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Regulatory Updates

Five New PFAS Added to EPA Regional Screening Levels (RSLs)

Victor Medina & Emily Larson | June 24, 2022

TRC is continually tracking environmental standards related to PFAS to provide timely information for our clients. In May 2022, the U.S. Environmental Protection Agency (EPA) announced the addition of five new PFAS to the list of RSLs. These PFAS are in addition to perfluorobutanesulfonic acid (PFBS), which was added to the RSLs in 2014 and updated in 2021:

  • Perfluorooctanesulfonic acid (PFOS)
  • Perfluorooctanoic acid (PFOA)
  • Perfluorononanoic acid (PFNA)
  • Perfluorohexanesulfonic acid (PFHxS)
  • Hexafluoropropylene oxide dimer acid (HFPO-DA), known as GenX chemicals

What are EPA Regional Screening Levels and How are They Used?

EPA RSLs are generic acceptable levels of contaminant concentrations in water, soil and air using risk assessment guidance from the Superfund program. RSLs are derived from standard exposure assumptions and EPA toxicity data. Generally, if a site has concentrations greater than the RSL, then further investigation is warranted. However, RSLs are not enforceable standards. The EPA usually requires a site-specific risk assessment for further evaluation of the potential exposure to contaminants of concern for receptors at the site. While it may be possible that concentrations exceed the RSL, a response action may not be required. The RSL can also be used as a preliminary remediation goal for guiding a Remedial Investigation/Feasibility Study. However, RSLs should not be used as final remediation goals because final remediation goals should be derived from a site-specific risk assessment.

The EPA uses toxicity data from several sources to generate RSLs. These sources include:

  • EPA Integrated Risk Information System (IRIS)
  • Agency for Toxic Substances and Disease Registry (ATSDR)
  • EPA Provisional Peer-Reviewed Toxicity Values (PPRTV)
  • California Environmental Protection Agency (CalEPA)
  • EPA Office of Water – Drinking Water Standards & Health Advisories (DWSHA)

What are the RSL Changes for PFAS and Why?

As previously stated, in spring 2022, the EPA issued new RSL tables that included several revisions regarding PFAS. It is important to note that the RSLs contain different forms of the PFAS, including the anion, acid and salt (cation) forms for PFBS and PFOS; the acid and anion forms for PFOA, PFNA, and PFHxS; and the acid and salt forms for HFPO-DA (GenX). While most PFAS exist in the anionic form in the environment, the RSL provided is the same regardless of the chemical’s form for each PFAS (with the exception of GenX chemicals, which have different values for the acid and salt forms).

A table with the updated toxicity reference data and new RSLs (as well as soil screening levels [SSLs]) is presented below. The reference dose (RfD) data and RSL data tables can be found at Regional Screening Levels (RSLs) – Generic Tables | US EPA.

Chemical EPA Regional Screening
Levels (RSLs)
Residential Soil (mg/kg) Industrial Soil (mg/kg) Tap Water (ug/L) Risk Based Protection of
Groundwater SSL (mg/kg)
Reference Dose (RfD) (mg/kg-day) RfD Source
New PFAS Chemicals
Perfluorooctanesulfonic acid
0.13 1.6 0.04 3.80E-05 2.00E-06 ATSDR
Perfluorooctanoic acid (PFOA) 0.19 2.5 0.06


3.00E-06 ATSDR
Perfluorononanoic acid
0.19 2.5 0.059 2.50E-04 3.00E-06 ATSDR
Perfluorohexanesulfonic acid (PFHxS) 1.3 16 0.39 1.70E-04 2.00E-05 ATSDR
Hexafluoropropylene oxide dimer acid (HFPO-DA)  (known as GenX) 0.23 3.5 0.06 N/A 3.00E-06 DWSHA
Existing PFAS Chemical
Perfluorobutanesulfonic acid
19 250 6.0 1.9E-03 3.0E-04 PPRTV


All RSLs shown in the table are based on noncancer toxicity.

The Residential and Industrial Soil RSLs for the salt form of HFPO-DA (ammonium perfluoro-2-methyl-3-oxahexanoate) and the SSL for the salt form of PFBS (potassium perfluorobutanesulfonate) are different than those listed for the acids.

mg/kg = milligrams per kilogram

ug/L = micrograms per liter

What are the Implications?

  • Since PFAS are not yet regulated federally, many states and entities will rely on the EPA RSL for guidance and to determine if further PFAS investigation is necessary at their sites.
  • Additional PFAS are being added to the RSL tables and revisions are resulting in lower screening levels, which may result in more sites being investigated for PFAS.
  • Any site with PFAS at, near, or over the RSLs should consider a site-specific evaluation to better understand if exposure may potentially cause adverse health effects.
  • Specialized waste treatment technologies for PFAS contamination or migration may need to be considered, including removal, treatment or remediation.

What Happens Next?

  • The timeline for establishing water regulatory standards (maximum contaminant levels [MCLs] and possibly secondary standards) includes a proposed rule in fall 2022 and a final rule in fall 2023.
  • PFAS reporting under Toxic Substances Control Act (TSCA) is expected in winter 2022.

What Can You Do?

  • Determine if there is any possibility that your site, installation, facility, or industry could be at risk for PFAS contamination. Consider conducting an audit of the processes and chemical formulations used on site.
  • Consider replacing PFAS materials with non-PFAS products.
  • Dispose PFAS materials appropriately and understand the potential for PFAS discharges in your waste stream.
  • Take actions to prevent further PFAS contamination/migration, including operational changes, removal or cleanup if necessary.

TRC is prepared to assist you with your PFAS-related and Environmental, Health and Safety (EHS) questions. For more information, please contact Victor Medina at or Emily Larson at

Victor Medina, Ph.D., P.E

Victor an Environmental Engineer and is TRC’s Technical Director for Water and Wastewater. Victor has 30 years of experience in remediation, water and wastewater treatment. Medina has a M.S. and Ph.D. in Civil/Environmental Engineering from the University of Southern California and is currently based in Jackson, Mississippi. Victor has five patents for innovative environmental technologies and specializes in developing effective solutions to challenging environmental problems. Contact Victor at

Emily Larson

Emily Larson has more than 10 years of experience modeling the bioaccumulation of semivolatile compounds and metals in ecological systems, modeling exposure to human and ecological receptors, and preparing human health and ecological risk assessments. She has experience conducting risk assessments with emerging contaminants, specifically per-and polyfluoroalkyl substances (PFAS). In addition, she serves as a technical expert on PFAS within the intermountain region for TRC. She has experience with Superfund (CERCLA) as well as several state-led programs specifically in the Inter Mountain West and Pacific Northwest regions. Emily has worked with several clients in both the private and the public (state and federal) sector. She can be reached at

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