Designing a Critical Interceptor in an Earthquake Prone Floodplain with Limited Access: The Santa Ana River Interceptor Relocation Project

The design team of Tetra Tech and HDR was retained by Orange County Flood Control District (OCFCD) to design the relocation of the existing Santa Ana River Interceptor (SARI) as part of the U.S. Army Corps of Engineers (Corps) Santa Ana River Mainstem Project. The SARI line is owned and operated by Orange County Sanitation District (OCSD), and a third agency, Santa Ana Watershed Project Authority (SAWPA), owns 30 MGD of capacity within SARI. The underlying project objective is to relocate the SARI line outside the limits of the Santa Ana River 100-year flood plain and provide complete maintenance access along the entire 3.9-mile route for this new 54-inch interceptor. This involves crossing a public golf course, constructing an 1,100-foot-long tunnel and inverted siphon under the Santa Ana River, tunneling up to 70 feet deep over an additional 2,800 feet of alignment in shallow groundwater, crossing a major earthquake fault and landslide area, working adjacent to a major freeway, crossing behind a recently constructed Corps of Engineers sheet pile and tieback system, and open cut construction up to 25 feet deep in narrow rights-of-way. All while protecting endangered species and riparian habitat.