A greyish liquid flowing down a drain outside a construction site may seem innocent enough. But few passing by would imagine it as being potent enough to damage plants and fish downstream. Concrete wash water is among the most common pollutants escaping from Australian sites and also one of the most overlooked.
Why Grey Water Is So Damaging?
Water for cleaning concrete vehicles, chutes, pumps and tools becomes contaminated with cement, fine sand and chemicals. Freshly mixed cement makes the water very alkaline, far more than what creeks and wetlands can handle. Without proper concrete waste water disposal, the water will not be treated before entering a creek, river or bay through a stormwater drain.
The damage occurs almost immediately. High levels of alkalinity can burn fish gills and cause death of the organisms that sustain aquatic life. Next, fine sediments accumulate at the bottom of creeks, smothering the plants and habitats of wildlife.
The soil suffers too. Repeated washing of the same area may damage it irreversibly even long after the build is completed.
What The Law Is Looking For?
Every state and territory treats concrete runoff as pollution, even though each has its own laws and penalties. Victoria has a general environmental duty, which says you’re supposed to cut down on any pollution risks as far as makes sense. Other states have similar pollution offences, with on-the-spot fines to back them up.
Councils slap on another layer with local stormwater rules. If there’s grey residue in a kerb, it’s an easy one for inspectors to spot, which is why it’s a pretty simple breach to prove. EPA Victoria’s guidance for building sites makes it clear that chute washings should be collected, then sent for proper treatment instead of just being left to soak or drain away.
And you’d be surprised how often it’s not just one person who gets hit with a fine. Builders, concreters, pump operators and site supervisors can all find themselves on the hook when wash water escapes.
Stopping Slurry From Taking A Leak Before It Happens
The good stuff starts with picking a washout area before you even start pouring the first load. It should be a spot that’s away from drains, gutters and slopes so that if there’s a spill it stays put. Some key containment methods are:
- Washout bays, which are purpose-built areas with some liners or bunding for repeated use.
- Portable washout containers, the trusty old workhorses on tight urban sites where there just isn’t much room.
- Dewatering bags, fabric filters that let the solid stuff sink to the bottom while letting the water seep out.
- Settling tanks, where the solid stuff gets to sink and then the water gets drawn off.
Each of those takes care of the solids, but none of them is going to fix the water’s acidity on its own. The WA Government’s stormwater guidance mentions that fabric filtration doesn’t do anything to change the pH levels, so even if the water has been filtered, it can still be a problem. So the water may need to be neutralised before it gets anywhere near a waterway.
Where that water ends up is all down to the local rules. Some sites have a trade waste agreement with the water authority and others have someone collect it for them. Even hobby builders have the same duty as everyone else, so it’s a good idea to check with the council, water authority or state environment regulator before the truck turns up to take away the waste.
Turning Waste Into A Resource
The industry is slowly starting to move away from just chucking concrete waste into the bin and towards finding ways to use it again. The solids from washouts can be crushed and then used in road base, fill or new aggregate. And the clean, treated water can often be reused for washing tools and trucks on the same site.
Government policies around circular economies are helping to push this along, by encouraging builders to keep materials in use for as long as possible. A lot of concrete plants are now recycling returned concrete and wash water straight in the batching yard.
Lower landfill fees and fewer truck trips often come as a result, which gives businesses a pretty good reason to change their ways.
Healthy Habits On The Job Site
Equipment only works if crews actually use it. A few minutes at the start of each pour to talk through the rules for washing the trucks and who’s going to check the washout area will set the tone for the rest of the day. Clear signs and a marked-out washout zone make sure everyone knows where they’re going and what they’re supposed to do, even if they’re a new subcontractor.
Having someone holding people accountable keeps the standards from slipping when deadlines get tight.
