Please note that this section of the manual may contain out-of-date information. It has been retained to provide general information and a revised version will be available soon.
This document is a guide to designing, constructing, operating and maintaining bunds or spill containment systems to minimise the risk of pollution from liquid spills and leaks.
Relevant standards and acts
Where applicable, the construction of bunds must comply with the requirements of:
- Australian Standard AS 1940B1993: The Storage and Handling of Flammable and Combustible Liquids
- Australian Standard AS 4452B1997: The Storage and Handling of Toxic Substances
- the Dangerous Goods Act 1975.
Standards Australia has published standards for a number of classes of dangerous goods, and these also give details of spill control requirements (see Further Reading)
What is a bund?
AS 4452B1997 defines a bund as:
an impervious embankment of earth, or a wall of brick, stone, concrete or other suitable material, which may form part or all of the perimeter of a compound that provides a barrier to retain liquid.
Since the bund is the main part of a spill containment system, the whole system (or bunded area) is colloquially referred to within industry as the "bund".
The bund is designed to contain spillages and leaks from liquids used, stored or processed above-ground, and to facilitate clean-up operations.
A bund consists of:
- an impervious bund wall or embankment surrounding the facility or tanks
- an impervious floor within the bunded area
- any joints in the floor or the wall, or between the floor and the wall
- any associated facilities designed to remove liquids safely from the bunded area without polluting the environment.
As well as being used to prevent pollution of the receiving environment, bunds are also often used for fire protection, product recovery and process isolation.
Minimising the risk of spills to the environment
Using bunding is only one way to minimise the risk of liquids entering the environment. All employees working with bunds should know how to:
- do regular inspections of valves, pumps, pipes and hoses
- use preventive maintenance
- use standard operating procedures in the event of an on-site or off-site emergency
- isolate a tank or bund
- use fire-fighting equipment
- stop substances entering the environment once they have escaped.
This guide does not address other issues that you must consider when storing liquids, including fire safety, storing compatible materials and restricting access.
Do I need to use bunding?
This guide applies to facilities that use or store liquids above-ground. Whether bunding is needed, and what type should be used, will be determined by:
- the level of risk at the site
- the type of facility
- the type of drainage.
Level of risk at the site
The level of sophistication that might be required of a bund depends on the level of risk posed to the environment from each facility. This would be based on a number of site-specific factors, including:
- the type of liquid being used or stored and its potential impacts on the environment
- the amount of liquid being used or stored
- the ability of the facility or storage system to prevent spillages or leakages, and hence the risk of a spill or leak occurring
- the duration of any temporary storage
- the sensitivity of the environment.
Type of facility
Facilities that should comply with the bunding requirements in this guide include:
- chemical storage facilities
- pesticide storage facilities
- petroleum storage facilities
- electrical transformers containing oil and/or PCBs
- facilities used to transfer stored liquids (such as transport facilities)
- drum storage areas, either temporary or permanent
- processing areas
- any other facilities that store substances other than water or uncontaminated stormwater. For example, milk (because of its high biological oxygen demand and solubility) can cause more environmental damage than oil (which floats on water and is removed relatively easily), so bunding might be required.
- any other locations where spills are common, including transfer points, workshops, factories, service stations, buildings or pieces of machinery, wash bays, and other areas in which a material is transferred from its container. In these situations, common forms of bunding are short brick or concrete walls, grading the ground towards a sump, or using "speed humps". Any method that contains the material and stops it entering the stormwater or environment might be acceptable.
The requirement for bunding has to be determined on a site-by-site basis, taking into account the factors listed in this section.
Type of drainage
Bunding is also recommended if the area drains to the sewer or a wastewater treatment plant. Spillages in these areas can either pass through the waste treatment process to the environment or severely damage the waste treatment process, resulting in damage to the environment.
If the storage or associated equipment were to fail and the liquid were to flow into a stormwater drain or creek, the situation would be considered differently to one in which the liquid would not reach the receiving waters. In both cases, there should be emergency management plans that assume a loss of liquid both on-site and off-site.
Designing and constructing bunds
In this section are some general rules to follow for the design and construction of bunds for tank and drum storages. The two diagrams illustrate many of the points that you should incorporate in your design.
Before any work starts on the construction of bunds, consider whether the local authority should be consulted regarding necessary approvals.
Example of bunding for bulk liquid storage tanks (adapted from EPA Victoria)
Net capacity of the bund AS 1940-1993 5.9.2, AS 3780-1994 5.7.2, AS 4452-1997
The net capacity of a bunded compound in a tank storage facility must be at least 100% of the net capacity of the largest tank. Make an additional allowance for rainwater according to the amount of rainfall in your area (that is, sufficient capacity to cope with a one-in-twenty-year 24-hour storm). Make sure you take into consideration the capacity displaced by other tanks within the same bunded area and any foundations. Treat interconnected tanks as a single tank of equivalent total volume for the purposes of the bund design criteria.
Example of bunding for liquid drums and containers (adapted from EPA Victoria)
If an automatic fire sprinkler system is installed in or over any bunded tank or drum storage compound, the capacity should be increased by a volume equal to the output from the sprinkler system for a period of at least 20 minutes.
If the material to be bunded is contained in drums (or other small containers), the bunded area must contain at least 25% of the total volume of the stored products.
In addition, provide for the containment of firewater on-site by designing and constructing adequate drainage controls, and by formulating emergency response plans. (See Best Practice Guidelines for Contaminated Water Retention and Treatment Systems, Department of Urban Affairs and Planning 1994.)
Materials used for bunding AS 1940-1993 5.9.3, AS 3780-1994 5.7.3
The bund floor and wall must be constructed of materials impervious to the contents of any tank or container within the bund. The bunded area must be capable of preventing the migration of any spillage or leakage to the surrounding environment. The bund must be built out of materials that can resist attack by any toxic substances that might be put inside it. A wall of brick, stone concrete or other suitable material could form part or all of the perimeter of a compound.
Earthen bunds are not recommended, except where there is no other viable alternative. Earth by itself, without a lining, does not satisfy the impermeability criteria. Any vegetation contained in the bund or on the banks will need to be maintained. The groundwater depth and subsidence of construction materials must be taken into consideration. A submission outlining remediation works and the disposal method for contaminated soil will be required at the development approval stage.
If vehicles will need access to the bunded area, use ramps, a change in grade, or speed humps to maintain an effective bund height.
Earthen bunds must be at least three times wider than they are high. There should be a flat section at the top at least 0.6 m wide. Earthen bunds should be higher than those built from brick or concrete, because there will be soil settling and erosion before the vegetation becomes established.
Strength of bunding floors and walls AS 1940-1993 5.9.3
The bund floors and walls must be strong enough to withhold any spillage from the storage facilities. The structural design should be approved by a structural engineer.
Bund heights and tank distance from the wall AS 1940-1993 5.9.3, AS 2865-1986
Wall-type bunds at tank storages should be from 0.5 m to 1.5 m high, depending on the required containment capacity and the distance to the tank - the closer the wall to the tank, the higher the wall has to be. The distance between the tank and bund walls must be at least 1 m. If bund walls are higher than 1 m above the compound floor, provide steps or ladders for quick escape. For bund walls close to the tank or higher than 1.5 m, apply the rules for confined spaces.
If you make the walls lower than 0.5 m you will need a large bunded surface area, which will collect more rainwater and be more exposed if there is a fire. Low walls are also more difficult for vehicle drivers to see, and so more likely to be damaged. If the walls are higher than 1.5 m it can be difficult to get out of the bund in a hurry, and high walls can make it hard to see what's in the bund. If the bund walls are to be higher than 1.0 m, install entry and exit ramps for general and emergency access as well as for reinforcement.
Storage of liquid classed as a "dangerous good"
If the liquid to be stored is classed as a dangerous good, make an allowance for the trajectory of a liquid leak, assuming a full tank with an elevated point of leakage. You might need to install a splatter shield, or have a generous distance between the tank and the bund wall - half the height of the tank would be appropriate. This is not necessary for drums if they are stored in such a way that a fence or wall stops them falling outside the bunded area.
Drainage AS 1940-1993 5.9.6, AS 3780-1994 5.7.4
A collection sump must be provided in the bund floor to make it easy to remove liquids. The floor must be graded in such a way that liquids collect in the sump. There must be no access to the stormwater system within the bund.
If bund drain valves are installed they must be leakproof and able to continue functioning in a fire. The controls must be outside the bunded area. They must be able to be opened manually, and the valve must be able to be locked in the closed position. The "open" and "closed" positions on the valve must be indicated and obvious.
Piping and pumping facilities AS 1940-1993 5.9.3, 5.9.6, AS 3780-1994 5.7.3
Piping and pumping facilities must be arranged in such a way that no leaks can escape the confines of the bund, and when the bund is full of liquid the pumps will still operate. If a pump has to be used to pump out flammable liquids or water containing flammable liquids, the pump must be flameproof.
All pipework should go over the bund walls; if pipework goes through the bund walls, the bund wall - pipework interface must remain gap-proof and crack-proof even in a fire. A sealant will be needed around all metal pipes that go through walls.
If there are hose couplings in the bund, place them in positions where leaks or spillages from the couplings are contained within the bund. If couplings are remote from the bund, you must provide a suitable means of collecting and retaining the leaks and spillages.
Disposal of waste
If there are processes operating within the bunded area, include a slop tank to facilitate the storage of wastes and spillages.
It is an offence under section 120 of the Protection of the Environment Operations Act 1997 to pollute waters. It is an offence under Part 5.6 of the POEO Act to unlawfully transport waste or to permit land to be used unlawfully as a waste facility.
If possible, provide a roof to stop rainwater getting in. Make sure that the roof will not cause a build-up of dangerous or poisonous gases, or restrict the application of water in an emergency. Incorporate a 12° from vertical overhang to help stop rain entering the bund from the side.
Roofing a dangerous goods storage
Not all dangerous goods storages have to be roofed. There are circumstances where a roof over a burning tank of flammable liquid could not only hinder firefighting operations, but also spread the flame laterally to other structures. Risk assessment and planning processes should be done on a case-by-case basis; they should explore the options of roofing or of safely disposing of rainwater that might collect in an open bund. Roofing the facility could be an advantage for non-flammable Class 6.1 and Class 8 dangerous goods.
Bunded tanks and accessories, including their bases and support structures, must be designed and constructed in such a way that they are resistant to fire and corrosion and do not react with spilled product.
It is sometimes acceptable to store drums temporarily on spill containment pallets. Each pallet should be capable of capturing the contents of at least one of the drums if there is a leak. If these pallets are to be used, the drums must be stored in a level area (to ensure full spill storage capacity), and they must be covered so that the pallets do not fill with rainwater.
For other temporary storages that hold less than 1000 L of liquid, it might be possible to avoid providing bunding if you follow good operational procedures. These procedures are:
- making sure it is possible to recover spilled material
- storing containers or drums under cover and on an impervious area, away from stormwater drains and pits
- keeping an absorbent on hand at all times.
Storage for more than 24 hours is not considered temporary.
Temporary bunding arrangements should ensure that there is only localised contamination in the event of a spill. As a condition of approval there must be a management plan for the remediation of the site and disposal of the waste. An example of temporary bunding is that needed for storage of fuel during forestry or mining operations.
Bunding involving the use of a graded floor or "speed bumps", so that the flow of any liquid leak is controlled and directed to a sump, might be acceptable. This technique is often used in locations where vehicle access is required.
Operating and maintaining bunds
Maintenance items requiring checking
The person responsible for operation and maintenance should check that:
- the drain valve remains in the fully closed position at all times when not in use and can be opened only by himself/herself
- the "open" or "closed" positions on the drain valve are clearly visible and locked when not in use
- the bund is under close supervision
- any authorised officer can gain access to inspect the drain valve
- the drain valve is routinely maintained to ensure it operates as designed
- the bund wall is routinely maintained to ensure it is always impervious to liquids
- pipework, valves and other equipment in the bund are routinely maintained
- spillages of solid or liquid material within the bunded areas are cleaned up immediately
- after rainfall, all bunds are emptied as soon as possible to maintain full capacity. Never allow rainwater to build up to a level where leaking dangerous goods can float over the top of the bund.
Testing and disposing of bund water
When the bund needs to be emptied, wherever practicable it should be pumped out, not emptied through a drain valve.
If you cannot determine whether the bund water is contaminated just by looking at it, the water must be tested before it is removed from the bund.
If a visual inspection indicates that the bund water is polluted, the concentration of the pollutants must be determined. The contaminated waters must be disposed of in a way that does not pollute the environment, such as to a liquid waste treatment facility.
Contaminated water and wastes contained within the bund must be disposed of in a way that does not pollute waters, in accordance with the POEO Act 1997. Liquid waste must be disposed of at a liquid waste disposal facility or company, or treated to an acceptable level for discharge to the sewer with the permission of the responsible authority.
Uncontaminated water contained within the bund can be used beneficially on-site for site enhancement, or directed to a grassed area to be absorbed into the ground, if this is practicable and possible.
Disposing of contaminated soil
If the soil has become contaminated, a decision will have to be made about how to deal with it. If the soil is to remain in situ, the degree of contamination, the proposed land use and the potential impact on groundwater will need to be assessed.
If a decision is made to remediate the soil, the hierarchy of solutions is:
- recover the contaminants
- treat on-site by whatever available means
- treat off-site
- dispose of on-site or off-site.
If the soil is put in a containment facility on-site, approvals are required from the local council or the Environment Protection Authority. Record information about the location of the containment with the Local Council. If the soil is disposed of off-site, it must go to an appropriate licensed waste facility.
The following standards are available from Standards Australia - phone 1300 654 646:
AS 1940-1993 The storage and handling of flammable and combustible liquids
AS 4326-1995 The storage and handling of oxidising agents
AS 3780-1994 The storage and handling of corrosive substances
AS 2507-1984 The storage and handling of pesticides
AS/NZS 4452-1997 The storage and handling of toxic substances
Department of Urban Affairs and Planning 1994, Best Practice Guidelines for Contaminated Water Retention and Treatment Systems, Hazardous Materials Policy Coordinating Committee, Department of Urban Affairs and Planning, Sydney
Hard copy ($11.00) available from the Department of Planning Infrastructure and Natural Resources:
20 Lee Street SYDNEY
Opening hours: 9.00am to 5.00pm Monday to Friday
t: 1300 305 695
f: 02 9762 8701
AS 2865-1986 The safe working in a confined space
AS 4081-1993 The storage, handling and transport of liquid and liquefied polyfunctional isocyanates
AS 2714-1993 The storage and handling of hazardous chemical materials - Class 5.2 substances (organic peroxides)