1 MEMORANDUM Subject: Response to Public Comments on Proposed Stationary Reciprocating Internal Combustion Engines NESHAP From: Sims Roy, ESD Combustion Group To: Robert Wayland, ESD Combustion Group On December 19, 2002, the EPA proposed national emission standards for hazardous air pollutants ( NESHAP) for stationary reciprocating internal combustion engines ( RICE) ( 67 FR 77830). The proposed rule fulfills the requirements of section 112( d) of the Clean Air Act ( CAA). The purpose of this document is to present a summary of the public comments that EPA received on the proposed standards and the responses developed by EPA. This summary of comments and responses serves as the basis for revisions made to the standards between proposal and promulgation.

The EPA received 64 public comments on the proposed rule. A listing of all persons submitting comments, their affiliation, and the document number for their comments is presented in Table 1. The comments can be obtained online from the EPA's Edocket website ( http:// www. epa. gov/ edocket). The docket number for this rulemaking is OAR 2002 0059. Each commenter has two document numbers, one number is the Edocket Document ID, and the other document number is for the legacy document numbering system. In this document, commenters are identified by the last three digits of the Edocket Document ID of their comments.

On January 21, 2003, a public hearing on the proposed NESHAP for stationary RICE was held at the EPA facility in Research Triangle Park, NC. Five speakers presented comments on the proposed rule and are listed at the end of Table 1. All of the commenters except one supplemented their comments at the public hearing with written comments submitted to the docket. Any comments from the public hearing that were not included in the written comments submitted to the docket are also summarized in this document. A transcript of the public hearing 2 is available from the Edocket website ( document ID OAR 2002 0059 0603).

Table 1. List of Commenters on the Proposed NESHAP for Stationary RICE Edocket ID Number Legacy Document Number Commenter, Addressee, Title or Description, etc. Date of Document OAR 2002 0059 0499 IV D 02 L. Eagan, Chair, STAPPA Air Toxics Committee and R. Colby, Chair, ALAPCO Air Toxics Committee, Washington, DC. 01 21 03 OAR 2002 0059 0500 IV D 01 J. Bardi, Administrative Assistant, ASTM International, W. Conshohocken, PA. 12 27 02 OAR 2002 0059 0526 IV D 04 G. M. Adams, Assistant Departmental Engineer Office Engineering Department, Los Angeles County Sanitation Districts ( LACSD), Whittier, CA. 02 12 03 OAR 2002 0059 0527 IV D 45 H. Malm Ph. D., Chief Technical Officer, REM Technology Inc., Calgary Alberta, Canada. 02 14 03 OAR 2002 0059 0528 jeanpublic@ yahoo. com undated OAR 2002 0059 0529 IV D 46 S. Kaderly, Air Quality Division Administrator, Nebraska Department of Environmental Quality, Lincoln, NE. 02 18 03 OAR 2002 0059 0530 IV D 12 J. P. LaCosse, President & Principal Scientist, Spectral Insights LLC, Durham, NC. 02 17 03 OAR 2002 0059 0533 IV D 10 M. Heseding, The European Association of Internal Combustion Engine Manufacturers ( EUROMOT), Frankfurt, Germany. 02 18 03 OAR 2002 0059 0536 IV D 18 J. Shefchek, Managing Director and Chief Environmental Officer, Alliant Energy Corp., Madison, WI. 02 13 03 OAR 2002 0059 0537 IV D 08 J. C. Weisbrod, JCW Technologies, Stevens Point, WI. 02 17 03 Edocket ID Number Legacy Document Number Commenter, Addressee, Title or Description, etc. Date of Document 3 OAR 2002 0059 0540 IV D 15 E. M. Adamo, North America Environmental, Air Products and Chemical Inc., Allentown, PA. 02 18 03 OAR 2002 0059 0542 IV D 56 M. W. Stroben, EHS Manager, Corporate Environment Health & Safety, Duke Energy, Charlotte, NC. 02 19 03 OAR 2002 0059 0544 IV D 47 J. C. deRuyter, Principal Consultant, DuPont Engineering Technology, Wilmington, DE. 02 20 03 OAR 2002 0059 0545 IV D 48 D. R. Schregardus, Deputy Assistant Secretary of the Navy, Washington, DC. 02 19 03 OAR 2002 0059 0546 IV D 44 D. E. Donohoue, Chief, Emissions Assessment Branch Stationary Source Division, Air Resources Board, Sacramento, CA. 02 20 03 OAR 2002 0059 0547 IV D 24 J. B. Frank, Counsel to the Class of ` 85 Regulatory Response Group, Baker Botts LLP, Washington, DC. 02 20 03 OAR 2002 0059 0548 IV D 49 G. Calvo, Counsel for the Utility Air Regulatory Group, Hunton & Williams, Washington, DC. 02 20 03 OAR 2002 0059 0549 IV D 54 T. Steichen, Sr. Regulatory Analyst, American Petroleum Institute, Washington, DC. 02 20 03 OAR 2002 0059 0550 IV D 55 K. King, Supervisor, Regulatory & Compliance Support Unit, Air Pollution Control Division, State of Colorado, Denver, CO. 02 14 03 OAR 2002 0059 0551 IV D 31 D. F. Hunter, Manager Regulatory Issues, ConocoPhillips, Houston, TX. 02 20 03 OAR 2002 0059 0552 IV D 50 J. Suchecki, Director Public Affairs, Engine Manufacturers Association, Chicago, IL. 02 20 03 Edocket ID Number Legacy Document Number Commenter, Addressee, Title or Description, etc. Date of Document 4 OAR 2002 0059 0553 IV D 23 J. Michael Geers, Cinergy Corp., Cincinnati, OH. 02 20 03 OAR 2002 0059 0554 IV D 51 Hanover Compression Limited Partnership, Houston, TX. 02 20 03 OAR 2002 0059 0555 IV D 32 T. R. Weeks, Chief, Engineering, San Diego County Air Pollution Control District, San Diego, CA. 02 20 03 OAR 2002 0059 0556 IV D 52 J. Dreyer, Director of Industry Affairs, Gas Processors Association, Tulsa, OK. 02 20 03 OAR 2002 0059 0557 IV D 20 J. C. Biechman, Vice President Government Affairs, The National Fire Protection Association ( NFPA), Arlington, VA. 02 19 03 OAR 2002 0059 0558 IV D 17 G. A. Wilkins, Manager Environmental Support, Marathon Ashland Petroleum LLC, Findlay, OH. 02 14 03 OAR 2002 0059 0559 IV D 33 D. L. Kraisinger, Vice President, Health, Safety & Environment, BP America Inc., Los Angeles, CA. 02 20 03 OAR 2002 0059 0560 IV G 01 T. Pugh, Manager Environmental Services, American Public Power Association ( APPA), Washington, DC. 02 24 03 OAR 2002 0059 0561 IV D 41 P. Faggert, Vice President and Chief Environmental Officer, Dominion Transmission Inc., Glen Allen, VA. 02 19 03 OAR 2002 0059 0562 IV D 34 R. J. Barkanic, Manager Environmental, PPL Services Corp., Allentown, PA. 02 13 03 OAR 2002 0059 0564 IV D 35 R. J. Morehouse, ExxonMobil Refining & Supply Company, Houston, TX. 02 19 03 Edocket ID Number Legacy Document Number Commenter, Addressee, Title or Description, etc. Date of Document 5 OAR 2002 0059 0565 IV D 36 J. J. Mayhew, Vice President Regulatory & Technical Center of Expertise, American Chemistry Council, Arlington, VA. 02 20 03 OAR 2002 0059 0566 IV D 13 J. R. Carson, Senior Staff Engineer Environmental Affairs, ISPAT Inland Inc., East Chicago, IN. 02 17 03 OAR 2002 0059 0567 IV D 14 J. T. Higgins, Director Bureau of Stationary Sources Division of Air Resources, New York State Department of Environmental Conservation, Albany, NY. 02 18 03 OAR 2002 0059 0569 IV D 16 R. W. Schenker, Manager Air Pollution Control, Corporate Environmental Programs, General Electric Company, Fairfield, CT. 02 18 03 OAR 2002 0059 0570 IV D 38 J. Jacobsen, General Counsel, Alyeska Pipeline, Fairbanks, AK. 02 18 03 OAR 2002 0059 0571 IV D 19 R. W. Stachowicz, Senior Development Engineer, Waukesha Engine Dresser, Inc., Waukesha, WI. 02 18 03 OAR 2002 0059 0572 IV D 21 J. A. Paul, Supervisor, Regional Air Pollution Control Agency, Dayton, OH. 02 11 03 OAR 2002 0059 0573 IV D 03 O. M. Dominguez, Director, Environmental Management Division, National Aeronautics and Space Administration ( NASA), Washington, DC. 02 06 03 OAR 2002 0059 0574 IV D 06 L. Eagan, Director, Bureau of Air Management, State of Wisconsin Department of Natural Resources, Madison, WI. 01 07 03 OAR 2002 0059 0575 IV D 07 A. G. Berwick, Associate Director, The Clean Energy Group, Concord, MA. 02 13 03 Edocket ID Number Legacy Document Number Commenter, Addressee, Title or Description, etc. Date of Document 6 OAR 2002 0059 0576 IV D 05 D. Samet, Associate Director, Standards Interpretation Group, Joint Commission on Accreditation of Healthcare Organizations ( JCAHO), Oakbrook Terrace, IL. 02 13 03 OAR 2002 0059 0577 IV D 09 B. H. McCully, President, American Society for Healthcare Engineering, Chicago, IL. 02 18 03 OAR 2002 0059 0578 IV D 39 N. Popa, Senior Environmental Planner, Consumers Energy, Jackson, MI. 02 12 03 OAR 2002 0059 0579 IV D 11 C. Hornback, Director, Regulatory Affairs, Association of Metropolitan Sewerage Agencies, Washington, DC. 02 18 03 OAR 2002 0059 0580 IV D 40 P. T. Cavanaugh, Vice President Federal and International Government Relations, ChevronTexaco, Washington, DC. 02 20 03 OAR 2002 0059 0581 IV D 27 R. Bessette, President, Council of Industrial Boiler Owners. 02 19 03 OAR 2002 0059 0582 IV D 30 V. Patton, Senior Attorney, Environmental Defense, Boulder, CO. 02 20 03 OAR 2002 0059 0583 IV D 28 P. A. Lacey, Senior Managing Counsel, American Gas Association, Washington, DC. 02 20 03 OAR 2002 0059 0584 IV D 29 E. W. Repa, Director Environmental Programs, National Solid Wastes Management Assoc., Washington, DC. 02 13 03 OAR 2002 0059 0585 IV D 22 N. Dee, Director of Environment and Safety, National Petrochemical & Refiners Assoc., Washington, DC. 02 19 03 OAR 2002 0059 0586 IV D 42 W. O'Sullivan, Acting Director, New Jersey Department of Environmental Protection ( NJDEP), Trenton, NJ. 02 14 03 Edocket ID Number Legacy Document Number Commenter, Addressee, Title or Description, etc. Date of Document 7 OAR 2002 0059 0587 IV D 37 L. Beal, Director Environmental Affairs, Interstate Natural Gas Association of America, Washington, DC. 02 19 03 OAR 2002 0059 0588 IV G 02 D. Olson, Administrator Air Quality Division, The State of Wyoming Department of Environmental Quality, Cheyenne, WY. 02 24 03 OAR 2002 0059 0593 IV D 25 R. D. Langford, Regulatory Affairs Manager, Celanese Acetate LLC, Narrows, VA. 02 20 03 OAR 2002 0059 0594 IV D 26 J. W. Sanderson, For the Colorado Utilities Coalition for Clean Air ( CUC), Denver, CO. 02 20 03 OAR 2002 0059 0595 IV G 03 R. Meyer, Manager of Environmental Affairs, American Municipal Power  Ohio Inc., Columbus, OH. 02 27 03 OAR 2002 0059 0598 IV G 04 M. Murray, Director, Environmental & Safety Policy, Sempra Energy, San Diego, CA. 02 28 03 OAR 2002 0059 0599 IV G 05 D. L. Chapman, Manager Global Environmental Services, The Goodyear Tire & Rubber Company, Akron, OH. 03 06 03 OAR 2002 0059 0600 IV G 06 A. Lawrence, Director Office of Environmental Policy and Guidance, Department of Energy, Washington, DC. 03 18 03 OAR 2002 0059 0604 R. L. Greene. 04 21 03 OAR 2002 0059 0605 IV D 43 J. Whynot, Planning and Rules Manager, Planning, Rule Development and Area Sources, South Coast Air Quality Management District, Diamond Bar, CA. 02 20 03 OAR 2002 0059 0606 R. Claybrook, Miratech Corporation. 08 07 03 Edocket ID Number Legacy Document Number Commenter, Addressee, Title or Description, etc. Date of Document 8 OAR 2002 0059 0603 ( transcript of public hearing) Speakers were: ( A) B. Nicholson, Chief of the Planning Section, NC Division of Air Quality, on behalf of the State and Territorial Air Pollution Program Administrators and the Association of Local Air Pollution Control Officials.

( B) S. Clowney, El Paso Pipeline Group, on behalf of the Interstate Natural Gas Association of America.

( C) C. Wait, Panhandle Pipe Line Companies, on behalf of the Interstate Natural Gas Association of America.

( D) M. Fisher, Wartsila North America.

( E) J. Sucheki, Engine Manufacturers Association.

Many commenters expressed support for the comments submitted by other commenters. Table 2 shows those commenters and the comments that they supported.

Table 2. List of Commenters Expressing Support for Other Comments Commenter Supports Comments of:

OAR 2002 0059 0542 OAR 2002 0059 0587 OAR 2002 0059 0544 OAR 2002 0059 0565 OAR 2002 0059 0551 OAR 2002 0059 0549, OAR 2002 0059 0585, OAR 2002 0059 0587 OAR 2002 0059 0554 OAR 2002 0059 0587 OAR 2002 0059 0556 OAR 2002 0059 0587 OAR 2002 0059 0559 OAR 2002 0059 0565, OAR 2002 0059 0549 Commenter Supports Comments of:

9 OAR 2002 0059 0561 OAR 2002 0059 0587 OAR 2002 0059 0564 OAR 2002 0059 0549, OAR 2002 0059 0565 OAR 2002 0059 0567 OAR 2002 0059 0499 OAR 2002 0059 0578 OAR 2002 0059 0587 OAR 2002 0059 0580 OAR 2002 0059 0549, OAR 2002 0059 0587 OAR 2002 0059 0581 OAR 2002 0059 0544 OAR 2002 0059 0583 OAR 2002 0059 0587 OAR 2002 0059 0595 Agrees with OAR 2002 0059 0594' s comments in commending the EPA for seeking comment on various aspects of CAA section 112( d)( 4). Defers to OAR 2002 0059 0594 on the use of RfDs.

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

I. Applicability A. Affected Source B. Applicability Cutoff C. Exemptions D. Emergency/ Limited Use E. Compression Ignition F. Subcategories G. Other II. Definitions A. Rich/ Lean Burn B. New/ Reconstructed C. Affected Source D. Other III. Dates A. Comment Period B. New/ Reconstructed C. Initial Notification D. Initial Compliance E. Other IV. Emission Limitations 10 A. Level B. Flexibility/ Options C. Compression Ignition/ DPF D. Other V. Monitoring, Recordkeeping, Reporting A. CO CEMS B. Operating Parameters 1. All Subcategories 2. 4SRB C. Initial Notification D. Startup, Shutdown, Malfunction Plan E. Reports F. Other VI. Testing A. Test Methods 1. CARB 430 2. FTIR 3. ASTM D6348 4. EPA Method 323 5. EPA SW 846 Method 0011 6. Other B. Performance Tests 1. Portable CO Monitor 2. Other VII. Cost/ Impact VIII. Risk IX. Emissions Data A. CSU Testing B. Other X. Other A. General Provisions B. Other 11 I. APPLICABILITY A. Affected Source I. A. 1 Comment: One commenter ( 569) expressed support for EPA's decision to limit the RICE maximum achievable control technology ( MACT) to major sources.

Response: The EPA has noted the commenter's support. The EPA will cover area sources and small engines under CAA sections 112( k) and 112( d), respectively, in a later rule.

I. A. 2 Comment: Two commenters ( 564, 565) requested clarification in the preamble that engines less than or equal to 500 horsepower ( HP) are included in the RICE affected source. One commenter ( 564) asked that EPA clarify that emergency/ limited use engines, and existing 2 stroke lean burn ( 2SLB), 4 stroke lean burn ( 4SLB), and compression ignition ( CI) engines are part of the affected source. Commenter 564 stated that the regulatory language ( § 63.6590( b)) appears to indicate that engines less than or equal to 500 HP, emergency/ limited use engines, and existing 2SLB, 4SLB, and CI RICE are part of the affected source but have exceptions from rule requirements. However, the preamble language in II. A ( 67 FR 77833) says " this proposed rule applies to you if..., except if your stationary RICE are all rated at or under 500 brake horsepower." The preamble language would suggest that RICE less than or equal to 500 HP are not subject to the rule and therefore are not in the affected source.

Response: Engines less than or equal to 500 HP are included in the RICE major source category, but are not covered by the final rule. The EPA is covering area sources and small engines in a later rule. The EPA recognizes that in the proposed rule it was unclear which engines were affected sources and has therefore made the appropriate revisions to the regulatory text in § 63.6590 to clearly indicate that the final rule applies to stationary RICE with a site rating of more than 500 HP located at major sources. Therefore, emergency power units, limited use units, engines with annual landfill and digester gas consumption 10 percent or more of the gross heat input on an annual basis, and existing 2SLB, existing 4SLB, and existing CI RICE are affected sources. Existing emergency power units, existing limited use units, existing engines that combust landfill gas or digester gas equivalent to 10 percent or more of the gross heat input on an annual basis, existing 2SLB, existing 4SLB, and existing CI engines have no requirements in the final rule. New and reconstructed emergency power units and new and reconstructed limited use units must only submit an initial notification. New and reconstructed engines that combust landfill gas or digester gas equivalent to 10 percent or more of the gross heat input on an annual basis must record and report the annual fuel usage in addition to submitting an initial notification.

I. A. 3 Comment: One commenter ( 545) asked that EPA clarify § § 63.6590( b), 63.6600( c), and 63.6640( f). These sections are missing the word " existing."

Response: The EPA agrees with the commenter and has added the word " existing" in front of " compression ignition" in § § 63.6590( b)( 3) ( previously § 63.6590( b)( 2)), 63.6600( c), and 12 63.6640( e) ( previously § 63.6640( f)). The EPA has also added " existing" in front of " 4SLB" in § 63.6600( c).

I. A. 4 Comment: One commenter ( 570) noted that § 63.6590( b)( 2) states that existing 2SLB, 4SLB, and CI do " not have to meet the requirements of this subpart and of subpart A of this part." The commenter stated that § 63.6600( c) leaves the impression, however, that some requirements for these sources beyond those listed in Tables 1( a), 2( a), 1( b), and 2( b) of the proposed rule do indeed apply. Similarly with § 63.6640( f). The commenter recommended removing § 63.6600( c) and modifying § 63.6640( f) to eliminate confusion.

Response: The EPA feels these sections are clear as written and do not need revision. The EPA thinks the revisions suggested would actually add confusion because it would omit important clarifying information.

I. A. 5 Comment: One commenter ( 585) requested clarification on what is considered an existing RICE unit for purposes of compliance. According to the commenter, using a date as a determination whether an engine is existing is confusing. The commenter stated that an engine takes on its identity when first assembled into an engine or when modified to be a different kind of engine, regardless of where that engine is ultimately installed or whether it is a spare on the shelf awaiting installation. Another commenter ( 565) asked that EPA clarify that an existing RICE unit is any engine that was assembled as a final unit before December 19, 2002, regardless of whether it was or has been installed in a stationary location.

One commenter ( 565) stated that the criteria that makes a RICE unit affected by the proposed rule does not limit the rule's effects to only units that operate. The proposed factors that determine applicability are construction date, manufacturer's nameplate rating, and specific inherent designs of units. None of these criteria as applied in the proposal include a requirement that the engine be operational. It is not uncommon for an owner or operator to have idle engines. Some may be installed and not in use. Others may be stored for later use as replacements or spare engines. Importantly, idle units are distinct from emergency power/ limited use units because an idle unit is not in any use. The commenter expressed that an idle RICE unit should have no compliance obligations imposed by the final RICE rule.

Response: The EPA disagrees with the first set of comments and feels that the date an engine was constructed is the date it was installed at the operator site and not when it was assembled as a final unit at the manufacturer. Thus, any engine constructed ( i. e., installed at the site of the operator) prior to December 19, 2002, is an existing engine for purposes of the final rule, while any engine constructed on or after that date is a new engine. For purposes of the final rule, the term " on site fabrication" in the definition of construction in 40 CFR § 63.2 shall refer to the final installation at the site of the final operator. This definition of construction is in line with how EPA generally defines construction, i. e., it is defined by when the unit is installed at the operator's location, rather than where it is first assembled. 13 The EPA feels it is appropriate to define " on site fabrication" as the final site of installation because even after a unit has been manufactured, several components necessary in order to be able to operate the unit must be considered and added. The owner or operator cannot go directly from purchasing the unit from the manufacturer to operation. The owner or operator must typically have a building to house the unit in, construct a pad for the unit, run utilities, install fuel supply tanks or run the natural gas line, have the catalyst vendor install the pollution control equipment, and finally test the unit on site. For larger engines ( e. g., 5,000 HP or greater), the installation process is even more pronounced. For these reasons, EPA finds it appropriate that the date that final installation of the unit at the site of operation is commenced should be considered the construction date.

Engines manufactured prior to December 19, 2002, but where installation was not commenced until after that date, are considered new engines and must comply with the requirements for new engines. The EPA expects that these units will be able to comply with the requirements especially since the control equipment is typically installed on the engine at the site of operation and does not come with the engine purchased from the manufacturer. Finally, no problems are expected to occur with retrofit controls because the control technology is relatively easy to retrofit, especially in units that are being installed initially at a site. If owners or operators anticipate problems, they can elect to purchase a new engine meeting the requirements if it is installed after that date.

With regard to the next comment, the EPA disagrees with the commenter's proposition that EPA needs to have a special provision to deal with engines that are installed but not in use. For new engines covered by the final rule, which will be the vast majority of the engines, the final rule does not apply until startup of the engine, which is when the engine begins operation. Therefore, new engines are not covered until they are operational, which already accomplishes the goal of the commenter. For existing engines, EPA feels that any engine that does not meet the definition of limited use engine, which includes engines that operate less than 100 hours per year, should not be relieved of compliance obligations. The EPA has written its definitions to distinguish emergency engines from limited use engines, which should reduce some confusion. An engine that does not operate at all is clearly a limited use engine, which by definition includes engines that operate 0 hours per year.

I. A. 6 Comment: One commenter ( 569) asked that EPA clarify the overlap between RICE subcategories. For example, it is not clear whether an emergency power unit with a nameplate rating of 400 HP is subject to the requirements of § 63.6590( b)( 1) or § 63.6590( b)( 2). One could argue that a 5 HP gasoline generator at a major source is subject to the initial notification requirements because it fits into the subcategory for emergency/ limited use engines. In the same manner, it is not clear whether an existing emergency power unit that is driven by a CI engine is subject to the requirements of § 63.6590( b)( 1) or § 63.6590( b)( 2) because the unit fits into two categories.

Response: The EPA has clarified the overlap between RICE subcategories in the final rule. For example, an emergency power unit with a nameplate rating of 400 HP would not be 14 subject to the rule since it is below 500 HP. Any engine rated at less than or equal to 500 HP is not covered by the final rule and does not have any requirements under the final rule. An existing emergency power unit that is driven by a CI engine would not be subject to any requirements of the rule since it is an existing emergency power unit. An existing emergency power unit greater than 500 HP that is driven by a 4 stroke rich burn ( 4SRB) engine would not be subject to any requirements of the rule either.

B. Applicability Cutoff I. B. 1 Comment: Eight commenters ( 542, 549, 551, 554, 583, 556, 580, 587) expressed that EPA should include an alternative applicability criteria based on 1 ton per year ( tpy) actual formaldehyde emissions.

Response: The basis for this comment is the Oil and Natural Gas Production and Natural Gas Transmission and Storage NESHAP ( promulgated on June 17, 1999). In that rule, hazardous air pollutants ( HAP) emissions from process vents at glycol dehydration units that are located at major HAP sources and from process vents at certain area source glycol dehydration units are required to be controlled unless the actual flowrate of natural gas in the unit is less than 85,000 cubic meters per day ( 3.0 million standard cubic feet per day), on an annual average basis, or the benzene emissions from the unit are less than 0.9 megagrams per year ( 1 tpy). The 1 tpy emission threshold in the Oil and Natural Gas Production and Natural Gas Transmission and Storage MACT is equivalent to the smallest size glycol dehydration unit with control of HAP emissions and is, therefore, based on equivalence, not risk. The information in the docket does not support a decision to provide an alternative applicability cutoff in this case. The EPA's decision to defer regulation of engines 500 HP or less was based on questions regarding how accurately the database reflected such engines. There was no such concerns raised based on whether an engine emitted formaldehyde above 1 tpy.

I. B. 2 Comment: Six commenters ( 542, 549, 551, 554, 556, 587) stated that the applicability limit for 2SLB should be increased to 1,100 HP to be consistent with the MACT floor. One commenter ( 565) stated that the small engine size cutoff should be changed from 500 HP to 650 HP. The commenter said that while EPA appropriately reasoned that small engines should not be subject to the requirements of the rule, EPA provided no explicit rationale for the selection of 500 HP as the appropriate small engine size cutoff. Ranking all engines in EPA's database from smallest to largest, the first engine size that has controls is 650 HP. Thus, the appropriate small engine size cutoff supported by the record is less than 650 HP instead of less than or equal to 500 HP.

One commenter ( 588) did not agree that 4SLB engines less than 500 HP are not regarded as significant sources of emissions. Since 1998, Wyoming has permitted approximately 350 571 F18GL engines rated at 400 HP. Of this number, 218 or 63 percent have permit conditions requiring the installation of oxidation catalyst to control formaldehyde. The commenter contends that 4SLB engines greater than 350 HP, located at major sources should be covered under the 15 MACT standard.

Response: First, EPA needs to clarify that engines 500 brake HP or less have not been exempted from regulation. Because EPA determined at the time of proposal that it did not have enough information to go forward with regulation of those engines at this time, EPA has deferred regulatory activity with regard to those engines. Pursuant to a consent decree signed on May 22, 2003, Sierra Club v. Whitman, Case Number 1: 01CV01537 ( D. C. D. C), a notice of proposed rulemaking regarding regulation of these engines under CAA section 112 is scheduled for October 31, 2006, with a final rule by December 20, 2007. At this time, it would be inappropriate to speculate on what level of control would be promulgated for these engines.

The EPA is aware of stationary engines as small as 650 HP that are equipped with add on HAP control devices. The EPA feels the database represented the population of engines between 500 HP and 1,100 HP reasonably well, so EPA does not feel it is appropriate to defer regulation of these engines to a later rule. Therefore, EPA does not feel it is appropriate to defer the regulation of engines up to 1,100 HP for 2SLB engines, or to include such engines in a separate subcategory. Although 650 HP is the smallest size unit that is known to have add on HAP control, EPA feels it is appropriate to limit the deferral to engines 500 HP or less because the control technology used for 650 HP units can be transferred to units at least as small as 500 HP in size. Oxidation catalyst technology is not limited to engines greater than 650 HP in size. In fact, information received during the public comment period supports our conclusion, where several engines rated at 400 HP were equipped with oxidation catalyst control. The EPA's deferral of engine regulation was based on the type of engines used below 500 HP and whether our database was adequate for such engines. The EPA feels the database for engines above 500 HP was adequate and that, in any case, the final rule for these engines are adequately justified in the record. The commenter does not adequately provide particular reasons to justify placing engines between 500 and 650 HP in a different subcategory from larger engines, and EPA does not feel such subcategorization has been shown to be appropriate.

The EPA acknowledges the information provided by the commenter regarding the Wyoming engines. This information could well be relevant when EPA reviews engines 500 HP and below and engines at area sources in the later rule.

I. B. 3 Comment: One commenter ( 555) asserted that the rule should be more explicit as to whether the 500 HP capacity level for exception from the rule and 5,000 HP capacity level for enhanced monitoring applies to an individual engine or applies to the aggregate capacity of a group of engines.

Response: The EPA intended for the 500 HP capacity level to apply to an individual engine, not the aggregate capacity of a group of engines. Similarly, the 5,000 HP capacity level for enhanced monitoring was intended to apply to an individual engine. However, EPA has not included a carbon monoxide ( CO) continuous emissions monitoring system ( CEMS) requirement in the final rule. Sources are free to use CO CEMS to demonstrate compliance; however, CO 16 CEMS are not required.

I. B. 4 Comment: One commenter ( 527) questioned if the rule is reasonable for engines. The commenter indicated that studies show that formaldehyde constitutes 90 percent or more of the total HAP emissions. The commenter stated that this means that natural gas fueled engines total HAP emissions cannot exceed 11.1 tpy.

Response: The EPA contacted the commenter for additional information regarding this comment and to clarify. The commenter stated that with respect to the rule for HAP, the commenter noted that a source would not be covered by the final rule if it emitted less than 25 tpy of all types of materials considered to be HAP. This means that a site could emit 9 tpy of formaldehyde, 8 tpy of a second HAP, and 7 tpy of a third HAP ( totaling 24 tpy) and still be below the rule limits. Numerous tests of emissions from natural gas engines have shown that these units emit primarily the formaldehyde HAP and very little other HAP. This is a direct result of combustion chemistry and is not likely to change by changes of operating conditions. The commenter further stated that nevertheless, the rule regulated sources that emit a single species of HAP at 10 tpy, which the commenter claims places an additional restriction on natural gas engines compared to other industrial sites that emit several HAP. The origin of the 11.1 tpy figure can from using an estimated emissions mix of 90 percent formaldehyde and 10 percent other HAP to estimate the maximum total HAP that could be emitted by a natural gas engine site ( 10 tpy + 10 tpy x 10 percent/ 90 percent = 11.1 tpy. The commenter therefore proposed that the rule for the maximum emissions of a single HAP be amended to enable the maximum emissions by a single HAP to be 20 tpy for the cases of engines using natural gas fuel. The commenter concluded by stating that because of combustion chemistry, such a rule would still ensure the site maximum would not exceed the 25 tpy.

The EPA is required by section 112 of the CAA to list categories and subcategories of major sources and area sources of HAP and to establish NESHAP for the listed source categories and subcategories. The final rule is limited to major sources. The CAA defines major sources of HAP to be those that have the potential to emit greater than 10 tpy of any one HAP or 25 tpy of any combination of HAP. Moreover, the determination of whether a source is a major source is made by counting the emissions of all stationary sources located within a contiguous area and under common control. Therefore, EPA cannot look at the emissions of an engine in isolation when determining whether it is located at a major source. The suggested revision and the logic underlying the comment are therefore not consistent with the specific requirements of the CAA. I. B. 5 Comment: One commenter ( 565) stated that EPA retains the authority to establish applicability criteria that focus the rule on the emission units emitting HAP using de minimis criteria. Despite the National Lime II and CKRC cases, EPA has not lost any of its discretion to establish applicability criteria that define the source category and the units subject to a MACT standard. The EPA should revisit its decision that it does not have de minimis authority. The EPA's interpretation, discussed in National Lime II, that it lost its inherent authority to relieve burdens of regulation where they yield trivial or no value is based on an incorrect analysis of the wrong provision of the statute. The commenter suggested that EPA should not take such a 17 restrictive position on its de minimis authority. The commenter suggested that EPA reexamine its policy that de minimis exclusions are unavailable when EPA calculates a floor, see National Lime II, supra at 640, because that policy was based on an incorrect analysis of the statute. Even if EPA does not alter that policy, the commenter noted that it does not affect EPA's inherent authority to craft de minimis exclusions unrelated to setting the MACT floor.

Response: The EPA thanks the commenter for its analysis. However, as the commenter does not relate the analysis to any particular decision of the Agency in the proposed rule, the EPA does not feel that it is necessary or appropriate to respond to the comment here. It would be more appropriate to review the legal analysis where it can be applied to a particular set of facts that are relevant to the particular regulatory action being addressed.

C. Exemptions I. C. 1 Comment: Two commenters ( 526, 579) requested that EPA exempt units ( new and existing) with non selective catalytic reduction ( NSCR) or oxidation catalyst that have been installed in compliance with other regulatory mandates to avoid potential conflict.

Response: The EPA does not agree with the commenters who suggested an exemption for existing and new units with NSCR or oxidation catalyst controls that have been installed in compliance with other regulations. The EPA has therefore not exempted units with NSCR or oxidation catalyst controls that have been installed in compliance with other regulations from the final rule. These units are covered and must demonstrate compliance. The EPA may look at the rule again at a later date following promulgation if some subgroup of new engines do not appear to be able to meet the standards either through the designated control technique or through other types of reasonable controls, but such evidence does not exist in this record. For existing engines, the Act understood that some engines are already controlled may not meet the requirements of the MACT, which is designed to achieve the control achieved by the average of the best controlled 12 percent of engines.

I. C. 2 Comment: One commenter ( 604) contended that the MACT should consider exempting any RICE using landfill gas. A diesel engine can operate at a landfill in a dual fuel mode using fuel oil and landfill gas. Tests have shown that a catalytic converter cannot be used because of siloxanes in the landfill gas, even if the engine operates with more than half the energy being supplied by the liquid fuel.

Six commenters ( 526, 544, 547, 565, 579, 584) expressed support for EPA's approach to deal with engines with landfill gas. Commenters 526, 579, and 584 agreed that fuel switching is an environmentally inferior option. Commenter 584 agreed with EPA that emissions reductions for landfill gas powered engines are not required.

Response: In the proposed rule, EPA had established a subcategory for landfill and digester gas fired units and defined the subcategory as those stationary RICE that combust 18 digester gas or landfill gas as the primary fuel. In the proposed rule, these units did not have to meet any emission limitation requirements but were subject to the initial notification requirements. The EPA agrees with the commenters supporting the proposed approach to landfill and digester gas fired engines. The EPA agrees that neither control technology, fuel switching, or other practices would be an appropriate or workable strategy for reducing HAP from these engines. The EPA agrees with the commenter that problems will occur when using landfill gas because of siloxanes in the fuel, even if the engine operates with more than half the energy being supplied by the liquid fuel. Therefore, EPA contacted sanitation districts and catalyst vendors for information. Based on the information obtained, EPA feels that firing greater than 10 percent landfill or digester gas will cause fouling of the oxidation catalyst, rendering the control device inoperable within a short period of time. All the sources EPA contacted indicated that there would be problems associated with catalyst deactivation due to siloxanes present in landfill and digester gas. For further information please refer to the memorandum entitled " Stationary Combustion Turbines and Reciprocating Internal Combustion Engines fired with Landfill or Digester Gas" available from EPA's Edocket Website ( Docket Number OAR 2002 0059 ( A 95 35)). While most units will operate using landfill or digester gas consumption above 50 percent of the time, there are times when such units may need to operate significantly below 50 percent landfill or digester gas consumption. The EPA feels a cutoff level of 10 percent of gross heat input is an appropriate level for defining these units, because operation below that percentage raises significant questions regarding whether the unit is still appropriately considered operating as a landfill or digester gas burning unit, and would raise concerns regarding circumvention of the requirements for other new units. In the final rule, EPA has defined the subcategory as those engines with annual landfill and digester gas consumption of 10 percent or more of the gross heat input on an annual basis. Engines in this subcategory must only comply with limited requirements of the final rule. Engines with an annual landfill and digester gas consumption of less than 10 percent of the gross heat input on an annual basis are subject to applicable emission limitations of the final rule in addition to other requirements.

I. C. 3 Comment: One commenter ( 605) requested that EPA consider the use of pre gas treatment for digester and landfill gas fired engines, thereby allowing use of oxidation catalysts for HAP reduction.

Response: The EPA investigated the use of pre gas treatment for digester and landfill gas fired engines. The EPA considered a pretreatment system. However the cost of such systems were deemed prohibitive. There is also very limited experience in the use of pretreatment systems to remove siloxanes. As a result, there is insufficient information on the siloxane removal effectiveness of pretreatment systems. The EPA is aware of pretreatment systems being applied to certain facilities. However, more testing is required to verify the long term performance of the pretreatment system and its effect on catalysts. Please refer to the memorandum entitled " Control Technology Options for Existing Digester Gas and Landfill Gas Engines," available from EPA's Edocket Website ( Docket Number OAR 2002 0059 ( A 95 35)) and the memorandum entitled " Stationary Combustion Turbines and Reciprocating Internal Combustion Engines fired with Landfill or Digester Gas" available from EPA's Edocket Website ( Docket Number OAR 2002 19 0059 ( A 95 35)) for more information.

I. C. 4 Comment: Two commenters ( 549, 551) asked for clarification on whether the rule intends to cover stationary internal combustion engines at refineries that are used for fuel testing. It is the commenters' understanding that this rule, as opposed to the Engine Test Cell/ Stand MACT governs those sources, as applicable.

Response: Stationary internal combustion engines at refineries that are used for fuel testing are covered by the final rule. Knock engines are used at refineries, and do not test the engine per se but instead test the fuels and lubricants for product quality and development purposes. They are therefore covered by this rule as opposed to the Engine Test Cell/ Stand MACT. The engines are typically smaller units and are similar to automotive engines commonly ranging from 100 to 200 HP in size. If the units used for fuel testing are 500 HP or less they would not be covered by the final rule.

I. C. 5 Comment: Four commenters ( 544, 547, 565, 569) expressed support for the Agency's decision not to require emissions limitations for existing 2SLB, existing 4SLB, existing CI, emergency power/ limited use, and 500 HP or less. One commenter ( 549) supported EPA setting a " No Control" floor and exemption for existing 2SLB, 4SLB, and CI stationary RICE. One commenter ( 565) also supported the exemption for stationary RICE test cells and stands. Commenter 575 agreed with the decision to subcategorize very small sources ( 500 HP or less) and to defer the standard setting decision, in light of the scarcity of data and apparently trivial emissions attributable to these units. One commenter ( 553) expressed support for EPA's exclusion of emergency and limited use engines.

One commenter ( 575) endorsed EPA's proposal to establish an emergency power subcategory for stationary RICE, with emergency defined with reference to the use of a stationary RICE as a power source when the primary power source for a facility has been rendered inoperable by an emergency situation ( without reference to a specific number of hours). The commenter also stated that the decision that the MACT floor is no emissions reduction is appropriate.

Response: The EPA acknowledges the commenters' support. Also note that engines less than or equal to 500 HP are not covered by the final rule. The EPA is covering area and small sources in a later rule.

I. C. 6 Comment: One commenter ( 594) stated that the proposal that the MACT floor for existing CI be no emissions reductions is endorsed. The finding that less than 1 percent of existing CI have controls is consistent with the commenter's experience and supports the floor finding.

Response: The EPA has noted the commenter's support.

I. C. 7 Comment: One commenter ( 584) stated that EPA should not develop NESHAP 20 for engines that utilize landfill gas because these engines are one of the control technologies mandated by the municipal solid waste landfill NESHAP. As such, EPA should not be regulating control devices with control devices.

Response: The commenter provided no legal support for its position that a pollution source should be exempt from CAA section 112( d) because it may have been installed to comply with other requirements. In any case, the commenter otherwise agreed with EPA's approach to regulating engines operating on landfill or digester gas, which are not required to meet emission limitations.

D. Emergency/ Limited Use I. D. 1 Comment: One commenter ( 544) stated that the limited use definition for RICE should be separated from the emergency power definition since these are really different applications. Another commenter ( 565) said that including both types of units in the same definition creates challenges in determining which criteria apply to each use and how to characterize a unit that may have both functions. Commenter 565 suggested that for clarity, the descriptions of each type of unit may require separation in the rule. Second, in defining each unit type EPA needs to also address related functions performed on each unit type that are required to support the primary function of the unit. This commenter also stated that EPA should clarify the application of the emergency power/ limited use definition to multi use units ( both emergency use and limited non emergency use).

Twenty three commenters ( 536, 540, 542, 544, 545, 547, 548, 551, 552, 553, 554, 556, 560, 562, 565, 566, 571, 573, 587, 593, 594, 595, 603( D)) stated that a limited use category should be included. One commenter ( 536) suggested using a flat annual threshold level of 1,000 hrs/ yr in lieu of 10 percent usage. Another commenter ( 545) recommended that the category include all units, not only peak shaving units. One commenter ( 551) recommended that this category should include all periods of testing and maintenance. Two commenters ( 548, 560) stated that in the event that a limited use RICE exceeds 876 hours in 1 year, EPA should allow 1 year for the owner or operator to meet the MACT standard. One commenter ( 595) agreed with EPA that limited use RICE are appropriate for subcategorization because " their use and operation are different compared to typical RICE." Two commenters ( 544, 565) suggested a 10 percent annual capacity factor for limited use.

Twenty seven commenters ( 526, 540, 542, 544, 547, 548, 549, 552, 554, 555, 556, 557, 558, 559, 560, 564, 565, 569, 571, 573, 575, 576, 577, 579, 581, 858, 587, 595) argued that the 50 hrs/ yr may not be sufficient. Six commenters ( 540, 558, 569, 576, 577, 581) noted that testing and maintenance should be included and not counted towards the 50 hrs/ yr. Two commenters ( 548, 560) recommended at least 250 hrs/ yr. In the event that an engine exceeds 250 hours in 1 year, EPA should allow 1 year for the owners and operators to meet the standard. One commenter ( 549) stated that the number of hours for emergency/ limited use exclusion should be increased to provide for periodic reliability and maintenance testing. One commenter ( 560) 21 recommended a 52 hour limit for routine maintenance and testing, then have no limit for true emergency use. Similarly, commenters 544 and 565 expressed that since routine or unscheduled maintenance and testing could require unknown time to complete, there should be no time limits on the use of emergency stationary RICE. Another commenter ( 555) contended that 52 hrs/ yr is satisfactory for most engines. However, engines located at airports can require up to 100 hrs/ yr and engines at nuclear power plants can require up to 200 hrs/ yr. Seven commenters ( 542, 552, 554, 556, 571, 573, 587) suggested 100 hrs/ yr for emergency generators. Two commenters ( 569, 564) recommended that the 50 hours should be extended to 10 percent. One commenter ( 547) asked that EPA clarify that testing is allowed as an emergency use. Two commenters ( 549, 559) recommended that the 50 hrs/ yr definition be changed to mean an engine whose operation is restricted by federally enforceable limits to less than 876 hrs/ yr. One commenter ( 595) stated that the subcategory should be redefined to include RICE that operate less than 500 hrs/ yr. In the event that an emergency power RICE exceeds 500 hours in 1 year, EPA should allow 1 year for the owners and operators to meet the MACT standard, if necessary. The 500 hours of operation would be consistent with Ohio Administrative Code 3745 31 03 ( A)( 4) which grants emergency generators greater than 50 HP a permit by rule permit to install exemption if the unit operates less than 500 hours per rolling 12 month period. Two commenters ( 526, 579) remarked that setting this exemption at 50 hrs/ yr down from the 100 or 200 hrs/ yr commonly seen in many State air pollution regulations, could have the net effect of increasing pollution by not allowing sufficient operating time for the engine to burn off hard deposits. One commenter ( 585) expressed that testing of engines be excluded from the 50 hrs/ yr or the threshold limit of this subcategory be changed from 50 hrs/ yr to be 10 percent of the annual capacity factor. One commenter ( 575) asked that these units should be allowed to run for normal maintenance purposes. Commenter 573 suggested that the testing of engines be excluded from the definition or the threshold limit of the subcategory be changed from 50 hours to be 10 percent of the annual capacity factor. One commenter ( 557) urged further study of the stringent testing time guidelines suggested and refrain from implementation until such data can be reviewed and offered in a proper consensus forum.

Two commenters ( 544, 565) stated that the operation of emergency power units should not be limited to only those times when the primary power source has been interrupted, but rather not time restricted at all, providing the primary design purpose of the unit is to provide emergency backup services, fire water, etc.

One commenter ( 555) asked that EPA clarify the definition of emergency/ limited use engines as to whether loss power that constitutes an emergency is limited to power supplied to the facility as a whole or includes power supplied to portions of the facility.

One commenter ( 552) suggested that EPA revise the definition of emergency power RICE to clarify the intent of the rule as the current definition does not adequately encompass the wide array of emergency uses of engines.

One commenter ( 594) endorsed the proposed subcategory of no emission reduction for RICE associated with emergency power/ limited use and the specific allowance for 50 hours of incidental 22 use in non emergency mode.

One commenter ( 565) felt that the description of an emergency engine is too restrictive. The emergency use description should describe more power loss emergencies than those affecting an entire facility at once. The commenter stated that EPA should clarify that emergency use also occurs when a standby or emergency unit activates to replace the function or perform an emergency function that arises from the sudden inoperability of one or more pieces of equipment on a site. The definition should also include uses for additional emergency types beyond power loss emergencies, e. g., fuel and raw material curtailments or fuel shortage emergencies applied by governments, utilities, or other suppliers may require the need to temporarily operate an engine, or some equipment may be operated to fight fires ( firewater pumps). Neither of these examples represent loss of power, but are still unplanned events.

One commenter ( 577) requested that EPA provide further clarification on the term to include provisions for scenarios such as power fluctuations and requests by local utility to run their generators.

One commenter ( 576) said that when healthcare facilities operate their emergency generators due to severe weather conditions or inability of the local utility to provide acceptable power, healthcare organizations should be allowed to operate their generators in support of equipment/ systems critical to patient/ resident care.

One commenter ( 573) noted that the definition should be revised to include operation at control centers for human spaceflight to provide power in and to allow for operation due to foreseeable but critical electrical outages or events anticipation of power failure due to severe storm activity.

One commenter ( 555) stated that the definition should be clarified, or extended, to allow for operations in anticipation of an emergency situation.

One commenter ( 567) remarked that this class of RICE ( engines having a capacity utilization of less than 10 percent) would operate mostly in the summer months when the public is more likely to be impacted by the emissions. Acetaldehyde, acrolein, and formaldehyde all have documented short term acute health effects. The EPA has failed to identify short term health effects throughout any of the risk analysis proposals. The commenter asserted that any subcategorization of these engines without controls is not protective of public health.

One commenter ( 566) contended that the subcategory of limited use must be tightly defined in terms of capacity and utilization, rather than the descriptive term " peak shaving," since limited use stationary RICE will perform functions other than just peak shaving. Since EPA has determined that these units will likely have a floor of no emissions reductions, it would not be appropriate to require anything other than an initial notification and a requirement to submit annual records of total operating hours. 23 One commenter ( 567) said that any subcategorization of RICE operated less than 876 hrs/ yr should include a permit requirement that these units operate less than 876 hrs/ yr. The commenter further noted that this class could have less onerous monitoring requirements as a way to lower costs for these engines especially when the low amount of operating hours are considered.

One commenter ( 553) expressed support for an " emergency use" subcategory that adds to the definition of " emergency use" units as alternative to limited use category. The commenter strongly supported an " emergency use" subcategory that construes " emergency use" more broadly to include the use of peak shaving units during periods of high demand. Inevitably, during periods of peak demand when nearly all the available generating units are dispatched, " capacity alerts" are declared. The alerts are issued with varying degrees of severity. The commenter supported the inclusion of " generation emergencies" in its definition of " emergency use." Specifically, the commenter supported a determination by EPA that, at a particular level of severity, the alerts constitute an " emergency," for which there is no limitation in terms of hours of percentage of capacity used.

One commenter ( 544) argued that the limited use definition for RICE should be separated from the emergency power definition since these are really different applications.

One commenter ( 585) stated that the definition of emergency should be expanded to include nonemergency hours of operation that are supportive of emergency situations. In addition, the definition should not have any time limits specified on emergency RICE units.

One commenter ( 544) indicated that the definition needs to allow for periodic testing of the RICE unit to ensure that it is reliable and available should an emergency occur, in addition to the time it may be required to provide emergency service.

One commenter ( 540) supported that the definition of emergency engine does not limit the number of emergency hours allowed for the unit.

One commenter ( 593) stated that the definition of emergency power/ limited use needs to be changed as it does not allow enough operating time for non emergency use of RICE and does not cover all the emergency uses of RICE. The definition should include non emergency hours of operation that are supportive of emergency mode operations. For example, the emergency use should also cover the periodic testing of the RICE unit to ensure that it is reliable and available should an emergency occur. The current language appears to limit these test periods to less than 50 hours per year. The EPA should clarify that emergency use occurs when a standby or emergency unit activates to replace the function or perform an emergency function that arises from the sudden inoperability of one or more pieces of equipment on a site. The commenter recommended modifying the definition to include periods of operation in response to plant emergency situations whether or not primary power is lost.

One commenter ( 564) suggested eliminating from the definition the reference to " when the 24 primary power source has been rendered inoperable." There are emergency conditions where the primary power source is still operable, but the emergency condition necessitates the startup of engines ( e. g., firewater pumps during a unit fire, instrument air back up engines). Another option would be to add the words " or is insufficient for an emergency situation" after the primary power source comment. In addition, the commenter stated that the definition for emergency RICE should include the testing of emergency engines to ensure their availability and reliability for emergency situations.

One commenter ( 548) remarked that the definition of emergency use/ limited power could be improved as follows: " An emergency power/ limited use unit means any stationary RICE that operates as a mechanical or electric power source during emergencies, when the primary power source for a facility has been rendered inoperable by an emergency situation and units that operate less than 250 hours per year in non emergency situations or for equipment testing and maintenance, including certain peaking units at electric facilities or stationary RICE at industrial facilities. One example of an emergency situation is when electric power from the local utility is interrupted. Another example is to pump water in the case of fire or flood."

Response: The preamble to the proposed rule proposed a subcategory for limited use stationary RICE and defined them as operating 50 hours or less per calendar year. Comments received indicated that the proposed 50 hours per year for limited use units was not sufficient and that many limited use engines would exceed the 50 hours per year just by routine testing and maintenance of the engine for readiness purposes. For this reason, EPA feels that few owners and operators would find this allowance useful and would not serve a purpose except to cover periods of testing and maintenance. The EPA has, therefore, found it appropriate to increase the number of hours for limited use operation. The EPA has specified in the final rule that limited use stationary RICE are stationary RICE that operate less than 100 hours per year. For limited use units, operation during routine testing and maintenance is counted towards the 100 hours per year.

In the preamble to the proposed rule, EPA solicited comments on creating a subcategory of limited use engines with capacity utilization of 10 percent or less ( 876 or fewer hours of annual operation). These units would have included engines used for electric power peak shaving. As a result of soliciting comments, EPA received several comments regarding the possibility of establishing a limited use subcategory with capacity utilization of 10 percent or less; some for and some against. The EPA considered all comments received and has decided not to include a subcategory of limited use stationary RICE with a capacity utilization of 10 percent or less in the final rule. Limited use units operating 876 hours per year are similar to other sources equipped with add on oxidation catalyst control and their operation only during peak periods does not preclude them from being equipped with add on oxidation catalyst control. Those commenters supporting a longer time period for the limited use engines did not provide persuasive arguments for such a subcategory. The commenters have not provided significant data indicating that engines operating up to 10 percent of the time ( or longer, as some commenters suggested) are unable to take steps similar to other RICE to reduce HAP. On the contrary, as stated previously, 25 such engines are similar to other stationary RICE that can be and have been equipped with add on oxidation catalyst control, and their operation only during peak periods does not preclude them from being equipped with workable add on control or from using other methods of emission control to reduce HAP. The 10 percent time limit would allow over a month of usage per year, which EPA feels is substantial enough both to be of concern environmentally and to take advantage of emission control strategies. Significant operation of these engines is expected and should be accounted for in the final rule.

By contrast, a limited use exemption covering only 100 hours per year of use is justified because usage in these cases in clearly exceptional and these engines would have the technical and usage concerns similar to emergency engines discussed in the proposed rule. These engines are categorically different from other engines in that they are only used in truly exceptional situations. For these reason, EPA has not established a limited use subcategory of units operating 876 hours per year in the final rule, but has included a limited use subcategory allowing engines to operate up to 100 hours per year.

The EPA does not agree with the commenters who suggested that in the event that a limited use engine exceeds the set amount, EPA should allow 1 year for the owners and operators to meet the standard. The EPA feels that when limited use engines are put into more than limited service, these engines should be required to meet applicable standards in the timeframe specified. Owners and operators of limited use engines should be well aware of the possibility of these engines needing to be put into regular service and should plan accordingly. Therefore, a 1 year compliance timeframe is not needed.

The EPA agrees with the comment that the emergency and limited use stationary RICE definition should be separated. The EPA has established separate definitions for emergency stationary RICE and limited use stationary RICE in the final rule.

In addition, in the final rule, the definition of emergency engine was written to indicate that loss of power that constitutes an emergency can include power supplied to portions of a facility. The EPA intended that the definition of emergency engine include operation during emergency situations, including times when the primary power source has been interrupted as well as other situations such as pumping water in the case of fire or flood, which was given as an example of emergency operation in the definition in the proposed rule. The definition has been clarified to clearly indicate that emergency operation is not limited to only times when the primary power source has been interrupted. The EPA contacted the commenter for more information about the types of curtailments with which they were concerned. The commenter provided only one example, which was shutdown of offshore wells during a hurricane. The EPA feels that the definition of emergency stationary combustion engine is sufficient to cover this particular scenario and it is not necessary to include more examples of emergency operation. It would be nearly impossible to provide examples of every potential type of emergency situation. The operation of emergency engines is not limited to a specific number of hours. Also, routine testing and maintenance to ensure operational readiness have been included in the definition of emergency 26 engine. However, the routine testing and maintenance must be within limits recommended by the engine manufacturer or other entity such as an insurance company. Emergency stationary RICE may also operate an additional 50 hours per year in non emergency situations. As stated previously, routine testing and maintenance have been included in the definition of emergency stationary RICE and, therefore, are not counted towards the 50 hours per year. The EPA does not agree that operation in anticipation of an emergency situation should be included in the definition of emergency engine and has not included such an allowance in the final rule.

In response to the commenter who urged further study of the stringent testing time guidelines suggested and refrain from implementation until such data can be reviewed and offered in a proper consensus forum, the EPA believes that the above response, which indicates that maintenance and testing of emergency engines have been included in the definition of an emergency engine, satisfies the commenter's concern. There is no limit on the number of hours allowed for testing and maintenance, but the routine testing and maintenance must be within limits recommended by the engine manufacturer or other entity such as an insurance company.

I. D. 2 Comment: One commenter ( 566) requested clarification on the following situation. The commenter has an emergency system that provides controlled cooling water to cool its number 7 blast furnace in case of a loss of electrical power or a mechanical pump failure. The system consists of an elevated water storage tank/ tower and two 600 HP diesel engines that must be started before the storage capacity is depleted during an emergency situation to maintain the minimum required cooling water flow by pumping to the tower/ tank. The rule clarification is required for the fact that this system is also utilized for furnace shutdowns to perform required maintenance work to avoid catastrophic failures/ emergencies. The commenter said the intent of this operation fits within the definition of emergency power/ limited use, but this is not clear by the specific definition.

Response: This specific example would fall under the definition of emergency operation.

I. D. 3 Comment: One commenter ( 547) stated that some limited use units do not have stacks that meet the performance specification requirements, and consequently, emissions testing on such units may require the prohibitively expensive construction of such stacks. As a result of these differences, the commenter stated that EPA should create a separate subcategory for limited use RICE. The commenter supported a subcategory of limited use RICE with annual capacity utilization of 10 percent or less.

Response: The EPA has included a provision for limited use units in the final rule which allows limited use units to operate up to 100 hours per year without being subject to the emission and operating limitation requirements of the final rule. The rationale for defining limited use as those units that operate less than 100 hours per year as opposed to those that operate less than 876 hours per year was discussed in the response to comment I. D. 1. If the units the commenter is concerned with qualify as limited use units, which they may since EPA has increased the limited use amount from 50 to 100 hours per year, owners and operators would not have to comply with 27 the emission and operating limitations and would not have to conduct performance tests. However, it is not clear from the comment whether the commenter is referring to performance specifications for CO CEMS or if the commenter is referring to performance test requirements. The EPA proposed requiring CO CEMS for large lean burn and large CI engines complying with the requirement to reduce CO emissions. However, based on comments received, EPA is no longer requiring CO CEMS. Sources have the option of using CO CEMS, but it is not required. Therefore, CO CEMS performance specifications should not be an issue for these sources. If these units are not limited use units, EPA cannot exempt them from performance testing requirements. Section 63.7( d) of the General Provisions requires owners and operators to provide adequate performance testing facilities, including a stack. The commenter did not provide any information supporting why the construction of such stacks would be prohibitively expensive. The EPA therefore cannot address that comment specifically.

E. Compression Ignition I. E. 1 Comment: One commenter ( 526) requested that EPA delay the portion of the rule dealing with CI engines to avoid potential issues with diesel engines in California and some other states being subject to two different regulatory regimes, one for particulate matter ( PM) and the other for formaldehyde, thereby requiring two different control technologies.

Response: The EPA cannot delay the portion of the rule dealing with CI engines because it is under statutory and court deadlines to promulgate standards under CAA section 112 for these engines. Also, section 112 of the CAA specifies the deadlines required for meeting standards once they are promulgated. However, EPA does not feel that its provisions will generally have the effects that the commenter discusses. The rule applies only to new CI engines, so existing CI engines will not be affected. Moreover, for those sources that may be subject to California's regulations on existing engines, they should be able to deal with such regulations by purchasing engines or technologies that comply with both requirements, thus reducing some costs. Unfortunately, EPA is not able to stop or delay the rule because of the possible plans of other regulatory agencies; nor can EPA stop or delay regulation of one type of pollutant because another agency may be regulating a different pollutant that the source also emits. Reduction of pollution sometimes requires multiple controls to deal with multiple pollutant types.

I. E. 2 Comment: One commenter ( 562) expressed that EPA has correctly concluded that the MACT floor for CI engines is no emissions reductions. The EPA states less than 1 percent of the existing CI engines have emission control equipment installed. Because the CAA specifies that the MACT floor is to be set at the average emission limitation achieved by the best performing 12 percent of existing sources, EPA must conclude that the MACT floor is no emissions reductions. Also, EPA has correctly concluded that the potential beyond the floor MACT alternatives, oxidation catalyst and fuel switching, are inappropriate for existing CI engines.

Response: The EPA acknowledges the commenter's support. This approach has been 28 retained in the final rule.

I. E. 3 Comment: One commenter ( 546) recommended that the rule include a provision to exempt diesel engines in California that meet the requirements of California's Stationary Diesel Engine Airborne Toxic Control Measure ( ATCM). The commenter also argued that the recordkeeping, reporting, monitoring and testing requirements of the rule are not appropriate for diesel engines meeting a diesel PM emission standard. The commenter also felt that the annual source testing requirement in the rule is not necessary, appropriate or cost effective for engines with diesel particulate filters ( DPF).

The commenter expressed the view that the rule is not health protective in that it only regulates organic gases and ignores diesel PM. The rule should allow State and local agencies to regulate diesel PM as a more health protective alternative for addressing the risk from diesel exhaust.

Response: The EPA disagrees with the suggestion to exempt diesel engines meeting California's Stationary Diesel Engine ATCM. The EPA cannot exempt sources in a source category from meeting the MACT requirements. The EPA understands that California has been regulating diesel engines separately to reduce PM from diesel engines. Such emissions are not regulated in the final rule. However, the fact that a source in California must meet the requirements of the ATCM does not excuse it from meeting the separate Federal requirements of CAA section 112. The commenter's reference to section 209 is unavailing. The provision that authorizes California to regulate mobile (" nonroad") engines is irrelevant to EPA's separate obligation under CAA section 112 to regulate stationary engines.

The specific pollutants covered in the final rule are distinguishable from what was regulated in the California Air Resources Board ( CARB) rule. While California may believe diesel PM to be a greater health concern, CAA section 112 does not permit EPA to ignore the regulation of listed HAP in order to accommodate the separate regulation of other pollutants. Moreover, the commenter does not contend that the NESHAP will increase levels of diesel PM from engines that have a PM filter.

Of course, any source that can meet the pollutant concentration requirements mandated in the final rule using a filter, as well as any engine out controls necessary or appropriate, need not employ a catalyst. If the information provided in the comment is accurate, a source could in fact use certain types of particulate filters ( likely a catalyzed filter would be used) to meet the requirements of the NESHAP.

The commenter does not explain why the recordkeeping, reporting, monitoring and testing requirements of the proposed rule are inappropriate. Numerous sources in numerous categories are required to meet the requirements of different standards promulgated by different authorities. The commenter does not explain why this requirement is fundamentally different from others in that respect. The EPA cannot suspend the requirement to show compliance with its regulations merely because another jurisdiction has required sources to show compliance with its regulations. 29 No source in California has requested the relief suggested by CARB.

I. E. 4 Comment: One commenter ( 533) indicated that the usage of oxidation catalyst is not recommended in context with CI engines burning fuels containing sulfur. Oxidation catalysts less sensitive to sulfur dioxide ( SO 2) deactivation usually oxidize a large proportion of the SO 2 to sulfate ( SO 3) and as an end result additional sulfate PM ( small particulate) is formed. Another consequence of sulfate formulation is clogging, deactivation, etc. of the catalyst. The commenter proposed that EPA take a similar standpoint with compression ignition engines operating on fuels containing sulfur as was taken on RICE burning digester and landfill gas.

Response: The EPA consulted catalyst vendors who stated that oxidation of SO 2 to acid mist can occur over a catalyst. However, SO 2 emissions from both natural gas and distillate oil fired engines are very low, therefore the impact on PM emissions would be very low. In addition, the catalyst can be installed at a location where the temperature and the residence time would help to minimize the potential for SO 3 formation. During EPA's testing at Colorado State University ( CSU), low sulfur fuel was used and only a minimal increase in PM emissions was detected ( about 3 percent on average). The EPA expects that if higher sulfur fuel is used, there would be increased PM emissions. However, EPA expects that owners and operators will use low sulfur fuel where the increase in PM is expected to be small. Low sulfur fuel and ultra low sulfur fuel are currently available and will become more available as EPA's regulations for on highway diesel fuel, and, as expected, nonroad diesel fuel, are phased in over the next several years.

F. Subcategories I. F. 1 Comment: One commenter ( 555) recommended that EPA evaluate the ability of engines associated with military tactical equipment to comply with the standard and the associated costs and cost effectiveness and environmental benefits, and a separate category for these engines be established if warranted. Engines associated with military tactical support equipment are not addressed in the proposal. These engines are often located at one location ( military base) for more than 12 months and hence may not qualify as nonroad engines. However, such engines often have unique requirements for deployability that may preclude the use of add on air pollution control equipment.

Response: The EPA contacted the commenter for additional information regarding this comment. Based on the information received, it appears that most of the engines the commenter is concerned with are typically small units. The EPA would expect that few of the engines in question would be greater than 500 HP in size. The final rule does not cover engines 500 HP in size or less. For the engines that are covered by the final rule, the engines located at one location for more than 12 months are likely being stored and not operated. If the engines do not operate, they do not have to comply with any specific requirements of the final rule. When these engines are deployed in the field and operate, they would be considered mobile sources and would not covered by the final rule for stationary RICE. For these reasons, EPA feels that no separate subcategory is needed for these engines. 30 I. F. 2 Comment: One commenter ( 555) recommended that EPA evaluate the ability of cyclic engines to comply with the standard and the associated costs and cost effectiveness and environmental benefits, and a separate category for engines with cyclic operations be established if warranted. The test results upon which the standards are based do not cover operations at less than 50 percent load. Engines in cyclic operations may spend a large part of their time idling or operating far below 50 percent load with only brief periods at high load. Since the control effectiveness for oxidation catalysts and NSCR depends on the exhaust temperature and exhaust temperature is expected to decrease at low loads, engines with cyclic operations may not be able to comply with the standards or be able to comply only with prohibitively expensive control systems.

Response: The EPA has specified in the final rule that performance tests must be conducted at high load conditions, defined as 100 percent ± 10 percent. Sources are not required to meet the emission limitations at low load.

I. F. 3 Comment: One commenter ( 577) urged EPA to consider establishing an exception for hospital based units that occasionally peak shave in response to excessively high spot market prices. Only a few hours of peak shaving can provide tremendous financial relief from highenergy prices while producing a relatively small contribution to HAP. An American Society for Health Care Engineering poll indicated that only 39 of 482 hospitals routinely or occasionally peak shave with a range of 121 161 hrs/ yr ( in addition to emergency operation). This practice falls well below the 10 percent utilization in the proposed limited use subcategory.

Response: In the final rule, EPA has defined limited use stationary RICE as stationary RICE that operate less than 100 hours per year. There is no limit on the amount of hours an emergency stationary RICE is allowed to operate for emergency purposes. Emergency stationary RICE may use an additional 50 hours per year for non emergency use. The EPA feels that allowing 50 hours per year is appropriate and a sufficient amount to assist owners of emergency units.

I. F. 4 Comment: One commenter ( 570) requested a subcategory for new and reconstructed stationary CI RICE located in the State of Alaska that exempts the engines from the control requirements of this proposed rule. The commenter stated that EPA has overlooked the fact that low sulfur fuels ( less than 500 ppm ( parts per million) ( 0.05 weight percent)) are necessary for CO oxidation catalysts to operate properly and that these fuels are not available in several areas of the United States including the State of Alaska. Sulfur can quickly degrade oxidation catalyst performance for controlling CO ( or formaldehyde) emissions by poisoning the precious metal substrate of the catalyst. In one study it was found that increasing the diesel sulfur content from 3 ppm to 350 ppm by weight resulted in a three fold increase in catalyst out PM emissions. In the same study, the performance of the diesel oxidation catalyst for controlling CO emissions from the higher sulfur fuel degraded by an average of 10 percent after the short term ( 250 hour) aging tests. In Alaska meeting the proposed MACT floor ( oxidation catalyst) for new CI RICE sources will be problematic because of the non availability of low sulfur diesel fuels ( 300 31 to 500 ppm sulfur content by weight). The permitted diesel fuel sulfur content, by weight, for most permitted stationary CI sources is between 0.1 percent and 0.5 percent ( 1,000 ppm to 5,000 ppm by weight). The Trans Alaska Pipeline System facilities operated by the commenter have permitted sulfur fuel content limits between 0.24 percent to 0.5 percent. The lowest fuel sulfur diesel that is available in the State of Alaska is an arctic grade fuel that has a sulfur content of approximately 0.1 percent. Petroleum refineries in the State are not required to produce lower sulfur fuels because Alaska is exempted ( see 40 CFR part 69 of 69 FR 34126) from EPA's low sulfur highway diesel fuel standards.

Response: The EPA feels it is unnecessary to establish a subcategory for new and reconstructed CI RICE located in the State of Alaska. Information received from the Alaska Department of Environmental Conservation ( DEC) indicated that there is a refinery in Alaska that can produce low sulfur fuel ( 300 to 500 ppm sulfur content by weight). The refinery can make low sulfur diesel that meets arctic pour point specifications. The information from the Alaska DEC also indicated that low sulfur fuel is generally available where there are roads in Anchorage, but not generally available on other parts of the road system, such as Fairbanks. Some remote villages do have low sulfur fuel. The EPA expects availability to grow further as EPA's final rule implementing new sulfur limits for highway fuel, including fuel in Alaska ( 68 FR 5002, January 18, 2001), is implemented beginning in 2006. The Alaska DEC said that Alaska has 200 small villages that are remote, and it may be difficult for these small villages to always have low sulfur fuel available. These villages tend to employ RICE to generate electricity and have between two to four stationary RICE in their power plants. These engines range from 6 to 4000 kilowatt ( kW), with an average of 300 kW. The Alaska DEC said that these engines are below the threshold for major sources, and that is also confirmed by HAP emission calculations. Since these villages would not be major HAP sites they would not be affected by the final rule. The nonavailability of low sulfur fuel at these remote villages would therefore not be an issue since these villages would not be subject to the rule since they are located at non major HAP sites. Finally, EPA has received information from catalyst vendors indicating that there are sulfur tolerant catalysts that have been commercialized and are suitable for use with fuels having a sulfur content between 3,000 and 5,000 ppm sulfur by weight. Sources that may not be able to obtain low sulfur fuel could use such catalysts to comply with the requirements of the final rule. For these reasons, EPA does not feel it is necessary to establish a separate subcategory for stationary CI RICE located in Alaska.

I. F. 5 Comment: One commenter ( 553) expressed strong support for EPA's proposal to create a subcategory specifically for CI engines.

Response: The EPA recognizes the commenter's support. The subcategory for CI engines has been retained in the final rule.

G. Other I. G. 1 Comment: One commenter ( 586) expressed the opinion that the health risks of 32 uncontrolled engines are sufficient to warrant consideration of making this MACT standard applicable to non major HAP facilities and other types of engines.

Response: The EPA is covering area sources and small engines under a later rule, which is expected to be proposed by October 31, 2006 and completed by December 20, 2007.

I. G. 2 Comment: One commenter ( 586) stated that the proposed MACT should also apply to existing lean burn engines, not only existing rich burn engines. Retrofitting an oxidation catalyst on a lean burn engine should not be much more complicated than retrofitting a nonselective catalyst to a rich burn engine.

Response: As established in section 112( d) of the CAA, the emission standards must be no less stringent than the MACT floor, which for existing sources is the average emission limitation achieved by the best performing 12 percent of existing sources. Review of the Population Database indicated that less than 1 percent of existing 2SLB stationary RICE, about 3 percent of existing 4SLB stationary RICE, and less than 1 percent of existing CI stationary RICE use oxidation catalyst systems or other emission reduction technologies or strategies. These percentages are all well below the criteria for a MACT floor that would require use of such systems, or equivalent emissions reductions for existing sources. The EPA concluded that the MACT floor for existing 2SLB, existing 4SLB, and existing CI stationary RICE is no emissions reductions. Unlike the case for lean burn and CI engines, the EPA determined that 27 percent of existing 4SRB stationary RICE are equipped with NSCR. Therefore it was appropriate to set the MACT floor for 4SRB stationary RICE at the level of HAP emissions reductions achieved by the use of NSCR systems. As discussed in the proposed rule, EPA also determined that it was not appropriate to require above the floor emissions reductions for the subcategories in this source category.

I. G. 3 Comment: One commenter ( 565) requested that EPA clarify applicability and exemptions with a flowchart.

Response: The EPA feels that the manner in which the applicability and exemptions of the rule are presented is sufficient.

I. G. 4 Comment: One commenter ( 585) requested clarification on the requirements for dual fuel engines. Reciprocating internal combustion engines are sometimes modified to use fuels such as diesel and natural gas. The dual fuels often are 5 percent diesel and 95 percent natural gas. Some clean burn dual RICE units use only 1 percent diesel and 99 percent natural gas. It is not clear how these engines should be defined for compliance. The commenter stated that it would be better to define the RICE units according to ignition instead of fuel. The commenter suggested the following wording concerning dual fuel RICE units: " Engines that are modified to reduce emission will be categorized or will continue to be categorized as natural gas engines if the ignition system is typical of a natural gas engine, i. e. spark ignition or diesel engine if the ignition system is typical of diesel engines, i. e. compression ignition." 33 One commenter ( 555) suggested that EPA evaluate the ability of dual fuel engines to comply with the standard and the associated costs and cost effectiveness and environmental benefits, and a separate category for these engines be established if warranted.

Response: In the rule, EPA defined CI engine as any stationary RICE " in which a high boiling point liquid fuel injected into the combustion chamber ignites when the air charge has been compressed to a temperature sufficiently high for auto ignition, including diesel engines and dualfuel engines and engines that are not spark ignition." Dual fuel engines in turn are defined as engines " in which a liquid fuel ( typically diesel fuel) is used for compression ignition and gaseous fuel ( typically natural gas) is used as the primary fuel." Therefore, dual fuel units as defined are required to comply with the emission limitation requirements established in the final rule for CI engines.

In response to the commenter who stated that EPA should evaluate the ability of dual fuel engines to comply with the standard, EPA does not have any reason to expect that dual fuel engines will not be able to meet the standards of the final rule. Information contained in several papers available from EPA's Edocket Website as attachments to Document ID Number OAR 2002 0059 0503 ( A 95 35 II D 78) shows that dual fuel engines equipped with oxidation catalysts can achieve CO removal efficiencies of 93 percent or more. Since the emission limitations EPA is requiring in the final rule range from 58 to 93 CO percent reduction, dual fuel engines should be able to meet the CO percent reduction emission limitations.

I. G. 5 Comment: One commenter ( 569) provided support for EPA's determination to set the MACT standard at the MACT floor. The commenter supported this approach for the following reasons:

( 1) The standard can be achieved by most existing and new sources in the source category in a cost effective manner; and ( 2) The standard will provide a sufficient level of emission controls to adequately protect the public and the environment.

Response: The EPA acknowledges the commenter's support. This approach has been retained in the final rule.

II. DEFINITIONS A. Rich/ Lean Burn II. A. 1 Comment: Six commenters ( 542, 549, 554, 556, 565, 587) stated that EPA should revise the definition of rich burn engine to eliminate engines that have been converted to operate as lean burn engines and to address older engines ( e. g., horizontal), where there is no recommended air/ fuel ratio. Commenter 587 recommended that EPA adopt the following 34 definition into the final rule:

" Rich burn engine means 4 stroke spark ignited engine where the manufacturers recommended air/ fuel ratio divided by the stoichiometric air/ fuel ratio at full conditions is less than or equal to 1.1. Engines originally manufactured as rich burn engines, but modified prior to ( promulgation date) with passive emission control technology for nitrogen dioxides ( such as precombustion chambers) shall be considered lean burn engines. Horizontal engines shall be considered lean burn engines. Also, older engines where there are no manufacturer's recommendations regarding air/ fuel ratio will be considered a rich burn engine if the excess oxygen content of the exhaust at full load conditions is less than or equal to 2 percent."

Commenter 549 recommended a similar definition.

Response: The EPA agrees with the commenter that it is necessary to address engines that have been converted from 4SRB engines to 4SLB engines and to also address older engines such as horizontal engines. The EPA has adjusted the definition of rich burn engine and has written the rich burn definition in the final rule as follows:

" Rich burn engine means any four stroke spark ignited engine where the manufacturer's recommended operating air/ fuel ratio divided by the stoichiometric air/ fuel ratio at full load conditions is less than or equal to 1.1. Engines originally manufactured as rich burn engines, but modified prior to December 19, 2002 with passive emission control technology for NOx ( such as pre combustion chambers) will be considered lean burn engines. Also, existing engines where there are no manufacturer's recommendations regarding air/ fuel ratio will be considered a rich burn engine if the excess oxygen content of the exhaust at full load conditions is less than or equal to 2 percent."

In addition, to avoid overlap with the definition of lean burn engine, the lean burn engine definition has also been adjusted and reads as follows in the final rule:

" Lean burn engine means any two stroke or four stroke spark ignited engine that does not meet the definition of a rich burn engine."

II. A. 2 Comment: One commenter ( 552) suggested that EPA revise the definition of rich burn engine to " A spark ignited engine that is designed to operate with an exhaust oxygen concentration of less than 2 percent by dry volume." The commenter was of the opinion that the current definition does not necessarily include all engines considered to be rich burn. In addition, according to the commenter, determining whether an engines falls into the rich burn category under the current definition is problematic since obtaining the data to calculate the ratio stated in the rule is very difficult.

Response: As described in response to comment II. A. 1, EPA has adjusted the definition of rich burn engine in the final rule. The EPA feels the definition of rich burn engine in the final rule satisfies the commenter's concerns. 35 II. A. 3 Comment: One commenter ( 527) observed that in the proposed rule there is no mention if a rich to lean conversion of a 4SRB engine is permitted. The commenter indicated that such a conversion should be permitted due to economic and environmental factors.

Response: The definition of a rich burn engine is based on the manufacturer's recommendation. Therefore, a conversion of a 4SRB engine to a 4SLB engine would not change the classification of the engine as a 4SRB engine, unless the engine was originally manufactured as a rich burn engine, but modified prior to December 19, 2002 with passive emission control technology for nitrogen oxides ( NOx) ( such as pre combustion chambers).

II. A. 4 Comment: One commenter ( 600) recommended that in order to eliminate the ambiguity that a CI RICE could be classified as a 2SLB or 4SLB RICE, the " lean burn engine" definition should be changed to reflect that it should be applicable only to spark ignited engines. The commenter recommended the following change: " Lean burn engine means any two stroke or four stroke spark ignited engine where the manufacturer's recommended operating air/ fuel ratio divided by the stoichiometric air/ fuel ratio is greater than 1.1." The proposed change is consistent with the language in the preamble where 2SLB and 4SLB are often preceded by either of the terms " spark ignited" or " spark ignition."

Response: The EPA agrees with the commenter and has incorporated parts of the commenter's recommendation into the definition of lean burn engine in the final rule. The definition of lean burn engine in the final rule is written as follows:

" Lean burn engine means any two stroke or four stroke spark ignited engine that does not meet the definition of a rich burn engine."

B. New/ Reconstructed II. B. 1 Comment: One commenter ( 546) asserted that the definition of a reconstructed source should be modified to exclude any cost incurred with the installation of a control device required by State and local emission standards. The addition of DPF could exceed the reconstruction cost threshold ( 50 percent of fixed capital cost to construct a comparable new source).

Response: Based on the information EPA has available on costs of DPF systems and costs of engines, EPA feels that the addition of DPF would not exceed the reconstruction threshold of 50 percent of the capital cost of a new engine. Information received from CARB indicate that the total cost of a DPF including equipment and installation is around $ 38/ HP. Engine costs estimated by CARB are $ 93/ HP for a new engine. Comparing the cost of a DPF system to the cost of a new engine shows that the addition of such a filter system would be less than 50 percent. Engine cost information available to EPA obtained from other sources indicate that engine costs are between $ 150$ 270/ HP. Using these engine costs, the addition of a DPF system would be an even less percentage of the cost of a new engine. Engine costs can be found in the memorandum entitled " National Impacts Associated with Reciprocating Internal 36 Combustion Engines" available from EPA's Edocket Website as Document ID Number OAR 2002 0059 0071 ( A 95 35 II B 48). The EPA has, therefore concluded that based on both information received from CARB and information EPA already has, the addition of a DPF would be less than 50 percent of the cost of a new engine.

In any case, EPA's policy regarding the inclusion of air pollution control equipment in determining reconstruction is that the costs associated with the purchase and installation of air pollution control equipment are included in the fixed capital cost to the extent that the equipment is required as part of the manufacturing or operating process. Therefore, it is EPA's policy not to include the fixed capital cost of air pollution control equipment that is not part of the operating process. Since DPF is not required in order to operate an engine, the cost for purchase and installation of DPF would not be included in determining whether a source is reconstructed. The commenter does not explain why EPA should deviate from its General Provisions based on compliance with State or local regulations. A source that is spending more than 50 percent of the capital cost needed for a new engine to meet the requirements should be in a position to make appropriate changes in its source at that time to meet the standards promulgated today. Moreover, the source may be able to comply with both requirements at the same time and may be able to meet the requirements using integrated controls ( if not the same controls) that would be best implemented at the same time.

II. B. 2 Comment: One commenter ( 552) recommended that EPA change the definition of new and reconstructed RICE to include those engines where construction or reconstruction is initiated after the date of publication of the final rule in the Federal Register. The commenter stated that this requirement is unreasonable since it places an unfair burden on owners who install RICE in the time period between publication of the draft rule and publication of the final rule. One issue the commenter raised was that since the final standards and requirements will not be known until the final publication data, any new RICE installed since December 19, 2002, could not possibly be in compliance on the final publication date and will have to shut down operations until compliance with all requirements can be assured.

Response: The EPA feels the definitions of new and reconstructed RICE as defined in § § 63.6590( a)( 2) and ( 3) of the final rule are appropriate. These definitions are also consistent with the General Provisions of part 63 and with the definitions in CAA section 112( a). Sources are required to install the proper equipment and meet the applicable emission limitations on startup; however, EPA allows sources 180 days to demonstrate compliance. In addition, if the promulgated standard is more stringent that the proposed standard, sources that commenced construction or reconstruction between proposal and promulgation have the option to comply with the proposed emission limitations when demonstrating initial compliance. Sources must then meet the final emission limitation within 3 years of the final rule and must conduct a second performance test to demonstrate compliance with the promulgated emission limitations within 3 years and 180 days after the date of the final rule.

II. B. 3 Comment: One commenter ( 553) stated that it strongly supports EPA's definition of " reconstructed" source. 37 Response: The EPA acknowledges the commenter's support.

C. Affected Source II. C. 1 Comment: Nine commenters ( 544, 549, 551, 553, 564, 565, 581, 585, 593) requested that EPA write the definitions of affected source, existing stationary RICE, new stationary RICE, and reconstructed stationary RICE such that they represent the " collection" of each type of source at a site, consistent with General Provisions § 63.2.

Response: Although § 63.2 of the General Provisions provides that EPA will generally adopt a broad definition of affected source, which includes all emission units within each subcategory which are located within the same contiguous area, this section also provides that EPA may adopt a narrower definition of affected source in instances where EPA determines that the broader definition would " create significant administrative, practical, or implementation problems" and " the different definition would resolve those problems." This is such an instance. There are several subcategories of stationary RICE, and a site could have engines from multiple subcategories, each having different compliance requirements. Use of the broader definition of affected source specified by the General Provisions would require very complex aggregate compliance determinations. The EPA feels such complicated compliance determinations to be impractical, and, therefore, has decided to adopt a definition which establishes each individual RICE as the affected source.

II. C. 2 Comment: One commenter ( 551) asked that EPA clarify the term " affected RICE" e. g., used in § 63.6595( c). The commenter stated that the term should be changed to " affected source" or " any stationary RICE that is part of an affected source" or " any stationary RICE subject to this provision," as appropriate to the intended context.

Response: The EPA agrees with the commenter and has replaced " affected RICE" with " affected source" in § 63.6595( c) of the final rule.

D. Other II. D. 1 Comment: One commenter ( 564) contended that the 1 year limitation on engines that are portable or transportable before they are categorized as stationary should be eliminated. For purpose of the RICE MACT, adding on control requirements, and the associated control systems, to engines that are portable is not practical.

Response: The commenter did not provide any information supporting why the addition of control equipment to portable and transportable engines that have remained at the same location for more than 1 year and that have become classified as stationary engines is not practical. Therefore, the EPA cannot justify eliminating the 1 year limitation without a reasonable basis.

II. D. 2 Comment: One commenter ( 555) said that " Gaseous fuel" should be defined as 38 being a gas at a standard temperature and pressure rather than " normally a gas."

Response: The EPA agrees with the commenter and has defined gaseous fuel according to the commenter's recommendation in the final rule.

II. D. 3 Comment: One commenter ( 555) questioned the definition of " Landfill gas" and stated that " Landfill gas" is defined as being " formed through anaerobic decomposition," which is usually but not always the case.

Response: The definitions of landfill gas and digester gas have been modified in the final rule to indicate that they are typically formed through anaerobic decomposition.

II. D. 4 Comment: One commenter ( 555) remarked that " Oxidation catalyst" is defined as " for lean burn engines" even though they can be used on rich burn engines with air injection.

Response: The EPA has adjusted the definition of oxidation catalyst in the final rule by removing " for lean burn engines."

II. D. 5 Comment: One commenter ( 555) provided the comment that " Propane" is defined as " suitable for use in spark ignited engines" when it could be used in a dual fueled engine as well.

Response: The EPA agrees with the commenter. The definition of propane has been adjusted to exclude the sentence " suitable for use in spark ignited engines" in the final rule.

II. D. 6 Comment: One commenter ( 555) made the observation that " Nameplate capacity" is not defined in the proposed rule. The commenter recommended that the term " manufacturers rating at maximum continuous load" be used.

Response: The EPA received several comments on the proposed rule stating that siterated HP should be used instead of manufacturer's nameplate HP. This was discussed in response to comment X. B. 1. For the reasons provided by EPA in response to X. B. 1, EPA feels it is appropriate to used site rated HP as the basis for the size threshold in the final rule.

II. D. 7 Comment: One commenter ( 564) recommended that the preamble should clarify that the definition of major source in the RICE MACT does not alter the definition of a major source in subpart HH of 40 CFR part 63 ( Oil and Natural Gas Production Facilities) and, therefore, does not affect subpart HH applicability. Similarly, commenter 549 stated that EPA should clarify in the preamble that major source status is MACT category specific and that area and major source determinations do not transfer between MACT categories.

Response: The EPA recognizes the commenter's concern regarding the definition of major source in the RICE NESHAP and its difference from the definition of major source in subpart HH. The EPA has, therefore, clarified in the preamble to the final rule that the definition of major source in the RICE NESHAP does not alter the definition of major source in subpart HH 39 ( or any other subpart), and, therefore, does not affect subpart HH applicability.

II. D. 8 Comment: Two commenters ( 564, 565) stated that the term, and definition of, " deviation" should be changed to " excursion" to avoid confusion with title V operating permit requirements and for consistency with other MACTs ( e. g., Hazardous Organic NESHAP).

Response: The EPA does not agree with the commenter that the definition of deviation should be changed to excursion. The term " deviation" has commonly been used in other MACT standards. The EPA has therefore not made this change.

II. D. 9 Comment: One commenter ( 604) stated that the standard exempts RICE whose primary fuel is landfill gas because catalytic converters will be rendered useless by siloxanes. The commenter said that primary fuel is not defined in the MACT.

Response: The EPA agrees that it is appropriate to provide guidelines for the usage of landfill and digester gas. As discussed elsewhere in this document, firing greater than 10 percent landfill or digester gas will cause fouling that will render an oxidation catalyst inoperable within a short period of time. Accordingly, EPA has defined this subcategory as engines with annual landfill and digester gas consumption of 10 percent or more of the gross heat input on an annual basis in the final rule.

II. D. 10 Comment: One commenter ( 549) expressed support for the definition of major source, except as follows:

The phrase " except when they are on the same surface site" should be removed from the end of part ( 1) of the RICE major source definition. This phrase is not present in the 40 CFR part 63, subpart HH major source definition that is the template for the RICE major source definition. Section 112( n)( 4) of the CAA of 1990 requires that wells and associated equipment not be aggregated even within the same surface site except as provided in part ( 3) of the RICE MACT major source definition.

In part ( 3) of the RICE major source definition, the phrase " storage vessel with flash emissions potential" should be changed to " storage vessel with the potential for flash emissions" to conform to the 40 CFR part 63, subpart HH definition.

The General Provisions major source definition presented in the RICE MACT is different from those found in the definition of major source in the NESHAP from Oil and Natural Gas Production Facilities ( 40 CFR 63.761). The significance of this difference is that sources that are area sources under subpart HH could possibly be rendered " Major Sources" under RICE. The EPA should acknowledge this possibility in the preamble to the final rule and clearly state that this does not change the source's status under subpart HH or any other MACT.

Response: The EPA agrees that the phrase " except when they are on the same surface site" should be removed from the end of part ( 1) of the RICE major source definition and the 40 phrase " storage tanks with flash emissions potential" in part ( 3) of the RICE MACT major source definition should be changed to " storage vessel with the potential for flash emissions." The EPA has incorporated the commenter's recommendations into the final rule.

The EPA recognizes the commenters' concern regarding the definition of major source in the RICE NESHAP and its difference from the definition of major source in subpart HH. The preamble to the final rule clarifies that the definition of major source in the RICE MACT does not alter the definition of major source in subpart HH, and therefore does not affect subpart HH applicability.

II. D. 11 Comment: One commenter ( 549) recommended that the definitions from 40 CFR subpart HH and 40 CFR subpart HHH for glycol dehydration unit, storage vessel with the potential for flash emissions, and production well should be included.

Response: The EPA agrees with the commenter that the definitions should be included in the RICE NESHAP. The definitions from 40 CFR subpart HH and 40 CFR subpart HHH for glycol dehydration unit, storage vessel with the potential for flash emissions, and production well have been added to the final RICE NESHAP.

III. DATES A. Comment Period III. A. 1 Comment: One commenter ( 603( B)) stated that a 60 day comment period was insufficient.

Response: The EPA feels the comment period was sufficient.

B. New/ Reconstructed III. B. 1 Comment: One commenter ( 570) stated that § § 63.6595( a)( 2) and ( 3) are not consistent with § 63.6590( a)( 2). " New stationary RICE" is defined as any RICE for which construction was commenced after December 19, 2002 in § 63.6590( a)( 2), while § 63.6595( a)( 2) and ( 3) indicate " new stationary RICE" are those for which construction commenced after the final publication date of the rule. The commenter suggested correcting the language in § § 63.6595( a)( 2) and ( 3). The commenter noted that the problem is also repeated in § § 63.6645( b) and ( c).

Response: The commenter's interpretation of the regulatory text is not accurate. Section 63.6590( a)( 2) states that a stationary RICE is new if construction of the stationary RICE was commenced on or after December 19, 2002 ( date of publication of the proposed rule in the Federal Register). Sections 63.6595( a)( 2) and ( 3) do not define new stationary RICE, rather they state when the new or reconstructed RICE must comply with the applicable emission limitations 41 depending on when startup occurred ( before or after publication of the final rule in the Federal Register).

C. Initial Notification III. C. 1 Comment: Four commenters ( 542, 554, 556, 587) remarked that EPA should provide 1 year for initial notification as in the glycol dehydration MACT.

Response: An initial notification is not a time consuming activity, and the EPA does not feel that 1 year is necessary to submit an initial notification.

D. Initial Compliance III. D. 1 Comment: Seven commenters ( 526, 548, 552, 595, 560, 571, 579) expressed the view that immediate compliance for new and reconstructed engines is unreasonable. The commenters felt that 1 year compliance time frame is more reasonable.

Response: The EPA feels that immediate compliance is appropriate for new and reconstructed engines and is consistent with the General Provisions of part 63. See also CAA section 112( i)( 1). The requirements of CAA section 112 contemplate that sources will be aware of their requirements at the time of proposal and, excluding requirements that are made more stringent between proposal and promulgation, new or reconstructed sources should be prepared to meet such requirements immediately, at the time of the final rule. Sources are required to install the proper equipment and meet the applicable emission limitations on startup; however, EPA allows sources 180 days to demonstrate compliance. In addition, because two of our emission requirements have been made more stringent since proposal, sources that commence operation between proposal and the final rule may show compliance with the proposed requirements for the first 3 years of the program.

III. D. 2 Comment: One commenter ( 569) supported the 3 year compliance period for existing affected sources provided in § 63.6595( a)( 1) because this amount of time will be required for the specification, purchase, manufacture, installation and testing of the required catalyst systems, particularly if many other sources are doing the same things at the same time.

Response: The EPA agrees with the commenter.

III. D. 3 Comment: Eight commenters ( 526, 540, 559, 564, 565, 569, 579, 585) stated that for area sources becoming major sources, the requirement to be in compliance at the time of the switch is unreasonable. Commenters 526 and 579 suggested allowing 1 year for the unit to come into compliance. One commenter ( 540) suggested that all area sources that become major should be allowed 3 years to achieve compliance or change the definition of a new stationary RICE to " A stationary RICE is new if you commenced construction of the stationary RICE after December 19, 2002, and you meet the applicability criteria for the subpart at the time you commenced construction." Six commenters ( 549, 569, 559, 565, 564, 585) suggested 3 years. 42 Response: The EPA agrees with the commenters that it is appropriate to allow existing area sources that become major sources 3 years to comply with the final rule. This has been specified in the final rule in § 63.6595( b)( 2). However, the EPA does not agree with the commenters that immediate compliance is unreasonable for new and reconstructed RICE located at area sources that are constructed or reconstructed at the same time the area source becomes a major source. These sources are aware in advance of their change in status from area source to major source and, therefore, should have sufficient time to plan for immediate compliance with the final rule. This has been specified in the final rule in § 63.6595( b)( 1). A period of 180 days is allowed to demonstrate compliance.

III. D. 4 Comment: Three commenters ( 542, 556, 587) requested that EPA provide 1 year to conduct the initial performance test, rather than 180 days provided by the General Provisions. Commenter 587 indicated that seasonal operations, such as storage facilities or compressor stations used in peak demand only, may not be operational during the 180 days provided to conduct the performance test. All existing 4SRB engines must conduct formaldehyde testing as a part of the initial performance test. It may be difficult to secure appropriate testing firms within the 180 days provided, especially since many may depend on Fourier Transform Infrared ( FTIR) testing.

Response: The EPA feels the time it allows sources to conduct the initial performance test is appropriate. Existing sources that must meet the requirements of the final rule have 3 years and 180 days to conduct the initial performance test and to demonstrate compliance. Therefore, existing 4SRB engines that must meet the formaldehyde emission limitations have sufficient time to secure an appropriate testing firm. In addition, the final rule does not only specify that FTIR can be used for formaldehyde testing, but that also EPA Method 323. This means it may not be necessary to secure testing firms specializing in FTIR measurements, and should increase the number of available testing firms. New sources that must meet the requirements of the final rule are aware in advance that their source will be covered by the final rule. The EPA feels that 180 days is sufficient time to secure appropriate testing firms and to conduct the initial performance test and feels that 1 year to conduct the initial performance test is not necessary. Regarding the comment concerning seasonal operations, new sources do not have to test until the unit is operating, so seasonal operation should not be a concern for new units. Also, for existing sources, EPA feels that seasonal operation should not be a problem since the unit has 3 years and 180 days to conduct the initial performance test, and surely the unit would be operational within that timeframe. Finally, the 180 day time period is consistent with the General Provisions of part 63.

III. D. 5 Comment: Two commenters ( 564 and 565) requested that idle ( not in service) units should have no immediate compliance obligation with the rule and should be given at least 1 year from the initial date of re activation to comply with the requirements.

Response: The EPA disagrees with the commenter. First, new stationary RICE are only required to meet emission limitations and testing after startup, which is when they are first operated. Existing engines that are not in operation would be considered limited use engines and 43 are not subject to immediate compliance with the emission limitations. However, EPA feels that when these engines are put into more than limited service, they should be required to meet applicable standards. Sources should be well aware of the possibility of their engines needing to be put into regular service and should plan accordingly.

E. Other III. E. 1 Comment: Two commenters ( 526, 579) asked that operators be allowed 1 year to design, execute and submit results of a testing program to define operating parameters. The commenters were of the opinion that if one should choose alternative formaldehyde limits developing site specific operating conditions would be cumbersome. The commenters stated that the concept behind the petitioning is meritorious in that it provides flexibility, many of the requirements border on research oriented items that perhaps only the largest and most knowledgeable operators are capable of performing. The EPA acknowledges at III. F. 3 of the proposed rule that it wishes to encourage alternative emission control technologies, hence the reason for formaldehyde concentration limits.

Response: The EPA does wish to encourage new and alternative emission control technology. However, the EPA anticipates that the information required to be submitted with the petition to the Administrator for approval of operating parameters would already be available to the owners and operators prior to installing the new technology. In other words, the owners and operators would have some basis for applying the new technology. Otherwise, EPA feels it would not be applied.

IV. EMISSION LIMITATIONS A. Level IV. A. 1 Comment: One commenter ( 552) asserted that the emission limitations are too stringent. The commenter stated that the proposed emission standards were based on information from only five engines and does not think that the proposed percent reductions and emission standards reflect the actual performance possible from the wide array of engine designs and sizes in the marketplace. For example, the formaldehyde reduction standard for rich burn engines in the proposed rule is set at 75 percent. However, the data in the docket show that results from eight test runs on two rich burn engines varied from 73 to 80 percent. If the reduction efficiency on two test engines under highly controlled conditions can vary by such a significant amount ( and to a level that does not meet the proposed standard), then it is highly likely that rich burn engines of different size and using different NSCR technology also would not be able to meet the standard. The EPA must consider the significant variability in RICE and adjust all final emissions standards and reduction percentages accordingly. The commenter recommended that the formaldehyde emission limits be revised upward by 10 percent to allow for variability in the RICE and aftertreatment system populations. 44 Three commenters ( 549, 551, 565) asserted that the MACT floor for existing 4SRB is not representative of the average emission limit achieved by the best performing 12 percent of existing sources.

One commenter ( 564) stated that the emission standard for existing 4SRB engines should be reassessed to be consistent with the requirements of CAA section 112( d). The commenter remarked that the Agency used the incorrect approach to set the emission limit for existing 4SRB engines, which logically should be lower percent removal than for new 4SRB engines. It was the commenter's opinion that the Agency should revisit the analysis and establish an emission limit for 4SRB engines more consistent with the required floor setting methodology.

Five commenters ( 526, 549, 551, 579, 564) expressed that the same emission limitation for existing and new 4SRB is unrealistic. Commenter 526 recommended considering 10 percent less restrictive emission reduction requirement for existing units. Another commenter ( 564) indicated that practically speaking, retrofitting existing equipment rarely achieves the optimum design available in new equipment.

One commenter ( 579) contended that 350 parts per billion by volume dry basis ( ppbvd) is too low. The chosen limit was achieved by the best performing engine during CSU testing while for other types of engines the highest emissions from the performance range had been chosen as the emissions limit.

Response: The EPA disagrees with comments that the MACT floor level proposed for existing 4SRB engines is inconsistent with the statute or not representative of the average emission level achieved by the best performing 12 percent of existing sources. The commenters do not dispute the accuracy of the data used or the representativeness of the engines tested. The commenters instead believe the manner in which the EPA used the data is not reflective of the average of the best performing 12 percent of existing sources. To clarify EPA's approach in the proposal, the EPA found the lowest percent reduction value for each of the two sources tested, which account for variability in results for each source. However, as EPA found that 27 percent of the engines in the subcategory use NSCR, EPA felt that it was appropriate to use only the higher of the two values to determine the MACT floor for existing engines. In essence, this treated the top performer as a surrogate for the top half of the population using NSCR or the top 13.5 percent of the population. This is more closely analogous to the level of the top 12 percent of sources than is a straight average of the two sources.

However, in reviewing EPA's method in response to these comments, EPA feels that it would be more appropriate to include in the analysis the data from the lower performing of the two engines tested, thus using more than a single data point in determining the MACT floor for existing engines. Because the test calculation for the MACT floor for existing engines is supposed to be based on the average of the top performing 12 percent of sources, it would be better to rely on a formula that does not rely solely on the highest performer. Also, it would not be appropriate to use a straight average between the two sources, because that would not be a fair approximation of the average of the top 12 percent of sources. Instead, it would approximate the average of the 1 The calculation of percentage reduction is as follows: ( lowest tested percentage reduction of the lower performing engine) * (. 222) + ( lowest tested percentage reduction of the higher performing engine) * (. 778) = ( 75.5)(. 222) + ( 76.2)(. 778) = 76.0. The calculation of ppbvd is as follows: ( highest tested ppbvd of the lower performing engine) * (. 222) + ( highest tested ppbvd of the higher performing engine) * (. 778) = ( 355)(. 222) + ( 348)(. 778) = 350.

45 best performing 27 percent of sources. Therefore, EPA feels a reasonable approach is to discount the lower performing source by 12/ 27, thus reducing the influence of that data point by the ratio of controlled sources ( 27 percent of the population) compared to the statutory level ( 12 percent). This leads to a weighted average where the data point for the lower performer will be worth 22 percent ( 50 percent) ( 12/ 27) and the level for the higher performer will be worth 78 percent.

To be consistent with the approach followed for other engine types, i. e., establish emission limitations based on test results conducted at high loads, EPA found it appropriate to exclude runs conducted at low loads in determining the lower and higher performer. This leads to a final MACT floor of 76 percent control efficiency or 350 ppbvd. 1 Though the formaldehyde reduction number differs slightly from the proposed level, it is very close. The proposed level for the alternative formaldehyde concentration emission limitation remains the same even after following the revised approach. This should not be particularly surprising. Though the emission values of the two engines were not identical, they were very close and the final value for either engines generally rounds to the same value.

For new 4SRB engines, the EPA proposed a formaldehyde reduction requirement of 75 percent and an alternative formaldehyde concentration emission limitation of 350 ppbvd. In reviewing the 4SRB emissions data EPA used to set the standard, EPA observed that the minimum percent efficiency achieved by the best performing engine was actually 76.2 percent formaldehyde reduction. Therefore, EPA acknowledges that the proposed formaldehyde reduction should have been set at 76 percent reduction for 4SRB engines and not 75 percent formaldehyde reduction and has written this in the final rule.

The commenters also seem to argue that the MACT floor levels for existing engines must be less stringent than those for new engines. While the criteria for the MACT floor for new engines is more stringent than for existing engines, it is not impossible or even illogical for the result to be the same, or at least very close. In this case, the best performing 12 percent of engines use the same control technology, and the emission values, as well as the emission reduction values, appear to be very close for these engines. Therefore, it is not surprising that the levels for the MACT floor for new and existing engines should be close. Moreover, EPA was using a very small data set in setting the final emission limits, thus limiting the variation in the data used. This led to a proposed level that used the same calculations for determining the MACT floor for both existing and new engines. The EPA has changed the manner of calculating the MACT floor for existing engines for the final rule, but the result is still the same as that for new engines. Again, this is because the results for both engines were very close. 46 Regarding the comment referring to the use of the average of the best five performing sources, this is only permitted when the category or subcategory has less than 30 sources. This is not the case with this subcategory. Given that EPA had usable data from only two sources, it is not clear that averaging the two sources would be appropriate to meet that requirement.

Regarding the comment that retrofitting existing equipment rarely achieved the optimum design available in new equipment, the commenters provide no data showing that emissions reductions from retrofitting existing engines would be reduced compared to those from new engines. Regardless, the MACT floor for new engines is not based on the optimum possible design for a new engine, but on the best level of control achieved in practice by the best controlled similar source, whether retrofitted or not. Similarly, the MACT floor for existing engines is based on a specific formula. The EPA based the MACT floor for new engines on the information available to EPA from existing engines. While individual existing sources may have some design constraints in installing the emission control technology, there is no evidence that the MACT floor is not achievable. The suggestion that is provided, a 10 percent discount for existing units, without a basis in the existing data, does not appear consistent with the requirements of CAA section 112( d).