We Made A Breakthrough (Curve): How Immobile Zone Properties and Breakthrough Curves Inform One Another

The prediction of solute transport through environmental and man-made systems is critical to the preservation of ecological and human health, influencing our ability to remediate contaminated rivers, protect groundwater aquifers, and permanently dispose of nuclear waste. However, natural environments tend to be rich in physical, biological, and chemical complexities, producing regions of negligible flow that retard transport and give rise to anomalous behaviors. Mobile-immobile models (MIMs) have successfully captured anomalous transport in different environments by accounting for simultaneous interactions between solutes and a collection of negligible-flow features. While effective, integrating retention over a host of features hinders our understanding of how any one feature affects transport. Through the use of physical experiments and numerical simulations, this thesis aims to (i) determine whether we can disentangle the role of individual immobile features on BTC dynamics and (ii) determine whether BTC features can be related back to specific retention mechanisms. We explore these questions in subsurface fracture networks, fluvial, and colloidal systems which, while quite diverse, can be similarly divided into mobile and immobile flow regions. We find that in subsurface fracture networks and streams, varying a single immobile zone characteristic (ie: thickness, substrate type, biofilm accumulation) exerts a noticeable signature on continuum scale transport. We then take initial steps in relating features of continuum scale data back to retention mechanisms in stream and colloidal systems by using regressive and inverse model- ing techniques. Although there is significant work ahead to establish a predictable relationship between individual immobile features and BTC behavior, this thesis lays the groundwork for such detailed analyses.