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1.0 INTRODUCTION 

On 6 July 2005, the U.S. Environmental Protection Agency (EPA) published final amendments 

to its 1999 Regional Haze Rule (RHR) in the Federal Register, including Appendix Y, the final 

guidance for Best Available Retrofit Technology (BART) determinations (70 FR 39104-39172). The 

rule applies to any BART-eligible source that ‘‘emits any air pollutant which may reasonably be 

anticipated to cause or contribute to any impairment of visibility” in any mandatory Class I federal area 

(Figures 1-1 through 1-4). States retain the authority to exempt certain BART-eligible sources based 

on dispersion modeling demonstrating that the source cannot reasonably be anticipated to cause or 

contribute to visibility impairment in a Class I area. States also have the authority to define the 

modeling procedures used to establish BART emissions limits on those sources for which controls are 

required. To assist the states, the EPA has offered guidelines for how BART modeling should be 

conducted (EPA, 2005). Although the Federal regulations implementing the BART requirement afford 

States latitude in establishing criteria for BART-exemptions and for determining levels of BART 

controls required on specific sources, the dispersion modeling analyses must either conform to 

established EPA guidance for regulatory modeling or demonstrate, through an acceptable modeling 

protocol, that alternative modeling methods are equally consistent with the overall aim of the RHR. 

States have the responsibility for preparing modeling protocols that describe both the modeling 

analyses for the ‘subject to BART’ test and the visibility improvement analyses as part of the BART 

determination. In developing modeling protocols, states are expected to collaborate with all 

stakeholders including Tribes, EPA, Federal Land Managers (FLMs), Regional Planning Organizations 

(RPOs) and the various source operators. Ultimately, EPA has the authority to approve or disapprove 

a state’s State Implementation Plan (SIP). A flawed BART modeling analysis, including deviations 

from an agreed upon protocol, would be considered in the SIP approval process. 

At least three CENRAP States (Iowa, Minnesota, and Texas) have already developed BART 

modeling protocols: 

> “CALPUFF Modeling Protocol in Support of Best Available Retrofit Technology 

Determinations”, (Johnson, 2005). Prepared by the Iowa Department of Natural 

Resources, Air Quality Bureau, Des Moines, IA 

> “Best Available Retrofit Technology (BART) Modeling Protocol to Determine Sources 

Subject to BART in the State of Minnesota”, (MPCA, 2005), prepared by the Minnesota 

Pollution Control Agency, St. Paul, MN. 

 > “Screening Analysis of Potentially BART-eligible Sources in Texas”, (ENVIRON, 

2005), prepared for the Texas Commission on Air Quality, Austin, TX. 

Protocols may be under development in other States as well. To promote consistency between states in 

the development of BART modeling protocols and to harmonize the approaches between adjacent 

RPOs, CENRAP commissioned the development of the BART Modeling Guidelines set forth in this 

document. These guidelines are intended to assist CENRAP states and source operators in the 

development of state-wide and source-specific modeling protocols specifically tailored to the needs 

and requirements of a given facility and Class I area(s). 

 In addition to the Iowa, Minnesota, and Texas protocols, the states of Colorado (CDPHE, 2005) 

and North Dakota (NDDH, 2005), VISTAS (VISTAS, 2005), the Midwest RPO (Baker, 2005; 
 

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LADCo, 2005) have also developed BART protocols. Since they all address a common subject, there 

is substantial overlap in the discussions of numerous topics such as Federal requirements, EPA 

guidance, CALMET/CALPUFF model descriptions, and recommended modeling procedures. 

Differences among the protocols exist, of course, due to local meteorology, topography, the location of 

Class I areas, the mix of BART-eligible sources, and established modeling procedures within the state, 

local and FLM groups. For consistency in BART modeling applications across the central U.S., in 

preparing these CENRAP Guidelines we have utilized relevant elements of each of these protocols. 

 The VISTAS protocol deserves special mention. It was prepared by members of the VISTAS 

Technical Analysis Work Group led by Ms. Pat Brewer, VISTAS’s Technical Advisor Dr. Ivar 

Tombach and Mr. Joe Scire of Earth Tech, Inc. The VISTAS BART protocol represents the 

culmination of several draft versions and considerable public discussion and input. At least two public 

workshops were convened in the autumn of 2005 to solicit comments and suggestions on draft versions 

and to receive input from EPA and FLM staff on evolving agency guidance. See full comments at: 

http://www.vistas-sesarm.org/BART/BARTComments.asp. Thus, element of the VISTAS protocol, 

reflecting the work of a very large number of organizations, were incorporated as appropriate into the 

CENRAP modeling recommendations.

 The guidelines presented in this document therefore represent the integrated writing efforts of 

many groups, especially the modelers and regulatory decision-makers instrumental in developing the 

VISTAS, MRPO, Iowa, Minnesota, Colorado and North Dakota protocols. 

 

1.1 Overview 

EPA’s BART requirements (70 FR, 39104-39172) are mandatory for electric generation units 

(EGUs) > 750 MW capacity. States are not required to follow the EPA BART guidelines for all 

sources, but are encouraged to apply the guideline concepts to all sources. States have the authority to 

make any or all aspects of the EPA BART guidelines mandatory for all BART determinations. 

Sources are BART-eligible if they meet three specific criteria including (a) emissions of at least 

250 tons per year of a visibility-impairing pollutant, (b) begin operation between 7 August 1962 and 7 

August 1977, and (c) are listed as one of the 26 listed source categories in the guidance. BART 

controls are required for any BART-eligible source that can be reasonably expected to “cause” or 

“contribute” to impairment of visibility in any of the 156 federal parks and wilderness (Class I) areas 

protected under the regional haze rule. Air quality modeling is an important tool available to the States 

in determining whether a source can be reasonably expected to contribute to visibility impairment in a 

Class I area. 

A “BART-eligible emission unit” is defined as any single emission unit that meets the BART 

criteria described above. A “BART-eligible source” is defined as the total of all BART-eligible 

emission units at a single facility. If a source has several emission units, only those that meet the 

BART-eligible criteria are included in the definition “BART-eligible source”. 

1.2. Objectives of These Guidelines 

Overall compliance with RHR visibility improvement goals in the CENRAP region entails four 

phases of visibility modeling: 
 

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> Single-source modeling to determine which BART-eligible sources are ‘subject to 

BART’; 

> Single-source modeling to determine the degree of visibility improvement attributable 

to proposed BART controls for each source subject to BART; 

> Cumulative modeling to determine the combined effect of proposed BART controls for 

sources subject to BART in each CENRAP state; and 

> Regional-scale modeling to determine if the combined effect of proposed BART 

controls for all CENRAP states ultimately satisfy the RHR visibility improvement 

goals. 

The responsibility for the first three modeling analyses belong to the individual states. CENRAP’s 

mandate is to assess the aggregate effects of controls on progress toward attaining the visibility goals 

across the domain. Tables 1-1 and 1-2 identify the Class I areas in and adjacent to the CENRAP 

domain. Figures 1-2 through 1-4 indicate the location of Class I areas by federal land manager. Figure 

1-5 identifies where visibility monitoring is currently occurring in the CENRAP region. 

This document applies only to the first two phases involving single-source modeling (i.e., 

screening to determine which BART-eligible sources are subject to BART, and single-source modeling 

to determine the degree of improvement related to the proposed BART control). The third phase will 

be addressed by the states in their Regional Haze SIPs due in 2008 and will most likely use the same or 

similar full-science modeling tools (CAMx or CMAQ) being used by the various RPOs dealing with 

the fourth phase. Individual CENRAP states will most likely conduct most, if not all, visibility 

modeling to determine which BART-eligible sources are subject to BART. Operators of sources 

determined to be ‘subject to BART’ may wish to conduct their own single-source modeling to 

determine the degree of visibility improvement, as they consider a variety of BART control options. 

The division of BART modeling between state and source operators will likely vary widely across the 

CENRAP states. Ultimately, it is the state’s responsibility to review and verify all single-source 

visibility modeling analyses. Note that all BART modeling for sources in the CENRAP states must 

follow a written and approved protocol either developed by the state for general application or by the 

source operator for a source-specific analysis. Thus, depending upon the state in which they operate, 

BART-eligible sources may or may not have to develop individual protocols. This issue must be 

worked out with the state and cognizant FLM. 

Given the focus on the first two visibility assessment phases, these guidelines focus on 

common procedures for air quality modeling in support of BART determinations, consistent with the 

EPA guidelines and harmonized with the methods employed by other RPOs. (Figure 1-6 depicts this 

process). The guidelines are intended to provide a common understanding among the organizations 

performing or reviewing BART analyses – CENRAP state and local air agencies, EPA, FLMs, source 

operators, and contractors. Each state retains responsibility for the processes and procedures it will 

follow in satisfying the requirements of the RHR. Nothing in the CENRAP process replaces States’ 

responsibility to determine BART controls. Therefore, this document describes suitable BART 

modeling systems and their application to two situations: 

> Air quality modeling to determine whether a BART-eligible source is “subject to 

BART” and therefore the BART analysis process must be applied to its operations. 
 

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 > Air quality modeling of emissions from sources that have been found to be subject to 

BART, to evaluate regional haze benefits of alternative control options and to document 

the benefits of the preferred option. 

These guidelines incorporate EPA final guidance and results of extensive public comments on BART 

modeling procedures recently proposed by several organizations. 

1.3 Overview of Recommended BART Modeling Procedures 

States must determine whether a source in their jurisdiction emits any air pollutant (SO2, NOx, 

PM, VOC) that “may reasonably be anticipated to cause or contribute to any impairment of visibility” 

in a Class I area. EPA identifies three options for the states to consider. First, a state might conclude 

that all BART-eligible sources are subject to BART. Alternatively, a state might demonstrate that all 

BART-eligible sources together do not cause or contribute to any visibility impairment. Finally, a 

state may seek to determine if the impact from each individual BART-eligible source on any day is 

greater than a threshold value. If so, then the source is subject to BART. 

The CENRAP states intend to pursue the third option, utilizing dispersion modeling to calculate 

impacts from individual sources with respect to a prescribed visibility threshold in Class I areas. This 

section discusses how the CALPUFF modeling system can be used to: (a) evaluate whether a BARTeligible source is exempt from BART controls, or to (b) quantify the visibility benefits of control 

options for sources that are determined to be subject to BART. 

 1.3.1 Three BART Modeling Approaches 

The visibility modeling methods described in these guidelines are grouped into three categories: 

 > Screening Modeling: The screening analysis uses the CALPUFF modeling system in 

default mode with pre-prepared modeling domains and model-ready meteorological 

inputs. This simple methodology, described in detail in Chapter 6, is intended to 

quickly distinguish between sources that have no significant impacts on Class I area 

visibility and those sources for which impacts are demonstrable or for which sourcespecific analyses are warranted. 

 > Source-Specific Modeling : A source-specific CALPUFF analysis (the subject of 

Chapter 7) is intended to remove some of the conservatism of the screening approach 

and bring more realism to bear in the analysis of a specific BART-eligible source. Here, 

the state or source operator may elect to introduce greater source specificity into the 

modeling through the use of variable background ammonia, ozone, and visibility levels; 

puff-splitting; finer horizontal grid meshes in the meteorological and air quality 

modeling, and so on. 

 > Alternative Modeling: Refined full-science modeling is available to states or source 

operators on a case-by-case basis. Described in Chapter 8, this entails the application of 

a state-of-the-science regional modeling system and readily available RPO visibility 

data bases for either single source or cumulative source impact assessments. 

For most sources in the CENRAP region, the use of the screening or source-specific approaches will 

satisfy the BART regulatory requirements. Separate chapters of this protocol are devoted to each of 
 

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these BART modeling approaches. Regardless of the approach, exemption modeling is the initial task 

at hand, followed if necessary by visibility impact modeling. 

 1.3.2 Exemption Modeling 

Exemption modeling is intended as a definitive test of whether a source is subject to BART. A 

state and/or source operator may use one or more of three modeling approaches just introduced in 

performing exemption modeling. For most sources, an initial screening assessment with CALPUFF 

should be considered to assess whether a BART-eligible source is subject to BART. As described in 

Chapter 6, a screening CALPUFF dispersion modeling analysis is performed to assess whether a 

particular source is exempt from BART, obviously ‘subject to BART’, or should consider additional 

source-specific modeling analyses to explore further its exemption status. Assumptions for the 

screening assessment are purposefully conservative so that a source that contributes to visibility 

impairment is not inadvertently exempted. If a source is shown not to contribute to visibility 

impairment using the CALPUFF screening assessment, the state may choose to exempt the source 

from BART or to require additional source-specific modeling to confirm it is not subject to BART. 

If a source is shown to contribute to visibility impairment in the screening assessment, the 

source has the option to undertake source-specific CALPUFF modeling to evaluate further whether it 

is subject to BART (see Chapter 7). Source-specific exemption modeling analysis can be used for 

sources that do not pass the screening analysis above or for which a more detailed modeling 

investigation is warranted. These analyses would typically include exercising CALPUFF with finer 

grid resolution (e.g., 1-2 km), more realistic estimates of background pollutant concentrations, sitespecific estimates of background natural visibility conditions, and so on. 

In some circumstances, a state or source operator may wish to apply full-science modeling 

methods to overcome CALPUFF’s inherent limitations (see Chapter 8). For example, sources close to 

Class I areas, sources located in proximity to other large industrial or urban source complexes, or 

sources located great distances from a Class I area may be better treated by a comprehensive fullscience modeling system. If alternative modeling is pursued, the requirements of the modeling protocol 

are increased. An alternative modeling protocol must justify the need for more advanced modeling 

methods, identify the availability of pertinent data sets, address model selection and configuration 

issues, and describe the methods to be used in applying the model to estimate visibility impacts. 

Discussions with state, EPA and FLM representatives should be conducted prior to development of an 

alternative modeling protocol to ensure all of the relevant issues are addressed in the document. 

1.3.3 Modeling the Effects of BART Controls on Visibility 

For sources determined to be ‘subject to BART’, the next step involves estimating the visibility 

benefits of possible BART control measures. These benefits are determined by re-running the 

dispersion model using the screening modeling procedures or more resolved source-specific inputs. A 

key difference from the exemption modeling is that the source terms and/or emissions data are 

modified to reflect the BART control measures being evaluated. The base case to which the 

effectiveness of BART controls is compared is the “current emissions” scenario for which the 

exemption modeling analysis was performed. The post processing steps and procedures are the same. 

Side-by-side comparison of the visibility impacts provides a direct estimate of the effectiveness of each 

control scenario relative to the base case. 
 

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1.3.4 Modeling Protocols 

Regardless of the BART modeling approach (e.g., screening, source-specific, or alternative 

modeling), a formal modeling protocol is required. A modeling protocol should be submitted for all 

modeling demonstrations regardless of the distance from the BART-eligible source to the Class I area. 

The protocol is typically written by the state or the source operator and then reviewed with state, EPA, 

and the FLM. EPA’s role in the development of the protocol is advisory only as the “States better 

understand the BART-eligible source configurations” and factors affecting their particular Class I areas 

(70 FR 39126). 

A protocol consists of many elements but mainly serves as a means for planning and 

communicating how a BART modeling study will be performed before it occurs. Examples of 

required elements in the modeling protocol: 

> The meteorological and terrain data that will be used; 

> The source-specific information (stack height, temperature, exit velocity, elevation, and 

emission rates, speciation and size fractionization of applicable pollutants); and 

> Receptor data from appropriate Class I areas. 

The protocol guides the technical details of a modeling study and provides a formal framework for 

reviewing technical assumptions, operational details, commitments and expectations of the 

participants. It also provides means for resolution of potential differences of technical and policy 

opinion in an open process within prescribed time and budget constraints. 

Modeling protocols all too often fall short of providing sufficient detail in the description of the 

modeling assumptions and procedures to be employed (Roth et al., 2005). To assist the states and 

source operators in development of a protocol specific to a particular facility, protocol templates are 

given in Chapters 6 and 7 containing key elements that should be include in screening and sourcespecific applications, respectively. Of course, each protocol will have some unique features depending 

on the nature of the sources(s) and the Class I area(s) of interest. Also, the requirements for technical 

detail escalate from a screening application to source-specific application and this should be reflected 

in the content of the protocol. 

1.4 Organization of this Document 

The remainder of this document describes available models and data bases and the 

recommended procedures for their application. Chapter 2 reviews EPA’s guidance for regional haze 

BART analysis modeling, as outlined in the 6 July 2005 Federal Register notice. Readers already 

familiar with the BART Rule may wish to skip to Chapter 3 where the CALPUFF model, EPA’s 

preferred tool for BART analyses, is introduced and its characteristics and limitations discussed. 

EPA’s guidance allows for the use of appropriate alternative models and Chapter 4 gives an overview 

of pertinent state-of-science regional photochemical/aerosol models and currently available data bases. 

However, these CENRAP guidelines focus primarily on the application the CALPUFF modeling 

system. Chapter 5 identifies existing data bases developed by CENRAP and others to support BART 

modeling. Then, Chapters 6, 7 and 8 present the three BART modeling approaches. 
 

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Chapter 6 discusses the specific steps needed to determine whether a BART-eligible source is 

subject to BART using the CALPUFF model in the screening mode using pre-compiled regional 

meteorological modeling data sets and CALPUFF run in a conservative mode. Procedures are also 

identified for evaluating the effects of BART controls on those sources that are identified as ‘subject to 

BART. For sources determined to be subject to BART based on screening analyses, additional sourcespecific CALPUFF modeling might be performed as described in Chapter 7. In a limited number of 

cases, it may be appropriate to use a full-science modeling system to develop more accurate estimates 

of a sources’ BART eligibility and/or to assess the effects of BART controls. Chapter 8 discusses the 

applications of state-of-science alternative models for this purpose. For each modeling approach 

described in Chapters 6 through 8, information regarding protocol development is provided as a 

template. Finally, a quality assurance methodology for CALMET/CALPUFF BART modeling is 

outlined in Chapter 9. 

Figure 1-1. Federal Class I Areas in the United States. 
 

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Figure 1-2. U.S. Forest Service Class I Areas. 
 

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Figure 1-3. National Park Service Class I Areas. 
 

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Figure 1-4. Fish and Wildlife Service Class I Areas. 
 

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Figure 1-5. Location of Visibility Monitoring Sites in the CENRAP Domain. 
 

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Figure 1-6. CANRAP BART Modeling Flow Chart.

Screening 

CALPUFF Application 

(2001-2003 at 6 km) 

High ∆dv 

> 0.5 

Source-Specific 

CALPUFF Application 

(2001-2003 at 1-6 km)

98% ∆dv 

> 0.5 

Source subject to BART controls

Source not subject 

to BART controls 

Source not subject 

to BART controls 

CENRAP BART 

Modeling Flow Chart 

NO

YES 

NO

YES 

YES 
 

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Table 1-1. Federally Mandated Class I Areas in the CENRAP States. 

U. S. Forest Service 

Caney Creek Wilderness (AR) 

Upper Buffalo Wilderness (AR) 

Boundary Waters Canoe Area (MN) 

Hercules - Glades Wilderness (MO) 

National Park Service 

Big Bend National Park (TX) 

Guadalupe Mountains National Park (TX) 

Voyageurs National Park (MN) 

U.S. Fish and Wildlife Service 

Wichita Mountains Wilderness (OK) 

Mingo Wilderness (MO) 

Breton Wilderness (LA) 

Table 1-2. Federally Mandated Class I Areas Near the CENRAP States. 

U.S. Forest Service 

Eagles Nest Wilderness (CO) 

Rawah Wilderness (CO) 

Pecos Wilderness (NM) 

Wheeler Peak Wilderness (NM) 

White Mountain Wilderness (NM) 

Sipsey Wilderness (AL) 

Rainbow Lakes Wilderness (WI) 

National Park Service 

Arches National Park (CO) 

Bandelier National Monument (NM) 

 Carlsbad Caverns National Park (NM) 

Chiricahua National Monument (NM) 

Great Sand Dunes National Monument (CO) 

Rocky Mountain National Park (CO) 

Badlands National Park (SD) 

Isle Royale National Park (MI) 

Theodore Roosevelt National Park (ND) 

Wind Cave National Park (SD) 

Mammoth Cave National Park (KY) 

U.S. Fish and Wildlife Service 

Bosque Del Apache Wilderness (NM) 

Salt Creek Wilderness (NM) 

Seney Wilderness (MI) 

St. Marks Wilderness (FL) 

Lostwood Wilderness (ND)