That safe drinking water threshold was set to protect infants from a potentially deadly condition known as blue baby syndrome, that leaves them without enough oxygen in their blood. But a growing body of medical literature links nitrates to other dangers, including birth defects, cancers, and reproductive problems — and at levels below the federal limit.

Broberg is among the tens of thousands of Minnesotans who get their water from private or municipal wells with nitrate levels that exceed the federal limit, some at rates many times that threshold. Nine percent of tested township wells have nitrate levels above the limit. So do 27 percent of samples from Minnesota streams, rivers, and lakes.

A recent analysis by the Environmental Working Group based on records obtained from the state health agency suggests about 150,000 Minnesotans were served by water systems with nitrate levels that exceeded federal health limits in at least one test from 2009 to 2018.

There’s no mystery as to why. Minnesota officials say the contamination comes largely from cropland. Nitrate leaches from agricultural soils into aquifers and waterways.

This isn’t a newly discovered problem. The state has known about it for years, leaning on voluntary measures to stem it.

When regulators finally proposed a set of enforceable rules, a political melee broke out.

State agriculture officials started by simply revising their two-decade-old guidebook of best practices farmers could voluntarily follow to reduce contamination, a move farm groups opposed. One form letter signed by farm groups insisted the 1990s guidelines were just as valid in 2013, despite rising nitrate problems over that period.

By the time Minnesota published the updated guidelines in 2015, state agriculture officials were convinced too few farmers followed such recommendations and many were over-applying fertilizer. Advice alone clearly was not reducing contamination.

Environmental groups urged lawmakers and state authorities to act, as did municipal leaders saddled with millions of dollars in rising water-treatment costs and a group — co-organized by Broberg — representing the 1.2 million Minnesotans who rely on private wells.

Officials started writing fertilizer regulations they could enforce.

“Voluntary participation or compliance was not going to be sufficient to get the kind of really significant change that the state’s situation required,” recalled Mark Dayton, Minnesota’s governor at the time.

The first draft, released in June 2017, would have prohibited many farmers in areas with vulnerable groundwater from applying fertilizer in the fall — when contamination risks rise without plants to suck up the nutrients — or on frozen soil. Exceptions were made for small-grain crops and research.

That kicked off one of the most ferocious fights of Dayton’s political career.

“We ran into stone walls,” he said.

Farmers and agriculture organizations packed public hearings, blitzed their legislators with statements, and filed formal comments that nitrate contamination was overhyped, caused by improperly sited or maintained wells rather than farms, and too costly to deal with the way the proposed regulation required. The Legislature passed a bill to block it. When Dayton responded with a veto, state House and Senate agriculture committees — including lawmakers who also worked as farmers — invoked an obscure provision to stall the rule.

Behind the scenes, the agency’s officials tried to convince politicians that fertilizers were a real and growing public health problem with a large scientific consensus, according to records obtained by Public Integrity and its partners. Those emails also show the agency defending the rule to angry farmers, including some who protested testing city-owned wells for contaminants out of fear that regulations would follow.

In public comments filed during rulemaking, the Minnesota Farm Bureau said voluntary efforts were effective and urged agriculture officials to prove that “elevated nitrate levels are actually the result of current nitrogen fertilizer practices, not due to other nitrogen sources or from fertilizer practices of past generations.”

Early versions of the rule set fertilizer restrictions in large land units, which worried farmers like Bruce Peterson. In just one of his fields, Peterson has a range of soil types and fertilizer needs. Agriculture officials revised it so smaller parts of a field could be restricted without limiting fertilizer application on other parts.

As the fight dragged on, department employees and staffers with the governor’s office softened their messaging, made more concessions to win over farm groups, and prepared talking points to deal with negative reactions from environmental groups.

During his last days in office, Dayton wrote a letter to his successor, Tim Walz, assuring him that the hard-fought nitrate rule was well-vetted and urgently necessary to protect the environment and public health, records show. Walz signed off, and the revised groundwater protection rule was enacted in 2019. Major farming groups no longer opposed it.

Peterson, in fact, said he expects the rule will have little impact on his operation and most others in southeastern Minnesota. “The vast majority of farmers have kind of gone away from fall nitrogen in these restricted areas already,” he said.

Environmental groups and well-owner organizations say that’s the problem with the rule: It was weakened so much, it does little to protect drinking water.

The state shrunk the number of areas where farmers cannot apply nitrogen fertilizers in the fall or on frozen soil. Other requirements meant to reduce contamination kick in only if nitrate levels near municipal wells worsen, rather than being broadly mandated, and do little to directly control how much fertilizer is applied or where it’s used. Much of the rule’s focus? Voluntary measures.

Agriculture officials also added a provision that requires the state to appoint and consult with a local advisory team as it responds to nitrate problems. Lost in the final rule: protections for privately owned wells like Jeff Broberg’s.

“It’s a whitewash,” Broberg said. “They basically regulated what was already being done.”

No easy answers

Bruce Peterson harvests grain in southeastern Minnesota, but one of the fields he leases was once a turkey farm. Though the birds were shipped out years ago, the lanky farmer can still pinpoint the exact spots they used to roam by pulling up a digital map on a laptop.

“We’ve collected yield data probably,” he said, “since the mid-’90s.” He adjusted the screen and clicking a multicolored map that shows dense corn and soybean growth in places where the turkeys deposited organic fertilizer. “Everything is grid-sampled.”

Software combining past harvest results with current soil samples creates digital maps that divide his 8,000-acre operation into smaller zones. The data uploads to a computer in the cab of Peterson’s tractor, which syncs up with GPS and automatically adjusts the rate fertilizer is applied as he drives over the cropland. Randy Souder, the Iowa farmer, uses a similar system.

Peterson says the technology hasn’t reduced his total fertilizer use, but the data-driven approach means he’s getting more crops per pound of nitrogen. Increasingly, farmers are adjusting fertilizer to give the most productive parts of their fields an extra dose and going lighter in places where crops are less productive. This approach helps them save money, has reduced fertilizer overapplication, and limits a source of reactive nitrogen that otherwise might contaminate water or become a greenhouse gas.

Agriculture groups point to these and other practices that boost farm profits while reducing environmental damage when they argue against mandates imposed on other polluting industries.

Even so, half the nitrogen applied as fertilizer is not used by crops and escapes into the environment, research shows. And though more efficient uses of nitrogen have increased across the U.S., there’s limited room for improvement. That’s because more and more fertilizer is required if global farm production doubles by 2050 as forecasted to keep up with population growth.

The targeted fertilizing that Peterson does is mainstream, but fewer farmers are employing other conservation practices that can prevent agricultural fertilizer from becoming a climate and environmental hazard.

Brent Larson is one of the outliers.

As the persistent rain soaking his northern Iowa farm paused one morning in late June, Larson snatched a spade and waded into a green quilt of grass. In the distance behind him, a corn ethanol refinery puffed out steamy fingers of vapor as a steady stream of 18-wheelers lined up to empty their trailers.

He slowed every now and then to jab at the earth. Suddenly, he stopped. Clearing the tip of the shovel with his hand, Larson pulled a clump close to his face and then disappeared into the waist-high thicket.