The MWRA has found eight projects where contractors have used couplings made by the same company that manufactured the massive pipe clamp that failed last Saturday, triggering a drinking water crisis for 2 million Greater Boston residents.

The discovery was revealed today at a board meeting of the Massachusetts Water Resources Authority as top officials discussed the investigation into the incident that forced people in 30 communities to boil water before drinking for 2 and a half days. Hundreds of millions of gallons of water also poured into the Charles River.

MWRA officials said the clamp that failed last Saturday was made by the Brico company and that they have found the same company has supplied clamps for eight other projects. The projects involved range in size from a half-mile length of pipe to projects that are several miles long.

They said the clamps used in the other projects range in size, and are often of different design.

MWRA officials stressed they do not yet know if the failure of the clamp – which was installed to close a gap between two massive water supply pipes -- was due to a manufacturing flaw.

The MWRA also said that their search of records showed that during construction, the design of how the two pipes were to be coupled together was changed once. They also said that the type of product used was changed twice. Such changes are common in construction, but the MWRA said it was not yet clear what prompted those specific alterations.

The contractor -- a consortium of companies called Shea, Traylor, Healy -- notified the MWRA in advance about its plans, and the MWRA agreed to the alterations before they was done, officials said.

As the board was meeting this afternoon at MWRA headquarter in Charlestown, efforts to find the missing the clamp were underway in Weston where the pipe failed on Saturday. The search began on Tuesday when State police divers went into the river; dredging began today.

But by late afternoon, the clamp remained missing. "We are starting to grow frustrated with our inability to find it,'' said Laskey. "This is a 15-foot-long piece of steel...It’s a huge piece of metal.''

Laskey said they had recovered the rubber gasket that lay underneath the clamp, a portion of which he showed off at the board meeting today. He said there is a remote possibility the missing clamp was buried under the concrete poured into the repaired pipe, but thought it was more likely swept away in the deluge.

In Weston, the dredging began at about 10:30 a.m. -- and when the work was halted at 3 p.m., the clamp had not been found.

During the day, large container trucks backed up to the banks of the Charles and an excavator dumped slushy dirt into them. The trucks, oozing from the sides with river water, dumped their loads onto an adjacent parking lot about 500 feet away, which had been prepared earlier with a perimeter of hay bales, a environmental precaution to prevent spillage.

On Wednesday, workers put into the river a 700-foot bright-orange boom with an anchored "siltration wall" to prevent sediment from drifting down the river during dredging.

The excavator dug mostly on the right side of a footbridge that crosses the Charles, linking Weston to Auburndale. Some MWRA officials have said it is more likely that the metal ring, measuring 10 feet in diameter and weighing about a ton, may be submerged to the left of that bridge, along the banks on the Weston side. That area will be dredged as well, officials said.

Dozens of pickup trucks were parked at the MWRA station, as were a bulldozer and other earth-moving vehicles belonging to Barletta Engineering, the company contracted by the MWRA to perform the dredging. Men in hard hats and steel-toe boots directed truck shipments of crushed stone, which was spread over a dirt path to the banks of the Charles, to stabilize the bank and prevent erosion.

Large wooden beams were hoisted by a bulldozer onto the water and served as a walkway for workers supervising the project. The busy pace throughout the morning subsided by noontime, when many of the workers ate lunch from their trucks, but by 1 p.m, the trucks began running again, and the workers donned their hardhats and headed back to the river's bank.

Near a small, red-brick water pumping station, about 20 feet west of where the underground main burst and washed out a large portion of an adjacent hill, workers walked an imaging machine over newly piled soil that had replaced the soil that was washed Saturday into the river.

On Wednesday, an excavator dug a deep hole at that spot, looking for fragments of the large ring that apparently broke and caused the main to rupture. The excavator did not dig up any such fragments and replaced the soil.

Meanwhile, a non-profit environmental organization collected water samples today after getting dozens of complaints from boaters about discolored water in the Charles.

Kate Bowditch, the director of projects for the Charles River Watershed Association, said the organization is concerned tha if the "total suspended solids," or TSS, exceeds 15 milligrams per liter, it would affect the herring migration up the Charles River.

"The herring are an indicator species that gauge the health of the ecosystem, and if the solids are too concentrated, they may turn back," she said.

Bowditch said the herring population has been growing because the water quality in the Charles and Boston Harbor has improved in the past few years.

Testing could take several days. The organization plans to take up to eight to 10 different samples, working its way from Weston toward Boston.

Bowditch said the results will be shared with the Department of Environmental Protection, and local conservation commissions. Based upon her personal observation, however, she said that the concentration probably isn't that high.

About a dozen loads of soil were taken from the river, evenly spread out to about 6 inches deep, along the parking lot by an excavator. Officials said there had been no sign of the ring, not even a small fragment.

After workers headed home, a flat-bed truck hauled another excavator to the site, joining two already there. The dredging is expected to resume at 7 a.m. Friday.