Bunbury Ocean Outlet Monitoring (BOOM)

Ocean outlet monitoring in Bunbury's coastal waters

Disposal of wastewater to the ocean adjacent to the Bunbury Wastewater Treatment Plant (WWTP) commenced in 2002 and continues to the present day. The volume of the wastewater has increased gradually from an of 6.2 in 2002 to 8.9 ML/d in 2009 in line with regional population growth.

Oceanica (in conjunction with MAFRL) has conducted monitoring on behalf of Water Corporation since the programme’s inception in 2002.

Regulatory framework

The Bunbury Ocean Outlet Monitoring (BOOM) programme is underpinned by Licence and Ministerial Conditions. Environmental monitoring is conducted pursuant to Conditions M6.1-6.2, Commitments P20-23 (pertaining to Marine Management) and Commitments P1.1-1.3 (pertaining to wastewater management). According to the Licence, the Licencee (Water Corporation) is to conduct monitoring three times per year (January, April and October). Results of the monitoring programme is summarized in the Annual Reports (see Downloads box).

Monitoring components

Treated Wastewater Characterisation

Monitoring of the treated wastewater (TWW) is conducted to provide information on contaminant inputs to the marine environment. Samples are analysed on a tri-annual basis in October, January and April. Comprehensive treated wastewater characterisation complements the regular sampling of treated wastewater undertaken by the Water Corporation.

The Treated Wastewater Characterisation analysis includes testing for the following parameters:

Biological Oxygen Demand (BOD)
Total suspended solids (TSS)
Electrical conductivity
Salinity
Ammonium (NH₄⁺ as ammonia NH₃)
Nitrate (NO₃^-) and Nitrite (NO₂^-)
Total Phosphorus (TP)
Thermo-tolerant coliforms (TTC)
Metals (Ag, As, Cd, Cr, Cu, Hg, Mo, Ni, Pb, Se, Zn)
Pesticides (organochlorine, organophosphates)
Herbicides (triazine, phenoxy acid)

Results of the Treated Wastewater Characterisation programme have indicated the following:

As the TWW is nearly all domestic, the characteristics of the influent to the wastewater treatment plant are relatively consistent;
The quality of the discharge varies with the level of treatment; and
All of the Environmental Quality Standards are met following initial dilution of the treated wastewater.

Numerical modelling

Numerical modelling has been used in the BOOM Programme as a tool to help understand 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 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 barotropic or baroclinic hydrodynamic models (refer definitions below). 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. For example, modelling and sampling have demonstrated that the discharge does not pose a risk to beach users.

Water quality monitoring

Licence Conditions stipulate that water quality is monitored in the vicinity of the Bunbury ocean outlet on a tri-annual basis in October, January and April. Water quality sampling is conducted by the Marine and Freshwater Research Laboratory (MAFRL), Murdoch University, under the direction of Oceanica.

The objectives of the programme are to monitor the potential impacts of treated wastewater on the surrounding marine environment. Regular monitoring provides information on the effect of treated wastewater on the physical-chemical and biological components of the ecosystem, which may serve as an early warning system for detection of long term ecosystem effects and /or potential risks to human health.

The monitoring programme was developed based on an understanding of the processes that occur during the discharge of the treated wastewater and knowledge of the potential effects of treated wastewater on the marine environment and human health. Thus, each of the components incorporates a specific set of sub-objectives.

Results of the Water Quality Monitoring programme continue to demonstrate that disposal of treated wastewater to the environment south of Bunbury is sustainable. This is indicated clearly in the meeting of each of the Environmental Quality Standards for each of the monitoring components. This is an outcome that the Water Corporation, Bunbury, is enormously proud of, and an outcome that Water Corporation has resolved to maintain.

The key components of the water quality monitoring programme, together with their respective sub-objectives are outlined below:

Physical-chemical profiles

To determine the effect of the treated wastewater plume on ambient oceanic conditions e.g. variable salinities in the vicinity of the outlet.
To provide a means for monitoring seasonal shifts in oceanographic characteristics - and therefore the potential for seasonal changes and/or fluctuations in treated wastewater impacts.

Nutrient and public health water quality monitoring

To monitor the potential for nutrient enrichment as a result of the treated wastewater discharge.
To determine microbiological counts in the vicinity of the outlet and surrounding environment.
Provide data to underpin the development of appropriate Environmental Quality Criteria for coastal waters adjacent to the Bunbury Ocean Outlet.
To assist the Water Corporation in developing a consistent approach to the management of ocean outlets in Western Australia.

Phytoplankton monitoring

To assess the influence of the treated wastewater discharge on phytoplankton communities. Nutrient enrichment associated with the discharge of treated wastewater may result in changes in phytoplankton community composition and abundances.
Determine if potentially toxic phytoplankton species are present in the coastal waters around the Bunbury Ocean Outlet and whether the concentrations exceed the Western Australian Shellfish Quality Assurance Program (WASQAP) Operations Manual (Department of Health and Department of Fisheries 2004) guideline concentrations.
Provide data to underpin the development of appropriate Environmental Quality Criteria for coastal waters around the Bunbury Ocean Outlet as part of the Environmental Quality Management Framework which may be implemented in the future.

Periphyton monitoring

To provide insight into the response of the periphyton to ambient and background nutrient concentrations.
Through differentiation of chlorophyll derivatives, provide information on the composition of the algal community present on the periphyton collectors.
Utilise the growth of periphyton on artificial collectors as an indicator (or sentinel) of the extent of nutrient enrichment in the coastal waters around the Bunbury Ocean Outlet.
Assess the influence of the treated wastewater discharge on periphyton chlorophyll content.

Seagrass health

Licence Conditions stipulate that seagrass is monitored in the vicinity of the ocean outlets on a tri-annual basis in October, January and April. To this end, the density of both seagrass leaves and seagrass shoots (rhizomes) at four compliance and four reference sites is determined in the spring (October), summer (January) and autumn (April) of each year. Sampling is conducted by the Marine and Freshwater Research Laboratory (MAFRL), Murdoch University, under the direction of Oceanica.

The monitoring programme was developed based on an understanding of the processes that occur during the discharge of the treated wastewater together with knowledge of the potential effects of treated wastewater on the marine environment.

The objectives of the programme are to monitor the potential impacts of treated wastewater on surrounding seagrass meadows in the vicinity of the ocean outlet. Regular monitoring provides information on the effect of treated wastewater on the density of seagrass shoots and leaves which inturn may serve as an early warning system for detection of long term ecosystem effects.

Results of the programme have demonstrated that the sea grass density is extremely variable. Data are indicative of striking variation on both a spatial and temporal (seasonal and inter-annual) scale, with no evidence to suggest differences between sea grass meadows exposed to treated wastewater, and those that are not. These results are of immense interest to marine ecologists who have used the data to demonstrate the magnitude of change (in leaf and shoot density) resulting from natural processes alone.

Specialist investigative studies

Sediment quality

Monitoring of sediment quality in the vicinity of the Bunbury Ocean Outlet was first undertaken in 2000. Results of initial investigation found the sediments to be clean and free from anthropogenic contaminants.

The objective of the sediment monitoring programme is to assess the condition of the marine sediments in the vicinity of the Bunbury Ocean Outlet, against the condition of similar sediments at appropriate references sites. The programme provides a means for detecting changes in the quality of the sediments, particularly those (i.e. eutrophication and organic matter contamination) that may be related to the anthropogenic effects of treated wastewater.

BOOM team

The BOOM project team comprises of a multi-disciplinary group of managers, technicians and scientists. Personnel from each organisation are responsible for carrying out monitoring and/or analytical tasks specific to their area of expertise.

BOOM Program Team
Involvement	Team Member	Organisation
Water Corporation Project Manager	Jenni Boyle	Water Corporation
Oceanica Project Director	Mark Bailey	Oceanica
Project Manager	Sarah Scott	Oceanica
Field Logistics and Sampling	Kris Wienczugow	MAFRL, Murdoch University
Treated Wastewater Characterisation	Dr Karen Hillman	Oceanica
Initial Dilution Modelling	Kellie Holloway	Oceanica
Water Quality Monitoring	Kris Wienczugow	MAFRL, Murdoch University
Phytoplankton Monitoring	Stuart Helleren	Dalcon Environmental
Seagrass Monitoring	Kris Wienczugow	MAFRL, Murdoch University
Annual Reporting	Sarah Scott	Oceanica
Microbial Analysis		Pathwest
Chemical Analysis		National Measurement Institute