Stormwater storage tanks: engineered for performance, compliance and long-term value

Stormwater management across the UK water sector is undergoing a notable transformation. Under AMP8 and increasing regulatory pressure, water companies are expected not only to reduce combined sewer overflow (CSO) discharges and improve environmental outcomes, but also to demonstrate that infrastructure is designed for long-term resilience. As a result, the industry is moving beyond a narrow focus on storage capacity toward solutions that are durable, maintainable and aligned with evolving compliance requirements.

Stormwater: a more complex reality

Stormwater is no longer considered simply rainwater; it is now recognised as a chemically complex runoff influenced by the environments it flows through. Research from organisations such as the Chartered Institution of Water and Environmental Management (CIWEM), the Environment Agency and National Highways highlight the diverse range of contaminants present in urban and highway runoff. These include hydrocarbons and fuel residues, heavy metals from brake and engine wear, polycyclic aromatic hydrocarbons (PAHs), tyre particles, road surface debris and microplastics.

If left unmanaged, these pollutants can accumulate in receiving waters and pose risks to aquatic ecosystems. Consequently, stormwater containment systems are increasingly designed with chemical exposure in mind, rather than focusing solely on hydraulic storage.

The importance of material selection

The composition of stormwater varies widely depending on land use, traffic density and environmental conditions. Even low concentrations of oils, fuels or solvents can affect the long-term performance of certain materials, particularly with prolonged exposure.

EPDM rubber has long been used in water containment due to its flexibility, weather resistance and durability. It remains suitable for many applications, especially where water quality is controlled. However, in environments where hydrocarbons are present, its performance can degrade over time. Repeated exposure may lead to swelling, softening, reduced tensile strength and gradual changes in mechanical properties. The extent of these effects depends on factors such as contaminant concentration, temperature and exposure duration.

In applications where chemical exposure is anticipated, alternative liner materials with enhanced resistance are often more appropriate.

Reinforced geomembranes: designed for demanding conditions

Reinforced geomembranes are widely used in containment systems where both durability and chemical resistance are essential. These engineered materials are designed to withstand a broad range of contaminants, with performance supported by manufacturer data. Their reinforced structure improves tensile and tear strength, while maintaining dimensional stability across varying temperatures. Consistent weldability also supports the formation of reliable, high-integrity seams.

Material selection should always be based on application-specific requirements and supported by relevant technical data and standards. For stormwater and wastewater applications where contaminant exposure is likely, Butek Tanks specifies reinforced geomembrane liners to achieve a balance of chemical resistance, mechanical durability and maintainability.

Liner systems for operational demands

Butek Tanks supplies Landflex™ ES as a standard liner option for stormwater and wastewater applications. Designed for environments where hydrocarbons and similar contaminants may be present, the company says it offers resistance to common pollutants while maintaining durability through its reinforced construction. It also provides dimensional stability across a range of operating temperatures.

For more demanding conditions, the company recommends its Landflex™ FT range, which provides a heavier-duty alternative. Engineered for higher mechanical stress and more intensive operational environments, it features factory-welded seams produced under controlled conditions and enhanced resistance to wear. The company says its robust construction makes it suitable for applications requiring increased durability, including those involving frequent cleaning or higher-duty use.

The selection of liner systems should be guided by operational requirements, expected loading conditions and maintenance strategies, supported by product-specific technical data.

Fabrication quality and assurance

The performance of geomembrane liners is closely linked to fabrication quality, particularly seam integrity. Since liners are formed from multiple welded panels, consistency in welding is essential to ensure system reliability.

Factory-controlled fabrication offers significant advantages, allowing welding processes to be carried out under consistent conditions with repeatable parameters. It also enables full traceability of materials and the application of documented quality assurance procedures. Testing methods such as vacuum box testing, spark testing and air-channel testing can be used to verify seam integrity before installation.

Materials may be specified in accordance with relevant standards, such as BS EN 13361, alongside project-specific design and installation requirements.

Modular steel tanks: practical advantages

Modular steel tanks with internal liners are increasingly used in stormwater storage due to their practical and operational benefits. Compared with traditional glass-fused-to-steel (GFS) or cast in-situ concrete structures, these systems can offer faster installation, reduced costs, reduced on-site complexity and manufacturing under controlled conditions. The design also allows improved access for inspection and maintenance.

A key advantage of modular lined systems is the separation of structural and containment functions. The steel structure provides strength, while the liner delivers an impermeable barrier. This separation enables liner repair or replacement without dismantling the tank structure, supporting efficient long-term asset management.

Protecting against mechanical damage

While chemical resistance is critical, mechanical protection remains equally important. Liner failures are most commonly caused by puncture, abrasion or localised stress. To mitigate these risks, liner systems are typically installed with protective measures such as geotextile cushioning layers beneath the liner and protective wall sheets, including HDPE panels. Careful step-by-step installation practices and inspections further reduce the likelihood of damage during construction.

Inspection and lifecycle management

Ongoing inspection and maintenance are essential to ensuring long-term performance. Good practice includes regular visual inspections, monitoring of liner condition and protective layers, and maintenance planning based on observed performance. Maintaining accurate inspection and maintenance records also supports compliance and asset reliability.

Butek Tanks provides guidance on inspection as well as liner replacement services, helping clients maintain performance throughout the asset lifecycle.

Supporting compliance and long-term performance

As regulatory expectations evolve, infrastructure providers are placing greater emphasis on demonstrable material compatibility, verified performance and controlled manufacturing processes. Traceability, documentation and predictable long-term behaviour are increasingly important in demonstrating compliance.

Modular steel tank systems incorporating reinforced geomembrane liners can support these objectives when properly specified, manufactured, installed and maintained.

Conclusion

Stormwater containment design is now shaped by both hydraulic demands and the need to manage chemically complex runoff. As a result, material selection, fabrication quality and lifecycle planning have become central to modern infrastructure design.

While traditional materials such as EPDM remain suitable in certain applications, environments with potential contaminant exposure benefit from liner systems designed for enhanced chemical resistance. By combining modular steel structures with reinforced geomembrane liners—and by adopting controlled fabrication and maintenance practices—stormwater storage systems can deliver reliable, long-term performance while meeting the evolving regulatory expectations of AMP8 and beyond.