It won't be as long as the 31-mile “Chunnel,” which carries trains beneath the English Channel between Great Britain and France.
And it won't be as well-known or busy as the Holland Tunnel, which is not even three miles long but allows 93,000 vehicles to travel between Manhattan and New Jersey every day without having to cross the Hudson River.
But in a public-works project that would be unique in local history, Fort Wayne officials are planning to drill a seven-mile tunnel through the bedrock about 150 feet below the city's surface – a project that could cost $150 million or more but, when complete, would dramatically reduce the amount of raw sewage pumped into the rivers during heavy rains.
Mandated by the Environmental Protection Agency to minimize the so-called “combined sewer overflows” that occur when the amount of liquid entering older combined storm and sanitary sewers exceeds their capacity, City Utilities has been working to reduce such discharges through the elimination of combined sewers and other methods. The entire project has been estimated to cost about $250 million.
The proposed “Fort Wayne Three Rivers Protection and Overflow Reduction Tunnel” is part of that effort but represents a more dramatic approach. Taking a still-undetermined route, the tunnel would stretch from the city's sewage treatment plant on Dwenger Avenue through the city and south toward Foster Park. The tunnel would have a circumference of about 12 and would be so large that specialized boring equipment would have to be brought in.
“Less than a dozen firms in the world do that sort of thing,” said Deputy Director of Engineering Matthew Wirtz, who stressed that many local contractors would also have the opportunity to bid on other aspects of the project.
Most sewers are less than 30 feet below the surface. By digging through deep bedrock, Wirtz said, the project will avoid unstable soil near the surface and existing utility lines and will also minimize the potentially expensive impact on buildings and property. Tunneling also allows the project to go under rivers. About 13 new vertical shafts of up to 40 feet in diameter will connect the smaller existing sewers with the new tunnel, allowing it to transport the contents of combined sewers to the plant for treatment while avoiding discharge into the rivers.
The tunnel will not be designed to carry people or vehicles, but will have enough capacity left after its sewers are installed that it could one day also serve as a conduit for fiber-optic lines or other uses.
Wirtz said much remains to be done before the project receives the final go-ahead, however. Few soil and rock samples have been taken at such a depth because they have not been necessary, and the results of coming tests could help determine the route. It's also unclear to what degree - if any - property owners' permission must be sought for a project so deep.
But the tunnel could be about 10 percent less expensive than comparable traditional sewers, Wirtz said.
Currently, the city discharges about 1 billion gallons of overflow into the rivers each year. The tunnel would help reduce that to about 10 million gallons – a level acceptable to the EPA.
“This would be a huge benefit,” Wirtz said. “We have CSOs (combined-sewer overflows) about 70 times a year now. We need to get that to four times or less.”
Work could start in 2017, take about six years to complete and would be funded by City Utilities fees.