Identification of chlorohydrocarbon degradation pathways in aquitards using dual element compound-specific isotope measurements in aquifers.

Compound-specific isotope analysis (CSIA) has been increasingly used to understand and quantify the (bio)degradation processes affecting chlorohydrocarbons in aquifer-aquitard systems. In this study, we aimed at investigating through reactive transport simulations if dual element (C, Cl) CSIA in aquifer samples can provide information about the occurring (bio)degradation pathways in the underlying aquitard. To that end, we modeled the continous dissolution of a 1,1,2,2-tetrachloroethane (TeCA) dense nonaqueous phase liquid (DNAPL) source in an aquifer as well as the resulting TeCA groundwater plume formation and diffusion into the underlying aquitard.

Environmental geochemistry and bioaccumulation/bioavailability of uranium in a post-mining context - The Bois-Noirs Limouzat mine (France).

Knowledge on the bioavailability of trace elements is essential in developing environmental quality standards. The purpose of this study was to explore the relationships between trace elements (in particular Uranium (U)) in sediments, porewater and their bioaccumulation by Chironomus riparius on a uranium mining site and river sediments upstream of the mine. The mobility and speciation of U in sediments was investigated using DGT.

An alternative sequential extraction scheme for the determination of trace elements in ferrihydrite rich sediments.

Sequential extraction schemes (SES) were evaluated to investigate the fractionation of Al, As, Cd, Cs, Cr, Co, Cu, Fe, Mn, Mo, Pb, Sr, U and Zn between the different mineral phases in iron oxide rich deposits of a former uranium mining site. Ineffective dissolution of iron oxide was observed when applying the BCR sequential extraction scheme. The hydroxylamine hydrochloride reagent in nitric acid could not effectively dissolve the iron oxide phase, even after several consecutive extractions.

Operator-splitting-based reactive transport models in strong feedback of porosity change: The contribution of analytical solutions for accuracy validation and estimator improvement.

Reactive transport is a highly non-linear problem requiring the most efficient algorithms to rapidly reach an accurate solution. The non-linearities are increased and the resolution is even more demanding and CPU-intensive when considering feedback of dissolution or precipitation reactions on hydrodynamic flow and transport, commonly referred to as the variable porosity case. This is particularly true near clogging, which leads to very stiff systems and therefore small time-steps.

Long-term reactive transport modelling of stabilized/solidified waste: from dynamic leaching tests to disposal scenarios.

Environmental impact assessment of hazardous waste disposal relies, among others, on standardized leaching tests characterized by a strong coupling between diffusion and chemical processes. In that respect, this study shows that reactive transport modelling is a useful tool to extrapolate laboratory results to site conditions characterized by lower solution/solid (L/S) ratios, site specific geometry, infiltration, etc. A cement solidified/stabilized (S/S) waste containing lead is investigated as a typical example.