[Federal Register: April 7, 2004 (Volume 69, Number 67)]
[Proposed Rules]               
[Page 18327-18338]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr07ap04-24]                         

-----------------------------------------------------------------------

ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 63

[OAR-2003-0189; FRL-7643-8]
RIN 2060-AK73

 
National Emission Standards for Hazardous Air Pollutants for 
Stationary Combustion Turbines

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

-----------------------------------------------------------------------

SUMMARY: The EPA is proposing to amend the list of categories of 
sources that was developed pursuant to section 112(c)(1) of the Clean 
Air Act (CAA) by deleting four subcategories from the Stationary 
Combustion Turbines source category. Final maximum achievable control 
technology (MACT) standards creating the following subcategories were 
published on March 5, 2004: lean premix gas-fired stationary combustion 
turbines, diffusion flame gas-fired stationary combustion turbines, 
emergency stationary combustion turbines, and stationary combustion 
turbines located on the North Slope of Alaska. This action is being 
taken in part to respond to a petition submitted by the Gas Turbine 
Association (GTA) and in part upon the EPA Administrator's own motion. 
Petitions to remove a source category from the source category list are 
permitted under section 112(c)(9) of the CAA. The proposed rule is 
based on EPA's evaluation of available information concerning the 
potential hazards from exposure to hazardous air pollutants (HAP) 
emitted from the four subcategories and includes a detailed rationale 
for removing the subcategories from the source category list. We 
request comment on the proposed rule.
    Although the proposed rule would delete certain subcategories from 
the Stationary Combustion Turbines source category, the MACT standards 
for the subcategories will take effect upon publication of the 
standards. Because the MACT standards require immediate compliance by 
new sources, some sources in the subcategories which we are proposing 
to delist may need to make immediate expenditures on emission controls 
which will not be required if we adopt a final rule to delete the 
subcategories. In view of our initial determination that the statutory 
criteria for delisting have been met for the subcategories, we consider 
it inappropriate and contrary to statutory intent to mandate such 
expenditures until after a final determination has been made whether or 
not the subcategories should be delisted. Accordingly, we are 
publishing elsewhere in this Federal Register a proposal to stay the 
effectiveness of the MACT standards for new sources in the 
subcategories during the pendency of the rule to delete the 
subcategories.

DATES: Comments. Written comments on the proposed rule must be received 
by June 7, 2004.
    Public Hearing. A public hearing regarding the proposed rule will 
be held if requests to speak are received by the EPA on or before April 
22, 2004. If requested, a public hearing will be held on May 5, 2004.

ADDRESSES: Comments. Comments may be submitted electronically, by mail, 
or through hand delivery/courier. Electronic comments may be submitted 
on-line at http://www.epa.gov/edocket/. Written comments sent by U.S. 

mail should be submitted (in duplicate if possible) to: Air and 
Radiation Docket and Information Center (Mail Code 6102T), Attention 
Docket ID Number OAR-2003-0189, Room B108, U.S. EPA, 1200 Pennsylvania 
Avenue, NW., Washington, DC 20460. Written comments delivered in person 
or by courier should be submitted (in duplicate if possible) to: Air 
and Radiation Docket and Information Center (Mail Code 6102T), 
Attention Docket ID Number OAR-2003-0189, Room B102, U.S. EPA, 1301 
Constitution Avenue, NW., Washington, DC 20460. The EPA requests a 
separate copy also be sent to the contact person listed below (see FOR 
FURTHER INFORMATION CONTACT).
    Public Hearing. If a public hearing is requested by April 22, 2004 
the public hearing will be held at the EPA facility complex, T.W. 
Alexander Drive, Research Triangle Park, NC May 5, 2004. Persons 
interested in presenting oral testimony should contact Ms. Kelly A. 
Rimer, Risk and Exposure Assessment Group, Emission Standards Division 
(C404-01), U.S. EPA, Research Triangle Park, North Carolina 27711, 
telephone number (919) 541-2962. Persons interested in attending the 
public hearing should also contact Ms. Rimer to verify the time of the 
hearing.

FOR FURTHER INFORMATION CONTACT: Ms. Kelly A. Rimer, Risk and Exposure 
Assessment Group, Emission Standards Division (C404-01), U.S. EPA, 
Research Triangle Park, NC 27711, telephone number (919) 541-2962, 
electronic mail address rimer.kelly@epa.gov.

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

----------------------------------------------------------------------------------------------------------------
                   Category                         SIC         NAICS         Examples of regulated entities
----------------------------------------------------------------------------------------------------------------
Any industry using a combustion turbine as             4911         2211  Electric power generation,
 defined in the regulation.                                                transmission, or stationary
                                                                           distribution.
                                                       4922       486210  Natural gas transmission.
                                                       1311       211111  Crude petroleum and natural gas
                                                                           production.
                                                       1321       211112  Natural gas liquids producers.
                                                       4931          221  Electric and other services combined.
----------------------------------------------------------------------------------------------------------------


[[Page 18328]]

    This table is not intended to be exhaustive, but rather provides a 
guide for readers regarding entities likely to be affected by this 
action. 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.
    Docket. The EPA has established an official public docket for this 
action under Docket ID Number OAR-2003-0189. The official public docket 
is the collection of materials that is available for public viewing at 
the EPA Docket Center (Air Docket), EPA West, Room B-108, 1301 
Constitution Avenue, NW., Washington, DC 20004. The Docket Center is 
open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding 
legal holidays. The telephone number for the Reading Room is (202) 566-
1744, and the telephone number for the Air Docket is (202) 566-1742.
    Electronic Access. An electronic version of the public docket is 
available through EPA's electronic public docket and comment system, 
EPA Dockets. You may use EPA Dockets at http://www.epa.gov/edocket/ to 

submit or view public comments, access the index of the contents of the 
official public docket, and access those documents in the public docket 
that are available electronically. Once in the system, select 
``search'' and key in the appropriate docket identification number.
    Certain types of information will not be placed in the EPA dockets. 
Information claimed as confidential business information (CBI) and 
other information whose disclosure is restricted by statute, which is 
not included in the official public docket, will not be available for 
public viewing in EPA's electronic public docket. The EPA's policy is 
that copyrighted material will not be placed in EPA's electronic public 
docket but will be available only in printed, paper form in the 
official public docket. Although not all docket materials may be 
available electronically, you may still access any of the publicly 
available docket materials through the EPA Docket Center.
    For public commenters, it is important to note that EPA's policy is 
that public comments, whether submitted electronically or in paper, 
will be made available for public viewing in EPA's electronic public 
docket as EPA receives them and without change unless the comment 
contains copyrighted material, CBI, or other information whose 
disclosure is restricted by statute. When EPA identifies a comment 
containing copyrighted material, EPA will provide a reference to that 
material in the version of the comment that is placed in EPA's 
electronic public docket. The entire printed comment, including the 
copyrighted material, will be available in the public docket.
    Public comments submitted on computer disks that are mailed or 
delivered to the docket will be transferred to EPA's electronic public 
docket. Public comments that are mailed or delivered to the docket will 
be scanned and placed in EPA's electronic public docket. Where 
practical, physical objects will be photographed, and the photograph 
will be placed in EPA's electronic public docket along with a brief 
description written by the docket staff.
    Comments. You may submit comments electronically, by mail, by 
facsimile, or through hand delivery/courier. To ensure proper receipt 
by EPA, identify the appropriate docket identification number in the 
subject line on the first page of your comment. Please ensure that your 
comments are submitted within the specified comment period. Comments 
submitted after the close of the comment period will be marked 
``late.'' The EPA is not required to consider these late comments.
    Electronically. If you submit an electronic comment as prescribed 
below, EPA recommends that you include your name, mailing address, and 
an e-mail address or other contact information in the body of your 
comment. Also include this contact information on the outside of any 
disk or CD ROM you submit and in any cover letter accompanying the disk 
or CD ROM. This ensures that you can be identified as the submitter of 
the comment and allows EPA to contact you in case EPA cannot read your 
comment due to technical difficulties or needs further information on 
the substance of your comment. The EPA's policy is that EPA will not 
edit your comment and any identifying or contact information provided 
in the body of a comment will be included as part of the comment that 
is placed in the official public docket and made available in EPA's 
electronic public docket. 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.
    Your use of EPA's electronic public docket to submit comments to 
EPA electronically is EPA's preferred method for receiving comments. Go 
directly to EPA Dockets at http://www.epa.gov/edocket, and follow the 

online instructions for submitting comments. Once in the system, select 
``search'' and key in Docket ID No. OAR-2003-0189. The system is an 
``anonymous access'' system, which means EPA will not know your 
identity, e-mail address, or other contact information unless you 
provide it in the body of your comment.
    Comments may be sent by electronic mail (e-mail) to 
a-and-r-docket@epa.gov, Attention Docket ID No. OAR-2003-0189. In contrast to 

EPA's electronic public docket, EPA's e-mail system is not an 
``anonymous access'' system. If you send an e-mail comment directly to 
the docket without going through EPA's electronic public docket, EPA's 
e-mail system automatically captures your e-mail address. E-mail 
addresses that are automatically captured by EPA's e-mail system are 
included as part of the comment that is placed in the official public 
docket and made available in EPA's electronic public docket.
    You may submit comments on a disk or CD ROM that you mail to the 
mailing address identified in this document. These electronic 
submissions will be accepted in WordPerfect or ASCII file format. Avoid 
the use of special characters and any form of encryption.
    By Mail. Send your comments (in duplicate, if possible) to: EPA 
Docket Center (Air Docket), U.S. EPA West, (MD-6102T), Room B-108, 1200 
Pennsylvania Avenue, NW., Washington, DC 20460, Attention Docket ID No. 
OAR-2003-0189.
    By Hand Delivery or Courier. Deliver your comments (in duplicate, 
if possible) to: EPA Docket Center, Room B-108, U.S. EPA West, 1301 
Constitution Avenue, NW., Washington, DC 20004, Attention Docket ID No. 
OAR-2003-0189. Such deliveries are only accepted during the Docket 
Center's normal hours of operation.
    By Facsimile. Fax your comments to: (202) 566-1741, Docket ID No. 
OAR-2003-0189.
    CBI. Do not submit information that you consider to be CBI through 
EPA's electronic public docket or by e-mail. Send or deliver 
information identified as CBI only to the following address: Kelly 
Rimer, c/o Roberto Morales, OAQPS Document Control Officer (C404-02), 
U.S. EPA, Research Triangle Park, NC 27709, Attention Docket ID No. 
OAR-2003-0189. You may claim information that you submit to EPA as CBI 
by marking any part or all of that information as CBI (if you submit 
CBI on disk or CD ROM, mark the outside of the disk or CD ROM as CBI 
and then identify electronically within the disk or CD ROM the specific 
information that is CBI). Information so marked will not be disclosed 
except in accordance with procedures set forth in 40 CFR part 2.
    In addition to one complete version of the comment that includes 
any

[[Page 18329]]

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 and EPA's electronic public docket. If you submit the 
copy that does not contain CBI on disk or CD-ROM, mark the outside of 
the disk or CD-ROM clearly that it does not contain CBI. Information 
not marked as CBI will be included in the public docket and EPA's 
electronic public docket without prior notice. If you have any 
questions about CBI or the procedures for claiming CBI, please consult 
the person identified in the FOR FURTHER INFORMATION CONTACT section.
    Worldwide Web (WWW). In addition to being available in the docket, 
an electronic copy of today's proposed rule will also be available on 
the WWW through the Technology Transfer Network (TTN). Following the 
Administrator's signature, a copy of the proposed rule will be placed 
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. If more 
information regarding the TTN is needed, call the TTN HELP line at 
(919) 541-5384.
    Outline. This preamble is organized as follows:

I. Background and Criteria for Delisting
II. Summary of Petitioner's Request and EPA's Initial Delisting 
Determination
III. Description of the Four Stationary Combustion Turbine 
Subcategories
IV. Analysis of Gas-Fired Subcategories
    A. Analytical Approach
    B. Planning and Scoping
    C. Source Characterization
    D. Emissions Characterization
    E. Air Dispersion Modeling
    F. Human Health Effects of Emitted HAP
    G. Human Health Values Used
    H. Human Health Risk Results--Air Pathway
    I. Multipathway Considerations
    J. Effects Due to Acute Exposure
    K. Environmental Effects Evaluation
V. Analysis of the Emergency Turbine Subcategory
VI. Analysis of the North Slope Turbine Subcategory
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
    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. Background and Criteria for Delisting

    Section 112 of the CAA contains a mandate for EPA to evaluate and 
control emissions of HAP from industry sectors called source 
categories. Section 112(b)(1) includes a list of 188 specific chemical 
compounds and classes of compounds identified as HAP. Section 112(c) 
requires the EPA to publish a list of all categories and subcategories 
of sources of HAP which will be subject to regulation. Each category or 
subcategory which includes major sources of HAP must be listed for 
regulation. Under section 112(d), the CAA requires EPA to establish 
national emission standards for major source categories based on MACT 
for each category or subcategory which is included in the list.
    The EPA published the initial source category list in the Federal 
Register on July 16, 1992 (57 FR 31576); you can find the most recent 
update to the source category list in the February 12, 2002 Federal 
Register (67 FR 6521).
    Section 112(c)(9) of the CAA provides for the deletion of a source 
category from the list of source categories. A source category may be 
deleted from the list under section 112(c)(9)(A) if the category no 
longer satisfies the criteria for inclusion on the list because of the 
deletion of one or more HAP from the HAP list pursuant to section 
112(b)(3) or a source category may be deleted from the list under 
section 112(c)(9)(B) if certain substantive criteria are satisfied. The 
EPA construes these provisions to apply to each listed subcategory as 
well. This construction is logical in the context of the general 
regulatory scheme established by the statute and is the most reasonable 
one because section 112(c)(9)(B)(ii) expressly refers to subcategories. 
If EPA takes final action to delete a listed source category or 
subcategory, this eliminates any requirement that MACT standards be 
promulgated for the category or subcategory in question. If MACT 
standards have already been promulgated, EPA will amend or rescind the 
standards in question.
    A proceeding to delete a listed category or subcategory under 
section 112(c)(9)(B) of the CAA may be commenced either in response to 
a petition or on the initiative of the EPA Administrator. A source 
category delist petition is a formal request to the EPA from an 
individual or group to remove a specific source category or subcategory 
from the source category list. The Administrator must either grant or 
deny a petition within 1 year after receiving a complete petition (64 
FR 33453). To grant such a petition, or to commence a proceeding to 
delete a category or subcategory on the Administrator's own motion, the 
Administrator must make an initial determination that:
    (1) In the case of HAP emitted by sources in the category or 
subcategory that may result in cancer in humans, a determination that 
no source in the category or subcategory emits such HAP in quantities 
that may cause a lifetime risk of cancer greater than 1 in 1 million to 
the individual in the population who is most exposed to emissions of 
such HAP from the source;
    (2) In the case of HAP that may result in adverse health effects in 
humans other than cancer, a determination that emissions from no source 
in the category or subcategory exceed a level which is adequate to 
protect public health with an ample margin of safety; and
    (3) In the case of HAP that may result in adverse environmental 
effects, a determination that no adverse environmental effect will 
result from emissions from any source in the category or subcategory.
    If the Administrator decides to deny a petition, the Agency 
publishes a written explanation of the basis for denial in the Federal 
Register. A decision to deny a petition is final Agency action subject 
to review. If the Administrator decides to grant a petition, the Agency 
publishes a written explanation of the Administrator's decision, along 
with a proposed rule to delete the affected source category or 
subcategory. After affording an opportunity for notice and comment, the 
Administrator will issue a final rule determining whether or not the 
affected category or subcategory will be delisted. If the final rule 
delists any affected source category or subcategory, the Administrator 
will also take all necessary actions to revise the source category list 
and to amend or to rescind affected MACT standards.
    We do not interpret section 112(c)(9)(B) of the CAA to require 
absolute certainty that a source category or subcategory will not cause 
adverse effects on human health or the environment before it may be 
deleted from the source category list. The use of the words ``may'' and 
``adequate'' indicate that the Agency must weigh the potential 
uncertainties and their likely significance. Uncertainties concerning 
risks of adverse health or environmental effects may be mitigated if we 
can determine that projected exposures are sufficiently low to provide 
reasonable assurance that such adverse effects will

[[Page 18330]]

not occur. Similarly, uncertainties concerning the magnitude of 
projected exposures may be mitigated if we can determine that the 
levels which might cause adverse health or environmental effects are 
sufficiently high to provide reasonable assurance that exposures will 
not reach harmful levels.

II. Summary of Petitioner's Request and EPA's Initial Delisting 
Determination

    On August 28, 2002, the GTA submitted a petition requesting EPA to 
create and then delete two subcategories from the Stationary Combustion 
Turbines source category: lean premix stationary combustion turbines 
firing natural gas as a primary fuel with limited oil backup 
capability, and a low-risk subcategory of stationary combustion 
turbines.
    Upon receiving a source category or subcategory deletion petition, 
EPA must first determine whether there is a match between the source 
category or subcategory to which the petition applies and a listed 
category or subcategory. When MACT standards have been promulgated for 
the category in question, EPA will consult the definitions in those 
standards to determine whether or not a petition refers to a listed 
category or subcategory.
    In this case, neither of the two subcategories to which the 
petition refers existed at the time the petition was received, nor do 
they coincide with the subcategories which we have recently adopted in 
the final MACT standards for stationary combustion turbines. However, 
based on the information and the arguments presented in the petition, 
we decided to conduct our own analysis on the subcategories as they 
were defined in the final MACT standards to determine whether any of 
the subcategories meet the criteria of section 112(c)(9)(B) of the CAA. 
In the analysis on which our initial determinations are based, we used 
the data and analysis presented in the petition in those instances 
where we felt it was relevant and technically appropriate to do so, and 
we collected additional data and performed further analysis where those 
in the petition were considered inadequate.
    We construe the issuance of the proposed rule to constitute a 
partial grant and a partial denial of the GTA petition. The lean premix 
gas-fired turbines subcategory in the final MACT standards is similar 
to one of the subcategories that the petitioner proposed: Namely, the 
lean premix stationary combustion turbine firing natural gas as a 
primary fuel with limited oil use. We have made an initial 
determination that the substantive criteria for delisting are satisfied 
for this subcategory. However, in the final MACT standards, we did not 
create any subcategory coinciding with the low-risk subcategory 
proposed by the petitioner. Therefore, we must deny that portion of the 
petition. Also, we have made an initial determination that several 
additional subcategories included in the final MACT standards satisfy 
the substantive criteria for delisting. These additional subcategories 
are: diffusion flame gas-fired stationary turbines, emergency 
stationary combustion turbines, and stationary combustion turbines 
located on the North Slope of Alaska.

III. Description of the Four Stationary Combustion Turbines 
Subcategories

    The final MACT standards (40 CFR 63.6175) define stationary 
combustion turbines as:

    All equipment including, but not limited to, the turbine, the 
fuel, air, lubrication and exhaust gas systems, control systems 
(except emissions control equipment), and any ancillary components 
and sub-components comprising any simple cycle stationary combustion 
turbine, any regenerative/recuperative cycle stationary combustion 
turbine, or the combustion turbine portion of any stationary 
combined cycle steam/electric generating system. Stationary means 
that the combustion turbine is not self-propelled or intended to be 
propelled while performing its function. A stationary combustion 
turbine may, however, be mounted on a vehicle for portability or 
transportability.

Currently, there are approximately 8,000 stationary combustion turbines 
operating in the United States.

    For the purposes of the MACT standards, stationary combustion 
turbines have been divided into eight subcategories. Four of the 
subcategories are the subject of the proposed delisting rule: (1) 
Stationary lean premix combustion turbines when firing gas and when 
firing oil at sites where all turbines fire oil no more than 1,000 
hours annually (also referred to as ``lean premix gas-fired 
turbines''); (2) stationary diffusion flame combustion turbines when 
firing gas and when firing oil at sites where all turbines fire oil no 
more than 1,000 hours annually (also referred to herein as ``diffusion 
flame gas-fired turbines''); (3) emergency stationary combustion 
turbines; and (4) stationary combustion turbines operated on the North 
Slope of Alaska (defined as the area north of the Arctic Circle 
(latitude 66.5[deg] North)).
    The stationary combustion turbines MACT standards also define the 
subcategories. The lean premix gas-fired turbines subcategory includes 
those stationary combustion turbines that use lean premix technology 
which was introduced in the 1990's and was developed to reduce nitrogen 
oxide (NOX) emissions without the use of add-on controls. In 
a lean premix combustor, the air and fuel are thoroughly mixed to form 
a lean mixture for combustion. Mixing may occur before or in the 
combustion chamber. Lean premix combustors emit lower levels of 
NOX, carbon monoxide (CO), formaldehyde and other HAP than 
diffusion flame combustion turbines.
    Diffusion flame gas-fired turbines operate in a different manner 
than lean premix units. In a diffusion flame combustor, the fuel and 
air are injected at the combustor and are mixed only by diffusion prior 
to ignition.
    Emergency stationary combustion turbines are stationary combustion 
turbines that operate in an emergency situation. Examples include 
stationary combustion turbines used to produce power for critical 
networks or equipment (including power supplied to portions of a 
facility) when electric power from the local utility is interrupted, or 
stationary combustion turbines used to pump water in the case of fire 
or flood, etc. Emergency stationary combustion turbines do not include 
stationary combustion turbines used as peaking units at electric 
utilities or stationary combustion turbines at industrial facilities 
that typically operate at low capacity factors. Emergency stationary 
combustion turbines may be operated for the purpose of maintenance 
checks and readiness testing, provided that the tests are required by 
the manufacturer, the vendor, or the insurance company associated with 
the turbine.
    The subcategory stationary combustion turbines located on the North 
Slope of Alaska refers to all stationary combustion turbines that are 
located north of the Arctic Circle. They have been identified as a 
subcategory due to operating limitations and uncertainties regarding 
the application of controls to these units.

IV. Analysis of Gas-Fired Subcategories

A. Analytical Approach

    In conducting the risk assessment for the four source 
subcategories, EPA uses a tiered, iterative process recommended by the 
National Research Council (NRC) of the National Academy of Sciences. 
This process begins with the use of relatively inexpensive screening 
techniques and moves to more resource-intensive levels of data-
gathering, model construction, and model application, as the particular 
situation warrants (NRC, 1994). In applying this approach, EPA

[[Page 18331]]

typically conducts the first (and in some cases the only) iteration of 
the risk assessment using limited amounts of data and simple, health-
protective assumptions. This results in risk estimates that we expect 
will over-predict the actual risk. If the initial estimates of risk 
exceed a level of concern, then successive refinements with regard to 
data and models may be useful to more accurately characterize the 
actual risk. If the initial estimates are below a level of concern, 
then a more sophisticated analysis may not be necessary for decision-
making purposes.
    The analysis discussed here represents an initial assessment based 
on simple, health-protective assumptions. This screening approach has 
not sought to modify the assumptions in a way that would yield exposure 
estimates that would correspond to an actual individual in the 
population who is most exposed. Instead, through the compounding of 
health-protective assumptions, we feel this approach yields exposure 
estimates that exceed exposures to the most exposed individuals in the 
population.

B. Planning and Scoping

    The first step in conducting a tiered, iterative risk assessment is 
to plan and scope the assessment. The EPA provides guidance for this 
step in the Risk Characterization Handbook (EPA, 2000) and in the 
Framework for Cumulative Risk Assessment (EPA, 2003). The general 
process of planning and scoping includes defining the elements that 
will or will not be included in the risk assessment and explaining the 
purposes for which the risk assessment information will be used (EPA, 
2000).
    We have already established the motivation for conducting the risk 
assessment. Prompted by a petition submitted by the GTA, we conducted 
the assessment under section 112(c)(9)(B) of the CAA to determine 
whether regulatory relief for the industry was warranted. The 
assessment needed to show whether or not any source in each of the four 
subcategories exceeds the human health and ecological criteria 
described in the statute. In designing the assessment, we considered 
the statutory requirements, the amount and type of available 
information on the subcategories to include in the assessment, and the 
available methods and models.
    Based on the criteria, we designed an assessment to estimate cancer 
risks and noncancer hazards from a worst-case exposure scenario which 
would likely exceed the exposure to the person most exposed. We began 
by conducting a human health risk analysis on stationary lean premix 
combustion turbines when firing gas and when firing oil at sites where 
all turbines fire oil no more than 1,000 hours annually, and stationary 
diffusion flame combustion turbines when firing gas and when firing oil 
at sites where all turbines fire oil no more than 1,000 hours annually. 
To evaluate the risks, hazards and potential for adverse environmental 
effects from the emergency turbines and north slope turbines 
subcategories, we used available information on the subcategories and 
the results of the assessment on the lean premix and diffusion flame 
subcategories.
    We designed the assessment to address cancer risks and noncancer 
hazards to humans from the air and ingestion pathways and also 
evaluated the potential for adverse environmental effects. As we 
describe above, we used a tiered, iterative approach to the assessment. 
Given that there are thousands of facilities in the four subcategories 
and that current information on the facilities is limited, it was not 
feasible to identify all turbines and their operating characteristics 
on a site-specific basis. Therefore, we used a number of health-
protective assumptions where we lacked data. This is an appropriate 
approach to evaluating whether to remove a source category or 
subcategory from regulation as the CAA specifies that in order to be 
delisted, ``no source in the category'' may exceed the cancer, 
noncancer or environmental criteria.
    We created a worst-case exposure scenario by using a combination of 
actual data and health-protective assumptions. For the air pathway, our 
approach was to:
    (1) Determine which type of turbine would result in the highest 
modeled air concentration of HAP.
    (2) Hypothetically ``place'' eleven of the turbines at an actual 
facility to create our model plant. (An actual facility is permitted 
for eleven turbines, but seven turbines are currently operated there.)
    (3) Calculate cancer risks, noncancer hazards and the potential for 
adverse environmental effects based on the highest ambient air 
concentrations of HAP calculated by the model.
    For the multipathway analysis, we developed and evaluated an 
exposure scenario for our model plant using meteorologic data from 
locations around the country: Allentown, PA; Baton Rouge, LA; 
Indianapolis, IN; Kansas City, KS; Los Angeles, CA; Minneapolis, MN; 
Seattle, WA; and Tampa, FL. Our goal was to account for the effect of 
meteorologic variability on the risks and hazards.
    We feel the health-protective assumptions we used, when compounded 
in the assessment, lead to very health-protective risk estimates. Given 
the combination of data and assumptions used, we conducted an 
assessment that adequately addresses the questions posed, that is 
responsive to the requirements in section 112(c)(9)(B) of the CAA, that 
overestimates actual risks, and that shows the statutory criteria for 
deletion are met. See the technical memo located in the docket for the 
a more detailed description of the analysis (Combustion Turbines Source 
Category Risk Characterization, January 2004).

C. Source Characterization

    Stationary combustion turbines can be operated in two basic cycles: 
simple cycle and combined cycle. The simple cycle mode consists of the 
combustion turbine-generator combination operating and producing 
electricity with the turbine exhaust vented through a stack directly to 
the atmosphere. In the combined cycle mode, the exhaust from the 
turbine is passed through a heat recovery steam generator to generate 
steam that is then used to produce additional electricity. The heat 
extraction at this step cools the exhaust gas stream resulting in a 
lower exhaust temperature (reduced plume buoyancy). Thus, emissions 
from a turbine operating in the combined cycle mode will often produce 
higher ground level pollutant concentrations. As a health-protective 
assumption, our analysis only examined the combined cycle units.
    To conduct our analysis, we used information on the physical 
characteristics of these turbines that was submitted by the petitioner 
after we determined the data were of sufficient quality to do so. The 
GTA provided data on a set of typical turbines ranging in power output 
from 5 to 253 megawatts (MW) each. These characteristics include 
turbine type (i.e., make and model), heat input, stack parameters 
(height, diameter, exit velocity, temperature), and building 
dimensions.

D. Emissions Characterization

    With regard to emissions, we agree with the petitioner that the 
following HAP are emitted from turbines when natural gas is used as the 
fuel: 1,3-butadiene, acetaldehyde, acrolein, benzene, ethylbenzene, 
formaldehyde, naphthalene, polycyclic aromatic hydrocarbons (PAH, which 
the EPA classifies as a subset of a larger group of HAP, polycyclic 
organic matter (POM)), propylene oxide, toluene, and xylenes (mixed). 
We also agree with the petitioner that the following non-

[[Page 18332]]

metallic HAP are emitted from turbines when distillate oil is used as 
the fuel: 1,3-butadiene, benzene, formaldehyde, naphthalene, and PAH. 
However, the petitioner claimed that metallic HAP are not detectable in 
distillate oil and are, thus, not present in turbine emissions; they 
subsequently amended this claim to state that only chromium and lead 
are emitted. We disagree with these claims and have collected 
additional data showing the following HAP metals can be emitted when 
turbines burn distillate oil, although the levels can vary by oil type: 
arsenic, beryllium, cadmium, chromium VI, lead, manganese, mercury, 
nickel and selenium. We used emission factors for the emitted HAP that 
are based on the most recent available data. Also, we developed 
separate emission factors for large and small turbines based on the 
burner design-type (lean premix or diffusion flame) and based on the 
differences in heat input between small versus large turbines. To 
develop health-protective, yet still realistic emission values, we 
calculated emission factors for each HAP by selecting the lesser of (1) 
the upper 95 percent confidence interval around the mean of each set of 
emission factors reported for the HAP or (2) the maximum emission 
factor reported for the HAP. We then developed turbine-specific 
emission estimates by multiplying the pollutant-specific emission 
factors with the heat input of each unit.

E. Air Dispersion Modeling

    The goal of our air dispersion modeling approach was to determine 
the maximum annual ambient average concentrations of all emitted HAP 
that a person living in the vicinity of a turbine could experience. We 
used these maximum annual ambient average concentrations, without 
regard to whether a person is actually exposed to these concentrations, 
as surrogates for exposure. This is a health-protective approach to 
assessing exposure.
    We used the SCREEN3 model (Version 96043) to estimate the maximum 
annual ambient average concentrations of all emitted pollutants. 
SCREEN3 consists of algorithms that tend to overestimate HAP 
concentrations in air, along with worst-case meteorologic conditions, 
to estimate ambient concentrations of HAP in air. This results in 
estimates of HAP concentrations in air that are likely to be an 
overestimate of what we expect people to actually breathe. We used this 
health-protective modeling approach to evaluate the four subcategories 
of stationary combustion turbines because it is not feasible to 
identify all turbines and their operating characteristics due to the 
large number of facilities. Also, we want to ensure that our assessment 
is not underestimating potential exposures and risks. This is an 
important consideration when we are evaluating whether to grant a 
petition to remove a source category from regulation as the CAA 
specifies that in order to be delisted, ``no source in the category'' 
may exceed the cancer, noncancer or environmental criteria.
    Our approach to modeling was to first determine which type of 
turbine (of the ten turbine types identified by the petitioner) 
produces the highest maximum annual ambient average concentrations 
using SCREEN3. We then simulated a facility and ran SCREEN3 for all HAP 
emitted from lean premix gas-fired turbines and also for diffusion 
flame gas-fired turbines, using regulatory default mode, full 
meteorology, building downwash, flat nearby terrain, rural dispersion, 
automated receptor arrangement (50-2000 meter), and a conversion factor 
of 0.08 to obtain annual average concentrations from maximum 1-hour 
concentrations. As stated above, we used turbine characteristics 
submitted by the petitioner and developed updated emission factors 
ourselves. We used these data as inputs into the SCREEN3 model in order 
to obtain the maximum annual average air concentrations from a worst-
case type of turbine. Our dispersion modeling showed that the W501F 
turbine resulted in the highest air concentrations.
    After establishing that maximum annual ambient average 
concentrations are the highest from the W501F turbine, we simulated 
another facility. We placed 11 W501F turbines at our simulated facility 
because the highest number of large turbines permitted to operate at an 
actual facility is 11. After accounting for source separation (see 
technical memo for details), we ran SCREEN3 on our simulated facility 
for four scenarios: (1) Assuming the 11 turbines are lean premix gas-
fired turbines collectively using 1,000 hours of oil per year; (2) 
assuming the 11 turbines are diffusion flame gas-fired turbines 
collectively using 1,000 hours of oil per year; (3) assuming the 11 
turbines are lean premix and burn only natural gas; and (4) assuming 
the 11 turbines are diffusion flame turbines and burn only natural gas. 
We conducted the analyses assuming the turbines burn only natural gas, 
and assuming the turbines burn natural gas plus 1,000 hours of oil per 
year because not all facilities use oil, and because emissions are 
different when only natural gas is used as fuel (no metals are emitted 
but formaldehyde emissions are higher). The maximum annual ambient 
average concentrations for each emitted pollutant for natural gas plus 
1,000 hours of oil per year and for natural gas only for the 11 W501F 
turbines can be found in Table 4 of the technical memo (see docket).
    We consider the maximum annual average concentrations resulting 
from our dispersion modeling analysis to be health-protective. That is, 
we feel that the resulting air concentrations over- rather than under-
estimate actual exposures to people. This is because our analysis used 
health-protective source parameters and atmospheric dispersion modeling 
methodology; relied on health-protective emission factors for all HAP; 
used the maximum annual ambient average concentrations of the emitted 
HAP as a surrogate for exposure; and assumed 70 years, 24 hours a day, 
365 days a year of continuous exposure. Even though actual emission 
rates, and thus ambient concentrations, of HAP may increase above 
annual average levels during certain short-duration transient 
operations such as unit startup, the health-protective analysis 
approach accounts for such transient increases in the health-protective 
estimates of annual average exposures. Thus, the analyses, even though 
they do not explicitly incorporate these short term events, reasonably 
account for these events and result in health-protective estimates of 
risk.

F. Human Health Effects of Emitted HAP

    Although numerous HAP may be emitted from combustion turbines, a 
few account for essentially all the mass of HAP emissions from 
stationary combustion turbines. These HAP are formaldehyde, toluene, 
benzene, and acetaldehyde. Other emitted HAP are of potential concern 
not so much because of the emitted amounts, but due to their high 
potency via the inhalation route. These include arsenic and PAH. Four 
of the emitted HAP are of potential concern from the ingestion route: 
PAH, which are of concern for cancer; and cadmium, lead and mercury 
which are of concern for noncarcinogenic effects.
    The HAP emitted in the largest quantity is formaldehyde. 
Formaldehyde is a probable human carcinogen and can cause irritation of 
the eyes and respiratory tract, coughing, dry throat, tightening of the 
chest, headache, and heart palpitations. Acute (short-term) inhalation 
has caused bronchitis, pulmonary edema, pneumonitis, pneumonia, and 
death due to respiratory failure. Chronic (long-

[[Page 18333]]

term) exposure can cause dermatitis and sensitization of the skin and 
respiratory tract.
    Other HAP emitted in significant quantities from stationary 
combustion turbines include toluene, benzene, and acetaldehyde. The 
health effect of primary concern for toluene is dysfunction of the 
central nervous system (CNS). Toluene vapor also causes narcosis. 
Controlled exposure of human subjects produced mild fatigue, weakness, 
confusion, lacrimation, and paresthesia; at higher exposure levels 
there were also euphoria, headache, dizziness, dilated pupils, and 
nausea. After-effects included nervousness, muscular fatigue, and 
insomnia persisting for several days. Acute exposure may cause 
irritation of the eyes, respiratory tract, and skin. It may also cause 
fatigue, weakness, confusion, headache, and drowsiness. Very high 
concentrations may cause unconsciousness and death.
    Benzene is a known human carcinogen. The health effects of benzene 
include nerve inflammation, CNS depression, and cardiac sensitization. 
Acute exposure can cause dizziness, euphoria, giddiness, headache, 
nausea, staggering gait, weakness, drowsiness, respiratory irritation, 
pulmonary edema, pneumonia, gastrointestinal irritation, convulsions, 
and paralysis. Benzene can also cause irritation to the skin, eyes, and 
mucous membranes. Chronic exposure to benzene can cause fatigue, 
nervousness, irritability, blurred vision, and labored breathing and 
has produced anorexia and irreversible injury to the blood-forming 
organs; effects include aplastic anemia and leukemia.
    Acetaldehyde is a probable human carcinogen. Inhalation exposures 
to acetaldehyde can cause irritation of the eyes, mucous membranes, 
skin, and upper respiratory tract, and CNS depression in humans. Acute 
exposure can cause conjunctivitis, coughing, difficult breathing, and 
dermatitis. Chronic exposure may cause heart and kidney damage, 
embryotoxicity, and teratogenic effects.
    Arsenic, a naturally occurring element, is found throughout the 
environment. For most people, food is the major source of exposure to 
arsenic. The EPA has classified inorganic arsenic as a human 
carcinogen. Acute high-level inhalation exposure to arsenic dust or 
fumes has resulted in gastrointestinal effects (nausea, diarrhea, 
abdominal pain); central and peripheral nervous system disorders have 
occurred in workers acutely exposed to inorganic arsenic. Chronic 
inhalation exposure to inorganic arsenic in humans is associated with 
irritation of the skin and mucous membranes. Chronic oral exposure has 
resulted in gastrointestinal effects, anemia, peripheral neuropathy, 
skin lesions, hyperpigmentation, and liver or kidney damage in humans. 
Inorganic arsenic exposure in humans, by the inhalation route, has been 
shown to be strongly associated with lung cancer, while ingestion of 
inorganic arsenic in humans has been linked to a form of skin cancer 
and also to bladder, liver, and lung cancer.
    Polycyclic aromatic hydrocarbons are a group of compounds that fit 
within the POM HAP category. Dermal exposures to mixtures of PAH cause 
skin disorders in humans and animals. No information is available on 
the reproductive or developmental effects of PAH mixtures in humans, 
but animal studies have reported that oral exposure to benzo(a)pyrene 
(BaP, a PAH compound) causes reproductive and developmental effects. 
Human studies have reported an increase in lung cancer in humans 
exposed to PAH-bearing mixtures including coke oven emissions, roofing 
tar emissions, and cigarette smoke. Animal studies have reported 
respiratory tract tumors from inhalation exposure to BaP and 
forestomach tumors, leukemia, and lung tumors from oral exposure to 
BaP. The EPA has classified seven PAH compounds: (BaP, 
benz(a)anthracene, chrysene, benzo(b)fluoranthene, 
benzo(k)fluoranthene, dibenz(a,h)anthracene, and indeno(1,2,3-
cd)pyrene) as Group B2, probable human carcinogens.
    The EPA reports in the Integrated Risk and Exposure Assessment 
(IRIS) that cadmium has been shown to cause kidney damage via the oral 
route. IRIS also reports that there are no positive cancer studies of 
orally ingested cadmium suitable for quantification. Consequently, we 
evaluated noncancer hazards only for cadmium ingestion. The major 
effect from chronic oral exposure to inorganic mercury is also kidney 
damage. Animal studies have reported effects such as alterations in 
testicular tissue, increased resorption rates, and abnormalities of 
development from oral exposure to inorganic mercury. Mercuric chloride 
(an inorganic mercury compound) exposure has been shown to result in 
forestomach, thyroid, and renal tumors in experimental animals. For 
lead, oral exposures can lead to central nervous system effects, as 
well as effects on the blood, blood pressure, kidneys and Vitamin D 
metabolism. Children are especially sensitive to the chronic effects of 
lead, and can exhibit slowed cognitive development and reduced growth.

G. Human Health Values Used

    We used the human health values currently used by EPA's air toxics 
program and available at: http://www.epa.gov/ttn/atw/toxsource/summary.html.
 These dose response values come from several sources 

including EPA's IRIS, the United States Department of Health and Human 
Service's Agency for Toxic Substances Disease Registry, and California 
EPA. See Table 5 in our technical memo for a summary of the human 
health values we used in our assessment.
    For formaldehyde, we do not use the dose-response value reported in 
IRIS. The dose-response value in IRIS is based on a 1987 study, and no 
longer represents the best available science in the peer-reviewed 
literature. Since that time, significant new data and analysis have 
become available. We based the dose-response value we used for 
formaldehyde on work conducted by the CIIT Centers for Health Research 
(CIIT). In 1999, the CIIT published a risk assessment which 
incorporated mechanistic and dosimetric information on formaldehyde 
that had been accumulated over the past decade. The risk assessment 
analyzed carcinogenic risk from inhaled formaldehyde using approaches 
that are consistent with EPA's draft guidelines for carcinogenic risk 
assessment. The CIIT model is based on computational fluid dynamics 
(CFD) models of airflow and formaldehyde delivery to the relevant parts 
of the rat and human respiratory tract, which are then coupled to a 
biologically-motivated, two-staged clonal growth model that allows for 
incorporation of different biological effects. These biological 
effects, such as interaction with DNA and cell proliferation, are 
processes by which formaldehyde may contribute to development of cancer 
at sites exposed at the portal of entry (e.g., respiratory tract). The 
two-staged model is a much more advanced approach for examining the 
relevance of tumors seen in animal models for human populations. The 
CIIT information and other recent information, including recently 
published epidemiological studies, are being reviewed and considered in 
the reassessment of our formaldehyde unit risk estimate (URE).
    We believe that the CIIT modeling effort represents the best 
available application of the available mechanistic and dosimetric 
science on the dose-response for portal of entry cancers due to 
formaldehyde exposures. We note here that other organizations, 
including

[[Page 18334]]

Health Canada, have adopted this approach. Accordingly, we have used 
risk estimates based on the CIIT airflow model coupled to a two-staged 
clonal growth model as the basis for the dose-response values for this 
analysis. The formaldehyde risk value obtained by extrapolating with 
the CIIT model that we used in our analysis differs slightly from the 
values used by the petitioner. The CIIT model incorporates state-of-
the-art analyses for species-specific dosimetry, and encompasses more 
of the available biological data than any other currently available 
model. As with any model, uncertainties exist, and the CIIT model is 
sensitive to the inputs, but we believe it represents the best 
available approach for assessing the risk of portal-of-entry cancers 
due to formaldehyde exposures.

H. Human Health Risk Results--Air Pathway

    We calculated the maximum excess lifetime cancer risk for the Air 
pathway that results from the exposure scenario described above. We 
estimated risks for both the primary firing of natural gas with 1,000 
hours of oil firing per year, per facility, and for the continuous 
firing of natural gas. Diffusion flame gas-fired turbines produced the 
highest risk. When firing natural gas plus 1,000 hours of oil per year, 
the total excess lifetime cancer risk from all the emitted pollutants 
from the diffusion flame turbines in our analysis is 7.7 x 
10-\7\. The total excess lifetime cancer risk from 
continuous burning of natural gas for our modeled scenario is 3.9 x 
10-\7\.
    In addition to estimating cancer risks, we evaluated noncancer 
hazards for each pollutant for which there is a noncancer human health 
value. To do this, we used a hazard quotient (HQ) approach and 
calculated the ratio of the exposure concentration to the noncancer 
human health value (e.g., inhalation reference concentration (RfC)) for 
each emitted HAP. This is represented by the formula HQ= (exposure 
concentration)/(RfC). The RfC is a peer-reviewed value defined as an 
estimate (with uncertainty spanning perhaps an order of magnitude) of a 
daily inhalation exposure to the human population (including sensitive 
subgroups) that is likely to be without appreciable risk of deleterious 
noncancer effects during a lifetime.
    We then generated hazard indices (HI) by summing HQ across HAP. We 
can generate two types of hazard indices. The first type is generated 
by adding HQ for all emitted HAP regardless of their target organ. This 
results in an HI that is considered health-protective since the HQ for 
all pollutants are added even though some pollutants cause distinctly 
different effects. For our modeled scenario, the total HI for the 
natural gas plus 1,000 hours of oil scenario is 0.6. The HI for the 
natural gas burning scenario is 0.4.
    We can also calculate HI by summing HQ from HAP that affect the 
same target organ. In this assessment, pollutants that affect the same 
target organ are acrolein and formaldehyde; they affect the respiratory 
system. These also are the two HAP with the highest individual hazard 
quotients. When accounting for the fact that acrolein and formaldehyde 
affect the same target organ, we calculate a HI of 0.4. None of the 
other HAP affect the same target organ, thus, we calculated a HI for 
the respiratory system only. The other HAP had HQ ranging from 
10-\6\ (nickel) to 0.1 (manganese).

I. Multipathway Considerations

    In order to fully characterize risks and hazards to humans from the 
subcategories, we considered exposures from ingestion as well as 
inhalation for four of the emitted HAP: cadmium, lead, mercury and PAH. 
We chose these HAP because of all the HAP emitted, only these four 
appear on lists of chemicals that EPA considers to be persistent, 
bioaccumulative, and toxic (PBT) substances under the Pollution 
Prevention Program, the Great Waters Program, or the Toxics Release 
Inventory. (See the multipathway HAP memo in the docket for more 
information.) Therefore, in addressing the potential for the 
subcategories to be of concern due to multipathway routes of exposure, 
we need to consider emissions of cadmium, lead, mercury and PAH.
    Several of the emitted PAH are carcinogenic via the ingestion 
pathway and, thus, we evaluated these pollutants in the multipathway 
analysis: benzo(a)anthracene, benzo(a)pyrene, benzo(b)fluoranthene, 
benzo(k)fluoranthene, chrysene, dibenz(a,h)anthracene, and indeno 
(1,2,3-cd)pyrene. We evaluated noncancer health effects for cadmium, 
lead, mercury and the following noncarcinogenic PAH: Acenaphthene, 
fluoranthene, fluorene, and pyrene.
    To evaluate the potential for these HAP to cause cancer risk or 
noncancer hazard to humans due to ingestion, we conducted a screening 
level multipathway analysis. As with the inhalation assessment, we did 
not have enough data to evaluate actual exposures across the entire 
source category. We did not structure this assessment to reflect actual 
exposures, rather we developed a worst-case exposure model scenario 
based on limited data and assumptions which, when considered in total, 
provide for a health-protective analysis. This approach ensures that we 
are not underestimating actual risks and hazards from emissions from 
the four subcategories.
    We structured this analysis to estimate maximum risks to an 
individual exposed via routes other than inhalation (e.g., ingestion of 
contaminated food) for HAP emitted from combustion turbines. We used 
our modeled facility and evaluated human ingestion of contaminated 
food, water and soil. We generally followed the Human Health Risk 
Assessment Protocol for Hazardous Waste Combustion Facilities (HHRAP) 
(U.S. EPA, 1998) to conduct the multipathway portion of the assessment. 
The HHRAP provided the primary source of chemical-specific parameter 
values and default environmental parameters. We started with the 
HHRAP's parameter values and replaced specific inputs as necessary, 
either due to updated science or due to policy choices that we made in 
order to be consistent with the mandate to assess risks to the 
individual most exposed.
    To evaluate a worst-case potential exposure from our modeled 
facility, we used a subsistence farmer scenario. This scenario reflects 
an adult living on a farm that we hypothetically assumed to be located 
close to our modeled facility. We assumed the farmer consumes meat 
(pork and beef), dairy, fruit, and vegetables that the farm produces as 
a portion of his/her diet. The animals raised on the farm subsist 
primarily on feed grown on the farm. We also assumed that the farmer is 
a recreational fisher and eats the fish he/she catches. Finally, we 
assumed that the farmer drinks treated, local surface water (water 
which has gone through minimal municipal treatment).
    For several reasons, we consider this approach to multipathway 
assessment scenario to be health-protective. We used the maximum 
ambient air concentrations from our modeled facility which, as we have 
stated above, produces higher ambient air concentrations than we expect 
to actually occur anywhere in the U.S. Also, we used a water body size, 
flow rate, watershed size and other parameters that were developed for 
the health protective analysis scenario analyzed in the Mercury Study 
Report to Congress. Further, we applied maximum pollutant deposition 
rates to the entire watershed. Thus, we feel our modeled scenario will 
over-predict

[[Page 18335]]

actual risks and hazards from ingestion and is, therefore, health-
protective.
    We estimated both cancer risk and noncancer hazards from all the 
ingestion pathways: water, meats, fruits, vegetables, soil, and fish. 
The results of our multipathway analysis show that the cancer risks 
from PAH are 0.16 in 1 million (1.6 x 10-\7\). This is below 
the statutory cancer risk criterion of 1 in 1 million. When we add 
these risks to the lifetime excess cancer risks of 7.7 x 
10-\7\ from the inhalation pathway, we get a total cancer 
risk of .93 in 1 million, which rounds to 0.9 in 1 million (0.9 x 
10-\6\). Such a summation of risks is appropriate only if it 
is plausible that the person with the maximum risks from the air 
pathway is also the person with the maximum risk from the ingestion 
pathway. Inherent in this assumption is that these two maximum 
concentrations (therefore, the maximum risk and hazards) occur at the 
exact same location. While we calculated risk and hazards for such a 
person, we feel it very unlikely that one person would be located at 
the point of highest impact from both inhalation and ingestion. If we 
had more site-specific data with which to conduct this assessment, we 
would likely have found that the maximum impact from inhalation was not 
in the same location as the maximum impact from ingestion, and the 
risks would be lower. We consider it inappropriate to use this combined 
inhalation/ingestion scenario because we consider it to be implausible. 
We feel that the actual combined risks, from all pathways, will be 
lower than 1 in 1 million and, therefore, the statutory criteria are 
met.
    We estimated noncancer hazards for cadmium and mercury, combining 
hazards from all ingestion pathways. The highest total hazard index for 
all ingestion pathways is 0.1. Noncancer hazards are driven by methyl 
mercury via ingestion of fish. The HQ for mercury for this route of 
exposure is also 0.1; it is clearly the driver for multipathway 
noncancer effects.
    The EPA uses a slightly different approach in order to assess the 
hazard from ingestion exposures to lead. In general, we use a protocol 
like that in HHRAP to obtain media concentrations. We use an additional 
model called the Integrated Exposure, Uptake and Biokinetic Model 
(IEUBK) to estimate blood lead levels. We then calculate an HQ. In this 
analysis, the inhalation HQ for lead was so low, 0.000008, that we 
found it unnecessary to take the additional step of modeling further 
with the IEUBK. Based on previous analyses we have conducted on lead, 
we do not feel that an air concentration that leads to an HQ of 
0.000008 would translate into an HQ of concern from the ingestion route 
of exposure. The ingestion HQ would have to be four to five orders of 
magnitude higher than the HQ from the air pathway to even approach a 
level of concern. Given the very low inhalation HQ for lead from 
exposure to the turbine subcategories, the lead emissions from the four 
subcategories do not exceed a level that is adequate to protect the 
public health with an ample margin of safety. Therefore, we conclude 
that both risks and hazards to humans due to multipathway exposures 
from all HAP emitted from the four combustion turbine subcategories 
meet the required human health criteria in CAA section 112(c)(9)(B).
    Emissions that result in the maximum modeled lifetime excess cancer 
risk of 0.9 in 1 million are within the statutory criteria. With regard 
to noncancer effects, we consider the emissions resulting in a target 
organ-specific HI of 0.4 from the turbine subcategories do not exceed a 
level that is adequate to protect the public health with an ample 
margin of safety. We consider the actual risks and hazards from the 
turbines in the four subcategories to be lower than what we estimated 
here due to the health-protective assumptions we included in this 
assessment. For example, in characterizing the physical and operational 
attributes of the turbines, we assumed all turbines were operating in 
combined cycle, used worst-case meteorology, and included the potential 
for building downwash. These assumptions lead to exposures which we 
feel are higher than what we would find from an actual plant. In 
addition, we assumed that individuals are exposed to the maximum 
modeled concentrations of HAP in the air continuously for their entire 
lives (which we approximated as 70 years), and we used the maximum 
annual average concentration as a surrogate for exposure. These 
assumptions are also health-protective.

J. Effects Due to Acute Exposure

    We determined that emissions from turbines are of concern for long-
term (chronic) exposures and not from short-term (acute) exposures. 
Short-term exposures may arise when a facility starts up or shuts down 
equipment, which may result in short bursts of high emissions due to 
the fact that the unit is not running at peak efficiency during the 
time it takes to start up or shut down. For other types of source 
categories, this can lead to exposures that result in adverse health 
effects. In the case of gas-fired turbines, we have determined that 
upon start up, they reach peak efficiency quickly, therefore, limiting 
any bursts of emissions. Shut downs take a short amount of time as 
well. The HAP emitted from combustion turbines have not been associated 
with acute health effects at the concentrations predicted in the 
analyses. While the short-duration emissions may slightly increase the 
overall cancer risks, this effect would be so small as to be 
inconsequential. Therefore, we conclude that the acute exposures to HAP 
emissions from stationary combustion turbines are not of concern.

K. Environmental Effects Evaluation

    In order to assess whether the emissions from our modeled facility 
could lead to adverse environmental effects, we performed a screening-
level ecological risk assessment. We evaluated the inhalation pathway 
for terrestrial mammals, the ingestion pathway for terrestrial 
wildlife, contact with sediment for benthic species, and contact with 
soil for terrestrial plants. We did not evaluate terrestrial plants 
exposed via direct contact with the air due to a lack of toxicity data.
    We contend that human toxicity values we used in this analysis for 
the inhalation route are protective of inhalation exposures that may be 
experienced by terrestrial mammals. The human health values were 
derived based on human studies and also considered studies on small 
laboratory animals, primarily rodents. These values are significantly 
less than the level to which an experimental animal was exposed. 
Because the maximum cancer risk and noncancer hazards to humans from 
inhalation exposure are all below a level of concern, we expect there 
to be no significant and widespread adverse effects to terrestrial 
mammals from inhalation exposures to HAP emitted from gas-fired 
turbines.
    In order to assess whether the continuing emissions from our 
modeled facility could contribute to adverse environmental effects from 
the ingestion pathway, we performed a screening-level ecological risk 
assessment. For screening purposes, we intentionally designed the 
assessment to be health-protective of ecological receptors. We did not 
intend the assessment to be used in predicting specific types of 
effects to individuals, species, populations, or communities, or to the 
structure and function of the ecosystem. We used the assessment to 
identify HAP which may pose potential risk or hazard to ecological 
receptors and, therefore, would need to be evaluated in a more refined 
level of risk assessment.

[[Page 18336]]

    For screening endpoints, we used the structure and function of 
generic aquatic and terrestrial populations and communities, including 
threatened and endangered species, that might be exposed to HAP 
emissions via soil or water. The assessment endpoints are relatively 
generic with respect to descriptions of the environmental values that 
are to be protected and the characteristics of the ecological entities 
and their attributes. We assumed in the assessment that these 
ecological receptors were representative of sensitive individuals, 
populations, and communities present near these facilities.
    The HAP we included in the quantitative ecological assessment are 
the same HAP that we evaluated in the multipathway human health 
assessment: cadmium, lead, mercury and PAH. We derived estimated media 
concentrations for each of these HAP from the media concentrations 
estimated in the multipathway exposures assessment. We chose exposure 
pathways to reflect the potential routes of exposure through sediment, 
soil, water, and air. We selected these environments because they are 
considered representative of locations of generic populations and 
communities most likely to be exposed to the HAP. Within these 
environments, the receptors evaluated consisted of two distinct groups: 
terrestrial and aquatic (i.e., including aquatic, benthic, and soil 
organisms; terrestrial plants and wildlife; and herbivorous, 
piscivorus, and carnivorous wildlife).
    The chronic ecological toxicity screening values used in the 
assessment were estimates of the maximum concentrations that would not 
be expected to affect survival, growth, or reproduction of sensitive 
species after long-term (more than 30 days) exposure to HAP. We 
screened HAP, pathways, and receptors using the ecological HQ method, 
which simply calculates the ratio of the estimated environmental 
concentrations to the selected ecological screening values.
    The results of our ecological assessment show that for all 
pollutants assessed, and for all pathways assessed, the ecological HQ 
values are less than 1. Therefore, it is not likely that any of the HAP 
emitted would pose an ecological risk to ecosystems near any of these 
facilities.
    With regard to endangered species, we assumed that the screening 
values were protective of sensitive species, including threatened or 
endangered species. There are no available ecological toxicity test 
data for threatened and endangered species for these HAP. As such, the 
actual sensitivities of any threatened or endangered species located in 
the vicinity of these facilities is unknown. However, in order to be 
health-protective, we selected ecological screening values for the most 
sensitive species available for use in the analysis. Also, we are not 
familiar with any species that have become threatened or endangered as 
a result of emissions of these chemicals from stationary combustion 
turbines. Therefore, we feel it is not likely that any threatened and 
endangered species, if they exist around these facilities, would be 
adversely affected by these HAP emissions.

V. Analysis of the Emergency Turbine Subcategory

    Emergency stationary combustion turbines are stationary combustion 
turbines that operate in an emergency situation. Examples include 
stationary combustion turbines used to produce power for critical 
networks or equipment (including power supplied to portions of a 
facility) when electric power from the local utility is interrupted, or 
stationary combustion turbines used to pump water in the case of fire 
or flood, etc. Emergency stationary combustion turbines do not include 
stationary combustion turbines used as peaking units at electric 
utilities or stationary combustion turbines at industrial facilities 
that typically operate at low capacity factors. Emergency stationary 
combustion turbines may be operated for the purpose of maintenance 
checks and readiness testing, provided that the tests are required by 
the manufacturer, the vendor, or the insurance company associated with 
the turbine.
    Usually one or two emergency turbines are located at a given 
facility. These units run mostly on oil and operate approximately 30 
hours per year, per turbine. Regular testing of these units (done to 
ensure they will be operational during an emergency) may bring the 
total operating hours for a turbine up toward 200 hours per year, per 
turbine, or approximately 400 hours per facility. Given that these 
units burn less oil than allowed under the MACT standards for lean 
premix and diffusion flame gas-fired turbines (1,000 hours per 
facility), we expect the maximum annual average HAP concentrations in 
air to be much less for emergency turbines. Therefore, we expect the 
risks and hazards to be less.

VI. Analysis of the North Slope Turbine Subcategory

    We have identified 120 stationary combustion turbines that are 
located on the North slope of Alaska. Of these, 112 are diffusion flame 
gas-fired units, and eight are lean premix gas-fired turbines. The 
total number of oil hours used, per year, by any facility we identified 
on the North Slope is much less than 1,000 hours. Because we have 
determined that facilities burning oil for fewer than 1,000 hours per 
year meet the statutory criteria for delisting, we concluded that 
stationary combustion turbines located on the North Slope of Alaska 
also meet the delisting criteria.
    Given the standard EPA risk assessment methods used, and the 
health-protective assumptions made in the assessment, we have made an 
initial determination that all sources in the four subcategories meet 
the human health and environmental criteria in CAA section 112(c)(9)(B) 
and should be removed from the source category list.

VII. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review

    Under Executive Order 12866 (58 FR 51735, October 4, 1993), EPA 
must determine whether the regulatory action is ``significant'' and, 
therefore, subject to Office of Management and Budget (OMB) review and 
the requirements of the Executive Order. The Executive Order defines 
``significant regulatory action'' as one that is likely to result in a 
rule that may:
    (1) Have an annual effect on the economy of $100 million or more or 
adverse affect in a material way the economy, a sector to the economy, 
productivity, competition, jobs, the environment, public health or 
safety, or state, local or tribal governments or communities;
    (2) Create a serious inconsistency or otherwise interfere with an 
action taken or planned by another agency;
    (3) Materially alter the budgetary impact of entitlements, grants, 
user fees, or loan programs, or the rights and obligation of recipients 
thereof; or
    (4) raise novel legal or policy issues arising out of legal 
mandates, the President's priorities, or the principles set forth in 
the Executive Order.
    Pursuant to the terms of Executive Order 12866, it has been 
determined that the proposed action constitutes a ``significant 
regulatory action'' because it may raise novel policy issues and is 
therefore subject to OMB review. Changes made in response to OMB 
suggestions or recommendations are documented in the public record (see 
ADDRESSES section of this preamble).

[[Page 18337]]

B. Paperwork Reduction Act

    This action does not impose an information collection burden under 
the provisions of the Paperwork Reduction Act, 44 U.S.C. 3501 et seq. 
The proposed action will remove two subcategories from the combustion 
turbine source category and, therefore, eliminate the need for 
information collection toward regulatory compliance under the CAA. 
Burden means the total time, effort, or financial resources expended by 
persons to generate, maintain, retain, or disclose or provide 
information to or for a Federal agency. This includes the time needed 
to review instructions; develop, acquire, install, and utilize 
technology and systems for the purposes of collecting, validating, and 
verifying information, processing and maintaining information, and 
disclosing and providing information; adjust the existing ways to 
comply with any previously applicable instructions and requirements; 
train personnel to be able to respond to a collection of information; 
search data sources; complete and review the collection of information; 
and transmit or otherwise disclose the information. An Agency may not 
conduct or sponsor, and a person is not required to respond to a 
collection of information unless it displays a currently valid OMB 
control number. The OMB control numbers for EPA's regulations are 
listed in 40 CFR part 9 and 48 CFR chapter 15.

C. Regulatory Flexibility Act

    The Regulatory Flexibility Act (RFA) generally requires an agency 
to prepare a regulatory flexibility analysis of any rule subject to 
notice and comment rulemaking requirements under the Administrative 
Procedure Act or any other statute unless the agency certifies that the 
rule will not have a significant economic impact on a substantial 
number of small entities. Small entities include small business, small 
organizations, and small governmental jurisdictions. For the purposes 
of assessing the impacts of today's proposed action on small entities, 
small entity is defined as: (1) A small business that meets the 
definitions for small business based on the Small Business Association 
(SBA) size standards which, for this proposed action, can include 
manufacturing (NAICS 3999-03) and air transportation (NAICS 4522-98 and 
4512-98) operations that employ less than 1,000 people and engineering 
services (NAICS 8711-98) operations that earn less than $20 million 
annually; (2) a small governmental jurisdiction that is a government of 
a city, county, town, school district or special district with a 
population of less than 50,000; and (3) a small organization that is 
any not-for-profit enterprise which is independently owned and operated 
and is not dominant in its field.
    After considering the economic impact of today's proposed action on 
small entities, I certify that the proposed action will not have a 
significant economic impact on a substantial number of small entities. 
In determining whether a rule has significant economic impact on a 
substantial number of small entities, the impact of concern is any 
significant adverse economic impact on small entities, since the 
primary purpose of the regulatory flexibility analysis is to identify 
and address regulatory alternatives ``which minimize any significant 
economic impact of the proposed rule on small entities.'' (5 U.S.C. 603 
and 604). Thus, an agency may certify that a rule will not have a 
significant economic impact on a substantial number of small entities 
if the rule relieves regulatory burden, or otherwise has a positive 
economic effect on all of the small entities subject to the rule. The 
proposed rule will eliminate the burden of additional controls to be 
applied to two subcategories of the combustion turbine source category, 
and associated operating, monitoring and reporting requirements. We 
have, therefore, concluded that today's proposed rule will relieve 
regulatory burden for all small entities. We continue to be interested 
in the potential impacts of the proposed rule on small entities and 
welcome comments on issues related to such impacts.

D. Unfunded Mandates Reform Act

    Title II of the Unfunded Mandates Reform Act of 1995 (UMRA), Public 
Law 1044, establishes requirements for Federal agencies to assess the 
effects of their regulatory actions on State, local, and tribal 
governments and the private sector. Under section 202 of the UMRA, EPA 
generally must prepare a written statement, including a cost-benefit 
analysis, for proposed and final rules with ``Federal mandates'' that 
may result in expenditures to State, local, and tribal governments, in 
the aggregate, or to the private sector, of $100 million or more in any 
1 year. Before promulgating an EPA rule for which a written statement 
is needed, section 205 of the UMRA generally requires EPA to identify 
and consider a reasonable number of regulatory alternatives and adopt 
the least costly, most cost-effective or least burdensome alternative 
that achieves the objectives of the rule. The provisions of section 205 
do not apply when they are inconsistent with applicable law. Moreover, 
section 205 allows EPA to adopt an alternative other than the least 
costly, most cost-effective or least burdensome alternative if the 
Administrator publishes with the final rule an explanation why that 
alternative was not adopted. Before EPA establishes any regulatory 
requirements that may significantly or uniquely affect small 
governments, including tribal governments, it must have developed under 
section 203 of the UMRA a small government agency plan. The plan must 
provide for notifying potentially affected small governments, enabling 
officials of affected small governments to have meaningful and timely 
input in the development of EPA regulatory proposals with significant 
Federal intergovernmental mandates, and informing, educating, and 
advising small governments on compliance with the regulatory 
requirements.
    Today's proposed rule contains no Federal mandates for State, 
local, or tribal governments or the private sector. The proposed rule 
imposes no enforceable duty on any State, local or tribal governments 
or the private sector. In any event, EPA has determined that the 
proposed rule does not contain a Federal mandate that may result in 
expenditures of $100 million or more for State, local, and tribal 
governments, in the aggregate, or the private sector in any 1 year. 
Because the proposed rule removes two subcategories from the combustion 
turbine source category from regulatory consideration, it actually 
reduces the burden established under the CAA. Thus, today's proposed 
rule is not subject to the requirements of sections 202 and 205 of the 
UMRA.

E. Executive Order 13132: Federalism

    Executive Order 13132 (64 FR 43255, August 10, 1999) requires EPA 
to develop an accountable process to ensure ``meaningful and timely 
input by State and local officials in the development of regulatory 
policies that have federalism implications.'' ``Policies that have 
federalism implications'' is defined in the Executive Order to include 
regulations that have ``substantial direct effects on the States, on 
the relationship between the national government and the States, or on 
the distribution of power and responsibilities among the various levels 
of government.''
    The proposed rule does not have federalism implications. It will 
not have substantial direct effects on the States, on the relationship 
between the national government and the States, or on the distribution 
of power and responsibilities among the various levels of government, 
as specified in

[[Page 18338]]

Executive Order 13132. Thus, Executive Order 13132 does not apply to 
the proposal.

F. Executive Order 13175: Consultation and Coordination With Indian 
Tribal Governments

    Executive Order 13175 (65 FR 67249, November 9, 2000) requires EPA 
to develop an accountable process to ensure ``meaningful and timely 
input by tribal officials in the development of regulatory policies 
that have tribal implications.'' The proposed rule does not have tribal 
implications, as specified in Executive Order 13175. The proposed 
action will eliminate control requirements for two subcategories from 
the combustion turbine source category and, therefore, reduces control 
costs and reporting requirements for any tribal entity operating a 
turbine contained in either of these subcategories. Thus, Executive 
Order 13175 does not apply to the proposed rule.

G. Executive Order 13045: Protection of Children From Environmental 
Health and Safety Risks

    Executive Order 13045 (62 FR 19885, April 23, 1997) applies to any 
rule that: (1) Is determined to be ``economically significant'' as 
defined under Executive Order 12866, and (2) concerns an environmental 
health or safety risk that EPA has reason to believe may have a 
disproportionate effect on children. If the regulatory action meets 
both criteria, the Agency must evaluate the environmental health or 
safety effects of the planned rule on children, and explain why the 
planned regulation is preferable to other potentially effective and 
reasonably feasible alternatives considered by the Agency.
    The EPA interprets Executive Order 13045 as applying only to those 
regulatory actions that are based on health or safety risks, such that 
the analysis required under section 5-501 of the Executive Order has 
the potential to influence the regulation. The proposed rule is not 
subject to Executive Order 13045 because it is not economically 
significant as defined in Executive Order 12866, and because the Agency 
does not have reason to believe the environmental health or safety 
risks addressed by this action present a disproportionate risk to 
children. This determination is based on the fact that the noncancer 
human health values we used in this analysis (e.g., RfC) are determined 
to be protective of sensitive sub-populations, including children. 
Also, while the cancer human health values do not always expressly 
account for cancer effects in children, the cancer risks posed by 
turbines in these two subcategories are sufficiently low so as not to 
be concern for anyone in the population, including children. In 
addition, the public is invited to submit or identify peer-reviewed 
studies and data, of which the Agency may not be aware, that assesses 
results of early life exposure to the HAP emitted by lean premix gas-
fired combustion turbines and diffusion flame gas-fired combustion 
turbines.

H. Executive Order 13211, Actions Concerning Regulations That 
Significantly Affect Energy Supply, Distribution, or Use

    The proposed rule is not subject to Executive Order 13211 (66 FR 
28355, May 22, 2001) because it is not a significant regulatory action 
under Executive Order 12866.

I. National Technology Transfer and Advancement Act

    Section 112(d) of the National Technology Transfer and Advancement 
Act of 1995 (NTTAA), (Public Law No. 104-113, section 12(d) 915 U.S.C. 
272 note), directs all Federal agencies to use voluntary consensus 
standards instead of government-unique standards in their regulatory 
activities unless to do so would be inconsistent with applicable law or 
otherwise impractical. Voluntary consensus standards are technical 
standards (e.g., material specifications, test method, sampling and 
analytical procedures, business practices, etc.) that are developed or 
adopted by one or more voluntary consensus standards bodies. Examples 
of organizations generally regarded as voluntary consensus standards 
bodies include the American Society for Testing and Materials, the 
National Fire Protection Association A), and the Society of Automotive 
Engineers. The NTTAA requires Federal agencies like EPA to provide 
Congress, through OMB, with explanations when an agency decides not to 
use available and applicable voluntary consensus standards. The 
proposed rule does not involve technical standards. Therefore, EPA is 
not considering the use of any voluntary consensus standards.

List of Subjects in 40 CFR Part 63

    Environmental protection, Air pollution control, Hazardous 
substances, Reporting and recordkeeping requirements.

    Dated: March 31, 2004.
Michael O. Leavitt,
Administrator.
[FR Doc. 04-7775 Filed 4-6-04; 8:45 am]

BILLING CODE 6560-50-P