Missouri Extension Service
MARSHFIELD, Mo. -- The Missouri Department of Natural Resources estimates there may be as many as one abandoned well or cistern for every 80 acres of land in the state. That translates to over 4,700 old wells or cisterns in most counties of southern Missouri.
"These old wells, which were once an asset, can become a serious liability," said Bob Schultheis, natural resource engineering specialist, University of Missouri Extension.
There are two major hazards associated with abandoned wells and cisterns. The first hazard is of someone falling into a dug well or cistern, which typically are 3- to 6-feet in diameter and 10- to 30-feet deep. The other hazard is the potential for the old well or cistern to be a source of contamination for the underground aquifer and neighboring wells.
Owner responsibility
"A well is considered abandoned when it can no longer be used or when it has not been in use for two years or more. It is the responsibility of the landowner to plug any abandoned wells on their property," Schultheis said.
State regulations allow landowners to plug wells on their property as long as they do so in accordance with the Missouri Well Construction Rules. Wells that are plugged improperly leave aquifers (water-bearing rock formations) susceptible to contamination.
"I've seen several situations where a new well tested bad for bacteria until the old well, several-hundred feet away, is plugged. Because of the fractured nature of Ozarks underground rocks, it's possible to pollute another person's water supply several miles away," Schultheis said.
Plugging typically costs $300 to $1,200, depending upon the type and depth of the well and whether a contractor is involved.
Plugging wells
Abandoned dug-wells and cisterns can be plugged by pushing in the upper three feet of the well lining, and then filling the well to within three feet of the surface with chlorinated clean fill, such as coarse gravel, rock or varied-size agricultural lime or sand.
The rest of the well should then be capped with clay-rich soil, mounded to allow for settling and to make sure surface-water drains away.
To plug a drilled bedrock well properly, a person needs to know the total depth, length of casing and depth to water. The pump should be removed and the casing cut off three feet below the ground surface. Chlorinated clean gravel, or varied-size agricultural lime, is added from the bottom of the well to 50 feet below the bottom of the casing.
Either neat-cement grout (a mixture of six gallons of water per 94-pound bag of Portland cement), bentonite grout (a bentonite-water slurry), or chipped bentonite clay is then added to fill the hole to within two feet of the ground surface.
"Concrete is not acceptable grout. If the casing depth is unknown, the well must be plugged full length with approved grout," Schultheis said.
According to Schultheis, the neat-cement or bentonite grout must be pumped to the bottom of the well, displacing any water out the top. The chipped bentonite clay, which swells when wet, can be slowly poured through standing water. The final two feet of the hole is then capped with clay-rich soil.
More information
Missouri law requires that the plugging of abandoned wells be registered with the DNR within 60 days of the work being completed. If the record shows that the well was plugged properly, a registration number and letter will be sent to the landowner. It is important to keep this documentation, because some lending institutions and local governments require such proof upon sale or refinancing.
For more information on plugging wells, contact the Missouri Department of Natural Resources' Wellhead Protection Section at 573-368-2165. Excellent resources for learning more about water protection in the Ozarks can be found online at http://extension.missouri.edu/webster/water.aspx.
If you have questions on this topic or other engineering concerns, contact Bob Schultheis at the Webster County Extension Center in Marshfield by telephone at (417) 859-2044, by email at [email protected], or online at extension.missouri.edu/webster.
Community on 08/27/2015