Mixed contaminants in soil and groundwater - some fundamental problems and their relevance to remediation and treatment

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Mixed contaminants pose major challenges in soil remediation and groundwater treatment. This proposal addresses the urgent need to study the effects of mixed contaminants in soil and groundwater. The proposed work will go beyond single classes of contaminants (e.g. lead, copper, zinc; petroleum hydrocarbon, brominated or fluorinated compounds). Significant gaps in current understanding of these contaminants include contaminant fate and transport in soil when present in mixtures, and transformation mechanisms, particularly in low-mobility zones, potential synergies among treatment technologies, and transport of mixed contaminants in plumes. My research is primarily focused on understanding fate and transport processes of contaminants, to help improve environmental protection and management practice, with the goals of preventing the spread of contaminants, and reducing adverse health and ecological risks. Many of the perfluoroalkyl and polyfluoroalkyl substances (PFASs) in drinking water are linked to specific sources, such as industrial sites, military fire-training areas and wastewater treatment plants. It is important to recognize that almost all PFAS-contaminated sites contain more than one contaminant in groundwater, often in commingled plumes, including fuel components such as petroleum products, chlorinated solvents and non-chlorinated compounds, e.g. simultaneously released to the sub-surface during fire-fighting training exercises. Despite this common co-existence of two or more contaminants, detailed study of the fate and transport of PFASs in relation to co-contaminants and co-contaminant remediation is largely missing to date. The proposed work will seek to provide insight into the fundamental fate and transport processes that control the impact of PFAS, as well as comingled polycyclic aromatic hydrocarbons (PAHs) and 1,4-dioxane, in groundwater. We will particularly focus on the release and transformation of polyfluoroalkyl to the more problematic perfluoroalkyl substances in source zones, as well as the degree of success of commonly employed remediation technologies, which tend to be based on single contaminants. The specific short-term objectives are to: (1) investigate the fundamental mechanisms controlling sorption and release of PFASs from complex soil media; (2) examine the diffusion and potential abiotic reactions of PFASs and comingled contaminants in low-permeability soils; and determine the effects of PAHs, 1,4-dioxane and degradation byproducts on breakthrough of PFASs and their degradation products in one-dimensional flow-through soil columns. The ultimate goal of improved insight into the fundamental fate and transport processes in these mixed contaminant systems is to facilitate the development and optimization of treatment strategies for management of PFAS-sites in which there are comingled co-contaminants.