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Te Mato Vai Stage 1 Upgrade – Making the ring main safe to carry water to households

Updated: Nov 24, 2020

As Landholdings Limited (Landholdings) prepares to reconnect upgraded sections of the ring main pipes to the public water supply, disinfecting the new pipes is an important step required to protect public health.

Pipe disinfection is standard practice when connecting any pipes or infrastructure to a water network, as pipes can become dirty during construction. One-off disinfection removes any contaminants such as bacteria or viruses that could have entered the pipes.

Under National Environment Service (NES) supervision, Landholdings will flush the pipes with a chlorine solution to ensure the new connections do not contaminate the water supply. They will do this before the system is connected, so none of the chlorine used will go into the public water supply.

After flushing, they will remove the chlorinated water and dispose of it responsibly, in line with methods approved by NES.

Will there be chlorine in our water supply?

No - while the new system will be cleaned using chlorine, this is done before the new structures are connected into the water supply. No chlorine will be added to the water supply at this stage.

Won’t there be some chlorine left in the pipes after they’ve been cleaned?

There may be a very small amount of chlorine left on the surface of the disinfected structures when we are ready for commissioning. We will wash this out and test the water to ensure there is no chlorine left in it before connecting the new system to the public water supply.

How do you dispose of the chlorinated water?

Landholdings is using one of two disposal methods approved by NES:

  1. Remove the chlorinated water from the pipe, pump it into a water cart and take it to the disused T&M Heather’s quarry for disposal.

  2. Remove the chlorinated water from the pipe, pump it into a to an aerated water tanker on site. Test the water for residual chlorine. When tests confirm there is no detectable chlorine in the water, discharge the water onto the ground.

How do you know this is safe for the environment?

NES have reviewed and approved both options and will supervise the work on site to ensure the most appropriate option is used for each location.

Chlorine is a gas at room temperature, and when it’s mixed with water its molecules escape into the air over time. This happens more quickly in warmer air and water temperatures, and when the water is aerated. This makes it easy to dispose of the chlorine solution used to disinfect the pipes, as long as it’s done in accordance with industry guidelines.

How are you monitoring the effects on the environment?

NES have approved the disposal methods and are supervising the disposal processes.

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