Hazard and risk assessment for indirect potable reuse schemes: An approach for use in developing Water Safety Plans

This paper describes research undertaken to develop an approach for facilitating an initial hazard assessment and risk characterisation for a proposed indirect potable reuse scheme, as part of the water safety plan recommended by the World Health Organization. The process involved a description and evaluation of the catchment, which was the sewerage system supplying the sewage treatment works that would provide the effluent to supply the pilot scale indirect potable reuse water treatment plant. Hazards, sources and barriers throughout the proposed system were identified and evaluated. An initial assessment of the possible hazards, highlighted chemical hazards as predominating, and assessment of risks, using a heat map as output, categorised most hazards as medium or high risk. However, this outcome has been influenced by a precautionary approach which assigned a high likelihood to the occurrence of hazards where no data was available on their occurrence in the system. As more data becomes available, and the waster safety plan develops, it is anticipated that the risk heat map will become more specific. Additionally, high quality targets, to drinking water standards, have been set, although water from the potable reuse plant will be discharged to receiving waters where it will undergo natural attenuation prior to further treatment to potable standards before distribution. The assessment has demonstrated the usefulness of the approach where data is initially limited, in generating a heat map allowing for prioritisation of hazards to a practical level.