Comparison of tools and protocols for groundwater sampling
Résumé
Prevention or management of pollution of groundwater is based on sampling. Sampling leads to determine the water quality and in case of deterioration, to understand its origin and evolution to better cope. Data must be reliable, the representativeness of a groundwater sample is essential. But obtain a sample which is “representative” of the water quality in the surrounding geological formation is partly related to the tools and protocols used. Remarkable progress have been done in site characterization, monitoring and field instrumentation over the past 25 years but some issues remain and profession lack of demonstration to clarify certain choices on tools (passive or active sampling techniques) and protocols (purging, sampling flow, filtration) best suited to the situation encountered and to the sampling purpose. A comparison of existing technology, whether or not conventionally employed by operators is currently underway by INERIS with academic and private partners - period 2014 to 2016. This work aims to produce a feedback and a cost benefit analysis on the various tools and protocols based on the results obtained at different scales- experimental tank (Figure 1) and real sites. This comparison process conducted on three sites (four campaigns by site) and on an experimental tank, will lead to the acquisition of a large amount of data. Interpretation of the results will allow to define some trends and to answer some questions mentioned above. At this stage, the acquired data concerning a surface sampling on two sites and tank show that for BTEX (benzene, toluene, ethylbenzene and xylenes), different sampling tools provide concentrations comparable (Figures 2 and 3, with Low-flow purging (LF), PDB, HydraSleeveTM, multiple packers coupling with bladder pump, bailer, pumps, discrete interval sampler). Work continues to assess reproducibility of these preliminary results to improve the state of the art.