2021-04-29_REPORT - C1981010 - Laserfiche WebLink

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The post-mining uses of ground water 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),which are 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 the point of compliance well GP-9 do not appear to have been impacted by mining at this time. However,given the elevated TDS 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. U. Impacts to ground water that CDRMS Elevated TDS levels in backfill aquifers are likely according adversely impact regulations to the PHC section of Trapper's permit. Well GD-3 is the postmining 4.05.1(2) and Comment completed in backfilled spoil. Well GD-2 is down-gradient land use within 4.05.11 of GD-3. The TDS levels in the backfill aquifer may be due the permit area to leaching from backfill material,reported levels are within their natural limits. In 2019,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. 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. Page 5