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Site investigations will help inform future wastewater system choices

Updated: Nov 24, 2020

We are underway with the next stage of investigations for the Mei Te Vai Ki Te Vai project to provide additional, vital information to support the wastewater treatment plant design and Government’s decision on either land-based or ocean outfall disposal options.

In 2018, the Mei Te Vai Ki Te Vai Project Management Unit (PMU) confirmed that septic tank systems in Muri’s sensitive coastal area are contributing to the seaweed growths in Muri Lagoon. This is because nutrients from both household and commercial wastewater treated in septic tanks enter the lagoon. These nutrients get into the lagoon by direct groundwater flow to the vulnerable lagoon environment, and also via the streams that flow in the wet season when the groundwater table is high.

This key finding has highlighted the need for a new reticulated wastewater system to service Muri’s coastal area. The new system will divert wastewater from households and businesses to a central treatment plant, where it will be treated to a much higher level than septic tanks and then disposed of more appropriately. Septic tanks can remain in use in less sensitive and less developed areas, where the wastewater nutrients don’t overload the land capacity and compromise the lagoon’s health.

The PMU has already done some preliminary work to identify the best type of reticulated wastewater system. The next stage of investigations has begun to inform the treatment plant design, and support the Cook Islands Government’s decision on the most suitable disposal method.

The PMU have a potential wastewater treatment plant site, and with landowners approval have done some geotechnical investigations and soil testing to confirm if the site is suitable. The proposed treatment plant will be designed to the latest standards, with common concerns such as smell and visual impact being actively addressed through the design.

More information is also needed before determining the best disposal option for treated wastewater. Both land-based and ocean outfall options would need to meet stringent public health and environmental guidelines, and require ongoing monitoring and reporting once operating.

The PMU is assessing both options, looking at topography and soil types to identify suitable land. The PMU is also engaging experts to lead oceanographic and marine ecological studies, together with the Ministry of Marine Resources, to see how an ocean outfall can meet the standards and guidelines. Locals and visitors may notice some activity in the Ngatangiia area while these investigations are being done.

Experts involved in the investigations include Dr Matt Blacka, Brett Miller and Dr Tracy Ainsworth from the University of New South Wales, Dr Lara Ainley of MMR and soil scientist and PMU environmental lead, Dr Murray Wallis.

For more information see our project website or contact the PMU directly on +682 28851.

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