by CHRIS ROGERS
In Winona’s latest water quality report, homeowners may have noticed the city met every standard for clean drinking water but one. Once again, a city water plant exceeded the limit for the naturally occurring contaminant radium. City staff fixed one radium problem last year, following high test results in 2016 and 2017, only to have a different water plant report high radium results in 2018.
Radium is a byproduct of naturally occurring uranium and thorium deposits deep underground. The radioactive element is a common problem for wells in deep Southeast Minnesota aquifers, though not an acute one. According to state officials, it takes many decades of radium exposure to cause significant increases in cancer risk. Minnesota Department of Health (MDH) regulators do not view high radium levels as an emergency, but rather a problem cities have some time to fix.
The state limit for radium in drinking water is 5.4 picocuries per liter (piC/L). Picocuries measure radioactivity. Last July, test results indicated water from the city’s Johnson Street water plant contained 5.9 piC/L.
It is normal for radium levels to fluctuate up and down, so a well might test high on one day and be fine the rest of the year. Winona Water Superintendent Brent Bunke also raised the prospect that the lab result may be have been incorrect. In any case, the over-the-limit test result triggered a requirement for the city to start testing for radium every quarter. So far, those tests have come back under the limit, and Bunke is hopeful that the rest of the quarterly tests will come in under the limit, suggesting the one high result was a fluke. If new tests come back with high radium levels, the city might have to consider purchasing treatment systems to remove radium.
“This next one would determine quite a bit in terms of what direction we would go — whether we try to do some kind of treatment for the future,” Bunke explained. “Whereas if this next one comes back low, we’d probably see how we do the rest of the year.”
Last year, the city fixed a radium problem at the city’s other water plant, the Westfield Water Plant, by installing a radium removal treatment system with the brand name TonkaZorb. Tests at the Westfield plant in 2016 and 2017 came back with radium levels of as high as 11.6 piC/L. “I’m not making light of it, but you’re looking at 0.5 pCi [over the limit], so you’re not nearly the radium that Westfield was,” Bunke said of the recent 5.9 piC/L result at the Johnson Street water plant.
The radium removal system uses the chemical potassium permanganate to remove radium. It solved the problem at Westfield and cost city $140,000.
The city’s full 2019 water quality report is available online at www.cityofwinona.com/city-services/public-works/water-plant.