EPA Approves Delaware's Plan to Keep Philly Air Particle-Free Until 2046
Published Date: 11/20/2025
Proposed Rule
Summary
The EPA is proposing to approve Delaware’s plan to keep the air clean in New Castle County, part of the Philadelphia area, by maintaining safe levels of tiny pollution particles through 2046. This plan helps protect people’s health and supports local transportation projects without extra costs. Comments on this plan are open until December 22, 2025, so everyone has a chance to weigh in!
Analyzed Economic Effects
4 provisions identified: 3 benefits, 1 costs, 0 mixed.
EPA proposes approval of Delaware PM2.5 plan
The EPA is proposing to approve Delaware’s Limited Maintenance Plan (LMP) for the New Castle County portion of the Philadelphia-Wilmington area for the 2006 24-hour PM2.5 standard. If approved, the plan covers the second 10-year maintenance period through September 4, 2034 and is intended to keep short-term fine particle levels below the 2006 24-hour NAAQS.
Transportation projects may avoid regional analysis
If the LMP is approved and found adequate, transportation conformity in New Castle County can be shown without a regional motor vehicle emissions analysis under 40 CFR 93.109(e). That means federally supported transportation plans and TIPs in the area may not need the regional emissions analysis tied to the 2006 24-hour PM2.5 standard while the LMP is adequate.
Contingency measures could impose controls
Delaware’s LMP includes contingency triggers and a menu of possible measures that would be implemented if pollution or emissions rise. A single-year 98th percentile 24-hour PM2.5 reading of 35.5 micrograms per cubic meter or greater, or a total PM2.5/NOX/SO2 emissions increase more than 10% above 2008 levels, can trigger a ‘warning level’ response; a three-year average (design value) of 35.5 micrograms per cubic meter or greater triggers an ‘action level’ response. Potential measures include tightening offset or control requirements for new or modified sources, diesel retrofit programs, vehicle inspection improvements, and other controls; implementation timelines set some actions to be in place within 30 months of the triggering event and regulatory steps to be completed within 12 months after modeling.
State will keep PM2.5 monitors running
Delaware (DNREC) committed to continue operating the PM2.5 air monitoring network in New Castle County throughout the second 10-year maintenance period and to periodically update emissions inventories. Ongoing monitoring is meant to verify continued attainment and to trigger contingency responses if needed.
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