New 10-mile-long sewage tunnel takes treated wastewater to the Atlantic Ocean

What's said to be the world's longest offshore sewage tunnel will begin transporting treated wastewater beyond Boston Harbor and dumping it deep into the ocean.

After nearly a decade of construction, the $390 million tunnel will carry sewage through 24-foot diameter pipes before discharging the waste nearly 10 miles at sea. Currently, the treated sewage is dumped several hundred feet off a treatment plant in Boston Harbor.

A similar wastewater disposal system is already in place in Southern California. The award-winning, recently completed South Bay Ocean Outfall in San Diego takes sewage treated at the South Bay International Wastewater Treatment Plant through an 11-foot diameter tunnel to a point 3.5 miles offshore.

Jonathan Yeo, spokesman for the Massachusetts Water Resources Authority, told the Associated Press that the discharge to the ocean will be at least 85% pure water because of primary and secondary treatment at the Deer Island plant in which solids are allowed to settle out of the sewage and bacterial and chemical treatment are used to clean it.

The pipe will carry an average of 320 million gallons a day, but is capable of carrying nearly four times that amount.

Opponents say the discharge could harm the marine ecosystem, but the water agency, which operates the tunnel, says federal guidelines and an aggressive monitoring system will limit the impact, reports AP.

Edited by Tracy Fabre
Managing Editor, Water Online