West Yost is designing upgrades and repairs to a water tank and pipelines for the City of San Bruno, California. The steel pipeline is 70 years old and in a hard to access area with steep slopes that can exceed 30% and covered in poison oak. Fixing leaks on this pipeline has proved to be very difficult for City staff, and a major failure of this pipeline would be problematic for the City. The 70 year old steel water tank has experienced severe corrosion from proximity to the Pacific Ocean.
Trenchless replacement options are being considered for the pipeline; however, the rugged terrain, remote location, and capacity requirements make those options very challenging. Instead, the pipeline design will likely utilize an open-cut construction method, which will introduce additional construction challenges caused by environmental considerations regarding the open space recreational area owned by the City, the San Francisco Public Utilities Commission, and the National Parks Service (Golden Gate National Recreation Area).
The tank, which will be replaced with a concrete tank, is located on a small project site with steep slopes and less than one mile from the San Andreas fault. The primary geotechnical consideration will be strong ground motion and West Yost is working closely with geotechnical and structural engineers to design a tank that will resist failure in an earthquake. We are also designing additional seismic measures that will automatically close valves to preserve water in the tank in the event of earthquake and a break in a water pipe. The site adds challenges for vehicular and construction access.