If you suspect soil contamination on your site, the first step is to stop any activities that could spread the contamination further and document what you know. From there, you are legally required to notify the relevant authorities and commission a formal site investigation to determine the nature, extent, and risk of the contamination. In Belgium, this process is governed by VLAREBO legislation and overseen by OVAM, the public waste agency. The sections below walk through each stage of that process, from initial suspicion to choosing a remediation strategy.
How do you know if your site is actually contaminated?
You can suspect soil contamination based on the site’s history, visible signs, or analytical testing. Historical land use is often the strongest indicator: sites that previously housed dry cleaners, fuel storage, metal processing, or industrial manufacturing carry a significantly elevated risk. Visible signs such as discolored soil, dying vegetation, or an unusual odor may point to contamination, but many serious contaminants are invisible and odorless at dangerous concentrations.
The only way to confirm contamination is through soil and groundwater sampling analyzed by an accredited laboratory. Sampling locations are selected based on the suspected source zones and potential migration pathways. For volatile organic compounds such as chlorinated solvents, groundwater monitoring wells are particularly important because these substances dissolve readily and can travel considerable distances from the original source.
Common indicators that warrant investigation include:
- Prior industrial or commercial use of the site
- Known or suspected underground storage tanks
- Neighboring sites with confirmed contamination
- Unusual vegetation patterns or soil discoloration
- Complaints from users or residents about odors or health effects
- Planned change of land use, construction, or sale of the property
If any of these factors apply, a formal assessment is warranted before proceeding with development or sale.
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What are your legal obligations when soil contamination is suspected?
In Flanders, the legal framework for soil contamination is established by VLAREBO, the soil remediation decree. If you are the owner, user, or operator of a site where contamination is discovered or reasonably suspected, you are legally obligated to report this to OVAM and to commission a preliminary site investigation. Failure to report can result in liability being extended to the current owner, even if the contamination predates their ownership.
Reporting obligations are triggered by specific events: a change of land use, a permit application, the sale or transfer of a property, or the cessation of a potentially contaminating activity. In some cases, OVAM may proactively require an investigation based on its own risk register. The obligation to investigate and remediate generally falls on the party responsible for the contamination, but ownership transfer rules mean that buyers and sellers must both exercise due diligence.
Non-compliance carries real consequences. OVAM can impose administrative measures, block permit applications, and in serious cases pursue legal enforcement. For project managers and site owners, the practical takeaway is straightforward: once contamination is suspected, acting promptly and within the regulatory framework protects both the project timeline and the organization’s legal position.
What is a preliminary site investigation and when is it required?
A preliminary site investigation, known in Flanders as an oriënterend bodemonderzoek (OBO), is a first-phase assessment that determines whether a site poses a risk of significant soil or groundwater contamination. It is required whenever a potentially contaminating activity has taken place on a site and a trigger event occurs, such as a sale, permit application, or change of use. The OBO must be carried out by a certified soil expert (erkend bodemsaneringsdeskundige).
The investigation combines a desk study of the site’s history with a limited field sampling program. The desk study reviews cadastral records, permit histories, aerial photographs, and any prior environmental reports. Field sampling targets the most likely contamination zones based on the historical analysis. Results are submitted to OVAM, which then classifies the site.
If the OBO confirms that contamination is present above threshold values, or that a significant risk cannot be excluded, OVAM will require a descriptive site investigation (beschrijvend bodemonderzoek, or BBO). The BBO is a more intensive characterization of the contamination, mapping its full extent, depth, and migration in soil and groundwater. This more detailed picture forms the basis for any subsequent remediation planning.
What happens after a site is classified as contaminated by OVAM?
Once OVAM classifies a site as contaminated following a descriptive investigation, the responsible party receives a formal decision that typically includes a remediation obligation. The nature and urgency of that obligation depend on the risk classification: whether the contamination poses an immediate risk to human health or the environment, or whether it is a lower-priority historical case that can be managed over a longer timeframe.
For high-risk sites, OVAM may require urgent interim measures to prevent further spread of the contamination before a full remediation plan is developed. For standard cases, the responsible party must draw up a soil remediation project (bodemsaneringsproject) that describes the chosen remediation technique, the target values to be achieved, the monitoring plan, and the timeline. This project must be approved by OVAM before implementation begins.
Throughout remediation, regular monitoring reports must be submitted to OVAM to demonstrate progress. Once target values are achieved and OVAM confirms the site meets the applicable standards, a declaration of conformity is issued. This declaration is essential for property transactions, building permits, and changes of use. Without it, development on a contaminated site is effectively blocked.
What are the main options for remediating contaminated soil?
The main remediation options for contaminated soil are excavation and off-site disposal, in-situ treatment techniques, and monitored natural attenuation. The appropriate method depends on the type and concentration of contaminants, the depth and extent of contamination, site-specific conditions such as groundwater depth and soil permeability, and the intended future use of the land.
Excavation and off-site disposal
Excavation involves physically removing contaminated soil and transporting it to a licensed treatment or disposal facility. It is the most familiar approach and delivers fast, verifiable results. However, it becomes impractical or prohibitively expensive when contamination is deep, located beneath structures, or present in large volumes. Groundwater contamination cannot be addressed by excavation alone.
In-situ treatment techniques
In-situ techniques treat contamination where it sits, without removing soil. These include pump-and-treat systems for groundwater, chemical oxidation or reduction, thermal treatment, and biological methods. Biological in-situ treatment, also called bioremediation, uses microbial activity to break down contaminants in place. For persistent contaminants such as chlorinated solvents (VOCl), biological soil remediation using specialized microbial consortia can achieve degradation that physical or chemical methods cannot replicate. Avecom specializes in this type of intervention, applying in-situ bioaugmentation supported by molecular monitoring tools to track remediation progress in real time.
Monitored natural attenuation
Natural attenuation relies on naturally occurring physical, chemical, and biological processes to reduce contamination over time without active intervention. It is only acceptable to OVAM under specific conditions and requires a robust monitoring program to demonstrate that attenuation is actually occurring at a sufficient rate.
How do you choose the right remediation approach for your site?
Choosing the right remediation approach starts with a clear understanding of the contaminant type, site conditions, and the regulatory targets that must be met. No single technique works for every situation. The selection process should weigh technical feasibility, cost, duration, and the degree of disruption to ongoing site activities or neighboring properties.
For many project managers, excavation feels like the safe default because it is familiar and delivers rapid results. But on sites with deep contamination, high groundwater tables, existing structures, or large affected volumes, excavation quickly becomes technically impractical or financially unviable. In these cases, in-situ biological treatment often represents a more proportionate solution, provided that the site conditions support microbial activity.
A key step before committing to any biological approach is a feasibility assessment. A microcosm test, which involves incubating site soil and groundwater samples under controlled laboratory conditions, can confirm whether the target contaminants are biodegradable under the specific conditions of that site. This relatively low-cost test avoids the risk of deploying a full remediation program on a site where biological degradation cannot proceed effectively. Avecom’s soil remediation services are built around exactly this kind of evidence-based screening, combining microcosm testing with molecular soil analysis to design interventions that are grounded in site-specific data rather than generic assumptions.
The remediation approach also needs to align with OVAM’s approval requirements. A well-documented technical rationale, supported by site-specific data, will move more smoothly through the regulatory review process than a generic proposal. Working with specialists who understand both the science and the regulatory framework can significantly reduce delays in obtaining approval and beginning active remediation.
If you are managing a site where classical techniques have not delivered results, or where excavation is not a viable option, a targeted biological approach may be worth evaluating. Learn more about Avecom’s approach to biological decontamination, or visit Avecom’s website to explore the full range of environmental remediation services available.