The Manitoba Hydro community of Pointe du Bois located in the Whiteshell Provincial Park services Manitoba Hydro’s oldest hydro generating stations: Pointe du Bois and Slave Falls. The community’s original infrastructure was built during the construction of the Pointe du Bois Generating Station, sometime between 1909 and 1926. Among the aging infrastructure was a gravity wastewater sewer system fabricated from vitrified clay pipe that remained in service until very recently.
Despite several rehabilitative upgrades, the system’s deteriorated pipes and manholes continued to allow excessive groundwater infiltration that overloaded the community’s wastewater treatment plant during spring melt periods and heavy rain events.
Manitoba Hydro retained KGS Acres to develop a permanent solution that managed environmental impact, while minimizing capital costs and maintenance. KGS Acres’ services included monitoring flows, diagnosing the problem, developing remedial alternatives, detailed designing of the preferred alternative and contract administration.
KGS Acres implemented a number of unique applications using modern engineering technologies, allowing the design team to efficiently diagnose the problem and develop an efficient, yet cost-effective design. These technologies included survey-grade GPS supplemented by a Light Detection and Ranging (LiDAR) survey of Pointe du Bois and the immediate surrounding region. The data produced from both ground surveys were used to develop a digital terrain model (DTM) of the existing topography using AutoDesk’s Land Development Desktop design software. KGS Acres also implemented ultrasonic flowmeters, installed in strategic locations within the existing system, to identify the sections that were experiencing extraneous flows.
KGS Acres’ unique solution retrofitted the existing gravity sewer by incorporating it as a protective conduit and alignment for the new high-density polyethylene which was installed within the old clay pipe. The system was converted from a gravity system to a low-pressure-sewer system. To provide the low pressure, each residence and building connected to the system was fitted with a 1-HP progressing cavity grinder pump housed within a 485-L capacity grinder pit. A total of 1,046 metres of new mainline piping was installed. Since completion of the project, flows have been stable and overall wastewater flows to the system have been reduced by 90%, well within license requirements.
The project, located in the Whiteshell Provincial Park, inherently adopted a low tolerance for environmental impact. The retrofit project was a unique and innovative solution that eliminated hydraulic overloading and minimized the human ‘footprint’ on the naturally pristine location. The construction technique itself was considered ‘green,’ requiring minimal excavation to install the new system and also reusing the old pipe network. The construction method also allowed the old wastewater collection system to be kept ‘live’ during construction, thereby minimizing interruptions to Manitoba Hydro’s day-to-day operations at Pointe du Bois.
The final construction costs were still below the original contract price even after implementing several value-added design changes during the construction phase. Ultimately, KGS Acres delivered the project within Manitoba Hydro’s timeframe and under the original construction budget.
Pointe du Bois is now home to Manitoba’s largest grinder-pump equipped low pressure sewer system.