### MEMORANDUM

TO: Jim Eddinger, U.S. Environmental Protection Age ncy, OAQPS/SPPD
FROM: Eastern Research Group

DATE: November 2011
SUBJECT: Revised (November 2011) MACT Floor Analysi s for the Industrial, Commercial, and

Institutional Boilers National Emission Standards f or Hazardous Air Pollutants – Area Source

The purpose of this memorandum is to present the re visions 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 a rea source boilers for the rule reconsideration. Rationale for determination of subcategory applicab ility to MACT versus GACT has not changed, and MACT floors are necessary only for coal boilers. A lso, the GACT methodology has not changed since the March 2011 Boiler Area rule, all work practice stan dards 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 Ana lysis Appendix B: Upper Prediction Limit (UPL) Calculatio ns 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, NYAE SGreenidgeDresden, Boiler 6 was the top performing unit and all calculations were based sol ely off data from this boiler. It was determined t hat the NYAESGreenidgeDresden boiler is classified as a utility boiler and as such is not applicable to ar ea source floors. There are now six boilers instead o f seven with applicable mercury data for coal units and the MACT floor is still only based off the best per forming 12% which is a single boiler. With that bo iler exclusion, a new top performer for coal Hg was sele cted and the Hg floor re-analyzed. It shall also be noted that the fuel variability fa ctor (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 sourc e of coal would also be Eastern bituminous and the 10.9 value would not change. After calculating th e 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 exis ting source MACT floor calculations.

Table 1. Hg MACT floor emissions limits for existi ng 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 sour ce, the new and existing floors are the same. The reconsideration new source coal Hg floor is differe nt from the March 2011 rule due to the same reason as the existing floors; the utility boiler was remo ved from the analysis and a new best performing uni t is used in the calculations. The new source Hg MACT f loor is shown in Table 2 and all calculations are provided in Appendix C.

Table 2. Hg MACT floor emissions limits for new so urces, 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 re visions 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 per cent confidence interval for all of the other emiss ion limits in the March 2011 rule. The petitioner poin ted out that if the data are highly variable, the 9 9 percent confidence interval should adequately refle ct the variability of emissions as well as for the data sets for other pollutants. The EPA is now proposin g to use a 99 percent confidence interval in order to maintain a consistent methodology with the developm ent 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 per formers each of these boilers shall have at least three test runs to ensure adequate variability is i ncorporated into the limits. This rationale is sim ilar to selecting the top performing unit for new source fl oors, 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 C O data and Appendix B for the existing source MACT floor c alculations.

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

Subcategory CO (ppm @ 3% O2) Coal 420

2.2 NEW SOURCES

For new sources the only revision was a modificatio n 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 th ree test runs was already enforced, so the top rank ed facility was not used in this analysis. The top pe rforming unit for the CO calculations did not chang e 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 so urces, rule reconsideration.

Subcategory CO (ppm @ 3% O2) Coal 420

Note:

• For CO, the calculated limit for new sources was le ss stringent than the calculated limit for existing sources and so the limit for existing sources was u sed 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 Indust rial, Commercial, and Institutional Boilers National Emis sion Standards for Hazardous Air Pollutants – Area Source. February 2011.