Use a Hold Study to Assess Distribution System Influent Water Quality
Citation:
Alexander, M., A. Dugan, AND D. Wahman. Use a Hold Study to Assess Distribution System Influent Water Quality. OPFLOW. American Water Works Association, Denver, CO, 45(5):16-19, (2019). https://doi.org/10.1002/opfl.1187
Impact/Purpose:
The environmental or health problem addressed by the study: A procedure to evaluate disinfectant residual stability and corresponding disinfection by-product formation. A general description of the work and results: Having an unstable disinfectant residual makes it challenging to maintain adequate residual throughout the distribution system (DS). Assessing the residual stability of the DS influent and corresponding disinfection byproduct (DBP) formation, whether it is coming directly from a water treatment plant, or into a consecutive system through a metered connection, provides information that enables systems to prioritize efforts to improve DS water quality. For example, if water entering a DS is very reactive and the residual rapidly decays, efforts focused on reducing chlorine-demand prior to distribution (e.g., improving natural organic matter removal) may be more effective than efforts to minimize water age in the DS (e.g., flushing or optimizing tank operations). Additionally, if a consecutive system has information showing the water they receive from the parent system is unstable or the disinfectant residual is too low to maintain an adequate residual in their system, that information may be used to initiate a dialogue among the two systems to cooperatively address water quality issues. The US Environmental Protection Agency’s Drinking Water Optimization Program promotes the use of a kinetic study to assess DS influent residual stability. Because DS influent water samples are collected and held for a predetermined time before analysis, the study is commonly referred to as a “hold study”. Because this study evaluates water stored in a chlorine demand-free bottle, it does not assess distribution system influences that can impact residual stability. However, the hold study is a relatively straightforward and cost-effective way to evaluate changes in bulk water quality over time. It can be used as a starting point to investigate more complex treatment or distribution system issues that may impact disinfectant residual stability. The long term importance or significance of the findings: Explains a methodology to evaluate disinfectant residual stability and corresponding disinfectant by-product formation. Who would be interested in or could apply the results (e.g. program or regional partners, general public, local communities): Drinking water utilities
Description:
The US Environmental Protection Agency’s Drinking Water Optimization Program promotes the use of a kinetic study to assess DS influent residual stability. Because DS influent water samples are collected and held for a predetermined time before analysis, the study is commonly referred to as a “hold study”. Because this study evaluates water stored in a chlorine demand-free bottle, it does not assess distribution system influences that can impact residual stability. However, the hold study is a relatively straightforward and cost-effective way to evaluate changes in bulk water quality over time. It can be used as a starting point to investigate more complex treatment or distribution system issues that may impact disinfectant residual stability.
