Date: March 18, 2013 

Subject: Reconsideration of the National Emission Standards for Hazardous Air Pollutants 

(NESHAP) Maximum Achievable Control Technology (MACT) Floor Analysis 

for Coal- and Oil-fired Electric Utility Steam Generating Units, Final Rule 

From: Stephen M. Boone (RTI International) 

To: Bill Maxwell and Nick Hutson 

 OAQPS/SPPD/ESG (D243-01) 

 U.S. Environmental Protection Agency 

 Research Triangle Park, NC 27711 

I. Introduction 

On February 16, 2012, the U.S. Environmental Protection Agency (EPA) published final rules 

entitled “National Emission Standards for Hazardous Air Pollutants from Coal- and Oil-fired 

Electric Utility Steam Generating Units and Standards of Performance for Fossil-Fuel-Fired 

Electric Utility, Industrial-Commercial-Institutional, and Small Industrial-CommercialInstitutional Steam Generating Units” (77 FR 9304). This rule is commonly referred to as the 

Mercury and Air Toxics Standards (MATS). Subsequently, on July 20, 2012, the EPA 

announced plans to reconsider certain standards applicable to new sources under the MATS. 

Section 112 of the Clean Air Act (CAA) requires that the EPA establish National Emission 

Standards for Hazardous Air Pollutants (NESHAP) for the control of the hazardous air pollutants 

(HAP) emitted from new sources in a source category. CAA section 112(d)(2) requires that these 

standards reflect the maximum degree of reduction in HAP emissions that “the Administrator, 

taking into consideration the cost of achieving such emission reduction, and any non-air quality 

health and environmental impacts and energy requirements, determines is achievable....” These 

standards are commonly referred to as “Maximum Achievable Control Technology” or “MACT” 

standards. 

CAA section 112(d)(3) states that MACT standards for new sources may not be “less stringent 

than the emission control that is achieved in practice by the best-controlled similar source, as 

determined by the Administrator.” In setting the minimum stringency level, or “MACT floor,” 

EPA uses available emission data or other information from the best performing source for each 

HAP or HAP surrogate in the source category. After EPA establishes the MACT floor, it 

considers the costs and non-air quality health and environmental impacts and energy 

requirements to determine whether a more stringent, or “beyond-the-floor,” level of control 

should be established. 

This memorandum describes the EPA’s process for establishing the new source MACT floors in 

the final reconsideration rule “Reconsideration of Certain New Source and Startup/Shutdown 

Issues: National Emission Standards for Hazardous Air Pollutants from Coal- and Oil-fired 

Electric Utility Steam Generating Units and Standards of Performance for Fossil-Fuel-Fired 
2 

Electric Utility, Industrial-Commercial-Institutional, and Small Industrial-CommercialInstitutional Steam Generating Units.” 

II. Scope of Reconsideration of New Source Standards 

As stated in the preamble to the final reconsideration rulemaking, the EPA reconsidered certain 

new source standards. Specifically, the EPA is finalizing new source standards for the identified 

HAP or HAP surrogates in the following subcategories (using the same subcategory numbers as 

were used in docket entry EPA-HQ-OAR-2009-0234-20132): 

1. Subcategory 1 – New EGUs designed to burn a coal having a calorific value (moist, 

mineral matter-free basis) of greater than or equal to 19,305 kJ/kg (8,300 Btu/lb) that are 

not coal-fired EGUs in the “unit designed for low rank, virgin coal” – particulate matter 

(PM), hydrochloric acid (HCl), mercury (Hg), sulfur dioxide (SO2), lead, and selenium. 

2. Subcategory 2 – New EGUs designed to burn and burning nonagglomerating virgin coal 

having a calorific value (moist, mineral matter-free basis) of less than 19,305 kJ/kg 

(8,300 Btu/lb) that are constructed and operated at or near the mine that produces such 

coal – PM, HCl, SO2, lead, and selenium.1

3. Subcategory 4 – New EGUs located inside the continental United States that burn liquid 

oil and have an annual oil-fired capacity factor of greater than or equal to 8 percent – PM 

4. Subcategory 7 – New EGUs that burn solid oil-derived fuel – PM and SO2.

In the December 16, 2011, final rule, the EPA used the stack test data with the lowest emission 

average submitted by each respondent to the MATS Information Collection Request (ICR) to 

identify the best performing similar source for each HAP or HAP surrogate. The EPA then 

calculated the new source MACT floors in the final rule using only the single best stack test 

available for the best performing sources, even if multiple tests were available for the best 

performing sources. During reconsideration, the EPA considered all available data in the record 

for the best performing sources when establishing the MACT floors for the final new source 

limits. 

The EPA used the following approach in establishing new source MACT floors for the HAP or 

HAP surrogate standards that are being finalized in this reconsideration rulemaking: 

Step 1. All available stack test data points (typically based on 3-run test averages) from the 

MATS ICR were ranked from lowest to highest for each HAP or HAP surrogate for 

each EGU in each subcategory (e.g., Subcategory 1- EGUs designed to burn a coal 

having a calorific value (moist, mineral matter-free basis) of greater than or equal to 

19,305 kJ/kg (8,300 Btu/lb) that are not coal-fired EGUs in the “unit designed for low 

rank, virgin coal”). 

 

1

 Subcategory 1 and 2 have the same limits for PM, HCl, SO2, selenium, and lead. Only the Hg 

limits are different between the two subcategories, and in the preamble to the proposed rule, EPA 

took comment on whether to revise the new source Hg limit for Subcategory 2. EPA did not 

include revisions to the Hg limit for Subcategory 2 in the final rule.
3 

Step 2. For each EGU within a given MACT floor data set (i.e., subcategory), the stack test 

data point with the lowest emissions rate for the relevant pollutant was determined 

and placed in a separate data set. 

Step 3. This separate data set was then ranked, with the highest ranking source (No. 1) 

defined as the member of the subcategory with the lowest reported “single-test, multirun average” emissions rate. 

Step 4. As part of selecting the best performing similar source, we evaluated the design of the 

unit and other aspects of the unit, including air pollution control equipment, to assess 

whether the unit was comparable to units built recently that are complying with all 

federal requirements, including the pre-construction requirements under the EPA’s 

New Source Review (NSR) program codified at 40 CFR 52.21 and 40 CFR 51.166. 

The NSR program includes requirements for new EGUs to achieve “the maximum 

degree of reduction” of regulated air pollutants, including particulate matter and 

sulfur dioxide (which are both HAP surrogates). The EPA undertook this analysis 

because in certain situations the controls for one pollutant can increase the emissions 

of, or negatively impact the control of, other pollutants. For example, for PM, if the 

highest ranked source did not have advanced flue gas desulfurization (FGD) system 

for SO2 control, the source was eliminated from consideration as the unit that 

demonstrates the level of control that could be achieved by a new EGU, because 

state-of-the-art FGD systems can add PM to the flue gas stream. We also eliminated 

stoker units as we did not believe that they represented the type of new boiler 

technology that is likely to be built in the future. 

Step 5. All available data for each best similar source were reviewed to determine if there 

were any quality assurance (QA) issues with the data for the unit. Data sets were 

evaluated using Tukey’s test to determine statistical outliers. Test data sheets were 

also evaluated to ensure that all method-specific QA measures were met during 

sampling. Data that did not pass QA measures within a relevant EPA reference 

method were not used to determine the MACT floor. 

Step 6. This step was dependant on the quantity and type of data available in the record for 

the best performing source. If data from three or more stack tests were available for 

the best performing source, test averages (typically the average of 3 runs) were used 

in the MACT floor calculations. If data from less than three stack tests were available 

in the record (i.e., one or two stack tests were available), data from the individual test 

runs were used in the MACT floor calculations. 

Step 7. Each set of run averages or test averages was evaluated for Kurtosis and skewness to 

determine if the data set for the best performing source was normally distributed. If 

these tests indicated the data set was normally distributed, the data set was treated as 

normally distributed in subsequent upper predictive limit (UPL) calculations. If either 

of these tests indicated the data set was not normally distributed, the data set was log 

transformed, and the log transformed data set was evaluated for Kurtosis and 

skewness. If these tests indicated the data set was log-normally distributed, the data 

set was treated as log-normally distributed in subsequent UPL calculations. If either 
4 

of these tests indicated the log transformed data set was not log-normally distributed, 

the data set was treated as non-normally distributed in subsequent UPL calculations. 

Step 8. After completing the determination of the type of data distribution for the best 

performing source’s data set, the data set was input to the series of calculations 

necessary to calculate the UPL as discussed on pages 5-9 of the MACT Floor Memo 

published at promulgation; the memo can be viewed in the rulemaking docket (EPAHQ-OAR-2009-0234) and at the following link: 

http://www.epa.gov/ttn/atw/utility/a1_egu_mact_floor_memo_121611.pdf

Step 9. For each pollutant, the results of the UPL calculation were compared to the emission 

limit value determined to be equivalent to 3 times the representative detection limit 

(3xRDL) of the relevant performance test method(s). If the calculated UPL value was 

less than the emission limit value determined to be equivalent to 3xRDL value, the 

3xRDL value was used as the basis for the standard because the 3xRDL value 

provides the lowest emission rate that can be measured using the performance test 

method while maintaining a relative method precision on the order of 10 to 20 percent 

of the measured value. If the UPL value was equal to or greater than the 3xRDL value, 

then the UPL value was used as the basis for the standard. See “Data and procedure 

for handling below detection level data in analyzing various pollutant emissions 

databases for MACT and RTR emissions limits” (docket entry EPA-HQ-OAR-2009-

0234-20062) for a discussion of the RDL approach generally, and the memo 

“Determination of Representative Detection Level (RDL) and 3 X RDL Values for 

Mercury Measured Using Sorbent Trap Technologies“ (docket EPA-HQ-OAR-2009-

0234) for a discussion of our approach for establishing an RDL for Hg. The RDL and 

3xRDL procedures are further described on pages 9 and 10 of the MACT Floor 

Memo at the link provided in Step 8. 

Exhibit II-1 presents the 10 standards finalized in the reconsideration rule.
5 

Exhibit II-1: Reconsidered New Source Standards 

Subcategory 

(Description) 

HAP or 

Surrogate 

Promulgated 

Standard2

Reconsidered 

Standard2

Best 

Performer 3xRDL3

Subcategory 1 

(New EGUs designed to burn a coal 

having a calorific value (moist, mineral matter-free basis) of greater than or equal to 19,305 kJ/kg (8,300 Btu/lb) that are not coal-fired EGUs in the “unit designed for low rank, virgin coal”) 

and Subcategory 2 

(New EGUs designed to burn and 

burning nonagglomerating virgin coal having a calorific value (moist, mineral matter-free basis) of less than 19,305 kJ/kg (8,300 Btu/lb) that are constructed and operated at or near the mine that produces such coal) 

Filterable PM 7.0E–3 lb/MWh 

(3xRDL) 

9.0E-2 

lb/MWh 

Springerville 

Unit 3 

6.40E-3 

lb/MWh 

Lead (Pb) 2.0E–3 lb/GWh 

(3xRDL) 

3.0E-2 

lb/GWh 

Weston 

Unit 4 

2.0E-3 

lb/GWh 

Selenium 

(Se) 

6.0E–3 lb/GWh 

(3xRDL) 

5.0E-2 

lb/GWh 

Logan 

Unit B01 

6.0E-3 

lb/GWh 

Hydrogen 

chloride (HCl) 

4.0E–4 lb/MWh 

(3xRDL) 

1.0E-2 lb/MWh5

 (beyond floor) 

Logan 

Unit B01 

4.0E-4 

lb/MWh 

Sulfur dioxide 

(SO2) 

4.0E–1 lb/MWh 1.0E0 lb/MWh6 Stanton 

Unit 10 

n/a 

Subcategory 1 

(New EGUs designed to burn a coal 

having a calorific value (moist, mineral matter-free basis) of greater than or equal to 19,305 kJ/kg (8,300 Btu/lb) that are not coal-fired EGUs in the “unit designed for low rank, virgin coal”) 

Mercury (Hg) 2.0E–4 lb/GWh 3.0E-3 

lb/GWh 

 (3xRDL) 

Nucla 

Unit 1 

3.0E-3 

lb/GWh 

2 The standard is derived either from the UPL calculation, from the 3xRDL comparison, or from a beyond-the-floo3 3xRDL: This value reflects the lowest emission rate that can be measured using the performance test method wh

relative method precision on the order of 10 to 20 percent of the measured value. The 3xRDL value is calculated bdiluent concentration and an F-factor of 9,780. 

4 Data Distribution Type: This is the data distribution of the sample set of runs or tests used in the MATS statistica5 Beyond-the-floor value; the calculated UPL floor value was 2.0E-2 lb/MWh. 6 Beyond-the-floor value; the calculated UPL floor value was 1.3E0 lb/MWh. 
6 

Subcategory 

(Description) 

HAP or 

Surrogate 

Promulgated 

Standard2

Reconsidered 

Standard2

Best 

Performer 3xRDL3

Subcategory 2 

(New EGUs designed to burn and 

burning nonagglomerating virgin coal having a calorific value (moist, mineral matter-free basis) of less than 19,305 kJ/kg (8,300 Btu/lb) that are constructed and operated at or near the mine that produces such coal) 

Mercury (Hg) 4.0E–2 lb/GWh7 3.0E-2 

lb/GWh 

Sandow 

Unit 5B 

3.0E-3 

lb/GWh 

Subcategory 4 

(New EGUs located inside the 

continental United States that burn liquid oil and have an annual oil-fired capacity factor of greater than or equal to 8 percent) 

Filterable PM 7.0E–2 lb/MWh 4.0E-1 

lb/MWh 

Port 

Everglades 

Unit PPE3 

6.40E-3 

lb/MWh 

Subcategory 7 

(New EGUs that burn solid oilderived fuel (e.g., petroleum coke-fired 

units)) 

Filterable PM 2.0E–2 lb/MWh 3.0E-2 

lb/MWh 

Northside 

Unit 1A 

6.40E-3

lb/MWh 

Sulfur dioxide 

(SO2) 

4.0E–1 lb/MWh 1.0 E0 

lb/MWh 

Hanford 

Unit CB1302 

n/a 

7 As stated in the preamble to the proposed rule, EPA took comment on whether to revise the Hg limit for Subcate

additional data in the record. The final reconsideration rule did not include revisions to the Hg limit for Subcatego