Managing stormwater

When excess rain water is directed to the sewer it can spill out into the environment.

Trade waste sites produce uncontaminated stormwater. This water is sent to stormwater drainage systems, under Environmental Protection Agency (EPA) requirements.

How to manage stormwater

First flush system

There are many options for managing stormwater. The most common is a first flush stormwater system, also called a stormwater diversion system.

The system catches the initial rainwater runoff, which is more polluted than later flows. The initial runoff is directed away from the stormwater system and the environment.

First flush systems are used at industrial sites with open areas for manufacturing or processing.

Installing a first flush system

How you connect a first flush system will depend on:

what your business does
your unroofed area
the sewer capacity
what pumps are available.

A first flush system must be designed and installed by a third party supplier.

Captured rainwater must be removed quickly so it doesn't contaminate other water on site.

Construction sites

Operators of construction sites should minimise stormwater runoff.

If stormwater needs to be discharged to the sewer, gross solids must be removed from the water before it’s discharged.

For more information on stormwater management during construction visit our page on Managing groundwater.

If we believe the land has been contaminated we may request a soil analysis or water quality report before issuing a trade waste agreement.

Discharging stormwater to the sewer

We will only accept stormwater to the sewer under a trade waste agreement when:

the stormwater is uncontaminated and flows from unroofed areas smaller than 20 square metres
the contaminated portion of stormwater is collected or diverted via a stormwater management system
the quality of all rainwater runoff is not acceptable for discharge to the stormwater system or the EPA has advised that all stormwater must be directed to sewer.

Unroofed areas under 20 square metres (m²)

Method	Discharged to sewer	Discharged to stormwater system	Trade waste charges	Suitable locations	Equipment and treatment
Gravity runoff	All rainwater runoff and wash water.	Nil	Yes	Car wash areas, mechanic workshops and panel beaters.	Straining Silt pit Any other treatment deemed necessary.

Method

Discharged to sewer

Discharged to stormwater system

Trade waste charges

Suitable locations

Equipment and treatment

Gravity runoff

All rainwater runoff and wash water.

Nil

Yes

Car wash areas, mechanic workshops and panel beaters.

Straining

Silt pit

Any other treatment deemed necessary.

Unroofed areas over 20 square metres (m²)

Method	Discharged to sewer	Discharged to stormwater system	Trade waste charges	Suitable locations	Equipment and treatment	Results of equipment or power failure
Slow rate pump to sewer with overflow to stormwater drainage.	Flow rate specified within trade waste agreement.	Rainwater with possible traces of pollutants.	Yes. A trade waste flow meter may need to be installed.	Areas up to 100m2 where minor pollution may occur. For example, bus washes, small loading areas, retail car yards.	Pump (limited to 3000 litres per hour) Silt pit for solids removal and oil interception.	Total flow to stormwater.
First flush system	Polluted rainwater runoff. To be discharged at a flow rate listed in your trade waste agreement.	Nil	Yes. A trade waste flow meter may need to be installed.	Abattoirs and large industrial facilities.	Large storage pond or holding facility. Tank Pump Flow meter	Eventual overflow to sewer or stormwater.
Diversion valve (operated by flow switch on water supply).	Polluted wash water directed to sewer only when water supply to area is operating.	Rainwater with possible traces of pollutants. Discharged when wash down is not taking place.	Yes. A trade waste flow meter may need to be installed.	Relatively clean wash down areas, no limit in size. For example, bus and truck washing and loading areas.	Stormwater diversion valve, or first flush valve. Compressor Control flow switch Silt pit for solids removal and oil interception.	Polluted water to stormwater or unpolluted water to sewer.
GWW-approved rain gauge.	Polluted wash water and rainwater runoff when rainfall is less than a pre- determined intensity in relation to size of area.	Rainwater with possible traces of pollutants.	Yes. A trade waste flow meter may need to be installed.	External processing and wash areas where pollution of the area is likely to occur when hoses are not being used. For example, bus washing, semi-trailer washing, transit and storage areas, processing areas.	Stormwater diversion valve, or first flush valve. Compressor Control flow switch Silt pit for solids removal and possibly oil interception.	Polluted water to stormwater drainage or unpolluted water to sewer.