Environmental guidance for your business in Northern Ireland & Scotland

Oil Separators for construction sites

Oil separators for use at construction sites

A well-maintained oil separator is very effective at removing petrol, diesel and oil from water.

Before you set up your site, decide how you will deal with run-off from car parks, storage areas and vehicle wash down areas. These may contain oil in water runoff.

You may need to channel run-off from your site to more than one method of treatment.

For example, if you use detergent to wash vehicles in a car park or vehicle wash down area the detergent will emulsify any oil in the water and make an oil separator ineffective.

Yard water may not require a separator if suitable sustainable drainage techniques (SuDS) can be used. See PPG 3 for further information.

PPG 3 Use and design of oil separators in surface water drainage systems (Adobe PDF – 78.6KB)

Discharges to water or sewer

Wheel washing at construction sites

What you must do

Sizing: consider separator design

Make sure that the oil separator is big enough to cope with the volume of water that will pass through it. If the flow of water is too fast, the water will be churned up and the separator may not work properly.

You may need to install a storage tank to regulate the flow of water through your separator.


Oil separators (interceptors) that are not maintained do not work properly. They require regular maintenance to ensure that they work correctly and efficiently.

The separator should be filled to its operating level with clean water when it is first installed and every time it is cleaned out.

Any surface scum or debris that has gathered behind the skimmer should be regularly removed and disposed of.

Oil absorbent pads can be used periodically to remove oil and fuel from the surface of the water within the separator (interceptor).

Do not leave oil absorbent pads on the water surface within the separator during periods of high water flow or for longer than the manufacturer's instructions suggest.

These should be disposed of as hazardous/special waste.

Hazardous / special waste

If you are hiring oil separators, contact the plant hire business to establish whether they can undertake their maintenance as part of your hiring agreement.


When planning the layout of your site, consider where the discharge from the oil separator (interceptor) will go and what authorisation you will need for the discharge.

Discharges to water or sewer

Duty of care - your waste responsibilities

Water use and abstraction

In this guideline

Bunds for oil and chemical storage on construction sites

Controlling surface water runoff from works near water

Dealing with silty water from construction sites

Dewatering excavations on a construction site

Oil Separators for construction sites

Groundwater protection when drilling or boring on a construction site

Sediment control using tanks or silt ponds on construction sites

Slurry (liquid wastes) from construction sites

Wheel washing on construction sites

Working close to water for construction sites

Construction phase SuDS

Drip trays to prevent spills on site

Working close to water for demolition businesses

Environmental News Blog

NetRegs on NetRegs on youTube

View our latest videos & subscribe to our channel.

NetRegs Update Newsletter

Free monthly email newsletter with environmental updates for Northern Ireland and Scotland

Sign up for free today!


NIEA - Apply online

SEPA - Application forms