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 January 2024)
IMAC Establishment SOP (updated April 2022)
IMAC Updates:
September 4, 2024
Public Notice on Request for IMACs for PFAS
The Division of Water Resources is providing notice and opportunity for comment on a request to establish Interim Maximum Allowable Concentrations (IMACs) for eight per- and polyfluoroalkyl substances (PFAS) for groundwater pursuant to 15A NCAC 02L .0202(c).
The Division received a request to establish IMACs on July 22, 2024 along with supporting data and documents.
The following proposed IMAC values will apply to Class GA and GSA groundwaters:
| Substance | Acronym | CAS Number | Concentration (ng/L) |
| Perfluorooctane sulfonic acid | PFOS | 1763-23-1 | 0.7* |
| Perfluorooctanoic acid | PFOA | 335-67-1 | 0.001* |
| Hexafluoropropylene oxide dimer acid | HFPO-DA (GenX) | 13252-13-6 | 10 |
| Perfluorobutane sulfonic acid | PFBS | 375-73-5 | 2,000 |
| Perfluorononanoic acid | PFNA | 375-95-1 | 10 |
| Perfluorohexane sulfonic acid | PFHxS | 355-46-4 | 10 |
| Perfluorobutanoic acid | PFBA | 375-22-4 | 7,000 |
| Perfluorohexanoic acid | PFHxA | 307-24-4 | 4,000 |
* The proposed 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 proposed IMAC for that chemical.
In accordance with 15A NCAC 02L .0202(c), the DWR Director intends to establish IMACs for eight PFAS at the values listed above on October 15, 2024.
Persons wishing to provide comments on the intended actions or the supporting information may submit electronically to IMACcomments@deq.nc.gov or may mail comments on or before October 4, 2024 to:
N.C. DEQ Division of Water Resources, Attn: Bridget Shelton
DWR Planning Section
1611 Mail Service Center
Raleigh, N.C. 27699-1611
If you have any questions, please contact Bridget Shelton at bridget.shelton@deq.nc.gov or 919-707-9022.
January 18, 2024
Public Memorandum Bentazon, Boscalid, Fluometuron, and Metolachlor IMAC Establishment
DWR received a request to develop interim maximum allowable concentrations (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:
| Substance | Concentration |
| Bentazon | 200 µg/L |
| Boscalid | 2,000 µg/L |
| Fluometuron | 90 µg/L |
| Metolachlor | 700 µg/L |
November 4, 2022
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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