PERMFILE114982

• Permit No: C1980004A
• IBM Index Class Name: Permit File
• Doc Date: 8/22/2006
• Section_Exhibit Name: Appendix N Probable Hydrologic Consequences
• 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, 19$5 Hydro-Geo Consultants report speculates the source of
water for the mine are surface streams and/or shallow aquifers from the upper
reaches of McClave Creek. This would indicate the flow through 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 1.7
million tons per year, using this five entry system, a total of 23,000 feet of
development would be required. This would expose 340,000
[(1,480)(23,000)!100] feet of rib. This amount of exposed rib would produce an
estimated maximum mine inflow as follows q =kia = (0.11) (340,000 x 8) (0.05) _
14,900 cubic feet per day 77 gpm.
Appendix N 2 11101