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Section 303(d) Frequently Asked Questions

What is the 303(d) list?

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

The 303(d) list is published by the Indiana Department of Environmental Management (IDEM). The 303(d) list is part of the more comprehensive Consolidated List that IDEM submits to U.S. EPA with the Indiana Integrated Water and Monitoring Assessment Report (IR) every two years. The IR and the Consolidated List are required by U.S. EPA under Section 305(b) of the Clean Water Act.

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 divides pollutant loadings among point and non-point sources. A TMDL provides information that can be used to guide watershed restoration activities aimed at mitigating the impairment(s) identified on the 303(d) list.

IDEM also uses the 303(d) list for the purposes of prioritizing IDEM’s monitoring efforts and to help prioritize watersheds for grant funding for watershed groups and other organizations working to improve water quality.

Why does IDEM develop the 303(d) list?

Section 303(d) of 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 (IR) every two years. The IR and the Consolidated List are required by U.S. EPA under Section 305(b) of the Clean Water Act.

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

Most of the data IDEM uses to develop the 303(d) list comes from IDEM’s surface water quality monitoring programs. Some data are collected using a rotating basin approach in which IDEM staff monitor at sites selected through a stratified random design in one of nine major water management basins each year. IDEM staff assess the data collected in each basin the following year. With this strategy, IDEM can monitor the entire state over a period of nine years. IDEM also uses data from its other water quality monitoring programs including its TMDL Watershed Characterization, statewide Fixed Station, and Fish Tissue Contaminants programs.

In addition, IDEM obtains data from other entities including the Ohio River Valley Water Sanitation Commission (ORSANCO) and Indiana University’s Clean Lakes Program.

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 and listing criteria to ensure our program complies with federal requirements.

U.S. EPA requires that states develop a document (the Consolidated Assessment and Listing Methodology or CALM) to guide impairment decisions. The CALM is updated for each assessment and listing cycle (every two years) to incorporate any changes to Indiana’s water quality standards or other criteria, the most recent U.S. EPA guidance, and new scientific information.

Using the CALM, IDEM staff review and assess water quality data and determine whether applicable water quality standards are being met. The CALM helps IDEM place waters into one of five categories which identify if the waterbody is "impaired", "not impaired", or if the current condition is unknown. The 303(d) list consists of waters in Category 5 that are impaired and for which TMDLs are required; categories 1-4 are described in more detail below. Staff also use the CALM to determine when a previously impaired waterbody should no longer be included on the 303(d) list.

Waterbody assessment decisions are applied through the use of assessment units, which are pre-defined sections of streams; assessment units may also comprise entire lakes or reservoirs. Stream and river assessment units have similar features, such as hydrology, surrounding land use, and potential sources of pollutants. Assessment units can vary from less than a mile up to 28 miles and may be composed of multiple small streams in a watershed to multiple-mile long sections of larger rivers. 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 similar given all the factors that could affect water quality such as the underlying geology or the presence of permitted facilities and farms. The use of assessment units allows IDEM to apply the results of a single sample location to a much larger area of the waterbody that shares similar features.

What Is the Difference Between the Consolidated List and the 303(d) List?

The Consolidated List is a list of all assessment units in Indiana including those that have been fully or partially assessed and those for which no assessments have yet been made. To develop the Consolidated List, IDEM places each assessment unit into one of five categories depending on the degree to which it supports the designated beneficial use in question. Designated beneficial uses for waterbodies are defined in Indiana Administrative Code and include protection of aquatic life, recreational uses, fish consumption, and use as a public water supply source.  Because IDEM makes use support assessments for three to four of the beneficial uses designated for each waterbody, a single waterbody may appear in one or more categories of the Consolidated List. The 303(d) list is a subset of the Consolidated List and includes all impairments identified in Category 5.

What are the categories on the Consolidated List?

Category 1: All designated uses for the assessment unit are supported, and no use is threatened. This category is used when all designated uses have been assessed as "not impaired".

Category 2: The available data and/or information indicate that some but not all the designated uses are supported. This category is used when at least one designated use is assessed as "not impaired" but at least one other designated use has not been assessed.

Category 3: The available data and/or information are insufficient to make a use support determination. This category is usually used when an assessment unit has not been assessed by IDEM.

Category 4: The available data and/or information indicate that at least one designated use is impaired or threatened, but a total maximum daily load (TMDL) is not required for one of the following reasons.

  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. The impairment is not caused by a pollutant. Category 4C may be used when impairments are determined to be due to natural causes such as drought.

Category 5: The available data and/or information indicate that at least one designated use is impaired or threatened and a TMDL is required. Waters may be listed in both 5A and 5B depending on the parameter(s) causing the impairment. Indiana’s 303(d) list is comprised of all waters in Category 5.

  1. The waterbody has one/more impaired biotic communities or is impaired for one/more pollutants.
  2. The waterbody is impaired due to the presences of presence of mercury, 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 is 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 4C of the Consolidated List. Naturally intermittent flow and other natural causes are typical of the impairments included in Category 4C, 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 the best use of limited resources. These impairments are listed in Category 4B of the Consolidated List.

Once a TMDL has been completed for an impairment, it may be removed from the 303(d) list, and placed in category 4A of the Consolidated List.

The completion of a TMDL is just the first step in remedying an impairment. Once a TMDL is completed, IDEM works with local watershed groups wherever possible to implement the recommendations in the TMDL document. These recommendations are intended to help restore the waterbody 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 45-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 submittal to U.S. EPA.

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