Managing Microbial Risk In Distribution Systems


  • Roger Arnold - Hazen and Sawyer

Microbial growth in distribution systems can contribute to a variety of adverse water quality consequences and potential health risks for consumers, and new regulations aim to improve how water systems manage microbial risk. The presentation will elucidate potential causes of microbial risk, regulatory impacts, and operational strategies for microbial control. The Revised Total Coliform Rule (RTCR) will become effective for public water systems on April 1, 2016, and the goal is to reduce potential pathways of contamination into the distribution system. A variety of factors such as disinfectant residual, maintenance/repairs, pipe materials, storage tanks, water age, backflow, and hydraulic transients can affect microbial risk in the distribution system. Furthermore, the Long Term 2 Enhanced Surface Water Treatment Rule requires a “detectable” chlorine residual in the distribution system, which may not provide adequate protection of the distribution system. Many states have adopted higher minimum chlorine residual requirements, and the AWWA Partnership for Safe Water specifies higher goals for distribution system residuals.

The presentation will highlight increasing regulatory scrutiny in Virginia on microbial risk associated with opportunistic pathogens in water systems, such as Legionella, Mycobacterium, and Naegleria Fowleri. For example, in 2013, the Centers for Disease Control and Prevention (CDC) reported that Legionella was the primary cause of waterborne illness outbreaks. However, regulations related to microbial risk do not specifically address control of opportunistic pathogens which can proliferate in biofilms. Strategies for reducing the occurrence of opportunistic pathogens can include disinfectant residual optimization, control of assimilable organic carbon (AOC), and water management in large buildings. Control of opportunistic pathogens in biofilms presents simultaneous compliance challenges due to potential impacts on Stage 2 Disinfection Byproducts Rule and the Lead and Copper Rule. Due to multiple causes of microbial risk, RTCR implementation presents an opportunity to adopt a holistic distribution system optimization approach to manage microbial risk from multiple sources.

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Horizons Fall 2017 (pdf)

Horizons showcases significant water, wastewater, reuse, and stormwater projects and innovations that help our clients to achieve their goals, and can help you achieve yours. Articles are written by top engineers and process group leaders, demonstrating and explaining the beneficial application of a variety of technologies and tools.

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