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Discover what is an interceptor and legal requirements in their maintenance. What is integrity testing and the importance of interceptor service as well as inspection.


Interceptors, sometimes called separators, are large underground tanks fitted on drainage systems to protect the environment from oil pollution. As rainwater runoff enters the interceptor most hydrocarbons would remain floating on the top and filtered water would be released into the drainage system. If you have interceptors on your site, they should be regularly inspected, serviced and maintained.



There are no specified legal requirements that deal with interceptors. However, this blog will discuss wider environmental obligations and how they apply to interceptors.

What do interceptors do?

Interceptors are designed as pollution prevention and control devises. They can be installed on the surface or foul drainage system and can be found in various areas on a site. They are usually in areas of high pollution risk like vehicle washes and fuel islands and/or at the outflow from the site. Water from your site will lead to the tank where pollutants can settle out. Oil will collect at the top while silt will settle to the bottom of the tank. Other pollutants such as detergent could emulsify oil and affect the effectiveness of the interceptor.

What do the regulations say?

There are no specified legal requirements that state how you should manage your interceptors. However, there are broader environmental obligations that do apply to interceptors. All businesses must prevent pollution. Under the Water Resources Act 1991, it is an offence to cause or knowingly permit any poisonous, noxious or polluting matter or any solid waste matter to enter any controlled waters.

This has two implications for interceptor management. Firstly, installing an interceptor will contribute to preventing pollution that could be caused by your site by intercepting oil and silt that may otherwise escape and cause environmental damage. Secondly, it you do not correctly manage your interceptor and carry out regular servicing, it could fail and release the pollutants it was designed to capture. When interceptors are in use, they can fill up with oil and silt, which, if not removed, can block interceptors or eventually release the accumulated pollutants in a concentrated form. Damaged interceptors could also be ineffective and cause pollution. Regular servicing should check your interceptors and report any damage and you should take action to repair when required.

Are there any other guidelines?

The Environment Agency provides a variety of guidance on an array of environmental matters. Their guidance on pollution prevention for business includes direction about when an interceptor is needed and the requirement to maintain and empty it as necessary. Additional guidance includes pollution prevention guidelines issued by the Environment Agency and the European Standard BS EN 858 that has been adopted by the UK for the design, use, selection, installation, operation and maintenance of prefabricated interceptors. Despite having now been revoked, Pollution Prevention Guideline 3 provides guidance on interceptors and is widely accepted by the industry. Both the PPG and the European Standard state that interceptors should be serviced every 6 months and that an interceptor integrity check should be completed every 5 years.

Interceptors are an essential piece of pollution prevention equipment. In order to ensure they remain effective and so you meet your legal obligations to prevent pollution, you must maintain and service them regularly.



What is involved in integrity testing?

Integrity testing for interceptors provides a more detailed analysis on the condition of the interceptors you have on site to ensure they are in good repair and continue to provide you with the best pollution prevention. In order to carry out an integrity test, the whole interceptor will need to be emptied of any contaminants (oil and silt) and all of the water. Confined spaces entry to inspect the condition of the tank is the usual method but can be carried out with specialist equipment and experience to avoid the requirement for confined spaces. After the test, the interceptor should be filled with clean water up to the static water level to ensure it continues to provide pollution protection and remove contaminants.

Why should I test the integrity of my interceptors?

During regular use, oil floats to the top of the tank while silt sinks to the bottom, allowing clean water to leave site. If the tank is damaged, or has worn, it may affect the effectiveness and contaminants could leave your site. Some trade effluent licences (for a reminder on what they are, click here) require effluent to be passed through an interceptor prior to discharge so you should ensure that the interceptor is working correctly and removing contaminants effectively to maintain compliance.

How often should interceptor integrity be tested?

As best practice, interceptors should be integrity tested every 5 years. This should be in addition to your interceptor servicing and maintenance visits, at least every 6 months.

What should I expect from integrity testing?

When you have your integrity test carried out, you should receive information on the specification of your interceptor, for example, its size, type and any associated equipment. You should also have a full report on the condition of the interceptor, including any areas of wear or anything that needs repairing or replacing. You should have recommendations, including frequency of integrity tests and you must review all of your recommendations and ensure that you action those necessary to maintain the effectiveness of your interceptors.

You should ensure that you address any issues or damage and take all possible actions to ensure your interceptors provide continued protection.



Why do interceptors need servicing?

Interceptors are an essential that will help make sure water discharges do not cause pollution or exceed the limits of a consent or license. However, they are only effective when they are in full working condition. Oil is separated from water as it is less dense and will float at the top of the tank. Once the tank fills with oil, it can no longer separate the pollutant from water discharges and oil will leave your site, potentially causing pollution. Interceptors can also be damaged or become worn and they will become less effective if the issues are not resolved quickly. A regular service visit can help ensure your interceptors remain effective and in good condition.

What does a service involve?

A service should involve more than emptying the tank; it should be a full inspection and assessment. The separator and all mechanical parts should be physically inspected to identify any areas of damage or wear and any associated electrical equipment such as alarms and separator management systems checked to ensure they are working correctly. The depth and accumulation of oil and silt should also be assessed. This will ensure that your interceptors are being serviced regularly enough and inform whether they should be emptied at more regular intervals.

A service should be followed up by information or a report on the work that has been carried out and any issues you should be made aware of. This should be used to take the appropriate measures to ensure your interceptors remain effective. If waste has been removed (e.g. oil, silt, water), you should have the appropriate waste documentation on file, including transfer paperwork, the waste carriers license of the contractor removing the waste and details of the site where the waste is being taken to.

How often should interceptors be serviced?

Interceptor servicing should be added to your regular PPM (Planned Preventative Maintenance) schedule to ensure they are regularly emptied and checked, the frequency of which will be informed by your site operations. Sites or interceptors servicing areas of higher risk, such as refueling areas, should be serviced more frequently as the likelihood of oil entering the drainage system is higher. Services can be every 3, 6 or 12 months, depending on the risks and findings of previous interceptor services.

Interceptors are essential pollution control devises that can assist sites in managing their environmental risks. However, sites must be aware of where their interceptors are and they should be checked and emptied regularly to ensure they remain in good condition and effective.



As part of your Planned Preventative Maintenance (PPM) schedule, you should regularly service your drains and interceptors (you can read more about why you should here). There are many different suppliers you can choose from, but what should you expect in terms of outcomes?

Full Service

It is important that your service covers all of your site interceptors and is completed to a high standard so that your interceptor maintains its purpose for pollution control. At a minimum, your interceptor service should include: • A regular check for silt and oil accumulation • A thorough visual inspection for any issues or faults • An inspection of all mechanical parts associated with the interceptor

If your inspection indicates so, you should empty your interceptor of oil and/ or silt that has accumulated there. You must make sure that anything removed from your interceptor is disposed of correctly as a waste and dealt with as hazardous if it is contaminated by oil.


A full and comprehensive interceptor service should be followed by an informative report. Some contractors will only provide you with an email confirming that they have visited your site, but this will not fully inform you of your site arrangements and potential risks. A comprehensive report should: • Detail the scope of works carried out – whether it was limited to an inspection or whether waste was removed or if an integrity test was carried out • Identify the current condition of your site interceptors • Recommend any further works required e.g. if the interceptor does require emptying • Include any additional issues with drainage or the surrounding area • Prove attendance, usually through photos • Highlight any missed interceptors and the reasons why e.g. not accessible

Your report should allow you to make management decisions regarding the state of your interceptors and any additional works that are required. A good report is also useful when proving maintenance of pollution controls during audits and showing purpose value for money when considering PPM budgets.

Interceptors should be regularly serviced, usually every 6 months. Your service should be comprehensive and include all of your site interceptors. When a service has been completed, a clear and full report will provide a service history of your interceptors and provide management information, so you can make a clear decision on interceptor management going forward.



Traditional interceptor management usually involves regular emptying of interceptors. This means that everything is emptied out of the interceptor and removed as a hazardous waste. This can get quite costly so is there an alternative?

How is traditional interceptor management carried out?

Historically, interceptors are regularly completely emptied out with a tanker, removing all water, oil, silt and other contamination; usually every 6 months or annually. This type of management does not take into account the levels of contamination and the whole load will usually be classified as hazardous waste. This can be a costly exercise taking into account the site visit, carrier charge and the cost of waste disposal. Additionally, you will need to make sure that the interceptor is filled up again with clean water or it won’t work properly as a pollution prevention device.

What can I do instead?

Although it may occasionally be necessary, it isn’t always essential to empty your interceptors. They should receive a regular maintenance visit (6 monthly or annually) and be checked for any issues or damage and to assess the level of oil or silt contamination. Where contamination is present, it will probably be removed, but the interceptor can be topped and tailed, leaving behind the non-contaminated water. This will reduce costs as you will be carrying and disposing of much less waste.

If your interceptors have not been serviced for a long time, you may need to remove all of the contaminated water and fill with clean water. However, after that, or if they are in good condition with little or no contamination, you should not need to empty your interceptors every time they are serviced. It is essential that you regularly service your interceptors (remind yourself why here) to ensure they continue to offer pollution protection by collecting oil and stop it from leaving site. However, it is not essential to completely empty an interceptor during every maintenance visit and more informed interceptor visits could save money while maintaining pollution management.



What is an interceptor inspection?

An interceptor inspection is a careful examination of your interceptor, the surrounding area and its contents to confirm quality and condition. A non-invasive check, the inspection will: • Check the area of the interceptor – is the interceptor accessible? Are there any damaged areas that could cause an issue? Can the manhole lid be lifted? • Check the accumulation of silt, oil and any other substances that could have got into the interceptor • A visual check of the interceptor itself, looking for any obvious damage • A visual check of any mechanical parts associated with the interceptor e.g. probes

Why should I have an interceptor inspection?

If you have never serviced your interceptors, an inspection is a great place to start to determine their current condition and effectiveness. An inspection will identify areas that need attention and assess any potentially underlying problems. For example, it will show if your interceptors are stuck fast (the manhole lid can’t be lifted) or full of oil. If your interceptors have been regularly serviced, an inspection in the interim between services can be beneficial to identify any issues that have developed, particularly if they are only serviced annually.

What do I do after an inspection?

Your inspection should be recorded to evidence that a check has been carried out. This should confirm areas where interceptor condition is acceptable and any areas where issues have developed. Following the inspection, you must follow up on any issues that have been discovered. If an interceptor has accumulated oil, you should arrange for a tanker to remove it. You may also want to investigate how any issues occurred and potentially consider increasing your service intervals.

Do I still need an interceptor service?

Yes! An inspection is a quick check of your interceptor to highlight any issues that develop between your service intervals, it is not intended to replace your regular servicing schedule. Interceptor services will be more thorough and cleaning is likely to occur to ensure continued servicing levels. Your service may also involve tanker work if oil or silt has accumulated in an interceptor.

Interceptor inspections are a good method of ensuring your interceptors continue to provide pollution protection from your site activities. You should carry out regular inspections and act on the results to ensure your pollution prevention control devices continue to work as designed. An inspection is not designed to replace an interceptor service but can be a good place to start if you have not had a service schedule in place previously.