[Federal Register Volume 64, Number 137 (Monday, July 19, 1999)]
[Notices]
[Pages 38706-38740]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-17774]
[[Page 38705]]
_______________________________________________________________________
Part II
Environmental Protection Agency
_______________________________________________________________________
National Air Toxics Program: The Integrated Urban Strategy; Notice
Federal Register / Vol. 64, No. 137 / Monday, July 19, 1999 /
Notices
[[Page 38706]]
ENVIRONMENTAL PROTECTION AGENCY
[FRL-6376-7; Docket No. A-97-44]
National Air Toxics Program: The Integrated Urban Strategy
AGENCY: Environmental Protection Agency (EPA).
ACTION: Notice.
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SUMMARY: This document provides an overview of EPA's national effort to
reduce air toxics, including stationary and mobile source standards,
cumulative risk initiatives, assessment approaches, and education and
outreach. This national air toxics program includes activities under
multiple Clean Air Act (Act) authorities to reduce air toxics emissions
from all sources, including major industrial sources, smaller
stationary sources, and mobile sources such as cars and trucks. By
integrating activities under different parts of the Act, EPA can better
address cumulative public health risks and adverse environmental
impacts posed by exposures to multiple air toxics in areas where the
emissions and risks are most significant.
In addition, this document describes a new major component of our
national effort, the Integrated Urban Air Toxics Strategy (Strategy)
developed under the authority of sections 112(k) and 112(c)(3) of the
Act. The Strategy reflects the public comments received on the draft
Strategy, which was published on September 14, 1998 (63 FR 49240).
The Strategy includes a description of risk reduction goals; a list
of 33 hazardous air pollutants (HAPs) judged to pose the greatest
potential threat to public health in the largest number of urban areas,
including 30 HAPs specifically identified as being emitted from smaller
industrial sources known as ``area'' sources; and a list of area source
categories which emit a substantial portion of these HAPs, and which
are being considered for regulation under section 112(d). Because
mobile sources are an important contributor to the urban air toxics
problem, the Strategy also describes actions under Title II (including
section 202(l)) of the Act to reduce toxics from these sources,
including those which address diesel particulate matter (PM).
The Strategy by itself doesn't automatically result in regulation
or control of emissions. The EPA will perform further analyses of HAP
emissions, control methods, and health impacts, as appropriate, for
stationary and mobile sources. These analyses will inform any ultimate
regulatory requirements that EPA develops under the Strategy.
ADDRESSES: A docket containing information relating to the development
of this notice (Docket No. A-97-44) is available for public inspection
and copying between 8:00 a.m. and 5:30 p.m., Monday through Friday
except for Federal holidays, in the Air and Radiation Docket and
Information Center (MC-6102), Room M-1500, U.S. Environmental
Protection Agency, 401 M Street, SW, Washington, DC 20460; telephone
(202) 260-7548. The docket office may charge a reasonable fee for
copying.
FOR FURTHER INFORMATION CONTACT: Laura McKelvey, Office of Air Quality
Planning and Standards (MD-13), U.S. Environmental Protection Agency,
Research Triangle Park, North Carolina, 27711, telephone number (919)
541-5497, electronic mail address: McKelvey.Laura''epa.gov.
SUPPLEMENTARY INFORMATION:
Plain Language
In compliance with President Clinton's June 1, 1998 Executive
Memorandum on Plain Language in Government Writing, this package is
written using plain language. Thus, the use of ``we'' in this package
refers to EPA. The use of ``you'' refers to the reader and may include
State, local or Tribal government agencies, industry, environmental
groups, or other interested individuals.
Executive Order 12866
Under Executive Order 12866 (58 FR 51735, October 4,1993), the
Agency must determine whether a regulatory action is ``significant''
and therefore subject to Office of Management and Budget (OMB) review
and the requirements of the Executive Order. The Order defines
``significant'' regulatory action as one that is likely to lead to a
rule that may either: (1) have an annual effect on this economy of $100
million or more, or adversely and materially affect a sector of 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 entitlement, grants, user fees, or loan programs or
the rights and obligations 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.
This notice was submitted to OMB for review. Any written comments
from OMB and written EPA responses are available in the docket.
Docket
The docket is an organized file containing information related to
the development of the Strategy. The main purpose of this docket is to
allow you to readily identify and locate documents relevant to the
development of the Strategy. The docket is available for public
inspection at the EPA's Air and Radiation Docket and Information
Center, which is listed in the ADDRESSES section of this document.
Electronic Access and Filing Addresses
You can get this notice and other background information in Docket
No. A-97-44 by contacting our Air and Radiation Docket and Information
Center (see ADDRESSES), or by visiting our website at ``http://
www.epa.gov/ttn/uatw/urban/urbanpg.html'' for electronic versions of
the notice and other information. For assistance in downloading files,
call the TTN HELP line at (919) 541-5384.
Outline
The information in this document is organized as follows:
I. National Efforts to Reduce Air Toxics
A. What is our overall air toxics program?
B. Why are we concerned about urban air in particular?
C. What is the Integrated Urban Air Toxics Strategy?
II. Federal Activities Related to the Integrated Urban Air Toxics
Strategy
A. What HAPs pose the greatest threat in urban areas?
B. How does EPA plan to address requirements for area sources of
HAPs?
C. What regulatory actions will EPA take to implement the
Strategy?
D. How do the various Federal authorities help EPA implement the
Strategy?
III. State, Local and Tribal Activities
A. Why are State, local and Tribal programs integral to the
process?
B. What are the objectives of State, local and Tribal
activities?
C. What were comments on the State/local/Tribal programs and how
are they being addressed in the Strategy development?
D. How can State, local or Tribal agencies participate in the
Strategy?
E. What elements should a State, local or Tribal program
contain?
IV. Assessment Activities
A. How will we assess progress toward goals?
B. What methods, tools, and data will we use to estimate risk?
C. What is our overall risk assessment approach for the
Strategy?
D. How will we design future assessments?
V. Knowledge and Tools
[[Page 38707]]
A. How will we review and expand ambient monitoring networks?
B. How will we update and maintain the emission inventory?
C. What air quality and exposure models will we use to implement
the Strategy?
D. What are the research needs and what is EPA doing to address
them?
VI. Public Participation and Communication
A. How will we encourage stakeholder involvement?
B. What is our overall timeline for action?
C. What reports will we prepare to communicate with the public?
Appendix A. Summary of other authorities, laws, rules, and programs
to help reduce HAP emissions
I. National Efforts to Reduce Air Toxics
The 1990 Clean Air Act Amendments provided the foundation for our
current air toxics program. This program is designed to characterize,
prioritize and equitably address the serious impacts of HAPs on the
public health and the environment through a strategic combination of
regulatory approaches, voluntary partnerships, ongoing research and
assessments, and education and outreach. Since 1990, we've made
considerable progress in reducing emissions of air toxics \1\ through
regulatory, voluntary and other programs. To date, our overall air
toxics program, summarized in section I.A., has focused on reducing
emissions of toxic air pollutants from major stationary sources through
the implementation of technology-based emissions standards as required
in section 112(d). These actions have resulted, or are projected to
result, in substantial reductions in HAP emissions.\2\ Additionally,
actions to address mobile and stationary sources under other Clean Air
Act programs are achieving reductions in HAP emissions (for example,
the phase-out of lead from gasoline). However, we expect that the
emission reductions that will result from these other actions are only
part of what will be necessary to protect public health and the
environment from toxic air pollutants. In identifying additional steps,
we'll use a risk-based focus to develop, implement and facilitate
additional Federal and local regulatory and voluntary measures.
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\1\ Our use of the terms ``air toxics'' or ``toxic air
pollutants'' in this notice refers specifically to those pollutants
which are listed under section 112(b) of the Act as ``hazardous air
pollutants'' or HAPs. There are currently 188 HAPs listed.
\2\ We project that by 2002, the full implementation of section
112(d) maximum achievable control technology (MACT) standards
adopted to date will yield emissions reductions of approximately one
million tons of HAPs per year. Within the next six years, completion
and full implementation of section 112(d) technology-based standards
for the remaining stationary source categories listed pursuant to
section 112(c) will contribute additional emissions reductions.
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In considering additional steps towards protecting human health and
the environment, we need to identify and focus on issues of highest
priority. Current information indicates that there are potentially
significant health risks associated with air toxics exposures affecting
large numbers of people in urban areas, as discussed in section I.B.
Recognizing this, Congress instructed us to develop a strategy for air
toxics in urban areas that includes specific actions to address the
large number of smaller, area sources,\3\ and that contains broader
risk reduction goals encompassing all stationary sources. More
specifically, section 112(k)(1) states:
\3\ Area sources are those stationary sources that emit, or have
the potential to emit, less than 10 tons per year of any one HAP or
less than 25 tons per year of a combination of HAPs. Examples
include hospital sterilizers and small publicly owned treatment
works.
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The Congress finds that emissions of hazardous air pollutants
from area sources may individually, or in the aggregate, present
significant risks to the public health in urban areas. Considering
the large number of persons exposed and the risks of carcinogenic
and other adverse health effects from hazardous air pollutants,
ambient concentrations characteristic of large urban areas should be
reduced to levels substantially below those currently experienced.
As the ambient concentrations of HAPs in urban areas result from a
combination of different sources (e.g., area, major,\4\ and mobile \5\)
emitting many of the same pollutants, we need to recognize
contributions from all types of sources in achieving the reductions in
ambient concentrations referred to in this subsection. Therefore, in
addition to addressing specific statutory requirements for area
sources, we've devised an integrated strategy for reducing cumulative
public health risks in urban areas posed by the aggregated exposures to
air toxics from all sources. The Integrated Urban Air Toxics Strategy
(the Strategy) presented here, and summarized in section I.C. below, is
one part of our overall national effort to reduce toxics. The basic
components of the Strategy consist of the same basic elements as those
of the overall air toxics program but with a specific focus on the
particular needs of urban areas.
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\4\ Major stationary sources are sources that emit, or have the
potential to emit, more than 10 tons per year of any one HAP or 25
tons per year of a combination of HAPs. Examples include chemical
plants, oil refineries, aerospace manufacturers and steel mills.
\5\ Mobile sources include motor vehicles (e.g., cars and
trucks) and off-road equipment (e.g., construction equipment and
lawn mowers), and their fuels.
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Before we describe the national efforts to control air toxics in
more detail, we want to provide a brief overview of what air toxics
are, their health and environmental effects, and their sources. These
topics are discussed in more detail later in the notice, but their
introduction here will help ensure that the remaining discussion in
section I is based on a common understanding of the nature of the air
toxics problem.
What are air toxics?
The Act identifies 188 compounds as HAPs. They include pollutants
like benzene found in gasoline, perchloroethylene emitted from dry
cleaners, methylene chloride used as an industrial solvent, heavy
metals like mercury and lead, polychlorinated biphenyls (PCBs), dioxins
and some pesticides. These pollutants may cause cancer or other serious
effects in humans or in the environment. Health concerns result from
both short-and long-term exposures to these pollutants. They may
disperse locally, regionally, nationally, or globally and after
deposition may persist in the environment and/or bioaccumulate in the
food chain, depending on their characteristics (such as vapor
pressures, atmospheric transformation rates). Although not specifically
listed as a HAP in section 112(b) of the Act, diesel emissions contain
many HAPs, and are thus collectively considered under our overall
program and the Strategy.
What health and environmental effects do they cause?
Hazardous air pollutants can cause many health effects. More than
half are known or suspected to be human carcinogens. Many are known to
have respiratory, neurological, immune or reproductive effects,
particularly for more susceptible or sensitive populations, such as
children. Many of the HAPs are known to also cause adverse effects in
many fish and animal species, including toxicity in fish or causing
reproductive decline in bird species, including endangered species.
These environmental effects may be felt by individual species within a
single level of the food chain or by the entire ecosystem where
multiple species are affected.
What are the sources of air toxics?
There are literally millions of sources of air toxics, including
large industrial complexes like chemical plants, oil refineries and
steel mills; small (area) sources such as dry cleaners, gas stations,
and small manufacturers; and mobile sources including cars, trucks,
buses, and nonroad vehicles like ships and farm equipment.
[[Page 38708]]
A. What is Our Overall Air Toxics Program?
Our overall approach to reducing air toxics reflects the mandates
under the Act to develop technology-based standards and then
subsequently to implement a risk-based program to ensure the protection
of public health and the environment. For example, in amending the Act
in 1990, Congress required us to establish national standards to reduce
emissions of air toxics from stationary and mobile sources. Under
section 112(d), Congress emphasized the implementation of technology-
based standards for stationary source categories emitting air toxics.
These emission standards are known as maximum achievable control
technology (MACT) standards, and generally available control technology
(GACT) standards. Section 112(k) requires us to list area source
categories and to ensure 90 percent of the emissions from area sources
are subject to standards pursuant to section 112(d). In addition, under
section 202, Congress requires us to set standards to control HAPs from
motor vehicles and their fuels.
Further, the Act contains additional provisions that have a risk-
based focus. Section 112(f) of the Act requires us to evaluate the risk
remaining after implementation of MACT standards (i.e., the ``residual
risk'') in order to evaluate the need for additional stationary source
standards to protect public health and the environment.
Under section 112(k), the Act specifically mandated that we develop
a Strategy (the subject of this notice) to address public health risks
posed by air toxics from area sources in urban areas and report to
Congress on this issue. In addition, section 112(k) of the Act also
mandates that the Strategy achieve a 75-percent reduction in cancer
incidence attributable to HAPs emitted by stationary sources.
Other sections of the Act call for study of other types of specific
air toxics problems including a focus on certain HAPs that persist and
bioaccumulate in the environment. These studies include the deposition
of air toxics to Great Waters,\6\ HAP emissions from electric
utilities, and the health and environmental effects of mercury
emissions, in particular.\7\
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\6\ The Great Lakes, Chesapeake Bay, Lake Champlain and coastal
waters are collectively referred to as the ``Great Waters.''
\7\ These studies are required by sections 112(m), 112(n)(1)(A),
and 112(n)(1)(B), respectively.
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Our current national air toxics goal was developed to meet
requirements of the Government Performance and Results Act (GPRA),
which requires us to report on the status of our progress in
implementing our programs. That goal is to reduce air toxics emissions
by 75 percent from 1993 levels and to significantly reduce the risk to
the public of cancer and other serious adverse health effects caused by
airborne toxics. Because our knowledge and tools to assess the impacts
of these emissions on public health and the environment were limited
when we set this current goal, it reflects the straightforward intent
to reduce total air toxics emissions as a means to reduce risks
associated with exposure to air toxics. However, as we extend our
knowledge, develop better assessment tools and begin to address the
risks associated with these emissions as required by the Clean Air Act,
we intend to modify our goal to one directed specifically at risk
reductions associated with exposure to air toxics. In working toward
such a risk-based goal, we'll focus particularly on populations and
areas disproportionately impacted, including, for example, densely
populated areas, children at risk of developmental effects and people
who are highly exposed to water and food affected by air toxics (e.g.,
subsistence fishers living near contaminated water bodies). For more
information on assessments, see section IV for an explanation of the
assessment methods.
We intend to progress toward the program goal through a combination
of our authorities, regulatory activities and voluntary initiatives.
The overall approach to reducing air toxics consists of the following
four key components:
Source-specific standards and sector-based standards. As
previously mentioned, section 112 specifies MACT/GACT standards, and
residual risk standards, as well as those area source standards which
are contemplated by the Integrated Urban Air Toxics Strategy.
Additionally, section 129 requires standards for solid waste
incineration and section 202(l) requires EPA, based on the mobile-
source related Air Toxics Study, to promulgate reasonable requirements
to control HAPs from motor vehicles and their fuels.
National, regional, and community-based initiatives to
focus on multi-media and cumulative risks. Section 112(k)(4) requires
us to ``encourage and support area wide strategies developed by the
State or local air pollution control agencies.'' Our risk initiatives
will include State, local and Tribal program activities consistent with
the Integrated Urban Air Toxics Strategy on the local level as well as
Federal and regional activities associated with the multimedia aspects
of HAPs, such as the Great Waters program \8\ and initiatives
concerning mercury, and other persistent bioaccumulative toxics (PBTs).
Other Agency initiatives include collaboration between the air and
water programs on the impact of air deposition on water quality (e.g.,
by accounting for the contribution of air deposition to the total
maximum daily load (TMDL) of pollutants to a water body), and
collaboration between offices within EPA's air program to assess the
risks from exposures to air toxics indoors and to develop non-
regulatory, voluntary programs to address those risks.
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\8\ Under section 112(m) of the Act, we assess and report to
Congress on the deposition of air pollutants in the Great Lakes,
Chesapeake Bay, Lake Champlain, and coastal waters. The third report
to Congress on ``The Deposition of Air Pollutants to the Great
Waters'' will be released later this year.
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National air toxics assessments (NATA). National air
toxics assessments will help us identify areas of concern, characterize
risks, and track our progress toward meeting our overall air toxics
program goals, as well as the risk-based goals of the various
activities and initiatives within the program, such as the Integrated
Urban Air Toxics Strategy. The NATA activities include expansion of air
toxics monitoring, improving and periodically updating emissions
inventories, national- and local-scale air quality, multi-media and
exposure modeling (including modeling which considers stationary and
mobile sources), continued research on health effects and exposures to
both ambient and indoor air, and use and improvement of exposure and
assessment tools. These activities will provide us with improved
characterizations of air toxics risk and risk reductions resulting from
emissions control standards and initiatives for both stationary and
mobile source programs.
Education and outreach. In light of the scientific
complexity inherent in air toxics issues, we recognize that the success
of our overall air toxics program depends in part on our ability to
communicate effectively with the public about air toxics risks and
activities necessary to reduce those risks. This includes education and
outreach efforts on air toxics in the ambient as well as indoor
environments.
Following is a more detailed discussion of the activities under
each of the four components of the national program.
[[Page 38709]]
1. Source-specific Standards and Sector-based Standards
Maximum achievable control technology. The 1990 Clean Air Act
Amendments required us to use a ``technology-based'' and a performance-
based approach to significantly reduce emissions of air toxics from
major sources of air pollution. These reductions are to be followed by
a risk-based approach to address any remaining, or residual risks.
Under the ``technology-based'' approach we develop standards for
controlling the ``routine'' emissions of air toxics from each major
source within an industry group (or ``source category''). These
standards--known as ``maximum achievable control technology (MACT)
standards''--are based on emissions levels that are already being
achieved by the better controlled sources in an industry. This approach
assures citizens nationwide that each major source of HAPs will be
required to employ effective measures to limit its emissions.
Under this program, we listed for regulation 174 source categories
that emit the 188 HAPs listed under section 112(b). To date, we've
promulgated 43 standards regulating 78 source categories. We've
proposed an additional 7 standards covering 8 source categories. Five
source categories have been delisted. We're continuing to develop
standards to cover the remaining source categories.
Combustion standards. We've also issued final rules to control
emissions of certain air toxics from certain types of solid waste
combustion facilities. These rules, required under section 129 of the
Act, set emission limits for new solid waste combustion facilities and
provide emissions guidelines for existing solid waste combustion
facilities. These rules affect municipal waste combustors and hospital/
medical/infectious waste incinerators, which account for 30 percent of
the national mercury emissions to the air. By the time these rules are
fully implemented we expect them to reduce mercury emissions from these
sources by about 90 percent from current levels, and reduce dioxin/
furan emissions by more than 95 percent from current levels. We're
working on additional rules to address industrial and commercial waste
incinerators, other solid waste incinerators and small municipal waste
combustor units.
Residual risk. The residual risk program, required under section
112(f) of the Act, is designed to assess the risk from source
categories after MACT standards are implemented. If we find a
remaining, or residual, risk, we're required, within 8 years of the
promulgation of the MACT standard, to set additional standards if the
level of residual risk doesn't provide an ``ample margin of safety to
protect public health'' or ``to prevent, taking into consideration
costs, energy, safety, and other relevant factors, an adverse
environmental effect.'' \9\
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\9\ The Residual Risk Report to Congress, March 3, 1999,
describes our approach on risk assessment methods for use across the
air toxics program, and our approach for conducting residual risk
analyses. (EPA-453-/R-99-001)
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In analyzing residual risk, we'll conduct risk assessments
consistent with the Agency's human health and ecosystem risk assessment
technical guidance and policies. We'll use a tiered approach, usually
first conducting a screening level assessment for a source category,
and move to a refined assessment only where the risks identified in the
screening assessment appear unacceptable. Depending on the
characteristics of the HAPs, these assessments will address single or
multiple pathways of exposure as well as human and ecological
endpoints.
Risk management decisions will be consistent with Agency policies.
For carcinogens, we'll use a linear dose-response model unless data
support nonlinear mechanisms. We'll follow the Agency's mixtures
guidelines where a source category emits multiple HAPs.
For non-cancer effects, we'll use the EPA reference concentration
or comparable criteria from other government agencies. As with the
cancer effects, we'll follow the mixtures guidelines for emissions of
multiple non-carcinogens.
In general, we'll base decisions on exposures predicted from
modeling HAP emissions in air and, where appropriate, other media.
Where available, we'll include monitoring data as part of our analysis
for refined assessments. We'll estimate the size and characteristics of
the exposed population, and conduct uncertainty and variability
analysis where appropriate.
Currently we're conducting analyses on 13 of the earliest standards
that we promulgated. We're conducting these analyses on a source
category basis. Depending on the outcome of these analyses, we may find
it necessary to modify our residual risk approach.
Mobile source standards. We started enforcing the first federal
emission standards for passenger cars in 1968. Since then, acting under
specific mandates from the Congress and under general authority, we've
developed emission standards for all types of highway vehicles, their
fuels, and engines used in virtually all varieties of mobile or
portable nonroad equipment such as tractors, construction vehicles,
recreational and commercial vessels, and lawn and garden equipment.
We've also made the emission standards more stringent over time. New
highway vehicles using gasoline are now all equipped with advanced
catalysts and computer-controlled fuel systems. Diesel vehicles and
most nonroad engines have been substantially redesigned to meet our
emission standards as well. Diesel buses in urban areas are subject to
a special limit on their emissions of particulate matter. All gasoline
and highway diesel fuel used in the United States is subject to
emission-reducing standards for volatility and sulfur, respectively.
About one-quarter of the gasoline used in the United States is now
subject to our reformulated gasoline program, and has lower volatility,
reduced concentrations of benzene and other aromatics, and other
beneficial changes. In May of this year, we proposed stringent new
standards for all cars and light trucks, and the gasoline they use. At
the same time we issued an advanced notice of proposed rulemaking to
solicit information relating to control of diesel fuel quality. This
year, we're also reviewing our standards for heavy-duty highway
vehicles. In 2001, we'll do the same for heavy-duty nonroad engines.
To date, most of our emission standards have been aimed at
improving urban air quality for the criteria pollutants carbon
monoxide, ozone, and PM10. However, the emission control equipment on
engines and vehicles, along with the fuel changes that have been needed
to meet our emission standards, are also effective at reducing
emissions of many HAPs. Our requirement to reduce and then end the use
of lead additives in gasoline is an example of a standard that
specifically reduced emissions of toxic pollutants. The reformulated
gasoline program is another example, as it includes a performance
standard for the emissions of several important HAPs.
Because of the time it takes for older vehicles to retire and be
replaced with newer vehicles that comply with the latest emission
standards, total mobile source toxics emissions will decline for many
years into the future.
While the toxic reductions from our emission standards have been
large, prior to 1990 we had no specific directions from Congress for a
planned program to control toxic emissions from mobile sources.
However, section 202(l), added by the Clean Air Act Amendments of 1990,
requires us to complete a study of motor vehicle-related air toxics,
and to promulgate
[[Page 38710]]
requirements for the control of HAPs from motor vehicles based on that
study. We completed the required study in 1993, and are presently
preparing an update to that study, and considering rulemaking under
section 202(l)(2). In addition, the 1990 Amendments give us
discretionary authority to control toxic emissions from nonroad mobile
engines. We plan to study the role of nonroad engines in the air toxics
problem over the next couple of years, and may propose standards if
appropriate.
2. National, Regional, and Community-based Initiative to Focus on
Multi-media and Cumulative Risks
The Clean Air Act requires a number of risk studies to help us
better characterize risk to the public and the environment from HAPs.
Information from these studies will provide information for rulemaking
in some cases but will also provide information to support national and
local efforts to address risks through other voluntary and pollution
prevention programs. The following paragraphs describe these studies.
Utility study. Section 112(n)(1)(A) of the Act requires ``a study
of the hazards to public health reasonably anticipated to occur as a
result of emissions by electric utility steam generating units of
pollutants listed under subsection [112(b)].'' We completed this study
in February of 1998. We're currently collecting additional information
to support a determination on whether regulations are appropriate and
necessary to address risks from HAPs from these sources. We expect all
test reports required under our information requests by May 31, 2000.
We'll use this information to conduct additional analysis of the
emissions of mercury from utilities and potential control technologies.
In addition, we'll continue the analysis of health-related issues. We
plan to make our determination about the need for regulation by
December 15, 2000.
Great Waters Program. Section 112(m) requires us to monitor, assess
and report on the deposition of HAPs to the ``Great Waters,'' which
include the Chesapeake Bay, Lake Champlain, the Great Lakes, National
Estuary Programs, and National Estuarine Research Reserves. We're
required to assess deposition to these waters by: establishing a
deposition monitoring network; investigating the sources of pollution;
improving monitoring methods; evaluating adverse effects; and sampling
for the pollutants in aquatic plants and wildlife. Pollutants of
concern to the Great Waters include mercury, lead, cadmium, nitrogen
compounds, polycylic organic matter/polynuclear aromatic hydrocarbons
(POM/PAHs), dioxin and furans, PCBs and seven banned or restricted
pesticides.
We're also required to provide an update to Congress every two
years on any new information relating to deposition of HAPs to the
Great Waters. We issued the first two reports to Congress in 1994 and
1997. In addition, in March 1998, we made a determination under section
112(m)(6) that we have enough authority under the Act to address the
HAPs impacting the Great Waters. The third report to Congress is
scheduled for September 1999, and will focus on the contribution of
atmospheric deposition, environmental and public health effects,
sources of pollution, and exceedences of standards.
As part of the Great Waters Program, we're funding special
monitoring studies at 13 different coastal areas. In addition, we're
expanding the National Atmospheric Deposition Program to include more
coastal sites for long-term deposition records. We'll continue to
develop a coastal monitoring network and to improve air deposition
monitoring methods.
In an effort to coordinate programs under the Clean Air Act and the
Clean Water Act, we're conducting a pilot study to link air dispersion
and deposition models with watershed fate and transport models. The
results of this study will help us to improve our multimedia analysis
efforts and will allow us to look at the connection between our legal
authorities under the two Acts.
Mercury study. Section 112(n)(1)(B) requires that we issue a report
to Congress on the sources and impacts of mercury. We released the
report in December 1997. The report included an assessment of the
emissions of mercury from all known anthropogenic sources in the United
States, the health and environmental implications of these emissions,
and the availability and cost of control of these emissions.
Urban Air Toxics Strategy. Section 112(k) of the Act requires us to
develop a strategy to identify and address risks to the public in urban
areas. We'll describe the Integrated Urban Air Toxics Strategy in more
detail in later sections of this document.
3. National Air Toxics Assessments (NATA)
As mentioned previously, in order for the national air toxics
program to move to a more risk-based program, it's imperative that we
have strong analytical tools to support activities to identify risks,
to track progress toward risk goals and to help prioritize our efforts
to address emissions and risks from air toxics. Several assessment
activities are under way to support the national air toxics program, as
described in the following paragraphs.
Federal air toxics monitoring. Ambient air toxics information is a
key component in supporting assessment activities, helping to determine
exposure, tracking progress of the air toxics program goals, and
evaluating models and other assessment tools. Because of the importance
of this information, we're currently developing an approach to
monitoring air toxics nationally and locally with State and local
agencies. We envision a monitoring network with some monitors operated
on the national level to track overall national trends. This monitoring
network may include both new monitoring sites located for air toxics
monitoring, as well as information leveraged from other national
monitoring networks including Photochemical Assessment Monitoring
Stations (PAMS) (which collect at least eight HAPs) and the PM2.5 sites
(which collect most of the metals). We'll also compile data from the
State toxics monitoring networks.
In order to optimize our monitoring resources, we're working with
our regulatory partners to expand monitoring networks by adding new
sites; merging existing Federal and States sites where appropriate
(e.g., PACS, PM2.5 and Speciation Trends sites); targeting urban
population-oriented sites; developing a common Acore'' list of
compounds to monitor; and implementing a phased approach to expanding
the number of sites and compounds to fill the data gaps.
Emissions inventories. Over the past several years we've worked to
build a program for a national inventory of air toxics emissions. We
now have data sets for the 1990 to 1993 period and a draft for 1996.
The 1996 National Toxics Inventory (NTI) will be used as part of the
NATA for modeling and data analyses. It includes information generated
from MACT standards development, as well as information provided by 36
States and various industries. The 1996 NTI is currently under review
by the State and local agencies. We expect the 1996 NTI to be final in
the fall of 1999.
Modeling. The NATA will include modeling efforts using information
from the emissions inventory and supported by the monitoring data.
We're working toward a future focus on integrated multi-media/
multipathway assessments. We intend to conduct assessments on the
national, regional, and local scales
[[Page 38711]]
to support activities at all levels of the air toxics program.
Initially we'll use the Assessment System for Population Exposure
Nationwide (ASPEN) model (used in the Cumulative Exposure Project) to
conduct national level assessments.
In the fall and winter of 1999, we'll conduct national level
assessments to estimate ambient concentrations of HAP and predict the
exposures that would result. This information will be released in the
spring of 2000. These assessments are described in more detail in
section IV.D.
In addition, we intend to use air quality and exposure models for
source-specific assessments and to look at selected urban areas. In the
near future, we expect to use the Total Risk Integrated Model (TRIM) to
address local or neighborhood scale applications. This model will have
the capability to address human health and ecological impacts. We
expect this to be available late in 2000. In addition, we're working on
a Models-3/Community Multi-scale Air Quality (CMAQ) Modeling System.
Initially, this model will support assessments on the urban-to
regional-scale. Eventually, however, it will be used for neighborhood-
scale assessments. By the end of 2000, we expect to have an operational
evaluation of the model using mercury and some semi-volatile compounds,
with a final evaluation completed by 2001. This model includes
capabilities to address ozone and PM, together with air toxics, and
will be able to link with a human exposure model.
4. Education and Outreach
We believe that public participation is vitally important in the
implementation of the overall air toxics program. We're committed to
work with cities, communities, State, local and Tribal agencies, and
other groups and organizations that can help implement our approach to
reducing toxics emissions. For example, we expect to work with the
cities, our regulatory partners, and other interested stakeholders in
the national air toxics assessments that will be conducted. In
addition, we'll continue to work with stakeholders on regulation
development. We intend to involve local communities and industries in
development of local risk initiatives such as the total maximum daily
load (TMDL) initiatives.
B. Why Are We Concerned About Urban Air in Particular?
In urban areas, toxic air pollutants raise concerns because sources
of emissions and people are concentrated in the same geographic area,
leading to large numbers of people exposed to the emissions of many
HAPs from many sources. Additionally, while urban exposures to some
pollutants may be fairly similar across the country, studies in a
number of urban areas indicate that exposures to other pollutants, and
any associated risks, may vary significantly from one urban area to the
next. The tools we rely on in our efforts to better characterize urban
health risks from air toxics each have associated uncertainties, which
may add to our concerns. We intend our NATA activities to improve our
ability to describe these uncertainties and where possible, reduce
them. As currently available, the various types of information (e.g.,
emissions, ambient air quality monitoring and modeling) that will be
central to our NATA activities illustrate the importance of focusing on
urban areas.
First, our baseline national emissions inventory \10\ for the air
toxics program indicates that the vast majority of HAP emissions
(approximately 75 percent of the total HAP emissions of all 188 HAPs
from all sources) are within counties with urban areas.\11\
Additionally, a greater number of different HAPs may be emitted from
the multiple sources present in urban areas than from the more limited
number and variety of sources present in rural areas. This is
particularly important because even in cases where individual pollutant
levels are low enough that exposure to any one pollutant wouldn't be
expected to pose harm, some pollutants may work together such that
their potential for harm increases and exposure to the mixture poses
harm. Thus, depending on exposure levels and characteristics of the
pollutants, multiple pollutant exposures, which may be prevalent in
urban populations, may pose increased public health risks.
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\10\ The baseline national toxics inventory (NTI) that we've
compiled over the past few years is representative of the years
1990-93. We believe that this is an appropriate baseline because
these years represent the ``pre-MACT'' emissions for HAP sources.
This baseline inventory contains information on major, area and
mobile sources for all 188 HAPs and provides information on whether
the emissions are urban or rural. A subset of this baseline
inventory is information collected and extensively reviewed by the
public to support analyses for this Strategy and regulatory actions
under section 112(c)(6).
\11\ In estimating the amount of emissions from urban areas,
we've totaled emissions from all U.S. counties that include a
metropolitan statistical area with a population greater than 250,000
or for which more than 50 percent of the population has been
designated ``urban'' by the U.S. Census Bureau. For a more detailed
description of emissions allocation, see the emissions information
prepared to support this Strategy (``Emissions Inventory of 40
Candidate Section 112(k) Pollutants; Supporting Data for EPA's
112(k) Regulatory Strategy''), available at www.epa.gov/ttn/uatw/
112k/112kfac.html.
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Second, ambient air monitoring information collected by States in
certain metropolitan areas during the 1990s demonstrate the
simultaneous presence of many HAPs in urban air and, thus, the
potential for urban population exposures to multiple HAPs. In assessing
the implications of these monitored HAP concentrations for potential
public health concerns, we combined the measured ambient HAP
concentrations with quantitative estimates of each HAP's cancer
potency. This limited evaluation of a subset of the small number of
HAPs monitored indicates the presence of HAPs in some cities that when
evaluated cumulatively is suggestive of upper bound estimates of
additional cancer risks at or above one in ten thousand.\12\ This type
of limited evaluation can provide indications of potential public
health concerns, but should not be considered a characterization of
actual health risks.
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\12\ The technical support documentation for this assessment
analysis is available from the public docket and includes a
presentation of ambient monitoring data in 17 cities for a variety
of HAPs. Also presented are the upper bound estimates of excess
cancer associated with continuous lifetime exposures at those
concentrations.
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Third, an early effort by the Agency to model ambient HAP
concentrations on a national scale performed for EPA's Cumulative
Exposure Project (CEP) suggests that HAP exposures are prevalent
nationwide, and that for some HAPs, in some locations, concentrations
are significantly higher than the concentrations that, if exposures are
continuous over a lifetime, are associated with a one-in-one million
lifetime excess cancer risk.\13\' \14\ As stated above, estimated
concentrations greater than risk-based concentrations should be viewed
as indicators of a potential public health problem and not as
characterizations of actual health risks. Illustrating the need for
special attention in urban areas, the early modeling analysis found
that for 75 percent of the HAPs modeled, the average estimated
concentrations in urban census tracts \15\ were greater, and in some
cases much greater, than the overall national average concentrations.
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\13\ SAIC. 1998. Final Report, Modeling cumulative outdoor
concentrations of hazardous air pollutants.
\14\ Woodruff, et al. 1998. Public Health Implications of 1990
Air Toxics Concentrations across the United States. Environ. Health
Persp. 106(5):245-251.
\15\ Census tracts with residential population density greater
than 750 persons per square kilometer.
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The concentration of activities in urban areas leads to the
presence of multiple emission sources and
[[Page 38712]]
proportionately higher emissions of multiple HAPs. Many of these
emission sources are area or mobile sources, and their emissions are
more likely to be released at ground level, where people are more
likely to be exposed to them. Because approximately 80 percent of the
U.S. population lives in metropolitan areas,\16\ exposures resulting
from urban air toxics emissions may pose a significant risk to public
health. Additionally, the prevalence of minority and low income
communities in urban industrial and commercial areas, where ambient
concentrations of HAPs may be greater, increases the likelihood of
elevated HAP exposures among these subgroups. The potential for air
toxics in urban areas, either directly or indirectly, to contribute to
elevated health risks among these and other subgroups (especially
including children, the elderly and persons with existing illness or
other potential vulnerability) demonstrates the need to assess risk
distributions across urban populations in order to address
disproportionate impacts of air toxics hazards.\17\
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\16\ U.S. Department of Commerce, 1997, Population Profile of
the United States. Current population reports, special studies P23-
194. Economic and Statistics Administration, Bureau of the Census,
Washington, D.C.
\17\ The reader should note that all of these examples
illustrate that there are different ways of representing urban
areas. These are all individually valid, but the result is that
different definitions lead to different approximations of the
affected population. In the remainder of the Strategy, we'll explain
which definition we're using in each particular context.
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As described earlier in this notice, we have been and are
continuing to develop various Federal standards for stationary and
mobile sources as part of the air toxics program and under other Clean
Air Act authorities. These standards, as well as standards developed by
State and local authorities, are expected to improve air quality in
urban areas. As part of the air toxics program, we will be assessing
what additional actions, both at the national and local level, are
needed to further improve air quality in urban areas. This is a primary
focus of the Integrated Urban Air Toxics Strategy, described more fully
in the rest of this notice. We will include State and local
authorities, and in particular mayors, in planning activities to assess
local air quality and to address concerns.
C. What is the Integrated Urban Air Toxics Strategy?
The Strategy presented in this notice has been developed in
response to the requirements of sections 112(k) and 112(c)(3) of the
Act, and also reflects activities to control mobile source emissions
required under section 202(l). As stated previously, the Strategy
represents an integration of our authorities to identify and address
risks from both stationary and mobile sources. In this section of the
notice, we describe the goals and major components of the Strategy,
while later sections describe more fully those components.
Additionally, section 112(k) of the Act also requires us to report to
Congress, on two occasions, regarding actions taken under the Strategy
and current information regarding public health risks posed by HAP
emissions in urban areas. We're currently preparing the first of these
two reports to Congress, and its release is planned for later this
year.
1. Goals of the Strategy
Our goals for the Strategy reflect both statutory requirements
stated in section 112(k) and the goals of our overall air toxics
program. These goals consist of the following:
Attain a 75-percent reduction in incidence of cancer
attributable to exposure to HAPs emitted by stationary sources. This is
relevant to all HAPs from both major and area stationary sources, in
all urban areas nationwide. Reductions can be the result of actions by
Federal, State, local and/or Tribal governments, achieved by any
regulations or voluntary actions.
Attain a substantial reduction in public health risks
posed by HAP emissions from area sources. This includes health effects
other than cancer posed by all HAPs. Reductions can be the result of
actions by Federal, State, local and/or Tribal governments, achieved by
any regulations or voluntary actions.
Address disproportionate impacts of air toxics hazards
across urban areas. This will necessarily involve consideration of both
stationary and mobile source emissions of all HAPs, as well as sources
of HAPs in indoor air. We intend to characterize exposure and risk
distributions both geographically and demographically. This will
include particular emphasis on highly exposed individuals (such as
those in geographic Ahot spots'') and specific population subgroups
(e.g., children, the elderly, and low-income communities).
The Act includes certain specific requirements for the Strategy.
First, we're required to identify at least 30 HAPs, ``which, as the
result of emissions from area sources, present the greatest threat to
public health in the largest number of urban areas'' (section
112(k)(3)(B)(i) of the Act). Second, we're required to assure that
sources accounting for 90 percent of the emissions of identified area
source HAPs are subject to standards (section 112(k)(3)(B)(ii) and
section 112(c)(3)). These steps will contribute to our progress toward
the Strategy's goals.
In meeting the Strategy's goals, we'll consider reductions in HAPs
resulting, not only from actions under our overall air toxics program
(e.g., MACT, residual risk standards, mobile source emission controls)
and measures resulting from programs to attain the national ambient air
quality standards for particulate matter and ozone (as well as our
other regulatory programs), but also from State, local and Tribal
measures. Further, we'll consider cumulative risks presented by
exposures to emissions of HAPs from sources in the aggregate. This is
consistent with the language of section 112(k)(1) of the Act, quoted
earlier. Further, consistent with the direction of section 112(k)(4) to
encourage and support area-wide strategies developed by State or local
air pollution control agencies, we'll work with State, local, and
Tribal air pollution control programs for additional progress toward
these goals.
Continuous advances in our knowledge and activities within the
broader air toxics program, both of which are expected to contribute
especially relevant information, will be integral to the implementation
of the Strategy. For example, certain air toxics, such as mercury, may
be deposited from the air into soil and/or water, taken up by organisms
into the food chain, and bioaccumulate so that concentrations increase
through each level of the food chain. The result is that humans and
wildlife can be exposed to these ``air'' toxics by eating contaminated
food, especially predatory fish from affected water bodies. We're
concerned about individuals in urban areas that eat more than the
average amount of fish from local sources, including urban subsistence
fishers. Under the Great Waters program, we monitor air toxics
deposition and evaluate potential adverse effects on public health and
the environment including those related to contaminated ecosystems and
fish. This information will assist us in assessing the potential for
certain HAPs to pose multipathway health risks to urban residents of
coastal areas (e.g., risks from both inhalation of HAPs and consumption
of fish contaminated by deposition of HAPs to waterways).
The indoor environments program is another Agency activity with
particular relevance to the Strategy because people in urban settings
spend as much as 80
[[Page 38713]]
to 90 percent of their time indoors.\18\ Additionally, outdoor air is
brought indoors through infiltration and mechanical ventilation and
there are also many sources of air toxics indoors. As part of this
Strategy, EPA will assess the current information on indoor emissions
and air concentrations of air toxics, and will use the data, to the
extent possible, to estimate exposures to air toxics in indoor
environments. As we continue to develop and enhance our knowledge of
exposures and risks from indoor air toxics through the indoor
environments program, we'll seek to include information on indoor
exposures in our characterization of risk associated with outdoor
sources and in the development of risk management options for air
toxics. We also intend to conduct additional research on indoor air
exposures to HAPs and on the relative significance of outdoor and
indoor concentrations of HAPs, as well as on the relationship between
outdoor emission sources and indoor concentrations of HAPs.
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\18\ The indoor environments program is a non-regulatory
program, working under the authority of Superfund Amendments and
Reauthorization Act (SARA) Title IV to perform research and provide
information to the public on the health problems associated with air
pollutants in the indoor environment. Most of the guidance provided
by the indoor environments program focuses on reducing pollutants
throughout buildings through proper building design, operation, and
maintenance, including management of indoor sources. The program
works through an extensive network of partners in providing training
and information on indoor air environmental issues throughout the
United States.
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2. Developing the Strategy
To address the problem of exposure to air toxics in urban areas, we
published a draft strategy on September 14, 1998 (63 FR 49240) that
addressed the urban air toxics risks from both stationary and mobile
sources. We asked for, and received, extensive public comment on the
draft strategy. We received over 120 letters and heard from numerous
speakers at stakeholder meetings in Alexandria, VA; Durham, NC;
Chicago, IL; and San Francisco, CA, as well as at other meetings
including a public meeting in New York City and meetings with the
National Environmental Justice Advisory Council. As discussed
throughout the following sections of this notice, we considered these
comments in developing the final Strategy. Comment letters, meeting
summaries, and material developed to analyze and respond to comments
are in the public docket (Docket No. A-97-44).
The Strategy being published today will produce a set of actions in
response to the cumulative public health risks presented by exposures
to emissions of multiple HAPs from multiple sources. We believe that by
considering urban air toxics emissions from all sources, we'll better
understand and address the relative risks posed by any one pollutant
and/or source category. Thus, by integrating activities under different
parts of the Act, we can more realistically address aggregate exposure
in areas where the emissions and risks are most significant and
controls are the most cost effective.
3. Components of the Strategy
Consistent with the broader overall air toxics program (described
in section I.A.), the Strategy is made up of four interrelated parts or
components for addressing the public health risk associated with urban
air toxics. Information from each of the four components provides
feedback to the others to inform the decisions needed to make progress
toward meeting our goals.
The first component includes our regulatory tools and programmatic
activities for source-specific and sector-based standard setting, as
well as those of States, local agencies, and Tribes, which contribute
to reductions in emissions of air toxics from major, area, and mobile
sources. This component includes activities such as selecting urban
HAPs, setting emission standards, conducting studies, developing
policies, and conducting enforcement and compliance assistance
activities. These actions result in emission reductions, as well as
associated reductions in risk. Sections II and III of this document
describe the regulatory activities we'll pursue to implement the
Strategy.
The second component of the Strategy involves local and community-
based initiatives to focus on multi-media and cumulative risks within
urban areas. These may include activities such as pilot projects to
identify and address risk, and may rely on some of the assessment
activities and tools described below. Section III of this document
describes the nature of some of these activities.
The third component is the urban component of NATA, which will
provide us with meaningful information and allow us to describe
progress that we've made in meeting our overall program and strategy-
specific goals. We'll identify the pollutants and sources that
contribute to any failures in meeting our risk reduction goals, and
provide meaningful information to support regulatory and policy
decisions needed to move us closer to meeting them. Section IV of this
document, Assessment Activities, describes how we'll design and conduct
these assessments. These activities rely on our improving base of
knowledge (e.g., concerning health effects and exposure
characteristics) and tools (e.g., emissions inventories, monitoring
networks, and computer models), which are described in section V, along
with our plans for their improvement and related research.
The fourth component, communicating about risk through education
and outreach to the public, ensures that the activities we undertake
are responsive to your concerns. We'll depend on stakeholder
involvement at the national and local levels to implement the Strategy.
Section VI explains how we'll communicate with the public on these
issues.
We've formulated an integrated Strategy to characterize,
prioritize, and equitably address the public health impacts of HAPs in
urban areas. The Strategy relies on a strategic combination of
regulatory approaches and voluntary partnerships, both of which are
based on ongoing research and assessments, and include educational
outreach. Sections II through VI of this document explain how the
components described above work, how they'll be expanded and improved,
and how we expect to meet our goals to reduce risk from HAPs.
4. Overview of the Strategy
The Integrated Urban Air Toxics Strategy, in conjunction with the
overall air toxics program, will continue to lower human exposure to
air toxics by reducing emissions. Progress will be achieved by:
Completing MACT standards.
Addressing residual risk.
Implementing the urban air toxics strategy.
Enhancing our ability to characterize risk and estimate
exposures.
Developing new tools for monitoring progress with the
goals of the air toxics program.
Developing a monitoring network.
Effectively implementing and enforcing standards.
We'll achieve these objectives by following the guiding principles
of the air toxics program:
Working cooperatively and effectively with State and local
communities.
Focusing on communities, susceptible populations, and
sensitive ecosystems.
Providing cost-effective, common-sense solutions to
problems, through flexible strategies.
Developing and executing an effective education and
outreach program.
[[Page 38714]]
The Strategy will bring together the four basic components
(standards, initiatives, assessment, and outreach). It will be an
iterative and evolving process that will use existing programs and
tools to target risk reduction and to continually assess risk and
measure progress.
II. Federal Activities Related to the Integrated Urban Air Toxics
Strategy
A. What HAPs Pose the Greatest Threat in Urban Areas?
This section provides further discussion of what air toxics are,
the concerns they present, and describes how we evaluated and selected
a list of HAPs to guide our actions under the Strategy. In brief, we
evaluated the health effects information available for the 188 HAPs,
estimated emissions from all known sources using a variety of
techniques, assessed available air quality monitoring data, reviewed
existing studies, and produced a list of pollutants based on the
relative hazards they pose in urban areas, considering toxicity,
emissions, and related characteristics. From this effort, we
established a list of urban HAPs which pose the greatest threats to
public health in urban areas, considering emissions from major, area
and mobile sources. Among these urban HAPs are a subset of the 30 HAPs
having the greatest emissions contribution from area sources (the
``area source HAPs'').
1. Air Toxics Defined
Section 112(b) of the Act identifies 188 toxic chemicals as HAPs.
Hazardous air pollutants include a wide variety of organic and
inorganic substances released from industrial operations (both large
and small), fossil fuel combustion, gasoline and diesel-powered
vehicles, and many other sources. The major categories of toxic air
pollutants include volatile organic compounds (known as VOCs), metals
and inorganic chemicals, and semi-volatile organic chemicals. Volatile
chemicals are usually released into the air as vapor, while semi-
volatile organics and metals may be released in the form of particles.
Additionally, 17 of the 188 HAPs are defined as chemical groups rather
than unique chemicals. In evaluating the health effects, emissions and
monitoring information for these chemical groups we made specific
decisions regarding our treatment of the available information for the
group or the individual chemicals represented by the group (see the
technical support document in the public docket for the identification
of the urban HAPs).
Of the 17 chemical groups, polycyclic organic matter (POM) posed
particular complications. Polycyclic organic matter is defined in
section 112(b) of the Act as organic compounds with more than one
benzene ring and a boiling point greater than or equal to 100 deg.C,
which encompasses a complex mixture of thousands of polynuclear
aromatic hydrocarbons (PAH). Among the many PAH constituents of POM are
seven compounds (benzo[a]anthracene, benzo[a]pyrene,
benzo[b]fluoranthene, benzo[k]fluoranthene, chrysene,
dibenzo[a,h]anthracene, and indeno[1,2,3-c,d]pyrene) that we've
identified as probable human carcinogens. For the evaluation of POM as
a potential public health threat in urban areas, and for the subsequent
source category analysis, we used this group (referred to as 7-PAH) as
a surrogate for the much larger, more complex and diverse mixture of
POM.
The 188 HAPs have been associated with a wide variety of adverse
health effects, including cancer, neurological effects, reproductive
effects and developmental effects. Additionally, the specific health
effects associated with the various HAPs may differ, depending on the
particular circumstances of exposure (e.g., the amount of chemical, the
length of time a person is exposed, the stage in life of the person
exposed). We've classified many of the HAPs as ``known,'' ``probable,''
or ``possible'' human carcinogens and have included this information in
our Integrated Risk Information System.\19\ The HAPs can also be
described with regard to the part of the human body to which they pose
threats of harm. For example, neurotoxic pollutants cause harm to the
nervous system. Other effects include cardiovascular, and respiratory
effects, as well as effects on the immune system and reproductive
system. The severity of harm can range from headaches and nausea to
respiratory arrest and death. The level of severity differs both with
the amount and length of exposure and the chemical itself (e.g., how it
interacts with individual components of the nervous system). Some
chemicals pose particular hazards to people of a certain age or stage
in life or even based on their ethnic background. For example, some
HAPs are developmental toxicants. That is, exposure to certain amounts
of these chemicals during a woman's pregnancy or exposure of infants or
children can prevent normal development into a healthy adult. Other
HAPs are reproductive toxicants, meaning they may have the potential to
affect the ability of adults to conceive or give birth to a healthy
baby.
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\19\ The Integrated Risk Information System (IRIS), prepared and
maintained here at EPA, is an electronic data base containing
information on human health effects that may result from exposure to
various chemicals in the environment. IRIS was initially developed
in response to a growing demand for consistent information on
chemical substances for use in risk assessments, decision-making and
regulatory activities. The information in IRIS is intended for those
without extensive training in toxicology, but with some knowledge of
health sciences. Further information about IRIS, including the
information it contains, can be found on the IRIS website at http://
www.epa.gov/iris.
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In addition, we're currently investigating the health risks
associated with the mixture of compounds that comprise diesel exhaust
which originates primarily from mobile sources. While not specifically
listed as one of the 188 HAPs, diesel exhaust includes many HAPs,
including chemicals that fall into the group of POM chemicals, as well
as some HAP metals and volatile organic compounds. In addition, we're
concerned about the potential health risks from the particulate matter
component of diesel exhaust. Diesel particles are characteristically
small and fall within the size range of inhalable particles addressed
by the national ambient air quality standards for particulate
matter.\20\ Our draft health assessment of diesel emissions identifies
lung cancer as well as several other adverse respiratory health
effects, including respiratory tract irritation, immunological effects,
and changes in lung function, as possible concerns for long-term
exposures to diesel exhaust.\21\ If new diesel engine models are used
in an increasing share of the light duty fleet,\22\ concerns regarding
potential
[[Page 38715]]
health risks from diesel exhaust will become more significant.
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\20\ Inhalable particles are defined as particles of aerodynamic
diameter less than or equal to 10 micrometers.
\21\ Health Assessment Document for Diesel Emissions, SAB Review
Draft, U.S. Environmental Protection Agency, Washington, D.C. EPA/
600/8-90-057C, February 1998. The evidence comes from studies
involving occupational exposures and/or high exposure animal
studies. The Health Assessment, when completed, will recommend how
the data should be interpreted for lower environmental levels of
exposure. The draft Health Assessment is currently being revised to
address comments from a peer review panel of the Clean Air Science
Advisory Committee (CASAC Review of the Draft Diesel Health
Assessment Document, U.S. Environmental Protection Agency Science
Advisory Board, Washington, D.C. EPA-SAB-CASC-99-001. The CASAC will
review these revisions later this year.)
\22\ Diesel engines in highway and nonroad mobile sources are
numerous and widespread. Heavy-duty highway and nonroad diesel
engines are the largest sources of diesel exhaust emissions. While
diesel engines are used in a relatively small number of cars and
light-duty trucks today, vehicle and engine manufacturers are
developing new engine models that may be used in an increasing share
of the light-duty fleet, particularly light-duty trucks.
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As described above, HAPs and mixtures containing HAPs have the
potential to pose a variety of health risks depending on their chemical
characteristics, as well as the circumstances of human exposure. In the
following two sections, we describe our identification of HAPs of
particular concern in urban areas nationally.
2. The URBAN HAPs
Although information is limited regarding actual health risks posed
by specific HAP emissions, the availability of various other types of
information is sufficient to achieve our objective of identifying those
HAPs posing the greatest potential public health concern in the largest
number of urban areas. For the purpose of meeting the requirements of
section 112(k) and section 112(c)(3), we've listed in Table 1 the 33
HAPs that, on a national scale, we believe pose the greatest threat to
public health in the largest number of urban areas. Of these 33 HAPs,
29 appeared on the draft urban HAPs list published in our September 14,
1998 Federal Register document (63 FR 49240). Changes to the list
resulted from changes made to the method for urban HAPs selection, the
input data and the final selection criteria upon consideration of
comments received on the draft list and its supporting methodology.
\23\
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\23\ The final list includes beryllium compounds,
hexachlorobenzene, polychlorinated biphenyls and 1,1,2,2
tetrachloroethane, which hadn't appeared on the draft list, and
doesn't include bis(2-ethylhexyl)phthalate (DEHP), 1,4-
dichlorobenzene, methyl chloride and methylene diphenyl diisocyanate
(MDI), which were on the draft list.
Table 1.--List of Urban HAPs for the Integrated Urban Air Toxics
Strategy
[``Urban HAPs List'']
------------------------------------------------------------------------
HAP CAS No.+HAP
------------------------------------------------------------------------
acetaldehyde............................................ 75070
acrolein................................................ 107028
acrylonitrile........................................... 107131
arsenic compounds....................................... ..............
benzene................................................. 71432
beryllium compounds..................................... ..............
1,3-butadiene........................................... 106990
cadmium compounds....................................... ..............
carbon tetrachloride*................................... 56235
chloroform.............................................. 67663
chromium compounds...................................... ..............
coke oven emissions*.................................... 8007452
1,2-dibromoethane*...................................... 106934
1,2-dichloropropane (propylene dichloride).............. 78875
1,3-dichloropropene..................................... 542756
ethylene dichloride (1,2-dichloroethane)................ 107062
ethylene oxide.......................................... 75218
formaldehyde............................................ 50000
hexachlorobenzene....................................... 118741
hydrazine............................................... 302012
lead compounds.......................................... ..............
manganese compounds..................................... ..............
mercury compounds....................................... ..............
methylene chloride (dichloromethane).................... 75092
nickel compounds........................................ ..............
polychlorinated biphenyls (PCBs)........................ 1336363
polycyclic organic matter (POM)......................... ..............
quinoline............................................... 91225
2,3,7,8-tetrachlorodibenzo-p-dioxin (and congeners and 1746016
TCDF congeners)........................................
1,1,2,2-tetrachloroethane............................... 79345
tetrachloroethylene (perchloroethylene)................. 127184
trichloroethylene....................................... 79016
vinyl chloride.......................................... 75014
------------------------------------------------------------------------
+ Chemical Abstracts System number.
* HAPs with less significant emissions contributions from area sources.
This list of 33 urban HAPs includes not only those with emissions
from area sources, but reflects the integrated nature of the Strategy
by including those posing public health concerns in urban areas
regardless of emissions source type. Included among the 33 urban HAPs
are the 30 HAPs with greatest emissions contributions from area sources
(i.e., the area source HAPs'').
In response to publication of our draft list of urban HAPs, we
received comments regarding our inclusion of HAPs emitted predominantly
from non-area sources. Several commenters said that it was
inappropriate to include HAPs for which area source contribution was
low or negligible. Although section 112(k)(3)(B)(i) only requires that
we list HAPs emitted from area sources, we believe that the public is
exposed to complex mixtures of pollutants, and that these pollutants
are emitted by all types of sources. In other words, the risk from
exposure to HAPs has public health implications regardless of the
source or source type from which they are emitted. Therefore, in the
interests of best protecting public health in urban areas, we've listed
the 33 HAPs in Table 1 considering the aggregate exposure potential of
mobile,
[[Page 38716]]
area, and major stationary source emissions combined. At the same time,
as described below, we've also identified the 30 HAPs with the greatest
area source contribution. Under section 112(k), there aren't any
specific regulatory implications of listing the other three HAPs.
However, we'll use all 33 HAPs in prioritizing efforts to address risk.
Section 112(k)(3)(B) of the Act requires us to identify not less
than 30 HAPs that are estimated to pose the greatest threat to public
health in the largest number of urban areas ``as the result of
emissions from area sources.'' The Act, however, doesn't state that
such threats must be exclusively the result of emissions from area
sources. Therefore, from the list of 33 urban HAPs (i.e., the HAPs that
pose the greatest threat to public health in urban areas because they
ranked highest relative to the other HAPs in the analysis discussed
above), we identified those 30 HAPs with the greatest contributions of
national urban emissions from area sources, thus ensuring consistency
with the specification in section 112(k)(3)(B)(i). Without these
contributions from area sources, the threat from these HAPs would not
be as great. Emissions of only the 30 area source HAPs were considered
in the area source category listing required under section 112(c)(3)
and section 112(k) and described in section II.B. of this document. The
other three HAPs in Table 1 for which area sources are less significant
contributors to total emissions (i.e., those HAPs noted on Table 1 with
an asterisk), can be addressed, as appropriate, using our other
existing authorities, as described in section II.C. of this document.
During the public comment period on the draft Strategy, we received
substantial comment regarding the role of diesel engine emissions among
urban air pollutants, with several commenters suggesting that we
include diesel exhaust among the priority urban HAPs. As described
earlier, diesel exhaust, although not specifically listed among the 188
HAPs in section 112(b) of the Act, is a particular type of emission
which is composed of many HAPs. We agree with commenters that diesel
exhaust plays an important role among urban air pollutants, and, as
previously mentioned, we're investigating the health risks associated
with diesel exhaust. Meanwhile, we plan to address diesel exhaust in
our section 202(l) rulemaking for air toxics from motor vehicles and
their fuels.
It's important to note that the list in Table 1 was generated based
on our best estimates representing 1990 national baseline air toxics
emissions and ambient concentrations for urban areas. For example,
implementation of technology-based standards for coke ovens has reduced
the benzene, coke oven gases, and POM from these sources by 80 percent
(or 1,408 tons per year) since 1993. In addition, certain urban areas
have reduced other benzene emissions by as much as 30 or 40 percent.
Much of this reduction is attributable to the implementation of mobile
source reformulated gasoline requirements. To insure that we
appropriately target reductions of urban air toxics to support the
protection of public health, it will be important to reevaluate our
priorities as we develop emissions estimates and obtain more
comprehensive monitoring information for more recent years.
3. Method to Identify the Urban HAPs.
This section summarizes how we identified HAPs for the urban HAPs
list. Our identification methodology included three separate analyses.
The results of these analyses were compared using specific criteria in
order to identify the urban HAPs. The three analyses relied on a
variety of information types including toxicity information, emissions
estimates, ambient monitoring, and air quality modeling. The
methodology is summarized here and more fully described in the
technical support document (``Ranking and Selection of Hazardous Air
Pollutants''), which is available through the public docket and on our
website.
In 1997, we conducted an initial screening evaluation using a
preliminary methodology. In addition to identifying HAPs for which we
separately conducted a public review of our national emissions
inventory information, this evaluation provided us with the opportunity
for peer review of our preliminary methodology. Like the methodology
relied on for our final list, this preliminary methodology relied on
various types of information relevant to potential health risks posed
by the 188 HAPs, and it integrated the results of three relative
rankings using the different types of information. This initial
screening run provided a starting point for focusing improvements in
the national emissions inventory and for evaluating and refining our
methodology for selecting the list of urban HAPs.
The preliminary methodology and screening analysis were reviewed by
a panel of outside experts. In early January of 1998, the preliminary
methodology was presented to the peer review panel in a written report.
A full day session of the peer review panel was held on January 21,
1998 to discuss the methodology and underlying data. The reviewers
evaluated all facets of the methodology and its suitability for
identifying HAPs for the urban HAPs list, the relative value of various
data sources, the availability of additional data sources, the
scientific validity of assumptions, consistency across the methodology
and appropriate presentation formats. Reviewers provided oral comments
at the January 21 meeting, as well as written comments before and after
the meeting. The final methodology described here has incorporated
revisions made to address comments raised by the January 1998 peer
review.
Comments were also received from the public in response to our
publication of the draft list of urban HAPs (September 14, 1998, 63 FR
49240). Consideration of issues raised by some commenters led us to
modify certain aspects of both the identification methodology and the
underlying data inputs. These changes were not inconsistent with
recommendations made by the 1998 peer review panel. Consistent with
peer reviewer recommendations to use the available information in the
most robust manner, our final identification methodology integrates the
results of three separate analyses. These ranking analyses are
discussed in the following sections. Because each analysis focused on
different aspects of the available information, such that no one
analysis fully captured all important aspects of the urban air toxics
information, we and the peer reviewers agreed that all three of the
analyses should be performed and their results integrated, to yield a
more comprehensive methodology.
a. Analysis 1: Risk-related ranking indices. In the first of the
three analyses, we ranked HAPs by combining surrogates for toxicity
with surrogates for exposure into ranking indices. The surrogates for
toxicity were risk-based concentrations (RBCs) for inhalation or risk-
based doses (RBDs) for ingestion. The RBCs and RBDs were derived from
acute and chronic (cancer and non-cancer) health-based reference
values.\24\
---------------------------------------------------------------------------
\24\ Acute RBCs were set equal to risk management exposure
guideline levels (e.g., Acute Exposure Guideline Levels (62 FR
58839-51) or Emergency Response Planning Guidelines (American
Industrial Hygiene Association, 1998. Emergency response planning
guidelines and workplace environmental exposure guidelines.) for
mild, transient or no effects from short exposure periods, when
available. Additionally, two chronic RBCs and two chronic RBDs were
derived for each HAP for which the requisite data were available.
For carcinogenic HAPs, we compared the continuous exposure levels
associated with predicted upper-bound lifetime increased cancer
risks of one-in-one million and one-in-ten thousand to the
continuous exposure level (e.g., EPA's reference concentration)
estimated to be without adverse non-cancer effects in human
populations, including sensitive subgroups. We then set the two
chronic RBC or RBD values to the lower two of those three levels.
For other HAPs, both of the two chronic RBC or RBD values were set
to the continuous exposure level estimated to be without adverse
non-cancer effects in human populations, including sensitive
subgroups. A fuller discussion of these steps is included in the
technical support document.
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[[Page 38717]]
Types of information used as surrogates for exposure included
measured ambient concentrations and yearly emission estimates from
area, major and mobile sources in all urban areas nationwide. To
address the potential for certain HAPs to pose significant risks of
exposure through pathways other than inhalation (primarily by consuming
food with accumulated HAPs), one set of indices also incorporated
measures of bioaccumulation potential. As described in more detail in
the technical support document, a total of seven separate indices \25\
were calculated using these different types of toxicity and exposure
information. Lack of the requisite data prevented all seven indices
from being calculated for all of the 188 HAPs. The indices were
combined into a single HAP ranking.
---------------------------------------------------------------------------
\25\ Four of the indices relied on chronic RBCs and emissions or
monitoring information, two other indices relied on chronic RBDs
plus emissions and bioaccumulation information, and the seventh
index relied on acute RBCs and monitoring information.
---------------------------------------------------------------------------
During the public comment period, we received comments stating that
the role of monitoring information in the methodology should be
strengthened. Because ambient concentrations directly influence
people's exposure to HAPs and there are differences among HAPs in the
many variables affecting their behavior after being emitted into the
air, we agree that it is important that the monitoring information play
a strong role in this analysis. Relying solely on emissions information
in selection of the urban HAPs would ignore the many factors which
influence ambient HAP concentrations. Since the publication of the
draft list, we've expanded our monitoring database to increase both the
number of pollutants for which we have monitoring information and the
number of measurement values. We've also improved our treatment of non-
detect measurements, first by assuming undetected HAPs are present at
one half the detection limit (instead of omitting the observation), and
by omitting data altogether for HAPs having fewer than ten percent of
observations above the detection limit. These changes have improved the
technical basis of the ambient indices.
We also received comment stating that inappropriate weight was
assigned to those HAPs for which the acute index was developed. In the
analysis for the draft Strategy, the requisite information for
calculating this index (both an acute RBC and an estimate of short-term
peak exposure) were available for only 21 of the 188 HAPs. We
appreciate the issue raised by the commenter that, because of the
relatively small number of HAPs for which this index could be
calculated, it was not necessarily assigning HAPs the appropriate
emphasis. Through our improvements to the ambient database described
above, and by increasing the number of acute RBCs, we have addressed
this issue and reduced bias in this index.
Commenters also recommended increased emphasis on persistent,
bioaccumulative and multipathway pollutants for which non-inhalation
exposure pathways may be important. It's important to recognize that
persistent bioaccumulative toxics (PBTs) are also often multipathway
pollutants, because the pattern of exposure is frequently other than
inhalation. However, not all multipathway pollutants are PBTs.
One commenter said ``EPA should consider multi-pathway exposures
under 112(k) when there is sufficient evidence demonstrating that
airborne emissions of the listed HAP have both direct and indirect
exposure pathways, which have been clearly identified.'' Another said,
``It is appropriate to include compounds with exposure pathways other
than inhalation because these pathways are a true concern in urban
areas where atmospheric deposition of particulate phase HAPs is
occurring (i.e., lead, mercury, cadmium, dioxin and PCBs) and being
taken up by fish, garden vegetables or hand-to mouth activity observed
in infants.'' With regard to the PBTs, some commenters said PBTs should
have been given more thorough consideration for listing. They said the
risks from PBT exposure are high, and the concentrations of many PBTs
are higher in the urban than non-urban areas. We support the use of the
multipathway analysis to assess total human exposure, particularly in
the case of PBTs.
Additionally, commenters said that indices should be calculated so
that the size of index value differences among HAPs could be more
clearly observed, and any bias related to different numbers of HAPs
ranked by each index removed. Because we believe that both of these
issues are important, we changed the index calculation methodology to
address these recommendations. This change had its greatest impact on
the food chain pathway index, in which HAPs with high bioaccumulation
potential and ingestion toxicity received much higher index values.
Primarily as a result of this change, Table 1 now includes two
additional persistent, bioaccumulative HAPs--PCBs and
hexachlorobenzene--that were absent from the September 1998 draft list.
Hexachlorobenzene and PCBs, as well as mercury, cadmium, lead, POM and
dioxin (also identified as urban HAPs in Table 1), are among the
pollutants of concern for our Great Waters program. Additionally, PCBs,
mercury and dioxin were identified as pollutants of concern in the
Great Lakes by the International Joint Commission of the United States
and Canada. Hexachlorobenzene, PCBs, dioxins, mercury, and alkyl-lead
were targeted for virtual elimination in the Great Lakes in the 1997
Canada-United States ``Strategy for the Virtual Elimination of
Persistent Toxic Substances in the Great Lakes'', known as the
``Binational Toxics Strategy''.
Some commenters said that the identification methodology emphasized
cancer as a health effect and didn't consider other health effects
including asthma, birth defects and reproductive effects. The
methodology does, however, consider health effects other than cancer.
Reference values (RBCs and RBDs) for each HAP used in the analysis were
developed for the health effects believed to occur at the lowest
exposure. In the case of HAPs which, in addition to these other health
effects, also pose cancer risks, we developed RBC/RBD values for one-
in-one million and one-in-ten thousand predicted lifetime cancer risk
levels. These risk levels have historically been used to inform
environmental regulatory action. The cancer risk-based values were
compared to RBC/RBD values for the most sensitive non-cancer health
effect, and the lowest two RBC/RBD values for each HAP were used in the
calculation of the chronic indices. This step, and the inclusion among
the seven indices of an acute toxicity index based entirely on effects
other than cancer, was intended specifically to recognize the
importance of health effects other than cancer for some HAPs. Thus, we
believe that the assessment methodology provides a balanced
consideration of all health effects associated with each HAP, with
index calculation and the resultant ranking depending significantly on
effects other than cancer.
We also received comments regarding the toxicity information used
in the analysis. More specifically, commenters
[[Page 38718]]
suggested that in the case of 1,3-butadiene and vinyl chloride, we
should rely on draft assessments in progress rather than on assessments
currently available on IRIS. In the case of 1,3-butadiene, we agree
that the IRIS risk estimate is not an appropriate basis from which to
extrapolate human risk and the updated assessment has progressed to the
point where it is appropriate for use here.\26\ Use of this new
assessment, however, does not affect the presence of 1,3-butadiene on
the urban HAPs list. In the case of vinyl chloride, we've chosen to use
the Agency consensus assessment currently in IRIS rather than a draft
assessment that may yet change significantly. However, we've confirmed
that using the draft assessment for vinyl chloride wouldn't change its
status on the final urban HAPs list.
---------------------------------------------------------------------------
\26\ See April 27, 1999 internal memo, available in the public
docket.
---------------------------------------------------------------------------
Some commenters questioned the use of cancer-based RBC or RBD
values for certain HAPs to which the Agency has assigned a ``C'' weight
of evidence for carcinogenicity (``possible human carcinogens''). We
evaluated the supporting data for each ``C'' carcinogen that had been
proposed for listing to verify the appropriateness of the assessments
for use in this analysis. Many of these substances are currently the
subjects of research studies and EPA reassessment activities. In the
case of 1,4-dichlorobenzene, the currently available information led us
to modify our analysis so that the RBC and RBD values were based on
effects other than cancer. For all other ``C'' carcinogens, we retained
the RBC and RBD values. As updated information and assessments become
available for these and other HAPs, we intend to use that information
in analyses supporting future regulatory actions under the Strategy.
Other commenters questioned our assumptions as to the predominant
species of chromium and nickel in emissions and monitoring data.
Because the national monitoring and emissions data used in this
analysis don't differentiate among species of metals, we had to make
certain assumptions. To address the likelihood, supported by limited
available data, that all nickel present in emissions or ambient air
isn't in the form that is thought to have carcinogenic potential (e.g.,
nickel subsulfide and other insoluble forms), we applied the cancer-
based RBC for nickel subsulfide to 25 percent of the total emissions
and the ambient measurements for total nickel. We based this decision
on the assumption that no more than 50 percent of ambient nickel is
present in the insoluble form and no more than 50 percent of that is
present in the crystalline form. In the case of the ingestion pathway,
the non-cancer-based RBD was used. Regarding chromium, the limited
emissions and monitoring information available for both hexavalent and
total chromium indicated that approximately two thirds of the chromium
present in ambient air or national emissions is likely to be other than
the hexavalent form. Thus, we applied the cancer-based RBC for
hexavalent chromium to 35 percent of the total emissions and to 35
percent of the ambient measurement.
A few commenters requested an analysis of uncertainties surrounding
the calculations. To the extent that it's possible to conduct an
uncertainty analysis, we believe the process already includes one. The
calculation and presentation of seven different ranking indices,
instituted in response to comments from the January 1998 peer review
panel, is presented in graphic form in the technical support document.
These graphs show the range of ranking indices for each HAP, which we
regard as a measure of some of the uncertainty associated with this
identification methodology.
b. Analysis 2: Review of existing risk assessments and hazard
rankings. For the second analysis, we reviewed a number of air toxics
risk assessments or hazard rankings conducted previously by EPA staff,
State agencies or others.\27\ We selected 14 of the available studies
for use in this analysis, because they were sufficiently broad in the
pollutants evaluated, they included area sources of HAPs, and they
focused on the risks presented in urban areas. Each study provided a
risk-based ranking of HAPs, with separate rankings for cancer and, when
available, other health effects. The rankings within each study were
converted to a scale common to all of the studies, and the values were
summed across the studies, providing a total score for each HAP.
Because section 112(k) places special emphasis on area sources of HAPs,
scores were developed both for studies that considered combined
emissions from major, area, and mobile sources, and for studies that
considered emissions from area sources alone. From this analysis, we
identified those HAPs that, when compared across studies, consistently
ranked high.
---------------------------------------------------------------------------
\27\ These assessments and rankings, and the details of this
analysis, are described in the technical support document for the
identification of the urban HAPs, which is available in the public
docket.
---------------------------------------------------------------------------
c. Analysis 3: Cumulative Exposure Project (CEP). In the third
analysis, we used information provided by the CEP.\28\ In the CEP, the
Assessment System for Population Exposure Nationwide (ASPEN) model was
used with preliminary estimates of 1990 HAP emissions from all source
types to predict long-term average concentrations at the census tract
level for 148 HAPs. For some pollutants, modeled concentrations were
augmented with estimates of background levels that were intended to
represent contributions from natural sources, as well as historic
emissions of persistent pollutants. The estimated ambient
concentrations were then compared to risk-based concentrations (termed
benchmarks by the authors) intended to represent either continuous
exposure levels associated with a one-in-a-million upper bound estimate
of excess lifetime cancer risk, or continuous lifetime exposure levels
associated with no significant risks of adverse non-cancer effects
(e.g., EPA's Inhalation Reference Concentration (RfC)). As stated
earlier, estimated concentrations greater than risk-based
concentrations should be viewed as indicators of a potential health
problem, and not as a characterization of health risks. While we
recognize certain limitations associated with this initial attempt at
modeling HAP concentrations nationwide, and its inappropriateness for
use in drawing conclusions at small geographic scales, this modeling
effort is useful as a national screening tool. In this analysis, we
used the information generated by the CEP for urban areas and
identified those HAPs for which the modeled concentrations exceeded
risk-based concentrations in the greatest number of urban census
tracts.
---------------------------------------------------------------------------
\28\ See footnotes 13 and 14.
---------------------------------------------------------------------------
We received comments on several aspects of our use of the CEP
analysis in our method for identifying the draft urban HAPs list. Some
commenters felt that the addition of background concentrations was
inappropriate. Additionally, some commenters questioned the
appropriateness of the reference values used for some HAPs. We
recognized that the background value for one of the HAPs (bis(2-
ethylhexyl)phthalate or DEHP) was wrong, and we agreed that we should
focus the analysis on modeled concentrations resulting from
controllable sources. Additionally, we're currently using updated risk-
based concentrations which, in some cases, differ from those used in
the CEP analysis. Consequently, prior to using this analysis as part of
our final methodology, we repeated the analysis
[[Page 38719]]
for the subset of affected HAPs using the modeled concentrations
resulting only from current area, major and mobile sources (i.e.,
without addition of a background value) and an updated set of risk-
based concentrations. We've described the details of this reanalysis in
the technical support document in the public docket.
d. Integration of the three analyses. In selecting the urban HAPs
for the integrated Strategy, we compared the results of these three
separate ranking analyses and applied the following criteria when
integrating their results. We selected those HAPs for which a publicly
reviewed baseline national emissions inventory was available \29\ and
which had been either:
---------------------------------------------------------------------------
\29\ On June 20, 1997 we published notice of a draft listing of
source categories for regulation under section 112(c)(6) of the Act
(62 FR 33625). As part of this notice, we requested public review
and comment on the baseline national emissions inventory for the
seven pollutants identified under section 112(c)(6). In the fall of
1998, we requested and obtained public review on our baseline
national emissions inventory for 40 HAPs, five of which had also
been reviewed as part of the rulemaking process under section
112(c)(6). During both of these public reviews, many comments were
received on various aspects of the emissions information, and we
considered these comments in making improvements to the baseline
national emissions inventory for those HAPs. Details concerning
these two public reviews and documentation of the resultant
inventory information are presented in two documents (``1990
Emissions Inventory of Section 112(c)(6) Pollutants: Final Report''
and ``1990 Emissions Inventory of 40 Candidate Section 112(k)
Pollutants'') available at www.epa.gov/ttn/uatw/112c6/112c6fac.html
and www.epa.gov/ttn/uatw/112k/112kfac.html, respectively. The public
reviews provided us with an inventory that was appropriate for our
use on a national scale, in the identification of the urban and area
source HAPs. However, this baseline inventory may require certain
modifications for small scale detailed analyses such as those
described in section II.B.
---------------------------------------------------------------------------
Identified by at least two of the three analyses
(regardless of area source contribution); or
Identified by at least one of the three analyses and
having an area source contribution to total emissions of at least 25
percent.
The second criterion was set in recognition of the area source
emphasis of this integrated Strategy. These criteria produced an
integrated list of 33 urban HAPs.
As discussed earlier, section 112(k)(3)(B) of the Act requires us
to identify not less than 30 HAPs that are estimated to pose the
greatest threat to public health in the largest number of urban areas
as the result of emissions from area sources (``the area source
HAPs''). To identify these 30 area source HAPs, we ranked the list of
33 urban HAPs by percent contribution to national urban emissions from
area sources and selected the 30 urban HAPs with the greatest area
source contributions. The remaining three urban HAPs (i.e., coke oven
emissions, 1,2-dibromoethane, and carbon tetrachloride) have less
significant emissions contributions from area sources and aren't among
the 30 area source HAPs considered in the area source category listing
described in section II.C.
Some commenters on the draft Strategy were concerned that the
percent contribution to national urban emissions from area sources was
too low for some of the HAPs on the draft area source HAPs list, thus
not placing enough emphasis on risks from area sources. While we note
that the percent contribution from area sources for the area source
HAPs ranges down to as low as 2.9 percent, these values apply to total
urban emissions nationally. In individual urban areas as well as in
local communities within large areas, area sources may play a much
larger role. Because the Act requires us to select not less than 30
area source HAPs and because the percentage of emissions from area
sources will vary, we consider this an appropriate approach to identify
the area source HAPs on which the Strategy will focus in reducing area
source emissions and any associated health risks in individual urban
areas nationwide.\30\ Accordingly, this list of 30 area source HAPs was
used in identifying the list of new area source categories for which
standards will be addressed as required by section 112(c)(3) and
section 112(k)(3)(B)(ii).
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\30\ Given the uncertainties and limitations associated with the
information upon which the 30 area source HAPs selection was based,
we don't believe that identifying greater than the statutory minimum
of 30 HAPs is warranted at this time.
---------------------------------------------------------------------------
B. How does EPA Plan to Address Requirements for Area Sources of HAPs?
1. Area Source Category Selection Approach in Draft Strategy
The Clean Air Act includes two provisions--sections 112(c)(3) and
112(k)(3)(B)(ii)--that instruct us to identify and list source
categories that contribute to the emissions of the 30 ``listed'' (or
area source) HAPs, and that are, or will be, subject to standards under
section 112 of the Act. The language in these two sections differs
slightly. Section 112(c)(3) requires us to list, pursuant to section
112(k)(3)(B), sufficient categories of sources ``to ensure that area
sources representing 90 percent of the area source emissions of the 30
[listed] hazardous air pollutants'' are subject to regulation under
section 112. As explained in the draft Strategy, this would seem to
allow us to regulate sources accounting for either 90 percent of the
combined emissions of all of the 30 area source HAPs, or 90 percent of
the emissions of each of the 30 area source HAPs. By contrast, section
112(k)(3)(B)(ii) requires us to identify sufficient categories to
``assure that sources accounting for 90 per centum or more of the
aggregate emissions of each of the 30 identified hazardous air
pollutants'' are subject to standards under section 112(d). This
language explicitly requires us to regulate sources accounting for 90
percent of the emissions of each of the 30 area source HAPs. As a
result, in the draft Strategy we adopted the interpretation that
allowed us to read the two provisions consistently, and assembled a
draft list of area source categories representing 90 percent of the
emissions of each of the 30 area source HAPs.
We adopted a two-step process for selecting the source categories
for the draft list. First we listed all of the area source categories
already subject to area source standards. For each of these source
categories we identified their percentage contribution to the total
area source emissions for each of the 30 area source HAPs. We then
listed additional area source categories as necessary, listing the
largest contributors first, until the list of area sources represented
90 percent of the emissions for each of the 30 area source HAPs.
2. Improvements in Area Source Category Information
Since issuing the draft Strategy, we've significantly improved our
emissions inventory data for many area source categories. (The final
information on the subset of pollutants of the baseline inventory used
in this analysis and a description of the changes made is in the
technical support document ``Emissions Inventory of 40 Candidate
Section 112(k) Pollutants; Supporting Data for EPA's Section 112(k)
Regulatory Strategy'' available at www.epa.gov/ttn/uatw/112k.) The
draft inventory for the subset of the HAPs of the baseline emission
inventory was available twice for public review. From this extensive
review, we received over 200 comments on the inventory, which were
addressed where data were provided. Based on the large number of public
comments, and information from internal comments, we've made many
changes to the baseline emissions inventory used to identify HAP
sources. In particular, better emission information for many of the
sources subject to section 112(d) MACT standards made a significant
difference in the inventory. The percent
[[Page 38720]]
contribution from major versus area sources for each source category
was also refined and updated based on better information. For many MACT
standards, we now have lists of regulated facilities, which allows for
better designation of major facilities in the inventory.
We received several comments requesting that the area source
categories designated as ``SIC combined'' be broken down into
individual SIC (or Standard Industrial Classification) codes. Examples
of these source categories from the draft Strategy were Electronic and
other Electric Equipment Manufacturing (SICs combined), Food Products
(SICs combined) and Instruments and Related Products (SICs combined).
The way in which the SIC codes were combined didn't reflect a technical
analysis of whether these SIC codes could in fact be combined into
single source categories for regulatory purposes. In general, the
combinations included large numbers of different industry types which
would later have to be broken down into separate projects and separate
source categories for regulation. In addition, it was difficult to
discern from the list which subsets of the multiple SIC codes were
actually emitting the pollutants of concern and would eventually be
subject to regulation.
For the final Strategy, we listed source categories (presented in
Table 3) that primarily represent single SIC codes in order to more
accurately identify the sources that may ultimately be subject to
regulation. The exception to this is when the source category was
derived directly from information obtained during the development of a
section 112(d) standard (e.g., Paint Stripping Operations), in which
case the area source category described for the standard may
incorporate multiple SIC codes.
Despite these improvements in the baseline, there are still
uncertainties in the emissions reported in some categories and in some
of the TRI reporting. Our awareness of these uncertainties is based on
our improved knowledge of some source categories and emission
estimation methods, and also on an improved recognition of the limits
of our data for other source categories. For the development of the
area source category listing, we needed to use the baseline inventory
information on a more refined scale (at the source category level) than
we did in development of the HAPs list where we used the baseline
inventory on a national scale. For this reason, we sometimes modified
the individual source category information in various ways, such as by
combining source categories' emission information. In a few cases, we
changed the emission information related to tonnage for some source
categories. These adjustments to tonnage didn't affect the total
emissions used on a national scale. As a result of these changes, the
information presented in the area source category analysis (source
category names and tonnage) may not always match the way source
categories are presented in the final baseline inventory.
Examples of some changes made in the area source category analysis
include combining all the emissions from human and animal cremation,
because they will be addressed under one rulemaking (Other Solid Waste
Incinerators). For the same reason, we combined all the emissions from
institutional and commercial heating, as this will be addressed under
one rulemaking (Institutional/Commercial Boilers). We also included the
area emission estimates for the source category Paint Stripping
Operations, because they were inadvertently excluded from the final
baseline inventory. We changed the name of the source category listed
as Chlorine Production in the baseline to Mercury Cell Chlor-Alkali
Plants. This revised source category name better represents the portion
of the industry which will be ``subject to standards''. Additional
changes are described in the technical support document for identifying
area source categories.
As discussed in section II.A.2., several of the 30 area source HAPs
listed in the draft Strategy have been replaced based on updated
information. The result is the addition of the following HAPs to the
list of 30 area source HAPs: beryllium compounds, hexachlorobenzene,
polychlorinated biphenyls (PCBs), quinoline, vinyl chloride, and
1,1,2,2,-tetrachloroethane. Quinoline was included in the draft
Strategy list for major sources only, but based on updated information
is now included for area sources. These changes in the area source HAPs
list have also led to changes in the area source categories list.
3. Area Source Category Selection Approach in Final Strategy
We've reviewed the provisions in sections 112(c)(3) and
112(k)(3)(B)(ii), and believe the most reasonable interpretation of the
Act is still the interpretation adopted in the draft Strategy. In order
to comply with the requirements of both sections, we must list those
source categories representing 90 percent of the emissions of each of
the 30 area source HAPs.
We have, however, changed our criteria for selecting the source
categories contributing to emissions of the 30 area source HAPs. Again
we've adopted a two-step approach with the first step being similar to
that in the draft Strategy. In the first step we've identified area
sources that contribute to emissions of the 30 area source HAPs, and
that are subject to existing standards, or will be subject to standards
that are currently being developed. These area source categories have
already been listed for regulation under the Act. As in the draft
Strategy, for each of these source categories we identified the percent
contribution to the total area source emissions for each of the 30 area
source HAPs.
In the second step, we've decided, at this time, to add only those
area source categories that contribute at least 15 percent of the total
area source emissions of any of the individual area source HAPs to the
list of source categories. We've adopted this criterion to account for
the uncertainties in our current inventory data. While we've been able
to significantly improve our baseline emissions inventory data, data
gaps and uncertainty still remain. This is particularly true as we move
to a more refined scale to determine emissions at a source category
level. As a result, we've decided to only list new categories of area
sources at this time if the inventory data demonstrate that each newly
listed area source category contributes at least 15 percent to the
national urban emissions of at least one of the 30 area source HAPs.
Once listed, we've counted the percent contribution, even if less than
15 percent, to emissions of any other area source HAPs, because once
the source is subject to regulation its emissions of any of the 30 area
source HAPs can be counted toward the 90-percent goal for each of the
area source HAPs. Likewise, when we subject these source categories to
regulation we'll evaluate regulation of all 188 HAPs, not just the 33
urban HAPs listed under this Strategy.
The result of these new criteria for the source selection process
is that the current list doesn't, at this time, contain area source
categories representing 90 percent of the emissions of each individual
HAP. It's important to make clear that we still intend to meet our
statutory obligation to list area sources accounting for 90 percent of
the emissions of each of the 30 area source HAPs. We've chosen to
complete this list in stages, adding to, deleting from, or shuffling
the list as we gather more and improved data. This first stage lists
those area source categories that contribute at least 15 percent, and,
[[Page 38721]]
therefore, we're confident add real contributions to the total area
source emissions of a particular area source HAP. As discussed in
section IV.D., we'll be conducting an initial national risk assessment
in the spring of 2000 that will be used in part to prioritize which
standards to pursue first. This initial assessment will use the much
better-developed 1996 NTI. We'll use this information as part of our
process to reevaluate the source categories listed in the Strategy.
Based on this updated information, we may decide to remove an area
source category listed here if, for example, the reason for the listing
was inaccurate (e.g., faulty reporting to TRI) or if no urban area
sources exist. We'll also use this assessment to evaluate area source
categories to be added to the list.
We believe this iterative approach is consistent with the general
scheme for listing and regulating area sources under section 112 of the
Act. Section 112 establishes two distinct steps for regulating
emissions of HAPs--one for listing source categories under 112(c) and
one for setting standards under 112(d). Section 112(k) incorporates
this two-step approach. The source category listing step (see for
example, sections 112(c)(1) and (9)) is intended to be an ongoing
process. Under section 112(e)(4), listing of a particular source
category isn't considered final agency action until EPA issues emission
standards for that source category. Thus, we feel the list of area
source categories is flexible both for the addition of new area source
categories and/or removal of area source categories, through public
notice. We believe our current approach for fulfilling the 90-percent
requirements in sections 112(k)(3)(B) and 112(c)(3) is consistent with
the overall structure of section 112 which authorizes us to treat the
list of area source categories as a work in progress.
One alternative to this iterative approach would be to attempt to
list all sources accounting for 90 percent of the emissions of each
individual area source HAPs as we did in the draft Strategy, and to
make changes in the future as data are collected and improved. We
decided against this approach because it would involve listing many
area source categories contributing very small amounts of a particular
HAP based on data that we consider in many instances to still have
significant uncertainty despite numerous improvements. In the end, we
believe the two approaches aren't meaningfully different. Even if we
officially ``listed'' these small contributors, their status on the
list would be tentative at best. Under the current approach, we've
identified all of these small contributors in the supporting materials
for this rulemaking, but we've chosen not to list them under section
112(c)(3) at this time, if the emissions currently appear to be less
than 15 percent of the total area source emissions of any individual
area source HAP. Under both approaches the list will likely change with
new and improved inventory data.
4. New Area Source Category List
With the two-step approach described above, we identified the area
source categories listed in Tables 2 and 3. In step one, we identified
those area source categories that contribute to emissions of the 30
area source HAPs, and that are subject to existing standards, or will
be subject to standards that are currently being developed. These
source categories are provided in Table 2. We've included Hazardous
Waste Combustors on this list, despite the fact that information
related to the percentage contribution from area source Hazardous Waste
Combustors hasn't yet been completely defined, because the Hazardous
Waste Combustor NESHAP (as proposed) would subject area sources to the
same standards as major sources. Once we determine the percentage of
urban area emissions from the area source categories affected by this
rule, their emissions will be counted toward the 90-percent requirement
for the appropriate HAPs.
Table 3 includes those new area source categories being listed
under section 112(c)(3) for the first time. These area source
categories were identified in step two of our selection process, which
identified area source categories contributing at least 15 percent of
the total area source emissions of any of the 30 area source HAPs.
Table 2.--Area Source Categories Already Subject to Standards or Which Will Be Subject to Standards
----------------------------------------------------------------------------------------------------------------
Chromic acid anodizing Industrial boilers
----------------------------------------------------------------------------------------------------------------
Commercial Sterilization Facilities.............. Institutional/Commercial Boilers.
Other Solid Waste Incinerators (Human/Animal Medical Waste Incinerators.
Cremation).
Decorative Chromium Electroplating............... Municipal Waste Combustors.
Dry Cleaning Facilities.......................... Open Burning Scrap Tires.
Halogenated Solvent Cleaners..................... Portland Cement.
Hard Chromium Electroplating..................... Secondary Lead Smelting.
Hazardous Waste Combustors....................... Stationary Internal Combustion Engines.
----------------------------------------------------------------------------------------------------------------
Table 3.--New Area Source Categories Being Listed
----------------------------------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------------------------------
Cyclic Crude and Intermediate Production..... Municipal Landfills.
Flexible Polyurethane Foam Fabrication Oil and Natural Gas Production.
Operations.
Hospital Sterilizers......................... Paint Stripping Operations.
Industrial Inorganic Chemical Manufacturing.. Plastic Materials and Resins Manufacturing.
Industrial Organic Chemical Manufacturing.... Publicly Owned Treatment Works.
Mercury Cell Chlor-Alkali Plants............. Synthetic Rubber Manufacturing.
Gasoline Distribution Stage I.
----------------------------------------------------------------------------------------------------------------
[[Page 38722]]
5. Meeting the Requirement To List Area Sources Representing 90 Percent
of Emissions
The current list of area source categories doesn't include
categories representing 90 percent of the emissions of each of the 30
area source HAPs. The current list meets the 90-percent or greater
requirement for 11 31 of the 30 area source HAPs. For 10
32 other HAPs, the list accounts for at least 80 percent of
the emissions, and for ethylene dichloride the list accounts for
approximately 78 percent of the emissions. Improved inventory data may
demonstrate that the current list of area sources already meets the 90-
percent requirement for some of these HAPs. The remaining HAPs on the
list represent less than 75 percent of the emissions: arsenic
compounds, cadmium compounds, chromium compounds, hexachlorobenzene,
lead compounds, manganese compounds, nickel compounds, and
polychlorinated biphenyl.
---------------------------------------------------------------------------
\31\ Including 1,1,2,2-tetrachloroethane, 1,2-dichloropropane,
polycyclic organic matter, acetaldehyde, acrolein, benzene, dioxin,
furans, ethylene oxide, formaldehyde, quinoline, and
tetrachlorethylene.
\32\ Including 1,3-butadiene, 1,3-dichloropropene,
acrylonitrile, beryllium compounds, chloroform, hydrazine, mercury
compounds, methylene chloride, trichloroethylene, and vinyl
chloride.
---------------------------------------------------------------------------
In the case of the metal compounds for arsenic, cadmium, chromium,
lead, manganese and nickel, we know we haven't listed enough new area
source categories to say that we've completely addressed the emissions
from these area source HAPs. In the case of the metal HAPs, there tend
to be numerous source categories, each contributing only a small
percentage of the HAPs. In many cases, this is because the source
categories have already reduced emissions due to other control programs
in place. However, because these pollutants can have significant health
effects, we'll be developing a separate strategy to specifically
address emissions of these metals. As part of our initial evaluation of
the area sources of these HAPs, we're including the following source
categories for further evaluation (our current data indicate that each
contributed five to twelve percent of area source emissions of one or
more of these metal HAPs):
Sewage Sludge Incineration.
Aluminum Foundries (castings).
Steel Foundries.
Secondary Copper Smelting.
Stainless and Nonstainless Steel Manufacturing--Electric
Arc Furnaces (EAF).
Iron Foundries.
Plating and Polishing.
Cadmium Refining and Cadmium Oxide Production.
Autobody Refinishing Paint Shops (called Paint
Applications in the baseline inventory).
Pressed and Blown Glass and Glassware Manufacturing.
We aren't listing these categories for possible regulation at this
time; however, after further evaluation of these categories, some or
all may be added to our area source category list.
We haven't listed any area source categories which specifically
contribute emissions of PCBs or hexachlorobenzene, although some of the
source categories listed may emit one or both of these HAPs. We've
decided to wait on listing any source categories contributing to area
source emissions of hexachlorobenzene or PCBs, because these HAPs
weren't included in the candidate list of HAPs for which we collected
detailed inventory data in preparation for the Strategy; therefore the
emissions inventory baseline for these HAPs didn't receive the same
level of review. We've already begun efforts that may supplement our
inventory data for these HAPs, and, as appropriate, we'll list new area
source categories when we collect more data and make the list available
through public notice. For example, we're currently researching the
sources of PCBs, and whether PCBs may be the product of incomplete
combustion. The findings of this research could significantly change
the emissions inventory for this pollutant. Even though we're not
listing source categories of these pollutants at this time, like the
metals, we're concerned about the potential health effects of these
pollutants, and we have a number of programs across EPA working to
address them (e.g., the PBT initiative and the Binational Toxics
Strategy).
We anticipate evaluating the source categories for these and the
other remaining HAPs for which we haven't reached a 90-percent emission
reduction, including the six metal HAPs, PCBs and hexachlorobenzene,
when we conduct the initial risk assessment in the spring of 2000
(discussed in section IV.D.). We intend to adjust this list in the
event that new information comes forward and will complete the list by
2003.
6. Comments on Specific Source Category Listings
Several comments on the draft Strategy addressed the need to add or
delete certain source categories. Many of these comments have been
addressed with the changes described above to the emissions inventory
and the urban HAPs list. Many of these commenters asked that we add
several source categories (such as dry cleaners, retail gas stations,
print shops, autobody shops, and beauty shops). Some of these source
categories are already addressed by area source MACT standards (e.g.,
dry cleaners). Many of the others involve organic emissions from
consumer products such as surface coatings, metal cleaning, solvents,
personal care products, and household cleaning products. While these
products may be responsible for a significant fraction of the emissions
of several of the 30 area source HAPs, we believe section 112 isn't
necessarily the most appropriate regulatory mechanism for controlling
them. For many of these emissions, we believe section 183(e) provides
the more useful authority. For example, in September 1998, we published
a VOC rule under section 183(e) for household consumer products. This
rule will affect approximately 220 consumer product manufacturers and
importers nationwide. At the same time we published two other national
rules which address VOC emissions from consumer and commercial
products: Architectural Coatings and Automobile Refinishing coatings.
These combined rules should provide reductions of over 2.4 million tons
of VOC per year. Automobile Refinishing is also included on our list
for further evaluation due to metals emissions.
Similarly, we don't believe section 112 is the most appropriate
tool to address refueling emissions at gas stations. Instead,
consistent with Congress' intent, we've chosen to regulate these
emissions through sections 182(b)(3) and 202(a)(6). The ``stage II''
and ``onboard requirements'' programs developed under these authorities
will lead to reductions of VOCs and HAPs of 300,000 to 400,000 tons per
year (63 FR 17844, April 10, 1998).
Commenters also said the list should focus on source categories
emitting the deadliest HAPs. As we explained in section II.A., toxicity
was one of the key criteria in all of the rankings used to develop the
list of 30 area source HAPs. As a result, pollutants such as dioxins
and beryllium compounds, because of their high toxicities, are included
on the list of 30 area source HAPs, despite relatively small overall
emissions in urban areas. Thus, toxicity is built into the list of
source categories selected for regulation because toxicity is built
into the list of pollutants used to select these source categories.
[[Page 38723]]
7. Additional Requirements for Area Source Categories Already Subject
to MACT
Several of the source categories listed today (e.g., Municipal
Landfills, and Publicly Owned Treatment Works) are already in source
categories covered by MACT standards for major sources. As discussed in
section II.C.1., we'll develop area source standards for the listed
area source categories. When it's practical during our rulemaking
activities, we'll attempt to combine information gathering for area and
major sources. A good example is the development of the MACT standard
for municipal landfills. This source category is required to be
evaluated for major sources as a MACT standard, and we've expanded our
data base to include area sources as well. In other instances, such as
for Publicly Owned Treatment Works, the MACT standard was already
proposed and is near promulgation, so it isn't possible to coordinate
rulemaking for the major and area sources at the same time.
In the cases where standards already apply to listed area sources
(e.g., Municipal Waste Combustors, Medical Waste Incinerators, Chromium
Electroplating, and Halogenated Solvent Cleaning), we'll coordinate the
need for additional regulation through assessments we'll be conducting
under the section 112(f) residual risk program. Information on how
we'll conduct assessments on residual risk are discussed in the
residual risk report.\33\ We'll also be evaluating the effectiveness of
the standards that are already in place through information provided by
State, local and Tribal air agencies. Also, as we continue to assess
our progress in meeting our air toxics Strategy goals, we'll reevaluate
the need for additional area source standards to ensure that the 90-
percent requirement and our other goals are met.
---------------------------------------------------------------------------
\33\ U.S. EPA. Residual Risk Report to Congress. EPA-453/R-99-
001. March 1999.
---------------------------------------------------------------------------
C. What Regulatory Actions Will EPA Take To Implement the Strategy?
Consistent with our goals, we intend to assess cumulative risks to
the public from HAP exposures resulting from stationary (area and
major) and mobile sources. Based on the outcome of these assessments,
we'll undertake the needed regulatory actions using the appropriate
authorities. These actions include developing area source standards,
which are discussed in sections II.C.1. though II.C.5. We'll also
regulate motor vehicle and fuel HAPs as described in section II.C.6.
Finally, we'll develop additional major source standards under section
112(d), section 112(f), and other programs under the Act, as needed to
reach our goals. The role of major stationary sources in the Strategy
is discussed in more detail in section II.C.7. Our approach for
addressing combinations of source types (e.g., at airports) is
described in section II.C.8.
1. Our Approach to Developing Area Source Standards
We plan to pursue a tiered approach that will consider three
standard setting processes. The specific process selected for a
particular source category will depend on the criteria outlined below.
The three tiers of standard setting processes that will be considered
are:
Tier 1--MACT standard process;
Tier 2--Source category specific GACT standard process;
and
Tier 3--Flexible GACT process.
We received a number of comments on the draft Strategy stating that
our regulatory intentions for area sources were unclear. In addition,
we received comments requesting flexibility for State/local/Tribal
governments and for emission sources in implementing these area source
standards. The following discussion attempts to provide the needed
clarifications and to explain our approach to developing a flexible
regulatory development process.
Tier 1--MACT standards. We'll develop MACT standards in accordance
with the process outlined in section 112(d)(3) for those area sources
whose emissions pose the greatest threat to human health and the
environment and for which the technology to achieve maximum reductions
in HAP emissions is appropriate. Section 112(d)(3) requires the
standards to reduce HAP emissions as much as is achievable, considering
the cost of these reductions, effects on health or the environment
(other than air), and energy requirements.
Section 112(d)(3) requires us to use a minimum statutory baseline
(``floor'') when setting MACT standards. For new sources, the MACT
standards for a source category or subcategory must be at least as
stringent as the emission control achieved in practice by the best
controlled similar source. The standards for existing sources can be
less stringent than standards for new sources, but they can't be less
stringent than the average emission limitation achieved by the best-
performing 12 percent of existing sources (excluding certain sources)
for categories or subcategories with 30 or more sources, or by the
best-performing 5 sources for categories or subcategories with fewer
than 30 sources.
We've issued MACT standards for area sources in previous cases. For
example, in the chromium electroplating national emission standards for
hazardous air pollutants (NESHAP), we developed MACT standards for area
sources because of the high toxicity of chromium. Similarly, in the
Portland Cement NESHAP, we determined that MACT controls were
appropriate because of the quantity and toxicity of the HAPs being
emitted from area sources. In addition, both of these source categories
have numerous, widespread sources.
Tier 2--Source category specific GACT standards. While we may
develop MACT standards for some area sources, we expect most sources
will be subject to GACT standards developed in accordance with section
112(d)(5). As with MACT standards, GACT standards would be developed
for a specific source category, but they would be based on the use of
GACT as opposed to the use of MACT. This approach will be used to
address source categories that present a human health risk or
environmental concern, but where GACT is a more appropriate approach
for reducing HAP emissions than MACT. To make these standard-setting
decisions, we'll consider economic feasibility and other factors that
could lead us to GACT.
Tier 3--Flexible GACT process.
Considering the large number and diversity of area sources and
limitations in the data and information currently available for many of
them, we expect it may be appropriate in some cases to develop flexible
requirements that would apply to several area source categories where
more flexibility is appropriate (e.g., where there are very few area
sources, they are confined to a limited geographic area or areas, or
they contribute to localized public health or environmental risks).
Under this option, we might develop general requirements such as a
process rule similar to section 112(g), which would be applicable to
area sources in several source categories. These general requirements
could outline procedures for determining what constitutes ``generally
available control technology'' in this context. By following these
procedures, States, local governments, and Tribal agencies could elect
to develop GACT for the area sources. We'd review the resulting
standards to ensure they were developed following the procedures
contained within the general requirements and, if appropriate, we'd
adopt the standards as GACT for these area sources.
We believe this approach presents several advantages. It could be
implemented in a manner that permits State, local and Tribal agencies
to
[[Page 38724]]
address cumulative risk posed by exposures to HAP emissions from many
different source categories. It also permits greater flexibility in
tailoring GACT to individual area sources or area source categories
which may contribute to an undue public health risk in a particular
area. For example, a State, local or Tribal agency could tailor GACT to
a particular source by requiring potentially more stringent controls
when the source contributes emissions that, when aggregated with
emissions from other sources in the area, pose health risk concerns.
They could also require less stringent controls when the source is in
an area where exposures to aggregated emissions don't present
significant concern.
To supplement our general requirements, we may choose to issue
control technique guidelines or alternative control technology
documents to provide information on generally available control
technologies for controlling HAP emissions.
2. The Legal Basis for Using GACT for Area Source Categories
Section 112(k)(3)(B)(ii) directs us to assure that the listed area
sources are subject to standards under section 112(d), which includes
two levels of standards--``maximum achievable control technology''
(MACT) and ``generally available control technology'' (GACT). We read
the requirement in section 112(k)(3)(B)(ii) to give us flexibility in
deciding which level of control to apply to a given source category.
Unlike MACT, which is specifically described in sections 112(d)(2)
and (3), the meaning of GACT, or of what is ``generally available,'' is
not defined in the Act. Section 112(d)(5) authorizes the Administrator
to:
[P]romulgate standards or requirements applicable to [area]
sources * * * which provide for the use of generally available
control technologies or management practices by such sources to
reduce emissions of hazardous air pollutants.
Section 112(d)(5) thus doesn't limit us to strict ``standard
setting'' in order to provide for the use of GACT. We read section
112(d)(5) to authorize promulgation of at least two types of rules:
rules that set emission levels based on specific controls or management
practices (analogous to MACT standard setting), and rules that
establish permitting or other regulatory processes that result in the
identification and application of GACT. As long as the result of the
section 112(d)(5) rulemaking is that sources use enforceable generally
available control technologies or management practices, section
112(d)(5) appears to give us flexibility in choosing between the
adoption of numerical emission limits and the promulgation of other
requirements that result in sources applying GACT.
As discussed previously, we intend to determine which of these
regulatory approaches is most appropriate when we conduct rulemaking on
the individual source categories. However, it's important to bear in
mind that we retain authority under section 112(d) to regulate any
listed area sources more stringently, under MACT, where appropriate, to
effectively address risk. In addition, we can lower the emission
thresholds for defining sources as ``major'' and, therefore, subject
what would have otherwise been area sources to major source
requirements (MACT).
3. Issues on the National vs. Local Scope of Area Source Standards
Section 112(k) requires that listed area source categories be
subject to standards under section 112(d).
Many commenters on the draft Strategy addressed the implications of
selecting a national versus a local scope for the area source
standards. Some said national area source standards are unfair and
inefficient, because they apply to sources located outside of urban
areas where they may pose less risk. However, others said failing to
apply the standards nationally creates an unlevel playing field for
businesses in urban areas, encourages urban sprawl, and creates a
disincentive for new businesses in brownfield and urban development
areas.
As indicated by our initiatives on urban development and brownfield
redevelopment, we share the concern of many commenters that applying
standards only in the urban areas could negatively impact economic
opportunities in the urban areas and could, in some cases, encourage
urban sprawl. In addition, we're also concerned about the
disproportionate public health risk for people, particularly sensitive
populations such as children, in smaller cities or rural areas that
might be located near area sources. However, we're aware that for some
area source categories it may be more practical and appropriate to
limit the applicability to urban areas. Thus, our expectations are to
apply area source standards under section 112(k) nationally; however,
for each individual area source category, we'll determine whether it's
more appropriate for area source standards to apply nationally or only
in urban areas.
For those area source categories where the standards only apply in
urban areas, we'll look to the consolidated metropolitan statistical
area (C/MSA) boundaries as a starting point to define the urban area.
Although we used the urban 1 and urban 2 definitions \34\ for the
development of the inventory to support the HAPs and source category
analysis, we believe the C/MSAs are more appropriate for defining
applicability of area source standards because the C/MSAs better
reflect the nature of population density, commercial development, area
growth, and air emissions that represent urban areas.
---------------------------------------------------------------------------
\34\ Urban 1 areas are those counties that have a population of
more than 250,000. Urban 2 areas are counties where at least 50
percent of the population is considered to be urban.
---------------------------------------------------------------------------
Although we generally believe that urban areas are those C/MSAs
with populations of more than 50,000, we recognize that the appropriate
area in which standards should apply may vary among area source
categories. Consequently, we believe the determination of the area in
which standards will apply should be made separately for each source
category.
4. Title V Permits for Area Sources
Under section 502(a) of the Act, area sources can be exempted from
Title V permitting if the Administrator determines that compliance with
Title V requirements is impracticable, infeasible, or unnecessarily
burdensome for the area sources in question. As specified in 40 CFR
63.1(c)(2), 70.3(b)(2) and 71.3(b)(2), individual standards promulgated
under part 63 will specify whether Title V permits are required for
area sources. Consequently, we'll determine in each subpart that is
developed for the Strategy whether area sources affected by the subpart
are subject to, or exempt from, Title V permitting.
Factors that might influence this determination were raised by
commenters. For example, many commenters felt that area sources are
often small businesses, and that requiring Title V permits for these
sources places an unfair resource burden on them. Other commenters felt
that these sources should be covered by Title V permits in order to
provide resources to the States through the collection of Title V fees,
and to provide an opportunity for community input on the establishment
of area source requirements. Title V, which is implemented through
regulations codified in 40 CFR parts 70 and 71, generally requires
owners or operators of area sources subject to section 112 standards to
obtain Title V permits.
[[Page 38725]]
We also received a number of comments in regard to Title V fees and
the Strategy. Some commenters requested that area sources subject to
the Title V program be charged an annual fee, rather than a per ton
fee. How Title V fees are assessed is determined by the individual
permitting authority and is subject to approval by EPA as part of the
permitting authority's Title V program submittal to the Agency.
Permitting authorities are free to assess fees based on criteria other
than emissions, including application fees or service-based fees.
Moreover, permitting authorities can assess fees differently among
Title V sources. Therefore, we don't have the authority under section
112(k) of the Act to establish a new basis for assessing Title V fees.
Other commenters requested that Title V fees be used to fund state
toxics reduction programs. We must emphasize that, according to 40 CFR
70.9(a), Title V fees are to be used solely to fund a permitting
authority's Title V program and not non-Title V activities.
5. Schedule for Area Source Standards
We've revised the time line we presented in the draft Strategy for
area source standards development. We believe the following milestones
reflect a more realistic estimate of the average 4 years it takes to
develop MACT/GACT standards. We intend to address the source categories
newly listed here by 2004, and address additional source categories
listed later in the process of implementing the Strategy in later years
(i.e., 2006-2009).
2004--promulgate the area source standards newly listed in
today's Strategy. We'll attempt to meet this demanding schedule as
expeditiously as practicable.
2006--promulgate additional area source standards to meet
the 90-percent requirement.
2009--promulgate all remaining area source standards
necessary to meet the 90-percent requirement.
2012--expected compliance under all standards.
We'll prioritize the order in which we regulate source categories
to address those posing the greatest risks first. This will be a part
of our initial assessments, which will be done in the spring of 2000.
We'll be developing standards between now and 2009. Compliance with
these standards is required within 3 years of promulgation. Therefore,
compliance with all standards is anticipated by no later than 2012.
6. Our Approach for Mobile Source Hazardous Air Toxic Controls
Title II of the Act provides several mechanisms to achieve
reductions in hazardous air pollutants from mobile sources. The most
direct of these is section 202(l) which requires us to identify the
need for and consider regulations for control of HAPs from motor
vehicles and their fuels.
Pursuant to section 202(l)(1) of the Act, we released the ``Motor
Vehicle-Related Air Toxics Study'' in 1993.\35\ This study summarized
information on emissions of toxic air pollutants associated with motor
vehicles and motor vehicle fuels, as well as estimated exposures, and
potential risks. The study also provided cancer risk estimates for
several air toxics for different years under various control scenarios.
We've recently completed draft analyses to update the emissions and
exposure analyses done for this study to account for new
information.\36,\ \37\ These draft analyses include base scenarios for
1990, 1996, 2007, and 2020, and control scenarios in 2007 and 2020. We
modeled toxic emissions and exposure for the following urban areas:
Chicago, Denver, Houston, Minneapolis, New York, Philadelphia, Phoenix,
Spokane, and St. Louis. We assessed emissions and exposure from
benzene, formaldehyde, acetaldehyde, 1,3-butadiene, and diesel
particulate. Experts and stakeholders are currently reviewing the
methodologies and assumptions used in the analyses, and work is on-
going to extend and revise the analyses.
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\35\ Motor Vehicle-Related Air Toxics Study, U.S. Environmental
Protection Agency, Office of Mobile Sources, Ann Arbor, MI, EPA
Report No. EPA 420-R-93-005, April 1993.
\36\ Estimation of Motor Vehicle Toxic Emissions and Exposure in
Selected Urban Areas. Prepared by Sierra Research, Inc., Radian
International Corp., and Energy & Environmental Analysis, Inc. for
U.S. EPA, Office of Mobile Sources, Assessment and Modeling
Division, Ann Arbor, MI, Report No. EPA420-D-99-002, March 1999.
\37\ Sierra Research, Inc. ``On-Road Motor Vehicle National
Toxics Exposure Estimates''. Memorandum from Philip Heirigs to Rich
Cook, U.S. EPA. October 15, 1998.
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As mentioned before, diesel particulate matter (PM), which is
emitted primarily by mobile sources, isn't included on the section
112(b) list of 188 HAP, and, as a result, isn't included on the urban
HAP list. However, we're currently investigating the health risks
associated with diesel PM and assessing its role in the urban air
toxics problem. We're concerned about the potential health risks
associated with exposures to the emissions of this pollutant mixture.
Diesel PM is a complex pollutant mixture that is emitted primarily
by mobile sources. Heavy-duty highway and nonroad diesel engines are
the largest sources of diesel PM, with the total on-road and non-road
diesel PM emissions for 1997 being 516,373 thousand tons.\38\ While
diesel engines are used in a relatively small number of cars and light-
duty trucks today, vehicle and engine manufacturers are developing new
engine models that may be used in an increasing share of the light-duty
fleet, particularly light-duty trucks. If sales of car and light trucks
with diesel engines increase substantially over time, the potential
health risks from diesel PM could also increase substantially.
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\38\ EPA National Air Pollutant Emissions Trends Update, 1970-
1997. December 1998, EPA-454/E-98-007. This number also represents
PM10 emissions, while PM-2.5 emissions are approximately 474 million
tons. Non-road emissions include locomotives, and the on-road
calculation excludes tire and brake wear.
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Diesel PM typically consists of a solid core, composed mainly of
elemental carbon, which has a coating of various organic and inorganic
compounds. The characteristically small particle size increases the
likelihood that the particles and the attached compounds will reach and
lodge in the deepest and more sensitive areas of the human lung. Both
the diesel particle and the attached compounds may be influential in
contributing to a potential for human health hazard from long term
exposure.
Section 202(l)(2) of the Act directs us to set standards to control
HAPs from motor vehicles, their fuels, or both. Those standards are to
be set based on available technology, taking existing standards, costs,
noise, energy and safety factors into account. The Act also specifies
that, at minimum, benzene and formaldehyde emissions must be addressed.
We're currently working on a proposal in compliance with section
202(l)(2).
In developing the section 202(l)(2) proposal, we'll draw on the
1993 study, and more recent analyses when completed, to describe the
magnitude of exposure and potential health risk to the public from
toxic emissions from motor vehicles and their fuels. We'll examine
exposure and potential risk in a number of urban areas, as well as on a
nationwide basis. With regard to control strategies, several of the
existing emission control programs developed under section 202(a)
(motor vehicle
[[Page 38726]]
controls) and section 211 (fuel controls) of the Act already limit many
HAP emissions from motor vehicles and their fuels. We'll consider these
programs, as well as our on-going regulatory activities (such as our
recent proposal for new light-duty ``Tier 2'' emission standards and
gasoline sulfur controls and our recent Advanced Notice of Proposed
Rulemaking for diesel fuel control), in our assessment of whether
additional controls are appropriate under section 202(l)(2).
In addition to fulfilling the requirement to examine emissions and
health risks from motor vehicles and their fuels, we'll continue our
efforts to ensure coordinated use of our standard-setting authorities
to address priority risks from mobile sources. In particular, as we
review existing regulations for a number of motor vehicle and nonroad
engine categories, the goal of reducing air toxics risks will be
considered. In addition, we envision that work done in the early stages
of implementing the Strategy, such as improving monitoring and
inventories, will help us compare options related to the various
emissions sources in urban areas and control authorities to provide the
best relative reduction of risk to the urban public.
7. Role Major Stationary Sources Play in the Strategy
As discussed in section I.C., section 112(k)(3)(B) requires that we
ensure that area sources accounting for 90 percent of the aggregate
emissions of each of the 30 area source HAPs are subject to standards.
However, in achieving required reductions in cancer incidences, section
112(k)(3)(C) permits us to consider reductions in public health risks
resulting from actions to reduce emissions from ``all stationary
sources and resulting from measures implemented by the Administrator or
by the States under this or other laws.'' Therefore, we'll consider
emission reductions from a combination of major and area sources in
conducting risk assessments to address this requirement.
These assessments will support regulatory efforts under the Clean
Air Act and other authorities, as necessary, to address the identified
risk. For example, any reductions resulting from MACT, the national
ambient air quality standards, and other programs that achieve
reductions in HAPs can be included in the assessment of reductions in
risks. Therefore, if we determine that a source category or an
individual source is presenting a significant health risk, then we'll
address it using the appropriate regulatory authority. For example, if
needed to provide an ample margin of safety to protect human health,
section 112(f) residual risk standards will be developed for source
categories currently subject to MACT. Additionally, if our analyses
reveal a major source category that is currently unregulated or
unlisted, but poses a public health risk, we'll list that source
category under the authority of section 112(c) and develop the
necessary regulations under section 112(d), or we may address it
through other activities like pollution prevention or voluntary
programs. Similarly, if a specific source is contributing to a local
risk problem, then the State, local or Tribal program may be more
appropriate for addressing that risk.
8. Our Approach for Combinations of Sources
We also intend to coordinate our authorities in addressing
cumulative risks posed by exposures to aggregate emissions from
multiple source types. For example, many commenters raised concerns
about the risks from airports to the communities that surround them.
Airports can be viewed as mini-cities, which produce numerous
pollutants from multiple sources and are governed by many different
authorities. We'll need to have an integrated strategy to reduce air
emissions and the many other environmental impacts associated with
aviation activities.
Although airports don't meet the definition of ``area'' or
``major'' source under section 112 of the Act, we're involved with
numerous efforts to better understand and reduce the environmental
impacts of aviation-related activities and their associated human
health risks. For example, we co-chair the EPA/Federal Aviation
Administration Voluntary Aircraft Emissions Reduction Initiative, a
multi-stakeholder process designed to identify and evaluate technically
feasible and cost-effective voluntary measures to reduce aviation
emissions. We're also participating with other stakeholders in the
development of the South Coast Ground Service Equipment memorandum of
understanding (MOU) in California to identify ways to achieve
additional emissions reductions from the commercial aviation community.
Implementation of the MOU, which should be finalized in the summer of
1999, should yield emission reductions through increased use of cleaner
engines, electrification, and alternative fuels. In addition, we're
developing a Green Airport Initiative to demonstrate innovative
strategies for reducing the environmental impacts of aviation-related
activities at an airport undergoing expansion. In April 1999, we
released a report that assesses the current and potential impact of
aircraft emissions on local air quality at ten selected airports. \39\
The regulatory and voluntary actions underway for aviation will produce
data that can inform this Strategy and begin to address the
environmental impacts of aviation-related activities and their
associated risks to the communities that surround them.
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\39\ ``Evaluation of Air Pollutant Emissions from Subsonic
Commercial Jet Aircraft,'' U.S. EPA, April 1999.
---------------------------------------------------------------------------
D. How do the Various Federal Authorities Help EPA Implement the
Strategy?
We've already made progress in addressing air toxics emissions
using existing programs. To put the problem in perspective, we estimate
that approximately 8.1 million tons of 188 HAPs were released in the
United States in 1993.\40\ We've already issued at least 43 MACT and
GACT standards and two section 129 standards with post-1993 compliance
dates, which will address these emissions. Emission controls for the
nation's cars, trucks and off-road equipment, and standards for fuels
add even more to these reductions. In this section, we'll discuss the
utility of these programs and others to achieve additional air toxics
emissions reductions.
---------------------------------------------------------------------------
\40\ ``Latest Finding on the National Air Quality: 1997 Status
and Trends,'' December 1998.
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Federal Regulatory Activities--Clean Air Act Section 112 Authorities
Section 112 of the Act provides several authorities for us to use
in meeting our air toxics goals. We've promulgated section 112(d) MACT
and GACT standards that are projected to reduce air toxics emissions by
approximately 1 million tons per year once fully implemented. Within
the next 10 years, as we complete more MACT and GACT standards, the air
toxics program is estimated to reduce emissions of toxic air pollutants
by well over 1.5 million tons per year.\41\ These nationwide emission
reductions will contribute significantly to reductions needed in urban
areas.
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\41\ See footnote 40.
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The need for section 112(f) standards, or ``residual risk''
standards, is under consideration for some of the early source
categories covered by MACT standards. Where justified, these standards
will address remaining public health and environmental impacts of HAPs
to ensure an ample margin of safety to protect public health and, in
consideration of other factors, to prevent adverse environmental
effects.
[[Page 38727]]
Consistent with the requirements of the Act, we'll evaluate the need
for residual risk standards for those area source categories covered by
MACT standards, and will consider such evaluation for those area source
categories for which GACT standards have been promulgated.
The chemical accident prevention regulations (``Risk Management
Program requirements'' or ``RMP rule''), were promulgated under section
112(r). These regulations require owners and operators handling more
than a threshold quantity of any substance listed in 40 CFR 68.130 in a
process, to develop risk management plans to prevent and address
accidental releases. Eighteen of these listed substances are HAPs. By
preventing accidental releases, the RMP rule will help reduce or
prevent emissions of these HAPs in the future.
We've already received several requests for permits under the
section 112(g) construction and reconstruction rule. This rule applies
to new or reconstructed major sources and requires them to install MACT
to reduce HAP emissions. In addition, the section 112(i)(5) rule (early
reductions) provides incentives for sources to reduce emissions by up
to 95 percent from 1990 levels prior to proposal of MACT for that
source category. Approximately 27 Title V permit applications have been
received, representing HAP reductions of over 6,800 tons.
Other CAA Authorities
Other programs under the Act also contribute to the reduction of
HAPs in urban areas. For example, section 109 requires States to
develop State implementation plans to attain compliance with the
national ambient air quality standards (NAAQS). Many of the activities
that are designed to address criteria pollutants (e.g., ozone,
particulate matter and lead) and attain the NAAQS also achieve
reductions in air toxics. For example, many of the VOCs that form ozone
are also air toxics, such as benzene and 1,3-butadiene. In addition,
some VOCs can react in the atmosphere to form HAPs such as
formaldehyde. Thus, controlling VOCs leads to reductions in air toxics.
Similarly, compliance with the PM standards will provide incidental,
but potentially significant, reductions in HAPs that are either emitted
in the form of particulate matter or that condense to form particles in
the atmosphere. These include polycyclic organic matter (POM),
chromium, mercury, and other metals. In addition, lead is a criteria
pollutant and lead compounds are listed as a HAP, so reducing lead
emissions through the lead NAAQS also reduces HAPs.
With regard to mobile sources, in addition to authority under
section 202(1) to address hazardous air toxics, other sections of Title
II that address mobile sources, including other parts of section 202
(motor vehicles), section 211 (fuel requirements), section 213
(emission standards for nonroad engines and vehicles), and section 219
(urban bus standards), are resulting in reductions in urban air toxics
by limiting VOCs, oxides of nitrogen, and particulate matter.
We've established section 129 performance standards for two source
categories for combustion sources. These are expected to result in over
50,000 tons per year in HAP reductions, much of which may be in urban
areas. Finally, actions taken under Title IV, the acid rain program,
and Title VI, stratospheric ozone layer protection, also reduce or
eliminate certain urban air toxic emissions.
Other Federal Laws
There are a number of other authorities, laws, rules, and programs
that will also help reduce emissions of HAPs and consequent exposures
and risks. We're evaluating the appropriateness of these statutes for
controlling emissions of HAPs as described under section 112(k)(3) and
intend to take further actions under these statutes as appropriate. The
contribution of other Federal programs to achieving the goals of the
strategy is discussed in more detail in Appendix A. Following is a list
of some relevant programs:
Superfund Amendments and Reauthorization Act (SARA) Title
IV.
Toxic Substances Control Act (TSCA).
Resource Conservation and Recovery Act (RCRA).
Comprehensive Environmental Response, Compensation and
Liability Act (CERCLA).
Clean Water Act (CWA).
Federal Insecticide, Fungicide and Rodenticide Act
(FIFRA).
Emergency Planning and Community Right-To-Know Act (EPCRA)
of 1986, especially Toxics Release Inventory requirements.
Pollution Prevention Act (PPA) of 1990.
Oil Pollution Act of 1990.
III. State, Local and Tribal Activities
A. Why are State, Local and Tribal Programs Integral to the Process?
The Act requires that the Strategy achieve the risk reduction goals
considering control of emissions of HAPs from all stationary sources,
using measures implemented by us under the Clean Air Act or other laws
or by the States. In addition, section 112(k)(4) requires us to
encourage State and local programs. By providing for State reductions
in achieving the goals, Congress acknowledged that there are many State
programs achieving HAP emissions reductions and, therefore, reducing
the chance for exposure and health risks, including cancer. For
example, before the Act was amended in 1990, many State, local and
Tribal governments developed their own programs for the control of air
toxics from stationary sources. Some of these programs have now been in
place for many years and, for some of the source categories, they may
have succeeded in reducing air toxics emissions to levels at or below
those required by the Federal standards. It's clear that Congress
intended State and local governments to be important partners in
carrying out the mandates of the Federal air toxics program, and this
Strategy provides a mechanism to recognize the reductions made by them.
Because of the varied nature of the emissions sources, legislative
structures, and other factors, the State, local and Tribal government
programs address air toxics in a number of ways. For example, some
programs have enacted technology standards for source categories that
require controls for specific HAPs, much like the MACT program. Other
programs apply a risk standard that prohibits emissions that result in
exceedances of a certain level of risk, or they use an ambient air
standard for air toxics that is based on threshold or exposure levels.
Still others may rely on reductions achieved through volatile organic
compound, particulate matter, or lead regulations developed under
section 110 or subpart D of the Act to meet national ambient air
quality standards. Regardless of the approaches used to address air
toxics, State, local and Tribal governments have accomplished and
continue to accomplish reductions in HAPs. As we proceed to implement
the Strategy, we'll work with these governments to better characterize
these reductions in emissions and the resulting reductions of public
health risks, including risk of cancer.
Developing the Strategy is a challenge at the national level
because urban air toxics problems vary significantly across the
country. Because of this variability, the Strategy works best if
approached as a partnership between EPA and State, local and Tribal
governments. These governments (including municipal
[[Page 38728]]
offices other than pollution control departments) have the most
experience with local air pollution issues, and can lend their
expertise and knowledge to address and resolve air toxics concerns that
are unique to cities. Many of these governments also have existing air
pollution control programs that currently address, and can effectively
continue to address, some or all of these issues. In addition, these
governments are often able to act much more quickly than we can to
address local concerns, which leads to less overall pollution,
particularly in the areas where pollution is of greatest concern.
At the Federal level, we can contribute Federal standards and
requirements using our authorities to develop and implement a national
regulatory program. We also have the resources and expertise to
evaluate, or to help other agencies evaluate, toxic pollution problems.
By integrating our relative strengths, we can provide a stronger, more
efficient, and more effective program to address toxic air pollution in
urban areas.
B. What Are the Objectives of State, Local and Tribal Activities?
The Strategy will be a partnership between EPA and State, local and
Tribal governments to address the risks from air toxics in urban areas.
Section I.C. of this document describes the goals of the Strategy.
Listed below are the objectives that we've identified to guide the
actions taken by us and our governmental partners, so that those
actions will be effective and efficient in achieving the goals of the
Strategy:
Establish appropriate Federal measures, through guidance,
policies, and rulemaking, which enable State, local and Tribal agencies
to be full partners. Many of the State, local and Tribal agencies may
be unable to do more than the Federal laws and rules require. These
agencies could benefit from Federal rulemaking guidance in addressing
local issues. At the same time, we recognize the need for flexibility
for these agencies to identify and address the local issues. We need
State, local and Tribal agencies' help to reach the Act's goals for
healthy air, and they'll benefit by being able to tailor the Strategy
to their specific needs.
Provide flexibility for strong State, local and Tribal
programs. Many of these governments have developed their own air
programs. In fact, we received many comments requesting that the
Strategy acknowledge programs that are already in place. Those
governments that have been pro-active in controlling air toxics can
benefit by tailoring the Strategy to their own needs, or by being able
to implement a program earlier than we can.
Provide incentives for State, local and Tribal action.
Since enabling through standards, policies and guidance and providing
flexibility can result in more effective and earlier controls of urban
HAPs, it will be beneficial to State, local, and Tribal governments, to
us, and to the public to facilitate State, local and Tribal actions.
Set priorities among urban areas and source categories.
Given the broad scope of the Strategy and the time it may take to
implement, it may be most effective to first identify and address those
areas and sources with the highest air toxic emissions or exposure
levels (including consideration of multipathway exposure where
appropriate).
Provide information to the public on HAPs and potential
risk in urban areas. The public benefits by having a sound basis to use
in setting their pollution control priorities and communicating their
priorities to us. Providing information to the public is also our
responsibility, and an informed public will be better equipped to help
us set priorities for appropriate State, local and Tribal HAP control
actions. This public outreach will include not only information on
exposure to air toxics, but also information on the link between water
quality and the deposition of air toxics.
Facilitate a focus on areas with disproportionate impacts
and greatest risks. The Strategy is intended to recognize the potential
for disproportionate impacts of air toxics hazards across urban areas.
State, local and Tribal governments can be particularly effective in
identifying and addressing disproportionate impacts of HAPs. We'll work
with our regulatory partners to provide technical and policy guidance
to help identify and address disproportionate impacts from HAPs,
including consideration of multipathway exposure as appropriate.
C. What Were Comments on the State/Local/Tribal Programs and How Are
They Being Addressed in the Strategy Development?
Commenters expressed a general desire for more information on the
State/local/Tribal agencies' roles and responsibilities in the
development and implementation of the Strategy. The nature of the
discussion in this part of the Strategy is general because our efforts
to develop urban air toxics strategies with State, local, and Tribal
governments are in an early stage of development. As described in a
later section, we plan to conduct assessments to better understand our
status with regard to the goals of the Strategy. We intend to use this
information and also gather more input from relevant parties in the
development of those programs through stakeholder meetings.
Commenters had a wide variety of opinions beyond a general desire
for more information. Some State, local or Tribal governments have
well-developed programs and ample resources for both the scientific and
regulatory aspects of an air program, while many others have less
experience and/or inadequate resources and don't do more than the
Federal government requires. As a result, some States believe that
their programs are mature enough to be given the flexibility to
identify HAPs and source categories to address the section 112(k)
requirements for themselves, and they and large industries located in
these States requested local flexibility. Other regulatory agencies,
small businesses and public health/environmental advocacy groups
recommended against such flexibility and requested national Federally-
mandated programs with Federal enforceability. We believe there are
valid points from all sides. Those wanting flexibility note that risk
reductions tailored to the local situation can be more effective than
national solutions and that this approach takes advantage of work they
already have in progress. Those wanting Federally-imposed programs note
that without such Federal mandates, the playing field wouldn't be level
for small businesses across different areas. In addition, some State,
local or Tribal programs wouldn't be able to address urban air toxics
without a Federal requirement. We will convene stakeholder meetings
early in the next fiscal year to resolve these issues on State, local
and Tribal programs. This time frame will allow for consideration of
information from our national assessment. We plan to bring stakeholders
together regularly for approximately six months and then take their
input, along with comments already received on the Strategy, to develop
a plan for implementing the State program. We intend to release this
plan no later than six months after the end of the stakeholder
meetings.
D. How Can State, Local or Tribal Agencies Participate in the Strategy?
The Strategy needs to be a partnership between EPA and State, local
and Tribal agencies in order to focus on local urban air toxics
concerns. But our relative roles may vary according to the needs of
particular urban areas and any limitations faced by State, local and
Tribal governments. With our regulatory
[[Page 38729]]
partners, we'll discuss and explore options for how the State, local
and Tribal agencies should participate in developing and implementing
the Strategy to address public and other environmental issues related
to air toxics.
We see a broad range of possibilities for State, local and Tribal
agency participation. For example, as indicated above, many regulatory
agency programs are designed to implement delegated Federal
requirements. However to provide additional flexibility, we may be able
to provide a Federal program that allows the agencies to either develop
and substitute their own requirements for an existing Federal program,
or, if they wish, to simply adopt and implement a risk reduction
program designed by us. For example, we could promulgate a Federal rule
describing how we'd develop and implement a local risk reduction
program. State, local or Tribal agencies could then either develop and
implement a program modeled on ours, or submit an alternative program
for our approval.
Alternatively, instead of promulgating a Federal rule setting out
the details of an acceptable risk reduction program, we could
promulgate a set of minimum elements that any local risk reduction
program--whether implemented by us or a State, local or Tribal agency--
must contain. This would provide agencies with more flexibility to
design and implement their own risk reduction programs that we could
approve.
The Federal role in developing additional risk reduction strategies
for urban areas could be smaller still. It may not be necessary for us
to directly guide development of State, local and Tribal programs. It
may be enough for us to encourage them to meet the goals of the
Strategy, and to provide necessary guidance. In the end, we (or the
State, local or Tribal agency) would still need to measure progress
against the mandatory goals of the Act. We might then need to determine
whether additional Federal action is warranted to meet the goals.
In evaluating and comparing the options we develop together, we and
our regulatory partners and other stakeholders will need to consider
how well each option addresses the objectives described in section
III.B. We'll also need to consider such other issues as practicality of
implementation, resource burden at each governmental level, and
possible adverse impacts on other Federal, State, local or Tribal
programs.
E. What Elements Should a State, Local or Tribal Program Contain?
No matter who develops and implements State, local or Tribal
programs, they should contain certain basic elements to allow them to
meet the risk reduction goals of the Strategy. For example, the
following list of elements should be considered:
Locally-focused assessment using existing information and
sufficiently refined tools to identify significant contributors to
urban risk, problem chemicals and sources, geographic ``hot spots''
within an urban area, and characteristics of at-risk populations.
A process, regulatory or otherwise, to develop strategies
aimed at reducing risk from those sources.
Opportunity for public review of both the baseline
assessment and the proposed risk reduction strategies.
A process and schedule for implementing the risk reduction
strategies.
Evaluation of whether the goals of the Strategy have been
met.
Provisions to implement additional risk reduction
strategies if the goals have not been met.
A process to encourage public participation.
At this point, this list is fairly general, because we don't have
enough information to more fully develop this program structure.
However, over the next couple of years, we'll be working to further
develop this aspect of the Strategy, to develop and use information
from assessments and other tools to guide our thinking, and to get
input from our stakeholders. For example, once we've completed the
initial assessment in the spring of 2000 (as described in section IV),
we'll know better our status with regard to risk reduction goals of the
Strategy. This will inform us about additional Federal activities
needed to meet those goals, and what additional State, local and Tribal
activities are needed to complement these activities. As described in
section IV, periodic assessments will continue to inform us about
needed programs over time. In the interim, while we're waiting for
completion of the initial assessment, we plan to meet with our State,
local and Tribal partners. We'll be reviewing the goals and the various
components of the Strategy and how they interrelate. In particular,
we'll focus on the assessment tools and their role in defining Federal,
State and local activities, and we'll exchange information to help
better refine the tools.
IV. Assessment Activities
This discussion of our assessment activities first focuses on how
we generally intend to assess progress in meeting the goals of the
Strategy. We then discuss our methods and tools for estimating health
risks and describe more specifically how we intend to apply these risk
assessment methods and tools in assessing progress and in supporting
implementation of the Strategy. However, it is important to remember
that the NATA assessments are designed to address all of the goals and
activities of our overall air toxics program.
Historically, Agency risk assessment and decision-making have
focused on the likelihood of health effects associated with exposure to
individual environmental contaminants. In recent years, as we move from
a focus on emissions reductions toward a focus on estimated risk
reduction, our risk assessment emphasis has shifted increasingly to a
greater consideration of multiple endpoints, pathways and routes of
exposure and holistic reduction of risk. This more complex assessment
is often called ``cumulative risk assessment,'' defined according to
who or what is at risk of adverse effects--from identifiable sources
and stressors--through several routes of exposure over varied time
frames. While various integrated approaches are now being used within
the Agency, we realize that there are significant gaps in methods,
models and data that limit our ability to assess cancer and non-cancer
risks associated with cumulative exposure to mixtures of pollutants
having different endpoints. We've identified both short-term and long-
term research needs to fill these gaps, highlighted in section V.D. of
this notice. Progress toward more refined assessments of cumulative
risks will depend upon the pace and evolution of our policy and
guidance on cumulative risk and the underlying research.
A. How Will We Assess Progress Toward Goals?
Assessing progress in reducing cumulative risk from HAPs will
require us to move away from a focus on assessing reductions in tons
per year emitted, toward a focus on estimating reductions in cancer and
non-cancer risks associated with lower emissions.
``Cancer'' describes a group of related diseases that affect a
variety of organs and tissues. Cancer results from a combination of
genetic damage and non-genetic factors that favor the growth of damaged
cells. At current cancer incidence rates, approximately one third
[[Page 38730]]
of U.S. residents may be expected eventually to contract some form of
cancer. Cancer is associated with a wide range of factors, of which
exposure to HAPs is only one. Other causes of cancer, including genetic
susceptibility, diet, smoking, background radiation, and lifestyle, are
thought to be the dominant factors determining total cancer incidence.
Given these complexities, the rate of cancers associated with HAPs
alone cannot be observed directly. Attributing cancer to specific
factors is also complicated by the fact that many cancers do not appear
for years, or decades, after exposure and, therefore, may have been
caused by exposures long past and in different locations. As a result,
we'll need to rely on modeled estimates of cancer risk rather than on
direct measurements for assessing the Strategy's progress toward the
goal of 75-percent reduction in cancer incidence associated with HAPs.
Adverse health effects other than cancer (``non-cancer risks'')
include a wide range of health endpoints in all organ systems (for
example, cardiovascular, immune, liver, kidney).\42\ As with cancer,
other factors such as diet, lifestyle, and other exposures (for
example, smoking) may exert a dominant influence over incidence of
adverse non-cancer health effects. Therefore, as with carcinogens, we
expect to rely primarily on risk estimates to assess progress, rather
than on direct measurements of changes in the incidence of adverse non-
cancer health impacts due to reductions in emissions.
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\42\ Some HAPs that cause cancer may also cause adverse non-
cancer health effects at environmentally relevant doses. Thus, when
we discuss ``non-carcinogens,'' we mean substances that may
potentially cause non-cancer effects in humans. Some of the same
substances may also be evaluated as carcinogens.
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The Act sets a clear numerical goal for reduction in cancer
incidence, but specifies only a ``substantial'' reduction in public
health risks for effects other than cancer. We see a need to define and
clarify this goal more fully as we work to implement this Strategy, but
we haven't yet developed a specific numerical goal for risk reduction
for various non-cancer effects. One major purpose of our non-cancer
risk assessments will be to provide a sound technical basis for
developing and defining non-cancer goals that are quantifiable,
attainable, and consistent with the Act.
Since cancer and non-cancer health impacts can't be directly
isolated and measured, we and others have spent more than two decades
developing an extensive set of risk assessment methods, tools and data
that serve the purpose of estimating health risks for many of our
programs. Our risk assessment science has been extensively peer-
reviewed, is widely used and understood by the scientific community,
and continues to expand and evolve as scientific knowledge advances. We
intend to use the most current and appropriate risk estimation methods
in tracking progress under the Strategy.
Our risk assessments, reflecting the risk paradigm set forth by the
National Academy of Sciences in 1983,\43\ are based in general on a
combination of two types of analyses. The first type of analysis
examines what adverse effects a substance causes (the ``hazard
identification''), and the specific exposures at which these effects
occur (the ``dose-response assessment''), and is usually based on human
or animal studies of high quality published in peer-reviewed scientific
journals. This type of analysis allows us to evaluate a chemical's
potential to cause cancer and other adverse health effects.
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\43\ National Research Council (NRC). 1983. Risk assessment in
the federal government: Managing the process. National Academy
Press, Washington, D.C.
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The second type of analysis estimates the levels of exposure that
people receive within the environment. We develop this ``exposure
assessment'' in stepwise fashion for air pollutants, with the first
step being the compilation of emissions data. Second, these data are
input to a dispersion model, which estimates ambient air
concentrations. These modeled ambient concentrations may be compared to
monitoring data in order to test and validate the models. Third, we
estimate exposures to ambient concentrations by applying models of
human behavior patterns, and incorporate measured personal exposure
information when available.
These two types of analyses--the exposure that causes harm and the
exposure people actually receive--are combined in a ``risk
characterization'' that describes the potential for real-world
exposures to cause harm, and the uncertainties surrounding the
characterization.
B. What Methods, Tools, and Data Will We Use To Estimate risk?
1. Evaluating a Chemical's Potential To Cause Cancer
Our dose-response assessments for carcinogens are based on
mathematical models and assumptions that support extrapolation from
high to low doses and from non-human test species to humans. As a
matter of science policy, many of these assumptions are protective, to
avoid underestimating cancer risks where data are incomplete. The most
important of these assumptions for most carcinogenic chemicals is that
risk is proportional to dose, with no threshold dose below which there
is no risk. Our dose-response assessments for inhalation of carcinogens
are expressed as a ``unit risk,'' that is, risk per microgram per cubic
meter of daily exposure during a lifetime. The unit risk is defined as
a conservative estimate of an individual's excess probability of
contracting cancer at the end of 70 years exposure to a continuous
level of one microgram per cubic meter. Risks from exposures to
concentrations other than one microgram per cubic meter are modeled as
proportional, with half the concentration producing half the estimated
risk, and so on.
Each word in the above definition of unit risk carries significant
meaning. First, the unit risk is a conservative rather than a ``best''
estimate. This means that the actual unit risk is unknown, and is very
likely to be lower than estimated and very unlikely to be higher.
Second, as already described, risks are estimated rather than measured.
Third, the unit risk applies to an individual, although cancer
incidence in a population can be estimated across a group by
aggregating the risk of each person. Fourth, unit risk estimates focus
only on the route of exposure being analyzed. Fifth, unit risks are
expressed in terms of probability. For example, we may determine the
unit risk of a particular HAP to be one in ten thousand per microgram
per cubic meter. This means that, of ten thousand people who
continuously inhale an average of one microgram per cubic meter of this
particular HAP for 70 years, no more than one would be expected to
contract cancer from the exposure. Sixth, risks are generally expressed
in terms of contracting cancer, not dying from it. Finally, exposures
are averaged over a 70-year lifetime, to account for long-term
exposures to low levels of carcinogens.
We intend to use unit risk estimates as the dose-response component
in estimating plausible reductions in cancer incidence achieved by this
Strategy.
2. Evaluating a Chemical's Potential To Cause Adverse Effects Other
Than Cancer
Adverse health effects other than cancer (``non-cancer risks'')
cover a wide range of health endpoints in all organ systems (for
example, cardiovascular, immune, liver, kidney).
[[Page 38731]]
For this reason, we've developed our non-cancer dose-response
assessment methods to address several additional sources of complexity
beyond those found in cancer assessments. First, organisms possess
varying abilities to eliminate, detoxify, and sequester many toxic
substances, and to repair some amount of damage that those toxic
substances may cause to tissues and organs. For this reason, most
chemicals don't cause observable adverse non-cancer health effects
until some threshold dose has been exceeded. Second, the appearance of
a toxic response when the threshold dose is exceeded is seldom
proportional to dose. The shape of ``dose-response curves'' (for
example, a graph of the number of individuals affected at varying dose
levels) varies substantially among chemicals, so there is no single
model that can be applied to all non-carcinogens. Third, available
information for most HAPs comes from animal studies, and significant
uncertainty is associated with extrapolating these results to humans to
support predictions of human dose-response curves.
For these reasons, non-cancer dose-response assessments for
inhalation are usually expressed in terms of a ``reference
concentration,'' defined as an estimate (with uncertainty spanning
perhaps an order of magnitude) of a continuous inhalation exposure to
the human population (including sensitive subgroups) that is likely to
be without an appreciable risk of deleterious non-cancer effects during
a lifetime. We intend to use reference concentrations as the dose-
response component for estimating reductions in non-cancer risk
achieved by this Strategy.\44\
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\44\ The uncertainty surrounding reference concentrations (RfCs)
varies substantially among HAPs, depending on the strength of the
supporting data. As a result, RfCs vary in their level of
protectiveness, with RfCs supported by strong toxicological data
tending to be less protective. We recognize this important
limitation to the use of RfCs, and may use more advanced dose-
response models for specific HAPs where they can be applied.
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3. Assessing Exposures and Characterizing Risks
In general, the choice of appropriate risk characterization
approaches will be influenced by both the availability of data to
support exposure assessment, and the level of detail and resolution
needed to support the purpose of the assessment. Possible approaches
span a wide range, from simple weighting adjustments of emissions data
or ambient concentrations, to detailed multipathway risk assessments.
We've identified four basic approaches that we plan to use for various
assessments to evaluate the progress of the Strategy in reducing
estimated risk. Each of these approaches uses the same dose-response
information described above, but relies on different types of data to
represent exposures. The four basic approaches we intend to use are:
(1) Emissions or ambient concentration weighting;(2) comparisons
between ambient concentrations and risk-based concentrations (RBCs)
\45\; (3) comparisons between estimated exposures and RBCs, that may
yield quantitative estimates of risk; and (4) quantitative estimates of
carcinogenic risk for individuals and populations.
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\45\ Risk-based concentrations for cancer are ambient
concentrations associated with specific levels of cancer risk,
assuming 70 years of continuous exposure. RBCs for non-cancer
effects are ambient concentrations that pose no appreciable risk to
humans, assuming continuous exposure. The use of RBCs does not imply
a judgement that the concentrations are either acceptable or
unacceptable, only that they have been derived in the same way for
all HAPs.
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Approaches (1) and (2) are considered hazard-based approaches, in
that they lack the dispersion and/or human exposure modeling steps of
an exposure assessment and therefore cannot provide quantitative
estimates of risk. However, they can provide valuable information,
subject to substantial uncertainty, that may be useful in evaluating
progress toward risk reduction goals. In contrast, approaches (3) and
(4) are considered risk-based approaches, in that they do incorporate
exposure assessments and thereby can provide quantitative risk
estimates.
(1) Weighted emissions or ambient concentrations. Weighting of
emissions or ambient concentrations is the least resource-intensive
approach of the four in terms of data needs and computational
requirements.\46\ This hazard-based approach combines HAP emissions or
monitored HAP concentrations (acting as surrogates for exposure) with
weighting factors (developed from unit risks and reference
concentrations) that account for differences in relative toxicity among
HAPs. Other weighting factors could also potentially be developed to
account for differences in dispersion characteristics or variations in
population density or behavior.
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\46\ Peer-reviewed examples of this approach include the EPA/
OPPT Risk-Screening Environmental Indicators, the EPA/OSW Waste
Prioritization Management Tool, and the EPA/OAQPS ranking analysis
for urban HAPs. See the public docket for a detailed list of risk
assessment references.
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The toxicity adjustment is intended to account for differences in
toxic potency among substances, placing all emissions data on the same
scale of hazard potential. For example, acrylamide is approximately 160
times more potent a carcinogen than benzene, such that weighting by
toxicity would consider one ton of acrylamide emissions equivalent to
160 tons of benzene. In a cumulative analysis, emissions or
concentrations of each HAP would be weighted by its relative toxicity
to allow for direct comparison and aggregation across HAPs (with
carcinogenic and non-carcinogenic estimates aggregated separately).
This type of analysis permits comparisons of relative hazard between
pollutants with large mass emissions and low toxicity (for example,
many non-chlorinated volatile compounds) against pollutants with small
mass emissions but high toxicity (for example, dioxin).
As discussed above, the weighted emissions-or concentration-based
approach lacks the last two steps of an exposure assessment, and
therefore doesn't provide a quantitative estimate of risk. Also,
because of the absence of these important exposure assessment steps, it
isn't possible to say how closely changes in weighted emissions or
concentrations will be related to changes in health risk. Nevertheless,
emissions and ambient concentrations clearly have a strong influence
over exposure and risk, and we anticipate that the toxicity-weighting
approach will provide useful information to estimate progress where
appropriate data for more refined assessment approaches aren't
available.
(2) Ratios of ambient concentrations to RBCs. A second type of
hazard-based approach is the comparison of ambient HAP concentrations
with RBCs.\47\ Ambient concentrations may be measured (as discussed in
section V.A.) or modeled (section V.C.). Appropriate modeling
approaches for estimating ambient concentrations at different spatial
scales using emissions data include national-scale and urban-to
neighborhood-scale air quality models, as well as multi-media models
for urban-to neighborhood-scale analyses.
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\47\ Peer-reviewed examples of the use of this approach include
the concentration-toxicity screen used by EPA's Superfund program to
select contaminants and exposures for detailed risk assessment, and
EPA's Cumulative Exposure Project, which compared modeled ambient
air concentration estimates with RBCs (termed Ahealth benchmarks''
by the authors) for 148 HAPs nationwide. See the public docket for a
detailed list of risk assessment references.
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The RBCs used for comparison are derived from unit risks or
reference concentrations. Specifically, cancer RBCs can be defined in
terms of a fixed risk level (for example, HAP concentrations
conservatively estimated to result in a one-in-ten-thousand or a
[[Page 38732]]
one-in-one-million upper-bound risk of contracting cancer from a
lifetime exposure at the RBC). Non-cancer RBCs can be defined in terms
of estimates of continuous exposure levels at which even sensitive
subgroups are likely to be without any appreciable risk of adverse
effects during a lifetime.
Because it is more complex than emissions-weighting, this type of
analysis brings two significant advantages. First, it supports a more
complete treatment of ambient HAP concentrations that are already below
non-cancer RBCs, for which further reductions may not carry significant
health benefits. Second, the use of dispersion models to predict
ambient concentrations can potentially account for variations in
factors such as location of exposed populations relative to sources of
HAPs, differences in meteorological conditions, and differences in fate
and transport characteristics among HAPs.
Nevertheless, this approach still lacks the third, human behavior-
related, step in an exposure assessment. Therefore, it doesn't provide
a quantitative estimate of risk, and its use in estimating progress is
subject to greater uncertainty than approaches (3) and (4), below.
Changes in health risk may not precisely track changes in
concentration/RBC ratios. However, because ambient concentrations are
important determiners of exposure and risk, we anticipate that the
concentration/RBC approach will provide useful information to estimate
progress where exposure assessment is not possible.
(3) Ratios of exposures to RBCs. A third type of approach begins
with measured or modeled ambient HAP concentrations, and adds further
refinement by overlaying estimates or measurements of population
exposures. Thus, this risk-based approach is qualitatively different
from the first two hazard-based approaches because it incorporates all
three steps of an exposure assessment.
While human exposures are directly affected by ambient
concentrations, they're also influenced by behavioral factors such as
time spent outdoors, periodic movements (such as commuting) within an
urban area, and activity levels. Exposures may be estimated with
exposure models, as discussed in section V.C., that simulate the
behavioral factors that determine exposure. Human exposure may also be
directly measured by personal monitoring, in which subjects wear small
air samplers and record their daily activities.
These estimated or measured exposures are then compared to RBCs
\48\ (as described above for approach (2)). Analogous to the
comparisons in approach (2), hazard potential would typically be
presented in terms of ratios of the exposure concentrations divided by
RBCs. The additional complexity of estimating exposure provides three
significant advantages over considering ambient concentrations alone.
First, it provides a more realistic comparison with RBCs, which are
based on unit risks and reference concentrations usually derived from
doses actually received by test organisms. Second, exposure estimates
can take into account behavioral differences between populations in
different cities, or between different demographic groups. Third,
exposure estimates support combining effects of multiple HAPs,
considering non-additivity and similarities or differences in toxic
mechanisms. Comparison of exposures with reference concentrations for
non-cancer effects (acting as RBCs) is currently the most advanced
approach available for assessing non-carcinogenic HAPs, although this
may change in the future for some substances.
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\48\ Peer-reviewed analyses of this type of analysis include
many single-substance risk assessments. Several examples concern the
fuel additives methylcyclopentadienyl manganese tricarbonyl (MMT)
and methyl tertiary butyl ether (MTBE). See the public docket for a
detailed list of risk assessment references.
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(4) Risk estimation. A fourth type of approach that can be used to
estimate cancer incidence is comprehensive risk estimation, focusing on
the most exposed individual or on entire populations or subgroups.\49\
We'll derive risk estimates by combining exposure estimates with dose-
response assessment results in terms of unit cancer risk estimates.
Risk estimates will also consider non-standard dose-response models and
complex interactions among different HAPs, if information is available.
Such risk estimates represent the most refined analysis of the four
approaches considered. Comprehensive assessments may contain modeling
to account for environmental fate and transport of released pollutants,
estimation of exposures to different subpopulations, detailed dose-
response assessments for each HAP, and information on complex, non-
additive interactions among HAPs. Results are expressed in terms of
probabilities of developing cancer during a lifetime. Cancer risks are
usually aggregated across HAPs by addition, but non-additive
interactions are included if data permit.
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\49\ Examples of such multi-chemical, multipathway risk
assessments include many performed by EPA's Superfund program under
the Risk Assessment Guidelines for Superfund. See the public docket
for a detailed list of risk assessment references.
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In its most complete form, risk estimation produces results in
probabilistic form (that is, with calculations considering a range of
cancer risks and the likelihood of each), expressed in terms of a
frequency distribution rather than as a single deterministic estimate.
Of currently available approaches, risk estimation, presented
probabilistically, provides the most complete, best-supported, and most
accurate presentation of both risk and the variability and uncertainty
surrounding it. However, this risk-based approach is much more
resource- and calculation-intensive than are simpler approaches.
4. Summary
We anticipate tracking progress in reducing estimated cumulative
risks from air toxics in urban areas by relying on estimates of health
risk rather than by directly observing reductions in adverse health
impacts in human populations. We consider these health risk estimates
to be reasonable and appropriate indicators of progress toward meeting
the goals of the Strategy. Their use is made necessary by the long
latency period for cancer, the high background rate of human cancer
from all sources, and complexities involved in attributing various non-
cancer health effects to specific environmental causes. Our assessments
will use a variety of approaches, including some that do not include
all exposure assessment steps. In some cases the information may be too
uncertain to support conclusions. We intend to evaluate these
approaches against each other, in terms of their ability to estimate
risk and their resource and data requirements, when supporting data
become available in early 2000. These results will assist us in
determining the scope, refinement, and precision of future assessments
developed to reflect different purposes under the Strategy.
C. What Is Our Overall Risk Assessment Approach for the Strategy?
In section I, we discussed the key role that assessing air quality,
exposure, and estimated risks will play in assessing progress toward
meeting the goals of this Strategy. In addition, these assessment
activities will, over time, also serve the following broader purposes:
Improve the definition of the goal for ``substantial''
reduction in non-cancer risk.
[[Page 38733]]
Support development of Federal area (as described earlier)
and mobile (as appropriate under section 202(l)) source standards.
Support decisions on how to conduct future risk
assessments.
Evaluate the effectiveness of each of the four approaches
to characterizing risk reductions, described above.
Provide guidance for State, local and Tribal agency
efforts in conducting local assessments and developing risk reduction
programs at the state and local levels.
Our assessment approach will be basically iterative in nature, so
as to take advantage of emerging science, new data, and improved tools
that become available at the time future assessments are performed.
Consistent with this approach, beginning in early 2000, we'll conduct
an initial set of assessments that will be based on final, updated
emissions data, as discussed in section IV.D. Subsequent assessments
will reflect the best available data, methods, and tools available at
the time the assessments are performed.
Our national database of air toxics emissions from major, area, and
mobile sources (including diesel exhaust), the NTI, will be a
fundamental component of our risk assessments. We are now completing a
baseline NTI representing the 1990-1993 period, and obtaining State
review of a draft 1996 NTI suitable for use as input data for
dispersion and exposure models (scheduled for completion in the fall of
1999). We plan to update the NTI every three years, and to conduct
subsequent risk assessments to coincide with these revisions. Monitored
air toxics concentrations will also be an important component of our
assessment activities, in part to help us evaluate and refine our air
quality models. We are now working with the States to design and
implement a national air toxics monitoring network that will provide
important information for future assessment activities. Our plans for
the ambient monitoring network are described in more detail in section
V.A.
1. How We Will Design Our Assessments
We'll tailor each assessment to the purpose(s) it is to serve
(e.g., measuring progress against the 75-percent estimated cancer
incidence reduction goal). Accordingly, assessments will vary in scope,
level of refinement, and, thus, data and resource requirements. The
scope of each assessment will generally be defined by the following
characteristics:
The number of HAPs to be evaluated (all 188 or some
subset);
Types of source included (area, major, mobile);
Spatial resolution (for example, aggregation of results on
the national, state, urban, or neighborhood scale); and
Pathways/media to be evaluated (inhalation/air only or
multipathway/multimedia).
Further, for each assessment, we need to specify an appropriate
approach to use in estimating progress toward our risk reduction goals,
since, as discussed above, it will not be possible to directly measure
reduction in cancer incidence or non-cancer risks attributable to
hazardous air pollutant emissions. Alternative approaches, discussed in
section IV.B., range from rough approximations to more precise risk
estimates, with data and resource requirements increasing for more
precise assessments that require greater refinement.
2. How Our Assessments Will Address Disproportionate Risks
Disparities in risks from air toxics in the urban environment may
exist between different cities, between neighborhoods or demographic
groups within a city, or within a similarly-exposed population that
includes sensitive groups. In our assessments, we intend to pay
particular attention to areas, populations, and sensitive groups with
substantially higher-than-average risks.
While differences in risk between different urban areas may be
discernible from national screening-level modeling, more refined
modeling will generally be needed to evaluate localized disparities
within any one urban area. This is because highly localized disparities
may be obscured by the simplifying assumptions that are necessarily
inherent in national screening-level assessments. For this reason, the
ability of EPA or State and local authorities to assess localized risk
disparities will depend on the availability of detailed data on
emissions and population distribution, local-scale models, and
sufficient resources.
D. How Will We Design Future Assessments?
We'll conduct a series of assessments starting in early 2000 and
periodically thereafter at appropriate times during the implementation
of the Strategy. The assessments will include both national-scale and
urban-scale analyses. All assessments will incorporate the most current
data, information, and assessment tools available at the time they are
performed. As the Strategy progresses, we may eventually use risk
assessment tools that are now only in early development, or perhaps
have not yet been envisioned. For this reason, we can't describe in
detail assessments that will be conducted several years from now.
1. Initial Assessments--National
We'll conduct an initial national assessment in early 2000. This
assessment will define an appropriate hazard-or risk-based approach
consistent with the limited available information on HAP emissions and
ambient concentrations. The principal limitation of the baseline
emissions information is that, although the baseline NTI will be a
comprehensive county-level inventory, it will lack the source-specific
information necessary to support air quality modeling.\50\ Thus, any
assessment of progress relative to the base year will be limited to
using either a weighted emissions or a weighted ambient concentration
analysis, since the other approaches include an air quality modeling
step. Future assessments, however, will not be limited in this way
because emission inventory data, beginning in 1996, will include
information needed for modeling.
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\50\ We note here, as discussed in sections I.B. and II.A., that
as part of the Agency's Cumulative Exposure Project, the ASPEN model
to estimate HAP ambient concentrations nationwide was developed and
tested using a 1990 emissions inventory that was based on the
limited HAP information available in the mid-1990s prior to the
substantial improvements that are now reflected in the baseline NTI.
While that first national-scale modeling exercise provided
screening-level information that we've used in conjunction with
other information in selecting the urban HAP list, we believe that
the uncertainties in the CEP's 1990 emission inventory are too large
to support a meaningful comparison with modeled concentrations for
future years that will result from the application of the ASPEN
model using updated emissions inventories. These updated
inventories, starting with the 1996 NTI, are specifically designed
to include sufficient source-specific information to support air
quality modeling.
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The initial assessment will serve several purposes. First, we'll
develop an estimate of progress that has already been made toward the
goals of the Air Toxics Program and the Strategy. Consistent with
section 112(k) of the Act as amended in 1990, which focuses on
reductions ``below those currently experienced,'' we've established
1990 as the base year for assessing progress. To estimate progress
since the base year, we'll compare the base year emissions inventory to
the inventory for 1996, due to be completed in fall of 1999, using a
weighted emissions analysis. This assessment will be limited to the
weighted-emissions approach because the base year inventory (although a
comprehensive county-level inventory) will lack the source-specific
information
[[Page 38734]]
necessary to support air quality modeling. Subsequent assessments,
however, will not be limited in this way because emission inventory
data, beginning in 1996, will include information needed for
modeling.\51\
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\51\ Peer-reviewed examples of this approach include the EPA/
OPPT Risk-Screening Environmental Indicators, the EPA/OSW Waste
Prioritization Management Tool, and the EPA/OAQPS ranking analysis
for urban HAPs. See the public docket for a detailed list of risk
assessment references.
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Second, the initial national assessment will provide basic
information to assist us in prioritizing HAPs and area, mobile, and
major source categories for regulations to be developed consistent with
section 112(k), section 202(l) and other authorities (e.g., residual
risk), respectively, based on their relative importance as contributors
of risk. Third, the assessment will provide the clearest and most
current picture of inter-urban and demographic disparities in risk, and
will provide insight on more refined analyses that may be appropriate
to identify types of sources associated with particularly high risk
levels. Fourth, we intend to use information from the initial
assessment to develop a more complete and quantitative goal for a
``substantial'' reduction in non-cancer risk. Finally, we'll use the
initial assessment to compare different hazard- and risk-based
approaches. In particular, we intend to correlate results of assessment
approaches (1) and (2) (which lack exposure assessments) with exposure
assessment-based approaches, to determine their relative accuracy and
to quantify uncertainties. These comparisons, in combination with data
and resource availability, will help us to scope the details of future
assessments and finalize our estimates of progress from 1990 to 1996.
We'll use all four types of approaches (emissions weighting,
comparisons between ambient concentrations and exposure estimates and
RBCs, and modeled estimates of risk) in the initial national
assessments, to the extent possible. As discussed in section V.C., we
plan to use the ASPEN model to estimate national air quality
concentrations in conjunction with the use of the Hazardous Air
Pollutant Exposure Model (HAPEM) to estimate national exposures. We'll
conduct screening level analyses before progressing to more refined
analyses, to ensure that we're allocating appropriate amounts of
resources to each assessment, given our information needs. The
assessment will focus on inhalation exposures, with the expectation of
including multipathway exposures, as appropriate, in subsequent
assessments. The initial assessment will include all urban areas in the
United States, and we anticipate presenting results with county- and/or
urban-scale resolution. The assessment will address as many HAPs as the
data support, but will include at least the 33 urban HAPs and diesel
PM.
2. Initial Assessments--Urban
We plan to conduct urban-scale assessments for a number of selected
cities to serve as case studies that may be particularly useful as
guidance for State, local and Tribal program assessments. We'll also
provide technical support and risk assessment tools for authorities
that wish to conduct their own local assessments to analyze area-
specific progress and intra-urban disparities. The experience we gain
through these analyses will also help us refine future assessments.
We'll develop these initial urban assessments using the specific
approaches that are appropriate for the quality of data available. Each
assessment will describe a single urban area, and we anticipate
presenting the results with high spatial resolution (for example, a 1-
kilometer grid). The scope of each assessment will address a subset of
HAPs that we identify as being priority HAPs for the particular urban
area being assessed. We plan to consider both inhalation and
multipathway exposures as appropriate and as available data permit.
3. Periodic Assessments
In the years following the initial national assessment, we'll
conduct new analyses at appropriate intervals as new data become
available. These periodic assessments will serve two principal
purposes. First, they'll measure progress toward the goals of the
Strategy, considering all actions taken that reduce HAP emissions
(including Federal, State, local and Tribal actions, as well as
voluntary initiatives by local communities and industry) for any
purpose. Second, they'll assist us in prioritizing which future
regulatory actions would be most effective in making needed further
progress. We'll develop the periodic assessments using the specific
approaches that have proved most efficient (that is, the least
resource-intensive approach that accomplishes the purpose of the
assessment). Assessments will include all urban areas in the United
States, with results presented on county- and urban-scale level
resolution. Assessments will address the full list of 188 HAPs, to the
extent to which emissions, monitoring, and health data are available.
If appropriate tools become available, periodic assessments for
bioaccumulative HAPs will include multipathway exposures.
By measuring ongoing progress, periodic assessments will also
inform us when we have met our goals, and will help us to measure the
degree to which we have reduced disparities in risk. The approaches
used for such goal-specific comparisons will be determined by the
results of earlier assessments, and developed to fit the Strategy's
purpose.
V. Knowledge and Tools
This section describes the activities we'll undertake to improve
our base of knowledge (e.g., concerning health effects and exposure
characteristics) and tools (e.g., emissions inventories, monitoring
networks, and computer models), along with our plans for their
improvement and related research.
A. How Will We Review and Expand Ambient Monitoring Networks?
1. Need for Ambient Data
As described in section IV, our iterative approach to risk
characterization looks at emissions as a rough surrogate for risks in
the near-term, while providing for a plan to periodically conduct more
refined analyses as risk tools and data are developed. In order to base
the air toxics program on risk assessments backed by sound science,
we'll need emissions and monitoring data to conduct good assessments.
Emissions data are one way we can attribute HAP exposures to specific
sources. On the other hand, ambient monitoring data allow us to
continually evaluate and improve our models and inventories, to deal
credibly with the difficult issue of background HAP concentrations, and
to measure progress more directly. Furthermore, each type of data
(source emissions data and ambient monitoring data) can be used to
improve our understanding of the other. For example, ambient data can
warn us when our inventory or models are seriously flawed, and modeled
exposures can be used in siting monitors and directing analyses for
both short- and long-term measurements.
2. Ambient Monitoring Network Program Design
Currently, we have limited data on ambient concentrations of air
toxics, because existing networks are limited, were developed for other
purposes, or weren't specifically designed to develop the data needed
to meet our current air toxic program goals. In fact, many commenters
raised concerns that the current monitoring network was
[[Page 38735]]
inadequate and that the draft Strategy didn't adequately address this
concern. Another problem is that ambient data can be both difficult and
expensive to obtain. Our long-term plan is to build an air toxics
monitoring network consistent with the goals of the air toxics program
and the Strategy.
Since it's not possible to monitor everywhere, we must develop a
monitoring network that is representative of air toxics problems on a
national scale, but that still provides a means of obtaining data on a
more localized basis as appropriate and necessary. The appropriateness
of a candidate monitoring site with respect to the projected uses of
its data is a key consideration in identifying sites for the national
network. For example, in selecting monitor locations we must evaluate
how well the location allows us to directly evaluate public exposure
and environmental impacts in the vicinity of the monitors. We'll also
need to site monitors to allow us to obtain data that can help us
establish an ambient baseline for toxics risk characterization, track
trends in ambient levels to assess progress in meeting our emission and
risk reduction goals, and assess the effectiveness of specific emission
reduction activities.
We'll design the monitoring network to address all of the needs of
the air toxics program and the Strategy, which should satisfy the
following objectives:
Measure pollutants of concern to the overall air toxics
program and the Strategy.
Use scientifically sound monitoring protocols to ensure
nationally consistent data of high quality.
Collect a sufficient amount of data to estimate annual
average concentrations at each monitoring site.
Complement existing national and State/local monitoring
programs.
Reflect Acommunity-oriented'' (i.e., neighborhood-scale)
population exposure, including inhalation and non-inhalation exposure.
Represent geographic variability in average ambient
concentrations.
3. Network Implementation Schedule
For the first 2 years of monitoring, we'll maximize our use of
existing State/local air toxics monitoring sites, Photochemical
Assessment Monitoring Stations (PAMS) sites, or planned particulate
matter chemical speciation sites. These sites should provide coverage
of both the largest metropolitan areas and neighborhood-scale sites,
which fits with our focus on population-oriented urban sites. If
existing platforms aren't suitable for characterization of population
exposure to air toxics, we'll strive to establish new community-
oriented monitoring stations or upgrade existing ones to include urban
HAP analyses. We'll also work to establish appropriate quality
assurance, data management, data analysis, and data submission
procedures, and will use established monitoring protocols in the next
few years.
After 2000, we expect the air toxics monitoring network to continue
to grow to cover more urban areas and to include monitors in rural
areas to permit estimates of background concentrations. We also expect
to place other fixed-site monitors in areas that may be subject to
localized high concentrations of air toxics. In some cases, temporary
or mobile monitors may be used to evaluate these areas. The long term
goal for a national network includes monitoring of sensitive ecosystems
and other environmental concerns. To this end, the national network
should incorporate the separately funded deposition monitoring
activities associated with the Great Waters Program. Our tentative
projection of the national network is 200 sites, but this will be
revised as additional information becomes available and as the network
itself expands.
B. How Will We Update and Maintain the Emission Inventory?
We plan to update the NTI every 3 years using the same principles
that we used when developing the 1996 NTI. The next version will be
known as the 1999 NTI. The 1996 and subsequent NTIs will be compiled
from State and local air toxics inventories. The State and local
emission inventory data are supplemented with data gathered to support
the development of MACT standards and Toxic Release Inventory (TRI) as
well as calculated emission estimates for the majority of area and
mobile sources. Unlike the baseline inventory developed for the
Strategy, the 1996 and subsequent NTIs will contain location- and
facility-specific data making the inventory suitable for input to
dispersion and exposure modeling. These additional data are used to
determine the exact types and location of facilities in urban and rural
areas. We also expect that the quality of information available to use
in developing future inventories will improve as data quality does and
as we learn more about the locations and sources we are studying.
As discussed in the rest of section V, we plan to obtain improved
monitoring data that will influence our inventory efforts, as well as
to undertake research projects to address our data needs. One tool
we're in the process of developing is the consolidated emissions
reporting rule, whose purpose is to simplify reporting, offer options
for data exchange, and unify reporting dates for various categories of
inventories.
C. What Air Quality and Exposure Models Will We Use To Implement the
Strategy?
A variety of mathematical models are often employed to assist in
risk assessment activities. While not designed specifically to address
urban areas, several models are currently available or under
development to help describe the fate and transport of toxic air
pollutant emissions. Although there is much associated uncertainty, the
output of such models is then used as input to models that estimate
human exposure and risk. This section discusses the model development
activities and models that will be used in the air toxic assessments
discussed in section IV.
We'll rely on a variety of fate and transport modeling tools that
vary in their complexity and the scale of the geographic area that
they're capable of handling. For example, we plan to use the Assessment
System for Population Exposure Nationwide (ASPEN) model to conduct
national screening modeling for ambient (i.e., outdoor) air toxic
concentrations. This model estimates annual average ambient air toxic
concentrations by modeling the dispersion of a nationwide inventory of
HAP emissions from major, area, and mobile sources. It can also address
simple chemical transformations of air toxics in the atmosphere.
Current developmental efforts are underway to add increased model
functionality to allow for testing of various ``what-if'' emission
reduction scenarios using the ASPEN model. We'll use the Industrial
Source Complex Short-Term (ISCST3) model to estimate both short-term
(one-hour) and long-term (annual) average concentrations at locations
from the urban to neighborhood scales. The ISCST3 model can predict not
only ambient air toxic concentrations, but the amount of air toxic
pollutants that will settle to the soil and/or into bodies of water.
These settling rates are sometimes used to track the fate of air toxic
pollutants where multimedia (air, water and/or soil) exposure and risk
are of concern (e.g., with mercury). When multimedia considerations are
of concern, we'll use the environmental fate and transport module of
the Total Risk Integrated Methodology (TRIM) to determine urban and
neighborhood scale impacts. Likewise, when a HAP
[[Page 38736]]
associated with complex chemical reactions in the atmosphere is being
considered, we'll use the Community Multiscale Air Quality (CMAQ)
Model. This model is currently being developed in the EPA's Models-3
Framework, and it can be used to predict regional and urban wide
concentrations values. The Models-3 Framework also employs a state-of-
the-art meteorological pre-processor for accurate and detailed
simulation of the meteorological data for input into the CMAQ model.
Model estimates of HAPs in the ambient air (and water and soil,
when appropriate) will provide input necessary for modeling exposures.
An exposure assessment takes into account the fact that most people
don't spend the majority of their lives in an outdoor environment. An
exposure model can track day-to-day activity patterns, simulating the
movement of population subgroups (e.g, children under 5 years of age)
through different ``micro-environments'' (e.g., in homes, vehicles,
school, work, or while bathing). These activity pattern relationships
are then used to estimate levels of exposures of population subgroups
to the HAPs. One such model that we've developed for determining
inhalation exposures is the Hazardous Air Pollutant Exposure Model
(HAPEM4). This model can work in tandem with the ASPEN model to predict
long-term nationwide-scale inhalation exposures to HAPs. Applications
requiring exposure estimates through multipathway routes (e.g., through
inhalation, ingestion and dermal contact) can use the TRIM module,
TRIM.Expo, which is currently under development. We're currently
developing several other exposure models for specific applications that
we may also consider in our air toxic assessments.
As is the case with any mathematical simulation, the more detailed
and accurate the simulation required, the more complex the input data
requirements become. The availability, type, and quality of input data
will directly influence the choice of the model or models selected for
specific assessment purposes. Where gaps between input data and the
required level of detail and accuracy are identified, we're making
efforts to supplement and improve our data sets (e.g., improvements in
the NTI, establishment of national monitoring networks) to make use of
the most state-of-the-art models available.
D. What are the Research Needs and What is EPA Doing to Address Them?
The Strategy describes the process we'll use for identifying the
various risks that may be present in an urban environment. Part of that
process is to determine gaps in our scientific information and to
identify the tools we'll need to assess urban risks and to implement
the risk reduction elements of the Strategy. To address this concern,
we plan to include a ``research needs'' chapter in our forthcoming
``Integrated Urban Air Toxics Report to Congress'' (Urban Report),
which will describe the activities and research that will be needed to
assist in our assessment and management of risks in urban
environments.\52\ The Urban Report will describe the research
activities we'll undertake with the support of our Office of Research
and Development, the research activities to be done by organizations
outside of EPA and funded through our Grants program, and the research
activities described in various other EPA reports that have relevance
to the Strategy. We're also developing an ``Air Toxics Research
Strategy'' (Research Strategy) which will expand on the planned urban
``research needs'' chapter, to include information that would assist in
assessing risks on a national or regional basis.\53\ This Research
Strategy would reflect the needs of other elements of the air toxics
program, such as the residual risk and Great Waters elements.
---------------------------------------------------------------------------
\52\ We hope to release the ``Integrated Urban Air Toxics Report
to Congress'' this summer.
\53\ The ``Air Toxics Research Strategy'' will be finalized in
fall 1999.
---------------------------------------------------------------------------
In our Urban Report, we plan to present research needs using the
risk assessment/risk management paradigm developed by the National
Academy of Sciences as the basis for the requested research. This
paradigm includes activities related to health and dose-response,
emissions and exposure characterization, a risk assessment, and risk
management. Briefly, the following identifies the research areas and
describes some of our current activities:
Urban HAP health effects and dose response needs.
Additional knowledge of both cancer and non-cancer health
effects will be accumulated. This will include determinations of
specific toxicities (determined from animal and human studies) as well
as the development of models to extrapolate across HAPs, species, time,
and routes of exposure. Any such determinations should address the
effects of HAPs or other factors which make sensitive subpopulations
(e.g., children, the elderly, persons with existing illnesses) more
vulnerable to exposure and effects.
Development and updating of HAP health reference values,
such as inhalation reference concentrations, acute reference exposure
values, and cancer unit risk factors.
Statistical methods for quantifying and reducing
uncertainty in risk assessments using acute and chronic data.
Emission characterization needs.
Development of methods for measuring HAPs in emissions and
for monitoring the ambient and indoor air, and the environment (e.g.,
deposition to water). The resulting measurements will be used to
improve the spatial characterization of potential exposures and to
establish a baseline against which modeling concentrations may be
compared.
Improved procedures to estimate and assess HAP emissions
in a representative number of cities, and to extrapolate results to
other locations.
Improved models that include multiscale air dispersion
models (neighborhood, urban, and regional) which consider atmospheric
transport, fate, and their potential transformation products and which
can simulate microenvironments when estimating inhalation exposures to
urban HAPs.
Exposure characterization needs.
Improved data to better understand the potential for
disproportionate impacts on those who are more susceptible to HAP
exposures including minority and low-income communities.
Improved understanding of human indoor and outdoor
activity patterns in urban environments, especially for children.
Improved understanding of the relationship between outdoor
and indoor air and HAP concentrations.
Improved monitoring to assess multipathway exposures to
foods, such as fish, vegetables and beef, contaminated by deposition of
urban HAPs.
Risk assessment needs.
Improved risk assessment methods for chemical mixtures.
Risk management needs.
Cost-effective control technologies for all HAPs and more
effective controls for those HAPs posing residual risks even after
applying currently available controls.
Some of the major air toxic research activities currently planned
or being undertaken by EPA include:
Health effects and dose-response assessment research highlights.
A proposed test rule under Toxics Substance Control Act
(TSCA) that would require testing of 21 HAPs.
Dose-response assessment efforts for mobile source
pollutants (such as benzene, 1,3-butadiene, and various fuel additives,
including
[[Page 38737]]
methylcyclopentadienyl manganese tricarbonyl (MMT)) and urban HAPs
shown in Table 1.
Reducing uncertainty in acute and chronic dose-response
assessments through the use of statistical (and other) methods.
Improved methods for identifying and quantifying the
health effects associated with exposures to mixtures of pollutants.
Development of a mixtures database to facilitate
assessments involving more than one chemical.
Emissions and exposure characterization research highlights.
A national air toxics monitoring network.
An updated, comprehensive emissions inventory of air
toxics (the National Toxics Inventory).
Various toxic emission characterization studies that
include addressing emissions speciation for HAPs such as mercury.
Improved nonroad and highway emission prediction models.
Improved air quality models, including long-range
transport models, a new model of acid deposition, and a modeling
system, the Total Risk Integrated Methodology (TRIM), which will
provide a framework for better assessing health and ecological risks
from multipathway exposure to air toxic (as well as criteria)
pollutants.
Various exposure assessment studies and methodologies.
Risk management research highlights.
Identification of processes contributing to the HAP
emissions from area source categories, and listing of control options
and Pollution Prevention alternatives for these processes.
In addition to those research needs and activities that will be
identified in the Urban Report, research designed to improve
quantitative risk assessment and management which may have relevance to
urban HAPs, can be found in various other EPA documents. For example,
we're developing a ``Mercury Research Strategy,'' which describes the
key research questions for mercury that we plan to address over the
coming 5 years. We expect that the mercury strategy will be finalized
during 1999 (following consideration of peer review comments). A
summary description of this and other research activities and the
documents in which they are found will be included in a separate
chapter of the Urban Report. As discussed earlier, we're also
developing an ``Air Toxics Research Strategy'' that, building on the
summary research descriptions in the Urban Report, will identify key
research questions and the additional research that will be conducted
to address those questions.
VI. Public Participation and Communication
A. How Will we Encourage Stakeholder Involvement?
Because of the scope of the Strategy, we realize that various
interests may perceive it differently. As a result, we'll make every
effort to address the unique perspectives of the key stakeholders to
this process, and we'll welcome their input to support an equitable
approach to meeting our risk reduction goals. As described earlier, we
intend to hold stakeholder meetings starting early in the next fiscal
year to discuss State, local, and Tribal authority and implementation
of the Strategy. With comments already received on the Strategy and
through input from various stakeholders in these meetings, we will
develop a plan for implementing the State, local and tribal programs.
Below we have also provided more information on different groups that
we plan to involve in implementing various aspects of the Strategy.
State, Local, and Tribal Governments
National standards for mobile and major sources may not adequately
address the human health risks in urban areas because of the combined
emissions from these sources and the many different types of sources.
For this reason, we expect State, local, and Tribal agencies to play an
active role in tailoring local approaches to reduce risks in urban
areas, and we'll ask for their help in developing practical programs to
implement the Strategy. More information on their role is presented in
section III.
In a parallel effort to address the issue of roles and
responsibilities, we'll be holding a series of meetings with State and
Territorial Air Pollution Program Administrators and the Association of
Local Air Pollution Control Officials (STAPPA/ALAPCO) to develop a plan
for the most efficient and effective interaction among regulators.
Additionally, over the next year, we plan to meet with other regulatory
partners including Tribal leaders and city mayors to help shape the
coordination process. In conducting urban scale assessments as
discussed in section IV, we'll work with local communities as
appropriate to characterize the air toxics emissions within a community
(through monitoring and emission inventories), estimate the risks
associated with these emissions, and identify actions which could be
taken to reduce air toxics. We'll also explore to what extent and how
to address air toxics indoors.
Environmental Justice Communities
The cumulative impact of multiple emission sources on minority
populations and low income populations in urban areas is of special
concern. The Strategy will help identify and plan actions to decrease
emissions that affect these communities. We're already coordinating
with the National Environmental Justice Advisory Council (NEJAC) to
establish mechanisms to work with communities to help solve urban air
toxics problems. We'll work with NEJAC to explore the formation of
groups such as round tables and panels as a means to involve
communities, and other stakeholders, including representatives from
universities and hospitals. These round tables/panels would explore
issues related to rulemaking coordination, risk assessments, and the
process of defining roles and responsibilities for Federal and State,
local and Tribal agencies in implementing the Strategy.
Public Health Groups and Environmental Groups
Public health concerns are a priority in this Strategy, especially
the impact of air toxics on susceptible groups like children. We plan
to identify and address health risks to children and seniors and
welcome input on these key issues. We'll also encourage these groups to
work with us on various aspects of the Strategy, such as defining the
roles and responsibilities of State, local, and Tribal agencies.
Small Business and Industry
Because the Strategy focuses on reducing emissions from area
sources, impacts of the ultimate standards may be felt by small
businesses. We'll strive, however, to ensure that regulations don't
unfairly impact them. We also plan to involve small businesses in pilot
projects to assess and design solutions to local air toxics risks.
An example of how we'll provide concrete support to small
businesses is our EPA Small Business Innovative Research (SBIR)
Program. Under this program, we can award Phase I contracts of up to
$70,000 over 6 months to small businesses with fewer than 500 employees
to develop and commercialize new environmental technologies. The awards
are based on the scientific merit and technical feasibility of the
proposed technology. The results of Phase I determine whether the
research idea is technically feasible, whether the firm can do high-
quality research, and whether sufficient
[[Page 38738]]
progress has been made to justify a larger Phase II effort. We can
award Phase II contracts for up to $295,000 over 2 years to
commercialize the technology or product. The FY2000 Phase I
Solicitation will open on August 11, 1999 and close on October 13,
1999. Copies of the solicitation will be posted on August 11, 1999 on
our website at: http://www.epa.gov/ncerqa. The solicitation will also
be available by fax at the EPA SBIR Helpline: 800-490-9194.
In addition, large businesses could be affected by programs and
regulations developed to implement the Strategy. As always, we'll work
with industry representatives to try to develop technically sound,
effective regulations that minimize the burden to affected sources.
Urban Developers
In designing the Strategy, we've tried to avoid unfairly limiting
the efforts of developers interested in creating business opportunities
in urban industrial sites or areas needing revitalization. We plan to
work with these interests to ensure that public health protection is
achieved and economic development is encouraged.
As with our previous air toxics regulatory development efforts, our
efforts under the Strategy will involve stakeholders as early as
possible in the process. We recognize that opportunities for public
participation beyond the required notice and comment process help
ensure we develop the most workable requirements that still achieve our
environmental goals. We'll use the established urban air toxics
Strategy website on the Internet (www.epa.gov/ttn/uatw/urban/
urban.pg.html) to update the public on ongoing activities and
opportunities to participate in implementation of the Strategy. This
will include updates on rule development, assessment activities, and
progress toward meeting all of the Strategy goals. You can find
information on all of our air toxics regulations at the following
website on the Internet: www.epa.gov/ttn/uatw.
B. What is our Overall Timeline for Action?
Many of the activities identified in the Strategy will require
further public notice and comment, and we'll provide further
opportunities for stakeholder input as they are developed. The public
will also be able to measure the progress of the Strategy by tracking
the following milestones projected in the coming five years:
1999
--Publish the Integrated Urban Air Toxics Strategy, including the
urban HAPs list and the area source category list.
--Issue the first Integrated Urban Air Toxics Strategy report to
Congress under section 112(k)(5).
--Complete 1996 NTI update.
--Begin State/local/Tribal stakeholder communication and
information exchange on implementing the Strategy.
--Propose motor vehicle and fuel standards under section 202(l).
2000
--Complete initial national and urban scale assessment.
--Complete motor vehicle and fuels standards development under
section 202(l).
--Start development of additional area source standards.
2002
--Complete 1999 NTI update.
2003
--Complete 1999 assessment.
--Finalize source category list.
2004
--Promulgate standards for the area source categories newly listed
in today's strategy.
We'll attempt to meet this demanding schedule as expeditiously as
practicable. We're currently engaged in significant efforts to develop
standards for stationary sources that were previously listed under
section 112(c). In addition, realistic schedule and resource
constraints suggest that our efforts to develop additional standards
should be phased in over time.
C. What Reports Will we Prepare To Communicate With the Public?
We're required under section 112 of the Act to provide two reports
to Congress on actions taken to reduce the risks to public health posed
by the release of HAPs from area sources. The Act also requires that
the reports identify specific metropolitan areas that continue to
experience high risks to public health as the result of emissions from
area sources.
We'll submit our first report in late 1999. This report will
provide more specific information about our Strategy, including further
details on the methodologies we used to develop the final urban HAPs
list and the list of source categories. The report will also provide an
overview of previous studies conducted in various cities to
characterize their respective urban air toxics problems and contain a
detailed discussion of the research needed to achieve the goals of the
Strategy. We also expect to report to the public about air toxics
emissions trends and air quality in urban and other areas in our annual
Air Quality and Emissions Trends Reports.
Dated: July 6, 1999.
Robert Perciasepe,
Assistant Administrator for Air and Radiation.
Appendix A--Summary of Other Authorities, Laws, Rules, and Programs to
Help Reduce HAP Emissions
There are a number of other authorities, laws, rules, and
programs that will help reduce emissions of HAPs and consequent
exposures and risks. Some of these are discussed below. We're
currently evaluating the appropriateness of these statutes for
controlling emissions of HAPs as described under section 112(k)(3)
and intend to take further actions under these statutes as
appropriate.
As discussed in section I., the Strategy involves collaboration
between offices within the air program to assess the risks from
exposures to air toxics indoors and will assimilate non-regulatory,
voluntary programs developed to address those risks. Title IV of the
Superfund Amendments and Reauthorization Act (SARA) provides EPA
with the authority to perform research and provide information to
the public on the health problems associated with air pollutants in
the indoor environment.
Under the Toxic Substances Control Act (TSCA), chemicals
produced or imported into the United States are evaluated as to
toxicity to human health and the environment. To prevent adverse
consequences of the many chemicals developed each year, TSCA
requires that any chemical that will reach the consumer marketplace
be tested for possible toxic effects prior to commercial
manufacture. Any existing chemical that is determined to pose health
and environmental hazards is tracked and reported under TSCA.
Procedures also are authorized for corrective action under TSCA in
cases of cleanup of toxic materials contamination. The TSCA is a
complementary authority to the Clean Air Act and has contributed to
decreased emissions of several HAPs. For example, concern over the
toxicity and persistence in the environment of polychlorinated
biphenyl (PCB) compounds led Congress to include in TSCA
prohibitions on the manufacture, processing, and distribution in
commerce of PCBs (TSCA section 6(e), 15 U.S.C. 2605(e)). In 1990,
TSCA authority was relied upon to eliminate chromium use in, and
emissions from, comfort cooling towers (i.e., industrial process
cooling towers used exclusively for cooling, heating, ventilation,
and air conditioning systems).
There are several provisions of the Resource Conservation and
Recovery Act (RCRA) and its amendments which may yield reductions of
urban air toxics. One impact evidenced in the 1990's is increased
recycling and recovery of hazardous waste, including solvents which
through volatilization contribute to HAP emissions. Section 3004(n)
of RCRA has been the basis of a three-phased regulatory program to
control air emissions from hazardous waste
[[Page 38739]]
treatment, storage and disposal facilities. The third phase would
address any risks remaining after implementation of the control
regulations issued in 1990 and 1994, which were estimated to reduce
organic emissions by more than one million tons per year. Any
resulting emissions and risk reductions can be considered in
assessing progress toward the 75-percent reduction in cancer
incidence from the baseline.
Under the Comprehensive Environmental Response, Compensation and
Liability Act, commonly known as Superfund, the clean-up of
abandoned hazardous waste sites may also reduce emissions of HAPs.
Where significant health risks from chemical releases to the air
have been identified at Superfund sites in urban areas, clean-up
will reduce risks from urban air toxics.
Under the Clean Water Act (CWA), controls on the discharge of
pollutants to surface water can also reduce the amount of HAPs
entering the environment. These controls may take the form of
national technology-based standards under the effluent guidelines
program or site-specific water quality-based controls to achieve
State water quality standards. In addition to providing control by
establishing discharge limitations on pollutants (including HAPs) in
the wastewater, process changes made in order to comply with these
limitations may also reduce fugitive emission sources.
As part of the effluent guidelines program under the CWA, we've
issued effluent limitations for the pharmaceuticals industry. Human
health benefits from these guidelines include reductions in excess
cancer risk through inhalation. The regulatory impact assessment
prepared for these guidelines estimates that the number of excess
cancer cases avoided per year nationwide ranges from 0.02 to 0.35.
These reductions are due to reductions in VOC emissions, including
10 carcinogens (principally chloroform and methylene chloride). We
can also point to air toxics benefits from the effluent guidelines
for the pulp, paper, and particleboard industry. These regulations,
coupled with the associated NESHAP, are expected to decrease
background emission of HAPs by 121,200 megagrams annually.
If a waterbody isn't meeting water quality standards even after
all technology-based controls under the effluent guidelines program
are in place, the State, local agency, or Tribe must list the water
as ``water quality limited'' and prepare a ``total maximum daily
load'' (TMDL) calculation that allocates the maximum amount of
pollution, with a margin of safety, that the waterbody can absorb
from point and nonpoint (including air deposited) sources. A plan
must then be developed to implement the TMDL, which might include
provisions to address air sources under Federal or State (or local
or Tribal) programs. We're conducting a pilot project in two
waterbodies to develop TMDLs identifying the relative contributions
of mercury from various air sources. This project will also examine
how Federal and State water programs can work together to reduce
mercury contamination of water.
The Federal Insecticide, Fungicide and Rodenticide Act (FIFRA)
provides Federal control of pesticide distribution, sale, and use.
Several HAPs listed in Clean Air Act section 112(b) have been used
as pesticides. An EPA registration is required of all pesticides
sold in the United States and is intended to ensure that pesticide
use, when in accordance with label specifications, doesn't cause
unreasonable harm to people or the environment. It's a violation of
FIFRA to use a pesticide in a manner inconsistent with its label.
Registered pesticides classified as ``restricted use'' may only be
used by registered applicators who have passed a certification exam.
This restricted use requirement minimizes the number of persons
having access to certain pesticides. The FIFRA regulations may also
reduce emissions and exposures by banning (canceling or denying
registration) or severely restricting pesticide use. Seven
individual HAPs and members of three HAP compound groups have been
banned or severely restricted in their use as pesticides.
Two other Federal laws, the Emergency Planning and Community
Right-To-Know Act (EPCRA) of 1986 and the Pollution Prevention Act
(PPA) of 1990, while not directly regulating air emissions of HAPs,
may influence decisions regarding chemical usage and storage, and
yield significant reductions in air toxics risks in urban areas. The
goal of EPCRA is to reduce risks to communities through informing
communities and citizens of chemical hazards in their areas.
Sections 311 and 312 of EPCRA require certain facilities to report
the locations and quantities of chemicals stored at their facilities
to State and local governments. This information is used by State
and local agencies in preparing for, and responding to, chemical
spills and similar emergencies.
Through EPCRA, Congress mandated that a Toxics Release Inventory
be made public. The TRI provides citizens with information about
potentially hazardous chemicals stored, manufactured and used in
their community. Section 313 of EPCRA specifically requires certain
manufacturers and all Federal facilities to report to EPA and State
governments, all releases of any of more than 600 designated toxic
chemicals to the environment (including most of the 188 HAPs). Each
year, more than 20,000 manufacturing facilities and 200 Federal
facilities submit information to us on the releases of chemicals to
the environment. We compile these data in an on-line, publicly
accessible national database, which is a significant source of
information regarding HAP emissions. Reporting requirements for TRI
became more comprehensive in 1991, highlighting the importance of
pollution prevention. In 1997 we added seven industry groups (metal
mining, coal mining, RCRA subtitle C TSD and solvent recovery,
petroleum distribution, electricity generating, and chemical
distribution). We believe that for the manufacturing sector this
public spotlight on releases and other waste management of toxic
chemicals has led to reductions in their environmental release.
We're also planning to lower the reporting thresholds under the TRI
for several persistent, bioaccumulative toxic chemicals, including
mercury and dioxin, that can cause human health and environmental
damage at very low levels, so that additional information on
releases will be available to the public.
The passage of the Pollution Prevention Act (PPA) established an
environmental hierarchy that establishes pollution prevention as the
first choice among waste management practices. Traditionally, much
environmental protection has involved controlling, treating or
cleaning up pollution. Pollution prevention, which eliminates or
minimizes pollution at the source, is most effective in reducing
health and environmental risks because it (1) eliminates any
pollutant associated risks, (2) avoids shifts of pollutants from one
medium (air, water or land) to another, which can result from
certain waste treatments, and (3) reduces waste of natural
resources. For waste that cannot be avoided at the source, recycling
is considered the next best option. A waste generator should turn to
treatment or disposal only after source reduction and recycling have
been considered. Pollution prevention strategies include redesigning
products, changing processes, substituting raw materials for less
toxic substances, increasing efficiency in the use of raw materials,
energy, water, land and other techniques. The EPA implements the PPA
by promoting voluntary pollution reduction programs, engaging in
partnerships, providing technical assistance, funding demonstration
projects and incorporating cost-effective pollution prevention
alternatives into regulations and other initiatives.
In addition, we've developed the ``Waste Minimization National
Plan,'' a voluntary, long-term effort to reduce the quantity and
toxicity of hazardous waste through waste minimization. The plan was
built on extensive stakeholder involvement and was released in 1994.
The plan focused on the following key objectives:
Prioritize pollution prevention efforts based on risk.
Promote source reduction over recycling.
Adopt a multi-media approach and prevent cross media
transfers.
Provide flexibility in implementing pollution
prevention activities.
Provide accountability and measure progress.
Involve the public.
The plan calls for a 50-percent reduction in the presence of the
most persistent, bioaccumulative and toxic (PBT) chemicals in
hazardous waste by 2005.
The starting point for selecting chemicals for the national
waste minimization list is EPA's ``Waste Minimization Prioritization
Tool,'' which is a software program that provides a screening-level
assessment of the potential chronic risks that chemicals pose to
human health and the environment, based on their persistence,
bioaccumulative potential, and human and ecological toxicity. This
software program contains full or partial PBT data for approximately
4,200 chemicals. The draft ``Waste Minimization Prioritization
Tool'' was released for public comment on June 23, 1997 (62 FR
33868). We made significant changes in response to public comment
and published a revised version on November 9, 1998 (63 FR 60332).
The revised software, in conjunction with a publicly
[[Page 38740]]
reviewed methodology, was used to generate a draft list of 53 PBT
chemicals, which is now in the process of being finalized.
[FR Doc. 99-17774 Filed 7-16-99; 8:45 am]
BILLING CODE 6560-50-P
