Dave Donaldson’s letter (8 Dec) lacks any scientific data justifying his claim that pumping wastewater, treated by the membrane bioreactor process, into the lake is ok. Too much nitrogen and phosphorus will remain. These chemicals are in fertilisers, enhancing plant growth, something we want less of, not more of, in Lake Rotorua.
Waste water into Lake Rotorua
Council has Certificate of Title, a legal lease agreement between the Crown, Council and landowners giving wastewater irrigation rights within Whakarewarewa Forest in perpetuity. Yes, we know the current land-based system isn’t working, primarily because of mismanagement and lack of maintenance by Council. To be effective spraying should occur in areas of 5-10yr old trees, thus irrigation sites must be relocated from time-to-time. This has rarely occurred.
In 2015 a Memorandum of Understanding was signed between Council and CNIIC to work towards vacating the forest by 2019, however, an MoU is not a legally binding document.
Currently, 755 tonnes of N/annum makes its way into the lake from all sources, 30t of which is from wastewater. To maintain a healthy lake, this needs to reduce to 435t.
Research by N Z Prof Dave Hamilton indicates that the MBR system, can remove only 90% N at best, leaving 4.3mg N/litre of water, thus, at current volumes approximately 30t N/annum will be discharged into the lake (much the same as now), rising to over 100t N/annum from the 70 million litre capacity, estimates suggest will be reached by 2035. This tonnage from wastewater alone!
No way! Council, improve, maintain and manage the existing land transfer system.