The St. Louis Metropolitan Sewer District is in the midst of a massive $7.2 billion, multifaceted infrastructure improvement program aimed at eradicating the sanitary sewer overflows that have plagued the city and surrounding St. Louis County for decades.

Called MSD Project Clear, the mammoth initiative also will improve water quality in the metro St. Louis area by eliminating the discharge of stormwater mixed with untreated wastewater into local waterways, says Bruce Litzsinger, MSD assistant director of engineering for planning.

“This is the largest capital improvement project in our utility’s history and I also can safely say it’s one of the largest such projects in the country,” Litzsinger says.

Project Clear started in 2012 and is expected to conclude in 2039. Jacobs Engineering, a consulting firm, helped the utility plan the project.

The complexity, scope and age of the MSD’s oldest infrastructure contributes significantly to the long timeline; the utility’s sewer system is the fourth largest system in the United States, featuring 9,058 miles of collection and trunk sewers and force mains, ranging in size from 6 inches to 29 feet in diameter.

“Some of the combined sewers are more than 170 years old,” Litzsinger points out.

More specifically, the MSD manages roughly 4,596 miles of wastewater sewers and force mains, approximately 2,998 miles of stormwater sewers and force mains and around 1,464 miles of combined sewers, mostly located in downtown St. Louis.

The utility serves nearly 1.3 million people in a service area that covers approximately 524 square miles, includes 88 different municipalities and features more than 1,500 creeks and 26 watersheds.

The primary components of the program include the repair of about 150 miles of sewer lines; the rehabilitation (primarily via pipe lining) of around 950 miles of existing sewer lines to stop stormwater inflow and infiltration; upsizing the capacity of approximately 150 miles of existing sewer lines; and building a network of aboveground storage tanks and “deep tunnel” storage facilities designed to hold wastewater until the sewer system can handle it, he explains.

Decades in the making

The genesis of Project Clear dates back to 2007, when the state of Missouri and the U.S. Environmental Protection Agency filed a lawsuit against the MSD to stop sanitary sewer overflows, which acted as relief valves that prevented wastewater backups when too much water entered the sewer system.

In the 1980s, more than 600 SSOs occurred. Those overflows dumped hundreds of millions of gallons of stormwater combined with untreated wastewater into local streams, creeks and rivers every year.

After years of negotiations, a federal judge approved a consent decree in April 2012 that required the utility to spend $4.7 billion during the ensuing 23 years to fix the overflows and make other system improvements. (That deadline later extended by four more years, to 2039.)

But the utility already was working to eliminate SSOs decades before, Litzsinger says.

From 1992 to 2012, the utility spent approximately $2.7 billion on system improvements that eliminated 350 overflows. As such, when Project Clear started, there were only 199 overflows left to fix. And as of last September, that number was down to 26, Litzsinger says.

“We achieved our mandated goal [from the consent decree] of eliminating 85% of our overflows by the end of 2023 and we did it ahead of schedule. We’re very happy about that.”

Stopping overflows

The initial focus of Project Clear was eliminating the SSOs. To do this, the utility spent the last decade concentrating on eliminating inflow and infiltration, primarily through pipe lining. “We’ve spent hundreds of millions of dollars on cured-in-place pipe,” Litzsinger explains. “We have a lot of vitrified 8-inch-diameter clay pipe with a lot of breakage and blockages and we rehabbed a lot of it early in the process to minimize the need for pipe replacements.”

The next step was strategic replacement of existing undersized sections of the sewer system with larger-capacity pipes. This required a thorough inspection of the sanitary sewer system to determine pipeline condition, followed by the installation of flowmeters to develop a hydraulic model for all sanitary sewers 12 inches in diameter or larger — about 17% of the system.

“That helped us to better understand the capacities of the system,” Litzsinger says.

One of the largest projects currently under construction is installing 7,900 feet of 66- to 78-inch-diameter pipes and 16,200 feet (about 3 miles) of 8- to 54-inch pipe to alleviate system surcharging in western St. Louis County.

Concurrent with all these efforts, the district also is building deep tunnels, adding/upgrading pump stations, and improving the capacity of its wastewater treatment plants to handle the additional flow.

Going deep

The centerpiece of Project Clear is the construction of six deep-tunnel storage facilities, bored through limestone as deep as 250 feet underground. Collectively, they will hold more than 360 million gallons of stormwater.

Two of the tunnels are complete. One is located in northern St. Louis and is 3,000 feet long and 28 feet in diameter, with a capacity of about 12 million gallons; the second, located in the middle of St. Louis County, is just under 4 miles long and 19 feet in diameter and holds 40 million gallons.

Two other tunnels currently are under construction to convey wastewater flows from the collections system to treatment plants. One is located in southern St. Louis County; it will be 36,000 feet long and 8 feet in diameter. The other one, located in northern St. Louis, will be 17,000 feet long and 7 feet in diameter.

The two remaining tunnels, currently in the design phase, will help alleviate combined sewer overflows. The first one, located in southern St. Louis, will be 32,000 feet long (about 6 miles) and 18 feet in diameter with a storage volume of 58 million gallons. The second one, located in southern St. Louis, is by far the largest of the six: 9 miles long and 30 feet in diameter with a storage capacity of 230 million gallons.

“These two tunnels are among the biggest components of the entire project,” Litzsinger says. “The biggest one is the crown jewel of Project Clear. When we finish that and all the collection sewer lines that flow into it, we’ll have basically met the terms of the consent decree.”

Both tunnels should be completed in 2039.

In addition, the project includes three already-completed, aboveground storage facilities for “wet-weather sanitary flow,” with a total capacity of about 22 million gallons, Litzsinger says.

Optimistic outlook

Project Clear has already delivered tangible results since ground was broken about a decade ago. Along with a dramatic reduction in SSOs, basement sewer backups have declined about 25%, says Sean Stone, the utility’s senior public affairs specialist.

“And that number looked a lot better before St. Louis got hit by two freak rain events in July of 2022 and last May,” he points out. “The July storm dropped 10 inches of rain in about 12 hours across our entire service area and was considered a 500-year rainfall. The May storm, which was more isolated, dropped about 6 inches in two to three hours and affected a significant swath of the most vulnerable parts of our system.”

The utility has already completed 650 individual projects as part of Project Clear, with 247 of them related to eliminating SSOs. That includes 50 miles of new, larger-capacity sewer pipes installed, 280 miles of sewer line rehabilitation, two deep tunnel storage facilities and two aboveground storage facilities.

Litzsinger looks forward to the day when all SSOs are eliminated, which will significantly improve the area’s water quality and make life easier for customers by mitigating basement backups. (The project will not eliminate combined sewer overflows, but their flows will be significantly reduced.)

“We’re super excited about the progress made so far,” he says. “A few years ago, meeting our deadline of eliminating 85% of sanitary sewer overflows by the end of 2023 seemed like a pretty daunting task.

“We were dealing with COVID-related issues such as labor shortages, rising prices for and scarcity of materials. … It was all very concerning. But now we’re largely on schedule and on budget. We’re very happy about and proud of that.”