THM Remediation

In 2021, staff were successful with the ICIP – Green Stream grant application to provide a solution to manage a water quality issue, caused by the formation of disinfection by-products (DBPs), mainly trihalomethanes (THMs), within the water distribution system.

DBPs, especially THMs, are formed when disinfectant, such as chlorine, reacts with natural organic matter. There are also environmental and treatment factors that influence DBP formation, including but not limited to, pH, contact time, temperature, season, disinfectant dose, and residual. Industry standards in terms of actions to eliminate or mitigate the formation of DBP consist of removal of THM precursors by enhanced treatment processes, implementing alternative disinfection methods and removal or THMs after formation.
The project funding of $3,500,000.00 is being allocated into the following components: comprehensive review, pilot project and desktop study, design and engineering, and full implementation.

Working with CIMA+, staff completed a comprehensive review and initial pilot project, which at the time indicated the best solution to reduce DBPs and therefore THMs, was through a process involving Powdered Activated Carbon (PAC). However, recent levels of THMs throughout the water distribution system have consistently exceeded the maximum allowable concentration and show no signs of returning to acceptable levels. In light of these persistent high levels, staff and CIMA+ have reassessed the available options to mitigate the THM issue. Consequently, a comprehensive plan comprising of two phases (both short-term and long-term) has been developed.

Phase One: the current filter media at the Deep River Water Treatment Plant (WTP) will be replaced with granular activated carbon (GAC) to achieve an immediate reduction in THM levels. This switch to GAC is expected to yield immediate improvements in THM reduction, providing a quick response to the ongoing water quality issue.

Phase Two: implementing chloramination as the method for secondary disinfection at the WTP. This more advanced disinfection process is scheduled for implementation in 2025 and will be completed by the grant completion deadline.

Phase three and beyond will be determined based on outcomes of the preliminary phases and budget.