Goulburn Mulwaree Council operate a single wastewater treatment plant at Ross Street with a connected equivalent population of approximately 22,000 people. The plant processes about four Megalitres of sewage per day. The Ross Street Plant was originally constructed in around 1915 and has had a number of augmentations since. The most recent augmentation involved the provision of new inlet infrastructure and storm pumps, which have significantly reduced the occurrence of uncontrolled overflows to the Wollondilly River during wet weather.
Sewage is collected and transferred to the Waste Water Treatment Plant via pump stations and a gravity reticulation network.
During wet weather significantly increased flows are experienced at the Waste Water Treatment Plant. This can be attributed to the poor condition of some existing pipes and illegal storm water connections. Existing pipes which are subject to infiltration from the surrounding ground are being renewed or replaced in the annual replacement program using trenchless techniques including relining and pipe bursting. This program is ongoing to help maintain and improve the sewer reticulation network.
The network consists of approximately 190km of sewer main ranging from small house drainage lines at 150mm to 750mm diameter carrier mains. Construction of the gravity network began in 1915, with much of the original pipe work still in service. Some of the earlier pipes are in poor condition and cause operational problems such as blockages. A variety of materials have been used in construction of the network including concrete, vitrified clay, asbestos cement, hobas, PVC and polyethylene.
Goulburn has a series of seventeen sewage pumping stations that collect sewage from sub-catchments within the city and transfer the sewage to the Waste Water Treatment Plant for treatment and reuse. The pump stations have been continuously constructed as the city has expanded. The first pump station was constructed at Bradley St in 1917, with the most recent being constructed at Clyde St in 2008. A majority of the pump stations are located along the Wollondilly and Mulwaree Rivers.
The majority of Marulan is serviced by a common effluent drainage system whereby the household maintains a septic tank and the effluent is collected and further treated. Eight sewage pump stations collect effluent in Marulan and transfer this to the treatment facility.
The Goulburn Waste Water Treatment Plant is a trickling filter plant, which provides primary and secondary treatment before the effluent is transferred to Gorman Road into storage dams and then irrigated at Council's farm, the Racetrack and the Cookbundoon Sporting Fields. Approximately 2300 Megalitres of effluent is treated each year, however this is subject to change depending upon rainfall.
The inlet works comprises an automatic step screen, bypass channel with manually raked bar screen, and vortex-style grit removal chamber. Effluent then passes via a splitter box to 4 primary sedimentation tanks of various configurations before passing to one of three trickling filters. Effluent from the trickling filters is dosed with alum to precipitate phosphorus before passing to 4 humus clarifiers and, ultimately, the effluent pumping station.
Effluent is transferred to Council's effluent irrigation farm located adjacent to the Wollondilly River at Gorman Road. The farm comprises 740ML of effluent storage in 3 linked ponds and 225 Ha of irrigable farm pasture. There is permanent irrigation equipment as well as some units and a combined irrigation pump station and UV disinfection system, which provide disinfected effluent "on demand" to the irrigation equipment via a pressurised reticulation network. The Gorman Road Pumping Station has been equipped with a precautionary discharge arrangement to reduce the frequency of uncontrolled overflows to the Wollondilly River.
The treatment facility at Marulan consists of a simple aeration/maturation process. The treated effluent is then pumped to a local Council owned property and used for irrigation purposes