Scott T. Potter, PhD, PE ARCADIS

Scott T. Potter, Ph.D., P.E., is a Vice President and Director of Hydrogeology and Modeling Services at ARCADIS U.S., Inc. He has been with ARCADIS for 20 years, and has more than 25 years of experience in groundwater hydrology and remediation. In his current role, he is Chief Hydrogeologist of ARCADIS providing technical leadership in hydrogeologic assessments and groundwater remediation projects throughout North and South America, and Europe.

Dr. Potter received his B.S. and M.S. in Environmental Engineering, and his Ph.D. in Civil Engineering from The Pennsylvania State University. Prior to working for ARCADIS, he spent nine years with the U.S. Department of Agriculture at the Northeast Watershed Research Center as a hydrologist and a research assistant investigating groundwater flow and solute transport problems in agriculture.

Presentation Description
Large Plume Remediation: Understanding the Mass Flux
Traditional remedial strategies and site investigations are typically focused inward, investing more resources to understand primary source areas and less on the down-gradient dissolved plume. The basis for this difference in allocation of resources is that the effects of transport processes on a plume moving through an aquifer are assumed to result in a relative uniformity in conditions; that we have a smoothing of concentration and mass flux down-gradient that can be characterized with relatively few investigative points. This interpretation of plume structure is driven by conceptualizations built from solutions to the advection-dispersion equation in homogeneous settings, where dissolved plume concentrations vary smoothly in the transverse direction, plume trajectories are unchanged, and peak concentrations and the center of mass travel at similar velocities.
A more realistic conceptualization of plume movement in aquifers recognizes that the majority of groundwater flow and contaminant mass flux occurs through the most permeable materials, and that these can represent a relatively small percentage of the overall aquifer volume. While flow occurs in the less permeable materials, it typically only represents a small proportion of the total ground water flow (Gillham et al., 1984 and Maidment, 1993). This aquifer structure influences solute transport by facilitating fast initial breakthrough due to “flow-focusing” and advection in the highly permeable materials, and diffusive exchange with lower permeability zones. This solute transport behavior is termed “non-ideal” and has been long-recognized in fractured rock and structured soils resulting in the development of various dual-domain non-equilibrium (DDNE) mass transfer models (Coats and Smith, 1964). Recent data-intensive studies of large plumes suggest that DDNE models are appropriate for most aquifers, even relatively “homogeneous” alluvial aquifers (Liu et al., 2007, Guan et al., 2008). Remediation-driven investigations of large plumes need to map (where possible) the major aquifer permeability features and large-scale anisotropy that control advective transport and overall plume orientation. In addition, the local scale aquifer properties that determine the plume behavior also should be characterized and measured to support the remediation system design.