11 Jan 2019

With the clock ticking on the Council’s self-imposed deadline to end temporary chlorination of the water supply within 12 months, Water Supply Improvement Programme Manager Helen Beaumont provides an update on how the work is tracking.

It has been a year since the Council voted to temporarily add chlorine to the city’s drinking water supply in response to advice from the Canterbury Medical Officer of Health. Over the past few months we have made significant progress on upgrading the wells that supply our water so that we can get back to having an unchlorinated water supply.

Helen Beaumont

Helen Beaumont is Christchurch City Council’s Water Supply Improvement Programme Manager

To date we have upgraded 25 per cent of our wells – by volume of water produced – to bring them up to a standard that exceeds the present requirements. We’ve set the bar higher than required because we anticipate that more stringent standards will be introduced by the Government shortly.

Upgrading each well takes between two and six weeks and we can only work on a limited number of wells at any one time because we still to need supply water to homes and businesses. We have been running a water conservation campaign asking people to use less water so we can continue work on the wells and we really appreciate the efforts people have been making.

Our data shows average water use to date is well below the summer averages for the past two years. If that keeps up we should be able to continue with the well remediation work as planned.

By May we expect to have completed interim upgrades on 19 below-ground wells and raised another 41 wells above ground, bringing the total number of secure wells to 98. Those wells collectively provide more than 60 per cent of the city’s water supply.

If we upgrade those wells as planned, we should have a sufficient volume of unchlorinated water to supply the city over the winter months when we use about 50 per cent less water than we do in the summer.

However, even after doing this work, providing chlorine-free water to everyone in every part of the city remains a challenge.

The water supply is delivered through nine discrete zones. The Central zone is our biggest water zone and supplies water to 42 per cent of the population. It is the oldest part of the city and where we have the most wells that need to be raised above ground. There is high demand for water relative to the available capacity in this zone and, therefore, very little excess capacity. This makes it difficult to do the necessary upgrades.

Ultraviolet treatment

To address the challenge in the Central zone, in addition to the interim upgrades on below-ground wells, we are also working to install ultra violet (UV) treatment at the Main Pump Station. The Main Pump station is the biggest supplier of water to the Central zone, and we are working with the contractor on ways that the installation can be sped up so water can be treated with UV instead of chlorine at this site.

We are also looking at whether we can transfer water across zone boundaries. There are technical challenges because of the different pressure levels in some of the zones. However, it may be possible for us to use some of the pump stations on the boundaries of the Central zone to push untreated water into that area.

In addition, we are investigating whether we can make use of two private wells on the Metro Sports Facility site. They tap into deep aquifers and were originally drilled for a ground-source heat pump that is no longer required. They may be suitable to supply potable water to homes and businesses in the Central zone.

We are confident that seven of the nine city supply zones will be chlorine free by May this year. It is likely that that we will have sufficient water from secure wells in the Ferrymead zone, and we are doing further modelling of water supply options and looking at opportunities to fast-track works in the Central zone.

In the meantime we are also looking at how we can reduce the amount of chlorine in the water.

Lowering the chlorine dose

At the pump stations where the chlorine has two minutes to react with the water and disinfect it before it reaches the first consumer we have been able to halve the dose of chlorine.

We are now looking at whether we can re-route the water at some of the other pump stations so we can give the chlorine a longer time to do its job before it reaches the first consumer. For example, if we can send the water around the block before it reaches people’s homes, there may be other pump stations where we can also reduce the dose.

Each pump station has between one and six wells supplying it. Where some wells are remediated and some are not, we have to chlorinate all of the water unless we can isolate the wells that haven’t been remediated. We can only do that when the demand for water is low.

When there are periods of low demand we aim to only use pump stations without chlorine. It is only when absolutely necessary, as water demand rises, that we bring the chlorinated pump stations into service.

We all want the chlorine out of our water and we are working hard to ensure we can have an unchlorinated water supply as soon as possible.