Another Sewer from Hell – The City of Richmond, British Columbia, Canada Experience

The City of Richmond has a population of approximately 180,000 and is located on a flood plain at approximately sea level. These physical attributes present numerous challenges with underground utility design, including sanitary sewers.On January 21, 2005 the City declared a local state of emergency near the intersection of No. 3 Road at Cook Road due to the development of a large sinkhole (10 × 8 × 1.5 metres deep). A commercial building had partially collapsed and the City's sanitary gravity main located at a depth of 4.5 metres, at an extreme flat grade of 0.27% and 2.0 metres off the face of a 100 metre long building, was no longer functional. City staff employed a unique methodology to return the sewer main to service and installed a City invented manhole pump/SCADA/bypass system to allow continuous sanitary service. All options to restore the collapsed sewer were exhausted starting with the seemingly least expensive methodology to repair the sewer at the collapse point leading to the adopted solution of re-routing the main. Construction of the re-routed main required a 5-metre deep excavation immediately adjacent to a 32-year old commercial building with substandard footings bearing on soft soils. With the ground water table at a depth of approximately 1.0 metre, uncontrolled dewatering would result in considerable building structural damage. Dewatering was further complicated by tidal fluctuations of the groundwater table. A grout curtain which is new technology not previously used by the City was constructed, leading to successful project completion.