"This site is EPA’s premier site for accessing EPA publications, with more than 7,000 in stock and 35,000 digital titles, free of charge! EPA’s print publications are available through the National Service Center for Environmental Publications (NSCEP), and EPA’s digital publications are stored in the National Environmental Publications Internet Site (NEPIS) database! You can search and retrieve, download, print and/or order only EPA publications from this site. "
Some of these reports will be also listed in various government databases, like NTIS, NTRL, MarciveWeb DOCS, and also in WorldCat and Google. (NTIS does not provide links or access to the full text.)
The EPA National Library Network has updated its Core List for an Environmental Reference Collection