Perth Long Term Ocean Outlet Monitoring (PLOOM)
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History of Ocean Outlet Monitoring in Perth's Coastal Waters
Pre 1993
Prior to 1993, ocean monitoring proceeded according to Licence Conditions associated with the operation of the Wastewater Treatment Plants. Licence Conditions specified that monitoring was to be conducted once annually in summer at 35 sites (arranged in a grid) in the vicinity of the outfalls (see image below). The location and number of sites varied depending on the trajectory of the plume on the day of sampling. Sampling grids exist for northerly, southerly and easterly flows. The Annual Summer Water Quality Monitoring Programme is, to this day, one of only two regulatory requirements imposed upon the operation of the Wastewater Treatment Plants (see Regulatory Framework section below).
1991-1995
In 1988 the then Water Authority of Western Australia (WAWA) requested approval from the EPA for duplication of the Ocean Reef wastewater outlet. EPA granted approval subject to a number of Conditions (EPA Bulletin 393, 1990). Conditions 2, 4 and 6 required WAWA to undertake studies in the vicinity of Ocean Reef to (a) determine circulation and flushing characteristics; (b) determine the effects of nutrient loads on marine communities; (c) survey contaminants (metals and pesticides) before 1992 and every three years thereafter (to be reviewed after 12 years) and (d) undertake studies to ascertain the 'nutrient assimilative capacity' of Perth's coastal waters. The Perth Coastal Waters Study (PCWS) was established to address Conditions 2, 4 and 6. A major recommendation of the PCWS was that WAWA conduct a five year ocean outlet performance monitoring programme. This led to the development of the PLOOM programme, which has been running continuously since 1995.
1995-Present Day
Commencing in 1995, the modern day PLOOM programme continues to focus on the potential effects of the three metropolitan ocean outlets. Monitoring is conducted primarily in summer (through the Annual Summer Water Quality Monitoring Survey and the Trial Compliance Monitoring Programme), though recent modifications to the Trial Compliance Monitoring programme have allowed for outlet-specific monitoring in autumn. The suite of monitoring conducted as part of the PLOOM programme is outlined in the Monitoring Components section below.
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Regulatory Framework
The operation of the Wastewater Treatment Plants and the discharge of treated wastewater to the marine environment is conducted under Licence Conditions set by the Department of Environment and Conservation. The Licence Conditions include requirements to:
- Measure treated wastewater flows and associated contaminant loads to ensure maximum nutrient loads are not exceeded; and
- Undertake an annual summer survey of ocean and beach water quality (nutrients, primary productivity and bacteria indicators) in the vicinity of the ocean outlets.
Further to the Licence Conditions, there are also Ministerial Conditions set as part of the proposal to duplicate the Ocean Reef outlet in 1988 and the proposal to construct and operate the Sepia Depression Ocean Outlet Land Line (SDOOL).
These Conditions include the requirement to undertake metals and pesticide surveys in the vicinity of the Ocean Reef and Sepia Depression outlets every three years.
Monitoring Components
Regulatory Commitments
The Licence Condition to undertake the annual summer survey is fulfilled each year via the implementation of the Annual Summer Water Quality Survey. Further Conditions to undertake triennial metals and pesticides surveys of marine sediments are fulfilled every three years. Part of this study involves 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. Mussels have been used in the past as additional indicators of water column contaminants, in addition to samples taken directly from marine sediments. The results of these programmes are available in the Annual Reports (see Downloads box).
Additional Monitoring
In demonstration of Water Corporation’s commitment to Perth’s coastal waters, several monitoring programmes are conducted in addition to those required by regulatory Conditions. These programmes are the most rigorous of the water quality monitoring programmes conducted to date. Indeed, data collected in the last ten years have been used to establish clear spatial and temporal trends in nutrient and chlorophyll a concentrations in Perth Coastal Waters. Apart from providing managers with information on the effects of Perth wastewater outlets, these data are an invaluable tool for establishing long term patterns of water quality in Western Australia’s temperate waters in general (see Specialist Investigative Studies – Long Term Environmental Water Quality Analysis).
Each of the monitoring components, including those required by Regulatory Conditions are summarised below:
Treated Wastewater Characterisation
On-going monitoring of the treated wastewater to provide information on contaminant inputs is addressed through annual comprehensive characterisation of the treated wastewater discharged from the Beenyup Wastewater Treatment Plant. The comprehensive wastewater characterisation complements the regular sampling of treated wastewater undertaken by the Water Corporation.
The objectives of the treated wastewater characterisation are to:
- Identify potential contaminants of concern from treated municipal wastewaters through literature reviews and expert advice;
- Analyse for the 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; and
- Utilise information on the treated wastewater quality to establish whether appropriate ANZECC/ARMCANZ (2000) Guidelines are being met.
Numerical Modelling
Numerical modelling has been used in the PLOOM Programme as a tool to help understand how discharged treated wastewater is diluted by seawater, and how it may be dispersed in the marine environment under the action of winds and currents. This modelling has enabled predictions of how the treated wastewater discharged from the ocean outlets may affect coastal water quality.
While numerical modelling programmes cannot provide definitive predictions of what will happen in the environment, a robust model provides a good approximation of what is likely to happen under a given set of environmental conditions.
The near-field dilution zone begins at the point of discharge on the seafloor, and extends to the point of maximum elevation (e.g. the point at which the plume first reaches the surface). The objective of near-field dilution modelling is to utilise information from the treated wastewater quality in conjunction with the modelled initial dilution rates and mixing zones for the Ocean Outlets to establish whether the appropriate ANZECC/ARMCANZ (2000) Guidelines are met.
Far-field advection and dispersion is best modelled with three-dimensional baroclinic hydrodynamic models. These three-dimensional hydrodynamic models can be used to predict the spatial and temporal advection and dispersion of the plume and the fate of reactive constituents (such as faecal coliforms or nitrogen) as such constituents spread outside the ‘near-field’ zone of initial mixing and dissipate under the influence of the prevailing water movement. These far-field models account for factors such as bathymetry and various forcing factors (e.g. wind, tide, surface elevation differences, density differences), and rely on the output from an initial dilution model as an input. The models can be run for a variety of scenarios, including different meteorological and oceanographic conditions, different flow conditions for the outlet, and varying discharge water quality.
Annual Summer Water Quality Monitoring Survey
The operation of each of the wastewater treatment plants in Perth’s Metropolitan region, and the discharge of treated wastewater to the marine environment is conducted under Licence Conditions set by the Department of Environment and Conservation. The Licence Conditions include a requirement to undertake annual summer surveys of ocean water quality to examine the effects of discharged treated wastewater on the marine environment. For consistency, the Water Corporation has implemented similar summer water quality surveys in the marine environment at all three ocean outlets (Ocean Reef, Swanbourne and Sepia Depression).
Sampling for the annual summer water quality monitoring surveys occurs at 35 offshore sites within a rectangular sampling grid appropriate for the prevailing flow conditions at each outlet on the day of the summer water quality survey, and at nine shoreline sites located along the coast adjacent to each of the outlets.
Trial Compliance Monitoring
The overarching objectives of the Trial Compliance Monitoring (TCM) programme are to:
- Assess the environmental impacts of the treated wastewater discharge through regular and intensive water quality monitoring;
- Add technical support to the development and refinement of appropriate Environmental Quality Criteria (EQC) for use in Perth’s coastal waters; and
- Ensure that the Environmental Values and Environmental Quality Criteria are met.
There are two levels of EQC; Environmental Quality Guidelines and Environmental Quality Standards. Each of the criteria are detailed below:
| Environmental Quality Criteria | Details |
| Environmental Quality Guideline (EQG) | EQGs are a threshold numerical value or narrative statement, that if met, indicate 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 (EQS) | EQSs are 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 2005a). 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. |
The objective of the TCM is to develop an appropriate monitoring programme capable of measuring environmental quality against the Environmental Quality Objectives (see also Treated Wastewater Ocean Disposal). The programme uses objective criteria to determine whether the Environmental Values for Perth’s Coastal Waters have been maintained. To this end, TCM programme represents one of the most important components of PLOOM. Results of the TCM programme can be found in the PLOOM annual reports (see Downloads box).
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Whole of Effluent Toxicity (WET) Tests
WET tests involve subjecting marine invertebrates (and occasionally fish) to different solutions of treated wastewater. All tests, where required, are undertaken with appropriate animal ethics approval. The tests are interested in the biological response of organisms to the wastewater, including: reproductive success, growth and behaviour.
The PLOOM programme conducts WET testing on a quarterly basis using the 1 hr sea urchin fertilisation test. The 1 hr sea urchin fertilisation test is an excellent sentinel test for the following reasons:
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It has a rapid turn around time of ~3 days (allowing for rapid management action if adverse results are detected); and
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High sensitivity to soaps & detergents (surfactants), one of the key contaminants contained within domestic wastewater;
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In the absence of National guidelines for surfactants – one of the key elements of domestic wastewater – the 1 hr sea urchin fertilisation fills the gap and provides an important additional line of evidence to support the notion that ocean disposal of waste water is ecologically sustainable.
The 1-hour sea urchin fertilisation test is carried out by Ecotox Services Australasia Pty Ltd (‘Ecotox’), Sydney, New South Wales. Wastewater samples are collected in HDPE containers supplied by Ecotox, with the volumes required identified by the laboratory prior to wastewater collection. Ecotox is an NATA-accredited laboratory.
The test determines the success of sea urchin fertilisation over a 1-hour period using the gametes of the sea urchin Heliocidaris tuberculata. The sperm of the sea urchin are exposed to dilute wastewater for a 1-hour period and then added to an egg suspension. The fertilised eggs are counted and the percent fertilisation calculated. These results are used to calculate the NOEC (no observed effects concentration), LOEC (lowest observed effects concentration) and EC50 (the concentration at which 50% mortality is achieved – or, in this case, fertilisation is achieved in 50% of cases).
In some circumstances, the results of the sea urchin WET tests may act as a 'trigger' for the full suite of WET testing; that is, an additional series of WET tests incorporating a suite of marine organisms from a variety of trophic levels. To trigger the full suite of WET tests, the NOEC must be ≤1.0% (equivalent to more than a 100-fold dilution).
Results of WET testing to date have indicated that the dilution of treated water (between the outlet diffuser and the surface of the water column) is sufficient to reduce contaminant concentrations to level well below ANZECC/ARMCANZ (2000) guideline trigger levels. These results indicate that the continuing disposal of treated wastewater to our coastal environment is safe, and in no way detrimental to local marine life.
Specialist Investigative Studies
In addition to the monitoring components outlined above, the PLOOM programme has historically undertaken a number of specialist investigative studies. These targeted studies are designed to compliment the information obtained as part of the standard monitoring programme.
Results of a number of Specialist Investigative Studies can be viewed by clicking on the images below
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| Seaglider Trial | Long-Term Environmental Water Quality Analysis | Fish Diversity |
PLOOM Team
The PLOOM project team comprises of a multi-disciplinary group of technicians, managers and scientists. Personnel from each organisation are responsible for carrying out monitoring and/or analytical tasks specific to their area of expertise.
| PLOOM Program Team | ||
| Involvement | Team Member | Organisation |
| Water Corporation Project Manager | Mark Nener | Water Corporation |
| Oceanica Project Director | Mark Bailey | Oceanica |
| Project Manager | Dr Glenn Shiell | Oceanica |
| Treated Wastewater Characterisation | Dr Karen Hillman | Oceanica |
| Initial Dilution Modelling | Kellie Holloway | Oceanica |
| Water Quality Monitoring | Kris Wienczugow | MAFRL, Murdoch University |
| Annual Summer Water Quality Surveys | Mark Nener | Water Corporation |
| Phytoplankton Monitoring | Stuart Helleren | Dalcon Environmental |
| Ecotoxicity Testing | Dr Rick Krassoi | Ecotox Services Australasia |
| Annual Reporting | Dr Glenn Shiell | Oceanica |
| Communications Material | Dr Glenn Shiell | Oceanica |
| Microbial Analysis | Pathwest | |
| Chemical Analysis | National Measurement Institute | |
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