Levels of 1,4 dioxane, an emerging contaminant that can cause cancer, doubled in raw water entering the Cape Fear Public Utility Authority’s Sweeney plant in Wilmington, according to testing conducted by the utility earlier this year.

The utility draws its water from the Cape Fear River. Raw river water had concentrations of 1,4 dioxane at 0.87 parts per billion in January and 1.8 ppb in February. The source of the contaminant is not currently known, nor is the reason for the spike in concentrations. Previous data showed that levels had been consistently low.

After treatment at the plant, the levels of 1,4 dioxane decreased to 0.5 ppb and 0.54 ppb in finished drinking water, respectively. The results became available earlier this week, said Vaughn Hagerty, public information officer for the utility, and were shared with state environmental regulators.

The January results of .5 ppb in finished water were from water taken when Sweeney’s ozone treatment was out of service for about a day, so it is not an accurate representation of typical 1,4-dioxane removal at Sweeney, Hagerty said. Ozone accounts for about half of the removal rates the plant achieves.

The compound is difficult to remove using conventional wastewater and water treatment systems, and usually requires a combination of granulated activated carbon and ozone.

Although there is no federal maximum contaminant level for 1,4 dioxane, the EPA has set a non-enforceable health advisory goal of .35 ppb in drinking water based on a 1 in 1 million cancer risk.

The utility discovered the increase in 1,4 dioxane after it replaced media in granulated activated carbon filters, which helps remove another class of emerging contaminants, PFAS. Utility officials wanted to monitor the impact of those replacements on 1,4 dioxane levels, and began testing for that compound more frequently, beginning in January.

The NC Department of Environmental Quality has identified 1,4 dioxane as a chemical of concern in the Cape Fear River. There are several industrial dischargers of the compound in the river basin. Reidsville, at the headwaters of the Haw River, which feeds the Cape Fear, is considered one potential source of the compound.

The Haw River is also the drinking water source for several communities, including Pittsboro, which has had to install additional treatment systems to manage the concentrations of 1,4 dioxane.

Along the Cape Fear itself, DAK Americas in Fayetteville, which manufacturers plastic resins, such as PET, has also been known to discharge 1,4 dioxane into the Cape Fear. According to the facility’s discharge permit, it conduct annual monitoring for 1,4 dioxane at one of its outfalls that funnels stormwater and wastewater into the river.