2014-01-09_REPORT - C1981010 - Laserfiche WebLink

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S. Restoration of ground water recharge to approximate pre- mining rate CDRMS regulation 4.05.12(3) Comment Each pit disrupts the potentiometric surface of confined aquifers. After reclamation, monitoring data show full recovery of the potentiometric surface outside of backfilled pits and partial recovery of potentiometric surface inside backfilled pits. Spoil springs may reduce groundwater recharge by diverting groundwater flow to surface flow. However, Trapper's expected total aggregate spoil spring discharge of less than 1 cfs will be too small to reduce recharge below the approximate pre - mining rate. The Probable Hydrologic Consequences (PHC) section of Trapper's mining and reclamation permit (Section 4. 83) discusses the possibility of a high -TDS plume of coal spoil leachate forming in the Third White Sandstone downgradient from the Trapper Mine in Section 29- T6N -90W. Such a plume would not be expected to form until several years, possibly decades, after the pit is reclaimed in the adjoining Section 32. Compared to pre - mining ground water conditions, such a plume would have elevated dissolved solids, which could possibly impair the use of ground water T. Prevention of in the Third White Sandstone. adverse impacts CDRMS to ground water regulation Comment Spoil leachate could also invade the alluvium in Flume systems outside 4.05.11 Gulch by seeping down into the subsurface from spoil the permit area springs flowing on the land surface in the gulch. The Third White Sandstone is monitored in the area of the possible plume in well GP -9, and the alluvium is monitored with the Coy well. Monitoring data from both wells indicate that a plume has not formed. For the Third White Sandstone, this could be the consequence of artesian conditions that are preventing invasion in the subsurface by spoil leachate. Page 6