Well water around Wichita: the Equus Beds and what to test for

Many well owners around Wichita draw from the same aquifer the city does, and decades of study by the U.S. Geological Survey, the Kansas Geological Survey and the city itself have mapped it in detail. Knowing a little about that water helps explain why some pumps fight sand, why some wells taste salty, and why testing matters more than people expect.

The Equus Beds

The Kansas Geological Survey describes the Equus beds as unconsolidated sand, silt and clay in varying mixtures, spread under parts of McPherson, Reno, Harvey, Sedgwick and Rice counties. The sand and gravel are thickest and most permeable around the Wichita well field, which started in southern Harvey County and was extended into northern Sedgwick County in 1949. K-State Research and Extension notes that most wells in south-central Kansas draw from unconfined aquifers like this one, which recharge directly from the surface and are harder to protect from what happens on the land above.

Today the City of Wichita takes about 40% of its supply from the Equus Beds and 60% from Cheney Reservoir. It has also put about $250 million into an aquifer storage and recovery project that treats high-flow river water and stores it underground.

Water levels have moved a lot

According to a 2015 USGS fact sheet, after the droughts of the late 1980s and early 1990s, aquifer water levels in 1993 were as much as 50 feet below where they stood in 1940. Wichita began artificially recharging the aquifer in 1997 with water from the Little Arkansas River. For a household well, the practical point is that the water level is not fixed. A pump set comfortably below the water decades ago may now sit closer to it after dry years, which shows up as air in the lines, sand, or a pump that loses suction in late summer.

Salt: the Burrton plume and the Arkansas River

The same USGS report describes a large chloride plume near Burrton, left by past oil and gas exploration, along with naturally high chloride from the Arkansas River, both moving toward the city's well field. Chloride above 250 mg/L, the EPA's secondary standard for taste, turned up in deep wells near Burrton and along the Arkansas River. KDHE's saltwater advisory lists Sedgwick, Harvey and Reno among the counties with contaminated areas from historic oilfield brine. Salty water is mostly a taste and corrosion issue, but it also eats at pump parts and fittings.

Arsenic and nitrate

Arsenic in the Equus Beds is natural, tied to clay layers with iron sulfide minerals. USGS sampling from 1995 to 2012 found it above the 10 micrograms-per-liter drinking water limit in about 12% of shallow monitoring-well samples and nearly 35% of deep ones. Nitrate is the other common concern. K-State's well testing guide gives the standard as 10 mg/L as nitrogen, explains that infants under six months are most at risk, and says levels above 20 mg/L should be corrected. Neither arsenic nor nitrate changes the taste, so only a lab test shows them.

How often to test

• Every year for bacteria and nitrate, the City of Wichita's recommendation for private wells, which K-State also gives.
• After any pump repair or replacement, once the well has been chlorinated and flushed. Sedgwick County requires chlorination after pump work.
• Once for arsenic and chloride, especially on deeper wells or west of Wichita toward Burrton.
• Before buying or selling a house with a well inside Wichita, where city code requires a well inspection before ownership changes.

K-State points out that no federal or state rule requires private well owners to test, so the job falls to the owner. A positive coliform result means checking the well for entry points (a loose cap, a cracked casing, a pit) and shock chlorinating, which ties back to the work on the repair and replacement pages. Once results come back, the well water test reader lines each number up against the EPA limit.

Questions people ask

Why does my well water taste salty?

Parts of the Wichita area sit near known chloride contamination from old oilfield brine, and the Arkansas River carries naturally salty water. A lab test for chloride will tell you how high it is.

Does a new pump fix bad-tasting water?

Usually not. Taste comes from the aquifer or from contamination getting into the well. A pump contractor can check the cap and seal, and a water test points to the treatment you need.

Is the Equus Beds aquifer running out?

USGS found 1993 levels as much as 50 feet below 1940 levels. Since then Wichita has leaned more on Cheney Reservoir and recharges the aquifer with river water, but local levels still rise and fall with drought, which can affect where a pump should be set.