Classic studies of subterranean flows end up recommending measurements of these flows at a particular time. But a proper cleanup is impossible unless we know how flows of water in an area have varied over time. Serge Brouyère and his team have developed a method for making dynamic measurements of water flowing underground.

Our region’s subsoils are still affected by contamination linked to the forms of heavy industry that formerly were very active in the region (coal mining, metallurgy, chemical plants…). There are even now a significant number of of waste areas and industrial and urban sites that are potentially contaminated. The rehabilitation and cleanup of these lands is an essential condition for their being used again for economic activities that are an important part of regional readaptation; in addition, it is necessary to comply with regional and European directives, already existing (Framework directive on water….) or soon to come (Directive on “soil”) that aim at limiting the potential impact at these sites on populations living nearby, and on the natural resources (water, ecosystems) that might be affected.

The subject is all the more pressing because the pollutants present in the soil are not just going to sit there forever: rainwater that soaks into the soil can carry pollutants deeper underground, toward underground streams whose waters eventually resurface. Thus it is essential to develop techniques that allow us to “see” what is going on underground. One such method has just been published in the Journal of Contaminant Hydrology (1). It was the result of research by Serge Brouyère and his colleagues at the laboratory of Hydrology and Environmental Geology at the University of Liège.

It’s not a secret to anyone: wherever they operated, heavy industries left polluted soils behind. On these sites, organic compounds have been found such as benzene derivatives, oils and solvents containing chlorine, heavy metals such as zing, lead, arsenic and cobalt, even pollutants like sulfate or cyanide compounds. The industries that polluted often used a lot of water, either as part of industrial processes or in order to bring raw materials in and send finished products out by ship. Thus they tended to be located near watercourses. The risk of migration of pollutants toward these watercourses, following underground streams that empty into surface waters, is quite high. This is the type of situation that the Liège researchers chose to study in order to develop their method. “Our specialty,” says Serge Brouyère, “is underground hydraulics (= hydrogeology) and the migration of pollutants by means of underground streams. In this context, we are at present studying closely the interaction between underground aquifers and rivers. When the level of a stream changes, what happens with the groundwater that is associated with it? How can we describe underground water flows? How much water flows toward an aquifer or away from it? And can we describe the flows of water and pollutants underground in this system?”

(1). A new tracer technique for monitoring grounwater fluxes : The Finite Volume Point Dilution Method; Serge Brouyère, Jordi Batlle-Aguilar, Pascal Goderniaux, Alain Dassargues. Journal of Contaminant Hydrology.