No atypical concentrations of 1,4-dioxane were detected in CFPUA’s daily monitoring of water from the Cape Fear River through July 16.
CFPUA began daily sampling on July 1 after the City of Greensboro said 1,4-dioxane had been detected at an average concentration of about 615 ppb in discharge from its T.Z. Osborne Wastewater Treatment Plant. The discharge eventually flows to the Cape Fear River and would be expected to undergo significant dilution before reaching CFPUA’s intakes at Kings Bluff.
To provide initial screening, the first few days’ samples were analyzed using a method that provides expedited results but is less precise and has a higher detection limit than the higher-resolution analysis used for CFPUA’s ongoing monthly 1,4-dioxane monitoring. Samples for higher-resolution analysis were added to monitoring related to the Greensboro discharge starting July 6. This higher-resolution analysis takes longer to process but provides more precise results and has a lower detection limit. Results of CFPUA’s higher-resolution analysis are listed in the table below:
Results in parts per billion (ppb) * |
Sample Date | Sweeney Raw Water | Sweeney Finished Water |
July 6, 2021 | 1.6 | 0.34 |
Saturday, July 10, 2021 | 1.7 | 0.4 |
Sunday, July 11, 2021 | 1.6 | 0.32 |
Monday, July 12, 2021 | 0.94 | 0.33 |
Tuesday, July 13, 2021 | 0.36 | <0.07 |
Wednesday, July 14, 2021 | 0.49 | 0.21 |
Thursday, July 15, 2021 | 0.94 | 0.14 |
Friday, July 16, 2021 | 1.3 | 0.16 |
|
*Detection limit is 0.07 ppb
These results are within the typical range of variation of results from CFPUA’s ongoing monthly 1,4-dioxane monitoring.
Based on current flow rates and other factors, CFPUA staff believes impacts from Greensboro’s discharge on 1,4-dioxane levels in Cape Fear River Water at the Kings Bluff raw water intakes would have been detected by July 14. As such, CFPUA has suspended daily 1,4-dioxane monitoring. Monthly monitoring will continue.
The Sweeney Water Treatment Plant treats water from the Cape Fear River to produce drinking water for about 80 percent of CFPUA customers. Sweeney is among the few facilities equipped to also treat for 1,4-dioxane. Ozonation and biological filters at Sweeney typically achieve about two-thirds removal of 1,4-dioxane from raw water during treatment.
An industrial solvent, 1,4-dioxane is considered by the U.S. Environmental Protection Agency to be a likely carcinogen. Although 1,4-dioxane is not regulated, the EPA has established a drinking water concentration of 0.35 ppb as presenting a 1-in-1 million cancer risk level for lifetime exposure to 1,4-dioxane. The N.C. Department of Environmental Quality states that U.S. EPA has a Drinking Water Health Advisory Level of 35 ppb based on a 1-in-10,000 cancer risk for lifetime exposure.