Environmental impact of deepwater discharge of sewage off Sydney, NSW, Australia

A comprehensive monitoring program (the EMP) was put in place to assess the environmental impacts of deepwater sewage discharge off Sydney (NSW, Australia). The EMP involves studies of environmental impacts on fish and macroinvertebrate community structure, on water quality in the ocean and at beaches, and of accumulation of contaminants in marine organisms and sediments. Comprehensive computer models of sewage plume behaviour were developed. The studies have shown that, since nearshore sewage discharge ceased, the extent and frequency of contamination of beaches by faecal bacteria has decreased with only small increases offshore, and there is little evidence of nutrient enrichment of offshore waters or of accumulation of contaminants in surface sediments near the outfalls. There has been a significant decrease in contamination of biota by trace metals and organochlorine compounds in nearshore areas, but no measurable increase in contaminants in organisms in offshore waters. Although no consistent pattern was observable, changes in offshore fish and invertebrate communities have occurred, manifested as increases and decreases in abundance. This intensive multidisciplinary study has allowed the accurate determination of the environmental impact of the deepwater sewage outfalls, and provides information to be used in the planning of any future discharges.