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Edited by Leon P. Zann
Great Barrier Reef Marine Park Authority, Townsville Queensland
Ocean Rescue 2000 Program
Department of the Environment, Sport and Territories, Canberra, 1995
ISBN 0 642 17406 7
Environment Protection Authority
Many major coastal cities in the world discharge their wastewaters to the ocean. Wastewater may consist of a combination of domestic, industrial and agricultural effluent. Domestic sewage contains nutrients and bacteria, whilst wastewaters from industrial processes contain trace metals and chemicals, and agricultural effluent may contain chemicals including pesticides. Ocean conditions prevailing around the world's coastlines vary, as do effluent discharge quality and practices. Discharges can be from multi-port diffusers in deep water, or single pipe outfalls at the shoreline. Levels of treatment of the sewage also vary. Table 1 presents data on sewage discharges from a number of coastal cities.
Depending on local ocean conditions and the sewage discharge configuration, effluent may be rapidly dispersed and diluted with little visible trace, or may remain in a highly visible and relatively undiluted plume in the vicinity of a discharge point. Studies in the 1970s led to the conclusion that the coastal waters offshore from Sydney had a significant capacity to accept non-toxic organic and inorganic wastes. This factor has been particularly significant in the development of strategies to minimise impacts associated with the disposal of Sydney's sewage (Water Board 1989).
Sydney's first sewers, laid in the 1850s, drained raw sewage into the harbour. In 1888, two interceptor sewers were commenced, one to the ocean at Bondi, and one to a sewage farm beside Botany Bay, which was later extended to the ocean at Malabar. On the northern side of Sydney Harbour, a sewer to an ocean outlet at North Head was commenced in 1916 (see Figure 1). The major coastal treatment plants were completed at Bondi (1960s), Malabar (1974) and North Head (1984), and were designed to remove screenings, grit, grease, and settleable solids (Water Board 1989).
The ocean discharge points at North Head, Bondi and Malabar received 80% of Sydney's total sewage flow. The effluent was discharged less than 10 metres below the surface from rocky headlands, through single pipe outfalls. The remaining 20% continues to discharge from smaller coastal and inland treatment plants. In the early 1980s, after years of planning, the final decision was taken to divert the effluent of the three major sewage treatment plants from the shoreline to offshore deepwater outfalls, using multi-port diffusers in water depths of 60 to 80 metres.
Through the 1980s, public opinion had increasingly demanded action to overcome often severe pollution of bathing beaches near the outfalls. The first deepwater outfall was commissioned at Malabar in September 1990. In December 1990, the North Head deepwater outfall came on line, and the Bondi deepwater outfall commenced full operation in August 1991.
The Water Board owns and operates Sydney's sewers and treatment plants, which collect and treat the effluent from domestic and industrial/commercial sources. The latter source accounts for approximately one third of the effluent quantity treated at the coastal treatment plants (Water Board 1989). The quality and quantity of the industrial/ commercial effluent entering the Water Board's sewers is controlled by the Board under trade waste agreements with each discharger. Construction of treatment plants, and the quality and quantity of discharges of treated effluent to the environment, are controlled by legislation administered by the NSW Environment Protection Authority (EPA).
Approvals and licences issued under the legislation may contain requirements for regular monitoring of discharged effluent and reporting to the EPA. Monitoring of the receiving environment may also be required. Approvals issued to the Water Board for construction of the Sydney deepwater outfalls had such a requirement.
After conducting early pilot studies, the Sydney deepwater outfall monitoring program was begun by the Water Board in 1989. Its aim was to quantify the environmental impact of the change to deepwater discharge of most of Sydney's sewage effluent. Monitoring commenced prior to commissioning of the deepwater outfalls, and is to continue for two years beyond the commissioning of the last deepwater outfall. Responsibility for the implementation of this environmental monitoring program was transferred by Government decision to the EPA in 1990.
Table 1: Data on coastal sewage outfalls
|Outfall||Service Population||Effluent Treatment||Water Depth (m)||Length (m)||Average Flow (ML/d)*||Risers x Ports|
|Malabar||1 500 000||Primary||80||2900||490||28 x 8|
|Bondi||600 000||Primary||60||1700||165||26 x 4|
|North Head||1 200 000||High Rate Primary||60||2900||385||36 x 6|
|The Hague||2 000 000||not known||15||2000||240||84|
|Los Angeles (Hyperion)||4 000 000||Adv. Primary||60||8000||1360||84 x 2|
|Rio de Janeiro||not known||Untreated||27||3300||not known||180|
|San Diego||1 300 000||Adv. Primary||63||3450||720||29 x 2|
* = megalitres per day Source: Camp Dresser & McKee (1989)
The monitoring program examines the complete sewage path, from treatment plant discharge, through dispersion in the ocean, and ending in accumulation in the biota and sediments. Oceanographic studies start with effluent discharge parameters, and examine the dispersive forces which act upon the discharged effluent using field-calibrated numerical models. Chemical and biological studies examine the fate of the effluent and its constituent pollutants, and measure the resulting environmental impacts. Particular studies examine levels of contaminants in fish and sentinel oysters, abundance and diversity of fish and macrobenthic organisms, and offshore and beach water quality. The monitoring program commenced in sufficient time to compile a set of baseline environmental data prior to commissioning of the first deepwater outfall. These data were to be compared with an equivalent set of post commissioning results.
The state of Sydney's marine environment is presented as it existed in 1991, during the period in which the deepwater outfalls were being commissioned. The major outfall at Bondi continued to discharge at the shoreline at this time. The results of the deepwater outfalls environmental monitoring program (EMP) are used to describe the situation.
Australian Water and Coastal Studies (1992) described the ocean off Sydney as having a predominance of southerly flowing ocean currents, and temperature stratification of the water column. As a result, diluted sewage from the deepwater outfalls generally moved south, whilst remaining trapped below the water surface.
Figure 2 presents data on the quality of bathing waters at Sydney's beaches between late 1990 and mid 1991, as distributions of two categories of faecal coliform densities, measured from water samples taken four days per week. The lower faecal coliform category, less than 300 colony forming units (cfu) per 100 mL, corresponds to a level where waters pass NSW Department of Health guidelines for bathing waters.
Figure 2 showed that beaches at greater distances from the main sewage outfalls (north from Shelly beach and south from Malabar Beach) had much greater occurrences of the lower category of faecal coliform densities in the water than those closer to outfalls. There were discontinuities at Bondi, Warriewood and Boat Harbour, near continuing shoreline sewage outfalls.
In the ocean at the commissioned deepwater outfall sites, the sewage plumes were normally trapped in stratified waters. In the deeper half of the water column (greater than 30 m depth), mean faecal coliform densities were up to several hundreds of cfu/100 mL. In the upper half (top 30 m) of the water column, mean levels were less than 10 cfu/100 mL (Philip et al 1993). At offshore sites away from the outfalls, mean faecal coliform levels in the upper 30 m of the water column were similarly low. Mean faecal coliform levels in the lower water column (greater than 30 m depth) at these sites were relatively higher, but of the same order of magnitude. This was attributed to the diluted deepwater plumes occasionally reaching these sites, whilst remaining at depth and being swept along by ocean currents.
Of a range of organochlorine compounds being investigated in sediments in 60 to 80 m water depth off Sydney, only hexachlorobenzene had been detected in the earliest samplings using relatively high detection limits. It was found in similar concentrations in locations across the study area, both close to and distant from the sewage outfalls (Philip et al 1993). Trace metals concentrations varied both spatially and temporally across the same locations. All levels detected lay within the 'low contaminant status' range as defined by Thomas (1987).
Various studies overseas have shown that natural materials and contaminants can concentrate in the thin layer of sea water (the microlayer) extending from the air-sea interface to a depth of about 50 micrometres. The microlayer can have toxic or sublethal effects on microscopic organisms such as the eggs and larval stages of fish. Off Sydney, chemical and bacteriological studies of microlayers have been conducted near the main Sydney outfalls during their shoreline discharge phase. Overall, the chemical concentrations found by the EMP work at the three outfalls were considerably lower than those found in the overseas studies (Table 2) that used comparable sampling equipment (Rendell 1993).
Contaminant concentrations in marine biota were included in the deepwater outfalls environmental monitoring program. However, the statistical designs of these contaminant projects required that the data be compiled for the full term of the study, before detailed statistical analyses were carried out. Observations about contaminant concentrations in marine biota are presented in the Trends section of this report.
Table 2: Comparisons of maximum concentrations of contaminants in microlayer samples from different studies.
|Study||Maximum microlayer concentration* ug/L|
|Total PAHs||Total metals||Total PCBs||Total pesticides|
|EMP (all sites)||0.28||50||0 (<0.004)||0.0069|
|Cross et al. (1987)||56||800||39||0.44|
|Hardy et al. (1987)||8000||4800||3.9||0.044|
|Sauer et al. (1989)||-||-||0.046||0|
|Hardy et al. (1990)||6.0#||73||-||-|
* Except for metals the totals may not be based on the sum of exactly the same constituents. Results below the detection limit were assumed to be zero. Total metal values were based on the sum of concentrations for cadmium, lead, zinc, silver, and copper in the sample as was used in Hardy et al. (1987). PAH - Poly Aromatic Hydrocarbon; PCB - Poly Chlorinated Biphenyl; # - Maximum mean over three sampling times. d. The trend from this poor environmental state to the present is reflected in Figure 4. This shows monthly coliform densities measured at Maroubra Beach near the Malabar sewage treatment plant, and spans the September 1990 commissioning date of the deepwater outfall. The reduction in bacterial densities was 100-fold. Most of Sydney's beaches now pass the NSW Health Department's bathing water quality guidelines 90% of the time (Beachwatch 1993).
The environmental state just described is predominantly the result of discharge of diluted sewage through the deepwater outfalls. Introducing results from 1988 to 1990, when all Sydney's sewage treatment plants were discharging at the shoreline, demonstrates the trends which have occurred in Sydney's marine environment over these years.
Prior to 1990, monitoring results showed that the marine waters and biota off Sydney had been significantly and adversely affected by the presence of sewage from treatment plants along some forty kilometres of Sydney's coastline. The seawater at many surfing beaches was often visibly discoloured, and contained particles of grease attributed in large part to the discharged sewage (CDM 1989). Water quality at beaches, in terms of levels of bacteria, did not meet Health Department guidelines for bathing waters on many occasions (Philip 1992). The flesh of some species of fish caught near the major shoreline discharge points contained contaminants at levels above residue limits set by the National Health and Medical Research Council (Mann & Ajani 1991).
Figure 3 presents the distribution of two categories of faecal coliform densities at Sydney's beaches between December 1989 and September 1990. It showed that famous Sydney beaches such as South Steyne (Manly) and Bondi failed the Health Department's bathing water quality guidelines more times than they passe
The results from analyses of oysters deployed at the North Head and Malabar shoreline outfall sites, spanning the times of commissioning of deepwater outfalls at these sites, confirmed the pre- to post commissioning trend observed for faecal coliforms.
Figure 5 (Philip et al 1993) shows that the concentrations of technical chlordane (*) in oysters dropped from significant levels to below the detection limit after commissioning in December 1990. Figure 6 shows a decrease in the concentration of technical chlordane (*) and dieldrin in one fish species, red morwong, known to be resident along the shoreline (P. Scanes , EPA, pers. comm.). This reduction in inshore contamination was a manifestation of the absence of the shoreline sewage plumes.
There has been wide variability in diversity and abundance of fish and seabed macro-invertebrates. A detailed interpretation of the state of Sydney's marine environment up to 1993, as determined by the EMP monitoring program is planned to be separately reported in late 1994.
The adverse impacts of the discharge of Sydney's urban sewage into the marine environment have been reduced by the commissioning of the deepwater outfalls. Improvements have occurred to the quality of the bathing waters at beaches close to the outfalls, and no increased adverse impacts have resulted at other Sydney beaches further away. Levels of contaminants measured in fish and deployed oysters along the shoreline have reduced.
Monitoring of the marine environment off Sydney is continuing, to determine whether the discharge of sewage in deep water, at greater dilutions than was previously achieved at the shoreline, will have any reduced impacts in the longer term. The continuing monitoring will also provide data to assist decision making on the need for improvements to the treatment processes, which would reduce the load of contaminants still being discharged into Sydney's marine environment.
Acknowledgments: The permission of the Environment Protection Authority (EPA) to present the material in this review is acknowledged. The work of EPA project teams and contractors, in carrying through the projects represented here, is gratefully acknowledged.
Australian Water and Coastal Studies P/L (AWACS) 1992, Sydney Deepwater Outfalls Environmental Monitoring Program, Ocean Reference Station Data September 1990 to August 1991, report for the Environment Protection Authority, Sydney.
Beachwatch Service 1993, Summer Season 1991/92 statistics, Environment Protection Authority, Sydney.
Camp, Dresser & McKee Consultants 1989, Review of Sydney's Beach Protection Programme, report to Minister for the Environment, Sydney, NSW.
Cross J.N., Hardy J.T., Hose J.E., Hershelman G.P., Antrim L.D., Gossett R.W. & Crecelius E.A. 1987, 'Contaminant concentrations and toxicity of sea-surface microlayer near Los Angeles, California', Marine Environment Research, vol. 23, pp. 307-323.
Hardy J.T., Crecelius E.A., Antrim L.D., Broadhurst V.L., Apts C.W., Gurtisen J.M. & Fortman T.J. 1987, 'The sea-surface microlayer of Puget Sound: Part II. Concentrations of contaminants and relation to toxicity', Marine Environment Research, vol. 23, pp. 251-271.
Hardy J.T., Crecelius E.A., Antrim L.D., Kiesser S.L. & Broadhurst V.L. 1990, 'Aquatic surface microlayer contamination in Chesapeake Bay', Marine Chemistry, vol. 28, pp. 333-351.
Mann R. & Ajani P. 1991, Sydney Deepwater Outfalls Environmental Monitoring Program Pre-commissioning Phase: Contaminants in Fish Project, State Pollution Control Commission, Sydney.
Philip, N. et al. 1994, Sydney Deepwater Outfalls Environmental Monitoring Program Commissioning Phase: Chemical and Biological Studies, Environment Protection Authority, Sydney,.
Philip, N.A. 1992, Sydney Deepwater Outfalls Environmental Monitoring Program Pre-Commissioning Phase: Volume 14-Overview, EPA, Sydney,
Rendell, P. 1993, Sydney Deepwater Outfalls Environmental Monitoring Program Pre-Commissioning Phase: Volume 8-Microlayer, EPA, Sydney.
Sauer T.C., Durell G.S., Brown J.S., Redford D. & Boehm P.D. 1989, 'Concentrations of Chlorinated Pesticides and PCBs in Microlayer and Seawater Samples Collected on Open-Ocean Waters off the U.S. East Coast and in the Gulf of Mexico', Marine Chemistry, vol. 27, pp. 235-257.
Thomas R.L. 1987, 'A protocol for the selection of process oriented remediated options to control in-situ sediment contaminants', Hydrobiologia, vol. 149, pp. 247-58.
Water Board 1989, Sydney's Deepwater Outfalls: Planning and Implementation, Sydney.
This technical paper by N. Philip was reviewed by Dr D.W. Connell & Professor J. Middleton.