“WHY I WANT TO BE A GEOLOGIST.” Allan Foster III, SA-8349, Colorado School of Mines


I want to become a geologist for one reason and that is to have a positive impact on the world. I want to make this positive impact on society through the pursuit of research, and the topic I have been focusing on and will continue to focus on is in the field of hydrogeology. My goal and the objective for my


research is to quantify phenomena controlling “anomalous” solute transport, where solutes do not move according to clas- sical theory. The broader implications of my research pursuit are substantial. Currently, humans have contaminated over fifty percent of their available freshwater sources and action needs to be taken in order to mitigate this. Given an expo- nentially growing population, there is going to be a day in which all available water resources are impacted by humans. Being able to accurately predict contaminant transport in highly heterogeneous natural systems is going to be a highly valued skillset as society moves forward. Geoscientists who understand where, when, and how contaminants are going to move through aquifers and freshwater resources will be called upon to help aid in the mitigation and cleansing of these vital resources. I want to be a part of engineering the solution to this phe- nomenon as a geolo- gist who is highly trained in hydrology


and engineering, in order to ensure that uncontaminated fresh water is not a term that is going to be lost in history. Recent work in Swanson and others (2015) shows that two similar zeolite clinoptilolites behaved significantly differently in terms of their solute transport behavior. Despite having the same intergranular and intragranular porosity, grain size and relative mineral composition, the manner in which solute was transported through them was different. Although not the focus of the publication, this difference led me to simply ask: why? Conceptually, from a hydrology perspective, these zeolites should behave in the exact same manner, but they do not. If these zeolites that are practically identical are behaving differently from a solute transport perspective, what does that mean when our knowledge is applied to extremely heteroge- neous natural systems? How would this impact contaminant transport in aquifers? I would like to tackle this problem. I hypothesize that increasing the heterogeneity of the geologic media within a system will lead to more anomalous solute transport behavior. However, when coupled with higher flow rates, the anomalous behavior will decrease and the system will begin to behave more in the way described by the advec- tion-dispersion equation (ADE). A visual representation of the difference between a breakthrough curve (a concentration his- tory through time) that experiences anomalous solute trans- port behavior and one that behaves like the ADE is provided below from my preliminary undergraduate research; the image below shows how the late-time behavior indicates increased storage of contaminants in gray. These breakthrough curves are from laboratory tracer tests performed on geologic media


www.aipg.org in one-dimensional flow columns.


To explore this hypothesis, I propose a series of experiments that include tracer tests. Logistically the experiments would be lab-based to maximize system control. The geologic material would consist of three different grain packings: homogeneous and heterogeneous sands, which contain only intergranular pore space, and homogeneous grain-sized crushed silica glass with both a lab-quantified intergranular and intragranular porosity. The research will use geophysics to measure bulk con- ductivities in addition to utilizing a fluid electrical conductivity cell to record fluid conductivities for the tracer experiments. During the tracer tests the relationship between the bulk conductivity and fluid conductivity will be used to study how different tracers flow through the column and how the resi- dence time of the tracers within the immobile pore space affects those fluid dynamics. This relationship will be studied through the simultaneous recording of bulk resistivity geophysical and fluid conductivity measurements during tracer experiments through geologic media. These measurements will be used to help quantify unknown control parameters on anomalous solute transport. Controls would be homogeneously packed, but the variations of packing configu- rations are endless. The purpose of the packing variations is to fully under- stand the solute transport behavior in a variety of differ- ent systems to apply


the results to natural systems.


The outcomes from the column experiments will be applied to developing a more appropriate numerical model for describ- ing transport phenomena through a natural system. Currently the ADE is commonly used to describe solute transport, but it fails to describe a majority of natural systems. To explore the parameters controlling solute transport, I will run a multitude of forward and inverse models to match measured break- through curves from the lab experiments. These data will be used to explore whether an alternate version of the ADE should be applied to predict the behavior of natural systems. This work will be vital for understanding contaminant transport as well as other processes, such as understanding greenhouse gas production from denitrification processes in hyporheic zones (zones within riparian systems where groundwater and surface water reactions occur) that have links to nitrous oxide in the atmosphere.


In addition to being a proponent for the science of hydrology, I am excited to be able to give back to the community through education about the field. Being able to connect science to broader societal application will help aid society in mitigating problems such as human controlled groundwater contamina- tion. In terms of the broader impacts of my work, my plan is to mentor high school students and share with them impacts of hydrologic principles and how their choices and actions impact groundwater resources. To do this, I would like to set up a “hydrology day” at my graduate institution, where I would develop hands-on lab and field components pertinent to hydrology and its broader impacts. Whether that may be


Jul.Aug.Sep 2017 • TPG 15


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