therefore not specifically required to have a
full sized valley fill drain. The 20MM yard refuse disposal area expansion also does classify as a
valley file according to Rule 1.04(148) and not required to have a full size valley fill drain. Rule
4.10.3(5) allows as alternative subdrainage system with approval of the Colorado Division of
Reclamation, Safety and Mining (CDRMS). Consideration of the possible water sources entering the
refuse disposal fill (storm infiltration, snowmelt, free water from fill material) and the low sensitivity
of pile stability to groundwater rise suggest a limited underdrain system would be prudent.
Potential water sources considered in designing the underdrain included surface water flows, storm
infiltration and groundwater. There are no known seeps, springs or sources of groundwater in the
refuse disposal area; therefore, groundwater contributions were not considered significant. Surface
water runoff will be controlled during and after construction by the temporary ditches and postmine
channels. Consequently, the primary sources of water to the underdrain system will be stormwater
infiltration and snowmelt both during and after construction.
Peak flows within the underdrain should be relatively small. Although infiltration of stormwater into
the pile could occur fairly quickly due to the course nature of the fill material at the surface, the
comparatively slow movement of the water down through the compacted fill, and then along the
ground surface to the center of the refuse disposal area will attenuate the peak flows.
The 10 -year, 24 -hour storm event was evaluated for both initial pile construction and for refuse pile
area closure (assuming no vegetative cover over the entire pile and all flows move toward the center
Hydro - Environmental Solutions, Inc.
5710' Street, Suite B
P.O. Box 772996
Steamboat Springs, CO 80477
Revised 09/09