by Tom Glanville
Agricultural and Biosystems Engineering Extension Specialist
Iowa State University Extension
Coliform bacteria are the most common health-related drinking water pollutants found in rural wells. According to the University Hygienic Laboratory, about 35 percent of the private well water samples submitted for testing in recent years have tested positive for coliform bacteria. Much of this is generally believed to be due to poor well construction or maintenance, not to widespread bacterial contamination of groundwater found at recommended well depths (50 feet or greater - depending on local geology).
One of the ways coliforms enter a well is through the wellhead when it is submerged – a situation that occurred more frequently than normal in Iowa this year due to widespread flooding and saturated soils. Although properly constructed wells have tight fitting caps that prevent entry of dirt, insects and rodents, well caps are rarely water tight. In fact, most well caps include a screened vent or “breather” to prevent a vacuum from forming inside the well when it is pumped. If the wellhead becomes submerged the vent allows contaminated water to enter the well.
Wells are at risk of being flooded when located in low-lying areas subject to heavy runoff, or if they are constructed inside a subsurface frost pit. Modern well construction regulations prohibit construction of new wells inside frost pits, but many older wells throughout the state are still located inside pits. During wet weather, when soils are saturated and water tables are high, leaky pits can fill with water. The solution to these problems is to contact a certified Iowa water well contractor and arrange to have the well casing extended.
A well located inside a frost pit can be extended to prevent flooding. In this situation, a new well casing is added to the original, extending the top of the well to at least one foot above ground, or above known local flooding levels. A special fitting, called a pitiless adapter, is added to the well so water can be discharged through the casing sidewall below frost line. Pressure tanks and other equipment are relocated to a nearby basement or heated building, the pit roof and walls are removed, and the hole is filled with compacted subsoil.
Procedures are similar, but less complicated, for wells that terminate above ground, but that do not extend sufficiently above local flooding levels. See original article in the October 2008 issue of Acreage Living for drawings and an additional information link .
The October issue of Acreage Living is available at www.extension.iastate.edu/acreage . Other articles include --
- Be a Smart Hay Buyer
- Keeping Companion Animals Safe