Columbia Sewer Rehabilitation Rehabilitating in Difficult Conditions

Abstract

The New Westminster Interceptor (NWI) Columbia Section - originally constructed in 1971 - is 1,622 metres long, and is predominately 1,067 to 1,524 millimetre diameter reinforced concrete pipe (RCP) with a significant grade of up to 5.5 percent in sections. Metro Vancouver has been assessing the condition of the NWI Columbia section over the last 20 years, the sewer has severely degraded since it entered service as a result of Hydrogen Sulphide corrosion. Due to the pipe condition and the hydraulic conditions Metro Vancouver has decided to rehabilitate this pipe section. Due to the pipe being located on an arterial road through a congested downtown business district, open-cut replacement was politically not considered an allowable method of construction. Metro Vancouver and Jacobs evaluated several rehabilitation methods and found live sliplining to be the preferred solution in order to reduce the overall construction and infrastructure footprint and community impacts. Work had to be timed to coincide with an upstream network pump station replacement that significantly reduced sewer flows through the pipe requiring rehabilitation. The pump station replacement facilitated the design of a live flow rehabilitation method with post replacement winter flows modelled to be 1.6 cubic meters per second (cms) and summer average dry weather flows were modelled to be 0.46 cms with anticipated average system velocities of 3.0 metres per second (m/s). These conditions whilst still challenging are a significant improvement from the pre pump station replacement conditions with peak flows of 4.7 cms and associated 6.0 m/s velocity.