North Stonington - It's not quite the "Big Dig," but heavy machinery was rumbling around Shunock Brook last week.

Archaeologist Michael Raber was directing a crew of contractors as he went about exploring the foundations of the old Town Hall Bridge, which washed out during the floods of March 2010.

The town needed to create a temporary driveway and move telephone poles before the dig began, and First Selectman Nicholas H. Mullane II said he was glad to have finished the work before the anticipated arrival of Hurricane Irene.

It's all part of a process to preserve and record the historical site of the old bridge that the town must complete before it builds a new Town Hall Bridge, Mullane said recently. The bridge is on the National Register of Historic Places and the town must comply with local, state and federal guidelines.

"It's required because it's in a federal historical district and we're getting federal funds for the replacement of a historic bridge," Mullane said. "We have to get that done before we build. (Raber) will do a historical review. He wants to understand how the bridge was built and he'll write a report of what was historically there."

Raber spent time at the site in April and released a large report with a historical abstract of the bridge and town, along with diagrams, figures and photographs of the bridge site.

Last week, he spent about two days in the brook, using an excavator, Bobcat and surveying equipment to learn more about the site and what "the very bottom courses were resting on."

He has no exact date, but Raber estimates the bridge was originally built in the early 1800s. Raber wanted to find the footings of the bridge this time around.

"I found the base of the arches, which were on big stone slabs and gravel," he said. "A lot of it seems pretty level."

The age of the bridge makes it an important piece of the state's architectural history, Raber said.

"This bridge was a significant example of a twin arch stone bridge," he said. "No two are exactly the same. This wasn't done by engineers, just masons who knew what they were doing."

Raber said he's finished his part but would most likely be back in a few weeks when the construction team builds the coffer dams. He said that process would expose more of the bridge footings and aid his research, which he'll turn into a second report to the town.

All aspects of construction of the bridge could cost close to $2 million, and a special town meeting was scheduled for Monday to approve the appropriation. The Federal Emergency Management Agency is set to pay 75 percent of the cost, meaning the town will pay approximately $485,000.

Mullane said the archaeological dig was a major hurdle and the project remains on schedule. If it continues as scheduled, Mullane said a new bridge could be open by the end of the year.

s.goldstein@theday.com