Theme: 7. Per- and Polyfluorinated Alkyl Substances (PFAS)

Topic Area: 7h2. PFAS Fate and Transport in Surface Water

Formatted Title:

Polymer-Based Per- and Polyfluoroalkyl Substances (PFAS) as Long-Term Source to Surface Water in the Alabama River System

Background/Objectives:

Much of the carpet manufacturing in the United States is concentrated in the headwaters of the Alabama river system near the city of Dalton in northwestern Georgia, USA. At least 23 million kilograms (kg) of PFAS-based polymers were used by facilities in Dalton to treat carpets for repellency characteristics from 1996 until the phase-out of PFAS for carpet treatment in 2019. The Alabama River headwaters near Dalton include the Conasauga River, a tributary of the Coosa River. Previous sampling of the Conasauga River upstream and downstream of Dalton indicated a significant source of PFAS to the river. The largest increase in PFAS concentrations in the Conasauga River is in the vicinity of the 9,600-acre land application system (LAS) used by the publicly-owned wastewater treatment works in Dalton. The LAS, which began operations in 1986, applies wastewater from Dalton Utilities’ wastewater treatment plants to the land surface via spray application. Concentrations of PFOA (~1,700 ng/L) and PFOS (~5,000 ng/L) in streams draining the LAS appear to represent some of the highest concentrations reported for surface waters.

Approach/Activities:

A mass balance approach was used to evaluate the mass flux of PFAS to the LAS, from the LAS to the Conasauga River, and in the Coosa River 150 miles downstream of the LAS in Gadsden, Alabama. A robust estimate of the mass flux in the Coosa River was calculated from the frequent monitoring of PFAS in the river from 2016 to 2022. The mass fluxes were calculated based on measured PFAS concentrations and stream flows. The stream flows were derived from U.S. Geologic Survey monitoring data and, for ungaged locations, on area-weighted calculations derived from runoff coefficients from nearby gaged watersheds. The amount of water sprayed at the LAS, used for calculating the mass flux to the LAS, was from data collected by Dalton Utilities.

Results/Lessons Learned:

Streams draining the LAS discharge approximately 1,000 kg per year of PFAS to the Conasauga River of which approximately 380 kg is PFOA and PFOS. The wastewater that is currently applied at the LAS accounts for less than 5% of the PFAS discharging to the Conasauga River. The current discharge of PFAS from the LAS to the river accounts for more than 60% of the PFOS and PFOA measured in the river 150 miles downstream in the Coosa River.

It has been more than a decade since 8+ chain PFAS (which can degrade to produce PFOS and PFOA) have been used widely in carpet facilities. As a result, the persistence of these compounds in the surface water flowing from the LAS cannot be attributed to ongoing releases. The presence and potential amount of PFAS-based polymers at the LAS has not been investigated as past soil, vegetation and biosolids sampling has not targeted these compounds. As a result, the significance of these polymers in the soil and vegetative matter has been overlooked as a long-term source of terminal PFAS in the environment.

Studies of PFAS-based polymers have shown degradation of the polymer with half-lives ranging from 10 to 112 years. Degradation is a two-step process: (1) cleavage of fluorinated side-chains from the polymer backbone and (2) degradation of the detached PFAS. The multi-step and long-degradation rates of the PFAS-based polymers likely accounts for the continuing releases of PFAS observed emanating from the LAS. The results of this study provide indirect evidence of the slow degradation of PFAS-based polymers as a continuing source of PFAS in the environment.

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Gary Davis