Monitored Natural Attenuation (MNA): decontamination technique

Moving towards a sustainable society is becoming an increasingly important area of development in the industrialized world. Concepts such as industrial ecology and "Cradle to Cradle aim to ensure that the objectives of – activities, such as sanitation –, take into account the effects on the environment and public health during and after these activities. These concepts are finding increasing support in our society. The basis of all sustainable development concepts is the economic and socio-ecological factor.

This development requires a thorough assessment of the socio-ecological cost-benefit balance of the action or technique envisaged. This applies not only to new investments and techniques, but also to the correction of environmental and human situations resulting from an industrial legacy.

In France and other industrialized countries, the trend towards a balanced approach between clean-up costs and environmental and human benefits is becoming increasingly clear. In the past, it was found that active groundwater remediation up to certain remediation standards (intervention standards or reference standards) often failed and was often unfeasible. As a result, the BATNEEC principle (Best Available Technique Not Entailing Excessive Cost) was not met. As a result, remediation is increasingly focused on human and environmental risk, using more extensive techniques. On the other hand, these techniques do not always restore the "pre-industrial" situation, but they do prevent unacceptable impacts on the environment and public health.

In this context, "Monitored Natural Attenuation" (MNA) is to be considered as a possible approach and an available remediation technique. Natural attenuation" is defined as all the natural processes (biological, geochemical, hydraulic and others) that are capable of reducing or limiting contamination or the risks associated with this contamination. The term "monitored natural attenuation" refers to reliance on natural attenuation processes. Far from being a laissez-faire philosophy, this technique can only be appropriate if its use is protective of human health and the environment, and if it is capable of achieving decontamination objectives within a reasonable timeframe compared with other alternatives.