Bunbury monitoring program

Treated wastewater discharged from the Bunbury Wastewater Treatment Plant is monitored to identify contaminants entering the marine environment. Samples are analysed in January, April and October. This complements our regular sampling of treated wastewater.

• 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)

Monitoring results indicate that:

• As most of treated wastewater is domestic, the characteristics of wastewater received at the plant are relatively consistent.
• The quality of the discharge varies with the level of treatment.
• All of the Environmental Quality Standards are met following initial dilution of the treated wastewater.

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.

Water quality surveys are conducted in January, April and October, by Marine and Freshwater Research Laboratory and Murdoch University, under the direction of Oceanica.

The key monitoring objectives, together with their respective sub-objectives are outlined below:

Physical-chemical profiles

• To determine the effect of 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 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 outfall.
• To assist us in developing a consistent approach to the management of ocean outfall in Western Australia.

Phytoplankton monitoring

• To assess the influence of 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 outfall and if 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 outfall, 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 outfall.
• Assess the influence of treated wastewater discharge on periphyton chlorophyll content.

We monitor seagrass in the vicinity of the Bunbury ocean outfall in January, April and October, to determine potential impacts of treated wastewater on the density of seagrass. Regular monitoring also provides an early warning system for detection of long term ecosystem effects.

The density of both seagrass leaves and shoots (rhizomes) at four compliance and four reference sites is determined annually in spring, autumn and summer. Sampling is conducted by Marine and Freshwater Research Laboratory (MAFRL) and Murdoch University, under the direction of Oceanica.

Results indicate that sea grass density is extremely variable, with differences on both a spatial (seasonal) and temporal (inter-annual) scale. There is no evidence to attribute these differences to exposure to wastewater. Marine ecologists have used the data to demonstrate the magnitude of change (in leaf and shoot density) resulting from natural processes.