Page 1 of 15 

# Technical Support Document

1

- Hour SO2 National Ambient Air Quality Standard
Recommended Air Quality Designations
for Specific Sources

September 18 , 2015

Colorado Department of Public Health and Environment
Air Pollution Control Division 4300 Cherry Creek Drive South Denver, Colorado 80246Page 2 of 15 

## Table of Contents

Introduction

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

Designation Recommendations

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

Overvi ew

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

History

................................ ................................ ................................ ................ 4
EPA Guidance on SO2 Designations

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

Future EPA SO2 Designations Process

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

## Analysis of Source Specific Designations

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

Public Service Company of Colorado

– Pawnee Power Plant

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

Pawnee Power Plant

– SO2 Emissions Analysis

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

SO2 Emissions in Morgan County

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

Modeling of Significant SO2 Emission Sources

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


### Colorado Springs Utilities

– Martin Drake Power Plant

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

Martin Drake Power Plant

– SO2 Emissions Analysis

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

SO2 Emissions in El Paso County

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

Modeling of Significant SO2 Emission Sources

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

SO2 Ambient Monitoring in El Paso County

................................ ................................ ......... 12Page 3 of 15 

# Introduction

Designation Recommendations

This Technical Support Document (TSD) provides the basis for the proposed source specific sulfur dioxide ( SO2 ) National Ambient Air Quality Standard (NAAQS) air quality designation
recommendations for the Public Service Company of Colorado

– Pawnee Power Plant and Colorado Springs Utilities

– Martin Drake Power Plant. The Division is requesting that the Air Quality Control Commission (Commission) recommend to the U.S. Environmental Protection Agency (EPA) that the nearby areas s urrounding both power plants be designated as unclassifiable as insufficient data and analysis is available to ascertain compliance with the 1

- hr SO2 NAAQS. The unclassifiable designation recommendations for both power plants will allow extra time to acqu ire more data to better analyze compliance with the SO2 standard.



### Overview

In 2010, the EPA promulgated a new NAAQS for SO2 as a 1

- hour average. The level was set at 75 p arts p er b illion (ppb) as the 3

- year average of the 9 9 th percentile 1

- hour daily maximum values. In 2011, Colorado submitted final recommendations of “attainment” and “attainment/unclassifiable” as applicable for all air quality control regions in the state. In August 2013, EPA promulgated a final rule establ ishing nationwide SO2 non

- attainment areas (none in Colorado) based on 2009

- 2011 monitoring data while acknowledging that EPA intended to address designations for other areas in separate future actions. EPA refers to the initial state designations based o n 2009

- 2011 SO2 monitoring data as “Round 1” designations.

In August 2013, the Sierra Club and Natural Resources Defense Council filed a complaint in federal District Court alleging that EPA failed to promulgate SO2 designations for all areas of the

countr y within the timeframe provided under the Clean Air Act ( Act ) . On March 2, 2015, a

Consent Decree was ordered that requires EPA to promulgate source specific designations on

certain SO2 sourc es no later than July 2, 2016

– this set of designations is refe rr ed to as “Round 2” designations. Th is section of the C onsent D ecree applies to any stationary source (1) emitting more than 16,000 t ons/year (t py ) of SO2 in 2012, or (2) emitting more than 2,600 tpy of SO2 and having an annual average emission rate of 0 .45 lbs SO2/MMBtu 1

1 MMBtu means one million British Thermal Units or higher in 2012.
Nationwide there are 6 8 coal

- fired power plants that are specifically listed in the C onsent

D ecree , including two in Colorado : Public Service Company of Colorado

– Pawnee Power Plant and Colorado Springs Utilities

– Martin Drake Power Plant. As a result of the Consent Decree,
states with certain affected sources meeting the criteria above must submit source specific designation recommendations, to assist EPA in promulgating “Round 2” designations, by September 18, 20 15 . The timing of the Consent Decree designation process does not provide
for consideration of post

- 2012 installed air pollution controls required pursuant to Regional

Haze State Implementation Plan.Page 4 of 15 

### History

Under the original annual and daily (24

- hour) S O2 standards (1971) there was extensive nationwide monitoring that indicated few SO2 non

- attainment problems ; accordingly, the nationwide SO2 monitoring network decreased in size from approximately 1,496 sites in 1980 to 488 sites operating in 2008. When the revised SO2 NAAQS was promulgated in 2010, only two SO2 monitors were operating in Colorado , both in the Denver Metro Area. Both monitors showed levels below the standard. Since there was very limited SO2 monitoring data on which to base designations , most of Colorado’s air quality control regions were recommended as “attainment/unclassifiable” during a public hearing of the Commission on March 17, 2011.

In response to the lack of SO2 monitoring data nationwide and associated concerns on whether large SO2 sources may emit levels exceeding the 1

- hour standard, EPA proposed the SO2 Data Requirements Rule (DRR) in May 2014 that solicit ed public comment on future monitoring or modeling requirements for large SO2 sources based on three proposed SO2 emission threshold options. The final SO2 NAAQS DRR was signed on August 10, 2015

. 

### EPA Guidance on SO2 Designations

In December of 2013, the EPA issued draft modeling guidance “SO2 NAAQS Designations Modeling Technical Assistance Document” (SO2 TAD Guidance) that provides direction to s tates on demonstrating compli ance with the SO2 NAAQS through modeling of source impacts. Unlike ambient monitoring, which requires 3 years of data acquisition to ascertain compliance with the NAAQS, m odeling provides for a rela tively quick conservative assessment of ambient air quality from stationary source impacts

. Ac cordingly, refined modeling is the preferred first approach to better characterize ambient air quality for both stationary source areas and the Division anticipa tes that refined modeling of the affected sources will be performed over an extended perio d likely spanning in to next year

.



### Future EPA SO2 Designations Process

Th e Data Requirements Rule establish es an SO2 emissions applicability threshold of 2,000 tons per year (tpy) that identifies priority sources subject to a source specific SO2 designations

process , referred to as “Round 3 ” designations . Th is process include s both the Public Service Company of Colorado

– Pawnee Power Plant and Colorad o Springs Utilities

– Martin Drake
Power Plant. S tates have three options under the DRR to characterize current air quality in areas with large SO2 sources (2,000 tpy or greater) : e stablish federally enforceable emission
limits (under 2,000 tpy) by January 13, 2017 ; conduct air quality modeling by January 13, 2017 ; or begin operating an appropriate monitoring network by January 1, 2017

. T he EPA will promulgate “Round 3” SO2 designations (by Court Order) no later than December 31, 2017

. F or

a ll other new monitored areas or remaining areas

, EPA will promulgate “Round 4” SO2 designations (by Court Order) no later than December 31, 2020. Consequently, the current
Division recommendat ion of unclassifiable for both power plants results in only a temp orary delay that will be resolved in future designation actions by EPA.Page 5 of 15 

# Analysis of Source Specific Designations

Public Service Company of Colorado

– Pawnee Power Plant

Pawnee Power Plant

– SO2 Emissions Analysis

T he March 2015 Consent Decree i dentified subject sources for inclusion in “ Round 2 ” designations based on 2012 continuous emissions monitoring data. In 2012 , the Pawnee Power
Plant had no SO2 controls aside from firing low

- sulfur coal 2

Table 1 ; consequently

, the facility ’s SO2

emissions were o ver the C onsent D ecree applicability threshold of 2,600 tpy a long with an annual average emission rate exceeding 0.45 lbs/MMBtu. In 2014, pursuant to Colorado’s Regional Haze SIP (approved by EPA in January 2013

, the Public Service Company of Colorado (PSCo) installed and commenced operation of a semi

- dry SO2 scrubber system (lime spray dryer) at the Pawnee Power Plant

. Pursuant to the Regional Haze SIP, t he scrubber system is subject to a federally enforceable permit limitation of 0.12 lbs/MMBtu based on a 30

- day rolling average emission rate. provides SO2 emissions data for the Pawnee Power Plant that is reported to the EPA Air Markets Program D ata system. As indicated in the below table, the recently installed semi

- dry SO2 scrub ber has result ed in a significant SO2 em ission
reduction of abou t 8 7 %.

Table 1 : Pawnee Power Plant SO2 Emissions

Year Number of Months Reported SO2 Annual Emissions (tons/year) SO2 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 ,7 00 ≈ 0.1 0 *SO2 lime spray dryer controls started in August 2014

SO2 Emissions in Morgan County

Table 2 includes the most current comprehensive emission inventory for Morgan County

, which
indicates that over 99 % of the 2013 SO2 emission s in Morgan 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 SO2 emissions in the future.

2 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.Page 6 of 15 Table 2 : 2013 SO2 Emission Inventory for Morgan County

Source Category SO2 Emissions ( tons/year )

Point Source 12, 575.3 Agriculture Burning 41.5
Railroad 8. 2

Motor Vehicles 2. 2

Non

- Road Vehicles 1. 0 Wood Burning 1. 0

Fuel Combustion 0.4

Oil & Gas Area 0. 4
Oil & Gas Point 0. 2
Aircraft 0. 1
Total: 1 2,6 30. 3

Table 3 includes the source specific emissions data from Air Pollutant Emissions Notice (APEN)
report s filed with the Division in the spring of 2014 using actual SO2 e missions data from 2013
or earlier. According to EPA Guidance 3

Table 3 : 2013 Point Source (Non

- Oil & Gas) SO2 Emissions for Morgan County on SO2 Designations Modeling, all sources expected to cause significant concentration gradients in the vicinity of the source of interest should be
evaluated. Based on a review of actual SO2 emissions in Morgan County , there are potentially

two significant SO2 sources (Western Sugar Cooperative and Cargill Meat Solutions) that need further evaluation for potential inclusion in a technical modeling analysis and demonstration
associated with the PSCo

– Pawnee Power Plant

.

Company 2013 Actual SO2 Emissions [tons/year]

Public Service Co

– Pawnee Power Plant * 12,46 7

. 55

Western Sugar Coop. 58.30 Cargill Meat Solutions 48.84 Brush Cogeneration Partners/Colorado Power 0. 18 Dairy Farmers of America, Inc. 0.16 City of Brush 0.16 Brushco Farms, Inc. 0.04 Brush Meat Processors, Inc 0.02

Public Service Co.

– Roundup Station 0.01 Heer Mortuary & Crematory 0.01 Leprino Foods Co. <0.01

Total: 12, 575 .3

* Includes 0.95 tpy from other sources at the facility

3 See Draft

- SO2 NAAQS Designations Modeling Technical Assistance Document , US EP A OAR

- OAQPS

- AQAD
December 2013Page 7 of 15 The Western Sugar Cooperative

– Fort Morgan Facility manufacture s sugar and sugar by

products from sugar beets in an annual 5

- month period that starts in about mid

- September. This period of operation, which can range from about 100 to 170 days and averages about 140 days, is called a “campaign”. During the campaign t he plant is in operation for 24 hours/day, seven days per week until all harvested beets have been processed . The facility has two
boilers 4 that fire low

- sulfur coal. In 1975, an application was made to convert the boilers from firing natural gas to coal and install a venturi scrubber system for controlling emissions. Each boiler was equipped with a venturi scrubber system . T he two boilers connect to common stack provided with a mist eliminator. The boilers do not have short

- term SO2 emission limits, but are subject to Regulation Number 1 emission limit of 1.8 lbs/MMBtu 5

Cargill Meat Solutions underwent a permit re newal in 2013 that specifies the SO2 emission limits. The facility has several boilers and a flare that fire either natural gas or bio

- gas, which results in some SO2 emissions. However, the SO2 emissions are emitted from a number of emission points at re latively low concentrations. Thus, this source is not expect ed to have a significant impact on the 1

- hr SO2 NAAQS in the local area. . According to EPA SO2 TAD Guidance, “air agencies may wish to conduct modeling using allowable or potential to emit (PTE) emi ssions.” In the situation of Western Sugar Cooperative, it is more appropriate to use actual emissions since the source only operates on a seasonal basis and the source PTE is much higher than actual emissions

.

Figure 1 identifies the three SO 2 sources to be evaluated. Cargill Meat Solutions is about 5.4 miles and Western Sugar Company is about 7.3 miles from the Pawnee Power Plant respectively.

Figure 1 : Significant SO2 Sources in Morgan County

4 Boiler manufacturer is Babcock & Wilcox with Detroit Stoker Model Rotograte RG

- 4. Each boiler is rated at 196 MMBtu/hour.

5 S ee Colorado Air Quality Control Commission (AQCC) Regulation Number 1, Section VI.A.3.a.(i)Page 8 of 15 Modeling of Significant SO2 Emission Source s In order to conduct the modeling necessary to predict the attainment status of the area surrounding the Pawnee Power Plant, the Division needs to develop appropriate short

- term
emission rates for the Pawnee Powe r Plant and the other two significant SO2 sources in
consultation with the sources and EPA. Since the SO2 NAAQS is an hourly standard, these
short

- term emission rates are necessary model inputs to properly characterize SO2 emissions that might impact the ambient air quality in Morgan County. Since controls have only recently been installed, PSCo is still acquiring short

- term emission rate data for Pawnee Power Plant.

T he Division anticipates that the refined modeling process could be completed in the nex t year

, which will provide information on the attainment status for SO2 air quality for Morgan County by the end of 2016

. 

### Colorado Springs Utilities

– Martin Drake Power Plant

Martin Drake Power Plant

– SO2 Emissions Analysis

The March 2015 Consent Decree i dentified subject sources to include in “Round 2” based on

2012 emission rates

. In 2012, the Martin Drake Power Plant had no SO2 controls, as ide from firing low

- sulfur coal 6

Drake Unit 5: 0.26 lb/MMBtu (30

- day rolling average) ; consequently the facilit y SO2 emissions were over the Consent Decree applicabil ity threshold of 2,600 tpy along with an annual average emission rate exceeding 0.45 lbs/MMBtu. Colorado Springs Utilities (CSU) is currently in the process of installing SO2
controls on Units 5, 6 and 7 to comply with Regional Haze emission limits

. At t he time of this analysis, CSU plans to install dry sorbent injection (DSI) on Unit 5 and lime spray dryers or equivalent on Units 6 and 7 with target control operational dates by December 31, 2016 and compliance dates no later than December 31, 2017 . CSU submitted a compliance schedule to the Division on March 28, 2013, which was published for public comment and subsequently approved by the Division on November 4, 2013 (for SO2 compliance

– the Division approved additional schedule changes for NOx in March 2015). The SO2 Best Available Retrofit Technology (BART) limits for the Martin Drake Power Plant are as follows:

Drake Unit 6: 0.13 lb/MMBtu (30

- day rolling average)

Drake Unit 7: 0.13 lb/MMBtu (30

- day rolling average)

Martin Drake Power Plant SO2 emissions by unit are indicated in Table 4 for the most recent three years of data that is reported to the EPA Air M arkets Program D ata system

.

6 The Martin Drake Power Plant generally fires a blend of sub

- bituminous and bituminous coal that has an average sulfur content ranging from 0.2 1 to 0. 53 percent from a variety of coal mines, including Power River Basin, ColoWyo, 20

- Mile Foidel Creek, and West Elk, located in western Colorado and Wyoming , based on 2006

- 2015
data

.Page 9 of 15 Table 4 : Martin Drake Power Plant SO2 Emissions

Year * Unit Number of
Months Reported SO2 Annual

Emissions (tons/year) SO2 30

- day Rolling Emission Rate (lb/MMBtu)

2012

5 12 1,108 0.52

2013 12 982 0.49 Average 1,045 0.51

2012

6 12 1,680 0.55

2013 12 1,595 0.50 Average 1,637 0.5 2

2012

7 12 2,004 0.56

2013 12 2,004 0.51 Average 2,004 0.5 3

2012 All 12 4,707 0.56

2013 12 4,580 0.51 Average 4,686 0.52

* * Drake Power Plant experienced a fire event that resulted in the unit s not operating for various periods of time

. Unit 6 was down for nine weeks. Unit 7 was down for 16 weeks. Therefore, 2014 is not included in recent
emission evaluations.
In comparison, the BART limits were based on emissions averaged from the years 2006

– 2008,
shown in Table 5

.
Table 5 : Martin Drake Power Plant BART baseline emissions (2006

- 2008)

Pollutant Unit 5 Unit 6 Unit 7
Annual
Emissions* (tpy) Annual
Emissions** (lb/MMBtu) Annual
Emissions* (tpy) Annual
Emissions** (lb/MMBtu) Annual
Emissions* (tpy) Annual
Emissions** (lb/MMBtu)

SO 2 1,269 0.63 2,785 0.82 4,429 0.83 *Using daily CEMs data from 2006

– 2008 calendar years

. **The Division calculated average emission rate (lb/MMBtu) from the 2006

- 2008 calendar years based on average daily reported data for each unit.

Emission differences between these two time frames are significan t. The percent in emission
reductions and resultant tons per year reductions (average of three years for 2006

– 2008 compared to 2012

– 201 3

, ) are listed below:

Drake Unit 5: 18% SO2 emission reduction (224 tons/year)

Drake Unit 6: 4 1 % SO2 emission re duction (1, 148 tons/year)

Drake Unit 7: 5 5 % SO2 emission reduction (2,4 25 tons/year)Page 10 of 15 There are several reasons for lower emissions in recent years: an overall increase in natural gas consumption, additional outages due to installation of Regional Haze controls, and a shift in coal types to lower sulfur coal 7

Drake Unit 5: 49% SO2 emission reduction . The emission l imits specified in the Regional Haze SIP will
result in further SO2 emission reductions from 2012

– 201 3 emissions. Using the most recent
two full years of data, the following perce nt emission reductions (from 2012

– 201 3 average) will occur by the end of 2017, based on the required 30

- day rolling average current emissions
and future limits:

Drake Unit 6: 7 5 % SO2 emission reduction

Drake U nit 7: 7 6 % SO2 emission reduction

SO2 Emissions in El Paso County
The 2013 emissions inventory is the most current inventory year that the Division has developed for El Paso County, except for motor vehicles, for which the most recent inventory is the year 2011. Table 6 below indicates that approximately 99% of emissions are from point

sources.

Table 6 : 2013 SO2 Emission Inventory for El Paso County

Source Category SO2 Emissions (tons/year)

Point Source 8,668.5

Motor Vehicles 30.5 Wood Burning 21.8
Aircraft 15.3

Railroad 9.6

Fuel Combustion 7.2

Non

- Road Vehicles 7.1 Agricultural Burning 0.3
Total: 8,760.4

Table 7 includes the source specific emissions data from Air Pollutant Emission Notice (APEN) reports filed with the Division in the spring of 2014 using actual SO2 emissions data from 2013
or earlie r. According to EPA Guidance 8

7 Sulfur content averaged 0.44% for 2006

- 2008 versus 0.25% for 2012

– June 2015 (plant

- wide). on SO2 Designations Modeling, all sources expected to cause significant concentration gradients in the vicinity of the source of interest should be
evaluated. The Nixon Power Plant , approximately 15 miles away from Drake, is t he only other significant SO2 source in El Paso County , and contributed about 46% of point source SO2
emissions in 2013 while Drake contributed 53%. As discussed in the modeling section below, air quality impacts from the Drake Power Plant have not been estimated due the lack of available representative meteorological data. When impacts from the Drake Power Plant are modeled, the Division will determine if contributions from Nixon and other off

- site sources to cumulative impacts need to be addressed.

8 See Draft

- SO2 NAAQS Designations Modeling Technical Assistance Document , US EPA OAR

- OAQPS

- AQAD
December 2013Page 11 of 15 Table 7 : 2013 Point Source (Non

- Oil & Gas) SO2 Emissions for El Paso County

Company 2013 Actu al SO2 Emissions ( tons/year )

Colorado Springs Utilities

- Martin Drake Power Plant 4,580.3 Colorado Springs Utilities

– Nixon Power Plant 3,955.1

Fort Carson US ARMY 34.5 Colorado Springs Utilities

– Clear Spring Ranch 23.6 Schmidt Construction Company

– Delta Drive Facility 23.2

Kiewet

– Colorado Springs Asphalt Plant 16.0

Martin Marietta Materials

– Fillmore 8.2

Schmidt Construction Company

– Menzer Facility 3.7 Penrose Community Hospital 3.7 U.S. Air Force Academy 2.5

Peterson Air Force Base 2.4

Homeward Bound 2.3 Rocky Mountain Materials & Asphalt Inc. 2.2

Fountain Landfill 1.6 Federal Express

– Colorado Tech 1.2 Fountain Valley Power

– Boca Raton 1.1 Pikes Peak Pet Crematory 1.0 Cheyenne Mountain Zoo 0.8 Holt Family Funeral Homes 0.7

UCH

- MHS Central 0.6

Hewlett

- Packard Corporation 0.6

Color Star Growers

– Peyton Greenhouse 0.6

Total: 8,668.5

*Sources reporting below 0.5 tpy were not included in this table due to extremely low emissions and contributions. This information is available upon request.

Modeling of Significant SO2 Emission Source s In EPA’s draft guidance on state implementation of the 1

- Hou r SO2 NAAQS (issued September 21, 2011), air quality modeling was identified as an alternative to monitoring for demonstrating

attainment. In October 2011, to prepare for this potential modeling exercise, the Division completed an asse ssment to determine if there was any available meteorological dataset(s) representative of transport and dispersion conditions at large stationary SO2 sources in
Colorado. The Division assesse s meteorological data repr esentativeness on the factors
discussed in Section 8.3 of EPA’s Guideline on Air Quality Models (40 CFR Part 51 Appendix W; November 2005). The only available meteorological data for the area is measured at the Colorado Springs Airport. Martin Drake Power Plant is located at the confluence of two large
creek d rainages, within and adjacent to terrain features that cause different meteorological conditions (e.g. wind directions/speeds, cloud cover) than at the Colorado Springs Airport.Page 12 of 15 Therefore , the D ivision concluded that there was no availab le representative meteorological
dataset for the Drake Power Plant.

The Division received air quality modeling from interested stakeholders regarding 1

- hour SO2 NAAQS compliance for the Drake Power Plant in October 2012 and September 2013. These modeling submittals use meteorological data from the Colorado Springs Airport. However,

m odeling with non

- representative meteorological data affects the magnitude an d location of impacts. T herefore, it would be inappropriate to base an attainment or nonattainment designation o n the modeling analyses submitted to the Division , which rely upon meteorological data from the Colorado Springs Airport, a non

- representative dataset

.

The Division is working with CSU to gather representative meteorological data. One year of meteorolog ical data will be collected and modeling is anticipated to require about 6 months to develop and finalize

. Consequently, the Division anticipates the final impact analysis to be complete in 2017.

SO2 Ambient Monitoring in El Paso County

The Division analy zed the potential to determine if the Drake Power Plant could be classified “attainment/nonattainment” based on current or historical ambient monitoring near the facility. Currently, there are four monitoring locations in operation in Colorado, of which o ne is located in Colorado Springs at Highway 24 and 8 th Street (AQS

- ID: 08

- 041

- 0015). This site may be relocated in the future when the Division approves a final modeling impact analysis based on maximum modeled impacts and siting relocation issues

.

Monitoring data for SO2 has never approached the level of any SO2 standard until this monitor was added in January 2013. Table 8 below details the concentrations at t he Highway 24 monitor over the past two years. This monitor has noted four total exceedances of the 75 ppb standard since monitoring began in 2013 through July 2015. However, the 99 th percentile value, as of July 2015, remains below the 75 ppb 1

- hour NAA QS at approximately 60 ppb (2015 data year is not complete).

Table 8 : CDPHE Highway 24 Monitor Data (2013

- present)

AQS Site ID Site
“Name” Address Year 1st Max 1

- hour 2nd Max 1

- hr 99 th % 1

- hour

08

- 041

-

0015 Highway 24 690 W. Highway 24 2013 99 81 58

2014 83 57 56
2015* 87 68 68 *Data year is from January 1, 2015

– July 15, 2015 (all data has not been QA/ QC ’ d )

Historically, there has been substantial SO2 monitoring in the Colorado Springs area , with up to ten monitors operating during different periods between 1988 and 2007, shown in Figure 2.Page 13 of 15 Figure 2 : Map of Historical and Current SO2 Monitoring Sites in Colorado Springs Metropolitan AreaPage 14 of 15 Monitors were dispersed across the metropolitan area, with multiple monitors located near the two major SO2 sources (Drake and Nixon Power Plants ) and one located at higher elevation (Chipita Park). The monitoring sites, operator, and years of operation are shown in Table 9

.

Table 9 : Historical and Current Colorado Springs Area Monitors

AQS Site ID Site “Name” Address Operator Operating Years

08

- 041

- 0015 Highway 24 690 W. Highway

24 CDPHE 2013

– present

08

- 041

- 6001 Nixon Base R.D. Nixon Power Plant (Exit 125 off

Interstate I

- 25) CSU 1988

– 2007

08

- 041

- 6002 Propane Air

- Plant 3550 Mark s heffel
Road CSU 1988

– 1990

08

- 041

- 6003 Nixon South R.D. Nixon Power Plan (Exit 123 off

Interstate I

- 25) CSU 1988

– 1991

08

- 41

- 6004 Woodmen 6000 Pulpit Rock

Drive CSU 1988

– 2007

08

- 41

- 6005 Pinello Ranch 4940 S. Highway 85/87 CSU 1988

– 1996

08

- 41

- 6006 Chipita Park 9400 Chipita Park
Road CSU 1988

– 1996

08

- 41

- 6009 Nixon North R.D. Nixon Power
Plan (Exit 123 off

Interstate I

- 25) CSU 1988

– 1996

08

- 41

- 6011 Colorado College 130 West Cache
La Poudre CSU 1989

– 2003

08

- 41

- 6013 Arvada Nevada 1699 S. Corona

Avenue CSU 1989

– 1996

08

- 41

- 6018 Sand Creek 4125 Center Park

Drive CSU 1997

– 2002

The monitors all showed widely variable concentration ranges from year to year. The two monitors closest to the Drake Power Plant (Colorado College and Arvada Nevada) ranged from 39 ppb for the lowest annual 1 st maximum value to 122 ppb for the highest. Moni tors located further from the power plants, but still within the Colorado Springs urban area (Woodmen, Pinello Ranch, Sand Creek, and Propane

- Air Plant) showed 1 st maximum values well below the standard, ranging from 10

- 20 ppb in some years to maximum valu es between 50

- 60 ppb in other years. These values were all recorded in the late 1990’s. The higher elevation site also
showed 1 st maximum values well below the standard, with the lowest at 18 ppb and the highest at 30 ppb. These values were recorded in the late 1980’s and mid 1990’s. It is important to
note that annual 99 th percentile values from all historical monitors near the Drake Power Plant never came close to exceeding the curren t 75 ppb NAAQS, with values lower for 3

- year 99 th
percentiles.Page 15 of 15 Si nce the majority of SO2 emissions in El Paso County are from the Drake and Nixon Power Plants, the Division assessed how SO2 emissions have changed from these sources since the historical monitoring period. Figure 3 and Figure 4 illustrate there has been a downward trend from both plants in past 20 years. This trend will continue due to Regional Haze SIP requirements for both plants. Although monitors are no longer dispersed throughout the Colorado Springs area, this information demonstrates that prior monitored values were below
the current 1

- hour SO2 standard and that SO2 emiss ion reductions have been both declining historically and will continue to decline in the future, resulting in lower ambient SO2

concentrations.

Figure 3 : Drake Power Plant Annual SO2 Emissions (tons/year) (1985

- 2014)

Figure 4 : Nixon Power Plant Annual SO2 Emissions (tons/year) (1985

- 2014) 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 100001985199019951996199719981999200020012002200320042005200620072008200920102011201220132014SO2 emissions (tons/year)

Year

0 1000 2000 3000 4000 5000 6000 7000 80001985199019951996199719981999200020012002200320042005200620072008200920102011201220132014SO2 emissions (tons/year)

Year