Sustaining Siphons Subsequent to Sewer Separation

Sewer separation provides many benefits to the receiving water and to the treatment facility. However, designers must be cognizant of potential negative impacts of reduced flows and velocities on downstream pipes, particularly siphons.This paper reviews siphon design principles, discusses the problem presented by sewer separation, and, through the use of a case study from Chicopee, Massachusetts, provides a potential solution. This case study reviews the installation and performance of North America's first Hydroflush GS flush-cleaning device, winner of the WEF 2007 Innovative Technology Award - Collection Systems. Continuous flow monitoring in the interceptor sewer has provided several months of data from which to compare flows and velocities in the siphons, before and after sewer separation, with and without the flush-cleaning device.