The Sydney Sewerage System
At home all the water that goes down your sinks, toilets and showers
ends up in the sewage system. The sewerage system for the Upper
Parramatta River Catchment is owned by Sydney
Industry must have a trade waste agreement with Sydney Water to
discharge to sewer. Industry may also have an Environment Protection
Licence (EPL) from the EPA where they fall into the schedule pursuant
to the POEO Act, or where they discharge to the environment. Industry
cannot discharge wastewater to the environment without an EPL unless
the discharge is deemed to be clean.
All connections to the sewage system must be authorised, or it
Where does the sewage go?
The sewage system in Sydney includes approximately 20,000 kilometres
of pipe owned and operated by Sydney Water and another 20,000 kilometres
located on private land, owned by customers. Most of the system
is gravity fed, following natural catchment drainage lines, although
transport to sewage treatment plants (STP’s) is assisted by 654
sewage pumping stations.
These pipes end up at one of 30 sewage treatment plants owned by
Sydney Water. All of the sewage in the upper Parramatta River catchment
is treated at the North Head Sewage Treatment Plant, Manly.
North Head Sewage Treatment Plant discharges 313 ML/day and serves
a population of over 1.1 million people. The sewage treatment process
is called high-rate primary and the effluent is discharged 3.7 km
off shore via deep ocean outfalls at a depth of 65 metres.
Why is there sewage pollution in our local creeks?
Sewage pollution gets into our local creeks when it escapes the
sewage system. This can happen when
- private or public sewer lines are cracked
- pipes are blocked by tree roots or other material
- sewage pumping stations fail
- sewage overflows cause discharges from designed overflows.
In wet weather, storm flows received may be in excess of system
capacity which can result in overflows from the sewerage pipe network
and/or partially treated discharges from the sewage treatment plants
Why does sewage pollution get so bad after rain?
The sewerage system has overflow points that act as safety valves.
They are designed to protect public health by preventing sewage
backing up into people’s homes if a problem occurs in the system.
In wet weather, overflows may be caused by rainwater getting into
the sewer through faults in pipes or illegal connections, exceeding
the capacity of the system. Overflows may also occur in dry weather
due to problems such as a blocked pipe.
Why is sewage pollution a problem?
Sewage pollution carries
- Pathogenic protozoa such as Giardia and Cryptosporium that are
a risk to human health
- Nutrients that can cause algal blooms and encourage weeds to
grow and can kill native vegetation
- Chemicals such as detergents
- increased dissolved solids.
What does the Trust do?
The Upper Parramatta
River Catchment Trust, Waterwatch
and local councils, regularly test
water quality around the catchment. The results from these tests
help us to identify problems.
Testing for Sewage Pollution
A number of indicators are used to test levels of sewage pollution
in creeks and rivers. An indicator is something that is easily tested
to show that sewage pollution is present. The indicator does not
tell you where the pollution came from (ducks, dogs, sewage system)
Faecal coliform are a bacteria that live in the guts of all warm
blooded animals. They are not harmful to human health but are used
to indicate the possibility of sewage pollution, which could mean
the presence of more harmful bacteria and viruses. Methods of identifying
viruses and bacteria directly are complicated and expensive, which
is why indicators like faecal coliform or enteracocci are used.
Levels of faecal coliforms greater than 1,000 cfu/100 mL exceed
the national guideline for secondary-contact recreational use of
waterways (eg canoeing, paddleboats).
In the upper Parramatta River catchment, levels generally exceed
the secondary contact standard by a small amount. For 48 hours after
rain levels are generally very high due to stormwater runoff and
Despite this, creeks such as Darling Mills Creek and Hunts Creek
in Baulkham Hills, North Rocks and Carlingford, generally better
the secondary contact standard in dry weather.Lake Parramatta now
complies with the secondary contact standards except after heavy
Parts of the Toongabbie Creek catchment can also be surprisingly
good, indicating that small improvements to the catchment will achieve
a great deal of benefit for water quality.
Ammonia is another substance monitored as an indicator of leakage
from the system. Like faecal coliforms, this substance is found
at high concentrations in raw sewage. While no specific guidelines
are set for total ammonia, levels of 1 mg/L help target areas for