2010-11-02_HYDROLOGY - C1981010 - Laserfiche WebLink

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Require- ment Requirement Regulation complied Comment with? (yes / not The post-mining uses of ground water in the permit area will be irrigation and livestock uses. 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 the impacts to ground past several years based on monitoring of wells P-5 and P-8, which water that CDRMS are in the East Pyeatt Gulch basin. Water from both wells, adversely impact regulations yes however, remains suitable for use by livestock and wildlife (see the postmining 4.05.1(2) and discussion in item L. above). land use within 4.05.11 Trapper believes the TDS and conductivity concentrations will the permit area 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. In 2009, as well as in previous years, elevated levels of TDS were detected in wells GF-7 and GF-11 (spoil backfill) and in well P-8 (the Third White Sandstone). These have been determined to be local impacts that do not impair potential use. Elevated TDS levels in well P-8 may be the result of spoil leachate discharging from A-pit, which is 1,100feet upgradient from the well, or they may be due to surface impacts, given that the well is only 35 feet deep and the well is completed in sandstone beds that are likely highly permeable. Furthermore, high nitrate content of samples in past years may indicate the well receives infiltration of surface water. V. Minimization of disturbance to the CDRMS hydrologic regulation yes balance within 4.05.1(1) and adjacent to the permit area W. Prevention of material damage CDRMS The only apparent significant impact to surface water outside the to the hydrologic regulation yes permit area has been TDS loading of surface streams, and this balance outside 4.05.1(1) impact has not impaired water use. There are no data indicating impacts to an aquifer outside the permit area. the ermit area Page 5