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Poison In The Water: How To Defeat Toxic Algae Like many municipalities, Hamilton, Ontario, is wary of harmful algal blooms and toxic cyanobacteria. To mitigate the threat and protect drinking water, a proactive, risk-based plan was developed. By Christopher Mills and Quirien Muylwyk H eavy rains, environmental conditions, and nutrients from runoff have created favorable conditions in the Great Lakes to promote more frequent and longer occurrences of algal blooms. The nutrient-rich environment and warm tem- peratures of the Great Lakes make them the perfect incubator for algal blooms, some of which can be harmful. Algal blooms and cyanobacte- ria not only impact the aesthetic appearance, odor, and taste of water supplies, they also can be detrimental to public health and impact the normal operations of a water treatment plant, including loss of produc- tion capacity during high demand periods. While several provinces and states are implementing long-term solu- tions to control the growth of algae, short-term solutions can minimize the impact of toxic algal blooms and avoid drastic measures like tem- porarily shutting off a community's water supply. Proactive planning can identify the right mix of short- and long-term solutions to prevent contamination of treated water with algal toxins, while also improving the understanding of the risk posed by algae and cyanotoxins at the plant. Located in the western end of Lake Ontario, five kilometers from the Burlington ship canal, the City of Hamilton's Woodward Avenue Water Treatment Plant (WTP), a 900 MLD (238 MGD) facility, is a good example of a utility taking a proactive, risk- based approach to managing its algal toxin risks. The Woodward WTP treats water from Lake Ontario using conventional treatment with intake chlorination, coagulation with polyaluminium chloride filtration with granular activated carbon, and chloramination. Depending on conditions on the lake, the plant's intake can be influenced by the water of the adjacent Hamilton Harbour, a water body in which cyanobacterial algal blooms have been observed due to its eutrophic conditions. Working with the City of Hamilton, CH2M HILL conducted a study to assess the potential impacts of algae and cyanobacteria on the performance of the Woodward Avenue WTP, in terms of aesthetics, public health, and plant operations. Using a proactive approach to iden- tify risks and recommendations for both short- and long-term control strategies, the study evaluated potential control strategies and empha- sizes opportunities to leverage the existing treatment plant infrastructure to address raw water quality conditions and risks. Source Water Conditions There are limited data available on the type and concentration of algae in the source water used by the Woodward Avenue WTP. However, monitoring data in the adjacent Hamilton Harbour are more prevalent than monitoring data in Lake Ontario. Since 1987, the city has been reviewing water quality data in Hamilton Harbour. Long-term monitoring trends indicate an overall average increase in water transparency and a dramatic shift in algal com- munity structure, with surface blooms becoming more frequent over the years. Also, after an approximately 10-year period of declining total phosphorus levels, there is a more recent trend of total phosphorus levels increasing. From analyzing and studying the water quality data, CH2M HILL helped the City of Hamilton better understand the potential impacts and risks associated with algae, cyanobacteria, and their metabo- lites observed in the source water. Previously, the city had not utilized the data to holistically identify these trends over the years. Based on the observed water quality trends in the source water, the study helped categorize the impact on water quality and the plant's operational performance. It was determined that the predominant algal species in Hamilton Harbour had shifted towards noxious algal taxa (from chlorophytes and diatoms to cyano- bacteria) over the past decade or longer. Per the literature, several species of cyanobacteria can produce algal metabolites that cause taste and odor (T&O;) — specifically geosmin and MIB, which are responsible for the majority of reported T&O; events — and/ or toxins. The study looked at water quality data from Hamilton Harbour as a worst-case scenario, and it was also confirmed that water exchange between Hamilton Harbour and western Lake Ontario does occur through the shipping canal, though water quality at the Woodward WTP intake is rarely influenced by this exchange. In some cases, however, algal species found in Hamilton Harbour were detected at the WTP intake, but at much lower levels. Therefore, because of the limited data available, it is difficult to draw conclusions about the linkage between water quality in Hamilton Harbour and western Lake Ontario, specifically at the Woodward WTP intake. For this study, a conservative assumption was made that algal spe- cies present in Hamilton Harbour could potentially influence water quality at the Woodward WTP intake, as this represents a worst-case scenario and is consistent with the delineation of Hamilton Harbour as Intake Protection Zone 3 for the Woodward WTP. The approach taken to assess the risk was based on deducing trends in the raw water intake data, based on groups of algae and cyanobacteria as opposed to individual algal species. Nevertheless, in order to mitigate risk using its existing infrastruc- ture, CH2M HILL utilized the city's risk management framework tool to interpret data and identify the components needed for managing 16 The "filter building" at the City of Hamilton's Woodward Avenue Water Treatment Plant wateronline.com ■ Water Innovations