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.

Nearly all oil poured down drains will find its way into streams, rivers, groundwater and the sea. In fact more oil ends up in the world's oceans from the disposal of waste oil down the drain than from any other source.

Fuel/oil separators, which were formerly known as interceptors, play an important role in helping to avert pollution by treating contaminated run-off and safely retaining oil until it can be removed.

They 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.

Fuel/oil separators were first introduced to the UK in the 1930s and they have come to the fore in recent years as new guidelines from Europe (EN 858) and the Environment Agency (PPG3) have been introduced to prevent oil pollution.

Although separators are now commonly used products, they are also very specialised and require careful specification to ensure that all risk factors are taken into account and that the correct type and class of separator is identified.

Firstly, specifiers need to identify when a separator is needed. Generally speaking, any site, where there is a risk of surface water contamination by oil, must have some measure in place to protect the environment.

Although a SUDS may offer sufficient protection for some low risk locations, separators are now mandatory for many sites, including roads, car parks, refuelling facilities and vehicle maintenance yards.

Having determined the need for a separator, specifiers should identify the correct class and type. 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.

The oil storage capacity of any separator must be sufficient to retain any foreseeable spillage. Capacity for silt storage must be provided according to the formula in PPG3 - the only published guidance on these products in the UK.

In terms of sizing, the nominal size of a separator in the UK is calculated by multiplying the surface of the area drained by 0.018 for full retention and 0.0018 for by-pass.

If an oil separator is needed then the discharge point must be determined at an early stage. If the product is to discharge into surface water drains or into the ground, Environment Agency permission may be needed.

If the separator is to discharge into a foul sewer, consent must be obtained from the local sewer provider. Discharge from areas such as scrap-yards, and storage and handling areas for chemicals, are likely to be contaminated with substances apart from oil and should usually drain to the foul sewer

A full retention separator must be fitted with a closure device so that it will prevent oil from escaping if the volume of oil exceeds the storage capacity.

All separators must be fitted with a warning system to prevent oil from overflowing. It is also advisable to have a silt level alarm on separators in areas such as quarries, builders' yards and major trunk roads, where large quantities of silt are likely to accumulate.

Other factors to bear in mind when specifying a separator are that these products must conform to the Construction Products Regulations 1991, which are enforced by Trading Standards.

Also, separators specified for permanent inclusion in construction works in the UK must conform to the BS EN 858-1:2002 standard. The Environment Agency holds a list of all manufacturers that comply.

Specifiers should advise purchasers to ensure that the separator is inspected every six months, or in accordance with the manufacturer's instructions, to ensure that it is working correctly and to remove any oil or silt.

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

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