2009-09-21_PERMIT FILE - C1980007

• Permit No: C1980007
• IBM Index Class Name: Permit File
• Doc Date: 9/21/2009
• Doc Name: NORTH FORK OF THE GUNNISON RIVER STREAM FLOW DEPLETION AND CONTRIBUTION
• Section_Exhibit Name: Exhibit 67 Windy Gap Process NF of the GR Stream Flow Depletion and Contribution Analysis
• Media Type: D
• Archive: No

Mountain Coal Company, LLC
Exhibit 67
West Elk Mine Windy Gap Process
the 2007 and 2008 Annual Hydrology Reports, as well as from the two highest coal
production (7.0+ million TPY) years to date (1999 and 2007), the average annual WWTP
discharge to the North Fork was 6.64 acre feet.
The discharges from WEM's two largest sediment ponds, MB-1 and MB-2R, during the
same three years averaged 52.4 and 110.3 acre-feet per year, respectively. Averaging
these two discharges (i.e. 81.35 acre-feet) and conservatively assuming that 50% of this
water was not from stormwater runoff, the average volume of return flows from the
sediment ponds is calculated to be 40.7 acre-feet per year. Similarly, the average amount
of treated mine water discharged annually during these three years was 429.4 acre-feet,
including WEM's non-tributary water right used as augmentation water. Conservatively
assuming that future mine water discharges will only be for augmentation during periods
of call on the North Fork (typically June through September each year, or about one
quarter of a year) 107.35 acre-feet of water will be pumped from the mine each year and
returned to the North Fork, even at maximum coal production levels.
Contributions
The natural mine water inflow is not directly proportional to the production rate, but is
chiefly affected by the areal extent mined and the geologic conditions. The production
rate does influence the areal extent of the mine because with higher production rates, a
greater area of the coal seam is mined to obtain that higher tonnage. WEM believes that
all mine water inflows, whether tributary or non-tributary sources, are a valid
contribution to the North Fork and the upper Colorado River basin because the water
would have remained isolated in fracture zones and/or perched, confined aquifers if
mining had not occurred. As such, mine inflows have been included as a part of the
return flows calculation (see above), albeit.a very conservative amount, when compared
to the actual amounts pumped from the WEM to the North Fork for more than a decade.
Net Depletion
No depletions were experienced at the WEM as a result of mining in the Box Canyon
Federal Lease COC-56447 (PR08). No depletions are anticipated as a result of mining in
either the South of the Divide Federal Lease C-1362 (PR10), the West Flatiron Federal
Lease COC-67011 (PR-11) or in the Dry Fork Lease COC-67232 (PR-12).
Based on maximum mining production rates and very conservative usage and return
flows, WEM's net depletion is calculated as follows.
Depletions (water usage) from the North Fork 201.8 acre-feet/year
Return Flows (including mine water contributions)
to the North Fork 154.7 acre-feet/year
NET DEPLETION 47.1 acre-feet/year
Exhibit 67-3 Revised 03105- PRI1; 01106- PR11; 03106- PRI1; 09109- 78118; 09109- TR119