Evidence of 1,4-Dioxane Attenuation at Groundwater Sites Contaminated with Chlorinated Solvents and 1,4-Dioxane

Abstract

There is a critical need to develop appropriate management strategies for 1,4-dioxane (dioxane) due to its widespread occurrence and perceived recalcitrance at groundwater sites where chlorinated solvents are present. A comprehensive evaluation of California state (GeoTracker) and Air Force monitoring records was used to provide significant evidence of dioxane attenuation at field sites. Temporal changes in the site-wide maximum concentrations were used to estimate source attenuation rates at the GeoTracker sites (median length of monitoring period = 6.8 years). While attenuation could not be established at all sites, statistically significant positive attenuation rates were confirmed at 22 sites. At sites where dioxane and chlorinated solvents were present, the median value of all statistically significant dioxane source attenuation rates (equivalent half-life = 31 months; n = 34) was lower than 1,1,1-trichloroethane (TCA) but similar to 1,1-dichloroethene (1,1-DCE) and trichloroethene (TCE). Dioxane attenuation rates were positively correlated with rates for 1,1-DCE and TCE but not TCA. At this set of sites, there was little evidence that chlorinated solvent remedial efforts (e.g., chemical oxidation, enhanced bioremediation) impacted dioxane attenuation. Attenuation rates based on well-specific records from the Air Force data set confirmed significant dioxane attenuation (131 out of 441 wells) at a similar frequency and extent (median equivalent half-life = 48 months) as observed at the California sites. Linear discriminant analysis established a positive correlation between dioxane attenuation and increasing concentrations of dissolved oxygen, while the same analysis found a negative correlation with metals and CVOC concentrations. The magnitude and prevalence of dioxane attenuation documented here suggest that natural attenuation may be used to manage some but not necessarily all dioxane-impacted sites.

A Multiple Lines of Evidence Framework to Evaluate Intrinsic Biodegradation of 1,4‐Dioxane

“…To date, there are over 30 published papers that document 1,4‐dioxane biodegradation in environmental and laboratory studies, and biological degradation of this compound is widely recognized. Indeed, environmental studies focusing on natural in situ biodegradation of 1,4‐dioxane are on the rise (Adamson et al., ; Chiang et al., ; Lippincott et al., ).…”

Sustainable Remediation Considerations for Treatment of 1,4‐Dioxane in Groundwater

“…Adamson et al. () report that attenuation of 1,4‐dioxane happens at a small yet significant number of project sites evaluated in California. This study also refers to Air Force databases in which some wells show an equivalent half‐life for 1,4‐dioxane of 2 to 5 years.…”

Editor's Perspective—1,4‐Dioxane Remediation Technology Developments

“…The natural attenuation research performed in the Adamson et al. () study discussed below revealed that 1,4‐dioxane was detected in 191 (32 percent) of the 589 California sites where it was part of the analytical suite. Presumably, the 1,4‐dioxane testing was related to other chlorinated solvent contamination and, therefore, this percentage may be biased higher than the total universe of contaminated sites; however, the results clearly demonstrate the prevalence of 1,4‐dioxane as a groundwater contaminant.…”