State Police divers are resuming their search of the Charles River Wednesday, near the site of the water main break that led to the boil water order that affected 30 communities in eastern Massachusetts over the weekend.
The divers are looking for a giant metal coupling, or "collar," which used to be wrapped around the pipe. It weighs about a ton and gave way when the main burst on Saturday. Investigators believe it is the key to figuring out what went wrong.
Massachusetts Water Resources Authority emergency preparedness director David Gilmartin says a contractor will begin dredging portions of the river Wednesday.
"It washed a lot of gravel into the river, so we'll be pulling a lot of that material out of there to look underneath the silt," Gilmartin said.
For a conversation about what investigators could find, WBUR turned to David Sykora, principal engineer for the Natick office of Exponent Failure Analysis Associates, a global firm that figures out how and why things crack and break.
Sykora said that the metal collar probably bears evidence of the story of Saturday's failure — but it could have any number of endings. "If it's a bolt, for instance, we'll be looking to see if the bolt was corroded in any way, or if the materials that were used to create the bolt were the proper materials."
Part of the mystery of this pipe break, said Sykora, is the fact that the pipe in question was only seven years old. "Typically, when you're dealing with newer materials, they have not been in the ground long enough to have corroded or deteriorated or aged," Sykora said.
Sykora said it is often a diverse range of experts dispatched to figure out problems like this one — including mechanical engineers, geologists and material scientists. "You don't know in advance just what you're going to learn," Sykora said.
Even if they don't find the collar, investigators may still come up with an explanation for last weekend's failure. For one thing, they already have the rubber gasket involved in the explosion, which wrapped itself around a telephone poll as water gushed out of the pipe.
"Because this was such a large failure and impacted so many people in the Boston area, there will be an important focus on trying to understand why this occurred," Sykora said.
This program aired on May 5, 2010.