© 2023 St. Louis Public Radio
Play Live Radio
Next Up:
Available On Air Stations

Deep under St. Louis County, a 7-mile tunnel is being built to relieve overflowing sewers

Nearly 200 feet below south St. Louis, Metropolitan St. Louis Sewer District workers are covered in safety gear, reflective jackets and work boots. They've entered a metal cage that a crane lowers to the entrance of a dimly lit, cavernous tunnel.

Soon, the muddy, dark, 22-foot-wide tunnel will house a machine that will dig a 7-mile tunnel to prevent wastewater overflows across the St. Louis area.

When completed in 2025, the 7-mile tunnel will take water to the Lower Meramec Treatment Plant near the confluence of the Meramec and Mississippi rivers. The $175 million tunnel is aimed at reducing overflow and improving water quality throughout the sewer district, said MSD Executive Director and CEO Brian Hoelscher.

“This gives us a bunch of different things,” Hoelscher said during a visit to the tunnel on Wednesday. “It helps the environment, helps us with the water quality and the cause of our problem with the water quality is the overflows that were occurring out onto the river.”

Brian Munoz
St. Louis Public Radio
Metropolitan St. Louis Sewer District workers and Environmental Protection Agency leaders lead a tour of the Lower Meramec Tunnel project on Wednesday, during a tour of the lower Meramec River Wastewater Tunnel near Arnold.

The tunnel will allow MSD to phase out its interim Fenton treatment facility, which is prone to flooding.

The sewer district is renovating the treatment center to expand its capacity to handle the large influx of water.

“[The renovation] is so that we're more prepared for those major events, those heavy rains that can really overwhelm our sewer system so that we're able to treat all the wastewater that St. Louis produces, and we can keep our local waterways clean,” said Bess McCoy, a public affairs specialist for MSD.

MSD is working with SAK Construction of O’Fallon, Missouri to dig the tunnel. The sewer district is using a tunnel-boring machine that can dig through soil and rock to create an 11-foot-diameter opening.

Brian Munoz
St. Louis Public Radio
Lights illuminate a starter tunnel that is part of the lower Meramec River Wastewater Tunnel on Wednesday, during a tour of the site near Arnold.

“It is a miraculous thing that you can tunnel for miles underground and hit a little hole when the machine pops out,” Holescher said. “They do a great job though of traveling so far underground, just making sure they hit those open holes that they've already excavated.”

MSD’s effort is among a number of such projects across the country. Many cities are using combined sewer systems that can easily get overwhelmed by stormwater and sewage. Existing tunnels across the country also are aging and in need of upgrades, EPA Deputy Director Janet McCabe said. Many regions need larger tunnels that can handle the excess from large storms that are becoming more frequent, due to climate change.

“We're seeing more severe storms with climate change,” McCabe said. “So when you put those two things together, it is really important to be putting money into these projects.”

Chad is a general assignment reporter at St. Louis Public Radio.

Send questions and comments about this story to feedback@stlpublicradio.org.