Groundwater IMACs

Groundwater Interim Maximum Allowable Concentrations (IMACs)

Any person may request the Division of Water Resources 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 2L .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:

January 18, 2024

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

The Division of Water Resources (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:

If you have any questions, please contact Bridget Shelton at  bridget.shelton@deq.nc.gov or 919-707-9022.

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.

If you have any questions, please contact Bridget Shelton at bridget.shelton@deq.nc.gov or 919-707-9022.

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