MEMORANDUM 

TO: Jim Eddinger, U.S. Environmental Protection Agency, OAQPS/SPPD 

FROM: Eastern Research Group 

DATE: November 2011 

SUBJECT: Revised (November 2011) MACT Floor Analysis for the Industrial, Commercial, and 

Institutional Boilers National Emission Standards for Hazardous Air Pollutants – Area 

Source

The purpose of this memorandum is to present the revisions in methodology and results of the 

maximum achievable control technology (MACT) floor determinations for mercury (Hg) and CO (as a 

surrogate for polycyclic organic matter (POM)) at area source boilers for the rule reconsideration. 

Rationale for determination of subcategory applicability to MACT versus GACT has not changed, and 

MACT floors are necessary only for coal boilers. Also, the GACT methodology has not changed since the

March 2011 Boiler Area rule, all work practice standards and PM limits are the same. See the 

memorandum provided with the March 2011 Boiler Area rule for full details of the MACT and GACT 

analysis.1 This memorandum is organized as follows: 

1.0 Revisions to Hg MACT Floor 

 1.1 Existing Sources 

 1.2 New Sources 

2.0 Revisions to CO MACT Floor 

 2.1 Existing Sources 

 2.2 New Sources 

3.0 References 

Appendix A: Ranked Emission Data for MACT Floor Analysis 

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

Appendix C: UPL Calculations for New Sources 
1.0 REVISIONS TO HG MACT FLOOR

1.1 EXISTING SOURCES 

The Hg MACT floor analysis was revised in light of additional information available about the top 

performing unit. For the March 2011 analysis, NYAESGreenidgeDresden, Boiler 6 was the top 

performing unit and all calculations were based solely off data from this boiler. It was determined that 

the NYAESGreenidgeDresden boiler is classified as a utility boiler and as such is not applicable to area 

source floors. There are now six boilers instead of seven with applicable mercury data for coal units and 

the MACT floor is still only based off the best performing 12% which is a single boiler. With that boiler 

exclusion, a new top performer for coal Hg was selected and the Hg floor re-analyzed. 

It shall also be noted that the fuel variability factor (FVF) is applicable for this analysis. In the

March 2011 rule, a FVF of 10.9 was calculated using data from Eastern bituminous coal. As the revised

top performing unit is from Massachusetts its source of coal would also be Eastern bituminous and the 

10.9 value would not change. After calculating the UPL and applying the FVF, the MACT floor for coal

Hg is as shown in Table 1. See Appendix A for the rankings of all Hg data and Appendix B for the existing 

source MACT floor calculations. 

Table 1. Hg MACT floor emissions limits for existing sources, rule reconsideration. 

Subcategory 

Hg

(lb/MMBtu) 

Coal 2.2 E-05 

1.2 NEW SOURCES 

For new sources, the MACT floor is calculated using the best performing source. Since the coal 

Hg existing floor is calculated using only one source, the new and existing floors are the same. The 

reconsideration new source coal Hg floor is different from the March 2011 rule due to the same reason 

as the existing floors; the utility boiler was removed from the analysis and a new best performing unit is 

used in the calculations. The new source Hg MACT floor is shown in Table 2 and all calculations are 

provided in Appendix C. 

Table 2. Hg MACT floor emissions limits for new sources, rule reconsideration. 

Subcategory 

Hg

(lb/MMBtu) 

Coal 2.2 E-05 
2.0 REVISIONS TO CO MACT FLOOR

2.1 EXISTING SOURCES 

The MACT floor calculations for CO underwent two revisions for this rule reconsideration. First, 

a 99% UPL is now applied instead of a 99.9% UPL. A petitioner requested reconsideration of this 

selection given the fact that the EPA used a 99 percent confidence interval for all of the other emission 

limits in the March 2011 rule. The petitioner pointed out that if the data are highly variable, the 99 

percent confidence interval should adequately reflect the variability of emissions as well as for the data 

sets for other pollutants. The EPA is now proposing to use a 99 percent confidence interval in order to 

maintain a consistent methodology with the development of the MACT floors for other pollutants. 

Second, the best performing 12% unit selection was revised. With 16 boilers with data, two 

units are in the top 12%. The top ranked facility with applicable data at the March 2011 rule is now 

excluded from the calculations because the CO data for this facility only included two test runs. It was 

determined that with only two units as the best performers each of these boilers shall have at least 

three test runs to ensure adequate variability is incorporated into the limits. This rationale is similar to 

selecting the top performing unit for new source floors, where the top performing unit must have at 

least three test runs. The CO floor is provided in Table 3. See Appendix A for the rankings of all CO data 

and Appendix B for the existing source MACT floor calculations. 

Table 3. CO MACT floor emissions limits for existing sources, rule reconsideration. 

Subcategory 

CO

(ppm @ 3% O2) 

Coal 420 

2.2 NEW SOURCES 

For new sources the only revision was a modification of the calculation methodology. Similar to 

existing sources, the CO MACT floor was calculated using a 99% UPL instead of a 99.9% UPL. For new 

sources the exclusion for boilers with less than three test runs was already enforced, so the top ranked 

facility was not used in this analysis. The top performing unit for the CO calculations did not change for 

new sources. The new source CO MACT floor is shown in Table 4 and all calculations are provided in 

Appendix C. 
Table 4. CO MACT floor emissions limits for new sources, rule reconsideration. 

Subcategory 

CO

(ppm @ 3% O2) 

Coal 420 

Note: 

• For CO, the calculated limit for new sources was less stringent than the calculated limit for existing

sources and so the limit for existing sources was used as the basis for the limit at new sources.
3.0 REFERENCES

1. Singleton, A. and Long, B., ERG. Revised MACT and GACT Floor Analysis for the Industrial, 

Commercial, and Institutional Boilers National Emission Standards for Hazardous Air Pollutants 

– Area Source. February 2011.