The city has received federal approval to build an estimated $200 million, 3.2-mile tunnel to move sewage from a Kane­ohe treatment plant to a Kailua wastewater facility.

The concrete tunnel, which will be 10 to 13 feet in diameter, will start at the Kane­ohe Pre-Treatment Facility near the Bayview Golf Course and end at the Kailua Regional Wastewater Treatment Plant in Aikahi. The proj­ect will entail boring a tunnel through One­awa Hill.

An environmental impact statement showed no significant impact along the planned route.

Construction is expected to begin in December 2013. The scheduled completion date is June 30, 2018.

The city rejected a proposal to build a 2.9-mile force main — a pressurized main pipe — 25 feet below the sea floor of Kane­ohe Bay and one that would have followed the path of the H-3 freeway.

The existing line, a 42-inch concrete main, is 3.1 miles long under Kane­ohe Bay Drive. The city is required to install a replacement under a 1995 legal settlement over sewage spills.

Various community groups, including the Sierra Club and the Surfrider Foundation, sued the city in 1992 because of wastewater discharges. Damaged lines in the current system have allowed groundwater and storm water to enter and overload the sewer system, resulting in spills. Floodwaters can also enter the system through manhole covers during heavy rain.

The city resolved the lawsuit in 1995 under a consent decree with the federal Environmental Protection Agency, with deadlines to complete improvements over 20 years.

Under the decree, a new discharge main running from the Kane­ohe Wastewater Pre-Treatment Facility to the Kailua Regional Wastewater Treatment Plant must be built.