REV04765

• Permit No: C1980007
• IBM Index Class Name: Revision
• Doc Date: 4/16/1985
• From: ANACONDA MINERALS CO
• To: MLRD
• Type & Sequence: PR4
• Media Type: D
• Archive: No

U.S. FISH AND MILDLIFE SERVICE °WINDY 6AP° MITIGATION PROCESS
Stream Flow Depletion and Contribution Analysis
of
West Elk Coal Company's Mt. Gunnison No. 1 Underground Mine
Somerset, Colorado
April, 1985
Depletions from the North Fork of the Gunnison River, a tributary
to the Colorado River, by WECC can be attributed to:
A. stream flow diversions;
B, evaporation from ponds and mine workings;
C. miscellaneous water uses.
Return flows to the North Fork from the Mt. Gunnison Mine can be
attributed to:
D. treated precipitation and mine water returns;
E. treated waste water returns.
A. Stream Flow Diversions
The Mt. Gunnison Mine pumps water from the North Fork of the
Gunnison River into a 10 acre-foot storage pond. Diversions to this
pond total approximately 30 acre-feet per year. This water is used
for drinking, showers, dust suppression, and fire suppression.
B. Evaporation from ponds and mine workings.
i. Pond evaporation losses. An estimate of 45 inches per
year for Class A pan evaporation near the mine was
obtained from USWB TP 37, 1959. A pan coefficient of 0.75
was used to obtain an annual pond evaporation estimate of
33.8 inches per year. Since all precipitation reaching
the ponds would be available for release or evaporation,
the net evaporation is 13.7 inches per year (using an
annual precipitation of 20.1 inches per year at the mine).
Thus for a total pond surface area of six acres, the
annual evaporation loss is 6.8 acre-feet.