KCCI Investigates: Underground water source hits record high nitrate levels

In the late 1800s, water use grew to the point Des Moines leaders needed a bigger operation.The answer: To build a 3.5-mile-long underground pipe system along the Raccoon River. This is known as the infiltration gallery and serves as a main source for drinking water along with the Des Moines and Raccoon Rivers. “It is a perforated pipe that naturally filters water from the Raccoon River,” says Tami Madsen, executive director of Central Iowa Water Works. “The infiltration gallery is the preferred source of water.”The gallery and the rivers now see higher levels of nitrates, one of the reasons for Monday’s announcement of a lawn-watering ban.Sand and gravel sit between segments of the pipe to naturally filter out contaminants. Nitrate levels are at all-time highs in the gallery. Data from CIWW show how many days in a year the gallery has had a reading above the EPA standard of 10 milligrams per liter. Here are the last five years and in 2026 so far:2021: 02022: 02023: 02024: 512025: 392026: 86”I think that that’s probably just a reflection of just how sustained and how high the nitrate levels have been in the river since going back to the last lawn watering ban last year,” says David Cwiertny, a professor at the University of Iowa and the director of the Center for Health Effects of Environmental Contamination.”If the gallery has been constantly barraged with river water that’s high in nitrate, it doesn’t give you that flexibility anymore, which is why they’ve had to run the nitrate removal system as long as they have,” Cwiertny says. The nitrate removal facility has run nearly 150 days.Central Iowa Water Works is also using Maffitt Reservoir to ensure treated water meets the EPA standard. It’s at 50% capacity. Matt Helmers is an Iowa State University professor and directs the Iowa Nutrient Research Center. He says rainfall has been pushing nitrates down the watersheds.”We expected that we would continue to see high nitrate this year, if we got rainfall and we’ve gotten rainfall,” he says.And there’s more in the forecast, which is why the ban on watering grass matters.”It’s communities working together that are really going to help with this long waiting situation right now,” says Madsen.Photos from construction of Des Moines Water Works infiltration galleryConstruction of the Des Moines Water Works infiltration gallery, which runs for more than 3 miles along the Raccoon River, began in 1884 and ended in 1931. Initial sections were made of wood, but in 1907, concrete rings were used. There’s over 9,000 concrete rings in all.DMWW officials say the gallery system is considered to be the longest in the world for a water utility. Scroll to see photos from construction of the gallery system: