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MEMORANDUM 

Date: August 2012 

To: Jim Eddinger, US EPA 

From: Eastern Research Group, Inc. 

Subject: CO CEMS MACT Floor Analysis (August 2012) for the Industrial, Commercial, and 

Institutional Boilers and Process Heaters National Emission Standards for Hazardous Air 

Pollutants – Major Source 

This memorandum describes the rationale, available data, and methodology for the 

alternative compliance option of a CO continuous emissions monitor (CEMS) MACT floor 

emission limit for the Boiler MACT amended final rule. This alternative is provided to increase 

compliance flexibility for boilers which already employ CEMS or may need to install CEMS for 

other regulations and it also provides flexibility for load-swinging units. 

The memorandum is organized as follows: 

1.0 Introduction 

2.0 CEMS MACT Floor Calculation Methodology – Existing Source 

2.1 Determining Best Performers 

2.2 Upper Prediction Limit Calculation 

2.3 Maximum Rolling Average of Top 6% 

2.4 Selection of CO CEMS MACT Floor 

3.0 CEMS MACT Floor Calculation Methodology - New Source 

4.0 Available CEMS Data 

5.0 CO CEMS MACT Floor Results 

5.1 Existing Source MACT Floors 

5.2 New Source MACT Floors 

6.0 References 

Appendix A: CO CEMS Subcategory Rankings and Raw Data 

Appendix B: CO CEMS Existing Source UPL Calculations 

Appendix C: CO CEMS New Source UPL Calculations 
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1.0 INTRODUCTION

For the Boiler MACT rule reconsideration proposal, a MACT floor analysis using the 

available CO CEMS data was performed in response to requests from petitioners.1 Commenters 

on the alternative CO CEMS limits in the reconsideration proposal provided additional CO 

CEMS data for certain subcategories for use in the current analysis. There were a few 

subcategories which still did not have data, but there was enough data available to analyze the 

options for most of the subcategories outlined in the amended final rule. Given the dataset 

available and definition changes regarding 10-day and 30-day rolling averages in the amended 

final rule, the CO CEMS MACT floors were computed using multiple methods. 

As will be discussed in the subsequent sections, the items mentioned below were changed 

for the amended final Boiler MACT rule from the December 2011 reconsideration proposal: 

1. In addition to 10-day rolling averages, 30-day rolling averages were calculated when 

sufficient data was provided to compute these longer averaging times; see section 4.0. 

2. Rolling averages were calculated using daily data and hourly data to provide four 

rolling average options; see sections 2.1 and 4.0. 

a. 10-day rolling averages 

b. 240-hour rolling averages (modified 10-day rolling average) 

c. 30-day rolling averages 

d. 720-hour rolling averages (modified 30-day rolling average) 

3. When multiple rolling averages were able to be calculated for a given subcategory, a 

hierarchy for use in UPL calculations was used: 720-hour rolling averages > 30-day 

rolling averages > 240-hour rolling averages > 10-day rolling averages; see sections 

2.1 and 4.0. 

4. The raw hourly or daily CO CEMS data were not used as inputs to the UPL equations 

for the MACT floor analysis, instead this data was reduced to the appropriate hourly 

or daily rolling averages, and the rolling average values themselves were used as 

inputs in the UPL calculations; see section 2.2. 

5. The UPL formula was modified such that the m parameter of the UPL equation—the 

test condition—now equals 1 instead of 1/the rolling average period; see section 2.2. 
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6. The highest value between the UPL and the maximum rolling average of the top 6 

percent was selected as the MACT floor for each subcategory; see section 2.3. This 

is consistent with the method presented in the alternative proposed CO CEMS 

emission limit for the December 2011 proposal. 

7. Alternative CO CEMS limit were not finalized for units designed to burn heavy 

liquids, light liquids, and non-continental liquids because facilities which did have 

CEMS data have permanently shut down since the December 2011 proposal; see 

section 4.0. 

8. Flagged periods of malfunction were included in the UPL calculation for the biomass 

suspension/grate subcategory; see section 4.0. 

2.0 CEMS MACT FLOOR CALCULATION METHODOLOGY – EXISTING SOURCE

2.1 DETERMINING BEST PERFORMERS 

For existing sources, MACT cannot be less stringent than the average emission limitation 

achieved by the best performing 12 percent of existing sources (for which emission information 

is available) for categories and subcategories with 30 or more sources or the best performing five 

sources for subcategories with less than 30 sources. The size of the subcategory was determined 

according to the number of units in the boiler and process heater inventory, not the number of 

units within each subcategory that had emission data available. 

To identify the universe of best performing units in each subcategory, we calculated 10-

day or 30-day rolling averages based on the available CO CEMS data. For the reconsideration 

proposal, 10-day rolling averages were calculated (with two exceptions where a 1-day block 

average and a 3-hr rolling average were calculated), but due to the availability of additional data 

and with the support of commenters, longer averaging periods were analyzed for the amended 

final rule. Furthermore, with the submittal of additional hourly CO CEMS data, rolling averages 

were calculated using hourly CEMS data in addition to daily data. When using hourly data, the 

30-day rolling average is more appropriately considered a 720-hour rolling average and the 10-

day rolling average equated to a 240-hour rolling average for the purposes of performing the 

MACT floor calculation and ranking. By using hourly data the variability which naturally occurs 
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due to fluctuations in boiler load were more adequately captured and operating days with only a 

few hours of operation do not skew the rolling averages over the course of a time period 

equivalent to 30 days and 24 hours of operation per day. If a subcategory has hourly CO CEMS 

available, then the ranking based on the 720-hour or 240-hour rolling averages superseded the 

rolling averages ranking based on daily averages. If however, a subcategory did not have hourly 

CEMS data available then daily rolling averages were used in the ranking and UPL analysis. In 

addition, if a subcategory had enough data to calculate a 30-day (720-hour) rolling average then 

10-day (240-hour) rolling averages were not considered when determining best performers. 

Instead, the longer rolling average available for each subcategory was used for the analysis. 

Selecting a longer averaging period when data are available to do so is more representative of 

unit operations over the long term. Since these CO CEMS emission limits apply at all times 

(excluding periods of startup and shutdown) it is appropriate to select the longer, more 

representative averaging times. See section 4.0 for details on calculating hourly and daily rolling 

averages. 

Within each subcategory, the minimum 10-day (240-hour) or 30-day (720-hour) rolling 

averages were ranked from lowest to highest to determine the best performing 12 percent. If the 

number of units in the subcategory was greater than 30, the best performing 12 percent was 

determined by multiplying the number of units in each subcategory with CEMS data by 12 

percent and rounding up to the nearest whole integer. Given the dataset, the top 12 percent 

represented a single combustion unit for all of the subcategories with greater than 30 units, 

except for wet biomass stoker, where the top 12 percent represented two units. If the number of 

units in the subcategory was less than 30, the units with the five lowest minimum 10-day (240-

hour) or 30-day (720-hour) rolling averages were identified as best performers; however, in these 

instances most subcategories only had a single unit with CO CEMS data, with the exception of 

the biomass fluidized bed subcategory which had four units with CO CEMS data. When 

determining the top 12 percent, the number of units which had either daily or hourly CEMS data 

available was used. This is seen in the wet biomass stoker rankings, where although only five 

units have enough data to calculate 720-hour rolling averages (which would equal one unit in the 

top 12 percent), the top 12 percent is based on all 13 units that reported CO CEMS data and thus 

two units were considered in the top 12 percent. The top two units in the wet biomass stoker 
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subcategory when ranking by hourly data were the same top performers as when ranking by 

daily CO CEMS data; therefore, the units in the floor calculation did not change when 

calculating the floor with hourly data instead of daily data and the use of hourly data led to a 

more robust and longer term dataset serving as the basis of the MACT floor emission limit. 

After ranking by minimum rolling averages, a comparison of the units used in the CO stack testbased floors were performed. Where we have CEMS data for units that were part of the stack 

test-based MACT floors, we also included the CEMS data from those units in the CEMS-based 

floors because those units were demonstrated best performers for CO when conducting stack 

tests. The rankings for all subcategories are provided in Appendix A-4. 

2.2 UPL CALCULATION 

With the best performing 12 percent for each subcategory determined, a 99 percent upper 

predictive limit (UPL) was calculated for each subcategory. This is the same level of confidence 

selected for the stack test-based emission limits. First, it was determined if each CO CEMS 

dataset was best characterized by a normal or lognormal distribution. To evaluate the distribution 

of the best performing dataset, we computed the skewness and kurtosis statistics and then 

conducted the appropriate small-sample hypothesis tests. When performing the statistical 

analyses for the CO CEMS UPL calculations, the rolling averages of the reported dataset were 

used. This differs from the reconsideration proposal analysis, where the raw reported data was 

used for the UPL analyses (for the reconsideration proposal the rolling averages were only used 

to determine the rankings). It was determined that use of rolling averages would provide more 

appropriate limits since the test condition requires that each rolling averages must be below the 

MACT floor. This revised UPL analysis provides a limit based on the conditions required by the 

amended final rule. 

The distribution of the rolling average datasets were determined using the same skewness 

and kurtosis techniques discussed in the December 2011 proposal analysis.1

 

For datasets that were determined to be normally distributed, the UPL is computed using 

a student’s t-test statistic. The t-statistic is calculated using the following Excel equation: 

t-statistic = TINV(2*(1-0.99),n-1) 
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Where: 

n = the number of rolling averages in the best performing 12 percent 

Next, the mean and standard deviation of the CO CEMS data were calculated and the 

UPL calculated via the following equation: 

Where: 

 the mean of rolling averages for the best performing 12 percent 

s

2

 = the standard deviation of the rolling averages in the best performing 12 percent 

n = the number of rolling averages in the best performing 12 percent 

For datasets that were determined to be lognormally distributed, the same t-statistic was 

applied, but a slightly different UPL equation was used. 

Where: 

 the mean of the natural log-transformed rolling averages for the best performing 12 

percent 

s

2

 = the standard deviation of the natural log-transformed rolling averages in the best 

performing 12 percent 

n = the number of rolling averages in the best performing 12 percent 

For each subcategory the analysis showed that the datasets were lognormally distributed. 

Note also that in each UPL formula, the term (1/m) was not included as was at the 

reconsideration proposal.1 At reconsideration, the ‘m’ represented the number of daily averages 

in the compliance average, but the equation has since been corrected such that it is set equal to 1. 

If the rule required a facility to demonstrate compliance by showing that the "average of 10" 10-
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day rolling averages is below the threshold, then m can be set equal to 10. However, the 

amended final rule requires an affected source to demonstrate compliance by showing that each 

of its rolling averages (regardless of them being 10-day or 30-day rolling averages) are below the 

threshold. 

Similar to the data validation rules used for the stack-test MACT floors and the 

December 2011 proposed CO CEMS-based MACT floors, for subcategories with one boiler in 

the top 12 percent, the top performing unit must be firing a fuel which is representative of and 

reasonable to obtain for the entire subcategory and not process specific nor based on co-fired 

configurations; this exception is the same as for new sources. The existing source calculations 

for the coal fluidized bed subcategory, however, were based on a boiler co-firing natural gas; see 

section 3.0 for additional details and discussion for inclusion of this boiler. 

2.3 MAXIMUM ROLLING AVERAGE OF TOP 6 PERCENT 

 In addition to calculating a UPL for each subcategory, the maximum rolling average of 

the top 6 percent for each subcategory was also determined. After the rankings were determined, 

the emissions of the top half of the best performing units (top 6 percent, or often the top single 

unit) were further analyzed. For each of these units the rolling averages were calculated, as 

shown in section 4.0, and reviewed to identify the maximum rolling average. After the maximum 

rolling average was determined for each unit, the highest maximum rolling average from the top 

half of the best performers for each subcategory was identified. In the CEMS-based compliance 

alternative, it is necessary for MACT floors to be achieved by the best performers at all times, 

even during large CO swings; the maximum rolling average value from the top half of the best 

performers is chosen as an alternative value to represent the performance of the average emission 

limitation achieved by the best performing 12 percent of existing sources (for which emission 

information is available). 

Since only one unit’s maximum rolling average is used for this option, the unit’s 

operation must be representative of the entire subcategory. Therefore, the unit selected must be 

firing a fuel which is reasonable to obtain for the entire subcategory and not process specific nor 

based on co-fired configurations; this exception is the same as for new sources. For the light 
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liquid subcategory, the top two ranked facilities are co-firing natural gas and are thus not 

representative of light liquid fuel boilers; the third ranked facility is used for the maximum 

rolling average. The new source calculations for the coal fluidized bed and biomass fluidized bed 

subcategories, however, were based on boilers co-firing natural gas; see section 3.0 for additional 

details and discussion for inclusion of this data. The maximum rolling average for the top 6 

percent of units in each subcategory is shown alongside the rankings in Appendix A-4. 

2.4 SELECTION OF CO CEMS MACT FLOOR 

 As a final step, the 99% UPL value from the top twelve percent of units was compared 

with the maximum rolling average from the top 6 percent of units to determine the MACT floor 

for each subcategory. This final step was included to ensure that best performers could 

demonstrate compliance with the CO CEMS limits at all times. Due to the variable nature of 

boilers and process heaters and the limited dataset for many subcategories it is known that 

significant CO swings do occur and CO values greater than the UPL may occur even for the best 

performers. To ensure this is not the case, the maximum value between the UPL and maximum 

rolling average of the top half of the best performers is chosen. Sections 5.1 and 5.2 show the 

data and final determinations of the MACT floor for each subcategory based on this comparison. 

3.0 CEMS MACT FLOOR CALCULATION METHODOLOGY - NEW SOURCE

A similar methodology used to calculate the existing source UPL and maximum rolling 

average of the top 6 percent was used to calculate the new source UPL and maximum rolling 

average of the best performer. For the new source calculations, however, only data from the top 

performing unit in each subcategory were used in the analyses. Since most of the subcategories 

only have one unit in the top 12 percent this makes little difference in the computed MACT 

floors. However, the top performing unit must be firing a fuel which is representative of and 

reasonable to obtain for the entire subcategory and not process specific nor based on co-fired 

configurations. If a boiler were not firing a similar fuel available to others in the same 

subcategory, then the new source floor could be biased. This same exception is also used in the 

new source floors for the CO stack test MACT floors. For the light liquid subcategory, the top 
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two ranked facilities are co-firing natural gas and are thus not representative of light liquid fuel 

boilers; the third ranked facility is used for the UPL. 

Data from boilers in two subcategories were from co-firing of natural gas, but were used 

for floor calculations. In light of the available data it was determined these were the best 

available option for performing the CO CEMS analyses. 

 Biomass fluidized bed, GATempleInlandRome, WF: Boiler was co-firing natural gas 

in small quantities but the other boiler with enough CEMS data to calculate 720-hour 

rolling averages (ALIPCourtland, No. 3 Combination Boier / 11CU301) was co-firing 

natural gas and process-specific fuel. 

 Coal fluidized bed, MITBSimonPowerPlant, Unit 4: Boiler was co-firing natural gas, 

but this was the only boiler for this subcategory with hourly data. 

There was also one additional step for new sources to ensure that the emission limit for 

new sources is not less stringent than the emission limit for existing sources in the same 

subcategory. If the value selected to represent the MACT floor value for new sources is less 

stringent than the emission limit selected to represent the MACT floor for existing sources, then 

the floor corresponding to the same subcategory for existing sources was used as the basis for the 

floor for new sources. Although the minimum average test run for the best performing source 

resulted in the lowest 10-day (240-hour) or 30-day (720-hour) CEMS rolling average, the 99 

percent UPL limit incorporates variability. As the sample size - in this case the number of hourly 

or daily CEMS values - gets smaller, the t-statistic increases. When the sample size is small, and 

there is large variability in the CEMS values, the calculated limit using the UPL approach can be 

larger than the variability among a larger set of data in the best performing 12 percent. 

4.0 AVAILABLE CEMS DATA

The CEMS data was obtained from two Information Collection Requests (ICRs) 

approved under OMB Control No. 2060-0616: ICR numbers 2286.01 and 2286.03, as well as 

additional voluntary data submittals.3,4,5,6,7 
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The ICR Phase I survey requested that owners submit CO CEMS data for the most recent 

30 days of operation (i.e., thirty 24-hour averages). Owners were asked to exclude data if they 

were from periods of start-up, shutdown, or malfunctions (SSM) and submittal was not required 

if the CEMs monitor was not installed for regulatory purposes. Owners were also requested to 

submit a “typical” operating rate, which often represented the average rate for the 30-day period, 

but it did not request daily load averages to correspond to the daily average CO CEMS emission 

concentrations. Phase II of the ICR requested 30 days of CEMS data, including hourly data and 

the corresponding hourly heat input and steam output of the boiler. The additional voluntary data 

submittals were provided as minute, hourly or daily averages. 

Consistent with the data eligibility criteria in the stack-test MACT floor analysis, when 

determining the applicable data for the CEMS analysis, the fuel fired during the CEMS analysis 

must meet a 90% heat input threshold to be considered for a subcategory.8 While the fuel was 

indicated for the majority of the data, assumptions for two boilers were necessary as described 

here: 

1. GATempleInlandRome, WF: Used oil along with wood bark are listed for certain 

data, but the percentage of used oil contributing to the heat input is not provided in all 

instances. For those instances when the percentage of used oil was provided it was 

always substantially less than 10 percent of total heat input, which would still allow 

the data to be considered in the biomass fluidized bed CEMS analysis. Also, only 6 

percent of the data points were from firing of used-oil with bark. It was assumed all 

CEMS data points for this unit meet the 90% threshold for biomass since used oil is 

typically burned in such small quantities. 

2. MITBSimonPowerPlant, Unit 4: Bituminous coal and natural gas are fired and the 

percentage each contributed to the heat input are not provided for the dates associated 

with the CO CEMS monitoring data. However, other fuel data for this boiler in other 

portions of the Phase I ICR survey showed that natural gas is burned in miniscule 

amounts. Therefore, it was assumed all CEMS data meets the 90% threshold for 

bituminous coal. 
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Three subcategories were impacted by the shutdown of boilers which were used to 

perform the CO CEMS analysis for the reconsideration proposal; heavy liquid, light liquid, and 

non-continental liquid. While these units were used to perform the analysis for the 

reconsideration proposal, if a boiler is permanently shutdown its data are no longer applicable to 

a subcategory. The resulting outcome for each subcategory is described: 

1. Heavy liquid: NJVinelandMuniElectric-HowardDown, Unit 9 has shut down. The 

heavy liquid subcategory now has one unit with CO CEMS data, 

TXOXEABayCity M-460, however this unit was co-firing natural gas and thus 

not representative of the heavy liquid subcategory. 

2. Light liquid: Four units at NYConEdHudsonAve have shut down; boiler 71, 

boiler 72, boiler 81, and boiler 82. The light liquid subcategory now has two units 

with CO CEMS data at the facility NJMerckRahway, E750011 - Boiler #11 and 

E750012 - Boiler #12, but they are co-firing natural gas and thus not 

representative of the light liquid subcategory. 

3. Non-continental liquid: USVIHovensa, H-4101A has shut down. No other CO 

CEMS data was available. 

Without additional data an alternative CO CEMS MACT floor will not be calculated for the 

heavy liquid, light liquid, or non-continental liquid subcategories. 

CO CEMS data from periods of malfunction were included in the analysis. This change 

was due to the fact that when facilities comply with the amended final Boiler MACT frequent 

periods of malfunction cannot qualify for the Affirmative Defense provisions in the amended 

final rule and these data will need to be included in the rolling averages. It would thus not be 

appropriate to exclude them from the calculations. Only one subcategory, biomass 

suspension/grate, provided data which specifically noted certain values were during a 

malfunction. Other subcategories flagged data as startup or shutdown periods, which were 

appropriately excluded from these analyses. The rolling averages for this subcategory include 

data from malfunctions. 
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With the submittal of additional data after the reconsideration proposal coupled with what 

was already available, most subcategories had a sufficient amount of CO CEMS data available to 

calculate an alternative CO CEMS MACT floor. Furthermore, there was additional data 

submitted as hourly averages which provided flexibility in determining floor limits. Given the 

data, we considered multiple rolling average periods for each dataset, with a focus on using 

hourly data to incorporate variability in the UPL limits. Using hourly rolling averages was also 

consistent with the requests from commenters, many of which had requested that EPA consider 

hourly data from the previous 240 or 720 operating hours when developing a CO CEMS-based 

MACT floor emission limit. The modified definitions in the amended final rule state that 

facilities were to use 240-hour or 720-hour rolling averages to comply with the finalized limits. 

When units reported hourly CO CEMS data, the following methodology was used to 

calculate 240 (or 720) hour rolling averages for each boiler. The hourly data points were sorted 

sequentially by hour and date. Then 240 (or 720) consecutive hours were averaged together to 

provide hourly rolling averages over the time period available. 

Daily averages were also calculated. For those subcategories without hourly data this was 

necessary because it was the source for the UPL calculations, while for those subcategories with 

hourly data the daily averages were used for comparison and to determine the number of units 

with CEMS data for each subcategory. To determine daily rolling averages where sources 

reported CEMS data on both an hourly and daily average basis we first reduced the hourly data 

into daily averages. The hourly data points for each boiler were sorted sequentially, grouped 

together by day, and then averaged to compute daily averages. Next, we combined the two 

datasets, sorted the data in sequential calendar date order and computed a series of 10-day (or 30-

day) rolling averages from each unit. 

The rolling averages represent sequential, but not necessarily continuous, calendar dates. 

In some cases the data reported by the facility skipped certain days due to unit downtime or data 

associated with startup or shutdown conditions. Also note that only data meeting the 90 percent 

fuel data validation criteria were included in the hourly and daily averages. 
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With a variety of data available, a hierarchy was selected to determine which data would 

be used in the UPL calculations. This order is as follows: (1) 30-day rolling average using hourly 

data to compute 720-hour rolling averages, (2) 30-day rolling averages using daily averages, (3) 

10-day rolling average using hourly data to compute 240-hour rolling averages, and (4) 10-day 

rolling averages using daily averages. Table 1 shows the subcategories which have hourly CO 

CEMS data available to calculate 240-hour or 720-hour rolling averages. The far right column 

denotes which, if either, of the hourly rolling averages was used for the UPL calculation. Table 2 

shows the subcategories which have daily CO CEMS data available to calculate 10-day or 30-

day rolling averages. Again, the far right column denotes which, if either, of the daily rolling 

averages was used for the UPL calculation. 

Table 1.  Available hourly CO CEMS data for each subcategory, to determine a 10‐day (240‐hour) or 30‐

day (720–hour) rolling average.

Fuel Category Combustor Design

Number of

Units in

Subcategory

Number of Units

with Hourly Avg

CO CEMS Data to

Compute 240‐Hr

Rolling Avgs

Number of Units

with Hourly Avg

CO CEMS Data to

Compute 720‐Hr

Rolling Avgs

Number

of Units

In Top

12%

Basis

for UPL

Calc

Coal

FB 35 1 1 1 720‐Hr

FB w/Heat Exchanger a a a a

PC 190 2 1 1 720‐Hr

Stoker/SlopedGrate/Other 391 2 1 1 720‐Hr

Biomass

Dutch Oven/Pile Burner 24 a a a a

FB 24 3 2 2 720‐Hr

Fuel Cell 14 a a a a

Suspension Burner 47 1 0 1 240‐Hr

Suspension/Grate 18 1 1 1 720‐Hr

Wet Biomass Stoker/SlopedGrate/Other 305 6 5 3 (b) 720‐Hr

Dry Biomass Stoker/SlopedGrate/Other 74 a a a a

Heavy Liquid N/A 320 a a a a

Light Liquid N/A 581 a a a a

Non‐Continental

Liquid N/A 44 a a a a

Process Gas N/A 129 a a a a

Note: 

a. Data was not available to calculate a rolling average on an hourly basis. 

b. Includes 1 unit which was a stack test best performer. The 12% of units with data is based on the 13 

units with hourly or daily data instead of just the 5 units with data available for 720-hr rolling averages. 
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Table 2.  Available daily average CO CEMS data for each subcategory, to determine a 10‐day or 30‐day

rolling average.

Fuel Category Combustor Design

Number of

Units in

Subcategory

Number of Units

with Daily Avg CO

CEMS Data to

Compute 10‐Day

Rolling Avgs

Number of Units

with Daily Avg

CO CEMS Data to

Compute 30‐Day

Rolling Avgs

Number

of Units

In Top

12%

Basis

for UPL

Calc

Coal

FB 35 6 5 1 b

FB w/Heat Exchanger 1 1 1 30‐Day

PC 190 3 1 1 b

Stoker/SlopedGrate/Other 391 6 0 1 b

Biomass

Dutch Oven/Pile Burner 24 1 a 1 10‐Day

FB 24 4 2 4 b

Fuel Cell 14 a a a a

Suspension Burner 47 2 0 1 b

Suspension/Grate 18 1 1 1 b

Wet Biomass Stoker/SlopedGrate/Other 305 13 5 3 (c) b

Dry Biomass Stoker/SlopedGrate/Other 74 a a a a

Heavy Liquid N/A 320 a a a a

Light Liquid N/A 581 a a a a

Non‐Continental

Liquid N/A 44 a a a a

Process Gas N/A 129 a a a a

Notes: 

a. Data was not available to calculate a rolling average on a daily basis. 

b. UPL computed using hourly data. 

c. Includes 1 unit which was a stack test best performer. 

5.0 CO CEMS MACT FLOOR RESULTS

5.1 EXISTING SOURCE MACT FLOORS 

After the CO CEMS MACT floor calculations were performed for each subcategory the 

same rounding technique used in the stack-test based MACT floors emission limits was applied. 

Each MACT floor was determined by rounding the limit up to two significant figures. Rounding 

up is appropriate for establishing emission standards that must be complied with at all times. The 

CO CEMS MACT floors for existing sources are summarized in Table 3. Both the UPL value 

and the maximum rolling average from the top 6% are shown for each subcategory; the value 

used for determining the MACT floor is highlighted. The rolling average basis for each 
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subcategory is also noted; 10-day, 240-hr, 30-day, or 720-hr. The rankings and maximum rolling 

average of the top 6% for each subcategory are shown in Appendix A and the UPL floor 

calculations for each subcategory are shown in Appendix B. 

In reviewing Tables 1 and 2 above, note there are six subcategories which do not have 

CO CEMS data available. While substituting a MACT floor from a different subcategory for the 

subcategories with no data was considered, ultimately it was determined that an alternative CO 

CEMS floor would not be provided for subcategories with no data. If other subcategories’ data 

were used to fill in incomplete subcategories, this data would not be representative of the 

applicable boilers operations and it would not be appropriate to subject boilers to a limit which is 

not based off representative data. 

Table 3.  Summary of CO CEMS MACT floor limits for existing boilers and process heaters, 10‐day (240‐

hr) or 30‐day (720‐hr) rolling averages.

Fuel Category Combustor Design

Category

Rolling

Average

Basis

99% UPL

Maximum

Rolling Avg

of Top 6%

Rounded CO

CEMS MACT

Floor (ppm @

3% O2)

Coal

FB 720‐Hr 224.0 164.7 230

FB‐Heat Exchanger 30‐Day 138.6 146.0 150

PC 720‐Hr 89.6 315.7 320

Stoker/SlopedGrate/Other 720‐Hr 309.9 336.9 340

Biomass

Dutch Oven/Pile Burner 10‐Day 516.5 220.1 520

FB 720‐Hr 268.3 305.5 310

Fuel Cell a a a a

Suspension Burner 240‐Hr 1929.2 1334.7 2000

Suspension/Grate 720‐Hr 848.3 893.9 900

Wet Biomass Stoker/SlopedGrate/Other 720‐Hr 718.9 297.4 720

Dry Biomass Stoker/SlopedGrate/Other a a a a

Heavy Liquid N/A a a a a

Light Liquid N/A a a a a

Non‐Continental Liquid N/A a a a a

Process Gas N/A a a a a

Notes: 

a. No applicable CO CEMS data available for this subcategory 

 Cells highlighted blue designate the value chosen for the MACT Floor. 

5.2 NEW SOURCE MACT FLOORS 
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 The new source CO CEMS MACT floors are summarized in Table 4 and the UPL 

calculations are provided in Appendix C. Both the UPL value and the maximum rolling average 

from the top performer are shown for each subcategory; the value used for determining the 

MACT floor is highlighted. The rolling average basis for each subcategory is also noted; 10-day, 

240-hr, 30-day, or 720-hr. Only one subcategory, wet biomass stoker/sloped grate/other, has a 

new source limit which is different than the existing source limit. 

Table 4. Summary of CO CEMS MACT floor limits for new boilers and process heaters, 10‐day (240‐hr)

or 30‐day (720‐hr) rolling averages.

Fuel Category Combustor Design

Category

Rolling

Average

Basis

99% UPL

Maximum

Rolling Avg

of Top 6%

Rounded CO

CEMS MACT

Floor (ppm @

3% O2)

Coal

FB 720‐Hr 224.0 164.7 230

FB‐Heat Exchanger 30‐Day 138.6 146.0 150

PC 720‐Hr 89.6 315.7 320

Stoker/SlopedGrate/Other 720‐Hr 309.9 336.9 340

Biomass

Dutch Oven/Pile Burner 10‐Day 516.5 220.1 520

FB 720‐Hr 271.6 305.5 310

Fuel Cell a a a a

Suspension Burner 240‐Hr 1929.2 1334.7 2000

Suspension/Grate 720‐Hr 848.3 893.9 900

Wet Biomass Stoker/SlopedGrate/Other 720‐Hr 380.01 297.4 390

Dry Biomass Stoker/SlopedGrate/Other a a a a

Heavy Liquid N/A a a a a

Light Liquid N/A a a a a

Non‐Continental Liquid N/A a a a a

Process Gas N/A a a a a

Notes: 

a. No applicable CO CEMS data available for this subcategory 

 Cells highlighted blue designate the value chosen for the MACT Floor. 

 
17

6.0 REFERENCES

1. Eastern Research Group, Inc. CO CEMS MACT Floor Analysis (November 2011) for the 

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

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

2. EPA. Data Quality Assessment: Statistical Methods for Practitioners. EPA QA/G-9S. 

February 2006. Available on-line at: http://www.epa.gov/quality/qs-docs/g9s-final.pdf

3. 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.

4. 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. 

5. Eastern Research Group, Inc. Handling and Processing of Corrections and New Data in the 

EPA ICR Databases. January 2011. 

6. Eastern Research Group, Inc. Handling and Processing of Corrections and New Data in the 

EPA ICR Databases – Revised November 2011. 

7. Eastern Research Group, Inc. Handling and Processing of Corrections and New Data in the 

EPA ICR Databases – Revised August 2012. 

8. 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. November 2011.