Pegasus Post: January 22, 2019

PEGASUS POST Latest Christchurch news at www.star.kiwi
Tuesday January 22 2019 7
News
Local
News
Now
What it takes to remove the chlorine
Fire rages, homes at risk
With the
clock ticking
on the city
council’s
self-imposed
deadline
to end
temporary
chlorination of the
water supply within
12 months, water
supply improvement
programme manager
Helen Beaumont gives
an update on how the
work is tracking
IT HAS been a year since the city
council voted to temporarily add
chlorine to the 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.
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.
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
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 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.
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.
PRECIOUS: Limit the time you
operate your garden hose.
Read more about Lucy’s story
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