Water Quality Standards

Triennial Review of Mississippi’s Water Quality Standards

The Clean Water Act requires all states to develop, review, revise, and adopt water quality standards every three years known as the triennial review.  Water quality standards must include three components: (1) the designated uses for the state’s waterbodies, (2) the water quality criteria (narrative or numeric) necessary to protect those uses, and (3) antidegradation provisions to protect water quality.

The public comment period for the triennial review of water quality standards began on February 11, 2021. A 10-day extension on the public comment period was requested by stakeholders and granted by MDEQ and comments were accepted up until April 9, 2021.

A public hearing was held regarding the proposed regulations on Tuesday, March 30, 2021 at 11:00 a.m. Due to issues associated with the COVID-19 pandemic, it was held telephonically. The public was invited to participate, to ask questions of the staff, to gain information regarding the proposed modifications to the regulations, and to present verbal comments on the proposed regulations.

A red-line version of the proposed regulations that includes changes in response to comments received by the public is published below.

On June 24, 2021, the Commission on Environmental Quality adopted amendments to Tile 11 of the Mississippi Administrative Code, Part 6, Chapter 2, entitled “Mississippi Commission on Environmental Quality Regulation for Water Quality Criteria for Intrastate, Interstate and Coastal Waters,” also known as Mississippi’s Water Quality Standards. This action is also reflected in Commission Order No. 7137-21 dated July 6, 2021.

In accordance with Miss. Code Ann. § 49-17-41, within thirty (30) days of the date of the Order, any interested person may request that a hearing be conducted regarding the issuance of this Order.  Such request must be made in writing to Mr. Chris Wells, Executive Director, Mississippi Department of Environmental Quality, P.O. Box 2261, Jackson, Mississippi 39225.

If there is no request for a hearing within 30 days of the Order, the next step in the triennial review process is to submit the Commission-adopted revisions of the Mississippi Water Quality Standards to EPA Region 4 for their review.

If you have questions or would like further information, please contact Kim Caviness at kcaviness@mdeq.ms.gov or Patrick Felch at pfelch@mdeq.ms.gov.

Draft Modifications to WQS for Triennial Review

Proposed Amendments to be presented to the Commission on Environmental Quality Regulations

Found below are the Public Comments that MDEQ Staff received during the Public Notice period along with MDEQ’s response to those comments.

To contact staff, click here.

About Water Quality Standards

Click here for the designated uses of the following streams:

  • Big Black River Basin
  • Coastal Streams
  • North Independent Streams
  • Pascagoula River Basin
  • Pearl River Basin
  • South Independent Streams
  • Tennessee River Basin
  • Tombigbee River Basin
  • Yazoo River Basin
About Water Quality Standards

Water quality standards are regulations that are designed to protect the surface waters of the State. They contain statements and numeric limits that are adopted through administrative rule-making procedures. The standards set forth the water quality needed to protect the uses of the water, such as swimming, public water supply, and the propagation and growth of aquatic life.

Under the Clean Water Act passed in 1972 by Congress, every state must develop and adopt water quality standards to protect, maintain, and improve the quality of the nation’s surface waters. The goal of the Clean Water Act is to “restore and maintain the chemical, physical, and biological integrity of the Nation’s waters”. The interim goal is to have “water quality which provides for the protection and propagation of fish, shellfish and wildlife, and provides for recreation in and on the water”, wherever attainable. The standards represent a level of water quality that will support the goal of “swimmable fishable” waters.

Water quality standards apply to ambient waters, as opposed to discharges. These ambient standards form the basis of water quality based permit limitations that regulate the discharge of pollutants into surface waters under the National Pollutant Discharge Elimination System (NPDES) permit program. The NPDES permit regulations are the implementation tools of the water quality standards.

Additionally, the standards do not apply directly to municipal drinking water supplies. Drinking water treatment and distribution is regulated by the Mississippi Department of Health, Water Supply Division.

State and Federal Laws and Regulations

Water quality standards requirements are embodied in both state and federal laws and regulations. State law mandates in Section 49-17-19 the protection of public health and welfare and the present use of waters for public water supplies, propagation of fish and aquatic life and wildlife, recreational purposes, and agricultural, industrial, and other legitimate uses. The adoption of water quality standards is the method of accomplishing the law’s purpose.

Mississippi’s water quality standards regulations are entitled Regulations for Water Quality Criteria for Intrastate, Interstate, and Coastal Waters. This document contains all the water quality standards applicable to the state’s surface waters.

The Federal Clean Water Act requires states to adopt water quality standards and hold a public hearing regarding the adoption once every three years. The Federal Regulations at 40 CFR 131 describe the required elements of a state’s water quality standards program. The federal laws and regulations can be viewed by clicking here.

Mississippi’s Water Quality Standards

Mississippi’s water quality standards include four major components:

  • designated uses,
  • narrative “free froms”,
  • numeric criteria, and
  • antidegradation provisions.
Designated Uses

Designated uses are those uses specified in water quality standards for each water body or segment whether or not they are being attained. They take into consideration the use and value of water for public water supplies, protection and propagation of aquatic life, recreation in and on the water (such as swimming and boating), and protection of consumers of fish and shellfish. Mississippi waters are classified into the following uses:

  • Public Water Supply
  • Shellfish Harvesting
  • Recreation
  • Fish and Wildlife
  • Ephemeral
    Attainment of these uses is based on specific numeric and narrative criteria which are also specified in the water quality standards.
Water Quality Criteria

Water quality criteria can include general narrative statements (narrative criteria) and specific numerical concentrations that are calculated to protect aquatic life and human health (numeric criteria). During each triennial review, the criteria are adjusted as needed to reflect changes in law and science.

Narrative “Free Froms”

Narrative “free froms” are general water quality criteria that apply to all surface waters. These criteria state that all waters shall be free from sludge, floating debris, oil and scum, color and odor producing materials, and substances that are harmful to human, animal, or aquatic life. The standards also read that there shall be “no toxics in toxic amounts,” which provides the regulatory basis for establishment and enforcement of Whole Effluent Toxicity (WET) limitations in NPDES permits.

Numeric Criteria

Numeric criteria are estimations of concentrations of chemicals and degree of aquatic life toxicity allowable in a waterbody without adversely impacting its designated uses. For aquatic life criteria, EPA determines both acute and chronic water quality criteria in fresh waters as well as salt waters.

EPA periodically compiles results of toxicity tests in which the sensitivity of aquatic organisms to regulated pollutants is determined. In these studies, fish and benthic macroinvertebrates are exposed to known concentrations of a chemical. The short term (acute) and long term (chronic) effects of the exposure are measured, and the results are used to set water quality criteria protective of the most sensitive of species.

Human health water quality criteria are derived based on studies done on the carcinogenic and neurological effects of chemicals to mammals, such as mice, which are then extrapolated to estimate the potential effects to humans.

Based on these tests, national criteria recommendations and guidelines are published by EPA. Mississippi uses these national criteria recommendations, along with other scientific information, to set appropriate water quality criteria for our surface waters. Mississippi adopts numerical criteria for approximately 36 chemicals, which are shown in Table 1 of the standards document. For those chemicals, which do not have a state-adopted water quality criterion, we refer to EPA’s latest national compilation of criteria recommendations. The latest compilation can be accessed by clicking here.

Numeric Nutrient Criteria

MDEQ is actively working to develop numeric nutrient criteria for Mississippi’s various water body types. MDEQ’s mission is to develop scientifically defensible criteria that are appropriate and protective of Mississippi’s waters. The criteria for each water body type will be coordinated with other water body types to ensure consistency across the state and protection from downstream impacts. Mississippi’s Nutrient Criteria Development Plan can be read by clicking on the link below.

Antidegradation Provisions

The antidegradation provisions describe the conditions under which water quality may be lowered in surface waters. Designated uses must be maintained and protected, and in no case may waters be degraded below the levels necessary to protect existing uses. Water quality better than that needed to protect designated uses must be maintained unless lower quality is deemed necessary to allow important economic or social development.

In theory, antidegradation protects water quality at three levels or “tiers”.

  • Tier 1 specifies that existing instream water uses and the level of water quality to protect the existing uses shall be maintained and protected. This means that as a minimum, all waters should meet adopted water quality standards.
  • Tier 2 protects water that is better than specified water quality standards. Only in limited circumstances may water quality be lowered in these waters.
  • Tier 3 are exceptional waters where no new, additional, or increased discharge of sewage, industrial wastes, or other pollution are allowed. These waters must be specifically listed in the regulation. To nominate a water for Outstanding National Resource Waters (ONRW) consideration, please follow the ONRW Nomination Guidance below.
Public Participation

Interested parties can provide input at any time to the department to be considered in the next triennial review. When water quality standards revisions are proposed, the public is notified of these revisions via newspapers, mailing lists, website, library and post office notifications. In accordance with federal requirements, a public hearing in Jackson, MS, is held to gather input and comments. Following consideration of comments and any necessary revisions, the standards are adopted by the Mississippi Commission on Environmental Quality. After adoption, the document is submitted to EPA for review and approval. Upon approval by EPA, the Standards become effective and can be implemented in NPDES permits, TMDL’s, and other affected programs.