MONITORING PLAN ? An important tool for the management of contaminated sites

When it comes to managing a polluted site, the development of an effective strategy depends, among other things, on the accuracy of the conceptual diagram. This diagram shows the sources, transfer routes, exposure media and receptors likely to come into contact with the pollutants. This diagram is not static. It may change, either because the information available was not exhaustive at the time of its creation, or because various elements making up the diagram have evolved over time (disappearance, modification or appearance of a source, a migration vector or a receptor). In addition, concentrations in the various media (source, transfer, exposure) evolve according to the measures taken, natural attenuation or other factors influencing pollutant mobilization or migration conditions.

Of all these parameters responsible for the dynamic nature of the conceptual diagram, it must be recognized that some are not easily foreseeable from the outset. This is why the management of a polluted site calls for iterative, progressive, evolutionary and interactive management processes. This is also why national policy on the management of polluted sites and soils has reiterated the importance of environmental monitoring throughout the process, and reaffirmed the primacy of measurement and interpretation in decision-making. This article looks at environmental monitoring and how it can contribute to the efficient management of a polluted site.

This monitoring gives the management strategy the extra reliability needed to win the assent and trust of stakeholders. Indeed, with the many factors of uncertainty that characterize polluted sites, confidence cannot be based solely on expert opinions and numerical modelling. Among the many factors of uncertainty are: gaps in our knowledge of the events at the origin of the pollution, the heterogeneity of the subsoil, the absence of direct visibility of underground phenomena, the inaccurate nature of subsoil science, the use of recent and as yet unproven treatment techniques, particularly in situ, and the difficulty of quantifying transfer and natural attenuation phenomena.

Measuring and monitoring the environment is therefore the key to correctly assessing impacts, and hence risk, over the long term. Their interpretation enables us to identify warning signals and take timely corrective action. As the phenomena involved are slow-moving, monitoring is carried out on a multi-year timescale. The article reviews the means and objectives of the quadrennial assessment, and devotes considerable space to feedback from a recent case study.