A tiered approach to the mathematical modeling of acid precipitation, its fate and effects, might include: (1) a steady-state susceptibility model to assess long-term effects from average annual atmospheric loadings on surface and groundwaters; (2) a dynamic, regional model to assess the role of long-range versus point-source pollutant loadings for regulatory purposes and (3) a three-dimensional dynamic event model to assess the maximum environmental insult to a specific ecosystem during critical conditions such as a snow-melt event. An integrated approach is needed which considers the fate of pollutants from their origin through terrestrial and aquatic ecosystems to the ultimate water resource, groundwater.