P. Suresh C. Rao Lee A. Rieth Chair & Distinguished Professor School of Civil Engineering Purdue University

Dr. Suresh Rao is the Lee A. Rieth Chair & Distinguished Professor of Environmental Engineering in the School of Civil Engineering at Purdue University. Prior to joining Purdue in 1999, he served for 25 years on the faculty at the University of Florida. Dr. Rao’s diverse range of research interests have spanned from lab-scale, process-level studies on environmental fate and transport of various contaminant classes to aquifer-scale and watershed-scale studies on water quality impacts of agricultural and industrial land uses. Dr. Rao has been involved in development and use of models for research purposes and for decision making, with applications in soil quality assessments, groundwater vulnerability, contaminated site remediation, and watershed management.

Presentation Description
Contaminant Mass Flux in Aquifers
Numerous techniques are now available for characterization of source zones and dissolved plumes at contaminated sites, and to monitor the performance of the remediation technologies implemented. These techniques can be broadly grouped into: (1) point measurements (e.g., soil coring and multi-level groundwater sampling), and (2) spatially or temporal integrated sampling (e.g., partitioning inter-well tracer tests; integral pump tests). The first group of techniques provides highly resolved data on spatial variations in site characteristics, but only generates synoptic information and suffers from significant uncertainties unless a large number of samples are collected. Spatially and/or temporally integrated site parameters that define the source zone and plume may be more useful and may have smaller uncertainties, but at the expense of the loss of spatial/temporal resolution needed for certain applications.

Recent studies have suggested the use of contaminant fluxes, J (M L-2 T-1)), and contaminant mass discharge, MD (MT-1), are useful as the integrated parameters that describe contaminant source behavior and provide a means to link source behavior to dissolved plume response. Contaminant mass discharge across a source control plane can be used as a measure of the source strength, while mass discharge at multiple control planes within the dissolved plume can be used to estimate plume-averaged contaminant degradation rates. Characterization of contaminant flux distribution at the source control plane also provides valuable information about the spatial distribution of source mass and helps in performance evaluation of aggressive source remediation. Over the past two decades, the theoretical underpinnings of the mass-flux approach have been critically examined, and the utility of this approach has been explored extensively in a series of lab- and field-scale studies conducted in the U.S., Europe, New Zealand, and Australia.

While there is now a general technical consensus that flux-based characterization and site management has a sound theoretical basis and that multiple flux-measurement techniques are available, this approach continues to find limited acceptance within the regulatory and user community. Why is practice lagging science? In this session, we will explore the varied reasons for this state of current practice. Prof. James Jawitz presents the keynote talk and give an overview of the theoretical basis for the flux-based approaches, and offers an interesting approach to estimating the required parameters. Dr. Murray Einarson then offers a practitioner's perspective as to why the user community has not widely adopted the flux-based approaches, and how the obstacles might be overcome. Next, Dr. Herb Levine presents a regulator's perspective on how mass-flux can be used as a performance measure in evaluating remedial actions at contaminated sites. Finally, Dr. Tamzen Macbeth presents the results from a case study of how mass-flux measurements were used at DNAPL site to evaluate the performance of in-situ bioremediation of a DNAPL source zone. Several posters on related topics are also being presented at the RemTec09 Summit.