Stormwater Risks to Sewer System

2 years ago | by

Smoke testing diagram

A long-term project by Coffs Harbour City Council to minimise the risk of harm to human and environmental health from sewage spills caused by stormwater accidentally or illegally entering the local sewer network is due to start in mid-August 2020.

“During wet weather, infiltration by stormwater into sewers can potentially overload the system increasing the chance of sewage backing up and spilling into streets, parks, waterways, beaches and even homes. Locally, wet weather sewer flows are currently reaching up to twice the actual capacity of the system,” said Mick Raby, Council’s Director Sustainable Infrastructure.

“We’re embarking on a long-term program, the Stormwater Inflow Reduction Project, to check every connection to our sewer system across the local government area because ensuring public safety and the health of our local environment is vitally important. There are also considerable cost savings to be gained from preventing an overload of our sewers and the water reclamation plants.

“A major contributor to this situation is suspected to be incorrect, or illegal, connections from the stormwater systems of residential homes into the sewer network.

“The Stormwater Inflow Reduction Project will undertake checks of all homes and commercial and public buildings linked to the sewer system – so we’re talking thousands of premises. It is expected to take a number of years.”

The first properties to be checked will be in and around the western end of Brodie Drive up to Glynn Street, Coffs Harbour.

Stormwater infiltration most commonly occurs when:

  • Rainwater from residential stormwater downpipes have been incorrectly or illegally connected into the sewerage rather than the stormwater system; and
  • Sewer overflow relief gullies (ORGs) on properties are broken or located in a position into which rainwater can flow.

The method of checking for incorrect connections is to use a non-toxic smoke which is pumped through the sewer main and then reappears out of stormwater downpipes. The local fire service will be advised in advance to avoid confusion. (See above diagram on how it works).

All property-owners will be notified two weeks ahead of testing in their area and contact will be made directly with each owner again three days before testing is planned to be carried out.

Both Council and property-owners have responsibility for different sections of sewer infrastructure. Drainage is the responsibility of the owner up to the property’s boundary. Council is responsible for the network beyond any private land boundaries.

If defects are identified, the owner will be issued with a rectification notice detailing the issues on their property and asking for them to be corrected in 90 days ahead of a further inspection.

Testing of public buildings such as medical centres and schools will be carefully coordinated.

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