PROVIDENCE -- Like some advanced type of moles, crews are boring a 3-mile tunnel under Rhode Island's capital city. It is this state's largest public works project to date, and will capture raw sewage that is now jettisoned into waterways during heavy rains.
All it takes is a half-inch of rain to overwhelm the combined sewer and stormwater system, some segments of which are 134 years old, that serves 360,000 residents of metropolitan Providence.
To relieve the backup, the contaminated water is released into local rivers, such as the Blackstone, Moshassuck, Providence, Seekonk, and Woonasquatucket rivers. Those empty into Narragansett Bay, fouling the water with fecal coliform bacteria and forcing the closure of shellfish beds that are a lifeblood of the commercial fishing industry.
The $318 million Combined Sewer Overflow Abatement project is Rhode Island's effort to stem the spills and clean the water. Work on the first phase of the Narragansett Bay Commission's project began in May 2001, and is scheduled to be completed in spring 2008. Two other phases are planned, which would involve building another miles-long underground tunnel.
Vincent Mesolella, chairman of the commission, called the Providence tunnel "a subway for water" that will improve the bay's health.
"It's absolutely critical," he added.
Scientists agree that the project will greatly reduce dangerous bacteria from local waters, but do not think it will meet federal requirements for the water to be fishable and swimmable.
"I would definitely not say outright this will make [the bay] fishable, swimmable, but this is certainly a major step, the major step," said Amos Colt, assistant director with the Rhode Island Sea Grant College Program, a partnership among federal and state agencies and universities to research marine issues.
The fishable, swimmable mandate comes from Congress, and is the reason why the commission looked at the problem in the first place. Other major cities with shared sewer and stormwater pipes also have opted to construct tunnels to capture excess wastewater. They include Boston, Chicago, Portland, Ore., and Milwaukee. Atlanta, Detroit, St. Louis, and Washington plan similar, multibillion dollar projects.
"It is an excellent solution, a proven technology," said Alexandra Dunn, general counsel for the Association of Metropolitan Sewerage Agencies in Washington.
There are 745 communities in the United States with combined sewer systems, most of them older cities concentrated in the Northeast and Great Lakes regions, said Jim Hanlon, director of office of wastewater management at the Environmental Protection Agency. As of July, about 59 percent of those municipalities have adopted solutions and are starting construction, he added.
"We're making progress," he said.
Newer communities have separate sanitary sewer and stormwater systems.
In Rhode Island, the tunnel under construction will stretch from the Field's Point wastewater treatment plant to a foundry complex just west of downtown. Its route roughly follows existing pipes along the Providence and Woonasquatucket rivers, then branches out under the south lawn of the State House before ending at the foundry complex, where one of the most active outfall pipes is located.
Engineers will close the outfall points and connect them to the current combined sewer network. The crews also will build "drop shafts" that will carry the excess wastewater downward to the new tunnel. The wastewater is then held in the 30-foot diameter tunnel, lined with concrete, until the Field's Point plant can process it.