Natural attenuation of PAHs under anaerobic conditions

Risk assessment for groundwater at contaminated sites uses flow and transport modelling. Taking into account the low mobility of PAH's, simulations are carried out for large time scale and natural attenuation, even if low, cannot be discarded. Sensitivity analysis have shown that the integration of biodégradation in the models has a strong effect on the results and on the conclusions of the risk assessment. At the moment, the position of the French Ministry of Environment is close to the position advocated by the Environmental Protection Agency (EPA) in the USA, based on the principle of precaution : "the phenomena of degradation of chemicals can be considered within the risk assessment only if irrefutable evidences of its existence can be brought ".