Each year, we discharge 100 billion litres of treated wastewater from Beenyup, Subiaco and Woodman Point wastewater treatment plants via ocean outfalls in Ocean Reef, Point Peron and Swanbourne.

The Perth Long Term Ocean Outlet Monitoring (PLOOM) program was established in 1995 and focuses on the potential effects of ocean on the marine environment. We have engaged an independent consultant, Oceanica Marine and Coastal Specialists, to conduct the program.

Monitoring is conducted primarily in summer, through the Annual Summer Water Quality Monitoring Survey and the Trial Compliance Monitoring Program, along with outlet-specific monitoring in autumn.

Regulatory framework and reporting

The operation of the Beenyup, Subiaco and Woodman Point wastewater treatment plants and the discharge of treated wastewater to the marine environment is conducted under our Licence Conditions set by the Department of Environment and Conservation (DEC). These include:
  • Measuring treated wastewater flows and associated contaminant loads to ensure maximum nutrient loads are not exceeded.
  • Undertaking an annual summer survey of ocean and beach water quality (nutrients, primary productivity and bacteria indicators) in the vicinity of the ocean outfalls.
Further to the Licence Conditions, there are also Ministerial Conditions, set by the Minister for Water, which include undertaking metals and pesticide surveys at the Ocean Reef and Point Peron (Sepia Depression) outlets every three years.

The Licence and Ministerial Conditions for the Perth Monitoring Program include annually reporting on our performance to the DEC and Minister for Water.

How we monitor our performance

Monitoring required by Licence and Ministerial Conditions

Our triennial metals and pesticide surveys involve the deployment of sentinel mussels. The filter feeding biology of mussels makes them ideal indicators of the concentration of pesticides and heavy metals in the water column.

These monitoring results are included in the Annual Summer Water Quality Monitoring Report.

Additional monitoring

We are committed to protecting our coastal water and undertake a number of additional rigorous water quality monitoring programs. The data collected over the past 10 years has been used to establish clear spatial and temporal trends in nutrient and chlorophyll a concentrations. It is also used as a tool for establishing long term patterns of water quality.

These monitoring results are included in the Ocean Reef, Sepia Depression and Swanbourne Annual Reports.

Specialist investigative studies

We also undertake a number of specialist investigative studies. These targeted studies are designed to complement the information obtained as part of the standard monitoring program.

Monitoring components

The components of the Perth Monitoring Program set out in our Licence Conditions are summarised below:

Treated wastewater discharged from the Beenyup Wastewater Treatment Plant is monitored to identify contaminants entering the marine environment. This complements our regular sampling of treated wastewater.

The objectives of treated wastewater characterisation are to:

  • Identify potential contaminants of concern from treated municipal wastewaters through literature reviews and expert advice.
  • Analyse for potential contaminants of concern in the final effluent discharged from the Beenyup Wastewater Treatment Plant to the marine environment via the ocean outlets at Ocean Reef.
  • Utilise information on treated wastewater quality to establish whether appropriate ANZECC/ARMCANZ (2000) Guidelines are being met.

Numeric modelling is used to develop a robust model of how discharged treated wastewater is diluted by seawater, and how it is dispersed in the marine environment under the action of winds and currents. This has enabled predictions of how treated wastewater discharged from ocean outlets may affect coastal water quality.

We conduct summer water quality surveys for the Ocean Reef, Swanbourne and Point Peron (Sepia Depression) ocean outlets. Samples are taken at 35 offshore sites within a rectangular sampling grid appropriate for the prevailing flow conditions at each outlet on the day of the survey, and at nine shoreline sites located along the coast adjacent to each of the outlets.

The compliance monitoring program is one of the most important components of the Perth Monitoring Program. It trials various monitoring program methods with the aim of developing a monitoring program capable of measuring environmental quality against the environmental quality objectives. The program uses objective criteria to determine if the environmental values have been maintained.

The overarching objectives of the Trial Compliance Monitoring program are to:

  • Assess the environmental impacts of treated wastewater discharge through regular and intensive water quality monitoring.
  • Add technical support to the development and refinement of appropriate Environmental Quality Criteria for use in Perth’s coastal waters.
  • Ensure that the Environmental Values and Environmental Quality Criteria are met.

There are two levels of Environmental Quality Criteria - Environmental Quality Guidelines (EQG)and Environmental Quality Standards (EQS), these are detailed below:

Environmental Quality Guidelines

A threshold numerical value or narrative statement, that if met, indicates there is a high degree of certainty that the associated environmental quality objective has been achieved. If the guideline is not met, there is uncertainty as to whether the associated environmental quality objective has been achieved and a more detailed assessment against an EQS is triggered.

Environmental Quality Standard

A threshold values or narrative statements that indicate a level beyond which there is a significant risk that the associated environmental quality objective has been not been achieved. EQSs involve a risk-based approach that considers multiple lines of evidence and integrates more refined measures of the surrogate indicators with more direct measures of the Environment Quality Objective (Environmental Protection Authority 2005). If an EQS is exceeded, it is considered that there is a significant risk that the associated Environmental Quality Objective has not been achieved, investigation of the cause is needed and an adaptive management response is triggered if the exceedance continues.

Results of the trial compliance monitoring program are provided in the Ocean Reef, Sepia Depression and Swanbourne annual reports.

Whole of Effluent Toxicity (WET) testing involves exposing organisms to different concentrations of treated wastewater and then measuring the growth and reproductive capability after a specific period of time. All tests, where required, are undertaken with appropriate animal ethics approval.

WET testing results indicate that the dilution of treated water is sufficient to reduce contaminant concentrations to levels well below ANZECC/ARMCANZ (2000) guideline trigger levels.

The Perth Monitoring Program conducts quarterly WET testing using the 1 hour sea urchin fertilisation test. This is an excellent sentinel test because:

  • It has a rapid turnaround time of approximately three days, allowing for rapid management action if adverse results are detected.
  • High sensitivity to soaps and detergents (surfactants), one of the key contaminants contained within domestic wastewater.
  • In the absence of national guidelines for surfactants, the test fills the gap and further confirms that ocean disposal of wastewater is ecologically sustainable.

The test is carried out by Ecotox Services Australasia, a NATA-accredited laboratory.

Contact details

The PLOOM program team comprises a multi-disciplinary group of scientists, responsible for carrying out monitoring and analytical tasks specific to their area of expertise.

For further information about the program, or to lodge any complaints, please contact us on 13 13 75.