An estimated half a million Minnesotans are drinking tap water contaminated with elevated levels of nitrate, a chemical associated with cancer and other serious health problems, according to a report by the Environmental Working Group.
“Many years of unaddressed nitrate from farm pollution have brought Minnesota to the brink of a public health crisis,” said Sarah Porter, senior GIS analyst with EWG and one of the report’s primary authors. “Now Minnesotans are paying for the state’s failure to hold farmers accountable for not keeping fertilizer and manure out of the water supply.”
EWG released its innovative analysis, which assembles five disparate streams of state and federal data, as the state begins to implement a new Groundwater Protection Rule – the first of its kind in the nation – to stem the farm pollution that is the primary cause of nitrate contamination of groundwater in Minnesota.
EWG’s report includes data from the Minnesota Department of Health indicating that more than 150,000 Minnesotans drink water from groundwater-based public water systems contaminated with nitrate at or above the legal limit of 10 milligrams per liter, or mg/L, which was set by the U.S. Environmental Protection Agency in 1991.
Research from recent decades indicates that half this amount – 5 mg/L – or even less is associated with higher risks of cancer and birth defects. Almost 300,000 people in Minnesota get water from systems with nitrate levels at or above 5 mg/L, and an additional 200,000 people drink tap water with 3 mg/L or more of nitrate. These tests were conducted by tap water utilities themselves, in accordance with federal regulations, between 2009 and 2018.
Although nitrate is found in many foods and occurs naturally in soil at low levels, a contamination level of 3 mg/L or higher indicates a human cause, according to the Minnesota Department of Health, which recently started requiring water utilities that hit that threshold to increase testing to once every quarter.
Private wells in the state are also contaminated with nitrate, EWG’s analysis shows. Tests conducted by the Minnesota departments of health and agriculture between 2009 and 2018 found more than 3,000 households drink from wells with nitrate contamination of 10 mg/L or higher, and over 7,600 wells tested at least once at or above 3 mg/L – 6,000 of them with nitrate of least 5 mg/L.
The widespread infiltration of nitrate in the state’s groundwater means that one in eight Minnesotans whose water comes from groundwater-based public water systems are affected by concerning levels of nitrate, as well as tens of thousands who drink from private wells.
The most contaminated systems and wells are located in southeastern, southwestern and central Minnesota, where the soil and geology make it easier for nitrate to seep into groundwater. The areas of highest vulnerability encompass almost one-quarter of the state, including 2.5 million acres of cropland and 6,287 livestock feedlots.
“Minnesota’s new nitrate rule is a necessary, important first step, but much more needs to be done – and soon,” said Anne Weir Schechinger, EWG senior economic analyst and the report’s co-author. “As written, this rule has too many loopholes allowing for continued contamination of tap water from farms.”
In 2017, the EPA began to revisit its legal limit for nitrate but abruptly halted that process in April 2019, saying it was no longer a priority for the agency.
EWG researchers recently released a peer-reviewed study that found that nitrate pollution of U.S. drinking water may cause up to 12,594 cases of cancer a year.