Consent granted for Whanganui Prison stormwater plan

Lake Wiritoa remains a popular spot for locals, despite being subject to algal blooms during summer. Photo / Bevan Conley

The Department of Corrections has been granted consent to continue discharging stormwater and associated contaminants from the Whanganui Prison to a channel connecting Lake Pauri and Wiritoa.

The original discharge consent ran out in December 2013, but the department applied for fresh consent within six months so discharge has continued legally since then.

The independent panel granted the Horizons Regional Council consent which runs until 2044.

At present, both lakes experience potentially toxic cyanobacteria blooms during most summers.

The Corrections' new proposal includes the installation of a proprietary filter capable of removing a minimum of 40 per cent of zinc and 30 per cent of nitrogen and phosphorus before the point of discharge, the preparation and implementation of a landscape plan, and works to reduce the annual load of phosphorus in the lakes system by a minimum of 9 kg per year.

The maximum discharge rate granted for the two outfall pipes will be 550 litres per second.

In addition, the discharge will be managed by a stormwater management plan, which is aimed at minimising adverse environmental effects and implementing opportunities for continual improvement in the discharge quality.

The consent hearing was held over three days in November 2020, with representatives from Department of Corrections and Horizons Regional Council meeting with public submitters and a panel of independent commissioners.

The application included statements from Antoine Coffin (iwi consultation and cultural impacts), stormwater management specialist Peter Cochrane, and Timothy Fisher, an expert in stormwater engineering.

Fisher said that flooding would not be worsened by the proposal, partly due to the fact that the catchment of the prison was only 2.4 per cent of the total catchment of the lakes system.

Cochrane said the concentration of total nitrogen at the point of the proposed discharge was 2.75 times lower than in the upstream waters of Lake Pauri and downstream waters of Lake Wiritoa.

Coffin argued the current status of the lake was due to decades of runoff from surrounding farming activities, and Corrections was not responsible for the degradation of the lake habitat.

But there were 17 submissions to the hearing, of which 15 were opposed to the proposal, one was neutral and one was in support.

Te Rūnanga o Tūhopo representative Jill Sheehy and Te Runanga o Nga Wairiki Ngati Apa's Chris Shenton were opposed to the discharge proposal, with Sheehy saying that recommendations put forward in the iwi's cultural reports had not been addressed by the Department of Corrections, and that the process was decided "before iwi were ever engaged".

The iwi report stated that discharge should not be put into Lake Pauri, Lake Wiritoa, or the connecting channel between the lakes, and a hybrid/co-design should be developed with iwi.

Sheehy said the hybrid/co-design option had not been sufficiently investigated before being discounted.

Submitter Dean Ranginui said, as a fourth generation eeler accessing the lakes for kai, he was bonded to the lakes along with his tipuna and mokopuna, and the historical algal blooms were "red flags" that something was wrong with the lakes.

Whanganui Prison is located near Lake Pauri (left) and Lake Wiritoa, with stormwater being discharged into the channel connecting the two bodies of water. Photo / File

Ranginui expressed his preference for an alternative stormwater plan, where the discharge was stored in tanks and reused as irrigation, or channelled into an engineered holding pond.

Alistair Duff, speaking on behalf of the Whanganui District Council Rural Community Board, raised concern about the high value of the lakes and the impact on those values from the proposed discharge.

Horizons' freshwater manager Logan Brown and senior consents planner Natasha Adsett both supplied evidence at the hearings in November with Adsett initially recommending the application be declined and that she could only support a three to five-year consent duration, to allow the prison to remain operational while alternative options were explored.

But after hearing Corrections' case Adsett concluded the proposal's impact on water quality would be "less than minor".

The panel ruled that the proposal included "demonstrable enhancement through
nutrient reduction and mitigation measures".

"We find this will assist with the restoration of the lakes to a less degraded state; and in turn, assist with the enhancement of the mauri of the lakes and working towards reversing of the trend of disconnectedness between iwi and the lakes.

"In considering the nature of the discharge and the sensitivity of the receiving
environment, the financial implications of other options, the current state of technical
knowledge and the likelihood the option can be successfully applied, we are satisfied
the application represents 'best practicable option'."