Key Considerations for PFAS Field Investigations
So, you have a PFAS problem. What’s next? In this article, I share some key considerations for planning and implementing a PFAS field investigation.
February 11, 2020
One of the most challenging aspects of investigating PFAS contamination is the very low concentrations that require measurement (usually, in the low parts per trillion) and the special sampling techniques required for these man-made chemicals. Over the past few years, LimnoTech has planned and implemented more than a dozen field investigations for PFAS in groundwater and soil where we have dealt with these challenges. I thought it might be helpful to take a step back and provide some considerations, from a broader perspective, that could help support planning and implementing a PFAS field investigation.
Know the Regulatory Environment
The scope of the investigation will depend on your interests and a state’s regulatory status regarding PFAS. Knowing the regulatory environment of a state is critical. Many states do not regulate PFAS, which means that the criteria driving the investigation and subsequent actions could change and/or are not clearly defined. If a state has not developed PFAS criteria, then only a federal value is available for data evaluations, which is an unenforceable Lifetime Health Advisory for end-of-pipe drinking water (70 ng/L for PFOA and PFOS). In these cases, it may be useful to propose site-specific criteria. For example, trying to delineate soil impacts to a non-detect level may be impossible at some sites where near-surface soil impacts have been randomly spread around the site by traffic, construction, and weather. But, if the responsible regulatory agency will approve site-specific soil criteria based on the EPA Regional Screening Level Calculator or some other rational method, it can help focus the investigation and limit expenditures.
States that have developed PFAS criteria, in general, do not have all types of environmental media included and address only a few compounds. To date, 21 states and 9 countries, including the U.S., have developed some type of PFAS criteria. For a complete list of criteria that is updated monthly by the ITRC, go to the PFAS Fact Sheets web page and the “Regulations, Guidance, and Advisories” section. Click on the Section 4 and Section 5 tables for an Excel file with the latest criteria.
It is important to note that not all of these standards are enforceable. Some of the standards are only screening levels or guidelines. Further complicating the site investigation planning process is the fact that different labs may report different lists of PFAS analytes, and in many cases these lists are being updated with the promulgation of new regulatory standards.
Given that information about PFAS and regulatory concerns is evolving rapidly and varies state by state, you will ultimately need to decide on an approach that will best support your interests and long-term goals. Questions that will need to be considered include:
- Should you test only for those compounds and for media that have criteria?
- Should you investigate for all compounds in media that currently have accepted analytical methods for identification and quantification?
- Should you limit your investigation to only compounds known or suspected to be present at the investigation site (see Initial Reconnaissance)?
In general, we recommend obtaining data for the most complete analyte list, provided there is no additional cost incurred or the client approves potential added costs. We recommend this approach because data for non-regulated PFAS compounds may be useful in understanding fate and transport, as well as source differentiation.
Evaluate Other Drivers
In some cases, non-regulatory drivers may influence the investigation plan. For example, public involvement, media attention and local issues can play a large role in directing the urgency and scope of a site investigation. A few states have been very proactive in addressing PFAS. For example, some states have implemented statewide sampling and reconnaissance programs to document PFAS impacts in surface waters and municipal supplies and to identify likely sources of PFAS. Consequently, the public may be more informed about PFAS issues in their community. The ubiquity of PFAS in the environment, the evolving understanding of adverse human health and environmental effects, and regulatory caution have resulted in a high degree of public interest and a higher-than-normal amount of media coverage in many markets. Even if the site is not currently subject to public or media scrutiny, it’s probably safe to assume it may be in the future.
The ubiquity of PFAS in the environment, the evolving understanding of adverse human health and environmental effects, and regulatory caution have resulted in a high degree of public interest and a higher-than-normal amount of media coverage in many markets.
Previous sampling by others may also influence investigation planning. States that have been proactive in PFAS evaluations may have a baseline of state-led PFAS investigation data to inform evaluations. Michigan is an example: starting in 2018, EGLE (Michigan Department of Environment, Great Lakes, and Energy) implemented a systematic sampling program of drinking water supplies in the State, and having knowledge of their findings has been useful in planning some of our investigations.
Review Available Hydrogeological Information
As with most subsurface investigations, starting with an initial understanding of local geology and hydrogeology by using available resources either from previous site investigations or the state geological survey is very helpful. In particular, identification of clay layers that may impede the downward migration of PFAS through the vadose zone is very important. LimnoTech has noted in several site investigations that PFAS concentrations can attenuate quickly in clay deposits within a few feet of the surface.
At one site, for example, we saw a PFOS concentration of 1,400 ug/kg in the upper half-foot of topsoil, but three feet deeper we saw PFOS at only 10 ug/kg in the shallow clay layer. In addition, if not already known, the likely direction of groundwater flow in the uppermost aquifer can be inferred based on the proximity and location of nearby surface water bodies and topography. However, perched groundwater and groundwater that follows preferential flow paths through sewer corridors can be significant vectors for dissolved PFAS compounds, just like with other soluble compounds.
Conduct Initial Reconnaissance
Similar to most field investigations, reviewing all available relevant historical information about the possible use and/or manufacture of PFAS at the site and nearby properties is informative. Potential sources of PFAS have been well documented in guidance documents from ITRC and the National Ground Water Association. Surface water flow, sewer networks, nearby surface water bodies and potential receptors will need to be identified to assist in the development of a targeted investigation approach.
Understand Potential Cross-Contamination
A primary issue driving PFAS investigations is their potential toxicity at extremely low concentrations in soils and water. Consequently, all site investigations have to incorporate safeguards for avoiding cross-contamination because of the ubiquitous nature of PFAS. Guidance documents have been developed (1,2) that recommend ways to avoid cross-contamination during site investigations, but some measures may come across as unnecessarily extreme. This raises the question, “Are all recommended measures justified?”
Until further studies have better documented the risks of cross-contamination from PFAS-containing sampling materials, the guidance document recommendations relevant to your site’s location should be followed.
LimnoTech has examined this concern on various projects through a limited evaluation of the potential for cross-contamination from Teflon tubing, soil core liners, and other materials, and found that, in most cases, there wasn’t an impact on the sample results. In our investigations, we’ve found that the use of field blanks, equipment blanks and duplicate samples goes a long way to produce a valid data set. Similarly, we always recommend testing of water supplies that will be used for equipment decontamination and collection of rinse blanks. However, until further studies have better documented the risks of cross-contamination from PFAS-containing sampling materials, the guidance document recommendations relevant to your site’s location should be followed. In addition, you may want to consider possible risks associated with sampling from existing monitoring wells which may have been installed with PFAS-containing materials (e.g., Teflon tape or synthetic pipe dope on casing joints, and/or permanent sampling pumps and dedicated tubing that are known or suspected to contain PFAS). An alternative option for groundwater sampling for PFAS is described in the section below (see Avoid Sample Dilution).
Avoid Sample Dilution
Vertical Aquifer Sampling (VAS) from temporary borings is an alternative or supplemental approach for aquifer characterization if existing wells are possibly compromised or insufficient. The potential influence of drilling fluids during VAS investigations will need to be monitored carefully because they may dilute the groundwater samples collected during the investigation. In many cases, purging is not conducted prior to groundwater sampling during VAS investigations if the sample is believed to be collected from an undisturbed section of the aquifer. We recommend some purge time prior to sampling to document general water quality data. Very low dissolved oxygen concentrations (well below 1 mg/L) are generally a good indicator that undiluted groundwater is being sampled. However, it’s important to know that some aquifers can have dissolved oxygen concentrations above 1 mg/L.
Decide to Start at the Source or Receptor
Another consideration is whether to initiate the investigation from a known or suspected source and move out from there, or vice versa. This will likely depend on potential imminent risks to receptors or cross-contamination concerns. If nearby receptors are thought to be at risk, then the investigation will likely start with an evaluation of the receptors (e.g., water well or source water sampling) and then proceed back to a potential source area. Evidence of foaming in surface or groundwater samples should be documented. As noted above, vertical characterization of soils is likely to show rapid diminishment of PFAS concentrations with depth if sampling is being conducted through a clay barrier.
Make a Lab Selection
The recent regulatory focus on PFAS has motivated many commercial labs to start offering PFAS analysis. However, there are currently no EPA-approved laboratory methods to measure PFAS in media other than drinking water. Organizations requiring PFAS testing need to ensure their data will withstand regulatory and public scrutiny.
Given the dynamic landscape around PFAS analytical methods and the emergence of new labs offering PFAS analysis, it can be challenging to determine if a given laboratory’s PFAS analytical procedure is right for your project needs. At LimnoTech, we recommend interviewing laboratories when planning a PFAS sampling program to make a better-informed selection. Specific points to note regarding analytical methods and lab selection are explained more fully in LimnoTech’s June 2019 Newsletter.
This article is the eighth in a series of articles authored by LimnoTech staff on PFAS-related issues. Follow us on LinkedIn or Twitter (@LimnoTech), and check the News and Media page on our website for more information and updates. Links to the other PFAS articles in this series are provided below:
The latest publication of the LimnoTech Currents newsletter, PFAS – Like Nothing We’ve Seen Before, also focuses on PFAS and covers a range of topics, including aviation and AFFF, potential issues and areas of concern for municipalities, analysis methods and laboratory considerations, and current regulations.
Joyce Dunkin, CPG, PG, is a Senior Hydrogeologist/Geologist at LimnoTech. Joyce has technical and project management experience in site investigations and assessments of numerous CERCLA- and RCRA-related projects. She has extensive experience in geologic and hydrogeologic investigations and data collection, synthesis, interpretation and analysis, including experience with surface/borehole geophysical data interpretation. Joyce’s technical skill areas and responsibilities have included senior project management for remedial investigations and feasibility studies; work plan and report preparation and review; field investigation methods development; soils and groundwater remedial design; field supervision, including soil and groundwater investigations for PFAS; groundwater modeling; groundwater supply studies; and management and field investigations to support 316(b) projects.