Nitrates: The canary in the coal mine and other concerns

January 28, 2019

When former MPCA Commissioner John Linc Stine asked for further study of nitrates in the groundwater of Southeast Minnesota’s karst region, it was a call for a better understanding of a very complex issue.

How complex?

While most experts working in the field — everyone from water experts at several state agencies to University of Minnesota professors and regional water authorities — would like to see more studies, what should be studied and what the results mean might be hard to pin down.

Here are several issues that need consideration as the Minnesota Environmental Quality Board considers taking up a general environmental impact statement on nitrates in the karst region.

A Little Bird Told Me

Jennifer Ronneberg, a principal planner for the Minnesota Department of Health who works with public water suppliers and wellhead protection, said that while the state’s 10 parts per million standard for nitrates is its own indicator of unhealthy drinking water. When nitrate amounts rise above the natural background of about 3 ppm, that means water-soluble contaminates are entering the aquifer.

Essentially, she said, nitrates are like the canary in the coal mine. Their presence is really an indicator of likely bigger issues of pesticides, herbicides and bacteria entering the aquifer.

“It means you have a pathway for whatever is up there to reach your well,” Ronneberg said.

A Toxin Cleanse

Calvin Alexander, a University of Minnesota Department of Earth Sciences professor, said aquifers that have been contaminated with nitrates and other toxins can be cleaned if the source of those toxins is shut off. An example of this occurred in Rochester near East Circle Drive where the Stonehenge Estates neighborhood replaced fields of row crop farming.

Once the farming — and fertilizing — stopped, the nitrate concentration in the groundwater downstream began to fall.

“It took about 10 years, but now it’s flattening off,” Alexander said, adding that the nitrate readings are now about 1 or 2 ppm. “That’s how long it takes to clean out the primary nitrate from crop fields.”

Stacks of Water

Everything from private wells to municipal wells in Southeast Minnesota get their water from underground aquifers. However, there isn’t just one aquifer, Alexander said, there are about a dozen in the region.

“There is a whole stack of aquifers going down about 1,500 feet,” Alexander said.

Most municipal wells in Southeast Minnesota are drilled into the Prairie du Chien-Jordan Aquifer, Alexander said, but private wells are usually dug to lesser depths depending on where and when they were drilled. For example most older wells were drilled into the upper-level Galena Aquifer.

The Galena, however, has taken the brunt of the contamination through the years. Today, well drilling firms are no longer allowed to drill into the Galena, said Dean Schrandt, water program manager for Dodge County Environmental Services.

“When most of these wells were drilled, most people had shallow wells,” Alexander said. “As those became contaminated, now wells are generally drilled 300 to 500 feet deep.”

And while those lower aquifers are generally cleaner, they get their water from the surface as well. “It’s just taking longer,” he said.

As Always, Water Flows

Like with surface rivers and streams, the water in aquifers flows downhill, eventually heading to the Mississippi River, Alexander said. In the karst region, the water moves through a matrix of underground systems that are analogous to the roads on which we drive.

Water, like cars, he said, spends most of its time in a complex matrix that can be thought of like a neighborhood or even a city. There, it moves slowly around that localized area among the fractured limestone and sandstone. But eventually, that water, like cars, hits the highway, moving more quickly.

But how the water flows from a source to a well can be tricky to gauge, Alexander said. And, as the water changes the underground topography, what we know today might change in the near future.

Brother, Can You Spare A Sample?

While the Township Testing Program and Volunteer Nitrate Monitoring Network have taken samples from thousands of wells across Southeast Minnesota, a new study — as called for by Stine – would likely need to gather new, and more, data.

The problem, Ronneberg said, is most well owners don’t want their wells tested as part of a state program.

“I’ve talked to these people who say, ‘I’ve been drinking from this well for 50 years,’” she said. “Well, you haven’t been drinking this concentration of nitrates for 50 years.”

Despite the testing that’s already underway, Ronneberg said to get a truly clear picture of contaminated groundwater many more wells will need to be sampled, and preferably over a period of time.

New MPCA Commissioner Laura Bishop said that while she looks forward to discussing the merits of the general environmental impact statement her agency has proposed, she hasn’t thought about the cost of all that testing, the role existing data has to play in it, or what goals a GEIS should have that would make her agency’s role of environmental review work better.

Sinkholes and Other Problems

Ronneberg said one of the biggest issues with the infiltration of contaminants into the groundwater is sinkholes or old, damaged wells that essentially act as sinkholes.

Schrandt said the number of known wells in Dodge County is around 2,000, but the number of actual wells — including those not registered and ones no longer in use but not properly sealed — could be double that.

“Old wells not being used are conduits to the aquifers,” Ronneberg said. “Locating old wells is one of the primary jobs we do.”

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