Existing Use Determinations
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Proposed Existing Use Determination and Rationale Documents
In accordance with Code of Maryland Regulations (COMAR) 26.08.02.04-1 and the Cold Water Existing Use Determinations: Policy & Procedures which is incorporated by reference into this regulation, the Department of the Environment previously shared for public review and comment seven (7) proposed cold water existing use determination and rationale documents.
The public comment period for these proposals was held from September 6, 2024 to December 9, 2024. The Department has reviewed the public comments received and the public comment response document is published here.
Four (4) existing use determinations were finalized and are posted under the dropdown below titled "Completed Existing Use Determinations". The Department is not making a final determination on three (3) existing use determinations on the North Branch Potomac River at this time. For more information, please refer to the Department's public comment response document. To access the original proposal documents, please see the dropdown below titled "Public Review Archive"
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In addition to defining designated uses as part of water quality standards, the implementing regulations of the CWA, found in Code of Federal Regulations (CFR) Title 40 § 131.3(e), also establish the concept of an “existing use”, one of the foundational principles for antidegradation policy. Here, 40 CFR § 131.3(e) defines existing uses as “…those uses actually attained in the water body on or after November 28, 1975, whether or not they are included in the water quality standards”. Federal regulations additionally discuss existing uses in 40 CFR § 131.12(a), part of the Code of Federal Regulations that establishes the basis for EPA and state’s Antidegradation Policy. Here the regulation asserts that “at a minimum…(1) Existing instream water uses and the level of water quality necessary to protect the existing uses shall be maintained and protected.” Existing uses therefore represent the highest level of use and water quality (necessary to support that use) that has been achieved since 1975. In this manner, existing uses function as the baseline or floor of water quality that must be maintained regardless of the codified designated use.
Maryland’s Code of Regulations (COMAR) also establishes protections for existing uses. Specifically, Maryland’s Antidegradation Policy regulation (COMAR regulation 26.08.02.04) echoes the federal regulations by saying “A. Waters of this State shall be protected and maintained for existing uses and the basic uses of water contact recreation, fishing, protection of aquatic life and wildlife, and agricultural and industrial water supply as identified in the Use Class designations.” and “B. Consistent with the Federal Act, existing uses and the level of water quality necessary to protect existing uses for any water body shall be maintained.”
Further, Maryland’s regulations provide Antidegradation Policy Implementation Procedures for the Tier I level of protection in COMAR 26.08.02.04-1 which state that “A. All waters of the State shall receive Tier I protection which requires the protection and maintenance of existing uses and designated uses.” and “B. Protections. Waters that have demonstrated an existing use that is not protected by the water quality criteria specified by the current designated use for this water body shall be protected so as to maintain the existing use and the water quality necessary to protect the existing use.”
MDE formed a Cold Water Advisory Committee composed of stakeholders and subject matter experts to assist the Department in developing MDE’s policy and procedures for identifying cold water existing uses and outlining steps designed to reduce regulatory uncertainty. This policy and procedures were formalized as the “
Cold Water Existing Use Determinations: Policy and Procedures” document that was incorporated by reference in COMAR 26.08.02.04-1.
Completed Existing Determinations
Recent data have shown that the current use classification of some Maryland surface waters was not protective of their existing use and specifically that of a cold water existing use. The existing uses of these streams are formally recognized by the Department and, as a result, some surface waters were reclassified to use Class III (or III-P) where data demonstrated that the Class III designated use and criteria were being attained. The following existing use determination documents provide justification for and describe the scale of existing use determinations and use classification changes where applicable. These existing uses are also shown on
MDE's Designated Uses Map.
No existing use determination documents are currently undergoing public review at this time.
2019 / 2022 Public Review
Nineteen (19) existing use determinations received public review and comment with the
2019 Triennial Review in March-April of 2022 and were made final in October 2022. MDE received EPA approval for the 2019 Triennial Review on June 28, 2023. The final documents can be found in the table under the Completed Existing Use Determinations dropdown.
2024 Public Review
A notice for seven (7) proposed existing use determinations was published in the September 6, 2024 edition of the Maryland Register. The public comment period for the following proposed existing use determination documents began on September 6, 2024 and closed on December 9, 2024. A public hearing was held both virtually and in-person on Monday, December 2, 2024 from 5:30 p.m. to 7:30 p.m. for the proposed North Branch Potomac River (Allegany) existing use determination and rationale document.
Four (4) of the existing use determinations for UT Jacks Hole (Harford County), UT Broad Creek (Harford County), UT Michaels Run (Harford County) and Dog Creek (Washington County) were made final in April 2026. These final documents can be found in the table under the Completed Existing Use Determinations dropdown. The Department has not made a determination on the three (3) existing use proposals along the North Branch Potomac River. The original proposal documents are provided below for public reference. For more information, please see the Department’s discussion in the published
comment response document.
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Last Updated 04/2026
