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: Compliant, but with the risks identified below
Period: August 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:
Current plant design and processes are inadequate for the connected population, resulting in non-compliance (specifically related to ammonia concentration in the effluent) which is affected by seasonal weather patterns.
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 has completed the first of a series of tests to determine the reason for a significant discrepancy between the inflow and the outflow measurements.
The 'Stage 1B Efficacy Report' is currently being updated and will be submitted with the Annual Report. Greater Wellington Regional Council will then be able to decide what action to take at Greytown.