83 FR 107 pgs. 25617-25632 - Interstate Transport Prongs 1 and 2 for the 2010 Sulfur Dioxide (SO2) Standard for Colorado, Montana, North Dakota, South Dakota and Wyoming
Type: PRORULEVolume: 83Number: 107Pages: 25617 - 25632
Pages: 25617, 25618, 25619, 25620, 25621, 25622, 25623, 25624, 25625, 25626, 25627, 25628, 25629, 25630, 25631, 25632Docket number: [EPA-R08-OAR-2018-0109; FRL-9978-72-Region 8]
FR document: [FR Doc. 2018-11846 Filed 6-1-18; 8:45 am]
Agency: Environmental Protection Agency
Official PDF Version: PDF Version
[top]
ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 52
[EPA-R08-OAR-2018-0109; FRL-9978-72-Region 8]
Interstate Transport Prongs 1 and 2 for the 2010 Sulfur Dioxide (SO 2 ) Standard for Colorado, Montana, North Dakota, South Dakota and Wyoming
AGENCY:
Environmental Protection Agency (EPA).
ACTION:
Proposed rule.
SUMMARY:
The Environmental Protection Agency (EPA) is proposing to approve portions of State Implementation Plan (SIP) submissions from Colorado, Montana, North Dakota, South Dakota and Wyoming addressing the Clean Air Act (CAA or Act) interstate transport SIP requirements for the 2010 Sulfur Dioxide (SO 2 ) National Ambient Air Quality Standards (NAAQS). These submissions address the requirement that each SIP contain adequate provisions prohibiting air emissions that will have certain adverse air quality effects in other states. The EPA is proposing to approve portions of these infrastructure SIPs for the aforementioned states as containing adequate provisions to ensure that air emissions in the states will not significantly contribute to nonattainment or interfere with maintenance of the 2010 SO 2 NAAQS in any other state.
DATES:
Comments must be received on or before July 5, 2018.
ADDRESSES:
Submit your comments, identified by Docket ID No EPA-R08-OAR-2018-0109 at http://www.regulations.gov. Follow the online instructions for submitting comments. Once submitted, comments cannot be edited or removed from www.regulations.gov. 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, the full EPA public comment policy, information about CBI or multimedia submissions and general guidance on making effective comments, please visit http://www2.epa.gov/dockets/commenting-epa-dockets.
FOR FURTHER INFORMATION CONTACT:
Adam Clark, Air Program, U.S. EPA Region 8, (303) 312-7104, clark.adam@epa.gov.
SUPPLEMENTARY INFORMATION:
I. Background
II. Relevant Factors To Evaluate 2010 SO 2 Interstate Transport SIPs
III. States' Submissions and EPA's Analysis
A. Colorado
1. State's Analysis
2. EPA's Prong 1 Evaluation
3. EPA's Prong 2 Evaluation
B. Montana
1. State's Analysis
2. EPA's Prong 1 Evaluation
3. EPA's Prong 2 Evaluation
C. North Dakota
1. State's Analysis
2. EPA's Prong 1 Evaluation
3. EPA's Prong 2 Evaluation
D. South Dakota
1. State's Analysis
2. EPA's Prong 1 Evaluation
3. EPA's Prong 2 Evaluation
E. Wyoming
1. State's Analysis
2. EPA's Prong 1 Evaluation
3. EPA's Prong 2 Evaluation
IV. Proposed Action
V. Statutory and Executive Order Reviews
I. Background
On June 2, 2010, the EPA established a new primary 1-hour SO 2 NAAQS of 75 parts per billion (ppb), based on a 3-year average of the annual 99th percentile of 1-hour daily maximum concentrations.1 The CAA requires states to submit, within 3 years after promulgation of a new or revised NAAQS, SIPs meeting the applicable "infrastructure" elements of sections 110(a)(1) and (2). One of these applicable infrastructure elements, CAA section 110(a)(2)(D)(i), requires SIPs to contain "good neighbor" provisions to prohibit certain adverse air quality effects on neighboring states due to interstate transport of pollution.
Footnotes:
1 ?75 FR 35520 (June 22, 2010).
Section 110(a)(2)(D)(i) includes four distinct components, commonly referred to as "prongs," that must be addressed in infrastructure SIP submissions. The first two prongs, which are codified in section 110(a)(2)(D)(i)(I), require SIPs to contain adequate provisions that prohibit any source or other type of emissions activity in one state from contributing significantly to nonattainment of the NAAQS in another state (prong 1) and from interfering with maintenance of the NAAQS in another state (prong 2). The third and fourth prongs, which are codified in section 110(a)(2)(D)(i)(II), require SIPs to contain adequate provisions that prohibit emissions activity in one state from interfering with measures required to prevent significant deterioration of air quality in another state (prong 3) or from interfering with measures to protect visibility in another state (prong 4).
[top] In this action, the EPA is proposing to approve the prong 1 and prong 2 portions of infrastructure SIP submissions submitted by: Colorado on July 17, 2013 and February 16, 2018; Montana on July 15, 2013; North Dakota on March 7, 2013; South Dakota on December 20, 2013; and Wyoming on March 6, 2015, as containing adequate provisions to ensure that air emissions in these states will not significantly contribute to nonattainment or interfere with maintenance of the 2010 SO 2 NAAQS in any other state. All other applicable infrastructure SIP requirements for these SIP submissions have been addressed in separate rulemakings.
II. Relevant Factors To Evaluate 2010 SO 2 Interstate Transport SIPs
Although SO 2 is emitted from a similar universe of point and nonpoint sources, interstate transport of SO 2 is unlike the transport of fine particulate matter (PM 2.5 ) or ozone, in that SO 2 is not a regional pollutant and does not commonly contribute to widespread nonattainment over a large (and often multi-state) area. The transport of SO 2 is more analogous to the transport of lead (Pb) because its physical properties result in localized pollutant impacts very near the emissions source. However, ambient concentrations of SO 2 do not decrease as quickly with distance from the source as Pb because of the physical properties and typical release heights of SO 2 . Emissions of SO 2 travel farther and have wider ranging impacts than emissions of Pb, but do not travel far enough to be treated in a manner similar to ozone or PM 2.5 . The approaches that the EPA has adopted for ozone or PM 2.5 transport are too regionally focused and the approach for Pb transport is too tightly circumscribed to the source. SO 2 transport is therefore a unique case and requires a different approach.
Given the physical properties of SO 2 , the EPA selected the "urban scale"-a spatial scale with dimensions from 4 to 50 kilometers (km) from point sources-given the usefulness of that range in assessing trends in both area-wide air quality and the effectiveness of large-scale pollution control strategies at such point sources.2 As such, the EPA utilized an assessment up to 50 km from point sources in order to assess trends in area-wide air quality that might impact downwind states.
Footnotes:
2 ?For the definition of spatial scales for SO 2 , please see 40 CFR part 58, Appendix D, section 4.4 ("Sulfur Dioxide (SO 2 ) Design Criteria"). For further discussion on how the EPA is applying these definitions with respect to interstate transport of SO 2 , see the EPA's proposal on Connecticut's SO 2 transport SIP. 82 FR 21351, 21352, 21354 (May 8, 2017).
As discussed in Section III of this proposed action, the EPA first reviewed each state's analysis to assess how the state evaluated the transport of SO 2 to other states, the types of information used in the analysis and the conclusions drawn by the state. The EPA then conducted a weight of evidence analysis, including review of each state's submission and other available information, including air quality, emission sources and emission trends within the state and in neighboring states to which it could potentially contribute or interfere.3
Footnotes:
3 ?This proposed approval action is based on the information contained in the administrative record for this action, and does not prejudge any other future EPA action that may make other determinations regarding any of the subject state's air quality status. Any such future actions, such as area designations under any NAAQS, will be based on their own administrative records and the EPA's analyses of information that becomes available at those times. Future available information may include, and is not limited to, monitoring data and modeling analyses conducted pursuant to the EPA's SO 2 Data Requirements Rule (80 FR 51052, August 21, 2015) and information submitted to the EPA by states, air agencies, and third party stakeholders such as citizen groups and industry representatives.
III. States' Submissions and EPA's Analysis
In this section, we provide an overview of each state's 2010 SO 2 transport analysis, as well as the EPA's evaluation of prongs 1 and 2 for each state. Table 1, below, shows emission trends for the five states addressed in this notice along with their neighboring states. The table will be referenced as part of the EPA's analysis for each state.4
Footnotes:
4 ?This emissions trends information was derived from EPA's webpage https://www.epa.gov/air-emissions-inventories/air-pollutant-emissions-trends-data.
| State | 2000 | 2005 | 2010 | 2016 | SO 2 reduction, 2000-2016 (%) |
|---|---|---|---|---|---|
| Arizona | 118,528 | 90,577 | 73,075 | 38,089 | 68 |
| Colorado | 115,122 | 80,468 | 60,459 | 20,626 | 82 |
| Idaho | 34,525 | 35,451 | 14,774 | 10,051 | 70 |
| Iowa | 265,005 | 222,419 | 142,738 | 48,776 | 81 |
| Kansas | 148,416 | 199,006 | 80,267 | 16,054 | 89 |
| Minnesota | 148,899 | 156,468 | 85,254 | 34,219 | 77 |
| Montana | 57,517 | 42,085 | 26,869 | 12,379 | 78 |
| Nebraska | 86,894 | 121,785 | 77,898 | 40,964 | 52 |
| New Mexico | 164,631 | 47,671 | 23,651 | 15,529 | 90 |
| North Dakota | 275,138 | 159,221 | 199,322 | 152,505 | 44 |
| Oklahoma | 145,862 | 169,464 | 136,348 | 73,006 | 50 |
| South Dakota | 41,120 | 28,579 | 16,202 | 2,642 | 93 |
| Utah | 58,040 | 52,998 | 29,776 | 15,226 | 73 |
| Wyoming | 141,439 | 122,453 | 91,022 | 57,313 | 59 |
A. Colorado
1. State's Analysis
[top] Colorado conducted a weight of evidence analysis to examine whether SO 2 emissions from Colorado adversely affect attainment or maintenance of the 2010 SO 2 NAAQS in downwind states. Colorado evaluated potential air quality impacts on areas outside the State through an assessment of whether SO 2 emissions from sources located within 50 km of Colorado's borders may have associated interstate transport impacts. Colorado's analysis included SO 2 emissions information in the State, with specific focus on sources and counties located within 50 km of Colorado's borders. Among these sources, Colorado provided an in-depth analysis of the two sources emitting over 100 tons per year (tpy) of SO 2 ; the Nucla Generating Station (47 km east of Utah border) and Rawhide Energy Station (15 km south of Wyoming border). Colorado also reviewed meteorological conditions at SO 2 sources within 50 km of the State's border, and the distances from identified SO 2 sources in Colorado to the nearest area that is not attaining the NAAQS or may have trouble maintaining the NAAQS in another state. Finally, Colorado reviewed mobile source emissions data from highway and off-highway vehicles in all of the Colorado counties which border other states. Based on this weight of evidence analysis, Colorado concluded that emissions within the State will not contribute to nonattainment or interfere with maintenance of the 2010 SO 2 NAAQS in neighboring states.
2. EPA's Prong 1 Evaluation
The EPA proposes to find that Colorado's SIP meets the interstate transport requirements of CAA section 110(a)(2)(D)(i)(I), prong 1 for the 2010 SO 2 NAAQS, as discussed below. We have analyzed the air quality, emission sources and emission trends in Colorado and neighboring states, i.e., Arizona, Kansas, Nebraska, New Mexico, Oklahoma, Utah and Wyoming. Based on that analysis, we propose to find that Colorado will not significantly contribute to nonattainment of the 2010 SO 2 NAAQS in any other state.
We reviewed 2014-2016 SO 2 design value concentrations at monitors with data sufficient to produce valid 1-hour SO 2 design values for Colorado and neighboring states.5 In Table 2, below, we have included monitoring data from four scenarios: (1) All of the monitor data from Colorado; (2) the monitor with the highest SO 2 level in each neighboring state; (3) the monitor in each neighboring state located closest to the Colorado border; and (4) all monitors in each neighboring state within 50 km of the border.
Footnotes:
5 ?Data retrieved from EPA's https://www.epa.gov/air-trends/air-quality-design-values#report.
| State/area | Scenario | Site ID | Distance to Colorado border (km)?* | 2014-2016 Design value (ppb)?6 |
|---|---|---|---|---|
| Arizona/Miami | 3 | 040070009 | 432 | 146 |
| Arizona/Hayden | 2 | 040071001 | 470 | 280 |
| Colorado/Denver | 1 | 080013001 | 127 | 18 |
| Colorado/Denver | 1 | 080310002 | 138 | 12 |
| Colorado/Denver | 1 | 080310026 | 135 | 14 |
| Colorado/Colorado Springs | 1 | 080410015 | 203 | 52 |
| Kansas/Trego County | 3 | 201950001 | 198 | 5 |
| Kansas/Kansas City | 2 | 202090021 | 640 | 34 |
| Nebraska/Omaha | 2 | 310550053 | 515 | 59 |
| Nebraska/Omaha | 3 | 310550019 | 676 | 27 |
| New Mexico/Fruitland | 4 | 350450009 | 28 | 3 |
| New Mexico/Waterflow | 2, 3, 4 | 350451005 | 22 | 8 |
| Oklahoma/Muskogee | 2 | 401010167 | 618 | 44 |
| Oklahoma/Oklahoma City | 3 | 401091037 | 437 | 3 |
| Wyoming/Cheyenne | 3, 4 | 560210100 | 20 | 9 |
| Wyoming/Casper | 2 | 560252601 | 206 | 25 |
| *?All distances throughout this notice are approximations. | ||||
The EPA reviewed ambient air quality data in Colorado and neighboring states to see whether there were any monitoring sites, particularly near the Colorado border, with elevated SO 2 concentrations that might warrant further investigation with respect to interstate transport of SO 2 from emission sources near any given monitor. As shown, there are no violating design values in Colorado or neighboring states apart from in the Hayden, Arizona and Miami, Arizona areas. In Colorado's analysis, the state reviewed its potential impact on the Hayden and Miami, Arizona 2010 SO 2 nonattainment areas, which are the only areas designated nonattainment in states bordering Colorado. Colorado noted the significant distance between its border and these nonattainment areas, as well as the larger distance between the nonattainment areas to the nearest major SO 2 source in Colorado (Nucla Generating Station-582 km).
Footnotes:
6 ?Id.
The data presented in Table 2, above, show that Colorado's network of SO 2 monitors with data sufficient to produce valid 1-hour SO 2 design values indicates that monitored 1-hour SO 2 levels in Colorado are between 16% and 69% of the 75 ppb level of the NAAQS. As shown, there are no Colorado monitors located within 50 km of a neighboring state's border. Three monitors in neighboring states are located within 50 km of the Colorado border, and these monitors recorded SO 2 design values ranging between 4% and 12% of the 2010 SO 2 NAAQS. Thus, these air quality data do not, by themselves, indicate any particular location that would warrant further investigation with respect to SO 2 emission sources that might significantly contribute to nonattainment in the neighboring states. However, because the monitoring network is not necessarily designed to find all locations of high SO 2 concentrations, this observation indicates an absence of evidence of impact at these locations but is not sufficient evidence by itself of an absence of impact at all locations in the neighboring states. We have therefore also conducted a source-oriented analysis.
As noted, the EPA finds that it is appropriate to examine the impacts of emissions from stationary sources in Colorado in distances ranging from 0 km to 50 km from the facility, based on the "urban scale" definition contained in Appendix D to 40 CFR part 58, Section 4.4. Colorado assessed point sources up to 50 km from state borders to evaluate trends and SO 2 concentrations in area-wide air quality. The list of sources of 100 tpy?7 or more of SO 2 within 50 km from state borders, provided by Colorado, is shown in Table 3 below.
Footnotes:
7 ?Colorado limited its analysis to Colorado sources of SO 2 emitting at least 100 tpy. We agree with Colorado's choice to limit its analysis in this way, because in the absence of special factors, for example the presence of a nearby larger source or unusual physical factors, Colorado sources emitting less than 100 tpy can appropriately be presumed to not be causing or contributing to SO 2 concentrations above the NAAQS.
[top]
| Colorado source | 2016 SO 2 emissions (tons)?* | Distance to Colorado border (km) | Distance to nearest neighboring state SO 2 source (km) | Neighboring state source 2016 emissions (tons) |
|---|---|---|---|---|
| Nucla Generating Station | 439 | 47 | 68 (Lisbon Natural Gas Processing Plant-San Juan County, Utah) | 499 |
| Rawhide Energy Station | 878 | 15 | 35 (Frontier Petroleum Refinery-Cheyenne, Wyoming) | 311 |
| *?Emissions data throughout this document were obtained using EPA's Emissions Inventory System (EIS) Gateway. | ||||
Table 3 shows the distance from the sources listed therein to the nearest out-of-state source emitting above 100 tpy of SO 2 , because elevated levels of SO 2 , to which SO 2 emitted in Colorado may have a downwind impact, are most likely to be found near such sources. In the case of the Nucla Generating Station, the distance between this source and the Colorado-Utah state border (47 km) and the nearest major SO 2 source in neighboring state Utah (68 km), indicate that emissions from Colorado are very unlikely to contribute significantly to problems with attainment of the 2010 SO 2 NAAQS in Utah. The EPA notes that Colorado recently revised the Nucla Generating Station NO X reasonable progress determination in its regional haze SIP to require the source to shut down before December 31, 2022, and the EPA has proposed approval of this SIP revision. See 83 FR 18244 (April 26, 2018).
With regard to the Rawhide Energy Station, because it is located within 50 km of the Frontier Petroleum Refinery in Cheyenne, Wyoming, the EPA has assessed potential SO 2 impacts from the Rawhide Energy Station on the Cheyenne area. First, the EPA reviewed available monitoring data in Cheyenne, Wyoming, 6 km northeast of the Frontier Petroleum Refinery. The 2014-2016 SO 2 design value for this monitor (Site ID 560210100-See Table 2) was 9 ppb. The maximum 1-hour SO 2 value measured at this monitor from January 1, 2011, (when it began operation) to December 31, 2017, was 31 ppb. A second monitor not listed in Table 2, located 3 km east of the Frontier Petroleum Refinery, recorded 1 year of data in Cheyenne to examine potential population exposure near the refinery.8 Between March 31, 2016, and April 3, 2017, this monitor recorded a maximum 1-hour SO 2 concentration of 44 ppb, with a fourth highest 1-hour daily maximum concentration of 16.7 ppb. All of these monitoring data combined indicate that SO 2 levels in Cheyenne, Wyoming, and therefore near the Frontier Petroleum Refinery, are not likely to exceed the 2010 SO 2 NAAQS or come near the level of a NAAQS exceedance.
Footnotes:
8 ?See Wyoming's 2016 Annual Monitoring Network Plan at pages 50-51: http://deq.wyoming.gov/aqd/monitoring/resources/annual-network-plans/.
The EPA also reviewed the location of sources in neighboring states emitting more than 100 tpy of SO 2 and located within 50 km of the Colorado border (see Table 4). This is because elevated levels of SO 2 , to which SO 2 emitted in Colorado may have a downwind impact, are most likely to be found near such sources. As shown in Table 4, the shortest distance between any pair of these sources is 84 km. Given the localized range of potential 1-hour SO 2 impacts, this indicates that there are no additional locations (apart from Cheyenne) in neighboring states that would warrant further investigation with respect to Colorado SO 2 emission sources that might contribute to problems with attainment of the 2010 SO 2 NAAQS. The Hayden and Miami, Arizona 2010 SO 2 nonattainment areas, which Colorado reviewed as part of its analysis, are over 400 km from the nearest Colorado border and so were not included in Table 4. Colorado asserted that the significant distance between its border and these nonattainment areas indicates that it is highly unlikely that SO 2 emissions generated in Colorado are contributing significantly to either nonattainment area in Arizona, and the EPA agrees with this conclusion.
| Source | 2016 SO 2 emissions (tons) | Distance to Colorado border (km) | Distance to nearest Colorado SO 2 source (km) | Colorado source 2016 emissions (tons) |
|---|---|---|---|---|
| San Juan Generating Station (Waterflow, New Mexico) | 2,913 | 22 | 160 (Nucla Generating Station-Nucla, Colorado) | 439 |
| Four Corners Steam Electric Station (Navajo Nation) | 4,412 | 34 | 172 (Nucla Generating Station-Nucla, Colorado) | 439 |
| Bonanza Power Plant (Uintah and Ouray Reservation) | 1,305 | 20 | 84 (Meeker Gas Plant-Rio Blanco County, Colorado) | 210 |
| Resolute Natural Resources Company-Aneth Unit (Navajo Nation) | 118 | 19 | 124 (Nucla Generating Station-Nucla, Colorado) | 439 |
| Clean Harbors Env. Services (Kimball County, Nebraska) | 218 | 17 | 104 (Pawnee Generating Station-Fort Morgan, Colorado) | 1,493 |
| *?We have not included sources that are duplicative of those in Table 3. | ||||
[top] In conclusion, for interstate transport prong 1, we reviewed ambient SO 2 monitoring data and SO 2 emission sources both within Colorado and in neighboring states. Based on this analysis, we propose to determine that
3. EPA's Prong 2 Evaluation
In its prong 2 analysis, Colorado reviewed potential SO 2 impacts on the Billings, Montana area, which is currently in "maintenance" status for the 2010 SO 2 NAAQS, noting the large distance between the nearest Colorado border and the Billings area (520 km). The EPA interprets CAA section 110(a)(2)(D)(i)(I) prong 2 to require an evaluation of the potential impact of a state's emissions on areas that are currently measuring clean data, but that may have issues maintaining that air quality, rather than only former nonattainment, and thus current maintenance, areas. Therefore, in addition to the analysis presented by Colorado, the EPA has also reviewed additional information on SO 2 air quality and emission trends to evaluate the State's conclusion that Colorado will not interfere with maintenance of the 2010 SO 2 NAAQS in downwind states. This evaluation builds on the analysis regarding significant contribution to nonattainment (prong 1). Specifically, because of the low monitored ambient concentrations of SO 2 in Colorado and neighboring states, and the large distances between cross-state SO 2 sources, the EPA is proposing to find that SO 2 levels in neighboring states near the Colorado border do not indicate any inability to maintain the SO 2 NAAQS that could be attributed in part to sources in Colorado.
As shown in Table 1, the statewide SO 2 emissions from Colorado and neighboring states have decreased substantially over time, per our review of the EPA's emissions trends data.9 From 2000 to 2016, total statewide SO 2 emissions decreased by the following proportions: Arizona (68% decrease), Colorado (82% decrease), Kansas (89% decrease), Nebraska (52% decrease), New Mexico (90% decrease), Utah (73% decrease) and Wyoming (59% decrease). This trend of decreasing SO 2 emissions does not by itself demonstrate that areas in Colorado and neighboring states will not have issues maintaining the 2010 SO 2 NAAQS. However, as a piece of this weight of evidence analysis for prong 2, it provides further indication (when considered alongside low monitor values in neighboring states) that such maintenance issues are unlikely. This is because the geographic scope of these reductions and their large sizes strongly suggest that they are not transient effects from reversible causes, and thus these reductions suggest that there is very low likelihood that a strong upward trend in emissions will occur that might cause areas presently in attainment to violate the NAAQS.
Footnotes:
9 ?Additional emissions trends data are available at: https://www.epa.gov/air-emissions-inventories/air-pollutant-emissions-trends-data.
As noted in Colorado's submission, any future large sources of SO 2 emissions will be addressed by Colorado's SIP-approved Prevention of Significant Deterioration (PSD) program.10 Future minor sources of SO 2 emissions will be addressed by Colorado's SIP-approved minor new source review permit program.11 The permitting regulations contained within these programs should help ensure that ambient concentrations of SO 2 in neighboring states are not exceeded as a result of new facility construction or modification occurring in Colorado.
Footnotes:
10 ?See EPA's final action of the PSD portions of Colorado's SIP, at 82 FR 39030, August 17, 2017.
11 ?Id.
In conclusion, for interstate transport prong 2, we reviewed additional information about emission trends, as well as the technical information considered for interstate transport prong 1. We find that the combination of low ambient concentrations of SO 2 in Colorado and neighboring states, the large distances between cross-state SO 2 sources, the downward trend in SO 2 emissions from Colorado and neighboring states, and state measures that prevent new facility construction or modification in Colorado from causing SO 2 exceedances in downwind states, indicates no interference with maintenance of the 2010 SO 2 NAAQS from Colorado. Accordingly, we propose to determine that Colorado SO 2 emission sources will not interfere with maintenance of the 2010 SO 2 NAAQS in any other state, per the requirements of CAA section 110(a)(2)(D)(i)(I).
B. Montana
1. State's Analysis
Montana relied on existing programs to assert that SO 2 emissions from Montana will not adversely affect attainment or maintenance of the 2010 SO 2 NAAQS in downwind states. Montana noted that sources within the State are subject to new source review and Montana Air Quality Permit (MAQP) requirements, as well as applicable Maximum Achievable Control Technology (MACT) and New Source Performance Standards (NSPS), and asserted that these requirements along with additional portions of Montana's SIP prevent sources within the State from contributing to nonattainment or interfering with maintenance of the 2010 SO 2 NAAQS in neighboring states.
2. EPA's Prong 1 Evaluation
The EPA proposes to find that Montana's SIP meets the interstate transport requirements of CAA section 110(a)(2)(D)(i)(I), prong 1 for the 2010 SO 2 NAAQS, as discussed below. We have analyzed the air quality, emission sources and emission trends in Montana and neighboring states, i.e., Idaho, North Dakota, South Dakota and Wyoming. Based on that analysis, we propose to find that Montana will not significantly contribute to nonattainment of the 2010 SO 2 NAAQS in any other state.
We reviewed 2014-2016 SO 2 design value concentrations at monitors with data sufficient to produce valid 1-hour SO 2 design values for Montana and neighboring states.12 In Table 5, below, we have included monitoring data from four scenarios: (1) All of the monitor data from Montana; (2) the monitor with the highest SO 2 level in each neighboring state; (3) the monitor in each neighboring state located closest to the Montana border; and (4) all monitors in each neighboring state within 50 km of the border.
Footnotes:
12 ?Data retrieved from EPA's https://www.epa.gov/air-trends/air-quality-design-values#report.
[top]
| State/area | Scenario | Site ID | Distance to Montana border (km) | 2014-2016 design value (ppb) |
|---|---|---|---|---|
| Idaho/Pocatello | 2, 3 | 160050004 | 162 | 39 |
| Montana/Helena | 1 | 300490004 | 178 | 2 |
| Montana/Richland County | 1 | 300830001 | 33 | 7 |
| Montana/Billings | 1 | 301110066 | 87 | 53 |
| North Dakota/Dickinson | 4 | 380070002 | 50 | 5 |
| North Dakota/Burke County | 2 | 380130004 | 120 | 23 |
| North Dakota/McKenzie County | 4 | 380530104 | 5 | 6 |
| North Dakota/McKenzie County | 4 | 380530111 | 2 | 7 |
| South Dakota/Sioux Falls | 2 | 460990008 | 608 | 6 |
| South Dakota/Rapid City | 3 | 461030020 | 118 | 4 |
| Wyoming/Gillette | 3 | 560050857 | 80 | 21 |
| Wyoming/Casper | 2 | 560252601 | 236 | 25 |
The EPA reviewed ambient air quality data in Montana and neighboring states to see whether there were any monitoring sites, particularly near the Montana border, with elevated SO 2 concentrations that might warrant further investigation with respect to interstate transport of SO 2 from emission sources near any given monitor. The data presented in Table 5, above, show that Montana's network of SO 2 monitors with data sufficient to produce valid 1-hour SO 2 design values indicates that monitored 1-hour SO 2 levels in Montana are between 2% and 70% of the 75 ppb level of the NAAQS. There is one Montana monitor located within 50 km of a neighboring state's border, and this monitor indicates a design value at 9% of the NAAQS. Three monitors in neighboring states are located within 50 km of the Montana border, and these monitors recorded SO 2 design values ranging between 6% and 9% of the 2010 SO 2 NAAQS. Thus, these air quality data do not, by themselves, indicate any particular location that would warrant further investigation with respect to SO 2 emission sources that might significantly contribute to nonattainment in the neighboring states. However, because the monitoring network is not necessarily designed to find all locations of high SO 2 concentrations, this observation indicates an absence of evidence of impact at these locations but is not sufficient evidence by itself of an absence of impact at all locations in the neighboring states. We have therefore also conducted a source-oriented analysis.
As noted, the EPA finds that it is appropriate to examine the impacts of emissions from stationary sources in Montana in distances ranging from 0 km to 50 km from the facility, based on the "urban scale" definition contained in Appendix D to 40 CFR part 58, Section 4.4. Therefore, we assessed point sources up to 50 km from state borders to evaluate trends and SO 2 concentrations in area-wide air quality, and determined that there are no such sources in Montana. The CHS Laurel Refinery, located 74 km north of the Wyoming border, is the Montana point source closest to another state's border. The large distances between Montana sources and the nearest neighboring state provide further evidence to support a conclusion that emissions from Montana will not contribute to problems with attainment of the 2010 SO 2 NAAQS in downwind states.
The EPA also reviewed the location of sources in neighboring states emitting more than 100 tpy?13 of SO 2 and located within 50 km of the Montana border (see Table 6). This is because elevated levels of SO 2 , to which SO 2 emitted in Montana may have a downwind impact, are most likely to be found near such sources. As shown in Table 6, the shortest distance between any pair of these sources is 75 km. This indicates that there are no locations in neighboring states that would warrant further investigation with respect to Montana SO 2 emission sources that might contribute to problems with attainment of the 2010 SO 2 NAAQS.
Footnotes:
13 ?We have limited our analysis to Montana sources of SO 2 emitting at least 100 tpy, because in the absence of special factors, for example the presence of a nearby larger source or unusual physical factors, Montana sources emitting less than 100 tpy can appropriately be presumed to not be causing or contributing to SO 2 concentrations above the NAAQS.
| Source | 2016 SO 2 emissions (tons) | Distance to Montana border (km) | Distance to nearest Montana SO 2 source (km) | Montana source 2016 emissions (tons) |
|---|---|---|---|---|
| Colony East and West Plants (Crook County, Wyoming) | 106 | 15 | 223 (Colstrip Station-Colstrip, Montana) | 1,335 |
| Elk Basin Gas Plant (Park County, Wyoming) | 641 | 2 | 75 (CHS Laurel Refinery-Laurel, Montana) | 272 |
In conclusion, for interstate transport prong 1, we reviewed ambient SO 2 monitoring data and SO 2 emission sources within Montana and in neighboring states. Based on this analysis, we propose to determine that Montana will not significantly contribute to nonattainment of the 2010 SO 2 NAAQS in any other state, per the requirements of CAA section 110(a)(2)(D)(i)(I).
3. EPA's Prong 2 Evaluation
[top] The EPA has reviewed available information on SO 2 air quality and emission trends to evaluate the state's conclusion that Montana will not interfere with maintenance of the 2010 SO 2 NAAQS in downwind states. The EPA notes that Montana's analysis does not independently address whether the SIP contains adequate provisions prohibiting emissions that will interfere with maintenance of the 2010 SO 2
Footnotes:
14 ?531 F.3d 896, 910-11 (D.C. Cir. 2008) (holding that the EPA must give "independent significance" to each prong of CAA section 110(a)(2)(D)(i)(I)).
As shown in Table 1, the statewide SO 2 emissions from Montana and neighboring states have decreased substantially over time, per our review of the EPA's emissions trends data.15 From 2000 to 2016, total statewide SO 2 emissions decreased by the following proportions: Idaho (70% decrease), Montana (78% decrease), North Dakota (44% decrease), South Dakota (93% decrease) and Wyoming (59% decrease). This trend of decreasing SO 2 emissions does not by itself demonstrate that areas in Montana and neighboring states will not have issues maintaining the 2010 SO 2 NAAQS. However, as a piece of this weight of evidence analysis for prong 2, it provides further indication (when considered alongside low monitor values in neighboring states) that such maintenance issues are unlikely. This is because the geographic scope of these reductions and their large sizes strongly suggest that they are not transient effects from reversible causes, and thus these reductions suggest that there is very low likelihood that a strong upward trend in emissions will occur that might cause areas presently in attainment to violate the NAAQS.
Footnotes:
15 ?Additional emissions trends data are available at: https://www.epa.gov/air-emissions-inventories/air-pollutant-emissions-trends-data.
As noted in Montana's submission, any future large sources of SO 2 emissions will be addressed by Montana's SIP-approved PSD program.16 Future minor sources of SO 2 emissions will be addressed by Montana's SIP-approved minor new source review permit program.17 The permitting regulations contained within these programs should help ensure that ambient concentrations of SO 2 in neighboring states are not exceeded as a result of new facility construction or modification occurring in Montana.
Footnotes:
16 ?See EPA's final action of the PSD portions of Montana's SIP, at 81 FR 23180, April 20, 2016.
17 ?Id.
In conclusion, for interstate transport prong 2, the EPA has incorporated additional information into our evaluation of Montana's submission, which did not include an independent analysis of prong 2. In doing so, we have reviewed information about emission trends, as well as the technical information considered for our interstate transport prong 1 analysis. We find that the combination of low ambient concentrations of SO 2 in Montana and neighboring states, the large distances between cross-state SO 2 sources, the downward trend in SO 2 emissions from Montana and surrounding states, and state measures that prevent new facility construction or modification in Montana from causing SO 2 exceedances in downwind states, indicates no interference with maintenance of the 2010 SO 2 NAAQS from Montana. Accordingly, we propose to determine that Montana SO 2 emission sources will not interfere with maintenance of the 2010 SO 2 NAAQS in any other state, per the requirements of CAA section 110(a)(2)(D)(i)(I).
C. North Dakota
1. State's Analysis
North Dakota conducted a weight of evidence analysis to examine whether SO 2 emissions from North Dakota adversely affect attainment or maintenance of the 2010 SO 2 NAAQS in downwind states. North Dakota cited the large distance between the State's SO 2 sources and the nearest SO 2 nonattainment and maintenance areas in downwind states, as well as the very low SO 2 values at intervening monitors. North Dakota also noted that SO 2 emissions within the State have been steadily decreasing over time, specifically noting a 35% point-source emissions decrease between 2002 and 2011. With regard to the interference with maintenance requirement, North Dakota discussed the low monitored ambient concentrations of SO 2 in neighboring states in the period up to and including 2011. Based on this weight of evidence analysis, North Dakota concluded that emissions within the State will not contribute to nonattainment or interfere with maintenance of the 2010 SO 2 NAAQS in neighboring states.
2. EPA's Prong 1 Evaluation
The EPA proposes to find that North Dakota's SIP meets the interstate transport requirements of CAA section 110(a)(2)(D)(i)(I), prong 1 for the 2010 SO 2 NAAQS, as discussed below. We have analyzed the air quality, emission sources, and emission trends in North Dakota and neighboring states, i.e., Minnesota, Montana and South Dakota. Based on that analysis, we propose to find that North Dakota will not significantly contribute to nonattainment of the 2010 SO 2 NAAQS in any other state.
To date, the only area in a state bordering North Dakota that has been designated nonattainment for the 2010 SO 2 NAAQS is Billings, Montana. The EPA designated the portion of Billings surrounding the PPL Corette Power Plant based on a 2009-2011 monitored design value, concluding that this source was the key contributor to the NAAQS violations during that period. See 78 FR 47191 (August 5, 2013). Following the permanent closure of the PPL Corette Plant in March 2015, which was accompanied by a significant decrease in monitored SO 2 values (which indicated attainment) in the nonattainment area, the EPA redesignated the former Billings 2010 SO 2 nonattainment area to attainment. See 81 FR 28718 (May 10, 2016). As shown in Table 7, below, the Billings, Montana area is located a large distance (343 km) from the North Dakota border, and recent monitoring data in the Billings area do not approach the 2010 SO 2 NAAQS. For these reasons, the EPA is proposing to find that emissions from North Dakota will not contribute significantly to nonattainment in the Billings, Montana area.
[top] As noted, North Dakota also referred to ambient monitor values in its transport analysis. We reviewed these, as well as the more recent 2014-2016 SO 2 design value concentrations at monitors with data sufficient to produce valid 1-hour SO 2 design values for North Dakota and neighboring states.18 In Table 7, below, we have included
Footnotes:
18 ?Data retrieved from EPA's https://www.epa.gov/air-trends/air-quality-design-values#report.
| State/Area | Scenario | Site ID | Distance to North Dakota border (km) | 2014-2016 Design value (ppb)19 |
|---|---|---|---|---|
| Minnesota/Minneapolis-St. Paul | 2 | 270370020 | 306 | 12 |
| Minnesota/Minneapolis-St. Paul | 3 | 270530954 | 278 | 5 |
| Montana/Richland County | 3, 4 | 300830001 | 33 | 7 |
| Montana/Billings | 2 | 301110066 | 343 | 53 |
| North Dakota/Dickinson | 1 | 380070002 | 50 | 5 |
| North Dakota/Burke County | 1 | 380130004 | 121 | 23 |
| North Dakota/Bismarck | 1 | 380150003 | 99 | 15 |
| North Dakota/Fargo | 1 | 380171004 | 4 | 2 |
| North Dakota/Dunn County | 1 | 380250003 | 115 | 5 |
| North Dakota/McKenzie County | 1 | 380530002 | 55 | 6 |
| North Dakota/McKenzie County | 1 | 380530104 | 5 | 6 |
| North Dakota/McKenzie County | 1 | 380530111 | 2 | 7 |
| North Dakota/Mercer County | 1 | 380570004 | 150 | 22 |
| North Dakota/Mercer County | 1 | 380570118 | 159 | 22 |
| North Dakota/Mercer County | 1 | 380570124 | 160 | 16 |
| North Dakota/Oliver County | 1 | 380650002 | 139 | 10 |
| South Dakota/Sioux Falls | 2 | 460990008 | 265 | 6 |
| South Dakota/Rapid City | 3 | 461030020 | 205 | 4 |
The EPA reviewed ambient air quality data in North Dakota and neighboring states to see whether there were any monitoring sites, particularly near the North Dakota border, with elevated SO 2 concentrations that might warrant further investigation with respect to interstate transport of SO 2 from emission sources near any given monitor. The data presented in Table 7, above, show that North Dakota's network of SO 2 monitors with data sufficient to produce valid 1-hour SO 2 design values indicates that monitored 1-hour SO 2 levels in North Dakota are between 2% and 31% of the 75 ppb level of the NAAQS. There are four North Dakota monitors located within 50 km of a neighboring state's border, and these monitors indicate design values between 2% to 9% of the NAAQS. Two SO 2 monitors have recently been installed in North Dakota to assist the state and the EPA in designating portions of North Dakota by 2020.20 These are source oriented monitors, and both the monitors and the source they are characterizing (the Tioga Gas Plant) are located over 80 km from the North Dakota border. There is one monitor in a neighboring state located within 50 km of the North Dakota border, and this monitor recorded an SO 2 design value of 9% of the 2010 SO 2 NAAQS. Thus, these air quality data do not, by themselves, indicate any particular location that would warrant further investigation with respect to SO 2 emission sources that might significantly contribute to nonattainment in the neighboring states. However, because the monitoring network is not necessarily designed to find all locations of high SO 2 concentrations, this observation indicates an absence of evidence of impact at these locations but is not sufficient evidence by itself of an absence of impact at all locations in the neighboring states. We have therefore also conducted a source-oriented analysis.
Footnotes:
19 ?Id.
20 ?See TSD: Final Round 3 Area Designations for the 2010 1-Hour SO 2 Primary National Ambient Air Quality Standard for North Dakota, in http://www.regulations.gov, document ID EPA-HQ-OAR-2017-0003-0600.
As noted, the EPA finds that it is appropriate to examine the impacts of emissions from stationary sources in North Dakota in distances ranging from 0 km to 50 km from the facility, based on the "urban scale" definition contained in Appendix D to 40 CFR part 58, Section 4.4. Therefore, we assessed North Dakota sources of 100 tpy?21 or more of SO 2 up to 50 km from neighboring state borders to evaluate trends and SO 2 concentrations in area-wide air quality in Table 8 below.
Footnotes:
21 ?We have limited our analysis to North Dakota sources of SO 2 emitting at least 100 tpy, because in the absence of special factors, for example the presence of a nearby larger source or unusual physical factors, North Dakota sources emitting less than 100 tpy can appropriately be presumed to not be causing or contributing to SO 2 concentrations above the NAAQS.
[top]
| North Dakota source | 2016 SO 2 emissions (tons) | Distance to North Dakota border (km) | Distance to nearest neighboring state SO 2 source (km) | Neighboring state source 2016 emissions (tons) |
|---|---|---|---|---|
| Drayton Sugar Mill | 330 | 2 | 75 (American Crystal Sugar-East Grand Forks, Minnesota) | 1,005 |
| Hillsboro Sugar Mill | 439 | 15 | 49 (American Crystal Sugar-Crookston, Minnesota) | 875 |
| University of North Dakota Heating Plant (Grand Forks) | 411 | 2 | 4 (American Crystal Sugar-East Grand Forks, Minnesota) | 1,005 |
| North Dakota State University Heating Plant (Fargo) | 123 | 2 | 4.5 km (American Crystal Sugar-Moorhead, Minnesota) | 373 |
| Wahpeton Sugar Mill | 227 | 1 | 44 km (Hoot Lake Plant-Fergus Falls, Minnesota) | 940 |
| Wahpeton Wet Corn Mill | 135 | 1 | 47 km (Hoot Lake Plant-Fergus Falls, Minnesota) | 940 |
As shown, there are six North Dakota sources within 50 kilometers of a cross-state source, and each neighboring state source is located in the State of Minnesota. The EPA has therefore assessed potential SO 2 impacts from North Dakota on each of the four Minnesota areas with SO 2 sources near the North Dakota border, specifically the Crookston, East Grand Forks, Moorhead and Fergus Falls, Minnesota areas.
With regard to the Grand Forks, North Dakota, and East Grand Forks, Minnesota combined metropolitan area, the EPA does not have monitoring or modeling data to indicate transport from Grand Forks, North Dakota, to East Grand Forks, Minnesota. On the contrary, wind roses for three local meteorological stations indicate prevailing winds to be north-south oriented as opposed to west-east that would be conducive to interstate transport.22 On this basis, the EPA is proposing to determine that emissions from Grand Forks, North Dakota, will not contribute significantly to nonattainment in East Grand Forks, Minnesota.23
Footnotes:
22 ?This wind rose data are available in a memo to the docket for this action, which can be found on http://www.regulations.gov.
23 ?The EPA is aware that the University of North Dakota has announced plans to replace its heating plant, though this change is not yet federally enforceable (See http://news.prairiepublic.org/post/und-replace-its-steam-plant-wont-be-asking-state-appropriation ). The EPA also notes that any changes to the current facility and construction of a new facility must go through the state's EPA-approved New Source Review program.
With regard to the Crookston, Minnesota area, the EPA finds the distance between the Hillsboro Sugar Mill and Crookston (49 km) makes it very unlikely that SO 2 emissions from the Hillsboro Sugar Mill could interact with SO 2 emissions from Crookston American Crystal Sugar in such a way as to contribute significantly to nonattainment in the Crookston area.
With regard to the Moorhead, Minnesota, and Fargo, North Dakota, combined metropolitan area, the EPA reviewed available monitoring data. There is one SO 2 monitor (Site ID 380171004-See Table 7) in the area, on the North Dakota side of the border, located 6.5 km northwest of the North Dakota State University Heating Plant, and 9.5 km northwest of the Moorhead American Crystal Sugar Mill. As shown, this monitor recorded a design value of 2 ppb from 2014-2016. Although this monitor is not sited to determine maximum impacts from either the Moorhead American Crystal Sugar Mill or the North Dakota State University Heating Plant, it does indicate that SO 2 levels are very low (2.6% of the NAAQS) in parts of the Fargo-Moorhead combined metropolitan area. Additionally, wind roses for a local meteorological station indicates prevailing winds to be north-south oriented as opposed to west-east that would be conducive to interstate transport.24 For these reasons, in addition to the relatively low level of SO 2 emissions from the North Dakota State University Heating Plant, the EPA is proposing to determine that emissions from the North Dakota State University Heating Plant will not contribute significantly to nonattainment in Moorhead, Minnesota.
Footnotes:
24 ?This wind rose data are available in a memo to the docket for this action, which can be found on http://www.regulations.gov.
Finally, with regard to the Fergus Falls, Minnesota area, air quality modeling submitted to the EPA by the State of Minnesota for the Hoot Lake Plant indicates that the highest predicted 99th percentile daily maximum 1-hour concentration within the modeling domain is 55.8 ppb.25 For this reason, the Fergus Falls area does not warrant further investigation with regard to potential significant contribution to nonattainment from North Dakota. Additionally, in our analysis of Minnesota's modeling in the context of designations for the 2010 SO 2 NAAQS, the EPA noted that the Wahpeton facilities' "modeled impact at that distance to the Hoot Lake area would be minimal and it's expected their impact would be represented by the background concentration."?26 The EPA continues to support this conclusion with respect to an interstate transport analysis for section 110(a)(2)(D)(i)(I).27
Footnotes:
25 ?See TSD: Intended Round 3 Area Designations for the 2010 1-Hour SO 2 Primary National Ambient Air Quality Standard for Minnesota, in http://www.regulations.gov, document ID EPA-HQ-OAR-2017-0003-0057. This information was not changed for the final version of the designation, as shown at document ID EPA-HQ-OAR-2017-0003-0618.
26 ?Id.
27 ?While the air quality modeling discussed here used by the EPA to support its final designation of the Fergus Falls area is also supportive of the Agency's analysis of North Dakota's 2010 SO 2 transport SIP, the designation itself or the use of this modeling in the specific context of that designation is not being re-opened through this separate proposed action.
In conclusion, for interstate transport prong 1, we reviewed ambient SO 2 monitoring data and SO 2 emission sources both within North Dakota and in neighboring states. Based on this analysis, we propose to determine that North Dakota will not significantly contribute to nonattainment of the 2010 SO 2 NAAQS in any other state, per the requirements of CAA section 110(a)(2)(D)(i)(I).
3. EPA's Prong 2 Evaluation
[top] In its prong 2 analysis, North Dakota reviewed potential SO 2 impacts on the Minneapolis-St. Paul, Minnesota area, which is currently in "maintenance" status for the 1971 SO 2 NAAQS, noting the large distance between the North Dakota border and the Minneapolis-St. Paul area (255 km), as well as NAAQS-attaining monitoring data in eastern North Dakota and in Minneapolis-St. Paul. The EPA interprets CAA section 110(a)(2)(D)(i)(I) prong 2 to require an evaluation of the potential impact of a state's emissions on areas that are currently measuring clean data, but that
As shown in Table 1, the statewide SO 2 emissions from North Dakota and neighboring states have decreased substantially over time, per our review of the EPA's emissions trends data.28 From 2000 to 2016, total statewide SO 2 emissions decreased by the following proportions: Minnesota (77% decrease), Montana (78% decrease), North Dakota (44% decrease) and South Dakota (93% decrease). This trend of decreasing SO 2 emissions does not by itself demonstrate that areas in North Dakota and neighboring states will not have issues maintaining the 2010 SO 2 NAAQS. However, as a piece of this weight of evidence analysis for prong 2, it provides further indication (when considered alongside low monitor values in neighboring states) that such maintenance issues are unlikely. This is because the geographic scope of these reductions and their large sizes strongly suggest that they are not transient effects from reversible causes, and thus these reductions suggest that there is very low likelihood that a strong upward trend in emissions will occur that might cause areas presently in attainment to violate the NAAQS.
Footnotes:
28 ?Additional emissions trends data are available at: https://www.epa.gov/air-emissions-inventories/air-pollutant-emissions-trends-data.
As noted in North Dakota's submission, any future large sources of SO 2 emissions will be addressed by North Dakota's SIP-approved PSD program.29 Future minor sources of SO 2 emissions will be addressed by North Dakota's SIP-approved minor new source review permit program.30 The permitting regulations contained within these programs should help ensure that ambient concentrations of SO 2 in neighboring states are not exceeded as a result of new facility construction or modification occurring in North Dakota.
Footnotes:
29 ?See EPA's final action of the PSD portions of North Dakota's SIP, at 82 FR 46681, October 6, 2017.
30 ?Id.
In conclusion, for interstate transport prong 2, we reviewed additional information about emission trends, as well as the technical information considered for interstate transport prong 1. We find that the combination of low ambient concentrations of SO 2 in North Dakota and neighboring states, our conclusions from our qualitative analysis of the identified sources of SO 2 emissions, the downward trend in SO 2 emissions from North Dakota and surrounding states, and state measures that prevent new facility construction or modification in North Dakota from causing SO 2 exceedances in downwind states, indicates no interference with maintenance of the 2010 SO 2 NAAQS from North Dakota. Accordingly, we propose to determine that North Dakota SO 2 emission sources will not interfere with maintenance of the 2010 SO 2 NAAQS in any other state, per the requirements of CAA section 110(a)(2)(D)(i)(I).
D. South Dakota
1. State's Analysis
South Dakota conducted a weight of evidence analysis to examine whether SO 2 emissions from South Dakota adversely affect attainment or maintenance of the 2010 SO 2 NAAQS in downwind states. South Dakota provided an inventory of each SO 2 source located in a county that borders another state, including the emissions for each source. South Dakota provided information on SO 2 reductions for the larger SO 2 sources in this inventory, noting that the State's largest SO 2 emissions source (Big Stone I) installed pollution controls between 2012 and 2015 to reduce SO 2 emissions at the facility by 80%. South Dakota also discussed how the State's second highest emitter (Ben French facility) shut down in 2012, and that the combination of reductions from these two facilities would result in a 75% reduction in SO 2 emissions throughout South Dakota from 2011 to 2016. South Dakota noted the large distance between the State and the nearest nonattainment areas in downwind states. South Dakota also considered the predominant northwesterly wind direction in the State, asserting that this made it very unlikely that South Dakota sources could impact SO 2 nonattainment in states to its west. Finally, South Dakota noted that its permitting programs would prevent new or modified sources from impacting nonattainment and maintenance areas in downwind states going forward. Based on this weight of evidence analysis, South Dakota concluded that emissions within the State will not contribute to nonattainment or interfere with maintenance of the 2010 SO 2 NAAQS in neighboring states.
2. EPA's Prong 1 Evaluation
The EPA proposes to find that South Dakota's SIP meets the interstate transport requirements of CAA section 110(a)(2)(D)(i)(I), prong 1 for the 2010 SO 2 NAAQS, as discussed below. We have analyzed the air quality, emission sources and emission trends in South Dakota and neighboring states, i.e., Iowa, Minnesota, Montana, Nebraska, North Dakota and Wyoming. Based on that analysis, we propose to find that South Dakota will not significantly contribute to nonattainment of the 2010 SO 2 NAAQS in any other state.
We reviewed 2014-2016 SO 2 design value concentrations at monitors with data sufficient to produce valid 1-hour SO 2 design values for South Dakota and neighboring states.31 In Table 9, below, we have included monitoring data from four scenarios: (1) All of the monitor data from South Dakota; (2) the monitor with the highest SO 2 level in each neighboring state; (3) the monitor in each neighboring state located closest to the South Dakota border; and (4) all monitors in each neighboring state within 50 km of the border.
Footnotes:
31 ?Data retrieved from EPA's https://www.epa.gov/air-trends/air-quality-design-values#report.
[top]
| State/Area | Scenario | Site ID | Distance from South Dakota border (km) | 2014-2016 Design value (ppb)?32 |
|---|---|---|---|---|
| Iowa/Muscatine | 2 | 191390020 | 462 | 113 |
| Iowa/Sioux City | 3, 4 | 191930020 | 19 | 9 |
| Minnesota/Minneapolis-St. Paul | 2 | 270370020 | 270 | 12 |
| Minnesota/Minneapolis-St. Paul | 3 | 270530954 | 250 | 5 |
| Montana/Richland County | 3 | 300830001 | 210 | 7 |
| Montana/Billings | 2 | 301110066 | 343 | 53 |
| Nebraska/Omaha | 2 | 310550053 | 136 | 59 |
| Nebraska/Omaha | 3 | 310550019 | 676 | 27 |
| North Dakota/Burke County | 2 | 380130004 | 300 | 23 |
| North Dakota/Bismarck | 3 | 380150003 | 99 | 15 |
| South Dakota/Jackson County | 1 | 460710001 | 83 | 3 |
| South Dakota/Sioux Falls | 1 | 460990008 | 10 | 6 |
| South Dakota/Rapid City | 1 | 461030020 | 62 | 4 |
| South Dakota/Sioux City | 1 | 461270001 | 6 | 4 |
| Wyoming/Casper | 2 | 560252601 | 178 | 25 |
| Wyoming/Weston County | 3, 4 | 560450800 | 12 | 3 |
The EPA reviewed ambient air quality data in South Dakota and neighboring states to determine whether there were any monitoring sites, particularly near the South Dakota border, with elevated SO 2 concentrations that might warrant further investigation with respect to interstate transport of SO 2 from emission sources near any given monitor. As shown, there are no violating design values in South Dakota or neighboring states apart from the Muscatine, Iowa area. In South Dakota's analysis, the State reviewed its potential impact on the Muscatine, Iowa 2010 SO 2 nonattainment area. South Dakota asserted that the significant distance between its nearest border and the Muscatine area (shown in Table 9), as well as the low emissions in southeastern South Dakota indicated no SO 2 impacts to the Muscatine SO 2 nonattainment area. The EPA agrees with South Dakota's analysis and conclusion with regard to the Muscatine, Iowa area. The EPA notes that during the 2014-2016 period, substantial reductions in SO 2 emissions occurred within the Muscatine SO 2 nonattainment area.33 For this reason, the last exceedance of the 2010 SO 2 NAAQS at the violating monitor listed in Table 9 (site ID 191390020) occurred in June 2015.34
Footnotes:
32 ?Id.
33 ?See TSD: Final Round 3 Area Designations for the 2010 1-Hour SO 2 Primary National Ambient Air Quality Standard for Iowa, in http://www.regulations.gov, document ID EPA-HQ-OAR-2017-0003-0616.
34 ?Data retrieved from EPA's https://www.epa.gov/outdoor-air-quality-data.
South Dakota also analyzed potential impacts to the Billings, Montana area, which was still in nonattainment status at the time of South Dakota's submission. As noted in the section of this notice about North Dakota, the EPA redesignated the former Billings 2010 SO 2 nonattainment area to attainment following the permanent closure of the PPL Corette Plant. See 81 FR 28718 (May 10, 2016). As noted by South Dakota, the Billings, Montana area is located a very large distance (343 km) from the nearest South Dakota border, and is upwind rather than downwind of South Dakota. Table 9 also shows that recent monitoring data in the Billings area do not approach the 2010 SO 2 NAAQS. For these reasons, the EPA agrees with South Dakota's conclusion that the emissions from South Dakota will not contribute significantly to nonattainment in the Billings, Montana area.
The data presented in Table 9, above, show that South Dakota's network of SO 2 monitors with data sufficient to produce valid 1-hour SO 2 design values indicates that monitored 1-hour SO 2 levels in South Dakota are between 4% and 8% of the 75 ppb level of the NAAQS. There are two South Dakota monitors located within 50 km of a neighboring state's border, and these monitors indicate design values between 5% and 8% of the NAAQS. There are two monitors in neighboring states located within 50 km of the South Dakota border, and these monitors recorded SO 2 design values between 4% and 12% of the 2010 SO 2 NAAQS. Thus, these air quality data do not, by themselves, indicate any particular location that would warrant further investigation with respect to SO 2 emission sources that might significantly contribute to nonattainment in the neighboring states. However, because the monitoring network is not necessarily designed to find all locations of high SO 2 concentrations, this observation indicates an absence of evidence of impact at these locations but is not sufficient evidence by itself of an absence of impact at all locations in the neighboring states. We have therefore also conducted a source-oriented analysis.
As noted, the EPA finds that it is appropriate to examine the impacts of emissions from stationary sources in South Dakota in distances ranging from 0 km to 50 km from the facility, based on the "urban scale" definition contained in Appendix D to 40 CFR part 58, Section 4.4. Therefore, we assessed point sources up to 50 km from state borders to evaluate trends and SO 2 concentrations in area-wide air quality. The list of such sources with greater than 100 tpy?35 of SO 2 within 50 km from state borders is provided in Table 10, below.
Footnotes:
35 ?We have limited our analysis to South Dakota sources of SO 2 emitting at least 100 tpy, because in the absence of special factors, for example the presence of a nearby larger source or unusual physical factors, South Dakota sources emitting less than 100 tpy can appropriately be presumed to not be causing or contributing to SO 2 concentrations above the NAAQS.
[top]
| Source | 2016 SO 2 emissions (tons) | Distance to South Dakota border (km) | Distance to nearest cross-State SO 2 source (km) | Cross-state source 2016 emissions (tons) |
|---|---|---|---|---|
| Big Stone Power Plant (Grant County, South Dakota) | 827 | 4 | 113 (Wahpeton Sugar Mill-Richland County, North Dakota) | 227 |
| Colony East and West Plant (Crook County, Wyoming) | 106 | 8 | 111 (GCC Dacotah-Rapid City, South Dakota) | 304 |
With regard to potential cross-state impacts from the Big Stone Power Plant, air quality modeling submitted to the EPA by South Dakota indicates that the highest predicted 99th percentile daily maximum 1-hour concentration within the modeling domain surrounding the power plant is 57.88 ppb.36 This predicted maximum concentration, which includes an estimate of the background concentration, indicates that this source alone could not cause nonattainment in South Dakota or any other state. Together with the distance between Big Stone and the nearest cross-state source (113 km), this indicates that the Big Stone Power Plant will not significantly contribute to nonattainment in any other state. The EPA continues to support this conclusion with respect to an interstate transport analysis for section 110(a)(2)(D)(i)(I).37
Footnotes:
36 ?See TSD: Final Area Designations for the 2010 SO 2 Primary National Ambient Air Quality Standard for South Dakota, in http://www.regulations.gov, document ID EPA-HQ-OAR-2014-0464-0359.
37 ?While the air quality modeling discussed here used by the EPA to support its final designation of the Grant County, South Dakota area is also supportive of the Agency's analysis of South Dakota's 2010 SO 2 transport SIP, the designation itself or the use of this modeling in the specific context of that designation is not being re-opened through this separate proposed action.
The EPA also reviewed the location of sources in neighboring states emitting more than 100 tpy of SO 2 and located within 50 km of the South Dakota border. This is because elevated levels of SO 2 , to which SO 2 emitted in South Dakota may have a downwind impact, are most likely to be found near such sources. As shown in Table 10, the only source within this distance of the South Dakota border is the Colony East and West Plant. The shortest distance between this source and the nearest source in South Dakota, the GCC Dacotah facility, is 111 km. This makes it very unlikely that SO 2 emissions from the GCC Dacotah facility could interact with SO 2 emissions from the Colony East and West Plants in such a way as to contribute significantly to nonattainment in the Crook County, Wyoming area.
In conclusion, for interstate transport prong 1, we reviewed ambient SO 2 monitoring data and SO 2 emission sources within South Dakota and in neighboring states. Based on this analysis, we propose to determine that South Dakota will not significantly contribute to nonattainment of the 2010 SO 2 NAAQS in any other state, per the requirements of CAA section 110(a)(2)(D)(i)(I).
3. EPA's Prong 2 Evaluation
The EPA has reviewed available information on SO 2 air quality and emission trends to evaluate the state's conclusion that South Dakota will not interfere with maintenance of the 2010 SO 2 NAAQS in downwind states. The EPA notes that South Dakota's analysis does not independently address whether the SIP contains adequate provisions prohibiting emissions that will interfere with maintenance of the 2010 SO 2 NAAQS in any other state. As noted, the "interfere with maintenance" clause of section 110(a)(2)(D)(i)(I) must be given "independent significance" by evaluating the impact of upwind state emissions on downwind areas that, while currently in attainment, are at risk of future nonattainment, considering historic variability.38 While South Dakota did not evaluate the potential impact of its emissions on areas that are currently measuring clean data, but that may have issues maintaining that air quality, the EPA has incorporated additional information into our evaluation of South Dakota's submission. This evaluation builds on the analysis regarding significant contribution to nonattainment (prong 1). Specifically, because of the low monitored ambient concentrations of SO 2 in South Dakota and neighboring states, and the large distances between cross-state SO 2 sources, the EPA is proposing to find that SO 2 levels in neighboring states near the South Dakota border do not indicate any inability to maintain the SO 2 NAAQS that could be attributed in part to sources in South Dakota.
Footnotes:
38 ?531 F.3d 896, 910-11 (DC Cir. 2008) (holding that the EPA must give "independent significance" to each prong of CAA section 110(a)(2)(D)(i)(I)).
As shown in Table 1, the statewide SO 2 emissions from South Dakota and neighboring states have decreased substantially over time, per our review of the EPA's emissions trends data.39 From 2000 to 2016, total statewide SO 2 emissions decreased by the following proportions: Iowa (81% decrease), Minnesota (77% decrease), Montana (78% decrease), Nebraska (52% decrease), North Dakota (44% decrease), South Dakota (93% decrease) and Wyoming (59% decrease). This trend of decreasing SO 2 emissions does not by itself demonstrate that areas in South Dakota and neighboring states will not have issues maintaining the 2010 SO 2 NAAQS. However, as a piece of this weight of evidence analysis for prong 2, it provides further indication (when considered alongside low monitor values in neighboring states) that such maintenance issues are unlikely. This is because the geographic scope of these reductions and their large sizes strongly suggest that they are not transient effects from reversible causes, and thus these reductions suggest that there is very low likelihood that a strong upward trend in emissions will occur that might cause areas presently in attainment to violate the NAAQS.
Footnotes:
39 ?Additional emissions trends data are available at: https://www.epa.gov/air-emissions-inventories/air-pollutant-emissions-trends-data.
[top] As noted in South Dakota's submission, any future large sources of SO 2 emissions will be addressed by South Dakota's SIP-approved PSD program.40 Future minor sources of SO 2 emissions will be addressed by South Dakota's SIP-approved minor new source review permit program.41 The permitting regulations contained within these programs should help ensure that ambient concentrations of SO 2 in neighboring states are not exceeded as a
Footnotes:
40 ?See EPA's final action of the PSD portions of South Dakota's SIP, at 82 FR 38832, August 16, 2017.
41 ?Id.
In conclusion, for interstate transport prong 2, the EPA has incorporated additional information into our evaluation of South Dakota's submission, which did not include an independent analysis of prong 2. In doing so, we have reviewed additional information about emission trends, as well as the technical information considered for interstate transport prong 1. We find that the combination of low ambient concentrations of SO 2 in South Dakota and neighboring states, the large distances between cross-state SO 2 sources, the downward trend in SO 2 emissions from South Dakota and surrounding states, and state measures that prevent new facility construction or modification in South Dakota from causing SO 2 exceedances in downwind states, indicates no interference with maintenance of the 2010 SO 2 NAAQS from South Dakota. Accordingly, we propose to determine that South Dakota SO 2 emission sources will not interfere with maintenance of the 2010 SO 2 NAAQS in any other state, per the requirements of CAA section 110(a)(2)(D)(i)(I).
E. Wyoming
1. State's Analysis
Wyoming conducted a weight of evidence analysis to examine whether SO 2 emissions from Wyoming adversely affect attainment or maintenance of the 2010 SO 2 NAAQS in downwind states. Wyoming primarily reviewed the potential impact of emissions from Wyoming on the Billings, Montana 2010 SO 2 maintenance area, which was designated as nonattainment at the time of Wyoming's submittal, because Montana was the only state bordering Wyoming that contained a nonattainment or maintenance area for this NAAQS. Wyoming reviewed wind rose data from northeast Wyoming, the location in Wyoming with the nearest significant SO 2 sources to the Billings area. Based on a review of this information, Wyoming concluded that winds in northeast Wyoming were predominantly from the north and west, and therefore made transport to Billings very unlikely. Wyoming also asserted that SO 2 sources within Wyoming were all located much further than 50 km from the Billings area. Finally, Wyoming noted that no neighboring state apart from Montana contained a 2010 SO 2 nonattainment area. Based on this weight of evidence analysis, Wyoming concluded that emissions within the State will not contribute to nonattainment or interfere with maintenance of the 2010 SO 2 NAAQS in neighboring states.
2. EPA's Prong 1 Evaluation
The EPA proposes to find that Wyoming's SIP meets the interstate transport requirements of CAA section 110(a)(2)(D)(i)(I), prong 1 for the 2010 SO 2 NAAQS, as discussed below. We have analyzed the air quality, emission sources and emission trends in Wyoming and neighboring states, i.e., Colorado, Idaho, Montana, Nebraska, South Dakota and Utah.42 Based on that analysis, we propose to find that Wyoming will not significantly contribute to nonattainment of the 2010 SO 2 NAAQS in any other state.
Footnotes:
42 ?The EPA also analyzed potential Wyoming SO 2 transport to the Wind River Reservation in Wyoming. The Northern Arapaho and Eastern Shoshone Tribes have been approved by the EPA for treatment in a similar manner as a state (TAS) status for CAA Section 126 (78 FR 76829, December 19, 2013). The Tribes' TAS application for Section 126 demonstrates an interest in how their air quality is impacted by Wyoming sources outside of the Reservation. We determined that the only source above 100 tpy of SO 2 within 50 km of the Wind River Reservation, the Lost Cabin Gas Plant, is located over 40 km downwind (see wind rose data in the docket for this action) from the Reservation. The area around this source contains a source-oriented monitor (Site ID 560130003) indicating a fourth highest 1-hour daily maximum below the 2010 SO 2 NAAQS in its first year of operation. Therefore, the available information indicates that emissions from Wyoming will not contribute significantly to nonattainment or interfere with maintenance of the 2010 SO 2 NAAQS at the Wind River Reservation.
Wyoming focused its analysis on potential impacts to the Billings, Montana area, which was still in nonattainment status at the time of Wyoming's submission. As noted, the EPA redesignated the former Billings 2010 SO 2 nonattainment area to attainment following the permanent closure of the PPL Corette Plant. See 81 FR 28718 (May 10, 2016). As asserted by Wyoming and shown in Table 11, the Billings, Montana area is located a large distance (87 km) from the Wyoming border. Further, the wind roses provided by Wyoming indicate that meteorology does not favor transport from Wyoming sources to the Billings area. Table 11 also shows that recent monitoring data in the Billings area do not approach the 2010 SO 2 NAAQS. For these reasons, the EPA agrees with Wyoming's conclusion that emissions from Wyoming will not contribute significantly to nonattainment in the Billings, Montana area.
We reviewed 2014-2016 SO 2 design value concentrations at monitors with data sufficient to produce valid 1-hour SO 2 design values for Wyoming and neighboring states.43 In Table 11, below, we have included monitoring data from four scenarios: (1) All of the monitor data from Wyoming; (2) the monitor with the highest SO 2 level in each neighboring state; (3) the monitor in each neighboring state located closest to the Wyoming border; and (4) all monitors in each neighboring state within 50 km of the Wyoming border.
Footnotes:
43 ?Data retrieved from EPA's https://www.epa.gov/air-trends/air-quality-design-values#report.
[top]
| State/Area | Scenario | Site ID | Distance to Wyoming border (km) | 2014-2016 Design value (ppb)?44 |
|---|---|---|---|---|
| Colorado/Denver | 3 | 080013001 | 127 | 18 |
| Colorado/Colorado Springs | 2 | 080410015 | 240 | 52 |
| Idaho/Pocatello | 2 | 160050004 | 120 | 39 |
| Idaho/Caribou County | 3, 4 | 160290031 | 45 | 26 |
| Montana/Billings | 2, 3 | 301110066 | 87 | 53 |
| Nebraska/Omaha | 3 | 310550019 | 676 | 27 |
| Nebraska/Omaha | 2 | 310550053 | 679 | 59 |
| South Dakota/Sioux Falls | 2 | 460990008 | 593 | 6 |
| South Dakota/Rapid City | 3 | 461030020 | 62 | 4 |
| Wyoming/Gillette | 1 | 560050857 | 80 | 21 |
| Wyoming/Cheyenne | 1 | 560210100 | 20 | 9 |
| Wyoming/Casper | 1 | 560252601 | 178 | 25 |
| Wyoming/Rock Springs | 1 | 560370300 | 83 | 21 |
| Wyoming/Weston County | 1 | 560450800 | 12 | 3 |
The EPA reviewed ambient air quality data in Wyoming and neighboring states to see whether there were any monitoring sites, particularly near the Wyoming border, with elevated SO 2 concentrations that might warrant further investigation with respect to interstate transport of SO 2 from emission sources near any given monitor. The data presented in Table 11, above, show that Wyoming's network of SO 2 monitors with data sufficient to produce valid 1-hour SO 2 design values indicates that monitored 1-hour SO 2 levels in Wyoming are between 4% and 33% of the 75 ppb level of the NAAQS. There are two Wyoming monitors located within 50 km of the state's border, and these monitors indicate design values between 4% and 12% of the NAAQS. Seven SO 2 monitors have recently been installed in Wyoming to assist the State and the EPA in designating portions of Wyoming by 2020.45 These are source oriented monitors, and none of these monitors or the sources they are characterizing are located within 50 km of the Wyoming border. There is one monitor in a neighboring state located within 50 km of the Wyoming border, and this monitor recorded an SO 2 design value of 35% of the 2010 SO 2 NAAQS. Thus, these air quality data do not, by themselves, indicate any particular location that would warrant further investigation with respect to SO 2 emission sources that might significantly contribute to nonattainment in the neighboring states. However, because the monitoring network is not necessarily designed to find all locations of high SO 2 concentrations, this observation indicates an absence of evidence of impact at these locations but is not sufficient evidence by itself of an absence of impact at all locations in the neighboring states. We have therefore also conducted a source-oriented analysis.
Footnotes:
44 ?Id.
45 ?See TSD: Final Round 3 Area Designations for the 2010 1-Hour SO 2 Primary National Ambient Air Quality Standard for Wyoming, in http://www.regulations.gov, document ID EPA-HQ-OAR-2017-0003-0608.
As noted, the EPA finds that it is appropriate to examine the impacts of emissions from stationary sources in Wyoming in distances ranging from 0 km to 50 km from the facility, based on the "urban scale" definition contained in Appendix D to 40 CFR part 58, Section 4.4. Therefore, we assessed point sources up to 50 km from state borders to evaluate trends and SO 2 concentrations in area-wide air quality. The list of sources of greater than 100 tpy?46 of SO 2 within 50 km from state borders is provided in Table 12 below.
Footnotes:
46 ?We have limited our analysis to Wyoming sources of SO 2 emitting at least 100 tpy, because in the absence of special factors, for example the presence of a nearby larger source or unusual physical factors, Wyoming sources emitting less than 100 tpy can appropriately be presumed to not be causing or contributing to SO 2 concentrations above the NAAQS.
| Wyoming source | 2016 annual SO 2 emissions (tons) | Distance to Wyoming border (km) | Distance to nearest neighboring state SO 2 source (km) | Neighboring state source 2016 emissions (tons) |
|---|---|---|---|---|
| Carter Creek Gas Plant | 130 | 11 | 76 (Devils Slide Plant, Holcim-Morgan County, Utah) | 187 |
| Frontier Petroleum Refinery | 311 | 14 | 35 (Rawhide Energy Station-Larimer County, Colorado) | 879 |
| Naughton Power Plant | 4,069.7 | 37 | 110 (Devils Slide Plant, Holcim-Morgan County, Utah) | 187 |
| Laramie Cement Plant | 165 | 30 | 67 (Rawhide Energy Station, Larimer County, Colorado) | 879 |
| Colony East and West Plants | 106 | 8 | 111 km (GCC Dacotah-Rapid City, South Dakota) | 304 |
| Elk Basin Gas Plant | 641 | 2 | 75 km (CHS Laurel Refinery-Laurel, Montana) | 272 |
With regard to the Frontier Petroleum Refinery in Cheyenne, the EPA has assessed potential SO 2 impacts from this source on the area near the Rawhide Energy Station, in Larimer County, Colorado.
[top] The EPA reviewed available monitoring data in Cheyenne, Wyoming. One monitor is located 6 km northeast of the Frontier Petroleum Refinery (Site ID 560210100-See Table 11), and recorded a 2014-2016 SO 2 design value of 9 ppb. The maximum 1-hour SO 2 value measured at this monitor from January 1, 2011 (when it began operation) to December 31, 2017, was 31 ppb. A second monitor not listed in Table 11, located 3 km east of the Frontier Petroleum Refinery, recorded 1 year of data in Cheyenne to examine potential population exposure near the Frontier Petroleum Refinery.47 Between March 31, 2016 and April 3, 2017, this monitor recorded a maximum SO 2 concentration of 44 ppb, with a fourth highest 1-hour daily maximum concentration of 16.7 ppb. Although
Footnotes:
47 ?See Wyoming's 2016 Annual Monitoring Network Plan at pages 50-51: http://deq.wyoming.gov/aqd/monitoring/resources/annual-network-plans/.
With regard to the Elk Basin Gas Plant, the EPA does not have information at this time suggesting that the State of Montana is impacted by emissions from Elk Basin Gas Plant or other emissions activity originating in Wyoming in violation of section 110(a)(2)(D)(i)(I). Therefore, we do not have evidence that demonstrates that emissions from this source will significantly contribute to nonattainment of the 2010 SO 2 NAAQS.
With regard to potential cross-state impacts from the Naughton Power Plant, air quality modeling submitted to the EPA by Wyoming indicates that the highest predicted 99th percentile daily maximum 1-hour concentration within the modeling domain surrounding the power plant is 56.3 ppb.48 This predicted maximum concentration, which includes an estimate of the background concentration, indicates that this source alone could not cause nonattainment in Wyoming or any other state. Together with the distance between Naughton and the nearest cross-state source (110 km), this indicates that the Naughton Power Plant will not significantly contribute to nonattainment in any other state. The EPA continues to support this conclusion with respect to an interstate transport analysis for section 110(a)(2)(D)(i)(I).49
Footnotes:
48 ?See TSD: Final Round 3 Area Designations for the 2010 1-Hour SO 2 Primary National Ambient Air Quality Standard for Wyoming, in http://www.regulations.gov, document ID EPA-HQ-OAR-2017-0003-0608, and TSD: Intended Round 3 Area Designations for the 2010 1-Hour SO 2 Primary National Ambient Air Quality Standard for Wyoming, at EPA-HQ-OAR-2017-0003-0033.
49 ?While the air quality modeling discussed here used by the EPA to support its final designation of the Lincoln County, Wyoming area is also supportive of the Agency's analysis of Wyoming's 2010 SO 2 transport SIP, the designation itself or the use of this modeling in the specific context of that designation is not being re-opened through this separate proposed action.
For the other sources listed in Table 12, the low levels of emissions and large distances between Wyoming sources within 50 km of a state border and the nearest SO 2 source in a neighboring state provide further evidence to support a conclusion that emissions from Wyoming will not contribute to problems with attainment of the 2010 SO 2 NAAQS in downwind states.
| Source | 2016 SO 2 emissions (tons) | Distance to Wyoming border (km) | Distance to nearest Wyoming SO 2 source (km) | Wyoming source 2016 emissions (tons) |
|---|---|---|---|---|
| Clean Harbors Env. Services (Kimball County, Nebraska) | 218 | 33 | 95 (Frontier Petroleum Refinery) | 311 |
| P4 Production Chemical Plant (Soda Springs, Idaho) | 478 | 45 | 132 (Naughton Generating Station) | 4,069 |
| Nu-West Industries Fertilizer Plant (Conda, Idaho) | 364 | 40 | 134 (Naughton Generating Station) | 4,069 |
| *?We have not included sources that are duplicative of those in Table 12. | ||||
The EPA also reviewed the location of sources in neighboring states emitting more than 100 tpy of SO 2 and located within 50 km of the Wyoming border (see Table 13). This is because elevated levels of SO 2 , to which SO 2 emitted in Wyoming may have a downwind impact, are most likely to be found near such sources. As shown in Table 13, the shortest distance between any pair of these sources is within 95 km. This indicates that there are no additional locations in neighboring states that would warrant further investigation with respect to Wyoming SO 2 emission sources that might contribute to problems with attainment of the 2010 SO 2 NAAQS.
In conclusion, for interstate transport prong 1, we reviewed ambient SO 2 monitoring data and SO 2 emission sources both within Wyoming and in neighboring states. Based on this analysis, we propose to determine that Wyoming will not significantly contribute to nonattainment of the 2010 SO 2 NAAQS in any other state, per the requirements of CAA section 110(a)(2)(D)(i)(I).
3. EPA's Prong 2 Evaluation
The EPA has reviewed the analysis presented by Wyoming and additional information on SO 2 air quality and emission trends to evaluate the State's conclusion that Wyoming will not interfere with maintenance of the 2010 SO 2 NAAQS in downwind states. The EPA notes that Wyoming's analysis does not independently address whether the SIP contains adequate provisions prohibiting emissions that will interfere with maintenance of the 2010 SO 2 NAAQS in any other state. As noted, the "interfere with maintenance" clause of section 110(a)(2)(D)(i)(I) must be given "independent significance" by evaluating the impact of upwind state emissions on downwind areas that, while currently in attainment, are at risk of future nonattainment, considering historic variability.50 While Wyoming did not evaluate the potential impact of its emissions on areas that are currently measuring clean data, but that may have issues maintaining that air quality, the EPA has incorporated additional information into our evaluation of Wyoming's submission. This evaluation builds on the analysis regarding significant contribution to nonattainment (prong 1). Specifically, because of the low monitored ambient concentrations of SO 2 in Wyoming and neighboring states and the large distances between cross-state SO 2 sources, the EPA is proposing to find that SO 2 levels in neighboring states near the Wyoming border do not indicate an inability to maintain the SO 2 NAAQS.
Footnotes:
50 ?531 F.3d 896, 910-11 (DC Cir. 2008) (holding that the EPA must give "independent significance" to each prong of CAA section 110(a)(2)(D)(i)(I)).
[top]
As shown in Table 1, the statewide SO 2 emissions from Wyoming and neighboring states have decreased substantially over time, per our review of the EPA's emissions trends data.51 From 2000 to 2016, total statewide SO 2 emissions decreased by the following proportions: Colorado (82% decrease), Idaho (70% decrease), Montana (78% decrease), Nebraska (52% decrease), South Dakota (93% decrease), Utah (73% decrease) and Wyoming (59% decrease). This trend of decreasing SO 2 emissions does not by itself demonstrate that areas in Wyoming and neighboring states will not have issues maintaining the 2010 SO 2 NAAQS. However, as a piece of this weight of evidence analysis for prong 2, it provides further indication (when considered alongside low monitor values in neighboring states) that such maintenance issues are unlikely. This is because the geographic scope of these reductions and their large sizes strongly suggest that they are not transient effects from reversible causes, and thus these reductions suggest that there is very low likelihood that a strong upward trend in emissions will occur that might cause areas presently in attainment to violate the NAAQS.
Footnotes:
51 ?Additional emissions trends data are available at: https://www.epa.gov/air-emissions-inventories/air-pollutant-emissions-trends-data.
As noted in Wyoming's submission, any future large sources of SO 2 emissions will be addressed by Wyoming's SIP-approved PSD program.52 Future minor sources of SO 2 emissions will be addressed by Wyoming's SIP-approved minor new source review permit program.53 The permitting regulations contained within these programs should help ensure that ambient concentrations of SO 2 in neighboring states are not exceeded as a result of new facility construction or modification occurring in Wyoming.
Footnotes:
52 ?See EPA's final action of the PSD portions of Wyoming's SIP, at 82 FR 18992, April 25, 2017.
53 ?Id.
In conclusion, for interstate transport prong 2, the EPA has incorporated additional information into our evaluation of Wyoming's submission, which did not include an independent analysis of prong 2. In doing so, we reviewed information about emission trends, as well as the technical information considered for interstate transport prong 1. We find that the combination of low ambient concentrations of SO 2 in Wyoming and neighboring states, the large distances between cross-state SO 2 sources, the downward trend in SO 2 emissions from Wyoming and surrounding states, and state measures that prevent new facility construction or modification in Wyoming from causing SO 2 exceedances in downwind states, indicates no interference with maintenance of the 2010 SO 2 NAAQS from Wyoming. Accordingly, we propose to determine that Wyoming SO 2 emission sources will not interfere with maintenance of the 2010 SO 2 NAAQS in any other state, per the requirements of CAA section 110(a)(2)(D)(i)(I).
IV. Proposed Action
The EPA is proposing to approve the following submittals as meeting the interstate transport requirements of CAA section 110(a)(2)(D)(i)(I) for the 2010 SO 2 NAAQS: Colorado's July 17, 2013 and February 16, 2018 submittals; Montana's July 15, 2013 submittal; North Dakota's March 7, 2013 submittal; South Dakota's December 20, 2013; and Wyoming's March 6, 2015 submittal. The EPA is proposing this approval based on our review of the information and analysis provided by each state, as well as additional relevant information, which indicates that in-state air emissions will not contribute significantly to nonattainment or interfere with maintenance of the 2010 SO 2 NAAQS in any other state. This action is being taken under section 110 of the CAA.
V. Statutory and Executive Order Reviews
Under the Clean Air Act, the Administrator is required to approve a SIP submission that complies with the provisions of the Act and applicable federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). Thus, in reviewing SIP submissions, the EPA's role is to approve state choices, provided that they meet the criteria of the CAA. Accordingly, these proposed actions merely approve state law as meeting federal requirements and do not impose additional requirements beyond those imposed by state law. For that reason, these proposed actions:
• Are not significant regulatory actions subject to review by the Office of Management and Budget under Executive Orders 12866 (58 FR 51735, October 4, 1993) and 13563 (76 FR 3821, January 21, 2011);
• are not Executive Order 13771 (82 FR 9339, February 2, 2017) regulatory actions because SIP approvals are exempted under Executive Order 12866;
• do not impose an information collection burden under the provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq. );
• are certified as not having a significant economic impact on a substantial number of small entities under the Regulatory Flexibility Act (5 U.S.C. 601 et seq. );
• do not contain any unfunded mandate or significantly or uniquely affect small governments, as described in the Unfunded Mandates Reform Act of 1995 (Pub. L. 104-4);
• do not have federalism implications as specified in Executive Order 13132 (64 FR 43255, August 10, 1999);
• are not economically significant regulatory actions based on health or safety risks subject to Executive Order 13045 (62 FR 19885, April 23, 1997);
• are not significant regulatory actions subject to Executive Order 13211 (66 FR 28355, May 22, 2001);
• are not subject to requirements of Section 12(d) of the National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 note) because this action does not involve technical standards; and
• do not provide the EPA with the discretionary authority to address, as appropriate, disproportionate human health or environmental effects, using practicable and legally permissible methods, under Executive Order 12898 (59 FR 7629, February 16, 1994).
In addition, these SIPs are not approved to apply on any Indian reservation land or in any other area where the EPA or an Indian tribe has demonstrated that a tribe has jurisdiction. In those areas of Indian country, the rule does not have tribal implications and will not impose substantial direct costs on tribal governments or preempt tribal law as specified by Executive Order 13175 (65 FR 67249, November 9, 2000).
List of Subjects in 40 CFR Part 52
Environmental protection, Air pollution control, Incorporation by reference, Intergovernmental relations, Nitrogen dioxide, Particulate Matter, Reporting and recordkeeping requirements, Sulfur dioxide, Volatile organic compounds.
Authority:
42 U.S.C. 7401 et seq.
Dated: May 29, 2018.
Douglas Benevento,
Regional Administrator, Region 8.
[FR Doc. 2018-11846 Filed 6-1-18; 8:45 am]
BILLING CODE 6560-50-P