1,4-Dioxane is a clear liquid primarily used as a solvent in manufacturing processes. It mixes easily with water and degrades slowly. The chemical is classified as a likely carcinogen by the U.S. Environmental Protection Agency, the U.S. Department of Health and Human Services, and the International Agency for Research on Cancer.
According to an EPA sampling program, North Carolina has the third-highest measured concentration of 1,4-dioxane in drinking water in the nation. The state ranked fourth highest in the number of impacted drinking water systems, with most detections occurring in the Cape Fear River Basin.
The EPA has a Drinking Water Health Advisory Level of 35 parts per billion (ppb) for 1,4 dioxane, based on a 1-in-10,000 cancer risk for lifetime exposure.
There are a number of potential sources of 1,4-dioxane in the Cape Fear River. One source identified by the N.C. Department of Environmental Quality (NCDEQ) is the City of Greensboro’s T.Z. Osborne Wastewater Treatment Plant, which discharges to a tributary of the Haw River, which flows into the Cape Fear River. The majority of 1,4-dioxane in T.Z. Osborne’s discharge originates from one or more of its industrial customers that send wastewater to the plant for treatment. The City of Greensboro is under a Special Order of Consent with NCDEQ to address elevated levels of 1,4-dioxane in the Cape Fear River tied to emissions from T.Z. Osborne.
Raw, untreated water sourced from the Cape Fear River is treated at the Sweeney Water Treatment Plant. Sweeney is among the most advanced treatment plants in North Carolina and one of the few treatment plants equipped to treat for 1,4-dioxane. Sweeney’s treatment technology includes ozonation and biological filters, which are able to remove an average of two-thirds of 1,4-dioxane from untreated water.
Since January of 2019, 1,4-dioxane levels in finished water from the Sweeney plant has only once gone over 2 ppb, still much lower than the health advisory level. (Over the same period of time, 1,4-dioxane levels in raw water have peaked over 4 ppb three times — again, that's well under the health advisory level).
The risk assessment concludes that North Carolinians are exposed to 1,4-dioxane concentrations that may be more than double the national average in drinking water and as much as four times the average in surface and groundwater.
DEQ enlisted assistance from experts in the field and used the latest scientific information to complete the assessment. DEQ’s human health risk assessment supports the application of a science-based cancer slope factor in determining a water quality standard for 1,4-dioxane that protects drinking water supplies.
DEQ continues to use its existing authority under state and federal law to address 1,4-dioxane discharges and protect public health and drinking water supplies.
The assessment is available online.