Multicomponent reactive transport simulation of the Elder problem: Effects of chemical reactions on salt plume development

A numerical modeling approach was used to investigate the relevancy of the feedback mechanisms between geochemical reactions and variable density flow during free convection. The problem was studied by reformulating the classic Elder problem as a reactive multicomponent transport problem. It was found that for the studied system, the importance of this feedback decreased with increasing density contrast between intruding salinized water and the ambient fresh water body. For the smaller density contrasts, the flow patterns that develop during intrusion in the reactive simulations are characterized by different convection cells, higher rates of plume descent, and an increase in the total mass of solutes by up to 22% at the end of the simulation compared to the nonreactive simulations. For field situations, the results suggest that it may be necessary to consider the feedback between reactions and variable density flow where subtle density variations drive flow such as in contaminant plumes. For seawater intrusion problems, however, the feedback mechanism appears to be negligible for most cases.