National Emission Standards for Coke Oven Batteries, 19992-20015 [05-6942]

Agencies

• ENVIRONMENTAL PROTECTION AGENCY

[Federal Register Volume 70, Number 72 (Friday, April 15, 2005)]
[Rules and Regulations]
[Pages 19992-20015]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 05-6942]



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Part II





Environmental Protection Agency





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40 CFR Part 63



National Emission Standards for Coke Oven Batteries; Final Rule

Federal Register / Vol. 70, No. 72 / Friday, April 15, 2005 / Rules 
and Regulations

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 63

[OAR-2003-0051; FRL-7895-8]
RIN 2060-AJ96


National Emission Standards for Coke Oven Batteries

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule; amendments.

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SUMMARY: On October 27, 1993 (58 FR 57898), pursuant to section 112 of 
the Clean Air Act (CAA), the EPA issued technology-based national 
emission standards to control hazardous air pollutants (HAP) emitted by 
coke oven batteries. This action amends the standards to address 
residual risks under section 112(f) and the 8-year review requirements 
of section 112(d)(6).

DATES: The final rule amendments will be effective on April 15, 2005. 
Existing sources will be required to comply with the final rule as 
amended on July 14, 2005. The incorporation by reference of certain 
publications listed in the final rule amendments is approved by the 
Director of the Federal Register as of April 15, 2005.

ADDRESSES: The EPA has established a docket for this action under 
Docket ID No. OAR-2003-0051. All documents in the docket are listed in 
the EDOCKET index at https://www.epa.gov/edocket. Although listed in the 
index, some information is not publicly available, i.e., confidential 
business information or other information whose disclosure is 
restricted by statute. Certain other information, such as copyrighted 
materials, is not placed on the Internet and will be publicly available 
only in hard copy form. Publicly available docket materials are 
available either electronically in EDOCKET or in hard copy form at the 
Air and Radiation Docket, Docket ID No. OAR-2003-0051, 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 (202) 566-1744, and the telephone number for the Air 
and Radiation Docket is (202) 566-1742.

FOR FURTHER INFORMATION CONTACT: Mr. Bob Schell, Emission Standards 
Division (C439-02), Office of Air Quality Planning and Standards, 
Environmental Protection Agency, Research Triangle Park, NC 27711, 
telephone number (919) 541-4116, e-mail address: schell.bob@epa.gov.

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

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                                      NAICS       Examples of regulated
             Category                code\1\            entities
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Industry.........................       331111  Existing by-product coke
                                        324199   oven batteries subject
                                                 to emission limitations
                                                 in 40 CFR 63.302(a)(2)
                                                 and nonrecovery coke
                                                 oven batteries subject
                                                 to new source emission
                                                 limitations in 40 CFR
                                                 63.303(b). These
                                                 batteries are subject
                                                 to maximum achievable
                                                 control technology
                                                 (MACT) requirements and
                                                 are known as ``MACT
                                                 track'' batteries.
Federal government...............  ...........  Not affected.
State/local/tribal government....  ...........  Not affected.
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\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 facility is regulated by this action, 
you should examine the applicability criteria in Sec.  63.300 of the 
national emission standards for coke oven batteries. 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. Worldwide Web (WWW). In addition to being 
available in the docket, an electronic copy of today's final rule 
amendments will also be available on the Worldwide Web (WWW) through 
the Technology Transfer Network (TTN). Following the Administrator's 
signature, a copy of the final rule amendments will be placed on the 
TTN's policy and guidance page for newly proposed or promulgated rules 
at https://www.epa.gov/ttn/oarpg. The TTN provides information and 
technology exchange in various areas of air pollution control.
    Judicial Review. Under section 307(b)(1) of the CAA, judicial 
review of the final rule amendments is available only by filing a 
petition for review in the U.S. Court of Appeals for the District of 
Columbia Circuit by June 14, 2005. Under section 307(d)(7)(B) of the 
CAA, only an objection to the final rule amendments that was raised 
with reasonable specificity during the period for public comment can be 
raised during judicial review. Under section 307(b)(2) of the CAA, the 
requirements that are the subject of this document may not be 
challenged later in civil or criminal proceedings brought by the EPA to 
enforce these requirements.
    Outline. The information presented in this preamble is organized as 
follows:

I. Background
II. Summary of the Final Rule Amendments
    A. What Are the Affected Sources and Emissions Points?
    B. What Are the Requirements?
III. Response to Major Comments
    A. Comments on the Overall Risk Program and Policy
    B. Risk Comments Specific to Coke Ovens
    C. Comments on Section 112(d)(6) Review Policy
    D. Specific Comments on Section 112(d)(6) Review of Coke Ovens
IV. 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 and Safety Risks
    H. Executive Order 13211: Actions That Significantly Affect 
Energy Supply, Distribution, or Use
    I. National Technology Transfer Advancement Act
    J. Congressional Review Act

I. Background

    EPA promulgated national emission standards for charging, door 
leaks, and topside leaks from coke ovens batteries at 58 FR 57898, 
October 27, 1993 (40 CFR part 63, subpart L) under section 112(d) of 
the CAA. Section 112(f)(2) of the CAA requires EPA to determine for 
each section 112(d) source category if the promulgation of additional 
standards is required ``in order to provide an ample margin of safety 
to protect public health.'' We also have

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discretion to impose a more stringent emissions standard to prevent 
adverse environmental effect if such action is justified in light of 
costs, energy, safety, and other relevant factors. On August 9, 2004 
(69 FR 48338), we proposed amendments to the national emission 
standards for coke oven batteries that included more stringent 
requirements for certain by-product coke oven batteries to address 
health risks remaining after implementation of the 1993 national 
emission standards. The proposed amendments also included provisions 
pursuant to the 8-year review requirements of CAA section 112(d)(6).
    In our proposal preamble, we presented the maximum individual risk 
(MIR) estimate for coke oven emissions from those emission points 
subject to the 1993 national emission standards. The MIR estimate was 
200 in a million (69 FR 48346). We also explained at proposal that, as 
required under the Benzene NESHAP \1\ decision framework (codified in 
section 112(f)(2)(A) and (B)), we considered the level of risk from the 
limits in the 1993 national emission standards (i.e., 200 in a million) 
to be acceptable after considering several factors (69 FR 48347-48350). 
These factors included the number of exposed people with cancer risk 
level estimates greater than 1 in a million (approximately 300,000 
people or 7 percent of the exposed population), the number of people 
for whom cancer risk levels are greater than 100 in a million (less 
than 10 people), the estimate of annual incidence of cancer (0.04), and 
the projected absence of adverse noncancer effects.\2\ Also considered 
in the evaluation in the proposal was the protective nature of many of 
the assumptions leading to these estimates of potential residual risk.
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    \1\ National Emission Standard for Hazardous Air Pollutants 
(NESHAP): Benzene Emissions from Maleic Anhydride Plants, 
Ethylbenzene/Stryene Plants, Benzene Storage Vessels, Benzene 
Equipment Leaks, and Coke By-Product Recovery Plants (54 FR 38044, 
September 14, 1989).
    \2\ All estimates of population risk and estimated annual 
incidence in these final rule amendments are based on an upper-bound 
cancer unit risk estimate, a 70-year exposure duration, and our best 
estimates of exposure concentrations; cancer risk estimates using 
best estimates for exposure duration and unit cancer risk would 
yield lower risk estimates.
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    Under section 112(o)(7) of the CAA, we are required to issue 
revised cancer guidelines prior to the promulgation of the first 
residual risk rule under section 112(f) (an implication being that we 
should consider these revisions in the various residual risk rules). 
Since our August 2004 proposal, we have issued revised cancer 
guidelines and also supplemental guidance which deal specifically with 
assessing the potential added susceptibility from early-life exposure 
to carcinogens. We have considered our decisions in these final rule 
amendments in light of the revised cancer guidelines and supplemental 
guidance. The supplemental guidance provides an approach for adjusting 
risk estimates to incorporate the potential for increased risk due to 
early-life exposures to chemicals that are thought to be carcinogenic 
by a mutagenic mode of action. For these chemicals, the supplemental 
guidance indicates that, in lieu of chemical-specific data on which age 
or life-stage specific risk estimates or potencies can be determined, 
default ``age dependent adjustment factors'' can be applied when 
assessing cancer risk for early-life exposures to chemicals which cause 
cancer through a mutagenic mode. In light of this guidance, EPA has 
evaluated the available scientific information associated with 
pollutants emitted by coke ovens and believes it is appropriate to 
apply the default factors in the risk assessment supporting today's 
final rule amendments. The chief HAP emitted by coke ovens, coke oven 
emissions, is specifically enumerated in CAA section 112(b)(1). Coke 
oven emissions are likely to cause cancer through a mutagenic mode of 
action. We base this conclusion on the data on coke oven emissions 
mutagenicity which has been summarized by EPA\3\ \4\ and the 
International Agency for Research on Cancer,\5\ and reported in 
numerous, more recent studies available in the peer-reviewed 
literature. The result of that determination is that our individual and 
population cancer risk estimates for lifetime exposures that begin at 
birth and extend through adulthood will increase from proposal by a 
factor of 1.6, \6\ a factor that considers the assumption of constant 
exposure over the 70-year exposure duration (birth to adulthood) we 
used in estimating individual and population risk. These further 
assumptions of increased cancer potency and birth to 70-year residence 
of the entire population in the area assessed were not part of the 
proposed rule amendments.
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    \3\ Carcinogen Assessment of Coke Oven Emissions: Final Report. 
U.S. Environmental Protection Agency, Office of Health and 
Environmental Assessment. EPA-600/6-82-003F. February 1984.
    \4\ ``Coke Oven Emissions.'' U.S. Environmental Protection 
Agency. Integrated Risk Information System (IRIS). 1989. Available 
at: https://www.epa.gov/irissubst/0395.htm.
    \5\ IARC Monographs Supplement 7. International Agency for 
Research on Cancer. 1987, page 176. Available at: https://www-
cie.iarc.fr/htdocs/monographs/suppl7/coke production.html.
    \6\ The ``Supplemental Guidance for Assessing Susceptibility 
from Early-Life Exposure to Carcinogens' recommends applying default 
adjustment factors to early life stage exposures to carcinogens 
acting through a mutagenic mode of action. The Supplemental Guidance 
recommends an integrative approach that can be used to assess total 
lifetime risk resulting from lifetime or less-than-lifetime exposure 
during a specific portion of a lifetime. The following adjustments 
represent the approach suggested in the Supplemental Guidance: (1) 
For exposures before 2 years of age (i.e., spanning a 2-year time 
interval from the first day of birth up until a child's second 
birthday), a 10-fold adjustment; (2) for exposures between 2 and 
less than 16 years of age (i.e., spanning a 14-year time interval 
from a child's second birthday up until their sixteenth birthday), a 
3-fold adjustment; and (3) for exposures after turning 16 years of 
age, no adjustment. In applying this factor to population risk, risk 
bins shown in appendix I of the risk assessment document were 
multiplied by 1.6, and the populations associated with those new 
risk bins were recounted depending on whether the bin risks were 
greater than 1 in a million, 10 in a million, or 100 in a million. 
The cancer incidence value was directly multiplied by the 1.6 
factor. The analysis and more detailed calculations may be found in 
the docket for this rulemaking.
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    Based on the supplemental guidance, we have revised our risk 
estimates by applying the default adjustment factors to account for 
increased susceptibility that might occur due to exposures that occur 
from birth to 16 years of age. The increased risk due to consideration 
of the exposures assumed to occur from birth to 16 years of age 
(included in the 70-year total exposure duration) results in a revised 
upper-bound estimate. For the source category associated with the 1993 
national emission standards, the revised MIR estimate is 300 in a 
million. We have chosen to also apply the default adjustment to other 
analyses used to support the determination that the MIR of 200 in a 
million was acceptable. However, we acknowledge that more refined 
modeling of exposure would be necessary to adequately express the 
effect of early life susceptibility to overall estimates of population 
risk. For example, not all individuals are expected to be born in the 
area assessed. Nonetheless, after application of the default adjustment 
factor, our conclusions in the proposed rule amendments do not change 
and further refinement of the assessment was not warranted. The 
assumptions of exposure initiation (at birth for all) and cancer risk 
for coke oven emissions based on the application of the supplemental 
guidance would affect the number of exposed people with cancer risk 
levels greater than 1 in a million (500,000 people or 12 percent of the 
exposed population), the number of people exposed to risk levels 
greater than 100 in a million (approximately 70 people), the annual 
incidence of cancer (0.06), and the uncertainty associated

[[Page 19994]]

with the estimates of risk. The remaining factors we considered (e.g., 
actual emissions versus allowable emissions and the projected absence 
of adverse noncancer effects) are unaffected.
    Although we are adjusting risk estimates upward to reflect the new 
supplemental guidance, these estimated risk increases must also be 
tempered by consideration of other factors that were discussed at 
proposal and in the risk assessment document, and the further 
protective assumption added to the risk assessment that all individuals 
are born in the assessed area. For example, the coke oven battery 
sources are consistently controlling emissions below the level allowed 
by the 1993 national emission standards, which results in a 30 percent 
reduction in the estimated MIR. Our 70-year exposure assumption 
includes exposures from birth to 70 years. If exposures were from 3 
years to 73 years, the adjustment factor would be less than 1.6. If 
exposures were from 16 years to 86 years, no adjustment would be 
necessary. In addition, we used a health-protective assumption of a 70-
year exposure duration in our risk estimates; however, using the 
national average residency time of 12 years would reduce the estimate 
of risk by a factor of six (69 FR 48347). Our 1984 unit risk estimate 
(URE) for coke oven emissions is considered a plausible upper-bound 
estimate; actual potency is likely to be lower. After considering all 
of these factors, we continue to consider the MIR due to emissions at 
the limits in the 1993 national emission standards to be an acceptable 
level of risk (within the meaning of the Benzene NESHAP decision 
framework discussed at 69 FR 48339-48340, 48347-48348). As mentioned in 
the recently published cancer guidelines, we will continue to develop 
and present, to the extent practicable, an appropriate central estimate 
and appropriate lower and upper-bound estimates of cancer potency. 
Development of new methods or estimates is a process that will require 
independent peer review.
    We also re-examined our decision as to what level of control is 
necessary to provide an ample margin of safety to protect human health 
in light of applying the early-life exposure default adjustment 
factors. The 2010 lowest achievable emission rate (LAER) levels (which 
we are adopting as residual risk standards in today's action) will 
reduce the MIR from exposure to coke oven emissions to 270 in a 
million. In addition, the reductions will result in approximately 
200,000 fewer people having excess lifetime cancer risks of greater 
than 1 in a million from exposure to these emissions. After considering 
these estimates and the other factors explained in detail in the 
preamble to the proposed rule amendments, we continue to believe that 
the 2010 LAER levels provide an ample margin of safety to protect 
public health.
    The proposal allowed a 60-day comment period ending October 8, 
2004. The EPA's EDOCKET system logged a total of 16 public comments in 
Docket Number OAR-2003-0051. Commenters included one state association, 
two state agencies, a coalition of three major environmental groups, 9 
industry trade associations, one steel company, and two individual 
commenters. Each of their comments is summarized in our response to 
comments document contained in the rulemaking docket.

II. Summary of the Final Rule Amendments

A. What Are the Affected Sources and Emission Points?

    The affected sources are each coke oven battery subject to the 
emission limitations in 40 CFR 63.302 or 40 CFR 63.303 (the 1993 
national emission standards). There are five affected sources in this 
category: Four existing by-product recovery batteries and one 
nonrecovery battery. The final rule amendments apply to emissions from 
doors, topside port lids, offtake systems, and charging on existing by-
product coke oven batteries. Provisions are also included for emissions 
from doors on new and existing nonrecovery batteries and charging on 
new nonrecovery batteries.

B. What Are the Requirements?

    For existing by-product batteries, the final rule amendments limit 
visible emissions from coke oven doors to 4 percent leaking doors for 
tall batteries and for batteries owned or operated by a foundry coke 
producer. Short batteries are limited to 3.3 percent leaking doors. 
Visible emissions from other emission points are limited to 0.4 percent 
leaking topside port lids and 2.5 percent leaking offtake systems. No 
change has been made to the limit for charging--emissions must not 
exceed 12 seconds of visible emissions per charge. Each of these 
visible emission limits is based on a 30-day rolling average. The final 
rule amendments replace the less stringent limits that became effective 
on January 1, 2003, for MACT track batteries and are equivalent to the 
limits that will become effective on January 1, 2010, for batteries 
subject to LAER track requirements. We have not changed the standards 
for new by-product batteries.
    The monitoring, reporting, and recordkeeping requirements in the 
existing national emission standards continue to apply to existing by-
product coke oven batteries on the MACT track. These requirements 
include daily performance tests to determine compliance with the 
visible emission limits. Each performance test must be conducted by a 
visible emissions observer certified according to the test method 
requirements. A daily inspection of the collecting main for leaks is 
also required. Specific work practice standards must also be 
implemented if required by the provisions in 40 CFR 63.306(c). Under 
the existing standards, companies must make semiannual compliance 
certifications; report any uncontrolled venting episodes or startup, 
shutdown, or malfunction events; and keep records of information needed 
to demonstrate compliance.
    We are also issuing amendments for the improved control of charging 
emissions from a new nonrecovery battery (i.e., constructed or 
reconstructed on or after August 9, 2004). Fugitive charging emissions 
are subject to an opacity limit of 20 percent. A weekly performance 
test is required to determine the average opacity of five consecutive 
charges for each charging emissions capture system. The certified 
observer must determine and record the highest 3-minute average opacity 
for each charge; compliance is based on the average of the highest 3-
minute averages for five consecutive charges. Emissions of particulate 
matter (PM), a surrogate for particulate HAP in coke oven emissions, 
from a charging emissions control device are limited to 0.0081 pounds 
per ton (lb/ton) of dry coal charged. A performance test using EPA 
Method 5 (40 CFR part 60, appendix A) is required to demonstrate 
initial compliance with subsequent performance tests at least once 
during each title V permit term. If any visible emissions are observed 
from a charging emissions control device, the owner or operator is 
required to take corrective action and follow up with a visible 
emissions observation by EPA Method 9 (40 CFR part 60, appendix A) to 
ensure that the corrective action had been successful. Any Method 9 
observation of the charging emissions control device greater than 10 
percent opacity must be reported as a deviation in the semiannual 
compliance report. The final rule amendments also require the owner or 
operator to implement a work practice standard designed to ensure

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that the draft on the oven is maximized during charging.
    We are also promulgating a work practice standard for the control 
of door leaks from all nonrecovery coke oven batteries on the MACT 
track. The owner or operator is required to observe each coke oven door 
after each charge and record the oven number of any door from which 
visible emissions occur. If a coke oven door leak is observed at any 
time during the coking cycle, the owner or operator must take 
corrective action and stop the leak within 15 minutes from the time the 
leak is first observed. After a door leak has been stopped, no 
additional leaks are allowed from doors on that oven for the remainder 
of that oven's coking cycle.
    We are allowing an exception to the 15-minute limit period for 
stopping a door leak. The owner or operator may have up to 45 minutes 
to stop a door leak no more than twice per battery during any 
semiannual reporting period. The limit of two occurrences does not 
apply if a worker must enter a cokeside shed to stop a leaking door 
under a cokeside shed. In that case, the owner or operator may have up 
to 45 minutes to take corrective action and stop the leak. The owner or 
operator also must operate the evacuation system and control device for 
the cokeside shed at all times that there is a leaking door under the 
cokeside shed.
    The owner or operator of a nonrecovery battery is also required to 
identify malfunctions that might cause a door to leak, establish 
preventative measures, and specify types of corrective actions for such 
events in its startup, shutdown, and malfunction plan. The final rule 
amendments also include recordkeeping and reporting requirements 
necessary to demonstrate initial and continuous compliance.
    We are also amending the provision in 40 CFR 63.303(a)(2) for 
existing nonrecovery batteries to state that the work practice standard 
for charging also applies to new nonrecovery batteries. These work 
practices are described in 40 CFR 63.306(b)(6).
    We are requiring that the owner or operator of existing by-product 
coke oven batteries on the MACT track comply by July 14, 2005. See CAA 
section 112(f)(4)(A), which states that existing sources must comply 
with section 112(f) residual risk standards within 90 days of the 
standard's effective date. We are also requiring that nonrecovery coke 
oven batteries on the MACT track comply by July 14, 2005 (or upon 
startup for a new nonrecovery battery for which construction commenced 
after August 9, 2004).
    The basis for the final rule amendments is set out in the preamble 
to the proposed rule amendments (69 FR 48338) unless otherwise 
explained in our responses to the major comments in this preamble. Our 
responses to all the comments are included in the docket.

III. Response to Major Comments

A. Comments on the Overall Risk Program and Policy

1. Ample Margin of Safety
    Comment: One commenter argued that CAA section 112(f)(2) makes 
clear that EPA's residual risk standards must reduce the lifetime risk 
to the single individual most exposed to emissions from any one of 
these sources to less than 1 in a million. In contrast, another 
commenter stated that EPA has properly construed the statute as 
establishing a trigger under which EPA must undertake a residual risk 
determination but not as establishing the level of risk reduction that 
must be achieved and further stated that EPA is not required to provide 
protection that achieves the 1 in a million excess cancer risk level.
    Response: The commenter's argument that the statute requires 
section 112(f) residual risk standards to reduce cancer risk to a most 
exposed individual to less than 1 in a million lacks a basis in the 
statutory text or in policy. Section 112(f)(2)(A) does indeed require 
us to promulgate standards if the ``lifetime excess cancer risk to the 
individual most exposed to emissions from a source in a category or 
subcategory'' is greater than 1 in a million. It does not establish 
what the level of the standard might be. See ``A Legislative History of 
the Clean Air Act Amendments of 1990,'' page 1789 (Conference Report), 
stating that ``[s]ection 112(f) contains a trigger for standards for 
non-threshold pollutants. * * *'' Rather, the level of the standard is 
to ``provide an ample margin of safety'' to protect public health. 
``Ample margin of safety'' is to be interpreted under the two-step 
formulation established by the Benzene NESHAP and CAA section 
112(f)(2)(B).
    Under that formulation, there is no single risk level establishing 
what constitutes an ample margin of safety (69 FR 48348). Rather, the 
Benzene NESHAP approach codified in section 112(f)(2) is deliberately 
flexible, requiring consideration of a range of factors (among them 
estimates of quantitative risk, incidence, and numbers of exposed 
persons within various risk ranges; scientific uncertainties; and 
weight of evidence) when determining acceptability of risk (the first 
step in the ample margin of safety determination) (54 FR 38045). 
Determination of ample margin of safety, the second step of the 
process, requires further consideration of these factors, plus 
consideration of technical feasibility, cost, economic impact, and 
other factors (54 FR 38046). As we stated in our ``Residual Risk Report 
to Congress'' \7\ issued under CAA section 112(f)(1), we do not 
consider the 1 in a million individual additional cancer risk level as 
a ``bright line'' mandated level of protection for establishing 
residual risk standards, but rather as a trigger point to evaluate 
whether additional reductions are necessary to provide an ample margin 
of safety to protect public health. This interpretation is supported by 
the interpretive language in the preamble to the Benzene NESHAP, which 
was incorporated by Congress in section 112(f)(2)(B).
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    \7\ Residual Risk Report to Congress. U.S. Environmental 
Protection Agency, Office of Air Quality Planning and Standards. 
EPA-453/R-99-001. March 1999.
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    We consequently believe that the commenter's bright line approach 
is not supported by the statute. Indeed, it is likely incorrect as a 
matter of law.\8\ In any event, EPA has concluded that the flexible 
approach to risk acceptability and ample margin of safety set forth in 
the Benzene NESHAP is desirable in light of the complex judgments EPA 
will make under section 112(f). The commenter's rigid approach lacks a 
basis in sound policy as well.
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    \8\ It is true that the Senate version of CAA section 112(f) 
mandated elimination of lifetime risks of carcinogenic effects 
greater than 1 in 10 thousand to the individual in the population 
most exposed to emissions of a carcinogen. (See ``A Legislative 
History of the Clean Air Act Amendments of 1990,'' pages 7598 and 
8518.) However, this version of the legislation was not adopted. The 
EPA believes that the (rejected) Senate version of section 112(f) 
shows that Congress was capable of mandating a level of risk 
reduction had it wished to do so.
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    Comment: Two commenters contended that EPA rejected a more 
stringent standard because the control technologies were not available 
at a reasonable cost. The commenters maintained that the more stringent 
standard would reduce risks to an acceptable level, and that the EPA 
does not have statutory authority to consider costs. According to one 
commenter, section 112(f) clearly calls for costs to be considered only 
in the area of adverse environmental effects.
    In contrast, a third commenter stated that EPA should not require 
any further reductions unless those reductions will produce discernible 
results stating that EPA justified the proposed additional reductions 
based on costs, yet noted that the reduction in cancer risk was so

[[Page 19996]]

small that it was within the noise level of EPA's ability to estimate. 
The commenter did not believe it was good policy to require additional 
reductions if EPA cannot be sure they will result in any benefit.
    Response: The first two commenters are mistaken regarding the 
consideration of costs in determining ``ample margin of safety.'' While 
it is correct that EPA does not consider costs in the first step (the 
``acceptability'' determination) of the ample margin of safety 
determination, costs are a factor which must be considered in the 
second step of the process (54 FR 38046).\9\ We have considered costs 
here in the authorized and required manner in assessing ample margin of 
safety after determining if baseline risk (level of risk remaining 
after imposition of MACT) is acceptable (54 FR 38045; 69 FR 48348-
48349).
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    \9\ See also the Vinyl Chloride opinion at 824 F.2d 1146.
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    In establishing an ample margin of safety, we weigh a range of 
factors, allowing flexibility on what constitutes an ample margin of 
safety (69 FR 48348). Some of the factors that can be considered are 
estimates of individual risk, incidence, numbers of exposed persons 
within various risk ranges, scientific uncertainties, weight of 
evidence, as well as potential standards' technical feasibility, cost, 
and economic impact. Balancing the above factors with the ability to 
achieve meaningful risk reductions is a critical component of the 
residual risk rulemaking process.
    We do not agree with the other commenter that the standards fail to 
produce discernible results. The emission limits are more stringent 
than the current MACT standards. The emissions reductions can be 
achieved at a nominal cost, they are technically feasible, and we 
estimate that the reductions will ensure that approximately 200,000 
fewer people having excess lifetime cancer risks of greater than 1 in a 
million.
2. Co-Located Sources and Facilitywide Risk
    Comment: One commenter said that many coke plants are part of a 
larger steel production complex; consequently, EPA should have 
considered the combined risk of all emission sources at the facility, 
including pushing, quenching, and battery stacks. The commenter also 
asserted that EPA should have considered the impact on residents near 
plants that are located in the same area (e.g., East Chicago and Gary, 
IN) and that the legislative history shows Congress' intent that EPA 
consider the combined risks of all sources of HAP emissions, regardless 
of source category, that are co-located. Specifically, Congress 
intended that the residual risk standards be stringent enough:

so that when all residual risk standards have been set, the public 
will be protected with an ample margin of safety from the combined 
emissions of all sources within a major source.\10\
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    \10\ Floor Statement of Senator Durenberger in ``A Legislative 
History of the Clean Air Act Amendments of 1990'', vol. 1, page 868 
(Senate Debate on Conference Report).

The commenter disagreed with EPA's statement that delaying a full 
assessment of risk was a practical necessity because of the lack of 
information on actual emissions from pushing, quenching, and battery 
stacks. The commenter argued, essentially, that we are obligated to 
develop standards for the totality of risks simultaneously.
    Another commenter also stated that EPA should consider the facility 
as a whole and requested stringent controls on each source category to 
ensure the goals of the residual risk provisions are met in an 
expeditious manner. The commenter also asked that EPA ensure health 
protection in cases where there are multiple facilities in close 
proximity.
    Three commenters voiced opposition to consideration of emissions 
other than those from the specific source category at issue. One 
commenter indicated that the initial trigger for determining whether a 
residual risk standard was required at all must be applied only to a 
particular ``category or subcategory of sources'' (quoting CAA section 
112(f)(2)(A)). The commenter argued that the provision in section 
112(f)(2)(A) requiring us to develop residual risk standards if risks 
from the source category exceed a certain level also serves as a 
limitation in that ``residual risk determinations are to be done on a 
category or subcategory basis, not on a source or facilitywide basis.'' 
The commenter concluded that facilitywide risk could not be considered 
at all when establishing residual risk standards. According to this 
commenter, the only exception to a source category approach would be a 
voluntary request for a facilitywide determination so that they could 
use the most cost-effective set of reductions.
    Another commenter maintained that residual risk determinations for 
facilities as a whole would be acceptable only if EPA were to do so on 
a source category-by-source category basis. This commenter continued 
that if EPA were to adopt that approach, then the Agency cannot impose 
more risk reduction requirements on one source category to compensate 
for risks posed by another (co-located) source category.
    Another commenter argued that statutory language prevents 
consideration of risks posed by anything but the source category at 
issue, and further argued that any other approach would be difficult 
and confusing to implement. The commenter asserted that although EPA 
can consider facilitywide risk, residual risk standards should not be 
applied disproportionately to the first of the co-located sources 
evaluated in the residual risk process.
    Three commenters disagreed with EPA's use of Senator Durenburger's 
statement as the basis for the Agency's ``facilitywide'' interpretation 
of the statute. One commenter contended that the statement of one 
Senator cannot overcome the statutory language of section 112(f)(2) or 
the congressional directive to follow the Benzene NESHAP, particularly 
when the Senator noted that his remarks were not providing EPA specific 
new direction. Another commenter added that it was inappropriate to 
rely on the Senator's statements because the Conference Committee Joint 
Explanatory Statement suggests that the Senate and House Managers did 
not agree to much with respect to the Senate bill, and the Conference 
Report contains no explanation of section 112(f) on which EPA can rely 
for support.
    One commenter stated that a facilitywide approach would be bad 
policy because it would constrain the ample margin of safety for 
individual source categories beyond the level intended in the Benzene 
NESHAP framework. Trying to reconcile aggregated risk from dissimilar 
sources that may be geographically far apart may be difficult to 
accomplish and may not identify better opportunities for emission 
reductions (than would serial analyses for individual source 
categories). The commenter also stated that Congress directed EPA to 
establish a list of source categories and was well aware that many 
plants would have emission units falling into more than one category. 
Congress also anticipated that standards under section 112(d) and (f) 
would be staggered over time. The commenter contended that a 
facilitywide analysis could be too complex, speculative, and costly for 
other residual risk standards; therefore, EPA cannot and should not 
mandate facilitywide analyses in standards under section 112(f).
    Response: First, we should clarify the scope of the issue. Some 
discussion of

[[Page 19997]]

this issue has used loose terminology (i.e., ``facilitywide,'' ``co-
located,'' ``background'') as an imprecise shorthand for the various 
pollutant sources to which an individual could be exposed. In fact, 
there is a continuum of possible sources of exposure to consider. One 
could consider, in the initial assessment of residual risk from a 
source category, exposure from: (1) The individual emission points 
regulated under the standards being evaluated--here, charging, doors, 
lids, and offtakes--excluding all other sources, including nearby 
sources in the same category; (2) emissions from the source category 
only, but including co-located sources in the same category; (3) 
emission points at a facility that are necessarily co-located because 
they are part of an integrated common activity (e.g. pushing, 
quenching, and battery stacks for coke ovens); (4) all emissions at a 
facility (i.e., a stationary source or group of sources in any source 
category in a contiguous area under common control); (5) emissions from 
similar (or all) nearby facilities (``closely-located'' sources) whose 
emissions affect all or some of the same individuals; or (6) all 
ambient HAP, regardless of their source (e.g., automobiles, HAP 
originating from global sources).\11\
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    \11\ Of course, in all of these cases, EPA would limit 
consideration to HAP emissions that are either the same as those 
emitted by the sources under evaluation or that have the same health 
effect or affect the same target organ.
---------------------------------------------------------------------------

    After considering the statute and the divergent views of commenters 
on these topics, EPA agrees with those commenters who stated that the 
natural reading of section 112(f) is that EPA should evaluate risks 
posed by the emissions only from the category or subcategory. Section 
112(f)(2)(A) instructs EPA to promulgate standards for ``each category 
or subcategory'' for which it has adopted MACT standards, if such 
standards are needed in order to provide an ample margin of safety to 
protect public health. The statutory ``trigger'' provision at the end 
of section 112(f)(2)(A), which mandates that EPA promulgate residual 
risk standards when ``cancer risks to the individual most exposed to 
emissions from a source in the category'' exceed a designated level, 
clearly is directed exclusively at emissions from the source category 
alone, and thus supports a reading that the ultimate requirement of the 
provision likewise applies only to emissions from the source 
category.\12\
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    \12\ Further, section 112(c)(9) authorizes EPA to delist a 
category or subcategory on the basis of specified risk criteria. 
This section does not require EPA to look beyond the relevant 
category or subcategory in making delisting decisions. It would be 
inconsistent for Congress to allow categories or subcategories to be 
delisted entirely from the section 112 regulatory program using a 
category specific analysis, yet require EPA to look beyond the same 
specific category when making similar risk assessments under section 
112(f).
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    We further agree, that while this is the first determination under 
section 112(f) since the adoption of the Clean Air Act Amendments of 
1990, Congress intended that EPA continue to apply the same test for 
determining when public health is protected with an ample margin of 
safety that was in effect before those amendments. Section 112(f)(2)(B) 
instructs EPA to use the ample margin of safety decision framework 
adopted in the Benzene NESHAP to make section 112(f) residual risk 
determinations, and indeed states that:

    [n]othing in subparagraph (A) or in any other provision of this 
section shall be construed as affecting, or applying to the 
Administrator's interpretation of this section, as * * * set forth 
in the Federal Register of September 14, 1989.

    In the Benzene NESHAP, EPA interpreted and applied the two-step 
test drawn from the D.C. Circuit's Vinyl Chloride opinion. Under that 
approach, EPA must first determine what level is ``safe'' ``based 
exclusively upon the Administrator's determination of the risk to 
health from a particular emission level.'' (See 54 FR 38055 (quoting 
Nat'l Res. Defense Council, Inc. v. EPA, 824 F.2d 1146 (D.C. Cir. 1987) 
(en banc)). The Court made clear, however, that ``safe'' does not mean 
``risk free.'' Id. Rather, the EPA must ``determine what inferences 
should be drawn from available scientific data and decide what risks 
are acceptable in the world in which we live.'' Id. In the second step 
under Vinyl Chloride and the Benzene NESHAP, once an ``acceptable 
risk'' level is determined, EPA must decide whether additional 
reductions are necessary to provide ``an ample margin of safety'' (54 
FR 38049). As part of this second decision, EPA may consider the costs 
of additional reductions, technological feasibility, uncertainties 
about available information or other relevant factors. Id.
    After examining the statutory scheme, the Benzene NESHAP, and sound 
policy concerns, EPA has concluded that, in its assessment of 
``acceptable risk'' for purposes of section 112(f), the agency will 
only consider the risk from emissions from that source category. This 
was the approach in the Benzene NESHAP, wherein EPA limited 
consideration of acceptability of risk to the specific sources under 
consideration (coke byproduct recovery plants, benzene storage vessels, 
benzene equipment leaks, ethylbenzene/styrene process vents, and maleic 
anhydride process vents) rather than to the accumulation of these and 
other sources of benzene emissions that may occur at an entire 
facility.\13\ See, e.g., 54 FR 38061 (stating in regard to 
consideration of natural background levels of a pollutant that 
``considering other sources of risk from benzene exposure and 
determining the acceptable risk level for all exposures to benzene, EPA 
considers this inappropriate because only the risks associated with the 
emissions under consideration are relevant to the regulation being 
established and, consequently, the decision being made.'') The Agency 
also rejected approaches that would have mandated consideration of 
background levels of benzene in assessing acceptability of risk. \14\
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    \13\ EPA will consider, consistent with the Benzene NESHAP 
decision, whether co-location of entities within the same source 
category ``significantly influences the magnitude of the MIR or 
other risk levels'' (54 FR 38051). In this rulemaking, EPA has 
concluded that the health risks from the emissions at issue in this 
rulemaking are not affected (let alone significantly affected) by 
co-location with other entities in the same source category.
    \14\ EPA concluded that ``comparison of acceptable risk should 
not be associated with levels in polluted urban air'' (54 FR 38061). 
Background levels of certain HAPs can be relatively high, perhaps 
even above a level that might be considered ``safe.'' These 
background levels (including natural background) are not barred from 
EPA's analysis, but EPA will consider them along with other factors, 
such as cost and technical feasibility, in the second step of its 
112(f) analysis. To decide otherwise, EPA would have to conclude--
inconsistent with the Benzene NESHAP and sound policy--that 112(f) 
requires EPA to shut down any source that emits a HAP in an area 
with high background pollution, even if the emissions from that 
source are extremely small and do not appreciably affect overall 
risk.
---------------------------------------------------------------------------

    EPA has concluded that the sound policy embodied in the Benzene 
NESHAP remains the approach that EPA should follow in determinations 
under section 112(f). At the first step, when determining ``acceptable 
risk,'' EPA will consider public health risks that result from 
emissions from the source category only. Not only is this 
interpretation supported by the text of the statute and prior 
regulatory practice, but we are impressed and daunted at the practical 
problems of implementing a compulsory facilitywide examination. For 
example, as commenters pointed out, in future rules, the myriad 
combinations of source categories present at different facilities could 
create situations where nationwide consideration of residual risk 
becomes a practical impossibility because every facility would present 
a different fact pattern of source categories. Yet section 112(f) 
contemplates national determinations, not case-by-case evaluations and 
standards.

[[Page 19998]]

    At proposal, EPA cited a portion of a floor statement by Senator 
Durenberger as support for the position that EPA must assess the risk 
from an entire facility. EPA agrees with the commenters who stated that 
this statement is not sufficient evidence of Congressional intent to 
justify a different response than that adopted in the Benzene NESHAP, 
especially when, later in the same statement, the Senator states that 
section 112(f) is intended to be a ``return to current law'' under the 
Benzene NESHAP. (See Legislative History, Vol. 1 at 875-76.) As noted 
above, EPA did not adopt standards covering entire facilities in the 
Benzene NESHAP.
    This said, EPA disagrees that section 112(f) precludes EPA from 
considering emissions other than those from the source category or 
subcategory entirely. EPA must still determine whether additional 
reductions should be required to protect public health with ``an ample 
margin of safety.'' EPA believes one of the ``other relevant factors'' 
that may be considered in this second step is co-location of other 
emission sources that augment the identified risks from the source 
category. The Benzene NESHAP does not explicitly identify this as a 
relevant factor under step two, but the decision does acknowledge that 
``multiple exposures to chemicals are important to understand and 
consider in the EPA's overall implementation of its public health 
mandates' despite the fact that EPA has concluded that these risks 
should not be ``routinely evaluated and considered in selecting'' the 
level of acceptable risk (the first step of the Benzene analysis) (54 
FR 38059).
    The decision today is an example of a situation in which EPA has 
determined such a relevant factor merits evaluation. Each of the 
facilities subject to today's rulemaking is also subject to MACT 
emission standards on coke oven emissions from pushing, quenching, and 
battery stacks. These sources are necessarily co-located--they are 
integral parts of the same industrial activity. In this instance, EPA 
has the authority, in establishing ``an ample margin of safety,'' to 
impose greater reductions on a particular source category when the 
agency concludes that several of these co-located sources categories 
have elevated the overall public health risk to unacceptable 
levels.\15\ While this evaluation could be performed during the 
development of an individual residual risk standard for any particular 
source category that is part of a larger facility with multiple source 
categories, such an analysis would necessarily require sufficient data 
regarding the total facility emissions and the costs and risk impacts 
of reducing those emissions. Such information may conceivably be 
available when EPA does the first residual risk rule applicable to a 
facility, but it is much more likely that an early evaluation of cross-
category risks will be inconclusive due to a lack of complete 
information regarding other emission points. (In this rule, for 
example, EPA does not yet have an accurate quantification of pushing 
and quenching battery emissions reflecting these sources' operations 
under MACT standards; such information is needed to reasonably assess 
risks, costs, and further technologically feasible emission 
reductions.) EPA expects to develop better information about what cost-
effective emission and risk reduction opportunities are available as 
more source categories are assessed. EPA believes, in the future, it 
may be able to identify potential emission reduction trade-offs between 
co-located source categories that result in more efficient risk 
reductions for less economic cost at a facility.
---------------------------------------------------------------------------

    \15\ This is not to say that the EPA may impose significant 
reductions across an entire source category to alleviate health 
risks posed by co-location at a subset of facilities. In these 
circumstances, EPA believes it should further parse its emissions 
standards so as to impose greater reductions only on those 
facilities with significant co-location of other emissions. Put 
another way, EPA may permissibly develop section 112(f) standards 
that could result in different controls for co-located source 
categories at a facility than for the same source category which is 
not co-located.
---------------------------------------------------------------------------

3. Actual Versus Allowable Emission Rates
    We explained at proposal that we modeled emissions at the rates 
allowed by the 1993 national emission standards because they represent 
the source's potential emissions and risks and is, therefore, 
consistent with the language in CAA section 112(f)(2).
    Comment: We received some comments that agreed with the use of 
allowable rather than actual emission rates while other comments stated 
that we should use actual emissions. According to one commenter, 
Congress meant for EPA to make realistic estimates of residual risk. In 
support, the commenter pointed to the language of section 112(f)(2) 
which refers to a different measure of risk (i.e., risk to the 
``individual most exposed to emissions from a source'' rather than 
``maximum exposed individual'' or ``maximum individual risk'' used in 
the Benzene NESHAP) and associated passages in the legislative history. 
The commenter stated that EPA has data on actual emissions and should 
use this information as the basis for the risk assessment for coke 
ovens. Another commenter agreed with the decision to assume that 
sources are complying with the 1993 national emission standards when 
estimating emissions. The commenter also agreed with efforts to 
evaluate actual versus ``worst case'' potential emissions when 
estimating population risks and encouraged appropriate adjustments in 
future risk assessments. Another commenter stated that the use of 
maximum allowable emissions is particularly inappropriate for 
industrial source categories with batch operations because they 
consistently operate at levels well below the allowable rate.
    One commenter stated that EPA should not assume perfect compliance 
with allowable emission limits since several of these facilities are 
out of compliance. The commenter believed that we must account for 
noncompliance in the emission estimates.
    Response: EPA believes it may evaluate potential risk based on 
consideration of both actual and allowable emissions. This approach is 
both reasonable and consistent with the flexibility inherent in the 
Benzene NESHAP framework for assessing ample margin of safety. As a 
general matter, allowable emissions are the maximum level sources could 
actually emit and still comply with the national emission standards, so 
modeling this level of emissions is inherently reasonable for 
evaluating potential risks associated with current standards. As 
discussed in other sections of this preamble, coke oven battery sources 
are consistently controlling emissions below the level allowed by the 
1993 national emission standards, which results in a 30 percent 
reduction in the estimated MIR.
    It is also reasonable that we consider actual emissions, when 
available, as a factor in both steps of the determination (i.e., 
determining both risk acceptability and ample margin of safety). See 54 
FR 38047, 38050-38051, 38053 (we acknowledge a probable overestimate of 
emission levels in determining that risk and overall incidence is 
probably less than the maximum estimated levels). For the final rule 
amendments adopted today, years of monitoring data show that actual 
emissions have been consistently lower than allowable levels (69 FR 
48346-48347). Moreover, there is a sound empirical basis for coke oven 
emissions to be lower than theoretically allowable levels. To allow for 
process variability, sources typically strive to perform better than 
required by emission standards so that the emission

[[Page 19999]]

increases which occur on individual days due to process variability 
remain below emission standards. Failure to consider these data in risk 
estimates would unrealistically inflate risk levels.
    It is incorrect that a large number of these coke batteries are out 
of compliance. The batteries are inspected every day to determine 
compliance with the emission limits for doors, lids, offtakes and 
charging. We have compiled the results of these compliance inspections, 
and the details are in the rulemaking docket. The inspection results 
show that the coke batteries are operating consistently below the 
established emission limits and have shown essentially continuous 
compliance.
4. Exposure Duration
    Comment: Two commenters disagreed with the use of a 24-hour per day 
exposure over a 70-year lifetime to estimate individual and population 
cancer risks for refined risk assessments. According to one commenter, 
this exposure assumption is inconsistent with the recommendations by 
the National Research Council and the Commission on Risk Assessment and 
Risk Management. In their Reports to Congress, these organizations 
support development of distributional approaches to exposure 
characterization based on knowledge of the characteristics of a 
population's variability. This commenter asked EPA to develop a refined 
exposure methodology that incorporates information available on 
population residency times that will more accurately reflect population 
risk estimates. The development of this exposure methodology should 
also include a probabilistic analysis of estimated exposures. The other 
commenter stated that the use of such an unrealistic assumption makes 
the results overly conservative and will lead to additional and 
unnecessarily stringent standards more frequently than necessary.
    Response: We agree that our assumption that people may be present 
at their homes for 24 hours per day over a 70-year lifetime represents 
a scenario that likely overestimates the actual exposures received by 
people living near the facilities. Most people have daily activities 
that take them to areas where exposure concentrations are different and 
move to new residences periodically. Both of these behaviors will tend 
to lower lifetime exposures and, therefore, risk. The most significant 
risk reductions would occur for the group of people who are the most 
exposed. For these reasons, we are currently developing a methodology 
that will allow us to consider a variety of parameters (e.g., residency 
time, socio-economic conditions, age distribution, demographics, size 
of the census block) that could affect exposure and risk to individuals 
and populations that live in the vicinity of facilities. Other factors 
(e.g., emigration out of and immigration into the ``exposure area,'' 
social factors that affect population mobility, and census block size) 
may also influence the mobility of populations and, therefore, affect 
estimates of exposure and risk. As part of this effort, we are also 
investigating whether similar probabilistic techniques can be applied 
to the MIR to develop meaningful alternative metrics of individual 
risk. While this methodology is currently under development, we did not 
have sufficient information to apply any of these factors to these coke 
oven facilities.
    Finally, regarding recommendations of the Commission on Risk 
Assessment and Risk Management, we note that our overall approach is 
consistent with some of those recommendations. For example, the Risk 
Commission recommended that ``exposure assessments should not be based 
on a hypothetical MEI * * * should rely on more representative 
estimates or a maximally exposed actual person* * *.'' Our approach was 
based on identifying the maximum concentration where the census data 
identified people as actually living, and we assumed, as discussed 
above, that exposure of this individual was for 70 years starting at 
birth. Where we varied from the Commission's recommendation in this 
area was in assuming a 70-year exposure duration for the population as 
well. As just noted, we are developing a methodology that will allow us 
to look at the exposure variability that might be seen in the exposed 
populations. See the ``Residual Risk Report to Congress'' (at pages 
128-130) summarizing similarity in approaches.
5. Hazard Index
    Comment: Five commenters disagreed with use of the hazard index 
(HI) of 1 as the safe or acceptable level for noncancer health effects. 
One commenter stated that the HI level of 1 should be the ample margin 
of safety level because the values which form the basis for calculating 
HI already contain sufficient layers of safety to represent the ample 
margin of safety. The commenter contended that the reference 
concentration (RfC) or reference dose (RfD) represents the most 
stringent ample margin of safety level EPA should adopt.
    Three commenters recommended that EPA avoid establishing any bright 
line for a safe or acceptable level for non-carcinogens. One of these 
commenters explained that the HI of 1 would define both the acceptable 
risk level and the ample margin of safety level in one step, which is 
inconsistent with the two-step Benzene NESHAP framework. This commenter 
argued that an HI of 1 is too conservative because ``the ample margin 
of safety would always be set at or below an HI of 1.0, which would 
have an effect equivalent to a cancer level of 10-4 within 
the Benzene framework.'' The Commission on Risk Assessment and Risk 
Management's report selected a threshold HI of 10 because the RfC on 
which the HI is based already includes many uncertainty factors that 
should not be compounded in the ample margin of safety decision.
    Another commenter stated that EPA needs to clarify that the case-
by-case flexibility in the Benzene NESHAP framework also applies when 
interpreting hazard quotients (HQ) and HI. Although the proposal 
preamble did not identify a bright line, EPA's risk assessment document 
stated that an HI of 1 for each facility should ordinarily represent 
the safe or acceptable level, and that the ample margin of safety level 
may be lower or equal to the acceptable level, but can never be higher. 
The commenter objected because EPA was talking about an HI for a 
facilitywide analysis (rather than a specific source category) and 
because a rigid adherence to an HI of 1 for determining acceptable risk 
is unwarranted. The EPA should reserve flexibility in interpreting and 
applying HI and HQ acceptability, even in the screening stage. The 
flexibility is needed because of the variability in uncertainty 
factors, quality and consistency of data content, and other underlying 
information and assumptions. The commenter provided additional specific 
observations:
     In some cases, an HI or HQ can represent negligible or 
zero risk. There is no means to translate an HI or HQ into a 
probability of an individual incurring the effect (as is done for 
carcinogen effects).
     The EPA should do the initial screening using a target 
organ specific HI and should not aggregate across target organs and HAP 
for either the initial screening or refined assessment. No health-based 
conclusion can be reached from aggregating across different organs. An 
HI ``roll up'' for multiple chemicals' HQ must be predicated on target 
organ end points that are the same and a common mechanism or mode of 
action.

[[Page 20000]]

     Neither a range of 0.2 to 0.8 for HI nor a conservative 
default of 0.2 is permissible under the CAA. The statute only refers to 
the emissions and risk posed by a source category.
    Response: Five commenters pointed out that a statement in the risk 
assessment document indicated that an HI of 1 is the safe or acceptable 
level. Our statement in the risk assessment document was incorrect and 
has been revised. We did not use an HI of 1 as the acceptable level in 
our analysis. In the proposal preamble, we explained that ``the maximum 
estimated target organ specific HI for the emissions of HAP that may 
cause effects other than