Administrative law - citizen suit/environment
Statute's requirement that there not be a pre-existing diligent prosecution of rights under the statute in order to permit a citizen suit is a substantive requirement, not a jurisdictional bar to suit.
A final judgment resulting from a diligent prosecution does not, in itself, remove the bar to citizen suit.
Diligent enforcement of outcome acts as a per se bar to citizen suit.
http://www2.ca3.uscourts.gov/opinarch/152041p.pdf
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.