Application of monitored natural attenuation in contaminated land management—A review and recommended approach for Europe

The prospect of more efficient, economically advantageous management strategies has driven the development of contaminated land management concepts particularly for large and complex contaminated sites during the last years. Consequently, the conscious and controlled use of naturally occurring degradation and retardation processes of pollutants in the subsurface (monitored natural attenuation—MNA) has gained increasing attention. Today, there are in principle two different MNA concepts available: risk-based MNA concepts as used, for example, in the USA, and MNA concepts which rely on a precautionary principle of soil and groundwater protection as developed, for example, in Germany. Based on a discussion of the virtues and limitations of these concepts, the manuscript provides a review and a synthesis of these concepts as well as recommendations for further improvements.