Balfour Beatty Infrastructure, Inc. began work in August 2007 on the Dorchester Tunnel in Boston, a $146 million job for the Massachusetts Water Authority. The three-year project is a joint venture with M. L. Shank, Co.

The work involves cutting an 11,000-foot tunnel to receive storm water runoff that will empty into a pump station. The tunnel is 17 feet in diameter and is constructed of a series of four-foot rings that create a watertight internal surface. The top of the tunnel lies 30 feet beneath the street.

A sophisticated cutting machine that tunnels through various materials -- clay, sand, organic material, gravel -- is progressing at a rate of 48 feet per day during the project’s two nine-hour shifts.