2012-08-31_PERMIT FILE - C1981012 ‎(2)‎

• Permit No: C1981012
• IBM Index Class Name: Permit File
• Doc Date: 8/31/2012
• Doc Name: Development Waste Disposal Area ‎(DWDA)‎ #2 Slope Stability Evaluations
• Section_Exhibit Name: Exhibit 37‎(1)‎ Development Waste Disposal Area ‎(DWDA)‎
• Media Type: D
• Archive: No

AAGAPITO ASSOCIATES, INC.
Mining & Civil Engineers & Geologists
715 HORIZON DR., STE 340
GRAND JUNCTION, CO 81506
USA
VOICE 970.242.4220
www agapito.com
May 25, 2012
Daniel I. Hernandez
Senior Environmental Protection Specialist
Colorado Division of Reclamation, Mining and Safety
1313 Sherman St., Room 215
Denver, CO 80203
Re: New Elk Mine (Permit No C- 1981 -012)
Technical Revision Application No. 66 (TR 66)
DWDA #2 Slope Stability Evaluations
Dear Mr. Hernandez,
GOLDEN OFFICE
303.271.3750
723 -01 T3
As you are aware, the existing development waste storage area (DWDA) referred to as
DWDA #2 was originally permitted to be constructed to a height of 30 feet (ft) with 1.5
horizontal(H):1 vertical(V) side slopes. New Elk Coal Company (NECC) would like to change
the permitted side slope design to a height of 50 ft with 2.0(H):1(V). Agapito Associates, Inc.
(AAI) has performed a slope stability evaluation of the DWDA #2 stockpile as submitted under
TR 66. This letter summarizes the results of the slope stability analysis and provides
recommendations for future construction of the DWDA #2.
Computer -Aided Modeling and Analysis
At present, DWDA #2 has a base (ground surface) width and length of approximately
150 ft by 1,250 ft, respectively. The toe of the waste rock embankment is at an elevation of
7,440 ft on the west end and at an elevation of 7,420 ft on the east end. The maximum height of
the embankment is intended to be 50 ft and the crest elevation would somewhat parallel the
ground surface and range from 7,480 ft on the west end to 7,450 ft on the east end. The general
configuration of the DWDA #2 embankment and the location of the section considered in the
analysis is shown in Figure 1.
The section analyzed was modeled with the mine waste rock embankment at 2(H):1(V)
side slopes and with the maximum proposed crest height of 50 ft. For conservatism, the section
also includes a wider crest of the waste rock mass to ensure that the greatest driving force is
realized. Several groundwater levels were evaluated including groundwater locations at the
existing ground surface, groundwater level at 5 ft, 10 ft and 20 ft above the existing ground
surface into and across the waste rock pile.
GEOENGINEERING • MINING ENGINEERING - CIVIL ENGINEERING
TR 66 Page E 37 -2 Revised 5/25/2012