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Sewage Pollution

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 Water.

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 is illegal.

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 sewage polultion.

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 rain.

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 investigation.


How can your help to reduce sewer overflows?


Tree roots can invade even the smallest cracks in pipes. As the roots grow, so does the size of the cracks. This lets in rainwater. Tree roots can also block the pipes causing sewers to backup and overflow. Cracked pipes have to be repaired or replaced. Careful thought needs to be given to the location of thirsty trees.


Broken pipes can occur in both Sydney Waters and householders systems. Sydney Water is responsible for inspecting, maintaining and repairing the mains system, and property owners are responsible for sewer pipes and downpipes on their land. Broken sewer pipes not only let stormwater in, they can also allow untreated waste to enter the soil and create unhealthy conditions. If you suspect broken pipes, have your system inspected by a licensed plumber.


Many, but not all, properties have a boundary trap. This acts as an inspection point on the sewerage system. It also stops sewer odours from reaching the property. If the boundary trap is set below ground level and it’s lid or concrete rim is damaged, stormwater can get in. There can also be a problem if the vertical riser is cracked.


Stormwater downpipes are not allowed to be connected to the sewerage system. All water from your roof should be connected to the local councils stormwater system. Sometimes direct connection to the sewerage system may seem easier. The effect of doing so is overflows of diluted raw sewage further down the system. This is a major cause of sewer overflows in the Upper Parramatta River Catchment.


Poorly fitting cracked or broken inspection holes on the mains sewer system can let water into the sewerage system. If you notice any problems with them, please call your nearest Sydney Water Customer Centre.


A gully is an open pipe which is covered with a grille and found just outside your building. It is there to release any backflow from blocked sewer pipes and make sure it doesn't overflow inside the house. If the ground around the gully is built up too high, it can let stormwater into the sewerage system. A plumber can lift the gully or lower the ground around it.


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