Fixing the holes where the rain gets in
NEWS RELEASE
16 December 2008
Fixing the holes
where the rain gets in
When it rains heavily,
stormwater gets into Wellington’s sewerage system –
sometimes causing it to overflow into the harbour and Cook
Strait – something which absolutely is not supposed to
happen.
The overflows pollute the harbour and
coastline and can make swimming and other recreational
activities unsafe.
The rogue incursions of
stormwater fill the sewage network beyond its designed
capacity. Not only do overflows occur from the network
throughout the city, but the huge volumes also overwhelm the
city’s sewage treatment plants. It means untreated or
partially-treated sewage must be allowed to ‘bypass’ the
plants and enter the sea
The Moa Point sewage
treatment plant, for example, is designed to deal with a
maximum inflow of 3000 litres of wastewater per second.
However during heavy rain the flow, swollen by stormwater,
can reach 4000 litres/sec. This extra 1000 litres/sec
can’t be treated and has to be pumped into Cook
Strait.
It’s estimated that about half of this
stormwater gets in through faults in the Council’s sewer
mains – and the other half via holes, cracks and faulty
joints in private drains.
The Council has spent
more than $130 million upgrading the sewerage network since
1993. However work is now required on the private network if
the overflow problem is to be overcome.
So the City
Council’s Strategy and Policy Committee has given the
go-ahead for a study on the possible ways of fixing the
holes and cracks.
And depending on the
recommendations in the report, property owners with leaky
drains may face hefty repair bills.
Cr Celia
Wade-Brown, the Council’s Environment Portfolio Chair,
says the ‘inflow and infiltration’ (I&I) problem is a
particularly challenging issue for the Council and the city
as a whole.
“This is one of those problems that
will be difficult for the Council to ‘sell’. Most people
don’t even realise there is a problem – because few of
us hang around Moa Point or the Karori sewage treatment
plant when it’s pouring with rain. So the sewage overflows
usually go unnoticed by the public.
“Most people
wouldn’t imagine that the sewer pipe running off their
property and safely buried in the ground could be cracked or
holed – and that it could contribute to big problems at
the beach or at the treatment plants.
“Even
further than that is the challenge of getting property
owners to realise that the private drain is their
responsibility.”
There are an estimated 50,000
private sewer drains across the city. Property owners faced
with renewing defective drains might be faced with costs
ranging from $1000 to $20,000-plus - with a likely average
cost from $4000 to $7000.
Council engineers and
consultants have been asked to spend the next three months
investigating and costing possible ways of dealing with
inflow and infiltration.
The possible options are
wide-ranging and expensive. They could
include:
Increasing the capacity of the Moa Point and
Western (Karori) treatment plants so they can deal with high
volumes without the need for overflows.
substantial
spending to increase the capacity of the infrastructure –
this would likely involve building very large underground
storage tanks at various locations around the city to hold
large volumes of wastewater during and after heavy
rains.
Requiring private property owners to upgrade or
replace private sewers – especially those running from
older properties.
A combination of several approaches,
including different ways of funding work.
It is
known that a small number of private sewer drain
replacements are done each year – generally in conjunction
with other building works, says Cr Wade-Brown. “Therefore
it’s likely that a negligible amount of maintenance is
occurring on most sewers on most properties.”
The
Council’s Infrastructure Planning Manager, Maria Archer,
says one means of compelling property owners to fix private
sewers could be by including information about the age and
presumed condition of the drains on land information
memoranda (LIMs).
“The Council could require that
private sewers and stormwater drains be inspected and, if
necessary, fixed as part of a property sale process – so
the condition and possible need for their replacement could
become a matter of negotiation between buyer and
vendor.”
Maria Archer says that, in conjunction
with all of these options, it will be recommended that the
Council fund an education campaign to inform property owners
of the
issues.
ends