Retail parks, outlet centres, mixed retail and leisure destinations, roadside developments and service stations play an important role in supporting local economies, employment and regional growth. However, many large commercial developments are located on sites where connection to the public sewer network is unavailable, impractical or unable to accommodate future development plans.
For developers, site owners, architects, planning consultants, consulting engineers, facilities managers and contractors, wastewater treatment infrastructure can therefore become a critical component of project success.
Retail formats continue to evolve across the UK, with retail parks showing strong resilience compared with some traditional retail locations. The British Retail Consortium reported retail park footfall growth of 2.0% year-on-year in February 2025, outperforming both high streets and shopping centres. Meanwhile, CBRE reported that investment in UK retail warehouse assets increased by 32% year-on-year during the first half of 2025.
At the same time, mixed-use developments continue to form an important part of the UK’s planning strategy, helping to support regeneration, employment opportunities and more efficient use of land.
As retail and mixed-use developments continue to evolve, wastewater treatment infrastructure must support long-term operational performance, environmental compliance and future growth.
Commercial developments commonly requiring off-mains drainage solutions
For larger retail and mixed-use developments, wastewater treatment requirements can extend far beyond those associated with small commercial premises. Sites serving more than 500 population equivalent (PE) often require a more strategic approach to wastewater treatment design, particularly where future expansion is planned.
These developments can include:
- Retail parks and outlet shopping centres
- Mixed retail and leisure developments
- Roadside and motorway service stations
- Visitor attractions with retail and hospitality facilities
- Food and beverage destinations
- Business parks incorporating customer facilities
- Commercial mixed-use schemes
- Phased commercial developments
These developments often experience significant fluctuations in visitor numbers, seasonal trading patterns and phased expansion, creating unique wastewater treatment challenges that must be considered during design and specification.
Why wastewater infrastructure should be considered early
Wastewater treatment infrastructure can represent a relatively small proportion of a commercial development’s overall capital expenditure, yet it can have a significant influence on planning approval, environmental compliance, future expansion and long-term operational costs.
Across the UK, regulators generally expect connection to the public sewer network to be considered before a private treatment solution is proposed. Where this is not feasible, developers must demonstrate that wastewater can be treated and discharged without causing environmental harm.
Early consideration of wastewater infrastructure enables project teams to assess:
- Population equivalent (PE) requirements
- Environmental constraints
- Available site footprint
- Ground conditions
- Proposed discharge locations
- Future development phases
- Whole-life operating costs
Addressing these factors early can help reduce planning delays, avoid redesign costs and support smoother project delivery.
Focusing on long-term value rather than lowest capital cost
While wastewater treatment infrastructure may represent only a small fraction of overall project costs, it will often remain operational for decades.
As a result, many developers, consulting engineers and facilities managers increasingly focus on long-term value rather than simply the lowest upfront capital cost.
Key considerations include:
- Whole-life operating costs
- Asset lifespan
- Maintenance requirements
- Operational reliability
- Future expansion capability
- Environmental compliance
- Business continuity
The most appropriate solution is often the one that delivers the best long-term outcome for the development and its users, while supporting future operational and environmental requirements.
For retail parks, outlet centres and mixed-use developments, wastewater treatment infrastructure supports critical site operations including public facilities, restaurants, cafés and tenant operations. Reliability and maintainability are therefore important considerations during specification.
Unplanned disruption to wastewater infrastructure can affect customer facilities, food and beverage operations, tenant activities and compliance obligations, making operational resilience an important consideration during system selection.
Common specification risks on large commercial developments
When seeking to reduce project costs, wastewater infrastructure can sometimes be viewed as a standard utility rather than a strategic asset.
Common specification risks include:
- Under sizing treatment capacity based on current occupancy only
- Failing to accommodate future development phases
- Not accounting for seasonal fluctuations in visitor numbers
- Selecting systems with high maintenance requirements
- Limited access for future servicing and upgrades
- Failing to consider environmentally sensitive locations
- Insufficient flexibility to accommodate future discharge requirements
For large commercial developments, addressing these risks during design is often significantly more cost-effective than attempting to rectify them after construction.
As environmental requirements continue to evolve, developers should also consider whether future discharge standards may become more stringent during the lifespan of the asset. Selecting solutions that can be upgraded, expanded or enhanced through additional treatment processes can help reduce future compliance risks.
New treatment plant or upgrading existing assets?
Many retail and mixed-use developments occupy sites with existing wastewater infrastructure that may no longer meet operational requirements, occupancy levels or environmental expectations. Complete replacement is not always necessary.
Depending on the condition of the existing asset, treatment performance can often be improved through:
- Refurbishing existing treatment assets or retrofitting new treatment technologies
- Repurposing existing onsite tanks, vessels and structures for new treatment processes
- Delivering tertiary treatment upgrades, including phosphorus reduction and enhanced effluent polishing technologies, to meet evolving environmental and discharge requirements
- Installing new modular off-site-built wastewater treatment plants where replacement or additional treatment capacity is required
This approach can help reduce capital expenditure, minimise disruption and extend the life of existing infrastructure while supporting future operational requirements.
For many projects, the most cost-effective solution may be improving existing assets rather than replacing them entirely.
Overcoming challenging commercial developments
Large retail and mixed-use developments often face site constraints such as restricted access, existing infrastructure, limited space, high groundwater levels, flood risk, operational requirements, discharge conditions and environmentally sensitive locations.
Standard treatment plants are not always suited to these challenges or to future expansion plans. Marlowe Environmental Services combines standard, customised and bespoke modular solutions with wastewater engineering expertise to deliver practical, site-specific systems.
Benefits can include:
- Faster installation and lower construction risk
- Minimal disruption to live operations
- Flexible phased expansion
- Reduced footprint requirements
- Improved access for constrained sites
- Greater design flexibility
- Lower maintenance needs
- Below-ground options to minimise visual impact
Modular off-site build solutions also help improve programme certainty while providing flexibility for future development phases.
Why engineering-led wastewater solutions deliver better outcomes
Large retail and mixed-use developments often require more than a standard treatment plant. Marlowe Environmental Services assesses each site individually to identify the most practical, compliant and cost-effective solution, whether that involves refurbishing existing assets, retrofitting new technologies into existing systems, repurposing onsite structures, delivering tertiary treatment upgrades, installing new modular treatment systems, or supporting refurbishment works with temporary mobile treatment hire.
With over 35 years of wastewater treatment expertise, we combine technical knowledge with a practical understanding of site operations to deliver solutions tailored to each development’s specific requirements.
By supporting projects from design and installation through to servicing and future upgrades, we help reduce project complexity, minimise risk and provide flexibility for future growth. Our modular, low-maintenance systems can be adapted for phased developments, seasonal fluctuations and long-term expansion requirements.
Whether upgrading existing infrastructure or delivering a new treatment system, the focus is always on achieving a practical, compliant and future-ready wastewater solution.
Need advice on off-mains drainage for a retail development?
Whether you’re planning a new site, expanding an existing development or assessing options for a sensitive location, Marlowe Environmental Services can help identify the most appropriate wastewater treatment solution for your site, growth plans and environmental requirements.