Protecting the nation's land, air and water would reasonably be considered to be in the "general welfare" of the US.
Ron Paul on the environment and the EPA:
Q: What makes you the strongest candidate on energy and the environment?
A: On environment, governments don't have a good reputation for doing a good job protecting the environment. (my comment: so much for the accomplishments of the Clean Air Act, Clean Water Act....). If you look at the extreme of socialism or communism, they were very poor environmentalists. (wtf? is the EPA a commie institution?) Private property owners have a much better record of taking care of the environment....
....
Q: What do you see as the role of the Environmental Protection Agency?
A: You wouldn't need it. Environmental protection in the U.S. should function according to the same premise as "prior restraint" in a newspaper....
http://www.grist.org/feature/2007/10/16/paul/
This is not someone I want in a position of responsibility for environmental policy.