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Where are separators needed?

Surface water may be contaminated by oil at a number of different sites. These sites need to have measures in place to prevent this oil from polluting the environment. These sites include:

  • Car parks typically larger than 800m2 in area or for 50 or more car parking spaces
  • Smaller car parks discharging to a sensitive environment
  • Areas where goods vehicles are parked or maneuvered
  • Vehicle maintenance areas
  • Roads
  • Industrial sites where oil is stored or used
  • Refueling facilities
  • Any other site with a risk of oil contamination

Trapped gully pots can provide adequate protection for car parks that are too small to justify the installation of a separator, but they must be properly maintained.

You might not need an oil separator if you use ‘sustainable drainage systems’ (SUDS). The SUDS approach should be used on all sites to minimise the impact of the development on the environment. In Scotland, the use of the SUDS approach is a legal requirement. Techniques that control pollution close to the source, such as permeable surfaces or infiltration trenches, can offer a suitable means of treatment for run-off from low-risk areas such as roofs, car parks and non-operational areas. In higher risk areas you might need other SUDS facilities such as constructed ponds, wetlands or swales. Where there is a high risk of contamination, it may be appropriate to use an oil separator as part of your SUDS scheme.

If you do need an oil separator, you will need to consider where it will discharge. It is important to speak to the Environment Agency as early as possible if you plan to discharge to surface water drains, to a watercourse or to the ground, as you might require consent. In Northern Ireland, any discharge from an oil separator will require consent. The Environment Agency does not issue these consents automatically and, if they allow a discharge, they might impose strict controls on the level of polluting substances in it such as oils. If you install a separator discharging to surface water you will need a Class 1 separator.

If your separator will discharge to a foul sewer, you must contact your local sewer provider before doing so. For discharges to a foul sewer, you will need a Class 1 or Class 2 separator. If your separator will discharge to a surface water sewer that is owned by the sewer provider, you must also contact them before you connect to that sewer.

Drainage from areas such as scrap yards, storage and handling areas for chemicals (solvents, acids etc.) and washing bays are likely to be contaminated with substances other than oil, and should normally drain to the foul sewer with the approval of the sewer provider. The local sewer provider might require the discharge to have a separator and you must consult them. Discharge from such areas is not suitable for drainage to surface water drain, a watercourse or to the ground.

Drainage containing detergents should not pass to a separator that discharges to surface water because the detergents prevent the separator from working properly.