ULiège is developing a technology that is unique in the world for measuring the flow of contaminated water underground
Engineers at the University of Liège have developed a technology that is unique in the world, capable of directly measuring the speed of water flow in aquifers, continuously monitoring variations in these flows and understanding their hydrodynamics. It's a promising technology that has already proved its worth in targeting areas where discharges of water and pollutants are the most significant, and therefore, where these pollutants present a risk. This patented technology will soon be transformed into a new spin-off company.
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roundwater is one of our planet's most critical natural resources. It needs to be adequately protected and managed. Although they appear to be protected from air pollution, groundwater is often contaminated (by old industrial activities, accidental discharges, diffuse pollution, etc.). Water infiltration into the ground then allows pollutants on the surface to reach the water table and spread at depth, increasing the risk of groundwater contamination. It is difficult to measure this flow exactly unless major and costly monitoring systems are put in place. This observation has not escaped the attention of the Hydrogeology and Environmental Geology Laboratory at the University of Liège, headed by Alain Dassargues and Serge Brouyère, who since the early 2000s have been developing the FVPDM (Finite Volume Point Dilution Method), a method that involves direct measurement of groundwater flows. As well as providing a better understanding of the dynamics of underground flows, this method makes it possible to calculate the mass fluxes of pollutants that migrate through aquifers and risk-reaching receptors (surface watercourses, drinking water production wells, etc.). By measuring these fluxes, it is possible to optimise management plans for polluted sites and substantially reduce the associated costs, while ensuring that the risks are controlled. In addition to the successful laboratory developments, researchers validated this patented technology on real industrial sites.
“The technology involves tracing by a single well dilution method, " explains Pierre Jamin, a ULiège's School of Engineering researcher and the project leader. In practical terms, a tracer is injected continuously into a well and its concentration is monitored over time. The greater the flux of groundwater naturally passing through the well, the more diluted the tracer will be and the lower its concentration in the well compared with the concentration injected. This method therefore makes it possible to continuously monitor variations in the flow of water in aquifers over several days, weeks or months, and to understand their hydrodynamics, which makes it unique in the world.”
"At the instigation of the Environmental consulting company Geolys, the ULiège team was contacted by the environment department of Elia, the Belgian high-voltage electricity transmission network operator, as part of the environmental management of one of its sites in Brussels. The alluvial aquifer beneath the site is contaminated with eight heavy metals and poses a risk of dispersion into the river adjacent to the site," explains Pierre Jamin. Elia, which is not responsible for this pollution, inherited a degraded site when it acquired the site, and has taken responsibility for managing the pollution. Since the assessment of dispersion risks based solely on conventional methods was unable to precisely quantify the risk of heavy metal discharge into the river, costly and time-consuming monitoring of the groundwater, surface water and sediments of the Senne, including 43 monitoring wells sampled twice a year for 30 years, had to be implemented".
Thanks to Elia's willingness to support innovation, and in collaboration with Geolys, the ULiège laboratory proposed an advanced risk assessment methodology based on the measurement and monitoring of groundwater fluxes as well as the quantification of dissolved metal fluxes and their potential discharge into the river. "Groundwater flow measurements were carried out on 43 monitoring wells, distributed like a control panel along the downstream border of the site. They enabled the spatial heterogeneity of groundwater flow to be characterised and the total discharge of water and metals across the site border feeding the river to be quantified."
"The study showed that, of the eight heavy metals present in the groundwater, the discharge of seven was insufficient to threaten the quality of the river water. The 'flux' approach also enabled us to better analyse changes over time in the extent of discharges," explains Roland Marchal, director of Geolys. A robust trend analysis has shown an overall decrease in total metal discharges since 2014, which was previously impossible to prove based on concentrations time series alone.
This study, validated by Brussels Environment (the administration of the Brussels-Capital region responsible for designing and implementing environmental policies), can be considered a reference case in the Brussels region. It was therefore possible to optimise the monitoring plan implemented on the site by monitoring only 18 of the 43 wells initially defined, with these 18 wells alone accounting for more than 95% of the metal mass discharge through groundwater. The monitoring period was also reduced from 21 to 9 years, saving almost 70% in monitoring costs. Geolys and Nagaré will present this reference case to all Brussels Environment staff at their next study day, to be held in October 2023.
"Elia attaches great importance to innovation and we are very pleased to have been able to support the development of this technology. Its application at our site has enabled us to provide a more accurate response to questions from Brussels Environment about the site's potential contribution to the quality of the water in the Senne river. In addition, future monitoring of the site has been optimised and costs reduced. The money saved can be allocated elsewhere in the company, which has many challenges to meet," explains Christophe Coq of Elia's environment department.
Nagaré, the company implementing this technology, which has benefited from the support of the Walloon Region through the First Spin-Off MFlux project, recently received an award from the NICOLE network, a major network of professionals in the field of sustainable management of polluted sites and soils. Nagaré received the NICOLE Innovative Project Award 2023 for "optimising management plans for the risks of pollutant dispersion in aquifers by using innovative approaches based on flow measurements". This award gives the future spin-off a high profile and recognition by its peers of the scientific relevance of the technology and its economic efficiency.
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