2022-06-02_REPORT - C1981010

• Permit No: C1981010
• IBM Index Class Name: Report
• Doc Date: 6/2/2022
• Doc Name: Annual Hydrology Report Adequacy Review
• From: DRMS
• To: Trapper Mining Company
• Email Name: RAR
• Email Name: JLE
• Media Type: D
• Archive: No

The post-mining uses of groundwater in the permit area will be
for agriculture and livestock/wildlife watering. Only the three
large sandstone aquifers within the upper Williams Fork
Formation at Trapper(Twenty Mile Sandstone, Second White
Sandstone,and Third White Sandstone)could reasonably be
expected to yield enough high quality water to serve as a local
supply source. Coal aquifers in the area possess neither the
deliverability nor water quality to be considered for reliable water
supplies.
The Second and Third White Sandstone aquifers overlie the
stratigraphic sequence being mined at Trapper. TDS concentrations
in both of these aquifers have increased over the years based on
monitoring of wells P-5 (2"d WSS),and P-8 (3,d WSS),located in the
East Pyeatt Gulch basin. Well GC-2 (2"d WSS)has shown an
increase in TDS from the mid 80's to early 90's,TDS levels appear
to have stabilized at levels above pre-mining levels. Sulfate Levels
in well P-8 are above the baseline levels. TDS and sulfate levels in
U. Impacts to the point of compliance well GP-9 do not appear to have been
ground water that CDRMS impacted by mining at this time. However,given the elevated TDS
adversely impact regulations and Sulfate levels in up-gradient well GC-2 and well P-8,elevated
TDS and sulfate levels may occur in the future at well GP-9.
the postmining 4.05.1(2) and
land use within 4.05.11 Elevated TDS levels in backfill aquifers are likely according to the
the permit area PHC section of Trapper's permit. Wells GD-3,GD-5,GF-7 and
GF-11 are completed in backfilled spoil. Well GD-2 is down-
gradient of GD-3. The elevated TDS levels in the backfill aquifers
may be due to leaching from backfill material,reported levels are
within their natural limits.
GMP-1,completed in the HI aquifer,continues to increase in
higher concentrations of TDS and Sulfate. This well is down
gradient from the reclaimed A-pit and is likely showing
fluctuations from the backfilled aquifer. According to the report,
other wells monitored in this specific area and aquifers have
TDS/Sulfate levels that naturally vary significantly over the area.
Trapper believes the TDS and conductivity concentrations will
eventually subside,possibly hundreds of years after mining and
reclamation,as discussed in Section 4.8.3 of the permit. The
suitability of Trapper's ground water for livestock and wildlife is
expected to continue into the future based on long-term trends in
Trapper's water quality data.
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