Bunded tank cleaning

Two separate areas

Primary tank and containment bund

Identify

Stored oil and the location of contamination

Scope of numeric rule

England business oil-storage guidance

Tank interior and secondary containment

The storage tank contains the product, while the bund provides secondary containment if product escapes. Deposits inside the tank and liquid or debris in the bund are therefore separate cleaning issues. An integrally bunded tank can also have different access limitations from an open concrete or masonry bund.

Under the cited GOV.UK business oil-storage guidance, a double-skinned or twin-walled tank does not by itself count as secondary containment for those rules. The installed design and its documentation establish what containment is provided.

Bund capacity requirements for oil storage

For a single fixed tank within the scope of England’s business oil-storage rules, secondary containment must hold at least 110% of the container capacity. A 2,500-litre container therefore requires at least 2,750 litres. This is a containment capacity rule, not an estimate of cleaning volume.

For multiple containers, the required capacity is the greater of 25% of their combined capacity or 110% of the largest container. Hydraulically linked containers have additional rules. The guidance has defined exceptions, and oil-storage requirements differ across the UK.

Contaminated liquid in the bund

Rainwater collected in a bund may contain oil or other contaminants. Its condition and the product history of the tank matter because contaminated bund water is not automatically suitable for discharge to surface-water drainage.

Cleaning does not repair a leaking tank or damaged containment. Defects and inspection findings remain separate maintenance issues even when contaminated liquid or sludge is removed at the same time.

Condition after cleaning

Tank capacity, bund arrangement, access and the location of contamination define the areas involved. Linked tanks and enclosed containment spaces can add further isolation and access considerations.

The condition required afterwards depends on the continued use of the tank and bund. Any entry into an enclosed tank or containment space requires a separate competent assessment.