SYDNEY’S DEEPWATER OCEAN OUTFALLS

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SYDNEYS DEEPWATER OCEAN OUTFALLSLong-term environmental performance

2007


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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, Sydneys beaches were polluted with primary sewage that was discharged fromcliff-face outfalls at North Head, Bondi and Malabar sewage treatment plants. Environmentalassessments from 1979 recommended deepwater ocean outfalls (that discharge treated effluent faroffshore) as the preferred option for managing wastewater. The assessments predicted that closing theold cliff-face outfalls would deliver significant environmental improvements close to the coast andbeaches, 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 haveassessed 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 withseawater on the continental shelf at depths of 60 to 80 metres. The primary treated effluent is conveyedthrough tunnels under the ocean floor, and is released through a series of diffusers. These diffusersrelease the effluent in fine jet streams, so it mixes immediately with seawater and disperses into thestrong East Australian Current. Because it is less dense than the salty seawater, the effluent movesupward and outward into the current as it disperses into an area called the mixing zone. At the sametime, the current continues to move it away from the coastline. Natural processes eventually break downthe 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 volumewould fill more than 1,000 Olympic swimming pools.

The deepwater ocean outfalls opened in 1990-91. For most of the preceding century, effluent wasdischarged from pipes along Sydneys shoreline. This degraded the coast and was the main cause ofpoor water quality at beaches.

The outfalls represent a long-term investment in protecting Sydneys coastline. They use much lessenergy than shoreline tertiary treatment and disposal, therefore producing less greenhouse gas, andthey use fewer chemicals. They also occupy less land, which keeps the coastline free of large sewagetreatment 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 Waterdevelop and implement a detailed environmental monitoring program (EMP).

The EMP ran between 1989 and 1993, and was one of the most comprehensive in Australia forassessing the impact of sewage discharges. It included pilot studies and extensive environmentalmonitoring that spanned before and after the commissioning of the outfalls. The extensive dataset itproduced has been the basis for ongoing assessment of ocean discharges along Sydneys 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 theenvironmental 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 performover the longer term.

Data is collected at 20 ocean monitoring sites (shown in Figure 1), from Terrigal on the NSW CentralCoast to Shoalhaven Bight south of Sydney, to detect any potential impacts on the marine ecology andsediments.

The monitoring program studies four main areas:

marine ecology

effluent toxicity

marine sediment characteristics

oceanography.

It forms part of the requirement of Sydney Waters Environmental Protection Licences for coastalsystems as required by the Department of Environment and Climate Change (DECC).


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Figure 1: Location of Sydneys 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 thedeepwater 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 evidentclose to the outfall, and less evident further away. At the Malabar Outfall, for example, monitoring isdone at intervals along the sea floor. Data is collected at the outfall, and at sites 3 km, 5 km and 7 kmaway.

The results are presented in Figure 2(a). A negative impact would show as four separate colouredclusters for each of the sites (such as the hypothetical case shown in Figure 2(b)). Instead, the sitescluster together as a mixed group regardless of distance from the outfall. This indicates there is noobvious difference in the marine ecology close to the outfall and that further away implying the outfallshave had no statistically significant effect on the environment even after 16 years of continuousoperation.

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

Marine AnimalGroups

Example Organisms

Mollusca Bivalves (e.g. clams) and snails

Annelida Marine worms (Polychaetes)

Arthropoda Crustaceans and isopods such aswater 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 Sydneys deepwater oceanoutfalls. 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 monitoringsites close to the deepwater ocean outfall to plot as a separate group from monitoring sites locatedfurther away (the expected scatter pattern for an impacted transect is shown in Figure 2(b)). The actualresults shown in Figure 2(a) show that there are no significant differences in the marine ecology atvarious distances from the deepwater ocean outfall.

Effluent toxicity testing

Toxicity testing became mandatory in 2004 under Sydney Waters DECC licences. The tests wereintroduced 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 toeffluent is observed to determine how likely the effluent is to affect organisms in receiving waters. Ifeffluent is not toxic to sensitive indicator species, it is unlikely to be toxic to others.

The sea urchin Heliocidaris tuberculatawas identified as an appropriate indicator species for Sydneyswaters, as it is particularly sensitive to toxins during its fertilisation lifecycle stage. Local Sydney seaurchins are specially cultured in the laboratory for the toxicity testing. The testing complies with therequirements of the NSW Animal Ethics Committee.

For each effluent sample, scientists determine the concentration required for a 50 per cent mortality offertilised sea urchins. The higher the effluent concentration required to achieve this mortality, the lesstoxic the effluent is.

The DECC sets stringent licence targets for toxicity. Results for all three deepwater ocean outfallscomply with licence targets over a number of years, with no evidence of ecotoxic effects in the effluentreleased from the deepwater ocean outfalls.

Results can be obtained from the Interactive sewage treatment plant (STP) map in Sydney Waters 2007online 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 chemicalparameters, 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 notappear to be associated with the deepwater ocean outfalls. In fact, concentrations of total organic carbonand metals (chromium, nickel, copper, cadmium, iron and zinc) are highest near the entrances to themajor 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

Sydneys deepwater ocean outfalls operate in a dynamic natural environment. Wave and currentconditions offshore are highly energetic. The outfalls harness this natural energy to disperse and breakdown effluent.

Oceanographic conditions affect how the deepwater ocean outfalls operate and how the marine ecologyand 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 kilometresoffshore from Bondi. The ORS measures and records oceanographic and meteorological variables, asshown in Table 3.

Data from the station is essential to the long-term oceanographic modelling used by a number ofcollaborative research projects. Sydney Water shares the data with agencies including the DECC, theBureau of Meteorology, the Defence Science and Technology Organisation, the CSIRO, the IntegratedMarine 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: OrganochlorinePesticides, PCBs

Polyaromatic Hydrocarbons

Cresols


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Plate 5: The Smith-McIntyre sampler used to collect sediment from the sea floor for the deepwaterocean 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, approximatelytwo kilometres off the Sydney coast. This device continually monitors ocean current and wave activityoffshore.


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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 environmentalperformance of the deepwater ocean outfalls. As a result of some of these reviews, a special edition ofthe Marine Pollution Bulletin in 1997 (Volume 33, Number 7-12)featured articles from a range ofscientific experts who had studied Sydneys deepwater ocean outfalls, including aspects such asoceanographic and physical processes, water quality and marine ecology. Topic areas studied in theMarine Pollution BulletinSpecial Edition on ocean outfalls are shown in Table 4.

The Marine Pollution Bulletinsummarised the scientists consensus as follows:

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

Table 4: Topic areas studied in the Marine Pollution BulletinSpecial 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 areaNo. studies

commissioned

Oceanography, Physical Processes & NumericalModelling

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 improvementin water quality at Sydney beaches.

Under the BeachWatch and HarbourWatch programs, the DECC continuously monitors swimmingconditions. Water quality samples are collected from beaches every six days and tested forconcentrations of two indicator bacteria: faecal coliforms and Enterococci. These bacteria are typicallyfound in sewage but are also commonly found in stormwater discharges. High concentrations canincrease the risk of infectious illnesses in humans.

Since the deepwater ocean outfalls opened, there has been a significant decrease in concentrations ofthese bacteria at Sydneys beaches. This is shown in the results from Bondi Beach in Figure 3. Thedeepwater 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 faecalcoliforms are associated with lower water quality. After the deepwaterocean outfalls opened, theconcentrations of faecal coliforms were markedly reduced across Sydneys Beaches, improvingswimming conditions.

Water Quality at Bondi Beach:

Faecal coliforms dur ing the Swimming Season

0

2

4

6

8

10

12

14

16

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

Year

No.ofsampleswherefaecalcoliforms

exceed100cfu

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 riversand estuaries, and eventually into the ocean. These diffuse source pollutants are a key source ofcontaminants and are generally associated with urban runoff and estuary flushing after wet weatherevents. 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 themonitoring program.

Plate 7: Freshwater flushing of the Hawkesbury Estuary

Climate change

The prolonged drought and evidence of climate change have reinforced the need for demandmanagement and other water saving initiatives.

As a result, lower consumption of water and recycling schemes have reduced inflows to sewagetreatment plants. Reduced inflows can mean higher concentrations of pollutants and other substances in

the wastewater.


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In summary

Sydneys deepwater ocean outfalls have delivered high-quality outcomes for the environment and thecommunity. 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 deepwaterocean outfalls. Sydney Water is committed to complying with its licence conditions and to meeting theexpectations of customers and the community.

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SYDNEY’S DEEPWATER OCEAN OUTFALLS