Interceptors for Spill Control and Drainage Compliance

Interceptors are a practical, front-line form of spill control that sit within your drainage system to capture oils, fuels, silt and other contaminants before they reach surface water drains, foul sewers, rivers or groundwater. They are widely used across industrial sites, transport hubs, depots and yards where there is a realistic risk of hydrocarbons or sediment being washed into drains during rainfall, washdown or de-icing operations.

Question: What is an interceptor and what problem does it solve?

Solution: An interceptor is a drainage separator designed to retain pollutants (typically oil, fuel and silt) so cleaner water can pass through the drainage network. In simple terms, it reduces the chance that day-to-day leaks, drips and runoff turn into an environmental incident. Interceptors are not a substitute for good housekeeping or emergency response, but they are an important layer of protection when used alongside spill kits, drain protection and bunding.

Question: When do you need an interceptor on site?

Solution: You should consider interceptors where any of the following apply:

• Vehicle movement, refuelling, maintenance or parking (risk of oil and diesel in runoff).
• Loading bays and external storage areas (risk of leaks from containers, IBCs and drums).
• Washdown areas (risk of oil, detergents, silt and suspended solids).
• Airfield aprons, de-icing and winter operations (risk of contaminated meltwater and runoff; see SERPRO guidance on managing de-icing related pollution pathways Airport De-Icing Spill Management).
• Sites near watercourses, sensitive drains or where discharge consent conditions apply.

As a rule, if a spill could reach a drain, you need a planned route to intercept it: physically (drain covers and drain mats), operationally (spill response) and structurally (interceptors and bunded areas).

Question: What is the difference between oil separators and silt traps?

Solution: Interceptors are often discussed in two broad functions:

• Oil/fuel separation: Captures hydrocarbons and floating oils. These are commonly called oil separators or oil interceptors.
• Silt and sediment capture: Retains heavier solids that would otherwise block drains and carry contaminants into the environment.

Many drainage designs combine both functions, because silt can reduce separator performance and shorten service life. This is especially relevant on high-traffic yards and unmade surfaces where sediment load is high.

Question: Are interceptors enough on their own for spill control?

Solution: No. Interceptors are designed for continuous, low-level pollution and limited contamination events. For best practice spill management, use interceptors as part of a layered approach:

• Prevent: Use bunding and secondary containment for stored oils, chemicals and fuels. Store drums and IBCs in bunded areas and use drip trays where decanting is routine.
• Protect drains: Use drain covers, drain seals and drain mats to stop a spill entering the drainage system in the first place, especially during an incident.
• Respond quickly: Keep spill kits accessible and train staff to deploy absorbents and isolate the source.
• Maintain drainage: Inspect and service interceptors so they are ready when you need them.

If you need additional measures around drains, see SERPRO Drain Protection and Spill Kits options.

Question: How do interceptors support environmental compliance in the UK?

Solution: Interceptors help demonstrate that you have taken proportionate steps to prevent pollution. This supports environmental compliance and can reduce the likelihood of reportable incidents, clean-up costs and enforcement action. They are particularly relevant where:

• runoff may discharge to surface water drains, watercourses or soakaways;
• your site operates under trade effluent or discharge consents;
• you handle hydrocarbons, lubricants, fuels or process liquids outdoors;
• you are expected to have pollution prevention measures as part of an environmental management system.

For wider spill control and compliance planning, see Bunding and Spill Control.

Question: What are common interceptor failure points and how do you avoid them?

Solution: Interceptors are often installed correctly but fail in practice due to avoidable operational issues:

• Lack of maintenance: Oil and silt accumulate, reducing separation performance and increasing overflow risk. Put a service schedule in place and keep records.
• Incorrect use of detergents: Some cleaning agents can emulsify oils, allowing them to pass through. Review washdown chemicals and procedures.
• High flow events: Heavy rain, rapid snowmelt or washdown can overwhelm poorly designed systems. Consider upstream silt control and flow management.
• Misplaced reliance during incidents: A large spill can bypass separation. Keep drain protection and spill response equipment ready for escalation.

Practical site control is often about the first 5 minutes: blocking drains, stopping the source and deploying absorbents can prevent an event from becoming a discharge.

Question: What does good practice look like on real sites?

Solution: Interceptors are most effective when matched to site risks and supported by procedures. Examples include:

• Distribution yard: Interceptor on surface water outfall, with drain mats at key gullies, spill kits at loading bays, and drip trays at routine coupling/uncoupling points.
• Engineering workshop: Bunded oil storage, controlled washdown, interceptor servicing regime, and a documented spill response plan.
• Airfield and winter operations: Targeted drainage protection around high-risk areas, contingency equipment for rapid isolation, and good housekeeping to reduce contaminants entering the drainage network (see Airport De-Icing Spill Management).

Question: What should you do next if you are reviewing your drainage spill controls?

Solution: Start with a simple risk walk:

1. Map where liquids are stored, transferred and used outdoors.
2. Trace the nearest drains and identify where they discharge.
3. Check whether existing interceptors are present, accessible and maintained.
4. Confirm you have rapid drain protection and spill kits for credible worst-case spills.

If you are improving containment around high-risk points, explore Drip Trays and Bunding. For emergency readiness, review Spill Kits and Drain Protection.

Sources and further reading

• SERPRO - Airport De-Icing Spill Management (spill pathways and controls)
• UK Government - Pollution prevention guidance
• NetRegs - Environmental guidance for businesses in the UK

Note: This page provides general information on interceptors for spill control and drainage protection. Specific interceptor selection, sizing and discharge requirements should be confirmed against your site drainage design, operational activities and any permits or consents.