Abatement notice issued for nitrogen levels in Hāwea oxidation pond

Queenstown Lakes District Council (QLDC) has received an abatement notice from Otago Regional Council (ORC) in relation to the performance of Hāwea Wastewater Treatment Plant, after the facility failed to achieve its 12 month rolling mean for nitrogen levels within treated wastewater discharged to its oxidation pond.

QLDC General Manager Property & Infrastructure, Tony Avery said while the breach and abatement notice were disappointing, environmental monitoring in Hāwea River showed there were no adverse effects associated with the treatment plant’s elevated nitrogen levels.

“Treated wastewater is discharged to land either via the facility’s land treatment area or an infiltration trench, both of which are located downstream from Lake Hāwea and ultimately drain through to Hāwea River. As a priority, staff are exploring further measures to improve performance and to bring the plant back into full compliance with its consent conditions,” said Mr Avery.

“We’ve been aware of fluctuating nitrogen levels in the treated wastewater and have attempted to resolve them through upgrades to the facility’s wastewater treatment processes in the recent past, and while these changes have resulted in significant improvements, nitrogen remains above consented limits.”

Monthly testing in Lake Hāwea, and in Hāwea River downstream from the wastewater treatment plant show no adverse effects associated with the current non-compliance.

Given historical non-compliance of Hāwea’s treatment plant and the need to cater for significant growth in the catchment, plans are already in place to connect the township to Project Pure/Wānaka Wastewater Treatment Plant.

This planned connection is part of the wider Upper Clutha Wastewater Conveyance Scheme project, which will see significant investment in wastewater management capacity across both the Hāwea and Wānaka schemes.

Funding for this project is included in the adopted QLDC Long Term Plan 2024-2034, with an overall budget of $80.1m which includes approximately $22m of funding from the Infrastructure Acceleration Fund.

ENDS|KUA MUTU.

Media contact: communications@qldc.govt.nz or call 03 441 1802.

FURTHER INFORMATION | Kā pāroko tāpiri:

Abatement Notice: https://www.qldc.govt.nz/media/mdtnsorw/enrma250015-abatement-hawea-wwtp.pdf

Map of Hāwea WWTP monitoring sites: https://www.qldc.govt.nz/media/2lrgygxu/qldc_hawea-wwtp-monitoring-map_apr25.pdf

Upper Clutha Wastewater Conveyance Scheme: https://www.qldc.govt.nz/your-council/major-projects/upper-clutha-wastewater-conveyance-scheme/

Hāwea Wastewater Treatment Plant – current treatment process:

Hāwea currently uses a Moving Bed Biofilm Reactor (MBBR) process and an oxidation pond to treat wastewater before returning it to the environment.

1. Wastewater enters the oxidation pond and undergoes conventional biological treatment, targeting a reduction in the biochemical oxygen demand of the wastewater.

2. Partially treated wastewater is then pumped from the outlet end of the oxidation pond into the MBBR tank which contains thousands of small, plastic pieces of media with a similar density to water, so they can move freely within the wastewater.

3. Bacteria form a biofilm on the surface of the plastic media.

4. Oxygen is provided to promote growth and activity of bacteria within the tank and to keep the plastic pieces moving around within the wastewater.

5. Bacteria breaks down and consumes organic matter in the wastewater, specifically converting ammonia to nitrate.

6. The water treated through the MBBR is then returned to the inlet end of the oxidation pond where the nitrate rich water mixes with the incoming ‘fresh’ wastewater, providing the correct environment for denitrification to occur.

7. Depending on the time of year, weather, and loading rates, the primary location of discharge is to the Land Treatment Area (LTA) adjacent to the plant where the treated wastewater is used as irrigation to grow a crop, and the secondary (and primary through winter) location is to a rapid infiltration trench which ultimately drains to Hāwea River.

Why Total Nitrogen is tested for:

Nitrogen helps plants grow. But if levels in water are too high, it can increase plant and/or algae growth and reduce water clarity and oxygen levels over time. This lack of oxygen can affect aquatic animals present within the water.