PHOENIX (AP) — A federal court has denied two legal challenges to federal clean-air regulators' plan for reducing haze by limiting emissions from the Navajo Generating station, a coal-fired plant in northern Arizona. Rulings Monday by the 9th U.S. Circuit Court of Appeals turn down challenges filed by the Hopi Tribe and by environmental and conservation groups. One ruling said the Environmental Protection Agency acted reasonably in setting limits on nitrous oxide emissions. The second said the agency adequately consulted with the Hopi Tribe during the agency's rulemaking process and didn't have to consider certain technology matters. The plant's owners announced in February they plan to close it in December 2019 when their lease with the Navajo Nation expires. The owners have cited availability of less expensive power generating by burning natural gas.