Establishing the prevalence and relative rates of 1,4-dioxane biodegradation in groundwater to improve remedy evaluations

Development of a Quantitative Framework for Evaluating Natural Attenuation of 1,1,1‐TCA, 1,1‐DCA, 1,1‐DCE, and 1,4‐Dioxanein Groundwater

“…As a result, it is possible that a site may have a limited dataset for 1,4‐dioxane, especially if it is a recent addition to the monitoring program. Several of the sites included in the field effort had little existing monitoring data on 1,4‐dioxane (Adamson et al 2022). In these cases, it may be difficult to establish a clear trend in concentration along a flowpath in groundwater at appropriate monitoring points.…”

“…This was accomplished by updating an existing Microsoft Excel spreadsheet application for evaluating chlorinated ethenes, the Biological Pathway Identification Criteria (BioPIC) (Lebrón et al 2015), so that it includes these new decision matrices for 1,4‐dioxane and the chlorinated ethanes. This leverages recent work that focused on developing and validating a 14 C‐1,4‐dioxane assay for 1,4‐dioxane biodegradation (Ramos‐Garcia et al 2022), as well as a study that documented the prevalence of this biodegradation capacity and other lines of evidence for 1,4‐dioxane attenuation at field sites (Adamson et al 2022). The resulting updated BioPIC tool for 2021 guides users on how to collect data that will serve as valuable lines of evidence for MNA for an expanded set of compounds.…”

“…The Decision Framework for 1,4‐dioxane was applied to 10 study sites where field data were collected; a summary of the site evaluations is provided in Adamson et al (2022) with additional details in Danko et al (2021). It is important to note that even when several lines of evidence for 1,4‐dioxane attenuation are positive at a particular site, it does not necessarily imply that all lines of evidence will be met.…”

“…For example, the 1,4‐dioxane summary assessment generated for one of these sites (Site 8 in Adamson et al 2022) after applying BioPIC is provided in Figure 1. This site is a former chemical waste disposal area where relatively large volumes of solvents and other chemical wastes were disposed for several decades.…”

“…In part, this reflects the current limitations in some of our diagnostic tools, including the use of groundwater from long-screened monitoring wells to evaluate degradation capacity and geochemical conditions that may be localized to specific depth intervals within an aquifer. For example, the 1,4-dioxane summary assessment generated for one of these sites (Site 8 in Adamson et al 2022) after applying BioPIC is provided in Figure 1. This site is a former chemical waste disposal area where relatively large volumes of solvents and other chemical wastes were disposed for several decades.…”