Abstracts

“Characterizing PFAS in Groundwater: Assessment of Tools and Fluorine Balances” by Dr. Charles Schaefer (ER21-5187)

This ongoing ESTCP project supports the Department of Defense’s efforts to understand the nature and quantity of PFAS at sites impacted with aqueous film forming foam (AFFF). Three tools for quantifying the total PFAS present at AFFF-impacted soil and groundwater samples are evaluated: extractable organic fluorine via combustion ion chromatography (EOF-CIC), the total oxidizable precursor (TOP) assay, and PFAS targeted, suspect and non-targeted workflows for the detection of PFAS. A solid phase extraction (SPE) method that maximizes PFAS retention while minimizing inorganic fluorine retention is described. This SPE method is then applied to collected soil and groundwater (source area and downgradient) samples from 12 AFFF-impacted DoD sites, with subsequent analysis using the three previously mentioned analytical tools. The PFAS-related fluorine mass balance is quantitively assessed for each site, focusing on repeatability of each method, comparison among the analytical methods, and potential impacts of site conditions (including source area versus downgradient groundwaters) on the appropriateness of each analytical tool.

“Using Real-Time Remote Sensors to Reduce the Cost of Long-Term Monitoring and Remediation Performance Monitoring at PFAS Vadose Source Zones” by Mr. Neth Walker (ER22-7381)

Mass discharge (i.e., mass flux) of key PFAS from vadose zone sources to groundwater is a key metric for evaluating the strength and long-term behavior of PFAS sources in the vadose zone. This project is developing sensor-based alternatives to complicated on-call field campaigns, where PFAS mass flux will be measured from a few key intermittent recharge events or from high-frequency routine sampling. With real time sensors and new process knowledge gained from this project, PFAS vadose zone sources can be remotely monitored to determine recharge rates and enable intelligent, more efficient sampling by targeting the key times to sample. Sensors are being tested at two DoD PFAS vadose zone sources (one in an arid climate, one in a wet/humid climate) over a two-year demonstration period. New guidance on how to directly measure the mass discharge (mass flux) of PFAS from vadose zone sources to groundwater will be developed, with a recommended three-tiered system for simple, intermediate, and complex sites. An indirect high-level goal is to provide enabling technology for the DoD to perform systematic, science-based portfolio reviews to determine which PFAS vadose source zones need to be remediated and which ones do not pose a significant threat to groundwater.

Speaker Biographies

Dr. Charles Schaefer is the Director of CDM Smith’s Research and Testing Laboratory in Bellevue, Washington. He has over 25 years of experience in the fate, transport, and treatment of organic contaminants in water, soil, and fractured rock. Dr. Schaefer has served as a principal or co-principal investigator for research projects funded by SERDP, ESTCP, the Air Force Civil Engineering Center, the Navy Environmental Sustainability Development to Integration Program, and the Water Research Foundation. He has over 90 peer-reviewed publications and has been awarded the SERDP/ESTCP Project of the Year award 3-times while serving as either a PI or co-PI. In addition, he has served as the technical lead on several site investigation and remedial efforts, supporting many state, municipal, industrial, and federal clients. Dr. Schaefer received his undergraduate and doctoral degrees in chemical and biochemical engineering from Rutgers University.

Mr. Kenneth “Neth” Walker is a senior geologist and engineer with GSI Environmental Inc. in Houston, Texas. He has over twelve years of experience in the environmental field. Mr. Walker has performed environmental site assessments and provided remediation support at sites impacted by chlorinated solvents, hydrocarbons, and PFAS. His activities have included data and statistical analyses, technology screening, green and sustainable remediation footprint analysis, and development and comparison of remedial alternatives. Mr. Walker was a key developer of the Thermal NSZD Dashboard and has designed and implemented thermal monitoring hardware for natural source zone depletion at LNAPL sites. He is a registered Professional Engineer (P.E.) in Texas and California, and a registered Professional Geologist (P.G.) in Texas and Alabama. He received a bachelor’s degree in geology from Washington and Lee University and a master’s degree in civil and environmental engineering from Stanford University.

Dr. Christopher P. Higgins is an environmental chemist at the Colorado School of Mines. He joined Mines in 2009, attaining the title of University Distinguished Professor in 2022. He was the recipient of the 2019 Huber Prize in Civil Engineering Research awarded by the American Society of Civil Engineers and was the lead Principal Investigator for the 2020 Environmental Restoration Project of the Year for the Strategic Environmental Research & Development Program (SERDP). His research focuses on the movement of contaminants in the environment. In particular, he studies chemical fate and transport in natural and engineered systems, with a focus on poly- and perfluoroalkyl substances (PFAS). Dr. Higgins has authored over 175 peer-reviewed publications. He received his A.B. in Chemistry from Harvard University, and graduate degrees in Civil and Environmental Engineering from Stanford University.