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Equus Beds Recharge Project
Science Center Objects
The water supply for the city of Wichita, south-central Kansas, currently comes from the Equus Beds aquifer and Cheney Reservoir. Because these sources are not expected to meet projected city water needs into the 21st century (Warren and others, 1995), artificial recharge of the Equus Beds aquifer was investigated as one alternative to meet future water-supply demands. An additional potential benefit of artificial recharge includes preventing degradation of the water quality of the aquifer by saltwater plumes from the Arkansas River to the southwest and the Burrton oil field to the northwest (Ziegler and others, 1999). Phase I of the full-scale artificial recharge project began in 2007 and continued through 2012. Phase II became operational in April 2013 and has a design capacity of 30 Mgal/day.
Phase I of the full-scale artificial recharge project began in 2007 and continued through 2012. For Phase I, the water pumped directly from the Little Arkansas River was treated to reduce sediment and remove atrazine before being recharged to the aquifer through recharge basins; water pumped from wells in the riverbank did not receive additional treatment before being recharged to the aquifer through recharge basins or wells (Debra Ary, city of Wichita, written commun., 2012). Phase II recharge facilities withdraw water from the Little Arkansas River and treat the water using ultrafiltration membranes and advanced oxidation techniques. The treated water can then be recharged into spreading basins or recharge wells throughout the area and stored in the aquifer for future use. Phase I has a design capacity of 10 Mgal/day. Phase II became operational in April 2013 and has a design capacity of 30 Mgal/day. Total construction costs for Phase I and II were about $247 million.
Map of Operations for Equus Beds Groundwater Recharge Project
City of Wichita Aquifer Storage and Recovery Program:
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
Water-quality changes associated with Phase I & Phase II recharge
- Kansas Underground Injection Control Area Permit Class V Aquifier Storage and Recovery, Kansas Permit No. KS-05-079-004
- Water-quality Data Compilation for 2010-2016
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).
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.
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.
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
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
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.
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
Equus Beds Surface-Water Quantity Results
- The source water for the Equus beds artificial recharge project is the Little Arkansas River. During the demonstration phase of the project through 2002, according to permit conditions set by the Kansas Department of Agriculture, Division of Water Resources, water could be diverted from the river for recharge under the following conditions:
- At the Halstead Recharge site, from April 1 through September 30, when streamflow at the USGS stream gage Little Arkansas River at Highway 50 near Halstead (07143672) exceeded 42 cubic feet per second (cfs).
- At the Halstead Recharge site, from October 1 through March 31, when streamflow at the USGS stream gage Little Arkansas River at Highway 50 near Halstead (07143672) exceeded 20 cfs.
- At the Sedgwick Recharge site, throughout the entire year, when streamflow at the USGS stream gage Little Arkansas River near Sedgwick, KS (07144100) exceeded 40 cfs.
- Permit guidelines for Phase I and Phase II full scale recharge operations established by the Kansas Department of Agriculture, Division of Water Resources, in August 2005, require the following conditions for water to be diverted from the river for recharge:
- At the Halstead Recharge site, from April 1 through September 30, when streamflow at the USGS stream gage Little Arkansas River at Highway 50 near Halstead (07143672) exceeds 57 cfs.
- At the Halstead Recharge site, from October 1 through March 31, when streamflow at the USGS stream gage Little Arkansas River at Highway 50 near Halstead (07143672) exceeds 20 cfs.
- At the Sedgwick Recharge site diverted water shall not cause the streamflow at the downstream Valley Center (07144200) site to fall below 30 cfs.
Surface water quantity data is also available for:
More Real-Time Water-Quality information for Kansas is available at http://nrtwq.usgs.gov/ks/.
|Site||Year||# of days when Q exceeded conditions||# of days when Q exceeded 70 cfs||# of days when Q exceeded 100 cfs|
|Little Arkansas River at Highway 50 near Halstead, KS (07143672)||1995||99||72||62|
|Little Arkansas River at Valley Center, KS (07144200)||1995||316||146||127|