mr. brownell: thank you, mr. chief justice. >> it should be affirmed for three basic reasons first because it is the most natural reading of the text. it harm allies is -- it harmonizes the regulations cause it applies the same regulatory logic to power plants that congress directed for every other source and that is whether to list for regulation based on health and environmental hazard alone and considering costs. and as matter of common sense and government practice, it was certainly appropriate to list power plants based solely on health and environmental hazards because that reflects the approach that congress chose not only in this regulatory program but all of the major regulatory programs under the clean air act. chief justice roberts: you can see, don't you, that epa could have interpreted the statutory action to allow cost? mr. verrilli: i think the best interpretation of the statute is it did not provide for the consideration of cost of the listings age -- chief justice roberts: appropriate and necessa

mr. brownell: your honor, it is cost, cost, cost and having -- under the statutory criteria that congresst. and then having to apply those standards at the end of the process. it makes one determination and light of the costs and impacts and other factors. justice kennedy: do you think when the word appropriate is used, it requires a cost-benefit analysis in any context? mr.brownell: your honor, in any context that is so broad. i do not think i can say. but in this context, that regulation has certain characteristics and consequences we have talked about this morning, including the fact that it opposes on a pollutant that has no public health risk. >> this is something we should be concerned about because there is this regulatory impact assessment that is the benefit -- that is an impact through the process. they have appropriately calculated. >> the co-benefits -- all of those benefits -- are co-benefits. those co-benefits that are in the regulatory impact analysis were not considered as part of the regulatory determination for good reason. their legal importance and relevance under the