What is three miles long, 26 feet in diameter, and 250 feet below Providence? The Narragansett Bay Commission’s new combined sewage overflow tunnel, which broke ground four years ago off Allens Avenue in the Fields Point section of Providence.
Last week, workers completed lining 12,000 feet of the 16,000-foot tunnel with concrete, said Jamie Samons, spokesman for the commission, which owns and operates two of the state’s largest wastewater treatment plants.
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The tunnel, pump station and seven drop shafts, with a price tag of about $342 million, are on schedule for completion by October 2008, she said. They’re the first phase of an effort to bring the city into compliance with the 1972 federal Clean Water Act, by stemming the flow of untreated sewage into the Narragansett Bay and its tributaries.
The remaining phases involve the construction of interceptors, tunnels and sewer separations in Pawtucket and Central Falls. The new infrastructure will transport a combination of storm sewer water and waste the primary treatment system cannot handle from those cities to the new tunnel in Providence, which runs from the Fields Point Wastewater Treatment Facility along the Providence River to the Foundry Building at the base of Smith Hill.
The project is expected to be completed in 2020. There is no set cost yet, but some early bidders quoted as much as $1 billion for the entire project (including the $342 million already allocated), said Richard Bernier, the Bay Commission’s construction manager.
Currently, when it rains “more than half an inch in 24 hours,” that backs up the aging sewer systems – Providence’s dates back to the 1870s – which overflow into the Bay and its tributaries, said John Torgan, spokesman for the environmental group Save The Bay.
The new tunnel will hold a maximum of about 63 million gallons of storm water and sewer overflow that would otherwise go directly into the Bay – from outfalls or discharge pipes along the Providence, Blackstone, Moshassuck, Seekonk, Woonasquatucket and West rivers – when the system’s 64 million gallon per day capacity is reached.
That overflow is a big cause of beach closings and shellfishing restrictions, Torgan said, which is why “we strongly supported this solution.” It will result in more open days for swimming and fishing, he said, whereas now the Providence River is permanently closed.
Joe Migliore, an environmental scientist for the Office of Water Resources at the R.I. Department of Environmental Management, said it’s unclear how much that will change.
Portions of the upper Bay are closed about 50 percent to 60 percent of the year, he said. Once the project is completed, those should improve to about 30 percent of the year.
Currently, the outfalls release about 2.2 billion gallons of untreated sewage per year, depending on rainfall. Phase one of this project will cut that by 40 percent, Bernier said.
The new tunnel will catch the overflow, Samons said, and a pumping station in Fields Point that is about the size of an NCAA basketball court will pump it to the surface to be treated.
At this point, this is the most expensive public works project in the city’s history, Samons said, although it will soon be eclipsed by the relocation of Interstate 195. And it is being paid for primarily through increases in the sewer rates paid by residents and businesses.
For example, the average annual residential sewage rate has risen from about $200, when the project started in 2002, to a projected $300 in 2007, Bernier said.
Torgan said some people refer to this project as Providence’s “Big Dig,” but he would disagree, because so far it has been “ahead of schedule and under budget.”
