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Addressing Per- and Poly-Fluoroalkyl Substances Through Source Water Assessments and Advanced Treatment Using Powdered Activated Carbon, Granular Activated Carbon, and Ion Exchange Samantha Black, Katie Walker, Gwen Woods-Chabane, Pete D’Adamo, and Dell Harney
P
er- and poly-fluoroalkyl substances (PFAS) are manmade fluorinated compounds of emerging concern in the water industry. The PFAS are persistent and stable in the environment due to the strong chemical bond between carbon and fluorine atoms. They have been used largely for their water- and oil-repellent properties in several applications, including consumer products and aqueous film-forming foam (AFFF) to fight petroleum-based fires. Communities in other countries and across the United States, including the City of Greensboro (city), N.C., have detected PFAS in drinking water supplies, typically at nanograms per liter (ng/L) concentrations. Elevated levels can be associated with facilities that use or manufacture these chemicals, such as airports (both domestic and military) and firefighting training facilities, as well as disposal sites of PFAS-contaminated wastes.
Treatment Plant (WTP), a 24-mil-gal-perday (mgd) conventional treatment facility. A schematic of the Mitchell WTP processes is provided in Figure 1. One of the city’s long-term goals is to provide a robust and flexible advanced treatment process capable of treating both emerging and regulated contaminants, and one family of emerging contaminants includes PFAS. The U.S. Environmental Protection Agency (EPA) has established a lifetime health advisory level (LHAL) of 70 ng/L for the sum of two PFAS: perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA). The PFOS and PFOA have been detected at trace concentrations in the city’s water supply at the Mitchell WTP, along with other PFAS. The LHALs for other PFAS are anticipated in mid-2022 and it’s expected that EPA will publish additional PFAS regulations in the next year.
City of Greensboro Mitchell Water Treatment Plant
Source Water Assessment
The city operates the Mitchell Water
During sampling, as part of the third Unregulated Contaminant Monitoring Rule
Samantha Black, Ph.D., P.E., is a water treatment process engineer and associate at HDR in West Palm Beach. Katie Walker, P.E., is a drinking water lead and associate at HDR in Raleigh, N.C. Gwen Woods-Chabane, Ph.D., is a drinking water quality lead and senior professional associate at HDR in Portland, Ore. Pete D’Adamo, Ph.D., P.E., is a water treatment technical lead and principal professional associate at HDR in Vienna, Va. Dell Harney is the water supply manager at the City of Greensboro in Greensboro, N.C.
(UCMR) from 2013 to 2015, some of the city’s water samples had combined levels of PFOS and PFOA that exceeded 100 ng/L. These findings led to a two-year watershed investigation to identify hotspots of PFAS contamination in the city’s raw water supply. This two-year study included monthly sampling of 30 sites throughout the city’s watershed, such as lakes that supply raw water to WTPs, streams that discharge into these lakes, ponds near potential
Figure 1. Simplified Process Schematic for the Mitchell Water Treatment Plant
10 July 2022 • Florida Water Resources Journal
