Southwest Wisconsin Groundwater and Geology (SWIGG) study

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The fractured bedrock aquifers of southwest Wisconsin are often overlain by shallow soils, so private wells are potentially vulnerable to contamination by nitrate and pathogens from the land surface.  The goal of this study is to evaluate the extent and causes of private well water contamination in three southwest Wisconsin counties.

Rural residents of southwest Wisconsin rely on private wells for water, and the fractured aquifers that provide water are potentially vulnerable to contaminants on or near the land surface, like nitrate and pathogens associated with agricultural practices and septic systems.  However, the extent and causes of groundwater contamination in the region are not well understood.  The Land and Water Conservation Departments of Grant, Iowa, and Lafayette Counties are partnering with researchers at USGS, USDA-ARS, and WGNHS to complete a study of private well water quality.

The objectives of this study are to:

1) determine the extent of private well contamination based on the presence of indicator bacteria or nitrate exceeding the drinking water standard of 10 mg/L,

2) identify the sources of fecal contamination (like manure and human wastewater) using microbial source tracking, and

3) assess factors related to private well contamination, like geology, precipitation, well construction, and land use.

Randomly selected wells were tested for nitrate and indicator bacteria during two synoptic sampling events to determine the extent of contamination.  Then, wells were randomly selected from those with indicator bacteria or nitrate greater than 10 mg/L to identify fecal contamination sources using genetic tests for microorganisms (e.g., bacteria and viruses) capable of distinguishing human wastewater and livestock manure (“microbial source tracking”).  Well test results are evaluated against potential contamination factors (like geology, precipitation) to inform water quality management.

Scientist collecting homeowner water sample

USGS scientist Joel Stokdyk collects a homeowner water sample in April 2019.

(Credit: K. Abbott, Iowa County LCD. Public domain.)