Greytown Wastewater Treatment
At the Greytown Wastewater Treatment plant, sewage flows through an aerated facultative pond, a maturation pond and ultraviolet treatment. Discharge of the treated effluent is managed to either an adjacent block of land by irrigation or to the Papawhai Stream, depending on the season, river levels and conditions of the Resource Consents.
The plant was granted new consents on 11 February 2016. These consents will continue for 35 years (expire 11 February 2051).
In general, the consents allow SWDC:
- to discharge treated wastewater to land via an irrigation system where there is a soil moisture deficit that is greater than the depth of discharged wastewater.
- to discharge treated wastewater to the Papawai Stream at an annual average daily flow of up to 750 cubic meters per day and at a maximum daily rate of up to 1,500 cubic meters per day.
- to discharge treated wastewater to land via seepage from the oxidation ponds
- to discharge contaminants and odours from the oxidation ponds within the boundary
- to discharge contaminants and odours from irrigation of treated wastewater to land within the boundary.
Current Status: Compliant, but with the risks identified below
Period: October 2023
Earlier in the year, Greater Wellington Regional Council issued letters requesting explanations of non-compliance. Wellington Water is implementing the required corrective actions where possible within the plant and resource constraints.
Major investment is required, and current funding levels do not meet this requirement.
Wellington Water is undertaking a programme of work to better manage the treated effluent discharge rates in relation to the stream flow rate.
A compliance upgrade project is currently underway however the scope of that does not currently allow for growth.
Items of significance:
Current plant design and processes are inadequate resulting in a risk of non-compliance.
WWL working through options to optimise discharge to land during the coming irrigation season, to avoid where possible a discharge to Papawai Stream during low flow (informed by ecological assessments).
A new inlet flowmeter has been installed.
Irrigation season kick-off meeting with the glider club & grazer. Improved irrigation conditions have been agreed.
WWL has commissioned the consent-required 'Stage 1B Efficacy Report' for submission to GWRC by 1 January 2024.