What is the standard for a successful challenge under section 509 of the Civil Code of Civil Procedure?

substantially prevailing party whenever it determines that such award is appropriate. 33 U.S.C. 1369(b)(3). We have interpreted section 509 to require the Christiansburg dual standard, however. See Saint John's Organic Farm v. Gem County Mosquito Abatement Dist., 574 F.3d 1054, 1063-64, n. 1 (9th Cir.2009). Thus an unsuccessful challenge under section 509 brought in federal court will ordinarily not result in a fee award against the plaintiff who brought the challenge.