Project of the Week: FY27 Large Diameter Sewer Inspection Project

Residents count on the City's sanitary sewer system every day - and behind the scenes, a team of inspectors, engineers, and contractors are constantly working to make sure that system keeps working properly.

On Tuesday, the City Council approved the FY2027 Large Diameter Sewer Inspection Project. The City's contractor will inspect the condition of over 82,000 feet of large diameter sanitary sewer mains throughout the city, as well as 277 manholes. The program will kick off in December and continue through January of 2028.

Inspectors will use closed-circuit television (CCTV), Sonar and LiDAR to inspect sanitary sewer mains and manholes. If any issues are found, they will be corrected with separate repair projects.

Sewer Utility Engineering Manager Ben Worrell says that managing such a large system requires a long-term, phased approach. The City aims to evaluate all City sewers - including the largest pipes - on roughly a ten-year cycle.

"Most of the reports have shown that the City's large sewers are in pretty good condition," Worrell says. "However, the most common issue we see are areas where the pipe is damaged and is allowing groundwater to flow into the sanitary sewer system. It's important to address those issues as soon as they are found, so that we make sure the sewer is not overwhelmed with water that is not supposed to be in the sanitary sewer system."

How inspections work

Inspectors will deploy remote-controlled, waterproof robotic cameras that can roll through sewer pipes and stream video to the surface. For larger sewers with higher wastewater flows, the inspection equipment is floated down the sewer on a raft and can collect data both above and below the water.

Inspectors can look for:

• Root Intrusions: Tree roots breaking through pipe joints over time.
• Cracks and Collapses: Structural failures from aging materials like clay, cast iron, or concrete.
• Corrosion or Joint Separation: Inspectors look for gaps between pipe segments that could let groundwater leak in.

If an inspection reveals a problem, City staff determine what repairs may be needed. Then they develop separate projects to make those repairs.

For example, several leaks were discovered during a previous phase of large diameter inspections in one of the sewers along A St. SW. In response, the City launched a new project to line that sewer and stop the leaks.

When traffic control is needed, the contractor submits a plan to the City before work begins, ensuring that any impacts to streets are limited and well-managed.

City staff are also inspecting smaller sewers and walking the sewers in our drainageways, looking for any damaged sewers or manhole lids that may have been pushed off by high flow. For example, earlier this month City staff discovered a 21-inch sewer main near 18^th St SW that was severely damaged after a tree fell into a waterway that the sewer main ran underneath. In response, the City set up pumps that bypassed the damaged line until repairs could be finished.

Critical upkeep

The areas chosen for inspection in the FY2027 plan include some of the City's most critical sewer lines, such as the main 96" sewer line that leads to the City's Water Pollution Control Facility. This line is just downstream of the City's downtown core - including the NewBo neighborhood, which saw basement flooding due to heavy rains earlier this year.

High flows and backups in the sanitary sewer system can put a stress on pipe joints and push off manhole lids. The City has checked thousands of manhole lids since the summer, and in some cases, had to put the lids back on.

"The sanitary sewer system needs to continue to be maintained to keep groundwater and stormwater out, so that capacity is available for future City growth," Worrell says.

During Tuesday's Council meeting, Mayor Tiffany O'Donnell expressed support for the vote that approved the FY2027 Large Diameter Sewer Inspection Project.

"I want to make sure that we celebrate this," O'Donnell said. "We know that the sewers are critical, and this kind of upkeep is not easy. It is tedious, but it is important."

You can learn more about City sewer maintenance here.

Project of the Week puts a spotlight on work happening all over the City every day. Each week, we will take a closer look at projects that are investing in our community's roads, trails, Flood Control System, and more. See previous installments here:

October 15: FY26 Downtown Sidewalk Repair
October 8: Ellis Lane Tie-Off
Oct. 1: 2^nd Street SW

September 24: ROADEO and winter snow training
September 17: Bever Avenue and Green Valley Terrace
September 10: 3^rd Street SE
September 4: Jacolyn Drive NW
August 27: Blairs Ferry Road Sidewalk Infill
August 20: Downtown Railroad Crossing Repair
August 13: 3^rd Street SW
August 6: CIPP Sewer Repairs

July 30: 6^th Avenue SW from 1^st Street to 2^nd Street
July 24: 4^th Street Trail Extension
July 17: 12^th Street SE/Coe Road
July 10: 34^th Street SE
July 3: Roundhouse

June 25: Mount Vernon Road
June 18: Grande Avenue SE
June 11: O Avenue NW Time Check Elevation Project
June 5: Nassau Street

May 28: Cedar Lake
May 21: Tree of Five Seasons Park
May 14: 20th Street NW
May 7: 18th Avenue SW
April 30: Alliant Energy LightLine™
April 23: 42nd Street
April 16: The 3rd Avenue Bridge