Located at the confluence of two rivers, the Athabasca and Clearwater Rivers, the community of Fort McMurray faces the risk of floods every spring when the rivers thaw. This risk was realized in spring 2020 when an ice jam on the Athabasca River caused water levels to rise rapidly, leading to widespread flooding and water damage. At the Water Treatment Plant, flood waters rose high enough to bypass two flow control gates, causing raw river water to enter the drinking water system. In order to protect public health, a boil-water order was immediately implemented. The Regional Municipality of Wood Buffalo, which operates the treatment facility, retained Associated Engineering to help recover the water system and coordinate the work necessary to lift the boil-water order.
The water system recovery plan was based on similar work performed by the Associated team following the wildfire in 2016. This latest river break flooding caused contaminated water to enter the treated water clearwells and disseminate throughout the water distribution network, necessitating a recovery method that focused on disinfection of any possible biological pathogens.
The water model demonstrated the efficacy of achieving disinfection in support of the water system recovery plan
Our project team coordinated with Alberta Environment and Parks and Alberta Health Services for their approval of the water system recovery plan before we started work. Associated Engineering was also responsible for executing the plan, providing technical support to the municipal operations staff, overseeing contracted field staff, documenting completed works, and reporting to the regulators to support lifting the boil-water order in a staged approach as the work was completed.
Starting at the Water Treatment Plant and working outward across the distribution system, every reservoir needed to be drained, cleaned, disinfected, and re-filled with regulatory-compliant water. As the disinfection and cleaning was completed at each reservoir, the clean water in the reservoir was then used to flush and disinfect each surrounding neighbourhood. Following disinfection, water quality samples were taken at the reservoirs and key locations within the distribution networks. The team submitted sample results and documentation to the regulators to lift the Boil Water Orders progressively as the works were completed.
Project Manager, Jason Vanderzwaag, tells us, “Our technical experts used Fort McMurray’s water distribution system model to demonstrate that a disinfection dose of 6 milligrams per litre free chlorine could be introduced into the water system, and with active flushing at the system extremities, we would achieve necessary saturation of disinfection dose across the distribution network. We also used the water model to identify key monitoring hydrants (e.g. critical points in the system that would be the last to receive the disinfection dose) and late-flush hydrants (e.g. points that needed to be flushed once the rest of the system has reached saturation).”
Once the flushing plans had been generated, Jason and his team provided technical oversight to the crews executing the work, including municipal operations staff and contracted crews. Due to the long initial flushing period of between 8 to 12 hours, plus the 16-hour disinfection time, the work was scheduled over continuous days, with crews rotating between day and night shifts. Thanks to the commitment and rapid work of the field crews, the work was completed and all the boil water orders lifted less than 60 days after the initial flood event, compared to an initial estimate of 120 days. This was regarded as a significant success by the Regional Municipality of Wood Buffalo.
Following the flood and the initial water recovery works, Associated Engineering worked with the operations staff to perform a root-cause analysis, and identify and repair all the failure mechanisms that led to the water contamination. Jason says, “Work is ongoing to address these issues, as well as to mitigate future contamination that may result from more frequent and extreme flood events as a result of climate change.”