Water Online

September 2017

Water Innovations gives Water and Wastewater Engineers and end-users a venue to find project solutions and source valuable product information. We aim to educate the engineering and operations community on important issues and trends.

Issue link: https://wateronline.epubxp.com/i/861825

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Page 14 of 38

source water, coordination with other Lake Erie users, and understanding and anticipating the behavior of the lake. The tiered monitoring approach considers location-specific factors at each plant, the time of year, and conditions observed in the source water to select the appropriate monitoring protocol. Factors such as shallow intakes, intakes situated close to the shore, and sources either directly on Lake Erie or impacted by Lake Erie were used to assess the risk at each of the Region's water treatment plants. Monitoring protocols for high-, moderate-, and low-risk plants were established for each of three temporal and water quality scenarios: • Tr a n s i t i o n a l s e a s o n monitoring, in spring and fall, using triggers to prompt routine summer monitoring; • Routine summer monitoring, when t h e l i k e l i h o o d of occurrence is relatively higher; and • Event monitoring, to determine the cause and effect during a confirmed cyanotoxin event. Triggers to move among the three scenarios included source water temperature, trends in cyanobacterial indicator parameters, the startup of prechlorination for zebra mussel control, and the detection of cyanotoxins in either the source water (above a threshold) or treated water (at any concentration). Understanding the monitoring logistics proved critical, given the breadth of possible monitoring parameters, locations, analytical methods, and timelines. Challenges of sampling and analytical logistics were overcome in the short term through collaboration with the local conservation authority, internal and external laboratories (including Provincial and Federal resources), along with increased staff-time commitments to monitoring. The tiered monitoring plan allowed the Region to obtain valuable information without the need to sample extensively at all six sites (potentially backing up analysis of critical samples), with the understanding that the interim logistics implemented for the 2016 season could be further refined in subsequent years. Local lab analytical capabilities and turnaround times were significant factors in the development of the monitoring plan. Existing Treatment Capabilities To understand the implications of the monitoring findings, a desktop assessment of the existing treatment capabilities of the DeCew Falls plant was undertaken. As a conventional treatment plant, DeCew Falls already featured chlorination (both intake and disinfection chlorination) with the potential to oxidize dissolved cyanotoxins. Existing chlorination practices were based on a range of goals, including preventing zebra mussel growth at the intake, minimizing d i s i n f e c t i o n by p ro d u c t formation, maintaining a level of pre-oxidation which helped the plant maintain pretreatment performance, and achieving pathogen disinfection requirements. With the introduction of an additional goal — managing cyanobacterial and cyanotoxin impacts — treatability tradeoffs for chlorination had to be considered. Once cyanobacteria were confirmed in the reservoir, prechlorination at the DeCew Falls plant was turned off in an effort to prevent lysis of cyanobacterial cells (and the release of any toxins contained within the cell membranes). However, the lack of prechlorination resulted in increased settled water turbidity and filter performance challenges, and prechlorination was ultimately resumed at a low level. Performance observations at the plant were integrated with industry information from a literature scan to develop preliminary chlorination guidelines for three scenarios. These guidelines were intended to provide a starting setpoint from which the plant could fine-tune operations, should it become necessary to consider cyanotoxin oxidation among the treatment goals for chlorination. 12 wateronline.com n Water Innovations MICROBIALCONTAMINANTS The tiered monitoring approach considers location-specific factors at each plant, the time of year, and conditions observed in the source water to select the appropriate monitoring protocol. Logistics are critical: Where should the monitoring occur? When should the samples be collected? Who will collect the samples? What should be tested for? What methods should be used? Who will analyze the samples? Can information be obtained quickly enough to react to a cyanotoxin event?

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