This paper discusses the reactive transport and evolution of arsenic along a selected flow path in a study plot within the central part of Datong basin. The simulation used the TOUGHREACT code. The spatial and temporal trends in hydrochemistry and mineral volume fraction along a flow path were observed. Furthermore, initial simulation of major ions and pH fits closely to the measured data. The study shows that equilibrium conditions may be attained at different stress periods for each parameter simulated. It is noted that the variations in ionic chemistry have a greater impact on arsenic distribution while reducing conditions drive the mobilization of arsenic. The study concluded that the reduction of Fe(III) and As(V) and probably SO4/HS cycling are significant factors affecting localized mobilization of arsenic. Besides cation exchange and water–rock interaction, incongruent dissolution of silicates is also a significant control mechanism of general chemistry of the Datong basin aquifer.