Blue Earth County, Minnesota: drinking water report. Blue Earth County in southern Minnesota has about 68,000 residents, with Mankato as the county seat.
Blue Earth County in southern Minnesota has about 68,000 residents, with Mankato as the county seat. The city draws water from the Blue Earth River and deep groundwater wells. The county sits in the heart of Minnesota's corn and soybean belt, where intensive row crop agriculture dominates the landscape. Tile drainage systems designed to move water off fields quickly also move dissolved nitrate directly into waterways.
The Blue Earth River is one of the most nitrate-impaired rivers in Minnesota. According to the Minnesota Pollution Control Agency's 2024 water quality data, nitrate concentrations at the Mankato gauge averaged 11.4 mg/L during March-June – above the MCL of 10 mg/L. Tile drainage from surrounding agricultural fields delivers nitrate directly to streams without the benefit of soil filtration.
A 2024 University of Minnesota Extension study found that 19% of private wells tested in Blue Earth County exceeded the nitrate MCL. The concentration pattern correlates closely with tile-drained cropland, confirming the agricultural pathway. PFAS from the Mankato Regional Airport has been detected at 7 ppt in nearby monitoring wells.
Southern Minnesota's tile drainage infrastructure creates a direct pipeline from farm fields to waterways and aquifers. If you are on a private well in Blue Earth County, nitrate testing is not optional – nearly one in five wells exceeds the safe limit.
Check your water for the latest data. For nitrate, reverse osmosis is the most reliable household treatment. Our water filter guide ranks certified nitrate removal systems. Pull your detailed report for local data, and visit our Minnesota page for statewide context.
Drinking water is one exposure route. These federal datasets also cover Blue Earth County, MN.
The EPA places Blue Earth County, MN in Zone 1 - the EPA's highest-risk category, where the predicted average indoor radon level is above 4 pCi/L. Zone maps predict an area's radon potential from geology and existing indoor readings; they say nothing about a specific house. Testing is the only way to know your own level.
53% of homes in Blue Earth County, MN were built before 1980, and 25% before 1950. Residential lead paint was banned in 1978, so housing age is the strongest available proxy for lead-paint exposure. This describes the county's housing stock, not any one home.
Modelled annual fine-particle pollution (PM2.5) in Blue Earth County, MN averages 6.3 µg/m³, within the EPA's annual standard of 9 µg/m³. These are CDC modelled county estimates rather than readings from a specific monitor.
How radon zones work · Air quality by county · Lead exposure guide