DOLICY AND PROCEDURES FOR IDENTIFYING, ASSESSING,  AND



REGULATING AIRBORNE SUBSTANCES POSING A RISK 0^ CANCER



                     PROPOSED RULE
     OFFICE OF AIR QUALITY PLANNING AND STANDARDS

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               Title 40 - Protection of the Environment
              CHAPTER 1 - ENVIRONMENTAL PROTECTION AGENCY
                      SUBCHAPTER C - AIR PROGRAMS
                         [               ]
  PART 61 - NATIONAL EMISSION STANDARDS FOR HAZARDOUS AIR POLLUTANTS
  POLICY AND PROCEDURES FOR IDENTIFYING, ASSESSING, AND REGULATING
          AIRBORNE SUBSTANCES POSING A RISK OF CANCER
AGENCY:    Environmental Protection Agency
ACTION:    Proposed Rulemaking
SUMMARY:   This notice proposes for comment a rule governing the policies
and procedures to be used by the Environmental Protection Agency in the
identification, assessment, and regulation under the Clean Air Act of
substances which, when emitted into the ambient air from stationary
sources, increase the risk of cancer to the general population.  In
concert with this proposal, EPA is publishing elsewhere in today's
Federal Register an advance notice of proposed rulemaking soliciting
comments on draft generic work practice and operational standards which
could be applied quickly to reduce emissions of airborne carcinogens
from certain source categories.
     Under the proposed policy., EPA would evaluate available information
to identify those substances, including radioactive materials, which
should be considered for regulation under the Clean Air Act as airborne
carcinogens.  Any air pollutant determined to present a significant
carcinogenic risk to human health as a result of air emissions from one
or more categories of stationary sources would be listed under section
112 as a hazardous air pollutant.  Listing under section 112 would be
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accompanied, where applicable, by the proposal of generic standards for
source categories producing or handling significant quantities of the substance.
The generic standards would rapidly effect reasonable control of emissions
while more detailed analyses are performed to establish priorities for
further regulation, determine available control technology, and assess
regulatory impacts.
     Final standards for source categories presenting significant risks
to public health would, as a minimum, require such sources to use best
available technology to reduce emissions.  If, however, the risk remaining
after the application of best available technology is determined to be
unreasonable, further control would be required.  Unreasonable residual
risk determinations would consider the risk remaining, the benefits
conferred by the substance or activity, the distribution of those benefits
versus the distribution of risks, the availability of substitutes, the
costs of further control of the substance or source categories, and
proposed sites in the case of new sources.  Standards would be reviewed
at no more than five-year intervals.
DATES:  Written comments should be postmarked no later than [60 days from
date of publication],  .nformal public hearings will  be held in Washington,
O.C. and Houston, Texas during the comment period.  Hearing dates and loca-
tions will be announced in the Federal Register.  Notices of intent to appear
at a public hearing should be postmarked no later than [45 days from date
of publication] and should be directed to Joseph Padgett, Director, Strategies
and Air Standards Division (MD-12), Environmental  Protection Agency, Research
Triangle Park, North Carolina  27711.  The record of each public hearing will
remain open for 30 days for submission of written comments responding to,
supplementing, or rebutting previous written or oral  comments.   EPA encourages

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interested parties to consi-der the comments of others and to submit such
additional comments.
ADDRESSES:  Pursuant to section 3Q7(d)(l)(N) of the Clean Air Act, 42 U.S.C.
7606(d)(l)(N), the provisions of section 307(d) apply to this rulemaking.  The
documents on which this proposal is based are contained in docket Number
OAQPS 79-14.  All comments received during the comment period will be added
to the docket promptly, and all documents upon which the final rule is based
will be included in the docket.  The docket will be open for public inspection
between 8:00 a.m. and 4:00 p.m. Monday through Friday at:
     Central Docket Section, Room 2903B
     Waterside Mall, 401 M Street, S.W.
     Washington, D.C.  20460
All written comments should be directed to the above address and should contain
the docket Number, OAQPS 79-14.
FOR FURTO INFORMATION CONTACT:  Joseph Padgett, Strategies and Air Standards
Division (MD-12). Office of Air Quality Planning and Standards, Environmental
Protection Agency, Research Triangle Park, North Carolina  27711.
AVAILABILITY OF RELATED INFORMATION:  As described above, documents upon
which this proposal is based are available for public inspection in the
rulemaking docket (OAQPS 79-14).  In addition to these materials, this notice
includes a supplemental statement of basis and purpose containing further
discussion of the legal basis for the proposed policy, various alternative
control strategies considered, and comparisons with other carcinogen policy
proposals.  This statement follows the text of the proposed rule.

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SUPPLEMENTARY INFORMATION:
I.  BACKGROUND:   THE NEED FOR A POLICY AND A REGULATORY MECHANISM
                            A.  INTRODUCTION
     The principal focus of the nation's air pollution control  program to
date has been the establishment and implementation of standards related to
six major pollutants (particulate matter, sulfur oxides, ozone, nitrogen
oxides, carbon monoxide, and lead).  Recently, increasing attention has
been directed towards those toxic components of air pollution which may not
be adequately controlled by current programs.  Pollutants that may contribute
to the occurrence of human cancer have received particular attention because
of the nature and seriousness of this group of diseases, and because of re-
cent findings suggesting that a large number of airborne chemicals and radio-
nuclides to which people are exposed may be implicated in cancer and other
                                   1 2 3
diseases related to genetic damage. ' '

                     B.  THE GENERAL CANCER PROBLEM
     The nature and magnitude of the cancer problem in the United States and
the fact that radioactive agents and some chemicals can produce cancer in
animals and humans have been well-doci merited and publicized.V  Some of the
more important aspects of the occurrence and causes of cancer and the role
played by air pollution are briefly summarized below.
(1) Nature and Magnitude of the Problem4'5'6'7'8
     Cancer is a group of diseases characterized by the unrestrained growth
of cells that have somehow lost an essential self-regulatory mechanism.  The
uncontrolled growth of these cells eventually threatens the life of the host
organism.  Cancer is currently the second leading cause of death in the
V  Detailed discussion of the general features of the problem havg been
    presented by the Occupational Safety and HealthgAdministration", the
    Consumer Product Safety Commission , and others ''.

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United States.  One American in four is expected to contract some form
of cancer in his or her lifetime, and one in five is expected to die
from the disease.  The most recent statistics show a continued increase
in total cancer incidence, due principally to increases in lung cancer.
     The social, economic, and human costs of cancer are immense.  Most
forms of cancer are difficult if not impossible to cure; less than one-half
of all cancer patients live longer than five years from the discovery of
their illness.  The elusiveness of cures is due largely to the fact that
cancer's basic biological  mechanisms at the cellular level are not well
understood.   Approximately 1.8 billion dollars are spent each year for
hospital care of cancer patients; significant additional costs not readily
estimated include doctor's fees, out-patient therapy, and drug costs.  In
addition, it is estimated that 1.8 million work-years are lost annually
because of cancer.
(2) Causes of Cancer:   Importance of Environmental Factors
     Studies of human cancer rates, their worldwide geographical variations,
and observations of incidence rates in migrant populations have revealed
that factors in the human environment are probably responsible for a
large proportion of cancers.  "Environmental factors" must be understood
in the broad sense to include chemical exposures from smoking, diet,
occupation,  drinking water, and air pollution; various forms of radiation,
including sunlight; and some forms of severe physical irritation.  Although
the uncertainties are great, estimates by the World Health Organization,
other prominent institutions, and individual experts have suggested that
                                                                  7 9
60 to 90 percent of all human cancers may be due to these factors. '

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     Studies of cancer incidence in particular groups have shown strong
statistical relationships between exposure to certain chemical  or radioactive
substances and specific cancers.  The connection between tobacco smoke and
lung and other cancers is the most widely known.    Significant increases in
leukemia and other forms of cancer have been noted among Japanese survivors
of atomic bomb explosions during World War II.  Markedly elevated cancer
rates are found among certain occupational groups in the United States and
other highly industrialized countries.  In general, cancer rates are higher
than average in urban areas.
     Unequivocal identification and quantification of the specific
factors that lead singly or in combination with other factors to specific
forms of cancer in humans is, however, an extraordinarily difficult task.
Observation from human experience is complicated by a number of factors.
Purposeful experimentation on humans, for example, is ethically unacceptable,
since the result would ofte.i be fatal.  Definitive epidemiological  studies
of occupationally exposed groups are often difficult because the relatively
small population exposed and inadequate information about duration, magnitude,
and circumstances of exposures may not permit statistically reliable conclu-
sions to be drawn.  Studies of the causes of cancer in the general  population
may be equivocal because of the complex modes of exposure, low exposure
levels, and other complicating factors.  In addition, synergistic and antagon-
istic interactions between chemicals may substantially complicate any
conclusions about the effects of a particular chemical.
     Another major difficulty in the interpretation of such studies is the
long latency period between exposure to carcinogens and onset of the disease.

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Most cancers observed in today's population probably had their origins in
exposures that began 15 to 40 years ago. '    Thus, epidemiological studies
in current populations must involve estimation of historical exposures.  The
latency period also means that epidemiology cannot detect effects of rela-
tively new substances until years of exposure have occurred.
     To date, epidemiological studies have identified only 26 environmental
                                                   12
agents believed to increase cancer risks in humans.    The causal
relationships implied by the statistical connections in these studies
have generally been supported by controlled experiments on animals.
With the possible exceptions of benzene and arsenic, those factors known
                                                               34
to produce cancer in humans also produce cancer in test animals  .
Animal experiments have also implicated many additional chemical substances
as potential human carcinogens.
     In addition to the potential that a substance acting alone may induce
cancer, there is evidence that exposure to certain combinations of
carcinogenic and non-carcinogenic agents may promote or potentiate the
carcinogenic response.  The disproportionate risk of lung cancer to
                                                           ?fi ^7
cigarette smokers occupationally exposed to asbestos fibers  '   is an
example of t!2 synergism of two known human carcinogens.  Non-carcinogenic
and co-carcinogenic substances may also act to promote or enhance the
human response to carcinogen exposure.
     Although airborne carcinogens may induce cancer at a number of body
sites, lung  cancer is thought to be the principal form of cancer related to
air pollution  .  While cigarette smoking is probably the most important
cause of lung cancer in the United States  '  , many scientists believe that
various air  pollutants increase the risk of cancer from smoking and other
carcinogenic insults.  Available estimates also indicate that occupational
exposures are responsible for a significant portion of lung cancer incidence
in the United States10'17.
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     Because of the difficulties inherent in studying the causes of cancer
and the multifactorial nature of human exposures, the role of each major
exposure pathway remains a matter of some debate.  While factors such as
smoking, occupational exposures, diet, and solar radiation are probably
responsible for a greater proportion of cancers than ambient air pollution
alone,  '      the dimensions of the problem posed by airborne carcinogens
remain significant.  Besides their contribution to cancers primarily
related to other pathways, airborne carcinogens themselves pose risks to
large numbers of people.  In certain industrialized areas, especially,
composite national figures may mask significantly higher air pollution-
related cancer risks.  And, in the vicinity of specific sources of
carcinogenic emissions, risks to individuals can reach very high levels.
     A preliminary EPA examination of chemical production, industries pro-
ducing radioactive materials, and air sampling results has identified over
fifty known or potential chemical carcinogens and numerous radioactive
materials which may be emitted to the atmosphere.  Many of these substances
are synthetic organic chemicals that have been in commercial  use only since
           1 g
the 1930's.    Since cancer induced by exposures to small  amounts of airborne
carcinogens may not appear for 15 to 40 years after exposure, it is still  too
early to detect the full impacts of these chemicals on human  health.  Thus,
                                    A
it is both prudent and, in view of the large number of people potentially
affected, important to reduce or contain emissions of known or suspected
atmospheric carcinogens in order to prevent future problems before they
actually are observed.
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               C.  PROBLEMS IN REGULATING AIRBORNE CARCINOGENS

(1) Introduction
     Although significant reductions in emissions of airborne carcinogens
have resulted indirectly from control  of pollutants such as particulate
      19                               20
matter   and volatile organic chemicals   under sections 109 and 111  of the
Clean Air Act,*/ EPA has taken direct regulatory action to control  air
carcinogens primarily under section 112*jV.  Section 112, National  Emission
Standards for Hazardous Air Pollutants (NESHAPs), provides for the listing
of pollutants which in the judgment of the Administrator cause or contribute
to air pollution which may reasonably be anticipated to result in an increase
in mortality or an increase in serious irreversible, or incapacitating revers-
ible, illness.  After a substance is listed as a hazardous air pollutant, EPA
must establish control requirements for various source categories which emit
the substance.  The standards must, in the judgment of the Administrator,
provide an ample margin of safety to protect the public health from such
hazardous air pollutants.  Carcinogens that have been listed under
section 112 to date include asbestos, beryllium,***/ vinyl chloride, and
benzene.   A number of specific emission source categories of these
                               21 22
substances have been regulated.  '
     A number of scientific, technical, and policy problems have arisen
which complicate the regulation of airborne carcinogens under section 112.
*/    42 U.S.C. Sections 7409 and 7411.
*V   42 U.S.C. Section 7412.  Since the Clean Air Act provides for separate
      treatment of mobile source emissions under Title II, this policy
      addresses only air emissions from stationary sources. At this time,
      carcinogenic emissions from stationary sources appear to present a
      larger and more diverse public health problem than mobile source emissions.
***/  Beryllium was listed because of its non-carcinogenic toxic properties.
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Significant delays in establishing standards have been associated with
determining the appropriate degree of control for certain sources of
listed carcinogens.  Although the determination of whether and to what
degree a particular chemical presents a risk of cancer to humans has not
yet been a significant source of delay under section 112, future disagreements
are anticipated.  This may be particularly true when dealing with substances
for which epidemiological data are not available.  These problems and
their consequences are discussed in the following sections.

(2) Difficulty in Determining Carcinogen!city
     The carcinogenic substances listed under section 112 to date were
recognized as human carcinogens on the basis of epidemiological evidence.
For most other chemical substances, however, such evidence will not be
available, and o~her means of assessing carcinoger.icity will have to be
employed.
     Protection of public health from current and future cancer risks there-
fore requires reliance on the results of laboratory tests, primarily involv-
ing animals, in the identification of probable human carcinogens.  Practical
limitations require that most animal tests be conducted with much smaller
numbers of subjects than the human populations they represent, and at
doses much higher than ambient exposure levels to improve the detectability
of carcinogenic effects.
     Evaluation of the carcinogenic risk to humans, based on such animal tests
of candidate substances, raises a number of issues.  Among these are the
differences between species, extrapolation from the high doses administered
to animals to the low concentrations present in the ambient air, differences
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in routes of exposure (e.g., ingestion versus inhalation), the significance
of benign tumors, and the question of no-effect "thresholds" at lower ex-
posures.  Since animal testing is of key importance in carcinogen identifi-
cation, policy decisions must be made and articulated on each of these issues.

(3) Problems Associated With the Large Number of Potential Air Carcinogens
    and Sources
     Further difficulties in dealing with air pollution-related cancer
result from the large number of potential atmospheric carcinogens and the
correspondingly large number of sources emitting them.  Preliminary analyses
have identified a number of source types which may emit carcinogenic substances
to the atmosphere.  Most of these types fall into one of the following six
broad groups:  (1) mining, smelting, refining, manufacture and end-use of
minerals and other -inorganic chemicals; (2) combustion; (3) petroleum refining,
distribution, and storage; (4) synthetic organic chemical  industries and
end-use applications, and waste disposal; (5) mining, processing, use, and
disposal of radioactive substances and radioactive by-products; and (6)
non-carcinogenic emissions which are chemically transformed into carcinogens
in the atmosphere.
     A survey of several thousand potential toxicants emitted from one
broad category, the synthetic organic chemical industry, has identified
                                                       18
over six hundred organic chemi'cals of possible concern.    Of these, over 140
showed some indication of possible carcinogenicity, mutagenicity, or terato-
genicity.  The results of a preliminary analysis of these substances suggest
that as many as 40 of these substances are of concern as potential air car-
        29
cinogens  .  Although the synthetic organic chemical industry comprises the
                                   11

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largest source grouping, a number of additional  organic and inorganic air
pollutants of concern, and a number of radioactive materials, are emitted
from the other source categories.
     Currently, EPA has only limited information on the emission rates,
sources, and atmospheric concentrations of most potential  airborne
carcinogens.   As a result of the generally low ambient concentrations
expected from emissions of many of these substances, as well  as their
large number, source emissions testing and atmospheric monitoring programs will
be more sophisticated and expensive, but less accurate or precise,
than traditional air pollution monitoring.  The resources necessary for
developing such programs and for evaluating the health effects and
control alternatives for this large number of substances and  sources far
exceed those currently available to EPA for the task.  Clearly, priorities
must therefore be established to maximize the public health benefits
obtainable with existing resources.

(4)  Difficulty in Determining the Appropriate Degree of Control
     As noted above, a central problem in establishing standards and require-
ments for air carcinogens under section 112 of the Clean Air  Act has been
determining the appropriate degree of control which should be required for
significant source categories.  The difficulty is related both to the character-
istics of carcinogens and to the requirement of section 112 that the public
health be protected with "an ample margin of safety."
     As discussed above, most identifications of substances as probable
human carcinogens have been based on studies of humans or animals exposed to
                                     12

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relatively high doses of the substances.   Whether the smaller doses generally
encountered in the ambient environment cause cancer or, whether instead,
some threshold or "safe" level  of exposure may exist is a matter of considerable
                  23
scientific debate.    EPA and other public health agencies and groups have,
as a matter of prudent health policy, taken the position that in the absence
of identifiable effect thresholds, carcinogens pose some risk of cancer
at any exposure level above zero.  The existence of risk at any exposure
level has created difficulty in setting required control levels.  Some
commenters have maintained that no risks  should be permitted from emissions
of carcinogens, while others argue that,  in view of the uncertainty that
any effect will occur at low exposure levels, only feasible and clearly
cost-effective controls should be required.
     This difficulty has been compounded  by the language of section 112
itself, which calls for the establishment of standards which, in the judgment
of the Administrator, provide "a-- ample margin of safety to protect the
public health" from hazardous air pollutants.  This language clearly mandates
that the primary factor in standard-setting under section 112, in contrast
to some other sections of the Act, such as section 111, be the protection of
public health.  How this mandate should be translated into standards for
airborne carcinogens, however, is not clear.  This uncertainty has led
to delay and litigation, with some arguing that the only factor that may
be considered is health effects, while others contend that EPA should
simply balance risk against the _cost of control and the benefits of the
activity, giving all factors equal weight.   While EPA has made limited
          21 22
statements  '   of its view of section 112, the Administrator has not
expressed a comprehensive interpretation of the provision as it applies
to the regulation of carcinogens until now.
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(5)  EOF Petition
     Citing concerns over the limited number of carcinogens listed as hazardous
air pollutants to date and the regulatory delays encountered in controlling
vinyl chloride, the Environmental Defense Fund (EOF), in November 1977,
petitioned EPA to adopt a generic approach for classifying and regulating
carcinogenic air pollutants under the Clean Air Act  .
     The EOF proposal is patterned on the classification system proposed by
OSHA and is based on scientific criteria similar to those articulated by
                                                       */
CPSC, OSHA, and EPA for carcinogenicity determinations.-   Suspect substances
would be grouped into three categories (confirmed, probable, possible) based
on the available evidence of carcinogenicity.  Under the main feature of the
policy suggested by EOF, a determination that an air pollutant is a confirmed
carcinogen would trigger the following responses:  (a)  immediate listing as
a hazardous air pollutant under section 112; and (b) proposal and promulgation
of regulations to (1) either ban the use of the material if a suitable
substitute exists, or to require the application of emissions or equipment
standards representing best available control technology; (2) establish a
timetable leading to the reduction of emissions to zero at both existing and
new sources; and (3) prevent any increase in emissions  from additions to or
replacements of existing facilities.
     In March 1978, EPA conducted a public meeting to receive comments on
the EOF proposal and any other suggestions regarding the Agency's regulatory
                                               31 32**/
process for the control of airborne carcinogens  '  — .  One major presen-
tation made at that meeting was by the American Industrial Health Council
(AIHC), advocating the use of a central board of non-governmental scientists
V A comparison of these approaches is presented in the supplemental
   statement which follows the text of the proposed rule.
j^VThe comments received at that meeting have been considered in the formulation
   of today's proposal.
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for evaluating carcinogenic!ty and carcinogenic potency of substances of
                                            33
interest for all federal regulatory agencies  .  The principles AIHC recom-
mended for determination of carcinogenicity differ somewhat from those
proposed by EPA, CPSC, and OSHA.  AIHC also recommended that standards be set
independently for each substance through a process of "balancing" predicted
cancer incidence, costs of control, and benefit of the substance regulated.
While AIHC gave examples of alternative balancing procedures which might be
used, it did not recommend any specific course of action to EPA for use under
section 112.

(6)  Need for an Air Carcinogen Policy
     The problems associated with the determination of carcinogenicity, the
large number of potential carcinogens, and the appropriate level of control
of emitting sources contribute to delays in decisions to list
carcinogenic substances as hazardous air pollutants as well as to delays
in establishing control requirements under section 112.  Indeed, EPA
has listed only three air pollutants as carcinogens under section 112
since 1S70.  Therefore, given the potentially large number of airborne
carcinogens which may require control, the general unavailability of epidemio-
logical data for determining carcinogenicity and potential risks, the require-
ments of section 112, and EPA's experience under section 112 to date, the
Administrator has concluded that the establishment of a comprehensive and
coherent policy and set of procedures for regulatory action in dealing with
airborne carcinogens is imperative.
     Specifically, publicly-stated, legally binding policies and regulatory
mechanisms are  needed for:  (1) determining the carcinogenicity and carcinogenic
risks of air pollutants for regulatory purposes;  (2) establishing priorities
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for evaluating the need for and accomplishing additional  regulatory action; (3)
specifying the degree of control required in general  under section 112 and how
that level of control will be determined in setting individual  standards;
and (4) providing more extensive public involvement in the Agency's decision-
making on the regulation of airborne carcinogens.    Among the benefits
of adopting such a policy, in addition to more expeditious control of
probable carcinogens, are increased public understanding  of and participation
in EPA's actions and the providing of earlier notice of EPA's findings and
intent to state and local regulatory authorities and to industries.

II.  DISCUSSION OF THE PROPOSED RULE

                               A.  INTRODUCTION
     The provisions of the proposed rule are stated formally at the end of'
this notice.  The following sections present the Agency's rationale for, and
describe the operation of, the proposed policy.  Certain  related issues,
including the detailed legal basis of the proposal, the consideration of
various alternatives, and a comparison vith other policies, are discussed in a
supplemental statement of basis and purpose following the text  of the pro-
posed rule.  The Administrator intends to publish a finding at  the time of
                                     *
the promulgation of this rule stating that the rule is based on determina-
tions of nationwide scope and effect.  The provisions of  section 307(b)
of the Act, 42 U.S.C. section 7607(b), will therefore limit judicial
review to the U.S. Court of Appeals for the District of Columbia Circuit,
and litigation of the issues posed by this rule will  not  be available in
connection with subsequent rulemakings in which it is applied.
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     Pending final  promulgation of the rule,  as  it may be modified after
public comment, EPA will generally follow the proposed policy and procedures
in actions taken in the interim.   Such actions are expected to be listing
decisions or regulatory proposals for specific substances, so that EPA will
be able to reflect, in final  regulatory action on such substances, any
changes made in the proposed rule after public comment.

     B.  IDENTIFICATION AND PRELIMINARY EVALUATION OF HEALTH RISKS
     This section describes the principles and procedures that EPA will use
in identifying potential airborne carcinogens and in determining whether
emissions of such substances pose significant risks to public health.
These principles and procedures address determinations in three fundamental
areas:  (1) the generic determination that the presence of airborne
carcinogens in ,'elatively low ambient concentrations warrants regulatory
action, (2) the identification of specific candidate substances for EPA
assessment, and (3) the assessment of whether such substances pose
significant risks to public health.

(1)  The Need for Concern About Relatively Low Doses
     The Administrator's belief that ambient concentrations of carcinogens
represent a significant public health risk warranting regulatory action is
based on the current understanding of the biological effects of these
substances at low concentrations.  Essentially, two hypotheses exist.
The non-threshold hypothesis assumes that cancer can result from the
interaction of as little as one molecule of a carcinogen with a critical
receptor in one cell.
                                   17

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     The threshold hypothesis, in contrast,  assumes that there is a no-

effect dose of a carcinogen below which induction of cancer cannot occur.

This hypothesis argues that, at small doses, chemical  carcinogens can be

detoxified througn metabolic processes, resulting in some level  of

exposure which produces no carcinogenic response, or that repair mechanisms

or cell death may prevent the development of cancer from a single damaged

cell.23

     The public health community has generally concluded that evidence for

identifiable dose thresholds does not exist for carcinogens.  Under this

view, any exposure to a carcinogenic substance carries a risk of cancer.
                                                   24
A recent report by the National Academy of Sciences   offers the following

observations in support of this conclusion:

     Consideration of the Dose-Response Relationship.   In considering
     the possibility of thresholds for ca-'cinogenesis, it is important
     to understand that there is no agenj-, chemical, or physical, which
     induces in man a form of cancer thai, does not occur in the absence
     of that agent.  In other words, when there is exposure to a material,
     we are not starting at an origin of zero cancers.  Nor are we starting
     at an origin of zero carcinogenic agents in our environment.  Thus,
     TTl's likely that any carcinogenic agent added to the environment will
     act by a particular mechanism on a particular cell population that
     is already being acted on by the same mechanism to induce cancers.
     This reasoning implies that the only way for a new carcinogen
     added to the environment to have a threshold in its dose-response
     curve would be if it were acting by a mechanism entirely different
     from that already being experienced by that tissue.

     Examination of Experimental Dose-Response Curves.  The most extensive
     information on carcinogenesis both in experimental animals and in
     humans is with ionizing radiation.  Although there is evidence impli-
     cating thresholds in some animal tissues, thresholds have in general
     not been established for most tissues.   If such thresholds exist,
     they occur at sufficiently low doses that it would require massive,
     expensive, and impracticable experiments to establish them.  In view
     of the common finding—for example, a linear dose-response relationshio
                                        18

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     (unaffected by dose-rate)--of cancer induction in  animals  by high
     LET [Linear Energy Transfer] radiation,  it is  unlikely that such thresholds
     exist.  Linearity is not essential  to the no-threshold argument since
     nonlinear, dose-response relationships do not  necessarily  imply the
     existence of thresholds...

     Heterogeneity of the Population.   The human population in  the United
     States—the population we are trying to  protect—is  a large, diverse,
     and genetically heterogeneous group exposed to a variety of toxic
     agents.  Genetic variability to carcinogenesis is  well-documented
     (Strong, 1976), and it is also known that individuals who  are deficient
     in immunological competence (for genetic or environmental  reasons)  are
     particularly susceptible to some forms of cancer (Cottier, et al.,  1974).

     It seems, therefore, that even if we were to postulate an  average
     threshold for a particular cancer induced by a particular  agent,  we
     would in practice need a series of thresholds  for  different individuals.
     It would be extremely difficult,  in practice,  to establish a single
     threshold.

     We conclude from these arguments  that, despite all  the complexities
     of chemical carcinogenesis, thresholds in the  dose-response relationships
     do not appear to exist for direct-acting carcinogens.  If  they do exist,
     they are unlikely to be detected and, hence, impossible to use.   This
     means that there can be no totally "safe" exposure to a particular
     carcinogen.  (Emphasis added.)

     EPA has there-ore made a generic  determination that, in view of the

existing state of scientific knowledge,  prudent public  health policy

requires that carcinogens be considered for regulatory  purposes to pose  some

finite risk of cancer at any exposure level above zero.   The Administrator

believes that this is consistent with  the mandate of section 112 requiring

the protection of public health against air pollutants  which "may reasonably

be anticipated" to cause or contribute to the health effects of concern,

and the application of an "ample margi-n  of safety"  in making such public

health judgments.
(2)  Identification and Screening of Potential  Airborne  Carcinogens

     Potential airborne carcinogens  are now and will  continue  to  be

identified through various EPA programs,  including  searches  of the scientific

literature, monitoring studies, and  biological  assays of substances  found

in ambient air and source emissions, as well  as by  examining information

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obtained from federal, state, or other regulatory authorities,  private  research
groups, and other scientific sources.  Suspect substances (compounds  or
mixtures) identified in this manner will  be screened to provide a  rough
estimate of the potential extent of public exposure resulting from ambient
air emissions.  Screening is essential for two reasons: first,  to  optimize
the use of Agency resources in view of the growing number of substances of
concern, and second, to distinguish between those substances which may,
through their presence in the air, present carcinogenic risks and  those
which, although probably carcinogenic, are not emitted in quantities
sufficient to pose such risks.
     Readily available information will be collected on the intentional and
inadvertent production of such substances and their uses, volatility, and
other chemical and physical properties.  Ambient air measurements  and
previous scientific assessments will be considered where available.
Appropriate offices within EPA and other relevant agencies will be contacted
to determine whether any regulatory actions, assessments, or screening
activities are underway.
     Suspect substances to which the screening process indicates the
public is probably exposed through ambient air will receive further
attention to evaluate the likelihood that they pose significant carcino-
genic risks.  Priorities for these evaluations will be assigned based on
the expected potential for public exposure to the substances.  In some cases,
EPA may determine after screening that regulatory actions under other  laws
administered by EPA or by other regulatory agencies eliminate the need for
further EPA action under the Clean Air Act.  Otherwise, potential  airborne
carcinogens will be evaluated for the likelihood that they pose significant
risks to public health.
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     These procedures are already in operation.  As noted above, screening
of over 140 potential airborne carcinogens has yielded a group of 40 for
which carcinogenicity determinations and preliminary exposure assessments
are underway.  These determinations are expected to be largely completed
by December 1979.

(3)  Evaluation of Significance of Risk to Public Health */
     The determination of significant carcinogenic risk will be based on
assessments in two areas:  the probability that the substance is a human
carcinogen, and the extent of human exposure via the ambient air.

(a)  Evaluation of the Probability of Human Carcinogenicity
     The criteria for evaluating the probability that an airborne substance
presents a carcinogenic risk to humans are not unique to the air, but are
conceptually the same as those for substances present in any exposure medium.
It would thus be inappropriate for EPA to use a novel set of criteria for
airborne substances alone.  Accordingly, in determining the carcinogenic risk
posed by air pollutants, EPA will use the criteria specified in general
guidelines adopted by the Agency.  The EPA "Interim Guideline for
Carcinogen Risk Assessment" ("Interim Guideline") issued on May 25, 197625
outlines the basic scientific criteria and policy judgments currently used
by EPA in evaluating evidence regarding suspect carcinogens.  This guidance
is supplemented by the recent release for comment by the Risk Assessment Work Group
     V Today's notice deals only with the carcinogenic hazards of an air
        pollutant.  A substance may also be regulated under section 112 due
        to its non-carcinogenic health effects, or due to a combination of
        carcinogenic and other serious effects.  Non-carcinogenic effects of
        substances being reviewed as possible airborne carcinogens will also
        be evaluated and considered where information on those effects is
        available.
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of the Interagency Regulatory Liaison Group (IRLG)V of a scientific review

of the principles and methods applicable to the identification and assessment
                               26
of human risk from carcinogens.

     In evaluating the likelihood that a substance is carcinogenic in

humans under EPA's Interim Guideline and the IRLG Work Group report, available

information is considered and judgments concerning the probability of

human carcinogenicity are made based on the quality and weight of evidence.

The information principally relevant to such an evaluation includes

epidemiological and animal or other laboratory studies.

     The available information is evaluated in light of the following criteria:

     Judgments about the weight of evidence involve considerations of the
     quality and adequacy of the data and the kinds of responses induced by
     the suspect carcinogen.  The best evidence that an agent is a human
     carcinogen comes from epidemiological  studies in conjunction with
     confirmatory animal tests.  Substantial evidence is provided by
     animal tests that demonstrate the induction of malignant tumors in one
     or more species including benign tumors that are generally recognized
     as early stages of malignancies.  Suggestive evidence includes the
     induction of only those non-life-shortening benign tumors which are
     generally accepted as not progressing to malignancy and indirect tests
     of tumorigenic activity, such as mutagenicity, in vitro cell transfor-
     mation, and initiation-promotion skin tests in mice.  Ancillary
     reasons that bear on judgments about carcinogenic potential, e.g.,
     evidence from systematic studies that relate chemical structure to
     carcinogenicity, should be included in the assessment.25
     This "weight of evidence" evaluation outlined in the Interim Guideline

does not involve automatic categorization of carcinogenic probability, but

rather evaluates the nature of the evidence in each case.  Once the evidence

has been weighed, of course, the conclusions must be useful  for regulatory

decisions.  For this reason, substances which have been evaluated
     IRLG Agencies include Environmental Protection Agency, Occuoational
     Safety and Health Administration, Consumer Product Safety Commission,
     Food and Drug Administration, and Foods Safety and Quality Service
     (U.S. Department of Agriculture).  The Occupational Safety and Health
     Administration, however, did not participate in the joint issuance of
     the Risk Assessment Work Group report.

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will be grouped into three broad categories (high, moderate, low) according
to the probability of carcino'genicity.  Assignment to a particular
regulatory category will be made on a case-by-case basis, and will reflect
the strength of the evidence that the substance in question is a human
carcinogen in comparison with the range of other substances which have been
evaluated for regulatory action.  In general, substances for which
"best" or "substantial evidence" as described above exists will be
considered for designation as high-probability human carcinogens for
purposes of section 112.  Substances for which only "suggestive" evidence
exists will be considered for designation as moderate-probability human
carcinogens.  Substances for which only "ancillary" evidence exists will
be considered for designation as low-probability human carcinogens.
     EPA recognizes that a range of scientific uncertainty exists within
these broad evidentiary classes.  For example, a substance which has
been found to be carcinogenic in all animal species and sexes tested may
be more likely to be carcinogenic in humans than a substance tested in
several species and found to produce tumors in only one sex of one species.
Although upon consideration of  the relative strength of evidence it may
be concluded that both substances should be considered high-probability
human carcinogens, the extent of uncertainty will be considered on a case-
by-case basis.

(b)  Preliminary Evaluation of  Ambient Exposure
     EPA will also determine whether a suspect airborne carcinogen is
emitted into or present in the  ambient air in such a way that significant
human exposure results.  While  the threshold of significance for the
ambient exposure determination  will be relatively low, some consideration
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of exposure levels is appropriate to avoid initiating regulatory action
under the Clean Air Act for substances such as "laboratory curiosities"
which are very unlikely to be present in the ambient air in measurable
quantities.  This preliminary exposure evaluation is designed to make
that distinction.
     In the preliminary assessment of ambient exposure, EPA will consider
available data on ambient concentrations of the substance, the number
and nature of emitting sources, and the number of people living near the
sources or in areas in which ambient concentrations have been reported.
Where possible, preliminary estimates of lifetime individual  risks to the
potentially most exposed individuals, based on estimates of carcinogenic
strength, will also be calculated.
     The preliminary exposure assessment will not be designed to produce
the more detailed information appropriate in deciding what control
measures may be necessary; that information, including detailed quantitative
assessments of risk, will also be developed where possible by EPA, but
is not required for the determination of significant ambient exposure.

      C.  INITIAL RESPONSES TO PRELIMINARY ASSESSMENTS OF HEALTH RISKS
          The evaluation of the significance of risk to public health will
be used to identify those substances for which, in the judgment of the
Administrator, there is sufficient evidence to warrant listing under
section 112 as airborne carcinogens.  For substances which fall short
of meeting the criteria for this determination, or for which available
information is not sufficient to make a determination, the proposed
policy provides for alternative responses.  The following paragraphs
describe EPA's specific responses to various possible evaluations under the
proposed rule.
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(1)  Listing Under Section 112:   Significant Risk
     Any substance judged by the Administrator to present significant
carcinogenic risks to the public will  be listed under section  112  as  a
hazardous air pollutant.  The finding  of significant carcinogenic  risk  is
based on the judgment that a substance has a high probability  of human
carcinogenicity, and evidence of significant public exposure via the  ambient
air from emissions from one or more categories of stationary sources.
     A high-probability carcinogen may also be listed under section  112 if a
preliminary quantitative risk assessment suggests that there is  a
significant risk to the potentially most exposed groups as a result  of
emissions of the substance.  These preliminary assessments of  risk will
be considered as supplemental evidence that listing is warranted where
the available evidence before the Administrator is otherwise insufficient
to indicate the existence of a significant risk.  In the judgment  of the
Administrator, it would hot be prudent health policy to base a decision not
to list upon a preliminary risk estimate in the presence of qualitative
evidence of significant human exposure.
     The limitation of the role of these preliminary risk assessments to
supplementary evidence in support of a finding of significant  risk is based
on the Administrator's judgment that these quantitative estimates  are too
imprecise and uncertain to use as a factor in deciding not to  list a  substance.
The Administrator does believe, however, that despite their considerable
uncertainty it would be impruderft to ignore assessments suggesting the
existence of significant risk, especially in light of the limited  direct
consequences of listing.  The Administrator's views concerning the use  of
quantitative risk assessment under this proposal are discussed in  greater
detail elsewhere in this notice.
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     The timing of the listing decision for a given airborne carcinogen
will depend on the nature of the information available to the Administrator.
Initially available information will often be adequate to conclude that
emissions of the substance present a significant risk to the public.  If so,
listing would occur immediately upon that finding.  Sometimes, however,
the preliminary assessments will not provide enough information to allow
the Administrator to decide if emissions of a substance present a significant
risk.  Where that is the case, further information will be obtained to
allow a determination to be made.  Substances for which exposures are
potentially substantial will be assigned high priority for this further
effort.
     The purposes of this "early" listing approach are:  to increase the
priority of a substance for further action, to facilitate the expeditious
application of clearly necessary control measures to certain sources, to
accelerate the process by which final regulatory decisions are made, and
to provide for earlier public notice of the Agency's views and increased
public participation in the regulatory decision-making process.  Paragraphs
(a) and (b) below describe the immediate consequences of listing under the
proposed policy.
(a)  Listing Where Generic Standards Are Applicable
     As explained more fully in a companion advance notice of proposed rule-
making (ANPR) elsewhere in today's Federal Register, EPA has developed a draft
set of low-cost and readily implemented control procedures and work practices
that can be applied to control emissions from various categories of
sources producing, consuming, and handling significant quantities of a
broad class of substances (volatile organic chemicals) sharing certain
properties.  Where substances listed as carcinogens under section 112
are emitted from source categories to which these "generic standards"
could apply, the application of the standards would be proposed immediately
upon listing.
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     The draft generic standards published elsewhere in the notice as an
Advance Notice of Proposed Rulemaking (ANPR) were developed from information
and efforts of EPA's Synthetic Organic Chemical Manufacturing Industry
(SOCMI) standards development program.  This program was initiated in
1976 to gather technical and cost data on the control of air pollution
from organic chemical manufacturing and to prepare (1) new source performance
standards (NSPS) for total volatile organic compound (VOC) emissions,
(2) control techniques guidelines (CTG) for VOC emissions, and (3)
section 112 standards for specific volatile organic chemical emissions.
     The SOCMI program has focused its efforts on four kinds of emissions:  (1)
emissions from storage tanks and transportation vessels, (2) fugitive leaks and
spills of VOC, (3) losses of VOC from liquid and solid wastes, and (4) emissions
from process vents.  Information-gathering, analysis, and standards develop-
ment are at various stages in these four areas, and the program's goal is to
develop generic standards in each area.  The draft generic standards in today's
ANPR, dealing with leaks and spills of VOC, represents the first generic
application of information developed by the SOCMI program to standards under
section 112.  As further information becomes available from the program relat-
ing to the other kinds of emissions under study, EPA intends to develop further
generic standards for use in conjunction with section 112.  EPA would expect
to follow a public participation and regulatory development process similar to
that of today's ANPR in connection with the development of additional generic
standards.
     The draft generic standards which are contained in today's ANPR would
apply to a large proportion of the organic chemical industry, and are based
on the similarity of many operations and equipment throughout the industry.
Examples of required procedures are the periodic inspection for and reporting
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of fugitive leaks and subsequent repair, and the painting of storage
tanks white to reduce volatilization of organics.   Since most of the
potentially carcinogenic chemical air pollutants identified by preliminary
surveys to date have been organic chemicals, these generic standards
would be expected to apply to the significant sources of most of the
chemical carcinogens which might be listed.
     In general, the applicability of the draft generic standards would be
dependent on the characteristics of source operations and the quantity of
the substance which is produced or handled.  The application of the draft generic
standards would be proposed only for sources dealing with significant quantities
of the listed substance, and some "tailoring" of the standards may be necessary
for source categories of each listed pollutant.  Sources currently meeting
the requirements of such standards would effectively be required to continue
doing so.   The purpose of the immediate proposal  of the generic standards is
to ensure that risk reductun which can quickly and easily be achieved through
the implementation of clearly appropriate "good housekeeping" measures is
not delayed by the further assessments and detailed analyses which will be
conducted before final regulatory decisions are made.
     These initial regulatory requirements would not be applicable to all
airborne carcinogens, and would not necessarily represent the degree of
control which may ultimately be required.   Because the draft generic
standards currently address only fugitive emission sources, further standards
will have to be developed individually to control  process emissions from
significant source categories.   As further generic standards are developed
for the remaining types of emission points and processes, the extent to which
further control requirements will have to be developed and applied on a
case-by-case basis will decrease significantly.
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(b)  Listing Where Generic Standards Are Not Applicable
     While a substantial majority of the substances  which will  be listed
under section 112 as airborne carcinogens are expected to be chemicals
to which generic standards could apply, there will  be other substances
such as inorganics or radioactive materials emitted  from source categories
for which generic standards have not been developed.  In these  cases,
listing of a substance will trigger the assignment of a priority for the
development of final emission regulations for significant categories of
sources emitting the substance.

(2)  Regulation Under Section 111:  Moderate Probability of Carcinogenicity
     and High Exposures
     Substances for which the probability of human carcinogenicity is  moderate
to low generally will not be considered for immediate regulation as carcinogens
under section 112.  If analy.is suggests high exposures to a substance of
"moderate probability," however, the resulting risk of cancer to the general
population remains of concern.  Such a substance will therefore undergo further
assessment and, unless that assessment indicates the substance  is a high-proba-
bility carcinogen, will be considered for interim regulation under section 111
of the Clean Air Act.
     Under section 111, new and existing sources may be regulated if they cause
or contribute to "air pollution which may reasonably be anticipated to endanger
public health or welfare."  WhiVe a substance of only moderate  probability of
carcinogenicity would not generally "be reasonably anticipated  to result in
an increase in mortality or an increase in serious irreversible or incapacitating
reversible illness," high exposures to that substance certainly may endanger
public health.  Such a substance may therefore be regulated under section 111.
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(3)  Further Assessment or Testing
     EPA will conduct, recommend,  or request that others  conduct further
biological  testing on low or moderate probability substances.   Testing may
include both cancer and other toxicity assays with priorities  based on the
extent of public exposures.
(4)  Quantitative Risk Assessments For Listed Carcinogens
     EPA will conduct a quantitative risk assessment,  if  possible,  for
any substance which has been listed under section 112  as  a carcinogen.
While such quantitative assessments are subject to considerable uncertainty,
the Administrator believes that they can provide useful  information for two
phases of the proposed policy:  establishing priorities  for regulation
of specific source categories of listed pollutants, and  determining the
degree of control required in final emission standards for those source
categories.  In assigning priorities for risk assessments, consideration
will be given to the likelihood of significant exposures, the  effect of
any generic standards proposed, carcinogenic strength  (potency), and the
feasibility of expeditious control.

(a)  Mature of Quantitative Risk Assessments
     Quantitative risk estimates at ambient concentrations involve  an
analysis of the effects of the substance in high-dose  epidemiological or
animal studies, and extrapolation of these high-dose results to relevant
human exposure routes at low doses.  The mathematical  models used for such
extrapolations are based on observed dose-response relationships for carcino-
gens and assumptions about such relationships as the dose approaches very
                   23 25 26
low levels or zero.  '  '    Examples of such models are  the linear non-
                                         25
threshold model and the log probit model.    Often, assumptions must be made
regarding the relevance of studies involving doses given  through feeding or
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other pathways in extrapolating to inhalation exposures.  Where only animal
studies exist, additional assumptions must be made concerning "mouse to man"
extrapolations.
     The risks to public health from emissions of a high-probability carcino-
gen may be estimated by combining the dose-response relationship obtained
from this carcinogenicity strength calculation with an analysis of the extent
of population exposure to the substance through the ambient air.  Exposure
in this context is a function of both the concentration of a substance and
the length of time the concentration is encountered.  A detailed exposure
analysis will estimate likely exposures for long-term temporal trends,
short-term maximum levels, and weighted averages for both the "total  population
exposed and subgroups whose exposures may be significantly greater or other-
wise different from the average.
     Although ambient monitoring data will be used whenever possible,
exposure analyses will often be based on the use of air quality models,
available estimates of emissions from significant source categories, and
approximations of population distributions near the source categories.
Similar models may be used to estimate exposure through other pathways
ultimately resulting from air emissions.  Detailed air quality models
will be used to estimate the range of pollutant exposures associated
with each major source category.  The air quality models used will
generally permit estimation of exposures of up to 20 kilometers and in
some cases 80 kilometers from individual sources.  Population and growth
statistics will be examined to allow projections to be made of future
exposures.  The information collected, together with the existing carcinogenic
strength determinations, will be used to provide estimates of the degree
of risk to individuals and the range of increased cancer incidence
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expected from ambient air exposures associated with source categories of
the carcinogenic air pollutant at various possible emissions levels.
(b)  Uncertainties in the Assessment of Risk
     The assumptions and procedures discussed above for extrapolation and
for exposure estimates are subject to considerable uncertainty.  Where
only animal data are available to assess the magnitude of cancer risk to
human populations, the differences in susceptibility between animal  species
and humans, and the need to extrapolate dose-response data to very low ambient
concentrations, result in risk estimates that must be regarded only as rough
                      25
indications of effect.
     Uncertainty in exposure estimates arises from the use of limited
monitoring, pollutant transport models, mobility of the exposed population
and other factors.  In combining these exposure estimates with dose-
response extrapolations to provide estimates of cancer incidence, the
total uncertainties are increased.
     The primary model that EPA will use to estimate carcinogenic risk from
exposure to a particular substance will be the linear non-threshold dose/
response model.  This model has bee,, chosen in order to avoid understating
the risks calculated from the extrapolation of the effects observed at
high doses to the lower doses characteristic of ambient exposure.  To the
extent possible, the range of uncertainty in the risks extrapolated from
animal studies to humans and from high to low doses will  be described.
     The decision to employ estimates of carcinogenic risks despite their
lack of precision rests on the belief that although they are subject to
considerable uncertainties, current analytical models and techniques can,
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with due consideration of the uncertainties, provide useful estimates of
relative carcinogenic strength and of the probable general ranges of excess
cancer incidence and individual risks.  This view has been supported by the
                             24                                    27
National Academy of Sciences,   the National Cancer Advisory Board,   and
others.28
D.   ESTABLISHMENT AND REVIEW OF EMISSION STANDARDS AND RELATED REQUIREMENTS

(1)  Introduction
     A central issue in developing a policy for the protection of public
health from carcinogens is the determination of the extent to which exposures
must be reduced.  Given the impossibility of identifying levels of carcinogens
with no associated risk, some have argued that no exposure should be tolerated
and that emissions should be reduced as expeditiously as practicable to zero.
Others contend that permissible exposures should be determined by an
unstructured balancing of risks, costs, and benefits.
     A number of approaches for addressing the appropriate level for control
of carcinogens have been considered or proposed by the federal regulatory
agencies, industrial groups, environmental organizations, and others.
Prominent examples include the OSHA proposal, the CPSC policy, V and the EOF
petition on airborne carcinogens.  A discussion of the suggested alternatives
is presented in the supplemental-statement which follows the text of the
proposed rule.  The following sections describe the approach proposed by
EPA.
V  The CPSC interim policy has been rescinded, 44 FR 23821 (April 23, 1979)
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(2)  The Proposed EPA Approach
     The standard-setting policy proposed today requires, as a minimum,
the use of "best available technology" (BAT) to control  emissions from
source categories presenting significant risks to public health.   The
policy would also require additional  controls, as necessary, to eliminate
"unreasonable residual risks" remaining after the use of best available
technology.  This approach is a judgmental one, designed to protect the
public health with an ample margin of safety from risks  associated with
exposure to airborne carcinogens.  The implementing procedure described
below puts prime emphasis on public health, consistent with section 112,
but permits consideration of economic impacts and benefits of the activity
in setting standards for each source category.  Uncertainties in the
assessments of risks, costs, and potential benefits, as  well as the
distributional (equity) problems of various situations,  would also be
considered in setting standards.

(a)  Source Categories Regulated
     The first step in establishing standards and requirements for
pollutants listed under section 112 under this proposed  policy is the
determination of which categories of sources emitting the pollutants
will be regulated, and in what order regulations will be developed.
Although a pollutant may have been listed because emissions from a
particular source category pose a significant risk, other source categories
may also emit the pollutant in lesser amounts.  This may occur, for
example, because the sources process very little of the  substance,
because the substance is present in only trace amounts in the sources'
raw materials, or because sources have installed adequate controls on
their own initiative or in response to other regulatory  requirements.
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     The Administrator will therefore propose regulations only for those
source categories which may pose significant risks to public health.
The determination of whether a source category emitting a listed pollutant
poses a significant risk will be made on essentially the same basis as
the listing decision, except that the more detailed exposure analysis
and risk assessment then available will be used in lieu of the prelim-
inary information used in the listing decision.  As in the listing
decision, the risk assessment will be used to indicate the existence of
a significant risk where the exposure analysis alone is insufficient,
but will not be used as evidence that a significant risk does not exist
where the exposure analysis indicates to the contrary.

(b)  Priorities for Development of Standards
     EPA anticipates that a substantial number of substances will be
listed as carcinogenic air pollutants under section 112 in the near
future.  It is also likely that many of these substances will be
emitted in significant quantities from more than one source category.
As a result, EPA will need to develop emission standards and other
requirements for a large number of source categories emitting these
substances.  At least until generic standards can be developed for
large groups of these sources, the resources that would be necessary
to complete this task immediately far exceed those available to EPA
for this purpose.  Today's proposal therefore provides for the assign-
ment of priorities to significant source categories for the development
of these regulations, through publicly stated criteria and announced
decisions.
     Under today's proposal, source categories posing significant risks
will be assigned priority status (high, medium, or low) for further
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regulatory action (beyond generic standards) on the basis of: (1) the
magnitude of projected total -excess cancer incidence associated with
current and future source emissions; (2) magnitude of cancer risks for
the most exposed individuals; (3) ease of expeditious standards development
and implementation; and (4) feasibility of significant improvements in
controls.  In addition, significant sources of more than one carcinogen
may be given priority over single-pollutant sources, based on the sum of
risks from the emitted substances.
     A high priority will be assigned, for example, to a source category
constituting an important problem requiring immediate attention, or
where risks are somewhat lower but an appropriate regulatory solution is
both feasible and readily available.  Source categories assigned medium
priority will generally be those that present lower risks and will be
scheduled for standard development as resources become available.  Lower
risk source categories for which the extent of feasibl > control may be
substantially limited will be assigned low priority for regulation
development.  Assignment to the low priority category will generally
mean that active development of regulations will not begin until there
is some change in the factors which led to the assignment, or until
higher priority actions have been completed.

(c)  Regulatory Options Analysis
     EPA will perform detailed analyses to identify alternative,
technologically feasible control options and the economic, energy, and
environmental impacts that would result from their application.  Where
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substitution is determined to.be a feasible option, the benefits of
continued use of the substance or process will be considered.  These
analyses will rely primarily on the procedures and techniques employed
by EPA for developing New Source Performance Standards under section 111
of the Act.
     The identification of feasible control options will initially
survey the existing control devices at the sources within a particular
category to determine the best controls currently in use.  The potential
emission points of the listed pollutant at a particular kind of facility
will also be identified, as will possible emissions of carcino.gens other
than the specific one under study.  EPA will, in addition, examine the
applicability of available technologies which are not currently used by
the industry to control the pollutant of concern (technology transfer)
but which have been demonstrated in pilot tests or other industrial
applications.  Finally, the availability and adequacy of substitutes
which would eliminate some or all emissions of the pollutant will be
assessed.
     Once the technologically feasible control alternatives, which may
range from no further control to a complete ban on emissions, have been
identified, the environmental, economic and energy impacts of these
options will be determined.  Considerations in these impact assessments
will include for each option:  the number of plant closures predicted
and the direct impact on employment and end product prices; the impact
on growth and expansion of the industry, the resulting changes in profit-
ability, capital availability for control equipment; the impacts from
the availability of substitute products and foreign imports; the poten-
tial increases in national energy consumption; and the impacts on other
                                        37

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environmental medial including increased water pollution and solid waste
disposal.  On the basis of these assessments, one of the control  options
identified will be designated as the "best available technology"  for the
control of emissions from the sources in the category.  This level of
control will be that technology, which in the judgment of the Administrator,
is the most advanced level of control adequately demonstrated, considering
economic, energy, and environmental impacts.
     The control level designated "best available technology" may be
different for new and existing facilities in a category.  For practical
purposes, this level of control for new sources will, as a minimum, be
equivalent to that which would be selected as the basis for a New Source
Performance Standard (NSPS) under section 111.  The requirement of "best
available technology" for new sources would consider "economic feasibility"
and woulc not preclude new construction.
     The selection of BAT for existing sources may require consideration
of the technological problems associated with retrofit and related
differences in the economic, energy, and environmental impacts.  In
practice, BAT for existing sources would consider economic feasibility
and would not exceed the most advanced level of technology that at least
most members of an industry could afford without plant closures.

(d)  Minimum Requirements for Existing Sources
     Final section 112 standards will require existing sources in any
regulated source category, as a minimum, to limit their emissions to the
levels corresponding to the use of "best available technology."  This
requirement is based on the Administrator's1 judgment that any risks
that could be avoided through the use of these feasible control measures
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are unreasonable.  Whether BAT controls are sufficient to protect public
health will be determined by a subsequent evaluation of the remaining
risks.

(e)  Determination of Unreasonable Residual Risk for Existing Sources
     Following the identification of BAT for existing sources, the
quantitative risk assessment described earlier will be used to determine
the risks remaining after the application of BAT to the source category.  If the
residual risks are not judged by the Administrator to be unreasonable,
further controls would not be required.  If, however, there is a finding
of unreasonable residual risk, a more stringent alternative would be
required.  Among the possible alternatives would be the immediate appli-
cation of more restrictive emission standards, including those based on
more extensive use of substitutes, and scheduler! or phased reductions in
permissible emissions.  The alternative selected would be that necessary,
in the Administrator's judgment, to eliminate the unreasonable residual
risks.
     Given the differences in the degree of certainty in risk estimates,
in the numbers of people exposed, in benefits, in the distribution of
risks and benefits, in the costs of controls, in the availability of
substitutes, and in other relevant factors, it is not possible to state
any precise formula for determining unreasonable residual risk.  The
determination will necessarily be a matter of judgment for each category
involved.  Nevertheless, the process followed and the various factors
involved can be outlined.
     The determination of unreasonable residual risk will be based
primarily on public health, and will require protection with an ample
                                   39

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margin of safety.  To the extent possible, quantitative or qualitative
estimates of various factors will be made for purposes of comparison.
Among these are:  (1) the range of total expected cancer incidence and
other health effects in the existing and future exposed populations
through the anticipated operating life of existing sources; (2) the
range of health risks to the most exposed individuals; (3) readily
identifiable benefits of the substance or activity; (4) the economic
impacts of requiring additional control measures; (5) the distribution
of the benefits of the activity versus the risks it causes; and (6)
other possible health and environmental effects resulting from the
increased use of substitutes.

(f)  The Degree of Control Required for New Sources
     The need to focus independently on new sources of carcinogenic
emissions stems principally from the nature of the threat posed by
airborne carcinogens.  Because of the lag time between exposure to a
carcinogen and onset of the disease, any assessment of the magnitude of
the problem posed by current exposure levels is subject to considerable
uncertainty, since the consequences have not yet become manifest.
Decisions on the appropriate level of control must take into account the
possibility that the dimensions of the current problem have been
underestimated.
     It also appears likely that the activities causing current carcinogenic
emissions will continue to expand, and that new ones will appear.   Since
new emissions would threaten an increased cancer incidence, it is  incumbent
upon the Agency to meet that threat in advance, especially if that can
be done free of some of the constraints associated with the reduction of
risks from existing sources.
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     The policy of developing separate requirements for new sources is
based on two additional considerations.  First, many of the factors
affecting risks can be controlled to a significant extent before new
construction takes place.  Foremost among these factors is siting:  new
sources in heavily populated areas create much greater cancer risks than
those locating in less populated areas.  In addition, new sources can
sometimes apply control technology more cheaply and effectively than
existing sources, since new sources: (1) are often larger and can thus
benefit from the economies of scale; (2) can engineer the integration of
emission controls from the ground up; and (3) do not have existing
control equipment which must be dismantled or scrapped.
     Second, given these differences, a determination of the appropriate
control level for new sources on the basis of unreasonable residual risk
may also weigh the relevant factors differently.  While the focus for
existing sources is primarily the balancing of health risks against the
costs of retrofit controls beyond BAT, for new sources the balance can
focus more heavily on siting, the benefits of the activity, and the
possibility of fundamental changes in the process which would lower
emissions.
     For these reasons, the Administrator proposes to include in this
policy a mechanism dealing specifically with new sources.  Under this
mechanism, described in more detail below, the standards applicable to
new and modified sources would be determined on a case-by-case basis,
and would consist of either (a) a presumptive emission standard, (b) the
best available technology standard, or (c) an alternative standard.
Regulations concerning procedures for the approval of construction or
modification under section 112 standards (40 CFR 61.07) would be amended
to reflect the requirements of the proposed policy, if it is adopted.
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     The Administrator recognizes that the mechanism proposed here is
somewhat complex.  After extensive consideration, however, this procedure
appears to be the approach most likely to satisfy the policy and practical
needs described above, within the constraints imposed by section 112.
The Administrator actively solicits comment on the procedure, and particularly
on possible alternative means to achieve the same objectives.

(1)  Presumptive Emission Standards
     EPA will prescribe a presumptive national emission standard for
each regulated source category.  This standard will prescribe a maximum
emission rate and will be based solely on potential health effects.
The presumptive standard will be designed to preclude the existence of
significant risks under projected worst case assumptions of plant size
and emissions, surrounding population density and distribution, and
meteorology.  Any proposed new source which would meet this limit would
be certified for construction under section 112(c) (1)(A) without further
demonstration or analysis.

(2)  Waiver to Best Available Technology
     Any new source meeting Risk Avoidance Criteria (described below)
specified for each regulated source category will be granted an auto-
matic waiver of the applicable presumptive emission standard, and will
instead be required to meet the best available technology standard.  Risk
Avoidance Criteria will be designed to recognize actual conditions more
favorable than the worst case assumptions used as the basis for the
presumptive emission standard.  Waivers will be granted, upon application
of the source during the certification process, where, as a result of
                                   42

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those different conditions, emissions greater than the level  of the
presumptive emission standard would not result in risks greater than those
associated with the presumptive emission standard.  The criteria to be
met, in general form, are:
     (a)(l)  Population density and distribution around the proposed
site at the source's proposed emission rate are within limits specified
by EPA.  These limits will be set to allow carefully-sited sources,
whose emissions using best available technology under specified siting
conditions would not result in significant risks, to receive automatic
waivers; and
        (2)  The proposed source is not within a specified distance of a
source of carcinogens regulated under section 112; or
     (b)  An offset against new emissions can be obtained either internally
(existing sources seeking to expand) or from existing sources of carcinogens
regulated under section 112 within a specified distance.  This criterion
is intended to allow automatic waivers to best available technology
where exposure to people already at risk from recognized carcinogenic
emissions would not increase as a result.

(3)  Establishment of Alternative Standard
     Any proposed source unable to qualify for an automatic waiver to
best available technology would be eligible to apply to EPA for the
establishment of an alternative standard applicable to that source.  The
alternative standard would be based on the avoidance of unreasonable
residual risk after the use of best available technology, and may range
from the presumptive emission standard to best available technology.  In
establishing an alternative standard, the Administrator would generally
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consider the same factors as in an unreasonable residual  risk determination
for existing sources.  The relevant factors include:
     (a)  the range of total expected cancer incidence and other serious
health effects associated with emissions of the source throughout its
anticipated operating life;
     (b)  the range of health risks to the most exposed individuals from
the source's emissions;
     (c)  existing risks to the affected population from emissions of
the listed pollutant and other carcinogenic air pollutants;
     (d)  readily identifiable benefits of the substances or the activity
producing the risk;
     (e)  the economic and technological feasibility of further control
measures;
     (f)  the distribution of the benefits of the activity versus the
distribution of risks;
     (g)  other possible health effects resulting from the use of substitutes
for the substance or activity; and
     (h)  the extent to which possible emissions offsets may be obtained.

     (3)  Summary of the Legal Basis for Proposed EPA Standard-Setting Approach
     As noted earlier, EPA has experienced considerable difficulty in
interpreting and applying the requirement of "an ample margin of safety
to protect the public health" in setting standards for carcinogenic air
pollutants under section 112 of the Clean Air Act.  The factual aspects
of the problem are first, as explained above, that airborne carcinogens
appear to have no identifiable thresholds (minimum exposure levels) for
adverse health effects; second, that in many cases the individual risks

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they present at ambient concentrations may be extremely small; and
third, that total elimination of those risks could require the closure
of some of the nation's basic industries.  The corresponding problem of
legal interpretation is that Congress does not appear to have addressed
this situation when enacting section 112.
     For the reasons discussed in more detail in the supplemental state-
ment of basis and purpose following this notice, the Administrator has
concluded that although it is possible to read section 112 as requiring
regulation designed to protect health absolutely, Congress has not
expressed any clear intention to require the total elimination of risks
posed by carcinogenic air pollutants.  The Administrator therefore
believes that, in light of the legislative history of section 112 and of
the Act as a whole, the most reasonable interpretation of that section
requires h1-m to focus principally on health orotection in regulating
airborne carcinogens but does not require the total elimination of risks
from such substances.  Consequently, it is the Administrator's judgment
that standards set under the policy proposed today will protect the
public health with an ample margin of safety.  These conclusions are
reinforced by the likelihood that Congress would have provided much
clearer guidance had it intended the drastic results that would flow
from a requirement to eliminate totally all risks from airborne carcino-
gens.

     (4)  Public Notification and Involvement

     (a)  Screening, Identification, and Assessment
     The results of the preliminary screening process, determinations of
carcinogenicity, preliminary exposure analyses, and decisions on listing,
                                   45

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proposal of generic regulations, and further analysis and testing will
be published in the Federal Register.  This notification will  serve to
advise the public, state and local agencies, and industry of the potential
hazards associated with the substances examined, will indicate which
substances are receiving further attention, and will  request the in-
volvement of interested parties.

     (b)  Listing, Quantitative Risk Assessments, and Determination of
          Regulatory Priorities
     The development of regulations is a time-consuming process.  While
the use of generic standards and the initial focus on regulating the
most significant sources first will accelerate the process of reducing
risks to public health, it is likely that regulation of medium and lower
priority sources will not be completed for a number of yfars.  To insure
that the public, industry, and the states are aware of the status of
federal regulatory efforts, the results of risk assessments and priority
determinations will be published in the Federal Register.  These notices
will include decisions and recommended actions on all substances under
review.

     (c)  Proposal and Promulgation of Standards
     Upon the proposal of generic or final regulations for source categories
of listed airborne carcinogens, EPA will hold public hearings and solicit
written comments on the proposed rulemaking.  Records of such hearings
and comments received will be made available for public inspection
througn the maintenance of public dockets.
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     (5)  Periodic Review
     At intervals of no more than five years, regulations promulgated
for each source category of airborne carcinogens will  be reviewed for
possible modification, based on recent technological  developments and
any new health effects information available.  This will provide an
opportunity to consider the tightening of standards for existing sources
to reflect new technology, and the application of innovative technologies
for new sources.  At the conclusion of each review, standards will be
revised to reflect more  stringent control requirements, or the existing
standards may be reaffirmed, as appropriate.
     [Authority:  Sections 111, 112, and 301(a) of the Clean Air Act, as
                  amended, 42 U.S.C. sections 7411, 7412, and 7601(a).]
Dated:
                                                                 Administrator
                                   47

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     The Administrator proposes to add the following rule as
Appendix C to Part 61  of Title 40 of the Code of Federal  Regulations:
                              APPENDIX C
         POLICY AND PROCEDURES FOR IDENTIFYING, ASSESSING, AND
        REGULATING AIRBORNE SUBSTANCES POSING A RISK OF CANCER

I.   INTRODUCTION
                              A.  SCOPE OF RULE
     This rule specifies the policies used by EPA in the regulation of
stationary sources of potentially carcinogenic air pollutants under
relevant Clean Air Act authorities, principally section 112.  The
rule does not affect regulation of non-carcinogenic hazardous substances
under section 112 ]V  or supplemental regulation of airborne carcinogens
under other Agency authorities where applicable.

                     B.  STATEMENT OF GENERAL POLICY
     (1) The EPA policy for regulation of sources emitting airborne carcinogens
under section 112 of the Clean Air Act is to protect the public health with
an ample margin of safety.  This protection will be achieved by requiring
the elimination of unreasonable residual risks from existing sources as
quickly as possible, and by preventing the development of such risks from
new sources.
     (2) The presence of "unreasonable residual risks" to an affected
population will be determined independently for each category of sources
regulated.  Primary emphasis in this determination will be on the level of
     V  A substance may also be regulated under section 112 due to its
         non-carcinogenic health effects, or due to a combination of
         carcinogenic and other serious effects.  Non-carcinogenic effects
         of substances being reviewed as possible airborne carcinogens will
         also be evaluated and considered where information on these effects
         is available.

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risk remaining after the installation of the "best available technology"
for the control of emissions from sources in the category.   In evaluating
this risk, consideration will  be given to the benefits conferred by the
substance or activity, the distribution of those benefits versus the distri-
bution of the risks presented by the substance or activity,  the availability
of substitutes, the cost of further control  of the substance or source
category, and the proposed siting of new sources.

II.  PRELIMINARY ASSESSMENT OF HEALTH RISKS
                 A.  IDENTIFICATION OF CANDIDATE SUBSTANCES
     Potential airborne carcinogens (candidate substances) will  be
identified through EPA programs, including searches of the scientific
literature, monitoring studies, and biological assays of substances
found in the embient air and source emissions, as well as by examining
information obtained from federal, state, or other public testing or
regulatory authorities, private research groups, and other scientific
sources.

                               B.  SCREENING
     Candidate substances will be screened to determine the potential
extent of exposure of the public through air emissions.
     (1) Screening of candidate substances will  consist of an analysis of
readily available information on their production, uses, properties, air
concentrations, and of other indices useful in assessing the potential
for public exposure.  EPA will also ascertain whether any other regula-
tory efforts are in progress with respect to these substances.
     (2) Substances which the identification and screening process indi-
cates (a) may be carcinogenic and (b) the public prooably is exposed
to via the ambient air will be evaluated to determine wnether they
                                   49

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pose a significant carcinogenic risk to the public.  Substances with the
greatest apparent potential for public exposure will be given highest
priority for this further examination.

                  C.  PRELIMINARY EVALUATION OF RISK
     The preliminary evaluation of the risks posed by a candidate substance
will consist primarily of an evaluation of the probability that it is a human
carcinogen and a preliminary evaluation of the extent of ambient exposure.

(1)  Evaluation of the Probability of Human Carcinogenicity
     Evaluation of the probability that a substance is a human carcino-
gen will be performed using criteria adopted by EPA for such determina-
tions.  These currently applicable criteria are summarized in the
Interim Guidelines for Carcinogen Risk Assessment  (41 FR 2 404; May 25,
1976). Using these criteria, the weight and quality of evidence of human
carcinogenicity for candidate substances will be assessed.  Based on such
assessments, including comparison with other substances which have been
evaluated for regulatory action, a judgment of the probability that a sub-
stance is a human carcinogen for regulatory purposes will be made roughly
as follows:
     (a)  High Probability of Human Carcinogenicity - Substances for
which "best" or "substantial" evidence exists from epidemiological
and/or at least one mammalian study.
     (b)  Moderate Probability of Human Carcinogenicity - Substances
for which "suggestive" evidence exists from epidemiological, animal, or
"short-term11 studies.
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     (c)  Low Probability of Human Carcinogenicity - Substances for


which only "ancillary" evidence exists, such as from structural correla-


tions, or for which epidemiological or animal results are judged to


indicate low probability.





(2)  Preliminary Evaluation of Ambient Exposure


     EPA will also conduct preliminary evaluations to determine whether


source emissions of high-probability carcinogens exist which cause or


contribute to air pollution posing significant carcinogenic risks to the


public.   Among the factors that this evaluation may take into account


are the number and types of sources emitting the substances in areas


where people may be exposed, the volume of their emissions, any ambient


concentrations which may have been reported, and the number of people


living near emitting sources or in the vicinity of ambient measurement


sites.  Where availab'a, estimates of carcinogenic strength may be used


to compute preliminary quantitative estimates of lifetime individual risks


to the potentially most exposed individuals.





III. INITIAL RESPONSES TO PRELIMINARY ASSESSMENT OF HEALTH RISKS


                             A.  LISTING


     Substances judged by the Administrator to present significant car-
                                       *

cinogenic risks to the public will be listed under section 112 as hazardous


air pollutants.  A substance will be judged to present a significant car-


cinogenic risk if (1) it is judged by the Administrator to have a high


probability of being a human carcinogen, and (2) there is evidence of significant


public exposure via the ambient air from emissions from one or more


categories of stationary sources.  Where the available evidence is otherwise


insufficient to indicate the existence of a significant risk, a high-probability


                                        51

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carcinogen also will be listed under section 112 if a preliminary
quantitative risk estimate suggests that a significant risk to the
potentially most exposed groups exists.  Where emissions or exposure
data indicate the existence of a significant risk, quantitative risk
estimates will not be considered evidence to the contrary.
                              B.  GENERIC STANDARDS
     Upon the listing of a substance, previously-developed generic standards
will be proposed for source categories of that substance to which they could
apply. Generic standards, developed based on the similarities among industrial
processes, will be "tailored" as necessary to fit the source categories for
which they are proposed.

            C.  MODERATE-PROBABILITY AND LOW-PROBABILITY CARCINOGENS
     EPA will recommend or require further biological testing of substances
initially judged to have a moderate or low-probability of being human
carcinogens.  Priorities for testing will be based on the extent of public
exposure.  Moderate-probability substances for which public exposures appear
to be high will be considered for regulation under section 111 of the
Clean Air Act.

                   D.  QUANTITATIVE RI-SK ASSESSMENTS
     Quantitative risk assessments on all high-probability carcinogens
will be performed, if possible.  These assessments will be undertaken based
on priorities designed to produce action most quickly on the most serious
problems pending at any given time.  The results of these assessments will
be used in the assignment of priorities for further regulation and in the
evaluation of residual risks.
                                        52

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(1)  The risk assessments will  examine:
     (a) detailed information on emission sources of the pollutants,  the
sources' control status and total emissions,  measured and predicted
ambient concentrations of the pollutants, and the production levels and
uses of the substances;
     (b)  distribution of the population around sources in specific
source categories;
     (c)  estimated duration and magnitude of exposures of the affected
population and the most exposed individuals;
     (d)  estimated carcinogenic strength (potency) of the substances;
     (e)  estimated range of expected cancer  incidence for the total
population and individual risks for the most  exposed individuals at
various possible emission levels;
     (f)  other serious health effects of the substances; and
     (g)  projected population growth around  existing sources.
(2)  The criteria to be considered in assigning priorities for quantita-
tive risk assessments include, in usual  order of importance:
     (a)  probable extent of exposure of the  public through air emissions;
     (b)  estimated carcinogenic strength;
     (z)  the effect of any generic standards proposed; and
     (d)  the feasibility of expeditious control.
(3)  The results of detailed risk assessments and determinations resulting
from the assessments will be published in the Federal Register and public
comments will be solicited.
IV.  ESTABLISHMENT AND REVIEW OF STANDARDS AND REQUIREMENTS
                        A.  SOURCE CATEGORIES REGULATED
     Emission standards in addition to generic standards will be proposed
for any source category whose emissions present a significant risk to
                                   53

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public health.  Such standards and other requirements will  be determined
independently for each regulated source category.   A source category emitting
a listed pollutant will be found to pose a significant risk if there is
evidence, from the detailed exposure analysis, that its emissions result in
significant public exposure to the pollutant via the ambient air.  Significant
risk also will be found in the absence of such evidence, if a detailed risk
assessment suggests that such a risk to the most exposed individuals or
to the population exists.  If emissions or exposure data indicate the existence
of a significant risk, the quantitative risk assessment will not be
considered as evidence to the contrary.
                    B.  PRIORITIES FOR FURTHER REGULATION
     Further standards and requirements for regulated source categories will be
developed according to the priority assigned to those source categories.  Source
categories will be assigned high, medium, or low priority based on the following
criteria:
     (1) magnitude cf the total expected and upper bound cancer incidence
associated with exposure to all carcinogens emitted by the source category;
     (2) degree of risk to the most exposed individuals;
     (3) ease of expeditious development and implementation of standards; and
     (4) feasibility of significant improvements in controls
                      C.  REGULATORY OPTIONS ANALYSIS
     EPA will conduct a regulatory options analysis to support decisions on
further required control measures.
     (1)  The analysis will identify technologically feasible control alter-
natives, their economic, energy, and environmental impacts, and, in the case of
substitutes, the benefits of continued use of the substance or process.
     (2)  The analysis will also designate levels of control considered
"best available technology" for new and for existing sources in a category.
                                     54

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The control level designated "best available technology" may be different
for new and existing facilities in a category.
     (a)  For new sources, "best available technology" is that technology
which, in the judgment of the Administrator, is the most advanced level  of
controls adequately demonstrated, considering economic, energy, and environ-
mental impacts.
     (b)  For existing sources, "best available technology" is that techno-
logy which, in the judgment of the Administrator, is the most advanced level
of controls adequately demonstrated, considering economic, energy, environ-
mental impacts, and the technological problems associated with retrofit.

                   D.  REQUIREMENTS FOR EXISTING SOURCES
     (1)  Existing sources in a regulated source category will be required,
as a minimum, to limit their emissions to the levels corresponding to the
use of "best available technology".
     (2)  Existing sources in a regulated source category also will be
required to limit their emissions in whatever additional amount is necessary,
in the Administrator's judgment, to eliminate unreasonable residual risks
to public health associated with those emissions.
     (3)  The principal emphasis in determining the level of additional
control required to eliminate unreasonable residual risk from an existing
source category will be on public health.  Factors which may be considered
in this judgment include:
     (a)  the range of total expected cancer incidence and other serious
health effects in the existing and future populations exposed, for the
anticipated operating life of existing sources in the category;
     (b)  the range of health risks to the most exposed individuals;
     (c)  readily identifiable benefits of the substance or activity  producing
the risk;
                                        55

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     (d)  the economic effects (especially plant closures) of requiring
additional control measures;
     (e)  the distribution of the benefits of the activity versus the
distribution of its risks; and
     (f)  other possible health effects resulting from the increased use
of substitutes.

              E.  REQUIREMENTS FOR NEW (INCLUDING MODIFIED) SOURCES
     (1)  Except as provided below, new sources in a regulated source
category will be required to meet a presumptive national  emission standard
designed to preclude the existence of significant risks under projected
worst case assumptions of plant size and emissions, surrounding population
density and distribution, and meteorology.
     (2)  Any proposed new source which shows, in the certification
process required by section 112(c)(l)(A), that it meets the requirements
of the Risk Avoidance Criteria (described below) applicable to that
source category will automatically be permitted to meet the applicable
best available technology standard instead of the applicable presumptive
national emission standard.  The sptcific terms of Risk Avoidance Criteria
will be prescribed separately for each source category.
     The criteria will generally require that either:
          (a) (1)  Population density and distribution around the proposed
                   site at the source's proposed emission rate are within
                   limits specified by EPA, and
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          (2)  The proposed source is not within a specified distance of
               a source of carcinogens regulated under section 112; or
          (b)  An offset against new emissions can be obtained either
               internally (existing sources seeking to expand) or from
               existing sources of carcinogens regulated under section
               112 within a specified distance.
     (3)  Any proposed new source which is unable to qualify for the
automatic waiver to best available technology described in paragraph (2)
may apply for the establishment of an alternative standard applicable to
the proposed source as part of the certification process required under
section 112(c)(l)(A).  The Administrator will establish an alternative
standard for that source at the best available technology standard or at
whatever more stringent level of control is necessary, in his/her judgment,
to prevent the existence of an unreasonable residual risk associated
with emissions from the proposed source.  Factors which may be considered
in this judgment include:
     (a)  the range of total expected cancer incidence and other serious
health effects associated with emissions oV the source throughout its
anticipated operating life;
     (b)  the range of health risks to .the most exposed individuals from
the source's emissions;
     (c)  existing risks to the affected population from emissions of
the listed pollutant and other carcinogenic air pollutants;
                                       57

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     (d)  readily identifiable benefits of the substance or the activity
producing the risk;
     (e)  the economic and technological feasibility of control
measures more stringent than BAT;
     (f)  the distribution of the benefits of the activity versus the
distribution of its risks;
     (g)  other possible health effects resulting from the use of substitutes
for the substance or activity; and
     (h)  the extent to which possible emission offsets have been obtained.

                   F.  REVIEW OF STANDARDS AND REQUIREMENTS
     Regulations promulgated for each source category of airborne carcinogens
will be reviewed and, if appropriate, revised at intervals of no more than
five years.
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                                   REFERENCES
1.   Pellizzari, E.  D., "Development of Methods  for  Carcinogenic  Vapor
     Analysis in Ambient Atmospheres".   Publication  No.  EPA-605/2-74-121 ,
     RTP, N.C. July 1974.

2.   Pitts, J., D. Grosjean, and T.  M.  Mischke,  "Mutagenic Activity of
     Airborne Participate Organic Pollutants,  Toxicology Letters.
     1:65-70 (1977).

3.   Sawicki, E. , "Chemical  Composition and Potential  Genotoxic Aspects
     of Polluted Atmospheres".   Mohr, U.,  Tomatis, L.,  and Schmahl , D. ,
     eds, in Air Pollution and  Cancer in Man,  International  Agency for
     Research on Cancer (IARC Scientific Publication No.  16).  Lyon,
     Franke (1977).

4.   Occupational Safety and Health  Administration,  "Identification,  Classifi-
     cation and Regulation of Toxic  Substances Posing  a Potential Occupational
     Carcinogenic Risk", 29 CFR Part 1990, 43  FR 54148, October 4, 1977.

5.   Consumer Product Safety Commission, "Interim Policy and Procedure
     for Classifying, Evaluating, and Regulating Carcinogens in Consumer
     Products", 43 FR 25658, June 13, 1978 (withdrawn  April  23, 1979
     44 FR_ 23821).

6.   "Carcinogens in the Environment",  in:  Council  on  Environmental
     Quality, Sixth Annual Report, Washington, D.  C. (1975).

7.   Cairns, J., "The Cancer Problem",  Scientific  American.  233(5): 64-78,
     (November 1975).

8.   Young, J. L., A. J. Asire, and  E.  S.  Pollack, "SEER Program:
     Cancer Incidence and Mortality  in  the United  States  1973-1976",
     OHEW Publication No. (NIH) 78-1837, National  Cancer Institute,
     Bethesda, Maryland (1978).

9.   "Prevention of Cancer", Report  of  a World Health  Organization Expert
     Committee, WHO Technical Report Series No.  276, Geneva,  1964.

10.  Fraumeni, J. E., Ed., Persons at High Risk  of Cancer:   An Approach
     to Cancer Etiology and Control. Academic Press,  Inc.,  New York
     (1975).

11.  Selikoff, Irving J. in Persons  at  High Risk of  Cancer;  An Approach
     to Cancer Etiology and Control. Academic Press,  Inc.,  New York
12.  Maugh, J. H., "Chemical  Carcinogens:   The  Scientific  Basis  for
     Regulation", Science 201:   1200-1205,  September  29, 1975.
                                   59

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13.  Mohr, V., L.  Tomatis,  P.  Schmahl,  Air Pollution  and  Cancer  in  Man,
     pp 169-253, International- Agency  for Research  on Cancer,  Publication
     No. 16, Lyon, France (1977).

14.  Cederloff, R., R.  Doll, B. Foyer,  L.  Friberg,  N. Nelson,  and V.  Vouk
     (ed), "Air Pollution and Cancer:   Risk Assessment Methodology  and
     Epidemiological Evidence".  Environmental  Health Perspectives.
     22:1-12, February 1978.

15.  Pike, M. C. et al.  "Air Pollution"  in Persons at High  Risk of
     Cancer:  An Approach to Cancer Etiology and Control.  Academic Press,
     Inc., New York (1975).

16.  "Cancer Facts and Figures", American Cancer Society,  New  York  (1974).

17.  "Estimates of the Fraction of Cancer Incidence in the United States
     Attributable to Occupational  Factors", National  Institute
     of Environmental Health Sciences,  Draft Summary, September  11,  1978.

18.  "Preliminary Scoring of Organic Air  Pollutants", EPA-450/3-77-008
     (1976).

19.  Faoro, Robert B. and J. A. Manning,  "Trends in Benzo(a)pyrene
     (1966-1975)", pre-publication 1978 copy, accepted for publication  in  JAPCA.

20.  Atmospheric Benzene Emissions, U.  S.  EPA,  RTP, N.C.  October, 1977
     (EPA-450/3-88-029).

21.  National Emission Standards for Hazardous  Air  Pollutants, Asbestos,
     Beryllium, and Mercury, EPA,  38 FR_ 8820 (1973).

22.  National Emission Standards for Hazardous  Air  Pollutants, Proposed
     Standard for Vinyl Chloride,  EPA,  40 FR 59532, December 24, 1975
     (final standard 41 FR 46560).

23.  Maugh, T. H., "Chemical Carcinogens:   How Dangerous  are Low Doses?"
     Science 202:   37-41, October 6, 1978.

24.  Drinking Water and Health, Part 1, Chapters 1-5, Draft, National Research
     Council, National  Academy of Sciences, Washington, D.C. (1977).

25.  EPA, "Health Risk and Economic Impact Assessments for Suspected
     Carcinogens", Interim Procedures  and Guidelines, 41  FR  24102,
     May 25, 1976.                                       ~~

26.  "Scientific Bases for Identification of Potential Carcinogens  and
     Estimation of Risks" Report by the Work Grouo  on Risk Assessment of
     the Interaaency Regulatory Liaison Group (IRLG)  44 FR 39858,
     July 6, 1979.


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27.  "General  Criteria for Assessing the Evidence  for  Carcinogenicity  of
     Chemical  Substances," Report of the Subcommittee  on  Environmental
     Carcinogenesis, National  Cancer Advisory Board, Journal  of  the  National
     Cancer Institute. 58:2, February,  1977.

28.  Hoel,  David G., et al.  "Estimation of Risks  of  Irreversible, Delayed
     Toxicity,"  Journal of Toxicology  and Environmental  Health  1:133-151.  1975.

29.  Bachmann, John  D. and John R. O'Connor,  "Identification, Assessment,
     and Regulation  of Toxic Air Pollutants"  presented at the Air Pollution
     Control  Association Speciality Conference,  February  14,  1979,
     Gainesville, Florida.

30.  "Petition for the Initiation of Rulemaking  Proceedings  to Establish
     a Policy Governing the Classification and Regulation of Carcinogenic
     Air Pollutants  under the Clean Air Act," Environmental  Defense  Fund,
     November 7, 1977.

31.  "Public Meeting—Regulation of Carcinogenic Air  Pollutants," EPA
     Internal  Memorandum from Joseph Padgett to  Walter C. Barber,
     May 17, 1978.

32.  "Summary of Responses and Proposals - Testimony and  Written Submissions,"
     U.S. EPA Public Hearings on Regulation of Carcinogenic  Air  Pollutants,
     Washington, D.  C., March 23, 1978.

33.  "Testimony on OSHA's Generic Carcinogen  Proposal,"  American Industrial
     Health Council, ilew York, May 16,  1978.

34.  "Quantitative Risk Assessment for  Ambient Exposure to Arsenic,"
     U.S. EPA Carcinogen Assessment Group, November 27, 1978.

35.  "Smoking and Health:  A Report of  the Surgeon General"  Public Health
     Service,  U.S. DHEW, January, 1979.

36.  I. J.  Selikoff, E.G. Hammond, and  J.  Churg  "Asbestos exposure,  smoking,
     and neoplasia"  JAMA 204(2): 106, April  8,"1968.

37.  "Asbestos Exposure, Cigarette Smoking,  and  Death  Rates"   E.C. Hammond,
     I.J. Selikoff,  and H. Seidman.  Presented at  the  International
     Conference on Health Hazards of Asbestos Exposure, New  York Academy
     of Sciences, June 24, 1978.
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                POLICY AND PROCEDURES FOR IDENTIFYING,
                  ASSESSING, AND REGULATING AIRBORNE
                  SUBSTANCES P'OSING A RISK OF CANCER
              SUPPLEMENTAL STATEMENT OF BASIS AND PURPOSE
     This document is intended as an elaboration of three aspects of the
basis and purpose of EPA's proposed rule for the regulation of airborne
carcinogens.  It should be read in conjunction with the preamble to the
Notice of Proposed Rulemaking for this action, which it supplements.  The
three aspects of the background of the proposal which are discussed in this
supplement are:   (1) a comparison of the EPA proposal with recent proposals
of other Federal agencies for regulating carcinogens; (2) various regulatory
approaches considered by the Administrator in formulating the proposed rule;
and (3) a fuller explanation of the underlying view of the meaning and
intent of section 112 of the Clean Air Act which led the Administrator to
choose the standard-setting approach actually proposed.
     I.   Comparison with Other Proposals
     The policies and regulatory approaches reflected in EPA's proposed
rule are similar in many important respects to those contained in recent
proposals by the Occupational Safety and Health Administration (OSHA)
                                                 2
and the Consumer Product Safety Commission (CPSC) .  There are also a
number of similarities to proposals made to EPA and other agencies by the
Environmental Defense Fund (EOF)  and to some extent by the American Indus-
trial Health Council (AIHC) .  The most important similarities and differences
among the various proposals are described below.
     The critical areas for comparison of the various proposals are:
(1) the scientific criteria underlying determinations of carcinogenicity
for regulatory purposes; (2) the use of those criteria in automatic classifi-
cation systems;  (3) the regulatory response to determinations of carcinogenicity;
and (4) the role of quantitative risk assessments.
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          A.   Carcinogenlclty Criteria
     The scientific criteria for determination of carcinogenicity under the
OSHA, CPSC, and EOF proposals are similar to the EPA Interim Guideline for
Carcinogen Risk Assessment .  All accept epidemiology as best evidence but
presume human cancer risk as a result of animal data alone.   All  accept the
principle that there is no safe level of exposure to carcinogenic substances.
Differences between the EPA and OSHA criteria are discussed  in some detail
in the EPA testimony at the OSHA hearing.  The major difference is that EPA
may consider the results of a single well-conducted animal study as sufficient
to classify a substance a high probability carcinogen, while the OSHA proposal
requires replication of such a study or a second "positive"  study in a different
species.  EPA feels that such a requirement is scientifically unnecessary
where the original study is of sufficient quality and could  result in
unnecessarily long delays while retesting takes place.
     Although the general scientific principles are similar, the OSHA and
CPSC statements are considerably more specific on a number of points than
are the EPA guidelines.  EPA believes that greater specificity and agreement
among the agencies are desirable, where possible, and has joined with the
Occupational Safety and Health Administration (OSHA), Consumer Product
Safety Commission (CPSC), Food and Drug Administration (FDA), and Food
Safety and Quality Service (FSQS) in the Interagency Regulatory Liaison
Group (IRLG) for the purpose of developing a uniform scientific basis for
determining the probability that a substance is carcinogenic.  The IRLG
has recently published a document dealing with these issues  .  Once the
document becomes final, the rule proposed today will be amended if necessary
and those principles will be used by EPA in regulating airborne carcinogens
under section 112.
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     There are a number of differences between the methods recommended by
AIHC for carcinogenicity determinations and EPA's Interim Guideline.   In
particular, AIHC suggests that greater weight be given to negative epidemiolo-
gical studies; that single-species animal  studies are insufficient to make a
presumption of human carcinogenicity; and  that short-term test results are
unsuitable for use in regulatory decisions.
     EPA feels that while "negative" epidemiological  evidence can sometimes
provide upper bounds on possible risks, epidemiology is normally not a
sensitive enough tool to provide proof that a substance which is carcinogenic
in animals is not carcinogenic in humans.   EPA considers well-conducted
single species tests and single tests results substantial evidence of
carcinogenicity.  Such tests are widely used in industry and government
laboratories.  In light of the available evidence, delaying the implementation
of controls for three or more years while  confirmatory tests are conducted
would not be a prudent policy.  The Agency feels that existing experience
with short-term tests is sufficient to suggest including results along with
other evidence in deciding the likelihood  of carcinogenicity.  In summary,
EPA feels that, given the available scientific evidence, protection of
public health requires the use of the criteria outlined in the Interim
Guideline.
     The AIHC also recommends establishment of a nine-member panel to evaluate
and classify carcinogens for all Federal agencies, suggesting that identifi-
cation and classification of carcinogens is too important and too complicated
to be left to government regulators alone.  EPA believes, however, that there
would be little advantage to this approach.  Agreement among the IRLG agencies
should make it unlikely that these Federal agencies would reach inconsistent
conclusions about a substance's carcinogenicity.  Having a single group—
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whether it be one agency or an outside group of scientists—perform these
evaluations would only add another layer of review, which could create
serious problems.  Among other things, establishing priorities that would
accomodate the needs of all affected agencies with their many different
regulatory responsibilities and deadlines would be complex and resource-
intensive.  In addition, if an outside group of scientists were used to
evaluate cancer risks, the scientists might be reluctant to take positions
on substances for which data are not definitive.  This would conflict with
the agencies' obligation to act upon the best available information rather
than to await definitive evidence.  Finally, it should also be noted that
current EPA procedures include an evaluation of carcinogenicity determinations
and risk assessments by the EPA Science Advisory Board, a review panel con-
sisting of scientists from outside of the Federal government.
     The AIHC makes no clear recommendation on techniques to be used in
evaluating excess cancer incidence other than to recommend that carcinogen
strength and cancer risks be evaluated as part of the regulatory process.
As EPA's proposal indicates, the Agency agrees that carcinogenic strength
and risk should play a role in that process.
          B.   Classification Systems
     In testimony at the OSHA hearings, EPA articulated its reservations
about the use of rigid, fixed criteria and automatic classification
schemes.  EPA is concerned that, since each determination is to some
extent unique, rigid classification schemes may not provide enough room
for the use of informed scientific judgment in making carcinogenicity
determinations.  Examples of the Agency's concerns are discussed in the
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EPA testimony .   EPA, therefore, prefers to continue to use a "weight of
evidence" approach which allows the use of informed scientific and policy
judgments in evaluating test results.
          C.   Response to Determinations of Carcinogenicity
     Under the policy proposed by OSHA (upon which the EOF petition is
modeled), substances classified as "confirmed carcinogens" would be automa-
tically regulated through an immediate emergency temporary standard including
exposure limits, monitoring, and work practices.  Within six months, a
permanent standard would be proposed to:  (1) effectively ban the substance
if a suitable substitute were available and (2) require exposures to be
reduced to lowest feasible level through technological means.
     The approach published by the CPSC establishes procedures for identifi-
cation and classification of carcinogens based on scientific criteria and
categories similar to those proposed by OSHA.  A major difference between
the CPSC and OSHA approaches is that if a substance is identified as a
confirmed carcinogen ("Category A"), CPSC would not automatically propose
a particular regulatory action.  Instead action would be taken on a case-
by-case basis, after a study of relevant factors.
     EPA believes that the appropriate regulatory response following the listing
of an airborne carcinogen under section 112 must take into consideration more
than a determination of carcinogenicity.  Given the large number of potential
airborne carcinogens, some means _of establishing priorities for regulating those
substances posing the greatest public health risks is necessary to ensure that
available Agency resources are used to the greatest effect.  The set of initial
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regulatory responses in the proposed EPA rule is designed to accomplish
that by accelerating the process of listing and initial regulation, and by
enabling the Agency to address the most significant sources and substances
first.
     The CPSC policy also recognizes the need for such procedures.  The
system for setting priorities for assessment proposed by EPA is conceptually
similar to that adopted by CPSC for establishing priorities for staff evalua-
tion and Commission appraisal of consumer products containg carcinogens.
     The OSHA and EOF proposals do not contain explicit procedures for
the establishment of priorities after carcinogenicity determinations.  Those
proposals would entail a fairly rigid schedule of regulatory responses to
notification or discovery of potential carcinogenicity.  After carcinogenicity
determinations, both the OSHA and EOF schemes would require automatic responses
without explicit consideration of risks or other indices of relative priority.
     One element of the OSHA proposal is the immediate imposition of an
emergency temporary standard.  The response is somewhat analagous to the
"generic standards" element of today's proposal.  Like OSHA, EPA believes
that there is no reason to permit the continued exposure to risks which
could be prevented by the use of clearly feasible control measures.  EPA
views the implementation of such measures as a high priority matter, espe-
cially since the application of pre-existing generic standards to specific
sources will not divert significant Agency resources from other control
efforts.
     EPA also believes, however, that a system for establishing priorities
for further regulatory actions is necessary in effectively implementing
section 112.  The Agency does not believe that a full system of automatic
responses, such as that proposed by OSHA, would be feasible for use
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under section 112, both because of the large number of airborne carcinogens
likely to be encountered and because of the differences in the statutory and
practical tasks EPA must perform.
          D.  Role of Quantitative Risk Assessment
     It is not clear what role, if any, quantitative risk estimates would
play in the approach OSHA intends  to employ.  As noted earlier, EPA believes
that, while cancer risk estimation is an imprecise endeavor involving many
uncertainties, such estimation can provide a rough measure of the magnitude
of carcinogenic risk posed by a substance.  EPA believes that consideration
of such estimates in establishing  regulatory priorities and in determining
the degree of additional control required beyond BAT is both useful and
appropriate under section 112.  This is particularly true in the Adminis-
trator's view with respect to exposures to carcinogens in the ambient
environment, which, in contrast to occupational exposures, can often be very
low and involve large populations.  Like OSHA, however, EPA does not view
these estimates as required for the decision that a particular substance
being emitted into the air should  be regulated as a hazardous pollutant,
once a determination of probable carcinogenicity and significant exposure
has been made.
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II.  Various Regulatory Approaches Considered
     A central issue in developing a policy for the protection of public
health from carcinogens is the determination of the extent to which exposures
must be reduced.  Given the impossibility of identifying levels of carcinogens
with no associated risk, some have argued that no exposure should be tolerated
and that emissions should be reduced as expeditiously as practical to zero.
Others contend, on the contrary, that permissible exposures should be deter-
mined by an unstructured balancing of risks, costs, and benefits.
     A number of approaches for addressing this problem have been considered
or proposed by the Federal regulatory agencies, industrial groups, environ-
mental organizations, and others.  Prominent examples include the OSHA
        12                      3
proposal , the CPSC policy , and the EOF petition  on airborne carcinogens.
This section discusses various suggested possibilities that have been consid-
ered by EPA, as well as the approach proposed today.
     The possible approaches and schemes suggested fall into essentially
four groups:  zero-oriented approaches; predetermined decision rules; special
approaches for new sources; and judgmental approaches.  The characteristics
of these approaches are discussed below in terms of their possible usefulness
in regulating carcinogens under section 112 of the Clean Air Act.
     A.  Zero-Oriented Approaches
     As discussed above, the lack of identifiable health effects exposure
thresholds for carcinogens suggests that exposure to even minute amounts of
such substances poses some finite risk, and that repeated exposures increase
the risk.  This has led to the proposition that for public health purposes,
no level of exposure to carcinogens can be considered absolutely "safe."  In
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particular, because section 112 emission standards must protect the public
health with an ample margin of safety, it has been argued that those standards
must therefore eliminate risk completely.
     The Administrator believes that his goal in administering section 112
must be to reduce exposures to carcinogens to the maximum extent possible.
While this implies at least a theoretical goal of zero emissions of these
substances, the immediate imposition of zero-emission requirements would
lead to the closing of most facilities now emitting carcinogenic air pollutants.
It is not now physically possible, for example, to manufacture, handle, and
store volatile organic compounds without some emissions, however small.
     As noted earlier, the Administrator does not believe that the immediate
imposition of zero-emission standards on a general basis, with their attendant
consequences, is appropriate under section 112.  Nevertheless, in setting
section 112 emission standards, public health considerations must be paramount.
Various mechanisms designed to minimize risk as part of certain zero-oriented
approaches may therefore be useful for purposes of section 112.  These
mechanisms include:
     (1)  Immediate Emission Control Requirements Beyond the use of Best
          Available Technology
     Standards more restrictive than those achievable through the use of
"best available technology" for existing sources, effective within between
ninety days and two years of promulgation, could result in the closure of
some sources.V  Depending on the degree of additional control judged necessary,
and on particular economic and technological factors, this could range from
V The meaning of the term "best available technology" as used here, is
   explained in the principal text accompanying the proposed rule.
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a few older, marginal facilities to industry closure.   Such requirement may
be appropriate where large residual risks remain after the use of best
available controls.
     (2)  Phased Control Requirements
     Although standards requiring controls beyond "best available" might not
be immediately feasible for certain affected emission sources, such controls
might be feasible if sufficient lead time were available before their required
achievement.  A form of phased control requirements, designed to force
technology improvements, is suggested by EOF in its petition.  This approach
would involve establishing a predetermined schedule for periodic tightening
of emission standards, leading ultimately to zero emissions.  EPA does not
regard this particular form of phased control as well-suited for use under
section 112, primarily because it fails to provide for consideration of the
consequences of a zero-emissions requirement in differing circumstances, and
because it could prove legally and practically infeasible for the Agency to
implement.
     The concept of technology forcing phased control  has, however, been
used in achieving ambient air standards and reducing automotive emissions,
and may be employed on a more selective basis under the proposed rule.  Such
requirements might entail somewhat accelerated closure of older, poorly
controlled plants, allowing time for funding and construction of better
controlled facilities and the development of improved control technology.
This approach could result in reduction of risks without extensive economic
dislocation or loss of the benefits associated with the activity or substance
involved.
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     (3)  Required Use of Substitutes
     The availability of safe and adequate substitutes for particular substances
or uses can be an important factor in determining the degree of control
required for a given source category.  It has been suggested, in fact, that
in order to eliminate emissions of the carcinogenic substance the use of
substitutes should be required whenever they exist.
     The main difficulty with this approach is that while partial or full
substitutes are often available, their consequences vary greatly.  In many
cases, for example, requiring the use of substitutes can result in prohibitive
economic penalties.  Substitutes available for some applications are also
often inadequate for other applications.  Moreover, the potential health
effects associated with substitutes will often be unknown.  Since adequate
substitutes are often similar to the originial substances, they may therefore
pose risks which could approach or exceed those of the banned substances.
     In addition, because carcinogens can be emitted in varying amounts  from
such diverse sources as fireplaces, chemical plants, automobiles, dry cleaning
establishments, steel manufacturing, and natural chemical and radioactive
emission sources, elimination of carcinogenic risks through substitution for
all these activities is clearly impractical.  Substitutes cannot therefore be
realistically considered a solution for all or even most airborne carcinogen
problems.
     In establishing control requirements under section 112, consequently,
EPA would consider measures requiring the use of substitutes.  In reaching a
decision, however, the Agency will also weigh the factors noted above to
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ensure that the net effect of-such requirements is consistent with the other
aspects of the proposed rule.
     B.  Predetermined Decision Rules
     A number of approaches, rejecting the zero risk concept, suggest that
the appropriate degree of control can be determined through uniform decision
rules, applied irrespective of individual circumstances.  While such decision
rules vary widely in their relative emphasis on factors such as risk, cost,
benefits, and technology, they share the central premise that regulatory
consistency can be achieved by prescribing in advance the weight to be
assigned to each of these factors under all circumstances.
     Although regulatory consistency is desirable, decisions made according
to predetermined rules are often unable to account adequately for unforeseen
or varying circumstances.  Because of the difficulty in anticipating all
possible combinations of the relevant factors, decisions bound by such rules
will frequently fail to produce desirable regulatory results.
     EPA feels that while it is important to articulate the way in which
relevant factors will be considered and weighed in determining control
requirements for airborne carcinogens, the complexity and unpredictability
of the situations that may arise dictate that some flexibility be maintained.
Predetermined decision rules will therefore not form the principal basis for
determining control requirements for airborne carcinogens under section 112.
Nevertheless, some elements of decision rule approaches may be useful as
benchmarks or guidelines.  These approaches are discussed below.
     (1)  Specification of a Fixed Target Carcinogenic Risk or Incidence Level
     This approach involves the selection of a target level of cancer risk
or incidence for purposes of regulatory action, and is based on the use of
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quantitative risk assessment techniques.  Under this approach, a fixed
numerical risk or expected cancer incidence rate target would be used in
determining the degree of control required for carcinogens.
     The use of target risk levels does have some precedent  as a basis for
regulatory decisions.  The FDA, for example, has regarded an upper bound
lifetime cancer incidence rate of less than one per million  people exposed
to carcinogenic residues in certain foods as "virtually safe".  EPA could
theoretically establish a similar goal for airborne carcinogens for use
under section 112.  If the predicted risk or incidence were  higher than the
target, the degree of control required would be that needed  to reach the
goal.
     While this approach might be consistent with the requirement that
section 112 standards place primary emphasis on protection of public health,
it suffers from two drawbacks.  Firrt, although current quantitative
risk assessment techniques for chemical carcinogens are useful decision-
making tools, considerable uncertainties are associated with the techniques
at their current stage of development.  Consequently, the Administrator
believes that in using quantitative risk assessments, he should generally
be free to consider the varying degrees of uncertainty that actual cancer
risks may be significantly above or below those predicted by the estimation
procedures, and not be bound by a fixed-target.
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     Second, a fixed target risk level, used as the determinant of
emissions standards, would also inadequately account for the varying
conditions characteristic of air pollution.   The suggested use of
target risk levels instead of a zero-risk requirement is based on the
importance of considering the various consequences of incremental risk
reductions to levels approaching zero, and it would be inconsistent with
this basis to use a fixed target risk level, irrespective of these varying
consequences, in setting standards.  These consequences differ greatly among
source categories of air pollutants, and a fixed target fails to provide
the flexibility necessary for an appropriate response.  Where risks
could be reduced beyond the target without significant costs, for example,
that should be permitted.  Likewise, where attainment of the goal would
eliminate a highly beneficial activity, the decision-maker should be
able to consider less stringent standards.
     (2)  "Cost-Per-Life" Goals
     Some have suggested that "acceptable" standards for carcinogens may be
developed by striking a predetermined balance of health risks, human lives,
economics, and social benefits.  Fundamental to this approach is the expression
of all these factors in economic terms and the adoption of a cost-per-life-
saved goal.  Under this decision rule scheme, regulations would require
control to, but not beyond, the point where the incremental costs associated
with saving an additional life were equivalent to the goal.  Proponents of
this approach argue that it would result in a more optimal allocation of
national resources.
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     The Administrator believes that several  aspects  of this  approach render
it unsuitable for standard-setting under section 112.   One such  aspect is
the basic assumption that it is appropriate to assign a single monetary
value to human life.  The Administrator regards that  task as  neither practical
nor ethically acceptable.  It is impractical  because  no consensus  criteria
exist which can be used to establish that cost value.   Indeed, the internalized
and external expenditures for protection of human lives in American society
ranges across a vast spectrum, and the very existence of this spectrum is
persuasive evidence that the society places heavy emphasis on the  surrounding
circumstances in "assigning" health protection values.  The approach is also
unacceptable in that it fails to consider the balance of equities  between
those benefiting from the activity creating the risk  and those who may die
as a consequence of the activity.  Finally, the fixed-cost approach also
necessarily ascribes more certainty to the risk assessment and cost estimates
underlying its use than is justifiable, in view of the uncertainties pre-
sent in both sets of estimates.  Therefore, although  cost-per-life estimates
may be used for perspective in considering control options, they will not
be used as decision rules in setting standards under  section  112.
     (3)  "Best Technology"
     Requirements for "best" control technology for emission  sources have
been advocated as an interim or ultimate approach which can be used without
difficult considerations of economics in determining  the degree  of control
required.  Although such a technology-based approach  at first appears rela-
tively simple to implement, it is soon apparent that  "best available technology"
cannot be defined by technical considerations alone.   For example, if an
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"add-on" control device achieves 90% control, then the installation of an
additional unit of similar capabilities could reduce remaining emissions by
an additional 90%.  Still further units could always be applied to marginally
reduce emissions.  Clearly, at some point in this process the costs associated
with marginal increases in control would be grossly disproportionate to the
incremental reductions in emissions.  Thus, "best available technology" must
be defined with at least some reference to economic considerations, as in
the case of new source performance standards under section 111 of the Clean
Air Act.
     "Best available technology" as defined in section 111 of the Clean Air
Act may not be an adequate level of control for purposes of section 112,
however, since "best available technology" does not consider the health
risks remaining after its use.  While "best available technology" may prove
a useful starting point, therefore, it is not itself sufficient for section
112 purposes without consideration of the residual health effects.
     C.  Special Approaches for New Sources
     A number of approaches and mechanisms have been suggested to contain or
minimize increases in risks which may be associated with operation of new
sources or carcinogenic air pollutants.  It has been argued that special
requirements for new sources are both necessary and justified because (1)
given existing uncertainties about the health effects associated with exposures
to various levels of carcinogens, those exposures should be limited as much
as possible, and (2) new sources can reasonably consider control and risk
avoidance options not readily available for existing sources.  Several
mechanisms for treatment of new sources are discussed below.
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     (1)  Stricter Standards for New Sources
     This approach would specify control  requirements for new sources that
are more stringent than those for existing sources.   In effect, this is
simply a modification of the best technology approach discussed above.   The
approach does have the advantage of limiting emissions from new facilities
to a greater degree than from existing facilities under a best technology
standard, and in that sense can be said to contain the risk somewhat.
     The approach could also involve consideration of residual risks associated
with projected typical new source siting conditions.   However, because it
cannot consider the residual health risks associated  with all of the varying
sets of population distributions in which a new source might actually be
located, the approach may not provide sufficient protection under actual
conditions.  Thus, like the best technology approach  for existing sources,
this approach can serve as a useful starting point,  but is not sufficient
alone.
     (2)  Regional Emissions Offsets
     An "offset" policy would require a reduction in  emissions of a given
carcinogenic air pollutant from existing sources in  an area as a precondition
for construction of new sources within a specified distance of the existing
sources.  To the extent that new sources desire to locate near existing
facilities, development of improved emissions control technology would be
encouraged by this approach and increases in risk to  health beyond existing
levels would be prevented.
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     The disadvantages of this approach as a general policy are that it
would have no effect at all on the establishment of sources at new locations,
and could prevent the expansion of sources which have already installed
advanced technology or do not present significant new risks.  In short, it
employs the somewhat arbitrary assumption that any increased risk in an area
with existing sources is not tolerable, but that increased risks in areas
with no existing sources are permissible.
     (3)  National Emissions Freeze
     Under this option, additional emissions from new or modified sources
would be prohibited except to the extent that offsets are obtained from
existing sources on a nationwide basis.  This approach would account from
some of the disadvantages of the regional emissions offset approach.  It
also provides incentives for technology-forcing and containment of risk.
     The main drawbacks of the approach are that it presumes that any additional
emissions create an intolerable risk, and that it would fall the most heavily
on the newest industries (those with the fewest existing sources) and on
those which have already forced technology the most.  It also fails to
provide incentives for careful siting of new sources.
     (4)  Case-by-Case Review of New Sources
     Under this approach, additional emissions in populated or high risk
areas would be permitted only after consideration of residual risks and
other relevant factors associated with each new source proposed.  In this
review, special emphasis would be placed on appropriate siting and the use
of improved control measures.
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     By evaluating risks, benefits,  controls,  and siting on a case-by-case
basis, this approach could significantly limit risk without arbitrariness
and over-regulation problems of either regional  or nationwide offset require-
ments.  Yet by requiring individual  reviews,  the pressure is maintained  for
both careful siting of new sources and improving technology where that
appears necessary.
     D.  Judgmental Approaches
     In contrast to the zero-oriented and fixed-decision rule approaches
outlined above, "judgmental" approaches posit that the degree of control
which is appropriate for airborne carcinogens cannot be predetermined in the
abstract for all cases and, to some extent, depends on the particular circum-
stances.  Circumstantial factors which might be considered, in addition  to
the risk to public health, include the costs of further control, the benefits
of the activity, the distribution o" risk versus benefits, and the availability
of substitutes.
     The use of a judgmental approach appears desirable to the Administrator
because it permits him to take advantage of the strong points of various
available approaches without suffering their drawbacks.  The specific approach
chosen, however, must be compatible with the mandate of section 112 to put
principal emphasis on public health protection, and each of the factors
involved must be assigned a weight consistent with this principle.
     Although protection of pub!re health must be paramount, the relative
importance of other factors can vary.  Society may be willing to pay more
for control or accept higher health risks associated with activities viewed
as important or essential.  The distributional aspects of control situations
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can differ even when the magnitude of risk,  costs,  and benefits  are similar.
Moreover, differing degrees of certainty in  the cancer incidence,  economic,
and benefits estimates can call  for different regulatory responses.  Given
this variety of circumstances and the frequent uncertainty of analyses,  the
Administrator believes that it is important  to consider different  situations
on their own merits.
     Judgmental approaches obviously place great responsibility  on decision-
makers to weigh the relevant factors carefully and  to reach judgments in the
best interest of the public.  The Administrator believes that such responsi-
bility, while heavy, is unavoidable if protection of public health is to be
maximized within the constraints of a world  of finite resources.  The policy
contained in the proposed rule is based on these views.
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III.  Legal  Basis For The Proposed EPA Approach
     A.   Congressional intent and the characteristics
         of airborne carcinogen	
     The main question the Administrator has  found  it  necessary  to  answer
in arriving at the interpretation of section  112  reflected  in  today's
proposal is whether Congress, in enacting that section,  had any  specific
intent about how an ample margin of safety would  be derived in setting
standards for air pollutants with the characteristics  of carcinogens.
If Congress had a specific intent, that would of  course  be  conclusive.
If, on the other hand, the situation presented by regulation of  airborne
carcinogens under section 112 falls in the interstices of congressional
intent, the Administrator is required by established legal  principles
to deduce and impute an intent in a reasonable way  that  is  consistent with
the overall purposes and scheme of the statues.V
               (1)  The focus of congressional attention:
                    "threshold" pollutants	
     In answering this question, the Administrator  has found it  helpful
to recall the pollution problem that Congress perceived  and addressed in
1970, when section 112 was enacted as part of a major  revision of the entire
Act.  The legislative history of the Clean Air Amendments of 1970 reveals
that the attention of Congress was at that time fixed  primarily  on  the
two problems perceived to be at the heart of  the  air pollution crisis:
stationary source emissions of various widely prevalent  pollutants  such
as sulfur dioxide, particulate matter, and photochemical oxidants;  and
V    See, e.g.. Mourning v. Family Publications Serv.,  Inc.,  411  U.S.
356, 371-373(1973); Morton v. Ruiz. 415 U.S.  199,  231(T974);
United States v. Southwestern Cable Co., 392 U.S.  157,  171-173  (1968);
International Harvester Co. v. Ruckeishaus, 473 F.2d 615,  648   (D.C.  Cir.,
1973).
                                      82

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automotive emissions of some of the same pollutants.   The statutory scheme
constructed for dealing with these pollutants reflected congressional
recognition of the view that the pollutants have exposure thresholds for
adverse health effects; that is, levels below which exposure to the pollu-
tants would not be expected to result in adverse health effects* /
     Because it is seldom scientifically feasible to identify precisely
the levels at which thresholds occur, the location of a threshold must
be estimated somewhere below the exposure level  (the "demonstrated effects
level") at which adverse health effects have been found to occur in empirical
research.  Congress therefore required in section 109 of the Act that "margins
of safety" be established to protect against unknown dangers below the
demonstrated effects levels.*jV  The Administrator believes that Congress
intended health effects to be the only consideration in setting standards
under section 109 under these circumstances, and this view has governed the
establishment of national ambient air quality standards (NAAQS) under section
109 to date.***/
*_/   Some physiological responses  (not producing adverse health effects)
may occur at exposure levels below the thresholds.
*V  S. Rep.  No. 91-1196, 91st Cong., 2d  Sess., at 9-10(1970).
***/ See, e.g.. 44 FR 8202  (February 8, 1979)  (revision of ozone standard).
Although Congress has precluded consideration of the feasibility of attain-
ing NAAQS in the standard-setting process, it has provided various means for
feasibility factors to be considered in connection with control  of the
pollutants described in section 108.  Control of pollutants listed under
section 108 can take account of feasibility through opportunities for
allocation of the burdens of control by the states under section 110, through
delays in compliance under sections 113(d) and 119, and through  attainment
date extensions under section 110(e).  Under section lll(d) of the Act,
feasibility is taken into account directly in connection with control of
certain similar, but less ubiquitous, pollutants emitted by discrete source
categories.
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     Congress also incorporated the "margin  of safety"  concept,  used  in
section 109 in dealing with the widespread apparent  threshold  pollutants
that were at the forefront of its awareness, into the  requirements  of
section 112.  The Administrator believes that this incorporation reflects
both a parallel intent and parallel assumptions.   Thus  section 112  standards
set to protect against adverse health effects characterized  by a threshold
must also be based solely on health^/, with  an "ample"  rather  than  an
"adequate" margin of safety to account for the greater  severity of  the pollu-
tants involved.^/  The apparent underlying  congressional  assumption, how-
ever — the existence of thresholds ~ also  leads the  Administrator to
believe, in the absence of significant contrary indications, that Congress
did not specifically foresee or address the  problems inherent  in applying
the margin of safety concept to air pollutants under fundamentally  different
circumstances.
               (2)  The carcinogen problem:   no apparent
                    thresholds	
     Regulation airborne carcinogens under section 112  does  require the
application of the margin of safety concept  under fundamentally different
circumstances.  Although carcinogens, as air pollutants which  may cause
an increase in mortality, are clearly among  the pollutants that the
Administrator is required to regulate under  section  112 of the Act,
V   This view was recently endorsed in Hercules,  Inc.  v.  EPA,     F.2d
	, 12 ERC 1376  (D.C. Cir., T978).
**/  This construction of the difference between "adequate"  and "amole"
was recently expressed by the U.S.  Court of Appeals for the  District  of
Columbia circuit in EDF(PCBs) v. EPA,     F.2d 	, 12  ERC 1353 (1978).
                                   34

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carcinogens must also (for the reasons discussed earlier) be regarded for
public health purposes as having no identifiable adverse health effects
thresholds.  The method used to establish a margin of safety for a thres-
hold pollutant -- setting the standard somewhere below the demonstrated
effects level at a point at which the absence of adverse health effects is
predicted -- therefore cannot be used to set standards (other than at zero)
for carcinogens under section 112, since risk of cancer is believed to exist
at any exposure level greater than zero.
     In establishing margins of safety for carcinogens, therefore, the task
is to determine how low the risk of the occurrence of cancer in an exposed
person or the projected incidence in an exposed population must be driven
before a margin of safety can be considered ample to protect the public
health.  Only two approaches are available for performing this task:
either the emission standards must be set at zero to eliminate the risk
of cancer incidence altogether, or some residual risk must be permitted.
Because Congress did not give specific consideration to this problem, the
Administrator does not believe that section 112 expresses an intent to
eliminate totally all r'-'sks from emissions of airborne carcinogens.V
Section 112 standards which permit small residual risks can, in the
Administrator's judgment, therefore provide an ample margin of safety to
protect the public health.
*/   While Congress apparently believed that some substances might be so
toxic that any'level of emissions should be prohibited  (see, e.g., A
Legislative History of the Clean Air Amendments of 1970, U.S. Government
Printing Office,  1974, at 227)(statement of Senator Muskie), it seems to
have had in mind  substances so poisonous that essentially any ambient
concentration would be expected to produce widespread serious health
effects, rather than substances with the characteristics of carcinogens,
which would produce only scattered, random health effects at very low
concentrations.
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               (3)  The consequences of a zero-risk
                    requirement	
     This view is based on several additional  factors.   Foremost among
these is the belief that if Congress had intended the drastic results  that
would flow from a requirement to eliminate all  risk from emissions  of
carcinogens, it would have spoken with much greater clarity.V
     A requirement that the risk from atmospheric carcinogen  emissions  be
reduced to zero would produce massive social  dislocations,  given the
pervasiveness of at least minimal levels of carcinogenic emissions  in
key American industries.  Since few such industries could soon operate  in
compliance with zero-emission standards, closure would be the only  legal
alternative.  Among the important activities  affected would be the  generation
of electricity from either coal-burning or nuclear energy;  the manufacturing
of steel; the mining, smelting, or refining of virtually any  mineral
(e.g., copper, iron, lead, zinc, and limestone); the manufacture of
synthetic organic chemicals; and the refining,  storage,  or  dispensing of
any petroleum product.^/  That Congress had  no clear intention of  mandating
such results seems self-evident.
     The conclusion that Congress d-'d not contemplate closure of the nation's
basic industries, or even widespread industry closures,  is  also supported
by the history and language of section 112.  First, Congress  in 1970 gave
the subject of plant closures only brief consideration in connection with
section 112.***/  While the legislative history makes clear that the
*/    Cf_. Brown v. EPA, 521 F.2d 827, 834  (9th Cir.,  1975),  vacated on
other grounds, 431 U.S.  99  (1977), opinion on remand,  566 F.2d 665  ("1977).
**/   One widespread, though non-industrial, activity  that would also be
affected is the burning of wood in home fireplaces.
***/  See, e.g., Legis. Hist., supra, at 133  (statement of Senator Muskie).
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Administrator is empowered to set standards under section 112 that
result in plant or industry closures where appropriate,*/ it is  by no means
clear that Congress intended that result for all  non-threshold hazardous
pollutants, or even that Congress really focused  on the problem.**/
Indeed, the very limited nature of the legislative history itself compels
the conclusion that closure of the nation's basic industries, irrespective
of the actual levels of risk involved, could not  have been contemplated.
That conclusion becomes even more inescapable in  light of the 1977 Amend-
ments, which added radioactive substances — long regarded as confirmed
carcinogens and emitted from a wide variety of sources — to the coverage
of the Act, with no mention anywhere of industry  closures as the inevitable
consequence.
     The language of section 112 is also consistent with today's proposal.
In using the phrase "margin of safety," Congress  was borrowing a concept
from the field of engineering, ***/ where it had  previously employed the
term.****/  By prescribing the use of a margin of safety for the load
*_/    See, Leqis. Hist., supra, at 133 (statement of Senator Muskie);
Adamo Wrecking Co. v. U.S., 434 U.S. 275, 54 L. Ed.2d 538, 555
(Stevens, J., dissenting).
*jV   In fact, the congressional expectation in 1970 was apparently
that only a few pollutants would ultimately be found "hazardous" within
the meaning of what became section 112.  See, S. Rep. No. 91-1196, supra,  at 20.
***/  See EOF (PCBs) vs. EPA, supra, slip opin. at 40.
****/ Federal Coal Mine Health and Safety Act of 1969, 314(a), 30 U.S.C.
l874"(a); see also 30 CFR 75.1401-1 (1977).
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factors of underground mine hoist cables in the 1969 Mine Safety Act,
for example, Congress surely did not intend to suggest that the safety
factor must guarantee a failure risk of zero.   Indeed, no reputable
engineer would say that even with a margin of safety an "adequately strong"
hoist cable*_/ presents a failure risk of absolutely zero.
     Nor does the use of the term "safety" necessarily imply a zero-risk
concept.  Where Congress has intended to require safety from the risk of
cancer to be absolute, it has known how to express that intention clearly,
as it did in the Delaney Clause of the Food and Drug Act,j^*_/ prohibiting
the use of any food additive found to induce cancer in man or animal  at any
level of exposure.  This provision was enacted years before section 112, and
the absence of comparable specificity in section 112 suggests that "an ample
margin of safety to protect the public health" need not be interpreted as
requiring the complete elimination of all risks.***/

     In interpreting the margin of safety concept in section 112 of the
Clean Air Act, moreover, there is no reason to believe that Congress
intended to make air pollution practically the sole facet of American life
from which the government would attempt to eliminate risk entirely.
*/   30 U.S.C  §874(a).
     21 U.S.C.  5348(c)(3)(A).
•***/ That Congress might have chosen an absolute safety rule for food
additives, but not for air pollution, is quite plausible on policy
grounds.  Cf . Doniger, "Federal Regulation of Vinyl Chloride,"  4
Ecology Law Quarterly 497, at 656-658  (1978).
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Not only is there no indication, as noted above, that Congress considered
the inevitable consequences of such a decision, but such an interpretation
would also be quite incongruous in view of the provisions of numerous other
public health statutes enacted during or since 1970.   These statutes deal
with, among other things, environmental carcinogens to which people are
equally or more exposed, and they all permit consideration of factors other
than risk in setting standards or taking comparable actions.^/
     In particular, the recent enactment of the Toxic Substances Control
Act, which was intended to address the problem of toxic substances compre-
hensively, supports the view that where Congress has  specifically considered
the problem of reducing risks posed by environmental  exposure to carcinogens,
it has not required complete elimination of those risks.  Taken together,
the Administrator believes that these statutes provide strong ev:dence
that the complete elimination of risk from environmental exposure to
carcinogens is not the task with which he has been charged by Congress.
     B.  Ample margins of safety under
         section 112	
     For reasons stated previously, the Administrator has concluded that
section 112 does not require him to base all emission standards for carcinogens
on a criterion of zero risk from exposure to such substances.  Once that  propo-
sition is accepted, at least limited consideration of factors other than  the
V   See, Federal Insecticide, Fungicide and Rodenticide Act,  as amended,
7 U.S.C.  136a et_ seg_.; Toxic Substances Control  Act,  15 U.S.C.   2601  et
seg.; Safe Drinking Water Act, 42 U.S.C.  300f et_ seq_.; Clean  Water Act,
as amended, 33 U.S.C.  1251 et_se£.; and Occupational  Safety and Health
Act of 1970, 29 U.S.C.  651 et seg.
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level of risk itself is unavoidable, since some criteria are needed in
order to judge whether or not the degree of public health protection
associated with a particular standard is "ample."V
     The Administrator believes that section 112 clearly requires this
determination to be based primarily on risk.  The Administrator also
believes, however, that he may consider other social and economic factors in
determining whether an ample margin of safety is provided by a given control
level.  These factors include the benefits of the activity or substance
producing risk; the distribution of the benefits versus the distribution
of the risks; the availability and possible environmental risks of sub-
stitutes for that substance or activity; and the cost of reducing the
risks further.
     The rule proposed today will provide an ample margin of safety in
several ways, consistent with this view.  First, it protects against the
unknown dangers of low-level exposures to airborne carcinogens by treating
them as pollutants presenting risks even at low exposure levels.  Next, it
places primary emphasis on risk in establishing standards for sources
regulated under section 112, and therefore requires at a minimum that such
sources use best available technology to reduce cancer risks from their
emissions.  Beyond that, additional control measures will be required
to eliminate residual risks judged unreasonable in light of the factors
noted above.  If necessary, this could entail closure of a source or even
an industry, although the Administrator is not now aware of any source
category whose carcinogenic emissions would be likely to require industry
closure.
V   As discussed above, this conclusion is of course limited to situations
where standards cannot be set on the basis of an adverse health effects
threshold.  Where standards can be set on that basis under section 112, fac-
tors other than health effects need not and may not be considered.
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     The proposal would also.carry out the public health mandate of
section 112 in two additional  ways:  first, by quickly imposing generic
standards where possible to eliminate swiftly certain existing sources of
carcinogenic emissions; and second, by applying the unreasonable risk
criterion to contain the risks posed by emissions from new sources.  The
Administrator believes that provisions dealing specifically with the other-
wise unpredictable increases in risks posed by emissions from new sources are
a necessary element of a policy under section 112 that requires the elimination
of unreasonable residual risks.  The Administrator also regards these provisions
as consistent with, if not required by, the policy of the Act to afford maximum
public health protection by preventing significant increases in exposure to
pollutants regulated by the Act.*/
     Finally, since the issues posed by today's proposal have not yet been
judicially resolved,*^' the Administrator regards the foregoing analysis of the
requirements of section 112 as a valid exercise of his discretion to interpret
the meaning of these complex provisions of the Act.***/  The interpretation
*_/   See, §§ I01(b)(2) and 160-169 of the Act,  42 U.S.C.  §§ 7401(b)(2) and
7470-7479; H. R. Rep. No. 95-294, 95th Cong., 1st Sess.  at 103-178  (1977).
The Administrator has previously expressed his  view that new sources of carcin-
ogen emissions should not be allowed to create  significant new risks to
exposed populations, 42 FR 28154, 28156  (June  2, 1977),  and that new sources
should be required to use improved emission control techniques, id.  at 28155.
**/  The Administrator does not regard the EDF(PCBs) and Hercules cases noted
above as controlling precedent for the interpretation expressed here.  Neither
of those cases involved regulations promulgated under section 112, and neither
dealt with the primary question involved here,  the regulation of carcinogens
-- nonthreshold pollutants -- under the Clean Air Act.
***/ See, e.g., Train v. NRDC, 420 U.S.  60  (1975).
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of section 112 stated here is the first detailed analysis the Administrator
has published of the application of the section to regulation of airborne
carcinogens.  It is, however, consistent with his initial (and subsequent)
actions in regulating asbestos, the first substance regulated under section
112 in part for carcinogenic effects.  In that initial rulemaking, despite
the absence of a known threshold level for carcinogenic effects, the
Administrator explicitly considered the technological and economic importance
of certain uses of asbestos and decided that, although a certain "minimal
risk to the public" would probably remain, emissions from certain of those
activities should be allowed to continue.V
     EPA also considered such factors in establishing emission standards for
vinyl chloride, the only other substance for which emission standards have been
set under section 112 to control carcinogenic effects.  The interpretations of
section 112 published in connection with that action are consistent with, though
not as detailed as, the analysis appearing here.W  Those interpretations were
reiterated, and the health-based nature of section 112 emphasized, in a proposal
to amend the vinyl chloride standards.***/  These publications make clear the
Administrator's consistent view that section 112 requires him to focus princi-
pally on health risks in regulating airborne carcinogens, but that it does
not require the elimination of all risks from carcinogens in establishing
am ample margin of safety to protect the public health.
*/   See 38 FR 8820  (April 6, 1973).
     See 40 FR 59532, 59534, 59535-59536  (December 24, 1975); 41 FR
46560, 46561-46562  (October 21, 1976).
***/  See 42 FR 28154  (June 2, 1977).

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                              REFERENCES
1.    Occupational  Safety and Health Administration,  Identification,  Classifi-
     cation and Regulation to Toxic Substances Posing a Potential  Occupational
     Carcinogenic Risk", 29 CFR Part 1990,  43 FR 54148, October 4,  1977.

2.    Consumer Products Safety Commission,  "Interim Policy and Procedure
     for Classifying, Evaluating, and Regulating Carcinogens in Consumer
     Products", 43 FR 25658, June 13, 1978.   Withdrawn, 44 FR 23821,  April  23,
     1979.

3.    "Petition for the Initiation of Rulemaking Proceedings to Establish
     a Policy Governing the Classification  and Regulation of Carcinogenic
     Air Pollutants under the Clean Air Act," Environmental Defense  Fund,
     November 7, 1977.

4.    "Testimony on OSHA's Generic Carcinogen Proposal,"  American  Industrial
     Health Council, New York.

5.    EPA, "Health Risk and Economic Impact  Assessments for Suspected
     Carcinogens', Interim Procedures and  Guidelines, 41  FR 21402,
     May 25, 1976.

6.    "Scientific Bases for Identification  of Potential Carcinogens  and
     Estimation of Risks" Report by the Work Group on Risk Assessment of
     the Interagency Regulatory Liaison Group (IRLG)  44 FR 39858,
     July 6, 1979.

7.    EPA's Testimony on OSHA's Proposed Cancer Policy, presented at  OSHA
     public hearings beginning May 16, 1978.
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                    ENVIRONMENTAL PROTECTION AGENCY
                           [40 CFR Part 61]
                    NATIONAL EMISSION STANDARDS FOR
                       HAZARDOUS AIR POLLUTANTS
                          Generic Standards
                 Advance Notice of Proposed  Rulemaking
     AGENCY:   Environmental  Protection Agency (EPA).
     ACTION:   Advance Notice of Proposed Rulemaking.
     SUMMARY:  This notice sets forth draft  generic standards that
EPA may propose for sources  of carcinogenic  organic chemicals that are
listed as hazardous air pollutants under section 112 of the Clean Air
Act.  Elsewhere in this issue of the FEDERAL REGISTER, EPA is proposing
a policy for the identification, assessment  and regulation o  airborne
carcinogens under section 112.  Under this policy, EPA would employ
generic standards where aoplicable to reduce emissions of airborne
carcinogens.   These generic standards would  be orooosed simultaneously
with the listing of a carcinogen as a hazardous air pollutant.  The
intent of this notice is to solicit comment on the generic standards EPA
is currently develooing.
     DATES:  written comments and information should be postmarked
on or before (60 days after the FEDERAL REGISTER notice date).
     ADDRESSES:
     Comments:  Written comments and information should be submitted to
the Central Docket Section  (A-130), U.S. Environmental Protection Agency,
Attn:  Docket No. A-79-13, 401 M Street, S.W., Washington, D.C. 20460.

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     Docket:  Docket No. A-79-13, containing material relevant to
this rulemaking, is located in the U.S. Environmental Protection Agency,
Central Docket Section, Room 2903B, 401 M Street, S.W., Washington, D.C.
20460.  The docket may be insoected between 8:00 a.m. and 4:00 p.m. on
workdays, and a reasonable fee may be charged for copying.
     FOR FURTHER INFORMATION CONTACT:  Environmental Protection
Agency, Office of Air Quality Planning and Standards, Emission
Standards and Engineering Division (MD-13), Research Triangle
Park, North Carolina 27711, Attention:  Mr. Don R. Goodwin, telephone
number (919) 541-5271.
     SUPPLEMENTARY INFORMATION:  Section 112 of the Clean Air Act
as amended, 42 U.S.C. 7412, requires EPA to regulate hazardous air
pollutants  by establishing emission standards and, where necessary.
certain other measures  to protect public health.  The rapidly developing
body of knowledge concerning toxicology indicates that many air pollutants,
primarily in the form of airborne carcinogens, may present significant
risks to public health.  Many of these air pollutants will likely be
volatile organic chemicals.  The technical complexity and diversity of
the organic chemical manufacturing industry and the stringency of Clean
Air Act time limits on  regulation of hazardous air pollutants indicate a
need to improve EPA's regulatory procedures in this area.  Accordingly,
as a significant part of the program for regulation of airborne carcinogens
contained in the rule oroposed elsewhere in today's FEDERAL REGISTER,
EPA is developing generic standards for use in reducing emissions of
organic chemical carcinogens listed under section 112 in the future.
The use of  generic standards would provide a quick, first steo in the
regulation  of organic chemical air carcinogens.
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                        GENERIC STANDARDS
     Generic standards used to regulate emission sources of carcinogenic
air pollutants are standards which are independent of process  or chemical
and are based on the similarity of operations and equipment throughout
an industry, such as the organic chemical manufacturing industry.   They
can be applied to similar emission sources and represent reasonable and
prudent measures a responsible plant owner or operator would take in
dealing with a carcinogenic air pollutant.
     Consistent with the mandate of section 112 that emissions of
hazardous air pollutants be reduced quickly, generic standards would be
proposed for applicable emission sources simultaneously with listing of
a volatile organic chemical determined to be an airborne carcinogen.
Depending on the nature of the listed organic chemical and the emission
sources of this chemical, generic standards may require "tailoring" in
certain cases to reflect unique or unusual situations.  Generic standards
and the rationale supoorting those standards would be published in the
FEDERAL REGISTER.  Additional documents outlining and summarizing the
information supporting the standards would not necessarily be published.
However, supporting information would be available at the time of proposal
for public inspection.  This supporting information would include general
assessments of the economic, energy, and environmental impacts of the
proposed standards.
     Proposal of generic standards for applicable organic chemical
emission sources would be followed by a public comment period and an

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opportunity for a public hearing.   EPA would evaluate the comments
submitted during the public hearing and comment period, make appropriate
changes to the proposed generic standards, and then promulgate the
generic standards.  Generic standards would be followed, in most cases,
by proposal of additional standards.  These additional standards would
be developed under the rule proposed today for regulation of airborne
carcinogens.
     As EPA identifies and develops additional standards, an evaluation
of the reasonableness of including these requirements in future
generic standards will be made.  As a result, the generic standards will
evolve and become more extensive as EPA's experience and expertise
increase.
             IMPLEMENTATION OF GENERIC STANDARDS
     As discussed below, the draft generic standards focus primarily
on reducing fugitive emissions through the use of an effective leak
detection and repair program.  There are a number of possible aporoaches to
implementing these generic standards.  The first approach would be to
require the attainment of specific performance levels by the sources
regulated.  For example, to control fugitive emissions from pumo seals,
a performance level could soecify that no more than a certain percentage
of pump seals leak.  Achievement of the performance level would be
enforced  through  tests of pump seals in a plant to determine what percent-
age of seals were leaking.  If more leaks were found than the percentage
allowed by  a performance level, the source would be out of compliance
and enforcement action would be taken.  This aoproach, therefore, would
be similar  to the approach followed in most existing new source performance

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standards and national emission standards for hazardous air pollutants.
Because this approach would depend on testing, rigorous enforcement of
the standards would be possible.  This approach also would provide each
plant with complete flexibility to institute its own method of achieving
and maintaining compliance with the standards.  Data to establish specific
performance levels, however, is not currently available, although
programs underway may provide some data which could be used for this
purpose.  If the data developed by these programs show that this approach
is feasible, future generic standards may incorporate performance levels
in some areas.
     A second approach to implementing generic standards would be to
specify that certain work practices be followed.  For example, to
control fugitive emissions from Dump seals, the standards would specify
(1) how often pump sea'is must be insoected for leaks, (2) the detection
technique and procedure for determining if a leak exists, and (3) the
time period within which any leak found must be repaired.  Compliance
with work practice requirements would be enforced through examination
of records kept by the plant showing that inspections were
carried out, leaks detected, and repairs made.  Compliance would be
monitored through use of routine reporting.  This approach would, of
course, provide less flexibility to the plant owner or operator.  The
reliance of this approach on self-reporting and recordkeeping could make
enforcing generic standards difficult.  However, data and information
are currently available which allow the development of v/ork practice
requirements.

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     A third approach to implementing generic standards would use the
standards as guidelines.  Guidelines would provide maximum flexibility
in the actions by industry; each plant could tailor its method of
locating and repairing leaks to its particular situation.  Guidelines
would also allow innovation in control techniques.  Guidelines, however,
would have no legal status.  Therefore, EPA could not enforce compliance
with guidelines.  Given the nature of the problem presented by public
exposure to hazardous air pollutants and the requirements of section
112, this approach is inadequate.
     The Manufacturing Chemists Association (MCA) has suggested an
approach similar to that of guidelines.  MCA's approach would require
owners and operators to prepare and implement plant-specific plans for
reducing fugitive emissions of the hazardous air pollutant.  The draft
generic standards would serve as guidelines for developing these plans.
Plans could depart from the guidelines if an owner or operator felt the
departure was justified.
     MCA's suggested approach is similar to an approach used by EPA in
oil pollution prevention regulation (40 CFR Part 112) promulgated in 1973
and in hazardous substance pollution prevention regulation (40 CFR Part 151)
proposed in 1978 under the Clean Water Act.  This approach provides each
plant with flexibility and allows innovation in control techniques.  In the
proposal, enforcement of this approach is triggered by an identifiable
event, such as discharge of hazardous substances in harmful quantities
as determined in 40 CFR Part 118, and focuses on a review of the effectiveness

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of the plan.  Enforcement of this approach is enhanced by surprise inspections
which focus on review of the olan.  After review of a olan, an owner or
operator may be required to amend the plan.   Also, the owner or operator
is liable for a civil penalty for violations of requirements of the
regulation.
     The plan preparation aporoach, if used to implement generic standards,
would be enforced through review of a plan to determine the effectiveness
of the plan.  Review of each olan would be required at some point in
time.  The mechanism for triggering review could be based on an identifi-
able event or could be based on an automatic or periodic review.
     In the example of the proposed regulation under the Clean Water
Act, review is triggered by an identifiable event, such as a discharge.
For emission sources covered by the draft generic standards, an identifi ible
event to trigger review of a plan is not readily apparent.  These emission
sources are spread out in an organic chemical plant and often require
a measurement device for detection.  A mechanism for triggering review
other than the identifiable event mechanism would be necessary.
     Another mechanism for triggering of review plans would follow
procedures similar to those used under 40 CFR Part 51 for development of
State Imolementation Plans.  These procedures would require automatic
preparation of clans and their_submittal to EPA for review.  After a
review to determine the effectiveness of a plan, the plan would be
approved or disapproved.  Approved plans would be incorporated into 40
CFR Part 61, thus assuring their implementation and allowing their
enforcement.  Incorporating olans into ^0 CFR Part 61 would be very time

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consuming.  The time and resources required to review and determine the
effectiveness of a plan and then to incorporate the plan into 40 CFR
Part 61 prohibit the use of this mechanism.
     Review of a plan to determine its effectiveness is central to
enforcement of the plan preparation approach.  The use of an identifiable
event to trigger review of a plan does not appear reasonable.  The use
of automatic review procedures similar to those used under 40 CFR Part 51
is prohibited by the time and resources required by the procedures.
Thus, the plan preparation approach is limited in its usefulness.
     EPA recognizes the general desirability of the performance level
approach to generic standards.  However, data and information are not
available to develop these types of generic standards at the present time.
Although EPA recognizes the possible use of the plan preparation
approach, the time and resources required to establish effective plans
prohibit the usefulness of this approach.  Therefore, in develooing the
draft generic standards, EPA has chosen the approach of specifying
detailed work procedures as the most viable approach now available.
This is consistent with EPA control techniques guidelines documents
which recommend this approach.  EPA invites public comment on advantages
and disadvantages of each of the approaches discussed above.
                     DRAFT GENERIC STANDARDS
     The  draft generic standards are outlined in Attachment A to this
notice.   These draft standards would be proposed for sources of carcinogenic
organic chemicals listed under section 112 of the Clean Air Act.  When

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proposing generic standards for regulation of carcinogenic organic
hazardous air pollutants, EPA would evaluate the aopropriateness  of each
standard outlined in Attachment A.   Tailoring may be required and therefore
in some instances, additions to these draft standards may be made, and
in other instances, deletions may be made.
     To achieve the goal of expeditious control  of carcinogenic emission
sources, the draft generic standards were based  on the following
selection criteria.  First, draft generic standards were selected which
are broadly applicable to organic chemical emission sources.  Second,
standards were selected which lend themselves to quick implementation
and third, standards were selected which do not  require substantial
capital expenditure.  Finally, standards were selected which would be
consistent with, any additional standards promulgated later; thus, the
generic standards could be instituted with confidence.
     The draft generic standards categorize emission sources of organic
chemicals into six groups.  These groups are:  fugitive emissions,
chemical storage, chemical transfer and handling, waste disposal, process
vents, and air pollution control devices.  All of these emission sources
lend themselves to control through the use of generic standards.   In
accordance with the selection criteria, the draft generic standards would
require control of these emission sources, for the most part, through
the use of improved operation, maintenance, and  housekeeping practices.
     The major focus of the draft generic standards is leak detection
and repair.  The draft standards would require inspection of ootential
fugitive emission sources at specific intervals  to locate leaks which

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require repair.  These fugitive emission sources consist of equipment
which comes into contact with any liquid or gaseous mixture containing
more than a specified minimum concentration of the listed pollutant.
Inspection includes routinely monitoring potential fugitive emission
sources to detect gaseous leaks, and routinely observing sources to
detect liquid leaks.  If an organic chemical concentration greater than
a defined action level is measured at the interface between the source
and the atmosphere using a portable detection device, it is considered
that a gaseous leak has been detected.  Upon monitoring, if a gaseous
leak is detected, the leak must be repaired within a specified repair
interval.  Upon observation, if a liquid leak is detected, the emission
source is monitored.  If a gaseous leak is detected, then repair is
required within the specified repair interval.  Repair of the leak would
be confirmed by muni toring the source to determine that the concentration
is less than the defined action level.  Inspection intervals ranging
from weekly to annually are currently being considered.  Values of 1  to
10 percent for the minimum concentration in the mixture, 5 to 15 days
for the repair interval, and 1000 to 10,000 parts per million by volume
measured as hexane Cppmv) as the action level or definition of a leak
are also currently being considered.
     If repair of a leak would result in more emissions than cumulative
emissions from the leak prior to a scheduled process or operation
shutdown, or if repair of a leak is not possible because of location,
service, or unavoidable circumstances, the required repair could be
delayed pending approval of EPA.  EPA Regional Enforcement Divisions
                                   10

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must be notified by telegram or telephone within a specified number of
days of requests for delay in the repair of a leak, and would retain the
authority to disapprove any requests.  If, however, EPA failed to respond
within a specified number of days to a request for delay in reoair of a
leak, approval of the request would be granted automatically.  Values of
2 to 5 days from the finding of a leak for requesting of a delay, and 2
to 5 days from receiving of a delay request for EPA response to the
request, are being considered.  Rather than follow this orocedure for
all leaks, EPA is considering this reporting procedure only for requests
for delays in repair of excessive leaks.  An excessive leak would be
defined as some emission concentration greater than the current 1000 to
10,000 ppmv range being considered as the definition of a leak.  For
example, an excessive leak could be defined as a concentration of equal
to or greater than 100,000 ppm.  Because either of these approaches is
"likely to require excessive resources and may be difficult to enforce,
EPA is requesting comment on their feasibility and alternative approaches
which could be employed.
     The numerical values of the specific requirements in the draft
generic standards were based on preliminary evaluation of various
engineering studies.  In most cases,'the requirements are illustrated by
a range of values that are being considered.  The inspection intervals,
which could vary from weekly to annually for equipment in liquid service
and from monthly to quarterly for equipment in gaseous service, were
based on data developed from test programs conducted within refinery and
                                    11

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petrochemical  plants.   In general,  the inspection intervals  are based
on the observed frequency of leaks  and their expected emission rates.
Preliminary evaluation of fugitive  emission sources  within benzene
production units of petroleum refineries indicates that the  inspection
interval influences potential emission reduction more than other factors,
such as definition of a leak, or repair interval.  Currently,  a monthly
inspection interval for equipment in gaseous and liquid service appears
the most reasonable inspection interval.
     The repair interval which ranges from 5 to 15 days was  based on
observations in the petroleum refinery and petrochemical industry and on
expected reporting requirements.  In many cases, repairs could be made
sooner than 5 days.  However, there are unavoidable circumstances which
can delay repair beyond 5 days.  Circumstances, such as a plant's parts
stock being depleted, are generally avoidable.  While a plant normally
stocks sufficient spare parts, there may be unique circumstances leading
to the depletion of a plant's parts stock.  Requests for delays in repair
of leaks will be approved only where repair is likely to result in
emissions in excess of the emissions resulting from the leak,  or where
repair is not possible because of circumstances which EPA considers
unavoidable.  Thus, the objective in selecting the repair interval was
to select a time interval consistent with the ability of a plant to
repair a leak expeditiously, but not to select a time interval so short
that it requires plants to continually request repair delays for
repair of routine leaks.  Preliminary evaluation of fugitive emission
                                    12

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sources within benzene production units of petroleum refineries indicates
that the emission reduction gained by going from 15 to 5 days is small.
Thus, the 15-day repair interval is currently considered reasonable.
     The purpose of specifying a minimum concentration level of the
pollutant in gaseous or liquid mixtures is to exclude process streams
with trace quantities of the hazardous pollutant.  The 10 percent upper
boundary for this concentration level is based on analogy with the
current vinyl chloride national emission standard.  The lower boundary
of 1 percent is based on estimates that this level, under certain
conditions, would allow emissions of less than 10 opmv of the hazardous
air pollutant.  Preliminary evaluation of fugitive emission sources
within benzene production units of oetroleum refineries indicates that
the 10 percent minimum concentration level is most reasonable.  Going
from 10 percent to 1 percent would greatly increase the number of
sources covered by the standards without a corresponding reduction in
emissions.  Therefore, 10 percent is currently considered the most
reasonable minimum concentration level.
     A hexane-based defi.'.ition of a gaseous leak at 10,000 opmv as
defined in an EPA control techniques guideline document, "Control of
Volatile Organic Compound Leaks from Petroleum Refinery Equipment"  (EPA-
450/2-78-036), was considered the maximum for use in regulating organic
hazardous air pollutants.  The 1000 ppmv definition of a leak is a
simple reduction of the value in the control techniques guideline.  The
1000 ppmv value aopears a reasonable lower value because some leakage
is unavoidable for emission sources covered by the draft generic standards.
The 10,000 ppmv and 1000 ppmv concentrations would be measured at the
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interface between the leak and the atmosphere.   These  values  are based
on a technical evaluation of leaks and are not based on an evaluation
of potential health risk of leaks.  Preliminary evaluation of fugitive
emission sources within benzene production units of petroleum refineries
indicates that the 10,000 ppmv action level is more reasonable than the
1000 ppmv action level.  Experience indicates that repair of leaks will
result in emission reduction with an action level of 10,000 ppmv.  However,
experience does not indicate that repair of leaks with concentrations
between 10,000 and 1000 ppmv will result in emission reduction.   Therefore,
10,000 ppm is currently considered the most reasonable action level.
                      MISCELLANEOUS ISSUES
     Continuous area-wide monitoring to measure ambient concentrations
of specific hazardous organic comoounds was considered.  EPA experience
with the effectiveness of area-wide monitoring indicates that this
technique is not as effective in locating leaks as a seal-by-seal
inspection, which is the technique outlined in the draft generic standards.
The use of area-wide monitoring may add to the effectiveness of seal-by-
seal inspection, but experier.:e indicates that this added effectiveness
is minimal.  Also, area-wide monitoring is a capital intensive technique.
Thus, continuous area-wide monitoring.seems imoractical for the draft
generic standards.
     On the other hand, some organic chemical facilities currently
have leak detection and repair programs based on continuous area-
wide monitoring of ambient air hydrocarbon concentrations.  In some
cases, these programs or other types of leak detection and repair

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programs might be as effective in reducing fugitive emissions as the
program described in the draft generic standards.   During meetings
with industry associations, it has been suggested that an alternative
to requiring duplication of equally effective leak detection and repair
programs should be developed.   This suggestion is reasonable.  However,
it depends upon determining equivalency of various programs with the
draft generic standards.  Three basic criteria seem necessary for any
technique for determining equivalency.  These criteria are:  (1) the
technique for determining equivalency should minimize both industry and
Agency resource requirements;  (2) the type of data necessary to demonstrate
equivalency should normally be available or easily developed; and (3)
the technique should be quantitative, with little room for discretion or
argument concerning equivalency.  EPA specifically invites comments on
possible approaches to determining equivalency that meet these criteria.
     The draft generic standards also include requirements for record-
keeping and reporting.  Recordkeeping and reporting are considered
necessary to insure that the improved operation, maintenance, and good
housekeeping practices generally required by the draft generic standards
are put into practice quickly, effectively, and consistently.  Detected
leaks would be recorded in a log and the corrective actions noted when a
leak is repaired.  EPA would be notified on a quarterly basis of leaks
not repaired within the specified repair interval; these quarterly
reports would include a listing of those units and components which
leaked past the specified repair interval, date and duration of these
leaks, and concentrations of the hazardous organic chemicals.  In some
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cases, recordkeeping and reporting would be ?. duplication of other EPA
requirements.  Where duplication is unnecessary, duplication would not
be required in the generic standards.
     In early versions of the draft generic standards, recordkeeping and
reporting requirements were the only measures used to ascertain comoliance
with the standards.  In meetings with environmental  groups, it was suggested
that either EPA or a certified independent contractor perform scheduled
inspections, observations and monitoring to confirm compliance with the
standards.  This suggestion would be extremely burdensome on EPA resources.
Therefore, it has not been included in the draft generic standards.  This
suggestion, however, did lead to incorporation of an aoproach requiring
the plant's owner or operator to notify EPA one week prior to the date
of certain inspections, observation  and monitoring.  This would give
EPA the opportunity to observe these activities and determine compliance
with the generic standards, without requiring extensive resource commitments.
EPA is actively seeking specific comments on this approach, to enforce-
ment of the draft generic standards, and specific comments on alternative
approaches.
     Minimal capital expenditure was a criterion for selection of the
draft generic standards.  The most readily identifiable capital expendi-
ture required by the draft standards is the purchase of the portable
organic vapor monitor.  The cost of two such monitors used by EPA
totals about $10,000.  A preliminary estimate of annual leak detection
and repair costs for benzene production units within a petroleum refinery
is about $25,000 per year.  This estimate includes the amortized cost of
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two monitors, annual  operating cost of the monitors,  annual  cost of
labor for leak detection, annual  parts and labor cost for leak  repair,
and annual cost of administrative support.  It does  not,  however,
include cost savings, which could be significant, for the value of the
retained organic chemicals.  EPA is interested in specific information
on the cost of the draft generic standards.
     The draft standards would also require the owner or  operator to
submit to EPA within four months following the promulgation of  a specific
generic standard an estimate of emissions of the hazardous air  pollutant.
This estimate would be based on nameplate operating  capacity and would
be categorized by emission source.
                         SPECIFIC REQUESTS
     EPA is requesting comments on the approaches discussed under the
Implementation of Generic Standards section of this  preamble.   EPA is
interested in comment on other approaches for implementing generic
standards and is specifically interested in any data and  information
which could lead to the development of performance level  generic standards
and means for enforcing the plan preparation approach advocated by MCA.
     EPA is also interested in specific comments on  the following
aspects of the draft generic standards:   (1) identification of  various
operations, procedures and equipment that are sources of emissions of
organic chemicals; (2) identification of demonstrated control  techniques
which can be broadly applied to these sources of emissions; (3) costs
associated with the requirements listed in the draft generic standards;
(4) standard equipment, designs, or operating and maintenance procedures
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(including periods of start-up and shutdown)  for controlling emissions
from operations that may emit organic chemicals; (5)  comments on the
various numerical ranges included in the draft generic standards;  (6)
comments on the aporoach of requiring requests for delays  in repair of
leaks or requests for delays in repair of excessive leaks  only,  and the
specified levels of an excessive leak; (7) identification  of techniques
or procedures which could be used to determine the equivalency of
alternative leak detection and repair programs; (8) identification of
ways to reduce the burden of recordkeeping and reporting on the  source
and EPA while maintaining the effectiveness of the draft generic standards;
(9) the enforcement approach of the draft generic standards and  alternative
approaches to the enforcement of these standards; and (10) specific
information on leak detection and repair programs similar  to the orogram
in the draft generic standard; for each program, the  information should
include (a) chemical name and the process used to produce  the chemical,
(b) a detailed description of the leak detection and  repair orogram, (c)
the number of pieces of each type of equipment affected by the orogram,
(d) separate cos.ts for monitoring, equipment,  installation of equipment,
labor for monitoring, repair parts, labor for  reoair,  and  overhead,  and
(e) an estimate of the emission reduction potential and the product
recovery credits, including an explanation of  the estimation method.
     This advance notice of proposed rulemaking is issued  under  the
authority of sections 112, 114, and 301(a) of  the Clean Air Act  as
amended [42 U.S.C. 7412, 741* and 7601(a)].
Date                          Administrator

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                                 Attachment A
                            Draft Generic Standards
   I.  Applicability.
     Except as noted below,  these standards would apply,  for applicable
emission sources, to the owner or operator of equipment affected by
these standards.  These standards would affect equipment  which  comes
into contact with a liquid mixture containing 1  [10]* percent or more by
weight, or a gaseous mixture containing 1 [10] percent or more  by volume,
of organic chemicals listed by EPA as carcinogenic hazardous-air pollutants
under §112 of the Clean Air Act.
*(NOTE:  Some requirements are illustrated with one  end of the  range  of
values currently being considered placed in brackets.)
  II.  Fugitive Emissions.
     (A)  All compressor seals and pipeline valves in gaseous service
shall be monitored as provided in section IX (A) quarterly [monthly].
Whenever a concentration of 1000 ppmv (parts per million  by volume as
hexane) [10,000 ppmv] is detected, a leak exists.  Whenever a leak
exists, it shall be repaired within 5 [15] days, except as provided in
sections II  (F) and (G).
     (B)  All pump seals, pipeline valves in liquid service, and process
drains shall be monitored as provided in section IX (A) annually [monthly].
Whenever a concentration of 1000 ppmv [10,000 ppmv]  is detected, a leak
exists.  Whenever a leak exists, it shall be repaired within 5  [15]
days, except as provided in sections II (F) and (G).
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     (C)  Pressure relief valves,  except those vented to a control
device, shall be monitored as provided in section IX (A) quarterly  [monthly].
Whenever a concentration of 1000 ppmv [10,000 ppmv]  is detected,  a  leak
exists.  Whenever a leak exists, it shall be repaired within 5 [15]
days, except as provided in sections II (F)  and (G).
     (D)  Whenever a rupture disk  installed  ahead of a pressure relief
valve ruptures, it shall be replaced within  5 [15] days.
     (E)  Pump seals shall be observed for liquid leaks weekly as provided
in section IX (B).  Whenever liquids are observed running or dripping
from a pump seal, the seal shall be monitored as provided in section IX (A).
Whenever a concentration of 1000 ppmv [10,000 ppmv]  is detected,  a  leak
exists.  Whenever a leak exists, it shall be repaired within 5 [15]
days, except as provided in sections II (F)  and (G).
     (F)  Where repair would clearly result  in emissions in excess  of
the emissions resulting from the leak, repair may be delayed, as  provided
in section VIII (G), until a regularly scheduled shutdown.  In determining
whether emissions from repair of a leak would exceed those resulting
from the leak, cumulative emissions over the time Until the regularly
scheduled shutdown shall be considered.
     CG)  Where repair is not possible because of location, service, or
unavoidable circumstances, repair may be delayed, as orovided in
section VIII (G), until a time when repair is possible.
     (H)  Housekeeping practices.
     (1)  All liquid spills shall  be cleaned up within 8 [24] hours.
Acceptable cleanup methods include siphoning into a  storage container
                                   20

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(e.g., a portable spill  tank), chemical  absorption and other appropriate
methods.  Cleanup methods shall be in compliance with requirements  under
40 CFR Part 151 (proposed).
     (2)  Wherever a valve is located at the end of a pipe or line,
the pipe or line shall be sealed with a  second valve, blind flange,
plug or cap.  This requirement does not  apply to pressure relief valves.
     (3)  Whenever liquid or gaseous samples are taken from lines
or equipment, a closeable container shall be used and sample valves
shall be closed between samples.  Liquid and gas that is bled from
sample lines shall also be collected.  All sample and bled material
shall be returned to the process or disposed as provided in section V.
 III.  Chemical Storage.
     For storage equipment of greater than 40 [150] cubic meters capacity:
     (A)  All fixed-roof storage vessels exposed to direct sunlight shall  be
painted white.  No more than 20 percent of the surface of the storage
vessel, or 20 square meters, whichever is less, shall be covered with
writing and figures.  This requirement shall not apply to insulated,
pressurized, or controlled temperature storage vessels and storage
vessels equipped with a refrigerated condenser, carbon adsorber,
incinerator, or any combination of these.
     (B)  Tank connection flanges and manway seals shall be monitored
as provided in section IX (A) quarterly [monthly].  Whenever a
concentration of 1000 oomv [10,000 pomv] is detected, a leak exists.
Whenever a leak exists, it shall be repaired within 5 [15] days, except
as provided in sections II (F) and (G).
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     (C)  Conservation vents on fixed roof storage vessels  shall  be
inspected and, if necessary, maintained quarterly [monthly].
     (D)  Seals on floating roof storage vessels  shall  be inspected and,
if necessary, maintained quarterly [monthly].
 IV.  Chemical Transfer and Handling.
     For equipment used in transferring and handling to or  from rail
cars, tank trucks, barges, and other transfer or  transportation vehicles,
all seals and fittings, excluding flanges, shall  be monitored as  provided
in section IX (A) quarterly [monthly].   Whenever  a concentration  of 1000
ppmv [10,000 ppmv] is detected, a leak exists.  Whenever a  leak exists,
it shall be repaired within 5 [15] days, except as provided in sections
II  (F) and (G).
  V.  Waste.
     (A)  For waste covered by regulation under the Resource Conservation
and Recovery Act (RCRA) and containing greater than 1[10] percent by
weight of a pollutant affected by section I, the  following  requirements
would apply:
     (1)  Waste from sampling shall be disposed by returning it to
the process stream, by reducing it in an appropriate air pollution
control device, or by absorbing or adsorbing it with a liquid or solid.
These absorbents and adsorbents, except those returned to the orocess
stream, shall then be wastes.
     (2)  Waste shall 5e stored in vapor-tight containers.
     (3)  A Regional Administrator may require an owner/operator, who
is demonstrating that treatment or disposal of a  volatile waste
(i.e., greater than 78 mm Hg) will not contribute airborne  contaminant
                                22

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to the atmosphere, as provided in the NOTE in 40 CFR 250.45 (proposed),
to demonstrate that treatment or disposal  of the pollutant affected by
section I will not contribute the airborne contaminant to the atmosphere
such that concentrations above the source  have the potential  to increase
risk to the public.
     (B)  For waste containing greater than 1[10] percent by  weight of a
pollutant affected by section I and not covered by regulation under
RCRA, the following requirements would apply:
     (1)  Disposal and treatment of waste  shall be in compliance with
standards for treatment/disposal, as provided in 40 CFR 250.45 (proposed).
     (2)  Disposal and treatment of waste  shall be in compliance with
sections V(A)(D, (2), and (3).
 VI.  Process Vents.
     Where a process vent may emit a hazardous organic chemical or any
mixture containing 1 [10] percent or more  by volume of hazardous
chemicals, procedures describing process operation, including start-up,
shutdown, normal and emergency procedures, shall be written and available
to appropriate process operators.  Operators shall receive an annual
minimum of two hours of training in these  procedures.
VII.  Air Pollution Control Devices.
     Where a control device is used to reduce air pollutant emissions of
a hazardous organic chemical, procedures outlining normal and emergency
procedures for the control device shall be written and available to
all operators.  These procedures shall include at least all operating
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and maintenance procedures recommended by the control  device manufacturer.
Operators shall receive an annual  minimum of two hours of training in
these procedures.
VIII.  Recordkeeping and Reports.
     (A)  When a leak is detected, the presence of the leak shall be
noted on a survey log as illustrated in Figure 1.  Other information as
shown shall be included on this survey log.  Figure 1  is used to illustrate
the minimum acceptable information to be recorded and is not a required
form.  A weatherproof and readily visible tag bearing an identification
number and the date that the leak was detected shall be affixed to the
leaking component.  After the leak has been repaired, the remaining
portion of the survey log shall be completed and the tag discarded.  The
survey log shall be retained for at least two years after th» repair is
completed.
     (B)  Quarterly reports shall be submitted to the appropriate EPA
Regional Office, Enforcement Division Director.  Each reoort shall
include a list as shown in Figure 2 of all leaks that were located since
the  last report  and not repaired within 5 [15] days.  Each report shall
include a separate list as shown in Figure 2 of all leaks which were
reported in a previous quarterly report and which have not been reoaired.
In addition, each report shall .include a statement signed by the plant
manager confirming that all weekly, [monthly], quarterly and annually
inspecting, observing and monitoring has been performed.
     (C)  When a spill occurs, records of the date and the time of the
spill and the  cleanup shall be maintained for a minimum of two years.

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The records shall include an estimate of the quantity of the lost material,
concentration of hazardous organic chemical, actions taken for the
cleanup, and method of final disposal.
     (D)  When an owner or operator must comply with requirements in
section VI, records of the times and aoproximate duration of all  safety
valve discharges shall be maintained for a minimum of two years.   A
summary of these safety valve discharges shall  be reported annually to
the appropriate EPA Regional Office, Enforcement Division Director.
     (E)  Written operating procedures as described in sections VI and
VII shall be maintained and updated as necessary.
     (F)  Within four months of the date of promulgation of this  section,
the owner or operator of any facility subject to this section shall
submit to the Administrator an evaluation of the emissions from the
sources of the hazardous pollutant specified in this paragraph.  This
evaluation shall be an engineering estimate and shall be subject to the
approval of the Administrator.  The evaluation shall include as a basis
the nameplate production rate, include the appropriate operating  pro-
duction rate, provide estimation of mass emissions from the sources in
sections II, III, IV, V, VI, and VII, and explain the technique for the
estimation.
     (G)  A request for delay in repairing a leak must begin within two
[five] days after locating the leak.  The owner or operator making a
delay request shall provide by telephone or telegram all necessary
information for making an evaluation at the time of the initial request
to the appropriate EPA Regional Office, Enforcement Division Director,
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and as required by the EPA Regional Office.   In evaluating the request,
the EPA Regional Office will consider the expected length of the delay,
the reasons for the delay, the consequences  of no delay, and other
relevant factors.  If the EPA Regional Office does not deny a requested
delay within two [five] days after receipt of the request, the delay
request will be granted automatically.
     (H)  Whenever an owner or operator is unable to comply with the
two [five]-day requirement as provided in section VIII (6), he shall
notify by teleohone or telegram the appropriate EPA Regional Office,
Enforcement Division Director, within one working day after determining
the inability to comply.  When notifying the appropriate EPA Regional
Office, the owner or operator shall provide  an explanation of the inability
to comply with section VIII (6).  In evaluating the inability to comply
with section VIII (G), the EPA Regional Office shall consider the reasons
for the inability to comply.  After evaluation, the EPA Regional Office
may allow application of section VIII (G) for delay requests after two
[five] days after the plant locates a leak.
     (I)  At least one working week orior to each [monthly], quarterly, or
annual inspections, observations, and monitoring, an owner or operator
shall notify the aopropriate EPA Regional Office, Enforcement Division
Director, by telephone or telegram that such inspections, observations,
or monitoring are scheduled.
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 IX.  Test Methods.
     (A)  Monitoring hazardous organic chemicals emissions.
     This test method describes the procedures used to detect volatile
organic chemical (VOC) leaks from sources of hazardous air pollutants.
A portable test device is used to survey individual equipment leak
sources.  The specifications and performance criteria for the test
instrument are included.
     (1)  Apparatus
     (a)  Monitoring Instrument
     The VOC detection instrument used in this procedure may be of
any type that is designed to respond to total hydrocarbons.   The
instrument must incorporate appropriate range options so that source
levels can be measured.  The instrument will be equipped with a pump so
that a continuous sample is provided to the detector.  The instrument
meter readout will be such that the scale can be read to +5 percent at
1,000 ppmv [10,000 ppmv].  The instrument must be capable of achieving
the performance criteria given in Table 1.  The definitions and evaluation
procedures for each parameter are given in subcategory (3).
     Table 1.  Monitoring Instrument Performance Criteria
            Parameter                      Specification
1.  Zero drift  (2-hour)              <5 ppmv
2.  Calibration drift (2-hour)       <5% of the calibration gas value
3.  Calibration error                <5% of the calibration gas value
4.  Response time                    <5 seconds

     The instrument must be subjected to the performance evaluation
test prior to being placed in service and every three months thereafter.
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The performance evaluation test is also required after any modification
or replacement of the instrument detector.
     (b)  Calibration Gases
     The VOC detection instrument is calibrated so that the meter
readout is in terms of ppmv hexane.   The calibration gases required
for monitoring and instrument performance evaluation are a zero gas
(air, <3 ppmv hexane} and a hexane in air mixture of about 1,000 ppmv
[10,000 ppmv].  If cylinder calibration gas mixtures are used, they must
be analyzed and certified by the manufacturer to be within +2 percent
accuracy.  Calibration gases may be prepared by the user according to
any accepted gaseous standards preparation procedure that will yield a
mixture accurate to within +2 percent.  Alternative calibration gas
species may be used in place of hexane if a relative response factor for
each instrument is determined so that calibrations with the alternative
species may be expressed as hexane equivalents on the meter readout.
     (2)  Procedures
     (a)  Calibration
     Assemble and start up the VOC analyzer according to the manufacturer's
instructions.  After the appropriate warm-up period and zero or internal
calibration procedure, introduce the 1,000 ppmv [10,000 ppmv] hexane or
hexane equivalent calibration gas into the instrument sample probe.
Adjust the instrument meter readout to correspond to the calibration gas
value.
     (b)  Individual Source Surveys
     Place the instrument sample probe inlet at the surface of the
component interface where leakage could occur.  During sample collection,
the probe should be moved along the interface surface with special
                                      28

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emphasis placed on positioning the probe inlet at the local  upwind
and downwind side of the component interface.   This general  technique is
applied to specific types of equipment leak sources as follows:
     (i)  Valves - The most common source of leaks from block (glove,
plug, gate, ball, etc.) and control valves is  at the seal  between the
stem and housing.  The probe should be placed  at the interface where
the stem exits the seal and sampling should be conducted on  all  sides
of the stem.  For valves where the housing is  a multipart assembly,
or where leaks can occur from points other than the stem seal, these
sources should also be surveyed with the probe inlet moved along the
surface of the interface.
     (ii)  Flanges and other connections - For welded flanges, the
probe should be placed at the outer edge of the flange-gasket interface
and samples collected around the circumference of the flange.  For
other types of non-permanent joints such as threaded connections,
a similar traverse is conducted at the component interface.
     (ill)  Pumps and compressors - A circumferential traverse is
conducted at the outer surface of the pump or  compressor shaft and
housing seal interface.  In cases where the instrument probe cannot
be placed in contact with a rotating shaft, the probe inlet  must be
placed within one centimeter of the shaft-seal interface.   In those
cases where the housing configuration of the pump or compressor prevents
the complete traversing of the seal periphery, all accessible portions
of the shaft seal should be probed.  All other joints where  leakage
could occur will also be sampled with the probe inlet placed at the
surface of the interface.  For pumps or compressors using sealing oil,
                                   29

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the vent from the seal oil. reservoir will be sampled by placing the
probe inlet at approximately the centroid of the vent area to atmosphere.
     (iv)  Pressure relief devices - The physical configuration of most
pressure relief devices prevents sampling at the sealing surface inter-
face.  However, most devices are equipped with an enclosed extension, or
horn.  For this type device, the probe inlet is placed at approximately
the centroid of the exhaust area to atmosphere.
     (v)  Process drains - For open process drains, the sample probe
inlet will be placed at approximately the centroid of the area open to
the atmosphere.  For covered drains, the probe should be placed at the
surface of the cover interface and a circumferential traverse shall be
conducted.
     (3)  Instrument performance evaluation procedures
     (a)  De-Tin itions
     Zero Drift - The change in the instrument meter readout over a
stated period of time of normal continuous operation when the VOC
concentration at the time of measurement is zero.
     Calibration Drift - The change in the instrument meter readout over
a stated period of time of normal continuous operation when the VOC
concentration at the time of measurement is the same known upscale
value.
     Calibration Error - The difference between the VOC concentration
indicated by the meter readout and the known concentration of a test gas
mixture.
     Response Time - The time interval from a step change in VOC con-
centration at the input of the sampling system to the time at which 95
percent of the corresponding final value is reached as displayed on the
instrument readout meter.
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     (b)  Evaluation Procedures
     At the beginning of the instrument performance evaluation test,
assemble and start up the instrument according to the manufacturer's
instructions for recommended warmup period and preliminary adjustments.
     (i)  Zero and calibration drift test - Calibrate the instrument per
the manufacturer's instructions using zero gas and a calibration gas
representing about 1,000 ppmv [10,000 ppmv].  Record the time, zero, and
calibration gas readings (example data sheet shown in Figure 3).  After
2 hours of continuous operation, introduce zero and calibration gases to
the instrument.  Record the zero and calibration gas meter readings.
Repeat for three additional 2-hour periods.
     (ii)  Calibration error test - Make a total of nine measurements by
alternately using zero gas and a calibration gas mixture corresponding
to about 1,000 ppmv [10,000 ppmv].  Record the meter readings (example
data sheet shown in Figure 4).
     (iii)  Response time test procedure - Introduce zero gas into the
instrument sample probe.  When the meter reading has stabilized, switch
quickly to the 1,000 ppmv [10,000 ppmv] calibration gas.  Measure the
time from concentration switching to 95 percent of final stable reading.
Perform this test sequence three (3) times and record the results (example
data sheet given in Figure 5).
     (iv)  The calibration error test and the response time test may be
performed during the zero and calibration drift test.
     (c)  Performance Calculations
     All results are expressed as mean values, calculated by:
                                1      n
                                —     s    Xi
                                n    i = 1
                                  31

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where:
     Xi = value of the measurements
     z  = sum of the individual values
     -  = mean value (the absolute value of the mean value)
     A
     n  = number of data points
     The specific calculations for each performance parameter are
indicated on the respective example data sheet given in Figures 3,
4, and 5.  The example data sheets are constructed so that performance
criteria tests can be conducted on 1,000 ppmv [10,000 ppmv] levels of
gas.
     (B)  Observing for liquid leaks of hazardous organic chemicals.
     This test method describes the procedures used to detect organic
chemical liquid leaks from sources of hazardous air pollutants.  The
method uses visual observations to determine the existence of a liquid
leak.
     (1)  Apparatus
     No apparatus is needed to perform this method.
     (2)  Procedure
     Observing from vantage points to sufficiently inspect the source,
determine if any chemicals are leaking.  A liquid leak exists if any
chemical liquid is observed running*or dripping from the surface of the
source.  When a chemical liquid is dripping to a surface which is in the
vicinity of a possible hazardous pollutant emission source, locate the
source of the liquid.
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Leak Detection and Repair Survey Log
Instrument Operator:
Recorder:
TAG
NUMBER

UNIT

COMPONENT

HAZARDOUS
ORGANIC
CHEMICAL
CONCENTRATION
IN STREAM
.
DATE
LEAK
LOCATED

DATE
MAINTEN-
ANCE
PERFORMED

COMPONENT RECIIECK
AFTER MAINTENANCE
DATE

INSTRUMENT
READING
(PPM)

        FIGURE 1.   Example Monitoring Survey Log Sheet.

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TAG
NUMBER

UNIT

COMPONENT

HAZARDOUS
ORGANIC
CHEMICAL
CONCENTRATION
IN STREAM
.
DATE
LEAK
LOCATED
T
DATE
MAINTEN-
ANCE
PERFORMED

DATES
MAINTEN-
ANCE
AFTEMPTED

REASONS REPAIRS POST-
PONED OR FAILED

FIGURE 2, Example Leak Report.
      31

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  Instrument ID:
                          Calibration Gas Data:
                                      ppmv
  Date and Time
    Zero
   Reading
    ppmv
 Zero
Drift
ppmv
Calibration
Gas Reading
   ppmv
Calibration
   Drift
   ppmv
Start

    1.

    2.

    3.

    4.
Mean  (1)
Value:
        Zero
        Drift =
    ppmv
Calibration Drift =
mean calibration drift
calibration gas value
      x 100 =
(1)
   Absolute Value
                Figure  3.   Zero  and  Calibration  Drift  Determination

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Instrument ID
                                                Instrument ID
                   Calibration Gas Mixture  Data

                            	ppniv
Run     Calibration Gas
No.    Concentration,  ppmv
  Instrument Meter
    Reading, ppmv
Difference,
   ppmv
                                                            (1)
1.
2.
3.
4.
5.
6.
7.
8.
9.

Mean Difference^2)

Calibration Error =
Mean Difference
               (2)
                    Calibration  Gas  Concentration
                                                                           Calibration Gas Concentration
                                                                                      ppmv
                                                95% Response Time:

                                                               Seconds
1.
2.
3.
 Seconds
"Seconds
                                                                          Mean Response Time
                                                                         Seconds
                                                   Figure 5.   Response Time Determination
LuCalibratlon Gas Concentration  -  Instrument Reading)
^'Absolute Value
            Figure 4.   Calibration  Error  Determination
                                                   32

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