Dr. Lloyd Steward
Praxis Environmental Technologies, Inc.
Dr. Stewart has over 30 years of experience in all aspects of environmental remediation research and development, including technology development; technology testing and evaluation; and remedial design. His hands-on experience includes laboratory testing, pilot-scale investigations, and full-scale implementations, supported by applied mathematical modeling. He has served as principal investigator on numerous innovative remediation and site characterization demonstrations for EPA, DoD, and SERDP and ESTCP. He has published papers and guidance on soil vapor extraction (SVE), vadose zone characterization, vapor intrusion, NAPL mass transfer, steam injection and UXO energetics release.
Evaluating and Applying Site-Specific NAPL Dissolution Rates During Remediation
Groundwater remediation of dense non-aqueous phase liquid (DNAPL)-impacted sites is costly and typically controlled by mass transfer constraints of DNAPL dissolution, even with enhancements. The Department of Defense (DoD) needs practical and scientifically sound methods to evaluate the effectiveness of past remediation, the potential benefit of additional treatment, and the post-remediation longevity of residual sources and back diffusion. Current approaches to predict the outcomes of DNAPL remediation include (1) screening models which lack a physical basis, and (2) coupled numerical transport and reaction models which are complex and costly. This presentation will describe an intermediate alternative, a volume-averaged model at dimensional scales of DNAPL sources and remedial actions. This approach employs well-established dissolution models using characteristic dimensions and DNAPL saturations combined with first- and second-order models of remedial processes. Volume-averaging minimizes spatial specificity, limits required site-specific inputs and reduces the burden of parameter estimation and calibration. As demonstrated with live calculations, the approach is flexible, incorporating a range of DNAPL architectures and processes, and is adaptable to the complexity of available data and remedial processes. Case studies include applications to enhanced biological degradation, in situ chemical oxidation (ISCO), and co-solvent treatment on the laboratory and field scales.