On December 20, 2017, EPA took the next step in completing the area designation process under the 2015 ozone standard. Specifically, the Agency issued “120-day letters” to the states proposing designations for all areas of the U.S. that were not designated as part of the Agency’s November 6, 2017 rulemaking designating 2,646 areas as either attainment or unclassifiable under the 2015 ozone standard. Under the Clean Air Act, states recommend area designations and if EPA intends to modify a state’s recommended designation, it must notify the state no later than 120 days prior to making the final designation and give the state an opportunity to respond.

Of the 30 letters that EPA issued to states, a few indicated that EPA agreed with the state’s initial recommendation. Most, however, indicated that EPA intended to make at least some adjustment to the boundaries of unclassifiable or nonattainment areas proposed by the state. Each letter was accompanied by a Technical Support Document, which, along with the 120-day letters, can be found here.

EPA has issued a pre-publication notice that will appear in the January 5, 2017 Federal Register, which will notify the public of the issuance of the 120-day letters and provide a 30-day comment period for interested parties to respond to the proposed designations. States receiving 120-day letters were given until February 28, 2018 to submit any information they would like EPA to consider in issuing final designations. Based on the date of the 120-day letters, final area designations are expected on or after April 19.