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Water Quality Standards

What are Water Quality Standards (WQS)?

Water Quality Standards (WQS) are the foundation of the water quality-based control programs mandated by the Clean Water Act. A standard can consist of either numeric or narrative criteria for a specific physical or chemical parameter and is used as the regulatory target for permitting, compliance, enforcement, and monitoring and assessing the quality of the state's waters. When assessments identify a waterbody as not meeting adopted water quality standards, the assessment may lead to a determination of impairment, initiating further action such as a Total Maximum Daily Load (TMDL) or other regulatory procedure aimed at addressing the impairment.

What are the components of WQS?

Water quality standards consist of:

  • Designated Uses: identification of how people, aquatic communities and wildlife use our waters (e.g., public water supply, protection and propagation of fish, shellfish, and wildlife, and recreation).
  • Water Quality Criteria: numeric or narrative in form and protect the designated uses. Numeric criteria are allowable concentrations of specific pollutants in a water body while narrative criteria are statements of unacceptable conditions in and on the water.
  • Antidegradation Policies: protection of existing uses and extra protection for high-quality or unique waters.

Where to find Indiana’s surface WQS and related implementation rules

Indiana surface waters are incorporated within either the Great Lakes system or the Mississippi River system. To account for differences in these systems, Indiana’s application of water quality standards is divided into three distinct categories of waters:

  1. Waters within the Great Lakes system (Lake Erie and Lake Michigan drainage basins);
  2. Waters not within the Great Lakes system (Ohio River and Illinois River drainage basins); and,
  3. The main stem of the Ohio River.

Indiana WQS are found in Title 327 of the Indiana Administrative Code (IAC) under Article 2 [PDF] and implementation procedures, such as the development of water quality-based effluent limitations (WQBELs), are found in Article 5. In addition, Indiana implements the Ohio River Valley Water Sanitation Commission Pollution Control Standards (ORSANCO Standards) for the main stem of the Ohio River.

U.S. EPA Approval of WQS Revisions

Under 40 CFR 131.21, U.S. EPA approval of revisions to Indiana WQS made on or after May 30, 2000 is required prior to their use for Clean Water Act purposes. These approvals are provided by letter from U.S. EPA Region 5. IDEM has received the following U.S. EPA approval letters for WQS rulemakings (2005 - Current):

Water Quality Standards Review

The federal Clean Water Act (CWA) requires all states to develop, review, revise, and adopt WQS. WQS must include the designated uses of the waterbody, water quality criteria necessary to protect those uses, and antidegradation provisions to protect the water quality.

Under the CWA, States are required to review their water quality standards every three years in a process known as the triennial review. This review is conducted to evaluate the need to update or revise the WQS to ensure that Indiana’s WQS reflect the best available science and support sound water quality management policies that improve and protect the surface water resources of the state.

2021 Water Quality Standards Review

The Indiana Department of Environmental Management (IDEM) initiated a review of its water quality standards (WQS) on March 24, 2021. IDEM held a public hearing to solicit public comment on Indiana’s WQS on May 12, 2021. The public comment period was open until close of business on May 23, 2021. IDEM did not receive comments regarding water quality standard updates or revisions during the public comment period or during the public hearing. IDEM also conducted an internal review among IDEM staff to rank priorities for revising and updating Indiana water quality standards.

IDEM prepared the 2021 Review of Indiana’s Water Quality Standards Final Report [PDF] to create a record of the WQS Review process. IDEM submitted this report to U.S. EPA Region 5 on July 22, 2021.

2024 Water Quality Standards Review

IDEM will be initiating the next WQS (triennial) review in 2024. Stay tuned for more information later this year on the 2024 WQS Review. Please subscribe below to receive updates via e-mail when the WQS page is updated.

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Additional Information

For additional information, please contact the Water Quality Standards Coordinator at the Office of Water Quality.

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