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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, propagation of aquatic life, 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. The Indiana Department of Environmental Management (IDEM) initiated a review of its water quality standards (WQS) on February 28, 2018. IDEM held a public hearing to solicit public comment on Indiana’s WQS on April 11, 2018. The public comment period was open until close of business on April 26, 2018. IDEM received three sets of comments [PDF] during the public comment period and one comment during the public hearing.

IDEM prepared the Review of Indiana Water Quality Standard - Final Report, July 2, 2018 [PDF] to create a record of the WQS Review process. IDEM submitted this report to U.S. EPA Region 5 on July 2, 2018.

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Additional Information

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

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