Could Thirsty Willows Help Masterton Wastewater Discharge?

Thursday, 13 June 2024, 9:00 pm
Article: Emily Ireland - Local Democracy Reporter

Sustainable Wairarapa [SW] says Masterton’s wastewater irrigation strategy has “shortcomings” with only about 30 per cent of wastewater being discharged to land.

A major upgrade to the Homebush Wastewater Treatment Plant was completed in 2015-16 at a cost of about $46 million.

And although multimillion improvements to the project have been signalled in the council’s Long-Term Plan [LTP], Don Bell of SW says the council should consider a halt “until the community and stakeholders have an opportunity to reconsider the issues”.

Bell’s recent submission to the LTP claims the council could achieve a greater discharge of wastewater to land by transitioning to a “willow-based strategy”.

The strategy involves discharging treated wastewater to surface-flow wetlands planted out with short rotation coppice [SRC] willow.

SRC willow are water-loving plants that have “an extraordinary ability to use water” compared to grass, Bell said.

He said a Canadian study showed that SRC willow can use more than seven times the volume of water compared to grass in a surface-flow wetland through evapotranspiration.

“The present pop-up valve and border-strip irrigation setup [at Homebush] could easily be adapted to mimic a surface-flow wetland,” Bell said.

“Much greater volumes of water could be discharged and held within the borders by a low bund.”

MDC project delivery and assets manager Phil Evans said the concept of short rotation cropping had been raised, "but these discussions are at a very early stage".

Under Greater Wellington Regional Council’s [GWRC] Natural Resources Plan, MDC will be required to further reduce treated wastewater discharged into the river.

Evans said the main limitations to discharging to land were the area of land available [currently 72 hectares], and the weather [wet weather limits discharging to land].

“The existing consent will expire in 2034, and the council has made budgetary provisions to prepare for the renewal of this consent, and will consult with our iwi partners and any other affected parties ahead of making any decisions."

In the council’s draft 2024-34 Long-Term Plan, $2.52 million has been set aside in Year 8 for the Homebush irrigation extension.

Another $2.5m has been set aside for Years 9 and 10 for the Homebush consent renewal and plant upgrade to stop treated wastewater discharges to the river when the current consent expires in 2034.

MDC's strategy involves identifying suitable land for treated wastewater irrigation available for purchase, lease, or collaboration with owners; gathering comprehensive data and information on flow and volume characteristics of water to be available to farmers and property owners; and developing means of onselling available water.

Bell said any plan to pump treated wastewater to privately-owned land was “potentially flawed”.

“Will farmers be able to sell to a market and receive a premium price when there is a real or perceived potential for the product to be contaminated with human waste?”

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