Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

1

Colorado Visibility and Regional Haze 

State Implementation Plan for the

Twelve Mandatory Class I Federal 

Areas in Colorado

Colorado Air Pollution Control Division

Revised Regional Haze Plan

Air Quality Control Commission, approved 01/07/2011
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

2

Table of Contents

Preface/Disclaimer........................................................................................................ 4

Chapter 1 Overview .................................................................................................. 5

1.1 Introduction .....................................................................................................................................5

1.2 Visibility Impairment........................................................................................................................7

1.3 Description of Colorado‟s Class I Areas .........................................................................................7

1.4 Programs to Address Visibility Impairment.....................................................................................8

1.5 Reasonable Progress Towards the 2064 Visibility Goals...............................................................9

2.1 Consultation with Federal Land Managers (FLM) ........................................................................10

2.2 Collaboration with Tribes ..............................................................................................................13

2.3 Consultation with Other States .....................................................................................................13

2.4 General Consultation....................................................................................................................14

Chapter 3 Monitoring Strategy............................................................................... 15

3.1 RAVI Monitoring Strategy in Current Colorado LTS.....................................................................15

3.2 Regional Haze Visibility Impairment Monitoring Strategy.............................................................16

3.3 Associated Monitoring Strategy Requirements ............................................................................17

3.4 Overview of the IMPROVE Monitoring Network...........................................................................18

3.5 Commitment for Future Monitoring...............................................................................................20

Chapter 4 Baseline and Natural Visibility Conditions in Colorado, and Uniform 

Progress for Each Class I Area.................................................................................. 22

4.1 The Deciview ................................................................................................................................22

4.2 Baseline and Current Visibility Conditions....................................................................................22

4.3 Monitoring Data ............................................................................................................................23

4.4 Natural Visibility Conditions ..........................................................................................................25

4.5 Uniform Progress..........................................................................................................................25

Chapter 5 Sources of Impairment in Colorado..................................................... 28

5.1 Natural Sources of Visibility Impairment.......................................................................................28

5.2 Anthropogenic Sources of Visibility Impairment ...........................................................................28

5.3 Overview of Emission Inventory System -TSS.............................................................................29

5.4 Emissions in Colorado..................................................................................................................29

Chapter 6 Best Available Retrofit Technology ..................................................... 39

6.1 Introduction ...................................................................................................................................39

6.2 Overview of Colorado‟s BART Regulation ...................................................................................39

6.3 Summary of Colorado‟s BART Determinations ............................................................................40

6.4 Overview of Colorado‟s BART Determinations ............................................................................45

Chapter 7 Visibility Modeling and Apportionment............................................. 102

7.1 Overview of the Community Multi-Scale Air Quality (CMAQ) Model..........................................102

7.2 CMAQ Modeling Results for 2018 ..............................................................................................102

7.3 Overview of Particulate Matter Source Apportionment Technology (PSAT) Modeling ..............103

7.4 PSAT Modeling Results for 2018 ...............................................................................................104

Chapter 8 Reasonable Progress.......................................................................... 106

8.1 Overview of Reasonable Progress Requirements .....................................................................106

8.2 Visibility Impairing Pollutants Subject to Evaluation ...................................................................106

8.3 Evaluation of Smaller Point and Area Sources of NOx for Reasonable Progress ....................109

8.4 Determination of Point Sources Subject to Reasonable Progress Evaluation ...........................112

8.5 Evaluation of Point Sources for Reasonable Progress ..............................................................116

Chapter 9 Long Term Strategy............................................................................. 147

9.1 LTS Requirements......................................................................................................................147

9.2 2004 RAVI Long-Term Strategy .................................................................................................148

9.3 Review of the 2004 RAVI LTS and Revisions ............................................................................151

9.4 Regional Haze Long Term Strategy ...........................................................................................151

9.5 Reasonable Progress Goals.......................................................................................................165
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

3

Chapter 10 Commitment to Consultation, Progress Reports, Periodic 

Evaluations of Plan Adequacy, and Future SIP Revisions .................................... 170

10.1 Future Consultation Commitments .........................................................................................170

10.2 Commitment to Progress Reports...........................................................................................171

10.3 Determination of Current Plan Adequacy ...............................................................................172

10.4 Commitment to Comprehensive SIP Revisions.....................................................................173

Chapter 11 Resource and Reference Documents.............................................. 175

List of Appendices – ................................................................................................. 176

Appendix A – Periodic Review of Colorado RAVI Long Term Strategy ................................................176

Appendix B – SIP Revision for RAVI Long Term Strategy....................................................................176

Appendix C – Technical Support for the BART Determinations............................................................176

Appendix D – Technical Support for the Reasonable Progress Determinations ..................................176
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

4

Preface/Disclaimer

The following document contains Colorado‟s State Implementation Plan for Regional 

Haze. Unless specifically stated in the text, all references to existing regulations or 

control measures are intended only to provide information about various aspects of the 

program described. Many of these controls are neither being submitted to EPA for 

approval nor being incorporated into the SIP as federally enforceable measures and are 

mentioned only as examples or references to Colorado air quality programs.

In developing and updating its Long Term Strategy (LTS) for reasonable progress, the 

State of Colorado takes into account the visibility impacts of several ongoing state 

programs that are not federally enforceable. These include statewide Colorado 

requirements applying to open burning, wildland fire smoke management, and 

renewable energy.

References in this SIP revision to such programs are intended to provide information 

that Colorado considers in developing its LTS and in its reasonable progress process. 

These programs are neither being submitted for EPA approval, nor for incorporation into 

the SIP by reference, nor are they intended to be federally enforceable. The Air Quality 

Control Commission Rules that govern them implement Colorado‟s programs and are 

not federally required. The state is precluded from submitting such programs for 

incorporation into this SIP by 25-7-105.1, C.R.S.

The following dates reflect actions by the Air Quality Control Commission associated 

with Colorado State Implementation Plan for Regional Haze:

Regional Haze Plan Approval Date

Original 12/21/2007

First Revision 12/19/2008

Second Revision

(Fully Replaces All Previous RH Plans)

01/07/2011
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

5

Chapter 1 Overview

1.1 Introduction 

The Clean Air Act (CAA) defines the general concept of protecting visibility in each of 

the 156 Mandatory Class I Federal Areas across the nation. Section 169A from the 

1977 CAA set forth the following national visibility goal:

“Congress hereby declares as a national goal the prevention of any future, 

and the remedying of any existing, impairment of visibility in mandatory 

Class I Federal areas which impairment results from man-made air 

pollution.”

The federal visibility regulations (40 CFR Part 51 Subpart P – Visibility Protection 

51.300 - 309) detail a two-phased process to determine existing impairment in each of 

the Class I areas; how to remedy such impairment; and how to establish goals to 

restore visibility to „natural conditions‟ by the year 2064. The federal regulations require 

states to prepare a State Implementation Plan (SIP) to:

include a monitoring strategy

address existing impairment from major stationary facilities (Reasonably 

Attributable Visibility Impairment)

prevent future impairment from proposed facilities

address Best Available Retrofit Technology (BART) for certain stationary sources

consider other major sources of visibility impairment

calculate baseline current and natural visibility conditions

consult with the Federal Land Managers (FLMs) in the development or change to 

the SIP

develop a long-term strategy to address issues facing the state

set and achieve reasonable progress goals for each Class I area

review the SIP every five years

Phase 1 of the visibility program, also known as Reasonably Attributable Visibility 

Impairment (RAVI), addresses impacts in Class I areas by establishing a process to 

evaluate source specific visibility impacts, or plume blight, from individual sources or

small groups of sources. Part of that process relates to evaluation of sources prior to 

construction through the Prevention of Significant Deterioration (PSD) permit program 

looking at major stationary sources. The plume blight part of the Phase 1 program also 

allows for the evaluation, and possible control, of reasonably attributable impairment 

from existing sources.

Section 169B was added to the Clean Air Act Amendments of 1990 to address Regional 

Haze. Since Regional Haze and visibility problems do not respect state and tribal 

boundaries, the amendments authorized EPA to establish visibility transport regions as 

a way to combat regional haze.

Phase 2 of the visibility program addresses Regional Haze. This form of visibility 

impairment focuses on overall decreases in visual range, clarity, color, and ability to 

discern texture and details in Class I areas. The responsible air pollutants can be 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

6

generated in the local vicinity or carried by the wind often many hundreds or even 

thousands of miles from where they originated. For technical and legal reasons the 

second part of the visibility program was not implemented in regulation until 1999. In 

1999 the EPA finalized the Regional Haze Rule (RHR) requiring States to adopt a State 

Implementation Plans (SIPs) to address this other aspect of visibility impairment in the 

Class I areas. Under current rules the Regional Haze SIP were to be submitted to the 

EPA by December 31st, 2007. Colorado adopted key components of the Regional Haze 

SIP in 2007 and 2008 which were submitted to EPA in 2008 and 2009, respectively. 

EPA subsequently noted deficiencies in the BART determination and Reasonable 

Further Progress elements, as well as other, more minor issues. Colorado has 

proceeded to take steps to remedy these alleged deficiencies. This SIP addresses

EPA‟s concerns. Updates to the BART evaluations and Reasonable Further Progress 

analyses constitute the major revisions to this 2010 plan. In addition, revisions to other 

chapters have been made to update emissions and monitoring data and descriptions of 

program changes impacting emissions regulations favoring improved visibility in the 

State.

The Regional Haze Rule envisions a long period, covered by several planning phases, 

to ultimately meet the congressionally established National Visibility Goal targeted to be 

met in 2064. Thus, the approach taken by Colorado, and other states, in preparing the 

plan is to set this initial planning period (2007-2018) as the “foundational plan” for the 

subsequent planning periods. This is an important concept when considering the nature 

of this SIP revision as compared to a SIP revision developed to address a 

nonattainment condition. The nonattainment plan must demonstrate necessary 

measures are implemented to meet the NAAQS by a specific time. On the other hand, 

the Regional Haze SIP must, among other things, set a Reasonable Progress Goal for 

each Class I area to protect the best days and to improve visibility on the worst days 

during the applicable time period for this SIP (2007-2018).

Colorado developed, and EPA approved, a SIP for the first Phase 1 of the visibility 

program. This Plan updates Phase 1 as well as establishing Phase 2 of the program, 

Regional Haze. The two key requirements of the Regional Haze program are:

Improve visibility for the most impaired days, and

Ensure no degradation in visibility for the least impaired days.

Though national visibility goals are targeted to be achieved by the year 2064,this plan is 

designed to meet the two requirements stated above for the period ending in 2018 (the 

first planning period in the federal rule), while also establishing enforceable controls to 

that will help to address the long term goal.

This SIP is intended to meet the requirements of EPA‟s Regional Haze rules that were 

adopted to comply with requirements set forth in the Clean Air Act. Elements of this 

Plan address the core requirements pursuant to 40 CFR 51.308(d) and the Best 

Available Retrofit Technology (BART) components of 40 CFR 50.308(e). In addition, 

this SIP addresses Regional Planning, State/Tribe and Federal Land Manager 

coordination, and contains a commitment to provide Plan revisions and adequacy 

determinations.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

7

1.2 Visibility Impairment

Most visibility impairment occurs when pollution in the form of small particles scatter or 

absorb light. Air pollutants come from a variety of natural and anthropogenic sources. 

Natural sources can include windblown dust and smoke from wildfires. Anthropogenic 

sources can include motor vehicles and other transportation sources, electric utility and 

industrial fuel burning, minerals, oil and gas extraction and processing and 

manufacturing operations. More pollutants mean more absorption and scattering of light 

which reduces the clarity and color of a scene. Some types of particles such as sulfates

scatter more light, particularly during humid conditions. Other particles like elemental 

carbon from combustion processes are highly efficient at absorbing light. Commonly, 

the receptor is the human eye and the object may be a single viewing target or a scene.

In the 156 Class I areas across the country, visual range has been substantially 

reduced by air pollution. In eastern parks, average visual range has decreased from 90 

miles to 15-25 miles. In the West, visual range has decreased from an average of 140 

miles to 35-90 miles. Colorado has some of the best visibility in the West but also has a 

number of areas where visibility is impaired due to a variety of sources. This SIP is 

designed to address regional haze requirements for the twelve mandatory Federal 

Class I areas in Colorado.

Some haze-causing particles are directly emitted to the air. Others are formed when 

gases emitted to the air form particles as they are transported many miles from the 

source of the pollutants. Some haze forming pollutants are also linked to human health 

problems and other environmental damage. Exposure to increased levels of very small 

particles in the air has been linked with increased respiratory illness, decreased lung 

function, and premature death. In addition, particles such as nitrates and sulfates 

contribute to acid deposition potentially making lakes, rivers, and streams less suitable 

for some forms of aquatic life and impacting flora in the ecosystem. These same acid 

particles can also erode materials such as paint, buildings or other natural and 

manmade structures.

1.3 Description of Colorado’s Class I Areas

There are 12 Mandatory Federal Class I Areas in the State of Colorado:

Black Canyon of the Gunnison National Park

Eagles Nest Wilderness Area

Flat Tops Wilderness Area

Great Sand Dunes National Park

La Garita Wilderness Area

Maroon Bells-Snowmass Wilderness Area

Mesa Verde National Park

Mount Zirkel Wilderness Area

Rawah Wilderness Area

Rocky Mountain National Park

Weminuche Wilderness Area

West Elk Wilderness Area
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

8

A detailed description of each of these areas, along with photographs, summaries of 

monitoring data containing an overview of current visibility conditions and sources of 

pollution in each area, is contained in individual Technical Support Documents (TSDs) 

for this plan (see list in Chapter 10). Each Class I area has been designated as 

impaired for visual air quality by the Federal Land Manager responsible for that area. 

Under the federal visibility regulations, the Colorado visibility SIP needs to address the 

visibility status of and control programs specific to each area. Figure 1-1 shows the 

location of these areas and the Inter-Agency Monitoring of Protected Visual 

Environments (IMPROVE) monitoring site that measures particulate air pollution 

representative of each Class I area.

Figure 1-1 Colorado Class I Areas and IMPROVE Monitor Locations

1.4 Programs to Address Visibility Impairment

Colorado adopted a Phase 1 visibility SIP to address the PSD permitting, source 

specific haze, and plume blight aspects of visibility in 1987. The most recent plan 

update was approved by the EPA in December 2006.

As stated in the preface to this Plan, unless specifically stated in the text, all references 

to existing regulations or control measures are intended only to provide information 

about various aspects of the program described and are neither being submitted to EPA 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

9

for approval nor being incorporated into the SIP as Federally enforceable measures. 

This comprehensive visibility plan, which now contains both Phase 1 and Phase 2 

visibility requirements, addresses all aspects of Colorado‟s visibility improvement 

program. Colorado has numerous emission control programs to improve and protect 

visibility in Class I areas. In addition to the traditional Title V, New Source Performance 

Standards, Maximum Achievable Control Technology and new source review permitting 

programs for stationary sources, Colorado also has Statewide emission control 

requirements for oil and gas sources, open burning, wildland fire, smoke management, 

automobile emissions for Front Range communities, and residential woodburning, as 

well as PM10 nonattainment/maintenance area requirements, dust suppression for 

construction areas and unpaved roads and renewable energy requirements.

Colorado adopted legislation to address renewable energy by establishing long-term 

energy production goals. This program is expected to reduce future expected and real 

emissions from coal-fired power plants. This renewable energy measure was 

considered a key feature of the Grand Canyon Visibility Transport Commission's 

recommendations. Although the Colorado renewable energy program was not 

specifically adopted to meet regional haze requirements, emissions from fossil-fuel fired 

electricity generation are avoided in the future.

Colorado is also setting emission limits (as part of this plan) for those sources subject to 

Best Available Retrofit Technology (BART) requirements of Phase 2 of the visibility 

regulations for Regional Haze (described in detail in Chapter 6 of this plan). To comply

with these BART limits sources subject to BART are required to install

and operate BART as expeditiously as practicable, but not later than 5 years after 

EPA‟s approval of the implementation plan revision.

As such, this Plan documents those programs, regulations, processes and controls 

deemed appropriate as measures to reduce regional haze and protect good visibility in 

the State toward meeting the 2018 and 2064 goals established in EPA regulations and 

the CAA.

1.5 Reasonable Progress Towards the 2064 Visibility Goals

As described in detail in Chapters 8 and 9 of this plan, reasonable progress goals for 

each Class I area have been established. The Division has worked with the Western 

Regional Air Partnership (WRAP) and with the WRAP‟s ongoing modeling program to 

establish and refine Reasonable Progress Goals (RPGs) for Colorado Class I Areas.

Technical analyses described in this Plan demonstrate emissions both inside and 

outside of Colorado have an appreciable impact on the State‟s Class I areas. Emission 

controls from many sources outside Colorado are reflected in emission inventory and 

modeling scenarios for future cases as detailed in the WRAP 2018 PRP18b control 

case. Progress toward the 2064 goal is determined based on emission control 

scenarios described in the WRAP inventory documentation plus the state‟s BART and 

reasonable progress determinations.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

10

Chapter 2 Plan Development and Consultation

This chapter discusses the process Colorado participated in to address consultation 

requirements with the federal land managers, tribes and other states in the Western 

Regional Air Partnership (WRAP) during the development of this Plan and future 

commitments for consultation.

Colorado has been a participating member of the WRAP since its inception. The WRAP 

completed a long-term strategic plan in 2003.1The Strategic Plan provides the overall 

schedule and objectives of the annual work plans and may be revised as appropriate. 

Among other things, the Strategic Plan (1) identifies major products and milestones; (2) 

serves as an instrument of coordination; (3) provides the direction and transparency 

needed to foster stakeholder participation and consensus-based decision making, which 

are key features of the WRAP process; and (4) provides guidance to the individual 

plans of WRAP forums and committees.

Much of the WRAP‟s effort is focused on regional technical analysis serving as the

basis for developing strategies to meet the RHR requirement to demonstrate 

reasonable progress towards natural visibility conditions in Class I national parks and 

wilderness areas. This includes the compilation of emission inventories, air quality 

modeling, and ambient monitoring and data analysis. The WRAP is committed to using 

the most recent and scientifically acceptable data and methods. The WRAP does not 

sponsor basic research, but WRAP committees and forums interact with the research 

community to refine and incorporate the best available tools and information pertaining 

to western haze.

2.1 Consultation with Federal Land Managers (FLM) 

Section 51.308(i) requires coordination between states and the Federal Land Managers

(FLMs). Colorado has provided agency contacts to the Federal Land Managers as 

required. In development of this Plan, the Federal Land Managers were consulted in 

accordance with the provisions of 51.308(i)(2). Specifically, the rule requires the State 

to provide the Federal Land Manager with an opportunity for consultation, in person,

and at least 60 days prior to holding any public hearing on an implementation plan or 

plan revision for regional haze. This consultation must include the opportunity for the 

affected Federal Land Managers to discuss their assessment of impairment of visibility 

in any mandatory Class I Federal area and recommendations on the development of the 

reasonable progress goal and on the development and implementation of strategies to 

address visibility impairment. The State must include a description of how it addressed 

any comments provided by the Federal Land Managers. Finally, the plan or revision 

must provide procedures for continuing consultation between the State and Federal 

Land Manager on the implementation of the visibility protection program required 

including development and review of implementation plan revisions and 5-year progress 

reports, and on the implementation of other programs having the potential to contribute 

to impairment of visibility in mandatory Class I Federal areas.

 

1

See http://www.wrapair.org/forums/sp/docs.html
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

11

Colorado participated in the WRAP to develop many elements of the SIP. The WRAP 

represents a conglomeration of stakeholder representing FLMs, industry, States, Tribes 

environmental groups and the general public. Through participation in this process, a 

significant portion of the consultation process with FLMs and other states has been met. 

In the WRAP process these stakeholders participated in various forums to help develop 

a coordinated emissions inventory and analysis of the impacts sources have on regional 

haze in the west. Coordination and evaluation of monitoring data and modeling 

processes were also overseen by WRAP participants. Through these coordinated 

technical evaluations, a regional haze-oriented evaluation of Colorado's Class I areas 

was constructed. Summaries of this information are available in the technical support 

documents of this Plan.

Public meetings were held at the Colorado Air Quality Control Commission in 2007 and 

2008 to provide a comprehensive review of the technical basis for the Plan. Following 

these meetings, additional meetings were held with the FLMs directly concerning each 

of the affected Class I areas and the development of the SIP. Prior to the requests for a 

public hearing on the Regional Haze SIP in August and September 2010, the Division 

again met with the FLMs to review additions, corrections and changes to the SIP made 

to address both FLM concerns over the analysis of additional controls on sources not 

subject to BART and the completion of BART analyses occurring after the 2008 

hearings (these new analyses and inventories are reflected later on in this SIP

document).

The FLMs have provided comments to the Division regarding proposed regional haze 

determinations over the course of several years in 2007 and 2008, and again in 2010. 

The state has carefully considered these comments and has made changes to many of 

its proposed determinations based in part on these comments. For example, the state 

has deleted its regulatory prohibition on consideration of post-combustion controls as 

part of the BART analysis. The state also revisited its earlier BART determinations that 

relied in some respects on EPA‟s so called „presumptive‟ emission limits for NOx and 

SO2, and in turn conducted robust facility-specific 5 and 4 factor analyses under BART 

and RP.

Most recently, the FLMs formally commented on the revised, proposed BART and RP 

determinations, as well as reasonable progress goals, in November and December 

2010. The National Park Service, the Fish and Wildlife Service and the U.S. Forest 

Service provided support for the modeling approach used by the state in the BART 

determinations, complimented the state on thorough 5 and 4 factor analyses, clear 

criteria, area source evaluations, and comprehensive/improved BART and RP 

determinations, and presented recommendations for cost/emission limit re-evaluations. 

The state appreciates the supportive input from the FLMs, especially in the areas of 

modeling and the establishment of the RPGs. The state gave serious consideration to 

the recent recommendations for revising cost estimates and lowering emission limits, 

but the comments ultimately did not alter the state‟s conclusions and resulting 

proposals.

Regarding the costs of control, the FLMs provided numerous recommendations for 

revising BART and RP control costs. The state notes that there is no regulatory 

approach for determining costs of controls. The state considered the relevant factors 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

12

for BART and RP determinations as set forth in the statute, the regulations and 

guidance, and consistent with the discretion expressly afforded to states under the 

statute and regulations. The state received detailed source-specific information for the 

facilities evaluated, checked this information using many different resources, and made 

adjustments/normalization when appropriate. The state employed engineering 

judgment and discretion when preparing BART and RP determinations, and found that 

the relevant present day and estimated future costs generally fell within the range of 

typical control costs nationwide. The state considered broader cost survey information 

to be relevant, and considered such information but did not find it dispositive; the state 

was informed more on facility-specific information as provided to the state to support its 

analyses and determinations. For most facilities even if different cost assumptions were 

employed or were re-assessed, expected visibility from the relevant control did not 

satisfy the state‟s guidance criteria for visibility improvement, and thus would not 

change the state‟s determination. Further, the state finds metrics like dollar per kilowatt 

hours or dollar per deciview of improvement of limited utility in considering the 5 or 4 

factors, and opted to use its own more straightforward approach to balance and weigh 

costs of control and related visibility improvement. The costs used by the state were 

determined to be appropriate and reasonable, were balanced with the state‟s 

consideration of related visibility improvement, and further revisions based on FLM 

comments were not incorporated. The resulting emissions reductions from the state‟s 

BART and RP determinations for NOx and SO2 are significant and will benefit Class I 

Areas.

Regarding CALPUFF modeling, the FLMs provided support for the state‟s BART and 

RP modeling efforts, including the modeling protocol and methodologies. However, the 

state respectfully disagrees with the FLMs recommendations to cumulate visibility 

improvement impacts from emission controls across multiple Class I Areas. It is the 

state‟s position that the approach employed is consistent with a straightforward 

application of the regional haze regulation, and that the approach suggested by the 

FLMs, while an option that could be considered, as a general rule is not appropriate. 

The Commission in making its determinations on certain BART sources was aware that 

emissions reductions would have some level of visibility improvement in other than the 

most impacted Class I Area. The CALPUFF modeling output files have been and 

continue to be available to the FLMs or to the public to perform such analyses.

Regarding BART and RP emission limits, the FLMs provided numerous comments to 

the state, identifying opportunities for tightening most of the proposed limits. The state 

notes that there is no regulatory formula for establishing limits in the Regional Haze rule 

and the state applied professional judgment and utilized appropriate and delegated

discretion in establishing appropriate emission limits. The stringency of the limits are 

tight enough to satisfy BART and RP requirements, but are not operationally 

unachievable. The emission limits fall within the range of limits adopted nationwide and 

were developed considering the requirements of the Regional Haze rule and related 

guidance.

Thus, between the WRAP, AQCC and individual meetings with the FLMs, the State has 

met the FLM consultation requirements.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

13

Colorado commits to continued coordination and consultation with the Federal Land 

Managers during the development of future progress reports and Plan revisions, in 

accordance with the requirements of 51.308(i)(4).

2.2 Collaboration with Tribes 

The Southern Ute Tribal lands in the southwest corner of Colorado are adjacent to 

Mesa Verde National Park, one of Colorado's Class I areas. As described above, 

Colorado participated in the collaborative WRAP process where Tribes were 

represented in all levels of the process. In addition, the Colorado Air Quality Control 

Commission had joint meetings with the Tribal Air Quality Council concerning regulatory 

and other processes related to air quality control and planning. The Southern Ute Tribe 

has numerous major and minor sources operating on their lands. Major source 

permitting is coordinated through a joint agreement with EPA Region IX. Minor sources 

on Tribal lands in Colorado are subject to the jurisdiction of the Tribes and this Plan 

contains no regulatory provisions for sources on Southern Ute lands in Colorado. The 

Tribes have the opportunity to develop Tribal Implementation Plans to address sources 

of pollution impacting visibility in their area.

2.3 Consultation with Other States

Pursuant to 40 CFR Section 51.308(d)(iv), Colorado consulted with other states during 

ongoing participation in the Regional Planning Organization, the Western Regional Air 

Partnership (WRAP), in developing the SIP. The WRAP is a collaborative effort of tribal 

governments, state governments and various federal agencies to implement the Grand 

Canyon Visibility Transport Commission's recommendations and to develop the 

technical and policy tools needed by western states and tribes to comply with the U.S. 

EPA's regional haze regulations. The WRAP is administered jointly by the Western 

Governors' Association and the National Tribal Environmental Council. WRAP activities 

are conducted by a network of committees and forums composed of WRAP members 

and stakeholders who represent a wide range of viewpoints. The WRAP recognizes 

that residents have the most to gain from improved visibility and that many solutions are 

best implemented at the local, state, tribal or regional level with public participation. 

Alaska, Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, North 

Dakota, Oregon, South Dakota, Utah, Washington, and Wyoming have agreed to work 

together to address regional haze in the western United States. Colorado held specific 

discussions with states that have a primary impact on Colorado Class I areas. These 

include California, Utah, New Mexico and Arizona regarding the impacts from sources in 

these states on Colorado Class I areas.

The major amount of state consultation in the development of SIPs was through the 

Implementation Work Group (IWG) of the WRAP. Colorado participated in the IWG 

which took the products of the WRAP technical analysis and consultation process 

discussed above and developed a process for establishing reasonable progress goals 

in the western Class I areas. A description of that process is discussed in Chapter 8 --

Reasonable Progress Section of the State SIP.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

14

Through the WRAP consultation process Colorado has reviewed and analyzed 

contributions from other states that reasonably may cause or contribute to visibility 

impairment in Colorado‟s Class I areas. While emissions from sources outside of 

Colorado have resulted in a slower rate of improvement in visibility than the rate that 

would be needed to attain natural conditions by 2064, most of these emissions are 

beyond the control of any state in the regional planning area of the WRAP. The 

emission sources include: emissions from outside the WRAP domain; emissions from

Canada and Mexico; emissions from wildfires and windblown dust; and emissions from 

offshore shipping. Colorado anticipates that the long-term strategies when adopted by 

other states in their SIPs and approved by EPA will include emission reductions from a

variety of sources that will reduce visibility impairment in Colorado‟s Class I areas.

Colorado‟s analysis of interstate impacts from specific nearby sources indicated the 

need for specific consultation with Nebraska, Wyoming, Utah, New Mexico and Arizona 

and California. In Nebraska the Gerald Gentleman Power Plant was analyzed for BART 

as part of the Nebraska RH process. Colorado commented to the State of Nebraska on 

this BART determination since emissions from this plant were indicated to impact Rocky 

Mountain National Park. Colorado similarly communicated with the State of Wyoming 

concerning BART determinations for its sources since impacts from Wyoming power 

plants were indicated to impact the Mt. Zirkel Wilderness Area. Colorado participated in 

the Four Corners Task force with Utah, New Mexico and Arizona and Tribal 

representatives to identify sources in the region adversely affecting air quality in the 

region. One element of that process was to consider sources impacting Mesa Verde or 

other Colorado Class I areas specifically for regional haze purposes. Through this 

process these States were made aware of Colorado‟s concerns about emissions from 

the Four Corners Power Plant, as it significantly impacts Mesa Verde. EPA Region IX 

was notified of Colorado‟s concerns with this facility since they are responsible for 

issuing and overseeing permits on this facility. Finally, California was contacted to 

discuss NOx emissions impacting Colorado Class I areas. California identified 

measures being taken in the State to reduce NOx emissions from mobile and other 

sources. Additional details concerning the Four Corners Task Force can be found in 

Section 9.5.5.3 of this Regional Haze SIP.

During the 2010 public hearing process, Colorado provided notification to the WRAPmember states and to other nearby states that a Regional Haze SIP revision had been 

prepared and invited review and comment on the plan and supporting documents.

By participating in the WRAP and the Four Corner‟s Task Force, and through specific

comments and communications with the participating states, Colorado has satisfied the 

state consultation requirement.

2.4 General Consultation

As part of the regional haze SIP development process Colorado will continue to 

coordinate and consult with parties as summarized in the long-term strategy described 

in Chapter 9.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

15

Chapter 3 Monitoring Strategy 

Federal regulations in 40 CFR 51.305 and 51.308(d)(4) require states to have a 

monitoring strategy in the SIP sufficient to characterize reasonable progress at each of 

the Class I areas, specifically Phase 1: reasonably attributable visibility impairment 

(RAVI) and Phase 2: regional haze visibility impairment in federal Class I areas within 

the state. Because Colorado adopted a visibility SIP to address the Phase 1 

requirements (51.305), a monitoring strategy is currently in place through an approved 

SIP. The State of Colorado utilizes data from the IMPROVE monitoring system which is 

designed to provide a representative measure of visibility in each of Colorado's Class I 

areas.

3.1 RAVI Monitoring Strategy in Current Colorado LTS

States are required by EPA to have a monitoring strategy for evaluating visibility in any 

Class I area by visual observation or other appropriate monitoring techniques. The 

monitoring strategy in the RAVI LTS is based on meeting the following four goals:

1. To provide information for new source visibility impact analysis.

2. To determine existing conditions in Class I areas and the source(s) of any certified 

impairment.

3. To determine actual affects from the operation of new sources or modifications to 

major sources on nearby Class I areas.

4. To establish visibility trends in Class I areas to evaluate progress towards meeting 

the national visibility goal.

Potential new major source operators must conduct visibility analyses utilizing existing 

visibility data. If data are adequate and/or representative of the potentially impacted 

Class I area(s), the permit holder will be notified of the visibility levels against which 

impacts are to be assessed. If visibility data are not adequate, pre-construction 

monitoring of visibility may be required.

If the Federal Land Managers (FLMs) or the State of Colorado certifies existing 

impairment in a Class I area, the Division will determine if emissions from a local 

source(s) operator(s) can be reasonably attributed to cause or contribute to the 

documented visibility impairment. In making this determination the Division will consider 

all available data including the following:

1. Data supplied by the FLM;

2. The number and type of sources likely to impact visibility in the Class I area;

3. The existing emissions and control measures on the source(s);

4. The prevailing meteorology near the Class I area; and

5. Any modeling that may have been done for other air quality programs.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

16

If available information is insufficient to make a decision regarding "reasonable 

attribution" of visibility impairment from an existing source(s) the State will initiate 

cooperative studies to help make such a determination. Such studies could involve the 

FLMs, the potentially affected source(s), the EPA, and others.

The monitoring strategy also included a commitment from the State to sponsor or share 

in the operation of visibility monitoring stations with FLMs as the need arises and 

resources allow.

The State commits to periodically compile information about visibility monitoring 

conducted by various entities throughout the State and assembling and evaluating 

visibility data.

Colorado law (C.R.S. 25-7-212(3)(a)) requires the federal land management agencies 

of Class I areas in Colorado (i.e., U.S.D.I. National Park Service and U.S.D.A. Forest 

Service) to “develop a plan for evaluating visibility in that area by visual observation or 

other appropriate monitoring technique approved by the federal environmental 

protection agency and shall submit such plan for approval by the division for 

incorporation by the commission as part of the state implementation plan.” The 

agencies indicated they developed, adopted, and implemented a monitoring plan 

through the Class I visibility monitoring collaborative known as IMPROVE. EPA‟s 

Regional Haze Rule (40 CFR 51.308(d)(4)) indicates, “The State must submit with the 

Implementation Plan a monitoring strategy for measuring, characterizing, and reporting 

regional haze visibility impairment representative of all mandatory Class I Federal 

areas within the State....Compliance with this requirement may be met through 

participating in the Interagency Monitoring of Protected Visual Environments 

[IMPROVE] network.” The federal agencies‟ monitoring plan relies on this network and 

ensures each Class I area in Colorado will have a monitor representative of visibility in 

the Class I area. In the LTS revision, submitted to EPA in 2008, the Division provided 

letters from the federal land managers and approval letters from the Division indicating 

this requirement was being met.

3.2 Regional Haze Visibility Impairment Monitoring Strategy

Under 40 CFR 51.308(d), a State must develop a monitoring strategy in the RH SIP to 

measure, characterize, and report regional haze visibility impairment representative of 

all federal Class I areas within the State. This monitoring strategy must be coordinated 

with the monitoring strategy described in Section 3.1 above, and will be met by 

participating in the IMPROVE network.

Colorado‟s monitoring strategy is to participate in the IMPROVE monitoring network. To 

insure coordination with the RAVI monitoring strategy, it includes the same four goals as 

in the RAVI LTS plus an additional goal:

To provide regional haze monitoring representing all visibility-protected federal 

Class I areas
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

17

3.3 Associated Monitoring Strategy Requirements

Other associated monitoring strategy requirements in 40 CFR 51.308(d)(4) and 

Colorado‟s associated SIP commitment are enumerated below:

1. Establishment of any additional monitoring sites or equipment to evaluate 

achievement of reasonable progress goals [40 CFR 51.308(d)(4)(i)].

a. Colorado will work collaboratively with IMPROVE, EPA, the Federal Land 

Managers and other potential sponsors to ensure that representative 

monitoring continues for all of its Class I areas. If necessary, additional 

monitoring sites or equipment will be established to evaluate the achievement 

of reasonable progress goals.

b. If funding for a site(s) is eliminated by EPA, the Division will consult with FLMs 

and IMPROVE to determine the best remaining site to use to represent the 

orphaned Class I areas.

2. Procedures describing how monitoring data and other information are used in 

determining the State‟s contribution of emissions to visibility impairment in any 

federal Class I area [40 CFR 51.308(d)(4)(ii)].

a. Colorado has participated extensively in the WRAP. One of the Regional 

Modeling Center (RMC) tools is the PSAT (PM Source Apportionment 

Technology) that relates emission sources to relative impacts at Class I areas. 

Details about PSAT are contained in the Technical Support Documents for 

each Class I area. Colorado will utilize the PSAT method and other models as 

needed and recommended by EPA modeling guidance for visibility evaluations, 

or other tools, to assist in determining the State‟s emission contribution to 

visibility impairment in any federal Class I area. As part of this process the 

State commits to consult with the EPA and FLMs or other entities as deemed 

appropriate when using monitoring and other data to determine the State‟s 

contribution of emissions to impairment in any Class I area.

b. Colorado will continue to review monitoring data from the IMPROVE sites and 

examine the chemical composition of individual specie concentrations and 

trends, to help understand the relative contribution of emissions from upwind 

states on Colorado Class I areas and any contributions from Colorado to 

downwind Class I areas in other states. This will occur no less than every five 

years in association with periodic SIP, LTS and monitoring strategy progress 

reports and reviews.

3. Provisions for annually reporting visibility monitoring data to EPA [40 CFR 

51.308(d)(4)(iv)].

a. IMPROVE data are centrally compiled and made available to EPA, states and 

the public via various electronic formats and websites including IMPROVE 

(http://vista.cira.colostate.edu/improve/) and VIEWS 

(http://vista.cira.colostate.edu/views/)Through participation in the IMPROVE 

network, Colorado will partially satisfies the requirement to annually report to 

EPA visibility data for each of Colorado‟s Class I areas.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

18

b. An annual compilation of the Colorado data will be prepared and reported to 

the EPA electronically.

4. A statewide emissions inventory of pollutants reasonably expected to cause or 

contribute to visibility impairment for a baseline year, most recent year data is 

available, and future projected year [40 CFR 51.308(d)(4)(v)].

a. Section 5.4 of this Plan includes a summary of Colorado statewide emissions 

by pollutant and source category. The inventory includes air pollution sources 

that can reasonably be expected to cause or contribute to visibility impairment 

to federal Class I areas.

i. The WRAP-developed Plan02d (March 2008) inventory is both the baseline 

and most recent year of data available for a statewide inventory. It is an 

inventory intended to represent typical annual emissions during the baseline 

period, 2000-2004. From the baseline/current inventory, projections were 

made to 2018. The WRAP‟s 2018 Base Case or PRP18b inventory was 

utilized for final model projections. This represented the most recent BART 

determinations reported by the States and EPA offices, projection of future 

fossil-fuel electric generation plants, revised control strategy rulemaking and 

updated permit limits for point and area sources in the WRAP region as of 

Spring 2009 (http://www.wrapedms.org/InventoryDesc.aspx). The emission 

inventory information was collaboratively developed between Division staff 

and the WRAP. A summarized western state and boundary condition 

inventory is available at: 

http://vista.cira.colostate.edu/TSS/Results/emis_smry_p02c_b18b_a5.xls

5. Commitment to update the emissions inventory [40 CFR 51.308(d)(4)(v)].

a. Colorado will update its portion of the regional inventory, on the tri-annual cycle 

as dictated by the Air Emissions Reporting Rule (AERR) (see section 3.5) in 

order to track emission change commitments and trends as well as for input to 

regional modeling exercises.

6. Any additional reporting, recordkeeping, and measures necessary to evaluate and 

report on visibility [40 CFR 51.308(d)(4)(vi)].

a. Colorado will provide any additional reporting, recordkeeping and measures 

necessary to evaluate and report on visibility but is unaware of the need for any 

specific commitment at this time beyond those made in this section and in the 

LTS section.

3.4 Overview of the IMPROVE Monitoring Network

In the mid-1980‟s, the IMPROVE program was established to measure visibility 

impairment in mandatory Class I Federal areas throughout the United States. The 

monitoring sites are operated and maintained through a formal cooperative relationship 

between the EPA, National Park Service, U.S. Fish and Wildlife Service, Bureau of 

Land Management, and U.S. Forest Service. In 1991, several additional organizations 

joined the effort: State and Territorial Air Pollution Program Administrators and the 

Association of Local Air Pollution Control Officials, Western States Air Resources 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

19

Council, Mid-Atlantic Regional Air Management Association, and Northeast States for 

Coordinated Air Use Management.

The objectives of the IMPROVE program include establishing the current visibility and 

aerosol conditions in mandatory Class I federal areas; identifying the chemical species 

and emission sources responsible for existing human-made visibility impairment; 

documenting long-term trends for assessing progress towards the national visibility 

goals; and support the requirements of the federal visibility rules by providing regional 

haze monitoring representing all visibility-protected federal Class I areas where 

practical.

The data collected at the IMPROVE monitoring sites are used by land managers, 

industry planners, scientists, consultants, public interest groups, and air quality 

regulators to better understand and protect the visual air quality resource in Class I 

areas. Most importantly, the IMPROVE Program scientifically documents for American 

citizens, the visual air quality of their wilderness areas and national parks.

In Colorado, there are six IMPROVE monitors that are listed under the site name in 

Figure 3-1. As shown, some monitors serve multiple Class I areas. For example, the 

monitor with site name Mount Zirkel is located just south of the Mount Zirkel Wilderness 

Area (on Buffalo Pass) but this monitor is also designated to represent the Rawah 

Wilderness Area.

Figure 3-1 Colorado Class I Areas and IMPROVE Monitor Locations

Figure 3-2 includes summary information for each IMPROVE monitor. The National 

Park Service (NPS) and the U.S. Forest Service (USFS) each operate and maintain 

three IMPROVE monitors in the State.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

20

Figure 3-2 Colorado IMPROVE Monitoring Site Information

Mandatory Class I Federal Area

Operating 

Agency

IMPROVE 

Monitor

Elevation 

[ft] Start Date

Great Sand Dunes National Park NPS GRSA1 8,215 5/4/1988

Mesa Verde National Park NPS MEVE1 7,142 3/5/1988

Mount Zirkel Wilderness USFS MOZI1 10,640 7/30/1994 Rawah Wilderness

Rocky Mountain National Park NPS ROMO1 9,039 9/19/1990

Weminuche Wilderness

Black Canyon of Gunnison NP USFS WEMI1 9,072 3/2/1988

La Garita Wilderness

Eagles Nest Wilderness

USFS WHRI1 11,214 7/17/2000 Flat Tops Wilderness

Maroon Bells-Snowmass Wilderness

West Elk Wilderness

3.5 Commitment for Future Monitoring

The State commits to continue utilizing the IMPROVE monitoring data and emission 

data to track reasonable progress. The State commits to providing summary visibility 

data in electronic format to the EPA on an annual basis from the IMPROVE monitoring, 

or other relevant sites. Also, the State commits to continue developing updated 

emission inventories on a tri-annual basis as required under the Air Emissions 

Reporting Rule sufficient to allow for the tracking of emission increases or decreases 

attributable to adopted strategies or other factors such as growth, economic downturn, 

or voluntary or permit related issues. These monitoring and emissions data will be 

available for electronic processing in future modeling or other emission tracking 

processes. Information collected from the monitoring system and emission inventory 

work will be made available to the public.

Colorado will depend on the Inter-Agency Monitoring of Protected Visual Environments 

(IMPROVE) monitoring program2to collect and report aerosol monitoring data for 

reasonable progress tracking as specified in the Regional Haze Rule (RHR). Because 

the RHR is a long-term tracking program with an implementation period nominally set 

for 60 years, the state expects the configuration of the monitors, sampling site locations, 

laboratory analysis methods and data quality assurance, and network operation 

protocols will not change, or if changed, will remain directly comparable to those 

operated by the IMPROVE program during the 2000-04 RHR baseline period. 

Technical analyses and reasonable progress goals in RHR plans are based on data 

from these sites. The state must be notified and agree to any changes in the IMPROVE 

program affecting the RHR tracking sites, before changes are made. Further, the state 

notes resources to operate a complete and representative monitoring network of these 

long-term reasonable progress tracking sites is currently the responsibility of the 

Federal government. Colorado is satisfying the monitoring requirements by participating 

in the IMPROVE network. Colorado will continue to work with EPA in refining monitoring 

 

2

http://vista.cira.colostate.edu/improve/ 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

21

strategies as new technologies become available in the future. If resource allocations 

change in supporting the monitoring network the state will work with the EPA and FLMs 

to address future monitoring requirements.

Colorado depends on IMPROVE program-operated monitors at six sites as identified in 

Figures 3.1 and 3.2 for tracking RHR reasonable progress. Colorado will depend on the 

routine timely reporting of monitoring data by the IMPROVE program for the reasonable 

progress tracking sites. Colorado commits to provide a yearly electronic report to the 

EPA of representative visibility data from the Colorado sites based on data availability 

from this network.

As required under 40 CFR 51.308(d)(4)(v) the State of Colorado has prepared a 

statewide inventory of emissions reasonably expected to cause or contribute to visibility 

impairment in Federal Class I Areas. Section 5.4 of this Plan summarizes the 

emissions by pollutant and source category.

The State of Colorado commits to updating statewide emissions on a tri-annual basis as 

required under the December 17, 2008 Air Emissions Reporting Rule (AERR). The 

updates will be used for state tracking of emission changes, trends, and input into any 

regional evaluation of whether reasonable progress goals are being achieved. Should 

no regional coordinating/planning agency exist in the future, Colorado commits to 

continue providing required emission updates as specified in the AERR and 40 CFR 

51.308(d)(4)(v).

The State will use the Fire Emissions Tracking System (FETS)3to store and access fire 

emissions data. Should this system become unavailable Colorado will work with the 

FLMs and the EPA to establish a process to track and report fire emissions data if 

continued use of such information is deemed necessary. The State will also depend 

upon periodic collective emissions inventory efforts by other states meeting emission 

reporting requirements of the AERR to provide a regional inventory for future modeling 

and evaluations of regional haze impacts. Colorado recognizes that other inventories of 

a nature more sophisticated than available from the AERR may be required for future 

regional haze or other visibility modeling applications. In the past, such inventories 

were developed through joint efforts of states with the WRAP, and it is currently beyond 

available resources to provide an expanded regional haze modeling quality inventory if 

one is needed for future evaluations. The State will continue to depend on and use the 

capabilities of the WRAP-sponsored Regional Modeling Center (RMC)4or other similar 

joint modeling efforts to simulate the air quality impacts of emissions for haze planning 

purposes. The State notes the resources to ensure data preparation, storage, and 

analysis by the state and regional coordinating agencies such as the WRAP will require 

adequate ongoing resources. Colorado commits to work with other states, tribes, the 

FLMs and the EPA to help ensure future multi-state modeling, monitoring or inventory 

processes can be met but makes no commitment in this SIP to fund such processes. 

Colorado will track data related to RHR haze plan implementation for sources for which 

the state has regulatory authority.

 

3

http://www.wrapfets.org/

4

http://pah.cert.ucr.edu/aqm/308/ 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

22

Chapter 4 Baseline and Natural Visibility Conditions in Colorado, and 

Uniform Progress for Each Class I Area 

4.1 The Deciview

Each IMPROVE monitor collects particulate concentration data which are converted into 

reconstructed light extinction through a complex calculation using the IMPROVE 

equation (see Technical Support Documents for any Class I area). Reconstructed light 

extinction (denoted as bext) is expressed in units of inverse megameters (1/Mm or Mm1

). The Regional Haze Rule requires the tracking of visibility conditions in terms of the 

Haze Index (HI) metric expressed in the deciview (dv) unit [(40 CFR 51.308(d)(2)]. 

Generally, a one deciview change in the haze index is likely humanly perceptible under 

ideal conditions regardless of background visibility conditions.

The relationship between extinction (Mm-1), haze index (dv) and visual range (km) are 

indicated by the following scale:

4.2 Baseline and Current Visibility Conditions

EPA requires the calculation of baseline conditions [(40 CFR 51.308(d)(2)(i) and (ii)]. 

The baseline condition for each Colorado Class I area is defined as the five year 

average (annual values for 2000 - 2004) of IMPROVE monitoring data (expressed in 

deciviews) for the most-impaired (20% worst) days and the least-impaired (20% best) 

days. For this first regional haze SIP submittal, the baseline conditions are the 

reference point against which visibility improvement is tracked. For subsequent RH SIP 

updates (in the year 2018 and every 10 years thereafter), baseline conditions are used 

to calculate progress from the beginning of the regional haze program.

Current conditions for the best and worst days are calculated from a multiyear average, 

based on the most recent 5-years of monitored data available [40 CFR 51.308(f)(1)]. 

This value will be revised at the time of each periodic SIP revision, and will be used to 

illustrate: (1) The amount of progress made since the last SIP revision, and (2) the 

amount of progress made from the baseline period of the program.

Colorado has established baseline visibility for the cleanest and worst visibility days for 

each Class I area based on, on-site data from the IMPROVE monitoring sites. A fiveyear average (2000 to 2004) was calculated for each value (both best and worst). The 

calculations were made in accordance with 40 CFR 51.308(d)(2) and EPA‟s Guidance 

for Tracking Progress Under the Regional Haze Rule (EPA-454/B-03-004, September 

2003). The IMPROVE II algorithm as described in the TSDs has been utilized for the 

calculation of Uniform Rate of Progress glide slopes for all Class I areas. Figure 4-4 

contains the baseline conditions for each IMPROVE monitor site in Colorado.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

23

4.3 Monitoring Data

Visibility-impairing pollutants both reflect and absorb light in the atmosphere, thereby 

affecting the clarity of objects viewed at a distance by the human eye. Each haze 

pollutant has a different light extinction capability. In addition, relative humidity changes 

the effective light extinction of both nitrates and sulfates. Since haze pollutants can be 

present in varying amounts at different locations throughout the year, aerosol 

measurements of each visibility-impairing pollutant are made every three days at the 

IMPROVE monitors located in or near each Class I area.

In addition to extinction, the Regional Haze Rule requires another metric for analyzing 

visibility impairment, known as the “Haze Index”, which is based on the smallest unit of 

uniform visibility change that can be perceived by the human eye. The unit of measure 

is the deciview (denoted dv).

More detailed information on the methodology for reconstructing light extinction along 

with converting between the haze index and reconstructed light extinction can be found 

in the Technical Support Documents for any of Colorado‟s twelve Class I areas.

The haze pollutants reported by the IMPROVE monitoring program are sulfates, 

nitrates, organic carbon, elemental carbon, fine soil and coarse mass. Summary data in 

Figures 4-1 and 4-2 are provided below for the worst and best days from the 6 

IMPROVE monitors for the 6 haze pollutants.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

24

Figure 4-1 Reconstructed Aerosol Components for 20% Worst Days (2000-2004)

Figure 4-2 Reconstructed Aerosol Components for 20% Best Days (2000-2004)

More detailed information on reconstructed extinction for each Class I area can be 

found in the Technical Support Document.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

25

4.4 Natural Visibility Conditions

The natural condition for each Class I area represents the visibility goal expressed in 

deciviews for the most-impaired (20% worst) days and the least-impaired (20% best) 

days that would exist if there were only naturally occurring impairment. Natural visibility 

conditions must be calculated by estimating the degree of visibility impairment existing 

under natural conditions for the most impaired and least impaired days, based on 

available monitoring information and appropriate data analysis techniques. [(40 CFR 

51.308(d)(iii)].

Figure 4-3, lists the 2064 natural conditions goal in deciviews for each Colorado Class I 

area. The natural conditions estimates were calculated consistent with EPA‟s Guidance 

for Estimating Natural Visibility Conditions Under the Regional Haze Rule (EPA-454/B03-005, September 2003). The natural conditions goal can be adjusted as new visibility 

information becomes available. The Natural Haze Level II Committee methodology was 

utilized as described in the TSD.

Figure 4-3: 2064 Natural Conditions Goal for Worst Days

4.5 Uniform Progress

For the worst days, uniform progress for each Colorado Class I area is the calculation of 

a uniform rate of progress per year to achieve natural conditions in 60 years [(40 CFR 

51.308(d)(1)(i)(B)]. In this initial SIP submittal, the first benchmark is the 2018 deciview 

level based on the uniform rate of progress applied to the first fourteen years of the 

program. This is also shown in Figure 4-4 in the column “2018 Uniform Progress Goal 

(Deciview)”.

For the 20% worst days, the uniform rate of progress (URP) in deciviews per year (i.e. 

slope of the glide path) is determined by the following equation:

URP = [Baseline Condition - Natural Condition] / 60 years

By multiplying the URP by the number of years in the 1st planning period one can 

calculate the uniform progress needed by 2018 to be on the path to achieving natural 

visibility conditions by 2064:

2018 UPG = [URP] x [14 years]
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

26

The 14 years comprising the 1st planning period includes the 4 years between the end 

of the baseline period and the SIP submittal date plus the standard 10-year planning 

period for subsequent SIP revisions.

More detailed information on the worst days along with the calculations and glide slope 

associated with each CIA can be found in Section 3 of the Technical Support 

Documents for any of Colorado‟s twelve Class I areas. This calculation is consistent 

with EPA‟s Guidance for Setting Reasonable Progress Goals Under the Regional Haze 

Rule (June 1, 2007).

For the best days at each Class I area, the State must ensure no degradation in visibility 

for the least-impaired (20% best) days over the same period. More detailed information 

on the best days, along with the determination of the best day‟s baseline for a particular 

CIA, can be found in Section 3 of the Technical Support Document.

Figure 4-4 provides the 2018 uniform rate of progress chart for the worst days and the 

baseline that must not be exceeded over the years in order to maintain the best days. 

As with natural conditions, uniform rate of progress can be adjusted as new visibility 

information becomes available.

Figure 4-4: Uniform Rate of Progress for Each Colorado Class I Area
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

27

Figure 4-5 provides a visual example of 2018 uniform progress glide slope for the worst 

days and the best days baseline.

Figure 4-5: Example of Uniform Progress for 20% Best & Worst Days at Rocky 

Mountain National Park
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

28

Chapter 5 Sources of Impairment in Colorado

5.1 Natural Sources of Visibility Impairment

Natural sources of visibility impairment include anything not directly attributed to humancaused emissions of visibility-impairing pollutants. Natural events (e.g. windblown dust, 

wildfire, volcanic activity, biogenic emissions) also introduce pollutants contributing to 

haze in the atmosphere. Natural visibility conditions are not constant; they vary with 

changing natural processes throughout the year. Specific natural events can lead to 

high short-term concentrations of visibility-impairing particulate matter and its 

precursors. Natural visibility conditions, for the purpose of Colorado‟s regional haze 

program, are represented by a long-term average of conditions expected to occur in the 

absence of emissions normally attributed to human activities. Natural visibility 

conditions reflect contemporary vegetated landscape, land-use patterns, and 

meteorological/climatic conditions. The 2064 goal is the natural visibility conditions for 

the 20% worst natural conditions days.

Natural sources contribute to visibility impairment but natural emissions cannot be 

realistically controlled or prevented by Colorado and therefore are beyond the scope of 

this plan. Current methods of analysis of IMPROVE data do not provide a distinction 

between natural and anthropogenic emissions. Instead, for the purposes of this SIP, 

they are estimated as described in Section 4.4.

5.2 Anthropogenic Sources of Visibility Impairment

Anthropogenic or human-caused sources of visibility impairment include anything 

directly attributable to human-caused activities producing emissions of visibilityimpairing pollutants. Some examples include transportation, agriculture activities, 

mining operations, and fuel combustion. Anthropogenic visibility conditions are not 

constant and vary with changing human activities throughout the year. Generally 

anthropogenic emissions include not only those anthropogenic emissions generated or 

originating within the boundaries of the United States but also international emissions 

transported into a state. Some examples include emissions from Mexico, Canada, and 

maritime shipping emissions in the Pacific Ocean.

Although anthropogenic sources contribute to visibility impairment, international 

emissions cannot be regulated, controlled or prevented by the states and 

therefore are beyond the scope of this planning document. Any reductions in 

international emissions would likely fall under the purview of the U.S. EPA 

administrator.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

29

5.3 Overview of Emission Inventory System -TSS

The Western Regional Air Partnership (WRAP) developed the Technical Support 

System (TSS) as an Internet access portal to all the data and analysis associated with 

the development of the technical foundations of Regional Haze plans across the 

Western US. The TSS provides state, county, and grid cell level emissions information 

for typical criteria pollutants such as SO2 & NOx and other secondary particulate 

forming pollutants such as VOC and NH3. Eleven different emission inventories were 

developed comprising the following source categories: point, area, on-road mobile, offroad mobile, oil and gas, anthropogenic fire, natural fire, biogenic, road dust, fugitive 

dust and windblown dust. Summaries of the emissions data for sources in Colorado are 

contained in subsequent Figures 5-1 through 5-8 in this section. In addition the 

Emissions Inventory TSD in this SIP contains a more detailed accounting of sources in 

Colorado used in the modeling exercise.

In the WRAP process, member states and the EPA agreed the tremendous amount of 

data collected, analyzed and maintained by the WRAP and the Regional Modeling 

Center would be impracticable and nearly infeasible to include in individual TSDs for 

individual States. For the purposes of administrative efficiency, WRAP data and 

analysis upon which the member states built their Regional Haze SIPs are available 

through the WRAP on the TSS Web site. For a more complete description of the 

emission inventory and process and for access information related to the web site 

containing comprehensive detail about the inventory please refer to the Emissions 

Inventory TSD in this SIP.

5.4 Emissions in Colorado

Federal visibility regulations (40 CFR 51.308(d)(4)(v)) require a statewide emission 

inventory of pollutants reasonably anticipated to cause or contribute to visibility 

impairment in any Class I area. The pollutants inventoried by the WRAP that Colorado 

used for this SIP include sulfur dioxide (SO2), nitrogen oxides (NOx), volatile organic 

compounds (VOC), primary organic aerosol (POA), elemental carbon (EC), fine 

particulate (Soil-PM2.5), coarse particulate (PM-2.5 to PM-10), and ammonia (NH3). An 

inventory was developed for the baseline year 2002, and projections of future emissions 

have been made for 2018. Colorado will provide updates to the EPA on this inventory 

on a three year basis as required by the AERR. Not all of the categories used for 

modeling purposes are contained in the AERR. A summary of the inventory results 

follows; the complete emission inventory is included in Section 5 of the Technical 

Support Document.

Emission inventories form one leg of the analysis stool to evaluate sources‟ impacts on 

visibility. Emission inventories are created for all of critical chemicals or species known 

to directly or indirectly impact visual air quality. These inventories become inputs to air 

quality models predicting concentrations of pollutants over a given space and time. For 

this SIP, the WRAP developed emission inventories for each state with input from 

participating stakeholders. A complete description of the development and content of 

the emission inventories can be found on the WRAP Technical Support System web 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

30

site: http://vista.cira.colostate.edu/TSS/Results/Emissions.aspx and a summary

description of the inventory is found in the Emission Inventory TSD.

Dispersion modeling predicts daily atmospheric concentrations of pollutants for the 

baseline year and these modeled results are compared to monitored data taken from 

the IMPROVE network. A second inventory is created to predict emissions in 2018 

based on expected controls, growth, or other factors. Additional inventories are created 

for future years to simulate the impact of different control strategies. The process for 

inventorying sources is similar for all species of interest. The number and types of 

sources is identified by various methods. For example, major stationary sources report 

actual annual emission rates to the EPA national emissions database. Colorado 

collects annual emission data from both major and minor sources and this information is 

used as input into the emissions inventory. In other cases, such as mobile sources, an 

EPA mobile source emissions model is used to develop emission projections. Colorado 

vehicle registration, vehicle mile traveled information and other vehicle data are used to 

tailor the mobile source data to best represent statewide and area specific emissions. 

Population, employment and household data are used in other parts of the emissions 

modeling to characterize emissions from area sources such as home heating. Thus, for 

each source type, emissions are calculated based on an emission rate and the amount 

of time the source is operating. Emission rates can be based on actual measurements 

from the source, or EPA emission factors based on data from tests of similar types of 

emission sources. In essence all sources go through the same process. The number 

of sources is identified, emission rates are determined by measurements of those types 

of sources and the time of operation is determined. By multiplying the emission rate 

times the hours of operation in a day, a daily emission rate can be calculated.

It is noted that certain source categories are more difficult to make current and future 

projections for. This is simply because market dynamics, growth factors, improvements 

in emission factors, types and number of sources, improvements in controls and 

changes in regulations make the future less predictable. Oil and gas sources in 

Colorado can be substantial for selected pollutants and significant efforts went into this 

SIP to improve emissions estimates for Colorado and other western states to help make 

the modeling as reflective as possible of known and future emissions. Future SIP 

updates will take into account any new information related to this, and other, source 

categories.

The following presents the Colorado emissions from the TSS, as provided to the WRAP 

early 2009. The “Plan 2002(d)” and “PRP 2018(b)” phrases on each of the emission 

inventory tables signify the version of inventories by year. A detailed explanation of 

each plan can be found in the Emission Inventory TSD. These inventories do not reflect 

the additional emission reductions that will result from the 2010 revised Best Available 

Retrofit Technology and reasonable progress determinations. An accounting of these 

emission reductions are presented in Chapter 9 of this plan.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

31

Figure 5-1 Colorado SO2 Emission Inventory – 2002 & 2018

Sulfur dioxide emissions produce sulfate particles in the atmosphere. Ammonium 

sulfate particles have a significantly greater impact on visibility than pollutants like dust 

from unpaved roads due to the physical characteristics causing greater light scattering 

from the particles. Sulfur dioxide emissions come primarily from coal combustion at 

electrical generation facilities but smaller amounts come from natural gas combustion, 

mobile sources and even wood combustion. Other than natural fire there are no 

biogenic SO2 emissions of significance in Colorado. Even allowing for those fire-related 

sulfur dioxide emissions to be counted as „natural‟ these represent only 3% of the 

statewide inventory. A 51% statewide reduction in SO2 emissions is expected by 2018 

due to planned controls on existing point sources, even with a growth consideration for 

electrical generating capacity for the State. Similar reductions in the West are expected 

from other states as BART or other planned controls take effect by 2018. The only 

sulfur dioxide category expected to increase is area sources. Area sources of sulfur 

oxides are linked to population growth as the activity factor. As population increases in 

Colorado from the base case to 2018, this category is expected to increase. A typical 

area source for sulfur dioxide would be home heating.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

32

Figure 5-2 Colorado NOx Emission Inventory – 2002 & 2018

Nitrogen oxides (NOx) are generated during any combustion process where nitrogen 

and oxygen from the atmosphere combine together under high temperature to form 

nitric oxide, and to a lesser degree nitrogen dioxide. Other odd oxides of nitrogen are 

also produced to a much smaller degree. Nitrogen oxides react in the atmosphere to 

form nitrate particles. Larger nitrate particles have a slightly greater impact on visibility 

than do sulfate particles of the same size and are much more effective at scattering light 

than mineral dust particles. Nitrogen oxide emissions in Colorado are expected to 

decline by 2018, primarily due to significant emission reductions from point, mobile and 

area sources. Off-road and on-road vehicles emissions will decline by more than 

80,000 tons per year from the base case emissions total of 204,000 tons per year. 

Increases in area sources, as with sulfur dioxide, are related to population growth with 

an expected 4,000 tons per year increase by 2018. Again, home heating would be a 

typical area source of NOx with growth in emissions related to population increases. Oil 

and gas development by 2018 is also expected to increase statewide emissions by 

about 10,000 tons per year.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

33

Figure 5-3 Colorado VOC Emission Inventory – 2002 & 2018

Volatile organic compounds (VOCs) are expected to decline slightly by 2018. Among 

other sources, volatile organic compounds from automobiles, industrial and commercial 

facilities, solvent use, and refueling automobiles all contribute to VOC loading in the 

atmosphere. Substantial natural emissions of VOCs come from vegetation. VOCs can 

directly impact visibility as emissions condense in the atmosphere to form an aerosol. 

Of more significance is the role VOCs play in the photochemical production of ozone in 

the troposphere. Volatile organic compounds react with nitrogen oxides to produce 

nitrated organic particles that impact visibility in the same series of chemical events that 

lead to ozone. Thus, strategies to reduce ozone in the atmosphere often lead to 

visibility improvements. The large increase in area sources is again related to 

population increases. Use of solvents such as in painting, dry cleaning, charcoal lighter, 

and windshield washer fluids, and many home use products, show up in the area 

source category and increases in this area are linked to population growth.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

34

Figure 5-4 Colorado Primary Organic Aerosol (POA) Emission Inventory – 2002 

& 2018

Primary Organic Aerosols (POAs) are organic carbon particles emitted directly from the 

combustion of organic material. A wide variety of sources contribute to this 

classification including cooking of meat to diesel emissions and combustion byproducts 

from wood and agricultural burning. Area sources and automobile emissions dominate 

this classification. Increases in areas sources are due to population increases. These 

increases are offset by expected improvements in automobile emissions and by 2018 

emissions from this category are expected to decline by about 5%.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

35

Figure 5-5 Colorado Elemental Carbon (EC) Emission Inventory – 2002 & 2018

Elemental carbon is the carbon black, or soot, a byproduct of incomplete combustion. It 

is the partner to primary organic aerosols and represents the more complete 

combustion of fuel producing carbon particulate matter as the end product. A carbon 

particle has a sixteen times greater impact on visibility than a coarse particle of granite 

has. Emissions, and reductions, in this category are dominated by mobile sources and 

expected new federal emission standards for mobile sources, especially for diesel 

engines, along with fleet replacement are the reason for these reductions.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

36

Figure 5-6 Colorado Soil (PM Fine) Emission Inventory – 2002 & 2018

Fine soil emissions are largely related to agricultural and mining activities, windblown 

dust from construction areas and emissions from unpaved and paved roads. A particle 

of fine dust has a relative impact on visibility one tenth as great as a particle of 

elemental carbon. Monitoring at all sites in Colorado indicates soil is present as a small 

but measurable part of the visibility problem. On any given visibility event where poor 

visual air quality is present in a scene, the impact of dust can vary widely. Overall, on 

the 20% worst days, fine soil has about the same impact as nitrate particles. 

Agricultural activities, dust from unpaved roads and construction are prevalent in this 

source category and changes in emissions are tied to population and vehicle miles 

traveled. Since soil emissions are not directly from the tailpipe of the vehicle, the 

category of mobile sources does not show any emissions and all vehicle related 

emissions from paved and unpaved roads show up in the fugitive dust category.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

37

Figure 5-7 Colorado Coarse Mass (PM Coarse) Emission Inventory – 2002 & 

2018

Particulate matter, also identified as coarse mass particles emissions, are closely 

related to the same sources as fine soil emissions but other activities like rock crushing 

and processing, material transfer, open pit mining and unpaved road emissions can be 

prominent sources. Coarse mass particles travel shorter distances in the atmosphere 

than some other smaller particles but can remain in the atmosphere sufficiently long 

enough to play a role in regional haze. Coarse mass particulate matter has the smallest 

direct impact on regional haze on a particle-by-particle basis where one particle of 

coarse mass has a relative visibility weight of 0.6 compared to a carbon particle having 

a weight of 10. Nevertheless, they are commonly present at all monitoring sites and are 

a greater contributor to regional haze than the fine soil component. Substantial 

increases in coarse mass are seen in the fugitive dust category. This is due to the fact 

that construction and emissions from paved and unpaved roads are lined to population, 

vehicle miles traveled and employment data. Growth in these factors results in these 

categories increasing from 2002 to 2018. For this planning period, the state evaluated 

PM from stationary sources, but not from natural sources.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

38

Figure 5-8 Colorado Ammonia (NH3) Emission Inventory – 2002 & 2018

Ammonia emissions come from a variety of sources including wastewater treatment 

facilities, livestock operations, and fertilizer application and to a small extent, mobile 

sources. Increases in ammonia emission from the base case year to 2018 are linked to 

population statistics and increased vehicular traffic. Ammonia is directly linked to the 

production of ammonium nitrate and ammonium sulfate particles in the atmosphere 

when sulfur dioxide and nitrogen oxides eventually convert over to these forms of 

particles. Expected growth in the mobile source emissions from 2002 to 2018 is due to 

the fact that no specific controls on mobile sources are implemented and increases in 

vehicle miles traveled links directly to increased ammonia emissions.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

39

Chapter 6 Best Available Retrofit Technology

6.1 Introduction

One of the principal elements of Section 169A of the 1977 Clean Air Act Amendments 

addresses the installation of Best Available Retrofit Technology (BART) for certain 

existing sources of pollution. The provision, 169A (b)(2), demonstrates Congress‟ intent 

to focus attention directly on pollution from a specific group of existing sources. The 

U.S. Environmental Protection Agency‟s (EPA) Regional Haze Rule requires certain 

emission sources that may reasonably be anticipated to cause or contribute to visibility 

impairment in downwind Class I areas to install BART. See 40 CFR §51.308(e); see 

also 64 Fed. Reg. 35714 et seq. (July 1, 1999). These requirements are intended to 

reduce emissions from certain large sources that, due to age, were exempted from 

other requirements of the Clean Air Act.

BART requirements pertain to 26 specified major point source categories including 

power plants, cement kilns and industrial boilers. To be considered BART-eligible, 

sources from these categories must have the potential to emit 250 tons or more of haze 

forming pollution and must have commenced operation in the 15-year period prior to 

August 7, 1977.

Because of the regional focus of this requirement in the Regional Haze Rule, BART 

applies to a larger number of sources than the Phase 1 reasonably attributable visibility 

impairment requirements. In addition to source-by-source command and control BART 

implementation, EPA has allowed for more flexible alternatives if they achieve greater 

progress toward the state‟s visibility goals than the standard BART approach.

This document demonstrates how Colorado has satisfied the BART requirements in 

EPA‟s Regional Haze Rule. Colorado‟s review process is described and a list of BARTeligible sources is provided. A list of sources that are subject to BART is also provided, 

along with the requisite modeling analysis approach and justification.

6.2 Overview of Colorado’s BART Regulation

Colorado‟s Air Quality Control Commission approved a State-only BART regulation 

(Regulation 3 Part F) on March 16, 2006, that became effective in May 2006. A 

summary of the Colorado BART program and determinations is set out below, in 

Section 6.3. More detail is provided in Regulation Number 3 Part F, Appendix C to this 

document, the Technical Support Document (TSD), and at the Division‟s BART website 

at: http://www.cdphe.state.co.us/ap/RegionalHazeBART.html.

Colorado‟s BART Rule includes the following major provisions:

1. Visibility impairing pollutants are defined to include SO2, NOx and particulate matter.

2. Visibility impact levels are established for determining whether a given source 

causes or contributes to visibility impairment for purposes of the source being 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

40

subject-to-BART (or excluded). The causation threshold is 1.0 deciview and the 

contribution threshold is 0.5 deciview. Individual sources are exempt from BART if 

the 98th percentile daily change in visibility from the facility, as compared against 

natural background conditions, is less than 0.5 deciview at all Class I federal areas 

for each year modeled and for the entire multi-year modeling period.

3. BART controls are established based on a case-by-case analysis taking into 

consideration the technology available, the costs of compliance, the energy and nonair quality environmental impacts of compliance, any pollution control equipment in 

use or in existence at the source or unit, the remaining useful life of the source or 

unit, and the degree of improvement in visibility which may reasonably be 

anticipated to result from the use of such technology. These factors are established 

in the definition of Best Available Retrofit Technology.

4. Provision that the installation of regional haze BART controls exempts a source from 

additional BART controls for regional haze, but does not exempt a source from 

additional controls or emission reductions that may be necessary to make 

reasonable progress under the regional haze SIP.

6.3 Summary of Colorado’s BART Determinations

Colorado‟s Air Quality Control Commission elected to assume that all BART-eligible 

sources are subject to BART, but required the Division to perform modeling to 

determine whether BART-eligible sources will cause or contribute to visibility impairment 

at any Class I area. The threshold for causing or contributing to impairment was 0.5 or 

greater deciview impact. BART-eligible sources that did not cause or contribute 0.5 or 

greater deciview impact would not be subject to BART.

Once the complete list of eligible sources had been assembled, the list was reviewed to 

determine the current status of each source. A number of sources were eliminated for 

various reasons. One plant was being shut down. Two others were found not to be 

subject to BART because the size of the boilers was less than the 250 MMBtu/hour limit 

identified in the EPA BART Rule. Two sources were not subject to BART because they 

had been re-constructed after the BART period, and two were exempt because VOCs 

are not a visibility impairing pollutant under Colorado's BART Rule. The final list of 

sources was modeled by the Division to determine if they met the “cause or contribute” 

criteria. The results of this modeling are reflected in Table 6 - 1 below.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

41

Table 6 - 1 Results of Subject-to-BART Modeling

Modeled BART–Eligible Source

Division 

Modeling

(98th 

percentile 

deltadeciview 

value)

Division 

Approved 

Refined Modeling 

from Source 

Operator

(98th percentile 

delta-deciview 

value)

Contribution 

Threshold

(deciviews)

Impact Equal 

to or Greater 

Than 

Contribution 

Threshold?

CEMEX - Lyons Cement Kiln & Dryer 1.533 0.5 Yes

CENC (Trigen-Colorado) Units 4 & 5 1.255 0.5 Yes

Cherokee Station – Unit 4 1.460 0.5 Yes

Comanche Station – Units 1 and 2 0.701 0.5 Yes

Craig Station – Units 1 & 2 2.689 0.5 Yes

Hayden Station – Units 1 & 2 2.538 0.5 Yes

Lamar Light & Power – Unit 6 0.064 0.5 No

Martin Drake Power Plant – Units 5, 6 & 7 1.041 0.5 Yes

Pawnee Station – Unit 1 1.189 0.5 Yes

Ray D. Nixon Power Plant – Unit 1 0.570 0.481 0.5 No

Suncor Denver Refinery 0.239 0.5 No

Valmont Station – Unit 5 1.591 0.5 Yes

Notes:

1. The contribution threshold has an implied level of precision equal to the level of precision reported 

from the model.

2. Source operator modeling results are shown only if modeling has been approved by Division.

3. Roche is not included because it is a VOC source and the Division has determined that anthropogenic 

VOC emissions are not a significant contributor to visibility impairment.

4. Denver Steam is not included because it is exempt by rule (natural gas only <250 MMBtu).

5. Holcim Cement (Florence) and Rocky Mountain Steel Mills (Pueblo) are not included because of 

facility reconstruction.

6. Changes to the Ray D. Nixon Power Plant modeling included refinement of the meteorological fields 

and emission rates. The Division has issued a permit modification for this facility that includes a 30-day 

rolling emission limit for SO2.

7. Suncor Denver Refinery (including the former Valero Refinery) was not included because it is a VOC 

source and the Division has determined that anthropogenic VOC emissions are not a significant 

contributor to visibility impairment. Moreover, Suncor has installed controls to comply with MACT 

standards.

Of the BART-eligible sources listed above, those sources with a visibility contribution 

threshold equal to or greater than 0.5 deciview were determined to be subject-to-BART. 

Tables 6 - 2 and 6 - 3 include the BART determinations that will apply to each source.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

42

Table 6 - 2 BART Determinations for Colorado Sources

Emission 

Unit

Assumed ** 

NOx Control 

Type

NOx Emission 

Limit

Assumed ** 

SO2 Control 

Type

SO2 Emission 

Limit

Assumed ** 

Particulate 

Control and 

Emission Limit

Cemex -

Lyons

Kiln

Selective 

Non-Catalytic 

Reduction 

System

255.3 lbs/hr

(30-day rolling 

average)

901.0 tons/yr

(12-month rolling 

average)

None 25.3 lbs/hr

(12-month 

rolling average)

95.0 tons/yr

(12-month 

rolling average)

Fabric Filter 

Baghouse *

0.275 lb/ton of 

dry feed

20% opacity

Cemex -

Lyons

Dryer

None 13.9 tons/yr None 36.7 tons/yr Fabric Filter 

Baghouse*

22.8 tons/yr

10% opacity

CENC

Unit 4

Low NOx 

Burners with 

Separated 

Over-Fire Air

0.37 lb/MMBtu 

(30-day rolling 

average)

Or

0.26 lb/MMBtu 

Combined 

Average for Units 

4 & 5 (30-day 

rolling average)

None 1.0 lb/MMBtu

(30-day rolling 

average)

Fabric Filter 

Baghouse*

0.07 lb/MMBtu

CENC

Unit 5

Low NOx 

Burners with

Separated 

Over-Fire Air, 

and Selective 

Non-Catalytic 

Reduction 

System

0.19 lb/MMBtu 

(30-day rolling 

average)

Or

0.26 lb/MMBtu 

Combined 

Average for Units 

4 & 5 (30-day 

rolling average)

None 1.0 lb/MMBtu 

(30-day rolling 

average)

Fabric Filter 

Baghouse*

0.07 lb/MMBtu

Comanche

Unit 1

Low NOx 

Burners*

0.20 lb/MMBtu

(30-day rolling 

average)

0.15 lb/MMBtu

(combined annual 

average for units 1 

& 2)

Lime Spray 

Dryer*

0.12 lb/MMBtu 

(30-day rolling 

average)

0.10 lb/MMBtu

(combined 

annual average 

for units 1 & 2)

Fabric Filter 

Baghouse*

0.03 lb/MMBtu
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

43

Table 6 - 2 BART Determinations for Colorado Sources

Emission 

Unit

Assumed ** 

NOx Control 

Type

NOx Emission 

Limit

Assumed ** 

SO2 Control 

Type

SO2 Emission 

Limit

Assumed ** 

Particulate 

Control and 

Emission Limit

Comanche

Unit 2

Low NOx 

Burners*

0.20 lb/MMBtu

(30-day rolling 

average)

0.15 lb/MMBtu

(combined annual 

average for units 1 

& 2)

Lime Spray 

Dryer*

0.12 lb/MMBtu

(30-day rolling 

average)

0.10 lb/MMBtu

(combined 

annual average 

for units 1 & 2)

Fabric Filter 

Baghouse*

0.03 lb/MMBtu

Craig

Unit 1

Selective 

Non-Catalytic 

Reduction 

System

0.28 lb/MMBtu

(30-day rolling 

average)

Wet 

Limestone 

scrubber*

0.11 lb/MMBtu

(30-day rolling 

average)

Fabric Filter 

Baghouse*

0.03 lb/MMBtu

Craig

Unit 2

Selective 

Catalytic 

Reduction 

System

0.08 lb/MMBtu

(30-day rolling 

average)

Wet 

Limestone 

scrubber*

0.11 lb/MMBtu

(30-day rolling 

average)

Fabric Filter 

Baghouse*

0.03 lb/MMBtu

Hayden

Unit 1

Selective 

Catalytic 

Reduction

System

0.08 lb/MMBtu

(30-day rolling 

average)

Lime Spray 

Dryer*

0.13 lb/MMBtu

(30-day rolling 

average)

Fabric Filter 

Baghouse*

0.03 lb/MMBtu

Hayden

Unit 2

Selective 

Catalytic 

Reduction

System

0.07 lb/MMBtu

(30-day rolling 

average)

Lime Spray 

Dryer*

0.13 lb/MMBtu

(30-day rolling 

average)

Fabric Filter 

Baghouse*

0.03 lb/MMBtu

Martin 

Drake

Unit 5

Ultra LowNOx Burners 

(including 

Over-Fire 

Air) 

0.31 lb/MMBtu

(30-day rolling 

average)

Dry Sorbent 

Injection

0.26 lb/MMBtu 

(30-day rolling 

average)

Fabric Filter 

Baghouse*

0.03 lb/MMBtu

Martin 

Drake

Unit 6

Ultra LowNOx Burners 

(including 

Over-Fire 

Air) 

0.31 lb/MMBtu

(30-day rolling 

average)

Lime Spray 

Dryer or 

Equivalent 

Control 

Technology

0.13 lb/MMBtu

(30-day rolling 

average)

Fabric Filter 

Baghouse*

0.03 lb/MMBtu

Martin 

Drake

Unit 7

Ultra LowNOx Burners 

(including 

Over-Fire 

Air)

0.29 lb/MMBtu

(30-day rolling 

average)

Lime Spray 

Dryer or 

Equivalent 

Control 

Technology

0.13 lb/MMBtu

(30-day rolling 

average)

Fabric Filter 

Baghouse*

0.03 lb/MMBtu

* Controls are already operating

** Based on the state's BART analysis, the "assumed" technology reflects the control option found to 

render the BART emission limit achievable. The "assumed" technology listed in the above table is 

not a requirement.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

44

Table 6 - 3 BART Determinations for PSCo’s BART Alternative Sources 5, 6, 7

Emission 

Unit

NOx Control 

Type

NOx Emission 

Limit

SO2 Control 

Type

SO2 Emission 

Limit

Particulate 

Control and 

Emission Limit

Cherokee

Unit 1

Shutdown

No later than 

7/1/2012

0 Shutdown

No later than 

7/1/2012

0 Shutdown

No later than 

7/1/2012

Cherokee

Unit 2 

Shutdown

12/31/2011

0 Shutdown

12/31/2011

0 Shutdown

12/31/2011

Cherokee

Unit 3

Shutdown

No later than 

12/31/2016

0 Shutdown

No later than 

12/31/2016 

0 Shutdown

No later than 

12/31/2016 

Cherokee

Unit 4

Natural Gas 

Operation 

12/31/2017

0.12 lb/MMBtu

(30-day rolling 

average) by 

12/31/2017

Natural Gas 

Operation 

12/31/2017

7.81 tpy (rolling 

12 month 

average)

Fabric Filter 

Baghouse*

0.03 lbs/MMBtu

Natural Gas 

Operation 

12/31/2017

Valmont

Unit 5

Shutdown

12/31/2017

0 Shutdown

12/31/2017

0 Shutdown

12/31/2017

Pawnee

Unit 1

SCR** 0.07 lb/MMBtu

(30-day rolling 

average) by 

12/31/2014

Lime Spray 

Dryer**

0.12 lbs/MMBtu 

(30-day rolling 

average) by 

12/31/2014

Fabric Filter 

Baghouse*

0.03 lbs/MMBtu

Arapahoe

Unit 3

Shutdown 

12/31/2013

0 Shutdown 

12/31/2013

0 Shutdown 

12/31/2013

Arapahoe

Unit 4

Natural Gas 

Operation

600 tpy (rolling 12 

month average) 

12/31/2014

Natural Gas 

operation 

12/31/2014 

1.28 tpy (rolling 

12 month 

average)

Fabric Filter 

Baghouse*

0.03 lbs/MMBtu

Natural Gas 

operation 

12/31/2014 

* Controls are already operating

** The "assumed" technology reflects the control option found to render the BART emission limit 

achievable. The "assumed" technology listed for Pawnee in the above table is not a requirement.

For all BART and BART alternative determinations, approved in the Federal State 

Implementation Plan, the state affirms that the BART emission limits satisfy Regional 

Haze requirements for this planning period (through 2017) and that no other Regional 

 

5

Emission rates would begin on the dates specified, the units would not have 30 days of data until 30 days following 

the dates shown in the table. 

6

500 tpy NOx will be reserved from Cherokee station for netting or offsets.

7

300 tpy NOx will be reserved from Arapahoe station for netting or offsets for additional natural gas generation.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

45

Haze analyses or Regional Haze controls will be required by the state during this 

timeframe.

6.4 Overview of Colorado’s BART Determinations

Colorado has been evaluating BART issues for many years and has closely followed 

EPA‟s proposals and final rules. The list of Colorado BART-eligible sources has been 

well known since the 1990‟s, based on EPA‟s expected applicability dates of between 

August 7, 1962 and August 7, 1977. Colorado has been involved in four BART-like 

proceedings involving known BART sources. Two of these determinations resulted 

from actions related to the Hayden and Craig power plants. These plants were 

identified in a certification of impairment made by the U.S. Forest Service regarding 

visibility impacts at Mt. Zirkel Wilderness Area, located northeast of Steamboat Springs. 

Colorado conducted two additional BART proceedings for all sources in 2007 and in 

2008, which were submitted to EPA for approval. A number of these determinations 

were revised in 2010 based on adverse comments from EPA; Table 6-2 presents the 

2010 BART determinations.

6.4.1 The State’s Consideration of BART Factors

In identifying a level of control as BART, States are required by section 169A(g) of the 

Clean Air Act to “take into consideration” the following factors:

(1) The costs of compliance,

(2) The energy and non-air quality environmental impacts of compliance,

(3) Any existing pollution control technology in use at the source,

(4) The remaining useful life of the source, and

(5) The degree of visibility improvement that may reasonably be anticipated from the 

use of BART.

42 U.S.C. § 7491(g)(2).

Colorado‟s BART regulation requires that the five statutory factors be considered for all 

BART sources. See, Regulation No. 3, Part E, Section IV.B.1. In making its BART 

determination for each Colorado source, the state took into consideration the five 

statutory factors on a case-by case basis, and for significant NOx controls the Division 

also utilized the guidance criteria set forth in Section 6.4.3 consistent with the five 

factors. Summaries of the state‟s facility-specific consideration of the five factors and 

resulting determinations for each BART source are provided in this Chapter 6. 

Documentation reflecting the state‟s analyses and supporting the state‟s BART 

determinations, including underlying data and detailed descriptions of the state‟s 

analysis for each facility, are provided in Appendix C of this document.

6.4.1.1 The costs of compliance. The Division requested, and the companies 

provided, source-specific cost information for each BART unit. The cost information 

ranged from the installation and operation of new SO2 and NOx control equipment to 

upgrade analyses of existing SO2 controls. The cost for each unit is summarized 

below, and the state‟s consideration of this factor for each source is presented in detail 

in Appendix C.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

46

6.4.1.2 The energy and non-air quality environmental impacts of compliance. 

This factor is typically used to identify non-air issues associated with different types of 

control equipment. The Division requested, and the companies provided, sourcespecific energy and non-air quality information for each BART unit. The state has 

particular concerns with respect to potential non-air quality environmental impacts 

associated with wet scrubber systems for SO2, as further described below.

6.4.1.3 Any existing pollution control technology in use at the source. The state 

has taken into consideration the existing PM, SO2 and NOx pollution control equipment 

in use at each Colorado source, as part of its BART determination process.

The Division has reviewed available particulate controls. Based on a review of NSPS, 

MACT and RACT/BACT/LAER, the state has determined that fabric filter baghouses are 

the best PM control available. The Portland cement MACT confirms that “a wellperforming baghouse represents the best performance for PM” see 74 Fed. Reg. 

21136, 21155 (May 6, 2009). The RACT/BACT/LAER Clearinghouse identifies 

baghouses as the PM control for the newer cement kilns and EGUs. Additional 

discussion of PM controls, including baghouse controls, is contained in the source 

specific analyses in Appendix C.

The Division also reviewed various SO2 controls applicable to EGUs and boilers. Two 

of the primary controls identified in the review are wet scrubbers and dry flue gas 

desulphurization (FGD). Based upon its experience, and as discussed in detail 

elsewhere in this Chapter 6, in Appendix C and in the TSD, the state has determined 

that wet scrubbing has several negative energy and non-air quality environmental 

impacts, including very significant water usage. This is a significant issue in Colorado 

and the arid West, where water is a costly, precious and scarce resource. There are 

other costs and environmental impacts that the state also considers undesirable with 

respect to wet scrubbers. For example, the off-site disposal of sludge entails 

considerable costs, both in terms of direct disposal costs, and indirect costs such as 

transportation and associated emissions. Moreover, on-site storage of wet ash is an 

increasing regulatory concern. EPA recognizes that some control technologies can 

have significant secondary environmental impacts. See 70 Fed. Reg. 39104, 39169 

(July 6, 2005). EPA has specifically noted that the limited availability of water can affect 

the feasibility and costs of wet scrubbers in the arid West. These issues were examined 

in each source specific analysis in Appendix C.

With respect to NOx controls, the state has assessed pre-combustion and postcombustion controls and upgrades to existing NOx controls, as appropriate

When determining the emission rates for each source, the state referred to and 

considered recent MACT, NSPS and RACT/BACT/LAER determinations to inform

emission limits. While relying on source specific information for the final limit, and 

considering that BART relates to retrofitting sources (vs. new or reconstructed facilities), 

a review of other determinations was used to better substantiate the source specific 

information provided by the source.

6.4.1.4 The remaining useful life of the source. None of Colorado‟s BART sources 

are expected to retire over the next twenty years. Therefore, this factor did not affect 

any of the state‟s BART determinations.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

47

6.4.1.5 The degree of visibility improvement which may reasonably be 

anticipated from the use of BART. The state took into consideration the degree of 

visibility improvement which may reasonably be anticipated from the use of BART. 

Modeling information for each BART determination is presented below and in Appendix 

C.

6.4.2 SIP Requirements from EPA’s Regional Haze Rule

The following section includes information addressing the SIP elements contained in 

EPA‟s Regional Haze Rule. The section numbers refer to provisions in 40 CFR § 

51.308(e), the BART provision of the Regional Haze Rule.

(i) A list of all BART-eligible sources within the State.

Table 6 - 3 below lists the initial group of Colorado sources subject to BART. 

This initial list was created based on historical information contained in the 

Division‟s source files and is based on the 1962-1977 time frame and source 

category list contained in Appendix Y. This list was then examined to see if 

any of the sources identified would be exempt from BART. EPA allows 

sources to be exempt from BART if they have undergone permitted 

reconstruction, emit de minimis levels of pollution, or are fossil-fuel boilers 

with an individual heat input rating below 250 million Btu/hour. Colorado‟s 

BART rule allows sources to be exempt from BART if modeling demonstrates 

the impact at any Class I area is below the “cause or contribute” thresholds of 

1.0 and 0.5 deciviews. Table 6 - 3 lists the current status of the original BART 

sources and notes which sources were exempted and why.

Table 6 - 4 Colorado’s BART Eligible Sources

Plant Name Source Owner

Rating, Heat 

Input or

Source type

Start 

Year Current Status

Cemex - Lyons

Kiln Cemex Portland 

Cement <1977 Subject-to-BART

Cemex - Lyons

Dryer Cemex Portland 

Cement <1977 Subject-to-BART

CENC

Unit 4

Colorado Energy 

Nations Company 

(CENC)

360 MMBtu/hr 1975 Subject-to-BART

CENC

Unit 5 CENC 650 MMBtu/hr 1979 Subject-to-BART

Cherokee

Unit 4 

Public Service 

Company of 

Colorado (PSCO)

350 MW 1968 Subject-to-BART

Comanche

Unit 1 PSCO 350 MW 1973 Subject-to-BART

Comanche

Unit 2 PSCO 350 MW 1976 Subject-to-BART

Craig

Unit 1

Tri-State 

Generation and 446 MW 1979 Subject-to-BART
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

48

Table 6 - 4 Colorado’s BART Eligible Sources

Plant Name Source Owner

Rating, Heat 

Input or

Source type

Start 

Year Current Status

Transmission, Inc.

Craig

Unit 2 Tri-State 446 MW 1979 Subject-to-BART

Hayden

Unit 1 PSCO 190 MW 1965 Subject-to-BART

Hayden

Unit 2 PSCO 275 MW 1976 Subject-to-BART

Martin Drake

Unit 5

Colorado Springs 

Utilities (CSU) 55 MW 1962 Subject-to-BART

Martin Drake

Unit 6 CSU 85 MW 1968 Subject-to-BART

Martin Drake

Unit 7 CSU 145 MW 1974 Subject-to-BART

Pawnee

Unit 1 PSCO 500 MW 1981 BART Alternative

Valmont

Unit 5 PSCO 188 MW 1964 Subject-to-BART

Denver Steam

Unit 1 PSCO Steam only 

210 MMBtu/hr 1972 Not subject-to-BART since this boiler is less than 250 MMBtu/hr, see 70 FR 39110

Denver Steam

Unit 2 PSCO Steam only 

243 MMBtu/hr 1974 Not subject-to-BART since this boiler is less than 250 MMBtu/hr, see 70 FR 39110

Holcim

Kiln Holcim Portland 

Cement <1977

Not subject-to-BART since Kiln built after 

BART time period. Other sources < 250 

TPY total emissions.

Lamar Utilities

City of Lamar 25 MW 1972 Plant will be shutdown; so will no longer 

be subject. 

Oregon Steel

Oregon Steel Steel Mfg. <1977

Not subject-to-BART since Arc furnace 

rebuilt after BART time period. Other 

sources < 250 TPY total emissions.

Ray Nixon

Unit 1 CSU 227 MW 1980

Not Subject-to-BART (enforceable 

emission limitations and refined CALPUFF 

modeling result in less than 0.5 dv visibility 

impact)

Roche

Roche Pharmaceutic

al Mfg. <1977

Not subject-to-BART since VOC 

determined as not a visibility impairing 

pollutant in CO

Suncor/Valero

Suncor Refinery <1977

Not subject-to-BART since VOC 

determined as not a visibility impairing 

pollutant in CO 

(ii) A determination of BART for each BART-eligible source.

Table 6 - 2 lists the state‟s BART determinations for sources that cause or 

contribute to visibility impairment in Class I areas.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

49

(iii) The determination of BART must be based on an analysis of the best system of 

continuous emission control technology available and associated emission 

reductions achievable for each BART-eligible source that is subject to BART within 

the State. In this analysis, the State must take into consideration the technology 

available, the costs of compliance, the energy and non-air quality environmental 

impacts of compliance, any pollution control equipment in use at the source, the 

remaining useful life of the source, and the degree of improvement in visibility 

which may reasonably be anticipated to result from the use of such technology.

Summaries of the state‟s facility-specific consideration of the five factors and resulting 

determinations are provided in this chapter 6. Documentation reflecting the state‟s 

analyses and supporting the state‟s BART determinations, including underlying data 

and detailed descriptions of the state‟s analysis for each facility, are provided in 

Appendix C of this document.

(iv) The determination of BART for fossil-fuel fired power plants having a total 

generating capacity greater than 750 megawatts must be made pursuant to the 

guidelines in Appendix Y of this part (Guidelines for BART Determinations Under 

the Regional Haze Rule).

Colorado has only one source with two BART eligible EGUs that have a combined 

rating exceeding 750 MW, which is Tri-State Generation and Transmission 

Association‟s Craig plant located in Moffat County. The Division‟s BART 

determination for the Craig facility is discussed in more detail below.

(v) A requirement that each source subject to BART be required to install and operate 

BART as expeditiously as practicable, but in no event later than 5 years after 

approval of the implementation plan revision.

This requirement is addressed in Colorado‟s BART Rule, and Regulation No. 3 

Part F Section VI.

(vi) A requirement that each source subject-to-BART maintain the control equipment 

required by this subpart and establish procedures to ensure such equipment is 

properly operated and maintained.

Operation and maintenance plans are required by the BART Rule, and Regulation 

No. 3. Part F Section VII.

6.4.3 Overview of the BART Determinations and the Five Factor Analyses for 

Each BART Source

This section presents an overview of the BART determinations for the subject to BART 

sources.

The Regional Haze rule requires states to make determinations about what is 

appropriate for BART, considering the five statutory factors:

(1) The costs of compliance,

(2) The energy and non-air quality environmental impacts of compliance,

(3) Any existing pollution control technology in use at the source,

(4) The remaining useful life of the source, and
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

50

(5) The degree of visibility improvement that may reasonably be anticipated from the 

use of BART.

The rule gives the states broad latitude on how the five factors are to be considered to 

determine the appropriate controls for BART. The Regional Haze rule provides little, if 

any, guidance on specifically how states are to use these factors in making the final 

determinations regarding what controls are appropriate under the rule, other than to 

consider the five factors in reaching a determination.8 The manner and method of 

consideration is left to the state‟s discretion; states are free to determine the weight and 

significance to be assigned to each factor.9

For the purposes of the five factor review for the three pollutants that the state is 

assessing for BART, SO2 and PM have been assessed utilizing the five factors on a 

case by case basis to reach a determination. This is primarily because the top level 

controls for SO2 and PM are already largely in use on electric generating units in the 

state, and certain other sources require a case by case review because of their unique 

nature. For NOx controls on BART electric generating units, for reasons described 

below, the state is employing guidance criteria to aid in its assessment and 

determination of BART using the five factors for these sources, largely because 

significant NOx add-on controls are not the norm for Colorado electric generating units, 

and to afford a degree of uniformity in the consideration of BART for these sources.

With respect to SO2 emissions, there are currently ten lime spray dryer (LSD) SO2 

control systems operating at electric generating units in Colorado.10 There are also two 

wet limestone systems in use in Colorado. The foregoing systems have been 

successfully operated and implemented for many years at Colorado sources, in some 

cases for over twenty years. The LSD has notable advantages in Colorado given the 

non-air quality consideration of its relatively lower water usage in reducing SO2 

emissions in the state and other non-air quality considerations. Each of these systems 

will meet EPA‟s presumptive limits, and in some cases surpass those limits.11 The 

 

8

The EPA “BART Guidelines” provide information relating to implementation of the Regional Haze rule, 

which the state has considered. However, Colorado also notes that Appendix Y is expressly not 

mandatory with respect to EGUs of less than 750 MWs in size, and Craig Station (Tri-State Generation 

and Transmission) is the only such BART electric generating unit in the state. See 70 Fed. Reg. at 39108. 

Thus, the state has substantial discretion in how it considers and applies the five factors (and any other 

factors that it deems relevant) to BART electric generating units in the state that are below this megawatt 

threshold, and for non-EGU sources. See, e.g., id. at 39108, 39131 and 39158.

9

See, e.g., 70 Fed. Reg. at 39170.

10 EGUs with LSD controls include Cherokee Units 3 & 4, Comanche Units 1, 2 & 3, Craig Unit 3, Hayden 

Units 1 & 2, Rawhide Unit 1, Valmont Unit 5.

11 In preparing Appendix Y, EPA conducted extensive research and analysis of emission controls on 

BART sources nationwide, including all BART EGU sources in Colorado. See 70 Fed. Reg. at 39134. 

Based upon this analysis, EPA established presumptive limits that it deems to be appropriate for large 

EGU sources of greater than 750 MW, including sources greater than 200 MW located at such plants. 

EPA‟s position is that the presumptive limits are cost effective and will lead to a significant degree of 

visibility improvement. Id. See also, 69 Fed. Reg. 25184, 25202 (May 5, 2004); Technical Support 

Document for BART NOx Limits for Electric Generating Units and Technical Support Document for BART 

NOx Limits for Electric Generating Units Excel Spreadsheet, Memorandum to Docket OAR 2002-0076, 

April 15, 2006; Technical Support Document for BART SO2 Limits for Electric Generating Units, 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

51

Division has determined in the past that these systems can be cost-effective for 

Colorado‟s BART sources, and the Air Quality Control Commission approved LSD 

systems as BART for Colorado Springs Utilities‟ Martin Drake Units #6 and #7 in 2008. 

With this familiarity and use of the emissions control technology, the state has assessed 

SO2 emissions control technologies and/or emissions rates for BART sources on a 

case by case basis in making its BART determinations.

With respect to PM emissions, fabric filter baghouses and appropriate PM emissions 

rates are in place at all power plants in Colorado. Fabric filter baghouse systems have 

been successfully operated and implemented for many years at Colorado sources, 

typically exceeding a control efficiency of 95%. The emission limits for these units 

reflect the 95% or greater control efficiency and are therefore stringent and appropriate. 

The state has determined that fabric filter baghouses are cost effective through their use 

at all coal-fired power plants in Colorado, and the Air Quality Control Commission 

approved these systems as BART in 2007. With this familiarity and use of the 

emissions control technology, the state has assessed PM emissions control 

technologies and/or emissions rates for BART sources on a case by case basis in 

making its BART determinations. Thus, as described in EPA‟s BART Guidelines, a full 

five-factor analysis for PM emissions was not necessary for Colorado‟s BART-subject 

units.

With respect to NOx emissions, post-combustion controls for NOx are generally not 

employed in Colorado at BART or other significant coal-fired electric generating units. 

Accordingly, this requires a direct assessment of the appropriateness of employing such 

post-combustion technology at these sources for implementation of the Regional Haze 

rule. There is only one coal-fired electric generating unit in the state that is equipped 

with a selective catalytic reduction (SCR) system to reduce NOx emissions, and that 

was employed as new technology designed into a new facility (Public Service Company 

of Colorado, Comanche Unit #3, operational 2010). There are no selective non-catalytic 

reduction (SNCR) systems in use on coal-fired electric generating units in the state to 

reduce NOx emissions.

In assessing and determining appropriate NOx BART controls for individual units for 

visibility improvement under the regional haze rule, the state has considered the five 

statutory factors in each instance. Based on its authority, discretion and policy 

judgment to implement the Regional Haze rule, the state has determined that costs and 

the anticipated degree of visibility improvement are the factors that should be afforded 

the most weight.12 In this regard, the state has utilized screening criteria as a means of 

generally guiding its consideration of these factors. More specifically, the state finds 

most important in its consideration and determinations for individual units: (i) the cost of 

controls as appropriate to achieve the goals of the regional haze rule (e.g., expressed 

as annualized control costs for a given technology to remove a ton of Nitrogen Oxides 

(NOx) from the atmosphere, or $/ton of NOx removed); and, (ii) visibility improvement 

 

Memorandum to Docket OAR 2002-0076, April 1, 2006; and Regulatory Impact Analysis for the Final 

Clean Air Visibility Rule or the Guidelines for Best Available Retrofit Technology (BART) Determinations 

Under the Regional Haze Regulations, U.S. EPA, June 2005.

12 See 70 Fed. Reg. at 39170 and 39137.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

52

expected from the control options analyzed (e.g., expressed as visibility improvement in 

delta deciview (Δdv) from CALPUFF air quality modeling).

- Accordingly, as part of its five factor consideration the state has elected to 

generally employ criteria for NOx post-combustion control options to aid in the 

assessment and determinations for BART – a $/ton of NOx removed cap, and 

two minimum applicable Δdv improvement figures relating to CALPUFF modeling 

for certain emissions control types, as follows.For the highest-performing NOx 

post-combustion control options (i.e., SCR systems for electric generating units) 

that do not exceed $5,000/ton of pollutant reduced by the state‟s calculation, and 

which provide a modeled visibility benefit on 0.50 Δdv or greater at the primary 

Class I Area affected, that level of control is generally viewed as reasonable.

- For lesser-performing NOx post-combustion control options (e.g., SNCR 

technologies for electric generating units) that do not exceed $5,000/ton of 

pollutant reduced by the state‟s calculation, and which provide a modeled 

visibility benefit of 0.20 Δdv or greater at the primary Class I Area affected, that 

level of control is generally viewed as reasonable.

The foregoing criteria guide the state‟s general approach to these policy considerations. 

They are not binding, and the state is free to deviate from this guidance criteria based 

upon its consideration of BART on a case by case basis.

The cost criteria presented above is generally viewed by the state as reasonable based 

on the state‟s extensive experience in evaluating industrial sources for emissions 

controls. For example, the $5,000/ton criterion is consistent with Colorado‟s retrofit 

control decisions made in recent years for reciprocating internal combustion engines 

(RICE) most commonly used in the oil and gas industry.13 In that case, a $5,000/ton 

threshold, which was determined by the state Air Quality Control Commission as a notto-exceed control cost threshold, was deemed reasonable and cost effective for an 

initiative focused on reducing air emissions to protect and improve public health.14 The 

$5,000/ton criterion is also consistent and within the range of the state‟s implementation 

of reasonably achievable control technology (RACT), as well as best achievable control 

technology (BACT) with respect to new industrial facilities. Control costs for Colorado 

RACT can be in the range of $5,000/ton (and lower), while control costs for Colorado 

BACT can be in the range of $5,000/ton (and higher).

In addition, as it considers the pertinent factors for regional haze, the state believes that 

the costs of control should have a relationship to visibility improvement. The highestperforming post-combustion NOx controls, i.e., SCR, has the ability to provide 

significant NOx reductions, but also has initial capital dollar requirements that can 

 

13 Air Quality Control Commission Regulation No. 7, 5 C.C.R. 1001-9, Sections XVII.E.3.a.(ii) (statewide 

RICE engines), and XVI.C.4 (8-Hour Ozone Control Area RICE engines).

14 The RICE emissions control regulations were promulgated by the Colorado Air Quality Control 

Commission in order to: (i) reduce ozone precursor emissions from RICE to help keep rapidly growing 

rural areas in attainment with federal ozone standards; (ii) for reducing transport of ozone precursor 

emissions from RICE into the Denver Metro Area/North Front Range (DMA/NFR) nonattainment area; 

and, (iii) for the DMA/NFR nonattainment area, reducing precursor emissions from RICE directly tied to 

exceedance levels of ozone.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

53

approach or exceed $100 million per unit.15 The lesser-performing post-combustion 

NOx controls, e.g., SNCR, reduce less NOx on a percentage basis, but also have 

substantially lower initial capital requirements, generally less than $10 million.16 The 

state finds that the significantly different capital investment required by the different 

types of control technologies is pertinent to its assessment and determination. 

Considering costs for the highest-performing add-on NOx controls (i.e., SCR), the state 

anticipates a direct level of visibility improvement contribution, generally 0.50 Δdv or 

greater of visibility improvement at the primary affected Class I Area.17 For the lesserperforming add-on NOx controls (e.g., SNCR), the state anticipates a meaningful and 

discernible level of visibility improvement that contributes to broader visibility 

improvement, generally 0.20 Δdv or greater of visibility improvement at the primary 

affected Class I Area.

Employing the foregoing guidance criteria for post-combustion NOx controls, as part of 

considering the five factors under the Regional Haze rule, promotes a robust evaluation 

of pertinent control options, including costs and an expectation of visibility benefit, to 

assist in determining what are appropriate control options for the Regional Haze rule.

6.4.3.1 BART Determination for Cemex’s Lyons Cement Plant

The Cemex facility manufactures Portland cement and is located in Lyons, Colorado, 

approximately 20 miles from Rocky Mountain National Park. The Lyons plant was 

originally constructed with a long dry kiln. This plant supplies approximately 25% of the 

clinker used in the regional cement market. There are two BART eligible units at the 

facility: the dryer and the kiln.

In 1980, the kiln was cut to one-half its original length, and a flash vessel was added 

with a single-stage preheater. The permitted kiln feed rate is 120 tons per hour of raw 

material (kiln feed), and on average yields approximately 62 tons of clinker per hour. 

The kiln is the main source of SO2 and NOx emissions. The raw material dryer emits 

minor amounts of SO2 and NOx; in 2008 Cemex reported SO2 and NOx emissions 

from the dryer as 0.89 and 10.41 tons per year respectively based on stack test results. 

Due to the low emission rates from the dryer the BART review focuses on the kiln.

Newer multistage preheater/precalciner kilns are designed to be more energy efficient 

and yield lower emissions per ton of clinker due to this when compared to the Cemex 

 

15 See, e.g., Appendix C, reflecting Public Service of Colorado, Comanche Unit #2, $83MM; Public 

Service of Colorado, Hayden Unit #2, $72MM; Tri-State Generation and Transmission, Craig Station Unit 

#1, $210MM.

16 See, e.g., Appendix C, reflecting CENC (Tri-gen), Unit #4, $1.4MM; Public Service Company of 

Colorado, Hayden Unit #2, $4.6MM; Tri-State Generation and Transmission, Craig Station Unit #1, 

$13.1MM

17 The EPA has determined that BART-eligible sources that affect visibility above 0.50 Δdv are not to be 

exempted from BART review, on the basis that above that level the source is individually contributing to 

visibility impairment at a Class I Area. 70 Fed. Reg. at 39161. The state relied upon this threshold when 

determining which Colorado‟s BART eligible sources became subject to BART. See, Air Quality Control 

Commission Regulation No. 3, Section III.B.1.b. Thus, a visibility improvement of 0.50 Δdv or greater will 

also provide significant direct progress towards improving visibility in a Class I Area from that facility.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

54

Lyons kiln. The newer Portland cement plants studied by EPA, utilize multistage 

preheater/precalciner designs that are not directly comparable. Cemex has a unique 

single stage preheater/precalciner system with different emission profiles and energy 

demands. New Portland cement plants have further developed the 

preheater/precalciner design with multiple stages to reduce emissions and energy 

requirements for the process. Additionally, new plant designs allow for the effective use 

of Selective Non-Catalytic Reduction (SNCR), which requires ammonia like compounds 

to be injected into appropriate locations of the preheater/precalciner vessels where 

temperatures are ideal (between 1600-2000oF) for reducing NOx to elemental Nitrogen.

Cemex submitted a BART analysis to the Division on August 1, 2006, with revisions 

submitted on August 28, 2006; January 15, 2007; October 2007 and August 29, 2008. 

In response to a Division request, Cemex submitted additional information on July 27 

and 28, 2010

CALPUFF modeling provided by the source, using a maximum SO2 emission rate of 

123.4 lbs/hour for both the dryer and kiln combined indicates a 98th percentile visibility 

impact of 0.78 delta deciview (Δdv) at Rocky Mountain National Park. The modeled 98th

percentile visibility impact from the kiln is 0.76 Δdv. Thus, the visibility impact of the 

dryer alone is the resultant difference which is 0.02 Δdv. Because the dryer uses the 

cleanest fossil fuel available and post combustion controls on such extremely low 

concentrations are not practical, the state has determined that no meaningful emission 

reductions (and thus no meaningful visibility improvements) would occur pursuant to 

any conceivable controls on the dryer. Accordingly, the state has determined that no 

additional emission control analysis of the dryer is necessary or appropriate since the 

total elimination of the emissions would not result in any meaningful visibility 

improvement which is a fundamental factor in the BART evaluation. For the dryer, the 

BART SO2 emission limitation is 36.7 tpy and the BART NOx emission limitation is 13.9 

tpy, which are listed in the existing Cemex Title V permit.

SO2 BART Determination for Cemex Lyons - Kiln

Lime addition to kiln feed, fuel substitution (coal with tire derived fuel), dry sorbent 

injection (DSI), and wet lime scrubbing (WLS) were determined to be technically 

feasible for reducing SO2 emissions from Portland cement kilns.

The following table lists the most feasible and effective options:

Cemex Lyons -Kiln

SO2 Control 

Technology

Estimated 

Control 

Efficiency

Annual Controlled 

Hourly SO2 

Emissions (lbs/hr)

Annual 

Controlled SO2 

Emissions (tpy)

Annual Controlled 

SO2 Emissions

(lb/ton of Clinker)

Baseline SO2 

Emissions 25.3 95.0 0.40

Lime Addition to Kiln 

Feed 25% 18.9 71.3 0.30 

Fuel Substitution

(coal with TDF) 40% 15.2 57.0 0.24
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

55

Cemex Lyons -Kiln

SO2 Control 

Technology

Estimated 

Control 

Efficiency

Annual Controlled 

Hourly SO2 

Emissions (lbs/hr)

Annual 

Controlled SO2 

Emissions (tpy)

Annual Controlled 

SO2 Emissions

(lb/ton of Clinker)

Dry Sorbent Injection 50% 12.6 47.5 0.20

Wet Lime Scrubbing

(Tailpipe scrubber)

90% 2.5 9.5 0.04 

The energy and non-air quality impacts of the alternatives are as follows:

Lime addition to kiln feed and dry sorbent injection - there are no energy or nonair quality impacts associated with these control options

Wet lime scrubbing - significant water usage, an additional fan of considerable 

horsepower to move the flue gas through the scrubber, potential increase in PM 

emissions and sulfuric acid mist

Tire-derived fuel – the community has expressed concerns regarding the 

potential for increased air toxics emissions, and opposed the use of tire derived 

fuel at this facility; a 2-year moratorium on use of permitted tire derived fuel was 

codified in a 2006 state enforcement matter for this facility. See, Cemex Inc., 

Case No. 2005-049 (Dec. 2006) Para. 1b.

There are no remaining useful life issues for the source, as the state has presumed that 

the source will remain in service for the 20-year amortization period. Cemex‟s 

limestone quarry may have a shorter life-span, but the source has not committed to a 

closure date.

The following table lists the SO2 emission reduction, annualized costs and the control 

cost effectiveness for the feasible controls:

Cemex Lyons - Kiln

SO2 Control Technology

SO2 

Emission 

Reduction 

Annualized 

Cost

Cost 

Effectiveness

Incremental 

Cost 

Effectiveness

(tons/yr) ($/yr) ($/ton) ($/ton)

Baseline SO2 Emissions -

Lime Addition to Kiln Feed 23.8 $3,640,178 $153,271

Fuel Substitution

(coal supplemented with TDF) 38.0 $172,179 $4,531 $243,368

Dry Sorbent Injection 47.5 Not 

provided -

Wet Lime Scrubbing (Tailpipe 

scrubber) 85.5 $2,529,018 $29,579 $49,618
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

56

The following table lists the projected visibility improvements for SO2 controls:

Cemex Lyons - Kiln

SO2 Control Method 98th Percentile 

Impact (Δdv)

98th Percentile 

Improvement (Δdv)

Maximum (24-hr max) 0.760

Baseline (95 tpy)* 0.731 -

Lime Addition to Kiln Feed (71.3 tpy)* 0.727 0.033

Fuel Substitution (57 tpy)* 0.725 0.034

Dry Sorbent Injection (47.5 tpy)* 0.725 0.036

Wet Lime Scrubbing (9.5 tpy)* 0.720 0.040

* Visibility impacts rescaled from original BART modeling

For the kiln, based upon its consideration and weighing of the five factors, the state has 

determined that no additional SO2 emissions control is warranted as the added 

expense of these controls were determined to not be reasonable for the small 

incremental visibility improvement of less than 0.04 deciviews. However, the use of low 

sulfur coal and the inherent control resulting from the Portland cement process provides 

sufficient basis to establish annual BART SO2 emission limits for the kiln of:

25.3 lbs/hour and

95.0 tons of SO2 per year

No additional controls are warranted because 80% of the sulfur is captured in the 

clinker, making the inherent control of the process the SO2 control. Additional SO2 

scrubbing is also provided by the limestone coating in the baghouse as the exhaust gas 

passes through the baghouse filter surface.

SO2 BART Determination for Cemex Lyons - Dryer

For the dryer, the state has determined that since the total elimination of the emissions 

would not result in any meaningful visibility improvement (less than 0.02 deciview), the 

SO2 BART requirement is 36.7 tpy, which is taken from the existing Title V permit.

Particulate Matter BART Determination for Cemex Lyons - Kiln and Dryer

The state has determined that the existing fabric filter baghouses and the existing 

regulatory emissions limits of 0.275 lb/ton of dry feed and 20% opacity for the kiln and 

10% opacity for the dryer represent the most stringent control option. The kiln and dryer 

baghouses exceed a PM control efficiency of 95%, and the emission limits are BART for 

PM/PM10. The state assumes that the BART emission limits can be achieved through 

the operation of the existing fabric filter baghouse.

NOx BART Determination for Cemex Lyons - Kiln

Water injection, firing coal supplemented with tire-derived fuel (TDF), indirect firing with 

low NOx burners, and selective non-catalytic reduction (SNCR) were determined to be 

technically feasible and appropriate for reducing NOx emissions from Portland cement 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

57

kilns. As further discussed in Appendix C, the state has determined that SCR is not 

commercially available for Portland cement kilns. Presently, SCR has not been applied 

to a cement plant of any type in the United States. Cemex notes that the major SCR 

vendors have indicated that SCR is not commercially available for cement kilns at this 

time. The state does not believe that a limited use - trial basis application of an SCR 

control technology on three modern kilns in Europe, constitutes “available” control 

technology for purposes of BART. The state believes that commercial demonstration of 

SCR controls on a cement plant in the United States is appropriate when considering 

whether a control technology is “available” for purposes of retrofitting such control 

technology on an existing source. Accordingly, the state has eliminated SCR as an 

available control technology for purposes of BART. Moreover, as further discussed in 

Appendix C, if SCR were considered commercially available, it is not technically feasible 

for the Lyons facility due to the unique design of the kiln.

The following table lists the most feasible and effective options:

Cemex Lyons - Kiln

NOx Control Technology

Estimated 

Control 

Efficiency

Annual Controlled 

Hourly NOx 

Emissions (lbs/hr)

Annual 

Controlled NOx 

Emissions (tpy)

Annual Controlled 

NOx Emissions

(lb/ton of Clinker)

Baseline NOx Emissions - 464.3 1,747.1 7.39

Water Injection 7.0% 431.8 1,624.8 6.87

Coal w/TDF 10.0% 417.8 1,572.3 6.65

Indirect Firing with LNB 20.0% 371.4 1,397.6 5.91

SNCR (30-day rolling) 45.0% 255.3 960.9 4.06

SNCR (12-month rolling) 48.4% 239.4 901.0 3.81

SNCR w/LNB 55% 208.9 786.2 3.33

The energy and non-air quality impacts of the alternatives are as follows:

Low-NOx burners - there are no energy or non-air quality impacts 

Water injection - significant water usage

Tire-derived fuel – the community has expressed concerns regarding the 

potential for increased air toxics emissions, and opposed the use of tire derived 

fuel at this facility; a 2-year moratorium on use of permitted tire derived fuel was 

codified in a 2006 state enforcement matter for this facility. See, Cemex Inc., 

Case No. 2005-049 (Dec. 2006) Para. 1b.

SNCR - none

There are no remaining useful life issues for the alternatives as the state has presumed 

that the source will remain in service for the 20-year amortization period. Cemex‟s 

limestone quarry may have a shorter life-span, but the source has not committed to a 

closure date.

The following table lists the emission reductions, annualized costs and the control cost 

effectiveness for the feasible controls:
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

58

Cemex Lyons - Kiln

NOx Control Technology

NOx Emission 

Reduction

Annualized 

Cost

Cost 

Effectiveness

Incremental 

Cost 

Effectiveness

(tons/yr) ($/yr) ($/ton) ($/ton)

Baseline NOx Emissions -

Water Injection 122.3 $43,598 $356 -

Coal w/TDF 174.7 $172,179 $986 $2,453

Indirect Firing with LNB 349.4 $710,750 $2,034 $3,083

SNCR (45.0% control) 786.2 $1,636,636 $2,082 $2,120

SNCR (48.4% control) 846.1 $1,636,636 $1,934 $1,864

SNCR w/LNB (55.0% control 

w/uncertainty) 960.9 $1,686,395 $1,755 $434

The following table lists the projected visibility improvements for NOx controls for the 

kiln:

Control Method

98th 

Percentile 

Impact

98th Percentile 

Improvement

(from 24-hr Max)

(Δdv) (Δdv)

24-hr Maximum (≈ 656.9 lbs/hr)) 0.760

Revised Baseline ( ≈ 464.3 lbs/hr)* 0.572 0.188

Original Baseline (≈ 446.8 lbs/hr)* 0.555 0.205

Water Injection (≈ 431.8 lbs/hr)* 0.540 0.220

Firing TDF (≈417.9 lbs/hr)* 0.526 0.234

Indirect Firing with LNB (≈ 371.4 lbs/hr)* 0.481 0.279

Original BART Limit – SNCR (≈ 268.0 lbs/hr) 0.380 0.380

Proposed BART Limit (30-day) – SNCR (≈ 255.3 lbs/hr)** 0.368 0.392

Proposed BART Limit (annual) – SNCR (≈ 239.0 lbs/hr)** 0.352 0.408

SNCR w/LNB (≈208.9 lbs/hr)** 0.322 0.438

The Cemex – Lyons facility is a unique kiln system most accurately described as a 

modified long dry kiln, the characteristics of a modified long dry kiln system are not 

similar to either a long wet kiln or a multi stage preheater/precalciner kiln. The 

temperature profile in a long dry kiln system (>1500oF) is significantly higher at the exit 

than a more typical preheater precalciner kiln (650oF). This is a significant distinction 

that limits the location and residence time available for an effective NOx control system. 

The combination of SNCR with LNB has an uncertain level of control due to unique 

nature of the Lyons kiln. Furthermore, the associated incremental reduction in NOx 

emissions associated with SNCR in combination with LNB would afford only a minimal 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

59

or negligible visibility improvement (less than 0.03 delta deciview). Therefore, the 

Division believes that SNCR is the best NOx control system available for this kiln.

For the kiln, because of the unique characteristics of the Cemex facility, the state has 

determined that the BART emission limits for NOx are:

255.3 pounds per hour (30-day rolling average) and

901.0 tons per year (12-month rolling average)

The emissions rate and the control efficiency reflect the best performance from the 

control options evaluated. This BART determination affords the most NOx reduction 

from the kiln (846.1 tpy) and contributes significant visibility improvement (0.38 Δdv). 

The determination affirms a prior Air Quality Control Commission BART determination 

for SNCR for this facility (2008). The state assumes that the BART emission limits can 

be achieved through the installation and operation of SNCR.

NOx BART Determination for Cemex Lyons - Dryer

For the dryer, the state has determined that since the total elimination of the emissions 

would not result in any meaningful visibility improvement (less than 0.02 deciview), the 

NOx BART requirement is 13.9 tpy, which is taken from the existing Title V permit.

A complete analysis that further supports the BART determination for the Cemex Lyons

facility can be found in Appendix C.

6.4.3.2 BART Determination for Colorado Energy Nations Company (CENC)

This facility is located adjacent to the Coors brewery in Golden, Jefferson County. 

Boilers 4 and 5 are considered BART-eligible, being industrial boilers with the potential 

to emit 250 tons or more of haze forming pollution (NOx, SO2, PM10), and having 

commenced operation in the 15-year period prior to August 7, 1977. Initial air 

dispersion modeling performed by the Division demonstrated that the CENC facility 

contributes to visibility impairment (a 98th percentile impact equal to or greater than 0.5 

deciviews) and is therefore subject to BART. Trigen (now CENC) submitted a BART 

Analysis to the Division on July 31, 2006. CENC also provided information in its “NOx 

Technical Feasibility and Emission Control Costs for Colorado Energy Nations, Golden, 

Colorado” Submittal provided on November 16, 2009, as well as additional information 

upon the Division‟s request on February 8, 2010, and May 7, 2010.

The CENC facility includes two coal-fired boilers that supply steam and electrical power 

to Coors Brewery. The boilers are rated as follows: Unit 4 at 360 MMBtu/hr and Unit 5 

at 650 MMBtu/hr. These are approximately equivalent to 35 and 65 MW power plant 

boilers, based on the design heat rates.

SO2 BART Determination for CENC - Boilers 4 and 5

Dry sorbent injection (DSI) and SO2 emission management were determined to be 

technically feasible for reducing SO2 emissions from Boilers 4 and 5. These options 

were considered as potentially BART by the Division. Lime or limestone-based wet 

FGD is technically feasible, but was determined to not be reasonable due to adverse 

non-air quality impacts. Dry FGD controls were determined to be not technically 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

60

feasible. SO2 emissions management uses a variety of options to reduce SO2 

emissions: dispatch natural gas-fired capacity, reduce total system load, and/or recue 

coal firing rate to maintain a new peak SO2 limit.

The following tables list the emission reductions, annualized costs and cost 

effectiveness of the control alternatives:

CENC Boiler 4 - SO2 Cost Comparison

Alternative Emissions 

Reduction (tpy)

Annualized Cost 

($)

Cost Effectiveness 

($/ton)

Baseline 0 $0 $0

SO2 Emissions Management 1.0 $44,299 $43,690

DSI – Trona 468.0 $1,766,000 $3,774

CENC Boiler 5 - SO2 Cost Comparison

Alternative Emissions 

Reduction (tpy)

Annualized Cost 

($)

Cost Effectiveness 

($/ton)

Baseline 0 $0 $0

SO2 Emissions Management 0.8 $65,882 $78,095

DSI – Trona 844.0 $2,094,000 $2,482

The energy and non-air quality impacts of the remaining alternative are as follows:

DSI - reduced mercury capture in the baghouse, and fly ash contamination with 

sodium sulfate, rendering the ash unsalable as a replacement for concrete and 

rendering it landfill material only.

There are no remaining useful life issues for the alternatives as the sources will remain 

in service for the 20-year amortization period.

The projected visibility improvements attributed to DSI are as follows:

SO2 Control Method

CENC - Boiler 4 CENC - Boiler 5

SO2 Emission 

Rate 

(lb/MMBtu)

98th 

Percentile 

Impact (Δdv)

SO2 Emission 

Rate 

(lb/MMBtu)

98th 

Percentile 

Impact (Δdv)

Daily Maximum (3-yr) 0.90 0.98

DSI – Trona (annual 

avg.)

0.26 0.08 0.29 0.13

SO2 emissions management was eliminated from consideration due to the high 

cost/effectiveness ratios and anticipated small degree of visibility improvement that 

would result from one tpy or less of SO2 reduction.

Based upon its consideration of the five factors summarized herein and detailed in 

Appendix C, the state has determined that SO2 BART is the following SO2 emission 

rates:
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

61

CENC Boiler 4: 1.0 lb/MMBtu (30-day rolling average)

CENC Boiler 5: 1.0 lb/MMBtu (30-day rolling average)

The state assumes that the BART emission limits can be achieved without additional 

control technology. Although dry sorbent injection does achieve better emissions 

reductions, the added expense of DSI controls were determined to not be reasonable 

coupled with the low visibility improvement afforded.

Particulate Matter BART Determination for CENC - Boilers 4 and 5

The Division has determined that for Boilers 4 and 5, an emission limit of 0.07 lb/MMBtu 

(PM/PM10) represents the most stringent control option. The units are exceeding a PM 

control efficiency of 95%, and the control technology and emission limits are BART for 

PM/PM10. The state assumes that the BART emission limit can be achieved through 

the operation of the existing fabric filter baghouses.

NOx BART Determination for CENC - Boilers 4 and 5

Low NOx burners (LNB), LNB plus separated overfire air (SOFA), selective noncatalytic reduction (SNCR), SNCR plus LNB plus SOFA, and selective catalytic 

reduction (SCR) were determined to be technically feasible for reducing NOx emissions 

at CENC Boilers 4 and 5.

The following tables list the emission reductions, annualized costs and cost 

effectiveness of the control alternatives.

CENC Boiler 4 - NOx Cost Comparisons

Alternative Emissions 

Reduction (tpy)

Annualized Cost 

($)

Cost Effectiveness 

($/ton)

Baseline 0 0 $0

LNB 59.9 $193,433 $3,227

SNCR 179.8 $694,046 $3,860

LNB+SOFA 209.8 $678,305 $3,234

LNB+SOFA + SNCR 368.0 $1,372,351 $3,729

SCR 515.4 $4,201,038 $8,150

CENC Boiler 5 - NOx Cost Comparisons

Alternative Emissions 

Reduction (tpy)

Annualized Cost 

($)

Cost Effectiveness 

($/ton)

Baseline 0 $0 $0

LNB 48.4 $249,858 $5,166

LNB+SOFA 127.3 $815,829 $6,383

SNCR 207.3 $923,996 $4,458

LNB+SOFA + SNCR 353.7 $1,739,825 $4,918

SCR 550.0 $6,469,610 $11,764
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

62

The energy and non-air quality impacts of the alternatives are as follows:

LNB – not significant

LNB + SOFA – may increase unburned carbon in the ash, commonly referred to 

as loss on ignition

SNCR – increased power needs, potential for ammonia slip, potential for visible 

emissions, hazardous materials storage and handling

There are no remaining useful life issues for the alternatives as the sources will remain 

in service for the 20-year amortization period.

The projected visibility improvements attributed to the alternatives are as follows:

NOx Control Method

CENC - Boiler 4 CENC - Boiler 5

NOx Emission 

Rate 

(lb/MMBtu)

98th 

Percentile 

Impact (Δdv)

NOx l Emission 

Rate 

(lb/MMBtu)

98th 

Percentile 

Impact (Δdv)

Daily Maximum (3-yr) 0.67 0.66

LNB (annual avg.) 0.45 0.05 0.30 0.17

SNCR (annual avg.) 0.35 0.07 0.24 0.21

LNB + SOFA (annual 

avg.)

0.32 0.08 0.24 0.21

LNB + SOFA + SNCR 

(annual avg.)

0.19 0.12 0.17 0.26

SCR 0.07 0.18 0.07 0.31

Based upon its consideration of the five factors summarized herein and detailed in 

Appendix C, the state has determined that NOx BART for Boiler 4 is the following NOx 

emission rates:

CENC Boiler 4: 0.37 lb/MMBtu (30-day rolling average)

Or

0.26 lb/MMBtu Boiler 4 and Boiler 5 combined average (30-day 

rolling average)

The state assumes that the BART emission limits can be achieved through the 

installation and operation of low NOx burners with separated over-fire air.

Although the other alternatives achieve better emissions reductions, achieving lower 

limits through different controls was determined to not be reasonable based on the high 

cost/effectiveness ratios coupled with the low visibility improvement afforded.

EPA Region 8 notes to the state that a number of control cost studies, such as that by 

NESCAUM (2005), indicate that costs for SNCR or SCR could be lower than the costs 

estimated by the Division in the above BART determination. However, assuming such 

lower costs were relevant to this source, use of such lower costs would not change the 

state's BART determination because the degree of visibility improvement achieved by 

SNCR or SCR is below the state's guidance criteria of 0.2 dv and 0.5 dv, respectively. 

Moreover, the incremental visibility improvement associated with SNCR or SCR is not 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

63

substantial when compared to the visibility improvement achieved by the selected limits 

(i.e., 0.04 dv for SNCR and 0.10 dv for SCR). Thus, it is not warranted to select 

emission limits associated with either SNCR or SCR for CENC Unit 4.

Based upon its consideration of the five factors summarized herein and detailed in 

Appendix C, the state has determined that NOx BART for Boiler 5 is the following NOx

emission rates:

CENC Boiler 5: 0.19 lb/MMBtu (30-day rolling average)

Or

0.26 lb/MMBtu Boiler 4 and 5 combined average (30-day rolling 

average)

The state assumes that the BART emission limits can be achieved through the 

installation and operation of low NOx burners with separated over-fire air and selective 

non-catalytic reduction.

For the emission limits above, the cost per ton of emissions removed, coupled with the 

estimated visibility improvements gained, falls within the guidance criteria discussed

above in section 6.4.3.

Boiler 5: $4,918 per ton NOx removed; 0.26 deciview of improvement

The dollars per ton control cost, coupled with notable visibility improvements, leads the 

state to this determination. Though SCR achieves better emissions reductions, 

achieving lower limits through SCR was determined to not fall into the guidance cost 

and visibility improvement criteria discussed in section 6.4.3.

EPA Region 8 notes to the state that a number of control cost studies, such as that by 

NESCAUM (2005), indicate that costs for SCR could be lower than the costs estimated 

by the Division in the above BART determination. However, assuming such lower costs 

were relevant to this source, use of such lower costs would not change the state's 

BART determination because the degree of visibility improvement achieved by SCR is 

below the state's guidance criteria of 0.5 dv. Moreover, the incremental visibility 

improvement associated with SCR is not substantial when compared to the visibility 

improvement achieved by the selected limits (i.e., 0.05 dv). Thus, it is not warranted to 

select emission limits associated SCR for CENC Unit 5.

A complete analysis that supports the BART determination for the CENC facility can be 

found in Appendix C.

6.4.3.3 BART Determination for Public Service Company Comanche Units 1 and 2

Comanche Units 1 and 2 are considered BART-eligible, being fossil-fuel steam electric 

plants of more than 250 MMBtu/hr heat input with the potential to emit 250 tons or more 

of haze forming pollution (NOx, SO2, PM10), and having commenced operation in the 15-

year period prior to August 7, 1977. These boilers also cause or contribute to visibility 

impairment at a federal Class I area at or above a 0.5 deciview change; consequently, 

both boilers are subject-to-BART. PSCo submitted a BART analysis to the Division on 

September 14, 2006 with revisions submitted on November 1, 2006 and January 8, 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

64

2007. In response to a Division request, PSCo submitted additional information on May 

25, and July 14, 2010.

SO2 BART Determination for Comanche - Units 1 and 2

Semi-Dry FGD Upgrades – As discussed in EPA‟s BART Guidelines, electric generating 

units (EGUs) with existing controls achieving removal efficiencies of greater than 50 

percent do not need to be evaluated for potential removal of controls and replacement 

with new controls. Therefore, the following dry scrubber upgrades should be 

considered for Comanche Units 1 and 2, if technically feasible.

Use of performance additives - The supplier of Comanche‟s dry scrubbing 

equipment does not recommend the use of any performance additive. PSCo is 

aware of some additive trials, using a chlorine-based chemical, for dry scrubbers. 

Because low-sulfur coal is used at Comanche, the use of performance additives 

on the scrubbers would not be expected to increase the SO2 removal.

Use of more reactive sorbent - PSCo is using a highly reactive lime with 92% 

calcium oxide content reagent that maximizes SO2 removal. The only other 

common reagent option for a dry scrubber is sodium-based products which are 

more reactive than freshly hydrated lime. Sodium has a major side effect of 

converting some of the NOx in the flue gas into NO2. Since NO2 is a visible gas, 

large coal-fired units can generate a visible brown/orange plume at high SO2

removal rates, such as those experienced at Comanche. There are no known 

acceptable reagents without this side effect that would allow additional SO2

removal in the dry scrubbing systems present at the Comanche Station.

Increase the pulverization level of sorbent – PSCo uses the best available 

grinding technologies, and other pulverization techniques have not been proven 

more effective.

Engineering redesign of atomizer or slurry injection system - The supplier offers 

no upgrade in atomizer design to improve SO2 removal at Comanche. PSCo 

asserts and the state agrees that a third scrubber module on Comanche Units 1 

and 2 is not feasible due to the current layout of the ductwork and space 

constraints around the scrubbers.

Additional equipment and maintenance - Comanche Units 1 and 2 are already 

achieving 30-day average emission rates of 0.12 lbs/MMBtu, 30-day rolling 

average, and 0.10 lbs/MMBtu, 12-month average for the two units combined, as 

adopted in 2007 by the Commission. It is not technically feasible to install an 

extra scrubber module at the site; therefore no additional equipment or 

maintenance will decrease SO2 emissions or achieve a lower limit.

Consequently, further capital upgrades to the current high performing SO2 removal 

system were deemed technically infeasible, and a lower emissions limit is not 

achievable.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

65

The projected visibility improvements attributed to the alternatives are as follows:

SO2 Control Method

Comanche – Unit 1 Comanche – Unit 2

SO2 Emission 

Rate 

(lb/MMBtu)

98th 

Percentile 

Impact (Δdv)

SO2 Emission 

Rate 

(lb/MMBtu)

98th 

Percentile 

Impact (Δdv)

Daily Maximum (3-yr) 0.75 0.74

Semi-Dry FGD (LSD) 

(annual avg.)

0.12 0.35 0.12 0.33

Semi-Dry FGD (LSD) 

(annual avg.)

0.08 0.37 0.08 0.36

Based upon its consideration of the five factors summarized herein and detailed in 

Appendix C, the state has determined that the following existing SO2 emission rates are 

BART:

Comanche Unit 1: 0.12 lb/MMBtu (30-day rolling average)

0.10 lb/MMBtu (combined annual average for units 1 & 2)

Comanche Unit 2: 0.12 lb/MMBtu (30-day rolling average)

0.10 lb/MMBtu (combined annual average for units 1 & 2)

The state assumes that the BART emission limits can be achieved through the 

operation of existing lime spray dryers (LSD). A 30-day rolling SO2 limit of 0.12 

lbs/MMBtu represents an appropriate level of emissions control associated with semidry FGD control technology. A complete analysis that supports the BART determination 

for the Comanche facility can be found in Appendix C.

Particulate Matter BART Determination for Comanche - Units 1 and 2

Based on recent BACT determinations, the state has determined that the existing Unit 1 

and 2 emission limit of 0.03 lb/MMBtu (PM/PM10) represents the most stringent level of 

available control for PM/PM10. The units are exceeding a PM control efficiency of 95%, 

and the state has selected this emission limit for PM/PM10 as BART. The state 

assumes that the BART emission limit can be achieved through the operation of the 

existing fabric filter baghouses.

NOx BART Determination for Comanche - Units 1 and 2

SNCR and SCR were determined to be technically feasible for reducing NOx emissions 

at Comanche Unit 1, and only SCR was determined feasible at Unit 2.

The following tables list the emission reductions, annualized costs and cost 

effectiveness of the control alternatives:
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

66

Comanche Unit 1 - NOx Cost Comparisons

Alternative Emissions Reduction 

(tpy)

Annualized Cost 

($)

Cost Effectiveness 

($/ton)

Baseline 0 $0 $0

SNCR 445.6 $1,624,100 $3,644

SCR 770.4 $12,265,014 $15,290

Comanche Unit 2 - NOx Cost Comparisons

Alternative Emissions Reduction 

(tpy)

Annualized Cost 

($)

Cost Effectiveness 

($/ton)

Baseline 0 $0 $0

SCR 1,480 $14,650,885 $9,900

The energy and non-air quality impacts of the alternatives are as follows:

SNCR and SCR – increased power needs, potential for ammonia slip, potential for 

visible emissions, hazardous materials storage and handling

There are no remaining useful life issues for the alternatives as the sources will remain 

in service for the 20-year amortization period.

The projected visibility improvements attributed to the alternatives are as follows:

NOx Control Method

Comanche – Unit 1 Comanche – Unit 2

NOx Emission 

Rate 

(lb/MMBtu)

98th 

Percentile 

Impact (Δdv)

NOx Emission 

Rate 

(lb/MMBtu)

98th 

Percentile 

Impact (Δdv)

Daily Maximum (1-yr) 

using new LNBs 0.20 0.20

SNCR (annual avg.) 0.10 0.11 Not Feasible –

SCR (annual avg.) 0.07 0.14 0.07 0.17

Based upon its consideration of the five factors summarized herein and detailed in 

Appendix C, the state has determined that NOx BART is the following existing NOx 

emission rates:

Comanche Unit 1: 0.20 lb/MMBtu (30-day rolling average)

0.15 lb/MMBtu (combined annual average for units 1 & 2)

Comanche Unit 2: 0.20 lb/MMBtu (30-day rolling average)

0.15 lb/MMBtu (combined annual average for units 1 & 2)

The state assumes that the BART emission limits can be achieved through the 

operation of existing low NOx burners. Although the other alternatives achieve better 

emissions reductions, the added expense of achieving lower limits through different 

controls were determined to not be reasonable based on the high cost/effectiveness 

ratios coupled with the low visibility improvement (under 0.2 delta deciview) afforded.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

67

EPA Region 8 notes to the state that a number of control cost studies, such as that by 

NESCAUM (2005), indicate that costs for SNCR or SCR could be lower than the costs 

estimated by the Division in the above BART determination. However, assuming such 

lower costs were relevant to this source, use of such lower costs would not change the 

State's BART determination because the degree of visibility improvement achieved by 

SNCR or SCR is below the state's guidance criteria of 0.2 dv and 0.5 dv, respectively. 

Moreover, the incremental visibility improvement associated with SNCR or SCR is not 

substantial when compared to the visibility improvement achieved by the selected limits 

(i.e., 0.10 dv for SNCR and 0.13 dv for SCR for Unit 1, and 0.17 dv for SCR for Unit 2). 

SNCR was found not to be technically feasible for Comanche Unit 2. Thus, it is not 

warranted to select emission limits associated with either SNCR or SCR for Comanche 

Units 1 and 2.

A complete analysis that supports the BART determination for PSCo‟s Comanche Units 

1 and 2 can be found in Appendix C.

6.4.3.4 BART Determination for Tri-State Generation and Transmission 

Association’s Craig Facility

Craig Units 1 and 2 are BART-eligible, being fossil-fuel steam electric plants of more

than 250 MMBtu/hr heat input with the potential to emit 250 tons or more of haze 

forming pollution (NOx, SO2, PM10), and having commenced operation in the 15-year 

period prior to August 7, 1977. These boilers also cause or contribute to visibility 

impairment at a federal Class I area at or above a 0.5 deciview change. Tri-State 

submitted a BART Analysis to the Division on July 31, 2006 with revisions, updates, 

and/or comments submitted on October 25, 2007, December 31, 2009, May 14, 2010, 

June 4, 2010 and July 30, 2010.

SO2 BART Determination for Craig - Units 1 and 2

Wet FGD Upgrades – As discussed in EPA‟s BART Guidelines, electric generating units 

(EGUs) with existing controls achieving removal efficiencies of greater than 50 percent 

do not need to be evaluated for potential removal of controls and replacement with new 

controls. Therefore, the following wet scrubber upgrades were considered for Craig 

Units 1 and 2, if technically feasible.

Elimination of bypass reheat: The FGD system bypass was redesigned to eliminate 

bypass of the FGD system except for boiler safety situations in 2003-2004.

Installation of liquid distribution rings: TriState determined that installation of 

perforated trays, described below, accomplished the same objective.

Installation of perforated trays: Upgrades during 2003-2004 included installation of a 

perforated plate tray in each scrubber module.

Use of organic acid additives: Organic acid additives were considered but not 

selected for the following reasons:

1. Dibasic Acid (DBA) has not been tested at the very low inlet SO2 concentrations 

seen at Craig Units 1 and 2.

2. DBA could cause changes in sulfite oxidation with impacts on SO2 removal and 

solids settling and dewatering characteristics.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

68

3. Installation of the perforated plate tray accomplished the same objective of 

increased SO2 removal.

Improve or upgrade scrubber auxiliary equipment: 2003-2004 upgrades included 

installation of the following upgrades on limestone processing and scrubber modules 

on Craig 1 and 2:

1. Two vertical ball mills were installed for additional limestone processing capability 

for increased SO2 removal. The two grinding circuit trains were redesigned to 

position the existing horizontal ball mills and the vertical ball mills in series to 

accommodate the increased quantity of limestone required for increased removal 

rates. The two mills in series also were designed to maintain the fine particle 

size (95% <325 mesh or 44 microns) required for high SO2 removal rates.

2. Forced oxidation within the SO2 removal system was thought necessary to 

accommodate increased removal rates and maintain the dewatering 

characteristics of the limestone slurry. Operation, performance, and 

maintenance of the gypsum dewatering equipment are more reliable with 

consistent slurry oxidation.

3. A ventilation system was installed for each reaction tank.

4. A new mist eliminator wash system was installed due to the increased gas flow 

through the absorbers since flue gas bypass was eliminated, which increased 

demand on the mist eliminator system. A complete redesign and replacement of 

the mist eliminator system including new pads and wash system improved the 

reliability of the individual modules by minimizing down time for washing deposits 

out of the pads.

5. Tri-State installed new module outlet isolation damper blades. The new blades, 

made of a corrosion-resistant nickel alloy, allow for safer entry into the nonoperating module for maintenance activities.

6. Various dewatering upgrades were completed. Dewatering the gypsum slurry 

waste is done to minimize the water content in waste solids prior to placements 

of the solids in reclamation areas at the Trapper Mine. The gypsum solids are 

mixed or layered with ash and used for fill during mine reclamation at Trapper 

Mine. The installed system was designed for the increased capacity required for 

increased SO2 removal. New hydrocyclones and vacuum drums were installed 

as well as a new conveyor and stack out system for solid waste disposal.

7. Instrumentation and controls were modified to support all of the new equipment.

Redesign spray header or nozzle configuration: The slurry spray distribution was 

modified during 2003-2004. The modified slurry spray distribution system improved 

slurry spray characteristics and was designed to minimize pluggage in the piping.

Therefore, there are no technically feasible upgrade options for Craig Station Units 1 

and 2. However, the state evaluated the option of tightening the emission limit for Craig 

Units 1 and 2 through the five-factor analysis and determined that a more stringent 30-

day rolling SO2 limit of 0.11 lbs/MMBtu represents an appropriate level of emissions 

control for this wet FGD control technology based on current emissions and operations. 

The tighter emission limits are achievable without additional capital investment. An SO2 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

69

limit lower than 0.11 lbs/MMBtu would likely require additional capital expenditure and is 

not reasonable for the small incremental visibility improvement of 0.02 deciview.

The projected visibility improvements attributed to the alternatives are as follows:

SO2 Control Method

Craig – Unit 1 Craig – Unit 2

SO2 Annual 

Emission Rate 

(lb/MMBtu)

98th 

Percentile 

Impact (Δdv)

SO2 Annual 

Emission Rate 

(lb/MMBtu)

98th 

Percentile 

Impact (Δdv)

Daily Maximum (3-yr) 0.17 0.16

Wet FGD 0.11 0.03 0.11 0.03

Wet FGD 0.07 0.05 0.07 0.05

Based upon its consideration of the five factors summarized herein and detailed in 

Appendix C, the state has determined that SO2 BART is the following SO2 emission 

rates:

Craig Unit 1: 0.11 lb/MMBtu (30-day rolling average)

Craig Unit 2: 0.11 lb/MMBtu (30-day rolling average)

The state assumes that the BART emission limits can be achieved through the 

operation of existing lime spray dryers (LSD). The 30-day rolling SO2 limit of 0.11 

lbs/MMBtu represents an appropriate level of emissions control associated with semidry FGD control technology.

Particulate Matter BART Determination for Craig - Units 1 and 2

The Division has determined that the existing Unit 1 and 2 emission limit of 0.03 

lb/MMBtu (PM/PM10) represents the most stringent control option. The units are 

exceeding a PM control efficiency of 95%, and the control technology and emission 

limits are BART for PM/PM10. The state assumes that the BART emission limit can be 

achieved through the operation of the existing pulse jet fabric filter baghouses.

NOx BART Determination for Craig - Units 1 and 2

Potential modifications to the ULNBs, neural network systems, selective non-catalytic 

reduction (SNCR), and selective catalytic reduction (SCR) were determined to be 

technically feasible for reducing NOx emissions at Craig Units 1 and 2.

The following tables list the emission reductions, annualized costs and cost 

effectiveness of the control alternatives:

Craig Unit 1 - NOx Cost Comparisons

Alternative Emissions Reduction

(tpy)

Annualized Cost 

($)

Cost Effectiveness 

($/ton)

Baseline 0 $0 $0

SNCR 779 $3,797,000 $4,877

SCR 3,855 $25,036,709 $6,445
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

70

Craig Unit 2 - NOx Cost Comparisons

Alternative Emissions Reduction 

(tpy)

Annualized Cost 

($)

Cost Effectiveness 

($/ton)

Baseline 0 $0 $0

SNCR 806 $3,797,000 $4,712

SCR 3,975 $25,036,709 $6,299

The energy and non-air quality impacts of SNCR are increased power needs, potential 

for ammonia slip, potential for visible emissions, and hazardous materials storage and 

handling.

There are no remaining useful life issues for the alternatives as the sources will remain 

in service for the 20-year amortization period.

The projected visibility improvements attributed to the alternatives are as follows:

NOx Control Method

Craig – Unit 1 Craig – Unit 2

NOx Annual 

Emission Rate 

(lb/MMBtu)

98th 

Percentile 

Impact (Δdv)

NOx Annual 

Emission Rate 

(lb/MMBtu)

98th 

Percentile 

Impact (Δdv)

Daily Maximum (3-yr) 0.35 0.35

SNCR 0.24 0.31 0.23 0.31

SCR 0.07 1.01 0.07 0.98

While potential modifications to the ULNB burners and a neural network system were 

also found to be technically feasible, these options did not provide the same level of 

reductions as SNCR or SCR, which are included within the ultimate BART Alternative 

determination for Units 1 and 2. Therefore, these options were not further considered in 

the technical analysis.

Based upon its consideration of the five factors summarized herein and detailed in 

Appendix C, the state has determined that NOx BART is the following NOx emission 

rates:

Craig Unit 1: 0.27 lb/MMBtu (30-day rolling average)

Craig Unit 2: 0.27 lb/MMBtu (30-day rolling average)

The state assumes that the BART emission limits can be achieved through the 

operation of SNCR. For the BART emission limits at Units 1 and 2, the cost per ton of 

emissions removed, coupled with the estimated visibility improvements gained, falls 

within the guidance criteria presented above.

Unit 1: $4,877 per ton NOx removed; 0.31 deciview of improvement

Unit 2: $4,712 per ton NOx removed; 0.31 deciview of improvement

The dollars per ton control costs, coupled with notable visibility improvements, leads the 

state to this determination. To the extent practicable, any technological application TriState utilizes to achieve these BART emission limits shall be installed, maintained, and 

operated in a manner consistent with good air pollution control practices for minimizing 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

71

emissions. Although emission limits associated with SCR achieve better emissions 

reductions, the cost-effectiveness of SCR for this BART determination was determined 

to be excessive and above the cost guidance criteria presented above. The state 

reached this conclusion after considering the associated visibility improvement 

information and after considering the SCR cost information in the SIP materials and 

provided during the pre-hearing and hearing process by the company, parties to the 

hearing, and the FLMs.

Per Section 308(e)(2) of EPA‟s Regional Haze Rule, as an alternative to BART (or 

“BART alternative”) it was proposed and the state agreed to a more stringent NOx 

emissions control plan for these BART units that consists of emission limits assumed to 

be associated with the operation of SNCR for Unit 1 and the operation of SCR for Unit 

2. These NOx emission rates are as follows:

Craig Unit 1: 0.28 lb/MMBtu (30-day rolling average)

Craig Unit 2: 0.08 lb/MMBtu (30-day rolling average)

Unit 1‟s 0.28 lb/MMBtu NOx emission rate equates to a 14% control and a NOx 

reduction of 727 tons per year, which is slightly less than the 15% control and a NOx 

reduction of 779 tons per year associated with the 0.27 lb/MMBtu BART emission rate

determination.

Unit 2‟s 0.08 lb/MMBtu NOx emission rate equates to a 74% control and a NOx 

reduction of 3,975 tons per year, which is much greater than the 15% control and a NOx 

reduction of 806 tons per year associated with the 0.27 lb/MMBtu BART emission rate

determination.

The total NOx emission reduction resulting from the BART determination is 1,585 tons 

per year (779 + 806 = 1,585 tons per year). The total NOx emission reduction resulting 

from the BART Alternative is 4,702 tons per year (727 + 3,975 = 4,702 tons per year). 

Given the far greater emission reduction achieved by the BART Alternative when 

compared to the BART determinations for the individual units, the state determines, in 

accordance with the federal Regional Haze regulations, that the BART Alternative

emission rates are appropriate for Craig Units 1 and 2 as providing greater reasonable 

progress than the application of BART as set forth in the federal BART Alternative 

regulation.

The state also evaluated the NOx emission reduction associated with both units (Craig 

1 & 2) in contrast to the existing NOx rates, presumptive BART NOx rate, source-bysource determination, and the final RH determination to determine the total NOx 

reduction benefit. In the below table, the existing NOx emissions from both units is 

10,562 tons/year which is much lower than the existing presumptive BART emissions of 

14,849 tons/year. The source-by-source BART determination resulted in NOx 

emissions of 8,978 tons/year which is well above the 5,860 tons/year in NOx emissions 

calculated to result from application of the BART Alternative. These tons/year 

calculations provide an emissions based comparison to demonstrate that the Craig 

BART Alternative provides greater reasonable progress than, and is superior to, source 

by source BART for these units. The table below is illustrative for demonstration 

purposes only. The tons per year projections provide an emission based comparison 

and are not enforceable requirements.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

72

NOx Analysis Units Craig 1 Craig 2 Total

Annual Average Heat Input* [MMBtu] 36,933,572 39,214,982

Annual Average NOx Rate* [lb/MMBtu] 0.28 0.27

Annual Average NOx Emissions* [tons/year] 5,190.3 5,371.6 10,562

Presumptive NOx Rate [lb/MMBtu] 0.39 0.39

Presumptive NOx Emissions [tons/year] 7,202.1 7,646.9 14,849

Source-by-Source Determination [lb/MMBtu] 0.27 0.27

Source-by-Source Determination [tons/year] 4,411.8 4,565.9 8,978

Final Regional Haze Determination [lb/MMBtu] 0.28 0.08

Final Regional Haze Determination [tons/year] 4,463.7 1,396.6 5,860

* Data from CAMD used for period (2006-2007)

Based on the above analysis and demonstration, the BART Alternative (final RH 

determination) achieves more NOx emissions reductions, which are well below the 

source-by-source BART determinations for each unit. Consequently, the BART 

Alternative will result in more visibility improvement at nearby Class I areas, and the 

state adopts this BART Alternative as appropriate to comply with the Regional Haze rule 

for these units. The state notes that this BART Alternative is not a trading program per 

Section 308(e)(2) and provisions associated with trading are not applicable.

Under EPA‟s Alternative to BART rule (40 CFR § 51.308(e)(2)), a state must show that 

the alternative measure or alternative program achieves greater reasonable progress 

than would be achieved through the installation and operation of BART. The 

demonstration addresses these requirements, as follows. (A complete description of 

these federal requirements is presented in section 6.4.3.7 below.)

1) 51.308(e)(2)(i)(A) A listing of all BART-eligible sources can be found in Table 

6-3 above.

2) 51.308(e)(2)(i)(B) The two BART-eligible sources are Craig Units 1 and 2.

3) 51.308(e)(2)(i)(C) The BART determinations presented herein describe the 

control information and the projected total NOx reduction of 1,585 tons per year

for source-by-source BART.

4) 51.308(e)(2)(i)(D) The BART Alternative achieves a projected NOx reduction of 

4,702 tons per year.

5) 51.308(e)(2)(i)(E) The BART Alternative achieves more than 3,100 tons of 

projected NOx reduction per year over what would be achieved by the 

installation of BART.

6) 51.308(e)(2)(iii) The Craig BART Alternative will be implemented as 

expeditiously as practicable but no later than five years after EPA‟s approval of 

this BART Alternative, as required by Regulation No. 3 Part F. The regulation 

requires that a compliance schedule be developed by the source and submitted 

to the state within six months from EPA‟s approval. The compliance and 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

73

monitoring provisions of the BART Alternative have also been incorporated into 

Regulation No. 3, Part F.

7) 51.308(e)(2)(iv) The emission reductions associated with the Craig BART 

Alternative have not been used for other SIP purposes, thus they are surplus.

8) 51.308(e)(2)(v) The state is not proposing a geographic enhancement for 

reasonably attributable impairment.

9) 51.308(e)(2)(vi) Since Colorado is not using a trading program for the Craig 

BART Alternative, this section does not apply.

10) 51.308(e)(3) There are only two units at the same facility under the Craig 

BART Alternative and thus there is no change in the distribution of emissions 

than under BART, and, as stated above, the alternative measure results in 

greater emission reductions than case-by-case BART. Therefore the Craig 

BART Alternative is deemed to achieve greater reasonable progress.

11) 51.308(e)(3)(i) Since the Craig BART Alternative includes only two units at the 

same facility, the state has determined that visibility does not decline in any 

Class I area due to the Craig BART Alternative when compared to case-bycase BART.

12) 51.308(e)(3)(ii) Because the Craig BART Alternative has been demonstrated to 

achieve more emission reductions than would occur through case-by-case 

BART, the state determines that there will be an overall improvement in 

visibility over all affected Class I areas.

13) 51.308(e)(4) Colorado is not participating in the CAIR program and cannot rely 

on this program for the Craig BART Alternative.

14) The state acknowledges that the core requirements will otherwise apply as set 

forth in the Regional Haze Rule.

15) 51.308(e)(6) No Colorado BART sources have applied for an exemption from 

BART.

A complete analysis that supports the BART determination and BART Alternative for 

Craig Station Units 1 and 2, including substantial cost information for NOx controls, can 

be found in Appendix C.

6.4.3.5 BART Determination for Public Service Company’s Hayden Station

Hayden Units 1 and 2 are considered BART-eligible, being fossil-fuel steam electric 

plants of more than 250 MMBtu/hr heat input with the potential to emit 250 tons or more 

of haze forming pollution (NOx, SO2, PM10), and having commenced operation in the 15-

year period prior to August 7, 1977. These boilers also cause or contribute to visibility 

impairment at a federal Class I area at or above a 0.5 deciview change; consequently, 

both boilers are subject-to-BART. Public Service Company (PSCo) submitted a BART 

analysis to the Division on September 14, 2006 with revisions submitted on November 

1, 2006 and January 8, 2007. In response to a Division request, PSCo submitted 

additional information on May 25, 2010.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

74

SO2 BART Determination for Hayden - Units 1 and 2

Semi-Dry FGD Upgrades – As discussed in EPA‟s BART Guidelines, electric generating 

units (EGUs) with existing controls achieving removal efficiencies of greater than 50 

percent do not need to be evaluated for potential removal of controls and replacement 

with new controls. Therefore, the following dry scrubber upgrades were considered for 

Hayden Units 1 and 2, if technically feasible.

Use of performance additives - The supplier of Hayden‟s dry scrubbing 

equipment does not recommend the use of any performance additive. PSCo is 

aware of some additive trials, using a chlorine-based chemical, for dry scrubbers. 

Because low-sulfur coal is used at Hayden, the use of performance additives on 

the scrubbers would not be expected to increase the SO2 removal. 

Use of more reactive sorbent - PSCo is using a highly reactive lime with 92% 

calcium oxide content reagent that maximizes SO2 removal. The only other 

common reagent option for a dry scrubber is sodium-based products which are 

more reactive than freshly hydrated lime. Sodium has a major side effect of 

converting some of the NOx in the flue gas into NO2. Since NO2 is a visible gas, 

large coal-fired units can generate a visible brown/orange plume at high SO2

removal rates, such as those experienced at Hayden. This side effect is 

unacceptable in a region with numerous Class I areas in close proximity to the 

source. There are no known acceptable reagents without this side effect that 

would allow additional SO2 removal in the dry scrubbing systems present at 

Hayden Station.

Increase the pulverization level of sorbent – PSCo uses the best available 

grinding technologies, and other pulverization techniques have not been proven 

more effective.

Engineering redesign of atomizer or slurry injection system - The supplier offers 

no upgrade in atomizer design to improve SO2 removal at Hayden. However, an 

additional scrubber module could be added along with spare parts and 

maintenance personnel in order to meet a lower emission limit. This option is 

technically feasible.

Additional equipment and maintenance - Hayden Units 1 and 2 can achieve a 

lower 30-day average emission rate limit than the 2008 State-adopted BART 

emission limit of 0.16 lbs/MMBtu by purchasing additional spare atomizer parts 

and increasing annual operating and maintenance through increased labor and 

reagent requirements. This emissions limit is 0.13 lbs/MMBtu, which is the 

current rolling 90-day limit.

The additional scrubber module, and additional spare atomizer parts with additional 

operation and maintenance were determined to be technically feasible for reducing SO2 

emissions from Units 1 and 2.

The following tables list the emission reductions, annualized costs and cost 

effectiveness of the control alternatives:
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

75

Hayden Unit 1 - SO2 Cost Comparison

Alternative Emissions 

Reduction (tpy)

Annualized 

Cost ($)

Cost Effectiveness 

($/ton)

Baseline 0 $0 $0

Semi-Dry FGD Upgrade – Additional 

Equipment and Maintenance 61 $141,150 $2,317

Additional Scrubber Module 488 $4,142,538 $8,490

Hayden Unit 2 - SO2 Cost Comparison

Alternative Emissions 

Reduction (tpy)

Annualized 

Cost ($)

Cost Effectiveness 

($/ton)

Baseline 0 $0 $0

Semi-Dry FGD Upgrade – Additional 

Equipment and Maintenance

39 $141,150 $3,626

Additional Scrubber Module 589 $4,808,896 $8,164

The additional scrubber module option was eliminated from consideration due to the 

high cost/effectiveness ratios and anticipated small degree of visibility improvement 

(less than 0.1 deciview) that would result from this upgrade.

There are no energy and non-air quality impact associated with the remaining semi-dry 

FGD upgrade alternative (additional equipment and maintenance).

There are no remaining useful life issues for the alternatives as the sources will remain 

in service for the 20-year amortization period.

The projected visibility improvements attributed to the alternatives are as follows:

SO2 Control Method

Hayden – Unit 1 Hayden – Unit 2

SO2 Emission 

Rate 

(lb/MMBtu)

98th 

Percentile 

Impact (Δdv)

SO2 Emission 

Rate 

(lb/MMBtu)

98th 

Percentile 

Impact (Δdv)

Daily Maximum (3-yr) 0.34 0.40

Existing Semi-Dry FGD 

(LSD) (annual avg.)

0.16 0.09 0.16 0.18

Semi-Dry FGD Upgrade 

(annual avg.)

0.13 0.10 0.13 0.21

Additional Scrubber 

Module (annual avg.)

0.07 0.14 0.07 0.26

Based upon its consideration of the five factors summarized herein and detailed in 

Appendix C, the state has determined that SO2 BART is the following SO2 emission 

rates:

Hayden Unit 1: 0.13 lb/MMBtu (30-day rolling average)

Hayden Unit 2: 0.13 lb/MMBtu (30-day rolling average)
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

76

The state assumes that the BART emission limits can be achieved through the 

operation of existing lime spray dryers (LSD). The state evaluated the option of 

tightening the emission limit for Hayden Units 1 and 2 and determined that a more 

stringent 30-day rolling SO2 limit of 0.13 lbs/MMBtu represents an appropriate level of 

emissions control for semi-dry FGD control technology. The tighter emission rate for 

both units is achievable with a negligible investment and the facility operator has offered 

to undertake these actions to allow for refinement of the emissions rate appropriate for 

this technology at this source despite the lack of appreciable modeled visibility 

improvement, and the state accepts this.

Particulate Matter BART Determination for Hayden - Units 1 and 2

Based on recent BACT determinations, the state has determined that the existing Unit 1 

and Unit 2 emission limit of 0.03 lb/MMBtu (PM/PM10) represents the most stringent 

level of available control for PM/PM10. The units are exceeding a PM control efficiency 

of 95%, and the state has selected this emission limit for PM/PM10 as BART. The state 

assumes that the BART emission limit can be achieved through the operation of the 

existing fabric filter baghouses.

NOx BART Determination for Hayden - Units 1 and 2

LNB upgrades, SNCR and SCR were determined to be technically feasible for reducing 

NOx emissions at Hayden Units 1 and 2.

The following tables list the emission reductions, annualized costs and cost 

effectiveness of the control alternatives:

Hayden Unit 1 - NOx Cost Comparisons

Alternative Emissions Reduction 

(tpy)

Annualized Cost 

($)

Cost Effectiveness 

($/ton)

Baseline 0 $0 $0

LNB 1,391 $572,010 $411

SNCR 1,391 $1,353,500 $973

SCR 3,120 $10,560,612 $3,385

Hayden Unit 2 - NOx Cost Comparisons

Alternative Emissions Reduction 

(tpy)

Annualized Cost 

($)

Cost Effectiveness 

($/ton)

Baseline 0 $0 $0

LNB 1,303 $992,729 $762

SNCR 1,610 $1,893,258 $1,176

SCR 3,032 $12,321,491 $4,064

The energy and non-air quality impacts of the alternatives are as follows:

LNB – not significant
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

77

SNCR and SCR – increased power needs, potential for ammonia slip, potential for 

visible emissions, hazardous materials storage and handling

There are no remaining useful life issues for the alternatives as the sources will remain 

in service for the 20-year amortization period.

The projected visibility improvements attributed to the alternatives are as follows:

NOx Control Method

Hayden – Unit 1 Hayden – Unit 2

NOx Emission 

Rate 

(lb/MMBtu)

98th 

Percentile 

Impact (Δdv)

NOx Emission 

Rate 

(lb/MMBtu)

98th 

Percentile 

Impact (Δdv)

Daily Maximum (3-yr) 0.61 0.37

LNB (annual avg.) 0.26 0.69 0.21 0.40

SNCR (annual avg.) 0.26 0.69 0.18 0.48

SCR (annual avg.) 0.07 1.12 0.06 0.85

Based upon its consideration of the five factors summarized herein and detailed in 

Appendix C, the state has determined that NOx BART is the following NOx emission 

rates:

Hayden Unit 1: 0.08 lb/MMBtu (30-day rolling average)

Hayden Unit 2: 0.07 lb/MMBtu (30-day rolling average)

The state assumes that the BART emission limits can be achieved through the 

installation and operation of selective catalytic reduction (SCR). For these emission 

limits, the cost per ton of emissions removed, coupled with the estimated visibility 

improvements gained, falls within the guidance criteria presented above.

Unit 1: $3,385 per ton NOx removed; 1.12 deciview of improvement

Unit 2: $4,064 per ton NOx removed; 0.85 deciview of improvement

The dollars per ton control costs, coupled with notable visibility improvements leads the 

state to this determination. The NOx emission limits of 0.08 lb/MMBtu (30-day rolling 

average) for Unit 1; and 0.07 lb/MMBtu (30-day rolling average) for Unit 2; are 

technically feasible and have been determined to be BART for Hayden Units 1 and 2.

A complete analysis that supports the BART determination for PSCo‟s Hayden Units 1 

and 2 can be found in Appendix C.

6.4.3.6 BART Determination for Colorado Springs Utilities’ Martin Drake Plant

Colorado Springs Utilities‟ Boilers 5, 6, and 7 are considered BART-eligible, being fossilfuel steam electric plants of more than 250 MMBtu/hr heat input with the potential to 

emit 250 tons or more of haze forming pollution (NOx, SO2, PM10), and having 

commenced operation in the 15-year period prior to August 7, 1977. The combined 

emissions of these boilers also cause or contribute to visibility impairment at a federal 

Class I area at or above a 0.5 deciview change; consequently, all three boilers are 

subject-to-BART. Initial air dispersion modeling performed by the Division 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

78

demonstrated that the Martin Drake Plant contributes to visibility impairment (a 98th

percentile impact equal to or greater than 0.5 deciviews) and is therefore subject to 

BART. Colorado Springs Utilities (CSU) submitted a BART Analysis to the Division on 

August 1, 2006 with updated cost information submitted on March 29, 2007. CSU also 

provided information in its “NOx and SO2 Reduction Cost and Technology Updates for 

Colorado Springs Utilities Drake and Nixon Plants” Submittal provided on February 20, 

2009 as well as additional information upon the Division‟s request on February 21, 

2010, March 21, 2010, May 10, 2010, May 28, 2010, June 2, 2010, and June 15, 2010.

SO2 BART Determination for Martin Drake - Units 5, 6 and 7

Dry sorbent injection (DSI) was determined to be feasible for all units and dry FGD were 

determined to be technically feasible for reducing SO2 emissions from Units 6, and 7. 

These options were considered as potential BART level controls by the Division. Lime 

or limestone-based wet FGD system is also technically feasible but was determined to 

be not reasonable due to adverse non-air quality impacts. Drake is conducting a trial on 

a new wet FGD system design (NeuStream-S) that uses much less water along with a 

smaller operational footprint that may provide, if successfully demonstrated, a 

reasonable alternative to traditional wet FGD systems.

The following tables list the emission reductions, annualized costs and cost 

effectiveness of the control alternatives:

Drake Unit 5 - SO2 Cost Comparison

Alternative Emissions 

Reduction (tpy)

Annualized Cost 

($)

Cost Effectiveness 

($/ton)

Baseline 0 $0 $0

DSI 762 $1,340,663 $1,760

Drake Unit 6 - SO2 Cost Comparison

Alternative Emissions 

Reduction (tpy)

Annualized Cost 

($)

Cost Effectiveness 

($/ton)

Baseline 0 $0 $0

DSI 1,671 $2,910,287 $1,741

Dry FGD (LSD) @ 82% control

(0.15 lb/MMBtu annual average)

2,284 $6,186,854 $2,709

Dry FGD (LSD) @ 85% control

(0.12 lb/MMBtu annual average)

2,368 $6,647,835 $2,808

Dry FGD (LSD) @ 90% control

(0.08 lb/MMBtu annual average)

2,507 $7,452,788 $2,973
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

79

Drake Unit 7 - SO2 Cost Comparison

Alternative Emissions 

Reduction (tpy)

Annualized Cost 

($)

Cost Effectiveness 

($/ton)

Baseline 0 $0 $0

DSI 2,657 $3,723,826 $1,405

Dry FGD (LSD) @ 82% control

(0.15 lb/MMBtu annual average)

3,632 $8,216,863 $2,263

Dry FGD (LSD) @ 85% control

(0.12 lb/MMBtu annual average)

3,764 $8,829,321 $2,345

Dry FGD (LSD) @ 90% control

(0.08 lb/MMBtu annual average)

3,986 $9,898,382 $2,483

The energy and non-air quality impacts of the remaining alternative are as follows:

DSI - reduced mercury capture in the baghouse, fly ash contamination with 

sodium sulfate, rendering the ash unsalable as a replacement for concrete and 

rendering it landfill material only

Dry FGD – less mercury removal compared to unscrubbed units, significant water 

usage

There are no remaining useful life issues for the alternatives as the sources will remain 

in service for the 20-year amortization period.

The projected visibility improvements attributed to the alternatives are as follows:

SO2 Control 

Method

Drake – Unit 5 Drake – Unit 6 Drake – Unit 7

SO2 

Emission 

Rate 

(lb/MMBtu)

98th 

Percentile 

Impact 

(Δdv)

SO2 

Emission 

Rate 

(lb/MMBtu)

98th 

Percentile 

Impact 

(Δdv)

SO2 

Emission 

Rate 

(lb/MMBtu)

98th 

Percentile 

Impact 

(Δdv)

Daily Max (3-yr) 0.94 1.00 0.99

DSI (annual 

avg.)

0.25 0.12 0.33 0.18 0.33 0.29

Dry FGD (LSD) 

(annual avg.)

Not

feasible

0.12 0.24 0.12 0.39

Dry FGD (LSD) 

(annual avg.)

Not

feasible

0.07 0.26 0.07 0.41

Based upon its consideration of the five factors summarized herein and detailed in 

Appendix C, the state has determined that SO2 BART for Unit 5 is the following SO2 

emission rate:

Drake Unit 5: 0.26 lb/MMBtu (30-day rolling average)

The state assumes that the BART emission limit can be achieved through the 

installation and operation of dry sorbent injection. Other alternatives are not feasible.

Unit 5: $1,760 per ton SO2 removed; 0.12 deciview of improvement
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

80

Based upon its consideration of the five factors summarized herein and detailed in 

Appendix C, the state has determined that SO2 BART for Unit 6 and Unit 7 is the 

following SO2 emission rates:

Drake Unit 6: 0.13 lb/MMBtu (30-day rolling average)

Drake Unit 7: 0.13 lb/MMBtu (30-day rolling average)

The state assumes that the BART emission limits can be achieved through the 

installation and operation of lime spray dryers (LSD). A lower emissions rate for Units 6 

and 7 was deemed to not be reasonable as increased control costs to achieve such an 

emissions rate do not provide appreciable improvements in visibility (0.02 delta deciview 

for both units respectively).

These emission rates for Units 6 and 7 provide 85% SO2 emission reduction at a 

modest cost per ton of emissions removed and result in a meaningful contribution to 

visibility improvement.

Unit 6: $2,808 per ton SO2 removed; 0.24 deciview of improvement

Unit 7: $2,345 per ton SO2 removed; 0.39 deciview of improvement

Particulate Matter BART Determination for Martin Drake - Units 5, 6 and 7

The state determines that the existing regulatory emissions limit of 0.03 lb/MMBtu 

(PM/PM10) for the three units represent the most stringent control options. The units 

are exceeding a PM control efficiency of 95%, and the emission limits are BART for 

PM/PM10. The state assumes that the BART emission limit can be achieved through the 

operation of the existing fabric filter baghouses.

NOx BART Determination for Martin Drake - Units 5, 6 and 7

Ultra low NOx burners (ULNB), ULNB including OFA, SNCR, SNCR plus ULNB, and 

SCR were determined to be technically feasible for reducing NOx emissions at Drake 

Units 5, 6 and 7.

The following tables list the emission reductions, annualized costs and cost 

effectiveness of the control alternatives:

Drake Unit 5 - NOx Cost Comparison

Alternative Emissions 

Reduction (tpy)

Annualized 

Cost ($)

Cost 

Effectiveness 

($/ton)

Baseline 0 $0 $0 

Overfire air (OFA) 154 $141,844 $923

Ultra-low NOx burners (ULNBs) 200 $147,000 $736

ULNBs + OFA 215 $288,844 $1,342

Selective Non-Catalytic Reduction (SNCR) 231 $1,011,324 $4,387

ULNB/SCR layered approach 626 $4,467,000 $7,133

Selective Catalytic Reduction (SCR) 626 $4,580,000 $7,314
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

81

Drake Unit 6 - NOx Cost Comparison

Alternative Emissions 

Reduction (tpy)

Annualized 

Cost ($)

Cost 

Effectiveness 

($/ton)

Baseline 0 $0 $0

Overfire air (OFA) 283 $104,951 $371

Selective Non-Catalytic Reduction (SNCR) 424 $1,208,302 $2,851

Ultra-low NOx burners (ULNBs) 452 $232,800 $515

ULNBs + OFA 509 $337,751 $664

ULNB/SCR layered approach 1,175 $6,182,800 $5,260

Selective Catalytic Reduction (SCR) 1,175 $6,340,000 $5,395

Drake Unit 7 - NOx Cost Comparison

Alternative

Emissions 

Reduction 

(tpy)

Annualized 

Cost ($)

Cost

Effectiveness 

($/ton)

Baseline 0 $0 $0

Overfire air (OFA) 416 $75,217 $181

Ultra-low NOx burners (ULNBs) 583 $386,000 $662

Selective Non-Catalytic Reduction (SNCR) 624 $2,018,575 $3,233

ULNBs + OFA 749 $461,217 $616

ULNB/SCR layered approach 1,709 $8,196,000 $4,797

Selective Catalytic Reduction (SCR) 1,709 $8,510,000 $4,981

The energy and non-air quality impacts of the alternatives are as follows:

OFA and ULNB – not significant

ULNB – not significant

SNCR and SCR – increased power needs, potential for ammonia slip, potential 

for visible emissions, hazardous materials storage and handling

There are no remaining useful life issues for the alternatives as the sources will remain 

in service for the 20-year amortization period.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

82

The projected visibility improvements attributed to the alternatives are as follows:

NOx Control 

Method

Drake – Unit 5 Drake – Unit 6 Drake – Unit 7

NOx 

Emission 

Rate 

(lb/MMBtu)

98th 

Percentile 

Impact 

(Δdv)

NOx 

Emission 

Rate 

(lb/MMBtu)

98th 

Percentile 

Impact 

(Δdv)

NOx 

Emission 

Rate 

(lb/MMBtu)

98th 

Percentile 

Impact 

(Δdv)

Daily Max (3-yr) 0.62 0.83 0.71

OFA (annual 

avg.)

0.30 0.07 0.33 0.18 0.31 0.22

ULNB (annual 

avg.)

0.28 0.08 0.28 0.193 0.28 0.24

ULNB + OFA 

(annual avg.)

0.27 0.08 0.27 0.20 0.25 0.26

SNCR (annual 

avg.)

0.27 0.08 0.29 0.19 0.28 0.24

ULNB + SCR 0.07 0.12 0.07 0.27 0.07 0.37

SCR (annual 

avg.)

0.07 0.12 0.07 0.27 0.07 0.37

Based upon its consideration of the five factors summarized herein and detailed in 

Appendix C, the state has determined that NOX BART for Units 5, 6 and 7 is the 

following NOx emission rates:

Drake Units 5 and 6: 0.31 lb/MMBtu (30-day rolling average)

Drake Unit 7: 0.29 lb/MMBtu (30-day rolling average)

The state assumes that the BART emission limits can be achieved through the 

installation and operation of ultra low-NOx burners (including over-fire air). 

Unit 5: $1,342 per ton NOx removed

Unit 6: $664 per ton NOx removed

Unit 7: $616 per ton NOx removed

The extremely low dollars per ton control costs leads the state to selecting this emission 

rate for each of the Drake units. SNCR is not selected as that technology provides an 

equivalent emissions rate, similar level of NOx reduction coupled with equivalent 

visibility improvement at a much higher cost per ton of pollutant removed along with 

potential energy and non-air quality impacts. SCR is not selected as the 

cost/effectiveness ratios for Units 5 and 6 are too high and the visibility improvement at 

all units do not meet the criteria guidance described above (e.g. less than 0.50 Δdv)

For Drake Units 5 and 6, EPA Region 8 notes to the state that a number of control cost 

studies, such as that by NESCAUM (2005), indicate that costs for SCR could be lower 

than the costs estimated by the Division in the above BART determination. However, 

assuming such lower costs were relevant to this source, use of such lower costs would 

not change the state's BART determination because the degree of visibility 

improvement achieved by SCR is below the state's guidance criteria of 0.5 dv. 

Moreover, the incremental visibility improvement associated with SCR is not substantial 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

83

when compared to the visibility improvement achieved by the selected limits (i.e., 0.04 

dv for SCR on Unit 5 and 0.07 dv for SCR on Unit 6). Thus, it is not warranted to select 

emission limits associated with SCR for Martin Drake Units 5 and 6.

For Drake Unit 7, EPA Region 8 notes to the state that a number of control cost studies, 

such as that by NESCAUM (2005), indicate that costs for SCR could be lower than the 

costs estimated by the Division in the above BART determination. However, assuming 

such lower costs were relevant to this source, use of such lower costs would not change 

the state's BART determination because the degree of visibility improvement achieved 

by SCR is below the state's guidance criteria of 0.5 dv. Moreover, the incremental 

visibility improvement associated with SCR is not substantial when compared to the 

visibility improvement achieved by the selected limits (i.e., 0.11 dv for SCR). Thus, it is 

not warranted to select emission limits associated with SCR for Martin Drake Unit 7.

A complete analysis that supports the BART determination for CSU‟s Martin Drake 

Units 5, 6 and 7 can be found in Appendix C.

6.4.3.7 BART Determination for Public Service Company’s Cherokee Unit 4, 

Valmont Unit 5 and the Pawnee Station as a BART Alternative, which Includes 

Reasonable Progress Determinations for Arapahoe Units 3 and 4 and Cherokee 

Units 1, 2 and 3

Background

Section 308(e)(2) of EPA‟s Regional Haze Rule allows a state to approve a BART 

alternative:

A State may opt to implement or require participation in an emissions trading 

program or other alternative measure rather than to require sources subject to 

BART to install, operate, and maintain BART. Such an emissions trading 

program or other alternative measure must achieve greater reasonable progress 

than would be achieved through the installation and operation of BART. For all 

such emission trading programs or other alternative measures, the State must 

submit an implementation plan containing the following plan elements and 

include documentation for all required analyses: (i) A demonstration that the 

emissions trading program or other alternative measure will achieve greater 

reasonable progress than would have resulted from the installation and operation 

of BART at all sources subject to BART in the State and covered by the 

alternative program. This demonstration must be based on the following: (A) A 

list of all BART-eligible sources within the State. (B) A list of all BART-eligible 

sources and all BART source categories covered by the alternative program. The 

State is not required to include every BART source category or every BARTeligible source within a BART source category in an alternative program, but 

each BART-eligible source in the State must be subject to the requirements of 

the alternative program, have a federally enforceable emission limitation 

determined by the State and approved by EPA as meeting BART in accordance 

with section 302(c) or paragraph (e)(1) of this section, or otherwise addressed 

under paragraphs (e)(1) or (e)(4) of this section.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

84

The PSCo BART Alternative Program (““PSCo BART Alternative”) was proposed by 

Public Service Company of Colorado (PSCo). The PSCo BART Alternative is not a 

trading program and does not include any complete source categories, although all 

facilities in the PSCo BART Alternative are electric generating units. The PSCo BART 

Alternative is based on reductions achieved as a result of a combination of unit 

shutdowns and the application of emissions controls planned as part of the Colorado 

HB 10-1365, the “Clean Air – Clean Jobs Act” ( § 40-3.2-201 C.R.S., et. seq.). The 

PSCo BART Alternative includes ten units at four facilities. The facilities included in the 

PSCo Alternative and the proposed controls are listed below.

Table 6-5: Actions and Dates under the PSCo Alternative

Facility Unit Action or Control Effective Date

Arapahoe Unit 3 Shutdown 12/31/2013

Unit 4 Operation on Natural Gas only 

(peaking unit)

12/31/2014

Cherokee Unit 1 Shutdown No later than 7/1/2012

Unit 2 Shutdown 12/31/2011

Unit 3 Shutdown No later than 12/31/2016

Unit 4 Operation on Natural Gas only 12/31/2017

Valmont Shutdown 12/31/2017

Pawnee SCR & LSD 12/31/2014

The state in evaluating the PSCo Alternative followed the EPA July 6, 2005, BART 

guidelines and the EPA October 13, 2006, regulation referred to as Provisions 

Governing Alternative to Source-Specific BART Determinations (71Fed.Reg. 60612-

60634 (10/13/2006); 40 CFR § 51.308(e)(2), “Alternative to BART rule”). Under the 

Alternative to BART rule, a state must show that the alternative measure or alternative 

program achieves greater reasonable progress than would be achieved through the 

installation and operation of BART. The demonstration must include five elements:

1) A list of all BART-eligible sources within the state;

2) A list of all BART-eligible sources and source categories covered by the 

alternative program;

3) An analysis of the best system of continuous emission control technology 

available and the associated reductions;

4) An analysis of the projected emissions reductions achievable through the 

alternative measure; and

5) A determination that the alternative measure achieves greater reasonable 

progress than would be achieved through the installation of BART. 

The PSCo Alternative includes both BART and non-BART sources. The non-BART 

sources are older than the BART timeframe, and in effect will all be controlled and 

reduce their NOx and SO2 emissions as a result of enforceable facility retirement dates 

and, for one unit, operating only on natural gas as a “peaking” unit. The BART sources, 

Cherokee 4, Pawnee and Valmont, will all be either controlled within the first planning 

period or shutdown with enforceable facility retirement dates.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

85

The state‟s alternative program satisfies the requirements of 40 CFR § 51.308, as 

further described in the preambles to the BART guidelines and the Alternative to BART 

rule. The state‟s analysis must include:

An analysis of the best system of continuous emission control technology 

available and associated emission reductions achievable for each source within 

the State subject to BART and covered by the alternative program. This analysis 

must be conducted by making a determination of BART for each source subject 

to BART and covered by the alternative program as provided for in paragraph 

(e)(1) of this section, unless the emissions trading program or other alternative 

measure has been designed to meet a requirement other than BART (such as 

the core requirement to have a long-term strategy to achieve the reasonable 

progress goals established by States). In this case, the State may determine the 

best system of continuous emission control technology and associated emission 

reductions for similar types of sources within a source category based on both 

source-specific and category-wide information, as appropriate.

40 CFR § 51.308(e)(2)(i)(C).

Colorado‟s alternative program was designed to meet a requirement other than BART; 

namely, Colorado‟s HB 10-1365. The express purpose of the legislation leading to the 

alternative program being proposed is:

THE GENERAL ASSEMBLY HEREBY FINDS, DETERMINES, AND DECLARES 

THAT THE FEDERAL "CLEAN AIR ACT", 42 U.S.C. SEC. 7401 ET SEQ., WILL 

LIKELY REQUIRE REDUCTIONS IN EMISSIONS FROM COAL-FIRED POWER 

PLANTS OPERATED BY RATE-REGULATED UTILITIES IN COLORADO. A 

COORDINATED PLAN OF EMISSION REDUCTIONS FROM THESE COALFIRED POWER PLANTS WILL ENABLE COLORADO RATE-REGULATED 

UTILITIES TO MEET THE REQUIREMENTS OF THE FEDERAL ACT AND 

PROTECT PUBLIC HEALTH AND THE ENVIRONMENT AT A LOWER COST 

THAN A PIECEMEAL APPROACH. A COORDINATED PLAN OF REDUCTION 

OF EMISSIONS FOR COLORADO'S RATE-REGULATED UTILITIES WILL 

ALSO RESULT IN REDUCTIONS IN MANY AIR POLLUTANTS AND 

PROMOTE THE USE OF NATURAL GAS AND OTHER LOW-EMITTING 

RESOURCES TO MEET COLORADO'S ELECTRICITY NEEDS, WHICH WILL 

IN TURN PROMOTE DEVELOPMENT OF COLORADO'S ECONOMY AND 

INDUSTRY.

§ 40-3.2-202, C.R.S. Similarly, Colorado‟s Clean Air – Clean Jobs Act further specifies 

that it is intended to address both current and reasonably foreseeable future 

requirements of the federal Clean Air Act. See, § 40-3.2-204, C.R.S.

PSCo BART Alternative measure for the subject coal-fired electric generating units is 

thus designed to meet the requirements of the regional haze rule, including BART, but 

also to address requirements beyond BART. This includes, for example, a revised 

national standard for ozone to be promulgated in 2011, other revised or to be revised 

national ambient air quality standards, or federal sector-specific regulations for 

hazardous air pollutants, among other federal regulatory requirements. Accordingly, the 

state will determine whether the PSCo BART Alternative represents the best system of 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

86

continuous emission control technology and associated emission reductions for the 

sources included in the alternative. In the preamble to the Alternative to BART rule, 

EPA discusses whether the option exists for states to use simplifying assumptions in 

determining the BART benchmark, or whether states must establish the BART 

benchmark through a source-by-source BART analysis. EPA states:

[T]here is no need to develop a precise estimate of the emissions reductions that 

could be achieved by BART in order simply to compare two programs. As EPA 

did in the CAIR, States should have the ability to develop a BART benchmark 

based on simplifying assumptions as to what the most-stringent BART is likely to 

achieve. The regulations finalized today therefore provide that where an emission 

trading program has been designed to meet a requirement other than BART, 

including the reasonable progress requirement, the State may establish a BART 

benchmark based on an analysis that includes simplifying assumptions about 

BART control levels for sources within a source category.

71 Fed. Reg. 60612, 60618 (October 13, 2006). EPA has thus determined that sourceby source BART is not required when it is not necessary where a state has determined 

that greater reasonable progress can be achieved by an alternative means. See also, 

70 Fed. Reg. 39104, 39137 (July 6, 2005). Thus, there is no need for states to conduct 

an extensive source-by-source BART assessment, and to then also go through the 

additional, resource intensive steps of developing an alternative program to BART. 

See, 71 Fed. Reg. at 60617.

Colorado has looked at several options to establish the BART benchmark. EPA 

establishes some criteria for the BART benchmark in the Alternative to BART rule, 

where the agency discusses simplifying assumptions.

In today‟s final rule, the regulations make clear that, with one exception, States 

must follow the approach for making BART determinations under section 

51.308(e)(1) in establishing a BART benchmark. This includes the requirement 

for States to use the BART guidelines in making BART determinations for EGUs 

at power plants of a certain size. As discussed above, the one exception to this 

general approach is where the alternative program has been designed to meet 

requirements other than BART; in this case, States are not required to make 

BART determinations under § 51.308(e)(1) and may use simplifying assumptions 

in establishing a BART benchmark based on an analysis of what BART is likely 

to be for similar types of sources within a source category. Under either approach 

to establishing a BART benchmark, we believe that the presumptions for EGUs 

in the BART guidelines should be used for comparison to a trading program or 

other alternative measure, unless the State determines that such presumptions 

are not appropriate for particular EGUs.

71 Fed. Reg. at 60619 (October 13, 2006). See also, id. at 60615 (“Where a trading 

program or other similar alternative program has been designed primarily to meet a 

Federal or State requirement other than BART, the State can use a more simplified 

approach to demonstrating that the alternative program will make greater reasonable 

progress than BART. Such an approach may be appropriate where the State believes 

the alternative program is clearly superior to BART and a detailed BART analysis is not 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

87

necessary to assure that the alternative program will result in greater reasonable 

progress than BART.”).

The PSCo BART Alternative includes only EGUs and, based on EPA‟s Alternative to 

BART rule, one option available is a comparison to the presumptive limits in the BART 

guidelines. Id. The presumptive limits represent a reasonable estimate of stringent case 

BART, particularly when developing a BART benchmark to assess an alternative 

program, because they are applied equally to EGU‟s of varying size and distance from 

Class I areas, and with varying impacts on visibility. Id. Because not all of the sources 

in the PSCo BART Alternative are BART sources, the state also considered other 

benchmarks that might be appropriate. For example, as part of the BART and 

reasonable progress analysis, the state has established guidelines for NOx based on 

control technology costs and visibility improvements. The state‟s analysis substantiates 

that the PSCo BART Alternative provides greater reasonable progress than would have 

been achieved without the alternative.

Analysis Under 40 CFR Part 51, § 308(e)

(2)(i)(A) A list of all Bart-eligible sources within the State.

A listing of all BART-eligible sources can be found in Table 6-3 in this Chapter 6 

of the Regional Haze State Implementation Plan.

(2)(i)(B) A list of all BART-eligible sources and all BART source categories covered by 

the alternative program. 

The State is not required to include every BART source category or every BARTeligible source within a BART source category in an alternative program. 

However, each BART-eligible source in the State covered by the PSCo BART 

Alternative in this case must be subject to the requirements of the alternative 

program, have a federally enforceable emission limitation determined by the 

State and approved by EPA as meeting BART in accordance with section 302(c) 

or section 308(e)(1), or otherwise be addressed under section 308(e)(1) or (e)(4). 

The BART sources covered by the PSCo BART Alternative are shown in Table 

6-6.

Table 6-6: Sources Included Within the PSCo Alternative

Facility Unit Action or Control

Arapahoe Unit 3 Shutdown

Unit 4 Operation on natural gas only 

Cherokee Unit 1 Shutdown

Unit 2 Shutdown

Unit 3 Shutdown

Unit 4 (BART-eligible) Operation on natural gas only

New nat. gas-fired EGU BACT where netting does not apply

Valmont (BART-eligible) Shutdown

Pawnee (BART-eligible) SCR & LSD
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

88

(2)(i)(C) An analysis of the best system of continuous emission control technology 

available and associated emission reductions achievable for each source within the 

State subject to BART and covered by the alternative program. This analysis must be 

conducted by making a determination of BART for each source subject to BART and 

covered by the alternative program as provided for in paragraph (e)(1) of this section, 

unless the emissions trading program or other alternative measure has been designed 

to meet a requirement other than BART (such as the core requirement to have a longterm strategy to achieve the reasonable progress goals established by States). In this 

case, the State may determine the best system of continuous emission control 

technology and associated emission reductions for similar types of sources within a 

source category based on both source-specific and category-wide information, as 

appropriate.

The PSCo BART Alternative includes the emission reductions achieved through 

Colorado HB 10-1365 (§ 40-3.2-201 C.R.S., et seq.). The PSCo BART 

Alternative was developed to address requirements other than BART, including 

to support the attainment of federal ambient air quality standards, to meet other 

federal requirements that can affect electric generating units, and improve air 

quality on the Front Range of Colorado. Since the PSCo BART Alternative was 

designed to address requirements other than BART, it meets the EPA SIP 

provision noted above that allows the state to determine the base case BART 

emissions using simplifying assumptions. This approach is discussed in EPA‟s 

Alternative to BART Rule. See, 71 Fed. Reg. at 60612 (October 13, 2006). 

Colorado has estimated base case BART emissions assuming that the plants 

included in the PSCo BART Alternative emit at the presumptive levels 

established by EPA for electric generating units of greater than 750 MW.18 The 

emissions resulting from the PSCo BART Alternative are then compared to the 

analysis of base case BART emissions to indicate the degree of emissions 

reduction improvement provided by the PSCo BART Alternative.

(2)(i)(D) An analysis of the projected emissions reductions achievable through the 

trading program or other alternative measure.

The emission reductions achievable through PSCo‟s Alternative include the 

reductions associated with the combination of shutdowns and retrofit controls 

established under PSCo‟s emissions reduction plan, endorsed by the state Public 

Utilities Commission pursuant to HB 10-1365, and codified and made 

enforceable by the elements reflected in this State Implementation Plan. The 

following emissions reductions provided by the PSCo BART Alternative are 

reflected in Tables 6-7 and 6-8, below. With respect to SO2 emissions, the PSCo 

BART Alternative will reduce SO2 emissions from these units by 21,493 tons per 

 

18 None of the BART units included in this Alternative are larger than 750MW, thus the presumptive 

emissions standards for electric generating units set forth in EPA‟s BART guidelines are not mandatory 

for these units. See, e.g., 70 Fed. Reg. at 39108. The non-BART units included in this Alternative are 

also not subject to the presumptive emissions standards as a mandatory element of Regional Haze. 

While not required as a matter of regulation the presumptive limits are employed in this instance solely for 

demonstrative and comparative purposes.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

89

year in the first planning period (2010 to 2018). With respect to NOx emissions, 

the PSCo BART Alternative will reduce NOx emissions from these units by 

15,994 tons per year in the first planning period (2010 to 2018).

(2)(i)(E) A determination under paragraph (e)(3) of this section or otherwise based on 

the clear weight of evidence that the trading program or other alternative measure 

achieves greater reasonable progress than would be achieved through the installation 

and operation of BART at the covered sources.

The PSCo BART Alternative has been evaluated according to the emissions 

based test discussed in EPA‟s Alternative to BART Rule. This is explained in 

further detail below, and demonstrates that for both SO2 and NOx, due to a 

combination of substantial retirements of coal-fired units and controls on other 

coal-fired units, the PSCo BART Alternative provides greater reasonable 

progress than would be afforded under BART at the covered sources.

(2)(ii) [Reserved] 

(2)(iii) A requirement that all necessary emission reductions take place during the period 

of the first long-term strategy for regional haze. To meet this requirement, the State 

must provide a detailed description of the emissions trading program or other alternative 

measure, including schedules for implementation, the emission reductions required by 

the program, all necessary administrative and technical procedures for implementing 

the program, rules for accounting and monitoring emissions, and procedures for 

enforcement.

The PSCo BART Alternative for these electric generating units will be implemented 

during the first long-term strategy period, by December 31, 2017. The PSCo BART 

Alternative as set forth in this SIP establishes an expeditious implementation schedule 

for the coordinated shutdown of, and installation of retrofit emissions controls on the 

covered coal-fired electric generating units. As reflected in Table 6-12, emission limits 

for SO2 and NOx at Pawnee, operation on natural gas at Cherokee Unit 4, operation on 

natural gas at Arapahoe Unit 4 as a peaking unit only, and shutdowns at Arapahoe Unit 

3, Cherokee Units 1, 2 and 3, and Valmont, will all occur during the first planning period. 

Some of the NOx emissions reductions will be reserved, and are not used in this 

alternative measure demonstration and not reflected in the emissions reductions in this 

SIP, to allow for natural gas replacement power at Cherokee and future “netting” or 

“offsets”. The compliance and monitoring provisions of the PSCo BART Alternative have 

been incorporated into Regulation No. 3, Part F. Compliance will be determined through 

the use of continuous emission monitors for those facilities that are not shutdown. 

Enforceability of the shutdown of coal-fired units under the PSCo BART Alternative is 

reflected in this State Implementation Plan, as well as in Regulation No. 3, Part F. 

Colorado will also amend the relevant permits to include enforceable shutdown dates.

(2)(iv) A demonstration that the emission reductions resulting from the emissions trading 

program or other alternative measure will be surplus to those reductions resulting from 

measures adopted to meet requirements of the CAA as of the baseline date of the SIP.

The emission controls associated with the PSCo BART Alternative have not been 

used for other SIP purposes, thus they are surplus. The reductions from the 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

90

shutdown of Arapahoe units 1 and 2 were used in an earlier PM SIP 

demonstration and are not included in this analysis. 

(2)(v) At the State's option, a provision that the emissions trading program or other 

alternative measure may include a geographic enhancement to the program to address 

the requirement under §51.302(c) related to BART for reasonably attributable 

impairment from the pollutants covered under the emissions trading program or other 

alternative measure.

The Division is not proposing a geographic enhancement for reasonably 

attributable impairment.

(2)(vi) For plans that include an emissions trading program that establishes a cap on 

total annual emissions of SO2 or NOx from sources subject to the program, requires the 

owners and operators of sources to hold allowances or authorizations to emit equal to 

emissions, and allows the owners and operators of sources and other entities to 

purchase, sell, and transfer allowances, the following elements are required concerning 

the emissions covered by the cap:

Since Colorado is not using a trading program for the PSCo BART Alternative, 

this section does not apply. Electric generating units subject to this alternative 

have unit-specific compliance requirements reflected in this SIP and in Reg. No. 

3, Part F.

(3) A State which opts under 40 CFR 51.308(e)(2) to implement an emissions trading 

program or other alternative measure rather than to require sources subject to BART to 

install, operate, and maintain BART may satisfy the final step of the demonstration 

required by that section as follows: If the distribution of emissions is not substantially 

different than under BART, and the alternative measure results in greater emission 

reductions, then the alternative measure may be deemed to achieve greater reasonable 

progress. If the distribution of emissions is significantly different, the State must conduct 

dispersion modeling to determine differences in visibility between BART and the trading 

program for each impacted Class I area, for the worst and best 20 percent of days. The 

modeling would demonstrate “greater reasonable progress” if both of the following two 

criteria are met: 

The Division has determined that the distribution of emissions under the PSCo 

BART Alternative is not substantially different than under BART, and the 

alternative measure results in greater emission reductions than case-by-case 

BART. The PSCo BART Alternative includes three BART units at four different 

facilities, all of which are in or immediately adjacent to the 8-Hour Ozone NonAttainment Area in the Front Range of Colorado. Like the other three facilities, 

the fourth is the Arapahoe facility and it is central to the non-attainment area, and 

is only 17 kilometers from the Cherokee facility.

(3)(i) Visibility does not decline in any Class I area, and

Since the Metro Denver BART eligible sources are included in the PSCo BART 

Alternative along with other non–BART sources in the area, and the overall 

visibility-impairing pollutants from these units decrease substantially, the Division 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

91

has determined that visibility does not decline in any Class I area in relation to 

this PSCo BART Alternative.

(3)(ii) There is an overall improvement in visibility, determined by comparing the 

average differences between BART and the alternative over all affected Class I areas.

The PSCo Alternative has been demonstrated to achieve more emission 

reductions than would occur through case-by-case BART. The reasons why the 

alternative provides greater reductions include:

a) Arapahoe Unit 3, Cherokee Units 1, 2 and 3, and Valmont (BART eligible 

unit), will be shutdown during the first planning period.

b) Arapahoe Unit 4 will operate on natural gas as a peaking unit.

c) Cherokee Unit 4 (BART eligible unit) will operate on natural gas only.

d) Pawnee Unit 1(BART eligible unit) will install and operate an LSD to control 

SO2 emissions and SCR to control NOx emissions in 2014.

(4) A State that chooses to meet the emission reduction requirements of the Clean Air 

Interstate Rule (CAIR) by participating in one or more of EPA’s CAIR trading programs

Colorado is not participating in the CAIR program.

(5) After a State has met the requirements for BART or implemented an emissions 

trading program or other alternative measure that achieves more reasonable progress 

than the installation and operation of BART, BART-eligible sources will be subject to the 

requirements of paragraph (d) of this section in the same manner as other sources.

The state acknowledges that the core requirements will otherwise apply as set 

forth in the Regional Haze Rule.

(6) Any BART-eligible facility subject to the requirement under paragraph (e) of this 

section to install, operate, and maintain BART may apply to the Administrator for an 

exemption from that requirement. An application for an exemption will be subject to the 

requirements of §51.303(a)(2)–(h).

No Colorado BART sources have applied for an exemption from BART.

Technical Analysis of the PSCo Alternative Emissions Reductions with Respect 

to the Section 308(e) Alternative Measure Demonstration

The following technical analysis of emissions reductions that result from the PSCo 

BART Alternative more fully demonstrates that the proposed alternative achieves 

greater reasonable progress than the installation of BART, as allowed under EPA‟s 

regional haze regulations. EPA‟s Regional Haze Rule requires that BART- eligible 

sources either install BART as determined for each source on a case-by-case basis, or 

install controls as required by a BART Alternative. EPA‟s BART guidance (70 Fed. 

Reg. 39104, July 6, 2005) and EPA‟s regulation on BART Alternatives (71 Fed. Reg. 

60612, October 13, 2006) both provide guidance on how to evaluate whether a BART 

Alternative proposal achieves greater reasonable progress under the regulation. This 

determination can be made based on an emissions comparison or through a modeling 

analysis if the state determines that is appropriate. If the geographic distribution of 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

92

emissions reductions from the programs is expected to be similar, the comparison can 

be made based on emissions alone. 70 Fed. Reg. at 39136; 71 Fed. Reg. at 60620. 

Because all the sources included in the PSCo BART Alternative are located in the same 

air shed and within a 100 mile area, the Division has determined that the BART eligible 

sources in the PSCo BART Alternative are in the same geographic region (namely, in

the Denver Metro Area and also in or immediately adjacent to the existing 8-Hour 

Ozone Non-Attainment Area) for purposes of regional haze. Thus an emissions 

demonstration is appropriate and modeling is not warranted for an alternative measure 

demonstration.

EPA‟s BART guidance does not specify a quantity of emission reductions an alternative 

must exceed to satisfy the “achieves greater reasonable progress” criteria. In its BART 

guidance, EPA provides an emission-based demonstration of how EPA determined the 

Clean Air Interstate Rule (CAIR) to be better than case-by-case BART on individual 

sources. In that instance, EPA demonstrated that more tons of emission reductions 

would result from the CAIR rule than with source-by-source BART. See, e.g., 70 Fed. 

Reg. at 39141. Similarly, the state has utilized the emission-based method to evaluate 

the PSCo BART Alternative. The state has determined that the PSCo BART Alternative 

achieves greater reasonable progress by evaluating the future emissions from the 

electric generating units under the operating scenarios reflected in the PSCo BART 

Alternative, and for demonstration purposes compared those emissions with the same 

units using the standard established by EPA of 95 percent removal or 0.15 lb/MMBtu for 

SO2 or a lb/MMBtu for NOx based on boiler and coal type. See 71 Fed. Reg. at 60619 

(“States establishing a BART benchmark based on simplifying assumptions as to the 

most stringent BART for EGUs may rely on the presumptions, as EPA did in the CAIR 

rule.”).

As previously discussed, the PSCo Alternative is based on a combination of emissions 

control retrofits and shutdowns resulting from Colorado HB 10-1365 and the PUC‟s 

actions. The PSCo BART Alternative includes Pawnee, Arapahoe Units 3 and 4, 

Valmont Unit 5, and Cherokee Units 1-4. Pawnee, Cherokee Unit 4 and Valmont Unit 5 

are the only BART eligible units. The sources involved in the PSCo BART Alternative 

are either BART eligible sources or sources that precede the BART timeframe. For 

demonstration purposes, the emissions from the entire group of electric generating units 

in the PSCo BART Alternative were compared to the emissions from the units if the 

presumptive levels were applied, as allowed under EPA‟s regulation. Table 6-7 

compares the tons of SO2 that would be emitted under the PSCo BART Alternative to 

the number of tons of SO2 that would be emitted by the same units if the standard of 

0.15 lb SO2/MMBtu were applied. The 0.15 lb/MMBtu standard comes from the 70 Fed. 

Reg. 39132 (7/6/2005) in which EPA establishes “BART limits of 95 percent SO2 

removal, or an emission rate of 0.15 lb SO2/MMBtu”. The MMBtu used for the analysis 

is an average of the actual MMBtu reported by the units to the Clean Air Markets 

Division for 2006, 2007 and 2008. For units that will be shutdown or operated on 

natural gas (Arapahoe unit 4) under the PSCo BART Alternative an emissions factor of 

0.0006 lb SO2/MMBtu was used for the alternative.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

93

Table 6-7: SO2 Reductions Beyond Presumptive BART for PSCo Alternative

Facility

MMBtu

Average 

2006 to 2008

SO2 TPY 

Average 

2006 to 

2008

SO2 TPY at 

0.15 

lb/MMBtu

Presumptive

SO2 TPY 

under PSCo

Alternative in 

2018

% Reduction 

Beyond 

Presumptive 

BART

Arapahoe

Unit 3 4,380,121 924.97 328.51 0.00 100.00%

Unit 4 8,545,791 1,764.70 640.93 1.2819 99.8%

Cherokee

Unit 1 8,311,352 2,220.80 623.35 0.00 100.00%

Unit 2 5,586,021 1,888.37 418.95 0.00 100.00%

Unit 3 8,159,889 743.00 611.99 0.00 100.00%

Unit 4 26,047,648 2,135.43 1,953.57 7.81 99.6 %

Valmont 13,722,507 758.47 1,029.19 0.00 100.00%

Pawnee 40,093,753 13,472.07 3,007.03 2,405.63 20.00%

Total 114,847,083 23,908 8,614 2,415 71.97%

The comparison with the standard of 0.15 lb SO2/MMBtu shows that the PSCo BART 

Alternative provides 72% lower SO2 emissions.

Figure 6-1 provides a year by year comparison of the PSCo BART Alternative to the 

0.15 lb SO2/MMBtu standard for this planning period.

Figure 6-1: SO2 reductions beyond presumptive BART for PSCo Alternative

 

19 Emission factor of 0.0006 lb SO2/MMBtu and 50% capacity factor.

0

5,000

10,000

15,000

20,000

25,000

30,000

2010 2011 2012 2013 2014 2015 2016 2017 2018

SO2 Tons/year

Year

SO2 Reductions

SO2 Presumptive

Alternative
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

94

A similar analysis was completed for NOx emissions. Table 6-8 compares the PSCo 

BART Alternative to a standard based on NOx limits established by EPA in 70 Fed. 

Reg. 39135 (7/6/2005). EPA provides a NOx lb/MMBtu level based on the boiler type 

and the coal type burned. The PSCo BART Alternative reflects 600 tpy of NOx emitted 

from Arapahoe 4 operating on natural gas as a “peaking” unit, 300 tpy of NOx reserved 

for “netting” or “offsets” from the Arapahoe facility, and 500 tpy of NOx reserved for 

“netting” or “offsets” from the Cherokee facility.

Table 6-8: NOx Reductions Beyond Presumptive BART for PSCo Alternative

Facility

MMBtu

Average 

2006 to 

2008

NOx TPY 

Average 

2006 to 

2008

NOx 

lb/MMBtu

Standard

TPY NOx 

at

Standard

TPY NOx 

Under PSCo

Alternative 

in 2018

% Reduction 

Beyond 

Presumptive 

BART

Arapahoe

Unit 3 4,380,121 1,770.47 0.23 503.71 0.00 100.00%

Unit 4 8,545,791 1,147.67 0.23 982.77 900.0020 8.42%

Cherokee

Unit 1 8,311,352 1,556.23 0.39 1,620.71 0.00 100.00%

Unit 2 5,586,021 2,895.20 0.39 1,089.27 0.00 100.00%

Unit 3 8,159,889 1,865.50 0.39 1,591.18 0.00 100.00%

Unit 4 26,047,648 4,274.00 0.28 3,646.67 2,062.8621 43.43%

Valmont 13,722,507 2,313.73 0.28 1,921.15 0.00 100.00%

Pawnee 40,093,753 4,537.73 0.23 4,610.78 1,403.28 69.57%

Total 114,847,083 20,361 15,966 4,366 72.65%

Figure 6-2 illustrates the year by year reductions achieved by the PSCo BART 

Alternative as compared to the standard derived from the EPA standard based on the 

configuration of each unit and the coal type burned by the unit in the PSCo BART 

Alternative.

 

20 600 tpy NOx from operation of Arapahoe 4 on natural gas as a “peaking” unit and 300 tpy NOx 

reserved for “netting” and “offsets” for additional natural gas generation. The 300 tpy NOx is associated 

with unit 4 for illustrative purposes, but may be associated with either unit.

21 Cherokee 4 operating on natural gas at 0.12 lb NOx/mmBTU and 500tpy NOx reserved for “netting” or 

“offsets”. The 500 tpy NOx is associated with unit 4 for illustrative purposes, but may be associated with 

any combination of the units.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

95

Figure 6-2: NOx Reductions Beyond Presumptive BART for PSCo Alternative

The PSCo BART Alternative provides a reduction of 15,994 tons per year of NOx and 

21,493 tons per year of SO2 from the baseline (average of 2006-2008 actuals) (89%

and 77% reduction, respectively). These SO2 and NOx reductions provide significantly 

greater reductions as compared to the application of the standard set forth in 70 Fed. 

Reg. 39132-39135 (7/6/2005) applied all the units in the PSCo BART Alternative. The 

PSCo BART Alternative provides a 71% improvement in NOx reductions (See Table 6-

8) over the presumptive levels, and a 72% improvement in SO2 reductions (See Table 

6-7) over the presumptive levels. This is a significantly higher reduction than would have 

been achieved through the application of the presumptive limits. The state‟s alternative 

program is thus “clearly superior” to source-specific BART. See 71 Fed. Reg. at 

60615. It provides not only for further emission reductions at units, but reflects the 

closure of numerous units, and thus the complete elimination of emissions from those 

units. Because these measures will provide greater emission reductions and will occur 

within the first planning period, the state has determined that they also satisfy 

reasonable progress for these sources. In this regard, Colorado has reasonably 

concluded that any control requirements imposed in the BART context also satisfy the 

RP related requirements in the first planning period. See U.S. EPA, “Guidance for 

Setting Reasonable Progress Goals Under the Regional Haze Program,” p. 4-2 (June 

2007).

Supplemental Technical Analysis Supporting the Alternative measure 

demonstration for the PSCo Alternative

0

5,000

10,000

15,000

20,000

25,000

2010 2011 2012 2013 2014 2015 2016 2017 2018

NOx Tons/year

Year

NOx Reductions

Nox Presumptive

Alternative
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

96

In addition to the foregoing demonstration that the PSCo BART Alternative satisfies the 

requirements of 40 CFR 51.308(e)(2) for an approvable alternative to EPA‟s BART 

regulation, the state undertook and provides the following additional technical analyses 

to support its determination that the PSCo BART Alternative demonstrates greater 

reasonable progress than the installation of BART on subject to BART units.

Colorado also evaluated the NOx reductions of the alternative program based on the 

criteria established by the state for BART and reasonable progress for NOx reductions. 

As part of its five factor consideration the state has elected to generally employ criteria 

for NOx post-combustion control options to aid in the assessment and determinations 

for BART – a $/ton of NOx removed cap, and two minimum applicable Δdv improvement 

figures relating to CALPUFF modeling for certain emissions control types, as follows.

- For the highest-performing NOx post-combustion control options (i.e., SCR systems 

for electric generating units) that do not exceed $5,000/ton of pollutant reduced by the 

state‟s calculation, and which provide a modeled visibility benefit on 0.50 Δdv or greater 

at the primary Class I Area affected, that level of control is generally viewed as 

reasonable.

- For lesser-performing NOx post-combustion control options (e.g., SNCR technologies 

for electric generating units) that do not exceed $5,000/ton of pollutant reduced by the 

state‟s calculation, and which provide a modeled visibility benefit of 0.20 Δdv or greater 

at the primary Class I Area affected, that level of control is generally viewed as 

reasonable.

For the PSCo BART Alternative sources included in the PSCo BART Alternative, SCR 

costs (where technically feasible) are greater than $5,000 per ton of NOx removed or 

the visibility improvement from SCR is less than 0.50 Δdv. See analysis in appendix C. 

Under the state‟s criteria this would eliminate SCR from further consideration as a 

control alternative for BART and reasonable progress. Thus, for demonstration 

purposes the state has compared the PSCo BART Alternative with the emission 

reductions achievable by SNCR. The division used study of SNCR on coal fired boilers 

in the size range of those in the PSCO BART Alternative. The study showed that the 

SNCR tested achieved a 35% reduction in NOx with less than 2ppm NH3 slip and 54% 

reduction with a 10ppm NH4 slip.22 Because of the high ammonia slip at the higher 

range of NOx removal the division determined that 50% removal was appropriate for 

this comparison. Thus, for comparative purposes for the PSCo BART Alternative, the 

state will assume that SNCR is applied at a level of NOx reduction, of 50%, to assess 

performance of presumed SNCR on these units as against the PSCo BART Alternative 

for NOx.23 Table 6-9 provides a comparison of the costs for SCR and SNCR as 

provided by PSCo, SNCR at a 50% reduction (calculated from an average of NOx 

actual from 2006-2008 as reported to the Clean Air Markets Division) and the PSCo 

BART Alternative.

 

22 Environmental Controls Conference, Pittsburgh, PA (5/16/2006 to 5/18/2006)

23 This level of NOx control efficiency is for comparative purposes only, is an assumed maximum potential 

level of performance, and is not intended to reflect that SNCR on these particular electric generating units 

could, in fact, achieve this level of NOx reduction performance from application of SNCR.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

97

Table 6-9: NOx reductions beyond state criteria for PSCo Alternative

Facility SCR $/ton SNCR 

$/ton

SNCR TPY at 

50%24

PSCo

Alternative 

TPY

% Reduction 

from SNCR at 

50% Control

Arapahoe

Unit 3 885.23 0 100.00%

Unit 4 573.83 90025-56.84%

Cherokee

Unit 1 N/A $8,737 778.12 0 100.00%

Unit 2 N/A $3,963 1,447.60 0 100.00%

Unit 3 $10,134 $3,485 932.75 0 100.00%

Unit 4 $6,252 $2,625 2,137.00 2,06226 3.47%

Valmont $8,647 $3,328 1,156.87 0 100.00%

Pawnee $4,371 $3,082 2,268.87 1,403 38.15%

Total 10,180 4,366 57.11%

The PSCo BART Alternative results in 55% more reduction in NOx than the assumed 

installation of SNCR at all units covered by the PSCo BART Alternative. A similar 

analysis was not completed for SO2 because the state did not look at SO2 controls for 

reasonable progress as all sources were already controlled.

For both SO2 and NOx the state also evaluated the PSCo BART Alternative against a 

source by source analysis. For SO2 the state has done source specific analyses for 

Arapahoe Unit 4, Cherokee Unit 4 and Pawnee. For the remainder of the sources, for 

demonstration purposes, the state applied an aggressive 95% control level assumption 

to the uncontrolled emissions from those sources. The 95% was taken both from 

current operations and from uncontrolled emissions calculated using AP-42.27 The 

analysis demonstrates that the alternative proposed is better than the source by source 

analysis by more than 52% as shown in Table 6-10. Figure 6-3 shows the reductions 

 

24 Fifty percent reduction was taken from an average of 2006-2008 actual NOx emissions as reported to 

the Clean Air Markets Division.

25 600 tpy NOx from operation of Arapahoe 4 on natural gas as a “peaking” unit and 300 tpy NOx 

reserved for “netting” and “offsets” for additional natural gas generation.

26 Cherokee 4 operating on natural gas at 0.12 lb NOx/MMBtu and 500 tpy NOx reserved for “netting” or

“offsets”.

27 This level of SO2 reduction efficiency is for comparative purposes only, is an assumed maximum 

potential level of performance, and is not intended to reflect that flue gas desulphurization systems on 

these particular electric generating units burning low-sulfur western coal, could, in fact, achieve this level 

of SO2 reduction performance. The AP 42 analysis reflects essentially the uncontrolled emissions from 

these facilities. This is different from the other analyses provided in this document, and when employing 

a 95% reduction assumption for demonstration purposes for an alternative measure makes the starting 

point for the sources in the Alternative more similar to uncontrolled eastern sources, where a higher sulfur 

content coal is generally utilized, which is more relevant to an assumed 95% reduction of SO2.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

98

from the PSCo BART Alternative as compared to the source by source evaluation on a 

year to year basis.

Table 6-10: SO2 Reductions Beyond Source-By-Source BART for PSCo 

Alternative

Facility SO2 TPY from 

AP-42

Source-bySource

SO2 TPY 

from PSCo

Alternative

% Reduction 

Beyond Sourceby-Source

Arapahoe

Unit 3 1,076.53 53.82 0.00 100.00%

Unit 4 2,322.21 1.28 1.28 0.00%

Cherokee

Unit 1 2,803.67 140.18 0.00 100.00%

Unit 2 2,662.17 133.10 0.00 100.00%

Unit 3 3,438.79 171.93 0.00 100.00%

Unit 4 9,779.27 1,953.5728 7.81 99.6%

Valmont 3,822.73 191.13 0.00 100.00%

Pawnee 8,342.36 2,405.6229 2,405.63 0.00%

Total 34,248 5,051 2,415 52.19%

Figure 6-3: SO2 Reductions Beyond Source-By-Source BART for PSCo 

Alternative

 

28 The Cherokee Unit 4 BART evaluation concluded that a 0.15 lb SO2/mmBTU limit was appropriate 

(See Appendix C). The TPY value was calculated from the average of 2006-2008 mmBTU values 

reported to the Clean Air Markets Division.

29 The Pawnee BART evaluation concluded that a 0.12 lb SO2/mmBTU limit was appropriate (See 

Appendix C). The TPY value was calculated from the average of 2006-2008 mmBTU values reported to 

the Clean Air Markets Division.

0

5,000

10,000

15,000

20,000

25,000

30,000

2010 2011 2012 2013 2014 2015 2016 2017 2018

SO2 TPY

Year

SO2 Comparison to Source-by-Source

Alternative

Source by Source
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

99

For NOx the state looked at a source by source analysis for Arapahoe Unit 4, Cherokee 

Unit 4 and Pawnee. For the remainder of the sources, for demonstration purposes, the 

state applied an aggressive 90% control level assumption to the sources. The 90% was 

taken from emissions calculated using AP-42.30 The source by source analysis 

considered the operation of Arapahoe Unit 4 with natural gas as a peaking unit and 

retaining 300 tpy of NOx for future netting or offsets from Arapahoe, the operation of 

Cherokee Unit 4 on natural gas at 0.12 lb/MMBTU and retaining 500 tpy of NOx from 

Cherokee for future netting, and control of Pawnee with SCR at 0.07 lb/MMBTU. The 

results of the comparison indicate that the alternative proposed is 49% better than the 

source by source analysis.

Table 6-11: NOx Reductions Beyond Source-By-Source BART for PSCo

Alternative 

Facility NOx TPY from 

AP-42

Source-bySource

NOx TPY from 

PSCo

Alternative

% Reduction 

Beyond Sourceby-Source

Arapahoe

Unit 3 2,149.15 214.91 0.00 100.00%

Unit 4 4,636.00 600 900.0031-50.00%

Cherokee

Unit 1 3,596.54 359.65 0.00 100.00%

Unit 2 3,415.03 341.50 0.00 100.00%

Unit 3 4,411.28 441.12 0.00 100.00%

Unit 4 7,878.04 2,735.0032 2,062.8633 24.58%

Valmont 2,061.04 206.10 0.00 100.00%

Pawnee 7,945.11 3,608.43 1,403.28 61.11%

Total 36,092 8,507 4,366 48.67%

 

30 This level of NOx reduction efficiency is for comparative purposes only, is an assumed maximum 

potential level of performance, and is not intended to reflect that flue gas desulphurization systems on 

these particular electric generating units, could, in fact, achieve this level of NOx reduction performance. 

The AP 42 analysis reflects essentially the uncontrolled emissions from these facilities. 

31 Natural gas operation as a peaking unit limited to 600 tpy with 300 tpy NOx reserved for offsets or

netting for additional natural gas generation.

32 Coal fired operation with SNCR at 0.21 lb NOx/MMBtu.

33 Natural gas operation at 0.12 lb NOx/MMBtu with 500 tpy NOx reserved for offsets or netting.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

100

Figure 6-4: NOx Reductions Beyond Source-By-Source BART for PSCo

Alternative

Conclusion

Under EPA regional haze regulations, Colorado has utilized an emission based 

comparison to demonstrate that that the PSCo BART Alternative provides greater 

reasonable progress than, and is clearly superior to, source by source BART. Although 

not necessary, as a means of further supporting its demonstration, the state has utilized 

other methodologies to demonstrate that the PSCo BART Alternative achieves greater 

reasonable progress than BART or individual reasonable progress requirements. The 

PSCo BART Alternative will result in early and significant reductions of visibility 

impairing pollutants.

0

5,000

10,000

15,000

20,000

25,000

2010 2011 2012 2013 2014 2015 2016 2017 2018

NOx TPY

Year

NOx Comparison to Source-by-Source

Alternative

Source by Source
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

101

Table 6-12: PSCo Alternative Emissions Limits34, 35, 36

Unit NOx Control

Type

NOx Emission

Limit

SO2 Control

Type

SO2 Emission

Limit

Particulate

Type And 

Limit

Cherokee

Unit 1

Shutdown

No later than 

7/1/2012

0 Shutdown

No later than 

7/1/2012

0 Shutdown

No later than 

7/1/2012

Cherokee

Unit 2 

Shutdown

12/31/2011

0 Shutdown

12/31/2011

0 Shutdown

12/31/2011

Cherokee

Unit 3

Shutdown

No later than 

12/31/2016

0 Shutdown

No later than 

12/31/2016

0 Shutdown

No later than 

12/31/2016

Cherokee

Unit 4

Natural Gas 

Operation

0.12 lb/MMBtu

(30-day rolling 

average) by 

12/31/2017

Natural Gas 

Operation

12/31/2017

7.81 tpy (12 month 

rolling average)

Fabric Filter 

Baghouse*

0.03 lbs/MMBtu

Natural Gas 

Operation 

12/31/2017

Valmont

Unit 5

Shutdown

12/31/2017

0 Shutdown

12/31/2017

0 Shutdown

12/31/2017

Pawnee

Unit 1

SCR** 0.07 lb/MMBtu

(30-day rolling 

average) by 

12/31/2014

Lime Spray 

Dryer**

0.12 lbs/MMBtu 

(30-day rolling 

average) by 

12/31/2014

Fabric Filter 

Baghouse*

0.03 lbs/MMBtu

Arapahoe

Unit 3

Shutdown 

12/31/2013

0 Shutdown 

12/31/2013

0 Shutdown 

12/31/2013

Arapahoe

Unit 4

Natural Gas 

Operation 

600 tpy (12 month 

rolling average) 

by 12/31/2014

Natural Gas 

operation 

12/31/2014

1.28 tpy (12 month 

rolling average)

Fabric Filter 

Baghouse*

0.03 lbs/MMBtu

Natural Gas 

operation

12/31/2014

 

** The "assumed" technology reflects the control option found to render the BART emission limit 

achievable. The "assumed" technology listed for Pawnee in the above table is not a requirement.

34

 Emission rates would begin on the dates specified, the units would not have 30 days of data until 30 

days following the dates shown in the table.

35 500 tpy NOx will be reserved from Cherokee Station for netting or offsets.

36

 300 tpy NOx will be reserved from Arapahoe Station for netting or offsets for additional natural gas 

generation.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

102

Chapter 7 Visibility Modeling and Apportionment

Modeling results and technical analyses indicate that Colorado sources contribute to 

visibility degradation at Class I areas. The modeling also shows out-of-state sources 

have the greatest impact on regional haze in Colorado. As such, this Plan anticipates 

local and regional solutions so that Colorado‟s 12 Class I areas make progress towards 

the 2018 and 2064 visibility goals.

7.1 Overview of the Community Multi-Scale Air Quality (CMAQ) Model

The Regional Modeling Center (RMC) Air Quality Modeling group is responsible the 

Regional Haze modeling for the WRAP. The RMC is located at the University of 

California - Riverside in the College of Engineering Center for Environmental Research 

and Technology.

The RMC modeling analysis is based on a model domain comprising the continental 

United States using the Community Multi-Scale Air Quality (CMAQ) model. The EPA 

developed the CMAQ modeling system in the late 1990s. CMAQ was designed as a 

“one atmosphere” modeling system to encompass modeling of multiple pollutants and 

issues, including ozone, PM, visibility, and air toxics. This is in contrast to many earlier 

air quality models that focused on single-pollutant issues (e.g., ozone modeling by the 

Urban Airshed Model). CMAQ is an Eulerian model - that is, it is a grid-based model in 

which the frame of reference is a fixed, three-dimensional (3-D) grid with uniformly sized 

horizontal grid cells and variable vertical layer thicknesses. The key science processes 

included in CMAQ are emissions, advection and dispersion, photochemical 

transformation, aerosol thermodynamics and phase transfer, aqueous chemistry, and 

wet and dry deposition of trace species.

A detailed summary of the CMAQ modeling for each Class I area is included in Section

6 of the Technical Support Document.

7.2 CMAQ Modeling Results for 2018

Figure 7-1 lists the 2018 Uniform Progress (UP) for each class I area along with the 

visibility modeling forecasts for 2018. These modeling results were released in 2006 by 

the WRAP and are preliminary; new modeling results with the latest emission estimates 

and control measure benefits are anticipated mid- to late 2007, and additional modeling 

is scheduled to be performed in 2008 and 2009. The results of this modeling will be 

utilized in defining (RPGs) for all 12 Colorado Class I areas by the year 2010 as 

described in Chapter 9.

As indicated by the 2006 modeling, reasonable progress for each Class I area falls 

short of meeting 2018 uniform progress for the 20% worst days, as indicated by the 

numbers in the blue highlighted box. Alternatively, all areas are forecast to maintain 

the best days in 2018.

More detailed information on the CMAQ modeling for a particular Class I area can be 

found in Section 6 of the Technical Support Document.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

103

Figure 7-1 Summary of CMAQ Modeling Progress Towards 2018 UP

7.3 Overview of Particulate Matter Source Apportionment Technology (PSAT) Modeling

The Regional Modeling Center (RMC) at the University of California – Riverside 

developed the PSAT algorithm in the Comprehensive Air quality Model with extensions 

(CAMx) model to assess source attribution. The PSAT analysis is used to attribute 

particle species, particularly sulfate and nitrate from a specific location within the 

Western Regional Air Partnership (WRAP) modeling domain. The PSAT algorithm 

applies nitrate-sulfate-ammonia chemistry to a system of tracers or “tags” to track the 

chemical transformations, transport and removal of emissions.

Each state or region (i.e. Mexico, Canada) is assigned a unique number that is used to 

tag the emissions from each 36-kilometer grid cell within the WRAP modeling domain. 

Due to time and computational limitations, only point, mobile, area and fire emissions 

were tagged.

The PSAT algorithm was also used, in a limited application (e.g. no state or regional 

attribution) due to resource constraints, to track natural and anthropogenic species of 

organic aerosols at each CIA. The organic aerosol tracer tracked both primary and 

secondary organic aerosols (POA & SOA). Appendix H includes more information on 

PSAT methodology.

More detailed information on the PSAT modeling can be found in Section 7 of the 

Technical Support Document for each Class I area.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

104

7.4 PSAT Modeling Results for 2018

Figure 7-2 provides the four highest source areas contributing sulfate and nitrate at 

each Class I area. As indicated, boundary conditions (BC) are the highest contributor to 

sulfate at all Colorado Class I areas. The boundary conditions represent the 

background concentrations of pollutants that enter the edge of the modeling domain. 

Depending on meteorology and the type of pollutant (particularly sulfate), these 

emissions can be transported great distances that can include regions such as Canada, 

Mexico, and the Pacific Ocean. Colorado appears to be a major contributor of 

particulate sulfate at those Class I areas near significant sources of SO2.

For nitrate, Colorado appears to be a major contributor at most of our Class I areas 

except for the Weminuche Wilderness, La Garita Wilderness and Black Canyon of 

Gunnison National Park. Although, boundary conditions also appear to be a major 

contributor of nitrate at all our Class I areas.

Figure 7-2 Summary of PSAT Modeling for 2018

Figure 7-3 identifies the change in the Colorado portion of particulate sulfate and nitrate 

concentrations, from 2002 to 2018 at each Class I area. For 2018, the PSAT modeling 

forecasts a reduction in the Colorado portion of sulfate at all Class I areas ranging from 

25% to 33%. These particulate sulfate reductions are due to reductions from point and

mobile source sulfur dioxide emissions (see Figure 5-1).

The 2018 forecasts for nitrate appear mixed with increases of 25% to 27% at the 

southwest Colorado Class I areas and nitrate reductions of 9% to 28% at all other 

areas. The increase in particulate nitrate in southwest Colorado is likely due to forecast 

increases in Colorado‟s and the region‟s NOx emissions from area sources and oil & 

gas development (see Figure 5-2). The projected particulate nitrate reductions at the 

remaining Class I areas are due to NOx reductions in mobile sources.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

105

Figure 7-3 Colorado Share of Modeled Sulfate and Nitrate Changes for 2018
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

106

Chapter 8 Reasonable Progress

8.1 Overview of Reasonable Progress Requirements

Based on the requirements of the Regional Haze Rule, 40 CFR 51.308(d)(1), the state 

must establish goals (expressed in deciviews) for each Class I area in Colorado that 

provide for Reasonable Progress (RP) towards achieving natural visibility conditions in 

2018 and to 2064. These reasonable progress goals (RPGs) are to provide for 

improvement in visibility for the most-impaired (20% worst) days over the period of the 

State Implementation Plan (SIP) and ensure no degradation in visibility for the leastimpaired (20% best) days over the same period.

In establishing the RPGs, the state must consider four factors: (1) the costs of 

compliance; (2) the time necessary for compliance; (3) the energy and non-air quality 

environmental impacts of compliance; and (4) the remaining useful life of any potentially 

affected sources. As well, the state must include a demonstration showing how these 

factors were taken into consideration in selecting the goals.

In establishing RPGs, the state must estimate the 2018 uniform rate of progress (URP) 

for each Class I area. The state must consider the URP and the emission reductions 

needed to achieve URP for the period covered by the plan. If the state ultimately 

establishes a Reasonable Progress Goal that provides for a slower rate of visibility 

improvement than would be necessary to meet natural conditions by 2064, the state 

must demonstrate that the uniform rate is not reasonable and that the state‟s alternative 

goal is reasonable, based on an evaluation of the 4 factors. In addition, the state must 

provide to the public an assessment of the number of years it would take to achieve 

natural conditions if improvement continues at the rate selected by the state. The 

detailed discussion of Reasonable Progress Goals can be found in Chapter 9, “Long 

Term Strategy”. The establishment of the pollutants for RP evaluations and the 

evaluation of significant sources for reasonable progress is presented below.

8.2 Visibility Impairing Pollutants Subject to Evaluation

The state conducted a detailed evaluation37 of the six particulate pollutants; ammonium 

sulfate, ammonium nitrate, organic carbon (OC), elemental carbon (EC), fine soil and 

coarse mass (CM) (both of which are commonly known as particulate matter (PM)), 

contributing to visibility impairment at Colorado‟s 12 mandatory Class I federal areas, 

and determined that the first Regional Haze Plan RP evaluation should focus on

significant point sources of SO2 (sulfate precursor), NOx (nitrate precursor) and PM 

emissions. Emission sources are best understood for these three visibility-impairing 

pollutants, and stationary, or “point” sources, dominate the emission inventories and 

apportionment modeling. This determination is based on the well documented point 

source emission inventories for SO2 and NOx, and the Regional Model performance for 

sulfate and nitrate was determined to be acceptable. Significant point source PM 

emissions are also evaluated because of the Q/d screening methodology (Q = total 

 

37 Significant Source Categories Contributing to Regional Haze at Colorado Class I Areas, October 2, 

2007. See the Technical support Document
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

107

SO2, NOx and PM emissions; d = distance from the nearest Class I area, as further 

described in section 8.3), which includes PM emissions. PM emissions from other 

anthropogenic and natural sources are not being evaluated at this time.

Mobile and area sources were also identified as significant contributors to nitrates, and 

the RP evaluation of these two source categories is presented in section 8.2 above.

Generally, the sources of other visibility impairing pollutants, OC, EC, and PM, are not 

well documented because of emission inventory limitations associated with natural 

sources (predominantly wildfires), uncertainty of fugitive (windblown) emissions, and 

poor model performance for these constituents. Without a sound basis for making 

emission control determinations for sources that emit these three pollutants, Colorado 

determines that it is not reasonable in this planning period to recommend emission 

control measures; the State intends to address these pollutants and their emissions 

sources in future plan updates.

Figure 8-1 provides the statewide projected 2018 SO2 emissions, which reflects “onthe-books (OTB)” and “on-the-way (OTW)” emission control measures as of January 

2009 (the latest year for a complete emissions inventory compiled by the Western 

Regional Air Partnership (WRAP)).

Figure 8-1: Relative Source Contributions to Colorado SO2 Emissions in 2018

As indicated, 78% of total statewide SO2 emissions are from point sources – largely 

coal-fired boilers. Area source SO2 emissions (14%) are dominated by thousands of 

boilers and internal combustion engines statewide that burn distillate fuel. Depending 

on use and fuel grade, the maximum sulfur content of distillate fuel ranges between 500 

ppm to 5000 ppm. SO2 emissions from natural fires are considered uncontrollable and 

vary from year-to-year depending on precipitation, fuel loading and lightning. Both offroad and on-road mobile sources are subject to federal ultra-low sulfur diesel (ULSD) 

fuel requirements that limit sulfur content to 15 ppm (0.0015 %) that was in widespread 

use after June 2010 for off-road mobile and June 2006 for on-road mobile.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

108

The state has determined that point sources are the dominant source of emissions and, 

for this planning period, the only practical category to evaluate under reasonable 

progress for SO2.

Figure 8-2 provides the statewide projected 2018 NOx emissions, which reflects OTB 

and OTW emission control measures as of October 2009 (the latest year for a complete 

emissions inventory compiled by the WRAP).

Figure 8-2: Relative Source Contributions to Colorado NOx Emissions in 2018

Point sources comprise 36% of total NOx emissions that are mostly coal-fired external 

combustion boilers and natural gas-fired internal combustion engines (in oil and gas 

compression service). On-road and off-road mobile sources comprise 16% and 14% of 

statewide NOx emissions respectively. A portion of the on-road mobile source NOx 

emissions reflect some level of NOx control because of the Denver metro-area vehicle 

inspection program (IM-240). Both on/off road mobile also benefit from fleet turnover to 

cleaner vehicles resulting from more stringent federal emission standards. Because 

mobile exhaust emissions are primarily addressed, and will continue to be addressed, 

through federal programs, mobile sources will not be evaluated by Colorado for further 

RP control in this planning period. NOx emissions from biogenic activity and natural fire 

are considered uncontrollable and vary from year-to-year. Non-oil and gas area 

sources comprise about 6% of NOx emissions that involve thousands of combustion 

sources that are not practical to evaluate in this planning period.

The state has determined that large point sources are the dominant source of emissions 

and for this planning period are practical to evaluate under reasonable progress for 

NOx. Also, certain smaller point sources and area sources of NOx will also be 

evaluated under RP.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

109

8.3 Evaluation of Smaller Point and Area Sources of NOx for Reasonable Progress

Oil and gas area source NOx emissions have been determined to significantly 

contribute to visibility impairment in Colorado‟s Class I areas. Because this source 

category is made up of numerous smaller sources, it is only practical to evaluate the 

category for RP control as a whole, unlike point sources where individual sources are 

evaluated separately. When reviewing O&G area sources, natural gas-fired heaters,

and reciprocating internal combustion engines (RICE), are identified as the largest NOx 

emission sources. When reviewing point sources, natural gas-fired turbines were also 

identified as significant for review for RP.

8.3.1 Oil and Gas Heater Treaters

A heater-treater is a device used to remove contaminants from the natural gas at or 

near the well head before the gas is sent down the production line to a natural gas 

processing plant. It prevents the formation of ice and natural gas hydrates that may 

form under the high pressures associated with the gas well production process. These

solids can plug the wellhead.

The latest 2018 emissions inventory for the state assumes approximately 23,000 tons of 

NOx per year from 26,000 natural gas heater-treaters in Colorado at an emissions level 

of 0.88 tpy NOx per gas well heater-treater. 

Emissions control research and control application for this source category is not well 

developed and has focused primarily on methane reductions. Though there are some 

technically feasible control options, the costs of compliance and the control 

effectiveness cannot be confidently determined. While the cumulative emissions make 

this a significant source category, the state determines that, for this planning period, 

requiring the control of 26,000 individual sources less than one ton per year in size is 

not practical or reasonable for reasonable progress.

A detailed 4-factor analysis for heater treaters can be found in Appendix D.

8.3.2 Reciprocating Internal Combustion Engines

Power generated by large reciprocating internal combustion engines (RICE) is generally 

used to compress natural gas or to generate electricity in remote locations. The 

designation “large” refers to RICE that have an engine rating of at least 100 horsepower 

(hp) for the purpose of this reasonable progress analysis. 

Stationary RICE produce power by combustion of fuel and are operated at various airto-fuel ratios. If the stoichiometric ratio is used, the air and fuel are present at exactly 

the ratio to have complete combustion. RICE are operated with either fuel-rich ratios at 

or near stoichiometric, which are called rich-burn engines (RB), or air-rich ratios below 

stoichiometric, which are called lean-burn engines (LB). Undesirable emissions from 

RICE are primarily nitrogen oxides (NOx; primarily nitric oxide and nitrogen dioxide), 

carbon monoxide (CO), and volatile organic compounds (VOCs). NOx are formed by 

thermal oxidation of nitrogen from the air. CO and VOCs are formed from incomplete 

combustion. Rich-burn engines inherently have higher NOx emissions by design, and 

lean burn engines are designed to have relatively lower NOx emissions. 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

110

Colorado has undertaken regulatory initiatives to control NOx emissions from RICE, 

beginning in 2004. For the Denver metro area/North Front Range ozone control area, 

Regulation No. 7 was revised to require the installation of controls on new and existing 

rich burn and lean burn RICE larger than 500 hp by May 1, 2005. Controls for rich burn 

RICE are non-selective catalytic reduction (NSCR) and an air-to-fuel ratio controller, 

which effectively controls NOx (95%), CO and VOCs. Controls for lean burn RICE are 

oxidation catalyst reduction, which effectively control CO and VOCs. An exemption 

from control for lean burn RICE could be obtained upon demonstration that cost of 

emission control would exceed $5,000 per ton. Selective catalytic reduction was 

considered for the control of NOx from lean burn engines, but was dismissed due to the 

high cost/effectiveness at approximately $22,000/ton (see Appendix D for complete 

analysis). EPA approved this requirement as part of the Colorado SIP on August 19, 

2005 (70 Fed. Reg. 48652 (8/19/05)). 

In December 2008, Colorado proceeded to adopt into Regulation No. 7 similar 

provisions for all existing RICE over 500 hp throughout the state. By July 1, 2010 all 

existing engines in Colorado, had to install controls as described in the paragraph 

above, with the one exception that the $5,000 per ton exemption applied to both lean 

burn and rich burn engines. The state-only provision for rich-burn RICE (which reduces 

NOx emissions and is codified in Regulation No. 7, Sections XVII.E.3. and 3.a.) is being 

included as part of the Regional Haze SIP to become federally enforceable upon EPA 

approval. 

For RICE NOx control under the Regional Haze rule, Colorado determines that the 

installation of NSCR on all rich burn RICE throughout the state satisfies RP 

requirements. The accompanying benefits of reducing VOCs and CO also support this 

RP determination. Additional NOx control for lean burn RICE throughout the state is not 

reasonable for this planning period.

For new and modified RICE of 100 hp or greater, the state is relying on emissions 

controls that are required by EPA's New Source Performance Standards (NSPS) Subpart 

JJJJ, 40 CFR Part 60 and EPA’s National Emissions Standards for Hazardous Air 

Pollutants (NESHAP) Subpart ZZZZ, 40 CFR Part 63. Colorado determines that this 

federal control program satisfies reasonable progress for these sources in this planning 

period.

For existing RICE less than 500 hp throughout the state, the state determines that no 

additional control is necessary for RP in this planning period. Colorado‟s emission 

inventory system indicates that in the 2007/2008 timeframe, there were 538 engines 

less than 500 hp in the state, and these engines emitted 5,464 tons/year of NOx. At an 

average of about 10 tons of NOx emissions per year, controlling engines of this size is 

not reasonable. Many of these smaller existing engines will eventually be brought into 

JJJJ and ZZZZ when modified in the future, so it is reasonable to assume that additional 

NOx reductions will occur.

The 2018 emissions inventory assumes approximately 16,199 tons of NOx per year 

from RICE of all sizes in Colorado. The NOx control achieved by controlling rich burn 

engines in the ozone control area (approximately 7,000 tons/year) is assumed in this 

number. Controlling the remaining rich burn engines statewide reduces the 2018 RICE 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

111

NOx emissions inventory by approximately 5,800 tons/year to approximately 10,400 

tons/year. For new RICE subject to the NSPS and NESHAP, NOx emissions reductions 

have not been estimated. Because the 2018 estimate of 16,199 tons/year of NOx 

assumed growth in uncontrolled engines and did not account for th NSPS and 

NESHAP, the 10,400 ton/year emissions in 2018 should be even lower. The remaining 

NOx from engines is attributed to existing lean burn engines which are uncontrolled for 

NOx (though they will eventually be brought into JJJJ and ZZZZ when modified in the 

future), existing rich burn engines after control, small engines, and new RICE after the 

application of JJJJ and ZZZZ.

A detailed 4-factor analysis for RICE can be found in Appendix D.

8.3.3 Combustion Turbines

Combustion turbines fueled by natural gas or oil are either co-located with coal-fired 

electric generating units or as stand-alone facilities. These units are primarily used to 

supplement power supply during peak demand periods when electricity use is highest. 

Combustion turbine units start quickly and usually operate only for a short time. 

However, they are capable of operating for extended periods. Combustion turbine units 

are also capable of operating together or independently.

Information regarding combustion turbine emissions is well recorded in the state‟s air 

emissions inventory. Typical emissions for this source type may be significant for NOx, 

but pipeline quality natural gas is inherently clean and low-emitting for SO2 and PM10 

emissions. Combustion turbines are subject to 40 CFR Part 60, Subpart GG –

Standards of Performance for Stationary Gas Turbines, which limit sulfur content to 0.8 

percent by weight, supported by monitoring and testing. Subpart GG also limits 

nitrogen oxides to 117.8 percent by volume at 15 percent oxygen on a dry basis 

(60.332(a)(1)), supported by monitoring and testing. The majority of combustion 

turbines are installed with Continuous Emissions Monitoring Systems (CEMs).

RP evaluations are triggered for turbines that are co-located at BART or RP sources 

that have been determined to be significant because they have a Q/d impact of greater 

than 20 (see section 8.3 below for a description of this “significance” determination). 

The state analyzed total state-wide combustion turbine emissions averaged over the 

2006 – 2008 Reasonable Progress baseline period. There are five Reasonable 

Progress facilities with combustion turbines – PSCo Valmont Generating Station, PSCo 

Arapahoe Generating Station, Colorado Springs Utilities Nixon Plant, Platte River Power 

Authority Rawhide Energy Station, and PSCo Pawnee Generating Station. Of these, 

only two turbines located at the Nixon Plant emit significant levels of visibility impairing 

emissions, as defined by the federal Prevention of Significant Deterioration (PSD) 

significance levels:

NOx – 40 tons per year

SO2 – 40 tons per year

PM10 – 15 tons per year
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

112

Facility – Turbine

Total 2006 –

2008 Averaged 

NOx Annual 

Emissions (tpy)

Total 2006 –

2008 Averaged 

SO2 Annual 

Emissions (tpy)

Total 2006 –

2008 Averaged 

PM10 Annual 

Emissions (tpy)

Greater than 

de minimis

levels?

Front Range Power 

Plant –

Turbine #1

159.6 2.9 4.9 Yes – NOx 

only

Front Range Power 

Plant –

Turbine #2

147.9 2.8 4.9 Yes – NOx 

only

The combustion turbines at the Front Range Power Plant were installed with advanced 

dry-low NOx combustion systems, and based on 2006 – 2008 CEMs data and AP-42 

emission factors, are achieving 89.4% and 90.1% NOx reductions, respectively.

There is one feasible emission control technology available for these turbines is adding 

post combustion technology – selective catalytic reduction (SCR) which, in good 

working order can achieve removal efficiencies ranging from 65 – 90 percent from 

uncontrolled levels.

Applying SCR would achieve up to an additional 90% control efficiency to both turbines 

and could result in about 275 tons of NOx reduced annually with a capital expenditure of 

at least $15 million. The state estimates that SCR for these turbines will range from 

approximately $57,000 - $62,000 per ton of NOx reduced annually. In the state‟s 

judgment for this planning period for Reasonable Progress, the potential 275 tons per 

year of NOx reductions are not cost-effective. The state has determined that NOx RP 

for combustion turbines is existing controls and emission limits.

A detailed 4-factor analysis for combustion turbines can be found in Appendix D.

8.4 Determination of Point Sources Subject to Reasonable Progress Evaluation

Colorado refined the RP analysis referred to in Section 8.2 (using the latest WRAP 

emission inventory data) to select specific point sources to evaluate for RP control38. 

This RP screening methodology involves a calculated ratio called “Q-over-d”, that 

evaluates stationary source emissions (mathematical sum of actual SO2, NOx and PM 

emissions in tons per year, denoted as “Q”) divided by the distance (in kilometers, 

denoted as “d”) of the point source from the nearest Class I area.

The State evaluated the visibility impact sensitivity of different Q/d thresholds and 

determined that a Q/d ratio equal to or greater than “20” approximated a delta deciview 

(Δdv) impact ranging from 0.06 Δdv to 0.56 Δdv. The resultant average of the range is 

about 0.3 Δdv, which is a more conservative RP threshold than the 0.5 Δdv that was 

used in determining which sources would be subject-to-BART under the federal BART 

regulations. The delta deciview impact was determined by evaluating CALPUFF 

 

38 Reasonable Progress Analysis of Significant Source Categories Contributing to Regional Haze at 

Colorado Class I Areas, March 31, 2010. See the Technical Support Document
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

113

modeling, conducted by the state in 2005, for the ten subject-to-BART stationary 

sources. Since the Q/d methodology involves consideration of PM emissions, the state 

has added PM (PM-10) emissions to the RP evaluation process.

The evaluation of potential RP sources involved all Colorado stationary sources with 

actual SO2, NOx or PM10 emissions over 100 tons per year based on Air Pollution 

Emissions Notice (APEN) reports from 2007. The one-hundred-thirteen (113) sources 

identified as exceeding the 100 tons/year threshold for any of the three pollutants (see 

Figure 8-3) were further analyzed, using ArcGIS mapping, to determine the exact 

distance from the centroid of the source to the nearest Class I area boundary. The Q/d 

was calculated for each source, and Table 8-1 lists the sixteen (16) point sources that 

are equal to or greater than the Q/d of 20 threshold. These sixteen sources will be 

referred to as “significant” sources for purposes of reasonable progress.

Figure 8-3: Point Sources with >100 TPY of Emissions
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

114

Table 8-1: Colorado Significant Point Sources with a Q/d 20

Note that the APEN reports may not represent actual annual emissions, as Colorado 

Regulation 3 requires APEN reports to be updated every five years if no significant 

emissions increases have occurred at the source. Further, sources do not pay APEN 

emission fees on fugitive dust, thus sources with significant fugitive dust emissions may 

report potential rather than actual emissions in the APEN. The state contacted sources 

to ensure that actual emissions were used as much as possible since many sources

over-estimate emissions in APENs. This ensures that correct emissions are used for 

the purposes of Reasonable Progress.

Set forth below are summaries of each of the sixteen significant sources. Many of these 

are BART sources, and emission control analyses and requirements for those sources 

are documented in Chapter 6 of this document. The BART determinations represent 

best available retrofit control and also satisfy RP requirements, and no further 

assessment of emissions controls for these facilities is necessary for reasonable 

progress during this planning period. In this regard, the state has already conducted 

BART analyses for its BART sources that are largely based on an assessment of the 

same factors to be addressed in establishing RPGs. Thus, Colorado has reasonably 

concluded that any control requirements imposed in the BART determination also 

satisfy the RP related requirements in the first planning period. See U.S. EPA, 

Guidance for Setting Reasonable Progress Goals Under the Regional Haze Program, p. 

4-2 (June 2007).

1. The state has determined that Platte River Power Authority‟s Rawhide Power Plant 

(unit 1) is a subject-to-RP source and has conducted an emission control analysis 

for the unit (see below).

2. The CEMEX Portland cement manufacturing facility in Lyons, Colorado, is a subjectto-BART source that the Division reviewed for best available retrofit controls for 

SO2, NOx and PM emissions. The state has determined that the CEMEX BART 

determinations for the kiln and the dryer (see Chapter 6) satisfy the SO2, NOx and 

PM BART/RP requirements in this planning period.

3. The Public Service Company of Colorado (PSCo) Valmont Power Plant (unit 5) is a 

subject-to-BART source that is included in a better than BART alternative for SO2 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

115

and NOx (see Chapter 6), which satisfies the SO2 and NOx BART/RP requirements 

in this planning period. For PM, the state has determined that the facility‟s closure 

by 2018 satisfies the PM BART/RP requirements in this planning period.

4. The Colorado Energy Nations Corporation (CENC) operates two subject-to-BART 

industrial boilers (boilers 4 & 5) that the state reviewed for best available retrofit 

controls for SO2, NOx and PM emissions. The CENC BART determination for these 

two boilers (see Chapter 6) satisfies the SO2, NOx and PM BART/RP requirements 

in this planning period. For boiler 3, the state has determined it to be subject-to-RP 

and has conducted an emission control analysis for the boiler (see below).

5. The PSCo Cherokee Power Plant has four units (1, 2, 3 & 4); unit 4 is a subject-toBART source. All of the units are included in a better than BART alternative for SO2 

and NOx (see Chapter 6), which satisfies the SO2 and NOx BART/RP requirements 

in this planning period. For PM, the closure of units 1, 2 and 3 by 2018 satisfies the 

PM RP requirements in this planning period. For unit 4, the BART determination for 

PM emissions satisfies the PM BART/RP requirements in this planning period.

6. The PSCo Arapahoe Power Plant (units 3 & 4) is a subject-to-RP source that is 

included in a better than BART alternative for SO2 and NOx (see Chapter 6), which 

satisfies the SO2 and NOx BART/RP requirements in this planning period. For PM, 

the closure of unit 3 by 2018 satisfies the PM RP requirements in this planning 

period; for unit 4 the conversion to repower from coal to natural gas satisfies the PM 

RP requirements in this planning period.

7. The PSCo Pawnee Power Plant (unit 1) is a subject-to-BART source that is included 

in a better than BART alternative for SO2 and NOx (see Chapter 6), which satisfies 

the SO2 and NOx BART/RP requirements in this planning period. The BART 

determination for PM emissions satisfies the PM BART/RP requirements in this 

planning period.

8. The Colorado Springs Utilities (CSU) Drake Power Plant (units 5-7) is a subject-toBART source that the state reviewed for best available retrofit controls for SO2, NOx 

and PM emissions. The Drake BART determination (see Chapter 6) satisfies the 

SO2, NOx and PM BART/RP requirements in this planning period.

9. The state has determined that the CSU Nixon Plant (unit 1) and the co-located Front 

Range Power Plant are subject-to-RP sources and has conducted emission control 

analyses for these sources (see below).

10.The state has determined that the Black Hills Energy Clark Power Plant (units 1 and 

2) is a subject-to-RP source and has conducted an emission control analysis for the 

source (see below).

11.The state has determined that the Holcim Portland cement manufacturing facility 

(kiln and dryer) is subject-to-RP and has conducted an emission control analysis for 

the source (see below).

12.The PSCo Comanche Power Plant (units 1 and 2) is a subject-to-BART source that 

the state reviewed for best available retrofit controls for SO2, NOx and PM 

emissions. The Comanche BART determination (see Chapter 6) satisfies the SO2, 

NOx and PM BART/RP requirements in this planning period.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

116

13.The state has determined that the Tri-State Generation and Transmission 

Association‟s Nucla Power Plant is subject-to-RP and has conducted an emission 

control analysis for the source (see below).

14.The state has determined that the PSCo Cameo Power Plant is subject-to-RP. With 

the closure of the facility by 2012, the SO2, NOx, and PM RP requirements are 

satisfied in this planning period. A regulatory closure requirement is contained in 

this chapter and in Regulation No. 3. 

15.The PSCo Hayden Power Plant (units 1 & 2) is a subject-to-BART source that the 

state reviewed for best available retrofit controls for SO2, NOx and PM emissions. 

The Hayden BART determination (see Chapter 6) satisfies the SO2, NOx and PM 

BART/RP requirements in this planning period.

16.The Tri-State Generation and Transmission Association‟s Craig Power Plant has 

three units (1, 2, and 3); units 1 & 2 are subject-to-BART that the Division reviewed 

for best available retrofit controls for SO2, NOx and PM emissions. The BART 

determinations for units 1 and 2 (see Chapter 6) satisfy the SO2, NOx and PM 

BART/RP requirements in this planning period. The state has determined that unit 3 

is subject-to-RP and has conducted an emission control analysis for the unit (see 

below).

Consequently, there are seven significant sources identified as subject-to-RP that 

Colorado has evaluated for controls in the RP analysis process:

Rawhide Unit 1

CENC Boiler 3

Nixon Unit 1 

Clark Units 1, 2

Holcim Kiln, Dryer

Nucla

Craig Unit 3

8.5 Evaluation of Point Sources for Reasonable Progress

In identifying an appropriate level of control for RP, Colorado took into consideration the 

following factors:

(1) The costs of compliance,

(2) The time necessary for compliance,

(3) The energy and non-air quality environmental impacts of compliance, and

(4) The remaining useful life of any potentially affected sources.

Colorado has concluded that it also appropriate to consider a fifth factor: the degree of 

visibility improvement that may reasonably be anticipated from the use of RP controls. 

States have flexibility in how they take these factors into consideration, as well as any 

other factors that the state determines to be relevant. See U.S. EPA, Guidance for 

Setting Reasonable Progress Goals Under the Regional Haze Program, p. 5-1 (June 

2007).
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

117

8.5.1 Rationale for Point Source RP Determinations

Similar to the process for determining BART as described in Chapter 6, in making its RP 

determination for each Colorado source, the state took into consideration the five 

factors on a case-by case basis, and for significant NOx controls the state also utilized 

the guidance criteria set forth in Section 6.4.3 consistent with the factors. Summaries of 

the state‟s facility-specific consideration of the factors and resulting determinations for 

each RP source are provided in this Chapter 8. Documentation reflecting the state‟s 

analyses and supporting the state‟s RP determinations, including underlying data and 

detailed descriptions of the state‟s analysis for each facility, are provided in Appendix D 

of this document and the TSD.

8.5.1.1 The costs of compliance. The Division requested, and the companies 

provided, source-specific cost information for each RP unit. The cost information 

relates primarily to the installation and operation of new SO2 and NOx control 

equipment. The cost for each unit is summarized below, and the state‟s consideration 

of this factor for each source is presented in detail in Appendix D.

8.5.1.2 The time necessary for compliance.

Regulation No 3, Part F, Section VI.B.4. requires facilities subject to RP determinations 

to submit a compliance plan within 60 days of SIP approval. Based on Colorado facility 

submittals, the Division anticipates that the time necessary for facilities to complete 

design, permitting, procurement, and system startup, after SIP approval, would be 

approximately 3 - 5 years. This timeframe may vary somewhat due to the necessary 

major maintenance outage with other regionally affected utilities.

8.5.1.3 The energy and non-air quality environmental impacts of compliance. 

This factor is typically used to identify non-air issues associated with different types of 

control equipment. The Division requested, and the companies provided, sourcespecific energy and non-air quality information for each RP unit. The state has 

particular concerns with respect to potential non-air quality environmental impacts 

associated with wet scrubber systems for SO2, as further described below.

8.5.1.4 The remaining useful life of the source. For those sources set to retire by 

2018, the state established a regulatory closure requirement in this chapter and in 

Regulation No. 3. For those sources not expected to retire over the next twenty years, 

this factor did not affect any of the state‟s RP determinations.

8.5.1.5 The degree of visibility improvement which may reasonably be 

anticipated from the use of RP. The state took into consideration the degree of 

visibility improvement which may reasonably be anticipated from the use of RP control, 

where relevant and the information was available, although degree of visibility 

improvement is not an express element of four factors to be considered during 

reasonable progress under EPA‟s federal regulations and guidelines. Modeling 

information where relevant and available for each RP determination is presented below 

and in Appendix D.

8.5.1.6 Overview of the RP Determinations for Each Source. This section presents 

an overview of the RP determinations for the significant point sources not addressed in 

Chapter 6.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

118

The regional haze rule gives the states broad latitude on how the four statutory factors, 

and any other factors a state deems to be relevant, may be considered to determine the 

appropriate controls for RP. The Regional Haze rule provides little, if any, guidance on 

specifically how states are to use these factors in making the final determinations 

regarding what controls are appropriate under the rule, other than to consider the 

factors in reaching a determination. The manner and method of consideration is left to 

the state‟s discretion; states are free to determine the weight and significance to be 

assigned to each factor.

The Division has reviewed available particulate controls applicable to RP facilities. 

Based on a review of NSPS, MACT and RACT/BACT/LAER, the state has determined 

that fabric filter baghouses are the best PM control available. The Portland cement 

MACT confirms that “a well-performing baghouse represents the best performance for 

PM”. See, 74 Fed. Reg. 21136, 21155 (May 6, 2009). The RACT/BACT/LAER 

Clearinghouse identifies baghouses as the PM control for the newer cement kilns and 

EGUs. Additional discussion of PM controls, including baghouse controls, is contained 

in the source specific analyses in Appendix D.

The Division also reviewed various SO2 controls applicable to EGUs and boilers. Two 

of the primary controls identified in the review are wet scrubbers and dry flue gas 

desulphurization (FGD). Based upon its experience, and as discussed in detail 

elsewhere in this Chapter 8, in Appendix D and in the TSD, the state has determined 

that wet scrubbing has several negative energy and non-air quality environmental 

impacts, including very significant water usage. This is a significant issue in Colorado 

and the arid West, where water is a costly, precious and scarce resource. There are 

other costs and environmental impacts that the state also considers undesirable with 

respect to wet scrubbers. For example, the off-site disposal of sludge entails 

considerable costs, both in terms of direct disposal costs, and indirect costs such as 

transportation and associated emissions. Moreover, on-site storage of wet ash is an 

increasing regulatory concern. EPA recognizes that some control technologies can 

have significant secondary environmental impacts. See, 70 Fed. Reg. 39104, 39169 

(July 6, 2005). EPA has specifically noted that the limited availability of water can affect 

the feasibility and costs of wet scrubbers in the arid West. These issues were examined 

in each source specific analysis in Appendix D.

With respect to NOx controls, the state has assessed pre-combustion and postcombustion controls and upgrades to existing NOx controls, as appropriate.

When determining the emission rates for each source, the state referred to the available 

literature and considered recent MACT, NSPS and RACT/BACT/LAER determinations 

to inform emission limits. While relying on source specific information for the final limit, 

and considering that RP relates to retrofitting sources (vs. new or reconstructed 

facilities), a review of other BART and RP determinations used to better substantiate the 

source specific information provided by the source.

For the purposes of the RP review for the three pollutants that the state is assessing for 

the seven facilities, SO2 and PM have been assessed utilizing the factors on a case by 

case basis to reach a determination. This is primarily because the top level controls for 

SO2 and PM are already largely in use on electric generating units in the state, and 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

119

certain other sources require a case by case review because of their unique nature. For 

NOx controls on reasonable progress electric generating units, for reasons described 

below, the state is employing guidance criteria to aid in its RP assessment, largely 

because significant NOx add-on controls are not the norm for Colorado electric 

generating units, and to afford a degree of uniformity in the consideration of control for 

these sources.

With respect to SO2 emissions, there are currently ten flue gas desulphurization lime 

spray dryer (LSD) SO2 control systems operating at electric generating units in 

Colorado.39 There are also two wet limestone systems in use in Colorado. The 

foregoing systems have been successfully operated and implemented for many years at 

Colorado sources, in some cases for over twenty years. The LSD has notable 

advantages in Colorado given the non-air quality consideration of its relatively lower 

water usage in reducing SO2 emissions in the state and other non-air quality 

considerations. The state has determined in the past that these systems can be costeffective for sources in Colorado. With this familiarity and use of the emissions control 

technology, the state has assessed SO2 emissions control technologies and/or 

emissions rates for the RP sources on a case by case basis in making its control 

determinations.

With respect to PM emissions, fabric filter baghouses and appropriate PM emissions 

rates are in place at all power plants in Colorado. Fabric filter baghouse systems have 

been successfully operated and implemented for many years at Colorado sources. The 

state has determined that fabric filter baghouses are cost effective through their use at 

all coal-fired power plants in Colorado. With this familiarity and use of the emissions 

control technology, the state has assessed PM emissions control technologies and/or 

emissions rates for the RP sources on a case by case basis in making its control 

determinations.

With respect to NOx emissions, post-combustion controls for NOx are generally not 

employed in Colorado. Accordingly, this requires a direct assessment of the 

appropriateness of employing such post-combustion technology at these sources for 

implementation of the Regional Haze rule. There is only one coal-fired electric 

generating unit in the state that is equipped with a selective catalytic reduction (SCR) 

system to reduce NOx emissions, and that was employed as new technology designed 

into a new facility (Public Service Company of Colorado, Comanche Unit #3, operational 

2010). There are currently no selective non-catalytic reduction (SNCR) systems in use 

on coal-fired electric generating units in the state to reduce NOx emissions.

In assessing and determining appropriate NOx controls at significant sources for 

individual units for visibility improvement under the Regional Haze rule, for reasonable 

progress, the state has considered the relevant factors in each instance. Based on its 

authority, discretion and policy judgment to implement the Regional Haze rule, the state 

has determined that costs and the anticipated degree of visibility improvement are the 

factors that should be afforded the most weight. In this regard, the state has utilized 

screening criteria as a means of generally guiding its consideration of these factors. 

 

39 EGUs with LSD controls include Cherokee Units 3 & 4, Comanche Units 1, 2 & 3, Craig Unit 3, Hayden 

Units 1 & 2, Rawhide Unit 1, Valmont Unit 5.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

120

More specifically, the state finds most important in its consideration and determinations

for individual units: (i) the cost of controls as appropriate to achieve the goals of the 

regional haze rule (e.g., expressed as annualized control costs for a given technology to 

remove a ton of Nitrogen Oxides (NOx) from the atmosphere, or $/ton of NOx removed); 

and, (ii) visibility improvement expected from the control options analyzed (e.g., 

expressed as visibility improvement in delta deciview (Δdv) from CALPUFF air quality 

modeling).

Accordingly, as part of its reasonable progress factor consideration the state has 

elected to generally employ criteria for NOx post-combustion control options to aid in 

the assessment and determinations for BART – a $/ton of NOx removed cap, and two 

minimum applicable Δdv improvement figures relating to CALPUFF modeling for certain 

emissions control types, as follows.

- For the highest-performing NOx post-combustion control options (i.e., SCR systems 

for electric generating units) that do not exceed $5,000/ton of pollutant reduced by 

the state‟s calculation, and which provide a modeled visibility benefit on 0.50 Δdv or 

greater at the primary Class I Area affected, that level of control is generally viewed 

as reasonable.

- For lesser-performing NOx post-combustion control options (e.g., SNCR 

technologies for electric generating units) that do not exceed $5,000/ton of pollutant 

reduced by the state‟s calculation, and which provide a modeled visibility benefit of 

0.20 Δdv or greater at the primary Class I Area affected, that level of control is 

generally viewed as reasonable.

The foregoing criteria guide the state‟s general approach to these policy considerations. 

They are not binding, and the state is free to deviate from this guidance criteria based 

upon its consideration of RP control on a case by case basis.

The cost criteria presented above is generally viewed by the state as reasonable based 

on the state‟s extensive experience in evaluating industrial sources for emissions 

controls. For example, the $5,000/ton criterion is consistent with Colorado‟s retrofit 

control decisions made in recent years for reciprocating internal combustion engines 

(RICE) most commonly used in the oil and gas industry.40 In that case, a $5,000/ton 

threshold, which was determined by the state Air Quality Control Commission as a notto-exceed control cost threshold, was deemed reasonable and cost effective for an 

initiative focused on reducing air emissions to protect and improve public health.41 The 

$5,000/ton criterion is also consistent with and within the range of the state‟s 

implementation of reasonably achievable control technology (RACT), as well as best 

achievable control technology (BACT) with respect to new industrial facilities. Control 

 

40 Air Quality Control Commission Regulation No. 7, 5 C.C.R. 1001-9, Sections XVII.E.3.a.(ii) (statewide 

RICE engines), and XVI.C.4 (8-Hour Ozone Control Area RICE engines).

41 The RICE emissions control regulations were promulgated by the Colorado Air Quality Control 

Commission in order to: (i) reduce ozone precursor emissions from RICE to help keep rapidly growing 

rural areas in attainment with federal ozone standards; (ii) for reducing transport of ozone precursor 

emissions from RICE into the Denver Metro Area/North Front Range (DMA/NFR) nonattainment area; 

and, (iii) for the DMA/NFR nonattainment area, reducing precursor emissions from RICE directly tied to 

exceedance levels of ozone.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

121

costs for Colorado RACT can be in the range of $5,000/ton (and lower), while control 

costs for Colorado BACT can be in the range of $5,000/ton (and higher). 

In addition, as it considers the pertinent factors for reasonable progress, the state 

believes that the costs of control should have a relationship to visibility improvement. 

The highest-performing post-combustion NOx controls, i.e., SCR, have the ability to 

provide significant NOx reductions, but also have initial capital dollar requirements that 

can approach or exceed $100 million per unit.42 The lesser-performing post-combustion 

NOx controls, e.g., SNCR, reduce less NOx on a percentage basis, but also have 

substantially lower initial capital requirements, generally less than $10 million.43 The 

state finds that the significantly different capital investment required by the different 

types of control technologies is pertinent to its assessment and determination. 

Considering costs for the highest-performing add-on NOx controls (i.e., SCR), the state 

anticipates a direct level of visibility improvement contribution, generally 0.50 Δdv or 

greater of visibility improvement at the primary affected Class I Area.44 For the lesserperforming add-on NOx controls (e.g., SNCR), the state anticipates a meaningful and 

discernible level of visibility improvement that contributes to broader visibility 

improvement, generally 0.20 Δdv or greater of visibility improvement at the primary 

affected Class I Area.

Employing the foregoing guidance criteria for post-combustion NOx controls, as part of 

considering the relevant factors for reasonable progress, promotes a robust evaluation 

of pertinent control options, including costs and an expectation of visibility benefit, to 

assist in determining what are appropriate control options for the Regional Haze rule.

 

42 See, e.g., Appendix C, reflecting Public Service of Colorado, Comanche Unit #2, $83MM; Public 

Service of Colorado, Hayden Unit #2, $72MM; Tri-State Generation and Transmission, Craig Station Unit 

#1, $210MM.

43 See, e.g., Appendix C, reflecting CENC (Tri-gen), Unit #4, $1.4MM; Public Service Company of 

Colorado, Hayden Unit #2, $4.6MM; Tri-State Generation and Transmission, Craig Station Unit #1, 

$13.1MM

44 The EPA has determined that BART-eligible sources that affect visibility above 0.50 Δdv are not to be 

exempted from BART review, on the basis that above that level the source is individually contributing to 

visibility impairment at a Class I Area. 70 Fed. Reg. at 39161. Colorado is applying these same criteria 

to RP sources, as a visibility improvement of 0.50 Δdv or greater will also provide significant direct 

progress towards improving visibility in a Class I Area from that facility.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

122

8.5.2 Point Source RP Determinations

The following summarizes the RP control determinations that will apply to each source.

Table 8-2 RP Control Determinations for Colorado Sources

Emission 

Unit

Assumed**

NOx Control 

Type

NOx Emission 

Limit

Assumed**

SO2 Control 

Type

SO2 Emission 

Limit

Assumed**

Particulate 

Control and 

Emission Limit

Rawhide

Unit 101

Enhanced 

Combustion 

Control*

0.145 lb/MMBtu

(30-day rolling 

average)

Lime Spray 

Dryer*

0.11 lb/MMBtu

(30-day rolling 

average)

Fabric Filter 

Baghouse*

0.03 lb/MMBtu

CENC

Unit 3

No Control 246 tons per year

(12-month rolling 

total)

No Control 1.2 lbs/MMBtu Fabric Filter 

Baghouse*

0.07 lb/MMBtu

Nixon

Unit 1

Ultra-low 

NOx burners 

with OverFire Air

0.21 lb/MMBtu

(30-day rolling 

average)

Lime Spray 

Dryer

0.11 lb/MMBtu

(30-day rolling 

average)

Fabric Filter 

Baghouse*

0.03 lb/MMBtu

Clark

Units 1 &2

Shutdown 

12/31/2013

0 Shutdown 

12/31/2013

0 Shutdown 

12/31/2013

Holcim -

Florence

Kiln

SNCR 2.73 lbs/ton clinker

(30-day rolling 

average)

2,086.8 tons/year

Wet Lime 

Scrubber*

1.30 lbs/ton 

clinker

(30-day rolling 

average)

721.4 tons/year

Fabric Filter 

Baghouse* 

246.3 tons/year

Nucla No Control 0.5 lb/MMBtu

(30-day rolling 

average)

Limestone 

Injection*

0.4 lb/MMBtu

(30-day rolling 

average)

Fabric Filter 

Baghouse*

0.03 lb/MMBtu

Craig

Unit 3

SNCR 0.28 lb/MMBtu

(30-day rolling 

average)

Lime Spray 

Dryer*

0.15 lb/MMBtu

(30-day rolling 

average)

Fabric Filter 

Baghouse*

0.013 lb/MMBtu

filterable PM

0.012 lb/MMBtu

PM10

Cameo Shutdown 

12/31/2011

0 Shutdown 

12/31/2011

0 Shutdown 

12/31/2011

* Controls are already operating

** Based on the state's RP analysis, the "assumed" technology reflects the control option found to 

render the RP emission limit achievable. The "assumed" technology listed in the above table is not a 

requirement.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

123

For all RP determinations, approved in the federal State Implementation Plan, the state 

affirms that the RP emission limits satisfy Regional Haze requirements for this planning 

period (through 2017) and that no other Regional Haze analyses or Regional Haze 

controls will be required by the state during this timeframe.

The following presents an overview of Colorado‟s RP control determinations:

8.5.2.1 RP Determination for Platte River Power Authority - Rawhide Unit 101

This facility is located in Larimer County approximately 10 miles north of the town of 

Wellington, Colorado. Unit 101 is a 305 MW boiler and is considered by the Division to 

be eligible for the purposes of Reasonable Progress, being an industrial boiler with the 

potential to emit 40 tons or more of haze forming pollution (NOx, SO2, PM10) at a facility 

with a Q/d impact greater than 20. Platte River Power Authority (PRPA) submitted a 

“Rawhide NOx Reduction Study” on January 22, 2009 as well as additional relevant 

information on May 5 and 6, 2010.

SO2 RP Determination for PRPA Rawhide Unit 101

Dry FGD Upgrades – As discussed in EPA‟s BART Guidelines, electric generating units 

(EGUs) with existing control achieving removal efficiencies of greater than 50 percent 

do not need to be evaluated for potential removal of controls and replacement with new 

controls. Rawhide Unit 101 operates a lime spray dryer FGD currently achieving over 

72 percent SO2 reduction. The state has elected to consider EPA‟s BART Guidelines 

as relevant to the RP evaluation of Rawhide Unit 101 and, therefore, the following dry 

scrubber upgrades were considered.

Use of performance additives: Performance additives are typically used with drysorbent injection systems, not semi-dry SDA scrubbers that spray slurry products. 

PRPA and the Division are not aware of SO2 scrubber performance additives 

applicable to the Unit 101 SDA system.

Use of more reactive sorbent: Lime quality is critical to achieving the current 

emission limit. PRPA utilizes premium lime at higher cost to ensure compliance with 

existing limits. The lime contract requires >92% reactivity (available calcium oxide) 

lime to ensure adequate scrubber performance. PRPA is already using a highly 

reactive sorbent, therefore this option is not technically feasible.

Increase the pulverization level of sorbent: The fineness of sorbents used in drysorbent injection systems is a consideration and may improve performance for these 

types of scrubbers. Again, the Unit 101 SO2 scrubber is a semi-dry SDA type 

scrubber that utilizes feed slurry that is primarily recycle-ash slurry with added lime 

slurry. PRPA recently completed SDA lime slaking sub-system improvements that 

are designed to improve the reactivity of the slaked lime-milk slurry.

Engineering redesign of atomizer or slurry injection system: The Unit 101 SDA 

scrubber utilizes atomizers for slurry injection. The scrubber utilizes three reactor 

compartments, each with a single atomizer. PRPA maintains a spare atomizer to 

ensure high scrubber availability. The atomizers utilize the most current wheel-
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

124

nozzle design. The state and PRPA concur that PRPA utilizes optimal maintenance 

and operations; therefore, a lower SO2 emission cannot be achieved with improved 

maintenance and/or operations.

Fuel switching to natural gas was determined by the source to be a technically feasible 

option for Rawhide Unit 101, and as provided by PRPA it was evaluated by the state.

The following tables list the emission reductions, annualized costs and cost 

effectiveness of the control alternatives.

Rawhide Unit 101 – SO2 Cost Comparisons

Alternative Emissions 

Reduction (tpy)

Annualized Cost 

($)

Cost Effectiveness 

($/ton)

Baseline 0 $0 $0

Fuel switching – NG 906 $237,424,331 $262,169

There are no energy and non-air quality impacts associated with this alternative.

There are no remaining useful life issues for the alternative as the source will remain in 

service for the 20-year amortization period.

The projected visibility improvements attributed to more stringent SO2 emission limits 

as a demonstration are as follows:

SO2 Control Method

SO2 Annual 

Emission Rate 

(lb/MMBtu)

98th Percentile 

Impact (∆dv)

Daily Maximum (3-yr) 0.11

Existing Dry FGD 0.09 0.01

Dry FGD – tighter limit 0.07 0.03

Fuel switching – NG 0.00 0.87

Based upon its consideration of the five factors summarized herein and detailed in 

Appendix D, the State has determined that SO2 RP is the following SO2 emission rates:

Rawhide Unit 101: 0.11 lb/MMBtu (30-day rolling average)

The state assumes that the RP emission limits can be achieved through the installation 

and operation of lime spray dryers (LSD). The state has determined that these 

emissions rates are achievable without additional capital investment through the fourfactor analysis. Upgrades to the existing SO2 control system were evaluated, and the 

state determines that meaningful upgrades to the system are not available. Lower SO2 

limits would not result in significant visibility improvement (less than 0.02 delta deciview) 

and would likely result in frequent non-compliance events and, thus, are not reasonable.

Particulate Matter RP Determination for PRPA Rawhide

The state has determined that the existing Unit 101 regulatory emissions limit of 0.03 

lb/MMBtu (PM/PM10) represents the most stringent control option. The unit is 

exceeding a PM control efficiency of 95%, and the emission limit is RP for PM/PM10. 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

125

The state assumes that the emission limit can be achieved through the operation of the 

existing fabric filter baghouses.

NOx RP Determination for PRPA Rawhide

Enhanced combustion control (ECC), selective non-catalytic reduction (SNCR), fuel 

switching to natural gas (NG), and selective catalytic reduction (SCR) were determined 

to be technically feasible for reducing NOx emissions at Rawhide Unit 101. Fuel 

switching to natural gas was determined by the source to be a technically feasible 

option for Rawhide Unit 101, and as provided by PRPA it was evaluated by the state.

The following tables list the emission reductions, annualized costs and cost 

effectiveness of the control alternatives.

Rawhide Unit 101 - NOx Cost Comparisons

Alternative Emissions 

Reduction (tpy)

Annualized Cost 

($)

Cost Effectiveness 

($/ton)

Baseline 0 $0 $0

ECC 448 $288,450 $644

SNCR 504 $1,596,000 $3,168

Fuel switching – NG 545 $237,424,331 $435,681

SCR 1,185 $12,103,000 $10,214

The energy and non-air quality impacts of SNCR are increased power needs, potential 

for ammonia slip, potential for visible emissions, hazardous materials storage and 

handling.

There are no remaining useful life issues for the alternatives as the sources will remain 

in service for the 20-year amortization period.

The projected visibility improvements attributed to the alternatives are as follows:

NOx Control Method

NOx Annual 

Emission Rate 

(lb/MMBtu)

98th Percentile 

Impact (∆dv)

Daily Maximum (3-yr) 0.302

ECC 0.126 0.45

SNCR 0.121 0.46

Fuel Switching – NG 0.118 0.47

SCR 0.061 0.59

It should be noted that the daily maximum (3-yr) value of 0.302 lb/MMBtu was a 

substituted value from CAMD. The next highest 24-hour value was 0.222 lb/MMBtu, 

26% lower than the modeled value. However, the Division did not conduct revised 

modeling since it was determined that it would not change the State‟s RP determination.

Switching to natural gas was eliminated from consideration due to the excessive 

cost/effectiveness ratio and degree of visibility improvement less than 0.5 dV.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

126

Based upon its consideration of the five factors summarized herein and detailed in 

Appendix D, the State has determined that NOx RP for Rawhide Unit 101 is the 

following NOx emission rate:

Rawhide Unit 1: 0.145 lb/MMBtu (30-day rolling average)

The state assumes that the RP emission limits can be achieved through the operation of 

enhanced combustion control. The dollars per ton control cost, coupled with notable 

visibility improvements of 0.45 delta dv, leads the state to this determination. Although 

SCR achieves better emission reductions, the expense of SCR was determined to be 

excessive and above the guidance cost criteria discussed in section 8.4 above. SNCR 

would achieve similar emissions reductions to enhanced combustion controls and would 

afford a minimal additional visibility benefit ( 0.01 delta deciview), but at a significantly 

higher dollar per ton control cost compared to the selected enhanced combustion 

controls, so SNCR was not determined to be reasonable by the state.

A complete analysis that supports the RP determination for the Rawhide facility can be 

found in Appendix D.

8.5.2.2 RP Determination for Colorado Energy Nations Company (CENC) Boiler 3

This facility is located adjacent to the Coors brewery in Golden, Jefferson County. 

Boiler 3 is considered by the State to be eligible for the purposes of Reasonable 

Progress, being an industrial boiler with the potential to emit 40 tons or more of haze 

forming pollution (NOx, SO2, PM10) at a facility with a Q/d impact greater than 20. 

CENC submitted a “Reasonable Progress Control Evaluation” on May 7, 2010 as well 

as additional relevant information on February 8, 2010. 

The CENC facility includes five coal-fired boilers that supply steam and electrical power 

to Coors Brewery. Three of the boilers emit above 40 tons or more of haze forming 

pollution. Of these three boilers, Units 4 and 5 are subject to BART, and Unit 3 is 

subject to RP. Unit 3 is rated as follows: 225 MMBtu/hr, which is approximately 

equivalent to 24 MW, based on the design heat rate.

SO2 RP Determination for CENC – Boiler 3

Dry sorbent injection (DSI) and fuel switching to natural gas were determined to be 

technically feasible for reducing SO2 emissions from Boiler 3. Dry FGD is not 

technically feasible for Boiler 3 due to space constraints onsite. These options were 

considered as potentially RP by the state. Fuel switching to natural gas was determined 

by the source to be a technically feasible option for Boiler 3, and as provided by PRPA it 

was evaluated by the state.

Lime or limestone-based wet FGD is technically feasible, but was determined to not be 

reasonable due to adverse non-air quality impacts. Dry FGD controls were determined 

to be not technically feasible.

The following tables list the emission reductions, annualized costs and cost 

effectiveness of the control alternatives:
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

127

CENC Boiler 3 - SO2 Cost Comparison

Alternative Emissions 

Reduction (tpy)

Annualized Cost 

($)

Cost Effectiveness 

($/ton)

Baseline 0 $0 $0

DSI – Trona 147 $1,340,661 $9,114

Fuel Switching – Natural Gas 245 $1,428,911 $5,828

DSI – Trona and fuel switching to natural gas were eliminated from consideration due to 

excessive cost/effectiveness ratio.

Because there are no reasonable alternatives, there are no energy and non-air quality 

impacts to consider.

There are no remaining useful life issues for the alternatives as the source will remain in 

service for the 20-year amortization period.

Based on CALPUFF modeling results for subject-to-BART CENC Units 4 and 5, the 

state determined the further CALPUFF modeling of smaller emission sources at the 

CENC facility would produce minimal visibility impacts (<<0.10 dv).

Based upon its consideration of the five factors summarized herein and detailed in 

Appendix D, the state has determined that SO2 RP is an emission rate of:

CENC Boiler 3: 1.2 lbs/MMBtu 

Although dry sorbent injection does achieve better emissions reductions, the added 

expense of DSI controls were determined to not be reasonable coupled with the low 

visibility improvement (<< 0.10 dv) afforded.

Particulate Matter RP Determination for CENC – Boiler 3

The state has determined that the existing Boiler 3 regulatory emissions limit of 0.07 

lb/MMBtu (PM/PM10) corresponding with the original Industrial Boiler MACT standard 

represents the most stringent control option. The units are exceeding a PM control 

efficiency of 90%, and the emission limit is RP for PM/PM10. The state assumes that 

the emission limit can be achieved through the operation of the existing fabric filter 

baghouse.

NOx RP Determination for CENC – Boiler 3

Flue gas recirculation (FGR), selective non-catalytic reduction (SNCR), rotating overfire 

air (ROFA) fuel switching to natural gas, and three options for selective catalytic 

reduction (RSCR, HTSCR, and LTSCR) were determined to be technically feasible for 

reducing NOx emissions at CENC Boiler 3. Fuel switching to natural gas was 

determined by the source to be a technically feasible option for Boiler 3, and as 

provided by CENC it was evaluated by the state. 

The following tables list the emission reductions, annualized costs and cost 

effectiveness of the control alternatives.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

128

CENC Boiler 3 - NOx Cost Comparisons

Alternative Emissions Reduction 

(tpy) Annualized Cost ($) Cost Effectiveness ($/ton)

Baseline 0 $0 $0

FGR 33.7 $1,042,941 $30,929

SNCR 50.6 $513,197 $10,146

Fuel switching – NG 84.3 $1,428,911 $16,950

ROFA w/ Rotamix 77 $978,065 $9,496

Regenerative SCR 96.3 $978,065 $10,160

High temperature SCR 125.6 $1,965,929 $15,651

Low temperature SCR 144.5 $2,772,286 $19,187

Because there are no reasonable alternatives, there are no energy and non-air quality 

impacts to consider.

There are no remaining useful life issues for the alternatives as the sources will remain 

in service for the 20-year amortization period.

Based on CALPUFF modeling results for subject-to-BART CENC Units 4 and 5, the 

state determined the further CALPUFF modeling of smaller emission sources at the 

CENC facility would produce visibility impacts below the guidance visibility criteria 

discussed in section 8.4 above.

All NOx control options were eliminated from consideration due to the excessive 

cost/effectiveness ratios and small degree of visibility improvement.

Based on review of historical actual load characteristics of this boiler, the state 

determines to be appropriate an annual NOx ton/year limit based on 50% annual 

capacity utilization based on the maximum capacity year in the last decade (2000). This 

annual capacity utilization will then have a 20% contingency factor for a variety of 

reasons specific to Boiler 3 further explained in Appendix D.

Based upon its consideration of the five factors summarized herein and detailed in 

Appendix D, the state has determined that NOx RP for Boiler 3 is the following NOx 

emission rate

CENC Boiler 3: 246 tons/year (12-month rolling total)

Though other controls achieve better emissions reductions, the expense of these 

options coupled with predicted minimal visibility improvement (<< 0.10 dv) were 

determined to be excessive and above the guidance cost criteria discussed in section 

8.4 of the Regional Haze SIP, and thus not reasonable

EPA Region 8 notes to the state that a number of control cost studies, such as that by 

NESCAUM (2005), indicate that costs for SNCR or SCR could be lower than the costs 

estimated by the Division in the above BART determination. However, assuming such 

lower costs were relevant to this source, use of such lower costs would not change the 

state's RP determination because the degree of visibility improvement achieved by 

SNCR or SCR is likely below the state's guidance criteria of 0.2 dv and 0.5 dv, 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

129

respectively (as demonstrated in the BART determination for CENC Boiler 4). 

Moreover, the incremental visibility improvement associated with SNCR or SCR is likely 

not substantial when compared to the visibility improvement achieved by the selected 

limits. Thus, it is not warranted to select emission limits associated with either SNCR or 

SCR for CENC Boiler 3.

A complete analysis that supports the RP determination for the CENC facility can be 

found in Appendix D.

8.5.2.3 RP Determination for Colorado Springs Utilities’ - Nixon Unit 1 

The Nixon plant is located in Fountain, Colorado in El Paso County. Nixon Unit 1 and 

two combustion turbines at the Front Range Power Plant are considered by the Division 

to be eligible for the purposes of Reasonable Progress, being industrial sources with the 

potential to individually emit 40 tons or more of haze forming pollution (NOx, SO2, PM10) 

at a facility with a Q/d impact greater than 20. Colorado Spring Utilities (CSU) provided

RP information in “NOx and SO2 Reduction Cost and Technology Updates for Colorado 

Springs Utilities Drake and Nixon Plants” Submittal provided on February 20, 2009 and 

additional relevant information on May 10, 2010.

SO2 RP Determination for CSU – Nixon

Dry sorbent injection (DSI) and dry FGD were determined to be technically feasible for 

reducing SO2 emissions from Nixon. These options were considered as potentially RP 

by the state. Lime or limestone-based wet FGD is technically feasible, but was 

determined to not be reasonable due to adverse non-air quality impacts. 

The following tables list the emission reductions, annualized costs and cost 

effectiveness of the control alternatives:

Nixon Unit 1 - SO2 Cost Comparison

Alternative

Emissions 

Reduction 

(tpy)

Annualized Cost 

($)

Cost Effectiveness 

($/ton)

Baseline 0 $0 $0

DSI – Trona 2,473 $9,438,692 $1,997

Dry FGD @ 78% control 

(0.10 lb/MMBtu annual average)

3,215 $12,036,604 $3,744

Dry FGD @ 85% control 

(0.07 lb/MMBtu annual average)

3,392 $13,399,590 $3,950

The energy and non-air quality impacts of the remaining alternatives are as follows:

DSI – reduced mercury capture in the baghouse, fly ash contamination with 

sodium sulfate, rendering the ash unsalable as replacement for concrete and 

rendering it landfill material only

Dry FGD – less mercury removal compared to unscrubbed units, significant 

water usage
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

130

There are no remaining useful life issues for the alternatives as the source will remain in 

service for the 20-year amortization period.

The projected visibility improvements attributed to the alternatives are as follows:

SO2 Control Method

Nixon – Unit 1

SO2 Annual Emission 

Rate (lb/MMBtu)

98th Percentile Impact 

(Δdv)

Daily Max (3-yr) 0.45

DSI 0.18 0.44

Dry FGD (LSD) 0.10 0.46

Dry FGD (LSD) 0.07 0.50

The state performed modeling using the maximum 24-hour rate during the baseline 

period, and compared resultant annual average control estimates. In the state‟s 

experience, 30-day SO2 rolling average emission rates are expected to be 

approximately 5% higher than the annual average emission rate. The state projected a

30-day rolling average emission rate increased by 5% for all SO2 emission rates to 

determine control efficiencies and annual reductions.

Based upon its consideration of the five factors summarized herein and detailed in 

Appendix D, the state has determined that SO2 RP is the following SO2 emission rate:

Nixon Unit 1: 0.11 lb/MMBtu (30-day rolling average)

The state assumes that the emission limit can be achieved with semi dry FGD (LSD). A 

lower emissions rate for Unit 1 was deemed to not be reasonable as increased control 

costs to achieve such an emissions rate do not provide appreciable improvements in 

visibility (0.04 delta deciview). Also, stringent retrofit emission limits below 0.10 

lb/MMBtu have not been demonstrated in Colorado, and the state determines that a 

lower emission limit is not reasonable in this planning period. 

The LSD control for Unit 1 provides 78% SO2 emission reduction at a modest cost per 

ton of emissions removed and result in a meaningful contribution to visibility 

improvement.

Unit 1: $3,744 per ton SO2 removed; 0.46 deciview of improvement

An alternate control technology that achieves the emissions limits of 0.11 lb/MMBtu, 30-

day rolling average, may also be employed.

Particulate Matter RP Determination for CSU – Nixon 

The state determines that the existing Unit 1 regulatory emissions limit of 0.03 lb/MMBtu 

(PM/PM10) represents the most stringent control option. The unit is exceeding a PM 

control efficiency of 95%, and the emission limits is RP for PM/PM10. The state 

assumes that the emission limit can be achieved through the operation of the existing 

fabric filter baghouse.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

131

NOx RP Determination for CSU – Nixon 

Ultra low NOx burners (ULNB), SNCR, SNCR plus ULNB, and SCR were determined to 

be technically feasible for reducing NOx emissions at Nixon Unit 1.

The following table lists the emission reductions, annualized costs and cost 

effectiveness of the control alternatives.

Nixon Unit 1 - NOx Cost Comparison

Alternative Emissions 

Reduction (tpy)

Annualized 

Cost ($)

Cost 

Effectiveness 

($/ton)

Baseline 0 $0 $0 

Ultra-low NOx Burners (ULNBs) 471 $567,000 $1,203

Overfire Air (OFA) 589 $403,000 $684

ULNBs+OFA 707 $907,000 $1,372

Selective Non-Catalytic Reduction (SNCR) 707 $3,266,877 $4,564

ULNB/SCR layered approach 1,720 $11,007,000 $6,398

Selective Catalytic Reduction (SCR) 1,720 $11,010,000 $6,400

The energy and non-air quality impacts of the alternatives are as follows:

OFA and ULNB – not significant

ULNB – not significant

SNCR – increased power needs, potential for ammonia slip, potential for visible 

emissions, hazardous materials storage and handling

There are no remaining useful life issues for the alternatives as the sources will remain 

in service for the 20-year amortization period.

The projected visibility improvements attributed to the alternatives are as follows:

NOx Control Method

Nixon – Unit 1

NOx Annual Emission Rate 

(lb/MMBtu)

98th Percentile 

Impact (Δdv)

Daily Max (3-yr) 0.26

ULNB 0.21 0.15

OFA 0.19 0.15

ULNB+OFA 0.18 0.16

SNCR 0.18 0.16

ULNB + SCR 0.07 0.24

SCR 0.07 0.24

SCR options were eliminated from consideration due to the excessive 

cost/effectiveness ratios and degree of visibility improvement.

The state performed modeling using the maximum 24-hour rate during the baseline 

period, and compared resultant annual average control estimates. In the state‟s 

experience and other state BART proposals, 30-day NOx rolling average emission rates 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

132

are expected to be approximately 5-15% higher than the annual average emission rate. 

The state projected a 30-day rolling average emission rate increased by 15% for all 

NOx emission rates to determine control efficiencies and annual reductions.

Based upon its consideration of the five factors summarized herein and detailed in 

Appendix D, the state has determined that NOx RP for Nixon Unit 1 is the following NOx 

emission rates:

Nixon Unit 1: 0.21 lb/MMBtu (30-day rolling average)

The state assumes that the emission limit can be achieved with ultra-low NOx burners 

with over fire air control. The Division notes that the ultra-low NOx burners with over-fire 

air-based emissions limit is the appropriate RP determination for Nixon Unit 1 due to the 

low cost effectiveness. SNCR would achieve similar emissions reductions at an added 

expense. Therefore, SNCR was determined to not be reasonable considering the low

visibility improvement afforded.

EPA Region 8 notes to the state that a number of control cost studies, such as that by 

NESCAUM (2005), indicate that costs for SNCR or SCR could be lower than the costs 

estimated by the Division in the above RP determination. However, assuming such 

lower costs were relevant to this source, use of such lower costs would not change the 

state's RP determination because the degree of visibility improvement achieved by 

SNCR or SCR is below the state's guidance criteria of 0.2 dv and 0.5 dv, respectively. 

Moreover, the incremental visibility improvement associated with SNCR or SCR is not 

substantial when compared to the visibility improvement achieved by the selected limits 

(i.e., 0.01 dv for SNCR and 0.09 dv for SCR). Thus, it is not warranted to select 

emission limits associated with either SNCR or SCR for Nixon Unit 1.

A complete analysis that supports the RP determination for the Nixon Plant can be 

found in Appendix D.

8.5.2.4 RP Determination for Black Hills Clark Facility Units 1 and 2

Black Hills/Colorado Electric Utility Company, LP informed the state that the Clark 

Station in the Cañon City, Colorado area will be shutdown 12/31/2013, resulting in SO2, 

NOx and PM reductions of approximately 1,457, 861, and 72 tons per year, 

respectively. Therefore, a four-factor analysis was not necessary for this facility and the 

RP determination for the facility is closure.

8.5.2.5 RP Determination for Holcim’s Florence Cement Plant

The Holcim Portland cement plant is located near Florence, Colorado in Fremont 

County, approximately 20 kilometers southeast of Canon City, and 35 kilometers 

northwest of Pueblo, Colorado. The plant is located 66 kilometers from Great Sand 

Dunes National Park.

In May 2002, a newly constructed cement kiln at the Portland Plant commenced 

operation. This more energy-efficient 5-stage preheater/precalciner kiln replaced three 

older wet process kilns. As a result, Holcim was able to increase clinker production from 

approximately 800,000 tons of clinker per year to a permitted level of 1,873,898 tons of 

clinker per year, while reducing the level of NOX, SO2, and PM/PM10 emissions on a 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

133

pound per ton of clinker produced basis. As a part of this project, Holcim also installed a 

wet lime scrubber to reduce the emissions of sulfur oxides.

The Portland Plant includes a quarry where major raw materials used to produce 

Portland cement, such as limestone, translime and sandstone, are mined, crushed and 

then conveyed to the plant site. The raw materials are further crushed and blended and 

then directed to the kiln feed bin from where the material is introduced into the kiln.

The dual string 5-stage preheater/precalciner/kiln system features a multi-stage 

combustion precalciner and a rotary kiln. The kiln system is rated at 950 MMBtu per 

hour of fuel input with a nominal clinker production rate of 5,950 tons per day. It is 

permitted to burn the following fuel types and amounts (with nominal fuel heat values, 

where reported):

coal (269,262 tons per year [tpy] @ 11,185 Btu/pound); 

tire derived fuel (55,000 tpy @ 14,500 Btu/pound); 

petroleum coke (5,000 tpy @ 14,372 Btu/pound);

natural gas (6,385 million standard cubic feet @ 1,000 Btu/standard cubic foot);

dried cellulose (55,000 tpy); and

oil, including non-hazardous used oil (4,000 tpy @ 12,000 Btu/pound). 

The clinker produced by the kiln system is cooled, grounded and blended with additives 

and the resulting cement product is stored for shipment. The shipment of final product 

from the plant is made by both truck and rail.

Emissions from the kiln system, raw mill, coal mill, alkali bypass and clinker cooler are 

all routed through a common main stack for discharge to atmosphere. These emissions 

are currently controlled by fabric filters (i.e., baghouses) for PM/PM10, by the inherent 

recycling and scrubbing of exhaust gases in the cement manufacturing process and by 

a tail-pipe wet lime scrubber for SO2, by burning alternative fuels (i.e., tire-derived fuel 

[TDF]) and using a Low-NOX precalciner, indirect firing, Low-NOX burners, staged 

combustion and a Linkman Expert Control System for NOX, and by the use of good 

combustion practices for both NOX and SO2.In addition to the kiln system/main stack 

emissions, there are two other process points whose PM/PM10 emissions exceed the 

Prevention of Significant Deterioration (PSD) significance level thresholds and were 

considered as a part of this Reasonable Progress analysis: 1) the raw material 

extraction and alkali bypass dust disposal operations associated with the quarry, and 2) 

the cement processing operations associated with the finish mill. Emissions from the 

quarry are currently controlled through a robust fugitive dust control plan and emissions 

from the finish mills are controlled by a series of baghouses.

Holcim did not initially complete a detailed four-factor analysis, though it did submit 

limited information on the feasibility of post-combustion NOX controls for the kiln system.

In late October through early December 2010, Holcim did submit detailed information, 

including data on baseline emissions, existing controls and additional control options, 

and visibility modeling to support the reasonable progress determination process. This 

section has been revised to reflect this additional information.

CALPUFF modeling was conducted by the Division for the kiln system, as a part of our 

original analysis, using a SO2 emission rate of 99.17 lbs/hour, a NOX emission rate of 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

134

837.96 pounds per hour (lbs/hour), and a PM10 emission rate of 19.83 lbs/hour. The 

modeling indicates a 98th percentile visibility impact of 0.435 delta deciview (Δdv) at 

Great Sand Dunes National Park. Holcim provided additional visibility modeling results 

in a submittal made in late October 2010.

Because of the high level of existing fugitive dust controls employed at the quarry and 

the baghouse controls already installed on the finish mill emission points, the state has 

determined that no meaningful emission reductions (and thus no meaningful visibility 

improvements) would occur pursuant to any conceivable additional controls on these

points. Accordingly, the state has determined that no additional visibility analysis is 

necessary or appropriate since even the total elimination of the emissions from the 

quarry and finish mill would not result in any meaningful visibility improvement. For the 

quarry, the current PM10 emission limitation is 47.9 tpy (fugitive) and for the finish mill it 

is 34.3 tpy (point source). These limitations are included in the existing Holcim Portland 

Plant construction permit.

SO2 RP Determination for Holcim Portland Plant – Kiln System

In addition to good combustion practices and the inherent recycling and scrubbing of 

acid gases by the raw materials, such as limestone, used in the cement manufacturing 

process, the Portland Plant kiln system has a tail-pipe wet lime scrubber. Holcim has 

reported that this combination of controls achieves an overall sulfur removal rate of 

98.3% for the kiln system, as measured by the total sulfur input in to the system versus 

the amount of sulfur emitted to atmosphere. Holcim has also reported that they estimate 

that the wet scrubber at the Portland Plant achieves an overall removal efficiency of 

over 90% of the SO2 emissions entering the scrubber. This control technology 

represents the highest level of control for Portland cement kilns. As a result, the state 

did not consider other control technologies as a part of this RP analysis.

The state did assess the corresponding SO2 emissions rates. The facility is currently 

permitted to emit 1,006.5 tpy of SO2 from the kiln system main stack. At a permitted 

clinker production level of 1,873,898 tpy, this equates to an annual average of 1.08 

pounds of SO2 per ton of clinker (the current permit does not contain an annual pound 

per ton of clinker or a short-term emission limit for SO2). The actual kiln SO2 emissions 

divided by the actual clinker production for the five-year baseline period used in this 

analysis (2004, 2005, 2006, 2007 and 2008) calculate to an overall annual average rate 

of 0.51 pound of SO2 per ton of clinker, with a standard deviation of 0.26 pound per ton. 

The highest annual emission rate in the baseline years was 0.95 pound per ton of 

clinker.

As a part of their submittals, Holcim analyzed continuous hourly emission data for SO2. 

The hourly emission data from 2004 to 2008 (baseline years) were used to calculate the 

daily emission rates. A 30-day rolling average emission rate was calculated by dividing 

the total emissions from the previous 30 operating days by the total clinker production 

from the previous 30 operating days. The 99th percentile of the 30-day rolling average 

data was used to establish the short-term baseline emissions limit of 1.30 pounds of 

SO2 per ton of clinker. The 99th percentile accounts for emission changes due to shortterm and long-term inherent process, raw material and fuel variability. The long-term 

annual limit was calculated at 721.4 tpy by multiplying the long-term baseline SO2 value 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

135

of 0.77 lb/ton (the mean of 0.51 pound per ton plus one standard deviation of 0.26 

pound per ton) by the annual clinker limit of 1,873,898 tpy, and then dividing by 2,000 

pounds per ton. 

Because there are no changes to the existing controls for SO2, there are no associated 

energy and non-air quality impacts for this determination. There are no remaining useful 

life issues for the source, as the state has presumed that the source will remain in 

service for the 20-year amortization period.

For the kiln system, based upon our consideration and weighing of the four factors, the 

state has determined that no additional SO2 emissions control is warranted given that 

the Holcim Portland Plant already is equipped with the top performing control 

technologies – the inherent recycling and scrubbing effect of the process itself followed 

by a tail-pipe wet lime scrubber. The RP analysis provides sufficient basis to establish a 

short-term SO2 emission limit of 1.30 pound per ton of clinker on a 30-day rolling 

average basis and a long-term annual emission limit of 721.4 tons of SO2 per year (12-

month rolling total) for the kiln system. There is no specific visibility improvement 

associated with this emission limitation.

Finally, on August 9, 2010, EPA finalized changes to the New Source Performance 

Standards (NSPS) for Portland Cement Plants and to the Maximum Achievable Control 

Technology standards for the Portland Cement Manufacturing Industry (PC MACT). The 

NSPS requires, new, modified or reconstructed cement kilns to meet an emission 

standard of 0.4 pound of SO2 per ton of clinker on a 30-day rolling average or a 90% 

reduction as measured at the inlet and outlet of the control device. While the new NSPS 

does not apply to the Holcim Portland Plant because it is an existing facility, it is 

important to note that the estimated level of control achieved by Holcim‟s wet scrubber 

(~90%) is consistent with the level of control prescribed by the NSPS for new sources.

Particulate Matter RP Determination for Holcim Portland Plant – Kiln System

The state has determined that the existing fabric filter baghouses installed on the kiln 

system represent the most stringent control option. Holcim has reported a nominal 

control efficiency for the kiln system baghouses at 99.5%. The units are exceeding a 

PM control efficiency of 95% and this control technology represents the highest level of 

control for Portland cement kilns. As a result, the state did not consider other control 

technologies as a part of this RP analysis.

The state did assess the corresponding PM10 emissions rates. The facility is currently 

permitted to emit 246.3 tpy of PM10 from the kiln system main stack (includes emissions 

from the clinker cooler). At a permitted clinker production level of 1,873,898 tpy, this 

equates to an annual average of 0.26 pound of PM10 per ton of clinker (the current 

permit does not contain an annual pound per ton of clinker or a short-term emission limit 

for PM10). The actual kiln system PM10 emissions divided by the actual clinker 

production for the five-year baseline period used in this analysis (2004, 2005, 2006, 

2007 and 2008) average to a rate of 0.16 pound of PM10 per ton of clinker (combined 

emissions from main stack). This value is derived from the limited annual stack test 

data, which are effectively snapshots in time, and does not take into account the shortterm inherent variability in the manufacturing process, raw material and fuel.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

136

Because there are no changes to the existing controls for PM10, there are no associated 

energy and non-air quality impacts for this determination. There are no remaining useful 

life issues for the source, as the state has presumed that the source will remain in 

service for the 20-year amortization period.

As a part of our original analysis, the state modeled possible visibility improvements 

associated with two emission rates – the baseline emission rate of 0.08 pound of PM10

per ton of clinker (19.83 lbs/hour) and a rate of 0.04 pound of PM10 per ton of clinker 

(9.92 lbs/hour). This analysis assumed the baseline emissions were all attributable to 

the kiln (i.e., no contribution from the clinker cooler) to assess the impact of a possible

reduction of the kiln emission limit. There was no change to the 98th percentile impact 

deciview value from 19.83 lbs/hour to 9.92 lbs/hour and therefore, no visibility 

improvement associated with this change. The state‟s modeling results showed that the 

most significant contributors to the visibility impairment from the Portland Plant were 

nitrates (NO3) followed by sulfates (SO4).The contribution of PM10 to the total visibility 

impairment was insignificant in the analysis. The level of PM10 emissions evaluated had 

no discernable impact on visibility.

For the kiln system, based upon our consideration and weighing of the four factors and 

the very limited impact of PM10 emissions from the kiln system on visibility impairment, 

the state has determined that no additional PM10 emissions control is warranted given 

that the Holcim Portland Plant already is equipped with the top performing control 

technology – fabric filter baghouses. These baghouses and the current permit limit of 

246.3 tpy of PM10 (12-month rolling total) from the kiln system main stack (including 

emissions from the clinker cooler) represent RP for this source. Furthermore, the 

Portland Plant is subject to the PC MACT and the recent amendments to the PC MACT 

include new, lower standards for PM emissions. As an existing facility, the Portland 

Plant kiln system will be subject to this standard once it becomes effective on 

September 9, 2013. Compliance with the new PC MACT PM emission standards will 

result in further reductions in the PM10 emissions.

NOX RP Determination for Holcim Portland Plant – Kiln System

There are a number of technologies available to reduce NOX emissions from the 

Portland Plant kiln system below the current baseline emissions level (the current 

configuration already includes indirect firing, low-NOX burners, staged combustion, a 

low-NOX precalciner, and a Linkman Process Control Expert system). These include 

water injection (the injection of water or steam into the main flame of a kiln to act as a 

heat sink to reduce the flame temperature), and selective non-catalytic reduction 

(SNCR). These technologies were determined to be technically feasible and appropriate 

for reducing NOX emissions from Portland cement kilns.

As further discussed in Appendix D, the state has determined that selective catalytic 

reduction (SCR) is not commercially available for the Portland Plant cement kiln system. 

Presently, SCR has not been applied to a cement plant of any type in the United States. 

Holcim notes that the major SCR vendors have either indicated that SCR is not 

commercially available for cement kilns at this time, or if they are willing to provide a 

quotation for an SCR system, the associated limitations that are attached with the quote 

severely undercut the efficacy of the system. The state does not believe that a limited 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

137

use - trial basis application of an SCR control technology on three modern kilns in 

Europe constitutes reasonable “available” control technology for purposes of RP at the 

Holcim Portland Plant. The state believes that commercial demonstration of SCR 

controls on a cement plant in the United States is appropriate when considering whether

a control technology is “available” for purposes of retrofitting such control technology on 

an existing source.

In the preamble to the recently finalized changes to the Portland Cement MACT/NSPS, 

EPA stated: “However, although SCR has been demonstrated at a few cement plants in 

Europe and has been demonstrated on coal-fired power plants in the US, the Agency is 

not satisfied that it has been sufficiently demonstrated as an off-the-shelf control 

technology that is readily applicable to cement kilns.” Based on our research and EPA‟s 

analysis for the MACT/NSPS standards, the state has eliminated SCR as an available 

control technology for purposes of this RP analysis.

The design of the Holcim Portland Plant does allow for the effective use of Selective 

Non-Catalytic Reduction (SNCR), which requires ammonia-like compounds to be 

injected into appropriate locations of the preheater/precalciner vessels where 

temperatures are ideal (between 1600-2000oF) for reducing NOX to elemental nitrogen.

Holcim has indicated to the state that SNCR is technically and economically feasible for 

the Portland Plant. In April 2008, Holcim provided information to the state on SNCR 

systems that was based on trials that were conducted at the plant in the 4th quarter of 

2006. Holcim estimated that NOX emissions could be reduced in the general range of 60 

to 80% (based on a 1,000 pound per hour emission rate) at an approximate cost of 

$1,028 per ton. This was based on a short-term testing and showed considerable 

ammonia slip which could cause significant environmental, safety and operational 

issues.

The facility is currently permitted to emit 3,185.7 tpy of NOX from the kiln system main 

stack. At a permitted clinker production level of 1,873,898 tpy, this equates to an annual 

average of 3.40 pounds of NOX per ton of clinker (the current permit does not contain 

an annual pound per ton of clinker or a short-term emission limit for NOX). The actual 

kiln NOX emissions divided by the actual clinker production for the five-year baseline 

period used in this analysis (2004, 2005, 2006, 2007 and 2008) calculate to an overall 

annual average rate of 3.43 pounds of NOX per ton of clinker, with a standard deviation 

of 0.21 pound per ton. The highest annual emission rate in the baseline years was 3.67 

pounds per ton of clinker.

As a part of their submittals, Holcim analyzed continuous hourly emission data for NOX. 

The hourly emission data from 2004 to 2008 (baseline years) were used to calculate the 

daily emission rates. A 30-day rolling average emission rate was calculated by dividing 

the total emissions from the previous 30 operating days by the total clinker production 

from the previous 30 operating days. The 99th percentile of the 30-day rolling average 

data was used to establish the short-term baseline emission rate of 4.47 pounds of NOX 

per ton of clinker. The 99th percentile accounts for emission changes due to short-term 

and long-term inherent process, raw material and fuel variability.

Holcim is permitted to burn up to 55,000 tpy of TDF annually and has been using TDF 

during the baseline years. Use of TDF as a NOX control strategy has been well 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

138

documented and recognized by EPA. A reduction in NOX emissions of up to 30% to 

40% has been reported. Since the TDF market and possible associated TDF-use 

incentives are unpredictable and TDF‟s long-term future availability is unknown, the 

baseline emission rate was adjusted upward by a conservative factor of 10% to account 

for the NOX reduction in the baseline years as a result of the use of TDF during this 

baseline period that might not be available in future years. This increased the baseline 

30-day rolling average emissions rate from 4.47 to 4.97 pounds of NOX per ton of 

clinker.

An SNCR control efficiency of 50% is feasible for the Portland Plant kiln that already 

has number of technologies available to reduce NOX emissions including indirect firing, 

low-NOX burners, staged combustion, a low-NOX precalciner, and a Linkman Process 

Control Expert system. However, to achieve the necessary system configuration and 

temperature profile, SNCR will be applied at the top of the preheater tower and thus the 

alkali bypass exhaust stream cannot be treated. To achieve the proper cement product 

specifications, the Portland Plant alkali bypass varies from 0 - 30% of main kiln gas 

flow. Adjusting by 10%, (conservative estimate) for the alkali bypass to account for the 

exhaust gas that is not treated (i.e., bypassed) by the SNCR system, the overall SNCR 

control efficiency for the main stack will be 45%.

Based on the above discussion, the 30-day rolling average short-term limit was 

calculated at 2.73 pounds of NOX per ton of clinker by adjusting upward the short-term 

baseline emission rate of 4.47 pounds of NOX per ton clinker by 10% for TDF and then 

accounting for SNCR 45% overall control efficiency [4.47/0.9*(1-0.45) = 2.73]. The longterm annual limit was calculated at 2,086.8 tpy by adjusting upward the annual baseline 

emission rate of 3.64 lbs/ton clinker (the mean of 3.43 pounds per ton plus one standard 

deviation of 0.21 pound per ton) by 10% for TDF and then accounting for SNCR 45% 

overall control efficiency [3.64/0.9*(1-0.45) = 2.23 lb/ton]. This calculated value of 2.23 

pounds per ton was then multiplied by the annual clinker limit of 1,873,898 tpy, and then 

divided by 2,000 pounds per ton to arrive at the 2,086.8 tpy NOX limit.

Because SNCR with existing LNB is technically and economically feasible, the state did 

not further consider water injection because the level of control associated with this 

option is not as high as with SNCR.

The following table lists the most feasible and effective option (SNCR):

NOx Control Technology

Estimated 

Control 

Efficiency

30-day Rolling

Average Emissions 

(lb/ton of Clinker) 

Annual Controlled 

NOx Emissions 

(tpy)

Baseline NOx Emissions - 4.97 3,185.7*

SNCR w/ existing LNB 45%** 2.73 2,086.8

* Defaulted to the permit limit since the calculated baseline was higher.

** This is calculated based on the 50% SNCR removal efficiency and 10% bypass

There are no significant associated energy and non-air quality impacts for SNCR in 

operation on a Portland cement plant. There are no remaining useful life issues for the
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

139

source, as the state has presumed that the source will remain in service for the 20-year 

amortization period.

The following table lists the emission reductions, annualized costs and the control cost 

effectiveness for the feasible controls:

Holcim Portland Plant – Kiln System

NOx Control 

Technology

NOx Emission 

Reduction

(tons/yr)

Annualized 

Cost ($/yr)

Cost 

Effectiveness

($/ton)

Incremental Cost 

Effectiveness

($/ton)

Baseline NOx 

Emissions -

SNCR w/existing LNB 

(45% control) 1,098.9 $2,520,000* $2,293 -

* Annualized cost is based on the estimates provided by Holcim. The state believes that the $2,293/ton 

value is generally representative of control costs for the scenario evaluated in this RP analysis.

As a part of their late October 2010 submittals, Holcim provided modeling data for their 

proposed NOX RP limitations. The following table lists the projected visibility 

improvements for NOX controls, as identified by Holcim:

Holcim Portland Plant – Kiln System

NOx Control Method 98th Percentile 

Impact (Δdv)

98th Percentile 

Improvement (Δdv)

Maximum (24-hr max)

(based on modeled emission rates of 1,363 

lb/hr NOx, 586 lb/hr SO2, 86.4 lb/hr PM10)

0.814 N/A

SNCR w/ existing LNB 

(45% overall NOX control efficiency)

Limits of 2.73 lb/ton (30-day rolling average) 

and 2,086.8 tons per year

(based on modeled emission rates of 750 lb/hr 

NOX, 586 lb/hr SO2, 86.4 lb/hr PM10)

0.526 0.288

For the kiln, the state has determined that SNCR w/existing LNB is the best NOX control 

system available with NOX RP emission limits of 2.73 pounds per ton of clinker (30-day 

rolling average) and 2,086.8 tons per year (12-month rolling total). The emissions rate 

and the control efficiency reflect the best performance from the control options 

evaluated. This RP determination affords the most NOX reduction from the kiln system 

(1,098.9 tpy) and contributes to significant visibility improvement.

A complete analysis that further supports the RP determination for the Holcim Portland 

Plant can be found in Appendix D.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

140

8.5.2.6 RP Determination for Tri-State Generation and Transmission 

Association’s Nucla Facility

The Tri-State Nucla Station is located in Montrose County about 3 miles southeast of 

the town of Nucla, Colorado. The Nucla Station consists of one coal fired steam driven 

electric generating unit (Unit 4), with a rated electric generating capacity of 110 MW 

(gross), which was placed into service in 1987. Nucla Unit 4 is considered by the 

Division to be eligible for the purposes of Reasonable Progress, being an industrial 

boiler with the potential to emit 40 tons or more of haze forming pollution (NOx, SO2, 

PM10) at a facility with a Q/d impact greater than 20. Tri-State Generation and 

Transmission Association (Tri-State) provided information relevant to RP to the Division 

on December 31, 2009, May 14, 2010, June 4, 2010 and July 30, 2010.

SO2 RP Determination for Nucla – Unit 4

Limestone injection improvements, a spray dry absorber (SDA) system (or dry FGD), 

limestone injection improvements with a SDA, hydrated ash reinjection (HAR), and HAR 

with limestone injection improvements were determined to be technically feasible for 

reducing SO2 emissions from Nucla Unit 4. Study-level information for HAR systems at 

Nucla or any other EGU in the western United States were not available for use in 

evaluating costs. Since the option to install a dry FGD alone (even without improving 

limestone injection) provides a better estimated control efficiency than a HAR system 

plus limestone injection improvements, the HAR system was not considered further in 

this analysis.

The following tables list the emission reductions, annualized costs and cost 

effectiveness of the control alternatives:

Nucla Unit 4 - SO2 Cost Comparison

Alternative Emissions 

Reduction (tpy)

Annualized Cost 

($)

Cost Effectiveness 

($/ton)

Baseline 0 $0 $0

Limestone Injection 

Improvements

526 $914,290 $4,161

Spray Dry Absorber (dry 

FGD)

1,162 $7,604,627 $6,547

Limestone Injection 

Improvements + dry FGD

1,254 $9,793,222 $7,808

A dry FGD system, or limestone injection improvements plus dry FGD system, were

eliminated from consideration by the state as unreasonable during this planning period

due to: 1) the excessive costs, 2) that they would require replacement of an existing 

system and installation of a completely new system (with attendant new capital costs 

and facility space considerations), and 3) the lack of modeled visibility affects 

associated with these particular SO2 reductions.

There is no energy and non-air quality impacts associated with limestone injection 

improvements. For dry FGD, the energy and non-air quality impacts include less 

mercury removal compared to unscrubbed units and significant water usage.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

141

There are no remaining useful life issues for alternatives as the source will remain in 

service for the 20-year amortization period.

Due to time and domain constraints, projected visibility improvements were not modeled 

by the state for this analysis.

Nucla already has a system in place to inject limestone into the boiler as required by 

current state and federal air permits. This system achieves an approximate 70% SO2 

emissions reduction capture efficiency at a permitted emission rate of 0.4 lbs/MMBtu 

limit. Increased SO2 capture efficiency (85%) with the existing limestone injection as an 

effective system upgrade, by use of more limestone (termed “limestone injection 

improvements”) was evaluated and determined to not be feasible under certain 

operating conditions. The system cannot be „run harder‟ with more limestone to achieve 

a more stringent SO2 emission limit; the system would have to be reconstructed or 

redesigned with attendant issues, or possibly require a new or different SO2 system, to 

meet an 85% capture efficiency.

Based upon its consideration of the five factors summarized herein and detailed in 

Appendix D, the state has determined that the existing permitted SO2 emission rate for 

Unit 4 satisfies RP:

Nucla Unit 4: 0.4 lb/MMBtu (30-day rolling average)

The state assumes that the emission limit can be achieved through the operation of the 

existing limestone injection system. 

PM10 RP Determination for Nucla – Unit 4

The state has determined that the existing regulatory emissions limit of 0.03 lb/MMBtu 

represents the most stringent control option. The unit is exceeding a PM control 

efficiency of 95%, and the emission limit is RP for PM/PM10. The state assumes that 

the emission limit can be achieved through the operation of the existing fabric filter 

baghouse.

NOx RP Determination for Nucla – Unit 4

Selective non-catalytic reduction (SNCR) was determined to be technically feasible for 

reducing NOx emissions at Nucla Unit 4. SCR is not technically feasible on a circulating 

fluidized bed coal-fired boiler, and is otherwise not cost-effective, as discussed in 

Appendix D. With respect to SNCR, however, there is substantial uncertainty 

surrounding the potential control efficiency achievable by a full-scale SNCR system at a 

CFB boiler burning western United States coal. The state and Tri-State‟s estimates 

vary between 10 – 40% NOx reduction potential, which correlates to between $3,000 -

$17,000 per ton NOx reduced and may result in between 100 to 400 tons NOx reduced 

per year.

The energy and non-air quality impacts of SNCR are increased power needs, potential 

for ammonia slip, potential for visible emissions, hazardous materials storage and 

handling.

There are no remaining useful life issues for the alternatives as the sources will remain 

in service for the 20-year amortization period.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

142

Due to time and domain constraints, projected visibility improvements were not modeled 

by the state for this analysis. There are several qualitative reasons that NOx controls 

may be warranted at Nucla. First, NOx control alternatives may result in between 100 –

400 tons of NOx reduced annually. Second, Nucla is within 100 kilometers in proximity 

to three Class I areas, depicted in the figure above, and within approximately 115 

kilometers to five Class I areas, including Utah‟s Canyonlands and Arches National 

Parks. Third, Nucla has a limited, small-scale SNCR system for emissions trimming 

purposes installed.

Based upon its consideration of the five factors summarized herein and detailed in 

Appendix D, the State has determined that NOx RP for Nucla Unit 4 is no control at the 

following NOx emission rate:

Nucla Unit 4: 0.5 lb/MMBtu (30-day rolling average)

Additional Analyses of SO2 and NOx Controls for Nucla

As state-only requirements of this Reasonable Progress determination, the Commission 

requires, and Tri-State agrees, that Tri-State conduct a comprehensive four factor 

analysis of all SO2 and NOx control options for Nucla using site-specific studies and 

cost information and provide to the state a draft analysis by July 1, 2012. A protocol for 

the four-factor analysis and studies will be approved by the Division in advance. The

analysis will include enhancements or upgrades to the existing limestone injection 

system for increased SO2 reduction performance, other relevant SO2 control 

technologies such as lime spray dryers and flue gas desulfurization, and all NOx control 

options. A final analysis that addresses the state‟s comments shall be submitted to the 

state by January 1, 2013. By January 1, 2013, Tri-State shall also conduct appropriate 

cost analyses, study and, if deemed necessary by the state and the source, testing, as 

approved by the Division, to inform what performance would be achieved by a full-scale 

SNCR system at Nucla to determine potential circulating fluidized bed (CFB) boilerspecific NOx control efficiencies. By January 1, 2013, Tri-State shall conduct CALPUFF 

modeling in compliance with the Division‟s approved BART-modeling protocol to 

determine potential visibility impacts the different SO2 and NOx control scenarios for 

Nucla. Finally, Tri-State shall propose to the state any preferred SO2 and NOx 

emission control strategies for Nucla by January 1, 2013.

A complete analysis that supports the RP determination for the Nucla facility can be 

found in Appendix D.

8.5.2.7 RP Determination for Tri-State Generation and Transmission 

Association’s Craig Facility Unit 3

The Tri-State Craig Station is located in Moffat County about 2.5 miles southwest of the 

town of Craig, Colorado. This facility is a coal-fired power plant with a total net electric 

generating capacity of 1264 MW, consisting of three units. Units 1 and 2, rated at 4,318 

mmBtu/hour each (net 428 MW), were placed in service in 1980, and 1979, 

respectively. Construction of Unit 3 began in 1981 and the unit commenced operation 

in 1984. Craig Units 1 and 2 are subject to BART. Craig Unit 3 is considered by the 

Division to be eligible for the purposes of Reasonable Progress, being an industrial 

boiler with the potential to emit 40 tons or more of haze forming pollution (NOx, SO2, 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

143

PM10) at a facility with a Q/d impact greater than 20. Tri-State Generation and 

Transmission Association (Tri-State) provided information relevant to RP to the Division 

on December 31, 2009, May 14, 2010, June 4, 2010 and July 30, 2010.

SO2 RP Determination for Craig – Unit 3

Dry FGD Upgrades - As discussed in EPA‟s BART Guidelines, electric generating units 

(EGUs) with existing controls achieving removal efficiencies of greater than 50 percent 

do not need to be evaluated for potential removal of controls and replacement with new 

controls. Craig Unit 3 operates a [lime spray dryer FGD] currently achieving over 80 

percent SO2 reduction. The state considers EPA‟s BART Guidelines relevant to the RP 

evaluation of Craig Unit 3 and, therefore, the following dry scrubber upgrades were 

considered.

Use of performance additives: Performance additives are typically used with drysorbent injection systems, not semi-dry SDA scrubbers that spray slurry products. 

Tri-State and the Division are not aware of SO2 scrubber performance additives 

applicable or commercially available for the Unit 3 SDA system. 

Use of more reactive sorbent/Increase the pulverization level of sorbent: The 

purchase and installation of two new vertical ball mill slakers improved the ability to 

supply high quality slaked (hydrated) lime. A higher quality slaked lime slurry means 

a more reactive sorbent. Typically, slakers are not designed for particle size 

reduction as part of the slaking process. However, the new vertical ball mill slakers 

are particularly suited for slaking lime that is a mixture of commercial pebble lime 

and lime fines. Fines are generated at the Craig facility in the pneumatic lime 

handling system. Therefore, the Division concurs that TriState cannot use a more 

reactive sorbent or increase the pulverization level of sorbent.

Engineering redesign of atomizer or slurry injection system: Both the slaked lime 

slurry and recycled ash slurry preparation and delivery systems were redesigned to 

improve overall performance and reliability. The improved system allows for slurry 

pressure control at both the individual reactor level and for each slurry injection 

header level on each reactor. Tri-State notes that consistent control of slurry 

parameters (pressure, flow, composition) promotes consistent and reliable SO2 

removal performance. The Division concurs that with the recent redesign of the 

slurry injection system and expansion to two trains of recycled ash slurry 

preparation, no further redesigns are possible at this time.

Therefore, there are no technically feasible upgrade options for Craig Station Unit 3. 

However, the state evaluated the option of tightening the emission limit for Craig Unit 3 

and determined that a more stringent 30-day rolling SO2 limit of 0.15 lbs/MMBtu 

represents an appropriate and reasonable level of emissions control for this dry FGD 

control technology. Upon review of 2009 emissions data from EPA‟s Clean Air Markets 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

144

Division website, the state has determined that this emissions rate is achievable without 

additional capital investment.

The projected visibility improvements attributed to the alternatives are as follows:

SO2 Control Method

Craig – Unit 3

SO2 Emission Rate 

(lb/MMBtu)

98th Percentile Impact 

(Δdv)

Daily Maximum (3-yr) 0.33

Dry FGD 0.15 0.26

Dry FGD 0.07 0.38

The current SO2 emission limits for Craig 3 are:

0.20 lb/MMBtu averaged over a calendar day, to be exceeded no more than 

once during any calendar month;

80% reduction of the potential combustion concentration of SO2, determined on 

a 30-day rolling average basis

2,125 tons/year annual emission limit

Based upon its consideration of the five factors summarized herein and detailed in 

Appendix D, the state has determined that SO2 BART is the following SO2 emission 

rates:

Craig Unit 3: 0.15 lb/MMBtu (30-day rolling average)

The state assumes that the emission limit can be achieved through the operation of 

existing dry FGD controls. An SO2 limit lower than 0.15 lbs/MMBtu would not result in 

significant visibility improvement (less than 0.2 delta deciview) and would likely result in 

frequent non-compliance events and, thus, is not reasonable.

PM10 RP Determination for Craig – Unit 3

The State has determined that the existing Unit 3 regulatory emissions limits of 0.013 

(filterable PM) and 0.012 lb/MMBtu (PM10) represents the most stringent control option. 

The unit is exceeding a PM control efficiency of 95%, and the emission limit is RP for 

PM/PM10. The state assumes that the emission limit can be achieved through the 

operation of the existing fabric filter baghouse.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

145

NOx RP Determination for Craig – Unit 3

Selective non-catalytic reduction (SNCR) and selective catalytic reduction (SCR) were 

determined to be technically feasible for reducing NOx emissions at Craig Unit 3.

The following table lists the emission reductions, annualized costs and cost 

effectiveness of the control alternatives:

Craig Unit 3 - NOx Cost Comparisons

Alternative Emissions 

Reduction (tpy)

Annualized Cost 

($)

Cost Effectiveness 

($/ton)

Baseline 0 $0 $0

SNCR 853 $4,173,000 $4,887

SCR 4,281 $29,762,387 $6,952

SCR was eliminated from consideration due to the excessive cost/benefit ratio.

The energy and non-air quality impacts of SNCR are increased power needs, potential 

for ammonia slip, potential for visible emissions, hazardous materials storage and 

handling.

There are no remaining useful life issues for the alternatives as the sources will remain 

in service for the 20-year amortization period.

The projected visibility improvements attributed to the alternatives are as follows:

NOx Control Method NOx Annual Emission Rate 

(lb/MMBtu)

98th Percentile Impact 

(∆dv)

Daily Maximum (2

nd half 2009) 0.365

SNCR 0.240 0.32

SCR 0.070 0.79

The state performed modeling using the maximum 24-hour rate during the baseline 

period, and compared resultant annual average control estimates. In the state‟s 

experience and other state BART proposals, 30-day NOx rolling average emission rates 

are expected to be approximately 5-15% higher than the annual average emission rate. 

The state projected a 30-day rolling average emission rate increased by 15% for all 

NOx emission rates to determine control efficiencies and annual reductions.

Based upon its consideration of the five factors summarized herein and detailed in 

Appendix D, the state has determined that NOx RP for Craig Unit 3 is the following NOx 

emission rates:

Craig Unit 3: 0.28 lb/MMBtu (30-day rolling average)

The state assumes that the RP emission limits can be achieved through the operation of 

SNCR. To the extent practicable, any technological application Tri-State utilizes to 

achieve this RP emission limit shall be installed, maintained, and operated in a manner 

consistent with good air pollution control practice for minimizing emissions. For SNCRbased emission rates at Unit 3, the cost per ton of emissions removed, coupled with the 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

146

estimated visibility improvements gained, falls with guidance cost criteria discussed in 

section 8.4 above.

Unit 3: $4,887 per ton NOx removed; 0.32 deciview of improvement 

The dollars per ton control cost, coupled with notable visibility improvements, leads the 

state to this determination. Although SCR achieves better emission reductions, the 

expense of SCR was determined to be excessive and above the guidance cost criteria 

discussed in section 8.4 above. The state reached this conclusion after considering the 

associated visibility improvement information and after considering the SCR cost 

information in the SIP materials and provided during the pre-hearing and hearing 

process by the company, parties to the hearing, and the FLMs.

A complete analysis that supports the RP determination for the Craig facility can be

found in Appendix D.

8.5.2.8 RP Determination for Public Service Company’s Cameo Station

Public Service Company informed the state that the Cameo Station east of Grand 

Junction, Colorado will be shutdown 12/31/2011, resulting in SO2, NOx and PM 

reductions of approximately 2,618, 1,140, and 225 tons per year, respectively. 

Therefore, a four-factor analysis was not necessary for this facility and the RP

determination for the facility is closure.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

147

Chapter 9 Long Term Strategy

The Long-Term Strategy (LTS) is required by both Phase 1 (Reasonably Attributable 

Visibility Impairment) and Phase 2 (Regional Haze) regulations. The LTS‟ of both 

phases are to be coordinated. 

This chapter contains:

LTS requirements;

An overview of the current Reasonably Attributable Visibility Impairment Long 

Term Strategies (RAVI LTS), adopted by the Commission in 2004 and 

subsequently approved by EPA;

A review of the 2004 RAVI LTS and a SIP revision;

A Regional Haze LTS; and

Reasonable Progress Goals for each of the state‟s 12 mandatory federal Class I 

areas.

9.1 LTS Requirements 

The LTS requirements for reasonably attributable visibility impairment, as described in 

40 CFR 51.306, are as follows:

Submittal of an initial RAVI LTS and 3-year periodic review and revision (since 

revised to 5-year updates per 40 CFR 51.306(g)) for addressing RAVI;

Submittal of revised LTS within three years of state receipt of any certification of 

impairment from a federal land manager;

Review of the impacts from any new or modified stationary source;

Consultation with federal land managers; and

A report to the public and EPA on progress toward the national goal.

The LTS requirements for Regional Haze (RH), as described in 40 CFR 51.308(d)(3), 

are as follows:

Submittal of an initial LTS and 5-year progress review per 40 CFR 51.308(g) that 

addresses regional haze visibility impairment;

Consult with other states to develop coordinated emission management 

strategies for Class I areas outside Colorado where Colorado emissions cause or 

contribute to visibility impairment, or for Class I areas in Colorado where 

emissions from other states cause or contribute to visibility impairment;

Document the technical basis on which the state is relying to determine its‟ 

apportionment of emission reduction obligations necessary for achieving 

reasonable progress in each Class I area it affects;

Identify all anthropogenic sources of visibility impairing emissions;

Consider the following factors when developing the LTS: 

(1) Emission reductions due to ongoing air pollution control programs, including 

measures to address reasonably attributable visibility impairment;

(2) Emission limitations and schedules for compliance to achieve the RP goal;

(3) Measures to mitigate the impacts of construction activities;
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

148

(4) Smoke management techniques for agricultural and forestry management 

purposes including plans as currently exist within the state for this purpose;

(5) Source retirement and replacement schedules;

(6) Enforceability of emission limitations and control measures; and

(7) The anticipated net effect on visibility due to projected changes in point, area, 

and mobile source emissions over the period addressed by the long-term 

strategy.

The following sections 9.2 and 9.3 address these LTS requirements.

9.2 2004 RAVI Long-Term Strategy

The RAVI LTS was adopted by the Commission in November 2004. It was 

subsequently approved by EPA in December 2006 and is summarized below.

9.2.1 Existing Impairment

The LTS must have the capability of addressing current and future existing impairment 

situations as they face the state. Colorado considers that Commission Regulation No. 3, 

Part B, 5XIV.D ("Existing Impairment") meets this LTS requirement regarding existing 

major stationary facilities and provides Federal Land Managers (FLMs) the opportunity 

to certify whether an existing stationary source(s) is likely reasonably attributable to 

existing visibility impairment and potentially subject to BART. The state believes 

existing regulations along with strategies and activities outlined below have together 

provided for reasonable progress toward the national visibility goal under Phase 1 of the 

visibility protection program. However, a specific requirement associated with the RH 

rule is found in 40 CFR § 51.306(c) and is intended to bring into harmony the 

reasonable attribution requirement in place since 1980 and the RH rule. As such, to 

meet one part of that requirement, the State of Colorado commits to review the longterm strategy as it applies to reasonably attributable impairment, and make revisions, as

appropriate, within three years of state receipt of any certification of reasonably

attributable impairment from a Federal Land Manager. This is consistent with the 

current LTS and State Regulation No. 3 noted above. In addition, Regulation 3, Part D, 

is amended as part of this SIP action to change the current 3 year review cycle to a 5 

year cycle to coordinate the RAVI and RH elements together as intended by the RH 

rule. Elsewhere in this SIP the state has documented measures to be adopted to 

address the RH element of the rule including BART determinations and strategies 

identified in Chapter 8- Reasonable Progress.

In a related action, this 5-year update will satisfy Colorado‟s requirement for developing 

emissions estimates from activities on federal lands (Colorado Revised Statute 25-7-

105(1)). The state commits to consult with Federal Land Managers to develop a 

consolidated emissions inventory, which will be brought to the Air Quality Control 

Commission as part of the 5-year LTS update and then submitted to EPA. After the 

2008 emission inventory data submittal, the Consolidated Emission Reporting Rule will 

be completely replaced by the Air Emissions Reporting Requirements Rule.

Following is a review of the elements contained in the LTS in a chronological order. 

During the five-year review required by the RH rule, the State of Colorado will add to or 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

149

revise this section as needed based on any new findings or actions taken related to 

RAVI notifications delivered to the state by a FLM.

9.2.1.1 Mt. Zirkel Wilderness

The U.S.D.A. Forest Service (USFS) concluded in its July 1993 certification letter to the 

State of Colorado that visibility impairment existed in the Mt. Zirkel Wilderness Area 

(MZWA) and local existing stationary sources, namely the Craig and Hayden power 

stations, contributed to the problem. In 1996 and again in 2001, settlement agreements 

between various parties and the Hayden and Craig (Units 1 and 2) Generating Stations, 

respectively, were completed. The state believes significant emission reductions of 

SO2 and PM effectively address the RAVI in the MZWA associated with the Hayden 

and Craig (Units 1 & 2) Generating Stations. The state further believes the Hayden and 

Craig Consent Decrees effectively resolve the certification of impairment brought by the 

U.S.D.A. Forest Service. The Forest Service indicated its complaint against Hayden 

and Craig had been satisfied.

9.2.1.2 BART and Emission Limitations

Although RAVI BART determinations were not made by the state regarding Hayden and 

Units 1 and 2 of Craig generating stations, emission limitations for the two power plants 

were incorporated into the LTS SIP in August 1996 (Hayden) and April 2001 (Craig 

Units 1 and 2) and these SIP revisions remain incorporated into the Colorado SIP. The 

contents of the August 1996 LTS SIP revision incorporating emission limitations, 

construction and compliance schedules, and reporting requirements for Hayden 

generating station Units 1 and 2 were incorporated into the 2004 LTS SIP by reference. 

EPA originally approved this SIP amendment on January 16, 1997. The contents of the 

April 2001 LTS SIP revision incorporating emission limitations, construction and 

compliance schedules, and reporting requirements for the Craig generating station Units 

1 and 2 were incorporated into the 2004 LTS SIP by reference. 

This RH SIP amendment establishes new limits on Hayden Units 1 and 2, and Craig 

Units 1 and 2, based on a full BART analysis under the current EPA guidelines. 

Chapter 6 of this SIP (and Appendix C as well as supporting technical support 

documents) and changes to Regulation No. 3 result in new control requirements for 

these units to meet BART.

9.2.1.3 Monitoring

It is important to track the effects of the emission changes on visibility and other Air 

Quality Related Values in and near Mt. Zirkel Wilderness Area and other Class I areas 

in Colorado. The Division committed in the 2004 LTS SIP amendment to coordinating a 

monitoring strategy with other agencies and to provide periodic assessments of various 

monitored parameters in "before" compared to "after" emission reductions periods. 

Colorado commits to maintain a monitoring strategy and periodically report to the public 

and the EPA on an annual basis to include trends, current levels and emission changes. 

In addition periodic emission inventory updates required by the national emissions 

reporting rule establish a 3-year reporting cycle for emissions updates. Finally, this RH 

SIP commits to a five year review process established by the RH rule. Through this, the 

state believes a demonstration of „before and after emission reductions‟ will be met.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

150

9.2.1.4 Other Stationary Sources and Colorado Class I Areas and Additional 

Emission Limitations and Schedules for Compliance

There are no outstanding certifications of Phase I visibility impairment in Colorado. For 

Regional Haze, Chapters 6 and 8 specifically delineate the comprehensive BART 

analysis and Reasonable Progress analysis of other sources. In these sections specific 

additional controls of selected stationary sources are detailed and emission reductions 

from these are reflected in the Appendices and technical support documents. The state 

believes the coordination of these added control measures meets the requirements of 

the LTS showing both emission limitations and schedules for compliance. In regard to 

any future certification of any RAVI, the state is prepared to respond to any future 

certifications as per AQCC Regulation No. 3 X1V.D in accordance with the five year 

limit established in 40 CFR § 51.306(c).

9.2.1.5 Ongoing Air Pollution Programs

In the 2004 LTS SIP revision, the state committed to:

Continue to attain and maintain the PM10 and PM2.5 standards which will have 

some effect on improving visibility in pristine and scenic areas;

Continue to provide technical support to efforts to understand and reduce the 

Brown Cloud in the Front Range of Colorado. Analysis of Brown Cloud data 

indicates it improved approximately 28% between 1991 and 2006, and data 

through 2009 indicates this trend continues as demonstrated in the APCD Annual 

Air Quality Data reports;

Continue to stay involved and inform the Colorado Air Quality Control 

Commission about emissions growth in the Four Corners area;

Continue to participate in any future work of the Rocky Mountain National Park 

research effort; and,

Continue to administer and follow existing regulations of point, area and mobile 

sources as specified in AQCC regulations.

9.2.2 Prevention of Future Impairment

The LTS must establish mechanisms to address the prevention of future impairment 

and outline strategies to ensure progress toward the national goal. The 2004 LTS 

summarized programs and activities providing reasonable progress toward the national 

goal under the Phase 1 RAVI program. Generally, Colorado considers its NSR and 

PSD programs meet the long-term strategy requirements for preventing future 

impairment from proposed major stationary sources or major modifications to existing 

facilities.

9.2.3 Smoke Management Practices

The LTS requires smoke management practices of prescribed burning be addressed. 

The 2004 LTS described Colorado‟s Regulation No. 9 regarding open burning and 

wildland fire smoke management. As the level and complexity of burning increases the 

Division committed to continually evaluate its regulatory program for this source of air 

pollution and surveyed its current activities in the 2004 LTS review. The addition of the 

Fire Emissions Tracking System (FETS) by the WRAP, FLMs and states allows 

Colorado to input fire emission data into the national tracking system thereby adding 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

151

more precise information for future inventories and studies. The state commits in this 

SIP to continue administration of Regulation 9 as part of this LTS, and to input data into 

the FETS as long as it is operational. Colorado will continue as part of Regulation 9 to 

maintain a database of fire related permits and actions - the basis for data entered into 

the FETS.

9.2.4 Federal Land Manager Consultation and Communication

The state committed to providing for the plans, goals, and comments of the Federal 

Land Managers during SIP and LTS revisions. The state will provide, at a minimum, the 

opportunity for consultation with the FLMs at least 60 days prior to any public hearing on 

any element of the Class I Visibility SIP including LTS revisions and review. In addition 

the state will publish as part of the SIP process any formal comments received by the 

FLMs as a result of their review along with a listing of responses the state made in 

regard to such comments.

9.3 Review of the 2004 RAVI LTS and Revisions

A July 2007 review of the 2004 RAVI LTS concluded that “The Division does not believe 

extensive and substantive revisions are necessary at this time to ensure reasonable 

progress toward the national goal under Phase I of the Class I Visibility Protection 

Program. However, small updates and edits are proposed so this part of the SIP does 

not become outdated.” Appendix A of this SIP document contains this review. The only 

other changes to this LTS relate to the change in the update period in Regulation 3, as

described above in section 9.2.1, and a commitment to utilize the FETS to track fire 

data as described above in section 9.2.3. The state commits to work with the FLMs to 

coordinate any changes to the RH/RAVI LTS on the five year cycle required by the 

regulation. This will include responding to any notification of impairment by the FLMs, 

providing an opportunity to comment 60 days prior to any public hearing on proposed 

changes to the RH/RAVI LTS, and to publish the FLM comments and state responses 

as part of that review process. Appendix B of this document contains the SIP revision 

for the RAVI LTS.

9.4 Regional Haze Long Term Strategy

The following presents Colorado‟s Long Term Strategy (LTS) for Regional Haze.

9.4.1 Impacts on Other States

Where the state has emissions reasonably anticipated to contribute to visibility

impairment in any mandatory Class I Federal area located in another state or states, the 

state must consult with the other state(s) in order to develop coordinated emission 

management strategies. Colorado has analyzed the output of the initial 2006 PSAT 

product from the WRAP and determined that emissions from the state do not 

significantly impact other states‟ Class I areas. The two largest Colorado visibility 

impacts are at Canyonlands National Park in Utah and Bandelier National Monument in 

New Mexico, where Colorado‟s total nitrate and sulfate contribution are only 1.0% and 

0.5%, respectively, of total haze at these Class I areas. This is not a meaningful level of 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

152

contribution, and all other modeled contributions at other Class I areas are of a smaller 

magnitude.

Table 9-1 Colorado’s Nitrate and Sulfate Impacts at Bandelier and Canyonlands

9.4.2 Impacts from Other States

Where other states cause or contribute to impairment in a mandatory Class I Federal 

area, the state must demonstrate it has included in its implementation plan all measures 

necessary to obtain its share of the emission reductions needed to meet the progress 

goal for the area. Chapter 7 presents modeling information that describes the 

contribution to visibility impairment in Colorado‟s Class I areas from other states. 

Colorado is establishing reasonable progress goals later in this chapter utilizing 

modeling results presented in Chapter 7, with supporting information in the technical 

support documents. This demonstration reflects the emission reductions achieved by 

the controls committed to by other states.

9.4.3 Document Technical Basis for RPGs

The state must document the technical basis (e.g., modeling) on which the state is 

relying to determine its apportionment of emission reduction obligations necessary for 

achieving reasonable progress in each mandatory Class I Federal area. This is 

addressed in the Technical Support Document, Chapter 7, and later in this Chapter 9.

9.4.4 Identify Anthropogenic Sources

The state must identify all anthropogenic sources of visibility impairment considered by 

the state in developing its LTS. Colorado presents comprehensive emission inventories 

in Chapter 5 and the TSD, and presents emissions control evaluations in Chapters 6 

and 8. Chapter 7 and the Technical Support Documents present information about 

source apportionment for each Class I area in Colorado. 

9.4.5 Emission Reductions Due to Ongoing Air Pollution Control Programs

Below is a discussion of ongoing air pollution control programs that reduce visibility 

impairing emissions throughout Colorado.

Numerous emission reduction programs exist for major and minor industrial sources of 

NOx, SO2 and particulates throughout the state, as well as in the Denver Metro 

Area/Northern Front Range region for VOCs, NOx, and particulates from mobile, area, 

stationary and oil/gas sources, and are contained in the following Colorado Air Quality 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

153

Control Commission Regulations:

Regulation Number 1: Emission Controls for Particulates, Smoke, Carbon Monoxide 

and Sulfur Oxides

o In the SIP (includes specific fugitive dust and open burning regulations)

Regulation Number 3: Stationary Source Permitting and Air Pollutant Emission 

Notice Requirements

o Parts A, B,D, F in the SIP or Submitted to EPA for inclusion in the SIP

o Part C is the Title V program and is delegated by EPA to the state

Regulation Number 4: New Wood Stoves and the Use of Certain Woodburning 

Appliances on High Pollution Days

o Regulation Number 4 is in the SIP. One provision, the Masonry Heater Test 

Method, is state only. Colorado is waiting for EPA to develop their own test 

method – the state will adopt it when EPA goes final

Regulation Number 6: Standards of Performance for New Stationary Sources

o Part A – Federal NSPS‟s adopted by the state – EPA has delegated authority 

to the state to implement; Colorado has requested delegation for the most

recent adoptions

o Part B – state-only NSPS regulations

Regulation Number 7: Control of Ozone Precursors

o The majority of Regulation Number 7 for VOC and NOx control is in the SIP 

or has been submitted for approval into the SIP – these provisions relate to 

VOC and NOx control measures for the Denver Metro Area/North Front 

Range 8-hour ozone nonattainment area and are summarized below

Regulation Number 9: Open Burning, Prescribed Fire and Permitting – state-only

Regulation Number 11: Motor Vehicle Emission Inspection Program – Parts A-F in 

the SIP

Regulation Number 16: Street Sanding Emissions – In the SIP

Some examples of these programs and the visibility-improving emission reductions they 

achieve are as follows. It is noted as to whether the program is federally enforceable, 

submitted by the state in an unrelated submittal for inclusion into the SIP, or state-only 

enforceable.

Early reductions from BART sources include approximately 24,000 tpy of SO2 from 

metro Denver power plants, approximately 6,500 tpy of SO2 from the Comanche 

power plant, and approximately 18,000 tpy of SO2 from the Craig and Hayden 

power plants – state-only

Oil and gas condensate tank control regulations for the Front Range region that 

have achieved approximately 52,000 tpy of volatile organic compounds (VOC) 

emission reductions by 2007 - in the SIP - with additional projected reductions of 

18,000 tpy by 2010 – Submitted for inclusion in the SIP

Existing industrial engine control regulations for the Front Range region that have 

achieved NOx and VOC emissions reductions of approximately 8,900 tpy – In the 

SIP

Oil and gas pneumatic actuated device control regulations for the Front Range 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

154

region that have achieved VOC emission reductions of approximately 8,400 tpy –

state-only

Mobile source emissions controls for VOCs and NOx through vehicle 

inspection/maintenance and lower volatility gasoline programs for the Front Range 

region is estimated to reduce emissions by approximately 8,000 tpy by 2011 –

Submitted for inclusion in the SIP

Statewide condensate tank control regulations that have achieved approximately 

5,600 tpy of VOCs emission reductions – state-only

Statewide existing industrial engine control regulations that are estimated to achieve 

NOx and VOC emissions reductions of approximately 7,100 tpy by 2010 – state-only

PM10 emission reduction programs in PM10 maintenance areas throughout the 

state – In the SIP

Fugitive dust control programs for construction, mining, vehicular traffic, and 

industrial sources state-wide – In the SIP

Smoke management programs for open burning and prescribed fire activities 

statewide – state-only

Renewable energy requirements that are driving current and future NOx, SO2 and 

PM emission reductions from coal-fired power plants - Ballot Initiative 37 – by 

requiring electricity to be obtained from renewable resources – state-only

Attaining and maintaining the PM10 and PM2.5 standards throughout the state 

Reducing Colorado Front Range Urban Visibility Impairment (Denver‟s Brown Cloud)

by 28% between 1991 and 2006) – state-only

Reducing Colorado emissions in the Four Corners area (which is upwind of 

numerous Class I areas in three states) through oil and gas control measures 

administered by the CDPHE and the Colorado Oil and Gas Conservation 

Commission, and by working with the Southern Ute Indian Tribe to develop a Title V 

permitting program and a minor source permitting program – state-only

Federal mobile source tailpipe exhaust reductions of approximately 55,000 tpy of 

VOC and NOx emissions by 2020 – gained through fleet turn-over

(Discussion of state-only measures in this Regional Haze SIP is informational only and 

not intended to make such measures federally enforceable. However, such measures 

could be included in future SIP revisions if found necessary to meet National Ambient 

Air Quality Standards or visibility requirements.)

Another comprehensive review of existing and ongoing programs as well as monitoring 

data and trends is contained in the Colorado Air Quality Control Commission‟s 2008-

2009 Report to the Public available at the following website:

http://www.cdphe.state.co.us/ap/rttplinks.html

As recently as 1995 Colorado had 12 “non-attainment” areas within the state for carbon 

monoxide, ozone, and/or PM10 health standards. Generally, all of these areas now 

maintain good air quality. This progress reflects the effects of local, statewide, regional, 

and national emission control strategies. This clean-up of Colorado‟s non-attainment 

areas also benefited Class I visibility conditions to some unknown degree.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

155

In the summer of 2003, the Denver metropolitan area violated the 8-hour ozone 

standard. EPA designated all or parts of 9 counties in northeastern Colorado as 

nonattainment for the 1997 8-hour ozone standard, though the nonattainment 

designation was deferred with the adoption of the Ozone Action Plan by the Colorado 

Air Quality Control Commission in March 2004 under EPA's Early Action Compact 

provisions. High concentrations of ground-level ozone during the 2005-2007 period put 

the nine-county Denver region in violation of the 1997 standard, and the deferred 

nonattainment designation became effective in November 2007. A detailed plan to 

reduce ozone was adopted by the Colorado Air Quality Control Commission in 

December 2008 and submitted to EPA for approval in 2009. This new plan contains 

additional VOC and NOx emission reduction measures to support achievement of 

compliance with the 1997 ozone standard by the end of 2010.

The table below shows the designation status for all current and former non-attainment 

areas.

Table 9-1 REDESIGNATION and PLAN AMENDMENT STATUS REPORT

PM10 Redesignations Plan Amendments

Aspen AQCC approved 1/11/01; EPA 

approved 5/15/03, effective 7/14/03

10-year update: AQCC approved 

12/16/10

Canon City AQCC approved 10/17/96; EPA 

approved 5/30/00, effective 7/31/00

10-year update: AQCC approved 

11/20/08; Legislature approved 2/15/09; 

submitted to EPA 6/18/2009

Denver AQCC approved 4/19/01; EPA 

approved 9/16/02, effective 10/16/02

Plan amendment developed with 

MOBILE6 to remove I/M from SIP; AQCC 

approved 12/15/05; EPA approved 

11/6/07, effective 1/7/08

Lamar AQCC approved 11/15/01; EPA 

approved 10/25/05, effective 

11/25/05

None

Pagosa 

Springs

AQCC approved 3/16/00; EPA 

approved 6/15/01, effective 8/14/01

10-year update: AQCC approved 

11/19/09; Legislature approved 2/15/10; 

submitted to EPA 3/31/2010

Steamboat 

Springs

AQCC approved 11/15/01; EPA 

approved 10/25/04, effective 

11/24/04

Telluride AQCC approved 3/16/00; EPA 

approved 6/15/01, effective 8/14/01

10-year update: AQCC approved 

11/19/09; Legislature approved 2/15/10; 

submitted to EPA 3/31/2010
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

156

Carbon 

Monoxide Redesignations Plan Amendments

Colorado 

Springs

AQCC approved 1/15/98; EPA 

approved 8/25/99, effective 9/24/99

- Amendment to drop oxyfuels approved 

by AQCC 2/17/00; EPA approved 

12/22/00, effective 2/20/01

- Amendment using MOBILE6 to 

eliminate I/M from SIP and revise 

emission budget approved by AQCC 

12/18/03; EPA approved 9/07/04, 

effective 11/08/04

- 10-year update: AQCC approved 

12/17/09; Legislature approved 2/15/10; 

submitted to EPA 3/31/2010

Denver AQCC approved 1/10/00; EPA 

approved 12/14/01, effective 1/14/02

- Amendment using MOBILE6 to revise 

emission budgets approved by AQCC 

6/19/03; EPA approved 9/16/04, effective 

11/15/04

- Amendment developed with MOBILE6 

to remove I/M & oxyfuels from SIP; 

AQCC approved 12/15/05; EPA approved 

8/17/07, effective 10/16/08

Ft. Collins AQCC approved 7/18/02; EPA 

approved 7/22/03, effective 9/22/03

10-year update: AQCC approved 

12/16/10

Greeley AQCC approved 9/19/96; EPA 

approved 3/10/99, effective 5/10/99

- Amendment using MOBILE6 to revise 

emission budget & to eliminate oxyfuels 

from the regulation/SIP & I/M from the 

SIP approved by AQCC 12/19/02; EPA 

approved 8/19/05, effective 9/19/05

- 10-year update: AQCC approved 

12/17/09; Legislature approved 2/15/10; 

submitted to EPA 3/31/2010

Longmont AQCC approved 12/19/97; EPA 

approved 9/24/99, effective 11/23/99

- Amendment using MOBILE6 to revise 

emission budget approved by AQCC 

12/18/03; EPA approved 9/30/04, 

effective 11/29/04

- Amendment developed with MOBILE6 

to remove I/M & oxyfuels from SIP; 

AQCC approved 12/15/05; EPA approved 

8/17/07, effective 10/16/08
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

157

Ozone Redesignations Plan Amendments

Denver/Nort

hern Front 

Range

AQCC approved 1-hour 

redesignation request and 

maintenance plan 1/11/01; EPA 

approved 9/11/01, effective 10/11/01

Early Action Compact 8-hour Ozone 

Action Plan approved by AQCC 

3/12/04; EPA approved 8/19/05, 

effective 9/19/05

- 8-hour OAP updated to include periodic 

assessments; AQCC approved 12/15/05; 

EPA approved //0, effective //0

- 8-hour OAP updated 12/17/06 by AQCC 

to incorporate Reg. 7‟s 75% oil and gas 

condensate tank requirements. EPA 

approved 2/13/08, effective 4/14/08

- Due to 2005-2007 ozone values, Front 

Range has violated the ozone standard 

and the nonattainment designation 

became effective 11/20/07; revised 

attainment plan approved by AQCC 

12/11/08; Legislature approved 2/15/09; 

submitted to EPA 6/18/2009

Lead Redesignations Plan Amendments

Denver EPA redesignated Denver 

attainment in 1984

Nitrogen 

Dioxide Redesignations Plan Amendments

Denver EPA redesignated Denver 

attainment in 1984

For larger stationary sources, the state of Colorado considers its New Source Review 

and Prevention of Significant Deterioration (PSD) programs as being protective of 

visibility impairment from proposed major stationary sources or major modifications to 

existing facilities.

9.4.6 Measures to Mitigate the Impacts of Construction Activities

Regulations 1 and 3 are currently part of Colorado‟s EPA-approved SIP and apply 

statewide. In part, provisions of Regulation 1 address emissions of particulate matter, 

from construction activities. Provisions of Regulation 3 cover issuance of permits 

applicable to sources defined in these regulations and air pollution emission notices 

required of specified sources. Provisions of Regulation 1, sections III.D.2.b apply to new 

and existing point and area sources. This section of the regulation addresses fugitive 

particulate emissions from construction activities. As such the state believes these 

regulations address common construction activities including storage and handling of 

materials, mining, haul roads and trucks, tailings piles and ponds, demolition and 

blasting activities, sandblasting, and animal confinement operations.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

158

Colorado believes point and area sources of emissions from these regulated sources 

are in part contributing to regional haze in Colorado. Colorado relies on the particulate 

emission controls specified in Regulation 1 to most directly address these sources of 

fine and course particles known to have a minor, but measured, impact on visibility in 

Class I areas of the state. Based on Coarse Mass Emissions Trace Analysis, described 

in Section 8 of the Technical Support Document for each Mandatory Class I Federal 

Area in Colorado included in this SIP, the greatest impact from coarse mass related 

construction in the state is expected in Rocky Mountain National Park. In RMNP slightly 

over 6% of the total impact on visibility on the 20% worst days is attributed to coarse 

mass particulate matter from construction activities. All other Class I areas have 

impacts from construction in the 2 to 3 percent range.

This regulatory provision requires applicable new and existing sources to limit emissions 

and implement a fugitive emission control plan. Various factors are specified in the 

regulation under which consideration in the control plan encompasses economic and 

technological reasonability of the control.

9.4.7 Smoke Management

For open burning and prescribed fire, Colorado believes its smoke management 

program reduces smoke emissions through emission reduction techniques and is 

protective of public health and welfare as well as Class I visibility.

Regulation No. 9 (Open Burning, Prescribed Fire, and Permitting) is the main vehicle in 

Colorado for addressing smoke management and preventing unacceptable smoke 

impacts. The rule applies to all open burning activity within Colorado, with certain 

exceptions. Section III specifically exempts agricultural open burning from the permit 

requirement45. Section III.A of the regulation requires anyone seeking to conduct open 

burning to obtain a permit from the Division. Regulation No. 9 also contains a number of 

factors the Division must consider in determining whether and, if so, under what 

conditions, a permit may be granted. Many of these factors relate to potential visibility 

impacts in Class I areas. A permit is granted only if the Division is reasonably certain 

that under the permit‟s conditions that include the prescribed meteorological conditions 

for the burn there will be no unacceptable air pollution (including visibility) impacts. 

Colorado‟s program also maintains an active compliance assistance and enforcement 

component. In 2005, the Division certified its smoke management program as 

consistent with EPA‟s Interim Air Quality Policy on Wildland Prescribed Fire, May 1998. 

Factors considered under Regulation No. 9, include, for example,

the potential contribution of such burning to air pollution in the area;

the meteorological conditions on the day or days of the proposed burning;

the location of the proposed burn and smoke-sensitive areas and Class I areas 

that might be impacted by the smoke and emissions from the burn;

 

45 The Division has determined that agricultural burning is not a significant source of emissions related to 

regional haze impairment. For example, 2004 estimates from the Division are that only 503 tpy of PM10 

were generated from agricultural burning in the entire State of Colorado. See TSD “Agricultural Burning in 

Colorado, 2003 and 2004 Inventories”.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

159

whether the applicant will conduct the burn in accordance with a smoke 

management plan or narrative that requires:

o that best smoke management methods will be used to minimize or 

eliminate smoke impacts at smoke-sensitive receptors (including Class I 

areas);

o that the burn will be scheduled outside times of significant visitor use in 

smoke-sensitive receptor areas that may be impacted by smoke and 

emissions from the fire; and

a monitoring plan to allow appropriate evaluation of smoke impacts at smokesensitive receptors.

The regulation requires all prescribed fire permitees to submit an application to the 

Division. A permit is granted only if the Division‟s assessment demonstrates that under 

the prescribed meteorological conditions for the burn there will be no unacceptable air 

pollution (including visibility) impacts. The Division reviews each permit application and 

determines if the burn can be conducted without causing unacceptable visibility impacts 

within Class I areas, as well as other smoke sensitive sites. In addition, the regulation 

provides for the Division to impose “permit conditions necessary to ensure that the burn 

will be conducted so as to minimize the impacts of the fire on visibility and on public 

health and welfare.” 

Permitted sources are also required to report actual activity to the Division. Depending 

on the size and type of fire, reporting may be a daily requirement. At a minimum, each 

year all permitted sources must return their permit forms with information indicating 

whether or not there was any activity in the area covered by the permit and, if so, how 

many acres were burned. The Division annually prepares a report on prescribed 

burning activity and estimated emissions. Reports from 1990 through 2009 are 

available by contacting the Division.

The regulation requires the draft permit for any proposed prescribed fire rated as having 

a “high” smoke risk rating be subject to a 30-day public comment period. The notice for 

the public comment period must contain information relating to the potential air quality 

and visibility impacts at smoke sensitive receptors, including Class I areas.

The Division‟s web site contains information about various aspects of Colorado‟s Smoke 

Management Program, downloadable forms and instructions, and links. It is also used 

to contain the notices for public comment periods for the draft permits subject to public 

comment. It is located at: http://www.cdphe.state.co.us/ap/smoke/

The addition of the Fire Emissions Tracking System (FETS) allows Colorado to input fire 

emission data into the national tracking system thereby adding more precise information 

for future inventories and studies. The state commits in this SIP to continue 

administration of Regulation 9 as part of this LTS, and to input data into the FETS as 

long as it is operational. Colorado will continue as part of Regulation 9 to maintain a 

data base of fire related permits and actions - the basis for data entered into the FETS.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

160

9.4.8 Emission Limitations and Schedules for Compliance to Achieve the 

Reasonable Progress Goal, and Enforceability of Emission Limitations and 

Control Measures

The emission limitations and compliance schedules for those sources specifically 

identified for control in this Regional Haze SIP can be found in Chapters 6 and 8, and 

Regulation Nos. 3 and 7. Enforceability of the requirements is ensured by codifying 

these requirements in regulation, inspecting the sources for compliance and initiating 

enforcement action under EPA-approved compliance regimes, and requiring monitoring, 

recordkeeping and reporting.

9.4.9 Source Retirement and Replacement Schedules

Source retirement and replacement schedules for those sources specifically identified 

for control in this Regional Haze SIP can be found in Chapters 6 and 8, and in 

Regulation No. 3. Unless otherwise indicated in those chapters or in Regulation No. 3, 

the state assumes that all other stationary sources will remain in operation through the 

end of this planning period. For mobile sources, the turnover of the fleet from older, 

higher-emitting vehicles to newer, lower-emitting vehicles is captured in the emission 

inventory presented in Chapter 5 – the fleet turn-over rate was developed utilizing EPAapproved methodologies. 

9.4.10 Anticipated Net Effect on Visibility

The WRAP has produced extensive analytical results from air quality monitoring, 

emissions inventories and air quality modeling. These data demonstrate that causes of 

regional haze in the West are due to emissions from a wide variety of anthropogenic 

and natural sources, some of which are controllable, some of which are natural, and 

some of which originate outside the jurisdiction of any state or the federal government 

and are uncontrollable. Analyses to date consistently show that anthropogenic 

emissions of haze causing pollutants will decline significantly across the West through 

2018, but overall visibility benefits of these reductions will be tempered by emissions 

from natural, international, and uncontrollable sources.

Colorado in this RH SIP addresses projections to 2018 anticipating growth and all 

committed to or reasonably expected controls at the time of modeling (emission 

inventories for Colorado are presented in Chapter 5). Note that at the time of this 2009 

WRAP modeling, Colorado had made BART determinations for each subject to BART 

unit in 2007 and 2008, and the associated emission reductions were included in the 

modeling. The inventories indicate a total SO2 emission reduction of 58,907 tons per 

year and a total NOx emission reduction of 123,497 tons per year by 2018. (SO2 and 

NOx are the primary emissions addressed by Colorado in this Regional Haze SIP.)

For the uniform rate of progress analysis and to establish Reasonable Progress Goal 

(RPGs), the modeling results from Chapter 7 are utilized. The modeled Uniform Rate of 

Progress and the progress made towards URP are presented below. Depending on the 

Class I area, the state has achieved 36 to 76 percent of the visibility improvement 

necessary to achieve URP. Note that this analysis does not include emission 

reductions that result from the BART and RP determinations presented in Chapters 6 

and 8.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

161

Figure 9-2 Summary of CMAQ Modeling Progress Towards 2018 URP

The total tons of visibility impairing pollutants reduced by 2018 due to the BART and RP 

measures adopted in 2010 are summarized below in Figures 9-4, 9-5 and 9-6.

2010 BART: 20,734 tons/year

2010 BART alternative: 37,488 tons/year

2010 RP: 12,624 tons/year

Total: 70,846 tons/year

The following figures also present “CALPUFF” modeling results that show the visibility 

benefits of each BART and RP determination. Though not additive to the visibility 

improvement values presented in Figure 9-2 above because different modeling 

platforms were used, the CALPUFF modeling illustrates that additional visibility 

improvement can be anticipated from the BART and RP controls.

Projected 

Amount of 

Progress by 

2018 Towards 

URP

Uniform 

Rate of 

Progress 

for 2018
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

162

Figure 9-3 Emission Reductions Achieved by 2010 BART Determinations
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

163

Figure 9-4 Emission Reductions Achieved by 2010 BART Alternative 

Determinations

Facility

NOx 

Emissions 

Average 

2006-2008 

(tpy)

NOx 

Emissions 

from 

Alternative 

(TPY)

Total NOx 

Emissions 

Reduced

(TPY)

SO2 

Emissions 

Average 

2006 -2008 

(tpy)

SO2 

Emissions 

from 

Alternative 

(TPY)

Total SO2 

Emissions 

Reduced

(TPY)

Arapahoe

Unit 3 1,770 0 925 0

Unit 4 1,148 90046 1,765 1.28

Cherokee

Unit 1 1,556 0 2,221 0

Unit 2 2,895 0 1,888 0

Unit 3 1,866 0 743 0

Unit 4 4,274 2,06347 2,135 7.81

48

Valmont 2,314 0 758 0

Pawnee 4,538 1,40349 13,472 2,40650

Totals 20,361 4,366 15,995 23,908 2,415 21,493

Total Emission Reductions Achieved: 37,488 tons per year

 

46 Includes 300 tpy NOx for offset or netting purposes and 600 tpy NOx from firing Arapahoe 4 on natural 

gas as a peaking unit.

47 Includes 500 NOx tpy for offset or netting purposes and emissions at 0.12 lb NOx/MMBtu

48 Emissions at 0.0006 lb SO2/MMBtu

49 Emissions at 0.07 lb NOx/MMBtu

50 Emissions at 0.12 lb SO2/MMBtu
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

164

Figure 9-5 Emission Reductions Achieved by 2010 RP Determinations

Of these 70,800 tons of SO2 and NOx reduced due to 2010 BART and RP, 

approximately 44,500 tons per year were not included in the WRAP‟s 2009 “CMAQ” 

modeling. Figure 9-6 below presents this analysis for each of the BART and RP 

sources.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

165

Figure 9-6 Difference Between the WRAP and Final BART/RP Emissions for 

NOx and SO2

These substantial additional emission reductions will further the amount of progress 

achieved by 2018.

Colorado believes the combination of WRAP‟s CMAQ modeling and the Division‟s 

BART and RP modeling adequately demonstrate the anticipated net positive visibility 

benefit or improvement for this SIP. Although the state of Colorado makes no 

commitment to produce comprehensive RH modeling unless resources are available 

and there is a need for such analysis (e.g., through the WRAP), it is anticipated in the 

five year review required by the RH rule and committed to in this SIP that additional 

regional CMAQ modeling will be done to evaluate compliance with the Reasonable 

Progress Goals for all the western states.

9.5 Reasonable Progress Goals

Based on the requirements of the Regional Haze Rule, 40 CFR 51.308(d)(1), the state 

must establish goals, for each Class I area in Colorado (expressed in deciviews) that 

provide for Reasonable Progress (RP) towards achieving natural visibility conditions in 

2018 and to 2064. The reasonable progress goals (RPGs) must provide for 

improvement in visibility for the most-impaired (20% worst) days over the period of the 

State Implementation Plan (SIP) and ensure no degradation in visibility for the leastimpaired (20% best) days over the same period.

Colorado is relying on the Western Regional Air Partnership‟s (WRAP‟s) CMAQ regional 

modeling performed in 2009 to establish these goals. As stated throughout this chapter, 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

166

all western states‟ reasonably foreseeable control measures at the time of modeling 

were included in the projections of 2018 visibility levels. Colorado determines that the 

2018 projections represent significant visibility improvement and reasonable progress 

upon the state‟s consideration of the statutory factors, and are the RPGs for each Class 

I area. Figure 9-7 presents these RPGs.

Figure 9-7 Reasonable Progress Goals for Each Class I Area

As required, each Class I area must 1) make improvement in visibility for the mostimpaired (20% worst) days over the period ending in 2018, and 2) allow no degradation 

in visibility for the least-impaired (20% best) days. This is demonstrated in Figure 9-5. 

As stated above in section 9.4.10, these goals reflect the emissions reductions achieved 

throughout Colorado (as reflected in the Chapter 5 inventories) and the nation. The 

additional emissions reductions from the BART and RP determinations will increase the 

amount of progress achieved by 2018.

In establishing the RPGs, the state considered the required four factors as per EPA 

regulations: (1) the costs of compliance; (2) the time necessary for compliance; (3) the 

energy and non-air quality environmental impacts of compliance; and (4) the remaining 

useful life of any potentially affected sources. Colorado describes in Chapter 8 how the 

four factors were used to select significant sources/source categories not already 

covered by BART or federal measures for control evaluation. The evaluations resulted 

No 

Degradation of 

Visibility for 

the Best Days

Reasonable 

Progress 

Goals for 

2018
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

167

in substantial emission reductions that build on the reductions already achieved by other 

measures.

Although the state used the four factors to determine reasonable and appropriate 

emission controls for subject facilities, Figure 9-7 illustrates that the RPGs do not 

achieve URP. The state realizes additional emissions reductions from both within and 

outside of the state are necessary to achieve URP. The state finds that the RPGs 

established in this SIP are reasonable for this planning period and that achieving URP 

in this planning period is not reasonable. In this SIP, Colorado has described, based 

upon its consideration of the statutory factors, why certain controls for specified BART 

and RP sources are reasonable, and why additional controls during this planning period 

are not reasonable. Similarly, the state has described why additional controls for certain 

area sources (such as oil and gas heater treaters and lean burn RICE engines) are not 

reasonable in this planning period. The emission reductions needed to achieve URP at 

each Class I area for this planning period cannot be determined with precision, due to 

limitations in calculating and modeling all of the visibility-impairing emissions. In the first 

5-year assessment, the state commits to begin evaluating this shortfall, first accounting 

for the degree of additional emission reductions achieved in Colorado and in other 

states that are not included in the modeling, and then assessing the inventory and 

modeling technical issues. 

Because RPGs are not achieving URP by 2018 and natural conditions by 2064, 

Colorado is required by the Regional Haze rule to re-calculate and state the length of 

time necessary to achieve natural conditions, as shown below and presented in Figure 

9-8. Instead of achieving natural conditions in 2064 (60 years) at all Class I areas, the 

year and the length of time is re-calculated as follows:

Sand Dunes: 2152 (148 years)

Mesa Verde: 2168 (164 years)

Zirkel & Rawah: 2106 (102 years)

Rocky Mountain: 2098 (94 years)

Black Canyon, Weminuche, & La Garita: 2119 (115 years)

Eagles Nest, Flat Tops, Maroon Bells & West Elk: 2083 (79 years)

The recalculated natural conditions timeline is based upon progress through 2018, 

though, as described above, the calculations do not consider the emission control 

requirements adopted by the state in 2010 and presented in Chapters 6 and 8. The four 

factors were used to evaluate significant sources of SO2, NOx (and PM from stationary 

sources) only as the state also determined that it was not reasonable to evaluate 

sources organic carbon, elemental carbon and particulate matter for control during this 

planning period. Thus, all reasonable control measures are presented in this SIP and it 

is acceptable under the Regional Haze rule that natural conditions are projected to be 

achieved beyond 2064.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

168

Figure 9-8 Re-Calculation of the Length of Time Necessary to Achieve Natural 

Conditions

The following figures for Mesa Verde National Park illustrate the re-calculations.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

169

Figure 9-9 Current Uniform Rate of Progress Glidepath for Mesa Verde and the 

Reasonable Progress Goal for 2018

Figure 9-10 Revised Glidepath for Mesa Verde Illustrating the Number of Years to 

Achieve Natural Conditions 
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

170

Chapter 10 Commitment to Consultation, Progress Reports, 

Periodic Evaluations of Plan Adequacy, and Future 

SIP Revisions

10.1 Future Consultation Commitments

10.1.1 FLM Consultation

As required by 40 CFR 51.308(i)(4), Colorado will continue to consult with the FLM on 

the implementation of the visibility protection program: and the following items

1. Colorado will provide the FLM an opportunity to review and comment on SIP 

revisions, the five-year progress reports, and other developing programs that may 

contribute to Class I visibility impairment. This report will include: 

a. Implementation of emission reduction strategies identified in the SIP as 

contributing to achieving improvement of worst-day visibility;

b. Summary of major new source permits issued;

c. Any changes to the monitoring strategy or monitoring stations that may 

affect tracking reasonable progress;

d. Work underway in preparing the five and ten year reviews

2. Colorado will afford the FLM with an opportunity for consultation in person and at 

least 60 days prior to holding any public hearing on a SIP revision. The FLM 

consultation must include the opportunity to discuss their assessment of visibility 

impairment in each federal Class I area; and to provide recommendations on the 

reasonable progress goals and on the development and implementation of the 

visibility control strategies. Colorado will include a summary of how it addressed 

the FLM comments in the revised RH SIP.

10.1.2 Tribal Consultation

Colorado will continue to remain in contact with those Tribes which may reasonably be 

anticipated to cause or contribute to visibility impairment in Colorado mandatory Class I 

Federal area(s). For those Tribes that adopted a RH TIP, Colorado will consult with 

them directly. For those Tribes without a RH TIP, Colorado will consult with both the 

Tribe and EPA. Documentation of the consultation will be maintained.

10.1.3 Inter-state Consultation/Coordination

In accordance with 40 CFR 51.308(d)(1)(iv) and 51.308(d)(3)(i), Colorado commits to 

continue consultation with Arizona, Nebraska, Kansas, Wyoming, New Mexico, Utah, 

and California, and any other state which may reasonably be anticipated to cause or 

contribute to visibility impairment in federal Class I areas located within Colorado. 

Colorado will also continue consultation with any state for which Colorado‟s emissions 

may reasonable be anticipated to cause or contribute to visibility impairment in those 

state‟s federal Class I areas.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

171

With regards to the established or updated goal for reasonable progress, should 

disagreement arise between another state or group of states, Colorado will describe the 

actions taken to resolve the disagreement in future RH SIP revisions for EPA‟s 

consideration. With regards to assessing or updating long-term strategies, Colorado 

commits to coordinate its emission management strategies with affected states and will 

continue to include in its future RH SIP revisions all measures necessary to obtain its 

share of emissions reductions for meeting progress goals.

10.1.4 Regional Planning Coordination

As per the requirements of [51.308(c)(1)(i)],Colorado commits to continued participation 

with one or more other States in a planning process for the development of future RH 

SIP revisions. Future plans will include:

1. Showing of inter-state visibility impairment in federal Class I areas based on 

available inventory, monitoring, or modeling information as per the requirements of 

[51.308(c)(1)(ii)].

2. Description of the regional planning process, including the list of states, which have 

agreed to work with Colorado to address regional haze, the goals, objectives, 

management, decision making structure for the regional planning group, deadlines 

for completing significant technical analyses and developing emission 

management strategies, and a schedule for State review and adoption of 

regulations implementing the recommendations of the regional group as per the 

requirements of ; [51.308(c)(1)(iii)].

4. Address fully the recommendations of WRAP, including Colorado‟s apportionment 

of emission reduction obligations as agreed upon through WRAP and the resulting 

control measures required [51.308(c)(1)(iv) and 51.308(d)(3)(ii)].

10.2 Commitment to Progress Reports

40 CFR 51.308(g), requires a State/Tribe to submit a progress report to EPA every five 

years evaluating progress towards the reasonable progress goal(s). The first progress 

report is due five years from the submittal of the initial implementation plan and must be 

in the form of an implementation plan revision that complies with Sections 51.102 and 

51.103. At a minimum, the progress reports must contain the elements in paragraphs 

51.308(g)(1) through (7) for each Class I area as summarized below.

1. Status of implementation of the RFP SIP measures for CIAs in Colorado and those 

outside the State identified as being impacted by emissions from within the state

2. Summary of emissions reductions in Colorado adopted or identified as part of the 

RFP strategy
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

172

3. A five year annual average assessment of the most and least impaired days for 

each CIA in Colorado including the current visibility conditions, difference between 

current conditions and baseline and change in visibility impairment over the five 

year period

4. Analysis, by type of source or activity of pollutant emission changes or activities

over the five year period from all sources contributing to visibility impairment in 

Colorado, based on the most recent EI with estimates projected forward as 

necessary to account for changes in the applicable five year period

5. Assessment of significant changes in anthropogenic emissions in or out of 

Colorado in the applicable five years which limited or impeded RFP;

6. Assessment of the current SIP sufficiency to meet reasonable progress goals both 

in Colorado and other States CIA identified as being significantly impacted by 

Colorado emissions 

7. Assessment of Colorado‟s visibility monitoring strategy and modifications of the 

strategy as necessary.

In accordance with the requirements listed in Section 51.308(g) of the federal regional 

haze rule, Colorado commits to submitting a report on reasonable progress to EPA 

every five years following the initial submittal of the SIP. That report will be in the form of 

an implementation plan revision. The reasonable progress report will evaluate the 

progress made towards the reasonable progress goal for each mandatory Class I area 

located within Colorado and in each mandatory Class I area located outside Colorado, 

which have been identified as being affected by emissions from Colorado.

The State will also evaluate the monitoring strategy adequacy in assessing reasonable 

progress goals.

10.3 Determination of Current Plan Adequacy

Based on the findings of the five-year progress report, 40 CFR 51.308(h) requires a 

State to make a determination of adequacy of the current implementation plan. The 

State must take one or more of the actions listed in 40 CFR 51. 308(h)(1) through (4) 

that are applicable. These actions are described below and must be taken at the same 

time the State is required to submit a five-year progress report.

1. If the State finds that no substantive SIP revisions are required to meet established 

visibility goals and emissions reductions, the State will provide a negative 

declaration that no implementation plan revision is needed.

2. If the State finds the implementation plan is, or may be, inadequate to ensure 

reasonable progress due to emissions from outside the State, the State shall notify 

EPA and the other contributing state(s) or tribe(s). The plan deficiency shall be 

addressed through a regional planning process in developing additional strategies 

with the planning efforts described in the progress report(s).

3. If the State finds the implementation plan is, or may be, inadequate to ensure 

reasonable progress due to emissions from another country, the State shall notify 

EPA and provide the available supporting information.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

173

4. If the State finds the implementation plan is, or may be, inadequate to ensure 

reasonable progress due to emissions from within the State, the State shall revise 

the plan to address the deficiency within a year.

Colorado commits, in accordance with 40 CFR 51.308(h), to make an adequacy 

determination of the current SIP at the same time a five-year progress report is due. 

10.4 Commitment to Comprehensive SIP Revisions

In addition to SIP revisions made for plan adequacy as specified in Section 10.3 of this 

plan, 40 CFR 51.308(f)(1-3)requires a State to revise and submit its regional haze 

implementation plan to EPA by July 31, 2018, and every ten years thereafter. Colorado 

commits to providing this revision and to evaluate and reassess elements under 40 CFR 

51.308(d) taking into account improvements in monitoring data collection and analysis, 

and control technologies. Elements of the future plans are summarized below.

10.4.1 Current Visibility Conditions

Colorado commits to determine and report current visibility conditions for the most and

least impaired days using themost recent five year period for which data is available and

to determine the actual progress made towards natural conditions. Current visibility 

conditions will be calculated based on the annual average level of visibility impairment.

10.4.2 Long Term Strategy Effectiveness

Colorado commits to determine the effectiveness of the long-term strategy for achieving 

reasonable progress goals over the prior implementation period(s) and to affirm or 

revise the RPG and monitoring strategy as specified in 10.4.3 and 10.4.4 of this section.

10.4.3 Affirmation of or Revisions to Reasonable Progress Goals

As part of this comprehensive SIP update and future ten year revisions, Colorado 

commits to affirm or revise the reasonable progress goals in accordance with the 

procedures set forth in 40 CFR 51.308(d)(1). For any goal which provided a slower rate 

of progress than needed to attain natural conditions by the year 2064, Colorado will 

perform the analysis of additional measures that could be adopted to achieve the 

degree of visibility improvement projected by the analysis contained in the initial 

implementation plan. This analysis of additional measures will be performed in 

accordance with the procedures set forth in 40 CFR 51.308(d)(1)(A) to include a 

consideration of the costs of compliance, energy and non-air quality environmental 

impacts of compliance, and the remaining useful life of any potentially affected sources, 

and a demonstration showing how these factors were taken into consideration in 

selecting the goal.

1. Colorado commits, in accordance with 40 CFR 51.308(d)(1)(B), to analyze and 

determine the rate of progress needed to attain natural conditions by the year 

2064 comparing baseline visibility to natural visibility conditions in each CIA 

considering the uniform rate of improvement and emission reduction measures 

needed to achieve RFP.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

174

2. As per 40 CFR 51.308(d)(1)(B)(ii) if Colorado establishes a RPG with a slower 

rate of progress than needed to attain natural conditions by 2064, Colorado will 

demonstrate, based on the factors listed in this section 10.4.3, the rate of 

progress is unreasonable and the established goal is reasonable. Colorado will 

provide for a public review, as part of the implementation plan revision in 2018, 

an assessment of the number of years it will take to attain natural conditions 

based on the RPG. 

3. As per 40 CFR 51.308(d)(1(B)(iv) Colorado will consult with States reasonably 

anticipated to cause or contribute to visibility impairment in the mandatory Class I 

Federal areas and where Colorado or another State cannot agree a RPG is 

appropriate, Colorado will describe, in the SIP submittal of 2018, actions taken to 

resolve disagreements.
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

175

Chapter 11 Resource and Reference Documents

There are a substantial number of documents that are referenced in this SIP and form 

the detailed technical basis for the proceeding Chapters. This Chapter is not the full 

Technical Support Document. It is a catalog of references used in the preparation of this 

SIP revision. The full Technical Support Document will be on the Air Pollution Control 

Division web site at http://www.cdphe.state.co.us/ap/regionalhaze.html

11.1 Class I Area Technical Support Documents (TSDs) TSDs are a comprehensive 

technical summary for each Class I area in Colorado. The individual Class I area TSDs

includes sections describing the Class I area; visibility monitoring; visibility conditions; 

haze impacting particles; emission source characterization; regional modeling; and PM 

source apportionment. Included in each TSD is the PSAT Modeling showing estimated 

source category impacts on Class I areas. Titles include:

Colorado State Implementation Plan for Regional Haze Technical Support 

Document – Black Canyon of the Gunnison National Park, Colorado Dept. of Public 

Health and Environment, Air Pollution Control Division, October 2007

Colorado State Implementation Plan for Regional Haze Technical Support 

Document –Eagles Nest Wilderness Area, Colorado Dept. of Public Health and 

Environment, Air Pollution Control Division, October 2007

Colorado State Implementation Plan for Regional Haze Technical Support 

Document –Flat Tops Wilderness Area, Colorado Dept. of Public Health and 

Environment, Air Pollution Control Division, October 2007

Colorado State Implementation Plan for Regional Haze Technical Support 

Document –La Garita Wilderness Area, Colorado Dept. of Public Health and 

Environment, Air Pollution Control Division, October 2007

Colorado State Implementation Plan for Regional Haze Technical Support 

Document – Maroon Bells Wilderness Area, Colorado Dept. of Public Health and 

Environment, Air Pollution Control Division, October 2007

Colorado State Implementation Plan for Regional Haze Technical Support 

Document –Mesa Verde National Park, Colorado Dept. of Public Health and 

Environment, Air Pollution Control Division, October 2007

Colorado State Implementation Plan for Regional Haze Technical Support 

Document –Mount Zirkel Wilderness Area, Colorado Dept. of Public Health and 

Environment, Air Pollution Control Division, October 2007

Colorado State Implementation Plan for Regional Haze Technical Support 

Document –Rocky Mountain National Park, Colorado Dept. of Public Health and 

Environment, Air Pollution Control Division, October 2007

Colorado State Implementation Plan for Regional Haze Technical Support 

Document –Rawah Wilderness Area, Colorado Dept. of Public Health and 

Environment, Air Pollution Control Division, October 2007
Colorado Visibility and Regional Haze State Implementation Plan for 12 Mandatory Class I Federal Areas

Colorado Dept. of Public Health and Environment, Air Pollution Control Division

Approved January 7, 2011

176

Colorado State Implementation Plan for Regional Haze Technical Support 

Document –Sand Dunes National Park, Colorado Dept. of Public Health and 

Environment, Air Pollution Control Division, October 2007

Colorado State Implementation Plan for Regional Haze Technical Support 

Document – Weminuche Wilderness Area, Colorado Dept. of Public Health and 

Environment, Air Pollution Control Division, October 2007

Colorado State Implementation Plan for Regional Haze Technical Support 

Document –West Elk Wilderness Area, Colorado Dept. of Public Health and 

Environment, Air Pollution Control Division, October 2007

11.2 Other Technical Support Documents In addition to the Class I area-specific TSDs, two 

other technical support documents have been developed. One for the IMPROVE lookalike monitors at Douglas Pass and Ripple Creek and another for agricultural burning in 

Colorado. Titles are:

Colorado State Implementation Plan for Regional Haze Technical Support 

Document –Douglas Pass and Ripple Creek Pass Sites, Colorado Dept. of Public 

Health and Environment, Air Pollution Control Division, June 2007

Colorado State Implementation Plan for Regional Haze Technical Support 

Document –Agricultural Burning in Colorado 2003-4 Inventory, Colorado Dept. of 

Public Health and Environment, Air Pollution Control Division, July 2007

Colorado State Implementation Plan for Regional Haze. Technical Support 

Document, Analysis of Colorado Visibility Impacts on Nearby Class I Areas, 

Colorado Dept. of Public Health and Environment, Air Pollution Control Division, 

March 2007

11.3 Long-Term Strategy Review Update In 2004, the State adopted this SIP revision in 

order to update the LTS. This SIP revision is intended to amend the 2002 LTS portion of 

the Class I Visibility SIP. This document is titled:

Long-Term Strategy Review and Revision of Colorado’s State Implementation Plan 

for Class I Visibility Protection Part II Revision of the Long-Term Strategy, Colorado 

Department of Public Health and Environment, Air Pollution Control Division, 

November 2004

List of Appendices –

Appendix A –Periodic Review of Colorado RAVI Long Term Strategy

Appendix B –SIP Revision for RAVI Long Term Strategy

Appendix C – Technical Support for the BART Determinations

Appendix D – Technical Support for the Reasonable Progress Determinations