The Current State of Modeling

Abstract

Today’s groundwater modeling tools are characterized by power, capability, and sophistication that was unthinkable even a few years ago. Boundary conditions (lakes, streams, wetlands) have advanced modules that allow more realistic depictions of the natural world. Models can simulate multiple scales conjunctively (Mehl and Hill 2005; Hunt 2006), or combine different formulations of the underlying mathematical governing equations (Haitjema et al. 2010). The unsaturated zone can be rigorously included (Jones and Woodward 2001; Radcliffe and Simůnek 2010), even on a large watershed scale using kinematic wave approximations (Niswonger et al. 2006). The ability to efficiently simulate unsaturated zone flow has been a critical advance to allow models to explicitly simulate groundwater and surface water interactions at the watershed scale (Therrien et al. 2006; Markstrom et al. 2008). At the same time groundwater flow modeling has attained an advanced state, contaminant transport models have continued to grow to provide improved simulation capabilities for complex field conditions. These include simulation of transport processes in highly heterogeneous media based on the dual-domain mass transfer formulation (Zheng et al. 2011), accommodation of a full suite of biogeochemical reactions through fully coupled multicomponent geochemical-transport models (Prommer et al. 2009; Ma et al. 2010; Parkhurst et al. 2010), and consideration of multiphase and multimedia processes (Pruess et al. 2011). Additionally, numerous efforts are ongoing to develop new or improved mathematical formulations that may deal more effectively with non-ideal contaminant transport behaviors arising from strong aquifer heterogeneity (Berkowitz et al. 2002; Zhang and Benson 2008). One example of such heterogeneity by Bianchi et al. (2011) shows decimeter-scale preferential flow paths with a varying degree of connectivity within a small aquifer cube (Figure 1). Groundwater flow and contaminant transport modeling have been greatly facilitated by rapid technological advances on two fronts: (1) the development of compact and large-memory field sensors that have yielded rich datasets for model calibration, (2) the exponential growth in computing power, which has substantially strengthened