Results helped minimize additional investigation requirements at bulk petroleum storage facility.
By Stephen Maxwell
Petroleum compounds can be readily identified using well developed forensic science techniques based on libraries of known products and well understood weathering processes. Unfortunately, the same cannot yet be said for poly- and perfluoroalkyl substances (PFAS). We set out to use a forensic source differentiation technique to evaluate the sources of PFAS at a bulk petroleum storage facility. The results enabled the owner to ultimately reduce the areal extent of site-related impacted shallow groundwater from 7 acres to 0.43 acres—a nearly 94 percent reduction of impacted area. The deep groundwater was also determined to be impacted with offsite contamination and eliminated from further evaluation. The following article describes the methods used.
Overview of Bulk Petroleum Storage Facility
The 7-acre bulk petroleum storage facility studied is located in a heavily industrialized urban area along a tidal water body in New Jersey. The site has been under investigation for petroleum impacted soil and groundwater since the 1990s, and there are also multiple potential offsite sources of PFAS, an environmentally persistent group of chemicals consisting of thousands of chemical species 1,2. Among the key PFAS sources is a Class B aqueous film forming foam (AFFF) fire suppression system used to combat Class B flammable fuel fires. Figure 1, depicts the site layout.
Monitoring wells have been installed to evaluate both shallow and deep groundwater for PFAS. Twenty-two shallow groundwater (defined as the water table to approximately 20 feet below ground surface (bgs)) monitoring wells have been installed; while six monitoring wells were installed to monitor deep groundwater (defined as from 20 feet bgs to approximately 40 feet bgs). Figure 1 shows the monitoring well locations.
The following AFFF formulations were present at the site:
• Legacy PFOS AFFF – 3M 6 percent [3]
• Legacy C8 AFFF – Ansulite 3 percent [4]
• Modern C6 AFFF – Universal Gold NMS #420 3 percent [5]
Samples of each AFFF formulation were sent for laboratory analysis to determine the total PFAS content. The samples were also subjected to a total oxidizable precursor (TOP) assay to evaluate the oxidized PFAS sample content.
Groundwater Sampling Collection Methods Reduce Contamination and Ensure Accuracy
To ensure accuracy and reduce contamination, the team collected groundwater samples using certified PFAS-free Proactive Monsoon submersible pumps with disposable high-density polyethylene (HDPE) tubing. The pumps were decontaminated using a four-step process:
1. Scrub and pump a solution of dilute ed Alconox
2. Rinse with tap water
3. Second rinse with tap water
4. Rinse with analytical laboratory provided certified PFAS-free deionized (DI) water
A field blank was collected from the decontaminated pump using certified PFAS free DI water provided by the analytical laboratory and analyzed with the samples. Prior to groundwater sample collection, a Solinist oil/water interface probe was used to measure the groundwater elevation in each monitoring well. The groundwater samples were collected in laboratory-provided 500-mL HDPE containers and analyzed using USEPA Method 1633. Samples of the AFFF formulations were collected from the manufacture’s container by pouring the AFFF concentrate into laboratory supplied HDPE containers. Table 1 shows the methods used to analyze each substance.
The 20 most common PFAS compounds detected in each sample were added to produce the total PFAS or ΣPFAS [6] of the sample. The concentration of each individual PFAS compound was divided by the ΣPFAS [6] to determine the relative abundance of each PFAS compound in the sample. This procedure was completed for each of the AFFF samples, the AFFF TOP results, and the groundwater sampling results. The PFAS relative abundance are placed on radar plots to depict the PFAS distribution and allow for interpretation and comparison.
New Jersey PFAS Groundwater Regulatory Standards
New Jersey has groundwater quality standards (GWQS) for PFOS, PFOA, PFNA, and hexafluoropropylene oxide dimer acid (HFPO-DA). HFPO-DA is not a significant contributor to PFAS in AFFF, was not regularly detected in the groundwater or AFFF samples and is not part of the ΣPFAS. The ΣPFAS in the groundwater samples ranged from 0.03329 µg/L at well MW-12 to 0.7299 µg/L at well MW-21D. The average ΣPFAS concentration in the shallow wells was 0.1157 µg/L, while the average ΣPFAS in the deep wells was 0.5425 µg/L.
Figure 2, shows the radar plots for each of the AFFF and oxidized AFFF formulations. The plots illustrate that the AFFF and oxidized AFFF for each formulation has a unique PFAS distribution. The distributions for oxidized C6 and C8 AFFF are somewhat similar; however, the oxidized C8 AFFF has higher percentages of long-chained (PFDA through PFTeDA) PFAS.
Three Distinct Types of PFAS Contamination Patterns in the Groundwater
The groundwater sample PFAS distributions identified three general patterns of PFAS; Figure 3 depicts the radar plot of the samples displaying each general pattern. The patterns include a background pattern dominated by PFOA (Figure 3A), a PFBA and PFOA dominated pattern (Figure 3B), and a PFOS pattern (Figure 3C).
The groundwater samples from all the deep monitoring wells contained PFAS distributions representing background conditions that are dominated by PFOA. This pattern was also identified in the groundwater samples from the up-gradient shallow wells MW-22 and MW-24.
The conceptual site model (CSM) for the site’s groundwater contamination is PFAS from AFFF entering the groundwater from surficial releases of AFFF. The ΣPFAS in the deep groundwater samples ranged from 0.4283 µg/L at well MW-24D to 0.7299 µg/L at well MW-21D. The average ΣPFAS in the deep well samples was 0.5425 µg/L, which is significantly greater than the average ΣPFAS of 0.1157 µg/L in the shallow wells. This indicates that the deep groundwater has been affected by an off-site source of PFAS.
The majority of the shallow groundwater samples contained the PFOA and PFBS dominated PFAS distribution pattern. The ΣPFAS for these samples ranged from 0.03329 µg/L in the sample from MW-12 to 0.1848 µg/L in the sample from MW-4. The PFOA portion of the PFAS distribution is at least partly associated with off-site PFOA migrating onto the site. This is documented in upgradient well MW-24, which had a ΣPFAS of 0.1091 µg/L and 64.9 percent of the ΣPFAS is PFOA. These results indicate that the PFOA is not a significant site-related contaminant.
The PFOS pattern samples are mostly located at the site’s northwestern corner, towards the tidal waterbody. The Perfluoroalkane Sulfonic Acids (PFSAs) detected in these samples were not detected in the background samples and it is possible that there is an onsite origin for these compounds. However, the distribution of PFAS in the PFOS pattern samples is not similar to either the fresh or oxidized legacy PFOS AFFF. Soil sampling will be completed in this area to evaluate if PFAS contamination is present resulting in a source of PFSAs to the groundwater. It is possible that the PFSAs are migrating on to the site from the former industrial site to the south. Additional groundwater gauging will be completed to provide additional data on the direction of groundwater flow in the area.
Technique Offers Line of Evidence for Source Differentiation
Multiple sources of PFAS to the environment and exceptionally low regulatory standards present significant challenges to site owners with PFAS issues. Since PFAS of regulatory interest are stable in the environment, PFAS distributions in samples and source materials can be used to evaluate the source of PFAS to a site. Using the relative abundance of PFAS in the groundwater to evaluate the source of PFAS provides a valuable line of evidence for source differentiation. | WA
Stephen Maxwell is Senior Hydrogeologist for Tetra Tech. He has worked as a project manager and technologist in the environmental industry for more than 30 years, primarily for manufacturing, chemical, solid waste, and utility market clients, as well as for state regulatory programs in New York and South Carolina. With his strong technical background and leadership, he has been successful in managing complex sites with multiple impacted media and stakeholders. He has also completed approximately 170 Phase I Environmental Site Assessments (ESAs) for properties ranging from complex large chemical manufacturing facilities to simple residential properties. Stephen has been a licensed Professional Geologist since 2003 and is currently registered in Pennsylvania. He has also been registered as a New Jersey Licensed Site Remediation Professional (LSRP) since 2008. He can be reached at [email protected].
References
- ITRC (Interstate Technology & Regulatory Council). 2026. PFAS Technical and Regulatory Guidance Document and Fact Sheets, PFAS-1. Washington, D.C.: Interstate Technology & Regulatory Council, PFAS Team. https://pfas-1.itrcweb.org/.
- 3M Company. 1999. Fluorochemical Use, Distribution and Release Overview.
- Legacy PFOS AFFF was created in the 1960s by 3M and manufactured in the United States from the late 1960s until 2002 exclusively by 3M. Legacy PFOS AFFFs contain PFOS and perfluorosulfonic acids (PFSAs), such as perfluorohexane sulfonate (PFHxS).
- Legacy Long-Chained (C8) Fluorotelomer AFFF was manufactured and sold in the United States from the 1970s until 2016 and encompass all other brands of AFFF besides 3M. Although they are reportedly not made with PFOA, they contain polyfluorinated precursors that degrade to PFOA and other terminal (environmentally stable) PFAS.
- Modern (C6) Fluorotelomer AFFF was developed in response to the USEPA 2010/2015 voluntary PFOA Stewardship Program. These formulations were developed to contain short-chained PFAS (< C7) that do not degrade to PFOA. Some long-chained PFAS (>C6) are present in the formulations.
- PFAS used for the ΣPFAS: 1H,1H,2H,2H-Perfluorodecanesulfonic Acid (8:2FTS), 1H,1H,2H,2H-Perfluorooctanesulfonic Acid (6:2FTS), N-Methyl Perfluorooctanesulfonamidoacetic Acid (NMeFOSAA), N-Ethyl Perfluorooctanesulfonamidoacetic Acid (NEtFOSAA), Perfluorooctanesulfonamide (PFOSA), Perfluorobutanoic Acid (PFBA), Perfluoroheptanoic Acid (PFHpA), PFHxA, Perfluoroheptanoic Acid (PFHpA), Perfluorooctanoic Acid (PFOA), Perfluorononanoic Acid (PFNA), Perfluorodecanoic Acid (PFDA), Perfluoroundecanoic Acid (PFUnA), Perfluorododecanoic Acid (PFDoA), Perfluorotridecanoic Acid (PFTrDA), Perfluorotetradecanoic Acid (PFTeDA), Perfluorodecanesulfonic Acid (PFDS), Perfluorooctanesulfonic Acid (PFOS), PFHxS and Perfluorobutanesulfonic Acid (PFBS).