Hydrologic Setting

The Ozark Aquifer is part of a larger system called the Ozark Plateau Aquifer system. This system includes the Springfield Plateau, Ozark, and the St. Francois Aquifers. The age of rocks that comprise this system range from Cambrian to Mississippian. The rocks consists of dolomite, sandstone, shale, and chert which tend to dip southward. The aquifer system reaches into southern Missouri and small portions of southeastern Kansas and eastern Oklahoma. The Ozark aquifer is by far the thickest aquifer in the northern aquifer system. The Ozark aquifer is comprised of limestone and dolomite with some areas containing chert, shale, and sandstone. These rocks date back to Late Cambrian to Middle Devonian. Most of the water that comes from the Ozark is used for agricultural purposes, although some of the water is used for industrial and municiple reasons. The aquifer is more than 3,000 feet thick in most places, but in central Arkansas it extends to 5,000 feet. In western Arkansas the Ozark aquifer is 1,500 feet or less (Renken, 1998).

There is a study unit that involves most of the aquifer which includes all four states. It has an area of 48,000 square miles. There are major water quality concerns in the study area that include elevated concentrations of nutrients, elevated concentrations of bacteria, trace elements, dissolved solids, and radionuclides in ground water. The area has a temperate climate with average annual precipitation around 38-48 inches per year. The study area has an average annual temperature of 56-60 degrees F, and evapotranspitation rates of 30-35 inches per year. The land surface area ranges from 200 feet to around 2300 feet. 2.3 million people live in this study area including the city of Springfield, Missouri. There is mining in all four states and the greatest amount occuring the the northwestern portion. Lead-zinc mining has been ecomnoically important in the past and coal is still being mined. The average annual runoff is about 14 to 20 inches per year in the Boston Mountians (Petersen et.al, 2005).

There are a few formations that can yeild a large portion of water. The Roubidoux and the Gunter Sandstones are a few that can yeild a lot of water. On the other hand, the Gasconade Dolomite yeilds little water. This formation is comprised of a cherty dolomite that is about 100 feet thick. The Roubidoux formation extends eastward across northern Arkansas and contains dolomite, quartz sandstone, and chert. The Gunter Sandstone is the main water yeilding formation in which it yeilds about 150 to 300 gallons per minute. The Gunter contains mostly quartz sandstone. The Ozark confining unit consists of mainly shale with some limestone with little permeability. The carbonate rocks in the upper parts of the aquifer are dissolved, leaving subsurface and surficial openings in the ground. Many of these openings leave caves, sinkholes and other openings which are called karst topography. Water can recharge into these openings either by infiltration through the soil, or by direct runoff into streams or sinkhole. There is a very large cavern system that runs underneath the surface. This is due to the fractures and partings in the bedding planes. The lithology of the three aquifers, confining units, and the hydraulic properties are consistent throughout a large area (Renken, 1998).

The main source of water that enters the Ozark aquifer is through precipitation that falls on and near the outcrop sites. Some of the water is infiltrated from the overlying aquifers. There is a confining unit called the Chattanooga Shale, that is thin or absent. The shale is fractured over the Ozark aquifer, in which the Springfield Plateau aquifer leaks downward, recharging the Ozark aquifer. Many studies have been done to explain the ground-water movement, and most people would say the the movement is controlled by the topographic relief. Some of the water moves towards major rivers, which indicates regional discharge. The regional water movement is northwestward, eastward, and southward from the St. Francois mountains. Ground-water flow is southeastward in the eastern part of the aquifer. There is thought to be a ground-water divide underneath the Boston Mountains. The Springfield aquifer is mainly used as a source of domestic water. The Ozark is used for domestic and public water. The Ozark aquifer reaches into Missouri and parts of Kansas and Oklahoma. A cone of depression was found in Springfield, Missouri many years ago due to the population amount in the area. People have now been moving into the rural areas which causes the cone to subside (Renken, 1998).

The Ozark aquifer extends into southern and central Missouri where it is used as mostly agriculture, domestic and public uses. The area is primarily forest and agriculture that includes pastures and cropland. Diciduous forest and evergreens make up the forest regions. Environmental consultants are worried about the number of contaminants entering the water through karst features. It has been shown that microbial activity in ground water can be affected by fractures, faults and karst due to losing streams, sinkholes and many other solution channels. In a recent study, 95 percent of of the public water is dependent upon the ground water. The ground water here is extremely susceptible to contamination and other harmful materials (Davis and Witt, 2005).

The ground-water contains mostly calcium or calcium magnesium bicarbonate. In some locations calcium sulfate or sodium chloride can be found where the aquifers are confined. The pH of the ground-water ranged from 5.2 to 8.3. Nitrate concentrations are also found in the Ozark aquifer as well as the Springfield Plateau. The Ozark aquifer is mainly used for agriculture. Some agricultural methods can increase concentrations of nutrients, bacteria, and trace elements into the ground-water. The chemical quality of the water is suitable for most uses. The concentration of dissolved solids is less than 1000 milligrams per liter. The numbers may be a little different as you move closer to the Mississippi River, probably because there is less karst as you move closer to the river. There is a large risk of contaminates entering into a sinkhole or any other opening in the ground. As the number of sinkholes increase, the risk of contamination of the aquifer increases. It is extremely important to not only monitor the water, but the movement of water as well (Renken, 1998).

In the study unit as talk about above, calcium magnesium bicarbonate is the main dissolved solid although in confined areas, calcium sulfate and sodium chloride are the dominate dissovled solids. There are many factors than affect the water quality. Some of them include climate, physiography, geology, soils and population. Most of the findings in the report note that the most contamination occured in or near agricultural land and industrial areas (Petersen et.al, 2005).

There are many things that can be done to stop the contamination of the aquifer and surficial water. The development in areas with subsidence could cause problems later, not only damage to the house but damage to the aquifer underneath the house. Another way to stop contaminations is to limit the amount of fertilizers in the area. The fertilizers have shown to seep into the aquifer by means of the karst topography. The last main point is to avoid major industrialization in the areas with the most subsidence. There are many pollutants that come from industries that enter the surface water and end up in the aquifers. They need to find a way to limit the amount of pollution entering the air and the ground. As seen in the graph above, agriculture use of the water is by far greater than any other use. The amount of fertilizers entering the soil could pose as a problem in the future.

As for a shortage of water, a city in Missouri has had problems in the last 10 years with an aquifer that has decreased its supply be nearly 3 feet per year. The city of Rolla, Missouri has depended entirely on the ground water of the Ozark aquifer. There is an average decline of 3 feet per year and in some places it is as much as 7 feet per year. There is a northeast trending cone of depresion about 4 miles long and 2 miles wide. There needs to be more options for a city like this that is home to a college, not to mention and engineering college, as well as many people that enjoy southern Missouri. They need to rely more on surface water than ground water (Vandike, 2001). As for southern Missouri, the population will continue to grow, but drought seasons will also continue. If southern Missouri has more droughts like they have had in the past, water will then move to southeast Kansas and northeast Oklahoma. Southern Missouri is losing water at a rapid pace, more options are needed to help this region.

Petersen, J. et.al., 2005. Water Quality in the Ozark Plateaus. National Water Quality Assessment Program. http://ar.water.usgs.gov/nawqa/ozark/setting.html

Renken, R. A., 1998. Ozark Plateau Aquifer System. http://capp.water.usgs.gov/gwa/ch_f/index.html

Vandike, J. E., 2001. Rolla's Shrinking Aquifer. No Standing News, Volume 2 Number 76. http://www.rollanet.org/~rwnash/nsn_1_76.pdf#search='Ozark%20aquifer'