2017-02-03_PERMIT FILE - C1980004 ‎(21)‎

• Permit No: C1980004
• IBM Index Class Name: Permit File
• Doc Date: 2/3/2017
• Section_Exhibit Name: Appendix N Probable Hydrologic Consequences
• Media Type: D
• Archive: No

dewatered. Experience gained by mining in the graben indicates initial flow rates will be
much greater than the flow rate after mining. Using Darcy's law to calculate the flow
rate in the graben after mining yields the following: q = kia = (0.11) (4,500 x 8) (0.05) _
198 cubic feet per day = 1.02 gpm. Where area is the length times height of
development 4500 feet times 8 feet and the hydraulic gradient is the slope of the coal
seam 5%. This calculation checks favorably with the estimated flow rate presented
above.
The February 18, 1985, Hydro -Geo Consultants report speculates the source of water
for the mine are surface streams and/or shallow aquifers from the upper reaches of
McClane Creek. This would indicate the flow though the coal seam is from the
northwest to the northeast. Therefore, long term flow into the mine will enter from the
exposed northwest coal ribs and the water should percolate into the downdip northeast
exposed coal ribs. The top or maximum elevation of the saturated coal zone is
projected at about 5580 feet. The elevation of the floor of the mine portals is about
5610 feet, over 30 feet above the saturated coal zone. Since the hydraulic gradient of
the saturated coal zone is below the elevation of the portals, perpetual mine discharge
is improbable. The coal at the portal would be saturated if the hydraulic gradient within
the mine plan area were high enough to cause perpetual mine discharge. There is no
compelling evidence (drill holes are all dry) that would indicate the mine workings will
intersect any substantial perched aquifer system that would alter the hydrologic
characteristics in the mine plan area.
The rate at which the saturated coal ribs are exposed should govern the maximum mine
inflow rate. A five entry system exposes 1,480 lineal feet of rib per 100 feet of advance
assuming 80 foot square pillars. That same 100 feet of development produces 5,400
tons of coal assuming an eight foot mining height. Based upon the k factor of 0.11 feet
per day, it takes about one year to dewater an 80 foot square pillar (40 feet / 0.11 feet
per day). Therefore, exposed coal ribs contribute to mine inflow for one year. At an
annual production rate of 0.5 million tons per year, using this five entry system, a total of
9,000 feet of development would be required. This would expose 133,000
[(1,480)(9,000)/100] feet of rib. This amount of exposed rib would produce an estimated
maximum mine inflow as follows q = kia = (0.11) (133,000 x 8) (0.05) = 5,900 cubic feet
per day. 30 gpm. A production rate of 1.7 million tons per year would increase the
projected water flow to about 100 gpm. The most recent mine inflow calculation for
2008 was 35 gpm (2008 AHR) which is in the same order of magnitude as that
calculated for the 0.5 million ton per year production rate.
Some of the mine inflow may be consumed underground during normal operations.
However, during periods of downtime, all of the mine inflow will be pumped to the
surface and discharged into East Salt Creek. For the purposes of projecting the effect
mine discharge will have on East Salt Creek, it will be assumed the maximum mine flow
rate is 100 gpm or 0.22 cfs.
The quality of the mine water as presented in the Hydro -Geo report indicates it is of
Appendix N — PR -02 - 2 - 10/10