MODELING THE EFFECTS OF AN ARTIFICIAL RECHARGE PROJECT ON STORAGE VOLUME IN THE EQUUS BEDS AQUIFER IN SOUTH-CENTRAL KANSAS

In 2006 the city of Wichita, Kansas initiated construction of the Equus Beds Aquifer Storage and Recovery (ASR) project. The aim of the ASR project is to increase the volume of water stored in the Equus Beds aquifer, a primary water supply source for the city, using artificial recharge. Water for artificial recharge is diverted from the Little Arkansas River during above base-flow conditions, treated, and injected into the aquifer via injection wells or allowed to infiltrate into the aquifer via recharge basins. The state of Kansas awards credits to the city for storage increases in the aquifer that can be attributed to ASR. The city can redeem these credits at a later time in exchange for the right to pump more than its allotted water right. In order to estimate storage changes that can be attributed to the ASR project’s artificial recharging, the city uses a groundwater-flow model. ASR credits are calculated annually by simulating the previous year with actual conditions (with artificial recharge) and with no artificial recharge, and the results of the simulations are compared to estimate the effect of the artificial recharge on the volume of water stored in the ASR project accounting area. During 2007 through 2008, the model-estimated storage volume in the ASR accounting area was 1,607 acre-feet higher with artificial recharge than in the no artificial recharge scenario. A contaminant transport model was also developed and coupled with the flow model using SEAWAT, and has been used to simulate the effect of artificial recharge on the movement of a saltwater plume in the Wichita well field vicinity. In an increased artificial recharge scenario, movement of the 250-mg/L chloride front toward the well field was slowed from about 0.8 ft/day to about 0.7 ft/day on average for the modeled period of 1990 through 2008. The ability to simulate the effects of artificial recharge can help the city to optimize ASR project operations and make long-term plans for managing use of the aquifer.