The Iowa Department of Natural Resources says large amounts of rains overwhelmed the sewage treatment plants in many areas of the state. The DNR’s Bill Gross says the south-central regional field office in particular had several calls following heavy overnight rainfalls.
“There was so much rainfall at one time, that systems weren’t sized for that much water to go through, so they overflow. Mainly at manhole areas,” Gross says. Cities reporting discharges in an 18-county area of south-central Iowa included: Chariton, Des Moines, Grinnell, Indianola, Melbourne, Redfield, Ogden, Waukee and West Des Moines.
The raw sewage gets into waterways, but Gross says the sewage is not very concentrated. “It’s very much diluted because of all the clear water from the rainfall event,” Gross says. He says each city will have to check their systems to see if the heavy water did more than blow out manhole covers.
“They evaluate the systems after the water goes back down, so that would be a case-by-case basis as to whether there would be damage to the system itself,” Gross says. Gross says they are seeing more wastewater discharges as the state gets more heavy rains in shorter periods of times.
“Cities have been working on upgrading their systems to try to prevent clear water from getting into them in the first place, so that has helped quite a bit,” according to Gross. He says cities have been working to keep sump pumps and clear water sources from running into the sewer system to reduce the amount of water that gets into those systems.