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Nonpoint Source Water Pollution

Nonpoint Source > Watershed Assessment > Impaired Waters - Integrated Report > IDEM’s Consolidated Assessment and Listing Methodology (CALM) IDEM’s Consolidated Assessment and Listing Methodology (CALM)

The Indiana Department of Environmental Management’s (IDEM’s) Consolidated Assessment and Listing Methodology (CALM) is a document (currently under development) that guides IDEM's Clean Water Act (CWA) Section 305(b) assessments and the Section 303(d) listing processes. The CALM describes IDEM’s methods for defining waterbody assessment units, which are streams or reaches of streams with similar features, such as hydrology, which makes them representative for assessment purposes. Lakes are each considered a single unit for the purposes of assessments.


  • Is based on federal CWA requirements and Indiana’s water quality standards;
  • Describes the type and amount of data needed to make water quality assessments for each designated use;
  • Describes the water quality criteria and other decision-making criteria used to determine, based on the available data, whether a waterbody meets its designated uses;
  • Provides the scientific rationale for any new or revised assessment methodologies;
  • Provides guidelines regarding the placement of Indiana waters into the appropriate category of the State’s Consolidated List for each designated use; and,
  • Explains the decision-making criteria for adding and removing waters from the State’s 303(d) list of impaired waters.

IDEM uses a rotating basin approach, which divides the state into five major water management basin, to monitor Indiana's waters. One basin is monitored each year, and data for the monitored basin is analyzed the following year.

IDEM’s monitoring programs provide most of the data used in water quality assessments. However, IDEM also solicits and reviews existing and readily available water quality data from external organizations for potential use in its 305(b) assessment and 303(d) listing processes. Once the water quality data for a basin has been compiled, IDEM makes its assessments in accordance with the processes documented in the CALM.

The CALM is updated every 2 years to incorporate changes in water quality standards, changes in U.S. EPA guidance, new scientific information, and other applicable criteria. In order to lend transparency and encourage public input to the Agency’s assessment and listing processes, IDEM always publishes the CALM and the draft 303(d) list together in one notice, when the 303(d) list is published for the state-mandated 90-day public comment period.