Assessing the efficiency of passive samplers for groundwater sampling
Résumé
Chlorinated solvents are among the most common soil and groundwater contaminants due to their widespread use as cleaning solvents or degreasing agents. Due to their physico-chemical properties, chlorinated solvents produce large-scale plumes of pollution in the groundwater. In the densely populated north western Europe, these pollution plumes often are situated under residential and urban development areas and, therefore, not easily accessible. Vapors can migrate through building slabs and affect the quality of indoor air. That is why the CityChlor project was created. It aims at improving the quality and minimizing pollution of soil and groundwater by developing an integrated approach to tackle the threats caused by contamination with chlorinated solvents in urban areas. One of the goals of the project is to define the most reliable, fast, and cost-effective techniques to detect, characterize, and delineate chlorinated solvent pollution in groundwater. In this context, passive sampling is an innovative way of sampling contaminants in groundwater in Europe, and it seems very promising. Therefore, tests are required at each country level to make regulations concerning these samplers, which will encourage consultants to use them. That is why the aim of this work was to assess the performance of 3 passive samplers to sample chlorinated solvents in groundwater and to compare the results to those obtained with the traditional groundwater sampling method, that is to say well purging prior to groundwater sampling with a pump. The pilot site chosen to conduct these experiments is an in-service facility located in France, 60 km east from Paris, in an urban area. In this factory, door locks and metal fittings have been produced since 1926 and chlorinated solvents are used to remove grease marks from metal fittings. On site, soils are composed of one layer of silty embankments (2 to 3 m) and then a sandy horizon. The water table is at around 2 m below the ground surface and it goes to 10 m deep. In order to test passive sampling, 5 dedicated water wells were installed on site. In this way, the design of the wells was totally known and passive samplers were tested in controlled conditions. One of them was screened from 2 to 8 m deep and the other ones were screened respectively from 2 to 3.5 m; 3.5 to 5 m; 5 to 6.5 m and 6.5 to 8 m. Three passive samplers were therefore tested: PDB (Polyethylene Diffusion Bags), Ceramic Dosimeters and Gore Sorber Modules. Multilevel sampling was done in the well screened from 2 to 8 m and one sampler was installed in the middle of each screened interval of the other wells. This was done for the 3 samplers tested. PDB were very easy to install and the cost of these samplers was lower than the one corresponding to the conventional method with the pump. In addition, these samplers exhibited a good reproducibility. Ceramic dosimeters were very easy to use as well, but results were not reproducible for some compounds. Some tests are still in progress to confirm this trend. For Gore Sorber Modules, the first sampling campaigns gave consistent results comparing to the pump. In general, passive samplers seemed to be very efficient to sample HVOC in groundwater and to be a good alternative to the standard method with purge and sampling with a pump.