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As local councils begin to negotiate stormwater quality,
the Dunedin City Council is reminding people that if pollutants
get into stormwater drains they flow untreated into waterways.
Contaminants that can be swept along for the ride range from
dog faeces from footpaths to oil and petrol-fumes from roads
and zinc released by metal roofs, says acting water and waste
services manager Laura McElhone.
Other problems include people pouring leftover paint into
drains and garden pesticides being washed by the rain off
footpaths and into gutters.
"Once it's in the stormwater pipe, it's going to the ocean
and people sometimes forget that."
In a few areas, groundwater from contaminated land may also
be seeping into stormwater pipes.
Stormwater is rain that is collected from the roof or that
flows over paved areas such as driveways, roads and
footpaths. It is different from wastewater, which comes from
domestic kitchens, bathrooms and laundries as well as from
commercial and industrial sources. Both are discharged into
the sea, but only wastewater goes to a treatment plant first.
The city's stormwater network includes 363km of pipe, ranging
in diameter from 100mm to 1800mm, and about 8000 mudtanks.
These grates in the kerb and channel are designed to separate
out litter and sediment but they don't catch all of it and
they don't stop chemicals.
Key concerns in Dunedin are the heavy metals: copper, zinc
and lead, along with bacterial contamination and polycyclic
aromatic hydrocarbons (typically derived from engine oil,
vehicle exhaust emissions, erosion of road surfaces and
In the central city, some of the pipes are
century-old,1.4m-high brick tunnels that Dr McElhone says are
in remarkably good condition and probably have about 40 years
left in them. There are also 11 stormwater pumping stations
but gravity and watercourses are used where possible to save
Ultimately, the stormwater ends up in the harbour or off the
coast via a series of outfalls, many of which have grilles to
prevent large pieces of litter going into the harbour.
Water quality has been in the spotlight recently, with the
Otago Regional Council changing its regulations to prevent
runoff in rural areas polluting waterways. Now the council is
turning its attention to stormwater discharges in urban
areas, where new contaminant standards will eventually be
Territorial authorities believe the policies implemented in
country areas and labelled too restrictive by many farmers
could flow on to urban areas.
The changes come as the Dunedin City Council applies to the
regional council for consent to discharge stormwater into
Andersons Bay Inlet, St Clair, Port Chalmers and the
Stormwater from residential catchments does not
requireapproval but these discharges are classified as a
controlled activity because they are from areas that have
trade and industrial premises.
The existing consents expire at the end of this month but
will stay in force until the two councils resolve any areas
of contention - a process which could be a lengthy one given
their oposing views.
Two issues are the level of treatment necessary and the use
of mixing zones - areas in the coastal waters where quality
standards can at present be exceeded to achieve reasonable
mixing of discharges.
The regional council says there should be regulations to
minimise contaminants from key sources such as industrial
sites and subdivisions and when old pipes need to be
replaced, the city council should take the opportunity to
install internationally accepted treatment devices, such as
vortex separators. If those things were done, mixing zones
should not be necessary in most cases.
The city council says costs and technical constraints make
this kind of catchment-wide treatment inappropriate and
spending large sums of money on end-of-pipe treatment may not
lead to measurable improvements in the harbour. It feels it
is better to control what goes into the stormwater at the
source, with targeted treatment where needed. A dedicated
stormwater bylaw would underpin this approach and more
industries might be required to have on-site treatment.
Dr McElhone says the council does need to reduce the
contaminant load because that is what the public has said it
wants. But the harbour is already a modified environment,
with sediments contaminated from early industries, and would
not suddenly flourish even if there were no stormwater in it.
"If you look at the pure science, our belief is that the
impact that stormwater is having on the harbour is not that
significant."Otago Regional Council resource management
director Dr Selva Selvarajah says that might be the case if
one took the whole harbour as an entity but not if one looks
at the receiving area.
"We've got to be mindful of the good practice that we can
adopt. Just because an environment provides a bit of mixing,
doesn't mean we'll continue to allow a large number of
contaminants into [it]."The applications have attracted seven
submissions and will be heard once a panel of independent
commissioners is appointed.
Stormwater do's and donts
THE FOLLOWING MATERIALS SHOULD NOT BE DUMPED INTO
STORMWATER DRAINS OR THE GUTTER because they will flow into
streams, lakes or the sea and can be toxic to wildlife:
• Automotive products, including motor oil, antifreeze, brake
fluid, diesel, transmission fluid, degreasers, petrol and
• Paints and solvents, including all types of paints, paint
thinners and strippers, rustproof coatings and
• Recreational products such as swimming-pool chlorine and
water, bilge water and spa-pool water.
• Pesticides, including insecticides, fungicides, rodent
baits, herbicides, molluscicides and wood
• Cleaning products, including caustic degreasers,
disinfectants, detergents, drain and toilet cleaners, leather
preservatives, dry-cleaning agents, polishing agents and
• Some hazardous materials can be recycled, while others
should be disposed of at a transfer station or landfill.
Contact your local council for more information.
WHAT YOU CAN DO:
• Wash your car on the lawn to stop detergent and oils
getting into drains.
• Wash your paintbrush at an inside sink or on the lawn or
• Pick up animal droppings.
• Put litter, including cigarette butts, in rubbish
• Dispose of excess paint and chemicals in the hazardous
waste area at landfills.
• Service your car regularly so oil does not leak into the
• Anyone doing building work involving earthworks must
prevent sediment leaving the site and may need a documented
sediment control plan.
• Industrial and commercial premises must comply with the
stormwater requirement in the trade waste bylaw and ensure
chemicals cannot get into the stormwater. In some cases they
may have to provide on-site treatment.
• If you see pollution in or near a waterway, contact the
Otago Regional Council's 24-hour pollution hotline, 0800 800
033. Dunedin residents who want more specific advice, or want
to report an accidental spill or the illegal tipping of
hazardous materials into a gully trap or manhole, should call
the Dunedin City Council on (03) 477 4000.
CONTAMINANTS PRESENT IN DUNEDIN'S
• Total Suspended Solids (TSS): Erosion, including
stream-bank erosion. Can be intensified by vegetation
stripping and construction activities.
• Arsenic (As): Combustion of fossil fuels; industrial
activities, including primary production of iron, steel,
copper, nickel, and zinc.
• Cadmium (Cd): Zinc products (Cd occurs as a contaminant),
aluminium soldering, ink, batteries, paints, oil spills,
• Chromium (Cr): Pigments for paints and dyes; vehicle
brake-lining wear; corrosion of welded metal plating; wear of
moving parts in engines; pesticides; fertilisers; industrial
• Copper (Cu): Vehicle brake linings; plumbing (including
gutters and downpipes); pesticides and fungicides; industrial
• Nickel (Ni): Corrosion of welded metal plating; wear of
moving parts in engines; electroplating and alloy
• Lead (Pb): Residues from historic paint and petrol (exhaust
emissions), pipes, guttering and roof flashing; industrial
• Zinc (Zn): Vehicle tyre wear and exhausts, galvanised
building materials (e.g. roofs), paints, industrial
• Polycyclic aromatic hydrocarbons (PAHs): Vehicle and engine
oil; exhaust emissions; erosion of road surfaces;
• Faecal coliforms/E.coli: Animal faeces (birds, rodents,
domestic pets, livestock), wastewater.
• Fluorescent Whitening Agents: Constituent of domestic