See The Tunnel

400 feet

Deer Island Wastewater Treatment Plant

Sea level

Shaft

Seafloor

THE PLAN

A Diffuser caps

A

B

Just after the 9-mile mark, the tunnel is too small for the Humvee to go farther. From there, a three-man team walked to the end of the tunnel, dragging a boat with equipment.

B

C

Riser leading to seafloor diffuser

C To remove each 65-pound plug, workers had to crawl deep inside a 30-inch-wide pipe, and then repeat that task 54 times.

Backup air supply

Risers

Tunnel

Bedrock

100 feet

To reach the diffusers, the five-man crew drove a Humvee; a trailer in tow carried a rack of liquid gas tanks as well as another Humvee that faced the opposite direction for easy exit. The tunnel is too narrow to allow a vehicle to turn around.

Main air supply

Trailer

Winthrop Logan Airport

BOSTON

el

n Tun

Diffusers

Deer MASSACHUSETTS Island BAY Harbor Islands

THE TUNNEL

( Areas of detail at right )

The tunnel was designed to carry treated sewer water more than 9 miles into Massachusetts Bay. The water exits the tunnel through 55 risers and diffuser caps, slowing and spreading out the flow of water.

Safety plug

Along the final mile or so of the tunnel, the floor ramps up and the width of the tunnel chokes down.

Boat Compacted rock

9.5 miles

SOURCES: Massachusetts Water Resources Authority, attorneys John Prescott and Robert Norton, and Globe archives