BEFORE THE

US ENVIRONMENTAL PROTECTION AGENCY

PROPOSED RECONSIDERATION OF NATIONAL EMISSION 

STANDARDS FOR INDUSTRIAL, COMMERCIAL AND INSTITUTIONAL 

BOILERS AND PROCESS HEATERS

(40 CFR 63 SUBPART DDDDD)

Docket ID No. EPA-HQ-OAR-2002-0058

COMMENTS OF AMEREN CORPORATION

Michael Hutcheson

Ameren Services

1901 Chouteau Avenue

PO Box 66149, MC 602

St. Louis, MO 63166-6149
Comments and Data Provided by Ameren 

on the US EPA Reconsideration of the Major Source Industrial Boiler MACT

Ameren Corporation is pleased to provide the following comments on the proposed 

Reconsideration of the final National Emission Standards for Hazardous Air Pollutants 

for Industrial, Commercial and Institutional Boilers and Process Heaters (Boiler MACT). 

Ameren Corporation is a producer and supplier of electricity and natural gas in three 

states in the Midwest. As a member of UARG, Ameren Corporation would like to herein 

endorse and adopt the comments submitted by UARG. 

In addition to the UARG comments, Ameren has prepared the following comments, 

information and data for US EPA’s consideration during the Boiler MACT 

reconsideration process. 

1. Ameren agrees with US EPA’s inclusion of a limited use boiler and process 

heater subcategory in the final rule. However, Ameren believes improvements to 

the definition of limited use boilers or process heaters can easily be made without 

compromising air quality. Ameren requests that US EPA reconsider the use of a 

straight hourly threshold for defining the limited use subcategory. As an 

alternative, US EPA should consider changing the definition of limited use to:

“Limited-use boiler or process heater that burns any amount of solid, liquid, or 

gaseous fuels, has a rated capacity of greater than 10 MMBtu per hour, and has an 

annual capacity factor of no more than 10 %.” The definition of annual capacity 

factor should then be added to the definitions in 40 CFR 63.7575 and it should be 

the same as the definition of annual capacity factor in both 40 CFR 60.41b and 40 

CFR 60.41c.

Ameren has several auxiliary boilers located at Ameren facilities for use when all 

facility electric generating units are offline at the same time. These units typically 

do not operate more than 876 hours per year and could meet the definition of 

limited use boilers. However, on rare occasions these boilers are required to 

operate more than 876 hours per year to return the electric generating facility to 

service. Ameren has recently encountered this issue during installation of flue gas 

desulfurization systems at one of our facilities. Because the outages for the tying 

in of two FGD systems at two units at one facility occurred over the course of 

several months, the auxiliary boiler at that facility was required to operate more 

than 876 hours over a 12 month period. Conversely, this auxiliary boiler never 

approached a capacity factor of 10 % despite operating for up to 1,950 hours 

during a 12 month period. 

Because emissions of HAPs are directly proportional to capacity factor as 

opposed to time on line, capacity factor is a much better substitute for defining the 

limited use subcategory. Emissions from the auxiliary boiler above never 

approached those of a boiler operating at design heat input for 876 hours as 

allowed under the current limited use exemption. Just because the boiler was 

needed for more than 876 hours to meet facility needs should not elevate the 

boiler out of the limited use subcategory if the capacity factor remains less than 

10 %.
Comments and Data Provided by Ameren 

on the US EPA Reconsideration of the Major Source Industrial Boiler MACT

Additionally, this MACT standard and other recently proposed MACT standards 

(EGU MACT) will require significant changes to air pollution controls at various 

sources in short time spans and long outages will result. In order to achieve 

compliance with these new standards the auxiliary boilers at Ameren facilities 

will have significantly increased demands on their time. Without a change to the 

definition of limited use boilers, Ameren’s auxiliary boilers may have to forgo 

limited use status in order to accommodate steam needs at their facilities while

other units at their facility upgrade pollution control devices to meet the new EGU 

MACT or other newly promulgated federal standards (Transport Rule). This will 

result in significant costs with little air quality benefit. 

For limited use boilers, the economics of installation of ESPs or fabric filters and 

activated carbon injection for Hg control, wet scrubbers for control of acid gases 

and potentially catalytic oxidizers for the control of organic HAPs is not cost 

effective. Assuming a no.2 fuel oil fired 250 MMBtu/hr auxiliary boiler with a 10 

% capacity factor and using AP-42 particulate emission factors, average PM2.5 

and Hg factors from the US EPA emission test database for the Boiler MACT 

rulemaking, the particulate emissions from that boiler is on the order of 1.5 tpy, 

PM2.5 on the order of .3 tpy and Hg on the order of 0.33 #/yr. Taking for granted 

the US EPA summary of Capital and Annual Costs for control in Table 11 of the 

Preamble of the proposed rule, the average annualized cost of control for existing 

liquid fuel fired boilers after considering fuel savings is $507,000 per boiler. In 

terms of cost effectiveness, assuming 100 % reduction of all three pollutants, the 

annualized cost of reduction is $338,000 per ton of PM reduction, $1,536,000 per 

ton of PM2.5 reduced and $1,690,000 per pound of Hg reduced. We include PM 

and PM2.5 for this analysis because US EPA’s benefits analysis for this proposed 

rule is based on PM2.5 reductions. At these costs, it does not make sense to 

require controls on limited use boilers even as large as 250 MMBtu/hr. 

In addition, in the case of limited use boilers/process heaters, it is not practicable 

economically to require sources which operate infrequently to undergo the 

expensive measurement methodologies at non-detectable levels. Ameren’s 

limited use/auxiliary boilers typically operate only during outages at the electrical 

generating units. Conducting stack testing during these infrequent outages which 

may last only very short periods at some plants is nearly impossible. Stack testing 

during significant EGU outages is not feasible due to the large numbers of 

contractors and maintenance personnel engaged in activities associated with 

returning electrical generating units back into service.

Ameren requests that US EPA reconsider the use of only a single subcategory for 

liquid fuel units. As Ameren and several other commenters noted during the 

comment period for the proposed rule, there are several physical differences 

between boilers designed to burn lighter fuel oils (#1 and #2) and those designed 

to burn heavier oils (#4 and #6). US EPA acknowledges those differences in its 

response to comments made by Randolph Price of Consolidated Edison (Pgs. 260 

to 262 of volume 2 of US EPA’s Response to Comments). Although elsewhere 
Comments and Data Provided by Ameren 

on the US EPA Reconsideration of the Major Source Industrial Boiler MACT

US EPA denies there is significant data or technical justification for a separate 

subcategory for heavy and light liquid fuel fired boilers or other non-petroleum 

based liquid fuels, in its response to comments from David Peightal of Dakota 

Gasification (Page 271 of Volume 2 of US EPA’s Response to Comments), it 

seems to come to a different conclusion when there are less differences separating 

gas fired units in the gas 1 and process gas subcategories. US EPA needs to

explain why it appropriate to subdivide boilers designed to burn gaseous fuels but 

is inappropriate to do the same for liquid fuel fired boilers even though there are 

significant differences between boilers designed to burn heavy fuel oils and those 

designed to burn light fuel oils. 

2. Ameren requests US EPA reconsider whether a threshold higher than 10 million 

Btu per hour meets the technical and economic limitations as specified in CAA 

section 112(h). Ameren raised this issue during comments on the proposed Boiler 

MACT but could not find that US EPA responded to this issue in the preamble or 

in the response to comments documents. Ameren believes that US EPA should

consider setting only work practice standards for all liquid fuel fired boilers and 

process heaters below 100 MMBtu/hr as it does for units of all sizes in the gas 1 

subcategory. Assuming a no.2 fuel oil fired 100 MMBtu/hr auxiliary boiler and 

using AP-42 particulate emission factors, average PM2.5 and Hg factors from the 

US EPA emission test database for the Boiler MACT rulemaking, the particulate 

emissions from that boiler is on the order of 6 tpy, PM2.5 on the order of 1.8 tpy 

and Hg on the order of 1.2 #/yr. Taking for granted the US EPA summary of 

Capital and Annual Costs for control in Table 11 of the Preamble of the proposed 

rule, the average annualized cost of control for existing liquid fuel fired boilers 

after considering fuel savings is $507,000 per boiler. In terms of cost 

effectiveness, assuming 100 % reduction of all three pollutants, the annualized 

cost of reduction is $84,500 per ton of PM reduction, $282,000 per ton of PM2.5 

reduced and $422,500 per pound of Hg reduced. We include PM and PM2.5 for 

this analysis because US EPA’s benefits analysis for this proposed rule is based 

on PM2.5 reductions. At these costs, it does not make sense to require controls on 

small liquid fuel fired boilers as small as 100 MMBtu/hr. 

3. Ameren requests that US EPA reconsider their position on whether CAA 

112(d)(3) requires that the MACT floors be based on test data from a minimum of 

5 sources. In the preamble to the final rule, US EPA when responding to 

comments that it is inappropriate to set limits for a category with more than 30 

sources using the testing from less than 5 sources only says that “the literal 

language of the provision appears to compel this result.” This is true only when 

EPA reads Section 112(d)(3) subparagraph (A) applying the parenthetical 

clarification to the term sources and presuming the clarification does not apply to 

all uses of that term in the paragraph. If the term sources is limited in the first 

part of the paragraph to only those sources which the administrator has emission 

information, then the term sources in the last part of the paragraph must have the 

same limitation. When the Act says “in the category or subcategory for categories 

and subcategories with 30 or more sources”, the term sources must not be read to 
Comments and Data Provided by Ameren 

on the US EPA Reconsideration of the Major Source Industrial Boiler MACT

be different than it is defined above in the same paragraph. Consequently, the 

number of sources in the category or subcategory is defined by the number of 

sources for which the administrator has emissions information. EPA errs when it 

reads the same term differently in the same paragraph. 

Ameren commented on this issue in comments on the draft rule, however, it did 

not appear that US EPA considered these comments as it did not respond to the 

assertion that it must read the same term in a paragraph the same way when it 

appears more than once. These comments are repeated here. Specifically, 

Ameren believes, Section 112(d)(2) of the Act states that the “Emission standards 

promulgated under this Subsection ... shall require the maximum degree of 

reduction of emissions of the hazardous air pollutants subject to this section...that 

the Administrator, taking into consideration the cost of achieving such emission 

reduction ... determines is achievable”. Section 112(d)(3) defines the maximum 

degree of reduction in emissions that is deemed achievable as (1) the emission 

control that is achieved in practice by the best controlled similar source for new 

sources and (2) no less than the average emission limitation achieved by the best 

performing 12 percent of existing sources or the best performing 5 sources in 

source categories (or subcategories) with fewer than 30 sources. A direct reading 

of this subsection of the Act indicates that if there is test data from fewer than 30 

sources, MACT standards can be no less than the average emission limitation 

achieved by the best performing 5 sources. The language in this section of the 

Act clarifies through parenthetical insertion that the number of sources in a 

subcategory is determined by the number of sources “for which the Administrator 

has emissions information”. It is incredulous to think that Congress wanted the 

US EPA to develop MACT standards for source categories with thousands of 

different sources from fewer than five (5) data points when it requires the use of 

at least 5 data points for categories with fewer than 30 sources. This is directly 

contrary to basic scientific and probabilistic principles and therefore contrary to 

the Administrators statements on the use of good science in making policy 

decisions. US EPA cannot believe that two dioxin/furan stack tests for coal-fired 

boilers can adequately represent the emission limitation achievable by top 

performing 12 % of boilers when there are 578 coal fired boilers affected by the 

rule. 

4. Ameren requests that US EPA reconsider their position on how to rank test results 

from individual sources. Ameren believes US EPA errs when it ranks the best 

controlled sources according to the single best test value when multiple test data 

are available. By using the single best test value, US EPA biases the rankings of 

the best performers and is not ranking the units according to the ability of a unit to 

achieve an emission limitation or a real qualitative assessment of the ability of a 

unit to control the pollutant in question. The Act requires that US EPA base the 

MACT floor on the best performing sources. According to US EPA in the 

preamble to the final rule, the test to determine a best performer for use in setting 

the MACT floor is how a unit performs during its single best emission test. 

Ameren believes a single test result is not an indication of a unit’s ability to 
Comments and Data Provided by Ameren 

on the US EPA Reconsideration of the Major Source Industrial Boiler MACT

achieve an emission limitation or an indication of a unit’s ability to control the 

pollutant when other test results for that source are higher than the test average 

used as the qualifier and indicate that the source does not control the pollutant as 

well as it is ranked. If a single test is to be used, the highest test value with a 

suitable variability factor applied (which takes into account the long term source 

variability) is a better indicator of a unit’s ability to consistently achieve an 

emission limitation not a single low test value. It is not reasonable, as US EPA 

asserts, to determine that one low test is indicative of the ability of a source to 

control a pollutant when other tests indicate otherwise. It is arbitrary to pick the 

lowest test results for sources with more than one test and to ignore the other tests 

when ranking that source. US EPA suggests that by taking into account the other 

tests during the UPL calculations, the US EPA has accounted for the data. 

However, this can’t substitute for incorrectly ranking sources by ignoring data 

indicating they are not as well controlled as the single best test might indicate. 

5. Ameren requests that US EPA reconsider how it determined MACT floors. As 

commented on during the comment period for the proposed Industrial Boiler 

MACT, Ameren thinks the MACT floor should be based on the 88th percentile of 

emission data not the average emission rate for the lowest emitting 12 % of 

sources. Ameren believes that the US EPA errs when it takes the average of the 

top 12 % of all data when determining the MACT floor. We believe the US EPA 

should actually be utilizing the 88th percentile of data instead of the average of 

the top 12 %. Ameren interprets Section 112(d)(3) of the Act to require that the 

MACT floor be based on an average emission rate that is achievable by all 12 % 

of the top performing sources. By using the average or mean of the top 12 % of 

sources, US EPA sets a MACT floor that is not achievable by those sources 

between the 88th and 94th percentiles. The use of the words “average emission 

limitation” would reflect that Congress intended that compliance with the 

limitation would be based on averaged data over a period of time such as a three 

run stack test. It does not reflect that Congress intended for the MACT floor to be 

based on an average of the top 12 % of test data. If the latter were true, as US 

EPA seems to believe, then Congress must have known that half the sources in 

the top 12 % could not have “achieved” the “average emission limitation 

achieved” making the word “achieved” superfluous. This is contrary to the basic 

rules for statutory construction. 

6. Ameren requests US EPA review Dioxin/Furan reporting used to establish the 

MACT Floor because it is inconsistent resulting in inaccurate characterization of 

the best performing sources. Dioxin/furan MACT Floor for the liquid fuel 

subcategory is based on 2 test results out of 13 after the emissions test database 

was purged of 4 tests after the proposed rule. The test results for dioxin/furan are 

reported as individual congeners and as a total which is the sum of the individual 

congeners. As previously commented on during the comment period on the 

proposed rule, the lowest TEQ results reported and used to establish the MACT 

floor for the liquid fuel subcategory only reported 17 congeners. All other 

Facilities reported either 21 or up to 25 congeners except the Virginia Newport 
Comments and Data Provided by Ameren 

on the US EPA Reconsideration of the Major Source Industrial Boiler MACT

News Shipbuilding facility boiler 78-E1 which was originally ranked 13th out of 

17 and now ranks 11th. The Newport News boiler test reported all congeners 

non-detect, however, because the detection limits reported for that test were much 

higher than most other tests, the reported TEQ level was higher than 10 others in 

the subcategory. Conversely, the MACT Floor was based on the only two other 

sources who reported only 17 congeners. By reporting fewer congeners, the 

sources used to establish the MACT floor have a biased low TEQ value which is 

the sum of the 17 congeners TEQ values. Because only one of the 17 Facilities 

reported detectable levels of dioxin/furans, the only basis to establish the two 

sources as the MACT floor is due to their limited reporting of congeners, if the 

other sources had reported only 17 congeners, the rankings may have been 

different. Because this MACT floor and the resulting standard are based on only 

seventeen congeners and the rest of the facilities reported additional congeners, 

the MACT floor is biased. US EPA should require that all reporting be 

consistent. The dioxin/furan floor must be based on test rankings which all report 

the same congeners and the same number of congeners.

7. Ameren requests that US EPA reconsider the Boiler MACT’s requirement to 

conduct an energy assessment to identify cost-effective energy conservation 

measures. Ameren believes that US EPA errs when it describes an energy 

assessment as a standard because it is “a requirement that can be enforced” (76 

FR 15633, March 21, 2011). US EPA knows that Section 112(d)(2) of the Act 

requires that MACT standards be “measures, processes, methods, systems or 

techniques including but not limited to measures which ... reduce the volume of, 

or eliminate emission of such pollutants through process changes, substitution of 

materials or other modifications.” As Ameren asserted previously in comments 

on the proposed rule, an energy audit is not a measure, process, method, system or 

technique that reduces the volume of, or eliminates emissions of any pollutants. 

An energy audit is a measure of the efficiency to which a system utilizes energy. 

An energy audit is not a requirement to change steam process to be more efficient. 

US EPA is correct that the audit itself can be enforced, but the audit cannot reduce 

the volume of, or eliminate emissions of any pollutants and therefore does not 

meet the definition in Section 112(d)(2) of the standards which must be 

promulgated. To assert otherwise is to claim that measuring a line can make the 

line shorter. 

Additionally, US EPA mischaracterizes the benefits from energy audits when it 

says that “the energy assessment will generate emission reductions through the 

reduction in fuel use beyond those reductions required by the floor.”(76 FR 

15632, March 21, 2011) A review of the efficiency measure upgrades in the

study completed by the US DOE upon which US EPA relies indicates that the 

some of the more cost effective efficiency upgrades will result in increased 

emissions and not reduced emissions. The US DOE study includes in its top 

recommendations fuel switching from Natural Gas to fuel oil to reduce fuel 

consumption . According to the DOE study, the energy efficiency upgrade that 
Comments and Data Provided by Ameren 

on the US EPA Reconsideration of the Major Source Industrial Boiler MACT

results in the most cost and energy savings is from switching from Natural Gas to 

the use of more efficient fuels such as fuel oil. This results in a more efficient 

fuel combustion process and reduced fuel use but also results in increased HAP 

emissions from fuel oil combustion. Implementing this recommendation would 

therefore result in an increase in HAP emissions. This “energy efficiency” project 

was actually proposed during the course of the US DOE study numerous times 

over the three study years and underlies the reduced fuel use assertions made by 

US EPA. Unfortunately, reduced fuel use in this case does not lead to reduced 

emissions. Consequently, US EPA cannot use this US DOE study as a basis for 

claiming energy assessments result in reductions in emissions. 

8. Ameren requests that US EPA review emission data used to develop the MACT 

Floor. Ameren believes that the emission test data for the BP facility in Decatur, 

Alabama is incorrectly listed as a liquid fuel fired boiler. Discussions with 

environmental representatives with the facility indicate that the boiler has not 

combusted the by-product fuel used for the compliance test used to establish the 

MACT floor for PM. Boiler AB-8301 normally combusts natural gas and the fuel 

used for the compliance test was burned only to reserve the capability to combust 

that fuel under the facility permit. Additionally, Ameren believes that it is 

improper to utilize data from the Milliken plant in South Carolina to establish 

liquid fuel fired boiler MACT floors. The boiler test data is based off of testing 

conducted at 4.3 MMBtu/hr which is significantly below the size limitations of 

the subcategory and is less than 50 % load for the unit (10.5 MMBtu/hr design 

rate). Testing for compliance with all NESHAP and NSPS standards is required 

to be conducted under representative load conditions (40 CFR 63.7(e)(1) and 40 

CFR 60.8(c). If representative conditions for this unit are at 4.3 MMBtu/hr, then 

the unit should not be included in a subcategory for units greater than 10 

MMBtu/hr. Additionally, testing at less than 50 % load will not produce the 

highest emission rates for a unit and creates a bias in the data. If this unit has 

been judged as a best performer simply because it operates significantly below its 

design rating during testing, then the unit should not be included as a best 

controlled source.