Using low-maintenance permeable surfaces that decontaminate hydrocarbons in an impound lot

Overview 

In 2025, Rouen Métropole launched a site development initiative to support the relocation of an existing car impound facility from the Flaubert neighbourhood. This relocation was a strategic move to free up land for housing developments in a densely urbanized sector of Rouen, France. The public authority required a new, robust, and environmentally sustainable location for the storage of vehicles – both damaged and intact, while also managing hydrocarbon contamination in ground soil. The new facility had to avoid the pitfalls of traditional impervious paving, such as soil degradation, poor stormwater management, and high maintenance costs. 

The proposed solution centered on a dual-layer system using two of Solmax’s advanced geosynthetic products: BIDIM® Accorder and OSMORIA® Indigreen® aquatextile. Together, these products offered a permeable, high-load-bearing surface with embedded stormwater management capacity and long-term environmental protection. 

The planning process began with early consultations in December 2022 during the annual Mayor’s event in Paris. The design phase followed in September 2023, with tender submissions in May 2024 and final installation scheduled for February 2025. The new impound area, located on a rehabilitated industrial site, would accommodate hundreds of vehicles while complying with modern environmental and infrastructural standards. 

This project sits at the intersection of site development and water management, addressing stormwater infiltration and ground protection in a high-impact urban context. The successful implementation delivers value not only to Rouen Métropole but also to surrounding communities and the environment. 

Challenge  

The project involved converting a brownfield industrial site into a functional vehicle impound lot. Before any installation could begin, the site had to be cleared of existing industrial waste and remediated to ensure it was suitable for new infrastructure. Unlike traditional construction, the client sought a permeable surface that could withstand frequent vehicular traffic without degrading over time or allowing pollutants to seep into the subsoil. 

One of the key challenges was persuading public authorities of the benefits of using this type of solution over more traditional methods such as concrete. This was the first project of its kind undertaken by the public authority, and decision-makers were initially hesitant to approve a solution that diverged from conventional concrete or rigid slab options. The use of aquatextiles in this context was still relatively novel, especially for car pound applications. 

Moreover, technical challenges existed in the design and installation phases. The site needed to handle repeated point loads from parked vehicles while maintaining water permeability and resisting rut formation. This required careful product selection, proper layering, and compatibility with aggregate infill. 

Solmax provided the design team at Viatech with comprehensive technical documentation, performance data, and product certifications. This information enabled the engineers to advocate confidently for the combined system in their specifications and secure final approval from the public authority. 

What made the solution particularly innovative was the integration of two distinct solutions – OSMORIA Indigreen aquatextile for stormwater treatment and BIDIM Accorder for load distribution – into a single working system. This dual functionality enabled the impound lot to manage structural loads and decontamination of hydrocarbons, reducing the environmental footprint while improving performance longevity. 

Solution 

The chosen solution used 3,300 m² of OSMORIA Indigreen depolluting aquatextile and an equal area of BIDIM Accorder, installed in sequential layers. The aquatextile was placed directly on the ground to optimize the soil's fixation and biodegradation functions in order to treat rainwater as it infiltrates. OSMORIA Indigreen manages hydrocarbon and PAH pollution and allows decontaminated water to infiltrate the subsoil, aligning with environmental protection goals and reducing long-term site degradation. 

BIDIM Accorder was installed above the aquatextile, to provide a matrix for aggregate retention and load distribution. Its honeycomb-like structure was filled with 80 mm (approximately 3.15 inches) of clean, well-graded draining aggregate. Once filled, the entire surface was compacted to create a solid yet permeable platform capable of supporting static and dynamic loads associated with vehicle storage. 

This dual-layer configuration offered several advantages over traditional materials: 

• It eliminated the need for impermeable concrete, reducing surface runoff and pressure on local stormwater infrastructure. 

• It prevented ruts and surface deformation over time, thanks to the properties of BIDIM Accorder. 

• It contributed to long-term sustainability with a lifespan exceeding 50 years and low maintenance requirements. 

• It improved soil protection by preventing hydrocarbon contamination. 

Initially, the public authority considered concrete paving or rigid permeable slabs. However, Solmax’s proposed system outperformed these alternatives in both functional longevity and environmental compatibility. Key selection factors included the low total cost of ownership, reduced maintenance needs, and the added ecological benefit of promoting stormwater treatment at the source. 

This project also served as a demonstration of how OSMORIA Indigreen and BIDIM Accorder can be effectively paired for heavy-duty applications such as parking facilities or impound lots. As long as the correct gravel size is used for the infill, the solution remains scalable, adaptable, and durable. 

The installation process itself was completed faster than expected, exceeding client expectations for timeline adherence. The client was especially satisfied with the speed and simplicity of the system’s deployment, which helped minimize disruption and allowed for rapid commissioning of the new car park. 

In the end, three primary reasons stood out for why the client would recommend this solution: 

• Sustainability: The system prevents soil contamination, supports stormwater infiltration, and contributes to long-term ground health. 

• Cost-efficiency: With no need for ongoing maintenance and a long service life, the overall lifecycle cost is significantly lower than traditional alternatives. 

• Performance: The combination of OSMORIA Indigreen and BIDIM Accorder delivers a high-performance surface that resists rutting, supports high loads, and maintains its function over decades. 

The successful delivery of this project strengthens the case for using integrated geosynthetic systems in municipal site development and opens the door for future collaborations with both Viatech and Rouen Métropole. The innovative pairing of a depolluting aquatextile and structural support geosynthetics sets a precedent for environmentally responsible urban infrastructure projects across Europe.