Louisville dumped nearly 600 million gallons of sewage and stormwater into Kentucky waterways during three days of record-breaking rains and flash flooding earlier this month.
The remnants of Tropical Storm Gordon dropped 3.84 inches of rain at the Louisville International Airport on Saturday, Sept. 8, a daily record. Rains and flooding spread across parts of Northern Kentucky and Southern Indiana into Sunday.
The Metropolitan Sewer District estimates it discharged about 572,788,056 gallons of sewage and stormwater into the Ohio River and Beargrass Creek over three days beginning Friday Sept. 7.
“With the increased intensity of severe storms, we’re asking those [combined sewer overflow] pipes to handle so much more volume than they are really designed to handle,” said Sheryl Lauder, MSD spokeswoman.
On the one hand, that’s less than the estimated four billion gallons the sewer district dumped while managing February’s deluge, the city’s largest river flooding since 1997.
On the other hand, MSD still dumped enough wastewater into the Ohio River to fill more than 867 Olympic-sized swimming pools.
The wastewater is full of fecal bacteria, household chemicals and everything the stormwater picks up on its way to the sewer pipe. It’s bad for the environment and for human health (Experts recommend avoiding contact with affected waterways for three days after it rains).
But the city has to do it because there’s nowhere else for the water to go.
Much of the city’s sewers, especially around downtown, are a combined system that uses the same pipes to carry household wastewater and storm water.
When it rains hard, the pipes fill-up. The city’s treatment plants don’t have the capacity to handle the volume and no one wants sewage backing up into their homes so the city discharges into door #3, aka the Ohio River and Beargrass Creek.
The city’s 590 miles of combined sewers were just never meant for a city this size.
“You have to remember the population of the city and the hard surfaces of the city were much less when these assets were put into the ground,” Lauder said.
Climate change is another contributing factor. The warmer the atmosphere, the more water vapor it can hold. As a result, the warming climate is expected to bring larger storms that produce more rainfall.
This year has been particularly wet. Already, Kentucky’s about 17 inches above average rainfall for this time of the year, said Tom Reaugh, forecaster at the National Weather Service in Louisville.
The recent flash flooding was one of at least two “top 10” rain events in the last month, said Trent Schade, National Oceanic and Atmospheric Administration hydrologist.
It would be inaccurate to conclude a single weather event is because of climate change, but it’s clear that these are the types of events that will become more frequent as the climate warms.
To solve the problem, the city is spending $900 million under a consent decree with the federal government to fix 98 percent of the city’s combined sewer overflows by 2020.
The city is building a series of storage systems to hold all of the excess sewage and stormwater until one of the city’s treatment centers can handle the load.
The largest project is the four-mile long Waterway Protection Tunnel that is under construction and will capture up to 55 million gallons of overflow. Additionally, the city is working on a series of storage basins.
The Logan Street Basin is already complete and can hold up to 15 million gallons; the Clifton Heights Basin should be ready by the end of the year. Two more are planned for completion before the 2020 deadline, Lauder said.