Applying reactive transport modelling in a chromium-contaminated site in the Matanza-Riachuelo basin, Buenos Aires, Argentina

Chromium (Cr) is one of the main pollutants affecting both soil and groundwater systems in some areas within the Matanza-Riachuelo River Basin (MRB) in Argentina. The particular site of study is located near an abandoned tannery and chemical industry facilities. Cr toxicity and mobility depend on its oxidation state: Cr(VI) is an active carcinogen, more soluble and mobile, whereas Cr(III) shows low toxicity and solubility, precipitating in the form of amorphous Cr(OH)3(am). This paper is devoted to elucidate the main key controls on the Cr(VI)-plume transport at this site using reactive transport (RT) modelling and uncertainty quantification analysis tools. RT results suggest a Cr source term on the surface to explain the observed Cr concentrations in both Pampeano and Puelche aquifers. UQ analysis indicates that the Cr(VI) concentrations in both aquifers are sensitive to hydraulic connectivity between them, the reaction reduction rates Cr(VI)-Cr(III) and the organic matter contents.