BSLC: A TOOL FOR BACTERIA SOURCE CHARACTERIZATION FOR WATERSHED MANAGEMENT

Abstract

The Total Maximum Daily Load (TMDL) program is an integrated watershed assessment and management processdesigned to address surface water quality impairments. The presence of pathogen indicator bacteria [fecal coliform andEscherichia 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 andwatershed planners in making informed immediate and long-term land-use-based watershed management decisions designedto control bacterial contamination and improve water quality. However, to use such models, accurate characterization ofbacteria sources present in a watershed is necessary. The objectives of this article are to describe the process developed andused by the Center for TMDL and Watershed Studies at Virginia Tech to characterize bacterial source inputs needed for awatershed-scale simulation model and to introduce a software tool, the Bacteria Source Load Calculator (BSLC), that aidsin the source characterization and TMDL allocation scenario development process. The BSLC uses externally generatedinputs, such as land use distribution and livestock, wildlife, and human population estimates, to calculate monthly bacterialland 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 inVirginia. The BSLC software greatly simplifies the creation of required data files needed by watershed-scale simulationmodels and provides consistency in data development and processing.