1

MEMORANDUM

Subject: Response to Public Comments on Proposed National Emission Standards for 

Hazardous Air Pollutants for Existing Stationary Reciprocating Internal 

Combustion Engines Located at Area Sources of Hazardous Air Pollutant 

Emissions or Have a Site Rating Less Than or Equal to 500 Brake HP Located at 

Major Sources of Hazardous Air Pollutant Emissions 

From: Melanie King, Energy Strategies Group 

To: EPA Docket EPA-HQ-OAR-2008-0708 

Date: August 10, 2010 

On March 5, 2009, the Environmental Protection Agency (EPA) proposed national emission 

standards for hazardous air pollutants (NESHAP) for stationary reciprocating internal 

combustion engines (RICE) that are either located at area sources of hazardous air pollutant 

(HAP) emissions or that have a site rating of less than or equal to 500 brake horsepower (HP) 

and are located at major sources of HAP emissions in 40 CFR part 63, subpart ZZZZ. EPA also 

proposed national emission standards for hazardous air pollutants for existing stationary 

compression ignition (CI) engines greater than 500 brake HP that are located at major sources of 

HAP emissions. It is important to note that the proposed rule covered both CI and spark ignition 

(SI) engines. The final rule is being promulgated in two parts. The first action covered CI 

engines only and was published in the Federal Register on March 3, 2010 (75 FR 9648). The 

comments on the proposed standards for CI engines and the responses to those comments were 

summarized in a separate document. The purpose of this document is to present a summary of 

the public comments that EPA received on the proposed standards for SI engines and the 

responses developed. This summary of comments and responses serves as the basis for revisions 

made to the standards between proposal and promulgation. 

EPA received 199 public comments on the proposed rule. A listing of all persons submitting 

comments, their affiliation, and the Document ID for their comments is presented in Table 1. 

The comments can be obtained online from the Federal Docket Management System at 

http://www.regulations.gov. The docket number for this rulemaking is EPA-HQ-OAR-2008-

0708. In this document, commenters are identified by the last three digits of the Document ID of 

their comments. Note that as stated above, this document includes the comments related to SI 

engines only. The comments that pertain to CI engines were summarized and responded to in a 

separate document (see document number EPA-HQ-OAR-2008-0708-0367 in the rulemaking 

docket). EPA received additional test data, information, and recommendations after the close of 

the public comment period; this information can also be obtained from the docket for this 

rulemaking. 
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Table 1. List of Commenters on the Proposed National Emission Standards for Hazardous 

Air Pollutants for Existing Stationary Reciprocating Internal Combustion Engines 

Document ID Commenter/Affiliation

EPA-HQ-OAR-2008-0708-0036 Bo Quick 

Southwire Company 

EPA-HQ-OAR-2008-0708-0038 

EPA-HQ-OAR-2008-0708-0062 

Jack Maley 

Director, Fleet Operations 

Exterran 

EPA-HQ-OAR-2008-0708-0039 

EPA-HQ-OAR-2008-0708-0180 

EPA-HQ-OAR-2008-0708-0242 

Stephanie R. Meadows 

Upstream Senior Policy Advisor 

American Petroleum Institute (API) 

EPA-HQ-OAR-2008-0708-0040 

EPA-HQ-OAR-2008-0708-0155 

Lisa Beal 

Director, Environment and Construction Policy 

Interstate Natural Gas Association of America (INGAA) 

EPA-HQ-OAR-2008-0708-0041 

Craig S. Harrison 

Hunton & Williams on behalf of the 

Utility Air Regulation Group (UARG) 

EPA-HQ-OAR-2008-0708-0042 R. L. Bedard 

EPA-HQ-OAR-2008-0708-0043 Anonymous 

EPA-HQ-OAR-2008-0708-0044 J. Hartz 

EPA-HQ-OAR-2008-0708-0045 

Mark Sutton 

Executive Director 

Gas Processors Association (GPA) 

EPA-HQ-OAR-2008-0708-0046 

Patrick J. Nugent 

Executive Director 

Texas Pipeline Association 

EPA-HQ-OAR-2008-0708-0047 Anonymous 

EPA-HQ-OAR-2008-0708-0048 Jorge Verde 

EPA-HQ-OAR-2008-0708-0050 Quinton Hancock 

Cree, Inc. 

EPA-HQ-OAR-2008-0708-0051 

Nancy C. Wrona 

Director, Air Quality Division 

Arizona Department of Environmental Quality (ADEQ) 

EPA-HQ-OAR-2008-0708-0052 K. W. Breeden Sr. 

EPA-HQ-OAR-2008-0708-0053 L. Jordan 

EPA-HQ-OAR-2008-0708-0054 Anonymous 

EPA-HQ-OAR-2008-0708-0055 Suneet K. Sikka 

Eastman Chemical Company 

EPA-HQ-OAR-2008-0708-0056 

Bruce Chrisman 

Manager of Engineering 

Cameron’s Compression Systems 

EPA-HQ-OAR-2008-0708-0057 

EPA-HQ-OAR-2008-0708-0059 

Gary L. Smith 

Consulting Engineer 

Cummings & Smith, Inc. 
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Document ID Commenter/Affiliation

EPA-HQ-OAR-2008-0708-0058 

EPA-HQ-OAR-2008-0708-0060 

Gary L. Smith 

Consulting Engineer 

Cummings & Smith, Inc. 

EPA-HQ-OAR-2008-0708-0061 Dan Popp 

PM Technologies 

EPA-HQ-OAR-2008-0708-0063 

Robert L. (Bobby) Myers II 

Principal 

Cirrus Consulting, LLC 

EPA-HQ-OAR-2008-0708-0064 

EPA-HQ-OAR-2008-0708-0070 

Chris Mello 

Program Manager, Rural Energy 

Alaska Energy Authority (AEA) 

EPA-HQ-OAR-2008-0708-0065 

EPA-HQ-OAR-2008-0708-0073 

Alice Edwards 

Acting Director 

Alaska Department of Environmental Conservation 

Division of Air Quality 

EPA-HQ-OAR-2008-0708-0066 

Support the comments of 

EPA-HQ-OAR-2008-0708-0064 

Scott Newlun 

General Manger 

Yakutat Power 

EPA-HQ-OAR-2008-0708-0067 L. Stevens 

EPA-HQ-OAR-2008-0708-0068 

Support the comments of 

EPA-HQ-OAR-2008-0708-0064 

Keith Berggren 

Generation Supervisor 

Inside Passage Electric Cooperative (IPEC) 

EPA-HQ-OAR-2008-0708-0069 Ron Sober 

RFS Consulting, Inc. 

EPA-HQ-OAR-2008-0708-0071 

Joy Wiecks 

Air Quality Technician 

Fond du Lac Band of Lake Superior Chippewa (The 

Band) 

EPA-HQ-OAR-2008-0708-0074 

Ken Daubert 

Plant Superintendent 

Kapaia Generating Station, Kauai Island Utility 

Cooperative (KIUC) 

EPA-HQ-OAR-2008-0708-0075 

Support the comments of 

EPA-HQ-OAR-2008-0708-0064 

Jodi Mitchell 

Chief Executive Officer (CEO)/General Manager and 

Keith Berggren 

Generation Supervisor 

Inside Passage Electric Cooperative (IPEC) 

EPA-HQ-OAR-2008-0708-0076 

EPA-HQ-OAR-2008-0708-0114 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0096 

EPA-HQ-OAR-2008-0708-0123 

EPA-HQ-OAR-2008-0708-0242 

David F. Wesson 

EH&S (Environmental Health and Safety) Global 

Regulatory Affairs The Dow Chemical Company (Dow) 
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Document ID Commenter/Affiliation

EPA-HQ-OAR-2008-0708-0077 

Robert E. Williams II 

Environmental Department 

FirstEnergy Corporation (FE) 

EPA-HQ-OAR-2008-0708-0078 

Russ D. Santiago 

Operations Superintendent, Port Allen Generating Station 

Kauai Island Utility Cooperative (KIUC) 

EPA-HQ-OAR-2008-0708-0079 

Bruce D. Alexander 

Environmental Regulatory Strategies Director 

Exelon Corporation 

EPA-HQ-OAR-2008-0708-0080 

Darryl Hoffman 

Utilities Program Manager 

Level 3 Communications, Inc. 

EPA-HQ-OAR-2008-0708-0081 

Kathleen Tobin 

Manager, Corporate Safety & Environmental Compliance 

Verizon Communications Inc. 

EPA-HQ-OAR-2008-0708-0082 

Don C. DiCristofaro 

CCM, President 

Blue Sky Environmental LLC 

EPA-HQ-OAR-2008-0708-0083 

Bruce J. Parker 

President and Chief Executive Officer (CEO), National 

Solid Wastes Management Association (NSWMA) and 

John H. Skinner 

Executive Director and Chief Executive Officer (CEO) 

Solid Waste Association of North America (SWANA) 

EPA-HQ-OAR-2008-0708-0084 

Incomplete Comment (No attachment) Innoventive Power, LLC & CPower, Inc. 

EPA-HQ-OAR-2008-0708-0085 

Support the comments of 

EPA-HQ-OAR-2008-0708-0084 

Demand Response Service Providers (DRSP Coalition) 

Innovative Power, LLC & CPower, Inc. 

EPA-HQ-OAR-2008-0708-0086 

Vincent St. Angelo 

Environmental Engineering 

Babcock & Wilcox Nuclear Operations Group 

(B&W NOG-L) 

EPA-HQ-OAR-2008-0708-0087 

Michael Garvin 

Assistant Vice President 

Scientific and Regulatory Affairs 

Pharmaceutical Research and Manufacturers of America 

(PhRMA) 

EPA-HQ-OAR-2008-0708-0088 

Michael Bradley 

 Director 

The Clean Energy Group (CEG) 
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Document ID Commenter/Affiliation

EPA-HQ-OAR-2008-0708-0089 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0112 

EPA-HQ-OAR-2008-0708-0155 

EPA-HQ-OAR-2008-0708-0242 

Kathleen M. Sgamma 

Director of Government Affairs 

Independent Petroleum Association of Mountain States 

(IPAMS) 

EPA-HQ-OAR-2008-0708-0090 

Steven A. Kent 

Manager -Standby Generation 

Industrial Energy Applications, Inc. (IEA) 

EPA-HQ-OAR-2008-0708-0091 

EPA-HQ-OAR-2008-0708-0096 

Joseph L. Suchecki 

Engine Manufacturers Association (EMA) 

EPA-HQ-OAR-2008-0708-0092 

Debbie Angotto 

Facilities Coordinator, on behalf of 

Thomas L. (surname illegible) 

Greenwich Hospital, Greenwich, CT 

EPA-HQ-OAR-2008-0708-0093 

EPA-HQ-OAR-2008-0708-0211 

Trina L. Vielhauer 

Chief, Bureau of Air Regulation 

Division of Air Resource Management 

Florida Department of Environmental Protection 

EPA-HQ-OAR-2008-0708-0094 

EPA-HQ-OAR-2008-0708-0165 

Laurel L. Kroack 

Chief, Bureau of Air 

Illinois Environmental Protection Agency (Illinois EPA) 

EPA-HQ-OAR-2008-0708-0095 

Reynaldo Tuazon 

Utilities Manager 

Adventist Hinsdale Hospital 

EPA-HQ-OAR-2008-0708-0097 

EPA-HQ-OAR-2008-0708-0163 

Kasey Gabbard 

Permits & Policy Group 

NiSource 

EPA-HQ-OAR-2008-0708-0098 

Brian W. Green 

Air Quality Specialist 

RRI Energy, Inc. 

EPA-HQ-OAR-2008-0708-0099 

Support the comments of 

EPA-HQ-OAR-2008-0708-0096 

Brady Winkleman 

Caterpillar Inc. 

EPA-HQ-OAR-2008-0708-0100 

EPA-HQ-OAR-2008-0708-0208 

Support the comments of 

EPA-HQ-OAR-2008-0708-0096 

Lynn Palmer 

Vice President, Engineering 

Dresser Waukesha 

EPA-HQ-OAR-2008-0708-0101 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0104 

EPA-HQ-OAR-2008-0708-0111 

EPA-HQ-OAR-2008-0708-0112 

EPA-HQ-OAR-2008-0708-0155 

EPA-HQ-OAR-2008-0708-0225 

EPA-HQ-OAR-2008-0708-0242 

Lee O. Fuller 

Independent Petroleum Association of America (IPAA) et 

al. 
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Document ID Commenter/Affiliation

EPA-HQ-OAR-2008-0708-0102 

Scott W. Snedden 

HSE Manager 

Westlake Longview Corporation 

EPA-HQ-OAR-2008-0708-0103 

John Dutton 

HSE Committee Chairman 

Gas Compressor Association (GCA) 

EPA-HQ-OAR-2008-0708-0104 

Angie Burckhalter 

Vice President, Regulatory Affairs 

Oklahoma Independent Petroleum Association (OIPA) 

EPA-HQ-OAR-2008-0708-0105 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0155 

Orland T. Pylant, 

Director, 

Compliance CenterPoint Energy-Mississippi River 

Transmission Corporation (MRT) 

EPA-HQ-OAR-2008-0708-0106 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0155 

Laura L. Guthrie 

Manager, Air Program 

CenterPoint Energy Field Services, Inc. (CEFS)

EPA-HQ-OAR-2008-0708-0107 

Phil Kairis 

Vice President 

Energy Alternatives 

EPA-HQ-OAR-2008-0708-0108 

Bruce Chrisman 

Manager, Engineering 

Cameron's Compression Systems 

EPA-HQ-OAR-2008-0708-0109 

Mark A. Young 

Executive Director 

Lowell Regional Wastewater Utility (LRWWU) 

EPA-HQ-OAR-2008-0708-0110 Union Pacific Railroad Company 

EPA-HQ-OAR-2008-0708-0111 

Frank Mortl 

President/Chief Executive Officer (CEO) 

Michigan Oil And Gas Association (MOGA) 

EPA-HQ-OAR-2008-0708-0112 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0155 

EPA-HQ-OAR-2008-0708-0242 

Johnny Dreyer 

Director of Industry Affairs 

Gas Processors Association (GPA) 

EPA-HQ-OAR-2008-0708-0113 

EPA-HQ-OAR-2008-0708-0222 

John P. Duraes 

President 

New England Healthcare Engineers' Society (NEHES) 

EPA-HQ-OAR-2008-0708-0115 

Christopher Collins 

Source Water Manager 

Pawtucket Water Supply Board (PWSB) 

EPA-HQ-OAR-2008-0708-0116 

G. Vinson Hellwig 

Michigan and 

Robert H. Colby 

Chattanooga, Tennessee, Co-Chairs, Air Toxic 

Committee 

National Association of Clean Air Agencies (NACAA) 
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Document ID Commenter/Affiliation

EPA-HQ-OAR-2008-0708-0117 Anonymous 

EPA-HQ-OAR-2008-0708-0118 

Robin Seguin 

CHMM, Environmental Manager, Qwest Risk 

Management 

Qwest 

EPA-HQ-OAR-2008-0708-0119 

EPA-HQ-OAR-2008-0708-0143 

Marie Robinson 

Chairperson, National Telecommunications Safety Panel 

(NTSP) AT&T Services, Inc. 

EPA-HQ-OAR-2008-0708-0120 

Matt Shields 

Milford Facilities Manager 

Milton Cat 

EPA-HQ-OAR-2008-0708-0121 

Valerie Ughetta 

Director, Stationary Sources 

Alliance of Automobile Manufacturers 

EPA-HQ-OAR-2008-0708-0122 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0155 

John B. Kuhn 

Global Air Leader 

Celanese Corporation 

EPA-HQ-OAR-2008-0708-0123 

EPA-HQ-OAR-2008-0708-0134 

Jim Griffin 

Senior Director 

American Chemistry Council (ACC) 

EPA-HQ-OAR-2008-0708-0124 

EPA-HQ-OAR-2008-0708-0235 

Tim Knox 

Vice President, Engineering and Production 

Compressor Systems, Inc. (CSI) 

EPA-HQ-OAR-2008-0708-0125 

Martin E. Rock, P.E., J.D. 

President & Senior Principal 

OMNI Professional Environmental Associates, P.A. 

EPA-HQ-OAR-2008-0708-0126 

F. William Brownell and Craig S. Harrison 

Hunton & Williams LLP on behalf of the 

Utility Air Regulatory Group (UARG) 

EPA-HQ-OAR-2008-0708-0127 

Julie Frazier 

Senior Environmental Specialist 

Butler County Water and Sewer Department (BCWS) 

EPA-HQ-OAR-2008-0708-0128 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0155 

Nicholas DeMarco 

Executive Director 

West Virginia Oil and Natural Gas Association 

EPA-HQ-OAR-2008-0708-0129 

Cathy Waxman 

Manager 

Air Quality Compliance, National Grid 

EPA-HQ-OAR-2008-0708-0130 

Steve Hensley 

Senior Director Regulatory Affairs 

USA Rice Federation 

EPA-HQ-OAR-2008-0708-0131 

John Dutton 

Manager, Operations 

J-W Power Company 
8

Document ID Commenter/Affiliation

EPA-HQ-OAR-2008-0708-0132 

Gerald Meinecke 

Vice President - Procurement & Compression 

Exterran 

EPA-HQ-OAR-2008-0708-0133 

Jim Griffin 

Senior Director 

American Chemistry Council (ACC) 

EPA-HQ-OAR-2008-0708-0135 

R. J. Riley 

Texas Agriculture Energy Users Association (TAEUA) 

and 

Texas Corn Growers Association 

EPA-HQ-OAR-2008-0708-0136 

EPA-HQ-OAR-2008-0708-0237 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0045 

EPA-HQ-OAR-2008-0708-0046 

EPA-HQ-OAR-2008-0708-0104 

EPA-HQ-OAR-2008-0708-0242 

Darren Smith 

Manager, Environmental Health and Safety (EHS) 

Devon Energy Corporation 

EPA-HQ-OAR-2008-0708-0137 

Tim Knox 

Vice President 

Engineering and Production 

Compressor Systems, Inc. (CSI) 

EPA-HQ-OAR-2008-0708-0138 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0101 

EPA-HQ-OAR-2008-0708-0104 

Gregory D. Russell 

Vorys, Sater, Seymour and Pease LLP on behalf of 

Ohio Oil and Gas Association (OOGA) 

EPA-HQ-OAR-2008-0708-0139 Craig Eckberg 

NRG Energy, Inc. 

EPA-HQ-OAR-2008-0708-0140 

Golder Associates Inc. on behalf of 

David A. Buff 

Principal Engineer 

Mosaic Fertilizer LLC (Mosaic) 

EPA-HQ-OAR-2008-0708-0141 

John Preczewski 

P.E., Assistant Director 

State of New Jersey Department of Environmental 

Protection (NJDEP) 

EPA-HQ-OAR-2008-0708-0142 

Michael S. Dae 

Wellfield and Environmental Compliance Manager 

Energy Developments, Inc. (EDI) 

EPA-HQ-OAR-2008-0708-0144 

Richard T. Wolbach 

CEM, Department of Physical Plant 

The University of Vermont (UVM) 

EPA-HQ-OAR-2008-0708-0145 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0155 

Debra A. Ristig 

Vice President, Engineering and Compliance 

CenterPoint Energy Gas Transmission Company (CEGT) 
9

Document ID Commenter/Affiliation

EPA-HQ-OAR-2008-0708-0146 

Karl M. Bhatnagar, P.E., 

ESH&M, Air Quality 

Northrop Grumman, Aerospace Systems (NGAS) 

EPA-HQ-OAR-2008-0708-0147 

David A. Buff 

Principal Engineer, Golder Associates Inc. on behalf of 

The Florida Sugar Industry (FSI)

EPA-HQ-OAR-2008-0708-0148 

Ethan W. Hinkley 

Environmental Compliance Specialist, Air Quality 

Red Cedar Gathering Company 

EPA-HQ-OAR-2008-0708-0149 

Kathryn Garcia 

Commissioner 

New York City Department of Environmental Protection 

(NYCDEP) 

EPA-HQ-OAR-2008-0708-0150 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0112 

EPA-HQ-OAR-2008-0708-0155 

EPA-HQ-OAR-2008-0708-0242 

Patrick J. Nugent 

Executive Director 

Texas Pipeline Association (TPA) 

EPA-HQ-OAR-2008-0708-0151 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0112 

EPA-HQ-OAR-2008-0708-0155 

EPA-HQ-OAR-2008-0708-0242 

Bruce Thompson 

 President 

American Exploration and Production Council (AXPC) 

EPA-HQ-OAR-2008-0708-0152 Shannon S. Broome 

Air Permitting Forum 

EPA-HQ-OAR-2008-0708-0153 

Marilyn Leland 

Executive Director 

Alaska Power Association 

EPA-HQ-OAR-2008-0708-0154 

Robert D. Bessette 

President 

Council of Industrial Boiler Owners (CIBO) 

EPA-HQ-OAR-2008-0708-0156 

Kevin D. Bailey 

Air Compliance Supervisor 

ExxonMobil Production Company 

EPA-HQ-OAR-2008-0708-0157 

EPA-HQ-OAR-2008-0708-0096 

EPA-HQ-OAR-2008-0708-0123 

EPA-HQ-OAR-2008-0708-0155 

EPA-HQ-OAR-2008-0708-0221 

EPA-HQ-OAR-2008-0708-0242 

Debra J. Jezouit and 

 Megan Berge 

Baker Botts L.L.P. on behalf of 

Class of '85 Regulatory Response Group 

EPA-HQ-OAR-2008-0708-0158 

Terry L. Steinert 

Environmental Compliance Manager 

Koch Carbon, LLC (Koch Carbon) 
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Document ID Commenter/Affiliation

EPA-HQ-OAR-2008-0708-0159 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0257 

Mary Uhl 

Chief, Air Quality Bureau (AQB) 

New Mexico Environment Department (NMED) 

EPA-HQ-OAR-2008-0708-0160 

EPA-HQ-OAR-2008-0708-0257 

Cynthia Finley 

Director, Regulatory Affairs 

National Association of Clean Water Agencies 

(NACWA) 

EPA-HQ-OAR-2008-0708-0161 

Dave Copeland 

Manager, Air Quality, Corporate Safety & Environmental 

Services Praxair, Inc. 

EPA-HQ-OAR-2008-0708-0162 

Kathryn R. Ross 

Senior Environmental Planner 

Consumers Energy Company 

EPA-HQ-OAR-2008-0708-0164 

Mary Uhl 

Air Quality Bureau 

New Mexico Environment Department (Incomplete) 

EPA-HQ-OAR-2008-0708-0166 

Andy Ly, PE CEM 

Director, Facilities Management & Planning, Energy 

Administration & Operations 

Boston University (BU) 

EPA-HQ-OAR-2008-0708-0167 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0121 

EPA-HQ-OAR-2008-0708-0154 

Lawrence W. Kavanagh 

Vice President 

American Iron and Steel Institute (AISI) and 

Bruce A. Steiner 

President 

American Coke and Coal Chemicals Institute (ACCCI) 

EPA-HQ-OAR-2008-0708-0168 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0126 

William T. Horton 

Senior Environmental Specialist 

Environmental Health and Safety Air Management 

Duke Energy Corporation (Duke Energy) 

EPA-HQ-OAR-2008-0708-0169 

Rick N. Soucy 

Senior Project Manager 

GZA GeoEnvironmental, Inc. 

EPA-HQ-OAR-2008-0708-0170 

Mark Macarro 

Tribal Chairman 

Pechanga Band of Luiseno Indians (Tribe) 

EPA-HQ-OAR-2008-0708-0171 

Mark J. Sedlacek 

Director 

Environmental Services 

Los Angeles Department of Water and Power (LADWP) 

EPA-HQ-OAR-2008-0708-0172 

Kerwei Sew 

Senior Environmental Engineer, Environmental 

Operations 

3M Company 
11

Document ID Commenter/Affiliation

EPA-HQ-OAR-2008-0708-0173 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0206 

T. Moser 

Chairman, Strategic Team and Resource Sharing 

(STARS) 

Integrated Regulatory Affairs Group 

EPA-HQ-OAR-2008-0708-0174 

Mark Maslyn 

Executive Director, Public Policy 

American Farm Bureau Federation (AFBF) 

EPA-HQ-OAR-2008-0708-0175 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0155 

EPA-HQ-OAR-2008-0708-0241 

Pamela A. Lacey 

Senior Managing Counsel 

American Gas Association (AGA) 

EPA-HQ-OAR-2008-0708-0176 

Deirdre K. Hirner 

Executive Director 

Illinois Environmental Regulatory Group (IERG) et al. 

EPA-HQ-OAR-2008-0708-0177 

Shawne C. McGibbon 

Acting Chief Counsel for Advocacy and 

Keith Holman 

Assistant Chief Counsel for Environmental Policy, Office 

of Advocacy 

U.S. Small Business Administration (SBA) 

EPA-HQ-OAR-2008-0708-0178 

Lisa Goldberg 

Director, Environment, Safety and Health 

Aerospace Industries Association of America (AIA) 

EPA-HQ-OAR-2008-0708-0179 

Marilyn Crockett 

Executive Director 

Alaska Oil and Gas Association (AOGA) 

EPA-HQ-OAR-2008-0708-0181 

EPA-HQ-OAR-2008-0708-0243 

Scott Davis 

Director, Environmental, Health & Safety 

Arizona Public Service (APS) 

EPA-HQ-OAR-2008-0708-0182 

Shawn Wade 

Director, Communications 

Plains Cotton Growers, Inc. (PCG) 

EPA-HQ-OAR-2008-0708-0183 

Don Mark Anthony 

Air Quality Engineer 

Alyeska Pipeline Service Company (Alyeska) 

EPA-HQ-OAR-2008-0708-0184 

Jack F. Alvey 

Vice President, Generation 

Indiana Municipal Power Agency (IMPA) 

EPA-HQ-OAR-2008-0708-0185 

Earl C. Burke 

Facilities Engineering Manager 

Baltimore Washington Medical Center (BWMC) 
12

Document ID Commenter/Affiliation

EPA-HQ-OAR-2008-0708-0186 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0112 

EPA-HQ-OAR-2008-0708-0155 

EPA-HQ-OAR-2008-0708-0242 

William W. (Bill) Grygar II 

Environmental and Regulatory Manager 

Anadarko Petroleum Corporation 

EPA-HQ-OAR-2008-0708-0187 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0096 

EPA-HQ-OAR-2008-0708-0155 

Karen St. John 

Director, Regulatory Affairs 

BP America Inc. (BP) 

EPA-HQ-OAR-2008-0708-0188 

Steve Donatiello, P.E. 

Senior Environmental Engineer 

Laclede Gas Company 

EPA-HQ-OAR-2008-0708-0189 

Rick A. Kress 

President 

Southern Gardens Citrus Holding Corporation 

EPA-HQ-OAR-2008-0708-0190 

Stuart Latham 

Manager, Land and Environmental 

Southern Star Central Gas Pipeline, Inc. (Southern Star) 

EPA-HQ-OAR-2008-0708-0191 

EPA-HQ-OAR-2008-0708-0239 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0083 

EPA-HQ-OAR-2008-0708-0126 

EPA-HQ-OAR-2008-0708-0155 

Skiles Boyd 

Vice President, Environmental Management and 

Resources 

DTE Energy 

EPA-HQ-OAR-2008-0708-0192 Terry Steinert 

Koch Carbon LLC 

EPA-HQ-OAR-2008-0708-0193 

James D. Jones 

Senior Consultant, EHS Services North America 

Alcoa Inc. 

EPA-HQ-OAR-2008-0708-0194 

Larry LeJeune 

Director, Pesticide and Environmental Programs Division, 

Office of Agricultural and Environmental Sciences 

Louisiana Department of Agriculture and Forestry 

EPA-HQ-OAR-2008-0708-0195 

Michael L. R. Housley 

President 

Legacy Energy Group, LLC 

EPA-HQ-OAR-2008-0708-0196 

Sarah E. Amick 

Environmental Counsel 

Rubber Manufacturers Association (RMA) 

EPA-HQ-OAR-2008-0708-0197 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0126 

Nilaksh Kothari 

General Manager 

Manitowoc Public Utilities (MPU) 

EPA-HQ-OAR-2008-0708-0198 

Bernard Milam 

Energy Manager 

University of Maryland Medical Center (UMMC) 
13

Document ID Commenter/Affiliation

EPA-HQ-OAR-2008-0708-0199 

Joseph Kubsh 

Executive Director 

Manufacturers of Emission Controls Association (MECA) 

EPA-HQ-OAR-2008-0708-0200 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0242 

Michelle Koch 

HES (Health/Environment/Safety) Professional 

Marathon Oil Corporation 

EPA-HQ-OAR-2008-0708-0201 

Chad Gregory 

Senior Vice President 

United Egg Producers (UEP) 

EPA-HQ-OAR-2008-0708-0202 

Theresa Pfeifer 

Regulatory Compliance Officer 

Metro Wastewater Reclamation District 

EPA-HQ-OAR-2008-0708-0203 

Caroline Choi 

Director, Energy Policy & Strategy 

Progress Energy 

EPA-HQ-OAR-2008-0708-0204 

Jon E. Kallen 

Manager, Environmental Policy and Strategy 

MidAmerican Energy Holdings Company 

EPA-HQ-OAR-2008-0708-0205 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0155 

Michael Tomko 

Counsel, Parsons Behle & Latimer on behalf of 

Utah Industry Environmental Coalition (UIENC) 

EPA-HQ-OAR-2008-0708-0206 

Amy Van Kolken Banister 

Senior Director, Air and Landfill Gas Programs and 

Kerry Kelly 

Director, Federal Public Affairs 

Waste Management (WM) 

EPA-HQ-OAR-2008-0708-0207 

EPA-HQ-OAR-2008-0708-0126 

John C. Butler 

Director, Operations Support 

Nuclear Energy Institute (NEI) 

EPA-HQ-OAR-2008-0708-0209 

Stephen R. Gossett, P.E. 

Senior Environmental Associate 

Eastman Chemical Company (ECC) 

EPA-HQ-OAR-2008-0708-0210 

Supports the comment of 

EPA-HQ-OAR-2008-0708-0155 

Vincent L. Brindley 

Principal Environmental Engineer 

El Paso Pipeline Group 

EPA-HQ-OAR-2008-0708-0212 

G. William Fowler 

Attorney, on behalf of the 

West Texas Gas Inc. (WTG) 

EPA-HQ-OAR-2008-0708-0213 

Ed Torres 

Director of Technical Services 

Orange County Sanitation District (OCSD) 

EPA-HQ-OAR-2008-0708-0214 

Brian Bonnell 

Senior Manager, Strategic Sourcing and Procurement 

Human Genome Sciences 
14

Document ID Commenter/Affiliation

EPA-HQ-OAR-2008-0708-0215 

Hilary Sinnamon 

Consultant 

Environmental Defense Fund (EDF) 

EPA-HQ-OAR-2008-0708-0216 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0088 

EPA-HQ-OAR-2008-0708-0157 

EPA-HQ-OAR-2008-0708-0207 

Rayburn L. Butts 

Director, Environmental Services 

Florida Power and Light Company (FPLC) 

EPA-HQ-OAR-2008-0708-0217 Michael Hutcheson 

Ameren Corporation 

EPA-HQ-OAR-2008-0708-0218 

EPA-HQ-OAR-2008-0708-0233 

Supports comments of 

EPA-HQ-OAR-2008-0708-0155 

Everette Johnson 

Director, Engineering 

Cameron Compression Systems 

EPA-HQ-OAR-2008-0708-0219 

Dan Pugliese 

Director, Engineering 

Hines 

EPA-HQ-OAR-2008-0708-0220 

Cathy S. Formigoni 

Legal Assistant, Hodge Dwyer & Driver on behalf of 

Illinois Municipal Electric Agency (IMEA) 

EPA-HQ-OAR-2008-0708-0221 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0112 

EPA-HQ-OAR-2008-0708-0155 

EPA-HQ-OAR-2008-0708-0242 

Deb Hastings 

Vice President, Environmental Affairs 

Texas Oil and Gas Association (TXOGA) 

EPA-HQ-OAR-2008-0708-0223 

Elizabeth A. Rubino 

SVP Human Resources 

QVC 

EPA-HQ-OAR-2008-0708-0224 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0155 

Edward L. Kropp 

Chair, Air Subcommittee, Environmental Committee 

West Virginia Chamber of Commerce 

EPA-HQ-OAR-2008-0708-0225 

Deborah Seligman 

Vice President, Governmental Affairs 

New Mexico Oil & Gas Association (NMOGA) 

EPA-HQ-OAR-2008-0708-0226 

Shawne C. McGibbon 

Acting Chief Counsel and 

Kevin Bromberg 

Assistant Chief Counsel, Environmental Policy, Office of 

Advocacy Small Business Administration (SBA) 

EPA-HQ-OAR-2008-0708-0227 

Quinn V. Kilty 

Manager 

Air/Water, Xcel Energy, Inc. 

EPA-HQ-OAR-2008-0708-0228 

Eric L. Riser 

Jorden Bischoff & Hiser 

PLC Counsel for Nucor Corporation 
15

Document ID Commenter/Affiliation

EPA-HQ-OAR-2008-0708-0229 

Carl H. Batliner 

Director, Environmental Affairs 

AK Steel Corporation 

EPA-HQ-OAR-2008-0708-0230 

Andrew C. Lawrence 

Director, Office of Nuclear Safety, Quality Assurance and 

Environment, Office of Health, Safety and Security 

U.S. Department of Energy (DOE) 

EPA-HQ-OAR-2008-0708-0231 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0112 

EPA-HQ-OAR-2008-0708-0155 

EPA-HQ-OAR-2008-0708-0242 

John Robitaille 

Vice President 

Petroleum Association of Wyoming (PAW) 

EPA-HQ-OAR-2008-0708-0232 

David R. Bell 

Sustainability Engineer, Facilities Supervisor 

Becton Dickinson Diagnostic Systems 

Baltimore Campus 

EPA-HQ-OAR-2008-0708-0234 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0112 

EPA-HQ-OAR-2008-0708-0155 

Ann W. McIver 

QEP, Director, Environmental Stewardship 

Citizens Gas 

EPA-HQ-OAR-2008-0708-0236 

John Quinn 

Director, Environmental Issues 

Constellation Energy 

EPA-HQ-OAR-2008-0708-0238 

EPA-HQ-OAR-2008-0708-0248 

EPA-HQ-OAR-2008-0708-0252 

Karl M. Kyriss 

President 

Aqua America, Inc. 

EPA-HQ-OAR-2008-0708-0240 

Bruce R. Byrd 

Vice President and General Counsel-Washington 

AT&T Services, Inc. 

EPA-HQ-OAR-2008-0708-0241 

Supports comments of 

EPA-HQ-OAR-2008-0708-0155 

EPA-HQ-OAR-2008-0708-0175 

William D. Schrand 

Administrator, Environmental Programs 

Southwest Gas Corporation 

EPA-HQ-OAR-2008-0708-0244 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0112 

EPA-HQ-OAR-2008-0708-0155 

Richard Bye 

Director, Environmental Services 

CenterPoint Energy, Inc. 

EPA-HQ-OAR-2008-0708-0245 

Ronald J. Schott Esq. 

Senior Corporate Counsel, Environment, Health and 

Safety 

Wyeth 

EPA-HQ-OAR-2008-0708-0246 Jim Valentine 

Combustion Components Associates, Inc. (CCA) 
16

Document ID Commenter/Affiliation

EPA-HQ-OAR-2008-0708-0247 

Supports the comments of 

EPA-HQ-OAR-2008-0708-0126 

EPA-HQ-OAR-2008-0708-0155 

EPA-HQ-OAR-2008-0708-0175 

Pamela F. Faggert 

Vice President and Chief Environmental Officer 

Dominion Resources Services, Inc. 

EPA-HQ-OAR-2008-0708-0249 

Kenneth D. Schisler 

Senior Director, Regulatory Affairs 

EnerNOC, Inc. (EnerNOC) 

EPA-HQ-OAR-2008-0708-0250 

Michael A. Caldarera 

Vice President, Regulatory and Technical Services 

National Propane Gas Association (NPGA) 

EPA-HQ-OAR-2008-0708-0251 

Marielle Daniels 

Manager, Patient Care Regulation 

Connecticut Hospital Association (CHA) 

EPA-HQ-OAR-2008-0708-0253 

EPA-HQ-OAR-2008-0708-0258 

EPA-HQ-OAR-2008-0708-0260 

Sean M. O’Keefe 

Director, Environmental Affairs 

Alexander & Baldwin, Inc. (A&B) 

EPA-HQ-OAR-2008-0708-0255 

John Otto 

Engineering Manager 

Brush Resources, Inc. 

EPA-HQ-OAR-2008-0708-0256 

Craig Wysong 

EHS Manager 

CARBO Ceramics, Inc. 

EPA-HQ-OAR-2008-0708-0259 

John Prescott 

Executive Vice President and General Manager 

Power Resources Cooperative (PRC) 

EPA-HQ-OAR-2008-0708-0261 

Michael H. Bernard 

President 

Mid-Continent Oil and Gas Association of Oklahoma 

(MCOGAO) 

EPA-HQ-OAR-2008-0708-0262 

Ed Hasely, Sr. 

Environmental Engineer 

Energen Resources 

EPA-HQ-OAR-2008-0708-0263 

Michael J. Kelly 

Director, Facilities Management 

University of Massachusetts Memorial Medical Center 

(UMassMMC) 

EPA-HQ-OAR-2008-0708-0264 

Chelly Reesman 

Environmental Engineer 

J.R. Simplot Company 

EPA-HQ-OAR-2008-0708-0265 

Scott Salisbury 

President 

Landfill Energy Systems 
17

Document ID Commenter/Affiliation

EPA-HQ-OAR-2008-0708-0267 

Jeffrey A. Smith 

Lead Environmental Scientist, Infrastructure Maintenance 

Division 

South Florida Water Management District 

EPA-HQ-OAR-2008-0708-0268 

Peter H. Zeliff 

President and CEO 

Innovative Energy Systems 

EPA-HQ-OAR-2008-0708-0269 Louisiana Farm Bureau Federation 
18

Summary of Public Comments and Responses 

The summary of public comments and responses is organized as follows:

1.0 General Approach 

2.0 Applicability 

2.1 Major Sources 

2.2 Area Sources 

2.3 Small Engines 

2.4 Natural Gas Engines 

2.5 Other 

3.0 Startup, Shutdown, and Malfunction 

4.0 Emissions 

 4.1 RICE Emissions Database 

 4.2 Surrogates 

 4.3 Engine Test Data 

5.0 Emission Limits 

 5.1 Major Sources 

 5.1.1 MACT Floor 

 5.1.2 Above-the-Floor 

 5.1.3 Subcategories 

 5.2 Area Sources 

 5.3 Emergency Engines 

 5.4 Small Engines 

 5.5 Landfill/Digester Gas Engines 

 5.7 Format of Standards and Other Issues Related to Standards 

 5.8 Technology 

6.0 Exemptions/Special Allowances 

 6.1 Limited Use Engines 

 6.2 Other Engines 

7.0 Management Practices 

 7.1 General Comments 

 7.2 Specific Requirements 

8.0 Parameter Monitoring 

9.0 Compliance 

 9.1 Test Procedures 

 9.2 Test Methods 

 9.3 Frequency 
19

 9.4 Other 

10.0 Recordkeeping, Reporting and Notifications 

11.0 Docket Materials/Transparent Regulatory Process 

12.0 Rule Impacts 

 12.1 Economic Impacts 

 12.2 Environmental/Health Impacts 

 12.3 Cost of Controls 

 12.4 Implementation and Enforcement 

 12.5 Energy Impacts 

 12.6 Small Businesses 

13.0 Miscellaneous 

 13.1 Definitions 

 13.2 Clarifications 

 13.3 Errors 

 13.4 Discrepancies 

 13.5 Other 
20

1.0 General Approach 

1.1 Comment: A few commenters (61, 94, 116) support EPA’s proposed rulemaking. One 

commenter (94) supports EPA’s proposed actions to reduce exhaust pollutants from existing 

stationary RICE that are located at area sources of HAP emissions and certain existing stationary 

RICE and stationary compression ignition (CI) engines that are located at major sources of HAP 

emissions. One commenter (116) commended the EPA for proposing a regulation that will 

reduce HAP and diesel emissions from the RICE source category. 

Response: No response is needed.

1.2 Comment: A few commenters (155, 224 and 242) are concerned with how the proposed 

rulemaking is in some cases the first in addressing recent Court decisions. Some of the recent 

issues include the following: 

• The Brick maximum achievable control technology (MACT) decision determined that 

EPA must set standards for HAP and cannot avoid standards in cases when the MACT 

floor is no control, 

• The Brick MACT decision indicated that EPA has to consider the range of emission level 

associated with the best performing sources; and 

• The rejection of the startup, shutdown and malfunction (SSM) exemption meaning that 

HAP emission standards must apply continuously. The Court expressed the need for 

some standard, but this does not mean an unchanging standard. 
21

The proposed rule is setting a precedent, but the commenters (155, 242) noted that there 

is no clear evidence of how EPA considered integrating these decisions into the rulemaking. 

Regarding the MACT floor decisions, the commenters (155, 242) believe the floor was based on 

flawed and deficient data. The commenters (155, 242) do not believe EPA has considered 

emissions variability. For SSM limits, the commenters (155, 242) said that EPA has set limits 

without any data from actual SSM events. The importance of integrating these Court decisions 

warrants considerable additional effort by EPA for this rulemaking, the commenters (155, 242) 

said. Commenters 155 and 242 specifically addressed each particular issue in separate 

comments, but noted that the issues reach beyond this rulemaking and will convey the Agency’s 

perspective that may be applied to future rulemakings. For these reasons, the commenters (155, 

242) firmly believe that EPA should provide guidance material to communicate to the public the 

Agency’s interpretation of Court decisions and how those will be incorporated into future rules. 

Response: EPA understands the commenters’ concerns with respect to recent court decisions 

affecting how the regulations for existing stationary engines at area sources and existing 

stationary engines less than or equal to 500 HP at major sources were developed. The U.S. Court 

of Appeals for the District of Columbia Circuit on March 13, 2007 vacated EPA’s MACT 

standards for the Brick and Structural Manufacturing category (40 CFR part 63, subpart JJJJJ). 

This is referred to as the “Brick MACT decision” (Sierra Club v. EPA, 479 F.3d 875 (D.C. Cir. 

2007).) EPA recognizes that it had limited emissions data when it developed the MACT floor 

standards for the proposed rule. EPA has on several occasions requested emissions data from 

industry and solicited data in the preamble to the proposed rule. However, EPA had to propose 

emission standards based on what data was available at the time. During the public comment 
22

period and the months following the close of the public comment period, EPA has worked with 

various groups and been able to gather additional emissions test data for stationary engines. EPA 

has reviewed the original emissions test data used to develop the proposed standards to ensure 

that engines were properly identified and categorized, as well as to determine if there was any 

other information that may indicate that the data was used inappropriately at proposal. 

For the proposed MACT floor for existing engines at major sources, EPA selected the 

best performing 12 percent of sources it had emissions data for within each engine subcategory. 

Commenters argued that EPA’s approach at proposal did not consider emissions variability. The 

approach at proposal counted each emissions test as a single data point. This meant that for 

cases where an engine was tested multiple times, the MACT floor may have included multiple 

data points from one engine, but only one data point from another engine. Commenters argued 

that this approach does not sufficiently take into account emissions variability or potentially 

inappropriately skews the MACT floor toward the one engine that was tested multiple times 

because with multiple data points emissions from that engine would have more weight in the top 

12 percent. EPA believes that it is appropriate to use a different approach for incorporating 

emissions variability in the final standards. Subsequently, EPA has reanalyzed the available 

emissions data and considered different ways of taking into account the range of emissions that 

can occur. EPA discussed the final approach in setting the MACT floor limits more extensively 

in the memo entitled “MACT Floor and MACT Determination for Existing Stationary SI RICE 

≤500 HP Located at Major Sources.” 

 Regarding the proposed SSM limits, EPA received numerous concerns from affected 

stakeholders on a range of issues. These issues are discussed in Section 3.0. EPA is not 

finalizing particularized numerical emission limits specifically for periods of SSM, but is issuing 
23

operational standards for periods of startup and including periods of shutdown and malfunction 

within the emission standards that generally apply to the various subcategories of stationary SI 

engines. The reasons for the approach we take in the final rule are discussed in the responses to 

comments in Section 3.0. 

EPA plans to make implementation and compliance material available to the regulated 

community following the promulgation of this rule. However, EPA cannot promise that such 

material will include the Agency’s interpretation of Court decisions and how those will be used 

in future rules. 

1.3 Comment: Several commenters (89, 93, 101, 104, 112, 129, 150, 151, 172, 186, 221, 231, 

242, 261, 264) noted concerns due to a complex proposed rulemaking and some commenters 

added that it is extra problematic to implement due to previous rulemakings issued that affect 

similar and sometimes the same engines. One commenter (242) noted that it has a number of 

outstanding and unresolved petitions submitted to EPA on the CI NSPS and SI new source 

performance standards (NSPS)/NESHAP, where it has questions concerning implementation and 

enforcement of those rules. There is ongoing confusion among State and regional agencies in 

implementing these rules, something that is exacerbated by EPA’s lack of response and guidance 

on several implementation questions, the commenter (242) said. According to the commenter 

(242), the inclusion of natural gas engines with diesel engines in this rulemaking will lead to a 

further increase in unresolved, issues complicating rule requirements and implementation. For 

example, for the SI NSPS/NESHAP, the commenter (242) pointed out various issues, which 

included a discussion on the integration of risk-based criteria for area source engines under the 

NESHAP. For that rulemaking, compliance with the NESHAP was mostly shown by 
24

demonstrating compliance with the NSPS, therefore it seems the comment went largely 

unanswered by EPA, the commenter (242) said. The commenter (242) indicated that it was 

hoping EPA would address this issue in this rulemaking, but has not. In general, the commenter 

(242) recommended that EPA develop and publish substantive compliance tools and provide 

assistance in interpreting rule requirements from multiple overlapping engine rules. 

Commenters 89, 101, 151, 221, 231 stated that the rules are complex because of their 

overlap with and references to the mobile source engine rules (i.e., for automobiles, boats, 

construction equipment, etc.). The commenters (89, 101, 151, 221, 231) believe that the mobile 

source rules are not well understood by the agencies and industries involved with the stationary 

source rules, and added that EPA has done little to aid the agencies and industry in understanding 

these rules. Additionally, the commenters (89, 101, 151, 221, 231) believe that EPA should 

delay promulgation of these rules until compliance assistance material can be developed to aid 

the state agencies and regulated community in their compliance efforts. 

One commenter (112) in the natural gas industry stated the member companies in his 

organization are interpreting and complying with five sweeping new federal engine regulations 

that have been promulgated in the last several years, which include 40 CFR part 63, subpart 

ZZZZ, the consolidated engine rule - MACT, subpart ZZZZ amendments for small engines, the 

consolidated engine rule – Generally Available Control Technology (GACT), subpart ZZZZ 

amendments for area source engines, 40 CFR part 60, subpart JJJJ (SI NSPS), and 40 CFR part 

60, subpart IIII (CI NSPS). 

Two commenters (112, 150) contended that each of these engine regulations has brought 

significant changes to control requirements, training, monitoring, recordkeeping, and reporting. 

In addition, the commenter (112) pointed out that both the Consolidated Engine Rule and the CI 
25

NSPS are still under litigation by API. The commenter (112) believes that the proposed 

regulations add tremendously to the current requirements by bringing existing engines under the 

rules with more stringent requirements than new or reconstructed sources. The commenter (112) 

stated that its member companies have serious concerns with interpreting the complex current 

and proposed compliance requirements and asked that EPA attempt to simplify existing federal 

engine rule requirements before the SI rules are finalized. 

 The commenter (112) noted that determining applicability of the rule requires companies 

to define engines as existing, new, or reconstructed, which is difficult, and often impossible, 

primarily because records that are required to determine if the engine has been reconstructed may 

be on multiple authorizations for expenditures (AFEs) or may simply not exist. The commenter 

(112) said that most, if not all, states have preconstruction authorizations that require companies 

to begin the permitting process well in advance of commencement of construction. The 

permitting process is complicated because specific regulatory requirements cannot be determined 

until the unit is overhauled and the final invoices are received, according to commenter 112. 

Frequently, engines are leased and returned to distributors and later purchased or leased by other 

companies and records get lost or possibly never obtained or maintained, making it nearly 

impossible for the new owner to establish a complete life history of an engine, commenter 112 

added. Commenter 112 also pointed out that competing companies may be reluctant or 

unwilling to share their records with new owners. Also, in absence of sufficient documentation, 

some companies may make the conservative assumption that the rule applies, while others will 

assume by lack of documentation that the rule does not apply, the commenter (112) said. 
26

Two commenters (112 and 150) said that a modified engine could be “new” under NSPS 

and “existing” under NESHAP because NESHAP considers only reconstruction and not 

modification, whereas NSPS considers both reconstruction and modification. 

The commenter (112) additionally indicated that subpart ZZZZ is already very complex 

due to the numerous cross references to the mobile source regulations in 40 CFR parts 90 and 

1068, as well as the 2008 amendments that added requirements for new small lean burn engines 

at major sites. The commenter (112) believes that adding this proposed major amendment to 

cover existing sources would make subpart ZZZZ even more difficult for both regulatory 

agencies and industry to interpret and for those who are subject, to comply. To simplify the 

proposed regulation, several commenters (89, 101, 112, 151, 221, 231, 242) recommended a new 

separate section, subpart ZZZZa. Commenter 261 suggested a similar separation of subsections 

and that EPA should delay promulgation until compliance assistance material can be developed 

to aid the State agencies and regulated community in their compliance efforts. 

One commenter (112) in the natural gas industry objected that the proposed rules are 

inflexible and the requirements are difficult with minimal or no added environmental benefit. 

The commenter (112) stated that the member companies in his organization are concerned with 

the overly prescriptive nature of the proposed requirements, particularly as they relate to testing, 

maintenance practices, reporting, and recordkeeping requirements. 

One commenter (104) in the oil and gas industry stated that the proposed rule requires a 

person with significant knowledge and experience with Clean Air Act (CAA) laws and rules in 

order to fully evaluate and understand the proposed rule. The commenter (104) was very 

concerned that many small businesses that operate crude oil and natural gas facilities, especially 

those that operate marginal wells, do not have the knowledge or the level of experience to fully 
27

understand and evaluate the proposed rule, and determine the impacts to their operations. The 

commenter (104) noted that the majority of the upstream crude oil and natural gas facilities have 

low emissions that fall below air permitting thresholds, and as such, are not familiar with air 

requirements. The commenter (104) was concerned that EPA will not receive feedback from 

many operators, especially the smaller businesses/companies who will be directly impacted by 

the proposed rule. 

Commenter 150 said that the complexity has been exacerbated by the fact that the 

applicability of some requirements is uncertain due to ongoing litigation. The commenter (150) 

believes that the proposed rules will add to the complexity by bringing in existing engines. The 

commenter (150) gave the following examples of instances when it will be difficult to determine 

which rules apply to which engines: 

• Applicable requirements are different depending on whether an engine had or had not 

been reconstructed. Making that determination would be difficult or impossible in some 

cases because records may be hard to locate and hard to access or they may no longer 

exist. 

• Requirements may differ based on whether a source is a major source or minor source. 

As engines were added or subtracted, the facility’s status could vary, and so could the 

applicable rules. In this regard, the commenter (150) believes that EPA should allow a 

facility sufficient time to come into compliance when a facility’s status changes due to 

addition or removal of equipment. The commenter (150) proposed a 3-year compliance 

period, which the commenter said was done in the NESHAP for natural gas transmission 

and storage [40 CFR 63.1270(d)(1)]. 
28

One commenter (93) provided an 18-page applicability flow chart to illustrate the 

permitting and compliance applicability requirements for the subject engines. The commenter 

(93) reported that differing state agency flow charts and guidance materials reviewed by them 

(Texas and Nebraska) have reached different interpretations regarding the applicability of the 

proposed rule. The commenter (93) stated that this highlights concerns regarding the rule’s 

complexities, which the commenter believed could result in inconsistent implementation 

throughout the country. The commenter (93) further reported that it had received numerous 

telephone calls from consultants outside of Florida asking for the commenter’s interpretation of 

the proposed changes in an effort to gain a general consensus of the states on the rule’s 

applicability. For example, a new category was proposed for existing emergency SI engines with 

a site rating of less than or equal to 500 HP located at a major source of HAP. The commenter 

(93) reported that they were able to determine the emission and operating limitations, 

maintenance requirements and equipment needed. However, they stated that the compliance 

requirements (40 CFR 63.6630 Table 5 in the Appendix) are clearly identified for only a few 

specific engine categories and then appear to group the rest of the engine categories in one large 

category of engines with a site rating of less than or equal to 500 HP located at a major source of 

HAP. The commenter (93) expressed that it is unclear if this large category is meant to be 

inclusive or exclusive of the remaining specific engines categories, such as emergency engines 

and SI engines. 

The commenter (93) recommended that EPA revise the NESHAP to specify all the 

applicable requirements under a given engine category subheading. The commenter (93) opined 

that, this way, applicability would then only need to be determined once for each engine category 
29

as the applicable requirements (emissions and operating limitations, general compliance 

requirements, etc.) would be specified by regulated engine category. 

Response: The engines that are subject to the NSPS are new engines and are not the focus of this 

rulemaking. EPA, therefore, does not believe that those issues will affect this rulemaking. EPA 

notes that it is required to promulgate standards for new engines under section 111 NSPS 

provisions and for new and existing engines under section 112 NESHAP provisions. Much of 

the complications commenters discuss results from the straightforward implementation of the 

requirements of the Clean Air Act. In terms of having a combined rulemaking for natural gas 

and diesel engines, EPA does not think that this complicates the rule. Issuing a rulemaking that 

addresses all types of stationary engines regardless of fuel type is consistent with how the 

original 2004 RICE NESHAP was developed. 

 It is not true that there are multiple overlapping engine rules for existing engines. This 

rule addresses engines that have not been addressed before, i.e., existing stationary engines at 

area sources and existing stationary engines less than or equal to 500 HP at major sources. EPA 

has not issued regulations for these engines previously, but noted in earlier final rules that EPA 

would be addressing these engines in the future. Since the final CI NSPS and SI NSPS rules 

covered only new stationary engines and the original 2004 RICE NESHAP covered only 

stationary engines at major sources greater than 500 HP, there are no other requirements 

affecting existing stationary engines at area sources. There are also no other requirements 

affecting existing stationary engines less than or equal to 500 HP located at major sources since 

again, the CI NSPS and SI NSPS rules covered only new stationary engines and the original 

2004 RICE NESHAP covered only stationary engines at major sources greater than 500 HP. 
30

Commenters expressed concern regarding overlap and references to mobile sources rules. 

It is not clear what the commenters’ concerns are because there are minimal references to the 

mobile source regulations in the proposed rule. EPA recognizes that individual owners and 

operators may not be familiar with the mobile source requirements. That is one reason why this 

rulemaking is focused on source-specific requirements and is not a manufacturer-based program. 

In the NSPS rules for new CI and SI stationary engines it made sense to implement a program 

that addresses emissions from engines at the point of manufacturing rather than when these 

engines are installed in the field, and to coordinate the requirements for new stationary engines 

with requirements for similar new mobile engines. The coordination of mobile and stationary 

engine requirements has in fact reduced the complexity of meeting EPA regulations for these 

new engines, since manufacturers and users of such engines can comply by meeting the same 

standards whether they are mobile or stationary. 

In this regulation, since it affects existing stationary engines, the engines are already 

located at the affected source. EPA has made reference to the mobile source rules only when 

absolutely necessary in order to demonstrate that for example certain control technologies or 

fuels are currently available and technically feasible. Other references include citing parts of 40 

CFR part 80, which contain the specifics of the fuel requirements for existing non-emergency 

diesel engines. Therefore, it is unclear what references to the mobile source rules the 

commenters are referring that are problematic. 

EPA cannot delay promulgation of the final rule due to a court-ordered schedule 

requiring EPA to finalize the regulation by August 10, 2010. As discussed elsewhere in this 

document, EPA has already previously delayed the rulemaking affecting existing stationary 
31

engines at area sources and existing stationary engines less than or equal to 500 HP at major 

sources. 

In the final rule, EPA has made an effort to promulgate requirements that are as clear as 

possible and that minimize the burden of implementing these requirements. In conjunction with 

the promulgation of the final rule, EPA is publishing this Response to Comments (RTC) 

Document, which summarizes the comments EPA received on the proposed rule and EPA’s 

responses to each comment. The RTC document explains and provides supporting rationale for 

EPA’s regulatory decisions. The document is also helpful as a compliance assistance tool in 

cases where commenters have asked for clarification on certain issues. Further, EPA also plans 

to provide other compliance assistance and implementation material to help sources in 

demonstrating compliance with the final rule. 

As far as the comment regarding the compliance period when a facility’s status changes 

from a minor to a major source, EPA already includes provisions in 63.6595(b) of the rule that 

allows an area source that becomes a major source, where construction or reconstruction is 

commenced before the date the area source becomes a major of HAP, up to 3 years to comply 

with the rule. EPA believes this addresses the commenter’s concern on this issue. 

1.4 Comment: Numerous commenters (38, 39, 41, 42, 45, 46, 130, 194, 205) believe that the 

comment period provided in the proposal was inadequate. Two commenters (45, 46) requested a 

90-day extension to the public comment period for the proposed rule, to August 3, 2009. The 

commenters (45, 46) believe that due to the breadth of coverage and implications for thousands 

of existing RICE, the proposed 60-day comment deadline is entirely inadequate to assess 

implications, review background documentation, and develop comments supported with 
32

complete technical data and facts. The commenters (45, 46) asserted that, in light of the pending 

EPA proposed rule that addresses Mandatory Reporting of Greenhouse Gases (GHGs) and 

affects the same stakeholders, failure to grant an extension will undermine the ability to provide 

necessary comments and respond effectively to either rule proposal. One commenter (39) 

requested an additional 90 days to comment in order to develop a more comprehensive analysis 

and subsequent comment submittal to EPA. Commenter 40 agreed with commenter 39, but said 

that if a 90-day extension was not provided that at least 60 days be provided. 

The commenter (45) added that it will take time to fully assess the implications of the 

proposed rule because it affects thousands of smaller engines at area source facilities that 

historically have been considered exempt or inconsequential emission sources. The commenter 

(45) asserted that his organization’s historical comments have been consistent with the 

administration goal of science-based decision making, and that a limited comment period will 

compromise scientific integrity in the decision making for the proposed rule. The commenter 

(45) understands that EPA’s schedule is constrained by a commitment to develop a final diesel 

engine rule, but believes that if a 90-day extension cannot be accommodated, at least an 

additional 60-days extension (i.e., 120 days total) is necessary. In the alternative, the commenter 

(45) suggested removing natural gas-fired engines from the proposal (see Section 1.2). 

Commenter 38 supported a 60-day extension. 

Due to the breadth of coverage and implications for thousands of existing engines, two 

commenters (41, 42) believe that the 60-day comment deadline is inadequate to assess 

implications, review background documentation, and develop comments substantiated with 

technical data and facts. Additionally, in order to prepare joint comment for its member 
33

companies, the commenter (41) must coordinate among its member companies, making location 

of relevant information and preparation of comments on the proposal in 60 days difficult. 

One commenter (194) requested on behalf of the agricultural industry in its state that 

EPA allow further consideration and review time to allow a more detailed comment to be 

submitted. 

Response: EPA provided a 30-day extension to the public comment period to allow additional 

time for commenters to prepare and submit their comments. EPA could not provide additional 

time beyond the 30 days due to the court-ordered deadline for the final rule of August 10, 2010. 

In addition, EPA attempted to the best of its ability to review information that came to the 

Agency from the public after the end of the comment period. 

1.5 Comment: Five commenters (89, 101, 151, 221, 231) stated that it is critically important that 

EPA enter into a deliberative, well-informed dialogue with the oil and natural gas industry so 

that regulations can be formulated that are both protective of the environment and conducive to 

existing and future oil and natural gas production activities.

Response: EPA agrees that it is important to involve different affected stakeholders during 

regulation development. EPA has a long history of actively engaging various segments of 

industry during the process of rule development. This rulemaking is no different and EPA has 

met with members of industry on several occasions. EPA has also contacted different industry 

groups and individual companies with an interest in this rulemaking by phone and email to 

obtain information on various issues related to stationary engines from control technology 
34

feasibility to the cost of installing and operating such controls, as well as to gather emissions data 

from stationary engines. 

1.6 Comment: Two commenters (176, 220) expressed that it is inappropriate for EPA to use 

section 112 of the CAA to target non-HAP pollutants. The commenter (176) opined that EPA 

addresses criteria pollutants, both in terms of the degree to which such pollutants are emitted 

from these types of engines, and the benefits that the proposed compliance requirements would 

have on criteria pollutants to justify regulation of engines located at area sources that have 

minimal impact on urban areas from HAP emissions. 

Response: EPA is not using the CAA to target non-HAP pollutants from existing stationary 

RICE, but is applying the use of a surrogate for HAP emissions from certain engines. Measuring 

emissions of HAP is in many cases much more expensive than measuring surrogate emissions 

and setting a standard in terms of a single pollutant would mean simpler and cheaper emissions 

testing. Formaldehyde is the HAP emitted in the largest quantity from stationary RICE and is 

related to the level of other HAP emissions. Therefore, formaldehyde is an appropriate 

representation of HAP emissions. EPA studied emissions data to determine if CO would be 

representative of HAP emissions. Because EPA determined that there is a relationship between 

CO and formaldehyde for certain engine types, EPA is using CO as a surrogate for HAP 

emissions for these engines. Also, while EPA’s standards are based on HAP reductions, there is 

no reason to ignore the co-benefits of the rule in terms of reduction in non-HAP pollutants when 

calculating the benefits of the rule. 
35

1.7 Comment: One commenter (69) opposes the proposed rulemaking because it imposes a 

tremendous hardship on the regulated community; strains the resources needed to demonstrate 

and/or achieve compliance, and is of marginal benefit, particularly for the oil and gas industry. 

The commenter (69) suggests that the proposal rule should be stayed indefinitely, or at least 

phased until a more favorable economic time. 

Response: EPA is required by statute to develop regulations for all existing stationary engines to 

address HAP emissions under sections 112(d), 112(c)(3) and 112(k) of the CAA. To the extent 

possible, EPA has attempted to minimize the burden on the regulated community, but EPA does 

not believe that the requirements are significantly burdensome. EPA does not have the option to 

delay the rulemaking due to consent decrees requiring EPA to finalize and issue the regulation 

by August 10, 2010. 

1.8 Comment: One commenter (220) proposed an alternative approach for regulating nonemergency units based on a nitrogen oxides (NOx) rulemaking in Illinois for the Chicago and 

Metro-East nonattainment areas. In that rulemaking sources may elect to comply by designating 

their units as low-use with operational limitations of no more than 8 million HP-hrs/yr or NOx

emissions less than 100 tons per year (tpy). Using AP-42 factors, the latter low-use option 

translates to an effective cap on HAP emissions of approximately 94 pounds per year, per 

municipality. 
36

Response: The commenter did not provide any information to support the comment that an 

emissions cap or limitation on operating hours would be appropriate as MACT for engines 

located at major sources or GACT for engines located at area sources. 

1.9 Comment: Several commenters (45, 46, 81, 97, 111, 112, 128, 130, 132, 150, 155, 175, 186, 

205, 224, 225, 242, 247) expressed concern over a combined rulemaking with natural gas and 

diesel engines and felt that a separate rulemaking and potential schedule should be developed for 

natural gas engines. Some commenters (155, 186, 242, 247) said that the information supporting 

the rule focuses on diesel particulate benefits and does not sufficiently address benefits 

associated with natural gas engines. In addition, the docket contains less information on gas 

engines than diesel engines, commenter 155 said. For this reason, the commenters (132, 155, 

175, 242, 247) believe that the rule is focused on diesel engines and that a separate rule based on 

data should be developed for natural gas engines. One commenter (81) said that the regulations 

should specifically exempt non-diesel engines. This would allow a more reasonable time for 

EPA to decide if it is necessary to promulgate rules for other engines and if so, to draft rules that 

deal appropriately with issues that those engines may have, according to the commenter (81) 

The commenters (155, 242) referred to how the Advanced Notice of Proposed 

Rulemaking (ANPRM) had discussed emissions from stationary diesel engines and that it did not 

expect a rule to be issued for natural gas engines following the same timeline as the diesel engine 

consent decree. In other words, the commenter (155) indicated that it was surprised by the 

proposed rule affecting natural gas engines and had it known, it would have been actively 

involved and in touch with EPA during the process of developing the proposal. The commenter 

(155) also noted that the ANPRM provided an opportunity for EPA to receive new diesel data, 
37

but that EPA is using the same, old data for gas engines. The proposed rulemaking is based on 

insufficient and flawed data for gas engines and the commenter (155) offered to assist EPA in 

addressing data gaps and other issues. However, the commenters 155 and 242 pointed out, such 

effort will take time. Commenters 155 and 242 recommended that EPA consider a different 

schedule for gas engines in order to gather sufficient and appropriate data and conduct a more 

thorough analysis on impacts, costs and benefits. This will allow EPA to engage stakeholders in 

the rule development process and to obtain appropriate information to support the rulemaking, 

commenters 155 and 242 expressed. 

A few commenters, including commenters 132, 155, and 242 indicated that they are 

willing to assist EPA in collecting additional data for natural gas engines, but that such an effort 

will be difficult to complete and it would be hard to incorporate the data resulting from such an 

effort into a rule that has to be finalized by February 2010. The commenter (242) offered to 

work with EPA to develop a plan to obtain test data and to come up with a revised rulemaking 

schedule for natural gas engines. Multiple commenters, including commenters 97, 132, 155, and 

242 asked that EPA negotiate a different schedule for natural gas engines and commenters 155 

and 242 asked that EPA develop a separate rulemaking for these engines. The commenter (132) 

believes that a minimum of 10 to 12 months is required to collect the emissions data, which 

includes; 60 days to develop and finalize a test plan, six to eight months for testing to occur, and 

60 days to develop a project test report. 

The commenters (155, 242) added that EPA’s current review and revision of the 

Integrated Risk Information System (IRIS) unit risk estimate (URE) for formaldehyde further 

supports the need for a separate rulemaking for natural gas engines. One commenter (224) 

suggested that EPA await the results on the ongoing formaldehyde URE review before adopting 
38

area source standards for natural gas-fired engines. The commenter (224) stated that EPA 

recently concluded that a lower URE is the current “best science” for formaldehyde, which is the 

primary HAP of concern from natural gas-fired engines. The commenter (224) further noted that 

area source standards are specifically established to reduce the risk to public health from area 

source emissions in urban areas, so the URE of formaldehyde is relevant to the proposed 

emission limits for area sources. 

Formaldehyde constitutes a large portion of the HAP emissions from natural gas engines. 

EPA’s review is not expected to be completed until late 2011 and the risk and urban source 

impacts due to formaldehyde emissions could be significantly impacted by the IRIS review, the 

commenters (155, 242) said. The outcome of the IRIS review may indicate a large reduction in 

the URE for formaldehyde leading to a reduced risk associated with natural gas engines and may 

also question the need for regulation. 

One commenter (225) believes that the current rulemaking timeline is too short to 

properly consider all of the issues raised by the commenters. The commenter (225) asserted that 

this proposed rule lacks supporting data in critical areas, and would have a significant impact on 

industry. Given that the current schedule would have the final rule promulgated in February 

2010 with compliance required by February 2013, the commenter (225) suggested that the rule 

be reconsidered and these areas addressed. 

One commenter (45) who requested an extension of the comment period for the proposed 

rule (see Section 1.1) recommended that EPA remove the natural gas-fired engines from the 

proposed rule if EPA believes that the court-ordered schedule for diesel engines precludes 

granting such an extension. The commenter (45) pointed out that the inflexible consent decree 

schedule requiring a February 2010 final rule only applies to diesel engines, and EPA elected to 
39

include natural gas RICE in the proposed rule. Thus, the commenter (45) believes that the 

specific deadline for non-diesel engines is self-imposed, and alternatives are available to provide 

a more reasonable opportunity for stakeholders to prepare constructive comments by choosing a 

different timeline for natural gas-fired engines. The commenter (45) stated that in this way, EPA 

will be provided an opportunity to engage affected stakeholders in the rule process to obtain 

credible information and support for emission limits, MACT floor determinations, and cost data 

that at present appear to be limited in scope and questionable in at least some cases. A second 

commenter (46) similarly recommended that, given a choice between (1) imposing unnecessarily 

tight deadlines on the comment period related to non-diesel engines based on a consent decree 

that does not relate to non-diesel engines, and (2) excluding non-diesel engines from this 

rulemaking, EPA should choose the latter. 

 These two commenters (45 and 46), whose initial comments focused on requesting 

extension of the commenter period, subsequently submitted substantive comments (112 and 150, 

respectively). The two commenters (112, 150) further emphasized that the rulemaking process 

related to natural gas-fired engines should be separated from the diesel engine rulemaking 

process so that more thorough consideration can be given to the proposed gas-fired engine 

standards. The commenters (112, 150) gave following reasons that the SI portion of the rule 

should be delayed: 

• Legal challenges [API petitions for review on the CI NSPS and consolidated SI engine 

rule (SI NSPS (40 CFR part 60, subpart JJJJ and RICE NESHAP (40 CFR part 63, 

subpart ZZZZ))] related to key issues implicated by the proposed rules have yet to be 

resolved. 

• The supporting docket material is limited and incomplete. 
40

• The proposed rules would significantly affect a large number of SI engines. 

Commenter 112 asserted that EPA has greatly underestimated the breadth and scope of 

this rule and there has been very little or no dialogue with the multitude of industries that 

will be affected. The commenter (112) believes that the current timeline is too short to 

educate those to be impacted and implement the required management practices and 

maintenance, recordkeeping, and reporting requirements. Commenter 150 added that 

rules that would have such an impact should receive a thorough review of economic 

impact and technical feasibility. The commenter (150) believes that the timeline is too 

short to properly consider all the important and precedent-setting issues related to natural 

gas-fired engines. 

• Commenter 112 also believes that the SI engine rulemaking should be separated from the 

CI rule because EPA has defined the MACT floor for SI engines lower than the courts 

have required. 

 Commenter 112 added that although EPA is required by recent Court Consent Decrees to 

finalize the SI area source rules, there is good reason not to finalize by February 10, 2010 

because no party is well served by the promulgation of a standard that is unattainable and has an 

unacceptable cost/benefit ratio. Several commenters, including commenters 112 and 186 

recommended that EPA negotiate with the Sierra Club to provide for an extended timeline so 

that all parties can better evaluate the assumptions in this proposal prior to promulgation of the 

final rule. 

One commenter (111) pointed out that the proposed rule lumps together natural gas-fired 

SI engines with diesel/CI engines, unlike the 2008 NSPS/NESHAP “new engine” rule. Because 

natural gas-fired SI engines are much cleaner burning and do not emit the metallic HAP and 
41

particulates associated with diesel/CI engines, the commenter (111) questioned the entire basis 

for the cost/benefit analysis since the majority of RICE in the analysis were CI (78 percent or 1 

million) versus SI (22 percent or 290,000). 

 One commenter (175) pointed out that in order to achieve a 75 percent reduction in 

cancer incidence attributable to HAP from stationary sources, the EPA is required by the CAA to 

ensure that area sources representing 90 percent of the emissions of the 30 urban HAP are 

subject to regulation. Information according to one study1 shows that the toxicity (cancer 

potency) of diesel emissions in a range from 38 to 81 times greater than the toxicity of natural 

gas emissions. To apply identical control requirements on diesel and natural gas engine 

emissions is to erroneously equate their toxicity, in the commenter’s (175) opinion. Therefore, 

the economic impact on operators of natural gas-fired engines would far exceed the emissions 

reduction benefit and consequently the commenter (175) believes that EPA should conduct a 

reasoned analysis of actual emissions, toxicity, and appropriate controls for natural gas-fired 

engines. 

Response: EPA initially proposed requirements for existing stationary engines located at area 

sources of HAP emissions and existing stationary engines less than or equal to 500 HP located at 

major sources of HAP emissions on June 12, 2006 (71 FR 33804). Therefore, it should come as 

no surprise that EPA intended to address emissions from existing stationary engines that were 

not included as part of EPA’s first stationary engine rulemaking in 2004 in 40 CFR part 63, 

subpart ZZZZ, which include natural gas engines. (40 CFR part 63, subpart ZZZZ addressed 

emissions from stationary engines greater than 500 HP located at major sources of HAP 

                                                           

1

 South Coast Air Quality Management District Staff Report, Proposed Rule 1194 – Commercial 

Airport Ground Access, August 2000.
42

emissions.) After the proposal of the 2006 rulemaking, the U.S. Court of Appeals for the District 

of Columbia Circuit issued a ruling, which impacted EPA’s ability to finalize the proposed 

standards of “no reduction” MACT standards for existing sources. Sierra Club v. EPA, 479 F.3d 

875 (D.C. Cir. 2007). EPA discussed in the preamble to the final rule that was published on 

January 18, 2008 (73 FR 3568) that EPA planned to reevaluate the MACT floors for existing 

stationary engines located at area sources of HAP emissions and existing stationary engines less 

than or equal to 500 HP located at major sources of HAP emissions. EPA informed the public in 

the final rulemaking in 2008 that a separate rulemaking would be developed to address HAP 

emissions from these sources that would likely be proposed in early 2009. Therefore, the 

timeline of a rulemaking for natural gas engines should not be a surprise. The commenters 

should have anticipated a rulemaking and EPA believes that industry has had ample time to 

participate in the development of the proposed rule. 

 EPA has over the past several years encouraged industry to submit stationary engine 

emissions data under various rulemakings. Industry has had the opportunity to provide 

emissions data over the last few years. EPA specifically asked commenter 242 in early 2007 if 

the commenter had any stationary engine testing data. At that time, commenter 242 had 

indicated that it was working on a testing program and would have engine test data available. 

Commenter 242 also indicated at that time that a rich burn engine test program might be 

developed in conjunction with other groups in order to collect data from rich burn engines with 

NSCR (EPA-HQ-OAR-2005-0030-0269). 

Nonetheless, in order to provide additional time post-proposal for the submittal of 

emissions data and other supporting information as requested by the commenters, EPA received 

a 6-month extension of the deadline for signature of the final rule for SI engines, from February, 
43

2010 to August, 2010. As a result, EPA received several documents providing further data for SI 

engines and EPA was able to use these documents in promulgating this final rule. 

 Regarding the comment related to the current review of the URE for formaldehyde, EPA 

does not have the ability to wait until results are available from that study. EPA is under courtorder deadline to finalize the rule by August 2010 and was not able to delay finalizing the rule 

until the formaldehyde URE review is complete. The consent decree that affects existing 

stationary engines located at area sources and existing stationary engines less than or equal to 

500 HP at major sources requires a final rule by August 10, 2010. So EPA must finalize 

requirements for all engines, including natural gas engines. Moreover, as formaldehyde is a 

listed hazardous air pollutant and section 112(d) of the CAA regulations are primarily 

technology-based, not risk based, and as stationary RICE emit several pollutants in addition to 

formaldehyde, it is not clear that waiting for such results would have any impact on the final 

regulations. 

 EPA does not believe that the legal challenges that the commenters refer to regarding the 

CI and SI NSPS rules will prevent or impact EPA in finalizing appropriate requirements in the 

NESHAP for natural gas engines and a delay in the natural gas portion of the rule is not 

necessary. 

1.10 Comment: Several commenters (89, 101, 103, 130, 136, 151, 155, 167, 172, 187, 221, 224, 

226, 231, 241, 242) said that EPA should attempt to harmonize the proposed rule requirements 

with requirements in the other stationary engine rules (2004 RICE NESHAP, CI NSPS, SI 

NSPS, and 2008 RICE NESHAP revisions) in order to simplify the implementation process. 
44

According to commenter 155, owners/operators of the stationary engine rules have experienced 

issues with implementing these rules. 

The commenter (242) thinks that EPA should simplify and harmonize the various engine 

rules to simplify the implementation and enforcement process. As mentioned, the regulated 

community has been having issues and a hard time implementing the various engine rules that 

have been issued by EPA over the years since 2004 when the first engine rule was published. 

This proposed rulemaking will add to the confusion with competing requirements and other 

issues, the commenter (242) said. EPA should revisit rule requirements and think about options 

to harmonize requirements across rulemakings, the commenter (242) recommended. The 

commenter (242) referred to EPA simplifying the reporting and recordkeeping requirements for 

engines subject to the NESHAP (new and reconstructed) under the 2008 rulemaking. Those 

engines were allowed to demonstrate compliance by meeting the NSPS. However, the current 

proposal affecting existing engines will result in these existing engines having more onerous 

recordkeeping and reporting requirements than what is required for new engines, the commenter 

(242) said. In addition, existing engines will in some cases have more stringent emission limits 

than new engines, the commenter (242) noted. The commenter (242) suggested that EPA think 

about separating the requirements for existing area sources and existing small engines at major 

sources into a new subpart (e.g., subpart ZZZZa). In the new subpart, EPA could clearly indicate 

that only certain provisions of 40 CFR part 63, subpart A GP (GP) apply to these engines so that 

similar reporting, recordkeeping and maintenance requirements apply for the NSPS and subpart 

ZZZZa affected engines, the commenter (242) recommended. 

Commenter 136 noted that the 2004 RICE MACT and 2008 Consolidated NSPS and 

NESHAP engine rule and this proposed rule are inconsistent; for example, the proposed 
45

standards for some existing RICE are more stringent than the recent emission standards for 

new/reconstructed RICE. Commenters 130 and 136 believe that EPA should allow areas source 

RICE that require control to comply with the NSPS requirements in lieu of NESHAP 

requirements. Further, the commenter (136) urged that EPA simplify and harmonize the rules to 

avoid contradictions and minimize the potential for compliance and enforcement confusion. 

One commenter (103) stated that the requirements for all of the different rules (original 

40 CFR part 63, subpart ZZZZ; part 60, subpart JJJJ; and now revised part 63, subpart ZZZZ) are 

overly burdensome. The commenter (103) indicated that EPA should consider having standards 

for area sources that are consistent for all rules, and noted that new sources already have this 

standard, but existing sources are treated differently under this proposal. 

 The commenter (103) asserted that specific surrogates for HAP are not needed for area 

sources if an overall level of performance can be demonstrated by the engine. The commenter 

(103) asserted that if the costs for controls for rural area sources can be justified, then surrogates 

for the existing engines should be the same as for new sources. As an example, the commenter 

(103) indicated that if an existing rich burn engine is operating at NSPS standards (2.0 grams per 

horsepower-hour (g/HP-hr) NOx, 4 g/HP-hr carbon monoxide (CO), and 1.0 g/HP-hr volatile 

organic compounds (VOC)) then the NSCR can be considered to be functioning correctly and 

HAP will be reduced even though formaldehyde is not measured directly. 

One commenter (172) noted that there were inconsistent thresholds between these 

proposed rules and the related SI and CI NSPS, creating complications. For instance, engine size 

in the CI NSPS is defined in terms of cylinder displacement, while HP or kilowatt (KW) ratings 

are used in other rules. 
46

Another commenter (172) noted that while EPA based setting the 300 HP subcategory for 

CI RICE and the 250 HP subcategory for SI RICE on where the greatest emission reductions are 

achieved, the multiple levels resulted in more confusion. The commenter (172) suggested that 

500 HP be kept as the cutoff to identify a “large” engine for greater consistency and clarity. 

Response: To the extent possible, EPA has attempted to harmonize requirements and make 

provisions consistent across rulemakings affecting stationary engines. Existing stationary 

engines addressed in this rulemaking are not covered in the NSPS rules. In the CI and SI NSPS 

rules, EPA is primarily relying on engine manufacturer certifications. For engines likely to be 

covered under a certification program, EPA believes it is more appropriate to lessen the 

recordkeeping, reporting, and testing requirements on the individual owners and operators 

because of engine certificates. However, for existing stationary engines covered in this 

rulemaking, EPA is relying on each individual owner and operator to demonstrate compliance 

with the requirements. Records and testing are necessary to demonstrate that the engine is 

meeting the emission standards and that other requirements in the rule are followed 

appropriately. Also, NESHAP and NSPS rulemakings are developed under different sections of 

the statute and address different pollutants. In the NESHAP, EPA must address HAP emissions, 

but in the NSPS, EPA must address criteria pollutants like NOx, CO, and PM. 

 Regarding the comments that requirements applicable to existing stationary engines may 

be more stringent than the requirements for new stationary engines, EPA understands the 

concerns. However, due to the recent Brick MACT decision, which said that EPA could not set 

MACT floors of no emission reduction, EPA had to take a different approach in setting standards 

for existing stationary engines than was taken in earlier regulations. The outcome of the Brick 
47

MACT decision and the SSM decision occurred after the previous engine rulemakings and 

therefore EPA cannot help the fact that standards may become more stringent for older engines 

under a different analysis. 

In response to the comment regarding inconsistent threshold across rules, EPA again 

notes that the rules, in particular the NESHAP versus NSPS rules, rules for new versus existing 

engines, and rules for engines at major sources versus area sources, are developed to address 

different statutory requirements. Further, in the rules targeting new engines, EPA relied heavily 

on a manufacturer-based certification program. For both NSPS regulations, but more so in the 

CI NSPS, EPA modeled emission standards and requirements in the nonroad engine rules 

affecting similar engines. In those two rules, the emission standards were mostly targeted to 

engine manufacturers and since EPA followed nonroad requirements in many cases, it made 

sense to adopt engine size thresholds and emission standards similar to, and in the same units as 

was done in the nonroad engine rules. 

2.0 Applicability 

2.1 Major Sources 

2.1.1 Comment: Two commenters (112, 148) noted that the requirements for individual engines 

are dependent upon the facility determination of major or area source status, which is subject to 

change as engines are added and removed from the site. The commenters suggested that major 

sources that become area sources should be provided a 3-year compliance period because some 

requirements proposed for area sources are more stringent than the comparable requirement for 
48

major sources. One of the commenters (112) stated that this is particularly important for 2-stroke 

lean burn (2SLB) engines that are at a major source that becomes an area source or is relocated 

to an area source.

Response: EPA does not agree with the commenter. Under EPA’s “once in, always in” 

interpretation, if the engine was located at a major source at any time after the first substantive 

compliance date of the MACT standard (subpart ZZZZ), which for existing engines more than 

500 HP at a major source is June 15, 2007, then the engine continues to be a major source for the 

purposes of subpart ZZZZ. To the extent the commenter is referring to relocated engines, we 

would need to analyze the facts and circumstances of each particular situation. The commenter 

can request an applicability determination regarding particular circumstances. 

2.2 Area Sources 

2.2.1 Comment: Numerous commenters (64, 66, 68, 75, 104, 111, 112, 124, 131, 132, 136, 148, 

150, 155, 175, 183, 187, 225, 226, 241, 247, 253, 261, 262) expressed concern over EPA’s 

decision to not distinguish between rural and urban engines at area sources in the proposed rule. 

Several commenters (64, 66, 68, 75, 104, 112, 136, 183, 226) requested that EPA reevaluate its 

congressional authority to regulate area HAP sources in rural areas. The commenter (112) 

believes that the proposal is inconsistent with 42 U.S.C. 7412(n)(4)(B) [CAA section 

112(n)(4)(B)], which states that: 

“The Administrator shall not list oil and gas production wells (with its associated equipment) as 

an area source category under subsection (c) of this section, except that the Administrator may 
49

establish an area source category for oil and gas production wells located in any metropolitan 

statistical area or consolidated metropolitan statistical area with a population in excess of 

1 million, if the Administrator determines that emissions of hazardous air pollutants from such 

wells present more than a negligible risk of adverse effects to public health.” 

 Three commenters (104, 112, 136) requested clarification of EPA’s rationale to regulate 

low levels of emissions from engines at oil and gas production facilities outside metropolitan 

areas, contending that EPA has applied this rule more broadly than the Congressional intent of 

the CAA, and requested that EPA reevaluate this issue of whether EPA can regulate rural area 

sources in light of the 42 U.S.C. 7412(n)(4)(B) language. 

One commenter (220) stated most of its members are located at area sources in non-urban 

locales, where HAP emissions from the affected engines, some of which are emergency engines, 

are unlikely to impact urban areas. Thus, engines located at non-urban sources should be exempt 

from the requirements of the proposed rule. Commenter 220 added that EPA has not made a 

case for such stringent regulation of units in non-urban areas, particularly where operation of 

such units is minimal. EPA should only impose requirements for non-emergency units in urban 

areas. 

Four commenters (111, 150, 187, 225) stated that EPA has based this rulemaking for area 

sources on sections of the CAA and its Urban Air Toxics Strategy that are intended to remove 

threats to public health in urban areas. The commenters (111, 150, 225) do not believe that the 

remote RICE at area sources in the oil and gas industry threaten public health in urban areas. 

Three of the commenter (150, 187, 225) noted that the NESHAP for glycol gas dehydrators (40 

CFR part 63, subpart HH) takes into account the location of area sources and does not apply the 

specific requirements of the rule to rural area sources. The commenters (150, 225) believe that 
50

the same approach should be used for the RICE rule, i.e., engines that are not located in or near 

populated areas should be exempt or subject to an alternative set of requirements so as not to 

force expensive requirements on remote engines that have no impact on public health. In 

particular, one of these commenters (150) stated that rural sources should be excluded from 

requirements relating to catalytic controls. 

 One commenter (111) questioned the rationale for the statement in the proposal preamble 

the “it would not be practical or appropriate to limit the applicability to urban areas....” 

Regarding practicality, the commenter (111) stated that urban area and urban cluster boundaries 

have been well defined by the Census Bureau (2000 Census) and that it would be easy to 

determine whether a facility is inside or outside these boundaries. Regarding appropriateness, 

the commenter (111) stated that the rationale in the proposal preamble does not relate the density 

of RICE to population density nor other HAP sources, both stationary and mobile, while the 

1999 Integrated Urban Air Toxics Strategy document (which is the basis of this proposal) stated 

that “the vast majority of HAP emissions...are within counties with urban areas. Additionally, a 

greater number of different HAP may be emitted from the multiple sources present in urban 

areas than from the more limited number and variety of sources present in rural areas.” The 

commenter (111) indicated that significant impacts from small sources in non-urban areas are 

dependent on them being additive to another major emitter (i.e., at major sources) or dependent 

on multiple sources of the same or different types being located within additive impact areas. 

 The commenter (111) noted that the monetized benefits of the proposed rule (74 FR 

9712) do not distinguish between rural and urban benefits. The commenter (111) anticipates that 

the risk avoidance benefits would be skewed to urban populations and requested that the benefits 

be analyzed in this manner if rural sources are to be included in the rule. In addition, the 
51

commenter (111) requested that the rule be limited to urban areas as defined in the 1999 Urban 

Air Toxics Strategy document or, at a minimum, be limited to major sources (RICE less than or 

equal to 500 HP) in rural areas if a clear positive cost/benefit can be demonstrated. 

Several commenters (112, 124, 131, 132, 148, 155, 175, 187, 241, 242, 247, 253, 261, 

262) cited rules where EPA considered urban proximity by allowing owners/operators to 

determine whether their engines were located in an urban area by the distance to an urban cluster 

as defined by the U.S. Census Bureau. For those rules, requirements and implementation 

schedules are based on location, and units that are considered non-urban show compliance by 

meeting work practices. 

Several commenters recommended that EPA follow 40 CFR part 63, subpart HH for 

existing stationary engines and only require work practices for area sources engines in rural 

areas. Commenter 241 concluded that following urban criteria ((defined as urban areas [UA] 

plus a 2 mile buffer area and urban clusters [UC] greater than 10,000)) that parallel 40 CFR part 

63, subpart HH, the final rule could provide an exemption for area source engines located in a 

rural area or require GACT work practices rather than MACT-equivalent emission limits. In 

addition, commenters 97 and 241 stated that with technology and cost limitations for emissions 

measurement and a lack of emissions data, EPA should consider section 112(h) of the CAA 

alternatives for promulgating design, equipment, work practice, or operational standards. 

Similarly, commenter 112 concluded that the proposed rules will be onerous and costly, and 

should not be imposed at area sources in rural areas unless the science supports the need for this 

type of regulation. 

Some commenters (97, 226, 247) believes that EPA should conduct an analysis of urban 

versus rural emissions and rural engine impacts on urban areas. Commenter 97 believes that the 
52

results of the analysis will warrant different standards, or overall exemption, for rural engines, 

especially those in remote locations. The commenter (97) stated that section 112(h) of the CAA 

provides alternative approaches to emission limits if it is infeasible to prescribe or enforce 

emission standards based on the technical and economic practicality of applying measurement 

methodology. The commenter (97) believes that EPA should consider additional opportunities 

to rely on management or operating practices for compliance. The commenter stated that 

management practices are warranted for area sources under GACT provisions, and for both area 

and major sources engines under CAA section 112(h). 

Response: EPA is finalizing its proposal to regulate existing stationary SI engines located at area 

sources on a nationwide basis. EPA believes that the CAA provides the Agency with the 

authority to regulate area sources nationwide. Section 112(k)(1) of the CAA states that “It is the 

purpose of this subsection to achieve a substantial reduction in emissions of hazardous air 

pollutants from area sources and an equivalent reduction in the public health risks associated 

with such sources including a reduction of not less than 75 per centum in the incidence of cancer 

attributable to emissions from such sources.” Consistent with this expressed purpose of section 

112(k) of the CAA to reduce both emissions and risks, CAA section 112(k)(3)(i) requires that 

EPA list not less than 30 HAP that, as a result of emissions from area sources, present the 

greatest threat to public health in the largest number of urban areas. Sections 112(c)(3) and 

(k)(3)(ii) of the CAA require that EPA list area source categories that represent not less than 90 

percent of the area source emissions of each of the listed HAP. Section 112(c) of the CAA 

requires that EPA issue standards for listed categories under CAA section 112(d). These 

relevant statutory provisions authorize EPA to regulate listed area source engines and not just 
53

engines located in urban areas. EPA believes that sections 112(c) and 112(k) of the CAA do not 

prohibit issuing area source rules of national applicability. 

 EPA also disagrees with the statement that the proposal was inconsistent with section 

112(n)(4)(B) of the CAA. The term “associated equipment” was defined for the purposes of 

subpart ZZZZ in the first RICE MACT rule not to include stationary RICE. EPA has not 

revisited that determination in this rule. In the discussion of the definition for “associated 

equipment” in the preamble to the NESHAP for Oil and Natural Gas Production Facilities (63 

FR 6287, 6300-02, February 6, 1998), EPA noted that while the CAA provides no definition of 

‘‘associated equipment,’’ the legislative history does indicate that the Congress, in drafting 

section 112(n)(4), believed that production wells and their associated equipment generally have 

low HAP emissions, but that, even if the wells are far apart, such emissions would be subject to 

aggregation under the definition of major source in section 112 because emissions from 

production wells in an oil or gas field are commonly owned and connected by pipeline. In that 

rulemaking, EPA rejected an approach suggested by industry that would have defined all 

equipment to the point of custody transfer to be associated equipment. Such an interpretation 

would define all such equipment as associated with a well, regardless of (1) the type of 

equipment, (2) any processing or commingling of streams that may occur, or (3) distance from 

the well, and would suggest that the Congress intended that aggregation of HAP emissions not be 

allowed within this industry under any circumstances. When viewed within the framework of 

section 112, the EPA did not believe this to be the case. 

 EPA noted that, for example, natural gas processing plants, which are generally situated 

prior to custody transfer, have numerous HAP emission points grouped together (e.g. glycol 

dehydrators, condensate storage vessels, gas treatment and separation steps, and various 
54

containers) that, when taken together, may emit above the levels associated with major sources. 

Inclusion of all of these equipment in the definition of “associated equipment” would likely leave 

the plants unregulated, despite the fact that the plant would emit the same level of emissions as 

found at major sources for other similar industries. EPA determined at that time that glycol 

dehydration units and storage vessels with the potential for flash emissions were not part of 

“associated equipment” because they were not the type of small HAP emission points that 

Congress intended to be included in the definition of associated equipment. 

 When EPA proposed the NESHAP for stationary RICE and stationary combustion 

turbines, EPA defined “associated equipment” as not including stationary RICE and stationary 

combustion turbines. Similar to glycol dehydration units and storage vessels, stationary RICE 

and combustion turbines are also not the type of small emission points that EPA believes 

Congress intended to be considered associated equipment. No adverse comments were received 

on that definition. Furthermore, it is EPA’s understanding that the stationary engines are 

typically located downstream of the well and glycol dehydrator, and therefore are not part of the 

operation of the well. EPA did not propose to revise its definition of associated equipment in the 

proposal for this rule and the commenters have not provided sufficient justification to justify 

reopening this definition. 

In response to the commenter who noted that the monetized benefits of the proposed rule 

did not distinguish between rural and urban benefits, the monetized benefits associated with 

reducing PM2.5 exposure by reducing precursor emissions such as NOx and VOC were estimated 

using national average benefit-per-ton estimates that are based on emissions and air quality 

modeling that reflect the current distribution of sources. Using this methodology in conjunction 

with a lack of information regarding the specific location of most of these engines, EPA is not 
55

able to provide an estimate of the fraction of monetized benefits that would occur in rural areas. 

This methodology does not systematically bias the benefits results as the underlying modeling 

reflects both urban and rural sources, these pollutants contribute to the secondary formation of 

PM2.5 well distant from the source, and PM2.5 can travel tens to hundreds of kilometers. EPA 

wase unable to monetize the benefits associated with reducing HAP emissions, CO emissions, 

ecosystem impairment, or visibility impairment. 

EPA reviewed its proposed requirements for existing SI engines at area sources based on 

comments received on the proposed rule. In the final rule, all existing stationary SI RICE that 

are 500 HP or less and located at area sources are required to meet management practices rather 

than numeric emission limitations. In addition, existing stationary RICE larger than 500 HP 

located at area sources that are 2SLB, landfill/digester gas-fired, or emergency stationary RICE 

are required to meet management practices. EPA received comments and supporting 

information indicating that EPA had underestimated the cost of emission controls and 

overestimated how many engines were already using these controls. EPA reevaluated the cost 

impacts associated with establishing numeric emission limitations for these engines and 

determined that the cost impacts would be unreasonable given the expected emission impacts 

both with and without the expectation of use of emission control technologies. For example, for 

4SRB engines, the annual cost per ton of HAP reduced, assuming the engine will have to install 

emission controls to meet the emission limit, is estimated to be $762,000 for a 50 HP engine and 

$167,000 for a 250 HP engine. For 2SLB and 4SLB engines at 250 HP, the annual cost per ton 

of HAP reduced is estimated to be $224,000 and $55,000, respectively, assuming the engines 

will have to install emission controls to meet the emission limit. Engine owners/operators have 

indicated that most of these smaller area source engines are not equipped with the control 
56

technologies required to meet these limits. Based on this information, EPA determined that 

management practices for these stationary SI RICE located at area sources of HAP are generally 

available and cost effective is promulgating management practices for these engines in the final 

rule. Additional information regarding this determination can be found in the memorandum 

titled, “MACT Floor and MACT Determination for Existing Stationary Non-Emergency SI 

RICE <100 HP and Existing Stationary Emergency SI RICE Located at Major Sources and 

GACT for Existing Stationary SI RICE Located at Area Sources,” which is available from the 

rulemaking docket. EPA believes that requiring management practices instead of specific 

emission limitations and/or control efficiency requirements on the majority of existing stationary 

CI engines at area sources alleviates concerns regarding costly and burdensome requirements for 

rural sources.

For existing non-emergency 4SRB and 4SLB stationary SI RICE greater than 500 HP at 

area sources that operate more than 24 hours per year, EPA determined for the final rule that it is 

appropriate to set numerical emission limits that EPA expects would be met using emission 

control technologies. The costs and economic impacts are reasonable and the control 

technologies that would be expected to be used are generally available for these area source 

engines. The cost per ton of HAP removed from a 500 HP 4SLB engine is $29,000 and is 

$16,000 for a 1,000 HP engine. For 4SRB engines, the cost per ton of HAP removed is $93,000 

for a 500 HP engine and $26,000 for a 1,000 HP engine. Information on the specific add-on 

control costs and cost per ton estimates can be found in the memorandum “Cost per Ton of HAP 

Reduced for Existing Stationary SI RICE,” available from the docket (EPA-HQ-OAR-2008-

0708). Also, the controls that are expected to be used on these engines will have the co-benefit 

of reducing volatile organic compounds (VOC), NOx, and CO emissions as well. Based on this, 
57

EPA believes it is appropriate to go beyond management controls for existing stationary nonemergency 4SLB engines greater than 500 HP at area sources. Therefore, EPA has determined 

that the final emission limits should be based on the use of oxidation catalysts for existing 

stationary non-emergency 4SLB engines greater than 500 HP that operate more than 24 hours 

per year that are located at area sources. 

EPA also believes that it is appropriate to establish emission limits for engines located in 

rural areas because their emissions can impact urban areas. HAP such as formaldehyde, 

acetaldehyde, acrolein, methanol, and benzene are emitted as gases. Regional photochemical 

model simulations, examining particular scenarios, have shown that gaseous HAP like 

formaldehyde and acetaldehyde can be transported hundreds of kilometers from their emissions 

source in distinct plumes.2

 Further, these emissions can contribute to regional air masses with 

elevated concentrations of gaseous HAP. These polluted air masses can be transported 

thousands of kilometers and affect locations well distant from the original emissions source. A 

nationwide rule also ensures an equal degree of protection to the public in both urban and rural 

areas. 

2.2.2 Comment: Two commenters (140, 148) suggested alternate ways to delineate major 

source RICE located in rural areas. Commenter 140 said its engines should not be regulated as 

major sources. Instead, EPA should clarify that RICE located in rural areas, used for mining or 

agricultural purposes, and operated for limited hours, will be subject to rules for area sources, 

even if such RICE are located at a major source. The commenter (140) concluded that there is 

                                                           

2

 U.S. Environmental Protection Agency (U.S. EPA). Air Quality Modeling Technical Support Document: Changes 

to the Renewable Fuel Standard Program, Office of Air Quality Planning and Standards, EPA 454/R-10-001. 

February. Available at <http://www.epa.gov/OMS/renewablefuels/454r10001.pdf>. 
58

no reason to impose new testing and emissions requirements on RICE units that, individually and 

collectively, are a very small source of HAP emissions. Alternatively, EPA could establish a 

separate subcategory of “rural” RICE under the major source category that would consider 

geographical location, emissions, and air quality impacts of these engines, the commenter (140) 

asserted. If established, this subcategory should have standards that are no more stringent than 

those promulgated for area sources, the commenter (140) said.

 

Response: EPA has to follow the definitions of a major source and an area source in CAA 

sections 112(a)(1) and (2). EPA is not at liberty to change those definitions, and EPA must 

regulate as major sources those stationary engines that are classified as being located at major 

sources under section 112(a). If a stationary engine is located at a source that has the potential to 

emit considering controls, in the aggregate, 10 tons per year or more of any HAP or 25 tons per 

year or more of any combination of HAP, it must be regulated as a major source. 

EPA is statutorily required to address HAP emissions from all existing major sources in 

listed source categories regardless of whether those sources are small or large or whether they 

are located in rural or urban areas. EPA is also required to use the specific procedures in section 

112(d) to determine MACT for engines, and the comment has provided no information to 

indicate MACT would be any different for the engines the commenter identified. 

2.2.3 Comment: Commenter (242) stated that EPA should evaluate whether generic risk-based 

applicability alternatives and work practice determinations are appropriate for natural gas 

engines. EPA should consider a tiered approach that takes into account engine size, distance to 

urban clusters, and emission-based exemptions. The commenter (242) asserted that annual 
59

formaldehyde area source emission exemptions or work practice requirements should be based 

on the generic risk assessment. A set of concentration curves using both the current and 

proposed URE by engine type, size and distance should be developed to be used to evaluate the 

impacts from rural area sources on urban clusters, the commenter (242) said. Finally, EPA 

should incorporate flexibility in the rule for each source to determine and show that if impacts 

are less than 1 in 1,000,000 formaldehyde risk levels an exemption from the rule or that only 

work practice standards are appropriate. 

Commenter (241) argued that because legislative history reinforces the perception that 

the fundamental purpose of the area source program is urban area risk reduction, EPA should 

incorporate risk in its consideration of cost effectiveness – for example, the cost effectiveness 

threshold for beyond the floor controls should consider the HAP of concern for different engine 

types. Further commenter (241) stated that any controls which do not contribute to significant 

reductions in risk cannot be considered cost effective or consistent with CAA section 112(k), and 

that this issue is even more compelling for natural gas-fired engines when considering the 

uncertainty in the Unit Risk Estimate for formaldehyde. 

Two commenters (74, 78) said that the section 112(k) of the CAA mandate seems 

specifically focused on sources in urban areas and does not appear to provide a basis for 

regulating area sources in nonurban areas. The commenters (74, 78) added that EPA’s 

determination that there are high concentrations of stationary RICE in rural areas does not mean 

that these area sources necessarily expose a large number of persons to HAP emitted by 

stationary RICE. According to the commenters (74, 78), EPA must demonstrate that stationary 

RICE at area sources in rural areas present significant risks to public health before imposing 

these regulations on area sources in rural areas. Any assessment of potential public health risks 
60

should also take into account Hawaiian meteorology, which enhances dispersion and thus 

reduces potential exposures, and the significantly lower population density that reduces the 

potential health risks. 

Commenter (136) asserted that application of an urban health risk standard to non-urban 

area sources is not justified and appears to be arbitrary and capricious and not otherwise in 

accordance with applicable law – the scope of the proposed rule for existing area sources RICE 

should be limited to those facilities with HAP emissions that pose an unacceptable risk to human 

health. 

Commenter (78) added that engines located in remote areas present a lower health risk 

than engines located in densely populated areas. EPA should consider excluding engines that do 

not present significant health risks from the retrofit requirements under this rule, commenter 78 

said. 

Four commenters (76, 150, 241, 242) noted that the uncertainty in the toxicological dose 

response values for formaldehyde should be considered when determining the regulation of 

RICE in non-urban areas. A commenter (150) asserted that the docket lacks support for the 

proposition that formaldehyde poses the sort of risk to human health that would justify the 

proposed rules, particularly in rural areas. Moreover, the commenter (150) indicated that the 

formaldehyde unit risk estimate (URE) is under review and may be revised. The commenter 

(150) believes that EPA should delay area source requirements for gas-fired engines until this 

review is complete and a technically sound risk assessment can be completed. 

Regarding the URE for formaldehyde, commenters 76 and 242 said that EPA should 

consider the fact that the formaldehyde URE review is ongoing. The review is not scheduled to 

be completed until August 2011. The outcome of the review is meaningful for classifying 
61

natural gas engines as key area sources, for estimating the cost-benefits associated with a 

NESHAP rulemaking, for risk relief from control of natural gas engines, and for determining if a 

separate category and de-listing from section 112 of the CAA is warranted for natural gas 

engines. 

Response: EPA does not agree that it should have conducted risk-based analyses for area 

sources. Section 112(d) rulemaking is intended to be technology based, with only certain 

provisions, not applicable here, dealing with risk. See also our responses to comments 2.2.1 and 

1.9 regarding the decision to regulate engines at rural locations and the URE for formaldehyde. 

2.2.4 Comment: Three commenters (104, 112, 136) stated that the physical and chemical 

properties of the HAP formaldehyde emitted by RICE should play a role in determining whether 

non-urban sources would be regulated in the proposed rule. One commenter (136) indicated that 

alternative standards for non-urban area source RICE are warranted considering the short halflife of formaldehyde in the atmosphere and the remote proximity to population clusters for the 

majority of RICE in the oil and gas upstream sector. This commenter (136) stated that EPA 

should consider a maintenance program in lieu of numeric standards for rural area source RICE, 

consistent with the precedent of the Oil and Gas MACT (40 CFR part 63, subpart HH) and 40 

CFR part 63, subpart GGGGG. 

One commenter (104) asserted that EPA has not adequately justified the need to regulate 

engines in rural areas at area sources, and requested that EPA re-evaluate this issue. The 

commenter (104) noted that EPA has proposed to limit emissions of HAP through emissions 

standards for formaldehyde for some engines and through emissions standards for CO for other 
62

engines. The commenter (104) stated that formaldehyde is short-lived compound that breaks 

down quickly by sunlight and other atmospheric conditions can shorten its life-span and rapidly 

disperse it, and also stated that carbon monoxide is short-lived. The commenter (104) asked 

what impacts there are to public health in rural, remote areas where there are no receptors in 

close proximity to engines at oil and gas production facilities. 

One commenter (112) requested that EPA reconsider the physical properties of 

formaldehyde and provide exemption status for area HAP sources in rural areas. The commenter 

(112) stated that formaldehyde is a naturally occurring and anthropogenic chemical that is 

neither persistent nor bioaccumulative. According to the commenter (112), formaldehyde is 

highly reactive and quickly removed from the environment: 

• When released to the atmosphere from combustion processes, formaldehyde is rapidly 

dispersed into ambient air. 

• Formaldehyde is removed from the atmosphere by direct photolysis and oxidation by 

photochemically produced hydroxyl radicals. 

• It is estimated that in the presence of sunlight the lifetime of formaldehyde in ambient air 

is approximately 1.6-19 hours. (Agency for Toxic Substances and Disease Registry, 

“Toxicological Profile for Formaldehyde” Section 5 – Potential for Human Exposure, 

pages 296-298; http://www.atsdr.cdc.gov/toxprofiles/tp111.html.) 

• Formaldehyde in air that reaches water and soil is expected to be rapidly biodegraded and 

would not be expected to be present to provide for exposure via ingestion of soils or 

water (ATSDR, 1999). (Agency for Toxic Substances and Disease Registry (ATSDR), 

1999. Toxicological Profile for Formaldehyde, Atlanta, July.) 
63

• It has been concluded that the bioavailability of formaldehyde from the ingestion of food 

is not expected to be significant (ATSDR, 1999; EPA, 1998). 

• There has been no evidence of bioaccumulation of formaldehyde into the aquatic or 

terrestrial food chain (HSDS, 2004). (Hazardous Substances Data Bank (HSDS), 2004. 

National Library of Medicine, queried on-line at www.nlm.nih.gov, July.) 

Response: Formaldehyde is a hazardous air pollutant regulated under section 112 of the CAA. 

As noted in the preamble of the final rule, standards under section 112(d) of the CAA are 

technology-based, not risk-based. EPA did take into account that formaldehyde is a probable 

human carcinogen, the magnitude of formaldehyde emissions from these engines, and the goal of 

providing equal protection for all communities, in determining not to exempt rural sources from 

regulation. 

While formaldehyde may have a short half-life in the presence of sunlight, secondary 

formation of formaldehyde from VOC precursors can be significant. Regional photochemical 

model simulations examining particular scenarios have shown that formaldehyde and 

acetaldehyde can be transported hundreds of kilometers from their emissions source in distinct 

plumes.3

 Further, these emissions can contribute to polluted air masses with elevated 

concentrations of gaseous HAP. These polluted airmasses can be transported thousands of 

kilometers and affect locations well distant from the original emissions source. 

                                                           

3 U.S. Environmental Protection Agency (U.S. EPA). Air Quality Modeling Technical Support Document: Changes 

to the Renewable Fuel Standard Program, Office of Air Quality Planning and Standards, EPA 454/R-10-001. 

February. Available at <http://www.epa.gov/OMS/renewablefuels/454r10001.pdf>.
64

2.2.5 Comment: One commenter (130) stated that the applicability of the rule (e.g., to all 

existing area source engines regardless of size) is not consistent with the legacy of affected units 

for other source categories. According to commenter 130, area sources and existing sources 

typically have lower control and assurance requirements than MACT source, not more stringent, 

as was proposed. For the area source regulation, EPA has chosen nationwide applicability, 

instead of considering proximity to urban areas as done in similar rules. The commenter (130) 

stated that formaldehyde is the primary HAP emitted by gas-fired sources and is used by EPA as 

an indicator and the commenter believed that using formaldehyde in this way is inappropriate 

because the formaldehyde URE is under review and may be revised, and also, formaldehyde has 

a short half life in the atmosphere thus receptors must be in close proximity for health affects to 

occur. The commenter recommended that a size-based exemption be added to the rule for area 

sources based on risk analysis. According to the commenter (130), rural sources should be 

excluded from catalytic controls similar to the oil and gas GACT for dehydrators. EPA should 

consider whether a size-based threshold can be included for engines as an emission limitation at 

major sources. 

Response: The commenter is correct that in some cases the proposed standards, and the final 

standards, for existing engines at area sources are more stringent than pre-existing standards for 

engines at major sources or new engines. This is a product of certain court decisions that have 

provided less flexibility in standard-setting under section 112 than EPA used in previous rules, as 

well as new and better information regarding emissions from existing engines. As discussed in 

response to comment 2.2.1, EPA determined that it is justified to finalize nationwide 

requirements that would apply equally to urban and rural area sources. EPA is finalizing 
65

management practices for the majority of existing SI engines at area sources (except nonemergency 4SLB and non-emergency 4SRB greater than 500 HP that operate more than 24 hours 

per year). For existing stationary non-emergency 4SLB and non-emergency 4SRB greater than 

500 HP that operate more than 24 hours per year, EPA determined that it was justified to require 

numerical emission levels that are based on levels expected with catalytic controls. Also, EPA 

must address existing stationary SI engines at area sources of all sizes, but small engines are 

under the final rule subject to management practices only, and not to numerical emission limits. 

EPA agrees that it is appropriate to distinguish smaller engines from larger engines for existing 

SI engines at major sources and has for the final rule established a subcategory of existing SI 

engines less than 100 HP. Existing SI engines less than 100 HP that are located at major sources 

are subject to maintenance practices under the final rule. 

EPA disagrees with the commenter that formaldehyde is not an appropriate surrogate for 

HAP emissions from stationary engines. Formaldehyde is the hazardous air pollutant that is 

emitted in the largest quantity from stationary engines and if formaldehyde emissions are 

reduced, HAP emissions are reduced. Formaldehyde is a HAP and must be regulated regardless 

of the formaldehyde URE being under review. 

2.3 Small Engines 

2.3.1 Comment: Numerous commenters (51, 96, 116, 121, 132, 150, 154, 176, 225, 228, 230, 

262) said EPA must provide an appropriate applicability cut-off for smaller rated engines. 

One commenter (262) noted that the proposed rule applies to all engines, regardless of 

size or emissions. The commenter (262) noted that there are maintenance and recordkeeping 
66

requirements and emission limits for engines as small as 50 HP. The commenter (262) said that 

the basis for extending these requirements to such small units is not clear or explained in the 

preamble. The commenter (262) noted that previous NESHAP rules have taken into account the 

size and emissions of the source when setting regulations. The commenter (262) recommended 

exempting engines below a minimum HP and minimum emissions, so as not to force expensive, 

burdensome requirements on small engines that do not have significant emissions. 

One commenter (176) reported that the state of Illinois exempts small engines from state 

permitting requirements when they are not covered from section 112 of the CAA. The 

commenter (176) asserted that the proposed rule would subject numerous owners and operators, 

who are not required to have a permit to operate their engines, to state permitting requirements. 

The commenter (176) expects that this would contribute to an increased delay in permitting and 

additional costs for owners and operators to obtain a permit. 

One commenter (51) believes that it is more important to regulate larger engines at all 

sources than to regulate small engines at area sources. One commenter (116) believed that it is 

inconsistent to exempt larger engines at major sources while requiring smaller engines to comply 

with the rule. The commenter (116) recommended that the standard include the same 

requirements for all categories of engines in excess of 500 HP at major and area sources. 

One commenter (118) noted the questionable value of regulating small RICE (between 50 

and 500 HP) at area sources. The commenter (118) noted that although the costs of the 

management practices would be minimal, some State rules are written such that they require any 

equipment subject to a MACT standard obtain a permit regardless how small the equipment may 

be. The commenter (118) felt that the air quality benefit of regulating these smaller sources is 

outweighed by the burden placed on area sources where a small engine may be their only 
67

equipment, and the administrative burden placed on the state agencies to administer permit 

programs for the large number of sources who would not otherwise be regulated. 

One commenter (225) stated that the proposed rule applies to all RICE regardless of size 

or emissions, with maintenance and recordkeeping requirements for engines less than 50 HP and 

emission limits for engines as small at 50 HP (4-stroke rich burn (4SRB)). The commenter (225) 

asserted that the basis for extending these requirements to such small units is not clear or 

explained in the preamble. The commenter (225) indicated that previous NESHAP (specifically 

40 CFR part 63, subpart HH for glycol gas dehydrators) took into account the size and emissions 

of the source and urged EPA to adopt this approach for the RICE rule. The commenter (225) 

believes that a HP threshold should be identified based on a risk analysis of emissions from the 

universe of potentially affected engines and their health effects, below which engines are exempt 

from the regulations. The commenter (225) stated that the focus is public health, so the rule 

should not force expensive requirements on small engines that do not have significant emissions. 

One commenter (132) believes that establishing a small natural gas-fired engine 

subcategory is a reasonable application of section 112(d)(1) of the CAA that will allow EPA to 

calculate defensible MACT floors, and also consider cost and other relevant factors in evaluating 

“beyond the floor” standards, appropriate GACT standards, and SSM requirements in accord 

with common sense and the reasonable meaning of the statute. The commenter (132) suggested 

using the following definition for the small natural gas-fired engine subcategory: 

“Small NG Rice means any SI RICE with HP less than 500 that is fueled by natural gas, located 

at a crude oil or natural gas production well, gathering station, processing station or otherwise 

included in SIC Major Group 13.” 
68

One commenter (96) believes that EPA should exempt engines less than 100 HP from the 

NESHAP. The commenter (96) said that it is not practical, feasible or cost effective to 

implement emission standards and requirements on all size engines. Small engines do not 

typically operate frequently and contribute little to the total HAP emissions and owners and 

operators of these engines have not been subject to regulation until now and may not be familiar 

with EPA or State requirements to demonstrate compliance, the commenter (96). Also, the cost 

of testing and compliance would be high for owners, States, and EPA, if such requirements are 

promulgated for the significant number of small engines. 

One commenter (150) stated that a size-based exemption should be added to the rule for 

area sources, such that smaller RICE (≤ 250 HP) would be exempt from the new requirements. 

The commenter (150) believes that this is appropriate because smaller engines create fewer 

emissions, so the air quality benefit of additional regulation is small in relation to the burden on 

operators. 

The commenter (150) also stated that EPA should exempt SI engines that emit less than 

0.5 ton/yr of formaldehyde because the cost per ton of mandatory controls is high while the 

public benefit is low. The commenter (150) noted that similar exemptions have been allowed in 

the 40 CFR part 63, subpart HH rules [see §63.764(e)(1)(ii)] and subpart GGGGG rules [see 

§63.7881(c)(1)], and pointed out that the exemption in subpart HH relates to emissions of 

benzene which is a known carcinogen that does not degrade as rapidly as formaldehyde. In the 

alternative, the commenter (150) suggested that such small sources of formaldehyde should only 

be required to adhere to work practice standards, not numerical emissions limits, thereby 

providing incentives and rewards to operators who are able to limit formaldehyde emissions.
69

Response: EPA is required to regulate all engines in the stationary engine source category. The 

source category includes stationary engines of all sizes at major sources of HAP emissions. As 

discussed in the memorandum entitled “Analysis of the Types of Engines Used to Estimate the 

CAA Section 112(k) Area Source Inventory for Stationary Reciprocating Internal Combustion 

Engines” which is in the docket for this rule, EPA has found that existing stationary emergency 

engines located at residential, commercial, and institutional facilities were not included in the 

original Urban Air Toxics Strategy inventory and were not included in the listing of urban area 

sources and are therefore not included in the source category. In the final rule, EPA has 

specified that those engines are not subject to subpart ZZZZ. However, with regard to other 

stationary engines, EPA does not agree with the commenter who said that EPA should treat 

emissions from smaller engines as de minimis. It is unclear whether a de minimis exemption is 

even possible under section 112(d) of the Act in these circumstances, see National Lime Ass’n v. 

EPA, 233 F. 3d 625, 640 (D.C. Cir, 2000), but in any case the commenter did not provide 

enough specific information to justify EPA making such a de minimis finding in this instance. 

Given the narrow and specific circumstances delineated by the court in Alabama Power v. 

Costle, 636 F.2d 323 (D.C. Cir. 1979) for making such a finding, and the lack of specific 

information from the commenter that these circumstances exist in this instance, we do not make 

a de minimis finding. However, in the final rule, EPA has attempted to minimize the regulatory 

burden particularly on smaller sized stationary engines. For stationary engines located at area 

sources, EPA has flexibility to set non-numerical limits in the form of management practices. 

EPA is promulgating management practices for all emergency stationary engines located at area 

sources, and for stationary SI engines smaller than 500 HP located at area sources. These 

management practices are discussed in more detail in section 7.0. For existing stationary SI 
70

engines below 100 HP located at major sources, EPA has determined that it is not feasible within 

the context of this rulemaking to prescribe or enforce a numerical emission standard because the 

“application of measurement methodology to this class of engine is not practicable due to 

technological and economic limitations.” This determination is discussed in more detail in the 

memorandum entitled “MACT Floor and MACT Determination for Existing Stationary NonEmergency SI RICE <100 HP and Existing Stationary Emergency SI RICE Located at Major 

Sources and GACT for Existing Stationary SI RICE Located at Area Sources.” As a result, 

existing engines below 100 HP located at major sources will be required to meet work practice 

standards to meet the maximum achievable control technology requirements for those engines. 

More information on the work practice standards can be found in the “MACT Floor and MACT 

Determination for Existing Stationary Non-Emergency SI RICE <100 HP and Existing 

Stationary Emergency SI RICE Located at Major Sources and GACT for Existing Stationary SI 

RICE Located at Area Sources” memorandum. 

Regarding the possibility of regulation under Title V, all stationary engines at area 

sources are exempted from Title V permit requirements under parts 70 and 71, as long as the 

sources do not otherwise have to meet such permit requirements. See 40 CFR § 63.6585(d). 

EPA understands the concerns of commenters regarding state permit requirements, but we 

believe that these concerns are best provided to the states in question. In addition, section 

112(c)(3) and 112(k) require that EPA regulate categories or subcategories of area sources 

representing 90 percent of the area source emissions of HAP presenting the greatest threat to 

public health in urban areas. Stationary engines located at area sources were included in that list 

of categories, and therefore must be regulated under section 112(c)(3). 
71

2.4 Natural Gas Engines 

2.4.1 Comment: One commenter (241) strongly felt that because EPA is basing the proposed 

rules for natural-gas-fired units on insufficient data and inadequate consideration of costs and 

benefits, the natural gas engine regulations should be withdrawn and developed through a more 

thoughtful, data driven, and transparent process. Commenter (241) claims the data for natural 

gas fired engines EPA is using is the same data previously indicated by EPA (in June 2004 final 

rulemaking for IC engines NESHAP) to be insufficient for rulemaking for existing natural gas 

fired engines less than 500 HP. 

This commenter (241) continues that the proposed rule has excluded natural gas 4SLB 

engines less than 50 HP and has based the emissions and service intervals on antiquated 

technologies. Commenter (241) also takes issue with EPA’s statement in Section IV, Subsection 

B, Paragraph 1a of the proposed rule preamble that there are no existing stationary RICE engines 

less than 50 HP that are lean burn SI of record, citing a new class of heat pump system available 

in the U.S, that have as a prime mover under 50 HP lean burn natural gas fueled RICE engines. 

Further, this commenter (241) sees no option for alternative maintenance intervals for natural gas 

powered 4SLB engines less than 50 HP in Table 2 of the preamble. Commenter 241 claimed 

that there are various small engines packaged that have proven service intervals ranging from 

6,000 to 10,000 hours, and that the emissions and cost impacts of the oil recycling, filter disposal 

and other maintenance proposed by EPA were not clear. While the emission requirements for 

4SLB engines less than 50 HP in preamble Table 1 generally specify formaldehyde as the target 

emission, it is unclear to the commenter (241) what test method will be used in the field, and this 
72

commenter also felt that the proposal did not define a clear emission target for natural gas 4SLB 

engines less than 50 HP. 

Response: EPA recognizes that it had limited emissions data available for the proposed 

rulemaking. However, at the time of the proposal, EPA was forced to use the emissions data it 

did have and propose emission standards based on that data set because that was all it had. Since 

proposal, EPA has attempted to gather additional engine test reports and has been able to obtain 

further emissions data to supplement the original database. Different industry groups have also 

gathered data and in some cases conducted testing programs to collect specific data that they 

believe was needed to develop a representative data set to base the emission standards on for the 

final rule. The commenter did not submit any data to show that the emission standards were not 

appropriate. 

 EPA did not exclude 4SLB engines less than 50 HP from the proposal. All engines less 

than 50 HP were in the same subcategory. In the final rule, EPA has promulgated work practice 

requirements or management practices for all engines at or below 100 HP. 

EPA received numerous comments stating that the proposed maintenance intervals were 

not appropriate. EPA has revised the proposed intervals to be consistent with and representative 

of current industry practices in the final rule based on the extensive comments received on this 

issue. EPA has also included in the final rule a provision allowing the use of an oil analysis 

program to extend the specified frequency for oil changes, which addresses the concern raised by 

the commenter. EPA clearly specified the test methods that should be used in the rule. 
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2.4.2 Comment: One commenter (135) requested that natural gas engines not be subject to 

emission standards. The commenter (135) noted that natural gas is a cleaner burning fuel than 

diesel, gasoline, and fuel oil. The commenter (135) explained how the proposed rule would 

affect owner/operators of natural gas engines that are used for irrigation purposes and are widely 

dispersed in rural areas. These owner/operators could either comply with the proposed rule or 

convert irrigators to electricity. Complying with the proposed rule would be costly, potentially 

putting some firms out of business, and result in increased fuel use and motor vehicle traffic 

(implying increased emissions from those sources) while yielding little benefit considering that 

they are located in rural areas. The other alternative, converting to electricity, would also be 

costly and is not even an option in some locations where electricity is not available or the local 

electric cooperative is already at full line load capacity. The commenter (135) considered both 

options infeasible and requested that natural gas engines not be subject to emission standards. 

Response: EPA is statutorily required to promulgate regulations for all existing stationary 

engines and is unable to exempt natural gas engines from emission standards. As discussed later 

in this document, the final rule contains revised requirements compared to the proposal. 

2.5 Other 

2.5.1 Comment: One commenter (242) said that the rule will require all existing engines to 

obtain an NSR permit. Exemptions that have existed in NSR programs for minor sources will no 

longer be available for sources having NESHAP requirements and the commenter (242) said that 
74

EPA has not taken into account the burden associated with obtaining NSR permits for these 

sources. These costs should be included in EPA’s benefit analysis, the commenter (242) said. 

Response: The costs of compliance with NSR are not clear and result from operation of those 

regulations. They are outside the scope of this rulemaking. The decision to regulate stationary 

engines located at area sources came through operation of section 112(c)(3) and 112(k) of the 

CAA and was decided in the urban air toxics rule, not this rule. 

2.5.2 Comment: One commenter (136) noted that there is no limit on construction date for 

existing RICE in the proposed rule. The commenter (136) stated that older engines were never 

designed to comply with these stringent emissions and some are not easily retrofitted with 

catalysts, if it can be done at all. The commenter (136) added that the expectation for older 

RICE to meet the MACT Floor or Beyond the MACT Floor will not be possible in many cases, 

and there is no data in the docket to support that these emission limits are achievable. The 

commenter (136) believes that industry could be faced with replacing thousands of existing 

engines that will not be able to comply with the emission limits in this proposed rule. 

Response: EPA proposed emission standards for certain existing stationary engines based on the 

use of add-on controls. In those cases, EPA expects that owners/operators would be able to 

retrofit their existing engines with readily available control technologies such as oxidation 

catalyst or NSCR. Based on available information at the time of proposal, there was no 

indication that the aftertreatment controls that the proposed emission standards were based on 
75

would not be feasible to apply to older engines. Oxidation catalyst and NSCR have been used 

for many years on existing and new stationary SI engines. 

 The commenter claims that the proposed emission standards that are based on retrofitting 

engines may not be achievable on older engines. The commenter does not define what is meant 

by older engines and further does not support the claim that the standards are not feasible. No 

details are provided as to why the proposed standards are not achievable, in the commenter’s 

opinion. 

2.5.3 Comment: One commenter (250) from the propane industry noted that the proposed rule 

only affects diesel and natural gas-fired RICE. The commenter (250) supported coverage only 

for natural gas-fired and diesel RICE because most existing propane-fired engines are ≤ 50 HP, 

and this population is small compared to the number of existing diesel and natural gas-fired 

engines at this site rating. The commenter (250) stated that the Emissions Database used by EPA 

lists no significant number of propane-fired engines such that any benefit could be derived 

through their regulation. 

 In addition, the commenter (250) indicated that it reviewed the support documents posted 

to the docket for the rulemaking and determined that there was no cost impact analysis 

performed for the propane industry nor was there any analysis to determine if any verified 

technologies exist for compliance with the proposed requirements by propane engines. The 

commenter (250) believes that had the intent of the proposal been to apply to propane-fired 

engines, such an analysis would have (and should have) been performed. The commenter (250) 

added that the propane industry is seeking to expand into the source categories listed under the 

proposal, but understands that future engines that are developed would need to meet the 
76

regulatory requirements of newly constructed engines, as opposed to the existing engines 

considered under this proposal. 

Response: The regulation covers all existing stationary SI engines that are located at area 

sources of HAP emissions and stationary SI engines less than or equal to 500 HP located at 

major sources of HAP emissions. EPA is required to address HAP emissions from all these 

engines and cannot exempt a subgroup of engines like propane-fired stationary engines solely 

based on the size of these engines and the commenter’s claim that there are very few such 

engines. The final rule contains work or management practice standards for all engines smaller 

than 100 HP, so existing propane engines are not subject to numeric emission limitations if they 

are less than 100 HP. 

2.5.4 Comment: One commenter (121) said EPA should exempt RICE used in product 

development, research, and testing operations at both major and area sources. For example, 

members of the commenter’s (121) organization employs engines to test transmissions, 

subsystems, and powertrain configuration using dynamometer facilities. EPA has traditionally 

excluded research activities from applicability of MACT standards, the commenter (121) said. 

Similarly, commenter 230 recommended modifying 63.6590(a) of the proposed rule to 

exclude stationary RICE used for research and testing because research engines operate for 

limited periods of time, and represent an insignificant source of emissions compared to the 

population of interest to EPA. 
77

Response: EPA does not agree that stationary SI engines used in product development, research, 

and testing operations should be exempted from subpart ZZZZ. The commenter did not provide 

any data to show that the emissions and operation from these engines are different and would 

justify exempting them from the rule. 

2.5.5 Comment: One commenter (138) urged EPA to adopt a small producer exemption that 

would exclude facilities that meet the definition of “marginal well production” as provided for by 

either the Interstate Oil and Gas Compact Commission (IOGCC) or the federal tax code. The 

commenter (138) is concerned that the proposed rule will lead to a loss of production and 

employment in its state (Ohio) during this difficult, recessionary economic time because it will 

impose additional regulatory costs even on the small engine sizes used in the marginal 

production context. Citing an IOGCC study (Marginal Wells: Fuel for economic Growth, 

2008), the commenter (138) indicated that 83 percent of the oil and 77 percent of the natural gas 

produced in its state (Ohio) comes from marginal wells (average of 0.43 barrels of oil per day 

and 5.5 Mcf of natural gas per day). The commenter (138) said that production from such 

marginal wells is continually at risk of being abandoned prematurely because of the attendant 

economics – economics that are getting worse with the declining economy, increasing taxes and 

fees, and more-threatening regulatory climate. The commenter quoted the IOGCC study as 

saying: “In addition to supplying much-needed energy, marginal wells are important to 

communities across the country, providing jobs and driving economic activity. In fact, every $1 

million directly generated by marginal production results in more than $2 million of activity 

elsewhere in the economy.” The commenter (138) believes that imposing additional regulatory 

requirements will threaten needed energy resource, jobs, and economic activity. 
78

Response: EPA cannot legally provide the exemption suggested by the commenter. 

2.5.6 Comment: Two commenters (147, 189) requested that stationary RICE that are less than 

300 HP, located in rural areas, used for agricultural purposes, and operated for a limited number 

of hrs/yr be exempted from numeric emission limitations and performance test requirements. 

The commenter (189) operates 74 stationary RICE that are spread out over a large geographic 

area. However, most of these are part of a single major source and would thus be subject to 

numeric emission limitations and performance test requirements. The commenter (189) asserted 

that it would be difficult, time-consuming and expensive to implement the proposed rule for all 

of these engines. The commenter (189) suggested two alternate methods for providing such an 

exemption: 

• Classify rural, agricultural engines as area sources, or 

• Create a separate subcategory of major sources consisting of RICE used for agricultural 

purposes. 

In either case, the commenter (189) suggested imposing O&M requirements on these engines in 

lieu of numeric emission limitations. 

The commenter (189) stated that the economic impact of the proposed rule on the 

commenter’s firm would be extremely high and would significantly outweigh any environmental 

benefit. The commenter (189) submitted data indicating total HAP emissions from all RICE 

operated by the commenter to be less than 0.2 tpy. Based on EPA’s estimates for performance 

test costs, the commenter (189) calculated a cost effectiveness for its firm of between $80,000 

and $260,000 per ton of HAP reduced assuming all of the HAP emissions were eliminated due to 
79

the proposed rule. The commenter (189) therefore requested that rural agricultural RICE be 

exempted from numeric emission limitations and performance test requirements. 

The commenter (189) asked EPA to revise the proposed rule to allow engines located in 

rural areas, used for agricultural purposes, and operated for limited hours to be subject to the 

standards for area sources even if these engines are located at, or adjacent to, a major source. 

Response: EPA cannot change the definition of a major source, which is defined as “any 

stationary source or group of stationary sources located within a contiguous area and under 

common control that emits or has the potential to emit considering controls, in the aggregate, 10 

tons per year or more of any hazardous air pollutant or 25 tons per year or more of any 

combination of hazardous air pollutants, unless the Administrator establishes a lesser quantity, or 

in the case of radionuclides, different criteria from those specified in this sentence.” EPA cannot 

change the definition of an area source either, which is defined as “any stationary source of 

hazardous air pollutants that is not a major source as defined in this part.” 

 Further, EPA is generally required to establish numerical limits for stationary engines 

located at major sources of HAP emissions and cannot exempt a certain group of engines from 

being subject to emission standards. With the exception of subcategories for which prescribing 

or enforcing a numerical emission standard is infeasible as defined in section 112(h) of the CAA, 

which has not been shown for the subcategory the commenter suggests, section 112 of the CAA 

requires numerical standards for major sources. EPA has made the finding required by section 

112(h) of the CAA for emergency engines and engines below 100 HP, but EPA cannot make that 

finding based on the record for agricultural engines above 100 HP located at major sources. 

However, for area sources, EPA may adopt alternatives to numerical limits that include work 
80

practice standards. The final rule requires all engines smaller than 500 HP located at area 

sources to meet management practice standards and does not require any emissions testing for 

those engines. This significantly impacts and minimizes the compliance burden on affected 

sources. 

2.5.7 Comment: One commenter (269) expressed opposition to the proposed rule. This 

commenter (269) stated that the proposed rule would affect more equipment than any other 

stationary source emission standard previously adopted by EPA and is concerned about the 

impact the proposed rule would have on farming and ranching operations. The commenter (269) 

explained that many farmers and ranchers have small stationary engines that are run on an as 

needed basis and require scheduled maintenance to keep operating properly. Under the proposed 

rule, these small engines used to power generators, pumps, and other production agriculture 

equipment would be treated no differently than a HAP major source facility. The commenter 

(269) opined that the proposed rule is not justified or necessary. This commenter (269) stated 

that a thorough review backed by reliable and accurate information must accompany EPA’s cost 

projections for implementation with the understanding that “one size does not fit all.” This 

commenter (269) suggested that EPA focus on incentive-based programs rather than regulation 

to achieve emission reductions. 

Response: EPA does not agree with the commenter’s statement that the proposed rule is not 

justified or necessary. EPA is obligated by statutory requirements under sections 112(d), 

112(c)(3), and 112(k) of the CAA to develop regulations for stationary engines. EPA took into 

consideration the differences that exist between engines and issued proposed standards and 
81

compliance requirements reflective of that. For existing stationary engines located at major 

sources, EPA must set emission standards that reflect the maximum degree of reduction of HAP 

that is achievable. For area sources, EPA has more flexibility in that it can consider emission 

standards that employ GACT or management practices. EPA established subcategories for the 

proposed rule in order to capture the distinct characteristics of engines and discussed the reasons 

for establishing those subcategories in supporting memoranda available from the docket. 

Additionally, EPA established different standards and requirements for the various 

subcategories, e.g., the proposed emission standards for smaller engines at major sources did not 

require the use of aftertreatment and EPA proposed management practices for smaller engines at 

area sources. When establishing the emission standards and requirements for smaller engines, 

EPA kept in mind the type of industries and applications that typically employ such smaller 

engines. In the final rule, EPA revised its proposed standards, allowing many more engines at 

area sources, including all engines below 500 HP at area sources, to meet management practices 

and requiring emergency engines and engines rated at or below 100 HP located at major sources 

to meet work practice requirements rather than numerical emission limits. 

2.5.8 Comment: One commenter (227) asked what the status is of 4SLB engines greater than 

500 HP at major facilities that were exempted from controls in the previous rule.

Response: Existing stationary 4SLB engines greater than 500 HP located at major sources that 

are subject to 40 CFR part 63, subpart ZZZZ, are still subject to the same requirements that were 

originally finalized in 2004. EPA is not making any changes to the requirements that apply to 
82

existing stationary 4SLB engines greater than 500 HP located at major sources during normal 

operation at this time. 

2.5.9 Comment: Two commenters (179 and 183) wanted clarification on whether the rule affects 

temporary replacement engines. One commenter (183) stated that EPA should clarify for 

temporary replacement engines that are considered stationary because that replace permanent 

engines at stationary sources may meet requirements of the NESHAP either by meeting the 

otherwise applicable requirements for stationary sources or by meeting the requirements for 

nonroad engines, including the use of certified engines. Two commenters (179, 183) stated that 

EPA should clarify in the preamble for temporary portable engines that do not trigger provisions 

in the definition of nonroad engine are not considered stationary engines and therefore would not 

be covered by the NESHAP. 

Response: If the engine in question meets the definition of a nonroad engine as defined in 40 

CFR 1068.30, the engine is not covered by this NESHAP. If the engine does not meet the 

definition of a nonroad engine in 40 CFR 1068.30, the engine would be subject to the NESHAP. 

Temporary portable engines that remain in one location for less than 12 consecutive months (or 

for less than the full season for seasonal sources) are considered nonroad engines and are subject 

to the requirements for nonroad engines unless they replace permanent engines at stationary 

sources. Temporary portable engines that remain in one location for more than 1 year (or a full 

season at seasonal sources) are considered stationary engines. EPA does not agree with the 

commenters who asked that EPA make a statement in the preamble that temporary portable 

engines that do not trigger the nonroad engine definition will not be considered stationary 
83

engines because they are in fact considered stationary sources. Therefore, this language has not 

been added. 

3.0 Startup, Shutdown, and Malfunction 

3.1 Comment: Several commenters (63, 74, 76, 78, 87, 89, 96, 97, 98, 99, 101, 103, 104, 112, 

121, 122, 124, 126, 129, 130, 131, 132, 134, 139, 146, 148, 150, 151, 152, 154, 155, 156, 157, 

160, 162, 167, 168, 175, 176, 177, 178, 183, 186, 187, 191, 197, 200, 202, 203, 204, 205, 207, 

209, 213, 216, 218, 221, 224, 225, 226, 227, 228, 229, 231, 236, 240, 242, 247, 253, 261, 262, 

264) expressed serious concern over the proposed emission standards for periods of SSM. The 

U.S. Court of Appeals for the District Columbia Circuit vacated the SSM exemption in 40 CFR 

part 63, subpart A on December 19, 2008. The decision requires the Agency to implement 

standards that apply at all times, including during SSM periods. Numerous commenters thought 

the quick response to the December 2008 Court decision on the SSM issue is premature and 

recommended that EPA wait for a final decision before incorporate elements from this case. 

Numerous commenters are of the opinion that EPA has not provided a technical basis for its 

establishment of SSM limits and that any SSM limits should be replaced with work practice 

standards and disagreed with the decision to include limits for SSM periods. In addition, several 

commenters said that emissions during SSM events cannot be measured and therefore cannot be 

confirmed and limits are not enforceable. One commenter (148) recommended that EPA require 

a SSM plan similar to the SSM plan currently required under 40 CFR part 63, subpart ZZZZ. 

The commenter (148) also pointed out that 40 CFR 63.6650(b) in the existing rule requires 

operators to operate and maintain their equipment in a manner consistent with good air pollution 
84

control practices at all times, including periods of SSM. The commenter (148) believes that this 

requirement in conjunction with a SSM plan will achieve the same goals as the proposed rules in 

a much more cost effective and logical manner. 

Based on CO baseline data presented by commenters (74, 78), EPA must consider a 

broader database of uncontrolled engines in determining what CO limits can be achieved during 

SSM periods. One commenter (78) asked how it can limit the concentration of CO to 40 ppmvd 

or less during startup and shutdown periods when catalytic control would not be effective, when 

CO emissions currently range for 160 to 382 ppmvd at 15 percent O2. Commenter 74 provided 

similar data and reached the same conclusion as commenter 78. 

Many commenters, including commenters 112, 155, 236, 242 and 247 recommended that 

EPA consider other alternatives to implement during SSM periods, such as possibly requiring 

work practice standards, which the commenters believe is the most reasonable approach and is 

justified under the CAA. Commenter 242 believes that work practices standards that minimize 

the emissions during of SSM periods is the most practical method of keeping HAP emissions 

from engines as low as possible. Commenter 242 offered to provide additional assistance and 

input in order to come up with reasonable work practices to include in the final rule. The 

commenter (155) also recommended that EPA describe the SSM requirements in the rule itself 

rather than in the GP. Alternatively, the commenter (155) recommended that the GP be revised 

due to confusing and conflicting requirements. 

 Several commenters, including commenters 96, 99, 156, and 242 said that there is no 

method to determine compliance during SSM periods. Commenter 242 said that it will be 

difficult or impossible to design a test program to describe emissions during SSM events, e.g., 

the commenter is not sure how a malfunction would be defined considering the unexpected and 
85

anomalous nature of the event. Therefore, emissions during these periods cannot be confirmed, 

commenter 242 said. Similarly, commenters 96 and 99 believe that it is not reasonable to set 

numerical limits during startup because there are no available or repeatable test methods or 

procedures for measuring emissions during startup or malfunction, plus there is no prescribed 

definition of what constitutes startup of an engine, which can vary significantly for a number of 

reasons such as engine and catalyst type, fuel, climatic conditions, application and load. 

Several commenters (63, 96, 104, 129, 139, 150, 162, 178, 191, 197, 242) expressed 

concern over the feasibility of measuring emissions during SSM events. One commenter (242) 

said that if EPA retains the SSM limits in the final rule that EPA must provide methodologies 

and details on how to determine compliance with the emission standards during these SSM 

events. The commenter (242) has previously stated its objection to SSM limits and favors work 

practice standards instead. However, if SSM limits are retained, two commenters (76, 242) said 

that EPA must specify how compliance is determined, e.g., the commenter (242) wondered how 

does a source determine compliance for SSM events that are short (which the majority of SSM 

events are) and less (e.g., 1 hour for warm startup) than the performance test length requirement 

of the average of three 1-hour tests. One commenter (96) said that this methodology (average of 

three 1-hour tests) is impossible to execute since startups usually take 30 minutes to complete. If 

EPA used Method 320 (FTIR) for short duration events, EPA should discuss any intent to 

modify the compliance method of taking the average of three 1-hour tests and state the length of 

a new tests, the commenter (242) said. The commenter (242) added that FTIR has the capability 

of taking short-term minute average concentration readings. 

One commenter (76) said that the rule should specify that concentration limit should be 

based on the time period of the startup or malfunction or a 1-hour period, whichever is longer. 
86

Another commenter (242) added that time is needed for catalyst elements to warm up and 

stabilize before CO and HAP are effectively reduced and uncontrolled or partially controlled 

emissions cannot comply with the proposed startup emission limits. Regarding malfunctions, the 

commenter (242) asserted that no assurance can ever be made in terms of emission limit 

compliance. The malfunction, by nature, is not predictable, unknown and undefined, of 

unknown frequency, and emissions cannot be predicted, implied or measured, the commenter 

(242) said and again urged EPA to adopt work practice standards that minimizes emissions 

during SSM events. 

 Finally, the commenter (242) noted that Title V operators would not be able to meet their 

obligation for compliance certification if the proposed SSM limits remain because affected 

sources would be required to show compliance with limits that have not been technically 

justified and will lead to implementation issues in the field. 

Since the rule offers no means of determining compliance during startup, one commenter 

(150) stated that clarification is needed on this issue. 

One commenter (129) stated that for a source that is not monitoring emissions with a 

CEMS, it is impossible to determine whether SSM limitations are being met. The commenter 

(129) added that the monitoring/testing requirements will not allow an operator to make a 

knowledgeable determination of compliance during SSM using available data. 

One commenter (99) said that there are no viable measurement methods available to 

measure CO, formaldehyde or VOC during transient operation and a review conducted by the 

commenter of Table 4 in the proposed rule shows the inconsistencies related to transient 

measurement acceptability with respect to stack gas moisture and flow rate, delays in the actual 

response of analyzers, issues in obtaining an accurate measurement during a transient test due to 
87

an axial diffusion function in long gaseous emissions sample lines, and field gaseous emission 

measurements require stack traverse as well for the emissions under measurement, per methods 

7, 10, 25, etc., which eliminates the possibility of getting an accurate measurement during 

transient events such as a startup. 

One commenter (152) claimed that issuance of numerical limits for SSM based on the 

emissions of the “best controlled sources prior to full warm up of the catalytic control” fails to 

consider emissions during malfunction of the engines themselves. The commenter (152) asserts 

that while EPA appropriately determined that during a control device malfunction, the floor and 

standard cannot be set assuming operation of the control device, EPA errs in limiting its analysis 

solely to operation of the controls since emissions can increase as a result of engine malfunctions 

as well. The commenter (152) noted that its experience is consistent with EPA’s statements that 

emissions during an engine malfunction may increase due to the effects on exhaust temperatures 

and composition. The commenter (152) concluded that emission limits would need to be based 

on the emissions level from the best performing sources without control while the engine is 

malfunctioning. Commenter 96 added that it does not make sense to set any numerical standards 

during a malfunction of an engine because inherent in the concept of a malfunction is that 

emissions will be malfunctioning as well. It is also not logical to apply the concept of “best 

performing” malfunctioning engine, the commenter (96) said. For these reasons, it is 

unreasonable for EPA to promulgate numerical emission limits for periods of malfunction, in the 

commenter’s (96) opinion. Emission testing for malfunctions would be near impossible to 

conduct given the sporadic and unpredictable nature of the events, the commenter (121) said. 

Commenter 154 said that the nature of malfunctions means it is not feasible to predict or 

simulate emissions that occur during periods of malfunctions. 
88

The commenter (152) asserted that with respect to engines, it is not technologically or 

economically feasible to apply measurement methodology for the emissions during SSM periods 

and further, that it is unreasonable for the Agency in the face of the lack of accurate emission 

measurements to simply set the standard at the level for normal operations (e.g., for sources not 

using a control device). The commenter (152) stated that this situation is precisely the 

circumstance in which Congress envisioned that a work practice standard would be established, 

and urged EPA to adopt a work practice standard applicable to malfunction and startup periods 

for engines consistent with section 112(h) of the CAA and not to apply the numerical limits for 

normal operations. 

 One commenter (157) believes that the startup and malfunction emission standards for 

RICE using catalytic controls should include maintenance checks and readiness testing, which 

are typically short in duration. Therefore, the commenter stated that the catalytic controls would 

not reach the required temperature for effective control. 

 One commenter (134) stated that EPA solicited comment on the level of specificity 

needed to define the periods of startup and malfunction. The commenter (134) believes the 

responses differ based on whether the event is a startup or malfunction. The commenter (134) 

noted that startup of an engine begins with the start of fuel flow to the engine and ends when the 

engine has achieved normal operating temperature and air to fuel flows as indicated by the 

manufacturers’ specifications, and while the initiation of a startup is predictable, its conclusion is 

not time-determined, but operationally-determined. The commenter (134) noted where a catalyst 

is used to control emissions; startup does not end until the required catalyst bed temperature has 

been achieved, however, this may happen before the engine air and fuel flows are normal and 

thus catalyst bed temperature is not the exclusive criterion that defines the end of the startup 
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period. The commenter (134) noted that the start of the malfunction should be defined as when 

the normal operation emission limit is exceeded and the end of the malfunction should be set as 

when the normal operation emission limit is restored or the engine is shutdown. The commenter 

(134) noted that malfunctions often require shutdown to address, but such shutdowns can be 

delayed because immediate engine shutdown would cause other upsets. Therefore, the 

commenter (134) believes it would not be reasonable to set any specific time limits on either 

startup or malfunction periods, because their duration can be a function of operational need. 

Similarly, one commenter (96) disagreed that it would be appropriate to set a specific limit on 

the time allowed for startup because not all engines experience the same type of startup and 

malfunction. The length of startup will depend on many factors including engine type, size, fuel 

type and duty cycle, plus the frequency of required startups will also vary greatly among engines 

because some engines are only used for intermittent operation. 

Some commenters, including commenters 74, 78, 96 and 99 thought that limiting the 

engine startup time is a reasonable method to limit emissions. Commenter 99 added that the 

most effective way to control emissions during startup for engines with catalysts is to limit the 

amount of time it takes to warm up the exhaust to initialize the catalyzation process and startup 

time can be easily monitored. The commenter (99) added that the time to be monitored at startup 

be defined as from the initial engine in-cylinder combustion, corresponding with continuous 

operation, up to the point that a defined catalyst inlet temperature is reached. The commenter 

(99) also recommended that owners/operators be able to request additional startup time if 

necessary in special circumstances, e.g., in extremely cold climates or where sufficient load 

cannot be reached within 30 minutes. Commenters 74, 78 recommended a limit of 1 hour for 

startup and 30 minutes for shutdown. The rule should not include a time limit for malfunctions, 
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as the length of time during which an engine will be out of compliance would depend on the type 

of malfunction, the commenters (74, 78) said. The commenters (74, 78) suggested that each 

affected source would be required to prepare a SSM plan, which would have to address 

appropriate actions and time limits for malfunctions. Commenter 112 suggested that for engine 

startups, the work practice should require loading the engine to normal operating load as soon as 

practicable so that the catalytic controls are within operating range as soon as practicable. 

Commenter 96 provided the following language to address the startup issue: 

“RICE startup operations, which constitute the time period from engine ignition to the time when 

the catalyst temperature is sufficient to enable effective catalyst operation, shall be minimized. 

Startup time shall not exceed 30 minutes or the manufacturer’s startup recommendations, unless 

the Administrator approves a longer time for certain engine classes or approves a longer startup 

time to address special conditions and requirements (e.g., cold weather installations) in response 

to a petition from the owner/operator. During initial commissioning of the engine/equipment 

installation, additional time may be required for the set-up procedures before normal catalyst 

operation can be expected. Malfunctioning RICE shall be shut down and repaired as soon as 

practicable based on the engine's application and use.” 

 Commenters (121, 154) do not support setting the same limits for SSM periods as for 

normal operations. Commenter (121) said that for engines with add-on controls, given that the 

catalysts have to reach a certain temperature to be effective, emissions during startup would be 

higher than during normal, steady state operation. The commenter (121) noted that EPA has a 

separate cold-start test with emission limits different from those required during the Federal Test 

Procedure. The commenter (121) attached a technical paper that illustrates the increased 

emissions during startup. Commenter (154) said there is no record support for this option and 
91

that any diesel engine could be expected to have different emissions as it starts up. Bag sampling 

by one industry member indicates CO emissions during startup are significantly higher (as much 

as double) than during steady state. 

 Commenters (121, 154) also objected to EPA’s proposed second option. Commenter 

(121) said the data are apparently derived from the best controlled engines not using catalytic 

controls. The commenter (121) said that emissions data from steady-state operation of 

uncontrolled engines does not account for the cooler engine and fuel temperature conditions 

during startup. Nor does the second option properly account for malfunctions. 

Two commenters (150, 154) said that EPA has not supported its assertion that emissions 

should not be different during periods of shutdown compared to normal operations. According 

the commenter (154), EPA has created no record to substantiate its assertion. The commenter 

(154) asserts that data would likely reveal variation among RICE shutdown emissions. For 

example, for RICE where there is a cool down period where the engine operates for a period of 

time (10 to 15 minutes) at reduced load and revolutions per minute, these conclusions could be 

wrong. All existing data has been acquired at 100 percent speed and load conditions, +/- 10 

percent. Normal operation can cover a wide range of speed and load conditions for which preand post-catalyst data do not exist. Without hard data at “off point” conditions, no defensible 

conclusion can be drawn, which makes EPA’s unsupported assertion arbitrary. The commenter 

(154) believes the best approach is for sources to follow appropriate operational procedures 

during shutdown periods. EPA should use section 112(h) of the CAA to allow facilities to 

establish source-appropriate procedures during shutdown, the commenter (154) said. 
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One commenter (154) stressed that EPA needs to evaluate each source category 

independently regarding the time required for shutting down equipment in a controlled fashion 

and the emission control equipment effectiveness during the shutdown period. 

 After the conclusion of litigation, if EPA pursues SSM limits for this category, it should 

consider precedents in the mobile source counterparts and the NSPS, according to commenter 

121. These engines are already well-controlled through other standards set by EPA, and 

additional requirements or changes are unnecessary under the RICE MACT, in the commenter’s 

(121) opinion. Another difficulty is defining the exact time period for “startup,” the commenter 

(121) noted. For new engines, the commenter (121) recommends that EPA and engine 

manufacturers work together to determine whether startup emissions can be addressed in the 

certification process. 

 Commenter 154 proposed two options for EPA to address emissions during SSM events, 

both of which are fully supported by law and could be fully supported through data. Alternative 

1 would be to treat SSM emissions as de minimis, using the D.C. Circuit rationale in Alabama 

Power Co. v. Costle. The commenter (154) noted that catalyst systems do not perform at low 

temperatures, and the SSM periods vary in duration and intensity, which can significantly impact 

actual emissions profiles. The commenter (154) provided examples of why an assumption that 

SSM emissions are identical to normal stable operations emissions is erroneous and a gross oversimplification of unit operations. 

 Commenter 162 said EPA should explain the justification behind setting CO and 

formaldehyde emission limits during periods of SSM. The commenter (162) does not see how 

one can assure compliance with an emission limit during a malfunction and does not know of 

any test methods that can be conducted during the relatively short periods of startup or shutdown. 
93

The commenter (162) asserted the compliance with SSM plans will ensure emissions are 

minimized during these times. By imposing emission limits during periods of SSM, RICE 

owner/operators will have to report deviations for each instance, even if the owner/operators took 

actions in compliance with their SSM plan, because a reliable compliance demonstration is not 

available for existing equipment, according to commenter 162. 

Five commenters (89, 101, 151, 221, 231) stated that SSM emission limits are unproven 

and cause compliance uncertainty. The commenters (89, 101, 151, 221, 231) indicated that EPA 

set the SSM emission limits assuming that emissions during SSM periods are the same as steady 

state engine operation before the catalyst. According to the commenters (89, 101, 151, 221, 

231), HAP emissions during SSM activities have not been studied, but are definitely not stable 

over hourly averages like the proposed standard assumes. With today’s knowledge, the 

commenters (89, 101, 151, 221, 231) believe that SSM emissions standards are not feasible. 

 Two commenters (112, 225) stated that operators of facilities with Title V permits may 

have concerns about the annual compliance certifications since compliance with the standards is 

unknown during startup and malfunction since emissions are rapidly changing during startup. 

One of these commenters (112) asserted that the SSM standards are instantaneous standards, not 

hourly averages, but no one knows if the proposed instantaneous limits can be met without test 

data. This commenter (112) indicated that compliance certifications for Title V permits may 

necessitate testing, which is not included in EPA’s cost analysis. 

 The commenter (150) believes that a clarification is needed regarding the co-proposal 

associated with Table 3 of the preamble (74 FR 9703). The commenter (150) believes that EPA 

is suggesting an amendment to existing regulations for certain categories of engines in order to 

set limits during periods of startup and malfunction, but the commenter finds the scope and 
94

possible applicability of this co-proposal unclear. If EPA is proposing that standards be relaxed 

during SSM events, the commenter (150) would support such a concept. 

Commenter 240 said that in contrast to other subcategories that allow for higher emission 

limits during periods of startup and malfunction, EPA requires that emergency CI engines meet 

the same 40 ppmvd CO at 15 percent O2 standard at all times. This commenter (240) looked at 

manufacturer specifications for new engines that show higher CO emissions at lower loads, with 

decreasing emissions as the engine progresses to higher loads. In addition to lower loads that 

may occur during a startup or malfunction event, good engineering practice for these engines is 

not to operate at full loads during normal operations or startup and malfunction. 

One commenter (76) noted that the NFPA Code 24 requires emergency diesel fire pump 

engines to be operated for 30 minutes per week to readiness testing purposes. It will raise 

difficult questions for the owners/operators of these engines if EPA requires emission limits 

during startup times, e.g., what should the owner do if the engine is unable to reach the required 

limits within the 30 minutes startup, the commenter (76) asked. The commenter (76) asked if the 

owner would be required to run the engine for longer e.g., up to 1 hour in order to reach steady 

state conditions. Even if the owner does not meet the limits, the owner will still have to conduct 

the weekly test under NFPA code and replacing emergency diesel fire pumps in a short 

timeframe is not practical, the commenter (76) said. Therefore, the commenter (76) indicated 

that it may not be able to comply with both the EPA and NFPA requirements for emergency 

diesel engines. 

Two commenters (103, 154) responded to EPA’s request on how to define a startup and 

malfunction. One commenter (154) said that EPA’s request reveals the profound lack of 

foundation that EPA has to propose rulemaking options for regulation of RICE SSM emissions. 
95

The commenter (154) will be pleased to assist EPA in developing a record for a future 

rulemaking to address SSM and noted that such an effort should also address the health and 

safety implications of regulating SSM events. 

Response: EPA received extensive comments on the proposed requirements applicable to 

existing stationary engines during SSM. Consistent with the recent Court decision that vacated 

the exemption in 40 C.F.R. 63.6(f)(1) and (h)(1) for SSM (Sierra Club v. EPA, 551 F.3d 1019), 

EPA has established standards in this rule that apply at all times. EPA disagrees with those 

comments suggesting that EPA was premature in proposing standards during periods of startup, 

shutdown and malfunction. The United States Court of Appeals for the District of Columbia 

Circuit issued its opinion vacating the SSM exemption in December 2008, and we appropriately 

accounted for that decision in proposing the rule in February 2009. EPA does not believe it is 

appropriate to promulgate final rules that are inconsistent with the decision of the D.C. Circuit. 

EPA has determined that the emissions from stationary SI engines during startup are 

significantly different than the emissions during normal operation. During startup, incomplete 

combustion of the diesel fuel causes variations in the pollutant concentrations and fluctuations in 

the flow rate of the exhaust gas. Incomplete combustion is due to cold areas of the cylinder 

walls that cause the temperature to be too low for efficient combustion. As the engine continues 

to operate, these cold regions begin to heat up and allow for more complete combustion of the 

diesel fuel and stabilization of the exhaust flow rate and pollutant concentrations. In addition, 

the engine experiences extreme transient conditions during startup, including variations in speed 

and load, poor atomization of the fuel injection, which leads to variable engine and engine 

exhaust temperatures, variable exhaust gas flow rates, and variable diluent pollutant 
96

concentration. Note for example the brief time spent at different load conditions as shown in 

Figure 1 of the attachment to EMA’s letter dated February 17, 2009 (EPA-HQ-OAR-2008-0708-

0019), which illustrates the transient nature of the engine startup phase. Other factors that cause 

emissions to be higher during startup, including for engines that are not equipped with oxidation 

catalyst, are a higher propensity for engine misfire and poorer atomization of the fuel spray 

during startup. Aftertreatment technologies like oxidation catalysts and NSCR must also reach a 

threshold temperature in order to reduce emissions effectively. In the February 17, 2009, EMA 

letter, EMA provided various graphs illustrating sample engine startup profiles and graphs 

demonstrating the effect of engine exhaust temperature on catalyst efficiency. Figure 6 of the 

attachment to EMA’s letter (EPA-HQ-OAR-2008-0708-0019.1) shows how the CO efficiency is 

a function of the catalyst inlet temperature. 

EPA has evaluated the criteria in section 112(h) of the CAA and carefully considered and 

reviewed the comments on this issue. EPA has determined that it is not feasible to prescribe a 

numerical emission standard for stationary SI engines during periods of startup because the 

application of measurement methodology to these engines is not practicable due to the 

technological and economic limitations described below. 

EPA test methods (e.g., 40 CFR part 60, appendix A, Methods 2, 3A, 4, 10, Method 320, 

and Method 323) do not respond adequately to the relatively short term and highly variable 

exhaust gas characteristics occurring during these periods. The innate and substantial changes in 

the engine operations during startup operations create rapid variations in exhaust gas flow rate as 

well as changes in both pollutant and diluent gas concentrations. Correlating the exhaust gas 

flow rates and the gas components concentration data for each fraction of time over the entire 
97

period of a startup operation is necessary to apportion the values appropriately and to determine 

representative average emissions concentrations or total mass emissions rate. 

Measuring flow and concentration data in the types of rapidly changing exhaust gas 

conditions characteristic of stationary SI engines is unachievable with current technologies 

applicable to stack emissions testing. For example, application of Method 2 to measure stack 

flow rate requires collecting data for velocity pressure and stack temperature at each of 12 

traverse points and a corresponding stack moisture and oxygen concentration (for molecular 

weight determination). This traverse operation requires about 30 minutes to complete to produce 

a single value for the test period, which is approximately the same amount of time as the engine 

startup period. Clearly a single flow rate value would not sufficiently represent the variable flow 

conditions nor allow appropriate apportioning of the pollutant concentration measurements over 

that same period for calculating a representative average emissions value. Even if the start-up 

period is longer than 30 minutes, the stack flow rate test period could not be short enough to 

represent the short term (e.g., minute-by-minute) result necessary for representative emissions 

calculations. These findings lead us to conclude that correlating the flow and concentration data 

as necessary to determine appropriate proportional contributions to the emissions rates or 

concentrations in calculating representative emissions over these short highly variable conditions 

with currently available field testing procedures is problematic for stationary SI engines. 

Method 323 would also be inadequate for testing stationary SI engines during start-up 

periods. Method 323 is capable of detecting concentrations on the order of 0.3 ppmv. Method 

323 can achieve this minimum detection level with a 24 liter sample (about 60 minutes of 

sampling time). Start-up time for these engines ranges from a few minutes in warm weather to 

over 20 minutes in cold weather climates. If one were to conduct Method 323 for these few 
98

minute periods representative of start-up, the method detection levels would range from about 1 

to 10 ppmv. Further, the method recommends that the target minimum concentration be about 

10 times the analytical detection level. This would translate to quantitation levels of 10 to 60 

ppmv for these shorter sampling times. Method 323 would not be adequately sensitive to 

measure compliance with applicable emissions limits on the order of a few ppmv to less than 1 

ppmv during a start-up period of a few minutes. One additional factor limiting the applicability 

of Method 323 to testing during start-up periods is the representativeness of a constant sampling 

rate, integrated sample for a rapidly changing flow and concentration matrix. The failure of the 

method to provide a proportionally accurate sample of such flow and concentration changes 

compromises the results, as well. 

In addition, even were it technically feasible to measure emissions during startups for 

stationary SI engines, the cost of doing so for every startup at every covered engine would 

impose a substantial economic burden. There are approximately 330,000 existing stationary SI 

engines that are subject to this rule; the cost for testing every one of these engines during engine 

startup could be more than $300 million. 

EPA is therefore finalizing an operational standard in lieu of a numerical emission limit 

during periods of startup in accordance with section 112(h) of the CAA. EPA is limited to the 

information before it, which, of course, includes any information provided by the commenters. 

See 112(d)(3)(A). In this case, EPA carefully analyzed all of the information before it, including 

that provided by commenters, and determined that this standard complies with the requirements 

of sections 112(d) and 112(h). The final rule requires that owners and operators of stationary 

engines limit the startup time to 30 minutes or less. Engine startup is defined as the time from 

initial start until applied load and engine and associated equipment reaches steady state or normal 
99

operation. For stationary engine with catalytic controls, engine startup means the time from 

initial start until applied load and engine and associated equipment reaches steady state or normal 

operation, including the catalyst. Based on information received from engine producers and 

operators of stationary existing SI engines, EPA believes that limiting the engine startup time to 

30 minutes or less is representative of the best controlled engines’ operation during startup. EPA 

expects that this amount of time is consistent with the warm-up time needed and would be 

sufficient in most cases. EPA believes that 30 minutes is reflective of what the best controlled 

existing stationary SI engines are currently doing in order to reduce HAP emissions during 

periods of startup. Therefore, the final rule requires that owners and operators of stationary 

engines limit the startup time to 30 minutes or less. EPA is also including a requirement in the 

final rule to minimize the engine’s time spent at idle and minimize the engine’s startup time at 

startup to a period needed for appropriate and safe loading of the engine, not to exceed 30 

minutes, after which time the otherwise applicable emission standards apply. As with any work 

practice, CAA section 112(h)(3) and EPA’s implementing regulations at 40 CFR 63.6(g) provide 

that major sources can petition the Administrator for approval of an alternative work practice, 

which must be at least as stringent as what is required in the regulation. 

Regarding shutdown, EPA determined that it was not necessary to establish different 

standards that would be applicable during shutdown for stationary SI engines. The commenters 

did not provide any information that shows emissions would be higher during shutdown than 

during normal operation. In addition, commenters are incorrect that compliance with the 

standards must be instantaneous. Compliance with these emission standards has always been 

based on the results of testing that is conducted over a three-hour period; EPA made this more 

explicit in the final rule published in March 2010. Since the shutdown period for stationary SI 
100

engines is typically only a matter of minutes, it is believed that even if a shutdown occurred 

during the performance test, the engine would still be able to comply with the emission 

limitation. In a letter dated February 17, 2009 (EPA-HQ-OAR-2008-0708-0019), EMA 

indicates that HAP emissions will be sufficiently controlled during periods of shutdown. EMA 

stated in its letter that according to manufacturers, emissions control equipment would most 

likely continue to reduce emissions as designed throughout the shutdown period. According to 

EMA, this is because engine emissions control systems and equipment are, during the start of an 

engine shutdown, at high enough temperatures to control HAP emissions and will continue to be 

sufficiently high until the engine shuts down. This trend is illustrated in the attachment to 

EMA’s February 17, 2009, letter to EPA, where EMA provided two graphs with sample engine 

shutdown profiles. Figure 2 of the attachment to EMA’s letter (EPA-HQ-OAR-2008-0708-

0019.1) shows catalyst temperatures versus minutes during engine shutdown and illustrate stable 

catalyst temperatures. 

In establishing the standards in this rule, EPA has taken into account startup periods and, 

for the reasons explained above, has established different standards for those periods. With 

respect to malfunctions, EPA proposed two options for subcategories where the proposed 

emission standard was based on the use of catalytic controls. The first proposed option was to 

have the same standards apply during normal operation and malfunctions. The second proposed 

option was that standards during malfunctions be based on emissions expected from the best 

controlled sources prior to the full warm-up of the catalytic control. For subcategories where the 

proposed emission standard was not based on the use of catalytic controls, we proposed the same 

emission limitations apply during malfunctions and periods of normal operations. EPA is 

finalizing the first option described above, which is that the same standards apply during normal 
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operation and malfunctions. In the proposed rule, EPA expressed the view that there are 

different modes of operation for any stationary source, and that these modes generally include 

startup, normal operations, shutdown, and malfunctions. However, after considering the issue of 

malfunctions more carefully, EPA believes that malfunctions are distinguishable from startup, 

shutdown and normal operations. Periods of startup, normal operations, and shutdown are all 

predictable and routine aspects of a source’s operations. However, by contrast, malfunction is 

defined as a “sudden, infrequent, and not reasonably preventable failure of air pollution control 

and monitoring equipment, process equipment or a process to operate in a normal or usual 

manner * * * ’’(40 CFR 63.2). EPA has determined that malfunctions should not be viewed as a 

distinct operating mode and, therefore, any emissions that occur at such times do not need to be 

factored into development of CAA section 112(d) standards, which, once promulgated, apply at 

all times. For example, we note that Section 112 uses the concept of “best performing” sources 

in defining MACT, the level of stringency that major source standards must meet. One 

commenter expressed the view that it is not logical to apply the concept of “best performing” to a 

source that is malfunctioning. Indeed, the goal of best performing sources is to operate in such a 

way as to avoid malfunctions of their units. Similarly, although standards for area sources are 

not required to be set based on “best performers,” we believe that what is "generally available" 

should not be based on periods in which there is a “failure to operate.” Moreover, even if 

malfunctions were considered a distinct operating mode, we believe it would be impracticable to 

take malfunctions into account in setting CAA section 112(d) standards for stationary SI engines. 

As noted above, by definition, malfunctions are sudden and unexpected events and it would be 

difficult to set a standard that takes into account the myriad different types of malfunctions that 
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can occur across all sources. Moreover, malfunctions can vary in frequency, degree, and 

duration, further complicating standard setting. 

Finally, EPA believes that malfunctions will not cause stationary SI engines to violate the 

standard that applies during normal operations. Stationary SI engines would in most cases shut 

down immediately or with very little delay in the event of a malfunction. Because the standard is 

expressed as the average of three one-hour runs, or a work or management practice, any 

emissions that occur prior to engine shutdown should not affect a source’s ability to comply with 

the standard. Commenters' concerns regarding compliance certifications should not be a concern 

for this same reason. This approach will also encourage shutdowns as soon as practicable when 

a malfunction that affects emissions occurs. In the very unlikely event that a source fails to 

comply with the applicable CAA section 112(d) standards as a result of a malfunction event, 

EPA would determine an appropriate response based on, among other things, the good faith 

efforts of the source to minimize emissions during malfunction periods, including preventative 

and corrective actions, as well as root cause analyses to ascertain and rectify excess emissions. 

EPA would also consider whether the source's failure to comply with the CAA section 112(d) 

standard was, in fact, “sudden, infrequent, not reasonably preventable” and was not instead 

“caused in part by poor maintenance or careless operation.” 40 C.F.R. § 63.2 (definition of 

malfunction). 

EPA does not agree with the commenter who said that EPA should treat SSM emissions 

as de minimis. It is doubtful whether a de minimis exemption is even possible under section 

112(d) of the Act in these circumstances, see National Lime Ass’n v. EPA, 233 F. 3d 625, 640 

(D.C. Cir, 2000), but in any case the commenter provides no specific information to justify EPA 

making such a de minimis finding in this instance. Given the very narrow and specific 
103

circumstances delineated by the court in Alabama Power v. Costle, 636 F.2d 323 (D.C. Cir. 

1979) for making such a finding, and the lack of specific information from the commenter that 

these circumstances exist in this instance, we do not make a de minimis finding. 

While commenters 74 and 78 do not provide emissions tests to verify the emissions they 

claim for their engines, EPA notes that, as discussed elsewhere in this document, it has revised 

its standards for existing stationary SI engines based on a broader database of engines, as 

suggested by the commenters, at various speed and load conditions, and this will affect the 

standards in place during periods of shutdown and malfunction. 

3.2 Comment: One commenter (99) said that it agrees with EPA that HAP emissions during 

shutdown are controlled by existing methods and technologies for engines that use catalysts 

because the exhaust will most likely be at a sufficient temperature for HAP control. 

Response: No response is needed. 

3.3 Comment: One commenter (134) believes the final rule must allow actions designed to 

prevent unsafe operations during SSM periods. The commenter (134) believes that by imposing 

numerical emission limits during startup and malfunction periods, this proposal could discourage 

sources from taking appropriate actions to respond to non-engine related emergencies since such 

actions could result in an emission noncompliance on the unit. The commenter (134) requested 

that the EPA include a provision in the final rule that allows sources to take actions necessary to 

protect life and property. The commenter (134) requested specific language be included in the 

final rule that allows an owner/operator of a RICE to take all appropriate actions when required 
104

to avoid unsafe conditions. The commenter (134) noted that this principle has been included in 

past rulemakings, e.g., 40 CFR §63.2450(p) of the Miscellaneous Organic NESHAP, as follows: 

“opening a safety device or taking other actions is allowed at any time conditions require it to 

avoid unsafe conditions.” 

Response: EPA shares the commenters’ concerns that engines must be operated safely. As EPA 

notes above, EPA believes the standard response to malfunction will usually be a fairly rapid 

shutdown of the engine, and given the fact that compliance is based on the average of three onehour tests, emissions during malfunction will not likely have a significant effect on compliance. 

In the highly unlikely event that a source fails to comply with the applicable CAA section 112(d) 

standards as a result of a malfunction event, EPA would determine an appropriate response based 

on, among other things, the good faith efforts of the source to minimize emissions during 

malfunction periods, including preventative and corrective actions, as well as root cause analyses 

to ascertain and rectify excess emissions. EPA does not think that any of the provisions in the 

final rule would preclude engine owners and operators from taking actions necessary to protect 

life and property. 

3.4 Comment: One commenter (228) believes that any numeric standards should have averaging 

times established consistent with the engine manufacturers’ averaging time for engine steady 

state operation. The commenter (228) noted that most engines are designed to operate under 

relatively steady-state conditions; however it may take some time for the engines to achieve that 

steady-state of operation. The commenter (228) stated that unless the SSM issues are resolved, 

EPA will need to ensure that there is an adequate averaging period to encompass both the startup 
105

period and the steady state period needed to stabilize engine emissions performance before 

expecting the engine to be able to demonstrate compliance with a standard based solely upon 

steady state conditions, which it appears that EPA’s emission database represents. 

Response: EPA is not finalizing numerical emission standards in the final rule for periods of 

startup. For the emission standards that are applicable during other operations, EPA has clarified 

that the standards are based on the average of three 1-hour runs. This provides an adequate 

averaging period for compliance demonstrations during periods other than startup. 

3.5 Comment: One commenter (112) suggested that EPA make it clear that emission limitations 

do not apply during maintenance activities, such as tuning of the air-to-fuel ratio controller 

(AFRC) and engine timing adjustments. The commenter (112) believes that EPA can find under 

CAA section 112(h)(1) that it is infeasible to prescribe or enforce an emission standard for 

control of HAP during such periods. 

Response: The commenter has not provided any data to demonstrate the need for a different 

emission limitation during maintenance activities. Nonetheless, EPA believes that performance 

testing during maintenance would not be optimal since operation during maintenance activities 

may not be sufficiently continuous and lengthy enough for the time needed to conduct the 

performance testing. 

4.0 Emissions 
106

4.1 RICE Emissions Database 

4.1.1 Comment: Multiple commenters (57, 78, 90, 96, 97, 103, 118, 124, 126, 130, 131,132, 

150, 155, 174, 175, 176, 178, 187, 205, 226, 241, 242, 247) believe that the emissions data for 

engines is not adequate to conduct an appropriate MACT floor analysis. EPA should collect 

additional data and redo the MACT floor analysis for gas engines, according to numerous 

commenters. The commenters (155, 241, 242, 247) believe that the data EPA used to develop 

the MACT floor is deficient and that certain data should be excluded from the analysis. The 

commenters (155, 187, 241, 242, 247) also stated that EPA did not consider emissions variability 

in setting the MACT floor. Commenter (78) stressed than an accurate inventory of engines by 

size is needed to accurately evaluate the costs, benefits, and feasibility of a proposed regulation. 

Several commenters offered to work with EPA to address the lack of data and determine where 

additional data can be supplemented. Some of the deficiencies noted by various commenters are: 

formaldehyde measurements using CARB Method 430, possible incorrect engine categorization, 

multiple tests for a single engine used as the basis for the MACT floor, and subcategory specific 

data deficiencies. These issues are discussed further below. 

 The commenters (132, 155, 241, 242) said that EPA should not rely on formaldehyde 

emissions data that was captured using CARB Method 430. It is understood that CARB Method 

430 produces unreliable results that should not be used to measure formaldehyde and EPA has 

acknowledged this is the document EPA-HQ-OAR-2005-0030-0009 and CARB Method 430 

data was excluded from HAP emission factors development in EPA-HQ-OAR-2005-0030-0009, 

commenters 155 and 242 said. 
107

 The commenters (155, 242) continued by stating that EPA has included in the MACT 

floor analysis for rich burn engines, units that should have been classified as lean burn engines 

based on EPA’s definition of a rich burn engine in 40 CFR §63.6675. According to the 

commenters (155, 242), only 1 of the 13 rich burn engines used in the MACT floor analysis 

would be defined as rich burn engines. The other engines operate at air-to-fuel ratios consistent 

with lean burn engines and should be excluded from the rich burn analysis, in the commenters’ 

(155, 242) opinion. 

The commenters (155, 242) said that because certain engines have been miscategorized, 

the ability to set accurate MACT floors has been hindered. Some examples are the 4SLB engine 

with test ID 20.1 used for the top 12 percent analysis that could possibly be a rich burn engine 

and test ID 20.2, which appears to be the same engine equipped with NSCR; a technology used 

for rich burn engines. EPA should further investigate the classification of the engines used for 

the MACT Floor analysis, several commenters (122, 154, 155, 242) said. (Note that the 

commenter (155) also said that this engine should be excluded on the basis of being tested with 

CARB Method 430). 

In addition, the commenters (155, 242) stated that EPA has not rationalized the use of test 

data for engines greater than 500 HP for 4SLB engines between 50 and 500 HP. The 

commenters (155, 242) said that the analysis for 4SLB is not clear and the commenter is not sure 

how EPA arrived at the MACT floor for CO. Following EPA’s documentation of its analysis, 

the commenters (155, 242) arrived at an average of 112 ppmvd for CO as opposed to the 95 

ppmvd that EPA proposed. Also, there are 6 emission tests that should be excluded based on the 

use of CARB Method 430. Doing so leaves 3 engines for the analysis, the commenters (155, 

242) said, plus these engines are all single-measurement tests. The commenters (155, 242) do 
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not believe that 3 data points is sufficient to identify the average of the best performing 12 

percent. The commenters (155, 242) also questioned the results from tests 29.33x and 29.41x 

and is currently looking into the test reports, which may include data that appear to be outliers. 

 Commenters 155 and 242 stated that it is inappropriate to use multiple tests of single 

engines as the basis for MACT floor determinations, e.g., 15 of the 16 tests for 2SLB engines are 

from a single engine at different operating conditions. The commenters (155, 242) added that 

this engine is also more representative of a large bore, slow speed engine and more illustrative of 

a unit above 1,000 HP as opposed to small engine. If the CARB Method 430 test is removed 

only one test remains in this subcategory, the commenters (155, 242) said. For 4SLB engines, 

there is only data from 8 engines and taking away tests measured with CARB Method 430 leaves 

only 3 engines, the commenters (155, 242) said. Two commenters (96, 155) are of the opinion 

that EPA should set a minimum number of sources necessary to determine the MACT floor, e.g., 

EPA has in some cases based the MACT floor on only one, two or three engines. Commenter 

155 does not believe that several test runs from a single engine is appropriate. 

 The two commenters (155, 242) stated that the MACT floors should not be based on data 

using single measurements, when three measurements are a standard requirement for 

demonstrating compliance. In the absence of multiple measurements, outliers and erroneous 

errors cannot be caught, according to the commenters (155, 242). 

 The commenters (96, 155, 242) said that EPA should use data from units of similar size 

to set standards for sources of the same size, e.g., emissions from a large engine should not be 

used to set standards for a 100 HP engine unless EPA can demonstrate that such an assumption is 

justified. The commenters (96, 155, 242) are concerned that the data EPA has used for the 

MACT floor analysis is not representative of the current population of engines. 
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One commenter (57) did not believe EPA has a relied on a valid database for the 

regulation of landfill gas fired SI engines larger than 500 HP. The commenter (57) cited a 

December 19, 2002 Federal Register notice of proposal for a prior rule that indicated that the 

MACT floor for landfill gas and digester fire engines is "no emissions reductions" (page 77840, 

center column), and also indicated that EPA was aware of no HAP emission control technologies 

which would work for this subcategory. Commenter (57) also cited a February 4, 2002 

memorandum from Melanie Taylor of Alpha-Gamma Technologies to Sims Roy of EPA, related 

to a proposed 2006 rulemaking that indicated (page 2) that for the digester gas and landfill gas 

subcategory, only 18 emissions tests were available and only one of those was for landfill gas 

fired engines. Commenter (57) stated that the landfill gas fired engine test was from a 1988 test 

on only one source, and that this is a rather thin record for setting emissions standards of 177 

ppm CO for landfill gas fired engines in excess of 500 HP. Commenter (57) is personally aware 

of one recently installed (2005) site with 3 engines which will not meet the proposed CO 

emissions limit, and believed many other existing and currently used engines for this source 

category will not be able to meet the proposed standard. Commenter (57) states that as EPA has 

correctly determined, there are no feasible add-on engine controls and no fuel cleaning methods 

which are applicable to this fuel source. 

Similar issues as those discussed for other engines apply to 2SLB engines, commenters 

155 and 242 said. The data used to set the floor were based on the average of two tests, where 

one of the tests were measured with CARB Method 430, the commenters (155, 242) said. 

Further, the 15 Colorado State University (CSU) data points that were part of the original data 

set are all single-measurement tests from one engine tested over a range of operating conditions 

and should be represented as one test, the commenters (155, 242) added. Also, the data gives 
110

EPA an opportunity to evaluate emission variability for a single engine, the commenters (155, 

242) said. Finally, and as mentioned before, the 2SLB engine tested at CSU, although 440 HP in 

size, is more representative of a larger EPA and therefore smaller engines are not represented in 

EPA’s data, according to commenters 155 and 242. 

 In conclusion, the commenters (155, 242) summarized that it agrees with EPA’s previous 

assertion from the 2004 RICE NESHAP that there are insufficient data to develop standards for 

natural gas engines less than 500 HP and EPA has not gathered additional data since then or 

engaged stakeholders in an attempt to obtain more data. Insufficient data and rationale have 

been used to develop this proposed rule, the commenters (155, 242) said. EPA should develop a 

more robust and complete database that is representative of the hundreds of thousands of engines 

it represents, the commenter (155) stated. The commenter (155) is working on gathering data 

from its members, but as previously stated, such an effort will take time. The commenter (155) 

provided several tables illustrating the test data that EPA used and opinions on which test results 

should be deleted for different reasons. 

Response: Section 112(d)(3) of the CAA requires EPA to set MACT standards based on the test 

data that is available to the Agency and this is what EPA did at proposal. EPA recognizes that it 

had limited emissions test data at the time it developed the proposed rule. However, EPA notes 

that it used the data that was available at the time of proposal. EPA requested additional test data 

to supplement the emissions database during the development of previous rules for stationary 

engines and also in an advance notice of proposed rulemaking for this rule and did not receive 

any data. EPA again requested additional test data during the comment period for the current 

engine rulemaking and made an additional effort post-proposal to reach out to industry and other 
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sources in order to supplement the existing emission data set. EPA did receive additional 

emissions data for stationary SI engines during the post-proposal period for this rulemaking. The 

additional data include tests for 619 stationary SI engines, ranging in size from 39 HP to 12,000 

HP. 

The commenters noted that certain test data is not appropriate for use in developing the 

MACT standards and EPA has reviewed that test data and have removed test data that was 

collected using the CARB 430 test method. The formaldehyde measurements collected by 

CARB Method 430 are considered invalid and EPA agrees that it would be inappropriate to use 

that data. 

EPA has reviewed the test data for each of the categories of engines to ensure that the 

engines are classified correctly and are included in the correct subcategory. In terms of the rich 

burn engines used for the original proposed MACT Floor analysis, where the commenter 

believes that only 1 of the 13 tests would be defined as a rich burn engine, EPA disagrees. For 

example, EPA confirmed with the engine manufacturer that Waukesha engine model 145, which 

is the engine tested under test IDs 7.10 and 7.11, would have been manufactured as a rich burn 

engine because during the time period that this engine family was manufactured, Waukesha did 

not produce any lean burn SI natural gas engine models. This information is included in the 

docket to the final rulemaking. Also, information reviewed, including Waukesha’s Gas Exhaust 

Emission Levels Dated 10/03, has led EPA to believe that Waukesha engine models 1197 are 

rich burn engines and were therefore included in the MACT Floor analysis for rich burn engines. 

These were engines tested under test IDs 7.3, 7.7, 7.8 and 7.12. However, this is no longer a 

concern since the 13 tests the commenter refers to used CARB Method 430 and data from all 13 

tests have been excluded from the final MACT Floor analysis. It is possible that the engine test 
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that the commenter refers to with test ID 20.1 could be a rich burn engine. However, again, 

CARB Method 430 was used to measure emissions from this test, as the commenter also pointed 

out, and has been excluded from EPA’s data set. 

EPA also considered the issue of emissions variability and has included emissions 

variability into the final emission standards. This is discussed in more detail in the response to 

comment 5.1.1.1. 

EPA acknowledges the commenters’ concerns in regards to the use of multiple tests from 

the same engine and using test data from larger engines to calculate the MACT floor for smaller 

engines. However, EPA again notes that it used the data that was available at the time of 

proposal and made the best judgment at the time regarding the use of available test data. EPA 

has requested additional test data from a number of industry trade groups, and must proceed with 

setting the MACT standards based on the current test data. For landfill gas engines, EPA has 

received numerous test reports that were included in the development of the final emission 

standards for existing landfill and digester gas engines. The landfill and digester gas community 

was eager to submit test data to EPA and followed-through with the submittal of numerous test 

reports. Emissions data from the additional test reports EPA received post-proposal was added 

to EPA’s existing dataset and the combination of data generate a complete and full data set. EPA 

also received test data following the proposed rule for other engine types, including 2SLB, 4SLB 

and 4SRB engines. In total, EPA received additional emissions test data for more than 600 

engines, including landfill and digester gas engines. The emissions test data included test results 

from engines ranging in size from 39 HP to 12,000 HP at loads between 11 and 100 percent. 

The additional test data EPA received is available from the docket (EPA-HQ-OAR-2008-0708). 

This test data was added to EPA’s analysis of MACT and GACT for the final rule. In addition, 
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in the final rule, EPA did not use multiple tests from a single engine to represent multiple 

engines for the purposes of determining the MACT floor. Each engine represented a single data 

point for the purposes of determining the best performing 12 percent of existing sources, as 

explained in response to comment 5.1.1.1 and more extensively in the memorandum titled 

“MACT Floor and MACT Determination for Existing Stationary SI RICE ≤500 HP Located at 

Major Sources.” 

4.1.2 Comment: One commenter (188) noted that its review of the database utilized by EPA in 

the process of developing this proposed rule contains no units manufactured before 1990 with 

catalytic controls, although EPA did not address it in its preamble. The commenter (188) 

concluded that EPA cannot demonstrate nor expect that units manufactured before 1990 can be 

economically retrofitted to comply with these proposed regulations and recommends that any 

units manufactured before 1990 should, by definition, be exempted from these regulations 

entirely.

Response: EPA is required to address HAP emissions from all existing stationary engines, not 

just stationary engines manufactured after the 1990s. EPA disagrees with the commenter that 

RICE units manufactured before 1990 should be exempt from the regulations. The commenter 

did not provide any information to support the claim that older engines could not be retrofit with 

emission controls. Manufacturers of control technology have demonstrated retrofit application 

of oxidation catalysts on older RICE units. These retrofit applications on older engines have 

proven to reduce HAP emissions. Therefore, EPA believes it is appropriate to require the use of 

control technology on units manufactured before 1990. 
114

4.1.3 Comment: Two commenters (265, 268) referred to EPA’s Method 10 that went into effect 

in May of 2006 as being more stringent than previous requirements, and specifies that 

stratification measurements must be performed on the exhaust stack to ensure that emission 

sampling is not conducted in areas of the stack that have lower levels of CO. In addition, the 

commenters (265, 268) reported that the analyzer is used to measure CO must be certified to 

demonstrate it can pass an interference test to ensure that it is not biased by the presence of other 

components in the exhaust gas. This commenters (265, 268) stated that the use of source data 

that pre-dates the use of Method 10 testing requirements may not be as accurate (or reliable) for 

use in the developing of standards, especially since the proposed rule compliance demonstrations 

will be required to adhere to the revised 2006 CO testing procedures. 

Response: Method 10 has always required interference checks for NOx, CO2, and SO2. The 

addition to the method was a requirement for the tester to identify any additional compounds 

present in the gas stream that might be an interference and to demonstrate that these additional 

compounds did not bias the test results. It is unlikely that there are significant additional 

interferences present in the exhaust from RICE that would cause a negative bias in the measured 

CO using Method 10. While measuring emissions from a stratified stack at a single point could 

significantly affect the results of a particular test, it is equally likely to bias the results high as it 

is low so that the average result from many tests is unlikely to be biased. Therefore, the overall 

effect of failing to account for stratification when using Method 10 on the emissions from RICE 

would be unlikely to bias the results in either direction. 
115

4.1.4 Comment: One commenter (121) reviewed the supporting data and determined that EPA 

failed to specify the actual RICE units from the Emissions Database comprising the top 12 

percent for the various floors. While the database can be queried, in some cases the data entries 

do not directly correspond to the subcategory name. A query for CO will not produce any 

results. In other cases, it is impossible to know whether the query results are the correct list of 

engines relied on by EPA in developing the floor. The commenter (121) gave specific examples 

of these issues. 

Response: All of the data used to calculate the MACT floor could be queried from the 

Emissions Database; however, EPA agrees that it was difficult to determine the exact data that 

was used to calculate the MACT floor. EPA has provided more documentation to the final rule 

to clearly show the data that was used to determine the emission standards. This documentation 

includes the top 12 percent of engines that are used to establish the floors for the various 

subcategories. This is shown in the memorandum, “MACT Floor and MACT Determination for 

Existing Stationary SI RICE ≤500 HP Located at Major Sources.” This memorandum includes 

the steps that were taken to develop the MACT floor for all the subcategories. 

4.2 Surrogates 

4.2.1 Comment: Several commenters (76, 96, 100, 104, 121, 129, 157, 216, 218, 225, 227, 229, 

242) said that an alternative surrogate for HAP is needed for rich burn engines, where EPA has 

currently determined that formaldehyde is the only option. Commenter 242 indicated that EPA 

was unable to confidently say that a different pollutant, such as for example, CO, could be used 
116

as a surrogate for HAP emissions from rich burn engines. To reach this conclusion, EPA has 

relied on analyses conducted for other rulemakings and the commenter (242) said that EPA 

should, at a minimum, include in the docket for this rulemaking specific references to relevant 

decision documents so that the previous analysis can be reviewed. Commenters 108, 218, 213 

and 229 also supported the use of CO. One commenter (76) requested that EPA include in the 

proposal, the reasons why such engines had limited data and why those engines are restricted in 

measuring formaldehyde rather than the surrogate parameter such as CO. 

As stated earlier, formaldehyde testing using FTIR is complex and expensive and the 

commenters (104, 225, 242) are concerned that industry testing capacity could be a problem. 

Identifying an alternative surrogate that is easier and less expensive to measure could simplify 

compliance, according to the commenter (242) and if EPA makes the analysis for determining 

that formaldehyde is the only valid surrogate available, the commenter could potentially assist 

with determining if there are alternative approaches available to FTIR testing. 

Commenter 104 recommended that CO or VOC be used a surrogate for formaldehyde 

because these tests are more economic and feasible. Commenter 96 also said that the proposed 

formaldehyde standards should be replaced with either VOC or CO emission standards in the 

final rule. As other commenters have also mentioned, this commenter (96) stated that measuring 

formaldehyde could be problematic and expensive. The commenter (96) recommended that EPA 

replace the formaldehyde standards with VOC standards as was done under the SI NSPS and 

incorporate the definition of VOC from the SI NSPS. Commenter 225 noted that CO is allowed 

as a surrogate for formaldehyde for lean burn engines in this rule and was proposed as a 

surrogate for HAP from boilers in 40 CFR part 63, subpart DDDDD, while the Consolidated 

Engine Rule allows VOC reductions across 4SRB NSCR catalysts to demonstrate formaldehyde 
117

reduction. Three commenters (129, 157, 216, 227) supported the use of VOC instead of HAP 

and commenter 129 asserted that a VOC standard would be equally effective in reducing HAP 

because such a standard would encompass the HAP that are considered VOC. Two commenters 

(129, 157) also stated that test procedures for VOC are more cost-effective and capable of 

providing real-time compliance determinations. 

One commenter (100) thinks that total hydrocarbons (THC) should be used instead of 

formaldehyde. The commenter (100) believes that using formaldehyde as a surrogate for HAP 

has placed an unnecessary compliance and cost burden of owners and operators of these engines, 

which significantly affects the sale of these engines. Because 4SLB and CI engines compete 

with 4SRB engines for sales and since 4SLB and CI engines have in EPA rulemakings been able 

to demonstrate compliance with NESHAP requirements by meeting CO limits or reductions, 

4SRB engines have been disadvantaged because of higher costs associated with testing for 

formaldehyde. In addition to replacing formaldehyde with THC, EPA should include THC 

percentage reductions options to add compliance flexibility and noted that the THC percent 

reduction should not be any more stringent than 40 to 60 percent, which is the level typically 

seen from rich burn engines with NSCR. The commenter (100) cited papers that conclude that 

there is a positive correlation between formaldehyde and THC emissions for various engine 

types, including rich burn engines. These papers were attached to the commenter’s (100) letter 

to EPA. In addition to these sources supporting the replacement of formaldehyde with THC in 

the final rule, commenter 100 volunteered to work with EPA to develop a test program to obtain 

additional data from rich burn engines to investigate the relationship between formaldehyde and 

THC on an engine, currently in the commenter’s (100) laboratory, equipped with NSCR to 
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support the recommendation that THC is a suitable surrogate for HAP emission reductions from 

rich burn engines. 

Response: EPA has documented the analysis that determined that CO was not an appropriate 

surrogate for HAP emissions for 4SRB engines. The documentation is in the docket for the 

original RICE NESHAP promulgation (EPA-HQ-OAR-2002-0059), which was incorporated into 

the record for this final rule. EPA received additional information following the proposal from 

engine manufacturer Waukesha, who conducted a testing program to investigate the correlation 

between THC and formaldehyde. The objective of the program was to determine if THC would 

be a valid surrogate for formaldehyde (and consequently HAP) for rich burn engines. Waukesha 

concluded that the information submitted supports the use of THC as a surrogate for HAP for 

4SRB engines. Waukesha also said that “There does not appear to be a good correlation between 

post-cat CH2O and either precat-CH2O or post-cat THC. However, that does not appear to be 

necessary as virtually complete CH2O reduction occurs regardless of the fairly broad conditions 

varied in this test.4” In EPA’s opinion, this conclusion is not substantial enough to support THC 

as a surrogate for formaldehyde. For example, results of the program indicated a large range in 

THC reductions while formaldehyde reductions remained fairly constant.5 Therefore, EPA 

believes that THC reductions are not a good indicator of catalyst performance. In fact, 

                                                           

4

 See page 2 of Email from Robert Stachowicz, Dresser Waukesha to Melanie King, USEPA. 

Additional Dresser-Waukesha Reciprocating Internal Combustion Engines (RICE) National 

Emission Standards for Hazardous Air Pollutants (NESHAP) Test Data and Comments. EPAHQ-OAR-2008-0708-0323.1. 

5

 See page 3 of Email from Robert Stachowicz, Dresser Waukesha to Melanie King, USEPA. 

Additional Dresser-Waukesha Reciprocating Internal Combustion Engines (RICE) National 

Emission Standards for Hazardous Air Pollutants (NESHAP) Test Data and Comments. EPAHQ-OAR-2008-0708-0323.2.
119

Waukesha stated that “The obvious conclusion to be drawn is that, for a properly functioning 

NSCR catalyst on a 4SRB engine, formaldehyde destruction will normally range from 94-97% 

across a very wide THC destruction range of 25-85%. Stated another way, the data show 

conclusively that, for a properly functioning NSCR catalyst on a 4SRB engine, formaldehyde 

destruction rates are uniformly very high and independent of the numeric THC destruction 

efficiency.6” EPA does not agree that it is not necessary to show a post-catalyst correlation. 

Regarding the commenters’ concerns about FTIR testing, EPA is promulgating Method 

323 for measuring formaldehyde as part of this final rule, which provides sources a lower cost 

method for compliance testing. 

 EPA does not disagree that CO and VOC testing would be more economical than 

formaldehyde testing. However, as stated, EPA previously determined that CO is not an 

appropriate surrogate for HAP for rich burn engines. In terms of VOC being used as a surrogate 

for HAP, EPA does not have any emissions data available in order to look at the relationship 

between VOC and HAP. Nor did commenters provide any emissions data to EPA to substantiate 

their claims. For the reasons discussed in this response, EPA is finalizing emission standards in 

terms of formaldehyde for rich burn engines where numerical limits are required. 

4.2.2 Comment: One commenter (242) believes that EPA has not taken into account the tradeoff that exists between formaldehyde and NOx emissions and between formaldehyde and CO 

emissions from rich burn engines and the commenter is uncertain whether rich burn engines that 

                                                           

6 See page 4 of Email from Robert Stachowicz, Dresser Waukesha to Melanie King, USEPA. 

Additional Dresser-Waukesha Reciprocating Internal Combustion Engines (RICE) National 

Emission Standards for Hazardous Air Pollutants (NESHAP) Test Data and Comments. EPAHQ-OAR-2008-0708-0323.2.
120

are tightly controlled for NOx (e.g., 0.5 or 1.0 g/HP-hr) can meet the proposed formaldehyde 

limits. The commenter (242) stated that EPA should gather emissions data to investigate 

whether rich burn engines with NSCR that are optimized for NOx control can meet the proposed 

formaldehyde standards, in addition to determining if these engines can maintain low levels of 

controls over time especially for smaller engines in remote locations where 1) application of 

NSCR has been limited thus far and 2) because of unmanned facilities limit operator 

attentiveness to control performance. 

Response: The HAP emission standards are based on what is achieved in practice by rich burn 

engines, based on the test data that EPA has received. The commenter provided no data to 

support the claim that these rich burn engines will be unable to meet the proposed formaldehyde 

limit. Therefore, EPA believes that the formaldehyde standards for rich burn engines are 

appropriate. 

4.3 Engine Test Data 

4.3.1 Comment: One commenter (141) provided stack test results for several large lean burn SI 

engines equipped with a CO oxidation catalyst, oxidation catalyst and SCR, or SCR. The data 

showed CO levels ranging from 18 to 58 ppmvd at 15 percent O2 for natural gas 4SLB engines. 

Response: EPA contacted the commenter and asked if they could provide EPA with the source 

test reports for the stack test data that were summarized in a table their comment, as EPA could 

not use the data without having the source test report. The commenter responded that they did 
121

not have the resources to provide copies of the documents to EPA. Since EPA did not have the 

test reports and could not review the data, EPA was unable to use the data submitted by the 

commenter in the MACT floor analysis. 

5.0 Emission Limits 

5.1 Major Sources 

5.1.1 MACT Floor 

5.1.1.1 Comment: Multiple commenters (89, 101, 103, 112, 122, 126, 150, 151, 155, 167, 187, 

205, 221, 225, 227, 228, 231, 242, 261) were concerned with how EPA set the MACT floor for 

the proposed rule. Several commenters, including 155, 205, 227, and 242 said that EPA has not 

considered variability in setting the MACT floor for the proposed rule. The commenter (155) 

cited the recent Brick MACT ruling which indicated that “floors may legitimately account for 

variability [in the best performing sources that are the MACT floor basis] because “each [source] 

must meet the [specified] standard every day and under all operating conditions.” The 

commenters (155, 242) stated EPA’s dataset is not sufficient in covering variability. The 

commenters (155, 242) expressed that it is willing to work with EPA to resolve the issue, but 

efforts may be hindered by the limited timeframe for finalizing the rule. It is necessary to collect 

additional data and conduct a thoughtful and scientifically sound review and analysis process, 

several commenters said (including commenters 122, 155, and 242). 
122

 In terms of a variability analysis, the commenters (155, 242) specifically suggested as 

one alternative that EPA identify the top 12 percent of engines based on average emissions 

operating at high load. Then, EPA could use lower load of other non-optimum operating 

emissions data to assess variability in the best performers, i.e., the MACT floor must be set less 

stringent than the highest data point for the best performers and lead to a less stringent standard. 

Alternatively, EPA could use all data in the average calculation meaning that data from all loads 

would be included, however, this is complicated due to the lack of low load data or data from 

various operating conditions for most tests. Lack of data is also an issue with the first suggested 

approach, the commenters (155, 242) said. In any event, the scarcity of data may necessitate 

additional, focused testing. Both commenters (155 and 242) are willing to work with EPA to 

resolve this issue. 

One commenter (261) noted that the Courts have been critical of EPA’s process for 

setting minimum allowable emission limits. The commenter (261) stated that EPA set the 

emission limits by averaging the best 12 percent of all performance tests for each subcategory, 

but did not consider operational variations of the units. The commenter (261) recommended that 

EPA set emission limits at the emissions level that is actually achieved under the worst 

reasonably foreseeable circumstances for the best performing 12 percent as allowed by the 

Courts in the Cement Kiln MACT and Brick Kiln MACT decisions. 

The commenter (126) acknowledged the difficulties with obtaining test data for RICE, 

however EPA cannot rely on the absence of emissions data to justify its proposed limits. The 

commenter (126) stated that EPA should have issued information collection requests to obtain 

adequate emission data for promulgating standards. 
123

Multiple commenters (97, 124, 132, 155, 175, 191, 224) suggested that EPA should 

consider a scenario under which lower temperatures and reduced catalyst efficiencies may occur 

due to reduced engine speed or load, resulting in lower temperatures and consider an alternative 

work practice under section 112(h) of the CAA for the situation. 

Two commenters (155, 224) noted that the emission standards in the proposed rule apply 

at all times, but that there is no data or information in the rulemaking docket that supports the 

proposed limits at low loads or at operating conditions other than high load. The commenters 

(155, 224) expressed that EPA should provide data and analysis that supports requiring emission 

limits to be met at all times. The commenter (155) said that it is inaccurate to assume that 

emission levels observed at one operating condition can be met at a different operation condition, 

e.g., high load emissions are not the same as low load emissions. The commenter (155) 

recommended that EPA consider technical and economic feasibility of requiring and enforcing 

emission limits at operating conditions where measurements are not technologically and/or 

economically feasible. If emission limits are based on high load emissions data and compliance 

is validated at high load, operating, design or work practices should be considered as an 

alternative way to demonstrate compliance under other operating scenarios, the commenter (155) 

said. Otherwise, the commenter (155) said that EPA needs to undertake a significant effort to 

add emissions data to the docket to support a standard that applies at all times. 

One commenter (155) said that EPA has not gathered data or provided a sound analysis 

to demonstrate that it is appropriate to set emission standards that apply at all times. EPA should 

show with an analysis and data that emission standards are achievable at operating conditions 

other than the MACT floor, commenter 155 said. However, if such a showing is not possible, 

EPA should consider alternatives under section 112(h) of the CAA to apply during periods other 
124

than high load, in commenters 155 and 224’s opinion. The commenter (155) said that EPA 

specifically did not consider emissions over different operating points, e.g., in the 2SLB 

emissions data from CSU. In that analysis, the commenter (155) indicated that instead of using 

the 15 available test run results from the one 2SLB engine in order to take into account 

variability in emissions, EPA looked at these tests as 15 separate tests and when setting the 

MACT floor used the two best performing, i.e., the best performing 12 percent. (Note that the 

total number of tests analyzed for this subcategory was 16). The commenter (155) expressed that 

it is not supportive of this approach. 

Again, the commenter (155) stated that it could not locate any information in the docket 

that is supportive of requiring emission standards to apply at all times and that the lack of data 

and analysis is a serious oversight on EPA’s part. Also, for compliance at all times, the 

commenter (155) asked what averaging times apply. The commenter (155) noted that there are 

several other similar questions that need to be answered. In the commenter’s (155) opinion, 

these compliance issues challenge the enforceability of the emission standards and therefore 

section 112(h) of the CAA applies. The commenter (155) believes that emission standards 

would still apply at high load and the performance test is performed at high load, but that for 

other operating conditions, section 112(h) of the CAA would form the basis for alternative 

compliance demonstrations through work or management practices. 

Response: Based on these comments, EPA reviewed all aspects of the MACT floor 

determination, and redid the MACT floor determinations for the final rule, making changes in 

several areas. These areas included the methodology for determining variability, the 

incorporation of additional data received into the MACT floor analysis, and the use of emissions 
125

data directly to determine the MACT floor, rather than through the gloss of the Population 

Database. 

The CAA requires EPA to set MACT standards based on the test data that is available to 

the Agency and this is what EPA did at proposal. EPA recognized that it had limited emissions 

test data at the time it was developing the proposed rule. However, EPA had requested 

additional test data to supplement the emissions database from commenters during the 

development of previous rules for stationary engines. In addition, EPA requested additional test 

data during the comment period for the current engine rulemaking. EPA made an additional 

effort post-proposal to reach out to industry and other sources in order to supplement the existing 

emission data set. EPA received data for an additional 619 engines during the post-proposal 

period; this data was incorporated into the MACT floor analysis for this final rule. 

 The U.S. Court of Appeals for the D.C. Circuit has recognized that EPA may consider 

variability in estimating the degree of emission reduction achieved by best-performing sources 

and in setting MACT floors. See Mossville Envt’l Action Now v. EPA, 370 F.3d 1232, 1241–42 

(D.C. Cir 2004). EPA has included a revised approach to variability in the MACT floor analysis 

for this final rule. The final emission standards are based on test data collected from stationary 

engines produced by different engine manufacturers, operating at various loads and other 

conditions, and located in various types of service and locations. The engines range in size from 

39 HP to 12,000 HP. The data includes engines operating at loads from 11-100 percent. To the 

extent commenters believed further data would have been beneficial to EPA, EPA must make its 

determinations based on the information available to it. EPA asked for further data, and EPA did 

receive further data following the proposal, which led to changes in the final regulations. For 

engines operating at reduced speed or loads resulting in a reduced exhaust temperature, EPA 
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believes that numerical emission requirements are still appropriate and there is no justification to 

only require work practice standards during these situations. We do not believe that the 

provisions of section 112(h) of the CAA are met (except as discussed elsewhere with regard to 

periods of start-up, emergency engines, and engines below 100 HP) because testing is not 

economically and technologically impractical and the emissions can be readily routed through a 

conveyance for purposes of emission testing. EPA believes that the final emission standards will 

reflect the numerous engine models and operating scenarios that can be expected from stationary 

engines. 

 EPA is not using the Population Database to determine a percentage of engines that have 

emission controls installed, as it did at proposal. In recent court cases, in particular the Cement 

Kiln and Brick MACT cases (Cement Kiln Recycling Coalition v. EPA, 255 F.3d 855 and Sierra 

Club v. EPA, 479 F.3d 875, respectively), the court rejected several MACT standards as not 

meeting the requirements of the statute “to reflect the emissions achieved in practice by the best 

controlled units.” The court in both cases rejected EPA decisions to determine the MACT floor 

by first determining the technology used by the median source in the top twelve percent of 

sources, using actual emissions data, and then basing the floor on emissions data from the 

highest emitter using that technology in the database. EPA argued that this ensured the standards 

were achievable by all units. The court found that the MACT floor must reflect the emissions 

actually achieved by the best controlled sources, and sources did not reflect such emissions 

merely because they shared the same technology. Both cases also fault EPA for relying solely 

on emissions control technology in determining the floor, and state that other factors also can 

affect emissions. Indeed, the court found that lower emissions need not be the result of a 

deliberate emission control strategy. “The Clean Air Act requires the EPA to set MACT floors 
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based upon the ‘average emission limitations achieved, it nowhere suggests that this achievement 

be the product of a specific intent.” 

The Population Database has not been updated since 2000. It contains information 

regarding whether or not an engine has emission controls, but does not generally contain other 

types of emission-related information, like engine-out emissions or operational controls, and it 

does not include any emissions concentration data, which is necessary to determine the MACT 

floor. EPA determined that it would be more appropriate and more defensible to base the MACT 

floor analysis directly on the emissions data that EPA has for stationary SI engines. 

In order to determine the MACT floor for each subcategory, EPA ranked all of the 

sources for which it had data based on their emissions and identified the lowest emitting 12 

percent of the sources based on the lowest test for each engine. EPA used all of the emissions 

data for those best performing engines to determine the emission limits for this final rule, 

accounting for variability. EPA assessed the variability of the best performers by using a 

statistical formula designed to estimate a MACT floor level that is achieved by the average of the 

best performing sources if the best performing sources were able to replicate the compliance tests 

in our data set. Specifically, the MACT floor limit is an upper prediction limit (UPL) calculated 

with the Student’s t-test using the TINV function in Microsoft Excel. The Student’s t-test has 

also been used in other EPA rulemakings (e.g., New Source Performance Standards for 

Hospital/Medical/Infectious Waste Incinerators, Proposed NESHAP for Industrial, Commercial, 

and Institutional Boilers and Process Heaters) in accounting for variability. A prediction interval 

for a future observation is an interval that will, with a specified degree of confidence, contain the 

next (or some other pre-specified) randomly selected observation from a population. In other 

words, the prediction interval estimates what future values will be, based upon present or past 
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background samples taken. Given this definition, the UPL represents the value which EPA can 

expect the mean of 3 future observations (3-run average) to fall below, based upon the results of 

an independent sample from the same population. In other words, if EPA were to randomly 

select a future test condition from any of these sources (i.e., average of 3 runs), EPA can be 99 

percent confident that the reported level will fall at or below the UPL value. To calculate the 

UPL, EPA used the average (or sample mean) and sample standard deviation, which are two 

statistical measures calculated from the sample data. The average is the central value of a data 

set, and the standard deviation is the common measure of the dispersion of the data set around 

the average. This approach reasonably ensures that the emission limit selected as the MACT 

floor adequately represents the level of emissions actually achieved by the average of the units in 

the top 12 percent, considering ordinary operational variability of those units. Both the analysis 

of the measured emissions from units representative of the top 12 percent, and the variability 

analysis, are reasonably designed to provide a meaningful estimate of the average performance, 

or central tendency, of the best controlled 12 percent of units in a given subcategory. 

 Regarding the comment asking about the averaging times that apply, EPA has clarified in 

the final rule that the emission standards are based on the average of three one-hour runs. 

 

5.1.1.2 Comment: Four commenters (132, 155, 175, 242, 247) stated that the majority of 

stationary engines subject to emission limits under the proposed rule would be forced to install 

add-on controls even though EPA made the statement that engines subject to emission standards 

based on an uncontrolled MACT floor are expected to meet the emission limitations without any 

aftertreatment controls. The commenters (155, 242, 247) do not believe that EPA has considered 

emission limit achievability or cost impacts of these requirements. The commenters (155, 242, 
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247) indicated that a high demand for aftertreatment controls could seriously affect market 

demand, feasibility of implementing add-on controls within the regulatory timeframe, and the 

cost-benefit analysis. The commenters (155, 242) are concerned that with the large number of 

engines that in its opinion will be required to install aftertreatment may lead to delays in 

permitting, delivery of aftertreatment controls, and vendor availability. These delays could result 

in service interruptions and potential safety concerns, ultimately possibly affecting the delivery 

of natural gas, the commenters (155, 242) said. 

With regards to emission limit achievability, the commenters (155, 242) said that since 

EPA’s analysis uses the average of the best performing source tests plus those tests are at high 

load, it is clear that these limits will not be achievable for most engines. Based on estimates 

provided in docket support information and the assumption that roughly half the natural gas 

engines would require catalytic control, the commenters (155, 242) stated that it is impractical or 

impossible to implement. The commenters (155, 242) recommended possible solutions to an 

enormous catalyst demand and compliance dilemma required by the proposed rule, which 

included obtaining data and analyzing data to arrive at a MACT floor that is more appropriate, 

compliance by requiring work practice standards rather than emission limits, and consideration 

of variability in setting the MACT floor. 

The commenters (155, 242) conducted a rough estimate of the number of engines (based 

on very conservative assumptions) that would have to install add-on controls and said that it 

estimated that the number would be approximately 150,000 natural gas engines. Commenter 242 

added that EPA has not indicated the basis for assuming that 80 percent of existing rich burn 

engines already have catalyst control. According to a survey conducted by the commenter (242), 

about 50 percent of rich burn engines above 500 HP have catalytic control and virtually no rich 
130

burn engines below 500 HP have catalyst control. Overall, about 10 percent of rich burn engines 

have add-on controls, the commenter (242) said. For that reason, commenter 242 thinks that 

EPA has overestimated the number of controlled engines. The commenter (242) pointed out that 

EPA current estimate contradicts the analysis of the Population Database, which indicate that the 

percentage is 5.6 percent for engines between 50 and 500 HP. There is also the issue of what 

engines should do when adding a catalyst is not an option or it is an option, but an extremely 

expensive one or engine replacement has to be considered, the commenter (242) said. 

 The commenters (132, 155, 242) asked EPA to develop a more complete review for the 

final RIA that adequately considers costs and compliance implementation issues resulting from 

requiring a large number of add-on controls and also that the final RIA be transparent. Finally, 

based on market constraints, the commenters (155, 242) asked that EPA consider the timing and 

schedule for demonstrating compliance. 

Response: EPA notes that the MACT standards are based on levels achieved in practice, not 

achievable. EPA has in any case revised the final standards to include additional test data that 

was received during the comment period. In addition, EPA has revised its approach to emission 

and operational variability into the final emission standards. In the final rule, the following 

engines have emission standards that are based on the use of add-on controls: 4SLB nonemergency engines 100-500 HP at major sources and 4SLB and 4SRB non-emergency engines 

larger than 500 HP at area sources. The remaining engines are either subject to emission 

standards that have been achieved by engines not equipped with add-on controls or are subject to 

work/management practice standards. The costs and economic impacts of the final rule are 

discussed in the RIA. The commenters did not provide any information to support the claim that 
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there would not be an adequate supply of catalysts, particularly given the three year lead time 

provided for meeting the standards. 

 Based on information submitted by the commenters, EPA revised the estimate of the 

number of 4SRB engines that are already equipped with NSCR. For the final rule, EPA assumed 

that 20 percent of engines already have NSCR, as opposed to the 80 percent number assumed for 

the proposal. The 20 percent estimate is based on information EPA gathered from a number of 

sources, including different EPA Regional Offices, the RICE Population Database, comments on 

the proposed rule and meetings with industry, and control technology vendors. This information 

is available from the rulemaking docket (EPA-HQ-OAR-2008-0708). EPA specifically 

contacted EPA Regions and MECA to get an estimate of how many existing rich burn engines 

have emission controls. The information collected generally indicated that a smaller percentage 

of stationary existing rich burn engines already have add-on controls compared to what EPA 

estimated at proposal. However, there was also a wide range in estimates EPA reviewed making 

it difficult to determine a percent of existing stationary rich burn engines with add-on controls 

that would be nationally representative and appropriate to use to calculate nationwide impacts 

associated with the final rule. With that said, analyzing the information received from all these 

sources, EPA believes that 20 percent is representative and reflects the best estimate EPA can 

develop with the information available. 

5.1.1.3 Comment: Four commenters (97, 132, 155, 175, 218, 224, 242) said that EPA has not 

provided proof that 90 percent reduction is readily achievable for all engines equipped with 

NSCR or oxidation catalyst. The docket does not contain any documentation supporting the 90 

percent reduction, the commenters (155, 242) said. According to the commenter (155), these 
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technologies require specific operating temperatures in order to reach such catalyst efficiencies 

and at temperatures that are lower, catalyst efficiency rapidly declines. EPA needs to determine 

the catalyst operating conditions that are necessary to achieve 90 percent reduction, commenter 

155 asserted. 

 The commenters (155, 224, 242) said that the 90 percent reduction contradicts the results 

from EPA’s CSU testing. The CSU testing indicated that the percent reduction from oxidation 

catalyst control is well below 90 percent for formaldehyde and CO for 2SLB, commenter 155 

said and EPA should explain why the percent control is different under this rulemaking. The 

commenter (155) stated that catalyst inlet data for the 2SLB engine tested at CSU exceed the 

proposed above-the-floor emission limits. In the 2004 RICE NESHAP, EPA concluded that the 

lower efficiencies observed at CSU were due to lower exhaust temperatures and EPA also found 

that with lower temperatures, the catalyst is more susceptible to poisoning, which also affects 

performance, the commenters (155, 242) said. Commenter 242 indicated that one of its members 

recently conducted temperature readings on a 1,350 HP Cooper GMVH-6 2SLB slow speed 

engine, which runs at approximately 300 rpm at 85 to 90 percent load. According to commenter 

242, the normal exhaust temperature immediately after the turbocharger was about 600°F. The 

temperature a few feet away where a potential catalyst would be placed was roughly 430° F, 

which is too low for efficient CO and formaldehyde removal. The commenters (155, 242) 

asserted, as noted in other comments by the commenters, that a separate subcategory may be 

warranted for 2SLB engines that may have lower exhaust gas temperatures impacting effective 

catalyst control. Commenter 102 made similar comments and suggested that the rule be 

modified to provide alternate emissions limits for existing 2SLB engines that operate with low 

exhaust temperatures below 500°F. The commenter (102) stated that the low exhaust 
133

temperatures of its engines are what make them unique and will make it difficult and perhaps 

impossible to achieve the proposed CO limit of 8 ppmvd CO in the exhaust, and the commenter 

noted that the preamble indicates that oxidation catalysts are the only proven and cost effective 

control technology for 2SLB engines. All oxidation catalysts have increased destruction 

efficiency at higher temperatures, so low exhaust temperatures limit the destruction efficiency of 

the catalyst. The commenter’s (102) units exhaust temperatures range between 330 and 500°F 

and oxidation catalysts have limited effectiveness below 500°F. 

Commenter 112 asserted that 2SLB engines often cannot be retrofitted with oxidation 

catalyst without significant additional modification/replacement of engine components; many 

older 2SLB engines cannot operate at the back-pressure caused by the catalyst; and 2SLB 

engines typically operate at slow speeds (i.e., 300 rpm), which causes pulsation and a greater 

potential for backfire, both of which are destructive to catalysts. The commenter (112) stated 

that older engines of all types typically consume more oil than new engines, which can also 

shorten the life expectancy of the catalyst. 

 Commenter 242 added that it disagrees with EPA’s methodology for determining the 

above-the-floor standards and the end results means that there are emission limits for existing 

engines that are more stringent than similar size new engines. For example, the commenter 

(242) said that 2SLB engines above 500 HP at major sources are subject to a 58 percent CO 

reduction while existing 2SLB engines above 500 HP at area sources have to meet a 90 percent 

reduction in CO, if the current proposed limits stand. Another example provided by commenter 

242 was that existing, new and reconstructed rich burn engines above 500 HP at major sources 

must reduce formaldehyde by 76 percent or limit formaldehyde by 350 parts per billion by 

volume, dry basis (ppbvd) while existing rich burn engines between 50 and 500 HP at major 
134

sources must under the proposed rule reduce formaldehyde emissions by 90 percent or limit 

those emissions to 200 ppbvd. 

Commenter (218) stated that the application of oxidation catalysts to 2SLB engines will 

not provide the desired reductions in CO and formaldehydes at all conditions of speed, load and 

ambient. The scavenging air requirements necessary to meet the current and projected NOx 

levels lower the engine exhaust gas temperatures sufficiently that a 90 percent catalyst reduction 

is not possible. The reduction is also highly dependent on whether the engine is turbocharged or 

naturally aspirated. EPA should consider alternative levels or categories for 2SLB engines with 

insufficient exhaust temperatures to apply oxidation catalyst technology. 

One commenter (102) further suggested the rule should be modified to allow a case-bycase determination of the emission limits for engines with low exhaust temperatures below 500 

°F. The commenter (102) attempted to contact 14 catalyst vendors to determine how it could 

comply with the proposed rule for their units and only 3 vendors responded and indicated a 

custom oxidation catalyst may be the solution for their units. Thus, based on the engine's 

operating parameters and the manufacturing capabilities of the catalyst vendors, the solution for 

each engine may be different; therefore, the commenter (102) believed that requiring all 2SLB 

engines to meet the same CO emission limit is not reasonable. 

Response: EPA received additional emissions data for stationary SI engines post-proposal. For 

the final rule, EPA has established a percent reduction emission limit only for non-emergency 

4SRB and 4SLB engines rated above 500 HP that operate more than 24 hours per year located at 

area sources. In those cases, EPA based the limit on emissions data that showed percent 

reductions that had been achieved in practice by stationary SI engines. For non-emergency 
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4SRB engines, the percent reduction emission limit established in the final rule is 76 percent. 

The 76 percent formaldehyde control efficiency is based on industry test results.7 These test 

results were used to set the final standards for stationary 4SRB engines greater than 500 HP at 

major sources and the 76 percent formaldehyde control efficiency is consistent with the current 

requirement for these engines. For non-emergency 4SLB engines, the percent reduction 

emission limit established in the final rule is 93 percent. The 93 percent CO control efficiency is 

based on the EPA-sponsored CSU testing conducted in 1999 to supporting the original RICE 

NESHAP rulemaking. This percent reduction is the average level of reduction achieved for the 

4SLB engines tested at CSU, which incorporates variability. The control efficiency of 93 

percent for CO for non-emergency 4SLB engines under this final rule is also consistent with the 

current requirements that apply to stationary 4SRB engines greater than 500 HP at major 

sources. For 2SLB engines, the final rule does not contain emission limits that are based on the 

use of add-on emission controls. 

5.1.1.4 Comment: Several commenters (51, 63, 96, 108, 116, 130, 141, 172, 176, 202, 204, 213, 

228) noted concerns over having limits that are more stringent for existing versus new engines, 

for smaller versus larger engines, or for area versus major sources. One commenter (96) 

expressed concern over the stringent emission limits proposed for existing rich burn engines 

below 500 HP that require compliance to formaldehyde levels much lower than what is required 

for larger engines, e.g., existing rich burn engines between 50 and 500 at major sources must 

                                                           

7

 Memorandum from Melanie Taylor and Jennifer Snyder, Alpha-Gamma Technologies, Inc. to 

Sims Roy, EPA OAQPS ESD Combustion Group. January 7, 2004. EPA-HQ-OAR-2002-0059-

0665. 
136

under the proposed rule meet at formaldehyde limit of 200 ppbvd (without the option of a 

percent reduction standard), which is 43 percent lower than required for larger sources. The 

commenter (96) also noted what it believed to be an inconsistency because the same engines at 

area sources can meet either a 200 ppbvd formaldehyde limit or a 90 percent formaldehyde 

reduction. The commenter (96) is of the opinion that smaller engines at major sources and area 

sources should not be subject to more stringent requirements than large engines. The commenter 

(96) also felt that the proposed requirements for smaller rich burn engines at major sources and 

all rich burn engines at area sources are inconsistent with what is proposed to be required for 

other engine types. For example, the 200 ppbvd formaldehyde limit that is required for these 

engines is much more stringent than both maintenance practices, which are required for 4SLB 

engines between 50 and 250 HP, and the 9 ppm CO standard that is required for 4SLB engines 

above 250 HP. The commenter (96) further noted that even under the best conditions with a 90 

percent efficient NSCR that 200 ppbvd may not be achievable and if EPA keeps the 

formaldehyde standard, EPA should adopt the standards that were finalized for rich burn engines 

above 500 HP at major sources of 350 ppbvd or a 75/76 percent formaldehyde reduction. 

One commenter (51) stated that EPA’s proposed rule places more stringent requirements 

on an engine at an area source than it does on an identical engine at a major source. The 

commenter (51) explained that the possibility exists that engines that fall into the exempt 

categories could also be located at area sources of HAP, in which case they would be subject to 

emission limits under the proposed rule. The commenter (51) believed it made little sense to 

exempt larger engines at major sources while requiring smaller engines to comply with the rule. 

The commenter suggested that MACT cover all categories of engines in excess of 500 HP at 

major sources as well as area sources. 
137

One commenter (228) stated that it is not clear why large (greater than 500 HP) existing 

2SLB, 4SLB, emergency RICE, limited use RICE, or RICE combusting landfill gas located at a 

major source should be exempt from regulation, while similar sources at area sources are 

regulated. The commenter stated that the same rules should apply to both, and EPA has provided 

no justification for exempting large existing RICE at major sources of HAP from subpart ZZZZ 

while requiring area sources to control the same units. The commenter (228) stated that if large 

units are going to be regulated at area sources, they should be regulated at major sources. 

One commenter (141) stated that the proposed rule includes SI engines and 

landfill/digester gas engines greater than 500 HP located at area sources and does not include the 

same size engines greater than 500 HP located at major sources and that, given the equipment is 

the same, the requirements should be the same. 

Commenter 63 expressed similar concerns to commenter 96 in terms of the proposed rule 

having more stringent limits for existing versus new sources and for small versus large sources. 

For example, commenter 63 cited as an example that the current rule has emissions limitations 

and operating limitations only for new stationary 4SLB RICE above 250 HP located only at a 

major source of HAP emissions (Tables 2a and 2b). Further, commenter 63 stated that proposed 

rule will place emissions limitations and operating limitations on these existing units whether 

located at a major source (Table 2c of the proposed rule) or at an area source (Table 2d of the 

proposed rule) and, consequently, existing units at a HAP source are subject to the regulation, 

but new ones at an area source will not be. Commenter (229) questioned how EPA expects 

existing engines to comply with an emission limitation standard that is more stringent than a 

standard for new engines. Commenter 213 is of the opinion that it would be better and more 
138

cost-efficient if the new standards are applicable to the new units only similar to what EPA 

finalized in the 2004 RICE NESHAP and the 2008 SI NSPS/NESHAP. 

Commenters 104, 111, 150, 151, and 225 expressed similar concerns in terms of the 

proposed standards being more stringent for existing sources than for new sources. Certain 

commenters said that the fact that existing equipment is older and typically less efficient tends to 

dramatically influence emissions output. Commenter 202 recommended that EPA limit the 

regulated source category to new or reconstructed engines. Other commenters (116, 141) 

expressed that the standards for all new/reconstructed engines should not be less stringent than 

for the same size existing RICE. 

The commenter (63) also claims the rule proposes more restrictive emissions limitations 

and operating limitations for small existing units (less than 500 HP) at major sources while those 

same existing sources greater than 500 HP are not regulated. The commenter (63) said that for 

example an existing 600 HP non-emergency 4SLB has no emissions limitation in Table 2c, but 

an existing 400 HP 4SLB does. 

One commenter (204) observed that EPA is proposing more stringent emissions limits for 

several categories of existing stationary RICE when compared to the limits proposed under the 

2004 and 2008 RICE rules, yet EPA fails to articulate a basis for this requirement. The 

commenter (204) further noted it would seem more reasonable to require additional or more 

stringent controls on units that are new or are being reconstructed as opposed to requiring 

expensive retrofits of existing units, some of which are nearing the end of their useful operating 

life. The commenter (204) also questioned how the EPA can establish different emissions limits 

for several of these categories when the same RICE emissions database was used for the 2004 

and 2008 rules as well as this proposed rule. 
139

Commenter 204 questioned why, in some cases, area source emissions limits are more 

restrictive than major source emissions limits. For example, an existing four stroke rich burn 

engine greater than 500 HP at a major source is subject to a 76 percent reduction of 

formaldehyde or 350 ppmvd. In contrast, the same exact engine at an area source is subject to a 

90 percent reduction of formaldehyde or 200 ppmvd. The commenter (204) noted that it is 

counterintuitive that the EPA would require more onerous emissions compliance limits for 

existing stationary RICE as well as area sources when compared to new/reconstructed units or 

units located at major sources. 

Response: As discussed in the response to comment 4.1.1, EPA received additional emissions 

data for stationary SI engines. This new data was incorporated into the MACT floor and MACT 

analysis, and the emission limits in the final rule are different than the proposed rule. Many of 

the concerns expressed by the commenters regarding the emission limits are no longer an issue 

with the final emission limits. For engines at or below 500 HP EPA is not requiring any engines 

under 100 HP to meet numerical standards and is only requiring 4SLB engines 101 HP to 500 

HP to meet standards that are likely to require emission controls. Moreover, the levels required 

in the final rule are less stringent than the proposed standards that were expected to require 

controls. 

 EPA notes that the standards for engines greater than 500 HP at major sources were 

developed under the 2004 rule and that the standards for new engines at area sources and at or 

below 500 HP at major sources were developed under the 2008 rule. Neither are the subject of 

this rule. Due to the Brick MACT decision, which said that EPA could not set MACT floors of 

no emission reduction, as well as other subsequent court decisions, EPA had to take a different 
140

approach in setting standards for the stationary engines regulated in this rule than was taken in 

earlier regulations. The outcome of the Brick MACT decision and the SSM decision occurred 

after the previous engine rulemakings and therefore have resulted in standards more stringent for 

older engines under a different analysis. 

5.1.1.5 Comment: One commenter (155) said that EPA should allow alternatives under section 

112(h) of the CAA for demonstrating compliance at reduced load and other reduced temperature 

operating conditions where catalytic control is required. The commenter (155) believes that it is 

not possible to set a standard based on add-on catalyst control that is applicable at all times. The 

performance of the catalyst is dependent on the load, engine type, engine make or model, catalyst 

formulation, catalyst age, and so on, and so therefore, it is infeasible to define a standard as a 

function of load and temperature, according to the commenter (155). The commenter (155) 

recommended that EPA consider a work practice standard to be used at reduced load or other 

reduced temperature conditions where aftertreatment is required to meet the standard. 

Alternatively, if EPA finalizes a catalyst-based standard that applies at all times, such a standard 

must be well rationalized and supported with data and a clear presentation of how the analysis 

was conducted, the commenter (155) said. 

Response: EPA agrees that it is appropriate to consider variability in developing the final rule. 

The final emission standards account for operational variability of the stationary engine. This 

includes engines operating at low loads and other reduced operating temperatures. EPA has also 

specified in the final rule that performance tests can be conducted during normal operating 

conditions. The final standards and other requirements are well explained and detailed 
141

documentation of how the analysis was conducted is included in the docket material. EPA does 

not believe that it would be justified in using the provision in 112(h) to establish work practice 

standards in lieu of emission limits since it is not technically or economically infeasible to 

measure emissions during the operating conditions discussed by the commenter. 

5.1.1.6 Comment: One commenter (96) stated that EPA has proposed CO standards for 4SLB 

engines between 50 and 250 HP of 95 ppmvd that are in conflict with the 540 ppmvd, which is 

required in the SI NSPS. 

Response: The emission standards in the NSPS and NESHAP cannot necessarily be compared 

because they were developed under different statutory sections of the CAA. For major sources, 

EPA is required to set an emission limit that is no less stringent than the MACT floor. For the 

final rule, the MACT floor for 4SLB engines 100 HP to 500 HP was determined to be 47 ppm 

CO, based on the sources for which EPA has data. 

5.1.1.7 Comment: One commenter (157) believes the MACT floor numbers of 8 ppmvd for 

2SLB and 9 ppmvd for 4SLB give 4SLB engines a 12 percent advantage in achieving the 90 

percent reduction. The commenter (108) noted previous NESHAP regulations (2004) required 

58 percent reduction of CO emissions for 2SLB and 93 percent reduction for 4SLB, which was 

based on the approximately 30 years of proven technology associated with 4SLB catalytic 

converters vs. the emerging (now 5 years) technology with 2SLB catalytic converters. The 

commenter (108) stated that the net result is that 2SLB engines are subject to a change 32 

percent lower in one step from the previous requirement and 4SLB engines are allowed a 3 
142

percent higher level from the previous requirement (the 2004 NESHAP regulations). Therefore, 

the commenter recommended that the MACT floor number be established for all engines at 9 

ppmvd. 

Response: EPA does not agree with the commenter that the emission limit for 2SLB engines 

should be the same as for 4SLB engines. However, as discussed in the response to comment 

5.1.1.1, the emission limits in the final rule are different than in the proposal. The limit for 2SLB 

engines at major sources is 225 ppm CO. The limit for 4SLB engines at major sources is 47 ppm 

CO. Therefore the concerns expressed by the commenter on the proposed limits are not 

applicable to the final limits. 

5.1.2 Above-the-Floor 

5.1.2.1 Comment: Several commenters (97, 112, 132, 155, 175, 241, 242) thought that the data 

used for EPA’s cost effectiveness analysis is flawed and based on limited and erroneous data and 

assumptions. Based on EPA’s analysis, it determined that catalytic controls were cost effective 

and appropriate for several natural gas engines, but the commenters (155, 242) believe that 

above-the-floor controls are not justified for natural gas engines based on using more realistic 

cost information. The commenters (155, 242) provided extensive detailed information 

supporting their view of EPA’s flawed cost data and assumptions. Some of the main points, 

which the commenters (155, 241, 242) believe indicate that different conclusions are justified 

and a reanalysis necessary, include the following: 
143

• Cost effectiveness estimates are significantly less than those presented for the 2004 RICE 

NESHAP and the commenter (155) believes that costs associated with the proposal are 

considerably underestimated by an order of magnitude or more. The commenter (155) 

should explain the difference between current cost estimates and the estimates from the 

2004 RICE NESHAP; 

• The underestimate of costs are mainly caused by underestimating control equipment 

capital cost, operating and compliance costs, and emission assumptions; and 

• Based on target cost effectiveness values and EPA conclusions from a document 

available from the docket, above-the-floor controls are not cost effective and not 

warranted for natural gas engines. 

The commenters (155, 242) suggested that EPA gather control technology cost data from 

several vendors and operators and independently validate cost quotes and performance claims to 

remove any potential conflict of interest from control technology vendor sales objectives. 

Additional flaws and inaccuracies in EPA’s cost data include AFRC costs not included in NSCR 

capital costs, as well as other associated necessary equipment; and the 20 years catalyst lifetime 

is not appropriate and 10 years or less would be more realistic. Commenter 242 said that 

elements that can affect catalyst life include: engine family, exhaust temperature, engine misfires 

and malfunctions, utilization and frequency of startup and shutdown, percent load and load 

swing cycles, catalyst cleaning frequency, element design and formulation, lubrication oil 

consumption and formulation, and fuel quality. The commenters stated that 90 percent reduction 

in emissions is not supported by data and information in the docket, e.g., EPA’s testing at CSU 

shows levels below 90 percent. According to the commenters, EPA should revise the cost 

effectiveness analysis using documented control efficiencies and for engines that cannot achieve 
144

90 percent, e.g., large 2SLB engines, control efficiencies should be reflective of those achievable 

in practice. 

Regarding the benefits from using NSCR on rich burn engines, the commenters (155, 

242) said that EPA has considered non-HAP reductions such as CO and NOx emissions, but that 

it has not included the impact of NSCR on all emissions. The commenters (155, 242) indicated 

that since rich burn engines are required to operate at a lower air-to-fuel ratio when equipped 

with NSCR, engine efficiency is decreased and greenhouse gas emissions will increase because 

more fuel carbon is oxidized leading to more carbon dioxide (CO2). Methane emissions may 

also increase, the commenter (155) said because NSCR control efficiency for methane is much 

lower than for HAP and CO. In addition, the commenters (155, 242) said that ammonia 

emissions are likely to increase with the use of NSCR, which is something that has been 

documented in recent studies. The commenters (155, 242) were also of the opinion that CO 

reductions are typically overestimated. 

The commenters (155, 242) said that the estimates it has provided are significantly higher 

than what EPA estimated for the proposed rule. If EPA conducts a re-estimate of the cost per ton 

of HAP removed from existing engines that are consistent with the estimates conducted by the 

commenters (155, 242) and presented in the above tables, the commenters are of the opinion that 

above-the-floor control cannot be justified for existing 2SLB, 4SLB and 4SRB engines. 

Response: In response to these comments on the cost effectiveness calculations for the 

proposed rule, EPA re-evaluated all aspects of the cost effectiveness calculations. EPA solicited 

and received additional information from stakeholders regarding the costs of oxidation catalyst 

and NSCR. This information has been incorporated into the cost effectiveness calculations for 
145

the final rule. EPA is including costs for AFRC in the cost analysis and has adjusted the 

equipment life to 10 years rather than 20. For the final rule, EPA is also using HAP emission 

factors specific to each subcategory, rather than using one HAP emission factor for all SI 

engines. The HAP emission factors EPA is using for the final rule to estimate cost per ton and 

emissions reductions are from AP-42 and are described in the memorandum titled “Emission 

Factors for Existing Stationary SI RICE.” Finally, EPA used emission reduction percentages 

that are based on emission reductions actually achieved in practice based on the emissions test 

data that EPA has. 

EPA agrees that rich burn engine efficiency might be affected as a result of operating 

with NSCR, but expects that any such decrease in efficiency would be negligible. Based on 

recommendations from commenters, EPA has incorporated a fuel penalty into the control costs 

used for the final rule. The specific fuel penalty costs EPA incorporated into the control costs for 

the final rule are included in the memorandum titled “Control Costs for Existing Stationary SI 

RICE.” The commenters did not provide any specific data to document the degree to which 

ammonia and greenhouse gas emissions will increase as a result of applying NSCR. EPA does 

not have any information on greenhouse gas emissions increases. It is true that ammonia 

emissions can increase across the catalyst, however the magnitude is unknown. Information 

published in the Four Corners Report,8

 states that “If NSCR is used on a large scale, it is believed 

ammonia emissions would result. However, it is not known if these emissions would be 

significant.” EPA does not have any other information on ammonia emissions to quantify the 

magnitude of ammonia emissions. However, according to the Four Corners Report,7ammonia 

                                                           

8

 Four Corners Air Quality Task Force Report of Mitigation Options. November 1, 2007. EPAHQ-OAR-2008-0708-0009. 
146

can be minimized by using a well-performing air/fuel ratio controller. The Four Corners Report 

states: “If a rich burn engine is operated with a properly functioning air/fuel ratio controller plus 

3-way catalyst, it will meet emissions requirements without producing a noticeable amount of 

ammonia.” EPA agrees with the findings of the Four Corners Report that with a tightly 

controlled air.fuel ratio controller, ammonia can be minimized. EPA also expects the ammonia 

increase to be minimal and would be offset by the substantial reduction in HAP, CO, VOC, and 

NOx emissions. 

5.1.2.2 Comment: A few commenters (76, 132, 155, 224, 242) said that EPA should define a 

cost effectiveness threshold for the above-the-floor analysis or identify a cost range and the basis 

for evaluating peripheral benefits and negative impacts if a specific threshold cannot be defined. 

Commenters 155, 186, and 242 also provided cost information for various engine subcategories. 

The commenters (155, 242) also asked that EPA discuss any differences in above-the-floor 

determinations between this proposed rule and the 2004 RICE NESHAP in terms of what costs 

are considered acceptable. 

One commenter (76) noted that the cost per ton of HAP removed was determined to be 

too significant and to outweigh the expected HAP reductions from non-emergency 4SLB 

50≤HP≤249 engines. The commenter (76) asked how EPA defined significant, and what was 

the basis for this determination. The commenter (76) stated that there was no data available in 

the preamble or the docket, and that this analysis should be reconsidered because the process that 

EPA used can be considered arbitrary. One commenter (76) asked how controls were justified 

and what criteria were used to establish the emission limitations for the non-emergency 4SLB 

50≤HP≤249 subcategory. 
147

One commenter (76) stated that MACT should be emission limits without add-on 

controls for non-emergency 4SRB engines 50≤HP≤500 located at major sources. The 

commenter (76) asked what is “reasonable” cost effectiveness for this subcategory and how was 

this number quantified. The commenter (76) recommended that CO be used as a surrogate for 

these types of engines rather than establishing formaldehyde limits. 

 Commenter 242 said that for the 2004 RICE NESHAP, EPA determined that above-thefloor controls were not cost effective. The cost per ton of HAP removed for lean burn engines 

for that rulemaking was between $13,000 and $21,000. However, for the current proposal, EPA 

has developed cost per ton estimates ranging from $5,000 to $33,000 for certain smaller 2SLB, 

4SLB, and 4SRB engines, where above-the-floor controls are not required. 

The commenters (155, 242) assumed that where above-the-floor controls were not required EPA 

is saying that the cost effectiveness is not reasonable. The commenters (155, 242) said that EPA 

considers cost of controls for 2SLB and 4SLB above 250 HP reasonable and based on an 

extrapolation of the cost per ton figures EPA presented for the proposal, the commenters (155, 

242) estimated that the cost per ton of HAP removed from a 250 HP lean burn engines is about 

$3,600. The commenter (242) added that the rule supporting information states that $2,900 and 

$3,000 per ton is reasonable for 2SLB and 4SLB engines, respectively. Therefore, the 

commenters (155, 242) concluded that the cost threshold for lean burn engines is approximately 

$3,600 per ton of HAP removed. 

 EPA has determined that cost per ton values for rich burn engines below 50 HP are 

significant and EPA did not go above-the-floor for this category of engines. This means that 

EPA is requiring add-on controls for rich burn engines that are above 50 HP, where the cost per 

ton range is $3,800 to $13,000. Therefore, the commenters (155, 242) said, it seems the cost 
148

threshold is between $13,000 and $33,000, since the latter represents the cost per ton for engines 

less than 50 HP. This indicates that EPA has determined that a higher cost per ton threshold is 

acceptable for rich burn engines, likely because of peripheral emission benefits the commenters 

(155, 242) said. However, it is not clear whether EPA has taken into account negative effects 

from NSCR, such as fuel penalties and a potential increase in greenhouse gas emissions, 

commenter 242 stated. Commenter 155 added for reference that EPA has indicated that $72,000 

per ton for diesel engines is too costly. 

 The commenters (155, 242) noted that EPA should consider the relative toxicity of HAP 

from natural gas engines and if the URE for formaldehyde is revised, the relative importance of 

reducing HAP may be marginalized and the cost effectiveness threshold would be lowered. 

Again, the commenters (155, 242) said that EPA should explain the basis for the cost 

thresholds and what specific criteria were considered in making decisions whether cost 

effectiveness values are reasonable or not. Commenters 155 and 242 have also previously 

indicated that they believe EPA has significantly underestimated the costs. Also, as mentioned 

earlier by commenters (155, 242), EPA should obtain more information on the cost of 

purchasing, installing, and operating controls, and providing a thorough explanation of how EPA 

reached its conclusions will assist in determining how much additional effort and information is 

needed to refine the cost analysis, e.g., if the cost effectiveness for a specific group of engines is 

significantly higher than the acceptable cost per ton threshold, then further analysis is not 

needed, but if the cost per ton is close, then additional cost effectiveness analysis may make 

sense to make sure adequate data has been reviewed and appropriate assumptions have been 

made. 
149

Response: EPA cannot define a specific cost per ton threshold that would be acceptable across 

the board. EPA does not think it is appropriate to discuss differences in the above-the-floor 

determinations in terms of which costs are justified and which are not between this rule and the 

2004 RICE NESHAP. Although consistency is preferable, it is not necessarily appropriate to 

make a comparison since the rules were developed at different times and under different 

conditions, cover different engines, and are based on different information and data. Note also 

that cost is not the only consideration in EPA’s determinations, but that EPA also considers other 

factors such as the benefits of reducing other non-HAP pollutants and non-air quality health and 

environmental impacts, and energy requirements. Therefore, EPA does not believe it would be 

appropriate to define a threshold that would be considered acceptable in all cases based solely on 

cost. The memorandum “Cost per Ton of HAP Reduced for Existing Stationary RICE” presents 

the cost per ton numbers for all engines and explains how these numbers were quantified. EPA’s 

decision for requiring emission standards under the final rule for certain engines is not arbitrary 

and EPA clearly presents the rationale and justification for the final limits in the the above-thefloor analysis in the memorandum titled “MACT Floor and MACT Determination for Existing 

Stationary SI RICE ≤500 HP Located at Major Sources” and the GACT analysis in the 

memorandum titled “MACT Floor and MACT Determination for Existing Stationary NonEmergency SI RICE <100 HP and Existing Stationary Emergency SI RICE Located at Major 

Sources and GACT for Existing Stationary SI RICE Located at Area Sources.” 

5.1.3 Subcategories 
150

5.1.3.1 Comment: Numerous commenters (112, 131, 132, 155, 156, 224, 242) thought that it 

might be necessary to establish additional subcategories or possible exemptions depending on the 

results of a re-analysis of the MACT floor. 

For example, the commenters (112, 131, 155, 242) said that certain 2SLB engines cannot 

reach the exhaust temperature necessary for effective catalyst performance and based on the 

proposed emission standards these engines would have to be replaced. Commenters 112 and 242 

said that existing 2SLB slow speed engines should either be exempted from the rule or be subject 

to only work practice standards. Commenter 112 asserted that controls on large bore, slow speed 

2SLB engines are particularly problematic for the following reasons: 

• The catalyst requires a temperature of at least 550°F to work properly. The temperature 

of the exhaust for 2SLB engines runs cooler than the temperature of the exhaust for 

4SRB. The commenter (112) submitted a list of 20 models of 2SLB engines with exhaust 

temperatures less than 550°F. 

• The exhaust temperature drops off sharply when the load is reduced, affecting the 

efficiency of the catalyst for 2SLB engines where the exhaust temperature at full load is 

over 550 F. The commenter (112) submitted a list of 38 models of 2SLB engines with 

exhaust temperatures greater than 550 F. 

• The 2SLB engines cannot be operated with more than a few inches of back pressure. A 

catalyst increases back pressure to the exhaust and would have to be designed 

accordingly. 

• Fouling of catalysts on 2SLB engines is much greater than for 4SLB or 4SRB engines 

due to units backfiring routinely, which either coats the catalyst or destroys it. 

Consequently, the catalyst will require frequent washing or replacement, which in turn 
151

results in additional performance tests, and additional notifications under 40 CFR part 63, 

subpart A, thereby greatly increasing the operating cost of the controls. 

 The commenter (112) attached to its comments a Case Study for retrofit of ten large 

2SLB engines with oxidation catalysts. In the case study, the catalysts were designed for 58 

percent reduction of CO because, as operator in the Case Study explained, a new catalyst may 

get approximately 90-percent reduction of CO but only for a few hours because oil masking 

begins immediately upon startup; within a few days, the efficiency is reduced below 70 percent 

and within approximately 3 months of continuous operation must be cleaned or replaced to 

ensure the control efficiency is kept at least 58 percent. The commenter (112) asserted that high 

reduction efficiency for catalysts on these types of engines is impossible to maintain long term. 

As a result, the commenter (112) believes that the rule would effectively require widespread 

replacement of the existing engines with newer models to meet the standards, which increases 

the cost of emissions reductions to nearly $250,000 per ton. The commenter (112) stated that 

replacement of these engines is both impractical and wasteful of valuable natural resources. The 

commenter (112) recommended that existing 2SLB engines be exempt from the standards. 

 Commenter (156) noted that existing 2SLB slow speed engines used to drive natural gas 

compressors are typically found in older producing gas fields, compressor stations, and gas 

plants; they are usually greater than 500 HP and are often more than 30 years old. The 

commenter (156) indicated that the engine and compressor are usually built with an integral 

design, meaning the engine cannot be replaced independently of the compressor; they usually 

operate at around 300 rpm and have characteristically low exhaust temperatures. The commenter 

(156) noted that this information can be found in the report of EPA’s study at CSU (EPA-454/R00-36a). According to the commenter (156), low exhaust gas temperatures mean that oxidation 
152

catalysts operate inefficiently, and in EPA’s study achieved CO control at best of about 65 

percent and formaldehyde control around 40 percent. The commenter (156) indicated that the 

cost to retrofit these engines is several orders of magnitude above what EPA used in the cost 

estimate for this rule (see Section 13.3), and even then will not achieve 90 percent control of CO 

as proposed. Thus, the commenter (156) believes that the only practical option is to replace 

these engines, which would be especially expensive since many are fit to integral compressors. 

With many of these engines located at older producing fields, this expense could be cost 

prohibitive, severely impacting field life economics, according to commenter 156. 

 As a solution to this problem, the commenter (156) asked EPA to give serious 

consideration to solutions offered by commenter 242 and that is adopting work practice 

standards in lieu of emissions standards for rural area sources and creating engine subcategories 

for engines with unique operating limitations that includes existing 2SLB slow speed engines. 

The commenter (156) believes that exempting existing 2SLB engines at area sources or adopting 

work practice standards specific to this engine type [as allowed under CAA sections 112(d)(5) 

and 112(h)] would resolve this issue in most all cases. Commenter 132 agrees that EPA should 

establish an additional subcategory for 2SLB for some of the same reasons as discussed above. 

Commenters 155 and 242 provided another example of engine types that would have 

difficulties meeting the proposed standard and those are air compressors commonly used in the 

natural gas transmission industry. According to the commenter (155), this type of engine has 

variable operation and operates for a brief time when operating. The engines used for this 

purpose are typically 4SRB engines above 100 HP and most compressor stations are located at 

major sources (consequently these engines would be subject to emission standards that require 

add-on controls), commenter 155 said. The commenters (155, 242) said that testing is not 
153

practical on these units because the unit will not operate at a steady load and for a period long 

enough to conduct a test. If the engine does not operate long enough exhaust temperatures are 

not likely to be sufficiently hot for catalyst function and cyclic load would challenge the air-tofuel ratio controller, according to the commenters (155, 242). For these reasons, the commenter 

(155) believes it is technically clear why emission standards and measurements are not feasible 

and a subcategory may be needed for these types of engines. Both commenters 155 and 242 

believe that a subcategory is necessary for cyclic duty operations. Examples of cyclical duty 

applications include air compressors, emergency generators, pumps, and cranes, commenter 242 

said. Commenters 131 and 132 agreed that a separate subcategory representing cyclic engines is 

appropriate. 

Other examples of engines possibly in need of separate subcategorization are units with 

limited run time, e.g., fire pumps or engines that operate infrequently based on demand, the 

commenter (155) said. The commenters (155, 242) thought a subcategory for these engines, i.e., 

limited use may be appropriate either because add-on controls might be necessary on a unit that 

rarely if ever operates to meet an emission standard or if the engine was subject to maintenance 

practices, the frequency of maintenance would require maintenance on an engine that has not be 

operated. Commenter 242 specifically suggested that a subcategory be created for intermittently 

used engines that operate less than 500 hrs/yr. Commenter 242 also believes that a subcategory 

should be established for emergency engines and these engines should only be subject to work 

practice standards. 

Response: EPA agrees with the commenters to some extent regarding the issues related to 2SLB 

engine operation and the use of oxidation catalyst. However, EPA has also reviewed information 
154

that appears to indicate 2SLB engines can operate successfully with oxidation catalyst and 

achieve substantial reductions.9,10,11,12 Nonetheless, EPA is finalizing numerical emission 

standards for existing stationary 2SLB engines at major sources that are expected to be met 

without the use of emission control aftertreatment. As discussed in the memorandum titled 

“MACT Floor and MACT Determination for Existing Stationary SI RICE ≤500 HP Located at 

Major Sources,” EPA determined that the MACT floor for existing stationary 2SLB engines 

greater than or equal to 100 HP and less than or equal to 500 HP is 225 ppmvd of CO at 15 

percent O2. EPA considered requiring oxidation catalyst, because EPA does believe the 

technology is feasible, but did not believe the costs justified going above-the-floor for this group 

of engines. The estimates of the cost per ton of HAP reduced were based on updated cost 

information, which was significantly increased to account for all necessary components and to 

reflect costs representative of oxidation catalyst costs for 2SLB engines. Cost per ton numbers 

used in considering the oxidation catalyst above-the-floor option for these engines were also 

calculated assuming a lower HAP control efficiency, i.e., 43 percent, compared to what EPA 

used at proposal. Even though oxidation catalyst could reduce HAP by more than 43 percent, 

EPA believes that this percentage is more reflective of expected in-use average reductions and is 

in fact based on the average HAP reduction observed during EPA’s 1999 CSU testing of a 2SLB 

                                                           

9 Article by Glen Sharkowicz and Bruce Chrisman. Development of Catalyst Friendly 

Lubricating Oil for Two-Stroke Lean-Burn Gas Engines. EPA-HQ-OAR-2008-0708-0471.

10 Development and Field Validation Testing of an Oxidizing Catalytic Converter and a 

Compatible Lube Oil for Two Stroke, Lean Burn Gas Engines. EPA-HQ-OAR-2008-0708-0490.

11 Article by Bruce Chrisman and Diane Slaughter. Staying Ahead of Exhaust Emission 

Regulations. June 2009. EPA-HQ-OAR-2008-0708-0494. 

12 Email from Bruce Chrisman, Cameron's Compression Engines to Tanya Parise, EC/R. 2SLB 

Engine Information. October 22, 2009. EPA-HQ-OAR-2008-0708-0500.
155

engine equipped with oxidation catalyst. For existing 2SLB engines at area sources, EPA is 

finalizing management practices, which were determined to be generally available. No other 

options beyond management practices were determined to be justified for existing stationary 

non-emergency 2SLB engines EPA is requiring management practices. EPA believes that the 

requirements EPA is finalizing for existing stationary 2SLB engines resolves the commenters’ 

concerns related to 2SLB engines and aftertreatment since oxidation catalyst is not expected to 

be necessary in order to demonstrate compliance with the final requirements under this rule. 

In response to concerns regarding variable load, for engines operating at reduced speed or 

loads resulting in a reduced exhaust temperature, EPA believes that numerical emission 

requirements are appropriate and there is no justification to only require work practice standards 

during these situations. EPA’s emission standards are based on emissions data from a engines 

operating across loads from 11 to 100 percent. EPA’s standard-setting approach also 

incorporates a statistical formula, which accounts for emissions variability. Note that with 

regard to 4SRB engines, only stationary existing non-emergency engines greater than 500 HP at 

area sources that are operated more than 24 hours per calendar year will most likely need 

aftertreatment, which means that variable load 4SRB engines between 100 HP and 500 HP at 

compressor stations at major sources will not have the issue of insufficient exhaust temperature 

for catalyst function. Existing non-emergency 4SRB engines greater than or equal to 100 HP 

and less than or equal to 500 HP are subject to a numerical emission limit, but the limit is at a 

level that would expected to be met without add-on controls. 

In response to the request for a subcategory of limited use engines, EPA does not believe 

such a subcategory is generally necessary, but is providing subcateogries for 4SLB and 4SRB 

engines greater than 500 HP located at area sources that operate less than or equal to 24 hours 
156

per year. EPA provides responses regarding this issue in section 6.1 of this document. EPA 

does not believe that a subcategory is justified solely based on what the commenters consider 

limited operation. The maintenance/management practices EPA is requiring under the final rule 

are specified as time intervals based on actual engine operating hours. Therefore, any 

management/maintenance practices that might apply to an engine operated infrequently would 

only be required based on actual operating time or annually, which would not constitute a 

burdensome requirement. 

Consistent with the proposed rule, EPA is retaining a subcategory for emergency engines 

in the final rule. EPA agrees with commenters that a subcategory for emergency engines is 

necessary to capture the different characteristics of these engines. 

5.1.3.2 Comment: One commenter (242) noted that a subcategory is justified for engines located 

on offshore platforms and in cold weather regions. According to commenter 242, due to space 

constraints on platforms, installation of add-on controls is expensive and/or impossible. In 

extreme cold weather it is difficult and sometimes impossible to maintain the exhaust hot enough 

for catalyst operation, particularly for emergency, limited use and intermittently used engines, 

the commenter (242) said. For these reasons, commenter 242 believes that it is reasonable that 

EPA create subcategories for non-continental areas/offshore platforms and for cold weather 

regions, i.e., less than 0°F as was done in 40 CFR part 60, subpart KKKK for stationary 

combustion turbines. The commenter (242) recommended that these special category engines 

only be subject to work practice standards. 
157

Response: The EPA does not agree that it would not be feasible to install add-on controls on 

offshore platforms. Catalyst manufacturers have had many experiences with installing controls 

in situations where space is a concern, for example in mobile source engines. Regarding engines 

located in cold weather regions, the commenter did not submit any data to show that the 

emission limitations could not be achieved by these engines. A subcategory for turbines located 

north of the Arctic Circle was created in subpart KKKK because the emission controls that are 

inherent to the turbines themselves did not operate as well in the cold weather, not because postcombustion controls such as oxidation catalyst were not feasible in these areas. 

5.1.3.3 Comment: One commenter (242) said that EPA has not considered fuel quality in 

determining appropriate subcategories for this rule and thinks that a separate subcategory is 

necessary for sulfur-containing fuels should be included. Sulfur in fuels can lead to the exhaust 

containing sulfur that impacts catalyst performance and reliability, the commenter (242). 

According to the commenter (242), fuel such as wellhead gas and other gases that contain 

hydrogen sulfide cannot use add-on controls due to catalyst poisoning. There are options to deal 

with this issue such as pre-treating the fuel, obtaining sulfur resistant catalysts, and replacing the 

catalyst on a more frequent basis. However, the commenter (242) said, such options may not be 

technically feasible and if feasible, would have costs well above reasonable cost effectiveness 

thresholds. The commenter (242) compared the issue to the issues related to landfill and digester 

gas that contain siloxanes, which because of the silicon-based compounds present in the fuel lead 

to catalyst inoperability. For these reasons, the commenter (242) asked that EPA create a 

subcategory for engines operating on non-pipeline gas (i.e., gas containing sulfur compounds) 
158

similar to what was done for landfill and digester gas fired engines. These engines should not be 

subject to above-the-floor controls, in the commenter’s (242) opinion. 

Response: The commenter did not provide any information to support the claim that a separate 

subcategory is needed for sulfur-containing fuels. As discussed in the response to comment 

6.9.5 on the NSPS for stationary SI engines (EPA Docket EPA-HQ-OAR-2005-0030-0249), 

there is information available that shows that there are aftertreatment control devices available 

which can operate efficiently with the presence of up to 500 ppm sulfur. Manufacturers of SI 

mobile source engines, like cars and trucks, successfully used catalysts on vehicles for many 

years when the sulfur content of gasoline was unregulated. 

5.1.3.4 Comment: One commenter (76) asked why EPA established a cutoff for non-emergency 

SI lean burn at 250 HP rather than at 300 HP. The commenter (76) stated that there was no data 

available in the preamble or the docket, and that this analysis should be reconsidered because the 

process that EPA used can be considered arbitrary. 

Response: The cutoff of 250 HP for non-emergency 4SLB engines was not arbitrary and was 

based on information EPA gathered for and decisions made for the SI NSPS and NESHAP 

finalized in 2008 for new engines. For example, see EPA’s discussion on this issue in response 

to comment 5.2 in EPA’s response to comments document for that rule.13 EPA also discussed 

                                                           

13 Memorandum from Jaime Pagán, EPA Energy Strategies Group to EPA Docket EPA-HQOAR-2005-0030. Response to Public Comments on Proposed Standards of Performance for 

Stationary Spark Ignition Internal Combustion Engines and National Emission Standards for 

Hazardous Air Pollutants for Stationary Reciprocating Internal Combustion Engines. EPA 

Docket EPA-HQ-OAR-2005-0030-0249. 
159

the appropriateness of the 250 HP cutoff in supporting documentation14 and in the preamble to 

that proposed rule (see 71 FR 33804). In the final rule, EPA has promulgated a single standard 

for all 4SLB engines rated from 100-500 HP located at major sources, which is equal to the 

MACT floor for those engines. 

5.2 Area Sources 

5.2.1 Comment: Four commenters (76, 96, 156, 216) do not believe that the emission standards 

for larger existing engines located at area sources should be more stringent than the same engines 

located at major sources. One commenter (76) asked how EPA determined what baseline was 

used to establish “reasonable” to justify GACT to be based on the same emission controls as 

MACT for area sources. Commenter 156 does not believe that EPA has presented adequate 

justification for this apparent discrepancy. Per 63.6590(b)(3), existing larger engines at major 

sources have no HAP requirements, the commenter (96) said. The commenter (96) was 

specifically referring to the proposed standards for existing 4SLB engines above 250 HP located 

at area sources and existing landfill and digester gas engines above 500 HP located at area 

sources. See areas marked “g” in the 4SLB and landfill/digester gas charts provided in the 

commenter’s (96) letter. 

One commenter (253) disagreed in the assessment that “costs associated with 

implementing HAP-reducing technologies are reasonable and justified, and there is no reason 

why GACT should be any different than MACT for larger engines located at area sources” (74 

                                                           

14 Memorandum from Jennifer Snyder and Tanya Parise, Alpha-Gamma Technologies, Inc. to 

Jaime Pagán, EPA Energy Strategies Group. Subcategorization of Stationary Reciprocating 

Internal Combustion Engines ≤500 HP. May 15, 2006. EPA-HQ-OAR-2008-0708-0012.
160

FR 9710). The commenter (253) believes that GACT by definition is a lesser degree of control 

than MACT, which requires a minimum level of emission control that is based upon the 

emissions achieved by the best-performing sources within a category or subcategory. The 

commenter (253) stated that EPA is not required to consider the MACT floor as a minimum 

standard for area sources, but may instead elect to promulgate standards or requirements for area 

sources which provide for the use of GACT or management practices by such sources to reduce 

emissions of HAP. The commenter (253) stated that EPA must consider not only the economic 

impacts and whether the methods, practices, and techniques are commercially available and 

appropriate for application by the sources in the category, but also the technical capabilities of 

the firms to operate and maintain the emissions controls systems. The commenter (253) pointed 

out that unlike engines located at major sources, which are often large industrial facilities, many 

engines at area sources are owned and operated by small businesses with little or no experience 

dealing with complex regulatory issues and with minimal technical and financial resources. The 

commenter (253) believes that EPA should reevaluate its GACT determinations for engines 

above 500 HP at area sources, and believes that management practices rather than emission 

limitations and add-on controls may be more appropriate for larger engines at area sources. 

Response: EPA has reviewed its proposed requirements for existing SI engines at area sources 

based on comments received on the proposed rule. For existing non-emergency 4SRB and 4SLB 

stationary SI RICE greater than 500 HP that operate more than 24 hours per year at area sources, 

EPA determined for the final rule that it is appropriate to set numerical emission limits that EPA 

expects would be met using emission control technologies. The emissions reductions associated 

with these requirements are substantial and the costs and economic impacts are reasonable. The 
161

estimated HAP reduction resulting from controlling these engines is 4,700 tpy. The total annual 

cost estimated for existing non-emergency 4SRB and 4SLB engines greater than 500 HP at area 

sources is approximately $150 million. The capital cost for controlling these engines is 

estimated at around $310 million. The control technologies that would be expected to be used, 

i.e., NSCR for 4SRB engines and oxidation catalyst for 4SLB engines, are generally available for 

these area source engines. Both technologies have been on the market for decades and are wellproven aftertreatment controls that are readable accessible and available. The aftertreatment 

control systems can be purchased through several different catalyst vendors and the location of a 

site would not preclude an owner from acquiring controls. The control systems are equally 

available to major and area sources and EPA does not see any reason why being located at an 

area sources would prevent such systems from being obtained. 

For the remaining existing stationary SI RICE at area sources, the final rule requires 

management practices. EPA received comments and supporting information indicating that EPA 

had underestimated the cost of emission controls and overestimated how many engines were 

already using these controls. EPA reevaluated the cost impacts associated with establishing 

numeric emission limitations for these engines and determined that the cost impacts would be 

unreasonable given the expected emission impacts both with and without the expectation of use 

of emission control technologies. For example, for 4SRB engines, the annual cost per ton of 

HAP reduced, assuming the engine will have to install emission controls to meet the emission 

limit, is estimated to be $762,000 for a 50 HP engine and $167,000 for a 250 HP engine. For 

2SLB and 4SLB engines at 250 HP, the annual cost per ton of HAP reduced is estimated to be 

$224,000 and $55,000, respectively, assuming the engines will have to install emission controls 

to meet the emission limit. The annual cost per ton of HAP reduced would be $128,000 for a 
162

500 HP 2SLB engine, respectively. According to engine operators, engines that operate on 

landfill gas are predominantly 4SLB. This is consistent with the landfill gas emissions data set 

that EPA used for the final rule. According to EPA’s landfill and digester gas dataset, which 

consists of 176 engines, the typical engine size for landfill gas-to-energy projects is between 

1,000 and 2,000 HP. Aftertreatment controls could in theory be applied to landfill and digester 

gas fired engines. However, siloxanes found in landfill and digester gas fuel foul the catalyst. 

Fouling of the catalyst causes the control device’s ability to reduce HAP to decline rapidly. 

Efforts have been made to pre-treat the fuel in order to remove impurities, but EPA is not aware 

of any technologies that are proven at this point. Therefore, because of feasibility issues in 

applying aftertreatment controls to engines operating on landfill and digester gas fuels, EPA is 

finalizing management practices for all landfill and digester gas engines. 

Engine owners/operators have indicated that most of these smaller area source engines 

are not equipped with the control technologies required to meet these limits. Based on this 

information, EPA determined that management practices for these stationary SI RICE located at 

area sources of HAP are generally available and cost effective is promulgating management 

practices for these engines in the final rule. Additional information regarding this determination 

can be found in the memorandum titled, “MACT Floor and MACT Determination for Existing 

Stationary Non-Emergency SI RICE <100 HP and Existing Stationary Emergency SI RICE 

Located at Major Sources and GACT for Existing Stationary SI RICE Located at Area Sources,” 

which is available from the rulemaking docket. 

5.3 Emergency Engines 
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5.3.1 Comment: Several commenters (36, 48, 74, 77, 79, 81, 86, 88, 90, 96, 97, 99, 112, 118, 

119, 121, 139, 140, 155, 157, 160, 161, 162, 167, 171, 173, 175, 176, 181, 196, 201, 209, 213, 

216, 220, 223, 224, 227, 229, 247, 249, 253, 256) expressed concern with the proposed limits for 

emergency engines. Numerous commenters stated that EPA should adopt management practices 

for emergency engines and not require emission limits from these engines. Emergency engines 

need special consideration, according to the commenter (155) due to minimal operation, and 

commenters 121 and 154 said that EPA should apply section 112(h) of the CAA because of this 

limited operation. Several commenters recommended that emergency engines be subject to only 

work practice standards that limit the number of hours allowed for operation during nonemergency events. 

For many existing engines in the field, add-on control technology is not feasible and not 

compatible with the engine and will cause potential performance problems as well as 

compromising functionality, commenter 121 said. Commenter 154 said that the numeric 

emission limits are not appropriate for emergency engines, because they cannot be met by most 

emergency engines as shown by available emissions test data on emergency engines. If EPA 

keeps emission limits for emergency engines, the commenter (155) thinks that EPA needs to 

provide justification as to the basis for such limits. Commenter 96 said that it is unreasonable to 

require existing emergency engines to meet numerical limits based on the best performing 12 

percent of sources, which consequentially leads to 88 percent of the engines not being able to 

meet the limits without installing some form of controls. EPA correctly concluded that add-on 

controls are inappropriate and too costly for emergency engines, some commenters said, 

including commenters 96 and 253, but the actual rule imposes limits not achievable in many 

cases without add-on controls, therefore forcing emergency engines to add emissions controls or 
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be replaced, which was not the Agency’s intent. Commenter 96 provided in its comments 

various charts for different engine categories of where it has shaded several areas where it 

believes that EPA should replace limits with operational hour limits. See areas marked “b” in 

the charts provided on pages 10, 12, 14, and 18, for diesel, 4SLB, rich burn, and landfill gas 

engines, respectively, of commenter 96’s comments. 

 Commenter 99 said that if EPA decides to go final with emission standards for 

emergency engines, the standards must be such that all properly maintained emergency engines 

can comply. As discussed above, as proposed, emergency engines cannot comply with the 

standards by altering operating characteristics and the commenter 99 explained that there are no 

“knobs” available to “turn down” HAP emissions. The commenter (99) expressed that if EPA 

finalizes the proposed standard for emergency engines it would obsolete many engines in this 

group leading to loss of reliable emergency power, which would be unacceptable to the public, 

will jeopardize public safety, will directly interfere with existing building codes, and a lead to a 

high cost to industry in lost production during emergencies. 

Two commenters (121, 162) said the proposed emission standards for existing emergency 

RICE are overly stringent. Commenter 121 added the proposed standards do not reflect what 

existing engines in this subcategory achieve in practice. The limits are significantly lower than 

the emission limits established for new engines in the 2008 NSPS and in some cases, they appear 

to be more stringent than standards established for comparable future nonroad engines, the 

commenter (121) said. The proposed standards also lack the flexibility of the nonroad programs, 

which typically provide for a selection of engine families and/or emission averaging and trading 

and engine certification, the commenter (121) added. 
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Without seeing which engines are in the specific floors, one commenter (121) was unable 

to perform an effective assessment of whether the proposed MACT limits appropriately reflect 

the average of the top 12 percent. However, test data from several existing emergency engines in 

the commenters’ (121) industry (automotive manufacturing) indicated they are unlikely to meet 

the proposed limits because they either pre-date or were produced to meet the established nonroad engine standards or similar standards that are less stringent than those proposed. The 

commenter (121) said it is likely that these engines will have to be replaced. 

Commenter (121) said that despite EPA’s claims that the agency is not requiring 

performance tests of emergency engines, major sources with existing emergency engines appear 

to have an implicit testing requirement to demonstrate that they comply with concentration 

limits. Such testing could significantly increase the time the typical emergency engine would be 

used in year and impose additional environmental impact and costs. The commenter (121) said 

EPA needs to resolve the conflict between the preamble and the regulatory language and replace 

the emission limits for emergency engines with work practices. Commenter (154) raised similar 

concerns about the apparent requirement for performance testing of emergency RICE due to 

ambiguous rule language and said it should be clarified to explicitly state that such testing is not 

required. Commenter (74) said the rule would require not only initial performance testing, but 

testing every 3 years. Because engine operation for performance testing would likely exceed 

typical operation for operational testing and maintenance, these testing requirements would result 

in increased operation of the engine with a corresponding significant increase in operating costs 

and emissions of other pollutants such as NOx. 

If EPA regulated emergency generators, the numerical limit for emergency engines rated 

greater than 500 HP must be eliminated, according to one commenter (81). It is not reasonable 
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for EPA to propose emissions limits for equipment and then state it does not require or expect 

owners of regulated equipment to test equipment to assure that it meets the those limits. This 

puts the regulated community in a precarious position, and it may cause owners to test their 

engines rather than risk a regulatory inspection that discovers that their equipment is not meeting 

required emission limits. 

One commenter (121) said EPA does not identify which engines were used for the 

proposed floor limit for existing SI emergency engines greater than 500 HP at area sources and 

concluded that GACT work practices are more appropriate for these engines. Assuming that 

EPA relied on the same data as used for emergency SI engines ranging from 50 to 500 HP, the 

commenter (121) is concerned that the floor limit does not reflect the average achieved in 

practice by the best performing emergency engines greater than 500 HP. Given the flexibility 

GACT provides and the limit use of emergency engines, the commenter (121) recommends EPA 

establish work practices and harmonize those requirements for these engines at major sources. 

One commenter (121) said a mandate for add-on controls would impose significant costs 

on engines that are run only an average of 26 hrs/yr. Commenter 48 pointed out that the 

proposed rule was too expensive and of limited benefit noting that emergency engines only run 

during emergencies. Instead, EPA should set management practices such as requirements to 

perform and record routine maintenance, retain copies of the engine manufacturer’s approved 

maintenance schedule or similar maintenance schedule, and mirror those requirements for 

engines located at major sources, according to commenter 121. 

One commenter (81) also disputed the rationale that established a numeric limit that EPA 

expects all emergency engines can meet without installing after treatment controls and, therefore, 

provides no additional environmental benefit. The commenter (81) concluded that EPA should 
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exempt all emergency engines at area sources. Other commenters (119) pointed to the minimal 

environmental benefit of regulating emergency engines and the unreasonable administrative 

burden of regulating such sources. 

One commenter (81) noted that the proposed limit is based on 100 percent load, which 

would seldom occur in the real world. This means the test limit would bear little relation to real 

operating conditions. In addition, testing may put the communication system at risk while the 

tests are being performed. Because few generators are likely installed to handle 100 percent 

loads, owners would likely have to use temporary load banks to meet test conditions. It may be 

necessary to disconnect the emergency engine from the network to test under load bank 

conditions, and the ability of the engine to respond effectively to an emergency situation will be 

reduced. 

 One commenter (81) added that if add-on controls are required to meet the limit, the short 

operating periods of emergency units would not trigger the usefulness of add-on controls. 

 One commenter (121) said EPA should allow owners or operators the option to follow 

either the engine manufacturers’ recommended maintenance schedules or the specific 

maintenance requirements proposed by EPA and that this provision apply to engines at either 

area sources or major sources. 

 One commenter (201) stated that EPA’s reasoning used to apply the MACT for engines 

at major sources as GACT for larger engines at area sources was deeply inconsistent in the case 

of large emergency engines at area sources. The commenter (201) pointed out that EPA decided 

not to require after-treatment controls for emergency engines under 500 HP located at major 

sources because of the low average annual operating time (50 hrs/yr), but did not make the same 

decision for larger emergency engines at area sources despite the same low average annual 
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operating times. The commenter stated that setting the GACT for large emergency engines at 

area sources the same as the MACT for non-emergency engines could not be justified given the 

high cost of the controls (estimated by the commenter (201) to be $4,000 to $20,000 per engine) 

and the low average annual operating time (estimated by the commenter (201) to be 25 to 50 

hrs/yr). The commenter (201) recommended that EPA eliminate numeric emission standards for 

emergency engines greater than 500 HP located at area sources and instead use the management 

practices and associated recordkeeping requirements proposed for small emergency engines 

located at area sources. 

One commenter (223) stated that EPA generators located at area sources should not be 

subject to emission standards under 40 CFR part 63, subpart ZZZZ. The commenter (223) stated 

that EPA is not required to promulgate emission standards for source categories located at area 

sources. The commenter (223) acknowledged the D.C. Court of Appeals ruling (Sierra Club v. 

EPA, 479 F.3d 875, 883 (2007)) on the NESHAP for Brick and Structural Clay Manufacturing 

and Clay Ceramics Manufacturing (which was vacated). The D.C. Court of Appeals ruling 

concluded that EPA’s use of work practice standards instead of emissions floors for certain 

subcategories of ceramic kilns located at major sources was not permitted under section 112(h) 

of the CAA and that EPA’s failure to set emissions reductions floors for certain major source 

brick kiln that do not use pollution control technology violated section 112(d)(3) of the CAA. 

This commenter (223) stated that for area sources under section 112(d)(5) of the CAA, EPA is 

allowed to promulgate alternative standards for “categories and subcategories of area 

sources....the Administrator may, in lieu of the authorities provided in [sections 112(d)(2) and 

(f) of the CAA, which provide, among other things, for the promulgation of emission standards 

for each category or subcategory of major sources and area sources,] elect to promulgate 
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standards or requirements applicable to sources in such categories or subcategories which 

provide for the use of generally available control technologies [(“GACT”)] or management 

practices by such sources to reduce emissions of hazardous air pollutants” (emphasis added). 

The commenter (223) stated that consistent with the Court’s finding in Sierra Club v. EPA, 

which applied to major sources only, EPA is not required under section 112 of the CAA to 

promulgate standards for listed source categories located at area sources, and emergency 

generators located at area sources should not be subject to emissions standards. 

This commenter (223) further stated that it believes it is appropriate to subcategorize 

emergency generators located at area sources under 40 CFR part 63, subpart ZZZZ. The 

commenter (223) cited section 112(d) of the CAA as stating that “[t]he Administrator may 

distinguish among classes, types, and sizes of sources within a category or subcategory in 

establishing...standards” as support. This commenter (223) believes that significant operational 

and economic circumstances governing emergency generators warrant the promulgation of a 

standard for these generators based on management practices rather than emission limits. The 

commenter (223) listed the following circumstances as support for its position: 

• Unlike non-emergency engines, emergency generators are only used during emergency 

situations (provided examples). 

• Because emergency generators are only used during unforeseen and typically infrequent 

emergency situations, their annual emissions are meaningfully lower than those from 

non-emergency engines. Noted that the annual NOx emission from the four emergency 

generators at its West Chester facility, for example, are capped by permit, ensuring that 

such emissions remain below 7.63 tons NOx on an annual basis. 
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• Emergency generators located at area sources are not subject to air quality permitting in 

many cases. The application of an emission standard under 40 CFR part 63, subpart 

ZZZZ could change a state’s current permitting approach toward emergency generators. 

State or interstate permitting authorities may establish more stringent Title V permitting 

requirements than mandated by the CAA, and therefore subject area sources to Title V 

permitting requirements. Furthermore, even in States that elect not to impose Title V 

permitting requirements on these sources, the mere fact that a source is subject to the 

NESHAP program could trigger State-level construction and operating permit 

requirements that otherwise would not apply. 

• It is economically infeasible for large emergency generators located at area sources to 

meet the applicable emission standards in the proposed rule. Table 2b of the proposed 

rule indicates that owners and operators of area source emergency generators greater than 

500 HP are required to limit the concentration of CO in the unit’s exhaust to 40 ppmvd or 

less at 15 percent O2 (including during periods of startup or malfunction). 74 FR 9723. 

Most of these generators would not be able to meet this standard without installing costly 

add-on control devices. The commenter’s (223) generators would need to add-on diesel 

oxidation catalyst technology that would be resistant to damage from mechanical or 

thermal shock and metallurgic erosion typically caused by engines. The cost of reducing 

CO emissions to 40 ppmvd using diesel oxidation catalyst technology for the 

commenter’s four emergency generators (whose combined emissions are limited to 7.63 

tons) would be approximately $33,000 per ton removed. Most facilities do not have the 

ability to account for the additional costs of installing and operating emissions control 

equipment as typical costs of doing business as they typically comprise of facilities that 
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rely on emergency generators for critical systems during emergencies and are not 

involved in manufacturing-based operations (e.g., hospital, commercial office buildings, 

and data centers). 

Based on the aforementioned circumstances, the commenter (223) concluded that EPA failed to 

recognize that facilities that depend on emergency generators to provide power for critical 

systems during emergencies would be burdened by having to comply with the proposed emission 

standards applicable to emergency generators greater than 500 HP, unlike their counterparts in 

the manufacturing/industrial sector. This commenter (223) asserted that, as with other engines 

that EPA concluded GACT to be management practices, these engines should also be 

subcategorized and GACT should be management practices. 

 Finally, this commenter (223) expressed that EPA failed to evaluate existing emergency 

RICE located at area sources in determining the basis and level of the proposed emission 

standards. The commenter (223) opined that if EPA had evaluated emergency RICE as a 

subcategory of engines at area sources (rather than by engine size and selected industry-type, 

without considering the costs of compliance specific to emergency engines), EPA would not 

have been able to have identified an appropriate emission standard for emergency RICE at area 

sources. 

 One commenter (76) supported using an equivalent MACT floor for emergency SI and 

CI engines between 50 and 500 HP using catalyst type control technology. The commenter (76) 

noted that the determination of the emission limit assumed that SI emergency and SI nonemergency engines are similar in operation and emissions. The commenter (76) also noted that 

the limits are based on limited data and no formal request for information was made. In addition, 

the commenter (76) noted that for engines operating less than 100 hours will require extensive 
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testing to establish startup and shutdown emissions. The commenter (76) supported the 

determination of emission limits without add-on controls for emergency CI engines between 50 

and 500 HP located at major sources. 

Response: : EPA reviewed the information submitted by the commenters and determined that it 

would be appropriate to require management practices for all emergency stationary SI engines at 

area sources. Because these engines are typically used only a few number of hours per year, the 

costs of emission control are not warranted when compared to the emission reductions that 

would be achieved. The proposed numeric emission levels are not GACT for emergency engines 

at area sources. Such engines rarely if ever use the type of emission controls that might have 

been necessary for many engines to meet the numeric standard, and such engines are rarely if 

ever subjected to emissions testing. Therefore, EPA determined that GACT for all stationary 

emergency engines at area sources is the use of management practices. 

EPA also analyzed the types of engines that were included in the area source category 

listing for stationary RICE. As a result of this analysis, EPA determined that emissions from 

existing stationary emergency engines located at residential, commercial, and institutional 

facilities that are area sources of HAP were not included in the 1990 baseline emissions 

inventory that was used as the basis for the listing of source categories needed to ensure that 90 

percent of area source emissions are regulated. Existing stationary emergency engines located at 

residential, commercial, and institutional facilities that are area sources are therefore not subject 

to this regulation. 

 For stationary emergency engines at major sources, EPA determined that it is not feasible 

to prescribe or enforce an emission standard because the application of measurement 
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methodology to this class of engines is impracticable due to technological and economic 

limitations. A more detailed discussion of this determination can be found in the memorandum 

entitled “MACT Floor and MACT Determination for Existing Stationary Non-Emergency SI 

RICE <100 HP and Existing Stationary Emergency SI RICE Located at Major Sources and 

GACT for Existing Stationary SI RICE Located at Area Sources.” EPA determined that it is 

impracticable to test stationary SI emergency engines using the test procedures specified in 

subpart ZZZZ because using these procedures would increase the required number of hours of 

operation beyond the routinely scheduled reliability testing and maintenance operation, thereby 

increasing emissions. While emergency engines have periods of operation for scheduled 

maintenance and reliability testing, those periods are usually several hours shorter than the 

number of hours that would be required to run the necessary emissions tests under subpart ZZZZ. 

CARB conducted a survey of stationary emergency engines in 200215 to determine the average 

number of hours that stationary emergency engines operate. The average hours of operation for 

maintenance and testing were 22 hours per year, which is less than two hours per month. For the 

engines that CARB surveyed, 86 percent operated less than 30 hours/year for testing and 

maintenance. Thirty percent operated less than 10 hours/year. National Fire Protection 

Association (NFPA) codes require that stationary engines that are used for emergency purposes 

are run 30 minutes per week (27 hours per year) for maintenance and testing purposes. It is 

impracticable to test emergency stationary engines as a result of emergency operation because 

emergencies are unplanned events and implementation of the procedures specified in subpart 

ZZZZ require advance planning before tests are conducted. In an emergency, the owner/operator 

                                                           

15 California Air Resources Board Staff Report: Initial Statement of Reasons for Proposed Rulemaking. Airborne 

Toxic Control Measure for Stationary Compression Ignition Engines. Stationary Source Division, Emissions 

Assessment Branch. September 2003. 
174

does not have the advance planning time necessary to implement subpart ZZZZ. In addition, it 

would be costly to test existing stationary SI emergency engines at major sources. 

 EPA expects that these changes from the proposed rule address the concerns expressed 

by the commenters about the requirements for stationary emergency engines. Regarding the 

comments pertaining to performance testing for emergency engines, EPA did not intend for the 

rule to require performance testing for emergency engines. The final rule does not contain any 

performance testing requirements for emergency engines. 

5.3.2 Comment: One commenter (96) pointed out that there are no standards for emergency 

engines above 500 HP at major sources, but that emergency engines less than 500 HP and 

emergency engines above 500 HP at area sources have emissions requirements. The commenter 

(96) asserted that any standards or work practices applicable to emergency engines should be 

consistent across size classes and should not include emission standards during startup 

operations. 

Response: This rulemaking and the one developed in 2004 for stationary engines above 500 HP 

at major sources were developed at different times. While EPA has attempted, to the degree 

possible and justified, to maintain consistency across rulemakings affecting the same or similar 

engines, recent court decisions regarding the way that MACT floors are determined and the 

startup/shutdown/malfunction exemptions in NESHAP have affected the way EPA develops and 

sets standards since the standards for stationary emergency engines above 500 HP at major 

sources were promulgated in 2004. For stationary emergency engines at area sources and less 

than 500 HP at major sources, EPA is statutorily required to set requirements. As discussed in 
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the response to comment 5.3.1, stationary emergency engines have to meet management or work 

practice requirements in the final rule. 

5.4 Small Engines 

5.4.1 Comment: Several commenters (96, 157, 216, 262) expressed opposition to EPA’s 

proposal to have emission standards apply to small engines. Three commenters (96, 157, 216) 

said that EPA should not finalize emission limits for engines less than 100 HP. One commenter 

(157) supported EPA’s proposed no compliance requirements beyond complying with the 

manufacturer’s instructions and no testing requirements for these engines. One commenter (96) 

argued that stationary engines that are less than 100 HP should be exempted from numerical 

HAP emission standards for some of the same reasons as those discussed by the commenter on 

the issue of emergency engine standards. In the commenter’s (96) opinion, it is not cost effective 

to install add-on controls on small engines or to purchase a new engine. The majority of engines 

in this size range are operated for intermittent household or other infrequent use and emissions 

are naturally limited, the commenter (96) said, and low emissions do not justify the costs 

associated with requiring a numerical HAP limit. As stated, commenter 96 is opposed to 

numerical emission limits for engines less than 100 HP and provided in its comments charts for 

different engine categories of where it has shaded several areas where it believes that EPA 

should replace limits with manufacturer’s engine maintenance. See areas marked “c,” “d” and 

“f” in the charts provided on pages 10, 12, 14, and 18, for diesel, 4SLB, rich burn, and landfill 

gas engines, respectively, of commenter 96’s comments. Finally, commenter 96 added that a 2 

ppmvd limit for formaldehyde is not achievable by diesel engines with a catalyst operating at 90 
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percent efficiency, catalysts are not cost effective for small engines, and 2 ppmvd is difficult to 

measure in lab conditions and impracticable in field measurements. 

One commenter (262) stated that because of how EPA conducted its MACT floor 

analysis, small engines may be forced to install add-on controls because the MACT floor was 

determined by the best 12 percent of engines. The commenter (228) is concerned that the 

proposed standards for RICE less than 50 HP will not meet the District of Columbia Circuit’s 

test for “work practice standards” set forth in the Sierra Club v. EPA (Brick Indus.), 479 F.3d 

875 (D.C. Cir. 2007), which allows work practice standards “only if measuring emission levels is 

technologically or economically impracticable.” The commenter (228) stated that emissions 

measurement likely meets these standards, but does not believe that measurement is 

economically practicable for a small unit as the cost of measurement will likely exceed the value 

of the unit itself. The commenter (228) urged EPA to exclude small sources from the category. 

Response: EPA has reanalyzed its proposed standards based on the information and data 

presented and EPA concludes that it is not feasible within the context of this rulemaking to 

prescribe emission limitations for existing stationary SI engines smaller than 100 HP located at 

major sources, because the measurement of emissions from these engines is not practicable due 

to technological and economic limitations. In order to measure the emissions from these engines 

on a ppmvd at 15 percent O2 basis, the following test methods are required: EPA Method 1 or 

1A for selection of sampling ports; EPA Method 3, 3A, or 3B for determining the O2

concentration; EPA Method 4 for measuring the moisture content, EPA Method 10 or ASTM 

D6522-00 (2005) for measuring the CO concentration; and EPA Method 320 or 323 or ASTM 

Method D6348-03 for measuring the formaldehyde concentration.. These test methods require 
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the sample point to be a certain distance between the engine and the exhaust. Because engines 

below 100 HP often have exhaust pipes with very small diameters and lengths, stack testing 

using these methods could require a modification or extension of the exhaust pipe to accomplish 

the test. The cost to do the testing ranges from approximately $1,000-$2,000 depending on the 

method used. The cumulative cost of testing existing stationary non-emergency engines below 

100 HP at major sources would be high. EPA estimates that there are more than 67,000 of these 

engines and to test these engines could cost as much as $135 million. Given the cost of the 

testing itself, the physical adjustments necessary to accomplish the test, and the particular 

circumstances pertaining to stationary engines below 100 HP, we believe that the application of 

measurement methodology to this class of engines is not practicable due to technological and 

economic limitations. Therefore, EPA is promulgating work practice standards for these 

engines. Additional detail regarding this analysis can be found in the memorandum entitled 

“MACT Floor and MACT Determination for Existing Stationary Non-Emergency SI RICE <100 

HP and Existing Stationary Emergency SI RICE Located at Major Sources and GACT for 

Existing Stationary SI RICE Located at Area Sources.” 

5.4.2 Comment: One commenter (76) asked how EPA established standards for less than 50 HP 

engines. The commenter (76) believes there is very limited data for these engines. The 

commenter (76) believes that the emission standards in Tables 1 and 2 in the preamble should be 

less than 100 HP instead of less than 50 HP engines. The commenter (76) further said that the 

proposed MACT floor for engines less than 50 HP is based on limited data and asked what is the 

percentage of these engines in the U.S. The commenter (76) asked if test data for this 

determination is available in the docket. 
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Response: EPA explained in the preamble to the proposed rule and in supporting documentation 

available from the rulemaking docket how the standards were developed for small engines less 

than 50 HP. See page 9706 of the proposed rule Federal Register notice and memoranda titled 

“Above-the-Floor Determination for Stationary RICE” and “Subcategorization and MACT Floor 

Determination for Stationary Reciprocating Internal Combustion Engines ≤500 HP at Major 

Sources” in Docket Number EPA-HQ-OAR-2008-0708. EPA has acknowledged that it had 

limited emissions data at the time of proposal; however, having limited data available does not 

exempt EPA from developing requirements. During the subcategorization determination for the 

final rule, EPA determined that a cutoff of 100 HP was the appropriate size to distinguish small 

existing stationary engines. EPA documents this in the memorandum “MACT Floor and MACT 

Determination for Existing Stationary SI RICE ≤500 HP Located at Major Sources.” The 

percentage of existing stationary engines that are less than 50 HP (or 100 HP) can be found in 

the memorandum titled “Impacts Associated with NESHAP for Existing Stationary SI RICE” 

available from the rulemaking docket. 

5.5 Landfill/Digester Gas Engines 

5.5.1 Comment: Several comments (57, 58, 83, 96, 99, 142, 149, 160, 191, 202, 206, 213, 260, 

262, 265, 268) provided input on the proposed provisions for landfill and digester gas engines. 

A few commenters (96, 99, 265, 268) noted EPA’s assertion in the preamble to the proposed rule 

regarding the feasibility of applying aftertreatment controls to landfill and digester gas fired 

engines where siloxanes in the fuel can foul fuel systems, combustion chambers, and post-
179

combustion catalysts and agreed with that. The commenter (96) said that in its experience, the 

most effective way of controlling HAP emissions from landfill and digester fueled sources is to 

control the fouling of the fuel system and combustion chamber by following manufacturer’s 

maintenance requirements. The commenter (96) recommended that landfill and digester gas 

engines should initially be required to be maintained according to the engine manufacturer’s 

maintenance practices and upon reconstruction be subject to the VOC standards for landfill and 

digester gas engines under the SI NSPS. If these engines will be subject to standard prior to 

reconstruction, something the commenter (96) does not recommend, the standard should be equal 

to the VOC reconstruction standard in the SI NSPS or less stringent. The commenter (96) also 

said that it is most appropriate in this case to use VOC over CO to maintain consistency. 

Commenter 99 also agreed that VOC should be used instead of CO for these sources. 

Commenter 99 added that landfill and digester gas engines deserve special consideration since 

these engines serve an important function of converting waste gases into useable energy, which 

reduces greenhouse gas emissions among other things. 

A few commenters (57, 83, 121, 206, 262) questioned the need for emission limits for 

landfill and digester gas engines. One commenter (57) stated that for existing and proposed 

landfill and digester gas fired engines at area sources, where MACT does not apply but GACT 

applies, EPA should very carefully document the need for the regulation and the ability of 

existing technologies to meet the proposed standard. Commenter 57 believes EPA should 

eliminate the regulation of both new and existing landfill gas fired and digester gas fired engines 

unless a well documented and significant list of sources can be shown to meet the proposed 

standard. 
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Commenter 121 said EPA’s proposed emission limits for existing engines burning 

landfill/digester gas are flawed, and work practices are more appropriate for engines in this 

subcategory at major and area sources. EPA’s proposed limit is significantly more stringent than 

the NSPS limit. Given that the NSPS was promulgated in 2006, the commenter (121) fails to see 

how the floor data can support a limit that is 30 percent higher than the NSPS. The MACT floor 

memo does not explain whether the CO data for the landfill/digester gas floor is in the Emissions 

Database or whether there is a separate database. There is no information on whether the 

engines included in the “latest information” are manufactured prior to 2006. The commenter 

(121) was unable to replicate EPA’s floor analysis, and cannot confirm whether the floor reflects 

the average of the top performing sources in the subcategory. 

One commenter (213) said that it supports keeping the subcategory of landfill and 

digester gas engines and the provision that allows these engines that are less than 500 HP to 

certify compliance with the NESHAP by following O&M requirements (e.g., change oil and 

filters every 500 hrs, etc.) The commenter (213) requested that this provision be provided for all 

landfill and digester gas engines regardless of size. 

Commenter (57) stated that if the proposed rule is promulgated as written, it is likely to 

cause the closure of most or all existing landfill gas fired engine facilities and the cessation of 

installation of new such facilities because the currently available engine technology cannot meet 

the 177 ppm CO standard. According to the commenter (57) this would be a great shame, as 

landfill gas energy production is an important method of landfill gas control and (referring to 

EPA's Landfill Methane Outreach Program) one which the EPA has devoted considerable time 

and money to promote. 
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Commenter 83 had similar concerns and stated that if EPA proceeds with the proposed 

NESHAP for landfill gas-powered RICE, it will be inconsistent with the efforts of Federal and 

State agencies to reduce GHG emissions, and promote renewable energy and distributed 

generation requirements. This commenter (83) expressed that landfill and digester gas have 

always been used as a significant source of additional renewable energy to reduce GHG 

emissions and displace dependence on fossil fuels. Examples provided by the commenter 

include: (1) EPA’s Landfill Methane Outreach Program, (2) California Executive Order S-06-

06, signed by Governor Schwarzenegger in April 2006, sets a target for maintaining and 

enhancing bio-energy production (including the use of landfill and digester gas) in California—

mandates the state meet a 20 percent target within the established state goals for renewable 

generation for 2010 and 2020; and (3) California’s recently enacted AB-32, which directs the 

state to reduce its GHG emissions to 1990 levels by the year 2020. This commenter (83) also 

provided that the California Climate Action Team has identified landfill gas as a significant 

source of potential additional renewable energy that could be used to displace our nation’s 

dependence on non-renewable energy sources, and the California Integrated Waste Management 

Board is actively engaged in identifying ways that such projects can be expanded and enhanced. 

The commenter (83) argued that any action to restrict or discourage use of landfill or digester gas 

to energy projects would be inconsistent with California’s multiple and integrated efforts to 

increase the use of renewable fuels. 

One commenter (83) stated that the landfill NESHAP finalized in 2003 addressed HAP 

emissions from engines using landfill gas. That rule determined that GACT for area source 

(non-NSPS/EG) landfills was no control. This commenter (83) believed that the issue of toxic 

emissions from landfills already has been resolved and that there is no need for EPA to further 
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address the issue in the proposed rule. The commenter (83) further stated that EPA has 

recognized in its revised AP-42 guidance for landfills that toxics in landfill gas have been 

decreasing with time, suggesting that there is no reason to reconsider the determinations already 

made in the landfill NESHAP. 

One commenter (83) opined that subjecting landfill and digester gas-fired RICE to the 

proposed new requirements would eliminate numerous and necessary energy projects. This 

commenter (83) stated that the proposed rule appears to include an exemption for landfill and 

digester gas-fired RICE located at major sources, but does not exempt stationary RICE located at 

area sources. The commenter (83) recommended that the exemption be extended to engines at 

area sources. The commenter (83) opined that, without such an exemption from the rule, since 

the proposed rule is for existing RICE, the rule would force existing renewable energy projects to 

shut down, resulting in flaring of landfill and digester gas. 

One commenter (83) justified exemption of landfill and digester gas fired RICE from the 

proposed rule for the following reasons: (1) Traditional fuel sources (e.g., commercial natural 

gas) differ from non-traditional fuel sources such as renewable landfill and digester gas; (2) 

impurities (e.g., siloxanes, sulfur compounds) in the landfill gas vary from site-to-site and can 

affect RICE emissions; (3) setting standards at the emission levels in the NESHAP, which appear 

only to be attainable with landfill gas RICE under best-case scenarios, EPA would be preventing 

the beneficial use of landfill gas as a renewable resource. This commenter (83) stated that 

regulating landfill and digester gas fired RICE under the proposed rule would discourage 

investment in landfill gas-to-energy technologies from lenders who will not fund a project 

without a guarantee that an engine will consistently and reliably meet the standards prescribed by 

the proposed rule. Currently, the commenter (83) reports that it has been unable to identify any 
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engine manufacturer who will warranty their engines will consistently and reliable meet the 

standards prescribed by the proposed rule. 

Because of the importance of encouraging the use of landfill gas as a renewable green 

energy fuel, the commenter (121) urges EPA to impose maintenance standards on all landfill gas 

engines regardless of the HP rating or whether the engine is located at a major or area source. 

EPA should not prevent engines from combusting landfill gas because they are incapable of 

complying with an emission limit. If EPA does impose a limit, it should harmonize it with the 

recently promulgated NSPS, 40 CFR 60 subpart JJJJ. The commenter (121) supports 

maintenance standards for this subcategory of engines and recommends that the owner or 

operator have the option to follow the engine manufacturer’s approved maintenance schedule or 

follow the maintenance schedule specified in the proposed rule. 

One commenter (206) expressed concern that the proposed RICE NESHAP would be 

imposing standards on landfill gas RICE that would discourage continued operation of existing 

renewable energy facilities that utilize landfill gas RICE. The commenter (206) believed that the 

excessive compliance obligations associated with the proposal would result in landfill gas to 

energy projects ceasing operations, thereby eliminating a significant opportunity for the 

continued reduction of GHGs through the offset of fossil fuels. This commenter (206) asserted 

that this result would be inconsistent with the pending Climate Change and Energy legislation.16

One commenter (262) stated that EPA has not provided data to justify a CO standard of 

177 ppmvd, because technology does not exist to reduce emissions of landfill gas RICE of the 

type that would be affected, because the proposed rule would require expensive emissions 

monitoring and source testing, and, overall, the proposed rule would reduce the production of 

                                                           

16 American Clean Energy and Security Act of 2009, HR 2454, 2009.
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electricity from a reliable, affordable, dispatchable, high capacity factor renewable resource. The 

commenter (259) stated the proposed rule could require Continuous Emissions Monitoring 

System (CEMS) at a cost of $15,000, and require annual source testing at such facilities at a cost 

of $20,000. The commenter (259) stated that these additional costs would limit the viability of 

renewable landfill gas-to-energy plants and increase costs to consumers. The commenter (259) 

proposed that EPA can make either of two potential changes to the proposed rule: set a GACT 

instead of a MACT standard for landfill gas RICE; or the agency can extend the exemption from 

CO regulations available for landfill gas RICE at major sources to the same engines at area 

sources. 

One commenter (202) supported the proposed provision that would allow landfill and 

digester fueled engines less than 500 HP to certify compliance by following prescribed operation 

limitations and maintenance practices and recommends that this provision be applied to all 

engines of this category regardless of their size because there are no viable controls for engines 

that combust landfill or digester gas. This commenter (202) stated that landfill and digester 

gases contain impurities that can foul add-on catalyst controls rendering them inoperable. 

One commenter (58) stated that in regards to the proposed emission limits of 177 ppm 

CO for landfill gas fired engines, the EPA should consider only recently permitted engines when 

considering what is achievable by current technology, because the emission rates for CO have 

increased in recent years as manufacturers have been required to lower the NOx emissions. The 

commenter (58) worried that if EPA bases the possible CO emissions on older units, the newer, 

currently available units will not be able to meet those limits because they have been designed 

for lower NOx requirements. 
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One commenter (160) representing the interests of nearly all publicly owned treatment 

works agencies nationwide provided support for the use of CO as surrogate for HAP, which it 

opined will simplify compliance and reduce costs for utilities. However, this commenter (160) 

felt that the CO emissions limits are too stringent for existing RICE, especially for those engines 

that use landfill or digester gas and those that are used for emergency situations. The commenter 

(160) stated that low emissions levels may be an appropriate requirement for new engines, but 

the cost to retrofit existing digester gas engines and install emissions controls has not been 

justified in the proposed rule. The commenter (160) suggested that EPA conduct a more-detailed 

analysis for digester gas engines. This commenter (160) stated that new emissions controls on 

existing engines are likely to cost millions of dollars for each utility and opined that utilities 

should be encouraged to continue using their existing digester gas engines, rather than face a 

situation where it is more cost-effective to purchase power from an electric utility and to waste a 

valuable fuel source by flaring the digester gas. Because of the technical problems associated 

with emissions controls for wastewater utilities (acknowledged by the EPA), EPA should either 

raise the CO emissions limits or substitute an operation limitations and maintenance practices 

standard for all existing digester gas RICE, as EPA has proposed for the area source RICE 

subcategory landfill/digester gas (50< HP < 500). The commenter (160) supports this 

maintenance and inspection standards and would support an identical or similar requirements for 

other subcategories of digester gas engines. 

One commenter (206) referred EPA to other information available for landfill gas RICE 

from Best Available Control Technology (BACT) determinations, AP-42, and NSPS 

rulemakings that show that CO emission limits that have been achieved in practice for the top 
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performing sources are in excess of the proposed MACT floor for landfill gas-fired RICE. The 

commenter (206) cited detailed information from the following sources: 

• “Stationary Spark Ignition Engines Using Landfill and Digester Gas” (Test results show 

that engine-out CO levels in the United States range from about 1.8 to about 2.5 g/HP-hr, 

which is also consistent with permit limits (Parise, T., Adams, L. Alpha-Gamma 

Technologies, Inc., Stationary Spark Ignition Engines Using Landfill and Digester Gas, 

Memorandum to Jamie Pagan, EPA Energy Strategies Group, December 11, 2007.)

• “Summary of State/Local Requirements Internal Combustion Engines” (Provides a 

summary of SCAQMD concentration limits for biogas engines which lists the current CO 

concentration limit of 2000 ppmvd (at 15 percent O2) and a CO limit of 250 ppmvd [at 15 

percent O2] effective July 1, 2012 [contingent upon the outcome of the mandated 2010 

technology review that will evaluate the feasibility of the 250 ppmvd limit]). (Nelson, B. 

EC/R Incorporated, Summary of State/Local Requirements for Stationary Internal 

Combustion Engines, Memorandum to Jamie Pagan, EPA OAQPS/SPPD/ESG, July 18, 

2008.)

• “Revisiting BACT for Lean Burn Landfill Gas Fired Internal Combustion Engines,” 

Frazier, R., Allen, C. White Paper, BAAQMD, February 26, 2009. (The BAAQMD 

concluded that the BACT CO limits achieved in practice within California as well as 

other states was between 2.1 and 3.02 g/HP-hr. The CO limits established by BAAQMD 

in the White Paper range from 2.1 to 2.5 g/HP-hr and may float up tot not to exceed 

emission limits between 3.0 and 4.2 g/HP-hr.)

• Background Information Document for Updating AP-42 Section 2.4 for Estimating 

Emissions from Municipal Solid Waste Landfills, September 2008. Eastern Research 
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Group, Inc., Prepared for Susan Thorneloe of the United States Environmental Protection 

Agency. (The emission factors in the Background Information Document are consistent 

with the Memorandum identified in the preceding bullet.)

• Standards of Performance for Stationary Spark Ignition Internal Combustion Engines 

(NSPS, 40 CFR part 60, subpart JJJJ). (Requires landfill/digester gas engines 

manufactured after the applicable dates to meet a CO emission limit of either 5.0 g/HP-hr 

or 610 ppmvd [at 15 percent O2]; states that “trying to control the CO in these engines 

beyond 5.0 g/HP-hr may cause instability and could affect the ability of the engine to 

reduce NOx levels.”).

• RACT/BACT/LAER Clearinghouse (RBLC). (RBLC Database entries with the BACT 

as the basis for the CO emission limit ranged between 2.0 and 3.0 g/HP-hr. The 

commenter (206) considers the 2.0 g/HP-hr to be an outlier as most of the BACT 

emission limits in the RBLC Database for CO were 2.75 g/HP-hr.)

The commenter (206), asserted that, according to the RIA for this rule, EPA determined 

that the MACT floor for stationary landfill/digester gas greater than or equal to 50 HP is the level 

achievable by existing landfill and digester gas engines operating without add-on controls. The 

commenter (206) stated that the logic of establishing the MACT floor for existing engines by 

considering recent test data and performance, and not emission (or permitted) limitations, is 

inconsistent with section 112(d)(3)(A) of the CAA. An “emission limitation,” according to the 

commenter (206) is not an achieved emission rate from a stack test, but a “requirement 

established by the State or the Administrator which limits the quantity, rate, or concentration of 

emissions” (See section 302(k) of the CAA). 
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The commenter (206) also reported that the MACT floor calculation for landfill and 

digester gas engines was not reproducible. The commenter (206) stated that the December 11, 

2007 memorandum that provides the data for 18 landfill RICE sources includes 9 sources with 

identified CO emissions in g/HP-hr emissions. The lowest figure is 1.74 g/HP (the remaining 

facilities show CO g/HP-hr values of 1.77, 1.95, 1.83, 2.44, 1.87, 1.9, 1.9, 2.36, 1.76, 1.99, 

2.173, 2.154, 2.030, 2.358, 2.26, 2.18, 2.33, 2.19, 2.392, and 1.74). The second table has six 

additional sources identified, with four of the sources having CO emissions identified in g/HP-hr 

of 1.76, 3.728, 7.027, 3.728, and 7.121). Based on EPA methodologies for converting 

concentration based limits to output based limits, the emission limitation of 177 ppmvd (at 15 

percent O2) is equivalent to approximately 1.44 g/HP-hr. Accordingly, the commenter stated that 

none of the stack test results used by EPA to establish the MACT floor can be achieved in 

practice, based on the stack test results, which were expressed in g/HP-hr. This commenter (206) 

further stated that, in examining Attachments 1 and 2 of the December 11, 2007 memorandum, 

three sites have emission limits expressed in terms of ppm concentration. Test results from four 

landfill gas-fired engines at the three sites indentify CO ppm concentrations of 228.6 ppm, 215.7, 

560 ppmv and 568 ppmv. Once again, the commenter (206) stated that none of the sites 

achieved the proposed MACT floor standard of 177 ppmvd (at 15 percent O2) in practice. The 

commenter (206) reported that the remaining stack tests for two facilities express results in lb/hr 

that could not be converted without examination of the underlying stack tests or additional data. 

Other commenters (265, 268) reported that the concentration (and mass emission rates) of 

CO that is emitted from landfill gas-fueled RICE does not remain constant with time. These 

emissions increase with increased equipment operating hours, even with the most stringent 

maintenance schedule. The commenters (265, 268) believed that EPA’s limited set of data used 
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to establish the RICE CO emission limit of 177 ppmvd corrected to 15 percent O2 (equivalent to 

a mass emission rate of approximately 0.7 g/HP-hr for the operation of CAT G3516 engine and 

1.5 g/HP-hr for the operation of the CAT G3520 engine) was insufficient to develop a full 

understanding of CO emissions from existing landfill gas fueled RICE. The commenters (265, 

268) pointed out specific CO emission variations, which exist as a function of fuel quality or 

engine operating hours, evident in the data set use by EPA to develop the proposed emission 

standard. The commenters (265, 268) stated that it has been operating landfill gas fueled RICE 

for over 15 years and has been required to perform numerous compliance/performance tests on 

this equipment (which is maintained to manufacturer’s specifications and industry standards). 

Comparing EPA’s proposed standard of 177 ppmvd corrected to 15 percent O2 , CO emission 

test results from its facilities and others, the commenter reported the following: 

• CAT G3516 and CAT G3520C RICE CO emission compliance results: None of the 

presented values demonstrate compliance with the proposed CO emission concentration 

limit. 

• Jenbacher RICE CO emission compliance test results: Only one of the 11 test results 

presented for this equipment appears to demonstrate compliance with the proposed CO 

emission concentration limit. 

The commenters (265, 268) opined that the results of the 52 area source tests assembled 

by EPA are an extremely limited set of data that does not accurately represent the levels of CO 

emissions that are exhausted from landfill gas-fueled RICE (and therefore inappropriate for 

standard development process). Attachment 2 of both of their letters included CO emission rate 

data by engine and HP rating. Innovative Energy Systems provided more comprehensive data 

that included the same data provided by Landfill Energy Systems. As indicated later in this 
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document, when these commenters (265, 268) compared EPA’s proposed RICE CO emission 

concentration limit of 177 ppmvd corrected to 15 percent O2, most of the compliance test CO 

emission concentrations did not meet EPA’s proposed standard for landfill gas-fueled RICE. 

A few commenters (83, 206) expressed concern with the data used to set the standards for 

landfill and digester gas engines. One commenter (83) expressed that the data used in the 

proposed rule to develop the landfill and digester gas-fired engine emission limits did not meet 

the transparency and technical requirements of the Data Quality Act (Public Law 106-554 

section 515). The commenter (83) stated that the data did not appear to be consistent with the 

information developed by the Bay Area Air Quality Management District (BAAQMD) as part of 

its revised BACT standard for landfill gas RICE (included as an attachment to the comment 

letter). The commenter (83) reported that for engine categories other than landfill and digester 

gas-fired engines, EPA at least provided data that identified the number of tests reviewed or the 

number of tests used to set the MACT floor. This commenter (83) stated that without this data, 

reviewers cannot properly analyze the proposed rule and its effects and it requested that this data 

be made available before a final rulemaking covering landfill and digester gas RICE is 

promulgated. 

The commenter (83) recommended that the EPA review the work of the BAAQMD 

regarding landfill gas-fired RICE (attached to its comment letter) when establishing BACT for 

RICE. The document states that RICE using landfill gas as fuel “generally perform at their best 

after overhaul events and that combustion performance tends to deteriorate as siloxane deposits 

form throughout the combustion surfaces. Notwithstanding this, source test histories are not 

extensive enough to show consistent trends demonstrating this deterioration, although there is 

ample evidence that significant variation exists around the Bay Area.” This document also finds 
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that “BACT for NOx and CO should be paired standards, and no longer evaluated separately.” 

The commenter (83) stated that the document concludes that CO limits for landfill gas-fired 

RICE should be as high as 3.4 to 3.9 g/HP-hr (over 2 times the proposed NESHAP). The 

commenter (83) opined that EPA’s information that landfill gas RICE can meet the proposed 

NESHAP limit is not reflective of actual conditions. 

Similarly, commenter 206 said that quality, objectivity, and reliability of the data used to 

establish emissions limits for landfill gas fired engines is unknown, and EPA has relied on an 

insufficient quantity of CO and HAP data for purposes of establishing a MACT floor for landfill 

gas-fired engines. The commenter (206) requested that, in order for EPA to comply with the 

March 9, 2009 Presidential Memorandum and its own data quality guidelines, and in order to 

comply with the proper MACT floor setting process under the CAA, EPA should defer 

publication of the new CO emission limit for landfill gas-fired RICE until such time that high 

quality data seta are available to support accurate, reliable and unbiased factors. The commenter 

(206) provided the following as support for its position: 

• The information EPA relied upon to establish the MACT floor for landfill gas-fired 

engines was not readily apparent from a review of the Emissions Database contained in 

the docket for the proposed rule (EPA-HQ-OAR-2002-0059). The database only 

contains information from a single test report in 1988 that does not address CO 

emissions. This commenter (206) concluded that EPA appeared to rely on information 

developed under Docket No. EPA-HQ-OAR-2005-0030, including a December 11, 2007 

memorandum that utilizes test results from engines at 18 landfills and concludes that no 

further controls are required for the landfill-gas-fired RICE. The commenter (206) 

opined that there was an insufficient number of landfill gas-fired engines and sites 
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considered for the MACT floor, and the test results used were heavily-biased California 

sites, and was not directly referenced in the proposed rulemaking. The commenter (206) 

argued that with the EPA being required to set an emission limit based on the emission 

limits associated with the top 12 percent of performing sources, it is important for the 

dataset to be representative and reliable. 

• Based on a review of the EPA Landfill Methane Outreach Program database, 

approximately 276 landfill gas fired engine projects are currently operational in the 

United States. (http://www.epa.gov/lmop/proj/index.hem#1) and setting a MACT floor 

based on 18 sets of engine data is contrary to the Information Quality Act and EPA 

guidelines, as well as the CAA. This commenter (206) stated that at least 37 landfill gasfired engine facilities were identified in the EPA 2002 Emissions Database. 

• In regards to transparency and quality of the data used to establish the MACT floor for 

landfill gas-fired engines, the information provided in the January 21, 2009 and 

December 11, 2007 memoranda and the Emission Database is insufficient and it is 

impossible to assess whether the data is representative. It is unclear from the January 

memorandum what information EPA relied on from the “recently obtained test reports” 

in establishing the MACT floor (contrary to EPA guidelines under the Information 

Quality Act). 

Two commenters (265, 268) stated that control requirements for existing and new 

stationary RICE, which combust landfill gas, with a site rating of more than 500 brake HP 

located at major sources of HAP are less stringent than those promulgated and proposed for new 

and existing stationary RICE, which combusts landfill gas, with a site rating of more than 500 

brake HP located at area sources of HAP. The commenters (265, 268) requested that control 
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requirements for existing stationary RICE, which combust landfill gas, with a site rating of more 

than 500 brake HP located at area sources of HAP consider the applicability of GACT or 

management practices and not be more stringent than those established for new stationary RICE 

located at area sources of HAP (i.e., a CO emission rate limit of 5.0 g/HP-hr). 

Three commenters (142, 149, 260) expressed concern over the requirements for landfill 

and digester gas engines. One commenter (260) was concerned over the seemingly inconsistent 

requirements that apply to landfill and digester gas engines. The commenter (206) requested that 

the “limited requirements” for certain existing landfill gas RICE within the current and proposed 

NESHAP RICE apply universally to existing landfill gas RICE. The commenter (206) explained 

that the proposed NESHAP RICE includes a specific change to 40 CFR part 63.6590(b)(3) that 

would allow for continued “limited requirements” for existing landfill gas RICE with a site 

rating of more than 500 HP located at major sources of HAP, but that this does not translate to 

other landfill gas-fired engines (e.g., existing landfill gas RICE at area sources of HAP and RICE 

with a site rating less than or equal to 500 HP located at major sources of HAP remain subject to 

the full requirements of NESHAP RICE). This inconsistency of handling landfill gas RICE 

appears again in 40 CFR part 63.6602 which requires compliance with the emission limitation 

(of 177 ppmvd CO or less at 15 percent O2) within Table 2c of the proposed rule for existing 

RICE with a site rating of equal to or less than 500 HP located at a major source of HAP. 

However, 40 CFR part 63.6603 requires existing stationary RICE located at an area source of 

HAP to comply with the limitations at Table 2d of the proposed rule. Table 2d of the proposed 

rule imposes management practices for landfill gas engines greater than 50 HP and less than or 

equal to 500 HP. The same Table 2d of the proposed rule also includes a limit for CO in the 

stationary RICE exhaust of 177 ppmvd or less (at 15 percent O2). The commenter (206) asserted 
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that, in one instance, the proposed rule appears more stringent for area sources, and in the other 

instance the proposed rule appears less stringent for area sources. The commenter (206) 

requested that the EPA require all existing landfill gas-fired RICE to comply with the same 

“limited requirements” currently applicable to existing landfill gas-fired RICE (See 40 CFR part 

63.6590(b)(3)). 

One commenter (149) urged EPA to clarify that the proposed rule does not apply to CI 

engines that burn landfill and/or digester gas at major sources and requests that the requirements 

for CI engines greater than 500 HP that burn landfill and/or digester gas at area sources be 

removed. The commenter (149) provided that it has 27 non-emergency CI engines ranging from 

520 to 3,174 HP that each combust 10 percent more of digester gas on an annual basis located at 

four of New York City’s 14 water pollution control plants. Based on commenter 149’s 

assessment, these engines that are currently classified as major sources as defined in 42 U.S.C. 

§7412(a)(1) would appear not to trigger the proposed rule. The commenter (149) requests 

clarification on whether the proposed rule governs these engines. The commenter (149) 

requested that EPA modify the final rule to state clearly that it does not apply to digester gas 

engines greater than 500 HP at major sources. The commenter (149) stated that if its 

interpretation is incorrect, the commenter believed the proposal did not provide adequate notice 

of EPA’s intention to apply emissions limits to these alternative fuel engines and that the rule 

must be republished with a regulatory analysis that includes the costs and benefits of applying 

emissions standards to digester gas engines (with adequate notice for wastewater utilities and 

other entities that use digester gas to power engines). The commenter (149) argued that 

compliance costs of strict emissions limits on digester gas engines would be so expensive that 
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the rule would result in a disincentive for digester gas use and would increase pressure on natural 

gas supplies and flaring of digester gas. 

The commenter (149) asked that EPA consider the following: 

• Emission control costs in New York City are greater than the benchmark control costs 

presented by EPA (provided that the design and construction costs associated with the 

installation of an emission control system for a 2,000 KW engine generator would be in 

the range of $1.5 million and that for them, the costs associated with the installation of 

emission control systems at all their facilities could be as high as $40 million). 

• The proposed rulemaking would be inconsistent with other national incentives that 

encourage the use of landfill and/or digester gas for power generation for cities to be 

sustainable. For example, in February 2009, the American Recovery and Reinvestment 

Act of 2009 allocated an additional $1.6 billion of new Clean Renewable Energy Bonds 

first authorized by the Energy Policy Act of 2005 to promote the use of alternative energy 

including anaerobic digester and landfill gas. 

• The proposed rulemaking is inconsistent with the national goals of reducing GHG 

emissions since it could be a disincentive for reducing the practice of flaring landfill 

and/or digester gas instead using these gases for energy generation, and would encourage 

the purchase of power from electric utilities and rely on limited non-renewable and more 

polluting sources of fuel (e.g., coal and residual oil). 

One commenter (142) noted that the current RICE NESHAP includes an exemption for 

existing stationary RICE at major sources that combust landfill gas or digester gas equivalent to 

10 percent or more of the gross heat input on an annual basis. The commenter (142) described 

the consequences if this exemption is not extended to engines at area sources, noting that most 
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municipal solid waste landfills in the U.S. are classified as area sources. Currently, collected 

landfill gas is used as a renewable energy source to fuel RICE. If these RICE are subject to the 

operational and economic impacts imposed by the proposed rule, they would likely opt to 

destroy the collected landfill gas through flaring to meet NSPS subpart WWW rather than reusing the landfill gas for renewable power generation. The commenter (142) noted that this 

could force the shutdown of such renewable energy projects with no resultant benefit at a time 

when the demand for renewable energy is growing. The commenter (142) requested that EPA 

extend the current exemption to landfill/digester gas RICE at area sources as a means of 

promoting the use of landfill gas as a renewable energy source. 

Two commenters (265, 268) recommended the following amendment to §66.6590(b)(3) 

of the proposed rule: 

(b)(3) ...an existing stationary RICE with a site rating of more than 500 brake HP located 

at a major source of HAP emissions that combusts landfill gas...equivalent to 10 percent 

or more of the gross heat input on an annual basis, does not have to meet the 

requirements of this subpart or of subpart A of this part. 

One commenter (142) questioned whether the data used to determine the emission limit 

for landfill/digester gas engines above 500 HP provide an adequate and accurate representation 

of engines currently operating at landfill gas-to-energy facilities. The commenter (142) provided 

data for his fleet of 51 RICE indicating mean emissions of 276 ppmvd CO and a median 

measurement of 278 ppmvd CO based on 93 discreet measurements of various engines 

conducted over the past eight years. The commenter (142) stated that none of these engines 

achieved the proposed standard of 177 ppmvd CO. The commenter (142) noted that, if the 

proposed limit accurately represented existing landfill/digester gas RICE in operation, some 
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portion of the commenter’s (142) fleet would be expected to meet the proposed limit, which is 

not the case. The commenter (142) recommended that EPA gather additional emissions data and 

re-evaluate the proposed emission limit. 

Similarly, commenter 213 asserted that the 177 ppmvd limit for CO is too stringent and 

that most engines operate around 1,000 ppm or more of CO. Reaching 177 ppm would require 

add-on controls, plus would necessitate the cleaning of the gas to remove impurities, according 

to the commenter. 

One commenter (191) stated that the database does not support, nor will newer 

landfill/digester gas engines be able to meet, the 177 ppmvd of CO limit. Recent tests on the 

commenter’s (191) new landfill fired gas engines show CO emissions of 411 ppm, more than 

twice the limit. The commenter (191) also noted that the assumption of 90 percent catalyst 

control of formaldehyde or CO as a surrogate for HAP has been associated with previous 

rulemaking and explain test data deviations from 90 percent control and the contradiction to 

previous testing. The commenter (191) added that the emphasis on reducing NOx emissions in 

recent years have resulted in an increase in CO emissions from landfill and digester gas fired 

engines. As a result these RICE may not be able to make the 177 ppmvd CO limit. The 

commenter (191) feels that efforts to lower the CO emissions in these engines would result in an 

increase in NOx emissions and notes that EPA has stated previously that catalytic oxidation does 

not work on such systems due to fouling of the catalyst by siloxanes in the raw fuel gas. 

Response: For existing stationary landfill and digester gas engines located at area sources, EPA 

cannot exempt such engines from regulation because stationary internal combustion engines 

were identified as a source category needed under section 112(k) of the CAA. EPA proposed 
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management practices for existing stationary landfill and digester gas engines greater than or 

equal to 50 HP and less than or equal to 500 HP located at area sources. EPA is retaining 

management practices for these engines in the final rule, as well as engines below 50 HP. For 

existing stationary landfill and digester gas engines greater than 500 HP at area sources, EPA 

proposed a CO concentration standard of 177 ppmvd at 15 percent O2. Based on an evaluation 

of generally available control technologies and management practices for these engines 

following the proposal, EPA is finalizing management practices for this group of engines. EPA 

has determined that for all existing stationary non-emergency landfill and digester gas engines at 

area sources management practices represent what is generally available among such engines to 

reduce HAP, and the practices will ensure that emissions are minimized and engines are properly 

operated. Specifically, existing stationary non-emergency landfill and digester gas engines at 

area sources must change the oil and filter every 1,440 hours of operation or annually, whichever 

comes first, except that sources can extend the period for changing the oil if the oil is part of an 

oil analysis program, inspect spark plugs every 1,440 hours of operation or annually, whichever 

comes first, and replace as necessary; and inspect all hoses and belts every 1,440 hours of 

operation or annually, whichever comes first, and replace as necessary. These specific 

management practices were developed based on input from different stationary engine operators 

(including landfill and digester gas engine operators) and engine manufacturers. A complete 

discussion of the analysis for landfill and digester gas engines at area sources can be found in the 

memorandum titled “MACT Floor and MACT Determination for Existing Stationary NonEmergency SI RICE <100 HP and Existing Stationary Emergency SI RICE Located at Major 

Sources and GACT for Existing Stationary SI RICE Located at Area Sources,” which is 

available from the rulemaking docket (EPA-HQ-OAR-2008-0708). 
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For existing stationary landfill and digester gas engines greater than or equal to 50 HP 

and less than or equal to 500 HP located at major sources, EPA proposed a CO concentration 

limit of 177 ppmvd at 15 percent O2. EPA is required to establish emission standards for 

stationary engines located at major sources of HAP emissions based on the average emission 

limit achieved by the best performing 12 percent of engines. Section 112 of the CAA requires 

EPA to regulate all stationary sources in the source category located at major sources. EPA 

cannot exempt subcategories of engines located at major sources from being subject to emission 

standards, which commenters appear to be suggesting by stating that landfill and digester gas 

engines deserve special consideration. Nor can EPA promulgate “no control floors” as was done 

in the first RICE MACT for stationary landfill and digester gas engines greater than 500 HP 

located at major sources. Recent court cases, in particular the “Brick MACT” case, have ruled 

such “no control floors” to be inconsistent with section 112(d) of the CAA. EPA therefore had 

to take a different approach in setting standards for existing stationary landfill and digester gas 

engines than was taken in earlier regulations. Moreover, EPA cannot promulgate work practice 

standards for existing stationary landfill and digester gas engines located at major sources 

because there is no evidence that the requirements for promulgating work practice standards 

under section 112(h) of the CAA have been met. 

EPA must therefore finalize a numerical emission limit for landfill and digester gas 

engines greater than or equal to 100 HP and less than or equal to 500 HP located at major 

sources. Following the proposed rule, EPA received additional test data for landfill and digester 

gas engines. EPA received emissions data for more than 150 engines and this data was 

incorporated into the MACT floor analysis for this final rule. As discussed in response to 

comment 5.1.1.1, EPA followed a revised approach in establishing the emission standards for the 
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final rule. In order to determine the MACT floor for existing non-emergency landfill and 

digester gas engines greater than or equal to 100 HP and less than or equal to 500 HP, EPA 

ranked the emissions of landfill and digester gas engines based on their emissions and identified 

the lowest emitting 12 percent (or 21 engines) based on the lowest test for each engine. EPA 

used all of the emissions data for those best performing 21 landfill and digester engines to 

determine the emission limits for this final rule, accounting for variability. EPA assessed the 

variability of the best performers by using a statistical formula (UPL) designed to estimate a 

MACT floor level that is achieved by the average of the best performing sources if the best 

performing sources were able to replicate the compliance tests in our data set. Again, details of 

this approach were discussed in response to comment 5.1.1.1 and this approach reasonably 

ensures that the emission limit selected as the MACT floor adequately represents the level of 

emissions actually achieved by the average of the units in the top 12 percent, considering 

ordinary operational variability of those units. Both the analysis of the measured emissions from 

units representative of the top 12 percent, and the variability analysis, are reasonably designed to 

provide a meaningful estimate of the average performance, or central tendency, of the best 

controlled 12 percent of units in a given subcategory. Following this approach, EPA determined 

that the final emission limit is 177 ppmvd of CO at 15 percent O2. Details on the MACT floor 

analysis, including the tests in EPA’s dataset, can be found in the memorandum titled “MACT 

Floor and MACT Determination for Existing Stationary SI RICE ≤500 HP Located at Major 

Sources,” which is available from the rulemaking docket (EPA-HQ-OAR-2008-0708). EPA 

believes that the final emission standards will reflect the numerous engine models and operating 

scenarios that can be expected from stationary engines. 
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In response to concerns from industry regarding the inclusion of emissions data from 

older units in EPA’s dataset, EPA is required by the CAA to set MACT standards based on the 

test data that is available to the Agency. EPA noted earlier in this response that it received a 

substantial amount of additional emissions data following the proposal, which has been 

incorporated into EPA’s dataset. The dataset is based on test results obtained from a variety of 

facilities across the United States for different engine makes, models and sizes primarily tested 

within the last decade. If commenters believed data from recently permitted units would have 

been more representative, commenters should have submitted test data to EPA for inclusion in 

the final dataset. EPA must make its determinations based on the information available to it and 

must base the final standard on actual data. 

The data at proposal may have been from facilities located in a particular area of the 

country, but it represented what EPA had available at the time and therefore was used to 

developed the proposed emission standards. The newly gathered emissions data expands on 

EPA’s dataset for landfill and digester gas engines and EPA’s dataset now includes test results 

from facilities in several different states, including New York, Maine, Vermont, Florida, North 

Carolina, Florida, Texas, California, Ohio and Illinois. 

Regarding comments that the standards are not achievable for existing engines, EPA 

notes that court cases have made clear that the appropriate criterion for determining the MACT 

floor under section 112(d) of the CAA is the emission levels that have been achieved by the best 

controlled sources. The test results indicate that all of the engines in the top 12 percent have 

achieved emission levels below the standard, as have an additional 7 engines in the subcategory. 

Engine settings can be adjusted to meet the emission standard. In any case, EPA believes that 
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most existing landfill and digester gas engines are located at area sources, as well as being 

greater than 500 HP. 

EPA cannot defer publication of requirements for existing stationary landfill and digester 

gas engines less than or equal to 500 HP located at major sources and for existing stationary 

landfill and digester gas engines located at area sources. EPA believes the dataset for landfill 

and digester gas engines, which consists of emissions tests for 176 engines, is comprehensive 

and representative. EPA cannot delay promulgation of the final rule and must finalize 

requirements for these engines due to a court-ordered schedule requiring EPA to promulgate the 

regulation by August 10, 2010. 

In reply to comments indicating that EPA should set any potential emission standard in 

terms of VOC and not CO, EPA believes that a standard that is in terms of CO, where EPA is 

finalizing a numerical emission limit, is appropriate for landfill and digester gas engines. EPA 

has previously determined that CO is an appropriate surrogate for HAP and believes that 

decision is still valid. Commenters did not provide any compelling evidence as to why the 

standard should be in terms of VOC and not CO, .e.g., no information was submitted to dismiss 

CO as a valid surrogate for HAP. Further, EPA does not agree that landfill and digester gas 

engines that are reconstructed should be subject to VOC standards currently required under 40 

CFR part 60, subpart JJJJ (SI NSPS). The SI NSPS was developed at a different time and under 

different statutory requirements. 

Further, EPA is not trying to discourage landfill and digester gas-to-energy projects. 

EPA is required to promulgate standards for stationary engines under section 112 of the CAA 

and EPA does not believe that this rule will be inconsistent with efforts to reduce greenhouse gas 

emissions. 
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In response to concerns regarding a numerical emission limit for stationary emergency 

landfill and digester gas engines, EPA has specified in the final rule that the numerical emission 

limit that applies to landfill and digester gas engines at major sources only applies to nonemergency engines. For all emergency engines, EPA is finalizing work or management 

practices. 

In response to comments that EPA’s analysis at the time of proposal lacked transparency, 

EPA has made an effort to be as clear as possible in materials developed to support the final 

rulemaking. EPA has presented the basis for regulatory decisions, and included all emissions 

data used to develop the final standard. All information used to support the final rulemaking is 

available from Docket Number EPA-HQ-OAR-2008-0708, however, note that some information 

may exist in prior dockets that are cited in the preamble to the final rule and include Docket 

Numbers EPA-HQ-OAR-2002-0059, EPA-HQ-OAR-2005-0029 and EPA-HQ-OAR-2005-0030. 

Regarding the request for clarification regarding CI landfill and digester gas engines, the 

final rule applies to all existing stationary landfill and digester gas engines that are less than or 

equal to 500 HP and located at major sources and to all existing stationary landfill and digester 

gas engines located at area sources, including those that may be compression ignition engines. 

Existing landfill and digester gas engines greater than 500 HP located at major sources were 

already subject to the RICE NESHAP finalized in 2004 and are regulated as landfill and digester 

gas engines, not CI engines. 

5.6 Format of Standards and Other Issues Related to Standards 
204

5.6.1 Comment: One commenter (242) said that there may be a large number of remotely 

located natural gas engines that are unmanned and there are issues related to air-to-fuel ratio 

controllers as far as continuous operational reliability and dependability are concerned. The 4-

Corners KSU study indicated that the following issues may exist: 

• Several remotely located engines will need a battery to be installed to power the AFRC 

and an alternator or solar panel to keep the battery charged; 

• It may be necessary to modify fuel and air handling systems to accommodate the control 

system; 

• There may be issues in reaching the precise air-to-fuel ratio on older engines; 

• In the beginning, frequent site visits are necessary to inspect and review technology 

performance such as the air-to-fuel ratio set point; 

• Fuel quality and variability issues; 

• Frequent site visits and system checks are required to ensure continuous operation and to 

assess any problems; and 

• Issues with test trailers accessing facilities located in difficult to access remote areas. 

The commenter (242) expressed that EPA should take into account the costs associated with the 

above issues in assessing the cost effectiveness for engines in rural area sources. 

 The commenter (242) cited a 2008 study where semi-continuous NOx and CO monitoring 

was installed on different rich burn engines with NSCR. Preliminary results suggested that 

NSCR systems are not able to demonstrate long-term consistent simultaneous control of NOx and 

CO to below 500 ppm, according to the commenter (242) with levels not being consistent from 

day-to-day or even within a few hours and the NSCR was not consistently able to reach 90 
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percent control during routine operation. This creates additional problems with respect to a 

standard applicable at all times, the commenter (242) said. 

Response: EPA is finalizing management practices for the majority of existing stationary 4SRB 

engines located at area sources. Only existing non-emergency 4SRB engines at area sources that 

are greater than 500 HP that operate more than 24 hours per year will be subject to numerical 

emission limitations, which are expected to necessitate the use of NSCR and air-fuel-ratio 

controllers. Existing 4SRB engines greater than 500 HP at area sources that operate more than 

24 hours per year must either meet a formaldehyde concentration standard of 2.7 ppmvd at 15 

percent O2 or reduce formaldehyde by 76 percent or more. Of the total population of affected 

4SRB engines at area sources, only 7 percent are estimated to be greater than 500 HP and subject 

to numerical emission limitations. The remaining 93 percent of 4SRB engines at area sources 

will be subject management practices. (EPA discussed the specific management practices that 

will be required of existing stationary 4SRB engines less than or equal to 500 HP located at area 

sources in response to comment 7.2.1). An even smaller percentage is estimated by industry who 

in a paper17 submitted to EPA indicated that only about 3 percent of 4SRB engines located at 

area sources are greater than 500 HP. Therefore, the majority of existing stationary 4SRB 

engines at located at area sources will not run into the potential issues related to the operation of 

air-to-fuel ratio controllers or the long-term emissions reductions from using NSCR because 

these engines are subject to management practices. EPA does not believe that the issues the 

commenter indicated may exist will be significant and in the event that a remote site may for 

                                                           

17 Support for Use of Management Practices in the National Emission Standards for Hazardous 

Air Pollutants Standards for Reciprocating Internal Combustion Engines at Area Sources in 

Rural Locations Prepared by David W. Heinold, CCM AECOM Environment. Prepared on 

behalf of American Petroleum Institute. November 2009. EPA-HQ-OAR-2008-0708-0300.
206

example need a battery to power the AFRC and an alternator or solar panel to keep the battery 

charge, the cost of this would not be significant. In the Four Corners Report the commenter 

cites, the cost for an alternator and battery or solar panel and battery is estimated at $350. EPA 

does not believe that this cost will put remotely located sites at a disadvantage. EPA does not 

believe that the impacts will be significantly greater for an engine in a remote area than in a nonremote area. Further, in a paper submitted to EPA by API supporting management practices for 

engines at area sources in rural locations12, API stated that “Oil and gas industry RICE are 

predominantly located in remote areas. Engines less than 500 HP are typically used for wellsite 

compression, while those greater than 500 HP are typically found at compressor stations and 

natural gas processing plants” (page 1 of API’s paper). Since engines greater than 500 HP are 

typically found at compressor stations and natural gas processing plants, EPA believes that the 

potential problems the commenter mentions in terms of potentially not having electricity or 

being staffed, may be less of an issue. This may be more of a concern for engines used for 

wellsite compression, but since these are typically less than 500 HP, this is not an issue since 

EPA is requiring management practices for 4SRB engines below 500 HP. EPA believes that the 

the changes made to the proposed rule in terms of requiring management practices for most 

existing stationary SI engines at area sources resolves the commenter’s main concerns. 

 EPA is not certain which study the commenter is referring to when it mentioned semicontinuous NOx and CO monitoring and the commenter did not provide the study or data to 

EPA. Therefore, EPA is not able to fully address this comment. EPA proposed a 200 ppbvd 

formaldehyde concentration or a 90 percent formaldehyde reduction for non-emergency 4SRB 

greater than or equal to 50 HP at area sources, but is, as stated, promulgating management 

practices for most engines at area sources. Where EPA is requiring standards based on levels 
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expected with aftertreatment, the final formaldehyde concentration standard is noticeably higher 

than what was proposed. Also, the formaldehyde reduction requirement EPA is finalizing is 

considerably lower than proposed, at 76 percent. 

5.6.2 Comment: Two commenters (96, 112) questioned the fact that some of the limits in the 

proposed rule for existing engines are more stringent than limits that apply to new engines. 

Older or existing engines are typically less advanced, have less available control options to 

reduce emissions, and are often times limited by physical space or engineering constraints, the 

commenter (96) said. Therefore, it is not possible to retrofit existing engines to the levels 

commensurate with that of new engines and certainly not to levels that are well below new 

engines, the commenters (96 and 112) expressed. For example, the NSPS requires new 4SLB 

engines above 250 HP to meet a CO limit of 270 ppmvd, while the proposed NESHAP requires 

existing engines to meet a CO limit of 9 ppmvd, the commenter (96) noted. Also, the standard 

applicable to new diesel emergency engines above 500 HP is simply notification requirements, 

while existing diesel emergency engines between 300 and 500 HP must meet a 40 ppmvd CO 

limit. The commenter (96) is of the opinion that such emission limits are inherently infeasible 

and impractical for existing engines when the limits for new engines can be two order of 

magnitude or greater. 

Commenter 112 particularly questioned the appropriateness of the 200 ppbvd 

formaldehyde limit proposed for existing 4SRB engines above 50 HP located at both major 

sources and area sources. The commenter (112) reported an investigation using FTIR testing 

that was performed by a member company in his organization on numerous makes and models of 

small rich burn engines to determine if the 200 ppbvd is achievable with AFRC and NSCR 
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controls. The commenter (112) indicated that the investigation found that reducing 

formaldehyde emissions by 90 percent is achievable, but meeting 200 ppbvd was not. 

 The commenter (112) indicated that a catalyst manufacturer and major supplier of 

aftermarket controls to the oil and gas industry typically guarantees the catalysts at 90-percent 

control or 0.04 g/HP-hr for formaldehyde for small rich burn engines, though the guarantee can 

vary slightly depending on the make and model of the engine and the catalyst. The commenter 

(112) stated that 200 ppbvd is equivalent to 0.001 g/HP-hr, which is approximately 40 times 

more stringent than what catalyst manufacturers are willing to guarantee under optimal 

temperature and fuel conditions. 

 The commenter (112) stated that data on controlled engines at member companies in his 

organization indicate that emissions are typically 6-10 ppmvd. The commenter (112) noted that 

meeting the proposed numerical standard would require an additional 98 percent reduction for 

this group of existing engines, which the commenter believes would be infeasible considering 

current control technologies. 

 The commenter (112) suggested that the numeric value for existing rich burn engines 

should be no more stringent than the most stringent numeric value for new sources (rich burn or 

lean burn) under 40 CFR part 63, subpart ZZZZ, which is 12 ppm or 0.048 g/HP-hr. 

Response: EPA is aware that some of the proposed emission standards for existing stationary SI 

engines were more stringent than what is currently applicable to new stationary SI engines. EPA 

responded to similar concerns for existing CI engines in the responses to comments18 when that 

                                                           

18 Memorandum from Melanie King, Energy Strategies Group to EPA Docket EPA-HQ-OAR2008-0708. Response to Public Comments on Proposed National Emission Standards for 

Hazardous Air Pollutants for Existing Stationary Reciprocating Internal Combustion Engines 
209

rule was finalized in early 2010. However, EPA is required to address HAP emissions from all 

existing stationary engines at major sources and based on the Brick MACT decision, EPA can no 

longer set floors of no emission reduction and must finalize numerical emission standards for 

engines located at major sources. EPA was not obligated to follow this approach during the 

2004 NESHAP and the provisions finalized under the NSPS regulations were developed under 

different statutory requirements and focused on criteria pollutants, not HAP. Furthermore, EPA 

must set limits based on the data available at the time of the rulemaking. EPA acknowledged 

that it had limited data available at the time of the proposed rule. Nevertheless EPA had to 

propose requirements even with a limited dataset. 

 As discussed in response to comment 5.1.1.1, EPA received a substantial amount of new 

emissions data following the proposed rule. For rich burn engines, EPA has emissions data for 

57 engines, which EPA analyzed for the final rule and established the final standards based on 

that data. For existing stationary non-emergency 4SRB engines greater than or equal to 100 HP 

and less than or equal to 500 HP at major sources, EPA is finalizing a formaldehyde 

concentration standard for 10.3 ppmvd at 15 percent O2. This standard incorporates emissions 

variability and is based on test data collected from stationary engines produced by different 

engine manufacturers, engines of different sizes, operating at various loads and other conditions, 

and located in various types of service. EPA discussed in response to comments in sections 5.1.1 

and 5.1.2 the approach for setting these standards and described the MACT floor, MACT and 

GACT analysis in the memoranda titled “MACT Floor and MACT Determination for Existing 

Stationary SI RICE ≤500 HP Located at Major Sources” and “MACT Floor and MACT 

                                                                                                                                                                                               

Located at Area Sources of Hazardous Air Pollutant Emissions or Have a Site Rating Less Than 

or Equal to 500 Brake HP Located at Major Sources of Hazardous Air Pollutant Emissions. 

EPA-HQ-OAR-2008-0708-0367.
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Determination for Existing Stationary Non-Emergency SI RICE <100 HP and Existing 

Stationary Emergency SI RICE Located at Major Sources and GACT for Existing Stationary SI 

RICE Located at Area Sources,” which are in the docket. 

5.6.3 Comment: Two commenters (96, 150) said that EPA should include the flexibility in the 

final rule of allowing all sources subject to emission standards the option of meeting either the 

concentration limit or the percent reduction standard. According to commenter 96, including 

such flexibility is necessary due to the large span in model year engines, emission characteristics 

and location conditions, and it may be more feasible to meet one compliance option over the 

other or even impossible to meet one of the options. 

 One commenter (99) asserted that where the percent reduction is available, it is generally 

attainable, but at a high cost. However, the numerical values proposed by EPA are not 

achievable, the commenter (99) said. 

Response: There is only one subcategory for which EPA did not provide a percent reduction 

option despite the fact that the standard is expected to require emission control technology. That 

is the subcategory of 4SLB engines rated at 100 HP to 500 HP located at major sources. The 

MACT floor for that subcategory is at a level that would likely require emission control 

technology. EPA did not allow a percent reduction option for that subcategory because a source 

could meet a percentage reduction level, but not meet the emission level required by the MACT 

floor. For all other subcategories that were expected to comply with the rule by applying add-on 

control technology, EPA provided the option of meeting either a concentration standard or a 

percent reduction requirement, e.g., non-emergency 4SRB and 4SLB engines greater than 500 
211

HP at area sources that operate more than 24 hours per year. Including an option to meet a 

percent reduction does not make sense for sources that are not expected to apply add-on controls, 

and furthermore, EPA would not know what that percentage would be if the standard was based 

on levels achievable without aftertreatment. EPA does not agree with the commenters that the 

emission standards are not achievable. The final standards are based on emissions data from 

existing stationary SI engines.

5.7 Technology 

5.7.1 Comment: One commenter (199) commended the EPA for its continuing efforts to develop 

and implement effective emission control standards for major sources of air pollution such as this 

category of engines. 

The commenter (199) agreed with EPA’s analysis that NSCR is a cost effective means to 

reduce HAP and NOx from existing stationary rich burn engines. The commenter stated that 

these technologies have been retrofitted on thousands of rich burn engines and have been verified 

by the CA ARB for use on large SI off-road engines. The commenter (199) noted that these 

verified technologies are also applicable to stationary rich burn engines. 

The commenter (199) recommended that EPA also consider the benefits of using 

selective catalytic reduction (SCR) to reduce both HAP and NOx emissions from stationary SI 

engines. The commenter (199) noted that one member company has installed over 400 SCR 

systems worldwide for stationary engines with varying fuel combinations. 
212

Response: EPA acknowledges the information regarding applicable control technology that is 

currently available to apply to existing stationary engines that the commenter provided. EPA 

generally agrees with the commenter that the technologies identified can be used by at least some 

existing stationary engines. EPA for the most part also concurs with the commenter’s assertions 

regarding the capabilities of the control technologies discussed as far as which pollutants they 

reduce and the effectiveness. EPA did not specifically consider SCR because this rulemaking 

focuses on reducing HAP emissions and SCR alone does not reduce emissions of HAP. In order 

for an SCR to reduce HAP, an oxidation catalyst would have to be part of the aftertreatment 

package. With that said EPA notes that it does not mandate any specific control technology in 

the final rule. Owners are free to select whichever control technology they feel is appropriate as 

long as they demonstrate compliance with the emission standards. 

5.7.2 Comment: One commenter (108) stated that the experience period for 2SLB engines with 

oxidizing catalysts is less than 5 years. The commenter (108) noted that Ajax has worked with 

oil manufacturers to identify suitable oil that does not contaminate the oxidation catalyst. 

Therefore the commenter (108) suggested that the EPA recognize this as an emerging technology 

and not make the requirements more stringent for 2SLB engines using this technology than the 

requirements for 4SLB engines.

Response: For 2SLB engines at major sources, EPA determined for the final rule that it would 

not be appropriate to go beyond the MACT floor and establish standards based on oxidation 

catalyst control. For 2SLB engines at area sources, the final rule establishes management 
213

practices. Thus, EPA does not expect that the requirement of the final rule would generally 

require the installation of oxidation catalysts on 2SLB engines. 

6.0 Exemptions/Special Allowances 

6.1 Limited Use Engines 

6.1.1 Comment: Multiple commenters (78, 97, 107, 110, 126, 129, 130, 139, 150, 162, 168, 170, 

177, 178, 179, 183, 191, 197, 202, 207, 216, 227, 236, 247, 253) wanted EPA to expand the 

definition of limited use engines. Several commenters (162, 168, 236) said that a limited use 

category should be included in this rulemaking for area source engines and engines less than 500 

HP, as was included in the rule for engines greater than 500 HP located at major facilities. 

Commenters 97, 168 and 236 thought that limited use engines should be exempt from 

performance testing. According to commenters 97, 168 and 236, limited use engines should only 

be required to track and report hours of operation. 

Commenter 168 asked that limited use be defined as 250 hrs/yr. Commenters 126, 150, 

162, 197, 216, 236 and 247 asked EPA to provide 300 hrs/yr for limited use engines. If 300 

hrs/yr is not provided, commenter 162 requested clarification that readiness testing and 

maintenance are excluded from the annual hours of operation. This will allow companies to 

perform the necessary maintenance and testing requirements without worry of exceeding the 100 

hour limit, which could be easily exceeded if a malfunction or repair required diagnosis and/or 

engine tuning, the commenter (162) said. 
214

Two commenters (177, 253) asked that limited use be defined as 500 hrs/yr. The current 

rule defines limited use as “any stationary RICE that operates less than 100 hrs/yr.” The 

commenter believes that because of the low capacity factor (approximately 5.7 percent for an 

engine that operates 500 hrs/yr), the emissions are inherently low and would not pose a 

significant health hazard to the public. Similarly, commenter 168 said that its limited use 

engines, which are predominantly CI engines are inherently low-emitting and would not pose a 

significant health hazard to the public. Given the short periods of time the commenter’s units 

operate (startup engines for large combustion turbines), imposing emission limits is impractical. 

Therefore, startup engines should either be included in the definition of emergency stationary 

RICE, or limited-use RICE should continue to be exempt from emission limitations and 

additional requirements, according to commenter 162. 

Two commenters (126, 247) stated that if EPA declines to exempt the current limited use 

category to include all limited use engines, then EPA should establish a new subcategory of 

limited use RICE that are used in electric grid security. The commenters (126, 247) noted there 

are 500 such engines that operate less than 300 hrs/yr that are used to support the integrity and 

voltage of various electric utility transmission and distribution grids. The commenter (126) 

stated that these engines are similar to emergency engines, except they are used to respond to 

sags in voltage on remote portions of the utility’s grid. The commenters (126, 247) noted that 

the proposed rule would require retrofitting of these engines with catalytic converters, but 

believes these retrofits in many cases are impractical. 

One commenter (226) noted that it was incredulous to require significant regulation for 

small engines, but determine that larger limited use engines require no regulation. The 
215

commenter (226) stated that the Regulatory Flexibility Act requires EPA to consider less 

burdensome alternatives, and this should be done for the final rule. 

One commenter (110) recommended that EPA include a de minimis usage threshold of 

50 hours/year, below which, equipment will be exempt from the requirements of the proposed 

rule. The commenter (110) is concerned that the proposed rule will require a significant 

investment of resources for testing, personnel training, recordkeeping and reporting relative to 

the hours of usage for emergency standby generators or other limited use engines that are 

operated only for exercise or testing for 1 to 2 hours per month or less. The commenter (110) 

believes that the benefits are insignificant relative to the compliance cost, instead, could have the 

unintended consequence of generating more emissions as a result of the travel to conduct testing. 

One commenter (78) said the cost effectiveness of adding control devices to low-use 

engines should be evaluated regardless of the size of the engine. The costs associated with the 

installation and maintenance of a control device on a low use unit can be quite high per ton of 

pollutant abated. 

One commenter (129) supported the creation of a subcategory of limited use RICE, such 

as those with a 10 percent capacity factor or less. The commenter (129) indicated that numerous 

RICE at natural gas utility companies have operating characteristics equivalent to emergency 

generators, generally RICE that operate only under unusual conditions such as extreme cold days 

or when normal gas supplies are disrupted. The commenter (129) stated that these systems are in 

place to insure gas is available to customers, particularly residential heating customers, during 

severe weather emergencies. Although they do not meet the definition of emergency equipment, 

the commenter (129) believes that their purpose, emissions, and operational use are essentially 

identical to that experienced by conventional emergency generators. The commenter (129) 
216

asserted that while emergency generators are spared post-combustion controls and testing, a 

similar engine used to insure the ability of residential heat during extreme winter conditions will 

be subject to onerous emissions limitations requiring post-combustion controls that would result 

in reduced dependability and significant cost increases. 

 The commenter (129) stated that there is a high cost per ton of HAP removed associated 

with installing an oxidation catalyst on low capacity factor engines. The commenter (129) noted 

that these limited use engines resemble emergency RICE in their operation, but fall outside that 

category because they are used during rare periods of high demand that are not defined as 

emergencies. The commenter (129) added that the infrequent use of such engines makes the 

application of pollution controls more difficult and costly than at “normal” RICE. 

believes that EPA’s rationale for proposing installation of an oxidation catalyst on engines 

greater than 300 HP also supports creation of a subcategory of limited use RICE. 

One commenter (202) recommended that an exemption for engines at an area source that 

is only used for backup purposes as long as the hours in any particular year do not exceed 500 

hours. The commenter (202) explained that it has four engines, each greater than 500 HP, that 

are maintained as backup units to ensure no digester gas build-up when the combustion turbines 

are off line. 

One commenter (107) proposed that EPA extend the exemption for limited use stationary 

engines that is currently available for engines above 500 HP at major sources to include existing 

engines at area sources that are above 300 HP. The commenter (107) noted that most of these 

engines are located at retail stores or office buildings where there are no other significant sources 

of HAP emissions and that the majority run less than 100 hrs/yr for backup power, peaking 

power, and maintenance combined. Additionally, the commenter (107) noted the proposed rule 
217

allows for an exemption for limited RICE rated greater than 500 HP at major sources, and the 

rule for area sources should not be more stringent than for units at major sources. 

One commenter (139) strongly supported the creation of a subcategory of limited use 

RICE, such as those with a 10 percent capacity factor or less. The commenter (139) believed 

that EPA’s rationale for proposing the installation of an oxidation catalyst on engines greater 

than 300 HP also supported the creation of a subcategory of limited use RICE, because in the 

proposed rule, EPA evaluates oxidation catalysts on a cost per ton HAP removal basis and 

concludes that the cost per ton increases as the size of the engine decreases. Similarly, the 

commenter (139) noted, there is a high cost per ton HAP removal associated with installing an 

oxidation catalyst on low capacity factor engines. The commenter (139) further noted that these 

limited use engines most closely resemble emergency RICE in their operation, but fall outside of 

that category because they do not meet the definition for emergency engines. Additionally, the 

infrequent use of limited use engines makes the application of pollution controls more difficult 

and costly. 

One commenter (78) said EPA should consider the distinction between baseload and 

peaking operation in developing the final regulation. Peaking engines typically operate far fewer 

hours each year than baseload engines (the commenter’s (78) peaking engines have capacity 

factors of 11 to 28 percent, which is typical). Retrofit requirements for engines in peaking 

operation will be far less cost effective because of the lower emissions benefits received. 

Another commenter (191) noted that many CI/diesel “peaker” units are not utilized 

simply in peak shaving, but more frequently act as “emergency” generation to stabilize the grid 

when requested by the regional electric Independent System Operator. The commenter (191) 

disagreed with EPA’s assumption of 1,000 hrs/yr operation times for peakers and provided data 
218

about their operating hours of peakers. Over the last 15 years, the commenter’s (191) 55 peaking 

units have averaged 40 operating hrs/yr. The maximum annual operating hours for any one site 

has been 269 hours in a year and the minimum 1 hour. The commenter (191) noted that in this 

circumstance the cost or emissions controls per ton of pollutant reduced becomes an order of 

magnitude greater and that EPA should lower the number of operating hours for which controls 

are not required to 300 per year. 

One commenter (130) requested that EPA expand the exemption for limited-use engines 

to include those used for rice irrigation. The commenter (130) specifically requested that the 

exemption be extended to area source engines that are less than or equal to 300 HP and that 

operate for 1,500 hours or less per year and provide that such engines only need to maintain 

records of annual operating hours to demonstrate that they comply with the limited-use 

exemption. To support the requested exemption, the commenter (130) noted that engines used 

for rice irrigation have a low capacity factor and are located in predominantly rural areas, thus 

presenting no significant health hazard to the public. Furthermore, the commenter (130) pointed 

out that EPA assumed the limited-use exemption would apply to engines used for electric power 

peak shaving that operate only during peak energy use periods, typically in the summer months. 

The commenter (130) asserted that, similarly, the use and operation of rice irrigation engines are 

different compared to typical engines because they are operated during limited periods of 

seasonal use and are mostly located in fields in rural areas. 

Response: EPA did not propose a category consisting of existing stationary limited use engines 

less than or equal to 500 HP located at major sources or existing limited use engines located at 

area sources. EPA did include a limited use category in the 2004 RICE NESHAP for existing 
219

and new stationary engines greater than 500 HP at major sources, defined as any stationary 

engine that operates less than 100 hours per year. However, that was a different rulemaking. It 

appears that some commenters might be commenting on that previous rule, which is not the 

subject of this action and EPA is not taking comment on requirements promulgated in 2004. 

EPA will revisit the 2004 regulation when the 8-year residual risk review must be conducted in 

2012. 

 EPA is required to address HAP emissions from all existing stationary engines less than 

or equal to 500 HP at major sources and existing stationary engines at area sources. Due to the 

Brick MACT decision, EPA can no longer set floors of no emission reduction for limited use 

engines at major sources, or any other engines for that matter, as was done in the 2004 RICE 

NESHAP that regulated existing and new stationary engines greater than 500 HP at major 

sources. 

 Various commenters requested that EPA establish a subcategory of limited use engines 

that would be allowed to operate up to 500 hrs/yr or a 10 percent capacity factor. Commenters 

argue that based on an engine’s limited annual operation that the emissions from the unit are not 

significant. EPA does not agree with this claim. EPA considered the input and 

recommendations by commenters on establishing a subcategory of limited use engines, but EPA 

disagrees that such a subcategory is justified for existing stationary engines less than or equal to 

500 HP located at major sources and existing stationary engines located at area sources. EPA 

expects that engines that operate up to 500 hours per year or more would be able to meet the 

same emission standards that apply to other stationary engines that may be operated more 

frequently. EPA does not see any reasons precluding these limited use engines from applying 

aftertreatment controls, in those cases where addition control measures are needed to meet the 
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final emission standards. EPA also points out that for many stationary engines at major sources, 

the final standards are not based on the use of add-on controls and many engines are expected to 

be able to meet these standards without aftertreatment. Limited use engines are expected to 

exhibit the same or similar exhaust emissions profile as other stationary engines. In addition, 

commenters provided strong opinions on creating a limited use subcategory of 500 hours or 10 

percent capacity factor in the final rule, but did not give EPA adequate and persuasive 

information supporting their opinions. There are an estimated 98,000 stationary SI nonemergency engines less than 500 HP located at a major source of HAP. The total emissions from 

these engines if they operated 500 hours each are estimated to be 850 tons of HAP and 32,000 

tons of NOx, so EPA does not agree that emissions from engines running 500 hours a year are 

insignificant. The majority of engines at area sources are subject to management practices in the 

final rule, so there is no need to create a distinction for limited use engines where the engines are 

only subject to management practices. For the area source engines that are subject to numeric 

emission limitations, which are the 4SLB and 4SRB non-emergency engines greater than 500 

HP, EPA determined that it would be appropriate to establish a distinction for engines that are 

used 24 hours or less per year. For these engines, EPA determined that the cost of emission 

controls are not justified given the small amount of reductions that would be achieved due to the 

limited yearly operation. 

6.1.2 Comment: A few commenters (88, 126, 129, 197, 247) were concerned about requirements 

that might apply to engines that startup turbines. Three commenters (126, 197, 247) suggested 

that RICE used to startup combustion turbines be exempt from the proposed rule, or deemed to 

fall under the “emergency” definition in 40 CFR §63.6675. The commenter (197) explained that 
221

turbine RICE only run for a few minutes to get the unit started and the total fuel consumption is 

not significant. The commenter (197) opined that the installation of expensive control equipment 

on RICE that has limited used does not make sense as the actual emissions for the RICE would 

be insignificant compared to the combustion turbine (burns more fuel oil in one minute of 

operation that the RICE would burn all year). 

Two commenters (88, 129) stated that EPA should not require post-combustion controls 

or emissions monitoring on engines serving gas turbine power facilities. The commenters (88, 

129) supported this exemption because post-combustion controls will result in reduced 

dependability and significant cost increases, with little change in actual emissions since these 

engines rarely run long enough for such controls to reach minimum operating temperatures. 

Two commenters (88, 129) noted that every major power plant in the United States is required to 

have black start capability, which typically involves a small combustion turbine (CT) equipped 

with a diesel engine used for startup of the CT. According to the commenter (129), the diesel 

starting engine, rated less than 500 HP, generally operates less than 10 minutes per CT start. The 

commenter (129) indicated that the majority of black start units only operate during emergencies 

or unusually high demand days, and that a review of the commenter’s company’s operating data 

determined that seven black start units in the system averaged 32 starts per year (which equates 

to less than 6 hours of operation per year, although some limited additional operation may occur 

as a result of routine maintenance and readiness testing). 

Commenter 88 stated that some engines serving electric sector facilities that play a role in 

maintaining reliable electric power supply and delivery, such as distribution company service 

buildings, customer call centers, and information technology data centers have similar concerns. 

The commenter (88) reported that these emergency engines typically operate less than 200 hrs/yr 
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and have low permitted capacity factors. The commenter (88) opined that emergency power at 

these facilities is critical to public safety and national security and should therefore not be subject 

to numerical emission limits, but to management practices instead. 

Response: In the final rule EPA has required that stationary engines used to startup combustion 

turbines meet work practice standards. EPA finds that the short time of operation for these 

engines (10-15 minutes per start) makes application of measurement methodology for these 

engines using the required procedures, which require continuous hours of operation, 

impracticable. Requiring numerical emission standards for these engines would actually require 

substantially longer operation than would occur normally in use, leading to greater emissions and 

greater costs. EPA also agrees with the commenters that it would not be appropriate to set 

emission limits that are based on the use of aftertreatment control for stationary engines that are 

used to startup combustion turbines. Catalyst control would not be effective for these engines 

due to their short time of operation (10-15 minutes per start). 

6.1.3 Comment: One commenter (127) expressed that it felt that it is unnecessary to limit the use 

of half of the 100 hours EPA has determined to be an acceptable cap for non-emergency 

generators under §63.6640 of the proposed rule. The commenter (127) requested that EPA 

remove the requirement limiting non-emergency operations to 50 hours for non-maintenance or 

testing purposes. The commenter (127) said that removing the requirement would make it easier 

for plant maintenance and recordkeeping purposes by allowing flexibility to use the hours (up to 

100) for non-emergency use without having to make the distinction of separately tracking and 

limiting the use of some of those hours. 
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Response: EPA disagrees with the commenter. EPA has already included flexibility in that 

stationary emergency engines can maintain their classification as an emergency unit, but are 

allowed to operate for non-emergency purposes of up to 50 hours per year as long as such 

operation is not used to generate income for a facility to supply power to an electric grid or 

otherwise supply power as part of a financial arrangement with another entity. If an emergency 

engine is operated differently than described, it would be classified as a non-emergency engine 

and would be subject to different emission standards and compliance requirements. Therefore, 

EPA must require that operation by emergency engines is tracked and documented to ensure the 

requirements of the rule are being met. As EPA discussed in the preamble to the proposed rule 

(74 FR 9712), it is not expected that the recordkeeping requirements associated with emergency 

engine operation will be a significant burden, plus many stationary emergency engines may 

already be recording this information. Finally, these requirements are consistent with those 

finalized for new SI and CI stationary engines. 

6.1.4 Comment: One commenter (77) finds the limit of 100 hours in the definition of limited use 

RICE at 40 CFR 63.6675 to be unduly restrictive. The commenter (77) believes that 100 hours 

is very close to the amount of time that could be consumed by just the routine “maintenance 

checks and readiness testing” for similar emergency units. 

The commenter (77) noted that the electric utility industry has various blackstart, startup, 

peaking, and other units that are depended on for grid reliability, and a portion of these units are 

important for the reliable and safe operation of nuclear and other power plants. According to the 

commenter (77), some of the latter units provide the capability to restore power to an electric 
224

generating facility (of whatever type) that has lost all station power and must rely on itself to 

restore power and operation of the facility. The commenter (77) added that these units also 

provide for safety when other station power has failed, which is very important to the nuclear 

power industry. The commenter (77) stated that some of these RICE may also be able to provide 

power to the electrical grid, but all of them operate at historically very low capacity factors 

because of the high cost of operation. The commenter (77) believes that a 3-year average 

capacity factor of 5.7 percent is a more appropriate limit than 100 hrs/yr. The commenter (77) 

noted that the 5.7 percent value is more in line with the restriction of 500 hours placed on 

emergency generators by the State of Ohio. The commenter (77) added that additional controls 

on this category of units would be extremely cost ineffective due to the low capacity factors and 

actual tons of emissions that would be reduced. The commenter (77) conceded that the 

definition of limited use RICE was not a subject of this rulemaking, but believes that it is 

appropriate to modify the definition since it is used to exempt some facilities from the present 

proposed rule at 40 CFR 63.6590(b)(3). 

Response: The 100 hrs/yr the commenters are referring to with respect to limited use engines is 

a provision that EPA included in the original RICE NESHAP affecting stationary engines above 

500 HP located at major sources that was finalized in 2004. EPA is not taking comment on 

aspects of that rule at this time. The engines relevant to this proposed rulemaking are existing 

stationary engines less than or equal to 500 HP located at major sources and existing stationary 

engines located at area sources. A limited use category of 100 hours per yearwas not proposed 

for these engines, nor will one be included in the final rule. See EPA’s response to comment 

6.2.1 on this issue. 
225

 Because EPA is revising 40 CFR part 63, subpart ZZZZ to add requirements for existing 

stationary engines less than or equal to 500 HP located at major sources and existing stationary 

engines located at area sources, it was necessary to modify section 63.6590(b)(3) of the proposed 

rule amendments in order to continue to exempt existing limited use stationary engines greater 

than 500 HP located at major sources. However, in terms of limited use engines, that section 

does not exempt any different or additional existing engines that were not already exempted from 

the original 40 CFR part 63, subpart ZZZZ promulgated in 2004. 

 

6.2 Other Engines 

6.2.1 Comment: One commenter (225) noted that there is no limit on construction date for 

existing RICE in the proposed rule. The commenter (225) stated that older engines were never 

designed to comply with these stringent emissions and some are not easily retrofitted with 

catalysts, if it can be done at all. The commenter (225) added that the expectation for old RICE 

to meet the MACT Floor or beyond-the-floor will be extremely challenging, and there is no data 

in the docket supporting whether the proposed emission limits are even possible. The 

commenter (225) believes that industry could be faced with replacing thousands of existing 

engines (most in rural areas) in order to meet the stringent standards in this proposed rule. 

Response: The commenter has not provided sufficient information to support the claim that 

existing engines cannot be retrofit with catalysts. EPA believes that older engines can use 

oxidation catalysts and is aware of installations of oxidation catalyst on older engines, both 

stationary and nonroad. Also, emission limits for many engines in the final rule do not rely on 
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engines having to be retrofitted, but the expectation is that many engines can meet the final 

emission standards without installing aftertreatment. In fact, for several categories, particularly 

emergency engines and engines less than 100 HP, EPA is not finalizing numerical emission 

limits, but is instead adopting work practices, or use restrictions, instead. 

6.2.2 Comment: One commenter (130) requested that generators used for residential purposes be 

exempted from the proposed rule. The commenter (130) stated that doing so would significantly 

lower the true economic impacts of the proposed rule. 

Response: In response to this comment, EPA analyzed the types of engines that were included in 

the area source category listing for stationary RICE. As a result of this analysis, EPA determined 

that emissions from existing stationary emergency engines located at residential, commercial, 

and institutional facilities that are area sources of HAP were not included in the 1990 baseline 

emissions inventory that was used as the basis for the listing of source categories needed to 

ensure that 90 percent of area source emissions are regulated. Therefore, EPA determined that 

these stationary engines will not be subject to this area source standard. 

6.2.3 Comment: One commenter (230) recommended that EPA allow state and local air 

agencies to determine appropriate exemptions from air permitting requirements, including Title 

V operating permit programs. The commenter cited several examples of state exemptions by 

engine type, size of engine and number of operating hours. The commenter noted that the 

proposed rule would require emergency engines to be incorporated into the Title V permit if 

located at a Title V source. The commenter also stated that states that allow Title V and minor 
227

source exemptions for area source RICE not regulated by EPA would no longer apply. The 

commenter believes the restrictions of hours and fuel types are adequate to limit HAP emissions. 

The commenter also noted that by EPA not proposing a permanent deferral for Title V area 

source permit applications, facilities subject to the proposed regulation will have to submit Title 

V area source applications, which the commenter believes will not enhance compliance and be 

unnecessarily burdensome.

Response: The provisions in 40 CFR 63.6585(d) indicate that area sources subject to 40 CFR 

part 63, subpart ZZZZ, would not be subject to permits under 40 CFR parts 70 or 71 solely 

because of this rule. That provision will apply to the existing stationary engines covered in this 

rulemaking, including existing stationary emergency engines that the commenter is concerned 

about. In addition, residential, institutional, and commercial existing stationary emergency 

engines at area sources are not subject to the final rule. 

6.2.4 Comment: One commenter (230) asked EPA to consider adding a provision to the rule that 

allows implementation of the relevant standards based on technological or economic feasibility 

similar to the 40 CFR 63 GP for reconstruction. 

Response: The requirements in the rule have already been determined to be technologically and 

economically feasible. Furthermore, affected sources have three years to comply with the rule. 

Therefore, EPA does not agree that the provision suggested by the commenter is necessary. 

7.0 Management Practices 
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7.1 General Comments 

7.1.1 Comment: One commenter (183) indicated that EPA did not contemplate the maintenance 

challenges for existing small (less than 50 HP) SI and CI RICE units located in remote 

unmanned locations. The commenter (183) stated that in Alaska remote locations, frequent visits 

for oil and filter changes every 200 hours and 500 hour belt inspections are impractical and 

unsafe. The commenter (183) noted that maintenance has been addressed by installation of large 

fuel tanks, winterization or expansion of the cooling systems, retrofit of oil reservoirs with 55 

gallon reservoirs, and the use of synthetic oils. The commenter (183) proposed that the rule be 

revised to exempt these types of remote unmanned sites from the maintenance interval 

requirements, or at least increase the maintenance intervals to an annual basis. 

Commenter 175 was also concerned about requiring specific maintenance activities for 

engines located in remote, unmanned area sources. The commenter (175) also pointed out that 

its members are developing and promoting new technologies to reduce CO2 emissions. Some of 

this new micro distributed energy covers engines less than 30 HP and it appears that these 

engines could be swept in under the proposed operations and maintenance standard for less than 

50 HP engines located at area sources. The commenter (175) said that it particularly worried that 

the proposed oil and filter replacement standards for such small engines would be overly 

burdensome, unnecessary and would persuade potential customers to instead install electric air 

conditioning and furnaces with a much larger carbon footprint and pollutant emissions measured 

from the source of the power generation (often coal-based) to the end use consumer. This will 
229

undermine efforts to reduce the carbon footprint of the commenter’s (175) members’ customers. 

The commenter (175) asked that EPA exempt area source engines less than 30 HP. 

Response: EPA cannot exempt area source engines less than 30 HP from the rule. EPA has, 

however, provided some flexibility for management practices. Sources have the ability to utilize 

an oil analysis program to extend the oil change frequency. Sources that may have special 

considerations, for example those in extreme cold weather locations, have the option to work 

with State permitting authorities pursuant to EPA’s regulations at 40 CFR subpart E (“Approval 

of State Programs and Delegation of Federal Authorities”) for approval of alternative 

management practices. 

7.2 Specific Requirements 

7.2.1 Comment: Numerous commenters (64, 66, 68, 75, 76, 89, 97, 101, 103, 104, 108, 111, 

112, 130, 131, 132, 136, 148, 150, 151, 154, 155, 159, 174, 176, 179, 183, 187, 204, 221, 224, 

225, 227, 228, 230, 231, 241, 242, 253, 261, 262, 264) did not agree with the specific 

management practices that EPA has proposed in the rule or recommended different maintenance 

practices. According to the commenters (103, 112, 131, 155, 179, 183, 224, 225, 241, 242), the 

maintenance frequency in the proposed rule exceeds current practices or is not supported in the 

proposed rule. Several commenters agreed that management practices are appropriate for the 

proper operation of the engines and is a reasonable means to reduce HAP emissions, however, 

did not agree with the specific maintenance practices proposed by EPA. Numerous commenters 
230

recommended that EPA allow owners/operators to follow engine manufacturers’ recommended 

practices or the owners/operators own site-specific maintenance plan. 

One commenter (155) states that the proposed rule requires oil changes every 200 hours 

and replacement of spark plugs every 500 hours for rich burn engines less than 50 HP. The 

commenters (155, 242) stated that such frequencies far exceed accepted practice and EPA has 

not presented the basis for these frequencies. EPA, in the commenters’ (155, 242) opinion, has 

not presented evidence that the proposed maintenance procedures are appropriate and the 

commenters asserted that EPA should consider other alternative practices or adopt a more 

reasonable frequency for conducting maintenance. 

Another commenter (225) in the oil and gas production industry asserted that there is no 

support in the proposed rule that there is a relationship between the frequent maintenance 

activities proposed and reduced emissions. 

One commenter (103) stated that while oil changes, spark plug changes, and belts and 

hoses checks are essential in maintaining engine reliability, the commenter did not understand 

the basis for the short-term intervals proposed for these maintenance practices. The commenter 

(103) assumes that EPA has tied the affected SI engines to the diesel and mobile source engine 

categories, and has applied similar maintenance practice strategies under the assumption that 

they will result in optimal emissions. The commenter (103) enclosed and summarized 

maintenance requirements for four makes of SI RICE commonly used in the natural gas 

compression industry (Ajax, Cummins, Waukesha, and Caterpillar) and summarized these 

recommendations, which vary widely, but are all less frequent (some much less frequent) than 

the proposed frequencies. The commenter (103) specifically said that air filters should be 

changed based on the differential pressure across the filter, per the manufacturer’s 
231

recommendations, rather than operating hours, to save on the environmental waste of discarding 

perfectly good filters. 

One commenter (112) pointed out that operators have a direct interest in maintaining 

engine oil, hoses, and belts, so the engine runs reliably, but the appropriate frequency for these 

maintenance practices are specific to engine design and are not “one size fits all.” 

One commenter (204) said that for certain existing stationary RICE located at area 

sources, the EPA has proposed specific maintenance schedules in lieu of actual emissions limits. 

For example, for nonemergency two stroke lean-burn engines greater than 50 HP but less than 

250 HP, the EPA would require that these engines change oil and filters every 500 hours, replace 

spark plugs every 1,000 hours; and inspect all hoses and belts every 500 hours and replace as 

necessary. The commenter (204) believed that the EPA has failed to provide a reasonable basis 

for these maintenance schedules and that the schedules exceed what is necessary for the 

effective, efficient, long-term operation of these engines. 

Ten commenters (89, 101, 103, 104, 150, 151, 155, 221, 231, 242, 264) recommended 

that EPA revise fixed maintenance (one-size-fits-all) requirements to maintenance plans. 

The commenters (89, 101, 151, 221, 231, 261) stated that, while fixed maintenance 

intervals work well for new mass produced engines similar to those in automobiles, they are 

inappropriate for the wide variety of existing engines used in the oil and gas, agriculture, and 

power generation industries across the nation. The commenters (89, 101, 151, 221, 231, 261) 

pointed out that EPA allows the use of operator-defined maintenance plans that are “consistent 

with good air pollution control practice for minimizing emissions” to be used in other portions of 

this same rule, and asserted that EPA should allow the use of operator-defined maintenance plans 

to greatly reduce cost and allow operators to optimize maintenance for each type of engine. 
232

 One of these commenters (221) added that current industry engine maintenance programs 

are driven by tried-and-true practices and since these practices effectively keep the engines 

running, they allow the products of the members of the commenter’s organization to go to 

market. The commenter (221) stated that additional, burdensome, frequent, and time-consuming 

maintenance requirements will cause the members of the commenter’s organization to morefrequently shut down engines and thus shut down production. 

The commenters (155, 242) said that if EPA keeps the management practices as 

proposed, the frequencies associated with conducting engine maintenance should be revised to 

be commensurate with today’s practices. The commenter (155) believes the maintenance 

practices, as proposed, are significantly burdensome and lack basis. According to the 

commenters (155, 242), EPA should replace the maintenance hour intervals with company 

recommended performance-based maintenance practices to be documented in an operatordefined maintenance plan consistent with requirements in 40 CFR part 60, subpart JJJJ. 

Two commenters (155, 242) recommended that EPA allow owner and operator-defined 

management practices, in addition to the specific management practices required by the rule. 

EPA has previously adopted a similar approach, e.g., in 40 CFR part 60, subpart JJJJ. In the 

commenters’ (155, 242) opinion, owners and operators of engines are knowledgeable in the 

operation of their engines and are best-suited for determining what practices are appropriate for 

their specific engines. Commenter 242 believed that owner and operator-defined maintenance 

practices will be more cost effective, lead to more consistent and stable combustion efficiency, 

and lower emissions. 

The commenters (155, 242) requested that, if EPA does not allow operator-defined 

maintenance practices, and if EPA cannot define a more appropriate maintenance frequency, 
233

EPA should enlist the assistance and input of industry to determine appropriate management 

practices. The commenter (155) believes that soliciting the participation from stakeholders on 

this matter will ensure management practices that are consistent with reasonable engine 

practices. In general, it seems that the majority of comments received on this issue are in favor 

of adopting engine manufacturer’s maintenance recommendations and not the specific 

maintenance requirements and frequencies that would be applicable to all engines across the 

board. 

 The commenter (103) appreciates the proposal of maintenance practices as an alternative 

to emissions limitations as GACT for small SI engines, but suggested the following alternatives 

to the proposed maintenance requirements: 

• Maintenance practices should be aligned with current industry preventative maintenance 

schedules. The final rule should require owners/operators to comply with the oil change, 

spark plug, and belt/hoses requirements on a schedule dictated by the company’s internal 

preventative maintenance schedules ensuring that the engine is operating at optimal 

conditions. These schedules would then be enforceable by the EPA under the final ruling 

and would require all of the maintenance practices to be conducted on these intervals. 

• As an alternative to aligning maintenance practices with existing preventative 

maintenance schedules, the commenter (103) suggested that the EPA consider operatordefined maintenance plans, which offer a solution to the issue regarding the different 

requirements for various engine make and models. These operator-defined maintenance 

plans should be formal documentation that is fully enforceable under the final rule by the 

EPA as well as state regulatory agencies. The commenter (103) also noted that operatordefined maintenance plans are the current strategy employed by the SI NSPS, 40 CFR 
234

part 60, subpart JJJJ. The commenter (103) believes that since this has been deemed 

appropriate for new sources, and it should also be deemed appropriate for existing 

sources 

 Another commenter (150) in the oil and gas industry agreed that the docket fails to 

demonstrate that the proposed requirements are reasonable or that they meet a cost/benefit test. 

The commenter (150) indicated that EPA should allow operators to engage in alternative 

practices so as to take into account the use of better, more efficient equipment as well as 

individual operators’ historical experience as to what operating and maintenance practices best 

fit their particular operations and facilities. The commenter (150) noted that allowing operators 

to develop their own maintenance practices would be consistent with the SI NSPS (40 CRF part 

60, subpart JJJJ). At a minimum, the commenter (150) believes that prescribed frequencies in 

the rule, if retained, must be revised to be consistent with current reasonable practices. In 

addition, the comment (150) stated that if maintenance frequency is defined in the rule, it should 

be specified in terms of operating hours. 

One commenter (264) supported EPA’s proposal to require non-emergency RICE at 

major sources to properly operate and maintain their stationary RICE and aftertreatment control 

device. However, the commenter (264) has experienced situations where manufacturers’ 

emission-related instructions are inferior to operating experience and that, for old equipment, it 

may be impossible to obtain manufacturer recommendations. The commenter (264) 

recommended that the option of operating according to a maintenance plan developed by the 

owner/operator for the engine be allowed. 

Seven commenters (76, 96, 99, 111, 130, 154, 242) recommended that EPA specify that 

the engine manufacturer’s prescribed requirements can be used to demonstrate compliance. 
235

The commenters (96, 99) thought that there is a better way to make sure owners and 

operators maintain and run their engines appropriately and that would be to follow the 

recommendations of the engine manufacturer. Engine manufacturer’s instructions and 

recommendations are specifically designed to ensure the engine is properly maintained and 

operated. Commenter 76 asserted that there are so many engine designs installed that the engine 

manufacturer is best-suited to determine the appropriate maintenance practices and schedules. 

Commenter 154 said that the Table 2d instructions of the proposed rule may not be 

specifically-designed to ensure proper engine maintenance and operation and may void the 

warranties provided by manufacturers. The commenter (154) recommended that EPA specify 

that the engine manufacturer’s requirements be prescribed to demonstrate compliance. 

According to the commenter (154), in the absence of appropriate specifications, EPA should 

indicate that the current requirements listed in Table 2d of the proposed rule must be followed. 

Another commenter (111) in the oil and gas production industry noted that EPA proposed 

its maintenance intervals with the expressed purpose “to ensure that emission control systems are 

working properly.” In the commenter’s (111) opinion, the manufacturers’ O&M manuals are 

both appropriate and sufficient to address this goal. The commenter (111) stated that 

manufacturer O&M procedures are typically conservative and driven by the equipment-specific 

design. 

One commenter (130) stated that rice irrigation engines may need to be operated beyond 

the proposed maintenance schedules during periods of flooding of rice fields and that relying on 

manufacturer’s suggested maintenance schedules would be more practical and appropriate. In 

some cases, warranty violations may occur if engines are maintained according to the proposed 

stringent schedules, according to commenter 130. 
236

Four commenters (99, 112, 204, 225) provided specific input on the proposed rule oil 

change and air filter requirements (including frequency). 

Commenter 112 noted that many operators use an oil testing program to determine oil life 

to reduce maintenance cost and used oil generated, while maintaining high engine reliability. 

The commenter (112) believes that EPA has failed to justify why recommended oil changes are 

included as a maintenance practice when oil changes have little to no effect on engine emissions. 

One commenter (204) noted that the vast majority of their applicable engines use a 

synthetic lubricant that does not need to be changed unless it is contaminated. This lubricant 

does not degrade over time and, in some instances, can be utilized in engines for over 30,000 

operating hours without requiring changing. The commenter’s (204) operating companies have 

in place sampling programs to ensure that the engine lubricant has not degraded and been 

contaminated. Air filters are regularly checked by determining the differential pressure across 

the filter to determine if a change is needed. The commenter (204) stated that by maximizing the 

useful life of oil and filters while maintaining a responsible maintenance schedule reduces costs 

and waste generation - a win-win proposition versus the proposed maintenance schedule that will 

increase the environmental impact from waste generation and the additional startup after 

maintenance of these engines as well as the costs of compliance for regulated entities. 

One commenter (225) stated that most of the engine manufacturers for the engines in the 

oil and gas industry recommend oil changes on a monthly schedule. The commenter (225) also 

indicated that it is common practice to periodically sample and test the engine oil to see if the oil 

properties are sufficient to extend this time period between oil changes. According to the 

commenter (225), this testing has shown in many cases that the oil change interval can be 

extended without any detrimental effects on the engine, which allows industry to maximize 
237

efficiencies, minimize oil usage, reduce waste, and streamline operations with no negative 

impacts to the engine or emissions. 

One commenter (112) expressed that inspection of hoses and belts has no impact on HAP 

emissions. Commenter 51 expressed that, generally, it agreed that performing maintenance on 

engines will help to reduce HAP emissions, but that while inspecting belts and hoses is an 

important part of general engine maintenance (and most sources likely conduct regular 

inspections of their engines), such inspections have no effect on emissions and should be 

removed from the proposed rule. 

EPA received the most information on the proposed frequency of changing the oil and 

filter. Many commenters indicated that the oil quality is often monitored through an oil testing 

program. Other commenters stated that several engines use a synthetic lubricant, which does not 

degrade as compared to other oil and can be use for extended periods of time without having to 

be replaced. Additional commenters indicating varying appropriate periods of oil and filter 

changes, including every 250 hours to 4,000 hours. 

Response: EPA proposed to require specific management practices for certain engines, primarily 

for smaller existing stationary engines at area sources where EPA thought that add-on controls 

were not GACT. EPA indicated at proposal that the management practices specified in the 

proposal reflected GACT and that such practices would provide a reasonable level of control, 

while at the same time ensuring that the burden on particularly small businesses and individual 

owners and operators would be minimized. EPA asked for comment on the proposed 

management practices and received comments on the proposal from industry. 
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 EPA agrees with the commenters that it is difficult to adopt a set of management 

practices that are appropriate for all types of stationary engines. Regardless, EPA must 

promulgate emission standards pursuant to section 112(d) of the CAA for all engines at area 

sources covered by the final rule. EPA still believes that a management practice approach 

reflects GACT for emergency engines and smaller engines at area sources. These management 

practices represent what is generally available among such engines to reduce HAP, and the 

practices will ensure that emissions are minimized and engines are properly operated. EPA does 

not agree with the commenters that it would be appropriate to simply specify that owners and 

operators follow the manufacturers recommended maintenance practices for the engine. EPA 

cannot delegate to manufacturers the final decision regarding the proper management practices 

required by section 112(d) of the CAA; nor can EPA allow management practices to change 

from engine to engine based on the views of multiple manufacturers. To address the comments 

that there may be special and unique operating situations where the management practices in the 

rule may not be appropriate, for example engines using a synthetic lubricant, EPA notes that 

owners/operators may work with state permitting authorities pursuant to 40 CFR subpart E 

(‘‘Approval of State Programs and Delegation of Federal Authorities’’) for approval of 

alternative management practices for their engines. Subpart E implements section 112(l) of the 

CAA, which authorizes EPA to approve alternative state/local/tribal HAP standards or programs 

when such requirements are demonstrated to be no less stringent than EPA promulgated 

standards. 

 The management practices EPA proposed for stationary engines greater than 50 HP 

included changing the oil and filter every 500 hours, replacing the spark plugs every 1,000 hours, 

and inspecting all hoses and belts every 500 hours and replacing as necessary. For engines less 
239

than 50 HP, EPA proposed to require that these engines change the oil and filter every 200 hours, 

replace spark plugs every 500 hours, and inspect all hoses and belts every 500 hours and replace 

as necessary. 

 According to the additional recommended maintenance procedures that EPA reviewed 

after the proposal for different engine makes and models, EPA agrees that there is a wide range 

of recommended maintenance procedures. Based on the different suggested maintenance 

recommendations EPA has reviewed, maintenance requirements appear to vary depending on 

whether the engine is used for standby, intermittent, or continuous operation. Maintenance is 

also dependent on the engine application, design, and model. Taking into consideration the 

information received from commenters on the proposed maintenance practices for oil and filter 

changes and carefully reviewing engine manufacturer recommended maintenance procedures, 

EPA has determined that for stationary non-emergency 4SLB and 4SRB engines, GACT will 

require the oil and filter to be changed every 1,440 hours of operation or annually, whichever 

comes first, which reflects the management practices that are generally available. Maintaining 

the oil is one of the most important activities operators can perform to minimize emissions and to 

ensure proper operation and performance. The specific oil change interval of every 1,440 hours 

of operation is based on recommendations received on the proposed rule and more specifically 

information received after the rule as a result of EPA’s effort to gain more knowledge on existing 

maintenance practices from Exterran, JW Power Company, and CSI (EJC).9

 These groups have 

extensive engine operation and preventative maintenance experience and indicated that a 

maintenance interval of every 1,440 hours of operation represent current industry practices. The 

maintenance interval in the final rule for non-emergency 4SLB and 4SRB engines is also 

supported by other engine operators, specifically INGAA, whose member companies operate 
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more than 6,000 stationary SI engines along natural gas pipelines. The API, an organization 

representing more than 400 companies in the oil and natural gas industry who operate thousands 

of engines, also concurred with these management practice recommendations. Therefore, EPA 

finds that these management practices and intervals are common practice and generally available 

and appropriate for the final rule. A maintenance interval of every 1,440 hours of engine usage 

will ensure that the components remain in proper condition and continue to perform the 

necessary functions to support proper engine operation, reduce HAP, and minimize emissions. 

EPA believes that the proposed levels of conducting maintenance were beyond current practice 

and would force unnecessary early replacement of the oil, filter and spark plugs, plus more 

frequent unneeded inspection intervals. The proposed rule would have required a significant 

number of oil changes per year. For example, for engines operating close to full-time, 17 oil 

changes would have been necessary per year. Based on comments received on the specific 

maintenance practices EPA proposed and additional information received post-proposal noted in 

the previous paragraph of this response, the proposed maintenance intervals were too frequent 

and inconsistent with current industry practice. 

For stationary non-emergency 2SLB engines, GACT will require the oil and filter to be 

changed every 4,320 hours of operation or annually. Two stroke lean burn engines have a longer 

maintenance interval than 4-stroke engines because 2SLB engines do not have combustion blowby gases entering the crankcase due to the engine configuration and therefore do not have as 

much oil contamination from the combustion blow-by gases. The 2SLB engines also operate at 

lower speeds and temperatures than 4-stroke engines, consequently the spark plug does not fire 

as frequently and fires at lower temperatures than 4-stroke engines. Therefore, 2SLB engines 

should have longer maintenance practice intervals than 4-stroke engines and consequently EPA 
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has determined that the proper interval for stationary non-emergency 2SLB engines is every 

4,320 hours of engine operation or annually, whichever comes first. The specific maintenance 

interval of every 4,320 hours of operation is based on comments received on the proposed rule 

and specific information received post-proposal from Exterran, JW Power Company, and CSI 

(EJC).19 These recommendations are supported by INGAA and API, and EPA agrees that these 

intervals are more appropriate for the standard based on generally available management 

practices. 

For stationary emergency engines, the final rule requires the oil and filter to be changed 

every 500 hours of operation or annually, whichever comes first. The changing of oil and the oil 

filter for stationary emergency engines is more frequent on an hourly basis than for nonemergency engines because of the nature of operation of these engines, which is for emergency 

use, with small amounts of additional run time for testing and maintenance, and thus requires 

less hourly use over the same period of time, and oil quality is reduced over time even during 

periods when the engine is not used. 

EPA also determined that it would be appropriate to include the option to use an oil 

analysis program in the final rule. EPA is including an alternative in the final rule for monitoring 

the quality of the oil through an oil analysis program. Sources have the option to use an oil 

change analysis program to extend the oil change frequencies. The analysis program must 

measure the total acid number (TAN), viscosity, and water content. If the TAN increases by 

more than 3.0 milligrams potassium hydroxide per gram from TAN of the oil when new, if the 

viscosity has changed by more than 20 percent from when the oil was new, or if the percent 

                                                           

19 Memorandum from Rebecca Rentz, Bracewell and Giuliani to Melanie King, EPA. Spark 

Ignited (SI) Recommended Management Practices. January 27, 2010. EPA-HQ-OAR-2008-

0708-0354.1. 
242

water content (by volume) is greater than 0.5, the oil must be changed prior to further operation 

of the engine. 

 EPA does not agree with the comments that inspecting belts and hoses has no impact on 

emissions. Ensuring that the engine is properly operated and maintained will help minimize the 

HAP emissions from the engine. Properly maintained belts and hoses allow the engine to 

operate at maximum efficiency. Hoses are generally used to move coolant through the engine to 

prevent the engine from overheating. Overheating of the engine can cause a malfunction in the 

combustion process, and may also burn the engine oil in the combustion chamber. Both of these 

conditions may increase pollutant emissions from the engine. Belts are commonly used for 

electrical generation and engine timing, and if worn or broken can cause damage to the engine 

and increase emissions. Therefore, EPA has required management practices that reflect GACT 

and that, in EPA’s view, will ensure the proper operation and maintenance of the engine. 

7.2.2 Comment: Several commenters (77, 118, 119, 129, 157, 205, 240) supported EPA’s use of 

maintenance and work practices standards and certain commenters said the management 

practices in Table 2d of the proposed rule (40 CFR 63 subpart ZZZZ) are consistent with the 

proper maintenance of engines, and that the management practices in the proposed RICE 

NESHAP are sufficient to ensure that the engines are properly maintained. 

One commenter (77) supported proposed 40 CFR 63.6625(e), which the commenter 

interprets as allowing owners/operators that must demonstrate compliance with a written 

maintenance plan the flexibility to operate and maintain their units according to either a plan 

written by the manufacturers or themselves “consistent with good air pollution control practice 

for minimizing emissions.” 
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Response: No response is necessary. 

7.2.3 Comment: One commenter (218) said that most of the 2SLB engines it manufactures 

require oil injected into the power cylinder for the critical purpose of lubricating the piston skirt. 

There is developing technology for catalyst friendly oils that do not affect or contaminate the 

catalyst. The commenter (218) added that any emission level claims include any contribution 

from the combustion of this oil. The commenter (218) recommended that there be no restriction 

of the burning of this very small amount of lube oil in the combustion chamber of a 2SLB 

engine. 

Response: EPA does not believe that any of the requirements in the final rule would restrict the 

operation of 2SLB engines as described by the commenter. 

8.0 Parameter Monitoring 

8.1 Comment: A few commenters (104, 126, 150, 155, 176, 220, 224, 242) had different 

remarks regarding parameter monitoring in the proposed rule. Three commenters (155, 220, 

224) wanted EPA to clarify whether parameter monitoring is required for any existing engines 

under the proposal. According to the commenter (155), the preamble and regulatory language 

contain conflicting information and the commenter is uncertain if EPA intended to require 

parameter monitoring for area sources. The commenters (155, 242) said that Table 6 of the 

proposed rule does not required parameter monitoring for area sources, but that the preamble 
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talks about such monitoring for larger area source engines. This should be clarified, commenters 

155 and 242 said. 

 Several commenters (128, 155, 176 and 242) are strongly against parameter monitoring 

for area source engines and three commenters (155, 176, 242) are of the opinion that EPA should 

take into account limitations that exist for these engines that may be located at unmanned 

facilities. In addition, area sources may not have electricity, which will be problematic in terms 

of continuous temperature monitoring, the commenters (155, 242) said. Monthly pressure drop 

readings may also be an issue, the commenters (155, 242) said. Parameter monitoring will add 

significant technical challenges and cost burden, according to the commenters (155, 242). EPA 

has failed to consider all factors, but if EPA decides to require area source parameter monitoring, 

analysis supporting that decision must be presented and justified, two commenters (155, 242) 

asserted. 

One commenter (128) expressed that it supports all of commenter (155) comment, but 

additionally noted in its comments that many of the area sources located in West Virginia are 

unmanned and in remote areas, where it may be difficult or impossible to conduct continuous 

monitoring of certain parameters. 

Two commenters (104, 150) noted that most oil and natural gas facilities are located in 

remote, rural areas, sometimes many hours from the home or field offices, and that many do not 

have access to electricity to monitor and record these parameters. The commenters (104, 150) 

believe that the proposed requirement is unreasonable and costly, and requested that the 

requirement be removed for engines located at area sources. 
245

One commenter (97) believes that EPA should not require parameter monitoring for area 

source engines. The commenter stated that the proposed rule should consider engine location 

and other site limitations if area source parameter monitoring is required.

Response: Parametric monitoring is required for existing non-emergency engines that are larger 

than 500 HP. EPA does not agree that parameter monitoring is not appropriate for area source 

engines. Parametric monitoring is appropriate for these engines because the parameters serve as 

surrogates of the catalyst performance. The pressure drop across the catalyst can indicate if the 

catalyst is damaged or fouled, in which case, catalyst performance would decrease. 

EPA disagrees with the commenters’ views that affordable, long-lasting, off-the-grid 

systems to measure and record temperatures and pressure differential at unmanned, remote 

locations do not exist. One instrument packager and vendor suggested use of his firm’s off-theshelf, battery-operated components. Stand-alone temperature measurements could be made and 

recorded using a single channel data logger ($129), a temperature sensor ($40), and a copy of 

software ($99), while stand-alone pressure differential measurements could be made and 

recorded using a multi-channel data logger ($485), a differential pressure sensor ($220), and a 

copy of software ($89). As the battery life for such systems is over 14 months and the data 

loggers can hold over 43,000 data points – more than 14 months of 15 minute readings – each 

system could operate unattended for more than a year. Assuming that an average source has 4 

engines, equipment costs for a stand-alone temperature system would be under $200 per point, 

while equipment costs for a stand-alone pressure differential system would be under $370 per 

point. Of course, these equipment costs could be further reduced by consolidating the number of 

data loggers. Given that off-the-shelf equipment is available and that plant personnel are 
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expected to visit each remote site at least once per year, when the data loggers could be 

downloaded or swapped out, we find no barriers for measuring and recording 15-minute 

temperature and pressure differential data at remote sites. 

8.2 Comment: A few commenters (112, 126, 150, 155, 176, 224, 227) suggested that EPA 

clarify in the final rule that during months when the engine does not operate, engine operation is 

limited, or the engine operates at reduced load, pressure drop measurements are not required. 

For example, the commenters (112, 155) thought that an engine that has been idle should not be 

started up solely to conduct a monthly pressure drop measurement. According to a few 

commenters, including commenters 155 and 224, there has been implementation issues with 

regards to monthly pressure drop monitoring since the 2004 RICE NESHAP was issued. The 

commenters (112, 155) said that without clarifying this requirement, owners/operators may be 

required to start an engine only to conduct a pressure drop measurement or be forced to 

artificially load the engine to 90 percent of rated load, which may not be possible. In the 

alternative, an owner/operator has to submit an alternative monitoring request to EPA for 

approval. The commenter (155) believes this is an unnecessary burden. The commenter (155) 

noted that it has asked EPA for guidance on this issue, but that the guidance that EPA provided 

in the form of a question and answer document (available at: 

http://www.epa.gov/ttn/atw/rice/riceq_a9-30-05.pdf), did not sufficiently address the issue of 

pressure drop monitoring. The commenter (155) had a number of specific recommendations that 

include the provision that if an engine does not operate during a specific month, does not reach 

100 percent load +/- 10 percent, or has limited operation and is shutdown prior to the 

owner/operator completing the pressure drop measurement, the owner/operator should not be 
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required to startup the engine solely to record the pressure drop. The commenter (155) also 

recommended that the owner/operator should record the pressure drop as soon as practical after 

the engine is started again. 

Similarly, one commenter (112) also asked EPA to clarify that temperature and pressure 

readings are only required when the engine is operating after startup. The commenter (112) 

noted that Tables 1b & 2b, item 1.b of the proposed rule, require the operator to maintain the 

temperature above a set point. However, the commenter (112) pointed out that when an engine 

is first started, there will be an unavoidable but short period of time (approximately 15 minutes) 

when the exhaust temperature is less than 450 F. The commenter (112) requested clarification 

that this startup period will be allowed without resulting in a noncompliance situation. 

One commenter (150) stated that EPA should provide exceptions to the monitoring 

requirements for idle or broken engines inasmuch as a given engine may not always be 

operating. The commenter (150) believes that the rules should be clear that no reporting is 

required for a particular period if, during that period, the engine did not operate. 

One commenter (224) requested that EPA clarify the requirements for re-establishing the 

baseline pressure drop and for conducting catalyst replacement tests. 

Response: EPA reiterates its existing policy that a company is not required to increase the load 

for the sole purpose of measuring pressure drop across the compressor stations, nor is it required 

to start an engine that is idle or broken for the sole purpose of measuring pressure drop. 

However, a company is required to measure the pressure drop once the load is increased to the 

target window, or when operations exceed 30 days (regardless of load), and to document the time 

periods when the RICE is operated below the target window in its required reporting. 
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8.3 Comment: Two commenters (112, 150) noted that when a catalyst must be cleaned or 

changed, the proposed rules require a 60-day notice prior to the retest. The commenters (112, 

150) requested clarification as to the operating values for the pressure drop across the catalyst 

that are to be used during this period, and added that it would appear impossible to operate the 

engine without generating a deviation during this period. The commenters (112, 150) 

recommended that EPA allow the use of an alternative test using a portable analyzer in this 

situation.

Response: The rule does require a 60-day notice prior to testing, however the owner/operator 

does not have to wait until after the catalyst is cleaned or changed to submit the notice. The test 

should be done as soon as possible after the catalyst is changed. Testing using a portable 

analyzer is already allowed by the rule. 

8.4 Comment: Several commenters (98, 126, 129, 157, 216, 220, 247) disagreed that 

owners/operators should conduct parameter monitoring continuously. Two commenters (98, 

129) stated that intervals for monitoring and recording temperature readings for catalysts should 

be reduced. The commenters (98, 129) asserted that measuring and recording catalyst 

temperature should only be required when the engine is operating. Commenter (98) believes that 

it is unnecessary to install continuous temperature monitoring equipment for recordkeeping 

purposes and that the requirements should be revised so that temperature is recorded each day 

that the unit is operated – it would then be at the operator’s discretion to decide to install 

continuous temperature monitoring equipment. The commenter (98) suggested that following 
249

revisions to the monitoring requirements, using as the basis of the revisions the language of the 

proposal preamble: 

“Owners and operators of existing stationary non-emergency 2SLB, 4SLB, 4SRB, and CI RICE 

that are greater than 500 HP and are located at a major/area source must continuously monitor 

and record catalyst inlet temperature at least once every 24-hour period the engine is operated if 

an oxidation catalyst or NSCR is being used on the engine. The pressure drop across the catalyst 

must also be measured monthly. If an oxidation catalyst is not being used on the engine, the 

owner or operator must continuously monitor and record the operating parameters (if any) 

approved by the Administrator.” 

Commenter (220) said EPA should not impose parameter monitoring requirements where 

there is minimal engine operation. 

Two commenters (126, 247) recommended that the inlet temperature testing be 

conducted during performance testing to verify that the inlet temperature is within the allowable 

range during normal operations. 

Response: EPA does not agree that the catalyst inlet temperature should not be monitored 

continuously. The temperature is an important determinate of catalytic activity and resulting 

emissions reduction. The continuous catalyst inlet temperature monitoring will help to 

demonstrate that the emission limitations are being achieved on a continuous basis. The rule 

already requires the catalyst inlet temperature to be testing during performance testing to verify 

that it is within the allowable range. 

9.0 Compliance 
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9.1 Test Procedures 

9.1.1 Comment: Several commenters (97, 112, 155, 224, 227, 242) recommended that EPA 

allow sequential pre and post-catalyst testing instead of simultaneous testing for engines 

complying with the percent reduction option. FTIR testing is expensive and will be a significant 

burden, but if sequential pre and post-catalyst testing is allowed the cost can be minimized. 

According to commenters (155, 242), most owners/operators will choose to comply with the 

percent reduction standard and not the concentration standard. Commenter 242 noted that this is 

because the level of the ppmv standards is very stringent and is exacerbated by the high percent 

efficiency that EPA has assumed. The commenters (155, 242) suggested that EPA allow 

sequential pre and post-catalyst testing for formaldehyde and CO percent reduction, while also 

prescribing practical quality assurance measures (e.g., engine load monitoring) to make sure that 

the sequential measurements before and after the catalytic control device are conducted at similar 

engine operation. 

Response: EPA does not believe the use of sequential pre and post-catalyst testing is appropriate 

for measuring percent reduction for a compliance standard. There are too many variables in the 

operation of an engine and the generated emissions to ensure that the percent reduction was 

being achieved. Changes in load, temperature, or fuel type can change during the test, which 

also affects the emissions. 
251

9.1.2 Comment: Several commenters (112, 132, 148, 150, 155, 186, 242) noted concerns 

regarding the testing requirements with respect to load, specifically regarding the requirement to 

test at high load. However, 90 percent efficiency may not be achievable at reduced load, 

according to the commenter (242) and compliance at all load conditions and SSM periods cannot 

be certified by the responsible official if the performance during off-load conditions is unknown. 

The commenter (242) recommended that EPA consider the broader use of management 

practices, which will lead to less engines requiring performance testing. 

Commenters 132 and 242 is in favor of test requirements at the highest load that is 

achievable in practice +/- 10 percent and this test condition should also limit the emission 

standard applicability to an hourly average period and normal operating condition(s). One 

commenter (155) said that it is supportive of performance testing at full load or the highest load 

that is achievable in order to demonstrate compliance, but that it suggests that EPA specifically 

adds language to the NESHAP to be consistent with the NSPS requirements, which include 

allowing the performance test to be conducted at the maximum load achieved in practice, e.g., if 

greater than 90 percent load is unattainable. Three commenter (145, 155, 242) recommended 

that EPA add the language “or the maximum load achieved in practice” to §63.6610(d)(5) of the 

proposed rule. Commenters 97 and 224 had a similar suggestion. Commenter 230 

recommended the text: 

“The test must be conducted at any load condition within plus or minus 10 percent; if the test 

cannot be conducted within this range, then the RICE cannot be operated at a load greater than 

10 percent of the load during the most recent performance test that complies with the emission 

limitations specified within this subpart.” 
252

The commenter (230) indicated that it is not capable of achieving 100 percent load +/- 10 

percent. 

Two commenters (150, 186) stated that engines should be allowed to be tested at 

maximum attainable load without need for an Alternative Testing Protocol obtained from the 

Administrator on a case-by-case basis. The commenters (150, 186) noted that the proposal 

requires testing at 100 percent load ± 10 percent, but does not specify whether it refers to full 

load for the engine rated at sea level or the site rating. The commenter (150) believes that 

because many engines physically cannot be operated at maximum rated HP for various reasons, 

the rule should contain some allowance to test at lower loads without requiring special approval 

on a case-by-case basis. The commenter (150) stated that the proposal retains high-load 

performance test requirements, but suggests that emission limits would apply at all loads 

including shutdown, while different limits for startup and malfunction. The commenter (150) 

believes that clarification is needed in this regard. Commenter (186) recommended that EPA 

include some allowance to test at lower loads without requiring operators to apply for and 

receive special approval from the administrator on a case-by-case basis. 

The commenter (155) also recommended that EPA indicate in the rule that the emission 

standards only apply at high load and that requirements for demonstrating compliance at other 

operating conditions should be shown with other alternatives. For demonstrating compliance 

and conditions other than high load, the commenter (155) believes that EPA should allow 

engines to use work practices. Requiring work practices would ensure that the engine is 

operating and performing as well as possible during periods other than high load and are 

appropriate since requiring emission standards is not technically and economically feasible, 

according to the commenter (155). The commenter (155) again mentioned that if EPA keeps 
253

emission standards that apply at all operating conditions, then data and a thorough analysis 

should be conducted and made evident and transparent in the rulemaking docket to support that 

decision. The commenter (155) reiterated how combustion chemistry does not support requiring 

the same emission standards at high and lower load, e.g., the commenter pointed to the testing 

conducted at CSU that was used to develop the 2004 RICE NESHAP. Finally, the commenter 

(155) added that the rule should address how cyclic operation and engines with a short run time 

should be addressed in terms of demonstrating compliance. Air compressors and other engines 

may need a separate subcategory that is allowed to demonstrate compliance using work practices 

and not emission standards, in the commenter’s (155) opinion. 

One commenter (112) asked that EPA allow engine testing at the maximum attainable 

load without requiring application for and receipt of special approval from the Administrator on 

a case-by-case basis. The commenter (112) noted that as proposed, engines tests must be 

conducted at load conditions of 100 +/- 10 percent, but the proposal does not specify whether 

that is 100 percent of full load for the engine rated at sea level or 100 percent of the site rating. 

The commenter (112) stated that many engines cannot physically be operated at the maximum 

rated HP due to gas field pressure, compressor restrictions, gathering system limitations, etc. 

 Another commenter (148) stated that many of the engines in the oil and gas industry are 

oversized for various reasons, such as the need to accommodate potential increases in future 

production, a decrease in the HP needed due to decreasing gas volumes being processed, or use 

of a larger engine than needed because it is available and it is not economical to purchase a 

smaller engine. The commenter (148) indicated that for these reasons it is not uncommon for an 

engine in the oil and gas field to operate at 60 to 80 percent load during the majority of its 

lifetime. The commenter (148) added that there are many instances when an engine cannot 
254

operate at full load due to gas pressure in the system, the size of the compressor that the engine is 

powering, site elevation, temperature, etc. The commenter (148) asserted that requiring the 

engine to be tested at 90 to 110 percent load is not always representative of actual operating 

conditions and could introduce situations where compliance with this requirement is not 

achievable. 

Response: EPA revised the emission standards to include additional data collected at loads less 

than 90 percent to capture the variability in stationary engine operation that can affect the HAP 

emissions. Since the emission limitations are based on operation over a range of loads, EPA 

believes that it would be appropriate to allow performance testing to be conducted at normal 

operation rather than during high load. In the final rule, EPA has included language specifying 

that performance testing can be conducted at normal operating conditions to demonstrate 

compliance with the emission standards. In addition, EPA has lowered the percent reduction 

requirements, and revised the consequent specified emission levels, to take into account 

operation at varying levels of operation, consistent with the testing that was used to develop the 

2004 NESHAP. EPA believes this satisfies the commenters’ concerns on this issue. 

9.1.3 Comment: One commenter (96) asked that EPA include in-use measurement allowances in 

the final rule. The commenter (96) said that EPA will need to include adequate measurement 

allowances to account for the relative accuracy and variability of in-use measurement systems 

when compared with laboratory-based CVS emissions measurement systems, like is being done 

for in-use NTE testing for mobile sources, in order to make sure those in-use tests are fairly 

comparable to any certification tests related to the engines at issue.
255

Response: EPA does not believe the inclusion of in-use measurement allowances is necessary or 

appropriate for the final rule. EPA believes that the QA/QC requirements that have been 

developed for the approved test methods and procedures are sufficient measures to ensure that 

the engines are meeting the requirements.

9.1.4 Comment: One commenter (76) indicated that it had provided significant comments in 

February 2009 on EPA’s Continuous Parameter Monitoring Systems proposal and believes that 

extensive revisions are needed of Performance Specifications 17 and 4. The commenter (76) 

asked that EPA review these procedures to determine their appropriateness for even larger 

engines and suggested that EPA remove the reference to 40 CFR 63.6(a)(2) from Table 8 of the 

proposed rule, i.e., change “Yes” to “No” for this paragraph of the General Provisions. 

Response: EPA does not agree with the commenter that the reference to 40 CFR 63.8(a)(2) 

should be “no”. The commenter did not provide any information to support the claim that the 

Performance Specifications and 40 CFR 63.8(a)(2) are not appropriate for stationary engines. In 

response to this comment, EPA reviewed the proposed Performance Specification and 

determined that it is appropriate for stationary engines, including spark ignition engines. In order 

to clearly indicate the requirements from the Performance Specification that should be followed 

for the stationary engines subject to this NESHAP, EPA has included the Performance 

Specification requirements in 40 CFR part 63 subpart ZZZZ. 
256

9.1.5 Comment: A few commenters (76, 188, 191) expressed concern over the cost of testing 

stationary engines, especially rich burn engines. One commenter (188) noted that in the 

proposed rule EPA chose to require an initial performance test only for stationary RICE located 

at area sources that are subject to numerical emission standards; however, if the engine is rebuilt 

or overhauled it must be re-tested to demonstrate that it meets emissions standards. Vendor 

estimates to comply with this requirement ranged from $40,000 to $50,000 to stack test one unit 

to demonstrate compliance with the requirement for 90 percent formaldehyde reduction. The 

commenter (188) felt that such costs are grossly out of proportion to the perceived benefit and 

that it would be very constructive if the EPA and stakeholders developed more economically 

practicable methodologies for monitoring relevant HAP from operations utilizing stationary 

RICE. The commenter (188) suggested that in cases where catalytic aftertreatment of stationary 

engine exhaust is warranted for HAP control, a potential regulatory alternative is to make 

catalytic converter vendors responsible (by warranty) for the performance of their products in 

lieu of expensive stack testing to as required for automotive catalysts. 

One commenter (76) noted that it currently tests three 4SRB engines greater than 3,000 

HP annually for formaldehyde. The commenter (76) stated that the performance test and 

sampling costs for these annual tests is approximately $35,000. The commenter (76) pointed out 

that EPA concluded that sources could test for CO/O2 for $500 to $1,000 per engine using a 

rented portable analyzer with the necessary calibration gases. The commenter (76) stated that it 

would seem reasonable and economical to test engines greater than 100 HP with portable 

analyzers, however it is not reasonable or economical to do formaldehyde testing on 4SRB 

engines 1/10th the size, but 10 times the population. 
257

One commenter (191) stated that there are issues with the formaldehyde test protocol and 

for small engines (less than 50 HP) the cost of the formaldehyde test may surpass the cost of a 

new engine that size. The commenter (191) suggested that CO as a surrogate is preferable to 

formaldehyde testing. 

Response: In the final rule, EPA is promulgating Method 323, which provides a lower-cost 

alternative for measuring formaldehyde. Performance testing is necessary to show that the 

emission limits in the rule are being met and EPA does not believe that the testing requirements 

in the rule are overly burdensome. For engines smaller than 500 HP, the rule requires an initial 

test only. EPA does not agree with the commenter who suggested that EPA rely on vendor 

guarantees in order to demonstrate compliance from sources using catalytic aftertreatment. For 

the engines that are subject to emission standards that necessitate the use of aftertreatment EPA 

believes it is appropriate and reasonable to require performance testing. 

9.1.6 Comment: Three commenters (76, 154, 188) supported the exemption of emergency 

and/or small engines from performance testing requirements. One commenter (188) noted that 

for smaller units at area sources, subject to numerical emission standards, it is unreasonable and 

not cost justified to require testing for such small emission units that in many cases only run a 

limited number of hrs/yr and produce negligible HAP emissions. The commenter (188) 

recommended that in the event EPA still believes testing is warranted for area sources, alternate, 

lower cost testing methodologies, i.e. grab samples of stack gas before and after the catalyst, 

should be allowed. 
258

Response: EPA agrees with the commenters that testing should not be required for emergency 

and small engines. The proposed rule specified that stationary emergency engines and stationary 

engines less than 100 HP were not subject to performance testing. EPA believed at proposal that 

it would not be reasonable to subject emergency engines at area sources to performance testing. 

In the final rule, stationary engines less than 100 HP and stationary emergency engines are 

subject to work practices or management practices, for which emissions performance testing are 

unnecessary and not required. EPA does believe that testing is warranted for stationary nonemergency 4SLB and 4SRB engines at area sources that are larger than 500 HP and operated 

more than 24 hours per calendar year. EPA does not believe that the costs for such testing are 

unreasonable and has specified that portable analyzers can be used for testing of CO, which 

reduces the cost of testing. 

9.1.7 Comment: Two commenters (193, 267) recommended adding a provision in the emissions 

testing protocol to allow for initial and subsequent emission testing to be performed on a single 

engine when a facility has multiple equivalent engines. The commenter (267) stated that the 

district operates and maintains over 2,000 miles of canals, 60 pumping stations, and 2,200 water 

control structures. It (267) reported that the district pump stations have multiple engines 

consisting of the same manufacturer, model, manufactured date, approximate operating hours, 

HP rating and maintenance program. The commenter (267) opined that it is not cost effective to 

perform formal testing on multiple engines if it can be demonstrated through contemporaneous 

screening of each engine that the worst case engine was selected. The commenter recommended 

the following insert: 
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“If a facility has multiple equivalent engines, the owner or operator can perform screening of 

each engine for the targeted pollutant using the applicable EPA Test Method. The formal testing 

must be performed on each engine until the readings are stable.” 

Response: For existing engines, EPA disagrees with the commenter that the performance of a 

compliance test on a single engine can be used to show compliance for the equivalent engines 

located at the same facility. EPA cannot be certain that the engines have been operated 

identically, have had the same operational, deterioration, and malfunction experiences, and have 

undergone the same maintenance, all of which could affect the emissions. Therefore, EPA does 

not believe that it is appropriate to allow the use of the test on a single existing engine to show 

compliance for other engines that are the same make and model. EPA has attempted to have as 

little testing as is necessary to ensure that engines are meeting the standard.

9.2 Test Methods 

9.2.1 Comment: A few commenters (97, 155, 224) support the CO test methods in the proposed 

rule, which include EPA Method 10, FTIR methods Method 320 and ASTM Method D6348-03, 

and ASTM Method D6522-00 (2005) using a portable analyzer. Two commenters (124, 132) 

also expressed that they support ASTM Method D6522. Commenter 242 also supports the use of 

EPA Method 10 and ASTM D6522 for CO testing. Commenters 124, 132, 155 and 242 said that 

EPA should also specify that alternative methods approved by the Administrator are allowed for 

portable analyzers and recommended the following specific language to be added to footnote a in 

Table 4 of the proposed rule: 
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“Alternative portable analyzer methods approved by the Administrator or delegated 

authority are also acceptable.” 

Response: Table 8 of the rule allows for the use of alternative test provisions as specified in 

§63.7(f) of the GP. This provision allows the owner or operator to petition the Administrator of 

their intention to use an alternative test method at least 60 days before the performance test is 

scheduled to begin. Therefore, EPA does not believe that the suggested footnote is needed to be 

added to Table 4 of the final rule. 

9.2.2 Comment: Two commenters (155, 224) were of the opinion that EPA should allow FTIR 

test methods in the final rule as acceptable methods for measuring CO percent reduction. The 

FTIR methods are already included for measuring concentration and the commenter (155) does 

not see why those methods should not also be included for percent reduction.

Response: EPA agrees that it is acceptable to measure the percent reduction of CO using the 

allowable FTIR methods and has specified that this is allowable in Table 4 of the final rule.

9.2.3 Comment: Many commenters (97, 112, 130, 132, 136, 150, 155, 186, 204, 213, 224, 225, 

241, 242) thought that EPA should reconsider whether EPA Method 323 could be included in the 

final rule or if there is another viable alternative to EPA Method 320. EPA Method 323 was 

published in the Federal Register on January 14, 2003 as a proposed test method to measuring 

formaldehyde from natural gas stationary combustion sources, but the method was never 

finalized. However, the commenters (155, 242) said that the method has been used on a 
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consistent basis to measure formaldehyde from gas engines for compliance and other purposes. 

EPA Region 8 has test results that indicate potential issues related to the reliability of EPA 

Method 323 and therefore method was therefore not included in this proposed rule. (The 

commenters (155, 242) said that they believe that testing errors may have been a factor in the 

anomalous results from EPA Region 8. The commenters (155, 242) have reviewed some of the 

test reports in question and noted potential calculation or testing errors.) The FTIR method, 

which is the single formaldehyde test method in the proposal, compared to Method 323 is more 

complex and often more expensive, according to two commenters (155, 242). In addition, 

several commenters (112, 136, 155, 186, 204, 242) have concerns about whether there will be a 

sufficient amount of available testing companies to meet the performance testing demands of the 

rule. For these reasons, several of the commenters said that EPA should look back at Method 

323 as a viable method and at the same time consider other alternatives for measuring 

formaldehyde. Commenter 150 and 225 believe that alternatives related to measurement 

feasibility must be considered, or an easier-to-measure surrogate for formaldehyde must be 

identified. After EPA proposed to remove Method 323 as a compliance test method, the Agency 

received test data comparing Method 323 to EPA Method 320. This information is available in 

the docket as Document ID Number EPA-HQ-OAR-2008-0708-0467.1.

Response: EPA Method 323 was first proposed as part of the NESHAP for Stationary 

Combustion Turbines published January 14, 2003, (68 FR 1888) for measuring formaldehyde 

emissions from natural gas-fired sources. However, the method was not included in the final 

Stationary Combustion Turbine NESHAP due to reliability concerns and EPA never 

promulgated EPA Method 323 as a final standard in 40 CFR part 63, appendix A. Despite this, 
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many sources chose to use the method for compliance testing and as EPA reviewed the results 

from the method two issues emerged. A few testers seemed to produce results with the method 

that were consistently biased low, and occasionally testers were unable to meet the performance 

requirement for collecting duplicate samples whose results agreed within ± 20 percent. Because 

EPA was unable to resolve these technical issues with the method, EPA found it appropriate to 

propose to remove the method from 40 CFR part 63, subpart ZZZZ. 

 After EPA proposed to remove Method 323 as a compliance test method, the Agency 

received test data comparing Method 323 to EPA Method 320. These comparison tests were run 

on five different engines with samples collected concurrently from co-located sampling systems. 

The results from the two methods showed good agreement and there was no evidence of bias in 

the results from Method 323. Also, during the comparison testing, there were no problems 

meeting the quality assurance requirement in Method 323 for agreement between duplicate 

samples. A careful review of the earlier data where some testers using Method 323 were 

consistently producing biased results showed that these testers did not always perform the 

method correctly. Based on the results of the comparison testing, EPA believes that when 

competent testers perform Method 323 according to all of its requirements, the method will 

produce accurate and consistent results and it is appropriate to allow sources the option to use 

Method 323 to demonstrate compliance with the formaldehyde emission limits in 40 CFR part 63 

subpart ZZZZ. Therefore, we are adding Method 323 to Appendix A of Part 63 in the final rule.

9.2.4 Comment: Seven commenters (104, 112, 130, 132, 136, 155, 225, 242) believe that CAA 

section 112(h) alternatives are necessary for measuring formaldehyde emissions from rich burn 

engines because testing will not be accessible due to FTIR test van access to remote locations, 
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cost, and commercial availability. Otherwise, an alternative surrogate for formaldehyde should 

be established, the commenters (155, 242) said. The commenters (155, 242) estimated that about 

80,000 rich burn engines will be have to conduct initial performance testing when the rule 

becomes effective based on population numbers EPA has provided in the docket. Based on this 

number and assuming that FTIR test van can test 150 engines per year, approximately 540 FTIR 

testing vans and personnel would be required, which the commenters (155, 242) do not believe 

are available. According to one commenter (155), quality testing personnel is about 10 percent 

of that number (540 x 10 percent = 54) and the commenter speculated that there is minimal 

incentive for new FTIR testing personnel to join the market since the engines are only subject to 

initial testing. Another commenter (242) estimated that even less industry expertise is available 

and said that less than 5 percent of the 540 FTIR testing vans anticipated to be required would be 

available. The commenters (155, 242) both also think that short-term demand for one-time 

testing may lead to unqualified testing companies entering the market. To solve these issues, the 

commenter (155) recommended that EPA implement more GACT management practices instead 

of emission limits for area source engines. The commenters (155, 242) expressed that section 

112(h) of the CAA alternatives (e.g., work practices) triggered by emissions measurement 

infeasibility must be considered, a simpler surrogate than formaldehyde for HAP emissions must 

be identified, and/or current issues preventing the inclusion of Method 323 in the final rule 

should be resolved. 

Commenter (112) asserted that requiring Method 320 exclusively poses the following 

significant implementation problems: 

• Many emissions testing contractors do not have FTIR technology nor qualified technical 

personnel to operate the equipment and interpret results. A significant increase in 
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demand for FTIR analysis would result in a serious shortage of qualified and sufficiently 

equipped testing firms. 

• Simultaneous pre-catalyst and post-catalyst testing would require two complete FTIR 

systems to determine destruction efficiency across the catalyst. 

• Engines located in remote areas, only accessible by dirt roads with difficult terrain, could 

be impassible for trailers large enough to conduct testing. FTIR instruments have 

delicate optics, often making it necessary to drive no more than 5 miles per hour down 

rough dirt roads. Increased drive times would significantly increase the cost of the test. 

• The cost of EPA Method 323 testing runs $1000 to $2,500 per test. FTIR testing is 

estimated at $4,000 to $4,500 per test ($8000 for pre- and post-catalyst). Increased costs 

will put a serious strain on both the gas industry and the stack testing industry. The 

number of additional tests for engines as small as 100 HP at remote area sites is 

enormous and unreasonable, with little or no benefit to the environment. 

Response: As discussed in the response to comment 9.2.3, EPA is promulgating Method 323 for 

formaldehyde as part of this final rule. This provides an alternative compliance method to FTIR 

testing. This addresses the concerns expressed by the commenters. Also note that the final rule 

requires more than 90 percent of engines located at area sources to meet management practice 

standards, which means that those engines will not have to do performance testing. 

 

9.2.5 Comment: One commenter (155) supports EPA’s decision in not using data measured with 

CARB Method 430 in the above-the-floor analysis. This commenter (155) and commenters 97 

and 228 agree that the method is non-quantitative and deficient and EPA should make sure that 
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no CARB Method 430 data is included in formaldehyde data used for the rulemaking. 

According to the commenter (155), CARB Method 430 tests are subject to a low bias for sources 

where NOx is present (e.g., natural gas engines) because NOx reacts and depletes the impinger 

solution. The MACT floor analysis includes formaldehyde data obtained used CARB Method 

430, the commenter (155) said, although EPA has generally said that CARB Method 430 data 

should be invalidated and eliminated from any analysis. EPA should explain why it has 

selectively chosen to use some CARB Method 430 data or eliminate CARB Method 430 entirely 

from any data used for the rulemaking.

Response: The proposed rule did include CARB Method 430 test data that was used to calculate 

the MACT floor and above-the-floor standards. Since that time, EPA has received numerous 

comments regarding the low bias of formaldehyde results due to the reaction of NOx and the 2,4-

dinitrophenyl hydrazine (DNPH) impinger solution. Because of this possible interference, EPA 

has removed all formaldehyde test data that was performed using the CARB 430 test method. 

EPA agrees that it is inappropriate to use any CARB Method 430 data. The final standards do 

not rely on any test data captured by CARB Method 430. 

9.2.6 Comment: Three commenters (121, 149, 150) stated that EPA should allow alternatives to 

performance testing. One commenter (121) said EPA should allow sources the option to use test 

results from other non-EPA test methods to demonstrate compliance as long as the data was 

gathered using an approved procedure. The commenter (121) said that its members (automotive 

manufacturing) indicated that the cost per sample run using Methods 1, 3, 4, and 10 could easily 

exceed $10,000, excluding costs to prepare for the sampling (i.e., scaffolding, stack extensions, 
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etc.). In addition to these cost considerations, as a practical matter, there would be significant 

difficulty in performing these EPA test methods on engine exhaust. To reduce the compliance 

burden, the commenter (121) suggested that EPA replace the emission limits with percent 

reduction and allow owners and operators to use portable analyzers for all performance testing, 

given the familiarity with this equipment and the significantly lower cost of this equipment. 

One commenter (150) stated that EPA should allow the use of portable analyzers (rather 

than EPA protocol testing) to assess CO emissions after catalyst replacement and 

overhaul/rebuild and for the 8,760-hour/3-year test. The commenter (150) indicated that this 

would be in keeping with state agency practice for sources that require periodic emission tests as 

part of their monitoring schedules. 

Response: EPA has already addressed the commenters’ concerns. The NESHAP allows the use 

or portable analyzers to show compliance with the CO emission standards. The method ASTM 

D6522-00 is a portable analyzer method.

9.3 Frequency 

9.3.1 Comment: One commenter (155) said that engines greater than 500 HP located at major 

sources that were rich burn engines had to conduct an initial performance test plus parameter 

monitoring and performance testing after catalyst replacement under the 2004 RICE NESHAP. 

The commenter (155) said that no subsequent testing was required for these engines, however, 

under the current proposal, engines greater than 500 HP at major sources are subject to periodic 

test requirements, which will include test requirements for rich burn engines affected by the 2004 
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RICE NESHAP. The commenter (155) expressed that EPA should reconsider this requirement 

and either clarify that additional testing is not required for existing rich burn engines between 

500 and 5,000 HP or provide an explanation and justification that supports adding new test 

requirements. 

Response: EPA did not intend to require additional periodic test requirements for rich burn 

engines greater than 500 HP at major sources and in the proposed rule. The same testing 

requirements in the 2004 RICE NESHAP still apply to these engines. This has been clarified in 

Table 3 in the final rule.

9.3.2 Comment: A few commenters (104, 150, 155) were unclear on the requirements related to 

when a catalyst is replaced. One commenter (155) said that EPA should clarify in the final rule 

that after a catalyst has been changed when the owner/operator conducts a performance test that 

this test fulfills the periodic test requirement. In other words, the schedule to perform future tests 

should be reset when the catalyst change test is completed, the commenter (155) said. The 

commenter (155) additionally noted that the rule does not specify the timing to conduct a 

performance test after a catalyst has been replaced. It was recommended that 63.6640(b) of the 

proposed rule be revised to indicate that 180 days is allowed to conduct this test, by commenter 

(155). Alternatively, the commenter (155) suggested that EPA revise 63.6610(a) to indicate that 

180 days applies to both initial testing and after a catalyst change. 

The commenter (155) also wanted EPA to clarify that temporary catalysts used during 

washing or cleaning should not trigger a catalyst change test. According to the commenter 

(155), the original catalyst may be cleaned offsite by a catalyst vendor and in a the meantime a 
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temporary catalyst is used. The commenter (155) said that an appropriate time period should be 

allowed to operate the temporary catalyst without having to conduct testing and recommended 

that sources be given 45 days to operate an engine with a temporary catalyst without conducting 

a test as long as the original catalyst is reinstalled following cleaning. 

One commenter (104) noted that proposed 40 CFR 63.6640 requires that when the 

catalyst is replaced, the operator must reestablish the values of the operating parameters 

measured during the initial performance test and then conduct a performance test to verify 

compliance and asked what the need for the initial test is as it may not be accurate. 

One commenter (150) stated that EPA should clarify the requirements regarding what 

testing is required after catalyst replacement. The commenter (150) believes that there is no need 

for a complete performance test after a catalyst is changed. 

Response: As the commenters noted, the rule does not specify a time for conducting a 

performance test after a catalyst change. However, the performance test after a catalyst change 

should be conducted as soon as possible to demonstrate that the engine is still in compliance with 

the applicable standards. It should be noted that the owner/operator must notify the EPA 

Regional office or the delegated authority 60 days prior to performing the test. The 

owner/operator may seek an adjustment to the 60 day notification requirement from the EPA 

Regional office or delegated authority if the owner wishes to conduct a performance test as soon 

as possible following the catalyst change. The performance test after a catalyst change can be 

used to satisfy the performance testing requirement. However, a request to waive the 

performance testing requirement must be submitted to the EPA Regional office or delegated 
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authority indicating that the catalyst change performance test will be used to satisfy the 

requirements for the required testing requirement under the rule. 

 In regards to the issue of whether a performance test is required when a temporary or 

“loaner” catalyst is being used while the primary catalyst is being washed or cleaned, EPA 

believes that this should be addressed on a site-specific basis and is dependent on additional 

information such as the type of “loaner” catalyst, the length of time the “loaner” catalyst is used, 

and the compliance history of the engine. After the primary catalyst has been washed or cleaned, 

a performance test may be required if the delegated agency has decided that the initial 

performance test is no longer representative of the performance of the affected source. EPA 

believes that routine washing of the catalyst is unlikely to cause the initial test to no longer be 

representative. However, this determination of whether a retest is required should be made by 

the delegated agency on a case-by-case basis. 

9.3.3 Comment: Two commenters (112, 242) expressed similar concerns regarding the test 

requirements for engines that are rebuilt or overhauled. One commenter (242) said that EPA 

should clarify in the final rule that additional performance tests are not required for engines 

between 100 and 500 HP after a rebuild or overhaul or alternatively explain and justify the cost 

and benefits of requiring such testing. According to the commenter (242), the preamble and rule 

text contain conflicting information on this topic and EPA must clarify this in the final rule. 

One commenter (112) asked that EPA allow alternative test procedures under certain 

conditions. The commenter (112) noted that while EPA stated in the proposal preamble that 

engines 110 to 500 HP do not require subsequent tests, an additional test must be carried out if 

the engine is rebuilt or overhauled. The commenter (112) indicated that based on the applicable 
270

definition, compressor engines may undergo an overhaul as often as every 2 to 3 years. The 

commenter (112) believes that requiring a reference test method each time an engine is 

overhauled is excessive and unnecessary. 

 The commenter (112) indicated that State agencies accept portable analyzer data with 

short duration runs (i.e., 6 minutes) as an acceptable means to facilitate measuring emissions 

from sources that require periodic emission tests. The commenter (112) added that these State 

agencies typically require the use of an approved protocol to ensure consistency and to provide a 

minimum level of quality assurance during the testing process. The commenter (112) asserted 

that EPA should allow the use of portable analyzer tests, using a State approved protocol for the 

State in which the engine is operating rather than the EPA Reference Method Performance Tests 

in the following circumstances: 

• Engine rebuild or overhaul, 

• Replacement of O2 sensor (which occurs every 3 months), 

• Catalyst washing or replacement, 

• Re-establishment of benchmark pressure drop. 

 The commenter (112) believes that if EPA intends to require performance tests in these 

situations, the increased cost should be captured in EPA’s economic analysis. The commenter 

(112) added that EPA should reevaluate the frequency of testing that is required above that of 

annual performance testing. 

Response: EPA believes that it is appropriate to require testing for stationary engines that have 

been rebuilt or overhauled even though the engines may only normally be required to conduct an 

initial performance test and no subsequent testing. The rebuilding or overhaul of the engine may 
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change the combustion characteristics of the engine. EPA does not believe that these 

performance tests after an engine is overhauled or rebuilt are excessive or unnecessary. The 

required testing will ensure that the rebuilt or overhauled engine still meet the applicable 

emission limits, therefore ensuring compliance with the applicable standards. 

 EPA has incorporated portable test methods that meet the QA/QC criteria of comparable 

EPA test methods. The rule does allow the petition of alternative test methods under 40 CFR 

§63.7(f) of the GP. This provision would allow the owner or operator to use an alternative test 

method from that specified in the standard provided that the owner notifies the Administrator of 

the intention to use an alternative test method at least 60 days before the performance test is 

scheduled to begin, uses Method 301 in appendix A of this part to validate the alternative test 

method, and submits the results of the Method 301 validation process along with the notification 

of intention and the justification for not using the specified test method. 

 In response to EPA including the costs of these tests for rebuilding or overhauling of 

engines, catalyst washing and replacement, or re-establishment of benchmark pressure drop, 

EPA does not believe that these additional testing costs need to be included because the analysis 

presented in the rule shows the costs in the year 2013, or the first full year after implementation 

of the rule, and it is unlikely these costs will be incurred in that year. For the replacement of the 

O2 sensor, EPA does not require testing and therefore the testing costs were not included in the 

economic analysis.

9.3.4 Comment: One commenter (76) asked that EPA modify 63.6612(b) of the proposed rule to 

allow past performance tests conducted in the last 5 years to be used instead of the 2 years that 

this paragraph currently requires. The commenter (76) believes that testing conducted in the last 
272

5 years is representative of current emissions in many cases and the commenter thinks that it is 

appropriate for EPA to allow such tests to be used to demonstrate compliance. 

 Another commenter (116) had a similar request that for areas sources that are subject to 

new testing requirements, this could be modified to allow tests that are not older than 3 years, 

since the promulgated rule will allow 3 years for compliance. The commenter (116) asserted that 

there are so many engines that will be required to be tested that it is reasonable to allow facilities 

more time to accomplish the testing before the compliance deadline. 

Response: EPA believes that the requirements in §63.6612(b) of the rule are appropriate. 

Performance tests older than 2 years may not be representative of the current emissions from the 

engine. Maintenance of the engine requires replacement of parts that may affect the combustion 

characteristics of the engine, which in turn will affect the emissions of the engine. In addition, 

EPA believes that the 2-year limit of performance test reports will also allow sufficient time for 

the sources to perform any applicable testing at their facility before the compliance deadline. 

9.3.5 Comment: Several commenters (87, 98, 112, 126, 139, 186, 197, 216, 227, 229, 236, 247) 

expressed that they disagreed with the testing requirements in the proposed rule. Multiple 

commenters (87, 112, 126, 139, 157, 186, 236) took issue with the testing requirements for nonemergency stationary RICE greater than 500 HP of every 8,760 hours of operation or 3 years. 

Two commenters (112, 186) indicated that strict adherence to a test schedule based on operating 

hours is difficult to manage in large fleets of engines due to availability of testing personnel, 

equipment breakdowns, weather conditions, safety considerations, etc. Consequently, the tests 

would necessarily be conducted more frequently than annually to ensure completion of tests for 
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the entire fleet within the operating hour time limit. Two commenters (112, 186) suggested that 

reduced test frequency should be allowed when two consecutive tests demonstrate compliance 

with emissions limitations (such as is allowed in the footnote to Table 6 of the proposed rule). 

The commenters (112, 186) added that upon any non-compliance with emissions limitations, the 

test frequency could revert to the original schedule. The commenter (112) also suggested that 

EPA should consider a reduced testing frequency, 3 years, for any engine in compliance for two 

consecutive performance tests, regardless of operating hours. 

Two commenters (236, 247) stated that EPA’s proposed frequency of performance tests 

(every 3 years) is excessive and recommends that frequency of performance testing be based on 

hours of operation. The commenter (236) noted that some engines are run very infrequently over 

their entire service life. 

Two commenters (126, 197) suggested that the frequency of performance tests be based 

on hours of operation. The commenter (197) asserted that many RICE have low dispatching 

hours and the required performance testing would contribute to a significant amount of their 

operating time. The commenter (197) recommended that limited use RICE should not be 

required to demonstrate that the control equipment is functional more than once.

One commenter (87) stated that the requirement to test every 3 years for units that do not 

run very often is unreasonable. The commenter (87) added that based on actual run time 

(including peak shavers) for 14 stationary RICE that would be subject to this testing requirement, 

the average 3 year cumulative run time was 105 hours, and without peak shavers, 37 hours. 

Further, the commenter (87) stated that most generator engines are not equipped with easyaccess test ports and would have to be modified for testing, the cost of which have not been 
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captured in this rule. The commenter (87) recommended that provisions for testing units that are 

not run frequently should be considered. 

One commenter (139) stated there is limited or no benefit for requiring owner and 

operators of non-emergency, limited use RICE greater than 500 HP to perform time-consuming 

and expensive tests every 3 years. The proposed rule would require owners and operators of all 

existing stationary non-emergency RICE greater than 500 HP to conduct an initial performance 

test and subsequent tests every 8,760 hours of operation or every three years, whichever comes 

first. For some RICE, operation would be required simply to conduct the testing, which is 

unreasonable. The commenter (139) urged EPA to revise the proposed rule so that subsequent 

testing of these engines is only required every 8,760 hours of operation. 

Commenter (227) said the proposed requirement for area sources to conduct an 

unnecessary and burdensome initial performance test should be replaced by an engine tune-up 

procedure, which would be adequate given the limited operation of the emergency engines. 

Commenter (216) said EPA should revise the proposed rule and limit performance testing 

requirements to non-emergency 2SLB and 4SLB engines greater than 250 HP and CI engines 

greater than 300 HP located at major sources. 

Commenter (229) believed that requiring a performance test for existing area source 

RICE greater than 500 HP (when the same engines at a major source facility are not required to 

be tested) seems completely unreasonable. Commenter (229) adds that the engines would be 

required to operate for the performance test when they would normally not be operating, creating 

emissions that would normally not be produced, and questioned the benefit of this, and asked 

what EPA would require the source to do if the test results were above the emission standard. 
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Commenter (229) noted that while EPA is stipulating that performance testing of existing 

engines is not required for major source facilities in the proposed rule, because an emission 

limitation is being proposed, this does not preclude state agencies from specifying performance 

test requirements as a compliance demonstration condition in Title V Permits . Accordingly, 

commenter (229) reiterated that appropriate work practice standards are the practical requirement 

for all existing emergency engines at major and area source facilities in lieu of any emission 

limitation standards. 

One commenter (98) argued that performance test requirements for non-emergency RICE 

greater than 100 HP at major sources are too broad in scope and must be revised to exclude 

limited use units in order to avoid the need to operate these units for the sole purpose of 

generating emissions data. The commenter (98) stated that the proposed language imposes initial 

performance test requirements on 2SLB and 4SLB engines 100≥HP≤250 and on CI engines 

100≥HP≤300 even though these engines are not required to install aftertreatment controls and 

emission standards are based on emissions from uncontrolled units. 

One commenter (98) argued that performance test requirements for non-emergency RICE 

greater than 500 HP at major and area sources are required too frequently. The commenter (98) 

asserted that many RICE in this category operate infrequently (less than 20 percent annual 

utilization) and consequently requiring a performance test every 3 years is too frequent. The 

commenter (98) noted that RICE in this category are required to monitor catalyst pressure drop 

and catalyst temperature to assure proper operation of the control device, which approach is 

similar to the Compliance Assurance Monitoring (CAM) Plan established in 40 CFR part 64. 

The commenter (98) believes that the required monitoring indicates proper performance of the 

control device, so frequent performance tests for these units are unnecessary and redundant. The 
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commenter recommended that the proposed rule language in 40 CFR 63.6615 be revised as 

follows: 

“Owners and operators of existing stationary non-emergency or non-limited use RICE that are 

greater than 500 HP and located at major/area sources must conduct an initial performance test 

and must test every 8,760 hours of operation or 3 5 years, whichever comes first, to demonstrate 

that they are achieving the required emission standards through required monitoring of aftertreatment control device(s). In the event that monitored parameters do not comply with specified 

after-treatment control equipment pressure drop and temperature criteria, corrective action or a 

performance test must be conducted to demonstrate that the emissions source is achieving the 

required emission standards. If corrective action involves modifications to the after-treatment 

control device which changes monitored parameters, a performance test must be conducted 

within 180 days of first operation of RICE after modification to the after-treatment control 

device occurred.” 

One commenter (157) believes these requirements are redundant and burdensome 

because many RICE in this category operate infrequently and are already subject to continuous 

monitoring of the catalyst pressure drop and catalyst temperature to assure proper operation of 

the control device. Therefore, the commenter (157) requested that the proposed rule only require 

subsequent testing of these units every 8,760 hours of operation. 

Response: EPA believes that the test frequency for stationary non-emergency existing 4SLB and 

4SRB engines greater than 500 HP located at area sources and operated more than 24 hours per 

year is appropriate to ensure compliance with the applicable standards. As stated in the preamble 

to the proposed rule, additional testing on a regular basis is appropriate and not excessive for 
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these engines because of their size and operating time. At most, these engines would be required 

to test yearly, which would actually be less than what is required for most of the engines subject 

to the 2004 RICE NESHAP. EPA believes that three years is an appropriate time between tests 

for larger engines to ensure that the emission standards are met on an ongoing basis. The option 

for reducing test frequency that the commenters cited in Table 6 allows for reducing from 

semiannual to annual testing; this proposal did not include any semiannual testing. The testing 

requirements are based on actual hours of operation. Regarding the comment that most 

generators are not equipped with easy access ports, the commenter did not submit any 

information to substantiate this claim. EPA does not agree that an engine tune-up would be an 

adequate replacement for an initial performance test as the tune-up would not provide any 

indication of what the emissions from the engine are. EPA has not required any performance 

testing for emergency engines at area sources. For stationary non-emergency SI engines at major 

sources larger than 100 HP, the final rule requires a performance test, which EPA has determined 

is necessary to adequately demonstrate that the engine is meeting the emission limitation. 

Emergency engines at major sources do not have emission limitations in the final rule, which 

addresses the concern expressed by the commenter regarding state agencies requiring testing to 

meet the emission limitations for these engines in the proposed rule. 

9.3.6 Comment: One commenter (264) supports EPA’s proposal to exclude existing nonemergency RICE located at major sources that are less than 100 HP and existing stationary 

emergency RICE located at major sources from the requirement to conduct performance testing. 

The commenter (264) expressed that it did not believe it was feasible to perform the testing base 

on size and potential configuration of equipment. This commenter (264) also supported EPA’s 
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proposal to exclude existing stationary RICE located at area sources that are subject to 

management standards from the requirement to conduct performance testing. The commenter 

(264) expressed that, based on the fact that these RICE are area sources of HAP and are for 

smaller-sized equipment, the maintenance standards, in its opinion, are an adequate means of 

ensuring emissions are minimized. 

Response: No response is needed.

9.3.7 Comment: One commenter (142) stated that, because landfill/digester gas RICE are 

typically operated 24 hours per day and 7 days per week, the proposed emission testing 

frequency would trigger testing approximately every 13 to 14 months considering typical 

downtimes experienced by these engines. The commenter (142) asserted that this requirement 

would result in a significant economic burden to sources operating landfill/digester gas RICE 

outweighing the value of periodic testing as a means of compliance assurance and creating a 

barrier to the utilization of landfill gas as a renewable energy source. 

Response: In the final rule, EPA did not promulgate requirements to conduct performance 

testing beyond the initial compliance test for landfill and digester gas engines. The only engines 

that have period compliance testing requirements in the final rule are 4SLB and 4SRB nonemergency engines greater than 500 HP at area sources of HAP that are operated more than 24 

hours per year. Landfill and digester gas engines at area sources have management practices 

rather than numeric emission limitations and are not required to conduct performance testing. 
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9.4 Other 

9.4.1 Comment: Several commenters (227, 229, 230, 253) expressed concern regarding potential 

performance testing for smaller engines. One commenter (227) said that while there is a 

proposed formaldehyde limit for existing stationary non-emergency RICE less than 100 HP at 

major sources and existing stationary emergency RICE at major sources, there are no testing 

requirements. These engines have maintenance and operating requirements to ensure 

compliance, based on manufacturer’s written emission-related instructions. Since testing is not 

required, the commenter (227) requested that EPA remove the emission standards for these 

RICE. 

One commenter (253) stated that there does not appear to be language in the proposed 

rule that would exempt emergency engines from this requirement. 

Commenter 229 noted that in Table 1, it appears that for all engines (emergency and nonemergency) less than 50 HP at a major source facility, EPA is proposing an emission limitation 

standard of 2 ppmvd formaldehyde. Commenter (229) questioned the purpose of this emission 

limit since EPA states that it does not expect any existing CI engines in this category to be 

operating at major source facilities, and if SI or CI engines less than 50 HP are operating at 

major source facilities, EPA is not stipulating a performance test for a compliance 

demonstration. Commenter 229 continued stating that this does not preclude state agencies from 

specifying performance test requirements or some other needless requirements as a compliance 

demonstration condition in Title V Permits. Commenter (229) therefore recommends that EPA 

exercise its de minimis authority under the CAA to exempt existing engines less than 50 HP 
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from the RICE NESHAP regulations for major and area sources since HAP emissions from these 

sources will be negligible and any regulatory requirements will be unwarranted. 

One commenter (230) recommended that EPA modify Table 4 to exclude small RICE 

from performance testing requirements. The commenter (230) stated that the rationale used for 

excluding performance testing for small stationary and emergency engines because of cost 

should be applied to the same engines at major sources. The commenter (230) does not believe 

there is a useful benefit in performance testing of small (less than 50 HP) RICE located at major 

or area sources. 

Response: In the final rule, EPA has determined that engines below 100 HP and emergency 

engines will be subject to work standards or management practices, and are not subject to testing. 

These engines do not have any numerical emission limitation. Regarding the comments that 

these engines should be exempted under de minimis, EPA does not believe that there is sufficient 

justification for a de minimis finding for these engines. 

9.4.2 Comment: Two commenters (157, 216) said EPA should allow performance test to be 

done during periods of planned operation. The commenters (157, 216) said this change would 

avoid unnecessary emissions produced just for the purposes of testing. 

Response: EPA agrees that it is unreasonable to startup an engine solely for the purpose of 

conducting a performance test and believes it is appropriate to incorporate flexibility when an 

engine is non-operational. In the final rule, EPA has included language in the performance 

testing section that allows stationary engines that are non-operational to conduct performance 
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testing when the engine is started up again. This is consistent with how EPA treats engines that 

must conduct monthly pressure drop readings (see EPA’s response to Question 22 in 

http://www.epa.gov/ttn/atw/rice/riceq_a_9-30-05.pdf) and does not require engines to be started 

up solely to record the pressure drop. 

9.4.3 Comment: One commenter (157) believes that EPA should revise the proposed initial 

performance test requirement for non-emergency 2SLB and 4SLB engines with a site rating 

between 100 HP and 250 HP, and CI engines with a site rating between 100 HP and 300 HP, 

because the proposed requirements conflict with EPA’s decision that such engines should not 

have to install controls. The commenter (157) states if one of these engines fails to meet the 

proposed emissions limit during the initial compliance test, then the owner is out of compliance 

unless the owner/operator reduces emissions from the engine, which will likely mandate the 

installation of controls. The commenter (157) noted that this is contrary to EPA’s determination 

that the cost of applying control to these engines is “too significant to outweigh the expected 

HAP reductions from these units.” Therefore, the commenter (157) believes that performance 

testing requirements should be limited to non-emergency 2SLB and 4SLB engines greater than 

250 HP and CI engines greater than 300 HP located at major sources. 

Response: Based on additional data received in the post-proposal period, EPA revised the 

MACT floor determination for these engines. The emission limitations for these engines in the 

final rule are higher than those at proposal. Therefore, EPA expects that the limits will be met 

without the use of add-on controls for many of these engines. For those engines that are required 

to use aftertreatment, this is the result of Congress’s mandate that standards be determined by 
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reviewing the emissions of the best controlled sources. This means that some engines whose 

uncontrolled emissions are high will need aftertreatment to meet the standard. EPA does not 

agree that performance testing should not be required for non-emergency engines; the testing is 

necessary to show that the engine is complying with the emission limitation and these engines 

are not subject to the special provisions that EPA has provided for engines used solely in 

emergency circumstances. 

9.4.4 Comment: Two commenters (193, 230) said that EPA should allow owners to use engine 

manufacturer information to demonstrate compliance with the rule. One commenter (230) asked 

that EPA allow the use of manufacturers testing data on all models of RICE below 300 HP 

instead of requiring performance testing. Commenter 193 stated that EPA should provide 

owners and operators of existing stationary RICE with a streamlined compliance demonstration 

option whenever they are able to obtain documentation from the engine manufacturer that attest 

to an engine’s compliance with the emission limits of this proposed rule. The commenter (193) 

encouraged EPA to construct a compliance option in the final rule for existing source RICE less 

than 500 HP, much like the compliance option it created in its January 2008 final rule (73 FR 

3596) and afford owners and operators the compliance option of obtaining certification 

documentation from engine manufacturers that attest to an engine’s compliance with the 

emission limits of this proposed rule. The commenter (193) noted that this alternative 

compliance option could apply if entities operate and maintain the certified stationary engine and 

control device according to the manufacturer’s emission-related written instructions, and the 

owner or operator keeps records of conducted maintenance to demonstrate compliance. Under 

this compliance option, no performance testing would be required of the owners or operators. 
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Response: EPA is not allowing owners of existing stationary engines to use manufacturer’s test 

data or any other information in lieu of conducting performance testing. EPA needs the 

assurance that each engine subject to performance testing is actually meeting the applicable 

emission standard. Manufacturer’s test data may be indicative of the engine performance when 

the engine is brand new, but may not be representative of the engine exhaust emissions after 

years in the field. Other factors that may affect the engine exhaust emissions include location, 

climate, fuel, controls, and how the engine has been operated and maintained over the years. The 

provisions the commenter is referring to in the January 2008 final rule on page 73 FR 3596 are 

for new stationary engines subject to the SI NSPS. For existing engines, EPA has no assurance 

that just because data from the manufacturer on the same model engine indicates that the engine 

is capable of meeting the emission standards when new, that the engine actually will after years 

of use in the field and EPA therefore believes that performance testing is justified and necessary.

10.0 Recordkeeping, Reporting and Notifications 

10.1 Comment: Numerous commenters (97, 103, 104, 112, 126, 150, 155, 158, 224, 241, 230, 

242, 247) expressed concern over the proposed recordkeeping and reporting requirements. 

One commenter (155) indicated that for the 2008 RICE NESHAP EPA acknowledged 

that the 40 CFR part 63 GP requirements were burdensome in certain cases and limited these 

requirements for new area source and small major source engines. Three commenters (155, 224, 

247) believe that EPA should make similar allowances for engines under this rulemaking and 

should not broadly apply the 40 CFR part 63 GP requirements to all existing engines. 
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Commenters 112, 155, and 241 are of the opinion that fewer requirements from the 40 

CFR part 63 GP should apply to area sources and smaller engines and said that EPA should 

exempt existing area source engines from 40 CFR part 63 GP requirements. Commenter 112 

believes that at minimum, EPA should consider the cost and benefit of subjecting 40 CFR part 

63 GP on area sources. Commenter 155 suggested that EPA review the requirements from the 

2008 RICE NESHAP and consider harmonizing the requirements in order to avoid 

implementation issues and adopt requirements that are similar for existing and new units. 

Commenter 241 stated under the proposed rule existing engines would have significantly 

more reporting and recordkeeping burden than new engines, and that requirements for new and 

existing engines should be complementary to avoid different implementation requirements. 

Commenter 242 suggested that EPA conduct additional analysis on costs and benefits 

associated with applying 40 CFR part 63 GP requirements and noted, like commenter 155, that 

the requirements for existing sources are more burdensome than those for new sources that 

comply with the NSPS. Two commenters (112, 242) specifically commented that it did not 

believe the hour estimate for emergency engines is accurate at 1 hr/yr and thought recordkeeping 

would take at least 15 minutes per occurrence, or at a minimum, at least once per month (3 

hrs/yr). The commenters (112, 242) further expressed that they did not believe EPA has 

accounted for the costs associated with overhead and profit in its emergency engines analysis. 

Commenters 112 and 242 also stated that it is not evident that EPA has considered any 

recordkeeping for engines requiring maintenance and that, based on its experience, significant 

recordkeeping is necessary for maintenance and SSM requirements. The commenters (112, 242) 

estimated that it would take 2 hrs/month and 1 hr/month for maintenance and SSM 

recordkeeping, respectively. In terms of reporting costs, the commenter (242) expressed that it 
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does not look like EPA considered the 167 percent overhead allowance, which would increase 

the reporting costs. 

The commenters (112, 242) added that EPA estimated 14 hours for reporting, but the 

commenter expressed that this is not sufficient time to become familiarized with the very 

complex rulemaking, which the commenters estimated would take about 40 hours. Commenter 

112 stated that EPA did not include the 167 percent overhead allowance in this calculation. 

Further, in terms of annual training, commenters 112 and 242 think this will take 8 hrs/yr. 

Considering the cumulative effect of notification, recordkeeping and reporting associated with 

the rule, the commenter (242) believes the rule will have an unprecedented impact on the 

regulated community and State agencies that will be implementing the rule. Commenters 155 

and 242 said that EPA has not recognized the extensive recordkeeping and reporting 

requirements in the 40 CFR part 63 GP and the commenters listed several requirements from the 

GP as examples of onerous and burdensome requirements (e.g., initial notification of 

applicability, various notifications including the notification of performance test, compliance 

reports, reporting related to SSM, various records required such as records of SSM, records of 

maintenance, records of monitoring). Based on the assumption that the average environmental 

professional will be responsible for 10 controlled engines, the commenter (112) estimated that 

19,800 environmental professionals will need to be trained at an initial cost of $58 million and 

annual cost of $12 million for refresher training, which does not include the cost for those 

professionals to educate field personnel about the requirements for which they are ultimately 

responsible. 

One commenter (126) believes the requirement for owners and operators to develop a 

maintenance plan that specifies how the management practices will be met provides little benefit 
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to anyone. If the manufacturer’s maintenance plan requirements are met, then the commenter 

(126) suggested that there be no maintenance plan and that the owner operator keep appropriate 

records to demonstrate that it has met those requirements. 

 Commenter 242 reported that the 40 CFR part 63 GP requirements are currently being 

reviewed as a result of the litigation concerning SSM. The commenter (242) said that the 

applicability of 40 CFR 63.7(e)(1), shown in Table 8 of the rule, adds significant confusion and 

the commenter believes it is inconsistent with the requirements of the rule. It is unclear whether 

a source needs to be in compliance outside of normal operating conditions because the section 

with these requirements says “as applies” and the commenter (242) urged EPA to clearly spell 

out all rule requirements. 

One commenter (158) stated that the management practices and recordkeeping 

requirements are not practical for low-use equipment because logs could need to be retained for 

years, even decades. For example, if a facility uses a 60 HP diesel-powered welder ten times per 

year for one hour per use, the proposed regulation would require that operating hours be recorded 

for 50 years in order to conduct scheduled maintenance. The commenter (158) stated that this is 

impractical and creates an unjustified compliance risk. 

One commenter (104) noted that the proposed 40 CFR 63.6665 section includes 

additional 40 CFR part 63 GP that apply to this rulemaking. The commenter (104) believes that 

these requirements increase the complexity of the rule on small businesses that operate engines at 

oil and gas facilities, especially those entities that have never been regulated before. The 

commenter (104) asked how EPA plans to simplify the process for these entities. 

One commenter (230) stated that the additional recordkeeping and reporting requirements 

in Table 2d for uncontrolled RICE are unnecessary if a comprehensive planned maintenance 
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program is utilized. The commenter believes that the oil and filter change management practices 

in Table 2d of the proposed rule may cause an inadvertent recordkeeping violation. The 

commenter recommends that the schedule should conform to an engine specific planned 

maintenance program, or the values in Table 2d of the proposed rule should provide an 

allowance for exceeding the recommended values during an emergency situation. 

Response: EPA believes the recordkeeping and reporting requirements are appropriate and 

justified in order to provide EPA with sufficient information to show that sources are in 

compliance with the rule. EPA does not believe that the requirements have to be the same for 

new and existing engines. In many cases, new engines are certified to achieve the emission 

limitations by the engine manufacturer and therefore EPA determined that these engines could 

have fewer recordkeeping and reporting requirements than what is in the part 63 General 

Provisions. EPA does not agree with the commenters that said that an estimate of one hour per 

year for recording emergency operation was not accurate. EPA did not include costs for 

recordkeeping for engine maintenance because EPA assumed that engine owners/operators 

would already be keeping these records even without this regulation. EPA believes that the costs 

estimated for recordkeeping and training are accurate. In terms of the cost of training and the 

impact of the rule on small businesses, EPA plans to provide implementation materials to assist 

affected facilities in complying with the final rule, which should decrease the amount of time 

needed to become familiar with the rule. 

In response to the comment regarding the 167 percent overhead allowance, EPA 

incorporated the 167 percent overhead and profit allowance in determining the labor rates, which 

means that the overhead allowance was included in the costs associated with emergency engines. 
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EPA documented this in the proposed rule impacts memo. However, EPA believes the way that 

this was written up in the proposed rule impacts memo may have been confusing and makes it 

seem as if 167 percent was added to the $68/hr rate, which is not the case. EPA has clarified this 

in the final rule impacts memo and believes this resolves the concern on this issue. 

 EPA does not agree with the commenter that developing a maintenance plan will provide 

little benefit. It is important that sources have a written plan spelling out the maintenance to be 

conducted on their stationary SI engines. This plan can certainly be based on the manufacturer’s 

recommended maintenance. 

 Regarding the comment that the applicability of 40 CFR 63.7(e)(1) shown in Table 8 is 

confusing, EPA is currently conducting a review of the part 63 General Provisions as a result of 

the court decision on startup, shutdown, and malfunction. EPA will revise the General 

Provisions as appropriate. 

 Regarding the comment that the recordkeeping requirements are not practical for low-use 

equipment, 40 CFR 63.10(b) specifies that records only need to be kept for five years after the 

date of the maintenance. Therefore, it will not be necessary for the records to be kept for 50 

years. EPA has specified in the final rule that the maintenance should be conducted at yearly 

intervals at a minimum. EPA has also specified that sources may petition for different 

maintenance requirements. Any exceedances of the maintenance requirements that occur during 

emergencies will be handled on a case-by-case basis. 

10.2 Comment: Several commenters (76, 81, 103, 104, 118, 119, 129, 136, 148, 150, 157, 225, 

240) suggested alternatives to requiring owners and operators having to maintain records on-site. 
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Several commenters (76, 81, 118, 136, 148, 240) suggested that EPA clarify that 

necessary records be kept in a central location and not on-site as currently required in 

63.6655(e). Commenter (76) recommended that §63.6660(c) be modified to allow records to be 

kept off-site at a central location for 5 years. According to the commenter (81), this is consistent 

with EPA and other Federal government efforts (e.g., electronic reporting). Commenter 119 

echoed these concerns and specifically requested that the final rule allow records to be 

maintained at an off-site location for engines located at area sources of HAP. 

One commenter (103), in the natural gas compression industry, noted that the vast 

majority of smaller HP engines are located at unmanned facilities in remote locations where 

maintaining records on-site would be quite burdensome and unreliable. The commenter (103) 

requested that EPA consider allowing records to be kept on-site, or at a nearby field office. 

Similarly, two other commenters (104, 150) in the oil and gas industry noted that most oil 

and gas facilities are in remote, rural areas, sometimes many hours from the home or field 

offices, so that there is no practical way to keep records on-site. These commenters (104, 150) 

requested that the requirement for on-site records be removed for oil and gas facilities, or that 

such records be allowed to be kept at the nearest manned field or home office. 

Another commenter (225), in the oil and gas industry also recommended that the 

requirement for maintenance records be expanded to include local field offices. This commenter 

(225) noted that, in some cases, maintenance may be conducted by a third-party contractor and 

recommended that retention of the records by a third party be allowed. 

One commenter (103) expressed that the proposed rule requires records to be kept on site 

unless a waiver is obtained. The commenter (103) believes that EPA and the states who will 

ultimately enforce the rule, do not have sufficient manpower to provide the thousands of waivers 
290

that will be requested and re-requested every time an engine is relocated. The commenter (103) 

asserted that a provision for keeping records at a field office should be written into the rule from 

the beginning because it is an unnecessary burden to require special waivers on items that are not 

only common place, but also the norm. 

Response: EPA agrees with the commenters that it would appropriate to allow records to be kept 

off-site at a central location. EPA has incorporated this requirement in the final rule. 

10.3 Comment: One commenter (112) in the natural gas industry asked that EPA change the 

initial notification date from "commence construction" to the date of on-site construction. The 

commenter (112) stated that “commence construction” was defined as the date the engine was 

ordered for consistency with the “entered into a contractual obligation” concept, which makes 

sense when discussing the applicability of the regulation or the construction of a major facility 

(i.e., a refinery, chemical plant or electrical generation facility). However, the commenter (112) 

believes that the initial notification requirements, in this case, should be revised so that the 

notification schedule is based on the date that the engine is sited rather than the date that the 

engine is ordered because often an engine is ordered without knowing at which site the unit will 

be installed. Commenter 150 expressed the same concerns. The commenter (112) noted that if 

the initial notification date is based on “commence construction,” the notification for these 

engines would contain only the engine make and model with no site location or date of 

installation, and the limited information provided would be of little use to the regulatory agencies 

receiving the notice. In addition, a subsequent notification would be required when the final 

location is determined to provide the balance of information required, which the commenter 
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(112) believes is onerous. The commenter (112) added that, for operators that have sites in 

multiple states, the notification would need to go to multiple states because even the state has not 

yet been identified. 

Response: The engines that are the subject of this rulemaking are existing engines that have 

already been constructed. The initial notification date for these engines is not tied to the date of 

construction and will be 120 days after the effective date of the final rule 

10.4 Comment: A few commenters (81, 129, 216) said the proposed recordkeeping requirements 

are unnecessarily rigid for emergency generators. The commenter (81) reported that it operates 

numerous remote, unoccupied, and often unmanned locations. Such areas are not easily accessed 

for the creation and maintenance of rigidly-defined documentation. The commenter requested 

that, should the recordkeeping requirements become too burdensome, it may become necessary 

to remove the use of emergency generators for use as needed backup power, potentially 

disrupting communications. 

Commenter (216) said EPA should reduce the proposed recordkeeping and reporting 

requirements for emergency engines. Most emergency RICE start automatically, and much of 

the equipment may be at remote locations. The requirement to record the purpose of all run 

events is a burden that will require additional manpower. 

Response: EPA does not agree that the recordkeeping requirements that were proposed for 

owners and operators of existing stationary emergency engines are too burdensome. EPA is 

finalizing requirements for emergency engines that do not require the application of 
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aftertreatment controls. EPA developed distinct subcategories for emergency and nonemergency engines to account for different characteristics between these types of stationary 

engines. The analysis that was conducted leading to the final requirements for emergency and 

non-emergency engines is based on those differences. Therefore, in order to demonstrate that an 

engine is truly an emergency engine as defined in the final rule, there must be some 

recordkeeping and documentation associated with the operation of the engine to confirm that the 

engine is operating according to the definition of an emergency engine and subsequently entitled 

to meet the less stringent standards. In the case the emergency engine is operated in a nonemergency manner, the more stringent standards that apply to non-emergency engines would 

apply. EPA believes that keeping track of the hours of operation and the purpose of operation is 

necessary in order to ensure that the engines are meeting the applicable standards. 

10.5 Comment: One commenter (162) said that semiannual compliance status reporting is overly 

onerous for emergency and limited-use stationary RICE at are sources. The commenter (162) 

described the specific burden his company would face. The commenter (162) particularly 

objected to filing reports for RICE that do not even have emission limitations. The commenter 

(162) requested that semiannual compliance reports be waived for area sources, or at least, for 

area sources with RICE that do not have emissions limitations. 

Response: EPA agrees with the commenter that semiannual compliance reporting, and other 

types of reporting required under the General Provisions of 40 CFR part 63 are not appropriate 

for area sources that are not subject to numerical emission standards. EPA believes that 

recording information and maintaining records will provide EPA with assurance that facilities 
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are meeting the work/management practices and other requirements applicable to their existing 

stationary engines. Further, EPA believes it is appropriate extend the same approach to any 

sources that are not subject to numerical emission standards, including existing stationary SI 

engines less than 100 HP and existing stationary emergency SI engines. Therefore, in the final 

rule, EPA has specified in 63.6645(a)(5) that these engines do not have to meet the notification 

requirements of the General Provisions that are specified in 63.6645(a). 

10.6 Comment: One commenter (103) stated that records of air filter change dates should only 

be required, if applicable, since not all engines contain air filters. 

Response: EPA agrees with the commenter. 

10.7 Comment: Several commenters (103, 104, 130, 150, 175, 227, 230, 255) provided 

comments on the requirement to maintain records of fuel consumption rates and/or the use of 

fuel and hour meters. 

Two commenters (103, 104) opined that having to install a fuel meter would impose a 

significant cost to owners and operators. On a similar topic, commenter 157 stated that the 

installation of the non-resettable hour meters requires a substantial monetary investment in either 

a computerized monitoring system or additional labor and requested that the reporting and 

recordkeeping requirements for existing engines should be the same reporting and recordkeeping 

requirements for new units. 

One commenter (103) requested that EPA drop the requirement to maintain records of 

fuel consumption rates. The commenter (103) stated that the majority of the smaller HP engines 
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operate on wellhead gas with a wide variety of gas constituents and Low Heating Value (LHV), 

and are not equipped with fuel meters or gas chromatographs to record the constituents of the 

fuel. The commenter (103) believes that it could prove to be a significant cost if fuel meters are 

required, and without a fuel meter, a field technician would have to calculate fuel consumption 

rates using engine technical data curves. 

Another commenter (104) in the oil and gas industry noted that the proposal preamble 

indicates that existing engines at area sources that are subject to management practices are 

required to record fuel consumption and hour data shown on hour meters. In Oklahoma, natural 

gas produced from the well is used to run the engines at the facility, and there are no meters 

installed to record fuel consumption. Operators typically use the manufacturer’s data to calculate 

fuel usage for small engines like pump jacks. The commenter (104) indicated that hour meters 

are not installed on these types of engines. This commenter (104) also stated that EPA has not 

specified the frequency that this data is to be kept, i.e., hourly, weekly, monthly, etc. The 

commenter (104) believes that the requirement to install a fuel meter will only increase capital, 

maintenance, and replacement costs without any environmental benefit, and that the proposed 

requirement will be unnecessarily costly and burdensome on small businesses and those 

companies that operate marginal crude oil and natural gas wells that operate on the lower edge of 

profitability. The commenter (104) requested that EPA remove these requirements for engines 

less than 500 HP that are located at area sources. 

One commenter (255) expressed that EPA should not apply the NESHAP meter 

requirement to existing emergency RICE which operate infrequently. The commenter (255) 

stated that the 100 hour per year limit (for which the meter requirement was established for) can 

be exceeded by petition or if state or local requirements mandate operation for more than 100 
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hrs/yr, in which case no petition is necessary. The commenter (255) requested that the 

requirement to install a non-resettable hour meter not be imposed on existing RICE that are 

dedicated to emergency service. If it is necessary to record and report the annual operation of 

such engines, the commenter (255) suggested that the operator be permitted to use other 

methods. This commenter (255) opined that the cost of installing a meter on existing RICE 

dedicated to emergency service is unwarranted given the prospective limited operation of such 

engines. Commenter 230 suggested the use of an operating log book and tracking fuel usage. 

The fuel usage could be calculated from consumption rates at minimum load and tracked as a 

rolling 12-month period. 

One commenter (130) stated that not all engines used for agricultural purposes have hour 

meters. The commenter (130) noted that this could be problematic during a field inspection and 

suggested allowing owners/operators to use their estimates of operating time for the purposes of 

conducting scheduled maintenance. 

One commenter (175) recommended that EPA establish a 100 hrs/yr threshold under 

which recordkeeping would apply. 

Response: EPA believes the commenters may have misunderstood the requirements in the 

proposed rule. The only engines that are required to keep track of their fuel consumption are 

new landfill and digester gas engines, which are not the subject of this rulemaking. EPA does 

not agree that existing emergency engines should not be required to install nonresettable hour 

meters. These meters will provide incontrovertible documentation of the total hours of operation 

for these engines, which would not be the case if fuel usage information is used. In response to 
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commenter 130, the commenter did not explain why it would be problematic for agricultural 

engines to install hour meters or why this would be problematic during field inspections. 

10.8 Comment: One commenter (103) in the natural gas compression industry noted that the 

proposed rule states that SSM records need to be kept for 5 years even if the facility is relocated 

or sold. The commenter (103) stated that in the case of rental equipment, the owner (lessor) 

typically has some records such as maintenance logs, and the operator (the lessee) has other 

records such as operational logs and testing results; when the engine driven package (the facility) 

is returned to the lessor, the records are rarely transferred to the lessor, yet the compliance period 

for the lessor as “Owner” has not ended. The commenter (103) also pointed out that the next 

lessee takes over as partial “Owner and Operator” with incomplete history. The commenter 

stated that since the requirements follow the RICE (for example performance testing 

frequencies), all of the parties are dependent on each other for historical records. The 

commenter (103) asserted that EPA should consider these dynamics when finalizing the rule. 

Response: This rule applies to both the owner and the operator, regardless as to whether the 

operator is an agent of the owner or merely a lessee. Because both the owner and operator are 

liable under the rule, the rental agreement should address who will conduct emissions testing or 

employ management practices for the specific engine, and who will create records, who will hold 

them for the statutory period and who will report. 

10.9 Comment: One commenter (104) noted that proposed 40 CFR 63.6640 requires each 

instance in which an operator did not meet each emission or operating limitation to be reported. 
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The commenter (104) questioned whether EPA really wants to know every instance an operator 

runs over an oil/filter or spark plug change or inspecting belts/hoses by 1 hour. The commenter 

(104) believes this reporting effort will be burdensome and costly and provide no environmental 

benefit. The commenter (104) requested that EPA remove this requirement when there is no 

specified emission limit for engines located at an area source. 

 Another commenter (150) also believes that the proposed reporting requirements are 

overbroad for operating requirements. The commenter (150) indicated that recordkeeping and 

reporting should be reserved for the most significant activities. 

Response: EPA believes that the reporting of failures to meet emission or operating limitations 

benefits the environment. This type of reporting provides information to the enforcing agency 

about the typical operation of the engine and therefore will help the enforcing agency better 

understand and identify problems and determine the compliance status of the affected source. 

The instances when the affected source does not meet the applicable emission or operating 

limitations are considered deviations and must be reported. These requirements are consistent 

with language in the General Provisions of 40 CFR part 63 and are appropriate for stationary 

engines subject to NESHAP. 

10.10 Comment: One commenter (104) noted that proposed 40 CFR 63.6645 requires existing 

stationary engines located at area sources to submit all notifications in accordance with 40 CFR 

63.9 (b) through (e), (g), and (h), which requires multiple notifications including a 120-day initial 

startup notification, a 60-day notification of an upcoming performance test, and notifications of 

compliance status. The commenter (104) stated that many states already have permitting or 
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other processes in place whereby the state is “notified” that a facility is beginning operations, 

conducting performance tests, and showing compliance. The commenter (104) asserted that 

additional, duplicative notifications to EPA are burdensome and costly and provide no 

environmental benefit. The commenter (104) requested that the notification requirements be 

removed for engines less than 500 HP that are located at area sources. 

Response: In most instances the State or local agency will be the delegated authority for 

ensuring compliance with the NESHAP and will receive the rule notifications. Moreover, even 

in cases where it is not, the requirement of sending two notifications where two different entities 

are regulating the engine, is neither overly burdensome or unnecessary. Therefore, EPA 

disagrees that the reporting efforts are duplicative, burdensome and costly. EPA has retained the 

reporting requirements as proposed. 

10.11 Comment: One commenter (134) believes that the proposed reporting and recordkeeping 

requirements are confusing and contraindicated for RICE at area sources. The commenter (134) 

noted that the proposed §63.6665 identifies which RICE will be exempt from complying with 

any of the requirements of the 40 CFR part 63 GP and includes a new or reconstructed RICE 

located at an area source. The commenter (134) stated that all other RICE located at area 

sources, whether subject to numerical standards or work practices, must comply with numerous 

GP requirements, such as developing and maintaining an SSM plan, keeping records of SSM 

events and actions taken during periods of SSM, periodic reporting of any SSM events linked to 

exceedances and immediate reporting of any malfunction, records of any startup or shutdown 

that causes exceedances. The commenter (134) stated that these SSM requirements are just a 
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few of the numerous requirements listed in Table 8 of the proposed rule. The commenter (134) 

stated while EPA has exempted existing RICE that are not subject to any numerical emission 

standards from complying with some notifications, we fail to understand, and EPA has not 

explained, why these RICE should be subjected to the onerous SSM recording and reporting 

requirements. The commenter (134) stated that it is unclear how RICE subject to work practice 

requirements will be able to record accurately the “duration” of a startup, shutdown or even a 

malfunction when there is no real technical ability to do so. The commenter (134) recommended 

that, for the “immediate reporting” requirements of §63.10(d)(5)(ii), these reports be 

incorporated into otherwise required periodic reports as provided for in other NESHAP for RICE 

subject to work practices at area sources. 

Response: New or reconstructed stationary RICE located at area sources do not have to comply 

with the part 63 General Provisions because they comply with subpart ZZZZ by complying with 

40 CFR part 60 subpart IIII or JJJJ as applicable, and therefore are subject to the 40 CFR part 60 

General Provisions. EPA does not agree with the commenter that the requirements in the part 63 

General Provisions are too burdensome. The recordkeeping and reporting requirements in the 

General Provisions allow EPA to determine whether sources are complying with subpart ZZZZ. 

The commenter did not provide any information to support the claim that it is not technically 

feasible to record the duration of startup, shutdowns, and malfunctions. 

10.12 Comment: One commenter (150) stated that the requirement to keep records of all 

maintenance activities would be onerous and unnecessary in practice. The commenter (150) 

recommended that the requirement be amended to require only records of key maintenance 
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activities such as oil and filter changes, spark plug replacement, overhaul, and rebuild, or 

associated activities that require an engine to be brought off-line. 

Response: EPA disagrees and does not believe that keeping records of maintenance performed 

on the engine is an onerous activity. In many cases maintenance records are already being kept 

and it is in the best interest of the owner and operator to maintain such documentation to ensure 

that the engine is properly taken care of. 

10.13 Comment: One commenter (174) asked that, for engines used for agricultural purposes, 

recordkeeping only be required of affected engines located in non-attainment areas. The 

commenter (174) stated that the public health impacts from agricultural engines located in rural 

areas would be lower than the impacts from engines located in urban, and particularly nonattainment areas. 

Response: EPA must address emissions from existing stationary engines in all areas. The 

determination of whether an area is in attainment or non-attainment with the National Ambient 

Air Quality Standards (NAAQS) applies only to the few criteria pollutants for which these 

standards have been established. Section 112 of the CAA pertains to HAP and only one 

hazardous air pollutant listed in section 112 of the CAA (lead) is subject to NAAQS. Therefore, 

the NAAQS attainment status of the engine location is not an appropriate distinction for 

reporting requirements in this NESHAP. 
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10.14 Comment: Two commenters (265, 268) noted that management practices are not 

specified for landfill gas fired RICE above 500 HP in Table 2d that is referenced in §63.6655(e) 

as follows: 

“(e) If you own or operate an existing stationary RICE . . . located at an area source of HAP 

emissions subject to management practices as shown in Table 2d to this subpart, you must keep 

records of the maintenance conducted on the stationary RICE in order to demonstrate that you 

operate and maintain the stationary RICE and aftertreatment control device (if any) according to 

your own maintenance plan.” 

The commenters pointed out that in the existing rule at 63.6655(c), the following requirement is 

included: “If you are operating a new or reconstructed stationary RICE which fires landfill gas 

or digester gas equivalent to 10 percent or more of the gross heat input on an annual basis, you 

must keep records of your daily fuel usage monitors.” 

Response: EPA is not clear on what the commenters are suggesting. It appears that the 

commenters are comparing the proposed requirements that apply to existing stationary landfill 

gas engines less than or equal to 500 HP at major sources and existing stationary landfill gas 

engines at area sources to the requirements that currently already apply for stationary landfill gas 

engines greater than 500 HP. The commenters seem to be pointing out that the management 

practices in Table 2d of the proposed rule are not consistent with the current requirements in 40 

CFR 63.6655(c). 

Table 2d of the proposed rule includes emission and operating limitations for existing 

stationary engines at area sources that are being addressed in this rulemaking. As item 12 in the 

proposed Table 2d indicates, existing landfill gas engines greater than 500 HP at area sources are 
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subject to an emission limitation. Existing landfill gas engines less than or equal to 500 HP at 

area sources are subject to maintenance practices as described in item 11. EPA discussed in the 

language of the proposed preamble the justification for the emission and operating limitations for 

landfill and digester gas engines. EPA notes that this rulemaking addresses a different set of 

stationary engines that had previously not been regulated under a NESHAP. The NESHAP that 

currently applies only addresses emissions from existing landfill gas engines above 500 HP at 

major sources, and does not cover smaller existing engines and existing engines at area sources. 

The provision in the 63.6655(c) of the current NESHAP that was promulgated in 2004 that the 

commenters are referring to do not apply to existing landfill gas engines addressed in this 

rulemaking because EPA is not including a fuel consumption threshold for these engines. The 

commenters did not provide any rationale as to why they were requesting a change, if the 

commenters were even suggesting that EPA should make the 63.6655(c) provision applicable to 

all landfill gas engines. 

11.0 Docket Materials/Transparent Regulatory Process 

11.1 Comment: Several commenters (76, 112, 130, 150, 155, 224, 242) thought the docket for 

the proposed rulemaking is inadequate and relies on outdated information, and that information 

in the docket is not always appropriately cited in order to provide a transparent and clear picture 

of how EPA developed the proposed rule. EPA has not met its objective in providing 

rulemaking transparency, the commenters (155, 224, 242) said. For example, the PSR database, 

which is the basis for population estimates, is not available in the docket because it is not a 
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public product, commenters 155, 224, 242 said. Therefore, the commenters (155, 224, 242) were 

unable to review and verify the information regarding the number and types of engines. 

The commenters (155, 242) said that the use of proprietary data is in conflict with the idea of 

transparency outlined by the Administrator and the short comment period did not allow for a 

FOIA request to be submitted. EPA should document and fully disclose all relevant calculations, 

equations, and assumptions related to the PSR database and any spreadsheets used to support 

assumptions should also be provided in the docket, the commenters (155, 242) said. One 

commenter (76) noted that was no discussion in the preamble regarding the population database 

that discusses how and when the database was populated. Similarly, test reports used by EPA to 

set the standards were not in the docket either, the commenter (155) said. For instance, 

commenter 242 said that the docket is missing EPA’s own 1999 study of a rebuilt and retrofitted 

for lean burn operation a Cooper Bessemer GMV-4TF (EPA-454/R-00-036a), which clearly 

demonstrates that 2SLB engines cannot meet the proposed requirements. Commenters 155 and 

242 added that the docket relies in large parts upon old data from other rules. For example, such 

as the Emissions Database, which contains data primarily from the 1990’s and control cost 

information gathered in 2003, commenters 112, 150, and 155 said. The commenters (155, 242) 

could not find evidence of a more recent data gathering effort and information and assumptions 

were adopted from older rulemakings without revisions to current levels. 

Commenter 242 said that EPA has not been adequate in supporting or justifying its 

MACT floor and above-the-floor decisions. The commenter (242) noted that in the 2004 RICE 

NESHAP, EPA made the statement that there was not sufficient information for engines less 

than 500 HP and therefore a regulation was postponed. However, the commenter (242) said, it 

appears that EPA has reversed this determination without supplementing with any new data and 
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is using a decade old database as the basis for setting standards. The commenter (242) stated that 

the docket is lacking in providing data and information supporting the MACT floor and abovethe-floor analysis for natural gas 2SLB, 4SLB and 4SRB engines. The commenter (242) agrees 

with EPA’s decision in 2004 that sufficient data was not available for small engines and the fact 

that additional data has not been collected since then means the database is still deficient. 

Therefore, the commenter (242) said, emissions and costs data is necessary to be collected in 

order to defend the final MACT floor and above-the-floor decisions. 

One commenter (224) stated that documents from previous rulemakings that were used in 

the development of the proposed rule were not appropriately cited in the docket and that this 

oversight hinders commenters’ ability to review and comprehend EPA’s analysis. The 

commenter (224) was specifically concerned with documents related to the cost analysis. The 

commenter (224) noted that a robust docket should be developed in order to support regulatory 

transparency.

 The commenter (150) also believes that EPA has failed to give proper consideration to 

urban vs. rural area regulatory distinctions and that the docket lacks support for the conclusion 

that emissions from remote area sources cause adverse human health effects (which is used as 

the basis for the proposal to require catalysts on certain engines even in rural areas). The 

commenter (150) indicated that the docket reference for capital equipment and operating and 

maintenance costs for controls is flawed in that EPA has failed to address and consider 

guaranteed life, expected life, catalyst replacement cost, tuning or maintenance 

recommendations, and potential costs related to retrofit applications versus new equipment. The 

commenter (150) also stated that limitations related to fuel quality limitations have not been 

properly considered. 
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One commenter (130) cited the following examples of EPA’s failure to comply with the 

new administration’s goals of science-based decision-making and transparent rulemaking: 

• Failure to conduct risk-based analyses for area sources; 

• Failure to consider the difference between urban and rural area sources; 

• Lack of transparency in cost-effectiveness determinations (e.g., based calculations on 

cost estimates from one vendor); 

• Failure to provide supporting data for proposed emission limits; and 

• Reversal of EPA’s previous assertion that the database developed for the 2004 RICE 

MACT contained insufficient data to regulate engines less than 500 HP by using the same 

database to develop the proposed rule, which includes emission standards for such 

engines. 

 The commenters (155, 242) expressed that it was in general difficult to understand EPA’s 

basis for regulatory decisions and in some cases information necessary to follow EPA’s analysis 

was not traceable. The commenter (155) stated that it was hindered in its review and indicated 

that it was not capable of providing complete input to EPA because of it. The commenter (155) 

believes EPA should obtain additional data, perform new analyses, and clearly present the 

analysis and supporting documentation in the docket for the regulated community to review. 

The commenters (155, 242) said that EPA has not met its goal of providing a transparent 

regulatory process. 

Response: The docket to the proposed rulemaking contained the information that was available 

to EPA at the time of the proposal development and that EPA used to support the proposed rule. 

While some of the information in the docket may be several years old, it was the best 
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information EPA had on hand at that time. In response to comments related to the use of older 

stationary engine test reports, EPA has repeatedly asked industry to provide emissions test data 

for different rulemakings over the last several years; however, the response and submittal of 

actual test data for stationary engines was minimal prior to the proposed rule. Since the 

publication of the proposal, EPA has received new test data for engines above and below 500 

HP. EPA has incorporated the new test data into its final MACT floors. 

EPA does not agree that information in the docket was not appropriately cited and EPA 

purposely tried to minimize duplication by referring to materials developed for previous 

rulemakings affecting the same and similar engines. EPA recognizes that commenters may not 

clearly have understood the analysis that was performed for the proposed rulemaking. EPA tried 

to answer any questions that were received post-proposal from industry and other affected 

stakeholders. For the final rulemaking, EPA has made an effort to be as clear as possible in 

support memoranda, preamble language, and other background materials, in order to provide at 

transparent rulemaking process. By clearly explaining rationale and assumptions, EPA believes 

the final rule is clear as far as the basis for regulatory decisions is concerned. 

Specifically, for the final rule, EPA has provided the original PSR figures that EPA used 

to develop population estimates. EPA has also clearly described in supporting documentation 

how the affected number of engines was estimated for the final rule. Both of these materials are 

available from the final rulemaking docket and commenters will be able to review and verify the 

information related to the stationary engine population. For more information on the population 

of engines affected by the final rule and the impacts associated with the final rule requirements, 

please refer to the memoranda entitled “Existing Population of Stationary RICE” and “Impacts 

Associated with NESHAP for Existing Stationary SI RICE.” EPA does not agree that it should 
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have conducted risk-based analyses for area sources. Section 112(d) rulemaking is intended to 

be technology based, with only certain provisions, not applicable here, dealing with risk. EPA 

explains its rationale for regulating area source SI engines in rural areas in section 2.0 of this 

document. EPA did provide the data to support the emission limitations via the RICE Emissions 

Database that is publicly available on EPA’s website. 

EPA has in supporting documents to the final rule made a significant effort in clearly 

describing the basis and information used for the final rule. EPA believes that the docket to the 

final rule contains the information necessary, and the information is presented in such a manner 

that it clearly illustrates the process for arriving at final decisions and provides a transparent 

rulemaking process. 

12.0 Rule Impacts 

12.1 Economic Impacts 

12.1.1 Comment: Several commenters (81, 89, 93, 97, 101, 103, 104, 111, 112, 121, 126, 130, 

132, 136, 140, 150, 151, 155, 176, 186, 187, 203, 204, 205, 207, 216, 220, 221, 224, 231, 241, 

242, 249, 251, 261) expressed that the costs are not representative of actual costs of 

implementing the rule and numerous commenters said that the proposed rule will have a 

significant financial impact on their sources. According to the commenters (155, 242), EPA has 

underestimated the cost impacts of the rule by an order of magnitude or more. Numerous 

commenters indicated that EPA has used old, faulty, and inappropriate data on the cost of 

controls, testing, recordkeeping and reporting to estimate the economic impacts of the rule. 
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Commenters 89, 101, 151, 221, and 231 indicated that EPA estimated the initial capital 

cost in this rule for control equipment to be $528 million and the annual cost to be $345 million, 

but that industry estimates the capital cost to be a factor of 10 higher and the annual cost to be a 

factor of 4 higher. Using a revised number of affected engines and EPA’s per-engine capital 

costs (which commenter 112 believes are low), the commenter (112) calculated total capital cost 

for controls of $892 million, as compared to $528 million estimated by EPA. The commenter 

(112) believes this difference is mostly attributable to the much higher number of 4SRB engines 

that it believes will be affected and requested that EPA examine this discrepancy to determine if 

the original estimate of 4SRB engines requiring controls is accurate. Commenter 151 asserted 

that EPA assumed that 80 percent of 4SRB engines are already controlled using NSCR, but only 

a tiny fraction of such engines below 500 HP are currently controlled. Commenter 112 does not 

believe that EPA’s assumption that 50 percent of all 4SRB engines are already controlled with 

NSCR and 5.7 percent of all 4SLB engines are already controlled with oxidation catalyst. The 

commenter (112) believes that this estimate is close for engines greater than 500 HP, but that 

few, if any, engines less that 500 HP are equipped with catalyst. 

The commenters (89, 101, 151, 221, 231) asserted that the following factors in EPA’s 

analysis resulted in a low estimate: 

• Not all existing engines requiring controls can simply add catalyst to the exhaust, so 

some engines must be replaced. (Commenter 151 added that this is primarily true of 

2SLB engines.) 

• EPA estimated performance tests to cost $250 to $500 each when the cost for many 

engines is approximately $8,000. Commenter 151 added that even 4SLB engine stack 

tests using portable analyzers for CO cost more than $250 to $500 due to the 3 hr/engine 
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test time. One commenter (104) did not believe that that re-testing costs have been 

included if an oxidation catalyst or NSCR is replaced because of routine replacement or 

failure, and requested that these costs be included. 

• EPA falsely assumes proposed maintenance requirements add no cost to industry. 

• The administrative burdens of the rule are underestimated or left out entirely. 

• Two commenters (112, 221) said EPA has overlooked potential costs in lost revenue 

resulting from shutting down engines used throughout the industry to operate pump jacks 

and to compress gas to booster stations and to consumers. Shut downs of engines will be 

required initially when retrofitting with controls and more routinely as a result of the 

burdensome, frequent, and time consuming maintenance requirements. 

Commenters 155 and 242 said that EPA should gather current information on the cost of 

controls and redo the cost calculations. The commenters (155, 242) provided specific examples 

of where they believe EPA has used inappropriate cost information in other comments in this 

RTC document, but the following also lists some main assertions: (Commenter 241 noted some 

of the same concerns in its comments). 

• EPA should present all costs associated with the rule in 2013 dollars and not in 2007 

dollars. 

• The models used to estimate the capital and annual costs of add-on controls 

underestimate the costs and not all equipment components have been included. 

• The population breakdown by engine type (i.e., 2SLB, 4SLB, etc.) is inaccurate. EPA 

has overestimated the number of 4SLB engines less than 500 HP and that in fact most 

engines are rich burn engines in that size range. Therefore, costs have been 

underestimated and a revised population breakdown will lead to increased costs since 
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add-on controls are required for rich burn engines down to 50 HP as opposed to 250 HP 

for 4SLB engines. Also, EPA’s analysis assumes that only engines subject to above-thefloor standards will need add-on controls, but in the commenters’ (155, 242) opinion, all 

engines subject to an emission limit will be installing add-on controls in order to 

demonstrate compliance. Consequently, costs will be higher. 

• The commenters (155, 242) noted that EPA assumed that about 80 percent of rich burn 

and diesel engines less than 500 HP are emergency, but that they disagree with this 

assumption. The commenters (155, 242) believe that the percentage is too high for 

natural gas engines. 

• EPA’s testing cost assumptions are too low and based on portable analyzer testing. 

Testing for formaldehyde will be conducted by FTIR, which is significantly more 

expensive than the $1,000 per engine testing cost EPA has estimated. Testing using 

FTIR is on the order of $5,000 per engine or more. Because the majority of engines 

affected are rich burn engines, the costs are underestimated by EPA. The commenters 

(155, 242) do not necessarily agree with EPA’s assumptions regarding engines being colocated at sources and the assumption that the $1,000 will cover testing for all engines at 

a facility. The commenters (155, 242) also said that they did not know whether the costs 

of subsequent testing (i.e., every 3 years of 8,760 hours, whichever comes first) have 

been included in the cost analysis, which the commenters thought should be. 

• Replacement costs may be incurred for 2SLB engines with lower exhaust temperatures 

since add-on controls may not be feasible. 

• Efficient HAP, CO and NOx control is highly dependent on engine operation and exhaust 

gas temperature and 90 percent reduction cannot be assumed. Actual CO reductions and 
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possible increases in GHG and ammonia emissions should be taken into account during a 

revised cost impact analysis. 

• Certain emission factors used for calculation purposes appear to be erroneous and should 

be revisited to confirm their appropriateness. For example, EPA used the same NOx

emission factor for 2SLB, 4SLB, 4SRB and diesel engines and CO emission factors are 

in units of lb/hr rather than lb/HP-hr. For engines below 500 HP, the emission factor 

based on data from engines less than 500 HP should be used (i.e., 4.78 x 10-4 lb/HP-hr). 

For rich burn engines, the AP-42 emission factor of 2.89 x 10-4 lb/HP-hr for HAP should 

be used. 

• Two commenters (104, 155) said that not all existing engines have hour meters. 

• Costs have not been considered for recordkeeping and reporting for small engines, or for 

area source engines and non-emergency SI engines, which must meet maintenance 

schedules in Table 2d of the proposed rule. Also, documentation is necessary for engines 

with add-on controls and that conduct testing. According to the commenter (104), EPA 

states there are no reporting requirements for engines less than 100 HP, emergency 

engines, and engines that are not subject to any numerical emission standards; however, 

40 CFR 63.6640 requires reporting of each instance in which an operator did not meet 

each emission limitation or operating limitation, which would apply to those instances 

when operators run over an oil/filter or spark plug change or inspection of belts/hoses. 

The commenter (104) requested that these costs be included. In addition, the commenter 

(104) requested that the cost of submitting information to both EPA (which enforces the 

engine standards because they have not been delegated to the State) and the State (which 

permits subject engines) be included in the analysis. 
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Similarly to the specific concerns listed above, commenters 112 and 186 believe that 

EPA has underestimated the total cost of this rule by underestimating the number of engines 

requiring the addition of catalyst; assuming that catalysts can simply be added to effectively 

control existing engines; overlooking the significant cost of field installation; and 

underestimating the complexity of and administrative/operational burdens added by this rule. 

The commenter (112) stated that the cost effectiveness of controls in $/ton are particularly 

concerning, because only the annual control cost of the catalyst and associated HAP reductions 

appear to have been considered and not all the additional costs after controls are added to an 

engine (i.e. performance testing, SSM and maintenance recordkeeping, reporting, lost 

production/revenue, etc.). The commenter (112) requested that EPA re-evaluate the economic 

analysis to include deficiencies in the cost estimates. 

Several commenters (90, 118, 146, 178, 184) provided comments about the economic 

impact of the rule on emergency units. One commenter (90) stated that overall the cost per ton 

of HAP or CO removal would be excessive for emergency CI engines since emissions were well 

below a ton/yr and the units use is very limited and intermittent. 

More specifically, one commenter (146) estimated only 2 of 14 emergency units at two of 

their major sources may be able to be retrofitted at a cost of $65,000 each. The others would 

need to be replaced at a cost of $1,350,000 plus an additional $110,000 each for source testing. 

The commenter’s (146) 9 area source RICE units that would be subject to a NESHAP emission 

standard would need to be replaced at $720,000 each. These costs would be for only 20 to 40 

hrs/yr of operation and thus resulting in minimal emissions reductions. Another commenter 

(178) noted that engine manufacturers do not recommend the use of after treatment devices for 

emergency engines, and that EPA appeared to support that position in the Regulatory Impact 
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Analysis, which states that cost per ton removal of HAP ranged from $1 million to $2.8 million 

for engines larger than 500 HP and from $3.7 million to $8.7 million for engines between 50 and 

500 HP. 

One commenter (184) provided calculations of worst and nominal cases emissions and 

cost per ton removal of CO to justify exemption of combustion turbine peaking unit devices. 

The worst case estimate was 0.13 tons of CO removed at a cost of $107,692 per ton and 0.016 

tons CO removed for the nominal case at a cost of $875,000 per ton. 

Four commenters (103, 186, 203, 204) believed that the true costs of the proposed rule 

are underestimated, especially 4SRB engines noted by commenter 103. One commenter (186) 

stated that the true costs of the rule are not fully understood and that the actual costs are much 

higher than EPA estimates and recommended that EPA re-evaluate the economic analysis to 

include more accurate cost estimates. The commenter (186) stated that the cost effectiveness of 

controls in $/ton are particularly concerning, since only the annual control cost of the catalyst 

and associated HAP reductions seem to be considered, but all of the other costs that this rule 

adds when an engine is controlled (i.e., performance testing, startup, shutdown and maintenance, 

recordkeeping, reporting, etc.) seem to be ignored. The commenter (103) added that the cost 

effective threshold should be based on current accepted science and not an arbitrary HP threshold 

intended to regulate a given percentage of engines. The commenter (103) also provided specific 

comments on the control cost analysis performed by EPA, which are summarized in section 13.3. 

 One commenter (204) believed, based on individual experience, that EPA had 

underestimated the actual cost estimates for several of the required emissions controls under the 

proposed rule, for example, the actual cost of the Continuous Parametric Monitoring System 

(CPMS), which is required to continuously monitor catalyst inlet temperatures, was grossly 
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underestimated. The commenter (204) noted that under the regulatory impact analysis, EPA 

estimated a cost to install a CPMS for a large engine at $531; however, their installation of a 

CPMS on a 4SRB RICE to comply with the 2004 rule resulted in the expenditure of nearly 

$150,000 (approximately $95,000 for labor costs and $50,000 for materials). 

 The commenter (204) also asserted that the EPA did not use accurate cost equations for 

determining the cost impacts of RICE add-on control technologies. For NSCR, the cost equation 

used by EPA was $19.70 x HP + $1,799, resulting in an estimated cost of compliance for a 500 

HP engine of $11,649. The commenter (204) believed that this cost estimate is grossly 

underestimated, especially for the retrofitting of existing engines, believing the cost is closer to 

$100,000 per engine when accounting for the actual NSCR installation, AFRC, modifications to 

the existing exhaust system and labor for the installation. In addition, depending on the 

configuration of the equipment, new supports and a foundation might also be necessary for the 

add-on controls. 

While reducing HAP is an important goal, one commenter (204) believed that the 

overbroad approach taken by EPA in subjecting all the RICE equipment in question to the 

requirements proposed, regardless of whether the equipment is located in urban or rural areas, 

particularly when considering the Congressional intent of reducing HAP in urban areas given the 

potential risks to public health, and the imposition of costs in excess of $528 million to reduce 

13,000 tons of HAP a year (i.e., a cost of $40,615 per ton) should be carefully scrutinized. 

 Another commenter (136) indicated that EPA’s estimates are low for the capital and 

operating costs associated with the use of catalytic control, and are based on pricing data from 

one vendor and a limited number of data points. The commenter (136) asserted that EPA’s 

capital estimate and annual operating cost estimate for catalytic controls are each low by an order 
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of magnitude of 2 to 3. The commenter (136) also stated that because beyond-the-floor 

standards (which require catalytic controls) are based on the cost per ton of HAP removed and 

EPA significantly underestimated capital and operating costs of catalytic controls, EPA must 

reanalyze the proposed rule with better cost data to determine when catalysts are economically 

practical. 

One commenter (81) said EPA’s cost estimates are based on a number of incorrect 

assumptions for emergency generators. The commenter (81) said EPA does not appear to 

consider any costs associated with testing emergency engines, even though owners may deem it 

prudent to test to confirm they are meeting the standard rather than risk an enforcement action if 

the unit does not meet the standard. Testing to comply with the 100 percent load requirement 

will require owners to purchase or rent load banks to meet the conditions contemplated in the 

standard, which can cost up to $10,000 per site. The load bank costs alone could add up to as 

much as $973 million. In addition, equipment modifications (sample ports) would be necessary 

to test emissions, and EPA has not included these costs in its calculations. 

 One commenter (121) said the cost information contained in the docket for test costs is 

not representative of the sampling costs required to comply with the standards as proposed. 

Members of the commenter’s (121) organization indicated that the cost per sample run using 

Methods 1, 3, 4, and 10 could easily exceed $10,000, excluding costs to prepare for the sampling 

(i.e., scaffolding, stack extensions, etc.). In addition to these cost considerations, as a practical 

matter, there would be significant difficulty in performing these EPA test methods on engine 

exhaust. 

 According to one commenter (81), if aftertreatment is required to meet the emergency 

engine numerical limitations, that cost must be considered. Because many emergency engines 
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are likely located in older buildings where space is limited, installation of controls could 

necessitate some reconfiguration of the building, at substantial costs with minimal environmental 

benefit. 

One commenter (140) said the primary impact of the proposed rule on the company is the 

requirement to conduct an initial performance test on each engine with an emission limit. Using 

EPA cost numbers, the company would spend at least $47,600 to test its units. However, 

because the RICE are spread over such a large area (500 square miles), the testing costs would be 

as much as $200,000 due to logistics, travel costs, additional labor for travel, access to remote 

areas, etc. Additional costs would be incurred if add-on controls were needed to meet the 

emission limits and due to O&M requirements, recordkeeping, and reporting requirements 

imposed by the rule. 

One commenter (111) asserted that the industry-specific cost estimates for Crude 

Petroleum & NG Production (Table 4-5 in the February 2009 supporting document) are 

underestimated by 1 to 2 orders of magnitude. The commenter (111) noted that this document 

estimated total nationwide capital costs for this industry sector at $3.77 million and annual costs 

at $7.23 million, but the commenter’s estimates for the State of Michigan alone are $34.8 million 

(capital cost) and $15.1 million (annual cost). The commenter (111) enclosed a table showing its 

organization’s estimate of costs per engine and total costs for the industry in Michigan (see 

section 13.3). The commenter (111) stated that while EPA’s cost analysis shows some 

omissions, it appears that most of the cost discrepancy is due to an underestimation of the 

number of oil and gas production RICE that would be subject to the rule. The commenter (111) 

added that because approximately 98 percent of natural gas production facilities in Michigan are 

located in rural areas, approximately 98 percent of the cost would be rural. 
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One commenter (103) submitted extensive comments regarding annual costs. Regarding 

direct annual costs, the commenter (103) stated that for all HP classes, the EPA assumed the 

direct annual costs associated with maintenance to be $260 per year, which the commenter (103) 

believes is considerably low compared to the actual cost of compliance for engines in the natural 

gas compression industry. The commenter (103) identified the following as some of the major 

issues that it claimed were not accounted for or inadequately accounted for by the EPA: 

• The required emissions tests for engines over 500 HP would cost $3,375 for a test with 

formaldehyde as the surrogate and $2,200 for a test requiring CO as the surrogate, with 

higher costs if a percent reduction method is used for compliance (due to the cost for 

equipment to simultaneously test pre- and post-control emissions). The commenter (103) 

based these estimates on the ability to test an engine in 3⁄4 of a day, which represents an 

average of some individual tests and some tests where multiple engines were tested as a 

group. The commenter (103) noted that EPA assumed $1,000 per test using a portable 

analyzer and made the assumption that all engines will be tested as part of a group (which 

the commenter believes is incorrect). 

• Catalyst elements need to be washed every year and replaced on an average of every 

3 years. Because most engines in the natural gas compression industry cannot be shut 

down long enough to allow the element to be shipped off for washing and returned, the 

commenter (103) believes that a rotation of elements will likely be used. The commenter 

(103) asserted that the cost to remove, ship, and clean an element should be included in 

the direct annual costs. Furthermore, if an element is changed, the commenter believes 

that the engine will have to be retested per proposed 40 CFR 63.6640(b). The commenter 

(103) stated that EPA should clarify in the final rule what circumstances do not require a 
318

re-test (for example equivalent replacement catalyst element in same housing). The 

commenter (103) believes that, as written, the language of proposed 40 CFR 63.6640(b) 

strongly implies that each engine must be retested when the catalyst is changed, which 

will result in engines being tested every year regardless of the HP of the engine. The 

commenter (103) asserted, therefore, that it must be assumed for purposes annual costs 

that all engines requiring catalytic controls will be subject to annual compliance testing. 

• In addition to the labor costs for the maintenance technician to remove and re-install 

elements for washing or replacement, there are often associated direct costs such as 

cranes on larger engines, and replacement parts such as gaskets and seals. 

• Engines must be shut down and restarted prior to maintenance activities. There are often 

two personnel involved (an operator and a maintenance technician), and in the case of 

rental compression, these often represent two different companies. The commenter (103) 

added that many companies require on-site safety reviews prior to work being started, 

and equipment has to be secured to isolate energy (lock-out, tag out) and allowed to cool 

down (especially exhaust) prior to working on the equipment. 

• Down time for maintenance activities has an associated loss in revenue for the operator 

of the engine that should be accounted for. The commenter (103) did not quantify or 

include the downtime in the annual cost estimates, but these are discussed below as 

“hidden costs.” 

• All of the other equipment associated with the installation of the control system has some 

required maintenance and some parts will occasionally fail. Many, such as batteries, 

have a finite life much shorter than the proposed capital recovery period of 10 years and 
319

will require routine replacement. This equipment includes thermocouples, AFR control 

boards, wiring, fuel valves, batteries, and alternators. 

• In addition to the maintenance and testing of individual equipment, there will be informal 

emissions tests performed using portable analyzers. Although these tests do not follow 

EPA protocol, they give the maintenance technician a good indication as to the overall 

performance of the engine and the control equipment and are necessary to ensure 

continuous compliance. 

Regarding indirect annual costs, the commenter (103) stated that the administrative burden for 

recordkeeping, reporting, and monitoring associated with the rule is much larger than assumed 

by the EPA. According to the commenter (103), every engine in the gas compression industry 

will be subject to one of several rules, all with different requirements that must not only be 

performed, but also documented. The commenter (103) also noted that the status of the engines 

will change periodically as the engines are relocated to different sites (major versus area source). 

The commenter asserted that all of these requirements combine to add a significant cost per 

engine for administrative costs in the range of $300 to $1,800 per engine per year. 

 Regarding total annual costs, the commenter (103) submitted cost information that 

indicated that the average total annual costs were 8 to 27 times higher than those estimated by 

EPA and noted that the numbers do not include lost revenue or additional fuel use, which are 

described below as “hidden costs.” 

The commenter (103) said that the HAP emission factor used for natural gas engines ( 

6.88 x 10-4 lb/HP-hr, which equates to about 0.31 g/HP-hr) is close to accurate for lean burn 

engines, but not for rich burn engines which have significantly lower emissions rates for HAP. 

Thus, the commenter (103) believes that the factor used by the EPA overstates the reduction 
320

benefit because it is 3 to 4 times higher than manufacturer's data and the factors in AP-42 for 

formaldehyde (which accounts for 60 to 75 percent of the total HAP in natural gas-fired RICE). 

The commenter (103) estimated that the cost per ton of HAP removed ranges from $8,200 to 

$92,400 based on using the commenter’s estimated total annual costs, a run time of 98 percent or 

8,585 hrs/yr, and a 90 percent reduction of AP-42 emissions factors for all HAP across catalytic 

controls. 

Commenter 103 submitted extensive comments regarding annual costs also identified two 

additional “hidden costs” that are associated with compliance of the rule, both of which have an 

impact on the cost of energy: (1) the cost associated with lost revenue when engines must be 

shut down, and (2) the cost associated with increased fuel burn at catalytic set points. 

 The commenter (103) claimed the following causes of additional shutdowns associated 

with the proposed rule: 

• Initial installation of controls. Some engines will be able to be retrofitted while not in 

use, but many will have to be shut down for the purpose of installing the controls. 

• Additional downtime associated with the maintenance frequencies proposed by the rule 

for smaller engines. 

• Additional downtime associated with catalyst cleaning and replacement. 

• Additional downtime associated with maintenance, repair, and replacement of various 

devices such as fuel valves, AFR control boards, sensors, thermocouples, etc. 

 The commenter (103) noted that in the case of a single engine installation, the cost of 

downtime is 100 percent of the revenue, which far exceeds the cost of the actual maintenance. 

According to the commenter (103), for the natural gas compression industry this cost is in the 

range of $30 to $90 per day per HP, based on lost natural gas production at $6.00 per MMBtu. 
321

At this rate, the commenter (103) estimated that it would cost the energy industry $159 million 

for just the HP owned by the commenter’s member companies (5.3 million HP), based on half of 

these member companies’ fleet HP requiring a 24-hour shutdown for the initial retrofit. The 

commenter (103) stated that additional downtime associated with maintenance will add a similar 

magnitude of cost on an annual basis. 

 The commenter (103) also stated that there is a cost associated with additional fuel 

burned from operating a 4SRB engine at a catalytic set point which is richer than normal 

operation. According to the commenter (103), the manufacturer's data for a 145 HP Caterpillar 

G3306 NA estimates the increase in brake specific fuel consumption (BSFC) to be 5 percent. 

The commenter (103) estimated an annual cost of $53 million (at $6.00 per MMBtu) for just the 

HP owned by the member companies, assuming that 50 percent of this overall fleet is affected in 

a similar manner. 

 Because of these claimed “hidden costs,” the commenter (103) recommended that EPA 

contact trade organizations that represent small, independent operators to determine if 

compliance with the rule will be overly burdensome on these companies that have limited human 

and capital resources. 

One commenter (150) stated that if the GP of 40 CFR part 63 are to be applied to engines 

that are the subject of this rulemaking, EPA should gather information on costs and complete a 

cost/benefit analysis for reporting and recordkeeping. 

One commenter (251) expressed that the proposed rule would put an incredible strain on 

not-for-profit entities, or hospitals, specifically. The commenter (251) reported that all of its 

hospitals are operating with negative margins and the cost of the proposed rule would pull 

resources from direct patient care. 
322

Commenter (249) contended that EPA’s proposed controls are cost prohibitive. This 

commenter (249) stated that the EPA should prepare a generic $/ton BACT analysis regarding 

the proposed controls that will be needed to meet proposed emission limits, and claimed that this 

analysis will clearly show that the $/ton costs are prohibitive. 

Commenter (249) noted that EPA is proposing to limit formaldehyde emissions to as low 

as 2 ppmvd for emergency SI engines. Commenter (249) claimed that costs to meet these rigid 

limits will be prohibitive and will impact emergency engines used throughout the United States 

at all kinds of facilities that provide vital safety requirements. 

Commenter (249) presented example cost quote and BACT analysis. Commenter’s (249) 

BACT analysis was prepared to reduce formaldehyde by 90 percent (from an emission rate of 

4.26 x 10-4 lb/hr to 4.26 x 10-5 lb/hr) using EPA recommended guidelines for a 0.5 MW (670 HP) 

engine. In commenter’s (249) analysis the cost effectiveness is calculated to be 

$109,639,280/ton (assuming 10 year amortization rate) for reducing formaldehyde base on 100 

hrs/yr of operation. By comparison, commenter (249) claimed that in most areas of the country, 

BACT is considered reasonable if the costs are approximately $5,000 to $10,000/ton depending 

on the pollutant. Commenter (249) noted that additional costs would be incurred for 

construction, maintenance and upkeep costs. 

Commenter (220) claimed that EPA has proposed compliance requirements that are more 

stringent than GACT requirements or management practices and that EPA has decided to 

institute MACT. However, even under MACT EPA can consider cost and energy impacts. The 

commenter (220) disagreed with EPA’s conclusion in the RIA that the rule will not likely have a 

significant impact on the supply, distribution, or use of energy. The commenter (220) said that 
323

the proposed standards could have a very detrimental impact on energy reliability, and many 

units may have to be shut down due to the cost of compliance. 

One commenter (261) believes that economic impact estimate by EPA is extremely low. 

The commenter (261) noted that EPA estimated the initial capital cost for control equipment to 

be $528 million and the annual cost to be $345 million. The commenter (261) stated that the 

industry believes that the capital cost is a factor of 10 higher and the annual cost to be a factor of 

4 higher. The commenter (261) gave the following reasons for EPA’s low estimate: 

• Not all existing engines requiring controls can simply add a catalyst, some engines must 

be replaced; 

• EPA estimated the performance test to cost $250-500 when the cost for many engines is 

approximately $8,000; 

• EPA falsely assumed the proposed maintenance requirements adds no cost to the 

industry; and 

• The administrative burdens of the rule were underestimated or left out entirely. 

One commenter (112) provided an estimate of the total cost of the proposed rule. The 

commenter (112) indicated that cost of controls reflects the affected engine count provided by 

EPA and the assumptions discussed in his comments on each component cost, but does not 

attempt to recalculate the capital or annual cost/engine. In comparing costs, the commenter 

(112) noted that its estimated costs exceed the EPA estimated costs by almost 2 billion dollars. 

 The commenter (112) believes that the examples included in its discussion of various 

component costs are indicative of a pattern of underestimation of the cost of this proposed 

regulation to the Oil and Gas industry. The commenter (112) asserted that the significant 

difference in estimated costs underscores the importance of re-evaluating the proposed regulation 
324

for SI engines to ensure that the final rule accomplishes EPA’s goals while not resulting in undue 

and onerous regulation for industry, especially in order to continue with operation of marginal 

locations. 

 The commenter (112) also stated that this cost summary does not correct all of the 

deficiencies that the commenter believes are present in the impact analysis, such as costs for 

catalyst control capital and annual costs, control maintenance costs, and maintenance work 

practice costs. In addition, the commenter’s (112) cost summary does not attempt to assign cost 

estimates to lost production, which the commenter believes would have to be estimated on a perwell or pipeline basis taking into account estimated engine down time due to adding controls and 

performing additional maintenance and the production of individual wells and/or pipeline 

throughput. The commenter (112) believes that these unaccounted for costs may be significantly 

greater than his cost corrections summarized above.

One commenter (242) said, as also noted in earlier comments by this commenter and 

others, that EPA has not considered the high demand of catalysts that will be the result of this 

rulemaking. The impacts of a large demand of catalysts should be included in EPA’s cost 

analysis to determine the effect based on vendor and catalyst availability, precious metal 

markets, and potential replacement costs, commenter (242) said.

Two commenters (104, 112) stated that EPA estimates of the cost of performance testing 

(based on performing test using a portable analyzer and discounts for testing multiple engines at 

every site) at $500 for engines less than 500 HP and $250 for engines greater than 500 HP. 

While the commenter (112) conceded that performance testing using portable testing equipment 

is less expensive for CO testing for lean burn and CI engines, the commenter believes $500/$250 

per test is an extremely low estimate. Commenters 104 and 112 stated that an FTIR test for 
325

formaldehyde (three 1-hour runs) may cost as much as $4,000 per test. The commenter (112) 

added that two tests (i.e., pre- and post-catalyst) are required to calculate a percent reduction 

across the catalyst, which results in an estimated cost for a performance test for one rich burn 

engine with NSCR of $8,000 per test. The commenter (112) stated that based on the number of 

affected non-emergency engines, industry expects to perform 46,947 initial tests for 

formaldehyde and 65,240 tests for CO for a total cost of $440.8 million in 2013, as compared to 

EPA’s estimate of $77 million.

 The commenter (112) also estimated that annual cost for subsequent performance testing 

of SI engines greater than 500 HP, which is required every 8,760 hours or 3 years, whichever 

comes first. The commenter (112) estimated that 75 percent of SI engines greater than 500 HP 

are in the oil and gas industry, where they typically have very high run time and will have to be 

tested every year, and the other 25 percent of the engines in other industries will be tested every 

3 years. Based on these assumptions, the commenter (112) estimated that the engines in the oil 

and gas industry would have annual testing costs of $44.6 million, the engines in other industries 

would have annual costs of $4.9 million, and the total annual cost of testing would be $49.5 

million per year. 

Response: EPA used the information it had available at the time of proposal to estimate the cost 

impacts associated with the rule. This information included cost data obtained for the 

development of previous stationary engine rulemakings, which EPA believed it would be 

appropriate to use for this rulemaking. As indicated clearly in this comment summary, several 

members of industry believe that EPA has underestimated the costs associated with the rule and 
326

used non-representative cost information. EPA points out, however, that some groups20 have 

indicated to EPA that the costs used, specifically those costs associated with aftertreatment 

controls are reasonable. EPA would also like to make the point that it has been requesting 

information on all facets related to stationary engines for years through various rulemakings and 

direct contact with members of industry and other affected stakeholders. Therefore, anyone 

interested in submitting information to EPA for consideration in this rulemaking or any other 

rulemaking has had ample opportunity to supply EPA with relevant cost information on controls, 

testing, recordkeeping and reporting reflective of today’s costs. Commenters also criticize 

EPA’s population estimate and again, EPA has on numerous occasions asked industry to provide 

breakdown estimates of the population of stationary engines in the U.S., but has been told that 

the estimates that EPA has from PSR is the best source of available information. If industry has 

had information available on the population of stationary engines that EPA could have used, 

EPA was not aware of that because such estimates were not provided to the Agency. For the 

final rule, EPA did supplement the population dataset with information from the USDA on the 

number of stationary SI engines used for agricultural purposes. 

Based on the significant number of comments received on the proposed rule costs, EPA 

believed it was appropriate to revisit the cost analysis and assumptions for the final rule. EPA 

has obtained additional and newer cost data and made an attempt to address the specific areas of 

concern commenters have pointed out that would benefit from more current and detailed cost 

inputs. EPA addresses comments related to the cost of controls in response to comment 12.3.1. 

                                                           

20 Email from Antonio Santos, MECA (Manufacturers of Emission Controls Association ) to 

Tanya Parise, EC/R. MECA Cost of Aftertreatment. January 21, 2010. EPA-HQ-OAR-2008-

0708-0380.
327

EPA has also described in detail the cost data and basis for assumptions in the memorandum 

“Control Costs for Existing Stationary SI RICE” available from the docket and asks commenters 

to refer to that document for the complete analysis. The revised capital and annual cost of 

controls are substantially higher than what was used for the proposal. For example, for a 300 HP 

rich burn engine, the capital control cost increased by an order of magnitude of above 1.5. The 

annual control costs increased by an order of magnitude of close to 4. EPA believes data and 

assumptions used to develop control costs for the final rule are accurate and representative of the 

current cost of controls. 

During the time of proposal, EPA looked at various sources of information in order to 

determine the number of existing 4SRB engines already equipped with aftertreatment controls. 

EPA reviewed State regulations and made a determination based on the applicability of the 

regulation on existing stationary rich burn engines and the applicable limit (typically NOx) 

whether such regulation would necessitate aftertreatment. EPA also compared that to 

information from a survey conducted in California related to the revisions implemented for 

South Coast AQMD’s Rule 1110.2 – Emissions from Gaseous and Liquid-Fueled Engines 

because the survey collected various information including types of engines and which controls 

are currently being used. Based on the information reviewed, EPA estimated for proposal that 

80 percent of existing rich burn engines are already equipped with NSCR. However, EPA notes 

that it was an estimate and certainly the percentage may fluctuate between State to State. Based 

on feedback on this assumption, EPA has made a reassessment for the final rule concerning how 

many existing rich burn engines already have aftertreatment. EPA agrees with commenters that 

the estimate of 80 percent was too high. As discussed in response to comment 5.1.1.2, EPA has 

gathered information from a number of different sources and has determined for purposes of 
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estimating impacts associated with the final rule, that an estimate of 20 percent is more 

appropriate to represent the number of already-controlled 4SRB engines. 

Regarding existing stationary 2SLB engines, EPA is finalizing emission standards for 

2SLB engines greater than or equal to 100 HP and less than or equal to 500 HP that have been 

met historically without oxidation catalyst. For existing 2SLB engines less than 100 HP and 

existing 2SLB engines at area sources, EPA is requiring maintenance/management practices. 

Based on updated cost of controls, EPA determined that aftertreatment was not justified for 

2SLB engines. EPA discussed how it conducted a re-analysis of the control of controls for 2SLB 

(and 4SLB and 4SRB) engines in response to comment 12.3.1. The data and methodology use 

for derive control costs are also presented in material21 available from the docket. EPA also 

discussed in response to comment 12.3.1 the range of control efficiencies that can be expected 

from 2SLB engines. EPA does not necessarily agree that 90 percent reduction is not achievable, 

particularly for CO and NOx. Nevertheless, for purposes of estimating the cost per ton of a 

potential add-on control option for 2SLB engines, EPA assumed a 43 and 65 percent control 

efficiency for HAP and CO, respectively, based on results seen at CSU. However, emissions 

data from the 4SLB engines tested at CSU shows an average CO reduction of 93 percent. For 

the final rule, for existing non-emergency 4SLB engines greater than 500 HP at area sources, 

EPA is requiring a 47 ppmvd at 15 percent O2 CO concentration standard or a 93 percent CO 

control efficiency. To estimate HAP reductions associated with this requirement, EPA agrees 

that it is not appropriate to assume a constant 90 percent reduction. Instead, for purposes of 

                                                           

21 Memorandum from Bradley Nelson, EC/R to Melanie King, EPA. Control Costs for Existing 

Stationary SI RICE. June 29, 2010. 
329

estimating emissions reductions for 4SLB engines, EPA has assumed a 71 percent HAP control 

efficiency, which was the average reduction observed for formaldehyde at CSU. Emissions data 

for 4SRB engines indicate an average NOx reduction of 97 percent, which is what EPA used to 

estimate the NOx reductions associated with the requirement for existing non-emergency 4SRB 

engines at area sources. These engines are subject to a 2.7 ppmvd formaldehyde standard at 15 

percent O2 or a 76 percent formaldehyde control efficiency. The 76 percent control efficiency is 

also based on the average level of reduction observed during testing. To estimate CO reduction 

from rich burn engines, EPA did not assume 90 percent, but used the average level of 49 percent 

seen during testing. Based on evidence in the docket, EPA believes that final standards that 

incorporate pollutant reduction efficiencies are appropriate and justified as well as the percent 

reduction efficiencies used to estimate impacts. 

 As far as emission factors are concerned, EPA again notes that it used what it believed to 

be the best information available at the time of proposal. EPA agrees that there is a possibility 

that more appropriate emissions data could have been used to estimate baseline emissions and 

reductions, but EPA disagrees that some of the emission factors were erroneous. One can argue 

the appropriateness of using lb/hr versus lb/HP-hr and EPA is not certain whether one is more 

suitable than the other, however, EPA used lb/hr emission factors for the original 2004 RICE 

NESHAP. EPA also used the same NOx emission factor for all engines under the 2004 RICE 

NESHAP. With that said, EPA reviewed the emission factors used at proposal considering the 

input provided by commenters. Regarding emission factors, for the final rule, EPA is using 

emission factors for HAP, VOC, CO, and NOx in consistent units, i.e., lb/HP-hr. EPA agrees 

with the commenters that it would be appropriate to use the AP-42 emission factor for 4SRB 

engines. EPA does not believe it is appropriate to use the HAP emission factor developed for 
330

natural gas engines below 500 HP (i.e., 4.78 x 10-4 lb/HP-hr) because the regulation addresses 

larger engines as well, that is existing stationary SI engines above 500 HP at area sources. Nor 

does EPA it is appropriate to use the same HAP emission factor for 2SLB and 4SLB engines, but 

believes a HAP emission factor that incorporates the differences between these two engine types 

is more appropriate. Therefore, for the final rule, EPA is using information from AP-4222 to 

derive emission factors in lb/HP-hr for 2SLB and 4SLB engines as well. EPA summed the 

individual HAP for each engine type to determine the emission factor in units of lb/MMBtu. 

EPA then converted the emission factor to lb/HP-hr using the conversion factor 0.002546 

MMBtu/HP-hr and an engine efficiency of 34 percent. For the final rule, EPA is using a HAP 

emission factor of 5.96 x 10-4, 5.41 x 10-4, and 2.43 x 10-4 lb/HP-hr, for 2SLB, 4SLB, and 4SRB, 

respectively. EPA also agrees that it is appropriate to distinguish between engine types in order 

to develop representative emission factors for CO and NOx too. The derivation of emission 

factors is presented in a memorandum available from the docket titled “Emission Factors for 

Existing Stationary SI RICE.” 

 EPA does not believe the testing costs used for the proposed rule were significantly 

unreasonable. Those costs were based on information available at the time, based on what 

testing firms have indicated to EPA. A cost of $1,000 is considered reasonable to EPA to test 

for CO at a site and for the purposes of estimating impacts, EPA has assumed that two engines 

can be tested for this cost ($500/engine). For FTIR/Method 320 or Method 323 testing, EPA has 

assumed a cost of $2,000, where with a multiple engine discount, EPA is assuming that two 

                                                           

22 AP 42, Fifth Edition, Volume I Chapter 3: Stationary Internal Combustion Sources Natural 

Gas-fired Reciprocating Engines. Supplement F, August 2000. 

http://www.epa.gov/ttn/chief/ap42/ch03/final/c03s02.pdf
331

engines can be tested for this cost (or $1,000/engine). EPA notes that this is an estimate and that 

testing costs can vary across the country. 

EPA disagrees that its assumption that maintenance requirements add no cost to industry 

is false and EPA does not agree that following maintenance/management practices will be a time 

consuming activity. The management practices EPA is requiring under the final rule are based 

on industry practice and normal maintenance procedures currently followed by stationary SI 

engine operators. It is in the best interest of owners that their engines are well-maintained and 

kept in proper condition. EPA believes engine operators would continue to follow maintenance 

procedures to keep their engines in proper working condition and would allocate funds for that 

purpose, in the absence of the rule. Therefore, EPA does not believe there will be any increased 

cost. In the event that engine owners and operators might expend additional effort as a result of 

the final rule in order to maintain their engines, such effort is expected to have a minimal effect 

on the cost, plus maintaining the engine properly might lead to a longer engine life and might 

even result in cost savings, which could offset the potential small increased cost owners and 

operators might experience. 

EPA does not agree that it used old, faulty, and inappropriate data to estimate the 

recordkeeping and reporting costs of the rule. EPA used information available at the time of 

proposal to develop the best estimate possible of the administrative burden associated with the 

rule. For the final rule, EPA is accounting for labor associated with recording the hours of 

operation for emergency SI engines and for engines tracking maintenance activities conducted on 

the engine. EPA estimated costs for keeping records that the work or management practices are 

being met, which includes keeping track of oil and filter change dates and, inspection and 

replacement dates for spark plugs, hoses, and belts, and records of other emission-related repairs 
332

and maintenance performed. EPA does not anticipate these recordkeeping requirements to be 

burdensome and expect minimal additional effort in terms of labor hours for owners/operators 

beyond what they are currently doing. In terms of reporting costs, EPA is accounting for 

activities required under the General Provisions, which include various notifications applicable 

to certain engines and additional reporting requirements like compliance reports that other 

engines must submit. More details on EPA’s estimate of testing, monitoring recordkeeping, and 

reporting costs are presented in the memorandum “Impacts Associated with NESHAP for 

Existing Stationary SI RICE” and in the RIA for the final rule. 

For the final rule, EPA estimated a total national capital cost of $406 million, with a total 

national annual cost of $261 million in year 2013 (the first year this final rule is implemented). 

EPA estimated that HAP emissions will be reduced by 6,000 tpy beginning in the year 2013. 

12.1.2 Comment: One commenter (242) said that EPA has not provided supporting information 

showing how it determined cost impacts for remotely and inaccessible rural engines. EPA has 

not considered the unique costs and requirements for engines located in rural areas where there 

may be issues like limited or poor accessibility and lack of electricity, the commenter (242) said 

and urged EPA to conduct a separate analysis of the impacts for rural remote area sources 

engines. In terms of the MACT floor, it is important that the analysis is conducted correctly to 

accurately reflect potential impacts for these sources, the commenter (242) said. Specifically, 

one commenter (104) said that EPA proposes that operators monitor the pressure drop across the 

catalyst and the temperature of the exhaust so they meet the proposed operating limitations for 

rich burn engines. Because many oil and gas facilities are located in remote, rural areas and do 
333

not have electricity to monitor or record these parameters, the commenter (104) requested that 

the cost for running electricity to a facility be included in the analysis. 

Response: EPA does not expect the cost impacts will be significantly greater for an engine in a 

rural area than in urban area. In terms of monitoring requirements to record the pressure drop 

and temperature associated with catalyst operation, recording these parameters are important to 

ensure proper functioning of the aftertreatment device. Lack of electricity at remote sites is not 

expected to be an issue because battery-operated equipment is available and affordable to 

measure and record temperature and pressure differential. Therefore, not having electricity is not 

a technical or economical obstacle and EPA does not believe costs will be greater for rural areas. 

It will not be necessary for sources in remote locations to run electricity solely to comply with 

monitoring requirements. EPA provides more cost details on such equipment in response to 

comment 8.1. 

12.1.3 Comment: One commenter (242) said that EPA should develop an estimate of the costs 

for implementing NESHAP requirements for existing area sources within synthetic minor 

permits. Sources have in the past opted to install controls beyond what is required in order to 

avoid Title V thresholds and to become synthetic minors for HAP. This is a problem because the 

proposed rule would apply many onerous provisions that were previously avoided, including 

more stringent emission limits, and will become a disadvantage for those sources that chose to 

over-control their engines in the past. 
334

Response: EPA has made several revisions to the proposed requirements and is finalizing a rule 

that in many cases significantly reduces the burden on existing stationary engines located at area 

sources. Therefore, EPA does not believe the final rule places many onerous or inappropriate 

provisions on the existing stationary engines the commenter is referring to. 

12.1.4 Comment: Two commenters (112, 220) were concerned with how the rule would 

economically affect their engines. One commenter (112) stated that the proposed amendment to 

the NESHAP for RICE is a regulation that will have a major operational and financial impact on 

the member companies in his organization, which operate thousands of engines continually 

throughout the year. The commenter (112) stressed that the operating and capital costs 

associated with compliance with this proposed regulation will be borne by the member 

companies and are expected to have a significant impact on the profitability of individual 

producing sites. The commenter (112) believes that marginal operating locations will likely 

become uneconomical due to additional costs of compliance with this rule, and gas and oil 

production will likely be impaired in locations that are not marginal. The commenter (112) 

added that engines that operate pump jacks, recover natural gas from wells, and transmit gas via 

pipelines will have to be temporarily shut down to retrofit controls and more routinely for 

additional proposed maintenance requirements. The commenter (112) noted that all of this is 

being proposed at a time when this country endeavors to become more energy independent. 

One commenter (220) provided an extensive discussion of the structure of the power 

generating structure of the Illinois Municipal Electric Agency. The commenter (220) provided 

this information to illustrate how vital these units are to the member municipalities, which are 
335

typically located in rural areas, have small populations, and are facing very tight budgets. The 

commenter (220) said the proposed rule will have drastic impacts on these communities. 

Response: EPA has attempted to minimize the burden on small businesses and individual 

owners and operators, and is finalizing management practices for most of the existing stationary 

engines located in area sources, which includes rural engines. However, EPA is required to 

address and develop regulations for all existing stationary engines less than or equal to 500 HP at 

major sources and existing stationary engines located at area sources. 

12.1.5 Comment: Three commenters (101, 104, 177) were concerned how the proposed rule 

would impact small business. Two commenters (101, 104) believe that the proposed rule will 

have an adverse impact on small businesses. One of these commenters (101) stated that over 80 

percent of America’s oil wells and approximately 74 percent of America’s natural gas wells are 

marginal wells, and that the overwhelmingly majority of these wells are operated by small 

businesses. The commenter (101) indicated that these wells require numerous engines to 

continue to operate and the current regulatory proposal would put many, if not most, of these 

wells at risk. The commenter (101) believes that the proposed regulations fail to consider the 

implications of the regulations on the small businesses that would be compelled to meet them. 

 The second commenter (104) noted that despite the low production rates, approximately 

19 percent of U.S. oil production and 8 percent of the natural gas produced in the lower 48 states 

comes from marginal wells. The commenter (104) indicated that most of these wells are located 

in older oil and gas producing regions like Oklahoma, Texas, and Appalachia. The commenter 

(104) said that marginal wells operate at the edge of profitability and are particularly sensitive to 
336

any increases in cost that might lead to their premature plugging and abandonment. According 

to the commenter (104) most marginal wells are operated by small businesses, which are nonintegrated companies that receive basically all of their revenues from production at the 

wellhead – thus, even the slightest increase in costs may have a disproportionate impact on their 

business as compared to large, integrated oil companies. The commenter (104) believes that 

special care must be taken to ensure that any increased regulatory costs are justified in light of 

the potential threat to these essential resources. The commenter (104) added that the negative 

impacts of the rule on small businesses that operate marginal wells are fundamentally 

inconsistent with efforts to protect national security by increasing domestic energy production. 

The commenter (104) requested that EPA reevaluate the impacts of the proposed action on the 

nation’s energy sources, supply, distribution, use, and the cost and benefit to the oil and gas 

industry in accordance with Executive Orders 12866 and 13211. 

One commenter (177) believes that the SSM limits could significantly impact small 

businesses and force them into noncompliance during startup, shutdown, or malfunction 

conditions. The sources will become subject to noncompliance penalties and other enforcement 

risks even though the engines have been operating in the same way for more than a decade. The 

commenter recommended that EPA suspend the SSM rulemaking and convene a Small Business 

Advocacy Review (SBAR) Panel on SSM under section 609(b) of the Regulatory Flexibility Act 

(RFA). 

Response: To the extent that it could, EPA did consider costs to small businesses in determining 

the requirements in the final rule. EPA cannot consider cost when determining the MACT floor, 

but it can and did consider cost when evaluating whether to go beyond the floor and also 
337

evaluating GACT for area sources. As discussed in the RIA for the final rule, EPA analyzed the 

impacts of the rule on small businesses and determined that it will not have a significant 

economic impact on a substantial number of small entities. See Section 6 of the RIA. 

The commenters did not provide any information to demonstrate why the proposed SSM 

requirements would have a more significant impact on small businesses than on other sources. 

Regardless, EPA in the final rule has specified work practices for startup that these sources can 

comply with that should not have a significant negative impact on these sources. As discussed in 

section 3.0, EPA has made changes in the final rule to the SSM requirements that were proposed, 

and EPA believes these changes will address the commenter’s concerns regarding the impacts of 

SSM on small entities. 

12.1.6 Comment: One commenter (104) believes that EPA estimates that a total of 180,291 SI 

engines at area sources will be impacted by the rule is inaccurate and the commenter believes 

that a greater number of facilities will be impacted. The commenter (104) stated that in 

Oklahoma there are approximately 122,000 oil and gas wells, and estimated that as many as 

67,000 facilities will have at least one engine that will be subject to the proposed rule. The 

commenter (104) requested that EPA re-evaluate the cost impacts to operators of oil and gas 

production facilities. 

Response: The impacts EPA estimated are based on population numbers that EPA developed 

from information available from the PSR database. The information from PSR is the best 

available information related to the number of engines in the United States. EPA has contacted 

industry on several occasions to obtain other estimates of the number of existing stationary 
338

engines; however, EPA has been told repeatedly that PSR is the best source of information and 

that industry does not have any better estimates of the national population of stationary engines. 

EPA described in a memorandum developed prior to the proposal how it arrived at the estimated 

number of stationary engines that would be affected by the rule. That document is available 

from the rulemaking docket at http://www.regulations.gov as Document ID Number EPA-HQOAR-2008-0708-0014. For the final rule, EPA has also made the PSR information that EPA 

used to develop the population estimates available and can be found in the docket as well. Based 

on the estimate for Oklahoma that the commenter provided, it seems that the number of engines 

in that State may be high compared to the total number of engines that EPA has estimated. 

However, EPA would be need similar estimates from each and every State in order to account 

for the total number of engines in the country. EPA would also need to determine the accuracy 

of estimate of the number of engines and to determine if the commenter over counted by, for 

example, including nonroad engines or engines that are otherwise not regulated (e.g. new 

engines) under the rule. EPA believes that it has used the best possible estimate of total 

stationary engines in the United States in order to develop impacts associated with the final rule. 

12.1.7 Comment: Two commenters (147, 194) expressed that the proposed rule would have a 

significant impact on agricultural sources. One commenter (194), on behalf of the agricultural 

industry in their state, stated that, because of the retroactive nature of the proposed rulemaking, it 

places a burden on agricultural operators without having viewed the costs of testing and other 

compliance measures for existing engines and lacks both economic and environmental 

justification. The commenter (194) stated that the operational use of engines used in the 

powering of irrigation and lift pump facilities has not been factored into EPA’s evaluation nor 
339

has data been submitted that supports a need beyond the normal replacement cycle of engines 

that is naturally occurring due to wear and tear of existing operating engines. The commenter 

(194) argued that the costs associated with requiring retroactive compliance does not recognize 

that the normal replacement process for such engines will produce the same reduction in 

emissions due to new engine performance standards being present when these existing engines 

are replaced without putting a burden on both the owners of the engines and on the regulatory 

agencies responsible for administering the programs. 

One commenter (147) stated that the economic impact of the proposed rule on the 

agriculture industry would be extremely high and would significantly outweigh any 

environmental benefit. The commenter (147) submitted data indicating total HAP emissions 

from all RICE operated by the Florida sugar industry to be less than 2 tpy. Based on EPA’s 

estimates for performance test costs, the commenter (147) calculated a cost effectiveness for this 

industry of $271,500 per ton of HAP reduced assuming all of the HAP emissions were 

eliminated due to the proposed rule. The commenter (147) therefore requested that rural, 

agricultural RICE be exempted from numeric emission limitations and performance test 

requirements. 

Response: EPA does not agree that it would be appropriate to wait until these engines are 

replaced to require emissions reductions. Stationary engines can in some cases operate for 

decades before they are replaced. EPA determined that the costs of the rule are justified 

considering the emissions reductions that will be achieved. The commenter did not provide any 

information to support the contention that stationary agricultural engines are significantly 

different enough from other applications to warrant a separate subcategory, or that standards 
340

would be different even if there were such a subcategory. EPA notes that in the final rule it has 

required management practices, not numerical emission limits, for all engines 500 HP and below 

located at area sources and has only required MACT standards at the MACT floor for engines at 

major sources, after determining the standards were justified for those engines, considering costs 

and other factors. EPA also notes that according to data received from the United States 

Department of Agriculture (USDA)23, the majority of engines used in agricultural applications 

are rated below 300 HP. For example, natural gas, propane, and gasoline agricultural engines 

below 300 HP represent more than 80 percent of the total population of agricultural SI engines, 

according to the USDA National Agricultural Statistics Service. 

12.1.8 Comment: One commenter (207) stated that EPA has underestimated the cost of the 

proposed rule for nuclear power plants. According the commenter (207), components installed in 

nuclear applications are subject to a variety of quality assurance requirements, specifications, and 

code requirements, and none of the current catalytic converter manufacturers are qualified to 

nuclear safety related standards. Further, commenter (207) claims that the cost of producing 

catalytic converters to nuclear safety related standards, estimated at $0.85 million, is expected to 

be 5 to 10 times the cost of commercial applications, that installation costs associated with 

additional piping, supports, fire protection, heating/ventilation/air conditioning, etc., are 

estimated to be $2 to 4 million per RICE, and the cost of providing additional structures to 

protect this equipment is estimated at $3 to 5 million per RICE. Commenter (207) estimates that 

with approximately 250 emergency RICE currently installed at nuclear power plants, the total 

                                                           

23 Email from Greg Zwicke, USDA to Melanie King, EPA. USDA National Agricultural 

Statistics Service. April, 7 2010. EPA-HQ-OAR-2008-0708-0495.
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cost would exceed $2 billion. Commenter (207) believes that this large cost is not justified by 

the insignificant amount of emission reduction that would result from adoption of the proposed 

rule. Similarly, Commenter 216 estimated that the cost of making modifications to existing 

emergency diesel generators configurations at nuclear power plants to result in capital costs that 

are 5 to 10 times greater due to additional NRC testing and evaluation requirements than would 

be the case at a non-nuclear regulated emergency diesel generators. 

Commenter (216) found the proposed rule to be a monetarily significant rule for 

regulated entities, thus adding a burden to their customers while yielding a minimal impact on 

emissions reductions. The cost and NRC conflicts and duplications within the proposed rule 

create significant concerns for nuclear facilities. The commenter (216) is concerned about safety 

conflicts with the NRC and the financial burden that would be imposed on nuclear facilities. 

Response: The EPA does not agree that the rule will have an unreasonable burden on engines 

used at nuclear power plants. For stationary emergency engines at nuclear power plants that are 

area sources of HAP or are less than 500 HP and at major sources of HAP, the final rule requires 

the engines to meet management practices rather than the emission limitations that were 

proposed. Therefore, these engines will not incur the cost of aftertreatment controls for their 

emissions, so there will be no concerns with having to operate these engines with catalyst control 

and the engines will not have to be modified. Emergency engines at nuclear power plants that 

are major sources of HAP and are greater than 500 HP are not the subject of this rulemaking. 

12.2 Environmental/Health Impacts 
342

12.2.1 Comment: Two comments (140, 147) believe the proposed rule will have little 

environmental benefit. Specifically, one commenter (140) noted that the HAP and formaldehyde 

emissions associated with RICE owned and operated by the company are very low. Since, EPA 

anticipates that all of these units could meet the standard without installing additional controls, 

there would be no environmental benefit. If controls are required, they are still only applied to 

low level emission sources. The cost effectiveness of any modifications or add-on controls for 

these engines would be extremely high. 

 The commenter (140) said the RICE operated by the company are scattered throughout 

approximately 322,000 acres, resulting in an average engine density of approximately one engine 

per 4,000 acres (6 square miles). For the most part, these engines are very remote any residences 

or population areas, according to commenter 140. Therefore, there would minimal or no health 

related improvements associated with imposing emission limits or control equipment on these 

engines, according to commenters 140 and 147. The commenter (147) noted that the engines 

operated for agricultural purposes typically are spread over a large geographic area that is in a 

remote location with respect to residences or population areas and, in most cases, are below 300 

HP. The commenter (147) pointed out that EPA acknowledged in the preamble to the proposed 

rule that it expects all engines below 300 HP to meet the proposed emission standards without 

any additional control. Therefore, the proposed rule imposes new, costly regulatory burdens 

without providing any environmental benefit. For this reason, the commenter (147) requested 

that rural, agricultural RICE be exempted from numeric emission limitations and performance 

test requirements (see comment above in section 6.4).
343

Response: EPA disagrees with the comment that the rule will have little environmental benefit. 

The rule will reduce emissions of HAP as well as CO, VOC, and NOx. EPA described the 

health effects of the HAP emitted from stationary diesel engines in the preamble to the original 

promulgation of subpart ZZZZ (69 FR 33474). These HAP emissions are known to cause or 

contribute significantly to air pollution which may reasonable be anticipated to endanger public 

health or welfare. The Regulatory Impact Analysis (RIA) for the final rule indicates that we 

expect $510 million to $1.2 billion in benefits nationwide associated with implementation of the 

rule due to reductions in PM precursor emissions that occur as a co-benefit of the HAP control 

requirements. 

EPA has determined that management practices are appropriate for small stationary 

engines at area sources as well as stationary emergency engines at area sources, which reduces 

the impact of the rule on those engines. 

12.2.2 Comment: One commenter (71) supports the proposed rule as issued by EPA in the 

Federal Register on March 5, 2009, in order to improve Reservation air quality and to help 

improve regional haze in nearby Class I areas. The commenter (71) also supports the EPA’s 

decision to help reduce greenhouse gas emissions through this rule. 

Response: EPA notes that this rulemaking is for HAP emissions and is not focused on reducing 

greenhouse gas emissions. 

12.2.3 Comment: Two commenters (146, 178) noted that from a life-cycle perspective, HAP 

emissions reductions attributable to replacement of emergency units (that are not recommended 
344

to have aftertreatment devices installed by their manufacturers) would be dwarfed by the carbon 

and HAP emissions that would result from manufacturing, transporting, and installing new 

replacement units that would be used for so few hrs/yr.

Response: EPA is not requiring the replacement of existing emergency engines in the rule. The 

commenter did not provide any information to explain why the emergency engines could not be 

retrofit with emission controls and would have to be replaced. In any case, the final rule does not 

require any numerical emission limits for emergency engines and requires only work or 

management practices. Therefore, EPA is unable to fully respond to this comment. 

12.2.4 Comment: One commenter (140) provided a profile of the phosphate fertilizer company’s 

engine population, including emission estimates based on actual engine operating hours and AP42 emission factors. As shown, HAP emissions are estimated at less than 0.5 pounds per hour 

(lb/hr) (based on organic HAP emissions). The commenter (140) concluded that these emissions 

are not significant compared to the HAP threshold for major source facilities. 

Response: No response is necessary.

12.3 Cost of Controls 

12.3.1 Comment: Several commenters (78, 103, 104, 111, 112, 150, 156, 216, 220, 225, 227) 

indicated concerns with EPA’s estimate of the cost of controls, specifically that such costs have 

been underestimated. Commenter 156 indicated that controlling 2SLB slow speed engines with 
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catalytic controls would be several orders of magnitude more expensive than the costs used by 

EPA in its cost estimate for the proposed rule. The commenter (156) stated that if EPA 

estimated the cost of retrofitting its own engine in its CSU study (EPA-454/R-00-36a) at today’s 

cost, the commenter believes the cost would be in the hundreds of thousands of dollars. The 

commenter (156) reviewed published industry studies from the mid-1990’s in which 2SLB slow 

speed engines were retrofit and stated that the following engine upgrades may be needed before a 

catalyst could be installed: 

• Install high-flow fuel valves. 

• Replace power cylinders with better designed inlet and exhaust port configurations. 

• Add a turbocharger for lean burn operation. 

• Deactivate scavenging pistons. 

• Change out ignition system for leaner air/fuel mixture. 

• Install a new engine control system. 

 The commenter (156) indicated that this retrofit plus catalyst is not expected to achieve 

90-percent control of CO, so the only practical solution is to replace the engine. Because many 

of these engines are fit to integral compressors, the commenter (156) indicated that replacement 

costs are higher (must replace both engine and compressor) – estimated at approximately $3,000 

per HP. At this replacement cost, the commenter (156) estimated that operator that still run 

2SLB slow speed engines will spend millions of dollars in replacement costs per engine with 

some, including the commenter, spending tens or even hundreds of millions of dollars depending 

on the number of such engines currently in service. The commenter (156) indicated that this 

could be cost prohibitive for some older producing fields, which may shut down to avoid 

incurring this expense. 
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Commenter 112 stated that no information has been provided for the figures EPA used 

for operating labor cost and cost of catalyst cleaning, replacement, and disposal. The commenter 

(112) noted that EPA used an annual maintenance cost of $260 for all engine types, which EPA 

based on the cost of maintenance for CDPF for diesel engines as calculated for the 2003 nonroad diesel engines rulemaking. The commenter (112) disagreed with EPA’s assumption that the 

cost of maintenance for both oxidation catalyst and NSCR was comparable to that for CDPF 

nonroad diesel engines for the following reasons: 

• Nonroad engines are at least somewhat mobile. The operator has the choice of bringing 

the engine to the shop for maintenance or taking the mechanic to the engine. With 

stationary engines in the oil and gas industry, there is no choice; the mechanic must go to 

the remote location of the engine which is often remote requiring additional travel time. 

• An engine with NSCR catalyst must be equipped with an AFRC per this regulation. 

Manufacturers recommend that the O2 sensor required for AFRC operating be replaced 

quarterly. Each time the O2 sensor is replaced, it is industry practice to verify the 

emissions with a portable analyzer to assure the sensor is functioning properly (failure of 

new O2 sensors has been known to occur). Many modern lean burn engines are also 

equipped with an AFRC to allow stable emission control. 

• CDPF maintenance mainly consists of removing inorganic material (metals and ash) from 

the control device. The source of the particulate is primarily fuel and lubrication oil. 

Spark ignition engines in the oil and gas industry are primarily fueled with natural gas, 

which has very low or no particulate in the exhaust. 

The commenter (112) believes that these factors increase the cost of maintenance for catalytic 

controls by a conservatively estimated factor of four. 
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 The commenter (112) noted that although he has not identified any EPA estimates on the 

cost of catalyst cleaning, replacement, and disposal; he is concerned about this cost especially on 

specific engine designs. In particular, 2SLB engines have been found to often require more 

frequent cleaning and replacement of the catalyst because they backfire routine (which coats or 

destroys the catalyst so that it must be frequently washed or replaced), and older and small 

engines that have higher lubrication oil consumption and/or lower fuel efficiencies, which may 

result in quick build-up of HC on the catalyst and cause them to require steam cleaning and more 

frequent disposal and replacement, according to commenter 112. 

Commenter 112 stated that the capital costs estimated in EPA’s support document are 

very low compared with industry’s experience. Based on a comparison of costs contained in 

“Four Corners Air Quality Task Force Report of Mitigation Options,” the commenter (112) 

believes that EPA’s low costs result from three major factors: 

• Industry finds that the purchased equipment costs (PEC) will be significantly higher than 

EPA’s memo finds. If catalyst and AFRCs were available for this price stated in the EPA 

memo, it is doubtful that the equipment would have the performance or life needed for 

industrial equipment to meet the regulatory requirements in this rulemaking. 

• The calculation method of multiplying the PEC by a factor ignores the fact that the effort 

required to install equipment is not linear relative to purchase price. Although a small 

unit does cost less to install than a large unit, a 100 HP unit does not cost 1/5th the cost to 

install a 750 HP unit as EPA’s estimates imply. 

• EPA’s calculations appear to assume that the cost of retrofitting an engine with controls 

is the same as installing the controls on a new engine, but existing equipment is always 

more expensive to retrofit because of having to travel to the engine site, remove old 
348

equipment from the engine, and to fabricate fittings to accept new equipment. All of this 

retrofit work is typically being done in the field, at often remote locations verses being 

done in a shop such as is typically done with new engines. 

 Commenter 103 believes that the following factors in EPA’s analysis resulted in a low 

estimate of capital costs: 

• The EPA used a single data point for all 4SRB engines and assumed the relationship was 

linear. The purchased equipment cost did not reflect all of the necessary components to 

perform a complete installation. 

• The EPA did not adequately account for the ancillary equipment that must be installed to 

enable the control device(s) to operate. For example, the vast majority of engines below 

500 HP do not have an electrical system capable of supporting Air/Fuel Ratio Controls 

(AFRC's). As a result, batteries and alternators must be installed on the engines to 

provide power to the AFRC's. 

• The assumption that retrofit costs are the same as a new installation is not realistic. It is 

more expensive to retrofit engines with controls, especially if it is not done in a shop 

environment. Many engines will have to be retrofitted in the field. 

 The commenter (103) provided an analysis of capital costs for equipping 4SRB engines 

with NSCR based on information gathered from four member companies in the natural gas 

compression industry. The commenter’s (103) analysis for these engines yielded a cost per HP 

($/HP) curve that is significantly steeper than EPA’s, which the commenter (103) believes shows 

that EPA’s assumptions significantly underestimate the cost for the smaller HP 4SRB engines. 

At the extreme, the commenter’s (103) figures show the cost for 75 HP units in excess of 
349

$150/HP, in contrast to less than $50/HP in EPA’s analysis. The commenter (103) noted, 

however, that their figures and EPA’s show good correlation for 4SRB engines above 800 HP. 

 The commenter (103) also indicated that the total capital investment to install oxidation 

catalysts on 4SLB engines was also underestimated by the EPA, but to a lesser degree. The 

commenter (103) stated that there are very few 4SLB engines below 400 HP, and the greatest 

disparity is on these smaller engines. 

 Two commenters (103, 227) noted that the majority of 2SLB engines operated by 

member companies (in the natural gas compression industry) are integral compressor packages 

manufactured by Ajax. The commenter (103) asserted that due to the nature of this engine and 

the design of the oxidation catalyst, the cost is dramatically higher than the EPA estimated using 

its standard factor for oxidation catalyst. 

 The commenter (103) estimated that the average cost to retrofit engines with the controls 

necessary to comply with the rule ranges between $50/HP and $70/HP. The range of this 

number is large because the exact makeup (models and HP) of each operator's fleet is 

proprietary. The commenter (103) further estimated that approximately 85 to 90 percent of the 

total fleet represented by the companies belonging to his organization (5.3 million HP) will 

require retrofit. Using the midpoint of the range ($60/HP) and an assumption of 87 percent of 

the HP being affected, the commenter (103) estimated that it will cost $346 million dollars for 

the initial capital investment on just the engines owned by these member companies. 

One commenter (225) made the general statement that EPA’s estimates are low for the 

capital and operating costs associated with the use of catalytic control, and are based on old 

pricing data from one vendor and a limited number of data points that were fit with a linear 

regression. The commenter (225) also stated that because above-the-floor standards (which 
350

require catalytic controls) are based on the cost per ton of HAP removed, EPA must reanalyze 

the proposed rule with better cost data to determine when catalysts are economically practical. 

One commenter (104) noted that proposed 40 CFR 63.6625(g) requires the use of AFRC 

with the operation of three-way catalysts/NSCR on 4SRB engines at area sources. The 

commenter (104) stated that AFRC are extremely costly and are not cost effective on smaller 

engines, while catalysts are not practical on engines that have variable loads such as pump jack 

engines. The commenter (104) indicated that in Oklahoma (where the commenter’s organization 

operates), catalysts and AFRC costs are estimated to be $8,000 to $16,000 ($2,000 to $4,000 for 

the catalyst and $6,000 to $12,000 for the AFRC), depending on the engine. The commenter 

(104) asserted that the proposed requirement will be costly for and burdensome on small 

businesses and those companies that operate marginal wells on the lower edge of profitability, 

and requested that the proposed requirement be dropped for all pump jack engines. 

 Commenter (220) said the cost data considered by EPA in developing the proposed rule 

is outdated and underestimates the costs to install, operate, and maintain the controls that will be 

necessary in order for owners and operators of RICE to comply with the proposed rule. The 

capital and annualized control cost formulas for oxidation catalysts only consider a small 

universe of engines. The commenter (220) collected vendor data on installation costs and 

concluded that EPA’s assumptions that these costs are the same for existing and new engines is 

incorrect. The commenter (220) concluded that EPA’s costs are too low (e.g., at least 40 

percent). Even assuming a 40 percent correction factor, the average capital cost is likely still low 

for retrofitting older units. In addition, the commenter (220) said that the annual operating costs 

for the oxidation catalyst control of these units would average about $31,000 per year at each 

generating facility. The commenter said EPA should gather current data to update the cost 
351

equations and provide a specific basis for assuming the cost to install controls on existing and 

new sources would be the same. 

 Commenter (220) said that because of the drastic underestimation of the cost of control, 

EPA has also mischaracterized the cost per ton of emission reduction. As the commenter’s (220) 

engines do not operate for lengthy periods of time, the cost per ton of reduction is high. Based on 

total emissions from the commenter’s (220) facilities of 45 tons of CO, the commenter (220) 

calculated an estimated cost of $111,000 per ton using EPA’s cost assumptions, and said the real 

number would be much higher. This cost is too high to justify the rule’s stringent requirements. 

Operation of engines in urban areas in accordance with acceptable management practices is 

sufficient to protect public health and the environment. 

 Commenter (220) said that because of the high costs to comply with the proposed rule, 

many municipalities may have to shut down units, affecting the viability of backup power 

supplies. Members’ units provide a vital source of power in emergency situations. Because 

these same units may be used in peaking circumstances, they do not qualify for emergency unit 

status and are subject to stringent retrofit controls. In addition, members use engines in sewer 

systems and along sewer lines to continue sewer operations during power outages. Such units 

would likely be subject to the prescriptive maintenance requirements in the proposed rule. Other 

true emergency type units may be large enough to implicate emission reduction requirements for 

larger emergency units. 

One commenter (111) stated that EPA’s estimated control costs appear low and provided 

estimates of control costs for oil and natural gas production facilities in the State of Michigan. 

The commenter (111) stated that formaldehyde testing costs for 4SRB engines were omitted 

from EPA’s cost analysis, but this cost is approximately $10,000 per test based on the test 
352

method required under the proposed rule. The commenter (111) also provided estimates of 

control costs for 4SRB engines above and below 500 HP and for 4SLB engines between 250 and 

500 HP and above 500 HP. 

Response: EPA estimated the cost impacts associated with the proposed rule based on 

information EPA had available at the time of proposal. That information included cost data for 

the purchase, installation, and operation of control technologies that would be necessary to 

employ in order to meet some of the proposed emission standards. Based on information 

available at the time of proposal, EPA derived cost equations for NSCR, the applicable 

technology for HAP reduction from stationary rich burn engines and for oxidation catalyst, the 

applicable technology for reducing HAP emissions from 2SLB and 4SLB SI engines. The 

capital cost and annual cost of NSCR were estimated as a function of engine size as were 

determined to be $19.7 x HP + $1,799 and $2.65 x HP + $657, respectively. At proposal, the 

capital cost and annual cost of oxidation catalyst were determined to be $11.3 x HP - $170 and 

$1.52 x HP + $393, respectively. EPA agrees with comments stating that these proposed costs of 

controls were low. 

As a result, EPA revisited the cost data used for the proposal. In addition, EPA requested 

additional cost data from industry to supplement the existing costs EPA had. EPA added specific 

costs received from industry for oxidation catalyst for 2SLB engines, oxidation catalyst for 4SLB 

engines, and NSCR for 4SRB engines. EPA used the available cost information to estimate the 

capital and annual control costs for different size model engines. EPA then took the capital and 

annual control costs estimated for each model engine and developed control cost equations as a 

function of engine size (HP). These cost equations were developed using a combination of 
353

information, including the original vendor equipment estimates EPA used at proposal updated to 

current costs, new cost information received following the publication of the proposed rule, 

including detailed cost information from API24,25 who presented each cost element specifically, 

information from Exterran, Anadarko Petroleum Corporation, and information from control 

technology trade association and vendors. For the majority of model engines, EPA used the 

equipment cost provided by the source, applied EPA’s control cost methodology, and determined 

the total capital cost for each model engine. In some cases, the total capital cost was provided by 

each source, in which case, EPA used that cost directly. In general, in order to determine the 

total annual cost for each model engine, and to be consistent, EPA used the information provided 

by API for the individual cost elements that contribute to the total annual cost, and applied 

EPA’s control cost methodology to determine the total direct and indirect annual costs. 

More information on how EPA estimated the cost of controls for the final rule is available in the 

memorandum titled “Control Costs for Existing Stationary SI RICE”, which can be found in the 

docket. 

For the final rule, the capital and annual cost of oxidation catalyst for 2SLB engines, as a 

function of engine size, was determined as $47.1 x HP + $41,603 and $11.4 x HP + $13,928, 

respectively. Compared to the costs developed for the proposal, EPA has increased its estimate 

of the cost to operate an oxidation catalyst, for example on a 500 HP 2SLB engine by a factor of 

                                                           

24 Reciprocating Internal Combustion Engine National Emission Standard for Hazardous Air 

Pollutants (RICE NESHAP) Proposed Revisions – Emission Control Cost Analysis Background 

for “Above the Floor” Emission Controls for Natural Gas-Fired RICE. Technical Report 

Prepared for: INGAA and API. Prepared by: Innovative Environmental Solutions. October 

2009. 

25 Letter from Tom McGrath, IES to Brad Nelson, EC/R, Melanie King, EPA, Lisa Beal, 

INGAA, et.al. Request for Additional Cost Detail for Gas-Fired Engines Emission Controls. 

April 19, 2010. 
354

17. Based comments received on the proposal and additional cost information obtained between 

proposal and promulgation, EPA learned that it would be appropriate to distinguish between the 

control costs for 2SLB and 4SLB engines, which, at the time of the proposal, EPA had used the 

same costs for both engines. Consequently, for the final rule, EPA developed separate control 

cost equations for 2SLB and 4SLB engines. EPA agrees that 2SLB engines may need more 

expensive catalysts and the final capital and annual controls costs reflect that. Stationary 2SLB 

SI engines typically have lower exhaust temperatures than other engines. For example, during 

the EPA-sponsored testing at CSU, the 2SLB exhaust temperature ranged from 451°F to 569°F, 

or an average of 530°F while the 4SLB exhaust temperature ranged 640°F to 734°F, or an 

average 691°F. Therefore, stationary 2SLB SI engines may have to use premium catalysts, 

which have a higher cost than regular catalysts. EPA obtained 2SLB catalyst equipment costs 

directly from a supplier of 2SLB catalyst, which were incorporated into data used to develop 

control costs for 2SLB. These costs were close to and consistent with other 2SLB catalyst cost 

data EPA obtained from, for example, API and INGAA and Exterran. 

For the final rule, the capital and annual cost of oxidation catalyst for 4SLB engines, as a 

function of engine size, was determined as $12.8 x HP + $3,069 and $1.81 x HP + $3,442, 

respectively. Compared to the control costs developed at proposal for oxidation catalyst, EPA 

has increased its annual control cost estimate by a factor of close to 4, for example for a 500 HP 

4SLB engine. For add-on controls on rich burn engines, EPA also increased its estimate of 

annual control costs by a factor of 4, between proposal and promulgation, on for example a 500 

HP 4SRB engine. For the final rule, the capital and annual cost of oxidation catalyst for 4SRB 

engines, as a function of engine size, was determined as $24.9 x HP + $13,118 and $4.77 x HP + 

$5,679, respectively. EPA believes that an AFRC is needed in order for proper functioning of 
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the NSCR and therefore agrees with the commenters that the cost of the AFRC should be 

included in the cost of NSCR. The above cited control cost equations include the cost of an 

AFRC for rich burn engines. The capital and annual control costs developed for the final rule for 

oxidation catalyst control for 2SLB and 4SLB, and NCSR for 4SRB engines are based on a 

sufficient number of data points that appropriately represent different model engines and sizes. 

For instance, for rich burn engines, EPA used 18 data points for engines ranging from less than 

50 HP to up to 3,000 HP. EPA believes the final control costs for all engines contain all 

necessary components and are reflective of current pricing for catalyst-based controls on 

stationary existing SI engines. 

In response to comments regarding the control efficiency capability of 2SLB engines, 

EPA agrees that it may not be possible for all 2SLB SI engines to achieve 90 percent reduction in 

CO emissions. EPA’s testing a CSU on a 440 HP Cooper Bessemer engine achieved CO control 

efficiencies between 58 and 69 percent. However, EPA believes catalyst could perform better 

than that. In fact, Cameron’s Compression Systems26, a supplier of oxidation catalysts for 2SLB 

engines, guaranteed 83 percent CO removal efficiency based on test results collect up until early 

2009. The supplier indicated to EPA that it has recently guaranteed a 90 percent CO removal 

efficiency. With that said, EPA is finalizing requirements for existing 2SLB SI engines that are 

not expected to require oxidation catalyst control. For existing 2SLB SI engines at area sources, 

EPA is requiring management practices. For existing 2SLB SI engines at major sources that are 

less than 100 HP, EPA is also requiring maintenance practices. For existing 2SLB SI engines at 

major sources that are greater than or equal to 100 HP and less than or equal to 500 HP, EPA is 

                                                           

26 Email from Bruce Chrisman, Cameron's Compression Engines to Tanya Parise, EC/R. 2SLB 

Engine Information. October 22, 2009. EPA-HQ-OAR-2008-0708-0500. 
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requiring a concentration standard of 225 ppmvd of CO at 15 percent O2. EPA considered 

oxidation catalyst for these engines, but determined it was not justified and reasonable to do so 

based on costs. For more information on EPA’s decision, please refer to the memorandum titled 

“MACT Floor and MACT Determination for Existing Stationary SI RICE ≤500 HP Located at 

Major Sources.” 

12.3.2 Comment: Two commenters (103, 112) stated that the equipment life used by EPA to 

compute the capital recovery factor (20 years) is too high. Commenter (103) believes this 

equipment life would be reasonable for the engines alone, but is very high for the add-on 

controls. In the commenter’s (112) experience, control equipment life expectancy is 

approximately 10 years for engines greater than 500 HP and approximately 5 years for smaller 

engines. The commenter (103) believes that the recovery period should be a maximum of 10 

years due to the following factors: 

• The economic life of the control equipment is 10 years, during which the element will 

still need to be replaced every 2-3 years. 

• The electronic technology often becomes unsupportable in a time span significantly less 

than 10 years. 

• It is unlikely that the regulatory environment will enable these controls to be used for 

20 years. Ever increasing regulations will likely obsolete the technology before the 

20 year recovery period has elapsed. 
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Response: EPA agrees with the commenter that the equipment life used to compute the capital 

recovery factor was too high. For the cost analysis in the final rule, EPA used an equipment life 

of 10 years, which is more accurate for these emission controls. 

12.3.3 Comment: Two commenters (78, 170) said that the cost effectiveness of adding control 

devices to older engines should be addressed, because it may not be cost effective to install 

controls on engines that are nearing the end of their useful life. Control devices such as 

oxidation catalysts must be designed and sized to match the engines on which they are installed, 

and one cannot automatically assume that a catalyst system designed for one engine can be used 

on another. In addition, attempting to retain the catalyst system for use on a replacement engine 

may limit the source’s option for replacement engines. Consequently, if the useful life of the 

control device is considered in cost effectiveness calculations, if the control device will not be 

used for its predicted useful life, then the calculations will underestimate the cost effectiveness of 

the device. 

Response: EPA does not agree with the commenter that it should determine the cost 

effectiveness of adding control devices to engines that are nearing the end of their useful life. It 

is not feasible to determine the cost effectiveness of every type of operating scenario. Affected 

sources will have 3 years to comply with this regulation and therefore can decide whether to 

replace older equipment rather than retrofitting. 

12.3.4 Comment: One commenter (103) in the natural gas compression industry believes that 

EPA has greatly underestimated the costs to comply with the proposed maintenance 
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requirements. The commenter (103) asked member companies in his organization to estimate 

these costs, and the following items were factored into the additional costs incurred as a result of 

the additional preventative maintenance trips required under the proposed rule: 

• Oil purchased for additional oil changes. 

• Oil filters purchased for additional oil changes. 

• Spark plugs purchased for additional spark plug changes. 

• Labor – the fully burdened labor rate was used for additional time. 

• Travel time 

• Waste oil and waste oil filters requiring hazardous disposal generated by additional 

changes. 

According to the commenter (103), the data from the member companies indicated the following 

costs: 

• Engines less than 50 HP: Average additional annual cost of $369.86 per HP, or 

approximately $18,123 annually for a 49 HP engine. 

• 2SLB engines 50 – 249 HP: Average additional annual cost of $45 per HP, or 

approximately $11,110 annually for a 249 HP engine. 

• 4SLB engines 50 – 249 HP: Average additional annual cost of $33 per HP, or 

approximately $8,127 annually for a 249 HP engine. 

The commenter (103) also stated that the realized emissions reductions greater than 

manufacturer’s recommended schedules at the given frequencies are null. 

Response: EPA has provided an option in the final rule to utilize an oil analysis program to 

extend the oil change frequency. EPA has also revised the intervals for work practices and 
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management practices in the final rule. EPA does not agree with the commenter that the 

management practices in the final rule are overly burdensome and would result in increased cost 

to the engine owner/operator. The management practices EPA is requiring under the final rule 

are based on industry practice and normal maintenance procedures currently followed by 

stationary SI engine operators. It is in the best interest of owners that their engines are wellmaintained and kept in proper condition. EPA believes engine operators would continue to 

follow maintenance procedures to keep their engines in proper working condition and would 

allocate funds for that purpose, in the absence of the rule. Therefore, EPA does not believe there 

will be any increased cost. In the event that engine owners and operators might expend 

additional effort as a result of the final rule in order to maintain their engines, such effort is 

expected to have a minimal effect on the cost, plus maintaining the engine properly might lead to 

a longer engine life and might even result in cost savings, which could offset the potential small 

increased cost owners and operators might experience. 

12.4 Implementation and Enforcement 

12.4.1 Comment: One commenter (112) believes that operators will have difficulty certifying 

compliance at major sources for engines that have emission limits, but have no testing 

requirements (i.e., emergency engines, 4SRB engines less than 100 HP, etc.). The commenter 

(112) requested that EPA insert the words, “Compliance is assumed if the operator follows 

maintenance practices as specified in their maintenance plan.” 
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Response: All of the engines that have emission limits in the final rule have to perform 

emissions testing to show compliance with the rule. 

12.4.2 Comment: Four commenters (104, 150, 191, 207) believe that the proposed compliance 

date of 3 years is too short. One commenter (132) believes that if the rule is promulgated as 

proposed, the resulting demand for catalytic controls would have serious implications for market 

demand and feasibility of installing controls within the 3-year timeline. The commenter (132) 

stated that these factors should be considered in the impacts assessment and rule schedule for 

compliance. One of the commenters (104) indicated that in Oklahoma alone there are an 

estimated 67,000 existing engines at oil and gas production sites. The commenter (104) believes 

that the sheer number of engines and the limited number of qualified companies available to 

conduct FTIR tests for formaldehyde on 4SRB engines (which are common at oil and gas 

facilities) limits a company’s ability to comply in the proposed time period. The commenter 

(104) suggested a compliance date of at least 6 years for area sources or, at a minimum, a longer 

compliance time for small businesses operating such facilities. 

 Because of the tens of thousands of engines that the commenter believes would have to 

be tested and modified and the limited number of qualified companies and personnel to perform 

these functions, commenter 150 urged EPA to extend all proposed compliance deadlines by at 

least 12 months. In the alternative, the commenter (150) suggested a phased-in approach based 

on engine size. The commenter (150) stated that 4SLB engines less than 250 HP should be the 

last engines required to comply because they are low-impact in terms of emissions and because 

they would be likely to be replaced since they would be unable to meet the standards without 

costly reconfigurations to install the catalytic controls necessary to comply. 
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One commenter (207) said that the compliance time would not be sufficient for 

installation of controls on back-up/emergency engines at nuclear power plants. According to the 

commenter (207) this is because components installed in nuclear applications are subject to a 

variety of quality assurance requirements, specifications, and code requirements, none of the 

current catalytic converter manufacturers are qualified to nuclear safety related standards, and 

the time frame for current vendors to meet the stringent quality assurance standards and produce 

an acceptable catalytic converter is estimated to be beyond the 3-year compliance period. 

Response The compliance date provided in §63.6595(a)(1) of the proposed rule for stationary 

existing engines less than or equal to 500 HP located at major sources and stationary existing 

engines located at area sources is consistent with the typical date of compliance given for 

existing sources, i.e., 3 years from the effective date of the rule, and is the maximum amount of 

time that EPA can provide under Clean Air Act section 112(i)(3). EPA believes this is sufficient 

time for sources to comply with the requirements and does not agree that a 6 year compliance 

period should be provided. EPA has not included additional compliance time in the final rule. 

 As discussed in the response to comment 12.1.8, stationary emergency engines at nuclear 

facilities are not subject to numerical emission limitations. Therefore, there is no justification for 

a longer compliance time for these engines. 

 

12.4.3 Comment: A few commenters (93, 104, 116) stated that the proposed rule will be onerous 

and costly on owners/operators of engines at oil and gas production facilities, and it will be also 

burdensome on EPA and the state agencies. The commenter (104) indicated that there are 

approximately 122,000 crude oil and natural gas wells in the state where her organization is 
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located (Oklahoma) and there may be as many as 67,000 oil and gas facilities that have at least 

one engine that would be subject to the proposed rule. The commenter (104) does not think EPA 

or the state agencies have the staff to implement or manage the proposed rule as written. The 

commenter (104) asked how EPA plans to address this issue. 

The commenter (104) stated that there is much confusion in implementing the current 

requirements for “new” engines that are less than 500 HP at area sources. The commenter (104) 

noted that currently the State of Oklahoma (where her organization is located) does not have 

primacy for the NSPS/NESHAP program as it relates to 40 CFR part 60, subpart JJJJ and 40 

CFR part 63, subpart ZZZZ; however, the state requires operators to obtain permits for these 

types of engines. The commenter (104) indicated that as a result, information required by the 

“new” engine rule is being submitted to the state as well as to EPA, which has placed additional 

burdens on small businesses and operators of marginal wells that are duplicative and unnecessary 

and provide no environmental benefit. The commenter (104) assumes that this same practice 

will be applied to any final rule for “existing” engines. The commenter (104) asserted that it 

would be very helpful to the regulated community if one agency implemented the program so 

that submittal of duplicate data was avoided. 

One state commenter (93) expressed that their main concerns with the proposed rule are 

that the complexity and organization of the rule may hinder compliance efforts and that 

implementing agencies may be overwhelmed by the increased workload. 

One local and state agency association commenter (116) recommended that EPA provide 

sufficient additional funds for state and local clean air agencies to carry out implementation of 

the proposed rule. They stated that, currently, federal grants fall short of what is needed to 

support state and local agencies in carrying out their existing responsibilities. Additional area 
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source programs, which are not eligible for Title V fees, will require significant new resources 

for state and local air agencies, above and beyond what is currently provided, according to 

commenter 116. This commenter (116) expressed that without increased federal grants, some 

state and local air agencies may not be able to adopt and enforce additional area source rules. 

Even for permitting agencies that do not adopt the rules, it is possible that implementation of the 

standards for area sources will increase the workload and resource needs of state and local 

agencies, the commenter (116) said. For example, synthetic minor permits (or Federally 

Enforceable State Operating Permits) may need to incorporate all applicable requirements, which 

would include the area source standards, the commenter (116) added. These requirements must 

also be enforced, according to the commenter (116). The commenter (116) explained that Title 

V permit fee funds are not available for those efforts and many state and local air agencies do not 

have sufficient resources for these responsibilities. 

Response: Providing additional funds for State and local implementation activities related to this 

rule, as requested by the commenter, is outside the scope of this rulemaking. EPA is planning on 

making implementation and guidance material available to the public following the promulgation 

of this rule. EPA believes such material will be helpful in implementing this rule. EPA has 

taken steps in the final rule that reduce the burden on both engine owners/operators and 

state/local agencies. For example, more than 90 percent of the existing engines at area sources 

are only subject to management practice standards and are not required to conduct performance 

testing or submit notifications and reports to state/local agencies. 
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12.4.4 Comment: One commenter (93) reiterated the February 25, 2008 request that EPA allow 

states to incorporate any new rules or revisions to rules at the next Title V revision or renewal as 

opposed to opening such permits for cause. The commenter (93) provided that the proposed rule 

will regulate thousands more engines than anticipated as it now includes: stationary engines of 

500 HP or less at major sources, stationary engines at area sources, and stationary CI engines of 

more than 500 HP at major sources. The commenter (93) stated that it heard from one existing 

Title V source that has over 300 engines that will be subject to the proposed rule. The 

commenter (93) requested that EPA consider the reasonableness and resources agencies would 

need to implement the 18 page flow chart for hundreds and possibly thousands of engines to 

determine permitting and compliance requirements. 

Response: EPA included provisions in the January 2008 final rule at 40 CFR 63.6585(d) that 

indicate that area sources subject to 40 CFR part 63, subpart ZZZZ, would not be subject to 

permits under 40 CFR parts 70 or 71 solely because of this rule. This provision will lessen the 

burden on numerous existing stationary engines located at area sources. EPA believes this 

should significantly reduce the commenter’s concern on this issue. In terms of the compliance 

burden and implementation process, EPA has made an effort to rely on management practices 

wherever appropriate, which will minimize the impact on particularly smaller sources and those 

individually owned and operated. Further, EPA has reserved regular performance testing for 

larger engines, though smaller engines subject to numerical emission limits will need to test at 

least once. Finally, EPA will be providing implementation material to assist affected sources in 

understanding the requirements of the final rule and implementing and demonstrating 

compliance with the specific provisions that apply to them. 
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12.5 Energy Impacts 

12.5.1 Comment: One commenter (176) recommended that EPA re-evaluate its energy impact 

determination and consider the impact of the proposed rule’s energy requirements on a broader 

scale rather than limiting its analysis to only sectors of the regulated community. The 

commenter (176) stated that EPA’s evaluation of the energy impact of the proposed rule only 

considered the electric power sector and failed to account for the impact on the non-industry 

sector. 

One commenter (176) provided that, under section 112(d) of the CAA, EPA can consider 

cost and energy impacts. EPA concluded in the RIA for the proposed rule that it “is not likely to 

have a significant impact on the supply, distribution, or use of energy.” RIA at 5-9. The 

commenter (176) disagreed with EPA’s conclusion and stated that engines are placed because of 

concerns as to the reliability of power for the source, particularly in rural areas. The commenter 

(176) stated that the proposed standards could have a very detrimental impact on energy 

reliability and many units may have to be shut down due to the cost of compliance. 

Response: EPA focused its analysis of energy impacts on the electric power sector because this 

sector experiences the greatest impact on energy costs of any of the affected sectors. Slightly 

more than half of the total annual costs of the final standard are incurred by the electric power 

sector (RIA at 4-39 and 5-2). EPA found that this industry would experience low annualized 

costs as a percent of industry revenue (less than 0.1 percent). This was also true for most of the 

other industries affected by the proposed standards. While EPA did not conduct an analysis for 
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sectors not regulated by the final standards, EPA did provide some information on how demand 

for the agriculture and construction industries may respond to an increase in price based on 

impacts from the proposal (RIA at 5-7). This information, taken from the Department of 

Energy’s Energy Information Administration, shows that the demand for agricultural products 

may fall 0.2 percent for a 1 percent increase in its product prices; for construction, the demand 

will fall 1 percent for a 1 percent increase in product prices. In response to the comment that 

engines may have to shut down due to the cost of compliance, EPA does not have the ability to 

estimate engine closures or shutdowns as part of the economic impact analysis in the RIA. EPA 

does not have sufficient firm-level or unit-level data to estimate such impacts, and EPA typically 

does not provide such estimates of impacts as part of our economic impact analyses. 

Nonetheless, EPA does not believe that any units would be shutting down as a result of this rule. 

The commenter did not provide any information to show that units would have to shut down and 

no other information is available to indicate that units would. 

12.6 Small Businesses 

12.6.1 Comment: A few commenters (226, 242) expressed concern over how the proposed rule 

might impact small businesses. One commenter (242) said that EPA has not properly 

communicated to small businesses (e.g., Small Business Administration), government 

installations (e.g., fire and police stations), and homeowners on the proposed rulemaking. The 

commenter (242) stated that EPA needs to quantify the potential impacts associated with 

regulating these sources since these sources are not exempt. Also, the commenter (242) said, 

EPA should conduct an outreach program to communicate the requirements of the rule to the 
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public. One commenter (226) stated that small businesses mostly use small engines and 

regulation of these engines yields the smallest emission benefits. 

Another commenter (226) had similar concerns stating that under the Regulatory 

Flexibility Act, EPA is required to analyze reasonable alternatives that minimize small business 

burdens while still achieving the statutory goals. The commenter (226) noted that in the 2002 

proposal that EPA acknowledged that small stationary RICE have generally not been regarded as 

significant sources of air pollution emissions, and solicited comment on ways to structure the 

proposed rule to focus on the facilities with significant risks and avoid the imposition of high 

costs on facilities that pose little risk to public health and the environment. However, the 

commenter (226) noted that the current proposal does not request any risk-based alternatives that 

would exclude small engines. 

One commenter (226) believes the proposed rule affects hundreds and thousands of small 

businesses that employ engines that are used in oil and gas production, natural gas pipeline 

companies, and agriculture. The commenter (199) stated that any slight increase in operating 

costs could lead to the shutdown of the facility, and given the heightened concern with energy 

cost and availability, EPA should carefully consider any new requirements. 

Response: In response to the concerns expressed by commenters about the potential impact of 

this rule on small businesses and homeowners, EPA conducted a review of the types of engines 

that were included in the area source category listing for stationary RICE. As a result of this 

analysis, EPA determined that emissions from existing stationary emergency engines located at 

residential, commercial, and institutional facilities were not included in the 1990 baseline 

emissions inventory that was used as the basis for the listing of source categories needed to 
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ensure that 90 percent of area source emissions are regulated. Therefore, EPA has determined 

that these engines are not part of this regulated source category, which will help address the 

commenters’ concerns about the impact of the rule on small businesses and homeowners. Both 

the proposed and final rule required small stationary engines at area sources to meet management 

practice requirements rather than emission limitations, which also lessens the burden of the rule 

on those engines. The final rule extends management practices to all emergency engines. In 

addition, the final rule requires only work practices for stationary engines less than 100 HP at 

major sources and management practices for stationary engines smaller than 500 HP at area 

sources, also decreasing the burden of the rule on owner/operators of small engines. Section 

112(d) of the CAA is generally technology-based, not risk-based. For engines at major sources, 

it requires regulation based on emissions data from existing engines. HAP emissions from these 

sources include carcinogens and HAP without health thresholds. The commenter does not 

explain how the very limited provisions of section 112(d)(4) or 112(c)(9) would be applicable to 

this source category. 

13.0 Miscellaneous 

13.1 Definitions 

13.1.1 Comment: One commenter (242) thinks that EPA should amend the definition of affected 

source to include area source engines and engines less than or equal to 500 HP at major sources 

to clarify rule applicability. 
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Response: EPA does not agree that it should revise the definition of affected source in subpart 

ZZZZ because the definition already includes engines located at area sources and engines less 

than or equal to 500 HP located at major sources. 

13.1.2 Comment: Three commenters (126, 158, 168) urged EPA to clarify and improve its 

definition of “stationary” RICE, contending that as written, it is difficult to clearly understand 

what constitutes a stationary RICE subject to regulation under the proposed rule. A problem 

with the current definition, according to commenter 168 arises when a mobile RICE that has 

been rented and has been moved to a power plant is deemed to become a stationary RICE under 

the nonroad definition in 40 CFR 1068.30. Further, commenter 168 claims that many RICE that 

would be regulated by the proposed subpart ZZZZ are temporary, rental diesel engines that 

provide outage power and compressed air during refueling and maintenance outages at nuclear 

power plants or during construction and maintenance activities at coal-fired power plants. 

Commenters 126 and 168 requested that, in the final rule, EPA revise the definition of stationary 

RICE or nonroad engine or otherwise revise the proposal to insure that rental, non-self propelled, 

portable nonroad diesel engines that are located at a utility power plant or area facility for more 

than 12 months during construction or extended maintenance are exempt from 40 CFR part 63, 

subpart ZZZZ. If portable RICE were deemed to be “stationary,” commenters 126 and 168 

requested that the final rule clarify that the owner of the diesel engine, and not the entity that 

rents and uses it, is required to comply with the rule, including required maintenance and 

performance testing. 

One commenter (158) requested that EPA clarify the types of engines that are considered 

“non-road engines” versus “stationary RICE.” For example, the commenter’s (158) firm 
370

operates power washers which can be either propelled (moved by hand) while being used or 

transported to a location at a facility, kept stationary while being used, and then transported to 

another location within the facility. The commenter (158) requested clarification as to whether 

such equipment would fit under 40 CFR 1068.30 section (1)(ii) or (1)(iii), which contain parts of 

the definition of “non-road engine.” As another example, the commenter’s (158) firm operates 

portable water pumps, generators, and welders which remain at a facility year-round and are 

moved to different locations on-site as needed. The commenter (158) requested clarification as 

to whether the engines powering such equipment would be excluded from the definition of “nonroad engine” because they remain at a location for more than 12 consecutive months, which is an 

exclusion specified in 40 CFR 1068.30. 

Response: EPA does not agree that the definition of stationary RICE should be revised. EPA 

intends for portable engines that remain in one location at a facility for more than 12 months to 

be considered stationary engines. For the example provided by commenter 168 of temporary 

rental diesel engines that provide power and compressed air at a facility, if the engines remain at 

the same location within the facility for more than 12 months, then they would be considered 

stationary engines. If the engines are located at the same facility but are moved around within 

the facility, then they would not be considered stationary. 

 Regarding the clarifications requested by commenter 158, those engines would be 

considered stationary engines only if they remain in the same location within the facility for 

more than 12 months. Engines that are located at a facility but moved around the facility are not 

stationary engines unless they remain at the same location within the facility for more than 12 

months. 
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 For engines that are rented, the final rule applies to both the owner and the operator, and 

the renter is the operator and is subject to the rule. Because both the owner and operator are 

liable under the rule, the rental agreement should address who will conduct emissions testing or 

employ management practices for the specific engine, and who will create records, who will hold 

them for the statutory period and who will report. 

13.1.3 Comment: One commenter (121) said EPA should include a definition for “commence 

construction” to clarify when new sources are covered by the RICE MACT because of the 

overlap between 40 CFR part 60, subparts JJJJ and IIII and the RICE MACT. Consistent with 

the NSPS, EPA should define “commence construction” as follows: 

“For purposes of this subpart, the date that construction commences is the date the engine is 

ordered by the owner or operator.” 

Engines at a closed facility may be relocated and installed at another facility. Clarifying the 

original order date will assist sources in understanding the applicability of the RICE MACT for 

engines in these situations, according to commenter 121. 

Response: EPA has already provided a definition of “commence construction” in the General 

Provisions for part 63. The definition can be found in 40 CFR 63.2. As the definitions and 

provisions for determining and regulating new engines have already been established, and this 

rule is concerned solely with existing stationary engines, EPA is not revisiting this issue in this 

rule. 
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13.1.4 Comment: One commenter (103) believes that the phrase “Owners and Operators” needs 

to be better defined as it relates to the requirements. The commenter (103) believes that while it 

is convenient for the EPA to avoid distinguishing between the two, the reality is that there are 

tens of thousands of engines where the roles of owner and operator are often represented by two 

independent companies. In the case of a rental compressor, the engine is owned by the lessor 

and rented to the lessee. According to the commenter (103), the lessor typically (but not always) 

provides: 

• Maintenance including preventative maintenance, repairs, and overhauls. This would 

include maintenance plans and the documentation of the work performed. 

• Adjustment of the engine parameters that control combustion such as ignition timing, 

air/fuel ratios, etc. 

The commenter (103) added that the lessee is typically (but not always) responsible for: 

• The day to day operation of the engine including starting, stopping, loading and 

unloading. 

• Emissions testing 

• Environmental permitting with the RICE along with the rest of surface equipment 

including burners, tanks, fugitive emissions, etc. 

 The commenter (103) stated that EPA was asked to clarify the roles and responsibilities 

of Owner and Operator as it relates to the NSPS (40 CFR part 60, subpart JJJJ) but has yet to do 

so, and added that the same mistake should not be made on this proposed rule. The commenter 

believes that the effects of this ambiguity include doubling or tripling the manpower required for 

tracking compliance on engines and for recordkeeping because all data not only must be 

gathered, compiled, sorted, and stored, but in order to transfer to counter parties (from Owner to 
373

Operator, for example) the data must then be carved out according to rental relationships and 

then conveyed to the other party. The commenter (103) also believes that there is an increased 

chance of noncompliance from each entity believing the other entity has complied with certain 

provisions. 

 The commenter (103) added that where there are rental engines in the natural gas 

compression industry, the “site” owner and operator will hold the state air permit for the site but 

is dependent on each of the rental companies for compliance on items such as maintenance plans, 

while the rental companies are dependent upon the site owner and operator for items such as 

permitting and testing. The commenter (103) asked the following questions: 

• What would happen when an annual emissions test is missed or failed and who is 

responsible? 

• Who is responsible? 

• If one company chooses not to comply, is the other company required to perform those 

functions, if it is even practical? 

The commenter (103) asserted that EPA should acknowledge that there are over 15,000 engines 

that have these issues every day due to its actions and inactions. 

Response: This rule applies to both the owner and the operator, regardless as to whether the 

operator is an agent of the owner or merely a lessee. Because both the owner and operator are 

liable under the rule, the rental agreement should address who will conduct emissions testing or 

employ management practices for the specific engine, and who will create records, who will hold 

them for the statutory period and who will report. The requirements under the rule are clear, 

divisible and openly subject to divided responsibility under a rental agreement. EPA is willing to 
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work with rental agencies to develop a standard rental agreement clause to ease recordkeeping 

and reporting. 

13.1.5 Comment: One commenter (83) recommended that EPA use the “major” definition for 

landfills contained in the NSPS/EG rule, which is also used in the federal Title V Program, as 

part of the final NESHAP when referencing landfill gas RICE. Under the landfill NSPS/EG 

definition of “major,” the design capacity of the landfill (2.5 million megagrams and 2.5 cubic 

meters) determines what are “major” and “minor” sources. The commenter (83) explained that, 

if EPA uses the typical NESHAP definition of “major,” most stationary RICE located at landfills 

will be “area” sources and subject to the stringent standards in the proposed rule and will not be 

able to take advantage of the 10 percent or greater landfill gas exclusion that is being proposed 

for “major” source RICE. 

Response: EPA has to follow the definitions of a major source and an area source in CAA 

sections 112(a)(1) and (2). EPA is not at liberty to change those definitions, and EPA must 

regulate as major sources those stationary engines that are classified as being located at major 

sources under section 112(a). If a stationary engine is located at a source that has the potential to 

emit considering controls, in the aggregate, 10 tons per year or more of any HAP or 25 tons per 

year or more of any combination of HAP, it must be regulated as a major source. 

13.1.6 Comment: Two commenters (90, 117) requested that the definition of emergency 

stationary RICE be modified to remove the clause that ICE that supply power “as part of a 

financial arrangement with another entity are not considered to be emergency engines.” One 
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commenter (117) noted that when applied to major sources, as in existing rules, the language 

may appropriately differentiate between true emergency engines and engines used in a 

commercial capacity. However, for smaller operations, it is common for multiple entities to 

share the cost and responsibility for providing emergency power. An example the commenter 

(117) cited is landlord-tenant relationships where as a part of the lease the landlord provides 

emergency backup power to the tenant. This occurs at multi-tenant facilities, such as shopping 

centers, where one tenant’s emergency power may be shared by others. The commenter (117) 

believed that EPA did not intend for these small operations to be excluded from consideration as 

emergency units. Another commenter (90) noted that most of their units would be excluded 

from consideration as emergency units under the proposed definition because they provide 

emergency backup power for clients such as grocery stores, data management centers, and small 

industrial facilities as part of a financial arrangement. Additionally, they may participate in 

voluntary utility curtailment programs where they have entered in financial arrangements to self 

generate power during brief times of utility constraints. 

Response: In the final rule published in March 2010, EPA revised the provisions applicable to 

emergency engines to clarify that engines that are operated as part of a financial arrangement but 

are used solely for emergency use (e.g. not for peak shaving) are still considered emergency 

engines. The examples provided by the commenters of a landlord that provides emergency 

backup power to a tenant or a company that provides emergency backup power to clients such as 

grocery stores, etc. are situations where the engines are still emergency engines (as long as they 

are operated per the requirements in §63.6640(f)). If the engine is used for a voluntary utility 

curtailment program to self generate power during times of utility constraints in return for 
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financial considerations, the engine would have to meet the requirements for non-emergency 

engines, with the exception that the engine can operate for up to 15 hours per year as part of an 

emergency demand response program, as specified in subpart ZZZZ. 

13.1.7 Comment: One commenter (253) stated that under §63.6675, a major source is defined as 

a stationary source or group of stationary sources located in a contiguous area and under 

common control that emits or has the potential to emit, considering controls, 10 tpy or more of 

any HAP or 25 tpy or more of any combination of HAP, while an area source is any stationary 

source of HAP that is not a major source. Therefore, the commenter (253) noted a farm which 

operates several small stationary irrigation pumps or a commercial building with an installed 

emergency generator would be classified as an area source, while a food processing facility with 

an industrial boiler, an emergency generator, and a backup fire pump might be classified as a 

major source of HAP, due primarily to its boiler emissions. The commenter (253) pointed out 

that if the farm covers a large area such that it is contiguous with both the food processing 

facility and an adjacent commercial area, and if all three facilities are owned and operated by the 

same company, then it appears that the farm, the commercial building, and the food processing 

facility would all be considered part of the same major source of HAP even if the facilities’ 

operations had nothing to do with one another. The commenter (253) pointed out that as 

individual facilities operating existing diesel engines not currently regulated under subpart 

ZZZZ, neither the farm nor the commercial building requires a Title V operating permit because 

neither meets the definition of a major source under 40 CFR part 70. Further, the commenter 

(253) stated that although the food processing facility does require a Title V permit as a major 

source, the adjacent farming and commercial building facilities are not considered part of the 
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Title V major source, despite being contiguous and under common ownership and control, 

because they belong to a different major industrial grouping than the food processing facility (see 

definition of major source under §70.2). The commenter (253) stated that as a result of being 

classified as a single major source of HAP under the proposed subpart ZZZZ, however, the 

combined farm/commercial building/food processing facility would also be considered a single 

major source under 40 CFR part 70; a Title V operating permit would therefore be required to 

cover all three operations. In addition, the commenter (253) stated that all existing stationary 

RICE at the farm and at the commercial building would be required to comply with standards of 

the proposed subpart ZZZZ applicable to RICE at major sources rather than those applicable to 

area sources. The commenter (253) believes that this situation is not an intended consequence of 

the proposed rule but is one that needs to be addressed. The commenter (253) strongly 

encouraged EPA to consider revising the definition of major source in §63.6675, or to otherwise 

modify the applicability provisions of the proposed subpart ZZZZ, to ensure that unnecessarily 

burdensome regulatory requirements are not imposed upon area sources with stationary RICE 

simply by virtue of their location adjacent to a major source of HAP. 

Response: EPA does not agree that the definition of major source needs to be revised. If the 

sources are located in a contiguous area and under common control, then they will be considered 

a major source. This is required by the statutory definition of major source in Clean Air Act 

section 112(a)(1), 42 USC § 7412. 

13.1.8 Comment: One commenter (126) requested that EPA provide guidance or clearly define 

the “source” with respect to RICE in the definition of reconstruction in 40 CFR §63.2. The 
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commenter (126) asked if ancillary components such as control panels be considered a 

component or are they excluded? The commenter (126) requested clarity in terms of 

reconstruction in subpart ZZZZ, and a generic statement that all ancillary equipment that are 

necessary to make the unit operate are exempt. 

Response: EPA has defined the term “engine” as constituting all parts necessary to operate the 

engine during emissions testing, including fuel and air intake components, cooling components, 

exhaust and pollution control components, control computers and the crankshaft, as well as the 

basic engine block and associated reciprocating engine parts. Control panels consisting 

exclusively of monitors and gauges and a throttle are not considered parts of the engine and thus 

are not part of the source. Engine computers that manage the engine in response to a throttle are 

considered part of the engine and thus of the source. EPA finds the term “ancillary equipment 

necessary to make the unit operate” ambiguous. The Agency will determine the applicability of 

any argument that a specific piece of “ancillary” equipment is not part of the source on a case by 

case basis, as provided for in the CAA. 

13.1.9 Comment: One commenter (213) asked that EPA specifically define what constitutes an 

area source (i.e., by including the amount of HAP emitted) and not rely on the current definition 

that defines an area source as any source that is not a major source. 

Response: The description of an area source provided in the regulations at 40 CFR 63.6585(c), 

which is the same definition of area source found in the statute in section 112(a)(2), and in the 

general provisions at 40 CFR part 63, is appropriate and consistent with what has been used for 
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previous rulemakings affecting stationary engines. EPA believes this definition is very clear and 

underscores that the universe of sources is made up of major sources or sources that are not 

major sources, which are called area sources. EPA is not finalizing a different definition. 

13.2 Clarifications 

13.2.1 Comment: Two commenters (155, 242) said that EPA needs to clarify that maintenance 

activities apply as appropriate because the specific maintenance requirements may not always 

make sense to conduct on an engine, e.g., 2SLB engines utilize continuous oil-feed so an oil 

change is illogical for this type of engine. 

Response: The two commenters who made the statement regarding oil changes being illogical 

for 2SLB engines, indicated in their comments that they could provide EPA with additional 

information on maintenance practices. EPA requested specific recommendations on 

maintenance practices from industry and from commenters 155 and 242 specifically. EPA 

received specific recommended maintenance practices for stationary SI engines, including 2SLB 

engines from Exterran, JW Power Company, and CSI (EJC).27 Commenters 155 and 242 did not 

submit separate recommendations, but during a meeting on March 22, 201028, API indicated that 

in terms of appropriate management practices for existing stationary SI engines, that it concurs 

                                                           

27 Letter from Rebecca Rentz, Bracewell and Giuliani to Melanie King, EPA. Management 

Practices for SI RICE Area Sources < 500 hp. January 27, 2010. EPA-HQ-OAR-2008-0708-

0354.1.

28 Memorandum from Tanya Parise, EC/R to Melanie King, EPA. Summary of the March 22, 

2010 Meeting between EPA and API to discuss the NESHAP for Existing Stationary SI RICE. 
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with the recommendations submitted by Exterran. Those recommendations supported an oil 

change interval of every 4,320 hours of operation for 2SLB engines. The oil change interval for 

2SLB engines is longer for than for other engines (i.e., 4SLB and 4SRB) because of the different 

engine configuration of 2SLB engines. EPA concurs with the recommendations submitted by 

Exterran et. al. and finds them appropriate for the final rule. Further, EPA is including an 

alternative in the final rule for monitoring the quality of the oil through an oil analysis program. 

Sources have the option to use an oil change analysis program to extend the oil change 

frequencies. Sources can also petition the Administrator pursuant to the requirements of 40 CFR 

63.6(g) for alternative work practices. Sources have the option to work with State permitting 

authorities pursuant to EPA’s regulations at 40 CFR subpart E (“Approval of State Programs and 

Delegation of Federal Authorities”) for approval of alternative management practices. 

13.2.2 Comment: Numerous commenters (112, 132, 154, 155, 162, 186, 227, 242) asked that 

EPA clarify in the rule where hours has been used to determine maintenance or testing frequency 

that it is operating hours and not calendar hours. Several commenters (112, 154, 155, 186, 242) 

said that EPA should clearly specify that the maintenance frequency in the rule are operating 

hours and not calendar hours. If the engine does not operate during a particular period, it is 

assumed that no wear, performance, or emissions degradation occur, the commenters (155, 242) 

said. Therefore, the commenters (155, 242) said, it is appropriate to specify that the maintenance 

interval is defined as operating hours. 

Similarly, commenter (162) said performance testing should be stipulated based on 

engine use and hours of operation instead of calendar years. Many of the commenter’s (162) 

engines are only operated seasonally. The number of hours operated varies greatly from year-to 
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year, and testing every 3 years seems burdensome given the variable and infrequent operation for 

this types of uses. 

Response: EPA agrees with the commenters that the rule should clarify that the maintenance and 

testing frequency are based on operating hours and has made this clarification in the final rule. 

EPA does not agree that it is burdensome to require testing every three years; this frequency is 

necessary to show that the engines are continuing to comply with the emission limitations in the 

rule. 

13.2.3 Comment: One commenter (155) expressed that EPA should provide allowances for 

cases where the maintenance schedule elapses during engine operation, e.g., an emergency could 

occur requiring an engine to operate for more than 200 hours and with a 200 hour maintenance 

schedule the commenter assumes that EPA did not intend for the engine to be stopped to 

complete an oil change. The final rule should include a provision that does not require engine 

shutdown solely for the purpose of conducting maintenance. 

Response: EPA agrees that there may be situations where an emergency engine is operating 

during an emergency and it is not possible to shut down the engine in order to perform the 

work/maintenance practice requirements on the schedule required in the final rule. EPA has 

added a provision in the final rule to indicate that if the stationary engine is operating during an 

emergency situation, then the maintenance activity can be delayed until the emergency is over. 

The maintenance should be performed as soon as practicable after the emergency has ended. 
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13.2.4 Comment: One commenter (96) indicated that it has found several issues with the 

proposed standards in terms of discrepancies, omissions, conflicts and other things that need 

correction. Specific comments by the commenter (96) are provided in other sections, but in 

general the commenter believes the rule is complex to follow. Especially since the proposed rule 

incorporates elements from previous engine rules, it is difficult to determine what requirements 

apply and commenters 96 and 132 urges EPA to provide guidance documents that will assist the 

regulated community in determining which requirements apply to the various types of engines. 

Response: EPA has made efforts in the final rule to be as clear as possible on the emission 

standards and other requirements that apply to existing stationary engines affected by the rule. 

EPA has also corrected discrepancies that were included in the proposed preamble and rule, 

which assists in making the final rule requirements as clear as possible. Finally, EPA will be 

developing guidance and implementation material for the final rule. This material will be 

available to affected stakeholders through EPA’s website and will help the regulated community 

in determining which requirements apply and demonstrating compliance. 

13.2.5 Comment: One commenter (96) noted that in 63.6603 of the proposed rule existing 

engines at area sources are required to meet operating limitations of Table 2b of the proposed 

rule, but that Table 2b indicates that it only applies to new and reconstructed sources. EPA 

should clarify what the intent is, the commenter (96) said. The commenter (96) provided various 

charts for different engine types where it believes that this clarification needs to be made. The 

commenter (96) believes that the areas marked “e” in the charts provided in the comment letter 

should be exempt from operating requirements. 
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Response: EPA agrees with the commenter that the title to Table 2b of the proposed rule on 

page 9721 of the Federal Register notice is confusing. EPA has clarified the title of Table 2b in 

the final rule to clearly indicate the applicability of operating limitations. EPA has also clarified 

and corrected various other inconsistencies that were included in the proposed rule and believes 

the final rule reads more easily and clearly. 

13.2.6 Comment: Numerous commenters (50, 81, 90, 96, 98, 116, 119, 126, 127, 129, 139, 157, 

167, 178, 196, 201, 216, 220, 240) referred to apparently conflicting language in the proposed 

preamble that appears to require initial performance testing of emergency generators and many 

of these commenters were opposed to requiring performance testing on emergency engines. Two 

commenters (96, 126) noted that in the preamble of the proposed rule at page 9711, EPA makes 

the statement “stationary non-emergency RICE located at major sources that are less than 100 

HP, stationary RICE located at area sources that are not subject to numerical emission standards, 

and all stationary emergency RICE are only subject to compliance requirements in the form of 

management practices to minimize emission levels.” The commenter (96) stated that this 

language contradicts later text requiring numerical emission standards for formaldehyde for 

engines below 50 HP, CO standards for diesel and 4SLB engines between 50 and 250 HP, and 

CO and formaldehyde standards for emergency engines at area sources greater than 500 HP. The 

commenter (96) thinks the preamble statement is the correct one and recommends that other 

language that conflicts with the preamble language be revised to clarify that only management 

practices, not numerical emission standards apply to these sources. One commenter (118) had 

similar concerns as those expressed by commenter 96. Commenters 188 and 203 also asked that 
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EPA clarify whether performance testing is required for these units because it is not clear from 

the rule text and specifically wanted explicit language in the final rule that exempts these units 

from performance testing. 

Commenter 119 received clarification from EPA that this was not the intent of the rule, 

and commenters 119 and 201 requested that EPA clarify this intent in the final rule. 

One commenter (162) said that performance testing of emergency RICE seems onerous, 

may not provide an accurate emissions profile, and should not be required. Emergency RICE 

emissions during short periods of readiness testing vary from the emissions profile achieved 

during longer periods of operation when they are used in emergency situations, the commenter 

(162) said. Commenters 167 and 196 expressed similar comments as 162. 

One commenter (127) stated, for example, that page 9711 section C of the preamble to 

the proposed rule states that “all stationary emergency RICE are only subject to compliance 

requirements in the form of management practices to minimize emissions.” However, the 

commenter (127) pointed out that, in Table 2 of the proposal preamble and Table 2d of the 

proposed rule, stationary emergency RICE with greater than 500 HP is listed as having emissions 

limits. 

One commenter (116) stated that it was not clear from the proposal whether existing 

emergency RICE less than 500 HP at major sources are required to conduct a performance test to 

demonstrate compliance with the emission limit. The commenter (116) noted that, in Table 2c of 

the proposed rule, emergency SI RICE between 50 and 500 HP have an emission limit for 

formaldehyde of 2 ppmv on a dry basis (ppmvd) or less at 15 percent O2. The commenter (116) 

also stated that the preamble to the proposed rule, section D.1 states that “[o]wners and operators 

of existing stationary non-emergency RICE located at major sources that are less than 100 HP 
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and existing stationary emergency RICE located at major sources do not have to conduct any 

performance testing,” but section 63.6612 of the proposed rule (requirements to conduct and 

initial performance test) states: “[i]f you own or operate an existing stationary RICE with a site 

rating of less than or equal to 500 brake HP located at major of HAP emissions...you are subject 

to the requirements of this section.” Section 63.6612 and Tables 4 and 5 do not distinguish 

between emergency RICE and non-emergency RICE. The proposed rule language suggests that 

if an engine has a numerical emission limit, a compliance test is required. The commenter (116) 

opined that the preamble language is incorrect, but if they are wrong, they suggested that EPA 

clarify that EPA does not intend to require emergency engines to be tested in Section 63.6612 

and in Tables 4 and 5 of the proposed rule. 

One commenter (90) noted there are conflicting statements in the preamble concerning if 

an initial compliance test is a requirement or not (e.g. on page 9704 of the proposed rule it states 

that area sources subject to an emission standard must do an initial compliance test while on 

Page 9705 of the proposed rule it states that operators of emergency RlCE are specifically 

excluded from the need to submit a notification of a compliance test). The commenter (90) 

stated that in EPA’s impacts memo, it is expressly stated that a compliance test for emergency 

use engines would not be required. The commenter (90) further stated that the most significant 

issue however is not that a compliance test is required for emergency use engines, but what the 

emission levels are for existing engines with no add-on controls. 

One commenter (176) recommended that EPA remove the testing requirements for 

emergency engines from the proposed rule. The commenter (176) stated that the preamble to the 

proposed rule provides that such engines are not subject to any performance testing 

requirements, but that the rule appears to include such testing requirements (i.e., in proposed 
386

Tables 3, 4 and 6 to 40 CFR part 63, subpart ZZZZ). The commenter (176) supported its 

recommendation by explaining that emergency engines only operate on a limited basis where 

periodic testing requirements are not necessary. 

One commenter (50) found the emissions testing and reporting requirements applicable to 

emergency generators to be contradictory. In Section III.E of the preamble (FR Page 9705), and 

again in part 63.6645, existing stationary emergency RICE are excluded from reporting 

requirements, including pre-emissions testing and post-emissions testing reporting requirements. 

However, emergency RICE greater than 500 HP are subject to emission limits and testing for CO 

per Table 2d, thereby making them subject to pre-testing and post-testing reporting requirements. 

The commenter requests that the rule be modified to clearly indicate that emergency generators 

are not subject to emissions testing and reporting requirements. 

Response: EPA understands the commenters’ points, but EPA disagrees that the statement on 

page 9711 of the proposed Federal Register notice that the commenters refer to conflicts with 

later text requiring numerical standards. The statement that the commenters refer to is in section 

IV.C. of the proposed preamble under the heading “How did EPA determine the compliance 

requirements.” That section of the preamble discusses the compliance requirements and how 

EPA determined appropriate compliance requirements, and is not a discussion of emission 

standards. Under the proposed rule, EPA did not require performance testing for stationary nonemergency engines at major sources that are less than 100 HP and stationary engines at area 

sources that are not subject to any numerical standards and stationary emergency engines. EPA 

explained why it believed it was appropriate to not require performance testing from these 
387

engines and this decision was not in conflict with the decision to require numerical emission 

standards from some of these engines at proposal. 

 The requirement that existing stationary engines at area sources subject to a numerical 

emission standard would be required to conduct an initial compliance test was intended for nonemergency engines at area sources and EPA does not believe that the requirement conflicts with 

the following statement that emergency engines are also not being subjected to performance 

testing. However, EPA sees that it may not have been absolutely clear in the proposed language 

and tables. Therefore, EPA has made clarifications in the final rule regarding which engines are 

subject to performance testing and believes this resolves the commenters’ concerns on this issue. 

EPA notes that several of the subcategories that were proposed to be subject to numerical limits 

have, in the final rule, been made subject to management practices or work practice standards, 

and thus would not be subject to performance testing. 

13.2.7 Comment: One commenter (96) indicated that it is not clear when new engines that are 

subject to SSM limits are supposed to comply and if these engines are supposed to comply as of 

the date of the proposed rulemaking, a date that has already passed, that is an impossible and 

unreasonable requirement the commenter (96) said. 

Response: New stationary engines should comply with the new requirements for SSM starting 

with the effective date of the final rule. 

13.2.8 Comment: One commenter (63) noted some inconsistencies or areas in need of 

clarification in the tables of the proposed rule and said that: 
388

• Table 1a, as drafted, appears to apply emissions limitations to all (existing, new and 

reconstructed) 4SRB engines of any HP, while Table 1b will apply operational 

limitations only to 4SRB engines greater than 500 HP at major and area sources of HAP. 

Should Table 1a also apply only to 4SRB engines greater than 500 HP, as Table 1a in the 

existing regulation does? 

• Table 1a establishes emissions limitations for all 4SRB RICE, whereas Table 2d 

establishes different emissions limitations for these existing units at area sources. Maybe 

Table 2.d, item 5 is supposed to be ‘non-emergency 4SRB 50>HP<500’ rather than 

4SRB > 50 HP, like Table 2.c? 

• There is a conflict between Table 1a and Table 2d items 13 and 14, if the engine is a 

4SRB emergency SI RICE. 

Response: In response to this comment, EPA clarified that Table 1a applies to 4SRB engines 

greater than 500 HP located at major sources of HAP.

13.2.9 Comment: One commenter (119) said there is some inconsistency between 40 CFR 

63.6625(e) and the referenced Table 2d of the proposed rule. Table 2d of the proposed rule 

explicitly outlines maintenance requirements for engines, but it does not include the provisions in 

40 CFR 63.6625(e) relating to manufacturer or owner/operator maintenance plans. Two 

commenters (118, 119) said EPA should insert the following clause to 40 CFR 63.6625(e): . . 

.you must operate and maintain the stationary RICE and aftertreatment control device (if any) 

according to the maintenance schedule in Table 2d, or you must operate and maintain the 

stationary RICE. . . 
389

 The commenter (119) recommended that a clause be added to Table 2d of the proposed 

rule indicating that as an alternative to the proposed schedules, owners and operators can 

maintain the stationary RICE according to the manufacturer’s emission-related written 

instruction or develop their own maintenance plan. 

 One commenter (104) stated that the text in proposed 40 CFR 63.6625 and 63.6655 

appears to allow the owner/operator of the engine to develop a maintenance plan in lieu of the 

requirements provided in Table 2d (i.e., proposed replacement schedule for oil/filters and spark 

plugs and inspection of hoses/belts). The commenter (104) requested that EPA clarify this issue 

in the text. 

Response: EPA does not agree with the commenters that there is an inconsistency. The 

maintenance requirements in Table 2d are not the only emission-related operating and 

maintenance requirements that are recommended by the engine manufacturer, and the language 

in §63.6625(e) requires owners and operators to follow those requirements. The maintenance 

plan should include the maintenance practices from Table 2d as well as other maintenance 

necessary for the engine.

13.2.10 Comment: One commenter (111) indicated that the proposal states that the pressure 

drop across the catalyst must be monitored monthly for engines greater than 500 HP at area 

sources (74 FR 9704) and later states that the pressure drop must be monitored continuously (74 

FR 9711). 
390

Response: The commenter is correct that there is an inconsistency in the preamble for the 

proposed rule. The language on page 9711 should have said that the pressure drop must be 

measured monthly, rather than continuously. 

13.2.11 Comment: One commenter (188) noted that the heading on the middle column of Table 

2d to subpart ZZZZ of part 63 of the proposed rule, states, “You must meet the following 

emission or operating limitations at all times, except during periods of startup, or malfunction.” 

The commenter (188) believed that this language may possibly be interpreted by overly zealous 

regulators in the field to require a continuous emissions monitoring system (CEMS) on every 

engine and noted that installing, maintaining and calibrating CEMS would be another 

unjustifiable and costly burden; especially when applied to small engines and/or those that are 

redundant/standby. The commenter (188) continued that the same comment applies regarding 

the heading at the top of the far right column of Table 2d to subpart ZZZZ of part 63 of the 

proposed rule, which states “[y]ou must meet the following emission or operating limitations 

during periods of startup, or malfunction.” The commenter (188) recommended that the EPA 

clearly state that CEMS is not required, and that EPA consider more realistic standards that 

operators are able to comply with; specifically, that the wording “at all times” be deleted. 

Response: Subpart ZZZZ does not require CEMS. Sources may elect to install CEMS, but they 

are not required. EPA does not agree that the wording “at all times” should be deleted because 

those requirements apply at all times except as indicated.
391

13.2.12 Comment: One commenter (160) requested that EPA clarify the status of the RICE 

landfill/digester gas engine subcategory for major sources. The commenter (160) stated that 

some engines that use digester gas with HP greater than 500 are CI engines, which makes it 

appear that they could fall under the major source RICE subcategory or non-emergency CI 

greater than 300 HP, with a 4 ppmvd CO or 90 percent CO reduction standard. The commenter 

(160) requested that EPA clarify that this standard only applies to diesel engines, and not to 

landfill/digester gas engines. 

Response: Engines that burn landfill or digester gas should meet the standards applicable to 

engines burning landfill or digester gas.

13.2.13 Comment: One commenter (256) expressed that the proposed rule is ambiguous as to 

how an owner or operator of a stationary emergency RICE is to demonstrate initial and 

continuous compliance with the proposed numerical emissions limitations. The commenter 

(256) stated that, if the EPA does not believe it is reasonable to subject stationary emergency 

RICE to performance testing, then there is no purpose for setting a numerical emissions 

limitation for any stationary emergency RICE. 

Response: The final rule does not contain any numerical emission limitations for emergency SI 

engines. These engines have to meet work or management practices. This addresses the 

concerns expressed by the commenter. 
392

13.2.14 Comment: One commenter (76) noted that Table 2 in the preamble identifies 

management practices of spark plug replacement for various 2SLB, 4SLB, and 4SRB 

subcategories. The commenter (76) asked EPA to clarify whether these categories include diesel 

or CI engines, as these engines can be manufactured as 2SLB, 4SLB, and 4SRB engines, but 

have no spark plugs to replace. 

Response: Section 63.6590 of the regulations defines 2SLB, 4SLB, and 4SRB engines as spark 

ignition engines. 

13.2.15 Comment: One commenter (76) asked if the requirements for less than 50 HP in Tables 

1 and 2 in the preamble apply to emergency or nonemergency engines. 

Response: The requirements in the preamble and rule tables for stationary engines less than 50 

HP apply to both emergency and non-emergency engines. The requirements were revised in the 

final rule. 

13.2.16 Comment: One commenter (193) requested that EPA clarify that the category of small 

engines (i.e., less than 50 HP) at both major and area sources is not a universally applicable 

category of engines that is separate, distinct, all encompassing, and not otherwise associated with 

any of the other listed engine sub-categories. The commenter (193) noted that the information 

presented in the referenced tables that contain compliance related requirements should be 

clarified to express that all engine types less than 50 HP, are not required to fulfill the stated 

requirements, or EPA should modify the information in its tables to reflect its stated belief that 
393

there will be no CI, or lean burn engines of this size. The commenter (193) suggested EPA limit 

the applicability of the less than 50 HP classification to only those four cycle, rich burn SI 

engines it used to establish the MACT floor. 

Response: The commenter is not correct. The category of engines less than 50 HP as proposed 

did include all stationary engines below 50 HP, not just 4SRB SI engines. This final rule only 

includes SI engines; SI engines under 50 HP have been grouped as one subcategory with SI 

engines 51-99 HP for the final rule and are subject to work or management standards.

13.2.17 Comment: One commenter (209) said the MACT standard for non-emergency 4SRB 

engines is off by a factor of 10. The commenter (209) pointed to discrepancies in the proposed 

rule and the background documents. The proposed formaldehyde standard is 200 ppbvd at 15 

percent O2 during steady state and 2,000 ppbvd at 15 percent O2 during startup or malfunctions. 

The January 21, 2009 Alpha-Gamma Technologies memo for the MACT floor determination for 

RICE less than 500 HP at major sources states that the MACT floor is 2 ppmvd of formaldehyde 

at 15 percent O2. To be consistent with this background document the proposed standards during 

steady state should be 2,000 ppbvd and the proposed standards during startup and malfunctions 

should be 20 ppmvd, not 2 ppmvd. 

Response: The proposed 2 ppmvd standard was the MACT floor for 4SRB engines. The 

standard in the proposed rule of 200 ppbvd was based on going beyond the MACT floor. The 

MACT and MACT floor determinations for 4SRB engines were revised in the final rule. 
394

13.2.18 Comment: One commenter (227) said that one of the standards (non-emergency RICE at 

major sources that are less than 50 HP and emergency RICE at major sources) requires the site to 

follow the manufacturer’s maintenance requirements, or develop a maintenance plan. The 

commenter (227) asked EPA to clarify whether a maintenance plan, if needed, could be 

developed for a company or must it be written for each site in a company. 

Response: The plan must include the maintenance for each engine at each site.

13.2.19 Comment: One commenter (126) requested that the SI and CI subcategories be defined 

and clarified. The commenter (126) believes that EPA intended to provide the SI category as a 

“catch-all” for any spark ignition engines that do not fall into other categories.

Response: There are definitions for SI and CI in §63.6675. The commenter did not provide any 

information regarding what needs to be clarified for these subcategories, therefore EPA is unable 

to fully respond to the comment. 

13.2.20 Comment: One commenter (157) requested that EPA confirm that Table 3 lists the 

correct site rating for 4SLB RICE greater than or equal to 250 HP. The commenter (157) stated 

that the heading for the table implies requirements for engine greater than 500 HP.

Response: Table 3 in the preamble to the proposed rule did include requirements for 4SLB 

RICE greater than or equal to 250 HP and the commenter is correct that this was not correctly 

indicated in the title of the Table. 
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13.2.21 Comment: One commenter (47) wanted to clarify that emergency SI engines less than 

50 HP are not subject to any requirements.

Response: Existing emergency SI engines less than 50 HP at major sources are subject to work 

practices. Existing emergency SI engines less than 50 HP at area sources are subject to 

management practices.

13.2.22 Comment: One commenter (213) requested clarification on whether landfill and digester 

gas engines are subject to continuous monitoring of catalyst parameters. 

Response: The final rule does not contain any continuous parametric monitoring requirements 

for landfill or digester gas engines. 

13.2.23 Comment: One commenter (175) asked for clarification on whether the requirements in 

Table 2d of the proposed rule apply to engines manufactured prior to June 12, 2004. The 

commenter (175) indicated that it thought that under 40 CFR 63.6590(c), the standard for new 

area source engines manufactured after June 12, 2006, would be equivalent to NSPS, and that the 

NSPS requires a maintenance plan that is not as prescriptive as the oil, filter and spark plug 

replacement schedule in the proposed rule for existing engines less than 50 HP. 

Response: The proposed Table 2d applies to existing stationary RICE located at an area source 

of HAP emissions. Section 63.6590 of subpart ZZZZ states that a stationary RICE located at an 
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area source of HAP emissions is considered existing if construction of the engine commenced 

before June 12, 2006. 

13.3 Errors 

13.3.1 Comment: Several commenters (63, 96, 99, 116, 146, 155, 159, 193, 224, 227, 242) noted 

errors in the use of mathematical symbols in the proposed rule preamble and rule tables and 

provided corrections to the tables. The commenters (155, 242) indicated that the “≥” symbol 

should be changed to “≤” in several cases, e.g., “50≥HP≤249” should be changed to 

“50≤HP≤249.” Commenter 99 said that for example 50>HP<500 should be changed to 

50<HP<500. 

Response: The commenters are correct that some of the mathematical symbols in the proposed 

rule were incorrect. EPA has corrected the typos concerning the use of the ≤, ≥, <, and > signs in 

the final rule. 

13.3.2 Comment: One commenter (242) stated that in the EPA Fact Sheet and February 27 

News Release EPA said that the rule sets emission standards for engines that “have a site rating 

of greater than 500 HP, are located at major sources of air toxics emissions, and were constructed 

or reconstructed before December 19, 2002.” The commenter (242) said that the referenced 

engines are the engines covered by the 2004 RICE NESHAP, where existing rich burn engines 

where the only existing sources that required add-on controls. The proposed rule sets new 

requirements for existing diesel engines, but not existing natural gas engines greater than 500 HP 
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at major sources. So it appears the EPA Fact Sheet and New Release contain errors, according to 

the commenter (242). It should be clarified in these publications that the proposed rule sets 

standards for existing diesel engines greater than 500 HP at major sources and SSM limits for 

natural gas rich burn engines greater than 500 HP at major sources. 

Response: EPA does not necessarily agree with the commenter that the February 25, 2009 Fact 

Sheet available at http://www.epa.gov/ttn/oarpg/t3/fact_sheets/rice_neshap_prop_fs_022509.pdf

was inaccurate. The applicability dates that distinguish stationary existing engines from 

stationary new engines are specified in 40 CFR 63.6590(a). Per 63.6590(a)(1)(i), stationary 

engines greater than 500 HP located at major sources of HAP emissions are considered existing 

if construction or reconstruction is commenced prior to December 19, 2002. This is consistent 

with bullet one, sub-bullet three, under the title “Action” in the February 25, 2009 Fact Sheet, 

which was intended for the existing stationary diesel engines greater than 500 HP located at 

major sources that EPA is addressing in this rulemaking. EPA could have been clearer in this 

bullet by stating that new emission standards only apply to existing diesel engines greater than 

500 HP at major sources, and not to natural gas engines, as well as specifying the applicability of 

the SSM limits that were being co-proposed. For the final rule, EPA has made sure that the Fact 

Sheet and other material are clear. 

13.3.3 Comment: One commenter (96) said that if EPA keeps standards for engines less than 50 

HP there needs to be a separate subcategory for emergency engines.
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Response: The commenter did not provide any information to justify the need for a separate 

subcategory for emergency engines smaller than 50 HP. In any case, both emergency and nonemergency engines smaller than 50 HP are subject to either work or management practices under 

the final rule. The practices for emergency engines are slightly different from those for nonemergency engines.

13.3.4 Comment: One commenter (186) noted that there is a typographical error on page 97111 

of the preamble where it says "of three years" instead of "or three years." 

Response: The commenter is correct. 

13.3.5 Comment: Two commenters (172, 178) said that §63.6603 of the proposed rule states that 

existing stationary RlCE located at an area source must comply with the operating limitations in 

Tables 1b and 2b of the rule. However, the operating limitations in Table 2b of the proposed rule 

appear to only apply to units at major sources. The EPA should remove the reference to Table 

2b of the proposed rule in section 63.6603 of the proposal. 

Response: It is not true that Table 2b of the proposed rule only applies to stationary engines at 

major sources. Table 2b of the proposed rule also applied to area sources and EPA disagrees that 

the reference to Table 2b should be removed from section 63.6603. 

13.4 Discrepancies 
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13.4.1 Comment: One commenter (193) noted that the §63.6640 requirement that precludes 

maintenance checks and readiness testing, unless it is recommended by governmental authorities, 

engine manufacturers, or insurance companies, conflicts with the proposed requirement 

§63.6625. The problematic wording of §63.6640(f) establishes a prohibition to the operation of 

an emergency RICE for maintenance and readiness testing purposes unless the owner or operator 

possesses a recommendation from one of the listed entities. The commenter (0193) believes that 

if EPA is to require owners and operators to develop plans for the maintenance and operation of 

emergency engines, in the absence of recommended practices from “Federal, State or local 

government, the manufacturer, the vendor, or the insurance company,” it should not construct 

accompanying regulatory requirements that do not include the owner or operator developed 

maintenance and operation plans as valid criteria for authorizing maintenance and readiness 

testing activities. 

Response: EPA does not agree with the commenter that §63.6640(f) should include maintenance 

checks developed solely by the owner/operator and having no input whatsoever from one of the 

entities listed in §63.6640(f). 

13.4.2 Comment: One commenter (178) noted discrepancies in the applicability of the rule as 

presented in the text and tables. The commenter (178) states that in several places the tables do 

not support the text concerning applicability of the rule to specific RlCE unit types. There are 

numerous inconsistencies between the requirements for large stationary engines and smaller 

ones, and between those located at major sources and those at area sources. Although there are 

many more examples, the following are instances of inconsistency: 
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• EPA should confirm that, in the descriptions to Table 2a and 2b of the proposed rule, the 

phrase “located at a Major Source . .” applies to all the categories of RlCE contained in 

those descriptions and not just the last category of RlCE in the titles. In Table 6, Item 11 

of the proposed rule, EPA should confirm that the phrase "located at major sources" 

applies to the universe of existing stationary RlCE >500 HP rather than just to 4SRB 

>500 HP. 

• Assuming that large engines have a larger potential impact, and that requirements 

proposed for small engines are not applicable to such larger engines, it is not reasonable 

to impose such requirements on small engines. For example, the requirements for an 

emergency stationary RlCE >500 HP does not have a 100 hr run-time restriction, yet 

smaller RlCE do. The commenter (178) suggested this requirement be removed for 

smaller engines. 

 

Response: The commenter is correct that the phrase “located at a Major Source . . .” applies to all 

of the RICE listed in the titles of Tables 2a and 2b. The run-time requirements for emergency 

stationary RICE greater than 500 HP at a major source were promulgated as part of the 2004 

RICE NESHAP and are not the subject of this rulemaking. EPA does not agree with the 

commenter that the 100 hour run-time restriction on maintenance and testing operation should be 

removed for stationary RICE smaller than 500 HP and stationary RICE located at area sources. 

Having a different requirement for large engines at major sources is not a sufficient justification 

for removing the 100 hour limit. 

13.5 Other
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13.5.1 Comment: A few commenters (103, 111, 150, 155, 224, 225) noted other regulations 

allows a 200 hour burn-in period for engines with catalysts that are new, reconstructed, or 

rebuilt. The commenters (155, 224) believe this allowance should also be provided for 

commissioning of an engine after major maintenance. Major maintenance may not always be 

considered a rebuild, however, an engine burn-in period would still be necessary to ensure that 

catalyst damage does not occur, the commenter (155) said. In addition, the commenter (155) 

also believes that existing engines that are retrofitted should be given a burn-in period. Again, 

the retrofit may not constitute a modification, reconstruction or rebuild, but necessary upgrades 

that require burn-in time to prevent catalyst damage may be appropriate, according to the 

commenter (155). The commenter (155) recommended that EPA revise the current language in 

§63.6640(d) to read as follows (the commenter’s (155) additions are shown in bold): 

“For new, reconstructed, and rebuilt stationary RICE, and stationary RICE that have 

undergone maintenance that could result in catalyst damage upon startup or equipment 

changes to comply with the requirements of this subpart, deviations from the emission or 

operating limitations that occur during the first 200 hours of operation from engine startup 

(engine burn-in period) are not violations.” 

One commenter (103) stated that EPA should incorporate a provision for a 

commissioning period into the rule whereby the RICE is allowed to operate prior to installation 

of catalytic elements in order to prevent damage to the catalytic elements during engine break in. 

The commenter (103) attributed the following quotation to EPA but gave no citation: 

“EPA understands the “commissioning period” to be the final phase of the construction 

process. Activities conducted during the commissioning period include: checking all 
402

mechanical, electrical, and control systems for the RICE and all related equipment; and 

confirming the performance measures specified in the purchase agreement. EPA 

understands that the commissioning period may take up to two weeks to complete. EPA 

does not consider the “commissioning period” as the initial startup of the unit as long as 

the RICE is not being used for its intended purpose or any other beneficial use at the 

facility during this time. Site-specific determinations of initial startup may be required 

for facilities that operate in a commissioning mode for excessive periods of time.” 

The commenter (103) indicated that in the natural gas compression industry, it is 

extremely rare that an engine can be operated under load to facilitate the commissioning without 

being used for its intended purpose. The commenter (103) believes that the requirement for a 

site-specific waiver is not an appropriate solution when it is a normal requirement, and asserted 

that the waiver should be written into the rule. 

 Two other commenters (111, 225) similarly noted that installation of the catalyst during 

the break-in period of a new or overhauled unit (typically 50-100 hours) is likely to result in 

catalyst malfunction due to fouling, masking, or poisoning of the catalyst element. 

 Another commenter (150) urged EPA to address the potential to generate a deviation 

during an SSM event consistent with the burn-in provisions set forth in 40 CFR 63.6640(d), 

which provides that “deviations from the emission or operating limits that occur during the first 

200 hours of operation from engine startup (engine burn-in period) are not violations.” This 

commenter (150) added that if the rules are promulgated not to allow burn-in time, costs would 

be increased due to the need to wash or replace catalyst which would be masked if left on during 

this period to meet emissions requirements. 
403

Response: EPA does not agree that it should provide a burn-in period in subpart ZZZZ for 

retrofitted engines or engines that have been subject to maintenance short of a rebuild. EPA does 

not have any information to indicate that retrofitted engines or engines subject to maintenance 

would not be able to meet the requirements of subpart ZZZZ immediately after the retrofit or 

maintenance, and therefore does not agree that such an exemption from the rule requirements 

should be provided. EPA notes that the pre-existing burn-in period for new, reconstructed and 

rebuilt engines has not been revised. Regarding the comments that stated that RICE should be 

allowed to operate prior to installation of catalyst elements, EPA does not agree that this is 

necessary because this rulemaking affects existing engines that have already been operated. In 

addition, sources have three years to comply with this rulemaking so they have sufficient time to 

operate their engines prior to catalyst installation and also have sufficient time to operate their 

engine following catalyst installation prior to the compliance date of the rule. 

13.5.2 Comment: One commenter (242) said that EPA’s failure to issue a proposed rule 

amendment with strikethrough and additions creates additional burden on the community and a 

rule with strikethrough and addition text would have eliminated the need to review and compare 

the previous rule text. The commenter (242) urged EPA to use this approach in future rule 

revisions to minimize rule interpretation issues and intent, inconsistencies, conflicts and 

unnecessary regulatory uncertainties. 

Response: EPA agrees with the commenter that a redline/strikeout copy of the rule would be 

useful in reviewing the amendments. However EPA does not agree that the failure to do so 

creates an undue burden on the community.