analyses with mean blood Pb levels closest to those of today’s U.S.
children, including the at-risk subpopulation.

Among the analyses presented in the proposal (Table 1), we note that six
study groups from four different studies have blood Pb levels
appreciably closer to the mean blood Pb levels in today’s young
children.  Mean blood Pb levels for these study groups range from 2.9 to
4.3 µg/dL, while mean blood Pb levels for the other three study groups
considered in the proposal range from 7.4 up to 9.7 µg/dL.  Further,
among the six slopes from analyses with blood Pb levels closest to
today’s blood Pb levels, four come from two studies, with these two
studies each providing two analyses of differing blood Pb levels.
Focusing on the single analysis from each of the four studies that has a
mean blood Pb level closest to today’s mean for U.S. children yields
four slopes ranging from -1.56 to -2.94, with a median of -1.75 IQ
points per µg/dL (Table 3).  Consistent with the evidence for
nonlinearity in the C-R relationship, the slopes for the C-R functions
from these four analyses are steeper than the slopes for the other
higher blood Pb level analyses.  In considering the C-R functions from
these four analyses with the air-related IQ loss framework in section
II.C.3.c below, we have placed greater weight on the median of the
group, giving less weight to the minimum or maximum values, recognizing
the uncertainty in determining the C-R relationship.Table 3.  Summary
of Quantitative Relationships of IQ and Blood Pb for Analyses with Blood
Pb Levels Closest to those of Children in the U.S. Today.

Blood Pb Levels

(µg/dL)

Study/Analysis	Average Linear SlopeA

(IQ points per µg/dL)

Geometric Mean	Range

(min-max)

2.9	0.8 – 4.9	Tellez-Rojo et al 2006, <5 subgroup	-1.71

3.24	0.9 – 7.4	Lanphear et al 2005B, <7.5 peak subgroup	-2.94

3.32	0.5 – 8.4	Canfield et al 2003 B, <10 peak subgroup	-1.79

3.8	1 - 9.3	Bellinger and Needleman 2003 B , <10 peak subgroup	-1.56

Median value	-1.75

A Average linear slope estimates here are for relationship between IQ
and concurrent blood Pb levels except for Bellinger & Needleman for
which study reports relationship fir 10 year old IQ with 24 month blood
Pb levels.

B The Lanphear et al. (2005) pooled International study includes blood
Pb data from the Rochester and Boston cohorts, although for different
ages (6 and 5 years, respectively) than the ages analyzed in Canfield et
al. (2003) and Bellinger and Needleman (2003).

Some commenters representing a business or industry association
recommended that EPA rely on the median estimate from the second set of
C-R functions presented in the proposal.  As their basis for this view,
these commenters made several points.  For example, they stated that the
extent and magnitude of nonlinearity in the IQ-blood Pb C-R relationship
is “highly uncertain,” and as part of their rationale for this
statement they cited studies by Jusko et al. (2007) and Surkan et al.
(2007) as not providing support for a nonlinear C-R function.  Other
statements made by these commenters in support of their view are that
the maximum slope in the first set is an “outlier,” that the second
set reflects a greater number of studies and subjects than the first
set, and that simply being closer to the blood Pb levels of today’s
children does not provide a better estimate than the median of the
second set, with some noting that the second set is inclusive of some
analyses with blood Pb levels similar to those in first set.

EPA disagrees with these commenters’ view that a focus on analyses of
children with blood Pb levels closer to today’s children is not an
important criterion for selecting a C-R function for use with the IQ
loss framework.  On the contrary, as stated above, EPA agrees with CASAC
that this is an essential criterion for this analysis.  While EPA
recognizes uncertainty in the quantitative characterization of the
nonlinearity in the blood Pb – IQ loss relationship, the weight of the
current evidence (described in detail in the Criteria Document) supports
our conclusion that the blood Pb – IQ loss relationship is nonlinear,
with steeper slopes at lower blood Pb levels.  While EPA agrees there
are a  greater number of studies and subjects in the second set, the
nonlinearity of the relationship at issue means that a focus on C-R
functions from the studies in that set involving children with
appreciably higher blood Pb levels could not be expected to identify a
slope estimate that would be reasonably representative for today’s
population of children.  In reviewing the available studies with this
important criterion in mind, as described above, we have identified four
different studies from which C-R functions can be drawn, and in
considering these functions in the context of the air-related IQ loss
framework, have focused on the median estimate for the group,
consequently avoiding focus on a single estimate that may be unduly
influenced by one single analysis.

With regard to the “new” studies cited by commenters above, EPA
notes that we are not relying on them in this review for the reasons
stated above in section I.C.  After provisional consideration of these
studies cited by commenters (discussed further in the Response to
Comments document), EPA has determined that the more recent cited
studies provide only limited information with regard to the shape of the
C-R curve and, in light of other recent provisionally considered studies
and those studies reviewed in the Criteria Document, do not materially
change EPA’s conclusion regarding nonlinearity that is well founded in
the evidence described in the Criteria Document.

(v) Role of Risk Assessment

Some commenters recommended that the Administrator place greater weight
on the risk estimates derived in the quantitative risk assessment, with
some (e.g., the Association of Battery Recyclers) concluding that these
estimates supported a level for the standard above the proposed range
and some (e.g., NRDC and Missouri Coalition for the Environment)
concluding that they supported a level at the lower end or below the
proposed range.  For the reasons identified in the proposal and noted in
section II.C.3.c below, the Administrator has placed primary weight on
the air-related IQ loss evidence-based framework in his decision with
regard to level, and less weight on risk estimates from the quantitative
risk assessment.  At the same time, as stated in section II.C.3.c below,
he finds those estimates to be roughly consistent with and generally
supportive of the estimates from the evidence-based framework.

c.   Conclusions on Level

Having carefully considered the public comments on the appropriate level
of the Pb standard, as discussed above, the Administrator believes the
fundamental scientific conclusions on the effects of Pb reached in the
Criteria Document and Staff Paper, briefly summarized above in sections
II.A.1 and II.A.2 and discussed more fully in sections II.A and II.B of
the proposal, remain valid.  In considering the level at which the
primary Pb standard should be set, as in reaching a final decision on
the need for revision of the current standard, the Administrator
considers the entire body of evidence and information, in an integrated
fashion, giving appropriate weight to each part of that body of evidence
and information.  In that context the Administrator continues to place
primary consideration on the body of scientific evidence available in
this review on the health effects associated with Pb exposure.  In so
doing, the Administrator primarily focuses on the air-related IQ loss
evidence-based framework summarized in section II.C.3.a above and
described in the proposal, recognizing that it provides useful guidance
for making the public health policy judgment on the degree of protection
from risk to public health that is sufficient but not more than
necessary.

As described in section II.E.3.d of the proposal and recognized in
section II.C.3.a above, the air-related IQ loss framework is used to
inform the selection of a standard level that would protect against
air-related IQ loss (and related effects) of a magnitude judged by the
Administrator to be of concern in subpopulations of children exposed  to
the level of the standard, taking into consideration uncertainties
inherent in such estimates.  This framework calls for identifying a
target degree of protection in terms of an air-related IQ loss for such
subpopulations of children (discussed further below), as well as two
other parameters also relevant to this framework -- a C-R function for
population IQ response associated with blood Pb level and an
air-to-blood ratio.

With regard to estimates for air-to-blood ratio, the Administrator has
further considered the evidence regarding air-to-blood relationships
described in section II.A.2.a.iii above in light of advice from CASAC
and comments from the public as described in section II.C.2.b above.
Accordingly, he recognizes that the evidence includes support for ratios
greater than 1:7 (the upper end of the range focused on in the
proposal), including estimates ranging from 1:8 to 1:10.  He also
recognizes that the estimates developed from the quantitative exposure
and risk assessments also include values greater than 1:7, including
values ranging up to 1:10 and some higher.  Additionally, as noted in
section II.A.2.a.iii above, the evidence as a whole also indicates that
variation in the value of the ratios appears to relate to the extent to
which the range of air-related pathways are included and the magnitude
of the air and blood Pb levels assessed, such that higher ratios appear
to be associated with more complete assessments of air-related pathways
and lower air and blood Pb levels.  Taking all of these considerations
into account, the Administrator concludes that the reasonable range of
air-to-blood estimates to use in the air-related IQ loss framework
includes ratios of 1:5 up to ratios on the order of 1:10.  He does not
consider lower ratios to be representative of the full range of
air-related pathways and the ratios expected at today’s air and blood
Pb levels.  The Administrator also concludes that it is appropriate to
focus on 1:7 as a generally central value within this range.

With regard to C-R functions, the Administrator has further considered
the evidence regarding quantitative relationships between IQ loss and
blood Pb levels described in section II.A.2.c above, in light of advice
from CASAC and comments from the public as described in section II.C.3.b
above.  He recognizes the evidence of nonlinearity and of steeper slopes
at lower blood Pb levels (summarized in section II.A.2.c above), and as
a result, he believes it is appropriate to focus on those analyses that
are based on blood Pb levels that most closely reflect today’s
population of children in the U.S., recognizing that the evidence does
not include analyses involving mean blood Pb levels as low as the mean
blood Pb level for today’s children.  He notes that, as described in
section II.C.3.b above,  a review of the evidence with this focus in
mind has identified four analyses that have a mean blood Pb level
closest to today’s mean for U.S. children and that yield four slopes
ranging from -1.56 to -2.94, with a median of -1.75 IQ points per µg/dL
(Table 3).  The Administrator concludes that it is appropriate to
consider this set of C-R functions for use in the air-related IQ loss
evidence based framework, as this set of C-R functions best represents
the evidence pertinent to children in the U.S. today.  In addition, the
Administrator determines that it is appropriate to give more weight to
the central estimate for this set of functions, which is the median of
the set of functions, and not to rely on any one function.

As noted in the proposal, in considering this evidence-based framework,
the Administrator recognizes that there are currently no commonly
accepted guidelines or criteria within the public health community that
would provide a clear basis for reaching a judgment as to the
appropriate degree of public health protection that should be afforded
to protect against risk of neurocognitive effects in sensitive
populations, such as IQ loss in children.  With regard to making a
public health policy judgment as to the appropriate protection against
risk of air-related IQ loss and related effects, the Administrator
believes that ideally air-related (as well as other) exposures to
environmental Pb would be reduced to the point that no IQ impact in
children would occur.  The Administrator recognizes, however, that in
the case of setting a NAAQS, he is required to make a judgment as to
what degree of protection is requisite to protect public health with an
adequate margin of safety.

The Administrator generally agrees with CASAC and the commenters who
emphasize that the NAAQS should prevent air-related IQ loss of a
significant magnitude in all but a small percentile of the population.
However, as discussed above in section II.C.3.b, it is important to note
that in selecting a target degree of public health protection that
should be afforded to at-risk populations of children in terms of
air-related IQ loss as estimated by the evidence-based framework being
applied in this review, the Administrator is not determining a specific
quantitative public health policy goal for air-related IQ loss that
would be acceptable or unacceptable for the entire population of
children in the United States.  Instead, he is determining what
magnitude of estimated air-related IQ loss should be used in conjunction
with this specific framework, in light of the uncertainties in the
framework and the limitations in using the framework.

In that context, the air-related IQ loss framework provides estimates
for the mean air-related IQ loss of a subset of the population of U.S.
children, and there are uncertainties associated with those estimates.
It provides estimates for that subset of children likely to be exposed
to the level of the standard, which is generally expected to be the
subpopulation of children living near sources who are likely to be most
highly exposed.  In providing estimates of the mean air-related IQ loss
for this subpopulation of children, the framework does not provide
estimates of the mean air-related IQ loss for all U.S. children.  The
Administrator recognizes, as discussed above, that EPA is unable to
quantify the percentile of the U.S. population of children that
corresponds to the mean of this sensitive subpopulation, nor can EPA
confidently develop quantified estimates for upper percentiles for this
subpopulation.  EPA expects that the mean of this subpopulation
represents a high, but not quantifiable, percentile of the U.S.
population of children.  As a result, the Administrator expects that a
standard based on consideration of this framework would provide the same
or greater protection from estimated air-related IQ loss for a high,
albeit unquantifiable, percentage of the entire population of U.S.
children.

In addition, EPA expects that the selection of a maximum, not to be
exceeded, form in conjunction with a rolling 3-month averaging time over
a three-year span, discussed in section II.C.2. above, will have the
effect that the at-risk subpopulation of children will be exposed below
the level of the standard most of the time.  In light of this  and the
significant uncertainty in the relationship between time period of
ambient level, exposure, and occurrence of a health effect, the choice
of an air-related IQ loss to focus on in applying the framework should
not be seen as a decision that a specific level of air-related IQ loss
will occur in fact in areas where the revised standard is just met or
that such a loss has been determined as acceptable if it were to occur.
Instead, the choice of such an air-related IQ loss is one of the
judgments that need to be made in using the the evidence-based framework
to provide useful guidance in making the public health policy judgment
on the degree of protection from risk to public health that is
sufficient but not more than necessary, taking into consideration the
patterns of air quality that would likely occur upon just meeting the
standard as revised in this rulemaking..

In considering the appropriate air-related IQ loss to accompany
application of the framework, the Administrator has considered the
advice of CASAC and public comments on this issue, discussed above in
section II.C.3.b.  The Administrator recognizes that comments on the
proposal have highlighted the ambiguity in using an air-related IQ loss
for the framework that is phrased in terms of a range.  For example, if
a range of 1-2 points IQ loss is selected, it is unclear whether the
intent is to limit points of air-related IQ loss to below 1, below 2, or
below some level in between.  For clarity, it is more useful to use a
specific level as compared to a range.  In addition, recognizing the
uncertainties inherent in evaluating the health impact of an IQ loss
across a population, as well as the uncertainties in the inputs to the
framework, the Administrator believes it is appropriate to use a whole
number for the air-related IQ loss level.

In consideration of comments from CASAC and the public and in
recognition of the uncertainties in the health effects evidence and
related information, as well as the role of a selected air-related IQ
loss in the application of the framework, the Administrator concludes
that an air-related IQ loss of 2 points should be used in conjunction
with the evidence-based framework in selecting an appropriate level for
the standard.  Given the uncertainties in the inputs to the framework,
the uncertainties in the relationship between ambient levels, exposure
period, and occurrence of health effects, and the focus of the framework
on the sensitive subpopulation of more highly exposed children, a
standard level selected using this air-related IQ loss, in combination
with the selected averaging time and form, would significantly reduce
and limit for a high percentage of U.S. children the risk of
experiencing an air-related IQ loss of that magnitude.

With this specific air-related IQ loss in mind, the Administrator
considered the application of this framework to a broad range of
standard levels, using estimates for the two key parameters –
air-to-blood ratio and C-R function – that are appropriate for use
within the framework, as shown in Table 4 below.  In so doing, the
Administrator recognized that, relying on the median of the four C-R
functions from analyses with blood Pb levels closest to those of
today’s children, a standard level in the lower half of the proposed
range (0.10 - 0.20 µg/m3) would limit the estimated mean IQ loss from
air-related Pb to below 2 points, depending on the choice of
air-to-blood ratio within the range from 1:5 to 1:10.

As noted above, however, the Administrator does not believe it is
appropriate to consider only a single air-to-blood ratio.  Using the
air-to-blood ratio of 1:7, a generally central estimate within the well
supported range of estimates, the estimates of air-related IQ loss are
below a 2-point IQ loss for standard levels of 0.15 µg/m3 and lower.
At a level of 0.15 µg/m3, the Administrator recognizes that use of a
1:10 ratio produces an estimate greater than 2 IQ points and use of a
1:5 ratio produces a lower IQ loss estimate.  Given the uncertainties
and limitations in the air-related IQ loss framework, the Administrator
views it as appropriate to place primary weight on the results from this
central estimate rather than estimates derived using air-to-blood-
ratios either higher or lower than this ratio.Table 4.  Estimates of
Air-related Mean IQ Loss for the Subpopulation of Children Exposed at
the Level of the Standard.

Potential Level

for Standard (µg/m3)	Air-related Mean IQ Loss (points) for the
subpopulation of children

exposed at level of the standard

	IQ loss estimate is based on median slope of 4 C-R functions with blood
Pb levels closer to those of today’s U.S. children

 (range shown for estimates based on lowest and highest of 4 slopes)

	Air-to-Blood Ratio

	1:10	1:7	1:5

0.50	>5*	>5*	4.4 (3.9-7.4)

0.40

4.9 (4.4-8.2)	3.5 (3.1-5.9)

0.30	5.3 (4.7-8.8)	3.7 (3.3-6.2)	2.6 (2.3-4.4)

0.25	4.4 (3.9-7.4)	3.1 (2.7-5.1)	2.2 (2.0-3.7)

0.20	3.5 (3.1-5.9)	2.5 (2.2 -4.1)	1.8 (1.6-2.9)

0.15	2.6 (2.3 -4.4)	1.8 (1.6-3.1)	1.3 (1.2-2.2)

0.10	1.8 (1.6-2.9)	1.2 (1.1- 2.1)	0.9 (0.8-1.5)

0.05	0.9 (0.8-1.5)	0.6 (0.5-1.0)	0.4 (0.4-0.7)

0.02	0.4 (0.3- 0.6)	0.2 (0.2 -0.4)	0.2 (0.2-0.3)

* For these combinations of standard levels and air-to-blood ratios, the
appropriateness of the C-R function applied in this table becomes
increasingly uncertain such that no greater precision than “>5” for
the IQ loss estimate is warranted.

The Administrator has also considered the results of the exposure and
risk assessments conducted for this review to provide some further
perspective on the potential magnitude of risk of air-related IQ loss.
The Administrator finds that these quantitative assessments provide a
useful perspective on the risk from air-related Pb.  However, in light
of the important uncertainties and limitations associated with these
assessments, as summarized in section II.A.3 above and discussed in
sections II.C and II.E.3.b of the proposal, for purposes of evaluating
potential standard levels, the Administrator places less weight on the
risk estimates than on the evidence-based assessment.  Nonetheless, the
Administrator finds that the risk estimates are roughly consistent with
and generally supportive of the evidence-based air-related IQ loss
estimates summarized above.

In the Administrator’s view, the above considerations, taken together,
provide no evidence- or risk-based bright line that indicates a single
appropriate level.  Instead, there is a collection of scientific
evidence and other information, including information about the
uncertainties inherent in many relevant factors, which needs to be
considered together in making the public health policy judgment to
select the appropriate standard level from a range of reasonable values.
 In addition, the results of the evidence-based framework are seen as a
useful guide in determining whether the risks to public health from
exposure to ambient levels of Pb in the air, in the context of a
specified averaging time and form, provide a degree of protection from
risk with an adequate margin of safety that is sufficient but not more
than necessary.

Based on consideration of the entire body of evidence and information
available at this time, as well as the recommendations of CASAC and
public comments, the Administrator has decided that a level for the
primary Pb standard of 0.15 µg/m3, in combination with the specified
choice of indicator, averaging time, and form, is requisite to protect
public health, including the health of sensitive groups, with an
adequate margin of safety.  The Administrator notes that this level is
within the range recommended by CASAC, the Staff Paper, and by the vast
majority of commenters.  The Administrator concludes that a standard
with a level of 0.15 µg/m3 will reduce the risk of a variety of health
effects associated with exposure to Pb, including effects indicated in
the epidemiological studies at low blood Pb levels, particularly
including neurological effects in children, and the potential for
cardiovascular and renal effects in adults.

The Administrator notes that the evidence-based framework indicates that
for standard levels above 0.15 µg/m3, the estimated mean air-related IQ
loss in the subpopulation of children exposed at the level of the
standard would range in almost all cases from above 2 points to 5 points
or more with the range of air-to-blood ratios considered.  He concludes,
in light of his consideration of all of the evidence, including  the
framework discussed above, that the protection from  air-related Pb
effects at the higher blood Pb levels that would be allowed by standards
above 0.15 µg/m3 would not be sufficient to protect public health with
an adequate margin of safety.

In addition, the Administrator notes that for standard levels below 0.15
µg/m3, the estimated mean IQ loss from air-related Pb in the
subpopulation of children exposed at the level of the standard would
generally be somewhat to well below 2 IQ points regardless of which
air-to-blood ratio within the range of ratios considered was used.  The
Administrator concludes in light of all of the evidence, including the
evidence-based framework, that the degree of public health protection
that standards below 0.15 µg/m3 would likely afford would be greater
than what is necessary to protect public health with an adequate margin
of safety.

The Administrator also recognizes that several commenters expressed
concern that the proposal did not adequately address the need for the
standard to be set with an adequate margin of safety.  As noted above,
in section I, the requirement that primary standards include an adequate
margin of safety was intended to address uncertainties associated with
inconclusive scientific and technical information available at the time
of standard setting.  It was also intended to provide a reasonable
degree of protection against hazards that research has not yet
identified.  Both kinds of uncertainties are components of the risk
associated with pollution at levels below those at which human health
effects can be said to occur with reasonable scientific certainty.
Thus, in selecting a primary standard that includes an adequate margin
of safety, the Administrator is seeking not only to prevent pollutant
levels that have been demonstrated to be harmful but also to prevent
lower pollutant levels that may pose an unacceptable risk of harm, even
if the risk is not precisely identified as to nature or degree.

Nothing in the Clean Air Act, however, requires the Administrator to
identify a primary standard that would be protective against
demonstrated harms, and then identify an additional “margin of
safety” which results in further lowering of the standard.  Rather,
the Administrator’s past practice has been to take margin of safety
considerations into account in making decisions about setting the
primary standard, including in determining its level, averaging time,
form and indicator, recognizing that protection with an adequate margin
of safety needs to be sufficient but not more than necessary .

Consistent with past practice, the Administrator has taken the need to
provide for an adequate margin of safety into account as an integral
part of his decision-making on the appropriate level, averaging time,
form, and indicator of the standard.  As discussed above, the
consideration of health effects caused by different ambient air
concentrations of Pb is extremely complex and necessarily involves
judgments about uncertainties with regard to the relationships between
air concentrations, exposures, and health effects.  In light of these
uncertainties, the Administrator has taken into account the need for an
adequate margin of safety in making decisions on each of the elements of
the standards.  Consideration of the need for an adequate margin of
safety is reflected in the following elements:  selection of TSP as the
indicator and the rejection of the use of PM10 scaling factors;
selection of  a maximum, not to be exceeded form, in conjunction with a
3-month averaging time  that employs a rolling average, with the
requirement that  each month in the 3-month period be weighted equally
(rather than being averaged by individual data) and that a 3-year span
be used for comparison to the standard; and, the use of a range of
inputs for the evidence-based framework, that includes a focus on higher
air-to-blood ratios than the lowest ratio considered to be supportable,
and steeper rather than shallower C-R functions, and the consideration
of these inputs in selection of 0.15 µg/m3 as the level of the
standard.  The Administrator concludes based on his review of all of the
evidence (including the evidence-based framework) that when taken as a
whole the standard selected today, including the indicator, averaging
time, form, and level, will be sufficient but not more than necessary to
protect public health, including the health of sensitive subpopulations,
with an adequate margin of safety.

Thus, after carefully taking the above comments and considerations into
account, and fully considering the scientific and policy views of the
CASAC, the Administrator has decided to revise the level of the primary
Pb standard to 0.15 µg/m3.  In the Administrator's judgment, based on
the currently available evidence, a standard set at this level and using
the specified indicator, averaging time, and form would be requisite to
protect public health with an adequate margin of safety.  The
Administrator judges that such a standard would protect, with an
adequate margin of safety, the health of children and other at-risk
populations against an array of adverse health effects, most notably
including neurological effects, particularly neurobehavioral and
neurocognitive effects, in children.  A standard set at this level
provides a very significant increase in protection compared to the
current standard.  The Administrator believes that a standard set at
0.15 µg/m3 would be sufficient to protect public health with an
adequate margin of safety, and believes that a lower standard would be
more than what is necessary to provide this degree of protection.  This
judgment by the Administrator appropriately considers the requirement
for a standard that is neither more nor less stringent than necessary
for this purpose and recognizes that the CAA does not require that
primary standards be set at a zero-risk level, but rather at a level
that reduces risk sufficiently so as to protect public health with an
adequate margin of safety.

D.  Final Decision on the Primary Lead Standard

For the reasons discussed above, and taking into account information and
assessments presented in the Criteria Document and Staff Paper, the
advice and recommendations of CASAC, and the public comments, the
Administrator is revising the various elements of the standard to
provide increased protection for children and other at-risk populations
against an array of adverse health effects, most notably including
neurological effects in children, including neurocognitive and
neurobehavioral effects.  Specifically, the Administrator has decided to
revise the level of the primary standard to a level of 0.15 µg/m3, in
conjunction with retaining the current indicator of Pb-TSP.  The
Administrator has also decided to revise the form and averaging time of
the standard to a maximum (not to be exceeded) rolling 3-month average
evaluated over a 3-year period.

Corresponding revisions to data handling conventions, including
allowance for the use of Pb-PM10 data in certain circumstances, and the
treatment of exceptional events are specified in revisions to Appendix
R, as discussed in section IV below.  Corresponding revisions to aspects
of the ambient air monitoring and reporting requirements for Pb are
discussed in section V below, including sampling and analysis methods
(e.g., a new Federal reference method for monitoring Pb in PM10, quality
assurance requirements), network design, sampling schedule, data
reporting, and other miscellaneous requirements.

III.	Secondary Lead Standard

A. Introduction

The NAAQS provisions of the Act require the Administrator to establish
secondary standards that, in the judgment of the Administrator, are
requisite to protect the public welfare from any known or anticipated
adverse effects associated with the presence of the pollutant in the
ambient air. In so doing, the Administrator seeks to establish standards
that are neither more nor less stringent than necessary for this
purpose. The Act does not require that secondary standards be set to
eliminate all risk of adverse welfare effects, but rather at a level
requisite to protect public welfare from those effects that are judged
by the Administrator to be adverse.

This section presents the rationale for the Administrator’s final
decision to revise the existing secondary NAAQS.  In considering the
currently available evidence on Pb-related welfare effects, there is
much information linking Pb to potentially adverse effects on organisms
and ecosystems.  However, given the evaluation of this information in
the Criteria Document and Staff Paper which highlighted the substantial
limitations in the evidence, especially the lack of evidence linking
various effects to specific levels of ambient Pb, the Administrator
concludes that the available evidence supports revising the secondary
standard but does not provide a sufficient basis for establishing a
secondary standard for Pb that is different from the primary standard.
SEQ CHAPTER \h \r 1

1. Overview of Welfare Effects Evidence

A secondary NAAQS addresses welfare effects and “effects on welfare”
include, but are not limited to, effects on soils, water, crops,
vegetation, manmade materials, animals, wildlife, weather, visibility
and climate, damage to and deterioration of property, and hazards to
transportation, as well as effects on economic values and on personal
comfort and well-being.  CAA section 302(h).  A qualitative assessment
of welfare effects evidence related to ambient Pb is summarized in this
section, drawing from the Criteria Document, Chapter 6 of the Staff
Paper and from the Proposed Rule.  The presentation here summarizes
several key aspects of the welfare evidence for Pb.  Lead is persistent
in the environment and accumulates in soils, aquatic systems (including
sediments), and some biological tissues of plants, animals and other
organisms, thereby providing long-term, multi-pathway exposures to
organisms and ecosystems.  Additionally, EPA recognizes that there have
been a number of uses of Pb, especially as an ingredient in automobile
fuel but also in other products such as paint, lead-acid batteries, and
some pesticides, which have significantly contributed to widespread
increases in Pb concentrations in the environment, a portion of which
remains today (e.g., CD, Chapters 2 and 3).

Ecosystems near smelters, mines and other industrial sources of Pb have
demonstrated a wide variety of adverse effects including decreases in
species diversity, loss of vegetation, changes to community composition,
decreased growth of vegetation, and increased number of invasive
species.  These sources may have multiple pathways for discharging Pb to
ecosystems, and apportioning effects between air-related pathways and
other pathways (e.g. discharges to water) in such cases is difficult.
Likewise, apportioning these effects between Pb and other stressors is
complicated because these point sources also emit a wide variety of
other heavy metals and sulfur dioxide which may cause toxic effects.
There are no field studies which have investigated effects of Pb
additions alone but some studies near large point sources of Pb have
found significantly reduced species composition and altered community
structures.  While these effects are significant, they are spatially
limited: the majority of contamination occurs within 20 to 50 km of the
emission source (CD, section AX<IP_ADDRESS>).

By far, the majority of air-related Pb found in terrestrial ecosystems
was deposited in the past during the use of Pb additives in gasoline.
Many sites receiving Pb predominantly through such long-range transport
of gasoline-derived small particles have accumulated large amounts of Pb
in soils (CD, p. AX7-98).  There is little evidence that terrestrial
sites exposed as a result of this long range transport of Pb have
experienced significant effects on ecosystem structure or function (CD,
section AX<IP_ADDRESS> and p. AX7-98).  Strong complexation of Pb by soil
organic matter may explain why few ecological effects have been observed
(CD, p. AX7-98).  Studies have shown decreasing levels of Pb in
vegetation which seems to correlate with decreases in atmospheric
deposition of Pb resulting from the removal of Pb additives to gasoline
(CD, section AX <IP_ADDRESS>).

Terrestrial ecosystems remain primarily sinks for Pb but amounts
retained in various soil layers vary based on forest type, climate, and
litter cycling (CD, section 7.1).  Once in the soil, the migration and
distribution of Pb is controlled by a multitude of factors including pH,
precipitation, litter composition, and other factors which govern the
rate at which Pb is bound to organic materials in the soil (CD, section
2.3.5).

Like most metals the solubility of Pb is increased at lower pH.
However, the reduction of pH may in turn decrease the solubility of
dissolved organic material (DOM).  Given the close association between
Pb mobility and complexation with DOM, a reduced pH does not necessarily
lead to increased movement of Pb through terrestrial systems and into
surface waters.  In areas with moderately acidic soil (i.e., pH of 4.5
to 5.5) and abundant DOM, there is no appreciable increase in the
movement of Pb into surface waters compared to those areas with neutral
soils (i.e., pH of approximately 7.0).  This appears to support the
theory that the movement of Pb in soils is limited by the solubilization
and transport of DOM.  In sandy soils without abundant DOM, moderate
acidification appears likely to increase outputs of Pb to surface waters
(CD, section AX <IP_ADDRESS>).

Lead exists in the environment in various forms which vary widely in
their ability to cause adverse effects on ecosystems and organisms.
Current levels of Pb in soil also vary widely depending on the source of
Pb but in all ecosystems Pb concentrations exceed natural background
levels.  The deposition of gasoline-derived Pb into forest soils has
produced a legacy of slow moving Pb that remains bound to organic
materials despite the removal of Pb from most fuels and the resulting
dramatic reductions in overall deposition rates.  For areas influenced
by point sources of air Pb, concentrations of Pb in soil may exceed by
many orders of magnitude the concentrations which are considered harmful
to laboratory organisms.  Adverse effects associated with Pb include
neurological, physiological and behavioral effects which may influence
ecosystem structure and functioning.  Ecological soil screening levels
(Eco-SSLs) have been developed for Superfund site characterizations to
indicate concentrations of Pb in soils below which no adverse effects
are expected to plants, soil invertebrates, birds and mammals.  Values
like these may be used to identify areas in which there is the potential
for adverse effects to any or all of these receptors based on current
concentrations of Pb in soils.

Atmospheric Pb enters aquatic ecosystems primarily through the erosion
and runoff of soils containing Pb and deposition (wet and dry).  While
overall deposition rates of atmospheric Pb have decreased dramatically
since the removal of Pb additives from gasoline, Pb continues to
accumulate and may be re-exposed in sediments and water bodies
throughout the United States (CD, section 2.3.6).

Several physical and chemical factors govern the fate and
bioavailability of Pb in aquatic systems.  A significant portion of Pb
remains bound to suspended particulate matter in the water column and
eventually settles into the substrate.  Species, pH, salinity,
temperature, turbulence and other factors govern the bioavailability of
Pb in surface waters (CD, section 7.2.2).

Lead exists in the aquatic environment in various forms and under
various chemical and physical parameters which determine the ability of
Pb to cause adverse effects either from dissolved Pb in the water column
or Pb in sediment.  Current levels of Pb in water and sediment also vary
widely depending on the source of Pb.  Conditions exist in which adverse
effects to organisms and thereby ecosystems may be anticipated given
experimental results.  It is unlikely that dissolved Pb in surface water
constitutes a threat to ecosystems that are not directly influenced by
point sources.  For Pb in sediment, the evidence is less clear.  It is
likely that some areas with long term historical deposition of Pb to
sediment from a variety of sources as well as areas influenced by point
sources have the potential for adverse effects to aquatic communities.
The long residence time of Pb in sediment and its ability to be
resuspended by turbulence make Pb likely to be a factor for the
foreseeable future.  Criteria have been developed to indicate
concentrations of Pb in water and sediment below which no adverse
effects are expected to aquatic organisms.  These values may be used to
identify areas in which there is the potential for adverse effects to
receptors based on current concentrations of Pb in water and sediment.

2. Overview of Screening Level Ecological Risk Assessment

This section presents a brief summary of the screening-level ecological
risk assessment conducted by EPA for this review. The assessment is
described in detail in Lead Human Exposure and Health Risk Assessments
and Ecological Risk Assessment for Selected Areas, Pilot Phase (ICF,
2006).  Various limitations have precluded performance of a full-scale
ecological risk assessment. The discussion here is focused on the
screening level assessment performed in the pilot phase (ICF, 2006) and
takes into consideration CASAC recommendations with regard to
interpretation of this assessment (Henderson, 2007a, b). The following
summary focuses on key features of the approach used in the assessment
and presents only a brief summary of the results of the assessment.

A screening level risk assessment was performed to estimate the
potential for ecological risks associated with exposures to Pb emitted
into ambient air.  A case study approach was used which included areas
surrounding a primary Pb smelter and a secondary Pb smelter, as well as
a location near a nonurban roadway. Soil, surface water, and/or sediment
concentrations were estimated for each of the three initial case studies
from available monitoring data or modeling analysis, and then compared
to ecological screening benchmarks to assess the potential for
ecological impacts from Pb that was emitted into the air. A
national-scale screening assessment was also used to evaluate surface
water and sediment monitoring locations across the United States for the
potential for ecological impacts associated with atmospheric deposition
of Pb.  An additional case study was identified to look at gasoline
derived Pb effects on an ecologically vulnerable ecosystem but various
limitations precluded any analyses.

The ecological screening values used in this assessment to estimate the
potential for ecological risk were developed from the Eco-SSLs
methodology, EPA’s recommended ambient water quality criteria, and
sediment screening values developed by MacDonald and others (2000,
2003). Soil screening values were derived for this assessment using the
Eco-SSL methodology with the toxicity reference values for Pb (USEPA,
2005d, 2005e) and consideration of the inputs on diet composition, food
intake rates, incidental soil ingestion, and contaminant uptake by prey
(details are presented in section <IP_ADDRESS> and Appendix L, of ICF, 2006).
Hardness specific surface water screening values were calculated for
each site based on EPA’s recommended ambient water quality criteria
for Pb (USEPA, 1984). For sediment screening values, the assessment
relied on sediment ‘‘threshold effect concentrations’’ and
‘‘probable effect concentrations’’ developed by MacDonald et al
(2000). The methodology for these sediment criteria is described fully
in section <IP_ADDRESS> and Appendix M of the pilot phase Risk Assessment
Report (ICF, 2006).

A Hazard Quotient (HQ) was calculated for various receptors to determine
the potential for risk to that receptor. The HQ is calculated as the
ratio of the media concentration to the ecotoxicity screening value, and
represented by the following equation:

HQ = (estimated Pb media concentration)/ (ecotoxicity screening value)

For each case study, HQ values were calculated for each location where
either modeled or measured media concentrations were available. Separate
soil HQ values were calculated for each ecological receptor group for
which an ecotoxicity screening value has been developed (i.e., birds,
mammals, soil invertebrates, and plants). HQ values less than 1.0
suggest that Pb concentrations in a specific medium are unlikely to pose
significant risks to ecological receptors. HQ values greater than 1.0
indicate that the expected exposure exceeds the ecotoxicity screening
value and that there is a potential for adverse effects.

There are several uncertainties that apply across case studies noted
below:

• The ecological risk screen is limited to specific case study
locations and other locations for which Pb data were available. Efforts
were made to ensure that the Pb exposures assessed were attributable to
airborne Pb and not dominated by non-air sources. However, there is
uncertainty as to whether other sources might have actually contributed
to the Pb exposure estimates.

• A limitation to using the selected ecotoxicity screening values is
that they might not be sufficient to identify risks to some threatened
or endangered species or unusually sensitive aquatic ecosystems (e.g.,
CD, p. AX7–110).

• The methods and database from which the surface water screening
values (i.e., the AWQC for Pb) were derived is somewhat dated. New data
and approaches (e.g., use of pH as indicator of bioavailability) may now
be available to estimated the aquatic toxicity of Pb (CD, sections
X<IP_ADDRESS> and AX<IP_ADDRESS>).

• No adjustments were made for sediment-specific characteristics that
might affect the bioavailability of Pb in sediments in the derivation of
the sediment quality criteria used for this ecological risk screen (CD,
sections 7.2.1 and AX<IP_ADDRESS>; Appendix M, ICF, 2006). Similarly,
characteristics of soils for the case study locations were not evaluated
for measures of bioavailability.

• Although the screening value for birds used in this analysis is
based on reasonable estimates for diet composition and assimilation
efficiency parameters, it was based on a conservative estimate of the
relative bioavailability of Pb in soil and natural diets compared with
water soluble Pb added to an experimental pellet diet (Appendix L, ICF,
2006).

The following is a brief summary of key observations related to the
results of the screening-level ecological risk assessment. A complete
discussion of the results is provided in Chapter 6 of the Staff Paper
and the complete presentation of the assessment and results is presented
in the pilot phase Risk Assessment Report (ICF, 2006).

For the case studies, the concentrations of Pb in soil and sediments in
various locations exceeded screening values for these media indicating
potential for adverse effects to terrestrial organisms (plants, birds
and mammals) and to sediment dwelling organisms.  While it was not
possible to dissect the contributions of air Pb emissions from other
sources, it is likely that, at least for the primary smelter, that the
air contribution is significant.  For the other case studies, the
contributions of current air emissions to the Pb burden, is less clear.

The national-scale screen of surface water data initially identified 15
areas for which water column levels of dissolved Pb were greater than
hardness adjusted chronic criteria for the protection of aquatic life
indicating a potential for adverse effect if concentrations were
persistent over chronic periods. Acute criteria were not exceeded at any
of these locations. The extent to which air emissions of Pb have
contributed to these surface water Pb concentrations is unclear. In the
national-scale screen of sediment data associated with the 15 surface
water sites described above, threshold effect concentration-based HQs at
nine of these sites exceeded 1.0. Additionally, HQs based on probable
effect concentrations exceeded 1.0 at five of the sites, indicating
probable adverse effects to sediment dwelling organisms. Thus, sediment
Pb concentrations at some sites are high enough that there is a
likelihood that they would cause adverse effects to sediment dwelling
organisms. However, the contribution of air emissions to these
concentrations is unknown.

B. Conclusions on the Secondary Lead Standard

  1. Basis for the Proposed Decision

d (1.5 μg Pb/m3, as a maximum arithmetic mean averaged over a calendar
quarter), the basis for which is summarized in section II.C.1.  At the
time the standard was set, the Agency concluded that the primary air
quality standard would adequately protect against known and anticipated
adverse effects on public welfare, as the Agency stated that it did not
have evidence that a more restrictive secondary standard was justified.
In the rationale for this conclusion, the Agency stated that the
available evidence cited in the 1977 Criteria Document indicated that
‘‘animals do not appear to be more susceptible to adverse effects
from lead than man, nor do adverse effects in animals occur at lower
levels of exposure than comparable effects in humans’’ (43 FR
46256). The Agency recognized that Pb may be deposited on the leaves of
plants and present a hazard to grazing animals. With regard to plants,
the Agency stated that Pb is absorbed but not accumulated to any great
extent by plants from soil, and that although some plants may be
susceptible to Pb, it is generally in a form that is largely unavailable
to them. Further the Agency stated that there was no evidence indicating
that ambient levels of Pb result in significant damage to manmade
materials and Pb effects on visibility and climate are minimal.

ary standard at or below the level of the then-current secondary
standard of 1.5 μg/m3.

Given the full body of current evidence, despite wide variations in Pb
concentrations in soils throughout the country, Pb concentrations are in
excess of concentrations expected from geologic or other
non-anthropogenic forces. There are several difficulties in quantifying
the role of recent air emissions of Pb in the environment: some Pb
deposited before the standard was enacted is still present in soils and
sediments; historic Pb from gasoline continues to move slowly through
systems as does current Pb derived from both air and nonair sources.
Additionally, the evidence of adversity in natural systems is limited
due in no small part to the difficulty in determining the effects of
confounding factors such as multiple metals or factors influencing
bioavailability in field studies.

The evidence summarized above, in the Proposed Rule, in section 4.2 of
the Staff Paper, and described in detail in the Criteria Document,
informs our understanding of Pb in the environment today and evidence of
environmental Pb exposures of potential concern.  For areas influenced
by point sources of air Pb that meet the current standard,
concentrations of Pb in soil may exceed by many orders of magnitude the
concentrations which are considered harmful to laboratory organisms (CD,
sections 3.2 and AX<IP_ADDRESS>). In addition, conditions exist in which Pb
associated adverse effects to aquatic organisms and thereby ecosystems
may be anticipated given experimental results. While the evidence does
not indicate that dissolved Pb in surface water constitutes a threat to
those ecosystems that are not directly influenced by point sources, the
evidence regarding Pb in sediment is less clear (CD, sections
AX<IP_ADDRESS>.2 and AX7.2.4). It is likely that some areas with long term
historical deposition of Pb to sediment from a variety of sources as
well as areas influenced by point sources have the potential for adverse
effects to aquatic communities. The Staff Paper concluded, based on
laboratory studies and current media concentrations in a wide range of
areas, that it seems likely that adverse effects are occurring,
particularly near point sources, under the current standard. The long
residence time of Pb in sediment and its ability to be resuspended by
turbulence make Pb contamination likely to be a factor for the
foreseeable future. Based on this information, the Staff Paper concluded
that the evidence suggests that the environmental levels of Pb occurring
under the current standard, set nearly thirty years ago, may pose risk
of adverse environmental effect.

In addition to the evidence-based considerations described in the
previous section, the screening level ecological risk assessment is
informative, taking into account key limitations and uncertainties
associated with the analyses. As discussed in the previous section, as a
result of its persistence, Pb emitted in the past remains today in
aquatic and terrestrial ecosystems of the United States. Consideration
of the environmental risks associated with the current standard is
complicated by the environmental burden associated with air Pb
concentrations that exceeded the current standard, predominantly in the
past. Concentrations of Pb in soil and sediments associated with the
case studies exceeded screening values for those media, indicating
potential for adverse effect in terrestrial organisms (plants, birds,
and mammals) and in sediment dwelling organisms. While the contribution
to these Pb concentrations from air as compared to non-air sources has
not  been quantified, air emissions from the primary smelting facility
at least are substantial (Appendix D, USEPA 2007b; ICF  2006).

The national-scale screens, which are not focused on particular point
source locations, indicate the ubiquitous nature of Pb in aquatic
systems of the United States today. Further, the magnitude of surface
water Pb concentrations in several aquatic systems exceeded screening
values and sediment Pb concentrations at some sites in the
national-scale screen were high enough that the likelihood that they
would cause adverse effects to sediment dwelling organisms may be
considered ‘‘probable’’.  A complicating factor in interpreting
the findings for the national-scale screening assessments is the lack of
clear apportionment of Pb contributions from air as compared to non-air
sources, such as industrial and municipal discharges.  While the
contribution of air emissions to the elevated concentrations has not
been quantified, documentation of historical trends in the sediments of
many water bodies has illustrated the sizeable contribution that
airborne Pb can have on aquatic systems (e.g., Staff Paper, section
2.8.1).  This documentation also indicates the greatly reduced
contribution in many systems as compared to decades ago (presumably
reflecting the phase-out of Pb-additives from gasoline used by cars and
trucks). However, the timeframe for removal of Pb from surface sediments
into deeper sediment varies across systems, such that Pb remains
available to biological organisms in some systems for much longer than
in others (Staff Paper, section 2.8; CD, pp. AX7–141 to AX7–145).

The case study locations included in the screening assessment, with the
exception of the primary Pb smelter site, are currently meeting the
current Pb standard, yet Pb occurs in soil and aquatic sediment in some
locations at concentrations indicative of a potential for harm to some
terrestrial and sediment dwelling organisms. While the role of airborne
Pb in determining these Pb concentrations is unclear, the historical
evidence indicates that airborne Pb can create such concentrations in
sediments and soil.

Based on its review of the Staff Paper, CASAC advised the Administrator
that “The Lead Panel unanimously affirms its earlier judgments that,
as with the primary (public-health based) Lead NAAQS, the secondary
(public-welfare based) standard for lead also needs to be substantially
lowered… Therefore at a minimum, the level of the secondary Lead NAAQS
should be at least as low as the level of the recommended primary lead
standard.” (Henderson, 2008a).  CASAC also recognized that EPA lacked
data to provide a clear quantitative basis for setting a secondary
standard that differed from the primary standard. (Henderson 2007a,
2008a)

In considering the adequacy of the current standard in providing
protection from Pb-related adverse effects on public welfare, the
Administrator considered in the proposal the body of available evidence
(briefly summarized above in section III.).  The proposal indicated that
depending on the interpretation, the available data and evidence,
primarily qualitative, suggests that there was the potential for adverse
environmental impacts under the current standard. Given the limited data
on Pb effects in ecosystems, it is necessary to look at evidence of Pb
effects on organisms and extrapolate to ecosystem effects. Therefore,
taking into account the available evidence and current media
concentrations in a wide range of areas, the Administrator concluded in
the proposal that there is potential for adverse effects occurring under
the current standard, although there are insufficient data to provide a
quantitative basis for setting a secondary standard different than the
primary. While the role of current airborne emissions is difficult to
apportion, deposition of Pb from air sources is occurring and this
ambient Pb is likely to be persistent in the environment similarly to
that of historically deposited Pb which has persisted, although location
specific dynamics of Pb in soil result in differences in the timeframe
during which Pb is retained in surface soils or sediments where it may
be available to ecological receptors (USEPA, 2007b, section 2.3.3).

Based on these considerations, and taking into account the observations,
analyses, and recommendations discussed above, the Administrator
proposed to revise the current secondary Pb standard by making it
identical in all respects to the proposed primary Pb standard (described
in section II.D above).

  2. Comments on the Proposed Secondary Standard

EPA notes that CASAC, in their July 2008 letter, did not provide
comments on the discussion and proposal regarding the secondary
standard.  Commenters who expressed an opinion on the proposed revision
to the secondary standard, including a number of national organizations,
individual States, Tribal associations, and local organizations, and
combined comments from various environmental groups supported the
position that the secondary Pb standard should be revised to the level
of the primary standard.  Some commenters recommended that the secondary
standard be no less stringent than the primary, one commenter
recommended that the standard be no more stringent than the primary, and
some commenters recommended that the secondary standard be identical to
the primary.  One commenter concurred with the Agency’s finding,
consistent with CASAC’s prior advice, that the current scientific
knowledge was lacking and that further research was necessary to
quantitatively inform an appropriate secondary standard.  For the
reasons discussed above and in the proposal, we agree with commenters
that the secondary standard should be at this time set equal to the
primary in indicator, level, form and averaging time and that more
research is needed to further inform the development of a secondary Pb
standard.

3.  Administrator’s Conclusions

In considering the adequacy of the current secondary standard in
providing requisite protection from Pb-related adverse effects on public
welfare, the Administrator has considered the body of available evidence
(briefly summarized above and in the proposal).  The screening-level
risk assessment, while limited and accompanied by various uncertainties,
suggests occurrences of environmental Pb concentrations existing under
the current standard that could have adverse environmental effects in
terrestrial organisms (plants, birds and mammals) and in sediment
dwelling organisms.  Environmental Pb levels today are associated with
atmospheric Pb concentrations and deposition that have combined with a
large reservoir of historically deposited Pb in environmental media.

In considering this evidence, as well as the views of CASAC, summarized
above, the Staff Paper and associated support documents, and views of
public commenters on the adequacy of the current standard, the
Administrator concurs with CASAC’s recommendation that the secondary
standard should be substantially revised and concludes that given the
current state of evidence, the current secondary standard for Pb is not
requisite to protect public welfare from known or anticipated adverse
effects.

C. Final Decision on the Secondary Lead Standard

The secondary standard is defined in terms of four basic elements:
indicator, averaging time, level and form, which serve to define the
standard and must be considered collectively in evaluating the welfare
protection afforded by the standards. With regard to the pollutant
indicator for use in a secondary NAAQS, EPA notes that Pb is a
persistent pollutant to which ecological receptors are exposed via
multiple pathways. While the evidence indicates that the environmental
mobility and ecological toxicity of Pb are affected by various
characteristics of its chemical form, and the media in which it occurs,
information is insufficient to identify an indicator other than total Pb
that would provide protection against adverse environmental effect in
all ecosystems nationally. Thus, the same rationale for retaining Pb-TSP
for the indicator apply here as for the primary standard.

Lead is a cumulative pollutant with environmental effects that can last
many decades.  There is a general lack of data that would indicate the
appropriate level of Pb in environmental media that may be associated
with adverse effects. The EPA notes the influence of airborne Pb on Pb
in aquatic systems and of changes in airborne Pb on aquatic systems, as
demonstrated by historical patterns in sediment cores from lakes and Pb
measurements (section 2.8.1; CD, section AX7.2.2; Yohn et al., 2004;
Boyle et al., 2005), as well as the comments of the CASAC Pb panel that
a significant change to current air concentrations (e.g., via a
significant change to the standard) is likely to have significant
beneficial effects on the magnitude of Pb exposures in the environment
and Pb toxicity impacts on natural and managed terrestrial and aquatic
ecosystems in various regions of the U.S., the Great Lakes and also U.S.
territorial waters of the Atlantic Ocean (Henderson, 2007a, Appendix E).
 The Administrator concurs with CASAC’s conclusion that the level of
the secondary standard should be set at least as low as the level of the
primary standard and that the Agency lacks the relevant data to provide
a clear, quantitative basis for setting a secondary Pb NAAQS that
differs from the primary in indicator, averaging time, level, or form.
Based on these considerations, and taking into account the observations,
analyses, and recommendations discussed above, the Administrator is
revising the current secondary Pb standard by making it identical in all
respects to the primary Pb standard.

IV. Appendix R— Interpretation of the NAAQS for Lead

EPA proposed to add Appendix R, Interpretation of the National Ambient
Air Quality Standards for Pb, to 40 CFR part 50 in order to provide data
handling procedures for the proposed Pb standard.  The proposed Appendix
R detailed the computations necessary for determining when the proposed
Pb NAAQS would be met. The proposed appendix also addressed data
reporting; sampling frequency and data completeness considerations; the
use of scaled low-volume Pb-PM10 data as a surrogate for Pb-TSP data (or
vice versa), including associated scaling instructions; and rounding
conventions.  The purpose of a data interpretation guideline in general
is to provide the practical details on how to make a comparison between
multi-day, possibly multi-monitor, and (in the unique instance of the
proposed Pb NAAQS) possibly multi-parameter (i.e., Pb-TSP and/or
low-volume Pb-PM10) ambient air concentration data to the level of the
NAAQS, so that determinations of compliance and violation are as
objective as possible.  Data interpretation guidelines also provide
criteria for determining whether there are sufficient data to make a
NAAQS level comparison at all.  When data are insufficient, for example
because of failure to collect valid ambient data on enough days in
enough months (because of operator error or events beyond the control of
the operator), no determination of current compliance or violation is
possible.

In the proposal, proposed rule text was provided only for the example of
a Pb NAAQS based on a Pb-TSP indicator, a monthly averaging time, and a
second maximum form.  The preamble discussed how the rule text would be
different to accommodate a Pb-PM10 indicator and/or a quarterly
averaging time with a not-to-be-exceeded form.

A. Ambient Data Requirements

1. Proposed Provisions

	Section 3 of the proposed Appendix R, Requirements for Data Used for
Comparisons with the Pb NAAQS and Data Reporting Considerations,
specified that all valid FRM/FEM Pb-TSP data and all valid FRM/FEM
Pb-PM10 data submitted to EPA's Air Quality System (AQS), or otherwise
available to EPA, meeting specified monitoring requirements in 40 CFR
part 58 related to quality assurance, monitoring methods, and monitor
siting shall be used in design value calculations.  Because 40 CFR 58
requirements were revised in 2006 and were proposed for further revision
in this rulemaking, and because the FRM/FEM criteria for Pb-PM10 are
being established for the first time in this rulemaking, EPA wanted to
provide clarity about whether data collected before the effective dates
of the 2006 revisions and of this final rule could be used for
comparisons to the NAAQS.  The proposal therefore provided that Pb-TSP
and Pb-PM10 data representing sample collection periods prior to January
1, 2009 (i.e., “pre-rule” data) would also be considered valid for
NAAQS comparisons and related attainment/nonattainment determinations if
the sampling and analysis methods that were utilized to collect those
data were consistent with the provisions of 40 CFR part 58 that were in
effect at the time of original sampling or that are in effect at the
time of the attainment / nonattainment determination, and if such data
are submitted to AQS prior to September 1, 2009.

This section of the proposed rule also required that in the future Pb
data be reported in terms of local temperature and pressure conditions,
but provided that Pb data collected prior to January 1, 2009 and
reported to AQS in terms of standard temperature and pressure conditions
would be compared directly the level of the NAAQS without re-adjustment
to local conditions, unless the monitoring agency voluntarily
re-submitted them with such adjustment.

	Finally, this section provided for the taking of make-up samples within
seven days after a scheduled sampling day fails to produce valid data.
It also specified that all data, including scheduled samples, make-up
samples, and any extra samples (i.e., non-scheduled samples that are not
eligible to be considered make-up samples because they either were taken
too long after the missed sample or another non-scheduled sample is
already being used as the make-up sample) would be used in calculating
the monthly average concentration.

2. Comments on Ambient Data Requirements

	One commenter argued that Pb concentrations should continue, as in the
past, to be reported in terms of standard temperature and pressure
conditions and that only those values should be compared to the level of
the NAAQS.  In support of this view, this commenter claimed generally
that ambient air Pb concentrations used in deriving relationships
between air Pb concentrations and blood Pb levels were in terms of
standard temperature and pressure.  Another commenter expressed a
similar but less specific concern about consistency between the
conditions for reporting concentrations and the logic used by the
Administrator to set the level of the NAAQS.  For reasons described in
the Response to Comments document, EPA rejects these arguments.

Another commenter supported the requirement for Pb concentrations to be
submitted in terms of local conditions and the option of monitoring
agencies to resubmit older data in those terms, but wanted EPA to
restrain monitoring agencies which do resubmit data from withdrawing the
data submitted earlier in terms of standard conditions.  EPA agrees that
the previously submitted data should not be withdrawn, but we will
instruct states to this effect through guidance rather than by
regulation, since nowhere now do the air monitoring or data
interpretation regulations address the possibility of data withdrawal.

However, for ease of reference for monitoring agency staff, in the final
rule the requirement for submitting Pb-TSP data in terms of local
conditions has been placed in 40 CFR 58.16 (Data submittal and archiving
requirements) rather than in Appendix R, so that it appears along with
various other requirements related to data submittal.  The corresponding
requirement for Pb-PM10 data is contained in the FRM method
specification in Appendix Q.  Appendix R retains a statement that this
is the manner in which both types of data are submitted.  Also, as
proposed, 40 CFR 50.3 is amended to say that Pb-TSP concentrations are
to be reported in terms of local conditions of temperature and pressure.

3. Conclusions on Ambient Data Requirements

	The final provisions of Appendix R regarding what ambient data are to
be used for comparisons to the NAAQS are as proposed.  Sections IV.C and
IV.D of this preamble also address certain related issues involving what
ambient data are to be used in making comparisons to the NAAQS.

B. Averaging time and Procedure

1.  Proposal on Averaging Time and Procedure

	EPA proposed in the alternative two averaging times for the revised
NAAQS: a monthly period and a calendar quarter.  In both approaches, the
averaging time would be based on non-overlapping periods, the 12
individual calendar months in the case of a monthly averaging time and
the 4 conventional calendar quarters (January – March, etc.) in the
case of calendar quarter.  In the case of a monthly averaging time all
valid 24-hour Pb concentration data from the month would be
arithmetically averaged to calculate the average concentration, and the
average would be considered valid depending on the completeness of the
data relative to the monitoring schedule, see section IV.C.  Similarly,
in the case of a quarterly average, all valid 24-hour data would be
averaged to calculate the quarterly average concentration.

2. Comments on Averaging Time and Procedure

	There were many public comments on the selection of the averaging time,
addressed in section II.C.2.  For the reasons discussed in that section,
the final rule establishes the averaging time as a rolling 3-month
period.  Also, the final rule contains a 2-step procedure for
calculating the 3-month average concentration, in which the average
concentration for individual calendar months are calculated from all
available valid 24-hour data in each month, and then three adjacent
monthly averages are summed and divided by three to form the 3-month
average concentration.  In this way, each month’s average will be
weighted the same in calculating the 3-month average even if the months
have different numbers of days with valid 24-hour concentration data.
As explained in section II.C.2, this reduces the possibility that any
one month’s concentration could be very high compared to the 3-month
average, compared to the proposed 1-step approach to calculating an
average over three months.

3. Conclusions on Averaging Time and Procedure

	The final rule establishes the averaging time as a rolling 3-month
period.  The final rule contains a 2-step procedure for calculating the
average concentration for a 3-month period.  First, the average
concentration for individual calendar months are calculated from all
available valid 24-hour data in each month giving equal weight to each
day with valid monitoring data.  Then, the three adjacent monthly
averages are summed and divided by three to form the 3-month average
concentration.

The final text of Appendix R also includes a provision that gives the
Administrator discretion to use an alternate 3-step approach to
calculating the 3-month average concentration instead of the 2-step
approach described above.  The Administrator will have this discretion
only in a situation in which the number of extra sampling days during a
month within the 3-month period is greater than the number of
successfully completed scheduled and make-up sample days in that month.
In such a situation, including all the available valid sampling days in
the calculation of a monthly average concentration (and thereby into the
calculation of a 3-month average concentration) might in result in an
unrepresentative value for the monthly average concentration.  This
provision is to protect the integrity of the monthly and 3-month average
concentration values in situations in which, by intention or otherwise,
extra sampling days are concentrated in a period or periods during which
ambient concentrations are particularly high or low.  As explained in
section IV.B, the final version of Appendix R does not apply a
completeness requirement to individual months, but instead applies the
completeness criteria to each 3-month averaging period as a whole.  As a
result, it is conceivable that a month used to form a valid 3-month
average may itself have as few as two scheduled sampling days with valid
data if the other two months have valid data for all five scheduled
sampling days.  In such a case, even a small number of extra samples
could dominate the monthly average, which would then in turn contribute
to the 3-month average with a weighting of one-third.  The extra
sampling days, however, may systematically tend to have been higher or
lower Pb concentration days.  For example, a monitoring agency might
have deliberately increased sampling frequency during episodes of high
Pb concentration in order to better understand the scope and causes of
high concentrations.  It is also possible for a monitoring agency to
pick days for extra sampling in ways that make those days tend to have
lower Pb concentrations, for example by paying attention to wind
direction or source operations.  If extra sampling days are
systematically related to concentration, the average of all data during
a month might not fairly represent the average of the daily
concentrations actually occurring across all the days in the month.  The
potential for the monthly average to become seriously distorted
increases as the number of extra sampling days increases.  Therefore,
the final rule does not trigger the discretion to use the alternate
3-step approach described below unless the number of extra sampling days
is greater than the number of scheduled and make-up days that have valid
data.

In the case of a Pb sampling schedule in which an ambient sample is
scheduled to be taken every sixth day, the first step in the 3-step
approach is to average all scheduled, make-up, and extra samples taken
on a given scheduled sample day and on any of the five days following
that sampling day.  Typically, there will be up to five such 6-day
averages in a month; there can be fewer 6-day averages if one or more of
the 6-day periods yielded no valid data.  The second step is to average
these 6-day averages together to calculate the monthly average.  This
approach has the effect of giving equal weight to each 6-day period
during a month regardless of how many samples were actually obtained
during the 6 days, which mitigates the potential for the monthly average
to be distorted.  The third step in calculating the 3-month average
would be to average the three monthly averages giving equal weight to
each month, as described above in the standard 2-step approach to
calculating the 3-month mean.

The above discussion has been simplified for easier understanding, by
not addressing all the possible situations that can arise and that are
addressed explicitly or implicitly by the final rule text.  The
following provides additional details.

 (1) The example presumes a one-in-six sampling schedule, which is the
minimum required in the final rule.  If the site is operating on a
one-in-three schedule, the first step in the alternate approach is to
average the daily concentrations over periods of three days, then those
three-day averages (up to 10, typically) are averaged to get the monthly
average.

(2) The first day of scheduled one-in-six sampling typically will not
fall on the first day of the calendar month, and there may be make-up or
extra samples on the 1 to 5 days (1 or 2 days in the case of
one-in-three sampling) of the same calendar month that  precede the
first scheduled day of the month.  These samples will stay associated
with their actual calendar month as follows.  Any extra and make-up
samples taken within the month but before the first scheduled sampling
day of the month will be associated with and averaged with the last
scheduled sampling day of the month and any days in the month following
the last scheduled sampling day.  In a 30-day month, this approach will
always associate the last scheduled day of the month with five
unscheduled days within the same month just as for the other scheduled
sampling days, even when it is less than five days from the start of the
next month, preserving the concept of giving equal weight to equal
calendar time.

(3)  In February, with 28 or 29 days, under the final rule’s alternate
approach one of the scheduled sampling days will end up associated with
fewer than five unscheduled days, but those days will nevertheless carry
equal weight with the four 6-day periods.  EPA recognizes this slight
departure from the concept of giving equal weight to equal calendar
time.

(4) In months with 31 days, there will also be a departure from the
concept of equal weight to equal calendar time.  Most often, one of the
“6-day” periods will actually have 7 days included in it.  Rarely,
the last day of a 31-day month will be a scheduled sampling day, and the
effect will be to give the Pb measurement from this day equal weight in
the monthly average as the five 6-day averages.  In such a case, the
Administrator may choose not to exercise the discretion to use the
alternate 3-step approach, for example if the measurement on the last
day of a 31-day month is unusually high or low.

C.  Data Completeness

1. Proposed Provisions

	EPA proposed that if a monthly averaging time were selected, the basic
completeness requirement for a monthly average concentration to be valid
would be that at least 75 percent of the scheduled sampling days have
produced valid reported data.  EPA also proposed that if the maximum
quarterly average concentration were selected, each month in the quarter
would be required to meet this completeness test.  Two “diagnostic”
tests involving data substitution were proposed, which in some cases
would allow a reasonably confident conclusion about the existence of an
exceedance or lack thereof to be made despite data completeness of less
than 75 percent.

EPA also asked for comment, but did not propose any specifics for, two
other tests that could allow conclusions about exceedances to be made in
additional situations when data completeness was substandard.  One of
these would compare the average monthly concentration to an unspecified
fraction of the level of the NAAQS, in effect applying a safety margin
to offset the risk of error caused by the small sample size of measured
concentrations.  The other test would create a statistically derived
confidence interval for the average monthly concentration based on the
daily data and then would test whether that interval was entirely above
(indicating an exceedance) or entirely below (indicating the lack of an
exceedance) the level of the NAAQS.  These same tests would be used
under the alternative proposal of a quarterly averaging time.  However,
in the proposal, EPA described these completeness tests only in the
context of a monthly average concentration (i.e., for the proposed
second maximum monthly average form).

2. Comments on Data Completeness

	No comments were received directly on the details of the proposal
regarding data completeness.  One commenter expressed concern that the
two diagnostic tests for use when data are less than 75 percent complete
could leave an indeterminate outcome even when the weight of evidence
indicates an exceedance or a lack of an exceedance.   EPA believes that
a proposed provision of Appendix R, which is included in the final rule,
allowing for case-by-case use of incomplete data with the approval of
the Administrator allows EPA to appropriately address such a situation.

 3. Conclusions on Data Completeness

	The final rule differs from the monthly averaging time version of the
proposal in the following aspects.  These changes have been made to
align Appendix R with the selected maximum rolling 3-month averaging
time and form of the NAAQS and the final requirement for one-in-six day
sampling (discussed in section V of this preamble).  Because one-in-six
sampling means that typically only five samples will be scheduled each
month, only a single sample could be missed (and not made up) without
completeness falling below the 75 percent level.  Therefore, requiring
75 percent completeness at the monthly level could easily result in one
month in a 3-year period being judged incomplete, making it impossible
to make a finding of attainment of the NAAQS even when the available
data in that and other months strongly suggest attainment.  To avoid
this, the final rule applies the 75 percent completeness requirement at
the 3-month level by averaging the three monthly completeness values to
get the 3-month completeness value.  Specifically, under the final rule
3-month completeness would be calculated and tested for every 3-month
period. This reduces the likelihood of an incompleteness situation for
an entire 3-year evaluation period due to as few as two missed samples
in a single month.

	In the proposed rule, the two diagnostic tests based on data
substitution were applied within an individual month that has incomplete
data relative to the 75 percent requirement.  In the final rule, the
tests remain and data are still substituted within the individual month
(i.e., if a day of concentration data is missing from January in one of
the three years, the missing concentration is substituted with the
highest or lowest (depending on which diagnostic test is being applied)
available measured Pb concentration from other days in the three
Januarys.  However, the last step of the diagnostic test, comparison of
the substituted average concentration to the level of the NAAQS, is done
for the 3-month average concentration not the monthly average
concentration since a 3-month averaging time has been selected.

	EPA is not finalizing any version of either of the two incompleteness
approaches on which comment was sought, described above, because they
may potentially result in incorrect conclusions regarding violations or
the lack thereof.  Because the number of valid daily concentration
values remaining after even only a few missed days of monitoring would
be quite small, a missing sample on a high-concentration day might make
a confidence interval derived from the available data appear smaller
than the actual variability of the daily concentrations, leading to an
incorrect conclusion about the probability of a NAAQS violation.  EPA
may continue to study these or similar approaches for application in
future NAAQS reviews.  Another possible application of these approaches
could be to inform the Administrator’s case-by-case decisions on
whether to use data that are incomplete for comparison to the NAAQS, as
was proposed and as the final rule allows the Administrator to do.

D. Scaling Factors to Relate Pb-TSP and Pb-PM10

1. Proposed Provisions

	EPA proposed that Pb-PM10 monitoring could be conducted to meet Pb
monitoring requirements at the option of the monitoring agency, but that
site-specific scaling factors would have to be developed to adjust the
Pb-PM10 concentrations to represent estimated Pb-TSP concentrations
before comparison to the level of the Pb-TSP NAAQS.  One year of
side-by-side measurement with both types of samplers would be required
to collect paired data for developing these scaling factors, and Pb-TSP
monitoring could not be discontinued at a Pb-PM10 monitoring site until
the factor for that site had been approved.  The proposed Appendix R
contained detailed requirements for the number of data pairs
successfully collected during the year of testing, the degree of
correlation required between the two types of measurements, and the
stability of the ratio of concentration averages from month to month,
and also provided the formula for calculating the scaling factor.

	EPA also asked for comment on the possibility of adopting a default
scaling factor, or a set of factors applicable in different situations,
instead of requiring the development of site-specific factors.  EPA
noted in the proposal that paired Pb-TSP and Pb-PM10 data from three
historical monitoring sites suggested that site-specific scaling factors
for source-oriented monitoring sites may vary between 1.1 and 2.0; but
that the range may also be greater.  EPA asked for comment on possible
default scaling factor values within a range of 1.1 to 2.0 for
application to Pb-PM10 data collected at source-oriented monitoring
sites.  EPA also noted in the proposal that it appears that
site-specific factors generally have ranged from 1.0 to 1.4 for
non-source oriented monitoring sites (with the factors for three sites
ranging from 1.8 to 1.9), and that the ratios may be influenced by
measurement variability in both samplers as well as by actual air
concentrations. EPA asked for comment on possible default scaling factor
values within a range of 1.0 to 1.9 for application to Pb-PM10 data
collected at monitoring sites that are not source-oriented.

 2. Comments on Scaling Factors

Many commenters addressed the scaling factor issues raised in the
proposal, often as part of overarching comments on the interrelated
issues of the choice of indicator, whether and for what locations the
final rule should allow Pb-PM10 monitoring instead of TSP-Pb monitoring,
and whether and how Pb-PM10 data, if collected, should be considered in
determining compliance with or violation of the Pb-TSP NAAQS.  Comments
on the specific subject of scaling factors to relate Pb-PM10
measurements to Pb-TSP concentrations are addressed here.  Other
comments related to the Pb-PM10 versus TSP-Pb monitoring and data use
aspects of the proposal are addressed in section IV.D.

Comment on scaling factors were overwhelmingly negative towards EPA’s
proposal to allow Pb-PM10 monitoring in place of Pb-TSP monitoring at
any site on the condition that the monitoring agency first develop a
site-specific scaling factor.  Most commenters also did not support the
alternative of establishing default scaling factors.  Some commenters
proposed that instead of allowing Pb-PM10 monitoring in place of Pb-TSP
monitoring and then applying site-specific or default scaling factors to
Pb-PM10 concentrations before comparison to the NAAQS, Pb-PM10
monitoring only be allowed at certain types of sites.

Some commenters said that it would be burdensome on state monitoring
agencies to have to develop site-specific scaling factors because two
kinds of monitoring equipment would have to be deployed at each site,
one set of which would become superfluous whether or not a scaling
factor was successfully developed.  Concerns were also expressed that
the actual ratio of the two parameters could vary over time, and
therefore that EPA’s proposal that a scaling factor could be used
indefinitely once developed on the basis of one year of paired
measurements would not be protective of public health.  No comments were
received on the specifics of the proposal regarding the amount and type
of data that would be required to be collected or the specific
correlation criteria and formula for developing a site-specific scaling
factor.

The final rule does not contain any provisions for the development of
site-specific scaling factors, for two reasons.  The proposed
requirement for a year of paired measurements would require considerable
initial investment of equipment, labor time, and laboratory costs by a
monitoring agency for paired measurement of both Pb-PM10 and Pb-TSP in
hopes of obtaining the option of indefinitely monitoring only for
Pb-PM10 thereafter.  The lack of any interest in this approach on the
part of monitoring agencies is one of the reasons it is not included in
the final rule.  Second, given the considerations leading to retaining
Pb-TSP as the indicator for the NAAQS, considerable caution should be
applied on any scaling factor approach because of the uncertainty
associated with the development and use of scaling factors.

Since issuing the proposal, EPA has engaged a statistical consultant to
review whether the proposed criteria regarding the amount and type of
data that would be required to be collected and the specific correlation
criteria and formula for developing a site-specific scaling factor were
practical and scientifically sound.  This assessment examined both the
proposed criteria which were structured around the proposed monthly
averaging time and a modified approach structured around a 3-month
averaging time.  The consultant’s report has been submitted to the
public docket. This assessment was able to “test drive” the proposed
criteria and formula only on a relatively small number of data sets
containing a sufficient number of Pb-TSP and high-volume Pb-PM10 data
pairs, and as such could not be completely definitive regarding the
merits of the criteria and formula when applied to low volume Pb-PM10
data.  Also, EPA does not necessarily endorse every aspect of the
assessment or its conclusions even apart from this data type disparity.
However, EPA believes based on our review of the consultant’s work
that there are significant unresolved issues with the proposed criteria
and formula with respect to their scientific adequacy and
appropriateness for the intended purpose, and that these issues could
result in not providing the protection intended by the Pb NAAQS.  This
is another reason why the site-specific scaling factor approach is not
included in the final rule.   One finding in the consultant’s report
is that among the 21 sites where sufficient paired exist to meet the
proposed data requirements for development of site-specific scaling
factors, the proposed criteria for month-to-month consistency of the
ratios of the two types of measurement and for overall correlation
between the two measurements across the year were met at only four
sites, three of which appear to be non-source oriented.  For the
non-source oriented sites and years of data for which all the proposed
criteria were met, the scaling factors mostly fell in the range of 1.2
to 1.4.  This indicates that while the observation at proposal was true
that there are three non-source oriented sites with some paired data
that result in ratios in the range of 1.8 to 1.9, the data from these
sites would be inadequate for developing site-specific scaling factors
under the criteria of the proposed rule.

 The alternative approach of establishing default scaling factors was
also opposed by virtually all commenters who addressed it, and no
commenter supported any specific default factor or set of default
factors.  Many commenters asserted that no reliable default factor or
factors could be developed and that all Pb measurements for comparison
to the NAAQS should be Pb-TSP measurements because of the possible
presence of ultra-coarse particles containing significant amounts of Pb.
 One commenter did not oppose the concept of default scaling factors but
even that commenter said that EPA should conduct more testing before
developing such factors.  A number of commenters said that if scaling
factors are used, they should be conservative, health protective factors
to ensure that the use of Pb-PM10 monitors does not result in increased
lead exposures; some of these commenters pointed to the case of a
particular Pb monitoring site that was reported in the preamble to the
proposed rule to have a scaling factor of 2.0.  Other commenters argued
that the data set from the site (in East Helena, MT) suggesting such a
high ratio of Pb-TSP to Pb-PM10 was not representative of the current
emissions profile of sources subject to emission standards adopted since
that data set was collected, and that a scaling factor for future
application should be lower than 2.0.

The final rule does not provide a default scaling factor or set of
factors for relating the two types of Pb concentration measurements.
Any default factor or factors would be subject to greater technical
pitfalls than would site-specific scaling factors.  EPA believes,
considering the data presented at the time of the proposal, the
comments, and the consultant’s assessment described above, that the
variability and thus the uncertainty in the relationship of the two
types of Pb measurement is not conducive to developing a default scaling
factor to address all situations in which it might be applied, unless it
were set so large that it effectively discouraged Pb-PM10 (see below).
Also, while in concept multiple default scaling factors applicable to
different situations should be more successful in avoiding this problem,
they could never be as good as site-specific factors about which EPA has
the technical reservations described above, in addition to the practical
reservations expressed by all monitoring agencies which commented on the
subject.  For these reasons, EPA is not adopting either site specific or
default scaling factors for use as described in the proposal.

However, as discussed below, the final rule does permit the use of
Pb-PM10 monitoring, and direct comparison of Pb-PM10 concentrations to
the Pb-TSP NAAQS, in certain situations in which EPA can be confident
that such monitoring and data comparisons will in fact be a protective
approach, and where such monitoring may be attractive for other reasons
that were described in the proposal and also noted by commenters.
Several commenters supported allowing Pb-PM10 monitoring to meet Pb
monitoring requirements in some situations and, in only those
situations, comparing Pb-PM10 data directly without any scaling factor
to the Pb-TSP indicator-based NAAQS.   The thrust of these comments was
that this approach to making use of Pb-PM10 monitors and their data
would be an acceptably protective approach provided that Pb-PM10
monitoring and associated comparison to the NAAQS is limited to sites
where there is good reason to expect that Pb-TSP concentrations are well
below the level of the NAAQS and/or that based on the nature of the
nearby sources the fraction of ultra-coarse Pb in Pb-TSP would be low.
Some commenters recommended this approach to monitoring only if the
NAAQS has been set at a particular level.  Because an appropriate
response to these comments involves many of the same facts and
considerations that EPA has taken into account in addressing the
comments explicitly about scaling factors, above, we address these
comments here as part of the discussion of data interpretation, noting
that section V of this preamble discusses in more detail the changes to
40 CFR 58 associated with our disposition of these comments.

EPA agrees that given the several attractions of low-volume Pb-PM10
monitoring as far as accuracy and representativeness over an area, it is
appropriate to allow for the use of Pb-PM10 monitors instead of Pb-TSP
monitors at locations where there is very little likelihood that Pb-TSP
levels will exceed the NAAQS.  We also believe that in general the
non-source oriented monitoring sites required in CBSAs with populations
over 500,000 (see Section V) meet this condition.  Our experience with
paired data at apparently non-source oriented sites, as detailed in the
Staff Paper and the preamble to the proposal, augmented by the
statistical consultant’s report mentioned above, supports the
conclusion that the ratio of Pb-TSP concentrations to Pb-PM10
concentrations at non-source oriented sites is consistently within the
range of 1.0 to 1.4.  The corresponding range of ultra-coarse Pb
fraction is zero to 0.3.  Also, a new EPA staff analysis, completed
since proposal, of recent Pb-TSP concentrations at existing monitoring
sites that appear to be non-source oriented (including all sites with
complete data from at least one Pb-TSP monitor, not just sites with
paired data) shows that nearly all of them have been well below the
final level of the NAAQS; in fact, nearly all have had 3-month average
Pb-TSP concentrations in 2005-2007 that do not exceed 50 percent of the
NAAQS.  Therefore there is, in the Administrator’s judgment, little
risk to the protective effect of the NAAQS in allowing the use of
Pb-PM10 monitors at such sites and in comparing the Pb-PM10 measurements
directly to the Pb-TSP NAAQS.  The final rule allows this, with two
safeguards to further ensure the protection intended by the Pb-TSP
NAAQS.  The first protection is a pre-condition that the available
Pb-TSP monitoring data at the site during the previous three years, if
any are available, do not show any 3-month average concentrations equal
to or greater than 0.10 µg/m3, which is 67 percent of the final NAAQS
level.  Thus unlike the proposed use of scaling factors, where an
approved scaling factor could have been applied to any and all recorded
measured levels of Pb-PM10, increasing the concern over the
protectiveness of this approach, here the use of Pb-PM10 data does not
raise similar concerns.  To guard against the possibility that any of
these required sites may be different in a way that contradicts the
previous experience at such sites and against the possibility that
source conditions around one or more of these monitoring sites may
change over time, the final rule also provides that if any 3-month
average concentration of Pb-PM10 is ever observed to be equal to or
greater than 0.10 µg/m3, a Pb-TSP monitor must be installed.  This 33
percent margin against the level of the NAAQS is protective for the long
run situation, given that the available data strongly suggest that
scaling factors will rarely if ever be greater than 1.4 at non-source
oriented sites.  If the 3-month average Pb-PM10 concentration at a site
was below 0.10 µg/m3and the scaling factor at that site was 1.4, the
3-month Pb-TSP concentration would be below the level of the NAAQS.  EPA
notes that some commenters suggested that this flexibility be
pre-conditioned on there being site-specific affirmative evidence that
Pb-TSP concentrations are less than 50 percent of the NAAQS.  However,
for many of the required monitoring sites of this type there will be no
pre-existing Pb monitoring data and in the absence of a dominant nearby
industrial source attempts to estimate Pb concentrations using air
quality modeling techniques would be very uncertain.  EPA believes that
the evidence from the many existing non-source oriented sites is
sufficient to support allowing this flexibility without a site-specific
hurdle, other than the provision tied to existing monitoring data if
there are any.

  EPA has also considered whether any of the required source-oriented
sites should be allowed to be monitored for Pb-PM10 rather than Pb-TSP,
also with the Pb-PM10 concentrations compared directly to the Pb-TSP
NAAQS.  As explained in Section V, the final requirements for monitoring
near sources of Pb are based on the quantity of Pb emitted being above
an emissions threshold.  We are extending the allowance for the use of
Pb-PM10 monitors to allow Pb-PM10 monitors without the use of scaling
factors for source-oriented monitors where Pb concentrations are
expected to be less than 0.10 µg/m3 (based on modeling or historic
data) and where the ultra-course Pb fraction is expected to be low.  We
are also requiring, as for non-source oriented sites, that a Pb-TSP
monitor be required at a source-oriented site if at some point in the
future the Pb-PM10 monitor shows that Pb-PM10 concentrations are equal
to or greater than 0.10 µg/m3.  A state may also operate non-required
Pb monitors at any other locations of its choosing, and these may be of
any type.

3. Conclusions on Scaling Factors

	The final version of Appendix R eliminates all reference to scaling
factors. As explained in detail in section V, the final rule allows
Pb-PM10 monitoring as a surrogate for Pb-TSP monitoring under certain
specified conditions, with continuation of such monitoring being
contingent on measured 3-month average Pb-PM10   concentrations
remaining without application of any scaling factor staying less than
0.10 µg/m3.  Section IV.D discusses how Pb-PM10 monitoring data will be
used as a surrogate for Pb-TSP in comparisons to the Pb-TSP NAAQS to
determine compliance with or violation of the NAAQS.

E. Use of Pb-TSP and Pb-PM10 Data

1. Proposed Provisions

The proposed text of Appendix R provided that complete Pb-TSP data would
be given precedence over both incomplete and complete (scaled) Pb-PM10
data, when both were collected in the same month at the same site, and
prohibited the mixing of the two types of data in calculating the
average Pb concentration for a single month.  Pb-TSP data would be used
in preference to Pb-PM10 data to form a monthly average Pb concentration
whenever the Pb-TSP data meets the test for completeness and valid
monthly average, i.e., whenever 75 percent of scheduled samples have
valid data or one or the other of the two diagnostic tests in the case
of less than 75 percent completeness results in a valid monthly average.
 If the Pb-TSP data were not complete enough to allow development of a
monthly average, the available scaled Pb-PM10 data from the site for
that month would be used provided they were complete enough.  Scaled
Pb-PM10 data could be used to show both compliance and violation of the
NAAQS.

2. Comments on Use of Pb-TSP and Pb-PM10 Data

No comments were received specifically on the proposed provisions of
Appendix R addressing the precedence between Pb-TSP and Pb-PM10 data.
However, the elimination of scaling factors from the final rule and the
inclusion of flexibility for Pb-PM10 monitoring only in limited
situations, done by EPA in the final rule in response to comments
summarized above, have required EPA to reconsider the proposed
provisions on the use of Pb-PM10 data and to make changes in the final
version of Appendix R.

	First, EPA has considered whether a comparison of Pb-PM10 monitoring
data to the NAAQS should be able to result in a conclusion that the
NAAQS has been violated if the comparison shows that a 3-month average
Pb-PM10 concentration is above the level of the Pb-TSP NAAQS.  This
situation could occur at a site that is required by the final rule’s
Pb monitoring requirement which is allowed to use Pb-PM10 monitoring in
place of Pb-TSP monitoring, although EPA believes it is unlikely given
the preconditions in the final rule regarding which required sites may
use Pb-PM10 monitoring.  It might also occur at a non-required site,
where the rule does not attempt to restrict the monitoring agency’s
flexibility to use Pb-PM10 monitoring and thus a monitoring agency might
choose not to adhere to the same preconditions.  Given that a Pb-PM10
monitor will generally capture somewhat less or at most the same
quantity of Pb as would a Pb-TSP monitor on a given day, EPA believes
that if a 3-month average of Pb-PM10 concentrations is based on data
that meets the 75 percent completeness test, including the associated
diagnostic data substitution tests described in IV.B, and is above the
level of the NAAQS, that situation should be considered to be a NAAQS
violation.

This should be the case even if a Pb-TSP monitor at the same site has
recorded a complete, valid 3-month average Pb-TSP concentration below
the NAAQS for the same 3-month period.  As just stated, a Pb-PM10
monitor will generally capture somewhat less or at most the same
quantity of Pb as would a Pb-TSP monitor on a given day. While it is
conceivable that a malfunction of a Pb-PM10 monitor, an operator error,
or simple variability could cause a single measured Pb-PM10
concentration to be higher than a valid same-day collocated Pb-TSP
concentration measurement, EPA expects based on experience that this
will be rare, particularly because 40 CFR part 58 appendix A and EPA
quality assurance guidance contain required and recommended procedures
to avoid equipment malfunctions and operator errors and to invalidate
any data affected by them before submission to EPA’s air quality data
base.  Also, since 3-month averages will be based on multiple
measurements, a significant effect on 3-month average concentrations
from such factors is an even more remote possibility.  EPA believes that
the only situation at all likely to arise in which a complete 3-month
average of Pb-PM10 indicates a NAAQS violation while a complete 3-month
average of Pb-TSP for the same period does not would be when the Pb-PM10
average includes more days of monitoring than the Pb-TSP average, and
those additional days tend towards high concentrations.  This can occur
if the Pb-PM10 measurements are being taken on a more frequent schedule,
if they are missing fewer days of scheduled data than for the Pb-TSP
measurements (counting make-up samples), or if more extra samples are
taken for Pb-PM10 than for Pb-TSP.  Regardless of which cause or causes
are responsible, EPA believes that the Pb-PM10 average based on more
days of sampling would generally be the more robust indication of
ambient concentrations, and the site should be considered to have
violated the NAAQS.

	Next, EPA has considered whether a comparison of Pb-PM10 monitoring
data to the NAAQS should be able to result in a conclusion that the
NAAQS has been met if the comparison shows that all the 3-month average
Pb-PM10 concentrations over a 3-year period are below the level of the
Pb-TSP NAAQS and there is no Pb-TSP data showing a violation, or should
such a comparison only lead to the more limited conclusion that there
has not been a demonstrated NAAQS violation.  In considering this issue,
EPA notes that while the final rule allows the use of Pb-PM10 monitoring
in place of Pb-TSP monitoring only at required non-source oriented
monitoring sites that by their nature are expected to have a low
fraction of ultra-coarse Pb, even a low fraction is not a zero fraction.
 Also, the expectation of a low ultra-coarse fraction may turn out to be
incorrect due to unexpected causes.  Also, monitoring agencies may also
deploy Pb-PM10 monitors at non-required sites which may have higher or
unknown fractions of ultra-coarse Pb.  Appendix R must anticipate the
availability of data from such sites, as EPA believes that such data
should not be ignored and that states should know in advance how it will
be used if collected.  Because Pb-PM10 data may include data from sites
with non-zero ultra-coarse fractions and may include data from sites
with high or unknown ultra-coarse factions, EPA believes it would
undermine the protectiveness of the NAAQS to always allow any Pb-PM10
data from any monitoring site to demonstrate compliance with the NAAQS.
Some site applicability restriction and/or compliance margin when using
Pb-PM10 data to show compliance would be needed to avoid undermining the
protectiveness of the NAAQS.   The technical issues to be overcome in
designing site applicability restrictions and/or compliance margins
would be the same as the issues that arise when considering default
scaling factors, described above.

	EPA is also mindful that the distinction between a finding of
compliance with the NAAQS and not making a finding of violation is much
more theoretical than practical.  The distinction is not important to
the initial stages of the implementation process for a revised NAAQS,
because (1) by the time of the initial designations very few Pb-PM10
monitoring sites will have three years of data so a finding of
compliance would not be possible anyway, and (2) there is no practical
difference in planning or implementation requirements between areas that
have been found to be in compliance with the NAAQS and areas for which
it can only be said that they have not been found to be in violation of
the NAAQS.  However, later, for an area initially designated
nonattainment, an affirmative finding that the area is complying with
the NAAQS is required in order for the area to be redesignated
attainment (also referred to as maintenance) after emission controls are
implemented.  In the latter situation, however, a Pb-TSP monitor should
be operating at any site that has initially shown a violation based on
either Pb-TSP or Pb-PM10, since Pb-TSP monitoring must begin at any site
where Pb-PM10 concentrations have exceeded even 50 percent of the NAAQS.
 This makes it moot whether Pb-PM10 data alone can be used to
redesignate a nonattainment area to attainment after emission controls
are implemented.  In light of the technical issues and the lack of any
substantive consequences, the final version of Appendix R does not allow
Pb-PM10 data to be used to show affirmative compliance with the NAAQS.

	The above discussion addresses the compliance versus violation
consequences of comparing Pb-PM10 and Pb-TSP data to the Pb-TSP NAAQS.
EPA has also considered the issue of how design values should be
determined when there is only Pb-PM10 data or there is a mixture of
Pb-PM10 data and Pb-TSP data for a single monitoring site over a given
period.  In addition to conveying the compliance or noncompliance status
of a monitoring site, design values are also used as an informative
indicator of pollutant levels more generally.  For the revised Pb NAAQS,
the design value in simple terms is the highest valid 3-month average
concentration at a monitoring site over whatever period of three years
is being reported.  It is necessary to be specific in Appendix R about
whether and when Pb-PM10 data can be used in the calculation of the
design value.  In the proposal, the simple principle applied was that
complete Pb-TSP data for a month or quarter always would have precedence
over scaled Pb-PM10 data, but that in the absence of complete Pb-TSP
data, scaled Pb-PM10 data would be used regardless of the resulting
value of the design value.  For the same reason described above that
Pb-PM10 data will not be allowed to support a finding of compliance with
the NAAQS, it would be inappropriate to use such data to develop a
design value whose value is below the level of the NAAQS.  Therefore,
the final version of Appendix R provides that the only situation in
which Pb-PM10 data will be used to calculate the design value is when
doing so results in a higher design value than using only Pb-TSP data
and that design value is above the level of the NAAQS.

3. Conclusions on Use of Pb-TSP and Pb-PM10 Data

	The final version of Appendix R specifies that the NAAQS is violated
whenever Pb-PM10 data or Pb-TSP data result in a 3-month average
concentration above the NAAQS level, but that compliance with the NAAQS
can only be demonstrated using Pb-TSP data.  Pb-PM10 data will be used
in the calculation of a design value only when doing so results in a
higher design value than using only Pb-TSP data and that design value is
above the level of the NAAQS.

F. Data Reporting and Rounding

1. Proposed Provisions

EPA proposed that individual daily concentrations of Pb be reported to
the nearest thousandth µg/m3 (0.xxx) with additional digits truncated,
and that monthly averages calculated from the daily averages would be
rounded to the nearest hundredth µg/m3 (0.xx). Decimals 0.xx5 and
greater would be rounded up, and any decimal lower than 0.xx5 would be
rounded down.  E.g., a monthly average of 0.104925 would round to 0.10
and a monthly average of 0.10500 would round to 0.11. Because the
proposed NAAQS level would be stated to two decimal places, no
additional rounding beyond what is specified for monthly averages would
be required before a design value selected from among rounded monthly
averages would be compared to the level of the NAAQS.

2. Comments on Data Reporting and Rounding

No comments were received on this aspect of the proposal.

3. Conclusions on Data Reporting and Rounding

The final version of Appendix R differs from that proposed because the
proposed version addressed a single month as the averaging time for the
NAAQS and the final NAAQS is based on a 3-month average concentration.
In the preamble to the proposal, EPA did not specifically address
whether and how, in the case of the NAAQS being based on a 3-month
averaging time, calculated monthly averages would be rounded before
being used to calculate the 3-month average.  The final version of
Appendix R specifies that all digits of the monthly average shall be
retained for the purpose of calculating the 3-month average, with the
3-month average then rounded to the nearest hundredth µg/m3, i.e.,
3-month average decimals 0.xx5 and greater would be rounded up and any
decimal lower than 0.xx5 would be rounded down.  Because individual
monthly averages are never compared to the level of the NAAQS there is
no need to specify a rounding convention for them, and retaining all
digits until the final comparison of the 3-month average to the NAAQS
allows a more precise determination of compliance compared to rounding
at both the monthly and 3-month levels.

G. Other Aspects of Data Interpretation

One implication of the selection of a rolling 3-month period as the
averaging time of the NAAQS is that there will be two 3-month periods
that span each pair of adjacent calendar years: November-January and
December-February.  EPA has considered whether, for any
three-calendar-year period, the 3-month averaging periods including one
or both of the two months of the year prior to those three years and/or
the averaging periods including one or both of the two months following
those three years will be included in determining whether a monitoring
site has met or violated the NAAQS.  This issue was not discussed in the
proposal, because the monthly average and calendar quarterly average
options discussed in the proposal do not raise this issue.  The final
version of Appendix R provides that the 3-month averages which include
either of the two months prior to a three-calendar-year period will be
associated with that 3-year period, and that the 3-month averages which
include either of the two months after the three-calendar-year period
will not be associated with it.  The latter two months would be within
the next 3-year period and their data would affect compliance during
that next 3-year period.  Thus, for example, the thirty-six 3-month
averages that will be considered in determining compliance with the
NAAQS for the 3-year “2010-2012” evaluation period will be based on
data from November and December of 2009, and all of 2010, 2011, and
2012.  Data from November 2009 will be used as part of the calculation
of one 3-month average, and data from December 2009 will be used as part
of the calculation of two 3-month averages.  Data from November and
December of 2012 will be used but only for 3-month averages which are
made up solely of months in 2012.  Thus, for the 2010-2012 period,
November 2009 through January 2010 is the first 3-month period and
October through December 2012 is the last 3-month period.

This approach has been selected for practical reasons, because the
once-per-year deadline for certifying data submitted to AQS means that
data from January and February of the year after a three-calendar-year
period will most often still be preliminary and uncertified as to
completeness and accuracy for 12 months beyond when data from the
three-calendar-year period itself (and the two previous months) are
final and ready to be used for compliance determinations.

Generally, a violation will have occurred if any of the 36 three-month
average concentrations of either Pb-TSP or Pb-PM10 exceeds the level of
the NAAQS, and a finding of compliance will require that all 36 3-month
averages of Pb-TSP be at or below the level of the NAAQS.  The final
Appendix R addresses the special situation of a new monitoring site
which has started sampling by January 15 of a certain year.  After the
first three years of data collection, only 34 3-month average
concentrations will be available.  In this situation, Appendix R
provides that a finding of compliance will be made if all 34 available
3-month average concentrations of Pb-TSP are at or below the level of
the NAAQS.

As discussed in Section V on monitoring requirements, EPA proposed and
is finalizing a change to the Pb monitoring requirements to no longer
allow monitoring agencies to combine several daily Pb-TSP filters for
chemical analysis, at required Pb monitoring sites.  The proposed
Appendix R presumed this change and did not address how data from such
“composite” samples would be used in comparisons to the NAAQS.
However, on further reflection EPA believes that whatever composite
sample data have been collected and submitted to AQS before the
prohibition on using the composite sample approach takes effect should
be considered for purposes of initial designations under the revised
NAAQS, if those data fall within the period on which designations will
be based.  The final version of Appendix R therefore includes specific
provisions addressing how to account for composite sample data in
determining data completeness and in calculating a monthly and 3-month
average concentration value.  These provisions will also govern the use
of any composite sample data that are collected at non-required
monitoring sites, indefinitely.  The only noteworthy issue EPA had to
consider in developing these provisions was what to do when the
submitted data for a monitoring site includes both a composite sample Pb
value and one or more individual daily sample Pb values.  Because it is
impossible to tell the exact days represented by a composite sample,
Appendix R specifies that either the composite sample or the available
daily data (if complete daily data were collected) will be used
depending on which has the lower pollutant occurrence code, but they
will not be combined because that might give double weight to some days.

V.	Ambient Monitoring Related to Revised Lead Standards

We are finalizing several changes to the ambient air monitoring and
reporting requirements for Pb to account for the revised NAAQS and to
update the Pb monitoring network.  Ambient Pb monitoring data are used
for comparison to the Pb NAAQS, for analysis of trends and
accountability in areas with sources that have implemented controls, in
the assessment of control strategies, for evaluating spatial variation
of Pb concentrations across an area, and as an input to health studies
used to inform reviews of the NAAQS.  Ambient data are collected and
reported by state, local, and tribal monitoring agencies (“monitoring
agencies”) according to the monitoring requirements contained in 40
CFR parts 50, 53, and 58.  This section summarizes the proposed changes
to the monitoring requirements in the May 20, 2008 notice of proposed
rulemaking, the major comments received on the proposed changes, and the
final changes to the Pb monitoring regulations being promulgated with
this action.  This section is divided into discussions of the monitoring
requirements for the sampling and analysis methods (including quality
assurance requirements), network design, sampling schedule, data
reporting, and other miscellaneous requirements.

A.	Sampling and Analysis Methods

We are finalizing changes to the sampling and analysis methods for the
Pb monitoring network.  Specifically, we are continuing to use the
current Pb-TSP Federal Reference Method (FRM, 40 CFR part 50 Appendix
G), but are finalizing a new Federal Reference Method (FRM) for
monitoring Pb in PM10 (Pb-PM10) for the limited situations where it will
be permitted, lowering the Pb concentration range required during Pb-TSP
and Pb-PM10 candidate Federal Equivalent Method (FEM) comparability
testing, and finalizing changes to the quality assurance requirements
for Pb monitoring.  The following paragraphs provide background,
rationale, and details for the final changes to the sampling and
analysis methods.

1.	Pb-TSP Method

No substantive changes are being made to the Pb-TSP method.  The current
FRM for Pb sampling and analysis is based on the use of a high-volume
TSP FRM sampler to collect the particulate matter sample and the use of
atomic absorption (AA) spectrometry for the analysis of Pb in a nitric
acid extract of the filter sample (40 CFR 50 Appendix G).  There are 21
FEMs currently approved for Pb-TSP.  All 21 FEMs are based on the use of
high-volume TSP samplers and a variety of approved equivalent analysis
methods.

a.	Proposed Changes

We stated in the NPR that if the final standard is based on Pb-TSP, we
believed it would be appropriate to continue use of the current
high-volume FRM for measuring Pb-TSP.  We proposed to make several minor
changes in 40 CFR 50 Appendix G to correct reference citations.
However, we did not propose any substantive changes to Appendix G.

In addition, we stated in the NPR that we believe that low-volume Pb-TSP
samplers might be superior to high-volume TSP samplers.  We pointed out
that presently, a low-volume TSP sampler cannot obtain FRM status,
because the FRM is specified in design terms that preclude designation
of a low-volume sampler as a FRM.  We also suggested that a low-volume
Pb-TSP monitoring system (including an analytical method for Pb) could
be designated as a FEM Pb-TSP monitor, if side-by-side testing were
performed as prescribed by 40 CFR 53.33.  We proposed amendments to 40
CFR 53.33 (described below in section V.A.3) to make such testing more
practical and to clarify that both high-volume and low-volume TSP
methods could use this route to FEM status.  We also held a consultation
with the CASAC Ambient Air Monitoring and Methods (AAMM) Subcommittee on
approaches for the development of a low-volume TSP sampler FRM or FEM.

b.	Comments on Pb-TSP Method

	This section addresses comments we received on our proposal to continue
the use of the Pb-TSP FRM as the monitoring method for the Pb NAAQS, and
comments on the use of low-volume TSP samplers as either a FEM or FRM
for Pb-TSP.  We also received comments on a number of related topics
that are not discussed in this section.  We received comments on the use
of Pb-PM10 as the Pb indicator, and those comments are addressed in
Section II.C.1 of this preamble. We received comments on the use of
scaled Pb-PM10, or other ways to supplement Pb-TSP monitoring data with
Pb-PM10 data, and those comments are addressed in Section IV.C, and in
Section V.B of this preamble.

We received a number of comments on our proposal to continue the use of
high-volume TSP samplers as the sampling method for Pb.   In their
comments on the proposed rule, CASAC reiterated their concerns over the
measurement uncertainty due to effects of wind speed and wind direction
on sampling efficiency.  These concerns were discussed in detail in our
proposed rule, and as such are not reiterated here.  However, CASAC
stated that if the final level of the NAAQS were to be set at 0.10 (g/m3
or above, then the high-volume Pb-TSP sampler should be used.  Some
public commenters also stated similar concerns with the performance of
the Pb-TSP sampler.

A large number of other commenters stated that the high-volume TSP
sampler should continue to be the sampler for determining compliance
with the Pb NAAQS.  They expressed concerns that PM10 samplers would not
capture ultra-coarse particles (i.e., particulate matter with an
aerodynamic diameter greater than 10 µm), and could greatly
underestimate Pb concentrations in the ambient air, especially near Pb
sources.

Despite some limitations with sampler performance and consistent with
CASAC advice for methods at the level of the NAAQS we have chosen, we
believe the high-volume sampler is the most appropriate currently
available sampler for the measurement of Pb-TSP in ambient air.
Ultra-coarse particulate matter (larger than PM10) can contribute to a
significant portion of the total Pb concentration in ambient air,
especially near Pb sources (Schmidt, 2008) where Pb-TSP concentrations
may be as much as twice as high as Pb-PM10.   Furthermore, we believe
the precision and bias of the high-volume TSP sampler are acceptable and
similar to those for other PM samplers (Camalier and Rice, 2007).

We received several comments supporting the need for the development of
a low-volume Pb-TSP sampler.  However, in our consultation with
CASAC’s AAMM Subcommittee, we were cautioned against finalizing a new
low-volume Pb-TSP FRM without an adequate characterization of the
sampler’s performance over a wide range of particle sizes.   We agree
with the interest for a low-volume Pb-TSP sampler and the desire for
such a sampler to be adequately characterized prior to being promulgated
as a new FRM.  Accordingly, we plan to further investigate the
possibility of developing a low-volume FRM in the future.

c.	Decisions on Pb-TSP Method

	We are maintaining the current FRM and FEMs for Pb-TSP as the sampling
and analysis methods for monitoring for the Pb NAAQS.  As proposed, we
are making minor editorial changes to 40 CFR 50 Appendix G (the FRM for
Pb-TSP) to correct some reference citations.  We are not making any
other substantive changes to Appendix G.

 2.	Pb-PM10 Method

	We are finalizing a new FRM for Pb-PM10 monitoring based on the use of
the low-volume PM10C FRM (40 CFR part 50, Appendix O) sampler coupled
with energy dispersive x-ray fluorescence (XRF) as the analysis method.
This section describes the proposed Pb-PM10 FRM, the comments we
received, and the final Pb-PM10 FRM requirements being promulgated with
this action.

a. 	Proposed FRM for Pb-PM10 Monitoring

We proposed a new Pb-PM10 FRM based on the use of the already
promulgated PM10C FRM coupled with XRF as the analysis method.  We
proposed to use the low-volume PM10C sampler for the FRM for Pb-PM10
rather than the existing PM10 FRM specified by Appendix J, for several
reasons.  The low-volume PM10C FRM sampler meets more demanding
performance criteria (Appendix L) than are required for the PM10
samplers described in Appendix J.   PM10C samplers can be equipped with
sequential sampling capabilities (i.e., the ability to collect more than
one sample between operator visits).  The low-volume PM10C sampler can
also precisely maintain a constant sample flow rate corrected to actual
conditions by actively sensing changes in temperature and pressure and
regulating sampling flow rate.  Use of a low-volume sampler for the
Pb-PM10 FRM would also provide network efficiencies and operational
consistencies with the samplers that are in widespread use for the PM2.5