Well‑testing program: 5% of private wells in Vernon County exceed nitrate health standard, study finds

A presentation to the Vernon County Board summarized results from a recent private‑well testing program that covered 163 residents. The study’s presenter for the Driftless Area Water Study said about 5% of samples were at or above the nitrate health standard of 10 parts per million, with an average nitrate concentration near 3 mg/L across the tested wells. The presenter added that “nitrate is a common groundwater contaminant in Wisconsin, primarily from agriculture, in some cases septic systems and lawn fertilizer.”

The presenter also reported that roughly 82% of tested wells showed hard water, which contributes mainly to aesthetic issues such as scale buildup, and that iron caused aesthetic problems in about 16% of samples (brown or red staining, occasional odor). Metals with health concerns were uncommon: “we had pretty much no occurrences of arsenic above the health standard,” the presenter said. Bacterial testing returned about 13% positive for coliform and roughly 1% positive for E. coli, the presenter noted, adding that E. coli indicates contamination from human or animal waste. The presenter offered to share slides and a PDF of the county maps showing spatial distribution of nitrate, iron and other test results.

Why it matters: Private wells are not regulated like municipal systems and are not required to be regularly tested, so the board heard that voluntary testing helps residents understand treatment needs and potential health risks. The presenter recommended annual bacteria testing and described treatment options — for example, reverse osmosis for elevated nitrate and water softeners for hard water. Several supervisors asked technical follow‑up questions about aquifer recharge and data sharing; the presenter said average groundwater recharge is about 10 inches per year but varies by precipitation and extraction.