CHAPTER 1

Introduction

Per- and polyfluoroalkyl substances (PFAS) are a class of more than 6,000 contaminants of emerging concern that can harm ecosystem and human health (1). PFAS contain strong carbon–fluorine bonds, which give them unusual—and commercially valuable—properties (2). For instance, PFAS repel both water and oils and are chemically stable (3). For these reasons, PFAS have been used since the mid-twentieth century in consumer products, industrial applications, and, notably, firefighting foams at airports and military installations (4).

However, the carbon–fluorine bonds that make PFAS useful also contribute to their hazard risk. The chemical stability of PFAS leads to their extreme environmental persistence, earning them the nickname “forever chemicals” (5). Further, PFAS bioaccumulate at high levels of the food chain (6). PFAS are associated with deleterious health endpoints, including kidney and testicular cancer, thyroid disease, increased cholesterol levels, lowered immune response, reproductive harm, and developmental delays, even at low levels of exposure (7).

PFAS regularly migrate from the source of their contamination through surface water and groundwater plumes, atmospheric deposition, and the engineered conveyance of impacted materials (8, 9). For example, PFAS may migrate from sources such as fire training areas or fields where wastewater biosolids are applied onto rights-of-way controlled by a department of transportation (DOT) (10). Fire training areas at military sites and airports, PFAS manufacturing sites, metal plating operations, land-applied wastewater biosolids, landfills, and pulp and paper mills are known sources of contamination from which PFAS may migrate (10). Because of their widespread use, persistence, and mobility, PFAS are now ubiquitous in soils and can be detected at low concentrations, even in soils distant from any likely source (11). However, these background concentrations are typically much lower than those near directly affected sites (12).

The following definitions are intended to clarify the terminology used within this report to refer to PFAS:

• PFAS (per- and polyfluoroalkyl substances): A class of at least 6,000 anthropogenic chemicals whose structures contain carbon bonded to fluorine. Precise definitions vary but encompass all compounds that contain multiple carbon–fluorine bonds and are used for their film-forming or water-, oil-, or grease-repellent properties, as well as their chemical precursors.
• PFCs (perfluorocarbons): Colorless, odorless gases containing only fluorine and carbon. Occasionally, this term is mistakenly applied to PFAS.
• PFOA (perfluorooctanoic acid): The eight-carbon (or C8) perfluorinated alkyl carboxylic acid. This is a single member of the PFAS class. Because PFOA is ubiquitous, it is sometimes mistaken for the entire PFAS class.
• PFOS (perfluorooctane sulfonate): The eight-carbon (or C8) perfluorinated alkyl sulfonate. This is a single member of the PFAS class. PFOS is sometimes mistaken for the entire PFAS class because of its ubiquity and the similarity of their names.

• Total PFAS: Methods such as total organic fluorine analysis or the total oxidizable precursor assay can quantify in aggregate nearly all PFAS in a sample but do not differentiate individual chemical species.

Despite long-standing evidence of PFAS toxicity, regulation of these compounds only began recently. The first federal maximum contaminant levels (MCLs) were proposed for drinking water in March 2023: the EPA-proposed MCLs at parts per trillion levels in drinking water for PFOA, PFOS, and four other PFAS (perfluorononanoic acid, hexafluoropropylene oxide dimer acid, perfluorohexane sulfonic acid, and perfluorobutane sulfonic acid) (13).

Additional federal rulemaking is also under way. Most notably, public comment has been completed for the designation of nine species, including PFOA, PFOS, and their chemical precursors, as hazardous substances under the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA, also known as the Superfund Act) (14). The designation of PFAS as hazardous substances would restrict how DOTs could handle and dispose of impacted materials (15). It would also give the EPA authority to direct and apportion liability for cleanup (16).

Several states regulate PFAS at varying concentrations. However, existing PFAS regulations vary according to environmental matrix (e.g., drinking water, land-applied solids, soil) and jurisdiction (17, 18, 19). Many of the states regulating PFAS in drinking water have equally stringent standards for groundwater. In the absence of federal regulation on soils or leaching standards, state and private entities (e.g., landfills) may individually evaluate the risk and liability of relocating PFAS-impacted soil.

Several states have developed action plans and interagency groups to mitigate the harm from PFAS. However, these action plans may not sufficiently address the effect of PFAS contamination on DOT construction and maintenance sites. Agencies including the Michigan DOT, Minnesota DOT, and New Hampshire DOT are navigating PFAS-related issues at significant expense. Situations include the following:

• DOT-owned legacy sites contaminated with PFAS;
• Road construction and improvement through soil and groundwater impacted by PFAS from aerial deposition, stormwater runoff, and groundwater migration;
• Increased assessment and analytical costs for soils to be graded, cut, or excavated;
• Storage and disposal of spoil materials from roadway maintenance in areas with PFAS aerial deposition;
• PFAS being found in dewatered construction groundwater, in excess of the requisite parts per trillion treatment goals; and
• Landfill testing requirements and restrictions leading to increased transportation and disposal costs.

Synthesis Objective

The objective of this synthesis is to document current state DOT practices for identifying locations of potential PFAS contamination and mitigating the impacts of PFAS related to highway construction and maintenance operations. This study considers PFAS impact and mitigation efforts in all phases of highway project development (i.e., planning, design, right-of-way acquisition), construction, and maintenance. The synthesis gathered information such as

• Written DOT policies and guidance for identifying and mitigating locations of PFAS contamination;
• Methodologies for identifying and mitigating PFAS impacts related to highway construction and maintenance operations (e.g., site screening, sampling, geographic tracking, new and

existing approved product lists, management and disposal considerations, pollutant source assessments, regulatory restrictions, liability considerations, ways to address legacy DOT right-of-way acquisitions impacted by PFAS);

• Timing and approaches used to screen for PFAS contamination in construction sites; and
• Identification of materials used currently or formerly by state DOTs on construction sites that may contain PFAS or be cross-contaminated (e.g., containers with PFAS).

Study Approach

This synthesis used a literature review, a practitioner survey, and case example interviews for data collection. First, an extensive literature review on PFAS provided the initial understanding of the current state of research and practice regarding the identification and mitigation of the effects of PFAS on highway construction projects and maintenance operations. The existing literature and previous discussions with DOTs assisted with the development of the survey questionnaire.

The survey was created to document current state DOT practices related to PFAS impacts, mitigation, and related procedures and practices. Under the guidance of the topic panel, the survey was divided into the following categories:

• Demographic information for respondents,
• Policies and procedures,
• Construction and maintenance site sampling,
• Sample evaluation,
• PFAS-containing materials, and
• Follow-up.

Once the final draft of the survey was approved, an e-mail request with the Qualtrics survey link and a PDF version of the survey were distributed to the voting membership of the AASHTO Committee on Environment and Sustainability (CES), and this list was supplemented when applicable by members of the CES Hazmat Working Group. Survey recipients constituted state DOT members from each of the 50 U.S. states and the District of Columbia. The recipients were asked to distribute the survey to individuals with knowledge of their DOT’s PFAS policies and processes. The complete survey is shown in Appendix A.

A total of 44 responses were collected, providing an 86% response rate from the 51 DOTs. The aggregated graphical representations of the survey responses and associated discussion are presented in Chapter 3. The aggregate and individual results of the survey are presented in Appendix B.

Following the analysis of the survey responses, subsequent case example interviews were conducted to gather further detailed information on the topic. Interviews were conducted with the following state DOTs based on their PFAS policies and procedures: Colorado, Illinois, Maine, Michigan, Minnesota, New Hampshire, Pennsylvania, and Tennessee. Details of the individual case examples are outlined in Chapter 4, and the questions asked during the interviews can be found in Appendix C.

This report seeks to document current DOT practices to identify and mitigate PFAS impacts on highway construction projects and maintenance operations. The authors’ charge in this report is to present information collected void of opinion and bias. The opinions expressed in the synthesis from detailed case examples are those of the state DOT professionals and should be viewed as such. The report is organized as follows:

• Chapter 2 is a review of available academic literature as well as published DOT procedures and policies for identifying and mitigating PFAS contamination,

• Chapter 3 summarizes the survey results,
• Chapter 4 provides the case example selection criteria and interviews with DOTs selected based on their procedures for identifying and mitigating PFAS contamination,
• Chapter 5 draws conclusions based on findings in previous chapters,
• Appendix A contains the survey questionnaire for state DOTs,
• Appendix B contains the results of the survey questionnaire, and
• Appendix C contains the case example interview questions.