Tunnel project nears its end

After eight months, South Coast Water District will wrap up a $5 million capital improvement project at Thousand Steps Beach by the end of August.

Workers, equipment and vehicles are expected to be off the beach by Aug. 31, Linda Homscheid, water district spokeswoman, said.

The district’s Emergency Sewer Tunnel Stabilization and Pipeline Protection project began in January to make improvements to an 800-foot section of a sewer tunnel inside the bluffs at Thousand Steps Beach.

The tunnel houses a major sewer line that conveys more than one million gallons a day of wastewater for treatment from South Laguna and northern Dana Point.

“As far as we know, we are the only sewer collection system in Southern California that has a sewer line inside of a tunnel,” said Mike Dunbar, South Coast Water District general manager.

“Prevention of sewer spills is the No. 1 priority for our sewer collection system,” said Dunbar. “Since 1954 when the tunnel was built, there have been no sewer spills from the sewer line onto the beach, and the District seeks to maintain that track record for the community and the environment.”

Engineering and geotechnical assessments had identified this section of the tunnel as needing emergency repairs due to severe deterioration, according to the district. The two-mile tunnel, built more than 50 years ago, runs inside the bluffs from Aliso Beach to Three Arch Bay.

The tunnel’s condition was a significant safety hazard for workers who inspect and maintain it, and a threat to the sewer line itself — which can crack or break due to falling rocks and rotting timber, Homscheid said.

Homes were not endangered by the deteriorating tunnel, district officials said.

From January to May, crews excavated, enlarged and fortified a particularly deteriorated area of the tunnel south of the Thousand Steps staircase.

A 35-foot passageway into the bluff and a 50-foot section of the tunnel containing the sewer line was improved, and concrete was poured around 800 feet of the sewer line for protection.

During the project, workers noticed accelerated deterioration of the tunnel’s ceiling and walls. As a result, crews excavated, enlarged and fortified an additional 350 feet of the tunnel from June to August.

Since the project began in January:

 49 work boats have landed at the beach, including one barge, to deliver supplies and equipment and remove debris;

 1,058 super-sacks of rocks and dirt and 77 pallets of timber were removed from the tunnel and taken away by work boats for disposal;

 264 super sacks of concrete were delivered by work boats and used to protect the sewer line; and

 7,862 bags of “shotcrete” (spray-on concrete) were delivered by work boats and sprayed onto the tunnel’s ceiling and walls.

The sewer tunnel was hand dug and blasted from the bluffs 53 years ago.

The 24-inch reinforced plastic sewer line inside of the tunnel — installed in the 1970s — still has more than 30 years of useful life, unless it’s damaged by the deteriorating tunnel, Homscheid said.

South Coast Water District has begun plans to make improvements inside the rest of the tunnel beyond Thousand Steps Beach, from Aliso Beach to Three Arch Bay.

The district is conducting an engineering assessment to determine the condition of the tunnel beyond Thousand Steps Beach, and will conduct a study to determine the environmental impacts of making improvements in the remainder of the tunnel.

The district plans to complete the assessment and study this year and to start design work on tunnel improvements next year.

Repair work in the rest of the tunnel could start in 2008, Homscheid said.