Teamwork Averts Disaster in Squamish
The District of Squamish is a rapidly growing community, located about halfway between Vancouver and Whistler. The current population is just over 21,000. Less than 10 years ago it was 15,000, and it’s projected to hit 30,000 by 2040.
In 2005 following a major upgrade at the Mamquam Wastewater Treatment Plant (WWTP), the District of Squamish made the decision to retain the old bioreactors and clarifiers as a means of redundancy for the new circular combined treatment unit (CTU) that had just been installed, and also to have added capacity during the wet months. It was a decision that would serve them well in the years to come.
Fast forward to January 18, 2018. A fairly standard winter day in Squamish – grey, cold, and heavy rain. One of the wastewater treatment plant Operators immediately knew something was wrong when she heard the clarifier ‘howling’ and ‘clunking’. The sound of metal on metal is not typical of the skimmer as it makes its slow lap of the tank. As with most mechanical failures, there were a series of things that went wrong. A shear pin failed to shear, and an over-torque sensor didn’t trigger the alarm. The exact cause of the failure is still unknown. As the Operators quickly reacted, the clarifier was twisting itself into scrap metal. Luckily, the team stopped the machine before the damage could get any worse.
With an average daily flow of just over 8,000m3/day that can double during the rainy winter months, the operations team knew it needed to act quickly. At the time of the failure, the CTU was treating 90% of incoming flow.
Chief Operator, Scott MacIntyre started to bring the old treatment train back online. The ‘old side’ consisted of four bioreactor tanks, two of which were already running to deal with the high seasonal flows. Scott worked to divert the water from the failed CTU to the old tanks. A 6” x 6” diesel pump was onsite within 24 hours.
Coincidentally, engineers from MPE Engineering were onsite completing a capital project to upgrade the controls at the facility and were able to work with the Operators to bring the old treatment train back online. The volume of incoming flow exceeded the design capacity of the process train, however MPE was able to create a program which allowed a single dissolved oxygen (DO) probe to operate all four tanks. MPE also helped to set up a return activated sludge (RAS) flow monitor.
Due to the volume of inflow and infiltration reaching the WWTP from all the rain, the secondary clarifiers were short-circuiting during peaks. When the inflows got excessive, the RAS was reduced, which reduced the mixed liquor suspended solids (MLSS) and was very helpful. Flocculent was added to the secondary clarifiers to improve settling before flow reached the weirs. With some programming tweaks, a plant with a capacity of 5,000 m3/day was running at 10,000 m3/day and meeting permitted discharge parameters.
Everyone on the team really came together. The Director of Public Works, Bob Smith took the lead on communicating with Council and the Ministry of Environment (MOE). Scott took the lead on continuing operations on the ‘old side’ while Utilities Supervisor Chris Stanger and Wastewater Collections chief Operator Dan Arnold were in charge of the repair work and getting the CTU back online as quickly as possible. The District Communications department did a press release to the community to keep the public aware of what was happening.
The CTU consists of a clarifier surrounded by a bioreactor, a wastewater treatment ‘doughnut’ if you will. This is a common approach when working within a small footprint. Often during the design and commissioning phases of a project, a small footprint is a positive. However, due to the design of the clarifier, the bioreactor also needed to be taken offline. During the repair the team noted that the apparatus was constructed with angular steel, which may have led to the failure. Furthermore, there were signs of older smaller failures on the angular steel thus weakening the entire structure. The repaired clarifier now contains new tubular steel as recommended by Westpro.
Throughout the entire emergency, the team was laser-focused on compliance with the MOE operating permit, allowing for total suspended solids (TSS) of 40mg/L. Sampling was completed daily throughout the repair work to prove compliance (normally only weekly samples are required). The MOE was helpful and engaged, and worked closely with the District to ensure protection of the environment.
The Squamish team looks back on this emergency event in a positive light and is reflective about the lessons learned along the way. The clarifier was brought back online and has been running at full capacity for close to a year. The whole process has been an incredible training opportunity for the Operators, the management team, and the rest of the District staff.