Bslc: A tool for bacteria source characterization for watershed management

The Total Maximum Daily Load (TMDL) program is an integrated watershed assessment and management process designed to address surface water quality impairments. The presence of pathogen indicator bacteria [fecal coliform and Escherichia coli (E. coli)] is reported to be the most widespread cause of water quality impairment in the United States. Watershed-scale simulation models, when used in a "what-if" scenario assessment mode, can assist stakeholders and watershed planners in making informed immediate and long-term land-use-based watershed management decisions designed to control bacterial contamination and improve water quality. However to use such models, accurate characterization of bacteria sources present in a watershed is necessary. Tire objectives of this article are to describe the process developed and used by the Center for TMDL and Watershed Studies at Virginia Tech to characterize bacterial source inputs needed for a watershed-scale simulation model and to introduce a software tool, the Bacteria Source Load Calculator (BSLC), that aids in the source characterization and TMDL allocation scenario development process.The BSLC uses externally generated inputs, such as land use distribution and livestock, wildlife, and human population estimates, to calculate monthly bacterial land loadings and hourly bacterial stream loadings. The program was developed using Visual Basic for Applications (VBA) in Microsoft Excel. The BSLC and its underlying methodology have been used in the development of 21 bacterial TMDLs in Virginia. The BSLC software greatly simplifies the creation of required data files needed by watershed-scale simulation models and provides consistency in data development and processing.