Soil analysis becomes a technical treatment decision by systematically matching the identified contaminant parameters against the requirements of available treatment methods. The key factors are the type, concentration, and combination of contaminants, as well as the physical and chemical properties of the soil material. The following sections explain which factors specifically play a role and which preliminary investigations are necessary.
Which analysis parameters determine the treatment path for contaminated soil?
The choice of treatment path depends primarily on the type of contaminant, the contaminant concentration, and the leaching behavior of the contaminated soil. Additionally, moisture content, fine particle fraction, organic content, and pH value play an important role, as they influence how soil can be technically processed and which treatment temperatures or methods are appropriate.
In detail, the following parameters are particularly relevant in contaminant analysis:
- Contaminant group: Volatile organic compounds such as BTEX, TPH, or PAHs behave differently under thermal treatment than inorganic contaminants such as heavy metals or cyanides.
- Concentration: High contaminant levels require more intensive treatment methods or longer residence times in the furnace.
- Binding form: Contaminants that are firmly bound to soil particles are harder to dissolve than those present in soil moisture.
- Particle size distribution: Fine-grained soils respond differently to thermal treatment than coarse gravel or rubble fractions.
- Moisture content: High moisture content increases energy demand and can affect treatment temperature.
- Organic matter content: A high humus content can intensify contaminant binding and complicate process control.
These parameters form the analytical foundation on which a well-founded treatment decision is built. Without complete knowledge of these values, safe and legally compliant disposal is not possible.
How do you decide whether thermal desorption is the right treatment method?
Thermal desorption is the right choice when contaminated soil contains organic pollutants that can be destroyed by heat or transferred to the gas phase, and when other methods such as biological or chemical-physical treatment are not sufficiently effective due to the type or concentration of contaminants.
The method is particularly suitable for soils contaminated with TPH, BTEX, PAHs, PCBs, phenols, PFAS/PFOS, PCDD/PCDF, nitroaromatics, cyanides, and chlorinated hydrocarbon compounds. For these substance groups, thermal treatment is often the only method that ensures complete and demonstrable contaminant destruction.
Thermal desorption is contraindicated when the soil is predominantly contaminated with inorganic substances, such as heavy metals, which cannot be destroyed thermally but are merely relocated. In such cases, stabilization, immobilization, or other methods of mechanical-physical treatment are the more sensible alternative.
In practice, the decision is rarely clear-cut. It requires a holistic assessment of the contaminant profile, economic viability, available capacity, and the legal requirements of the respective project.
What happens when soil contains multiple contaminants simultaneously?
When soil contains multiple contaminants simultaneously, the most demanding contaminant determines the treatment requirements. This means: treatment conditions must be selected so that all contaminants present are safely treated, even if individual ones would allow for a milder method on their own.
In practice, multiple contaminations frequently occur, for example at decommissioned industrial sites, gasworks, or military facilities, where decades of various production processes have left behind different contaminants. Typical combinations include TPH together with PAHs, BTEX with phenols, or heavy metals combined with chlorinated hydrocarbons.
In cases of multiple contamination, thermal desorption is often the method of choice because it treats a broad spectrum of organic contaminants in a single process step. The treatment temperature and residence time in the rotary kiln are set so that even the less volatile compounds are safely destroyed. At the same time, the downstream exhaust gas treatment must be tailored to the resulting gas mixtures to reliably comply with all emission limits.
If heavy metal contamination is also present, it must be assessed whether thermal treatment could convert it into a more critical form. In such cases, close coordination between analytics and process engineering is essential.
What preliminary investigations are required before accepting contaminated soil?
Before accepting contaminated soil, a complete contaminant analysis, a characterization of the physical soil properties, and a review of the waste law classification are required. These preliminary investigations form the basis for the admissibility of acceptance and the planning of the treatment path.
In detail, the necessary preliminary investigations typically include the following steps:
- Analytical basic characterization: Determination of all relevant contaminants by an accredited laboratory, including eluate analyses in accordance with applicable standards.
- Physical characterization: Particle size distribution, moisture content, density, and where applicable, the calorific value of the material.
- Waste law classification: Assignment to the correct waste codes in accordance with the European Waste Catalogue and verification of whether hazardous waste is involved.
- Proof of origin: Documentation of the place of origin and the usage history of the site, particularly for brownfield or contaminated land sites.
- Admissibility review: Comparison of analysis results with the acceptance conditions of the respective treatment facility and the regulatory permits.
Only when these documents are complete can a reliable treatment decision be made and acceptance of the material approved. Material flow management plays a central role here, as it ensures that every material takes the correct disposal route.
When is soil analysis alone insufficient to make a treatment decision?
Soil analysis alone is insufficient when the analysis results are contradictory, when unknown contaminants are suspected, when sampling was not representative, or when the physical properties of the soil present a particular process engineering challenge that cannot be fully captured by laboratory values alone.
Specific situations in which an extended assessment is necessary:
- Heterogeneous contamination: When the distribution of contaminants across the site varies greatly, individual samples are not representative. In this case, composite samples or a higher sampling density are required.
- Unknown site history: When the usage history of a site is unclear, relevant contaminants may be missing from the analysis program.
- Findings close to limit values: When contaminant concentrations are just below or at limit values, analysis alone is often insufficient to reliably determine the treatment method.
- Complex material composition: Construction rubble, slags, or mixtures of different waste types frequently require supplementary tests, such as thermal desorbability tests or leaching tests under process conditions.
- Regulatory requirements: Some permitting procedures require specific evidence that goes beyond standard analysis.
In such cases, close collaboration between the client, an experienced expert, and the treatment facility is crucial. Only by combining analytical data, site knowledge, and process engineering experience can a safe and legally defensible treatment decision be made. Information on quality management in acceptance and treatment can be found in the Quality Management section.
How ARE Deutzen supports treatment decisions for contaminated soils
ARE Deutzen GmbH accompanies civil engineering companies and industrial clients from the initial contaminant analysis through to the verified treatment of contaminated material. With over 30 years of experience in thermal soil treatment and more than 2.5 million tonnes of treated mineral materials, ARE Deutzen has the technical expertise to safely assess and treat even complex contaminations.
The range of services specifically includes:
- Expert review of analytical data and support with acceptance planning
- Thermal desorption in a rotary kiln at temperatures up to approximately 600 °C, depending on the material and contaminant load
- Treatment of soils contaminated with TPH, BTEX, PAHs, PCBs, PFAS/PFOS, PCDD/PCDF, cyanides, nitroaromatics, and chlorinated hydrocarbon compounds
- Multi-stage exhaust gas treatment with thermal post-combustion, flue gas scrubbing, and activated carbon filtration
- Material flow management for soils, dredged material, construction rubble, and process residues
- Certified waste management company in accordance with § 52 KrWG with permits under BImSchG
If you are facing a concrete treatment decision and want to know whether your material is suitable for thermal soil treatment, speak directly with the specialists at ARE Deutzen. The contact persons will advise you objectively and solution-orientedly so that your remediation project can be implemented safely and efficiently.