Scientific evidence has shown that atmospheric deposition of sulfur and nitrogen compounds can harm ecosystems. Title IV of the Clean Air Act Amendments of 1990 (CAAA or the Act) addresses the problem of such effects by mandating reductions in emissions of sulfur and nitrogen oxides, the major precursors of acidic deposition. Coupled with Titles I and II of the Act, which address new and existing stationary and mobile sources of sulfur and nitrogen oxides, implementation of Title IV is expected to provide significant benefits to the United States and Canada. These benefits include decreases in the acidity of lakes and streams, concomitant improvements in fish population diversity and health, decreases in soil degradation and forest stress, improvements in visibility (especially to scenic vistas), decreases in damage to materials and cultural resources, and a reduction in human health effects. Congress included Section 404 in Title IV (Appendix B of the Act) requiring the Environmental Protection Agency (EPA or the Agency) to provide a report to Congress on the feasibility and effectiveness of an acid deposition standard or standards to protect sensitive and critically sensitive aquatic and terrestrial resources. Specifically, Congress listed six areas to be addressed in the report:
             · Identification of sensitive and critically sensitive aquatic and terrestrial resources in the U.S. and Canada which may be affected by the deposition of acidic compounds;
             · Description and specification of a numeric value for an acid deposition standard sufficient to protect such resources;
             · Description of the use of such standard or standards in other Nations or by any of the several States in acidic deposition control programs;
             · Description of measures that would be needed to integrate such standard or standards with the control program required by Title IV of the Clean Air Act;
             · Description of the sta...