WRRF 11-10: Defining the Costs and Benefits of “Fail-Safe” Direct Potable Reuse

Direct Potable Reuse (DPR) can be defined as the incorporation of highly purified recycled water into a drinking water source without an environmental buffer such as a groundwater basin or a lake, river, or reservoir. Because of extreme water shortages, DPR is now being implemented in New Mexico and Texas, and the State of California has mandated that State regulators evaluate DPR in the near future. DPR has inherent risks different from traditional source waters and different from conventional indirect potable reuse (IPR). The potential impact of DPR treatment process upsets can be far greater than for IPR or traditional drinking water treatment of a less impaired source. Many questions must be answered about DPR. Are existing treatment barriers for IPR sufficient? What is the value of the environmental buffer and how can it be replaced with an engineered system? How can we use online monitoring to ensure water quality and public health protection?.To answer these questions, Carollo is leading WateReuse Research Foundation Project 11-10, Evaluation of Risk Reduction Principles for Direct Potable Reuse. The project team includes key utilities across California and outside experts on risk reduction. The result will be an understanding of what engineering practices could be incorporated into our approach to the design, control, operation, and maintenance of advanced treatment systems for DPR. Topics under consideration include:1) Qualifying engineering redundancy necessary to reduce engineer practice mistakes;2) Qualifying design redundancy to ensure production of high quality water;3) Qualifying monitoring, operational, and maintenance characteristics required to reduce risk; and4) Quantifying the inherent trade-offs and costs associated with the identified redundancy and quality assurance/quality control (QA/QC) measures.To date, the investigation suggests that existing IPR treatment technologies sufficiently protect public health, if they are well maintained and monitored. The use of the Hazard Analysis Critical Control Point (HACCP) methodology looks promising to minimize treatment process failure and to reduce the impact of such failures. The project team is now performing detailed DPR HACCP analysis and investigating new methods to continuously monitor DPR effluent quality. The projectfindings will be presented in early 2013.