E&S Environmental Chemistry, Inc., working together with the U.S. Environmental Protection Agency (EPA) and under the direction of the USDA Forest Service (USFS), assisted the USFS in the development of a decision-support system (DSS) for critical loads (CL) of atmospheric sulfur (S) deposition in the southeastern United States. The spatial coverage of the study region included the Ridge and Valley and Central Appalachian ecoregions in Virginia and West Virginia and the Blue Ridge Ecoregion in Virginia, West Virginia, North Carolina, and Tennessee. The research team developed the DSS in this project as an application of the Ecosystem Management Decision Support (EMDS) system, originally developed at the USFS PNW Research Station. EMDS is an application framework for knowledge-based decision support for environmental analysis and planning at multiple geographic scales. The system integrates geographic information with logic- and decision-modeling technologies to provide a spatial analysis system for data management and environmental risk assessment. E&S compiled water chemistry data across the study region from a variety of EPA and USFS water quality databases. The final data set included water chemistry measurements at 933 stream sites. Dynamic model estimates of base cation weathering were developed for 140 of the 933 water chemistry sites, and were used to develop regional predictions of steady-state CLs, based on tests of a variety of multivariate modeling techniques. All data were upslope averaged to develop potential predictor variables above each pour point in GIS. Project completion date was April 2012.