Lessons Learned from the CIPP Lining of a 72-inch Sewer Interceptor Amidst Wetlands and Landfills

Abstract

The City of Palo Alto (City) owns, operates, and maintains the 72-inch RCP gravity Joint Intercepting Sewer (JIS). Originally constructed in 1972, the 9,000-foot long JIS is the main sanitary sewer transmission system to the Regional Water Quality Control Plant (Plant), conveying more than half of the Plant’s influent flow. Following a condition assessment in 2020, the City determined that approximately 2,400 feet of the JIS pipeline immediately upstream of the Plant’s headworks required urgent rehabilitation. The JIS is buried 25 feet deep beneath a public trail adjacent to Byxbee Park and the Baylands Nature Preserve along the South San Francisco Bay shoreline. The park and shoreline include a heavily used hiking network, including a trail over this portion of the JIS. Additionally, Byxbee Park is constructed on a closed landfill, and active leachate pumping is discharged to the JIS. The JIS is also close to a wetland, home to protected migratory birds, foxes and other wildlife treasured by the regional community. The JIS rehabilitation design used cured-in-place pipe (CIPP) lining and non-structural rehabilitation of three maintenance holes originally planned for completion in 2024. Several construction challenges resulted in the project being delayed, and planning to finalize construction in 2025. This paper highlights construction challenges and lessons learned that resulted in the successful rehabilitation of the downstream portion of the JIS.