SPECIFYING THE RIGHT FUEL/OIL SEPARATOR by Stephen LeTissier, technical sales manager for Klargester, a leading manufacturer of these products

Oil and fuel are the most common types of water pollutant investigated by the Environment Agency in England and Wales, and cleaning up such spillages costs UK business around £100m per year.

Fuel/oil separators play an important role in helping to avert pollution by treating contaminated run-off and safely retaining oil until it can be removed. They are mandatory for many sites, including roads, car parks, refuelling facilities and vehicle maintenance yards.

Fuel/oil separators can also form an important part of a SUDS (Sustainable Urban Drainage) System, since they can even out flows, improve groundwater recharge and treat minor organic pollution.

Although separators are commonly used products, they are also very specialised and can therefore be difficult to specify. There are two main classes of separator and three main types.

Class 1 separators must always be used for discharge to surface water drains or discharge to groundwater via a filtration device such as a soakaway or filtration trench. In test conditions, the effluent from these contains < 5mg/l oil. Class 2 separators are sometimes used for discharges to the foul sewer. In test conditions, the effluent from these contains < 100mg/l oil. Discharge from a separator direct to groundwater is prohibited.

The main types of separator are known as full retention, bypass and forecourt. Full retention separators treat all design flow that can be delivered by the drainage system up to a rainfall intensity of 65mm/hr. They are used where there is a risk of regular contamination and a foreseeable risk of significant spillages e.g. at goods yards, maintenance depots, industrial sites, refuelling facilities and airports.

By-pass separators treat all design flows delivered by the drainage system during rainfall of up to 6.5mm/hr. Flows above this rate are allowed to by-pass the separator. These products are suitable for locations where full treatment for high rainfall flows is not considered necessary, where only small spillages can occur and where the risk is low e.g. short stay car parks.

A forecourt separator must be used at all sites where liquid fuel dispensing occurs, including non-retail and diesel only sites. It must be sized in two ways applying the greater of the two - the flow that can be delivered by the drainage system and the size of any potential spillage.

To conclude, there are many issues that need to be taken into account when specifying a separator and a thorough risk assessment should always be conducted beforehand to ensure best practice and safety.

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