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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.
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.