[Federal Register: June 12, 2006 (Volume 71, Number 112)]
[Proposed Rules]
[Page 33803-33855]
[DOCID:fr12jn06-35]

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Part II

Environmental Protection Agency

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40 CFR Parts 60, 63, et al.

Standards of Performance for Stationary Spark Ignition Internal
Combustion Engines and National Emission Standards for Hazardous Air
Pollutants for Reciprocating Internal Combustion Engines; Proposed Rule

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 60, 63, 85, 90, 1048, 1065, and 1068

[EPA-HQ-OAR-2005-0030, FRL-8176-1]
RIN 2060-AM81 and 2060-AN62

Standards of Performance for Stationary Spark Ignition Internal
Combustion Engines and National Emission Standards for Hazardous Air
Pollutants for Reciprocating Internal Combustion Engines

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: EPA is proposing new source standards of performance for
stationary spark ignition internal combustion engines. EPA is also
proposing national emission standards for hazardous air pollutants for
stationary reciprocating internal combustion engines that either are
located at area sources of hazardous air pollutant emissions or that
have a site rating of less than or equal to 500 brake horsepower and
are located at major sources of hazardous air pollutant emissions.

DATES: Comments must be received on or before September 11, 2006, or 60
days after date of public hearing if later. Under the Paperwork
Reduction Act, comments on the information collection provisions must
be received by the Office of Management and Budget (OMB) on or before
July 12, 2006. Public Hearing. If anyone contacts us requesting to
speak at a public hearing by July 3, 2006, a public hearing will be
held on July 12, 2006. If you are interested in attending the public
hearing, contact Ms. Pamela Garrett at<PHONE_NUMBER> to verify that a
hearing will be held.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-HQ-
OAR-2005-0030, by one of the following methods:
     http://www.regulations.gov: Follow the on-line instructions for

submitting comments.
     E-mail<EMAIL_ADDRESS>     Fax:<PHONE_NUMBER>.
     Mail: Air and Radiation Docket and Information Center,
Environmental Protection Agency, Mailcode: 6102T, 1200 Pennsylvania
Ave., NW., Washington, DC 20460. Please include a total of two copies.
EPA requests a separate copy also be sent to the contact person
identified below (see FOR FURTHER INFORMATION CONTACT). In addition,
please mail a copy of your comments on the information collection
provisions to the Office of Information and Regulatory Affairs, Office
of Management and Budget, Attn: Desk Officer for EPA, 735 17th St.,
NW., Washington, DC 20503.
     Hand Delivery: Air and Radiation Docket and Information
Center, U.S. EPA, Room B102, 1301 Constitution Avenue, NW., Washington,
DC. Such deliveries are only accepted during the Docket's normal hours
of operation, and special arrangements should be made for deliveries of
boxed information.
    Instructions: Direct your comments to Docket ID No. EPA-HQ-OAR-
2005-0030. EPA's policy is that all comments received will be included
in the public docket without change and may be made available on-line
at http://www.regulations.gov, including any personal information

provided, unless the comment includes information claimed to be
Confidential Business Information (CBI) or other information whose
disclosure is restricted by statute. Do not submit information that you
consider to be CBI or otherwise protected through http://www.regulations.gov

or e-mail. The http://www.regulations.gov Web site is an ``anonymous access''

system, which means EPA will not know your identity or contact
information unless you provide it in the body of your comment. If you
send an e-mail comment directly to EPA without going through
http://www.regulations.gov, your e-mail address will be automatically captured

and included as part of the comment that is placed in the public docket
and made available on the Internet. If you submit an electronic
comment, EPA recommends that you include your name and other contact
information in the body of your comment and with any disk or CD-ROM you
submit. If EPA cannot read your comment due to technical difficulties
and cannot contact you for clarification, EPA may not be able to
consider your comment. Electronic files should avoid the use of special
characters, any form of encryption, and be free of any defects or
viruses.
    Public Hearing: If a public hearing is held, it will be held at
EPA's campus located at 109 T.W. Alexander Drive in Research Triangle
Park, NC or an alternate site nearby.
    Docket: All documents in the docket are listed in the
http://www.regulations.gov index. We also rely on documents in Docket ID Nos.

A-96-55 and A-2000-01, and incorporate those dockets into the record
for this proposed rule. Although listed in the index, some information
is not publicly available, e.g., CBI or other information whose
disclosure is restricted by statute. Certain other material, such as
copyrighted material, will be publicly available only in hard copy.
Publicly available docket materials are available either electronically
in http://www.regulations.gov or in hard copy at the Air and Radiation Docket,

EPA/DC, EPA West, Room B102, 1301 Constitution Ave., NW., Washington,
DC. The Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday
through Friday, excluding legal holidays. The telephone number for the
Public Reading Room is<PHONE_NUMBER>, and the telephone number for the
Air Docket is<PHONE_NUMBER>.

FOR FURTHER INFORMATION CONTACT: Mr. Jaime Pag[aacute]n, Energy
Strategies Group, Sector Policies and Programs Division (D243-01),
Environmental Protection Agency, Research Triangle Park, North Carolina
27711; telephone number<PHONE_NUMBER>; facsimile number (919) 541-
5450; email address<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION: Organization of This Document. The following
outline is provided to aid in locating information in the preamble.

I. General Information
    A. Does this action apply to me?
    B. What should I consider as I prepare my comments for EPA?
II. Background
III. Summary of This Proposed Rule
    A. What is the source category regulated by this proposed rule?
    B. What are the pollutants regulated by this proposed rule?
    C. What are the proposed standards?
    D. What are the requirements for sources that are modified or
reconstructed?
    E. What are the requirements for demonstrating compliance?
    F. What are the reporting and recordkeeping requirements?
IV. Rationale for Proposed Rule
    A. Which control technologies apply to stationary engines?
    B. How did EPA determine the basis and level of the proposed
standards?
    C. How did EPA determine the compliance requirements?
    D. How did EPA determine the reporting and recordkeeping
requirements?
    E. Why did EPA determine to exempt area sources from title V
permit requirements?
V. Summary of Environmental, Energy and Economic Impacts
    A. What are the air quality impacts?
    B. What are the cost impacts?
    C. What are the economic impacts?
    D. What are the non-air health, environmental and energy
impacts?
VI. Solicitation of Comments and Public Participation
VII. Statutory and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review
    B. Paperwork Reduction Act
    C. Regulatory Flexibility Act
    D. Unfunded Mandates Reform Act of 1995

    E. Executive Order 13132: Federalism
    F. Executive Order 13175: Consultation and Coordination With
Indian Tribal Governments
    G. Executive Order 13045: Protection of Children From
Environmental Health Risks and Safety Risks
    H. Executive Order 13211: Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution, or Use
    I. National Technology Transfer and Advancement Act

I. General Information

A. Does this action apply to me?

    Regulated Entities. Categories and entities potentially regulated
by this action include:

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                  Category                    NAICS \1\               Examples of regulated entities
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Any manufacturer that produces or any              2211  Electric power generation, transmission, or
 industry using a stationary internal            622110   distribution.
 combustion engine as defined in this            335312  Medical and surgical hospitals.
 proposed rule.                                  333912  Motor and generator manufacturing.
                                                 333992  Pump and compressor manufacturing.
                                                  48621  Welding and soldering equipment manufacturing.
                                                 211111  Natural gas transmission.
                                                 211112  Crude petroleum and natural gas production.
                                                  92811  Natural gas liquids producers.
                                                         National security.
----------------------------------------------------------------------------------------------------------------
\1\ North American Industry Classification System.

    This table is not intended to be exhaustive, but rather provides a
guide for readers regarding entities likely to be regulated by this
action. To determine whether your engine is regulated by this action,
you should examine the applicability criteria of this proposed rule. If
you have any questions regarding the applicability of this action to a
particular entity, consult the person listed in the preceding FOR
FURTHER INFORMATION CONTACT section.

B. What should I consider as I prepare my comments for EPA?

    1. Submitting CBI. Do not submit this information to EPA through
regulations.gov or e-mail. Clearly mark the part or all of the
information that you claim to be CBI. For CBI information in a disk or
CD ROM that you mail to EPA, mark the outside of the diskor CD ROM as
CBI and then identify electronically within the disk or CD ROM the
specific information that is claimed as CBI. In addition to one
complete version of the comment that includes information claimed as
CBI, a copy of the comment that does not contain the information
claimed as CBI must be submitted for inclusion in the public docket.
Information so marked will not be disclosed except in accordance with
procedures set forth in 40 CFR part 2. Send or deliver information
identified as CBI to only the following address: Mr. Jaime
Pag[aacute]n, c/o OAQPS Document Control Officer (Room C404-02), U.S.
EPA, Research Triangle Park, NC 27711, Attention Docket ID No. EPA-HQ-
OAR-2005-0030.
    2. Tips for Preparing Your Comments. When submitting comments,
remember to:
    (a) Identify the rulemaking by docket number and other identifying
information (subject heading, Federal Register date and page number).
    (b) Follow directions. EPA may ask you to respond to specific
questions or organize comments by referencing a Code of Federal
Regulations (CFR) part or section number.
    (c) Explain why you agree or disagree; suggest alternatives and
substitute language for your requested changes.
    (d) Describe any assumptions and provide any technical information
and/or data that you used.
    (e) If you estimate potential costs or burdens, explain how you
arrived at your estimate in sufficient detail to allow for it to be
reproduced.
    (f) Provide specific examples to illustrate your concerns, and
suggest alternatives.
    (g) Explain your views as clearly as possible, avoiding the use of
profanity or personal threats.
    (h) Make sure to submit your comments by the comment period
deadline identified.
    Docket. The docket number for this proposed rule is Docket ID No.
EPA-HQ-OAR-2005-0030.
    World Wide Web (WWW). In addition to being available in the docket,
an electronic copy of this proposed rule will be posted on the WWW
through the Technology Transfer Network Web site (TTN Web). Following
signature, EPA will post a copy of this proposed rule on the TTN's
policy and guidance page for newly proposed or promulgated rules at
http://www.epa.gov/ttn/oarpg. The TTN provides information and

technology exchange in various areas of air pollution control.

II. Background

    This action proposes new source performance standards (NSPS) that
would apply to new stationary spark ignition (SI) internal combustion
engines (ICE). New source performance standards implement section
111(b) of the Clean Air Act (CAA), and are issued for categories of
sources which cause, or contribute significantly to, air pollution
which may reasonably be anticipated to endanger public health or
welfare. The standards apply to new stationary sources of emissions,
i.e., sources whose construction, reconstruction, or modification
begins after a standard for those sources is proposed. The NSPS for
stationary SI ICE would be promulgated under 40 CFR part 60, subpart
JJJJ.
    This action also proposes national emission standards for hazardous
air pollutants (NESHAP) from existing, new, and reconstructed
stationary reciprocating internal combustion engines (RICE) with a site
rating of less than or equal to 500 horsepower (HP) located at major
sources, and existing, new, and reconstructed stationary RICE located
at area sources. We are proposing these requirements to meet our
statutory obligation to address hazardous air pollutants (HAP)
emissions from these sources under sections 112(d) and 112(k) of the
CAA. The final NESHAP for stationary RICE would be promulgated under 40
CFR part 63, subpart ZZZZ, which already contains standards applicable
to stationary RICE with a site rating above 500 HP located at major
sources.
    We are proposing these two sets of regulations under one notice of
proposed rulemaking because the source categories being addressed are
practically identical. In other words, stationary engines located at
major and area sources of HAP will also be affected by NSPS
regulations. Based on the similarities, we decided that it would be
appropriate to propose the regulations at the same time and attempt to
bring some consistency between them.

III. Summary of this Proposed Rule

A. What is the source category regulated by this proposed rule?

    The proposed NSPS apply to new stationary SI ICE. A stationary
internal combustion engine means any internal combustion engine, except
combustion turbines, that converts heat energy into mechanical work and
is not mobile. Stationary ICE differ from mobile ICE in that a
stationary internal combustion engine is not a nonroad engine as
defined at 40 CFR 1068.30, and is not used to propel a motor vehicle or
a vehicle used solely for competition. Stationary ICE include
reciprocating ICE, rotary ICE, and other ICE, except combustion
turbines. The proposed NESHAP applies only to stationary RICE. To our
knowledge, no rotary or other types of stationary ICE exist at this
time.
    The SI NSPS address emissions from new, modified and reconstructed
stationary SI engines. An SI engine is either a gasoline-fueled engine;
or any other type of engine, with a spark plug (or other sparking
device) and with operating characteristics significantly similar to the
theoretical Otto combustion cycle. Spark ignition engines usually use a
throttle to regulate intake air flow to control power during normal
operation. Dual-fuel 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 at an annual average ratio of
less than 2 parts diesel fuel to 100 parts total fuel on an energy
equivalent basis are considered SI engines for purposes of this
proposed rule.
    The NESHAP address emissions from existing, new, and reconstructed
stationary engines less than or equal to 500 HP located at major
sources and all stationary engines located at area sources. A major
source of HAP emissions is a plant site that emits or has the potential
to emit any single HAP at a rate of 10 tons (9.07 megagrams) or more
per year or any combination of HAP at a rate of 25 tons (22.68
megagrams) or more per year, except that for oil and gas production
facilities, a major source of HAP emissions is determined for each
surface site. An area source of HAP emissions is a source that is not a
major source.
    If you are an owner or operator of an area source subject to this
proposed rule, you are exempt from the obligation to obtain a permit
under 40 CFR parts 70 or 71, provided you are not required to obtain a
permit under 40 CFR 70.3(a) or 40 CFR 71.3(a) for a reason other than
your status as an area source under this proposed rule.
1. SI NSPS
    New source performance standards for stationary SI engines are
issued under section 111(b) of the CAA. All new, modified and
reconstructed stationary SI engines are covered regardless of size. The
NSPS apply to stationary SI engines combusting any fuel (natural gas,
gasoline, liquefied petroleum gas (LPG), compressed natural gas,
landfill gas, digester gas, and any other applicable fuel). New source
performance standards require these sources to control emissions to the
level achievable by best demonstrated technology (BDT), considering
costs and any non-air quality health and environmental impacts and
energy requirements.
    Under section 111 of the CAA, 42 U.S.C. 7411, the Administrator is
required to publish, and periodically update, a list of source
categories that in his or her judgment cause, or contribute
significantly to, air pollution which may reasonably be anticipated to
endanger public health or welfare. This list appears in 40 CFR 60.16.
The list reflects the Administrator's determination that emissions from
the listed source categories contribute significantly to air pollution
that may reasonably be anticipated to endanger public health or
welfare, and it is intended to identify major source categories for
which standards of performance are to be promulgated.
    EPA has determined that for purposes of NSPS regulations, the
stationary internal combustion engine source category should be split
into two source categories--SI engines and compression ignition (CI)
engines. Proposed NSPS for stationary CI engines were published on July
11, 2005 (70 FR 39870).
2. NESHAP
    The NESHAP portion of this action is a revision to the regulations
in 40 CFR part 63, subpart ZZZZ, currently applicable to stationary
RICE greater than 500 HP located at major sources, which were
promulgated in 2004. Subpart ZZZZ of 40 CFR part 63 does not currently
cover stationary engines located at area sources of HAP emissions, nor
does it apply to stationary engines located at major sources with a
site rating of 500 HP or less. When the subpart ZZZZ of 40 CFR part 63
regulations were promulgated in 2004 (69 FR 33474), EPA deferred
promulgating regulations with respect to stationary engines 500 HP or
less at major sources until further information on the engines could be
obtained and analyzed. It was decided to regulate these smaller engines
at the same time as we regulate engines located at area sources.
    This action proposes to revise 40 CFR part 63, subpart ZZZZ, in
order to address HAP emissions from stationary RICE less than or equal
to 500 HP located at major sources and stationary RICE located at area
sources. For stationary engines less than or equal to 500 HP at major
sources, EPA must determine what is the appropriate maximum achievable
control technology (MACT) for those engines under section 112(d)(3) of
the CAA.
    For stationary engines located at area sources, we have the
flexibility to promulgate standards based on generally available
control technology (GACT) under CAA section 112(d)(5). We are required
to address HAP emissions from stationary RICE located at area sources
under section 112(k) of the CAA, based on criteria set forth by EPA in
the Urban Air Toxics Strategy described in the paragraph below.
    On July 19, 1999, EPA announced in the Federal Register its plan
for addressing exposure to air toxics in urban areas. The Urban Air
Toxics Strategy (64 FR 38706) listed several source categories that
emit one or more of the air toxic pollutants of greatest concern in
urban areas. The stationary engine source category was one of the
source categories listed and, as such, EPA is required to consider it
for regulation. The strategy addressed sections 112(c)(3) and
112(k)(3)(B)(ii) of the CAA that instruct us to identify not less than
30 HAP which, as the result of emissions from area sources, present the
greatest threat to public health in the largest number of urban areas,
and to list sufficient area source categories or subcategories to
ensure that emissions representing 90 percent of the 30 listed HAP are
subject to regulation. The strategy included a list of 33 HAP judged to
pose the greatest potential threat to public health in the largest
number of urban areas (the urban HAP) and a list of area source
categories emitting the listed HAP (area source HAP). Once listed,
these area source categories shall be subject to standards under
section 112(d) of the CAA.
    We have divided the source category into the following
subcategories: Stationary RICE less than 50 HP, landfill and digester
gas stationary RICE, CI stationary RICE greater than or equal to 50 HP,
and SI stationary RICE greater than or equal to 50 HP. The CI
stationary RICE greater than or equal to 50 HP subcategory was further
subcategorized into emergency and non-emergency engines, as was the

subcategory of SI stationary RICE greater than or equal to 50 HP. Spark
ignition non-emergency stationary RICE greater than or equal to 50 HP
were then subcategorized into 2 stroke lean burn (2SLB), 4 stroke lean
burn (4SLB), and 4 stroke rich burn (4SRB) stationary RICE.
    The regulatory approach being proposed in this action
differentiates between gasoline, LPG, natural gas, and digester and
landfill gas. Gasoline and LPG are fuels more commonly used in nonroad
engines than stationary engines. Nonroad SI engines less than or equal
to 19 kilowatt (KW) (25 HP) typically use gasoline. It is estimated
that about 68 percent of SI nonroad engines above 19 KW (25 HP) use
LPG. A smaller percentage of nonroad SI engines above 19 KW (25 HP) use
gasoline (about 23 percent) and even less use compressed natural gas
(about 9 percent). Natural gas fuel is more common in larger,
stationary applications. Natural gas engines refer to all gaseous-
fueled engines except those fueled by landfill and digester gas.
Natural gas is primarily composed of methane and typically contains
very low levels of sulfur. Other fuels used with stationary SI engines
are landfill and digester gases. These gases are by-products of
wastewater treatment and land application of municipal reuse. Landfill
and digester gases, which are formed through anaerobic decomposition of
organic materials, are principally comprised of methane and carbon
dioxide, but small quantities of other compounds such as hydrogen
sulfide, ammonia, volatile organic compounds, and particulate matter
(PM) may also be present. These gases have a lower methane content than
natural gas and may range from 50 to 65 percent. Although similar in
composition to natural gas, there are some differences in the emissions
from combustion of landfill and digester gases due to e.g., chlorinated
compounds typically not found in natural gas. Both landfill and
digester gases contain a family of silicon-based gases collectively
called siloxanes. Combustion of siloxanes forms compounds that have
been known to foul fuel systems, combustion chambers, and post-
combustion catalysts.

B. What are the pollutants regulated by this proposed rule?

    New source performance standards are developed under the authority
of section 111 of the CAA. Emissions of criteria pollutants (those
pollutants identified under section 110 of the CAA) are generally
regulated under section 111 of the CAA, while HAP are regulated under
section 112 of the CAA. Emissions from stationary engines contribute
significantly to air pollution and cause adverse health and welfare
effects. The pollutants to be regulated by the proposed NSPS for
stationary SI engines are nitrogen oxides (NOX), carbon
monoxide (CO), and non-methane hydrocarbons (NMHC). In addition, a
sulfur limit on gasoline is being proposed.
    Nitrogen oxides are listed as criteria pollutants and are regulated
due to their contribution to the formation of ozone. Nitrogen oxides
are precursors to ozone formation. Exposure to ozone has been linked to
health and welfare impacts. Health and welfare risks include impaired
respiratory function, eye irritation, deterioration of materials such
as rubber, and necrosis of plant tissue. Nitrogen oxides are also a
major precursor for nitrate PM. Particulate matter, also regulated as a
criteria pollutant, is associated with premature mortality and a number
of serious adverse respiratory and cardiovascular effects, especially
in children, the elderly, and people with existing heart or lung
disease. Particulate matter also reduces visibility and damages
building materials. Nitrogen oxides are also associated with various
other health and welfare effects. Nitrogen dioxide can cause irritation
of the lungs and can also reduce the resistance to respiratory
infection. Nitrogen oxides are one of the major pollutants emitted from
stationary ICE and stationary ICE are considered to cause or contribute
significantly to nationwide releases of NOX emissions.
    Carbon monoxide is a criteria pollutant and is considered harmful
to public health and the environment. Carbon monoxide has been linked
to increased risk for people with heart disease, reduced visual
perception, cognitive functions and aerobic capacity, and possible
fetal effects. Stationary engines emit CO and are considered to
contribute to several areas failing to attain the National Ambient Air
Quality Standards for CO.
    Emissions of NMHC from stationary engines contribute to the
formation of ozone. In addition, emissions of NMHC include air toxics
such as benzene, formaldehyde, acetaldehyde, 1,3-butadiene, and
acrolein. These substances are known or suspected to be human or animal
carcinogens, or having noncancer health effects such as irritation or
corrosion of the eyes, nose, throat, and lungs; pulmonary and
respiratory problems; and dermatitis and sensitization of the skin and
respiratory tract. Stationary engines contribute to nationwide releases
of NMHC emissions.
    Sulfur dioxide (SO2) is a criteria pollutant emitted
from stationary SI engines due to sulfur in gasoline. It contributes to
respiratory illness, particularly in children and the elderly, and
aggravates existing heart and lung diseases. It also contributes to
acid deposition, damaging forests, aquatic ecosystems, crops, and
building materials. Sulfur dioxide undergoes chemical reactions in the
atmosphere to form sulfate PM. The health effects of PM were previously
described in this section. This proposed rule reduces SO2
and sulfate PM by requiring the use of gasoline with lower sulfur
levels, thus improving air quality, public health, and public welfare.
    The NESHAP being proposed in this action would regulate emissions
of HAP. Available emissions data show that several HAP are emitted from
stationary engines, which are formed during the combustion process or
that are contained within the fuel burned. Many HAP have been detected
from the stationary engine exhaust, but only a handful of HAP represent
the majority of HAP emissions from stationary engines. These HAP are
formaldehyde, acrolein, methanol, and acetaldehyde. We described the
health effects of these HAP and other HAP emitted from the operation of
stationary ICE in the preamble to 40 CFR part 63, subpart ZZZZ,
published on June 15, 2004, on page 33474 of the Federal Register.
These HAP emissions are known to cause, or contribute significantly to
air pollution, which may reasonably be anticipated to endanger public
health or welfare.
    Under the RICE NESHAP, we are proposing to limit emissions of HAP
through emissions standards for NMHC and formaldehyde. We have
determined that it is appropriate to use NMHC and formaldehyde or CO
emissions as a surrogate for HAP emissions. For the RICE MHAP
promulgated in 2004 (69 FR 33474) for engines greater than 500 HP
located at major sources, EPA chose to select a single pollutant to
serve as a surrogate for HAP emissions. Formaldehyde is the hazardous
air pollutant present in the highest concentration from stationary
engines. In addition, emissions data show that formaldehyde emission
levels are related to other HAP emission levels. For the NESHAP
promulgated in 2004, EPA also found that there is a strong relationship
between CO emissions reductions and HAP emissions reductions from 2SLB,
4SLB, and CI stationary engines. Therefore, CO emissions reductions
were chosen as a surrogate for HAP emissions reductions for 2SLB, 4SLB,
and CI stationary

engines operating with oxidation catalyst systems for that rule. For
the standards being proposed in this action, EPA believes that
previously made decisions regarding the appropriateness of using
formaldehyde and CO as surrogates for HAP are still valid. For this
proposal, EPA conducted an analysis using available emissions data to
look at the relationship between formaldehyde (a surrogate for HAP) and
NMHC. Based on statistical results of engine exhaust data, these data
indicate that there is a significant relationship between formaldehyde
and NMHC emissions from 2SLB, 4SLB, and CI stationary RICE. For this
reason, EPA believes it is appropriate to use NMHC emissions as a
surrogate for formaldehyde, and consequently, also as a surrogate for
HAP emissions. Much of the HAP being regulated are hydrocarbons; e.g.,
formaldehyde, an oxygenated hydrocarbon, is the HAP emitted in largest
quantities from stationary engines. For more information on EPA's
analysis of NMHC as a surrogate for HAP, refer to the docket for this
proposal.

C. What are the proposed standards?

    A description of the proposed standards is provided in the
following sections.
1. SI NSPS
    a. Stationary SI Engines < =19 KW (25 HP). EPA is proposing emission
standards that will affect manufacturers, owners, and operators of
stationary SI engines. Engine manufacturers must certify their
stationary SI engines with a maximum engine power less than or equal to
19 KW (25 HP) that are manufactured after January 1, 2008, to the
certification emission standards for new nonroad SI engines in 40 CFR
part 90, as applicable. The standards applicable to these engines are
shown in Table 1 of this preamble.

  Table 1.--NOX, HC, NMHC, and CO Emission Standards in g/KW-hr (g/HP-hr) for Stationary SI Engines < =19 KW (25
                                                       HP)
----------------------------------------------------------------------------------------------------------------
                                       Emission requirement in g/KW-hr (g/HP-hr)
           Engine classc           ------------------------------------------------      Manufacture date\b\
                                        HC+NOX         NMHC+NOXa          CO
----------------------------------------------------------------------------------------------------------------
I.................................            16.1            14.8
                                            (12.0)          (11.0)
I-A...............................              50  ..............             610  January 1, 2008.
                                              (37)  ..............           (455)
I-B...............................              40              37
                                              (30)          (27.6)
II................................            12.1            11.3
                                             (9.0)           (8.4)
----------------------------------------------------------------------------------------------------------------
aNMHC+NOX standards are applicable only to natural gas fueled engines at the option of the manufacturer, in lieu
  of HC+NOX standards.
bModified and reconstructed engines manufactured prior to January 1, 2008, must meet the standards applicable to
  engines manufactured after January 1, 2008.
cClass I-A: Engines with displacement < 66 cubic centimeter (cc); Class I-B: Engines with displacement greater
  than or equal to 66 cc and less than 100 cc; Class I: Engines with displacement greater than or equal to 100
  cc and less than 225 cc; Class II: Engines with displacement greater than or equal to 225 cc.

    b. Stationary SI Gasoline Engines >19 KW (25 HP) and Rich Burn LPG
Engines >19 KW (25 HP). Engine manufacturers must certify their
stationary SI engines with a maximum engine power greater than 19 KW
(25 HP) and less than 500 HP that use gasoline or rich burn engines
greater than 19 KW (25 HP) and less than 500 HP that use LPG that are
manufactured after January 1, 2008, to the certification emission
standards for new nonroad SI engines in 40 CFR part 1048, as
applicable. Engine manufacturers must certify their stationary SI
engines with a maximum engine power greater than or equal to 500 HP
that use gasoline or rich burn engines greater than or equal to 500 HP
that use LPG that are manufactured after July 1, 2007, to the
certification emission standards for new nonroad SI engines in 40 CFR
part 1048. The standards applicable to engines greater than 19 KW (25
HP) that are gasoline or rich burn engines that use LPG are shown in
Table 2 of this preamble.

 Table 2.--NOX, HC, and CO Emission Standards in g/KW-hr (g/HP-hr) for Stationary SI Gasoline Engines >19 KW (25
                                  HP) and Rich Burn LPG Engines >19 KW (25 HP)
----------------------------------------------------------------------------------------------------------------
                                                                                Emission requirement in g/KW-hr
                                                                                (g/HP-hr) a, b
             Maximum engine power                      Manufacture date        ---------------------------------
                                                                                HC+NOX             CO
----------------------------------------------------------------------------------------------------------------
25< HP< 500 c..................................  January 1, 2008................             2.7              4.4
                                                                                (2.0)            (3.3)
                                               January 1, 2008................             2.7            130.0
                                               (severe duty)..................            (2.0)           (97.0)
HP>=500 d....................................  July 1, 2007...................             2.7              4.4
                                                                                (2.0)            (3.3)
                                               July 1, 2007...................             2.7            130.0
                                               (severe duty)..................            (2.0)           (97.0)
----------------------------------------------------------------------------------------------------------------
a You may optionally certify your engines according to the following formula instead of the standards in Table 2
  of this preamble: (HC+NOX)xCO0.784< =8.57. The HC+NOX and CO emission levels you select to satisfy this
  formula, rounded to the nearest 0.1 g/kW-hr, become the emission standards that apply for those engines. You
  may not select an HC+NOX emission standard higher than 2.7 g/kW-hr or a CO emission standard higher than 20.6
  g/kW-hr.
b Provisions in 40 CFR part 1048 allow engines with a maximum engine power at or below 30 KW (40 HP) with a
  total displacement at or below 1,000 cubic centimeters (cc) to comply with the requirements of 40 CFR part 90.

c Modified and reconstructed engines between 25 and 500 HP manufactured prior to January 1, 2008, must meet the
  standards applicable to engines manufactured after January 1, 2008.
d Modified and reconstructed engines greater than or equal to 500 HP manufactured prior to July 1, 2007, must
  meet the standards applicable to engines manufactured after July 1, 2007.

    In addition to the emission standards shown in Table 2 of this
preamble, there are separate field testing standards required under 40
CFR part 1048 that are part of the certification requirements for
engine manufacturers.
    c. Stationary Non-Emergency SI Natural Gas Engines 19< KW< 37
(25< HP< 50) and Lean Burn LPG Engines 19< KW< 37 (25< HP< 50). Owners and
operators who purchase stationary SI engines with a maximum engine
power between 19 and 37 KW (25 and 50 HP) that are natural gas engines
or lean burn engines using LPG that are manufactured after January 1,
2008, must limit their exhaust emissions of NOX to 2.0 grams
per HP-hour (g/HP-hr), emissions of CO to 4.0 g/HP-hr, and emissions of
NMHC to 1.0 g/HP-hr. More stringent emission standards take effect 3
years later, i.e., for stationary natural gas engines 19 to 37 KW (25
to 50 HP) and lean burn engines using LPG between 19 and 37 KW (25 and
50 HP) manufactured after January 1, 2011. These engines must comply
with a NOX standard of 1.0 g/HP-hr, a CO standard of 2.0 g/
HP-hr, and a NMHC standard of 0.7 g/HP-hr. Engine manufacturers have
the option to certify their stationary SI engines to these emission
standards. However, the certification is only voluntary, and it is up
to the manufacturer to decide if it believes certification is feasible
and beneficial. Also, engine manufacturers have the option to certify
stationary SI engines between 19 and 37 KW (25 and 50 HP) that are
natural gas engines or lean burn engines using LPG to the emission
standards in 40 CFR part 1048, as shown in Table 2 of this preamble.
Additionally, engine manufacturers may certify engines between 19 and
30 KW (25 and 40 HP) with a displacement of 1,000 cc or less to the
provisions of 40 CFR part 90 (shown in Table 1 of this preamble), which
is consistent with similar provisions applicable to nonroad engines in
this displacement and size category. A summary of the proposed
standards for stationary non-emergency SI natural gas engines between
19 and 37 KW (25 and 50 HP) and stationary non-emergency lean burn LPG
engines between 19 and 37 KW (25 and 50 HP) is provided in Table 3 of
this preamble.
    d. Stationary Non-Emergency SI Natural Gas Engines 50< =HP< 500 and
Lean Burn LPG Engines 50< =HP< 500. EPA is proposing emission standards
in two stages for these engines. Owners and operators who purchase
stationary SI engines with a maximum engine power between 50 and 500 HP
that are natural gas engines or lean burn engines using LPG that are
manufactured after January 1, 2008, must limit their exhaust emissions
of NOX to 2.0 g/HP-hr, emissions of CO to 4.0 g/HP-hr, and
emissions of NMHC to 1.0 g/HP-hr. Again, engine manufacturers may
voluntarily certify these stationary SI engines to these emission
standards, but the certification is not required by this proposed rule.
Stationary SI engines with a maximum engine power between 50 and 500 HP
that are natural gas engines or lean burn engines using LPG that are
manufactured after January 1, 2011, must limit their exhaust emissions
of NOX to 1.0 g/HP-hr, emissions of CO to 2.0 g/HP-hr, and
emissions of NMHC to 0.7 g/HP-hr. A summary of the emission standards
EPA is proposing for these engines is shown in Table 3 of this
preamble.

                            Table 3.--NOX, NMHC, and CO Emission Standards in g/HP-hr for Stationary SI Engines >19KW (25 HP)
                                                       [Except Gasoline and Rich Burn LPG Engines]
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Emission standards in g/HP-hr
          Engine type and fuel               Maximum  engine power             Manufacture date a        -----------------------------------------------
                                                                                NOX             CO             NMHC
--------------------------------------------------------------------------------------------------------------------------------------------------------
Non-Emergency SI Natural Gas             25< HP< 500 a.................  January 1, 2008..................             2.0             4.0             1.0
                  and

Non-Emergency SI Lean Burn LPG.........  ............................  January 1, 2011..................             1.0             2.0             0.7
Non-Emergency SI Natural Gas             HP< =500.....................  July 1, 2007.....................             2.0             4.0             1.0
                  and

Non-Emergency SI Lean Burn LPG.........  ............................  July 1, 2010.....................             1.0             2.0             0.7
Landfill/Digester Gas..................  HP>=500.....................  January 1, 2008..................             3.0             5.0             1.0
                                                                       January 1, 2011..................             2.0             5.0             1.0
                                         HP>=500.....................  July 1, 2007.....................             3.0             5.0             1.0
                                                                       July 1, 2010.....................             2.0             5.0             1.0
Emergency..............................  All Sizes...................  January 1, 2009..................             2.0             4.0             1.0
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Stationary SI natural gas and lean burn LPG engines between 19 and 37 KW (25 and 50 HP) may comply with the requirements of Table 2 of this
  preamble, instead of this table, as applicable.

    e. Stationary Non-Emergency SI Natural Gas Engines >=500 HP and
Non-Emergency Lean Burn LPG Engines >=500 HP. EPA is proposing emission
standards in two stages for stationary non-emergency SI natural gas
engines greater than or equal to 500 HP and non-emergency lean burn LPG
engines greater than or equal to 500 HP. Owners and operators who
purchase stationary SI engines with a maximum engine power greater than
or equal to 500 HP that are natural gas engines or lean burn engines
using LPG that are manufactured after July 1, 2007, must limit their
exhaust emissions of NOX to 2.0 g/HP-hr, emissions of CO to
4.0 g/HP-hr, and emissions of NMHC to 1.0 g/HP-hr. Engine manufacturers
may voluntarily certify these stationary SI engines to these emission
standards, but the certification is not required by the rule, as
proposed. Stationary SI engines with a maximum engine power greater
than or equal to 500 HP that are natural gas engines or lean burn
engines using LPG that are manufactured after July 1, 2010, must limit
their exhaust emissions of NOX to 1.0 g/HP-hr, emissions of
CO to 2.0 g/HP-hr, and emissions of NMHC to 0.7 g/HP-hr. Again,
manufacturers may voluntarily certify their engines to these emission
standards. A summary of the emission standards EPA is proposing for
these engines is shown in Table 3 of this preamble.

    f. Stationary SI Landfill/Digester Gas Engines. Similar to other
stationary SI engines, EPA is proposing emission standards in two
stages for landfill and digester gas fired engines. Owners and
operators who purchase stationary landfill or digester SI engines that
are manufactured after July 1, 2007, that are greater than or equal to
500 HP must limit their exhaust emissions of NOX to 3.0 g/
HP-hr, emissions of CO to 5.0 g/HP-hr, and emissions of NMHC to 1.0 g/
HP-hr. Stationary landfill and digester gas SI engines greater than or
equal to 500 HP that are manufactured after July 1, 2010, must limit
their exhaust emissions of NOX to 2.0 g/HP-hr, emissions of
CO to 5.0 g/HP-hr, and emissions of NMHC to 1.0 g/HP-hr. Again, engine
manufacturers may voluntarily certify these stationary SI engines to
these emission standards, but the certification is not required by the
rule, as proposed. Stationary SI engines that use landfill or digester
gas that are less than 500 HP are given an extra 6 months to comply
with the standards. The first stage of limits of 3.0, 5.0, and 1.0 g/
HP-hr, for NOX, CO, and NMHC, respectively, applies to
landfill and digester gas engines manufactured after January 1, 2008.
The second stage of limits of 2.0, 5.0, and 1.0 g/HP-hr, for
NOX, CO, and NMHC, respectively, applies to landfill and
digester gas engines manufactured after January 1, 2011. A summary of
the emission standards EPA is proposing for these engines is shown in
Table 3 of this preamble.
    g. Stationary Emergency SI Engines. For stationary SI engines that
are emergency engines, EPA is proposing a single stage of emission
limits. Owners and operators who purchase stationary emergency engines
that are manufactured after January 1, 2009, must limit their exhaust
emissions of NOX to 2.0 g/HP-hr, emissions of CO to 4.0 g/
HP-hr, and emissions of NMHC to 1.0 g/HP-hr.
    h. Fuel Requirements. In addition to emission standards, EPA is
proposing that owners and operators who use gasoline in their
stationary SI engine must use gasoline that meets the requirements of
40 CFR 80.195. The requirements include a gasoline sulfur per gallon
cap of 80 parts per million (ppm).
2. NESHAP
    a. Engines < =500 HP at Major Sources. We are proposing that owners
and operators of new and reconstructed stationary SI engines with a
site rating of equal to or less than 500 HP located at a major source
of HAP emissions must generally meet the same NMHC emission standards
for new SI engines as proposed for the NSPS in 40 CFR part 60, subpart
JJJJ.
    One major difference between the SI NSPS and NESHAP requirements is
that owners and operators of new or reconstructed 4SLB SI stationary
engines between 250 and 500 HP located at a major source are required
to either reduce CO emissions by 93 percent or more, or limit the
concentration of formaldehyde in the stationary engine exhaust to 14
ppm by volume, dry basis (ppmvd) or less, at 15 percent oxygen
(O2). These engines would not be required to meet the NMHC
standard. The formaldehyde standard is more stringent than the NMHC
stage 1 and stage 2 emission standards of 1.0 and 0.7 g/HP-hr,
respectively.
    Under the NESHAP, owners and operators of new and reconstructed
landfill and digester gas fired engines and new and reconstructed SI
emergency engines are subject to the NMHC emission standards that are
being proposed under the SI NSPS. New and reconstructed landfill and
digester gas engines must, under the NESHAP, meet NMHC emission
standards consistent with the SI NSPS, i.e., a NMHC standard of 1.0 g/
HP-hr. Owners and operators of stationary landfill and digester gas
engines must meet the NMHC standard if they are manufactured after
January 1, 2008.
    For new and reconstructed stationary SI engines with a site rating
of equal to or less than 500 HP located at a major source of HAP
emissions that are emergency engines, owners and operators who purchase
such engines that are manufactured after January 1, 2009, must limit
their exhaust emissions of NMHC to 1.0 g/HP-hr.
    Finally, owners and operators of new and reconstructed stationary
CI engines with a site rating of equal to or less than 500 HP located
at a major source of HAP emissions that purchase 2007 model year and
later stationary CI engines must meet the NMHC and PM emission
standards for new CI engines specified in 40 CFR part 60, subpart IIII.
Those standards are generally based on the certification emission
standards for new nonroad CI engines. A summary of the standards being
proposed for stationary engines less than or equal to 500 HP located at
major sources is presented in Table 4 of this preamble.
    Owners and operators of existing stationary engines with a site
rating of equal to or less than 500 HP located at a major source of HAP
emissions have an emissions standard of no emission reduction and are
not subject to any specific requirements under subpart ZZZZ or subpart
A of 40 CFR part 63. A stationary RICE is existing if it commences
construction or reconstruction before June 12, 2006.

     Table 4.--Emission Standards for Stationary RICE < =500 HP Located at Major Sources of HAP Emissions and
                            Stationary RICE Located at Area Sources of HAP Emissions
----------------------------------------------------------------------------------------------------------------
       Engine type and fuel            Maximum engine power          Manufacture date a       Emission standards
----------------------------------------------------------------------------------------------------------------
Existing All Fuels and All Types.  All Sizes..................               No Emission Reduction.
New/Reconstructed SI.............  < =25 HP....................  January 1, 2008............  Meet 40 CFR part 60
                                                                                subpart JJJJ.
New/Reconstructed SI Gasoline and  25>HP<500..................  January 1, 2008............  Meet 40 CFR part 60
 Rich Burn LPG.                    HP>=500....................  July 1, 2007...............   subpart JJJJ.
New/Reconstructed Non-Emergency    25< HP< 500 a................  January 1, 2008............  1.0 g/HP-hr NMHC.
 SI Natural Gas.
               and

New/Reconstructed Non-Emergency    ...........................  January 1, 2011............  0.7 g/HP-hr 2011
 SI Lean Burn LPG b.                                                                          NMHC.
New/Reconstructed Non-Emergency    HP>=500....................  July 1, 2007...............  1.0 g/HP-hr NMHC
 SI Natural Gas.
HP< =500..........................  July 1, 2007...............  1.0 g/HP-hr NMHC...........

               and

New/Reconstructed Non-Emergency    ...........................  July 1, 2010...............  0.7 g/HP-hr NMHC.
 SI Lean Burn LPG.
New/Reconstructed Non-Emergency    250< HP < =500...............  January 1, 2008............  93% CO Reduction or
 SI 4SLB at Major Sources (except                                                             14 ppmvd
 landfill and digester gas) b.                                                                formaldehyde.
CI All Fuels.....................  All Sizes..................  2007+ Model Year...........  Meet 40 CFR part 60
                                                                                subpart IIII.
Landfill/Digester Gas............  HP< 500.....................  January 1, 2008............  1.0 g/HP-hr NMHC.
                                   HP>=500....................  July 1, 2007...............  1.0 g/HP-hr NMHC.
Emergency SI.....................  All Sizes..................  January 1, 2009............  1.0 g/HP-hr NMHC.
----------------------------------------------------------------------------------------------------------------
a Stationary SI natural gas and lean burn LPG engines between 19 and 37 KW (25 and 50 HP) may comply with the
  requirements of Table 2 of this preamble, instead of this table, as applicable.
b New and reconstructed non-emergency 4SLB engines at major sources with a site rating between 250 and 500 HP
  are not required to meet the 1.0 and 0.7 g/HP-hr NMHC emission standards.

    b. Engines at Area Sources. We are proposing that owners and
operators of new and reconstructed stationary engines located at area
sources of HAP emissions generally meet the same requirements that
apply to new and reconstructed stationary engines with a site rating of
equal to or less than 500 HP located at a major source of HAP
emissions. New and reconstructed stationary engines located at area
sources with a site rating greater than 500 HP are required to meet the
same NMHC standard as proposed in the SI NSPS for the engine's HP
classification, or the same NMHC and PM standards as proposed in the CI
NSPS for the engine's HP classification.
    There is only one difference between the requirements for new and
reconstructed stationary engines located at area sources and new and
reconstructed stationary engines with a site rating of equal to or less
than 500 HP located at major sources. Owners and operators of new or
reconstructed 4SLB SI stationary engines between 250 and 500 HP located
at area sources are not required to reduce CO emissions by 93 percent
or more, or limit the concentration of formaldehyde in the stationary
engine exhaust to 14 ppmvd or less at 15 percent O2. New and
reconstructed stationary SI engines located at area sources must,
however, meet the NMHC emission standards shown in Table 4 of this
preamble.
    Owners and operators of existing stationary engines located at an
area source of HAP emissions have an emission standard of no emission
reduction and are not subject to any specific requirements under
subpart ZZZZ or of subpart A of 40 CFR part 63.

D. What are the requirements for sources that are modified or
reconstructed?

1. SI NSPS
    The proposed standards apply to stationary SI engines subject to
the SI NSPS that are modified or reconstructed after June 12, 2006. The
guidelines for determining whether a source is modified or
reconstructed are given in 40 CFR 60.14 and 40 CFR 60.15, respectively.
    Stationary SI ICE less than or equal to 19 KW (25 HP) manufactured
prior to January 1, 2008 that are modified or reconstructed after June
12, 2006 are required to meet the standards that apply to engines
manufactured after January 1, 2008.
    Stationary SI gasoline and rich burn LPG engines between 25 HP and
500 HP manufactured prior to January 1, 2008 that are modified or
reconstructed after June 12, 2006 are required to meet the standards
applicable to engines manufactured after January 1, 2008.
    Stationary SI gasoline and rich burn LPG engines greater than or
equal to 500 HP manufactured prior to July 1, 2007 that are modified or
reconstructed after June 12, 2006 are required to meet the standards
applicable to engines manufactured after July 1, 2007.
    Stationary SI natural gas and lean burn LPG engines less than 500
HP manufactured prior to January 1, 2008 that are modified or
reconstructed after June 12, 2006 are required to meet a NOX
emission standard of 3.0 g/HP-hr, a CO standard of 4.0 g/HP-hr, and a
NMHC standard of 1.0 g/HP-hr.
    Stationary SI natural gas and lean burn LPG engines greater than or
equal to 500 HP manufactured prior to July 1, 2007 that are modified
after June 12, 2006, are required to meet a NOX emission
standard of 3.0 g/HP-hr, a CO standard of 4.0 g/HP-hr, and a NMHC
standard of 1.0 g/HP-hr.
    Stationary SI landfill and digester gas engines less than 500 HP
manufactured prior to January 1, 2008 that are modified or
reconstructed after June 12, 2006 are required to meet a NOX
emission standard of 3.0 g/HP-hr, a CO standard of 5.0 g/HP-hr, and a
NMHC standard of 1.0 g/HP-hr. Stationary SI landfill and digester gas
engines greater than or equal to 500 HP manufactured prior to July 1,
2007 that are modified after June 12, 2006 are required to meet a
NOX emission standard of 3.0 g/HP-hr, a CO standard of 5.0
g/HP-hr, and a NMHC standard of 1.0 g/HP-hr.
    Stationary SI emergency engines manufactured prior to January 1,
2009 that are modified or reconstructed after June 12, 2006 are
required to meet a NOX emission standard of 3.0 g/HP-hr, a
CO standard of 4.0 g/HP-hr, and a NMHC standard of 1.0 g/HP-hr.
2. NESHAP
    Similar concepts as those discussed above apply to engines subject
to 40 CFR part 63 regulations; however, the concept of modification is
not included in 40 CFR part 63. The proposed standards apply to
stationary engines subject to the NESHAP that commence reconstruction
on or after June 12, 2006. The reconstruction criteria are provided in
40 CFR 63.2.

E. What are the requirements for demonstrating compliance?

    The following sections describe the requirements for demonstrating
compliance under the stationary SI NSPS and NESHAP.
1. SI NSPS
    Owners and operators of stationary engines subject to the
requirements of the SI NSPS must operate and maintain

their stationary engine and after treatment control device (if any)
according to the manufacturer's written instructions. Manufacturers of
stationary SI engines required to certify their engines must
demonstrate compliance by certifying that their stationary SI engines
meet the emission standards, as specified in 40 CFR part 60, subpart
JJJJ, as applicable, using the certification procedures in subpart B of
40 CFR part 90 and subpart C of 40 CFR part 1048, as applicable, and
must test their engines as specified in those parts. Manufacturers who
conduct voluntary certification must follow the same test procedures
that apply to large SI nonroad engines under 40 CFR part 1048, but must
use the D-2 cycle in International Organization for Standardization
(ISO) 8178-4 for stationary engines. The test cycle requirements that
manufacturers who conduct voluntary certification should follow are
provided in Table 3 to 40 CFR 1048.505.
    Manufacturers who opt to voluntary certify their stationary SI
engines to the emission standards specified in this subpart must
certify their engines using fuel that meets the definition of pipeline-
quality natural gas, which according to the proposed definition must be
composed of at least 70 percent methane by volume or have a gross
calorific value between 950 and 1,100 British thermal units per
standard cubic foot.
    If the manufacturer chooses to certify its stationary SI engines to
another fuel, the manufacturer must specify the properties of that fuel
and what adjustments the owner or operator must make to the engine
during installation in the field in order to meet the emission
standards. The manufacturer must also perform certification testing on
the engine on that fuel, as it would if it was certifying to pipeline-
quality natural gas, in order to assure compliance with the emission
standards. Manufacturers who conduct voluntary certification of
stationary SI ICE must also provide instructions to the owner and
operator for configuring the stationary engine to meet the emission
standards on fuels that meet the pipeline-quality natural gas
specifications and fuels that do not meet the pipeline-quality natural
gas specifications. The manufacturer must provide information to the
owner and operator of the certified stationary SI engine regarding the
particular fuels to which the engine is certified, and instructions
regarding configuring the engine in a manner most appropriate for
reducing pollutant emissions for engines operating on such fuels.
Owners and operators may operate their certified engine on other fuels
that the engine is not certified to, but the engine would no longer be
considered a certified engine and the owner or operator would be
required to test the engine to demonstrate compliance with the emission
standards.
    EPA is proposing to allow owners and operators of natural gas
engines to use propane as back up fuel for emergency purposes for no
more than 100 hours per year. If propane is used for more than 100
hours per year in an engine that is not certified to the emission
standards when using propane, the owners and operators are required to
conduct a performance test to demonstrate compliance with the emission
standards.
    Owners and operators that operate engines that have been certified
by the engine manufacturer are not required to perform any performance
testing unless the engine is operated outside of the fuel properties
specified by the manufacturer. If the owner or operator uses fuels that
are outside of the fuel specifications or does not follow the
adjustments specified by the manufacturer, the engine is no longer
considered a certified engine and the owner or operator must test the
engine to demonstrate compliance. If the engine is no longer considered
a certified engine, the owner or operator must test the engine
according to the test procedures that are specified for uncertified
engines, as specified in this proposed rule.
    Owners and operators subject to the emission standards specified in
this proposed rule who use stationary SI engines with a maximum engine
power of less than or equal to 19 KW (25 HP) or who use stationary SI
engines with a maximum engine power greater than 19 KW (25 HP) and use
gasoline or are rich burn engines greater than 19 KW (25 HP) using LPG
must demonstrate compliance by using an engine certified to the
emission standards specified in 40 CFR part 90 or 1048, as applicable.
    Owners and operators subject to this proposed rule who use
stationary SI engines with a maximum engine power greater than 19 KW
(25 HP) that use fuels other than gasoline and that are not rich burn
engines greater than 19 KW (25 HP) that use LPG, must demonstrate
compliance by either using an engine certified to the emission
standards specified in Table 3 of this preamble or by conducting an
initial performance test to demonstrate compliance with the emission
standards specified in Table 3 of this preamble. If the owner or
operator purchases a certified engine, performance testing would not be
required (unless the engine is operated differently than specified by
the manufacturer). Owners and operators of uncertified engines that are
greater than 500 HP must conduct subsequent performance tests every 3
years, or 8,760 hours of operation, whichever comes first.
2. NESHAP
    Consistent with the requirements for owners and operators subject
to the SI NSPS, owners and operators of stationary engines subject to
the requirements of the NESHAP must also operate and maintain their
stationary engine and exhaust aftertreatment device (if any) according
to the manufacturer's written instructions. This requirement applies to
stationary SI and CI engines regulated under this proposed rule.
    Owners and operators subject to the NESHAP who use stationary SI
engines must demonstrate compliance by meeting the NMHC emission
standards specified in 40 CFR part 60, subpart JJJJ (unless they are
new or reconstructed non-emergency 4SLB SI stationary RICE between 250
and 500 HP located at major sources). Under 40 CFR part 60, subpart
JJJJ, as described in the previous section, certain stationary SI
engines must be certified to the emission standards in 40 CFR part 90
or 1048, as applicable.
    Owners and operators of uncertified SI engines subject to the
emission standards proposed in the NESHAP must conduct an initial
performance test to demonstrate compliance with the emission standards.
Owners and operators of certified engines are not required to conduct
any performance testing (unless the engine is operated differently than
procedures specified by the manufacturer or procedures developed by the
owner or operator that are approved by the engine manufacturer). Owners
and operators of uncertified engines that are greater than 500 HP,
subject to the emission standards proposed in this action must conduct
subsequent performance tests every 3 years, or 8,760 hours of
operation, whichever comes first. Owners and operators of uncertified
engines subject to emission standards that are less than or equal to
500 HP are not required to perform subsequent performance tests after
the initial performance test, unless the stationary engine is rebuilt
or undergoes major repair or maintenance.
    Owners and operators of new and reconstructed non-emergency 4SLB
engines between 250 and 500 HP that are located at major sources of HAP
emissions must demonstrate compliance

by conducting an initial performance test. These engines must also
conduct subsequent performance test semiannually if they are complying
with the requirement to reduce CO emissions and not using a continuous
emissions monitoring system, and if they are complying with the
requirement to limit the concentration of formaldehyde in the
stationary engine exhaust.
    Owners and operators subject to the NESHAP who use stationary CI
engines must demonstrate compliance by using an engine certified to the
NMHC and PM emission standards specified in 40 CFR part 60, subpart
IIII, and by operating their engine properly, as stated above. The only
exception is for owners and operators of stationary CI engines with a
displacement of greater than or equal to 30 liters per cylinder who
must demonstrate compliance through performance testing.

F. What are the reporting and recordkeeping requirements?

    The following sections describe the reporting and recordkeeping
requirements that are required under the SI NSPS and the NESHAP.
1. SI NSPS
    Owners and operators of all engines (certified and uncertified) are
required to maintain records of proper maintenance. An initial
notification is required for owners and operators of engines greater
than 500 HP that are not certified. Also, owners and operators who
conduct performance testing are required to report the test results
within 30 days of each performance test.
    Owners and operators of emergency engines are required to keep
records of their hours of operation. Owners and operators must install
a non-resettable hour meter on their engines to record the necessary
information. Emergency stationary engines may be operated for the
purpose of maintenance checks and readiness testing, provided that the
tests are recommended by the Federal, State or local government, the
manufacturer, the vendor, or the insurance company associated with the
engine. Maintenance checks and readiness testing of such units is
limited to 100 hours per year. Owners and operators can petition the
Administrator for additional hours, beyond the allowed 100 hours per
year, if such additional hours should prove to be necessary for
maintenance and testing reasons. A petition is not required if the
hours beyond 100 hours per year for maintenance and testing purposes
are mandated by regulation such as State or local requirements. There
is no time limit on the use of emergency stationary engines in
emergency situations, however, the owner or operator is required to
record the length of operation and the reason the engine was in
operation during that time. Records must be maintained documenting why
the engine was operating to ensure the 100 hours per year limit for
maintenance and testing operation is not exceeded.
2. NESHAP
    Consistent with the SI NSPS (and the already proposed CI NSPS),
owners and operators of stationary emergency engines (SI and CI) are
required to keep records of their hours of operation under the NESHAP.
Owners and operators must install a non-resettable hour meter on their
engines to record the necessary information. Emergency stationary
engines may be operated for the purpose of maintenance checks and
readiness testing, provided that the tests are recommended by Federal,
State or local government, the manufacturer, the vendor, or the
insurance company associated with the engine. Maintenance checks and
readiness testing of such units is limited to 100 hours per year.
Owners and operators can petition the Administrator for additional
hours, beyond the allowed 100 hours per year, if such additional hours
should prove to be necessary for maintenance and testing reasons. A
petition is not required if the hours beyond 100 hours per year for
maintenance and testing purposes are mandated by regulation such as
State or local requirements. There is no time limit on the use of
emergency stationary engines in emergency situations. Owners and
operators must also maintain records documenting the reason the engine
was in operation.
    The above proposed requirement to limit the operation of
maintenance and testing operation to 100 hours per year is different
than the requirement that was finalized for stationary engines greater
than 500 HP located at major sources. Currently, stationary emergency
engines greater than 500 HP located at major sources are required to
limit non-emergency operation to 50 hours per year. Multiple comments
received during the public comment period for NSPS for stationary CI
engines argued that EPA should allow 100 hours per year for emergency
engines to conduct necessary maintenance and testing. Based on those
comments, EPA believes it would be appropriate to propose to allow 100
hours per year for maintenance and testing operation for emergency
engines. As discussed, EPA is proposing 100 hours per year for
maintenance and testing operation under the SI NSPS and the NESHAP
being proposed in this action for stationary engines with a site rating
of 500 HP or less located at major sources and stationary engines
located at area sources. EPA believes it is appropriate to propose to
amend the requirements of stationary engines greater than 500 HP
located at major sources to allow emergency engines to operate 100
hours per year for maintenance and testing purposes. It is crucial to
allow sufficient hours for maintenance and readiness testing to ensure
that the emergency engine will respond as expected in the event of an
emergency and EPA believes that 100 hours per year is adequate. EPA
also believes it is appropriate to amend the emergency engine hour
limitation in the NESHAP for stationary RICE greater than 500 HP
located at major sources to ensure consistency between regulations
affecting the same or similar sources. Further, as discussed, based on
information received since the promulgation of the NESHAP for
stationary RICE greater than 500 HP located at major sources, the 50
hours per year allowance currently in that regulation would not be
sufficient to address necessary maintenance, testing, and readiness
operation for emergency engines, and EPA is, therefore, proposing to
increase the limitation to 100 hours per year.
    Owners and operators of new and reconstructed stationary RICE which
fire landfill or digester gas equivalent to 10 percent or more of the
gross heat input on an annual affected by subpart ZZZZ of 40 CFR part
63, must monitor and record the fuel usage daily with separate fuel
meters to measure the volumetric flow rate of each fuel.

IV. Rationale for Proposed Rule

A. Which control technologies apply to stationary engines?

    EPA reviewed various control technologies applicable to stationary
engines. For detailed information on the control technology review that
EPA conducted, refer to information in the docket for this proposed
rule. The following sections provide general descriptions of currently
available controls that can be used to reduce emissions from stationary
engines.
    Non-selective catalytic reduction (NSCR) has been commercially
available for many years and has been widely used on stationary
engines. The technology can be applied to rich burn stationary engines
and is capable of reducing NOX emissions by 90 percent or
more. The technology also reduces CO by about 90 percent. Emissions of
NMHC and HAP are also reduced by

using the catalyst and significant reductions have been recorded. Based
on our information, NSCR appears to be technically feasible for rich
burn engines down to 19 KW (25 HP).
    Selective catalytic reduction (SCR) is applicable to lean burn
stationary engines, but has not been widely used on stationary SI
engines. This technology is capable of achieving NOX
reductions of at least 90 percent. An oxidation catalyst is often used
in conjunction with SCR to reduce emissions of CO, NMHC, and HAP. The
technology has not been commonly applied to stationary engines and if
applied, the applications have typically been on larger lean burn
engines. Costs of SCR are generally high, including significant
equipment, installation, and operating costs.
    Oxidation catalyst is another type of aftertreatment that can be
applied to stationary engines and is typically used with lean burn
engines. The technology can be applied to either diesel or gas fired
lean burn engines. Emissions of CO can be reduced by 90 percent or more
and significant NMHC and HAP reductions are also possible. Applying the
technology to diesel fired engines can reduce PM by about 25 to 30
percent. Oxidation catalyst control has been widely used and has been
available for decades for use with lean burn stationary engines.
    Catalyzed diesel particulate filters (CDPF) are applicable to CI
engines using diesel fuel and are primarily used to reduce PM
emissions. The technology is a newer technology than other
aftertreatment control devices, but is becoming increasingly
widespread. Applying CDPF can reduce PM emissions by 90 percent or
more, and reductions in CO and HAP can be significant. The technology
appears to be applicable to a wide range of diesel engines, except
there may be issues with respect to applying the technology to smaller
engines (less than 19 KW (25 HP)), and potentially also to extremely
large engines (several thousand HP). Catalyzed diesel particulate
filters are the basis for the Tier 4 emission standards for PM for most
nonroad CI engines regulated by 40 CFR part 1039 and also for most new
non-emergency stationary CI engines regulated under 40 CFR part 60,
subpart IIII. Recently finalized standards for stationary CI engines in
California are also based on the use of particulate filters in some
cases.
    Stationary SI engines burning natural gas typically have low levels
of PM in the order of 0.01 g/HP-hr, according to engine manufacturers.
This level is comparable to Tier 4 levels that nonroad and stationary
CI engines will achieve with CDPF. For these reasons, EPA is not
proposing PM emission standards for stationary SI engines. Emissions of
sulfur oxides (SOX) are usually low from natural gas fired
engines since, in most cases, the fuel is inherently very low in
sulfur. There are no controls currently available to control
SOX in the exhaust from stationary engines; the only way to
limit SOX is to minimize sulfur in the fuel.
    Although aftertreatment devices can help achieve very significant
reductions in exhaust emissions from stationary engines, there are
other strategies available which can help reduce emissions. For
example, lean burn technology alone produces much lower levels of
NOX than rich burn engines. In a lean burn engine, excess
air is introduced into the engine with the fuel, reducing the
temperature of the combustion process, which in turn reduces the
NOX significantly compared to a rich burn engine. Also,
because excess O2 is available, combustion is more
efficient, so more power is produced with the same amount of fuel.
Another example of an emission reduction strategy that prevents the
formation of NOX is exhaust gas recirculation. Exhaust gas
recirculation has been widely used in automotive engines for many years
to reduce NOX emissions and could potentially be used in
stationary engine applications. Also, in SI engines, modifications of
the combustion chamber and fuel metering system can help improve mixing
of the fuel and air, thus improving NMHC emissions. Spark-timing
calibrations can also help reduce CO and NMHC emissions.

B. How did EPA determine the basis and level of the proposed standards?

1. SI NSPS
    Section 111 of the CAA states that a standard of performance
``means a standard * * * which reflects the degree of emission
limitation achievable through application of the best system of
emission reduction which (taking into account the cost of achieving
such reduction and any non-air quality health and environmental impact
and energy requirements) the Administrator determines has been
adequately demonstrated.''
    The following discussion provides additional information by
identifying specific technologies (referred to hereafter as ``BDT'')
that EPA anticipates to be used to meet the NSPS. It must be noted,
however, that EPA's proposal is that the best system of emissions
reductions that has been adequately demonstrated is a set of emissions
standards, including an averaging, banking and trading program, where
applicable, that allows for the use of other potential technologies
that meet or exceed the standards.
    a. Stationary SI Engines < =19 KW (25 HP). For stationary SI engines
less than or equal to 19 KW (25 HP), the technologies that are the
basis of the proposed standards are expected to be the same as the
technologies that are the basis for the nonroad SI engine Phase 2
standards in this size range. The Phase 2 nonroad engine program will
lead to increased use of automotive-style overhead valve technology for
nonhandheld engines and is expected to be the technology that is relied
upon to meet Phase 2 emission standards. Stationary engines less than
or equal to 19 KW (25 HP) are required to be certified to the emission
standards for new nonroad SI engines as specified in 40 CFR part 90.
These standards are separated by the class of the engine (Class I
through Class V) and each class is determined by the use of the engine,
i.e., handheld or nonhandheld, and engine displacement. Phase 1
standards took effect for most new handheld and nonhandheld engines
beginning in model year 1997. Phase 2 standards for nonhandheld engines
are being phased in between 2001 and 2007. Phase 2 standards for
handheld engines have been phased in starting in 2002. EPA believes it
is appropriate to require new stationary SI engines less than or equal
to 19 KW (25 HP) to meet the Phase 2 emission standards for nonhandheld
nonroad SI engines, as nonhandheld engines would be more similar to
stationary engines than handheld engines, and because by definition, a
stationary engine cannot be a handheld engine. EPA believes that it is
appropriate that the emission standards for new stationary SI engines
less than or equal to 19 KW (25 HP) are the same as those for nonroad
SI engines in this size range. To determine the BDT for these size
engines, EPA analyzed the emission control strategies selected for the
nonroad SI engine rule for engines less than or equal to 19 KW (25 HP).
EPA concluded that the level and implementation timing of the nonroad
SI engine standards are the most appropriate that can be justified for
this size group of engines. EPA believes a manufacturer-based
certification program is also appropriate for this group of engines and
that there is little difference, if any, between nonroad and stationary
SI engines in this size range. Engine manufacturers are already
familiar with and have experience in

certifying their engine families according to EPA's certification
program. For the reasons provided, BDT for stationary SI engines less
than or equal to 19 KW (25 HP) is determined to be the control
technologies used to comply with Phase 2 emission standards for
nonhandheld nonroad SI engines under 40 CFR part 90. EPA is also
proposing to allow manufacturers to certify any engine with a maximum
engine power between 19 and 30 KW (25 and 40 HP) with total
displacement of 1,000 cc or less to the nonhandheld nonroad SI engine
standards under 40 CFR part 90. This option is already available for
nonroad engines with these maximum power and displacement
characteristics.
    EPA expects to propose new standards in the near future applicable
to nonroad SI engines less than or equal to 19 KW (25 HP) that will be
more stringent than Phase 2 standards, giving appropriate lead time for
the requirements. EPA will consider incorporating these more stringent
standards into its stationary SI NSPS regulations as they apply to
stationary SI engines in this HP range at the same time it revises its
nonroad standards for SI engines.
    EPA requests public comment on the issue of evaluating the
appropriateness of future small non-road engine emission standards as
they may apply to stationary SI engines less than or equal to 19 KW (25
HP).
    b. Stationary SI Gasoline Engines >19 KW (25 HP) and Rich Burn LPG
Engines >19 KW (25 HP). For stationary SI engines greater than 19 KW
(25 HP) that use gasoline and rich burn engines greater than 19 KW (25
HP) that use LPG, the technology that is the basis of the proposed
standards are the technologies used by nonroad SI engines greater than
19 KW (25 HP) to comply with the emission standards in 40 CFR part
1048. The majority of nonroad SI engines greater than 19 KW (25 HP) use
LPG, but some operate on gasoline or natural gas. There are two tiers
for nonroad SI engines in this size category. Tier 1 standards were
scheduled to begin in 2004; Tier 2 standards will begin in 2007. The
upcoming Tier 2 standards are based on three-way catalyst systems with
electronic, closed-loop fuel systems. For stationary SI engines greater
than 19 KW (25 HP) that use gasoline or are rich burn engines greater
than 19 KW (25 HP) that use LPG, EPA believes these engines are very
similar to nonroad SI equipment, and the same engines designed for use
in nonroad applications are used in stationary applications. Therefore,
for stationary SI engines greater than 19 KW (25 HP) that use gasoline
and rich burn engines greater than 19 KW (25 HP) that use LPG, the BDT
is the technology that is the basis for the Tier 2 emission standards
for nonroad engines above 19 KW (25 HP) regulated under 40 CFR part
1048.
    c. Stationary Non-Emergency SI Natural Gas Engines 25< HP< 500 and SI
Lean Burn LPG Engines 25< HP< 500. For stationary non-emergency SI
natural gas and lean burn LPG engines between 25 and 500 HP, EPA
believes that these engines can be different than nonroad SI engines in
the same size range that use gasoline or that are rich burn engines
using LPG, and that more stringent standards are possible for these
engines provided that sufficient lead time is given. Therefore, EPA
evaluated currently available control technologies to reduce criteria
pollutant emissions from these stationary SI engines. However, EPA is
proposing to allow manufacturers to certify any SI natural gas or lean
burn LPG engines between 19 and 37 KW (25 and 50 HP) to the standards
for nonroad engines in this power range in 40 CFR part 1048 as an
alternative to the standards being proposed in the SI NSPS. EPA
believes that engines between 19 and 37 KW (25 and 50 HP) can be
similar to nonroad engines in this size range and, therefore, feels it
is appropriate to provide engine manufacturers with the option to
certify these engines to 40 CFR part 1048. However, for engines greater
than 37 KW (50 HP), EPA is not including this option. EPA believes that
natural gas engines and lean burn LPG engines greater than 37 KW (50
HP) are different than those less than 37 KW (50 HP), which tend to be
more like mobile engines and for that reason is proposing the emission
standards discussed below.
    For natural gas rich burn stationary engines, the technology that
is the basis for the proposed standards is NSCR and is essentially the
same technology as a three-way catalyst. As discussed, NSCR is widely
available and has commonly been used on stationary rich burn engines
across the U.S. The technology was the basis for the emission standards
for HAP for the NESHAP for stationary RICE greater than 500 HP located
at major sources and is also the basis for many State requirements for
rich burn engines. Non-selective catalytic reduction has primarily been
installed to reduce emissions of NOX, but is also effective
in reducing CO and NMHC emissions from stationary rich burn engines. No
other technology was identified as applicable to rich burn engines that
would achieve equivalent or higher emission reductions than NSCR. The
technology can be purchased, installed, and operated for a reasonable
cost on new engines and requires no extensive operator training or
expertise. The technology is available from many catalyst vendors and
is simple to acquire. For the reasons provided, BDT for rich burn
engines between 25 and 500 HP that use fuels other than gasoline and
LPG is NSCR.
    As discussed, EPA is proposing a stage 1 NOX emission
limit of 2.0 g/HP-hr for stationary non-emergency SI engines between 25
and 500 HP that burn natural gas or that are lean burn engine using
LPG. This limit would apply to engines manufactured after January 1,
2008. EPA believes that January 1, 2008, will provide sufficient time
for engine manufacturers and owners and operators to make the necessary
adjustments and preparations in order to develop and certify engines
that are able to achieve the proposed standards. These engines would
also have to meet a CO emission limit of 4.0 g/HP-hr and a NMHC
emission limit of 1.0 g/HP-hr. EPA received information on the
emissions from new stationary SI engines from various engine
manufacturers. The average NOX engine-out levels for rich
burn engines without aftertreatment were in the order of 12 to 15 g/HP-
hr. It is estimated that applying NSCR to new uncontrolled rich burn
engines would be able to achieve controlled NOX levels
between 1.2 and 1.5 g/HP-hr, perhaps lower if the catalyst is designed
for higher NOX reduction. Based on these estimates, EPA
feels it is reasonable to require a stage 1 NOX emission
limit of 2.0 g/HP-hr, which is based on engines using aftertreatment
control. A stage 1 limit of 2.0 g/HP-hr takes into account uncertainty
associated with meeting the standard. The engine may be capable of
emitting an average of 1.5 g/HP-hr, but NOX emissions may
fluctuate above and below that level. A standard of 2.0 g/HP-hr
provides the necessary flexibility to account for such fluctuations,
which may occur from the engine control or aftertreatment systems,
operational conditions, and/or variations in fuel quality.
    For stage 2, EPA is proposing a more stringent NOX
emission limit of 1.0 g/HP-hr for stationary SI engines manufactured
after January 1, 2011. Again, EPA is incorporating adequate lead time
to account for steps engine manufacturers and owners and operators must
take between stages 1 and 2 to achieve the standards throughout the new
engine category. EPA has analyzed emissions information from several
stationary rich burn engines and has concluded that the

1.0 g/HP-hr limit for NOX is appropriate for the second
stage of emissions requirements. As the uncontrolled NOX
levels indicate, levels lower than 1.5 g/HP-hr are possible with an
NSCR reducing NOX by 90 percent. In addition, a catalyst can
be designed to optimize NOX reduction and with an increased
reduction efficiency, the proposed stage 2 NOX emission
limit can be achieved. The stage 2 limit beginning with engines
manufactured after January 1, 2011, also gives manufacturers time to
improve the design of their engines, which would make the stage 2
NOX emission limits more easily attainable.
    For CO, a similar approach was followed. The average engine-out CO
levels for rich burn engines without aftertreatment controls vary
between 7 and 13 g/HP-hr. A stage 1 CO limit would be easily achievable
through application of NSCR. Similarly, using NSCR, the stage 2 limit
for CO is expected to be achievable by all rich burn engines. The stage
2 standards recognize the inverse relationship between NOX
and CO emissions. In order to optimize NOX emission
reductions, CO emission reductions may not be as large. EPA believes
the stage 2 CO limit is achievable by new rich burn engines by using
NSCR and expects significant reductions from uncontrolled levels.
    Finally, for NMHC, EPA is proposing a limit of 1.0 g/HP-hr for
stage 1 and a limit of 0.7 g/HP-hr for stage 2. As with the
relationship between NOX and CO, the relationship between
NOX and NMHC, in terms of their formation during combustion,
is inverse in nature. Uncontrolled NMHC emissions from new rich burn
engines are between 0.6 and 1.0 g/HP-hr. Therefore, EPA believes that
the proposed limit for NMHC is achievable.
    For SI lean burn engines, EPA considered SCR. The technology is
effective in reducing NOX emissions, as well as other
pollutant emissions, if an oxidation catalyst element is included.
However, the technology has not been widely applied to stationary SI
engines and has mostly been used with diesel engines and larger
applications thousands of HP in size. The technology requires a
significant understanding of its operation and maintenance requirements
and is not a simple process to manage. Installation can be complex and
requires experienced operators. Costs of SCR are high, and have been
rejected frequently by States for this reason. EPA does not believe
that SCR is a reasonable option for stationary SI lean burn engines.
Stationary lean burn engines are, by design, low NOX
emitting units and have sometimes been favored over rich burn engines
in areas with stringent air pollution control requirements due to their
lower NOX level. There are no other currently available add-
on control technologies on the market to further reduce NOX
emissions from stationary SI lean burn engines, but low NOX
emission strategies and design are currently being used to minimize
NOX levels. Based on information received from engine
manufacturers who produce such engines, average NOX levels
from 4SLB engines are between 1.0 and 2.0 g/HP-hr, which are comparable
to engine-out NOX levels from a rich burn engine with a
catalyst. Carbon monoxide levels are also low from these engines and
can be as low as 2.0 g/HP-hr. Stationary SI uncontrolled lean burn
engines are much cleaner than uncontrolled rich burn engines. Levels of
CO in lean burn engines are much lower than rich burn engines. Although
oxidation catalysts can be installed in lean burn engines, EPA believes
that no further controls are needed, given the already-low engine-out
CO and NMHC emissions from them. The CO levels emitted from new lean
burn SI engines are comparable to controlled levels from rich burn
engines. For these reasons, the BDT for stationary SI lean burn engines
is the low emitting level achieved by design and on-engine controls,
and other combustion optimization techniques employed in new stationary
SI lean burn engines. The BDT is the level achieved by new lean burn
engines.
    There are a few new stationary natural gas fired 2SLB sold per year
in the U.S., but the total number manufactured and sold in the U.S. is
insignificant compared to the number of other engine designs sold. In
addition, there are only a few manufacturers who produce such engines.
Available information shows that 2SLB engines that are pre-chamber
combustion designs have similar emissions to natural gas fired 4SLB
engines, and one manufacturer indicated that nearly all of the engines
it sells for the U.S. are pre-chamber combustion engines.
    d. Stationary Non-Emergency Natural Gas Engines >=500 HP and Lean
Burn LPG Engines >=500 HP. For natural gas fired rich burn engines
greater than or equal to 500 HP, the technology that is the basis for
the proposed standards is NSCR. The technology was discussed in
previous sections of this preamble and for the reasons discussed in
that section, NSCR represents BDT for natural gas fired rich burn
engines 500 HP and above.
    The technology that is the basis for the proposed standards for
lean burn natural gas and LPG engines greater than or equal to 500 HP
is the level achieved by design and on-engine controls, and other
combustion optimization techniques employed in new stationary SI lean
burn engines. As discussed previously, EPA considered the use of SCR,
but rejected the technology as BDT based on several factors. Emission
levels from SI lean burn engines are comparable to controlled levels
from rich burn engines and engine-out emissions from SI lean burn
engines are at already low levels. New stationary natural gas engines
greater than or equal to 500 HP and lean burn LPG engines greater than
or equal to 500 HP must comply with two stages of limits. The first
stage, effective for engines manufactured after July 1, 2007, requires
these engines to comply with a NOX limit of 2.0 g/HP-hr, a
CO limit of 4.0 g/HP-hr, and a NMHC limit of 1.0 g/HP-hr. A second
stage of limits, effective for engines manufactured after July 1, 2010,
requires these engines to comply with a NOX limit of 1.0 g/
HP-hr, a CO limit of 2.0 g/HP-hr, and a NMHC limit of 0.7 g/HP-hr. EPA
is proposing that stage 1 limits apply to engines manufactured after
July 1, 2007, to provide enough lead time to make the necessary
preparations and adjustment in order to meet the proposed limits. An
extra 3 years is being proposed to reach compliance with stage 2 limits
to account for further redesign, manufacturing and implementation
issues that manufacturers and owner and operators must handle in order
to meet these limits. EPA believes it is appropriate to distinguish
between less than 500 HP engines and greater than or equal to 500 HP
engines with respect to effective dates of stage 1 and stage 2 limits.
In order to spread out resources and costs, EPA believes it is
appropriate to provide additional time for engines less than 500 HP to
meet the standards.
    e. Stationary SI Landfill/Digester Gas Engines. For stationary
landfill and digester gas fired engines, EPA evaluated currently
available control technologies. Chemicals in landfill and digester gas
fuels called siloxanes poison the catalyst in add-on control
technologies such as SCR, NSCR, and oxidation catalysts, rendering them
ineffective in very short periods of time. (See discussion below.)
Emission standards requiring aftertreatment controls from such engines
have typically not been required due to poisoning of the catalyst
leading to poor reduction efficiencies and eventually destroying the
add-on control device.

For this reason, EPA did not consider add-on control for landfill and
digester gas applications.
    The technology that is the basis for the proposed standards for
landfill and digester gas engines is the level achieved by new lean
burn engines. EPA has been told that lean burn engines are the
preferred choice for landfill and digester gas applications because
these engines have the lowest NOX emissions without add-on
control. Information EPA gathered during the proposal also shows that
the majority of landfill applications use lean burn engines. There may
be some rich burn engines being used in wastewater applications, and
EPA is requesting comment on how common rich burn engine designs are in
landfill and digester gas applications.
    Test results EPA has obtained from various sanitation districts and
regulatory control agencies indicate that landfill and digester gas
engines are capable of meeting similar emission levels to those engines
that are using natural gas fuels. However, there is a lot of
variability in landfill and digester gas, and the methane content can
change considerably from day to day. For these reasons, EPA is
proposing emission standards that are similar to, but somewhat less
stringent than, the standards for engines combusting natural gas. Lean
burn engines are lower NOX emitting units. EPA wishes to
promote cleaner technology through proposing emission standards based
on low NOX design.
    For stationary landfill and digester gas fired engines, EPA is
proposing separate effective dates based on the size of the engine. In
order to prepare the market for regulations applicable to these
engines, EPA is proposing stage 1 limits for landfill and digester gas
engines less than 500 HP that are manufactured after January 1, 2008.
Stage 2 limits are required for landfill and digester gas engines less
than 500 HP manufactured after January 1, 2011. Again, EPA believes it
must provide adequate time between stages 1 and 2 in order for the
market to make the necessary adjustments to meet stage 2 standards. EPA
is proposing that landfill and digester gas engines greater than or
equal to 500 HP meet stage 1 limits if they are manufactured after July
1, 2007, and stage 2 limits after July 1, 2010.
    All landfill and digester gas engines are required to meet a
NOX limit of 3.0 g/HP-hr for stage 1 and a NOX
limit of 2.0 g/HP-hr for stage 2. The stage 2 CO and NMHC limits for
these engines are not more stringent than stage 1, but remain the same
for both stages at 5.0 and 1.0 g/HP-hr for CO and NMHC, respectively.
EPA believes that trying to control the CO in these engines beyond 5.0
g/HP-hr may cause instability and could affect the ability of the
engine to reduce NOX levels; therefore, the same CO limit is
being proposed for both stages. Emissions of NMHC are similar to
natural gas fueled engines, but in order to provide landfill and
digester gas engines with some flexibility to account for variability
in the fuel, which can be beyond the control of the operator, EPA is
proposing a NMHC limit that remains the same between stage 1 and stage
2 and is not proposing a more stringent limit for NMHC for the second
stage.
    f. Stationary Emergency SI Engines. As with landfill and digester
gas fired applications, add-on controls have typically not been
required on stationary emergency engines. Stationary engines used for
emergency purposes are operated infrequently, and aftertreatment has
often been avoided because of factors such as high costs per ton of
pollutant removed due to short periods of operation. EPA's recently
proposed regulations for stationary CI engines that required only in-
engine controls for emergency engines, and did not require stringent
standards based on add-on controls for stationary CI engines used for
emergency purposes. Similarly, the RICE NESHAP promulgated in 2004 (69
FR 33474) did not require emergency engines to meet emission control
requirements.
    Engine manufacturers expressed during the proposal process that
emergency SI engines should be exempt from emission standards, citing
similar reasons to those provided above. However, we do not agree that
emergency engines should be exempt from the standards.
    Therefore, we have established that the technology that is the
basis for the standards for stationary emergency engines is the level
achieved by new lean burn engines. Lean burn engines are available in
the power ranges that include emergency engines. EPA expects that the
emission standards for emergency engines will be met with lean burn
engines. Lean burn engines are available and represent the cleanest
technology available without the use of exhaust aftertreatment.
    EPA is providing stationary emergency engines significant lead-time
to prepare to meet the proposed standards for emergency engines. This
is particularly appropriate because emergency engines have generally
not previously been subject to emission standards and therefore have
not necessarily been optimized for emissions performance.
    EPA is proposing a single stage of emission standards for emergency
engines beginning in January 1, 2009. Stationary SI emergency engines
manufactured after this date must meet a NOX limit of 2.0 g/
HP-hr, a CO limit of 4.0 g/HP-hr, and a NMHC limit of 1.0 g/HP-hr. As
previously discussed in this preamble, stationary SI lean burn engines
emit low levels of NOX, in the range of 1.0 to 2.0 g/HP-hr,
which means the limit being proposed for NOX is achievable.
Similar conclusions can be made regarding CO and NMHC as well.
    g. Modified and Reconstructed Stationary SI Engines. EPA is
proposing that owners and operators of stationary SI natural gas and
lean burn LPG engines that are modified or reconstructed and become
subject to this proposed rule limit their exhaust emissions of
NOX to 3.0 g/HP-hr, emissions of CO to 4.0 g/HP-hr, and
emissions of NMHC to 1.0 g/HP-hr. These emission standards are
consistent with the proposed Stage 1 emission standards for new natural
gas and lean burn LPG engines, except that a less stringent
NOX emission standard is being proposed for these engines.
    There are technical difficulties in reaching a NOX level
of 2.0 g/HP-hr for modified and reconstructed engines that were not
originally built to meet a 2.0 g/HP-hr standard, and such a level, even
where technically feasible, would in many cases require extensive work.
In addition, lowering emissions of NOX down to 2.0 g/HP-hr,
even where possible, would often be very costly. EPA discussed this
issue in one of the final rules associated with the NOX
State Implementation Plan call (69 FR 21604, 21617-21621). Therefore,
EPA believes it is more appropriate to propose to require that modified
and reconstructed engines manufactured prior to the dates when the 2.0
g/HP-hr standard takes effect must meet a NOX emission
standard of 3.0 g/HP-hr. This level can be achieved with retrofit
technology without extensive hardware replacements and can be achieved
without unreasonable costs.
2. NESHAP
    Section 112 of the CAA requires that we establish NESHAP for the
control of HAP from new and existing sources in regulated source
categories. The CAA requires the NESHAP for major sources to reflect
the maximum degree of reduction in emissions of HAP that is achievable.
This level of control is commonly referred to as the MACT.
    The MACT floor is the minimum control level allowed for NESHAP and
is defined under section 112(d)(3) of the

CAA. In essence, the MACT floor ensures that the standards are set at a
level that assures that all major sources achieve the level of control
at least as stringent as that already achieved by the better controlled
and lower emitting sources in each source category or subcategory.
    For new sources, the MACT floor cannot be less stringent than the
emission control that is achieved in practice by the best controlled
similar source. The MACT standards for existing sources can be less
stringent than standards for new sources, but they cannot be less
stringent than the average emission limitation achieved by the best
performing 12 percent of existing sources in the category or
subcategory (or the best performing 5 sources for categories or
subcategories with fewer than 30 sources).
    In developing MACT, we also consider control options that are more
stringent than the floor. We may establish standards more stringent
than the floor based on the consideration of cost of achieving the
emissions reductions, any non-air quality health and environmental
impacts, and energy requirements.
    Section 112 of the CAA allows EPA to establish subcategories among
a group of sources, based on criteria that differentiate such sources.
The subcategories that have been developed for stationary RICE were
previously listed and are necessary in order to capture the distinct
differences, which could affect the emissions of HAP from these
engines. The complete rationale explaining the development of these
subcategories is provided in the memorandum titled Subcategorization of
Stationary Reciprocating Internal Combustion Engines 500 HP available
from the docket.
    a. Engines < =500 HP at Major Sources. For the MACT floor
determination, EPA s Office of Air Quality Planning and Standards RICE
Population Database (hereafter referred to as the ``Population
Database'') was consulted. The Population Database, which was developed
for the stationary RICE NESHAP for engines greater than 500 HP at major
sources, represents the best information available to EPA.
    Information in the Population Database was obtained from several
sources and is further described in the notice of proposed rulemaking
for the RICE NESHAP (67 FR 77830). EPA queried the Population Database
to determine how many stationary RICE less than or equal to 500 HP have
catalyst type controls. According to the Population Database, neither
engines less than 50 HP, landfill/digester gas fired engines, CI
emergency engines, CI non-emergency engines, SI emergency engines, nor
non-emergency 2SLB engines are equipped with catalyst type controls.
The Population Database indicates that 32 (3.7 percent) out of 861 non-
emergency use 4SLB engines are equipped with catalyst type controls.
Out of a total of 3,533 non-emergency 4SRB engines 50 to 500 HP, 197
are using catalyst type controls (5.6 percent). The percentage for 4SRB
engines may or may not be representative of current conditions, and EPA
requests comments on this issue. For further information on EPA's
analysis on the Population Database, refer to the docket for this
proposed rule.

MACT Floor for Existing Sources

    The MACT floor for existing stationary RICE must be no less
stringent than the average emission limitation achieved by the best
performing 12 percent of existing sources. According to information in
the Population Database, there are no existing engines less than 50 HP,
landfill/digester gas fired engines, CI emergency engines, CI non-
emergency engines, SI emergency engines, or non-emergency 2SLB engines
that use catalyst type controls. Therefore, the MACT floor for these
subcategories is no further emissions reductions.
    For existing non-emergency 4SLB engines between 50 and 500 HP,
there are insufficient numbers of engines using add-on controls that
may reduce HAP to support basing the MACT floor on the use of add-on
controls. The percentage (3.7) is below the criteria for a MACT floor
that would require emissions reductions for existing stationary 4SLB
engines. Therefore, the MACT floor for existing non-emergency use
stationary 4SLB engines 50 to 500 HP is no further emissions
reductions.
    The percentage for existing non-emergency 4SRB engines is also
below the criteria for a MACT floor that would require emissions
reductions for existing 4SRB engines. Therefore, the MACT floor for
existing non-emergency use stationary 4SRB engines 50 to 500 HP is no
further emissions reductions.

MACT for Existing Sources

    As stated, for existing sources, the MACT floor for each of the
subcategories is no emission reduction, and the MACT standard must be
no less stringent than the MACT floor.
    EPA considered one regulatory option more stringent than the MACT
floor for existing 2SLB and existing 4SLB engines, i.e., requiring a
specific HAP reduction through the use of an oxidation catalyst.
Oxidation catalysts provide significant reductions of HAP emissions, as
well as considerable reductions of CO. Catalyst cost information was
obtained from vendors of catalytic control equipment and annual costs
were derived from the data. Estimates of cost per ton of applying
oxidation catalyst to various size engines were developed. The cost of
oxidation catalysts was determined to outweigh the potential HAP
emission reduction benefits for these subcategories. Therefore, the
beyond-the-floor option was determined as inappropriate for these
subcategories. Non-air quality health, environmental impacts and energy
effects were also not significant factors. EPA is not aware of any
other options which could serve as the basis for MACT to reduce HAP
emissions from existing 2SLB and existing 4SLB engines. Therefore, MACT
is equal to the MACT floor for these engines. For specific details on
this analysis, refer to memorandum entitled ``Regulatory Alternatives
and MACT for Stationary Reciprocating Internal Combustion Engines < =500
HP at Major Sources,'' available from the docket for this proposed
rule.
    EPA considered one regulatory option more stringent than the MACT
floor for existing 4SRB engines, i.e., requiring a specific HAP
reduction through the use of NSCR.
    An NSCR, or three-way catalyst, is a catalytic post-combustion
control device that oxidizes HAP emissions, and also reduces criteria
pollutants such as NOX and CO. To operate effectively, NSCR
requires stoichiometric conditions to enhance both oxidation and
reduction reactions in the exhaust stream. Removal efficiencies for
NSCR were previously discussed in this preamble. Again, cost
information was obtained from catalyst vendors and annual NSCR costs
were estimated based on these data. The costs per ton of pollutant
removed by applying NSCR to various size 4SRB engines were calculated,
and are documented in information included in the docket. Based on the
costs per ton of HAP removed from existing 4SRB engines, it was
determined that requiring NSCR on existing engines would not be
appropriate and, therefore, the MACT for existing 4SRB engines is the
MACT floor, i.e., no emission reduction. No other technology was
identified as appropriate for reducing HAP from 4SRB engines.
    Cost per ton estimates are presented in the memorandum entitled
``Cost per Ton of HAP Reduced for Stationary RICE,'' included in the
docket. EPA's analysis of regulatory alternatives

beyond-the-floor is presented in the memorandum entitled ``Regulatory
Alternatives and MACT for Stationary Reciprocating Internal Combustion
Engines 500 Horsepower at Major Sources.''
    EPA considered one regulatory option more stringent than the MACT
floor for existing CI engines, which is the use of CDPF. A description
of the technology and potential emission reductions were previously
discussed in this preamble. Using available information, the cost for
applying CDPF to existing CI engines was estimated. Based on the
estimated cost per ton of HAP removed, EPA determined that requiring
the use of CDPF would be too high for existing CI engines. Therefore,
the MACT for existing CI engines is the MACT floor, i.e., no emission
reduction.
    The MACT floor for existing digester and landfill gas stationary
engines is no emission reduction. The use of oxidation catalysts to
reduce HAP emissions from this subcategory of RICE was found to be
technically infeasible. This is due to the fact that digester gases and
landfill gases contain a family of silicon-based compounds called
siloxanes. Combustion of siloxanes can foul post-combustion catalysts,
rendering them inoperable within a short period of time. Because of
these technical issues associated with applying oxidation catalyst
control, there are no viable beyond-the-floor regulatory options for
these stationary RICE. Therefore, no emission reduction is MACT for
existing digester and landfill gas stationary RICE.
    Emission control technologies which reduce HAP emissions from
stationary RICE have not been applied to stationary RICE which operate
exclusively as emergency units. Thus, the MACT floor is no emission
reduction. In considering the application of HAP emission control
technologies to stationary RICE which operate exclusively as emergency
units, there are a number of concerns regarding the technical
feasibility, primarily in the areas of the long term durability and
effectiveness of emission control. Whether such concerns are warranted
or not, however, emission control is not considered cost effective
because of the very small reductions in HAP emissions which might be
achieved through the use of such technologies. In addition, non-air
quality health, environmental impacts and energy effects were not
significant factors. As a result, MACT for existing stationary RICE
which operate exclusively as emergency engines is no emission
reduction.

MACT Floor for New Sources

    The MACT floor for new stationary RICE must be no less stringent
than the emission control achieved in practice by the best controlled
similar source. Since the Population Database indicates that there are
no existing engines less than 50 HP, landfill/digester gas fired
engines, CI emergency engines, CI non-emergency engines, SI emergency
engines, or non-emergency 2SLB engines that are using catalyst type
controls, the MACT floor for these new stationary RICE is no further
emissions reductions.
    As discussed, EPA established a subcategory for non-emergency 4SLB
engines between 50 and 500 HP. However, based on information received
by EPA, there are few, if any, stationary 4SLB engines less than 250
HP. Information regarding the smallest 4SLB engines produced is
available from the docket. The additional cost and complexity of
components associated with lean burn engine design is not cost
effective for smaller engines (less than 400 HP), according to
industry.
    Stationary 4SLB engines greater than or equal to 250 HP tend to be
similar to larger engines, i.e., those that are greater than 500 HP,
and on a mass basis, engines greater than or equal to 250 HP emit more
than smaller engines. In addition, engines of such size have
traditionally been treated by States as larger engines, rather than
smaller engines, and stationary 4SLB SI engines below 250 HP have
generally been regulated as smaller engines. In some cases, engines
greater than 250 HP may be required to meet more stringent emission
standards than smaller engines. In addition, the type of add-controls
that can be applied to 4SLB engines greater than or equal to 250 HP are
the same as those that can be applied to larger engines, i.e., those
greater than 500 HP, and those engines are capable of achieving very
similar emission reductions as larger engines. Further, larger engines
are typically employed in different applications than smaller engines
are and may be more likely to be used in electric power generation and
gas transmission and processing. In addition, smaller engines may tend
to be used more by small businesses or for agricultural purposes and
may resemble nonroad engines more than those greater than or equal to
250 HP, which are more similar to traditional stationary engines. For
these reasons, EPA believes that non-emergency 4SLB engines greater
than or equal to 250 HP more closely resemble larger engines and should
be treated in a similar manner as the engines greater than 500 HP were
treated.
    The Population Database indicates that there are non-emergency 4SLB
engines in the size range of 250 to 500 HP employing catalyst type
controls, and according to the Population Database, the smallest 4SLB
engine equipped with catalyst control is 270 HP. However, EPA received
additional information indicating that there is a 260 HP engine
operating with oxidation catalyst control and is, therefore, the
smallest existing 4SLB engine of which EPA is aware that is equipped
with add-on control.
    EPA believes it is unreasonable to require new 4SLB engines smaller
than 250 HP to meet emission standards based on add-on control. The
cost per ton for new 4SLB engines between 250 and 500 HP located at
major sources is reasonable. Looking at the cost effectiveness for
engines smaller than 250 HP, the cost per ton of HAP removed rapidly
increases with decreasing size. EPA believes an appropriate cutoff for
requiring emission standards based on add-on controls is 250 HP. This
conclusion is consistent with other findings, including an analysis of
the Population Database of the smallest engine with catalyst control
and information from other sources. This conclusion is also consistent
with the MACT floor decision for new 4SLB engines greater than 500 HP
located at major sources. For these reasons, the MACT floor for new
4SLB engines between 250 and 500 HP located at major sources is the
level of control achieved by application of oxidation catalyst
controls. The MACT floor for new 4SLB engines between 50 and 250 HP is
no further HAP emission reduction.
    We request comment on our proposed approach for MACT requirements
for new 4SLB engines (250-500 HP). EPA's Population Database indicates
that oxidation catalysts are used in some of these engines, and this
technology forms the basis of the proposed standards. It is likely that
these oxidation catalysts are used to meet State requirements developed
as part of EPA programs such as New Source Review (NSR) and Prevention
of Significant Deterioration (PSD), which focus on the control of
criteria pollutants, rather than HAP. However, oxidation catalysts
installed to control CO and NMHC can also reduce HAP emissions. We
request comment on EPA's determination that oxidation catalysts should
be the basis of the MACT floor for new 4SLB engines in the size range
of 250 to 500 HP.
    The Population Database indicates that there are non-emergency 4SRB

engines 50 to 500 HP operating with catalyst type controls, and,
therefore, the MACT floor for new non-emergency 4SRB engines between 50
and 500 HP is the level achieved by the use of NSCR.

MACT for New Sources

    For 2SLB, there are no engines in the Population Database that are
using catalyst type controls. Therefore, the MACT floor for new
stationary 2SLB is no further emissions reductions. In addition, the
cost effectiveness of adding an oxidation catalyst to a new 2SLB engine
was not determined to be economically feasible, and MACT for new 2SLB
engines is, therefore, no emission reduction. This determination is
different than MACT for engines greater than 500 HP located at major
sources because for those engines, the Population Database indicates
that there are existing 2SLB engines greater than 500 HP operating with
catalytic controls. As stated, no existing 2SLB engines less than or
equal to 500 HP are using catalytic controls, according to the
Population Database. However, we are proposing to require these engines
to meet NMHC emission standards that are based on the use of on-engine
controls in order to reduce levels of HAP.
    For engines less than 50 HP, EPA evaluated beyond-the-floor options
for engines less than or equal to 19 KW (25 HP) and engines above 19 KW
(25 HP) separately. Stationary SI engines less than or equal to 19 KW
(25 HP) are required under the proposed SI NSPS to meet the
certification standards for new nonroad SI engines in 40 CFR part 90
for nonhandheld engines. The technologies that are the basis for those
standards rely on engine-based controls. Under the SI NSPS, those
controls were determined to be BDT for new stationary SI engines less
than or equal to 19 KW (25 HP). The beyond-the-floor analysis for
stationary SI engines less than or equal to 19 KW (25 HP) considered
the use of those technologies, and EPA believes it is appropriate to
set MACT for these engines at the level of control required by the SI
NSPS.
    The emission standards for nonhandheld engines include limits for
HC + NOX (or NMHC + NOX standards for natural gas
fueled engines, at the option of the manufacturer) and CO. EPA has
determined that NMHC can be used as a surrogate for HAP and, therefore,
believes it is appropriate to require a standard based on NMHC as
opposed to a HAP standard. For more information on EPA's decision to
use NMHC as a surrogate for HAP, refer to the memorandum entitled
``Non-methane Hydrocarbons as a Surrogate for Hazardous Air Pollutants
for Stationary Internal Combustion Engines,'' available from the
docket.
    For new stationary SI engines between 19 and 37 KW (25 and 50 HP),
EPA evaluated beyond-the-floor options based on the requirements for
new stationary SI engines under the SI NSPS. Under the SI NSPS, engines
greater than 19 KW (25 HP) that use gasoline or that are rich burn
engines greater than 19 KW (25 HP) that use LPG, are required to be
certified to the emission standards in 40 CFR part 1048. The
technologies that are the basis for those standards are three-way
catalyst systems (NSCR) with electronic, closed-loop fuel systems.
These technologies were determined to be BDT for new stationary SI
engines greater than 19 KW (25 HP) that use gasoline and rich burn
engines greater than 19 KW (25 HP) that use LPG under the SI NSPS.
These are the same engines that would be covered by the NESHAP, and,
therefore, EPA believes it is appropriate to go beyond-the-floor for
these engines and require that owners and operators of these engines
meet the standards proposed in the SI NSPS.
    The nonroad standards for SI engines greater than 19 KW (25 HP)
include HC + NOX standards and standards for CO. The engine
has to meet the numerical emission standard based on NMHC emissions if
the engine is fueled by natural gas. As discussed, EPA has determined
that NMHC is an appropriate surrogate for HAP, and EPA believes it is
appropriate to require the nonroad SI engine standards in 40 CFR part
1048 for these engines. In addition, these engines are the same engines
that are covered by the SI NSPS and would be subject to certification
requirements of 40 CFR part 1048 even in the absence of the NESHAP.
    Finally, EPA would like to ensure consistency and avoid conflicting
requirements between regulations affecting the same or similar source
categories. Therefore, EPA believes it is appropriate to set MACT for
these engines at the level of control required by the SI NSPS.
    For stationary SI engines between 19 and 37 KW (25 and 50 HP) that
use natural gas or are lean burn LPG engines, EPA described that
requiring engine certification would be inappropriate for various
reasons. For the SI NSPS, EPA determined that it was more appropriate
to rely on a voluntary engine certification program combined with
requirements for owners and operators. EPA considers this approach as a
reasonable beyond-the-floor option for new stationary SI engines
between 19 and 37 KW (25 and 50 HP) located at major sources. Again,
the same engines would be covered under the SI NSPS, and would, under
that rule, be required to meet NOX, CO, and NMHC emission
standards. Therefore, EPA considers the NMHC emission standards from
the SI NSPS as the most appropriate beyond-the-floor option.
    It was previously discussed that it is appropriate to use NMHC as a
surrogate for HAP. The SI NSPS propose different NMHC emission
standards and timing based on the type and size of the engine. The SI
NSPS propose a NMHC limit of 0.7 or 1.0 g/HP-hr, which EPA believes is
reasonable to require for engines under the NESHAP as well. For
stationary SI engines between 19 and 37 KW (25 and 50 HP) that use
natural gas or are lean burn engines using LPG, MACT is determined to
be the level required for these engines under the SI NSPS, i.e., an
emission standard of 0.7 or 1.0 g/HP-hr for NMHC. The NMHC limit of 1.0
g/HP-hr is required for natural gas fired engines less than 500 HP and
lean burn engines less than 500 HP using LPG that are manufactured
after January 1, 2008. The limit of 0.7 g/HP-hr for NMHC is required
for natural gas fired engines less than 500 HP and lean burn engines
less than 500 HP that use LPG that are manufactured after January 1,
2011. EPA believes that the implementation dates are the most stringent
that can be justified that provide engine manufacturers with sufficient
time to prepare their products for compliance.
    According to the Population Database, there are existing 4SLB
stationary engines currently operating with oxidation catalyst systems.
No technology achieving greater emission reductions was found. We
previously discussed the decision to set the MACT floor for new 4SLB
engines between 250 and 500 HP located at major sources based on the
use of oxidation catalyst. For new 4SLB engines between 50 and 250 HP,
the MACT floor is no emission reduction. We also discussed in an
earlier section that we believe non-emergency 4SLB engines between 250
and 500 HP are more similar to large engines, i.e., those greater than
500 HP. The formaldehyde level required by the existing 40 CFR part 63,
subpart ZZZZ, for new 4SLB engines greater than 500 HP located at major
sources is based on using oxidation catalyst. A formaldehyde
concentration level of 14 ppmvd at 15 percent O2 was
promulgated for those engines. As an alternative, a 93 percent
reduction of CO was provided.
    EPA believes these levels are reasonable for new 4SLB engines

between 250 and 500 HP located at major sources as well. EPA expects
the capabilities of the oxidation catalyst to be the same for engines
between 250 and 500 HP as they are for engines greater than 500 HP. For
these reasons, MACT is the level of control achieved by using oxidation
catalyst, i.e., either a 93 percent reduction of CO or a formaldehyde
outlet concentration limit of 14 ppmvd at 15 percent O2.
    For new 4SLB engines between 50 and 250 HP located at major
sources, the proposed MACT standard is equal to the NMHC standard
required under the proposed SI NSPS.
    The MACT standard for new 4SRB stationary RICE must be at least as
stringent as the MACT floor for existing 4SRB stationary RICE.
Regulatory options more stringent than the MACT floor include requiring
the use of NSCR; no other technology achieving greater emissions
reductions was found.
    As discussed, EPA generally believes it is appropriate to base the
MACT standards for new stationary SI engines on the standards being
proposed in the stationary SI NSPS (except for new and reconstructed
4SLB engines between 250 and 500 HP located at major sources). This
conclusion affects new stationary rich burn engines. EPA discussed
selecting NSCR as BDT for most new stationary rich burn engines earlier
in this preamble. We discussed the appropriateness of following the SI
NSPS for new SI engines less than or equal to 19 KW (25 HP) and new SI
engines greater than 19 KW (25 HP) that use gasoline or that are rich
burn engines greater than 19 KW (25 HP) that use LPG. For the reasons
previously discussed, MACT for new 4SRB engines between 25 and 500 HP
located at major sources are the NMHC standards that are required in
the SI NSPS. EPA also discussed the appropriateness of requiring