On a summer day, residents and tourists often flock to one of Toronto’s many Lake Ontario beaches. However, leisure activities can be curtailed by high levels of Escherichia coli (E. coli) in the lake water. Although most E. coli strains are harmless, some can cause serious health problems to humans who swallow them or swim in water that has been contaminated by them. To protect the public, Ontario warns against swimming when tests show 100 E. coli-colony-forming units per 100 millilitres (CFU/100 mL) of water at a specific beach and has set this value as a Provincial Water Quality Objective (PWQO).
As a local natural gas-fired power plant with a community focus and an active ecological sustainability strategy, the Portlands Energy Centre (PEC) is well aware of the threats E. coli pose to nearby Cherry Beach, an eco-labelled Blue Flag beach for its adherence to strict global standards.
The 550-megawatt (MW) PEC was built in 2008 to meet 25 per cent of Toronto’s electricity needs, primarily during peak demand times, and offset emissions from Ontario’s coal-fired generating stations. During operation, it takes water from Toronto Harbour’s ship channel and turning basin for generation processes and cooling, treats it on site, then releases it into the discharge channel and back to Lake Ontario’s Outer Harbour.
Some E. coli in sanitary sewer and stormwater runoff from Toronto neighbourhoods north of the plant enters the ship channel and turning basin from two of the city’s overflows and then enters PEC’s water intake. From there, it may be inadvertently transferred to the Outer Harbour through normal discharge of cooling water, and could potentially reach the popular Cherry Beach.
As part of its Certificate of Approval for water permits, the Ministry of the Environment (MOE) requires the PEC to implement an E. coli control program for the water it uses, but the plant’s management chose to go further.
In 2008, it hired EcoMetrix Inc., an environmental consulting firm, and embarked on a comprehensive four-year E. coli monitoring program during the summer months that included the ship channel, the discharge channel, the intake basin, the Outer Harbour, Cherry Beach, and the Eastern Gap.
During the first summer, the firm established a baseline by measuring E. coli concentrations before the plant was operational. As expected, these data revealed no direct relationship between E. coli in the discharge channel or the ship channel during pre- operations.
The consulting firm followed this research in 2009 by looking for relationships between E. coli levels and various aspects of the plant operations. This included studying the effects of operational factors, including volume and temperature of the cooling water intake discharge flows. The team also studied how rainfall influenced E. coli concentrations. In the third summer, team members collected daily samples for 22 weeks to research potential associations between E. coli in cooling water effluent and E. coli at Cherry Beach.
Efforts also included measuring E. coli levels throughout the Outer Harbour after significant rainfall events to narrow down the most probable source of E. coli that could potentially impact Cherry Beach. Findings suggested that the Keating Channel running from the Don River, via the Eastern Gap, was the most likely source of E. coli to affect the popular beach.
Monitoring studies found that changes to flow volume and water temperature caused by plant operations did not appear to influence E. coli concentration in the cooling water effluent. Similarly, E. coli levels in the discharge water were generally the same as those in the intake basin. From this they concluded that on its own, discharged water from the plant was unlikely to increase E. coli concentrations at Cherry Beach.
The same could not be said for precipitation. “We saw E. coli concentrations typically spike to 3,600 to 8,700 CFU/100 mL, during the two to seven hours after we received at least 10 millimetres (mm) of rain within a 24-hour period,” explains Robert J. Eakins, an associate and senior fisheries ecologist at EcoMetrix. “Our modelling studies further indicated that when these E. coli levels reach 3,500 CFU/100 mL, they could potentially cause corresponding levels at Cherry Beach to rise above 100 CFU/100 mL.”
More importantly, in 2011, the team began to test the effectiveness of using a specialized hyper chlorination process to treat the cooling water effluent to reduce E. coli in it. They pumped a small amount of sodium hypochlorite into the effluent, followed by sodium bisulfate to neutralize and reduce chlorine concentrations to levels below 0.01 milligrams per litre before it’s discharged, as specified in the Certificate of Approval. The impact was almost immediate; E. coli levels in the effluent decreased by approximately 90 per cent within five seconds of treatment.
“With these results, we began to ask what steps we could take to treat more than the mandated amount of water we use and create farther reaching benefits,” says Curtis Mahoney, general manager at PEC. “We coordinated with the City of Toronto and the MOE to implement a larger-scale control program to mitigate E. coli that threatens Cherry Beach and help maintain Blue Flag swimming conditions, even during seasonal periods of heavy rainfall.”
Building on four years of research, the team developed an E. coli control program for 2012 and implemented it during the June to Labour Day beach season. Each treatment was triggered by a rainfall in excess of 10 mm within 24 hours, so E. coli was reduced when concentrations were potentially high. Treatment began once the rainfall threshold was reached and continued for 24 hours after the rain had stopped. Since evaluation was a priority, E. coli levels were carefully monitored with water tested from both the plant’s intake and discharge waters.
Results were promising, showing chlorination significantly reduced E. coli concentrations in the effluent relative to the levels measured in the intake water. In fact, E. coli levels in the effluent were usually well below the PWQO of 100 CFU/100 mL after treatment. Furthermore, Cherry Beach was only posted as unsafe for two days in 2012, compared to an average of six days during the previous five years.
This summer, the team plans to collect hourly samples before, during, and after significant rainfall events to explore potential program refinements, such as shortening the duration of each chlorination treatment.
With PEC’s program and concerted efforts from other organizations, this summer should offer residents and tourists many carefree hours enjoying Toronto’s Cherry Beach.