Preventing Stormwater Pollution

As we discussed in our article: What is Stormwater Management and Why is it important. After a rain event, water will either settle on the surface (until it soaks into the ground or evaporation occurs), or will be discharged into the stormwater network where it will eventually enter local waterways.

Almost 80% of all stormwater is untreated or recycled.

Untreated stormwater runoff containing amongst other potential contaminants, chemicals, animal waste, fertilisers and microorganisms from the soil have the capacity to upset the delicate ecological balance of our waterways, affecting water quality, and harming marine plants and animals.


An example of this is nutrient pollution, which occurs due to excessive nitrogen and phosphorus from fertilisers and other chemicals entering a waterway, causing algal blooms. Algal blooms have the potential to leach toxins into the water and block sunlight.

Algae also consumes dissolved oxygen as it decomposes, reducing oxygen levels in the water that marine plants and animals rely on to survive. And, as an example of the rapid ‘flow on’ effect that can occur due to pollution, the decomposition of marine plants and animals due to algae contributes even further to depleting dissolved oxygen levels.

Other contaminants such as oil can leave a skin on the surface of the water and affect marine plants and animals more directly by making it harder to breathe. * It is against the law to allow oil or oily waste to enter the stormwater network.

Below is a table indicating describing common sources of pollution and the negative consequences they can have on waterways ans aquatic plants and animals.

Source of Pollution Outcomes
Engine oil. Cooking Oil. Grease
In abundance can form a layer on the surface of the water, decreasing dissolved oxygen and limiting biological activity. 

Examples of this include:

– Reducing the water repelling ability of aquatic bird feathers
– Ingestion resulting in death
– Reduces the ability to insulate against cold temperatures
– Slows growth in fish, and causes reproductive problems, including incubation of eggs.

Organic matter
Plant clippings, lawn clippings, leaves, nitrates and phosphates
Reduces dissolved oxygen as the bacteria contained within consume oxygen, resulting in less dissolved oxygen for aquatic marine and plant life.
Animal Waste
Animal and bird faeces
Reduces dissolved oxygen due to contained bacteria. Alters PH balance of aquatic system, unsettling the natural ecological balance.
Chemicals and Fertilisers
Pesticides, Acidic and Alkaline Chemicals
Can result in Algal blooms which reduces dissolved oxygen. 

Pesticides can be lethal to many aquatic species and builds up over time in tissue and blood.

Arsenic, Mercury, Lead, Zinc and Nickel
Can cause contamination in fish life making them unsafe for human consumption.


Fines and Legal Action

While untreated stormwater runoff resulting in pollution is obviously a major concern, fines may also be issued to business owners through local council or the EPA.

Depending on the extent of the offence, on the spot fines may be issued or the matter may be taken significantly further based on the extent of the breach.

It’s also important for business owners to be aware that they are responsible for their staff and any activities resulting in pollution.

If you are unaware of your environmental responsibilities or have concerns about non-compliance it’s advised to contact your local council or state department. Contact information is available here.


There are some simple ways businesses can reduce the risk of pollution as a result of stormwater runoff.

Reduce litter

Ensure the car park and other areas where litter builds up and could potentially be washed into a stormwater drain are kept clean and monitored.

If you operate a business that deals directly with the public, ensure there are adequate rubbish bins to encourage customers to dispose of litter and items such as cigarette butts. Use impactful signage so customers are aware of where bins can be found.

Ensure standards are kept high with regard to litter in the workplace, encourage your staff to maintain a tidy work area, it not only benefits the environment, customers will appreciate it also.

Protect your Drains

There are a number of products available to filter or block contaminants from entering stormwater drains. These include:

Dewatering bags: Dewatering bags are used to filter silt from stormwater discharge. They are mainly used to control sediment typically seen around construction sites. In large scale applications they are an effective secondary measure e.g. after diverted stormwater is screened.

Stormwater screens: Stainless steel screens mostly used as pre-treatment screens in trade waste systems. Screen stop larger particles entering the trade waste system reducing the impact on filters and pumps.

Silt pits: A complete unit containing a stormwater pit with silt basket and grated drain cover. This product will remove more than 99% of all particles under 3mm in size without restricting water flow.

Baffled silt pits: These are similar to the stormwater pit except also contain a baffle system that retains hydrocarbons that settle on the surface of the silt basket. Baffled silt pits are more effective at controlling pollution for areas up to 1200m2 than a standard end of line treatment system.

Weighted drain covers: Weighted drain covers are used to completely seal drains, preventing contamination during a spill even. It’s a simple, affordable option that requires no specific training or ongoing costs.

Automated Systems

DD600 Automated Wash Down Diversion System
Unless wastewater runoff is diverted to a treatment system or holding tank, during a washdown activity e.g vehicle washdown, pollutants are very likely to enter the stormwater network from your business premises.

Automated washdown systems such as the DD600, detect washdown activity and automatically open the diversion valve, diverting wastewater runoff for treatment or storage.

First Flush Systems
Car parks and wash down areas where oils and detergents may present a risk can utilise products such as a first flush diverter which diverts the ‘first flush’ of water during a storm event. The ‘first flush’ typically contains all the loose contaminants found on the surface and reduces the possibility of pollutants entering the stormwater network.

Store and handle contaminants safely

Ensure best practices are followed when storing or handling potential contaminants e.g. fertilisers and chemicals.

  • Use a dedicated washdown area
    Chemicals found in cleaning products e.g. detergents can promote the growth of algae and other aquatic weeds reducing dissolved oxygen in the water. Untreated washdown runoff should be treated before entering the stormwater network.
  • Store potential liquid contaminants away from stormwater drains
  • Utilise bunding to protect against liquid spills

Train Staff

Staff that undertake activities that may result in stormwater runoff should receive training in both preventing pollution causing activity along with how to minimise the environmental harm caused by a liquid spill or unsafe business practice. * Remember the business owner is accountable for pollution as a result of staff activity.


Untreated wastewater runoff causes pollution. Pollution affects us all in various ways, and aside from the impacts on our local waterways including aquatic animal and plant life there is also the risk of heavy fines and/or legal consequences for business owners.

Trade Enviro offers a number of effective solutions that can help your business greatly reduce its risk of causing stormwater pollution. If you are unsure of your requirements or simply want expert advice on how to avoid running into environmental compliance problems contact Paul today.

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