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Flooding May Have Polluted More Than 140,000 Residential Wells In Missouri

May 29, 2019 A kayaker paddles down flooded Main Street west of Grafton. The river had reached 32 feet, on its way to a projected crest of 36.3 feet, which would be the second highest on record and less than two feet below the record set in 1993.
File Photo | Brent Jones | St. Louis Public Radio
The National Ground Water Association estimates that more than 140,000 private wells in Missouri could have been contaminated by flooding. Missouri health officials think the extent of well contamination was overstated.

Recent flooding could have contaminated more than 140,000 private wells in Missouri, according to an estimate by the National Ground Water Association.

However, the Missouri Department of Health and Senior Services only has about 130,000 registered in its database, said Jeff Wenzel, chief of the department’s environmental epidemiology bureau.

Floodwaters can spread pathogenic bacteria, like E. coli and chemicals used in home gardening and agriculture. During large floods, water can rise over wells and expose private water supplies to contaminants.

Wenzel said the nonprofit group's estimate likely overstates the problem.

“That would mean that all the wells we know about plus a few more are affected,” he said.

The National Ground Water Association’s estimate is based on U.S. Census data in counties that reported flooding this year. The census data, however, dates back to the 1990s.

“There likely hasn’t been a huge change [in number of wells] since then,” said Bill Alley, science and technology director at the National Ground Water Association. “We have encouraged the census over time to include that question.”

The nonprofit recommends that homeowners test their wells for bacteria and nitrates. If residents live near a power plant that stores coal ash waste in ponds, residents may also want to test for heavy metals, like arsenic, Alley said. Wells that are old or have not been maintained in some time are at a greater risk of being contaminated during floods.

Contamination could become more of a concern in the future as flooding increases in the Midwest, Alley said. Several reports, including the 2018 National Climate Assessment, predicts that the Midwest region of the U.S. will experience more frequent and intense river flooding.

“If that’s the new normal as some people think, then this is going to be more of an issue than it has in the past,” Alley said.

The state health department offers free testing services for residents with wells.

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Eli is the science and environment reporter at St. Louis Public Radio.

Send questions and comments about this story to feedback@stlpublicradio.org.