Walk around any industrial site in Australia, and you will see a mix of humps, grates, and tanks. But if you ask the Site Manager what each one does—or if it’s actually working—you often get a blank stare.
Stormwater infrastructure on industrial sites is frequently misunderstood. Many operators assume that a “drain is a drain.” This is a dangerous assumption.
Industrial stormwater systems are engineered to target specific pollutants. Using a Gross Pollutant Trap (GPT) to catch oil won’t work. Relying on bunding without a shut-off valve is a recipe for disaster.
To stay compliant with EPA regulations and avoid costly fines, you need the right tool for the right pollutant. Here is a breakdown of the three critical lines of defence: Bunding, Separators, and GPTs.
1. Bunding: The First Line of Defence (Containment)
What is it?
Bunding is a physical barrier (usually a concrete or rubber kerb) designed to contain spills before they enter the drainage network.
What it targets:
Catastrophic spills. It is not for cleaning water; it is for stopping liquid from escaping.
Do you need it?
If you store liquids (fuel, chemicals, oil) in drums or tanks, Yes.
Australian Standards (AS 1940) generally require bunding to hold 110% of the volume of the largest tank within the bund. This ensures that if the tank ruptures, the liquid stays inside the bund rather than flowing into the stormwater pit.
The Common Fail:
- “Drive-over” bunds that have flattened out: Forklifts destroy rubber bunding over time. If the bund is flat, it’s useless.
- Open valves: We often see bunds with a drain valve left permanently open to let rainwater out. This defeats the purpose. If a spill happens, it flows straight out the open valve.
2. Oil/Water Separators: The “Refinery” (Treatment)
What is it?
A device designed to strip hydrocarbons (oil, grease, petrol, diesel) from water. Common types include Coalescing Plate Separators (CPS) and Vertical Gravity Separators (VGS).
What it targets:
Hydrocarbons. It separates oil from water based on density (oil floats, water sinks).
Do you need it?
If you have un-roofed hardstand areas where vehicles are parked, washed, or refuelled, Yes.
Rainwater washing over a dirty car park picks up oil and grease. You cannot discharge this oily water into the stormwater system. It must pass through a separator (usually discharging to the sewer under a Trade Waste Agreement) to reduce oil content to <10ppm.
The Common Fail:
- Lack of maintenance: Separators rely on internal plate packs to “coalesce” small oil droplets into big ones. If these plates get clogged with mud, the system fails.
- Emulsifying detergents: Using the wrong cleaning chemicals (like heavy degreasers) can break the oil down so much that the separator can’t catch it.
3. Gross Pollutant Traps (GPTs): The “Garbage Can” (Filtration)
What is it?
A primary filter installed underground at the end of your stormwater line, just before it leaves your property.
What it targets:
Physical debris. Plastic wrappers, pallet timber, styrofoam, organic matter (leaves), and coarse sediment.
Do you need it?
If you have a large open yard, logistics apron, or car park, Yes.
Most Councils mandate GPTs to stop industrial litter entering local creeks.
The Common Fail:
- “Out of Sight, Out of Mind”: Because they are underground, GPTs are rarely checked. When full, they go into “bypass,” allowing all subsequent pollution to flow straight into the environment.
- Wrong Type: Installing a simple “trash screen” in a yard with heavy silt runoff. The screen blocks instantly, causing site flooding.
The “Golden Rule” of Industrial Stormwater
Separation is key.
- Roof Water is (usually) clean. It should go straight to the stormwater drain or a rainwater tank.
- Process Water (from wash bays) is dirty. It must go to the Sewer (via a separator).
- Yard Runoff is potentially contaminated. It must go through a GPT (and possibly a separator) before hitting the stormwater drain.
Mixing these streams is where most compliance breaches occur. If you wash a forklift on a driveway that drains to a GPT, you are polluting. A GPT catches trash, not soapy, oily wash water.
Summary
You cannot manage environmental risk if you don’t know what assets you have.
Take a walk around your site today. Look at your drains. If you don’t know where they go or what device protects them, you are flying blind.
Need a Site Audit?
[Contact Stormwater Services Australia] for a comprehensive Environmental Site Audit. We will map your drains, inspect your separators and GPTs, and tell you exactly what is required to make your site compliant.
