Field applications of hydrogeochemical modeling: What we can learn about complex interactions between transport, geochemistry, and biology

Gene-Hua Crystal Ng, Assistant Professor, Department of Earth Sciences, University of Minnesota

The spread of contaminants through our groundwater systems involve complex interactions among physical, geochemical, microbial, and plant ecological processes.  Reactive-transport models provide a tool for evaluating these dynamical links.  Two examples will be presented that demonstrate how field observations and reactive-transport modeling together generate insights into the multiple factors controlling contaminant fate.  The first example looks at secondary water quality impacts at a crude oil spill site near Bemidji, MN, which has served as a long-term research site for over 35 years.  Its uniquely extensive dataset was used to develop a reactive-transport model that describes secondary plumes in aquifers - such as those of iron and methane - that are triggered as the primary hydrocarbon contaminant biodegrades.  The second example describes on-going research on the Iron Range in northeast Minnesota examining groundwater's influence on how high sulfate concentrations in lakes and streams impact wild rice.  A suite of newly collected physical and geochemical field measurements are integrated with a reactive-transport model to evaluate how the regional groundwater system and surface water interact with the stream bed hyporheic zone where wild rice grows.  In both examples, a process-based model represent coupled interactions not readily measured, while data are crucial for ensuring that models simulate field-scale relevant processes.