Air Plan Approval; Delaware; 2006 24-Hour Fine Particulate Matter Limited Maintenance Plan for the Philadelphia Nonattainment Area

ENVIRONMENTAL PROTECTION AGENCY <CFR>40 CFR Part 52</CFR> <DEPDOC>[EPA-R03-OAR-2025-0205; FRL-11969-01-R3]</DEPDOC> <SUBJECT>Air Plan Approval; Delaware; 2006 24-Hour Fine Particulate Matter Limited Maintenance Plan for the Philadelphia Nonattainment Area</SUBJECT> <HD SOURCE="HED">AGENCY:</HD> Environmental Protection Agency (EPA). <HD SOURCE="HED">ACTION:</HD> Proposed rule. <SUM> <HD SOURCE="HED">SUMMARY:</HD> The Environmental Protection Agency (EPA) is proposing to approve a limited maintenance plan (LMP) submitted by the Delaware Department of Natural Resources and Environmental Control (DNREC). This LMP is a revision to Delaware's state implementation plan (SIP) and addresses the New Castle County portion of the Philadelphia-Wilmington, PA-NJ-DE area (Philadelphia Area). The EPA is proposing to approve the New Castle County portion of the Philadelphia Area LMP because it provides for the maintenance of the 2006 24-hour fine particulate matter (PM <E T="52">2.5</E> ) national ambient air quality standard (NAAQS) through the end of the second 10-year maintenance period. In addition, the EPA is initiating the process to find the LMP adequate for transportation conformity purposes. This action is being taken under the Clean Air Act (CAA). </SUM> <EFFDATE> <HD SOURCE="HED">DATES:</HD> Written comments must be received on or before December 22, 2025. </EFFDATE> <HD SOURCE="HED">ADDRESSES:</HD> Submit your comments, identified by Docket ID No. EPA-R03-OAR-2025-0205 at <E T="03">www.regulations.gov,</E> or via email to <E T="03">gordon.mike@epa.gov.</E> For comments submitted at <E T="03">Regulations.gov,</E> follow the online instructions for submitting comments. Once submitted, comments cannot be edited or removed from <E T="03">Regulations.gov</E> . For either manner of submission, the EPA may publish any comment received to its public docket. Do not submit electronically any information you consider to be confidential business information (CBI) or other information whose disclosure is restricted by statute. Multimedia submissions (audio, video, etc.) must be accompanied by a written comment. The written comment is considered the official comment and should include discussion of all points you wish to make. The EPA will generally not consider comments or comment contents located outside of the primary submission ( <E T="03">i.e.</E> on the web, cloud, or other file sharing system). For additional submission methods, please contact the person identified in the <E T="02">FOR FURTHER INFORMATION CONTACT</E> section. For the full EPA public comment policy, information about CBI or multimedia submissions, and general guidance on making effective comments, please visit <E T="03">www.epa.gov/dockets/commenting-epa-dockets.</E> <FURINF> <HD SOURCE="HED">FOR FURTHER INFORMATION CONTACT:</HD> Sarah McCabe, Planning & Implementation Branch (3AD30), Air & Radiation Division, U.S. Environmental Protection Agency, Region III, 1600 John F Kennedy Boulevard, Philadelphia, Pennsylvania 19103. The telephone number is (215) 814-5786. Ms. McCabe can also be reached via electronic mail at <E T="03">mccabe.sarah@epa.gov.</E> </FURINF> <SUPLINF> <HD SOURCE="HED">SUPPLEMENTARY INFORMATION:</HD> On April 15, 2024, DNREC submitted a revision to the State's SIP. This revision is a LMP for the second 10-year maintenance period for the 2006 24-hour PM <E T="52">2.5</E> NAAQS for the New Castle County portion of the Philadelphia-Wilmington, PA-NJ-DE area. The Philadelphia Area is comprised of New Castle County in Delaware; Burlington, Camden, and Gloucester Counties in New Jersey; and Bucks, Chester, Delaware, Montgomery, and Philadelphia Counties in Pennsylvania. This action is expected to ensure that the State of Delaware meets CAA requirements. <HD SOURCE="HD1">I. Background</HD> <HD SOURCE="HD2"> A. The PM <E T="54">2.5</E> NAAQS </HD> Under section 109 of the CAA, the EPA has established NAAQS for certain pervasive air pollutants (referred to as “criteria pollutants”) and conducts periodic reviews of the NAAQS to determine whether they should be revised or whether new NAAQS should be established. The EPA sets the NAAQS for criteria pollutants at levels required to protect public health and welfare. <SU>1</SU> <FTREF/> The EPA's particulate matter standards address particles with diameters that are generally two and half micrometers or smaller (fine particulate matter or PM <E T="52">2.5</E> ) and particles with diameters that are generally 10 micrometers or smaller (PM <E T="52">10</E> ). PM <E T="52">2.5</E> is one of the ambient pollutants for which the EPA has established health-based standards. <FTNT> <SU>1</SU>  For a given air pollutant, “primary” national ambient air quality standards are those determined by the EPA as requisite to protect the public health. “Secondary” standards are those determined by the EPA as requisite to protect the public welfare from any known or anticipated adverse effects associated with the presence of such air pollutant in the ambient air. CAA section 109(b). </FTNT> Fine particulate matter contributes to effects that are harmful to human health and the environment, including premature mortality, aggravation of respiratory and cardiovascular disease, decreased lung function, visibility impairment, and damage to vegetation and ecosystems. Individuals particularly sensitive to PM <E T="52">2.5</E> exposure include older adults, people with heart and lung disease, and children. <E T="03">See</E> 78 FR 3086 at 3088 (January 15, 2013). PM <E T="52">2.5</E> can be emitted directly into the atmosphere as a solid or liquid particle (primary PM <E T="52">2.5</E> or direct PM <E T="52">2.5</E> ) or can be formed in the atmosphere (secondary PM <E T="52">2.5</E> ) as a result of various chemical reactions among precursor pollutants such as nitrogen oxides (NO <E T="52">X</E> ), sulfur dioxide (SO <E T="52">2</E> ), volatile organic compounds (VOCs), and ammonia (NH <E T="52">3</E> ). <SU>2</SU> <FTREF/> <FTNT> <SU>2</SU>  EPA, Air Quality Criteria for Particulate Matter, No. EPA/600/P-99/002aF and EPA/600/P-99/002bF, October 2004. </FTNT> On July 18, 1997 (62 FR 38652), the EPA revised the NAAQS for particulate matter to add new standards for PM <E T="52">2.5</E> . The Agency established primary and secondary annual and 24-hour standards for PM <E T="52">2.5</E> . The annual standard was set at 15.0 micrograms per cubic meter (µg/m <SU>3</SU> ) based on a 3-year average of annual mean PM <E T="52">2.5</E> concentrations, and the 24-hour (daily) standard was set at 65 µg/m <SU>3</SU> based on the 3-year average of the annual 98th percentile values of 24-hour PM <E T="52">2.5</E> concentrations at each population-oriented monitor within an area. <SU>3</SU> <FTREF/> <FTNT> <SU>3</SU>  The primary and secondary standards were set at the same level for both the 24-hour and the annual PM <E T="52">2.5</E> standards. </FTNT> On October 17, 2006 (71 FR 61144), the EPA promulgated the 2006 PM <E T="52">2.5</E> NAAQS. It retained the annual average NAAQS at 15.0 µg/m <SU>3</SU> but lowered the level of the 24-hour PM <E T="52">2.5</E> NAAQS to 35 µg/m <SU>3</SU> based on a 3-year average of the annual 98th percentile values of 24-hour concentrations. <SU>4</SU> <FTREF/> <FTNT> <SU>4</SU>  Under EPA regulations at 40 CFR part 50, the primary and secondary 2006 24-hour PM <E T="52">2.5</E> NAAQS are attained when the annual arithmetic mean concentration, as determined in accordance with 40 CFR part 50, appendix N, is less than or equal to 35 µg/m <SU>3</SU> at all relevant monitoring sites in the subject area, averaged over a 3-year period. </FTNT> On December 14, 2012, the EPA promulgated the 2012 PM <E T="52">2.5</E> NAAQS, including lowering the annual standard to 12.0 µg/m <SU>3</SU> based on a 3-year average of annual mean PM <E T="52">2.5</E> concentrations. The EPA maintained the 24-hour standard of 35 µg/m <SU>3</SU> based on a 3-year average of the 98th percentile of 24-hour concentrations. <E T="03">See</E> 78 FR 3086 (January 15, 2013). On February 7, 2024, the EPA revised the NAAQS for particulate matter to add new standards for PM <E T="52">2.5</E> . The EPA strengthened the level of the annual primary PM <E T="52">2.5</E> standard from 12.0 µg/m <SU>3</SU> to 9.0 µg/m <SU>3</SU> . The EPA retained the primary and secondary 24-hour PM <E T="52">2.5</E> standards, secondary annual PM <E T="52">2.5</E> standard, and primary and secondary PM <E T="52">10</E> standards. <E T="03">See</E> 89 FR 16202 (March 6, 2024). <HD SOURCE="HD2"> B. Designation of PM <E T="54">2.5</E> NAAQS Nonattainment Areas and Subsequent Actions </HD> Following promulgation of a new or revised NAAQS, the EPA is required by CAA section 107(d) to designate areas throughout the nation as attaining or not attaining the NAAQS. On November 13, 2009 (74 FR 58688), the EPA designated the Philadelphia Area as nonattainment for the 2006 24-hour PM <E T="52">2.5</E> NAAQS. Initially, the EPA did not assign classifications for PM <E T="52">2.5</E> for the 2006 24-hour NAAQS ( <E T="03">e.g.</E> marginal, moderate, etc.). Subsequently, on January 4, 2013, the Court of Appeals for the District of Columbia remanded the EPA's implementation rule as a result of <E T="03">Natural Resources Defense Council</E> v. <E T="03">EPA,</E> 706 F.3d 428 (D.C. Cir. 2013), regarding the failure of the EPA to assign classifications for PM <E T="52">2.5</E> for the 2006 24-hour NAAQS. The Court concluded that the EPA had improperly based the 2007 implementation rule for the 2006 24-hour PM <E T="52">2.5</E> NAAQS solely upon the requirements of Title I, part D, subpart 1 of the CAA, and had failed to ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Preview showing 10k of 53k characters. 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