A Practical Guide to:

BS EN 858-2:2003 Separator Systems for Light Liquids (e.g. Oil & Petrol)

Ensuring legal compliance and environmental protection for interceptor systems.

Overview

BS EN 858-2:2003 is the national and European standard providing detailed guidance on the specification, installation, operation, and maintenance of separator systems (also referred to as interceptors) used to treat light liquid pollutants, including oil and petrol.

Introduced across the EU in 2002 and adopted by the British Standards Institution (BSI) in 2003, this standard applies to sites where surface water run-off from impermeable areas - such as forecourts, vehicle washdown areas, and industrial yards - may become contaminated with hydrocarbons.

By following BS EN 858-2:2003, businesses can reduce pollution risk, meet legal expectations, and support good environmental stewardship.

Legal Context & Regulatory Obligations

UK law requires businesses to prevent pollution through proper management of oil storage and contaminated water. Several legal instruments reinforce the need for correctly specified and maintained separators, including:

 

  •  The Environmental Permitting (England and Wales) Regulations 2016
  •  The Pollution Prevention and Control (Scotland) Regulations 2012
  •  The Water Environment (Oil Storage) (Scotland) Regulations 2006
  •  The Control of Pollution (Oil Storage) (Amendment) Regulations (Northern Ireland) 2011
  •  The Pollution Prevention and Control Act 1999

These legal requirements are supported by BS EN 858-2:2003 and GPP 3 (Guidance for Pollution Prevention) to help site operators understand what is expected and how to demonstrate compliance.

✅ Key Point: Regulatory authorities will evaluate not just legal non-compliance but also whether best practices outlined in BS EN 858-2:2003 have been implemented in the event of a pollution incident.

Key Requirements of BS EN 858-2:2003

Routine Operation & Maintenance (Section 6)

All separator systems in use must be serviced at least every six months by qualified personnel. The following checks must be completed:

  •  Sludge Trap: Measure sludge volume and remove if approaching 50% capacity
  •  Separator Unit: Measure the layer of light liquids (e.g. oil thickness); Inspect the automatic closure device; Assess coalescing devices for permeability; Test the warning alarm system
  •  Sampling Shaft: Clean the drain channel to ensure functionality

Five-Year Integrity Inspections

Regardless of Audit frequency, separators must be emptied and fully inspected at least once every five years, covering:

  •  Structural condition and tightness
  •  State of internal coatings and components
  •  Adjustment and function of closure and warning devices
  •  Functionality of any electrical installations

In rare cases where personnel need to enter the unit, it must be completely drained and properly ventilated, with all relevant health and safety procedures followed.

Documentation & Record-Keeping

Maintaining up-to-date service records is a mandatory requirement of BS EN 858-2:2003. Logs must:

  •  Be accessible upon request by regulators
  •  Detail all maintenance activities, including dates, inspections, and remedial work
  •  Include notes on unusual events such as accidents, system failures, or repairs

Why Compliance is Critical

Environmental & Legal Risks 

Non-compliance can result in:

  •  Environmental pollution from oil run-off or slow leaks
  •  Prosecution and significant fines, especially where negligence is found
  •  Reputational damage from being associated with pollution events

Business Continuity Impacts 

Pollution incidents often lead to:

  •  Operational downtime for emergency clean-ups
  •  Long-term site investigations and audits
  •  Higher future costs for remediation and insurance

✋ A poorly maintained or incorrectly installed separator is a significant business risk.

Best Practices for Implementation

To remain compliant with BS EN 858-2:2003:

  1. Install correctly: Ensure systems are correctly specified and installed based on site activity, catchment area, and discharge destination.
  2. Maintain regularly: Audit separators every 6 months, with additional inspections after heavy use or adverse weather
  3. Inspect every 5 years: Perform a full integrity test at least once every five years.
  4. Fit and monitor warning devices: Ensure alarms are operational and tested regularly.
  5. Keep records accessible: Maintain organised, complete, and accessible logs of all inspections, servicing, and incidents.

How GPT Environmental Can Support Your Compliance

  •  Scheduled servicing and maintenance (in line with the 6-monthly requirement)
  •  Separator alarm installation and testing
  •  Five-yearly integrity inspections and reporting
  •  Comprehensive compliance documentation and record management
  •  Remedial works and emergency support where needed

Your next steps... 

  •  Confirm your current separator system is correctly sized and installed
  •  Schedule your next 6-monthly service
  •  Conduct a compliance review of your records
  •  Plan for your next 5-year integrity test
  •  Speak to a professional for guidance and ongoing support