Achieving Chesapeake Bay Program (CBP) nutrient and sediment reduction goals will require securing reductions largely from agricultural and urban nonpoint sources. While state and local governments rely largely on best management practices (BMPs) to achieve these goals, uncertainty surrounds the pollutant control effectiveness of these investments. Currently, the variation of BMP performance is not well documented or characterized in the CBP. Furthermore, knowledge gaps exist surrounding the sources and extent of the variation surrounding BMP performance. The purpose of this workshop was to make recommendations for improving the documentation and characterization of BMP performance uncertainty and to suggest how more detailed information on BMP uncertainty could be used to inform management decisions. Through this report, the workshop participants make several recommendations for characterizing uncertainty during the process of generating BMP effectiveness estimates (BMP Expert Panel Process). These include recommendations that the Chesapeake Bay Program partnership take measures to:

1. Systematically document and represent uncertainties throughout the BMP treatment process;
2. Produce information about the distribution of removal effectiveness of each BMP;
3. Develop a method for simply and effectively communicating the degree and type of uncertainty across all approved BMPs; and
4. Provide additional guidance for how to most effectively solicit “best professional judgment” as part of the expert panel process, including best practices for structured literature syntheses, identifying and avoiding potentially inappropriate heuristics (shortcuts) and biases when obtaining expert opinion, and expert elicitation.