A potentially cancer-causing chemical recently detected in the groundwater of two north metro cities has officials using stopgap measures to ensure the water supply is safe until they can make multimillion-dollar upgrades to their treatment plants.

Those measures include shutting off some wells, temporarily connecting to a Minneapolis water main, and shutting down splashy kids' parks to conserve water.

The industrial chemical — 1,4 dioxane — comes from the long-closed Twin Cities Army Ammunition Plant (TCAAP) in Arden Hills and only recently emerged as a contaminant.

Now it's showing up in the groundwater supply used by New Brighton and St. Anthony.

"Two things have happened to make it a concern today: We now have the ability to detect it in the water, and we have additional information about potential health risks," said Amy Hadiaris, a Minnesota Pollution Control Agency hydrogeologist and manager for the TCAAP Superfund site.

The U.S. Environmental Protection Agency (EPA) labeled dioxane a likely human carcinogen about four years ago, adding it to a watch list of contaminants to be monitored in public water supplies.

While the EPA has no set standards for the chemical, the Minnesota Department of Health set health risk limits for it in 2013. To reduce the risk of an additional case of cancer in a population of 100,000 exposed people, the state recommends keeping exposures at or below 1 part per billion over a lifetime of constant exposure.

While no human cancer cases have been linked to dioxane, it has been found to cause liver cancer in animal experiments, according to the Health Department.

"Testing technology has become more sophisticated," St. Anthony Mayor Jerry Faust said. "It's probably been present the whole time. It's just there was no diagnostic equipment for the MPCA to test for it."

Hadiaris said news of an emerging contaminant can be unsettling to those who have been drinking the same water for years.

"That is very much on everyone's mind. At any given point in time, we work with the information and technology we have," she said. "It's a good thing that it continues to evolve. It brings us new tools and we learn new things."

'A preventive action'

Scientists have detected trace amounts of 1,4 dioxane in 19 of Minnesota's 700-plus municipal water systems. Only New Brighton has exceeded the state limits, said Doug Schlutz, a Health Department spokesman.

New Brighton officials shut down six wells where dioxane was detected last year, leaving the city with four remaining wells that are safe. This summer, the city is restricting lawn sprinkling and will temporarily connect to the Minneapolis water system, which largely draws from surface water, at a cost of $2.7 million.

Now the goal is to upgrade the city's water treatment plant by 2018 with technology that can remove the dioxane. That could cost $15 million to $20 million, according to preliminary estimates.

"I am very pleased to be able to report the substantial progress that has been made since this time last year, and to assure you that the water you are receiving and will be receiving is safe," wrote New Brighton City Manager Dean Lotter.

Neighboring St. Anthony has stopped pumping from one of its wells with higher levels of 1,4 dioxane, and also is planning a $10 million water treatment plant upgrade. Officials there are using conservation efforts, restricting lawn sprinkling and closing both of the city's popular splash pads — which use 30 million gallons a year, or 10 percent of the city's total annual water usage.

"First and foremost, we understand it's going to be inconvenient," said St. Anthony City Manager Mark Casey. "When it comes to water quality, we act with an abundance of caution. This is a preventive action."

Army to pay for upgrades

This isn't the first time TCAAP has affected the region's water supply.

Minnesota has monitored water quality around the federal Superfund site for decades and treated water for trichloroethylene (TCE), a degreaser at the munitions plant that has been labeled harmful to human health. According to the MPCA, dioxane was a chemical used to stabilize TCE.

"When TCE was no longer useful, they would take it outside in 55-gallon drums and pour it into holes in the ground or they would pour it into big pools and light [it] on fire," Lotter said.

The U.S. Army likely will pay for upgrades to the two cities' water treatment plants, Hadiaris said. "The Army has committed to pay for the design and the installation of these additional remediation systems," she said.

New Brighton and St. Anthony sued the U.S. Department of Defense, the Army and the federal government in the 1980s, demanding that they pay for cleanup of the water supply. The parties reached settlements.

In 2014, New Brighton again took the federal government to court for water treatment costs and won an additional $59.4 million.

Both cities have sent detailed letters to residents about the ongoing process.

"We are being proactive and trying to get out ahead of this so we are not exceeding the state standard," Faust said. "We want to be able to ensure we have pure drinking water for ourselves and our children for future generations."

Shannon Prather • 612-673-4804