Equus Beds: An Aquifer on the Road to Recovery

Table of Contents

Hydrologic Setting

Properties of the Aquifer

A Water Resource

Contamination Issues

Conclusion

References

Map download from Equus Bed Information Site at Equus info

Hydrologic Setting of Equus Beds

The Equus Beds Aquifer is a local aquifer located in South-Central Kansas. The south-central area of Kansas has a temperate climate and average 28-32 inches of precipitation per year. Most of the precipitation occurs in the spring as rain or in the winter as snow. This is when much of the recharge to the aquifer occurs via infiltration. Other sources of recharge are seepage through the beds of streams and rivers, downward percolation of irrigation water, and ground water inflow from underlying permeable rock. The average annual runoff for the area is 10 inches and includes surface and ground discharge into streams. Valley fill located along the Arkansas River is considered part of the aquifer when it is hydraulically connected to it. The valley fill allows water to flow directly between the stream and aquifer and back. Hot, dry summers tend to dry the area, causing water loss to evapotranspiration. The south-central Kansas area is home to two of the state larger population areas (Hutchinson and Wichita). South-Central Kansas area also supports many farms with crops that are irrigated and non irrigated. Increases in the population and irrigation have drawn down the aquifer below recharge levels - reaching its lowest's levels in 1990. Efforts in the last ten years to limit, replace and treat contamination are resulting in encouraging progress toward restoring the aquifer.

The area overlying Equus Beds is drained by the Little Arkansas, Arkansas and Ninnescah rivers as well as several smaller creeks. Cheney Reservoir is located on the southern edge of the aquifer. It was built on the north fork of the Ninnescah River by the Bureau of Reclamation, U.S. Department of the Interior, between 1962 and 1965 Cheney Lake serves as an additional water source for Wichita. It also helps recharge the aquifer by inflitration.

Properties of the Aquifer

The Equus Beds Aquifer consists mainly of unconsolidated Quaternary and Tertiary sand and gravel. These were deposited as stream alluvium over a lower bed of Permian rocks consisting mostly of shale, siltstone, sandstone, gypsum, anhydrite dolomite,limestone and halite. Equus Beds is considered part of the High Plains Aquifer which is located thorough out Nebraska, Kansas Colorado and Texas. The aquifer overlays part of the North American craton - an area of old, stable rock. It has been subjected to deformation as revealed by faults and down and upwards faults which can be seen over the entire area. The area gradually slopes from west to east resulting in a general ground flow gradient in the same direction. The unconsolidated layers of sand and gravels are interspersed with thin layers of silt and clay. These layers may act as a leaky confining layer at best because of their thinness, discontinuity or complete absence. North of the Arkansas River the ground may be saturated with precipitation raising the water table to ground level or even above with local artesian conditions if a confining layer is present. South of the Arkansas the clay area thickens. This area is also covered with dune sands which readily absorbs precipitation and allow it to infiltrate and recharge the aquifer. The Arkansas River is considered a confining unit between the west-east flow of groundwater. The Permian rock that underlies the Equus Beds Aquifer contains salt deposits. Ground water percolates through the salt layers dissolving the salt and other minerals. This increases the salinity when this ground water is hydraulically connected to the aquifer. The specific yield of the Equus Beds aquifer, which is the ratio of the volume of water that the saturated aquifer material would yield by gravity to the volume of the aquifer material, is estimated here as 20 percent. (USGS, 2006)In the Wichita well field, the aquifer consists of about 80 percent solid materials and about 20 percent open pore space where ground water is stored (Stramel, 1956).

Maps showing the rock formations of Nebraska, Kansas and Missouri downloaded from http://capp.water.usgs.gov/gwa/ch_d/

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A Water Resource

The Equus Beds Aquifer is the primary water source for most of the population living above it. In Reno County, the total water used in 2000 was 69.67 million gallons/day. Irrigation accounts for 45.57% of this water used, while pubic consumes 8.35% and industrial uses an additional 11.59%. (USGS, 2005) Groundwater is the only source for this water. Wichita (population -344284 )is located on the southeastern edge of the aquifer, in Sedgwick County. From 1940 to 1993, Wichita used Equus Beds to supply 1/2 of its water requirements. In 1993,Wichita developed surface water sources (Cheney Reservoir) to augment its water supply. Though the Cheney water required more extensive treatment prior to use, it was necessary to find another source of water. The water levels of the Equus Beds Aquifer was declining dramatically (40 feet since 1940). Between 1993-2002, the city relied of Equus Beds Aquifer for only 1/3 of its water requirements. Higher than average precipitation and reduced pumping enabled the aquifer to recover approximately 182,000 acre-feet of storage volume. This raised the level of most wells 10 ft above the record low in 1992.

Annual Equus Bed Aquifer level chart downloaded from USGS, 2006. Wichita water level consumption charts obtained from http://ks.water.usgs.gov/Kansas/pubs/fact-sheets, 2006

In 1997, Wichita started a study on the feasibility of artificially recharging the Equus Beds Aquifer. It created two recharge sites: one in Halstead, the other in Sedgwick. These sites diverted excess water from the Little Arkansas River. After the water was treated, it was inserted in the aquifer via basin, trench and injection wells. During its testing period (1997 -2002) the artificial recharge contributed 3% of the municipal use by Wichita. The feasibility study ended in 2002, but recharge continues when the steam flow of the Little Arkansas River permits. The Demonstration Project showed localized water-level rises near the Halstead and Sedgwick recharge sites. The plan for full production would add millions of gallons of water per day that would be available for city use during times of need. The Artificial recharge storage and recovery (ASR) Phase I plan was to start construction in 2004. Its initial output upon completion is projected to be 10 million gallons of water/day.

Schematic downloaded from USGS Equus Beds Studies, 2006,

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Contamination Issues

For communities that rely on ground-water as their only source of water - any contamination is of concern. Contamination by toxic waste disposal, water discharge, agriculture chemical and bio waste as well as untreated human wastes all are issues that need to be addressed. The Equus Beds Aquifer however, faces two major sources of contamination: one is from the naturally occurring saltwater infusions, the other is from the Obee superfund site located east of Hutchinson.

Salt Water Contamination

One impetus for Wichita's ASR plan was the threat of saltwater intrusion from the west. Currently, the salinity of groundwater increases westward from the Arkansas River. It reaches levels considerably above 500 mg/L. The Kansas Department of Health and Environment (KDHE) maintains that levels above 500 are unsuited for irrigation and public consummation. The Arkansas River acts as a confining unit keeping the higher salinity water from mixing with the fresh water east of the river. A recent study (Young, 2001)indicates that the Arkansas River confining unit may have been breached northwest of Hutchinson, allowing the higher levels of salt water to be introduced into the fresh water aquifer to the east. Also, a study of the bedrock and water flows indicate that another salt contamination source may be the aquifer in GMD#5. Although uncertainties are high, the estimates suggest local penetration from the Permian bedrock in GMD#2 and down gradient flow from GMD#5. Sources are not uniformly distributed, but are probably associated with lows and paleochannels in the bedrock. A suspected location of a paleochannel parallels part of Rattlesnake Creek. The fact that it is oriented parallel to the groundwater flow direction means that it has the potential to serve as conduit for relatively rapid, long-distance transport of high-salinity water (Rubin, 2000). Another source of salt contamination may be wastes associated with the salt mining industry in Hutchinson. The KDHE is monitoring this site and an oil field brine site near Halstead.

From: Salt Contamination of Groundwater in South-Central Kansas, Public Information Circular No. 2, Kansas Geological Survey map showing natural salt contamination areas in Stafford, Pratt, Reno, Sedgwick, Sumner, and Cowley counties

Obee Road Superfund Site

The Obee Road Site was designated as a superfund site and placed on the National Priorities List (NPL) in July 1987. Two contaminated subsites have been identified: the old Hutchinson Landfill located east of the Hutchinson Airport (Obee sub site) and an East fourth street Industrial facility (Airport Rd sub site) located in Hutchinson. The Department of Defense (DOD) operated the Hutchinson Airport until 1963 and may have contributed to the contamination. While the landfill was operating (until 1983), it accepted unknown quantities of industrial wastes as well as solvents from local plants. KDHE detected levels of volatile organic compounds (VOC) including benzene, tetrachlorethylene, chloroform and vinyl chloride. Initial remediation actions included supplying local residents with an alternative source of water. This was accomplished in 1985 via a water line constructed by the City of Hutchinson. A pump and treat system is being utilized to contain the contaminant plume at the Obee site until a final remediation can be achieved. The final Remedial Design/Remedial Action (RD/RA) Work Plan for the Obee site was submitted in December 1996. It requires institutional controls including deed restrictions for the affected area and ground water monitoring. The report was executed in March, 1997 and its first 5 year review completed in June, 2000.

The responsible parties have complete the Remedial Investigations Airport Rd sub site. Further action has been delayed pending a TMDL for chloride which may effect groundwater treatment. Interim measures taken in 1993 included installations of two remedial pumping wells, two air stripping towers and a discharge line on the East Fourth facility. A second phase consisting of additional pumping wells located in the southeastern portion of the site began in 1997. Cessna has extended rural water to homes in the area that have contaminated wells. These interim actions will remain until final solutions are in place.

Image courtesy of Enviromapper, http:epa.gov, (20 April, 2006)

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Conclusion

Water use and regulation can be an intensely volatile issue when the lives and livelihoods of the using population is at stake. The task of cleaning and maintaining a healthy Equus Beds Aquifer requires close cooperation between several Federal and State of Kansas agencies, local municipalities, mineral rights owners, area farmers and livestock producers. The State of Kansas has developed a Kansas Water Plan which controls the use, development, conservation and management of the water sources available in Kansas. The KWP was developed from the recommendations of the various appointed Water Authority Board Members. It is updated when necessary. Additionally the Equus Beds Groundwater Management District #2(GMD#2) as well as two Intensive Groundwater Use Control Areas in McPherson and Burrton also help in the management of Equus Beds and its recharge area. The GMD#2 was formed in 1975 and operated with a "safe Yield" concept. The Safe Yield requires that the annual water withdrawn equals the annual recharge for the area. To maintain the quality of the Equus Beds Aquifer, the water removed must be replaced eventually to prevent further salt contamination. In additonal the EPA is working with local and state agencies to insure that the contaminated sites at the Obee and Airport subsites are cleaned so as to pose no threat to the population. The restoration of aquifer water levels and elimination of contaminants are both vital to a healthy Equus Beds Aquifer.

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References

http://ks.water.usgs.gov/Kansas/studies/equus

http://www.kgs.ku.edu/Hydro/Equus/OFR00_30/index.htm

Buddemeier, R.W., Sawin,R.S., Whittemore, D.O. and Young, D.P., Salt Contamination of Groundwater in South-Central Kansas, Public Information Circular No. 2, Kansas Geological Survey

EnviroMapper for Envirofacts, http://www.epa.gov/(date accessed 20 April 2006)

GROUND WATER ATLAS of the UNITED STATES, Kansas, Missouri, and Nebraska. HA 730-D. http://capp.water.usgs.gov/gwa/ch_d/

Obee Road, National Priorities List, http://www.epa.gov/region7/cleanup/npl_files/ksd980631766.pdf

Ross, H.C., Myers, N.C., and Aucott, W.R. Increased Use of Cheney Reservoir for Wichita Area Water Supply Benefits Equus Beds Aquifer, http://ks.water.usgs.gov/Kansas/pubs/fact-sheets/fs.156-97.html (date accessed April 20, 2006)

Hansen, C.V. and Aucott, W. R., Status of Ground-Water Levels and Storage Volume in the Equus Beds Aquifer Near Wichita, Kansas, January 2000-January 2003. Prepared in cooperation with the City of Wichita. http://pubs.usgs.gov/wri/wrir034298/

Kansas NPL Site Narrative for Obee Road, http://www.epa.gov/superfund/sites/npl/nar827.htm (date accessed, April 20, 2006)

Rubin, H., Young, D. P., and Buddemeier, R. W., 2000. Sources, Transport and Management of Salt Contamination in the Groundwater of South-Central Kansas: Kansas Geological Survey Open-File Report 2000-30 (V1.0) Kansas Geological Survey, The University of Kansas, Lawrence, Kansas. http://ks.water.usgs.gov/Kansas/pubs/fact-sheets/fs.156-97.fig3.gif

Stramel, G.J., 1956, Progress report on the ground-water hydrology of the Equus Beds area: Kansas Geological Survey Bulletin 119, Part 1, 59 p.

Young, D.P., Buddemeier, R. W., Whittemore, D. O. and Rubin, H. Final Summary and Data Report: The Equus Beds Mineral Intrusion Project, KGS Open File Report 2000-30, Kansas Geological Survey, University of Kansas. March, 2001

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