Outdoor chemical storage presents a distinct set of challenges that indoor containment simply does not. Exposure to rain, temperature fluctuations, UV degradation, and the proximity of surface water drains and watercourses means that the consequences of a containment failure are far more likely to cause serious environmental harm. UK legislation is correspondingly strict, and enforcement by both the Environment Agency and the Health and Safety Executive has intensified over recent years.
The Legal Framework
Secondary containment for outdoor chemical storage is governed by several interlocking pieces of legislation. The Environmental Permitting (England and Wales) Regulations 2016 set out requirements for pollution prevention, while the Water Resources Act 1991 makes it a criminal offence to cause or knowingly permit water pollution. The Control of Pollution (Oil Storage) (England) Regulations 2001 specifically require secondary containment for above-ground oil storage exceeding 200 litres at industrial, commercial, and institutional sites. Scotland has its own equivalent under the Water Environment (Oil Storage) (Scotland) Regulations 2006.
Failure to comply can result in unlimited fines, environmental remediation costs (which are typically eye-watering), and criminal prosecution of individuals as well as organisations.
What Secondary Containment Must Achieve
Effective secondary containment must be capable of holding 110% of the largest container stored within it, or 25% of the total volume stored — whichever is greater. This 110% rule is the standard benchmark and is non-negotiable for oil storage under the Control of Pollution regulations. For other chemicals, the same principle applies as best practice even where not explicitly mandated.
Key Considerations for Outdoor Bunding
- Material compatibility: The bund must be chemically resistant to the substances stored. Concrete is suitable for many applications but can be attacked by certain acids and solvents. GRP (glass-reinforced plastic) and polyethylene bunds offer broader chemical resistance and are worth considering for aggressive substances.
- Rainwater accumulation: Outdoor bunds will accumulate rainwater. Any drain valve or outlet must be normally closed and only opened after confirming the water is uncontaminated. Leaving a bund drain open defeats the purpose entirely and is a compliance failure.
- UV and weather resistance: Not all bund materials perform equally in outdoor conditions. Check manufacturer specifications for UV resistance and temperature ratings, particularly in exposed locations.
- Impermeable base and walls: The bund must have no cracks, gaps, or penetrations that could allow liquid to escape. Inspection of bund integrity should be a regular maintenance task.
- Access for deliveries: Design the containment area to allow safe access for deliveries while maintaining containment integrity. Drive-over bunds and kerb systems allow vehicle access without creating gaps in containment.
- Distance from drains and watercourses: Locate outdoor chemical stores as far as practicable from surface water drains, soakaways, and watercourses. Where proximity is unavoidable, additional protection such as drain seals and interceptors should be in place.
- Signage: Outdoor chemical stores must be clearly signed with hazard information, emergency contact details, and substance identification in line with the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR) where applicable.
Choosing the Right Containment System
For drum and IBC storage, modular polyethylene bund pallets and spill decks provide a flexible, relocatable solution that meets both the 110% containment rule and the practical needs of a working site. For larger fixed installations, concrete bunds with chemical-resistant lining or purpose-built GRP containment bays offer a more permanent solution.
Our range of outdoor bunding and secondary containment products includes options suitable for single drums right up to multi-IBC storage compounds. We also stock drain protection products for additional environmental safeguarding.
Inspection and Maintenance
Secondary containment is not a fit-and-forget solution. Inspect bunds and containment systems regularly for signs of cracking, corrosion, or damage. Check that drain valves are closed and in good condition. Remove accumulated rainwater promptly and dispose of it correctly — contaminated bund water must be treated as hazardous waste. Document all inspections.
Summary
Outdoor chemical storage demands a rigorous approach to secondary containment. The environmental and legal consequences of getting it wrong are severe. Invest in the right containment system, maintain it properly, and you will have a defensible compliance position and a lower environmental risk profile.
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