Lower Northwest Interceptor Pipeline

​The Lower Northwest Interceptor (LNWI) wastewater pipeline is a 19-mile sewer line that serves as a critical link from West Sacramento/Natomas to the Sacramento Regional Wastewater Treatment Plant in Elk Grove. The LNWI is an ambitious project by the Sacramento Regional County Sanitation District (SRCSD) and is a result of a cooperative effort among area governments to ensure that the entire region is provided with the highest quality sewer service possible. The overall program includes two new pump stations, five pipeline projects, and 14 tunneled crossings, two of which are under the Sacramento River.

SC Solutions was engaged to provide seismic evaluation of the Southern and Northern Sacramento River Crossings for the LNWI. The seismic model consisted of the launching and receiving shaft, embedded pipes within the shafts, and a buried tunnel region that extends below the river. Seismic time history analyses were performed for both crossings. The analyses focused on determining the expected level of pipe steel strain in the tunnel region and determining the relative axial displacements and rotations through the pipe couplings. Effective soil springs (i.e.: force-displacement relations) were varied in the analyses to determine overall system sensitivity.

The advanced seismic analyses provided by SC Solutions supported the verification of seismic performance and provided an overall schedule reduction as well as cost savings to the project.