Senior Environmental Engineer
Dr. David Adamson has more than 14 years of environmental project experience in academic research and environmental consulting, and he is a licensed Professional Engineer in Texas. He has worked as a post-doctoral research associate at Cornell University, and he has held lecturer, research scientist, and Adjunct Assistant Professor positions at Rice University in the Civil and Environmental Engineering Department. He has conducted and published research on a variety of areas related to subsurface contamination and biological remediation. Since joining GSI in 2004, Dr. Adamson’s professional experience includes site investigation, characterization, and remediation, with projects in the U.S., Europe, Latin America, and the Middle East, including the design, implementation, and management of full-scale remediation projects. He has extensive expertise in projects dealing with natural attenuation, source zone characterization, emerging contaminants, matrix diffusion, and the developm ent and testing of innovative treatment technologies. He has served as a Principal Investigator or co-Principal Investigator on several DoD-sponsored research projects, including those focused on 1,4-dioxane, innovative long-term monitoring strategies, enhanced amendment delivery systems, and improved characterization and treatment methods for contaminants in low permeability matrices.
Implications of Matrix Diffusion on 1,4-Dioxane Persistence at Contaminated Groundwater Sites
Management of groundwater sites impacted by 1,4-dioxane can be challenging due to the migration potential of 1,4-dioxane and its perceived recalcitrance. This study examined how diffusion of mass into and out of lower-permeability zones contribute to dioxane’s persistence relative to co-released chlorinated solvents. Different release scenarios were evaluated within a two-layer aquifer using a modeling framework designed to estimate the distribution of 1,4-dioxane and TCA during the period when the source was loading the low-permeability zone via diffusion, as well as the period when the source was depleted and back diffusion of contaminant mass occurred. Despite 1,4-dioxane’s much shorter loading period, the mass of 1,4-dioxane stored within the low-permeability zone was much larger than that predicted for TCA. Even 80 years after release, this mass resulted in aqueous 1,4-dioxane concentrations that were still several orders-of-magnitude higher than potentially-applicable criteria. Within the downgradient plume, diffusion contributed to higher concentrations and enhanced penetration of 1,4-dioxane into the low-permeability zones relative to TCA. This study highlights that 1,4-dioxane’s behavior follow its release to the subsurface results in present-day source zones that are much different than those for chlorinated solvents. 1,4-dioxane mass within the transmissive portions of the source zone is quickly depleted due to characteristics that were shown to favor both diffusion-based storage as well as groundwater transport, leaving little mass to treat using conventional means. Furthermore, the results suggest that back diffusion of 1,4-dioxane mass from the low-permeability zones may be serving as the dominant long-term “secondary source” at many contaminated sites.