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What is an ocean outfall?

Updated: Nov 24, 2020

Ocean outfall involves dispersing treated effluent deep into the ocean beyond the reef, using a special ‘diffuser’. The ocean currents disperse and dilute the treated wastewater, and the sea life consumes any remaining nutrients and organic matter it contains.

What impact would an outfall have on the environment?

Ocean outfalls typically have minimal environmental impact because the ocean has a very high capacity to disperse treated wastewater.

We are preparing a comprehensive Environmental Impact Assessment (EIA) for an ocean outfall to help inform Government’s decision about which treated wastewater disposal option should be progressed. The EIA will be published, so the public will have an opportunity to understand the impacts. If the Cook Islands Government chooses an ocean outfall, it would be designed to meet strict international environmental and public health standards.

Once in operation, regular and on-going testing of the treatment plant and water quality at the discharge site would be necessary.

How much land does it use?

The ocean outfall for the developed Muri coastal area will need about 2 hectares (5 acres) for the treatment plant and a pumping station to send treated wastewater to the outfall. One advantage of an outfall is that it could cope with future growth, without needing more land.

How would you decide where to put the outfall?

The MTVKTV project has engaged a number of technical specialists to do extensive monitoring and assessment to identify the most suitable location for an outfall.

Ocean outfall location is dictated by a number of things, including the depth of the outfall, wind, waves, ocean currents and distance from the wastewater treatment plant. Ocean outfalls are always located and designed to protect both the environment and public health, so recreational activities along the coastline would not be impacted.

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