Water Journal : Water Journal September 2012-1
refereed paper potable reuse water SEPTEMBER 2012 53 Abstract A framework has been developed to inform the public health risk assessment process for indirect potable reuse schemes. A stepwise framework has been designed to 1) prioritise chemicals in recycled water using a risk-based approach; and 2) incorporate chemical characteristics and the natural barrier when guideline exceedances are detected. Triggers in the framework include method detection limits exceeding health guidelines, chemicals considered persistent/bioaccumulative/toxic and chemicals detected routinely for which it is possible to produce a probability distribution function. Of the 468 chemicals monitored in the purified recycled water scheme of South- East Queensland, only 4% were classed as Category 1. Of these 20 chemicals, 16 were included in Category 1 due to method detection limits exceeding the Queensland Public Health Regulation. Examples are provided for specific chemicals to illustrate triggers in the assessment process and the benefits of the natural barrier in reducing water concentrations. Further work is required to fully integrate chemical fate and reservoir hydrodynamic models with the assessment framework. Introduction When undertaking public health risk assessments for planned indirect potable reuse (IPR) schemes it is important to monitor the quality of recycled water and account for the effect that the natural barrier may have on the concentration of chemicals. Monitoring data can be used for comparison with guidelines and to determine ongoing monitoring requirements, particularly when chemicals are not detected or only occur at very low concentrations. Accounting for the effect that the natural barrier will have on water concentrations further informs the risk assessment by demonstrating how chemical transformation processes and dilution may change the risk profile of particular chemicals. A process has been developed to inform the public health risk assessment of purified recycled water (PRW). A step- wise framework has been designed that can both identify priority chemicals in PRW and also assess the likely risk of health guideline exceedances. Figure 1 summarises the approach taken, both during this prioritisation exercise (1) but also in dealing with possible exceedances in the future (2). In the prioritisation exercise, monitoring data was synthesised in probability distribution function (PDF) charts, as discussed in Khan (2010). These charts provide a measure of the likelihood of potential exceedance of current human health guidelines from the Queensland Public Health Regulation Schedule 3b (QPHR) and the Australian Drinking Water Guidelines (ADWG). Some 468 parameters were monitored; however, not all of these have a current guideline value and some were monitored purely for operational or contract purposes (e.g., conductivity, pH, total organic carbon). The QPHR contains approximately 360 standards for chemicals, while the ADWG provides approximately 220 guideline values for chemicals. In Queensland, when dealing with recycled water for augmentation of drinking water supplies, the QPHR take precedence over the Australian Guidelines for Water Recycling (Phase 2) Augmentation of Drinking Water Supplies (AGWR) and the ADWG. Where no guideline was available, an interim guideline was derived using the framework described in the AGWR. This paper outlines the process developed to prioritise chemicals according to available monitoring data, human health significance and with an example of how a natural barrier (reservoir or storage) can be incorporated into the risk assessment. FDL Leusch, D Middleton, ME Bartkow Development and application of a tool to estimate the likelihood and significance of exceedances HUMAN HEALTH-BASED CHEMICAL GUIDELINES IN PURIFIED RECYCLED WATER Figure 1. Approach for the prioritisation exercise (1) and dealing with exceedances (2). Note that expert assessment is required if a chemical triggers a PBT (persistence, bioaccumulation, toxicity) alert (red box in this diagram).
Water Journal November 2012-1
Water Journal August 2012