Equus Beds Aquifer Water Quality Nearly Unchanged between 2001 and 2016

Water quality in the Little Arkansas River and in the Equus Beds aquifer has not substantially changed since 2001, according to a new study by the U.S. Geological Survey in cooperation with the city of Wichita, Kansas.

“The Equus Beds aquifer is a critical water resource. Long-term monitoring of water quantity and quality allows the USGS to evaluate changing conditions and to provide water managers with science-based information to optimize decision-making,” said Mandy Stone, a USGS hydrologist and the lead author on the study.

The Equus Beds aquifer, located in south-central Kansas, provides drinking water to about a half million people and is the primary water supply for the city of Wichita, Kansas. Groundwater pumping for municipal and irrigation uses, as well as during periodic drought conditions, has led to water-level declines and concerns about future water supply. For this reason, the city of Wichita developed the Equus Beds Aquifer Storage and Recovery project, or ASR, to artificially recharge the aquifer and help meet water needs during drought conditions.

USGS scientists looked at water-quality characteristics for the Equus Beds aquifer and the Little Arkansas River over a 15-year period from 2001 through 2016. Scientists collected 4,700 samples and analyzed them for more than 300 chemicals. Findings show that water chemistry was within historical ranges of variability over the study period.

Exceedances of federal human-health benchmarks occurred in both untreated surface water and groundwater over the study period for chloride, sulfate, nitrate, iron, manganese and arsenic. Large chloride concentrations continue to persist in the aquifer within a plume near Burrton, Kansas, from past oil and gas activities and also along the Arkansas River. Nitrate concentrations were largest in the shallow part of the aquifer and exceedances occurred in the southeastern part of the aquifer. Larger arsenic concentrations occurred in the central part of the aquifer and near the Little Arkansas River. Atrazine exceeded drinking water criteria in 39% of samples from surface water but not in any groundwater samples.

The ASR is part of an 80-year cooperative water science effort with the city of Wichita. In 2007, the ASR called for water to be pumped out of the Little Arkansas River during high flows and injected into the Equus aquifer to help meet demands during drought. In 2013 phase two of the ASR included treating river water using EPA drinking water standards and guidelines before injecting into the aquifer. The total amount of water diverted into the aquifer from the Arkansas River between 2001 and 2016 was about 9,930 acre-feet of water or about 20% of the average annual water withdrawals from the aquifer for irrigation and public supply. The USGS will continue to work with the city of Wichita to monitor water-level and water-quality changes in the Equus Beds aquifer.

More information is available on USGS efforts related to defining and understanding water quantity and quality of the Equus Beds aquifer on the USGS Kansas Water Science Center website.

The USGS provides information in a number of states related to preservation of water supplies in artificial recharge and aquifer storage and recovery. For more information visit the USGS artificial groundwater recharge website.

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