1 

MEMORANDUM

TO: Jim Eddinger, EPA/SPPD

FROM:   Eastern Research Group, Inc.

DATE:    August 2012

SUBJECT: Revised MACT Floor Analysis (August 2012) for the Industrial, Commercial, and

Institutional Boilers and Process Heaters National Emission Standards for

Hazardous Air Pollutants – Major Source

1.0 INTRODUCTION

The purpose of this memorandum is to present the revised results of the maximum

achievable control technology (MACT) floor determinations for boilers and process heaters at

major sources of hazardous air pollutants (HAP).  We determined the MACT floors using data

obtained from two recently implemented Information Collection Requests (ICRs) approved

under OMB Control No. 2060‐0616:  ICR numbers 2286.01 and 2286.03, as well as new data and

data corrections received before, during and after the public comment period on the

reconsideration proposal.1,2,3 This memo is a follow‐up to the memorandum prepared to

document the MACT floor methodology in the December, 2011 proposed reconsideration of

the major source boiler and process heater rule.4 This feature highlights only the changes to the

methodology and results since the previous analysis.

This memorandum is organized as follows:

1.0 Introduction

2.0 MACT Floors for Existing Sources

3.0 MACT Floors for New Sources

4.0 Analysis of CO and Formaldehyde Paired Data

5.0 References

Appendix A:  Hg, HCl, and TSM Variability as a Function of Fuel Variability
2 

Appendix B:  Ranked Emission Data for MACT Floor Analysis

Appendix C:  Upper Prediction Limit (UPL) Calculations for Existing Sources

Appendix D:  Summary of Statistical, Fuel, and RDL Variability for Existing Sources

Appendix E:  UPL Calculations for New Sources

Appendix F:  Summary of Statistical, Fuel, and RDL Variability for New Sources

Appendix G: Analysis of Paired CO and NOx Data for New Sources

Appendix H: Analysis of Paired CO and Formaldehyde Data

   
3 

2.0 MACT FLOORS FOR EXISTING SOURCES

The methods and assumptions used to calculate MACT floors for existing sources are

identical to the methods and assumptions used in the MACT floor analysis for the proposed

reconsideration of the rule, with a few minor exceptions.  The methods and assumptions used

to calculate MACT floors for the proposed reconsideration of the rule are documented in

another memorandum.4 The exceptions to the methods and assumptions that were used for

analysis for the promulgated rule are provided below:

1. For the proposed reconsideration of the rule, a TSM alternative limit was not

provided as an option for boilers or process heaters designed to combust liquid fuels

(including those units located in non‐continental states or territories).  The

promulgated rule contains a TSM alternative for liquid subcategories, and thus

MACT floors were calculated for these subcategories and are presented in the

appendices to this memorandum.  A TSM alternative was calculated and included in

the proposed reconsideration of the rule, and the methods for conducting that

calculation remain the same.

2. For boilers and process heaters designed to combust coal or other solid fossil fuels,

the proposed reconsideration of the rule provided PM and TSM emission limits

parsed by combustor design.  The promulgated rule combines all boilers or process

heaters designed to burn these fuels into a single subcategory, units design to burn

coal or solid fossil fuel, and all units in this subcategory are subject to a single PM

limit (or TSM alternative limit).

3. The methods used to incorporate instrument calibration and measurement error for

CO emissions have changed slightly since the previous analysis.  The change in the

analysis affected CO emissions from all subcategories, and the revised methodology

is discussed in another memorandum.5

4. One TSM fuel analysis sample was provided with comments from a facility

containing non‐continental liquid units.  For the MACT floor analysis for the

proposed reconsideration of the rule, no TSM emissions or fuel analysis data were

available from non‐continental liquid units and the UPL was instead based on a value
4 

calculated from available emissions and fuel analysis data from boilers or process

heaters combusting residual fuel oil in continental locations.  With the newly

provided TSM fuel analysis data, the non‐continental liquid subcategory no longer

has any data gaps; all MACT floors for the subcategory were calculated based on

actual data from units in the subcategory.

5. For two subcategories, the existing source MACT floor was calculated based on the

emissions from a unit other than the top‐ranked unit:

a. The PM MACT floor for Biomass/Bio‐based Solid Suspension Burners is

calculated from the emissions from the #3 ranked unit.  The #3 ranked

unit was also selected in the reconsideration proposal. The top 12

percent for this subcategory equates to a single unit, and the units

ranked #1 and #2 each reported data from the co‐firing of natural gas.  As

discussed in the memorandum for the previous analysis, MACT floors

calculated from a single source must be based on emissions data

combusting 100% of the fuel represented by the subcategory.4

b. The TSM MACT floor for Biomass/Bio‐based Solid Suspension Burners is

calculated from the emissions from the #2 ranked unit.  The top 12

percent for this subcategory equates to a single unit, and the top‐ranked

unit only has two valid test runs. The third test run did not pass data

review procedures for TSM that were conducted since the

reconsideration proposal.  As discussed in the memorandum for the

previous analysis, MACT floors calculated from a single source must be

based on at least three runs of data.4

6. The 99 percent UPL computed for CO in the biomass/bio‐based solid suspension

burner subcategory is over seven times the maximum reported test run from the

best performing unit.  None of the other UPL calculations resulted in a value that

was so much higher than the maximum test run from the best performers. Instead

the UPL calculations for other subcategories resulted in a value between 0.2 and 3.6

times the maximum test run, with an average of 1.3. As a result we set the floor for

CO at this subcategory equal to the maximum test run instead of the UPL in order to
5 

establish an emission limit not less stringent than the performance achieved by the

best performing unit.

7. After further review of certain best performer test reports to assess data quality,

some tests were removed from the analysis because they did not pass a quality

review.  Efforts were made to correct erroneous data when laboratory appendices

were available to re‐compute the numbers, but this was not possible in all cases

based on the data available at the time of this rulemaking.  A discussion of the

approaches used and findings from the data quality review process are available in

another memorandum.6

8. Minimum CO emission limits of 130 ppm @ 3% O2 for all new and existing unit

subcategories were implemented based on a review of paired CO and formaldehyde

data.  A discussion of this new analysis is presented in Section 4.0.

Fuel analysis variability was calculated using the same methods and assumptions used in

the previous analysis with one exception. For the solid fuel subcategory the March 2011 final

rule and the reconsideration proposal did not adopt a fuel variability factor into the MACT floor

emission limit. However, in response to petitions for reconsideration on this issue and public

comments received on the solid fuel subcategory a fuel variability factor was adopted in this

analysis for the amended final rule, where data was available. Given that the solid fuel category

does exhibit some heterogeneous fuel make‐up amongst the top performing units, the EPA

adopted the average fuel variability ratio for each pollutant instead of the maximum fuel

variability ratio. This average value, calculated from only those fuel samples where the FVF ratio

was greater than one, was selected to not overestimate fuel variability for a subcategory that

has a mix of biomass, coal, and other solid fossil stack test data factored into the 99% UPL

calculations, but it recognizes that some additional fuel variability is present in the best

performing units that may not be represented by the stack test data alone. While the 99% UPL

calculation incorporates variability between test runs resulting from variability in

measurements, unit operations, and control device operations and performance, the FVF ratio

incorporates variability in fuel feedstocks that occur at best performing units during periods not

covered by the stack tests.  The FVF ratio, as described in previous memoranda4

, compares the

fuel constituents during the test with the fuel constituents during other periods of operation in
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order to evaluate the full range of fuels consumed by these best performing units.  

Detection level variability was again calculated and compared to the calculated MACT

floor.  The methods used to assign detection level variability are discussed in another

memorandum.7 The methods used calculate fuel variability, and the methods used to compare

the detection level variability to the MACT floor are discussed in the memorandum for the

proposed reconsideration analysis.4 A summary of the fuel analysis variability is provided in

Appendix A.  The ranked emissions data used in the MACT floor calculations are provided in

Appendix B.  The MACT floor calculations for existing sources for each subcategory are provided

in Appendix C.  A summary of all variability calculations for existing sources is provided in

Appendix D.  An analysis of paired CO and formaldehyde data is presented in Appendix H. The

finalized existing source emission limits for each subcategory are provided in Table 1, below.
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Table 1:  Summary of Calculated MACT Floor Limits for Existing Boilers and Process Heaters at Major Sources of HAP

Subcategory

Filterable

Particulate

Matter

(lb/MMBtu)

TSM 8

(lb/MMBtu)

Hydrogen

Chloride

(lb/MMBtu)

Mercury

(lb/MMBtu)

CO

(ppm @ 3% O2)

All Solid Fuels 0.022 5.7E‐06

Coal/Fossil Solid 0.040 5.3E‐05

FB 130 B

FBHE 140

PC 130 B

Stoker/Other 160 A

Biomass/Bio‐based

Solid

Dutch Oven/Pile

Burner 0.28 2.0E‐03 770A

FB 0.11 1.2E‐03 470 A

Fuel Cell 0.020 5.8E‐03 1,100 A

Suspension Burner 0.051 6.5E‐03 2,400 A

Suspension/Grate 0.44 4.5E‐04 2,800 A

Wet Biomass

Stoker/Other 0.037 2.4E‐04 1,500 A

Dry Biomass

Stoker/Other 0.32 4.0E‐03 460

Liquid 0.0011 2.0E‐06

Heavy Liquid 0.062 2.0E‐04 130 B

Light Liquid 0.0079 6.2E‐05 130 B

Non‐Continental

Liquid 0.27 8.6E‐04 130 B

Process Gas 0.0067 2.1E‐04 0.0017 7.9E‐06 130 B

Notes:

 Red text indicates at least one test run used to calculate the UPL limit was reported as non‐detect data.  

 Blue shaded cells indicate limits that incorporate fuel analysis variability. The Hg floor for liquid units

incorporates both the 3*RDL value and fuel analysis variability. This value represents the 3*RDL multiplied

by the FVF.

 Although default maximum calibration errors were used for CO, if data was flagged as non‐detect when

initially reported it was still considered to be non‐detect data even if the value defaulted to the calibration

error.

 Orange cells indicate limits that are based on the maximum top performer test run value.

A CO MACT floor is based on adjusted data that consider measurement error for measurements obtained

with an instrument test method. (See details explained in Reference 8).

B CO MACT floor is based on a minimum emission limit of 130 ppm as discussed in Section 4.0.  

3.0 MACT FLOORS FOR NEW SOURCES

As with existing sources, the methods and assumptions used to calculate MACT floors

for new sources are identical to the methods and assumptions used in the MACT floor analysis

for the proposed reconsideration of the rule, with a few minor exceptions.  The methods and
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assumptions used to calculate MACT floors for the proposed reconsideration of the rule are

documented in another memorandum.4 The exceptions to the methods and assumptions that

were used for analysis for the promulgated rule are provided below:

1. Identical to the MACT floor analysis for the proposed reconsideration of the rule,

new source MACT floors were calculated on emissions from a unit other than the

top ranked unit in the subcategory under a few circumstances.  MACT floors for new

sources were calculated based on a lower‐ranked unit if the emissions data from the

top ranked unit met one of the following criteria:

a. Fewer than three total test runs. Using the lowest emitting unit with three

test runs ensures that adequate variability can be incorporated into the limit to

guarantee that future sources can repeatedly meet the limit during their

compliance tests.

b. Emissions data based on the co‐firing of fuels from separate

subcategories. A unit co‐firing natural gas or other fuels outside the

subcategory is not considered to be representative of the best similar source

for the subcategory because not all units have the ability to co‐fire fuels.

c. Emissions data based on the combustion of process‐specific fuel (i.e.,

sludges, anhydrides waste, etc.). Since process‐specific fuels cannot be

reasonably purchased or obtained by other sources in the subcategory, these

fuels are not representative of the best single source for the subcategory.

A list of the specific subcategories for which substitutions were made in calculating

the new source MACT floor can be found in Appendix E‐9.

2. For the CO MACT floor for each subcategory, the relationship between the top

performer’s CO and NOx emissions was investigated because the degree of NOx

control is constrained by the onset of CO emissions.  That is, the combustion

controls used to reduce NOx have the reverse effect on CO emissions.  NOx

reduction mechanisms including controlling the rate of fuel‐air mixing, reducing

oxygen availability in the initial combustion zone, and reducing peak flame

temperatures.  These NOx reduction mechanisms can potentially promote CO

formation.  Thus, a unit that operates to reduce the emissions of one pollutant
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which cause the emissions of another pollutant to increase cannot be reasonably

considered a “best performing unit.”   

The relationship between NOx and CO was evaluated from units that reported

paired NOx and CO emission tests.  If the reported NOx emissions were at least 50

times higher than their paired CO emissions, that test was not considered to be

representative of a best performer because its emissions of CO were very low at the

expense of increased NOx emissions. Based on the review of the paired CO and NOx

data, some of the best performing units emitting the lowest CO levels had NOx

levels much higher than the other top performing units.  In these cases, that unit

was disregarded from the MACT floor calculation since it does not represent a best

performing unit.  Many facilities have limitations on NOx emissions via permits or

other regulations.  As specified in public comments, testing configurations that

minimize CO often result in higher emissions of NOx; it is not expected that facilities

with NOx emission limitations would be able to demonstrate simultaneous

compliance with a CO limit if the CO limit was calculated based on a low CO emission

level that yielded a high‐NOx value.  This CO‐NOx relationship was investigated for

both existing and new sources, but substitutions were only made for new sources

since the MACT floor is calculated from the emissions from a single source.  For

existing sources, the presence of emissions data from additional sources increased

the variability such that the correlation between CO and NOx emissions had less of

an impact on the calculation and further EPA does not have paired emissions data

from all of the best performing units in the existing source floor calculations.  For the

subcategories where the existing source MACT floor was calculated from a single

unit, the NOx‐to‐CO ratio did not exceed 50 and therefore no tests were disqualified.  

However, there were three subcategories for new sources where the ratio was

exceeded, and another test was used to represent the CO emissions performance of

best performing unit in the subcategory:  Coal/Fossil Solid Pulverized Coal,

Coal/Fossil Solid Stoker/Sloped Grate/Other, and Heavy Liquid.  However, since the

resultant CO MACT floor for the Heavy Liquid subcategory was less stringent than
10 

the existing source MACT floor the new source CO emission limit was established a

level equal to the existing source limit.

3. Minimum CO emission limits of 130 ppm @ 3% O2 for all new and existing unit

subcategories were implemented based on a review of paired CO and formaldehyde

data.  A discussion of this new analysis is presented in Section 4.0.

The MACT floor calculations for new sources for each subcategory are provided in

Appendix E.  A summary of all variability calculations for existing sources is provided in

Appendix F.  An analysis of the paired CO and NOx emissions data is provided in Appendix G.  

An analysis of paired CO and formaldehyde data is presented in Appendix H. The finalized new

source emission limits for each subcategory are provided in Table 2, below.

Table 2:  Summary of Calculated MACT Floor Limits for New Boilers and Process Heaters at Major Sources of HAP

Subcategory

Filterable

Particulate

Matter

(lb/MMBtu)

TSM 8

(lb/MMBtu)

Hydrogen

Chloride

(lb/MMBtu)

Mercury

(lb/MMBtu)

CO

(ppm @ 3% O2)

All Solid Fuels 0.022 8.0E‐07

Coal/Fossil Solid 0.0011 2.3E‐05

FB 130 C

FBHE 140

PC 130 C

Stoker/Other 130 C

Biomass/Bio‐based

Solid

Dutch Oven/Pile

Burner 0.0032 3.9E‐05 330 A

FB 0.0098 8.3E‐05 230

Fuel Cell 0.020 2.9E‐05 910 A

Suspension Burner 0.030 6.5E‐03 2,400 A

Suspension/Grate 0.026 4.4E‐04 1,100 A

Wet Biomass

Stoker/Other 0.030 2.6E‐05 620 A

Dry Biomass

Stoker/Other 0.030 4.0E‐03 460

Liquid 0.00044 4.8E‐07B

Heavy Liquid 0.013 7.5E‐05 130 C

Light Liquid 0.0011 2.9E‐05 130 C

Non‐Continental

Liquid 0.023 8.6E‐04 130 C

Process Gas 0.0067 2.1E‐04 0.0017 7.9E‐06 130 C

Notes:

• Red text indicates at least one test run used to calculate the 99% UPL limit was reported as non‐detect

data.  
11 

 Blue shaded cells indicate limits that incorporate fuel analysis variability. The Hg, floor for liquid units

incorporates both the 3*RDL value and fuel analysis variability. This value represents the 3*RDL multiplied

by the FVF.

• Yellow shaded cells indicate limits where the calculated limit for new sources was less stringent than the

calculated limit for existing sources, so the limit for existing sources was used as the basis for the limit at

new sources.

• Green cells indicate limits that are based on the 3*RDL approach.

• Although default maximum calibration errors were used for CO, if data was flagged as non‐detect when

initially reported it was still considered to be non‐detect data even if the value defaulted to the calibration

error.

• Orange cells indicate limits that are based on the maximum top performer test run value.

• Red cells indicate limits that are based on a beyond‐the‐floor limit.

A CO MACT floor is based on adjusted data that consider measurement error for measurements obtained

with an instrument test method (See details explained in Reference 8).

B MACT floor limit is based on 3x RDL and also incorporates fuel analysis variability.

C CO MACT floor is based on a minimum emission limit of 130 ppm as discussed in Section 4.0.  

4.0 Analysis of CO and Formaldehyde Paired Data

Several stakeholders presented concerns in their comments about establishing a

minimum CO level such that the level is a representative proxy for organic HAP destruction.  In

order to evaluate whether or not a minimum CO level was an appropriate indicator for organic

HAP destruction in each subcategory, we evaluated the relationship between CO and

formaldehyde data using the phase I and II ICR data as well as subsequent data submittals.1,2,3

Formaldehyde was selected as the basis of the organic HAP comparison because it was the

most prevalent HAP in the ICR datasets and a large number (over 300) paired test runs existed

for CO and formaldehyde.  Looking at Chart H‐1a in Appendix H, the relationship between CO

and formaldehyde emissions exhibits a high R2 value for CO levels above 130 ppm, supporting

the selection of CO as a surrogate for organic HAP emissions at higher CO levels. Chart H‐1b in

Appendix H displays the relationship between CO and formaldehyde emissions for various

levels of CO for levels below 1000 ppm @ 3% O2 CO. Although the R2 values are not significantly

high for any of the four ranges of CO shown on this chart, the chart shows the lowest R2 value

for the relationship between formaldehyde and CO emissions at levels below 130 ppm,

suggesting that at these low CO levels, CO is not a good proxy for formaldehyde destruction

when looking across all of the paired CO and formaldehyde tests for this source category. In

addition to assessing the correlation between CO and formaldehyde at various levels of CO

emissions, a trend can be seen that mean formaldehyde levels are lowest when CO emissions

are in the range of 150 to 300 ppm. At levels lower than 150 ppm, the mean levels of

formaldehyde appear to increase (over two times the mean formaldehyde levels observed from
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units emitting CO levels between 130 and 300 ppm), as does the overall maximum value and

variability in formaldehyde emissions.  Fitting a quadratic regression line to the paired CO levels

as shown in Chart H‐1c, a slight increase in formaldehyde emissions is observed at CO levels

below 206 ppm @ 3% O2, suggesting a similar breakdown in the CO‐formaldehyde relationship

at low CO levels that is observed in Chart H‐1b.  

Due to limited paired dataset, a specific CO threshold below which formaldehyde

emissions stopped decreasing could not be established across the entire dataset. Therefore we

next looked at the relationship between CO and formaldehyde emissions in each subcategory

impacted by CO emission limits lower than 300 ppm @ 3% O2 in order to evaluate how the CO

threshold might be impacted by each combustor design.

Table 3:  Summary of Formaldehyde Emission Data for Various CO Emission Ranges

  

Corresponding Formaldehyde Levels

(ppm @ 3% O2)

Reported CO Level

(ppm @ 3% O2) Mean

Standard

Deviation Min Max

0 to 130 0.25 0.45 6.97E‐05 2.16

130 to 300 0.10 0.17 5.14E‐04 1.09

300 to 500 0.34 0.52 4.86E‐04 1.67

500 to 1000 0.58 1.07 1.96E‐04 5.27

The data in Table 3 show that CO is a poor surrogate for formaldehyde at levels below

130 ppm.  For this reason, a minimum CO emission limit of 130 ppm was established for all

existing and new source subcategories where the calculated 99% UPL was less than 130 ppm.  

Tables 4 and 5 summarize the subcategories for which the minimum CO standard was

established.

Table 4:  Summary of Selected CO MACT Floor Emission Levels for Existing Sources After Considering Minimum CO Emission

Limits
13 

Subcategory

Minimum CO

Emission Limit

(ppm @ 3% O2)

99% UPL CO Floor

from Methodology

in Section 2.0

(ppm @ 3% O2)A

Difference Between

Minimum CO Limit

and 99% UPL

(ppm @ 3% O2)

Rounded Amended

Final MACT Floor

Value and Basis

Coal‐FB 130 49  ‐81 130

(Minimum CO Limit)

Coal‐PC 130 62  ‐68 130

(Minimum CO Limit)

Heavy Liquid 130 12  ‐118 130

(Minimum CO Limit)

Light Liquid 130 6  ‐124 130

(Minimum CO Limit)

Non‐Continental

Liquid 130 32  ‐98 130(Minimum CO Limit)

Process Gas 130 5  ‐125 130

(Minimum CO Limit)

A See appendix D for a summary of calculated values discussed in Section 2.0.

Table 5:  Summary of Selected CO MACT Floor Emission Levels for New Sources After Considering Minimum CO Emission

Limits

Subcategory

Minimum CO

Emission Limit

(ppm @ 3% O2)

99% UPL CO

Floor from

Methodology in

Section 2.0

(ppm @ 3%

O2)A

Difference Between

Minimum CO Limit

and 99% UPL

(ppm @ 3% O2)

Rounded Amended

Final MACT Floor

Value and Basis

Coal‐FB 130 25  ‐105 130

(Minimum CO Limit)

Coal‐PC 130 60  ‐70 130

(Minimum CO Limit)

Coal‐Stoker/Sloped

Grate/Other 130 19  ‐111 130(Minimum CO Limit)

Heavy Liquid 130 12  ‐118 130

(Minimum CO Limit)

Light Liquid 130 3  ‐127 130

(Minimum CO Limit)

Non‐Continental Liquid 130 25  ‐105 130

(Minimum CO Limit)

Process Gas 130 5  ‐125 130

(Minimum CO Limit)

A See appendix F for a summary of calculated values discussed in Section 3.0.
14 

5.0 REFERENCES

1) Phase I ICR 2008 Combustion Survey. [ICR No. 2286.01]. OMB Control No. 2060‐0616 ‐ 

Information Collection Effort for Facilities with Combustion Units. Approved by OMB on

August 1, 2008.

2) Phase II ICR Test Plan Requesting Emission Testing from Boilers, Process Heaters, and

CISWI. [ICR No. 2286.03]. OMB Control No. 2060‐0616 ‐ Information Collection Effort for

Facilities with Combustion Units. Approved by OMB on May 21, 2009.

3) Eastern Research Group, Inc. Handling and Processing of Corrections and New Data in

the EPA ICR Databases. Revised August 2012.

4) Eastern Research Group, Inc. Revised MACT Floor Analysis (November 2011) for the

Industrial, Commercial, and Institutional Boilers and Process Heaters National Emission

Standards for Hazardous Air Pollutants – Major Source. Revised November 2011.

5) Eastern Research Group, Inc.  Incorporating Measurement Error in Reported Carbon

Monoxide (CO) and Total Hydrocarbon (THC) Data (Revised August 2012).  August 2012.

6) Eastern Research Group, Inc.  Revised (August 2012) Summary of Test Report Data

Review from Best Performing Units at Industrial, Commercial, and Institutional Boilers

and Process Heaters National Emission Standards for Hazardous Air Pollutants ‐ Major

Source. August 2012.

7) Eastern Research Group, Inc.  Revised (August 2012) Analysis of Minimum Detection

Levels from Industrial, Commercial, and Institutional Boilers and Process Heaters

National Emission Standards for Hazardous Air Pollutants ‐ Major Source.  August 2012.

8) Westlin, Peter.  U.S. EPA OAQPS/SPPD.  Measurement Detection Capabilities for EPA for

Instrumental Test Methods.  April 10, 2012.