Risk-based approach to on-site wastewater treatment

Abstract

On-site wastewater treatment system siting and design has commonly been based on site specific conditions with little regard to the surrounding environment or the cumulative effect resulting from clusters of systems. The numerous cases of poor treatment performance of on-site systems reported over the years highlight the need for a risk-based approach underpinned by strong scientific knowledge for the management of on-site wastewater treatment systems.

A study is being conducted in the Gold Coast City region in collaboration with the Gold Coast City Council for the development of an integrated risk based approach for the siting, design and management of on-site wastewater treatment systems. The inclusion of relevant stakeholders through a series of workshops during various phases of project development has been crucial for the development of the risk assessment process. An initial risk zoning of the region was developed based on the integration of scientific and qualitative data relating to the themes; soil suitability for effluent disposal, planning criteria and environmental sensitivity. This entailed the development of an appropriate framework for the integration of these diverse qualitative and quantitative data. The use of multivariate statistical techniques such as Principal Component Analysis and multicriteria decision making aids such as PROMETHEE and GAIA enabled the finding of significant correlations and patterns between selected soil physical and chemical data. The initial risk zones thus developed have subsequently undergone a series of refinements based on the outcomes of comprehensive soil analysis. The availability of risk zoning in terms of on-site wastewater treatment would assist the Gold Coast City Council in land development planning and the development of appropriate strategies to ensure improved management of on-site wastewater treatment. Investigations into nutrient and microbiological contamination of ground and surface waters are currently being conducted to develop risk assessment frameworks for environmental and public health factors. Subsequently, the developed soil suitability framework will be combined with the environmental and public health assessment frameworks to develop an integrated risk assessment process for on-site wastewater treatment systems.