Presented on January 26, 2023 | Presentation Slides

“Evaluating and Applying Site-Specific NAPL Dissolution Rates during Remediation” by Dr. Lloyd Stewart, Dr. Michael Kavanaugh, and Dr. Mark Widdowson (ESTCP Project ER19-5223)

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 outcomes 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. The approach is flexible, incorporating a range of DNAPL architectures and processes, and the complexity is adaptable to the data available and to the processes under consideration. Case studies include applications to biological, in situ chemical oxidation (ISCO), and co-solvent treatment. 
 

“Remote Monitoring of Natural Source Zone Depletion Using Temperature Data to Support Long-Term Passive Management Strategies” by Dr. Thomas McHugh and Dr. Kenneth Walker (ESTCP Project ER19-5091)

Many DoD sites are affected by historical releases of light non-aqueous phase liquids (LNAPL) such as fuels, lubricants, and heating oil. Traditionally, costly active treatment technologies like hydraulic recovery, air sparging, multi-phase extraction, or soil vapor extraction have been used to remediate LNAPL sites. These technologies have large carbon footprints, are unsustainable, costly and often not effective enough to meet regulatory closure requirements. As a result, natural source zone depletion (NSZD) is gaining broader acceptance as a practical and effective remedy for mature LNAPL releases. NSZD remedies are far more sustainable and cost-effective than active remedies. Further, natural depletion rates commonly exceed what can be achieved with active remedies. A promising approach to documenting LNAPL NSZD is real-time monitoring of subsurface temperatures and utilizing the heat signature from NSZD to estimate NSZD rates. Similar to a compost pile, the bacterial degradation of LNAPL in the subsurface generates heat. After a one-time field installation, continuous, remote monitoring essentially eliminates routine site visits and operations and maintenance, which further improves the environmental impact of monitoring and the health and safety of field personnel. This presentation will discuss the application of remote temperature monitoring at two DoD sites impacted by LNAPL. These demonstrations were used to validate remote monitoring of NZSD using temperature data with a focus on (1) evaluation of second-generation temperature monitoring systems to improve data quality and reduce costs, (2) demonstration of improved methods to separate the heat signal associated with biodegradation of petroleum from seasonal and other sources of temperature fluctuations in soils (i.e., improved background correction), and (3) demonstration that temperature-based approaches to quantifying NSZD rates are particularly suited for LNAPL source areas located below buildings or other paved surfaces. The demonstration results show that remote temperature monitoring is an effective approach for documenting and quantifying NSZD at LNAPL-impacted sites. 
 

Dr. Lloyd “Bo” Stewart is the vice president of Praxis Environmental Technologies, Inc. in Burlingame, California. He has 35 years of experience in applied research related to environmental restoration including technology development, technology testing and evaluation, and remedial design. Dr. Stewart’s hands-on experience includes laboratory testing, pilot-scale field investigations, and full-scale field implementations. His work on different remediation technologies includes mathematical modeling of soil vapor extraction (SVE), thermal enhanced extraction, steam injection, enhanced bioremediation, and in situ chemical oxidation. He has served as principal investigator on numerous innovative remediation and site characterization demonstrations for the Air Force Civil Engineer Center, Army Environmental Center, Department of Energy, U.S. Environmental Protection Agency, SERDP and ESTCP. He is a registered mechanical engineer in California. Dr. Stewart received a bachelor’s degree from North Carolina State University, a master’s degree from Georgia Institute of Technology, and a doctoral degree from the University of California, Berkeley, all in mechanical engineering.
 

Dr. Michael Kavanaugh is a senior consultant with Geosyntec Consultants, Inc. with over forty years of consulting experience. Dr. Kavanaugh has served project engineer, project manager, principal-in-charge, or technical director for over 400 projects conducted in the U.S. and internationally on a broad range of environmental topics. He has authored or co-authored more than 40 peer-reviewed technical papers, and has edited and contributed to six books on water quality, water treatment, groundwater remediation, and aquifer restoration. He has served as principal or co-principal investigator for several SERDP and ESTCP projects. Dr. Kavanaugh is a registered chemical engineer in California, a Board Certified Environmental Engineer, and a Fellow of the Water Environment Federation. He was elected to the National Academy of Engineering in 1998 for his contributions to water quality management . and remediation of contaminated sites. He earned bachelor’s and master’s degrees in chemical engineering from Stanford and the University of California, Berkeley, respectively, and a doctoral degree in civil and environmental engineering from the University of California, Berkeley.
 

Dr. Mark A. Widdowson is a professor and the department head of the Charles E. Via Jr. Department of Civil and Environmental Engineering at Virginia Tech. His research activities include studying the fate and transport of chemicals of concern in groundwater systems, remediation of subsurface contamination, and groundwater resource management. His site remediation expertise includes modeling and decision-support tools for Remedial Investigation/Feasability Study (RI/FS) and long-term site management at Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) sites. Dr. Widdowson is the author and principal investigator of the software tools Sequential Electron Acceptor Model, 3D transport (SEAM3D) and Natural Attenuation Software (NAS), which are used to evaluate remedial strategies to address site remediation objectives in conjunction with economic and risk assessment models. He is a registered professional engineer in South Carolina. He received a bachelor’s degree in civil engineering from the University of Cincinnati, a master’s degree in water resources engineering from the University of Kansas, and a doctoral degree in civil engineering from Auburn University.
 

Mr. Kenneth “Neth” Walker is a senior geologist and engineer with GSI Environmental Inc. in Houston, Texas. He has over eleven years of experience in the environmental field and has performed environmental site assessments and provided remediation support at numerous facilities across the United States under the applicable state and federal regulatory programs, including CERCLA/Superfund, for multiple contaminants in soil, solid waste, soil gas, surface water, and groundwater. His activities have included data and statistical analyses, technology screening, green and sustainable remediation footprint analysis, and development and comparison of remedial alternatives. Mr. Walker was a key developer of the Thermal NSZD Dashboard and has designed and implemented thermal monitoring hardware for natural source zone depletion at LNAPL sites. Mr. Walker is a registered Professional Engineer (P.E.) in Texas and California and a registered Professional Geologist (P.G.) in Texas and Alabama. He received a master’s degree in Civil and Environmental Engineering, Environmental Fluid Mechanics and Hydrology, from Stanford University, and a bachelor’s degree in Geology from Washington and Lee University.