Contamination in the Ozark Aquifer
Created By:
John Goldsmith, 27 April 2010
Emporia State University
GO571 Hydrogeology
Aquifer Background Information
The Ozark aquifer is a large significant source of water for communities, rural
districts, industry, and much agriculture in Southern Missouri, Southeast Kansas,
and Northern Oklahoma. There are several areas of the aquifer; each area has its
own name and individual characteristics. The area extending into southeast
Kansas from southwest Missouri is the confining system of the aquifer. The area
of most interest with contamination is in the Tri-State mining area in the region
where Oklahoma, Missouri, and Kansas’s borders all meet. This small area of the
Ozark Aquifer, which covers almost the entire state of Missouri, encompasses two
areas of the aquifer, the Springfield Plateau Aquifer and Ozark Confining areas
(Pugh & Adamski, 2003). Figure 1 below shows a map of the different aquifers
and their specific locations.
Hydrological Setting
The area of study projected below in figure 1 is the Western Interior Plains
confining systems and the Springfield Plateau aquifer. This part of the Ozark
Aquifer is in the Tri-State mining area. The Tri-State area was a mining district in
the past for lead and zinc minerals and for strip-mining for coal as well. The
average annual rainfall in this area is about 46 inches per year (Miller & Appel,
1997). The evapotranspiration rates vary across the entire aquifer from very high
to low from west to east. Overall average across the area is medium to high at
around 37 inches per year in the Tri-state region (Miller & Appel, 1997). The
annual air temperature is about 56.7 degrees Fahrenheit (Miller & Appel, 1997).
The area is in a largely diverse topographic region on the boundary of the Ozark
Plateau and the Lowland Plains. The above sea level elevations are quite different
throughout the area. The area is located at the base of the Ozark Mountains and
can be very hilly with large elevation gains over a few miles. Near Pittsburg,
Kansas, the average elevation is 947ft, but in the Miami, OK region, it is closer to
800ft. The highest average elevation in the study area is most likely the Joplin,
MO area with an average elevation of just over 1,000ft above sea level (Miller &
Appel, 1997). The recharge of the Ozark Aquifer system is mainly from
precipitation in the aquifer outcrop areas. It occurs in the Northern part of
Arkansas and in the Southwestern part of Missouri. (Figure 1)
Figure 1
Retrieved with permission from USGS
There are also limited amounts of vertical recharge from the much shallower
Springfield Plateau Aquifer into the Ozark Aquifer. The Springfield Plateau aquifer
sits on top of the Ozark Aquifer. (Figure 2) Fractures and limited permeability
allow water from the Springfield Plateau to enter the Ozark Aquifer vertically
(Miller & Appel, 1997).
Figure 2
Retrieved with permission from KGS
Most of the ground-water flow is controlled topographically from high recharge
areas along short flow paths, and is discharged as base flow in nearby streams.
The ground water resides and flows through the fractures and in between
bedding planes in the carbonate rock that exist in the aquifer. The fractures and
bedding planes are significantly enlarged over time do to the dissolution of the
carbonate rocks (Miller & Appel, 1997). The runoff in this regional area is around
8-10 inches per year. This runoff makes its way into the local streambeds and
rivers and nearby lakes. The limestone rock that is abundant in the area has great
permeability allowing ground water to move downward towards the aquifer. This
provides a good recharge system for the aquifer.
Geologic Properties of the Aquifer
Many geological formations comprise this aquifer. They range from Ordovician to
Pennsylvanian in age. (Figure3) The Ozark Aquifer is a carbonate aquifer
composed largely of limestone and dolomite, although sandstone chert and shale
are interbedded at some depths. The main water-yielding formations are the
Upper Cambrian Potosi Dolomite, the Lower Ordovician Gasconade Dolomite, and
Roubidoux Formation. The aquifer ranges from less than 1,000 to over 3,000 feet
in thickness (Miller & Appel, 1997). (Figure3)
Figure 3
Retrieved with permission from DNR
In the area at its maximum, the Springfield Plateau aquifer is in between 0-450ft
in thickness. The rocks are much different in the Plateau Aquifer and in the
confining units than in the large Ozark Aquifer. The Ozark Aquifer has much
thinner beds of limestone and has some thin shale beds. The confining boundary
of the aquifer in all areas of the region that include the Ozark Aquifer, the
Springfield Plateau, and the confining units, is a Pre-Cambrian age igneous and
metamorphic rock combination with low porosity and permeability. This creates
a great lower confining boundary with very limited infiltration from the top or
bottom (Pugh & Adamski, 2003). The rocks in all three parts of the aquifer all
contain great porosity for holding high water yields (Pugh & Adamski, 2003). The
formations almost all are composed of limestone there for they create good
fractures in a block like sequence that forms good permeability for the water to
move through the rock sequence. The entire aquifer is composed of sedimentary
rocks with great pore space that structure an even, almost homogeneous setting.
Hydraulic Properties in Tri-State Area
Wells in the Springfield Plateau aquifer and in the confining units in southeast
Kansas have low in yields (Pugh & Adamski, 2003). These wells typically can be
pumped around 20 gallons per minute. The storativity of the area is near 5.1
trillion gallons of water (Pugh & Adamski, 2003). The hydraulic conductivity is
considered quite higher in this area versus the large part of the Ozark Aquifer.
This along with thin bedding planes causes the water in Springfield Plateau to
average 90ft higher than the Ozark Aquifer. 30-40 million gallons of water a year
leaks from the Springfield Plateau Aquifer into the Ozark Aquifer due to the
stratification differences of elevation. Water in the Springfield Plateau is typically
lower in mineralization when in comparison to the Ozark Aquifer. It is calciumbicarbonate rich water due to its large affiliation and direct contact with the
limestone rock prevalent in the area (Pugh & Adamski, 2003). This causes the
water confined in the aquifer to be quite hard.
Water as a Resource
The water in the Tri-State area aquifers are used in a variety of ways. The water
can be used to supply communities, rural districts, industry, and a large
agriculture area. The aquifer supplies an area of about 8,700 square miles. This
includes about 12.5 percent of Missouri, thus causing somewhat of a problem due
to its large demand with limited resources. The groundwater level can fluctuate
year to year by about 15ft (Pugh & Adamski, 2003). Most of the aquifers
municipal supply is to Joplin and Springfield Metropolitan Area. Figure 4 below
shows the Springfield Metro area has continued to grow in population the last
100 years. Pittsburg, Kansas, and Miami, Oklahoma are two other small cities in
the region that use the aquifer as a water source as well. These four communities
alone total more than a half a million people. Much of the ground water is used
predominately for agriculture purposes. This causes the water level of the aquifer
to fluctuate. In a year with more than average rainfall, less irrigation is used on
crops. Less water drawn from the aquifer allows time for recharge, leading to a
higher water level throughout the area.
Figure 4
Retrieved with permission from FAIR
Contamination of the Aquifer by Coal Mining
In most places the Ozark Aquifer does not contain harmful contaminates, only
naturally occurring minerals. The quality of water is acceptable in this case and is
used for many purposes including drinking water. In the Ozark Aquifer,
concentrations average less the 1,000 milligrams per liter except in the most
western parts and eastern parts (Miller & Appel, 1997). But, the Tri-State Mining
area has caused many problems within the aquifer in this region. Concentrations
of dissolved solids in this area average between 200-500 milligrams per liter, but
were recorded as high as 10,000 in the deeper aquifers (Pope, Mehl, Coiner,
2009). This includes the most southeast part of Kansas, southwest Missouri,
northeast Oklahoma, and a small area of Northwest Arkansas. This problem is
contributed partially by the coal mining in the area. The coal mines in the area
were predominately strip pits. This type of mining was used to retrieve the thin
shallow beds of coal. The pits usually only hundred feet wide could be up to a
hundred feet deep, thus the strip pits collect water from precipitation and cause
runoff. The runoffs from the coal strip pits have many affects on the natural
water. The runoff increases conductivity, acidity, and sulfate levels, iron and
magnesium concentrations, and lowers the pH levels (Fantz, Heatherly, Yasger,
2010). One of the sources from the coal mines is the gob piles left behind. Gob
piles are piles of discarded coal-waste and fractured rock. These piles contain
iron pyrite also known as fool’s gold. Pyrite is iron sulfide and when it is exposed
to water and oxygen, it goes through a chemical reaction that produces sulfuric
acid, iron oxides, and hydroxides (Brosius, 2005). The different oxides and
sulfides can have a large impact on the pH level of the water it meets. Sulfuric
acid is harmful because it pollutes the water and soils it meets. It is not
considered toxic but it can be very corrosive. These two types of pollution from
the mines are considered Acid Mine Drainage (AMD). The acidic water not only
causes harm and corrosion to the elements it comes in contact with like boats,
coverts, piers, pumps, and other metal equipment, it causes the destruction of
smaller living organisms and causes the water to be unacceptable for recreational
purposes and drinking (Fantz, Heatherly, Yasger, 2010).
AMD can enter the environment several different ways. One way is from the
draining of the gob piles that expel during large events of precipitation. The
flowing water transports large amounts of acid into nearby runoff streams and
rivers (McKinley, 2008). The second and possibly most devastating way for ADM
to effect the aquifer is when in enters vertically underground below the piles.
This contaminates large amounts of water once it enters into the aquifer because
of how shallow the coal beds are, and many of them directly over lay the aquifer.
Any of the acidic runoff trapped in ponds, lakes, or any other holding body of
water eventually can leach into the groundwater supply as well (McKinley, 2008).
Coalmines or strip pits also cause pollution from one aquifer to another. This is by
the mining efforts of the past that actually connect different aquifers to each
other by piercing principal confining layers. They can even provide direct
pathways from surface to groundwater. This is very harmful to the aquifer
because it creates a direct route for surface contaminates to reach the ground
water supply without passing through a protective filter of unsaturated zone
(Buchanan & Buddemeier, 1993).
Contamination of the Aquifer by CBM Production
Another source of groundwater contamination in the Tri-State area is through the
presence and production of Coal Bed Methanes (CBM). CBM is a gas that is
generated during the coalification process and is sorted with the coal on internal
surfaces. There are different environmental issues that come into play with the
production of CBM. “Environmental groups believe that the extraction,
production, and distribution of CBM can have severe impacts on rural agricultural
communities” (Fisher, 2001). CBM can development can affect all aspects of the
ecological system, including, land, water, wildlife, and communities. One of the
issues with CBM production is the large amounts of water that are accompanied
with it. When CBM is produced out of the ground, the large amounts of water
existing with it come from two places. One of these is that CBM is developed in
aqueous solutions. Without the presence of water, CBM cannot be created. This
makes producing CBM without producing water nearly impossible. Another
object that makes producing CBM without water nearly impossible, is the coal
beds in place have a significant amount of porosity. This makes the coal beds
ideal for holding large gas reserves (Fisher, 2001). Many times injection wells
must be set up to push the gas towards the pumping wellhead. The large
amounts of water that are produced along side with the CBM create a significant
disposal problem. The surface discharge of saline produced waters or produced
waters contain vast amounts of organics or inorganic toxins. These toxins include
ammonia or hydrogen sulfide. If insufficient natural flow of water cannot dilute
the discharged water on the surface, than there can be substantial, damage
possible to the environment (Fisher, 2001). Another source of contamination
associated with CBM is involved with the movement and migration of CBM.
Methane can move from coal reservoirs to shallow sub-surfaces and or to the
ground surface. This is a huge environmental concern as well. Seeping methane
can disturb and contaminate shallow groundwater, kill vegetation, and produce
fire and explosion hazards within structures, seeping can be prevented through
better human practices. Seepage normally happens through natural fractures, in
uncemented annular spaces behind existing well casings, through water wells, or
through improperly abandoned oil and gas exploration wells (Fisher, 2001).
Conclusions and Actions Taken
Coal beds in the Tri-State area and other factors, such as the gases they contain,
and human influences of mining, cause groundwater pollution in the aquifers in
the region. This has been a problem for several years and has been addressed to
some extent. There have been new regulations and legislation passed to try and
further control the pollution by the governing the production practices of CBM.
The two governing bodies that investigate and report on the contamination are
both state agencies. In Kansas, the governing body that enforces the clean up is
the Kansas Department of Health and Environment (KDHE). In Missouri, the
enforcer is the Missouri Department of Natural Resources (DNR). With joint
efforts in the region, the two combined have done well at slowing down the
pollution factor immensely, but groundwater remediation or clean up is not only
difficult but also expensive. In many locations, pollution in the groundwater is
known about, but the natural filtration process is relied on to clean it up. In other
places, pump stations for municipal water supplies have to include a filtration
process to get the water to a good quality level (Fisher, 2001). With new mining
and production techniques, and better awareness of the situation, it is hopeful
that the water quality can be preserved for our future generations.
Resources
Brosius, L., (2005, May 4). Coal Mining in Kansas: Kansas Geological Survey Online
Publication. Available at
http://www.kgs.ku.edu/Extension/cherokee/coalmining.html. Accessed on April
27, 2010.
Buchanan, R. and R.W. Buddemeier, (1993). Kansas Ground Water: Kansas
Geological Survey Bulletin ED 10. Pgs. 1-5. Available online at
http://www.kgs.ku.edu/Publications/Bulletins/ED10/05_qual.html. Accessed on
April 25, 2010.
Fantz, D.K., W.G. Heatherly, and P.A. Yasger (2010). Watershed Inventory and
Assessment: Missouri Department of Conservation Assessment. Pgs. 69-80.
Available online at http://extra.mdc.mo.gov/fish/watershed/wosage/watqual/.
Accessed on April 29, 2010.
Fisher, J.B. (2001). Environmental Issues and Challenges in Coal Bed Methane
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http://pubs.usgs.gov/ha/ha730/ch_d/index.html. Accessed April 26, 2010.
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Pope, L.M., H.E. Mehl, and R.L. Coiner. (2009). Quality characteristics of ground
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http://pubs.usgs.gov/sir/2009/5093/. Accessed on April 24, 2010.
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Accessed on April 25, 2010.