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Characterization and modeling of arsenic occurrence in the alluvial aquifer nearby Venice lagoon

Excess of arsenic in groundwater is a worldwide problem threatening the health of the millions of people directly exposed to As-rich water intake. The problem is particularly acute in naturally occurring unconsolidated aquifers where As-rich groundwater is an easily-accessible resource of drinking water, such as in India, Bangladesh and Vietnam. Naturally occurring high concentrations of As in groundwater also notoriously mark the Venetian Alluvial Plain (VAP) in Italy, affecting in particular the shallower confined aquifers. The VAP is characterized by a patchy As distribution with variable extensions and concentrations. Although empirical evidences exist about the relationship between As occurrence and other factors controlling As, several aspects regarding the physical and geochemical processes controlling As in the VAP aquifers remain unclear. This study aims to elucidate the geochemical conditions that control As mobilization in the VAP, in order to improve the knowledge about As-controlling processes in the study area and use them as a proxy to evaluate occurrence of As in other world regions characterized by a similar hydrogeological and geochemical settings, such as the Bengal Delta Plain. To this end, we focused in detail on an agricultural zone nearby the Venice lagoon, affected by As contamination (called “Aree Agricole West”, AAW). The available data, collected by several hydrogeological surveys, show a spatial and temporal variability of As concentration, which can be associated to a variety of hydro-geochemical processes such as redox variations, sorption or reductive dissolution of As-rich iron oxy-hydroxides. Multicomponent 1D reactive transport modeling is applied to elucidate the leading As-controlling processes and their relevance on the AAW and VAP in general. The results provide the initial input for a 2D/3D reactive transport model aiming at highlighting As control by other mechanisms, including influence of recharge due to agricultural activities, supporting regional-scale environmental management and future stakeholders’ decision procedures.

Arsenic ; Venice lagoon ; 1D reactive transport modelling ; groundwater management

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