Cleaning a bunded wall involves removing accumulated rainwater, chemical residue, and debris from the containment area to maintain its full holding capacity and structural integrity. Because bunds are designed to hold 110% of the largest tank’s volume in case of a spill, any buildup of water or sludge directly reduces that protective capacity. Regular cleaning keeps you compliant with environmental regulations and prevents long-term damage to the bund lining.
Why Bund Cleaning Matters
A bund wall is your second line of defense against chemical spills, fires, or tank failures. It surrounds storage tanks or drum areas holding flammable or toxic liquids, and its entire purpose depends on having enough empty volume to contain a worst-case release. When rainwater, leaves, sediment, or chemical residue accumulate inside the bund, that available volume shrinks. Enough buildup and you risk overtopping, where a spill simply flows over the wall and reaches the surrounding environment.
There’s also a chemical compatibility issue. If the substance stored in your tanks is incompatible with water (certain acids, reactive chemicals, or oil-based products), allowing rainwater to pool inside the bund creates a hazard on its own. The UK’s Health and Safety Executive specifically flags this as a common and preventable failure, particularly at remote or less-visited sites where maintenance tends to slip.
Assess the Bund Before You Start
Before any cleaning, you need to know what’s in the bund. This step is non-negotiable because it determines your safety precautions, your disposal method, and potentially your legal liability. Walk the perimeter and visually inspect for oil sheens, discoloration, chemical odors, or visible residue on the walls and floor. Check the drain valve if one exists, as many bunds have a manually operated valve at the base for routine water removal.
If you suspect contamination from stored chemicals, the water and residue inside the bund may legally qualify as hazardous waste. Under U.S. regulations, you’re required to perform a hazardous waste determination on any waste material you generate. This often involves laboratory testing using a procedure called the Toxicity Characteristic Leaching Procedure, which checks whether contaminants in the liquid exceed safe thresholds. Until you know the results, treat the contents as potentially hazardous.
Also inspect the bund walls and floor for cracks, coating damage, or joint failures. Cleaning is the ideal time to catch these problems since the surfaces are exposed and visible. A cracked bund that looks fine from the outside can fail completely during an actual spill.
Safety Equipment You’ll Need
The level of personal protective equipment depends entirely on what chemicals the bund contains. For a straightforward rainwater-only cleanout around diesel or fuel oil tanks, standard PPE typically includes chemical-resistant gloves, safety boots, eye protection, and coveralls. If you’re working with or near substances that produce harmful vapors, you’ll need respiratory protection and potentially a full chemical-resistant suit.
Air monitoring is critical when cleaning bunds around tanks holding volatile or toxic materials. Use direct-reading instruments like combustible gas meters or detector tubes to check for explosive atmospheres, oxygen deficiency, or toxic vapor concentrations before entering the bund area. OSHA requires this type of monitoring at hazardous sites, and it applies even if the bund looks clean. Residual vapors can settle into the low-lying containment area and concentrate to dangerous levels.
For situations where chemical exposure could cause serious harm or where the hazards aren’t fully identified, OSHA guidance calls for Level B protection at minimum: a chemical splash suit with a self-contained breathing apparatus. If skin absorption is a concern, fully encapsulating suits (Level A) are required. Most routine bund cleanings won’t reach this level, but if you’re unsure about what’s in the bund, err on the side of more protection rather than less.
Removing Standing Water
Most bunds accumulate rainwater between cleanings. The simplest removal method is opening the bund’s drain valve, which should be part of your daily or weekly operating routine. Before opening the valve, visually confirm the water is uncontaminated: no sheen, no unusual color, no chemical smell. Clean rainwater can typically be discharged to a surface water drain or storm sewer, though local rules vary.
For larger volumes or where no drain valve exists, use a pump. A submersible or diaphragm pump works well for most situations. Position the discharge hose into an appropriate collection point: a holding tank, tanker truck, or approved drain. Never pump bund water directly into a watercourse or storm drain without confirming it’s uncontaminated.
If the water shows any signs of contamination, it must be collected and tested before disposal. You cannot dilute contaminated water as a shortcut to meet disposal standards. Regulations explicitly prohibit dilution as a substitute for proper treatment. Contaminated water typically needs to go to a licensed waste treatment facility, and as the generator of that waste, you remain legally responsible for it from creation through final disposal.
Cleaning the Walls and Floor
Once the standing water is removed, the actual cleaning begins. Start by removing loose debris: leaves, dirt, and sediment that have settled on the floor and collected against the walls. A shovel, broom, or wet/dry vacuum handles most of this. For larger bunds, a small skid-steer or similar equipment may be needed to remove heavy sludge buildup.
For chemical residue on the walls and floor, pressure washing is the most common method. Use hot water where possible, as it’s more effective at breaking down oil films and chemical deposits. Work from the top of the wall down so contaminated wash water flows to the lowest point for collection. In some cases, you may need a degreasing agent or a cleaning solution compatible with both the bund’s lining material and the chemicals stored nearby. Avoid anything that could damage coatings, sealants, or concrete surfaces.
All wash water generated during cleaning needs the same hazardous waste consideration as the standing water you removed earlier. Collect it, test it if there’s any possibility of contamination, and dispose of it through appropriate channels. Keep records of what you collected, how much, what testing was done, and where it went. These records matter during inspections.
Inspect and Repair After Cleaning
A clean bund is your best opportunity to spot problems. Walk the entire interior and check for cracks in concrete walls or floors, deterioration of coatings or liners, gaps at joints or penetrations where pipes pass through the wall, and any signs of chemical attack on the bund material. Pay close attention to the junction between the wall and floor, which is the most common failure point.
Repair any damage before refilling or returning the bund to service. Cracks in concrete can be sealed with appropriate fillers. Damaged coatings should be stripped and reapplied. If the bund has a membrane liner, patch any holes or tears with compatible material. A bund with compromised integrity isn’t just a regulatory problem; it’s a containment system that will fail when you need it most.
How Often to Clean
The EPA’s SPCC rule, which governs oil storage facilities in the U.S., does not prescribe a specific cleaning frequency. Instead, it’s a performance-based regulation: your facility’s Professional Engineer sets the inspection and maintenance schedule based on good engineering practices and industry standards for your specific situation. This means frequency depends on your local climate, what you’re storing, and how quickly water and debris accumulate.
As a practical baseline, drain accumulated rainwater daily or after every significant rainfall event. This is the single most important routine maintenance task for any bund. A full cleaning and inspection, including wall scrubbing and residue removal, is commonly done quarterly or semi-annually, though high-risk sites or those in heavy rainfall areas may need monthly attention. Document every cleaning and inspection with dates, findings, and any repairs made. This documentation is what regulators will ask for, and it’s your evidence that the containment system was properly maintained if a spill ever occurs.