A quarter century of coal mining and hydrogeologic research in southeastern Montana
Book
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OSTI ID:361621
- Univ. of Montana, Butte, MT (United States). Bureau of Mines and Geology
Two valuable natural resources coexist in eastern Montana--coal and ground water. Water related issues are the major concerns during coal mine permit decisions. Due to the concerns about mining related impacts, ground water in the vicinity of coal mines has been continuously monitored since 1970. The continuity and duration of the Montana Bureau of Mines and Geology monitoring program under a variety of geologic, mining, and post-mining conditions have provided a fundamental knowledge on impacts to water levels and water quality. Coal beds are among the most dependable and utilized aquifers in eastern Montana, due to their lateral continuity and fracture-related transmissivity. In response to coal strip mining, water levels in coal-bed aquifers have dropped at distances as far as 2 miles away from mines near Colstrip, and as far as 15 miles from mines near Decker. Water levels typically return to pre-mining levels within several years after pits are backfilled. Mining-induced drawdown in stratigraphically deeper aquifers exceed those in mined aquifers in some areas, and relate to inadequately plugged boreholes from older exploration drilling programs. Dissolved-solids concentrations of water in the spoils aquifers have increased by 50 to 200% due to the dissolution of newly available salts of calcium, magnesium, sodium and sulfate. However, in some sites freshening of the water appears to be occurring as initial salt loads are flushed through the systems. Water-quality impacts are expected in off-site and deeper aquifers due to normal ground-water flow, and in deeper aquifers due to poorly plugged exploration drill holes. However, downgradient impacts to water quality are rarely observed. Future ground-water monitoring should document stable water levels and improving water quality as spoils aquifers reach equilibrium with local undisturbed hydrologic systems.
- OSTI ID:
- 361621
- Report Number(s):
- CONF-9805185--
- Country of Publication:
- United States
- Language:
- English
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