How are TMDLs developed?

How are TMDLs developed?

First, the water body must be identified, based on scientific monitoring, as an impaired water body. MDEQ collects data and information that lead to an assessment of the quality of the water. Waters that are impaired by a pollutant are included in the state’s Section 303(d) list. Waters on this list are scheduled for TMDL development. TMDLs are developed for the most sensitive environmental conditions, i.e., stream flow, temperature, weather conditions, etc., using data compiled in a particular geographic area or watershed. Scientifically accepted mathematical methods are used to develop the TMDL. Computer models that represent what is happening in nature are used for the more complex situations to predict how certain pollutants behave in the water body. A GIS (geographic information system) format may be used to provide the framework for the model’s information, particularly land use distribution, land elevations, and soils information. Data and information may include the relative contribution of point and nonpoint sources of pollutants. These computer models can be used to add or remove simulated pollutant loads to calculate the maximum amount allowable.