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GCC Report to the Legislature Public Awareness of Groundwater Health Risk

Unlike public water systems, protection and maintenance of a private well is largely the responsibility of homeowners. The agencies use a variety of ways to increase awareness and promote testing. Many recommendations for which contaminants private well owners should test for are location-specific, but some contaminants should be tested for by all private well owners.

The GCC agencies recommend all private well owners test their water at least once a year for coliform bacteria, so the percent of potable private wells tested annually for total coliform bacteria can be considered a proxy for groundwater health risk awareness.

Of the estimated 509,000 potable private wells* in Wisconsin, about 32,000 total coliform samples were taken annually on average during the past 5 years (2011-2015)**. Therefore, the average percent of potable private wells tested annually for total coliform bacteria is about 6% statewide. This is similar to results from a recent public health survey*** that found that about 10% of private well owners have tested their well for any contaminant in the past year. Total coliform is by far the most frequently analyzed contaminant; around 30% of all reported sample results for private wells are for total coliform.


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* Estimating the number of potable private wells — the number of potable private wells in each county is estimated based on the total number of well construction reports filed for each county. Abandoned, reconstructed and replacement wells are excluded for the purposes of this count, as are any reports associated with public, non–potable or industrial purposes. Some wells have no report. This is more common in areas along the western border of the state (e.g., Douglass, Burnett, Pierce, Buffalo, LaCrosse, Vernon and Crawford counties) and in areas with a large number of drive point wells such as the Central Sands (e.g., Portage, Wood and Juneau counties). In those areas, it is possible that as many as half of potable private wells do not have a well construction report, but statewide it is generally expected that closer to 10% of active wells are missing a report.

** Estimating the number of total coliform samples — the number of total coliform samples in each county is estimated from four data sources:
1. samples required by NR 812.41 after new construction or pump work in potable private wells;
2. samples voluntarily reported to the Lab Data Entry System (primarily from the Wisconsin State Laboratory of Hygiene);
3. samples voluntarily reported to the Groundwater Retrieval Network; and
4. samples analyzed by the UW–Stevens Point Water and Environmental Analysis Lab.

Samples are screened for overlap between the first three sources and there is no expected overlap with the fourth source. This does not account for any samples analyzed at a private or local lab that are not subsequently reported to one of these four sources, so this approach likely underestimates the total number of samples. Statewide, the magnitude of this underestimate seems balanced by the underestimate of the number of wells, but this may vary from county to county.

***Schultz, A., Malecki, K. C. 2015. Reducing Human Health Risks from Groundwater: Estimating Private Well Testing Behaviors and Water Use among Private Well Owners in Wisconsin.

Last revised: Wednesday January 04 2017