The next phase of Metropolitan Sewer District’s plan to prevent sewage from overflowing into the Ohio River begins next week.

Construction on the $200 million project will close sections of two downtown city blocks for nearly two years.

It’s part of Louisville’s deal with the federal government to stop pouring raw sewage and stormwater into Kentucky waterways by 2020.

MSD’s plan is to build a storage basin to collect sewage and stormwater. That way, the city has more time to treat the sewage before dumping it into Louisville waterways, said MSD spokeswoman Sheryl Lauder.

“If it rains really hard this afternoon and it overloads the system, it will go into the river so this tunnel will capture that and eliminate 98 percent overflows into the river,” Lauder said.

Construction started in January on the so-called “Waterway Protection Tunnel.”

When complete, it will be 2.5 miles long, 20 feet in diameter and buried 18 stories underground.

In total, it will be able to hold 37 million gallons of sewage and stormwater, enough to fill 56 Olympic-size swimming pools.

But even after it’s complete, the city will still have overflows during really big storms, like the one seen in February.

“That one was so intense and put down so much rain in such a short period of time that Saturday night, it probably would still overwhelm the system at that point,” Lauder said.

Construction on the next phase of the project begins next week. MSD will close downtown sections of River Road, West Washington Street and Seventh Street until March of 2020.

Metropolitan Sewer District

Closures will begin May 14 and last until March of 2020, according to MSD.

MSD will use that time to drill a 200-foot drop shaft that will help move waste and stormwater into the tunnel. The actual shaft will be in the median at Seventh and Washington streets.

In the meantime, businesses in the area will remain open.

“All the businesses and attractions are open on West Main Street and their parking lots are open. You just have to take a detour and the detours will be marked,” Lauder said.

Construction on another drop shaft will cause a road closure at Lexington Road and Baxter Avenue at the end of the month.

Metropolitan Sewer District

Closures will begin May 21 and last until August 2018, according to MSD.

Ryan Van Velzer is WFPL's Energy and Environment Reporter.