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Boston Globe Features MetroWest Water Supply Project

Far below Boston's western suburbs, massive machines are boring their way through miles of bedrock to carve out a new water supply tunnel.

It's a distinction that will probably never find its way into the tourist brochures alongside Beacon Hill and the Old North Bridge, but Greater Boston is well on its way to claiming the title of America's premier deep-rock tunneling city.

Hard on the heels of several other major tunneling projects, three gigantic machines are now deep underground below the western suburbs, starting to chew through some of the hardest rock ever attacked by boring machines to carve out a 17.6-mile water-supply tunnel running from Marlborough to Weston.

The work, some of it taking place the equivalent of 40 stories below ground, promises a much more reliable water supply for Greater Boston's 2.5 million residents sometime early in 2004. At an annual cost of about $80 for at least 20 years on the average consumer's bill, the tunnel will supplement and replace weak links in the chain of aqueducts and reservoirs that ferries water from the Quabbin and Wachusett reservoirs to the distribution network that fans out from Weston.

Among US cities, Boston has come to rank as a leader in the use of tunnel-boring machines for construction projects, beginning inauspiciously back in the 1960s with a machine that dug just 300 feet of a Dorchester water tunnel before it got stuck and was replaced by miners wielding drills and dynamite.

Since then, newer machines have successfully been used on a Danvers-Beverly water tunnel, part of the MBTA Red Line between Porter and Davis Squares in Cambridge and Somerville, and the MWRA's 14 miles of sewer tunnels going from Nut Island to Deer Island and from Deer Island to the outfall pipes in Massachusetts Bay, says Robin Dill, a Boston geotechnical engineer who worked on several of the projects.

"Boston is by far the most active city in the country right now for deep tunneling like this," said Michael McBride, the deputy capital construction manager overseeing the new MetroWest Water Supply Tunnel for the Massachusetts Water Resources Authority.

But MWRA engineer John W. Critchfield laments that "one of the problems with tunneling is that the average person can't see the work product. All they can see is the mess. Very few people will ever get a chance to get down here and see this thing. That makes it a tough public-relations problem."

The recent tunneling boom was a lucky break for the authority and its contractors, including Modern Continental/Obayashi and J.F. Shea/Traylor Brothers/S.A. Healy: They can draw on a readily available, knowledgeable workforce of non-claustrophobic tunnel workers, operating engineers, and electricians.

Among them is Brian McCormick, an operating engineers Local 4 veteran who spent more than four years on the overnight shift drilling the nine-mile outfall pipe from Deer Island, and now has signed up for five years under Framingham.

After all that time grinding rock and never seeing sunshine, what could entice a man to go back to the life of a mole? "Money," McCormick joked one recent day as he prepared to climb into the crane-borne metal cage that serves as the elevator at the 400-foot-deep shaft below Framingham where the tunneling began last month.

With overtime, McCormick is looking at making upwards of $25 an hour for the next several years, but he admits to some excitement about what will surely rank as one of the state's historic construction feats.

"It's a challenge. I take everything the rock gives me, and I just try to give it a little more myself," said McCormick.

"We love it down here," agreed McCormick's colleague Tom Brown, a day foreman working out of Framingham who has spent 22 of his 41 years digging tunnels as far away as Hawaii. His brother, Jim, works the overnight shift. "It's our life, this job. It gets in your blood."

Already, two of the three $8 million boring machines have drilled several hundred feet east and west from the Framingham shaft - located, conveniently enough, at the New England Sand and Gravel Company, which is taking 70,000 truckloads of rock as partial payment for leasing the site. It will use most of the rock to fill quarried areas.

The third machine, which will bore the segment west from the Sudbury Reservoir dam in Southborough to a planned water treatment plant near the Ken's Foods salad-dressing factory at Walnut Hill in Marlborough, has been lowered into the 280-foot shaft piece by piece and assembled. It should start crunching through rock in another week or so.

The 16-foot-diameter water tunnel will provide a long-overdue replacement for the Hultman Aqueduct, which carries water just under ground level from the Wachusett to the Norumbega Reservoir in Weston, where it is fed into pipes that serve most of the communities inside Route 128.

The new tunnel will snake along the same route, but hundreds of feet below the 58-year-old Hultman. The aqueduct leaks in at least 35 places, MWRA officials say, but because it carries 85 percent of all of the metropolitan area's water, it can't be shut down for repairs. Even digging around the 12-foot-diameter aqueduct to find and fix leaks could cause a catastrophic failure that would leave entire neighborhoods dry for weeks, force hundreds of thousands of people to boil their tap water and probably shut down Boston's financial district and many of its hospitals for days or weeks. Some specialists say a failure of the aqueduct could mean $100 million in economic losses a day.

By world standards, the length of the new tunnel is not remarkable. But the granite, quartz and other rock to be gouged out "is some of the hardest rock that has ever been mined anywhere," said McBride.

In many areas, according to MWRA engineer Critchfield, an international tunneling veteran, the rock is nine to 15 times tougher to crack than the typical city sidewalk.

The machines that will do the cracking differ slightly in specifications, but all are locomotive-sized cylindrical giants that work the same way. Ringed by giant "shoes" that press outward to grip the tunnel walls, they press forward with huge cutting heads containing dozens of super-hardened steel wheels.

As their heads turns counterclockwise at a rate of 6 to 12 revolutions a minute, pushed by 2,400- horsepower electric motors that could easily pull a freight train, the 17-inch diameter wheels - each weighing easily 300 pounds - score a pattern of concentric circles on the rock face.

Lateral cracks between the circles cause the rock to drop out in cheeseburger-sized chunks that are then carried by a scoop on the cutting wheel to a conveyor belt. As often as once a week, depending on the rock, the wheels must be removed and remachined to stay sharp.

While the twin Atlas Copco Robbins machines in Framingham move six feet at a time, the CTS machine that will move west from Southborough has the capacity to move continuously. In a maneuver operators call "the shuffle shoe," it can grip the tunnel wall with two shoes, slide its other two about 24 inches forward, and repeat the process so it never stops grinding ahead. A laser mounted on the side of the tunnel projects a beam through an opening in the machine onto the rock face. Aided by computers, the machine operator - riding in a cab just behind the boring head - uses the laser as a target to make sure the tunnel stays within inches of the proper alignment over the 17 miles. That's an accuracy of better than 99.9998 percent.

As the machines move forward, tunnel workers can drill through slots in the shoes to install grouting, support rods, and mesh to shore up weaker sections of rock.

On a good day, working three shifts, crews can push through 150 to 200 feet of rock. But engineers expect there will be days - especially going through two inactive fault zones - when 40 or 50 feet will be a success. Framingham resident engineer Tony Stewart of the engineering firm of Stone & Webster, which is managing the project for the MWRA, says "some healthy competition" has already sprung up between the crews headed east and west from the entry shaft. As impressive as the huge boring machines are, they are only one aspect of the tunnel construction, which also includes these elements:

Five "risers" to convey water from the new aqueduct to municipal water departments will be excavated from the bottom up to minimize truck traffic on residential streets in Framingham, Southborough and Weston. Four-foot-diameter augers will drop rock into the tunnel to be carried out by conveyors.

In Southborough and Weston, vertical shafts will be drilled to move water between the Hultman and the new tunnel, so three segments of the Hultman can be shut down for repairs. In Framingham, the MWRA built a $3 million water treatment plant to collect the water that leaks into the tunnel from the surrounding rock and drains down into a living-room-sized sump well 210 feet below sea level, the project's deepest point.

Because by the time the tunnel is completed late in 2003 as much as 4 million gallons a day of groundwater could be seeping toward the Framingham shaft, the MWRA had to develop a way to filter out sand and pollution before discharging the water into the Sudbury River.

"The last thing we want is some sort of plume going out into the river," said Critchfield, "so we have a treatment plant here that would be suitable for a small municipality."

Once all the tunnel segments are bored, they will be lined with a 12-inch layer of concrete, reinforced in some fragile areas with steel panels.

Next the MWRA will fill the tunnel with water, add a huge dose of chlorine for disinfection, and use the hydraulic force generated by the Wachusett Reservoir 390 feet above sea level to flush the slug of chlorine through the pipe with more water.

Near the Charles River in Weston, the chlorine will be chemically deactivated and then pumped into the river under close monitoring.