The victim's foot reportedly got caught under the tread, which pulled him under.
Officials say the operator of excavator tried to shut it down, but it was too late.
The 49-year-old man, a contractor for United Water, was pronounced dead at the scene.
The operator was taken to Valley Hospital in Ridgewood for treatment of shock.
The worker was employed by J. Fletcher Creamer & Son, according to authorities. He was installing the water main for United Water as part of a long-term construction project.
The state's Office of Occupational Safety and Health Administration will investigate the death.