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The Investigation Procedure

The Investigation Procedure

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The Tiered Investigation Approach

The German methodology operates through progressive verification stages, each building upon the previous one.
At each stage, authorities decide about necessary further steps based on information available at that time.
As investigation steps increase in complexity and scope, so do specific costs and reliability of conclusions.

This stepwise procedure leads to a more detailed information available at each step, allowing sites with low or no risks to be excluded from further investigation at an early stage, whereas acute hazards may demand immediate measures and monitoring. The process typically progresses through distinct phases, as shown on the diagramm below. 


 The Tiered Investigation Framework. Figure created by author based on LfULG(2020) Licensed under CC BY-NC-SA 4.0


At each assessment stage, authorities make one of three determinations based on investigation findings and comparison with legally defined trigger and action values:

No action required/suspicision cleared
If contamination is absent or remains below trigger values, the suspicion of harmful soil change is considered ruled out. The site exits the investigation process, subject only to documentation and record-keeping requirements. This outcome, shown by the green pathway in the investigation flowchart, allows sites with minimal risk to be released from further regulatory oversight at an early stage.

Ongoing monitoring
When contamination exceeds trigger values but remains below action values, or when site-specific conditions create uncertainty, authorities may require continued monitoring under regulatory oversight. Sites in this status are subject to monitoring, periodic sampling and evaluation, allowing authorities to assess whether contamination levels are stable, increasing, or decreasing. This response, shown by the blue pathways in the flowchart, recognizes that not all contamination require immediate active intervention.

Action required
Where action values are exceeded or an acute hazard is identified, authorities must determine appropriate intervention measures. Depending on site-specific conditions and the proportionality principle, this may include immediate protective measures, active remediation, containment systems, institutional controls, or intensified monitoring. The red pathway in the flowchart indicates situations in which regulatory action is required to prevent or manage unacceptable risks to receptors: human health or the environment.