Section Manager/Emerging Contaminants Lead
Burns & McDonnell
Brian Hoye is a Section Manager at Burns & McDonnell with in-depth experience in the fields of remediation and site investigation. He is the emerging contaminants and per-and polyfluoroalkyl substances (PFAS) lead at Burns & McDonnell. In this role, Brian leads multi-disciplinary teams working to overcome challenges associated with the investigation and remediation of PFAS. He also participates in various PFAS work groups and regulatory coalitions that are influencing the national response to PFAS. He earned a bachelor's degree in geology and environmental studies from Cornell College, and a master's degree in environmental science from Florida Gulf Coast University and is a Registered Professional Geologist in multiple states.
PFAS Site Characterization: Why We Need to Rethink Our Approach to Remedial Investigations
Remediating PFAS in groundwater presents numerous challenges due to the complexities and unknowns associated with this class of compounds. The wide variety of potential PFAS sources, limited knowledge of the physicochemical characteristics associated with these compounds, and the low concentration screening levels that continue to be established for PFAS and drive plume delineation have confounded site characterization efforts. Specific PFAS characteristics that drive uncertainties and site characterization challenges include high solubility; generally low, but also variable (depending on the PFAS compound class) adsorption affinity; high recalcitrance (terminal PFAS are not biodegradable); surfactant behavior (attracted to air-water interfaces); and susceptibility to electrostatic forces (due to ionic form in solution). The typical industry-approach to site characterization for most contaminants (e.g., chlorinated volatile compounds [cVOCs], petroleum hydrocarbons, pesticides/herbicides) has been to identify the location of the release to the subsurface (source area) and then proceed with a groundwater sampling program that involves “stepping out” from the source area until reported contaminant concentrations are below the established regulatory criteria. However, considering the complex PFAS chemistry, potential for multiple sources, chemical persistence, and very low (part per trillion) screening concentrations and detection limits, the conditions governing site characterization differ greatly from those associated with other contaminants, necessitating a site characterization workflow that differs from the industry standard. A step out, “plume chasing” approach to plume delineation is not recommended for most PFAS sites primarily because it has high potential to result in the flawed association of PFAS impacts with other sources. Additionally, this can be cost prohibitive and require many rounds of investigation and forensic analysis if PFAS groundwater detections are not clearly associated with the source and pathway of the PFAS release being characterized.
A more strategic, effective approach to characterizing the nature and extent of a PFAS plume is to first define potential migration pathways from the source area to potential receptors. This provides a three-dimensional map of permeability architecture that will inform the collection of groundwater samples away from the source area. Such 3D subsurface mapping can be accomplished using Environmental Sequence Stratigraphy (ESS) (Shultz, M.R., et.al, EPA/600/R-17/293). Many PFAS-impacted sites have an existing groundwater monitoring network and lithologic data from existing boreholes. These existing data sources can be leveraged to conduct an ESS analysis and define the hydrostratigraphic units (HSUs) that control contaminant migration prior to entering the field. The ESS framework can then be used to target the PFAS groundwater sampling program, collecting only the data that is needed to address critical data gaps and preventing the collection of unnecessary or misleading/problematic data.
Utilizing the approach for PFAS site investigation described above provides multiple benefits when responding to and investigating PFAS groundwater impacts. These include: reducing the effects of the aforementioned challenges specific to PFAS sites, limiting the cost and duration of PFAS investigations, and providing a process-based CSM that can be used to assess risk and design more efficient remedial solutions for PFAS.