New stage of harbor cleanup set to start

Two decades ago, frustration with the frequently murky waters along the beaches of Dorchester and South Boston helped spur a court battle and a judge's order for the state to clean up Boston Harbor.

Now, after billions of dollars in sewer work have transformed the labyrinth of underground sewer tunnels at the harbor, work is beginning on a 2-mile sewer overflow tunnel that will virtually eliminate the release of sewage and storm water into the harbor and dramatically reduce beach closings.

"The folks that have been justifiably worried about going swimming anytime near when it rains in Boston will be able to feel much safer about having their children in the water when this project is finally implemented," said Peter Shelley, vice president of the Conservation Law Foundation and one of the lawyers who initially sued government agencies over the discharge of raw sewage into Boston Harbor in 1983. "This project is really being done for the people who use the beaches of Boston, and it's about time."

A massive boring machine arrived in the Boston Harbor from Japan last week, and officials will gather in South Boston this morning to mark the start of work on the project, set to cost about $215 million and take four years to complete.

The tunnel will store storm water during a storm and send it to a new pumping station at Conley Terminal. The pumping station will then push storm water to the Deer Island sewer treatment plant.

Under normal conditions, rain and sewage are piped to Boston's water treatment plant. But during heavy storms, runoff can overwhelm the sewer system, forcing runoff and sewage into relief valves that empty into the harbor. High bacteria levels after storms have forced the closing of beaches in South Boston an average of 21 times a year. The new tunnel and pumping station will hold overflows from all but the largest storms.

"This is a really important project to fulfill the promise of truly clean water in Boston Harbor," Ian Bowles, secretary of energy and environmental affairs, said in a telephone interview. "It also has dramatic environmental benefits in terms of the mix of species you will find in the water."

When the new system is in place, engineers will open gates when heavy rainfall approaches that will direct the combined sewer flow to the new North Dorchester Bay Combined Sewer Overflow Tunnel, where it will sit until the storm ends, before being pumped out. "This will give us real-time management of a storm," said Fred Laskey, executive director of the Massachusetts Water Resources Authority.

Since the vast majority of work on the tunnel will be underground, disruption to residents, workers, and beachgoers should be minimal, Laskey said. He said the authority has agreed not to conduct above-ground work during the beach season.

The M.L. Shank Co. of Providence is the lead contractor on the tunneling, Laskey said. Shank is joined by London-based engineering firm Balfour Beatty and Canton-based Barletta Engineering Corp. The work will be treacherous, Laskey said.

The 350-ton machine, custom-built for the project, will include a train more than 300 feet long. A driver will direct the train as it bores a hole about 19 feet in diameter 30 to 50 feet under William J. Day Boulevard. The tunnel will extend 2.1 miles from the Massachusetts Port Authority's Conley Container Terminal to the State Police barracks at the head of Carson Beach.

An average of 25 people will be working underground and 30 people above-ground at any given point during construction, said Massport spokeswoman Ria Convery.

"While the machine does a lot of the work, the support functions that allow it to work can be grueling at times," Laskey said.

While the MWRA previously has dug three deep-rock tunnels, this is the first tunnel of this size the authority is digging through soft rock. That means workers will have to stabilize the rock as they dig to prevent sinkholes from forming above.

Bruce Berman, spokesman for the group Save the Harbor/Save the Day, called the North Dorchester tunnel "the payoff for the Boston Harbor cleanup."

"We're going to have the cleanest urban beaches in America," he said. "It took a lot of patience and a lot of process to get everyone to agree that the goal wasn't a technical solution, but a real one that works for the people of Boston."

John C. Drake can be reached at jdrake@globe.com.