The South Coast Water District plans to present revisions to a proposed project that would shore up a two-mile underground tunnel and replace an aging sewer pipeline in South Laguna.

City planning commissioners will review the changes to the estimated $80-million project when they meet next week.

Concerned about the possibility of traffic and construction-related noise, residents called for changes to how the work would be implemented during an October Planning Commission meeting.

Those requests were taken into considerations when the proposed changes were drafted, district spokesman Steve Greyshock said.

The district has proposed a 15,000-square-foot staging area at Fourth Avenue and South Coast Highway that would provide an area for work-related vehicles to come and go.

To mitigate possible noise, the proposal calls for the three sides of the staging area that face houses to have 12-foot-tall sound walls, except for a 10-foot sliding gate for vehicles to enter and exit along Fourth, Greyshock said.

"There was a section of the sound wall abutting Virginia Way that was proposed at 10 feet, but the district has amended the plan to build that section up to 12 feet in response to its dialogue with residents," Greyshock said in an email.

A portion of the side facing Virginia Way would have 12-foot-tall beams, but the sound wall would be only 10 feet, Greyshock said.

The district will conduct noise surveys once construction begins — twice in the first month and once each in the second and fourth months, according to a November district letter to commissioners and Community Development Director John Montgomery.

"The sound wall is modular, so if the sound retention goals can be achieved at a lower height, and residents would like it at a lower height, the district has the ability to [lower the wall's height]," Greyshock said in an email.

Residents were also concerned about construction vehicles using Virginia Way to access the staging area.

District officials listened to those concerns and proposed that vehicles use only Fourth and South Coast Highway to access the staging area and not Virginia, Greyshock said.

The district does not plan any changes to the underground portion of the project, Greyshock said.

The district is seeking conditional use and coastal development permits to repair the tunnel, which is six feet wide by six feet high, and runs parallel to Coast Highway. The stretch is primarily located beneath privately owned oceanfront properties that span from about Three Arch Bay to Aliso Beach Park, according to a district staff report.

The tunnel is deteriorating and repairs are needed to prevent it and the sewer pipe from failing, according to the report.

The tunnel, with an interior of earth, rock and timber supports, houses a sewage pipeline that handles 1 million gallons of sewage daily from South Laguna and Dana Point, according to the district website.

District officials want to shore up the tunnel's interior with "shotcrete," a spray-on form of concrete.

The five-year project is expected to cost $80 million, Director of Operations Joe McDivitt said.

Construction could begin in 2014.

District staff also took the public on tours of the sewer tunnel after the October planning commission meeting, which Greyshock said fostered community involvement.

The Planning Commission will take place at 6:30 p.m. Wednesday in City Council chambers at City Hall, 505 Forest Ave.