The largest desalination plant on the Eastern Seaboard – featuring two marine tunnels to be constructed by purpose-built Tunnel Boring Machines from Germany – is now under construction on Queensland’s Gold Coast.
Located in Tugun, Queensland and adjacent to the Gold Coast Airport, the 125ML/day facility is being constructed by the GCD Alliance comprising John Holland Constructions, Veolia Water Australia, Sinclair Knight Merz and Cardno.
The Alliance will also operate the plant for 10 years following its commissioning in November 2008.
Owned by the Queensland State Government and Gold Coast City Council, the plant will provide an emergency bulkwater supply for South East Queensland.
One of the project’s key milestones in 2007 is the arrival of two 130 tonne Herrenknecht Tunnel Boring Machines (TBMs) from Germany in May.
Shaft excavation is currently underway, with 24-hour operations to commence shortly. The top 35 metres of the two shafts have been constructed with diaphragm walls due to the local geology.
After being lowered 70 metres down the shafts, the TBMs will each bore a marine tunnel (3.4 metre external diameter) from the plant site to inlet and outlet risers 1500 metres out to sea.
These high-tech machines were purpose-built for the project and were chosen because of the significantly reduced impact on the environment and the community, and the safety of construction of the tunnels, 40 metres below the seabed.
The 2.2 kilometre (in length) intake tunnel will draw seawater to the plant, where it will undergo Reverse Osmosis (RO), a process which involves pushing seawater (under high pressure) through a semi-permeable membrane that traps the salt and other impurities.
Measuring 1.3 kilometres from the shoreline and 700 metres from the plant, the outlet will be slightly north of the intake. The distance between the two and the depth of water will allow for the brine to be returned to the ocean and dispersed efficiently, without affecting the quality of the intake water or the marine environment.