Back diffusion + Plume persistence

PhD students Changmin Kim and Seonggan Jang studied solute transport in aquitards, a critical factor for groundwater contaminant remediation and also more broadly solute exchange between subsurface layers encountered throughout geosciences disciplines. Other specific applications include landfill liners and nuclear waste repositories. 

We developed analytical solutions for solving finite domain problems, the solutions were validated with new laboratory experimental data, and the solutions were further applied to diffusion data that spans a large range of scales, both length (cm to m) and temporal (days to millions of years).  

This work demonstrates how measured field data can be used to help understand and manage contaminated sites. The issue of back diffusion is of significant current interest at contaminated aquifer sites (see left). Field-measured data (aquitard concentration profiles) can provide characteristic signatures of plume life cycle stage. 

Based on the shapes of concentration profiles in the aquitard, we can describe the timing of the transitions between aquifer source zone dissolution, dissolution combined with back diffusion from an aquitard, and back diffusion alone. This work supports assessment of plume persistence and human exposure risk. Furthermore, this study addresses proper timing of site management actions in relation to both aquifers and aquitards.