Water Journal : Water Journal December 2011
small wastewater systems refereed paper technical features 76 DECEMBER 2011 water In several of these cases hydraulic pathways to the estuary were confirmed, indicating that contaminated groundwater from OWMS was entering surface drains and quickly entering the estuary following heavy rainfall events (Geary, 2005). More detailed investigations followed to identify the sources of faecal contamination that an unsewered development was making to both surface runoff and groundwater entering the estuary. In addition to the microbial faecal indicators regularly used in such studies, water samples were collected and analysed for faecal sterol compounds in order to determine whether faecal contamination was human-derived. Interpretation of the various sterol compounds indicated that while there had been occasions where human- derived faecal contamination had entered the estuary, the majority of the faecal contamination at that time was sourced from herbivores in the catchment upstream (Geary et al., 2007). While the estuary was closed, estuary and catchment remediation works were initiated by the local Council. A catchment management plan was commissioned which recommended a number of improved management practices be adopted and an estuary response model developed. When a sewerage options study indicated that the cost of a reticulated system for the small community adjacent to the estuary was prohibitively expensive, a number of standard designs for improved OWMS were developed and failing systems were required to be upgraded. One of the OWMS designs adopted by Council which has proved very successful in overcoming the problems associated with the high groundwater table is the sand (Wisconsin) mound. These systems are considered secondary treatment systems, as primary-treated effluent is pumped into an above-ground distribution system constructed in imported permeable soil. Effluent then percolates through this material where treatment occurs prior to it entering the groundwater. As a mitigation measure, 58 mounds which receive primary treated effluent, and nine which receive secondary-treated effluent from aerated treatment systems, have been constructed. Monitoring has shown that the overall efficacy of the treatment system can be directly linked to the increased vertical separation distance to the groundwater provided by the mound and the periodic dose loading of effluent from the septic tank (Whitehead and Geary, 2009). A Wisconsin Mound OWMS. Similar audits conducted in the Kalang River estuary have found that a number of OWMS which have been approved by the local Council are failing. Studies have been undertaken using tracers such as fluorescein, rhodamine and bromide, along with microbiological faecal indicators, to determine the source of the human contamination in the estuary waters. While there are unsewered and sewered urban settlements adjacent to the river, and a variety of other agricultural land use activities upstream which may be contributing to the faecal contamination detected in these oyster-growing areas, the source of the human contamination has yet to be found and the estuary remains closed to oyster harvesting. This situation, as in the former example, has had a profound effect on the commercial viability of the oyster growing industry in each of these estuaries and a consequent loss in consumer confidence in the product. There are also other estuaries where there is concern with respect to the increasing faecal bacterial counts in oyster-growing waters and the potential which exists for contamination to be human-derived from adjacent or nearby small unsewered communities. Conclusion Demonstrating direct linkages between the wastewater management practices of small communities and estuarine water quality is difficult at the catchment scale and may not be possible using standard monitoring techniques and typical microbiological indicators. While Gardner et al. (2006) has suggested that there is little evidence of the impact that unsewered communities have on water quality, the fact that human viruses can periodically be found in oysters suggests current monitoring programs at high-risk estuary locations need to be improved. In developing new monitoring programs, consideration should be given to either more regular assays for human viruses in oysters, or in measuring chemicals associated with human metabolism and activity, which can also be present in human faecal material such as caffeine, faecal sterols and various pharmaceutical compounds. Fluorescent whitening compounds (FWCs), which are present in the majority of wastewaters containing laundry products, are also now being assessed as studies elsewhere (Gilpin et al., 2002) have shown that they too can be used to assist with identifying human faecal sources in environmental water samples. Contamination incidents such as those discussed in this paper demonstrate the close relationship and the sometimes inherent conflict between managing wastewater in small communities, increasing urban and rural development, and the need to maintain estuarine water quality so that aquaculture such as oyster growing can be undertaken without compromising human health. The Authors Phil Geary (email: phil.geary@newcastle. edu.au) is an Associate Professor at the School of Environmental & Life Sciences, University of Newcastle, NSW. Joe Whitehead (email: joewhitehead@ whiteheadenvironmental.com.au) is Principal of Whitehead and Associates Environmental Consultants, Director of the Centre for Environmental Training and Senior Lecturer at the University of Newcastle. References Gardner E, Vieritz A & Beal C, 2006: Are on-site systems environmentally sustainable? Water, 33(1), pp 36--46. Geary PM, 2005: Effluent tracing and the transport of contaminants from a domestic septic system, Water Science and Technology, 51(10), pp 283--290. Geary PM, Lucas SA, Dunstan RH & Coombes PJ, 2007: Distinguishing wastewater contamination from on-site systems in mixed land use watersheds, In 11th National Symposium on Individual and Small Community Sewage Systems Proceedings (Ed. K. Mancl), American Society of Agricultural Engineers, St Joseph, Michigan, US. Gilpin BJ, Gregor JE & Savill MG, 2002: Identification of the source of faecal pollution in contaminated rivers, Water Science and Technology, 46(3), pp 9--15. Kardamanidis K, Corbett SJ & Zammitt AP, 2009: Hepatitis A: Wallis Lake revisited, NSW Public Health Bulletin, 20(1--2), pp 29--30. Whitehead J & Geary PM, 2009: Sand mounds for effective domestic effluent management, Water, 36(1), pp 27--32.
Water Journal April 2012
Water Journal November 2011