This report is intended to provide the reader with an understanding of the use of models in the development and implementation of total maximum daily loading (TMDL) studies.

The report focuses on the types of models used for TMDLs, the key assumptions underlying the models, how models are selected for specific surface waters and impairments, the data required to apply the models to a specific surface water and impairment, and how the predictive capability of the models is assessed.