Groundwater IMACs

Groundwater Interim Maximum Allowable Concentrations (IMACs)

Any person may request the Division of Water Resources (DWR) Director to establish an interim maximum allowable concentration (IMAC) for a substance for which a groundwater standard has not been established. The requestor is required to submit relevant toxicological and epidemiological data, study results, and calculations necessary to establish a standard in accordance with the groundwater rules in 15A NCAC 02L .0202. 

If there is not enough information available to establish a standard or interim maximum allowable concentration for a substance, then that substance is not permitted in groundwater above detectable concentrations. A detectable concentration is defined as a detection of that substance at or above the practical quantitation limit (PQL). The practical quantitation limit is the lowest concentration of a substance that can be reliably achieved by a laboratory. Note that the practical quantitation limit may vary slightly from lab to lab due to sample matrix interference, dilution and other factors.

IMAC Table (updated October 2024)

IMAC Establishment SOP (updated April 2022)

IMAC Updates:

Tab/Accordion Items

Public Memorandum PFAS IMACs Establishment

DWR received a request to develop IMACs in groundwater for eight per- and polyfluoroalkyl substances (PFAS) on July 22, 2024 along with supporting data and documents. In accordance with 15A NCAC 02L .0202, the data supporting the request have been reviewed by DWR. The data and supporting information for the establishment for these IMACs are available in the following document: PFAS IMACs Supporting Information

The intent to establish these IMACs was public noticed (Public Notice on Request for IMACs for PFAS) on September 4, 2024, with the opportunity for any interested party to submit a comment within a 30-day period.

Comments Received:

Public Comments Received via Email (It is recommended that you open this file in Adobe Acrobat or Adobe Acrobat Reader. This file is a PDF portfolio, and other PDF readers may not support it.)

Public Comment Received via Mail

DWR appreciates all comments received. The toxicological and epidemiological data, study results and calculations submitted with the request were in accordance with 15A NCAC 02L .0202. As 15A NCAC 02L .0202(d) states that the standard shall be the least of, and 15A NCAC 02L .0202(e) establishes the order of preference for references, no revisions to the proposed IMAC values included in the public notice are recommended as a result of the public comments received. As required, the Director will make a recommendation to the Environmental Management Commission (EMC) within 12 months of the date of the memorandum as to whether any of the below IMACs should be replaced by a new groundwater standard or expire.

The Director has concluded that the establishment of these IMACs will not degrade the quality of the groundwaters, will not likely cause or contribute to pollution of the waters of the state, and will be protective of public health. The following interim maximum allowable concentrations are hereby established for Class GA and GSA groundwaters effective October 15, 2024:

SubstanceAcronymCAS NumberConcentration (ng/L)
Perfluorooctane sulfonic acidPFOS1763-23-10.7*
Perfluorooctanoic acidPFOA335-67-10.001*
Hexafluoropropylene oxide dimer acidHFPO-DA (GenX)13252-13-610
Perfluorobutane sulfonic acidPFBS375-73-52,000
Perfluorononanoic acidPFNA375-95-110
Perfluorohexane sulfonic acidPFHxS355-46-410
Perfluorobutanoic acidPFBA375-22-47,000
Perfluorohexanoic acidPFHxA307-24-44,000

* The IMACs for PFOA and PFOS are below detection level or the Practical Quantitation Limit (PQL).  A measurement at or above the current PQL of 4 ng/L for PFOA and PFOS as reported in EPA Test Method 1633 would constitute an exceedance of the IMAC for that chemical.

Public Memorandum Bentazon, Boscalid, Fluometuron, and Metolachlor IMAC Establishment

DWR received a request to develop IMACs in groundwater for bentazon, boscalid, fluometuron, and metolachlor: IMAC Establishment Request August 2023. In accordance with 15A NCAC 02L .0202, the data supporting the request have been reviewed by DWR. The data and supporting information for the establishment for these IMACs are available in the following document: Bentazon, Boscalid, Fluometuron, and Metolachlor IMAC Supporting Information.

The intent to establish these IMACs was public noticed (Public Notice) on November 22, 2023, with the opportunity for any interested party to submit a comment within a 30-day period.

The following IMACs are hereby established for Class GA and GSA groundwaters effective January 18, 2024:

SubstanceConcentration
Bentazon200 µg/L
Boscalid2,000 µg/L
Fluometuron90 µg/L
Metolachlor700 µg/L

Public Memorandum PFOA IMAC Removal

The DWR Director received a request for removal of the IMAC for perfluorooctanoic acid (PFOA) on June 17, 2022: PFOA IMAC Removal Request. In accordance with 15A NCAC 02L .0202, the data supporting the request have been reviewed by DWR. The data and supporting information for the removal of this IMAC are available in the following document: Perfluorooctanoic Acid (PFOA) IMAC Supporting Information.

The intent to remove this IMAC was public noticed (Public Notice) on September 26, 2022, with the opportunity for any interested party to submit a comment within a 30-day period. The Division appreciates all comments received.

The Director has concluded that the removal of this IMAC will not degrade the quality of the groundwaters, will not likely cause or contribute to pollution of the waters of the state, and will be protective of public health. The interim maximum allowable concentration for PFOA is hereby removed effective November 4, 2022. In accordance with 15A NCAC 02L .0202 (c), PFOA shall not be permitted in groundwater in concentrations at or above the practical quantitation limit.


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