SYDNEY’S DEEPWATER OCEAN OUTFALLS Long-term environmental performance

2007

Table of contents Introduction.................................................................................................................................................3

Environmental monitoring...........................................................................................................................4

Independent reviews ................................................................................................................................11

Contributing to clean beaches ..................................................................................................................12

Meeting future challenges ........................................................................................................................13

In summary...............................................................................................................................................14

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Introduction Until the early 1990s, Sydney’s beaches were polluted with primary sewage that was discharged from cliff-face outfalls at North Head, Bondi and Malabar sewage treatment plants. Environmental assessments from 1979 recommended deepwater ocean outfalls (that discharge treated effluent far offshore) as the preferred option for managing wastewater. The assessments predicted that closing the old cliff-face outfalls would deliver significant environmental improvements close to the coast and beaches, while opening the outfalls further offshore would have minimal new impact on the environment, due to the natural high-energy mixing processes of the ocean. Since then, extensive studies have assessed the environmental performance and public health benefits of the deepwater ocean outfalls. This paper outlines their performance and benefits.

What are deepwater ocean outfalls and how do they work?

Deepwater ocean outfalls release treated sewage two to four kilometres off the coast where it mixes with seawater on the continental shelf at depths of 60 to 80 metres. The primary treated effluent is conveyed through tunnels under the ocean floor, and is released through a series of diffusers. These diffusers release the effluent in fine jet streams, so it mixes immediately with seawater and disperses into the strong East Australian Current. Because it is less dense than the salty seawater, the effluent moves upward and outward into the current as it disperses into an area called the mixing zone. At the same time, the current continues to move it away from the coastline. Natural processes eventually break down the effluent components, which are by now very highly diluted. Sydney Water operates deepwater ocean outfalls at North Head, Bondi and Malabar. These serve almost 2.9 million Sydneysiders and treat up to 1,040 million litres of wastewater a day. This volume would fill more than 1,000 Olympic swimming pools. The deepwater ocean outfalls opened in 1990-91. For most of the preceding century, effluent was discharged from pipes along Sydney’s shoreline. This degraded the coast and was the main cause of poor water quality at beaches. The outfalls represent a long-term investment in protecting Sydney’s coastline. They use much less energy than shoreline tertiary treatment and disposal, therefore producing less greenhouse gas, and they use fewer chemicals. They also occupy less land, which keeps the coastline free of large sewage treatment infrastructure and reduces costs and disruption to the community.

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Environmental monitoring History

Approval for construction of the deepwater ocean outfalls was granted on the proviso that Sydney Water develop and implement a detailed environmental monitoring program (EMP). The EMP ran between 1989 and 1993, and was one of the most comprehensive in Australia for assessing the impact of sewage discharges. It included pilot studies and extensive environmental monitoring that spanned before and after the commissioning of the outfalls. The extensive dataset it produced has been the basis for ongoing assessment of ocean discharges along Sydney’s coast. The EMP aimed to determine if the outfalls would make beaches safe for swimming and fish safe to eat, and if they would protect the marine environment. The program found that the ocean outfalls performed well, meeting or exceeding the predictions of the environmental impact statements, and mitigated all of the previous environmental problems associated with the old cliff-face outfalls.

The EMP resulted in a series of peer-reviewed scientific reports and publications on:

ocean and beach water quality

sewage plume dispersal

contamination of fish and molluscs

seabed ecology and sediments

plankton

fish communities

the effects of organic contaminants.

Current monitoring

Sydney Water has an ongoing monitoring program to assess how the deepwater ocean outfalls perform over the longer term. Data is collected at 20 ocean monitoring sites (shown in Figure 1), from Terrigal on the NSW Central Coast to Shoalhaven Bight south of Sydney, to detect any potential impacts on the marine ecology and sediments.

The monitoring program studies four main areas:

marine ecology

effluent toxicity

marine sediment characteristics

oceanography.

It forms part of the requirement of Sydney Water’s Environmental Protection Licences for coastal systems as required by the Department of Environment and Climate Change (DECC).

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Figure 1: Location of Sydney’s deepwater ocean outfalls (red bars) and the ocean monitoring site (yellow diamonds). An additional monitoring site is located in the Shoalhaven Bight.

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Marine ecology Sydney Water compares the diversity and abundance of seafloor organisms at sites close to the deepwater ocean outfalls, to those at control sites far from the outfalls. Examples of the organisms sampled under this program are listed in Table 1 and are shown in Plates 1-4. If a deepwater ocean outfall were damaging the local marine ecology, the effects would be most evident close to the outfall, and less evident further away. At the Malabar Outfall, for example, monitoring is done at intervals along the sea floor. Data is collected at the outfall, and at sites 3 km, 5 km and 7 km away. The results are presented in Figure 2(a). A negative impact would show as four separate coloured clusters for each of the sites (such as the hypothetical case shown in Figure 2(b)). Instead, the sites cluster together as a mixed group regardless of distance from the outfall. This indicates there is no obvious difference in the marine ecology close to the outfall and that further away – implying the outfalls have had no statistically significant effect on the environment even after 16 years of continuous operation.

Table 1: Animal groups that are monitored in the marine ecology component.

Marine Animal

Groups Example Organisms

Mollusca

Bivalves (e.g. clams) and snails

Annelida

Marine worms (Polychaetes)

Arthropoda

Crustaceans and isopods such as water slaters

Poriphera

Sea sponges

Echinodermata

Starfish, sea urchins

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Plates 1-4: Marine organisms sampled from the sea floor in the vicinity of Sydney’s deepwater ocean outfalls. A comprehensive and ongoing marine ecology monitoring program (conducted over 16 years) has not detected any adverse impacts of the deepwater ocean outfalls on the local marine life.

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Figure 2 (a) Figure 2(b)

Figure 2(a): Cluster diagram of actual marine ecology results for the Malabar Deepwater Ocean Outfall. If this deepwater ocean outfall was negatively impacting the marine ecology, we would expect monitoring sites close to the deepwater ocean outfall to plot as a separate group from monitoring sites located further away (the expected scatter pattern for an impacted transect is shown in Figure 2(b)). The actual results shown in Figure 2(a) show that there are no significant differences in the marine ecology at various distances from the deepwater ocean outfall.

Effluent toxicity testing Toxicity testing became mandatory in 2004 under Sydney Water’s DECC licences. The tests were introduced to better measure the impact on the environment of treated effluent. To test for toxicity, indicator organisms are chosen for their sensitivity. Their reaction when exposed to effluent is observed to determine how likely the effluent is to affect organisms in receiving waters. If effluent is not toxic to sensitive indicator species, it is unlikely to be toxic to others. The sea urchin Heliocidaris tuberculata was identified as an appropriate indicator species for Sydney’s waters, as it is particularly sensitive to toxins during its fertilisation lifecycle stage. Local Sydney sea urchins are specially cultured in the laboratory for the toxicity testing. The testing complies with the requirements of the NSW Animal Ethics Committee. For each effluent sample, scientists determine the concentration required for a 50 per cent mortality of fertilised sea urchins. The higher the effluent concentration required to achieve this mortality, the less toxic the effluent is. The DECC sets stringent licence targets for toxicity. Results for all three deepwater ocean outfalls comply with licence targets over a number of years, with no evidence of ecotoxic effects in the effluent released from the deepwater ocean outfalls.

Results can be obtained from the Interactive sewage treatment plant (STP) map in Sydney Water’s 2007 online Annual Report.

Expected scatter for an impacted transect

0 km

3 km

5 km

7 km

Expected scatter for an impacted transect

Malabar benthic macrofauna 2002, replicate data, 1L corrected

0 km

3 km

5 km

7 km

Stress = 0.15Dimensions 2 and 3 of 3 Actual scatter at the Malabar transect

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Marine sediments Marine sediments at the monitoring sites are surveyed each year for a range of physical and chemical parameters, shown in Table 2. The sediment sampler is shown in Plate 5. To date, sediment results have varied between the monitoring sites. However, the variations do not appear to be associated with the deepwater ocean outfalls. In fact, concentrations of total organic carbon and metals (chromium, nickel, copper, cadmium, iron and zinc) are highest near the entrances to the major Sydney waterways – Broken Bay, Port Jackson, Botany Bay and Port Hacking. This suggests that general urban pollution generated in Sydney is the major source of low-level, background pollution in the marine sediments. Research is continuing to confirm these patterns.

Table 2: Parameters studied in the Marine Sediments Monitoring Program

Oceanography Sydney’s deepwater ocean outfalls operate in a dynamic natural environment. Wave and current conditions offshore are highly energetic. The outfalls harness this natural energy to disperse and break down effluent. Oceanographic conditions affect how the deepwater ocean outfalls operate and how the marine ecology and sediments behave. To better understand how the outfalls interact with oceanographic forces, Sydney Water operates a permanent Ocean Reference Station (ORS) (see Plate 6), three kilometres offshore from Bondi. The ORS measures and records oceanographic and meteorological variables, as shown in Table 3. Data from the station is essential to the long-term oceanographic modelling used by a number of collaborative research projects. Sydney Water shares the data with agencies including the DECC, the Bureau of Meteorology, the Defence Science and Technology Organisation, the CSIRO, the Integrated Marine Observing System, universities and local governments.

Sediment parameters

• Nutrients: Nitrogen and Phosphorus • Total Organic Carbon • Metals: Aluminium, Iron, • Heavy Metals: Arsenic, Chromium,

Copper, Lead, Nickel, Zinc, Cadmium, Mercury, Selenium, Silver

• Organic Compounds: Organochlorine Pesticides, PCBs

• Polyaromatic Hydrocarbons • Cresols

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Plate 5: The Smith-McIntyre sampler used to collect sediment from the sea floor for the deepwater ocean outfall monitoring program. This device is deployed on a line from a boat, and automatically collects a sediment sample when it reaches the sea floor.

Plate 6: The Ocean Reference Station is housed in a permanently moored marine buoy, approximately two kilometres off the Sydney coast. This device continually monitors ocean current and wave activity offshore.

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Table 3: Variables measured at the Ocean Reference Station

Independent reviews Sydney Water has commissioned several independent, detailed reviews of the environmental performance of the deepwater ocean outfalls. As a result of some of these reviews, a special edition of the Marine Pollution Bulletin in 1997 (Volume 33, Number 7-12) featured articles from a range of scientific experts who had studied Sydney’s deepwater ocean outfalls, including aspects such as oceanographic and physical processes, water quality and marine ecology. Topic areas studied in the Marine Pollution Bulletin Special Edition on ocean outfalls are shown in Table 4.

The Marine Pollution Bulletin summarised the scientists’ consensus as follows:

“Generally, the environmental monitoring program has found that the outfalls are performing well, ie that sewage plume dilutions exceed design specifications, and that they have reduced the degree of beach pollution in the Sydney area as well as leading to the recovery of degraded areas in inshore waters. The studies … demonstrate that the outfalls appear to have, to date, created no new problems in ocean waters near the outfalls or in the adjacent sediments.” (p. 121)

Table 4: Topic areas studied in the Marine Pollution Bulletin Special Edition on ocean outfalls.

Oceanographic variables: • Ocean current speed and direction [vertical profile] • Ocean temperature [vertical profile] • Ocean salinity [vertical profile] • Wave height and length

Meteorological variables:

• Wind speed and direction

Topic area No. studies commissioned

Oceanography, Physical Processes & Numerical Modelling 3

Water Quality & Potential Contaminants 5

Marine Ecology 6

Beaches 2

Community 1

General Environmental Monitoring & Design 4

TOTAL 21

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Contributing to clean beaches One of the most positive outcomes of the deepwater ocean outfalls has been the marked improvement in water quality at Sydney beaches. Under the BeachWatch and HarbourWatch programs, the DECC continuously monitors swimming conditions. Water quality samples are collected from beaches every six days and tested for concentrations of two indicator bacteria: faecal coliforms and Enterococci. These bacteria are typically found in sewage but are also commonly found in stormwater discharges. High concentrations can increase the risk of infectious illnesses in humans. Since the deepwater ocean outfalls opened, there has been a significant decrease in concentrations of these bacteria at Sydney’s beaches. This is shown in the results from Bondi Beach in Figure 3. The deepwater ocean outfalls have been very effective in safeguarding beaches from bacterial pollution. Water quality has greatly improved, making it safe to swim except after rain due to urban runoff and sewer overflows.

Figure 3: Water quality at Bondi Beach before and after the opening of the deepwater ocean outfalls. One indicator for water quality is the concentration of faecal coliforms. Higher concentrations of faecal coliforms are associated with lower water quality. After the deepwater ocean outfalls opened, the concentrations of faecal coliforms were markedly reduced across Sydney’s Beaches, improving swimming conditions.

Water Quality at Bondi Beach:Faecal coliforms during the Swimming Season

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Opening of deepwater ocean outfalls

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Meeting future challenges

Diffuse source pollutants

Pollutants generated by a large city and its surrounding catchment inevitably find their way into rivers and estuaries, and eventually into the ocean. These diffuse source pollutants are a key source of contaminants and are generally associated with urban runoff and estuary flushing after wet weather events. Freshwater flushing of the Hawkesbury Estuary is shown in Plate 7. Distinguishing between diffuse source and deepwater ocean outfall effects is a major challenge of the monitoring program.

Plate 7: Freshwater flushing of the Hawkesbury Estuary

Climate change

The prolonged drought and evidence of climate change have reinforced the need for demand management and other water saving initiatives. As a result, lower consumption of water and recycling schemes have reduced inflows to sewage treatment plants. Reduced inflows can mean higher concentrations of pollutants and other substances in the wastewater.

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In summary Sydney’s deepwater ocean outfalls have delivered high-quality outcomes for the environment and the community. Beaches and harbours are cleaner and the marine environment is healthy.

Since the deepwater ocean outfalls opened 16 years ago,

swimming conditions have significantly improved

beach grease has been eliminated

there has been no detectable negative effect on marine ecology or sediments

effluent discharged has consistently been shown to be non-toxic at its diluted state.

Sydney Water will continue to monitor and report on the environmental performance of the deepwater ocean outfalls. Sydney Water is committed to complying with its licence conditions and to meeting the expectations of customers and the community.