Gippsland Water has many wastewater treatment facilities, see the map below and the following table.

Wastewater treatment lagoons

Gippsland Water has five separate wastewater lagoons at Dutson Downs which act as a series of waste stabilisation lagoons. These use physical and biological treatment processes incorporating anaerobic and aerobic digestion to break down the suspended and colloidal matter trapped in the waste. The liquid flows through the lagoon over a 60 day period into the final No. 2 Storage Lagoon, where it is retained for a further 30 days thereby producing a secondary treated effluent for discharge into Bass Strait.

The lagoons have a capacity to hold 3,000 megalitres of wastewater and can treat at least 15,000 megalitres of wastewater, produced by domestic and industrial customers, per year.
The wastewater is discharged to Bass Strait through an ocean outfall 1.2km out to sea. This outfall contains 27 diffusers that allow waste to be dispersed into the ocean. This allows wastewater to be disposed in the ocean at a rate of 1 in 100 dilution ratio. The quality of the wastewater is monitored for a wide range of chemical and biological parameters as required in the EPA licence.

Wash down and formation waters from oil and gas plant operations has its own saline treatment pond located at the Dutson Downs treatment facility. Approximately 10 megalitres of these wastewaters are received each day via one large pipeline into the saline treatment pond. This wastewater undergoes a 50-day biological treatment and evaporation process to remove oily compounds, nutrients and sulphide. Once this process is complete it is discharged to the fourth lagoon at Dutson and hence to the ocean outfall pipeline to Bass Strait.

Wastewater ocean outfalls

Treated wastewater is discharged at a rate of approximately 36 megalitres per day to Bass Strait. The treatment process has removed over 98% of the biochemical oxygen demand and suspended solids, as well as 99.999% of the bacteria. It is discharged at a depth of 15 meters and normally achieved a dilution of over 100ml of sea water to 1ml of wastewater on immediate discharge.

Monitoring of the discharge site over the past 10 years has shown that the discharge is not toxic and that there is no evidence of bioaccumulation of heavy metals or organic compounds in marine organisms.