Overview of the Ozark Aquifer In Southern Missouri

Neal Farrar GO-571 Applied Hydrogeology Emporia State University Spring 2009

Description of the Ozark Aquifer

The Ozark Aquifer consists primarily of Dolomitic rocks of Ordovician and Cambrian ages. Its thickness ranges from a few hundred feet adjacent to the Saint Francois Mountains to over 1400 feet thick in much of southern Missouri.  The Ozark Aquifer underlies an area of approximately 35,000 square miles (Page 1, Miller and Vandike 1997) and fully comprises what is referred to as the Salem Plateau Groundwater Province (Page 1 Miller and Vandike 1997).  The Ozark Aquifer is represents the first bedrock encountered at many locations.  In other locations it is overlain by younger formations some of which are also water bearing.  The location and extent of the Ozark Aquifer and its spatial relationship to adjacent groundwater provinces is shown on Figure 1 (Figure 88, Miller and Appel 1997) below.

The formations which typically comprise the Ozark Aquifer in southern Missouri  from top to base is as follows: Cotter Dolomite, Jefferson City Dolomite, Roubidoux Formation, Gasconade Dolomite (Upper and Lower), Eminence Dolomite and Potosi Dolomite.  The upper formations are generally considered to produce less water than the lower formations and in many areas the Cotter Dolomite is considered to behave as an aquitard.  Both the Roubidoux and the Gunter Sandstone member of the Gasconade dolomite are both considered desirable completion targets as the sandy nature of both formations are capable of producing significant quantities of groundwater.  Figure 2 (Slide 18, Power point presentation Vandike 1997) shown below provides a diagrammatic view of the Ozark Aquifer and the overlying Springfield Plateau Aquifer that is present in some locations.  The figure also shows the confining unit that is present between the two aquifers.

Figure 2

The Ozark Aquifer is the principal potable water supply aquifer in most of southern Missouri and is used for municipal and private water supply and for industrial uses.  Sustained flow pumping rates vary considerably from location to location and well to well and is typically related to the presence of fractures, the depth of the well and the thickness of the sandy dolomite (Roubidoux and Gunter) members that are encountered.  Generally speaking the deeper the well, the more exposed formations, the more water column the greater the sustainable well yield.  Typical sustained flow rates vary from 10 gallons per minute (gpm) for a private domestic well with up to 200 feet of Ozark Aquifer penetrated to over 750 gpm for a municipal water well with over 1000 feet of Ozark Aquifer penetrated.  Estimated water storage of the Ozark Aquifer is 223 trillion gallons (Page 1 Miller and Vandike 1997).  Most southern Missouri rural area utilize the Ozarks Aquifer for at least some of their drinking water.  Approximately 1 million people are served by the Ozark Aquifer as a source of their drinking water.  The area that the Ozark Aquifer occupies in southern Missouri is typically steep, rugged terrain with extensive small and large scale faulting.  There are several major lakes and rivers that provide some re-charge to the Ozark Aquifer.  During dry times many southern Missouri rivers and streams receive most of their flow from springs and groundwater seeps. (Page 32, Miller and Vandike 1997).

Water Quality

Water Quality is variable within the Ozark Aquifer but is generally considered to be very good in much of Southern Missouri.  Dissolved solids are typical calcium-magnesium bicarbonate type and range from less then 50 to 1000 milligrams per liter (mg/l) over much of southern Missouri.  Areas to the north, west and south contain excessive dissolved solids primarily in the form of chlorides.  Some of these areas also exhibit elevated raidionuclide concentrations thought to be related to geochemical reactions due to the increased chloride levels (Page 17, Miller and Vandike 1997).  However this relationship does not appear to be consistent in all locations where elevated radionuclides are present (Vandike personal communication 2009).  The Ozark Aquifer that underlies areas within southeast Kansas are almost entirely saline and is considered non-potable and seldom used for drinking water.  There is concern that extensive pumping of water from the Ozark Aquifer in western Missouri could eventually drawn these saline waters into areas of currently good quality water.  Table 1 below provides a summary of general chemistry data for select municipal water supply wells located across Missouri (Table 6 page 60, Miller and Vandike 1997). 

Table 1

Susceptibility to Groundwater Contamination

Karst development and therefore Karst features are quite common in southern Missouri within the carbonate formations that comprise the Ozark Aquifer and the overlying Mississippian aged formations.   These Karst features such as sinkholes and losing drainages allow surface or near surface contamination to rapidly enter the groundwater.   These contaminants include human and animal wastes from lagoons and septic tanks, leaks or spills from containers both above ground and underground of fuels or other hazardous substances.  Run-off from agricultural, industrial, urban and other non-point sources containing fertilizers, oil and antifreeze to enter the groundwater rapidly and easily via these Karst features.  These same Karst features that allow contaminants to quickly enter the groundwater can also facilitate the rapid transportation and spreading and in some instances dilution of certain contaminants.  The Missouri Department of Natural Resources (MDNR) in an effort to minimize contamination of the Ozark Aquifer from surface or near surface contamination has developed, implemented and enforces well installation and construction rules.  The rules are area and well type specific and set out drilling, casing and grout sealing requirements in an attempt to prevent degradation of groundwater quality by attempting to limit migration of contaminants from either surface water and or shallow groundwater to the deeper aquifers.

Hydrogeologic Characteristics

The Ozark Aquifer is heterogeneous in most if not all of its hydrogeologic characteristics.  The presence, size and extent of fractures and the thickness of known high production zones that consist predominantly of sandy zones within the dolomite determines the variability's of many of the hydrogeolgoic characteristics as they relate to the production of groundwater from wells.  The Ozark Aquifer while not confined in all areas behaves as a confined aquifer due primarily to the presence of lower permeability rock overlying higher permeability rock in most instances.  Table 2 (Table 5 page 59. Miller and Vandike 1997) provides a summary of flow rates, transmissivity and storage coefficient for selected municipal wells all completed in the Ozark Aquifer.

Recharge to the Ozark Aquifer occurs thru the soil via percolation of precipitation (Page 23, Miller and Vandike 1997) generally forming a perched water layer atop the bedrock that then recharges the bedrock.  Significant recharge to the Ozark Aquifer during periods of precipitation is thru direct and large scale runoff directly into the Ozark Aquifer via Karst features (Page 27, Miller and Vandike 1997).  There are thousands of sinkholes, hundreds of miles of losing drainages and thousands of springs in southern Missouri (Page 30, Miller and Vandike) many of which overlie and or directly influence the Ozark Aquifer.  Southern Missouri receives approximately 38 inches of precipitation annually with evapotranspiration averaging approximately 28 inches per year.  While no specific estimates of recharge via precipitation solely within the Ozark Aquifer, it is estimated that total recharge statewide is 4.85 trillion gallons per year (Page 27, Miller and Vandike 1997).  Much of the water that enters the aquifer during precipitation rapidly exits via springs.  Many of these springs are significant and increase flow to the streams that they discharge to.  Table 3 (Page 45, Table 12 Brookshire 1997) below provides a summary of flow data for Missouri's largest springs. 



Table 2


Water that enters these karst features can travel long distances over a short duration prior to discharging via a spring or springs and no discussion of the Ozark Aquifer in southern Missouri would be complete without photographs of some of Missouri's spectacular springs.  Photos (MDNR website link below) below show some of these karst features that are quite common in southern Missouri


Table 3




Blue Spring


Greer Spring


Double Spring


Big Springs





The Ozark Aquifer of southern Missouri is a high quality extensive water bearing zone that provides clean drinking water for much of rural Missourian's.  It's springs provide rare beauty and recreation that is not common in many areas within the United States.  Due to its extensive karst features such as sinkholes and losing drainages the Ozark Aquifer is very susceptible to contamination sources and therefore protection of these resource is required.




Goodwin Hollow Losing Drainage



Miller, A. James and Appel, L. Cynthia  Groundwater Atlas of the United States, Kansas, Missouri and Nebraska.  USGS Publication HA-730-D published in 1997 http://pubs.usgs.gov/ha/ha730/ch_d/D-text5.html

Salem Plateau Groundwater province, Missouri Department of Natural Resource http://www.dnr.mo.gov/env/wrc/groundwater/education/provinces/salemplatprovince.htm

Brookshire, N. Cynthia Missouri Water Quality Assessment, Water Resources Report 47, Missouri State Water Plan Series Volume III.

Miller, E. Don, and Vandike, E., James, Groundwater Resources of Missouri, Water Resources Report #46, Missouri State Water Plan Series Volume II, 1997

Vandike, James Missouri Groundwater 101Power Point Presentation, Groundwater Issues in Southwest Missouri.  Orginally presented at the Ozark Aquifer Forum, Missouri Southern University, Joplin, Missouri.  November 20, 2007.  http://ks.water.usgs.gov/studies/OzarkAquifer/SWMOkansasmotalk.ppt