The Lower Walnut Creek Sanitary Sewer Interceptor project provided 16,000 LF of new 64- and 72-inch pipeline that maintains safe wastewater conveyance through Raleigh’s largest sewer basin and increases sewer capacity to meet the area’s needs until 2040. The Walnut Creek Sewer Basin covers approximately 38% of the city’s sewer service area.
Prior to this project, the Lower Walnut Creek sanitary sewer had been in service for nearly 40 years. This aging infrastructure transported millions of gallons of raw sewage to the wastewater treatment plant each day. Pipeline failure would have had significant environmental impacts on the area. Raleigh Water originally hired McKim & Creed to replace and/or rehabilitate approximately 16,000 linear feet— approximately three miles—of 48- and 54-inch sewer pipeline. After researching numerous methodologies and technologies, the team concluded that the most effective solution was to install and interconnect new 66- and 72-inch pipeline parallel to the original infrastructure. This extended infrastructure service life, increased capacity, and allowed for future rehabilitation and reutilization of the abandoned 48- and 54-inch pipelines for even more capacity if needed in the future.
The Raleigh Water / McKim & Creed team employed such innovative technologies as physical modeling and advanced design for siphons, subsurface utility engineering (SUE), microtunneling, and polymer junction/ siphon box design. The $27.2-million project was completed for 8 percent under budget and nearly five months ahead of schedule. The American Council of Engineering Companies of North Carolina awarded McKim & Creed and Raleigh Water with a 2021 Grand Engineering Excellence award for their work on this project.