Wichitas Equus Beds aquifer storage and recovery project

Wichita is the largest city in Kansas and is located in the south-central part of the state, just south of the Equus Beds aquifer, the 'eastern most extension of the High Plains aquifer system' (Equus Beds Information Resource, 2005). In the 1930s, Wichita established wells in the Equus Beds and began pumping groundwater for municipal use. Running through the Equus Beds area is the Little Arkansas River, which joins the Arkansas River at Wichita.

Until the early 1990s, Wichita drew heavily from the Equus Beds aquifer. Extensive groundwater use by Wichita and irrigating farmers drew down the aquifer approximately 13 m in some locations, with a total loss of approximately 24.6 million cubic metres of water from aquifer storage from the time heavy pumping began in the 1940s. Irrigators with water rights junior to Wichita's water rights may have to shut down their wells if the water table keeps dropping. In addition to the lowering of the water table, the other problem in the region is a large, underground saltwater plume located north-west of the Wichita wells, migrating towards the city's well field.

Wichita is working on an ASR project to replenish the Equus Beds for the benefit of both Wichita and irrigators as well as to provide a hydraulic barrier to impede the migration of the saltwater plume moving towards the Wichita well field. The basis of the ASR project is that flood and other higher-than-normal-flow water seeps down into the banks of the Little Arkansas River, is held there and can be withdrawn for recharge into the deeper Equus Beds aquifer. The plan is to refill the depleting aquifer with flood water.

A demonstration project from 1995 to 2004 showed that engineering aspects of the ASR project were feasible, but there were legal problems because of inadequate statutes and regulations. In response, the DWR worked with Wichita and promulgated a new set of regulations designed explicitly for 'aquifer storage and recovery permitting' (Kansas Administrative Regulations, 2005, ยงยง5-12-1, et seq.). Each applicant for an ASR project must file applications for two types of appropriation permits: (i) to divert water either directly from the river or from bank storage; and (ii) to divert water from the Equus Beds aquifer for its ultimate use. The applicant must also comply with relevant regulations of the Kansas Department of Health and Environment regarding the quality of the injected or artificially stored water.

In applying for the first permit to divert water from the river or from bank storage, the applicant must describe the volumetric area in which the water will be stored. The bottom of the basin storage area is the lowest level that has occurred within 10 years of the application; the top is the elevation representing the maximum storage potential, i.e. the pre-development water table elevation. The applicant must also include a methodology of accounting for the water stored on an annual basis to enable 'recharge credits' to be calculated. The regulation seeks an accounting system that sets up a 'water balance' for the water entering and leaving the storage area, considering recharge, groundwater inflow and outflow, evapotranspiration, groundwater pumpage of recharge credits, and all non-domestic wells in the basin storage area.

Wichita's ASR project covers four phases to be completed in 2015, with a goal of 378.5 million litres per day capacity. Phase I, scheduled for completion in 2007, will have a capacity of 37.85 million litres per day. At a public hearing held by the DWR in December 2004 to consider Wichita's Phase I permit applications, the public expressed concerns about the unknowns - the effect of the ASR project on groundwater quality, downstream water right holders and downstream riparian owners. The interested participants in the project (Wichita, the GMD, DWR and the public) must continually review the data and analyse the goals, objectives and performance of the project, and modify it when necessary if its twin goals of recharging the Equus Beds aquifer and halting movement of the saltwater plume for the benefit of Wichita and area irrigators are to be met.

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