and capricious. Cf. NRDC v. Costle, 568 F.2d 1369, 1380 (D.C.Cir.1977) (“[W]hen numerical effluent limitations are infeasible, EPA may issue permits with conditions designed to reduce the level of effluent discharges to acceptable levels.”). In the face of the severe technological limitations on monitoring, it was reasonable for EPA to decline to require monitoring for parameters for which it is currently impractical to collect and analyze samples. Functionality monitoring and biological indirect monitoring are the only feasible options at present to assure com pliance with the permit. We defer to EPA’s decision that functionality monitoring and biological indicator monitoring, when used in combination, offer an acceptable “other measurement.” See Auer, 519 U.S. at 461, 117 S.Ct. 905 (<HOLDING>). b. Monitoring Requirements for WQBELs
holding that courts should defer to agencys interpretation of its own regulations if not plainly erroneous or inconsistent with the regulation holding that deference is owed to an agencys interpretation of its own categorical exclusion regulations so long as that interpretation is not plainly erroneous or inconsistent with the regulation holding that an agencys interpretation of its own regulations is controlling unless plainly erroneous or inconsistent with the regulation citation and quotation marks excluded holding that an agencys interpretation of its own regulations is entitled to deference holding that a secretarys interpretation of a departments regulation is controlling unless plainly erroneous or inconsistent with the regulation