The Twists and Turns of Rehabbing a 70-Year-Old Trunk Sewer and Manholes in an Established Neighborhood

Lauderdale, located in north central Edmonton, has an 8 m deep 1950 trunk sewer system consisting of 750 mm diameter and 900 mm diameter RCP combined sewers, with several incoming lateral connections—including a 600 mm connection and seven sanitary manholes, one being a drop manhole. Following a series of inspection and condition assessment programs, the conveyance system was identified to be in poor-to-very poor structural condition. The wall loss alone was estimated to range between 50% and 80%, indicating a high risk of imminent localized failure. Additionally, 24 “Water Level Sag” defects were found along the trunk sewer. Wastewater samples revealed a high level of biological activity, possible anaerobic conditions, and high sulfide content, which were evident by the degree of H₂S-induced deterioration observed and the odor nuisance issues in the neighborhood. The technical viability and overall suitability of various renewal methodologies were evaluated. Consideration was given to sanitary flow bypass requirements, trunk sewer structure and hydraulic capacity requirements, site constraints, and service life extension. CIPP was identified as the most viable renewal option for the sewer and geopolymer and epoxy coating for the manholes. Some project “twists and turns” included: (1) an 8 m deep sinkhole due to collapse of a section of the trunk sewer during the planning phase, (2) the existing drop-manhole was to be relocated away from the right-of-way of the future LRT project and to be replaced with a new 2,400 mm manhole, (3) the 2,400 mm manhole was to be installed at the sinkhole location, and it was to house a Hydro Vortex Flow Insert system required to address drop flow and odor issues, (4) chasing competent concrete along the RCP sewer for reconnection on both sides of the 2,400 mm manhole, leading to ~20 m long unexpected excavation, (5) five sections along the sewer with significant sagging were earmarked for open-cut replacement prior to re-lining. Liquification and soil sloughing were encountered, causing the team to change course, and (6) the 600 mm service pipe and one of the 250 mm CB leads reside beneath the right-of-way of the future LRT project, triggering the need to comply with applicable railway crossing design standards. This article shows how the rehabilitation activities leveraged collaborative and adaptive team efforts, as well as industry best practices and innovative solutions. Multiple lessons learned will be shared, as well as rehabilitation options evaluation, design criteria, constructability constraints and considerations, stakeholders’ management, construction approach, and QAQC requirements.