Sewer project in the pipeline

South Coast Water District will be digging up some pricey dirt if proposed repairs to a tunnel and replacement of a sewer pipeline are approved.

The 55-year-old tunnel runs for about two miles from South La Senda Drive in Three Arch Bay north to Aliso Beach. The project and its effect on the environment are outlined in a recirculated draft environmental impact report available to residents for review at the district office and on its website. Written comments may be submitted through 6 p.m. Oct. 11. Oral and written comments were also solicited at a Sept. 9 public hearing.

"At one point they were going to gain access to the tunnel through [Three Arch] properties and the community was quite upset, but they are not going to do that," said former Mayor Kathleen Blackburn, a long-time homeowner in the gated community. "It is a big project and it was going to be disruptive to a good number of rate payers and that was a big consideration."

Project plans call for the enlargement and stabilization of the tunnel in a horseshoe shape so pipeline failures can be averted and the access made safer for district personnel who maintain and inspect the facility.

The tunnel measures about 6 feet wide and 6 feet high. It burrows through sections of the San Onofre Formation brecia, sandstone and siltstone. Most of it is located within beach cliffs, and it runs generally parallel to the cliff.

Loose rock and rotten timber supports that could harm workers or the sewer line will be removed and a new pipeline installed with the older line remaining in place. The existing grades will be maintained so lift stations will not be needed and there will be no operational changes in terms of function or capacity because of the project, according to Joe McDivitt, district director of operations.

The project will be scheduled to prevent any interruption of service.

About 1 million gallons of sewage from some 14,000 homes and businesses served by South Coast flow daily through the 24-inch pipeline, which will be left in place when the proposed new pipeline is installed.

The tunnel is presently unlined and unsupported in several sections, although some sections have been repaired since the tunnel was constructed in 1954. A 750-foot-long section was enlarged and fortified with shotcrete — sprayed-on concrete — or backfilled with sand in 2007. Those emergency repairs will be integrated with the proposed rehabilitation.