The System for Urban Stormwater Treatment and Analysis Integration (SUSTAIN) was developed by the U.S. Environmental Protection Agency (EPA) to provide stormwater managers with a decision support system for the cost-efficient selection and placement of stormwater best management practices (BMPs) in urban watersheds. The SUSTAIN modeling system integrates simulation based on sound science and engineering principles, with cost estimation tools, and optimization to support users in selecting the best solutions on the basis of cost and effectiveness. This report documents the enhancements to the system since the initial release of version 1.0 in October 2009. Two case studies also provide insight into the application of the system, and demonstrate the utility of SUSTAIN in evaluating the use of green infrastructure (GI) in communities addressing the mitigation of combined sewer overflows (CSOs). SUSTAIN's innovative integration of optimization and simulation of BMP performance in a watershed setting provides significant capabilities to support the evaluation of various configurations of BMPs, the impact of local site conditions on BMP placement, and the types and relative costs of the BMPs available.