In 1905, N. H. Darton described the geology and underground‐water resources of the central Great Plains in his classic report that emphasized the importance of the Dakota aquifer to this region of the United States. Since Darton's work, many investigators have studied Dakota‐aquifer hydrology with regard to development of local or statewide resources. Preliminary mapping of relatively recent fluid‐level data by the U.S. Geological Survey indicates regional potentiometric trends similar to those interpreted by Darton, but altitudes substantially lower in part of the area. The classic artesian‐system concept of the Dakota aquifer is not consistent with some of the data and observations of the past several decades. The simple aquifer geometry and effective lateral hydraulic continuity normally associated with that concept do not appear to characterize the Dakota aquifer regionally.
Introduction Watershed C06 Summary of premining conditions Data collection during mining Groundwater hydrology during mining Groundwater quality during mining 13 Watershed M09 15 Summary of premining conditions Data collection during mining Groundwater hydrology during mining 15 Groundwater quality during mining
The Dakota aquifer, composed of the Dakota Sandstone and stratigraphically equivalent sandstone units of Cretaceous age, is the upper‐most regional aquifer underlying the extensively developed High Plains aquifer of the midwestern United States. The concentration of dissolved solids in ground water of the Dakota aquifer ranges from less than 500 milligrams per liter in calcium bicarbonate type water in the eastern outcrop area to more than 100,000 milligrams per liter in sodium chloride type oilfield brine in the Denver Basin to the west. Preliminary maps showing the distribution of dissolved solids confirm the complex nature of the Dakota aquifer as inferred from stratigraphic and hydraulic evidence. Extensive vertical leakage through confining layers, local recharge at the truncated eastern boundary, and a barrier to recharge along the western edge of the Denver Basin are consistent with the distribution of hydraulic head and dissolved solids.
Three regional aquifer systems were investigated in a 370,000-square-mile area extending from the foothills of the Rocky Mountains in Colorado to the Mississippi River in eastern Missouri, and from South Dakota to mountainous parts of Arkansas and Oklahoma. These aquifer systems and internal confining systems are composed of sedimentary rocks ranging in age from Cambrian through Cretaceous. The study area is informally divided into the Plains subregion and Ozark subregion. Al A2 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST aquifer system was simulated. Pumping rates are small compared to the large natural rates of recharge and discharge.
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