The amount of raw sewage discharged into public waters in Greater Cincinnati was higher than average last year, thanks to higher than average rainfall.
Cincinnati has a combined sewer system, where human sewage shares the same pipes as stormwater runoff. High-intensity rainstorms can overwhelm the system, causing a combination of human waste and stormwater to overflow into the Ohio River, Mill Creek, and other areas.
The Metropolitan Sewer District of Greater Cincinnati has been working for decades to reduce how often these combined sewer overflows happen. In 2006, MSD averaged 14 billion gallons of sewage overflow a year; the current average is about 6 billion gallons.
"In 2024 our overflow was 7.8 billion gallons," said MSD Director Diana Christy, pointing to higher than average rainfall last year.
RELATED: Listen to Cincinnati Public Radio's podcast Backed Up
"It's not just the overall rainfall in a year that matters, it's really the intensity of specific storms," Christy said. "The rainfall that we get in this region comes less frequently, so we have fewer storms, but it's dumping so much rain in those very short periods of time. And those storms just completely overwhelm the combined sewer system."
Another problem that can be related to combined sewer systems is sewer backups, where untreated sewage is pushed back through the pipes into basements through floor drains or toilets.
In 2024, MSD received reports of a sewer backup at 2,871 properties. After investigating each property, MSD determined 371 of those were likely caused by incapacity in the public sewer (or another MSD-related cause, like a blockage in the public sewer). Those properties are offered cleanup services paid for by MSD.
Christy says a full investigation of each report takes much longer than this initial determination; in 2024, only 129 backups were the result of the public sewer.
MSD has several strategies to reduce sewer backups, including overall efforts to increase system capacity (which also reduces combined sewer overflows). Certain properties with chronic sewer backups can be eligible for MSD to install a prevention device, but that only protects one home at a time. MSD has installed over a thousand of these devices since 2006, including 35 last year.
Christy says one project completed in 2024 involved more than 50 homes in Mt. Washington that were eligible for prevention devices because of frequent sewer backups.
"It was not only going to be very costly ... the property owners didn't want it," Christy said. "They didn't want MSD coming in and digging up their yards or their basements to install these solutions. They really challenged us to find another way."
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MSD opted to separate the combined sewer system in that area by building new pipes for stormwater only, eliminating the risk of heavy rain causing sewer backups. Christy says it's not cost-effective or even possible to separate the system everywhere, but it was a good solution for this location.
Tracking progress on sewer backups can be difficult, because it's heavily dependent on rainfall, and because homeowners have to report a backup to MSD. More reports in any given year could be caused by heavier rain or more public awareness about how to report, or a combination of the two.
"The problem is not solved, and we're well aware of that," Christy said.
MSD posts monthly reports on its sewer backup program online.
Learn more about sewage infrastructure in Backed Up, a podcast from Cincinnati Public Radio: wvxu.org/backedup
