Wellington Scoop

Harbour search continues for new fresh water supply

News from Wellington Water
With the New Year, the harbour bores project has resumed its drilling programme with the barge and drilling rig Tuhora heading back out. Drilling is expected to continue for up to 30 days, weather dependent, at a new location near Somes Island.

We’ve chosen this site based on data from the first bore site which indicated that whilst the Waiwhetu aquifer has treatable quantities of freshwater in a viable yield, there is potential for better results at a second site.

This site also allows us to triangulate results using data on water from the land-based bore on Somes which also draws on the Waiwhetu aquifer.

The barge and drilling rig has had modifications to the leg bases to ensure stability in the softer sea bed conditions.

Earlier report – 28 August
The first exploratory Wellington Harbour bore has discovered fresh water in sufficient volume that it could be used as an emergency supply. As we expected it would require treatment to be used for drinking as early tests have identified levels of manganese, iron, and ammonia. The exploratory bores are part of wider initiatives by Wellington Water and the Wellington Regional Council to build the region’s water resilience in event of an emergency.

The barge and drilling rig Tuhora found freshwater in both the upper Waiwhetu and the Morera aquifers in the first bore at a site approximately 800 metres off the Mirimar Peninsula. The bore hole has been sealed to protect against any cross contamination between the upper and lower sections of the aquifers and any seawater contamination.

The first bore has been a scientific success enabling one of the most significant studies of the aquifers and the seabed to be carried out by partners GNS Science and the National Institute of Water and Atmospheric Research. The data about the freshwater resource and a collection of core samples of the seabed will be analysed providing first insights into the geological nature of the sites.

We’re investigating ways to provide Wellington city with an increased and more resilient water supply.
Miramar map March web size 2017

Recent surveys found that the Waiwhetu Aquifer may extend under Wellington Harbour as far out as the harbour entrance. We’re drilling exploratory bores in up to four locations (depending on results) in the harbour to determine if permanent water bores could be viable. If their viability is proven, the under harbour bores could be a cheaper and more resilient alternative to a cross-harbour pipeline.

The exploratory bores are being drilled off the northern coast of the Miramar Peninsula in Kau Bay. The closest bore will be approximately 550 metres off the coast with the others 200 metres apart heading towards Eastbourne. One may be further out – approximately 2km off shore. Exploratory drilling began in early July. The drilling equipment is well lit to ensure it’s visible to marine traffic.
Update 24 July 2017

Late last week the barge and drilling rig team reached freshwater in the upper aquifer at a depth of about 23 metres under the seabed. Water samples are now being tested to see if it is drinkable and/or could be easily treated and we’re continuing to drill into the aquifer until we reach the lower aquifer. If the laboratory testing shows the water quality at this location is not acceptable, the barge and rig will be moved and exploratory bore hole drilling will continue at a second location.

If the tests show the water is of a high enough quality, we’ll then move onto pump testing using larger production bores to obtain flow rate data from the aquifer. This will help determine whether we can draw useful quantities of water from the aquifer without impacting it.

We’d expect that stage to start late 2017, subject to water tests and it would take around 3-4 months.

What the tests will achieve

Once the exploratory bore is achieved, we’ll pump water from the bore for seven days (a pump test). The flow of extracted water will be measured and its quality will be checked. We’ll also monitor the impact of the test bores on the existing aquifer.

How the bores will be drilled

People will be able to see a barge which acts as a temporary platform for the drilling to take place from.
Environmental controls

Respecting our environment is one of Wellington Water’s core values. Environmental consents for the exploratory bores have been granted from Greater Wellington Regional Council and there are strict controls in place to manage all activities. Controls include managing the discharge of sediment and contaminants. The test bores will not harm the marine environment.

The Waiwhetu Aquifer
Frequently asked questions

Why does Wellington need a new water supply?

Wellington city’s drinking water supply comes from three sources: the Waiwhetu Aquifer via the Waterloo Water Treatment Plant, the Wainuiomata and Orongorongo rivers via the Wainuiomata Water Treatment Plant and the Hutt River via the Te Marua Water Treatment Plant. It’s piped to Wellington along the State Highway 1 and 2 corridors. In the event of an earthquake, it’s likely that these main water pipelines will break and could take months to repair. We want to improve the resilience of Wellington city’s water supply by providing a pipe that does not cross known faultlines.

How was the location selected?

In February 2016, the National Institute of Water and Atmospheric Research (NIWA) carried out an acoustic survey of the area to better define the extent and depth of the gravels that comprise the fresh water Waiwhetu Aquifer. The study observed the gravel layer extends into Evans Bay and off Point Halswell and Point Jerningham. The thickness of the gravels is estimated to be approximately 11-12m.

What happens if the tests prove the bores are not viable?

If the investigations prove that a permanent water supply is not possible from the bores then we’ll continue investigating a cross-harbour pipeline. It’s likely that a small monitoring bore will be left in place to record the behaviour of the aquifer.

What happens if the tests prove the bores are viable?

If the investigations prove the viability of the bores, then resource consent will be sought to build a permanent bore field and pipeline to collect the water and pipe it to an existing network.
Barge and drilling rig on its way

Barge and drilling rig on its way

What tests will be carried out on the water samples?

Tests include physical analyses such as pH, temperature and conductivity; alkalinity and hardness; chemical analyses (for chloride, fluoride, salt, various metals); and microbiological testing for coliforms.

How long would it take to establish permanent under-harbour water bores?

A permanent bore could be operational within two years following the successful completion of the investigations.

How would permanent bores look?

Any permanent bore would be located below the seafloor so would be invisible from above. It would consist of a concrete cap on the seabed and a pump located beneath the seafloor. It would pump the water through a buried pipe to the Miramar Peninsula.

Has offshore drilling for water been done before in New Zealand or internationally?

We are aware of a similar undersea water exploration project in the United States, but it is still in the planning stage. However, bores are frequently situated along coastlines and can draw water in from under the sea back towards the shore – although we are unaware of any sea floor bores.

In Wellington, we are exploring sub-harbour bores due to favourable geology and the need to provide the city with a resilient emergency water supply. In New Zealand, as we far as we can determine, there is not a similar drilling project.

We do know that a very small offshore bore was established for Matiu/Somes Island in 1942 which supplies approx. 2,000 litres of drinking water per day. The exploratory harbour bore project aims to provide an alternative supply of up to 30 million litres a day.

How much will it cost?

Subject to what we find, we estimate the cost of the exploration phase at around $5 million. If we find a viable source of drinking water, the cost of installing permanent bores and supplying it onto the Miramar Peninsula and into reservoirs would be up to $45 million.

What other options have you considered?

The next most feasible option is a cross-harbour pipeline from Lower Hutt. The costs would likely be approximately $90 million. This could still be an option if we are unable to establish offshore bores and may be considered in the future for increased resilience.

Will this project draw more from the aquifer?

No. This project would not increase existing consented water take from the aquifer which is currently drawn in the Hutt Valley and piped to Lower Hutt and into Wellington. Rather, it aims to provide an alternative access point into the aquifer to supply the city in an emergency if the main pipelines fail.

Will it have any negative impacts on the environment?

We expect the project to have very little – if any – environmental impacts. This aspect was rigorously assessed as part of our application for resource consent. Even noise and vibration from the drilling rig will not disturb fish. Specialist advice received indicates that of the few mammals that may sense the noise/vibrations, none of them are known to live in the harbour. The harbour is not known to be a feeding, breeding or resting area for these species, and only two are known to visit the harbour. If they happen to pay a visit during drilling operations, the duration and levels of noise/vibration emitted are not expected to cause them any concern.

Impacts on the seabed will be minimal and temporary due to the drilling of a thin, 20cm diameter bore down into the upper and possibly lower aquifer. The bores will be capped to prevent sea water infiltration into the freshwater aquifer and the seabed will be reinstated after bore completion.

How are you protecting the aquifer from bore contamination?

For the exploratory bores, there are several lines of defence.

All ground-engaging drilling equipment such as the drill rods and casings, has been purchased brand new so has never been in contact with soil or contaminants from other sites. All equipment is also rinsed with freshwater before use.

All drilling fluids are non-toxic and environmentally friendly – though no fluids at all are used to advance the actual bore hole.

We’re capping all bore holes using industry standard techniques to prevent transfer of sea water between the aquifer and the harbour water. This involves reinstating the bore holes with grout, which expands once the drilling casing is removed to blend with the ground layers under the harbour – effectively creating an impermeable seal.

We are also monitoring the aquifer continuously to ensure there is no salt water intrusion, with monitoring bores at Matiu/Somes Island, on the Petone foreshore and further up the Hutt Valley.

For the second stage of investigations (involving pump testing in larger production bores), we have a design concept in place which includes environmental protection, which will be finalised once the outcomes of current testing and analysis is known.

If you find drinking water, could it provide a day-to-day supply, or is it just for emergency use?

We haven’t yet decided on this but it is a possibility, depending on the quality of the water found. The drilling will significantly increase our understanding of the aquifer and how best to manage the resource.

If you find drinking water, will the council make money from it, such as by selling it commercially?

The purpose of the project is not commercial. It is to increase the resilience of Wellington’s water supply.

What about other parts of Wellington – how will they get emergency water?

The focus has been on this area of Wellington as it has been identified as the most vulnerable. However, we’re looking at other initiatives to make the region’s water more resilient including establishing alternative networks using new bores, streams, small scale treatment and water bladders.

If you’ve already found fresh water why do you need to drill more?

To properly understand the aquifer we need to drill in more than one location. At this first site, we’ve found freshwater with treatable levels of ammonia, iron and manganese, and in sufficient quantities and flow levels to be used as an emergency supply. With the second exploratory bore we’ll drill in a different location and run the same tests to see if there is any difference in quality and quantity. Depending on results we may drill a third exploratory bore.

What does ammonia in the water mean?

Ammonia at low levels in drinking water is safe. But, water with high levels of ammonia, when treated with chlorine, can react and make it unsafe to drink. The water we have found at this first bore site has high levels of ammonia, which can be removed using an ion-exchange treatment process.

Are iron and manganese treatable?

Yes. Iron and manganese are treated through the normal water treatment processes of pre-oxidation, coagulation, flocculation, sedimentation, and filtration.