Outfall Levee Repair

Outfall Levee Repair

The South Bayside System Authority (SBSA) owns and operates a regional wastewater treatment system serving the communities of southern San Mateo County on the bay side of Skyline Blvd. The SBSA facilities include a 60-inch diameter outfall used to transport treated water to a diffuser located approximately 6000 feet off shore in the San Francisco Bay deep water channel. The outfall crosses under the Redwood Shores outer levee approximately one-quarter mile north of Steinberger Slough. The outfall pipe is constructed with reinforced concrete with bell & spigot "o-ring" joints. The pipe segments are twelve to fifteen feet in length. Localized settlement in the vicinity of the levee has caused separation of several pipe joints under the levee. During high tide and outfall flow conditions, the joint separations can leak with leakage resulting in erosion on the bay side and land side of the outer levee. Divers have been employed to repair the leaky joints from the inside of the pipeline. However, their efforts have not achieved the complete cessation of the leaks. The work on this project is to replace approximately 220 lineal feet of the existing pipeline with a more flexible pipeline material that will accomodate future anticipated localized differential settlements and eliminate future leakage. A steel sheet-pile coffer dam will be constructed enclosing the existing pipe, the existing pipe removed, new bedding and pipe placed. The coffer dam will serve as a temporary trestle from which the work will be performed. All work access will be from the treatment plant site. Repairs will also be made to restore the stability of the levee by replacing the eroded material with native bay mud. The work needs to be completed as soon as possible and is planned to be completed by fall 2005.

Redwood City

San Mateo