Probability of Non-Exceedance of Arsenic Concentration in Groundwater Estimated Using Stochastic Multicomponent Reactive Transport Modeling

Stochastic multicomponent reactive transport modeling is a powerful approach to quantify the probability of non-exceedance (PNE) arsenic (As) critical concentration thresholds in groundwater. The applied well-characterized shallow alluvial aquifer near Venice, Italy. Here, As mobility depends primarily on rainfall-controlled redox-dependent precipitation-dissolution iron hydroxides. A Monte-Carlo analysis based calibrated three-dimensional flow and model targeted geochemical initial conditions as main source uncertainty concentrations studied aquifer. It was found that, during 115 simulated days, fraction entire volume with > 10 ?gL?1 decreased average from ~43% ~39% ~32 ~27 ?gL?1. Meanwhile, PNE increased 55% 60% when set target threshold, 71% 78% for 50 time dependence attenuation can be ascribed increase oxidizing rainfall-dependent recharge, which causes sorption precipitating When computing same statistics shallowest 6 m, even more evident. 10?gL?1 dropped 40% 28% 31 20 ?gL?1, whereas 58% 70% < 86% Thus, wells screen depth aspect estimating risk, owing depth-dependent relative change redox rainfall events.