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Inflow and infiltration – these words are the dread of public works departments and all those who oversee sewer and drainage systems. When combined with an aging pipe infrastructure such as the city of Davenport, Iowa’s 150-year-plus old system, “I&I,” as they’re commonly known, can spell disaster.

“One of our biggest challenges, like many other cities of our age, is I&I,” Public Works Director Michael Clarke says. “Many of our sewage pipes are cracked and broken in some places … as rainwater seeps through the ground after a storm, it can completely surround and infiltrate the sewage pipes.”

An infrastructure project in Daven­port will target failing sewers while improving the capacity and flow of the city’s sewer system. The system handles a flow of roughly 30 million gallons of sewage a day.

The $31 million West Side Diver­sion Tunnel project will directly connect an interceptor pipe running parallel to the Mississippi River to sewage collector pipes on the western and western-central sides of the city. The tunnel will replace several older sections of pipe that connect to many homes and businesses, Clarke says.

The project is broken into three phases. Foley Construction Company of Davenport began work on the $12 million phase one in 2009. It involves replacing one mile of sewer lines.

Phase one is expected to conclude in November 2011, three months later than its initially anticipated August completion, because two recent floods impeded progress. The pipes being replaced in the phase are 10 to 30 feet below ground and are in a floodplain, Clarke says. Workers needed to plug the upstream side of newly installed pipes while pumping out the flooded downstream pipe portions, in addition to having to wait while flood waters receded or were removed.

The second phase of the project started in June 2011 with the awarding of a $14.3 million contract to Jay Dee Contractors Inc. of Livonia, Mich. This portion of the project includes installing a deep tunnel up to 160 feet underground; this roughly one-mile-long tunnel will intercept the discharge from other nearby sewers. This phase is projected to conclude in 2013.

The awarded phase two contract is well below initial engineering estimates of $32 million. “The estimate was done a number of years ago, and was valid under the economic conditions of the time, but those conditions have since changed, and contractors have responded by being more competitive in their bidding,” Clarke says.

The project’s third phase will add shallow-depth trunk sewers into the city’s relatively undeveloped northwestern sector. This phase is pending further development in the area.

Future sewer-related projects in­clude a projected $49 million equalization basin adjacent to the city’s water treatment plant. The basin will hold and prevent excess stormwater from entering the sewers, Clarke says.

Constant Contact

Close communication with contractors, homeowners, businesses and other stakeholders is a key to the project’s success, Clarke says. City officials met with contractors and subcontractors in a formal partnering session before work commenced, and executive sessions are held quarterly. Project engineers and supervisors meet weekly to ensure construction proceeds smoothly.

Residents and business owners are also kept informed about temporary sewer hookups and other potential im­pacts to their service through both face-­to-face visits and local ward meetings.

The city has worked closely with other entities including the Bur­ling­ton Northern Santa Fe during the project to coordinate digging beneath tracks around train schedules. Much of the railroad-adjacent digging work was performed on weekends.

Top Priorities

The West Side Diversion Tunnel project is the largest ongoing public works project in Davenport this year. Other infrastructure projects underway in the city include street resurfacing and bridge replacement projects, as well as a sanitary sewer-lining program. 

“It’s been a pretty good year; we’ve been able to maintain our emphasis on street and sewer maintenance and re­pair even in an austere budget year,” Clarke says. “Maintaining our streets and sewers is a high priority of our city council, and we are executing that priority well.”