Project Location: South Laguna
A two-mile sewer tunnel built in 1954 runs deep inside the ocean-facing cliffs from Three Arch Bay to Aliso Beach in South Laguna. The tunnel houses a sewer line that conveys one million gallons of wastewater a day from South Laguna and north Dana Point by gravity flow to the Coastal Treatment Plant in Aliso Canyon. the volume of wastewater carried by the line is approximately 25% of the District's total daily load. The tunnel is undersized, deteriorating and unsafe, posing risks of injury to workers and risks of damaging or breaking the sewer line itself and causing a sewage spill onto the beaches along the two-mile South Laguna coast.
Project Goals
- To prevent sewer spills. The District has zero tolerance to sewer spills and there have been no spills from this line onto the beach or ocean since it was built, due to ongoing inspection, maintenance, and emergency repairs.
- To prevent worker injury or death. Job safety is #1. District crews and contractors inspecting or repairing the sewer line risk critical injuries due to falling rocks and beams inside the deteriorating, cramped tunnel. The improved tunnel will allow line repairs to occur safely and much more quickly – minimizing the potential for sewage to spill into the ocean.
No workers have been injured and no sewer spills have occurred in the tunnel.
The District seeks to maintain that track record.
Project Background
Twenty-five percent of the wastewater collected every day in the District flows through the two-mile tunnel and sewer line.
- Two-thirds of the wastewater originates from Niguel Shores, Monarch Bay, Monarch Beach, the Headlands and other communities in northern Dana Point -- about 670,000 gallons per day.
- One-third of the wastewater originates from residents living on or near the bluffs in South Laguna -- about 330,000 gallons per day.
The tunnel was originally hand-dug and blasted from the cliffs in 1954. At that time, there were very few homes on the South Laguna bluffs, and the communities of Monarch Bay, Niguel Shores and others were not built. Over the years, as more homes and people arrived, the original 21-inch sewer line in the tunnel was replaced with a 24-inch line.
Back in 1954, the Districts’ customers, engineers, and elected officials had a vision to minimize visual impacts, maintenance and operating costs by constructing a unique sewer tunnel tucked away in the bluffs. The two-mile sewer line conveys wastewater 100% by gravity to a single lift station – eliminating the need to build three or more lift stations along the coast and incur significant pumping costs.
Project Description
On average, the tunnel is 6 feet wide and tall, but much smaller in many places. The support timbers are deteriorating and the earth and rock walls are crumbling. The pipeline has sustained damage and is at risk. With 10-inch beams protruding into the tunnel and at 2-foot diameter pipeline running through it, there is not much room for maintenance workers to maneuver safely and perform necessary repairs.
In 2007, the District enlarged and stabilized a 750-foot segment of the tunnel as part of an emergency repair project at Thousand Steps Beach, which took eight months and cost $5 million.
The District estimates that the remainder of the tunnel rehabilitation, about 10,000 feet, and the installation of a new pipeline will take six years and cost about $50 million.
- Tunnel stabilization. To stabilize the interior of the tunnel, the District must enlarge it to reach solid rock, due to the soil geology of the area. The enlarged tunnel also provides a safe, improved work environment. The reconstructed tunnel will be about 7.5 feet in diameter, possibly larger in sections, structurally reinforced and lined with concrete.
- Pipeline replacement. The 24-inch pipeline installed in 1974 will be completely encased by a concrete floor throughout the length of the tunnel and retained for possible emergency use. A new 24-inch pipeline will be installed on the concrete floor above the old line.
Reserves, operating revenues and proceeds from the recent sale of District bonds will pay for a portion of the estimated $50 million project. Additional bonds could be sold in the future. Bond financing is a long-term funding mechanism that spreads costs to future customers who will also benefit from the project.
The reconstructed tunnel is expected to last 100 years without major rehabilitation.
Project Status
The public contributed numerous comments during the Environmental Impact Report (EIR) process. Following 12-months of meetings, workshops, community outreach, and public input, the Board certified the EIR (see documents below) on November 11, 2010.
An extensive permitting process is now underway with state, county and local agencies and is expected to take a year. Acquisition of necessary easements from residents for the tunnel work is also in progress. Project design is at 60%.
Given the project’s scope and complexity, the District is employing a Constructability Review Process for contractor selection. Two pre-qualified contractors will be asked to work directly with the District and its tunnel engineers for several months before submitting final project design plans, project cost estimates, and target contract prices. The contract will be awarded and construction will start in 2012.
Project Process
- Secure necessary permits
- Secure necessary easements
- Award construction contract
- Mobilize 4th Ave. staging area. A fenced staging area will be located on District property at 4th Ave. and South Coast Highway during the project.
- Start construction
- Mobilize temporary staging areas on Thousands Steps Beach, Camel Point Beach and Aliso Beach according to construction schedule.
- Complete tunnel reconstruction and pipeline installation (2017-2018)
Project Information & Documents
