Understanding Leaching and Mobility of Per and Polyfluoroalkyl Substances (PFAS) in Concrete
Dr. Tamzen Wood Macbeth, Ph.D., PE, BCEE, Senior Vice President, Remediation Practice Leader, CDM Smith
There are thousands of sites across military (DOD) and public sector (e.g., airports) facilities where aqueous film-forming foam (AFFF) has been used and released, leading to contamination of drinking water resources with per and poly-fluoroalkyl substances (PFAS), such as surface water and groundwater. These facilities have millions of tons of PFAS-contaminated concrete in fire training areas, hangars, runways, aprons, and taxiways/roadways across the United States. In addition, construction and demolition (C&D) materials generated from renovation and demolition projects are typically disposed of in non-hazardous unlined landfills. Consequently, contaminated concrete and solid waste from C&D activities require proper management to prevent PFAS releases at unacceptable levels to groundwater, surface water, and drinking water sources. Recent studies are exploring ways to understand and control PFAS retention and release in soils and concrete. At many facilities, releases of AFFF have resulted in egress and diffusion into and adsorption onto concrete surfaces rendering them potential sources for PFAS leaching. Recent SERDP projects are advancing the science around understanding and controlling PFAS retention and release in soils and concrete. However, concrete has profoundly different compositions and morphological variations, depending on its relative abundance, mineralogy, and geochemistry. Fresh and aged concrete also vary due to slow (re)crystallization and leaching of cations, anions, and reactive silica. In most cases, concrete remains as a monolith with often minimal renewal or repair over its operational lifetime. All of these factors can affect how PFAS migrates or is retained within the concrete matrix. A summary of studies will illustrate some of the PFAS concrete sorption complexity which depends on sorbate and sorbent properties and solution chemistry. PFAS sorption in concrete is controlled by similar mechanisms to that of soils and sediments, as a combination of hydrophobic and electrostatic interactions and interfacial accumulation. However, PFAS sorption to cementitious and aggregate surfaces in concrete also varies temporally due to changes in components (e.g., cement), mineralogy (e.g., incipient recrystallization/Ostwald ripening in concrete), or changes in porosity (e.g., pore-filling secondary minerals in concrete). Additionally, sampling, and analysis methods such as the SPLP (Method 1312) and LEAF (Method 1315) have been used to evaluate PFAS leaching from concrete. Analytical data to evaluate total PFAS using target and non-target analysis will be presented in the context of the potential of PFAS precursor transformation as future sources of PFAS leaching from concrete. Finally, the long-term modeling of desorption and diffusion of PFAS from impacted concrete will be presented in the context of better understanding the timeframe these materials may leach PFAS into the environment.
Dr. Tamzen Macbeth is an internationally recognized remediation expert with 22 years of technical leadership, designing and implementing investigation, design, and remediation programs, including seven years of PFAS site characterization. She has served as the principal investigator or engineering lead for more than 100 complex investigations for federal, state and private clients. She possesses an in-depth understanding of the science of PFAS sampling and analysis, fate and transport and treatment in multiple media. She leads multi-disciplinary project teams, executing simple to complex investigation programs to understand site conditions, evaluating unacceptable impacts, and selecting effective remedial actions. She has successfully transferred the knowledge gained in research and development to engineering practice through authoring more than 100 technical papers, presentations, training manuals and guidance documents, seminars and short courses on remediation topics for the ITRC, USACE, Navy RITS, EPA, AWWA.
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