“Cost-Effective and High-Resolution Subsurface Characterization Using Hydraulic Tomography” by Dr. Chin Man Mok
Inaccurate or inadequate delineation of groundwater flow fields at appropriate resolution has resulted in poor remediation performance at many recalcitrant sites with complex hydrogeology. Characterizing such sites by conventional methods is often difficult and expensive. This ESTCP project demonstrated that Hydraulic Tomography (HT) is a cost-effective high-resolution site characterization technique for delineating the spatial distributions of hydraulic conductivity (K) and storativity, which is critical for better management of contaminated groundwater sites. HT involves conducting a series of aquifer pumping tests by perturbing the hydraulic stresses in the subsurface differently in each test, which is analogous to hydraulically scanning the subsurface from many different angles. Then, the complete data sets of observed hydraulic head responses over a well network are jointly analyzed. This presentation described the demonstrations at a local-scale site and a field-scale site. The results confirmed that HT provides more accurate site characterization than conventional techniques. The results also illustrate that HT can be readily applied at other DoD sites using existing networks of groundwater extraction/injection and observation wells. In addition, this presentation described further enhancements by integrating HT with geophysical tomography as well as applications to remediation reliability evaluation and optimization.
“Contaminant Flux Reduction Barriers for Managing Difficult-to-Treat Source Zones in Unconsolidated Media” by Ms. Poonam Kulkarni
Groundwater flow reduction using physical barriers (e.g., permeation grouting, slurry walls) may be an underutilized technology for managing difficult-to-treat chlorinated solvent source zones. The physical barrier approach provides two benefits for improving groundwater quality at chlorinated volatile organic carbon (CVOC) sites. The well-known benefit involves physically reducing the mass flux of contaminants leaving the source zone, thereby reducing risk and making the downgradient plume more amenable for management by natural attenuation processes. A lesser-known benefit involves increasing the Natural Source Zone Depletion (NSZD) rate within the CVOC source zone by diverting competing electron acceptors (e.g., dissolved oxygen, nitrate, and sulfate), thereby creating an enhanced reductive dechlorination zone (ERDZ). This presentation described the following from a recently completed ESTCP project: (1) results from a small-scale field demonstration of the permeation grouting technology; (2) a permeation grouting decision flowchart which informs the user which sites are and are not appropriate for a permeation grouting barrier; and (3) the ESTCP Source Barrier Toolkit which explains the types, applicable sites and approximate costs of three different types of physical barriers (permeation grouting, slurry walls, sheet pile wall), and provides insights and a calculator illustrating the benefits that will accrue if a physical barrier around a chlorinated solvent source zone is installed.
Dr. Chin Man (Bill) Mok is a Vice President and Principal with GSI Environmental Inc. in Oakland, California, as well as an adjunct professor at the University of Waterloo and Rice University. He has over 30 years of consulting experience in environmental, water resources, geotechnical/geological and seismic projects. Stochastic groundwater flow and subsurface chemical transport has been one of his areas of research and practice since his doctoral studies. He has served as a principal investigator on several high-resolution site characterization projects funded by the ESTCP, Air Force and Department of Energy on delineation of subsurface heterogeneity and preferential pathways by hydraulic and geophysical tomography. He is a licensed Civil Engineer, Geotechnical Engineer and Geologist, and a Rudolf Diesel Industry Fellow of the Technical University of Munich. He earned a bachelor's degree in civil and structural engineering from the University of Hong Kong and master's and doctoral degrees in civil and environmental engineering from the University of California at Berkeley.
Ms. Poonam Kulkarni is an Environmental Engineer with GSI Environmental Inc. in Houston, TX. She has over 12 years of experience in engineering and environmental consulting. She has served as co-principal investigator on multiple DoD-sponsored research projects that apply innovative strategies to characterize and treat conventional and emerging contaminants in groundwater at a wide range of sites. These include the development of an innovative enhanced bioattenuation technology for dense non-aqueous phase liquid (DNAPL) sites, characterization of the nature and extent of per- and polyfluoroalkyl substances (PFAS), methods to evaluate and reduce variability in groundwater monitoring data, as well as a demonstration of passive soil vapor extraction technologies. She also has extensive professional experience in methods to evaluate and enhance Natural Source Zone Depletion (NSZD) at hydrocarbon sites with a focus on thermal monitoring and temperature enhancements of biodegradation. In addition, she specializes in the analysis and interpretation of large public and private databases focusing on the extent and attenuation of constituents and their key driving factors, including the effectiveness of remediation efforts. Ms. Kulkarni earned a bachelor’s degree in chemical engineering from the University of Texas, Austin and a master’s degree in civil and environmental engineering degree from Rice University.