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Note: This guidance is for facilities performing a BART analysis. The MPCA used 

modeling to determine which units contribute to visibility impairment in a Class I area 

and are therefore “subject to BART”. The MPCA requests facilities with emission units 

that are subject to BART to complete a BART analysis within 6 months of notification. 

Section IV of EPA’s “Guidelines for BART Determinations under the Regional Haze 

Rules” [40 CFR Part 51, Appendix Y] is reprinted below. The EPA’s Guidelines were 

written for states to use in making BART determinations. The MPCA is asking facilities 

to follow these Guidelines in completing their BART analysis. The MPCA has inserted 

notes (in grey boxes) into the Guidelines text below to clarify expectations for a BART 

analysis. The MPCA will use the BART analysis to make the actual BART 

determinations, subject to EPA approval. 

In each step of the analysis, facilities are asked to clearly document rationale, data 

sources, etc. Facilities are requested to submit the BART analysis using the format in 

Attachment 3. 

IV. The BART Determination: Analysis of BART Options 

This section describes the process for the analysis of control options for sources subject to BART. 

A. What factors must I address in the BART review?

The visibility regulations define BART as follows: 

Best Available Retrofit Technology (BART) means an emission limitation based on the degree of reduction 

achievable through the application of the best system of continuous emission reduction for each pollutant which is 

emitted by . . . [a BART-eligible source]. The emission limitation must be established, on a case-by-case basis, 

taking 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 or in existence 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. 

The BART analysis identifies the best system of continuous emission reduction taking into account: 

(1) The available retrofit control options, 

(2) Any pollution control equipment in use at the source (which affects the availability of options and their 

impacts), 

(3) The costs of compliance with control options, 

(4) The remaining useful life of the facility, 

(5) The energy and non-air quality environmental impacts of control options 

(6) The visibility impacts analysis. 

B. What is the scope of the BART review?

Once you determine that a source is subject to BART for a particular pollutant, then for each affected emission unit, 
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you must establish BART for that pollutant. The BART determination must address air pollution control measures for 

each emissions unit or pollutant emitting activity subject to review. 

Example: Plantwide emissions from emission units within the listed categories that began operation within 

the “time window” for BART 11 are 300 tons/yr of NOX, 200 tons/yr of SO2, and 150 tons/yr of primary 

particulate. Emissions unit A emits 200 tons/yr of NOX, 100 tons/yr of SO2, and 100 tons/yr of primary 

particulate. Other emission units, units B through H, which began operating in 1966, contribute lesser 

amounts of each pollutant. For this example, a BART review is required for NOX, SO2, and primary 

particulate, and control options must be analyzed for units B through H as well as unit A. 

11 That is, emission units that were in existence on August 7, 1977 and which began actual operation on or 

after August 7, 1962. 

C. How does a BART review relate to Maximum Achievable Control Technology (MACT) Standards under 

CAA section 112, or to other emission limitations required under the CAA?

For VOC and PM sources subject to MACT standards, States may streamline the analysis by including 

a discussion of the MACT controls and whether any major new technologies have been developed 

subsequent to the MACT standards. We believe that there are many VOC and PM sources that are well 

controlled because they are regulated by the MACT standards, which EPA developed under CAA 

section 112. For a few MACT standards, this may also be true for SO2. Any source subject to MACT 

standards must meet a level that is as stringent as the best-controlled 12 percent of sources in the 

industry. Examples of these hazardous air pollutant sources which effectively control VOC and PM 

emissions include (among others) secondary lead facilities, organic chemical plants subject to the 

hazardous organic NESHAP (HON), pharmaceutical production facilities, and equipment leaks and 

wastewater operations at petroleum refineries. We believe that, in many cases, it will be unlikely that 

States will identify emission controls more stringent than the MACT standards without identifying control 

options that would cost many thousands of dollars per ton. Unless there are new technologies 

subsequent to the MACT standards which would lead to cost-effective increases in the level of control, 

you may rely on the MACT standards for purposes of BART. 

We believe that the same rationale also holds true for emissions standards developed for municipal waste 

incinerators under CAA section 111(d), and for many NSR/PSD determinations and NSR/PSD settlement 

agreements. However, we do not believe that technology determinations from the 1970s or early 1980s, including 

new source performance standards (NSPS), should be considered to represent best control for existing sources, as 

best control levels for recent plant retrofits are more stringent than these older levels. 

Where you are relying on these standards to represent a BART level of control, you should provide the public with a 

discussion of whether any new technologies have subsequently become available. 

MPCA Note: The MPCA intends to streamline the analysis of PM and VOC sources subject to MACT standards in a 

BART analysis. The MPCA agrees with U.S. EPA’s assertion that it is unlikely that states will identify controls more 

stringent than the MACT standards without incurring much higher costs. Therefore, the MPCA will rely on MACT 

standards to represent BART level of control for those visibility-impairing pollutants addressed by the MACT 

standard unless there are new technologies subsequent to the MACT standards, which would lead to cost-effective 

increases in the level of control. For example, if a BART-eligible emissions unit emits PM10 and NOx and the unit is 

subject to a MACT limit for PM10, then a full BART analysis need only address NOx. 

If you have units emitting visibility-impairing pollutants that are addressed by a MACT standard(s), then please list 

those units or groups of units in section III of the BART analysis (see Attachment 3). Please include the MACT 

standard, the limit imposed on the unit by the MACT standard, the MACT limit converted into a pounds/day value, 

and document your rationale as to why the MACT standard represents BART. No further analysis is needed of 

those units for that visibility-impairing pollutant. 

If you believe that recent application of a BACT or NSPS standard represents BART for an emission unit, please 

consult with MPCA staff early in the BART analysis process for further guidance on the expected level of analysis. 
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D. What Are the Five Basic Steps of a Case-by-Case BART Analysis?

The five steps are: 

STEP 1—Identify All12 Available Retrofit Control Technologies, 

12 In identifying “all” options, you must identify the most stringent option and a reasonable set of options 

for analysis that reflects a comprehensive list of available technologies. It is not necessary to list all 

permutations of available control levels that exist for a given technology—the list is complete if it includes 

the maximum level of control each technology is capable of achieving. 

STEP 2— Eliminate Technically Infeasible Options, 

STEP 3— Evaluate Control Effectiveness of Remaining Control Technologies, 

STEP 4— Evaluate Impacts and Document the Results, and 

STEP 5—Evaluate Visibility Impacts. 

1. STEP 1: How do I identify all available retrofit emission control techniques? 

1. Available retrofit control options are those air pollution control technologies with a practical potential for application 

to the emissions unit and the regulated pollutant under evaluation. Air pollution control technologies can include a 

wide variety of available methods, systems, and techniques for control of the affected pollutant. Technologies 

required as BACT or LAER are available for BART purposes and must be included as control alternatives. The 

control alternatives can include not only existing controls for the source category in question but also take into 

account technology transfer of controls that have been applied to similar source categories and gas streams. 

Technologies which have not yet been applied to (or permitted for) full scale operations need not be considered as 

available; we do not expect the source owner to purchase or construct a process or control device that has not 

already been demonstrated in practice. 

2. Where a NSPS exists for a source category (which is the case for most of the categories affected by BART), you 

should include a level of control equivalent to the NSPS as one of the control options13 The NSPS standards are 

codified in 40 CFR part 60. We note that there are situations where NSPS standards do not require the most 

stringent level of available control for all sources within a category. For example, post-combustion NOX controls (the 

most stringent controls for stationary gas turbines) are not required under subpart GG of the NSPS for Stationary 

Gas Turbines. However, such controls must still be considered available technologies for the BART selection 

process. 

13 In EPA's 1980 BART guidelines for reasonably attributable visibility impairment, we concluded that NSPS 

standards generally, at that time, represented the best level sources could install as BART. In the 20 year 

period since this guidance was developed, there have been advances in SO2 control technologies as well 

as technologies for the control of other pollutants, confirmed by a number of recent retrofits at Western 

power plants. Accordingly, EPA no longer concludes that the NSPS level of controls automatically 

represents “the best these sources can install.” Analysis of the BART factors could result in the selection of 

a NSPS level of control, but you should reach this conclusion only after considering the full range of control 

options. 

3. Potentially applicable retrofit control alternatives can be categorized in three ways. 

• Pollution prevention: use of inherently lower-emitting processes/practices, including the use of control 

techniques (e.g., low-NOX burners) and work practices that prevent emissions and result in lower 

“production-specific” emissions (note that it is not our intent to direct States to switch fuel forms, e.g., from 

coal to gas), 
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• Use of (and where already in place, improvement in the performance of) add-on controls, such as 

scrubbers, fabric filters, thermal oxidizers and other devices that control and reduce emissions after they 

are produced, and 

• Combinations of inherently lower-emitting processes and add-on controls. 

MPCA Note: At a minimum, taconite plants should consider the control technologies and work practices/operational 

changes in the table below as retrofit control alternatives for their BART-eligible indurating furnaces: 

Pollutant Description Comments 

SCR 

IFGR Burners 

Low-NOx burners Including ultra-low NOx 

burners 

Ported Kiln Only for rotary kilns 

Control Technologies: 

LoTOx 

NOx CEM Also investigate other 

forms of monitoring to 

ensure combustion 

efficiency 

NOx 

Work Practices/ 

Operational Changes: 

Alternative fuels Evaluate use of biomass 

as fuel 

High efficiency wet scrubber (> 90% 

removal) 

Low efficiency wet scrubber (> 50% 

removal) 

Control Technologies: 

Lime/Limestone wet slurry scrubbing Look at various 

alternatives to enhance 

SO2 collection efficiency 

of existing web scrubbers 

SO2

Work Practices/ 

Operational Changes: 

Alternative fuels 

4. In the course of the BART review, one or more of the available control options may be eliminated from 

consideration because they are demonstrated to be technically infeasible or to have unacceptable energy, cost, or 

non-air quality environmental impacts on a case-by-case (or site-specific) basis. However, at the outset, you should 

initially identify all control options with potential application to the emissions unit under review. 

5. We do not consider BART as a requirement to redesign the source when considering available control 

alternatives. For example, where the source subject to BART is a coal-fired electric generator, we do not require the 

BART analysis to consider building a natural gas-fired electric turbine although the turbine may be inherently less 

polluting on a per unit basis. 

6. For emission units subject to a BART review, there will often be control measures or devices already in place. For 

such emission units, it is important to include control options that involve improvements to existing controls and not 

to limit the control options only to those measures that involve a complete replacement of control devices. 

Example: For a power plant with an existing wet scrubber, the current control efficiency is 66 percent. 

Part of the reason for the relatively low control efficiency is that 22 percent of the gas stream bypasses the 

scrubber. A BART review identifies options for improving the performance of the wet scrubber by 

redesigning the internal components of the scrubber and by eliminating or reducing the percentage of the 

gas stream that bypasses the scrubber. Four control options are identified: (1) 78 percent control based 

upon improved scrubber performance while maintaining the 22 percent bypass, (2) 83 percent control 

based upon improved scrubber performance while reducing the bypass to 15 percent, (3) 93 percent 

control based upon improving the scrubber performance while eliminating the bypass entirely, (this option 
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results in a “wet stack” operation in which the gas leaving the stack is saturated with water) and (4) 93 

percent as in option 3, with the addition of an indirect reheat system to reheat the stack gas above the 

saturation temperature. You must consider each of these four options in a BART analysis for this source. 

7. You are expected to identify potentially applicable retrofit control technologies that represent the full range of 

demonstrated alternatives. Examples of general information sources to consider include: 

• The EPA's Clean Air Technology Center, which includes the RACT/BACT/LAER Clearinghouse (RBLC); 

• State and Local Best Available Control Technology Guidelines—many agencies have online information—

for example South Coast Air Quality Management District, Bay Area Air Quality Management District, and 

Texas Natural Resources Conservation Commission; 

• Control technology vendors; 

• Federal/State/Local NSR permits and associated inspection/performance test reports; 

• Environmental consultants; 

• Technical journals, reports and newsletters, air pollution control seminars; and 

• The EPA's NSR bulletin board—http://www.epa.gov/ttn/nsr;

• Department of Energy's Clean Coal Program—technical reports; 

• The NOX Control Technology “Cost Tool”—Clean Air Markets Division Web page—

http://www.epa.gov/airmarkets/arp/nox/controltech.html;

• Performance of selective catalytic reduction on coal-fired steam generating units—final report. OAR/ARD, 

June 1997 (also available at http://www.epa.gov/airmarkets/arp/nox/controltech.html); 

• Cost estimates for selected applications of NOX control technologies on stationary combustion boilers. 

OAR/ARD June 1997. (Docket for NOX SIP Call, A–96–56, item II–A–03); 

• Investigation of performance and cost of NOX controls as applied to group 2 boilers. OAR/ARD, August 

1996. (Docket for Phase II NOX rule, A–95–28, item IV–A–4); 

• Controlling SO2 Emissions: A Review of Technologies. EPA–600/R–00–093, USEPA/ORD/NRMRL, 

October 2000; and 

• The OAQPS Control Cost Manual. 

You are expected to compile appropriate information from these information sources. 

8. There may be situations where a specific set of units within a fenceline constitutes the logical set to which controls 

would apply and that set of units may or may not all be BART-eligible. (For example, some units in that set may not 

have been constructed between 1962 and 1977.) 

9. If you find that a BART source has controls already in place which are the most stringent controls available (note 

that this means that all possible improvements to any control devices have been made), then it is not necessary to 

comprehensively complete each following step of the BART analysis in this section. As long as these most stringent 

controls available are made federally enforceable for the purpose of implementing BART for that source, you may 

skip the remaining analyses in this section, including the visibility analysis in step 5. Likewise, if a source commits to 

a BART determination that consists of the most stringent controls available, then there is no need to complete the 
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remaining analyses in this section. 

MPCA Note: The MPCA will consider on a case-by-case basis whether a BACT determination or NSPS limit for a 

particular pollutant at a BART-eligible unit satisfies BART requirements. The MPCA will take into account the age of 

the BACT determination or NSPS limit, whether any new technologies have subsequently become available 

(including work practices that reduce emissions), and the visibility analysis that was performed for the BACT 

determination. The MPCA encourages facilities to consult with MPCA staff during the development of their BART 

analysis if they believe a BACT determination or NSPS limit represents BART and that no further analyses are 

required for a particular visibility-impairing pollutant. 

2. STEP 2: How do I determine whether the options identified in Step 1 are technically feasible? 

In Step 2, you evaluate the technical feasibility of the control options you identified in Step 1. You should document 

a demonstration of technical infeasibility and should explain, based on physical, chemical, or engineering principles, 

why technical difficulties would preclude the successful use of the control option on the emissions unit under review. 

You may then eliminate such technically infeasible control options from further consideration in the BART analysis. 

In general, what do we mean by technical feasibility? 

Control technologies are technically feasible if either (1) they have been installed and operated successfully for the 

type of source under review under similar conditions, or (2) the technology could be applied to the source under 

review. Two key concepts are important in determining whether a technology could be applied: “availability” and 

“applicability.” As explained in more detail below, a technology is considered “available” if the source owner may 

obtain it through commercial channels, or it is otherwise available within the common sense meaning of the term. 

An available technology is “applicable” if it can reasonably be installed and operated on the source type under 

consideration. A technology that is available and applicable is technically feasible. 

What do we mean by “available” technology? 

1. The typical stages for bringing a control technology concept to reality as a commercial product are: 

• Concept stage; 

• Research and patenting; 

• Bench scale or laboratory testing; 

• Pilot scale testing; 

• Licensing and commercial demonstration; and 

• Commercial sales. 

2. A control technique is considered available, within the context presented above, if it has reached the stage of 

licensing and commercial availability. Similarly, we do not expect a source owner to conduct extended trials to learn 

how to apply a technology on a totally new and dissimilar source type. Consequently, you would not consider 

technologies in the pilot scale testing stages of development as “available” for purposes of BART review. 

3. Commercial availability by itself, however, is not necessarily a sufficient basis for concluding a technology to be 

applicable and therefore technically feasible. Technical feasibility, as determined in Step 2, also means a control 

option may reasonably be deployed on or “applicable” to the source type under consideration. 

Because a new technology may become available at various points in time during the BART analysis process, we 

believe that guidelines are needed on when a technology must be considered. For example, a technology may 

become available during the public comment period on the State's rule development process. Likewise, it is 
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possible that new technologies may become available after the close of the State's public comment period and 

before submittal of the SIP to EPA, or during EPA's review process on the SIP submittal. In order to provide certainty 

in the process, all technologies should be considered if available before the close of the State's public comment 

period. You need not consider technologies that become available after this date. As part of your analysis, you 

should consider any technologies brought to your attention in public comments. If you disagree with public 

comments asserting that the technology is available, you should provide an explanation for the public record as to 

the basis for your conclusion. 

MPCA note: For the purpose of the BART analysis, please consider all available technologies as of the date of 

submittal of the BART analysis. 

What do we mean by “applicable” technology? 

You need to exercise technical judgment in determining whether a control alternative is applicable to the source type 

under consideration. In general, a commercially available control option will be presumed applicable if it has been 

used on the same or a similar source type. Absent a showing of this type, you evaluate technical feasibility by 

examining the physical and chemical characteristics of the pollutant-bearing gas stream, and comparing them to the 

gas stream characteristics of the source types to which the technology had been applied previously. Deployment of 

the control technology on a new or existing source with similar gas stream characteristics is generally a sufficient 

basis for concluding the technology is technically feasible barring a demonstration to the contrary as described 

below. 

What type of demonstration is required if I conclude that an option is not technically feasible? 

1. Where you conclude that a control option identified in Step 1 is technically infeasible, you should demonstrate that 

the option is either commercially unavailable, or that specific circumstances preclude its application to a particular 

emission unit. Generally, such a demonstration involves an evaluation of the characteristics of the pollutant-bearing 

gas stream and the capabilities of the technology. Alternatively, a demonstration of technical infeasibility may 

involve a showing that there are unresolvable technical difficulties with applying the control to the source (e.g., size 

of the unit, location of the proposed site, operating problems related to specific circumstances of the source, space 

constraints, reliability, and adverse side effects on the rest of the facility). Where the resolution of technical 

difficulties is merely a matter of increased cost, you should consider the technology to be technically feasible. The 

cost of a control alternative is considered later in the process. 

2. The determination of technical feasibility is sometimes influenced by recent air quality permits. In some cases, an 

air quality permit may require a certain level of control, but the level of control in a permit is not expected to be 

achieved in practice (e.g., a source has received a permit but the project was canceled, or every operating source at 

that permitted level has been physically unable to achieve compliance with the limit). Where this is the case, you 

should provide supporting documentation showing why such limits are not technically feasible, and, therefore, why 

the level of control (but not necessarily the technology) may be eliminated from further consideration. However, if 

there is a permit requiring the application of a certain technology or emission limit to be achieved for such 

technology, this usually is sufficient justification for you to assume the technical feasibility of that technology or 

emission limit. 

MPCA note: Air emission permits are available online at http://www.pca.state.mn.us/air/permits/issued/index.html . 

3. Physical modifications needed to resolve technical obstacles do not, in and of themselves, provide a justification 

for eliminating the control technique on the basis of technical infeasibility. However, you may consider the cost of 

such modifications in estimating costs. This, in turn, may form the basis for eliminating a control technology (see 

later discussion). 

4. Vendor guarantees may provide an indication of commercial availability and the technical feasibility of a control 

technique and could contribute to a determination of technical feasibility or technical infeasibility, depending on 

circumstances. However, we do not consider a vendor guarantee alone to be sufficient justification that a control 

option will work. Conversely, lack of a vendor guarantee by itself does not present sufficient justification that a 

control option or an emissions limit is technically infeasible. Generally, you should make decisions about technical 

feasibility based on chemical, and engineering analyses (as discussed above), in conjunction with information about 
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vendor guarantees. 

5. A possible outcome of the BART procedures discussed in these guidelines is the evaluation of multiple control 

technology alternatives which result in essentially equivalent emissions. It is not our intent to encourage evaluation 

of unnecessarily large numbers of control alternatives for every emissions unit. Consequently, you should use 

judgment in deciding on those alternatives for which you will conduct the detailed impacts analysis (Step 4 below). 

For example, if two or more control techniques result in control levels that are essentially identical, considering the 

uncertainties of emissions factors and other parameters pertinent to estimating performance, you may evaluate only 

the less costly of these options. You should narrow the scope of the BART analysis in this way only if there is a 

negligible difference in emissions and energy and non-air quality environmental impacts between control 

alternatives. 

3. STEP 3: How do I evaluate technically feasible alternatives? 

Step 3 involves evaluating the control effectiveness of all the technically feasible control alternatives identified in 

Step 2 for the pollutant and emissions unit under review. 

Two key issues in this process include: 

(1) Making sure that you express the degree of control using a metric that ensures an “apples to apples” 

comparison of emissions performance levels among options, and 

(2) Giving appropriate treatment and consideration of control techniques that can operate over a wide 

range of emission performance levels. 

What are the appropriate metrics for comparison? 

This issue is especially important when you compare inherently lower-polluting processes to one another or to addon controls. In such cases, it is generally most effective to express emissions performance as an average steady 

state emissions level per unit of product produced or processed. 

Examples of common metrics: 

• Pounds of SO2 emissions per million Btu heat input, and 

• Pounds of NOX emissions per ton of cement produced. 

MPCA Note: For EGUs, please provide compare emissions in units of pounds per million Btu heat input. For 

indurating furnaces at taconite facilities, please compare emissions as follows: for SO2 and NOx use lb/ hour. All 

emissions should also be provided on a lb/day basis as these are the units that will be used for modeling purposes. 

In evaluating the reductions attainable from the use of a NOx CEM on indurating furnaces to improve combustion 

practices, you may assume a 20 percent reduction unless you have information to support another value. The 

MPCA believes that potential reductions range from 15 to 35 percent due to improved operational information. 

How do I evaluate control techniques with a wide range of emission performance levels? 

1. Many control techniques, including both add-on controls and inherently lower polluting processes, can perform at 

a wide range of levels. Scrubbers and high and low efficiency electrostatic precipitators (ESPs) are two of the many 

examples of such control techniques that can perform at a wide range of levels. It is not our intent to require 

analysis of each possible level of efficiency for a control technique as such an analysis would result in a large 

number of options. It is important, however, that in analyzing the technology you take into account the most 

stringent emission control level that the technology is capable of achieving. You should consider recent regulatory 

decisions and performance data (e.g., manufacturer's data, engineering estimates and the experience of other 
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sources) when identifying an emissions performance level or levels to evaluate. 

2. In assessing the capability of the control alternative, latitude exists to consider special circumstances pertinent to 

the specific source under review, or regarding the prior application of the control alternative. However, you should 

explain the basis for choosing the alternate level (or range) of control in the BART analysis. Without a showing of 

differences between the source and other sources that have achieved more stringent emissions limits, you should 

conclude that the level being achieved by those other sources is representative of the achievable level for the source 

being analyzed. 

3. You may encounter cases where you may wish to evaluate other levels of control in addition to the most stringent 

level for a given device. While you must consider the most stringent level as one of the control options, you may 

consider less stringent levels of control as additional options. This would be useful, particularly in cases where the 

selection of additional options would have widely varying costs and other impacts. 

4. Finally, we note that for retrofitting existing sources in addressing BART, you should consider ways to improve the 

performance of existing control devices, particularly when a control device is not achieving the level of control that 

other similar sources are achieving in practice with the same device. For example, you should consider requiring 

those sources with electrostatic precipitators (ESPs) performing below currently achievable levels to improve their 

performance. 

4. STEP 4: For a BART review, what impacts, am I expected to calculate and report? What methods does 

EPA recommend for the impacts analysis? 

After you identify the available and technically feasible control technology options, you are expected to conduct the 

following analyses when you make a BART determination: 

Impact analysis part 1: Costs of compliance, 

Impact analysis part 2: Energy impacts, and 

Impact analysis part 3: Non-air quality environmental impacts. 

Impact analysis part 4: Remaining useful life. 

In this section, we describe how to conduct each of these three analyses. You are responsible for presenting an 

evaluation of each impact along with appropriate supporting information. You should discuss and, where possible, 

quantify both beneficial and adverse impacts. In general, the analysis should focus on the direct impact of the 

control alternative. 

MPCA Note: The Guidelines do not explicitly mention how to deal with collateral increases in another regulated 

pollutant as a result of a control alternative. For example, use of furnace sorbent injection to control SO2 in a boiler 

could result in an increase in PM emissions. This increase could trigger other air quality requirements such as 

NSPS or NSR. The MPCA asks that you identify any collateral increases in other regulated pollutants in your 

analysis. If you select a control that has collateral increases as proposed BART, then the MPCA asks that your 

BART analysis also identify any regulatory requirements that are triggered. 

a. Impact analysis part 1: how do I estimate the costs of control? 

1. To conduct a cost analysis, you: 

(1) Identify the emissions units being controlled, 

(2) Identify design parameters for emission controls, and 
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(3) Develop cost estimates based upon those design parameters. 

2. It is important to identify clearly the emission units being controlled, that is, to specify a well-defined area or 

process segment within the plant. In some cases, multiple emission units can be controlled jointly. However, in other 

cases, it may be appropriate in the cost analysis to consider whether multiple units will be required to install separate 

and/or different control devices. The analysis should provide a clear summary list of equipment and the associated 

control costs. Inadequate documentation of the equipment whose emissions are being controlled is a potential 

cause for confusion in comparison of costs of the same controls applied to similar sources. 

3. You then specify the control system design parameters. Potential sources of these design parameters include 

equipment vendors, background information documents used to support NSPS development, control technique 

guidelines documents, cost manuals developed by EPA, control data in trade publications, and engineering and 

performance test data. The following are a few examples of design parameters for two example control measures: 

 

------------------------------------------------------------------------ 

 Control device Examples of design parameters 

------------------------------------------------------------------------ 

Wet Scrubbers......................... Type of sorbent used (lime, limestone, etc.). 

 Gas pressure drop. 

 Liquid/gas ratio. 

Selective Catalytic Reduction......... Ammonia to NOX molar ratio. 

 Pressure drop. 

 Catalyst life. 

------------------------------------------------------------------------ 

4. The value selected for the design parameter should ensure that the control option will achieve the level of 

emission control being evaluated. You should include in your analysis documentation of your assumptions 

regarding design parameters. Examples of supporting references would include the EPA OAQPS Control 

Cost Manual (see below) and background information documents used for NSPS and hazardous pollutant 

emission standards. If the design parameters you specified differ from typical designs, you should document 

the difference by supplying performance test data for the control technology in question applied to the same 

source or a similar source. 

5. Once the control technology alternatives and achievable emissions performance levels have been 

identified, you then develop estimates of capital and annual costs. The basis for equipment cost estimates 

also should be documented, either with data supplied by an equipment vendor (i.e., budget estimates or bids) 

or by a referenced source (such as the OAQPS Control Cost Manual, Fifth Edition, February 1996, EPA 

453/B–96–001)14. In order to maintain and improve consistency, cost estimates should be based on the 

OAQPS Control Cost Manual, where possible15. The Control Cost Manual addresses most control 

technologies in sufficient detail for a BART analysis. The cost analysis should also take into account any 

site-specific design or other conditions identified above that affect the cost of a particular BART technology 

option. 

14 The OAQPS Control Cost Manual is updated periodically. While this citation refers to the latest 

version at the time this guidance was written, you should use the version that is current as of when 

you conduct your impact analysis. This document is available at the following Web site: 

http://www.epa.gov/ttn/catc/dir1/cs1ch2.pdf .

15 You should include documentation for any additional information you used for the cost 

calculations, including any information supplied by vendors that affects your assumptions regarding 

purchased equipment costs, equipment life, replacement of major components, and any other 

element of the calculation that differs from the Control Cost Manual. 
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MPCA note: Please reflect all costs in year 2005 dollars. 

For EGUs greater than 100 MW, the MPCA requests that you use CUECOST to perform cost calculations 

unless MPCA staff has agreed to the use of an alternative method. Please provide a printout of the input & 

calculation summary used in CUECOST. If you do not use default values, explain your rationale. 

b. What do we mean by cost effectiveness? 

Cost effectiveness, in general, is a criterion used to assess the potential for achieving an objective in the 

most economical way. For purposes of air pollutant analysis, “effectiveness” is measured in terms of tons of 

pollutant emissions removed, and “cost” is measured in terms of annualized control costs. We recommend 

two types of cost-effectiveness calculations—average cost effectiveness, and incremental cost effectiveness. 

c. How do I calculate average cost effectiveness? 

Average cost effectiveness means the total annualized costs of control divided by annual emissions 

reductions (the difference between baseline annual emissions and the estimate of emissions after controls), 

using the following formula: 

Average cost effectiveness (dollars per ton removed) = Control option annualized cost 16 

16 Whenever you calculate or report annual costs, you should indicate the year for which the costs 

are estimated. For example, if you use the year 2000 as the basis for cost comparisons, you would 

report that an annualized cost of $20 million would be: $20 million (year 2000 dollars). 

Baseline annual emissions—Annual emissions with Control option 

Because you calculate costs in (annualized) dollars per year ($/yr) and because you calculate emissions 

rates in tons per year (tons/yr), the result is an average cost-effectiveness number in (annualized) dollars per 

ton ($/ton) of pollutant removed. 

MPCA Note: Consider “average cost effectiveness” to simply be “cost effectiveness,” since the Guidelines 

do not specify what terms are to be averaged. Use 2005 dollars for this calculation. To determine the 

"annualized cost," follow the methodology provided in the EPA AIR POLLUTION CONTROL COST 

MANUAL, Sixth Edition (EPA/452/B-02-001, January 2002). Use seven percent as the interest rate in these 

calculations. Assume a 20 year control equipment life. If a 20 year life is not appropriate for the control 

scenario considered, document your rationale for use of another value. 

d. How do I calculate baseline emissions? 

1. The baseline emissions rate should represent a realistic depiction of anticipated annual emissions for the 

source. In general, for the existing sources subject to BART, you will estimate the anticipated annual 

emissions based upon actual emissions from a baseline period. 

2. When you project that future operating parameters (e.g., limited hours of operation or capacity utilization, 

type of fuel, raw materials or product mix or type) will differ from past practice, and if this projection has a 

deciding effect in the BART determination, then you must make these parameters or assumptions into 

enforceable limitations. In the absence of enforceable limitations, you calculate baseline emissions based 

upon continuation of past practice. 

3. For example, the baseline emissions calculation for an emergency standby generator may consider the 

fact that the source owner would not operate more than past practice of 2 weeks a year. On the other hand, 

baseline emissions associated with a base-loaded turbine should be based on its past practice which would 

indicate a large number of hours of operation. This produces a significantly higher level of baseline 

emissions than in the case of the emergency/standby unit and results in more cost-effective controls. As a 
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consequence of the dissimilar baseline emissions, BART for the two cases could be very different. 

MPCA Note: To estimate the baseline tons per year for non-EGU, calculate the actual annual emissions 

based on the highest emissions in 24-consecutive months from January, 1996 to December, 2005 for each of 

the visibility-impairing pollutants. The baseline emission factor should be correlated to the appropriate 

operational parameters over this 24-month period. For example, if the baseline NOx emission rate from a 

furnace is 1000 lb/hour and the maximum number of operating hours over 24-consecutive months was 

16,000 hours, then the NOx baseline tons per year for the furnace would be 4000 tons. 

For EGU, calculate the baseline annual emissions based on the highest emissions in 12-consecutive months 

from January, 2001 to December, 2005 for each of the visibility-impairing pollutants. Use CEM data if it is 

available to determine the highest emissions in 12-consecutive months. If CEM data is not available (as for 

PM10), correlate the baseline emission factor to the appropriate operational parameters over the 12-month 

period. For example, if the baseline PM10 emission rate from an EGU is 0.04 lb/MMBtu and the maximum 

heat input is 5,000,000 MMBtu over a 12-month period, then the PM10 baseline tons per year would be 100 

tons. 

(This method is based on the PSD baseline calculation method.) 

e. How do I calculate incremental cost effectiveness? 

1. In addition to the average cost effectiveness of a control option, you should also calculate incremental cost 

effectiveness. You should consider the incremental cost effectiveness in combination with the average cost 

effectiveness when considering whether to eliminate a control option. The incremental cost effectiveness 

calculation compares the costs and performance level of a control option to those of the next most stringent 

option, as shown in the following formula (with respect to cost per emissions reduction): 

Incremental Cost Effectiveness (dollars per incremental ton removed) = 

(Total annualized costs of control option) − (Total annualized costs of next control option) ÷ (Control option 

annual emissions) − (Next control option annual emissions) 

Example 1: Assume that Option F on Figure 2 has total annualized costs of $1 million to reduce 

2000 tons of a pollutant, and that Option D on Figure 2 has total annualized costs of $500,000 to 

reduce 1000 tons of the same pollutant. The incremental cost effectiveness of Option F relative to 

Option D is ($1 million − $500,000) divided by (2000 tons − 1000 tons), or $500,000 divided by 1000 

tons, which is $500/ton. 

Example 2: Assume that two control options exist: Option 1 and Option 2. Option 1 achieves a 

1,000 ton/yr reduction at an annualized cost of $1,900,000. This represents an average cost of 

($1,900,000/1,000 tons) = $1,900/ton. Option 2 achieves a 980 tons/yr reduction at an annualized 

cost of $1,500,000. This represents an average cost of ($1,500,000/980 tons) = $1,531/ton. The 

incremental cost effectiveness of Option 1 relative to Option 2 is ($1,900,000 − $1,500,000) divided 

by (1,000 tons − 980 tons). The adoption of Option 1 instead of Option 2 results in an incremental 

emission reduction of 20 tons per year at an additional cost of $400,000 per year. The incremental 

cost of Option 1, then, is $20,000 per ton − 11 times the average cost of $1,900 per ton. While 

$1,900 per ton may still be deemed reasonable, it is useful to consider both the average and 

incremental cost in making an overall cost-effectiveness finding. Of course, there may be other 

differences between these options, such as, energy or water use, or non-air environmental effects, 

which also should be considered in selecting a BART technology. 

2. You should exercise care in deriving incremental costs of candidate control options. Incremental costeffectiveness comparisons should focus on annualized cost and emission reduction differences between 

“dominant” alternatives. To identify dominant alternatives, you generate a graphical plot of total annualized 

costs for total emissions reductions for all control alternatives identified in the BART analysis, and by 

identifying a “least-cost envelope” as shown in Figure 2. (A “least-cost envelope” represents the set of 
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options that should be dominant in the choice of a specific option.) 

View or download PDF 

Example: Eight technically feasible control options for analysis are listed. These are represented 

as A through H in Figure 2. The dominant set of control options, B, D, F, G, and H, represent the 

least-cost envelope, as we depict by the cost curve connecting them. Points A, C and E are inferior 

options, and you should not use them in calculating incremental cost effectiveness. Points A, C and 

E represent inferior controls because B will buy more emissions reductions for less money than A; 

and similarly, D and F will buy more reductions for less money than C and E, respectively. 

3. In calculating incremental costs, you: 

(1) Array the control options in ascending order of annualized total costs, 

(2) Develop a graph of the most reasonable smooth curve of the control options, as shown in Figure 

2. This is to show the “least-cost envelope” discussed above; and 

(3) Calculate the incremental cost effectiveness for each dominant option, which is the difference in 

total annual costs between that option and the next most stringent option, divided by the difference 

in emissions, after controls have been applied, between those two control options. For example, 

using Figure 2, you would calculate incremental cost effectiveness for the difference between 

options B and D, options D and F, options F and G, and options G and H. 

4. A comparison of incremental costs can also be useful in evaluating the viability of a specific control option 

over a range of efficiencies. For example, depending on the capital and operational cost of a control device, 

total and incremental cost may vary significantly (either increasing or decreasing) over the operational range 

of a control device. Also, the greater the number of possible control options that exist, the more weight 

should be given to the incremental costs vs. average costs. It should be noted that average and incremental 

cost effectiveness are identical when only one candidate control option is known to exist. 

5. You should exercise caution not to misuse these techniques. For example, you may be faced with a 

choice between two available control devices at a source, control A and control B, where control B achieves 

slightly greater emission reductions. The average cost (total annual cost/total annual emission reductions) 

for each may be deemed to be reasonable. However, the incremental cost (total annual costA – B/total annual 

emission reductionsA – B) of the additional emission reductions to be achieved by control B may be very great. 
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In such an instance, it may be inappropriate to choose control B, based on its high incremental costs, even 

though its average cost may be considered reasonable. 

6. In addition, when you evaluate the average or incremental cost effectiveness of a control alternative, you 

should make reasonable and supportable assumptions regarding control efficiencies. An unrealistically low 

assessment of the emission reduction potential of a certain technology could result in inflated costeffectiveness figures. 

MPCA Note: The MPCA does not expect that you develop a least cost envelope such as that shown in the 

figure. The MPCA expects that the top-down nature of the BART analysis and the information requested in 

the analysis will be sufficient for BART determination purposes. 

f. What other information should I provide in the cost impacts analysis? 

You should provide documentation of any unusual circumstances that exist for the source that would lead to 

cost-effectiveness estimates that would exceed that for recent retrofits. This is especially important in cases 

where recent retrofits have cost-effectiveness values that are within what has been considered a reasonable 

range, but your analysis concludes that costs for the source being analyzed are not considered reasonable. 

(A reasonable range would be a range that is consistent with the range of cost effectiveness values used in 

other similar permit decisions over a period of time.) 

Example: In an arid region, large amounts of water are needed for a scrubbing system. Acquiring 

water from a distant location could greatly increase the cost per ton of emissions reduced of wet 

scrubbing as a control option. 

g. What other things are important to consider in the cost impacts analysis? 

In the cost analysis, you should take care not to focus on incomplete results or partial calculations. For 

example, large capital costs for a control option alone would not preclude selection of a control measure if 

large emissions reductions are projected. In such a case, low or reasonable cost effectiveness numbers may 

validate the option as an appropriate BART alternative irrespective of the large capital costs. Similarly, 

projects with relatively low capital costs may not be cost effective if there are few emissions reduced. 

h. Impact analysis part 2: How should I analyze and report energy impacts? 

1. You should examine the energy requirements of the control technology and determine whether the use of 

that technology results in energy penalties or benefits. A source owner may, for example, benefit from the 

combustion of a concentrated gas stream rich in volatile organic compounds; on the other hand, more often 

extra fuel or electricity is required to power a control device or incinerate a dilute gas stream. If such benefits 

or penalties exist, they should be quantified to the extent practicable. Because energy penalties or benefits 

can usually be quantified in terms of additional cost or income to the source, the energy impacts analysis 

can, in most cases, simply be factored into the cost impacts analysis. The fact of energy use in and of itself 

does not disqualify a technology. 

2. Your energy impact analysis should consider only direct energy consumption and not indirect energy 

impacts. For example, you could estimate the direct energy impacts of the control alternative in units of 

energy consumption at the source (e.g., BTU, kWh, barrels of oil, tons of coal). The energy requirements of 

the control options should be shown in terms of total (and in certain cases, also incremental) energy costs 

per ton of pollutant removed. You can then convert these units into dollar costs and, where appropriate, 

factor these costs into the control cost analysis. 

3. You generally do not consider indirect energy impacts (such as energy to produce raw materials for 

construction of control equipment). However, if you determine, either independently or based on a showing 

by the source owner, that the indirect energy impact is unusual or significant and that the impact can be well 

quantified, you may consider the indirect impact. 
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4. The energy impact analysis may also address concerns over the use of locally scarce fuels. The 

designation of a scarce fuel may vary from region to region. However, in general, a scarce fuel is one which 

is in short supply locally and can be better used for alternative purposes, or one which may not be 

reasonably available to the source either at the present time or in the near future. 

5. Finally, the energy impacts analysis may consider whether there are relative differences between 

alternatives regarding the use of locally or regionally available coal, and whether a given alternative would 

result in significant economic disruption or unemployment. For example, where two options are equally cost 

effective and achieve equivalent or similar emissions reductions, one option may be preferred if the other 

alternative results in significant disruption or unemployment. 

MPCA Note: Please report energy impacts on a $ per ton of pollutant removed basis. Please document all 

assumptions made in calculating energy costs. 

i. Impact analysis part 3: How do I analyze “non-air quality environmental impacts?” 

1. In the non-air quality related environmental impacts portion of the BART analysis, you address 

environmental impacts other than air quality due to emissions of the pollutant in question. Such 

environmental impacts include solid or hazardous waste generation and discharges of polluted water from a 

control device. 

2. You should identify any significant or unusual environmental impacts associated with a control alternative 

that have the potential to affect the selection or elimination of a control alternative. Some control 

technologies may have potentially significant secondary environmental impacts. Scrubber effluent, for 

example, may affect water quality and land use. Alternatively, water availability may affect the feasibility and 

costs of wet scrubbers. Other examples of secondary environmental impacts could include hazardous waste 

discharges, such as spent catalysts or contaminated carbon. Generally, these types of environmental 

concerns become important when sensitive site-specific receptors exist or when the incremental emissions 

reductions potential of the more stringent control is only marginally greater than the next most-effective 

option. However, the fact that a control device creates liquid and solid waste that must be disposed of does 

not necessarily argue against selection of that technology as BART, particularly if the control device has 

been applied to similar facilities elsewhere and the solid or liquid waste is similar to those other applications. 

On the other hand, where you or the source owner can show that unusual circumstances at the proposed 

facility create greater problems than experienced elsewhere, this may provide a basis for the elimination of 

that control alternative as BART. 

3. The procedure for conducting an analysis of non-air quality environmental impacts should be made based 

on a consideration of site-specific circumstances. If you propose to adopt the most stringent alternative, then 

it is not necessary to perform this analysis of environmental impacts for the entire list of technologies you 

ranked in Step 3. In general, the analysis need only address those control alternatives with any significant or 

unusual environmental impacts that have the potential to affect the selection of a control alternative, or 

elimination of a more stringent control alternative. Thus, any important relative environmental impacts (both 

positive and negative) of alternatives can be compared with each other. 

4. In general, the analysis of impacts starts with the identification and quantification of the solid, liquid, and 

gaseous discharges from the control device or devices under review. Initially, you should perform a 

qualitative or semi-quantitative screening to narrow the analysis to discharges with potential for causing 

adverse environmental effects. Next, you should assess the mass and composition of any such discharges 

and quantify them to the extent possible, based on readily available information. You should also assemble 

pertinent information about the public or environmental consequences of releasing these materials. 

j. Impact analysis part 4: What are examples of non-air quality environmental impacts? 

The following are examples of how to conduct non-air quality environmental impacts: 

(1) Water Impact
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You should identify the relative quantities of water used and water pollutants produced and 

discharged as a result of the use of each alternative emission control system. Where possible, you 

should assess the effect on ground water and such local surface water quality parameters as ph, 

turbidity, dissolved oxygen, salinity, toxic chemical levels, temperature, and any other important 

considerations. The analysis could consider whether applicable water quality standards will be met 

and the availability and effectiveness of various techniques to reduce potential adverse effects. 

(2) Solid Waste Disposal Impact

You could also compare the quality and quantity of solid waste (e.g., sludges, solids) that must be 

stored and disposed of or recycled as a result of the application of each alternative emission control 

system. You should consider the composition and various other characteristics of the solid waste 

(such as permeability, water retention, rewatering of dried material, compression strength, 

leachability of dissolved ions, bulk density, ability to support vegetation growth and hazardous 

characteristics) which are significant with regard to potential surface water pollution or transport into 

and contamination of subsurface waters or aquifers. 

(3) Irreversible or Irretrievable Commitment of Resources

You may consider the extent to which the alternative emission control systems may involve a tradeoff between short-term environmental gains at the expense of long-term environmental losses and 

the extent to which the alternative systems may result in irreversible or irretrievable commitment of 

resources (for example, use of scarce water resources). 

(4) Other Adverse Environmental Impacts

You may consider significant differences in noise levels, radiant heat, or dissipated static electrical 

energy of pollution control alternatives. Other examples of non-air quality environmental impacts 

would include hazardous waste discharges such as spent catalysts or contaminated carbon. 

k. How do I take into account a project's “remaining useful life” in calculating control costs? 

1. You may decide to treat the requirement to consider the source's “remaining useful life” of the source for 

BART determinations as one element of the overall cost analysis. The “remaining useful life” of a source, if it 

represents a relatively short time period, may affect the annualized costs of retrofit controls. For example, 

the methods for calculating annualized costs in EPA's OAQPS Control Cost Manual require the use of a 

specified time period for amortization that varies based upon the type of control. If the remaining useful life 

will clearly exceed this time period, the remaining useful life has essentially no effect on control costs and on 

the BART determination process. Where the remaining useful life is less than the time period for amortizing 

costs, you should use this shorter time period in your cost calculations. 

MPCA Note: For units being evaluated in the OAQPS Control Cost Manual, any time period that is less than 

the lifetime of the control equipment set in the Control Cost Manual, e.g., the remaining life of the equipment, 

should be supported with a rationale that includes an assessment of why it is not reasonable to assume the 

facility will maintained or reconstructed for continued operation, thus allowing the control equipment to be 

used for an extended period. 

2. For purposes of these guidelines, the remaining useful life is the difference between: 

(1) The date that controls will be put in place (capital and other construction costs incurred before 

controls are put in place can be rolled into the first year, as suggested in EPA's OAQPS Control 

Cost Manual); you are conducting the BART analysis; and 

(2) The date the facility permanently stops operations. Where this affects the BART determination, 

this date should be assured by a federally- or State-enforceable restriction preventing further 
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operation. 

3. We recognize that there may be situations where a source operator intends to shut down a source by a 

given date, but wishes to retain the flexibility to continue operating beyond that date in the event, for 

example, that market conditions change. Where this is the case, your BART analysis may account for this, 

but it must maintain consistency with the statutory requirement to install BART within 5 years. Where the 

source chooses not to accept a federally enforceable condition requiring the source to shut down by a given 

date, it is necessary to determine whether a reduced time period for the remaining useful life changes the 

level of controls that would have been required as BART. 

If the reduced time period does change the level of BART controls, you may identify, and include as part of 

the BART emission limitation, the more stringent level of control that would be required as BART if there 

were no assumption that reduced the remaining useful life. You may incorporate into the BART emission 

limit this more stringent level, which would serve as a contingency should the source continue operating 

more than 5 years after the date EPA approves the relevant SIP. The source would not be allowed to 

operate after the 5-year mark without such controls. If a source does operate after the 5-year mark without 

BART in place, the source is considered to be in violation of the BART emissions limit for each day of 

operation. 

5. Step 5: How should I determine visibility impacts in the BART determination? 

The following is an approach you may use to determine visibility impacts (the degree of visibility improvement 

for each source subject to BART) for the BART determination. Once you have determined that your source 

or sources are subject to BART, you must conduct a visibility improvement determination for the source(s) as 

part of the BART determination. When making this determination, we believe you have flexibility in setting 

absolute thresholds, target levels of improvement, or de minimis levels since the deciview improvement must 

be weighed among the five factors, and you are free to determine the weight and significance to be assigned 

to each factor. For example, a 0.3 deciview improvement may merit a stronger weighting in one case versus 

another, so one “bright line” may not be appropriate. [Note that if sources have elected to apply the most 

stringent controls available, consistent with the discussion in section E. step 1. below, you need not conduct, 

or require the source to conduct, an air quality modeling analysis for the purpose of determining its visibility 

impacts.] 

Use CALPUFF17, or other appropriate dispersion model to determine the visibility improvement expected at a 

Class I area from the potential BART control technology applied to the source. Modeling should be 

conducted for SO2, NOX, and direct PM emissions (PM2.5 and/or PM10). If the source is making the visibility 

determination, you should review and approve or disapprove of the source's analysis before making the 

expected improvement determination. There are several steps for determining the visibility impacts from an 

individual source using a dispersion model: 

17 The model code and its documentation are available at no cost for download from 

http://www.epa.gov/scram001/tt22.htm#calpuff.

• Develop a modeling protocol. 

Some critical items to include in a modeling protocol are meteorological and terrain data, as well as sourcespecific information (stack height, temperature, exit velocity, elevation, and allowable and actual emission 

rates of applicable pollutants), and receptor data from appropriate Class I areas. We recommend following 

EPA's Interagency Workgroup on Air Quality Modeling (IWAQM) Phase 2 Summary Report and 

Recommendations for Modeling Long Range Transport Impacts18 for parameter settings and meteorological 

data inputs; the use of other settings from those in IWAQM should be identified and explained in the protocol. 

18 Interagency Workgroup on Air Quality Modeling (IWAQM) Phase 2 Summary Report and 

Recommendations for Modeling Long Range Transport Impacts, U.S. Environmental Protection 

Agency, EPA–454/R–98–019, December 1998. 

One important element of the protocol is in establishing the receptors that will be used in the model. The 
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receptors that you use should be located in the nearest Class I area with sufficient density to identify the 

likely visibility effects of the source. For other Class I areas in relatively close proximity to a BART-eligible 

source, you may model a few strategic receptors to determine whether effects at those areas may be greater 

than at the nearest Class I area. For example, you might chose to locate receptors at these areas at the 

closest point to the source, at the highest and lowest elevation in the Class I area, at the IMPROVE monitor, 

and at the approximate expected plume release height. If the highest modeled effects are observed at the 

nearest Class I area, you may choose not to analyze the other Class I areas any further as additional 

analyses might be unwarranted. 

You should bear in mind that some receptors within the relevant Class I area may be less than 50 km from 

the source while other receptors within that same Class I area may be greater than 50 km from the same 

source. As indicated by the Guideline on Air Quality Models, this situation may call for the use of two 

different modeling approaches for the same Class I area and source, depending upon the State's chosen 

method for modeling sources less than 50 km. In situations where you are assessing visibility impacts for 

source-receptor distances less than 50 km, you should use expert modeling judgment in determining visibility 

impacts, giving consideration to both CALPUFF and other EPA-approved methods. 

In developing your modeling protocol, you may want to consult with EPA and your regional planning 

organization (RPO). Up-front consultation will ensure that key technical issues are addressed before you 

conduct your modeling. 

MPCA Note: For determining visibility impacts of the various control alternatives, use the modeling protocol 

developed by the MPCA titled “BART Modeling Protocol to Determine Sources Subject-to-BART and for 

BART Determinations in the State of Minnesota, Final Draft, <insert date>”. It is available at: 

http://www.pca.state.mn.us/air/regionalhaze.html <Note this document has not yet been finalized which 

means it has not been approved by EPA as part of the regional haze SIP. The specific emissions and stack 

parameter inputs used for each facility in the subject-to-BART modeling will be available at 

http://www.pca.state.mn.us/air/regionalhaze.html . The Final Draft version should be available in February, 

2006> 

If you did not estimate PM2.5 emissions in the Request for Information spreadsheet to identify BART-eligible 

sources, then the MPCA estimated a maximum 24-hour average actual PM2.5 emission rate using the PM10 

The MPCA estimated PM2.5 by scaling the PM10 emissions to PM2.5 using the PM2.5/PM10 ratio 

calculated by the MPCA for the 2002 emissions inventory. To quantify PM2.5 emissions in the 2002 

emissions inventory, the MPCA used three different methods: 1) If the facility didn’t submit PM10 stack test 

data, MPCA estimated both the PM2.5 and PM10 primary emissions (filterable +condensable) using 

uncontrolled emission factors from EPA’s FIRE database and applying MPCA default control efficiencies; 2) 

If the facility did submit PM10 stack test data, MPCA estimated the PM2.5 by scaling the existing ration of 

PM2.5/PM10 primary emissions derived from method #1; or 3) If the facility’s SCC were not available in 

FIRE, MPCA estimated the PM2.5 using EPA’s PM Calculator 

http://www.epa.gov/ttn/chief/software/pmcalc/index.html

Thus, PM2.5 emissions will be the scaled PM2.5 (fine PM) and the remainder (PM 2.5-10 ) will be assigned to 

PM10 (coarse PM). It is possible the PM2.5/PM10 ratio for the control alternative will not be the same as the 

base case ratio. If the ratio will not be the same, it is recommended that you use the method used by the 

MPCA to estimate PM2.5 emissions for the various control alternatives evaluated. Don Sheperd of the 

National Park Service has developed PM10 speciation methods for various emission units (large coal-fired 

boilers, thermal dryers, oil boilers, and cement kilns) with control applied. If you have a BART-eligible 

emission unit for which PM10 speciation data is available, then you may use that method instead. <These 

methods are still under development and not yet available on-line. Contact Don Sheperd at 

don_shepherd@nps.gov, if you would like the most recent drafts.> If speciation data for particulate matter 

emissions is available from stack testing, then such speciation may be used in the modeling provided the 

basis for speciation is documented. Please consult with MPCA staff if you plan to use stack test data to 

speciate particulate matter for modeling purposes. 

• For each source, run the model, at pre-control and post-control emission rates according to the 

accepted methodology in the protocol. 
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Use the 24-hour average actual emission rate from the highest emitting day of the meteorological period 

modeled (for the pre-control scenario). Calculate the model results for each receptor as the change in 

deciviews compared against natural visibility conditions. Post-control emission rates are calculated as a 

percentage of pre-control emission rates. For example, if the 24-hr pre-control emission rate is 100 lb/hr of 

SO2, then the post control rate is 5 lb/hr if the control efficiency being evaluated is 95 percent. 

MPCA Note: Provide tables with the pre-control and post-control inputs used for the modeling runs. See the 

suggested format in Attachment 3. 

• Make the net visibility improvement determination. 

Assess the visibility improvement based on the modeled change in visibility impacts for the pre-control and 

post-control emission scenarios. You have flexibility to assess visibility improvements due to BART controls 

by one or more methods. You may consider the frequency, magnitude, and duration components of 

impairment. Suggestions for making the determination are: 

• Use of a comparison threshold, as is done for determining if BART-eligible sources should be subject to a 

BART determination. Comparison thresholds can be used in a number of ways in evaluating visibility 

improvement (e.g., the number of days or hours that the threshold was exceeded, a single threshold for 

determining whether a change in impacts is significant, or a threshold representing an x percent change in 

improvement). 

MPCA Note: The MPCA will not be providing you with a comparison threshold for evaluating visibility 

improvement. The MPCA does not believe that the degree of visibility improvement should be contingent 

upon perceptibility. This approach is consistent with EPA’s Guidelines and EPA’s subsequent clarification of 

the Guidelines. In its Guidelines, EPA did not recommend a deciview threshold for states to use in evaluating 

the degree of visibility improvement factor for a BART determination. 

• Compare the 98th percent days for the pre- and post-control runs. 

Note that each of the modeling options may be supplemented with source apportionment data or source 

apportionment modeling. 

MPCA Note: See Attachment 3 for the MPCA’s suggested format to use in providing results of the 98th

percentile days for the pre- and post-control runs for each of the model years as well as the combination of 

all three model years. In addition, the MPCA is asking that you report the number of days above 0.5 

deciview for each of the three model years as well as the combination of all three model years. The use of 

0.5 is not intended as a threshold, but merely another metric by which to understand visibility modeling 

results.

E. How do I select the “best” alternative, using the results of Steps 1 through 5? 

1. Summary of the Impacts Analysis 

From the alternatives you evaluated in Step 3, we recommend you develop a chart (or charts) displaying for 

each of the alternatives: 

(1) Expected emission rate (tons per year, pounds per hour); 

(2) Emissions performance level (e.g., percent pollutant removed, emissions per unit product, 

lb/MMBtu, ppm); 
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(3) Expected emissions reductions (tons per year); 

(4) Costs of compliance—total annualized costs ($), cost effectiveness ($/ton), and incremental cost 

effectiveness ($/ton), and/or any other cost-effectiveness measures (such as $/deciview); 

(5) Energy impacts; 

(6) Non-air quality environmental impacts; and 

(7) Modeled visibility impacts. 

2. Selecting a “best” alternative 

1. You have discretion to determine the order in which you should evaluate control options for BART. 

Whatever the order in which you choose to evaluate options, you should always (1) display the options 

evaluated; (2) identify the average and incremental costs of each option; (3) consider the energy and non-air 

quality environmental impacts of each option; (4) consider the remaining useful life; and (5) consider the 

modeled visibility impacts. You should provide a justification for adopting the technology that you select as 

the “best” level of control, including an explanation of the CAA factors that led you to choose that option over 

other control levels. 

MPCA Note: The MPCA would like you to use a top-down approach to evaluate control strategies. If you 

determine that the most stringent alternative in the ranking does not impose unreasonable costs of 

compliance, taking into account both average and incremental costs, the analysis begins with the 

presumption that this level is selected. Under this, you would then proceed to consider whether energy and 

non-air quality environmental impacts would justify selection of an alternative control option. If there are no 

outstanding issues regarding energy and non-air quality environmental impacts, the analysis is ended and 

the most stringent alternative is identified as the “best system of continuous reduction.” If you determine that 

the most stringent alternative is unacceptable due to such impacts, this approach would require you to 

document the rationale for this finding. Then, the next most effective alternative in the listing becomes the 

new control candidate and is similarly evaluated. This process continues until you identify a technology 

which does not pose unacceptable costs of compliance, energy and/or non-air quality environmental impacts. 

MPCA staff will be available to work with you during your BART analysis preparation to address your 

questions and concerns, such as the specific concern that a particular technology favored by you would be 

eliminated under a top-down approach. In making the BART determination itself, all factors will be 

considered, including the degree of visibility improvement. 

2. In the case where you are conducting a BART determination for two regulated pollutants on the same 

source, if the result is two different BART technologies that do not work well together, you could then 

substitute a different technology or combination of technologies. 

3. In selecting a “best” alternative, should I consider the affordability of controls? 

1. Even if the control technology is cost effective, there may be cases where the installation of 

controls would affect the viability of continued plant operations. 

2. There may be unusual circumstances that justify taking into consideration the conditions of the 

plant and the economic effects of requiring the use of a given control technology. These effects 

would include effects on product prices, the market share, and profitability of the source. Where 

there are such unusual circumstances that are judged to affect plant operations, you may take into 

consideration the conditions of the plant and the economic effects of requiring the use of a control 

technology. Where these effects are judged to have a severe impact on plant operations you may 

consider them in the selection process, but you may wish to provide an economic analysis that 

demonstrates, in sufficient detail for public review, the specific economic effects, parameters, and 

reasoning. (We recognize that this review process must preserve the confidentiality of sensitive 

business information). Any analysis may also consider whether other competing plants in the same 
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industry have been required to install BART controls if this information is available. 

4. Sulfur dioxide limits for utility boilers 

You must require 750 MW power plants to meet specific control levels for SO2 of either 95 percent control or 

0.15 lbs/MMBtu, for each EGU greater than 200 MW that is currently uncontrolled unless you determine that 

an alternative control level is justified based on a careful consideration of the statutory factors. Thus, for 

example, if the source demonstrates circumstances affecting its ability to cost-effectively reduce its 

emissions, you should take that into account in determining whether the presumptive levels of control are 

appropriate for that facility. For a currently uncontrolled EGU greater than 200 MW in size, but located at a 

power plant smaller than 750 MW in size, such controls are generally cost-effective and could be used in 

your BART determination considering the five factors specified in CAA section 169A(g)(2). While these levels 

may represent current control capabilities, we expect that scrubber technology will continue to improve and 

control costs continue to decline. You should be sure to consider the level of control that is currently best 

achievable at the time that you are conducting your BART analysis. 

For coal-fired EGUs with existing post-combustion SO2 controls achieving less than 50 percent removal 

efficiencies, we recommend that you evaluate constructing a new FGD system to meet the same emission 

limits as above (95 percent removal or 0.15 lb/mmBtu), in addition to the evaluation of scrubber upgrades 

discussed below. For oil-fired units, regardless of size, you should evaluate limiting the sulfur content of the 

fuel oil burned to 1 percent or less by weight. 

For those BART-eligible EGUs with pre-existing post-combustion SO2 controls achieving removal efficiencies 

of at least 50 percent, your BART determination should consider cost effective scrubber upgrades designed 

to improve the system's overall SO2 removal efficiency. There are numerous scrubber enhancements 

available to upgrade the average removal efficiencies of all types of existing scrubber systems. We 

recommend that as you evaluate the definition of “upgrade,” you evaluate options that not only improve the 

design removal efficiency of the scrubber vessel itself, but also consider upgrades that can improve the 

overall SO2 removal efficiency of the scrubber system. Increasing a scrubber system's reliability, and 

conversely decreasing its downtime, by way of optimizing operation procedures, improving maintenance 

practices, adjusting scrubber chemistry, and increasing auxiliary equipment redundancy, are all ways to 

improve average SO2 removal efficiencies. 

We recommend that as you evaluate the performance of existing wet scrubber systems, you consider some 

of the following upgrades, in no particular order, as potential scrubber upgrades that have been proven in the 

industry as cost effective means to increase overall SO2 removal of wet systems: 

(a) Elimination of Bypass Reheat; 

(b) Installation of Liquid Distribution Rings; 

(c) Installation of Perforated Trays; 

(d) Use of Organic Acid Additives; 

(e) Improve or Upgrade Scrubber Auxiliary System Equipment; 

(f) Redesign Spray Header or Nozzle Configuration. 

We recommend that as you evaluate upgrade options for dry scrubber systems, you should consider the 

following cost effective upgrades, in no particular order: 

(a) Use of Performance Additives; 
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(b) Use of more Reactive Sorbent; 

(c) Increase the Pulverization Level of Sorbent; 

(d) Engineering redesign of atomizer or slurry injection system. 

You should evaluate scrubber upgrade options based on the 5 step BART analysis process. 

5. Nitrogen oxide limits for utility boilers 

You should establish specific numerical limits for NOX control for each BART determination. For power plants 

with a generating capacity in excess of 750 MW currently using selective catalytic reduction (SCR) or 

selective non-catalytic reduction (SNCR) for part of the year, you should presume that use of those same 

controls year-round is BART. For other sources currently using SCR or SNCR to reduce NOX emissions 

during part of the year, you should carefully consider requiring the use of these controls year-round as the 

additional costs of operating the equipment throughout the year would be relatively modest. 

For coal-fired EGUs greater than 200 MW located at greater than 750 MW power plants and operating 

without post-combustion controls (i.e., SCR or SNCR), we have provided presumptive NOX limits, 

differentiated by boiler design and type of coal burned. You may determine that an alternative control level is 

appropriate based on a careful consideration of the statutory factors. For coal-fired EGUs greater than 200 

MW located at power plants 750 MW or less in size and operating without post-combustion controls, you 

should likewise presume that these same levels are cost-effective. You should require such utility boilers to 

meet the following NOX emission limits, unless you determine that an alternative control level is justified 

based on consideration of the statutory factors. The following NOX emission rates were determined based on 

a number of assumptions, including that the EGU boiler has enough volume to allow for installation and 

effective operation of separated overfire air ports. For boilers where these assumptions are incorrect, these 

emission limits may not be cost-effective. 

 

Table 1_Presumptive NOX Emission Limits for BART-Eligible Coal-Fired Units19

--------------------------------------------------------------------------------------------------------------------- 

 NOX presumptive 

 Unit type Coal type limit (lb/ 

 mmbtu) 20

--------------------------------------------------------------------------------------------------------------------- 

Dry-bottom wall-fired......... Bituminous............ 0.39 

 Sub-bituminous........ 0.23 

 Lignite............... 0.29 

Tangential-fired.............. Bituminous............ 0.28 

 Sub-bituminous........ 0.15 

 Lignite............... 0.17 

Cell Burners.................. Bituminous............ 0.40 

 Sub-bituminous........ 0.45 

Dry-turbo-fired............... Bituminous............ 0.32 

 Sub-bituminous........ 0.23 

Wet-bottom tangential-fired... Bituminous............ 0.62 

------------------------------------------------------------------------ 

19 No Cell burners, dry-turbo-fired units, nor wet-bottom tangential- 

 fired units burning lignite were identified as BART-eligible, thus no 

 presumptive limit was determined. Similarly, no wet-bottom tangential- 

 fired units burning sub-bituminous were identified as BART-eligible. 

20 These limits reflect the design and technological assumptions 

 discussed in the technical support document for NOX limits for these 

 guidelines. See 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, 2005. 
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Most EGUs can meet these presumptive NOX limits through the use of current combustion control 

technology, i.e. the careful control of combustion air and low-NOX burners. For units that cannot meet these 

limits using such technologies, you should consider whether advanced combustion control technologies such 

as rotating opposed fire air should be used to meet these limits. 

Because of the relatively high NOX emission rates of cyclone units, SCR is more cost-effective than the use 

of current combustion control technology for these units. The use of SCRs at cyclone units burning 

bituminous coal, sub-bituminous coal, and lignite should enable the units to cost-effectively meet NOX rates 

of 0.10 lbs/mmbtu. As a result, we are establishing a presumptive NOX limit of 0.10 lbs/mmbtu based on the 

use of SCR for coal-fired cyclone units greater than 200 MW located at 750 MW power plants. As with the 

other presumptive limits established in this guideline, you may determine that an alternative level of control is 

appropriate based on your consideration of the relevant statutory factors. For other cyclone units, you should 

review the use of SCR and consider whether these post-combustion controls should be required as BART. 

For oil-fired and gas-fired EGUs larger than 200MW, we believe that installation of current combustion control 

technology to control NOX is generally highly cost-effective and should be considered in your determination 

of BART for these sources. Many such units can make significant reductions in NOX emissions which are 

highly cost-effective through the application of current combustion control technology21 

21 See 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, 2005. 

MPCA Note: While the MPCA has not yet made the determination that CAIR substitutes for BART, we would 

like you to conduct a BART analysis for CAIR EGU at your facility that the MPCA has determined contribute 

to visibility impairment in a Class I area. We would like the analysis to include an evaluation of technology to 

reduce emissions to at least presumptive BART levels regardless of EGU size. 

V. Enforceable Limits/Compliance Date 

To complete the BART process, you must establish enforceable emission limits that reflect the BART 

requirements and require compliance within a given period of time. In particular, you must establish an 

enforceable emission limit for each subject emission unit at the source and for each pollutant subject to 

review that is emitted from the source. In addition, you must require compliance with the BART emission 

limitations no later than 5 years after EPA approves your regional haze SIP. If technological or economic 

limitations in the application of a measurement methodology to a particular emission unit make a 

conventional emissions limit infeasible, you may instead prescribe a design, equipment, work practice, 

operation standard, or combination of these types of standards. You should consider allowing sources to 

“average” emissions across any set of BART-eligible emission units within a fenceline, so long as the 

emission reductions from each pollutant being controlled for BART would be equal to those reductions that 

would be obtained by simply controlling each of the BART-eligible units that constitute BART-eligible source. 

You should ensure that any BART requirements are written in a way that clearly specifies the individual 

emission unit(s) subject to BART regulation. Because the BART requirements themselves are “applicable” 

requirements of the CAA, they must be included as title V permit conditions according to the procedures 

established in 40 CFR part 70 or 40 CFR part 71. 

Section 302(k) of the CAA requires emissions limits such as BART to be met on a continuous basis. 

Although this provision does not necessarily require the use of continuous emissions monitoring (CEMs), it is 

important that sources employ techniques that ensure compliance on a continuous basis. Monitoring 

requirements generally applicable to sources, including those that are subject to BART, are governed by 

other regulations. See, e.g., 40 CFR part 64 (compliance assurance monitoring); 40 CFR 70.6(a)(3) (periodic 

monitoring); 40 CFR 70.6(c)(1) (sufficiency monitoring). Note also that while we do not believe that CEMs 

would necessarily be required for all BART sources, the vast majority of electric generating units potentially 

subject to BART already employ CEM technology for other programs, such as the acid rain program. In 

addition, emissions limits must be enforceable as a practical matter (contain appropriate averaging times, 
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compliance verification procedures and recordkeeping requirements). In light of the above, the permit must: 

• Be sufficient to show compliance or noncompliance (i.e., through monitoring times of operation, 

fuel input, or other indices of operating conditions and practices); and 

• Specify a reasonable averaging time consistent with established reference methods, contain 

reference methods for determining compliance, and provide for adequate reporting and 

recordkeeping so that air quality agency personnel can determine the compliance status of the 

source; and 

• For EGUS, specify an averaging time of a 30-day rolling average, and contain a definition of “boiler 

operating day” that is consistent with the definition in the proposed revisions to the NSPS for utility 

boilers in 40 CFR Part 60, subpart Da. 22. You should consider a boiler operating day to be any 24-

hour period between 12:00 midnight and the following midnight during which any fuel is combusted 

at any time at the steam generating unit. This would allow 30-day rolling average emission rates to 

be calculated consistently across sources. 

MPCA Note: While the MPCA will determine the compliance date and emission limit, we encourage you to 

suggest a compliance schedule and to propose a BART limit consistent with the above guidance 

The MPCA will allow you to “average” emissions across any set of BART-eligible emission units within a 

fenceline, so long as facility-wide emission reductions from each pollutant being controlled for BART would 

be equal or greater than those reductions expected by simply controlling each of the BART-eligible units at a 

BART-eligible source. 

.