2013-07-29_PERMIT FILE - C1982056 ‎(4)‎

• Permit No: C1982056
• IBM Index Class Name: Permit File
• Doc Date: 7/29/2013
• Doc Name: COAL REFUSE DISPOSAL AREA EXPANSION
• Section_Exhibit Name: Exhibit 08EE Coal Refuse Disposal Area Expansion Drainage Designs
• Media Type: D
• Archive: No

_A&Ya691 Foidel Creek Mine' Refuse Disposal Area Zipmion — Surface Water Control Plan • Page 6
TABLE 3
20MM Yard Expansion Culvert Desians
Calvert
Peak Flow
WS)
Maximum
Headwater (ft)
Design
Diameter
inches
Multiples
36-inch
48 -inch
RDA -lc
43.0
3.0
48
2
1
RDA-3
2.0
2.0
10
Install minimum 18 -Inch
Expansion
Area Toe
53.2
3.0
60
3
2
Haul Road
58.4
3.5
54
4
3
Note: "Expansion Area Tod' culvert collects runoff from Channels RDA -lb, RDA4 and RDA-& The
design peak flow is a summation of the peak flows calculated in the channel design demonstrations.
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. 103(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 Jisposal 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 ..
of the fill). :The possibility of infiltrating water moving downward into the underlying' spoil or.
natural soils was ignored even though this could reduce future peak flows through the underdrain.
Hydro-Environmental Solutions, Ine.
571& Street, Suite B
P.O. Box 772996
Steamboat Springs, CO 80477