U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2004-3086

August 2004

Monitoring Water-Level and Water-Quality Response to 

Conservation Measures in the Sparta Aquifer of the Union 

County, Arkansas Area

Printed on recycled paper

The Union County Water Conservation Board is 

overseeing a conservation plan to reduce withdrawals from the Sparta aquifer and allow water levels 

to recover to a level that can be maintained through 

managed ground-water withdrawals. One major 

aspect of the plan is to replace ground water with 

surface water from the Ouachita River to supply large 

industrial demands in El Dorado, Arkansas. Construction of a river intake and pumping facility (fig. 1) 

and 5 miles of 48-inch pipeline was completed in 

2002. The facility will be capable of producing 65 

million gallons per day (Mgal/d). A new power plant 

and local industries will use the surface water in lieu 

of ground water from the Sparta aquifer (Burns and 

McDonnell, 2003).

Background

The Sparta aquifer is a primary source of ground water 

for industrial, municipal, and agricultural uses in southern 

Arkansas and northern Louisiana. In Union County, 

Arkansas, withdrawals from the Sparta aquifer increased 

since development related to the oil boom began in the early 

1920’s until the 1960’s, resulting in water-level declines of 

over 250 feet in El Dorado. The water level in U.S. Geological 

Survey (USGS) well 17S15W18DBB1 (A in fig. 4) declined 

256 feet from 1942 to 2002 (fig. 2). In addition, the chloride 

concentration of water within the Sparta aquifer has increased 

in some wells in Union County as usage has increased (Broom 

and others, 1984). Optimization and ground-water flow 

models developed by the USGS show that 1997 withdrawals 

of 21 Mgal/d from the Sparta aquifer in Union County must 

be reduced to 28 percent or about 6 Mgal/d to maintain water 

levels at or above the top of the Sparta Sand (Hays, 2000; 

McKee and Clark, 2003; McKee and others, 2004).

In 1996, the Arkansas Soil and Water Conservation Commission designated five counties in southern Arkansas, including 

Union County, as a “Critical Ground-Water Area” because 

water levels were below the top of the Sparta Sand or waterlevel declines of greater than 1 ft/yr were occurring. This 

encouraged Union County officials and citizens to form the 

Union County Water Conservation Board (UCWCB) in 1999. 

Under the management of the UCWCB, with cooperation from 

Union County, the city of El Dorado, and local industry, several 

water-conservation measures were implemented in Union 

County to reduce ground-water withdrawals (Robert Reynolds, 

Union County Water Conservation Board, written commun., 

2003):

• The city of El Dorado installed a gray-water irrigation

system on two local golf courses

• Local industries built a pipeline to allow sharing of used 

industrial water 

• Citizens have reduced domestic and business consumption 

through implementation of conservation practices

• The citizens of Union County voted for a temporary 1-cent 

sales tax to help pay for a facility on the Ouachita River to 

supply surface water to local industry

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Figure 1. Ouachita River intake and pumping facility (photograph by 

John Czarnecki, U.S. Geological Survey).

Figure 2. Ground-water levels at well A in El Dorado and total withdrawal rate from wells in Union County, Arkansas.
The combined results of all conservation measures are 

expected to reduce usage from the Sparta aquifer in Union 

County by about 15 Mgal/d. In 2002, the UCWCB received a 

grant from the U.S. Environmental Protection Agency to study 

how the conservation measures affect the ground water in the 

Sparta aquifer. As part of the study, the USGS is monitoring 

the recovery of water levels and changes in water quality in the 

Sparta aquifer in cooperation with the UCWCB, with assistance 

from Burns and McDonnell and the Union County Conservation 

District. Monitoring the response of the Sparta aquifer will 

increase understanding of the behavior of the Sparta aquifer and 

help planners and managers plan for future withdrawals.

Sparta Aquifer

In Union County, the Sparta aquifer comprises a sequence of 

sand units within the Sparta Sand, a formation of the Claiborne 

Group, that transmit economically important quantities of 

water. The sand units of the aquifer are interbedded with clay 

and silt units, and confined by clay units in the overlying Cook 

Mountain Formation and underlying Cane River Formation 

(fig. 3). The most productive upper and lower sand units of the 

Sparta aquifer in Union County are referred to as the “Green 

sand” and “El Dorado sand,” respectively (Hays, 2000). 

Recharge to the aquifer is by direct infiltration in the outcrop 

and by leakage from overlying alluvium and from other aquifers 

with higher heads (Payne, 1968). Regional direction of groundwater flow is generally to the east and south in southern

Arkansas, and to the east in northern Louisiana although 

large ground-water withdrawals, such as at El Dorado (fig. 

4), alter the direction of flow toward the center of pumping 

(Broom and others, 1984; Schrader, 2004).

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Ouachita

County

Union County

CITY OF

EL DORADO

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Figure 3. Conceptualized hydrogeologic section of the Sparta aquifer in 

southern Arkansas.

Figure 4. Location of water-level and water-quality monitoring wells and potentiometric surface of the Sparta aquifer.

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Union

Calhoun

Bradley Ouachita

Columbia

Claiborne Union

ARKANSAS

LOUISIANA

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Monitoring Program

There are three major aspects of the monitoring program: 

characterizing the hydrogeology, monitoring water levels, and 

monitoring water quality. Preliminary to monitoring the water 

levels and water quality, the hydrogeology is characterized.

 The hydrogeology is characterized to identify the major 

lithologic units, determine approximate depth to unit boundaries, and define the physical properties of the Sparta Sand and 

overlying/ underlying units. Local discontinuities and variations 

in Sparta aquifer unit thicknesses necessitate the gathering of 

this information, especially where monitor wells are located, 

to determine the source of ground water in the wells and to 

identify major sand units, the Sparta Sand, confining units, and 

their boundaries. This information is obtained from geophysical 

logs, drillers’logs, drill cuttings, and past historical records for 

wells. Two new wells were drilled in 2003 to gather hydrogeologic information and monitor the ground-water level (waterlevel sites 1 and 2 in fig. 4). The geophysical and lithologic logs 

from well 1 (fig. 5) illustrate how geophysical logs are used to 

interpret lithologies and their boundaries.

Figure 6. Water-level monitoring equipment (photograph by Ralf

Montanus, U.S. Geological Survey).

The most observable effect of reducing ground-water withdrawals is a rise in the ground-water level elevation. This is 

monitored through a network of eight wells that penetrate the 

Sparta aquifer in Union and Columbia Counties, Arkansas, and 

Union and Claiborne Parishes, Louisiana (fig. 4). Where the 

Sparta aquifer is confined by an overlying confining layer, such 

as the Cook Mountain Formation, the water is under pressure 

and will rise in a well that penetrates the confining layer. The 

altitude to which the water level rises is defined as the potentiometric surface (fig. 4) (Bates and Jackson, 1980). Each well 

is equipped with a pressure transducer to measure water levels, 

a digital recorder to store the data, and a phone modem (fig. 6) 

to transmit water-level data to the USGS office in Little Rock, 

Arkansas. The water-level data are automatically processed and 

updated every 6 hours on the USGS web site

http://ar.waterdata.usgs.gov/ (fig. 7).

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Figure 5. Geophysical and lithologic logs of well 1 in El Dorado, Arkansas.

Large withdrawal rates and low water levels can create conditions that induce encroachment of saltwater into 

the Sparta aquifer increasing the chloride concentration 

(Broom and others, 1984). As withdrawal rates are reduced 

and water levels rise because of conservation efforts, the 

chloride concentration is expected to decrease; therefore, the 

need for water-quality monitoring. Water quality is monitored through a network of 12 actively-pumped public-supply wells located near the city of El Dorado and adjacent 

areas in southern Arkansas and northern Louisiana (fig. 4). 

Water samples are collected from each well twice per year 

and measured for temperature and specific conductance, and 

analyzed for chloride concentration. 
Figure 8. A U.S. Geological Survey employee demonstrates how the groundwater level is monitored in a well at a school in Union County, Arkansas (photograph by Ginger Risinger, Union County Conservation District).

Managing for the Future

Education, conservation, and monitoring will play key roles 

in managing the Sparta aquifer resource in the future. Education of government officials and citizens on the condition of 

the resource (fig. 8) will enable wise and informed decisions to 

be made. Conservation by officials, industry, and citizens will 

help to restore withdrawals to a sustainable level. Monitoring 

water levels and water quality in the Sparta aquifer will provide 

information on the condition of the resource to help managers 

plan future withdrawals and to protect the resource.

References

Bates, R.L., and Jackson, J.A., eds., 1987, Glossary of geology 

(3d ed.): Falls Church, Va., American Geological Institute,

788 p.

Broom, M.E., Kraemer, T.F., and Bush, W.V., 1984, A reconnaissance study of saltwater contamination in the El Dorado 

aquifer, Union County, Arkansas: U.S. Geological Survey 

Water-Resources Investigations Report 84-4012, 47 p.

Burns and McDonnell, 2003, Sparta Aquifer Recovery Study, 

February 2003 - October 2003: 2nd Semi-Annual Report,

18 p.

Hays, P.D., 2000, Sustainable yield estimation for the Sparta 

aquifer in Union County, Arkansas: U.S. Geological Survey 

Water-Resources Investigations Report 99-4272, 17 p.

McKee, P.W., and Clark, B.R., 2003, Development and calibration of a ground-water flow model for the Sparta aquifer of 

southeastern Arkansas and north-central Louisiana and simulated response to withdrawals, 1998-2027: U.S. Geological 

Survey Water-Resources Investigations Report 03-4132, 71 p.

McKee, P.W., Clark, B.R., and Czarnecki, J.B., 2004, Conjunctive-use optimization model and sustainable-yield estimation 

for the Sparta aquifer of southeastern Arkansas and northcentral Louisiana: U.S. Geological Survey Water-Resources 

Investigations Report 03-4231, 30 p.

Payne, J.N., 1968, Hydrologic significance of the lithofacies 

of the Sparta Sand in Arkansas, Louisiana, Mississippi, and 

Texas: U.S. Geological Survey Professional Paper 569-A,

17 p.

Schrader, T.P., 2004, Status of water levels and selected waterquality conditions in the Sparta-Memphis aquifer in Arkansas 

and the Sparta aquifer in Louisiana, spring-summer 2001: 

U.S. Geological Survey Scientific Investigations Report 

2004-5055, 52 p.

— Daniel S. Yeatts

Any use of trade, product, or firm names is for descriptive 

purposes only and does not imply endorsement by the U.S. 

Government.

Information on technical reports and hydrologic data 

related to this study can be obtained from:

District Chief

U.S. Geological Survey

401 Hardin Road 

Little Rock, AR 72211

Email: dc_ar@usgs.gov

Phone: (501) 228–3600

FAX: (501) 228-3601

World Wide Web: http://ar.water.usgs.gov/ 

Figure 7. Water-level data for well 1 as displayed on U.S. Geological 

Survey web site.