A report prepared for the Council on Environmental Quality *I would like to acknowledge the helpful comments and suggestions

and William Watson. Of course I bear sole responsibility for any errors, and for all judgments, interpretations, and conclusions. DISCLAIMER Although prepared with EPA funding, this report has neither been reviewed nor approved by the U.S. Environmental Protection Agency for publication as an EPA report. The contents do not necessarily reflect the views or policies of the U.S. Environmental Protection Agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use. CHAPTER