The EPA has a vast web presence but offers various means of navigating it. For basic information check out their "Learn the Issues" tab. More detailed scientific information on a variety of subjects is under "Science and Technology." There's also an interactive map for finding information by geographic area.
Here is their major page dealing with the topic of Sustainability.
Some other major subsidiary sites of EPA are:
Some important reports in the Library's government documents stacks:
Major tools for finding government information: