2014-01-09_REPORT - C1981010 - Laserfiche WebLink

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Page 7 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 U. Prevention of concentrations in both of these aquifers have increased over impacts to ground the past several years based on monitoring of wells P -5 and water that CDRMS P -8, which are in the East Pyeatt Gulch basin. adversely impact regulations 4.05.1(2) and Comment In 2011, elevated levels of TDS were detected in wells the postmining land use within 4.05.11 GD -2 and GD -3 (spoil backfill). GD -2 is down - gradient of the permit area GD -3 which has increased in TDS in 2008 to 2012 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 2012, GMP -1 well indicated higher levels of TDS. 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 aquifer have TDS 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. V. Minimization of disturbance to the CDRMS hydrologic regulation Yes balance within 4.05.1(1) and adjacentto the permit area Page 7