For any industrial or commercial site in the UK, drainage risk assessments are not merely best practice — they are a regulatory expectation. The Environment Agency (EA) and local authorities actively enforce pollution prevention standards, and a poorly managed drainage system can result in prosecution under the Environmental Permitting (England and Wales) Regulations 2016 and the Water Resources Act 1991. This guide walks you through how to conduct a site drainage risk assessment that satisfies regulatory requirements and protects your site from costly incidents.
Why Drainage Risk Assessments Matter
Every site that handles chemicals, fuels, oils, or other polluting substances has the potential to cause a water pollution incident. Rainwater runoff, firefighting water, and accidental spills can all reach surface water or groundwater via site drainage if adequate controls are not in place. The EA takes a zero-tolerance approach to pollution events — even a one-off incident can trigger enforcement action, civil claims, and significant reputational damage.
Step-by-Step: Conducting Your Drainage Risk Assessment
Step 1: Map Your Drainage System
Begin by producing or obtaining an accurate drainage plan showing all surface water drains, foul drains, interceptors, and outfall points. Identify which drains connect to surface water (rivers, streams, soakaways) and which connect to the foul sewer. This distinction is critical — surface water drains have no treatment before reaching a watercourse.
Step 2: Identify Pollution Hazards
Walk the site and catalogue all potential pollution sources: chemical storage areas, vehicle wash-down zones, fuel bunkering points, waste skips, and loading bays. Note the substances involved and their volumes. Use your COSHH assessments and site plans as reference.
Step 3: Assess Likelihood and Consequence
For each hazard, assess the likelihood of a release reaching the drainage system and the potential consequence to the receiving watercourse. A risk matrix approach is widely used and accepted by regulators.
Step 4: Identify and Implement Controls
Controls should follow the hierarchy from elimination through to monitoring. Common site drainage controls include:
- Drain guards and drain covers to prevent spill ingress
- Oil/water interceptors or petrol interceptors on surface water outfalls
- Bunding around chemical and fuel storage areas
- Spill kits positioned at key risk points
- Interceptor bypass alarms for high-risk outfalls
- Secondary containment for IBC and drum storage areas
Drainage Risk Assessment Summary Table
| Assessment Step | Key Output | Regulatory Relevance |
|---|---|---|
| Drainage mapping | Accurate site drainage plan | Required for EA permit applications |
| Hazard identification | Pollution source register | Supports COSHH and DSEAR assessments |
| Risk rating | Risk matrix/register | Demonstrates due diligence to EA |
| Control measures | Drain protection equipment list | Satisfies PPG (Pollution Prevention Guidelines) |
| Review and monitoring | Inspection schedule | Required for permitted sites |
EA Pollution Prevention Guidelines (PPGs)
The EA publishes a suite of Pollution Prevention Guidelines covering specific activities — from vehicle washing to chemical storage. While many PPGs have been withdrawn and replaced with the consolidated Prevention of water pollution from industrial sites guidance, the underlying principles remain enforceable. Your drainage risk assessment should demonstrate alignment with this guidance.
Emergency Drain Protection
No risk assessment is complete without emergency response provisions. Keep drain seals and inflatable drain stoppers on site to isolate drainage in the event of a spill. Our range of drain protection products includes fast-deploy covers, drain socks, and chemical-resistant plugs suitable for all standard UK gully and channel sizes.
Need expert advice? Call 01744 520 110