An innovative approach for groundwater contamination characterization : passive samplers coupled with vertical flow measurement
Résumé
In France, passive sampling is an emerging method to measure groundwater quality and as a consequence to monitor contaminated sites. Coupled with natural vertical flow measurements in monitoring wells it appears very efficient for a vertical characterization of the pollution in groundwater. Nevertheless passive samplers are not widely used in France because there is a need to provide feedback and guidelines to consultants to promote their use in a regulatory context. That is why, in the frame of a European research project (the CityChlor project), tests were performed on passive samplers in different conditions (concentration ranges and hydrogeological conditions) to measure groundwater quality at a site contaminated with chlorinated solvents. Prior to the use of passive samplers, the groundwater contamination on site was characterized and 5 monitoring wells were installed at different depths. 4 passive samplers were tested in these wells: PDBs (Polyethylene Diffusion Bags), Ceramic Dosimeters, Gore Sorber Modules and Dialysis Membranes. The tests consisted in comparing the concentrations in groundwater given by these passive samplers to those obtained with the conventional sampling method, that is to say well purging prior to groundwater sampling with a pump. Chlorinated solvent concentrations in groundwater given by the tested passive samplers were consistent with the ones obtained from the conventional sampling method. Therefore, passive samplers seem very interesting to monitor groundwater at a contaminated site. In addition, they are very easy to use, generally cheaper than the conventional sampling method (particularly the PDBs) and cross-contamination is avoided. They can as well offer complementary information compared with traditional sampling method because they allow depth discrete and multi-level sampling in a well. Consequently, they seem to be very promising tools for the long term monitoring of groundwater on well-characterized contaminated sites.