Separators stem tide of unseen pollution
More oil finds its way into oceans from spills into drains than tanker leaks. Specifying the correct separator for a site's risk level can prevent spills ending up in the watercourse - and ensure compliance with new legislation, writes Andy Thompson.The fact that oil and fuel are among the most common types of water pollutant investigated by the Environment Agency (EA) in England and Wales probably will not surprise many people. What may be a surprise will be the hefty clean-up cost for UK business, currently estimated at around £100M a year.
Legislation has been introduced that means, generally speaking, any site where there is a risk of surface water contamination by oil must now have some measure in place to protect the environment.
But, despite this and additional guidance from government agencies, there are concerns that preventative measures that have been implemented are either inadequate, or are not being properly maintained.
Oil and fuel pollution, not surprisingly, is most closely associated with vehicle use, so sites that are most at risk from pollution include petrol forecourts, roads and car parks. Oil drips and fuel spills from vehicles or pumps contaminates surface water that then drains into the sewage system. From there, it is discharged directly into a watercourse or indirectly into ground water via a soakaway.
Oil pollution in our oceans is most commonly associated with a grounded oil tanker and the devastating effect the leaking oil has on eco-systems. But it is believed more oil ends up in the world's oceans from waste oil contamination via drains, and then watercourses, than from any other source.
The EA has published guidance on surface water disposal, either at the point of source, or when it leaves the site. The techniques are collectively known as sustainable urban drainage systems (SUD) which, as many of you will be aware, aims to even out flow rates (preventing flash flooding), replenish groundwater and treat minor organic pollution - at source, where practical.
The measures that should be implemented under SUDS, not surprisingly, depend on the likely scale of the problem.
Low-risk areas such as small car parks (less than 15 spaces) may need only a simple solution such as permeable surfaces or infiltration trenches. But areas such as roads, refuelling facilities, large car parks and vehicle maintenance yards require a more robust solution for dealing with oil spillages.
For all these situations it is now mandatory to install a separator (formerly known as an interceptor).
Separators are - in appearance at least - large underground tanks that are designed to prevent any pollution reaching drains or ground water by treating contaminated run-off and safely retaining oil until it can be removed.
They 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.
According to Mike Norton, technical director of Kingspan Environmental (Klargester and Titan Pollution Control), although separators are now fairly commonplace, they are also very specialised.
"It's important that the correct type and class of separator is installed. A thorough risk assessment should always be conducted beforehand and regular ongoing maintenance is also required to ensure efficient working, best practice and safety," says Norton.
"We have seen units installed in situations where operating regimes permit more oil than water to be fed to separators. Clearly, they cannot operate in this scenario."
The point about maintenance is particularly important.
"All separators should be inspected every six months, or in accordance with the manufacturer's instructions, to ensure that they are working correctly and to remove any oil or silt," says Norton.
Of particular concern is whether separators at facilities nationwide are being maintained by teams on site. They may not know if they even have a separator on site, let alone what is needed to maintain their efficient operation.
If a separator is not cleaned regularly, oil or silt will back-up and it will stop working. In those instances, oil will simply bypass the separator and discharge directly into groundwater - which is both illegal and an environmental hazard.
One way to guard against any failure of the process is to fit the separator with a warning system to prevent oil from overflowing. PPG and EN858 recommend oil level alarms be fitted to all separators.
"If in doubt about the presence or otherwise of a separator, the site manager should review the site's drainage layout drawings. These will allow you to identify their exact location; otherwise the only visible sign at ground level will be a manhole cover," adds Norton.
· Class 1 separators reduce the oil content to less than 5mg/l in water under laboratory conditions when fed with a concentration of 500mg/l of oil. Use when discharging to storm-water drains
· Class 2 separators can be used where lower quality requirements apply - discharges to the foul sewer, for instance. Their output must contain less than 100mg/l oil, again under the above test conditions
· Full retention separators are used where there is a risk of regular contamination and of significant spillages - goods yards, maintenance depots, industrial sites, refuelling facilities and airports
· Bypass separators are suitable where there is a low risk of small spillages only, such as short-stay car parks. Also relevant to large catchment areas where full retention units would be impractical
· A forecourt separator must be used where liquid fuel-handling involves road tankers and dispensing occurs, including non-retail and diesel-only sites. Not required on domestic tanker delivery sites
Andy Thompson is market development manager at Kingspan Environmental Division, which includes Klargester Environmental and Titan Pollution Control.
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