In this interview, Geosyntec’s Kathleen Brannen-Donnelly discusses the importance of understanding a site’s history and geology when designing PFAS sampling plans. Kathleen will present “Background Concentrations of PFAS: Guidance for Site Evaluation” at the Society of American Military Engineers Joint Engineer Training Conference & Expo on Thursday, May 21, 2026, in Portland, Oregon.

About the Interviewee

Kathleen Brannen-Donnelly, PhD, PE, is a Senior Hydrogeologist based in Georgia who focuses on aqueous geochemistry, environmental statistics, and site characterization. She offers expertise evaluating per- and polyfluoroalkyl substances (PFAS), metals, volatile organic carbon compounds, polychlorinated biphenyls, and radionuclides in soil, groundwater, sediment, and building materials.

Q&A

Tell us about your professional background.

I have degrees in biology and geology, and I specialize in environmental forensics and site characterization. I started working with PFAS many years ago, when they were just becoming known as an emerging contaminant. In my 10 years at Geosyntec, I have focused on trying to understand where PFAS are in the environment, how they got there, and who contributed to the PFAS in the environment.

Why is it important to understand background levels versus site impacts when dealing with PFOS?

First and foremost, PFAS are a large group of chemicals that include thousands of substances.

What we’ve found is that because they are such a big group of chemicals, the way they move through the environment varies. In addition, PFAS are now largely considered to be ubiquitous. That is, when we go into an area where we don’t expect to find a source, we still end up finding PFAS in soil and groundwater.

When we’re evaluating a site for contamination using standards like the EPA’s levels for drinking water contamination or the CERCLA hazardous substance levels, we are trying to understand the PFAS impacts to the site. We have to ask, are we finding PFAS deposited there through groundwater or rainwater? Or is it from a point source like manufacturing or use of AFFF on the site?

This is what makes PFAS unique when compared with contaminants like PCBs: we often can’t delineate PFAS without considering background levels.

How do you sample a site when you know that there’s going to be a background level of PFAS?

One of the first things we recommend is having a good understanding of the site’s history and operations. There are obvious things, such as considering what manufacturing processes happened on the site or whether any sort of fire training was happening there.

Then you might have to look further afield. Is surface water or freshwater being used at the site in any capacity? If so, is that water being pulled from a source that has PFAS in it? Does the site regularly receive heavy rain that could be transporting PFAS? Do any of the adjoining properties use PFAS in large concentrations?

When a site has multiple types of PFAS at different concentrations, it becomes particularly important to think about where in the site’s history PFAS could have come on to the site.

How do you design a site sampling plan to account for PFAS regulations when those regulations are changing?

PFAS screening levels have progressed over the years. I remember when combined screening levels for PFOS and PFOA in drinking water were at 70 nanograms per liter. Now, EPA regulations for drinking water MCLs (maximum contaminant levels) are roughly 9 times lower for both PFOS and PFOA.

At the higher level, it was easier for clients to delineate their impacts at their site. At these new lower levels, they can’t do that without considering possible background sources.

It has now become important to consider the background sources earlier in site characterization. You might need to collect more samples or you might need a higher level of engagement with the state regulatory agency, earlier in the process—or both.

What are some of the current limitations of sampling and analytical methods? And what’s the best way forward?

Often during site characterization, we do a targeted analysis, comparing what is found in a sample to a screening level. Other times, when we are trying to meet multiple objectives during sampling, it might be necessary to take a bigger picture view of what is at the site.

For example, PFAS have the nickname, forever chemicals, because they don’t break down quickly or easily. However, some PFAS do break down into other components like PFOS and PFOA that can also be measured in an environmental sample. A site can have both the original PFAS and these other components at relatively high concentrations. In this case, you might have to do a different analysis.

When it comes to analytical methods and getting a good understanding of your site characteristics, the best way to start is with a good understanding of your site history. This, in turn, will allow you to develop and implement an efficient method of environmental sampling.