FAQ

Our area has many shops, a hospital and several schools. What kind of pollution does it produce?
This type of catchment area – with permanent, regularly used establishments – consistently produces large amounts of light pollution, such as plastic packaging, polystyrene, paper, etc. This light litter will move down the drainage system quickly. It takes very little rain to transport and very little time for it to travel long distances.

Is silt a major problem in drainage systems?
Sediment is mainly generated by residential and commercial building sites. A catchment with construction activity will have sediment running into the stormwater system. The amount of sediment is directly proportional to the amount of construction activity within the catchment.

Downstream of these areas there is an increase in the amount of silt and sediment that builds up in the streams and culverts of the drainage system. Silt and sediment are heavy and therefore move at a slower rate down the stormwater systems.

There is therefore a time lag from the time that the construction work finishes to the time that the sediment begins to show up in the drainage system or stormwater trap.

I have recently moved into a manufacturing area. With industry being forced to clean up, can I expect to see any pollution entering our drains?
Catchment areas with heavy or light manufacturing industries produce larger volumes of oils, both heavy and light hydrocarbons, and cooking oil and heavy plastics than other catchments.

These catchments also generate heavy plastics – for example, industrial packaging material and off-cuts from plastic injection mouldings. This type of pollution is still evident despite the efforts of the Environment Protection Authority and other bodies.

A positive aspect of industrial pollution is that the pollution has distinctive characteristics. For example, heavy and light hydrocarbons have specific characteristics. It is easy to distinguish sump oil from diesel fuel, from hydraulic oil from cooking oils. All these oils have different colours, smells and viscosity and can be traced to a particular industry or activity. Industrial packaging is often labelled, making it easier to identify and address the source of the pollution.

Is organic material a problem for stormwater traps?
Catchments with large numbers of deciduous trees create enormous volumes of organic matter, which ends up in the stormwater systems. The volume of organic matter influences the performance of pollution traps. In most traps, the volume of leaf litter caught in the trap makes up between 35% and 60% of the total rubbish volume. Organic matter that has been saturated in water is very heavy. If it has been sitting in a wet confined space for any length of time it will begin to decompose anaerobically, which leads to odours, gases and a reduction in available oxygen.

Many councils are asking residents to collect and compost organic material rather than allow this material to enter drainage systems.

Our urban development is required to install stormwater pollution traps. How can we ensure they perform well and don't cause problems?
The key often is regular cleaning. Points to note:

• A clean trap should perform to the designer/manufacture’s specification. All traps and pollution-control systems work more efficiently when their grills, bars, nets, booms or sumps are empty and clean.
• Any filter that is fine enough to stop cigarette butts and small pieces of polystyrene will block up very quickly with the volume of pollution coming down the stormwater systems.
• Once the trap or filter is full or blocked the pollution will overflow, defeating the purpose for installing the trap.
• SQIDs (stormwater quality improvement devices or pollution traps) that are catching large volumes of light litter need more frequent maintenance than traps that predominantly catch silt and sediment. Plastics and polystyrene will finally break up and be forced through grills and bars during storms if they are left to sit in the trap, week after week.

An important point when you are choosing a stormwater trap is access.

Before you decide and install any stormwater trap consider how easy it will be to maintain and clean. Simply, the easier it is to access the trap, the easier it is to clean and the lower the long-term maintenance costs.

Access becomes more important when you need to use machinery to clean stormwater traps.

Another tip. DO NOT install a SQID under power lines if it requires a crane for cleaning.

Our council area has numerous traps with different amounts of rubbish. What's the best way to co-ordinate cleaning?
Economies of scale can be an advantage where there is more than one trap in the vicinity. Cleaning services should address multiple traps in a scheduled manner to increase their efficiency and save time and money.

We currently use our staff to clean our in-ground stormwater traps. What matters should we take into account to minimise worker risk?
Points to be aware of concerning in-ground stormwater traps and pits, and the confined spaces in which they are located:

• There is not enough oxygen.
• The surfaces inside are contaminated.
• Liquids and gasses may enter the space in an uncontrolled manner.
• There is a risk of suffocation and/or explosion.

There is a lot that can go wrong when working in confined spaces. For this reason only properly trained and equipped personnel should enter or work inside these systems.

What happens to the pollution that is collected?
It must be disposed off in a way that meets environmental and public health regulations. In NSW, the State Government's Waste Services now classifies stormwater pollution as “special waste” and charges $92 per tonne for disposal. In many cases it is necessary to fax through a request to Waste Services before the pollution can be taken to their depots. Some of the information required includes catchment details, how the waste was collected and the content of the waste material.

NSW Waste Services places the following restrictions on the disposal of stormwater pollution:

• No free liquids.
• No sharp items.
• No odours.

Each state government and jurisdiction has its own rules.