EPA Region 6 issued a Revised Designation Decision on December 9, 2024, determining that stormwater discharges from small Municipal Separate Storm Sewer Systems (MS4s) operated by Los Alamos County, the New Mexico Department of Transportation, and Los Alamos National Laboratory in Los Alamos and Santa Fe Counties, New Mexico are contributing to violations of New Mexico Water Quality Standards and require NPDES permit coverage under the Clean Water Act. This decision revises EPA's December 16, 2019 designation, which had been remanded by the U.S. Court of Appeals for the Tenth Circuit, and responds to a 2014 petition filed by Amigos Bravos.12