By Silvia Vlad, Monique Waller, and Quirien Muylwyk
A case study from Lake Erie shows the value of adaptable monitoring plans and how to get ready to respond to dynamic situations.
In the summer of 2016, the Region of Niagara — a regional municipality on the Canadian shore of Lake Erie serving 450,000 residents — faced the challenge of developing and implementing a cyanobacterial monitoring and response plan within a single season, while managing an active cyanobacterial event with the potential to impact one of the Region’s six water treatment plants.
An increasing number of municipalities are affected by cyanobacteria or cyanobacterial metabolites each year, and many utilities have noted blooms appearing earlier in the spring and lasting longer into the fall. Several risks are inherent to a drinking water supply impacted by cyanobacteria — notably metabolite toxins (cyanotoxins), which can harm human and animal health, as well as the taste-and-odor compounds 2-methylisoborneol (MIB) and geosmin. While a range of options is available to utilities managing the risks posed by these blooms, tradeoffs exist between the costs of monitoring, using temporary mitigation techniques, or implementing permanent treatment measures. These challenges are further complicated by the intermittent nature of cyanobacterial events, for which the occurrence, duration, and magnitude are not easily predicted.
In Spring 2016, operators at the DeCew Falls treatment plant reported needing to clean the intake bar screens of algal debris more often than in past years. Although no toxins had yet been detected, the Region wanted to understand the potential implications of finding cyanobacteria in their source — including potential cyanotoxin production, a timeline for toxin intrusion into the plant, and barriers needed to prevent the toxin from entering the water supply. The Region of Niagara engaged CH2M to obtain answers to their questions when elevated algal activity was confirmed in the raw water storage reservoir upstream of the DeCew Falls plant.
CH2M worked with the Region through the summer and early fall to:
Recommendations were developed for monitoring the source, in-plant, and treated water for algae, cyanobacteria, and their metabolites across six of the Region’s treatment plants, to provide supplemental information beyond what was obtained through monitoring practices already in place.
The monitoring plan was used to identify both the occurrence of algae, cyanobacteria, or their metabolites, and their impact on plant performance using a variety of tools, including visual observations of the 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:
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 disinfection byproduct 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.
In concert with the analysis of existing treatment capabilities, bench-scale testing was completed at the DeCew Falls plant to identify modifications to the existing treatment which the Region could implement relatively quickly if toxins were detected at the plant. Based on the results of the bench-scale study, operating with an enhanced coagulation dose of the existing plant coagulant (alum) was selected as the preferred short-term solution that used the existing infrastructure, and a range of potential polymers was screened. The polymer investigations identified a product which could assist in forming a fast-settling, heavy floc to promote better settling of cyanobacterial cells and prevent re-suspension of the sludge. Once a preferred polymer was selected, logistical considerations such as the availability of supply, location for injection, make-down system requirements, and regulatory approvals for implementation of a new chemical system were addressed, and the Region prepared to enact treatment augmentations, if necessary.
Recognizing that further fine-tuning of plant operations may be required under changing water quality conditions throughout a cyanobacterial event, a training program for the Region’s staff was incorporated in the bench-scale studies. Increasing the Region’s in-house capacity to develop and carry out jar test plans will provide greater flexibility in determining the appropriate response and implementation for subsequent events, including continued examination of coagulant, chlorine, and polymer doses.
Monitoring Implementation, Response Readiness, And A Cyanotoxin Framework
Within the 2016 cyanobacterial season, a tiered monitoring plan was implemented by the Region of Niagara, and while cyanotoxins were only ever detected upstream of the DeCew Falls treatment plant (never at the plant itself ), the Region was ready to use existing chlorination capabilities to manage dissolved toxins and had obtained approvals from the regulator to implement a polymer system for augmented removal of cyanobacterial cells, should it have become necessary.
The Region successfully navigated the potential pitfalls of gathering data about a cyanobacterial event, analyzing the data to understand the implications, and preparing a treatment response plan. A teamwork approach to communication, monitoring logistics, implication analysis, and decision execution was integral to the process, and included O&M staff, summer interns, quality and compliance staff, the Region’s laboratory staff, Public Health officials, the local conservation authority, university researchers, and other municipalities.
Ultimately, a monitoring and response framework was developed to support the Region in managing potential cyanobacterial impacts going forward. While circumstances might differ between events or evolve throughout the duration of an event, the framework will allow the Region to obtain needed and actionable information, understand the current treatment capabilities and augmentation options, and have the in-house training to further fine-tune the treatment parameters. By ensuring that tiered monitoring and response measures are in place, issues such as sample frequencies and locations, preliminary treatment set-points, and media release timelines will be addressed ahead of time, allowing the Region’s staff to focus on critical questions rather than laboratory logistics during future events.
About The Authors
Silvia Vlad is a water treatment engineer in CH2M’s Toronto, Canada office and holds a Masters of Applied Science from the University of Waterloo, where her thesis focused on the treatment of the cyanotoxin anatoxin-a in drinking water. Silvia is delighted to be part of an industry that strives towards a resilient global water supply through ambitious policy initiatives, open communications, and effective engineering solutions.
Monique Waller obtained her Master’s degree in civil engineering from the University of Toronto in 2008, after which she joined CH2M’s Kitchener office. Monique has supported a range of municipal drinking water treatment and distribution projects, including water quality and optimization studies, environmental assessments, and hydraulic modeling of water distribution systems.
Quirien Muylwyk, MASc., P.Eng., is the National Practice Leader for Water Quality with AECOM. Quirien has more than 20 years of experience in strategic planning for regulatory compliance and growth, the design and construction of new works, and process optimization for municipal water systems. Her work has focused on making the link between performance inside the treatment plant and performance in the distribution system, all with the purpose of promoting public health.