PERMFILE50679

• Permit No: C1980004A
• IBM Index Class Name: Permit File
• Doc Date: 5/13/2002
• Section_Exhibit Name: APPENDICES K - P
• Media Type: D
• Archive: Yes

• Mining into the saturated coal bed will produce mine inflows as the coal bed is
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) (4,300 x 8) (0.05) _
189.2 cubic feet per day = 0.98 gpm. Where area is the length times height of
development 4300 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 above calculation indicates postmining inflow will be quite low. The maximum area
that can be opened up in the permit area is about 15,000 feet within the saturated
zone. Assuming two seams are mined over this entire area, which is unlikely, the
maximum long term flow rate into the mine will be q = kai = (0.11) (15,000 x 16) (0.05) _
6.8 gpm.
The February 18, 1999, 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.

Appendix N - 2 • 12/99