Equus Beds Aquifer Storage and Recovery (ASR) Project Active

The Equus Beds ASR Project is a recent part of an 80-year cooperative water science effort with the city of Wichita, Kansas that began in the 1920s as the city began its water-supply development (Stone, 2017). Current (2023) water-quality monitoring efforts provides data to characterize real-time and changing water-quality measurements and allows the city of Wichita to make informed municipal water-supply decisions.  

The city of Wichita, Kansas, uses the Equus Beds aquifer as a primary municipal water-supply source. Equus Beds aquifer water levels have decreased substantially (Hansen and others, 2014; Whisnant and others, 2015; Klager, 2016) because historically, irrigator, industrial, and municipal pumpage volumes exceeded the natural aquifer recharge rate. The Wichita well field is susceptible to saltwater (including chloride) contamination from the Arkansas River and intrusion from existing upgradient plumes near Burrton, Kansas, caused by oil field evaporation pits remaining from the 1930s (Klager and others, 2014). The Equus Beds ASR project was created by the city of Wichita to help meet future water demands. 

The Equus Beds ASR project currently (2023) consists of two coexisting phases: 

1. Phase I began in 2007 and has the capacity to capture 10 million gallons per day (Mgal/d) of Little Arkansas River water and indirect streambank-diversion well water for recharge activity with water injection in four wells and two recharge basins. Directly diverted stream water is treated using membrane filtration and advanced oxidation to reduce sediment and remove organic material before being recharged through the two recharge basins; streambank-diversion well pumped water is not treated further before recharge through the injection wells or basins (Garinger and others, 2011). 

2. Phase II began in 2013 and includes a 30-Mgal/d surface-water treatment facility, a 60-Mgal/d river intake facility equipped to divert 30 Mgal/d and treat 15 Mgal/d, eight recharge-injection wells, and a recharge basin. The facility capacity of 30 Mgal/d requires a streamflow of about 100 cubic feet per second (ft3/s) or greater at the Little Arkansas River near Sedgwick, Kans., streamgage (USGS station 07144100; fig. 1) to operate. Water is directly diverted from the Little Arkansas River at the intake structure when streamflow exceeds about 100 ft3/s at this site. The city of Wichita has a National Pollutant Discharge Elimination System (NPDES) permit (Kansas Permit number I-LA24-PO01; Federal Permit number KS0099694) to discharge waste from the ASR phase II surface-water treatment facility to the Little Arkansas River. 

Sources/Usage: Public Domain.

Figure 1. Location of the Equus Beds ASR project study area near Wichita, south-central Kansas. 

Equus Beds ASR project study highlights: 

1. The amount of aquifer water volume has recovered since the historic 1993 low because of less pumping, more natural recharge, and ASR (Klager, 2016).  

2. The chloride plume near Burrton, Kans. (figs 1, 2, and 3), moves about 0.6 foot per day eastward toward the Wichita well field regardless of pumping (fig. 2; Klager and others, 2014).  

Sources/Usage: Public Domain.

Figure 2. Animation showing simulated chloride transport in the deep layer of the Equus Beds aquifer under existing pumping conditions from 1990 through 2008 (Klager and others, 2014). 

Sources/Usage: Public Domain.

Figure 3. Equus Beds ASR Project study area map showing shallow aquifer water-level changes from predevelopment to 1993 and chloride plume in deep wells that exceed U.S. Environmental Protection Agency drinking water criterion (>250 milligrams per liter) during 2006–12 moving eastward. 

3. Water-quality constituents of concern collected during 1995 through 2012 did not increase substantially during and concurrent with Phase I activity and were likely more affected by climatological and natural processes than artificial recharge (Tappa and others, 2015). 

4. A Hydrobiological Monitoring Project (HBMP) study using data collected during 2011–2014 showed that Phase II recharge activities did not result in substantial changes in Little Arkansas River or Equus Beds aquifer water quality; most Little Arkansas River water chemistry and biology (macroinvertebrates and fish) changes were largely attributable to hydrology (Stone and others, 2016). 

5. Little Arkansas River water-quality constituent concentrations collected during 2001 through 2016 did not increase in comparison to sampling that preceded (1995 through 2012; Tappa and others, 2015) the study. Constituents of concern in the Equus Beds aquifer exceeded their respective Federal criteria throughout the study period and included chloride, sulfate, nitrate plus nitrite, Escherichia coli bacteria, total coliforms, and dissolved iron and arsenic species. (table 1; Stone and others, 2019).  

Table 1. Little Arkansas River surface-water and Equus Beds index well groundwater water-quality summary statistics during 2001–16. 

Sources/Usage: Public Domain.

Figure 4. Average A, nitrate plus nitrite and B, dissolved arsenic concentrations in the shallow parts (depths below land surface equal to or less than 80 feet) of the Equus Beds aquifer 2001–16. 

6. Little Arkansas River real-time computations of water-quality constituents for three Little Arkansas sites are available at the USGS National Real-Time Water Quality website (https:// nrtwq.usgs.gov) and include dissolved solids, primary ions (including bromide), nutrients, sediment, dissolved arsenic, and pesticides (including atrazine; Stone and Klager, 2022; Stone and Klager, 2023).  

7. Little Arkansas River long-term (1995–2021) trend analyses showed that, generally, flow-normalized bromide, nitrate, and total phosphorus concentrations decreased; total organic carbon increased; and sediment concentrations neither increased or decreased. About one-quarter to one-half of the river loads, including nutrients and sediment, were transported during 1 percent of the time during the study (Stone and Klager, 2023).