# Approval and Promulgation of Air Quality Implementation Plans; Delaware; Regional Haze State Implementation Plan for the Second Implementation Period > Briefs, arguments, decisions, and more. URL: https://www.frixlaw.com/law-library/documents/fr%3A2024-18174 ## Record - **Collection:** Federal Register - **Document type:** Proposed Rule - **Published:** August 19, 2024 - **Citation:** 89 FR 67018 ## Text ENVIRONMENTAL PROTECTION AGENCY 40 CFR Part 52 [EPA-R03-OAR-2023-0301; FRL-10191-01-R3] Approval and Promulgation of Air Quality Implementation Plans; Delaware; Regional Haze State Implementation Plan for the Second Implementation Period AGENCY: Environmental Protection Agency (EPA). ACTION: Proposed rule. SUMMARY: The Environmental Protection Agency (EPA or “the Agency”) is proposing to approve the regional haze State implementation plan (SIP) revision submitted by Delaware on August 8, 2022, and supplemented on March 7, 2024, as satisfying applicable requirements under the Clean Air Act (CAA) and EPA's Regional Haze Rule (RHR) for the program's second implementation period. Delaware's SIP submission addresses the requirement that States must periodically revise their long-term strategies for making reasonable progress towards the national goal of preventing any future, and remedying any existing, anthropogenic impairment of visibility, including regional haze, in mandatory Class I Federal areas. The SIP submission also addresses other applicable requirements for the second implementation period of the regional haze program. EPA is taking this action pursuant to sections 110 and 169A of the CAA. DATES: Written comments must be received on or before September 18, 2024. ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R03-OAR-2023-0301 at www.regulations.gov. For comments submitted at www.regulations.gov, follow the online instructions for submitting comments. Once submitted, comments cannot be edited or removed from www.regulations.gov. 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 ( i.e., on the web, cloud, or other file sharing system). For additional submission methods, please contact the person identified in the FOR FURTHER INFORMATION CONTACT section. For the full EPA public comment policy, information about CBI or multimedia submissions, and general guidance on making effective comments, please visit www.epa.gov/dockets/commenting-epa-dockets. FOR FURTHER INFORMATION CONTACT: Adam Yarina, U.S. Environmental Protection Agency, Air & Radiation Division, U.S. Environmental Protection Agency, Region III, Four Penn Center, 1600 John F Kennedy Boulevard, Philadelphia, Pennsylvania 19103. The telephone number is (215) 814-2108. Mr. Yarina can also be reached via electronic mail at yarina.adam@epa.gov. SUPPLEMENTARY INFORMATION: Table of Contents I. What action is EPA proposing? II. Background and Requirements for Regional Haze Plans A. Regional Haze Background B. Roles of Agencies in Addressing Regional Haze III. Requirements for Regional Haze Plans for the Second Implementation Period A. Identification of Class I Areas B. Calculations of Baseline, Current, and Natural Visibility Conditions; Progress to Date; and the Uniform Rate of Progress C. Long-Term Strategy for Regional Haze D. Reasonable Progress Goals E. Monitoring Strategy and Other State Implementation Plan Requirements F. Requirements for Periodic Reports Describing Progress Towards the Reasonable Progress Goals G. Requirements for State and Federal Land Manager Coordination IV. EPA's Evaluation of Delaware's Regional Haze Submission for the Second Implementation Period A. Background on Delaware's First Implementation Period SIP Submission B. Delaware's Second Implementation Period SIP Submission and EPA's Evaluation C. Identification of Class I Areas D. Calculations of Baseline, Current, and Natural Visibility Conditions; Progress to Date; and the Uniform Rate of Progress E. Long-Term Strategy for Regional Haze a. Delaware's Response to the Six MANE-VU Asks b. EPA's Evaluation of Delaware's Response to the Six MANE-VU Asks and Compliance With 40 CFR 51.308(f)(2)(i) c. Additional Long-Term Strategy Requirements F. Reasonable Progress Goals G. Monitoring Strategy and Other Implementation Plan Requirements H. Requirements for Periodic Reports Describing Progress Towards the Reasonable Progress Goals I. Requirements for State and Federal Land Manager Coordination V. Proposed Action VI. Incorporation by Reference VII. Statutory and Executive Order Reviews I. What action is EPA proposing? On August 8, 2022, the Delaware Department of Natural Resources and Environmental Control (DNREC) submitted a revision to its SIP to address regional haze for the second implementation period; with a supplement submitted on March 7, 2024. DNREC made this SIP submission to satisfy the requirements of the CAA's regional haze program pursuant to CAA sections 169A and 169B and 40 CFR 51.308. EPA is proposing to find that the Delaware regional haze SIP submission for the second implementation period meets the applicable statutory and regulatory requirements and thus proposes to approve Delaware's submission into its SIP. II. Background and Requirements for Regional Haze Plans A. Regional Haze Background In the 1977 CAA Amendments, Congress created a program for protecting visibility in the nation's mandatory Class I Federal areas, which include certain national parks and wilderness areas. 1 CAA 169A. The CAA establishes as a national goal the “prevention of any future, and the remedying of any existing, impairment of visibility in mandatory Class I Federal areas which impairment results from manmade air pollution.” CAA 169A(a)(1). The CAA further directs EPA to promulgate regulations to assure reasonable progress toward meeting this national goal. CAA 169A(a)(4). On December 2, 1980, EPA promulgated regulations to address visibility impairment in mandatory Class I Federal areas (hereinafter referred to as “Class I Areas”) that is “reasonably attributable” to a single source or small group of sources. (45 FR 80084, December 2, 1980). These regulations, codified at 40 Code of Federal Regulations (CFR) 51.300 through 51.307, represented the first phase of EPA's efforts to address visibility impairment. In 1990, Congress added section 169B to the CAA to further address visibility impairment, specifically, impairment from regional haze. CAA 169B. EPA promulgated the RHR, codified at 40 CFR 51.308, 2 on July 1, 1999. (64 FR 35714, July 1, 1999). These regional haze regulations are a central component of EPA's comprehensive visibility protection program for Class I Areas. 1 Areas statutorily designated as mandatory Class I Federal areas consist of national parks exceeding 6,000 acres, wilderness areas and national memorial parks exceeding 5,000 acres, and all international parks that were in existence on August 7, 1977. CAA 162(a). There are 156 mandatory Class I Areas. The list of areas to which the requirements of the visibility protection program apply is in 40 CFR part 81, subpart D. 2 In addition to the generally applicable regional haze provisions at 40 CFR 51.308, EPA also promulgated regulations specific to addressing regional haze visibility impairment in Class I Areas on the Colorado Plateau at 40 CFR 51.309. The latter regulations are applicable only for specific jurisdictions' regional haze plans submitted no later than December 17, 2007, and thus are not relevant here. Regional haze is visibility impairment that is produced by a multitude of anthropogenic sources and activities which are located across a broad geographic area and that emit pollutants that impair visibility. Visibility impairing pollutants include fine and coarse particulate matter (PM) ( e.g., sulfates, nitrates, organic carbon, elemental carbon, and soil dust) and their precursors ( e.g., sulfur dioxide (SO 2 ), nitrogen oxides (NO X ), and, in some cases, volatile organic compounds (VOC) and ammonia (NH 3 )). Fine particle precursors react in the atmosphere to form fine particulate matter (PM 2.5 ), which impairs visibility by scattering and absorbing light. Visibility impairment reduces the perception of clarity and color, as well as visible distance. 3 3 There are several ways to measure the amount of visibility impairment, i.e., haze. One such measurement is the deciview, which is the principal metric used by the RHR. Under many circumstances, a change in one deciview will be perceived by the human eye to be the same on both clear and hazy days. The deciview is unitless. It is proportional to the logarithm of the atmospheric extinction of light, which is the perceived dimming of light due to its being scattered and absorbed as it passes through the atmosphere. Atmospheric light extinction (b ext ) is a metric used to express visibility and is measured in inverse megameters (Mm−1). The EPA's Guidance on Regional Haze State Implementation Plans for the Second Implementation Period (“2019 Guidance”) offers the flexibility for the use of light extinction in certain cases. Light extinction can be simpler to use in calculations than deciviews since it is not a logarithmic function. See, e.g., 2019 Guidance at 16, 19, www.epa.gov/visibility/guidance-regional-haze-state-implementation-plans-second-implementation-period, The EPA Office of Air Quality Planning and Standards, Research Triangle Park (August 20, 2019). The formula for the deciview is 10 ln (b ext )/10 Mm−1). 40 CFR 51.301. To address regional haze visibility impairment, the 1999 RHR established an iterative planning process that requires both States in which Class I Areas are located and States “the emissions from which may reasonably be anticipated to cause or contribute to any impairment of visibility” in a Class I Area to periodically submit SIP revisions to address such impairment. CAA 169A(b)(2); 4 see also 40 CFR 51.308(b), (f) (establishing submission dates for iterative regional haze SIP revisions); (64 FR 35714 at 35768, July 1, 1999). Under the CAA, each SIP submission must contain “a long-term (ten to fifteen years) strategy for making reasonable progress toward meeting the national goal,” CAA 169A(b)(2)(B); the initial round of SIP submissions also had to address the statutory requirement that certain older, larger sources of visibility impairing pollutants install and operate the best available retrofit technology (BART). CAA 169A(b)(2)(A); 40 CFR 51.308(d), (e). States' first regional haze SIPs were due by December 17, 2007, 40 CFR 51.308(b), with subsequent SIP submissions containing updated long-term strategies originally due July 31, 2018, and every ten years thereafter. (64 FR 35714 at 35768, July 1, 1999). EPA established in the 1999 RHR that all States either have Class I Areas within their borders or “contain sources whose emissions are reasonably anticipated to contribute to regional haze in a Class I Area”; therefore, all States must submit regional haze SIPs. 5 Id. at 35721. 4 The RHR expresses the statutory requirement for states to submit plans addressing out-of-state Class I Areas by providing that states must address visibility impairment “in each mandatory Class I Federal area located outside the State that may be affected by emissions from within the State.” 40 CFR 51.308(d), (f). 5 In addition to each of the fifty states, the EPA also concluded that the Virgin Islands and District of Columbia must also submit regional haze SIPs because they either contain a Class I area or contain sources whose emissions are reasonably anticipated to contribute regional haze in a Class I area. See 40 CFR 51.300(b), (d)(3). Much of the focus in the first implementation period of the regional haze program, which ran from 2007 through 2018, was on satisfying States' BART obligations. First implementation period SIPs were additionally required to contain long-term strategies for making reasonable progress toward the national visibility goal, of which BART is one component. The core required elements for the first implementation period SIPs (other than BART) are laid out in 40 CFR 51.308(d). Those provisions required that States containing Class I Areas establish reasonable progress goals (RPGs) that are measured in deciviews and reflect the anticipated visibility conditions at the end of the implementation period including from implementation of States' long-term strategies. The first planning period RPGs were required to provide for an improvement in visibility for the most impaired days over the period of the implementation plan and ensure no degradation in visibility for the least impaired days over the same period. In establishing the RPGs for any Class I Area in a State, the State was required to consider four statutory factors: the costs of compliance, the time necessary for compliance, the energy and non-air quality environmental impacts of compliance, and the remaining useful life of any potentially affected sources. CAA 169A(g)(1); 40 CFR 51.308(d)(1). States were also required to calculate baseline (using the five year period of 2000-2004) and natural visibility conditions ( i.e., visibility conditions without anthropogenic visibility impairment) for each Class I Area, and to calculate the linear rate of progress needed to attain natural visibility conditions, assuming a starting point of baseline visibility conditions in 2004 and ending with natural conditions in 2064. This linear interpolation is known as the uniform rate of progress (URP) and is used as a tracking metric to help States assess the amount of progress they are making towards the national visibility goal over time in each Class I Area. 6 40 CFR 51.308(d)(1)(i)(B), (d)(2). The 1999 RHR also provided that States' long-term strategies must include the “enforceable emissions limitations, compliance schedules, and other measures as necessary to achieve the reasonable progress goals.” 40 CFR 51.308(d)(3). In establishing their long-term strategies, States are required to consult with other States that also contribute to visibility impairment in a given Class I Area and include all measures necessary to obtain their shares of the emission reductions needed to meet the RPGs. 40 CFR 51.308(d)(3)(i) and (ii). Section 51.308(d) also contains seven additional factors States must consider in formulating their long-term strategies, 40 CFR 51.308(d)(3)(v), as well as provisions governing monitoring and other implementation plan requirements. 40 CFR 51.308(d)(4). Finally, the 1999 RHR required States to submit periodic progress reports—SIP revisions due every five years that contain information on States' implementation of their regional haze plans and an assessment of whether anything additional is needed to make reasonable progress, see 40 CFR 51.308(g), (h)—and to consult with the Federal Land Manager(s) 7 (FLMs) responsible for each Class I Area according to the requirements in CAA 169A(d) and 40 CFR 51.308(i). 6 EPA established the URP framework in the 1999 RHR to provide “an equitable analytical approach” to assessing the rate of visibility improvement at Class I Areas across the country. The start point for the URP analysis is 2004 and the endpoint was calculated based on the amount of visibility improvement that was anticipated to result from implementation of existing CAA programs over the period from the mid-1990s to approximately 2005. Assuming this rate of progress would continue into the future, EPA determined that natural visibility conditions would be reached in 60 years, or 2064 (60 years from the baseline starting point of 2004). However, EPA did not establish 2064 as the year by which the national goal must be reached. 64 FR 35714 at 35731-32, July 1, 1999. That is, the URP and the 2064 date are not enforceable targets, but are rather tools that “allow for analytical comparisons between the rate of progress that would be achieved by the state's chosen set of control measures and the URP.” (82 FR 3078 at 3084, January 10, 2017). 7 EPA's regulations define “Federal Land Manager” as “the Secretary of the department with authority over the Federal Class I area (or the Secretary's designee) or, with respect to Roosevelt-Campobello International Park, the Chairman of the Roosevelt-Campobello International Park Commission.” 40 CFR 51.301. On January 10, 2017, EPA promulgated revisions to the RHR, (82 FR 3078, January 10, 2017), that apply for the second and subsequent implementation periods. The 2017 rule made several changes to the requirements for regional haze SIPs to clarify States' obligations and streamline certain regional haze requirements. The revisions to the regional haze program for the second and subsequent implementation periods focused on the requirement that States' SIPs contain long-term strategies for making reasonable progress towards the national visibility goal. The reasonable progress requirements as revised in the 2017 rule (referred to here as the “2017 RHR Revisions”) are codified at 40 CFR 51.308(f). Among other changes, the 2017 RHR Revisions adjusted the deadline for States to submit their second implementation period SIPs from July 31, 2018 to July 31, 2021, clarified the order of analysis and the relationship between RPGs and the long-term strategy, and focused on making visibility improvements on the days with the most anthropogenic visibility impairment, as opposed to the days with the most visibility impairment overall. EPA also revised requirements of the visibility protection program related to periodic progress reports and FLM consultation. The specific requirements applicable to second implementation period regional haze SIP submissions are addressed in detail below. EPA provided guidance to the States for their second implementation period SIP submissions in the preamble to the 2017 RHR Revisions as well as in subsequent, stand-alone guidance documents. In August 2019, the EPA issued “Guidance on Regional Haze State Implementation Plans for the Second Implementation Period” (“2019 Guidance”). 8 On July 8, 2021, EPA issued a memorandum containing “Clarifications Regarding Regional Haze State Implementation Plans for the Second Implementation Period” (“2021 Clarifications Memo”). 9 Additionally, EPA further clarified the recommended procedures for processing ambient visibility data and optionally adjusting the URP to account for international anthropogenic and prescribed fire impacts in two technical guidance documents: the December 2018 “Technical Guidance on Tracking Visibility Progress for the Second Implementation Period of the Regional Haze Program” (“2018 Visibility Tracking Guidance”), 10 and the June 2020 “Recommendation for the Use of Patched and Substituted Data and Clarification of Data Completeness for Tracking Visibility Progress for the Second Implementation Period of the Regional Haze Program” and associated Technical Addendum (“2020 Data Completeness Memo”). 11 8 Guidance on Regional Haze State Implementation Plans for the Second Implementation Period. www.epa.gov/visibility/guidance-regional-haze-state-implementation-plans-second-implementation-period . The EPA Office of Air Quality Planning and Standards, Research Triangle Park (August 20, 2019). 9 Clarifications Regarding Regional Haze State Implementation Plans for the Second Implementation Period. www.epa.gov/system/files/documents/2021-07/clarifications-regarding-regional-haze-state-implementation-plans-for-the-second-implementation-period.pdf . The EPA Office of Air Quality Planning and Standards, Research Triangle Park (July 8, 2021). 10 Technical Guidance on Tracking Visibility Progress for the Second Implementation Period of the Regional Haze Program. www.epa.gov/visibility/technical-guidance-tracking-visibility-progress-second-implementation-period-regional. The EPA Office of Air Quality Planning and Standards, Research Triangle Park. (December 20, 2018). 11 Recommendation for the Use of Patched and Substituted Data and Clarification of Data Completeness for Tracking Visibility Progress for the Second Implementation Period of the Regional Haze Program. www.epa.gov/visibility/memo-and-technical-addendum-ambient-data-usage-and-completeness-regional-haze-program. The EPA Office of Air Quality Planning and Standards, Research Triangle Park (June 3, 2020). As previously explained in the 2021 Clarifications Memo, EPA intends the second implementation period of the regional haze program to secure meaningful reductions in visibility impairing pollutants that build on the significant progress States have achieved to date. The Agency also recognizes that analyses regarding reasonable progress are State-specific and that, based on States' and sources' individual circumstances, what constitutes reasonable reductions in visibility impairing pollutants will vary from state-to-state. While there exist many opportunities for States to leverage both ongoing and upcoming emission reductions under other CAA programs, the Agency expects States to undertake rigorous reasonable progress analyses that identify further opportunities to advance the national visibility goal consistent with the statutory and regulatory requirements. See generally 2021 Clarifications Memo. This is consistent with Congress' determination that a visibility protection program is needed in addition to the CAA's National Ambient Air Quality Standards and Prevention of Significant Deterioration programs, as further emission reductions may be necessary to adequately protect visibility in Class I Areas throughout the country. 12 12 See, e.g., H.R. Rep No. 95-294 at 205 (“In determining how to best remedy the growing visibility problem in these areas of great scenic importance, the committee realizes that as a matter of equity, the national ambient air quality standards cannot be revised to adequately protect visibility in all areas of the country.”), (“the mandatory class I increments of [the PSD program] do not adequately protect visibility in Class I Areas”). B. Roles of Agencies in Addressing Regional Haze Because the air pollutants and pollution affecting visibility in Class I Areas can be transported over long distances, successful implementation of the regional haze program requires long-term, regional coordination among multiple jurisdictions and agencies that have responsibility for Class I Areas and the emissions that impact visibility in those areas. In order to address regional haze, States need to develop strategies in coordination with one another, considering the effect of emissions from one jurisdiction on the air quality in another. Five regional planning organizations (RPOs), 13 which include representation from State and Tribal governments, EPA, and FLMs, were developed in the lead-up to the first implementation period to address regional haze. RPOs evaluate technical information to better understand how emissions from State and Tribal land impact Class I Areas across the country, pursue the development of regional strategies to reduce emissions of particulate matter and other pollutants leading to regional haze, and help States meet the consultation requirements of the RHR. 13 RPOs are sometimes also referred to as “multi-jurisdictional organizations,” or MJOs. For the purposes of this rulemaking, the terms RPO and MJO are synonymous. The Mid-Atlantic/Northeast Visibility Union (MANE-VU), one of the five RPOs described above, is a collaborative effort of State governments, Tribal governments, and various Federal agencies established to initiate and coordinate activities associated with the management of regional haze, visibility, and other air quality issues in the Mid-Atlantic and Northeast corridor of the United States. Member States and Tribal governments (listed alphabetically) include: Connecticut, Delaware, the District of Columbia, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Penobscot Indian Nation, Rhode Island, St. Regis Mohawk Tribe, and Vermont. The Federal partner members of MANE-VU are EPA, U.S. National Parks Service (NPS), U.S. Fish and Wildlife Service (FWS), and U.S. Forest Service (USFS). III. Requirements for Regional Haze Plans for the Second Implementation Period Under the CAA and EPA's regulations, all 50 States, the District of Columbia, and the U.S. Virgin Islands are required to submit regional haze SIPs satisfying the applicable requirements for the second implementation period of the regional haze program by July 31, 2021. Each State's SIP must contain a long-term strategy for making reasonable progress toward meeting the national goal of remedying any existing and preventing any future anthropogenic visibility impairment in Class I Areas. CAA 169A(b)(2)(B). To this end, 40 CFR 51.308(f) lays out the process by which States determine what constitutes their long-term strategies, with the order of the requirements in 40 CFR 51.308(f)(1) through (3) generally mirroring the order of the steps in the reasonable progress analysis 14 and paragraphs (f)(4) through (6) containing additional, related requirements. Broadly speaking, a State first must identify the Class I Areas within the State and determine the Class I Areas outside the State in which visibility may be affected by emissions from the State. These are the Class I Areas that must be addressed in the State's long-term strategy. See 40 CFR 51.308(f), (f)(2). For each Class I Area within its borders, a State must then calculate the baseline, current, and natural visibility conditions for that area, as well as the visibility improvement made to date and the URP. See 40 CFR 51.308(f)(1). Each State having a Class I Area and/or emissions that may affect visibility in a Class I Area must then develop a long-term strategy that includes the enforceable emission limitations, compliance schedules, and other measures that are necessary to make reasonable progress in such areas. A reasonable progress determination is based on applying the four factors in CAA section 169A(g)(1) to sources of visibility-impairing pollutants that the State has selected to assess for controls for the second implementation period. See 40 CFR 51.308(f)(2). A State evaluates potential emission reduction measures for those selected sources and determines which are necessary to make reasonable progress. Those measures are then incorporated into the State's long-term strategy. After a State has developed its long-term strategy, it then establishes RPGs for each Class I Area within its borders by modeling the visibility impacts of all reasonable progress controls at the end of the second implementation period, i.e., in 2028, as well as the impacts of other requirements of the CAA. The RPGs include reasonable progress controls not only for sources in the State in which the Class I Area is located, but also for sources in other States that contribute to visibility impairment in that area. The RPGs are then compared to the baseline visibility conditions and the URP to ensure that progress is being made towards the statutory goal of preventing any future and remedying any existing anthropogenic visibility impairment in Class I Areas. 40 CFR 51.308(f)(2) and (3). 14 EPA explained in the 2017 RHR Revisions that we were adopting new regulatory language in 40 CFR 51.308(f) that, unlike the structure in 40 CFR 51.308(d), “tracked the actual planning sequence.” (82 FR 3078 at 3091, January 10, 2017). In addition to satisfying the requirements at 40 CFR 51.308(f) related to reasonable progress, the regional haze SIP revisions for the second implementation period must address the requirements in 40 CFR 51.308(g)(1) through (5) pertaining to periodic reports describing progress towards the RPGs, 40 CFR 51.308(f)(5), as well as requirements for FLM consultation that apply to all visibility protection SIPs and SIP revisions. 40 CFR 51.308(i). A State must submit its regional haze SIP and subsequent SIP revisions to EPA according to the requirements applicable to all SIP revisions under the CAA and EPA's regulations. See CAA 169A(b)(2); CAA 110(a). Upon EPA approval, a SIP is enforceable by the Agency and the public under the CAA. If EPA finds that a State fails to make a required SIP revision, or if EPA finds that a State's SIP is incomplete or disapproves the SIP, the Agency must promulgate a Federal implementation plan (FIP) that satisfies the applicable requirements. CAA 110(c)(1). A. Identification of Class I Areas The first step in developing a regional haze SIP is for a State to determine which Class I Areas, in addition to those within its borders, “may be affected” by emissions from within the State. In the 1999 RHR, EPA determined that all States contribute to visibility impairment in at least one Class I Area, 64 FR 35714 at 35720-22 (July 1, 1999), and explained that the statute and regulations lay out an “extremely low triggering threshold” for determining “whether States should be required to engage in air quality planning and analysis as a prerequisite to determining the need for control of emissions from sources within their State.” Id. at 35721. A State must determine which Class I Areas must be addressed by its SIP by evaluating the total emissions of visibility impairing pollutants from all sources within the State. While the RHR does not require this evaluation to be conducted in any particular manner, EPA's 2019 Guidance provides recommendations for how such an assessment might be accomplished, including by, where appropriate, using the determinations previously made for the first implementation period. 2019 Guidance at 8-9. In addition, the determination of which Class I Areas may be affected by a State's emissions is subject to the requirement in 40 CFR 51.308(f)(2)(iii) to “document the technical basis, including modeling, monitoring, cost, engineering, and emissions information, on which the State is relying to determine the emission reduction measures that are necessary to make reasonable progress in each mandatory Class I Federal Area it affects.” B. Calculations of Baseline, Current, and Natural Visibility Conditions; Progress to Date; and the Uniform Rate of Progress As part of assessing whether a SIP submission for the second implementation period is providing for reasonable progress towards the national visibility goal, the RHR contains requirements in 40 CFR 51.308(f)(1) related to tracking visibility improvement over time. The requirements of this section apply only to States having Class I Areas within their borders; the required calculations must be made for each such Class I Area. EPA's 2018 Visibility Tracking Guidance 15 provides recommendations to assist States in satisfying their obligations under 40 CFR 51.308(f)(1); specifically, in developing information on baseline, current, and natural visibility conditions, and in making optional adjustments to the URP to account for the impacts of international anthropogenic emissions and prescribed fires. See 82 FR 3078 at 3103-05 (January 10, 2017). 15 The 2018 Visibility Tracking Guidance references and relies on parts of the 2003 Tracking Guidance: “Guidance for Tracking Progress Under the Regional Haze Rule,” which can be found at www.epa.gov/sites/default/files/2021-03/documents/tracking.pdf. The RHR requires tracking of visibility conditions on two sets of days: the clearest and the most impaired days. Visibility conditions for both sets of days are expressed as the average deciview index for the relevant five-year period (the period representing baseline or current visibility conditions). The RHR provides that the relevant sets of days for visibility tracking purposes are the 20% clearest (the 20% of monitored days in a calendar year with the lowest values of the deciview index) and 20% most impaired days (the 20% of monitored days in a calendar year with the highest amounts of anthropogenic visibility impairment). 16 40 CFR 51.301. A State must calculate visibility conditions for both the 20% clearest and 20% most impaired days for the baseline period of 2000-2004 and the most recent five-year period for which visibility monitoring data are available (representing current visibility conditions). 40 CFR 51.308(f)(1)(i) and (iii). States must also calculate natural visibility conditions for the clearest and most impaired days, 17 by estimating the conditions that would exist on those two sets of days absent anthropogenic visibility impairment. 40 CFR 51.308(f)(1)(ii). Using all these data, States must then calculate, for each Class I Area, the amount of progress made since the baseline period (2000-2004) and how much improvement is left to achieve in order to reach natural visibility conditions. 16 This rulemaking also refers to the 20% clearest and 20% most anthropogenically impaired days as the “clearest” and “most impaired” or “most anthropogenically impaired” days, respectively. 17 The RHR at 40 CFR 51.308(f)(1)(ii) contains an error related to the requirement for calculating two sets of natural conditions values. The rule says “most impaired days or the clearest days” where it should say “most impaired days and clearest days.” This is an error that was intended to be corrected in the 2017 RHR Revisions but did not get corrected in the final rule language. This is supported by the preamble text at 82 FR 3078 at 3098: “In the final version of 40 CFR 51.308(f)(1)(ii), an occurrence of “or” has been corrected to “and” to indicate that natural visibility conditions for both the most impaired days and the clearest days must be based on available monitoring information.” Using the data for the set of most impaired days only, States must plot a line between visibility conditions in the baseline period and natural visibility conditions for each Class I Area to determine the URP—the amount of visibility improvement, measured in deciviews, that would need to be achieved during each implementation period in order to achieve natural visibility conditions by the end of 2064. The URP is used in later steps of the reasonable progress analysis for informational purposes and to provide a non-enforceable benchmark against which to assess a Class I Area's rate of visibility improvement. 18 Additionally, in the 2017 RHR Revisions, EPA provided States the option of proposing to adjust the endpoint of the URP to account for impacts of anthropogenic sources outside the United States and/or impacts of certain types of wildland prescribed fires. These adjustments, which must be approved by EPA, are intended to avoid any perception that States should compensate for impacts from international anthropogenic sources and to give States the flexibility to determine that limiting the use of wildland-prescribed fire is not necessary for reasonable progress. See 82 FR 3078 at 3107, January 10, 2017, footnote 116. 18 Being on or below the URP is not a “safe harbor”; i.e., achieving the URP does not mean that a Class I area is making “reasonable progress” and does not relieve a state from using the four statutory factors to determine what level of control is needed to achieve such progress. See, e.g., 82 FR 3078 at 3093 (January 10, 2017). EPA's 2018 Visibility Tracking Guidance can be used to help satisfy the 40 CFR 51.308(f)(1) requirements, including in developing information on baseline, current, and natural visibility conditions, and in making optional adjustments to the URP. In addition, the 2020 Data Completeness Memo provides recommendations on the data completeness language referenced in 40 CFR 51.308(f)(1)(i) and provides updated natural conditions estimates for each Class I Area. C. Long-Term Strategy for Regional Haze The core component of a regional haze SIP submission is a long-term strategy that addresses regional haze in each Class I Area within a State's borders and each Class I Area that may be affected by emissions from the State. The long-term strategy “must include the enforceable emissions limitations, compliance schedules, and other measures that are necessary to make reasonable progress, as determined pursuant to (f)(2)(i) through (iv).” 40 CFR 51.308(f)(2). The amount of progress that is “reasonable progress” is based on applying the four statutory factors in CAA section 169A(g)(1) in an evaluation of potential control options for sources of visibility impairing pollutants, which is referred to as a “four-factor” analysis. The outcome of that analysis is the emission reduction measures that a particular source or group of sources needs to implement in order to make reasonable progress towards the national visibility goal. See 40 CFR 51.308(f)(2)(i). Emission reduction measures that are necessary to make reasonable progress may be either new, additional control measures for a source, or they may be the existing emission reduction measures that a source is already implementing. See 2019 Guidance at 43; 2021 Clarifications Memo at 8-10. Such measures must be represented by “enforceable emissions limitations, compliance schedules, and other measures” ( i.e., any additional compliance tools) in a State's long-term strategy in its SIP. 40 CFR 51.308(f)(2). Section 51.308(f)(2)(i) provides the requirements for the four-factor analysis. The first step of this analysis entails selecting the sources to be evaluated for emission reduction measures; to this end, the RHR requires States to consider “major and minor stationary sources or groups of sources, mobile sources, and area sources” of visibility impairing pollutants for potential four-factor control analysis. 40 CFR 51.308(f)(2)(i). A threshold question at this step is which visibility impairing pollutants will be analyzed. As EPA previously explained, consistent with the first implementation period, EPA generally expects that each State will analyze at least SO 2 and NO X in selecting sources and determining control measures. See 2019 Guidance at 12, 2021 Clarifications Memo at 4. A State that chooses not to consider at least these two pollutants should demonstrate why such consideration would be unreasonable. 2021 Clarifications Memo at 4. While States have the option to analyze all sources, the 2019 Guidance explains that “an analysis of control measures is not required for every source in each implementation period,” and that “[s]electing a set of sources for analysis of control measures in each implementation period is . . . consistent with the Regional Haze Rule, which sets up an iterative planning process and anticipates that a State may not need to analyze control measures for all its sources in a given SIP revision.” 2019 Guidance at 9. However, given that source selection is the basis of all subsequent control determinations, a reasonable source selection process “should be designed and conducted to ensure that source selection results in a set of pollutants and sources the evaluation of which has the potential to meaningfully reduce their contributions to visibility impairment.” 2021 Clarifications Memo at 3. EPA explained in the 2021 Clarifications Memo that each State has an obligation to submit a long-term strategy that addresses the regional haze visibility impairment that results from emissions from within that State. Thus, source selection should focus on the in-State contribution to visibility impairment and be designed to capture a meaningful portion of the State's total contribution to visibility impairment in Class I Areas. A State should not decline to select its largest in-State sources on the basis that there are even larger out-of-State contributors. 2021 Clarifications Memo at 4. 19 19 Similarly, in responding to comments on the 2017 RHR Revisions EPA explained that “[a] state should not fail to address its many relatively low-impact sources merely because it only has such sources and another state has even more low-impact sources and/or some high impact sources.” Responses to Comments on Protection of Visibility: Amendments to Requirements for State Plans; Proposed Rule (81 FR 26942, May 4, 2016) at 26987-26988. Thus, while States have discretion to choose any source selection methodology that is reasonable, whatever choices they make should be reasonably explained. To this end, 40 CFR 51.308(f)(2)(i) requires that a State's SIP submission include “a description of the criteria it used to determine which sources or groups of sources it evaluated.” The technical basis for source selection, which may include methods for quantifying potential visibility impacts such as emissions divided by distance metrics, trajectory analyses, residence time analyses, and/or photochemical modeling, must also be appropriately documented, as required by 40 CFR 51.308(f)(2)(iii). Once a State has selected the set of sources, the next step is to determine the emissions reduction measures for those sources that are necessary to make reasonable progress for the second implementation period. 20 This is accomplished by considering the four factors—“the costs of compliance, the time necessary for compliance, and the energy and nonair quality environmental impacts of compliance, and the remaining useful life of any existing source subject to such requirements.” CAA 169A(g)(1). EPA has explained that the four-factor analysis is an assessment of potential emission reduction measures ( i.e., control options) for sources; “use of the terms `compliance' and `subject to such requirements' in section 169A(g)(1) strongly indicates that Congress intended the relevant determination to be the requirements with which sources would have to comply in order to satisfy the CAA's reasonable progress mandate.” 82 FR 3078 at 3091 (January 10, 2017). Thus, for each source it has selected for four-factor analysis, 21 a State must consider a “meaningful set” of technically feasible control options for reducing emissions of visibility impairing pollutants. Id. at 3088. The 2019 Guidance provides that “[a] state must reasonably pick and justify the measures that it will consider, recognizing that there is no statutory or regulatory requirement to consider all technically feasible measures or any particular measures. A range of technically feasible measures available to reduce emissions would be one way to justify a reasonable set.” 2019 Guidance at 29. 20 The CAA provides that, “[i]n determining reasonable progress there shall be taken into consideration” the four statutory factors. CAA 169A(g)(1). However, in addition to four-factor analyses for selected sources, groups of sources, or source categories, a state may also consider additional emission reduction measures for inclusion in its long-term strategy, e.g., from other newly adopted, on-the-books, or on-the-way rules and measures for sources not selected for four-factor analysis for the second planning period. 21 “Each source” or “particular source” is used here as shorthand. While a source-specific analysis is one way of applying the four factors, neither the statute nor the RHR requires states to evaluate individual sources. Rather, states have “the flexibility to conduct four-factor analyses for specific sources, groups of sources or even entire source categories, depending on state policy preferences and the specific circumstances of each state.” 82 FR 3078 at 3088, January 10, 2017. However, not all approaches to grouping sources for four-factor analysis are necessarily reasonable; the reasonableness of grouping sources in any particular instance will depend on the circumstances and the manner in which grouping is conducted. If it is feasible to establish and enforce different requirements for sources or subgroups of sources, and if relevant factors can be quantified for those sources or subgroups, then States should make a separate reasonable progress determination for each source or subgroup. 2021 Clarifications Memo at 7-8. EPA's 2021 Clarifications Memo provides further guidance on what constitutes a reasonable set of control options for consideration: “A reasonable four-factor analysis will consider the full range of potentially reasonable options for reducing emissions.” 2021 Clarifications Memo at 7. In addition to add-on controls and other retrofits ( i.e., new emission reduction measures for sources), EPA explained that States should generally analyze efficiency improvements for sources' existing measures as control options in their four-factor analyses, as in many cases such improvements are reasonable given that they typically involve only additional operation and maintenance costs. Additionally, the 2021 Clarifications Memo provides that States that have assumed a higher emission rate than a source has achieved or could potentially achieve using its existing measures should also consider lower emission rates as potential control options. That is, a State should consider a source's recent actual and projected emission rates to determine if it could reasonably attain lower emission rates with its existing measures. If so, the State should analyze the lower emission rate as a control option for reducing emissions. 2021 Clarifications Memo at 7. EPA's recommendations to analyze potential efficiency improvements and achievable lower emission rates apply to both sources that have been selected for four-factor analysis and those that have forgone a four-factor analysis on the basis of existing “effective controls.” See 2021 Clarifications Memo at 5, 10. After identifying a reasonable set of potential control options for the sources it has selected, a State then collects information on the four factors with regard to each option identified. EPA has also explained that, in addition to the four statutory factors, States have flexibility under the CAA and RHR to reasonably consider visibility benefits as an additional factor alongside the four statutory factors. 22 The 2019 Guidance provides recommendations for the types of information that can be used to characterize the four factors (with or without visibility), as well as ways in which States might reasonably consider and balance that information to determine which of the potential control options is necessary to make reasonable progress. See 2019 Guidance at 30-36. The 2021 Clarifications Memo contains further guidance on how States can reasonably consider modeled visibility impacts or benefits in the context of a four-factor analysis. 2021 Clarifications Memo at 12-13, 14-15. Specifically, EPA explained that while visibility can reasonably be used when comparing and choosing between multiple reasonable control options, it should not be used to summarily reject controls that are reasonable given the four statutory factors. 2021 Clarifications Memo at 13. Ultimately, while States have discretion to reasonably weigh the factors and to determine what level of control is needed, 40 CFR 51.308(f)(2)(i) provides that a State “must include in its implementation plan a description of . . . how the four factors were taken into consideration in selecting the measure for inclusion in its long-term strategy.” 22 See, e.g., Responses to Comments on Protection of Visibility: Amendments to Requirements for State Plans; Proposed Rule (81 FR 26942, May 4, 2016), Docket Number EPA-HQ-OAR-2015-0531, U.S. Environmental Protection Agency at 186; 2019 Guidance at 36-37. As explained above, 40 CFR 51.308(f)(2)(i) requires States to determine the emission reduction measures for sources that are necessary to make reasonable progress by considering the four factors. Pursuant to 40 CFR 51.308(f)(2), measures that are necessary to make reasonable progress towards the national visibility goal must be included in a State's long-term strategy and in its SIP. 23 If the outcome of a four-factor analysis is a new, additional emission reduction measure for a source, that new measure is necessary to make reasonable progress towards remedying existing anthropogenic visibility impairment and must be included in the SIP. If the outcome of a four-factor analysis is that no new measures are reasonable for a source, continued implementation of the source's existing measures is generally necessary to prevent future emission increases and thus to make reasonable progress towards the second part of the national visibility goal: preventing future anthropogenic visibility impairment. See CAA 169A(a)(1). That is, when the result of a four-factor analysis is that no new measures are necessary to make reasonable progress, the source's existing measures are generally necessary to make reasonable progress and must be included in the SIP. However, there may be circumstances in which a State can demonstrate that a source's existing measures are not necessary to make reasonable progress. Specifically, if a State can demonstrate that a source will continue to implement its existing measures and will not increase its emission rate, it may not be necessary to have those measures in the long-term strategy in order to prevent future emission increases and future visibility impairment. EPA's 2021 Clarifications Memo provides further explanation and guidance on how States may demonstrate that a source's existing measures are not necessary to make reasonable progress. See 2021 Clarifications Memo at 8-10. If the State can make such a demonstration, it need not include a source's existing measures in the long-term strategy or its SIP. 23 States may choose to, but are not required to, include measures in their long-term strategies beyond just the emission reduction measures that are necessary for reasonable progress. See 2021 Clarifications Memo at 16. For example, states with smoke management programs may choose to submit their smoke management plans to EPA for inclusion in their SIPs but are not required to do so. See, e.g., 82 FR 3078 at 3108-09, January 10, 2017 (requirement to consider smoke management practices and smoke management programs under 40 CFR 51.308(f)(2)(iv) does not require states to adopt such practices or programs into their SIPs, although they may elect to do so). As with source selection, the characterization of information on each of the factors is also subject to the documentation requirement in 40 CFR 51.308(f)(2)(iii). The reasonable progress analysis, including source selection, information gathering, characterization of the four statutory factors (and potentially visibility), balancing of the four factors, and selection of the emission reduction measures that represent reasonable progress, is a technically complex exercise, but also a flexible one that provides States with bounded discretion to design and implement approaches appropriate to their circumstances. Given this flexibility, 40 CFR 51.308(f)(2)(iii) plays an important function in requiring a State to document the technical basis for its decision making so that the public and EPA can comprehend and evaluate the information and analysis the State relied upon to determine what emission reduction measures must be in place to make reasonable progress. The technical documentation must include the modeling, monitoring, cost, engineering, and emissions information on which the State relied to determine the measures necessary to make reasonable progress. This documentation requirement can be met through the provision of and reliance on technical analyses developed through a regional planning process, so long as that process and its output has been approved by all State participants. In addition to the explicit regulatory requirement to document the technical basis of their reasonable progress determinations, States are also subject to the general principle that those determinations must be reasonably moored to the statute. 24 That is, a State's decisions about the emission reduction measures that are necessary to make reasonable progress must be consistent with the statutory goal of remedying existing and preventing future visibility impairment. 24 See Arizona ex rel. Darwin v. U.S. EPA, 815 F.3d 519, 531 (9th Cir. 2016); Nebraska v. U.S. EPA, 812 F.3d 662, 668 (8th Cir. 2016); North Dakota v. EPA, 730 F.3d 750, 761 (8th Cir. 2013); Oklahoma v. EPA, 723 F.3d 1201, 1206, 1208-10 (10th Cir. 2013); cf. also Nat'l Parks Conservation Ass'n v. EPA, 803 F.3d 151, 165 (3d Cir. 2015); Alaska Dep't of Envtl. Conservation v. EPA, 540 U.S. 461, 485, 490 (2004). The four statutory factors (and potentially visibility) are used to determine what emission reduction measures for selected sources must be included in a State's long-term strategy for making reasonable progress. Additionally, the RHR at 40 CFR 51.308(f)(2)(iv) separately provides five “additional factors” 25 that States must consider in developing their long-term strategies: (1) emission reductions due to ongoing air pollution control programs, including measures to address reasonably attributable visibility impairment; (2) measures to reduce the impacts of construction activities; (3) source retirement and replacement schedules; (4) basic smoke management practices for prescribed fire used for agricultural and wildland vegetation management purposes and smoke management programs; and (5) the anticipated net effect on visibility due to projected changes in point, area, and mobile source emissions over the period addressed by the long-term strategy. The 2019 Guidance provides that a State may satisfy this requirement by considering these additional factors in the process of selecting sources for four-factor analysis, when performing that analysis, or both, and that not every one of the additional factors needs to be considered at the same stage of the process. See 2019 Guidance at 21. EPA provided further guidance on the five additional factors in the 2021 Clarifications Memo, explaining that a State should generally not reject cost-effective and otherwise reasonable controls merely because there have been emission reductions since the first planning period owing to other ongoing air pollution control programs or merely because visibility is otherwise projected to improve at Class I Areas. Additionally, States should not rely on these additional factors to summarily assert that the State has already made sufficient progress and, therefore, no sources need to be selected or no new controls are needed regardless of the outcome of four-factor analyses. 2021 Clarifications Memo at 13. 25 The five “additional factors” for consideration in 40 CFR 51.308(f)(2)(iv) are distinct from the four factors listed in CAA section 169A(g)(1) and 40 CFR 51.308(f)(2)(i) that states must consider and apply to sources in determining reasonable progress. Because the air pollution that causes regional haze crosses State boundaries, 40 CFR 51.308(f)(2)(ii) requires a State to consult with other States that also have emissions that are reasonably anticipated to contribute to visibility impairment in a given Class I Area. Consultation allows for each State that impacts visibility in an area to share whatever technical information, analyses, and control determinations may be necessary to develop coordinated emission management strategies. This coordination may be managed through inter- and intra-RPO consultation and the development of regional emissions strategies; additional consultations between States outside of RPO processes may also occur. If a State, pursuant to consultation, agrees that certain measures ( e.g., a certain emission limitation) are necessary to make reasonable progress at a Class I Area, it must include those measures in its SIP. 40 CFR 51.308(f)(2)(ii)(A). Additionally, the RHR requires that States that contribute to visibility impairment at the same Class I Area consider the emission reduction measures the other contributing States have identified as being necessary to make reasonable progress for their own sources. 40 CFR 51.308(f)(2)(ii)(B). If a State has been asked to consider or adopt certain emission reduction measures, but ultimately determines those measures are not necessary to make reasonable progress, that State must document in its SIP the actions taken to resolve the disagreement. 40 CFR 51.308(f)(2)(ii)(C). EPA will consider the technical information and explanations presented by the submitting State and the State with which it disagrees when considering whether to approve the State's SIP. See id.; 2019 Guidance at 53. Under all circumstances, a State must document in its SIP submission all substantive consultations with other contributing States. 40 CFR 51.308(f)(2)(ii)(C). D. Reasonable Progress Goals Reasonable progress goals “measure the progress that is projected to be achieved by the control measures States have determined are necessary to make reasonable progress based on a four-factor analysis.” 82 FR 3078 at 3091 (January 10, 2017). Their primary purpose is to assist the public and EPA in assessing the reasonableness of States' long-term strategies for making reasonable progress towards the national visibility goal. See 40 CFR 51.308(f)(3)(iii) and (iv). States in which Class I Areas are located must establish two RPGs, both in deciviews—one representing visibility conditions on the clearest days and one representing visibility on the most anthropogenically impaired days—for each area within their borders. 40 CFR 51.308(f)(3)(i). The two RPGs are intended to reflect the projected impacts, on the two sets of days, of the emission reduction measures the State with the Class I Area, as well as all other contributing States, have included in their long-term strategies for the second implementation period. 26 The RPGs also account for the projected impacts of implementing other CAA requirements, including non-SIP based requirements. Because RPGs are the modeled result of the measures in States' long-term strategies (as well as other measures required under the CAA), they cannot be determined before States have conducted their four-factor analyses and determined the control measures that are necessary to make reasonable progress. See 2021 Clarifications Memo at 6. 26 RPGs are intended to reflect the projected impacts of the measures all contributing states include in their long-term strategies. However, due to the timing of analyses, control determinations by other states, and other on-going emissions changes, a particular state's RPGs may not reflect all control measures and emissions reductions that are expected to occur by the end of the implementation period. The 2019 Guidance provides recommendations for addressing the timing of RPG calculations when states are developing their long-term strategies on disparate schedules, as well as for adjusting RPGs using a post-modeling approach. 2019 Guidance at 47-48. For the second implementation period, the RPGs are set for 2028. Reasonable progress goals are not enforceable targets, 40 CFR 51.308(f)(3)(iii); rather, they “provide a way for the states to check the projected outcome of the [long-term strategy] against the goals for visibility improvement.” 2019 Guidance at 46. While States are not legally obligated to achieve the visibility conditions described in their RPGs, 40 CFR 51.308(f)(3)(i) requires that “[t]he long-term strategy and the reasonable progress goals must provide for an improvement in visibility for the most impaired days since the baseline period and ensure no degradation in visibility for the clearest days since the baseline period.” Thus, States are required to have emission reduction measures in their long-term strategies that are projected to achieve visibility conditions on the most impaired days that are better than the baseline period and show no degradation on the clearest days compared to the clearest days from the baseline period. The baseline period for the purpose of this comparison is the baseline visibility condition—the annual average visibility condition for the period 2000-2004. See 40 CFR 51.308(f)(1)(i), 82 FR 3078 at 3097-98 (January 10, 2017). So that RPGs may also serve as a metric for assessing the amount of progress a State is making towards the national visibility goal, the RHR requires States with Class I Areas to compare the 2028 RPG for the most impaired days to the corresponding point on the URP line (representing visibility conditions in 2028 if visibility were to improve at a linear rate from conditions in the baseline period of 2000-2004 to natural visibility conditions in 2064). If the most impaired days RPG in 2028 is above the URP ( i.e., if visibility conditions are improving more slowly than the rate described by the URP), each State that contributes to visibility impairment in the Class I Area must demonstrate, based on the four-factor analysis required under 40 CFR 51.308(f)(2)(i), that no additional emission reduction measures would be reasonable to include in its long-term strategy. 40 CFR 51.308(f)(3)(ii). To this end, 40 CFR 51.308(f)(3)(ii) requires that each State contributing to visibility impairment in a Class I Area that is projected to improve more slowly than the URP provide “a robust demonstration, including documenting the criteria used to determine which sources or groups [of] sources were evaluated and how the four factors required by paragraph (f)(2)(i) were taken into consideration in selecting the measures for inclusion in its long-term strategy.” The 2019 Guidance provides suggestions about how such a “robust demonstration” might be conducted. See 2019 Guidance at 50-51. The 2017 RHR, 2019 Guidance, and 2021 Clarifications Memo also explain that projecting an RPG that is on or below the URP based on only on-the-books and/or on-the-way control measures ( i.e., control measures already required or anticipated before the four-factor analysis is conducted) is not a “safe harbor” from the CAA's and RHR's requirement that all States must conduct a four-factor analysis to determine what emission reduction measures constitute reasonable progress. The URP is a planning metric used to gauge the amount of progress made thus far and the amount left before reaching natural visibility conditions. However, the URP is not based on consideration of the four statutory factors and therefore cannot answer the question of whether the amount of progress being made in any particular implementation period is “reasonable progress.” See 82 FR 3078 at 3093, 3099-3100 (January 10, 2017); 2019 Guidance at 22; 2021 Clarifications Memo at 15-16. E. Monitoring Strategy and Other State Implementation Plan Requirements Section 51.308(f)(6) requires States to have certain strategies and elements in place for assessing and reporting on visibility. Individual requirements under this section apply either to States with Class I Areas within their borders, States with no Class I Areas but that are reasonably anticipated to cause or contribute to visibility impairment in any Class I Area, or both. A State with Class I Areas within its borders must submit with its SIP revision a monitoring strategy for measuring, characterizing, and reporting regional haze visibility impairment that is representative of all Class I Areas within the State. SIP revisions for such States must also provide for the establishment of any additional monitoring sites or equipment needed to assess visibility conditions in Class I Areas, as well as reporting of all visibility monitoring data to EPA at least annually. Compliance with the monitoring strategy requirement may be met through a State's participation in the Interagency Monitoring of Protected Visual Environments (IMPROVE) monitoring network, which is used to measure visibility impairment caused by air pollution at the 156 Class I Areas covered by the visibility program. 40 CFR 51.308(f)(6), (f)(6)(i) and (iv). The IMPROVE monitoring data is used to determine the 20% most anthropogenically impaired and 20% clearest sets of days every year at each Class I Area and tracks visibility impairment over time. All States' SIPs must provide for procedures by which monitoring data and other information are used to determine the contribution of emissions from within the State to regional haze visibility impairment in affected Class I Areas. 40 CFR 51.308(f)(6)(ii) and (iii). S ection 51.308(f)(6)(v) further requires that all States' SIPs provide for a statewide inventory of emissions of pollutants that are reasonably anticipated to cause or contribute to visibility impairment in any Class I Area; the inventory must include emissions for the most recent year for which data are available and estimates of future projected emissions. States must also include commitments to update their inventories periodically. The inventories themselves do not need to be included as elements in the SIP and are not subject to EPA review as part of the Agency's evaluation of a SIP revision. 27 All States' SIPs must also provide for any other elements, including reporting, recordkeeping, and other measures, that are necessary for States to assess and report on visibility. 40 CFR 51.308(f)(6)(vi). Per the 2019 Guidance, a State may note in its regional haze SIP that its compliance with the Air Emissions Reporting Rule (AERR) in 40 CFR part 51, subpart A satisfies the requirement to provide for an emissions inventory for the most recent year for which data are available. To satisfy the requirement to provide estimates of future projected emissions, a State may explain in its SIP how projected emissions were developed for use in establishing RPGs for its own and nearby Class I Areas. 28 27 See “Step 8: Additional requirements for regional haze SIPs” in 2019 Regional Haze Guidance at 55. 28 Id. Separate from the requirements related to monitoring for regional haze purposes under 40 CFR 51.308(f)(6), the RHR also contains a requirement at 40 CFR 51.308(f)(4) related to any additional monitoring that may be needed to address visibility impairment in Class I Areas from a single source or a small group of sources. This is called “reasonably attributable visibility impairment.” 29 Under this provision, if EPA or the FLM of an affected Class I Area has advised a State that additional monitoring is needed to assess reasonably attributable visibility impairment, the State must include in its SIP revision for the second implementation period an appropriate strategy for evaluating such impairment. 29 EPA's visibility protection regulations define “reasonably attributable visibility impairment” as “visibility impairment that is caused by the emission of air pollutants from one, or a small number of sources.” 40 CFR 51.301. F. Requirements for Periodic Reports Describing Progress Towards the Reasonable Progress Goals Section 51.308(f)(5) requires a State's regional haze SIP revision to address the requirements of paragraphs 40 CFR 51.308(g)(1) through (5) so that the plan revision due in 2021 will serve also as a progress report addressing the period since submission of the progress report for the first implementation period. The regional haze progress report requirement is designed to inform the public and EPA about a State's implementation of its existing long-term strategy and whether such implementation is in fact resulting in the expected visibility improvement. See 81 FR 26942, 26950 (May 4, 2016), (82 FR 3078 at 3119, January 10, 2017). To this end, every State's SIP revision for the second implementation period is required to describe the status of implementation of all measures included in the State's long-term strategy, including BART and reasonable progress emission reduction measures from the first implementation period, and the resulting emissions reductions. 40 CFR 51.308(g)(1) and (2). A core component of the progress report requirements is an assessment of changes in visibility conditions on the clearest and most impaired days. For second implementation period progress reports, 40 CFR 51.308(g)(3) requires States with Class I Areas within their borders to first determine current visibility conditions for each area on the most impaired and clearest days, 40 CFR 51.308(g)(3)(i), and then to calculate the difference between those current conditions and baseline (2000-2004) visibility conditions in order to assess progress made to date. See 40 CFR 51.308(g)(3)(ii). States must also assess the changes in visibility impairment for the most impaired and clearest days since they submitted their first implementation period progress reports. See 40 CFR 51.308(g)(3)(iii), (f)(5). Since different States submitted their first implementation period progress reports at different times, the starting point for this assessment will vary State by State. Similarly, States must provide analyses tracking the change in emissions of pollutants contributing to visibility impairment from all sources and activities within the State over the period since they submitted their first implementation period progress reports. See 40 CFR 51.308(g)(4), (f)(5). Changes in emissions should be identified by the type of source or activity. Section 51.308(g)(5) also addresses changes in emissions since the period addressed by the previous progress report and requires States' SIP revisions to include an assessment of any significant changes in anthropogenic emissions within or outside the State. This assessment must include an explanation of whether these changes in emissions were anticipated and whether they have limited or impeded progress in reducing emissions and improving visibility relative to what the State projected based on its long-term strategy for the first implementation period. G. Requirements for State and Federal Land Manager Coordination Clean Air Act section 169A(d) requires that before a State holds a public hearing on a proposed regional haze SIP revision, it must consult with the appropriate FLM or FLMs; pursuant to that consultation, the State must include a summary of the FLMs' conclusions and recommendations in the notice to the public. Consistent with this statutory requirement, the RHR also requires that States “provide the [FLM] with an opportunity for consultation, in person and at a point early enough in the State's policy analyses of its long-term strategy emission reduction obligation so that information and recommendations provided by the [FLM] can meaningfully inform the State's decisions on the long-term strategy.” 40 CFR 51.308(i)(2). Consultation that occurs 120 days prior to any public hearing or public comment opportunity will be deemed “early enough,” but the RHR provides that in any event the opportunity for consultation must be provided at least 60 days before a public hearing or comment opportunity. This consultation must include the opportunity for the FLMs to discuss their assessment of visibility impairment in any Class I Area and their recommendations on the development and implementation of strategies to address such impairment. 40 CFR 51.308(i)(2). In order for EPA to evaluate whether FLM consultation meeting the requirements of the RHR has occurred, the SIP submission should include documentation of the timing and content of such consultation. The SIP revision submitted to EPA must also describe how the State addressed any comments provided by the FLMs. 40 CFR 51.308(i)(3). Finally, a SIP revision must provide procedures for continuing consultation between the State and FLMs regarding the State's visibility protection program, including development and review of SIP revisions, five-year progress reports, and the implementation of other programs having the potential to contribute to impairment of visibility in Class I Areas. 40 CFR 51.308(i)(4). IV. EPA's Evaluation of Delaware's Regional Haze Submission for the Second Implementation Period A. Background on Delaware's First Implementation Period SIP Submission DNREC submitted its regional haze SIP for the first implementation period to EPA on September 25, 2008. EPA approved Delaware's first implementation period regional haze SIP submission on July 19, 2011 (76 FR 42557). Delaware has no Class I Areas within its borders but was identified as influencing the visibility impairment of the Brigantine National Wildlife Refuge Class I Area (“Brigantine” or “Brigantine Wilderness Class I Area”), located in the State of New Jersey. EPA's approval included the portions of the plan that addressed the reasonable progress requirements and Delaware's implementation of Best Available Retrofit Technologies (BART) on eligible sources. The requirements for regional haze SIPs for the first implementation period are contained in 40 CFR 51.308(d) and (e). 40 CFR 51.308(b). Pursuant to 40 CFR 51.308(g), Delaware was also responsible for submitting a five-year progress report as a SIP revision for the first implementation period, which it did on September 24, 2013. EPA approved the progress report into the Delaware SIP on May 5, 2014. See 79 FR 25506. B. Delaware's Second Implementation Period SIP Submission and EPA's Evaluation In accordance with CAA sections 169A and the RHR at 40 CFR 51.308(f), on August 8, 2022, DNREC submitted a revision to the Delaware SIP, titled “Delaware's Visibility SIP Revision Final August 2022” to address its regional haze obligations for the second implementation period, which runs through 2028. DNREC subsequently submitted a supplemental SIP submittal to EPA on March 7, 2024, referred to as “Supplemental Submission for Delaware's Second Regional Haze SIP”, which included title V permit provisions for three facilities owned by Calpine Mid-Atlantic Generation, LLC to be incorporated into the Delaware SIP. These permits and their associated public notice and transmittal letters are included in the rulemaking docket for this action. 30 30 DNREC provided a clarification of this supplemental SIP submittal on May 28, 2024, that specified which provisions of the Title V permits it intended to be incorporated by reference into the Delaware SIP. The following sections describe Delaware's SIP submission, including analyses conducted by MANE-VU and Delaware's determinations based on those analyses, Delaware's assessment of progress made since the first implementation period in reducing emissions of visibility impairing pollutants, and the visibility improvement progress at the nearby Class I Area. This rulemaking also contains EPA's evaluation of Delaware's submission against the requirements of the CAA and RHR for the second implementation period of the regional haze program. C. Identification of Class I Areas Section 169A(b)(2) of the CAA requires each State in which any Class I Area is located or “the emissions from which may reasonably be anticipated to cause or contribute to any impairment of visibility” in a Class I Area to have a plan for making reasonable progress toward the national visibility goal. The RHR implements this statutory requirement at 40 CFR 51.308(f), which provides that each State's plan “must address regional haze in each mandatory Class I Area located within the State and in each mandatory Class I Area located outside the State that may be affected by emissions from within the State,” and (f)(2), which requires each State's plan to include a long-term strategy that addresses regional haze in such Class I Areas. Delaware does not have a Class I Area located within its borders, but has been identified as influencing the visibility impairment of the Brigantine Wilderness Class I Area, located in the State of New Jersey. For the second implementation period, MANE-VU performed technical analyses 31 to help assess source and State-level contributions to visibility impairment and the need for interstate consultation. MANE-VU used the results of these analyses to determine which States' emissions “have a high likelihood of affecting visibility in MANE-VU's Class I Areas.” 32 Similar to metrics used in the first implementation period, 33 MANE-VU used a greater than 2 percent of sulfate plus nitrate emissions contribution criteria to determine whether emissions from individual jurisdictions within the region affected visibility in any Class I Areas. The MANE-VU analyses for the second implementation period used a combination of data analysis techniques, including emissions data, distance from Class I Areas, wind trajectories, and California Puff Model (CALPUFF) dispersion modeling. Although many of the analyses focused only on SO 2 emissions and resultant particulate sulfate contributions to visibility impairment, some also incorporated NO X emissions to estimate particulate nitrate contributions. 31 The contribution assessment methodologies for MANE-VU Class I Areas are summarized in appendix 1-1 of the DE Regional Haze SIP submission, “Selection of States for MANE-VU Regional Haze Consultation (2018)” in the docket. 32 Id. 33 See docket EPA-R03-OAR-2011-0289 for MANE-VU supporting materials. One MANE-VU analysis used for contribution assessment was CALPUFF air dispersion modeling. The CALPUFF model was used to estimate sulfate and nitrate formation and transport in MANE-VU and nearby regions originating from large electric generating unit (EGU) point sources and other large industrial and institutional sources in the eastern and central United States. Information from an initial round of CALPUFF modeling was collated for the 444 EGUs that were determined to warrant further scrutiny based on their emissions of SO 2 and NO X . The list of EGUs was based on an enhanced “Q/d” analysis 34 that considered recent SO 2 emissions in the eastern United States and an analysis that adjusted previous 2002 MANE-VU CALPUFF modeling by applying a ratio of 2011 to 2002 SO 2 emissions. This list of sources was then enhanced by including the top five SO 2 and NO X emission sources for 2011 for each State included in the modeling domain. A total of 311 EGU stacks (as opposed to individual units) were included in the CALPUFF modeling analysis. Initial information was also collected on the 50 industrial and institutional sources that, according to 2011 Q/d analysis, contributed the most to visibility impact in each Class I Area. The ultimate CALPUFF modeling run included a total of 311 EGU stacks and 82 industrial facilities. The summary report for the CALPUFF modeling included the top 10 most impacting EGUs and the top five most impacting industrial/institutional sources for each Class I Area and compiled those results into a ranked list of the most impacting EGUs and industrial sources at MANE-VU Class I Areas. 35 34 “Q/d” is emissions (Q) in tons per year, typically of one or a combination of visibility-impairing pollutants, divided by distance to a class I area (d) in kilometers. The resulting ratio is commonly used as a metric to assess a source's potential visibility impacts on a particular class I area. 35 See tables 34 and 35 of appendix 8-5 of the DE 2022 Regional haze SIP submission, “2016 MANE-VU CALPUFF Modeling Report” in the docket. The second MANE-VU contribution analysis used a meteorologically weighted Q/d calculation to assess States' contributions to visibility impairment at MANE-VU Class I Areas. 36 This analysis focused predominantly on SO 2 emissions and used cumulative SO 2 emissions from a source and a State for the variable “Q,” and the distance of the source or State to the IMPROVE monitor receptor at a Class I Area as “d.” The result is then multiplied by a constant (C i ), which is determined based on the prevailing wind patterns. MANE-VU selected a meteorologically weighted Q/d analysis as an inexpensive initial screening tool that could easily be repeated to determine which States, sectors, or sources have a larger relative impact and warrant further analysis. MANE-VU's analysis estimated SO 2 emission contribution from Delaware sources of less than 2% of visibility impairment for all seven MANE-VU Class I Areas. Although MANE-VU did not originally estimate nitrate impacts, the MANE-VU Q/d analysis was subsequently extended to account for nitrate contributions from NO X emissions and to approximate the nitrate impacts from area and mobile sources. MANE-VU therefore developed a ratio of nitrate to sulfate impacts based on the previously described CALPUFF modeling and applied those to the sulfate Q/d results in order to derive nitrate contribution estimates. Several States did not have CALPUFF nitrate to sulfate ratio results, however, because there were no point sources modeled with CALPUFF. 36 See appendix 8-2, “Contribution to Regional Haze in the Northeast and Mid-Atlantic United States: Preliminary Update Through 2007.” To develop a final set of contribution estimates, MANE-VU weighted the results from both the Q/d and CALPUFF analyses. The MANE-VU mass-weighted sulfate and nitrate contribution results were reported for the MANE-VU Class I Areas (the Q/d summary report included results for several non-MANE-VU areas as well). If a State's contribution to sulfate and nitrate concentrations at a particular Class I Area was 2 percent or greater, MANE-VU regarded that State as contributing to visibility impairment in that area. Delaware's highest mass-weighted sulfate and nitrate contribution to any Class I Area was 0.6% to the Brigantine Wilderness Class I Area. Even with a contribution level below 2 percent threshold, Delaware agreed to participate in the consultation process, as part of the MANE-VU RPO. As explained above, the EPA concluded in the 1999 RHR that “all [s]tates contain sources whose emissions are reasonably anticipated to contribute to regional haze in a Class I Area,” 64 FR 35714 at 35721 (July 1, 1999), and this determination was not changed in the 2017 RHR. Critically, the statute and regulation both require that the cause-or-contribute assessment consider all emissions of visibility-impairing pollutants from a State, as opposed to emissions of a particular pollutant or emissions from a certain set of sources. Consistent with these requirements, the 2019 Guidance makes it clear that “all types of anthropogenic sources are to be included in the determination” of whether a State's emissions are reasonably anticipated to result in any visibility impairment. 2019 Guidance at 8. First, as an aside, the screening analyses on which MANE-VU relied are useful for certain purposes. MANE-VU used information from its technical analysis to rank the largest contributing States to sulfate and nitrate impairment in five Class I Areas within MANE-VU States and three additional, nearby Class I Areas. 37 The rankings were used to determine upwind States that were deemed important to include in state-to-state consultation (based on an identified impact screening threshold). Additionally, large individual source impacts were used to target MANE-VU control analysis “Asks” 38 of States and sources both within and upwind of MANE-VU. 39 EPA finds the nature of the analyses generally appropriate to support decisions on States with which to consult. However, we have cautioned that source selection methodologies that target the largest regional contributors to visibility impairment across multiple States may not be reasonable for a particular State if it results in few or no sources being selected for subsequent analysis. 2021 Clarifications Memo at 3. Delaware has participated in the MANE-VU visibility analysis and has provided information in its SIP submission on the magnitude of visibility impacts from certain Delaware emission sources, specifically the Indian River Generating Station and the Edge Moor Energy Center (EMEC), on nearby Class I Areas. 37 The Class I Areas analyzed were Acadia National Park in Maine, Brigantine Wilderness in New Jersey, Great Gulf Wilderness in New Hampshire, Lye Brook Wilderness in Vermont, Moosehorn Wilderness in Maine, Shenandoah National Park in Virginia, James River Face Wilderness in Virginia, and Dolly Sods/Otter Creek Wildernesses in West Virginia. 38 As explained more fully in section IV.E.a, of this document MANE-VU refers to each of the components of its overall strategy as an “Ask” of its member states. 39 The MANE-VU consultation report (appendix D) explains that “[t]he objective of this technical work was to identify states and sources from which MANE-VU will pursue further analysis. This screening was intended to identify which states to invite to consultation, not a definitive list of which states are contributing.” With regard to the analysis and determinations regarding Delaware's contribution to visibility impairment at out-of-state Class I Areas, the MANE-VU technical work focuses on the magnitude of visibility impacts from certain Delaware emissions on its Class I Area and other nearby Class I Areas. However, the analyses did not account for all emissions and all components of visibility impairment ( e.g., primary PM emissions, and impairment from fine PM, elemental carbon, and organic carbon). In addition, Q/d analyses with a relatively simplistic accounting for wind trajectories and CALPUFF applied to a very limited set of EGUs, and major industrial sources of SO 2 and NO X are not scientifically rigorous tools capable of evaluating contribution to visibility impairment from all emissions in a State. We again clarify that each State is obligated under the CAA and RHR to address regional haze visibility impairment resulting from emissions from within the State, irrespective of whether another State's contribution is greater. See 2021 Clarifications Memo at 3. Additionally, we note that the 2 percent or greater sulfate-plus-nitrate threshold used to determine whether Delaware's emissions contribute to visibility impairment at a particular Class I Area may be higher than what EPA believes is an “extremely low triggering threshold” intended by the statute and regulations. In sum, based on the information provided, it is clear that emissions from Delaware contribute to visibility impairment at out-of-state Class I Areas. However, due to the low triggering threshold implied by the Rule and the lack of rigorous modeling analyses, we do not necessarily agree with the level of the State's 2% contribution threshold. Delaware determined that sources and emissions within the State contribute to visibility impairment at three out-of-state Class I Areas. 40 Furthermore, the State took part in the emission control strategy consultation process as a member of MANE-VU pursuant to the regulatory requirements. As part of that process, MANE-VU developed a set of emissions reduction measures identified as being necessary to make reasonable progress in the five MANE-VU Class I Areas. This strategy consists of six “Asks” for States within MANE-VU and five “Asks” for States outside the region that were found to impact visibility at Class I Areas within MANE-VU. 41 Delaware's submission discusses each of the “Asks” and explains why or why not each is applicable and how it has complied with the relevant components of the emissions control strategy MANE-VU has laid out for its States. Delaware worked with MANE-VU to determine potential reasonable measures that could be implemented by 2028, considering the cost of compliance, the time necessary for compliance, the energy and non-air quality environmental impacts, and the remaining useful life of any potentially affected sources. As discussed in further detail below, the EPA is proposing to find that Delaware has submitted a regional haze plan that meets the requirements of 40 CFR 51.308(f)(2) related to the development of a long-term strategy. Although we have concerns regarding some aspects of MANE-VU's technical analyses supporting States' contribution determinations, we propose to find that Delaware has nevertheless satisfied the applicable regulatory requirements for making reasonable progress towards natural visibility conditions in Class I Areas that may be affected by emissions from the State. 40 Brigantine in NJ, James River Face in WV and Shenandoah National Park in VA. 41 See appendix 9-1 of the DE Regional Haze SIP submittal, “Statement of the Mid-Atlantic/Northeast Visibility Union (MANE-VU) Concerning a Course of Action within MANE-VU toward Assuring Reasonable Progress for the Second Regional Haze Implementation Period (2018-2028), (August 2017).” D. Calculations of Baseline, Current, and Natural Visibility Conditions; Progress to Date; and the Uniform Rate of Progress Section 51.308(f)(1) requires States to determine the following for “each mandatory Class I Federal area located within the State”: baseline visibility conditions for the most impaired and clearest days, natural visibility conditions for the most impaired and clearest days, progress to date for the most impaired and clearest days, the differences between current visibility conditions and natural visibility conditions, and the URP. This section also provides the option for States to propose adjustments to the URP line for a Class I Area to account for visibility impacts from anthropogenic sources outside the United States and/or the impacts from wildland prescribed fires that were conducted for certain, specified objectives. 40 CFR 51.308(f)(1)(vi)(B). Delaware does not have any Class I Area within its borders therefore, § 51.308(f)(1) and its requirements do not apply. 42 42 While Delaware noted that it was not required to comply with 40 CFR 51.308(f)(1), elsewhere in its SIP submission (section 8.10), Delaware included a visibility metric graph of a nearby Class I area, which was taken from a MANE-VU report referenced in their SIP submittal, titled “Mid-Atlantic/Northeast U.S. Visibility Data 2004-2019 (2nd RH SIP Metrics) (May 1, 2020 revisions) (January 21, 2021 revision).” E. Long-Term Strategy for Regional Haze a. Delaware's Response to the Six MANE-VU Asks Each State having a Class I Area within its borders or emissions that may affect visibility in a Class I Area must develop a long-term strategy for making reasonable progress towards the national visibility goal. CAA 169A(b)(2)(B). As explained in the Background section of this rulemaking, reasonable progress is achieved when all States contributing to visibility impairment in a Class I Area are implementing the measures determined—through application of the four statutory factors to sources of visibility impairing pollutants—to be necessary to make reasonable progress. 40 CFR 51.308(f)(2)(i). Each State's long-term strategy must include the enforceable emission limitations, compliance schedules, and other measures that are necessary to make reasonable progress. 40 CFR 51.308(f)(2). All new ( i.e., additional) measures that are the outcome of four-factor analyses are necessary to make reasonable progress and must be in the long-term strategy. If the outcome of a four-factor analysis and other measures necessary to make reasonable progress is that no new measures are reasonable for a source, that source's existing measures are necessary to make reasonable progress, unless the State can demonstrate that the source will continue to implement those measures and will not increase its emission rate. Existing measures that are necessary to make reasonable progress must also be in the long-term strategy. In developing its long-term strategies, a State must also consider the five additional factors in 40 CFR 51.308(f)(2)(iv). As part of its reasonable progress determinations, the State must describe the criteria used to determine which sources or group of sources were evaluated ( i.e., subjected to four-factor analysis) for the second implementation period and how the four factors were taken into consideration in selecting the emission reduction measures for inclusion in the long-term strategy. 40 CFR 51.308(f)(2)(iii). The following section summarizes how Delaware's SIP submission addressed the requirements of 40 CFR 51.308(f)(2)(i). Specifically, it describes MANE-VU's development of the six Asks and how Delaware addressed each one. States may rely on technical information developed by the RPOs of which they are members to select sources for four-factor analysis and to conduct that analysis, as well as to satisfy the documentation requirements under 40 CFR 51.308(f). Where an RPO has performed source selection and/or four-factor analyses (or considered the five additional factors in 40 CFR 51.308(f)(2)(iv)) for its member States, those States may rely on the RPO's analyses for the purpose of satisfying the requirements of 40 CFR 51.308(f)(2)(i) so long as the States have a reasonable basis to do so and all State participants in the RPO process have approved the technical analyses. 40 CFR 51.308(f)(3)(iii). States may also satisfy the requirement of 40 CFR 51.308(f)(2)(ii) to engage in interstate consultation with other States that have emissions that are reasonably anticipated to contribute to visibility impairment in a given Class I Area under the auspices of intra- and inter-RPO engagement. Delaware is a member of the MANE-VU RPO and participated in the RPO's regional approach to developing a strategy for making reasonable progress towards the national visibility goal in the MANE-VU Class I Areas. MANE-VU's strategy includes a combination of: (1) measures for certain source sectors and groups of sectors that the RPO determined were reasonable for States to pursue, and (2) a request for member States to conduct four-factor analyses for individual sources that it identified as contributing to visibility impairment. MANE-VU refers to each of the components of its overall strategy as an Ask of its member States. On August 25, 2017, the Executive Director of MANE-VU, on behalf of the MANE-VU States and Tribal nations, signed a statement that identifies six emission reduction measures that comprise the “Asks” for the second implementation period. 43 The “Asks” were “designed to identify reasonable emission reduction strategies that must be addressed by the states and tribal nations of MANE-VU through their regional haze SIP updates.” 44 The statement explains that “[i]f any State cannot agree with or complete a Class I State's Asks, the State must describe the actions taken to resolve the disagreement in the Regional Haze SIP.” 45 43 See appendix 9-1 of the DE Regional Haze SIP submittal, “Statement of the Mid-Atlantic/Northeast Visibility Union (MANE-VU) Concerning a Course of Action within MANE-VU toward Assuring Reasonable Progress for the Second Regional Haze Implementation Period (2018-2028), (August 2017).” 44 Id. 45 Id. MANE-VU's recommendations as to the appropriate control measures were based on technical analyses documented in the RPO's reports and included as appendices to or referenced in Delaware's regional haze SIP submission. One of the initial steps of MANE-VU's technical analysis was to determine which visibility-impairing pollutants should be the focus of its efforts for the second implementation period. In the first implementation period, MANE-VU determined that sulfates were the most significant visibility impairing pollutant at the region's Class I Areas. To determine the impact of certain pollutants on visibility at Class I Areas for the purpose of second implementation period planning, MANE-VU conducted an analysis comparing the pollutant contribution on the clearest and most impaired days in the baseline period (2000-2004) to the most recent period (2012-2016) 46 at MANE-VU and nearby Class I Areas. MANE-VU found that while SO 2 emissions were decreasing and visibility was improving, sulfates still made up the most significant contribution to visibility impairment at MANE-VU and nearby Class I Areas. According to the analysis, NO X emissions have begun to play a more significant role in visibility impacts in recent years, especially at the Brigantine Wilderness Class I Area. The technical analyses used by Delaware are included in their submission and are as follows: 46 The period of 2012-2016 was the most recent period for which data was available at the time of analysis. • The Nature of the Fine Particle and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual description (NESCAUM, November 2006, Revised August 2010 and July 2012) (Appendix 8-1) • Contributions to Regional Haze in the Northeast and Mid-Atlantic United States: Preliminary Update Through 2007 (NESCAUM, March 2012) (Appendix 8-2) • MANE-VU Updated Q/d*C Contribution Assessment. (MANE-VU, April 2016) (Appendix 8-3) • 2016 Updates to the Assessment of Reasonable Progress in MANE-VU Class I Areas (MARAMA, January 2016) (Appendix 8-4) • 2016 MANE-VU Source Contribution Modeling Report—CALPUFF Modeling of Large Electrical Generating Units and Industrial Sources (MANE-VU, April 2017) (Appendix 8-5) • Regional Haze Metrics Trends and HYSPLIT Trajectory Analysis. (MANE-VU, May 2017) (Appendix 8-6) • Permit Cancellation Documents for McKee Run Generating Station, City of Dover. (DNREC, November 2021) (Appendix 8-7) • Recommendation on Approaches to Selecting the 20% Most Impaired Days. (MANE-VU, March 2017) (Appendix 8-8) • Analysis of Speciation Trends Network Data Measured at the State of Delaware, Philip K. Hopke and Eugene Kim, Center for Air Resources Engineering and Science Clarkson University. (January 2005) (Appendix 8-9) To support development of the “Asks,” MANE-VU gathered information on each of the four statutory factors for six source sectors it determined, based on an examination of annual emission inventories, “had emissions that were reasonabl[y] anticipated to contribute to visibility degradation in MANE-VU:” electric generating units (EGUs), industrial/commercial/institutional boilers (ICI boilers), cement kilns, heating oil, residential wood combustion, and outdoor wood combustion. 47 MANE-VU also collected data on individual sources within the EGU, ICI boiler, and cement kiln sectors. 48 Information for the six sectors included explanations of technically feasible control options for SO 2 or NO X, illustrative cost-effectiveness estimates for a range of model units and control options, sector-wide cost considerations, potential time frames for compliance with control options, potential energy and non-air-quality environmental impacts of certain control options, and how the remaining useful lives of sources might be considered in a control analysis. 49 Source-specific data included SO 2 emissions 50 and existing controls 51 for certain existing EGUs, ICI boilers, and cement kilns. MANE-VU considered this information on the four factors as well as the analyses developed by the RPO's Technical Support Committee when it determined specific emission reduction measures that were found to be reasonable for certain sources within two of the sectors it had examined—EGUs and ICI boilers. The “Asks” were based on this analysis and looked to either optimize the use of existing controls, have States conduct further analysis on EGU or ICI boilers with considerable visibility impacts, implement low sulfur fuel standards, or lock-in lower emission rates. 47 See MANE-VU's “Four Factor Data Collection” Memo at 1, March 30, 2017, available at otcair.org/MANEVU/Upload/Publication/Reports/Four-Factor%20Data%20Collection%20Memo%20-%20170314.pdf. The six sectors were identified in the first implementation period pursuant to MANE-VU's contribution assessment; MANE-VU subsequently updated its information on these sectors for the second implementation period. 48 See appendix 8-4 “2016 Updates to the Assessment of Reasonable Progress for Regional Haze in MANE-VU Class I Areas, January 31, 2016.” 49 Id. 50 See docket document, “MANE-VU's “Four Factor Data Collection Memo” March 30, 2017, table 1 contains 2011 SO 2 data from specific sources. 51 The “Status of the Top 167 EGUs that Contributed to Visibility Impairment at MANE-VU Class I Areas during the 2008 Regional Haze Planning Period” July 25, 2016, reviews the existing and soon to be installed, at the time of the report, emission controls at individual EGU sources that were a part of the MANE-VU Ask from the first implementation period. Available at: otcair.org/MANEVU/Upload/Publication/Reports/Status%20of%20the%20Top%20167%20Stacks%20from%20the%202008%20MANE-VU%20Ask.pdf. MANE-VU Ask 1 is “ensure the most effective use of control technologies on a year-round basis to consistently minimize emissions of haze precursors or obtain equivalent alternative emission reductions” at EGUs with a nameplate capacity larger than or equal to 25 megawatts (MW) with already installed NO X and/or SO 2 controls. 52 52 See appendix 8-12 “MANE-VU Regional Haze Consultation Report.” To address Ask 1, first, Delaware indicated that all the units that burn fuel oil are covered year-round by a Delaware low sulfur fuel regulation at Title 7 Delaware Administrative Code (7 DE Admin Code) 1108, 53 that was approved into the SIP on July 11, 2022 (87 FR 41074). Delaware's SIP-approved low sulfur fuel regulation reduces the SIP-approved maximum allowable sulfur content limit for distillate fuels from 3,000 ppm to 15 ppm, for residual fuel from 1% to 0.5% by weight, and for any other fuel, the sulfur content would remain at 1.0% by weight. Based on that, the State asserted that it met the request to ensure SO 2 controls year-round under Ask 1. 53 7 DE Admin Code 1108 “Sulfur Dioxide Emissions from Fuel Burning Equipment.” See 87 FR 41074, July 11, 2022. Delaware then focused its efforts on the control of NO X emissions and identified 10 EGUs with nameplate capacity larger than or equal to 25 MW, of which four had permits that did not require the use of NO X controls year-round on some of their units. The four sources are Christiana Energy Center (ChEC), Edge Moor Energy Center (EMEC), Garrison Energy Center (GEC), and Hay Road Energy Center (HREC), which are all owned by Calpine Mid-Atlantic Generation, LLC (Calpine). To meet the Ask, Delaware requested the EGUs to perform four-factor analyses on the pertinent units to determine if year-round NO X controls are feasible. Details of the EGUs' four-factor analyses with regard to Ask 1 can be found in a technical support document (TSD) of this proposed rulemaking action; specifically, it describes how Delaware addressed each Ask. Based on the four-factor analyses performed by the sources to evaluate adding or expanding NO X controls year-round, only one of the sources, ChEC, concluded that it was feasible to operate the existing controls for an additional period throughout the year. Based upon that conclusion and in order to meet the Ask, Delaware updated applicable permits in May 2021 to reflect the new measures, and submitted the redacted permits for incorporation into the SIP. Additional details can be found in the TSD (section III-a.-1. at 8). Delaware therefore concluded that it met Ask 1. MANE-VU Ask 2 requests that States “perform a four-factor analysis for reasonable installation or upgrade to emissions controls” for specified sources. MANE-VU developed its Ask 2 list of sources for analysis by performing modeling and identifying facilities with the potential for 3.0 inverse megameters (Mm −1 ) or greater impacts on visibility at any Class I Area in the MANE-VU region. 54 Delaware explained that it has no facilities that were modeled by MANE-VU to impact visibility at any Class I Area by 3.0 Mm −1 or more and concluded that it is currently meeting Ask 2. While Delaware did not select sources that fell under MANE-VU's 3.0 Mm −1 threshold for four-factor analysis, it did provide supplemental information about a large source that was identified by commenters and explanation supporting its decision not to request the facility to evaluate measures for reasonable progress because the facility is effectively controlled. 54 See appendix 8-12 “MANE-VU Regional Haze Consultation Report.” Specifically, commenters asserted that Delaware should have selected the Delaware City Refinery Company, LLC (DCRC) for a four-factor analysis of possible controls. In its SIP submission, Delaware explained the reasons it did not conduct a four-factor analysis for DCRC. First, based on MANE-VU's modeling results, DCRC showed that its impact on visibility impairment was low; 55 second, Delaware relied on the threshold that was agreed to by all MANE-VU States, including those that have Class I Areas within their boundaries; and third, the source is well controlled for SO 2 and NO X through existing State regulations and several consent decrees. Section 8.13.2 of the SIP submission contains a detailed description of controls required for SO 2 and NO X emissions, pursuant to two Federal consent decrees, an agreement governing the acquisition and operation of the facility, and State and Federal regulations that DCRC is subject to. 56 More details about Delaware's response to Ask 2 can be found in the TSD of this proposed rulemaking action. 55 The Q/d for this facility, as calculated by MANE-VU, ranged from 0.36-3.25 for the eight Class I Areas in the MANE-VU analysis, with Brigantine Wilderness Area being at the top of this range; see docket documents, “Delaware Response to EPA Regional Haze Info Request 11-3-23” and “Attachment E—QDCPointOnly—Delaware1.xlsx”. In addition, this facility was not one of the 82 Industrial, Commercial, and Institutional sources identified by MANE-VU's CALPUFF modeling as having emissions similar in magnitude to the EGUs modeled in this exercise or that are close enough to a Class I area that they would have the potential for visibility impacts. 56 See the DE Regional Haze SIP submittal at 91. MANE-VU Ask 3 requests that “each MANE-VU State that has not yet fully adopted an ultra-low fuel oil standard as requested by MANE-VU in 2007”, to “pursue this standard as expeditiously as possible and before 2028, depending on supply availability.” The Ask includes percent by weight standards for #2 distillate oil (0.0015% sulfur by weight or 15 parts per million (ppm)), #4 residual oil (0.25-0.5% sulfur by weight), and #6 residual oil (0.3-0.5% sulfur by weight). Delaware explained that, in 2013, it adopted the 7 DE Admin Code 1108 low-sulfur fuel regulation 57 which went into effect on July 1, 2016. Delaware therefore concluded that it is meeting Ask 3. Additional details about Delaware's response to Ask 3 can be found in the TSD of this proposed rulemaking action at 24. 57 See 87 FR 41074 (July 11, 2022). MANE-VU Ask 4 requests States to “pursue updating permits, enforceable agreements, and/or rules to “lock in” lower emissions rates for SO 2 , NO X and PM” at emission sources larger than 250 million British Thermal Units (MMBtu) per hour heat input that have switched to lower emitting fuels. 58 Based on Delaware's SIP submission, two EGUs fell under Ask 4. The first source is Calpine's EMEC, which had switched operations to lower emitting fuels and had its permits updated to lock in lower emission rates for SO 2 , NO X and PM. A second source, City of Dover McKee Run Generating Station, had its permits cancelled in November 2021. 59 Based on these updates, Delaware concluded it is meeting Ask 4. More details about Delaware's response to Ask 4 are included in the TSD of this proposed rulemaking action. 58 See appendix 8-12 “MANE-VU Regional Haze Consultation Report.” 59 See appendix 8-7 “McKee Run Permit Cancellation Letter.” MANE-VU Ask 5 requests that MANE-VU States “where emission rules have not been adopted, control NO X emissions for peaking combustion turbines that have the potential to operate on high electric demand days (HEDD)” by either: (a) striving to meet NO X emissions standards specified in the Ask for turbines that run on natural gas and fuel oil, (b) performing a four-factor analysis for reasonable installation of or upgrade to emission controls, or (c) obtaining equivalent alternative emission reductions on HEDD. 60 The Ask requests States to strive for NO X emission standards of no greater than 25 ppm for natural gas and 42 ppm for fuel oil, or at a minimum, NO X emissions standards of no greater than 42 ppm for natural gas and 96 ppm for fuel oil. 60 See appendix 8-12 “MANE-VU Regional Haze Consultation Report.” For Ask 5, Delaware identified seven sources with units affected by HEDD, 61 and two of the seven sources met the emission limits provided in option (a). Delaware requested that each of the remaining five sources perform four-factor analyses as stated in option (b) of the Ask because their current Title V permits do not meet the NO X standards from option (a). 62 Based on the four-factor analyses conducted by the five sources to evaluate potential control options for HEDD units, three of them found it economically feasible to operate existing controls during two additional months adjacent to the ozone season, for which Delaware updated their Title V permits accordingly and submitted the permits for incorporation into the SIP. For the remaining two sources, Delaware reviewed the facilities' estimates of compliance costs 63 of $192,000/ton of NO X removed for one and $334,897/ton of NO X removed for the other to upgrade their respective units, 64 and Delaware concluded that it was not an economically feasible option for these sources to upgrade their existing control given the limited operational time and low level of reported annual NO X emissions within the State as shown on table 10-5 of the SIP submittal. In addition, Delaware evaluated various potential new control options for the five sources but found that these were neither economically nor technically feasible. Because Delaware conducted four-factor analyses on the selected sources, Delaware concluded it has satisfied Ask 5 through option (b). More details about Delaware's EGUs four-factor analyses with regards to Ask 5 can be found in the TSD of this proposed rulemaking action. 61 See table 10-4 (Delaware Units Affected by HEDD “Ask #5”) of the DE Regional Haze SIP submittal at 110. 62 See table 10-5 (Average Operating Hours and NO X Emissions for Units Under “Ask #5”) of the DE Regional Haze SIP submittal at 111. 63 Per the DE Regional Haze SIP submittal section 10.5, costs were based on similar projects in other states for the one facility, and vendor quotes and EPA's Air Pollution Control Cost Manual for the other facility. 64 See section 10.5 of the DE Regional Haze SIP submittal. MANE-VU Ask 6, requests that “each State should consider and report in their SIP measures or programs to: (a) decrease energy demand through the use of energy efficiency and (b) increase the use within their State of Combined Heat and Power (CHP) and other clean Distributed Generation technologies including fuel cells, wind and solar.” 65 Delaware stated that it implemented a number of measures with regard to this Ask. Some of these include the Energy Task Force Executive Order signed on April 26, 2002, the Delaware Energy Efficiency Advisory Council (EEAC), the 2005 Renewable Energy Portfolio Standards Act which is the basis for Delaware's renewable energy portfolio standards (RPS), and the Regional Greenhouse Gas Initiative (RGGI), to name a few. Based on these measures, Delaware concluded it is meeting Ask 6. Additional details about Delaware's response to Ask 6 can be found in the TSD of this proposed rulemaking action. 65 See appendix 8-12 “MANE-VU Regional Haze Consultation Report.” b. EPA's Evaluation of Delaware's Response to the Six MANE-VU Asks and Compliance With 40 CFR 51.308(f)(2)(i) EPA is proposing to find that Delaware has satisfied the requirements of 40 CFR 51.308(f)(2)(i) related to evaluating sources and determining the emission reduction measures that are necessary to make reasonable progress by considering the four statutory factors. Through Ask 1, MANE-VU instructed States to “ensure the most effective use of control technologies on a year-round basis to consistently minimize emissions of haze precursors or obtain equivalent alternative emission reductions” at EGUs with a nameplate capacity larger than or equal to 25 megawatts (MW) with already installed NO X and/or SO 2 controls. 66 66 Id. EPA reviewed and evaluated Delaware's response to the four-factor analyses on the four sources with permits that did not require NO X controls year-round on some of their units and found that the State agreed with Calpine's conclusions for each of the sources. For ChEC and EMEC, Delaware agreed that it is not economically feasible to operate their NO X existing controls year-round because the units' operation and, hence, NO X emissions are both limited. On the other hand, for GEC and HREC, Delaware agreed that it is not technically feasible to retrofit the sources' NO X existing controls to operate year-round due to the same conclusion that operation and NO X emissions are limited. To support their conclusion, on table 10-2 of the SIP submittal, Delaware included the annual average operating hours and NO X emissions of the sources for a five-year period, which demonstrate the generally limited operation and the significantly low NO X emissions in recent years ( i.e., the tons of NO X emitted per unit per year ranging from less than two to less than 150). EPA agrees with Delaware that it is not reasonable to upgrade any of the sources' NO X existing controls due to the extremely low emission reductions that would have been achieved, and that the costs of compliance, as demonstrated through the four-factor analyses, are not justified by the low amount of NO X emission reductions that the sources would achieve if these were reconfigured. More information on the amount of NO X emitted from these units can be found in the TSD at 32-33. EPA also reviewed and evaluated the State's selection and modification of the applicable EGUs' title V permits to incorporate the regional haze requirements of the second planning period. To meet Ask 1, DNREC updated ChEC, EMEC, and HREC's title V permits after conducting four-factor analyses. For ChEC, DNREC added the 88 ppm NO X emission limit during April and October. For EMEC and HREC, DNREC added language requiring the facilities to operate and maintain their existing NO X control systems in accordance with Calpine's maintenance protocol. Based on the above, EPA thus agrees with Delaware's conclusions and proposes to find that Delaware reasonably satisfied Ask 1. For Ask 2, MANE-VU requested that States “perform a four-factor analysis for reasonable installation or upgrade to emissions controls” for specified sources. MANE-VU developed its Ask 2 list of sources for analysis by performing modeling and identifying facilities with the potential for 3.0 inverse megameters (Mm −1 ) or greater impacts on visibility at any Class I Area in the MANE-VU region. 67 67 See appendix 8-12 “MANE-VU Regional Haze Consultation Report.” As an initial matter, EPA does not necessarily agree that MANE-VU 3.0 Mm −1 visibility impact is a reasonable threshold for source selection. The RHR recognizes that, due to the nature of regional haze visibility impairment, numerous and sometimes relatively small sources may need to be selected and evaluated for control measures in order to make reasonable progress. See 2021 Clarifications Memo at 4. As explained in the 2021 Clarifications Memo, while states have discretion to choose any source selection threshold that is reasonable, “[a] state that relies on a visibility (or proxy for visibility impact) threshold to select sources for four-factor analysis should set the threshold at a level that captures a meaningful portion of the State's total contribution to visibility impairment to Class I Areas.” 2021 Memo at 3. In this case, the 3.0 Mm −1 threshold did not identify sources in Delaware (only 22 across the entire MANE-VU region), indicating that it may be unreasonably high. 68 68 Even though MANE-VU's 3.0 Mm −1 threshold did not identify sources in Delaware, two EGU sources were selected for CALPUFF modeling and identified as impacting two Class I Areas, Shenandoah National Park (SHEN) and James River Face National Park (JARI). These sources were the Indian River and the Edge Moor Energy Centers, whose highest impacts to these Class I Areas were at 1.7 Mm 1 in 2011 and 0.5 Mm −1 in 2015 from Indian River to SHEN, 1.1 Mm −1 in 2011 and 0.7 Mm −1 in 2015 from Indian River to JARI, 0.2 Mm −1 in 2011 and none in 2015 from Edge Moor to SHEN, and 0.4 Mm −1 in 2011 and none in 2015 from Edge Moor to JARI. Nonetheless, their impacts were well below the 3.0 Mm −1 threshold during the selected base years of 2011 and 2015. See DE Regional Haze SIP submittal at 75. However, EPA proposes to find that Delaware reasonably determined that it has satisfied Ask 2. As explained above, we do not necessarily agree that a 3.0 Mm −1 threshold for selecting sources for four-factor analysis results in a set of sources the evaluation of which has the potential to meaningfully reduce the State's contribution to visibility impairment. MANE-VU's Ask 2 did not identify any source in Delaware for a four-factor analysis; however, as part of EPA's evaluation, we note that other MANE-VU Asks identified multiple sources and sectors for four-factor analyses in Delaware, and Delaware did evaluate additional control measures and conducted four-factor analyses through other Asks to meet the regional haze requirements for the second planning period. Ask 2 is not the only source selection process for this State, and thus EPA is basing this proposed finding on the State's consideration of the four factors and units and sectors analyzed in Asks 1, 3, and 5. Ask 3 requests that, for “each MANE-VU State that has not yet fully adopted an ultra-low fuel oil standard as requested by MANE-VU in 2007”, to “pursue this standard as expeditiously as possible and before 2028, depending on supply availability.” EPA proposes to find that Delaware reasonably relied on MANE-VU's four-factor analysis for a low-sulfur fuel oil regulation, which engaged with each of the statutory factors and explained how the information supported a conclusion that a 15 ppm-sulfur fuel oil standard for fuel oils is reasonable. Delaware's ultra-low sulfur fuel oil regulations, 69 which, as previously stated, were approved into Delaware's SIP on July 11, 2022 (87 FR 41074), are consistent with Ask 3. EPA therefore proposes to find that Delaware reasonably determined that it has satisfied Ask 3. 69 See 7 DE Admin Code 1108 “Sulfur Dioxide Emissions from Fuel Burning Equipment.” MANE-VU Ask 4 requests that States “pursue updating permits, enforceable agreements, and/or rules to lock-in lower emission rates for SO 2 , NO X , and PM” at “EGUs and other large point emission sources larger than 250 MMBTU per hour heat input that have switched to lower emitting fuels.” Ask 4 also states that “the permit, enforceable agreement, and/or rule can allow for suspension of the lower emission rate during natural gas curtailment.” Delaware concluded that no additional updates were needed to meet Ask 4 because the EGU that fell under this Ask, Calpine EMEC, switched operations to lower emitting fuels and has already locked into the lower emission rates for NO X , SO 2 , and PM by permits. In addition, the McKee Run Generating Station, that fell under this Ask, had its permits cancelled on November 12, 2021. Finally, modified units in Delaware are required to amend their permits through the New Source Review (NSR) process if they plan to switch back to coal or a fuel that will increase emissions. A change in fuel, unless already allowed in the permit, would generally be a modification, 70 and Delaware's operating permits regulations require that an application to modify the permit be submitted prior to the change in fuel. 71 70 See 7 DE Admin Code 1101, defining “Modification” means [Text truncated at 120,000 characters. The full text is on the page linked above.] --- Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2024-18174. Public record. Not legal advice.