Iowa’s largest drinking water utility has started operation of its nitrate removal facility this week, as it said nitrate levels in raw water sources have increased.
The last time Des Moines Waterworks had to use its nitrate removal facility was in 2017.
This year's rainy spring weather is partly to blame, said Ted Corrigan, the CEO and general manager of Des Moines Water Works.
"One of the things that we see is very dry conditions - like we had the last two years - tend to result in less nitrate in the river, because there just isn't the water coming off the landscape upstream. But that nitrate just stores — that excess nutrient stores on the landscape." he said.
"And then when we have heavy rains in the spring and the rivers rise, we see very high nitrate concentration. So this was no surprise. This is what happens in Des Moines in a wet spring after a dry fall or a dry year."
This has affected nitrate levels in many different raw water sources that the utility uses, Corrigan said.
The nitrate concentrate in the Raccoon River is about 14 milligrams per liter, while its infiltration gallery, which is shallow groundwater, is over 9 mg/L, he said.
The U.S. Environmental Protection Agency’s Safe Drinking Water Standard for nitrate is 10 mg/L.
Corrigan said Water Works employees are carefully monitoring the water, and it remains safe to drink for the 600,000 central Iowans who get their water from the utility.
However, running the nitrate removal facility can be a significant expense that’s passed on to ratepayers, he said.
"The cost of running the facility can be as high as $10,000 a day," Corrigan said. "And that includes everything from labor to power to chemicals to the fee that we have to pay to [the wastewater reclamation authority] to send a waste stream to them for treatment."
The amount it time it will have to run depends on weather, but the water utility is predicating it will run for several weeks "given the concentrations that we're seeing in the river now," he said.
Public health research has tied elevated levels of nitrate in drinking water to a range of issues such as colorectal cancer, thyroid issues and birth defects.
The elevated nitrate concentrations in Iowa's rivers and streams are linked to land use practices upstream, such as the use of agricultural fertilizer on farms, Corrigan said.
"It just highlights the fact that we really need to see conservation practices implemented at scale - on millions of acres of farmland," he said.
