Wastewater troubles are bubbling up within Horizons Regional Council area - and fixing those issues could cost ratepayers millions.

Of the 46 wastewater treatment plants in the region at least 24 will need an upgrade, costing between $330m and $500m.

However in Horowhenua the situation is not that bleak, but it is not perfect either.

Rules are stricter now than when previous resource consents were granted, and Horowhenua has been working on discharging all treated wastewater effluent to land, rather than into water.

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Both Foxton and Tokomaru plants have been identified by Horizons as significantly non-compliant, while Waiterere complies but is at risk of non-compliance due to minor ponding in its irrigation area.

Waitarere is going through the consent renewal process, and its consent expired on June 27, 2007, according to a Horizons' report from last year. Tokomaru is also going through an application renewal, while Foxton's application is complete.

Council has budgeted approximately $11.5million to fix all wastewater treatment plant issues in the district.

"In the Horowhenua District there are seven Wastewater Treatment Plants (WWTP), five of which were compliant at date of last assessment," Council strategy and regulation group manager Dr Nic Peet said.

"Two WWTPs were significantly non-compliant - Foxton and Tokomaru. Both of these non-compliances are being addressed through new consent applications.

"Foxton's consenting process is now complete, however upgrades will clearly take some time to occur. Tokomaru is currently going through the renewal process," Dr Peet said.

Horowhenua District Council said it is changing what it does with wastewater, and is well advanced.

"The quality of river water near where treated wastewater effluent is discharged from the Foxton and Tokomaru wastewater treatment plants does not always meet the water quality standards for the presence of nitrates, ammonia and E. Coli under the National Policy Statement for Freshwater Management," Maurice McGunnigle, Water Services Engineer for Horowhenua District Council said. "They are more stringent now than the standards required when the Resource Consents for these wastewater treatment plants were originally granted.

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"Horowhenua District Council is moving towards discharging treated wastewater effluent from all of its wastewater treatment plants to land, which will alleviate any potential future river water quality compliance issues and also improve and protect our waterways.

"In consultation with iwi and the Foxton and Tokomaru communities, Council is working on proposals to carry out upgrades to the Foxton and Tokomaru wastewater treatment plants that will enable the treated wastewater effluent from these plants to be discharged to land," Mr McGunnigle said.

In September 2018, an interim Environment Court decision allowed the council to built a facility to discharge treated Foxton wastewater on to an island in the River Loop.

"Council is now focusing on gaining consent for land discharge for treated wastewater effluent from Tokomaru. Once these upgrades are completed, this would make Horowhenua District Council one of only a few councils in the country, if not the only one, to discharge all of its treated wastewater effluent to land and not into our waterways."

"The work in Foxton and Tokomaru is part of a long-term commitment by Council to discharge treated wastewater effluent to land instead of into waterways across the district," he said.

"Treated wastewater effluent from the Levin Wastewater Treatment Plant has been discharged to land at The Pot for over 30 years, using the first pressurised wastewater spray irrigation system in New Zealand.

"In 2017, Horowhenua District Council became the first council in New Zealand to use a purpose-made native ecosystem for irrigation and further treatment of wastewater effluent when it began replacing pine trees at The Pot with mānuka and kānuka as part of a five-year trial to assess environmental benefits.

Levin Wastewater Treatment Plant - Trickling filters (foreground), secondary clarifier, treatment pond.
Levin Wastewater Treatment Plant - Trickling filters (foreground), secondary clarifier, treatment pond.

In 2016, Council upgraded the Shannon Wastewater Treatment Plant so treated wastewater effluent could be used to irrigate Council-owned farmland instead of being discharged into the Manawatū River for 355 days of the year.

At the Waiterere plant Horizons has found a small ponding issue in the irrigation area, which the council rectified. Waitarere's plant was granted a new consent last June for 26 years, expiring on 1 July 2044.

Although resource consents for Foxton and Tokomaru wastewater treatment plants have expired, they can continue to operate if an application to renew the consent has been lodged at least six months before expiry.

"It is common for the decision process to take a long time. Horowhenua District Council had lodged applications for renewal of these consents within the statutory timeframes, and is currently operating under the conditions of the expired consents pending approval of the new consent applications. This is essential to keep infrastructure that is essential for public health operating," said McGunnigle.

Council has applied for a new consent to discharge treated wastewater onto land in Foxton and is installing a flow control valve on the outlet pipe from the plant that will shut off the flow to the river once the maximum daily discharge limit is reached.

In Council's Long Term Plan 2018-2038, about $9.5 million has been allocated for upgrading of the wastewater treatment plant, including design and installation of a new land irrigation system.

"Council is awaiting the final decision from the Environment Court on its application. Once released, the decision will be subject to appeal for 15 working days.

In July 2016 Council applied to renew its existing Tokomaru consent and is currently consulting with Horizons. Treated wastewater is currently discharged onto land and to the adjacent land drainage system.

"The non-compliance with exceeding the daily discharge limit has been due to isolated incidents of opening the valve during and after periods of extreme heavy rainfall events, to manage water levels in the land treatment area at the plant to prevent treated wastewater effluent from overflowing on to neighbouring farmland," he said.

"Council has budgeted approximately $2 million in the Long Term Plan 2018-2038 to upgrade the wastewater treatment plant, which will include expanding the capacity of the land discharge system."