Environmental guidance for your business in Northern Ireland & Scotland

Secondary containment systems (Bunding)

Secondary containment systems (Bunding)

Secondary containment systems (SCS) are used to catch any leaking oil, overfilling or other spills from a primary container, such as a tank, and its pipework. If you store oil on your premises you may have to comply with the Oil Storage Regulations which set minimum requirements to use SCS when storing oil. Bunds and drip trays are examples of SCS.


What you must do

Follow requirements for secondary containment or bunding

If you are required to use secondary containment, you must store oil containers within a bund, drip tray or any other suitable SCS.

For oil tanks, intermediate bulk containers (IBCs) and mobile bowsers, a bund is the main form of secondary containment. A drip tray is usually used for single or multiple oil drums.

For oil tanks, IBCs and mobile bowsers, your SCS must be able to hold at least 110 per cent of the maximum volume of a single container.

If you have more than one container stored in the same system, the SCS must be able to hold whichever of the following is greater:

  • 110 per cent of the largest container's storage volume
  • 25 per cent of the total volume of the containers.

For drum storage, your drip tray must be able to hold at least 25 per cent of the total storage capacity of the drums.

When you calculate the capacity of your SCS remember to deduct the volume taken up by the container supports, pipework and pumps. If you are located in a high rainfall area, you may need to increase the capacity or install a protective roof to stop water entering the SCS.

You must ensure that the base and walls of your bunds are impermeable to water and oil with no drainage outlets.

Always ensure there is ample space between the primary container and its SCS. A minimum distance of 750 millimetres between your tank and the bund wall is advisable so you have room to inspect and maintain the tank and bund.

You must locate your SCS away from areas where it could be damaged by impact, for example vehicle movements. If this is not possible you must take steps to minimise the risk of damage. You could provide protection, such as a barrier or bollards, for the SCS.

SEPA: Oil storage guidance for Scotland

No pipes, valves or other openings to drain down the system must penetrate the base or wall of the SCS. All fill pipes and draw-off pipes from the tank that pass through the bund must be sealed carefully to prevent oil escaping. See the page in this guideline: Oil container pipework and fittings requirements


Comply with agricultural fuel oil regulations

In Northern Ireland, if you store oil for agricultural use on a farm, for example to produce heat or power, there are separate regulations that govern how you must store it.

Storing and using oil for Agriculture


Good practice to avoid causing pollution

Even if the Oil Storage Regulations do not apply, you should still use secondary containment for your oil containers.

GPP 2 Above ground oil storage tanks (Adobe PDF - 276KB)

You should have a pollution prevention plan in place, in case rainwater enters the bund and becomes contaminated with oil. Use an enclosed, proprietary tank system or roof over an open bund to prevent rainwater collecting.

If you have an open bund it may have a sump or low point that collects rainwater or spilt oil in the base of the bund. You can remove any unwanted liquids using a manual pump or by hand bailing.

You could use an automatic pumping system in remote locations which can distinguish between oil and water in the bund. However, to install one of these systems, you must find out from the Northern Ireland Environment Agency or SEPA where you can discharge the water.

Any water removed from the bund may be contaminated with oil, and you must dispose of it as hazardous/special waste.

Hazardous/special waste


Further information

NIEA and SEPA Water Pollution Hotline 0800 80 70 60

DAERA: Oil storage guidance for Northern Ireland

SEPA: Oil storage guidance for Scotland

GPP 2 Above ground oil storage tanks (Adobe PDF - 276KB)

GPP 21: Pollution incident response planning

In this Guideline

Where to locate your oil storage container

Requirements for your oil storage container

Secondary containment systems (Bunding)

Pipework and fittings for oil storage

Mobile bowsers for oil and fuel

Maintaining your oil storage containers

Prevent pollution: dealing with oil spills

Oil storage - Further information

Oil storage environmental legislation

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