The Black hills area in western South Dakota is an elongated dome that was uplifted during the Laramide Orogeny. Surrounding this dome are layers of sedimentary rock; many of which contain aquifers. (Strobel and Galloway) One of these sedimentary layers is the Madison Limestone, sometimes known as the Pahasapa Limestone (Davis, 1995). This limestone formation is found across areas of Montana, North Dakota, South Dakota, Nebraska and Wyoming (Oberst, 2002). The Madison Aquifer usually consists of the upper portions of the limestone unit that are saturated with grounds water (Davis, 1995). Its confined status and 1,000ft. thick base, makes the Madison the largest artesian aquifer in the United States (Oberst, 2002).
The Madison Aquifer is underlain by the Englewood Formation and the Deadwood Aquifer. It is overlain by the Minnelusa Aquifer, separated by shale; but these two aquifers are hydraulically connected in some areas (Strobel andGalloway). This interconnectedness results in leakage from the Madison Aquifer of about 8 cubic ft/s (Long and Putnam, 2002). Figure:1 shows a cross-section of the madison ers
Figure: 1 (Strobel and Galloway)
There is substantial recharge to the aquifer by stream losses and precipitation and surface water through outcrop areas where the limestone is present at the surface (Long and Putnam, 2002). The eroded cracks, tunnels, and caves of this protruding limestone take in large volumes of water and transport it down into the aquifer (Oberst, 2002). There are several streams that cross paths with the Madison Aquifer. Two of these streams combine lose an average of 1,400,000 gallons per day, while another stream loses all of its water and contributes about 220,000 gallons per day to the aquifer (Kirk, 2001). During dry periods, streamflow recharge is about 27 cubic ft/s and areal recharge is 11 cubic ft/s. During wet periods, recharge to the aquifer is 68 cubic ft/s and 36 cubic ft/s respectively (Long and Putnam, 2002).
In its geologic past, the Madison Limestone was exposed at the surface for about 50 million years. During this time, widespread erosion and karstification took place that created many fracture and some tourist attracting caves. Due to the dome-shaped formation of the Black Hills, groundwater flows radially outward as shown in figure 2. This flow may be slightly interrupted in some areas by folds or faults (Strobel and Galloway). Figure:2 shows this flow of water with respect to the geographic features of the area.
The water of this aquifer is of a calcium bicarbonate type with dissolved solids concentrations of usually less that 500mg/L. The water near some of the springs and outcropped areas, the water is of a sodium sulfate type and has dissolved solids concentrations of up to 4,303 mg/L (Stacey and Lidstone, 2003). There are also parts of the aquifer that are magnesium carbonate, calcium magnesium sulfate, calcium sodium sulfate, and calcium sulfate in type. There are areas that are enriched in fluoride as well. The following is a list of some of the other properties of the Madison Aquifer:
The Madison Aquifer is one of the highest yielding aquifers in the United States (Stacey and Lidstone, 2003). There have been reports of well yields up to 2,500 gal/min in some areas (Long and Putnam, 2002). Normal flow yields are between 400-600gal/min. It is of great importance to many of the states that have access it. It is used for livestock, irrigation, industry, and recreation. Beyond these, it is used for many municipal water systems because it is of great quality (2005, Environment). In some places, there is really no need to treat the water at all. The aquifer contains about 66 million acre-feet of drinking water in South Dakota and about 90% of the state depends on this ground water (Davis, 1995). It is probably the most important aquifer to the entire state of Wyoming because they rely on it so heavily (2005, Environment).
Mining activity, irrigation, forest management activities, recreational development, and urbanization pose as potential threats to the degradation of the water-quality in the Madison Aquifer (Black). There is also a concern with the radioactive atom (radionuclide) concentrations that have been discovered in some areas (2005, Environment). The increasing population puts stress on the aquifer and other water resources, and periodic droughts in the region add to the issue (Black).
With the wide array of domestic, industrial, and recreational activities that are happening over much of area in which the Madison Aquifer resides, one would think that there would be many contamination issues. The vulnerability of the aquifer to contamination of drinking water is extremely high due to the rapid transport of water (Davis, 2000). There have been no threatening cases of contamination in the aquifer, but research of the area is always expanding. There are especially stringent wastewater restrictions in outcropped areas of the Madison Aquifer to protect it from any future contamination (Davis, 2000).
Black Hills Hydrology Study. United States Geological Survey. http://sd.water.usgs.gov/projects/bhhs/Intro.html [retrieved: 25 April 2007].
Davis, Arden. 2000. More about Arden Davis. South Dakota School of Mines and Technology. http://sdmines.sdsmt.edu [retrieved 26 April 2007].
Davis, Arden. 1995. Madison Aquifer. West Dakota Water Development District. http://www.northern.edu [retrieved: 25 April 2007].
Kirk, K.B. and Custer, S.G. 2001. Potential of the Madison Aquifer for a City Water Supply in Bozeman, Montana, paper no. 4-0. The Geological Society of America.http://gsa.confex.com/gsa/2001AM/finalprogram/abstract_26719.htm [retrieved: 25 April 2007].
Long, A.J. and Putnam, L.D. 2002. Water-Resources Investigations Report 02-4185. United States Geological Survey. http://www.usgs.gov [retrieved: 25 April 2007].
Oberst, G. 2002. A Geologistís View of Montanaís State Parks. Montana Fish Wildlife and Parks. http://fwp.mt.gov [retrieved 25 April 2007].
Stacey, M.E., and Lidstone, C. 2003. Water Flows Underground from Mountains in Central Montana to Manitoba. Wyoming Sate Water Plan, http://waterplan.state.wy.us [retrieved: 21 April 2007].
Strobel, M.J. and Galloway, J.M. Potentiometric Surface of the Madison Aquifer in the Black Hills Area, South Dakota. United States Geological Survey. http://www.pubs.usgs.gov [retrieve: 25 April 2007].
2005. Environment and Natural Resources. Johnson County Comprehensive Land Use Plan. http://johnsoncountywyoming.org [retrieved: 25 April 2007].
April 27, 2007