Environmental response to acidic deposition occurs through the vehicle of water movement in the ecosystem. As a part of the environmental studies for acidic deposition in the ecosystem, output-based hydrologic classification was done from basin hydrologies based on the distribution of the baseflow, snowmelt, and the direct runoff sources. Because of the differences in the flow paths and exposure duration, those components were assumed to represent distinct geochemical responses. As a first step, user-friendly software has been developed to calculate the baseflow based on the separation of annual hydrographs. It also generates the hydrograph for visual analysis using trial separation slope. After the software was completed, about 1200 stream flow gauging stations in Northeastern U.S. were accessed for flow separation and other hydrologic characteristics. At the final stage, based on the output from the streamflow analysis, cluster analysis was performed to classify the streamflow behaviors in terms of acidic inflow. The output from the cluster analysis shows more efficient regional boundaries of the subregions than the current regional boundaries used by U.S. Environmental Protection Agency (U.S.E.P.A.) for the environmental management in terms of acidic deposition based on the regional baseflow properties.