Duvauchelle treated wastewater options

 The Duvauchelle Wastewater Treatment Plant was built in 1988, with minor upgrades completed in 1996 and 2002. It serves a community of about 250 dwellings, many of which are holiday homes.

The wastewater receives primary and secondary treatment and goes through an ultraviolet disinfection process before being discharged into Akaroa Harbour via a 1760-metre long marine outfall. Sludge is taken to the Christchurch Wastewater Treatment Plant at Bromley for processing into biosolids.

What is wastewater?

Wastewater, or sewage, is the used water from households, businesses and industries.

It includes everything flushed down toilets and water used for bathing and showering, laundry and dishwashing. It also includes any groundwater and stormwater that may get into the network.  

Given the requirements of the Resource Management Act, our own policy frameworks, and Ngāi Tahu cultural values, it is extremely unlikely we would get a new consent to discharge wastewater to the harbour because feasible land-based alternatives exist.

In discussion with the Akaroa Golf Club, the Duvauchelle Wastewater Working Party and Ngāi Tahu we investigated 12 feasible options. We eventually settled on the two options that you are able to have your say on here. 

Key considerations

All options considered had to meet criteria including:

Relevant law

Local Government Act (LGA) - Options must take into account social, cultural, economic and environmental wellbeing.

1. Efficient, effective and appropriate
2. Consentable as sustainable management under the Resource Management Act

Resource Management Act (RMA) - our current consent to discharge treated wastewater to Akaroa Harbour expires in 2023. It is a condition of that consent that we investigate alternative land-based options.

Te Tiriti o Waitangi – the Treaty of Waitangi

In recognition of Crown obligations under the Treaty, we provide opportunities for iwi to contribute to and participate in our decision making.

Ngāi Tahu rights and interests associated with Akaroa Harbour are strongly focused on mahinga kai (food gathering). Discharging treated wastewater into the harbour is culturally offensive to Ngāi Tahu and incompatible with customary use of the harbour as a food basket.

As tāngata whenua, Ngāi Tahu has kaitiaki (guardianship) rights and responsibilities to actively protect natural resources of the harbour for future generations.

Ngāi Tahu told us they will not accept any option that discharges wastewater to water.

Te Wai ora o Tāne Integrated Water Strategy

Council adopted this strategy in September 2019. It provides a holistic approach to our management of water supply (drinking water), wastewater, stormwater, surface water and groundwater. It recognises water as a taonga (treasure) and identifies the need to manage water resources in ways that support the environmental, social, cultural and economic wellbeing of current and future generations.

Goals include to:

• Reduce the effects of wastewater overflows
• Manage wastewater systems to meet community needs
• Develop long-term solutions for the disposal of treated wastewater from the Akaroa Harbour communities
• Develop an adaptive response to the effects of climate change
• Promote water conservation

New Zealand Coastal Policy Statement 2010

This national policy guides local authorities in their day-to-day management of the coastal environment.

It states that the discharge of treated wastewater to water in the coastal environment is not allowed unless:

• There has been adequate consideration of alternatives
• The decision to allow it is informed by an understanding of tangata whenua values and the effects on them
• Objectives, policies and rules in any plans that allow such a discharge were subject to early and meaningful consultation with tangata whenua

Risks

Risks identified with the chosen option will be managed appropriately during the design and construction stages, and through the resource consenting process.

Available land

The Akaroa Golf Course is the only land area big enough in Duvauchelle to receive the volume of wastewater produced. We own the land and lease it to the Akaroa Golf Club.

We would like your feedback on the options below.

Both the short-listed options use treated wastewater on the golf course land.

The first option beneficially reuses the wastewater for irrigation when needed and applies the treated wastewater to trees when not needed on the golf course.

The second option drip irrigates trees on the margins of the golf course and on another nearby property.
We are talking with a landowner who is keen to use treated wastewater to irrigate native trees on his property. However, at the time of publication, an agreement had not been confirmed.

Common to both options

Treatment process

• All wastewater is highly treated and disinfected at the treatment plant
• The scheme includes storage for treated wastewater
• The scheme is designed and engineered to be resilient to earthquakes, land slips, storms, flooding and with future growth taken into account

Golf course

We have worked closely with the Akaroa Golf Club over many years to narrow the options down to the two outlined here. Both options retain the Akaroa Golf Course as an 18-hole course.

Option 1 – Spray and drip irrigate Akaroa Golf Course

This is the preferred option.

In dry conditions (summer), it would be used to spray irrigate tees, greens and fairways.

In wet conditions (winter), it would be used to drip irrigate the planted margins around the golf course, including the area uphill of the golf course (already planted in trees).

In wet weather, when ground conditions on trees, greens and fairways are too wet for spray irrigation, the treated wastewater would be used to drip irrigate eight hectares of trees around the golf course.

Storage tanks for treated wastewater would be needed. Their total capacity would be 3,800 cubic meters (more details of this are available in the Beca report appendices(external link)). 

The treatment plant would be upgraded to treat the wastewater to the standard required for spray and drip irrigation to land used for recreation.

The capital cost would be about $13.1 million. 

The estimated annual operating cost would be about $240,000 (more details of this are available in the Beca report appendices(external link)).

Our wellbeing assessment shows:

• Cultural wellbeing: Ngāi Tahu supports this option because there is no discharge to the harbour.
• Social wellbeing: This option provides for true beneficial reuse of highly treated wastewater in a way that supports a valued community venue for recreation.
• Economic wellbeing: The capital and operational costs are higher than for Option 2 as the new wastewater plant would require significantly higher specifications to treat the wastewater to the standard needed for spray irrigation on a golf course and more irrigation and drainage work would be needed.
• Environmental wellbeing: Any negative effects on the environment would be minimal, with little effect on water resources. There are carbon benefits and the need to take water from the stream to irrigate Akaroa Golf Course will significantly reduce.

Staff opinion

We prefer this option because it meets expectations, national policies, and our strategic direction. It reuses the treated wastewater at one site – the golf course.

It satisfies the strong desire of Ngāi Tahu that we cease discharging treated wastewater into Akaroa Harbour.

The golf clubs supports this option and, from our discussions with the Duvauchelle Wastewater Working Party, it appears there is community support for using treated wastewater in this way.

Although this is the more expensive option, there are benefits in significantly reducing water use from the stream for irrigation, and the scheme's capacity for future growth.

Option 2 –  Irrigate Akaroa Golf Course and another property

Irrigate planted course margins, including areas uphill of the golf course. Retain an 18-hole course and irrigate a nearby property. The golf course playing areas would not be irrigated with treated wastewater.

We would use treated wastewater to drip irrigate the planted areas around the golf course and trees on private land nearby. The golf course playing area would not be irrigated.

The treatment plant would need only a minor upgrade for drip irrigation.

Approximately 9.4 hectares of trees will be required for this drip irrigation option.

Storage capacity of 3,200 cubic meters would be needed (more details of this are available in the Beca report appendices(external link)). 

The capital cost would be about $8.2 million.

The estimated annual operating cost is $200,000 (more details of this are available in the Beca report appendices(external link)). 

Our wellbeing assessment shows:

• Cultural wellbeing: Ngāi Tahu supports this option because there is no discharge to the harbour.
• Social wellbeing: We see no issues.
• Economic wellbeing: The capital cost is lower than it is for Option 1. We would need to buy land or come to a land-lease arrangement for the wastewater to be used at the second property.
• Environmental wellbeing: Any negative effects on the environment would be minimal, with little effect on water resources, although the golf club would still take water from the stream for irrigation. There are carbon benefits in planting new areas of native trees.

Staff opinion

We like this option because it has a good costs-benefits balance and offers good operational flexibility.

It meets the expectations of the law, national policies, and our strategic direction. 

It satisfies the strong desire of Ngāi Tahu that we cease discharging treated wastewater into Akaroa Harbour.

We are in discussion with the owner of a nearby property who has expressed an interest in using treated wastewater to irrigate native plants.

Options considered and rejected (Listed in no particular order)

For more information, please refer to the technical report [PDF, 1.3 MB](external link) (produced by BECA). The technical BECA report appendices can be accessed via Google Drive(external link)(external link). 

1. How much will this project cost?

The total budget for the project is $14.4 million, however the capital costs for the two options that we are looking at are $13.1 million (option 1) and $8.2 million (option 2).

2. Can I have more information about the golf course drainage improvements involved with option 1?

A more detailed map of this plan is shown on page 2 of appendix B(external link).
An initial concept investigation identified 18 areas where drainage upgrades are proposed. Indicative details of these are provided in Appendix E3.(external link)
In future stages of this project these concepts will require further work to develop the preliminary and detailed design. We will do this in coordination with the Akaroa Golf Club to incorporate the course requirements.

3. What level of treatment will be given to the wastewater in each of the options?

There are no New Zealand guidelines for using treated wastewater in recreational areas, so we have used the Australian Guideline for Water Recycling. This specifies the level of treatment required to protect human health, with 99.999% of pathogens removed (also known as 5 log reduction). Both options achieve this but through different means:

Option 1 – the treatment standard would be achieved by upgrading the wastewater treatment plant to include membrane filtration and a UV disinfection unit.

Option 2 -  the treatment standard would be achieved through dripper irrigation (the likelihood of people ingesting wastewater applied using drippers is considerably less than if it is spray applied), and access restrictions (i.e. stand down periods or exclusion zones). An example of stand down periods would be through night-time irrigation. If unrestricted access is to be provided (i.e. no stand down period or exclusion zone), a UV disinfection unit would need to be added to the treatment plant.

Please refer to the Beca technical report section 3.2 Wastewater Treatment plant(external link), and Appendix D1(external link) and D2(external link) for more detail.

4. What does ‘golf course margins’ mean in option 2?

The “Golf Course margins” mean the non-playing surfaces of the Akaroa Golf Course property. Some of these are already planted in trees while others would need to be planted.

5. What is the ‘minor upgrade’ of the treatment plant described in option 2?

This is a simple disc filter to make sure that the dripper nozzles don’t block.

If unrestricted access is to be provided (refer to FAQ #3), Option 2 would also require a UV disinfection unit (the approximate capital cost of this would be less than $200,000).

6. There is a rumour going around that land that is irrigated with wastewater isn’t suitable for cows. If it is not suitable for cows, how is it safe for humans to interact with?

As part of our early look into options, we investigated irrigating a property that is used for dairy farming. This was not a viable option as Fonterra does not accept milk from cows that have been fed grass or hay which has been irrigated with human wastewater, no matter how well treated. The reason for this is because of the public perception of risk for their international market, not because of safety concerns. Both options are safe for people, pets and farm animals in areas where public access is permitted.

7. How much run-off will occur on land below the golf course?

For both options, we would be irrigating at a rate at which the grass or trees can take up the water, so there would be no runoff. We would not irrigate when the soil is wet and instead would store the treated wastewater until conditions were suitable for irrigation again. There is adequate storage to hold surplus wastewater until more irrigation is needed.

8. What kind of modelling has been done for the ‘worst-case scenario’ in terms of storage tank failure?

In all scenarios that have been modelled, the existing gullies managed the wastewater without any overland flow onto neighbouring properties. The scenarios were for previous options which weren’t shortlisted and which had larger storage volumes.

9. Will there be any adverse effects on the preschool and school grounds?

No, our resource consent will ensure that any potential adverse effects on neighbouring properties are avoided, remedied or mitigated.