Southwest Wisconsin groundwater and geology study (SWIGG)

September 22, 2020

by Linda Deith

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Farmland and tree-covered rolling hills of the Driftless Area in southwest Wisconsin (photo by Eric Carson, WGNHS) Southwest Wisconsin has fractured bedrock beneath generally thin soils, putting groundwater at risk for contamination.

The purpose of this study is to improve our understanding of groundwater quality in southwest Wisconsin and to better understand how local hydrogeology and well construction characteristics affect groundwater quality.

Project objectives

Evaluate private well contamination using indicator bacteria (total coliform and E. coli) and nitrate;
Assess well construction and geological characteristics (e.g., well age, depth to bedrock) that affect total coliform and nitrate contamination; and
Identify the source of contamination (people, cows, or pigs) in a subset of wells that tested positive for total coliform and nitrate.

Frequently asked questions

Are 91% of private wells in rural southwest Wisconsin really polluted?

No. This is a confusing misconception. The percentage of affected wells is lower. In our first round of sampling, 42% of wells were contaminated. In the second sampling event, 27% of wells were affected.

Later resampling targeted wells known to be contaminated in order to try to identify the source(s) of that contamination.

Is more sampling planned?

No. We have now completed four rounds of sampling. The following results show the percentage and number of resampled wells that tested positive for contamination of fecal origin from humans, cattle, and/or swine:

Spring 2019: Contamination found in 32 of 35 private wells (91%)
Summer 2019: Contamination found in 25 of 34 private wells (73%)
Fall 2019: Contamination found in 27 of 34 private wells (79%)
Spring 2020: Contamination found in 21 of 35 private wells (60%)

What happens next?

Team researchers will continue to analyze the data looking for correlations between water quality, geology, and well construction. The study’s final report should be complete in 2021.

Should I have my well tested if it was not part of this study?

Private drinking water wells should be tested annually or more frequently if you notice a change in the water or in nearby land use. More information is listed below in “Resources for private well owners.”

Resources for private well owners

Information for private well owners (Wisconsin Department of Natural Resources)
Identify your water’s symptoms (Wisconsin Department of Natural Resources)
Homeowner well water testing (University of Wisconsin–Stevens Point)
Well water quality viewer—interactive map (University of Wisconsin–Stevens Point)