1 Draft Technical Support Document

Colorado Area Designations for the 2010 SO 2 Primary National Ambient Air Quality Standard

Summary

Pursuant to section 107(d) of the Clean Air Act (CA A), the U.S. Environmental Protection Agency (EPA, or the Agency) must designate areas as either “unclassifiable,” “attainment,” or
“nonattainment” for the 2010 one-hour sulfur dioxid e (SO 2 ) primary national ambient air quality standard (NAAQS). The CAA defines a nonattainment a rea as one that does not meet the NAAQS or that contributes to a violation in a nearb y area. An attainment area is defined as any
area other than a nonattainment area that meets the NAAQS. Unclassifiable areas are defined as
those that cannot be classified on the basis of ava ilable information as meeting or not meeting the NAAQS.

Colorado submitted updated recommendations on Septe mber 18, 2015, ahead of a July 2, 2016, deadline for the EPA to designate certain areas est ablished by the U.S. District Court for the
Northern District of California. This deadline is t he first of three deadlines established by the court for the EPA to complete area designations for the 2010 SO 2 NAAQS. Table 1 below lists
Colorado’s recommendations and identifies the count ies or portions of counties in Colorado that the EPA intends to designate by July 2, 2016 based on an assessment and characterization of air quality through ambient air quality data, air dispe rsion modeling, other evidence and supporting information, or a combination of the above.

Table 1. State’s recommended and EPA’s intended des ignations
Area Colorado’s

Recommended
Area Definition Colorado’s

Recommended Designation EPA’s Intended

Area Definition EPA’s Intended

Designation

Colorado Springs,
Colorado Unspecified (Area

around source) Unclassifiable El Paso County,
Colorado Unclassifiable

Morgan County,
Colorado Unspecified (Area

around source) Unclassifiable Morgan County,
Colorado Unclassifiable2 Background

On June 3, 2010, the EPA revised the primary (healt h based) SO 2 NAAQS by establishing a new one-hour standard at a level of 75 parts per billio n (ppb) which is attained when the three-year average of the 99th percentile of one-hour daily ma ximum concentrations does not exceed 75 ppb. This NAAQS was published in the Federal Regist er on June 22, 2010 (75 FR 35520) and is
codified at 40 CFR 50.17. The EPA determined this i s the level necessary to protect public health with an adequate margin of safety, especially for c hildren, the elderly and those with asthma. These groups are particularly susceptible to the he alth effects associated with breathing SO 2 . The two prior primary standards of 140 ppb evaluated ov er 24 hours, and 30 ppb evaluated over an entire year, codified at 40 CFR 50.4, remain applic able. 1 However, the EPA is not currently designating areas on the basis of either of these t wo primary standards. Similarly, the secondary
standard for SO 2, set at 500 ppb evaluated over 3 hours has not been revised, and the EPA is also not currently designating areas on the basis of the secondary standard.

General Approach and Schedule

Section 107(d) of the Clean Air Act requires that n ot later than one year after promulgation of a new or revised NAAQS, state governors must submit t heir recommendations for designations and boundaries to EPA. Section 107(d) also requires the EPA to provide notification to states no less than 120 days prior to promulgating an initial area designation that is a modification of a
state’s recommendation. If a state does not submit designation recommendations, the EPA will promulgate the designations that it deems appropria te. If a state or tribe disagrees with the EPA’s intended designations, they are given an opportunit y within the 120 day period to demonstrate why any proposed modification is inappropriate.

On August 5, 2013, the EPA published a final rule e stablishing air quality designations for 29
areas in the United States for the 2010 SO 2 NAAQS, based on recorded air quality monitoring data from 2009 - 2011 showing violations of the NAA QS (78 FR 47191). In that rulemaking, the EPA committed to address, in separate future action s, the designations for all other areas for which the Agency was not yet prepared to issue desi gnations.

Following the initial August 5, 2013 designations, three lawsuits were filed against the EPA in different U.S. District Courts, alleging the Agency had failed to perform a nondiscretionary duty under the CAA by not designating all portions of th e country by the June 2013 deadline. In an effort intended to resolve the litigation in one of those cases, plaintiffs Sierra Club and the
Natural Resources Defense Council and the EPA filed a proposed consent decree with the U.S.
District Court for the Northern District of Califor nia. On March 2, 2015, the court entered the
consent decree and issued an enforceable order for the EPA to complete the area designations according to the court-ordered schedule.

1 40 CFR 50.4(e) provides that the two prior primary NAAQS will no longer apply to an area one year aft er its designation under the 2010 NAAQS, except that for a reas designated nonattainment under the prior NAAQS as of August 22, 2010, and areas not meeting the requirem ents of a SIP Call under the prior NAAQS, the prior NAAQS will apply until that area submits and EPA approves a SIP providing for attainment of the 2010 NAAQS. Neither El Paso County nor Morgan County were designated nonat tainment under the prior NAAQS or were failing to m eet SIP Call requirements under the prior NAAQS, so the exception does not apply.3

According to the court-ordered schedule, the EPA mu st complete the remaining designations by three specific deadlines. By no later than July 2, 2016 (16 months from the court’s order), the EPA must designate two groups of areas: (1) areas t hat have newly monitored violations of the
2010 SO 2 NAAQS and (2) areas that contain any stationary sou rces that had not been announced as of March 2, 2015 for retirement and that accordi ng to the EPA’s Air Markets Database emitted in 2012 either (i) more than 16,000 tons of SO 2 or (ii) more than 2,600 tons of SO 2 with an annual average emission rate of at least 0.45 po unds of SO 2 per one million British thermal units (lbs SO 2 /mmBTU). Specifically, a stationary source with a coal-fired unit that as of January 1, 2010 had a capacity of over 5 megawatts and otherwise meets the emissions criteria, is excluded from the July 2, 2016 deadline if it ha d announced through a company public announcement, public utilities commission filing, c onsent decree, public legal settlement, final state or federal permit filing, or other similar me ans of communication, by March 2, 2015, that it will cease burning coal at that unit.

The last two deadlines for completing remaining des ignations are December 31, 2017, and December 31, 2020. The EPA has separately promulgat ed requirements for states and other air agencies to provide additional monitoring or modeli ng information on a timetable consistent with these designation deadlines. We expect this informa tion to become available in time to help inform these subsequent designations. These require ments were promulgated on August 21, 2015 (80 FR 51052), in a rule known as the SO 2 Data Requirements Rule (DRR).

Updated designations guidance was issued by the EPA through a March 20, 2015 memorandum from Stephen D. Page, Director, U.S. EPA, Office of Air Quality Planning and Standards, to Air Division Directors, U.S. EPA Regions I-X. This memo randum supersedes earlier designation guidance for the 2010 SO 2 NAAQS, issued on March 24, 2011, and it identifies factors that the EPA intends to evaluate in determining whether area s are in violation of the 2010 SO 2 NAAQS. The guidance also contains the factors the EPA inte nds to evaluate in determining the boundaries for all remaining areas in the country, consistent with the court’s order and schedule. These factors include: 1) Air quality characterization vi a ambient monitoring or dispersion modeling results; 2) Emissions-related data; 3) Meteorology; 4) Geography and topography; and 5) Jurisdictional boundaries. This guidance was supple mented by two technical assistance
documents intended to assist states and other inter ested parties in their efforts to characterize air quality through air dispersion modeling or ambient air quality monitoring for sources that emit
SO 2 . Notably, the EPA released its most recent version s of documents titled, “SO 2 NAAQS Designations Modeling Technical Assistance Document ” (Modeling TAD) and “SO 2 NAAQS Designations Source-Oriented Monitoring Technical A ssistance Document” (Monitoring TAD)
in December 2013.

Based on ambient air quality data collected between 2012 and 2014, no violations of the 2010
SO 2 NAAQS have been recorded in any undesignated part of the State. 2 However, there are 2

2 For designations based on ambient air quality moni toring data that violates the 2010 SO 2 NAAQS, the consent
decree directs the EPA to evaluate data collected b etween 2013 and 2015. Absent complete, quality assu red and certified data for 2015, the analyses of applicable areas for the EPA’s intended designations will be informed by data
collected between 2012 and 2014. States with monito rs that have recorded a violation of the 2010 SO 2 NAAQS4

sources in the State meeting the emissions criteria of the consent decree for which the EPA must complete designations by July 2, 2016. In this draf t technical support document, the EPA discusses its review and technical analysis of Colo rado’s updated recommendations for the areas that we must designate. The EPA also discusses any intended modifications from the State’s
recommendation based on all available data before u s.

The following are definitions of important terms us ed in this document: 1) 2010 SO 2 NAAQS – The primary NAAQS for SO 2 promulgated in 2010. This NAAQS is 75 ppb, based on the three year average of the 99th percentile of the annual distribution of daily maximum one-hour average concentrations. S ee 40 CFR 50.17. 2) Design Value - a statistic computed according to th e data handling procedures of the NAAQS (in 40 CFR part 50 Appendix T) that, by compa rison to the level of the NAAQS, indicates whether the area is violating the NAAQS. 3) Designated nonattainment area – an area which the E PA has determined has violated the
2010 SO 2 NAAQS or contributed to a violation in a nearby ar ea. A nonattainment designation reflects considerations of state recomm endations and all of the information
discussed in this document. The EPA’s decision is b ased on all available information including the most recent 3 years of air quality mo nitoring data, available modeling analysis, and any other relevant information. 4) Designated unclassifiable area – an area which the EPA cannot determine based on all
available information whether or not it meets the 2 010 SO 2 NAAQS. 5) Designated unclassifiable/attainment area – an area which the EPA has determined to
have sufficient evidence to find either is attainin g or is likely to be attaining the NAAQS.
The EPA’s decision is based on all available inform ation including the most recent 3 years of air quality monitoring data, available mod eling analysis, and any other relevant
information. 6) Modeled violation – a violation based on air disper sion modeling. 7) Recommended attainment area – an area a state or tr ibe has recommended that the EPA designate as attainment. 8) Recommended nonattainment area – an area a state or tribe has recommended that the EPA designate as nonattainment. 9) Recommended unclassifiable area – an area a state o r tribe has recommended that the EPA designate as unclassifiable. 10) Recommended unclassifiable/attainment area – an are a a state or tribe has recommended that the EPA designate as unclassifiable/attainment

. 11) Violating monitor – an ambient air monitor meeting all methods, quality assurance and siting criteria and requirements whose valid design value exceeds 75 ppb, based on data analysis conducted in accordance with Appendix T of 40 CFR part 50.

during these years have the option of submitting co mplete, quality assured and certified data for cale ndar year 2015 by April 19, 2016to the EPA for evaluation. If afte r our review, the ambient air quality data for the area indicates that no violation of the NAAQS occurred between 201 3 and 2015, the consent decree does not obligate th e EPA to complete the designation. Instead, we may designate the area and all other previously undesignated are as in the State on a schedule consistent with the prescribed timing of the court order, i.e., by December 31, 2017, or December 31,
2020.5 Technical Analysis for the Colorado Springs, Colora do Area

Introduction

The Colorado Springs area contains a stationary sou rce that according to the EPA’s Air Markets Database emitted in 2012 either more than 16,000 to ns of SO 2 or more than 2,600 tons of SO 2 and had an annual average emission rate of at least 0.45 pounds of SO 2 per one million British thermal units (lbs SO 2 /mmBTU). As of March 2, 2015, this stationary sourc e had not met the specific requirements for being “announced for reti rement.” Specifically, in 2012, the Martin Drake Power Plant emitted 4,792 tons of SO 2 , and had an emissions rate of 0.56 lbs
SO 2 /mmBTU. Pursuant to the March 2, 2015 court-ordered schedule, the EPA must designate the area surrounding the facility by July 2, 2016.

In its submission, Colorado recommended that the ar ea surrounding the Martin Drake Power Plant be designated as unclassifiable based on an a ssessment and characterization of air quality from the facility and other nearby sources which ma y have a potential impact in the area of analysis where maximum concentrations of SO 2 are expected. This assessment and
characterization was based on consideration of the data available to the State, including attaining monitoring data with fewer than 3 total years of da ta that Colorado did not determine was located
in the area of maximum concentration. After careful review of the State’s assessment, supporting documentation, and all available data, the EPA agre es with the State’s recommendation for the area, and intends to designate the areas as unclass ifiable. However, because the State did not provide specific boundaries in its recommendation, the EPA’s intended boundary consists of El Paso County.

The Martin Drake Power Plant is located in Colorado Springs, Colorado in the western portion of El Paso County. As seen in Figure 1 below, the faci lity is located in southwestern Colorado Springs. Also included in the figure are nearby emi tters of SO 2 (specifically the Nixon Power Plant, indicated in green). Figure 2, below, shows the intended unclassifiable area (El Paso County) in blue, with a red star which indicates th e location of the Martin Drake facility.

Figure 1. The EPA’s intended designation for El Pas o County, Colorado6

Figure 2. The EPA’s intended unclassifiable designa tion for El Paso County, Colorado7

The discussion and analysis that follows below will reference the State’s use of the Modeling TAD, the EPA’s assessment of the State’s modeling i n accordance with the Modeling TAD, and
the factors for evaluation contained in the EPA’s M arch 20, 2015 guidance, as appropriate.

Detailed Assessment

Air Quality Data

This factor considers the SO 2 air quality monitoring data in the area surroundin g Martin Drake Power Plant. The facility is located in El Paso Cou nty, and the State included all available monitoring data from the one SO 2 monitor currently operating in El Paso County. Thi s monitor, which began collecting SO 2 data in 2013, is located about .5 miles northwest of the Martin Drake Power Plant. The table below shows information prov ided by the State related to the monitor located in El Paso County.

Table 2. Available Air Quality Data for the Area Cl osest to Martin Drake Power Plant

County State

Recommendation Air Quality

Systems (AQS)
Monitor ID Monitor Location Distance to
Martin Drake
Power Plant (km) 2013 – 2015

SO 2 Design Value in ppb

El Paso Unclassified 08-041-0015 690 W. Highway
24 .8 km 56 ppb8

Based on available ambient air quality collected at the Highway 24 monitor, the county surrounding Martin Drake Power Plant does not show a violation of the 2010 SO 2 NAAQS at its monitor. Colorado did not attempt to use the Highwa y 24 monitoring data to justify an attainment designation, nor did the State attempt t o demonstrate that the monitor is appropriately sited at a point of expected maximum SO 2 concentration. EPA therefore does not consider the Highway 24 data to be a sufficient technical justif ication to rule out that an exceedance of the

2010 SO 2 NAAQS may occur at another location near the facil ity.

Emissions and Emissions-Related Data

Evidence of SO 2 emissions from the source meeting the emissions cri teria of the March 2, 2015 consent decree, i.e., Martin Drake Power Plant, is an important factor for determining whether the immediate area is experiencing elevated levels of SO 2 concentrations. Other considerations for this factor include county level SO 2 emissions data and data for sources located within 50 km.

As part of its recommendation, Colorado included th e annual emissions for all point sources in El Paso County emitting at or above 0.5 tons per ye ar of SO 2 . Colorado obtained the data for these sources and their emissions from the yearly f acility reports that are submitted to the State.

These emissions data are summarized below.

Table 3: SO 2 Emissions from Martin Drake Power Plant and Other L ocal Sources

County Company Distance to Martin
Drake Power Plant 2013 Actual SO 2

Emissions (tons/year) El Paso Colorado Springs Utilities -

Martin Drake Power Plant 4,580.3

El Paso Colorado Springs Utilities –

Nixon Power Plant 24 km 3,955.1

El Paso Fort Carson US ARMY 7.5 km 34.5 El Paso Colorado Springs Utilities –

Clear Spring Ranch 23.5 km 23.6

El Paso Schmidt Construction Company

– Delta Drive Facility 6.5 km 23.2

El Paso Kiewit – Colorado Springs

Asphalt Plant 16.0

El Paso Martin Marietta Materials –

Fillmore 8.2

El Paso Schmidt Construction Company

– Menzer Facility 3.7

El Paso Penrose Community Hospital 3.7 El Paso U.S. Air Force Academy 2.5
El Paso Peterson Air Force Base 2.4
El Paso Homeward Bound 2.39

El Paso Rocky Mountain Materials &

Asphalt Inc. 2.2

El Paso Fountain Landfill 1.6 El Paso Federal Express – Colorado

Tech 1.2

El Paso Fountain Valley Power – Boca

Raton 1.1

El Paso Pikes Peak Pet Crematory 1.0 El Paso Cheyenne Mountain Zoo 0.8 El Paso Holt Family Funeral Homes 0.7
El Paso UCH-MHS Central 0.6 El Paso Hewlett-Packard Corporation 0.6 El Paso Color Star Growers – Peyton

Greenhouse 0.6

* Distance was only measured for sources with emiss ions equal to or greater than 20 tons per

year

Emissions Controls

The EPA recognizes that control strategies implemen ted after the release of the 2011 NEI may not be reflected, or may warrant further discussion . The State indicated that Colorado Springs Utilities (CSU) is currently in the process of inst alling SO 2 controls on Units 5, 6 and 7 to comply with Regional Haze emission limits. At the t ime of this analysis, CSU plans to install dry sorbent injection (DSI) on Unit 5 and lime spray dr yers or equivalent on Units 6 and 7 with target control operational dates by December 31, 20 16 and compliance dates no later than December 31, 2017.

Meteorology (Weather & Transport Patterns)

In its designation recommendation, Colorado indicat ed that there are no available representative meteorological datasets for the transport and dispe rsion conditions at the Martin Drake Power Plant. Following its designation recommendation, Co lorado submitted to EPA a document describing why it did not consider the nearest avai lable meteorological data, at the Colorado Springs Airport over 11 kilometers east of the Mart in Drake Power Plant, to be representative of EPA’s Guideline on Air Quality Models (40 CFR Part 51 Appendix W; November 2005). This document, “Meteorological Determination for the Mar tin Drake Power Plant,” was submitted to EPA on October 6, 2015.

In its “Meteorological Determination” document, Col orado noted that winds at/near Martin Drake are expected to flow up the valley of Fountai n Creek during most daytime hours and up the valley of Monument Creek at a much lower freque ncy due to differential heating and the proximity of the power plant to Pikes Peak (see Fig ure 3, below). During nighttime and early morning hours, drainage winds flowing from the vall eys of Fountain Creek and Monument Creek towards the power plant are expected.10 Figure 3. Expected Wind Directions at the Martin Dr ake Power Plant and Colorado Springs Airport

By contrast, the State determined that the upslope and downslope winds at the Colorado Springs Airport are driven by the higher terrain to the nor th of the airport, the Palmer Divide. There are no other significant terrain features that influenc e the winds at the airport. This makes the wind directions at the airport predominantly northerly ( downslope) and southerly (upslope).

The State also indicated that during inversion cond itions with light surface winds during which the highest impacts from the power plant are expect ed to occur, the light drainage winds transporting the plumes from Martin Drake are espec ially likely to follow along Fountain Creek. Finally, Colorado stated that wind speeds at the ai rport are expected to be higher than at the
Martin Drake Power Plant.

All of these factors led Colorado to conclude that there are no available meteorological datasets that are representative of transport and dispersion conditions of the Martin Drake Power Plant plumes due to the differences in meteorological con ditions between the Colorado Springs Airport11

and the Martin Drake Power Plant. As a result, Colo rado Springs Utilities erected a sound detection and ranging (SODAR) tower just south of M artin Drake in fall 2015 in order to gather representative meteorological data to more accurate ly inform future modeling.

EPA agrees with Colorado’s determination that the m eteorological data from the Colorado Springs Airport are not representative of meteorolo gical conditions at the Martin Drake Power Plant. Therefore, EPA does not consider modeling wh ich relies on meteorological data from the Colorado Springs Airport to be sufficient as the so le basis for a designation of the area impacted by emissions from the Martin Drake Power Plant. A d iscussion and analysis of other information the EPA received, including air dispersion modeling relying on these non-representative meteorological conditions, follows in the section t itled, “Other Relevant Information.”

Geography and Topography (Mountain Ranges or Other Air Basin Boundaries)

The Martin Drake Power Plant is located near the co nfluence of two large creek drainages;

Fountain Creek and Monument Creek. It is about two miles west of Rocky Mountain foothills, which rise dramatically in elevation. The wind flow s impacting the plumes at Martin Drake Power Plant generally follow Fountain Creek.

Jurisdictional Boundaries

Once the geographic area associated with the immedi ate area surrounding the Martin Drake Power Plant, other nearby sources, and background c oncentrations are determined, existing jurisdictional boundaries are considered for the pu rpose of informing our intended unclassifiable area. Specific attention will be given to clearly d efined legal boundaries.

The EPA believes that our intended unclassifiable a rea, consisting of El Paso County, is comprised of clearly defined legal boundaries, and we find these boundaries to be a suitably clear basis for defining our intended unclassifiable area

.

Other Relevant Information

The EPA received air dispersion modeling results fr om the Sierra Club (with modeling conducted by Wingra Engineering, S.C.), in which th e submitter asserts that SO 2 emissions from the Martin Drake Power Plant, when considered alone or in tandem with other local sources, are causing a violation of the NAAQS.

In its modeling analysis, Sierra Club used meteorol ogical data from the Colorado Springs Airport. As noted, the State has determined that th e “meteorological data from the Colorado Springs Airport is not representative of transport and dispersion conditions of the Drake Power Plant plumes due to the differences in meteorologic al conditions at the Colorado Springs Airport
and the Drake Power Plant. The use of the Colorado Springs Airport data to model the Drake Power Plant is inconsistent with the TAD and Append ix W.” EPA agrees with Colorado’s
conclusion.12

In addition to its review of meteorological data, t he state of Colorado reviewed the methodology and model inputs in the Sierra Club’s modeling eval uation to determine if they were consistent with recommendations in the Modeling TAD, procedure s for regulatory applications of
AERMOD that are addressed in U.S. EPA’s Guideline on Air Quality Models

‐ Appendix W to 40 CFR 51 (Appendix W) and the U.S. EPA’s AERMOD Im plementation Guide (AIG), and relevant clarification memos issued by U.S. EPA. 3 Based on its review, the state of Colorado determined that several inputs were inconsistent wi th EPA guidance. Specifically, the State concluded;

1. A downwash analysis was not used in Sierra Club’s e valuation. Building parameters (including downwash) should be used in the modeling since there are structures at both plants that will cause plume downwash.
2. The National Elevation Dataset (NED) in the Sierra Club evaluation was developed using
base data from 1947. Since all of the modeled emiss ion units were built after this date, plant survey data would provide more accurate base elevations.
3. Sierra Club’s evaluation assumed that Martin Drake is located in a rural area based on
examination of land use/cover. Colorado concluded t hat it would be more appropriate to model Drake as an urban source using the population density procedure and 2010 Census
Tract data.
4. Receptor elevations and hill heights were determine d using the NED in the Sierra Club evaluation. Colorado noted use of higher resolution NED is more appropriate.
5. A flagpole height of 1.5 meters was used for all re ceptors in the Sierra Club evaluation. Colorado concluded that ground-level receptors woul d be more appropriate per the TAD and Appendix W.

Similar to the state of Colorado, EPA also has conc erns with the assumptions used in the modeling conducted by the Sierra Club to support a nonattainment classification. EPA finds that certain modeling inputs do not conform to EPA guida nce or are not sufficiently supported for use in AERMOD for the characterization of ambient air q uality with significant SO 2 emission sources. Specifically, the components of the Sierra Club modeling analysis that EPA finds inconsistent with EPA guidance or are not sufficien tly supported include:
1. The use of a version of AERMOD/AERMET dated 14134 a nd AERMINUTE dated 14237. In a proposed rulemaking published in the Ju ly 29, 2015 Federal Register (80 FR 45340), EPA released a revised version of AERMOD (1 5181), which replaces the previous version of AERMOD dated 14134. The latest version of AERMINUTE is also 14337. The latest release of the AERMOD platform is recommended for use in regulatory applications.
2. The use of receptors placed 1.5 meters above ground -level. EPA Modeling TAD and Appendix W do not recommend that receptors be place d at levels other than ground level for comparison to the NAAQS.

3 Colorado considered the memos “Applicability of Ap pendix W Modeling Guidance for the 1

‐ hour SO 2 NAAQS”, August 23, 2010; “Additional Clarification Regardin g Application of Appendix W Modeling Guidance for t he 1

‐ hour NO2 National Ambient Air Quality Standard” Mar ch 1, 2011.13

3. The use of actual stacks heights for modeling actua ls and allowable emissions. For the purposes of modeling with actual emissions to chara cterize air quality for use in the SO 2 designations process, EPA guidance recommends the u se of actual stack heights. If allowable emissions are modeled, EPA guidance recom mends that the GEP stack height policy be used in the model.
4. Not considering building downwash. EPA guidance rec ommends careful consideration of the information for any nearby buildings, such as l ocation and orientation relative to stacks and building size parameters. Given that the re are structures at both the Drake and Nixon Power plant, building downwash should be cons idered to represent actual
conditions.
5. The use of rural dispersion coefficients. EPA’s gui dance recommends two methods for determining land classification as either urban or rural. The methods include analyzing land use or population density with the most recent and representative information. It is
not clear that the information used in the Sierra C lub analysis is the most recent or representative of the area to support the use of ru ral dispersion coefficients.
6. The assumed background concentration of 75.9 μ g/m 3 based on monitor information at a site about 100 km from the source. EPA’s guidance r ecommends that air quality data in the vicinity of the source should be used to determ ine the background concentrations. EPA is aware of monitoring data closer to the sourc es that should be considered for determining the background concentrations. Also, th e assumed value may not be a representative background concentration because it may be impacted by other nearby sources. Based on the information provided by the S ierra Club, it does not appear that the calculation excluded periods when the dominant sour ces could have been influencing the monitored concentrations. EPA’s modeling TAD recomm ends approaches for correcting for source impacted background data which Sierra Cl ub apparently did not take into

account.

For these reasons, and due to the use of unrepresen tative meteorological data, EPA finds that the results of the Sierra Club modeling should not be u sed as the basis for a nonattainment designation for Colorado Springs, as Sierra Club ha s recommended in their evaluation of compliance with the 1-hour NAAQS for SO 2

.

EPA has also received information from residents of Colorado Springs and nearby communities. Like Sierra Club, these individuals have advocated that the area around Martin Drake be designated as nonattainment for the 2010 SO 2 NAAQS. EPA has not yet fully addressed the information provided by these individuals given tim e constraints and the expectation of additional technical information to support their s pecific claims. EPA will review and take in to account all of the information received by these an d other parties as part of its final designation process for the Colorado Springs area.

Conclusion

After careful evaluation of the State’s recommendat ion and supporting information, as well as all available relevant information, the EPA intends to designate the area around Martin Drake Power
Plant as unclassifiable for the 2010 SO 2 NAAQS. Specifically, the boundaries are comprised of the entirety of El Paso County, Colorado. The EPA i s basing this conclusion on the lack of14

sufficient technical information on which to base a determination regarding whether the area is meeting or not meeting the NAAQS.

At this time, our intended designations for the Sta te only apply to this area. Consistent with the conditions in the March 2, 2015 court-ordered sched ule, the EPA will evaluate and designate all remaining undesignated areas in Colorado by either December 31, 2017 or December 31, 2020.15 Technical Analysis for the Morgan County, Colorado Area

Introduction

Morgan County, Colorado contains a stationary sourc e that according to the EPA’s Air Markets Database emitted in 2012 either more than 16,000 to ns of SO 2 or more than 2,600 tons of SO 2 and had an annual average emission rate of at least 0.45 pounds of SO 2 per one million British thermal units (lbs SO 2 /mmBTU). As of March 2, 2015, this stationary sourc e had not met the specific requirements for being “announced for reti rement.” Specifically, in 2012, the Pawnee Power Plant emitted 13,510 tons of SO 2 , and had an emissions rate of 0.76 lbs SO 2 /mmBTU. Pursuant to the March 2, 2015 court-ordered schedul e, the EPA must designate the area surrounding the facility by July 2, 2016.

In its submission, Colorado recommended that the ar ea surrounding the Pawnee Power Plant be designated as unclassifiable based on an assessment and characterization of air quality from the facility and other nearby sources which may have a potential impact in the area of analysis where
maximum concentrations of SO 2 are expected. This assessment and characterization was based
on consideration of the data available to the State . After careful review of the State’s assessment, supporting documentation, and all available data, t he EPA agrees with the State’s recommendation for the area, and intends to designa te the areas as unclassifiable. However, because the State did not provide specific boundari es in its recommendation, the EPA’s intended boundary consists of Morgan County.

The Pawnee Power Plant is located roughly 8.5 km so utheast of Fort Morgan, Colorado in the central portion of Morgan County (see Figure 4, bel ow). Also included in the figure are nearby
emitters of SO 2 (the green dot demarks Cargill Meat Solutions). Fig ure 5 shows the EPA’s intended unclassifiable designation for the area (i .e. Morgan County), in blue, with the Pawnee Power Plant indicated by the red star.

Figure 4. Pawnee Power Plant and other sources in M organ County, Colorado16

Figure 5. EPA’s intended unclassifiable area, which consists of Morgan County, Colorado.17

The discussion and analysis that follows below will reference the State’s use of the Modeling TAD, the EPA’s assessment of the State’s modeling i n accordance with the Modeling TAD, and
the factors for evaluation contained in the EPA’s M arch 20, 2015 guidance, as appropriate.

Detailed Assessment

Air Quality Data

This factor considers the SO 2 air quality monitoring data in the area surroundin g Pawnee Power Plant. The facility is located in Morgan County; ho wever, there are no ambient air quality monitors located in this county. The State did not include the most recent 3 years of monitoring data, i.e., 2012 – 2014, in its recommendation for the closest neighboring county, i.e., Adams County. The table below shows information related t o the monitor(s) located in Adams County, which were confirmed through the EPA’s 2014 design value report for SO 2

. 4

Table 4: Available Air Quality Data for the Area Cl osest to Pawnee Power Plant

County State

Recommendation Air Quality

Systems (AQS)
Monitor ID Monitor Location Distance to
Martin Drake
Power Plant (km) 2012 – 2014

SO 2 Design Value in ppb

Adams None 08-001-3001 3174 E. 78 th Ave. Welby, Colorado 110 km 25 ppb

4 The design value report for SO 2, as well as each of the other NAAQS, can be found at this link: http://www3.epa.gov/airtrends/values.html18

Due to the large distance from the nearest monitor (in Welby, Colorado) to the Pawnee Power Plant, the information from this monitor is not inf ormative as to a designation of the area surrounding Pawnee.

Emissions and Emissions-Related Data

Evidence of SO 2 emissions from the source meeting the emissions cri teria of the March 2, 2015 consent decree, i.e., Pawnee Power Plant, is an imp ortant factor for determining whether the immediate area is experiencing elevated levels of S O 2 concentrations. Other considerations for this factor include county level SO 2 emissions data and data for sources located within a significant concentration gradient. 5

As part of its recommendation, Colorado included th e annual emissions for all point sources in Morgan County emitting SO 2 . Colorado obtained the data for these sources and their emissions from the yearly facility reports that are submitted to the State. These emissions data are

summarized below.

Table 5: SO 2 Emissions from Martin Drake Power Plant and Other L ocal Sources

County Company Distance to Pawnee
Power Plant* 2013 Actual SO2

Emissions [tons/year] Morgan Public Service Co – Pawnee

Power Plant 12,467.55

Morgan Western Sugar Coop. 12 km 58.30 Morgan Cargill Meat Solutions 8.6 km 48.84 Morgan Brush Cogeneration

Partners/Colorado Power 0.18

Morgan Dairy Farmers of America, Inc. 0.16 Morgan City of Brush 0.16 Morgan Brushco Farms, Inc. 0.04 Morgan Brush Meat Processors, Inc 0.02 Morgan Public Service Co. – Roundup

Station 0.01

Morgan Heer Mortuary & Crematory 0.01 Morgan Leprino Foods Co. <0.01

5 The State addressed the sources within a significa nt concentration gradient of Pawnee, citing EPA’s M odeling
TAD.19

* Distance was only measured for sources with SO 2 emissions greater or equal to 20 tons per

year.

Emissions Controls

The EPA recognizes that control strategies implemen ted after the release of the 2011 NEI may not be reflected, or may warrant further discussion . As part of its designation recommendation,

Colorado submitted information on emissions reducti ons resulting from controls put into place after the date of the emissions inventory data prov ided in the table above.

Pursuant to Colorado’s Regional Haze SIP (77 FR 768 71, December 31, 2012), a semi-dry SO 2 scrubber system was installed at the Pawnee Power P lant. The controls began operating in August 2014, and have resulted in an SO 2 reduction of about 87%. Table 6, below, was includ ed

in Colorado’s recommendation and demonstrates the s ignificant decrease in SO 2 emissions following the installation of the new scrubber syst em.

Table 6: Pawnee Power Plant Emissions

Year Number of Months

Reported SO 2 Annual

Emissions (tons/year) SO 2 Annual

Emission Rate (lb/MMBtu) 2012 12 13,510 0.76 2013 12 12,467 0.72 2014 12 5,508* 0.34 2015 (partial) 3 476 0.08 2015 (projected) - ≈ 1,700 ≈ 0.10
* SO 2 lime spray dryer controls installed August 2014

Meteorology (Weather & Transport Patterns)

Evidence of source-receptor relationships between s pecific emissions sources and high SO 2 concentrations in the surrounding area is another i mportant factor in determining the appropriate

extent of the EPA’s intended unclassifiable area.20

Geography and Topography (Mountain Ranges or Other Air Basin Boundaries)

The Pawnee Power Plant is located on the plains of eastern Colorado about 7 km south of the South Platte River. There are no significant topogr aphical features impacting the area near the

Pawnee Power Plant.

Jurisdictional Boundaries

Once the geographic area associated with the immedi ate area surrounding the Pawnee Power Plant, other nearby sources, and background concent rations are determined, existing jurisdictional boundaries are considered for the pu rpose of informing our intended unclassifiable area. Specific attention will be given to clearly d efined legal boundaries.

The EPA believes that our intended unclassifiable a rea, consisting of Morgan County, is comprised of clearly defined legal boundaries, and we find these boundaries to be a suitably clear basis for defining our intended unclassifiable area

.

Conclusion

After careful evaluation of the State’s recommendat ion and supporting information, as well as all available relevant information, the EPA intends to designate the area around Pawnee Power Plant
as unclassifiable for the 2010 SO 2 NAAQS. Specifically, the boundaries are comprised of the entirety of Morgan County, Colorado.

EPA is basing this conclusion on the lack of suffic ient technical information on which to base a determination regarding whether the area is meeting or not meeting the NAAQS. As indicated, no modeling has been conducted, and the appropriate modeling parameters are not understood. Further, ambient air quality data that properly rep resents the areas of predicted maximum concentrations in the vicinity of Pawnee Power Plan t are not available.

At this time, our intended designations for the Sta te only apply to this area. Consistent with the conditions in the March 2, 2015 court-ordered sched ule, the EPA will evaluate and designate all remaining undesignated areas in Colorado by either December 31, 2017 or December 31, 2020.