Preliminary quantitative risk assessment for the Salisbury stormwater ASTR project

[摘要] EXECUTIVE SUMMARY: This report extends the preliminary qualitative risk assessment prepared by Swierc et al. (2005) for the Salisbury Aquifer Storage Transfer Recovery (ASTR) project by incorporating the results of water quality monitoring undertaken in 2006. Overall the quality of the stormwater entering the holding basin/cleansing reed bed pre-treatment system was similar to that reported in the literature, but below average rainfall during this period may not be representative of normal operating conditions. In addition to the traditional water quality monitoring, sediment analysis and passive samplers for assessment of micropollutants were trialled as tools for risk assessment where concentrations of hazards are below standard laboratory detection limits. While no micropollutants or enteric pathogens were detected using the conventional water or sediment monitoring programs, the passive samples detected trace quantities of micropollutants throughout the system of which diuron, simazine and chlorpyrifos appeared to be most significant. The results of the monitoring program were used to construct a water and chloride balance for the holding storage and cleansing reed bed components of the ASTR system as a step to quantitatively assess their treatment performance for physical, chemical and microbial hazards. The performance of the system over August-September 2006 was found to have removal efficiencies of 0.66, 0.77 and 0.64 for total nitrogen, phosphorous and organic carbon respectively. The water produced after the cleansing reed bed was of near-potable quality, with the exceptions of colour caused by elevated iron concentrations and small numbers of faecal indicator bacteria caused by indigenous fauna in the cleansing reed bed. In addition to the treatment performance, a quantitative risk assessment (QRA) for several index pathogens (rotavirus, Campylobacter and Cryptosporidium) and chemicals (diuron, simazine, and chlorpyrifos) was also performed. The QRA incorporated a Monte Carlo simulation to describe the behaviour of these hazards in the ASTR system - from stormwater harvesting through to the water user. For the micropollutants, final estimated concentrations were compared to the appropriate water quality guidelines. However, for the pathogens, the exposure estimate was then used as an input to a dose-response model to estimate the risk in terms of public health burden using the disability adjusted life years (DALYs) metric. The QRA indicated that the risks posed by the index microbial and chemical hazards were currently unacceptable for use of the recovered water for drinking. These initial QRA results stem from the uncertainty of subsurface treatment component. If the recovered water is to be intended for drinking, the treatment provided by the aquifer must be quantified and validated to be incorporated into the multi-barrier approach of a risk management plan. Recommendations for the risk assessment and management of the system focus on specific actions for partners with milestones that are detailed in Section 7. This includes monitoring and acquiring information to refine the risk assessment, involving the surface catchment, the stormwater capture and treatment system and aquifer processes. This leads to recommendations concerning communication about the risks and other steps required before recovered water could be introduced into mains supplies.

[发布机构] CSIRO

[学科分类] 地球科学(综合)