2010-01-21_PERMIT FILE - M2009082 ‎(10)‎

• Permit No: M2009082
• IBM Index Class Name: PERMIT FILE
• Doc Date: 1/21/2010
• Doc Name: Stability Analysis
• From: Deere & Ault Consultants, Inc.
• To: DRMS
• Email Name: JLE
• Media Type: D
• Archive: No

Table 3: Highwall Setback DRMS Analysis Results

Model
Setback

Distance (feet) Calculated

Factor of

Safety
Required Factor

of Safety
Phase I A 47 1.03 1.0
Phase 1B 39 1.01 1.0
Phase IC 30 1.06 1.0
Phase 2 Eastside 39 1.01 1.0
Phase 2 Westside 37 1.03 1.0
Phase 3 25 1.15 1.0
Phase 4A 25 1.01 1.0
Phase 4B 25 1.11 1.0
Phase 4C 25 1.03 1.0
Phase 5A 25 1.02 1.0
Phase 513 and 5C 26 1.02 1.0
Longterm Case 47 1.57 N/A
The setback distance in Table 2 is calculated from the crest of the mine highwall to the potential failure
surface intersection with the existing ground.
Inflow and Outflow Structures
In order to mine within 400 feet of the Cache la Poudre River, the Division of Reclamation Mining and
Safety (DRMS) requires the construction of engineered inflow and outflow structures. A single
inflow/outflow structure will be required for each of the following mining phases: 1C, 3, 4B, 4C, 5A,
5B, and 5C. Each inflow/outflow structure will be a native grass-lined trapezoidal channel excavated to
a depth of two feet with 4:1 (horizontal: vertical) side slopes. Because flow can be bi-directional, these
channels are to be constructed with no longitudinal slope. Each channel is approximately 200 feet in
length with the exception of the channel for Phase 4B which is approximately 300 feet in length.
The bottom width of the trapezoidal channel will vary from 20 to 100 feet depending on the size of the
phase. Phases 1 C, 3, 5A, and 5C require a bottom width of 20 feet while Phases 4B and 5B require a
bottom width of 50 feet and Phase 4C requires a bottom width of 100 feet. The rate of inflow from the
river will vary as the river stage rises above the invert of the inflow/outflow structure based on HEC-
RAS modeling of the inflow/outflow structures. For the 200-ft channel with a bottom width of 20 feet,
the inflow would be 30 cfs, 60 cfs, and 120 cfs at river stages of 1.0 feet, 1.5 feet, and 2.0 feet above the
channel invert, respectively. The 200-ft channel with a bottom width of 50 feet would convey inflows
of 60 cfs, 140 cfs, and 270 cfs at similar stages of 1.0 feet, 1.5 feet, and 2.0 feet, respectively. For the
300-ft channel with a bottom width of 50 feet, these inflows would decrease slightly to 50 cfs, 120 cfs,
and 220 cfs at similar stages of 1.0 feet, 1.5 feet, and 2.0 feet, respectively. The inflow through the 200-
ft channel with a bottom width of 100 feet would be 120 cfs, 280 cfs, and 510 cfs at stages of 1.0 feet,
1.5 feet, and 2.0 feet respectively.
At these inflow rates, the cells will fill from the normal water line to the invert of the inflow/outflow
channel in approximately 5 to 14 hours at a river stage of 1.0 foot above the channel invert. Fill time
decreases to 3 to 6 hours with the stage at 1.5 feet above the channel invert and further decreases to 1 to
3 hours at 2.0 feet above the channel invert. Based on the 2003 floodplain study of the Cache la Poudre
Parsons Mine
DRMS 112 Permit
Page SE6 of SE7