United States
Environmental Protection
Agency
Office of
Radiation Programs
Washington, D.C. 20460
EPA 520/1-84-023-2
October 1984
Radiation
Radionuclides
Response to Comments
for Final Rules
Volume II
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EPA 521-84-023-2
40 CFR Part 61
National Emission Standards for
Hazardous Air Pollutants
RESPONSE TO COMMENTS
FINAL RULES FOR RADIONUGLIDES
VOLUME II
October 22, 1984
Office of Radiation Programs
U.S. Environmental Protection Agency
Washington, D.C. 20460
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TABLE OF CONTENTS
1.0 INTRODUCTION 1
2.0 EPA's RESPONSE TO THE SCIENCE ADVISORY BOARD SUBCOMMITTEE
COMMENTS ON RISK ASSESSMENT 2
2.1 Responses to Procedural Recommendations 3
2.2 Response to Technical Comments and Recommendations 6
3.0 COMMENTS ON THE SCIENCE ADVISORY BOARD SUBCOMMITTEE FINAL
REPORT ON RISK ASSESSMENT 19
4.0 UNDERGROUND URANIUM MINES 22
5.0 ELEMENTAL PHOSPHORUS PLANTS 26
5.1 Sampling Locations/Procedures 26
5.2 Particle Size 26
5. 3 Demons trated Technology 27
5.4 Cos ts 31
5.5 References 36
6.0 GENERAL 37
APPENDICES: INDEX TO COMMENTERS
A. Federal Government 42
B. Members of Industry .' 43
C. Members of the Public 45
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1.0 INTRODUCTION
On April 6, 1983, EPA published in the Federal Register (48 FR
15076) proposed standards for certain categories of radionuclides.
Volume I of the Response to Comments (EPA 521/1-84-023-1) summarizes
major concerns and issues arising from written and oral comments on the
April 6 proposal, as well as EPA's response to these.
In December 1983, the Administrator of the EPA formed a Science
Advisory Board Subcommittee to review the methodology used by the Office
of Radiation Programs in assessing health risks from airborne release of
radionuclides. in addition, new technical data was gathered which
included the results of radionuclide emission testing at calciners at
three elemental phosphorus plants. New information also became available
on the cost and effectiveness of methods for reducing radon emissions
from underground uranium mines. Because the Agency intended to consider
this new information in the ongoing rulemaking, public comment was
requested on the new information, (49 FR 33695, August 24, 1984).
This document summarizes public comments on the new information and
EPA's response to them. In addition, Section 2 of the document contains
EPA's response to the Science Advisory Board Subcommittee's comments.
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2.0 EPA's REPONSE TO THE SCIENCE ADVISORY BOARD SUBCOMMITTEE COMMENTS ON
RISK ASSESSMENT
In response to criticism that the Agency did not have sufficient
outside review of its methods used to assess risks due to radionuclides,
the Administrator formed a subcommittee of the Agency's Science Advisory
Board (SAB) to review the scientific basis of the proposed standards for
radionuclides. The subcommittee held three public meetings: the first
on January 16, 1984, the second on February 21-22, 1984, and the third on
March 22, 1984. At these meetings, the Subcommittee was briefed by
Agency staff on the methods used in estimating risks caused by airborne
radionuclides. The panel heard from members of the public on the
Agency's risk assessments as well. The Subcommittee also held executive
sessions to consider the information presented by the Agency and the
public.
Transcripts of the public meetings are available in the Docket. The
Subcommittee's final report, entitled "Report on the Scientific Basis of
EPA's Proposed National Emissions Standards for Hazardous Air Pollutants
for Radionuclides," was transmitted to the Administrator on August 17,
1984. A copy of this report is available in the Docket.
In the Executive Summary of its report, the Subcommittee noted that
its activities could be viewed as addressing two interrelated questions.
First, did the Agency's staff collect the scientifically relevant data
and use scientifically defensible approaches in modeling the transport of
radionuclides through the environment from airborne releases, in cal-
culating the doses received by persons inhaling or ingesting this
radioactivity, and in estimating the potential cancer and genetic risks
of the calculated doses? Second, are the individual facts, calculational
operations, scientific judgments, and estimates of uncertainty documented
and integrated in a clear and logical manner to provide a risk assessment
that can be used as a scientific basis for risk management purposes,
i.e., standard-setting? With regard to the first question, the
Subcommittee concluded that EPA had gathered the appropriate scientific
information needed for a risk assessment in a technically proficient
manner.
The Subcommittee's greatest criticism in its report was related to
the second question. They concluded that EPA had not assembled and
integrated the available scientific data in the format of a risk
assessment that provides a scientifically adequate basis for regulatory
decisions on airborne radionuclides. The panel suggested that an inter-
mediate step was necessary between the collection of the relevant
technical information and the selection of regulatory options.
Specifically, they encouraged the Agency to assemble an integrated risk
assessment document that would lead a decisionmaker step-by-step from the
identification of emission sources, through the calculation of radiation
doses and health risks and the associated degree of uncertainty. They
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believe that such an assessment would enable the decisionmakers to better
evaluate the variety of regulatory options available. Only in this way,
did the Subcommittee feel that a policymaker could be presented with all
the facts necessary to make a responsible regulatory decision. Further,
this analysis would enable the scientific community and the public to
understand the rationale and basis for the Agency's actions.
The Subcommittee made several technical suggestions on how EPA could
improve its assumptions, models, and methods for estimating risks. Most
of the technical suggestions have been incorporated into EPA's risk
assessment procedures. The risk assessment for the final rule reflects
all of these modifications. Responses to each of the technical comments
are presented later in this report. Some of these technical suggestions
involve additional research to improve future risk assessment methods.
These suggestions will be used as EPA conducts new studies.
The Agency recognizes and is concerned about the adverse criticism
of its processes by its own Science Advisory Board. The Agency does
believe that, on balance, its risk estimates for specific sources of
radionuclide emissions are accurate within the limitations inherent in
making such estimates. However, it acknowledges that the criticism of
the Board does cloud the rulemaking record, and that the Subcommittee's
concerns, by their very nature, cannot be fully addressed within the time
available for this decision. Nevertheless, the final Background
Information Document has been greatly modified to encompass the format
and suggestions of the Subcommittee to the extent possible. The
Subcommittee has not yet had an opportunity to review this revised
document.
The Subcommittee made six procedural suggestions for improving
the Agency's risk assessment methods. These recommendations will be
incorporated into the Agency's procedures and processes. Responses to
these six recommendations are presented in Section 2.1 of this report.
The Subcommittee also made six recommendations for areas in which
additional research would be helpful. The Agency appreciates receiving
these recommendations and will work with the radiation research community
to try to promote additional studies in these areas.
2.1 Responses to the Procedural Recommendations
Recommendation Number 1; ...that procedures be established to
delineate more clearly the risk assessment and risk management aspects
of the total radiation standards development process.
Response; The Subcommittee was not particularly clear as to the
specific problem this recommendation was addressing, and how the Agency
could best accommodate their concerns. However, during their
deliberations it appeared that several of the Subcommittee's members had
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difficulty distinguishing and separating risk assessment and risk
management issues. To accommodate this recommendation, EPA will adopt
procedures to more clearly delineate risk assessment and risk management.
They will include determining the appropriate time to schedule reviews by
SAB and the scientific community, determining the nature of the materials
to be submitted for scientific review, and determining the role of the
scientific review in the risk management process,
Recommendation Number 2; ...that for each regulatory action
considered, the risk assessment process includes development of a risk
assessment document which makes reference, as appropriate, to more
detailed analyses found in the scientific literature.
Response; The Agency will include a risk assessment document for
each of its regulatory actions involving radiation. The Subcommittee
suggested that such a document include the conceptual framework for
assessing radiation risks, starting with identifying sources of
radionuclide emissions, analyzing the movement of radionuclides from a
source through environmental pathways, calculating doses received by
individuals and populations, estimating genetic and somatic health
effects, and presenting a statement of uncertainty in the risk
estimates. They indicated that uncertainty should be expressed as with
lower and upper bounds around central estimates for cancer and genetic
end points.
The Agency will prepare its risk assessment documents for radiation
along the general framework recommended by the Subcommittee. However, it
is important to note that, at least for radiation risk assessments
performed in the near future, the ability to evaluate uncertainties is
limited. Each element of the risk assessment has uncertainties.
Consequently, to develop an overall estimate of the uncertainty, it is
necessary to have techniques which can propagate uncertainties throughout
the assessment. The development of such techniques is currently in the
research stage. Well established models and techniques are not
available. EPA and other groups are working to improve analytical
capabilities in uncertainty analysis, but it will be several years before
satisfactory methods are available. In the meantime, EPA will provide a
qualitative evaluation of uncertainties in the various elements of the
risk assessment. This will include determining which elements have the
greatest uncertainty and which uncertainties have the greatest impact on
the risk estimates. The Agency will provide quantitative estimates of
uncertainty to the extent feasible, but it must be recognized that such
estimates are likely to be based primarily on scientific judgment rather
than rigorous mathematical analysis.
Recommendation Number 3; ...that such a risk assessment document be
prepared for airborne radioactivity as a basis for making any further
risk management decisions on the airborne radionuclides emission
standards, including promulgation of final standards.
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Response: The Agency has prepared an integrated risk assessment
document for the final radionuclide rule following the framework
suggested by the Subcommittee.
This integrated risk assessment is the final Background Information
Document. It is organized into two volumes. The first volume contains
background information on radiation protection and a detailed description
of the Agency's procedures and methods for estimating radiation dose and
risk due to radionuclide emissions to the air. Volume II contains
detailed risk estimates for each source of emissions, which were
performed according to the procedures given in Volume I. Each chapter
contains a general description of the source category, a brief
description of the processes leading to emissions of radionuclides to the
air, a summary of emissions data, and estimates of radiation doses and
health risks to both nearby individuals and larger populations.
The Agency has had only about two months between officially
receiving the Subcommittee's report and the deadline established by the
court for final action. Completion of this integrated risk assessment in
such a short period has been a monumental task . It would have been
desirable to have had more time to refine the risk assessment.
Nonetheless, the Agency believes that the risk assessment performed for
the final rule reflects the state-of-the-art in assembling, analyzing,
evaluating, and presenting the relevant scientific information.
Recommendation Number 4 ...that a standing committee be created as
a part of the EPA Science Advisory Board to review risk assessments for
radiation standards and to provide advice on the full range of scientific
activities of the Office of Radiation Programs.
Response: EPA believes that a standing subcommittee would be useful
and is in the process of establishing such a subcommittee. However, the
charter will be broader than just reviewing the activities of the Office
of Radiation Programs. It will review the scientific activities of all
of the programs in EPA that deal with radiation.
Recommendation Number 5 ...that procedures be developed for
soliciting and receiving public comment and SAB review on radiation risk
assessments before proposed standards are developed.
Response; EPA agrees that it would be beneficial to have its
scientific assessments reviewed prior to the development of standards.
This would help remove risk management issues from the scientific review,
and it would enable scientists to focus on the scientific issues in a
well structured, unhurried manner. EPA will schedule the review of risk
assessments in accordance with this recommendation, to the extent
practical. Complying with this recommendation may add one year or more
to the period needed to complete a rulemaking. Court ordered deadlines
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and other constraints sometimes hinder the Agency's ability to conduct
such extensive reviews prior to the development of proposed rules and
other risk management decisions. The Agency is aware of the difficulties
encountered when scientific reviews are conducted after standards have
been proposed and will try to avoid such conflicts, if possible.
Recommendation Number 6 ...that steps be taken to enhance
communication between the Office of Radiation Programs and other staff
offices of the Agency and the scientific community on issues related to
risk assessment.
Response; The Office of Radiation Programs was one of the first
offices in EPA and the Federal Government to perform risk assessments
methods. Many of the techniques used for radiation risk assessments have
been adapted for use in estimating risks from toxic chemicals. Still,
EPA agrees that technical exchange between all scientific groups
performing risk assessments could be improved.
The Agency is taking several steps to foster better communication.
A forum has been established at EPA to exchange information pertinent to
risk assessments among the program offices. Guidelines are being
developed to insure that scientific information is evaluated in a
consistent manner. EPA has requested the National Academy of Sciences to
undertake a new review of the effects on exposure to low levels of
ionizing radiation. This review will consider the effects of high and
low LET (linear energy transfer) radiation. Further, the Agency is
planning to seek advice from the National Council on Radiation Protection
(NCRP) on various scientific issues, including risk assessment for
airborne emissions of radionuclides.
2.2 Response to Technical Comments and Recommendations
Comment 1: The Subcommittee raises several questions about the.
basic structure of the food chain section of AIRDOS-EPA. For example,
the processes of resuspension, rain splash, absorption of surficial
deposits into foliar tissues, and soil ingestion by beef and dairy cattle
do not seem to be included in the code. (Page 17) Note: Page number
refers to that in "Report on the Scientific Basis of EPA's Proposed
National Emission Standards for Hazardous Air Pollutants for
Radionuclides."
Response: The degree of detail required in a risk assessment model
depends on the purposes for which the model is being used. In the case
of radionuclide air emissions, the major impact on human health is due to
the inhalation of airborne radioactivity. The AIRDOS-EPA ingestion model
is clearly adequate to establish the relative importance of the food
pathway, and to demonstrate that the food pathway is not particularly
significant in estimating the total risk from emissions to air.
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Consequently, the food pathway is not an important consideration in
making regulatory decisions regarding radionuclide emissions. Moreover,
many of the processes explicitly identified by the Subcommittee have not
been neglected, e.g., resuspension, rain splash, and absorption. The
values for the intercept fraction (that fraction of deposited activity
which is intercepted by plant surfaces) used in the calculations are
based on field measurements which include the effects of these
processes. The measured values do not, however, allow the effects to be
quantified separately. Soil ingestion by livestock is not included, as
EPA is unaware of any concensus on values for this parameter. In view of
the low significance of the food pathway, it is difficult to envision
that this process would affect regulatory decisions concerning air
emissions.
Comment 2; Furthermore, several basic human food types are not
explicitly modeled, such as fish, cheese, poultry, eggs, and red meats
other than beef. These omissions do not appear to be offset by higher
human consumption rates of similar food directly modeled. (Page 17)
Response: These omissions were offset by adjusting consumption data
for similar foods. For most radionuclides, good data on transfer
coefficients to meats are available only for beef. Therefore, we have
used the concentration in beef as a surrogate for that in other meat and
then used a meat utilization factor which includes the consumption of
poultry and other meats as well as beef. This "offset by higher human
consumption rates of similar foods" is discussed in chapter six of the
final BID. We agree that the model should be augmented to include
specific transfer coefficients for additional foodstuffs as data become
available, so that it will be more useful for situations where ingestion
is a significant pathway. In the case of interest here, there would be a
negligible change in the total risk if we had detailed data for all food
stuffs, since the food pathway contributes only a small fraction of the
total risk.
Comment 3: AIRDOS-EPA appears to be structured to average across
seasons ... disregards the significant seasonal fluctuations ... A
further limitation of this constant-parameter, steady-state model becomes
clear if it is applied to radionuclide releases which are short-term,
time-variant, or sporadic. (Pages 17-18)
Response; The air emissions of concern are chronic releases which
are expected to be fairly uniform throughout the year. AIRDOS-EPA
computes average intakes and exposures across seasons for the various
pathways to man. If releases of radionuclides had a strong variation
which was particularly significant to the assessment, AIRDOS-EPA would be
modified. Limitations of the AIRDOS methodology are considered when
performing and evaluating risk assessments so that it is not used
inappropriately.
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Comment 4; subcommittee statement: "... it would seem more
reasonable to adopt NRPB values," ... than "EPA values for
gastrointestinal absorption of transuranic radionuclides." (Page 21)
Response: The Agency has included the cited lower NRPB values in
the final BID. EPA believes inclusion of both the EPA and the NRPB
values for gastrointestinal absorption is appropriate since both sets are
now being considered by the ICRP in their ongoing revision of ICRP
Publication 19, "The Metabolism of Compounds of Plutonium and Other
Actinides." It should be noted, however, that the EPA Science Advisory
Board's Subcommittee on High Level Waste recommended that the EPA values
be used in the assessment of the risk from transuranic wastes.
The World Health Organization has adopted the NRPB estimates for gut
absorption of transuranics (Environmental Health Criteria 25: Selected
Radionuclides, WHO, Geneva, 1983; Nuclear Power: Health Implications of
Transuranic Elements, European Series No. 11; WHO, Copenhagen, 1982).
However, they noted that the estimate was based on animal studies and
"Qualitative support for the plutonium numbers is provided by autopsy
data from a group of reindeer-herding northern Finns, who ingest large
quantities of plutonium-rich reindeer liver [M3]. Their plutonium
burdens seem to be no higher than those of southern Finns, who do not
ingest these relatively large quantities of plutonium. A difference
should have been apparent if the fraction absorbed from the
gastrointestinal tract had been much greater than 10~4."
(Environmental Health Criteria 25, 1983).
Reports from the Finnish investigators (H. Mussalo-Rauhamaa,
Accumulation of Plutonium from Fallout in Southern Finns and Lapps,
University of Helsinki, Finland, 1981; H. Mussalo-Rauhamaa, et al.,
Plutonium in Finnish Lapps - An Estimate of the Gastrointestinal
Absorption of Plutonium by Man Based on a Comparison of the Plutonium
Content of Lapps and Southern Finns, Health Physics 46:549-559, 1984)
show that such a difference was observed. Further, they estimate the
gastrointestinal absorption of soluble plutonium in man to be 8 x 10~4
to 9 x 10~4. If they are correct, the EPA would not underestimate
absorption but the NRPB would.
There are no comparable data for other transuranics, but studies in
swine, selected because "the primary strengths of swine as the animal
model are their remarkable anatomic and physiologic likeness to man with
respect to the cardiovascular system, digestive tract, skin, nutritional
needs, bone development and mineral metabolism," have provided new data
on americiura (G.R. Eisele, e_t al., Americium Absorption from the
Gastrointestinal Tract of the Pig, NVO-252, Oak Ridge Associated
Universities, Oak Ridge, Tennessee, 1982). They found net absorption of
241Ara from the gastrointestinal tract of swine varied from 0.7 x 10~3
to 1.6 x 10~3 and the absorption was estimated at 1.1 x 10~3, similar
to the EPA estimated absorption in man.
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Differences between NRPB values and those used by EPA in preparing
the draft BID are appreciable only for plutoniura oxides. Unlike the
NRPB, EPA takes account of the fact that the solubility of plutoniura
oxides varies, depending on the temperature at which they are formed, and
that, even in the oxide form, high specific activity plutonium isotopes
have greater solubility than plutonium-239. Therefore, the NRPB
estimates may underestimate absorption. In any case, except for
Plutonium oxides and organically-bound transuranics (not considered by
the NRPB), the EPA values for gastrointestinal absorption are only twice
the NRPB values. Although use of the EPA values rather than the NRPB
values increases the dose estimate for the sources considered in this
rulemaking, this would have a negligible effect on the final risk
estimates because there is very little emission of transuranic
radionuclides from the source categories considered, and the ingestion
pathway as a whole contributes only a small fraction of the total risk.
Comment 5; (five) ... technical areas of AIRDOS-EPA, RADRISK and
DARTAB where improvements may be required in the future:
a: "... in the calculation of external dose, it was assumed that
the deposited radioactivity stays on the surface of the earth for 100
years and never weathers into the soil. This assumption would seriously
overestimate the dose from long-lived radionuclides." (Pages 22-23)
Response; The subcommittee is in error. A 100-year retention
without environmental removal is not assumed in the calculation of
external dose. Rather, EPA has assumed a 2% per year removal constant
for deposition in rural areas and a 10% per year removal constant for
urban areas. Removal of deposited radioactivity is of course highly
dependent on such considerations as chemical form of the radionuclide
soil composition and chemistry, and precipitation, irrigation and
evapo-transpiration. The values we have used are comparable to those
predicted by the model proposed by Hoffman and Baesd) and those
calculated from the changes in time of fallout products (1-^Cs and
90Sr) in food stuffs as reported by UNSCEAR^. A discussion of
environmental removal from soil has been included in Volume I, Chapter 6
of the final BID.
Hoffman P.O. and Baes C.F. Ill, A Statistical Analysis of Selected
Parameters for Predicting Food Chain Transport and Internal Dose of
Radionuclides, NUREG/CR-1004, Oak Ridge National Laboratory, Oak Ridge,
Tennessee 37831, 1979).
(2) united Nations Scientific Committee on the Effects of Atomic
Radiation, Ionizing Radiation Sources and Biological Effects, 1982 Report
to the General Assembly, with Annexes, United Nations, New York, 1982.
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b: The documentation for AIRDOS-EPA also indicates that a constant
absolute humidity value of 8 g/m3 is used. Since absolute humidity is
typically much lower than 8 g/m3 in much of the U.S., this assumption
leads to an underestimation of dose. It would be more appropriate, and
not difficult, to use site-specific values for absolute humidity.
Response; This comment pertains to the assessment of the dose from
tritium. While the Agency agrees that site specific values for the
absolute humidity would be appropriate in cases where the dose from
tritium would be particularly important for decisionmaking, this is not
an important factor for the tritium releases considered in the draft
BID. In the absence of site specific data, the Agency has followed the
expert advice of Etnier, "a default value of 8 g/m3 would yield dose
estimates which are within a factor of two of the individual site
specific data" (Etnier, E. L. "Regional Site Specific Absolute Humidity
Data for Use in Tritium Dose Calculations").
The Agency has not analyzed, for this rulemaking, significant
releases of tritium in areas of low humidity and precipitation, where
8 g/m3 would be an inappropriate value. Rather, the only facility
assessed that had significant release of tritium was the Department of
Energy's Savannah River Facility in South Carolina. Etnier, cited above,
calculates absolute humidity in South Carolina to be in the range of 9.1
to 10.2 g/m3. Therefore, the Agency believes that the value used for
the Savannah River assessment does not differ significantly from these
values. However, we agree with the main thrust of the subcommittee's
comment that site specific values should be used where they would
significantly affect the result, i.e., in arid climates.
c: The physiological models and other input data required for the
calculation of dose for internally absorbed radionuclides is equally
important, and in many areas the data are incomplete. EPA should support
work aimed at expanding the technical basis for many of the input
parameters.
Response: The Agency is supporting work in this area by cooperating
with other Federal agencies in the efforts of the International
Commission on Radiological Protection to provide more complete and,
particularly, age-specific data for dose calculations.
d: These three calculational programs do not now consider the
important factor of uncertainty in each of the input parameters. The
Subcommittee does not have specific suggestions as to how such data could
be included, but believes that it is important for the EPA to develop
methods that would indicate to the user the uncertainty or "noise" in the
final values of REF. This uncertainty plays an important role in the
setting of standards.
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Response; The Agency agrees with the Subcommittee that a complete
quantification of the effect of uncertainty in all of the input param-
eters on the final results is desirable. A methodology that utilizes a
Monte Carlo approach to ascertain the probability distribution of the
uncertainty is being developed by ORNL and others, in cooperation with
the EPA, but it is unlikely to be useful for several years.
Nevertheless, the final BID provides additional information on the degree
of uncertainty in all components of the risk assessment.
e: Although scientifically sound, the units of REF are difficult
for the lay person, or even the scientist, to grasp. Alternatively,
consideration might be given to developing and using a common unit of
risk that could apply to all radiation hazards and be more readily
understood.
Response; The Agency agrees. In the final BID for the rulemaking
(as in the draft BID), risks have been expressed in terras of the
probability of inducing fatal cancer without reference to a risk
equivalent factor (REF).
Comment 6: In estimating cancer risk, the ORP approach was weakened
by the use of a single dose-response model, the linear nonthreshold
model. A preferred approach would have been to present a range of models
as discussed in the BEIR-3 report. (Page 24)
Response: The draft BID was based on the 1972 BEIR I report, which
used only the linear nonthreshold model. Additional models described in
the 1980 BEIR III report were discussed by EPA in "Basis for EPA
Radiation Risk Estimates," prepared for the Subcommittee in January
1984. This report, which is incorporated into the final BID, presents
the range of risk estimates obtained using all of the various dose
response and risk projection models discussed in the BEIR III report.
Risk estimates in the final BID are not based on a single model of
dose response, but include estimates made using the linear quadratic
model as well as the linear model. The difference in estimated risks for
these two dose response models is about a factor of 2.5. The reasons why
the Agency selected these two models and rejected the BEIR III quadratic
model are described in Chapter 8 of the final BID.
Comment 7; "The calculations of dose per unit intake of radio-
activity apparently do not use an age-dependent factor." (Page 24)
Response; Age-dependent factors were used in the draft BID for
estimating the risk due to radon progeny inhalation. Unfortunately,
there are insufficient metabolic data for children to estimate age
specific doses for all radionuclides. For the case of radon, the
calculated lifetime risk obtained using age-specific data is 22% greater
than that calculated using a dosimetry appropriate for adults only. The
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Agency has developed, in conjunction with Oak Ridge National Laboratory,
dosimetric models that will allow the inclusion of age-dependent factors
for children when sufficient metabolic data becomes available. For a few
radionuclides, including iodine-131, analyses of the risk using age
dependent factors are made in the final BID. These results are then
compared to the risks calculated using ICRP metabolic data for adults.
The greatest increased risk based on age-dependent calculations was for
lifetime exposure to 1-131, which was 60% higher. However, until
ICRP-23, "Reference Man," and ICRP-30, "Limits for Intake of
Radionuclides for Workers," are revised to include physiological and
metabolic data for children, it will not be practical to apply this
approach to all radionuclides.
Comment 8; It was also not clear if, following radionuclide intake,
the dose was assumed to be instantaneously delivered or protracted in
time...the great detail of the life table approach is not matched by the
details of the dose calculations. (Pages 24-25)
Response; The usefulness of the life table analysis is not confined
to assessing the risk for time-dependent doses. In the EPA assessment,
organ doses are not assumed to occur instantaneously, but are protracted
over a period of time corresponding to the time each annual intake is
retained within the body. Dealing with this type of exposure situation
is one of the strengths of the life table approach. Moreover, the risk
estimates derived by the BEIR III Committee are age-dependent and can be
considered explicitly in our analysis only by using a life table
approach. See also the prior comment.
Comment 9; Also, the fetus is generally considered to be very
radiosensitive, but no calculation of in utero dose is made. (Page 25)
Response: The draft BID was based on the BEIR I report (WAS 1972).
In that report, the cancer risk due to lifetime exposure at a constant
dose rate of 100 mrera per year was calculated with and without in utero
exposure. The difference in the estimated lifetime risk was small -
1 percent to 10 percent, depending on which risk model was used. In the
final BID, presentations of estimates of cancer risk are patterned after
those of the BEIR III Committee. The BEIR III risk estimates excluded
the small risk from in utero doses because the Committee believed that
the risk information was not sufficiently reliable for this age group.
Moreover, as a practical matter, there is almost no information in the
literature on the in utero dose from internal emitters in humans. Even
though a complete analysis of in utero doses for all radionuclides is
beyond the state of the art at this time, the final BID discusses in
utero health effects in some detail.
Comment 10: Radiobiological data exist which indicate the
likelihood that, at low doses and low dose rates, biological effects may
be less than that suggested by a linear nonthreshold relationship. In
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this regard, the radiobiological literature developed from experimentation
using many different biological systems are a useful supplement to the
human data, and ORP should examine this information and make greater use
of it. (Page 25)
Response; The radiobiological data that the Subcommittee appears to
be referring to are animal studies. While the Agency agrees that animal
data can sometimes serve as a useful supplement to human data on
radiation carcinogenesis, it does not believe decisions regarding the
shape of dose response models should be based exclusively on animal
data. The animal data have not been confirmed in studies of exposed
humans and are, in fact, contradicted by some observations of radiogenic
cancer in exposed humans. For example, the BEIR III Committee concluded
that for breast cancer across a wide range from low to high doses, even
with fractionation, and for thyroid cancer across a wide range of doses,
the response was adequately described by a linear nonthreshold model.
H.I. Kohn and R.J.M. Fry (Radiation Carcinogenesis, N. Engl. J. Med.
31C):504-511, 1984) recently pointed out, "Just what the shape of the
curve should be for any human cancer risk awaits further investigation.
When the mechanisms involved are unknown, there is not compelling reason
to suppose that one type of curve or model will be superior to all
others. In fact, it is likely that different decisive factors are at
work in various situations, even if the initial biophysical step in each
case is the same. Experiments have demonstrated how diverse dose-effect
curves can be in the mouse for example, for the induction of a single
class of reticular-tissue tumors: myeloid leukemia, roughly linear;
thymic sarcoma, a negative slope to a reduction in incidence of 50
percent, followed by a plateau." It would appear that a single model
based on "animals" is not predictive of response in a single species,
much less being a universal model for many species.
The World Health Organization (WHO) has considered this problem in
"Environmental Health Criteria 25" (WHO Geneva 1983) from a somewhat
different viewpoint that is worthy of consideration.
"466. In experimental animals and in man late somatic
and hereditary effects may exhibit different shapes of the
dose-effect relationships, according to a large number of physical
and biological variables operating in each particular system.
Linear, linear-quadratic, quadratic or complex relationships have
been described in various circumstances. No generalization may be
gained by the consideration of all existing experience, except
perhaps that each specific system responds according to different
kinetics of action and that biologically complex effects usually
correspond to more complex types of relationships. It would be
impossible to set up a rationale for a system of radiation
protection by considering each case separately. To overcome this
difficulty the assumption is made that late somatic and hereditary
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effects of irradiation follow a non-threshold linear function of
dose. This assumption is simple and there is evidence that it is
also a conservative assumption in most cases."
Comment 11; The Subcommittee also believes that the use of the BEIR
III report, which for cancer risks is based largely on human data at high
doses and brief exposures, should be supplemented with other radio-
biological data when extrapolations are made to very low doses
accumulated over decades. The Subcommittee assertion is not intended as
a criticism of the BEIR III panel's evaluation, for that report was not
designed as a risk assessment for standard setting at very low level of
exposure. (Page 26)
Reponse: The BEIR III Committee's report is entitled "The Effects
on Populations of Exposure to Low Levels of Ionizing Radiation: 1980."
Contrary to the Subcommittee's indication that the BEIR III Committee's
report was not to be used in risk assessments for standard setting, the
transmittal letter for this report to the Agency (page IV in NAS BEIR-3)
from the President of the Academy clearly indicates otherwise, i.e., "We
believe that the report will be helpful to the EPA and other agencies as
they reassess radiation protection standards. It provides the scientific
basis upon which standards may be decided after nonscientific social
values have been taken into account." In this context, it is important
to recognize that the term low level must always refer to dose rates that
are at least 0.1 rad per year since this is the average yearly dose from
naturally occurring background radiation in the United States. The
Agency has assessed the size of incremental doses due to radionuclide
emissions that are in addition to this background dose rate. We believe
that the Academy envisioned the use of their risk estimates near back-
ground levels because the Federal Radiation Protection Guides published
in 1960 apply to dose rates as low as 170 mrad per year. Further, the
NAS studies were commissioned by EPA to help assess risks at levels near
background. The radiological data the Subcommittee has identified is
based on various animal studies. The Agency has considered animal data
and other radiobiological information in its calculation of risk
estimates. However, we do not believe it should be relied on more than
human data when it is contradicted by studies of human cancer in exposed
populations.
Comment 12: ... to assess the risk from radon daughters ...ORP
again selected a single value, three percent lung cancer increase per
WLM, as the relative risk coefficient. A range of values would have been
more appropriate.... (Page 26)
Response: A range of values is used in the final BID. The draft
BID used three percent because this is an average value for exposed
miners (Indoor Radiation Exposure Due to Radium-226 in Florida Phosphate
Lands, EPA 520/4-78-013, USEPA, Washington, D.C., 1978; V.E. Archer, E.P.
Radford, and 0. Axelson. Factors in Exposure-Response Relationships of
Radon Daughter Injury, pp. 324-367 in Conference/Workshop on Lung Cancer
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Epidemiology and Industrial Applications of Sputum Cytology. Colorado
School of Mines, Golden, 1979). The report, "Basis for EPA Radiation
Assessments" provided to the Subcommittee during its review compares six
models for assessing the risk due to inhaling radon daughters. This
information is also included in Chapter 8 of the final BID, along with
corresponding risk estimates for representative models. While estimates
of radon risk vary by about a factor of six, the UNSCEAR and ICRP models
yield estimates within a factor of two of the EPA and BEIR III models.
The BEIR III risk estimates for radon inhalation are nearly identical to
those of EPA.
The more credible models included in the final BID are those of EPA,
BEIR III, and AECB. All these models address lifetime risk for lifetime
exposure as might be appropriate for a population.
The ICRP model addresses only exposure during the working lifetime
and expression of cancer risk during a 30-year followup period, not
appropriate for a population estimate.
The UNSCEAR model uses a lifetime exposure but only addresses cancer
expression during a 40-year followup period. Such a short followup
period is not really appropriate for a population estimate.
The NCRP model addresses lifetime risk for lifetime exposure.
However, it assumes that the effect of exposure diminishes exponentially
with a 20-year half-life. No scientific support for this assumption is
currently available.
Comment 13; The Subcommittee is concerned that ORP uses the
conservative or worst case linear extrapolation for carcinogenesis, i.e.,
extrapolation from acute high-dose exposures, while simultaneously using
the chronic low-dose exposure extrapolation procedure for genetic
effects. For genetic effects, the endpoint of concern is the nucleus.
It is most likely that the nucleus is also the relevant target for
important aspects of induction of somatic effects since scientists now
recognize the role of oncogenes and chromosome rearrangement in
carcinogenesis. Thus, state-of-the-art understanding of the mechanism of
cancer induction can no longer justify ignoring "dose-rate effects" in
favor of linear high-dose extrapolation. Scientific panels organized by
the National Academy of Sciences, the United Nations Scientific Committee
on the Effects of Atomic Radiation (UNSCEAR), the National Council on
Radiation Protection (NCRP) and ICRP are in general agreement that some
dose-rate effect occurs, and each of these groups uses this assumption in
calculating best estimates. (Page 27)
Response: The BEIR III report provided dose-response estimates for
three of the many possible models of dose-response. Of the three models
the BEIR Committee evaluated, the linear model is most conservative.
Even so, numerical risk estimates based on the linear model are within
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the range of uncertainty of risk estimates based on the less conservative,
linear quadratic model.
Although the linear model is generally conservative, it is clearly
not a worst case model. There are a number of other dose-response models
that would yield higher risks at low doses. For example, a model that
takes account of the variation of radiosensitivity among members of a
heterogeneous population would estimate the risk at low doses to be
higher than the risk estimate from a linear model (Problems in Assessing
the Cancer Risks of Low-Level Ionizing Radiation Exposure, U.S. General
Accounting Office, 1981).
The Agency agrees that many scientists believe that reduced
radiocarcinogenesis may be possible at low dose rates. These views are
based on the body of evidence arising from cellular and animal studies.
However, there is no human cancer data to support this view (H.I. Kohn
and R.J.M. Fry, Radiation Carcinogenesis, N. Engl. J. Med., 310:504-511,
1984), and currently available studies of both radiogenic breast cancer
and thyroid cancer in humans appear to contradict it. Breast cancer
incidence has been shown to be linear in the dose range from less than 20
rad to more then 300 rad, with no sign of a quadratic term at high
doses. Moreover, when the dose to breast tissues is fractionated into
many small doses, less than a rad, the cancer risk is not reduced,
contrary to the effect that would be predicted in a dose-rate effect.
Similarly, thyroid doses of less than 10 rad are as carcinogenic per unit
dose as are much larger doses, a few hundred rad. While these examples
indicate that the linear model may not overestimate risks for some types
of cancer, EPA does not believe that all types of radiogenic cancers will
necessarily follow the same dose-response model. The final BID includes
risk estimates based on reducing radiocarcinogenesis at low dose rates
for low LET radiations. This will enable the public and Agency
decisionmakers to observe the significance of using alternative dose
response models. In general, whether one uses the linear model or the
model that reduces risk for low dose rates, the difference in risk
estimates is a factor of 2.5. Even so, the Agency believes that it is
reasonable and prudent to give considerable credibility to estimates
based on a linear response since this model has the least conflict with
the data observed from human cancer studies.
Comment 14: In addition, in cases where ORP proposes to use a years
of life lost estimate per rad exposure for calculating the risk of
somatic effects, a parallel approach should be applied to deriving a
statement of genetic risk (see UNSCEAR 82). (Page 21)
Response: Although the Agency presented a method for calculating
the average number of years of life lost due to premature cancer deaths
in its presentation to the Subcommittee, it did not include such results
in either the draft or final BID. Although analyzing years of life lost
due to premature cancer death is an interesting concept, EPA has not
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attempted to incorporate it into decisionmaking. It is premature to
develop similar estimates for genetic effects until more complete
information on reduction in life expectancy, severity of impairment
during the life span, and impact on family and society for a large
variety of genetic effects (or "endpoints of genetic effects") is
published. The Agency notes that the 1982 UNSCEAR report stressed the
uncertainty of its estimates of years of life lost and years of life
impaired for genetic effects, and the virtual absence of estimates for
irregularly inherited conditions or recessive conditions.
Comment 15; Finally, BEIR III estimates for genetic effects are low
because the mouse female data are inappropriate for human extrapola-
tion. The immature mouse oocyte cannot be used to detect mutations since
an ionization traversal through the cell membrane kills the cell (Dobson,
1983). Faced with this scientific uncertainty it would be judicious for
ORP to also give an alternative estimate, assuming equivalent mutability
for both sexes, until there is other evidence to the contrary. (Page 27
and 28)
Response; EPA has included alternative estimates in the final BID
that assume equal mutability for both sexes. These alternative estimates
of genetic damage are about 40% larger than those in the BEIR III report,
where the female is considered to be 60% less sensitive to mutations than
the male. This change is small compared to the range of uncertainty in
the BEIR III estimates for genetic effects which may be several hundred
percent.
Comment 16; ORP's selection of relative versus absolute risk models
for estimating cancer risks is another instance where a more detailed
analysis and presentation would have been useful. Both approaches have
their strengths and weaknesses which should have been elaborated. If one
approach was to be selected over the others then it would be appropriate
to clearly document why it was selected and how it is reflected in the
uncertainty of the final risk estimates. (Page 28)
Response; Absolute and relative risk models are discussed in the
Final BID in two aspects: as transportation models for use in applying
risks observed in one group to another having different demographic
characteristics and as risk projection models for estimating the lifetime
risk from radiation exposure beyond the years of observation. The
limitations introduced by the selection of a particular model are
discussed in the Final BID, along with the degree of uncertainty inherent
in the Agency's use of an average of relative and absolute risk
projections for all cancers except leukemia and bone cancer. The choice
of a relative or absolute risk population model is not important for
leukemia and bone cancer because the duration of expression is apparently
less than the period of observation in epidemiological studies. In such
cases, either model yields the same estimated risk, as noted in the Final
BID.
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Comment 17; The factor of twenty for high LET radiation appears
appropriate when used by ICRP and inappropriate when used by ORP. ICRP
has a dose-rate factor for low LET radiation. In contrast, ORP uses a
high dose rate for low LET to compare with high LET. The factor of
twenty is thus too great. (Page 28)
Response: The Agency agrees. In the draft BID, the Agency followed
the same procedure as then used by the BEIR III Committee, in which the
risk of alpha emitters was divided by 20 to estimate low LET risks using
a linear model. However; EPA agrees that risk estimates based on the
ICRP quality factor of 20 and risks observed for acute low LET exposures
should take account of a dose rate effectiveness factor (DREF). Risk
estimates for internally-deposited alpha particle emitters have been
revised in the final BID to reflect the information supplied by the
Subcommittee, i.e., risk estimates for internally-deposited alpha
particle emitters are twenty times the risk estimated using the BEIR III
linear dose response model, and a DREF of 2.5.
The comments by the Subcommittee on pages 28 and 29 were the result
of a misconception on the part of the Subcommittee. Subsequent
discussion with the Subcommittee member who made the comment indicated
that he thought that the arguments made by EPA in developing an RBE of 20
for genetic effects due to alpha radiation were the basis for the quality
factor of 20 the Agency used to estimate the risk of carcinogenesis due
to alpha radiation. This is not the case. The EPA analysis of the RBE
for genetic effects is independent of the ICRP choice of a quality factor
of 20 for carcinogenesis due to alpha radiation. Both the RBE for
genetic effects the ICRP quality factor apply to the risk of alpha
radiation compared to low dose rate low LET radiation. For genetic
effects, the BEIR III Committee (and EPA) used a dose rate effectiveness
factor (DREF) of 3. The Subcommittee agreed with this choice for genetic
effects. The SAB Subcommittee informed EPA that the ICRP had used a DREF
of 2.5 in developing their cancer risk estimates for low dose rate low
LET radiations and that their choice of a quality factor of 20 was based
on this assumption. Cancer risk estimates for alpha particle emitters in
the final BID were recalculated accordingly.
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3.0 COMMENTS ON THE SCIENCE ADVISORY BOARD SUBCOMMITTEE FINAL REPORT ON
RISK ASSESSMENT
This section responds to comments received from the general public
related to the Science Advisory Board Subcommittee report on risk
assessment.
Comment 3.1.a: The commenters agree with the SAB comments that the
proposed regulations lack a scientifically adequate basis for regulatory
decisions for radionuclides and that a risk assessment document must be
completed and submitted for review. (1-1, 1-6, 1-8, 1-11)
Comment 3.1.b: Commenter supports SAB recommendation that EPA
prepare a range of risk estimates in future work regarding NESHAPS for
radionuclides and more clearly delineate its risk assessments from its
risk management decisions. (1-3)
Response (Comments 3.1.a and b): These comments have been addressed
in Section 2.1. The appropriate sections are indicated below:
Comment 3.1.a - See response to Recommendation Numbers 2, 3, 4, and
5.
Comment 3.1.b - See response to Recommendation Numbers 1, 2, 3, and
4.
Comment 3.2a: The suggestions of the Science Advisory Board go
beyond their mandate and should not be allowed to impede prompt
completion of the Agency's obligations to produce final standards. (P-6)
Comment 3.2b: The report authored by the Science Advisory Board
should be excluded from consideration when considering the final national
emission standards for radionuclides. (P-5)
Response (Comments 3.2a and b): The SAB was charged with a review
of the Agency's risk assessment methodology. That review was to focus on
such items as identifying the health hazards from exposure to radiation,
analyzing the movement from sources through various pathways, estimating
a dose received by humans, calculating the probability of health effects,
and presenting a statement of uncertainty in the risk estimates. The
Committee, in some instances, focused and commented on risk management
which includes such things as comparing the risk estimates to risks from
other hazards to assist in judging significance, developing alternate
control strategies, analyzing the social and economic aspects of the
status quo and alternative actions, and deciding on an appropriate course
of action.
The Agency separated the risk assessment issues and comments from
the risk management issues and comments and considered only the former in
arriving at its decisions.
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Comment 3.3; The Science Advisory Board Subcommittee's
recommendation that EPA abandon the ALARA regulatory approach in favor of
the "probable risk" approach is beyond the Subcommittee's mandate to
consider only the scientific basis of EPA's risk assessment and is
contrary to both the Clean Air Act and the tenets of radiation
protection. (P-6)
Response: The Agency agrees. The discussion of ALARA as the basis
for decisions is clearly a discussion of a possible approach to risk
management. It was the charge of the SAB to review the Agency's risk
assessment methodology.
Comment 3.4; Commenter requests EPA to reconsider and withdraw the
listing of radionuclides as hazardous air pollutants. This is based on
the SAB Subcommittee report which states: (1-2)
— the health impacts from radioactive emissions being discharged
from all the U.S. facilities ... were calculated to be much less
than one cancer per year for the entire country.
Response; The record strongly supports the conclusion that
radionuclides meet the criterion for a hazardous air pollutant in Section
112 of the Act because extensive scientific evidence indicates that
exposure to radiation increases the risks of developing fatal and
nonfatal cancers. This information is based on animal and human studies
at levels only a few times greater than potential environmental
concentrations. Therefore, the original decision to list radionuclides
as a hazardous air pollutant is adequately supported.
Comment 3.5: The SAB has confirmed that EPA's proposal to regulate
airborne radionuclides lacks any scientifically adequate basis for
regulatory decisions for this pollutant; therefore, commenters suggest
that EPA should withdraw the proposed rule. (1-1, 1-4, 1-10, 1-11, 1-12)
Response; The Agency announced its withdrawal of four proposed
standards for radionuclide emissions under Section 112 of the Clean Air
Act and affirmed its original decisions not to regulate emissions from
the other five source categories considered. The announcement and
reasons for the action appear in the Federal Register.
Comment 3.6; EPA's risk assessment should emphasize "upper bound"
estimates, rather than "central" estimates, as recommended by the Science
Advisory Board Subcommittee.
Response: This commenter has also said, "We do not object to a risk
assessment document that displays a range of models or assumptions, along
with their resulting risk assessments." In the Background Information
Document, EPA considered several models. The Agency did not attempt to
arrive at a "central" estimate, through some sort of averaging procedure.
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EPA does not agree that it must always select the model that yields
the highest risk estimates, for an "upper bound" on risk. See the
response to Comment 2.2.If in Volume 1 of this document.
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4.0 UNDERGROUND URANIUM MINES
Comment 4.1: Neither the information in the original docket nor the
new information recently added justify regulation of radon from uranium
vents at the standard proposed by EPA. (1-2)
Response: The Agency proposed a standard that would limit the
annual average radon-222 concentration in air due to emissions from an
underground mine to 0.2 pci/l above background in any unrestricted area.
The standard was expected to be met by one of the following procedures:
(1) reducing the percentage of time the mine operates, (2) increasing the
effective height of the release, or (3) controlling land around the
mine. EPA expected that mine operators would most likely try to control
land within about 2 kilometers of the mine vents in order to comply with
the standards. EPA did not choose to issue a direct emission standard
for radon from underground uranium mines because available information
suggested that radon could not be collected by available pollution
control equipment before being released from the vents and reductions
afforded by better bulkheading or sealants were highly uncertain.
Comments on the proposed rule indicated that controlling land around the
mine might not be feasible because private owners of land surrounding the
mine might be unwilling to make their land available to the mine owners
or might be willing to sell only at prices higher than fair market value.
Analysis of the likely reduction in health risks afforded by the
proposed standards showed that while risks to nearby individuals were
reduced by a factor of about 10, the risks to the total population were
only negligibly reduced. The lack of population risk reduction was due
to the fact that radon releases would not be mitigated, they would only
be more widely dispersed.
Several comments were received stating that the EPA had overestimated
the risks from radon-222 emissions from underground uranium mines. It
was suggested that the Agency had used overly conservative assumptions in
the dispersion and risk calculations and that it used greater risk
coefficients than recommended by other recognized radiation experts. EPA
has reevaluated the risk estimates from radon-222 emissions and revised
the parameters used for emission rates, plume rise, and equilibrium
ratios. Estimates of the lifetime risks to individuals living near these
mines range from one in one thousand to one in one hundred. The potential
exists for even higher risks in some situations, e.g., a person living
very close to several horizontal mine vents or in areas influenced by
multiple mine emissions. Lifetime risk in these situations can be as
high as one in ten. The fatal cancer risk to the total population, both
regionally and nationally, is 5 fatal cancers/year. The Agency considers
these risks to be significant and believes action is needed to protect
populations and individuals living near underground uranium mines.
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Because radon-222 is a noble gas and the volume of air discharged
through mine vents is very large, there is no practical method to remove
radon-222 from the mine exhaust air- Absorption onto activated charcoal
is the most widely used method for removing noble gases from a low volume
air stream. However, application of this method to the removal of
radon-222 from mine ventilation air at the volumes of air which must be
treated would require large, complex, unproven systems which would be
extremely costly. Therefore, it is the Administrator's judgment that it
is not feasible to prescribe or enforce an emission standard for
radon-222 emissions from underground uranium mines because radon-222
cannot be emitted through a conveyance designed to capture the gas under
current conditions. Instead, EPA has decided to begin development of
work practice, design, equipment, or operation standards to control radon
releases from underground uranium mines.
To this end, EPA has issued an Advanced Notice of Proposed Rulemaking
to acquire information/data in a number of subject areas. The Advanced
Notice of Proposed Rulemaking (ANPR) on this subject solicits information
in the following areas:
(1) amounts of emissions of radon-222 from underground uranium mines;
(2) applicable design, equipment, work practice or operational
standards;
(3) ability to predict releases of radon from underground uranium
mines without controls and with various types of bulkheads,
sealants, or other controls;
(4) effectiveness, feasibility, and costs of such controls; and
(5) estimates of impacts on nearby individuals and populations due
to radon-222 emissions before and after such controls.
Comment 4.2a: Additional evidence supports the conclusion that
technology is available to allow uranium mines to achieve significantly
more stringent emission limitations for radon than those proposed by EPA.
(P-2)
Comment 4.2b: EPA fails to consider radon exposure from mines in the
context of total exposure to all major sources of radon. (P-2)
Comment 4.2c: EPA should set its standard at a level which will
avoid any increased deaths attributable to radon from uranium mines when
considered as part of the total radon exposure above natural background
experienced by a person living in uranium mining districts. (P-2)
Response (Comment 4.2a through c): EPA has issued an Advanced Notice
of Proposed Rulemaking for uranium mines. The Agency has solicited
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information in a number of subject areas, including radionuclide emission
levels and control options and strategies (also see response to Comment
6.1). These data will be used to develop work practice, design, equipment
and/or operational standards to control radon releases from uranium
mines. It is the Agency's intent to evaluate the risk of radon exposure
in the context of total exposure to all major sources, including exposure
in the home.
Comment 4.3: Any standards for underground uranium mines should be
developed to protect actual individuals from actual exposure that could
produce significant risks of harm. Similarly, any exemption program
should be based on the same conditions. In short, if no real individual
is subject to such exposures, imposition of standards is unnecessary.
(1-2)
Response: The main concern in this comment seems to be that the
method does not relate to actual people. In the final BID, maps are
included to show where individuals are located near mine vents.
Comment 4.4: Commenters state that release data are outdated and
that many mines are now closed. (1-2, 1-6)
Response; Estimates of emissions were revised on the basis of mine
age and size in 1982. This methodology is described in Volume II of the
Background Information Document.
Comment 4.5: Commenters state that costs of controls for underground
uranium mines are prohibitive. (1-2, 1-6)
Response: The cost for controls has been updated in the final BID.
These costs will be reconsidered when the Agency examines the feasibility
of a work practice standard. See also response to Comment 4.1.
Comment 4.6: The Gaussian dispersion model is very conservative and
its level of uncertainty in rough terrain is unknown; the relevance of the
model mine in areas of multiple mines is questionable; the radon emission
data for the Ambrosia Lake area are dated; Droppo's comments on the
importance of plume rise, vent orientation, and local meteorology are well
taken. (1-2)
Response: In response to this comment, EPA has changed the model
used to estimate radon concentrations in air. The model now used
(developed by Droppo) is better able to predict the influence of multiple
mines (see Volume I of the Background Information Document).
Comment 4.7; EPA should compare the risk of lung cancer associated
with radon releases from uranium mines against the risk of lung cancer
from natural background causes, not against the risk of lung cancer
associated with preventable exposure to anthropogenic agents, such as
cigarette smoking. (P-2)
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Response: EPA disagrees. Between 1 and 3 percent of fatal cancers
have been attributed to the natural radiation background. This risk is
significant (approximately 2 in 1000). EPA has concluded that the level
of risk associated with background radiation should not be judged
acceptable just because it is unavoidable. Therefore, the natural
radiation background is not a good benchmark for hazardous material
emission limits that are intended to be protective of public health with
an ample margin of safety.
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5.0 ELEMENTAL PHOSPHORUS PLANTS
All of the comments included in this Section relate to the following
reports prepared by Midwest Research Institute for EPA: (1) Analysis of
Achievable Po-210 Emission Reductions and Associated Costs for FMC's
Pocatello, Idaho, Plant and (2) Analysis of Achievable Po-210 Emission
Reductions and Associated Costs for Monsanto's Elemental Phosphorus Plant
at Soda Springs, Idaho.
5.1 SAMPLING LOCATIONS/PROCEDURES
Comment 5.1.1; Monsanto commented that no control system inlet
sampling was performed so no control efficiencies could be calculated
(1-10).
Response; The control efficiency of the existing scrubber was not
necessary for estimating the emission reductions that could be achieved
with add-on scrubbers, baghouses, or ESP's. It was assumed that the
existing emission control devices would continue to be operated and that
new control devices would be added to the exhaust gas stream of the
existing control devices. Therefore, testing only the outlet was needed
to estimate performance that could be achieved with new control devices.
Comment 5.1.2: Monsanto commented that since the outlet sampling
location did not meet EPA Reference Method 1 criteria, the usefulness of
the data is limited and adequate only for relative comparisons (1-10).
Response: The sampling data obtained at the Monsanto plant are,
under the circumstances, acceptable for the purpose of estimating of the
Po-210 emissions. As indicated in Section 6.3.4 of the final BID, the
sampling location at the Monsanto plant was not adequate for particle
size measurements. Therefore, particle size distributions measured at
the FMC plant were used to estimate particle size distributions for the
Monsanto plant (see response to Comment 5.2.1 below).
5.2 PARTICLE SIZE
Comment 5.2.1: Monsanto commented that the SASS and Anderson
particle size distribution methodologies are incompatible for comparison
purposes (1-10).
Response; To estimate particulate emissions and the Po-210
associated with the particulate emissions from Monsanto, it was assumed
that the distribution of particle size and the distribution of Po-210
associated with the particles would be the same at Monsanto as it was at
FMC. The comparison of data from the SASS and Andersen trains merely
showed that the particle size distributions were not grossly different.
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Comment 5.2.2; Monsanto commented that the extrapolation of the
particle size distribution below 0.6 micrometer (pm) for the Anderson
impactor, and below 1 vim for the SASS train is without merit (1-12).
Response: Extrapolation of data, such as particle size
distribution, is commonly used in the design of pollution control
equipment. The extrapolation of particle size data is reasonable for
estimating the performance that can be achieved by properly designed and
properly operated pollution control equipment.
Comment 5.2.3: FMC, in the attachment to its comment letter, noted
that size distribution curves are typically plotted as a logarithmic
normal function. They comment that the plot in the report minimizes the
percentage of particles in the less than 0.1 ym fraction (1-12).
Response: The plot presented in the report is of actual data and
was not extrapolated to smaller particle sizes.
Comment 5.2.4: FMC, in its attachment, commented that assuming that
the Po-210 is evenly distributed over the respective size fractions
overstates the predicted control efficiency (1-12).
Response; There are no data to show just how the Po-210 is
distributed across each size fraction. In the absence of such data EPA
has assumed a uniform distribution of Po-210 over particle size ranges.
EPA believes that the assumed distribution is as likely as any other
distribution.
5.3 DEMONSTRATED TECHNOLOGY
General
Comment 5.3.1: FMC contends that none of the proposed technologies
are demonstrated. Both Monsanto and FMC suggest that pilot scale testing
of the technologies would be required prior to full scale installation
(1-10, 1-12).
Response: None of the control technologies evaluated are either
emerging or novel applications. The scrubber pressure drops evaluated
are well within the range of those used in other industrial applications.
In addition, this industry is familiar with scrubber technology, albeit
at lower pressure drops. Wet ESPs are used in a variety of industries,
including one in this industry. Fabric filters, while not used in this
industry, are widely used for fine particulate control in other
industries, including on sources having saturated, or near saturated,
exhaust streams. EPA would not argue against pilot scale testing of
these technologies. It was not the purpose of EPA's study to provide an
exact engineering job, complete with site study, such as would be
required for ultimate installation. However, both EPA and MRI
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representatives were on-site during the period of the test program.
During this visit, observations were made of the facility and its
layout. These observations were used in the analysis.
Comment 5.3.2: Both Monsanto and FMC contend that no technology has
been shown that will meet the 1 curie/year proposed standard (1-10, 1-12).
Response: The purpose of the study was to analyze what emission
level could be achieved at what cost at the two facilities. The analysis
was based on the use of existing control technology operating within
reasonable process bounds. This analysis showed that significant
reductions in Po-210 emissions could be achieved through the use of
additional control equipment.
Wet Scrubbers
Comment 5.3.3; Monsanto commented that the Calvert model was used
with an empirical factor, f, equal to 0.5. The factor appears to be
high, thus, overstating scrubber efficiency (1-10).
Response: The factor f has a value of 0.5 for full scale scrubbers
on industrial sources of air pollution and, thus, is appropriate for this
modeling effort.^-'^ There is no data to indicate that it is
inappropriate.
The f values may range from a low of 0.10 to a high of 0.70 with
typical values in the range of 0.25 to 0.50.3 por hydrophobic
particles (lacking affinity for water), an f value of 0.25 is
recommended.^ For hydrophilic particles (with strong affinity for
water), f values are significantly higher (0.4 to 0.5).2
Comment 5.3.4; FMC noted that there are significant uncertainties
in the prediction of collection efficiency. The assumptions of f factor
and particle density could be 20 percent high and together could
introduce a 20 percent error in estimated penetration. The calculation
also relies on a droplet size correlation developed over 40 years ago by
Nukiyama and Tanasawa (1-12).
Response: The factors noted should be considered to properly design
equipment to meet the emission levels that have been estimated. Small
variations in these values do not change the estimate of what can be
achieved by properly designed and operated control equipment.
Vet Electrostatic Precipitators
Comment 5.3.5: Monsanto and FMC noted that emission tests were
performed on a wet ESP at one plant and the particle size distribution at
another plant was used. MRI selected a precipitation rate parameter (w)
based on one plant using a different type of calciner. It is unlikely
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that the precipitation rate parameters are the same and it is unlikely
that the Deutsch-Anderson equation accurately predicts performance for
this particle size distribution, which is generally smaller than 0.5 pm
(1-10, 1-12).
Response: The precipitation rate parameter (w) is influenced by the
characteristics of the dust, including particle size and resistivity. An
effective precipitation rate parameter is commonly used that is based on
field experience rather than theory. Using field data (which included
particles less than 0.5 pm in diameter), a value of 5 ft/min for the
precipitation rate parameter was calculated for the smallest particle
diameter (i.e., 0.35 pm). The Cunningham Correction Factor was used to
adjust the precipitation rate parameter for particles smaller than
5 ym.4
The properties of the gas and particulates at the two evaluated
plants are similar to those at the plant using the wet ESP. Therefore,
for estimating what can be achieved by properly designed control
equipment, it is reasonable to use the precipitation rate parameters
(based on actual data) for both plants. To actually design the control
equipment, a plant may wish to use data that is specific to that plant.
Comment 5.3.6: FMC commented that there is uncertainty and
variability in expected collection efficiencies using the
Deutsch-Anderson equation. Even more elaborate models are also entirely
theoretical resulting in difficulties in predicting actual efficiency
(1-12).
Response: The Deutsch-Anderson equation is commonly used for
estimating particle collection efficiency. Factors such as particle
reentrainment, gas leakage, and the physical and chemical properties of
the particles and gases are often unknown and cannot be accounted for in
an analysis. The equation and analysis performed is typical of
procedures used to predict collection efficiencies.
Fabric Filters
Comment 5.3.7; Monsanto commented that the application of fabric
filter technology to their Soda Springs, Idaho, facility would require
extensive research and analysis to demonstrate the level of emission
reduction claimed in the report. FMC commented that fabric filters (in
particular, fabric filters controlling exhaust gas streams from wet
scrubbers) do not represent a demonstrated control technology for
reduction of Po-210 emissions and that pilot plant testing would be
required to verify the fabric filter efficiency projected in the report
(1-10, 1-12).
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Response; The MRI analysis of fabric filter performance was based
on the application of conventional fabric filter technology to a gas
stream whose characteristics had been determined through testing. This
approach was adequate to develop an estimate of the cost to reduce Po-210
emissions from phosphate rock calciners.
The application of fabric filter technology to control particulate
emissions from mineral processing industries is well-established and has
been studied extensively. However, EPA agrees that the elemental
phosphorus manufacturing industry has no direct experience in the use of
fabric filters to control Po-210 emissions from moisture-laden gas
streams. Therefore, pilot scale testing may be required to optimize
design and operating parameters for a fabric filter in this application
(see response to Comment 5.3.1).
Comment 5.3.8: FMC commented that the report contains no data to
establish the collection efficiency of a fabric filter when collecting
particles less than 0.5 pro in diameter. FMC also noted that the report
does not discuss the uncertainty and variability of expected collection
efficiency by a fabric filter. (Related comments by a private consultant
to FMC state that the report reinforces the hazards of using particle
size distribution data on fine particles to predict collection
efficiency. This consultant states that MRI applied a 97 percent
collection efficiency to particles less than 0.5 ym in diameter when
the data do not extend below 0.2 ym. He further states that between
30 and 80 percent of the particles in question are less than 0.2 ym in
diameter.) (1-12)
Response; No reliable in situ sampling techniques exist to measure
particle size when the particles are less than 0.3 ym in diameter. MRI
utilized the best information available when projecting the performance
of a fabric filter on fine particles at the FMC plant. The expected
collected efficiency used in the MRI analysis is consistent with observed
collection efficiencies of fabric filters in other mineral industries.
Insufficient data exist to analyze the uncertainty and variability
of the expected collection efficiency of a fabric filter on this
application. Collection efficiency can vary as a result of numerous
design and operating parameters (air-to-cloth ratio, pressure drop,
cleaning frequency, cloth type, cleaning mechanism). The predicted
collection efficiency is based on the best available information for this
application using a control technology that is well established on
similar sources of particulate emissions.
The statement by FMC's consultant that 30 to 80 percent of the
particles are less than 0.2 ym is inconsistent with FMC's comment that
the particle size distribution below 0.5 ym in FMC's stack emissions is
unknown. Further, the source of this consultant's data is not
identified, and these data did not come from the MRI report.
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Coimnent 5.3.9; Monsanto commented that MRI did not consider what
happens to Po-210 in the presence of a gas flame during reheating of the
exhaust gas from a wet scrubber before the gas enters a fabric filter.
Monsanto noted that Po-210 could vaporize and not be collected by the
fabric filter (1-10).
Response: The scrubber exhaust gas is heated by a natural gas-fired
burner to increase its temperature from 145°F to approximately 200°F to
prevent moisture from condensing on the fabric filter bags. The scrubber
exhaust gas stream does not pass through a direct flame; the burner is
not in-line with the gas flow, external combustion air was provided, and
the flame would not be in direct contact with the Po-210. Therefore,
volatilization of Po-210 should not occur. Even if Po-210 did volatilize
during the indirect heating of the scrubber exhaust gas, the gas
temperature at the fabric filter bags is approximately 200°F. Therefore,
any Po-210 that had been vaporized upstream would recondense at the lower
temperature and would be captured as particulate matter by the fabric
filter.
Comment 5.3.10; FMC commented that fluoride emissions would be
2.5 times the allowable limit if 14 percent of the calciner exhaust gas
bypassed the wet scrubber and was used to reheat the inlet gas stream to
a fabric filter. FMC stated that all of the calciner exhaust gas would
need to be ducted to the scrubber for fluoride control and then be
reheated to prevent bag binding in the fabric filter (1-12).
Response: Calciner exhaust gases must be scrubbed to remove
fluoride at this facility to meet the State ambient air standard for
fluorides. MRI has revised the design of the control system at this
facility accordingly and has developed the capital and annualized costs
for a natural gas-fire burner to heat the entire exhaust gas stream from
the wet scrubber. These costs are shown in response to Comment 5.4.9.
5.4 COSTS
General
Comment 5.4.1; Monsanto and FMC commented that EPA has
underestimated the cost of controls for reducing Po-210 emissions at
elemental phosphorous plants by a factor of 3 or 4. Costs have been
underestimated for a number of reasons but primarily because of the use
of carbon steel rather than stainless steel for the equipment (1-10,
1-12).
Response: EPA disagrees that is has overestimated these costs by a
factor of 3 or 4. A reevaluation of the cost estimates by MRI, taking
into consideration the comments received and using more conservative
assumptions in the calculations (so as not to underestimate costs) shows
annualized cost increases of no more than a factor of 2 (see Tables 5.1
and 5.2).
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TABLE 5.1 SUMMARY OF REVISED RESULTS FOR THE
ROTARY KILN CALCINER--MONSANTO
Oriqinal
Control
technology
Scrubber
15 in. AP
30 in. AP
45 in. AP
ESP
200 SCAb
300 SCA
400 SCA
Fabric Filter
Capital
costs,3 $
1,090,600
1,455,400
1,989,400
2,851,200
3,182,400
4,330,200
4,147,900
Annual ized
costs ,a $/yr
879,800
1,405,800
1,954,600
782,800
861,600
1,065,800
1,286,900
Revised
Capital
costs,9 $
3,005,600
3,494,600
4,217,600
6,297,500
7,735,900
10,538,100
6,078,600
Annualized
costs, a $/yr
1,238,200
1,807,000
2,425,800
1,431,300
1,585,300
2,050,000
1,784,700
aBased on January 1984 dollars.
bSCA = Specific collection area in ft2/1,000 acfm.
TABLE 5.2 SUMMARY OF REVISED RESULTS FOR
CALCINER NO. 2—FMCa
Original
Control
technology
Scrubber
15 in. AP
30 in. AP
45 in. AP
ESP
200 SCAC
300 SCA
400 SCA
Fabric Filter
Capital
costs, k $
1,032,000
1,377,000
1,870,000
2,596,000
2,949,000
3,346,000
3,672,000
Annualized
costs, b $/yr
792,000
1,270,000
1,769,000
699,000
771,000
868,000
927,000
Revised
Capital
costs, b $
2,166,200
2,628,600
3,291,400
6,512,600
7,374,800
8,344,800
6,921,900
Annualized
costs, b $/yr
1,017,600
1,526,800
2,099,800
1,318,700
1,470,800
1,657,900
1,945,200
aTotal costs for both calciners can be estimated by doubling the
Calciner No. 2 values.
bflased on January 1984 dollars.
CSCA = Specific collection area in ft2/!,000 acfra.
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In preparing a regulatory impact analysis (EPA 520/1-84-025) for
emission standards for elemental phosphous plants, EPA analyzed the
regulatory impact of higher costs than those included in the MRI
reports. Therefore, the Agency has already considered how somewhat
higher costs would affect these plants. More specific responses to
comments on costs follow below.
Comment 5.4.2: Monsanto commented that their experience with the
CARD manual, which was the basis for the costing, has been that the
resulting cost estimates are significantly lower than actual costs,
especially when devices are being added to an existing system (1-10).
Response; The CARD manual is accepted, and used, by the EPA for
estimating the costs of air pollution control systems. These costs are
typically accepted to have a +30 percent error range. It is recognized
that site-specific factors may influence the costs to a large extent.
However, the manual, and the resulting costs, are valuable for providing
a consistent basis for comparing various control options. Methods are
available to update the costs to any period desired and these methods
were followed in preparing the Monsanto and FMC reports.
Comment 5.4.3; Monsanto commented that the costs presented by MRI
did not include costs for fabrication labor, foundations, supports,
contingencies, or engineering (1-10).
Response; As noted later in Monsanto's comment letter, the CARD
manual uses a modified "Lang Method" approach to cost estimating. This
approach applies cost factors for installation to the cost of equipment.
Factors for all of the items noted by Monsanto are included and,
therefore, were utilized in the cost estimates.
Comment 5.4.4: Monsanto questioned as being low the $16/ton value
used for waste disposal if the material were to be classified as a
hazardous waste (1-10).
Response; The $16/ton value noted by Monsanto is a 1978 value
obtained from information gathered by the EPA on a variety of sources.
It was updated to $23.50/ton (January 1984 dollars) for use in estimating
the costs. The disposal cost was used as a what-if, conservative
estimate. Some plants, including Monsanto, recycle the wastes to the
process, thus eliminating the waste disposal costs. In any case, waste
disposal costs would be relatively small compared to the total annualized
costs.
Comment 5.4.5: Monsanto and FMC both commented that MRI understated
the capital costs of the control technologies by a factor of three to
four. The primary reason for the understatement of costs was the use of
carbon rather than stainless steel for the equipment. (Other factors were
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also noted for each control device. These factors will be addressed in
later sections.) The commenters believe carbon steel to be unacceptable
because of corrosion problems (1-10, 1-12).
Response: The commenters are correct in stating that carbon steel
was used in the cost analyses. However, as noted in the response to
Comment 5.4.7, certain other considerations were taken to account for the
corrosion problem.
The commenter's allegation that carbon steel is unacceptable and
that stainless steel is preferred is not supported in the literature. In
a list presented in the Mcllvaine Scrubber Manual, 316 stainless steel
carries a lower rating that does carbon steel for use with hydrofluoric
acid (i.e., 316 stainless steel is considered unsatisfactory for use
while carbon steel is suitable for limited service).5 The recommended
materials for use with hydrofluoric acid are plastics (e.g., epoxy
resins). These compounds are also higher rated for use with sulfuric
acid. Thus, epoxy-lined carbon steel would provide better corrosion
resistance than would 316 stainless steel. The cost of epoxy lining is
addressed in the response to Comment 5.4.7.
Comment 5.4.6: FMC indicated that an 11-year life should be used in
determining the capital recovery factor rather than 20 years as done in
the MRI analyses. They indicated that 11 years is currently accepted as
book life and approximates actual equipment life (1-12).
Response: Using the 11 year life rather than 20-year life would
increase the capital recovery factor from 11.746 percent to
15.396 percent. While this is a 31 percent increase in the value of the
capital recovery factor, it only translates into a 5 to 14 percent
increase in the annualized cost using the cost values reported in the
August 1984 report for FMC. With epoxy-lined components, a 20-year life
is believed appropriate. EPA analyzed the effect of a 10-year life on
the annualized costs of these control systems in a regulatory impact
analysis (EPA 520/1-84-025).
Wet Scrubbers
Comment 5.4.7: Both commenters stated their concern that the
capital costs of wet scrubbers are understated for a variety of reasons
but primarily as a result of the use of carbon steel (1-10, 1-12).
Response: In its initial analysis, MRI costed the use of a rubber
liner for the carbon steel Venturi scrubber for corrosion resistance.
Although rubber is also listed in the Mcllvaine Scrubber Manual as being
unsatisfactory for use with hydrofluoric acid, its cost range is the same
as that for epoxy.6 Thus, the cost of corrosion resistance has been
accounted for.
However, in responding to these comments, both the basis and the
estimated costs for a Venturi scrubber at these facilities have been
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reexamined. The cost factors utilized in the "Lang Method" can be
adjusted depending on the circumstances. Tables 5.1 and 5.2 present the
revised costs for Monsanto and FMC, respectively. Liner costs have been
calculated per square foot where possible. Where the area cannot be
determined, the costs have been increased by 15 percent (the maximum
percent of liner cost versus wet scrubber cost).
Wet Electrostatic Precipitators
Comment 5.4.8: Again both commenters noted their concern about the
understatement of costs and the use of carbon steel (1-10, 1-18).
Response: Wet ESPs were included in the reexamination of the
control device costs. The revised costs are included in Tables 5.1
and 5.2. The multiplier for wet vs. dry ESPs has been increased from
1.15 to 2.0 to more adequately account for lining and corrosion
protection. The revised values may more accurately reflect estimated
costs.
Fabric Filters
Comment 5.4.9: Both commenters expressed their concern regarding
the understated costs and the use of carbon steel. Monsanto commented
that reheat of the gas stream will lead to slagging and that the heat
requirement calculations do not account for heat losses. Monsanto also
provided information as to their natural gas costs and altitude.
Additional comments by Monsanto relate to the use of V-belt drives in the
calculations. Monsanto also contends that no provision was made for
mixing the two streams.
FMC commented that the gas volume to be treated has been
understated. The cost of the baghouse is alleged to be understated
because of the use of the reheat bypass stream. FMC also contends that
an air-to-cloth ratio (A/C) of 2:1 would be more appropriate than the
selection of 4:1 (1-10, 1-12).
Response: Revised costs for fabric filters are included in
Tables 5.1 and 5.2. In costing a fabric filter for use on these gas
streams, it was assumed that the existing scrubber, with demisting
equipment, would be retained. Proper demisting would remove entrained
water droplets from the gas stream and thus prevent, or greatly reduce,
the slagging that could result from dissolved solids in entrained water
droplets. By designing the heating system to raise the gas stream in
excess of 50°F above the wet bulb temperature, heat losses are allowed
for. Additional ductwork and insulation have been included in the
revised costs as recommended by Monsanto. Changes have also been made
for the increased natural gas cost and altitude. Direct drive units were
costed in the original estimates, rather than V-belt drives as believed
by the commenter. As noted earlier, MRI has reevaluated the "Lang" cost
factors for fabric filters. No justification can be found for raising
the end value to 4 as suggested by Monsanto. The original values are
believed to be adequate for this study.
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In providing their comments, FMC was not aware that a fabric filter
for their facility with a gas-fired reheater similar to that at Monsanto
had also been costed. This approach would alleviate their concerns with
regard to increased fluoride emissions. It is still believed that a
fabric filter placed downstream of the fluoride scrubber provided with
reheat capability, and utilizing an A/C ratio of 4:1 is a less-costly
approach to solving the problem than that suggested by FMC. The air
flows used in the analysis were based on those determined during the test
program. The costs in Table 5.2 are those for the gas-fired reheater
system.
5.5 REFERENCES
1. Sparks, L.E., Particle Collection Using a Venturi Scrubber.
ACCESS. September/October 1982. pp. 24-29.
2. Calvert, S. Scrubbing. In: Air Pollution Volume 4. p. 281.
3. U.S. Environmental Protection Agency. Control Techniques for
Particulate Emissions from Stationary Sources. Volume 1.
Publication No. EPA-450/3-81-005a. September 1982. p. 4.5-21.
4. Wark, K., and C.F. Warner. Air Pollution: Its Origin and Control.
IEP. New York. 1976. p. 216.
5. Mcllvaine Scrubber Manual. Volume I, Chapter III. pp. 1.21-1.22.
6. Mcllvaine Scrubber Manual. Volume III, Chapter XI. p. 8-6.
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6.0 GENERAL
Comments 6.1; The specified review period was not sufficient to
perform a review. A request was made for an extension of the docket
period. (G-l, 1-7)
Response: The Agency is committed by statute and policy to public
participation in the decisionmaking process for its environmental
regulations. This policy encourages and solicits communications and
comments to the public docket. Contributions are desired from as many
diverse views as possible. At times, extenuating circumstances cause
EPA's docket periods to vary in length. In the present case, the U.S.
District Court for the Northern District of California ordered EPA to
take final action on its proposed standards by October 23, 1984. On
August 24, 1984 (49 FR 33695), EPA opened Docket A-79-11, Section IV.
until September 21, 1984, to allow for public comment on new information
developed or received since our proposed rulemaking. This left the
Agency with about 30 days for docket review, docket analysis, options
evaluation, and preparation of final rulemaking documentation to comply
with the court order. Accordingly, the Agency was not in a position to
extend the docket period.
Comment 6.2; Persons have lived in naturally radioactive areas
("hot spots") without apparent harm. There is thus obviously doubt as to
the productive value to the taxpayer of the proposed standards. (P-l)
Response: See Section 2.2 of Response to Comments Final Rules for
Radionuclides, Volume I.
Comment 6.3; Risks associated with exposure to radon released
during the operational phase of uranium mills compel immediate action by
EPA. (P-2)
Response: EPA has issued an Advanced Notice of Proposed Rulemaking
for uranium mills. The Agency has solicited information in a number of
subject areas, including:
(1) radionuclide emissions from these facilities;
(2) applicable control options and strategies, including work
practices;
(3) feasibility and cost of control options and strategies; and
(4) local and regional impacts due to emissions of radon-222 from
active uranium mills.
These data will be used to develop work practice, design, equipment
and/or operational standards to control radon releases from uranium mills.
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Comment 6.4; Commenter believes that consideration of the potential
increase from airborne radionuclide emissions from DOE facilities would
strongly demonstrate the need for EPA regulation of such emissions.
(P-6)
Response: It is the Administrator's judgment that the present
record does not support a conclusion that regulation of DOE facilities
for radionuclide emissions to air is necessary to protect the public
health with an ample margin of safety, within the meaning of the Clean
Air Act. The DOE currently has a program to keep exposure to the public
to levels that are as low as reasonably achievable. This program is
operated by the Department in keeping with the longstanding
recommendations of the National Council on Radiation Protection and
Measurements, the International Commission on Radiological Protection,
and the Federal Radiation Council to avoid radiation exposure where
practical. While the Agency recognizes that DOE facilities maintain very
large quantities of radionuclides in their inventories at many of the
facilities, there has been a general trend at most facilities for
radionuclide emissions to be reduced over the years. See, also, the
Federal Register Notice of Withdrawal.
Comment 6.5; It is inappropriate to establish standards below 500
mrems for known individuals and 170 mrems for members of the general
public because these existing standards include a margin of safety. (1-2)
Response; Such levels of radiation exposure are generally
recognized to represent a significant level of risk, especially if the
exposure lasts for many years. Therefore, they are maximum permitted
levels that should not be approached without good reasons, and people
should not be exposed to such levels for any length of time. They do not
represent an exposure level that provides, over a long term, an ample
margin of safety for the public. Furthermore, they apply to the sum
total of exposure to an individual from all pathways and all sources.
They are not appropriate as limits for a single facility and a single
pathway.
Comment 6.6; EPA's calculated cost of implementing the proposed
standard is extraordinarily large in comparison with the health effects
averted. (1-1)
Response; The Clean Air Act requires EPA to establish emission
standards which, in the Administrator's judgment, provide an ample margin
of safety to protect public health from hazardous air pollutants. In
developing standards, EPA evaluates the availability, practicality, and
cost of control technology to achieve reduced health effects. This
consideration contributed to the Agency's decisions to withdraw the
proposed standard for elemental phosphorus plants and not to regulate
coal-fired boilers.
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Comment 6.7: Notwithstanding the Science Advisory Board Committee's
comments and recommendations, EPA's risk assessment is adequate to
support the Agency's decision not to regulate emissions from coal-fired
power plants. (1-9)
Response: EPA did not propose standards for coal-fired boilers for
a number of reasons, including the assessment that the risks to nearby
individuals and the total risk to populations due to radionuclides, as
the result of particulate controls already in place, are not large.
Particulate emissions from new utility and new large industrial
boilers are controlled by new source performance standards issued under
Section III of the Clean Air Act, reflecting best demonstrated technology.
EPA has also proposed new source performance standards for smaller
industrial boilers. Existing utility and industrial boilers are
regulated for particulate emissions by State implementation plans as
required by the Clean Air Act.
EPA believes that it is unreasonable to issue a standard that
duplicates current regulations. As a practical matter, the Clean Air Act
regulations for particulates limit radionuclide emissions to low levels
and protect the public health with an ample margin of safety (as far as
radionuclide emissions are concerned).
After carefully considering all comments, EPA has affirmed its
initial decision not to regulate radionuclide emissions from coal-fired
boilers at this time.
Comment 6.8; EPA's dispersion modeling is suspect so long as the
results have not been validated. (1-6)
Response: EPA attempts to model environmental transport of
radioactivity as realistically as possible. As noted in the science
Advisory Board Subcommittee's report (p. 13), the level of uncertainty
associated with dispersion models such as AIRDOS-EPA over flat terrain
and for long-term averages ranges from a factor of about two for nearby
receptors to a factor of four for more distant receptors.
Comment 6.9; A recent review of the lung cancer risk resulting from
radon exposure to the general public concludes that:
a. Ionizing radiation is carcinogenic,
b. Radiation exposure is a significant cause of lung cancer,
c. Existing epidemiologic data may underestimate the risk of low
dose exposures,
d. Low dose exposure may be more harmful in terms of unit dose than
high dose exposure, and
e. The most appropriate method for determining health effects to
the general public is the relative risk model.
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Response: EPA agrees with the thrust of this comment. There is no
scientific dispute that ionizing radiation is carcinogenic. EPA has
estimated the risk of fatal lung cancer resulting from emissions of
radionuclides. These estimates can be found in Volume II of the
Background Information Document, EPA 520/1-84-022-2, October 1984.
Since 1978, EPA has based risk estimates of cancer resulting from
inhaled radon-222 progeny on a linear dose response function, a relative
risk projection model, and a minimum induction period of 10 years.
Lifetime risks are projected on the assumption that exposure to 1 WLM
increases the age-specific risk of lung cancer by 3 percent over the
age-specific rate in the U.S. population as a whole.
In reviewing this model in terms of the more recent information, EPA
has found that our major assumptions, linear response and relative risk
projection, have been affirmed. The A-bomb survivor data clearly
indicate that the absolute risk of radiogenic lung cancer has continued
to increase among these survivors while their relative risk has remained
reasonably constant. The UNSCEAR, ICRP, and 1980 MAS Committee have
continued to use a linear dose response to estimate the risk of lung
cancer resulting from inhaled radon progeny. Thomas and McNeill's
analysis indicates that the use of linearity is not unduly conservative
and may, in fact, underestimate the risk at low doses. The 1980 MAS BEIR
Committee reached a similar conclusion.
The major weakness of the EPA model is the uncertainty in the
relative risk coefficient used, a 3 percent increase per WLM. This value
is based on the excess mortality resulting from lung cancer among exposed
miners of various ages, many of whom smoked. Therefore, it is an average
value for a mixed population of smokers and nonsmokers. Furthermore, the
fact that smoking was more prevalent among some of the groups of miners
studied than it is among the U.S. general population today may lead to a
somewhat conservative risk estimate. In a recent paper, Radford and
Remard reported on the results of a long-term study of Swedish iron
workers who were exposed to radon progeny. This study is unique in that
most of the miners were exposed to less than 100 WLM, and the risks to
smokers and nonsmokers were considered separately. The absolute risk of
the two groups was similar, 20 fatalities per 10" person WLM year for
smokers compared to 16 for nonsmokers. The total number of lung cancer
fatalities for nonsmokers is small, making the estimate of 16 not too
reliable. Nonsmokers have a much lower baseline incidence of lung cancer
mortality than smokers. This means that risk for the nonsmoking exposed
miners relative to unexposed nonsmokers was about four times larger that
the relative risk for exposed smokers. This large relative risk,
however, does not compensate for the lower baseline incidence of
nonsmokers. Therefore, the study of Swedish iron miners indicates that
a 3 percent per WLM relative risk coefficient is conservative for the
population as a whole. Further follow-up of this mining group may
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provide more reliable data on the risk to nonsraokers, and we expect to
incorporate separate consideration of smokers and nonsmokers into EPA
analyses as more data become available.
A more detailed discussion of risk to low dose exposure appears in
Chapter 8 "Estimating the Risk of Health Effects Resulting from
Radionuclide Air Emission," EPA 5201/1-84-022-1, Volume I, October 1984.
EPA has considered the possibility that a linear dose-response model
may underestimate the risk associated with low doses. See the response
to Comment 13 in Section 2 of this volume.
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APPEMDIX A. GOVERNMENT COMMENTERS
I.D. Docket Date of Date
Code Number Conunenter Submission Docketed
G-l IV-D-13 Martin E, Rivers 9-20-84 9-25-84
Director of Environmental
Quality
Tennessee Valley Authority
Knoxville, Tennessee 37902
42
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APPENDIX B. INDUSTRY COMMENTERS
I.D. Docket ' Date of Date
Code Number Commenter Submission Docketed
1-1 IV-D-2 Don G. Scroggins 9-10-84 9-19-84
Beveridge and Diamond, P.C.
1333 New Hampshire Ave. N.W.
Washington, D.C. 20036
1-2 IV-D-4 J. Allen Overton, Jr. 9-21-84 9-21-84
American Mining Congress
1920 N. Street N.W.
Washington, D.C. 20036
1-3 IV-D-6 Gary D. Myers 9-21-84 9-21-84
The Fertilizer Institute
1015 18th Street N.W.
Washington, D.C. 20036
1-4 IV-D-8 G.C. Sorensen 9-20-84 9-20-84
Washington Public Power
Supply System
P.O. Box 968
3000 George Washington Way
Richland, Washington 99352
1-5 IV-D-11 Robert G. Beverly 9-19-84 9-24-84
Umetco Minerals Corporation
P.O. Box 1029
Grand Junction, Colorado 81502
1-6 IV-D-12 J.C. Stauter 9-21-84 9-24-84
Kerr-McGee Corporation
Kerr-McGee Center
Oklahoma City, Oklahoma 73125
1-7 IV-D-14 Gary H. Baise 9-21-84 9-26-84
Beverly and Diamond, P.C.
1333 New Hampshire Ave., N.W
Washington, D.C. '20036
(Counsel, The Idaho
Mining Association)
1-8 IV-D-15 Middle South Services, Inc. 9-20-84 9-26-84
P.O. Box 61000
New Orleans, LA 70161
43
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APPENDIX B. INDUSTRY COMMENTERS (cont1)
I.D. Docket Date of Date
Code Number Commenter Submission Docketed
1-9 IV-D-16 Henry V. Nickel, et al. 9-21-84 10-01-84
Hunton and William
2000 Pennsylvania Ave., N.W.
P.O. Box 19230
Washington, D.C. 20036
(Counsel, Utility Air
Regulatory Group)
1-10 IV-D-17 J.P. Hyland 9-21-84 10-05-84
Monsanto Industrial Chemical Co.
800 N. Lindbergh Blvd.
St. Louis, Missouri 63167
1-11 IV-D-18 The Idaho Mining Association 9-21-84 10-11-84
Statehouse Square
802 Banock, Suite 301
Boise, Idaho 83701
1-12 IV-D-19 FMC Corporation 9-21-84 10-11-84
200 Market Street
Philadelphia, PA 19103
44
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APPENDIX C. PUBLIC COMMENTS
I.D. Docket Date of Date
Code Number Commenter Submission Docketed
P-l IV-D-1 C.G. Bacon No date 9-05-84
2960 Hannah Ave.
Norristown, PA 19401
P-2 IV-D-3 Dr. Ellen Silbergold, et al. 9-21-84 9-21-84
Environmental Defense Fund
1405 Arapahoe Avenue
Boulder, Colorado 80302
P-3 IV-D-5 Leonard D. Hamilton 9-20-84 9-21-84
Brookhaven National Laboratory
Upton, Long Island,
New York 11973
P-4 IV-D-9 James B. Morton 9-20-84 9-20-14
Environmental Defense Fund
1405 Arapahoe Avenue
Boulder, Colorado 80302
P-5 IV-D-10 Gloria C. Rains 9-17-84 9-21-84
Manasota 88
5314 Bay State Road
Palmetto, Florida 33561
P-6 IV-D-7 Barbara A. Finamore 9-21-84 9-12-84
Suite 300
Natural Resources Defense Council, Inc.
1350 New York Avenue N.W.
Washington, D.C. 20005
45
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