Engineers Looking For Possible Big Dig Sinkhole

State contractors are boring into the ground in an effort to determine whether a sinkhole has formed under a Big Dig tunnel and if so, how to plug it.

Highway officials revealed the existence of the possible sinkhole several months ago but said it posed no public safety risk.

While constructing the Interstate 90 Connector Tunnel more than a decade ago, Big Dig engineers chemically froze some of the ground near the Fort Point Channel to prevent it from caving in or leaking. Officials expected the ground would eventually thaw and slowly begin to settle, but they were surprised to discover that the rate of settling was about an inch a month.

Contractors plan to dig four, 135-foot-deep holes and take samples of earth they hope will reveal the extent of the problem.