The review came about following several scientific studies that were commissioned to find out what was behind the growth of periphyton (algae), downstream of the Totara Road wastewater Treatment Plant, in the Manawatū River during periods of low flow.
The Review Hearing will be heard by independent commissioners later this year and will determine what, if any, resource consent conditions may need to be changed.
Palmerston North City Council chief executive Paddy Clifford says that throughout the process, Council has been guided by peer reviewed scientific research.
"It has been a long journey," says Mr Clifford, "from when the issue was first raised to working proactively with Horizons Regional Council to coming up with a scientifically backed action plan."
Paddy Clifford says both parties agree the treated discharge is having more of an effect than was anticpated when Horizons initially gave Council consent.
"It's the extent of the effect and the remedies proposed where we differ."
"We are looking forward to finally having the matter resolved through the process of a pre-hearing meeting and then the formal hearing by independent Commissioners."
River Accord, offered to install a tertiary Disk Filtration System to reduce total phosphorus in the discharge with the intention of limiting periphyton growth to approximately the rates predicted when the 25 year consent was originally granted.
Council is currently carrying out research to find out what effect the installation of the filter will have on other algae present in the river. The project is included in the 2014/15 Annual Plan which is currently out for public consultation and if approved construction will begin in the next financial year.
Rob Green says having read Horizon's response he and his team acknowledge the differences of opinion held by both Councils and welcomes the opportunity for independent commissioners to consider the evidence.
The hearing will be held mid this year.
Wastewater Treatment Plant - notes
In 2003 Council was granted a 25 year consent for the wastewater discharge and embarked on a $16million upgrade of the treatment plant. A clarifier was built and alum dosing commenced which significantly improved the quality of the discharge into the river by reducing the amount of dissolved reactive phosphorus or DRP in the discharge. An ultra violet light treatment process was introduced which allowed Council to meet bacteriogical standards.
The discharge consent expires in 2028. Typically with large consents of this nature planning for renewal commences 5 to 7 years before expiry.
Council is a member of the Manawatū River Leaders Accord and has been working to reduce the number of treated wastewater discharges throughout its catchment to enhance the water quality of the river. The discharges are being redirected to the Totara Road plant which provides higher quality treatment than offered at the smaller plants. The overall project has an $8million budget and once completed the city will have only one point of discharge into the river. Linton and Aokautere have been redirected, Ashhurst will be redirected next month (April, 2014), construction of the Longburn connection is about to start and next year construction of the Bunnythorpe connection will begin.
In 2011 HRC assessed the discharge as not complying and causing a significant adverse effect on aquatic life due to its impact on periphyton growth and the macro-inverterbrate community during low flow conditions. This led to a joint PNCC-HRC Monitoring Programme by consulting ecologist Keith Hamill.
The Consent conditions recognise there would be more periphyton growth downstream of the plant however Mr Hamill's report found it was growing at a rate faster than expected causing mayflys to move downstream. The report also found more DRP in the river than could be explained by the discharge alone.
As a result of the report Horizons Regional Council is carrying out a formal review of the Consent conditions and Palmerston North City Council adopted a $1.7M Wastewater Action Plan. The plan included a review of treatment processes and mitigation options, an increase in alum dosing at higher flows, investigation into the causes of the higher periphyton growth downstream of the plant, de-sludging of the aerated ponds (due to occur later this year) and a marketing campaign aimed at encouraging residents to use non phosphorus based detergents.
Keith Hamill's studies continued throughout last summer during the worst drought in 70 years, thereby providing a unique opportunity to study the effects at extended periods of low flow. His full report is available here.