Arsenic release from pyrite ash waste over an active hydrogeological system and its effects on water quality.

Arsenic is a potentially toxic element of concern for environmental compartments, and it is a frequent pollutant in many abandoned industrial sites. In this study, geochemical and hydrogeological tools were used to determine the long-term effects of As-rich pyrite ash disposal (83,000 m3 as estimated by geostatistical tools) in a brownfield located over a quaternary alluvial aquifer. Throughout the site, soil pollution and water table oscillation led to leachates in the form of both run-off and infiltration waters, thereby reducing (ground)water quality (e.g. pH, electrical conductivity) and, in particular, increasing the concentration of arsenic (average approx. 4000 μg/l for one hydrological year). By means of laboratory and in situ measurements, the main mechanisms through which the sulphide remaining in the pyrite ash leaches were identified. In addition, to evaluate the effects of the polluted groundwater on the nearby main river, a mathematical approach using the Domenico analytical groundwater transport model revealed potential concentrations of 49 μg/l of arsenic in the junction between the study aquifer and the river, equivalent to an annual quantity of 49 kg of this element.