by ZACH KAYSER
Although the Mississippi River flows next to Winona, the water that pours from your faucet doesn’t come from there. It comes from deep underground, out of natural storage in the Mount Simon aquifer, a great deal cleaner than the river.
It’s also sometimes slightly radioactive, and tests from earlier this year showed the radioactivity in the city’s water exceeded federal standards.
The Mount Simon aquifer is unusually high in radium, a naturally occurring element that famed Polish scientist Marie Skłodowska Curie studied in order to discover radioactivity (along with her French husband, Pierre). To honor Curie’s legacy, levels of radium/radioactivity are expressed in picocuries. The federal Environmental Protection Agency has an acceptable limit of 5.4 picocuries per liter of drinking water (piC/L). The ideal rate is zero.
According to the Minnesota Department of Health (MDH), surface waters like lakes and rivers generally don’t have enough radium to make a difference. It is only underground where radium levels are a concern, after the water absorbs the element from the metaphorical sponge that is the aquifer. Radium occurs naturally, and often in larger concentrations the deeper one goes in the ground.
“Different doses of radiation cause different health effects,” the MDH webpage on radium says. “Drinking water that has radionuclides in it puts you in contact with very low doses of radiation every day. You have a higher risk of getting cancer if you drink water with radionuclides in it every day for many years.”
For five years, Winona has worked to get its radium levels under control. Eight wells draw water from the Mount Simon aquifer, drilling down from 500 to 1,100 feet below the surface. Multiple water plants have tested high for radium at different times, forcing the city water department to play a game of radioactive whack-a-mole.
Winona discovered a radium problem with its water via wells and pumps from two main facilities: Johnson Street near Levee Park and Westfield. Normally, in the instances where the city does not have to worry about radioactive particles, the intake plants do two things: filter out particles using a pressure sand filter, and treat the raw water with chemicals, chlorine and fluoride. Water workers had to add a third chemical to the mixture at the Westfield plant in 2018, a proprietary mixture called TonkaZorb, designed to remove radium. Radium levels there had gotten as high as 11.6 piC/L before the system was installed. At the Johnson Street plant, in 2019, radium was creeping up to levels as high as 5.9 piC/L. The citywide average/highest single result was also 5.9 piC/L in 2020. At the Johnson Street plant in particular, results indicated a 6.2 piC/L reading in January. So in late March, the city installed a second TonkaZorb system to stave off the problem, this time at the Johnson plant.
Public Works Director Brian DeFrang and Water Superintendent Brent Bunke said the active ingredient in TonkaZorb is manganese, another basic element. Manganese bonds with radium so that the resulting clumps will not fit through the filter, and are sorted out from the water. To put it in very simplified terms, one can think of the manganese as elemental kitty litter and the radium as the waste a cat leaves behind. The litter does not destroy the waste, it simply makes it possible to sift out easily.
Bunke said the deeper the wells are drilled, the more radium will show up into the water. However, he was hesitant to say that the problem will necessarily get worse over time. The older TonkaZorb at the Westfield plant has shown excellent results since it was put in, to the degree that a recent test found no discernable traces of radium at all, he said. What’s more, the Johnson Street plant does not have as high of an initial reading as the Westfield plant did, Bunke said. The drill hole at Johnson Street is east of the Westfield one, and since it was in a different position on the Mount Simon aquifer, its radium contamination was delayed compared to Westfield’s, he said.
Containing radioactivity isn’t cheap: Bunke said the TonkaZorb costs about $14 a gallon. The Johnson plant averages about 20 gallons a day, for $280 in total costs. And since the system is already running at Westfield, overall the city spends more than $500 a day to limit the amount of radium in the water. An earlier estimate of the Westfield plant put the cost of adding TonkaZorb at $140,000 annually.
The cost in dollars is worth avoiding the potential costs to health, from the city’s point of view.
“During the year, we had an ongoing violation for combined radium,” the city’s 2020 water quality report said. “Some people who drink water containing radium 226 or 228 in excess of the MCL over many years may have an increased risk of getting cancer. Our system has signed an agreement with MDH, we continue to monitor radium levels quarterly, and we are studying alternatives available for corrective action.”
The latest test sample was sent off to MDH earlier this month. Due to a long turnaround time on test results, the city does not yet know how effective the TonkaZorb is at filtering radium at the Johnson Street plan, Bunke said. Still, the treatment was the best chance the city had at reducing the radioactivity.
“This was our best solution, our best scenario,” Bunke said.
For home water treatment guidance, visit the MDH’s website at www.health.state.mn.us/communities/environment/water/factsheet/hometreatment.html.