A large scale pilot study of a GIS based risk assessment system for on-site wastewater management in New South Wales, Australia

Following an outbreak of Hepatitis A disease associated with consumption of oysters from Wallis Lake, New South Wales (NSW), Australia in 1996, the NSW Government has invested A$3.8M over the past four years (1998-2002) in a SepticSafe program to assist local government authorities (local councils) to implement systematic management of sanitation risks related to onsite wastewater management. Part of this investment was directed to the development of an integrated system of sewage risk assessment in coastal areas, particularly oyster growing areas and drinking water catchments (watersheds). An On-site Risk Assessment System (OSRAS) has been developed to bring together information held by local councils and State Government agencies. The OSRAS uses GIS layering techniques and transparent logic matrices to model the fate of sewage pollution from decentralised sewage management facilities, in relation to identified disease vectors and sensitive environmental receptors, and to generate risk "maps". The output will enable councils and State Government agencies to assess the likely scale of impact and relative risk of sewage pollution in unsewered residential areas. The OSRAS is currently being trialed in the Hawkesbury Lower Nepean catchment, covering 20 Local Government Areas in the Sydney hinterland with approximately 50,000 on-site wastewater management systems. The large scale pilot study involves the development of a data management system, data integrity review, application of the OSRAS methodology to the Hawkesbury Lower Nepean catchment, consultation with local councils and State Government agencies and field validation, prior to the release of the OSRAS for use in other areas of coastal NSW.