Waikato District Council has a consent to discharge treated wastewater to the lake from its treatment plant that services the surrounding urban area. The quality of the discharge varies throughout the year and although it will be compliant for much of the year, at times it is failing.
“Council’s current discharge consent was issued in July 2013 when the population of Te Kauwhata was lower. The current discharge consent does not expire until 2028 but the population of Te Kauwhata has now increased so we have much more wastewater to process through the plant and yet we still have to keep within limits that were set when the population and the wastewater generated was much lower,” said Special Infrastructure Projects Manager, Ian Cathcart.
Mr Cathcart said that the amount of treated wastewater from the plant entering the lake is incredibly small compared to the overall contribution of water from waterways entering the lake.
“With urgency we are putting in place the upgrades of the wastewater treatment plant to reduce the overall impact on the lake and meet its targets in the discharge consent,” he said.
Council is rebuilding the treatment plant to include a new UV unit to be commissioned in December 2021 and a Membrane Aerated Biofilm-Reactor (MABR) plant, which is scheduled to be commissioned by April 2022. This technology is expected to bring the treated wastewater discharge back into compliance with the consent.
The upgraded facilities are partly funded by a $16.2 million loan from Government’s Housing Infrastructure Fund that was put in place to assist local authorities in areas of significant projected population growth.
“We have been working on the current upgrade of the plant since 2019 when it became apparent we were not able to keep within the current consents for nitrogen, phosphorus and E.coli,” said Mr Cathcart.
“The new design will process the wastewater to a better quality so we can process higher amounts of wastewater but remain within consent levels. But, since the new designs were agreed, and since early last year with the onset of COVID-19, we have run into international supply chain difficulties that have held up the parts that we have ordered,” he said.
Aside from upgrading and maintaining the wastewater treatment processes collaboratively with mana whenua and key stakeholders, Council also works closely with partners, landowners and volunteers to contribute to the management of the lake through the Waikato Regional Council’s catchment management plan for Lake Waikare and the Whangamarino wetland.
Lake Waikare is the largest of several lakes in the upper floodplain of the Waikato River. It is located to the east of Te Kauwhata. The water in the lake is in poor condition due to its shallow nature (2m deep at its deepest), the heavy use of fertiliser in the surrounding district, the large population of Koi Carp, and to a lesser extent wastewater discharge from the local treatment plant.
• The UV plant is used to kill E.coli and viruses while the MABR plant will reduce suspended sediments, nitrogen and phosphorous.
• E. coli levels are monitored regularly in the treated wastewater before discharge. The ultraviolet disinfection unit which will be constructed by the end of the year will bring E. Coli levels in the treated wastewater to almost zero.
• E. coli has many sources including animals and birds in the catchment. The net contribution of the treated wastewater to the overall lake E. coli concentrations is likely very low.