Kraft Pulp Mills New Source Performance Review 

(40 CFR Part 60, Subpart BBa)

Final Amendments

Response to Public Comments on

May 23, 2013 Proposal

U.S. Environmental Protection Agency

Office of Air Quality Planning and Standards

Sector Policies and Programs Division

Research Triangle Park, NC 27711

March 13, 2014
i

Table of Contents

Page

1. Introduction................................................................................................................................. 6

2. Technology Review .................................................................................................................... 8

2.1 General Comments................................................................................................................ 8

2.2 Recovery Furnace, Lime Kiln, and Smelt Dissolving Tank Technology........................... 13

2.3 Digester and Brown Stock Washer Technology................................................................. 26

3. Continuous Emission Monitoring System Data Review .......................................................... 31

3.1 Data Evaluation and Quality Analysis................................................................................ 31

3.1.1 General Quality Analysis................................................................................................ 31

3.1.2 Operating Period............................................................................................................. 33

3.2 Opacity Limits .................................................................................................................... 46

3.3 TRS Limits.......................................................................................................................... 48

3.4 Startup and Shutdown Performance Data ........................................................................... 49

4. Startup, Shutdown, and Malfunction ........................................................................................ 51

4.1 Periods of Startup and Shutdown........................................................................................ 51

4.2 Periods of Malfunction ....................................................................................................... 80

4.3 Affirmative Defense............................................................................................................ 86

5. Testing and Monitoring........................................................................................................... 100

5.1 Emissions Testing ............................................................................................................. 100

5.2 Parameter Monitoring ....................................................................................................... 104

5.2.1 Incinerator Parameter Monitoring ................................................................................ 104

5.2.2 Recovery Furnace Parameter Monitoring..................................................................... 106

5.2.3 Smelt Dissolving Tank Parameter Monitoring............................................................. 108

5.2.4 Lime Kiln Parameter Monitoring ................................................................................. 110

5.2.5 Digester Parameter Monitoring .................................................................................... 111

5.3 TRS CEMS Data O2 Correction Procedure ...................................................................... 111

5.4 Averaging Times............................................................................................................... 117

5.5 Electronic Reporting ......................................................................................................... 121

5.6 Other Testing and Monitoring Comments........................................................................ 122

6. Cost and Impacts..................................................................................................................... 126

7. Greenhouse Gas Emissions..................................................................................................... 127
ii

List of Tables

Page

Table 1. List of Commenters on 40 CFR Part 60, Subpart BBa, Proposed May 23, 2013

(78 FR 31316).................................................................................................................. 7

Table 2. Typical Uncontrolled TRS Emissions from Salt Cake Mix Tanks and Processes

Covered Under the Kraft Pulp NSPS............................................................................. 15

Table 3A. Summary of Recovery Furnace COMS Data Sets Analyzed....................................... 38

Table 3B. Summary of Lime Kiln COMS Data Sets Analyzed ................................................... 39

Table 3C. Summary of Recovery Furnace TRS CEMS Data Sets Analyzed............................... 40

Table 3D. Summary of Lime Kiln TRS CEMS Data Sets Analyzed ........................................... 41

Table 4. Example Lime Kiln O2 Corrections.............................................................................. 113

List of Figures

Page

Figure 1. 99th Percentile of the TRS Averaging Periods (NSPS and Non-NSPS Furnaces) .......18

Figure 2. 99th Percentile of the TRS Averaging Periods by APCD (NSPS Furnaces) ............... 19

Figure 3. 99th Percentile of TRS Averaging Periods for Lime Kilns (NSPS Kilns Only.............20

Figure 4. Opacity Monitoring Allowance Data for Recovery Furnaces ....................................42

Figure 5. Opacity Monitoring Allowance Data for Lime Kilns ..............................................43

Figure 6. TRS Monitoring Allowance Data for Recovery Furnaces Subject to the Subpart BB 

NSPS Limit (5 ppm) .............................................................................44

Figure 7. TRS Monitoring Allowance Data for Lime Kilns Subject to the Subpart BB NSPS 

Limit (8 ppm) ....................................................................................45
iii

List of Acronyms and Units of Measure

Act Clean Air Act

ADTP air-dried ton(s) of pulp

ADTPD air-dried ton(s) of pulp per day

AF&PA American Forest & Paper Association

AFS EPA’s Air Facility System

Agency U.S. Environmental Protection Agency

AIRS EPA’s Aerometric Information Retrieval System

ALAPCO Association of Local Air Pollution Control Officers

APCD air pollution control device

Ass’n Association

BACT best available control technology

BID background information document

BLO black liquor oxidation

BLRBAC Black Liquor Recovery Boiler Advisory Committee

BLS black liquor solids

BSER best system of emission reduction

BSW brown stock washer

CAA Clean Air Act

CaCO3 calcium carbonate

CAM compliance assurance monitoring

CaO calcium oxide (lime)

CCA Clean Condensate Alternative

CDX EPA’s Central Data Exchange

CEDRI EPA’s Compliance and Emissions Data Reporting Interface

CEMS continuous emissions monitoring system

cert. certiorari (writ seeking judicial review)

cf. confer (compare)

CFR Code of Federal Regulations

CH4 methane

Cir. Circuit Court

CMS continuous monitoring system

CO carbon monoxide

CO2 carbon dioxide

CO2e CO2 equivalents

col. column

COMS continuous opacity monitoring system

Court United States Court of Appeals for the District of Columbia Circuit

CPM condensable PM

CPMS continuous parameter monitoring system

CROMERR Cross Media Electronic Reporting Rule

CWA Clean Water Act

D.C. District of Columbia

D.C. Cir. United States Court of Appeals for the District of Columbia Circuit

DAS data acquisition system(s)
iv

DBESP dry-bottom ESP

DCE direct contact evaporator

dscf dry standard cubic foot

e.g. exempli gratia (for example)

EPA Environmental Protection Agency

ERT Electronic Reporting Tool

ESP electrostatic precipitator

etc. et cetera (and other things)

FIP Federal Implementation Plan

FR Federal Register

GHG greenhouse gas

GHGRP Greenhouse Gas Reporting Program

gr grain(s)

H2S hydrogen sulfide

HAP hazardous air pollutant

hr hour

HVLC high-volume low-concentration

i.e. id est (that is)

ICR information collection request

id. idem (the same)

LAER lowest achievable emission rate

lb pound

LVHC low-volume high-concentration

MACT maximum achievable control technology

mg milligram(s)

MMBtu million British thermal unit(s)

N2O nitrous oxide

Na2CO3 sodium carbonate

Na2S sodium sulfide

Na2SO4 sodium sulfate

NaOH sodium hydroxide

NCASI National Council for Air and Stream Improvement, Inc.

NCG non-condensable gas

NDCE non-direct contact evaporator

NESHAP national emissions standards for hazardous air pollutants

No. Number

NOX nitrogen oxides

NRDC Natural Resources Defense Council

NSPS new source performance standards

NSSC neutral sulfite semichemical

O2 oxygen

p. page

PM particulate matter

PM2.5 PM ≤ 2.5 microns in diameter (fine PM)

pp. pages

ppm part(s) per million
v

ppmdv part(s) per million of dry volume

QA quality assurance

QC quality control

RACT reasonably available control technology

RBLC RACT/BACT/LAER Clearinghouse

RTR residual risk and technology review

S/S startup(s) and/or shutdown(s)

SAB EPA’s Science Advisory Board

SCBR scrubber

scfm standard cubic feet per minute

SDT smelt dissolving tank

SIP State Implementation Plan

SO2 sulfur dioxide

SSM startup, shutdown, and malfunction

STAPPA State and Territorial Air Pollution Program Administrators

tpd ton(s) per day

tpy ton(s) per tear

TRS total reduced sulfur

U.S. United States

U.S.C. United States Code

v. versus

VOC volatile organic compound

WBESP wet-bottom ESP

WPR wet PM return

WWW World Wide Web
6

1. Introduction

Section 111(b)(1)(B) of the CAA requires the EPA to review and, if appropriate, revise existing 

NSPS at least every 8 years. As part of the review, the EPA considers what degree of emission 

limitation is achievable through the application of the BSER, which (taking into account the cost 

of achieving such reduction and any nonair quality health and environmental impact and energy 

requirements) the Administrator determines has been adequately demonstrated. The EPA also

considers the emission limitations and reductions that have been achieved in practice.

In addition to conducting the NSPS review, the EPA evaluated the SSM provisions in light of the 

D.C. Circuit Court of Appeals decision in Sierra Club v. EPA, 551 F.3d 1019 (D.C. Cir. 2008), 

which held that the SSM exemption provisions in the General Provisions in 40 CFR part 63 

violated the CAA’s requirement that some standard apply continuously. In the Sierra Club case, 

the D.C. Circuit vacated the SSM exemption provisions in the General Provisions of 40 CFR part 

63 for non-opacity and opacity standards. The Court explained that under section 302(k) of the 

CAA, emission standards or limitations must be continuous in nature. The Court then held that 

the SSM exemption violates the CAA’s requirement that some section 112 standard apply 

continuously. In light of the Court’s reasoning, all rule provisions must be carefully examined to 

determine whether they provide for periods when no emission standard applies. The EPA 

believes the reasoning behind the D.C. Circuit’s decision in Sierra Club v. EPA applies equally 

to CAA section 111 and section 129 rules. The EPA’s general approach to SSM periods has been 

used consistently in promulgating new NSPS standards under CAA section 111, and in section 

112 and section 129 rulemaking actions, since the D.C. Circuit’s decision in Sierra Club. See, 

e.g., New Source Performance Standards Review for Nitric Acid Plants, Final Rule, 77 FR 

48433 (August 14, 2012); New Source Performance Standards for New Stationary Sources and 

Emission Guidelines for Existing Sources; Commercial and Industrial Solid Waste Incineration 

Units, Final rule, 76 FR 15704, (March 21, 2011); Oil and Natural Gas Sector: New Source 

Performance Standards and National Emission Standards for Hazardous Air Pollutants 

Reviews; Final rules, 77 FR 49490, (August 16, 2012).

The NSPS for kraft pulp mills (40 CFR part 60, subpart BB) were promulgated in 1978 and last

reviewed in 1986. To address the latest NSPS review, SSM exemptions and other changes, the 

EPA proposed new standards on May 23, 2013, which apply to affected sources at kraft pulp

mills for which construction, modification or reconstruction commences after the May 23, 2013 

proposal date. A 60-day period ending July 23, 2013 was provided for the public to submit 

comments to EPA on the proposal. The following sections of this document summarize the 

public comments received on the proposal and present EPA’s responses to those comments:

 Section 2–Technology Review

 Section 3–Continuous Emission Monitoring System Data Review

 Section 4–Startup, Shutdown, and Malfunction

 Section 5–Testing and Monitoring

 Section 6–Costs and Impacts

 Section 7–Greenhouse Gas Emissions
7

A total of six separate sets of written comments were received on the proposal. (See 

www.regulations.gov, Docket ID No. EPA-HQ-OAR-2012-0640, for the complete comments.)

Table 1 below lists the names of the commenters providing written comments, their affiliations, 

and the document numbers assigned to their comments. For simplicity, only the last four digits of 

the document numbers specific to each commenter are presented in this document (e.g., 

commenter 0055, instead of commenter EPA-HQ-OAR-2012-0640-0055). One commenter 

submitted comments in multiple documents and is identified by the number of the first document 

submitted (i.e., commenter 0059 for documents 0059, 0060, and 0062).

Table 1. List of Commenters on 40 CFR Part 60, Subpart BBa, Proposed May 23, 2013

(78 FR 31316)

Docket ID No. 

EPA-HQ-OAR2012-0640 Commenter name Affiliation

0055 E. Christopher 

Abruzzo

Pennsylvania Department of Environmental 

Protection

0056 Stephen E. Woock Weyerhaeuser

0057 Vera P. Pardee and 

Helen Kang

Center for Biological Diversity, Greenpeace, Inc., 

and Port Townsend Air Watchers

0058 Vipin K. Varma National Council for Air and Stream Improvement

0059, 0060, 0062 Paul Noe American Forest & Paper Association

0061 Russell Frye SSM Coalition
8

2. Technology Review

2.1 General Comments

2.1-01 Comment: Commenter 0059 agreed with EPA’s decision not to include additional 

pollutants in its kraft pulp mill NSPS review. According to the commenter, the 8-year review 

provision in CAA section 111(b)(1)(B) by its terms addresses only review of existing standards,

not imposing additional performance standards.1The commenter pointed out that there is no 

statement in the statute establishing any deadline for EPA to consider whether to adopt NSPS for 

new pollutants or new emission sources not covered by the current regulations.

The commenter argued that EPA was not even required to complete a comprehensive review of

the current subpart BB regulations. According to the commenter, CAA section 111(b)(1)(B) 

gives EPA the option of determining that periodic review “is not appropriate in light of readily 

available information on the efficacy” of the existing NSPS.2The commenter noted that they 

provided EPA with information that they believed demonstrated that EPA could and should have 

made such a finding, rather than going through a full review of the existing standards.3

Noting that EPA nevertheless chose to conduct a review of the kraft pulp mill NSPS, the 

commenter argued that EPA had broad discretion to determine the sources that it would evaluate 

and the pollutants for which it would consider establishing standards. The commenter contended 

that EPA’s decision not to expand the sources or the pollutants currently covered under subpart 

BB was well within that discretion.

According to the commenter, EPA is under no obligation to add pollutants, nor to consider 

adding pollutants, to those already regulated under subpart BB. The commenter argued that 

nothing in CAA section 111 requires that NSPS cover all pollutants emitted by a source, and that 

EPA has never interpreted it that way.4The commenter contended that, before expanding the 

kraft pulp mill NSPS to cover additional pollutants, EPA would have to justify its departure from 

its prior decisions about which pollutants the NSPS should cover.5The commenter stated that 

 

1

See also Portland Cement Ass’n v. EPA, 665 F.3d 177, 193 (D.C. Cir. 2011) (“it is unclear whether EPA has such a 

duty with respect to pollutants it has not previously regulated”).

2

See 78 FR 31322.

3

See, e.g., AF&PA November 22, 2011 comments on EPA’s October 24, 2011, proposed plan for periodic review 

of NSPS, 76 FR 65655 (document no. EPA-HQ-OAR-2010–0223-0008).

4

See, e.g., National Lime Ass’n v. EPA, 627 F.2d 416, 426 (D.C. Cir. 1980) (observing that, while EPA had 

determined that lime plants were sources of NOx, CO, and SO2 as well as particulates, standards of performance

were proposed and ultimately promulgated only for PM); 70 FR 9706, 9711 (Feb. 28, 2005) (declining to set NOx 

limits for boilers below 100 MMBtu/hr heat input, based on current emission levels, available technologies, and

costs); 74 FR 51950, 51957 (Oct. 8, 2009) (“The statutory scheme thus provides EPA with significant discretion to 

determine which pollutant(s) should be regulated under the NSPS.”); 75 FR 54970, 54996 (Sept. 9, 2010) (declining 

to set CO limits for cement kilns in part because new emission units “are designed to combust fuel as efficiently as 

possible, and CO emissions from fuel combustion are minimized, regardless of any potential emission limit”).

5 Clearly the fact that pulp mill sources emit VOCs, NOx, CO, and GHGs, none of which are subject to emission 

limitations in the kraft pulp mill NSPS, has been known for many years. See, e.g., RTI March 29, 2013 

memorandum, Technology Review and Regulatory Options for the Kraft Pulp Mill NSPS, document no. EPA-HQOAR-2012-0640-0048, p. 10. If EPA were required to include in NSPS every pollutant that is emitted by a source 

category, that objection to the kraft pulp mill NSPS should have been raised years ago.
9

EPA is under no obligation to include pollutants in NSPS before EPA, in its discretion, 

determines that it has enough information to decide whether Federal standards of performance 

are necessary or appropriate for the pollutant.6

The commenter further argued that, as a practical matter, there would be little benefit to 

expanding the number of pollutants subject to emission limitations in the kraft pulp mill NSPS. 

First of all, the commenter pointed out that there are relatively few new affected facilities being 

constructed, and so there would be relatively little to be gained by EPA spending the resources to 

develop NSPS for additional pollutants. The commenter noted that EPA has recognized that this 

is an appropriate reason for choosing not to promulgate NSPS.7 According to the commenter, 

there has not been a greenfield chemical pulp mill built in the U.S. in over 20 years. Because of a 

variety of factors, including stringent environmental controls and reduced access to forest fiber 

supplies due to land development and access to Federal forests, the commenter stated that there 

almost certainly will be few if any new pulp mills built in the U.S. in the coming 8 years. 

Moreover, because of overcapacity, environmental regulations, and the like, the commenter said 

that there likely will be only a few new subpart BB affected facilities installed in the next 

8 years. The commenter pointed out that, in the decade from 1990 to 1999, 21 new kraft recovery 

furnaces and 25 new lime kilns came on-line in the U.S. According to the commenter, from 2000

to 2010, only 3 new kraft recovery furnaces and 3 new lime kilns came on-line (and one recovery 

furnace and one lime kiln were at a mill that has since shut down). The commenter contended 

that new source standard technology reviews should be more than adequate to assure that these 

few new units use the best emission control technology.

Secondly, the commenter noted that other CAA regulations already comprehensively address 

emissions from kraft pulp mills, such that adding pollutants to the kraft pulp mill NSPS would

provide little if any incremental benefit. According to the commenter, MACT standards in 

40 CFR part 63, subpart S require mills to control emissions of volatile HAPs, through collecting 

and incinerating vent gases or using clean condensates to minimize release of volatile HAPs, 

which also controls VOC emissions (as do measures to minimize total reduced sulfur (TRS)

emissions under the existing subpart BB NSPS). The commenter noted that EPA very recently 

completed a review and revision of those subpart S standards.8The commenter pointed out that 

EPA has acknowledged, in its proposed plan for reviewing and prioritizing NSPS, that MACT 

standards result in effective control of criteria pollutants as well.9

In addition, the commenter indicated that all kraft pulp mills are large enough sources of 

conventional pollutants to be above the “major stationary source” threshold for major source new 

source review requirements and that new source review regulations will require BACT or LAER 

for pollutants (other than HAPs) at new and modified sources that might be addressed in current 

or revised kraft pulp mill NSPS. According to the commenter, the statutory criteria for those 

technology requirements make them at least as stringent as, and generally more stringent than,

NSPS.

 

6 Cf. 78 FR 31321.

7

See 76 FR 65655, 65658-59 (Oct. 24, 2011).

8

See 77 FR 55698 (Sept. 11, 2012).

9

See 76 FR 65655, 65658-59 (Oct. 24, 2011); see also, e.g., 75 FR at 54996 (declining to set NSPS for VOC 

emissions from cement kilns because VOCs would be adequately controlled by NESHAP limits on THC emissions).
10

Moreover, the commenter stated that a number of recently promulgated or pending EPA 

regulations that are not specifically directed at pulp mills will impose additional limits on their 

emissions, because they will require further reductions from large sources of the types of

pollutants emitted by pulp mills. According to the commenter, these regulations include, for 

example, more stringent ambient air quality standards and EPA requirements for implementation 

of those standards, such as the NOx SIP call; visibility protection and regional haze programs; 

other regional pollutant transport programs; and Boiler MACT standards in 40 CFR part 63,

subpart DDDDD. The commenter contended that these and other programs will require pulp 

mills to spend billions of dollars on additional emission controls (for existing as well as new 

sources) in the coming years.

Response: We acknowledge this comment in support of focusing the NSPS review on the 

current standards for PM and TRS due for review under CAA section 111(b)(1)(B).

2.1-02 Comment: Commenter 0059 stated that the EPA was justified in choosing not to expand 

the list of “affected facilities” covered by the kraft pulp mill NSPS. According to the commenter, 

as with adding pollutants to the list of those covered by subpart BB, the CAA does not require 

EPA to review its previous decision not to include other emission units in the NSPS, nor does it 

require EPA to regulate, or even consider regulating, all emission units at a source category for 

which EPA chooses to promulgate NSPS.

10 The commenter noted that EPA in fact often has 

chosen to regulate only some emission units at industrial plants.11

The commenter also noted that there is no reason for EPA to consider adding other affected 

facilities to the kraft pulp mill NSPS because EPA regulated “all process gas streams which have 

been identified as major sources of TRS compounds or particulate matter at kraft pulp mills” in 

the original subpart BB NSPS,

12 and that conclusion remains valid today. The commenter noted

that EPA chose not to address boiler emissions when it initially promulgated the kraft pulp mill 

NSPS, even though they were a significant source of emissions at pulp mills, because EPA 

anticipated promulgating NSPS for industrial boilers,

13 which have since been promulgated, and 

reviewed and revised.

14 In addition, the commenter noted that EPA has also recently 

promulgated MACT standards for industrial boilers and process heaters.15 The commenter also 

noted that the NESHAPs applicable to kraft pulp mill processes, subparts S and MM, thoroughly 

regulate the process sources of volatile HAP and HAP metals, and therefore the sources of TRS 

and PM, at kraft pulp mills, applying technology requirements at least as stringent as could be

imposed under NSPS. Because these NESHAPs already cover additional emission points not 

addressed by the NSPS, the commenter argued that there would be no practical benefit from 

adding those emission points to the kraft pulp mill NSPS, which the commenter said EPA had

recognized.16

 

10 See CAA section 111(a)-(b).

11 See, e.g., 73 FR 35838, 35848, 35868 (June 24, 2008) (adding fluid coking units, not previously regulated, to list 

of affected facilities in Petroleum Refineries NSPS

12 See 41 FR 42012, 40213 (Sept. 24, 1976).

13 See id. at 40213.

14 See 40 CFR part 60, subparts Db and Dc.

15 See 40 CFR part 63, subpart DDDDD.

16 See 78 FR 31322.
11

Response: We acknowledge this comment in support of focusing the NSPS review on the 

current standards due for review under CAA section 111(b)(1)(B). The kraft pulp mill NSPS 

limits emissions of PM and TRS from the most significant and measurable sources of these 

emissions from kraft pulp mills that are not covered under other NSPS, such as the boiler NSPS.

2.1-03 Comment: Commenter 0059 stated that the EPA was correct in determining not to 

expand NSPS to other chemical pulping processes. The commenter pointed out that, when 

subpart BB was originally promulgated, EPA considered setting standards for sulfite and NSSC 

pulping processes, as well as for the kraft process. The commenter noted that EPA determined at 

that time that there would be little benefit to establishing an NSPS for those types of mills, and 

the commenter stated that the considerations that led EPA to that conclusion are even stronger 

today, noting that sulfite and NSSC pulping have become even less prevalent.17

Response: We acknowledge this comment in support of continuing to focus the kraft pulp mill 

NSPS on mills that use the kraft pulping process, which is the predominant pulping process used 

by the most mills in the U.S. We agree that the use of other chemical pulping processes is 

becoming less prevalent.18

2.1-04 Comment: Commenter 0057 argued that the technology-forcing nature of section 111 

requires EPA to consider all realistic means of emission control for each emission source in 

conducting its NSPS review. According to the commenter, the courts have indicated that EPA 

may consider emerging technologies and the benefits of raising standards to promote technology 

innovation.19 The commenter stated that EPA’s entire emission control technology review 

apparently considered only emission limitations achieved in practice by existing kraft pulp mills, 

which the commenter said falls short of BSER. The commenter contended that other 

technologies exist and have been adequately demonstrated to achieve additional emission

reductions and should be incorporated into the revised NSPS.

Response: We disagree that our analyses of the BSER fell short of what is required under CAA 

section 111. The technology review focused on the emission limitations that have been 

adequately demonstrated to be achieved in practice, taking into account the cost of achieving 

such reduction and any non-air quality health and environmental impact and energy 

requirements. Determining the BSER that has been adequately demonstrated and the emission 

limitations achieved in practice necessarily involves consideration of emission reduction 

methods in use at existing kraft mills. To determine the BSER, the EPA performed an extensive 

review of several recent sources of information including:

 Process, equipment, and control device details from industry responses to EPA’s 2011 

pulp and paper industry ICR;

 

17 U.S. Environmental Protection Agency. Screening Study on Feasibility of Standards of Performance for Two 

Wood Pulping Processes. Document no. EPA-HQ-OAR-2012–0640-0029. November 1978.

18 Hanks, K., Holloway, T., and Gooden, C., RTI International. Projections of the Number of New, Modified, and 

Reconstructed Emission Units for the Kraft Pulp Mill NSPS Review. Memorandum to U.S. Environmental Protection 

Agency. February 4, 2013.

19 See, e.g., Sierra Club v. Costle, 657 F.2d 298, 346 (D.C. Cir. 1981).
12

 Permit limits from permits submitted with the ICR and collected from state agencies;

 RACT/BACT/LAER Clearinghouse;

 A 2010 European Commission document titled Integrated Pollution Prevention and 

Control (IPPC): Reference Document on Best Available Techniques in the Pulp and 

Paper Industry;

 A document from STAPPA/ALAPCO titled Controlling Fine Particulate Matter Under 

the Clean Air Act: A Menu of Options;

 Stack test data for PM and TRS;

 COMS data for recovery furnaces and lime kilns;

 TRS CEMS data for recovery furnaces, lime kilns, and NCG sources; and

 Technical bulletins prepared by NCASI, a major source of environmental data affecting 

the pulp and paper industry.

The conclusions from review of the above information are consolidated in a March 29, 2013 

report titled, “Technology Review and Regulatory Options for the Kraft Pulp Mill NSPS,” 

available in Docket ID No. EPA-HQ-OAR-2012-0640. Additional reports that are also available 

in the docket provide a detailed discussion of the data sets and information sources described 

above:

 Review of the Air Permits for Kraft Pulp Mills. April 26, 2013;

 Review of the Continuous Emission Monitoring and Continuous Opacity Monitoring 

Data from the Pulp and Paper Information Collection Request Responses Pertaining to 

Subpart BB Sources. April 5, 2013;

 Updated Review of the Continuous Emission Monitoring and Continuous Opacity 

Monitoring Data from the Pulp and Paper ICR Responses for NSPS Sources. February 

28, 2014;

 Summary of RBLC and Other Findings to Support Section 111(b) Review of Kraft Pulp 

Mill NSPS. October 18, 2012; and

 Emissions Test Data for the Kraft Pulp Mill NSPS Review. April 22, 2013.

In our review of the ICR data, permits, the RBLC, and literature, we looked for new and 

innovative emissions reduction technologies that would result in greater emissions reductions 

than are currently required by the NSPS. In our comprehensive reviews of CEMS data and 

emissions test data, we looked specifically at the PM and TRS emission limitations that are 

achieved in practice at nearly all kraft mills. Next, we identified options for reducing the 

promulgated NSPS emission limits and analyzed the impacts of reducing the limits.

20 Based on 

the analyses described above, the EPA is increasing the stringency of the NSPS PM limit for new 

and reconstructed recovery furnaces; new and reconstructed SDTs associated with new and 

reconstructed recovery furnaces; and new, modified, and reconstructed lime kilns. The EPA is 

also increasing the stringency of monitoring limits for opacity and TRS by tightening or placing 

restrictions of use of the monitoring allowances in the current NSPS. In the sections below, we 

 

20 Holloway, T. and Hanks, K., RTI International. Emissions Inventory for Kraft Pulp Mills and Costs/Impacts of the 

Section 111(b) Review of the Kraft Pulp Mills NSPS. Memorandum to U.S. Environmental Protection Agency.

February 4, 2013.
13

address commenters’ specific examples of other technologies that they believe should have been 

incorporated into the NSPS review.

2.1-05 Comment: Commenter 0056 noted that EPA generally did not find any advances in 

technology that were adequately demonstrated beyond certain more stringent emission limits for 

PM already established for the same types of sources and systems in 40 CFR part 63, subpart 

MM.21 As a result, the commenter noted that EPA proposed to reset the NSPS for certain new 

and reconstructed sources to the same PM levels established for new sources in the NESHAP, 

and to adjust the PM limit only for modified lime kiln sources to the NESHAP existing unit 

limit. The commenter supported the rationale that EPA used for the proposed emission limit 

changes.

Similarly, commenter 0059 agreed with EPA’s conclusion in the preamble that the technologies 

being used to control PM and TRS emissions from sources regulated under NSPS subpart BB

have not changed. The commenter noted that PM emissions are controlled by ESPs and 

scrubbers, and TRS emissions are reduced using process controls, scrubbers, or incineration. 

According to the commenter, there have been no changes in the technologies used in the industry 

since the last review of subpart BB (or since implementation of the pulp and paper MACT 

standards) to control PM, TRS, or any other criteria pollutants.

Response: We acknowledge the support of commenter 0056 for the proposed changes to the 

numeric emission limits for PM and TRS, and the support of both commenters for our 

conclusions regarding advances in technology. The EPA proposed to:

 Reduce the NSPS PM limit for new and reconstructed recovery furnaces from 0.044 

gr/dscf to the new source PM limit of 0.015 gr/dscf found in the subpart MM NESHAP.

 Maintain the current NSPS TRS limits for recovery furnaces (5 ppmdv for straight

recovery furnaces and 25 ppmdv for cross recovery furnaces).

 Reduce the NSPS PM limit for new and reconstructed SDTs associated with new or 

reconstructed recovery furnaces from 0.2 lb/ton BLS to the new source PM limit of 0.12 

lb/ton BLS in the subpart MM NESHAP.

 Reduce the NSPS PM limit for lime kilns from 0.066 gr/dscf for gas-fired kilns and 0.13 

gr/dscf for liquid-fired kilns (in subpart BB) to the PM limits found in the subpart MM

NESHAP for all fuels, 0.064 gr/dscf for modified lime kilns and 0.010 gr/dscf for new or 

reconstructed lime kilns.

 Maintain the current NSPS TRS limit for lime kilns at 8 ppmdv.

The reductions in the emission limits are being promulgated as proposed. 

2.2 Recovery Furnace, Lime Kiln, and Smelt Dissolving Tank Technology

2.2-01 Comment: Commenter 0057 argued that EPA must consider control techniques that are 

currently used in some mills when making the BSER determination for emissions from recovery 

furnace process units. According to the commenter, the process of mixing collected PM salt from 

 

21 See 66 FR 3180.
14

a recovery furnace ESP with strong black liquor before the liquor is injected into the recovery

furnace is a large source of TRS, VOC, and HAP emissions at a kraft pulp mill. The commenter 

stated that, in the design of modern kraft recovery furnaces, precipitator mix tanks are part of the

recovery furnace process unit. The commenter provided a real-life narrative illustrating the 

significance of controlling the process gases from the hot concentrated black liquor in recovery 

furnace precipitator mix tanks.22

In the narrative, a malfunction caused process gas from the mix tanks to be redirected from a 

SDT to the recovery furnace, resulting in a TRS excursion exceeding 5 ppm and complaints of 

strong odors. In response to the complaints and ongoing regulatory attention, the mill operator 

re-directed the precipitator mix tank process gas flow to an available HVLC vent system 

discharged to a combustion unit, eliminating the TRS, VOC, HAP, and significant odors that had 

previously been emitted by the precipitator mix tank and discharged virtually uncontrolled from 

the SDT low-energy weak wash scrubber vent.

The commenter pointed to this re-direction of gas from a precipitator mix tank to a combustion 

unit as an example of an enhanced control alternative for TRS, VOC, and HAP and noted that 

combustion units are widely used throughout the industry to control emissions. The commenter 

contended that EPA must consider this technique for emissions reductions as part of its BSER 

determination. However, the commenter noted that they found no review and consideration of 

precipitator mix tank TRS and VOC process gas emissions within the proposed kraft pulp mill 

NSPS.

The commenter further suggested that the revised NSPS for kraft pulp mills should rule out 

precipitator mix tank designs at the base of ESPs that allow mix tank off-gases to reach recovery

furnace fuel gas emission points, stating that such designs cannot meet section 111 requirements 

for the BSER that has been adequately demonstrated.

Response: The commenter refers to emissions from salt cake mix tanks, which are used to 

collect the Na2SO4 (salt cake) and Na2CO3 captured in the recovery furnace ESP for reuse in the 

pulping process in order to conserve chemicals. The Na2SO4 recycled back to the recovery 

furnace is reduced to Na2S, a cooking liquor chemical, in the reducing zone of the furnace. 

Reprocessing of the Na2S and Na2CO3 into cooking liquor continues in the SDT.23

Emissions of TRS from salt cake mix tanks, and emissions of VOC and HAP, were considered to 

be outside the scope of this NSPS review because the review focused on the current PM and TRS 

standards that were due for review under CAA section 111(b)(1)(B). In addition, HAPs are 

regulated under the authority of a separate section of the CAA (section 112). Salt cake mix tanks 

are not known to be a source of PM (i.e., no PM data are available for salt cake mix tanks alone 

uncombined with other exhaust streams). Furthermore, salt cake mix tanks typically are not a 

significant source of TRS compared to the emission units currently regulated for TRS under the 

 

22 This narrative concerns the 1200 tpd ADP bleached kraft pulp mill constructed by Champion International

Corporation in 1986 in Quinnessec, MI.

23 U.S. Environmental Protection Agency. Technical Support Document: Chemical Recovery Combustion Sources at 

Kraft and Soda Pulp Mills. Office of Air Quality Planning and Standards. Research Triangle Park, NC. Publication 

No. EPA-453/R-96-012. October 1996. p. 5-13.
15

NSPS, as shown in Table 2. Similarly, emission factor calculations reveal that typical emissions 

of VOC and HAP (methanol) from salt cake mix tanks are also less than 1 tpy. 

Table 2. Typical Uncontrolled TRS Emissions from Salt Cake Mix Tanks and Processes 

Covered Under the Kraft Pulp NSPS

Process TRS emissions, tpy

a

Recovery furnace b2,700

Condensate stripper system 360

Digester system 270

Evaporator system 180

Lime kiln 144

BSW system 54

SDT 36

BLO system 18

Salt cake mix tank c0.6

a. Uncontrolled emissions of TRS are based on information in Table 2.1 (p. 2-5) of the 1983 NSPS review BID, 

entitled Review of New Source Performance Standards for Kraft Pulp Mills, Publication No. EPA-450/3-83-

017, September, 1983. Emission estimates are based on a kraft mill producing 1000 ADTPD, operating 360 

days per year. Conversions used included 1.6 tons BLS/ADTP and 0.275 tons lime (CaO)/ADTP.

b. Based on a range of data from DCE and NDCE recovery furnaces.

c. Salt cake mix tank emission estimates are based on a TRS emission factor of 0.0022 lb sulfur/ton BLS in

NCASI Technical Bulletin No. 849 (August 2002). 

We provide typical emissions estimates for salt cake mix tanks above. However, we 

acknowledge that there can be variability in equipment configuration and emissions from mill to 

mill. The commenter describes a malfunction event caused by blockage of the process gas 

evacuation in gas flow to the SDT vent at one mill as a reason why they believe salt cake mix 

tanks should be covered under the NSPS. The EPA does not consider malfunctions to be valid 

operating conditions for which emission standards are set. The pulp and paper ICR data collected 

by EPA confirms that the mill noted by the commenter continues to route salt cake mix tank 

emissions to their HVLC system for control, and therefore has resolved the problem noted by the 

commenter. The ICR data also indicate that the practice of routing salt cake mix tank emissions 

through a collection system to incineration-based control is used for approximately 20 percent of 

salt cake mix tanks in the kraft pulping industry (e.g., tanks where variability in operations may 

have led to odors the mill has opted to eliminate). Considering the typically low emissions from 

salt cake mix tanks and the variability in operations from mill to mill, the fact that some mills 

have opted to route salt cake mix tank emissions to their HVLC collection system for 

incineration-based control does not necessarily mean that this practice is reasonable for all kraft 

mills, as we show below.

The annualized cost for HVLC systems was recently estimated to be $1.89 million per year.24 A 

typical HVLC system designed for subpart S regulated equipment handles around 133,525 

 

24 Holloway, T., Hanks, K., and Gooden, C., RTI International. Costs, Environmental, and Energy Impacts for the 

Promulgated Subpart S Risk and Technology Review. Memorandum to U.S. Environmental Protection Agency. May 

15, 2012.
16

scfm.

25,26 The average flow rate of uncontrolled vent gas streams from salt cake mix tanks is 

5,045 scfm based on the 2011 ICR responses. The average flow of exhaust from salt cake mix 

tanks is about 4 percent of the typical HVLC gas flow. Adding this exhaust stream would require

new stainless steel duct work (and the associated moisture removal and pressure relief 

components). Considering that HVLC system costs are related to the gas flow transported, the 

estimated cost of the additional components to an HVLC system to accommodate the salt cake 

mix tank would be roughly $71,000 for 1 ton of TRS emissions controlled (e.g., $71,000/ton),

assuming an incineration device is available to accept the salt cake mix tank gas flow. If 

additional incineration capacity would be required, costs would rise significantly. Thus, even 

though salt cake mix tanks were not addressed in the proposed NSPS review, after further 

analysis, we conclude in response to this comment that it would not be cost-effective to regulate 

TRS (or VOC) emissions from salt cake mix tanks under the NSPS.

2.2-02 Comment: Commenter 0057 argued that the proposed rule failed to fully consider 

changes in technology since the last review, resulting in a 5 ppm TRS limit for recovery furnaces 

that is very likely too lax. The commenter noted that when the standard was first promulgated in 

1978, it was based on the use of direct contact black liquor evaporation, black liquor oxidation, 

and control of black liquor sulfidity.27 The commenter pointed out that, while modern mills still 

rely on control of sulfidity as a process-specific means of limiting TRS emissions and controlling 

pulping process chemistry, direct contact evaporation and black liquor oxidation is outdated 

technology, and no new kraft recovery furnaces will be constructed in this fashion.

The commenter argued that the 8 ppm TRS standard for lime kilns is also based on old 

technology. The commenter noted that under the 1978 rule, a lime kiln would comply through 

the maintenance of effective lime mud washing, good operational and combustion practice, and 

wet scrubbing (which was not required to be caustic scrubbing).28 However, according to the 

commenter, EPA made very clear in the final rule that caustic scrubbing was an appropriate and 

demonstrated control for H2S and TRS emissions that performed in a superior manner to noncaustic assisted wet scrubbing for TRS control, but EPA did not explain why it did not require 

caustic scrubbing for TRS control, even though it was the demonstrated BSER. The commenter 

recommended that the lime kiln TRS standard be revised to reflect the fact that today’s lime kilns 

are designed with greater TRS control technology and that caustic scrubbing is a demonstrated 

BSER for TRS.

Response: In general, we disagree with the commenter that we have not considered modern

technology. We performed an extensive review of recent information on the processes, emissions 

controls, and emission data for the pulp and paper industry. This information was obtained by 

EPA through a very detailed (and costly) ICR completed by the pulp and paper industry in 2011. 

 

25 Oommen, R., Radian Corp. Changes made to the Design and Unit Costing of Equipment used to Transport, Treat, 

and Control Emissions from Pulp and Paper Vents. Memorandum to U.S. Environmental Protection Agency. 

Docket ID No. A-92-40, item IV-B-13. February 26, 1996.

26The 133,525 scfm value is the sum of gas flows from HVLC components, including weak liquor storage tanks, 

knotters/screens, deckers, pulp storage tanks, vacuum washers, and associated tanks and chests, and O2

delignification for a kraft mill processing 1000 ADTPD.

27 Kraft Pulp Mills Standards of Performance for New Stationary Sources, Final Rule, 43 FR 7568 (Feb. 23,

1978).

28 Id.
17

Our review of the ICR data, permit limits, the RBLC, and other relevant literature is documented 

in a series of technical reports available in Docket ID No. EPA-HQ-OAR-2012-0640, including:

 Review of the Continuous Emission Monitoring and Continuous Opacity Monitoring 

Data from the Pulp and Paper Information Collection Request Responses Pertaining to 

Subpart BB Sources. April 5, 2013

 Updated Review of the Continuous Emission Monitoring and Continuous Opacity 

Monitoring Data from the Pulp and Paper ICR Responses for NSPS Sources. February 

28, 2014

 Emissions Test Data for the Kraft Pulp Mill NSPS Review. April 22, 2013

 Summary of RBLC and Other Findings to Support Section 111(b) Review of Kraft Pulp 

Mill NSPS. October 18, 2012

 Review of the Air Permits for Kraft Pulp Mills. April 26, 2013

 Technology Review and Regulatory Options for the Kraft Pulp Mill NSPS. March 29, 

2013

 Review of Pulp and Paper Information Collection Request (ICR) Responses Pertaining to 

Startup and Shutdown of Subpart BB Equipment. March 22, 2013

 Projections of the Number of New, Modified, and Reconstructed Emission Units for the 

Kraft Pulp Mill NSPS Review. February 4, 2013

 Emissions Inventory for Kraft Pulp Mills and Costs/Impacts of the Section 111(b) Review 

of the Kraft Pulp Mills NSPS. February 4, 2013

 Economic Impact Analysis for the Section 111(b) Review of the Kraft Pulp Mills New 

Source Performance Standards Subpart BB. February 22, 2013

This extensive body of information builds on and supersedes conclusions from the 1978 original 

NSPS and 1986 NSPS review.

Recovery furnaces. We agree with the commenter’s assessment that there will never be a new 

DCE recovery furnace and associated BLO system in the U.S. The last of these systems was 

installed in 1989. Non-direct contact evaporator recovery furnaces are now the prevailing design. 

The original NSPS promulgated in 1978 considered DCE with BLO and NDCE recovery furnace 

designs and concluded that a TRS limit of 5 ppm reflected the best demonstrated technology

(i.e., use of an NDCE or DCE with sufficient black liquor oxidation to meet 5 ppm). This limit 

was reaffirmed in the 1986 NSPS review, and was reaffirmed again in the 2013 proposed NSPS 

review based on review of a very comprehensive TRS CEMS data set for recovery furnaces in 

use today (roughly 3/4 of which are NDCE recovery furnaces). Given the extensive data set 

evaluated, we disagree with the commenter that we did not evaluate the performance of today’s 

recovery furnace technology. We considered data from all recovery furnaces and then focused 

only on the recovery furnaces that have triggered NSPS to examine the performance of newer or 

upgraded recovery furnaces relative to the 5 ppm limit. Figure 1 below shows the 99th percentile 

of the TRS concentrations measured by CEMS for each recovery furnace, including recovery 

furnaces that are not currently subject to NSPS.

29 Figure 1 shows that most DCE recovery 

furnaces do not perform as well on TRS as NDCE recovery furnaces. Non-NSPS recovery 

 

29 The 99th percentile indicates the emission limitation consistently met by each emission unit considering emissions 

variability (i.e., 99 percent of the TRS averages measured by the CEMS were at or below the 99th percentile value 

shown for each recovery furnace).
18

furnaces are not subject to the same low TRS limit as NSPS furnaces. Figure 2 presents the 99th

percentile TRS concentrations for the recovery furnaces subject to the subpart BB NSPS broken 

out by DCE and NDCE design and control device type. Two of the three DCE recovery furnaces 

subject to subpart BB had 99th percentile TRS values above the 5 ppm limit, while the majority 

of NDCE recovery furnaces met the 5 ppm limit regardless of control device design. Based on 

the data in Figures 1 and 2, we agree with the commenter that DCE recovery furnaces do not 

perform as well on TRS as NDCE recovery furnaces and that DCE recovery furnaces would be 

challenged to meet a 5 ppm TRS limit. Thus, we can conclude based on the data that the 5 ppm 

NSPS TRS limit effectively deters installation of new DCE recovery furnaces. Any DCE 

recovery furnaces that trigger NSPS through modification or reconstruction are expected to 

either convert to NDCE technology or use another means of demonstrating compliance with the 

5 ppm limit (e.g., through improved process controls, additional black liquor oxidation stages, 

and switching to oxidized black liquor in the wet-bottom ESP). In either case, modified and 

reconstructed recovery furnaces are held to the same level of performance as NDCE recovery 

furnaces.

Figure 1. 99th Percentile of the TRS Averaging Periods (NSPS and Non-NSPS Furnaces)
19

Figure 2. 99th Percentile of the TRS Averaging Periods by APCD (NSPS Furnaces)

Lime kilns. Based on our evaluation of an extensive TRS CEMS data set and other literature, we 

disagree with the commenter that caustic scrubbing represents the BSER for lime kilns. Lime 

kiln control technology has evolved since promulgation of the NSPS in 1978, as has the pool of 

available emissions data upon which we based our conclusions for the 2013 proposed NSPS 

review. In addition to good mud washing and operational practices, today’s lime kiln control 

technologies include wet scrubbers, ESPs, and ESP/scrubber combination controls. Electrostatic 

precipitators are becoming increasingly common for lime kiln PM control. We evaluated all of 

these control systems for the proposed NSPS review and found that wet scrubbers (regardless of 

caustic addition), ESPs, and ESP/scrubber combinations all performed similarly with regard to 

TRS. The fact that ESP-controlled kilns performed as well as scrubber-controlled kilns (when 

ESPs are not designed for TRS control) suggests that process factors such as mud washing and 

good combustion of NCGs are important factors in reducing lime kiln TRS emissions. Figure 3

below affirms that 8 ppm is the emission level that has been achieved in practice and adequately 

demonstrated as the BSER.30

 

30 Spence, K., U.S. Environmental Protection Agency. Updated Review of the Continuous Emission Monitoring and 

Continuous Opacity Monitoring Data from the Pulp and Paper ICR Responses for NSPS Sources. Memorandum to 

Docket ID No. EPA-HQ-OAR-2012-0640. February 28, 2014.

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15 TRS (ppmdv @ 8% O2

)

DCE - WBESP DCE - WBESP/SCBR NDCE - WBESP

NDCE - DBESP-WPR NDCE - DB-WBESP NDCE - WBESP

Figure 6. 99th Percentile of the 12-hour TRS Averaging Periods by APCD (NSPS Furnaces)

Current NSPS limit for straight RF (DCE and NDCE) = 5 ppm @ 8% O2

One 99th percentile omitted: NSPS NDCE (49 ppm)
20

Figure 3. 99th Percentile of TRS Averaging Periods for Lime Kilns (NSPS Kilns Only)

One issue with wet scrubbers is that the scrubbing liquid must not introduce reduced sulfur 

compounds into the lime kiln exhaust gas stream. Lime kiln scrubber makeup water can be a 

source of TRS emissions if the scrubber uses process water (e.g., process condensates) 

contaminated with reduced sulfur compounds. Reduced sulfur compounds can be stripped from 

the scrubber makeup water as the hot kiln flue gases pass through the scrubber. Caustic (or weak 

wash) scrubbing is not effective on all TRS compounds and is not necessary to achieve the 8 

ppm limit.31

Review of lime kiln TRS emissions data and the technologies used to reduce TRS emissions 

from lime kilns suggests that use of process controls such as good lime mud washing and 

avoidance of scrubbing liquid contaminated with reduced sulfur compounds continues to be 

adequately demonstrated as the BSER.

2.2-03 Comment: Commenter 0059 agreed that it is appropriate to revise the PM and opacity 

limits in subpart BBa for new and reconstructed lime kilns and recovery furnaces to match the

PM and opacity limits in MACT subpart MM. The commenter noted that the new source PM and 

opacity limits in MACT subpart MM are more stringent than those in NSPS subpart BB and that

these limits represent what new and reconstructed kilns and furnaces have achieved and that the 

units would have to meet the new source MACT standards anyway. The commenter further 

noted that there is no cost impact for this change.

 

31 Hanks, K. and Holloway, T., RTI International. Technology Review and Regulatory Options for the Kraft Pulp 

Mill NSPS. Memorandum to U.S. Environmental Protection Agency. March 29, 2013.
21

The commenter also agreed that it is appropriate only to change the PM limit for 

new/reconstructed SDTs that are associated with new recovery furnaces. The commenter noted 

that facilities often replace or reconstruct existing SDTs without modifying the associated 

recovery furnace or modifying the existing SDT scrubber. Therefore, the commenter agreed that 

it is not cost-effective to lower the PM limit for these units because a lower PM limit would 

likely require a scrubber replacement for a reconstructed SDT.

Response: We acknowledge the comment in favor of the proposed limits for new and 

reconstructed lime kilns and recovery furnaces. The numeric values for the PM and opacity 

limits for lime kilns and recovery furnaces are being promulgated as proposed. We also 

acknowledge the commenter’s agreement with our conclusion to reduce the PM limit from 0.2 to 

0.12 lb/ton BLS for new and reconstructed SDTs that are associated with new recovery furnaces.

The numeric limits for SDTs are being promulgated as proposed.

2.2-04 Comment: Commenter 0057 contended that EPA’s discussion of TRS emission control is 

flawed, since it incorrectly assumes that the terms “white liquor scrubber,” “caustic scrubber,” 

and “wet scrubber” all are directly equivalent and interchangeable when addressing TRS 

emission control for lime kilns, SDT vents, and recovery furnaces. According to the commenter, 

all white liquor scrubbers and caustic scrubbers are wet scrubbers, but a wet scrubber using water 

is never considered as a caustic scrubber or white liquor scrubber. The commenter further noted 

that all white liquor scrubbers are caustic scrubbers, but a caustic scrubber using only sodium or 

potassium hydroxide is not a white liquor scrubber. Commenter 0057 noted that white liquor 

scrubbers use white liquor, which is a solution of Na2CO3, Na2S, and NaOH obtained from the 

kraft pulp mill process, for re-circulating wet scrubbing systems. The commenter argued that 

grouping together white liquor scrubbers, caustic scrubbers, and wet scrubbers that only use 

water instead of caustic compounds is a technical error because they do not have equivalent

emission control reduction effects. The commenter recommended that these scrubber types be 

addressed as separate categories for TRS emissions data review, control efficacy, and analysis, 

and each should be separately analyzed for purposes of the final rule on required emissions 

limitations.

According to the commenter, the reason this distinction is important is that the substantial Na2S

contained in re-circulating white liquor scrubbers will cause formation of H2S, Na2CO3, and 

Na2SO4 in the flue gas from reactions with CO2 and water contained in the recovery furnace and 

lime kiln flue gas. The commenter stated that, due to this chemical reaction, EPA cannot 

accurately conclude that white liquor scrubbing, caustic scrubbing, and scrubbing with water all 

have the same emission control efficacy and thus the same percentage reduction control for H2S

emission concentrations relative to the inlet gas stream H2S and methyl mercaptan

concentrations.

The commenter concluded that EPA must analyze whether the control technology level achieved 

by caustic scrubbing for TRS control on lime kilns, recovery furnaces, and SDT vents does in 

fact constitute the BSER as required by section 111. The commenter recommended that EPA 

require caustic scrubbing wet scrubber control of TRS (as opposed to white liquor scrubbing) in 

the final rule and establish that position by ensuring appropriate subcategorization of its TRS 
22

emission control database analysis determination on each process unit under the rule and in all 

emissions database analyses.

Response: The commenter appears to be confused by the complexities of the kraft pulping 

process, the location and types of emissions controls that can appear within the process v. end-ofpipe, and the summary of findings from our technology review that was condensed considerably 

for the preamble. The technical memoranda in the docket for the proposed rule explain the 

subject matter in greater detail. We also explain the differences in scrubber types here in 

response to this comment. 

“White liquor” is a solution of NaOH and Na2S that is used for cooking wood chips. “White 

liquor scrubbers” are not end-of-pipe controls used on recovery furnace or lime kiln flue gases as 

described by the commenter. White liquor scrubbers are in-process scrubbers installed at some 

mills to reduce sulfur in an NCG stream prior to incineration of that stream in a combustion 

device. White liquor scrubbers may also be referred to as “NCG scrubbers” or “NCG prescrubbers.” The intended purpose of white liquor scrubbers is to remove sulfur compounds from 

NCG streams prior to combustion in order to reduce SO2 emissions that result from combustion 

of TRS-laden NCG streams. The effectiveness of white liquor scrubbers has been determined to 

be process-specific and dependent on the molecular makeup of the NCG stream scrubbed. As 

part of the NSPS review, EPA evaluated whether use of white liquor scrubbers prior to 

incineration of TRS results in reduced emissions of residual TRS following combustion. The 

EPA found no conclusive evidence that white liquor scrubbing reduces post-combustion TRS 

emissions.32

“Wet scrubbers,” as we refer to them in the NSPS review documentation are end-of-pipe

scrubbers regardless of the scrubbing liquid used, whether water alone or water with addition of 

caustic or other liquids. Kraft pulp mills are large industrial users of water, so mills recycle and 

reuse water within their processes whenever possible without causing adverse effects. Often,

mixtures of fresh water and other process liquids are used for scrubbing. The ICR requested data 

on scrubbing liquid, and a wide variety of responses were received which do not group neatly 

into “water only” or “caustic” scrubbers. There are many different sources of scrubbing liquid

and process-specific ranges in concentrations of caustic that could be added to scrubbing liquids

or are already present in liquids recycled from another process. Some common scrubbing liquids 

are described below.

 “Water” can be various forms of mill water including surface water (e.g., from a 

river), groundwater, and/or water that has already been used in some aspect of the 

process.

 “Condensates” are process liquids that condense from various pulping processes 

which may be treated for removal of HAP and reduced sulfur compounds with

condensate strippers or in-process biological treatment systems. Treated “clean”

condensates and other condensates with low concentrations of nuisance compounds 

are often reused in the pulping process as scrubbing liquid or for another purpose. 

 

32 See Figure 7 of the February 28, 2014 EPA memorandum entitled Updated Review of the Continuous Emission 

Monitoring and Continuous Opacity Monitoring Data from the Pulp and Paper ICR Responses for NSPS Sources, 

Appendix E, for NSPS kilns with no NCG, NCG, and pre-scrubbed NCG.
23

Care must be taken to avoid use of contaminated condensates (i.e., condensates with a 

high concentration of reduced sulfur compounds) in scrubbers, as this would result in 

TRS emissions.

 “Weak wash” is the lime mud washer filtrate. Lime mud is predominantly CaCO3. 

Weak wash is often used in SDT scrubbers and then drains into the SDT, where the 

weak wash dissolves recovery furnace smelt. Based on the ICR data, we observe that 

weak wash typically has a pH of 10 or greater. Additional alkali (caustic) may be 

added if necessary to further increase the pH of the scrubbing medium.

As discussed in a previous response, TRS CEMS data for wet scrubbers on lime kilns subject to 

the NSPS exhibited similar performance regardless of scrubbing liquid used, so it was not 

necessary to distinguish among scrubber types, especially given that wet scrubbers are not the 

only lime kiln control technology in use today. Based on the data, we can conclude that caustic 

scrubbing is not the one and only BSER for TRS from lime kilns. Review of lime kiln TRS 

emissions data and the technologies used to reduce TRS emissions from lime kilns shows that 

use of process controls such as good lime mud washing and avoidance of scrubbing liquid 

contaminated with reduced sulfur compounds represents the BSER.

Wet scrubbers are only present on 6 of the 149 recovery furnaces in the U.S., including 3 DCE 

furnaces and 3 NDCE furnaces. Four of the scrubbers are preceded by a recovery furnace ESP 

system. Regardless of whether the scrubbing fluid used contained caustic, scrubber-controlled 

recovery furnaces did not achieve TRS emissions lower than their ESP-controlled counterparts. 

Thus, we can conclude that caustic scrubbing does not constitute BSER for TRS from recovery 

furnaces.

Similarly, caustic scrubbing alone does not constitute the BSER for SDTs. In our NSPS review, 

we concluded that variability in SDT TRS emissions can be attributed to process factors unique 

to individual facilities, that no one specific process factor alone dictates TRS emissions from mill 

to mill, and that control of SDT TRS emissions depends on more than scrubbing alone (i.e., the 

scrubbing solution, scrubber variables, and site-specific process parameters all play a role). The 

TRS emissions arise from the sulfide present in the smelt and in the scrubbing liquid. Scrubbers 

with scrubbing solution that is high in sulfides can contribute to TRS emissions rather than 

reducing them. Therefore, the BSER for SDTs was determined to be the use of water that is not 

highly contaminated with dissolved sulfides for dissolving the smelt and for scrubbing. In 

addition to ensuring that the scrubbing and smelt dissolving liquid is not contaminated with 

sulfides, TRS removal can be enhanced through use of an alkaline scrubbing medium at mills 

where the principle TRS compounds are acidic (e.g., H2S, and to some extent methyl mercaptan). 

Review of the ICR data base indicates that the vast majority of SDTs are using alkaline solutions 

such as weak wash or a combination of water (or weak wash) and caustic as the scrubbing 

medium.33

Whether or not a salt cake mix tank vents into the SDT for control by the SDT scrubber could 

also affect SDT emissions at some mills, depending on the concentration and specific TRS 

compounds attributable to the salt cake mix tank. As mentioned elsewhere, one mill found it 

necessary to implement a process change to remove a salt cake mix tank vent from the SDT 

 

33 Hanks, K. and Holloway, T., RTI International. Technology Review and Regulatory Options for the Kraft Pulp 

Mill NSPS. Memorandum to U.S. Environmental Protection Agency. March 29, 2013.
24

scrubber system in order to meet the SDT TRS limit. However, this is not typical of salt cake 

mix tank emissions from all mills, and the configuration of the salt cake mix tank vent with 

respect to the SDT can be different from mill to mill (e.g., some may route salt cake mix tanks to 

the SDT scrubbers, others may not).

The current NSPS limit for TRS emissions from SDTs is 0.033 lb as H2S/ton BLS. The original 

1976 SDT TRS limit of 0.0168 lb/ton BLS was raised to 0.033 lb/ton BLS during the 1986 NSPS 

review because some SDTs with wet scrubbers could not meet the original limit. During the 

1986 NSPS review, it was determined that there was a larger range of variation in TRS emissions 

from well-controlled SDTs than indicated by data obtained during NSPS development.

Rather than attempt to estimate and account for every equipment design and operating variable in 

SDT and scrubber systems that could potentially affect TRS emissions, we took the more direct 

and accurate approach of analyzing SDT TRS stack test measurements to evaluate the 

performance of today’s SDTs. Emissions test data collected at the SDT scrubber stack account 

for all of the process- and scrubber-related factors that affect SDT emissions. A total of 106 TRS 

stack tests performed between 1987 and 2011 (on 90 SDTs) were reviewed for purposes of the 

NSPS review. All but seven of the tests were performed as recently as 2004. The TRS emissions 

test data allowed us to determine the emission limitation that has been achieved in practice 

though the combination of process changes and controls that have been demonstrated at modern 

kraft mills. We determined that the emission limitation achieved in practice considering process 

variability and cost is 0.033 lb as H2S/ton BLS. 

2.2-05 Comment: Commenter 0057 noted that SDT emissions could be substantially reduced

through application of control methods used on other equipment at pulp mills. The commenter 

noted that historically, the kraft pulp mill sector has generally used low-pressure scrubbing plus

demisters, or demisters only, as the sole emission control techniques applied to PM and TRS

emissions from SDT vents. According to the commenter, such PM and TRS emissions could be 

better controlled by high-energy wet scrubbing, spray towers, packed towers, and caustic 

scrubbers and through process modification if the facility employed recovery furnace precipitator 

salt-strong black liquor mixing tanks that are vented to the SDT process vent. The commenter 

pointed out that some of these same controls are applied to other kraft pulp mill process 

equipment and could be applied to SDT process vents. The commenter recommended that EPA 

evaluate these controls as part of its BSER determination.

Response: The commenter suggests that SDT emissions could be further reduced if SDTs 

employed various types of scrubbers (i.e., high-energy wet scrubbers, spray towers, packed 

towers, or caustic scrubbers) instead of low-energy wet scrubbers or demisters, or presumably if 

salt cake mix tanks were not vented though the SDT. If a salt cake mix tank vent were removed 

from the SDT scrubber, then the salt cake mix tank would either be completely uncontrolled, or 

possibly routed through an HVLC collection system to incineration-based control. We discussed

the typical TRS and VOC emission reduction that could be achieved and high cost of routing salt 

cake mix tank emissions through an HVLC system in response to comment 2.2-01, where we 

concluded that this practice is not adequately demonstrated as the BSER considering costeffectiveness.
25

Regarding scrubber controls, we discussed caustic scrubbing of SDT emissions in response to 

comment 2.2-04, where we concluded that caustic scrubbing alone is not the BSER and that 

additional process factors were accounted for through our analysis of recent stack test data. 

Spray towers are a form of low-energy wet scrubber, having pressure drops that are typically 

lower than other types of scrubbers.34 Various types of wet scrubbers are used that differ not only 

in their design (e.g., spray tower, venturi, packed-bed, etc.), but in how they are operated (e.g., 

operating pressure drop, type of scrubbing liquid used, pH, etc.).35

The combination of scrubber design and operating variables makes each scrubber system 

somewhat mill-specific, necessitating some level of generalization in nationwide analyses. 

Rather than attempt to account for every equipment design and operating variable, we analyzed 

SDT TRS stack test measurements to evaluate the performance of today’s SDTs. In our analysis 

of TRS stack test data for SDTs, we grouped SDTs with demisters, packed-bed scrubbers, and all 

other types of wet scrubbers separately. Information on the type of scrubbing solution used 

during TRS emissions testing was limited in the stack test reports. However, review of the ICR 

data base indicated that the vast majority of SDTs in the U.S. are using weak wash or a 

combination of fresh water and caustic as the scrubbing medium. Figures D-1 and D-2 in our 

technology review presented the emissions test data for SDT scrubbers.

36 We concluded based 

on the emissions test data and additional information from prior studies of SDT TRS emissions 

that:

 The baseline level of SDT TRS emissions of 0.033 lb/ton BLS has been achieved in 

practice. 

 The technological basis for this limit (use of water in the smelt tank and scrubber with 

low sulfide content) has not changed since the 1986 NSPS review.

 Because many SDTs have achieved levels below 0.0168 lb/ton BLS, it would be 

appropriate to evaluate the cost effectiveness and environmental impacts of reducing the 

NSPS limit for new, modified, and reconstructed SDTs to the original NSPS and 

emissions guidelines level of 0.0168 lb/ton BLS.

37

 

34 U.S. Environmental Protection Agency. Air Pollution Control Cost Manual - Sixth Edition. Publication No. EPA 

452/B-02-001. Section 6, Chapter 2 - Wet Scrubbers for Particulate Matter. July, 15 2002. Table 2.1. Available at 

http://www.epa.gov/ttn/catc/dir1/cs6ch2.pdf.

35 U.S. Environmental Protection Agency. Air Pollution Control Technology Fact Sheet: Packed-bed/Packed-Tower 

Wet Scrubber. Publication No. EPA-452/F-03-015. July 15, 2003. Available at 

http://www.epa.gov/ttn/catc/dir1/fpack.pdf.

U.S. Environmental Protection Agency. Air Pollution Control Technology Fact Sheet: Spray-Chamber/Spray-Tower 

Wet Scrubber. Publication No. EPA-452/F-03-016. July 15, 2003. Available at

http://www.epa.gov/ttn/catc/dir1/fsprytwr.pdf.

U.S. Environmental Protection Agency. Air Pollution Control Technology Fact Sheet: Venturi Scrubber. Publication 

No. EPA-452/F-03-017. July 15, 2003. Available at http://www.epa.gov/ttn/catc/dir1/fventuri.pdf.

U.S. Environmental Protection Agency. Air Pollution Control Cost Manual - Sixth Edition. Section 6, Chapter 2 -

Wet Scrubbers for Particulate Matter . Publication No. EPA 452/B-02-001. July, 15 2002. Available at 

http://www.epa.gov/ttn/catc/dir1/cs6ch2.pdf.

36 Hanks, K. and Holloway, T., RTI International. Technology Review and Regulatory Options for the Kraft Pulp 

Mill NSPS. Memorandum to U.S. Environmental Protection Agency. March 29, 2013.

37 Id.
26

We considered use of a high-energy wet scrubber in our cost and impacts analysis. We 

concluded that the costs to upgrade to a high-energy scrubber were not justified by the 

incremental TRS emission reductions that would be achieved (assuming the scrubber reduced 

emissions from 0.033 to 0.0168 lb/ton BLS). Although not justified for TRS, a high-energy wet 

scrubber was determined to be the BSER for PM emissions from new and reconstructed SDTs

associated with new or reconstructed recovery furnaces. The same high-energy wet scrubbers 

used for SDT PM control would also be used for SDT TRS control in the future.

2.3 Digester and Brown Stock Washer Technology

2.3-01 Comment: Commenter 0057 argued that the proposed rule has not fully evaluated the 

actual TRS emissions reductions with combustion units or non-combustion units. The 

commenter contended that non-combustion units are typically not as effective for reducing TRS 

in discharge gases from digester systems, BSW systems, evaporator systems, and condensate 

stripper systems. Thus, the commenter concluded that EPA must consider the actual reductions 

achievable with combustion-controlled systems and revise the TRS standard to ensure that all 

pulp mills are reducing TRS emissions accordingly.

The commenter also stated that the TRS limit should be expressed as a percentage reduction to 

ensure that the emissions reductions available through the BSER are actually achieved at all pulp 

mills. The commenter noted that the current TRS limit is expressed as 5 ppm, but pointed out 

that emissions reductions with combustion units are typically in the range of 98 percent to 

greater than 99 percent destruction efficiency for both TRS and VOC contained in the process 

gases. The commenter concluded that this percentage reduction may very well put TRS 

emissions consistently below 5 ppm.

Response: Regarding the commenter’s statements about combustion versus non-combustion 

technology, it appears that the commenter is referring to the TRS compliance option for digester, 

BSW, evaporator, and condensate stripper systems in §60.283a(a)(1)(v), where a noncombustion control device must meet a TRS limit of 5 ppm. In the proposal preamble, we stated 

that incineration remains the best demonstrated technology and that 5 ppm remains the 

appropriate limit, and noted that:

Alternatives to incineration, such as scrubbing, are less effective at the removal of TRS 

because only two of the four TRS compounds (H2S and methyl mercaptan) are acidic 

enough to be removed with alkaline scrubbing, resulting in a removal efficiency much 

lower than that achieved by incineration.38

In response to the commenter, we note that the NSPS does not dictate which controls must be 

used, as long as the emission limit is met. The 5 ppm emission limit in §60.283a(a)(1)(v) for 

non-combustion is equivalent to the 5 ppm TRS emission limit for incineration-based control in 

§60.283a(a)(1). We identified only a few facilities using the 5 ppm non-combustion TRS 

standard in §60.283a(a)(1)(v) to show compliance. Even though the vast majority of facilities use 

incineration-based control, facilities are not precluded from using other forms of control that 

achieve the TRS emission limit. This construction of NSPS allows for innovation of new 

 

38 78 FR 31322.
27

technologies in the future that can show compliance with the same 5 ppm limit as required for 

incineration-based control. 

We disagree with the commenter that the 5 ppm limit should be replaced with a percent 

reduction limit for several reasons. First, percent reduction requirements would not necessarily 

equate to emissions below 5 ppm. In circumstances where uncontrolled emissions are highly 

concentrated (e.g., 5000 ppm), a percent reduction would not reduce emissions to 5 ppm (e.g., a 

99 percent reduction in concentration would be 50 ppm, as compared to the currently required 

5 ppm limit). Emissions of this magnitude would not be unusual for kraft mill digester, 

evaporator, or condensate stripper systems if left uncontrolled. Typical uncontrolled TRS 

concentrations from digester, evaporator, BSW, and condensate stripper systems would be or the 

order of 9500, 6700, 30, and 5000 ppm, respectively.39 Thus, requiring a percent reduction 

instead of a 5 ppm limit, in most cases, would effectively relax the low TRS limits that have 

reflected the level of control achieved in practice for over 30 years.

Second, while it may seem that reducing low-concentration gas streams by 99 percent would 

result in emissions below 5 ppm, this may not be reasonably achievable (considering cost, 

environmental, and energy impacts), as would a 5 ppm limit. Dilute gas streams such as a highvolume BSW gas stream with a 30 ppm TRS concentration are more difficult and costly to 

control in a thermal oxidizer than concentrated gas streams because of the high air flow volumes 

that must be incinerated.

40 Large amounts of supplemental fuel would be needed to sustain 

combustion of the dilute gas stream in a thermal oxidizer, which in turn would result in 

emissions of additional criteria pollutants and GHGs. Instead of prescribing a specific emission 

reduction be met, the NSPS contains multiple compliance options including the 5 ppm TRS limit 

or equivalent combustion of vent gases in process equipment such as lime kilns, recovery 

furnaces, or boilers where capacity of these devices to treat HVLC air flow volumes is available. 

Lime kilns, recovery furnaces, and boilers do not suffer from the supplemental fuel requirements 

needed for thermal oxidizers and have been demonstrated in practice to achieve low TRS 

emissions.

Finally, percent reduction limits would require periodic emissions testing at the inlet and outlet 

of the control device, whereas continuous TRS monitoring in the stack is used to demonstrate 

compliance with the 5 ppm limit. Inlet-outlet testing of TRS vent gas streams entering 

incineration devices poses a safety hazard and is particularly impractical for process equipment 

such as lime kilns, recovery furnaces, and boilers because outlet emissions are confounded by 

emissions from sulfur compounds that enter the process in other ways (e.g., with the BLS or lime 

mud). Measurement of inlet-outlet concentrations is also complicated in situations where 

multiple inlet streams are introduced separately into the control device which has one comingled 

exhaust, or in situations where gases from multiple emissions units are combined in a common 

duct that can be split and routed to more than one control device (e.g., a primary control device 

and backup control device), 

2.3-02 Comment: Commenter 0057 recommended that the EPA clarify that digester process 

gases released into the interiors of buildings that house digester process equipment should be 

 

39 U.S. Environmental Protection Agency. Review of New Source Performance Standards for Kraft Pulp Mills.

Publication No. EPA-450/3-83-017. September 1983.

40 Id.
28

considered a discharge to the atmosphere. The commenter noted that digester process equipment, 

including continuous digesters, chip bins, chip hoppers, knotter cyclones, low and high pressure 

feeders, pre-steaming vessels, flash tanks, etc. are usually housed together in the digester process 

building, which also includes a ventilation system. The commenter further noted that chip 

steaming is often used to charge digesters in kraft pulp mills, thereby making beneficial use of 

low-grade steam, but the common industry practice of using contaminated flash steam during 

chip steaming can also lead to the release of TRS, VOC, and HAP.

The commenter noted that these emissions are typically first released into the building that 

houses the kraft mill digester, and then released to the outside through building ventilation fans. 

According to the commenter, this occurs when the chip bin is charged with an excessive amount 

of flash steam and the low pressure feeder from the chip hopper to the chip bin is breached with 

process gases entering the chip hopper. The commenter further noted that knotter cyclones are 

used to charge chip bins with incompletely digested wood knots that are recycled from the output 

of continuous digesters and digester blow-down tank/pre-brown stock pulp management. The 

commenter stated that such cyclones are another potential source of emissions to the air in

digester buildings.

The commenter also cited the following passage in the proposed rule:

(a) On and after the date on which the performance test required to be conducted by 

§60.8 is completed, no owner or operator subject to the provisions of this subpart must 

cause to be discharged into the atmosphere...41 (emphasis added)

The commenter contended that this language is vague and may allow for uncontrolled release of 

process gases from equipment inside of buildings that are not directly ducted to a vent or stack 

on the exterior of the building. The commenter was concerned that this terminology could be 

misinterpreted to mean that there must be an intentional, direct release of air pollutants to the 

outside atmosphere, which the commenter feared may create a loophole in some states to which 

EPA has delegated authority for NSPS implementation. The commenter noted that, in certain 

states, process gases emitted into the interior of buildings are considered solely under the 

purview of occupational health regulation.

Response: The proposed subpart BBa language “cause to be discharged into the atmosphere”

applies for both captured and uncaptured (fugitive) emissions that are discharged into the 

atmosphere.

Federal air pollution regulations address the most significant sources of emissions from the pulp 

and paper industry, including captured emissions emitted through a conveyance and fugitive 

emissions. Any remaining fugitive emissions not explicitly addressed under Federal regulations 

that could potentially escape from digester buildings are likely to be very minor in comparison to 

regulated emissions, and any such remaining emissions may be best characterized as episodic 

equipment leaks that are not part of normal operations. Such emissions would first pose an 

occupational hazard if they are emitted in significant concentrations, along with nuisance odors, 

 

41 Kraft Pulp Mills NSPS Review, Proposed Rule, 43 FR 31336 (May 23, 2013), citing proposed §60.283a(a).
29

and potential non-compliance with air regulations (especially if a mill has interpreted the 

regulations loosely, as the commenter contends).

We believe the broad language in the NSPS, which is further enhanced by the collection and 

control requirements under NESHAP subpart S, already ensures that releases of air pollutants 

into digester buildings from regulated equipment are subject to control. “Digester systems” are 

defined broadly in the NSPS to include each continuous digester or each batch digester used for 

the cooking of wood in white liquor, and associated flash tank(s), blow tank(s), chip steamer(s), 

and condenser(s). In addition, the NSPS contains broad definitions for other NCG-producing 

equipment subject to the TRS limitations. For example, the definition of a “brown stock washer 

system” includes BSWs and associated knotters, vacuum pumps, and filtrate tanks used to wash 

the pulp following the digester system. Thus, the equipment referred to by the commenter 

(continuous digesters, chip bins, chip hoppers, knotter cyclones, low and high pressure feeders, 

pre-steaming vessels, and flash tanks) are addressed by the NSPS equipment definitions.

Similarly, under the subpart S NESHAP, broad definitions cover the equipment referred to by the 

commenter. For example, under subpart S, the definition of an “emission point” includes open 

pieces of process equipment and equipment leaks. As defined in subpart S, a “chip steamer” is a 

vessel used for the purpose of preheating or pretreating wood chips prior to the digester, using 

flash steam from the digester or live steam. A subpart S “knotter system” includes the knotter, 

knot drainer tanks, ancillary tanks, and any other equipment serving the same function. The 

subpart S NESHAP contains specific standards for capture of HAP emissions from affected 

facilities (see §63.450 – Standards for enclosures and closed-vent systems) which involve VOC 

leak detection as a surrogate for HAP. The subpart S NESHAP, which was promulgated in 1998,

results in refined monitoring and control of NCG emission sources beyond that required in the 

NSPS. Collection, control, and leak detection of HAP emissions under subpart S results in 

collection, control, and leak detection of TRS emissions in the same NCG streams covered under 

the NSPS. To ensure that the collection system requirements under subpart S are implemented 

under subpart BBa, and to promote consistency between these two Federal rules, we are revising 

§§60.283a(a)(1)(i)-(iii) and (v) of the proposed subpart BBa to reference the §63.450 collection 

system standards in subpart S. We believe that the applicable Federal air regulations (NSPS and 

NESHAP together), combined with worker safety regulations, leave little opportunity for any 

significant emissions of TRS, VOC, or HAP from modern digester buildings. 

In addition to incorporating the §63.450 standards for closed-vent systems, as an outgrowth of 

this comment, we are changing the final NSPS to clarify that chip bins using live steam (flash 

steam) are considered to be chip steamers within the definition of digester system in the NSPS. 

Emission factor estimations show that the uncontrolled TRS emissions associated with digester 

chip bins using live steam are significantly greater than digester chip bins using fresh steam. For 

example, if uncontrolled, a digester chip bin could emit on the order of 40 tpy TRS, while an 

uncontrolled digester chip bin using fresh steam would emit only 0.1 tpy TRS. In light of these 

data, we are revising the NSPS definition of “digester system” to clarify that “chip steamer(s) 

including chip bins using live steam” are subject to the NSPS. 

2.3-03 Comment: Commenter 0057 stated that the proposed limits for TRS include an 

exemption for BSWs that could allow uncontrolled TRS emissions. The commenter noted that 

the proposed regulation states that BSWs do not have to comply with the TRS requirements if 
30

the Administrator is convinced that “incinerating the exhaust gases from a new, modified, or 

reconstructed brown stock washer system is technologically or economically unfeasible.”42

The commenter argued that this subsection creates an impermissible exception based on 

economic considerations. The commenter noted that section 111 directs the Administrator to take 

account of cost when making a determination of what constitutes BSER for each standard of 

performance.43 Once the Administrator has determined what reductions are available under this 

standard, the commenter argued there is no longer a statutory basis for avoiding compliance 

based on cost. The commenter contended that the subsection as drafted opens the possibility of

avoiding the statutory duty to implement the standards of performance.

The commenter further argued that the Administrator’s determination of what constitutes BSER 

has already established what constitutes BSER from a technical standpoint, so taking a second 

bite at the apple in this subsection simply allows the circumvention of a determination already 

made. According to the commenter, even if the exemption in the proposed regulation at 

§60.283a(a)(1)(iv) could be justified, it fails to explain what the alternative standard would be if

an exemption were granted. The commenter cited the court ruling in Sierra Club v. EPA, which 

stated that Congress intended that “constant or continuous means of reducing emissions must be 

used to meet these requirements. By the same token, intermittent or supplemental controls or 

other temporary, periodic, or limited systems of control would not be permitted as a final means 

of compliance.”44 Although this case related to CAA section 112, the commenter argued the 

drafting of section 111 is highly analogous, which the commenter said EPA recognized in the 

proposed rule.45

According to the commenter, the proposed regulation as it is currently drafted does not state 

what standard will apply to exempted BSWs. The commenter stated that this must be remedied 

to ensure that, as required by law, adequate and continuous controls for TRS will be in place, 

even for exempt BSWs.

Response: The exemption codified in §60.283a(a)(1)(iv) continues the same exemption that 

EPA previously promulgated and codified in §60.283(a)(1)(iv) in Subpart BB. This exemption 

was originally promulgated in 1978 and was reconsidered and retained in the subsequent NSPS 

review that was concluded in 1986. In this rulemaking, EPA did not invite comment on this 

exemption or otherwise reopen this exemption for comment, and is not reconsidering it. 

 

42 Kraft Pulp Mills Standards of Performance for New Stationary Sources, Final Rule, 43 FR 7568 (Feb. 23,

1978).

43 See 42 U.S.C. 7411(a)(1).

44 See Sierra Club v. EPA, 551 F.3d 1019, 1027 (D.C. Cir. 2008).

45 See Proposed Rule, supra, at 31317.
31

3. Continuous Emission Monitoring System Data Review

3.1 Data Evaluation and Quality Analysis

3.1.1 General Quality Analysis

3.1.1-01 Comment: In commenter 0058’s review of CEMS/COMS data, the commenter found 

multiple instances of inclusion of erroneous/inappropriate data (e.g., negative values, values 

corresponding to “zero production,” etc.),46 some of which were also cited by commenter 0056.47

Commenter 0058 acknowledged that the EPA was tasked with the analysis of a large quantity of 

fairly complex data sets in a short period of time. However, according to the commenter, the lack 

of consistency in applying QA/QC procedures has the potential to significantly impact the 

conclusions from this data analysis, especially given the need to ascertain that performance is 

“adequately demonstrated” even when including S/S periods. The commenter contended that a 

thorough review of NSPS unit performance that includes a consistent QA of all data, including 

those related to S/S conditions, is essential in order to support the “adequately demonstrated” 

conclusion.

Citing the CEMS/COMS data review memorandum,48 commenter 0058 contended that, while 

omitting abnormally large values that occur during periods of “process downtime” (zero 

production) is appropriate, the inclusion of any data used during “process downtime” can 

artificially skew the averages. Commenter 0056 cited a specific example where EPA included 

zeros in its calculation of the 12-hour block average for TRS for one of their mills.49

Commenter 0058 noted that inclusion of zeros during times of non-operation not only artificially 

lowers calculated averages but also inflates the count of averaging periods containing numeric 

data. According to the commenter, the count of averaging periods with numeric data appears in 

the denominator when the percentage of periods exceeding a proposed limit (20 percent opacity, 

8 ppmdv TRS @ 10 percent O2, or 5 ppmdv TRS @ 8 percent O2) is calculated. Thus, the

commenter noted that inclusion of these values in the analyses results in artificially low 

“monitoring exceedance” percentage calculations as well.

Response: The COMS and TRS CEMS data sets analyzed by EPA prior to proposal were 

provided as part of ICR responses. The ICR respondents handled erroneous/inappropriate

monitoring data in a variety of ways: (a) some respondents replaced invalid measurements with 

text which prevented the data from being used in EPA’s calculations, (b) some respondents

added a note when invalid measurements occurred but did not remove the data, and (c) some 

respondents did not provide any indication when invalid measurements occurred. In response to 

comments on our analysis of the CEMS and COMS data, EPA scrutinized the data sets to ensure 

the following types of data were removed:

 

46 See comment 0058, p. 9.

47 See comment 0056, pp. 6-7.

48 U.S. Environmental Protection Agency. Review of the Continuous Emission Monitoring and Continuous Opacity 

Monitoring Data from the Pulp and Paper Information Collection Request Responses Pertaining to Subpart BB 

Sources. Document no. EPA-HQ-OAR-2012-0640-0039. April 5, 2013.

49 See comment 0056, p. 7. 
32

 Negative opacity and negative TRS concentration measurements

 Measurements corresponding with periods of zero (or negative) production values or 

labeled as “process down” times

 Measurements recorded during monitoring system malfunctions, out-of-control periods 

or repairs, and monitor QA/QC checks, calibration checks, or zero or span adjustments to 

the extent that these time periods were labeled in the data sets.

The EPA also resolved double TRS O2 corrections for units pointed out by commenters 0056 and 

0058 below, rechecked calculation references, ensured any O2 correction calculations added to 

the data sets were based on the 12-hour average TRS concentration and 12-hour average O2

concentration (consistent with the rule), and updated other information as needed.

The resultant “cleaned” data sets after removal of the erroneous/inappropriate data described 

above were used for further analysis of the promulgated standards. These data sets are described 

in an updated documentation memorandum, available in the docket for the final rule.

50 The 

cleaned data sets and revised memorandum replace and supersede the pre-proposal data sets and 

analysis. 

3.1.2-03 Comment: Commenters 0056 and 0058 stated that some of the TRS data have been 

double-corrected for O2. Commenter 0058 noted that in the CEMS/COMS data review 

memorandum,

51 the EPA assumed that the data submitted in certain TRS CEMS datasheets were 

uncorrected because the percent O2 correction data provided in the adjacent column of the 

spreadsheet(s) were not reported as 8 percent or 10 percent. The commenter indicated they have

obtained confirmation from two facilities so far that O2-corrected TRS data were provided as 

requested, and that the 12-hour O2 averages used to correct the data to 8 percent or 10 percent, as

appropriate, were reported in the “% O2 correction” column. Thus, commenter 0058 concluded, 

the TRS data for units 109.RB3, 109.RB4, 109.LK1, and 112.AA-110 have been erroneously 

double-corrected for O2 in the EPA’s analysis.

Response: The EPA removed the double-O2 correction for TRS from recovery furnaces

109.RB3 and 109.RB4 and lime kilns 109.LK1 and 112.AA-110 identified by the commenters

and used the data provided in the original submissions for these units. The EPA did not change 

the O2 corrections for other units unless they were specifically identified as double-corrected by 

commenters. However, EPA did review the TRS data sets to determine the number of CEMS

data sets for which double correction may have occurred and the potential effects of the double 

correction. We determined that double correction may have occurred (e.g., a 50/50 chance) in up 

to seven additional recovery furnace CEMS data sets and seven additional lime kiln CEMS data 

sets submitted by multiple companies. Upon further examination of the data sets, we determined 

that the impact of the potential double correction on our conclusions relative to the proposed 

emissions limits and monitoring allowances is insignificant because the number of exceedances 

 

50 U.S. Environmental Protection Agency. Updated Review of the Continuous Emission Monitoring and Continuous 

Opacity Monitoring Data from the Pulp and Paper ICR Responses for NSPS Sources. Memorandum to Docket ID 

No. EPA-HQ-OAR-2012-0640. February 28, 2014.

51 U.S. Environmental Protection Agency. Review of the Continuous Emission Monitoring and Continuous Opacity 

Monitoring Data from the Pulp and Paper Information Collection Request Responses Pertaining to Subpart BB 

Sources. Memorandum to Docket ID No. EPA-HQ-OAR-2012-0640. April 5, 2013.
33

of the proposed standard was similar in the original TRS ppm column and the potentially doublecorrected TRS ppm column of each CEMS data sheet. Therefore, we did not burden ICR 

respondents with follow-up questions on the TRS CEMS data, nor did we remove the 14 

potentially double-corrected data sets from the analysis.

3.1.2 Operating Period

3.1.2-01 Comment: Commenter 0055 believes that the semiannual basis for determining the 

monitoring allowance is more appropriate than the quarterly basis, stating that a semiannual basis 

for this requirement would not result in an increase in emissions, but would decrease the 

opportunity for reported violations. According to the commenter, this alleviates some of the 

burden on the industry without harming the environment. The commenter stated that this 

approach is consistent with ICR data accumulated by the EPA and includes limitations that are 

achievable so long as the current SSM exemption is maintained. The commenter noted that 

industry has concerns that by removing the current SSM exemption, it would be difficult to meet 

the proposed 1 percent allowance.

Response: The EPA acknowledges the commenter’s support for using a semiannual basis for 

determining monitoring allowance and has chosen to finalize this requirement consistent with the 

semiannual reporting frequency in §60.288a(a). The EPA agrees the semiannual allowance 

calculation basis will reduce reporting burden on the industry without harming the environment. 

As proposed, the EPA is eliminating the SSM exemption for reasons discussed in section 4 of 

this document.

3.1.2-02 Comment: Commenter 0058 stated that the EPA did not evaluate whether compliance 

with the proposed monitoring allowances had been “adequately demonstrated” under the 

currently proposed quarterly reporting basis or the alternative semiannual reporting basis. The 

commenter concluded that achieving compliance on an annual basis is not equivalent to 

achieving compliance on a quarterly or a semiannual basis. The commenter noted that a 1

percent annual monitoring allowance of the 730 TRS reporting periods in a year corresponds to 

a maximum of seven reporting periods of excess emissions without triggering a violation of the 

standard (provided the applicable proposed cap is not exceeded). The commenter further noted 

that, when considered on a quarterly or semiannual basis, this corresponds to 1.8 (rounded up to 

2) reporting periods per quarter or 3.6 (rounded up to 4) reporting periods semiannually. 

According to the commenter, a facility with seven or fewer reporting periods in a year would 

therefore be in compliance on an annual basis, but if more than two excursions occurred in any 

given quarter, or more than four occurred in a semiannual period, the facility would fail to meet 

the requirement on either a quarterly or a semiannual basis. The commenter stated that EPA,

therefore, cannot conclude, based on a review of annual performance data, that compliance with 

the proposed quarterly-based standards has been adequately demonstrated. To illustrate his point, 

the commenter provided two specific examples.

52

 In the first example, the annual average TRS from a current NSPS recovery furnace 

[NDCE-WBESP] is reported as 0.75 ppm @ 8 percent O2 (99th percentile = 2.55 ppm @ 

8 percent O2) for the year 2009. In the same year, five exceedances of the 5 ppmdv limit 

 

52 Comment 0058, p. 2.
34

were reported. Data were available from 694 of 730 possible 12-hour averaging periods. 

On an annual basis, it would appear that the data from this NSPS recovery furnace 

demonstrate that the proposed standards are achievable. However, even though the 

annual percentage of averaging periods that exceeded 5 ppmdv was less than 1 percent 

(5/694 = 0.72 percent), 4 of the 5 exceedances occurred in the third quarter, and the fifth 

exceedance occurred in the following quarter. If the proposed standards were applicable 

to this NSPS unit, the 1 percent monitoring allowance would be exceeded on a quarterly 

basis, and also on a semiannual basis.

 In the second example, another NSPS recovery furnace [NDCE-DBESP] in the data set

has an annual average TRS of 0.30 ppm @ 8 percent O2 and a 99th percentile of 4.44 ppm 

@ 8 percent O2. Six exceedances of the 5 ppmdv emission limit were reported (all during 

periods of S/S) with data available for 726 reporting periods. The percentage of averaging 

periods exceeding 5 ppmdv was calculated on an annual basis to be less than 1 percent 

(6/726 = 0.83 percent). However, all 6 exceedances occurred on four consecutive days in 

one quarter while trying to bring the recovery furnace back online. During this period, 

BLS were fired at a reduced rate along with supplementary fossil fuel firing. As indicated 

in Table 1 of the comment, 3.3 percent (6/180) of averaging periods in the third quarter 

exceeded 5 ppmdv. The example also indicates that the 1 percent monitoring allowance 

would not be adequate when periods of S/S are included. Hourly production and 12-hour

TRS data for this unit were plotted in Figure 1 of the comment.

Commenter 0058 noted that EPA’s data analysis also included some examples of recovery 

furnaces reported to be meeting the proposed 20 percent opacity limit and 2 percent monitoring 

allowance on an annual basis, but unable to meet the requirements on a quarterly basis. Table 2 

of the comment compared the quarterly and annual evaluation of exceedances for an NSPS 

NDCE-DBESP recovery furnace, reported to have an annual average opacity of 13.07 percent

excluding exceedances.53 While the recovery furnace achieved the 2 percent allowance on an 

annual basis (at 1.33 percent), it did not achieve it for the 1st quarter of the year, with 2.24 

percent of the averaging periods for the quarter exceeding 20 percent opacity. Table 3 of the 

comment provided the same comparison for another NSPS NDCE-DBESP recovery furnace 

reported to have an annual average opacity of 5.71 percent excluding exceedances.54 Similar to 

the other recovery furnace, this furnace met the 2 percent allowance on an annual basis (at 1.31 

percent), but did not achieve it for the 3rd quarter, with opacity greater than 20 percent for 2.28 

percent of the averaging periods for that quarter.

Commenter 0058 further noted that EPA, in its review of COMS data from recovery furnaces, 

ascertained that only 12 out of 160 recovery furnaces were unable to meet these limits and 

thereby concluded that compliance at these levels was adequately demonstrated. However, the 

commenter pointed out that EPA’s assessment of performance used annual performance data (as 

opposed to quarterly or semiannual). The commenter also noted that 7 out of the 12 furnaces that 

were unable to meet the limits were subject to NSPS, indicating that achievability is an issue for 

NSPS units. The commenter recommended that EPA carry out a thorough review of NSPS unit 

performance using the same averaging time as proposed in the standard, in order to support the 

“adequately demonstrated” conclusion.

 

53 Id., Table 2.

54 Id., Table 3.
35

Commenter 0059 supported the conclusions of commenter 0058, stating that the EPA’s approach 

in analyzing COMS and CEMS data does not adequately support the proposed changes in 

monitoring allowances. The commenter asserted that it is inappropriate to assess the ability of 

NSPS units to comply with a proposed quarterly percent exceedance requirement using annual

exceedance data. Given that percent exceedance is a function of the total number of exceedances 

in the applicable “period,” the commenter argued that the use of a longer analysis period has the 

potential to overstate the unit’s performance and yield erroneous conclusions on the ability of 

furnaces and lime kilns to meet the allowances on a quarterly basis.

Response: The EPA is finalizing a semiannual period for the monitoring allowance calculation

consistent with the semiannual reporting frequency in §60.288a(a). In an updated analysis of the 

TRS CEMS and COMS data, the EPA repeated monitoring allowance calculations based on a 

semiannual reporting period instead of the annual basis used for the proposal. Details of this 

analysis can be found in the memorandum titled, Updated Review of the CEMS and COMS Data 

from the Pulp and Paper ICR Responses for NSPS Sources, found in Docket ID No. EPA-HQOAR-2012-0640. We address commenter 0058’s specific examples below.

In the first example provided by commenter 0058, an NDCE-WBESP recovery furnace 

(226.RECB2) indicated by EPA prior to proposal to have a 99th percentile TRS concentration of 

2.55 ppm and 5 exceedances for the year was reassessed by the commenter on a semiannual

basis. The commenter found that 4 of the 5 exceedances occurred in the 2nd reporting period,

which would exceed the 1 percent allowance for that period. In EPA’s updated assessment, data 

for 111 reporting periods included in the pre-proposal assessment were removed due to “process 

down” or “0 production” periods. The new assessment showed zero exceedances in the first 

semiannual reporting period and one exceedance in the second reporting period, resulting in a 

monitoring allowance usage of 0.3 percent (1 exceedance/331 reporting periods). This unit 

would be in compliance with the 5 ppm TRS limit and 1 percent monitoring allowance for both 

semiannual reporting periods based on the 2009 data analyzed.

In the second example provided by commenter 0058, an NDCE-DBESP recovery furnace 

(180.D001) analyzed by EPA prior to proposal to have a 99th percentile TRS concentration of 

4.44 ppm and 6 exceedances for the year was reassessed by the commenter and found to have

exceedances occurring in the 3rd quarter, resulting in the need for a 3.3 percent monitoring 

allowance. In EPA’s updated assessment based on semiannual reporting, there were zero 

exceedances in the first semiannual reporting period and six in the second, resulting in an 

exceedance of 1.6 percent (6 exceedances/365 reporting periods). This unit would not be in 

compliance with the 5 ppm TRS limit and 1 percent monitoring allowance for both semiannual

reporting periods of the year. 

Table 2 of comment 0058 shows the commenter’s reanalysis of an NDCE-DBESP recovery 

furnace (174.G-32) that EPA analyzed prior to proposal and found met a 20 percent opacity limit 

with a 2 percent monitoring allowance. The commenter’s assessment shows that the unit would 

not meet the standard if assessed on a quarterly basis. The EPA’s updated assessment, based on 

semiannual reporting periods, shows that the unit exceeded 20 percent opacity in 2.13 percent of 

valid readings in the first semiannual reporting period (847/39,771) and by 0.59 percent in the 
36

second period (254/43,165). This unit could be out of compliance with the 20 percent opacity 

limit and 2 percent monitoring allowance for the first reporting period of the year if the 

enforcement authority does not round the 2.13 percent allowance down to 2 percent.

Table 3 of comment 0058 shows the commenter’s reanalysis of an NDCE-DBESP recovery 

furnace (195.003) that EPA proposed could meet a 20 percent opacity limit with a 2 percent 

monitoring allowance. The commenter’s assessment shows that the unit would not meet the 

standard if assessed on a quarterly basis. The EPA’s updated assessment based on semiannual

reporting and with the removal of data associated with periods of no production shows that the 

unit exceeded 20 percent opacity for 0.63 percent of readings in the first reporting period 

(173/27348) and 1.54 percent of readings in the second reporting period (665/43297). This unit 

would be in compliance with the proposed 20 percent opacity limit and 2 percent monitoring 

allowance calculated on a semiannual basis.

Tables 3A through 3D below summarize the number of CEMS and COMS data sets analyzed for 

new, modified (or reconstructed), and existing recovery furnaces and lime kilns. The number of 

data sets in compliance with the proposed standards and monitoring allowances before proposal 

and in the final data sets is indicated. The values presented from the proposal analysis represent 

calculation of the monitoring allowances on an annual basis, while the values from the final 

analysis reflect the revised data sets and calculation of monitoring allowances on a semiannual 

basis. Use of a semiannual basis for calculating the allowances resulted in only minor differences 

in the number of emission units that would not be in compliance with the proposed standards and 

monitoring allowances. The semiannual allowance calculation would change the compliance 

outcome for:

 3 out of 160 recovery furnace COMS data sets,

 0 out of 29 lime kiln COMS data sets,

 2 out of 141 recovery furnace TRS data sets, and

 2 out of 110 lime kiln TRS data sets.

As shown in Tables 3A through 3D below, EPA’s revised analysis accounts for the reason a unit 

became subject to the NSPS (e.g., new or modified [including reconstructed]). The majority of 

data sets for new and modified recovery furnaces and lime kilns demonstrate compliance with 

the proposed standards. For opacity, the majority of the data sets for existing (non-NSPS) 

recovery furnaces and lime kilns also showed compliance with the proposed 20 percent opacity 

limit and monitoring allowance. A number of existing (non-NSPS) data sets also showed 

compliance with the proposed TRS limits and allowances. Therefore, EPA maintains that the 

proposed standards are adequately demonstrated based on the final revised data sets with the 

proposed monitoring allowances calculated on a semiannual basis. Considering the large number 

of data sets analyzed for this NSPS review (including most of the emission units in the U.S.) and 

the preponderance of emission units meeting the proposed standards, we do not believe it is 

necessary for every single data set and emission unit analyzed to have shown compliance with 

the standards and monitoring allowances proposed for subpart BBa in order for EPA to conclude 

that the proposed standards are adequately demonstrated and achievable. Subpart BBa is not 

immediately applicable to the emission units analyzed, but will become applicable to emission 

units as they are newly installed, modified, or reconstructed in the future.
37

Figures 4 through 7 depict the semiannual monitoring allowance calculations for lime kilns or 

recovery furnaces. The monitoring allowance represents the percent of CEMS or COMS 

averaging periods exceeding the applicable emission limit for each emission unit. Figure 4 

shows that the 2 percent monitoring allowance (calculated on a semiannual basis) for recovery 

furnace opacity is achieved by the majority of recovery furnaces in the U.S. Figure 5 shows that 

a 1 percent opacity monitoring allowance (calculated on a semiannual basis) is achieved by most 

lime kilns with ESPs in the U.S. Figures 6 and 7 show that the majority of recovery furnaces and 

lime kilns subject to subpart BB achieved a 1 percent TRS monitoring allowance on a 

semiannual basis. TRS data for existing non-NSPS (subpart BB) sources are omitted from

Figures 6 and 7 because existing non-NSPS sources are subject to TRS limits less stringent than 

the current NSPS limits

.
38

Table 3A. Summary of Recovery Furnace COMS Data Sets Analyzed

Unit NSPS 

Classification1

Proposal data set with 

monitoring allowance 

calculated on an annual 

basis

Final data set with 

monitoring allowance 

calculated on an 

semiannual basis Notes

No. of COMS data sets 160

 New 52

 Modified 32

 Existing (not subject to NSPS) 76

No. of COMS meeting 20% opacity 

with a 2% allowance

144 141

 New 45 44

 Modified 30 30

 Existing (not subject to NSPS) 69 67

No. of COMS not meeting 20% 

opacity with a 2% allowance

16 19

 New 7 8 Installation dates ranged from 1978 to 1991. 

The semiannual percentage of periods 

exceeding 20% opacity ranged from 0.59 to 

8.05%. Four of the 8 units in the final data set 

achieved a 4% allowance on a semiannual 

basis.2

 Modified 2 2 Two stacks having separate COMS on a 

furnace that became subject to the NSPS in 

1990. The semiannual percentage of periods 

exceeding 20% opacity ranged from 1.26 to 

7.72%. Neither of these COMS achieved a 

4% allowance. 2

 Existing (not subject to NSPS) 7 9 5 of the 9 units in the final data set achieved a 

4% allowance on a semiannual basis. 2 The 

semiannual percentage of periods exceeding 

20% opacity ranged from 0.39 to 35.2%.

1. New and modified units are defined in terms of the subpart BB NSPS 1976 applicability date (not the more recent subpart MM applicability 

date).

2. See response to comment 3.2-01 for more discussion of the commenter-requested 4% monitoring allowance.
39

Table 3B. Summary of Lime Kiln COMS Data Sets Analyzed

Unit NSPS 

Classification1

Proposal data set with 

monitoring allowance 

calculated on an annual 

basis

Final data set with 

monitoring allowance 

calculated on an 

semiannual basis Notes

No. of COMS data sets 29

 New 23

 Modified 2

 Existing (not subject to NSPS) 4

No. of COMS meeting 20% opacity 

with a 1% allowance

27 27

 New 21 21

 Modified 2 2

 Existing (not subject to NSPS) 4 4

No. of COMS not meeting 20% 

opacity with a 1% allowance

2 2

 New 2 2 Exceedances of the 1% allowance were 

1.84% and 2.19% on a semiannual basis. 

These ESP-controlled kilns became subject to 

the NSPS in 1997 and 1994, respectively 

(prior to establishment of the subpart MM 

opacity monitoring requirements).

 Modified 0 0

 Existing (not subject to NSPS) 0 0

1. New and modified units are defined in terms of the subpart BB NSPS 1976 applicability date (not the more recent subpart MM applicability 

date).
40

Table 3C. Summary of Recovery Furnace TRS CEMS Data Sets Analyzed

Unit NSPS 

Classification1

Proposal data set with 

monitoring allowance 

calculated on an annual 

basis

Final data set with 

monitoring allowance 

calculated on an 

semiannual basis Notes

No. of TRS CEMS data sets 141

 New 51

 Modified 28

 Existing (not subject to NSPS) 62

No. of CEMS meeting 5 ppm with a 

1% allowance

95 93

 New 45 45

 Modified 26 26

 Existing (not subject to NSPS) 24 22

No. of CEMS not meeting 5 ppm 

with a 1% allowance

46 48

 New 6 6 Installation dates range from 1977 to 1992.

 Modified 2 2 Modified in 1989 and 1990.

 Existing (not subject to NSPS) 38 40 Includes 33 DCE recovery furnace CEMS. 

The TRS emission guideline for existing 

DCE recovery furnaces is 20 ppm.

4 of these existing units were DCE furnaces 

in the final data set that have since been 

replaced with or converted to NDCE 

technology (in 2011-2012 after the data were 

collected).

1. New and modified units are defined in terms of the subpart BB NSPS 1976 applicability date (not the more recent subpart MM applicability 

date).
41

Table 3D. Summary of Lime Kiln TRS CEMS Data Sets Analyzed

Unit NSPS 

Classification1

Proposal data set with 

monitoring allowance 

calculated on an 

annual basis

Final data set with 

monitoring allowance 

calculated on an 

semiannual basis Notes

No. of TRS CEMS data sets 112 110 2 data sets (for 1 new kiln and 1 existing kiln) 

were removed from the final analysis due to 

data quality issues.

 New 48 47

 Modified 11 11

 Existing (not subject to NSPS) 53 52

No. of CEMS meeting 8 ppm with a 

1% allowance

68 64

 New 45 44

 Modified 7 7

 Existing (not subject to NSPS) 16 13

No. of CEMS not meeting 8 ppm 

with a 1% allowance

44 46

 New 3 3 Installed 1997, 1989, and 1994.

 Modified 4 4 Modified in pre-1990, pre-1995, and 2007. 

Scrubber-controlled. Some of these kilns 

were up and down and had data availability 

issues throughout the year.

 Existing (not subject to NSPS) 37 39 The TRS emission guideline for existing lime 

kilns is 20 ppm.

1. New and modified units are defined in terms of the subpart BB NSPS 1976 applicability date (not the more recent subpart MM applicability 

date).
42

Figure 4. Opacity Monitoring Allowance Data for Recovery Furnaces 
43

Figure 5. Opacity Monitoring Allowance Data for Lime Kilns 
44

Figure 6. TRS Monitoring Allowance Data for Recovery Furnaces Subject to the Subpart BB NSPS Limit (5 ppm)
45

Figure 7. TRS Monitoring Allowance Data for Lime Kilns Subject to the Subpart BB NSPS Limit (8 ppm)
46

3.2 Opacity Limits

3.2-01 Comment: Commenter 0056 does not support EPA’s decision to propose making the 

opacity limit more stringent for modified recovery furnace units under the NSPS. The 

commenter noted that EPA proposes to reset the current 35 percent opacity limit to a 20 percent

limit,55 which, except for reducing the allowances percentage, is equivalent to that for new and

reconstructed units under the subpart MM NESHAP. The commenter argued that, as the EPA 

found no reason to reduce PM for modified recovery furnaces, it is not logical to reduce the 

opacity limit to the level for new and reconstructed units under the NESHAP either. The 

commenter noted that opacity is a continuous compliance monitoring demonstration for the PM 

limit,

56 long recognized as an approximate PM surrogate. The commenter believes the EPA may 

have reached these opposite decisions on related parameters as a consequence of conducting the 

opacity COMs analyses of the ICR data separately from the PM analyses and in part, as a 

consequence of the potential errors in the opacity analyses identified in previous comments.

Commenter 0058 stated that EPA’s analysis of COMS data does not sufficiently support the 

decision to propose lowering the opacity limit and monitoring allowance for modified recovery 

furnaces. According to the commenter, EPA’s COMS data analysis does not (a) distinguish 

between new/reconstructed and modified furnaces and (b) assess the performance of modified 

recovery furnaces using the proposed quarterly or semiannual period. Therefore, it is unclear to 

the commenter whether compliance with the proposed 20 percent opacity limit, at the 2 percent

monitoring allowance level, is adequately demonstrated for modified NSPS recovery furnaces.

Commenter 0059 made similar conclusions and stated that, given uncertainties in the data 

analysis, EPA should reconsider the proposal to lower the opacity monitoring allowance to 2

percent and instead consider a higher allowance of 4 percent, calculated on a semiannual basis, 

to account for the differences between furnaces and be consistent with the reporting requirements

under subpart BB and proposed for subpart BBa.

57

Commenter 0055 supports EPA’s decision to propose an opacity limit of 20 percent for new, 

modified and reconstructed units subject to subpart BBa. The commenter believes that the 20

percent opacity requirement should be achievable for modified sources. According to the 

commenter, this opacity standard has been an existing requirement in their state for over 30 years 

(25 PA Code §123.41) and has been achieved by the owners and operators of the affected 

facilities.58 The commenter also cited this standard as support for EPA’s decision to establish a 

20 percent opacity requirement on lime kilns where an ESP control device is used. The 

commenter believes that the 20 percent opacity limit proposed is practicable and achievable for 

lime kilns and noted that their opinion is supported by the EPA’s own data.

Response: Our responses to the commenters’ concerns in the context of recovery furnaces and 

lime kilns are provided below.

 

55 See proposed §60.284a(d)(1)(ii).

56 See 78 FR 31323.

57 See §60.288a(a).

58 25 PA Code §123.41: “A person may not permit the emission into the outdoor atmosphere of visible air 

contaminants in such a manner that the opacity of the emission is either of the following: (1) Equal to or greater than 

20 percent for a period or periods aggregating more than 3 minutes in any 1 hour. (2) Equal to or greater than 60 

percent at any time.”
47

Recovery furnaces. The subpart MM NESHAP specifies a 20 percent opacity limit for new and 

reconstructed recovery furnaces and a 20 percent opacity corrective action threshold for existing 

recovery furnaces (which includes existing recovery furnaces that are modified under NSPS 

definitions). In addition to the precedent for a 20 percent opacity limit under subpart MM, the 

EPA reviewed state permits and found many recovery furnaces with state permit limits of 

20 percent opacity.59 As an example, commenter 0055 noted that a 20 percent opacity limit for 

recovery furnaces has been the Pennsylvania state requirement for over 30 years.

The opacity limit under subpart BBa is part of the emission standards set forth in §60.282a. 

Therefore, it was reviewed independently from the PM limit. Table 3A above summarizes the 

COMS data reviewed for recovery furnaces. Most of the recovery furnaces in the U.S. were 

included in this analysis. Of the COMS data sets analyzed, 141 of 160 total data sets achieved 

the 20 percent opacity limit with a 2 percent monitoring allowance proposed for subpart BBa. In 

response to comments on the proposal, EPA broke the recovery furnace COMS data into new, 

modified, and existing sources based on the reason each recovery furnace became subject to the 

NSPS following the 1976 applicability date (e.g., new units installed after 1976, modifications 

occurring after 1976). While a few recovery furnaces that became subject to the NSPS when they 

were installed new or were modified did not achieve the limit proposed for subpart BBa, we note 

that these units all became subject to the NSPS over 20 years ago. Recovery furnaces that have 

come online as new units or been upgraded over the past decade showed compliance with the 

proposed 20 percent opacity limit with a 2 percent monitoring allowance. The EPA is unaware of 

any technological reason that would hinder modified units from meeting this limit, especially 

considering that the majority of existing sources not subject to the NSPS already meet the 

proposed limit.

Although a 4 percent monitoring allowance (suggested by commenter 0059) would provide some 

additional flexibility, it would not resolve the issues noted for all of the new and modified NSPS 

units in Table 3A that did not meet 20 percent opacity with a 2 percent allowance. The two 

modified recovery furnaces that did not meet the 2 percent allowance also would not meet a 

4 percent allowance. We fail to see any basis for the 4 percent allowance suggested by the 

commenter. 

Our analysis of the COMS data shows that 20 percent opacity (with a 2 percent monitoring 

allowance calculated on a semiannual basis) has been achieved by most of the recovery furnaces 

in the U.S. Based on that analysis, and given the opacity levels established under subpart MM 

and permit limits, we maintain that this opacity limit has been adequately demonstrated, and we 

are finalizing this limit in subpart BBa.

Lime kilns. The EPA proposed to add an opacity standard to subpart BBa for lime kilns 

controlled by ESPs alone (i.e., without a scrubber) based on the subpart MM 20 percent opacity 

corrective action level for new and existing lime kilns and our review of 29 COMS data sets for 

27 lime kilns (including 2 kilns with separate COMS in dual stacks), showing that 20 percent 

opacity with a 1 percent monitoring allowance has been adequately demonstrated under periods 

 

59 U.S. Environmental Protection Agency. Review of the Air Permits for Kraft Pulp Mills. Memorandum to Docket 

ID No. EPA-HQ-OAR-2012-064. April 26, 2013.
48

of normal operation and during S/S. The lime kiln opacity data sets were reanalyzed and broken 

out by NSPS applicability to address public comments on the proposed NSPS review. Based on 

reanalysis of the data, we maintain that 20 percent opacity and a 1 percent monitoring allowance 

has been adequately demonstrated for lime kilns. Only two ESP-controlled kilns that became 

subject to the NSPS in 1994 and 1997 as new units were unable to meet the 20 percent opacity 

limit with a 1 percent monitoring allowance. One of these kilns exceeded the 20 percent opacity 

limit during 1.84 percent of averaging periods in one semiannual period, but achieved the

allowance (at 0.27 percent) in the other semiannual period. The second kiln exceeded the 20 

percent opacity limit during 2.19 percent of averaging periods in the only semiannual period for 

which data were provided. The remaining 25 kilns (with 27 COMS), including existing and 

modified kilns, showed compliance with the proposed opacity standard and monitoring 

allowance calculated on a semiannual basis. We maintain that the 20 percent opacity limit with a 

1 percent monitoring allowance calculated on a semiannual basis is adequately demonstrated to 

be achieved in practice because the majority of ESP-controlled kilns achieved this standard.

3.3 TRS Limits

3.3-01 Comment: Commenter 0055 believes that adding an upper limit of 30 ppmdv @ 8

percent O2 to the monitoring allowance for TRS for recovery furnaces tightens emissions 

limitations without undue burden to the industry. However, the commenter believes that there is 

an inconsistency in how the upper limit of TRS for recovery furnaces is applied. For straight 

kraft recovery furnaces, which have a limit of 5 ppmdv @ 8 percent O2, the commenter noted 

that this never-to-exceed limit is 600 percent of the normal requirement. For cross recovery 

furnaces, which have a limit of 25 ppmdv @ 8 percent O2, the commenter noted that this neverto-exceed limit is only 20 percent above the normal limit. The commenter stated that it is 

inappropriate to establish limits for cross recovery furnaces because there is a lack of data. The 

commenter also added that data for straight recovery furnaces should not be used to establish 

limits for cross recovery furnaces. The commenter agreed with establishing the upper limit of 22 

ppmdv @ 10 percent O2 for TRS emissions from lime kilns.

Response: The EPA agrees with commenter 0055 that the calculated upper limit for TRS from 

recovery furnaces (30 ppm) should be specified to be for straight recovery furnaces, and the final 

rule language has been edited for clarification. This 30 ppm upper limit was based on analysis of 

data for straight recovery furnaces and also coincides with the span of the TRS monitor required 

in §60.284a(a)(2)(i) for straight recovery furnaces.

The cross recovery furnace TRS emission limit is higher than the straight recovery furnace TRS 

emission limit for three technical reasons. First, the sulfur content of the semichemical liquor is 

higher than traditional kraft liquor. Second, the heat content of the liquor is lower because it 

contains less organic material than kraft liquor due to higher pulping yields. Third, the heavier 

sulfur loading and the lower operating temperature puts a restriction on the amount of excess O2

available to oxidize the sulfur compounds. If we were to base a cross recovery furnace upper 

limit on the straight recovery furnace data, the limit would be 150 ppmdv (600 percent x 25 

ppmdv, to utilize the same ratio). This limit is unreasonable because the span of the monitors are 

required to be set at 50 ppmdv. Because we do not have continuous monitoring data for cross 

recovery furnaces to analyze (with no known cross recovery furnaces subject to NSPS at this 

time), we are setting the upper TRS limit for cross recovery furnaces at the instrument span of 50 
49

ppmdv for these units. This upper limit can be reevaluated during the next NSPS review should 

data become available for cross recovery furnaces in the future. 

3.4 Startup and Shutdown Performance Data

3.4-01 Comment: Commenter 0058 stated that the EPA needs to consider performance data 

under S/S conditions before proposing more stringent monitoring allowances that include S/S

periods. According to the commenter, their targeted review of ICR data has identified instances

where S/S data were either excluded from data submittals or inappropriately labeled/included, 

which has the potential to influence EPA’s conclusions on the ability of NSPS units to comply 

with the proposed monitoring allowances, when also including S/S periods. The commenter 

noted that EPA indicated in its CEMS review that 29 NSPS lime kilns were achieving the 

proposed 1 percent monitoring allowance on an annual basis. The commenter stated that (1) 13 

of the 29 lime kilns did not include any S/S data; (2) a mixture of blank cells and values were 

included for 4 kilns during periods of S/S; and (3) 2 additional mills included comments that they 

are required to maintain records of startup, shutdown and/or malfunction only when an emission 

standard is exceeded. In cases where shutdown data were included and identified in a data set, 

they were sometimes reported as ‘zero’ and corresponded to periods of ‘zero’ production, 

artificially overstating unit performance, and potentially impacting the results and conclusions.

The commenter also stated that it is inappropriate to include periods when only oil (or other 

fossil fuel) is fired during periods of S/S in the analyses because excess emissions are defined as 

periods when BLS are fired (for recovery furnaces). The commenter stated that they were not 

able to substantially comment on S/S due to insufficient time to fully evaluate the extensive data.

In a similar comment, commenter 0056 stated that EPA may have inadvertently misconstrued 

portions of the ICR data used in the proposed rulemaking, raising concerns that EPA used 

impaired analyses to reach certain conclusions that may in reality be unsupported. As an 

example, the commenter cited the proposal to eliminate the monitoring exemptions for excess 

emissions during SSM periods and instead require the normal operating emission standards to be 

met at all times. The commenter cited reports finding that the EPA based some facility 

demonstrations of achievability on emissions performance measured on an annual basis by 

evaluating the annual percentage of the excess emissions allowances, but when the actual 

regulated quarterly performance was examined, the allowance would not have been adequate and 

the facility would have had un-allowed excess emissions subject to enforcement. The commenter 

also noted another example reporting the apparent misidentification of S/S data, or the lack 

thereof, in a large fraction of the 29 units that EPA analyzed in its analysis of lime kiln TRS 

CEMS data; the commenter said that this analysis led EPA to a probably erroneous conclusion 

that kilns could meet the emission standard given a 1 percent monitoring allowance even while 

including S/S periods.

In another comment, commenter 0059 stated that the 2011 ICR did not include data during S/S in 

all cases. Therefore, the commenter concluded that EPA may not have adequately considered all 

operating scenarios and data associated with S/S conditions in its analysis. Consequently, the 

underlying conclusions about performance during S/S conclusions are also potentially in error.

Commenter 0059 referred specifically to the focused review of NSPS data by commenter 0058, 
50

which the commenter said identified instances where facilities either excluded60 or mislabeled 

data collected during S/S periods. According to commenter 0059, this exclusion of relevant data 

could extend to a larger subset of evaluated sources, is a cause for concern, and has the potential 

to lead to wrong conclusions about S/S periods. The commenter also noted that there also is the 

potential for overstatement of unit performance as a result of the use of annual data in assessing

compliance with a proposed quarterly allowance. The commenter indicated that the potential 

exclusion of S/S data from ICR data sets may further impact the “adequately demonstrated” 

conclusion associated with the monitoring allowances.

Response: The EPA analyzed the data available to the Agency collected through ICR responses. 

The ICR requested that S/S periods be included and labeled in the CEMS and COMS data sets. 

The EPA used the data that it received to assess each unit’s performance for all operating 

periods, which would have included S/S periods that were not labeled as such. Approximately 75 

percent of COMS data sets and 60 percent of TRS data sets EPA analyzed contained S/S periods 

that were clearly labeled. Based on this review, EPA proposed to add a 1 percent monitoring 

allowance for lime kiln TRS to account for process variability (including S/S) in light of removal 

of the SSM exemption. Previously, there was no monitoring allowance for lime kiln TRS.

EPA reviewed the continuous monitoring data again following proposal and has addressed 

commenters’ concerns by removing all values associated with zero BLS or lime mud throughput

and negative values. The EPA has also reanalyzed the data using a semiannual basis for 

calculation of the monitoring allowance, consistent with the final rule. Following reanalysis of 

the continuous monitoring data, EPA maintains that the proposed monitoring allowances have 

been adequately demonstrated. The commenter has not provided any specific information to the 

contrary.

 

60 In many cases, state reporting requirements require facilities to exclude S/S data from periodic reports.
51

4. Startup, Shutdown, and Malfunction

4.1 Periods of Startup and Shutdown

4.1-01 Comment: Commenter 0057 supported EPA’s decision to review the NSPS for kraft pulp 

mills and apply the standards continuously, including during times of SSM, which the 

commenter said was undoubtedly correct and well supported.

Response: We acknowledge the commenter’s agreement with our proposal to apply the 

standards continuously and have decided to finalize a continuous standard, including during 

times of SSM.

4.1-02 Comment: Regarding the elimination of exemptions from excess emissions monitoring 

during SSM periods, commenter 0056 requested that the EPA re-evaluate how SSM periods will 

be treated, (a) in light of the potential data analysis errors regarding the ability of many sources 

to meet normal operating condition emission limits at all times, and (b) with respect to the EPA’s 

legal view of SSM provisions of the CAA. The commenter noted that EPA is proposing to 

eliminate the exemptions from the emission standards for S/S events as its response to the 2008 

decision by the U.S. Court of Appeals for the D.C. Circuit vacating certain aspects of the 

emission exemption under the NESHAP rules, a decision EPA says it believes “applies equally 

to section 111 rules.”

61 According to the commenter, the EPA concludes, based on its ICR data 

analyses, that “affected units will be able to comply with the proposed standards at all times” 

including the operating parameter limits during S/S periods, and consequently did not propose a 

new standard for these periods separate from the operating emission standards.

Commenter 0056 does not believe that the Sierra Club court decision requires the EPA to set 

numerical emission limits for S/S periods. As noted by the commenter, the Sierra Club

decision62 vacated the broad emission standard exemption during SSM events contained in the 

40 CFR Part 63, Subpart A, General Provisions, under CAA section 112. The commenter 

contended that EPA, in the proposed NSPS revisions, proposes to change regulations that have 

been in place for many years and change SSM provisions that were never challenged in court, 

without any justification of its authority to do so and without adequate factual analysis of the 

statutory criteria for standard-setting. The commenter also contended that the court did not say 

that the same emission limitations that the EPA has derived for normal operations must also 

apply during SSM events, and, therefore, it did not preclude the EPA from applying different 

standards during SSM events than standards that apply during normal operations. According to 

the commenter, applying the same emission standards during SSM periods is not compelled by 

the statute or applicable case law, and the commenter said EPA has several options for setting 

NSPS for such periods, including establishing a design, equipment, work practice, or operational 

standard under CAA section 111(h). The commenter also pointed out that, even under the 

NESHAP regulations promulgated after the Sierra Club decision, such as for the Boiler MACT, 

EPA has established work practices for S/S periods rather than applying the same emission limits 

that are in effect during normal operating periods or even setting separate numerical emission 

limits.63

 

61 See 78 FR 31317.

62 Sierra Club v. EPA, 551F.3d 1019 (D.C. Cir. 2008), cert. denied, 130 S. Ct. 1735 (2010).

63 See 40 CFR 63.11201(d).
52

In a related comment, commenter 0061 believes that the approach the EPA took in its review of 

the kraft pulp mill NSPS fails to account adequately for emissions that occur during SSM 

periods. Commenter 0061’s comments on this issue are also supported by commenter 0056 and 

adopted by reference. According to commenter 0061, the EPA based its actions on insufficiently 

supported assumptions about SSM events and emissions during SSM periods. The commenter 

asserted that the EPA has for decades recognized, in technology-based standards under the CAA

and other statutes, that in many cases it is not feasible, using the identified technology, to achieve 

the same emission limitations established for normal operations during SSM periods. According 

to the commenter, the EPA has not justified departing from that practice in the proposed rule, nor 

has the EPA demonstrated that the amended standards it is proposing reflect the performance 

actually demonstrated by best-performing existing sources. The commenter argued that applying 

the same emission standards during SSM periods is not compelled by the statute or applicable 

case law and that EPA has several options for setting NSPS for such periods, including 

establishing a design, equipment, work practice, or operational standard under CAA section 

111(h).

Another commenter (0059) noted that nothing fundamental has changed as it relates to the 

technologies available to control TRS emissions at kraft pulp mills or the ability of those 

technologies to mitigate or eliminate the unavoidable excess emissions during some operational

periods. Absent such new or improved technologies, the commenter said there is no basis for 

EPA to revise the standards to indicate that they apply at all times.

Commenter 0059 also stated that the proposed rule contains a number of changes that affect 

mills’ compliance obligations during periods of SSM. For the most part, the commenter said 

those changes are not the result of EPA’s assessment of developments concerning demonstrated 

control technology for kraft pulp mills, but rather an expression of EPA policy preferences that 

are at odds with 40 years of EPA interpretation and application of CAA section 111. Commenter 

0059 stated that they are familiar with and support comments being filed on this proposed rule by 

commenter 0061, which they incorporated by reference. Commenter 0059 also noted that they 

provided extensive comments during the MACT Subpart S RTR related to the necessity of 

having provisions that address startup, shutdown, and safety-related venting for pulp mill sources 

that they have included in attachments to their comments.

Response: The General Provisions in 40 CFR part 60 provide that emissions in excess of the 

level of the applicable emission limit during periods of SSM shall not be considered a violation 

of the applicable emission limit unless otherwise specified in the applicable standard. See 40 

CFR 60.8(c). The General Provisions, however, may be superseded by language in individual 

subparts as we are doing in subpart BBa. The EPA proposed standards in subpart BBa that apply 

at all times (as specified in the proposed §§60.282a(b) and 60.283a(b)) based on EPA’s view that 

the reasoning of the Sierra Club decision calls into question the legality of source categoryspecific SSM exemptions in rules promulgated pursuant to section 111. That reasoning guided 

our review of continuous monitoring data and parametric methods for demonstrating continuous 

compliance with the emission standards. For the final rule the EPA is superseding §60.8(c) with 

revised language in §60.285a(a) of subpart BBa. The EPA also revised the proposed wording of 

§§60.282a(b) and 60.283a(b) to further clarify that the standards in subpart BBa apply at all 
53

times as specified in the monitoring and testing sections of the rule. In the paragraphs below, we 

describe the analyses and considerations that support applying the standard at all times. 

Prior to proposal EPA reviewed numerous COMS and TRS CEMS data sets that included

periods of SSM, and concluded the affected units would be able to comply with the proposed 

standards at all times. The proposed rule specified excess emissions monitoring allowances 

based on review of the COMS and CEMS data. In light of public comments questioning certain 

aspects of our analysis, we have reanalyzed the COMS and TRS CEMS data following proposal 

(as described in Section 3). The reanalysis supports our original conclusions in the proposal 

regarding the ability of sources to meet the proposed standard during both normal operations and 

periods of S/S.64 The COMS and TRS CEMS data analyzed included COMS and TRS CEMS 

data for most of the recovery furnaces in the U.S., TRS CEMS data for most of the lime kilns in 

the U.S., and COMS data for most of the lime kilns using ESP control in the U.S. Thus, the bestperforming units were included in the analysis.

The EPA also reviewed the incinerator temperature, ESP, and wet scrubber parametric 

monitoring requirements prior to proposal.

65 The EPA proposed several provisions to help ensure 

the feasibility of parametric monitoring limits during S/S. In addition to specifying a 3-hour

block averaging time for incinerator temperature monitors, the EPA proposed to define excess 

emissions as periods below the minimum temperature of 1200°F when TRS emissions are fired 

(i.e., periods when an incinerator is not burning TRS, such as during warm-up and cool-down or 

when an alternative control device is used, would not be considered violations). To address the 

need for ESPs to warm to a specified temperature (typically above 200°F) before full power is 

applied to the transformer-rectifier set, EPA proposed to define excess emissions as ESP 

parameter measurements below the minimum requirements during times when BLS or lime mud 

is fired (as applicable) based on several responses to the ICR indicating that mills must bring 

their ESP online before introducing BLS or lime mud into the recovery furnace or lime kiln, 

respectively. The EPA also proposed language that would allow affected units to use wet 

scrubber liquid flow rate (or liquid supply pressure) to demonstrate compliance during periods of 

S/S because pressure drop is difficult to achieve during these periods. The EPA is finalizing 

these provisions substantially as proposed, and, in response to comments, is adding to the final 

rule a provision that will allow facilities to use only ESP secondary voltage to show compliance 

with the ESP parameter limits for combined ESP/scrubber systems during S/S because of the 

difficulty in achieving the secondary current or total secondary power operating limits during 

S/S. (See comment 4.1-09 for details).

The commenters question the application of the Sierra Club decision to a section 111 rule. The 

EPA does not claim that the Sierra Club case constrains its authority to prescribe unique 

standards for SSM periods or directly addresses the legality of SSM exemptions for section 111 

standards. The EPA’s view is that the reasoning of the Sierra Club decision calls into question 

 

64 U.S. Environmental Protection Agency. Updated Review of the Continuous Emission Monitoring and Continuous 

Opacity Monitoring Data from the Pulp and Paper ICR Responses for NSPS Sources. Memorandum to Docket ID 

No. EPA-HQ-OAR-2012-0640. February 28, 2014. 

65 Hanks, K. and Gooden, C., RTI International. Review of Pulp and Paper Information Collection Request (ICR) 

Responses Pertaining to Startup and Shutdown of Subpart BB Equipment. Memorandum to U.S. Environmental 

Protection Agency. March 22, 2013.
54

the legality of source category-specific SSM exemptions in rules promulgated pursuant to section 

111. The EPA has concluded that applying the subpart BBa standards at all times is both 

practical and achievable. We disagree with the commenters’ argument regarding the Sierra Club

court decision, and we have set a numerical limit applicable during S/S. We have evaluated 

whether different standards during S/S periods are justified, and in this case, we have concluded 

different standards are not warranted for subpart BBa given the monitoring allowances and 

parametric monitoring provisions provided.

We believe the monitoring allowances set here recognize that kraft pulp mills may have brief 

periods where production conditions occur leading to excess emissions above the emission limits 

set in the standard. Commenters 0056, 0058 and 0059 discussed those types of circumstances in 

their comments on this proposal and the previous subpart S NESHAP RTR proposal. For 

example, there is a 1 percent monitoring allowance for TRS emissions above the 5 ppm limit for

straight recovery furnaces and the 8 ppm limit for lime kilns. However, the CAA requires that a 

continuous standard must be in place. Consequently, for periods covered by the TRS monitoring 

allowance, we set an upper limit for periods of excess emissions of 30 ppm for straight recovery 

furnaces and 22 ppm for lime kilns. Regarding the suggestion that a separate S/S standard 

should be considered, industry commenters had previously noted that production events that lead 

to excess emissions can occur in both normal operation and during S/S. Our analysis of the ICR 

data confirmed that observation, so consequently we chose neither to restrict the application of 

this monitoring allowance to normal operation nor to set an alternative standard that applied to 

periods of S/S. The flexibility inherent in the monitoring allowance approach to setting a 

continuous standard applies at all times here. A thorough explanation of our S/S analysis is 

discussed in our responses to comments 4.1-04 and 4.1.05.

The commenters have not suggested any specific work practices for subpart BBa equipment that 

could be used in place of the numeric limits during S/S periods, nor have the commenters 

provided data to show that the standards (demonstrated through continuous opacity monitoring, 

TRS emissions monitoring, or parametric monitoring) cannot be met during those times.

Although commenter 0059 suggests that there is no basis for revising the standards so they will 

apply at all times absent new and improved technologies, we note that changes in control 

technologies are not a prerequisite for EPA to update monitoring procedures for demonstrating 

continuous compliance to square them with recent legal precedent or to reflect what review of 

monitoring data shows is achievable with current technology. Also, commenters 0056 and 0061

incorrectly suggest that EPA proposed to change previous NSPS, which included SSM 

provisions. The subpart BBa proposal did not take actions regarding any previous NSPS or 

equipment currently permitted to be in compliance with an NSPS, including subpart BB.

We acknowledge the subpart S RTR comments provided by commenter 0059 that pertain to 

startup, shutdown, and safety-related venting for pulp mill sources. Closed-vent collection 

systems are discussed further in comments 4.1-06 and 4.1-07 below.

4.1-03 Comment: Commenter 0061 argued that EPA has not justified its rejection of relief from 

numerical emission limitations that it has provided in NSPS for decades. According to the 

commenter, for the past 40 years, EPA has recognized that often it is unreasonable to require 

sources to meet technology-based emission standards, such as NSPS promulgated under CAA 
55

section 111, during SSM periods.66 The commenter noted that the existence of such an allowance 

for SSM events has been an important element of court decisions, concluding that EPA 

established reasonable NSPS for particular source categories. Despite that fact, the commenter 

stated that EPA proposes that the emission limitations in the revised NSPS for kraft pulp mills 

would be applicable at all times, even during SSM events.67

The commenter contended that there is ample precedent for EPA applying a different standard 

during SSM events. According to the commenter, prior to the CAA Amendments of 1977 (which 

defined “emission limitation” and “emission standard” to be something that “limits the quantity, 

rate, or concentration of emissions of air pollutants on a continuous basis”) and since that time, 

EPA has not required sources to meet NSPS emission limitations under CAA section 111 

established for normal operations, during SSM events.68 The commenter argued that there is 

nothing in the legislative history of the 1977 amendments to the CAA that suggests Congress 

intended to overturn that practice.69 Moreover, the commenter stated that court decisions both 

before and after the CAA Amendments of 1977, some of which the commenter cited below, have 

affirmed the appropriateness of including special SSM provisions in standards issued under 

section 111. 

According to the commenter, an emission limitation that applies during SSM events does not 

meet the requirement of CAA section 111(a) that EPA establish “standards of performance”

under that section that are “achievable” with the “best” emission control technology, “taking into 

consideration the cost of achieving such emission reduction, and any nonair quality health and 

environmental impact and energy requirements” that has been “adequately demonstrated,” if in 

fact EPA has not demonstrated that the limitation is reasonably “achievable” with available 

technology during S/S or malfunction events.

 

66 See 40 CFR 60.8(c).

67 See, e.g., 78 FR 31317, 31322 & 31328; proposed §§60.282a(b) and 60.283a(b).

68 See 40 CFR 60.8(c).

69 Congress’s insertion of the “continuous basis” language in the definition of “emission limitation” or “emission 

standard” in CAA section 302(k) in 1977 related to a debate in Congress about whether sources should be allowed to 

use temporary or intermittent pollution control technologies, as the D.C. Circuit recognized in Sierra Club v. EPA, 

551 F.3d 1019, 1027 (D.C. Cir. 2008), cert. denied, 130 S. Ct. 1735 (2010), citing Kamp v. Hernandez, 752 F.2d 

1444, 1452 (9th Cir.1985). See also Conference Report on H.R. 6161 (the CAA Amendments of 1977), H. Rep. No. 

95-564 (August 3, 1977) at 129 (requirement to use “continuous emission controls” “clarifies that intermittent or 

alternative control measures are not permissible means of compliance”), 172; S. Rep. No. 94-717 (March 29, 1976) 

at 78 (definition of “emission limitation” being amended to clarify that “[i]ntermittent controls or dispersion 

techniques are unacceptable as a substitute for continuous control of pollutants” and contrasting intermittent 

controls, which vary based on predicted changes in pollutant dispersion due to meteorological predictions, with 

continuous controls such as flue-gas cleaning equipment); National Lime Ass’n v. EPA, 627 F.2d 416, 434 n.54 

(D.C. Cir. 1980) (“The ‘intermittent’ controls that concerned Congress were any of those which entailed temporary 

reductions in emissions when weather conditions were poor.”). When it added the language in the definition of 

“emission standard” about “continuous reduction,” Congress did not in any way address the question of what 

emission limitations may apply during SSM periods, nor take any issue with EPA’s established practice of 

exempting excess emissions during SSM events from its performance standards applicable to normal operations. In 

fact, the legislative history indicates Congress was aware that alternative emission limitations might at times be 

necessary, even though the emission limitations were established based on the capability of “continuous controls” 

like scrubbers. See, e.g., S. Rep. No. 94-717 at 78 (“It is recognized that the source controls may not be available to

achieve the full reduction required of a particular source under particular circumstances. In such case, supplementary 

programs can and should be developed. But this flexibility occurs only after imposition of the continuous emission

limitation.”).
56

Commenter 0061 asserted that this plain-language reading of the applicable statutory 

requirements is echoed by extensive case law. The commenter said that the courts have long 

recognized that a “technology based standard discards its fundamental premise when it ignores 

the limits inherent in technology.”70 As an example, the commenter cited Portland Cement Ass'n 

v. Ruckelshaus, 486 F.2d 375, 398 (D.C. Cir. 1973), a decision reviewing standards under CAA 

section 111, wherein the D.C. Circuit recognized the concern that “‘start-up’ and ‘upset’ 

conditions, due to plant or emission device malfunction, are an inescapable aspect of industrial 

life and that allowance must be made for such factors in the standards that are promulgated.”71

Similarly, in Essex Chem. Corp. v. Ruckelshaus, 486 F.2d 427, 432 (D.C. Cir. 1973), cert. 

denied, 416 U.S. 969 (1974), another section 111 case, the commenter noted that the court held 

that SSM provisions are “necessary to preserve the reasonableness of the standards as a 

whole.”72 The commenter also cited National Lime Ass’n v. EPA, 627 F.2d 416 (D.C. Cir. 1980), 

another case reviewing emission standards promulgated under CAA section 111, wherein the 

court held that the CAA requirement that NSPS be “achievable” means that the standards must 

be capable of being met “under most adverse circumstances which can reasonably be expected to 

recur....”73

Commenter 0061 noted that courts have reached a similar conclusion when considering the 

analogous CWA requirements that EPA establish technology-based effluent limitations based on 

the best available control technology. According to the commenter, in one such case, the court 

held that where EPA knew that there would be periods where a discharger, even with “exemplary 

use of” the identified best technology, would exceed the effluent limitations because of 

conditions “beyond the control of the permit holder,” EPA had violated the CWA by failing to 

provide an “upset provision” to address those periods.74,75,76

The commenter noted EPA’s assertion that it “is required to ensure that section 111 emissions

standards are continuous,” citing the definition of “emission limitation” and “emission standard” 

 

70 NRDC v. EPA, 859 F.2d 156, 208 (D.C. Cir. 1988).

71 See also Portland Cement Ass'n v. Ruckelshaus, at 399.

72 See also Essex Chem. Corp. v. Ruckelshaus, at 433.

73 See also National Lime Ass’n v. EPA, at 431n.46.

74 Marathon Oil Co. v. EPA, 564 F.2d 1253, 1273-74 (9th Cir. 1977).

75 See also, e.g., NRDC v. EPA, 859 F.2d at 207 (distinguishing between technology-based effluent limitations, 

where some provision for “upsets” is required, and water-quality-based effluent limitations, which are tied to 

achieving water quality standards rather than being based on available technology, and therefore need not include an 

upset provision).

76 The Weyerhaeuser Co. v. Costle decision, 590 F. 2d 1011 (D.C. Cir. 1978), which EPA cites in the proposed rule, 

78 FR 31329, does not support EPA’s position. In that case, the court was discussing a “technology forcing” 

standard, rather than one, like NSPS, that is to be based on what has already been demonstrated to be achievable. 

Also, the SSM events that EPA acknowledges are expected to occur at sources subject to the proposed standards are 

a far cry from the “’uncontrollable acts of third parties,’ such as strikes, sabotage, operator intoxication, or insanity” 

that the Weyerhaeuser Court was considering in the passage quoted by EPA, see id. Industry is not requesting that 

EPA establish NSPS that can be met even during those exceedingly unusual types of events, and just because there 

may be certain kinds of malfunctions that EPA could not reasonably account for in the NSPS does not mean that 

EPA is free to ignore all types of malfunctions when it establishes the standards. Just as importantly, the

Weyerhaeuser decision came long before NRDC v. EPA, 859 F.2d 156 (D.C. Cir. 1988), which, as noted above, 

affirmed the need for an upset provision to address circumstances where compliance with effluent limitations is 

impossible through no fault of the permittee, and which endorsed Marathon Oil.
57

in CAA section 302(k) and Sierra Club v. EPA, 551 F.3d at 1021.77 The commenter remarked 

that this statement fails entirely to justify EPA’s abandonment of its longstanding provisions 

excusing sources from complying with numerical emission limitations (but imposing operational 

requirements) during SSM periods.78

Commenter 0061 noted that EPA’s argument with respect to the definition of “emission 

limitation” and “emission standard” in CAA section 302(k) seems to be that the statement in the

definition that an emission limitation is “a requirement...which limits the quantity, rate, or 

concentration of emissions of air pollutants on a continuous basis...” means that the same 

limitation must apply at all times; in other words, that by describing emission limitations as 

applying “on a continuous basis,” Congress intended to require that processes and associated 

pollution control equipment operate perfectly at all times and without variation. The commenter 

argued that there is no basis for that position, and contended that there are many indications that 

EPA’s (new) position about the effect of the definition of “emission limitation” is wrong.

The commenter pointed out that, on its face, a “requirement” that limits emissions “on a 

continuous basis” does not have to impose the same limitation at all times, nor does the form of 

the limitation have to always be the same.

79 According to the commenter, a set of regulations that 

imposes numerical limitations on the mass or concentration of pollutants emitted during normal

operations, but that also includes conditions during which those numerical limitations do not 

apply, still represents a continuously applicable requirement. The commenter stated that the 

NSPS regulations spell out the circumstances under which a kraft pulp mill affected facility

would be allowed to deviate from the numerical emission limitations that apply during normal 

operations, and they impose requirements for the operation of the facility during SSM events and 

for reporting of those events.80 The commenter remarked that it is simply inaccurate to describe 

these regulations as not providing for control of emissions on a continuous basis.

According to the commenter, EPA’s attempt to give overarching significance to the phrase “on a 

continuous basis” is also undercut by the language of CAA section 302(k). The commenter 

pointed out that section 302(k) defines “emission limitation” and “emission standard” to be not 

solely a numerical limit on the quantity, rate, or concentration of emissions of an air pollutant on 

a continuous basis, but rather “a requirement... which limits” the quantity, rate, or concentration

of emissions of air pollutants on a continuous basis. The commenter stated that the statute does

not say that requirement must be expressed as a single, numerical, not-to-be-exceeded-at-alltimes limitation. The commenter also noted that the remainder of CAA section 302(k) provides 

alternatives to a specific limitation on the quantity, rate, or concentration of emissions: “any 

requirement relating to the operation or maintenance of a source to assure continuous emission 

 

77 See 78 FR 31329.

78 See 40 CFR 60.7(b)-(c), 60.8(c), 60.11.

79 The D.C. Circuit also reached that conclusion in Sierra Club v. EPA, acknowledging that section 302(k)’s 

“inclusion of [the] broad phrase” “any requirement relating to the operation or maintenance of a source to assure

continuous emission reduction” in the definition of “emission standard” suggests that EPA can establish MACT 

standards consistent with CAA section 112 “without necessarily continuously applying a single standard.” 551 F.3d 

at 1027. “Indeed, this reading is supported by the legislative history of section 302(k).” Id. See also id. at 1021 

(“accepting that ‘continuous’ for purposes of the definition of ‘emission standards’ under CAA section 302(k) does 

not mean unchanging”).

80 See 40 CFR 60.2 (definition of malfunction), 60.7(b)-(c), 60.8(c), 60.11.
58

reduction,” and “any design, equipment, work practice or operational standard promulgated 

under” the Act (hereafter, a “work practice standard”).81

The commenter claimed that, as section 302(k) is constructed, the portion of section 302(k) that 

mentions “continuous basis” does not even apply to work practice standards. But even if it did,

the commenter argued that a requirement to, for example, use, on a continuous basis, a particular 

work practice to minimize emissions in no way mandates that emissions be constant as a

consequence, nor that the work practice must avoid any level of emissions during startup, 

shutdown, or malfunction that is higher than during steady-state operations. The commenter 

stated that EPA and the courts have recognized on many occasions the fact that just because a 

particular set of processes and air pollution controls are properly designed to minimize emissions 

does not mean that those emissions will be at the same level at all times, nor does it mean that 

the properly designed equipment or work practice will operate flawlessly, free from any variation 

in emissions associated with, for example, startup, shutdown, or unavoidable malfunctions.82

According to the commenter, EPA offers no explanation how the statutory definition of 

“emission limitation” and “emission standard” could support or compel its insertion of language 

in the proposed rule that states that the limitations apply at all times (and, according to the

preamble to the proposed rule, thereby preventing reliance on the SSM provisions of the NSPS 

General Provisions), when EPA contemporaneously has promulgated categorical standards 

imposing “emission limitations” or “emission standards” under CAA section 112 that expressly 

do not apply during periods of startup, shutdown, or malfunction.

83

The bottom line, according to the commenter, is that an “emission limitation” can include a 

design, equipment, work practice, or operational standard (which would include an SSM 

provision, which specifies required actions during SSM events to qualify for an exemption for

otherwise-applicable emission limitations), and the work practice standards expressed in an SSM 

provision apply continuously, if at all. According to the commenter, the rhetorical arguments in 

the preamble to the proposed rule notwithstanding, the longstanding SSM provisions of EPA’s 

NSPS regulations (that EPA now suggests fail to comply with the CAA because they do not 

constitute “emission limitations”) in fact fall well within the statutory definition of that term.

The commenter further argued that Sierra Club v. EPA did not involve NSPS at all, but rather 

concerned an open-ended blanket exemption from applicable category-specific NESHAPs 

contained in a generic provision in the NESHAP General Provisions. According to the 

commenter, the Court concluded that this blanket exemption did not attempt to reflect the 

emission limitations achieved by the best-performing sources, as required by CAA section 

112(d), and so did not satisfy the CAA requirement that MACT standards be “section 112-

 

81 See id.

82 See, e.g., Portland Cement Ass'n v. Ruckelshaus, 486 F.2d at 399 (“‘start-up’ and ‘upset’ conditions due to plant 

or emission device malfunction, is an inescapable aspect of industrial life and...allowance must be made for such 

factors in the standards that are promulgated”); Sierra Club v. EPA, 551 F.3d at 1027.

83 See, e.g., 78 FR 7138 (Jan. 31, 2013), 40 CFR 63.7500(f) and subpart DDDDD Table 3 (numerical emission 

limitations for hazardous pollutants for Industrial Boilers do not apply during S/S; sources must follow work 

practices); 77 FR 9304 (Feb. 16, 2012), 40 CFR 63.10000(a) (numerical emission limitations for hazardous 

pollutants for Utility Boilers do not apply during S/S; sources firing natural gas are not even subject to work 

practices during those periods).
59

compliant” at all times.84 The commenter pointed out that the Court did not say anything about

standards of performance under CAA section 111 and the requirement of section 111 that those 

standards reflect the performance achieved by demonstrated control technologies. Even more

importantly, the commenter pointed out that the decision did not concern whether EPA could 

apply different emission limitations, even for HAPs, during SSM events, nor did it consider 

whether EPA could address SSM events through work practice standards, including work 

practices that result in different levels of emissions during SSM. The commenter noted that EPA 

did not argue that the NESHAP General Provisions SSM exemption that the Court struck down 

in Sierra Club was a work practice standard under CAA sections 112(h) or 302(k), and so that

issue was not before the Court,

85 but the Sierra Club panel did imply that EPA could establish 

emission standards under CAA section 112 that specify numerical emission limits during normal 

operations and a work practice standard for SSM periods, as noted above. The commenter 

pointed out that no court has struck down an SSM provision in a specific NESHAP standard, of 

which there are many.86

Response: We disagree with the commenter’s statement that “EPA has not justified its rejection 

of relief from numerical emission limitations that it has provided in NSPS for decades.” The 

EPA did not propose to take actions regarding any previous existing NSPS or equipment 

currently permitted to be in compliance with an existing NSPS, including subpart BB. Instead, 

the EPA proposed a new standard (subpart BBa) for which the Agency analyzed continuous 

monitoring data and parametric methods for demonstrating continuous compliance and 

developed rule provisions pertaining to continuous monitoring that encompass or address S/S 

periods. With such provisions, EPA concluded that outright exemption from the standards during 

S/S is unnecessary. The EPA also added affirmative defense provisions to address malfunctions 

(discussed further in Sections 4.2 and 4.3 below). We also disagree with the comment that EPA 

did not show that the emission standard was achievable with available technology during S/S. As 

discussed in the response comment 3.4-01, EPA analyzed the data collected through the ICR, 

which contained data for S/S periods. Our analysis shows that the standard is achievable at all 

times, including during periods of S/S. 

The EPA disagrees with the commenter who asserts the case law supports its assertion that an 

NSPS cannot satisfy the requirements in CAA section 111(a)(1) if that NSPS applies at all times 

(i.e. during malfunctions). For malfunctions, the EPA recognizes that even equipment that is 

properly designed and maintained can sometimes fail and that such failure can cause a violation 

of an emission standard, but does not agree with commenters that argue that the EPA’s approach 

to malfunctions is flawed. As discussed in the preamble to the final rule, the relevance of the 

cases such as Portland Cement and Essex Chemical Corp. are called into question in light of 

subsequent case law and the 1977 amendments to the CAA’s definition of “emission standard” 

requiring that such standards be continuous. In any event, even if those cases are relevant, as also 

explained in the preamble to the final rule, the EPA’s overall approach to malfunction events in 

this rule, including the promulgation of an affirmative defense, is consistent with the approach 

set forth in EPA’s 1972 proposed rules cited favorably in Portland Cement in that both the 

 

84 Sierra Club v. EPA, 551 F.3d at 1021.

85 See 551 F.3d at 1028, 1030.

86 Since the Sierra Club v. EPA decision on the NESHAP General Provisions SSM exemption, EPA has taken it 

upon itself to remove SSM provisions from existing NESHAPs as EPA revises them. No court has upheld such a 

revision to categorical NESHAPs on the merits, either.
60

EPA’s approach today and in 1972 impart a construction of "reasonableness" to the standards as 

a whole and adopts a more flexible system of regulation than can be had by a system devoid of 

"give." Portland Cement at 399. Portland Cement criticized the EPA regulations that contained 

no specific provisions to address malfunctions and the EPA‘s assertion that malfunctions would 

be dealt with by the informal exercise of discretion in the Agency’s enforcement activities. 

Those decisions did not require exemptions or less stringent standards for malfunction events as 

the commenter suggests. The EPA’s approach to malfunctions goes further than reliance on the 

informal exercise of enforcement discretion in that it includes regulatory provisions establishing 

an affirmative defense to civil penalties for exceedances of emission limits that are caused by 

malfunctions. The court in Marathon Oil Co. v. EPA, 564 F.2d 1253, 1272 (9th Cir. 1977) held 

that the EPA must formalize its approach to upsets under the Clean Water Act. The affirmative 

defense does so. See, Mont. Sulphur & Chem. Co. v. United States EPA, 2012 U.S. App. LEXIS 

1056 (5th Cir. Jan 19, 2012) (in rejecting industry argument based on Marathon Oil that reliance 

on the affirmative defense was not adequate, court stated “[h]owever, here the EPA does not rely 

on enforcement discretion alone, but specifically promulgates an affirmative defense in the FIP, 

which clearly defines the requirements to avoid penalties.”). But see, Weyerhaeuser v Costle, 

590 F.2d 1011, 1057-58 (D.C. Cir. 1978) (holding that an informal approach is adequate). In 

fact, the affirmative defense comports with the court’s suggestion in Marathon Oil that the EPA 

place the burden on the permit holder of producing the relevant data and proving that the upset 

could not have been prevented. Id.

Regarding Sierra Club, the EPA does not claim that the Sierra Club case constrains its authority 

to prescribe unique standards for SSM periods or directly addresses the legality of SSM 

exemptions for section 111 standards. The EPA’s view is that the reasoning of the Sierra Club 

decision calls into question the legality of source category-specific SSM exemptions in rules 

promulgated pursuant to section 111. Our concerns regarding the legality of SSM exemptions in 

section 111 rules prompted us to identify alternatives to an SSM exemption in the newly 

proposed subpart BBa to ensure that the standards are applied continuously (see our response to 

comment 4.1-02). The EPA disagrees with the commenter’s suggestion that the existence of an 

SSM exemption in rules implementing section 111 in 1977 when Congress enacted the 

continuous basis language in the definition of emission standard is evidence that Congress 

approved of that regulatory SSM exemption. We do not believe the legislative history and the 

other evidence cited supports that Congress was aware or approved of that exemption. 

The commenters state in several different ways that they believe that the ‘continuous standard’ 

principle allows EPA to set a different standard during S/S than applies during normal operation. 

We generally agree and, as they cite, have set different standards during S/S in rules (e.g., Boiler 

MACT [78 FR 7138] and Utility MACT [77 FR 9304]. We have evaluated whether different 

standards during S/S periods are justified for subpart BBa, and we believe different standards are 

not warranted. Here, our analysis showed that the best-performing sources could achieve a 

continuous emission limit that was applicable at all times if we set monitoring parameters that 

allowed brief excursions above the baseline limit, but set a cap on any exceedance or ensured 

that the source was continuously monitored in some way. By setting a cap on the standards 

monitored with TRS CEMS, a continuous standard remains in place during the allowance. 

Technically, the commenter is correct in stating that we did not set a separate baseline standard 

during S/S. However, we did recognize that sources with the best-performing control technology

may briefly exceed the continuously monitored baseline emission limit from time to time, 
61

including during S/S periods. Thus we accommodated those circumstances, which we 

acknowledged as having the potential to occur during S/S, with an allowance. Again, setting a 

cap on the allowance sets a standard that applies continuously. Not limiting the periods that the 

capped exceedance was available, for example to just S/S periods, we believe adds flexibility to 

the use of the capped exceedance. We also added a provision to subpart BBa that would allow 

enforcement authorities to consider an alternative compliance calculation that allows TRS 

emissions to be uncorrected for O2 during S/S periods because the O2 correction equation could 

cause an otherwise-compliant TRS measurement to exceed the applicable concentration emission 

limit when O2 levels in the stack approach ambient conditions. For opacity monitors, we 

provided an opacity monitoring allowance to address excess emissions during any times 

including S/S periods, and added an ESP parametric monitoring requirement to ensure the 

opacity standard is continuous. Furthermore, as described in response to the previous comment, 

we developed provisions for parametric monitors that would allow flexibility during S/S events 

while ensuring the standards apply continuously (e.g., monitoring one of two wet scrubber or 

ESP parameters during S/S so that transient parameters with potential to be unachievable during 

S/S are not used for enforcement during those times). We believe that the suggestion that perhaps 

EPA should have developed a separate emission limit or work practice standard for S/S periods 

for subpart BBa would have added an unnecessary layer of complexity to the standard, not 

flexibility. For example, the Boiler MACT and Utility MACT work practices necessitated 

definitions of startup and shutdown, and specification of when startup ends and “clean fuels” that 

could be burned during startup. These concepts have been the subject of many comments, and 

continue to persist as reconsideration issues. The commenters have not suggested any specific 

work practices that could be used in place of the numeric limits during S/S periods for subpart 

BBa, nor have the commenters provided data to show that the standards (demonstrated through 

continuous opacity monitoring, TRS emissions monitoring, or parametric monitoring) cannot be 

met during those times.

The commenter makes several arguments regarding the definitions of “emission limitation” and 

“emission standard” in CAA section 302(k) to essentially argue that EPA can provide for SSM 

exemptions in its NSPS by promulgating separate work practice standards that apply during SSM 

events, and those separate work practice standards for SSM events need include nothing more 

than what is currently contained in the general duty clause in 40 CFR 60.11(d). As explained 

earlier, EPA agrees that it may promulgate separate standards for S/S events that, together with 

the standards that apply during normal operations, constitute standards that apply at all times. 

EPA also agrees that those standards – either for normal operations or S/S events – may be in the 

form of numerical emissions limits or work practice standards (assuming the requirements of 

CAA section 111(h) are met). However, The EPA flatly disagrees that we can promulgate an 

NSPS that includes an exemption from those standards during SSM events. To promulgate such 

a standard would be to perpetuate another form of an SSM exemption, which means that no 

standard would apply during an SSM event. As explained above and in the preambles for both 

the proposed and final rules, EPA does not believe the Sierra Club decision allows for such an 

exemption.

87

 

87 See section 5 of the proposed rule preamble (Periods of startup, shutdown and malfunction) at 78 FR 31328-

31330, May 23, 2013, and section B (Startup, Shutdown and Malfunction) in the “Summary of Significant Changes 

Following Proposal” section of the final rule preamble.
62

As explained earlier, in the final rule we are setting standards that apply during startup and 

shutdown periods in response to the Sierra Club decision. We have explained in the preambles 

for the proposed and final rules our rationale for not setting a separate standard for S/S events for 

this source category. The commenter has not provided information to support development of 

alternative standards that would apply during S/S events or offered any evidence, information or 

other specific argument regarding why these facilities cannot meet the standard that applies 

during normal operations during its S/S events given the monitoring allowances and other 

flexible provisions included in the final rule. Therefore, EPA is promulgating the same standards 

that apply during normal operation for periods of startup and shutdown. 

4.1-04 Comment: Commenter 0061 argued that EPA must fully justify applying the same 

emission limitations during S/S as during normal operations. The commenter noted that, in the 

preamble to the proposed rule, EPA does not say that it is precluded from adopting different 

emission limitations that would apply during S/S periods.88 The commenter pointed out that EPA 

has done just that in some other recent NSPS and NESHAP rulemakings. Instead, according to 

the commenter, EPA asserts that because “periods of startup, normal operations and shutdown 

are all predictable and routine aspects of a source’s operations” and because “in developing the 

proposed standards, it reviewed numerous continuous opacity and TRS monitoring data sets that 

included periods of startup and shutdown,” EPA concludes that “the affected units will be able to 

comply with the proposed standards at all times.”89 (The commenter noted that EPA also 

proposes a provision that would allow enforcement authorities to consider an alternative 

compliance calculation that allows TRS emissions to be uncorrected for O2 during S/S periods 

because the O2 correction equation could cause an otherwise-compliant TRS measurement to 

exceed the applicable concentration emission limit when O2 levels in the stack approach ambient

conditions.90)

Commenter 0061 noted that its members do not have sufficient information to comment on

applying the emission limitations derived for normal operations at all times, including during 

SSM events. The commenter was concerned, however, that EPA does not seem to apply the 

same rigor in analyzing that question as it does when deriving the emission limitations for 

normal operations. According to the commenter, under CAA section 111, EPA must determine 

that emission limitations that are based on steady-state operation but will apply during S/S are 

”achievable” using emission reduction technology that the Administrator determines is the “best” 

and has been “adequately demonstrated.” The commenter contended that EPA cannot conclude 

that special provisions for emissions during S/S are not needed based on “mere speculation.”91

According to the commenter, it is not apparent from the preamble to the proposed rule that EPA 

has conducted a sufficient analysis to demonstrate the achievability of the proposed emission 

limits during S/S events. Although EPA stated that it reviewed numerous continuous opacity and 

TRS monitoring data sets that included periods of S/S,

92 the commenter was skeptical that EPA 

had done a sufficient analysis, because adequate emissions data for such an analysis often are not 

available for periods of S/S.

 

88 See 78 FR 31328 col. 2.

89 See id. at 31328- 31239.

90 See id. at 31328.

91 See NRDC v. EPA, 859 F.2d 156, 210 (D.C. Cir. 1988).

92 See 78 FR 31328.
63

According to the commenter, there are several reasons why adequate data often do not exist to 

allow EPA to conclude that an emission limitation established for normal operations also

represents the performance of the best demonstrated control technology during S/S:

 To the extent emissions data come from required performance tests, the applicable 

regulations generally prohibit testing during SSM conditions and require that data not be 

used for compliance purposes if obtained during a startup, shutdown, or malfunction 

event.93

 To the extent EPA evaluates emissions data collected through continuous monitoring, the 

applicable regulations often require, or allow, the source to exclude from its reporting of 

continuous monitoring any data reflecting SSM conditions.

 Also, atypical pollutant concentrations and other stack conditions that may exist during 

S/S can result in the continuous monitoring system producing unusable data because the 

pollutant concentration may be outside of the monitoring equipment’s span or the stack 

conditions may not meet monitoring system QA/QC parameters, or the data may be 

truncated on the high end because of limitations of the monitoring equipment.94

(Conversely, the commenter noted that, once an NSPS numerical emission limitation has been 

established that applies during S/S, if unusual stack conditions during a S/S event are outside the 

QA/QC parameters for a continuous monitor that is installed and calibrated to monitor normal 

operations, then the source may be in violation of the NSPS because of monitor unavailability, 

even if the emissions during S/S, if they could have been measured adequately, would not have 

caused the source to exceed the average emission limitation.)

According to the commenter, these factors would cause EPA to calculate an average emission 

limitation that understates emissions occurring during S/S. The commenter also pointed to an 

additional problem, in that it can be unclear whether a condition that leads to excess emissions

should be characterized as a S/S event or a malfunction event. According to the commenter, 

without a clear demarcation (both in EPA regulations and in practice), EPA may be analyzing 

data sets that exclude events that were treated as malfunctions but that EPA would say should be 

included in calculating average performance as S/S conditions.

While EPA said that it determined from continuous monitoring data that the proposed standards 

would be met all of the time,

95 the commenter said it is not apparent whether or how that analysis 

adjusted for the limitations in monitoring data for periods of S/S described above. According to 

the commenter, S/S events, by their very nature, can vary considerably in both duration and

effect on emission rate. The commenter stated that EPA would need to analyze monitoring data 

for an extended period of time and for numerous facilities to try to establish emission limitations 

 

93 See, for example, the General Provisions applicable to NSPS, which state that performance tests can only be 

conducted under representative conditions and which specify that: “Operations during periods of startup, shutdown, 

and malfunction shall not constitute representative conditions for the purpose of a performance test....” 40 CFR 

60.8(c).

94 Data from periods when the monitoring system is malfunctioning or being repaired is required to be excluded 

from emission averages under the NSPS General Provisions, 40 CFR 60.13(h).

95 See 78 FR 31328, col. 2.
64

that could be met during S/S (with the level of control technology provided in CAA section 111). 

The commenter further stated that expressing an emission limitation as a long-term average, 

while helping to address higher emissions during S/S, could also fail to account adequately for 

the potential wide variation in emissions during S/S events, which could be masked if EPA 

simply assumed that calculating a long-term-average emission rate from existing monitoring data

would adequately address S/S.

According to the commenter, there are a number of ways in which EPA could better ensure that 

the standards applicable during S/S comply with the criteria for NSPS in CAA section 111:

 For certain types of sources and stack configurations, EPA may be able to conduct stack 

testing during S/S events to better delineate the variations in emissions occurring during 

S/S (rather than extrapolating from continuous emissions or parametric monitoring).

 In a more thorough analysis, EPA may be able to analyze continuous monitoring data 

specific to S/S events, and at more facilities.96

The commenter indicated that these data could enable EPA to set alternative emission standards 

that apply during S/S, or to conclude with greater certainty that sources with the identified 

control technology would be able to meet emission limitations established for normal operations 

during S/S periods, as well. The commenter suggested it would be appropriate for EPA to defer 

promulgating any emission limitations that apply during periods of S/S until after EPA obtains 

such data. According to the commenter, EPA also could study facilities’ operational logs to be 

sure it has chosen an averaging time for an emission standard sufficiently long that typical S/S 

periods would not cause an exceedance of the standard.

The commenter indicated that EPA also might determine, based on the infeasibility of collecting

representative data during S/S events, that it is necessary and appropriate to promulgate a design, 

equipment, work practice, or operational standard, pursuant to CAA section 111(h) and/or 

section 302(k), in lieu of deriving limitations on the mass or concentration of pollutants emitted 

during S/S. According to the commenter, as set forth in section 111(h)(2), EPA may determine 

that it is “not feasible to prescribe or enforce a standard of performance” because it is not 

feasible to capture the pollutant and emit it through a particular conveyance, or because it is not 

practicable to measure emissions “due to technological and economic limitations.” In the case of 

S/S events, the commenter said that one or both of these circumstances often will apply. 

Commenter 0061 contended that EPA cannot, consistent with CAA sections 111 and 302(k), 

simply ignore the possibility of using some type of work practice, etc. standard during SSM 

events, instead of an unachievable emission limitation based on normal operations.

According to the commenter, the preceding paragraphs demonstrate that EPA had a number of 

ways to approach NSPS for S/S conditions that would be consistent with the CAA. The 

 

96 As suggested above, emissions testing or continuous monitoring during S/S will not be an option in all cases, 

because it may not be possible to obtain accurate sampling of exhaust gases during S/S periods of certain types of 

process or pollution control equipment. Stack sampling procedures may not apply or may not produce accurate 

results during the abnormal flow and concentration conditions present during S/S periods. During some S/S events, 

gas streams may have to be diverted from the control device, and thus from the stack being monitored, altogether for 

a time. This is a particular concern where the gas streams being controlled are potentially flammable or explosive, as 

is the case at kraft pulp mills.
65

commenter argued that the approach EPA took in the proposed rule—assuming there is no 

problem based on only a limited analysis of the performance actually achieved—was not

consistent with the CAA. The commenter recommended that EPA defer establishment of any 

standards under CAA section 111 for S/S periods until the Agency either can collect and analyze 

the necessary data or determine the appropriate work practice or operational standards to 

establish “emission standards”—either the same as or less stringent than those established for 

normal operations—that apply during S/S.

Response: The EPA has used an extensive amount of information collected from pulp and paper 

ICR responses (not “mere speculation”) to justify applying the same emission limits during S/S

as during normal operations. Again, we agree with the commenter’s suggestion that EPA can set 

alternative standards during S/S. We have evaluated whether different standards during S/S

periods are justified in this case; we believe different standards are not warranted and did not 

propose them for subpart BBa. Prior to proposal, we analyzed continuous monitoring data and 

parametric methods for demonstrating continuous compliance and developed rule provisions 

pertaining to continuous monitoring that encompass or address S/S periods. These proposed 

provisions include:

 Monitoring allowances which specify a certain number of exceedances that will not be 

considered as violations, developed through review of TRS CEMS and COMS data sets 

that included SSM periods.97

 A provision for enforcement authorities to consider the uncorrected TRS concentration 

during periods of S/S if O2 levels in the stack approach ambient conditions where the O2

correction equation could cause an otherwise-compliant TRS measurement to exceed the 

applicable emission limit.

 For ESP parameter monitors, provisions that define excess emissions as ESP parameter 

measurements below the minimum requirements during times when BLS or lime mud is 

fired (as applicable).

 For wet scrubber parameter monitors, language that allows facilities to use wet scrubber 

liquid flow rate (or liquid supply pressure) to demonstrate compliance during periods of 

S/S because pressure drop is difficult to achieve during these periods.

 For temperature monitors, a lengthened 3-hour block averaging time, and provisions that 

acknowledge that the minimum temperature of 1200°F is not met during periods when an 

incinerator is not burning TRS (e.g., during incinerator warm-up and cool-down or when 

an alternative control device is used).

The EPA is finalizing these provisions substantially as proposed, and, in response to comments, 

is adding to the final rule a provision that will allow facilities to use only ESP secondary voltage 

to show compliance with the ESP parameter limits for combined ESP/scrubber systems during 

S/S because of the difficulty in achieving the secondary current or total secondary power 

operating limits during S/S. (See comment 4.1-09 for details).

With the above monitoring provisions that address periods of S/S, EPA concluded that 

alternative standards (e.g., work practices) during S/S are unnecessary. Again, we believe that 

 

97 The TRS monitoring allowances are capped with an upper TRS ppm limit and ESP parameter monitoring is 

required during the times when the opacity monitoring allowance is used, resulting in standards that are 

continuously applied and monitored at all times even during times when the allowances are invoked. 
66

the suggestion that perhaps EPA should have developed a separate emission limit or work 

practice standard for S/S periods would have added an unnecessary layer of complexity to the 

standard, not flexibility. The EPA added affirmative defense provisions to address malfunctions 

(discussed further in Sections 4.2 and 4.3 below).

The commenter questions our rigor and whether we “conducted a sufficient analysis to 

demonstrate the achievability” of the proposal. We believe we did. Two technical memos were 

provided at proposal to document our analysis of monitoring systems during S/S for pulp and 

paper processes subject to subpart BBa:

 Review of the Continuous Emission Monitoring and Continuous Opacity Monitoring 

Data from the Pulp and Paper Information Collection Request Responses Pertaining to 

Subpart BB Sources. April 5, 2013 (EPA-HQ-OAR-2012-0640-025)

 Review of Pulp and Paper Information Collection Request (ICR) Responses Pertaining to 

Startup and Shutdown of Subpart BB Equipment (March 22, 2013) (EPA-HQ-OAR2012-0640-039 thru 045)

The first memo has been updated following proposal to reflect additional analysis of the CEMS 

and COMS data. The revised memo, Updated Review of the Continuous Emission Monitoring 

and Continuous Opacity Monitoring Data from the Pulp and Paper ICR Responses for NSPS 

Sources, is available in the docket for the final rule.

The commenter appears to believe that sufficient information is unavailable on operations during 

SSM because compliance testing is precluded during those periods and sources have the option 

of excluding CEMS and COMS data collected during SSM from reports to regulatory authorities. 

However, contrary to this assertion, we collected extensive TRS CEMS and COMS data 

covering SSM periods. Actual monitoring data (not summary reports) were collected and 

analyzed prior to proposal. Our ICR specified that SSM periods be included in the data provided 

to EPA, so numerous data sets including these periods were available to EPA and analyzed for 

the proposal. Opacity and TRS emissions occurring during periods of SSM were retained in the 

continuous monitoring data averages analyzed in order to evaluate whether the updated NSPS 

should distinguish between periods of S/S and normal operation as revised emission limits were 

considered. A memorandum in the docket, Updated Review of the Continuous Emission 

Monitoring and Continuous Opacity Monitoring Data from the Pulp and Paper ICR Responses 

for NSPS Sources, documents the extensive amount of data that was received. The commenter 

suggests that EPA needs to analyze monitoring data for an extended period of time and for 

numerous facilities. The CEMS and COMS data sets EPA analyzed included an entire year of 

data for most of the pulp mill recovery furnaces and lime kilns in the U.S. We believe this data 

set was sufficient to represent the sources with the best-performing technology and to support 

our conclusion that with the proposed monitoring allowances there is no need for a separate 

standard for S/S periods.

The commenter suggests that “atypical pollutant concentrations and other stack conditions that 

may exist during S/S can result in the continuous monitoring system producing unusable data” in 

terms of monitor span, monitor QA/QC requirements, or monitoring system malfunction or 

repairs. Periods of monitor QA/QC and monitor malfunction or repairs are excluded from the 
67

data set used to determine compliance, so these periods are irrelevant.98 See §60.284a(c)(5)-(7). 

We did not find exceedances of monitoring system span during periods of S/S to be a persistent 

problem in our analysis, and, at the best-performing sources, any such exceedances would be 

accounted for with the monitoring allowance.

99 There is no upper limit on the COMS monitoring 

allowances because ESP parameter monitoring also applies, ensuring a continuous standard. We 

reviewed the highest values reported to establish the upper limits on continuously monitored 

TRS emissions. We noted a few high values that would be considered malfunctions (subject to 

the affirmative defense provisions), prior to establishing the TRS upper limit caps at the highest 

representative values observed including periods of S/S (22 ppm for lime kilns and 30 ppm for 

recovery furnaces).100

Regarding the commenters’ concern that it may be unclear whether a condition that leads to 

excess emissions should be characterized as a S/S event or a malfunction event, we note that the 

40 CFR part 60 General Provisions provides generic definitions of “startup,” “shutdown,” and 

“malfunction” to help facilities determine how to label their emissions data. The EPA has not 

included rigorous, equipment-specific definitions of these terms in subpart BBa because defining 

these terms on an equipment-specific basis adds complexity to the rule and inevitably would 

create issues where a “one-size-fits-all” definition is not a good fit for the entire population of 

subpart BBa affected emission units. Most mills are likely to have site-specific criteria that they 

use in distinguishing S/S within the framework of the General Provisions definitions. Regarding 

labeling of the data sets EPA analyzed, EPA’s analysis treated periods labeled as “S/S” as S/S 

and periods labeled as “malfunctions” as malfunctions, and EPA has no reason to believe that 

data were mislabeled. Even if data were mislabeled (or not labeled at all), it would have little 

effect on the outcome of our analysis because all SSM periods were retained in the CEMS and 

COMS data sets analyzed whether labeled or not. See also our response to comment 3.4-01.

For emission units where compliance is based on stack testing and continuous parameter 

monitoring (as opposed to continuous emissions monitoring), the EPA collected ICR responses 

to equipment-specific questions seeking information on parameter limits that may be difficult to 

meet during periods of S/S. These responses were analyzed and used to design the continuous 

parameter monitoring provisions listed above to address periods of S/S.

When stack tests are the sole means of directly measuring emissions (i.e., when continuous 

emissions monitors are not used), we recognize the commenter’s point that emissions data are 

not available for SSM periods because performance testing is not conducted during periods of 

SSM. Subpart BBa does not require stack testing during periods of SSM, and in fact, through 

incorporation of the §60.8(c) language as superseded by §60.285a(a), prevents stack testing 

during SSM.

The commenter makes three additional suggestions. First, it is suggested that EPA conduct stack 

testing during S/S rather than extrapolate from continuous emissions or parametric monitoring. 

We disagree that stack testing during S/S is necessary or appropriate because subpart BBa does 

 

98 See §60.284a(c)(5)-(7).

99 Our response to comment 5.3-03 further addresses our position with respect to use of values above the instrument 

span for compliance determination.

100 U.S. Environmental Protection Agency. Updated Review of the Continuous Emission Monitoring and Continuous 

Opacity Monitoring Data from the Pulp and Paper ICR Responses for NSPS Sources. February 28, 2014
68

not require (and in fact precludes) stack testing during S/S. Continuous compliance with subpart 

BBa (including periods of S/S) is determined based on continuous monitoring of emissions or 

parameters.

Second, it is suggested that operational logs be studied closer. We believe our analyses of the 

CEMS/COMS data and ICR responses to SSM questions related to parametric monitoring are 

sufficient in that regard. The ICR provided information on S/S times that EPA took into account 

when establishing the 12-hour block averaging times for ESP and scrubber parameters, and the 

temperature monitoring provisions. The proposal requested additional data, but none were 

received for EPA to analyze further.101

Third, it is suggested that it might be appropriate for EPA to “promulgate a design, equipment, 

work practice, or operational standard.” As mentioned above, we did not “ignore the possibility 

of using some type of work practice” as the commenter insinuates. Instead, we built flexibility 

into the monitoring provisions to accommodate S/S periods. The EPA requested information in 

the ICR on work practices that could apply during S/S, but received no useful information. The 

ICR responses did provide CEMS and COMS data and valuable information on the duration of 

S/S periods and their effects on operating parameters. This information was used in constructing 

monitoring requirements that encompass S/S periods for sources using the best-performing 

control technologies.

4.1-05 Comment: Commenter 0059 argued that EPA was not justified in reversing longstanding 

practice and current NSPS regulations by eliminating the exemption for SSM events meeting 

certain criteria. According to the commenter, EPA has recognized, for the past 40 years, that 

often it is unreasonable to require sources to meet technology-based emission standards, such as 

NSPS promulgated under CAA section 111, during SSM periods. Accordingly, the commenter 

noted, 40 CFR 60.8(c) provides that “emissions in excess of the level of the applicable emission 

limit during periods of startup, shutdown, and malfunction [shall not] be considered a violation 

of the applicable emission limit unless otherwise specified in the applicable standard.” The 

commenter pointed out that other provisions require facilities to keep records of the occurrence 

and duration of any SSM event and to report to EPA about periods of excess emissions that 

occur during SSM events (or that no excess emissions occurred).102 As noted by the commenter, 

when EPA promulgated the emission limitations currently contained in subpart BB, it was with 

the understanding that those emissions limitations would not apply during periods that qualified 

as SSM, as defined in 40 CFR 60.2.

The commenter further noted that the proposed rule includes nothing explicitly stating that the 

above-cited regulations in the General Provisions would not apply to subpart BBa. The 

commenter remarked that this apparently is what EPA intended to accomplish, however, by 

adding language, in proposed §§60.282a(b) and 60.283a(b), that stated: “The standards in this 

 

101 See 78 FR 31328. “The EPA solicits comment on whether the proposal to apply these standards at all times is 

practicable and achievable. In particular, the EPA notes that the General Provisions in part 60 require facilities to 

keep records of the occurrence and duration of any startup, shutdown or malfunction (40 CFR 60.7(b)) and either 

report to the EPA any period of excess emissions that occurs during periods of startup, shutdown or malfunction (40 

CFR 60.7(c)(2)) or report that no excess emissions occurred (40 CFR 60.7(c)(4)). In light of this requirement, 

comments that contend that sources cannot meet the proposed standard during startup and shutdown periods should 

include data and other specifics supporting this claim.”

102 See 40 CFR 60.7(b), (c)(2), (c)(4).
69

section apply at all times.”103 The commenter argued that this proposed action is not only 

unclear, but is also directly contrary to past EPA interpretations of the statute and of the 

operative facts.

Commenter 0059 noted that CAA section 111(a) requires that NSPS be “achievable” with the 

“best” emission control technology,” taking into consideration the cost of achieving such 

emission reduction, and any non-air quality health and environmental impact and energy

requirements,” that has been “adequately demonstrated.” According to the commenter, NSPS 

that will cause facilities to be in noncompliance, due to unavoidable variation in emissions 

associated with SSM, do not meet those statutory criteria. The commenter stated that the courts 

have been explicit about this. As an example, the commenter cited Portland Cement Ass'n v.

Ruckelshaus, 486 F.2d 375, 398 (D.C. Cir. 1973), a decision reviewing standards under CAA 

section 111, wherein the D.C. Circuit recognized the concern that “‘start-up’ and ‘upset’ 

conditions, due to plant or emission device malfunction, are an inescapable aspect of industrial 

life and that allowance must be made for such factors in the standards that are promulgated.”104

Similarly, in Essex Chem. Corp. v. Ruckelshaus, 486 F.2d 427, 432 (D.C. Cir. 1973), cert. 

denied, 416 U.S. 969 (1974), another section 111 case, the commenter noted that the court held 

that SSM provisions are “necessary to preserve the reasonableness of the standards as a 

whole.”105 The commenter also cited National Lime Ass’n v. EPA, 627 F.2d 416 (D.C. Cir. 

1980), another case reviewing emission standards promulgated under CAA section 111, wherein 

the court held that the CAA requirement that NSPS be “achievable” means that the standards 

must be capable of being met “under most adverse circumstances which can reasonably be 

expected to recur ....”106 The commenter was not aware of a single court decision that reached a 

different conclusion with respect to NSPS. Thus, the commenter contended that EPA’s proposal 

to simply delete long-standing provisions accommodating excess emissions during SSM events 

is directly contrary to judicial precedent.

Commenter 0059 referred to EPA’s suggestion that it is appropriate to remove the 40 CFR

60.8(c) SSM exemption from applicability to subpart BBa because the statutory definition of

“emission limitation” and “emission standard” specifies a requirement that limits air pollutant 

emissions “on a continuous basis.” The commenter indicated there are multiple problems with 

that argument:

 The qualifier that an emission limitation must apply on a continuous basis was adopted to 

preclude the use of intermittent or temporary controls (e.g., controls that operate only 

during “dirty air” periods), and nothing in the legislative history suggests that Congress 

intended to overturn existing EPA regulations that recognize the need for relief from 

otherwise-applicable emission standards during SSM events.107

 The “continuous basis” language was inserted into the definition of “emission limitation” 

in 1977, before the D.C. Circuit’s 1980 National Lime Ass’n decision affirming the need 

 

103 See 78 FR 31328-29.

104 See also id. at 399.

105 See id. at 433.

106 See id. at 431 n.46.

107 Sierra Club v. EPA, 551 F.3d 1019, 1027 (D.C. Cir. 2008), cert. denied, 130 S. Ct. 1735 (2010), citing Kamp v. 

Hernandez, 752 F.2d 1444, 1452 (9th Cir.1985). See also Conference Report on H.R. 6161 (the CAA Amendments 

of 1977), H. Rep. No. 95-564 (August 3, 1977) at 129, 172; S. Rep. No. 94-717 (March 29, 1976) at 78.
70

for NSPS to be achievable even during anticipated SSM events. It also was followed by 

30 years of EPA promulgating NSPS that incorporated the SSM exemption in 40 CFR

60.8(c) and other SSM provisions.

 The court decision EPA cited on the “continuous” issue, Sierra Club v. EPA, 551 F.3d 

1019, 1021, did not say anything about standards of performance under CAA section 111 

and the requirement of section 111 that those standards reflect the performance achieved 

by demonstrated control technologies. Rather, that decision addressed what the Court 

concluded was a requirement of section 112 that MACT standards be “section 112-

compliant” at all times.108 Moreover, the Sierra Club decision interpreted the definition 

of “emissions standard” in CAA section 302(k) not to require “unchanging” standards 

and to allow EPA to promulgate MACT standards “without necessarily continuously 

applying a single standard.”109

 The definition of “emission standard” in CAA section 302(k) does not in any way suggest 

that the requirement that standards limit emissions of air pollutants on a continuous basis 

means that the standard must be the same at all times. Moreover, section 302(k) 

specifically recognizes that this requirement can be met through “any requirement 

relating to the operation or maintenance of a source to ensure continuous emission 

reduction” or “any design, equipment, work practice or operational standard promulgated 

under” the CAA (hereafter, “work practices”). The current kraft pulp mill NSPS conform 

to this definition: Although the numerical emission limitations that apply during normal 

operations do not apply during incidents that meet the definition of SSM, pursuant to 40 

CFR 60.8(c), there are requirements related to the operation and maintenance of the 

source or work practices that do apply during SSM events.110

Commenter 0059 referred to EPA’s conclusion, which applies only to S/S, that affected facilities 

can in fact meet the emission standards during S/S. For the reasons set forth elsewhere in their 

current comment and in their previously submitted comments (included in attachments to their 

current comment), the commenter argued that this conclusion is not factually accurate, and 

indicated that, in fact, short-term venting of gas streams controlled under the NSPS will be 

unavoidable during some S/S events. According to the commenter, EPA has recognized that it 

could set alternative emission standards for S/S periods, however, if needed to make the NSPS 

consistent with the performance achieved by demonstrated control technology.111 The 

commenter argued that EPA is inaccurate in its assumption that mills can meet the numerical and

other emission limitations in the proposed subpart BBa standards at all times during S/S, and,

therefore, the commenter concluded that EPA was not justified in eliminating the 40 CFR 60.8(c) 

provision for excess emissions during S/S.

Response: As discussed in response to comment 4.1-02, 40 CFR 60.8(c) of the NSPS General 

Provisions provides that emissions in excess of the level of the applicable emission limit during 

 

108 See id.

109 551 F.3d at 1021, 1027.

110 See, e.g., 40 CFR 60.11(d) (operator “shall, to the extent practicable, maintain and operate any affected facility 

including associated air pollution control equipment in a manner consistent with good air pollution control practice 

for minimizing emissions,” at “all times, including periods of startup, shutdown, and malfunction”).

111 See 78 FR 31328; see also, e.g., 77 FR 52554, 52558 (August 29, 2012) (same conclusion with respect to NSPS 

for gas turbines); 75 FR 54970, 54991 (September 9, 2010) (establishing different standards to apply to cement 

plants during S/S).
71

periods of SSM shall not be considered a violation of the applicable emission limit unless 

otherwise specified in the applicable standard. The General Provisions, however, may be 

amended for individual subparts. The EPA is finalizing standards in subpart BBa that apply at all 

times (as specified in §§60.282a(b) and 60.283a(b)) based on EPA’s view that the reasoning of 

the Sierra Club decision calls into question the legality of source category-specific SSM 

exemptions in rules promulgated pursuant to section 111, and following review of continuous 

monitoring data and parametric methods for demonstrating continuous compliance with the 

emission standards. We evaluated whether different standards during S/S periods are justified, 

and, in this case, we concluded different standards are not warranted for subpart BBa given the 

monitoring allowances and parametric monitoring provisions provided. For periods of 

malfunction, which are addressed in Section 4.2 and 4.3 of this document, we set a standard for 

affirmative defense.112

The commenter cites several historical facts regarding the development of NSPS, including the 

subpart BB NSPS and the development of its SSM standard. First, we did not perform a sourcecategory specific evaluation to support a separate standard for periods of SSM either in the 1978 

standard or in the 1986 review of subpart BB. Consequently, there is no historical basis for the 

comparison the commenter attempts to make.

Following review of this comment and other comments related to SSM, we recognize that 

applicability of certain sections of the General Provisions should be clarified. We offer the 

following clarifications:

 The definitions of startup, shutdown, and malfunction in §60.2 apply to subpart BBa.

 The requirement to maintain records of SSM periods and periods when CMS are 

inoperative under §60.7(b) applies to subpart BBa.

 The requirements under §60.7(c)(2) to identify in the excess emissions report each period 

of excess emissions that occurs during SSM, and the nature of any malfunction apply to 

subpart BBa.

113

 Inclusion of S/S in the summary report format provided in §60.7(d) applies for subpart 

BBa.

 The §60.11(c) exemption from the opacity standards during SSM is superseded for

subpart BBa by §60.282a(c).

 The §60.11(d) requirement to use good air pollution control practices at all times 

including SSM applies to subpart BBa.

In addition, in the final rule, we have explicitly clarified the relationship between §60.8(c), the 

§§60.284a(d) and (e) excess emissions definitions and allowances, and §§60.282a(b) and 

60.283a(b) which state that the standards apply at all times. We changed §§60.282a(b) and 

60.283a(b) to state that the standards apply at all times as specified in §§60.284a and 60.285a 

(the monitoring and testing provisions). We added a statement to §60.285a(a) that §60.8(c) shall

be read as:

 

112 See 78 FR 31328.

113 Note that sections within subpart BBa in addition to §60.7(c)(2) also pertain to malfunction recordkeeping and 

reporting.
72

“Performance tests shall be conducted under such conditions as the Administrator shall 

specify to the plant operator based on representative performance of the affected facility.

The owner or operator shall make available to the Administrator such records as may be 

necessary to determine the conditions of the performance tests. Operations during periods 

of startup, shutdown, and malfunction shall not constitute representative conditions for 

the purpose of a performance test.”

The SSM exemption phrase “nor shall emissions in excess of the level of the applicable emission 

limit during periods of startup, shutdown, and malfunction be considered a violation of the 

applicable emission limit unless otherwise specified in the applicable standard” has been

eliminated from the revised wording of §60.8(c) incorporated into §60.285a(a) of subpart BBa.

Section §60.285a(a) in subpart BBa now supersedes §60.8(c).

The commenter cites several court rulings and claims that our removal of the SSM exemption is 

inconsistent with those rulings which the commenter considers to compel EPA to recognize and 

address SSM periods. We believe that we have built provisions into subpart BBa that address 

SSM and render subpart BBa consistent with the court rulings cited by the commenter. As noted 

elsewhere in this section, emissions testing during SSM is not required (and in fact is prohibited), 

monitoring provisions are used to demonstrate continuous compliance, and these monitoring 

provisions (along with their associated definitions of excess emissions and allowances) have 

been reviewed and developed, giving special consideration to their achievability during SSM 

periods. For example, continuous compliance is demonstrated through:

 TRS monitoring provisions that contain a monitoring allowance with an upper limit cap 

based on S/S periods;

 Wet scrubber liquor flow rate monitoring only during S/S, not pressure drop monitoring, 

because pressure drop varies considerably over the S/S timeframe; and

 ESP secondary voltage monitoring only during S/S, not ESP secondary current or total 

secondary power because these parameters are expected to vary considerably over the S/S 

timeframe.

Other examples of flexibility built into subpart BBa to accommodate SSM, such as the ability to 

consider TRS emissions uncorrected for O2 when O2 reaches ambient levels, are discussed 

throughout this section in other comment-responses. Thus, we believe we have considered SSM 

thoroughly and reasonably in the construction of subpart BBa and that this new subpart is 

consistent with the rulings cited by the commenter. 

Regarding the commenter’s interpretation of the CAA terms “emission limitation” and “emission 

standard,” EPA disagrees with the suggestion that the existence of an SSM exemption in rules 

implementing section 111 in 1977 when Congress enacted the continuous basis language in the 

definition of emission standard is evidence that Congress approved of that regulatory SSM 

exemption.

We acknowledge the commenter’s prior and current comments related to the unavoidable shortterm venting of pulping closed-vent gas streams during S/S events for safety reasons. This topic 

is addressed in responses to comments below.
73

4.1-06 Comment: Commenter 0059 noted that EPA added language at §§60.282a(b) and 

60.283a(b) that states “the standards in this section apply at all times.” The commenter argued 

that it is not feasible to comply with the standards at all times. To provide context, the 

commenter noted the following:

 The TRS emission standard that applies to affected digester systems, BSW systems, 

multiple-effect evaporator systems, or condensate stripper systems is (a) 5 ppm TRS or 

(b) combustion in a lime kiln, recovery furnace, boiler, or incinerator. Exhaust gases from 

these systems are collected and conveyed to a combustion device in order to meet the 

standard.

 The current NSPS subpart BB states that excess emissions occur when there is a period in 

excess of 5 minutes where these gases are not combusted at a temperature of at least 

1200°F.114

 Excess emissions that occur during periods of SSM are recorded and reported according 

to 40 CFR 60.7.

 These systems are also subject to MACT standards at 40 CFR part 63, subpart S. Subpart 

S allows periods of excess emissions up to 1 percent of the time for LVHC pulp mill gas 

collection systems (e.g., digester, evaporator, and stripper off-gases) and up to 4 percent 

of the time for HVLC gas collection systems (e.g., BSW gases), including periods of 

SSM.

Commenter 0059 noted that the proposed subpart BBa is more stringent than either MACT 

subpart S or NSPS subpart BB, as EPA has added language to subpart BBa that states the 

standards apply at all times, and changed the definition of excess emissions as all 3-hour block 

averages during which the combustion temperature is less than 1200°F.115 The commenter noted 

that there are no provisions in this standard specifically addressing short periods of safety-related

venting. According to the commenter, best available technology includes unavoidable periods 

wherein all vent gases cannot be routed to the control device for safety reasons and/or when the

control device is inoperable or necessarily operating at a reduced rate due to a malfunction. The 

commenter noted that they provided more detail in previously submitted comments, which they 

included in attachments to their current comment.

Commenter 0059 requested that EPA add the words “, as provided in §§60.284a and 60.285a.” to

the end of the statements in proposed §§60.282a(b) and 60.283a(b) that say “The standards in 

this section apply at all times.” The commenter stated that this change is necessary to avoid 

confusion about EPA’s intent in adding these short, unqualified statements to the sections 

describing the PM and TRS standards. The commenter stated that it may be obvious that the 

monitoring and performance testing sections that follow, including provisions defining excess 

emissions, govern implementation of the emission limitations, but the wording in proposed 

§§60.282a(b) and 60.283a(b) might be misinterpreted. (As an example, the commenter noted that 

§60.283a as proposed might be misunderstood to impose TRS limitations on recovery furnace 

emissions even during periods when BLS are not being fired.)

 

114 See §60.284(d)(3).

115 See §60.284a(d)(3).
74

Response: We acknowledge the comments on subpart S provided previously and attached by 

commenter 0059 that pertain to startup, shutdown, and safety-related venting for pulp mill 

sources. We also acknowledge that there are overlapping requirements in subpart S and subpart 

BBa for digester systems, BSW systems, multiple-effect evaporator systems, and condensate 

stripper systems. Vent gases from these systems are collected in LVHC or HVLC collection 

systems meeting the closed-vent collection system standards in §63.450 of subpart S. The 

closed-vent collection system standards in subpart S were promulgated in 1998 and work in 

tandem with the NSPS requirements to ensure and document that pulping vent gases are routed 

through a closed-vent collection system to the control device. In response to this comment and 

comment 2.3-02 on the proposed subpart BBa, and in order to promote consistency between 

subpart S vent gas standards and the subpart BBa TRS standards (which use the same collection 

and incineration systems), we have added a reference to the subpart S closed-vent collection 

system standards in the subpart BBa standards in §§60.283a(a)(1)(i)-(iii) and (v). We have also 

added definitions and criteria related to closed-vent collection systems to §60.281a and 

§§60.284a(d) and (e) to ensure the standards are implemented consistently. Furthermore, as 

stated in response to the comment above, we have clarified the language in §§60.282a(b) and 

60.283a(b) by adding the phrase “as specified in §§60.284a and 60.285a” to ensure that 

§§60.282a(b) and 60.283a(b) are not misinterpreted as being inconsistent with the monitoring 

and performance testing sections in subpart BBa.

4.1-07 Comment: Commenter 0059 recommended that EPA adopt the excess emissions 

provisions in MACT subpart S for digesters, BSWs, evaporators, and strippers covered by NSPS 

subpart BBa. According to the commenter, the excess emission provisions in the MACT subpart 

S regulations reflect EPA’s careful determination, after years of study of a large quantity of 

emissions information and public comments, that the MACT “floor,” representing the emissions 

of the “best performers,” includes emissions during unavoidable periods of releases of 

uncontrolled or partially controlled pulping process vent gases.116 The commenter cited the 

following text from the preamble to the final subpart S rule:

“EPA established appropriate excess emission provisions to approximate the level of 

backup control that exists at the best-performing mills and the associated period of time 

during which no control device is available.”117

After “an analysis of the public comments and the available data regarding excess

emissions and the level of backup control in the industry,” EPA determined that the

“best-performing mills achieve a one percent downtime in their LVHC system control

devices” and “best-performing mills achieve a four percent downtime in the control

devices used to reduce emissions from their HVLC system to account for flow balancing 

problems and unpredictable pressure changes inherent in HVLC control systems.”118

 

116 See 63 FR 18504, 18529 (April 15, 1998).

117 See id.

118 See id.
75

“The allowances address normal operating variations in the LVHC and HVLC system 

control devices for which the equipment is designed. The variations would not be 

considered startup, shutdown, or malfunction under the Part 63 General Provisions....”119

Commenter 0059 pointed out that EPA adopted the excess emission provisions after reviewing 

extensive data from continuous monitoring systems and considering industry comments that,

although some mills had backup combustion devices as part of their LVHC control system, 

venting of NCGs is an essential safety practice (because of their explosion hazard) even for those 

systems with backup control devices, since the startup of, and transfer of vent gases to, the 

backup controls cannot be immediate or automatic for safety reasons, and operating variability in 

the control devices themselves was unavoidable for process and other reasons.120 For HVLC 

systems, the commenter noted that few mills had backup controls that could handle the large 

volume of vent gases, so any standard that required the use of backup devices would have been 

beyond the MACT “floor” and would not have been cost-effective due to the low concentration 

of pollutants in the large gas stream.121

In short, the commenter stated that the MACT determinations that EPA made when 

promulgating the subpart S emission standards correctly concluded that best available 

technology includes unavoidable periods wherein all vent gases cannot be routed to the control 

device, and/or when the control device is inoperable or necessarily operating at a reduced rate.

The commenter noted that the subpart S emission standards (including the excess emission 

provisions) were designed to reflect the performance of the MACT technology and the actual

performance of the “best-performing” mills. The commenter indicated there have been no 

technology developments for new/modified sources that would change the conclusions reached

under subpart S. Without any excess emission provisions, the commenter said that subpart BBa 

emissions standards would impose limitations not achieved even by the “best performers” and 

not demonstrated as achievable at any facility.

Commenter 0059 noted that provisions for a small amount of LVHC and HVLC system venting 

and stripper downtime were developed as part of the MACT “floor,” based on the fact that even 

the best-performing units could not meet the standards at all times. According to the commenter, 

as the technology for the collection and treatment of HAPs under subpart S has not changed, 

neither has the capability for mills to operate without needing these provisions. The commenter 

insisted that these provisions are necessary due to process variability and not for situations

defined as SSM. The commenter said that these events generally are not due to situations where 

 

119 See 63 FR 18530.

120 See, e.g., U.S. Environmental Protection Agency, Pulp, Paper and Paperboard Industry – Background 

Information for Promulgated Air Emission Standards – Final EIS, Publication No. EPA-453/R-93-050b, October 

1997 (“BID”) at pp. 4-81, 4-82 to 4- 84; AF&PA April 18, 1994 comments on the proposed MACT standards for 

Pulp and Paper Mills, p. MACT-61 (events resulting in venting of NCGs are “integral to process variability,” and 

combustion devices will “predictably” not perform at their design efficiency ” some small percentage of the time, 

even when they are being operated properly and all equipment is in order”); id. P0. MACT-173-74.

121 See 63 FR 18529; BID at pp. 4-81 to 4-82; AF&PA April 18, 1994 comments at p. MACT-61 (degree of venting 

allowance needed is “independent of the availability of backup combustion devices because of the safety and 

engineering concerns”); id. at p. MACT-174 (backup combustion devices for HVLC systems could be an additional 

cost of $1 billion).
76

some equipment has broken down and must be repaired to correct the situation, but are due to 

process variability and safety interlocks which have caused a situation that requires a release.

Regarding LVHC systems, commenter 0059 noted that LVHC NCG gases (e.g., those from 

digesters and evaporators) are potentially explosive and cannot be burned safely without 

supplemental fuel. The commenter noted that most mills have both a primary and back-up 

control device122 for the treatment of LVHC gases. The commenter stated that these gases must 

be incinerated with support fuel and be interlocked to failsafe on loss of support fuel, combustion 

air, and/or boiler load. The commenter noted that flame safety system will not permit the gases to 

be admitted until the burner is operating on supplemental fuel and ignition is proven. Therefore, 

for gases to be introduced into any control device, the commenter said several conditions, also 

known as permissives, must be met, and the system has a series of interlocks that will not allow 

the introduction of gases unless all conditions are satisfied. The commenter pointed out that these 

conditions are required for both safety and protection of process equipment. The commenter 

noted that safety interlocks are required by both Factory Mutual Insurance and the National Fire

Protection Association for burning of these NCGs. Also, when these gases are burned in a 

recovery furnace, the commenter indicated there are safety guidelines issued by BLRBAC.

Regarding HVLC systems, commenter 0059 noted that the HVLC system (used to collect gases 

from sources such as BSWs) is similar to the LVHC system in causes of venting events: “The 

best-performing mills achieve a four percent downtime in the control devices used to reduce 

emissions from their HVLC system to account for flow balancing problems and unpredictable 

pressure changes inherent in HVLC systems.”

123 According to the commenter, the main

difference is that most HVLC systems do not have back-up control devices. Therefore, the 

commenter noted, when boiler/firing permissives prevent the incineration of these gases, the mill 

must decide if emissions will be best minimized by waiting for the control device to become 

available or shutting down the HVLC sources.

Regarding TRS emissions during startup, shutdown, and safety venting, commenter 0059 noted 

that, for each type of release, it is not possible to estimate emissions on a site- or event-specific

basis. According to the commenter, emissions will vary based on the cause, location, and source 

of the release. The commenter pointed out that emissions will vary not only between mills and 

sources but between the same sources at the same mill under different circumstances. 

Commenter 0059 noted that commenter 0058 has developed limited data sets for main vents 

(vents immediately prior to the control device that include gases from all collected sources) 

under normal operations, but noted that that site-specific data cannot be collected for the releases 

listed above, because the events cannot be anticipated, the events are typically short in duration, 

and it is unsafe to perform sampling. Therefore, the commenter concluded it is not possible to 

develop or suggest a TRS standard that might apply during these periods.

 

122 Common control devices for LVHC gases include power boilers, lime kilns, stand-alone incinerators, and 

recovery furnaces.

123 See 63 FR 18529 (April 15, 1998).
77

Commenter 0059 noted that, for subpart S, EPA decided to develop MACT “floors” on a unit 

(i.e., system) basis.”124 The commenter asserted that development of a numerical emissions 

standard (other than tracking vent time) is not feasible due to limitations in technology. The 

commenter indicated that there are no data available to quantify site-specific emissions from the 

vents of LVHC and HVLC systems.

Regarding procedures to minimize TRS emissions during startup, shutdown, and safety venting, 

commenter 0059 noted that, under subpart S, mills were required to develop SSM plans, and 

stated that the same procedures are followed for sources subject to NSPS subpart BB, even 

though SSM plans are not required. The commenter indicated that mills use these plans and 

standard operating procedures to define the work practices mills must follow to minimize 

emissions during a release. As an example, the commenter noted that during extended steam 

stripper downtimes (that exceed the buffering capacity of the condensate collection tank), many 

facilities route their condensates to the secondary wastewater treatment system. According to the 

commenter, depending on process and system design, mills also monitor the location and 

duration of releases from NCG systems by detecting changes in pressure (most popular), valve 

position, temperature at the vent location, or flow meters. The commenter noted that facilities 

have instituted standard operating procedures and corrective actions to minimize these 

intermittent venting periods and record this information either electronically or in log books and 

report events, causes, and corrective actions.

Response: As stated previously, the closed-vent collection system standards in subpart S were 

promulgated in 1998 and work in tandem with the NSPS requirements to ensure and document 

that pulping vent gases are routed through a closed-vent collection system to the control device.

In order to ensure consistency between the subpart S vent gas standards and the subpart BBa 

TRS standards (which use the same collection and incineration systems), we have added a 

reference to the subpart S closed-vent collection system standards in the subpart BBa standards 

in §§60.283a(a)(1)(i)-(iii) and (v). We have also added definitions and criteria related to closedvent collection systems to §60.281a and §§60.284a(d) and (e) to ensure the standards are 

implemented consistently.

While we appreciate the overview of the subpart S MACT determinations provided by the 

commenter, we are not responding in detail to this discussion because it is outside the scope of 

the subpart BBa rulemaking. The preamble to the final subpart BBa rule discusses the timing of 

future actions related to the industry’s subpart S petition for reconsideration of the final subpart S 

RTR rule relating to safety-related venting of pulp mill vent gases.

4.1-08 Comment: Commenter 0055 agreed with the EPA’s approach to define excess emissions 

as ESP parameter measurements below the minimum requirements during times when BLS or 

lime mud is fired. The commenter also believes the use of wet scrubber liquid flow rate (or liquid 

supply pressure) by the affected units to demonstrate compliance during periods of S/S to be 

reasonable. In addition, it is the commenter’s understanding that, due to the requirements of 40 

CFR 60.7(b), (c)(2), and (c)(4), these exceedances were already required to be reported and, in 

conjunction with the monitoring allowances, are not considered violations unless they exceed the 

 

124 U.S. Environmental Protection Agency. Pulp, Paper, and Paperboard Industry—Background Information for 

Promulgated Air Emission Standards: Manufacturing Processes at Kraft, Sulfite, Soda, Semi-Chemical, 

Mechanical, and Secondary and Non-wood Fiber Mills. Publication No. EPA-453/R-93-050b. October 1997. p. 4-6.
78

proposed upper limits. Therefore, the commenter stated, compliance is practicable and 

achievable.

Response: We appreciate the support. We are promulgating our approach to define excess 

emissions as ESP parameter measurements below the minimum requirements during times when 

BLS or lime mud is fired as proposed. We are also promulgating the use of only wet scrubber 

liquid flow rate (or liquid supply pressure) to demonstrate compliance during periods of S/S as 

proposed. Similarly, as discussed in comment 4.1-09 below, we are promulgating a provision 

that requires only the use of ESP secondary voltage (as opposed to both ESP secondary voltage 

and current, or total secondary power) to be included in the compliance demonstration during 

periods of S/S.

The commenter is correct that the recordkeeping and reporting requirements of 40 CFR 60.7(b), 

(c)(2), and (c)(4) apply.

4.1-09 Comment: Commenter 0059 supported the following provisions from the proposed rule 

and believes they are necessary:

 EPA did not propose alternate standards during periods of S/S, but instead proposed some 

adjustments and clarifications to accommodate S/S periods for incinerators, recovery 

furnaces, and lime kilns.

 EPA clarified that the TRS limits for recovery furnaces and lime kilns only apply when 

BLS or lime mud is being fired.

 EPA has also allowed the use of uncorrected TRS concentrations during S/S when the O2

concentration is greater than 15 percent.

 Because incineration devices must warm to 1200°F during control startup prior to firing 

TRS gases (and subsequently cool to below 1200°F during control shutdown), the EPA 

proposed to allow facilities to omit 5-minute recorded temperature measurements from 

the 3-hour block averages when no TRS emissions are fired. This means that when the 

incinerator is not burning TRS (e.g., during incinerator warm-up and cool-down periods 

when TRS gases are not being burned or when an alternative control device is used), the 

low temperature does not constitute a violation.

 To address the need for ESPs to warm to a specified temperature before full power is 

applied to the transformer-rectifier set, the EPA proposed to define excess emissions as 

ESP parameter measurements below the minimum requirements during times when BLS

or lime mud is fired (as applicable).

 The EPA is also proposed language that would allow affected units to use only wet 

scrubber liquid flow rate (or liquid supply pressure) to demonstrate compliance during 

periods of S/S because pressure drop is difficult to achieve during these periods.

Commenter 0059 believes it is appropriate for EPA to acknowledge that operations of control

equipment are different during periods of S/S than during periods of steady state, normal 

operation and indicated that the proposed monitoring provisions that accommodate these 

differences in operation are appropriate. However, the commenter stated that additional

provisions are needed to more fully account for S/S periods, as discussed in the following 

paragraphs.
79

Startup and ESPs. With PM emissions from recovery furnaces (and some lime kilns) controlled 

using ESPs, commenter 0059 noted that subpart BBa as proposed does not require compliance 

with the opacity standard until BLS or lime mud is being fired, which provides time for the 

operators to warm up the equipment on auxiliary fuel, such as fuel oil or natural gas. Noting that 

the ESP cannot practicably be engaged until a certain flue gas temperature is reached, the 

commenter said that premature starting of this equipment would lead to short-term stability 

problems that could result in unsafe actions and longer term degradation of ESP performance due 

to fouling, increased chances of wire damage, or increased corrosion within the chambers. The 

commenter pointed out that vendors providing this equipment incorporate these safety and 

operational concerns into their standard operating procedures.125

According to the commenter, during periods of startup, auxiliary fuel (e.g., fuel oil or natural 

gas) is introduced to the furnace or kiln and the ESP warms up on a designated curve that could 

last for a few hours. The commenter noted that some ESPs have O2 sensors and alarms that shut 

down the ESP at high flue gas O2 levels to avoid a fire in the unit. The commenter further noted 

that the O2 level is typically high during startup, so the ESP may not engage due to these safety 

controls until more stable operating conditions are reached. In addition, the commenter noted 

that when the furnace or kiln is started on residual oil, the ESP cannot be engaged until a certain 

temperature is reached to avoid fouling the plates.

The commenter pointed out that operators have a financial incentive to minimize the time spent 

in startup. According to the commenter, when units are starting up, they are not operating in the 

most efficient mode, auxiliary fuel is being burned, and the process is not operating optimally. 

Therefore, the commenter indicated that furnaces and kilns are started up as expeditiously as 

possible, but safety concerns cannot be ignored, and proper procedures must be followed. The 

commenter stated that EPA was correct in applying the opacity standard only after BLS or lime 

mud is introduced into the furnace or kiln. However, the commenter pointed out that ESPs are 

operated using a power management system to ensure the most efficient mode of operation. 

According to the commenter, the efficient functioning of an ESP means minimizing power

consumption and maximizing dust collection. The commenter noted that these automated power 

management systems sense the amount of loading and adjust the amount of current applied

accordingly, based on the spark rate. Therefore, the commenter stated, at low loads during S/S

when BLS or lime mud is being fired at less than normal operation, the secondary current may 

not be within the range achieved during the last performance test, but the ESP would still be 

operating optimally. As a result, the commenter explained, the first 12-hour block average 

secondary current or total secondary power reading could be less than the established operating 

parameter range, but the PM emissions and opacity could below the standards.

Therefore, the commenter requested that EPA exclude from the definition of excess emissions all 

12-hour average measurements of secondary current or total power during S/S that are less than 

the site-specific operating parameter limits, as it has done for scrubber pressure drop.126 Given 

the difficulties associated with maintaining steady secondary current, and extending the logic 

behind allowing liquid flow rate (as opposed to pressure drop) for scrubbers during S/S, the 

 

125 See Appendix I of AF&PA’s August 23, 2010 comments on the June 4, 2010 proposed Boiler MACT rule for an 

excerpt of an ESP operational manual.

126 See §60.284a(d)(4)(ii) and (5)(ii).
80

commenter requested that EPA also allow facilities to monitor only secondary voltage during

S/S.

Longer averaging times. In addition to incorporating provisions that address the S/S issues raised 

above, commenter 0059 requested that EPA also incorporate a longer averaging time to the 

various emission standards (e.g., 24-hour average) to better account for short safety venting

episodes and short excursions during S/S. The commenter also requested that the definition of

excess emissions in subpart BB127—as a period in excess of 5 minutes where gases are not 

combusted at a temperature of at least 1200°F—should be retained in subpart BBa. The 

commenter argued that EPA had not provided a sufficient rationale for its elimination. The 

commenter noted, however, that a longer averaging time or a 5-minute allowance would not be 

sufficient to account for the time needed to safely start up digester, evaporator, stripper, and 

BSW systems, and, thus, the commenter indicated other changes are necessary, as discussed 

above.

Response: The commenter supports and understands correctly our proposals regarding operating 

parameters and the applicability of TRS limits during recovery furnace and lime kiln operation. 

Similarly, they understand and support our proposal on O2 correction of TRS CEMS readings. 

We appreciate their support and are finalizing those sections of the proposal. These monitoring 

provisions were developed in recognition that selected parameters during S/S periods may 

different from parameters observed during normal steady-state operations.

The commenter’s observation regarding ESP secondary current during periods of low load, such 

as would occur during S/S, is helpful. The commenter notes that for control systems where an 

ESP is followed by a wet scrubber, the ESP secondary current (or total secondary power which is 

calculated using secondary current) can be below the established operating parameter range 

while the PM and opacity limits meet the standard. We agree with the commenter that secondary 

current (or total secondary power) can vary during startup and shutdown. We have changed the 

definition of ESP-related excess emissions for combined ESP/scrubber controls in 

§60.284a(d)(5) of the final rule to include all 12-hour block averages of ESP secondary voltage 

below the minimum operating limit at all times (including S/S), and all 12-hour block averages 

of secondary current or total secondary power below the minimum operating limit at all times 

except during S/S. The rule changes make the S/S accommodations proposed for wet scrubbers 

and those for this type of ESP comparable. This change does not apply for systems that only 

employ an ESP and have longer averaging periods in conjunction with an opacity limit.

Given the 12-hour averaging times for most parameters and other changes incorporated into the 

final rule to promote consistency between subpart S and subpart BBa, we do not believe it is 

necessary to also lengthen the averaging time for continuously monitored parameters or to 

reinstate the definition of excess emissions as a period in excess of 5 minutes where gases are not 

combusted at a temperature of at least 1200°F. 

4.2 Periods of Malfunction

 

127 See §63.284(d)(3)(ii).
81

4.2-01 Comment: Commenters 0059 and 0061 contended that EPA is required to take 

malfunctions into account when adopting NSPS. According to the commenters, EPA 

categorically asserts that “section 111 does not require that emissions that occur during periods 

of malfunction be factored into development of CAA 111 standards,”128 but offers very little 

support for that assertion, other than stating its own, often counterintuitive, conclusions.

Commenter 0059 indicated that the plain language of section 111 and the explicit direction of all 

of the relevant case law state that malfunctions must be accommodated by the NSPS if they in 

fact are to be achievable when using the best demonstrated control technology on which the 

NSPS are based. Commenter 0061 argued that EPA cannot simply change its mind without 

providing a factual analysis supporting its new conclusion that NSPS need not include the 

allowances for malfunctions that were included in dozens of NSPS issued over the past 40 

years.129

Commenter 0059 rejected EPA’s claim that the technology basis for NSPS incorporates the 

notion of “operating units in such a way as to avoid malfunctions” and setting emission standards 

at levels “achieved by a well-performing non-malfunctioning source.”130 The commenter stated 

that EPA’s claim has no basis in the statutory language or the case law. According to the 

commenter, rather than set standards of performance that reflect what is achieved by 

demonstrated technology as the statute requires, the EPA has instead assured that the proposed 

NSPS are inconsistent with the statutory criteria for NSPS, by assuring that sources will be in 

violation of the standards despite installation of the identified control technology.131 Far from 

being “consistent with section 111 and... a reasonable interpretation of the statute,”132 the 

commenter argued that EPA’s approach to malfunctions disregards congressional intent that 

NSPS be achievable with demonstrated technology and instead sets limits EPA knows sources 

will violate even if they install that technology and operate and maintain it properly.

According to commenters 0059 and 0061, EPA asserts that emissions during malfunctions 

should not be used to characterize the source’s operations for purposes of deriving NSPS. The 

commenters cited EPA’s argument that NSPS should be characterized only by a source’s 

emissions during normal operations, because “accounting for malfunctions would be difficult, if 

not impossible, given the myriad different types of malfunctions that can occur across all sources 

in the category and given the difficulties associated with predicting or accounting for the 

frequency, degree and duration of various malfunctions that might occur.”

133 Commenter 0061 

contended that, on its face, acknowledging that malfunctions are part of the affected facility’s 

operation, but then excluding emissions during malfunctions when determining emission 

limitations for the affected facility, makes no sense.

According to commenter 0061, EPA acknowledges that even properly designed and operated 

equipment will sometimes exceed emission limitations based on steady-state operation, due to

 

128 See 78 FR 31329, col.1.

129 See, e.g., Transactive Corp. v. United States, 91 F.3d 232, 237 (D.C. Cir. 1996) (agency must provide a 

“reasoned analysis” to support departing from prior practice).

130 See 78 FR 31329.

131 See id. (recognizing that “even equipment that is properly designed and maintained” can be expected to fail 

sometimes, and therefore not to achieve the emission limitations EPA is proposing).

132 See 78 FR 31329.

133 See id.
82

malfunctions.134 The commenter stated that operators of the affected facility must treat 

malfunctions as very distinct events from steady-state operations, depending on the severity of 

the malfunction, requiring anything from shutdown of the unit to emergency fire response

actions. The commenter agreed with EPA’s conclusion that the factual complexity of differing 

processes and of the severity, frequency, and duration of malfunctions makes standard-setting 

difficult.135 In addition, the commenter pointed out that it is often impossible to gather emission 

data during malfunctions either for standard-setting or for compliance demonstration purposes. 

According to the commenter, malfunctions are by definition unexpected, so it is not possible to 

plan to have test equipment in place to measure emissions when one occurs. The commenter also 

pointed out that, even if test or monitoring equipment is in place, emissions during malfunctions 

often are not routed to a stack where they can be measured, and upsets during stack testing 

invalidate the test results under EPA’s approved test methods.

Rather than supporting EPA’s decision to ignore the fact that SSM events can lead to higher 

emissions even at well-operated facilities with the best control equipment, commenters 0059 and 

0061 said these findings should lead EPA to its authority under CAA section 111(h) to prescribe 

alternative design, equipment, work practice, or operational standards where it is not feasible to 

set or enforce a numerical emission limit. Commenter 0059 pointed out that EPA has done so in 

subpart BB and should do so in subpart BBa as well.136 The commenters argued that EPA cannot 

rationally defend its articulated view that applying the concept of “best system of emission 

reduction which ... has been adequately demonstrated” to periods during which a source is 

malfunctioning “presents difficulties.”137 The commenters contended that this ignores the fact 

that there are work practices that represent the best practices for minimizing emissions during a

malfunction. While the measures that represent these best practices will depend on facilityspecific issues, such as process design, pollution control train, and other factors, the commenters 

said they are nonetheless the “best system of emission reduction which ... has been adequately 

demonstrated.”138

Commenter 0061 noted EPA’s claim that “accounting for malfunctions when setting standards of

performance under section 111...could lead to standards that are significantly less stringent than 

levels that are achieved by a well-performing non-malfunctioning source.”139 According to the 

commenter, that “end justifies the means” rationale ignores the congressional directive that 

NSPS are to represent limitations that have been achieved in practice and that reflect operation of 

 

134 See id.

135 See id.

136 EPA suggests that its position is supported by Weyerhaeuser Co. v. Costle, 590 F.2d 1011 (D.C. Cir. 1978). But 

that opinion: (a) involved a CWA “technology-forcing” requirement that is different from the best demonstrated 

technology requirement of CAA section 111; (b) was issued long before the D.C. Circuit concluded in NRDC v. 

EPA, 859 F.2d 156 (D.C. Cir. 1988) that the CWA technology-based effluent limitations must include an upset 

provision to address circumstances where compliance with effluent limitations is impossible through no fault of the 

permittee; and (c) in any event speaks to highly unusual events (“’uncontrollable acts of third parties,’ such as 

strikes, sabotage, operator intoxication, or insanity”) rather than to anticipated inability of identified control 

technology to meet specified emission limitations 100 percent of the time. See 590 F.2d at 1058. Moreover, the fact 

that there may be certain kinds of malfunctions that EPA could not reasonably account for in the NSPS does not in 

any way demonstrate that EPA is justified in ignoring all types of malfunctions when it establishes the standards.

137 See 78 FR 31329.

138 See id.

139 See id.
83

the “best” control technology, taking into account various statutory factors, including cost and 

energy impacts...not limitations that represent the highest level of pollution control achievable. 

The commenter argued that it is not reasonable and inconsistent with congressional intent for 

EPA to ignore the undisputed existence of malfunctions even at best-performing sources, and 

then claim falsely that the best-performing sources “achieve” emission levels that they 

undisputedly do not achieve part of the time. According to the commenter, since EPA described

malfunctions as being sometimes unavoidable or “not reasonably preventable,” despite proper 

design and maintenance of equipment, there is no basis for EPA’s conclusion that malfunction 

events are not representative of best-performing sources.140 The commenter acknowledged that

one goal (although not “the goal”) of best-performing sources is “operating in such a way as to 

avoid malfunctions of their units,”

141 but the commenter said that is all the more reason why 

EPA must acknowledge the fact that those sources nevertheless experience malfunction events, 

rather than assume those emissions away.

Commenter 0061 argued that, by proposing an NSPS that EPA recognizes even sources with the 

best demonstrated control technology cannot achieve at all times, the Agency failed to meet the 

statutory requirement that NSPS be adequately demonstrated. The commenter stated that this is

especially obvious when one considers the multitude of conditions EPA proposes to impose on 

sources during malfunctions, in order to be excused from civil penalties. According to the 

commenter, EPA made no attempt to justify those conditions as reasonable “taking into

consideration the cost of achieving such reduction and any nonair quality health and

environmental impact and energy requirements....”142

Commenter 0061 also noted that EPA did not present any substantiation for its belief that “it 

would be difficult, if not impossible, to take malfunctions into account in setting CAA section

111 standards.”143 According to the commenter, it is indefensible for EPA to acknowledge that 

malfunctions are inevitable, even for the best-performing sources, and yet refuse to include 

emissions data representing malfunctions in its calculations of the emission limitations for the 

proposed standards. The commenter contended that, if it is possible to gather sufficient

representative data reflecting emissions during malfunctions, then EPA is obligated to consider 

these data in its calculations of NSPS for steady-state operating conditions. To the extent EPA 

had access to continuous monitoring data for emission units using technology on which the 

proposed standards are based that included malfunction periods, the commenter said EPA could 

have conducted analyses of emissions levels during malfunction events.144 The commenter also 

noted that many types of sources are required by many state agencies to submit deviation reports 

or malfunction reports when they experience a malfunction that causes an exceedance of an 

applicable limitation. The commenter stated that EPA did not appear to have made any attempt 

to obtain and analyze such reports, in order to assess what type of requirement might reasonably 

apply to the subject emission units during malfunctions.

 

140 See id.

141 Cf. id.

142 See CAA section 111(a)(1).

143 See 78 FR 31329.

144 Even if the continuous monitoring data are for parameters not regulated by the proposed standards, analysis of 

monitoring data for those other parameters during malfunction events might form a reasonable basis for EPA’s 

assessment of what standards are achieved or achievable during malfunctions.
84

According to commenter 0061, there are several options EPA could use for setting NSPS under 

CAA section 111 that would apply during malfunction events. The commenter noted that EPA, 

for example, could establish an emission limitation that applies at all times, but that has an 

averaging time of sufficient duration that short, infrequent spikes in emissions due to 

malfunctions would not cause the source to exceed the emission limitation (while at the same 

time ensuring that the source does not operate in a way that causes frequent, lengthy excursions 

above the normal controlled emission rate). The commenter stated that EPA did not appear to

have done any analysis that would show whether the averaging times proposed would 

accommodate excess emissions during malfunctions typical of this source category.

Commenter 0061 noted that EPA also could use the flexibility accorded by CAA section 302(k) 

(defining “emission limitation” and “emission standard” to include “any requirement relating to

the operation or maintenance of a source to ensure continuous emission reduction, and any 

design, equipment, work practice or operational standard promulgated under” the CAA) to 

address emissions during malfunction events through operational requirements rather than by 

applying the same limits on pollutant concentrations in exhaust gases that apply during normal 

operations. According to the commenter, EPA could have concluded, as explained for S/S events 

above, that it has grounds to exercise its authority under CAA section 111(h) to promulgate a 

design, equipment, work practice, or operational standard, or combination thereof, because it is 

not feasible to prescribe or enforce an emission standard. The commenter noted that EPA might 

also use several of these approaches in combination.

According to commenter 0061, there is no indication in the proposed rule that EPA gave much, if 

any, consideration to these types of options. The commenter said that, in short, there are ample 

reasons to reject EPA’s conclusory assertions that it cannot take malfunctions into account when

setting NSPS for kraft pulp mills. The commenter argued that EPA’s failure to evaluate these 

options thoroughly renders the proposed rule arbitrary and requires EPA to develop a new 

proposal.

Like commenters 0059 and 0061, commenter 0056 also objected to EPA’s argument that the 

CAA does not require them to include malfunction periods in development of NSPS emission 

standards.145 While commenter 0056 agreed with EPA that the emissions from malfunction 

events typically cannot reasonably be measured or monitored, making those emissions not 

amenable to regulation under specific emission limits, the commenter contended that setting a 

single emission limitation that applies at all times, even though it cannot be met during some 

malfunctions (or S/S) events, does not represent a limitation “achievable,” as required by CAA

section 111. The commenter noted that the original NSPS standards for pulp mill chemical 

recovery and combustion sources were written with the understanding that excess emissions 

associated with SSM events would not be considered violations of the standards. Because of the 

court decision and the underlying CAA achievability criteria, the commenter said EPA must 

focus its reassessment of malfunction standards applicable to the pulp mill chemical recovery 

processes in a way that captures the fundamental information on best performers on which the 

current standards were based. For practical reasons, the commenter said EPA should either reevaluate and provide adequate monitoring allowances to cover malfunctions as part of the 

standard, or establish work practices that are feasible to implement during a malfunction (i.e., 

 

145 See 78 FR 31329.
85

best engineering and safety practices). According to the commenter, setting appropriate 

allowances or work practice standards as the NSPS during malfunction events is the legally 

defensible and feasible approach.

Response: The EPA disagrees with the comment that it is required to take malfunctions into 

account when adopting NSPS and that a separate standard be set for periods of malfunction. As 

explained in the preamble, the EPA has determined that CAA section 111 does not require that 

emissions that occur during periods of malfunction be factored into development of CAA section 

111 standards. As the EPA further explained, accounting for malfunctions would be difficult, if 

not impossible, given the myriad different types of malfunctions that can occur across all sources 

in the category and given the difficulties associated with predicting or accounting for the 

frequency, degree, and duration of various malfunctions that might occur. Setting work practice 

standards under section 111(h) as the commenters suggest presents the same issues as setting 

numerical emission limits given the varied nature of malfunctions. The commenters have not 

suggested any specific work practices for subpart BBa equipment that could be used in place of 

the numeric limits during periods of malfunction. Consequently, to assure continuous 

compliance for periods of malfunction, we added affirmative defense provisions to subpart BBa.

The EPA also disagrees with the comment that our approach ignores congressional intent that the 

NSPS be achievable with demonstrated technology because the proposed NSPS does not 

accommodate malfunctions. The affirmative defense provisions give the EPA the flexibility to 

both ensure that its emission standards are “continuous,” as required by 42 U.S.C. 7602(k), and 

account for unplanned upsets and thus support the reasonableness of the standard as a whole.

The EPA also disagrees that we “ignore the undisputed existence of malfunctions even at bestperforming sources.” We recognized that malfunctions occur even at the best-controlled sources 

and included the affirmative defense provisions for this standard in order to address them. Also, 

the comment that EPA did not consider malfunction events from the CEMS/COMS ICR data is 

incorrect. We collected and evaluated malfunction data in our CEMS/COMS analysis.

We appreciate the commenter’s suggestion regarding the use of an “averaging time of sufficient 

duration [to ensure] that short, infrequent spikes in emissions due to malfunctions would not 

cause the source to exceed the emission limitation (while at the same time ensuring that the 

source does not operate in a way that causes frequent, lengthy excursions above the normal 

controlled emission rate).” We also appreciate their evaluation of the averaging approaches 

proposed for §60.284a, though we disagree with the commenter’s assessment of the utility of 

such averaging approaches regarding malfunctions. The EPA has determined that CAA section 

111 does not require that emissions that occur during periods of malfunction be factored into 

development of CAA section 111 standards, as stated elsewhere in this response. Consequently,

we did not perform a specific “analysis that would show whether the averaging times proposed 

would accommodate excess emissions during malfunctions typical of this source category.” Our 

proposal sought to establish reasonable averaging periods that reflect the BSER at the bestcontrolled sources. Our initial and subsequent analyses (see section 3 of this response) both 

confirm this BSER assessment. Establishing an averaging period is an acknowledgment that 

even the best sources experience some level of process variability. Further, we recognize that 

averaging periods can encompass events that some sources might characterize as minor 

equipment malfunctions. Such an accommodation is inherent in any averaging approach. This 
86

aspect of averaging periods serves to limit the circumstances where affirmative defense might 

apply to events that are significant malfunctions, with excess emissions defined in §§60.284a(d) 

and (e). Again, these excess emission definitions were reviewed using recent ICR data collected 

at the best-controlled sources. Consequently, we do not believe that affirmative defense will be 

frequently applicable since new, reconstructed and modified sources will need to employ control 

technology already in use at the best sources and the prospect of affirmative defense assures that 

these control systems will be properly maintained.

4.3 Affirmative Defense

4.3-01 Comment: Commenter 0059 referred to EPA’s suggestion that its position on use of an 

affirmative defense was supported by a recent 5th Circuit decision in Luminant Generation LLC 

v. EPA, 714 F.3d 841 (2013). The commenter indicated there are many problems with that 

assertion.

1. The Luminant decision addressed EPA’s discretion to approve and disapprove SIPs under 

CAA section 110; it had nothing to do with establishment of standards achievable with 

best demonstrated technology under CAA section 111.

2. The Luminant decision largely dealt with whether EPA’s approval of the Texas SSM 

provisions was consistent with the CAA enforcement authorities in section 113(e), which 

again does not bear on whether use of the affirmative defense is an adequate substitute 

for establishing achievable NSPS under section 111.

3. The Luminant court sustained EPA’s approval of a Texas SIP affirmative defense 

provision that includes unplanned S/S events, while EPA takes the position in the 

proposed subpart BBa preamble that an affirmative defense is not appropriate for S/S

events.

4. The Luminant decision currently is the subject of a petition for writ of certiorari pending 

before the Supreme Court.

Response: As stated in the proposed rule preamble (at 78 FR 31330 (col. 1)), the Luminant

decision is cited to support EPA’s view that an affirmative defense provision is consistent with 

CAA section 113(e), which is only one part of the discussion supporting EPA’s promulgation of 

an affirmative defense for malfunction events. See 78 FR 31329-330. Notwithstanding the 

comments summarized above concerning the Luminant decision, EPA stands by both its citation 

of Luminant for the specific proposition for which it was cited and the overall basis for the 

affirmative defense as discussed in the proposed rule preamble.

4.3-02 Comment: Commenter 0061 argued that the proposed affirmative defense is not a 

substitute for addressing malfunction events in the performance standards themselves. The 

commenter noted EPA’s acknowledgement that the sources that will be subject to the proposed 

rule sometimes will be unable to comply with the proposed standards because of malfunctions, 

even if their equipment is properly designed and maintained, through no fault of the source.146

 

146 See 78 FR 31329.
87

Rather than promulgate a standard of performance that eliminates that situation, so that the 

regulated emission sources will be subject to differentiated requirements, achievable with the 

identified best demonstrated technology, during malfunction events, the commenter noted that 

EPA offered instead an “affirmative defense.” According to the commenter, the proposed 

affirmative defense shifts the burden to the source to prove that a myriad number of criteria are 

met and actions were taken by the source (which criteria bear no direct relation to the statutory 

factors for standards of performance under CAA section 111), in order to avoid “civil penalties.” 

The commenter contended that inclusion of the affirmative defense does not cure EPA’s failure 

to set emission standards that are achievable during malfunctions. The commenter argued that 

the proposed standards, incorporating the affirmative defense, still do not represent emission 

limitations that have been “adequately demonstrated” to be “achievable” through use of the best

control technology under CAA section 111(a)(1).

According to commenter 0061, it is unclear where EPA found the legal authority in the CAA to 

shift the burden to the regulated community of proving (or disproving) essential elements of an

alleged violation. The commenter noted that the statute is silent as to the issue and “the ordinary 

default rule [is] that plaintiffs bear the risk of failing to prove their claims.”147 While the 

Supreme Court has recognized exceptions such as affirmative defenses, the commenter noted 

that courts retain the authority to establish such rules unless Congress acts to delegate that 

authority. In this instance, the commenter said EPA had not provided any statutory authority, nor 

any real justification, for requiring a source to prove its innocence...moreover, to fully 

demonstrate its innocence when reporting the event...without even being charged. The 

commenter suggested that if EPA adopts an approach along the lines of the proposed affirmative 

defense, it should be stated instead in terms that, once a source has claimed that its excess 

emissions were related to a malfunction, it will not be considered to be in violation of the 

standards unless the enforcement authority demonstrates that the source is not entitled to claim 

the malfunction.

Furthermore, according to commenter 0061, EPA offered no defensible rationale for excluding 

S/S events from the proposed affirmative defense. As the commenter noted above, EPA has for 

decades recognized in NSPS regulations that it may not be possible to meet normally applicable 

emission limitations, even using the best demonstrated technology, during SSM events. The 

commenter argued that, if EPA persisted in its proposal not to provide separate emission 

limitations for S/S of regulated units, and if in fact excess emissions from those units could not 

reasonably be avoided during a S/S event, not because of failure of a process or equipment but 

because of the nature of conditions while starting up or shutting down the source, there is no 

justification for EPA not to provide the same kind of affirmative defense that it proposes to 

provide for malfunctions. The commenter noted EPA’s statement that, through analysis of 

“numerous continuous opacity and TRS monitoring data sets that included periods of startup and 

shutdown...the affected units will be able to comply with the proposed standards at all times,”148

 

147 Shaeffer v. Weast, 546 U.S. 49 (2005), quoting McCormick on Evidence §337, at 412 (“The burdens of pleading 

and proof with regard to most facts have and should be assigned to the plaintiff who generally seeks to change the 

present state of affairs and who therefore naturally should be expected to bear the risk of failure or proof or 

persuasion”); C. Mueller & L. Kirkpatrick, Evidence §3.1, p. 104 (3d ed. 2003) (“Perhaps the broadest and most 

accepted idea is that the person who seeks court action should justify the request, which means that the plaintiffs 

bear the burdens on the elements in their claims”).

148 See 78 FR 31328.
88

and said that, even if this assumption is true, it would not justify excluding startup and 

malfunction events from the affirmative defense, to cover those situations where the S/S event is 

of such a duration or magnitude that it causes an exceedance of the emission limitation.

Commenter 0061 maintained that, even if the proposed affirmative defense were not 

unreasonably restrictive, as discussed below, being able to assert a defense obviously is not the 

same as being able to comply with emission limitations that properly reflect the limitations of

available technology as required by CAA section 111. The commenter pointed out that, although 

a source believes it qualifies for the affirmative defense, it may be considered to have violated 

the standards—and may have to report violations, certify noncompliance, etc.—until there has 

been an enforcement proceeding and the source has successfully asserted the affirmative defense. 

The commenter contended that the affirmative defense places the source in the position of 

proving its innocence, rather than EPA or another enforcement authority having to prove that the 

source violated the CAA.149

Furthermore, commenter 0061 remarked that it is not even clear what the affirmative defense 

covers. The commenter noted that, in the proposed rule, EPA states that the affirmative defense 

is “to civil penalties that are caused by malfunctions.”150 The commenter inquired whether the

term “civil penalties,” which was not defined in the proposed rule, was intended to apply as well 

to a “civil administrative penalty” imposed by EPA under CAA section 113(d). (The commenter 

noted that the term “civil penalty” in other contexts means only penalties imposed by a court.)

The commenter also inquired whether the affirmative defense applies to “noncompliance 

penalties” under CAA section 120 (which apply, inter alia, to noncompliance with a section 111 

NSPS). According to the commenter, in order to meet the purported purpose of the affirmative 

defense, which is to provide relief from emission limitations that cannot be met at times even 

with equipment that is properly designed and maintained,

151 the affirmative defense would need 

to apply to civil and administrative penalties, including noncompliance penalties.152

Commenter 0061 remarked that it is also unclear how the affirmative defense would apply to 

enforcement actions by state and local governments, or to private citizen enforcement actions

under CAA section 304. The commenter noted that the preamble to the proposed rule, for 

example, spoke only in terms of application of the affirmative defense in an EPA enforcement

action.153 The commenter said that an affirmative defense should clearly state that it is applicable 

to enforcement actions by states or citizen-suit plaintiffs, as well.

 

149 See, e.g., Portland Cement, 486 F.2d at 398 n.1 (enforcement discretion is not a lawful means of curing rules that

create uncertain compliance obligations).

150 See, e.g., 78 FR 31322, 31329, 31330.

151 See id. at 31329.

152 EPA states that, if a source cannot prove its entitlement to the affirmative defense, “appropriate penalties could 

be assessed in accordance with section 113 of the CAA (see also 40 CFR 22.77).” 78 FR 31329, col.3. This does not 

answer the questions stated above. Moreover, there is no “part 22.77” in the July 1, 2012, edition of Title 40 of the 

Code of Federal Regulations. The proposed rule, therefore, is unclear on this key issue of what the affirmative 

defense is intended to cover.

153 See 78 FR 31329, col.3 (“In any judicial or administrative proceeding, the Administrator may challenge the 

assertion of the affirmative defense....”) (emphasis added).
89

Regarding the statement in the proposed rule that “The affirmative defense shall not be available 

for claims for injunctive relief,”154 commenter 0061 noted that the preamble to the proposed rule 

gave no explanation for why the affirmative defense would not apply to injunctive relief.155

According to the commenter, if the excess emissions associated with the equipment or process 

failure are not reasonably preventable, then there is no apparent reason why injunctive relief 

should not be available either.156 The commenter noted that, in fact, as a matter of law, injunctive 

relief may not be available in cases where a civil penalty cannot be imposed.157

Commenters 0059 and 0061 stated that EPA’s plan to limit the affirmative defense to civil 

penalties only and maintain liability for injunctive relief renders the affirmative defense 

inadequate for the purpose EPA has claimed. Since injunctive relief would be available even 

where a malfunction was unavoidable despite installation and operation of the identified “best” 

control technology, the commenters argued that mills still would be subject to enforcement 

action, including citizen suits, and liability for remedial action and citizens group attorneys’ fees, 

under emission standards that are supposed to be achievable using demonstrated technology. 

Consequently, the affirmative defense would not accomplish EPA’s stated objective of providing 

relief in situations where the emission limitations cannot be met despite proper design and 

operation of process and control equipment. For the affirmative defense to provide relief from

violations that were unavoidable with the specified technology, the commenters said it cannot be 

limited to civil penalties alone.

Commenter 0061 contended that EPA had not addressed these and other apparent limitations and 

shortcomings of the affirmative defense, which the commenter said made it an inadequate 

substitute for setting NSPS that include provisions for SSM events. Commenter 0059 contended 

that EPA’s proposal to allow an affirmative defense to civil penalties for a malfunction, if the 

source can meet extensive criteria, does not cure the Agency’s failure to set NSPS that are 

achievable in the first place. According to both commenters, EPA had provided no analysis that 

would supersede its long-standing determination that it is not desirable to rely on enforcement, 

rather than regulatory language, to address the inability to comply with technology-based 

standards during SSM events.158 The commenters said that the courts have adopted the same 

view.159,160,161

 

154 Proposed §60.286a.

155 See 78 FR 31330.

156 EPA does not explain how excluding injunctive relief from the affirmative defense would in practice achieve any 

greater protection of air quality. The affirmative defense is only available in the first place where the problem was 

sudden, unpredictable, beyond the control of the operator, incapable of being avoided by better design or operation 

and maintenance, expeditiously repaired, etc. Under those particular circumstances, it is hard to see what the basis 

would be for a court to impose injunctive relief. Nor is it apparent how a court order, issued long after the event but 

directed at these unavoidable, unpredictable circumstances, would improve air quality or otherwise implement 

requirements of the CAA.

157 See Sierra Club v. Otter Tail Power Co., 615 F.3d 1008 (8th Cir. 2010) (under concurrent remedy doctrine, 

injunctive relief for a CAA violation is barred when civil penalty is barred by statute of limitations).

158 See 37 FR 17214 (Aug. 25, 1972) (establishing SSM provision in NSPS).

159 See National Lime, 627 F.2d at 431 n.46 (the promised flexibility in enforcement “will not render ‘achievable’ a 

[NSPS] which cannot be achieved on a regular basis, either for the reasons expressly take into account in 

compliance determination regulations (here startup, shutdown and malfunction), or otherwise.”).

160 See also Marathon Oil Co. v. EPA, 564 F.2d at 1253, 1273 (9th Cir. 1977) (explaining why EPA’s proffered 

assurances that it would not take enforcement action against sources that exceeded effluent limitations because of 
90

At a minimum, commenter 0061 recommended that EPA should state that the affirmative 

defense applies to civil penalties, civil administrative penalties, noncompliance penalties, and 

injunctive relief, in an action brought by EPA, a state, or a citizen-suit plaintiff. The commenter 

recommended that EPA also should revise the “affirmative defense,” so that it states that a 

source “will not be deemed in violation of” the NSPS for excess emissions or other deviations 

from the standards, associated with a startup, shutdown, or malfunction event, unless the event, 

and the source’s response to the event, do not meet the criteria spelled out in the regulations.162

The commenter argued that, configured in that way, this provision should be called something

other than an “affirmative defense,” such as an “alternative standard for SSM events.”

Like commenters 0059 and 0061, commenter 0056 also argued that EPA’s affirmative defense

approach for excess emissions during periods of malfunction is flawed. Commenter 0056 said 

that EPA, rather than structure a discrete and achievable emissions standard for malfunction

events, had instead placed those events in a netherworld where the emission limitations 

otherwise applicable during normal operating conditions may or may not be enforced depending 

on how well a facility meets, in EPA’s eyes, a broad and mixed set of precise quantitative 

conditions and actions with “eye-of-the-beholder” qualitative conditions. The commenter also 

noted that EPA provided an affirmative defense provision against civil penalties that requires a 

“preponderance” of evidence to support.163 According to the commenter, the affirmative defense

policy EPA proposed to codify as potential legal protection when malfunctions lead to emissions 

that exceed standards, does not adequately address the issue. On its own, the commenter said the 

policy is overly complex in its documentation and reporting requirements that would be difficult, 

if not impossible, to meet during extreme or catastrophic malfunction events. The commenter 

said the policy also is objectionable in that it shifts to the operator the burden of proof, turning 

the doctrine of “innocent until proven guilty” on its head.

Response: The EPA disagrees with comments regarding our decision to use affirmative defense 

provisions to address malfunction events. To assure continuous compliance for periods of 

malfunction, we added affirmative defense provisions to subpart BBa.

 

upset events was “not an adequate response” to the argument that standards that cannot be met during unavoidable 

upsets fail to reflect available technology).

161 Commenter 0061noted that they are not suggesting that EPA lacks authority to include an affirmative defense

provision in NSPS, but rather that doing so is not an adequate substitute for establishing NSPS that are achievable 

under anticipated operating conditions in the first place. The EPA has broad discretion in how it fashions NSPS. The 

EPA can carve out types of sources or circumstances that do not have to meet the emission limitations that would 

otherwise be imposed by an NSPS, and it frequently has. See, e.g., exemptions for engines in certain uses in the 

NSPS for Compression Ignition Internal Combustion Engines, §60.4200; exemption from control requirement for 

BSWs at mills where controls would be technologically or economically infeasible, §60.283. Using work practice 

standards under section 111(f) is also a way that EPA sometimes has provided relief from compliance with certain

numerical standards. Contrary to objections that some have raised to affirmative defense language in NESHAPs, 

EPA does not usurp the role of the courts in enforcing emission standards when EPA includes an affirmative defense 

provision in those emissions standards; it simply is designing those emission standards so that they will, in EPA’s 

judgment, meet the letter and intent of the relevant statutory requirement.

162 Cf., e.g., 40 CFR 80.613 (stating that persons demonstrating specified defenses “will not be deemed in violation” 

and are not “deemed liable for a violation” of diesel fuel sulfur program regulations).

163 See 78 FR 31329.
91

The EPA disagrees with comments that we failed to set “emission limitations that have been 

adequately demonstrated to be achievable through use of the best control technology.” As noted 

previously, the affirmative defense provisions give the EPA the flexibility to both ensure that its 

emission standards are “continuous,” as required by 42 U.S.C. 7602(k), and account for 

unplanned upsets and thus support the reasonableness of the standard as a whole.

The EPA also disagrees with comments that criticize the affirmative defense for shifting the 

burden of proof. The affirmative defense does not require a facility to prove its innocence instead 

of requiring an enforcement authority to prove a violation of the CAA or change the burden of 

proof with respect to establishing a violation. The affirmative defense applies to penalties and 

thus is only utilized where a violation has been established. The burden of proof remains with the 

plaintiff in an enforcement action.164 If a violation has been established and a source wishes to 

assert the affirmative defense with respect to penalties, the source does bear the burden of 

establishing that the elements of the affirmative defense have been met. This burden-shifting is 

appropriate because the source is in a better position to determine the facts required to establish 

the defense.165

The EPA further disagrees that we have offered “no defensible rationale for excluding S/S events 

from the proposed affirmative defense.” As explained in the preamble, the EPA believes that 

malfunction events should be treated differently than periods of S/S, which are predictable and 

routine aspects of a source’s operations. In contrast, the EPA has determined that CAA section 

111 does not require that emissions that occur during malfunctions be factored into development 

of CAA section 111 standards. Because S/S periods are part of a source’s normal operations, the 

same approach to compliance with, and enforcement of, applicable emissions standards during 

those periods should apply as otherwise applies during a source’s operations. Further, as 

explained above, periods of S/S—but not malfunctions—are taken into account when 

establishing section 111 emissions standards. For these reasons, the EPA does not believe it is 

appropriate to apply the affirmative defense provision to S/S periods. Additionally, this argument 

is not accurate since malfunctions that occur during S/S would be eligible for coverage under the 

affirmative defense. Consequently, the EPA is promulgating the affirmative defense for 

malfunctions only, not for periods of S/S.

The commenter correctly observes that the affirmative defense provisions do not relieve a source 

from any reporting obligations required by the standard or noncompliance certifications under 

the CAA. Sources are required to comply with the standards at all times, including periods of 

malfunction. To the extent a source experiences a malfunction that causes the source to exceed 

the excess emission allowances defined in §60.284a(d) and (e), the source is in noncompliance 

and subject to penalties unless the source demonstrates that the affirmative defense applies. The 

source will need to include in its malfunction report the additional calculations and an 

explanation to demonstrate that the source complied with the standard notwithstanding the 

malfunction event.

 

164 See, e.g., 40 CFR 22.24.

165 See, e.g., Arizona Pub. Serv. Co. v. EPA, 562 F.3d 1116, 1120, 1129-30 (10th Cir. 2009) (rejecting industry

challenge to the EPA’s use of an affirmative defense to address excess emissions during malfunction events).
92

The commenter indicates the coverage of affirmative defense or its applicability to injunctive 

relief is not clear. The affirmative defense applies to civil penalties, including civil 

administrative penalties and penalties under section 120, but does not apply to injunctive relief or 

criminal penalties. The affirmative defense is available in any civil action to enforce the 

standards set forth in this rule, whether such action is brought by EPA, a state or local authority 

or a citizen. The EPA agrees that in some cases, injunctive relief may not be appropriate if all the 

criteria of the affirmative defense have been satisfied. In such cases, liability for attorney’s fees 

is not a real issue. However, some form of injunctive relief may be appropriate. The Sierra Club 

v. Otter Tail Power Co. case cited by commenters is not on point and does not undermine EPA’s 

ability to limit the affirmative defense to penalty claims. The concurrent remedy doctrine 

provides that where a party's legal remedies are time-barred, a party's concurrent equitable 

claims generally are barred. The affirmative defense is not a time-bar to civil penalties. The EPA 

does not intend to provide an affirmative defense to criminal charges, as the very nature of 

criminal charges is that there is alleged to be a knowing violation (CAA section 113(c)(1) 

through (3)), or a knowing or negligent release that threatens imminent danger to persons (CAA 

section 113(c)(4) and (5)). In these circumstances, it is likely that the source did not do all that 

could be done to prevent the excess emissions. However, if there are circumstances that justify a 

knowing release, such circumstances can be raised in any enforcement action and may be the 

basis for a defense. The affirmative defense is available in any action to enforce the standards set 

forth in this rule, whether such action is brought by EPA, a state or local authority or a citizen. 

Although the preamble‘s reference to the ‘Administrator’ may have caused some confusion, 

there is nothing in the language of the regulatory text establishing the affirmative defense that 

suggests that the affirmative defense is limited to EPA enforcement actions.

The commenter indicates that coverage of affirmative defense to private citizen actions under 

CAA section 304 is unclear. The EPA’s view is that the affirmative defense is consistent with 

CAA section 304, as well as section 113(e). Section 304 gives district courts jurisdiction “to 

apply appropriate civil penalties.” Section 113(e)(1) identifies the factors that the Administrator 

or a court shall take into consideration in determining the amount of a penalty to be assessed 

only after it has been determined that a penalty is appropriate. The affirmative defense regulatory 

provision is not relevant to the amount of any penalty to be assessed under section 113(e), 

because if a court determines that the affirmative defense elements have been established, then a 

penalty is not appropriate, and penalty assessment pursuant to the section 113(e)(1) factors does 

not occur. In exercising its authority under section 111 to establish emission standards (at a level 

that meets the stringency requirements of section 111), the EPA necessarily defines conduct that 

constitutes a violation. The EPA’s view is that the affirmative defense is part of the emission 

standard and defines two categories of violation. If there is a violation of the emission standard 

and the source demonstrates that all the elements of the affirmative defense are met, only 

injunctive relief is available. All other violations of the emission standard are subject to 

injunctive relief and penalties. The CAA does not require that all violations be treated equally. 

Further, a citizen suit claim under section 304 allows citizens to commence a civil action against 

any person alleged to be in violation of “an emission standard or limitation under this chapter.” 

The CAA, however, allows the EPA to establish such “enforceable emission limitations.” Thus, 

the citizen suit provision clearly contemplates enforcement of the standards that are defined by 

the EPA. As a result, where the EPA defines its emissions limitations and enforcement measures 

to allow a source the opportunity to prove its entitlement to a lesser degree of violation (not 
93

subject to penalties) in narrow, specified circumstances, as the EPA did here, penalties are not 

“appropriate” under section 304. The EPA’s view is that an affirmative defense to civil penalties 

for exceedances of applicable emission standards during periods of malfunction appropriately 

balances competing concerns. On the one hand, citizen enforcers are concerned about additional 

complications in their enforcement actions. On the other hand, industrial sources are concerned 

about being penalized for violations caused by malfunctions that could not have been prevented 

and were otherwise appropriately handled (as reflected in the affirmative defense criteria). The 

EPA has utilized its section 301(a)(1) authority to issue regulations necessary to carry out the 

Act in a manner that appropriately balances these competing concerns.

The EPA disagrees with the statement that we are relying “on enforcement, rather than 

regulatory language, to address the inability to comply with technology-based standards during 

SSM events.” EPA‘s approach to malfunctions goes further than reliance on the informal 

exercise of enforcement discretion, in that it includes regulatory provisions establishing an 

affirmative defense to civil penalties for exceedances of emission limits that are caused by 

malfunctions. Regarding Marathon Oil, the Court clearly states the following in its opinion

regarding an affirmative defense: “here the EPA does not rely on enforcement discretion alone, 

but specifically promulgates an affirmative defense in the FIP, which clearly defines the 

requirements to avoid penalties.” The affirmative defense comports with the court‘s suggestion 

in Marathon Oil that EPA place the burden on the permit holder of producing the relevant data 

and proving that the upset could not have been prevented.

4.3-03 Comment: Commenter 0061 argued that the proposed affirmative defense as written is 

unreasonable and impracticable. According to the commenter, if EPA refuses to set alternative 

emission standards that apply during SSM periods and continues to rely instead on the proposed 

affirmative defense, the affirmative defense must be substantially modified for it to provide any 

significant relief. First, as noted above, the commenter said the affirmative defense needs to state 

clearly that a source that qualifies for the affirmative defense shall not be deemed to have 

violated the applicable standards during that time. The commenter indicated that if EPA does 

that, it may be unnecessary to state also that the affirmative defense relieves the source from 

liability for all types of penalties and injunctive relief (save criminal penalties), but that should 

be the clear effect of qualifying for the affirmative defense.

Commenter 0061 suggested that affirmative defense should be available not only for 

malfunctions, but also for excess emissions, if any, during S/S. As the commenter stated above, 

there is no logical reason why a source that experiences excess emissions during S/S periods that 

were not reasonably preventable (either because the source experienced conditions EPA did not 

anticipate in setting the standards, or because EPA’s assumption about the achievability of those 

standards during S/S periods was wrong) should be excluded from the affirmative defense.

Commenter 0061, with the support of commenter 0059, argued that many aspects of the 

affirmative defense would make it unavailable as a practical matter for many, if not most 

malfunctions. According to commenter 0061, many of the limitations on the affirmative defense 

are not directly related to the question of whether an exceedance of the emission limitations due 

to a malfunction should be excused. Commenter 0061 further stated that EPA needs to 

substantially revise and streamline the proposed affirmative defense for it to be of practical 

value. Commenters 0059 and 0061 both noted that EPA has estimated that there will be no more 
94

than two instances of a mill seeking to avail itself of the affirmative defense during the first 3

years after the subpart BBa standards are promulgated.166 Commenter 0061 argued that this is 

inconsistent with EPA’s recognition of the fact that mills with the identified technology still will 

experience unavoidable exceedances from time to time, and its estimate that nearly 20 emission 

units will be subject to subpart BBa during that period.167 According to commenters 0059 and 

0061, EPA’s assumption that those mills will not even attempt to invoke the affirmative defense 

even once a year is a clear indication that the affirmative defense as proposed fails entirely to 

meet the statutory requirement that NSPS be set at a level that facilities will be able to meet with 

the identified control technology.

According to commenter 0061, several of the conditions for establishing an affirmative defense 

in proposed §60.286a list numerous items which may be appropriate considerations in 

determining whether excess emissions during a malfunction should be considered a violation, but 

which ought not to be listed as mandatory criteria, all of which have to be met in order for an

exceedance to be excused. For example, the commenter cited proposed §60.286a(a)(1)(i), which 

requires that the excess emissions must have been “caused by a sudden, infrequent, and 

unavoidable failure of air pollution control and monitoring equipment, process equipment, or a 

process to operate in a normal or usual manner....” The commenter remarked that there is no 

apparent reason why a “sudden” and “unavoidable” equipment failure or process upset leading to 

emissions greater than the NSPS should be considered a violation of the standards if it is not 

“infrequent,” even though it is “not part of a recurring pattern indicative of inadequate design, 

operation, or maintenance” and “[c]ould not have been prevented through careful planning, 

proper design or better operation and maintenance practices.”168

Commenter 0061 noted that a number of the conditions for establishing an affirmative defense 

use phrases that are subject to a wide range of interpretations, and that on their face do not 

recognize any need for reasonableness or cost-effectiveness. The commenter inquired how the 

enforcement authority, or a judge, would determine whether “proper design” or “better operation 

and maintenance practices” could have prevented a malfunction (§60.286a(a)(1)(ii)), whether a 

recurring malfunction is a result of “inadequate design” (§60.286a(a)(1)(iv)), whether repairs 

were made “as expeditiously as possible” (§60.286a(a)(2)), whether the source took “all possible 

steps” to minimize the impact of the excess emissions (§60.286a(a)(5)), and whether emissions 

monitoring and control systems “were kept in operation if at all possible” (§60.286a(a)(6))? The 

commenter contended that affirmative defense, as proposed, leaves open the possibility that a 

source will be considered to be in violation because the enforcement authority decides that in one 

or more respects it would have been “proper” or “possible” for the source to take further steps to 

prevent or minimize the malfunction. According to the commenter EPA or the court may, in 

effect, impose an extreme version of best demonstrated technology, during malfunction periods. 

The commenter contended that the vague and unqualified descriptors in the criteria for 

demonstrating the affirmative defense will, at a minimum inevitably lead to varying conclusions 

as to whether a violation has occurred, resulting in inconsistency from one jurisdiction to the 

next.

 

166 See 78 FR 31333.

167 See 78 FR 31332.

168 See §60.286a(a)(1)(ii) and (iv).
95

Noting that proposed §60.286a(a)(6) requires, as a condition for the affirmative defense, that all 

emissions “control systems were kept in operation if at all possible,” commenter 0061 argued 

that the phrase “if at all possible” should not be used because it is an extreme term that bears no 

relation to good air pollution control practices. The commenter also argued that this provision 

should be qualified, as EPA has qualified similar provisions in the NSPS General Provisions in 

40 CFR 60.11(d) and the NESHAP General Provisions in 40 CFR 63.6. As an example, the 

commenter advised that these conditions should be qualified with caveats that the operation must 

be consistent with safety and good air pollution control practices, that it does not require the 

source to make further efforts to reduce emissions below what the standards require, and that it 

does not require regular operation of backup or standby pollution control equipment.169

According to the commenter, EPA has long recognized, in the General Provisions applicable to 

NSPS, that it is appropriate to require sources to operate the affected facility and related air 

pollution control technology “to the extent practicable ... consistent with good air pollution 

control practice for minimizing emissions” during SSM periods, not “if at all possible.”170 The 

commenter argued that EPA cannot abandon those rational approaches and adopt the kind of 

absolute requirements implied by the proposed rule, without an explanation of why it is 

necessary and appropriate to do so.

According to commenter 0061, proposed §60.286a(a)(4) would preclude a facility from taking 

advantage of the affirmative defense if the malfunction involved bypassing control equipment or 

a process and the bypass was not “unavoidable to prevent loss of life, personal injury, or severe 

property damage.” The commenter argued that this language is stated in such strong terms that it 

may be difficult or impossible for a source to demonstrate that it met this criterion, even though 

bypassing the control equipment or the process was an appropriate exercise of good air pollution 

control practices. As an example, the commenter noted that a bypass can constitute the best air 

pollution control practice in response to an upset in order to prevent excess emissions, e.g., to 

avoid fouling of pollution control equipment media that in turn would result in reduced pollution 

control equipment efficiency or increased pollution control equipment downtime. The 

commenter noted that there can be substantial room for disagreement about what constitutes 

“severe” property damage. Besides the unclear and subjective nature of these criteria, the 

commenter said there is nothing inherent to standards of performance under CAA section 111 

that requires a source to avoid bypassing control equipment to such a degree. Lastly, the 

commenter contended that it is not apparent at all why the CAA would disfavor bypassing “a 

process”—as opposed to pollution control equipment—in this way.

Commenter 0061 noted that, under proposed §60.286a(a)(5), a source claiming the affirmative 

defense must prove that “[a]ll possible steps were taken to minimize the impact of the excess 

emissions on ambient air quality, the environment and human health.” In addition to the 

subjective term “all possible steps,” the commenter argued that this provision again presents a 

disconnect between the absolute and extreme requirement of the affirmative defense and the 

 

169 See, e.g., 40 CFR 63.483(a), 76 FR 22566, 22583, 22588 (April 21, 2011), where EPA agreed it was appropriate 

to include such a qualifier in comparable language in NESHAPs: “The general duty to minimize emissions does not 

require the owner or operator to make any further efforts to reduce emissions if levels required by this standard have 

been achieved.” EPA also determined it was appropriate to include those kinds of caveats in its regulation requiring 

proper operation and maintenance of wastewater treatment facilities, in 40 CFR 122.41(e).

170 See 40 CFR 60.11(d).
96

provisions of the CAA designed to attain ambient air quality standards and protect human health 

and the environment. Commenter 0061 argued that the CAA does not require sources to take “all 

possible steps” to control emissions; the commenter pointed out that, even for HAPs, the CAA 

specifies a level below which further reductions are not required.171 In addition, the commenter 

said it is unclear how this criterion for qualifying for the affirmative defense differs from 

proposed §60.286a(a)(3), which requires that the frequency, amount, and duration of excess 

emissions “were minimized to the maximum extent practicable.” Unless EPA explains what 

additional showing would be needed by §60.286a(a)(5), the commenter recommended that it 

should be eliminated.

According to commenter 0061, the requirement proposed in §60.286a(a)(8)—that the source 

must show that “[a]t all times, the affected source was operated in a manner consistent with good 

practices for minimizing emissions” (emphasis added)—could be read to go way beyond an 

analysis of why equipment may have malfunctioned and place an overwhelming burden on the 

source to meet a “good practices” standard (undefined) for the whole industrial plant or 

commercial premises. The commenter pointed out that this factor potentially could allow a 

regulatory enforcement official to judge the entirety of operations at a site against a multitude of 

arbitrary “good practices” and subjectively find the stationary source lacking, thereby denying 

the source the ability to assert an affirmative defense for NSPS applicable to a particular 

operation at the site. If EPA retains this condition for the affirmative defense, of demonstrating 

operation consistent with good practices for minimizing emissions, the commenter insisted the 

Agency must clarify that this condition applies to the “affected facility,” as that term is defined 

in 40 CFR 60.2. If EPA really does intend for this condition to apply to operation of the entire 

site, and not just “the apparatus to which a standard is applicable,”172 the commenter insisted that 

EPA must explain why it has the statutory authority to shift the focus of the proposed standards 

from the apparatus subject to the NSPS to the plant as a whole. The commenter indicated that 

this does not appear to be EPA’s intention, however, since, in apparent response to their 

comments, EPA changed the similar provision in the final NSPS for Nitric Acid plants to read 

“the affected facility was operated,” rather than “the affected source was operated” in a manner 

consistent with good practices for minimizing emissions.173

Commenter 0061 argued that the requirement in proposed §60.286a(a)(9) that the source prepare 

a “written root cause analysis...to determine, correct, and eliminate the primary causes of the 

malfunction and the excess emissions resulting from the malfunction event at issue” again does 

not implement the statutory criteria for standard-setting under section 111. The commenter said 

that read literally, the provision would mean that a source could never take advantage of the 

affirmative defense if the source was unable to determine the primary cause of the malfunction 

or was unable to correct that cause. Noting that EPA has defined a malfunction as an event that is 

“unavoidable” and unforeseeable, and “not reasonably preventable,”174 the commenter said that 

it, therefore, may not always be possible to identify and address the specific causes of the 

 

171 See CAA sections 112(d) and (f).

172 See 40 CFR 60.2 definition of “affected facility.”

173 See 40 CFR 60.74a(a)(8), 77 FR 48433, 48447 (Aug. 14, 2012).

174 See proposed §60.286a(a)(1)(i) and (iii) and 40 CFR 60.2.
97

malfunction or the excess emissions associated with it.175 The commenter also noted that 

requiring the facility to eliminate the primary causes of the malfunction, without regard to 

“taking into account the cost of achieving such” elimination and the “nonair quality health and 

environmental impact and energy requirements” associated with its elimination is unreasonable 

and entirely inconsistent with the criteria for NSPS established under CAA section 111(a)(1).176

Commenter 0061 also reported as unreasonable and unnecessary the requirement in proposed 

§60.286a(b) to submit a written report to the Administrator “with all necessary supporting 

documentation,” indicating that the source met all of the multitude of criteria for the affirmative 

defense, which report is to be included in the first periodic compliance, deviation or excess 

emission report. The commenter stated that it is novel at best for a person to be determined to 

have acted unlawfully unless the person has submitted his or her entire defense before he or she 

is even notified of a potential enforcement action. The commenter argued that, in many cases, it 

would be obvious to the enforcement authority, based on the kind of short malfunction or 

deviation report sources already submit under many air programs, that an exceedance of the 

proposed standards resulted from an unforeseen and unavoidable equipment failure or process 

upset. According to the commenter, it is extremely inefficient and burdensome, for both sources 

and regulators, to require a complete justification of the affirmative defense before the 

enforcement authority has indicated any need for further investigation.

Commenter 0061 noted that, according to proposed §60.286a(b), if the compliance, deviation or 

excess emission report is due less than 45 days after the initial occurrence of the violation, the 

affirmative defense report may be included in the second compliance deviation report or excess 

emission report due after the initial occurrence of the violation of the relevant standard. The 

commenter noted that the proposed minimum 45-day period for submitting a written report 

demonstrating that the source qualifies for the affirmative defense commences on the date of “the 

initial occurrence of the exceedance of the standard.”177 The commenter said this presents several 

problems. According to the commenter, much of the required content of that written report could 

not be created until the malfunction event ceased—which could be days or even weeks after the 

malfunction commenced. The commenter said this could make the amount of time the source 

would have, in practice, to prepare the report much less than it might seem.

Response: We disagree with the commenter’s statement that qualification for affirmative 

defense should absolve a source from any violation of the applicable standard. That is not our 

intent. Sources are required to comply with the standards at all times, including periods of 

 

175 EPA has long acknowledged this reality in the General Provisions applicable to NSPS, which require that written 

reports of excess emissions include the “nature and cause of any malfunction, if known....” See 40 CFR 60.7(b)(2)

(emphasis added).

176 For example, it might be theoretically possible to eliminate the excess emissions associated with the malfunction 

by installing totally redundant pollution control equipment, or pollution control equipment with far more capacity 

than needed for normal operations. But this would not reflect control technology that has been “adequately 

demonstrated,” nor would the NSPS take cost and other factors into consideration as the statute requires. On the 

other hand, even with redundancy and extra capacity certain sources can incur malfunctions that would result in 

excessive emissions. Moreover, the proposed requirement to eliminate “the primary causes of the malfunction” and 

not just to eliminate “the excess emissions resulting from the malfunction event” lies entirely outside of EPA’s 

authority under the CAA, which is limited to establishing and enforcing emission limitations, not dictating plant 

operations.

177 See proposed §60.286a(b).
98

malfunction. To the extent a source experiences a malfunction that causes the source to exceed 

the excess emission limits defined in §§60.284a(d) and (e), the source is in noncompliance and 

subject to penalties unless the source demonstrates that the affirmative defense applies. If there is 

a violation of the emissions standard and the source demonstrates that all the elements of the 

affirmative defense are met, only injunctive relief is available.

The commenter appears unclear about the availability of an affirmative defense during S/S. As 

stated above, the affirmative defense is available for malfunctions that occur during S/S and 

during the normal course of operations.

We do not agree with the opinion that our estimate on the future use of the affirmative defense in 

subpart BBa indicates that it is not a practical standard. Rather, we believe that our proper 

application of BSER serves to limit the circumstances where the affirmative defense might apply 

to events that are significant malfunctions, with excess emissions defined in §§60.284a(d) and 

(e). The NSPS excess emission definitions were reviewed using ICR data collected at the bestcontrolled sources. Consequently, we do not believe that the affirmative defense will be 

frequently applicable since new, reconstructed and modified sources will need to employ control 

technology already in use at the best sources and the prospect of the affirmative defense assures 

that these control systems will be properly maintained.

The commenter questions the use of several terms and phrases used to describe circumstances 

characterizing malfunctions eligible for the affirmative defense – ‘sudden,’ ‘infrequent,’ ‘proper 

design,’ ‘better operation and maintenance practices,’ ‘unavoidable to prevent loss of life, 

personal injury, or severe property damage,’ ‘all possible steps,’ ‘good practices,’ etc. The 

commenter describes these phrases as vague, unqualified descriptors and “extreme terms” that 

should not become mandatory criteria. The commenter expresses concern that terminology will 

be applied inconsistently. We disagree. These words and phrases provide parameters needed to 

facilitate assessments made by delegated authorities responsible for determining the 

reasonableness of an affirmative defense claim. Contrary to the commenters concerns, these 

terms have a successful history of consistent application. Many were modeled after the 

conditions of the affirmative defense in EPA‘s 1999 SIP SSM policy, which several states have 

adopted into their SIPs. We do not have any indication that parties to enforcement proceedings 

have had any significant difficulties applying the terms of these SIP affirmative defenses. Other 

conditions are modeled after a FIP promulgated by EPA.178 The EPA’s view is that use of 

consistent terms in establishing affirmative defense regulations and policies across various CAA 

programs will promote consistent implementation of those rules and policies. The EPA disagrees 

with suggestions that it is unnecessary to satisfy all of the requirements of the affirmative 

defense. As noted above, the requirements set forth in the affirmative defense provisions are 

modeled after the conditions of the affirmative defense in EPA’s SIP SSM policy. Additionally, 

affirmative defense provisions are now in multiple rules, and EPA has both received comment 

and made reasonable adjustments to the terms we have proposed.179 The EPA disagrees that 

other terms and conditions in §60.286a or in the other conditions of the affirmative defense are 

overly subjective or extreme or need further qualification. EPA acknowledges that some of the 

criteria may overlap to some extent and under some circumstances but does not believe it is 

necessary to change the requirements. To the extent there is overlap, the same information can be 

 

178 See 40 CFR 50.1312.

179 See, e.g., EPA-HQ-OAR-2009-0559-0171 chapter 15.
99

used to meet the provisions in question. Consequently, we have concluded that establishing these 

parameters for evaluating malfunctions is the best approach to determining eligibility for the 

affirmative defense provisions.

We disagree with the comment on root cause analyses. The EPA believes that a minor 

administrative burden will result in sources analyzing their violative emissions to reduce or avoid 

those emissions in the future, which is an environmental benefit. A root cause analysis is only 

required if a source seeks to assert an affirmative defense. However, such an analysis is 

beneficial in resolving or preventing violations and excess emissions whether the source seeks to 

assert the affirmative defense or not. A root cause analysis is one example of what constitutes 

good air pollution control practices to minimize emissions. A root cause analysis is not required 

for every malfunction - only those malfunctions for which the source chooses to assert an 

affirmative defense. Not every malfunction is so significant that it would require asserting an 

affirmative defense. The EPA believes that sources seeking to minimize emissions will endeavor 

to find out what went wrong anytime there is a minor or major malfunction. The facility should 

decide what level of investigation is needed in each instance. Sources should use appropriate 

techniques of analysis to achieve the desired results and conclusions in the event of a 

malfunction. The EPA joins the commenter in seeking meaningful results which successfully 

identify and address the cause of the malfunction. However, if the malfunction rises to the level 

of one that the source seeks to avail themselves of the affirmative defense, then a root cause 

analysis is required. In the context of section 111, the term “root cause analysis” was used 

generically to imply an analysis of sufficient depth and complexity to indicate whether a 

malfunction did indeed cause a failure to meet a standard, provide sufficient information on the 

nature and causes of a malfunction to determine whether the source had a malfunction that met 

the definition of a malfunction, and whether civil penalties are an appropriate sanction for the 

violation, if one occurred. The term “root cause analysis” is not defined in subpart A (the part 60 

General Provisions) or in the subpart being promulgated, subpart BBa. The EPA did not intend 

to prescribe a specific methodology, given that “root cause analysis” is not a defined term in the 

applicable subparts of part 60.

With respect to the commenter’s suggestions on the timing of the reporting requirements, the 

written reports required to demonstrate that the affirmative defense provisions have been met 

may be submitted electronically, providing the facility with greater flexibility on the timing of 

the reporting requirements. In addition, the facility has the option to submit a request for an 

extension of the deadline for these reports, and this request may also be submitted electronically.

Consequently, we believe the reporting requirements to be reasonable and have decided to 

finalize the reporting requirements as proposed.

We believe affected industries which are making good-faith efforts to meet the standards will on 

the whole welcome a regularized means of informing the Agency in detail of the circumstances 

surrounding unavoidable emission excesses.
100

5. Testing and Monitoring

5.1 Emissions Testing

5.1-01 Comment: Commenters 0058 and 0059 noted that EPA is proposing under subpart BBa

to require initial and repeat CPM emissions testing in conjunction with filterable PM testing, 

citing the lack of CPM data and the need to develop a better understanding of CPM emissions 

from pulp and paper sources. The commenters contended that initial and repeat performance 

testing of CPM may not help address current data gaps, given the unresolved method artifact and 

bias issues associated with the new EPA Method 202. According to the commenters, recent work 

carried out by commenter 0058 has identified several unresolved issues with the new version of 

EPA Method 202, which was promulgated in December 2010. The commenters provided a 

summary of the significant findings from the ongoing technical studies on CPM measurement 

and emissions (with the details provided in an attachment to commenter 0058’s comments). The 

summary items are listed below.

1. Method evaluation studies carried out by commenter 0058 indicate that the new Method 

202 yields train blank values ~6.0 mg. The EPA’s field evaluation study also yielded an 

average train blank of 5.33 mg, with values ranging from 4.6 to 6.2 mg. However, the 

currently promulgated version of Method 202 only allows a maximum blank correction 

of 2 mg. The resulting positive bias associated with subtracting only 2 mg (as opposed to 

the observed ~6.0 mg) can be a significant component of the total CPM measured during 

tests on low-emitting sources.

2. Commenter 0058’s studies on a low-emitting source (natural gas package boiler) using 

the new Method 202 also indicate the potential for positive bias due to the capture of SO2 

in the impingers and subsequent characterization of this SO2 as sulfate (and CPM) in the 

method. The positive biases resulting from (a) the use of an inappropriate blank 

correction and (b) the formation of method artifacts are also relevant for the sources 

covered by this rulemaking.

3. Commenter 0058 recently carried out characterization studies on concurrently collected 

filterable particulate (EPA Method 5–front half) and CPM (new EPA Method 202–back 

half) samples from a DCE recovery furnace. The primary cation captured in the CPM 

train was ammonium, while the anions included sulfate, chloride, and carbonate. By 

comparison, the front half sample did not contain any ammonium, suggesting that the 

ammoniumcaptured in the back-half cannot be attributed to a partial breakthrough of 

filterable particulate. The presence of sodium in the front-half catch, and its absence in 

the back-half catch, further confirms that there was no breakthrough of filterable 

particulate (Na2SO4 particulate is captured on the front-half filter). These results indicate 

the potential for positive bias in CPM measurements in the presence of free ammonia. 

Any free ammonia in stack gases would pass through the front-half filter, react with any 

acid gases to form ammonium sulfate or ammonium chloride, and be characterized as 

CPM during subsequent gravimetric measurements. Ammonium was also identified as 

the predominant cation on CPM filters obtained from wood-fired boilers.

4. Commenter 0058 has also carried out characterization studies on the CPM catches from 

three DCE furnaces and three NDCE furnaces. Ammonium accounted for ~30 percent of 

the total CPM mass captured in two of the three DCE furnaces and 5 to 10 percent of the 
101

total CPM mass in the three NDCE furnaces.180 Ammonium accounted for 15 to 25 

percent of CPM mass collected during sampling on six lime kilns and from 10 to 35 

percent of CPM mass in three SDTs.181 These results indicate the potential for positive 

bias in CPM measurements due to free ammonia: (a) is relevant for the sources covered 

in this rulemaking (recovery furnaces), and (b) merits a more thorough investigation.

Commenter 0058 is carrying out additional CPM method evaluation studies as part of the 

ongoing technical studies program, including (a) identifying the source and extent of SO2 and 

other method artifact biases, (b) comparing the performance of Method 202 against other 

equivalent test methods, and (c) developing modifications to mitigate these issues. Therefore, 

commenters 0058 and 0059 recommended that EPA defer proposing the CPM testing 

requirement until more information on the unresolved method issues becomes available. 

According to the commenters, any CPM data generated in the interim will be of questionable 

quality and will further contribute to the uncertainty surrounding CPM emissions.

Response: The EPA acknowledges and appreciates the independent efforts of commenter 0058 

to improve the implementation of EPA’s reference method for CPM (Method 202). The EPA 

also acknowledges the commenter’s concern with the current implementation of the method by 

the testing community. The EPA is working to address those issues with implementation by the 

testing community and will collect and consider the blank levels in the use of the data. The 

comments listed above (Nos. 1 through 4) are addressed one-by-one in the paragraphs below.

1. Field blanks in this context represent material present in the sampling system that was not 

removed from initial cleaning and material carryover that was not removed when samples 

were collected during serial use of the sampling equipment. The intent of the field blank 

is to alert the tester to residual material beyond that determined to be an inherent 

correction to the method to enable the tester to identify the cause of the residual material 

and implement best practices to minimize this residual. Field blanks reported to EPA 

from the testers using Method 202 range from less than 2 mg per sampling train to more 

than 10 mg. Testing firms that measure less than 2 mg per sampling train of residual 

condensable mass have identified and instituted best practices to routinely maintain this

low residual mass in their field blanks. Proof blanks described in the method can be used 

to determine if a particular tester has an inherent blank or contamination issue that should 

be resolved before routine implementation of this method. The EPA disagrees that the 

excess (greater than 2.0 mg) field blank resulting from commenter 0058’s tests is

attributable to artifacts. The field test data supplied by the commenter do not contain 

documentation that the glassware was heated to over 300oC or that a proof blank was 

performed to verify that particulate residue was not introduced from improper sample 

train preparation. If one assumes that the sample trains were appropriately prepared and 

discounts the lack of documentation, any residue in the field blank is likely to originate 

from either contamination or residual particulate which was not removed during the 

sample train recovery process. Neither the inability to control contamination nor the 

inability to recover all of the PM collected by the sample train is an indication that the 

additional residue is an artifact.

 

180 Unpublished results from NCASI study.

181 See id.
102

2. The EPA acknowledges that Method 202 sampling runs of longer duration accumulate 

additional condensed moisture and run the potential to generate SO2 artifact in much the 

same way as the previous version of Method 202 behaved. The positive biases resulting 

from increased potential for SO2 absorption in the condensed water combined with longer 

exposure to this greater accumulation of moisture can be overcome by periodic removal 

and purging of the moisture as allowed in the method. The EPA recommends that 

commenter 0058 institute this best practice to minimize the impact of the longer sampling 

runs they feel necessary to achieve sensitivities necessary for use of the Method 202

CPM data.

3. The EPA acknowledges that ion characterization studies of filterable particulate and 

CPM samples showed the primary cation captured in the CPM train was ammonium with 

potential balancing anions of sulfate, chloride, and carbonate. The comparison of the ion 

characterization of the filterable and condensable fraction provides an incomplete 

assessment of the stack matrix and how it interacts with the sampling train and 

immediately in the atmosphere. Also, as indicated in several published studies,182 higher 

concentrations of ammonia are known to react quickly with SO2 at ambient temperature 

to form primary ammonium sulfate particulate near or at the stack exit. Therefore, we 

believe Method 202 correctly measures primary ammonia particulate and should be 

characterized as CPM during subsequent gravimetric measurements. We have included

these published studies in our docket for those who are interested in a better 

understanding of this issue.

4. The EPA appreciates information and comparison of reference Method 202 results with 

other “equivalent test methods” to further understand the differences between the 

methods. The EPA eagerly anticipates comparison data to further evaluate the 

performance of Method 202.

The EPA is retaining the requirement to conduct CPM testing in conjunction with filterable PM 

testing for the final rule. This requirement will apply for new, modified, and reconstructed 

recovery furnaces, SDTs, and lime kilns that become subject to subpart BBa over time. As we 

noted in the proposal, the CPM data collected will build experience with implementation of 

Method 202 and will aid in research to develop a broader understanding of CPM emissions from 

pulp and paper combustion sources and to determine mechanisms for reducing CPM. Because 

subpart BBa references Method 202, any improvements to the method that are codified in the 

CFR over time will automatically be referenced in subpart BBa.

5.1-02 Comment: Commenter 0056 supported EPA’s decision to continue basing the PM 

emission limits compliance tests on filterable PM as measured by EPA Method 5. The 

commenter noted that this is the approach used under the current NSPS subpart BB and 

NESHAP subpart MM. The commenter further noted that EPA is not proposing separate 

standards for filterable PM2.5 (“fine PM”), recognizing the limited availability of PM2.5 emission 

data for kraft pulp mill sources, the lack of a reliable method for measuring PM2.5 emissions 

 

182 See, e.g., Burke, J. and Johnson, K., Radian Corp. Ammonium Sulfate and Bisulfate Formation in Air Preheaters.

Prepared for U.S. Environmental Protection Agency. DCN 81-202-187-68-14. February 1981.
103

from sources equipped with wet control devices, and the limited effectiveness of traditional PM 

control technologies in removing filterable PM2.5. Likewise, the commenter noted that EPA is 

not proposing to base limits on condensable PM.183

Response: We acknowledge this comment and appreciate the commenter’s support for 

continuing to base the emission limits on filterable PM measured with EPA Method 5.

5.1-03 Comment: Commenter 0059 noted that EPA has proposed to require repeat testing at 

least once every 60 months for PM and TRS. The commenter requested that, to provide 

operational flexibility, the testing be required once every 5 calendar years, at any time during the 

fifth calendar year.

Response: We agree it is reasonable for facilities to have some operational flexibility in when 

they do the repeat testing and have amended the final rule text to refer to repeat testing every “5 

years.”

5.1-04 Comment: Commenter 0057 stated that the test methods in the proposed rule do not 

address instances in which SDT emission vents consist only of a demister pad with no extending 

stack. In such situations, the commenter indicated that it is impossible to use a Method 5 probe to 

accurately determine the PM emission rate. The commenter suggested that the rule be revised to 

require a stack with a suitable emission point for a Method 5 PM stack test and suitable emission 

test point for TRS emissions.

The commenter also suggested that EPA state what procedures should be used when making a 

Method 5 and/or Method 16, 16a, 16b, or 16c determination during high-aerosol, relatively lowtemperature conditions in SDTs.

Response: Section 60.8 of the NSPS General Provisions specifies performance testing 

requirements. Section 60.8(e)(1) requires that the owner or operator provide sampling ports 

adequate for test methods applicable to such facility including: (i) constructing the air pollution 

control system such that volumetric flow rates and pollutant emission rates can be accurately 

determined by applicable test methods and procedures, and (ii) providing a stack or duct free of 

cyclonic flow during performance tests, as demonstrated by applicable test methods and 

procedures. These General Provisions requirements address the commenter’s concern regarding 

SDT demisters with no extending stack. 

Regarding the commenter’s concern about testing during periods of high-aerosol and lowtemperature conditions within the SDT, we note that §60.8(c), as incorporated into subpart BBa 

and superseded with §60.285a(a), requires that emissions testing be performed under 

representative operating conditions. We also note that testing is performed at the outlet of the 

control device (usually a wet scrubber) that would entrain aerosols from the SDT. Method 5 is a 

widely used method applicable for the determination of PM emissions from stationary sources, 

including those controlled by wet scrubbers. Similarly, Methods 16, 16A, 16B, 16C are 

applicable for SDT scrubber stacks. The EPA is not aware of any reason why these methods

could not be applied under the SDT conditions described by the commenter.

 

183 See 78 FR 31321.
104

5.2 Parameter Monitoring

5.2-01 Comment: Commenter 0056 supported making the monitoring, recordkeeping and 

reporting requirements more consistent with the current subpart MM NESHAP requirements.

Response: We acknowledge the commenter’s support.

5.2.1 Incinerator Parameter Monitoring

5.2.1-01 Comment: Commenter 0055 noted that the EPA is proposing to allow facilities to omit 

5-minute recorded temperature measurements from the 3-hour block averages when no TRS 

emissions are fired and requests comment on the 3-hour averaging time for incinerator 

temperature monitoring, especially as it relates to temperature data recording and averaging 

practices specified for individual mills under the subpart S NESHAP. The commenter agreed

with the 5-minute frequency and the omission of all 5-minute recorded temperature

measurements from the 3-hour block averages when no TRS emissions are fired.

Response: We acknowledge the commenter’s support for our decision to use a 5-minute

frequency for recording temperature measurements. As proposed, the 5-minute temperature 

readings will be used in a 3-hour block average of the incineration temperature. The 3-hour block 

averaging period is consistent with the averaging time many mills use for subpart S NESHAP

compliance. 

We also acknowledge the commenter’s support for omitting the 5-minute recorded temperature 

measurements from the 3-hour block averages when no TRS emissions are fired. We are 

finalizing this provision as proposed in order to account for incinerator warm-up and cool-down 

periods before TRS emissions are generated or when an alternative control device is used.

5.2.1-02 Comment: Commenter 0059 stated that the reference to temperature monitoring for 

incinerators controlling emissions of BLO systems in §§60.284a(b)(1) and 60.287a(b)(3) should 

be removed because NSPS subpart BBa does not require control of black liquor oxidation 

systems.

Response: We agree with the commenter about removing the provisions in §§60.284a(b)(1) and 

60.287a(b)(3) that include BLO systems in the list of processes for which incinerator temperature 

monitoring is required. When subpart BB was reviewed in 1983, the requirement to control TRS 

emissions from BLO systems was rescinded, but BLO systems were erroneously retained in the 

incinerator temperature monitoring provision. The same wording including BLO systems was 

carried over into the proposed subpart BBa. We have removed mention of BLO systems from 

§§60.284a(b)(1) and 60.287a(b)(3) in subpart BBa for the final rule. We have also removed the 

definition of BLO system because this term no longer appears in subpart BBa following its 

removal from §§60.284a(b)(1) and 60.287a(b)(3).

5.2.1-03 Comment: Commenter 0059 noted the following:
105

 Most facilities control TRS emissions from affected digesters, evaporators, BSWs, and 

condensate strippers by ducting the exhaust gases to a combustion device.

 If the gases are ducted to a stand-alone incinerator, temperature monitoring is used to 

ensure the device is operating at a temperature of at least 1200°F.

 If the gases are ducted to a combustion device such as a lime kiln, recovery furnace, or 

power boiler, they are injected either with the primary fuel, with the combustion air, or 

into the flame zone, as allowed.

 The same emissions control scheme is used for HAP emissions control from these 

sources under MACT subpart S, which does not require temperature monitoring when the 

gases are controlled in a lime kiln, recovery furnace, or power boiler, per §63.443(d)(4).

Commenter 0059 recommended that EPA make the clarification in NSPS subpart BBa that 

temperature monitoring is only required when TRS control is achieved in a stand-alone 

incinerator. The commenter cited the 1983 NSPS review BID, which indicated that there is no 

need to monitor combustion temperature from devices other than an incinerator because these 

devices normally operate at temperatures higher than 1200°F.184

The commenter suggested the clarification be made as follows:

§60.284a(d)(3)(ii): All 3-hour block averages during which the combustion temperature 

at the point of incineration is less than 650°C (1200°F), where the provisions of 

§60.283a(a)(1)(iii) apply and an incinerator is used as the combustion device. 

§60.287a(b)(3): Records of the incinerator combustion temperature at the point of 

incineration of effluent gases which are emitted from any digester system, brown stock 

washer system, multiple effect evaporator system, black liquor oxidation system, or 

condensate stripper system where the provisions of §60.283a(a)(1)(iii) apply and an 

incinerator is used as the combustion device. 

The commenter supported EPA’s proposed incinerator temperature monitoring provisions at

§60.284a(c)(2) that require 3-hour averages for determining compliance status, as this approach 

is required in MACT subpart S.

Response: We agree with the commenter’s suggested changes to §§60.284a(d)(3)(ii) and 

60.287a(b)(3) to clarify that temperature monitoring would not be required for combustion 

devices such as a lime kiln, recovery furnace, or power boiler, since those devices normally 

operate at temperatures higher than 1200°F. These changes will make the subpart BBa 

provisions consistent with the monitoring methods mills use to comply with subpart S. 

Accordingly, we have revised §§60.284a(d)(3)(ii) and 60.287a(b)(3) in subpart BBa for the final 

rule.

 

184 U.S. Environmental Protection Agency. Review of New Source Performance Standards for Kraft Pulp Mills.

EPA-450/3-83-017. September 1983. p. 9-2.
106

5.2.2 Recovery Furnace Parameter Monitoring

5.2.2-01 Comment: Commenter 0055 noted the following from the subpart BBa proposal:

 The EPA is proposing that ESP secondary voltage and secondary current (or total 

secondary power) be monitored and averaged over the same calendar quarter as the 

opacity monitoring allowance.

 The 2 percent opacity monitoring allowance will only be available for recovery furnaces 

with ESP parameters that are above the minimum limits established during the PM 

performance test (i.e., above the minimum secondary current and secondary voltage or 

above minimum total secondary power).

 Subpart BB currently requires that the opacity allowance be calculated based on the 

percent of the total number of possible contiguous periods of excess emissions in a 

quarter.

 The EPA is soliciting comment on the proposed requirement, specifically whether a 

semiannual basis would be more appropriate based on the semiannual reporting 

requirement.

Commenter 0055 noted that the previous opacity allowance of 6 percent allowed a maximum of 

1,314 contiguous periods of excess emissions in a quarter (131.4 hours). According to the 

commenter, the proposed opacity allowance of 2 percent reduces the maximum number of 

contiguous periods of excess emissions to 438 per quarter (43.8 hours). The commenter stated 

that this is consistent with data accumulated by the EPA, and tightens the limitations without 

undue burden so long as the current SSM exemption is maintained. The commenter noted that 

industry has concerns that by removing the current SSM exemption, it would be difficult to meet 

the proposed 2 percent allowance. The commenter has determined that a semiannual basis for 

this requirement would not result in an increase in emissions, but would decrease the opportunity 

for reported violations. According to the commenter, this alleviates some of the burden on the 

industry without harming the environment. Therefore, the commenter supported the semiannual 

basis for the opacity allowance.

The commenter stated that sources using a COMS should not be required to conduct parametric 

monitoring for the ESP. In addition, the commenter stated that sources should be allowed to use 

alternative methods of compliance in lieu of the specified parametric monitoring requirements as 

proposed. As an example, the commenter suggested that facilities could correlate opacity to PM

emissions and then monitor the opacity to show compliance with the PM standards. The 

commenter noted that this is a similar approach to that used in CAM plans approved under 40 

CFR part 64.

Response: We acknowledge the commenter’s support for using a semiannual basis to determine 

the opacity allowance. As mentioned previously, EPA is promulgating a semiannual basis for 

calculation of monitoring allowances consistent with the semiannual reporting requirement in 

§60.288a(a).

Regarding the commenter’s statement that sources using COMS should not be required to 

conduct ESP parameter monitoring, we proposed ESP parameter monitoring in addition to 
107

COMS use to enable affected units to show continuous compliance with the PM concentration 

standards at all times, including periods when the opacity monitoring allowance is used. As 

discussed in section 4.1 of this document, the EPA has included language in subpart BBa to 

clarify that the standards apply at all times as specified in the §§60.284a and 60.285a monitoring 

and testing provisions in the rule. The ESP monitoring requirements were added to provide a 

measure of continuous compliance in order to enable retention of an opacity monitoring 

allowance in the NSPS. The 2 percent opacity monitoring allowance will only be available for 

recovery furnaces with ESP parameters that are above the minimum limits established during the 

PM performance test (i.e., above the minimum secondary current and secondary voltage or above 

minimum total secondary power).

Regarding the commenter’s request that sources be allowed to use alternative methods of 

compliance in lieu of the proposed parametric monitoring requirements, it should be noted that 

sources are allowed to request alternative monitoring requirements under 40 CFR 60.13(i).

5.2.2-02 Comment: Commenter 0055 noted the following from the subpart BBa proposal:

 The EPA is proposing to require ESP and wet scrubber parameter monitoring for 

recovery furnaces equipped with an ESP followed by a wet scrubber because opacity is 

not a suitable monitoring requirement for recovery furnaces with wet scrubber stacks.

 The EPA is specifying that the scrubber parameters would be measured and recorded at 

least once every 15 minutes and these 15-minute measurements used to calculate 12-hour

block averages.

 The EPA is requesting comment on the use of parameter monitoring instead of opacity 

monitoring in systems that utilize both an ESP and a wet scrubber.

 The EPA is also requesting comment on the parameter recording frequency and 

averaging time for ESP parameters and wet scrubber parameters.

Commenter 0055 requested that EPA clarify whether a source controlled by an ESP/scrubber 

combination is relieved from meeting the 20 percent opacity requirement. The commenter also

requested that EPA clarify if it is EPA’s intention to relieve a recovery furnace controlled solely 

by a scrubber from the 20 percent opacity requirement. 

Commenter 0055 believes that the use of a scrubber, either solely or in combination with an ESP, 

should relieve the source from the 20 percent opacity requirement. The commenter agreed with 

the use of parametric monitoring in lieu of opacity monitoring. The commenter concurred with 

the proposed parametric monitoring and recording on the ESP and wet scrubber every 15

minutes, and the 12-hour block averaging time for ESP parameters and wet scrubber parameters.

However, the commenter believes that sources should be allowed to use alternative methods in 

lieu of the specified parametric monitoring requirements as proposed using an approach similar 

to that used in CAM plans approved under 40 CFR part 64. According to the commenter, the 

TRS CEMS would demonstrate that the scrubber is working properly and would preclude the 

need to do parametric monitoring for the scrubber.

Response: Recovery furnaces with either a scrubber alone or an ESP/scrubber combination 

control are not required to monitor opacity. Section 60.282a(a)(1)(ii) and (a)(2)(ii) clarify that 
108

the opacity limit only applies for recovery furnaces with ESP controls. Section 60.284a(b) 

specifies wet scrubber parameter monitoring requirements for recovery furnaces, and 

§60.284a(b)(4) of subpart BBa states that opacity monitoring is not required for ESP/scrubber 

combination controls.

We acknowledge the commenter’s support for the proposed 15-minute recording frequency and 

12-hour block averaging time for recovery furnace ESP and scrubber parameter monitoring. 

Regarding the commenter’s request that sources be allowed to use alternative methods of 

compliance in lieu of the proposed parameter monitoring requirements, it should be noted that 

sources are allowed to request alternative monitoring requirements under 40 CFR 60.13(i).

The commenter suggests that TRS CEMS would demonstrate that a scrubber is working properly 

and would preclude the need to do parametric monitoring for the scrubber. However, we note 

that TRS emissions are affected by more than scrubber operation alone (e.g., process factors play 

a role which could potentially be more significant than scrubber operation in reducing TRS 

emissions). Thus, any alternative monitoring request that TRS CEMS replace scrubber parameter 

monitoring should contain justification explaining why TRS CEMS would be appropriate.

5.2.2-03 Comment: In the event EPA decides to finalize its proposed secondary voltage, 

secondary current, and alternative secondary power CPMS monitoring requirement for ESPs 

serving recovery furnaces, commenters 0056 and 0059 believe that EPA’s rule language at 

proposed §60.284a(e)(1)(ii)185 for recovery furnace ESPs should add secondary power as an 

alternate to secondary voltage and secondary current, similar to its inclusion at proposed 

§60.284a(e)(1)(iv) for lime kiln ESPs.

186

Response: We agree with the clarification to subpart BBa provided by the commenters and have 

made the suggested change to §60.284a(e)(1)(ii) of the final rule.

5.2.3 Smelt Dissolving Tank Parameter Monitoring

5.2.3-01 Comment: Commenter 0055 noted that the EPA is proposing a 12-hour averaging time 

for wet scrubber parameters recorded at least once every 15 minutes rather than retaining the 

current NSPS requirement to record wet scrubber parameters only once per shift at SDTs. The 

commenter also noted that EPA is soliciting comment on the SDT scrubber parameter 

monitoring requirements, especially the recording frequency and the averaging time for wet 

scrubber parameters.

The commenter agreed with the proposed SDT scrubber parameter monitoring and recording 

frequency of 15 minutes and the 12-hour averaging time for wet scrubber parameters. The 

commenter also believes that sources should be allowed to use alternative methods of 

compliance in lieu of the specified parametric monitoring requirements as proposed using an 

approach similar to that used in CAM plans approved under 40 CFR part 64.

Response: We acknowledge the commenter’s support for the proposed 15-minute frequency and 

12-hour block averaging time for SDT scrubber parameter monitoring. Regarding the 

 

185 See 78 FR 31339.

186 See 78 FR 31324.
109

commenter’s request that sources be allowed to use alternative methods of compliance in lieu of 

the proposed parameter monitoring requirements, it should be noted that sources are allowed to 

request alternative monitoring requirements under 40 CFR 60.13(i).

5.2.3-02 Comment: Commenter 0057 argued that the monitoring requirements and test methods 

for SDTs in the proposed rule are insufficient. As support for this argument, the commenter 

noted the following:

 SDT vent emissions can increase during recovery furnace conditions in which there is a 

temporary loss of combustion on part of the smelt bed at the base of the recovery furnace 

and subsequent sluicing of such uncombusted material into the hot SDT.

 Dimethyl sulfide, dimethyl disulfide and potentially other sulfur compounds (i.e. methyl 

mercaptan, ethyl mercaptan, phenyl mercaptan, etc.) contained in uncombusted 

concentrated black liquor can then be carried over on the surface of the smelt bed and 

conveyed into the SDT.

 Once in the tank, such organic sulfur compounds can boil off as process gas emissions 

from the SDT. 

The commenter contended that because problems during the operation of recovery furnaces can 

influence SDT vent emissions of TRS and other sulfur compounds, continuous TRS monitoring

of such tank vents should be required as part of the continuous monitoring requirements under

proposed §60.284a. Alternatively, the commenter suggested that continuous parameter 

monitoring be required for (a) SDT vent scrubbers to ensure a minimum level of causticity and 

(b) sulfidity of green liquor.

Response: The situation described by the commenter of a temporary loss of combustion on part 

of the recovery furnace smelt bed and discharge of uncombusted concentrated black liquor into 

the SDT is not a normal operating condition, and would be considered a malfunction. 

Malfunctions are not valid operating conditions for which EPA establishes emissions standards.

The commenter requests that the NSPS require TRS CEMS on SDT stacks, or alternatively 

parameter monitoring to ensure a minimum level of causticity (e.g., pH monitoring) or sulfidity 

of green liquor. Regarding the commenter’s suggestion to monitor TRS emissions and sulfidity, 

the BID for the original NSPS stated the following:

Since the standard for smelt dissolving tanks is expressed in a format of pollutant mass 

per unit of production, the gas flow rate and the production rate would have to be 

measured simultaneously to reduce the TRS concentrations measured by the monitor to 

units of the proposed standard. Inaccuracies would arise from measuring velocities 

continuously, and the production rate cannot be measured accurately except over 

relatively long periods of time. The inaccuracies involved in continuously measuring 

emissions from the smelt dissolving tank are felt to be sufficiently large that EPA has 

determined that the direct monitoring of TRS emissions from the smelt dissolving tank is 

not practical.

Another method exists for continuously monitoring the proper operation of smelt 

dissolving tanks to ensure that TRS emissions are well controlled. The TRS emissions 
110

from the smelt dissolving tank are related to the concentration of dissolved sulfides in the 

smelt dissolving tank water and in the water used in the scrubber. The concentration of 

the dissolved sulfides could be monitored, but neither EPA nor the industry have 

experience with this type of monitoring. The proposed standards therefore do not require 

the monitoring of dissolved sulfides in the smelt dissolving water or the scrubber 

water.187

The concerns noted in the original NSPS BID regarding continuous SDT monitoring remain 

valid today. The mass per unit production format of the SDT TRS standard has not changed. 

Sulfidity is not measured directly, but is calculated based on the concentration of multiple 

chemicals in solution which would to be continuously measured individually in order to allow 

for continuous calculation of sulfidity. 

Even if SDT TRS monitoring were practical, the typical TRS emissions from SDTs (36 tpy) are 

too low to make TRS monitoring a cost-effective monitoring option, compared to typical 

uncontrolled TRS emissions from sources that are required to conduct TRS monitoring (e.g., 

2,700 tpy from recovery furnaces, 144 tpy from lime kilns). Nevertheless, we have strengthened 

the continuous compliance requirements for SDTs relative to subpart BB. In addition to 

specifying a minimum 15-minute recording time and 12-hour averaging time for wet scrubber 

parameters (as opposed to a once-per-shift reading), the NSPS revisions for subpart BBa require

5-year repeat testing for all NSPS affected sources, which includes TRS tests for SDTs, ensuring 

ongoing compliance with the SDT TRS limit.

5.2.4 Lime Kiln Parameter Monitoring

5.2.4-01 Comment: Commenter 0055 noted the following from the subpart BBa proposal:

 The EPA is proposing a 12-hour averaging time for wet scrubber parameters recorded at 

least once every 15 minutes (instead of the current NSPS requirement to record wet 

scrubber parameters only once per shift).

 Excess emissions for lime kilns with ESP/scrubber combination controls would be any 

12-hour block ESP or scrubber parameter below its respective site-specific limit 

(established during the performance test) during times when lime mud is fired in the kiln.

 The EPA is requesting comment on the 12-hour averaging time specified for ESP and 

scrubber parameters, and whether a 3-hour averaging time (such as that specified under 

the subpart MM NESHAP for wet scrubber parameters) would be more appropriate and 

adequately account for periods of process variability in the absence of a monitoring 

allowance.

Commenter 0055 agreed with the proposed parametric monitoring and recording frequency of 

once every 15 minutes and averaging time of 12 hours. The commenter did not consider the 

necessity to calculate a 3-hour average for 40 CFR part 63, subpart MM and a 12-hour average 

for this NSPS to constitute an undue burden.

 

187 U.S. Environmental Protection Agency. Standards Support and Environmental Impact Statement Volume 1: 

Proposed Standards of Performance for Kraft Pulp Mills. Publication No. EPA-450/2-76-014-a. September 1976. 

Section 9.8.
111

According to the commenter, compliance with the 3-hour average would imply compliance with 

the 12-hour average. The commenter noted that EPA has expressed concern that a 3-hour

average may not account for process variability and recommended that, if EPA decides to pursue 

the 3-hour averaging time, any violation indicated by the 3-hour averaging block be examined 

from the 12-hour averaging standpoint before determining if a violation has occurred.

The commenter also stated that sources should be allowed to use alternative methods of 

compliance in lieu of the specified parametric monitoring requirements as proposed using an 

approach similar to that used in CAM plans approved under 40 CFR part 64.

Response: We acknowledge the commenter’s support for the proposed 15-minute frequency and 

12-hour block averaging time for scrubber parameter monitoring. The final rule retains the 12-

hour averaging time for wet scrubber parameters and ESP parameters (when an ESP is used in 

combination with a wet scrubber). The commenter is correct that compliance with the 3-hour

average would imply compliance with the 12-hour average. Regarding the commenter’s request 

that sources be allowed to use alternative methods of compliance in lieu of the proposed 

parameter monitoring requirements, it should be noted that sources are allowed to request 

alternative monitoring requirements under 40 CFR 60.13(i).

5.2.5 Digester Parameter Monitoring

5.2.5-01 Comment: Commenter 0057 argued that the proposed NSPS do not contain sufficient 

monitoring requirements to assure compliance with digester emission limitations and TRS

control requirements from digester chip bins. According to the commenter, an operator of a kraft 

pulp mill using a continuous digester and having the potential to emit digester process gases 

from chip bins to the atmosphere cannot assure compliance with the proposed TRS emission 

limitations without monitoring and instrumentation. The commenter recommended that such 

monitoring should, at the very least, include parameter monitoring for chip steaming bin gas 

pressure and exhaust temperature. The commenter contended that a minimum level of digester 

process monitoring, recordkeeping and reporting is needed to assure that digester process gases 

are not released because the operator has maintained below-atmospheric pressure chip bin 

steaming conditions.

Response: We address applicability of the NSPS to digester chip bins in response to comment 

2.3-02 above. Chip bins in which flash/live steam is introduced are part of the digester system, 

and digester process gases are required to meet the NSPS emission limits for TRS. In addition to 

the NSPS emission limits, the subpart S NESHAP contains detailed collection system 

requirements (see §63.450–Standards for enclosures and closed-vent systems) that further ensure 

emissions from all digester emission points are routed to a control device. These closed-vent 

system standards have been incorporated into the subpart BBa TRS standards. Therefore, we 

believe it is unnecessary to include parametric monitoring requirements specific to chip bins, 

which are one component of the digester system, in the NSPS.

5.3 TRS CEMS Data O2 Correction Procedure

5.3-01 Comment: Commenter 0059 agreed with EPA’s rationale in allowing facilities to use 

uncorrected TRS concentrations during periods when stack O2 values are greater than or equal to
112

15 percent. According to the commenter, these high stack O2 periods are typically indicative of 

(a) periods of S/S or (b) transient changes in boiler/lime kiln loading that have not been reflected 

in air flows. The commenter stated that the ability to use uncorrected TRS concentrations 

mitigates the use of an artificially inflated (and inappropriate) O2 correction factor.

The commenter noted that EPA has, however, limited the applicability of this approach by 

further stipulating that it can be used only during periods of S/S where the uncorrected TRS

concentrations are below applicable limits (5 ppm for recovery furnaces and 8 ppm for lime 

kilns). The commenter countered that there are two operating scenarios that are applicable:

1. Periods of S/S where uncorrected TRS concentrations are below the respective upper 

restriction levels (30 ppm and 22 ppm for recovery furnaces and lime kilns, respectively) 

and stack O2 concentration is greater than or equal to 15 percent; and

2. Limited normal operating periods where uncorrected TRS concentrations are below the 

respective upper restriction levels (30 ppm and 22 ppm for recovery furnaces and lime 

kilns, respectively) and stack O2 concentration is greater than or equal to 15 percent.

Commenter 0059 noted that EPA concluded in the COMS/CEMs background document188 that 

brief spikes in recovery furnace TRS concentrations (greater than 5 ppm) occurred during S/S

periods and that the proposed upper restriction of 30 ppm adequately encompasses these spikes, 

after addressing extreme-value outliers. Noting that spikes greater than 5 ppm do occur during 

S/S periods, the commenter concluded that it is only logical to allow the use of uncorrected TRS 

concentrations for these instances (uncorrected values below upper restriction level AND stack 

O2 greater than or equal to 15 percent). The commenter stated that this option would be of 

limited use if TRS “limits” (as opposed to “upper restriction levels”) are stipulated as a threshold 

for applicability.

Commenter 0059 noted that the scenario identified in Item 2 above (normal operation) also can 

occur. Given that EPA is proposing a standard that includes all operating periods, including S/S, 

the commenter concluded that EPA should allow the use of this approach for all operating 

periods when the uncorrected TRS concentration is below the applicable upper restriction level 

and stack O2 greater than or equal to 15 percent.

Response: We acknowledge the commenters’ support for the provision allowing facilities and 

enforcement authorities to consider the TRS concentration uncorrected for O2 when determining 

compliance with the excess emissions provisions for TRS during periods of S/S when stack O2

percentage approaches ambient conditions. We are retaining this provision as proposed.

The purpose of O2 correction is to prevent circumvention of the concentration standards for 

combustion sources by dilution (e.g., through leakage of ambient air in the control device or 

exhaust ductwork). Although the NSPS General Provisions (§60.12) prohibit circumvention of 

the concentration standards by dilution, it is difficult to distinguish between process air needed 

 

188 U.S. Environmental Protection Agency. Review of Continuous Emission Monitoring and Continuous Opacity 

Monitoring Data from the Pulp and Paper Information Collection Request Responses Pertaining to Subpart BB 

Sources. Docket ID. No. EPA-HQ-OAR-2012-0640. April 5, 2013.
113

for combustion and dilution air. Therefore the O2 correction provision is needed to correct for 

excess air in-leakage in the outlet stream.189

The O2 correction procedure increases the reported TRS concentration when O2 levels exceed the 

correction value of 8 percent or 10 percent for recovery furnaces or lime kilns, respectively. 

These O2 correction values were established when the NSPS were originally promulgated based 

on analysis of the O2 concentrations in recovery furnace and lime kiln exhaust streams, and are 

still representative today. Table 4 below provides some examples for a lime kiln to help illustrate 

this point. 

Table 4. Example Lime Kiln O2 Corrections

Measured TRS 

ppm (limit for 

lime kilns)

Measured 

O2 %

TRS ppm 

corrected to 

10% O2 Note

5 6 3.7 O2 levels lower than the 10% correction standard 

reduce the corrected TRS ppm. Dilution is not 

suspected.

5 10 5 There is no change to the reported TRS ppm when 

measured O2 equals the O2 correction value (10%)

5 15 9.2 Higher O2, potentially from dilution during normal 

operation, increases the corrected TRS ppm.

5 20 55 Very high O2 levels, possibly symptomatic of 

excessive dilution under normal operation, 

malfunction, or transient O2 levels under S/S

conditions, inflate the TRS ppm.

5 20.9 550

O2 correction equation: Corrected ppm = Measured ppm x (21-10)/(21-measured O2)

The proposed rule language to allow otherwise compliant uncorrected TRS concentrations

(5 ppm and 8 ppm for recovery furnaces and lime kilns, respectively) to be considered when 

stack O2 percentage approaches ambient conditions was limited to periods of S/S because in 

some cases the stack gas O2 percentage may not be stable during these times and could approach 

ambient levels if combustion conditions do not consume the O2 in the process air. We disagree 

that the 30 ppm and 22 ppm upper limits are appropriate values to represent the uncorrected TRS 

concentrations because the 30 ppm and 22 ppm upper limits were derived from analysis of O2-

corrected values. We also disagree that extending the provision to normal operations is 

appropriate because this would contradict the purpose of O2 correction to prevent dilution. 

We believe the rule, as proposed, provides ample flexibility. In addition to allowing facilities to 

dismiss otherwise compliant TRS values inflated by the O2 correction equation during S/S, 

monitoring is based on a 12-hour averaging period that works to smooth out variability in the 

hourly TRS and O2 measurements during all time periods. We further note that removal of 

periods in which no BLS or lime mud is processed through the recovery furnace or lime kiln, 

 

189 U.S. Environmental Protection Agency. Standards Support and Environmental Impact Statement Volume 1: 

Proposed Standards of Performance for Kraft Pulp Mills. Publication No. EPA-450/2-76-014-a. September 1976. 

Chapter 9.
114

respectively, also addresses times when O2 levels may be high due to changing combustion 

conditions.

5.3-02 Comment: Commenter 0059 requested clarification on the procedure used to calculate 

the 12-hour corrected TRS concentrations used to demonstrate compliance with (a) the 

applicable TRS limits and (b) the applicable “upper restriction level” during periods when the 

monitoring allowance is invoked. The commenter noted that the need to consider uncorrected 

TRS concentrations during periods when stack O2 levels are greater than or equal to 15 percent is 

another reason for requesting this clarification.

According to commenter 0059, the currently proposed procedure in §60.284a(c)(1) involves 

(a) calculating the 12-hour uncorrected TRS concentrations, (b) calculating the corresponding 

12-hour O2 concentrations, and (c) carrying out the O2 correction on the 12-hour average.

Commenter 0059 noted that §60.284(e)(3) states that “If the measured TRS concentration 

uncorrected for O2 is less than the applicable.....during periods of startup or shutdown when the 

stack O2 concentration is 15 percent or greater, then the Administrator will consider the TRS 

average to be in compliance.” According to commenter 0059, a procedure that performs the O2

correction on 1-hour uncorrected TRS data, and subsequently uses hourly corrected values to

calculate the 12-hour average may be more appropriate given this new O2 correction

requirement. Commenter 0056 concurred that EPA needed to consider a procedure for 

incorporating uncorrected TRS values in support of the proposed policy of using uncorrected 

data when stack O2 concentration approaches ambient levels. Commenters 0056 and 0059 

recommended that EPA use the following procedure developed by commenter 0058 for 

calculating the corrected 12-hour TRS concentrations:

1. Compute 1-hour averages of uncorrected TRS concentrations;

2. Calculate the 1-hour averages of stack O2 concentrations;

3. Skip to step 5 if the uncorrected 1-hour average TRS concentration is less than the 

applicable TRS limit190 AND the 1-hour stack O2 greater than or equal to 15 percent;

4. Carry-out the O2 correction according to equation in §60.284a(c)(1)(iii), if the 1-hour

stack O2 is less than 15 percent to obtain the corrected 1-hour TRS concentration; skip to 

step 6;

5. Use uncorrected 1-hour TRS concentration to calculate the 12-hour block average;

6. Repeat steps 1 through 5 for each hourly average in the 12-hour block; and

7. Roll-up the hourly averages to calculate the 12-hour block average concentration.

According to commenter 0059, the procedure outlined above would help streamline the 

calculations required to demonstrate compliance with the 12-hour block average TRS standard, 

while accommodating the need to comply with upper restriction levels and the need to use

uncorrected TRS values in certain instances. The commenter suggested that this procedure could 

be added as an option in §60.284(c)(1).

Response: We are not adopting the commenter’s calculation procedure. It was not EPA’s 

intention to completely overhaul the longstanding NSPS TRS and O2 data reduction procedures 

with the proposed rule. As the commenter notes, the data reduction procedure in the rule 

 

190 Commenter 0059 proposed that EPA modify this to the TRS upper restriction level.
115

involves computing 1-hour TRS and O2 values from valid monitoring data, and then averaging

the 1-hour values to arrive at 12-hour TRS and O2 values. The O2 correction is performed using 

the 12-hour averages for TRS and O2 to arrive at each 12-hour block O2-corrected TRS 

concentration that is either characterized as a compliant 12-hour block or as a 12-hour block 

period of excess emissions. Next, the total number of possible contiguous 12-hour blocks in the 

semiannual reporting period is compared with the number of 12-hour blocks that are excess 

emissions to calculate the monitoring allowance and determine if a violation of the standards has 

occurred. The intent of the proposed rule was not to significantly alter the fundamental data 

reduction procedure, but to insert some additional criteria for defining invalid data and 

characterizing 12-hour blocks considered to be excess emissions or violations. See also our 

response to comment 5.4-01 for reasons why we chose not to use a shorter averaging time. We 

clarify the key steps in the data reduction procedure below and have added the words “12-hour” 

or “12-hour average” to the final rule to clarify when the 12-hour block average is used for a 

particular calculation.

Step 1. Removing invalid data and calculating the 12-hour average. Sections 60.284a(c)(5)-(7) 

require operation of TRS CEMS to collect data at all required intervals at all times the affected 

facility is operating, except for periods of monitoring system malfunctions or out-of-control 

periods, repairs associated with monitoring system malfunctions or out-of-control periods, and 

required monitoring system quality assurance or quality control activities including, as 

applicable, calibration checks and required zero and span adjustments. Data recorded during 

monitoring system malfunctions or out-of-control periods, repairs associated with monitoring 

system malfunctions or out-of-control periods, or required monitoring system quality assurance 

or control activities are considered invalid data. Invalid data may not be used in calculations, 

such as the 1-hour average values rolled into the 12-hour block average TRS and O2 calculations 

required under §60.284a(c)(1).

Following removal of invalid data as described in §§60.284a(c)(5)-(7), the 12-hour block 

averages of TRS and O2 are calculated and subsequently used to calculate the 12-hour O2-

corrected TRS concentration following the procedures in §§60.284a(c)(1)(i)-(iii).

Step 2. Determining which 12-hour blocks are excess emissions. Next, each O2-corrected 

12-hour block average is evaluated to determine if it is (1) a compliant block, or (2) an excess 

emissions block. Excess emissions from recovery furnaces and lime kilns are defined as all 

12-hour block averages above the TRS ppm limit corrected for O2 when BLS or lime mud is 

fired. Thus, 12-hour blocks during which no (zero) BLS or lime mud is fired are not considered 

to be excess emissions even if the TRS concentration is higher than the applicable 5 or 8 ppm 

limit (possibly because of startup or shutdown conditions contributing to near-ambient O2). We 

recognize that some 12-hour blocks may only include a brief time when BLS or lime mud was 

fired. As noted in our response to comment 5.4-03, such blocks were included in the data sets 

used to reevaluate the TRS standards, and, therefore, are appropriate for evaluation as compliant 

or excess emissions blocks.

While subpart BBa does not specify rigorous procedures for monitoring and averaging of BLS 

and lime mud throughput data, we note that production monitoring data are readily available and 

are required under subpart MM. Mills are expected to match the available production data with 
116

the 12-hour block TRS averages for purposes of identifying 12-hour blocks in which there was 

zero throughput. Furthermore, §60.7(b) requires recordkeeping of startup and shutdown periods,

which will aid in identifying 12-hour periods of zero throughput.

Step 3. Determining whether excess emissions are in violation of the standard. Excess emissions 

and violations are determined using the 12-hour block averages. Excess emissions are not 

considered to be violations if good air pollution practices are used (per §60.284a(e)(2)) and the 

percentage of the total number of possible contiguous periods of excess emissions in the 

semiannual period does not exceed:

 One percent for TRS emissions from straight recovery furnaces, provided that the 

12-hour average TRS concentration does not exceed 30 ppm corrected to 8 percent O2. 

(§60.284a(e)(1)(i))

 One percent for TRS emissions from lime kilns, provided that the 12-hour average TRS 

concentration does not exceed 22 ppm corrected to 10 percent O2. (§60.284a(e)(1)(ii))

Except as provided in §60.284a(e)(3), all O2-corrected 12-hour average TRS concentrations that 

exceed the upper TRS limits (22 ppm for lime kilns and 30 ppm for straight recovery furnaces) 

are considered to be violations. In addition, if the 1 percent monitoring allowance is exceeded, 

then other 12-hour periods of excess emissions would also be considered in violation of the 

standards.

Section 60.284a(e)(3) states that the 12-hour average TRS concentration uncorrected for O2 may 

be considered when determining compliance with the excess emissions provisions during periods 

of startup or shutdown when stack O2 percentage approaches ambient conditions. If the 12-hour 

average TRS concentration uncorrected for O2 is less than the applicable limit (5 ppm for 

recovery furnaces or 8 ppm for lime kilns) during periods of startup or shutdown when the

12-hour stack O2 concentration is 15 percent or greater, then the Administrator will consider the 

TRS average to be in compliance. This provision only applies during periods of affected facility 

startup and shutdown.

Given the multiple nested criteria in §60.284a(e)(3)–that they only apply during S/S, that 

uncorrected TRS must not exceed 5 or 8 ppm, and that O2 must exceed 15 percent–the provision 

was not intended to be programmed into DAS, but instead was intended to provide mills and 

enforcement personnel with some recourse should the O2 correction requirement during S/S be 

the only reason a violation would have been recorded. It is expected that mills exceeding the 

1 percent monitoring allowance would carefully review their TRS CEMS data in order to explain 

violations to enforcement personnel. During this review, the monitoring allowance could be 

recalculated following removal of any blocks meeting all of the conditions in §60.284a(e)(3) to 

determine if it still exceeds 1 percent.

While it was not EPA’s intent that extensive reprogramming of DAS be completed in order to 

comply with the subpart BBa standards, mills are free to program their software as they choose, 

if they wish to incorporate §60.284a(e)(3) into the programming logic, as opposed to using this 

provision as an after-the-fact consideration should they exceed the 1 percent monitoring 
117

allowance. It is expected that some reprogramming of DAS would be helpful to address the 22 

and 30 ppm upper limits.

5.3-03 Comment: Commenters 0056, 0058, and 0059 requested that EPA clarify the procedure 

for the reporting and treatment of uncorrected TRS concentrations that exceed the span value (30 

ppmdv) for the TRS CEMS instrument. One approach that the commenters suggested was to (a) 

allow the use of uncorrected TRS measurements for readings up to 60 ppmdv (2 times the 

instrument span) for calculating the 1-hour uncorrected averages and (b) for those measurements 

greater than 60 ppmdv, require the use of 60 ppmdv in averaging calculations. According to the 

commenters, this approach minimizes the use of extreme-value data that typically have high 

levels of measurement uncertainty.

Response: When a CEMS reads between the calibrated span and instrument range, the values

the CEMS reads should be used in the emissions average calculation. While these data fall 

outside a calibrated instrument span, we recognize that the data have value and must be included 

in any CEMS hourly average or other long-term rolling average calculation. Otherwise, facilities 

could inappropriately dismiss non-compliant values as invalid data. Additional language has 

been added to the final rule in §60.284a(a)(2) to state that the range of the continuous monitoring 

system must encompass all expected concentration values, including the zero and span values 

used for calibration.

When a CEMS reads above the instrument range, the instrument range value should be used in 

the emissions average calculation. Where an instrument signal output has “flat lined” because it 

has reached its maximum signal, that value must be included in any CEMS hourly average or 

other long-term rolling average calculation. In this case, the source would need to flag these data 

so that the enforcement agency knows they are likely biased low and the agency can develop an 

appropriate response (e.g., consider if the facility should increase the range of their instrument). 

5.3-04 Comment: Commenter 0059 recommended that EPA make the following editorial 

changes to TRS and O2 monitoring:

 Under §60.284a(c)(1)(ii), change the cross-reference from “paragraph (c)(1) of this 

section” to “paragraph (c)(1)(i) of this section.”

 Under §60.284a(c)(1)(iii), revise the definition of the Cmeas term as follows: Cmeas = the 

measured 12-hour average concentration uncorrected for O2.

 Under §60.284a(e)(1)(i) and (iii), provide clarification to indicate a “12-hour average” 

TRS concentration.

Response: We agree with the clarifications to subpart BBa provided by the commenter and have 

made the suggested changes to subpart BBa for the final rule.

5.4 Averaging Times

5.4-01 Comment: Commenter 0057 recommended that the kraft pulp mill NSPS be revised to 

require rolling averages over shorter intervals, or, at a minimum, reporting of 12-hour block 

averages each hour. The commenter noted that the proposed TRS standard retains 12-hour block 

averaging times, which, according to the commenter, allows excursions from the TRS standard
118

to occur. The commenter contended that under the proposed rule, instances of elevated emissions 

could be avoided by cherry picking which 12-hour block is reported.

Commenter 0057 indicated that the use of 12-hour block averages appears to be based on 

technology from the 1970s when the NSPS were first promulgated, but stated that current 

technology makes possible both the ability to average over shorter intervals and to use rolling 

averages. The commenter pointed out that, when the kraft pulp mill NSPS were first proposed in 

1976, TRS emission limitations for the digester process group, lime kilns, and recovery furnaces

were all proposed as 4-hour averages for purposes of emission limitation, compliance evaluation,

and monitoring/recordkeeping/reporting data integration.191 The commenter noted that the final 

NSPS, however, included a less stringent TRS standard and required only 12-hour block

averaging.192

While not explained, the commenter indicated that this decision seems to reflect a concern that 

pulp mills existing at the time would have been unable to comply with more stringent 

requirements. According to the commenter, none of the subsequent rulemakings has justified the 

12-hour averaging times or provided any review or consideration of shorter averaging times for 

TRS emissions. The commenter further noted that EPA generally does not provide for such long 

12-hour averaging times in the NSPS for other sources. The commenter concluded that EPA, at a 

minimum, must explain why shorter averaging times have been rejected.

Response: The EPA disagrees that block averages allow for cherry picking data to avoid 

reporting elevated emissions. Block averages are fixed averaging periods (e.g., 12 midnight to 

12 noon and 12 noon to 12 midnight) and will include periods of elevated emissions. 

The majority of mills are using 12-hour block averaging times for their TRS monitors and have 

12-hour averaging times written into their state permits. Data from 12-hour average data sets for 

most mills in the U.S. were analyzed for the NSPS review and used to reevaluate the TRS 

emission limit and monitoring allowances. In order to review the NSPS TRS limit, it was 

necessary to compare 12-hour average data to the NSPS limit, which is currently enforced on a 

12-hour average. To deviate from a 12-hour averaging time would require reconsideration of the 

TRS concentration limit (e.g., reducing the averaging time could necessitate increasing the TRS 

concentration limit). The recordkeeping requirements of 12-hour TRS averages reflect the 

majority of the data analyzed and the compliance requirements by the state enforcement 

authorities, and, therefore, were retained for the final rule. Stack testing (which does not involve 

12-hour averages) is also used in addition to TRS monitoring for enforcement purposes, as 

explained in our response to the comment below.

5.4-02 Comment: Commenter 0057 requested that EPA clarify how to evaluate stack test reports 

for purposes of TRS compliance determinations. The commenter stated that EPA’s proposed rule 

does not explain or indicate how and whether TRS test method run results will be evaluated in 

order to determine compliance with a 12-hour average TRS emission limitation. According to the 

 

191 Kraft Pulp Mills Standards of Performance for New Stationary Sources, Proposed Rule, 41 FR 42012, 42016 

(Sept. 24, 1976).

192 Kraft Pulp Mills Standards of Performance for New Stationary Sources, Final Rule, 43 FR 7568 (Feb. 23,

1978).
119

commenter, the proposed rule at §60.285a(d) contemplates Method 16 (or related TRS approved 

determination method) runs in which “[t]he sampling time must be at least 3 hours, but no longer 

than 6 hours.” The commenter 0057 stated that, while the 5-year intervals on compliance stack 

testing are shown as performance tests, there is no explanation, method or narrative in the 

proposed rule that explains how to make a determination of compliance with a 12-hour TRS 

emission limitation on the basis of a 3 to 6-hour sampling time using EPA Methods 16 through 

16c testing.

Response: Stack testing and continuous emissions monitoring are two separate and independent 

methods for determining compliance with the TRS emission limits. Stack testing is used to 

determine initial compliance, and is repeated in 5-year intervals as one method of determining 

continuous compliance. Continuous monitoring of TRS emissions is also used by the regulating 

authorities to determine continuous compliance and excess emissions, with data averaged and 

reported on a 12-hour basis. The stack test uses Method 16, 16A, 16B, or 16C, in which three 

test runs with sampling times of 3 to 6 hours are averaged together for one emission value to 

determine compliance. The data from stack tests may be compared to continuous monitoring 

data, but are not averaged or intermingled with the CEMS data. The stack test and the CEMS 

12-hour averages are both used to demonstrate compliance, but are used individually.

5.4-03 Comment: Commenter 0059 noted that the proposed rule requires calculation of 12-hour

block average TRS concentrations for the two consecutive periods of each operating day and 3-

hour block averages for several parameters. The commenter further noted that monitoring is not 

required during S/S of affected sources when TRS gases are not being fired in an incinerator, 

when black liquor is not being fired in a recovery furnace, or when lime mud is not being fired in 

a lime kiln. For purposes of demonstrating compliance, the commenter noted the following

concerns:

 These 12-hour and 3-hour block average “periods” are fixed (12 midnight to 12 noon and 

vice versa), i.e., the start of the 12-hour block does not coincide with equipment startup.

 Facilities need flexibility to be able to S/S in line with process demands.

 If a recovery furnace is starting up and begins firing black liquor at 11:00, there is only 

1 hour of data that will be used to calculate the 12-hour block average TRS concentration.

 If the operation is not stable, such that TRS emissions are below 5 ppm, that 1 operating 

hour will result in excess emissions for that 12-hour average.

 Similarly, if a source starts up at 12:00, begins firing BLS or lime mud, and then 

operators need to shut the source down within an hour or 2 because operations are not 

stable and emissions are greater than 5 ppm, 1 operating hour will result in excess 

emissions for that 12-hour average.

Commenter 0059 stated that, because EPA has proposed to apply the standards at all times, 

sources will no longer be able to rely on the NSPS General Provisions to excuse excess 

emissions during periods of SSM. Therefore, to address these situations, the commenter

recommended that EPA establish that a 12-hour TRS block average must contain at least 8 hours 

of data and a 3-hour block average temperature must contain at least 2 hours of data.

Response: For the reasons below, we are denying the commenter’s request for a minimum data 

availability requirement for TRS and temperature monitoring under the NSPS.
120

First, we point out that monitoring requirements do not affect a mill’s ability to start up and shut

down in line with process demands. It is not expected that process equipment S/S periods are to 

coincide with the block averaging periods under the NSPS. 

Second, we would like to address any confusion about when monitoring is required. Contrary to 

the commenters statement that “[m]onitoring is not required during S/S of affected sources when 

TRS gases are not being fired in an incinerator, when black liquor is not being fired in a 

recovery furnace, or when lime mud is not being fired in a lime kiln,” we point out that 

monitoring is required during these times. The monitoring data required to be collected during 

these times are considered specially: (a) when calculating the 3-hour average incinerator 

temperature, or (b) in the assessment of which monitoring data constitute excess emissions (zero 

production periods). Monitoring is required during S/S. Section 60.284a(c)(5) through (7) 

requires continuous monitoring systems to collect data at all times the affected facility is 

operating except for periods of monitoring system malfunctions or out-of-control periods, repairs

associated with monitoring system malfunctions or out-of-control periods, and required 

monitoring system QA or QC activities including, as applicable, calibration checks and required 

zero and span adjustments. These monitor downtime and QA periods are to be excluded from 

calculations used to report emissions or operating limits. Otherwise, failure to collect required 

data is a deviation of the monitoring requirements. 

Taken together, several aspects of the monitoring requirements combine to provide significant 

flexibility for mills in their efforts to demonstrate compliance with the standard. We discuss 

several below.

Rather than specifying that entire block averages be discarded if they do not meet a minimum 

data availability requirement (e.g., the 8 hours per 12-hour block, or 2 hours per 3-hour block 

suggested by the commenter), the provisions in §60.284a(c)(5) through (7) maximize the number 

of recorded readings that are included in block averages, and increase the number of block 

averages acquired over each semiannual period. Maximizing the number of recording readings 

and block averages over the semiannual period is a more robust approach to monitoring, 

particularly for subpart BBa, which contains monitoring allowances and relatively long 

averaging periods for TRS and most operating parameter limits. Temperature is the only 

operating parameter limit for which a 3-hour block average is required (based on at least 36

readings recorded every 5 minutes or less). The ESP and scrubber operating parameter limits are 

based on a 12-hour block average (comprised of at least 48 readings recorded in 15-minute

intervals or less). Electrostatic precipitator parameters monitored in conjunction with opacity are 

based on a semiannual average (e.g., over 17,000 readings). 

The TRS data analyzed by EPA to reevaluate the NSPS included S/S periods occurring at 

varying times in relation to the 12-hour block average TRS data. The data set analyzed by EPA 

included situations where positive process throughput was only reported for 1 hour of the 12-

hour block TRS calculation. Such 12-hour block periods were retained in the data set and 

considered in the evaluation of the monitoring allowance. Twelve-hour block averages calculated 

with less than 12 hours of data do not automatically render the 12-hour block in violation of the 

applicable TRS concentration limit. In order for a violation to occur, the emission limit first must 
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be exceeded, and then the 1 percent semiannual monitoring allowance must also be exceeded.193

As mentioned by the commenter, 12-hour blocks characterized as zero-throughput blocks would 

not be considered as excess emissions. Also, under §60.284a(e)(3), otherwise-compliant blocks 

where the 12-hour O2-corrected TRS emissions exceed the limit solely because the O2

percentage exceeded 15 percent during S/S periods, would be considered compliant.

Section 60.284a(c)(2) states that temperature measurements recorded when no TRS emissions 

are fired in the incinerator (e.g., during incinerator warm-up and cool-down periods when no 

TRS emissions are generated or an alternative control device is used) may be omitted from the 

block average calculation. Thus temperature is recorded during incinerator warm-up and cooldown, but is not used in the 3-hour block average calculation when TRS emissions are not fired 

in the incinerator. Given this requirement and the requirement to exclude monitor downtime and 

QA periods from calculations of the 3-hour block average, we recognize that some 3-hour blocks 

will be comprised of less than 3 hours of valid data. Addition of a minimum data availability 

requirement for temperature monitoring would serve to omit 3-hour block averages from 

consideration for compliance purposes when TRS emissions are fired into the incinerator for a 

portion of the block. Use of less than 3 hours of data does not automatically render a block out of 

compliance with the 1200°F incinerator temperature operating limit. Incineration devices used to 

combust vent gas streams containing TRS are also used to comply with NESHAP subpart S,

which requires a higher temperature (1600°F) for the incineration of HAP. Incineration devices 

are usually brought up to the required incineration temperature prior to accepting vent gases 

containing TRS or HAP for safety reasons, and backup controls may be used in the interim. It is 

very unlikely that TRS emissions would be fired into an incinerator when the combustion 

temperature is less than 1200°F, even for a partial block comprised of less than 3 hours of data. 

5.5 Electronic Reporting

5.5-01 Comment: Commenter 0059 argued that EPA has included a new reporting requirement 

in proposed subpart BBa that was not justified and would be excessively burdensome to industry. 

The commenter cited proposed §60.288a(b) and (c), which state that, within 60 days of 

completing each performance test and CEMS performance evaluation test, the owner/operator 

must submit the test data to the EPA’s CDX by using the ERT, when the data and methods are 

compatible with the ERT.

Commenter 0059 pointed out that facilities are already required to submit performance test data 

to regulatory agencies and provide certifications on their semiannual compliance reports that 

they have performed the required monitoring and will provide information on any deviations 

from the testing requirements. According to the commenter, additional performance test report 

submittals to EPA provide no useful purpose, environmental or otherwise, and would be an 

additional administrative burden on operating facilities. The commenter stated that ERT 

continues to be revised and updated due to various flaws. The commenter argued that it would be

unreasonable to put sources at risk of violations (late reporting) because of EPA reporting tool 

issues or availability. As an example, the commenter noted that the CDX system went down on 

 

193 Note however that 12-hour block averages exceeding the applicable ppm upper violation limits (e.g., 30 ppm for 

straight recovery furnaces, 22 ppm for lime kilns) are automatic violations unless the 12-hour block met the criteria 

in §60.284a(e)(3).
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July 1, 2013, the due date for TRI reports, and that many facilities were unable to submit reports 

electronically until July 2.

Commenter 0059 noted that a number of states already specify that performance test results be 

submitted in an electronic format. The commenter requested that EPA remove its reporting 

format requirement from the rule and work more closely with states to develop a universal 

reporting system that is not costly or redundant, does not require different electronic reporting 

formats, and that is not problematic and labor-intensive for data entry. The commenter contended 

that, as proposed, the rule’s ERT requirement is an extra, excessive burden for mills and stack 

testing vendors. The commenter concluded that EPA needs to defer any electronic collection of 

data until the CDX system is fully functional, user-friendly, and streamlined with states.

Response: The EPA acknowledges that there may be existing reporting programs in place. 

However, the compliance test reporting requirement in this rule allows for quick and easy access 

of the data by state, local, and tribal entities, as well as the public. As of January 1, 2012, the 

CEDRI has been fully functional. Since that time, ERT submittals via CEDRI and the CDX were 

transferred into EPA’s WebFIRE database, which is publicly accessible. WebFIRE provides a 

convenient location, which is already used to store source test data allowing regulatory 

authorities access to CROMERR compliant test reports. As EPA and state/local agency data 

systems mature, information provided through the ERT will be used to populate these data 

systems. We are currently upgrading the AIRS/AFS and expect to replace manually entered 

information with electronic population from the ERT. We are also working with several state and 

local agencies to adopt the use of the ERT for delivery of compliance test reports. We disagree 

that all systems to receive and process the compliance data must be operational prior to 

establishing the requirement for regulated sources to submit compliance data electronically.

5.6 Other Testing and Monitoring Comments

5.6-01 Comment: Commenter 0056 was concerned that, with this proposal, EPA has reduced or 

eliminated the compliance margin and increased the complexity of the NSPS. The commenter

stated that the proposed incremental changes in surrogate (opacity for PM) and parametric 

monitoring requirements, in excess emissions monitoring allowances, and in exemptions during

SSM periods unnecessarily reduces or eliminates the compliance margin for future new, 

reconstructed or modified facilities. According to the commenter, monitoring allowances and 

SSM exemptions were built into the current NSPS based on the large, complex and multifaceted 

processes. The commenter pointed out that existing facilities have worked to achieve compliance 

margins that take into account these allowances and exemptions because they are necessary to 

maintain and assure compliance and provide operating flexibility. The commenter expected that 

future facilities will have the same concerns, but noted that EPA has not really identified new 

cost-effective technology to rebuild those margins. The commenter also noted that, while this is a 

technology-based review, there are no new identified health risks, and, as EPA has noted, no

major pollutant reductions.194 Thus, the commenter concluded that this proposal may severely 

narrow compliance margins for new, reconstructed or modified units, adding significant cost and 

reducing operating flexibility of those units without improving emissions or reducing health risk.

 

194 See 78 FR 31332.
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According to the commenter, examples of going beyond the NESHAP subpart MM are the 

proposals to:

 Reduce the opacity limit for modified recovery furnaces from 35 percent to 20 percent;

 Reduce the monitoring allowance for opacity from 6 percent of the monitoring periods 

during a quarter while excluding SSM periods, to 2 percent of the monitoring periods 

while including SSM periods;

 Require CPMS monitoring and establishing operating limits of secondary voltage and 

secondary current of each ESP field serving a recovery furnaces and lime kiln where 

opacity already is monitored195 and then using the CPMS measurements to potentially 

eliminate the ability to use the monitoring allowance, and;

 Substitute the current use of CPMS measurements that fall outside of established 

operating limits as deviations warranting corrective actions (which if not corrected and 

exceed certain limits becomes an excess emission under the NESHAP), to instead define 

them immediately as excess emissions subject to enforcement whether or not an actual 

emission limit for a concentration regulated parameter (PM, TRS) has been exceeded.196

The commenter noted that current NSPS and NESHAP and rules applicable to pulp mill systems 

are complex enough that it is sometimes difficult to manage all the compliance requirements, 

even for sophisticated and dedicated staff at advanced companies. According to the commenter, 

as the standards are applied through SIPS by states and other authorities, differing approaches 

emerge that further challenge standardized compliance efforts. To illustrate the problem, the 

commenter provided an example. With operations in multiple states, the commenter’s company

has observed state-by-state differences in current monitoring and reporting practices, and even 

within states, differences among mills, with facilities considering the pros and cons of including 

or excluding monitor downtimes or QA/QC adjustment periods or even including SSM period 

emissions when they could legally be excluded from compliance calculations. The commenter 

explained that facilities do this because the effort to separate reportable values during normal 

monitor operating periods from monitor downtimes or SSM periods is viewed as excessively 

burdensome. The commenter noted that, in some cases, states require facilities to include nonnormal periods in reports of monitoring data. By doing this approach, the commenter said 

monitoring and reporting burdens are reduced, while emissions during SSM periods are 

conservatively included when they otherwise could be exempt. The commenter noted that air 

pollution control systems and processes have been developed to establish compliance margin to 

accomplish this. 

The commenter stated that the incremental and multiple monitoring additions,197 the setting of 

CPMS operating limits as enforceable excess emissions points instead of corrective action 

triggers, and reduced monitoring allowances converge to make the proposed kraft pulp mill 

NSPS more complex, rather than achieving regulatory flexibility and consistency with current 

NESHAP and other regulations. The commenter requested that EPA address the additional 

complexities it is proposing, and, at a minimum, re-evaluate the potentially flawed analyses, as 

 

195 See proposed §63.284a(b)(3) and (b)(4).

196 See NESHAP subpart MM §63.864(k) v. proposed NSPS subpart BBa §60.284a(d) and (e).

197 Such as the proposed ramp-up in opacity restrictions, to which EPA also adds ESP secondary voltage and current 

monitoring and operating limits as “another indicator of ESP performance” [78 FR 31324]) .
124

identified by commenter 0058, that EPA used to develop its proposals to increase restrictions. As 

a partial solution, commenter 0056 believes re-proposing a more equitable set of monitoring 

allowances would substantially alleviate many of these concerns.

Response: In support of their comments on compliance margin and rule complexity, the 

commenter refers to four changes from subpart BB:

 Reduction in opacity limit;

 Additional ESP monitoring requirements/operating limits (secondary voltage and current)

where opacity is already monitored;

 Setting operating limits as enforceable excess emissions points instead of corrective

action triggers; and

 Reduction in monitoring allowances.

We have conducted a review of the data used in developing the proposed opacity limit. Table 3A

above summarizes the COMS data reviewed for recovery furnaces. Most of the recovery 

furnaces in the U.S. were included in this analysis. Of the COMS data sets analyzed, 141 of 160 

total data sets achieved the 20 percent opacity limit with a 2 percent monitoring allowance 

proposed for subpart BBa. In response to comments on the proposal, EPA broke the recovery 

furnace COMS data into new, modified, and existing sources based on the reason each recovery 

furnace became subject to the NSPS following the 1976 applicability date (e.g., new units 

installed after 1976, modifications occurring after 1976). While a few recovery furnaces that 

became subject to the NSPS when they were installed or modified did not achieve the limit 

prosed for subpart BBa, we note that these units all became subject to the NSPS over 20 years 

ago. Recovery furnaces that have come online as new units or been upgraded over the past 

decade showed compliance with the proposed 20 percent opacity limit with a 2 percent 

monitoring allowance. The EPA is unaware of any technological reason that would hinder 

modified units from meeting this limit, especially considering that the majority of existing 

sources not subject to the NSPS already meet the proposed limit.

Based on our analysis of the COMS data showing that 20 percent opacity (with a 2 percent 

monitoring allowance calculated on a semiannual basis) has been achieved by most of the 

recovery furnaces in the U.S., and given the opacity levels established under subpart MM and 

permit limits, we maintain that 20 percent opacity (with a 2 percent monitoring allowance 

calculated on a semiannual basis) has been adequately demonstrated and we are finalizing this 

limit in subpart BBa.

Regarding the commenter’s concern that sources using COMS should not also be required to 

conduct ESP parameter monitoring, we proposed ESP parameter monitoring in addition to 

COMS use so affected units would have a mechanism to show continuous compliance with the 

PM concentration standards at all times, including periods when the opacity monitoring 

allowance is used. As discussed in section 4.1 of this document, the EPA has included language 

in subpart BBa to clarify that the standards apply at all times as specified in the monitoring and 

testing provisions in the rule. The ESP monitoring requirements were added to provide a 

measure of continuous compliance in order to enable retention of an opacity monitoring 

allowance in the NSPS. The 2 percent opacity monitoring allowance will only be available for 

recovery furnaces with ESP parameters that are above the minimum limits established during the 
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PM performance test (i.e., above the minimum secondary current and secondary voltage or above 

minimum total secondary power).

Regarding the commenter’s concern about the reduction in excess emissions monitoring 

allowances for opacity from 6 percent of the monitoring periods while excluding periods of S/S, 

to 2 percent of the monitoring periods while including periods of S/S, the proposed rule specified 

these allowances based on our review of the COMS data. In light of comments questioning 

certain aspects of our analysis, we have reanalyzed the COMS data following proposal (as 

described in Section 3). The reanalysis supports the original conclusions in the proposal 

regarding the ability of sources to meet the proposed standard during both normal operations and 

periods of S/S. The most significant change we are making as a result of our reanalysis of the

COMS data is to require calculation of the opacity monitoring allowance on a semiannual basis 

instead of quarterly. 

We acknowledge that simultaneous implementation of NSPS, NESHAP, and state rules is 

complex and that there could be some inconsistencies especially while EPA is in the process of 

updating Federal rules to address SSM. While the revised NSPS subpart BBa may seem more 

complicated than subpart BB, we note that EPA has added language to the revised NSPS to 

update the NSPS requirements to be consistent with the NESHAP and clarify how emissions are 

to be reported during time periods that previously were not required to be addressed (e.g., S/S 

periods). Several of the new requirements added to the revised NSPS were included to ensure 

adequate flexibility was maintained in the NSPS in light of the need to address SSM periods. 

Review of the NESHAP (subpart MM) is forthcoming and will provide an opportunity for EPA 

to address SSM in a manner consistent with the revised NSPS. While EPA hopes that state rules 

will be consistent with Federal rules, we note that state rules, and the timing in which state 

requirements are made consistent with Federal rules as they are updated, may vary, and this 

timing is not entirely within EPA’s control. Finally, as the commenter mentioned, this is a 

technology-based review, so health risks cannot be a consideration for this rule. No health risk 

assessment has been conducted for this rule.
126

6. Cost and Impacts

6-01 Comment: Commenter 0059 submitted comments on the costs associated with the 

proposed NSPS review, specifically the costs associated with lowering the NSPS PM emission 

limits for modified and reconstructed SDTs and for modified lime kilns. These comments were 

previously submitted to EPA prior to proposal and can be found in the document titled, Meeting 

Notes for the March 14, 2013 meeting with AF&PA and NCASI, in the docket for the proposed 

rulemaking.

Response: We received and evaluated the aforementioned comments prior to proposal of the 

NSPS review and took them into account in preparing the costs of the proposal, which can be 

found in the memorandum titled, Emissions Inventory for Kraft Pulp Mills and Costs/Impacts of 

the Section 111(b) Review of the Kraft Pulp Mills NSPS, in the docket for the proposed 

rulemaking. We appreciate the commenter’s input to the cost estimates for the proposed rule.

6-02 Comment: Commenter 0056 supported EPA’s decision and rationale for maintaining the 

modified recovery furnace PM limit. The commenter noted that, because modified unit status 

under the NSPS has no equivalent status trigger under the NESHAP regulations, EPA evaluated

the cost effectiveness of moving the PM limit for such modified units to the more restrictive PM 

limits under the subpart MM NESHAP for new and reconstructed units. The commenter further 

noted that EPA found “poor cost effectiveness” as a result, especially for modified units, that for 

economic reasons would need to attempt to comply with more stringent limits by upgrading 

existing controls, and that EPA chose to retain the current NSPS limit.198 The commenter agreed 

that this was an appropriate choice.

Response: We appreciate the commenter’s support for our decision to maintain the current PM 

emission limit for modified kraft recovery furnaces.

 

198 See 78 FR 31323.
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7. Greenhouse Gas Emissions

7-01 Comment: Commenters 0057 and 0059 presented opposing arguments regarding the 

regulation of GHGs from kraft pulp mills. Commenter 0059 argued that EPA has ample practical

reasons not to consider adding GHGs to the kraft pulp mill NSPS. The commenter stated that 

EPA is not required to promulgate NSPS for all, or indeed for any, pollutants emitted by a 

particular source category. Although EPA has made an “endangerment finding” with respect to 

GHG emissions from motor vehicles,199 the commenter contended that this finding does not by 

its terms address GHG emissions from pulp mills. But even if it did, the commenter argued that 

section 111 contains no requirement that EPA include emission limitations in current NSPS for 

all air pollutants that are emitted by a given source category, even for pollutants that EPA has 

determined may reasonably be anticipated to endanger public health or welfare,200 in contrast to 

section 202(a)(1), which requires EPA to set standards for emissions of “any air pollutant” from 

new motor vehicles that, in the Administrator’s judgment, cause or contribute to air pollution that 

“may reasonably be anticipated to endanger public health or welfare.” 

Commenter 0059 contended that, in any event, including GHGs in the kraft pulp mill NSPS

would be premature. First, the commenter noted that no court has held that EPA is authorized to 

use NSPS under CAA section 111 to combat climate change.201 According to the commenter, 

there are numerous reasons why CAA section 111 is not an appropriate vehicle for addressing 

climate change. Among other things, the commenter cited the fact that GHG emissions do not 

have local effects, but have been identified as a concern only as they build up in the global 

atmosphere, which, according to the commenter, means that controlling their emissions from 

new and modified sources using the best demonstrated technology is likely not to be the most 

cost-efficient way of achieving desired reductions in global GHG emissions. The commenter 

stated that virtually everyone agrees that stabilizing GHG concentrations in the global 

atmosphere would be an enormously costly proposition, and, therefore, it is particularly 

important that any GHG reductions be obtained in a cost-effective manner. The commenter 

pointed out that NSPS, which by statute must be based on an evaluation of the best-performing

emission control technology for a particular emission unit, do not incorporate any explicit 

consideration of whether the same or greater reduction in GHGs could be achieved at lower cost 

through other measures. The commenter also pointed out that NSPS typically are expressed as 

uniform emission rates for every unit in a particular source category or subcategory, without 

providing for consideration of site-specific factors or incorporating the flexibility necessary to 

minimize the cost of emission reductions on a global scale.

Commenter 0059 contended that including GHGs in the kraft pulp mill NSPS would be 

premature on technical grounds, as well. According to the commenter, technologies for control 

of GHGs are just beginning to be developed, and it could actually be counterproductive for EPA 

 

199 74 FR 66496 (Dec. 15, 2009).

200 Compare CAA sections 111(b)(1)(A), (f)(2)(B), and (g)(2).

201 See, e.g., EPA’s Combined Motion To Govern Further Proceedings and Response to Environmental and State 

Petitioners’ Motion To Govern Further Proceedings in New York v. EPA, D.C. Cir. No. 06-1322, June 18, 2007, at 8

(“To date neither Massachusetts nor any other judicial decision has specifically addressed either the legal or policy 

aspects of the potential regulation of greenhouse gas emissions under section 111 of the Act....”).
128

to establish NSPS for GHGs, which likely would not be reviewed for at least another 8 years, 

based on current technologies. The commenter also noted that a large portion of GHG emissions 

from kraft pulp mills comes from biomass, and pointed out that EPA is currently in the midst of 

developing its policy with respect to regulation of biogenic GHG emissions, in light of the 

carbon cycle.202 As an example, the commenter indicated that a recovery furnace can be viewed 

as an energy efficiency device—recovering energy value from a byproduct of the pulping

process that would otherwise be wasted—and also a device whose carbon emissions displace 

carbon emissions from fossil fuel that otherwise would be transformed from subsurface deposit 

to atmospheric pollutant. The commenter stated that EPA does not yet have the conceptual

framework to address these distinct qualities of pulp mill GHG emission sources. Thus, 

according to the commenter, there are numerous legal and practical reasons for EPA to exercise 

its ample discretion not to include GHGs in the kraft pulp mill NSPS.

By contrast, commenter 0057 argued that GHG emissions, especially CO2, should be 

inventoried, monitored, and analyzed for future review of the NSPS for kraft pulp mills. 

According to the commenter, estimates for the pulp and paper industry as a whole indicate that 

CO2 emissions from biogenic sources, such as black liquor and other waste biomass at pulp mills,

are approximately double the emissions from other fuel combustion.203 The commenter noted, 

however, that these substantial biogenic CO2 emissions are not currently reported for the purpose 

of GHG inventories. Consequently, the commenter indicated there are no accurate measures of 

the total GHG emissions from pulp mills. Commenter 0057 contended that these biogenic 

emissions should be inventoried just as fossil sources are currently inventoried for GHG 

emissions. Even though these CO2 emissions are biogenic in origin, the commenter stated that 

EPA must consider how they could be reduced through improvements in efficiency or other 

methods.

Response: We agree with commenter 0059 that GHG emissions, regardless of biogenic or nonbiogenic origin, were outside the scope of the proposed NSPS review. The proposed NSPS 

review focused on the PM and TRS emission standards in subpart BB that were due for review 

under CAA section 111(b)(1)(B).

Even though GHG emissions were outside of the scope of the proposed NSPS review, 

commenter 0057 raises other topics that we would like to address here. First, we disagree with 

commenter 0057 that CO2 emissions from the combustion of black liquor and biomass are not 

reported for the purpose of GHG inventories and that there are no accurate measures of the total 

GHG emissions from pulp mills. The pulp and paper industry reports biogenic CO2 emissions 

from black liquor and biomass combustion through EPA’s GHGRP, and has done so since 2010. 

Under the GHGRP, biogenic CO2 emissions are reported separately from the CO2e emissions 

associated with (a) CO2 from burning fossil fuels, (b) CH4 and N2O from burning biomass and 

fossil fuels, and (c) process-related CO2 (e.g., from sorbent or make-up chemical use). Based on 

reporting year 2012 data from the GHGRP, commenter 0057 is correct that biogenic CO2

emissions from the pulp and paper industry are higher than emissions of non-biogenic CO2e (42

million metric tons). 

 

202 See 76 FR 43490 (July 20, 2011).

203 U.S. Environmental Protection Agency. Available and Emerging Technologies for Reducing Greenhouse Gas 

Emissions from the Pulp and Paper Industry. 2010.
129

Given the scientific and technical issues surrounding biogenic CO2 (e.g., carbon cycle 

considerations), since 2010 and while EPA has been collecting biogenic CO2 emissions data 

from the pulp and paper industry under the GHGRP, EPA has also taken a number of actions 

related to biogenic CO2 emissions from stationary sources. These EPA actions include issuing a 

call for information on GHG emissions associated with bioenergy and other biogenic sources and 

drafting an Accounting Framework for Biogenic CO2 Emissions from Stationary Sources for peer 

review by a SAB panel specially convened to study the scientific and technical issues associated

with biogenic CO2. The final peer review report from the SAB panel on the draft framework was 

published on September 28, 2012. The EPA is currently in the process of determining the 

appropriate next steps with respect to biogenic CO2.

We also note that the EPA is taking common-sense steps to regulating GHG emissions from 

stationary sources, beginning with the largest sources of GHG (i.e., power plants). According to 

data from the GHGRP, GHG emissions from the pulp and paper industry are only a small 

fraction of the approximately 2 billion metric tons of GHG emissions from the power sector, 

even considering biogenic CO2 emissions.