Greytown wastewater treatment plant connections  

What’s happened? 

A recent technical assessment from Wellington Water Limited (WWL) of Greytown’s wastewater treatment plant (GWWTP) has recommended an immediate stop to approving all new connection applications to the public wastewater network in Greytown, until treatment plant capacity is planned for and funded. 

Connection constraints
Wellington Water have advised South Wairarapa District Council (SWDC) that future connections to the treatment plant need to be carefully considered and SWDC taken this advice on board. Effective immediately SWDC will be pausing new wastewater connections in Greytown with the exception of:

• residential and developer consents and permits that have already been approved – these will be honoured.   
• residential and developer consents and permits that are still in the process of being approved – these will be honoured.   
• applications from existing landowners of urban sections who are yet to apply for a single residential connection to the wastewater system will be considered.

While the GWWTP is not under an abatement notice, WWL have identified an increased risk of non-compliance; therefore, Council believes it is necessary to take this step to help mitigate the risk of adverse impacts on the environment.   

Background  

In 2023 SWDC initiated a health check of its four wastewater treatment plants after the pause on accepting new connections to the Martinborough public wastewater network. In that report, that was publicly released, it was noted that we were facing similar constraints in all our wastewater treatment plants to varying degrees. 

This month, an updated technical health check by WWL was initiated after the review of a pre-application assessment for a potential 200 lot development planned for Greytown. A development of this size would increase Greytown’s population by 10-15%.  In their advice, WWL considered the wastewater system constraints, and risks and opportunities to enable new development connections to support growth in Greytown. 

The conclusion was that the Greytown Wastewater Treatment Plant (GWWTP) currently does not have the capacity to support a development of this size. The proposed development would also increase constraints on the existing water supply, particularly regarding water supply pressure and fire-fighting requirements. There was also a risk of flooding issues. Population growth in Greytown is moderate but ongoing, and future demand models predict further strain on the water network.  

The existing population of Greytown is approximately 2,720. Greytown’s population was estimated at 2,202 in the 2013 census, 2466 in 2018 census and is projected to increase to 3674 by 2051.  

The Greytown WWTP was designed to service approximately 2200 people and the existing population exceeds this by around 500 people.

Context 

South Wairarapa has a smaller population than many council districts, and our settlements are widespread. This means our infrastructure is multiplied throughout the area as opposed to metro areas where services are typically centralised into one large asset. We have four wastewater systems in Martinborough, Featherston, Greytown and Lake Ferry.  

At the Greytown Wastewater Treatment plant, wastewater (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 Papawai stream, depending on the season, river levels and conditions of the Resource Consents. 

The current consent WAR6080254 in which the treatment plant operates requires SWDC to operate in accordance with the application made in 2014. At the time, no additional growth was expected, based on Statistic NZ projections, with a small buffer expected from existing observed loading. The consent required initial upgrades for ultraviolet disinfection and an initial land disposal field, a further stage of land disposal from 2030 and finally winter storage from 2039 to effectively remove discharge of treated wastewater from Papawai Stream.  

The plant was granted new consents on 11 February 2016. These consents will continue for 35 years (expiring 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 pond 
• 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. 

Paying for water services for the small populations living in our three distinct urban areas and rural areas is our biggest challenge and has the largest impact on rates increases.  

Looking ahead  

Following an abatement notice on the Martinborough wastewater treatment plant in 2022, SWDC commissioned WWL to undertake a ‘health-check’ on South Wairarapa’s other treatment plants. The results of the checks were produced promptly by WWL and a copy is available for the public here.  

There are several initiatives underway working towards addressing capacity at Greytown wastewater treatment plant. These include the following:  

Desludging 
Following the health-check, SWDC then engaged engineering consultant Stantec to advise on the compliance pathways for both Martinborough and Greytown. They advised that the most critical action we must take in all WWTPs was to desludge. Phase one of this work for the GWWTP is scheduled for the current 2024-25 financial year and will be completed in the next financial year. The MWWTP will be fully desludged this financial year.  
 
Capacity study 
SWDC are urgently progressing a wastewater network capacity study for Greytown which will provide information required to plan and design options for upgraded or new infrastructure. 
 
Irrigation trials  
Part of our resource consent obligations is to discharge some of South Wairarapa’s wastewater to land (except during high river flow conditions). This past summer as part of a trial run by WWL to help optimise the performance of the plant, the district has seen a 170% increase in treated (cleaned) wastewater that’s been put to land in South Wairarapa, rather than the rivers or ocean.   
 
Funding and Plant upgrades  
Funding for the required stages 2 and 3 of treated wastewater disposal as required in our consent have been foreshadowed in our Long-Term Plan (LTP) investment advice from WWL. 

Funding for plant upgrades to address capacity constraints is not yet confirmed as the capacity growth study is needed to inform the requirements. It is anticipated that significant additional funding in Council’s 2025-34 LTP will be required. 

For example, upgrades to provide additional treatment capacity (such as aerators or baffling) could be safely installed on the pond without adverse effect on other treatment aspects. Adding this equipment to the pond could unlock additional potential for growth in Greytown but the design team engaged must define what is possible on this pond system, in line with the results of the growth study defining expected future loadings. Proposed upgrades will also need to be reviewed with Greater Wellington Regional Council, to understand whether they can be achieved within the existing consent conditions. 

What does this mean for the local community and businesses? 

South Wairarapa District Council appreciates the impact this decision will have on developers and people seeking to build new homes in Greytown. We regret having to make this decision which we know will temporarily slow growth. New connections will be paused only for as long as necessary.  

All permits, resource management and building consents that have been received and approved by Council will be honoured and a connection to the wastewater network made. 

A domestic on-site wastewater treatment and disposal system is an alternative to a direct connection to the wastewater treatment plant. Greater Wellington Regional Council is responsible for managing discharges to land and they are available to advise you on your options: Greater Wellington — Contact Us

Documents

Technical assessment Greytown Connections Advice (June 2024)
WWL high level statement on capacity of SWDC wastewater treatment plants (May 2023)

FAQs