Overview
EN 12255-2:2026 is a European standard developed by CEN that defines the requirements for storm water management systems specifically within wastewater treatment plants. This standard does not address storm water management in sewer networks or collection systems, but focuses on handling, storing, and treating storm water that reaches the treatment plant itself. The document provides guidance for flow management, separation, storage, treatment, discharge, and return of storm water, helping operators and designers mitigate the impact of storm events on both treatment processes and the environment.
By setting out consistent requirements and recommended practices, EN 12255-2:2026 supports the design, operation, and maintenance of robust storm water management systems at municipal and industrial wastewater treatment plants, promoting safer, more effective handling of storm flows and protecting water quality.
Key Topics
- Scope of Application: Requirements for storm water management apply only within the boundaries of wastewater treatment plants - not to the sewer or conveyance systems.
- Flow Management Systems: Techniques for separating and controlling influent to ensure that treatment capacity is not overwhelmed during storms.
- Storm Tanks: Design and use of storm water storage tanks, including blind storm tanks (units without environmental overflow) and regular tanks, with guidance on sizing, sequencing, and operation.
- Return and Discharge: Procedures for returning stored storm water to treatment after flows subside, and for overflow discharge, including screening and solids removal.
- Tank Cleaning and Maintenance: Recommended cleaning systems and maintenance practices, scaled according to plant size and local requirements.
- Measurement and Control: Guidance on measuring flows, monitoring system status, and applying automation or manual control depending on plant capacity.
- Regulatory Alignment: Reference to related standards such as EN 752 and EN 16933 for integration with external sewer and stormwater systems.
Applications
EN 12255-2:2026 is essential for:
- Municipal and industrial wastewater treatment plants: Ensuring adequate storm water management is in place to handle sudden increases in influent without compromising treatment performance or causing environmental impact.
- Engineering and consulting firms: Providing a technical framework for the planning, design, and specification of storm water management solutions within treatment plant projects.
- Operators and maintenance teams: Supporting the consistent operation and upkeep of storm water tanks, flow control systems, and monitoring equipment.
- Regulatory compliance: Helping plants demonstrate alignment with best practices and national/international regulations for storm water overflows and environmental protection.
- Asset upgrades and retrofits: Guiding modernization and expansion of facilities to meet new storm water management requirements, particularly in response to climate change and increased frequency of extreme weather events.
By following EN 12255-2:2026, stakeholders can improve system resilience, minimize pollutant discharges during storm events, and extend the life and reliability of critical treatment infrastructure.
Related Standards
- EN 752: Drain and sewer systems outside buildings - Management of sewer networks and pumping installations.
- EN 12255-1: Wastewater treatment plants - General construction principles.
- EN 12255-3: Preliminary treatment processes at wastewater treatment plants.
- EN 12255-4: Primary treatment specifications.
- EN 16932: Drain and sewer systems - Pumping systems.
- EN 16933: Drain and sewer systems - Design.
- EN ISO 20456: Electromagnetic flowmeters for liquids.
- ISO 4359, ISO 12242: Flow measurement techniques for treatment plants.
For complete storm water management and compliance at wastewater treatment facilities, EN 12255-2:2026 should be used in conjunction with these and other relevant standards to ensure comprehensive coverage of design, operation, and environmental needs.
Keywords: storm water management, wastewater treatment plants, storm tanks, flow management, overflow control, EN 12255-2, European standard, stormwater systems, treatment plant design, CEN, water quality, environmental protection.