Equus Beds Water Quality
Rasmussen, P.P., Eslick, P.J., and Ziegler, A.C., 2016, Relations between continuous real-time physical properties and discrete water-quality constituents in the Little Arkansas River, south-central Kansas, 1998-2014: U.S. Geological Survey Open-File Report 2016–1057, 20 p.
Stone, M.L., Garrett, J.D., Poulton, B.C., and Ziegler, A.C., 2016, Effects of aquifer storage and recovery activities on water quality in the Little Arkansas River and Equus Beds aquifer, south-central Kansas, 2011–14: U.S. Geological Survey Report 2016–5024, 88 p.
Presentation: The Role of Science in Managed Aquifer Recharge—the Equus Beds aquifer near Wichita, Kansas 1938–2016+
Whisnant, J.A., Hansen, C.V., Eslick, P.J., 2015, Groundwater-level and storage-volume changes in the Equus Beds Aquifer near Wichita, Kansas, predevelopment through January 2015: U.S. Geological Survey Scientific Investigations Report 2015-5121, 27p.
Equus Beds summary of USGS activities
Tappa and others, 2015. Water quality of the Little Arkansas River and Equus Beds Aquifer before and concurrent with large-scale artificial recharge, south-central Kansas, 1995–2012
Since 1995, water-quality samples have been collected from more than 10 surface-water sites and more than 100 groundwater
sites as a part of the Equus Beds Groundwater Recharge Project. More than 10,000 water-quality samples have been collected
and analyzed for more than 400 compounds, including most of the compounds on the U.S. Environmental Protection Agency’s
Maximum Contaminant Level (MCL) List for drinking water. The station names and numbers for water-quality monitoring sites
are listed in the following link—
Equus Beds Groundwater Recharge Project water-quality monitoring sites.
Klager and others, 2014. Preliminary Simulation of Chloride Transport in the Equus Beds Aquifer and Simulated Effects of Well Pumping and Artificial Recharge on Groundwater Flow and Chloride Transport near the City of Wichita, Kansas, 1990 through 2008
The USGS model (Kelly and others, 2013; Klager and others, 2014) simulated groundwater flow and chloride transport during 1990 through 2008, and was used to test how various theoretical well-field management scenarios affect groundwater levels and chloride movement toward the Wichita well-field. the USGS model was developed to assist
resource managers in making decisions on how to best protect Wichita water resources. If chloride levels are high the water is less usable as a drinking-water source and for crop irrigation without additional treatment.
Equus Beds aquifer model presentation
Compared to current irrigation and city pumping:
If all Wichita and irrigation pumping was discontinued, water levels would be about five feet higher.
If Wichita pumping was doubled and with existing groundwater pumping, water levels would be about five feet lower.
If artificial recharge were increased by 2,300 acre-feet per year in the Phase 1 sites near Burron, Kansas water levels would increase by about 0.5 feet.
With actual well-pumping and artificial-recharge rates, the simulated chloride plume near Burrton moved toward the Wichita well field at about 0.8 feet per day.
With all agricultural and Wichita pumping removed, movement of chloride plume near Burrton would slow to about 0.7 feet per day.
Doubling the municipal pumping of the city of Wichita from the well field increased the simulated rate of movement of the plume to about 1.0 foot per day.
- Increasing the amount of water artificially recharged to the aquifer by 2,300 acre-feet per year near the Phase 1 recharge locations slowed the simulated rate of movement of the plume to about 0.7 feet per day.
- Animations of simulated chloride movement in the Equus Beds aquifer can be accessed here: http://pubs.usgs.gov/of/2014/1162/downloads
Equus Beds groundwater-flow and chloride-transport model archives available on request. Contact GS-W-KS_equus@usgs.gov
Ziegler and others, 2010. Water Quality in the Equus Beds Aquifer and the Little Arkansas River Before Implementation of Large-Scale Artificial Recharge, South-Central Kansas, 1995-2005
Baseline (before artificial recharge) sampling and during demonstration phase defined the constituents of concern
(>5% of samples exceed water quality standards) for artificial recharge;
(Surface Water detection table,
Ground water detection table)
Sampling has continued to define the water quality of surface and groundwater.
Surface Water Summary Table
Groundwater Summary Table
- A number of organic compounds have been detected, but no concentrations exceed water-quality standards.
- Burrton Chloride plume has moved about 3 miles in past 45 years.
- Chloride in Little Arkansas River exceeds 250 mg/L in 21% to 58% of samples.
- Chloride in deep index wells exceeds 250 mg/L (SMCL) 8% of time—5% in shallow wells—with higher values near Burrton and along the Arkansas River.
- Sulfate exceeds 250 mg/L (SMCL) in 18% of shallow and 13% of deep groundwater.
- Nitrate exceeds 10 mg/L (MCL) in about 15% of shallow groundwater- little nitrate in deep groundwater.
- Arsenic exceeds 10 ug/L (MCL):
- In surface water about 10% of samples and usually during low flow.
- In shallow groundwater in 12% of the samples.
- In deep groundwater in 34% of samples.
- Atrazine concentrations in the Little Arkansas River exceed 3 ug/L in about 19% to 42% (MCL – as annual average) of the samples mostly in late spring through early fall.
- Atrazine is detected in 56% of shallow wells indicating infiltration from field application.
- Coliform and E. coli are detected in nearly all surface water samples.
- Total coliforms were detected in 25% of shallow index wells and 12% of deep index wells.
Concentrations and load estimates for select locations of the Little Arkansas River
indicate that the sources of the loads of chloride and fecal coliform bacteria are
upstream of Highway 50. The concentrations and load estimates also indicate
that atrazine loads are distributed throughout the basin. For further information refer to
“Regression Analysis and Real-Time Water-Quality Monitoring to Estimate Constituent Concentrations, Loads, and Yields in the Little Arkansas River, South-Central Kansas, 1995-99.”
In addition, hourly estimates of concentrations and loads for these sites from 1999 to today are available at
Expected effects of artificial recharge
- Will increase water levels and storage in the aquifer.
- Will slow down southeast movement of chloride near Burrton and along the Arkansas River.
- As water levels increase, concentrations of some metals may temporarily increase until reaches geochemical equilibria.
- Recharge of oxygenated water will decrease concentrations of metals—as long as it remains oxygenated.
Effects of Induced Stream-Water and Artificial Recharge on the Equus
Beds Aquifer, South Central Kansas, 1995-2004, were defined using simple
mixing, solute-transport, and theoretical geochemical models. Simple mixing
and solute-transport models indicated that about 75% of the water in the
diversion well at Halstead originates from the nearby stream. Geochemical
modeling indicated that if fully oxygenated water is injected in the aquifer,
chemical precipitation of calcite and iron oxyhydroxide are likely and may
reduce the efficiency of the injection wells.
Water-quality changes associated with Phase I recharge
- Water-quality Data Compilation for 2006-2015
- The Equus Beds Aquifer Storage and Recovery (ASR) Project Phase I began in 2006
“to inject surface water into the Equus Beds Aquifer for the purpose of storage and later
recovery of the groundwater and to form a hydraulic barrier to a known brine plume” (
Kansas Underground Injection Control Area Permit Class V Injection Well, Kansas Permit No.
The project diverts water from the Little Arkansas River through bank storage (diversion) wells,
completed adjacent to the stream, when flow in the Little Arkansas River
exceeds base flow (Equus Beds surface water quantity). The
diverted water is artificially recharged into the Equus Beds aquifer through
injection wells and recharge basins. The following link provides more information on
the Equus Beds Aquifer Storage and Recovery (ASR) Project Phase I. Equus
Beds Aquifer Storage and Recovery Project Phase 1.
- As of December 2012, artificially recharged water reached the monitoring wells at RB-1, RB-2, RRW3, and RRW4
- Average concentrations of several constituents increased during Phase 1 recharge (2006-2015) compared to pre-Phase 1 (1995-2005) conditions at all Index Well sites, including:
- Specific Conductance
- Decreasing concentrations:
- Oxidation-Reduction Potential
Water-quality changes associated with Phase I & Phase II recharge
Statistical exceedance information on all sites sampled from February 1995- December 2015 as part of the Equus
Beds Groundwater Recharge Project:
Aquifer Storage and Recovery Project Phase I site maps:
What controls the water quality?
- Chloride- proximity to Burrton and Arkansas River and possible dilution by recharge water or increased hydraulic head slowing the movement of the chloride plume.
- Arsenic, iron, and manganese—presence in aquifer materials, distribution of clays, chemically reducing conditions, and areas of larger water level declines
- If oxygenated water is recharged into a reducing aquifer, concentrations of dissolved arsenic, iron and manganese will decrease because these constituents will precipitate from solution
- Nitrate, atrazine, and bacteria in surface water, – controlled by runoff and agricultural land use
Chloride concentrations exceeded the SDWR of 250 mg/l in less than 8% of the shallow and deep parts of the aquifer. Crop yields decrease if concentrations >350 mg/L (Bauder and others, 2007).
Average chloride concentrations in shallow wells, 1995-2012, in milligrams per liter
Average chloride concentrations in shallow wells, 2013 only, in milligrams per liter
Chloride concentrations for the shallow wells for 2013 have decreased or have diluted in the Burrton area over the 16-year period (1995-2013). However, the extent of the chloride plume near Burrton has expanded, migrating to the south and east.
Average chloride concentrations in deep wells, 1995-2012, in milligrams per liter
Average chloride concentrations in deep wells, 2013 only, in milligrams per liter
In the deep wells, chloride concentrations between the 16-year averages (1995-2012) are similar to the concentration averages for 2013. The migration of the 250 and 500 mg/L fronts associated with the Burrton plume appear to be limited/confined by artificial recharge associated with Phase I sites (green).
Concentrations larger than 500 mg/L were found near Burrton, where previous oilfield brine disposal occurred. These brines have moved about 3 miles in the past 45 years. Also, large concentrations of chloride from the Arkansas River are moving into the aquifer because of ground water declines caused by agricultural and city pumping.
Chloride is moving……..slowly….. Phase 1 artificial recharge may have helped stabilize chloride concentrations from 2004 to 2010 and likely again in 2013. Concentrations increased in 2011 and 2012 due to curtailed recharge as a result of drought-related low flows in the Little Arkansas River, but corresponding with Phase I & II recharge activities: 2013 chloride concentrations are again showing signs of stability while ASR is operated.
Chloride concentrations at IW-05 wells as a result of Phase I recharge activities at RRW3
Why is Arsenic an issue in the Equus Beds Aquifer?
- There is an EPA Maximum contaminant level (MCL) of 10 micrograms per liter (ppb). Before 2006, the criterion was 50 ppb. Annual samples are required. If the criterion is exceed, then quarterly are required. The MCL is the annual average of the collected samples.
- Background concentrations (before recharge) for arsenic exceeded 10 ppb in several wells and in the Little Arkansas River.
- Arsenic is naturally present in the aquifer sediments.
- Arsenic is controlled by the geochemistry of the aquifer material and the oxygen conditions in the aquifer.
Arsenic concentrations in groundwater in the United States, 2000, in micrograms per liter
BASELINE (1995-2013) Arsenic concentrations in shallow groundwater (well less than 80 feet deep)
- Arsenic concentrations exceed 10 ppb in 12% of samples
- Arsenic concentrations exceeding 10 ppb are associated with low (no) oxygen, clays, and areas of water-level declines
Average arsenic concentrations in shallow wells, 1995-2012, in micrograms per liter
Average arsenic concentrations in shallow wells, 2013 only, in micrograms per liter
Arsenic concentrations for the shallow wells in 2013 are similar to the 1995-2012 averages, with the exceptions of slight increases in the southeastern parts of the study area near the Little Arkansas River and a substantial decrease near IW-04 in the northwestern part of the study area.
BASELINE (1995-2012) Arsenic concentrations in deep groundwater
- Concentrations exceed 10 ppb in 35 % of deep groundwater
- Concentrations are controlled by low (no) oxygen, more clay, and possibly thicker aquifer
Average arsenic concentrations in deep wells, 1995-2012, in micrograms per liter
Average arsenic concentrations in deep wells, 2013 only, in micrograms per liter
In the deep wells, arsenic concentrations for 2013 have remained nearly the same as the 16-year (1995-2012) average.
Computed dissolved arsenic concentration in the Little Arkansas River at Highway 50 near Halstead, KS
- When streamflow exceeds 57 cfs, arsenic doesn’t exceed 10 ppb, therefore, arsenic in treated surface water is not a problem for artificial recharge.
- From 1999-2012, Arsenic exceeded 10 ppb about 15% of time. However, due to low flows in 2013, computed arsenic concentrations exceeded 10 ppb about 75% of the time.
Duration curve of dissolved arsenic in the Little Arkansas River at Highway 50 near Halstead, KS, 2013
Arsenic variability is much greater than chloride variability.
General Geochemical controls for Arsenic
- Minerals important for recharge and geochemistry
- Calcite (calcium carbonate)
- Pyrite (iron sulfide) (can contain arsenic)- Sources
- Iron hydroxides (both source and sink)
- Oxygen (oxidation-reduction potential or Eh)
Natural geochemical process of arsenic concentrations in an aquifer
- Controlled by:
- Sources–clay-rich areas have more pyrite (and sorbed arsenic)
- Oxygen(or lack of oxygen); more oxygen = less dissolved arsenic
- Infiltrating water quality and receiving aquifer quality
- What does this mean in the aquifer?
- Dewatered areas oxygenate and destabilize arsenic-containing pyrites
- Arsenic and iron are dissolved or leached
- As a result of increasing oxygen concentrations from either dewatering or the recharge of oxygenated water, amorphous iron oxides (hydroxides, oxyhydroxides) may form.
- Dissolved arsenic species can be scavenged by or sorb to the surfaces of precipitated iron oxide species, and are, therefore, removed from groundwater
- In summary, a new equilibrium is reached in the aquifer that is primarily controlled by oxygen availability
- Before recharge, natural arsenic concentrations exceed the MCL of 10 ppb in 35% of deep groundwater, 12% of shallow groundwater, and in the Little Arkansas River 11% of the time since 1995.
- Arsenic concentrations exceeding 10 ppb are associated with low (or no) oxygen, areas with more clay in the aquifer and areas where water levels have declined and are now recovering.
- Increases in arsenic can be minimized by maintaining similar oxygen levels between the aquifer and recharge water.
- If oxygen-rich water is recharged;
- iron and calcite likely will precipitate and may coat the aquifer materials,
- arsenic concentrations in the aquifer water will decrease if oxygen is maintained, improving the overall water quality in the aquifer will improve with respect to arsenic.