Citation: Sharon Beder, 'Fallout on Outfalls', Engineering World, April 1991, pp10-11.


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The choice of deepwater outfalls as a solution to Sydney's sewage pollution problems is but one example, some may think it an extreme example, of how engineering practice falls short of what is required for an ecologically sustainable future.

Sydney's deepwater outfalls were designed to meet negotiated standards set in 1974. They were also designed to meet the political objective of removing the large stains surrounding the shoreline outfalls. The engineers involved felt they were discharging their responsibilities in meeting these requirements and did not set out to protect the environment, per se, nor to design a sustainable solution that would meet the requirements of future generations. This has until now been acceptable engineering practice.

The water quality standards that the deepwater outfalls had to meet, WP-1, "Design Criteria for Ocean Outfalls," were negotiated between the Water Board and the State Pollution Control Commission after both organisations had decided that the deepwater outfalls were a good idea. WP-1 included criteria for toxic substances and faecal coliform in terms of concentrations rather than maximum quantities. This in itself encouraged an engineering solution that provided dilution rather than treatment before discharge.

The deepwater outfalls were designed to achieve dilution, dispersal, and die-off of faecal coliform not to ensure bathing waters were free of pathogens. Faecal coliform are organisms which occur naturally in the human gut and do not cause disease themselves. They are used as indicators of sewage pollution. They die relatively quickly in the ocean (1-9 hours) unlike pathogenic bacteria and viruses which can live for long periods of time in the ocean (sometimes months). Caldwell Connell, the Water Board's consultants, did experiments on the die-off rates of faecal coliform but not on disease causing organisms.

Similarly the outfalls were designed to dilute and disperse the toxic waste so that concentrations of heavy metals and chlorinated hydrocarbons at the boundary of an initial dilution zone would be less than the levels specified in WP-1. There was little effort made to discover the mechanisms that might cause these toxic substances to concentrate in sediments and marine life. In fact WP-1 ensured that more toxic waste would be allowed to be discharged into the ocean each year when the deepwater outfalls were built because they provided many times the dilution than achieved by the shoreline outfalls. Caldwell Connell, the Water Board's consultants did not test fish for bioaccumulation but a Water Board employee did some tests for himself in 1973. These tests showed clear evidence that heavy metals were even at this early date accumulating in marine life.

The deepwater outfalls were also designed to ensure the sewage field would remain submerged below the surface of the ocean for most of the time in summer so that it would not be seen, even from the air. The submerged field would travel in the direction of the deeper ocean currents rather than in the direction of the surface currents and the wind. The fate of a sewage field driven inshore by currents travelling shoreward was not investigated. Nor was the eventual fate of the sewage which travelled southwards as it was supposed to.

The deepwater outfalls were supposed to substitute for upgraded onshore treatment (currently only 10-15% of suspended solids are removed before the sewage is discharged). In this way the deepwater outfalls would meet the legal and political requirements but not necessarily the requirements of ecological sustainability.

Not only did the engineers involved accept the standards in WP-1 as sufficient, the engineers of both the Water Board and the SPCC were actively involved in setting those standards and then engineers in both organisations and their consultants helped to persuade the public that the deepwater outfall was an adequate long-term solution.

In recent years the inadequacy of the deepwater outfalls as a long-term solution has been confirmed by an independent team of engineers, Camp, Dresser & McKee commissioned by the NSW government to review the Water Board's Beach Protection Programme. Yet such is the engineering culture that the same firm of engineers, had it been given the brief given to Caldwell Connell (that is to come up with the most cost-effective solution to meet WP-1) may also have proposed the deepwater outfalls.

The engineers who work in the Water Board claim they have been caught out because of changing community requirements. Yet now that they are being forced to upgrade the treatment at the main Sydney outfalls they are still aiming for the cheapest possible technologies: dissolved air flotation at the North Head plant, chemically assisted sedimentation at the Bondi plant and Sirofloc magnetite precipitation at the Malabar plant. These will improve the removal of suspended solids and are cheaper than installing secondary treatment, which is the norm elsewhere in Australia and legally required in the United States.

In order to sell these minimum solutions to the public they are labelling them "secondary standard" technologies, although they are technically called "advanced primary" and do not treat anything that is dissolved in the sewage. They are less efficient at removing heavy metals, organochlorines and grease. The credibility of Water Board engineers suffered before because they failed to design solutions that would protect the environment and they do not seem to have learnt from that.

The engineering profession as a whole will similarly suffer from a loss of credibility if its members continue to only do the minimum required by law to protect the environment and to cater to their clients lack of social responsibility. The community has come to expect more than this and if engineers fail to put the public interest first then they may find themselves losing both status and autonomy.

It is time engineers re-evaluated their role in both private and government organisations and took a wider view of their responsibilities. We have the choice. We could easily become the villains of a bygone age. Far better to take a leading role in helping Australia achieve sustainability.