Use of Flushing as a Corrective Action Under the Revised Total Coliform Rule

Water main flushing is a commonly used (and often misused) utility maintenance practice to maintain or improve water quality and to address contamination issues in distribution systems. Flushing is also identified in the Revised Total Coliform Rule as a corrective action to address sanitary defects; however, there is no guidance available to utilities as to whether it is appropriate for a particular coliform response situation or how it should be applied and monitored. When improperly applied, flushing can worsen a situation and increase risks to public health. A WRF tailored collaboration research project 4653, Use of Flushing as a Corrective Action Under the Revised Total Coliform Rule, was conducted with two large Pacific Northwest utilities – Portland Water Bureau and Seattle Public Utilities – to field-evaluate the effectiveness of unidirectional flushing (UDF) to remove microbially active sediment/biofilm from pipe walls and to reduce disinfectant demand associated with legacy deposits; as well as to characterize the benefits, limitations, and risks of conventional flushing. This webcast focused on key findings from the project field trials and provides industry guidance for utility operations, including a framework and protocols on how and when to optimally conduct flushing as it relates to addressing microbial water quality upsets.