What are the risks?
The presence of a contaminant in the soil is not a hazard in itself. What is risky is a contaminant that can be mobilized and affect plants, animals or people. Examples include being absorbed into the roots of an edible plant or passing into an aquifer* that supplies a drinking water network. In short, the danger arises when there is a source of pollution, a pathway, such as a plant or water, and a target, such as people or the environment. A site that was contaminated long ago rarely causes hazards and immediate risks for local residents. Accidental pollution, however, can sometimes present an immediate danger. In certain cases, the risk can come from exposure to low doses over a long period, sometimes an entire lifetime. Fortunately, this type of situation is rare.

Determining remediation objectives
Remediating a contaminated site is expensive, with costs running from half a million to several tens of millions of euros. As a result, decisions need to be well founded.
In any case, it is important to determine the remediation objectives. Several countries have set ceilings on the acceptable amount of residual contamination, such as 3 grams of cadmium per metric ton of soil.

In France, as in most industrialized nations, the maximum level of residual contamination and the confinement measures to be taken to keep pollution from reaching a target are based on the admissible risk for future use of the site. This, of course, can vary. For example, a site that is destined to become a parking lot does not need to be treated as extensively as one that will have homes with vegetable gardens or a nursery school built on it.
Remediation decisions are based on risk assessment. This method demonstrates that a remediated site cannot be used for all types of activity. Obviously, one would not want to add a new pathway, such as vegetables, or a new target, such as children playing eight hours a day. This is why it is important to list restrictions in zoning documents and in a national database such as the one maintained by BRGM in France.