Equus Beds Ground-Water Recharge Demonstration Project, South-Central Kansas: Baseline Water Quality and Preliminary Effects of Artificial Recharge on Ground-Water Quality

Abstract

The Equus Beds Ground-Water Recharge Demonstration Project began in 1995 to help meet future water needs and is sponsored by the city of Wichita and Bureau of Reclamation, U.S. Department of Interior. During the project, high flows from the Little Arkansas River are captured and recharged into the aquifer through infiltration basins, a trench, or an injection well. The U.S. Geological Survey collected data from February 1995 through September 1997 to document baseline concentrations of inorganic, pesticide, volatile organic, acid-base neutral organic, and bacterial constituents in ground and surface water and to document the preliminary effects of artificial recharge. Baseline sampling indicated that the primary constituents of concern were chloride and atrazine. The U.S. Environmental Protection Agency drinking-water standard for chloride is 250 mg/L (milligrams per liter) and for atrazine is 3 Î/L (micrograms per liter) as an annual average. Concentrations of chloride ranged from 5.8 to 290 mg/L and concentrations of atrazine ranged from <0.05 to 1.6 Îg/L in water samples collected from the 24 ground-water wells. The concentrations of chloride and atrazine, as well as other constituents, were monitored in ground-water wells at two artificial recharge sites --Halstead and Sedgwick.

From May 1997 through May 1998, about 250 million gallons of water were recharged at the Halstead site. During high flows, water from the Little Arkansas River is induced into the alluvium and diverted for recharge by a pumping well immediately adjacent to the river. Chloride concentrations in the diverted water ranged from 52 to 80 mg/L, and atrazine concentrations ranged from 0.025 to 0.13 Îg/L. As of May 1998, chloride concentrations in the monitoring wells at the Halstead site are similar to that of the diverted water. The maximum atrazine concentration detected in the wells was 0.09 Îg/L. From October 1997 through June 1998, about 12 million gallons of water have been recharged at the Sedgwick site. During high flows, water is diverted from the Little Arkansas River, treated to remove sediment and atrazine, and recharged at the Sedgwick site. Chloride concentrations in the diverted water ranged from 38 to 180 mg/L and atrazine concentrations ranged from <0.10 to 6.8 Îg/L. Chloride concentrations in shallow wells (40 to 60 feet deep) ranged from 4.5 to 78 mg/L. As of June 1998, water from one of two deep wells sampled (190 feet deep) has shown a decrease in chloride concentrations, whereas concentrations in the other deep well remain unchanged. The maximum atrazine concentration detected in the shallow wells was 0.3 Îg/L. Atrazine was not detected in the deep wells.

Preliminary effects of recharge at both the Halstead and Sedgwick recharge sites indicate that concentrations of chloride and atrazine have increased in some of the wells, although concentrations remain within the range of baseline values in the Equus Beds aquifer and are considerably less than drinking-water standards. However, enough water has not been recharged at the Sedgwick site to date to determine the overall effects.

Additional information on the Equus Beds Project can be found at: http://ks.water.usgs.gov/studies/equus/

Ziegler, A.C., Christensen, V.G., and Ross, H.C., 1998, Equus Beds Ground-Water Recharge Demonstration Project, South-Central Kansas: Baseline Water Quality and Preliminary Effects of Artificial Recharge on Ground-Water Quality [abst.], in Proceedings of Midwest Groundwater Conference, October 12-14, 1998.