Potential effects of surface coal mining on the hydrology of the Bloomfield coal tract, Dawson County, eastern Montana

Water-Resources Investigations Report 83-4229




The Bloomfield coal tract in Dawson County, Montana, contains about 420 million tons of recoverable coal reserves within the Pust coal bed. About 136 million tons of coal within the tract is Federally owned, of which 98 million tons has been identified for potential lease sale. A hydrologic study has been conducted in the potential lease area to describe existing hydrologic systems and to assess potential impacts of surface coal mining on local water resources. Shallow ground-water resources in the tract are limited to sandstone and coal aquifers in the Tongue River Member of the Fort Union Formation (Paleocene age). These shallow aquifers have small values of hydraulic conductivity; yields to wells generally range from 1 to 10 gallons per minute. Water from shallow sandstone and coal aquifers is used primarily for livestock watering and domestic supply. Chemical analyses indicate that water from most shallow aquifers is dominated by calcium and magnesium cations and sulfate and bicarbonate anions. Surface-water resources in the tract consist primarily of small reservoirs used for livestock watering. All streams in the tract are ephemeral, making them unreliable as a source of livestock water. Mining of the Pust coal bed would cause certain impacts on local water resources. About 15 stock and domestic wells and 13 small stock reservoirs would be destroyed by mining. Shallow coal and sandstone aquifers would be permanently removed from parts of the tract. Leaching of soluble salts from mine spoils may cause a long-term degradation of the quality of water in shallow aquifers in or near the coal tract. Impacts on the local water resources could be mitigated by development of alternative ground-water supplies from deeper aquifers in the Fort Union and in the Upper Cretaceous Hell Creek and Fox Hills Formations. Reservoirs destroyed by mining could be reconstructed during mine reclamation. (USGS)

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Potential effects of surface coal mining on the hydrology of the Bloomfield coal tract, Dawson County, eastern Montana
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Water-Resources Investigations Report
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U.S. Geological Survey,
iv, 37 p. :ill., maps ;28 cm.