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Polluted site: can we build ? 

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15/10/2024

In our day and age, managing industrial liabilities is a key issue when it comes to real estate development in France. Besides their potential role in containing urban sprawl, contaminated brownfields are receiving considerable attention for their often strategic locations and urban connections.

However, despite the attraction, there’s still the thorny issue of pollutants and their impact on:

  • the environment
  • the project’s budget

Besides the financial aspects, managing a contaminated site requires knowledge of geology, chemistry and geochemistry, hydrogeology, health, risks, construction work, etc. The behaviour of pollutants in the various soil strata, as well as underground water and gases, creates a complex equation that calls into question conventional interpretations and mitigation solutions. Each polluted site is unique – and so is its management.


Understanding polluted sites

Afin de connaître l’ampleur et la nature de la contamination, il est nécessaire de réaliser une étude historique, investiguant l’utilisation antérieure du lieu. Les terrains, ayant préalablement accueilli des activités industrielles intensives ou des infrastructures telles que des stations-service ou des zones de stockage de déchets, présentent souvent une charge polluante élevée. L’enquête historique s’avère essentielle pour tracer les origines de la contamination. La gestion d’un site pollué requiert la mise en place d’une stratégie de caractérisation sur la base d’une série d’études de données historiques (origine du site, cession/vente, modification des process…), de données de la qualité des sols, des eaux souterraines, des gaz du sol, des interactions entre les polluants, leur milieu et l’environnement, de données de dimensionnement des travaux à mettre en œuvre pour la réhabilitation du site et enfin des travaux. Toutes ces étapes sont aujourd’hui normées et font appel à une règlementation et une méthodologie sur la gestion des sites et sols pollués parfaitement maitrisées par les acteurs des Sites et Sols Pollués en France (SSP).

Understanding a polluted site therefore requires a multi-disciplinary set of skills and stakeholders, as well as investors willing to take up the twofold challenge of:

  • reducing these sites’ impact on the environment
  • limiting the transformation of natural, agricultural and forest land for construction purposes

These benefits are what makes brownfield sites so attractive on the commercial property market today.



The challenges of decontamination in a highly regulated sector

Building on polluted brownfields requires a rigorous process when preparing bids and applying for planning permission. The data on these sites can easily be called into question. GSE therefore establishes clear phases and milestones for communication on each project. During the sales phase, our in-house expert advice on polluted sites helps to reassure the various stakeholders regarding the levels of risk (planning, budgets, discovery, etc.) and the technical solutions suited to each issue. The aim is to implement virtuous projects while guaranteeing the highest levels of safety, pragmatic management and cost effectiveness.

Meanwhile, regulations and standardised methodologies for contaminated sites guarantee the quality of the advice and work provided by specialised contractors and a competent administration

France’s Sites et Sols Pollués methodology published on 9 April 2017 brings together all the best practices and willing stakeholders to respond to the shortage of land and contain urban sprawl. Today, regulations make it possible to qualify all of the environmental issues related to a site’s liabilities: historical study, soil and groundwater diagnosis, implementation of a pollution mitigation plan, risks associated with residual pollution, works design plan and works execution. These stages are codified, making it easy to understand the operations carried out, their relevance to each project and the associated guarantees.

Owners and developers are required to comply with these standards, which include mandatory protocols for diagnosis, clean-up and post-rehabilitation environmental monitoring. This combination of technical expertise and regulatory compliance is essential to ensure the environmental rehabilitation and safe use of polluted sites.

Diagnosis, rehabilitation and adaptation to the environment

Providing an accurate picture of the impacts of human activity on the environment or on an industrial site requires sampling, surveys, modelling and reporting. And beyond the metrics, thinking about the site’s future use is essential in rehabilitation projects. In addition to financial considerations, the long-term vision is key to the planning of rehabilitation efforts. Simply put, the level of remediation of a site will not be the same for a future industrial facility and a future daycare centre. The rehabilitation effort will depend on the intended future use, the amenities to be offered and the target audience. This will enable local users to adopt the revitalised site. Through thoughtful redevelopment, we avoid the risk of seeing the plot turn once again to wasteland – in another 5 or 10 years’ time – and give it a place in the future urban landscape.



What about technology in this grand scheme of things?

Today, in mature markets, companies specialising in depollution have a range of technical solutions to meet the demands of planning, cost and environmental & human risks.

These techniques fall into 3 categories:

Off-site techniques: these solutions handle depollution “off-site”, by excavating materials and removing them. This may include:

Off-site techniques : these solutions handle depollution “off-site”, by excavating materials and removing them. This may include :

  • Grounb excavations
  • Off-site washing

On-site techniques : these solutions process matérials on site once the polluted soil has been removed. There is an initial management phase, followed by impact treatment. For exemple (depending on the nature of the contamination) :

  • Ground excavation and particle size sorting
  • Ground excavation and mounding (biological or not)
  • Composting
  • Thermal desorption

In situ or “in the ground” techniques : these solutions process matérials from the surface, without and dedicated earth movement. Several subsoil strata can be treated at the same time, for exemple (depending on the nature of the contamination) through :

  • Venting of the unsaturated zone
  • In situ spaging
  • In situ chemical exidation/reduction
  • Pumping-skimming

Multi-disciplinary collaboration therefore plays an essential role in remedying pollution and promoting environmental sustainability.

The joint work of GSE’s environmental engineer and our Polluted Sites and Soils (PSS) expert is essential. They have a major responsibility in assessing environmental impacts and developing strategies to mitigate them. Our environmental engineer always aims to preserve the local biodiversity specific to brownfield sites (fauna and flora), to orchestrate the sustainable management of the species identified and to encourage the reconstitution of ecosystems through the renaturation of sealed soils. This final stage enables us to propose the on-site management of contaminated materials (heavy metals in particular) by implementing landscaping solutions with appropriate plant cover, thereby reducing the site’s environmental & health impacts as well as the project’s carbon footprint.

Practical case : Ecological rehabilitation of an industrial site

A GSE project: Creil – les Marches de l’Oise.

This site, formerly used for industrial activities, was severely contaminated by heavy metals. The project’s configuration was constrained by a flood control plan (PPRI) near the site. The strategy adopted was to create vegetated rain gardens in line with the recommendations of the water regulations dossier, while treating 18,000 m3 of soil contaminated by heavy metals. The creation of the gardens enabled rainwater to be managed at the plot level, while securing reabsorption through rehabilitated soil. These steps and opportunities for rehabilitation were proposed to our client, who approved the operations.

A construction project on a polluted site is a challenge that requires multidisciplinary expertise and a rigorous approach. Despite the difficulties, with effective remediation methods, a clear understanding of regulations and a commitment to environmental protection, it is possible to transform degraded land into thriving spaces that serve the community. With 30% of our projects built on brownfield, the challenge of building on a contaminated site is fully within our grasp.

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