To date, steps 1 and 2 have been completed and
steps 3 and 4 are ongoing. In Step 1, a list of common
terminologies associated with leakage and water main
breaks was developed to ensure the project team, the
project partners, and the final report has clearly defined
terms for developing a risk-based response strategy. In
addition, a utilities questionnaire was completed to solicit
input from 27 operating utilities on their current main
break repair processes. Recently a series of “featured
programs” for main break responses was completed
to offer best management practices for what could be
considered a model utility main break response program.
Quantitative microbial risk assessment (QMRA) was
developed in another Foundation project, Managing
Distribution System Low Transient Pressure for
Water Quality (LeChevallier et al., 2011, project
#4152) ,and was adapted into the current project to
study microbial infection risks caused by main breaks.
In Step 2, four pieces of information were collected:
( 1) the disinfect demand of the contaminating material,
( 2) the inactivation kinetics of the contaminant,
( 3) the effectiveness of removal of contamination by
flushing, and ( 4) the risk of the material remaining after
disinfection and/or flushing. The major tasks of this step
have been mostly completed.
In April 2012 the project team (HDR Inc. and American
Water) hosted a Risk Management Workshop and the
participants included the project advisory committee
(PAC), utility partners, and regulators. The purposes of
the workshop were to ( 1) confirm the applicability of the
risk model to be presented at the workshop, ( 2) confirm
the risk model input parameters (e.g., disinfectant
concentration, flushing velocity), ( 3) identify field
activities for the next phase of the study, and ( 4) discuss
the applicability of this project as the technical basis for
future revision of AWWA Standard C651-05 (Disinfecting
Water Mains). Participants explored three major topics:
( 1) procedure-maintaining flow and pressure during repair,
( 2) disinfection criteria-free chlorine and chloramine, and
( 3) flushing criteria, including what velocity is needed.
The Foundation held a Webcast in late May to provide a
summary of the workshop.
The project outcome will help utilities improve responses
to main breaks and depressurization events to better
protect public health. Also, the results from this project
may provide the sound technical recommendations for a
future revision of AWWA Standard C651-05.