Water Environment Federation (WEF)

Methodology for Forensic Investigation of Potable Water Quality in Municipal Distribution Systems

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Courtesy of Courtesy of Water Environment Federation (WEF)


During routine regulatory potable water quality sampling in distribution systems related to the Total Coliform Rule, utilities can sometimes experience anomalous detections of total coliform bacteria and/or fecal coliform bacteria in the distribution system samples. Frequently, the regulatory-required retesting of the same sample locations reveals no detection of bacteria, and thus no direct cause can be immediately determined for the detection episodes. The utilization of a structured approach which focuses on the investigation of critical base parameters within the raw water, treatment processes, and transmission network of a municipal potable water supply and distribution system can help utilities isolate probable causes of detected water quality episodes, and help expedite the implementation of corrective measures to reduce the likelihood of future episodes. In order to perform a comprehensive analysis which would provide the greatest chance of revealing a probable cause for the detection episodes, a detailed methodology was developed to closely examine each segment of the municipal water system - raw water source, raw water supply wells, and raw water transmission system, water treatment plant processes, disinfection system, application, and operation, distribution system conditions, utility operation and maintenance practices, and laboratory and sampling protocols. Anecdotal investigations include structured interviews with system operations and maintenance, laboratory, and plant staff. Engineering investigations include plant profiling, computation fluid dynamics modeling of
system storage elements, disinfectant decay and water age modeling, pipe bio-film analysis, system flushing analyses, and system-wide sample tap swab and biospeciation. The developed plan provides a systematic protocol for the examination and elimination of various probable causes by implementing tasks which utilize specific scientific analysis and repetitive sampling, geographic information system (GIS) mapping, statistical correlations, visual and field observations, system operation reviews, operator analyses, hydraulic modeling, and water quality modeling. The compiled results create a relational database logging the many system parameters recorded during the detection episodes for use in correlating any future coliform bacteria detections, and to assist in the determination of probable cause. By implementing a similar protocol, water utilities can react more efficiently to detection episodes, show proactive progress to regulators, and focus on rectifying or eliminating the identified probable causes.

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