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.
Resource consents
Plant performance
Current Status: Non-compliant
Period: September 2024
Commentary:
In 2023, 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 approved funding levels do not meet this requirement.
A compliance upgrade project is currently underway (excluding growth). The plant is already operating beyond its design loading capacity and so new connections have been paused.
Funding has been approved to complete a Growth-Capacity Study in conjunction with Martinborough's study.
The degree of desludging that will be achieved at Greytown is not yet determined. Further funding may be required to complete.
Items of significance:
The 2024-2024 Annual Report was submitted to GWRC. Current plant design and processes are inadequate for the connected population, resulting in non-compliance (specifically related to nutrient concentrations in the effluent).
The biannual CLG meeting was held in September
New connections have been paused while a Growth-Capacity study is undertaken to determine how to ensure the WWTP can operate compliantly with new connections.
Wellington Water identified a leak from the 1st maturation pond discharging partially treated effluent to the Papawai Stream. This has been temporarily isolated while the permanent isolation works are planned. An Incident Report was submitted to GWRC explaining the likely volumes and reason for this leak route.
The 'Stage 1B Efficacy Report' is currently being updated and was submitted with the Annual Report.