2014-07-25_REPORT - C1981010

• Permit No: C1981010
• IBM Index Class Name: Report
• Doc Date: 7/25/2014
• From: DRMS
• To: Trapper Mining, Inc
• Permit Index Doc Type: Annual Reclamation Report
• Email Name: JLE
• Media Type: D
• Archive: No

S. Restoration of
ground water
recharge to
approximate pre-
mining rate
CDRMS
regulation
4.05.12(3)
Comment
Each pit disrupts the potentiometric surface of confined
aquifers. After reclamation, monitoring data show recovery
of the potentiometric surface outside of backfilled pits and
partial recovery of potentiometric surface inside backfilled
pits. Spoil springs may reduce groundwater recharge by
diverting groundwater flow to surface flow. However,
Trapper's expected total aggregate spoil spring discharge of
less than 1 cfs will be too small to reduce recharge below the
approximate pre- mining rate.
The Probable Hydrologic Consequences (PHC) section of
Trapper's mining and reclamation permit (Section 4.83)
discusses the possibility of a high -TDS plume of coal spoil
leachate forming in the Third White Sandstone
downgradient from the Trapper Mine in Section 29 -T6N-
90W. Such a plume would not be expected to form until
several years, possibly decades, after the pit is reclaimed in
the adjoining Section 32. Compared to pre- mining ground
water conditions, such a plume would have elevated
dissolved solids, which could possibly impair the use of
ground water in the Third White Sandstone.
Spoil leachate could also invade the alluvium in Flume
Gulch by seeping down into the subsurface from spoil
springs flowing on the land surface in the gulch.
T. Prevention of
adverse impacts
CDRMS
The Third White Sandstone is monitored in the area of the
to ground water
regulation
Comment
possible plume in well GP -9, and the alluvium is monitored
systems outside
4.05.11
with the Coy well. Monitoring data from both wells indicate
the permit area
that a plume has not reached these wells. Well GC -2
completed in the 3rd White Sandstone up- gradient of well
GP -9 is showing evidence of the predicted plume with
elevated TDS levels and Sulfate levels that have increased
over time but have since stabilized. However, up- gradient
mining /de- watering near well GC -2 may be playing a role in
the groundwater at this well. Other wells down - gradient of
spoil backfill such as well P -8 completed in the Third White
Sandstone and well GD -2 completed in the R aquifer are
also showing signs of elevated TDS /Sulfate likely leaching
from backfilled spoils. TDS Levels in well P -8 appear to
have stabilized after a large increase in around 1995 but are
remaining above baseline levels. TDS /Sulfate levels in the
alluvial wells have fluctuated significantly over the years but
appear to be within natural levels according to the report.
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