Page 1 of 15



# Technical Support

Document

1

- Hour SO 2 

# National Ambient Air Quality Standard

Recommended Air Quality Designation Boundaries

for

“Round 2” Sources

April 19, 2016

Colorado Department of Public Health and Environment

Air Pollution Contro l Division 4300 Cherry Creek Drive South Denver, Colorado 80246Page 2 of 15 

## Table of Contents

Introduction

................................ ................................ .......................... 3

Designation Boundary Recommendations

................................ ..................... 3

EPA Guidance on SO 2 

### Designations

................................ ................................ 3

Future EPA SO 2 

### Designations Process

................................ ............................ 3



## A nalysis of Source Specific Designations

................................ .......... 4

Public Service Company of Colorado

– Pawnee Power Plant

..................... 4

Air Quality Characterization: Ambi ent Monitoring or Dispersion Modeling Results

. 4

Emissions

- Related Data

................................ ................................ ................................ ....... 5

Meteorology (Weather & Transport Patterns)

................................ ................................ 6

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

........ 7

Jurisdictional Boundaries

................................ ................................ ................................ .... 7

Other Relevant Information

................................ ................................ ............................... 8

Conclusion

................................ ................................ ................................ ............................. 8


### Colorado Springs Utilities

– Martin Drake Power Plant

............................. 10

Air Quality Characterization: Ambient Monitoring or Dispersion Modeling Results 10

SO2 Ambient Monitoring in El Paso County

................................ ................................ ... 10

Dispersion Modeling

................................ ................................ ................................ ........... 10

Emissions

- Related Data

................................ ................................ ................................ ..... 10

Meteorology (Weather & Transport Patterns)

................................ .............................. 11

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

...... 12

Jurisdictional Boundaries

................................ ................................ ................................ .. 12

Other Relevant Information

................................ ................................ ............................. 1 2

Conclusion

................................ ................................ ................................ ........................... 13Page 3 of 15 

# Introduction

Designation Boundary Recommendations

This Technical Support Document (TSD) p rovides the basis for the source specific sulfur dioxide ( SO 2 ) National Ambient Air Quality Standard (NAAQS) air quality designation boundary recommendations for the Public Service Company of Colorado

– Pawnee Power Plant and Colorado Springs Utilities

– M artin Drake Power Plant. These sources must be designated pursuant to “Round 2” of EPA’s Data Requirements Rule (DR R) (80 FR 51056)

. The Colorado Department of Public Health and Environment (CDPHE) Air Pollution Control Division ( Division ) recommended, a nd the U.S. Environmental Protection Agency (EPA) proposed, to designate specific areas surrounding both power plants as unclassifiable regarding compliance with the 1

- hr

SO 2 NAAQS. These areas will be subject to future additional designation requirements

under the Data Requirements Rule (DRR)

.



### EPA Guidance on SO 2 

### Designations

Pursuant to the letter EPA sent to Governor Hickenloope r on February 16, 2016, the

Division is providing additional information that EPA should consider prior to finalizing

these d esignations. In the attached Technical Support Document of EPA’s letter, it is noted that updated designations guidance issued by EPA through a Mar ch 20, 2015 memorandum supersede s earlier designation guidance and identifies factors that the

EPA intends t o evaluate in determining area boundaries under the 2010 SO 2 NAAQS.

These five factors are: 1) Air quality characterization via ambient monitoring or dispersion modeling results; 2) Emissions

- related data; 3) Meteorology; 4) Geography and topography; 5) Jurisdictional boundaries. In this TSD, CDPHE considers each of these five factors along with other relevant information regarding each of the detailed area boundary recommendations for

Pawnee and Drake Power Plants

.



### Future EPA SO 2 

### Designations Process

Th e DRR establish es an SO 2 emissions applicability threshold of 2,000 tons per year (tpy) that identifies priority sources subject to a source specific SO 2 designation

process

. S tates have three options under the DRR to characterize current air quality

in areas with large SO 2 sources (2,000 tpy or greater) : (1) e stablish federally

enforceable emission limits (under 2,000 tpy) by January 13, 2017 ; (2) conduct air quality modeling by January 13, 2017 ; or (3) begin operating an appropriate monitoring network by January 1, 2017

. T he EPA will promulgate Round 3 SO 2 designations (by Court Order) no later than December 31, 2017 for areas with sources

that are modeled

. F or sources that are monitored and any remaining undesignated

areas , EPA will promulgate Round 4 SO 2 designations (by Court Order) no later than December 31, 2020. The Pawnee Power Plant and Martin Drake Power Plant will be subject to future DRR promulgations.Page 4 of 15



# Analysis of Source Specific Designations

This section of the TSD analyzes each of the fiv e factors set forth in EPA’s March 20,

2015 memorandum for the Pawnee Power Plant and the Martin Drake Power Plant. Boundary recommendations are presented at the conclusion of each five factor analysis.



### Public Service Company of Colorado

– Pawnee Power P lant

Air Quality Characterization : A mbient M onitoring or D ispersion M odeling R esults

As EPA noted previously, the nearest ambient SO 2 monitor in Adams County is over 60 miles away to the southwest

. Due to the fact that there has never been ambient SO 2

mon itoring in Morgan County, t here is not any current or historical ambient monitoring for the Pawnee Power Plant available. Therefore, refined dispersion modeling is currently being conducted for this facility in consultation with the source

and EPA.

For D RR modeling, EPA recommends that the model domain be based on the determination of significant concentration gradients and distance from source. The

SO 2 Modeling Technical Assistance Document ( TAD ) states the following:

“Concentration gradients associated with a particular source will be generally largest between the source and the distance to the maximum ground level concentrations from the source. Beyond that distance, gradients tend to be smaller and more spatially uniform...a general guideline that the d istance between a source and its maximum ground level concentration is generally 10 times the stack height 1 in flat terrain. However, the potential influence of terrain can impact the location and magnitudes of significant concentration gradients. The use of significant concentration gradients can help inform the decision on the size of the modeling domain and sources to consider for modeling.” The Division notes that 10 times the stack height of Pawnee Power Plant is: 550 feet x 10 = 5,500 feet (roughly 1 mile or

1.7 k ilo m eters (km) ). This radius would be considered too narrow considering the meteorological data, including potential terrain influences, and other nearby sources

in the area.

EPA’s March 1, 2011 Memo, which is referenced in the TAD, also sta tes the following:

“Even accounting for some terrain influences on the location and gradients of

maximum 1

- hour concentrations, these considerations suggest that the emphasis on determining which nearby sources to include in the modeling analysis should fo cus on the area within about 10 kilometers of the project location 2 in most cases. The routine inclusion of all sources within 50 kilometers of the project location, the nominal distance for which AERMOD is applicable, is likely to produce an overly

1 EPA SO2 NAA QS Designations Modeling Technical Assistance Document, page 8.

2 Additional Clarification Regarding Application of Appendix W Modeling Guidance for the 1

- hour NO2 National Ambient Air Quality Standard, March 1, 2011, page 16.Page 5 of 15

conser vative result in most cases.” Based on the TAD and this Memo, the Division believes the modeling analysis should focus on the area within a 10 km radius of the

Pawnee Power Plant.

Figure 1 identifies SO 2 sources in the vicinity of the Pawnee Power Plant. Cargill Meat Solutions is about 5.4 miles (8.7 kilometers) and Western Sugar Company is about 7.3 miles (11.8 kilometers) from the Pawnee Power Plant respectively.

Figure 1: Significant SO 2 Sources in Morgan County

When CDPHE initially submitted Round 2 designation recommendations on September 18, 2015, the appropriate area for air quality characterization had not yet been

determined. Upon review of the EPA TAD and Memo, CDPHE proposes that a radius of 10 km captures potential terrain influences and the affected populations in the town of Brush and a portion of the city of Fort Morgan. The Division anticipates that the refined modeling process to be completed in 2016, which will then provide additional

information for the attainment status of the Pawnee Power Plant.

Emissions-Related Data

Pawnee Power Plant

– SO 2 Emissions Analysis

The March 2015 Consent Decree (CD) identified subject sources for inclusion in Round 2 designations based on 2012 continuous emissions monitoring data. In 2012, the

Pawnee Power Plant had no SO 2 controls aside from firing low-sulfur coal 3 ; consequently, the facility’s SO 2 emissi ons were over the CD’s applicability threshold of 2,600 tpy along with an annual average emission rate exceeding 0.45 lbs/MMBtu. In 2014, pursuant to Colorado’s Regional Haze S tate Implementation Plan (SIP)

3 The Pawnee Power Plant generally fires sub-bituminous coal that has an average sulfur content ranging from 0.24 to 0.42 percent from the Powder River Basin area in Wyoming.

Copyrighted map removedPage 6 of 15

(approved by EPA in January 2013), the Public Service Company of Colorado (PSCo) installed and commenced operation of a semi

- d ry SO 2 scrubber system (lime spray dryer) at the Pawnee Power Plant. Pursuant to the Regional Haze SIP, the scrubber system is subject to a federally enforceable (allowable) permit limitation of 0.12

lbs/MMBtu based on a 30

- day rolling average emission ra te. Table 1 provides SO 2 emissions data for the Pawnee Power Plant that is reported to the EPA Air Markets Program Data system. As indicated in the below table, the recently installed semi

- dry

SO 2 scrubber has re sulted in a significant SO 2 emission reduction of about 86 %

.

Table 1 : Pawnee Power Plant SO 2 Emissions (updated with 2015 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 12 1,810 0.08
*SO2 lime spray dryer controls started in August 2014

SO 2 Emissions in Morgan County

T he most current comprehensive emiss ion inventory available from Division records

for Morgan County indicates that over 99% of the 201 3 SO 2 emissions in the county are from point sources. As indicated above, the Pawnee Power Plant began operating a

semi

- dry scrubber system in August of 2014 that will significantly lower SO 2 emissions

in th e future. The Pawnee Power Plant comprised 98.7% of the SO 2 emissions in Morgan County (as of 2013).

Meteorology (Weather & Transport Patterns)

The local winds are a combination of the mountain/valley winds in the South Platte and Beaver Creek Valleys and large scale weather features (synoptic winds). During the night and early morning hours the down valley winds in the South Platte River or Beaver Creek Valleys dominate. The winds in Beaver Creek Valley are most likely enhanced by synoptic conditions. Th e annual 60

- meter windrose , which is similar to winds at plume height, is depicted in Figure 2 below

. Generally, over a year, a variety of synoptic type forcings cause winds to flow from either the west through northeast or from the south through southeas t most of the time.Page 7 of 15

Figure 2 : Annual 60

- meter Windrose (Pawnee Power Plant meteorological data)

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

The Pawnee Power Pl ant is located on the southern slope of t he South Platte River Valley and on the west side of Beaver Creek. Near this location the South Platte River

turns from the southeast to the northeast and continues in this direction into

Nebraska. Beaver Creek flows from the south to the north into the S outh Platte River. Outside of the South Platte River Valley the terrain gently slopes up, north to the Cheyenne Ridge and south to Monument Ridge.

Jurisdictional Boundaries

The Pawnee Power Plant is not located within any defined town or city boundaries,

b ut rather within the rural areas of Morgan County. The closest town is Brush (population 5,501 as of 2013 ) , which is located approximately three miles (4.8 km) to the northeast. The closest city is Fort Morgan (population 11,407 as of 2013 ) , located

appro ximately five miles (8 km) to the northwest. As of 2013, the population of Morgan County was 28,404 people 4

. The populations of these two nearby communities comprise about 60% of Morgan County’s population.

4 All population statistics are from the United States Census Bureau.Page 8 of 15

Other Relevant Information

None.

Conclusion

Upo n consideration of the five factors, CDPHE recommends applying a radius of 10 km (6.2 miles) around the Pawnee Power Plant as the boundary for the unclassifiable area designation , shown in Figure 3. This is based on the following information:

 EPA’s Modeli ng TAD and March 1, 2011 Memo distance guidelines indicate that a 10 km radius normally establishes an appropriate modeling domain. SO 2 modeling for the area around the Pawnee Power Plant will not be complete d before the court ordered deadline for making Round 2 designations. No SO 2 ambient monitoring data is available for this area. Without completed modeling results or ambient monitoring data, it is appropriate to base the SO 2 area boundary on the 10 km radius outlined in EPA’s March 1, 2011 Memo ;

 SO 2 e mi ssions from the Pawnee Power Plant have been significantly reduced

since the installation of the semi

- dry lime scrubber in 2014 . Emissions from Cargill Meat Solutions are captured by the 10 km radius. The Western Sugar

Co operative facility is located further than 10 km from the Pawnee Power Plant, a nd has significantly lower emissions than the power plant ;

 There are no significant meteorological, geographical or topographica l features

that make the 10 km radius an inappropriate area designation b oundary ;

 The nearby town of Brush and the affected areas of the city of Fort Morgan closest to the Pawnee Power Plant are included in this proposed radius 5

.

5 Town and city boundaries appl icable as of April 2016.Page 9 of 15

Figure 3 : Pawnee Power Plant Boundary RecommendationPage 10 of 15



### Colorado Sprin gs Utilities

– Martin Drake Power Plant

Air Quality Characterization : A mbient M onitoring or D ispersion M odeling R esults

SO2 Ambient Monitoring in El Paso County

Currently, there are four SO 2 monitoring locations in operation in Colorado, of which

one is lo cated in Colorado Springs at Highway 24 and 8 th Street (AQS

- ID: 08

- 041

- 0015). This site might be relocated in the future , depending on the results of any final modeling impact analysis and site availability

.

Historical m onitoring data for SO 2 in Colorad o Springs (and the rest of the state) never approached the level of any SO 2 standard prior to the installation of the Highway 24 monitor in January 2013. T here has been substantial SO 2 monitoring in the Colorado Springs area, with up to ten monitors opera ting during different periods between 1988

and 2007

. Table 2 below details the concentrations at the Highway 24 monitor over the past three years. This monitor has noted four total exceedances of the 75 ppb

stand ard since monit oring began in 2013 through the end of 2015. However, these

exceedances do not indicate nonattainment because the 99 th p ercentile value through

the end of 2015 remains below the 75 ppb 1

- ho ur NAAQS

, with the 2013

- 2015 design value at 56 ppb

. The last exceedance was in March 2015.

Table 2 : CDPHE Highway 24 Monitor Data (2013

- present)

AQS Site

ID Site

“Name” Address Year 1st Max 1

- hour (ppb) 2nd Max 1

-

h ou r (ppb) 99 th % 1

- hour

(ppb)

08

- 041

- 0015 Highway

24 690 W.

High way 24 2013 99 81 58

2014 83 57 57

2015 87 70 53

2013

- 2015 n/a n/a 56

Dispersion Modeling

The Division concluded that there was no available representative meteorological

dataset for the Drake Power Plant i n S e p t e m b e r 2 0 1 5 ( a n d p r o v i d e d E P A w i t h

a d d i t i o n a l i n f o r m a t i o n i n D e c e m b e r 2 0 1 5 )

. Colorado Springs Utilities ( CSU ) be gan gather ing representative meteorological data in October 2015

. At least o ne year of meteorological data will be collected . Subsequently, after the quality assurance process is completed for the entire year of acquired meteorological data, mo deling is anticipated to span about s i x mon ths . Consequently, the Division anticipates the final impact a nalysis to be complete in 2017.

Emissions

- Related Data

Martin Drake Power Plant

– SO 2 Emissions Analysis CSU is currently in the process of ins talling SO 2 control s on Units 6 and 7 to comply with Regional Haze S I P emission limits effective December 31, 2017 . The scrubber for Drake Unit 7 is installed and in testing phases while the scrubber for Unit 6 will begin operational testing at the end of 2016. E missions from the Drake Power Plant arePage 11 of 15

shown in Table 3 below (from the EPA Air Markets Program Data system )

. Additionally, t he CSU Board voted January 20, 2016 to decommission Drake Unit 5 by December 31, 2017. CSU plan s to accept a federal ly enforceable plant

- wide SO 2 emission limit of l e s s t h a n 2,000 tons per year per the DRR , effective on or before January 13, 2017 . This l i m i t will reduce a c t u a l SO 2 emissions by approximately 2,800

tons in the year 2017 (based on initial pre

- applicat ion meetings with the Division).

Table 3 : Martin Drake Power Plant SO 2 Emissions

Year* Unit Number of

Months Reported SO 2 Annual

Emissions (tons/year) SO 2 30

- day Rolling

Emission Rate (lb/MMBtu)

2012

5 12 1,108 0.52

2013 12 982 0 .49

2015 12 580 0.42

2012

6 12 1,680 0.55

2013 12 1,595 0.50

2015 12 1,448 0.47

2012

7 12 2,004 0.56

2013 12 2,004 0.51

2015 12 2,004 0.53

2012

All 12 4,707 0.56

2013 12 4,580 0.51

2015 12 3,960 0.45

2015** 6 & 7 12 3,452 0.47

* Drake Pow er Plant experienced a fire event that resulted in the units not operating for various periods

of time. Unit 6 was down for nine weeks. Unit 5 was down for 16 weeks. Therefore, 2014 is not

included in recent emission evaluations.

**This row is included since Unit 5 operated at 70% of average operating hours (years 2006

- 2013) in the year 2015 to give perspective regarding the operation of Units 6 and 7

.

SO 2 Emissions in El Paso County The most current comprehensive emission inventory avail able from Divis ion records for El Paso County indicates that approximately 99% of the 2013 SO 2 emissions in the county are from point sources. The Nixon Power Plant, approximately 15 miles away from Drake, is the only other significant SO 2 source in El Paso County, and contributed about 46% of point source SO 2 emissions in 2013 while Drake contributed 53%. As

discuss ed in the modeling section , air quality impacts from the Drake Power Plant

have not been estimated due to the lack of available representative meteorologica l

data. However, preliminary analysis indicates that SO 2 emission concentration gradients and potential hotspots from the Drake and Nixon Power Plants do not overlap because of geographical distance and terrain features that result in each plant existing in separate airsheds with regard to SO 2

.

Meteorology (Weather & Transport Patterns)

As noted , the Division determined there is not currently available representative meteorological da tasets for the transport and dispersion conditions at the Drake Power Plant. EPA agreed with this determination in its February 16, 2016 letter andPage 12 of 15

associated draft technical support document. The Division anticipates representative

meteoro logical data w ill be collected by the end o f 2016 that will then be quality

assured to be used for air dispersion modeling purposes along with allowing for the development of a representative annual wind rose for the Drake Power Plant

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

Fountain Creek and Monument Creek converge just to the west of the Drake Power Plant, which directly impact the plume and wind flows. The re are two prominent

terrain f eatures that affect wind conditions at the Drake P ower Plant: Pikes Peak approximately two miles to the west and the Palmer Divide approximately five miles

to the north.

Jurisdictional Boundaries

C learly defined legal boundaries can be used to determine an appr opriate geographic area regarding potential NAAQS impacts from the Martin Drake Power Plant. The city of Colorado Springs is the largest city in Colorado by land area , encom passing 194 square miles , and the second largest in population ( 4 4 5

, 8 3 0 a s o f 2 0 1 4 6 ) . M any scattered unincorporated county designated areas are enc losed within city limits

. The Drake Power P lant is located at the western edge of downtown Colorado Springs

. Therefore, it is appropriate to examine roadway intersections as major defining lines for the designation boundary since city limits extend much f arther east than the areas

t h a t monitoring, meteorological and topographical analyses suggest are being impacted. The Division also considers the city of Manitou Springs to be a clearly defined legal boundary that should be included in the designation a rea due to

Fountain Creek air flows and potential impacts i n t h e areas of the foothills.

Other Relevant Information

The Division used CDPHE’s public

- facing Community Health Equity Map (2010

- 2014 data) 7 to examine census

- tract level geographic disparities f or selected social determinants of health, including income/poverty levels and race/ethnicity population percentages, and key health conditions and outcomes, including asthma

related hospitalization rates, heart disease mortality rates, and preventable

con ditions. An example of these maps (income/poverty rates) is shown below in Figure 4

. Several areas in the southern area of the city clearly indicate above average poverty rates, increased minority populations as well as higher t han state averages for

asthma

- related hospitalization rates , heart disease mortality rates, and preventable condition hospitalization rates. The Division also reviewed population d ensity using this Map to incorporate appropriate potentially affected popul ations a n d a s s e s s

p o p u l a t i o n d e n s i t y i n t h e m o u n t a i n s w e s t o f M a n i t o u S p r i n g s a n d C o l o r a d o S p r i n g s

. This information is important in considerin g boundary area recommendations for a source located in an urbanized area with varied population factors.

6 All population statistics are from the United States Census Bureau.

7 http://www.cohealthmaps.dphe.state.co.us/cdphe_community_health_equity_map/

-Page 13 of 15

Figure 4 : CDPHE Community Health Equity Map Example (Income/Poverty Rate)

Conclusion

Upon consideration of the five factors and other relevant information, CDPHE recommends a boundary around a portion of the city of Colorado Springs, including enclosed unincorporated county areas, bounded to the north by East Woodmen Road,

N orth Academy Boulevard, and city limits, to the east by North/South Powers Boulevard, and to the south and west by city limits, with the addition of the ‘ census designated place ’ termed “Stratmoor” bounded by South Academy Boulevard for the designation bou ndary , shown in Figure 5 8 . This conclusion is ba sed on the following

information :

 Preliminary monitoring and emissions

- related data shows that this boundary incorporates the primary source (Martin Drake Power Plant) . Emissions f rom the only other notable SO 2 source in the vicinity are in a separate airshed ;

 Meteorological and topographical information indicate that potential impacts would be contained within this boundary;

 The mountains that generally begin just to the west of th e cities of Colorado Springs and Manitou Springs constitute a geographical boundary limit ;

 Basing the area boundary on the guideline 10 km radiu s for a modeling domain

is not appr opriate because of the complex terrain and urban demographics ;

 Affected popu lations, including sensitive subpopulations, within the city of Colorado Springs, including those living in unincorporated enclosed county areas, and the city of Manitou Springs are located within this boundary . EPA has previously approved area boundaries for other Round 2 SO 2 designation

8 C ity boundaries appl icable as of April 2016.Page 14 of 15

boundaries that align with roadways, rather than the outermost jurisdictional boundaries of a unit of local government 9

.

9 North Dakota Mercer County (portion) SO 2 Designation : road boundaries specified in Technical Support

Document (February 16, 2016)Page 15 of 15

Figure 5 : Martin Drake Power Plant Boundary Recommendation