Water Journal : Water Journal December 2011
refereed paper small wastewater systems water DECEMBER 2011 75 however where human viruses are found in estuarine filter feeders such as oysters, a human source of contamination such as failing OWMS or sewerage treatment plant discharge has to be responsible. In January 1997 in Wallis Lake, a Hepatitis A virus affected approximately 274 people in NSW (one fatally) and, in all, 422 people throughout Australia. In a subsequent investigation by NSW Health, it was concluded that the oyster contamination was waterborne and potentially from contamination by human faecal waste (Kardamanidis et al., 2009). While the estuarine waters were contaminated by human faecal and nutrient pollution from unsewered small communities and other sources, the specific source of the waste was not able to be determined. Failing OWMS were, however, considered highly likely to have been primarily responsible due to their reported high rates of failure and the large number of unidentified unsewered premises in the catchment. In July 2005 part of the State's second largest producer of oysters with an annual value of A$5 million (behind Wallis Lake with an annual value of A$14 million) was closed to commercial oyster harvesting due to a similar contamination incident. Samples of oyster tissue tested positive using PCR analysis for human Adenovirus and Norovirus in the Tilligerry Creek estuary in Port Stephens. In this case (as in Wallis Lake), faecal contamination from failing OWMS was considered responsible, although agricultural sources of contamination were also significant in terms of the overall faecal load to the estuary. The estuary remained closed to commercial harvesting for over two years, resulting in a substantial loss of income from which the industry in that region has yet to recover. More recently, in 2008 outbreaks of gastroenteritis have been linked to a common batch of oysters harvested from the Kalang River estuary in northern NSW. The presented symptoms were consistent with Norovirus infection and the estuary subsequently closed to the commercial harvesting of oysters by the NSW Food Authority. Investigations are still underway as to the source or sources of the human faecal contamination and the estuary still remains closed to harvesting. Possible human sources of the contamination are considered to be a number of OWMS adjacent to the estuarine waters and a downstream sewerage treatment plant discharge from a nearby community wastewater system. Responses In response to the outbreak in the Wallis Lake estuary, a number of Local and State Government agencies collaborated in estuary and catchment remediation works. Over the 13 years since the incident, these works have resulted in significantly improved estuarine water quality and commercial oyster growing is again thriving. In 2004 the Great Lakes Council was awarded a major prize for best practice in river and catchment management and environmental repair in Australia (Kardamanidis et al., 2009), although the actual source of the contamination incident has never been identified. In response to the closure of the Tilligerry Creek estuary to oyster harvesting, a sanitary survey of the estuary and river shorelines was conducted by the NSW Food Authority and Port Stephens Council undertook OWMS inspections. An audit of approximately 300 OWMS in the community adjacent to the estuary found that a small number of systems were faulty and that human effluent had the potential to contaminate ground and surface estuarine waters where the oysters were grown and harvested. In this study a number of individual OWMS were dosed, using bromide and lithium salts and fluorescein dye to determine whether direct linkages existed between the OWMS and surface and groundwaters. An aerial photo of Wallis Lake Estuary. Aerial photo of an upstream part of Tilligerry Creek Estuary, Port Stephens, showing mixed land uses.
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