The Challenge with Gravity: How to Build a Better Trunk Sewer

The Eastside Trunk Sewer (ESTS) is a gravity sewer that conveys approximately half of the wastewater from the City of Rohnert Park, California (population ~45,000) to the City’s main pump station. This 5.6 km (3.5 mile), 460- to 1,060 mm (18- to 42-in) pipeline conveys up to 53 ML/d (14 mgd) from various contributing sewers and traverses City commercial and residential corridors.Planning and design for the ESTS required managing various challenges such as flat terrain; highway and creek crossings; high groundwater and poor soils; and minimizing infiltration and inflow (I/I). As the ESTS progressed through three project phases from 2005 to 2015, new construction materials and techniques were incorporated into the project. Materials and construction techniques focused on the following goals: 1) keeping manholes and pipelines water tight; 2) extending the useful life of assets to reduce future rehabilitation needs; and 3) increased construction efficiency and quality.