Multifunctional Assessment of Porous Pavements with Reservoir Structures: In situ and Modeling using Extreme Environmental Externalities

Context
France loses 65,000 hectares of land each year due to urbanization. This urbanization expansion significantly exacerbates stormwater runoff and contributes to the degradation of urban water quality. By promoting soil sealing, urbanization increases runoff volume. At the same time, the increasing frequency and intensity of weather events (flood, heat waves, …) increase the vulnerability of territories. Local adaptation strategies are essential to preserve water resources. In Grand-Est region, 46,200 km for municipal roads represents a high potential for soil de-sealing.
Pervious roads incorporating storage structure offer a promising approach to address this challenge by combining mechanical functions required for vehicle travel and traffic support with hydraulic functions, such as stormwater storage before infiltration in the underlying soil layers. These functions are interconnected with geochemical processes (desorption) biological processes (assimilation, biodegradation) that can influence the fate and mobility of contaminants throughout the structure and even into the underlying soil. Understanding these mechanisms is essential to assess the long-term effectiveness of the solution while managing environmental impacts.

Permeable pavement and ecosystemic services
Permeable pavements are multifunctional technologies that provide a range of ecosystemic services whose performance depends on the local geoclimatic context, the use of the structure, the properties of the constituent
materials, and the characteristics and dynamics of the surrounding ecosystem. In this context, there is a growing need to develop appropriate metrics able to assess the different services provided by permeable pavements, including hydrological regulation, water quality regulation, supporting services, and thermal regulation. A comprehensive understanding of the hydraulic, thermal, acoustic, and mechanical functions associated with these services, as well as the factors controlling their evolution over the long term, remain major scientific challenges.
Processes such as clogging and freeze–thaw cycles are only two examples of the mechanisms that may progressively alter pavement performance. Indeed, a permeable pavement should not be considered as an isolated
technical structure, but rather as a component of a broader urban metasystem. Its long-term performance depends not only on its initial design and material properties, but also on its management over time and its integration within the surrounding urban environment.

Permeable pavements and road pollutants
Despite the extensive research conducted over the past three decades on the retention of conventional road
pollutants—such as suspended solids (SS), heavy metals, hydrocarbons, and de-icing salts (NaCl)—by porous
asphalt reservoir pavements, several scientific and technical challenges remain. For example, the potential risk of
chronic contamination of receiving environments, including soils. Recent literature (Lokesh et al., 2026) reports
overall removal efficiency for road-related micropollutants ranging from approximately 40 to 90% in permeable
pavements, with these findings being supported by several other studies (Jayakaran et al., 2019; Holzer & Poor,
2024).
However, removal performance varies substantially depending on the physicochemical properties of the
contaminants and their partitioning between particulate and dissolved phases. Elements strongly associated with
particles, such as Pb, Al, and Fe, tend to be more effectively retained than more mobile species predominantly
occurring in the aqueous phase, including Cu, Zn, and Mn (Zhang et al., 2018). Similarly, polycyclic aromatic
hydrocarbons (PAHs), which are widely detected in road runoff, are generally effectively retained within
permeable pavement structures. Nevertheless, these removal efficiency depends on several interacting factors,
including pavement configuration and loading conditions, the reactivity of the constituent materials, contaminant
physicochemical properties, and hydrological conditions. This highlights the need for a better understanding of the
mechanisms governing contaminant transport, retention, and fate within these structures. Such an understanding
must also account for the progressive evolution of these mechanisms during pavement ageing and clogging in order
to assess the long-term sustainability and durability of pollutant removal performance.
Beyond the priority pollutants traditionally monitored in road runoff, increasing attention is now being given to
emerging pollutants of concern (Valeo et al., 2026). This term covers a wide spectrum of substances detected in
road runoff (Maurer et al., 2023). Among them, microplastics are of particular concern, including tire and road
wear particles (TRWP) generated by tire and pavement abrasion, as well as tire-derived additives such as
plasticizers and 6PPD and its transformation product, 6PPD-quinone. Recent studies suggest that permeable
pavements may provide an effective means of limiting the transfer of these contaminants into receiving
environments (Mitchell & Jayakaran, 2024).
Another major group of emerging contaminants consists of per- and polyfluoroalkyl substances (PFAS). Their
inclusion in the assessment of permeable pavement systems is particularly important due to their high persistence
and their mobility in the aqueous phase, which may allow them to migrate through the depth of the filter media and
potentially reach the underlying soil (Beryani et al., 2024).
Reactive transport modelling of micropollutants
Most studies investigating the fate of micropollutants in reservoir pavements has relied on laboratory experiments
or field monitoring. These studies have generally aimed to characterize contaminant removal within pavement
systems using material and layer characteristics, hydrological operating conditions, and pollutant loading. In
contrast, mechanistic modelling approaches for reactive micropollutant transport, through the different pavement
layers and into the underlying soil remain very limited. The diversity of contaminants represents one of the main
challenges for developing such modelling approaches. An additional difficulty lies in describing their fate, which
results in a combination between hydrodynamics, material properties and reactivity, sorption/desorption processes,
physicochemical and potentially microbiologically transformation occurring within the different pavement
compartments. A major scientific challenge is therefore to develop and validate a multi-contaminant reactive
transport model capable of coupling the hydrological functioning of permeable pavements with the interactions
between micropollutants and the road materials, particularly within the reservoir structure.

3
Thesis objectives
The thesis aims to:
1) conduct a literature review of rules and state of the art regarding reservoir-structured pavements: typology,
design, operation, and services associated
2) select functions which will provide a better understanding of the interaction between water, heat, and
pollution flows, etc.
3) Study the influence of external and internal factors—such as the properties of porous and impermeable
asphalt mixtures—on the generation of particulate pollution resulting from tire wear and the road
pavements themselves.
4) Develop a numerical model simulating hydrological and physicochemical processes and their impact on the
regulatory functions of porous pavements with a reservoir structure, as well as the onset of clogging. A
focus will be done on the robustness of pavements in the face of extreme external events.
Thesis structure
The thesis consists of an experimental component and a numerical component:
• The experimental component will be based on:
- A field study (rue Neuve, Strasbourg) aims to monitor the hydrological behavior and contaminant fate
within the two road sections with contrasting operating characteristic (porous media vs. impervious
media leading to reservoir structure)
- A laboratory-based approach using columns (Cerema platform, Nancy agency), replicating road
surfaces and some hydrological operating conditions or climatic, while ensuring control over the
upstream pollutant load (type and micropollutants concentration)
• the numerical component will be based on contaminant transport, both a field scale and in experimental
columns. It will aim to produce a mechanistic multi contaminant model designed to predict retention or
transport of contaminant depending on the layers considered. Software such as HYDRUS 1D, designed to
model flow in porous media, may be used and coupled with PHREEQC to better understand the reactive
transport of micropollutants.

Host Institutions
The thesis will take place:
• At ICube lab (UMR 7357) specifically in Mecaflu team. Icube is internationally known for conducting
transdisciplinary research on topics related to engineering for health, environment and sustainable
development. Mecaflu team is recognized for its expertise in understanding and modeling fluid flow,
pollutant transport and environmental processes.
• At Cerema (Centre d'études et d'expertise sur les risques, l'environnement, la mobilité et l'aménagement),
more precisely at Team team (Transferts et interactions liés à l'eau en milieu construit). Team works aims
to better understand the impact of built environments (cities and transportation infrastructure) on water
discharges, pollutant discharges, rising local temperature.

- Master degree or Engineering Degree in Environmental Science/Water science
• Experience related to environmental studies
• Programming and numerical modelling skills
• Interest in fieldwork
• Teamwork skills and ability to work independently
• Excellent English and/or French language skills (written and spoken)