Proposed rule · 2025-24200

Proposed Revisions of the Nonattainment Designation for the 2008 and 2015 Ozone Standards and Clean Data Determinations for the 2008 and 2015 Ozone Standards: Cecil County, MD and New Castle County, DE

The Environmental Protection Agency (EPA) is proposing to approve two separate requests from Maryland and Delaware to revise the designation for the Philadelphia-Wilmington-Atlantic City, PA-NJ-MD-DE nonattainment area (hereafter referred to as the Philadelphia nonattainment area) for the 2008 primary and secondary ozone national ambient air quality standards (NAAQS) and the 2015 primary and secondary ozone NAAQS. Due to the concurrent requests from Maryland and Delaware, the EPA is proposing to revise the existing Philadelphia nonattainment area boundary into three distinct nonattainment areas that together cover the identical geographic area of the existing area. The EPA is also proposing to issue clean data determinations (CDDs) for the revised Maryland and Delaware nonattainment areas for both the 2008 and 2015 ozone NAAQS. The EPA is taking this action pursuant to Clean Air Act (CAA) sections 107, 110, 172, and 182.