| Popis: |
Development of energy-related resources in the northern Great Plains of the US will require large quantities of ground water. Because Montana, North Dakota, and Wyoming are semiarid, the primary local sources of nonappropriated water are the deep bedrock aquifers of Paleozoic and Mesozoic age. The US Geological Survey undertook a 4-year interdisciplinary study that has culminated in a digital-simulation model of the regional flow system and incorporates the results of geochemical, hydrologic, and geologic studies. Rocks of Paleozoic and Mesozoic age form at least five artesian aquifers that are recharged in the mountainous areas of Montana, South Dakota, and Wyoming. The aquifers extend for more than 600 mi to discharge areas in the northeastern part of North Dakota and in Manitoba. In general, the direction of flow in each aquifer is east to northeast, but flow is deflected to the north and south around the Williston basin. Flow through the Williston basin is restricted because of brine (200,000-350,000 mg/l), halite beds, geologic structures, and decreased permeability of rocks in the deeper parts of the basin. Fracture systems and lineaments transverse the entire area and act either as conduits or as barriers to ground-water flow, depending on their hydrogeologic and geochemicalmore » history. Vertical leakage from the aquifers is restricted by shale with low permeability, by halite beds, and by stratigraphic traps or low-permeability zones associated with petroleum accumulations. However, interaquifer leakage appears to occur through and along some of the major lineaments and fractures. Interaquifer leakage may be a major consideration in determining the quality of water produced from wells.« less |
