Pollution prevention and spill containment stop contaminants reaching drains and watercourses at source, rather than treating them after the fact. The governing principle is a hierarchy: prevent a release first, contain what escapes, and treat only as a last resort. Get drainage segregation, bunding and spill response right and most pollution incidents never happen.
Why prevent pollution at source instead of treating it?
Once a spill reaches a surface-water drain it is usually seconds from an open watercourse, and dilution makes recovery impractical — a few litres of oil can sheen a large stretch of river. Source control is therefore ordered as a strict hierarchy:
Prevent — eliminate or substitute the hazard, reduce inventory, use closed transfer.
Contain — bunds, sumps, interceptors and shut-off valves keep an escape on site.
Treat — only what cannot be prevented or contained is treated end-of-pipe.
Effort and cost should be weighted heavily toward the first two tiers.
Prevention is also the cheaper strategy over an asset life: a bund and a drainage plan cost far less than the remediation, clean-up charges and prosecution that follow a pollution event. This article covers prevention and containment at source. Setting the numeric limits that treated effluent must meet is dealt with separately in our guide to effluent discharge standards in the UK, and consent to discharge to the public sewer in our guide to trade effluent consent.
How should site drainage be segregated?
Most industrial sites run two independent drainage systems, and confusing them is a leading cause of pollution:
- Foul drainage carries process effluent, wash-water and sanitary flow to the public sewer or an on-site treatment plant, under a trade effluent consent.
- Surface-water drainage carries clean rainwater from roofs and yards, usually discharging untreated and directly to a soakaway, ditch or watercourse.
A wrong connection — a process drain or a contaminated yard gully plumbed into the surface-water system — sends pollutants straight to the environment with no treatment. Every site should hold an up-to-date drainage plan with foul and surface-water runs colour-coded (the long-standing convention is red for foul and blue for surface water), and manhole covers marked to match. Where a yard drains to surface water, protect it with a penstock or shut-off valve and an oil/silt interceptor so a spill can be isolated before it leaves site. Verify actual connections with a dye or CCTV survey — drawings are frequently wrong.
What is the 110% rule for secondary containment (bunding)?
Secondary containment (bunding) is an impermeable barrier around a tank or drum store that catches leaks, overfills and firewater. The sizing rules are well established:
For a single tank: Vbund ≥ 1.10 × Vtank.
For multiple tanks in one bund: Vbund ≥ the greater of 110% of the largest tank or 25% of the aggregate stored volume.
The base and walls must be impermeable and resistant to the stored liquid; there must be no drain or outlet through the bund wall.
For oil stored above ground in England, the Oil Storage Regulations 2001 (The Control of Pollution (Oil Storage) (England) Regulations 2001) apply to most commercial, industrial and institutional stores above 200 litres, and require a bund of at least 110% of the container (or 25% of aggregate for multiple containers). Fill points, draw-off, valves, sight gauges and vent pipes must all sit within the bund so a drip or a burst hose is caught. At the time of writing the detailed thresholds differ across England, Scotland, Wales and Northern Ireland — always verify the current rules for your nation on GOV.UK or with the relevant regulator (Environment Agency, SEPA, Natural Resources Wales, or NIEA).
Worked example: sizing a bund
Size the secondary containment for a store holding three chemical tanks in a single bund: one of 25 m³ and two of 15 m³ each.
- Rule A — largest vessel: 1.10 × 25 = 27.5 m³.
- Rule B — aggregate: total stored = 25 + 15 + 15 = 55 m³; 25% × 55 = 13.75 m³.
- Governing capacity: take the greater of the two → 27.5 m³.
If the bund footprint is a rectangle 6 m × 5 m (30 m² plan area), the minimum wall height to hold 27.5 m³ is 27.5 / 30 = 0.92 m — before allowing for the volume the tanks themselves displace and freeboard for rainfall and firewater. In practice you would design the walls to roughly 1.0–1.1 m and confirm the net free volume after subtracting the tank plinths. Always carry the calculation to the net containable volume, not the gross box.
What is Guidance for Pollution Prevention (GPP)?
The authoritative UK best-practice reference is the Guidance for Pollution Prevention (GPP) series, published jointly by the environmental regulators via NetRegs. GPP replaced the former Pollution Prevention Guidelines (PPGs), which were withdrawn in England — so any specification or method statement still citing a "PPG" number is out of date and should be updated to the equivalent GPP. Key documents include:
| Reference | Subject |
|---|---|
| GPP 1 | Understanding your environmental responsibilities |
| GPP 2 | Above-ground oil storage tanks |
| GPP 5 | Works and maintenance near water |
| GPP 8 | Safe storage and disposal of used oils |
| GPP 21 | Pollution incident response planning |
| GPP 22 | Dealing with spills |
Treat GPP as the go-to source for containment and drainage detail. The series is periodically revised and some documents are region-specific, so confirm the current version and its applicability to your nation before relying on it. If you need help translating GPP into a site design, our team can support a site pollution-prevention and compliance review.
What does a good spill response system look like?
Even a well-run site needs a tested response for the escape that does happen. The essentials:
- Spill kits — absorbents, booms and pads sized to the largest credible spill, stationed where releases are likely (transfer points, stores, loading bays) and inspected/restocked on a schedule.
- Drain protection — drain mats/covers and inflatable drain plugs to seal gullies fast, plus the penstock valves noted above.
- Trained responders — staff who know the drainage plan, where kits are, and the stop-the-source-then-contain sequence.
- Notification — if pollution reaches or threatens a watercourse or groundwater, report it without delay to the Environment Agency incident hotline on 0800 80 70 60 (in England; equivalent numbers apply for SEPA, NRW and NIEA).
- Remediation and review — recover and dispose of contaminated material as controlled waste, then investigate root cause and close the gap.
Absorbents and contaminated soil become hazardous or controlled waste, so plan disposal routes in advance rather than during the incident.
What is a Pollution Incident Response Plan (PIRP) and the legal duty?
A Pollution Incident Response Plan (PIRP) is the written, site-specific document tying the above together: it maps drainage and receptors, lists inventories and their containment, sets the response actions and roles, and holds emergency contacts. GPP 21 sets out what it should contain. A PIRP is a permit condition for many regulated activities and simply good practice for the rest.
The legal backdrop makes prevention non-optional. Under the Environmental Permitting (England and Wales) Regulations 2016 it is an offence to cause or knowingly permit a water discharge or groundwater activity without, or in breach of, a permit — a strict "cause" limb means you can be liable without intent or negligence. The Environmental Damage (Prevention and Remediation) Regulations 2015 add a "polluter pays" duty to prevent imminent damage and to remediate environmental damage to water, land and protected species. Separately, the waste duty of care requires you to store, describe and transfer waste (including contaminated absorbents) responsibly. This is a summary at the time of writing, not legal advice — verify the current legislation and regulator guidance on GOV.UK for your circumstances and nation.
How to build a site pollution-prevention plan
- Map drainage and receptors. Produce or verify a colour-coded drainage plan (foul vs surface water) with a dye/CCTV survey, and identify nearby watercourses, drains and groundwater at risk.
- Inventory the hazards. List all liquids stored and handled with volumes and locations, and rank each by likelihood and consequence of a release.
- Provide containment. Bund tanks and stores to 110% of the largest vessel (or 25% of aggregate), fit interceptors and penstock/shut-off valves on surface-water routes, and confirm impermeable bases.
- Equip and train for spills. Site spill kits and drain protection sized to the largest credible spill, and train staff in the stop-source, contain, notify sequence.
- Write and test the PIRP. Document the plan (per GPP 21) with contacts including the incident hotline, then run a drill and correct any gaps.
- Review and maintain. Inspect bunds, interceptors and kits on a schedule, and update the plan after any change, incident or near-miss.
Frequently asked questions
What is the difference between primary and secondary containment?
Primary containment is the vessel itself — the tank, drum or IBC holding the liquid. Secondary containment is the independent barrier around it, typically a bund, that catches leaks, overfills and firewater if the primary vessel fails. Secondary containment must be impermeable, have no drain through the wall, and hold at least 110% of the largest vessel.
How big does a bund need to be?
For a single vessel a bund must hold at least 110% of that vessel's volume. Where several vessels share one bund, it must hold the greater of 110% of the largest vessel or 25% of the total aggregate stored. Allow additional freeboard for rainfall and firewater, and design to the net volume after tanks and plinths are subtracted.
Do the oil storage regulations apply to my site?
In England the Oil Storage Regulations 2001 apply to most commercial, industrial and institutional above-ground oil stores over 200 litres, requiring secondary containment of 110% (or 25% of aggregate). Thresholds and scope differ across the UK nations and there are exemptions, so verify the current rules on GOV.UK or with your regulator before relying on this.
What should I do first when a spill happens?
Stop the source if it is safe to do so, then contain the spread — deploy drain covers or plugs and absorbent booms to keep it out of gullies and watercourses. Only then clean up. If pollution reaches or threatens water, call the Environment Agency incident hotline on 0800 80 70 60 (or your nation's equivalent) without delay.
What replaced the Pollution Prevention Guidelines (PPGs)?
The Guidance for Pollution Prevention (GPP) series replaced the older PPGs, which were withdrawn in England. GPP is now the go-to best-practice reference for drainage, storage, bunding and incident planning. If a document still cites a PPG number, update it to the equivalent GPP and check you are using the current version for your nation.
Is it an offence to cause water pollution even by accident?
Yes. Under the Environmental Permitting Regulations it is an offence to cause or knowingly permit an unpermitted water discharge. The "cause" limb is effectively strict liability, so an operator can be prosecuted for an accidental release without proof of intent or negligence — which is exactly why containment and a response plan matter. This is general information, not legal advice.