HEXAFLUOROPROPYLENE OXIDE (HFPO) DIMER ACID (Gen-X) cleanup levels in Pennsylvania

These are the Pennsylvania Department of Environmental Protection's published values for HEXAFLUOROPROPYLENE OXIDE (HFPO) DIMER ACID (Gen-X), from its PFAS groundwater table, updated 7/10/2024. Each value is shown as the agency prints it, with the same number written out beside it where that reads differently.

Pennsylvania: Statewide Health Standard Medium-Specific Concentrations

DEP's PFAS groundwater table

DEP's file dated July 24, 2024.

Pennsylvania Department of Environmental Protection

The United States Environmental Protection Agency (EPA) has established maximum contaminant levels (MCL) for the per- and polyfluoroalkyl substances (PFAS) compounds listed below. These MCLs will become the Statewide health standard medium-specific concentration (MSC) values for groundwater effective June 25, 2024. The new values are:

HEXAFLUOROPROPYLENE OXIDE (HFPO) DIMER ACID (Gen-X)^*

Used Aquifers, TDS ≤ 2500

Column	Value	Code
R (µg/L)	0.01	M
NR (µg/L)	0.01	M

Used Aquifers, TDS > 2500

Column	Value	Code
R (µg/L)	1	M
NR (µg/L)	1	M

Nonuse Aquifers

Column	Value	Code
R (µg/L)	0.01	M
NR (µg/L)	0.01	M

Footnotes to DEP's PFAS groundwater table, as the agency prints them

* In addition to meeting the individual MSC, if more than one of the marked compounds (Gen-X, PFBS, PFHxS, PFNA) are detected at any concentration in a sample, a Hazard Index (HI) must be calculated using the equation below. The HI MSC is met in this case by maintaining a rolling average HI of less than one for the most recent four quarters of samples utilizing the equation:

HI = (C_Gen-X/0.01)+(C_PFBS/2)+(C_PFNA/0.01)+(C_PFHxS/0.01)

Where: All concentrations are in µg/L

C_Gen-X = concentration of Gen-X

C_PFBS = concentration of PFBS

C_PFNA = concentration of PFNA

C_PFHxS = concentration of PFHxS

Updated: 7/10/2024

Pennsylvania Department of Environmental Protection

PFAS Soil MSC Notice (January 2026)

PA DEP has determined that the Hazard Index portion of the EPA’s April 26, 2024 PFAS MCL Rule does not apply to soil. The rationale behind that decision is explained in the Technical Notice below.

January 2026 Technical Notice (PDF)

The agency's current table governs. This page is a reference copy and not a cleanup decision. Check the agency's page for a newer table before relying on a value.

Source

• Pennsylvania Department of Environmental Protection, Statewide Health Standard Medium-Specific Concentrations.
• PFAS groundwater table: DEP's file dated July 24, 2024, read October 5, 2026.