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: March 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.
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.
Consent is required for earthworks to site geobags (for desludging); the Greytown location has some currently unresolved sensitivities.
Items of significance:
Current plant design and processes are inadequate resulting in a risk of non-compliance (specifically related to Ammonia concentration in the effluent) and possible growth restrictions.
So far this season, 55,000m3 of treated effluent has been discharged to land; this meets the current season's targets. Critically, discharge to Papawai Stream during low flows has been avoided, as informed by ecological assessments. An additional ecological study will be undertaken to determine the baseline effect of this current season's discharge operation.
Community Liaison Group meeting held 26 March.
Greater Wellington Regional Council's peer reviewer is assessing the 'Stage 1B Efficacy Report' and WWL will continue to work with them to understand how the plant operation can be further optimised to achieve the full intention of the consent at Stage 1B.