Part of a large estuary along the eastern Australian coastline (150 kilometres north of Sydney, NSW) used for shellfish production was closed to harvesting for over 18 months. Monitoring in 2005 showed human viral contamination of oyster tissue and surveys of drainage channels and the estuary indicated regular exceedances of standards set for shellfish growing waters, particularly following heavy rainfall. The contamination was attributed to urban runoff, agricultural wastes and failing on-site wastewater systems. In particular there were significant land capability constraints to the on-site dispersal of treated wastewater due to the high groundwater tables and permeable sandy soils. For this reason, and because human viruses were recorded in the shellfish, domestic wastewater systems were considered an important source of the contaminants recorded in the estuary. As part of the current estuary remediation program, the local regulatory authority (Port Stephens Council) required that appropriately sized sand mounds be constructed at sites where systems had been assessed as failing and also at new housing sites with severe land capability constraints due to the high groundwater levels. Two of the sand mound systems have been monitored in detail since midway through 2007 for a period of six months using a variety of soil water samplers and groundwater bores. Water use has been monitored at each property along with a suite of wastewater contaminants in each septic tank, the vadose zone and shallow groundwater. Only some of the monitoring results are presented in this paper, but on the basis of these results, it is clear that the two sand mounds are performing effectively as a treatment system resulting in significantly reduced contaminant concentrations entering the groundwater. There is substantial interest in the overall performance of these systems as little research has been conducted in Australia on wastewater treatment using sand mounds.
Onsite and Decentralised Sewerage & Recycling Conference. Proceedings of Onsite and Decentralised Sewerage & Recycling Conference: Coming Clean: Sustainable Backyards and Beyond! (Benalla, Vic. 12-15 October, 2008) p. 325-333