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Nonpoint Source Water Pollution

Nonpoint Source > Watershed Assessment > Impaired Waters - Integrated Report > Section 303(d) List of Impaired Waters > Section 303(d) Frequently Asked Questions Section 303(d) Frequently Asked Questions

What is the 303(d) list?

The 303(d) list identifies where many of Indiana’s water quality problems exist and the nature of those impairments.

The 303(d) list is published by Indiana Department of Environmental Management (IDEM) as part of the more comprehensive Indiana Integrated Water Monitoring and Assessment Report (IR) every two years.

How does IDEM use the 303(d) list?

In accordance with the federal Clean Water Act, the primary purpose of the 303(d) list is to identify impairments for which a total maximum daily load (TMDL) study is needed. A TMDL identifies the maximum amount of pollutant that a waterbody can receive and still meet water quality standards, and allocates pollutant loadings among point and non-point sources. A TMDL provides information that can be used to guide restoration activities in the watershed aimed at mitigating the impairment(s) identified on the 303(d) list.

IDEM also uses the 303(d) list for the purposes of prioritizing monitoring efforts and to help prioritize watersheds for grant funding for water quality improvement practices.

Why does IDEM develop the 303(d) list?

The federal Clean Water Act requires states to provide a list of impaired waters to the United States Environmental Protection Agency (U.S. EPA).

The 303(d) list is part of the more comprehensive Consolidated List that is submitted to U.S. EPA with the Indiana Integrated Water and Monitoring Assessment Report every two years.

Where does IDEM get the data to develop the 303(d) List?

The large majority of the data used IDEM uses to develop the 303(d) list is collected by IDEM staff using a rotating basin approach. Using this approach, IDEM has divided Indiana into five major water management basins and monitors one of the five major basins each year. Therefore, each major basin is sampled by IDEM once every five years. IDEM staff assess the data collected in each basin within the following year.

IDEM obtains data from other entities, as well, including the United States Geological Survey, Indiana University’s School of Public and Environmental Affairs, and the Indiana State Department of Health.

IDEM also solicits water quality data from other colleges and universities and local organizations, such as county health departments, cities and towns, and watershed management groups.

How does IDEM make its 303(d) listing decisions?

IDEM follows U.S. EPA guidance in its assessment methodology, listing criteria, and actual listings to ensure our program complies with federal requirements.

To make decisions about impairments, IDEM uses a document called the Consolidated Assessment and Listing Methodology (CALM), which it has developed and updates based on federal Clean Water Act requirements and Indiana’s water quality standards. The CALM is revised to varying extents for each assessment and listing cycle (every two years) in order to incorporate any changes to Indiana’s water quality standards, and other applicable criteria, the most recent U.S. EPA guidance and new scientific information.

Using the CALM, IDEM staff review water quality data and determine which “assessment units,” or predetermined sections of streams, do not meet water quality standards or other applicable criteria. Staff also uses the CALM to determine when an assessment unit should no longer be listed on the 303(d) list.

Finally, the CALM also helps IDEM place waters in one of five categories, according to available data that make up Indiana’s Consolidated List. The 303(d) list consists of waters in Category 5 that are impaired and for which TMDLs are required.

Assessment units are areas of streams that are predetermined and have similar features, such as hydrology. Other factors considered when assessment units are developed are potential sources of pollutants, as well as whether the area is rural or urban. Assessment units can vary from less than a mile to 35 miles. This is because IDEM’s goal when defining the size of a given assessment unit is to determine the distance over which we can reasonably expect water quality conditions to be the same/similar given all the factors that could affect water quality such as land use, hydrology, the presence of permitted facilities and farms, etc. These factors will vary from stream to stream. So, the assessment units will also vary.

What are the categories on the Consolidated List?

Category 1 Attaining the water quality standard and other applicable criteria for all designated uses and no use is threatened.

Category 2 Attaining some of the designated uses; no use is threatened; and insufficient data and information are available to determine if the remaining uses are attained or threatened.

Category 3 Insufficient data and information is available to determine if any designated use is attained.

Category 4 Impaired or threatened for one or more designated uses, but does not require the development of a total maximum daily load (TMDL).

  1. A TMDL has been completed that is expected to result in attainment of all applicable water quality standards and has been approved by U.S. EPA.
  2. Other pollution control requirements are reasonably expected to result in the attainment of the water quality standards in a reasonable period of time.
  3. Impairment is not caused by a pollutant.

Category 5 The water quality standards or other applicable criteria are not attained.

  1. The waters are impaired or threatened for one or more designated uses by a pollutant(s), and require a TMDL.
  2. The waters are impaired due to the presence of mercury or PCBs, or both in the edible tissue of fish collected from them at levels exceeding Indiana’s human health criteria for these contaminants.

How does IDEM remove impairments from the 303(d) list (Category 5)?

U.S. EPA reviews Indiana’s draft 303(d) list and all the changes to the 303(d) list discussed in the Notice of Comment Period to ensure that all federal policies regarding listing and delisting are met. U.S. EPA also reviews IDEM’s CALM to ensure its consistency with Indiana’s water quality standards and other applicable criteria and that any changes to the methodology are consistent scientifically and within the context of federal policy.

No waters may be removed from the 303(d) list without U.S. EPA approval.

The following are considered by U.S. EPA to be acceptable reasons for removing impairments from a state’s 303(d) List of Impaired waters:

  • New data indicates that the impairment no longer exists.
  • IDEM has changed its assessment or listing methodology and, based on the new methodology, the water body would no longer be impaired.
    • IDEM’s CALM is considered by IDEM to be a living document and may be revised to reflect new science and/or changes in U.S. EPA policy.
    • Any time the CALM is revised, previous assessments must be revised to ensure that they are consistent with the new methods. In cases where they are not and their associated impairment decisions are found to no longer be valid, the impairment would be removed from the 303(d) list.
  • The impairment is not caused by a pollutant. The 303(d) list identifies impairments that require the development of a TMDL. Streams including stressors for which a load cannot be calculated are placed in Category 4(c). Naturally intermittent flow and other natural causes are typical of the impairments included in this Category 4(c), although it is not commonly used.
  • If it there are other means to ensure that the impairment is remedied. For example, if the impairment is caused solely by a permitted facility, IDEM would work with the facility to fix the problem rather than develop a TMDL for the impairment. This allows IDEM to make best use of limited resources.

Once a TMDL has been completed for the impairment, it may be removed from the 303(d) list, and placed under category 4 on the integrated list.

The completion of a TMDL is just the first step in remedying an impairment. Once a TMDL is completed, IDEM will work with local watershed groups wherever possible to implement the recommendations in TMDL document, which are intended to help restore the water body to the point at which it meets water quality standards.

Why does IDEM publish the 303(d) list and the CALM for public comment?

IDEM is required by state law to publish the draft 303(d) list for a 90-day public comment period. Publishing the list for public comment lends transparency to IDEM’s processes. IDEM also publishes its CALM with the draft 303(d) list to provide the public the opportunity to provide input regarding the assessment and listing processes that go into the development of the 303(d) list. Public input is important to these processes because it can potentially provide additional information for use in developing the 303(d) list. U.S. EPA also reviews IDEM’s draft 303(d) list and provides comments, which IDEM evaluates together with comments from the public to determine if changes are needed to the draft list prior to its approval by U.S. EPA.

The public notice period also allows the U.S. EPA an opportunity to begin reviewing the 303(d) list and provide comment. During this time, IDEM works to finalize the 303(d) list. The comments provided by U.S. EPA, like those submitted by the public, help to ensure the accuracy of the finalized 303(d) list prior to it submission to U.S. EPA for formal approval.