The 4th french exchange days on contaminated sites and soils were held on June 18 and 19, 2015 in Geneva. This event was organized both by the GESDEC, the L’Ucie association and the OFEV. Hélène Demougeot-Renard was invited to speak on the topic “Site contaminated with chlorinated hydrocarbons – Assessing the potential of natural biodegradation using a detailed analysis of monitoring data“.