2014-07-25_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 Twenty Mile Sandstone is the only regionally extensive aquifer in the vicinity of the Trapper Mine. It is several hundred feet deeper than the deepest mining at Trapper and has shown no effect from Trapper's mining based on monitoring data from well GF -1 and previously from well GD -1(2). 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 (2nd WSS) and P -8 (3rd WSS), which are in the East Pyeatt Gulch basin. Well GC -2 (2nd 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 does 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 U. impacts to TDS and sulfate levels may occur in the future at well GP -9. ground water that CDRMS adversely impact regulations Comment Elevated TDS levels in backfill aquifers is likely according to the postmining 4.05.1(2) and the PHC section of Trapper's permit. In 2011, elevated land use within 4.05.11 levels of TDS were detected in wells GD -2 and GD -3. Well the permit area GD -3 is completed in backfilled spoil. Well GD -2 is down - gradient of GD -3 and has increased in TDS in 2008 to 2013 which could be the movement of higher concentrations from GD -3 area to well GD -2. The TDS levels in the backfill aquifer may be due to leaching from backfill material, but these levels were reported to be well within their natural limits. In 2013, GMP -1 well completed in the HI aquifer indicated significantly higher levels 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. Page 8