Recent US EPA data show that seven of the twenty highest 1,4-dioxane concentrations in US drinking water occur in communities located in the Cape Fear River watershed of North Carolina. 1,4-Dioxane is a likely human carcinogen, and a one-in-a-million excess cancer risk is associated with the lifetime consumption of drinking water containing 0.35 mg/L 1,4-dioxane. Objectives of this research are (1) to establish the spatial and temporal variability in 1,4-dioxane concentrations and mass flows in the Cape Fear River watershed, and (2) to assess the effectiveness of water treatment processes and point-of-use (POU) treatment devices for 1,4-dioxane removal. Over 50 sampling points were strategically selected in the Cape Fear River watershed to bracket possible sources, and monthly samples were taken between October 2014 and October 2015. Occurrence data suggest that wastewater discharges from three municipalities are primarily responsible for the elevated 1,4-dioxane levels. Concentrations as high as 1,700 mg/L were measured downstream of municipal wastewater discharges. Results for two conventional drinking water treatment plants showed that 1,4-dioxane concentrations were not attenuated. At a third utility, raw and settled water ozonation oxidized ~67% of the influent 1,4-dioxane. Bench-scale experiments showed that 1,4-dioxane levels of ≤ 0.35 mg/L can be reached with feasible ozone doses when ozone is added to settled water. However, high background levels of bromide in the Cape Fear River yielded bromate levels above the drinking water standard of 10 mg/L Finally, pitcher filters and refrigerator filters were evaluated. POU filter performance varied dramatically in terms of adsorptive 1,4-dioxane removal, and desorption of 1,4-dioxane lowered the effectiveness of POU devices when high influent 1,4-dioxane concentrations were followed by low influent 1,4-dioxane concentrations.
