What is a Bunding

In industries that store, handle, or process liquids, the risk of accidental spills and leaks is ever-present. These spills can have devastating consequences, contaminating soil and groundwater, threatening public health, and damaging infrastructure. To mitigate these risks, protective barriers known as bunds are constructed. Bunding refers to the design and installation of secondary containment systems, typically walls or embankments, built around storage tanks, chemical containers, or industrial sites to contain liquid spills in the event of failure or overflow.

Bunding is an essential safety measure across many sectors, including water treatment, fuel storage, agriculture, chemical manufacturing, and environmental protection. In the United Kingdom, as well as internationally, it is mandated by law in many circumstances, with strict regulations outlining construction standards and maintenance requirements.

What is bunding

Bunding is the construction of a barrier, wall, or embankment around a tank, drum store, or liquid-handling area, designed to contain any accidental discharge. The contained space, known as a bund, functions as a catchment area, preventing hazardous liquids from escaping into the wider environment.

The size of the bund is generally calculated to hold at least 110% of the capacity of the largest tank within it, or 25% of the total volume stored, whichever is greater. This ensures that even in the event of catastrophic failure or simultaneous spills, the liquid remains confined.

Historical development

The origins of bunding can be traced back to the early days of industrialisation, when catastrophic fuel and chemical spills highlighted the need for secondary containment. In the nineteenth century, as oil and chemical industries expanded, bund walls were first constructed around storage facilities. These early bunds were often simple earth embankments, relying on sheer volume rather than engineering precision.

By the mid-twentieth century, formal standards began to emerge, particularly as environmental awareness grew and governments responded to pollution incidents. The widespread oil storage regulations introduced in the UK and Europe during the latter half of the century made bunding a legal requirement. Since then, bund design has become increasingly sophisticated, incorporating impermeable liners, reinforced concrete, and advanced monitoring systems.

Types of bunds

Bunding can take many forms depending on the application and the nature of the liquids stored:

• Earth bunds: Constructed from compacted clay or soil, often lined with geomembranes to ensure impermeability.

• Concrete bunds: Durable and widely used in industrial facilities, providing strength and chemical resistance.

• Masonry bunds: Brick or block walls used in smaller installations, sometimes with protective coatings.

• Steel or composite bunds: Prefabricated systems for drums or small tanks, often portable and modular.

• Double-skinned tanks: A modern alternative where the tank itself incorporates an integral bund between its inner and outer walls.

Each type has its advantages and limitations, and selection depends on site conditions, liquid characteristics, and regulatory requirements.

Functions of bunding

The primary purpose of bunding is containment, but its functions extend beyond simple storage:

• Prevents spills from contaminating soil and groundwater.

• Protects drainage systems and watercourses from hazardous discharges.

• Provides a controlled area for recovery and clean-up operations.

• Reduces fire risks by containing flammable liquids.

• Ensures compliance with environmental legislation and health and safety regulations.

In wastewater treatment and drainage contexts, bunding is critical for preventing untreated or toxic effluents from escaping during plant failures or accidental releases.

Design considerations

Effective bunding requires careful design to ensure both containment and long-term durability. Key factors include:

• Capacity: The bund must meet or exceed minimum volume requirements specified by regulations.

• Material compatibility: Walls and liners must resist chemical attack from the stored liquids.

• Impermeability: The bund must be watertight, with no cracks or leaks.

• Drainage: Bunds should include sump areas and controlled drainage points to facilitate safe removal of rainwater or spilled liquid.

• Accessibility: Designs must allow for safe inspection and maintenance of tanks within the bund.

• Structural integrity: Walls must withstand hydrostatic pressure from potential spills and external loads.

Modern bunds may also incorporate leak detection sensors and automatic pumping systems to manage accumulated liquids.

Regulations and standards

In the United Kingdom, bunding requirements are set out under several pieces of legislation. The Control of Pollution (Oil Storage) Regulations 2001 is particularly significant, requiring secondary containment for oil storage in many domestic, commercial, and industrial settings. Other regulations, such as the Environmental Permitting Regulations and the Health and Safety at Work Act, also impose duties to prevent pollution.

British Standards, such as BS EN 858 for oil separators and related containment systems, provide technical guidance on bund design. The Environment Agency also issues best practice notes, advising operators on bund capacity, construction materials, and maintenance procedures.

Failure to comply with bunding regulations can result in prosecution, fines, and liability for clean-up costs, which in some cases can reach millions of pounds.

Common problems and failures

Despite their importance, bunds are not infallible. Problems often arise due to poor design, inadequate maintenance, or improper use. Common issues include:

• Cracks and leaks in concrete bunds leading to loss of containment.

• Blocked drainage points causing bunds to fill with rainwater and lose effective capacity.

• Chemical attack degrading liners or wall materials.

• Poor housekeeping, with bunds used as storage areas for drums, tools, or waste.

• Structural collapse due to overloading or lack of reinforcement.

These failures not only undermine safety but also create legal liabilities for operators. Regular inspection and maintenance are therefore essential.

Maintenance and inspection

A bund is only effective if it is properly maintained. Best practices for bund maintenance include:

• Regular inspection of walls and floors for cracks, leaks, or signs of chemical damage.

• Removal of accumulated rainwater or liquid, ensuring it is tested and disposed of correctly.

• Checking that drains, valves, and sumps are functioning and secure.

• Ensuring that the bund is free from clutter and remains accessible for emergency use.

• Periodic integrity testing to confirm watertightness.

Many organisations adopt inspection schedules in line with regulatory requirements, often quarterly or annually, depending on the risk level.

Bunding in wastewater and drainage systems

In wastewater treatment plants, bunding is often used around chemical dosing systems, sludge storage tanks, and fuel tanks for standby generators. These facilities handle potentially hazardous liquids such as acids, alkalis, or oils, all of which must be contained securely.

In drainage engineering, bunds can also be used to protect sensitive watercourses from contaminated stormwater runoff, especially in industrial estates or chemical storage yards. By capturing and holding pollutants, bunds reduce the risk of uncontrolled discharges into sewers or rivers.

Environmental significance

The environmental benefits of bunding are substantial. By preventing spills from spreading, bunds protect groundwater, rivers, and soil ecosystems from pollution. They reduce the risk of long-term contamination, which can take decades to remediate and often involves enormous costs.

Bunding also plays a role in climate resilience. As extreme weather events such as floods increase, the risk of storage tank failure rises. Properly designed bunds add a layer of security, ensuring hazardous substances do not spread during disasters.

Future developments

The future of bunding lies in integrating traditional containment with modern monitoring and sustainability approaches. Smart bunds equipped with sensors can provide real-time alerts of leaks or rising liquid levels. Improved liner technologies and chemical-resistant composites are extending the lifespan of bund structures.

There is also growing emphasis on sustainability, with bunds increasingly designed using recycled aggregates, low-carbon concrete, and permeable membranes that combine durability with environmental responsibility.

In the context of circular economy principles, bunds are no longer seen simply as passive barriers but as active components of risk management and environmental stewardship.

Conclusion

Bunding is a critical protective measure in plumbing, drainage, wastewater management, and industrial operations. By providing secondary containment, bunds prevent liquid spills from causing pollution, protect public health, and ensure compliance with strict regulations. Whether constructed from earth, concrete, steel, or advanced composites, their effectiveness depends on proper design, maintenance, and adherence to standards.

While often overlooked compared to more visible infrastructure, bunds are essential guardians of the environment. Their role in safeguarding soil, water, and ecosystems against hazardous spills will remain central as industries adapt to stricter environmental standards and the challenges of a changing climate.