Document ID: EPA-HQ-OAR-2006-0735-5895
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2008-10-16T04:00Z

ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 50, 51, 53 and 58

[EPA-HQ-OAR-2006-0735; FRL-_____- _]

RIN 2060-AN83

	National Ambient Air Quality Standards for Lead

AGENCY:  Environmental Protection Agency (EPA).

ACTION:  Final rule.

SUMMARY:  Based on its review of the air quality criteria and national
ambient air quality standards (NAAQS) for lead (Pb), EPA is making
revisions to the primary and secondary NAAQS for Pb to provide requisite
protection of public health and welfare, respectively.  With regard to
the primary standard, EPA is revising the level to 0.15 µg/m3.  EPA is
retaining the current indicator of Pb in total suspended particles
(Pb-TSP).  EPA is revising the averaging time to a rolling 3-month
period with a maximum (not-to-be-exceeded) form, evaluated over a 3-year
period.  EPA is revising the secondary standard to be identical in all
respects to the revised primary standard.

EPA is also revising data handling procedures, including allowance for
the use of Pb-PM10 data in certain circumstances, and the treatment of
exceptional events, and ambient air monitoring and reporting
requirements for Pb, including those related to sampling and analysis
methods, network design, sampling schedule, and data reporting. 
Finally, EPA is revising emissions inventory reporting requirements and
providing guidance on its approach for implementing the revised primary
and secondary standards for Pb.    

DATES:  This final rule is effective on [insert date 60 days after date
of publication in the Federal Register].  

ADDRESSES:  EPA has established a docket for this action under Docket ID
No. EPA-HQ-OAR-2006-0735.  All documents in the docket are listed on the
  HYPERLINK "http://www.regulations.gov"  www.regulations.gov  website. 
Although listed in the index, some information is not publicly
available, e.g., confidential business information or other information
whose disclosure is restricted by statute.  Certain other material, such
as copyrighted material, will be publicly available only in hard copy
form.  Publicly available docket materials are available either
electronically through   HYPERLINK "http://www.regulations.gov" 
www.regulations.gov  or in hard copy at the Air and Radiation Docket and
Information Center, EPA/DC, EPA West, Room 3334, 1301 Constitution Ave.,
NW, Washington, DC.  The Public Reading Room is open from 8:30 a.m. to
4:30 p.m., Monday through Friday, excluding legal holidays.  The
telephone number for the Public Reading Room is (202) 566-1744 and the
telephone number for the Air and Radiation Docket and Information Center
is (202) 566-1742.  

FOR FURTHER INFORMATION CONTACT:  For further information in general or
specifically with regard to sections I through III or VIII, contact Dr.
Deirdre Murphy,  Health and Environmental Impacts Division, Office of
Air Quality Planning and Standards, U.S. Environmental Protection
Agency, Mail code C504-06,  Research Triangle Park, NC 27711; telephone:
919-541-0729; fax: 919-541-0237; email:   HYPERLINK
"mailto:Murphy.deirdre@epa.gov"  Murphy.deirdre@epa.gov . With regard to
section IV, contact Mr. Mark Schmidt, Air Quality Analysis Division,
Office of Air Quality Planning and Standards, U.S. Environmental
Protection Agency, Mail code C304-04,  Research Triangle Park, NC 27711;
telephone: 919-541-2416; fax: 919-541-1903; email:   HYPERLINK
"mailto:Schmidt.mark@epa.gov"  Schmidt.mark@epa.gov .  With regard to
section V, contact Mr. Kevin Cavender, Air Quality Analysis Division,
Office of Air Quality Planning and Standards, U.S. Environmental
Protection Agency, Mail code C304-06,  Research Triangle Park, NC 27711;
telephone: 919-541-2364; fax: 919-541-1903; email:   HYPERLINK
"mailto:Cavender.kevin@epa.gov"  Cavender.kevin@epa.gov .  With regard
to section VI, contact Mr. Larry Wallace, Ph.D., Air Quality Policy
Division, Office of Air Quality Planning and Standards, U.S.
Environmental Protection Agency, Mail code C539-01, Research Triangle
Park, NC 27711; telephone: 919-541-0906; fax: 919-541-0824; email:  
HYPERLINK "mailto:Wallace.larry@epa.gov"  Wallace.larry@epa.gov .  With
regard to section VII, contact Mr. Tom Link, Air Quality Policy
Division, Office of Air Quality Planning and Standards, U.S.
Environmental Protection Agency, Mail code C539-04, Research Triangle
Park, NC 27711; telephone: 919-541-5456; email:   HYPERLINK
"mailto:Link.tom@epa.gov"  Link.tom@epa.gov .

SUPPLEMENTARY INFORMATION:

Table of Contents 

	The following topics are discussed in this preamble:

I.  Summary and Background

A. Summary of Revisions to the Lead NAAQS

B. Legislative Requirements

C. Review of Air Quality Criteria and Standards for Lead

D. Current Related Control Requirements

E. Summary of Proposed Revisions to the Lead NAAQS

F. Organization and Approach to Final Lead NAAQS Decisions

II. Rationale for Final Decisions on the Primary Lead Standard

A. Introduction

  1. Overview of Multimedia, Multipathway Considerations and Background

  2. Overview of Health Effects Information

	a.  Blood Lead

	b.  Array of Health Effects and At-risk Subpopulations

	c.  Neurological Effects in Children

  3. Overview of Human Exposure and Health Risk Assessments

 B. Need for Revision of the Current Primary Lead Standard

  1. Introduction

  2. Comments on the Need for Revision

  3. Conclusions Regarding the Need for Revision

C. Conclusions on the Elements of the Primary Lead Standard

  1. Indicator

		a. Basis for Proposed Decision

		b. Comments on Indicator

		c. Conclusions on Indicator

  2. Averaging Time and Form

a. Basis for Proposed Decision

		b. Comments on Averaging Time and Form

		c. Conclusions on Averaging Time and Form

  3. Level

a. Basis for Proposed Range

b. Comments on Level

c. Conclusions on Level

D. Final Decision on the Primary Lead Standard

III.  Secondary Lead Standard

A. Introduction

  1. Overview of Welfare Effects Evidence

  2. Overview of Screening Level Ecological Risk Assessment

B. Conclusions on the Secondary Lead Standard

  1. Basis for Proposed Decision

  2. Comments on the Proposed Secondary Standard

  3. Administrator’s Conclusions 

C. Final Decision on the Secondary Lead Standard

IV.  Appendix R - Interpretation of the NAAQS for Lead

A. Ambient Data Requirements

   1. Proposed Provisions

   2. Comments on Ambient Data Requirements

   3. Conclusions on Ambient Data Requirements

B. Averaging Time and Procedure

   1. Proposed Provisions

   2.  Comments on Averaging Time and Procedure

   3. Conclusions on Averaging Time and Procedure

C. Data Completeness

   1. Proposed Provisions

   2. Comments on Data Completeness

   3. Conclusions on Data Completeness

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

   1. Proposed Provisions

   2. Comments on Scaling Factors

   3. Conclusions on Scaling Factors

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

   1. Proposed Provisions

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

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

F. Data Reporting and Rounding

    1. Proposed Provisions

    2. Comments on Data Reporting and Rounding

    3. Conclusions on Data Reporting and Rounding

G. Other Aspects of Data Interpretation

V. Ambient Monitoring Related to Revised Lead Standards

A.   Sampling and Analysis Methods

   1.  Pb-TSP Method

    	a. Proposed Changes

    	b. Comments on Pb-TSP Method

    	c. Decisions on Pb-TSP Method

  2.  Pb-PM10 Method

    	a. Proposed FRM for Pb-PM10 Monitoring

    	b. Comments on Proposed Pb-PM10 FRM

    	c. Decisions on Pb-PM10 FRM

  3.  FEM Requirements

    	a. Proposed FEM Requirements

    	b. Comments 

    	c. Decisions on FEM Requirements

  4.  Quality Assurance Requirements

    	a. Proposed Changes

    	b. Comments 

    	c. Decisions on Quality Assurance Requirements

B.  Network Design

  1. Proposed Changes

  2.  Comments on Network Design

	a.Source-oriented monitoring

	b. Non-source oriented monitoring

	c. Roadway Monitoring

	d.  Use of Pb-PM10 Monitors

	e.  Required timeline for monitor installation and operation

  3.  Decisions on Network Design Requirements

C.  Sampling Frequency

D.  Monitoring for the Secondary Standard

E.  Other Monitoring Regulation Changes

  1.  Reporting of Average Pressure and Temperature

  2.  Special Purpose Monitoring

  3.  Reporting of Pb-TSP Concentrations

VI. Implementation Considerations

 A. Designations for the Lead NAAQS

1.  Proposal

2.  Comments and Responses

3.  Final 

  B. Lead Nonattainment Area Boundaries

1.  Proposal

2.  Comments and Responses

3.  Final

  C. Classifications

	1.  Proposal

2.  Comments and Responses

3.  Final

  D. Section 110(a)(2) Lead NAAQS Infrastructure Requirements

	1.  Proposal

2.  Final

  E. Attainment Dates

	1.  Proposal

2.  Comments and Responses

3.  Final

  F. Attainment Planning Requirements

1. RACM/RACT for Lead Nonattainment Areas

	a.  Proposal

	b.  Comments and Responses 

	c.  Final

2. Demonstration of Attainment for Lead Nonattainment Areas

	a.  Proposal

	b.  Final

3. Reasonable Further Progress (RFP)

	a.  Proposal

	b.  Comments and Responses 

	c.  Final

4. Contingency Measures

	a.  Proposal

	b.  Comments and Responses 

	c.  Final

5. Nonattainment New Source Review (NSR) and Prevention of Significant
Deterioration (PSD) Requirements

	a.  Proposal

	b.  Comments and Responses 

	c.  Final

6. Emissions Inventories

	a.  Proposal

	b.  Comments and Responses 

	c.  Final

7. Modeling

	a.  Proposal

	b.  Comments and Responses 

	c.  Final

  G. General Conformity

1.  Proposal

2.  Final

  H. Transition From the Current NAAQS to a Revised NAAQS for Lead

  	1.  Proposal

2.  Final

VII. Exceptional Events Information Submission Schedule for Lead NAAQS

A.  Proposal

B.  Comments and Responses

C.  Final

VIII. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review

B. Paperwork Reduction Act

C. Regulatory Flexibility Act

D. Unfunded Mandates Reform Act

E .Executive Order 13132: Federalism

F Executive Order 13175: Consultation and Coordination with Indian
Tribal Governments

G Executive Order 13045: Protection of Children from Environmental
Health & Safety Risks

H Executive Order 13211: Actions that Significantly Affect Energy
Supply, Distribution or Use

I. National Technology Transfer and Advancement Act

J. Executive Order 12898: Federal Actions to Address Environmental
Justice in Minority Populations and Low-Income Populations

K. Congressional Review Act 

References

I. Summary and Background

A. Summary of Revisions to the Lead NAAQS

Based on its review of the air quality criteria and national ambient air
quality standards (NAAQS) for lead (Pb), EPA is making revisions to the
primary and secondary NAAQS for Pb to provide requisite protection of
public health and welfare, respectively.  With regard to the primary
standard, EPA is revising 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.  EPA is revising the level to 0.15 µg/m3.  EPA is retaining
the current indicator of Pb in total suspended particles (Pb-TSP).  EPA
is revising the averaging time to a rolling 3-month period with a
maximum (not-to-be-exceeded) form, evaluated over a 3-year period.  

EPA is revising the secondary standard to be identical in all respects
to the revised primary standard.

EPA is also revising data handling procedures, including allowance for
the use of Pb-PM10 data in certain circumstances, and the treatment of
exceptional events, and ambient air monitoring and reporting
requirements for Pb, including those related to sampling and analysis
methods, network design, sampling schedule, and data reporting.

B. Legislative Requirements

Two sections of the Clean Air Act (Act) govern the establishment and
revision of the NAAQS.  Section 108 (42 U.S.C. 7408) directs the
Administrator to identify and list each air pollutant, emissions of
which “in his judgment, cause or contribute to air pollution which may
reasonably be anticipated to endanger public health and welfare” and
whose “presence . . . in the ambient air results from numerous or
diverse mobile or stationary sources” and to issue air quality
criteria for those that are listed.  Air quality criteria are to
“accurately reflect the latest scientific knowledge useful in
indicating the kind and extent of all identifiable effects on public
health or welfare which may be expected from the presence of [the]
pollutant in ambient air . . .”.   Section 109 (42 U.S.C. 7409)
directs the Administrator to propose and promulgate “primary” and
“secondary” NAAQS for pollutants listed under section 108.  Section
109(b)(1) defines a primary standard as one “the attainment and
maintenance of which in the judgment of the Administrator, based on [air
quality] criteria and allowing an adequate margin of safety, are
requisite to protect the public health.”  A secondary standard, as
defined in section 109(b)(2), must “specify a level of air quality the
attainment and maintenance of which, in the judgment of the
Administrator, based on criteria, is requisite to protect the public
welfare from any known or anticipated adverse effects associated with
the presence of [the] pollutant in the ambient air.”

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. Lead Industries Association v. EPA, 647 F.2d 1130, 1154
(D.C. Cir 1980), cert. denied, 449 U.S. 1042 (1980); American Petroleum
Institute v. Costle, 665 F.2d 1176, 1186 (D.C. Cir. 1981), cert. denied,
455 U.S. 1034 (1982).  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 primary standards that include 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.  The CAA does not require the Administrator to establish a
primary NAAQS at a zero-risk level or at background concentration
levels, see Lead Industries Association v. EPA, 647 F.2d at 1156 n. 51,
but rather at a level that reduces risk sufficiently so as to protect
public health with an adequate margin of safety.

The selection of any particular approach to providing an adequate margin
of safety is a policy choice left specifically to the Administrator’s
judgment.  Lead Industries Association v. EPA, 647 F.2d at 1161-62.  In
addressing the requirement for an adequate margin of safety, EPA
considers such factors as the nature and severity of the health effects
involved, the size of the population(s) at risk, and the kind and degree
of the uncertainties that must be addressed.  In setting standards that
are “requisite” to protect public health and welfare, as provided in
section 109(b), EPA’s task is to establish standards that are neither
more nor less stringent than necessary for these purposes.  Whitman v.
American Trucking Associations, 531 U.S. 457, 473.  Further the Supreme
Court ruled that “[t]he text of § 109(b), interpreted in its
statutory and historical context and with appreciation for its
importance to the CAA as a whole, unambiguously bars cost considerations
from the NAAQS-setting process. . .”  Id. at 472.  

Section 109(d)(1) of the Act requires that “[n]ot later than December
31, 1980, and at 5-year intervals thereafter, the Administrator shall
complete a thorough review of the criteria published under section 108
and the national ambient air quality standards promulgated under this
section and shall make such revisions in such criteria and standards and
promulgate such new standards as may be appropriate in accordance with
section 108 and subsection (b) of this section.”  Section 109(d)(2)(A)
requires that "The Administrator shall appoint an independent scientific
review committee composed of seven members including at least one member
of the National Academy of Sciences, one physician, and one person
representing State air pollution control agencies."  Section
109(d)(2)(B) requires that, "[n]ot later than January 1, 1980, and at
five-year intervals thereafter, the committee referred to in
subparagraph (A) shall complete a review of the criteria published under
section 108 and the national primary and secondary ambient air quality
standards promulgated under this section and shall recommend to the
Administrator any new national ambient air quality standards and
revisions of existing criteria and standards as may be appropriate under
section 108 and subsection (b) of this section."  Since the early
1980's, this independent review function has been performed by the Clean
Air Scientific Advisory Committee (CASAC) of EPA’s Science Advisory
Board.

C. Review of Air Quality Criteria and Standards for Lead

On October 5, 1978, EPA promulgated primary and secondary NAAQS for Pb
under section 109 of the Act (43 FR 46246).  Both primary and secondary
standards were set at a level of 1.5 micrograms per cubic meter
(μg/m3), measured as Pb in total suspended particulate matter 
(Pb-TSP), not to be exceeded by the maximum arithmetic mean
concentration averaged over a calendar quarter.  This standard was based
on the 1977 Air Quality Criteria for Lead (USEPA, 1977). 

A review of the Pb standards was initiated in the mid-1980s.  The
scientific assessment for that review is described in the 1986 Air
Quality Criteria for Lead (USEPA, 1986a), the associated Addendum
(USEPA, 1986b) and the 1990 Supplement (USEPA, 1990a).  As part of the
review, the Agency designed and performed human exposure and health risk
analyses (USEPA, 1989), the results of which were presented in a 1990
Staff Paper (USEPA, 1990b).  Based on the scientific assessment and the
human exposure and health risk analyses, the 1990 Staff Paper presented
options for the Pb NAAQS level in the range of 0.5 to 1.5 µg/m3, and
suggested the second highest monthly average in three years for the form
and averaging time of the standard (USEPA, 1990b).  After consideration
of the documents developed during the review and the significantly
changed circumstances since Pb was listed in 1976, the Agency did not
propose any revisions to the 1978 Pb NAAQS.  In a parallel effort, the
Agency developed the broad, multi-program, multimedia, integrated U.S.
Strategy for Reducing Lead Exposure (USEPA, 1991).  As part of
implementing this strategy, the Agency focused efforts primarily on
regulatory and remedial clean-up actions aimed at reducing Pb exposures
from a variety of nonair sources judged to pose more extensive public
health risks to U.S. populations, as well as on actions to reduce Pb
emissions to air, such as bringing more areas into compliance with the
existing Pb NAAQS (USEPA, 1991). 

EPA initiated the current review of the air quality criteria for Pb on
November 9, 2004 with a general call for information (69 FR 64926).  A
project work plan (USEPA, 2005a) for the preparation of the Criteria
Document was released in January 2005 for CASAC and public review.  EPA
held a series of workshops in August 2005, inviting recognized
scientific experts to discuss initial draft materials that dealt with
various lead-related issues being addressed in the Pb air quality
criteria document.  In February 2006, EPA released the Plan for Review
of the National Ambient Air Quality Standards for Lead (USEPA 2006c)
that described Agency plans and a timeline for reviewing the air quality
criteria, developing human exposure and risk assessments and an
ecological risk assessment, preparing a policy assessment, and
developing the proposed and final rulemakings.

The first draft of the Criteria Document (USEPA, 2005b) was released for
CASAC and public review in December 2005 and discussed at a CASAC
meeting held on February 28-March 1, 2006.  A second draft Criteria
Document (USEPA, 2006b) was released for CASAC and public review in May
2006, and discussed at the CASAC meeting on June 28, 2006.  A subsequent
draft of Chapter 7 - Integrative Synthesis (chapter 8 in the final
Criteria Document), released on July 31, 2006, was discussed at an
August 15, 2006 CASAC teleconference.  The final Criteria Document was
released on September 30, 2006 (USEPA, 2006a; cited throughout this
preamble as CD).  While the Criteria Document focuses on new scientific
information available since the last review, it integrates that
information with scientific information from previous reviews.

In May 2006, EPA released for CASAC and public review a draft Analysis
Plan for Human Health and Ecological Risk Assessment for the Review of
the Lead National Ambient Air Quality Standards (USEPA, 2006d), which
was discussed at a June 29, 2006 CASAC meeting (Henderson, 2006).  The
May 2006 assessment plan discussed two assessment phases:  a pilot phase
and a full-scale phase.  The pilot phase of both the human health and
ecological risk assessments was presented in the draft Lead Human
Exposure and Health Risk Assessments and Ecological Risk Assessment for
Selected Areas (ICF, 2006; henceforth referred to as the first draft
Risk Assessment Report) which was released for CASAC and public review
in December 2006.  The first draft Staff Paper, also released in
December 2006, discussed the pilot assessments and the most
policy-relevant science from the Criteria Document.  These documents
were reviewed by CASAC and the public at a public meeting on February
6-7, 2007 (Henderson, 2007a).

Subsequent to that meeting, EPA conducted full-scale human exposure and
health risk assessments, although no further work was done on the
ecological assessment due to resource limitations.  A second draft Risk
Assessment Report (USEPA, 2007a), containing the full-scale human
exposure and health risk assessments, was released in July 2007 for
review by CASAC at a meeting held on August 28-29, 2007.  Taking into
consideration CASAC comments (Henderson, 2007b) and public comments on
that document, we conducted additional human exposure and health risk
assessments.  A final Risk Assessment Report (USEPA, 2007b) and final
Staff Paper (USEPA, 2007c) were released on November 1, 2007.

The final Staff Paper presents OAQPS staff’s evaluation of the public
health and welfare policy implications of the key studies and scientific
information contained in the Criteria Document and presents and
interprets results from the quantitative risk/exposure analyses
conducted for this review.  Further, the Staff Paper presents OAQPS
staff recommendations on a range of policy options for the Administrator
to consider concerning whether, and if so how, to revise the primary and
secondary Pb NAAQS.  Such an evaluation of policy implications is
intended to help “bridge the gap” between the scientific assessment
contained in the Criteria Document and the judgments required of the EPA
Administrator in determining whether it is appropriate to retain or
revise the NAAQS for Pb.  In evaluating the adequacy of the current
standard and a range of alternatives, the Staff Paper considered the
available scientific evidence and quantitative risk-based analyses,
together with related limitations and uncertainties, and focused on the
information that is most pertinent to evaluating the basic elements of
national ambient air quality standards:  indicator, averaging time,
form, and level.  These elements, which together serve to define each
standard, must be considered collectively in evaluating the public
health and welfare protection afforded by the Pb standards.  The
information, conclusions, and OAQPS staff recommendations presented in
the Staff Paper were informed by comments and advice received from CASAC
in its reviews of the earlier draft Staff Paper and drafts of related
risk/exposure assessment reports, as well as comments on these earlier
draft documents submitted by public commenters.

Subsequent to completion of the Staff Paper, EPA issued an advance
notice of proposed rulemaking (ANPR) that was signed by the
Administrator on December 5, 2007 (72 FR 71488).  The ANPR is one of the
key features of the new NAAQS review process that EPA has instituted
over the past two years to help to improve the efficiency of the process
the Agency uses in reviewing the NAAQS while ensuring that the
Agency’s decisions are informed by the best available science and
broad participation among experts in the scientific community and the
public.  The ANPR provided the public an opportunity to comment on a
wide range of policy options that could be considered by the
Administrator.  

A public meeting of CASAC was held on December 12-13, 2007 to provide
advice and recommendations to the Administrator based on its review of
the ANPR and the previously released final Staff Paper and Risk
Assessment Report.  Transcripts of the meeting and CASAC’s letter to
the Administrator (Henderson, 2008a) are in the docket for this review
and CASAC’s letter is also available on the EPA web site (  HYPERLINK
"http://www.epa.gov/sab"  www.epa.gov/sab ).  

A public comment period for the ANPR extended through January 16, 2008
and comments received are in the docket for this review.  Comments were
received from nearly 9000 private citizens (roughly 200 of them were not
part of one of several mass comment campaigns), 13 State and local
agencies, one federal agency, three regional or national associations of
government agencies or officials, 15 nongovernmental environmental or
public health organizations (including one submission on behalf of a
coalition of 23 organizations) and five businesses or industry
organizations.  

The proposed decision (henceforth “proposal”) on revisions to the Pb
NAAQS was signed on May 1, 2008 and published in the Federal Register on
May 20, 2008.  Public teleconferences of the CASAC Pb Panel were held on
June 9 and July 8, 2008 to provide advice and recommendations to the
Administrator based on its review of the proposal notice.  CASAC’s
letter to the Administrator (Henderson, 2008b) is in the docket for this
review and also available on the EPA web site (  HYPERLINK
"http://www.epa.gov/sab"  www.epa.gov/sab ).  

The EPA held two public hearings to provide direct opportunities for
oral testimony by the public on the proposal.  The hearings were held
concurrently on June 12, 2008 in Baltimore, Maryland and St Louis,
Missouri.  At these public hearings, EPA heard testimony from 33
individuals representing themselves or specific interested
organizations.  Transcripts from these hearings and written testimony
provided at the hearings are in the docket for this review. 
Additionally, a large number of written comments were received from
various commenters during the public comment period on the proposal. 
Comments were received from EPA/s Children’s Health Protection
Advisory Committee, the American Academy of Pediatrics, the American
Medical Association, the American Thoracic Society, two organizations of
state and local air agencies (National Association of Clean Air Agencies
and Northeast States for Coordinated Air Use Management), approximately
40 State, Tribal and local government agencies, approximately 20
environmental or public health organizations or coalitions,
approximately 20 industry organizations or companies, and approximately
6200 private citizens (roughly 150 of whom were not part of one of
several mass comment campaigns).  Significant issues raised in the
public comments are discussed throughout the preamble of this final
action.  A summary of all other significant comments, along with EPA’s
responses (henceforth “Response to Comments”), can be found in the
docket for this review.

The schedule for completion of this review has been governed by a
judicial order in Missouri Coalition for the Environment, v. EPA (No.
4:04CV00660 ERW, Sept. 14, 2005).  The court-ordered schedule governing
this review, entered by the court on September 14, 2005 and amended on
April 29, 2008 and July 1, 2008, requires EPA to sign, for publication,
a notice of final rulemaking concerning its review of the Pb NAAQS no
later than October 15, 2008.

Some commenters have referred to and discussed individual scientific
studies on the health effects of Pb that were not included in the
Criteria Document (EPA, 2006a) (“'new' studies”).  In considering
and responding to comments for which such “new” studies were cited
in support, EPA has provisionally considered the cited studies in
conjunction with other relevant “new” studies published since the
completion of the Criteria Document in the context of the findings of
the Criteria Document.  

As in prior NAAQS reviews, EPA is basing its decision in this review on
studies and related information included in the Criteria Document and
Staff Paper, which have undergone CASAC and public review.  In this Pb
NAAQS review, EPA also prepared an ANPR, consistent with the Agency’s
new NAAQS process.  The ANPR discussed studies that were included in the
Criteria Document and Staff Paper.  The studies assessed in the Criteria
Document and Staff Paper, and the integration of the scientific evidence
presented in them, have undergone extensive critical review by EPA,
CASAC, and the public.  The rigor of that review makes these studies,
and their integrative assessment, the most reliable source of scientific
information on which to base decisions on the NAAQS, decisions that all
parties recognize as of great import. NAAQS decisions can have profound
impacts on public health and welfare, and NAAQS decisions should be
based on studies that have been rigorously assessed in an integrative
manner not only by EPA but also by the statutorily mandated independent
advisory committee, as well as the public review that accompanies this
process.  EPA’s provisional consideration of these studies did not and
could not provide that kind of in-depth critical review. 

This decision is consistent with EPA’s practice in prior NAAQS reviews
and its interpretation of the requirements of the CAA.  Since the 1970
amendments, the EPA has taken the view that NAAQS decisions are to be
based on scientific studies and related information that have been
assessed as a part of the pertinent air quality criteria, and has
consistently followed this approach.  This longstanding interpretation
was strengthened by new legislative requirements enacted in 1977, which
added section 109(d)(2) of the Act concerning CASAC review of air
quality criteria.  See 71 FR 61144, 61148 (October 17, 2006) (final
decision on review of PM NAAQS) for a detailed discussion of this issue
and EPA’s past practice.  

As discussed in EPA’s 1993 decision not to revise the NAAQS for ozone,
‘‘new’’ studies may sometimes be of such significance that it is
appropriate to delay a decision on revision of a NAAQS and to supplement
the pertinent air quality criteria so the studies can be taken into
account (58 FR at 13013–13014, March 9, 1993).  In the present case,
EPA’s provisional consideration of ‘‘new’’ studies concludes
that, taken in context, the ‘‘new’’ information and findings do
not materially change any of the broad scientific conclusions regarding
the health effects and exposure pathways of ambient air Pb made in the
air quality criteria.  For this reason, reopening the air quality
criteria review would not be warranted even if there were time to do so
under the court order governing the schedule for this rulemaking. 

Accordingly, EPA is basing the final decisions in this review on the
studies and related information included in the Pb air quality criteria
that have undergone CASAC and public review.  EPA will consider the
“new” studies for purposes of decision-making in the next periodic
review of the Pb NAAQS, which EPA expects to begin soon after the
conclusion of this review and which will provide the opportunity to
fully assess these studies through a more rigorous review process
involving EPA, CASAC, and the public. Further discussion of these
‘‘new’’ studies can be found in the Response to Comments
document.	

D.Current Related Lead Control Programs

States are primarily responsible for ensuring attainment and maintenance
of national ambient air quality standards once EPA has established them.
 Under section 110 of the Act (42 U.S.C. 7410) and related provisions,
States are to submit, for EPA approval, State implementation plans
(SIPs) that provide for the attainment and maintenance of such standards
through control programs directed to sources of the pollutants involved.
 The States, in conjunction with EPA, also administer the prevention of
significant deterioration program (42 U.S.C. 7470–7479) for these
pollutants.  In addition, Federal programs provide for nationwide
reductions in emissions of these and other air pollutants through the
Federal Motor Vehicle Control Program under Title II of the Act (42
U.S.C. 7521–7574), which involves controls for automobile, truck, bus,
motorcycle, nonroad engine, and aircraft emissions; the new source
performance standards under section 111 of the Act (42 U.S.C. 7411); and
the national emission standards for hazardous air pollutants under
section 112 of the Act (42 U.S.C. 7412).

As Pb is a multimedia pollutant, a broad range of Federal programs
beyond those that focus on air pollution control provide for nationwide
reductions in environmental releases and human exposures.  In addition,
the Centers for Disease Control and Prevention (CDC) programs provide
for the tracking of children’s blood Pb levels nationally and provide
guidance on levels at which medical and environmental case management
activities should be implemented (CDC, 2005a; ACCLPP, 2007).  In 1991,
the Secretary of the Health and Human Services (HHS) characterized Pb
poisoning as the “number one environmental threat to the health of
children in the United States” (Alliance to End Childhood Lead
Poisoning. 1991).  In 1997, President Clinton created, by Executive
Order 13045, the President’s Task Force on Environmental Health Risks
and Safety Risks to Children in response to increased awareness that
children face disproportionate risks from environmental health and
safety hazards (62 FR 19885).  By Executive Orders issued in October
2001 and April 2003, President Bush extended the work for the Task Force
for an additional three and a half years beyond its original charter (66
FR 52013 and 68 FR 19931).  The Task Force set a Federal goal of
eliminating childhood Pb poisoning by the year 2010 and reducing Pb
poisoning in children was identified as the Task Force’s top priority.
 

Federal abatement programs provide for the reduction in human exposures
and environmental releases from in-place materials containing Pb (e.g.,
Pb-based paint, urban soil and dust, and contaminated waste sites). 
Federal regulations on disposal of Pb-based paint waste help facilitate
the removal of Pb-based paint from residences (68 FR 36487).  Further,
in 1991, EPA lowered the maximum levels of Pb permitted in public water
systems from 50 parts per billion (ppb) to 15 ppb measured at the
consumer’s tap (56 FR 26460).

Federal programs to reduce exposure to Pb in paint, dust, and soil are
specified under the comprehensive federal regulatory framework developed
under the Residential Lead-Based Paint Hazard Reduction Act (Title X). 
Under Title X and Title IV of the Toxic Substances Control Act (TSCA),
EPA has established regulations and associated programs in the following
five categories:   (1) training and certification requirements for
persons engaged in lead-based paint activities; accreditation of
training providers; authorization of State and Tribal lead-based paint
programs; and work practice standards for the safe, reliable, and
effective identification and elimination of lead-based paint hazards;
(2) ensuring that, for most housing constructed before 1978, lead-based
paint information flows from sellers to purchasers, from landlords to
tenants, and from renovators to owners and occupants; (3) establishing
standards for identifying dangerous levels of Pb in paint, dust and
soil; (4) providing grant funding to establish and maintain State and
Tribal lead-based paint programs, and to address childhood lead
poisoning in the highest-risk communities; and (5) providing information
on Pb hazards to the public, including steps that people can take to
protect themselves and their families from lead-based paint hazards.  

Under Title IV of TSCA, EPA established standards identifying hazardous
levels of lead in residential paint, dust, and soil in 2001.  This
regulation supports the implementation of other regulations which deal
with worker training and certification, Pb hazard disclosure in real
estate transactions, Pb hazard evaluation and control in Federally-owned
housing prior to sale and housing receiving Federal assistance, and U.S.
Department of Housing and Urban Development grants to local
jurisdictions to perform Pb hazard control.  The TSCA Title IV term
"lead-based paint hazard" implemented through this regulation identifies
lead-based paint and all residential lead-containing dust and soil
regardless of the source of Pb, which, due to their condition and
location, would result in adverse human health effects.  One of the
underlying principles of Title X is to move the focus of public and
private decision makers away from the mere presence of lead-based paint,
to the presence of lead-based paint hazards, for which more substantive
action should be undertaken to control exposures, especially to young
children.  In addition the success of the program will rely on the
voluntary participation of States and Tribes as well as counties and
cities to implement the programs and on property owners to follow the
standards and EPA's recommendations.  If EPA were to set unreasonable
standards (e.g., standards that would recommend removal of all Pb from
paint, dust, and soil), States and Tribes may choose to opt out of the
Title X Pb program and property owners may choose to ignore EPA's advice
believing it lacks credibility and practical value.  Consequently, EPA
needed to develop standards that would not waste resources by chasing
risks of negligible importance and that would be accepted by States,
Tribes, local governments and property owners.  In addition, a separate
regulation establishes, among other things, under authority of TSCA
section 402, residential Pb dust cleanup levels and amendments to dust
and soil sampling requirements (66 FR 1206).

On March 31, 2008, the Agency issued a new rule (Lead: Renovation,
Repair and Painting [RRP] Program, 73 FR 21692) to protect children from
lead-based paint hazards.  This rule applies to renovators and
maintenance professionals who perform renovation, repair, or painting in
housing, child-care facilities, and schools built prior to 1978.  It
requires that contractors and maintenance professionals be certified;
that their employees be trained; and that they follow protective work
practice standards.  These standards prohibit certain dangerous
practices, such as open flame burning or torching of lead-based paint. 
The required work practices also include posting warning signs,
restricting occupants from work areas, containing work areas to prevent
dust and debris from spreading, conducting a thorough cleanup, and
verifying that cleanup was effective.  The rule will be fully effective
by April 2010.  The rule contains procedures for the authorization of
States, territories, and Tribes to administer and enforce these
standards and regulations in lieu of a federal program.  In announcing
this rule, EPA noted that almost 38 million homes in the United States
contain some lead-based paint, and that this rule’s requirements were
key components of a comprehensive effort to eliminate childhood Pb
poisoning.  To foster adoption of the rule’s measures, EPA also
intends to conduct an extensive education and outreach campaign to
promote awareness of these new requirements. 

Programs associated with the Comprehensive Environmental Response,
Compensation, and Liability Act (CERCLA or Superfund) and Resource
Conservation Recovery Act (RCRA) also implement abatement programs,
reducing exposures to Pb and other pollutants.  For example, EPA
determines and implements protective levels for Pb in soil at Superfund
sites and RCRA corrective action facilities.  Federal programs,
including those implementing RCRA, provide for management of hazardous
substances in hazardous and municipal solid waste (see, e.g., 66 FR
58258).  Federal regulations concerning batteries in municipal solid
waste facilitate the collection and recycling or proper disposal of
batteries containing Pb.  Similarly, Federal programs provide for the
reduction in environmental releases of hazardous substances such as Pb
in the management of wastewater (  HYPERLINK "http://www.epa.gov/owm/" 
http://www.epa.gov/owm/ ).

A variety of federal nonregulatory programs also provide for reduced
environmental release of Pb-containing materials through more general
encouragement of pollution prevention, promotion of reuse and recycling,
reduction of priority and toxic chemicals in products and waste, and
conservation of energy and materials.  These include the Resource
Conservation Challenge (  HYPERLINK
"http://www.epa.gov/epaoswer/osw/conserve/index.htm" 
http://www.epa.gov/epaoswer/osw/conserve/index.htm ), the National Waste
Minimization Program (  HYPERLINK
"http://www.epa.gov/epaoswer/hazwaste/minimize/leadtire.htm" 
http://www.epa.gov/epaoswer/hazwaste/minimize/leadtire.htm ), “Plug in
to eCycling” (a partnership between EPA and consumer electronics
manufacturers and retailers;   HYPERLINK
"http://www.epa.gov/epaoswer/hazwaste/recycle/electron/crt.htm#crts" 
http://www.epa.gov/epaoswer/hazwaste/recycle/electron/crt.htm#crts ),
and activities to reduce the practice of backyard trash burning ( 
HYPERLINK "http://www.epa.gov/msw/backyard/pubs.htm" 
http://www.epa.gov/msw/backyard/pubs.htm ).

μg/dL and a level of 3.9 μg/dL for the 90th percentile child in the
2003-2004 National Health and Nutrition Examination Survey (NHANES) as
compared to median and 90th percentile levels in 1988-1991 of 3.5 μg/dL
and 9.4 μg/dL, respectively
(http://www.epa.gov/envirohealth/children/body_burdens/b1-table.htm). 
These levels (median and 90th percentile) for the general population of
young children are at the low end of the historic range of blood Pb
levels for general population of children aged 1-5 years.  However, as
recognized in section II.A.2.b, levels have been found to vary among
children of different socioeconomic status and other demographic
characteristics (CD, p. 4-21) and racial/ethnic and income disparities
in blood Pb levels in children persist.  The Agency has continued to
grapple with soil and dust Pb levels from the historical use of Pb in
paint and gasoline and from other sources.  

In addition to the Pb control programs summarized above, EPA’s
research program, with other Federal agencies, identifies, encourages
and conducts research needed to locate and assess serious risks and to
develop methods and tools to characterize and help reduce risks.  For
example, EPA’s Integrated Exposure Uptake Biokinetic Model for Lead in
Children (IEUBK model) for Pb in children and the Adult Lead Methodology
are widely used and accepted as tools that provide guidance in
evaluating site specific data.  More recently, in recognition of the
need for a single model that predicts Pb concentrations in tissues for
children and adults, EPA is developing the All Ages Lead Model (AALM) to
provide researchers and risk assessors with a pharmacokinetic model
capable of estimating blood, tissue, and bone concentrations of Pb based
on estimates of exposure over the lifetime of the individual.  EPA
research activities on substances including Pb focus on better
characterizing aspects of health and environmental effects, exposure,
and control or management of environmental releases (see   HYPERLINK
"http://www.epa.gov/ord/researchaccomplishments/index.html" 
http://www.epa.gov/ord/researchaccomplishments/index.html ).

E. Summary of Proposed Revisions to the Lead NAAQS

For reasons discussed in the proposal, the Administrator proposed to
revise the current primary and secondary Pb standards.  With regard to
the primary Pb standard, the Administrator proposed to revise the level
of the Pb standard to a level within the range of 0.10 µg/m3 to 0.30
µg/m3, in conjunction with retaining the current indicator of Pb in
total suspended particles (Pb-TSP) but with allowance for the use of
Pb-PM10 data.  With regard to the averaging time and form, the
Administrator proposed two options:  to retain the current averaging
time of a calendar quarter and the current not-to-be-exceeded form,
revised to apply across a 3-year span; and to revise the averaging time
to a calendar month and the form to the second-highest monthly average
across a 3-year span.  With regard to the secondary standard for Pb, the
Administrator proposed to revise the standard to make it identical to
the proposed primary standard.

F. Organization and Approach to Final Lead NAAQS Decisions

	This action presents the Administrator’s final decisions regarding
the need to revise the current primary and secondary Pb standards. 
Revisions to the primary standard for Pb are addressed below in section
II.  The secondary Pb standard is addressed below in section III. 
Related data completeness, data handling, data reporting and rounding
conventions are addressed in section IV, and related ambient monitoring
methods and network design are addressed below in section V. 
Implementation of the revised NAAQS is discussed in section VI, and the
exceptional events information submission schedule is described in
section VII.  A discussion of statutory and executive order reviews is
provided in section VIII.

	Today's final decisions are based on a thorough review in the Criteria
Document of scientific information on known and potential human health
and welfare effects associated with exposure to Pb in the environment. 
These final decisions also take into account:  (1) assessments in the
Staff Paper and ANPR of the most policy-relevant information in the
Criteria Document as well as quantitative exposure and risk assessments
based on that information; (2) CASAC Panel advice and recommendations,
as reflected in its letters to the Administrator, its discussions of
drafts of the Criteria Document and Staff Paper, and of the ANPR and the
notice of proposed rulemaking at public meetings; (3) public comments
received during the development of these documents, either in connection
with CASAC Panel meetings or separately;  and (4) public comments
received on the proposed rulemaking.

II.	Rationale for Final Decision on the Primary Standard

A.	Introduction

This section presents the rationale for the Administrator’s final
decision that the current primary standard is not requisite to protect
public health with an adequate margin of safety, and that the existing
Pb primary standard should be revised.  In developing this rationale,
EPA has drawn upon an integrative synthesis in the Criteria Document of
the entire body of evidence published through late 2006 on human health
effects associated with Pb exposure.  Some 6000 studies were considered
in this review.  This body of evidence addresses a broad range of health
endpoints associated with exposure to Pb (EPA, 2006a, chapter 8), and
includes hundreds of epidemiologic studies conducted in the U.S.,
Canada, and many countries around the world since the time of the last
review (EPA, 2006a, chapter 6).  

As discussed below, a significant amount of new research has been
conducted since the last review, with important new information coming
from epidemiological, toxicological, controlled human exposure, and
dosimetric studies.  Moreover, the newly available research studies
evaluated in the Criteria Document have undergone intensive scrutiny
through multiple layers of peer review, with extended opportunities for
review and comment by the CASAC Panel and the public.  As with virtually
any policy-relevant scientific research, there is uncertainty in the
characterization of health effects attributable to exposure to ambient
Pb.  While important uncertainties remain, the review of the health
effects information has been extensive and deliberate.  In the judgment
of the Administrator, this intensive evaluation of the scientific
evidence provides an adequate basis for regulatory decision making at
this time.  This review also provides important input to EPA's research
plan for improving our future understanding of the relationships between
exposures to ambient Pb and health effects.

The health effects information and quantitative exposure and health risk
assessment were summarized in sections II.B and II.C of the proposal (73
FR at 29193-29220) and are only briefly outlined below in sections
II.A.2 and II.A.3.  Responses to public comments specific to the
material presented in sections II.A.1 through II.A.3 below are provided
in the Response to Comments document. 

Subsequent sections of this preamble provide a more complete discussion
of the Administrator’s rationale, in light of key issues raised in
public comments, for concluding that the current standard is not
requisite to protect public health with an adequate margin of safety and
that it is appropriate to revise the current primary Pb standard to
provide additional public health protection (section II.B), as well as a
more complete discussion of the Administrator’s rationale for
retaining or revising the specific elements of the primary Pb standards
(section II.C), namely the indicator (section II.C.1), averaging time
and form (section II.C.2), and level (section II.C.3).  A summary of the
final decisions on revisions to the primary Pb standards is presented in
section II.D.

1.	Overview of Multimedia, Multipathway Considerations and Background

This section briefly summarizes the information presented in section
II.A of the proposal and chapter 2 of the Staff Paper on multimedia,
multipathway and background considerations of the Pb NAAQS review.  As
was true in the setting of the current standard, multimedia distribution
of and multipathway exposure to Pb that has been emitted into the
ambient air play a key role in the Agency’s consideration of the Pb
NAAQS.  Some key multimedia and multipathway considerations in the
review include:

(1) Lead is emitted into the air from many sources encompassing a wide
variety of stationary and mobile source types.  Lead emitted to the air
is predominantly in particulate form, with the particles occurring in
various sizes.  Once emitted, the particles can be transported long or
short distances depending on their size, which influences the amount of
time spent in aerosol phase.  In general, larger particles tend to
deposit more quickly, within shorter distances from emissions points,
while smaller particles will remain in aerosol phase and travel longer
distances before depositing.  As summarized in sections II.A.1 and
II.E.1 of the proposal, airborne concentrations of Pb at sites near
sources are much higher, and the representation of larger particles is
greater, than at sites not known to be directly influenced by sources.  

(2) Once deposited out of the air, Pb can subsequently be resuspended
into the ambient air and, because of the persistence of Pb, Pb emissions
contribute to media concentrations for some years into the future. 

(3) Exposure to Pb emitted into the ambient air (air-related Pb) can
occur directly by inhalation, or indirectly by ingestion of
Pb-contaminated food, water or other materials including dust and soil. 
This occurs as Pb emitted into the ambient air is distributed to other
environmental media and can contribute to human exposures via indoor and
outdoor dusts, outdoor soil, food and drinking water, as well as
inhalation of air.  These exposure pathways are described more fully in
the proposal.

(4) Air-related exposure pathways are affected by changes to air
quality, including changes in concentrations of Pb in air and changes in
atmospheric deposition of Pb.  Further, because of its persistence in
the environment, Pb deposited from the air may contribute to human and
ecological exposures for years into the future.  Thus, because of the
roles of both air concentration and air deposition in human exposure
pathways, and because of the persistence of Pb once deposited, some
pathways respond more quickly to changes in air quality than others. 
Pathways most directly involving Pb in ambient air and exchanges of
ambient air with indoor air respond more quickly while pathways
involving exposure to Pb deposited from ambient air into the environment
generally respond more slowly.  

Additionally, as when the standard was set, human exposures to Pb
include nonair or background contributions in addition to air-related
pathways.  Some key aspects of the consideration of air and nonair
pathways in the review (described in more detail in the proposal) are
summarized here:

(1) Human exposure pathways that are not air-related are those in which
Pb does not pass through ambient air.  These pathways as well as
air-related human exposure pathways that involve natural sources of Pb
to air are considered “policy-relevant background” in this review.  

(2) The pathways of human exposure to Pb that are not air-related
include ingestion of indoor Pb paint, Pb in diet as a result of
inadvertent additions during food processing, and Pb in drinking water
attributable to Pb in distribution systems, as well as other generally
less prevalent pathways, as described in the proposal (73 FR 29192) and
Criteria Document (CD, pp. 3-50 to 3-51).  

(3) Some amount of Pb in the air derives from background sources, such
as volcanoes, sea salt, and windborne soil particles from areas free of
anthropogenic activity and may also derive from anthropogenic sources of
airborne Pb located outside of North America (which would also be
considered policy-relevant background).  In considering contributions
from policy-relevant background to human exposures and associated health
effects, however, policy-relevant background in air is likely
insignificant in comparison to the contributions from exposures to
nonair media.

(4) The relative contribution of Pb from different exposure media to
human exposure varies, particularly for different age groups.  For
example, some studies have found that dietary intake of Pb may be a
predominant source of Pb exposure among adults, greater than consumption
of water and beverages or inhalation, while for young children,
ingestion of indoor dust can be a significant Pb exposure pathway (e.g.,
via hand-to-mouth activity of very young children).  

(5) Estimating separate contributions to human Pb exposure from air and
nonair sources is complicated by the existence of multiple and varied
air-related pathways, as well as the persistent nature of Pb.  For
example, Pb that is a soil or dust contaminant today may have been
airborne yesterday or many years ago.  The studies currently available
and reviewed in the Criteria Document that evaluate the multiple
pathways of Pb exposure, when considering exposure contributions from
indoor dust or outdoor dust/soil, do not usually distinguish between
air-related and other sources of Pb or between air-related Pb associated
with historical emissions and that from recent emissions.  

(6) Relative contributions to a child’s total Pb exposure from
air-related exposure pathways compared to other (nonair-related) Pb
exposures depends on many factors including ambient air concentrations
and air deposition in the area where the child resides (as well as in
the area from which the child’s food derives) and access to other
sources of Pb exposure such as Pb paint, tap water affected by plumbing
containing Pb, and lead-tainted products.  Studies indicate that in the
absence of paint-related exposures, Pb from other sources such as
stationary sources of Pb emissions may dominate a child’s Pb
exposures.  In other cases, such as children living in older housing
with peeling paint or where renovations have occurred, the dominant
source of Pb exposure may be lead paint used in the house in the past. 
Depending on Pb levels in a home’s tap water, drinking water can
sometimes be a significant source.  In still other cases, there may be
more of a mixture of contributions from multiple sources, with no one
source dominating.  

2.	Overview of Health Effects Information 

This section summarizes information presented in section II.B of the
proposal pertaining to health endpoints associated with the range of
exposures considered to be most relevant to current exposure levels.  In
recognition of the role of multiple exposure pathways and routes and the
use of an internal exposure or dose metric in evaluating health risk for
Pb, the following section summarizes key aspects of the internal
disposition or distribution of Pb, the use of blood Pb as an internal
exposure or dose metric, and the evidence with regard to the
quantitative relationship between air Pb and blood Pb levels (section
II.A.2.a).  This is followed first by a summary of the broad array of
Pb-induced health effects and recognition of at-risk subpopulations
(section II.A.2.b) and then by a summary of neurological effects in
children and quantitative concentration-response relationships for blood
Pb and IQ (section II.A.2.c).  

a.	Blood Lead 

(i)	Internal Disposition of Lead

Lead enters the body via the respiratory system and gastrointestinal
tract, from which it is quickly absorbed into the blood stream and
distributed throughout the body.  Lead bioaccumulates in the body, with
the bone serving as a large, long-term storage compartment; soft tissues
(e.g., kidney, liver, brain, etc) serve as smaller compartments, in
which Pb may be more mobile (CD, sections 4.3.1.4 and 8.3.1.).  During
childhood development, bone represents approximately 70% of a child’s
body burden of Pb, and this accumulation continues through adulthood,
when more than 90% of the total Pb body burden is stored in the bone
(CD, section 4.2.2).  Throughout life, Pb in the body is exchanged
between blood and bone, and between blood and soft tissues (CD, section
4.3.2), with variation in these exchanges reflecting “duration and
intensity of the exposure, age and various physiological variables”
(CD, p. 4-1).  

The bone pool of Pb in children is thought to be much more labile than
that in adults due to the more rapid turnover of bone mineral as a
result of growth (CD, p. 4-27).  As a result, changes in blood Pb
concentration in children more closely parallel changes in total body
burden (CD, pp. 4-20 and 4-27).  This is in contrast to adults, whose
bone has accumulated decades of Pb exposures (with past exposures often
greater than current ones), and for whom the bone may be a significant
source long after exposure has ended (CD, section 4.3.2.5).	

(ii)	Use of Blood Pb as Dose Metric

d Pb levels below 10 μg/dL and the data demonstrating that no
“safe” threshold for blood Pb had been identified, and emphasizing
the importance of preventative measures (CDC, 2005a, ACCLPP, 2007). 

Since 1976, the CDC has been monitoring blood Pb levels in multiple age
groups nationally through the National Health and Nutrition Examination
Survey (NHANES).  The NHANES information has documented the dramatic
decline in mean blood Pb levels in the U.S. population that has occurred
since the 1970s and that coincides with regulations regarding leaded
fuels, leaded paint, and Pb-containing plumbing materials that have
reduced Pb exposure among the general population  (CD, sections 4.3.1.3
and 8.3.3; Schwemberger et al., 2005).  The Criteria Document summarizes
related information as follows (CD, p. E-6).  

μg/dL in 1976-1980 to ~1-2 μg/dL in the 2000-2004 period.  

While blood Pb levels in the U.S. general population, including
geometric mean levels in children aged 1-5, have declined significantly,
levels have been found to vary among children of different socioeconomic
status (SES) and other demographic characteristics (CD, p. 4-21), and
racial/ethnic and income disparities in blood Pb levels in children
persist.  For example, as described in the proposal, blood Pb levels for
lower income and African American children are higher than those for the
general population.  The recently released RRP rule (discussed above in
section I.C) is expected to contribute to further reductions in blood Pb
levels for children living in houses with Pb paint.

(iii) Air-to-Blood Relationships 

As described in section II.A.1 above and discussed in section II.A of
the proposal, Pb in ambient air contributes to Pb in blood by multiple
pathways, with the pertinent exposure routes including both inhalation
and ingestion (CD, sections 3.1.3.2, 4.2 and 4.4; Hilts, 2003).  The
quantitative relationship between ambient air Pb and blood Pb (discussed
in section II.B.1.c of the proposal), which is often termed a slope or
ratio, describes the increase in blood Pb (in µg/dL) estimated to be
associated with each unit increase of air Pb (in µg/m3).  

The evidence on this quantitative relationship is now, as in the past,
limited by the circumstances in which the data are collected.  These
estimates are generally developed from studies of populations in various
Pb exposure circumstances.  The 1986 Criteria Document discussed the
studies available at that time that addressed the relationship between
air Pb and blood Pb, recognizing that there is significant variability
in air-to-blood ratios for different populations exposed to Pb through
different air-related exposure pathways and at different exposure
levels.

In discussing the available evidence, the 1986 Criteria Document
observed that estimates of air-to-blood ratios that included air-related
ingestion pathways in addition to the inhalation pathway are
“necessarily higher”, in terms of blood Pb response, than those
estimates based on inhalation alone (USEPA 1986a, p. 11-106).  Thus, the
extent to which studies account for the full set of air-related
inhalation and ingestion exposure pathways affects the magnitude of the
resultant air-to-blood estimates, such that fewer pathways included as
“air-related” yields lower ratios.  The 1986 Criteria Document also
observed that ratios derived from studies focused only on inhalation
pathways (e.g., chamber studies, occupational studies) have generally
been on the order of 1:2 or lower, while ratios derived from studies
including more air-related pathways were generally higher (USEPA, 1986a,
p. 11-106).  Further, the current evidence appears to indicate higher
ratios for children as compared to those for adults (USEPA, 1986a),
perhaps due to behavioral differences between the age groups.

Reflecting these considerations, the 1986 Criteria Document identified a
range of air-to-blood ratios for children that reflected both inhalation
and ingestion-related air Pb contributions as generally ranging from 1:3
to 1:5 based on the information available at that time (USEPA 1986a, p.
11-106).  Table 11-36 (p. 11-100) in the 1986 Criteria Document (drawn
from Table 1 in Brunekreef, 1984) presents air-to-blood ratios from a
number of studies in children (i.e., those with identified air
monitoring methods and reliable blood Pb data).  For example,
air-to-blood ratios from the subset of those studies that used quality
control protocols and presented adjusted slopes include adjusted ratios
of 3.6 (Zielhuis et al., 1979), 5.2 (Billick et al., 1979, 1980); 2.9
(Billick et al., 1983), and 8.5 (Brunekreef et al, 1983).

Additionally, the 1986 Criteria Document noted that ratios derived from
studies involving higher blood and air Pb levels are generally smaller
than ratios from studies involving lower blood and air Pb levels (USEPA,
1986a. p. 11-99).  In consideration of this factor, the proposal
observed that the range of 1:3 to 1:5 in air-to-blood ratios for
children noted in the 1986 Criteria Document generally reflected study
populations with blood Pb levels in the range of approximately 10-30
µg/dL (USEPA 1986a, pp. 11-100; Brunekreef, 1984), much higher than
those common in today’s population.  This observation suggests that
air-to-blood ratios relevant for today’s population of children would
likely extend higher than the 1:3 to 1:5 range identified in the 1986
Criteria Document.

More recently, a study of changes in children’s blood Pb levels
associated with reduced Pb emissions and associated air concentrations
near a Pb smelter in Canada (for children through age six in age)
reports a ratio of 1:6, and additional analysis of the data by EPA for
the initial time period of the study resulted in a ratio of 1:7 (CD, pp.
3-23 to 3-24; Hilts, 2003).  Ambient air and blood Pb levels associated
with the Hilts (2003) study range from 1.1 to 0.03 µg/m3, and
associated population mean blood Pb levels range from 11.5 to 4.7
µg/dL, which are lower than levels associated with the older studies
cited in the 1986 Criteria Document (USEPA, 1986). 

The proposal identified sources of uncertainty related to air-to-blood
ratios obtained from Hilts (2003).  One such area of uncertainty relates
to the pattern of changes in indoor Pb dustfall (presented in Table 3 in
the article) which suggests a potentially significant decrease in Pb
impacts to indoor dust prior to closure of an older Pb smelter and
start-up of a newer facility in 1997.  Some have suggested that this
earlier reduction in indoor dustfall suggests that a significant portion
of the reduction in Pb exposure (and therefore, the blood Pb reduction
reflected in air-to-blood ratios) may have resulted from efforts to
increase public awareness of the Pb contamination issue (e.g., through
increased cleaning to reduce indoor dust levels) rather than reductions
in ambient air Pb and associated indoor dust Pb contamination.  In
addition, notable fluctuations in blood Pb levels observed prior to 1997
(as seen in Figure 2 of the article) have raised questions as to whether
factors other than ambient air Pb reduction could be influencing
decreases in blood Pb.   

In addition to the study by Hilts (2003), we are aware of two other
studies published since the 1986 Criteria Document that report
air-to-blood ratios for children (Tripathi et al., 2001 and Hayes et
al., 1994).  These studies were not cited in the 2006 Criteria Document,
but were referenced in public comments received by EPA during this
review.  The study by Tripathi et al. (2001) reports an air-to-blood
ratio of approximately 1:3.6 for an analysis of children aged six
through ten in India.  The ambient air and blood Pb levels in this study
(geometric mean blood Pb levels generally ranged from 10 to 15 µg/dL)
are similar to levels reported in older studies reviewed in the 1986
Criteria Document and are much higher than current conditions in the
U.S.  The study by Hayes et al. (1994) compared patterns of ambient air
Pb reductions and blood Pb reductions for large numbers of children in
Chicago between 1971 and 1988, a period when significant reductions
occurred in both measures.  The study reports an air-to-blood ratio of
1:5.6 associated with ambient air Pb levels near 1 µg/m3 and a ratio of
1:16 for ambient air Pb levels in the range of 0.25 µg/m3, indicating a
pattern of higher ratios with lower ambient air Pb and blood Pb levels
consistent with conclusions in the 1986 Criteria Document.  

In their advice to the Agency prior to the proposal, CASAC identified
air-to-blood ratios of 1:5, as used by the World Health Organization
(2000), and 1:10, as supported by an empirical analysis of changes in
air Pb and changes in blood Pb between 1976 and the time when the
phase-out of Pb from gasoline was completed (Henderson, 2007a).

In the proposal, beyond considering the evidence presented in the
published literature and that reviewed in Pb Criteria Documents, we also
considered air-to-blood ratios derived from the exposure assessment for
this review (summarized below in section II.A.3 and described in detail
in USEPA, 2007b).  In that assessment, current modeling tools and
information on children’s activity patterns, behavior and physiology
(e.g., CD, section 4.4) were used to estimate blood Pb levels associated
with multimedia and multipathway Pb exposure.  The results from the
various case studies included in this assessment, with consideration of
the context in which they were derived (e.g., the extent to which the
range of air-related pathways were simulated), are also informative to
our understanding of air-to-blood ratios.  

For the general urban case study, air-to-blood ratios ranged from 1:2 to
1:9 across the alternative standard levels assessed, which ranged from
the current standard of 1.5 µg/m3 down to a level of 0.02 µg/m3.  This
pattern of model-derived ratios generally supports the range of ratios
obtained from the literature and also supports the observation that
lower ambient air Pb levels are associated with higher air-to-blood
ratios.  There are a number of sources of uncertainty associated with
these model-derived ratios.  The hybrid indoor dust Pb model, which is
used in estimating indoor dust Pb levels for the urban case studies,
uses a U.S. Department of Housing and Urban Development (HUD) survey
dataset reflecting housing constructed before 1980 in establishing the
relationship between dust loading and concentration, which is a key
component in the hybrid dust model (as described in the Risk Assessment
Report, Volume II, Appendix G, Attachment G-1).  Given this application
of the HUD dataset, there is the potential that the nonlinear
relationship between indoor dust Pb loading and concentration (which is
reflected in the structure of the hybrid dust model) could be driven
more by the presence of indoor Pb paint than contributions from outdoor
ambient air Pb.  We also note that only recent air pathways were
adjusted in modeling the impact of ambient air Pb reductions on blood Pb
levels in the urban case studies, which could have implications for the
air-to-blood ratios.

For the primary Pb smelter (subarea) case study, air-to-blood ratios
ranged from 1:10 to 1:19 across the same range of alternative standard
levels, from 1.5 down to 0.02 µg/m3.  Because these ratios are based on
regression modeling developed using empirical data, there is the
potential for these ratios to capture more fully the impact of ambient
air on indoor dust Pb, and ultimately blood Pb, including longer
timeframe impacts resulting from changes in outdoor deposition. 
Therefore, given that these ratios are higher than ratios developed for
the general urban case study using the hybrid indoor dust Pb model
(which only considers reductions in recent air), the ratios estimated
for the primary Pb smelter (subarea) support the evidence-based
observation discussed above that consideration of more of the exposure
pathways relating ambient air Pb to blood Pb, may result in higher
air-to-blood Pb ratios.  In considering this case study, some have
suggested, however, that the regression modeling fails to accurately
reflect the temporal relationship between reductions in ambient air Pb
and indoor dust Pb, which could result in an over-estimate of the degree
of dust Pb reduction associated with a specified degree of ambient air
Pb reduction, which in turn could produce air-to-blood Pb ratios that
are biased high. 

In summary, EPA’s view in the proposal was that the current evidence
in conjunction with the results and observations drawn from the exposure
assessment, including related uncertainties, supports consideration of a
range of air-to-blood ratios for children ranging from 1:3 to 1:7,
reflecting multiple air-related pathways beyond simply inhalation and
the lower air and blood Pb levels pertinent to this review.  EPA invited
comment on this range as well as the appropriate weight to place on
specific ratios within this range.  Advice from CASAC and comments from
the public on this issue are discussed below in section II.C.3.

b.	Array of Health Effects and At-risk Subpopulations

Lead has been demonstrated to exert “a broad array of deleterious
effects on multiple organ systems via widely diverse mechanisms of
action” (CD, p. 8-24 and section 8.4.1).  This array of health effects
includes effects on heme biosynthesis and related functions;
neurological development and function; reproduction and physical
development; kidney function; cardiovascular function; and immune
function.  The weight of evidence varies across this array of effects
and is comprehensively described in the Criteria Document.  There is
also some evidence of Pb carcinogenicity, primarily from animal studies,
together with limited human evidence of suggestive associations (CD,
sections 5.6.2, 6.7, and 8.4.10).

ranging down to as low as 2 to 8 μg/dL” (CD, p. E-9).  

We note that many studies over the past decade, in investigating effects
at lower blood Pb levels, have utilized the CDC advisory level or level
of concern for individual children (10 µg/dL)  as a benchmark for
assessment, and this is reflected in the numerous references in the
Criteria Document to 10 µg/dL.  Individual study conclusions stated
with regard to effects observed below 10 µg/dL are usually referring to
individual blood Pb levels.  In fact, many such study groups have been
restricted to individual blood Pb levels below 10 µg/dL or below levels
lower than 10 µg/dL.  We note that the mean blood Pb level for these
groups will necessarily be lower than the blood Pb level they are
restricted below.

Threshold levels, in terms of blood Pb levels in individual children,
for neurological effects cannot be discerned from the currently
available studies (CD, pp. 8-60 to 8-63).  The Criteria Document states
“There is no level of Pb exposure that can yet be identified, with
confidence, as clearly not being associated with some risk of
deleterious health effects” (CD, p. 8-63).  As discussed in the
Criteria Document, “a threshold for Pb neurotoxic effects may exist at
levels distinctly lower than the lowest exposures examined in these
epidemiologic studies” (CD, p. 8-67).

As described in the proposal, physiological, behavioral and demographic
factors contribute to increased risk of Pb-related health effects. 
Potentially at-risk  subpopulations, also referred to as sensitive
sub-populations, include those with increased susceptibility (i.e.,
physiological factors contributing to a greater response for the same
exposure), as well as those with greater vulnerability (i.e., those with
increased exposure such as through exposure to higher media
concentrations or resulting from behavior leading to increased contact
with contaminated media), or those affected by socioeconomic factors,
such as reduced access to health care or low socioeconomic status.  

While adults are susceptible to Pb effects at lower blood Pb levels than
previously understood (e.g., CD, p. 8-25), the greater influence of past
exposures on their current blood Pb levels (as summarized above in
section II.A.2.a) leads us to give greater prominence to children as the
sensitive subpopulation in this review.  Children are at increased risk
of Pb-related health effects due to various factors that enhance their
exposures (e.g., via the hand-to-mouth activity that is prevalent in
very young children, CD, section 4.4.3) and susceptibility.  While
children are considered to be at a period of maximum exposure around
18-27 months, the current evidence has found even stronger associations
between blood Pb at school age and IQ at school age.  The evidence
“supports the idea that Pb exposure continues to be toxic to children
as they reach school age, and [does] not lend support to the
interpretation that all the damage is done by the time the child reaches
2 to 3 years of age” (CD, section 6.2.12).  The following
physiological and demographic factors can further affect risk of
Pb-related effects in some children.

particular genetic polymorphisms (e.g., presence of the
δ-aminolevulinic acid dehydratase-2 [ALAD-2] allele) have increased
sensitivity to Pb toxicity, which may be due to increased susceptibility
to the same internal dose and/or to increased internal dose associated
with same exposure (CD, p. 8-71, sections 6.3.5, 6.4.7.3 and 6.3.6).

Some children may have blood Pb levels higher than those otherwise
associated with a given Pb exposure (CD, section 8.5.3) as a result of
nutritional status (e.g., iron deficiency, calcium intake), as well as
genetic and other factors (CD, chapter 4 and sections 3.4, 5.3.7 and
8.5.3). 

Situations of elevated exposure, such as residing near sources of
ambient Pb, as well as socioeconomic factors, such as reduced access to
health care or low socioeconomic status (SES) (USEPA, 2003, 2005c) can
also contribute to increased blood Pb levels and increased risk of
associated health effects from air-related Pb.  

As described in the proposal (sections II.B.1.b and II.B.3), children in
poverty and black, non-Hispanic children have notably higher blood Pb
levels than do economically well-off children and white children, in
general.

c.	Neurological Effects in Children

Among the wide variety of health endpoints associated with Pb exposures,
there is general consensus that the developing nervous system in
children is among the, if not the, most sensitive.  While blood Pb
levels in U.S. children have decreased notably since the late 1970s,
newer studies have investigated and reported associations of effects on
the neurodevelopment of children with these more recent blood Pb levels
(CD, chapter 6).  Functional manifestations of Pb neurotoxicity during
childhood include sensory, motor, cognitive and behavioral impacts. 
Numerous epidemiological studies have reported neurocognitive,
neurobehavioral, sensory, and motor function effects in children with
blood Pb levels below 10 μg/dL (CD, sections 6.2 and 8.4).  As
discussed in the Criteria Document, “extensive experimental laboratory
animal evidence has been generated that (a) substantiates well the
plausibility of the epidemiologic findings observed in human children
and adults and (b) expands our understanding of likely mechanisms
underlying the neurotoxic effects” (CD, p. 8-25; section 5.3).  

	Cognitive effects associated with Pb exposures that have been observed
in epidemiological studies have included decrements in intelligence test
results, such as the widely used IQ score, and in academic achievement
as assessed by various standardized tests as well as by class ranking
and graduation rates (CD, section 6.2.16 and pp 8-29 to 8-30).  As noted
in the Criteria Document with regard to the latter, “Associations
between Pb exposure and academic achievement observed in the above-noted
studies were significant even after adjusting for IQ, suggesting that
Pb-sensitive neuropsychological processing and learning factors not
reflected by global intelligence indices might contribute to reduced
performance on academic tasks” (CD, pp 8-29 to 8-30).  

With regard to potential implications of Pb effects on IQ, the Criteria
Document recognizes the “critical” distinction between population
and individual risk, identifying issues regarding declines in IQ for an
individual and for the population.  The Criteria Document further states
that a “point estimate indicating a modest mean change on a health
index at the individual level can have substantial implications at the
population level” (CD, p. 8-77).  A downward shift in the mean IQ
value is associated with both substantial decreases in percentages
achieving very high scores and substantial increases in the percentage
of individuals achieving very low scores (CD, p. 8-81).  For an
individual functioning in the low IQ range due to the influence of
developmental risk factors other than Pb, a Pb-associated IQ decline of
several points might be sufficient to drop that individual into the
range associated with increased risk of educational, vocational, and
social failure (CD, p. 8-77).

 Pb levels below 10 μg/dL (CD, section 6.2.5 and pp. 8-30 to 8-31). 
The evidence for the role of Pb in this suite of effects includes
experimental animal findings (discussed in CD, section 8.4.2.1; p.
8-31), which provide strong biological plausibility of Pb effects on
learning ability, memory and attention (CD, section 5.3.5), as well as
associated mechanistic findings.  

	The persistence of such Pb-induced effects is described in the proposal
and the Criteria Document (e.g., CD, sections 5.3.5, 6.2.11, and 8.5.2).
 The persistence or irreversibility of such effects can be the result of
damage occurring without adequate repair offsets or of the persistence
of Pb in the body (CD, section 8.5.2).  It is additionally important to
note that there may be long-term consequences of such deficits over a
lifetime.  Poor academic skills and achievement can have “enduring and
important effects on objective parameters of success in real life”, as
well as increased risk of antisocial and delinquent behavior (CD,
section 6.2.16).  

 in the range of 5 to 10 μg/dL, and some analyses indicate Pb effects
on intellectual attainment of children for which population mean blood
Pb levels in the analysis ranged from 2 to 8 μg/dL (CD, sections 6.2,
8.4.2 and 8.4.2.6).  Thus, while blood Pb levels in U.S. children have
decreased notably since the late 1970s, newer studies have investigated
and reported associations of effects on the neurodevelopment of children
with blood Pb levels similar to the more recent, lower blood Pb levels
(CD, chapter 6; and as discussed in section II.B.2.b of the proposal).

The current evidence reviewed in the Criteria Document with regard to
the quantitative relationship between neurocognitive decrement, such as
IQ, and blood Pb levels indicates that the slope for Pb effects on IQ is
nonlinear and is steeper at lower blood Pb levels, such that each μg/dL
increase in blood Pb may have a greater effect on IQ at lower blood Pb
levels (e.g., below 10 μg/dL) than at higher levels (CD, section
6.2.13; pp. 8-63 to 8-64; Figure 8-7).  As stated in the CD, “the most
compelling evidence for effects at blood Pb levels <10 μg/dL, as well
as a nonlinear relationship between blood Pb levels and IQ, comes from
the international pooled analysis of seven prospective cohort studies
(n=1,333) by Lanphear et al. (2005)” (CD, pp. 6-67 and 8-37 and
section 6.2.3.1.11).  Using the full pooled dataset with concurrent
blood Pb level as the exposure metric and IQ as the response from the
pooled dataset of seven international studies, Lanphear and others
(2005) employed mathematical models of various forms, including linear,
cubic spline, log-linear, and piece-wise linear, in their investigation
of the blood Pb concentration-response relationship (CD, p. 6-29;
Lanphear et al., 2005).  They observed for this pooled dataset that the
shape of the concentration-response relationship is nonlinear and the
log-linear model provides a better fit over the full range of blood Pb
measurements than a linear one (CD, p. 6-29 and pp. 6-67 to 6-70;
Lanphear et al., 2005).  In addition, they found that no individual
study among the seven was responsible for the estimated nonlinear
relationship between Pb and deficits in IQ (CD p. 6-30).  Others have
also analyzed the same dataset and similarly concluded that, across the
range of the dataset’s blood Pb levels, a log-linear relationship was
a significantly better fit than the linear relationship (p=0.009) with
little evidence of residual confounding from included model variables
(CD, section 6.2.13; Rothenberg and Rothenberg, 2005).  

es predominant at blood-Pb levels greater than 10 μg/dL.

The current evidence includes multiple studies that have examined the
quantitative relationship between IQ and blood Pb level in analyses of
children with individual blood Pb concentrations below 10 μg/dL.  In
comparing across the individual epidemiological studies and the
international pooled analysis, the Criteria Document observed that at
higher blood Pb levels (e.g., above 10 μg/dL), the slopes (for change
in IQ with blood Pb) derived for log-linear and linear models are almost
identical, and for studies with lower blood Pb levels, the slopes appear
to be steeper than those observed in studies involving higher blood Pb
levels (CD, p. 8-78, Figure 8-7).  In making these observations, the
Criteria Document focused on the curves from the models from the 10th
percentile to the 90th percentile saying that the “curves are
restricted to that range because log-linear curves become very steep at
the lower end of the blood Pb levels, and this may be an artifact of the
model chosen”.

The quantitative relationship between IQ and blood Pb level has been
examined in the Criteria Document using studies where all or the
majority of study subjects had blood Pb levels below 10 μg/dL and also
where an analysis was performed on a subset of children whose blood Pb
levels have never exceeded 10 μg/dL (CD, Table 6-1).  The datasets for
three of these studies included concurrent blood Pb levels above 10
µg/dL; the concentration-response (C-R) relationship reported for one
of the three was linear while it was log-linear for the other two.  For
the one study among these three that reported a linear C-R relationship,
the highest blood Pb level was just below 12 μg/dL and the population
mean was 7.9 µg/dL (Kordas et al., 2006).  Of the two studies with
log-linear functions, one reported 69% of the children with blood Pb
levels below 10 μg/dL and a population mean blood Pb level of 7.44
μg/dL (Al-Saleh et al., 2001), and the second reported a population
median blood Pb level of 9.7 μg/dL and a 95th percentile of 33.2 μg/dL
(Lanphear et al., 2005).  In order to compare slopes across all of these
studies (linear and log-linear) in the Criteria Document, EPA estimated,
for each, the average slope of change in IQ with change in blood Pb
between the 10th percentile blood Pb level and 10 μg/dL (CD, Table
6-1).  The resultant group of reported and estimated average linear
slopes for IQ change with blood Pb levels up to 10 μg/dL range from
-0.4 to -1.8 IQ points per μg/dL blood Pb (CD, Tables 6-1 and 8-7),
with a median of -0.9 IQ points per μg/dL blood Pb (CD, p. 8-80).   
These slopes from Tables 6-1 and 8-7 of the Criteria Document are
presented in the second set of slopes in Table 1 below (adapted from
Table 1 of the proposal).  In this second set are studies (included in
the Criteria Document Table 6-1) that examined the quantitative
relationships of IQ and blood Pb in study populations for which most
blood Pb levels were below 10 µg/dL and for which a linear slope
restricted to blood Pb levels below about 10 µg/dL could be estimated.

Among this group of quantitative IQ-blood Pb relationships examined in
the Criteria Document (CD, Tables 6-1 and 8-7), the steepest slopes for
change in IQ with change in blood Pb level are those derived for the
subsets of children in the Rochester and Boston cohorts for which peak
blood Pb levels were <10 μg/dL; these slopes, in terms of IQ points per
µg/dL blood Pb, are -1.8 (for concurrent blood Pb influence on IQ) and
-1.6 (for 24-month blood Pb influence on IQ), respectively.  The mean
blood Pb levels for children in these subsets of the Rochester and
Boston cohorts are 3.32 (Canfield, 2008) and 3.8 μg/dL (Bellinger,
2008), respectively, which are the lowest population mean levels among
the datasets included in the table.  Other studies with analyses
involving similarly low blood Pb levels (e.g., mean levels below 4
μg/dL) also had slopes steeper than -1.5 points per µg/dL blood Pb. 
These include the slope of -1.71 points per µg/dL blood Pb for the
subset of 24-month old children in the Mexico City cohort with blood Pb
levels less than 5 μg/dL (n=193), for which the mean concurrent blood
Pb level was 2.9 μg/dL (Tellez-Rojo et al 2006, 2008), and the slope of
-2.94 points per µg/dL blood Pb for the subset of 6-10 year old
children whose peak blood Pb levels never exceeded 7.5 μg/dL (n=112),
and for which the mean concurrent blood Pb level was 3.24 μg/dL
(Lanphear et al 2005; Hornung 2008a).  Thus, from these subset analyses,
the slopes range from -1.71 to -2.94 IQ points per μg/dL of concurrent
blood Pb, as shown in the first set of slopes in Table 1.  In this first
set are studies that included quantitative relationships for IQ and
blood Pb that focused on lower individual blood Pb levels (below 7.5
µg/dL).  We also note that for blood Pb levels up to approximately 3.7
µg/dL, the slope of the nonlinear C-R function in which greatest
confidence is placed in estimating IQ loss in the quantitative risk
assessment (the LLL function)  falls intermediate between these two
values.  Table 1.  Summary of Quantitative Relationships of IQ and
Blood Pb for Two Sets of Studies Discussed Above.

Study/Analysis	Study Cohort	Analysis

Dataset	N	Range BLLA

(µg/dL)	Geometric Mean BLLA (µg/dL)

	Form of Model from which Average Slope Derived	Average Linear SlopeB

(points per µg/dL)

Set of studies from which steeper slopes are drawn in the proposal 

Tellez-Rojo <5 subgroup	Mexico City, age 24 mo	Children - BLL<5 µg/dL
193	0.8 – 4.9	2.9	Linear	-1.71

based on Lanphear et al 2005C,

 Log-linear with low-exposure linearization (LLL)	Dataset from which the
log-linear function is derived is the pooled International dataset of
1333 children, 

age 6-10 yr, having median blood Pb of 9.7 µg/dL and 5th -95th
percentile of 2.5-33.2 µg/dL. 	LLLD:                 -2.29 at 2 µg/dL

-1.89 at 3 µg/dL

Lanphear et al 2005C, <7.5 peak subgroup	Pooled International, age 6-10
yr	Children - peak  BLL <7.5 µg/dL	103	0.9-7.4	3.24	Linear	-2.94

Set of studies with shallower slopes (Criteria Document Table 6-1)
presented in the proposal E 

Canfield et al 2003C, <10 peak subgroup	Rochester, age 5 yr	Children-
peak BLL <10 µg/dL	71	0.5 – 8.4	3.32	Linear	-1.79

Bellinger and Needleman 2003C 	Boston B,F	Children - peak BLL <10 µg/dL
48	 1 - 9.3 F	3.8F	Linear	-1.56

Tellez-Rojo et al 2006 	Mexico City, age 24 mo	Full dataset	294	0.8 –
9.8	4.28	Linear	-1.04

Tellez-Rojo et al 2006 full – loglinear	Mexico City, age 24 mo	 Full
dataset	294	0.8 – 9.8	4.28	Log-linear	-0.94 G

Lanphear et al 2005C, <10 peakCsubgroup	Pooled International, age 6-10
yr	Children - peak BLL <10 µg/dL	244	0.1 - 9.8	4.30	Linear	-0.80

Al-Saleh et al 2001 full – loglinear	Saudi Arabia, age 6-12 yr	 Full
dataset	533	2.3– 27.36 H	7.44	Log-linear	-0.76 G

Kordas et al 2006, <12 subgroup	Torreon, Mexico, age 7 yr	Children -
BLL<12 µg/dL	377	2.3 - <12	7.9	Linear	-0.40

Lanphear et al 2005C full – loglinear	Pooled International, age 6-10
yr	Full dataset	1333	0.1 – 71.7	9.7 (median)	Log-linear	-0.41 G

Median value 	-0.9D

A Blood Pb level (BLL) information provided here is drawn from
publications listed in table, in some cases augmented by study authors
(Bellinger, 2008; Canfield, 2008a,b; Hornung, 2008a,b; Kordas, 2008;
Tellez-Rojo, 2008).

BAverage linear slope estimates here are for relationship between IQ and
concurrent blood Pb levels (BLL), except for Bellinger & Needleman which
used 24 month BLLs with 10 year old IQ.

C 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. 

DThe LLL function (described in section II.C.2.b) was developed from
Lanphear et al 2005 loglinear model with a linearization of the slope at
BLL below 1 µg/dL.  In estimating IQ loss with this function in the
risk assessment (section II.A.3) the nonlinear form of the model with
varying slope was used for all BLL above 1 µg/dL.  The slopes shown are
the average slopes (IQ points per µg/dL blood Pb) associated with
application of the LLL functions from zero to the blood Pb levels
identified (2 and 3 µg/dL).

E These studies and quantitative relationships are discussed in the
Criteria Document (CD, sections 6.2, 6.2.1.3 and 8.6.2). 

F The BLL for Bellinger and Needleman (2003) are for age 24 months.

G For nonlinear models, this is the estimated average slope for change
in IQ with change in blood Pb over the range from the 10th percentile
blood Pb value in study to 10 µg/dL (CD, p. 6-65).   The shape of these
models is such that the average slopes from the 10th percentiles to a
value lower than 10 µg/dL are larger negative values than those shown
here (e.g., the slopes to 5 µg/dL are ~50% larger negative values).

H 69% of children in Al-Saleh et al (2001) study had BLL<10 µg/dL

3.	Overview of Human Exposure and Health Risk Assessments

To put judgments about risk associated with exposure to air-related Pb
in a broader public health context, EPA developed and applied models to
estimate human exposures to air-related Pb and associated health risk
for various air quality scenarios and alternative standards.  The design
and implementation of the risk assessment needed to address significant
limitations and complexity that go far beyond the situation for similar
assessments typically performed for other criteria pollutants.  The
multimedia and persistent nature of Pb and the role of multiple exposure
pathways add significant complexity as compared with other criteria
pollutants that focus only on the inhalation exposure.  Not only was the
risk assessment constrained by the timeframe allowed for this review in
the context of the breadth of information to address, it was also
constrained by significant limitations in data and modeling tools for
the assessment, as described in section II.C.2.h of the proposal.  

The scope and methodology for this assessment were developed over the
last few years with considerable input from the CASAC Pb Panel and the
public, as described in the proposal (section II.C.2.a).  The following
sections provide a brief summary of the quantitative exposure and risk
assessment and key findings.  The complete full-scale assessment,
including the associated uncertainties, is more fully summarized in
section II.C of the proposal and described in detail in the Risk
Assessment Report (USEPA, 2007b).

a.	Design Aspects and Associated Uncertainties

As discussed in section II.C.2 of the proposal, EPA conducted exposure
and risk analyses to estimate blood Pb and associated IQ loss in
children exposed to air-related Pb.  As recognized in section II.A.2
above and discussed in the proposal notice and Criteria Document, among
the wide variety of health endpoints associated with Pb exposures, there
is general consensus that the developing nervous system in children is
among, if not, the most sensitive, and that neurobehavioral effects
(specifically neurocognitive deficits), including IQ decrements, appear
to occur at lower blood Pb levels than previously believed.  The
selection of children’s IQ for the quantitative risk assessment
reflects consideration of the evidence presented in the Criteria
Document as well as advice received from CASAC (Henderson, 2006, 2007a).

The brief summary provided here focuses on blood Pb and risk estimates
for five case studies that generally represent two types of population
exposures: (1) more highly air-pathway exposed children (as described
below) residing in small neighborhoods or localized residential areas
with air concentrations somewhat near the standard being evaluated, and
(2) location-specific urban populations with a broader range of
air-related exposures.

The case studies representing the more highly air-pathway exposed
children are the general urban case study and the primary Pb smelter
case study.  The general urban case study case study is not based on a
specific geographic location and reflects several simplifications in
representing exposure including uniform ambient air Pb levels associated
with the standard of interest across the hypothetical study area and a
uniform study population.  Additionally, the method for simulating
temporal variability in air Pb concentrations in this case study relied
on national average estimates of the relationships between air
concentrations in terms of the statistics considered for different forms
of the standard being assessed and the annual ambient air concentrations
required for input to the blood Pb model.  Thus, while this case study
provides characterization of risk to children that are relatively more
highly air pathway exposed (as compared to the location-specific case
studies), this case study is not considered to represent a high-end
scenario with regard to the characterization of ambient air Pb levels
and associated risk.  The primary Pb smelter case study provides risk
estimates for children living in a specific area that is currently not
in attainment with the current NAAQS.  We have focused on a subarea
within 1.5 km of the facility where airborne Pb concentrations are
closest to the current standard and where children’s air-related
exposures are most impacted by emissions associated with the Pb smelter
from which air Pb concentrations were estimated.

The three location-specific urban case studies focus on specific
residential areas within Cleveland, Chicago, and Los Angeles to provide
representations of urban populations with a broader range of air-related
exposures due to spatial gradients in both ambient air Pb levels and
population density.  For example, the highest air concentrations in
these case studies (i.e., those closest to the standard being assessed)
are found in very small parts of the study areas, while a large majority
of the case study populations reside in areas with much lower air
concentrations.

Based on the nature of the population exposures represented by the two
categories of case study, the first category (the general urban and
primary Pb smelter case studies) relates more closely to the air-related
IQ loss evidence-based framework described in the proposal (sections
II.D.2.a.ii and II.E.3.a) with regard to estimates of air-related IQ
loss.  As mentioned above, these case studies, as compared to the other
category of case studies, include populations that are relatively more
highly exposed by way of air pathways to air Pb concentrations somewhat
near the standard level evaluated.

The air quality scenarios assessed include (a) the current NAAQS (for
all five case studies); (b) current conditions for the location-specific
and general urban case studies (which are below the current NAAQS); and
(c) a range of alternate standard levels (for all case studies).  The
alternative NAAQS scenarios included levels of 0.50, 0.20, 0.05 and 0.02
µg/m3, with a form of maximum monthly average, as well as a level of
0.20 µg/m3, with a form of maximum quarterly average.  Details of the
assessment scenarios, including the Pb concentrations for other media
are presented in Sections 2.3 and 5.1.1 of the Risk Assessment Report
(USEPA, 2007b).

Exposure and associated blood Pb levels were simulated using the IEUBK
model, as more fully described and presented in the Risk Assessment
Report (USEPA, 2007b).  Because of the nonlinear response of blood Pb to
exposure and also the nonlinearity reflected in the C-R functions for
estimation of IQ loss, this assessment first estimated total blood Pb
and risk (air- and nonair-related), and then separated out those
estimates of blood Pb and associated risk associated with the pathways
of interest in this review.  We separated out the estimates of total
(all-pathway) blood Pb and IQ loss into a background category and two
air-related categories (referred to as “recent air” and “past
air”).  However, significant limitations in our modeling tools and
data resulted in an inability to parse specific risk estimates into
specific pathways, such that we have approximated estimates for the
air-related and background categories. 

Those Pb exposure pathways tied most directly to ambient air, which
consequently have the potential to respond relatively more quickly to
changes in air Pb (i.e., inhalation and ingestion of indoor dust Pb
derived from the infiltration of ambient air Pb indoors), were placed
into the "recent air" category.  The other air-related Pb exposure
pathways, all of which are associated with atmospheric deposition, were
placed into the “past air” category.  These include ingestion of Pb
in outdoor dust/soil and ingestion of the portion of Pb in indoor dust
that after deposition from ambient air outdoors is carried indoors with
humans (as noted in section II.A.1 above).

Among the limitations affecting our estimates for the air-related and
background categories is the apportionment of background (nonair)
pathways.  For example, while conceptually indoor Pb paint contributions
to indoor dust Pb would be considered background and included in the
“background” category for this assessment, due to technical
limitations related to indoor dust Pb modeling, dust from Pb paint was
included as part of "other" indoor dust Pb (i.e., as part of past air
exposure).  The inclusion of indoor paint Pb as a component of "other"
indoor dust Pb (and consequently as a component of the “past air”
category) represents a source of potential high bias in our prediction
of exposure and risk associated with the “past air” category because
conceptually, exposure to indoor paint Pb is considered part of
background exposure.  At the same time, Pb in ambient air does
contribute to the exposure pathways included in the “background”
category (drinking water and diet), and is likely a substantial
contribution to diet (CD, p. 3-48).  We could not separate the air
contribution from the nonair contributions, and the total contribution
from both the drinking water and diet pathways are categorized as
“background” in this assessment.  As a result, our “background”
risk estimate includes some air-related risk representing a source of
potential low bias in our predictions of air-related risk.

Further, we note that in simulating reductions in exposure associated
with reducing ambient air Pb levels through alternative NAAQS (and
increases in exposure if the current NAAQS was reached in certain case
studies) only the exposure pathways categorized as “recent air”
(inhalation and ingestion of that portion of indoor dust associated with
outdoor ambient air) were varied with changes in air concentration.  The
assessment did not simulate decreases in “past air” exposure
pathways (e.g., reductions in outdoor soil Pb levels following reduction
in ambient air Pb levels and a subsequent decrease in exposure through
incidental soil ingestion and the contribution of outdoor soil to indoor
dust).  These exposures were held constant across all air quality
scenarios. 

In summary, because of limitations in the assessment design, data and
modeling tools, our risk estimates for the “past air” category
include both risks that are truly air-related and potentially, some
background risk.  Because we could not sharply separate Pb linked to
ambient air from Pb that is background, some of the three categories of
risk are underestimated and others overestimated.  On balance, we
believe this limitation leads to a slight overestimate of the risks in
the “past air” category.  At the same time, as discussed above, the
"recent air" category does not fully represent the risk associated with
all air-related pathways.  Thus, we consider the risk attributable to
air-related exposure pathways to be bounded on the low end by the risk
estimated for the “recent air” category and on the upper end by the
risk estimated for the “recent air” plus “past air” categories.

As discussed in the proposal notice and in greater detail in the Staff
Paper and Risk Assessment Report, exposure and risk modeling conducted
for this analysis was complex and subject to significant uncertainties
due to limitations, data, models and time available.  Key assumptions,
limitations and uncertainties, which were recognized in various ways in
the assessment and presentation of results, are listed here, beginning
with those related to design of the assessment or case studies, followed
by those related to estimation of Pb concentrations in ambient air,
indoor dust, outdoor soil/dust, and blood, and estimation of Pb-related
IQ loss.

Temporal Aspects:  During the 7-year exposure period, media
concentrations remain fixed and the simulated child remains at the same
residence (while exposure factors and physiological parameters are
adjusted to match the age of the child).  

General Urban Case Study:  The design for this case study employs
assumptions regarding uniformity that are reasonable in the context of a
small neighborhood population, but would contribute significant
uncertainty to extrapolation of these estimates to a specific urban
location, particularly a relatively large one.  Thus, the risk estimates
for this general urban case study, while generally representative of an
urban residential population exposed to the specified ambient air Pb
levels, cannot be readily related to a specific large urban population.

Location-specific Urban Case Studies:  Limitations in the ambient air
monitoring network limit our characterization of spatial gradients of
ambient air Pb levels in these case studies.

Air Quality Simulation:  The proportional roll-up and roll-down
procedures used in some case studies to simulate current NAAQS and
alternate NAAQS levels, respectively, assume proportional changes in air
concentrations across the study area in those scenarios for those case
studies.  EPA recognizes that it is extremely unlikely that Pb
concentrations would rise to just meet the current NAAQS in urban areas
nationwide and that there is substantial uncertainty with our simulation
of such conditions in the urban location-specific case studies.  There
is also significant uncertainty in simulation conditions associated with
the implementation of emissions reduction actions to meet a lower
standard. 

Outdoor Soil/Dust Pb Concentrations:  Uncertainty regarding soil/dust Pb
levels and the inability to simulate the influence of changing air Pb
levels related to lowering the NAAQS contributes uncertainty to
air-related risk estimates.

Indoor Dust Pb Concentrations:  Limitations and uncertainty in modeling
of indoor dust Pb levels, including the impact of reductions in ambient
air Pb levels, contributes uncertainty to air-related risk estimates.

Interindividual Variability in Blood Pb Levels:  Uncertainty related to
population variability in blood Pb levels and limitations in modeling of
this introduces significant uncertainty into blood Pb and IQ loss
estimates for the 95th percentile of the population.

Pathway Apportionment for Higher Percentile Blood Pb and IQ Loss: 
Limitations in data, modeling tools and assessment design introduce
uncertainty into estimates of air-related blood Pb and IQ loss for the
upper ends of population distribution.

IQ Loss Concentration-response Functions:  Specification of the
quantitative relationship between blood Pb level and IQ loss is subject
to significant uncertainty at lower blood Pb levels (e.g., below 5
µg/dL concurrent blood Pb).

b.	Summary of Blood Pb Estimates 

Key observations regarding the blood Pb estimates from this analysis are
noted here:

As shown in Table 2 of the proposal (73 FR 29215), median blood Pb
levels for the current conditions air quality scenario in the urban case
studies ranged from 1.7-1.8 µg/dL for the location-specific case
studies up to 1.9 µg/dL for the general urban case study.  These values
are slightly larger than the median value from NHANES for children aged
1-5 years old in 2003-2004 of 1.6 µg/dL (  HYPERLINK
"http://www.epa.gov/envirohealth/children/body_burdens/b1-table.htm" 
http://www.epa.gov/envirohealth/children/body_burdens/b1-table.htm ). 
Blood Pb level estimates for the 90th percentile in the urban case
studies are also higher than the NHANES 90th percentile blood Pb levels.
 We note, however, that ambient air Pb levels in the urban case studies
are higher than those at most monitoring sites in the U.S., as described
in section II.C.3.a of the proposal.

With regard to air-to-blood ratios, estimates for the general urban case
study ranged from 1:2 to 1:9 with the majority of the estimates ranging
from 1:4 to 1:6.   Because the risk assessment only reflects the impact
of reductions on recent air-related pathways in predicting changes in
indoor dust Pb for the general urban case study (as noted in section
II.C.3.a of the proposal), however, the ratios generated are lower than
they would be if they had also reflected other air-related pathways
(e.g., changes in outdoor surface soil/dust and dietary Pb with changes
in ambient air Pb).  

Air-to-blood ratios estimated for the primary Pb smelter subarea ranged
from 1:10 and higher.  One reason for these estimates being higher than
those for the urban case study may be that the dust Pb model used may
somewhat reflect ambient air-related pathways other than that of ambient
air infiltrating a home.

c.	Summary of IQ Loss Estimates

As described more fully in the proposal notice and in the Risk
Assessment Report (USEPA, 2007b, section 5.3.1), four sets of IQ loss
estimates were derived from the blood Pb estimates, one for each of four
concentration-response functions derived from the international pooled
analysis by Lanphear and others (2005).  Each of these four functions
utilizes a different approach for characterizing low-exposure IQ loss,
thereby providing a range of estimates intended to reflect the
uncertainty in this key aspect of the risk assessment.  As described in
section II.C.2.b of the proposal (and in more detail in section 2.1.5 of
the Risk Assessment Report), we have placed greater confidence in the
log-linear function with low-exposure linearization (LLL) and present
risk estimates based on that function here.

The risk estimates summarized here are those considered most relevant to
the review in considering whether the current NAAQS and potential
alternative NAAQS provide protection of public health with an adequate
margin of safety (i.e., estimates of IQ loss associated with air-related
Pb exposure).  In considering these estimates, we note that IQ loss
associated with air-related Pb is bounded on the low end by risk
associated with the recent air category of exposure pathways and on the
upper end by the recent plus past air categories of pathways (as
described above in section II.A.3.a).  Key observations regarding the
median estimates of air-related risk for the current NAAQS and
alternative standards include:

As shown in Table 2 below (Table 3 in the proposal), in all five case
studies, the lower bound of population median air-related risk
associated with the current NAAQS exceeds 2 points IQ loss, and the
upper bound is near or above 4 points.

Alternate standards provide substantial reduction in estimates of
air-related risk across the full set of alternative NAAQS considered,
particularly for the lower bound of air-related risk which includes only
the pathways that were varied with changes in air concentrations (as
shown in Table 2).

In the general urban case study, the estimated population median
air-related risk falls between 1.9 and 3.6 points IQ loss for an
alternative NAAQS of 0.50 µg/m3, maximum monthly average, between 1.2
and 3.2 points IQ loss for an alternative NAAQS of 0.20 µg/m3 and
between 0.5 and 2.8 points IQ loss for an alternate NAAQS of 0.05
µg/m3, maximum monthly average, (as shown in Table 2).  Higher risk
estimates are associated with a maximum quarterly averaging time (USEPA,
2007b).

At each NAAQS level assessed, the upper bound of population median
air-related risk for the primary Pb smelter subarea, which due to
limitations in modeling is the only air-related risk estimate for this
case study, is generally higher than that for the general urban case
study, likely due to differences in the indoor dust models used for the
two case studies (as discussed in section II.C.3.b of the proposal). 

Compared to the other case studies, the air-related risk for the
location-specific case studies is smaller because of the broader range
of air-related exposures and the population distribution.  For example,
the majority of the populations in each of the location-specific case
studies resides in areas with ambient air Pb levels well below each
standard level assessed, particularly for standard levels above 0.05
µg/m3, maximum monthly average.  Consequently, risk estimates for these
case studies indicate little response to alternative standard levels
above 0.05 µg/m3 maximum monthly average (as shown in Table 2).

Table 2.  Summary of risk attributable to air-related Pb exposure. 

NAAQS Level Simulated 

(μg/m3 max monthly,

 except as noted below)	Median air-related IQ loss A

	General urban case study	Primary Pb  smelter (subarea) case study B, C
Location-specific urban case studies

	Cleveland

(0.56 μg/m3)	Chicago

(0.31 μg/m3)	Los Angeles

(0.17 μg/m3)

1.5 max quarterlyD

	3.5 - 4.8	< 6	2.8 - 3.9 E	3.4 - 4.7 E	2.7 - 4.2 E

	(1.5 - 7.7)	<(3.2 - 9.4)	(0.6 - 4.6)	(1.4 - 7.4)	(1.1 - 6.2)

0.5	1.9 - 3.6	< 4.5	0.6 - 2.9	F	F

	(0.7 - 4.8)	<(2.1 - 7.7)	(0.2 - 3.9)

0.2	1.2 - 3.2	< 3.7	0.6 - 2.8	0.6 - 2.9	0.7 - 2.9 G

	(0.4 - 4.0)	<(1.2 - 5.1)	(0.1 - 3.2)	(0.3 - 3.6)	(0.2 - 3.5)

0.05 	0.5 - 2.8	< 2.8	0.1 - 2.6	0.2 - 2.6	0.3 - 2.7

	(0.2 - 3.3)	<(0.9 - 3.4)	(<0.1 - 3.1)	(0.1 - 3.2)	(0.1 - 3.2)

0.02	0.3 - 2.6	< 2.9	<0.1 - 2.6	0.1 - 2.6	0.1 - 2.6

	(0.1 - 3.1)	<(0.9 - 3.3)	(<0.1 - 3.0)	(<0.1 - 3.1)	(<0.1 - 3.1)

A -  Air-related risk is bracketed by “recent air” (lower bound of
presented range) and “recent” plus “past air” (upper bound of
presented range).  While differences between standard levels are better
distinguished by differences in the “recent” plus “past air”
estimates (upper bounds shown here), these differences are inherently
underestimates. The term “past air” includes contributions from the
outdoor soil/dust contribution to indoor dust, historical air
contribution to indoor dust, and outdoor soil/dust pathways; “recent
air” refers to contributions from inhalation of ambient air Pb or
ingestion of indoor dust Pb predicted to be associated with outdoor
ambient air Pb levels, with outdoor ambient air also potentially
including resuspended, previously deposited Pb (see section II.C.2.e of
the proposal). Boldface values are estimates generated using the
log-linear with low-exposure linearization function.  Values in
parentheses reflect the range of estimates associated with all four
concentration-response functions. 

B – In the case of the primary Pb smelter case study, only recent plus
past air estimates are available.  

C – Median air-related IQ loss estimates for the primary Pb smelter
(full study area) range from <1.7 to <2.9 points, with no consistent
pattern across simulated NAAQS levels. This lack of a pattern reflects
inclusion of a large fraction of the study population with relatively
low ambient air impacts such that there is lower variation (at the
population median) across standard levels (see section  4.2 of the Risk
Assessment, Volume 1).

D – This corresponds to roughly 0.7 - 1.0 μg/m3 maximum monthly mean,
across the urban case studies

E - A “roll-up” was performed so that the highest monitor in the
study area is increased to just meet this level. 

F – A “roll-up” to this level was not performed.  

G – A “roll-up” to this level was not performed; these estimates
are based on current conditions in this area.

B. Need for Revision of the Current Primary Standard	

The initial issue to be addressed in the current review of the primary
Pb standard is whether, in view of the advances in scientific knowledge
reflected in the Criteria Document and Staff Paper, the existing
standard should be revised.  In evaluating whether it is appropriate to
revise the current standard, the Administrator builds on the general
approach used in the initial setting of the standard, as well as that
used in the last review, and reflects the broader body of evidence and
information now available.  The approach used is based on an integration
of information on health effects associated with exposure to ambient Pb;
expert judgment on the adversity of such effects on individuals; and
policy judgments as to when the standard is requisite to protect public
health with an adequate margin of safety, which are informed by air
quality and related analyses, quantitative exposure and risk assessments
when possible, and qualitative assessment of impacts that could not be
quantified.  The Administrator has taken into account both
evidence-based and quantitative exposure- and risk-based considerations
in developing conclusions on the adequacy of the current primary Pb
standard.

The Administrator’s proposed conclusions on the adequacy of the
current primary standard are summarized below in the Introduction
(section II.B.1), followed by consideration of comments received on the
proposal (section II.B.2) and the Administrator’s final decision with
regard to the need for revision of the current primary standard
(II.B.3).

1. Introduction

As described in section II.D.1.a of the proposal, the current standard
was set in 1978 to provide protection to the public, especially children
as the particularly sensitive population subgroup, against Pb-induced
adverse health effects (43 FR 46246).  The standard was set to provide
protection against anemia (as well as effects associated with higher
exposures), with consideration of impacts on the heme synthesis pathway
leading to anemia (43 FR 46252-46253).  In setting the standard, EPA
determined that “the maximum safe level of blood lead for an
individual child” should be no higher than 30 µg/dL, and described 15
µg/dL Pb as “the maximum safe blood lead level (geometric mean) for a
population of young children” (43 FR 46247, 46253).  The basis for the
level, averaging time, form and indicator are described in section
II.D.1.a of the proposal.  

extending to as low as 10 to 15 μg/dL or, possibly, below) as being
associated with slowed physical and neurobehavioral development, lower
IQ, impaired learning, and/or other indicators of adverse neurological
impacts; and (b) other pathophysiological effects of Pb on
cardiovascular function, immune system components, calcium and vitamin D
metabolism and other selected health endpoints” (CD, pp. 8-24 to
8-25).  This evidence is discussed fully in the Criteria Document.  

In the proposal, EPA explained its evidence-based considerations
regarding the adequacy of the current standard.  With regard to the
sensitive population, while the sensitivity of the elderly and other
particular subgroups is recognized, as at the time the current standard
was set, young children continue to be recognized as a key sensitive
population for Pb exposures.

With regard to the exposure levels at which adverse health effects
occur, the proposal noted that the current evidence demonstrates the
occurrence of adverse health effects at appreciably lower blood Pb
levels than those demonstrated by the evidence at the time the standard
was set.  This evidence is reflected in changes over the intervening
years in the CDC’s identification and description of their advisory
level for Pb in individual children’s blood (as described above in
section II.A.2.a).  The current evidence indicates the occurrence of a
variety of health effects, including neurological effects in children,
associated with blood Pb levels extending well below 10 µg/dL (CD,
sections 6.2, 8.4 and 8.5).  For example, as noted in the Criteria
Document with regard to the neurocognitive effects in children, the
“weight of overall evidence strongly substantiates likely occurrence
of [this] type of effect in association with blood-Pb concentrations in
range of 5-10 μg/dL, or possibly lower … Although no evident
threshold has yet been clearly established for those effects, the
existence of such effects at still lower blood-Pb levels cannot be ruled
out based on available data.” (CD, p. 8-61).  The Criteria Document
further notes that any such threshold may exist “at levels distinctly
lower than the lowest exposures examined in these epidemiological
studies” (CD, p. 8-67).

In considering the adequacy of the current standard, the Staff Paper
considered the evidence in the context of the framework used to
determine the standard in 1978, as adapted to reflect the current
evidence.  In so doing, the Staff Paper recognized that the health
effects evidence with regard to characterization of a threshold for
adverse effects has changed since the standard was set in 1978, as have
the Agency’s views on the characterization of a safe blood Pb level. 
As summarized in the proposal (73 FR 29237-38) and described in the
Staff Paper (section 5.4.1), parameters for this framework include
estimates for average nonair blood Pb level, and air-to-blood ratio, as
well as a maximum safe individual and/or geometric mean blood Pb level. 
For this last parameter, the Staff Paper for the purposes of this
evaluation considered the lowest population mean blood Pb levels with
which some neurocognitive effects have been associated in the evidence.

Based on the current evidence, the Staff Paper first concluded that
young children remain the sensitive population of primary focus in this
review and that “there is now no recognized safe level of Pb in
children’s blood and studies appear to show adverse effects at
population mean concurrent blood Pb levels as low as approximately 2
µg/dL (CD, pp. 6-31 to 6-32; Lanphear et al., 2000)” (USEPA, 2007c). 
The Staff Paper further stated that “while the nonair contribution to
blood Pb has declined, perhaps to a range of 1.0-1.4 µg/dL, the
air-to-blood ratio appears to be higher at today’s lower blood Pb
levels than the estimates at the time the standard was set, with current
estimates on the order of 1:3 to 1:5 and perhaps up to 1:10” (USEPA,
2007c).  Adapting the framework employed in setting the standard in
1978, the Staff Paper concluded that “the more recently available
evidence suggests a level for the standard that is lower by an order of
magnitude or more” (USEPA, 2007c, p. 5-17).

Since completion of the Staff Paper and ANPR, the Agency further
considered the evidence with regard to adequacy of the current standard
using an approach other than the adapted 1978 framework considered in
the Staff Paper.  This alternative evidence-based framework, referred to
as the air-related IQ loss framework, shifts focus from identifying an
appropriate target population mean blood lead level and instead focuses
on the magnitude of effects of air-related Pb on neurocognitive
functions.  This framework builds on a recommendation by the CASAC Pb
Panel to consider the evidence in a more quantitative manner, and is
discussed in more detail in section II.E.3.a.ii of the proposal.

In this air-related IQ loss framework, EPA draws from the entire body of
evidence as a basis for concluding that there are causal associations
between air-related Pb exposures and population IQ loss.  We also draw
more quantitatively from the evidence by using evidence-based C-R
functions to quantify the association between air Pb concentrations and
air-related population mean IQ loss.  Thus, this framework more fully
considers the evidence with regard to the concentration-response
relationship for the effect of Pb on IQ than does the adapted 1978
framework, and it also draws from estimates for air-to-blood ratios.  

In the proposal, while we noted the evidence of steeper slope for the
C-R relationship for blood Pb concentration and IQ loss at lower blood
Pb levels (described above in sections II.A.2.c), we stated that for
purposes of consideration of the adequacy of the current standard we
were concerned with the C-R relationship for blood Pb levels that would
be associated with exposure to air-related Pb at the level of the
current standard.  For this purpose, we focused on a median linear
estimate of the slope of the C-R function from study populations for
which most blood Pb levels were below 10 µg/dL and for which a linear
slope restricted to blood Pb levels below about 10 µg/dL could be
estimated (described in CD, pp. 6-65 to 6-66 and summarized in section
II.B.2.b of the proposal).  The median slope estimate is -0.9 IQ points
per µg/dL blood Pb (CD, p. 8-80).  Applying estimates of air-to-blood
ratios ranging from 1:3 to 1:5, drawing from the discussion of
air-to-blood ratios in section II.B.1.c of the proposal, to a population
of children exposed at the current level of the standard is estimated to
result in an average air-related blood Pb level above 4 µg/dL. 
Multiplying these blood Pb levels by the slope estimate, identified
above, for blood Pb levels extending up to 10 µg/dL (-0.9 IQ points per
µg/dL), would imply an average air-related IQ loss for such a group of
children on the order of 4 or more IQ points.

In the proposal, EPA also explained its exposure- and risk- based
considerations regarding the adequacy of the current standard.  EPA
estimated exposures and health risks associated with air quality that
just meets the current standard (as described in the Risk Assessment
Report) to help inform judgments about whether or not the current
standard provides adequate protection of public health, taking into
account key uncertainties associated with the estimated exposures and
risks (summarized above in section II.C of the proposal and more fully
in the Risk Assessment Report).  In considering the adequacy of the
standard, the Staff Paper considered exposure and risk estimates from
the quantitative risk assessment, taking into account associated
uncertainties.  The Staff Paper first considered exposure/risk estimates
associated with air-related risk, which as recognized in section II.A.3
above (and summarized in section II.C.2.e of the proposal and described
more fully in the Risk Assessment Report) are approximated estimates,
provided in terms of upper and lower bounds.  The Staff Paper described
the magnitude of these estimates for the current NAAQS as being
indicative of levels of IQ loss associated with air-related risk that
may “reasonably be judged to be highly significant from a public
health perspective” (USEPA, 2007c).

As discussed in section II.D.2.b of the proposal, the Staff Paper also
describes a different risk metric that estimated differences in the
numbers of children with different amounts of Pb-related IQ loss between
air quality scenarios for current conditions and for the current NAAQS
in the three location-specific urban case studies.  The Staff Paper
concluded that these estimated differences “indicate the potential for
significant numbers of children to be negatively affected if air Pb
concentrations increased to levels just meeting the current standard”
(USEPA, 2007c).  Beyond the findings related to quantified IQ loss, the
Staff Paper recognized the potential for other, unquantified adverse
effects that may occur at similarly low exposures as those
quantitatively assessed in the risk assessment.  In summary, the Staff
Paper concluded that taken together, “the quantified IQ effects
associated with the current NAAQS and other, nonquantified effects are
important from a public health perspective, indicating a need for
consideration of revision of the standard to provide an appreciable
increase in public health protection” (USEPA, 2007c).

In their letter to the Administrator subsequent to consideration of the
ANPR, the Staff Paper and the Risk Assessment Report, the CASAC Pb Panel
advised the Administrator that they unanimously and fully supported
“Agency staff’s scientific analyses in recommending the need to
substantially lower the level of the primary (public-health based) Lead
NAAQS, to an upper bound of no higher than 0.2 µg/m3 with a monthly
averaging time” (Henderson, 2008a, p. 1).  The Panel additionally
advised that the current Pb NAAQS “are totally inadequate for assuring
the necessary decreases of lead exposures in sensitive U.S. populations
below those current health hazard markers identified by a wealth of new
epidemiological, experimental and mechanistic studies”, and that “it
is the CASAC Lead Review Panel’s considered judgment that the NAAQS
for Lead must be decreased to fully-protect both the health of children
and adult populations” (Henderson, 2007a, p. 5).  CASAC drew support
for their recommendation from the current evidence, described in the
Criteria Document, of health effects occurring at dramatically lower
blood Pb levels than those indicated by the evidence available when the
standard was set and of a recognition of effects that extend beyond
children to adults.

At the time of proposal, in considering whether the current primary
standard should be revised, the Administrator carefully considered the
conclusions contained in the Criteria Document, the information,
exposure/risk assessments, conclusions and recommendations presented in
the Staff Paper, the advice and recommendations from CASAC, and public
comments received on the ANPR and other documents to date.  In so doing,
the Administrator noted the following:  (1) a substantially expanded
body of available evidence, described briefly in section II.A above and
more fully in section II.B of the proposal and discussed in the Criteria
Document, from that available when the current standard was set three
decades ago; (2) evidence of the occurrence of health effects at
appreciably lower blood Pb levels than those demonstrated by the
evidence at the time the standard was set in 1978; (3) the currently
available robust evidence of neurotoxic effects of Pb exposure in
children, both with regard to epidemiological and toxicological studies;
(4) associations of effects on the neurodevelopment of children with
blood Pb levels notably decreased from those in the late 1970s; (5)
toxicological evidence including extensive experimental laboratory
animal evidence that substantiates well the plausibility of the
epidemiologic findings observed in human children; (6) current evidence
that suggests a steeper dose-response relationship at recent lower blood
Pb levels than at higher blood Pb levels, indicating the potential for
greater incremental impact associated with exposure at these lower
levels.  

In addition to the evidence of health effects occurring at significantly
lower blood Pb levels, the Administrator recognized in the proposal
that, as at the time the standard was set, the current health effects
evidence together with findings from the exposure and risk assessments
(summarized above in section II.A.3) supports a finding that air-related
Pb exposure pathways contribute to blood Pb levels in young children by
inhalation and ingestion.  Furthermore, the Administrator took note of
the information that suggests that the air-to-blood ratio (i.e., the
quantitative relationship between air concentrations and blood
concentrations) is now likely larger, when air inhalation and ingestion
are considered, than that estimated when the standard was set.  

At the time of proposal, the Administrator first considered the current
evidence in the context of an adaptation of the 1978 framework, as
presented in the Staff Paper, recognizing that the health effects
evidence with regard to characterization of a threshold for adverse
effects has changed dramatically since the standard was set in 1978.  As
discussed in the proposal, however, limitations in the application of
that framework to the current situation, where (unlike when the standard
was set in 1978) there is not an evidentiary basis to determine a safe
level for individual children with respect to the identified health
effect, led the Administrator to focus primarily instead on the
air-related IQ loss evidence-based framework, described in section
II.D.2.a.ii of the proposal, in considering the adequacy of the current
standard.

As discussed in the proposal, the Administrator judged that air-related
IQ loss associated with exposure at the level of the current standard is
large from a public health perspective and that this evidence-based
framework supports a conclusion that the current standard does not
protect public health with an adequate margin of safety.  Further, the
Administrator provisionally concluded that the current evidence
indicates the need for a standard level that is substantially lower than
the current level to provide increased public health protection,
especially for at-risk groups, including most notably children, against
an array of effects, most importantly including effects on the
developing nervous system. 

At the time of proposal, the Administrator also considered the results
of the exposure and risk assessments conducted for this review as
providing some further perspective on the potential magnitude of
air-related IQ loss, although, noting uncertainties and limitations in
the assessments, the Administrator did not place primary reliance on the
exposure and risk assessments.  Nonetheless, the Administrator observed
that in areas projected to just meet the current standard, the
quantitative estimates of IQ loss associated with air-related Pb
indicate risk of a magnitude that in his judgment is significant from a
public health perspective and also recognized that, although the current
monitoring data indicate few areas with airborne Pb near or just
exceeding the current standard, there are significant limitations with
the current monitoring network and thus there exists the potential that
the prevalence of such Pb concentrations may be underestimated by
currently available data. 

Based on all of these considerations, the Administrator provisionally
concluded that the current Pb standard is not requisite to protect
public health with an adequate margin of safety because it does not
provide sufficient protection, and that the standard should be revised
to provide increased public health protection, especially for members of
at-risk groups.

2. Comments on the Need for Revision

In considering comments on the need for revision, the Administrator
first notes the advice and recommendations from CASAC with regard to the
adequacy of the current standard.  In the four letters that CASAC has
sent the Agency providing advice on the Pb standard, including the most
recent one on the proposal, all have repeated their unanimous view
regarding the need for substantial revision of the Pb NAAQS (Henderson,
2007a, 2007b, 2008a, 2008b).  For example, as stated in their letter of
March 2007, the “unanimous judgment of the Lead Panel is that … both
the primary and secondary NAAQS should be substantially lowered”
(Henderson, 2007a).  

General comments based on relevant factors that either support or oppose
any change to the current Pb primary standard are addressed in this
section.  Comments on elements of the proposed primary standard and on
studies that relate to consideration of the appropriate indicator,
averaging time and form, and level are addressed below in sections
II.C.1, II.C.2, and II.C.3, respectively.  Other specific comments
related to the standard setting, as well as general comments based on
implementation-related factors that are not a permissible basis for
considering the need to revise the current standards are addressed in
the Response to Comments document.

The vast majority of public comments received on the proposal generally
asserted that, based on the available scientific information, the
current Pb standard is insufficient to protect public health with an
adequate margin of safety and revisions to the standard are appropriate.
 Among those calling for revisions to the current standards are medical
groups, including the American Academy of Pediatrics, the American
Medical Association and the American Thoracic Society, as well as two
groups of concerned physicians and scientists, and the Agency’s
external Children’s Health Protection Advisory Committee (Marty,
2008).  Similar conclusions were also submitted in comments from many
national, state, and local environmental and public health
organizations, including, for example, the Natural Resources Defense
Council (NRDC), the Sierra Club, and the Coalition to End Childhood Lead
Poisoning.  All of these medical, public health and environmental
commenters stated that the current Pb standard needs to be revised to a
level well below the current level to protect the health of sensitive
population groups.  Many individual commenters also expressed such
views.  Additionally, regional organizations of state agencies,
including the National Association of Clean Air Agencies (NACAA), and
Northeast States for Coordinated Air Use Management (NESCAUM) urged that
EPA revise the Pb standard.  State and local air pollution control
authorities or public health agencies who commented on the Pb standard
also supported revision of the current Pb standard, including the New
York Departments of Health and Environmental Conservation, Iowa
Departments of Natural Resources and Public Health, the Missouri
Departments of Natural Resources and Health and Senior Services, as well
as the Missouri Office of the Attorney General, among others.  All
tribal governments and tribal air and environmental agencies commenting
on the standard, including the InterTribal Council of Arizona, Inc (an
organization of 20 tribal governments in Arizona), the Lone Pine
Paiute-Shoshone Reservation, as well as the Fond du Lac Band of Lake
Superior Chippewa, commented in support of revision of the Pb NAAQS.  

In general, all of these commenters agreed with EPA’s proposed
conclusions on the importance of results from the large body of
scientific studies reviewed in the Criteria Document and on the need to
revise the primary Pb standard as articulated in EPA’s proposal.  Many
commenters cited CASAC advice on this point.  The EPA generally agrees
with CASAC and these public commenters’ conclusions regarding the need
to revise the primary Pb standard.  EPA agrees that the evidence
assessed in the Criteria Document and the Staff Paper provides a basis
for concluding that the current Pb standard does not protect public
health with an adequate margin of safety.  Comments on specific aspects
of the level for a revised standard are discussed below in section
II.C.3 below.  

Some of these commenters also identified ‘‘new’’ studies that
were not included in the Criteria Document as providing further support
for the need to revise the Pb standards.  As noted above in section I.C,
as in past NAAQS reviews, the Agency is basing the final decisions in
this review on the studies and related information included in the Pb
air quality criteria that have undergone CASAC and public review, and
will consider the newly published studies for purposes of decision
making in the next Pb NAAQS review.  Nonetheless, in considering these
comments related to these more recent studies (further discussed in the
Response to Comments document), EPA notes that our provisional
consideration of these studies concludes that this new information and
findings do not materially change any of the broad scientific
conclusions regarding neurotoxic and other health effects of lead
exposure made in the 2006 Criteria Document.  For example, “new”
studies cited by commenters on neurocognitive and neurobehavioral
effects add to the overall weight of evidence and focus on findings of
such effects beyond IQ in study groups with some studies including lower
blood Pb levels than were available for review in the Criteria Document.

Three industry associations (National Association of Manufacturers,
Non-Ferrous Founders’ Society, and Wisconsin Manufacturers& Commerce)
commented in support of retaining the current primary Pb standard. 
These commenters generally state that most health risks associated with
Pb exposures are more likely to result from past air emissions or nonair
sources of Pb, such as lead-based paint, and that reduction of the Pb
standard will not provide meaningful benefits to public health.  They
additionally cite costs to those industries on whose part action will be
required to meet a reduced standard.  While EPA recognizes that nonair
sources contribute Pb exposure to today’s population, EPA disagrees
with the commenters’ premise that Pb exposures associated with any
past air emissions are not relevant to consider in judging the adequacy
of the current standard.  Further, EPA disagrees with commenters,
regarding the significance of health risk associated with air-related Pb
exposures allowed by the current standard.  As discussed in summarized
in section II.B.1 above and discussed in section II.B.3 below, EPA has
concluded that the health risk associated with air-related Pb exposures
allowed by the current standard is of such a significant magnitude that
a revision to the standard is needed to protect public health with an
adequate margin of safety.  EPA further notes that, as discussed above
in section I.B, under the CAA, EPA may not consider the costs of
compliance in determining what standard is requisite to protect public
health with an adequate margin of safety.  

3. Conclusions Regarding the Need for Revision

Having carefully considered the public comments, 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 section II.B.1, remain valid.  In considering
whether the primary Pb standard should be revised, the Administrator
places primary consideration on the large body of scientific evidence
available in this review concerning the public health impacts of Pb,
including significant new evidence concerning effects at blood Pb
concentrations substantially below those identified when the current
standard was set.  As summarized in section II.A.2.b, Pb has been
demonstrated to exert a broad array of adverse effects on multiple organ
systems, with the evidence across this array of effects much expanded
since the standard was set, with the key effects most pertinent to
ambient exposures today including neurological, hematological and immune
effects for children and hematological, cardiovascular and renal effects
for adults.  The Administrator particularly notes the robust evidence of
neurotoxic effects of Pb exposure in children, both with regard to
epidemiological and toxicological studies.  While blood Pb levels in
U.S. children have decreased notably since the late 1970s, newer studies
have investigated and reported associations of effects on the
neurodevelopment of children with these more recent blood Pb levels. 
The toxicological evidence includes extensive experimental laboratory
animal evidence that substantiates well the plausibility of the
epidemiologic findings observed in human children and expands our
understanding of likely mechanisms underlying the neurotoxic effects. 
Further, the Administrator notes the current evidence that suggests a
steeper dose-response relationship at these lower blood Pb levels than
at higher blood Pb levels, indicating the potential for greater
incremental impact associated with exposure at these lower levels.  

In addition to the evidence of health effects occurring at significantly
lower blood Pb levels, the Administrator recognizes that the current
health effects evidence together with findings from the exposure and
risk assessments (summarized above in section II.A.3), like the
information available at the time the standard was set, supports our
finding that air-related Pb exposure pathways contribute to blood Pb
levels in young children, by inhalation and ingestion.  Furthermore, the
Administrator takes note of the information that suggests that the
air-to-blood ratio (i.e., the quantitative relationship between air
concentrations and blood concentrations) is now likely larger, when all
air inhalation and ingestion pathways are considered, than that
estimated when the standard was set.  

The Administrator has considered the evidence in the record, and
discussed above, in the context of an adaptation of the 1978 framework,
as presented in the Staff Paper, recognizing that the health effects
evidence with regard to characterization of a threshold for adverse
effects has changed dramatically since the standard was set in 1978.  As
discussed in the proposal (73 FR 29229), however, the Administrator
recognizes limitations to this approach and has focused primarily
instead on the air-related IQ loss evidence-based framework described in
section II.B.1 above, in considering the adequacy of the current
standard.

In considering the application of the air-related IQ loss framework to
the current evidence as discussed above in section II.B.1, the
Administrator concludes that in areas projected to just meet the current
standard, the quantitative estimates of IQ loss associated with
air-related Pb indicate risk of a magnitude that in his judgment is
significant from a public health perspective, and that this
evidence-based framework supports a conclusion that the current standard
does not protect public health with an adequate margin of safety. 
Further, the Administrator believes that the current evidence indicates
the need for a standard level that is substantially lower than the
current level to provide increased public health protection, especially
for at-risk groups, including most notably children, against an array of
effects, most importantly including effects on the developing nervous
system.

In addition to the primary consideration given to the available
evidence, the Administrator has also taken into consideration the
Agency’s exposure and risk assessments to help inform his evaluation
of the adequacy of the current standard.  As at the time of proposal,
the Administrator believes the results of those assessments provide some
further perspective on the potential magnitude of air-related IQ loss
and thus inform his judgment on the adequacy of the current standard to
protect against health effects of concern.  While taking into
consideration the uncertainties and limitations in the risk assessments,
the Administrator again observes that in areas projected to just meet
the current standard, the quantitative estimates of IQ loss associated
with air-related Pb indicate risk of a magnitude that in his judgment is
significant from a public health perspective.  Further, although the
current monitoring data indicate few areas with airborne Pb near or just
exceeding the current standard, the Administrator recognizes significant
limitations with the current monitoring network and thus there is the
potential that the prevalence of such Pb concentrations may be
underestimated by currently available data.  The Administrator thus
finds that the exposure and risk estimates provide additional support to
the evidence-based conclusion, reached above, that the current standard
needs to be revised. 

Based on these considerations, and consistent with the CASAC Panel’s
unanimous conclusion that EPA needed to substantially lower the level of
the primary Pb NAAQS to fully protect the health of children and adult
populations, the Administrator agrees with the vast majority of public
commenters that the current standard is not sufficient and thus not
requisite to protect public health with an adequate margin of safety and
that revision is needed to provide increased public health protection,
especially for members of at-risk groups. 

C.	Conclusions on the Elements of the Standard

The four elements of the standard – indicator, averaging time, form,
and level – serve to define the standard and must be considered
collectively in evaluating the health and welfare protection afforded by
the standard.  In considering comments on the proposed revisions to the
current primary Pb standard, as discussed in the following sections, EPA
considers each of the four elements of the standard as to how they might
be revised to provide a primary standard for Pb that is requisite to
protect public health with an adequate margin of safety.  The basis for
the proposed decision, comments on the proposal, and the
Administrator’s final decision on indicator are discussed in section
II.C.1, on averaging time and form in section II.C.2, and on a level for
the primary Pb NAAQS in section II.C.3.  

1. Indicator

a. Basis for Proposed Decision 

In setting the current standard in 1978, EPA established Pb-TSP as the
indicator.  In comments on the 1977 proposal, EPA received comments
expressing concern that because only a fraction of airborne particulate
matter is respirable, an air standard based on total air Pb would be
unnecessarily stringent and therefore the standard should be limited to
respirable size Pb particulate matter.  Such a standard might have led
to a Pb NAAQS with an indicator of Pb in particulate matter less than or
equal to 10 µm in diameter (Pb-PM10) as the indicator.  The Agency
considered this recommendation, but did not accept it.  Rather, EPA
reemphasized that larger particles of air-related Pb contribute to Pb
exposure through ingestion pathways, and that ingestion pathways,
including those associated with deposition of Pb from the air, can be a
significant component of Pb exposures.  In addition to these ingestion
exposure pathways, nonrespirable Pb that has been emitted to the ambient
air may, at some point, become respirable through weathering or
mechanical action, thus subsequently contributing to inhalation
exposures.  EPA concluded that total airborne Pb, both respirable and
nonrespirable fractions, should be addressed by the air standard (43 FR
46251).  The federal reference method (FRM) for Pb-TSP specifies the use
of the high-volume sampler.

In the 1990 Staff Paper, this issue was again considered in light of
information regarding limitations of the high-volume sampler used for
the Pb-TSP measurements, such as the variability discussed below.  The
continued use of Pb-TSP as the indicator was recommended in the Staff
Paper (USEPA, 1990b): 

Given that exposure to lead occurs not only via direct inhalation, but
via ingestion of deposited particles as well, especially among young
children, the hi-vol provides a more complete measure of the total
impact of ambient air lead. … Despite its shortcomings, the staff
believes the high-volume sampler will provide a reasonable indicator for
determination of compliance . . .

As in the past, and discussed in the proposal, the evidence available
today indicates that Pb in all particle size fractions, not just
respirable Pb particles, contributes to Pb in blood and to associated
health effects.  Further, the evidence and exposure/risk estimates in
the current review indicate that ingestion pathways dominate air-related
exposure.  Lead is unlike other criteria pollutants, where inhalation of
the airborne pollutant is the key contributor to exposure.  For Pb it is
the quantity of Pb in ambient particles with the potential to deposit
indoors or outdoors, thereby leading to a role in ingestion pathways,
that is the key contributor to air-related exposure.  The evidence
additionally indicates that airborne Pb particles are transported long
or short distances depending on their size, such that the representation
of larger particles is greater at locations near sources than at sites
not directly influenced by sources.

In the current review, the Staff Paper evaluated the evidence with
regard to the indicator for a revised primary standard.  This evaluation
included consideration of the basis for using Pb-TSP as the current
indicator, information regarding the sampling methodology for the
current indicator, and CASAC advice with regard to indicator (described
below).  Based on this evaluation, the Staff Paper recommended retaining
Pb-TSP as the indicator for the primary standard.  The Staff Paper also
recommended activities intended to encourage collection and development
of datasets that will improve our understanding of national and
site-specific relationships between Pb-PM10 (collected by low-volume
sampler) and Pb-TSP to support a more informed consideration of
indicator during the next review.  The Staff Paper suggested that such
activities might include describing a federal equivalence method (FEM)
in terms of PM10 and allowing its use for a TSP-based standard in
certain situations, such as where sufficient data are available to
adequately demonstrate a relationship between Pb-TSP and Pb-PM10 or, in
combination with more limited Pb-TSP monitoring, in areas where Pb-TSP
data indicate Pb levels well below the NAAQS level. 

The ANPR further identified issues and options associated with
consideration of the potential use of Pb-PM10 data for judging
attainment or nonattainment with a Pb-TSP NAAQS.  These issues included
the impact of controlling Pb-PM10 for sources predominantly emitting Pb
in particles larger than those captured by PM10 monitors (i.e.,
ultra-coarse), and the options included potential application of Pb-PM10
FRM/FEMs at sites with established relationships between Pb-TSP and
Pb-PM10, and use of Pb-PM10 data, with adjustment, as a surrogate for
Pb-TSP data.  The ANPR broadly solicited comment in these areas.

As noted in the proposal, the Agency in setting the standard and CASAC
in providing their advice (described below) both recognized that
ingestion pathways are important to air-related Pb exposures and that Pb
particles contributing to these pathways include ultra-coarse particles.
 Thus, as noted in the proposal, choosing the appropriate indicator
requires consideration of the impact of the indicator on the protection
provided from exposure to air-related Pb of all particle sizes,
including ultra-coarse particles, by both the inhalation and ingestion
pathways.

As discussed in the proposal (sections II.E.1 and V.A), the Agency
recognizes the body of evidence indicating that the high-volume Pb-TSP
sampling methodology contributes to imprecision in resultant Pb
measurements due to variability in the efficiency of capture of
particles of different sizes and thus, in the mass of Pb measured. 
Variability is most substantial in samples with a large portion of Pb
particles greater than 10 microns, such as those samples collected near
sources with emissions of ultra-coarse particles.  As noted in the
proposal, this variability contributes to a clear risk of
underestimating the ambient level of total Pb in the air, especially in
areas near sources of ultra-coarse particles, by underestimating the
amount of the ultra-coarse particles.  This variability also contributes
to a risk of not consistently identifying sites that fail to achieve the
standard.  

The Agency also recognizes, as discussed in the proposal, that the
low-volume PM10 sampling methodology does not exhibit such variability
due both to increased precision of the monitor and the decreased spatial
variation of Pb-PM10 concentrations, associated with both the more
widespread distribution of PM10 sources and aerodynamic characteristics
of particles of this size class which contribute to broader distribution
from sources.  Accordingly, there is a lower risk of error in measuring
the ambient Pb in the PM10 size class than there is risk of error in
measuring the ambient Pb in the TSP size class using Pb TSP samplers. 
We additionally noted in the proposal that, since Pb-PM10 concentrations
have less spatial variability, such monitoring data may be
representative of Pb-PM10 air quality conditions over a larger
geographic area (and larger populations) than would Pb-TSP measurements.
 The larger scale of representation for Pb-PM10 would mean that reported
measurements of this indicator, and hence designation outcomes, would be
less sensitive to exact monitor siting than with Pb-TSP as the
indicator.  

As discussed in the proposal, however, there is a different source of
error associated with the use of Pb-PM10 as the indicator, in that
larger Pb particles not captured by PM10 samplers would not be measured.
 As noted above, these particles contribute to the health risks posed by
air-related Pb, especially in areas influenced by sources of
ultra-coarse particles.  As discussed in the proposal, there is
uncertainty as to the degree to which control strategies put in place to
meet a NAAQS with a Pb-PM10 indicator would be effective in controlling
ultra-coarse Pb-containing particles.  Additionally, the fraction of Pb
collected with a TSP sampler that would not be collected by a PM10
sampler varies depending on proximity to sources of ultra-coarse Pb
particles and the size mix of the particles they emit, as well as the
sampling variability inherent in the method discussed above.  Thus, this
error is of most concern in locations in closer proximity to such
sources, which may also be locations with some of the highest ambient
air levels.  

Accordingly, we stated in the proposal that it is reasonable to consider
continued use of a Pb-TSP indicator, focusing on the fact that it
specifically includes ultra-coarse Pb particles among the particles
collected, all of which are of concern and need to be addressed in
protecting public health from air-related exposures.  We additionally
recognized that some State, local, or tribal monitoring agencies, or
other organizations, for the sake of the advantages noted above, and
described more fully in the proposal, may wish to deploy low-volume
Pb-PM10 samplers rather than Pb-TSP samplers.  Thus, we also considered
several approaches that would allow the use of Pb-PM10 data in
conjunction with retaining Pb-TSP as the indicator.  These approaches,
discussed more fully in the proposal (sections II.E.1 and IV), include
the development and use of site-specific scaling factors and the use of
default scaling factors for particular categories of monitoring sites
(e.g., source-oriented, non-source-oriented).  Additionally, we
solicited comment on changing the indicator to Pb in PM10, in
recognition of the potential benefits of such a revision discussed
above.

In their advice to the Agency during the current review, the CASAC Pb
Panel provided recommendations to the Agency on the indicator for a
revised standard in conjunction with their recommendations for revisions
to level and averaging time.  As noted above in section II.B and below
in section II.C.3, the Panel recommended a significant lowering of the
level for the standard, which they noted would lead to a requirement for
additional monitoring over that currently required, with distribution of
monitors over a much larger area.  In consideration of this, prior to
the proposal, the CASAC Pb Panel, as well as the majority of the CASAC
Ambient Air Monitoring and Methods (AAMM) Subcommittee, recommended that
EPA consider a change in the indicator to PM10, utilizing low-volume
PM10 sampling (Henderson, 2007a, 2007b, 2008a, 2008b; Russell, 2008a). 
They found support for their recommendation in a range of areas, as
summarized in the proposal (73 FR 29230).  In advising a revision to the
indicator, CASAC also stated that they “recognize the importance of
coarse dust contributions to total Pb ingestion and acknowledge that TSP
sampling is likely to capture additional very coarse particles which are
excluded by PM10 samplers” (Henderson 2007b).  They suggested that an
adjustment of the NAAQS level would accommodate the loss of these
ultra-coarse Pb particles, and that development of such a quantitative
adjustment might appropriately be based on concurrent Pb-PM10 and Pb-TSP
sampling data (Henderson, 2007a, 2007b, 2008a).  

For reasons discussed in the proposal and recognized above, and taking
into account information and assessments presented in the Criteria
Document, Staff Paper, and ANPR, the advice and recommendations of CASAC
and of members of the CASAC AAMM Subcommittee, and public comments
received prior to proposal, the Administrator proposed to retain the
current indicator of Pb-TSP, measured by the current FRM, a current FEM,
or an FEM approved under the proposed revisions to 40 CFR part 53.  The
Administrator also proposed an expansion of the measurements accepted
for determining attainment or nonattainment of the Pb NAAQS to provide
an allowance for use of Pb-PM10 data, measured by the new low-volume
Pb-PM10 FRM specified in the proposed appendix Q to 40 CFR part 50 or by
a FEM approved under the proposed revisions to 40 CFR part 53, with
site-specific scaling factors.  The Administrator also solicited comment
on providing States the option of using default scaling factors instead
of conducting the testing that would be needed to develop the
site-specific scaling factors.  Additionally, the Administrator invited
comment on an alternative option of revising the indicator to Pb-PM10.

b. Comments on Indicator 

In considering comments received on the proposal, EPA first notes the
advice provided by CASAC concerning the proposal in a July 2008 letter
to the Administrator (Henderson, 2008b).  In that advice, CASAC repeated
their prior recommendations regarding the indicator and level of the
revised standard, and emphasized that these recommendations “were
based, in part on an assumption that the level of the primary Pb NAAQS
would be ‘substantially’ lowered to the EPA Staff-recommended range
(with an TSP indicator) of between 0.1 to 0.2 µg/m3 as an upper bound
and 0.02 to 0.05 µg/m3 as a lower bound (with the added consideration
that the selection be made somewhat ‘conservatively’ within this
range to accommodate the potential loss of ultra-coarse lead with a PM10
Pb indicator)” (emphasis in original) (Henderson, 2008b).  They
additionally noted that “at most population-oriented monitoring sites,
levels of PM10 Pb are essentially the same as TSP Pb, but at
source-oriented monitoring sites with high coarse mode particulate lead
emissions, TSP Pb was roughly twice as high as PM10 Pb” and that this
“factor-of-two difference … could be readily accommodated by
considering a slightly more conservative upper bound of 0.1 µg/m3
rather than 0.2 µg/m3” (Henderson, 2008b).  The CASAC panel concluded
that “a transition to a PM10 indicator would be preferable, but only
at a level conservatively below an upper bound of 0.2 µg/m3 or lower”
(Henderson, 2008b).  EPA interprets this advice on the whole to be
supportive of Pb-TSP as the indicator for any standard level greater
than 0.10 µg/m3, particularly when the level has been selected with
recognition of the inclusion of ultra-coarse particles in Pb-TSP
measurements.

The EPA received many public comments on issues related to the indicator
for Pb.  The large majority of public comments were in support of
EPA’s proposal to retain Pb-TSP as the indicator for Pb.  Represented
in this group were many state agencies, as well as some Tribes and
tribal environmental agencies, and local environmental agencies.  Many
commenters supported Pb-TSP as the indicator regardless of a level for
the standard, variously citing evidence also cited by EPA in the
proposal notice, such as the relevance of all sizes of Pb particles to
exposures, blood Pb levels and effects and the omission of ultra-coarse
particles with PM10 samples.  In support of Pb-TSP as the indicator, a
few commenters also stated that air-to-blood ratios used in the
evidence-based framework for considering a level for the standard are
generally based on Pb-TSP data.  Some comments, similar to CASAC,
supported Pb-TSP as the indicator for levels above the lower end of the
proposed range (i.e., above 0.10 µg/m3), including a level of 0.15
µg/m3.  One commenter (NESCAUM) specifically recommended an indicator
of Pb-TSP for a NAAQS with a level of 0.15 µg/m3, recommending a
revision to Pb-PM10 only if some other, much lower, level (0.05 µg/m3)
was selected.  

EPA generally agrees with CASAC and the large number of public
commenters with regard to the appropriateness of a Pb-TSP indicator for
the level of the standard identified for the revised standard in section
II.C.3 below.  This conclusion is supported by the current scientific
evidence, discussed above in section II.C.1.a, recognizing the range of
particle sizes inclusive of ultra-coarse particles which contribute to
Pb exposures, evidence of the presence of ultra-coarse particles in some
areas, particularly near sources, and variation in the relationship
between Pb-TSP and Pb-PM10 at such sites, which together contribute to
uncertainty about the sufficiency of public health protection associated
with a Pb-PM10 standard at the level of 0.15 µg/m3. 

A few commenters (including the National Association of Clean Air
Agencies) recommended transition to a Pb-PM10 indicator for the standard
at levels below 0.2 µg/m3.  These commenters stated that low-volume
PM10 samplers measure Pb much more accurately than high-volume TSP
samplers, referring to EPA’s discussion in the proposal that
recognized the variability of Pb-TSP measurements associated with wind
speed and direction, and also referred to support among CASAC AAMM
members and the July 2008 comments from CASAC on indicator.  These
commenters, however, did not provide rationales as to why a Pb-PM10
indicator might be justified in light of the health considerations
identified by EPA in the proposal.  Further, as noted above, EPA
interprets CASAC’s July 2008 comments on the whole to be supportive of
Pb-TSP as the indicator for any standard level greater than 0.10 µg/m3.
 

A few commenters, including both state and industry commenters,
recommended transition to Pb-PM10 without reference to a particular
level.  Some of these commenters, like CASAC, noted concerns with the
high-volume TSP sampling methodology and advantages of the PM10
monitoring method in reduced variability of the measurements.  Two
industry commenters additionally suggested consideration of an indicator
based on Pb-PM2.5, stating as their rationale that almost all airborne
Pb in air is in “the small size fraction”, ambient sampling for PM10
and PM2.5 size fractions is already required, and precision which might
be greater with PM10 monitors is needed for “lower” standards.  None
of this group of commenters provided a rationale as to why a Pb-PM10
indicator might be justified in light of the health considerations
identified by EPA in the proposal.  

EPA disagrees with this group of commenters, noting the potential
presence at some sites of particles that would not be captured by PM10
or PM2.5 samplers yet would contribute to human exposure to Pb and
associated health effects.  As discussed below, EPA believes that, in
light of the evidence of all particle sizes of Pb contributing to blood
Pb and health effects by both ingestion and inhalation pathways, the
available data on relationships between Pb-TSP and Pb-PM10 (discussed in
section II.E.1 of the proposal and in section IV.C below) are inadequate
to support development of a Pb-PM10- based NAAQS that would provide
sufficient but not more than necessary protection of public health, with
an adequate margin of safety, across the wide variety of ambient Pb
circumstances affecting this relationship, and at the level selected by
the Administrator.  Although, EPA did not consider relationships between
Pb-TSP and Pb-PM2.5 in the proposal, EPA notes the more restricted
particle size range associated with PM2.5 measurements than with PM10
measurements, and the associated omission of substantially more Pb that
contributes to blood Pb and associated health effects. 

A number of comments were received regarding the potential use of
site-specific or default scaling factors to relate Pb-PM10 data to a
Pb-TSP-based standard, with the large majority of these comments being
opposed to these options.  With regard to site-specific scaling factors,
commenters note the temporal variability of the relationship between
Pb-TSP and Pb-PM10 at individual sites, raise concerns about
defensibility of attainment and nonattainment decisions based on the use
of scaling factors, and question whether there are benefits associated
with allowance of such scaling factors.  

As discussed below in section IV, EPA generally agrees with these
commenters and has not adopted a provision allowing the use of
site-specific scaling factors.  A few commenters supported the use of
default scaling factors that would be developed by EPA, as an approach
that would be most easily implemented.  EPA, however, concludes that the
limited available data on relationships between Pb-TSP and Pb-PM10 are
inadequate to support development of appropriate default scaling factors
as described below in section IV.

Although commenters generally opposed the use of scaling factors that
would relate Pb-PM10 data to specific corresponding levels of Pb-TSP for
all levels of Pb-PM10 and for all purposes related to implementation of
the standard, many commenters supported some uses of Pb-PM10 monitoring
with a Pb-TSP-based NAAQS.  One example of such a use that was suggested
by commenters is at sites well below the standard and in areas without
ultra-coarse particle sources.  EPA agrees with these commenters that
such a limited use of Pb-PM10 data in such areas is desirable in light
of the advantages of Pb-PM10 monitoring described in section II.C.1.a
above, and does not raise the concerns discussed above about sufficiency
of public health protection when considering ambient air Pb
concentrations that are closer to the level of the standard.  Such uses
allowed by this rulemaking are recognized below in section II.C.1.c and
discussed more fully in sections IV and V below.  

Some States noted agreement with the view expressed by EPA in the
proposal that low-volume TSP sampling offers advantages over high-volume
TSP sampling (the federal reference method for Pb).  Issues regarding
the sample collection method for the TSP indicator are discussed in
section V below.

c.	Conclusions on Indicator

Having carefully considered the public comments, as discussed above, and
advice and recommendations from CASAC on this issue, the Administrator
concludes that it is appropriate to retain Pb-TSP as the indicator for
the Pb NAAQS at this time.  The Administrator agrees with CASAC that use
of a Pb-TSP indicator is necessary to provide sufficient public health
protection from the range of particle sizes of ambient air Pb, including
ultra-coarse particles, in conjunction with the selected level (see
section II.C.3 below).  The Administrator recognizes that Pb in all
particle sizes contributes to Pb in blood and associated health effects
(as discussed in section II.E.1 of the proposal and II.C.1.a above). 
The Administrator additionally notes that selection of the standard
level does not include an adjustment or accommodation for the difference
in Pb particles captured by TSP and PM10 monitors which, as discussed
elsewhere (section II.E.1 of the proposal, section II.C.1.a above, and
section IV.D below) may be on the order of a factor of two in some
areas.  The Administrator also recognizes the quite limited dataset,
particularly for source-oriented sites, that is available to the Agency
from which to characterize the relationship between Pb-TSP and Pb-PM10
for purposes of identifying the appropriate level for a Pb-PM10 based
standard.  Further, the Administrator recognizes there is uncertainty
with regard to whether a Pb-PM10-based NAAQS would also effectively
control ultra-coarse Pb particles, which, as noted above, may have a
greater presence in areas near sources where Pb concentrations are
highest.  In light of these considerations, the Administrator concludes
that it is appropriate to retain Pb-TSP as the indicator to protect
against health risks from ultra coarse particulate Pb emitted to ambient
air.

With regard to the use of scaling factors to relate Pb-PM10 data to a
Pb-TSP indicator, the Administrator concludes that the limited available
data on relationships between Pb-TSP and Pb-PM10 are inadequate to
support a use of scaling factors to relate all valid Pb-PM10
measurements to specific levels of Pb-TSP concentrations for all
purposes of a Pb-TSP-based standard.

The Administrator concurs with the comments from CASAC and public
commenters that recognize the potential value of providing a role for
Pb-PM10 in the monitoring required for a Pb-TSP standard.  Such comments
emphasize the similarity of Pb-TSP and Pb-PM10 measurements at
non-source-oriented locations, while recognizing the potential for
differences at sites near sources, and recognize the sufficiency of
public health protection when Pb-PM10 levels are well below the level of
the standard.  EPA believes that use of Pb-PM10 measurements at sites
not influenced by sources of ultra-coarse Pb and where Pb concentrations
are well below the standard would take advantage of the increased
precision of these measurements and decreased spatial variation of
Pb-PM10 concentrations, without raising the same concerns over a lack of
protection against health risks from all particulate Pb emitted to the
ambient air that support retention of Pb-TSP as the indicator. 
Accordingly, the Administrator is expanding the types of measurements
which may be considered with regard to implementation of the Pb NAAQS. 
This expansion, as discussed more fully in sections IV and V below,
provides a role for Pb-PM10 data under certain limited circumstances and
with certain conditions.  The circumstances and conditions under which
such data are allowed, as described in sections IV and V below, are
those in which the Pb concentrations are expected to be substantially
below the standard and ultra-coarse particles are not expected to be
present.

2. Averaging Time and Form 

a. 	Basis for Proposed Decision

The averaging time and form of the current standard is a
not-to-be-exceeded or maximum value, averaged over a calendar quarter. 
The basis for this averaging time and form reflects consideration of the
evidence available when the Pb NAAQS were promulgated in 1978.  At that
time, the Agency had concluded that the level of the standard, 1.5
µg/m3, would be a “safe ceiling for indefinite exposure of young
children” (43 FR 46250), and that the slightly greater possibility of
elevated air Pb levels for shorter periods within the quarterly
averaging period, as contrasted to the monthly averaging period proposed
in 1977 (43 FR 63076), was not significant for health.  These
conclusions were based in part on the Agency’s interpretation of the
health effects evidence as indicating that 30 µg/dL was the maximum
safe level of blood Pb for an individual child, and the Agency’s views
that the distribution of air concentrations made it unlikely there could
be sustained periods greatly above the average value and that the
multipathway nature of Pb exposure lessened the impact of short-term
changes in air concentrations of Pb.  

In the 1990 Staff Paper, this issue was again considered in light of the
evidence available at that time.  The 1990 Staff Paper concluded that
“[a] monthly averaging period would better capture short-term
increases in lead exposure and would more fully protect children’s
health than the current quarterly average” (USEPA, 1990b).  The 1990
Staff Paper further concluded that “[t]he most appropriate form of the
standard appears to be the second highest monthly average in a 3-year
span.  This form would be nearly as stringent as a form that does not
permit any exceedances and allows for discounting of one ‘bad’ month
in 3 years which may be caused, for example, by unusual meteorology.” 
In their review of the 1990 Staff Paper, the CASAC Pb Panel concurred
with the staff recommendation to express the lead NAAQS as a monthly
standard not to be exceeded more than once in three years.

As summarized in section II.A above and discussed in detail in the
Criteria Document, the currently available health effects evidence
indicates a wider variety of neurological effects, as well as immune
system and hematological effects, associated with substantially lower
blood Pb levels in children than were recognized when the standard was
set in 1978.  Further, the health effects evidence with regard to
characterization of a threshold for adverse effects has changed since
the standard was set in 1978, as have the Agency’s views on the
characterization of a safe blood Pb level.  

In the proposal (section II.E.2), we noted various aspects of the
current evidence that are pertinent to consideration of the averaging
time and form for the Pb standard.  We noted those aspects pertaining to
the human physiological response to changes in Pb exposures and also
aspects pertaining to the response of air-related Pb exposure pathways
to changes in airborne Pb.  The latter aspects are more complex for Pb
than for other criteria pollutants because the exposure pathways for
air-related Pb include both inhalation pathways and deposition-related
ingestion pathways, which is not the case for other criteria pollutants.
 The persistence of Pb in multiple media and in the body provides an
additional complication in the case of Pb.  

With regard to the human physiological response to changes in Pb
exposures, as summarized in the Staff Paper and discussed in more detail
in the Criteria Document, the evidence indicates that blood Pb levels
respond quickly to increased Pb exposures, such that an abrupt increase
in Pb uptake results in increased blood Pb levels.  Contributing to this
response is the absorption through the lungs and the gastrointestinal
tract (which is both greater and faster in children as compared to
adults), and the rapid distribution (within days), once absorbed, from
plasma to red blood cells and throughout the body.  As noted in the
proposal, while the evidence with regard to sensitive neurological
effects is limited in what it indicates regarding the specific duration
of exposures associated with effects, it indicates both the sensitivity
of the first three years of life and a sustained sensitivity throughout
the lifespan as the human central nervous system continues to mature and
be vulnerable to neurotoxicants (CD, section 8.4.2.7).  In general, the
evidence indicates the potential importance of exposures on the order of
months (CD, section 5.3).  The evidence also indicates increased
vulnerability during some developmental periods (e.g., prenatal), the
length of which indicates a potential importance of exposures as short
as weeks to months.

As noted in the proposal with regard to the response of human exposure
pathways to changes in airborne Pb, data from NHANES II and an analysis
of the temporal relationship between gasoline consumption and blood Pb
indicate a month lag between changes in Pb emissions from leaded
gasoline and the response of children’s blood Pb levels and the number
of children with elevated blood Pb levels (EPA, 1986a, p. 11-39;
Rabinowitz and Needleman, 1983; Schwartz and Pitcher, 1989; USEPA,
1990b).  As noted in the proposal with regard to consideration of
air-related Pb exposure pathways, the evidence described in the Criteria
Document and the quantitative risk assessment indicate that today
ingestion of dust can be a predominant exposure pathway for young
children to air-related Pb.  Further, the proposal noted that a recent
study of dustfall near an open window in New York City indicates the
potential for a response of indoor dust Pb loading to ambient airborne
Pb on the order of weeks (Caravanos et al., 2006; CD, p. 3-28).

In the proposal, we additionally noted that the health effects evidence
identifies varying durations in exposure that may be relevant and
important to the selection of averaging time.  In light of uncertainties
in aspects such as response times of children’s exposure to airborne
Pb, we recognized, as in the past, that this evidence provides a basis
for consideration of both quarterly and monthly averaging times.

In considering both averaging time and form in the proposal, EPA
combined the current calendar quarter averaging time with the current
not-to-be exceeded (maximum) form and also combined a monthly averaging
time with a second maximum form, so as to provide an appropriate degree
of year-to-year stability that a maximum monthly form would not provide.
 We also observed in the proposal (73 FR 29235) that the second maximum
monthly form provides a roughly comparable degree of protection on a
broad national scale to the current maximum calendar quarter averaging
time and form.  This observation was based on an analysis of the
2003-2005 monitoring data set that found a roughly  similar number of
areas not likely to attain alternate levels of the standard for these
two combinations of averaging time and form (although a slightly greater
number of sites would likely exceed the levels based on the second
maximum monthly average).  We also noted, however, that the relative
protection provided by these two averaging times and forms may differ
from area to area.  Moreover, we noted that control programs to reduce
average Pb concentrations across a calendar quarter may not have the
same protective effect as control programs aimed at reducing average Pb
concentrations on a monthly basis.  Given the limited scope of the
current monitoring network, which lacks monitors near many significant
Pb sources, and uncertainty about Pb source emissions and possible
controls, the proposal noted that it is difficult to more quantitatively
compare the protectiveness of standards defined in terms of the maximum
calendar quarter average versus the second maximum monthly average.

In their advice to the Agency prior to the proposal, CASAC recommended
that consideration be given to changing from a calendar quarter to a
monthly averaging time (Henderson, 2007a, 2007b, 2008a).  In making that
recommendation, CASAC has emphasized support from studies that suggest
that blood Pb concentrations respond at shorter time scales than would
be captured completely by a quarterly average.  With regard to form of
the standard, CASAC has stated that one could “consider having the
lead standards based on the second highest monthly average, a form that
appears to correlate well with using the maximum quarterly value”,
while also indicating that “the most protective form would be the
highest monthly average in a year” (Henderson, 2007a).  Among the
public comments the Agency received on the discussion of averaging time
in the ANPR, the majority concurred with the CASAC recommendation for a
revision to a monthly averaging time.

On an additional point related to form, the 1990 Staff Paper and the
Staff Paper for this review both recommended that the Administrator
consider specifying that compliance with the NAAQS be evaluated over a
3-year period.  As described in the proposal, a monitor would be
considered to be in violation of the NAAQS based on a 3-year period, if,
in any of the three previous calendar years with sufficiently complete
data (as explained in detail in section IV of the proposal), the value
of the selected averaging time and form statistic (e.g., second maximum
monthly average or maximum quarterly average) exceeded the level of the
NAAQS.  Thus, a monitor, initially or after once having violated the
NAAQS, would not be considered to have attained the NAAQS until three
years have passed without the level of the standard being exceeded.  In
discussing the merits of this approach in the proposal, we noted that
variations in Pb source emissions and in meteorological conditions
contribute to the potential for a monitor to record an exceedance of a
particular level in one period but not in another, even if no permanent
controls have been applied to the nearby source(s).  We further noted
that it would potentially reduce the public health protection afforded
by the standard if areas fluctuated in and out of nonattainment status
so frequently that States do not have opportunity and incentive to
identify sources in need of more emission control and to require those
controls to be put in place.  We noted that the 3-year approach would
help ensure that areas initially found to be violating the NAAQS have
effectively controlled the contributing lead emissions before being
redesignated to attainment.

At the time of proposal, the Administrator considered the information
summarized above (described in more detail in Criteria Document and
Staff Paper), as well as the advice from CASAC and public comments on
the ANPR.  The Administrator recognized that there is support in the
evidence for an averaging time as short as monthly consistent with the
following observations:  (1) the health evidence indicates that very
short exposures can lead to increases in blood Pb levels, (2) the time
period of response of indoor dust Pb to airborne Pb can be on the order
of weeks, and (3) the health evidence indicates that adverse effects may
occur with exposures during relatively short windows of susceptibility,
such as prenatally and in developing infants.  The Administrator also
recognized limitations and uncertainties in the evidence including the
limited available evidence specific to the consideration of the
particular duration of sustained airborne Pb levels having the potential
to contribute to the adverse health effects identified as most relevant
to this review, as well as variability in the response time of indoor
dust Pb loading to ambient airborne Pb.

Based on these considerations and the air quality analyses summarized
above, the Administrator concluded that this information provided
support for an averaging time no longer than a calendar quarter. 
Further, the Administrator recognized that if substantial weight is
given to the evidence of even shorter times for response of key exposure
pathways, blood Pb, and associated effects to airborne Pb, a monthly
averaging time may be appropriate.  Accordingly, the Administrator
proposed two options with regard to the form and averaging time for the
standard, and with both he proposed that three years be the time period
evaluated in considering attainment.  One option was to retain the
current not-to-be-exceeded form with an averaging time of a calendar
quarter, and the second option was to revise the averaging time to a
calendar month and the form to the second highest monthly average.  

b.	 Comments on Averaging Time and Form

In considering comments on averaging time for the revised standard, the
Administrator first notes that the CASAC Pb Panel, in their comments on
the proposal, restated their previous recommendation to reduce the
averaging time from calendar quarter to monthly (Henderson, 2008b).  In
repeating this recommendation in their July 2008 letter, CASAC noted
that “adverse effects could result from exposures over as few as 30
days’ duration” (Henderson, 2008b).  Many public commenters also
supported the option of a monthly averaging time, generally placing
great weight on the recommendation of CASAC.  Some of these commenters
also provided additional reasons for their support for a monthly
averaging time.  These reasons variously included concerns regarding the
lack of a “safe” blood Pb level; evidence that children’s blood Pb
concentrations respond over time periods shorter than three months;
evidence for very short windows of susceptibility to some effects during
prenatal and infant development; concerns that dust Pb responds
relatively quickly to air Pb; and concerns for large near-source
temporal variability in airborne Pb concentrations and the exposure and
risk contributed by “high” months, which, given the persistence of
Pb, may occur for some time subsequent to the “high” month.

Some other commenters supported retaining the current quarterly
averaging time stating that the proposed option of a monthly averaging
time is not well founded in the evidence.  In supporting this view, the
commenters variously stated that no evidence has been presented to show
a relationship between a shorter-term air concentration and air-related
blood Pb levels contributing to neurological effects; there is little
known regarding the relationship between neurocognitive effects such as
IQ and a monthly exposure period;  there is uncertainty regarding the
time over which indoor dust, a key pathway for air-related Pb, responds
to indoor air; and, the World Health Organization and European Community
air criteria or guidelines for Pb are based on a yearly average.  

In considering advice from CASAC and comments from the public, EPA
recognizes that the evidence indicates the potential for effects
pertinent to this review to result from Pb exposures (e.g., from
ingestion and inhalation routes) on the order of one to three months, as
summarized in section II.C.2.a and described more fully in the proposal.
 EPA additionally notes the greater complexity inherent in considering
the averaging time for the primary Pb standard, as compared to other
criteria pollutants, due to the persistence and multimedia nature of Pb
and its multiple pathways of human exposure.  Accordingly, in
considering averaging time in this review, in addition to considering
the evidence with regard to exposure durations related to blood Pb
levels associated with neurological effects, a key consideration for the
Agency is how closely Pb exposures via the major air-related Pb exposure
pathways reflect temporal changes in ambient air Pb concentrations,
recognizing that the averaging period involves the duration over time of
ambient air concentrations, and is not a direct measure of the duration
or degree of exposure.  

With regard to exposure durations related to blood Pb levels associated
with neurocognitive effects, EPA notes that, as described in section
II.A.2.c above, the concurrent blood Pb metric (i.e., blood Pb measured
at the time of IQ test) has been found to have the strongest association
with IQ response.  Further, a concurrent blood Pb measurement is most
strongly related to a child’s exposure events within the past few
(e.g., one to three) months.  This is supported by multiple aspects of
the evidence (e.g., CD, chapter 4; USEPA, 1986a, chapter 11), including
evidence cited by CASAC and commenters, such as the findings of the
significant contribution to blood Pb of gasoline Pb sales in the past
month (e.g., Schwartz and Pitcher, 1989; Rabinowitz and Needleman,
1983). 

EPA also recognizes, as noted by some commenters and discussed in the
Criteria Document and summarized in the Staff Paper, ANPR and proposal,
that the evidence demonstrates sensitivity of the early years of life
and increased vulnerability of specific types of effects during some
developmental periods (e.g., prenatal) which may be shorter than a
calendar quarter.  EPA notes uncertainty, however in some aspects of the
linkages between airborne Pb concentrations and these physiological
responses, including time-related aspects of the exposure pathways
contributing to such effects.

In considering the evidence regarding how blood Pb levels respond to
changes in ambient air Pb concentrations along the multiple exposure
pathways to blood, EPA recognizes several pertinent aspects of the
evidence.  First, the evidence in this area does not specify the
duration of a sustained air concentration associated with a particular
blood Pb contribution.  Accordingly, we are uncertain as to the precise
duration of air concentration(s) reflected in any one air-to-blood ratio
and the ways in which an air-to-blood ratio may vary with the duration
of the air Pb concentration.  However, as discussed in section II.C.2.a
above, the evidence supports the importance of time periods on the order
of three months or less, and as discussed below, in light of the
prominent role of deposition-related pathways today, EPA concludes the
evidence most strongly supports a time period of approximately three
months.

Given the varying complexities of the multiple air-related exposure
pathways summarized in section II.A.1 above, exposure durations
pertinent for each pathway may be expected to vary.  The most immediate
and direct exposure pathway is the inhalation pathway, while the
ingestion pathways are more indirect and to varying degrees (across the
range of pathways) less immediate.  For example, as mentioned above,
when leaded gasoline was a predominant source of air-related exposure
for people in the U.S., the evidence indicates that blood Pb levels were
strongly associated with average sales of leaded gasoline during the
previous month (e.g., Schwartz and Pitcher, 1989).  We note that
exposures to the generally fine particles produced by combustion of
leaded gasoline, which remain suspended in the atmosphere for many days
(USEPA, 1986a, p. 5-10), provide a greater role for inhalation pathways
(e.g., as compared to deposition-related ingestion pathways, such as
indoor dust ingestion) than would exposures to generally larger Pb
particles (which tend to more readily deposit).  Further, as recognized
in the Staff Paper and the proposal, air-related ingestion pathways are
necessarily slower to respond to changes in air concentrations than the
immediate and direct pathway of inhalation.  The ingestion pathways are
affected by a variety of factors that play a lesser, if any, role in
inhalation exposure.  For example, human behavior (e.g., activity,
cleaning practices and frequency) and other building characteristics
(e.g., number of windows, presence of screens, air conditioning) would
be expected to modulate the response of indoor dust to changes in
ambient air Pb (Caravanos et al., 2006; CD, p. 3-28).  

As noted previously, the evidence and the results of the quantitative
risk assessment indicate a greater role for ingestion pathways than
inhalation pathways in contributing to the air-related exposures of
children today.  Accordingly, the relatively greater focus today (than
at the time of leaded gasoline usage) on deposition-related pathways of
exposure to air-related Pb such as indoor dust ingestion would tend to
support consideration of an averaging time longer than a month.  We
additionally note results from dust Pb modeling analyses performed as
part of the quantitative risk assessment.  These results provide an
estimate of approximately four months as the time over which an increase
in air Pb will reach 90% of the final steady-state change in dust Pb
(USEPA, 2007b, section G.3.2.2).  Additionally, we note that multiple
studies have observed blood Pb levels to exhibit seasonal patterns,
perhaps related to seasonality in exposure variables (e.g., Rabinowitz
et al., 1985).  

Some commenters who supported a monthly averaging time cited concern for
the potential for the occurrence of single month average air Pb
concentration, within a quarter that met the standard, to be
substantially above the level of the standard.  For example, one
commenter suggested that a monthly averaging time would be more likely
to capture exceedances related to periodic activities (such as
industrial activity, construction or demolition).  Another commenter
submitted examples of such temporal variability in ambient air
concentrations at specific monitoring sites, one of which indicated a
quarter in which the current standard of 1.5 µg/m3 was met, while a
single month within that quarter was some 30% percent higher (2.07
µg/m3).  In considering this example, we consider the likelihood of
differing blood Pb responses between children in two different
situations:  one in which the 3-month average Pb concentration just met
the level of the standard but a single month within the quarter was 30%
higher than that level (with the other two months below the standard
level), and the other in which each of three consecutive monthly average
Pb concentrations just met the level of the standard.  The current
evidence is limited with regard to the consideration of this issue. 
Given the range of air-related blood Pb exposure pathways and the
processes involved in their relationships with airborne Pb (e.g., the
response of indoor dust Pb to ambient air Pb), it is highly uncertain,
based on the evidence available today, whether there would be
appreciable differences in blood Pb levels between the children in these
two scenarios as a result of these different 3-month periods.  That is,
in this example, we consider it unlikely that a single relatively higher
month of air Pb followed by two months of relatively lower air Pb would
translate into a similar single high month of blood Pb followed by two
months of relatively low blood Pb.  Rather, it is expected that the high
month would tend to be modulated into a more extended and less
pronounced month-to-month change in blood Pb levels.

In considering this issue, however, we recognize that greater
month-to-month variability in air concentrations than that described by
this example is possible, and as such variability increases, it becomes
more likely that a month’s air Pb concentration might result in a more
pronounced impact on blood Pb concentrations.  

Another example offered by the commenter described more extreme
month-to-month variability in a quarter in which the current standard
was met.  This example indicated a monthly average that was more than 3
times the average for the quarter.  The allowance for this seemingly
implausible occurrence results from the current calculation method for
the current quarterly average standard.  The current method takes an
average across all valid measurements in a quarter, without according
equal weight to each month’s measurements.  In situations where a
significantly different number of measurements occur in each month of
the quarter, the current method can have the effect of giving greater
weight to multiple measurements occurring over a relatively short
period.  In the specific example cited by the commenter, the few very
high measurements in a single month were outweighed by a much larger
number of lower measurements occurring in each of the other two months
of the quarter, thus biasing the resulting quarterly average.  EPA
agrees with the commenter that the allowance of such significant
month-to-month variability within a 3-month period is inappropriate and
may not provide appropriate protection of public health.  In
consideration of this issue, the Agency has identified changes to the
method used to derive the 3-month average that would yield an average
that is more representative of air quality over the 3-month period and
lessen the likelihood and frequency of occurrence of cases where such
extremely high months would be allowed in a 3-month averaging period
that met the standard.  More specifically, as discussed below in section
IV, the Agency considers it appropriate to average the measurements
within each month prior to deriving the 3-month average as a way to
avoid the allowance of such large monthly variability as noted by the
commenter.

In considering comments specifically on the current use of a block
calendar quarter average, the Administrator first notes that the CASAC
Pb Panel, in their comments on the proposal, stated that “there is no
logic for averaging only by ‘calendar’ quarter as there is nothing
unique about effects that may occur exclusively during the four calendar
seasons” and that a “ ‘rolling’ three-month (or 90-day) average
would be more logical than a ‘calendar’ quarter” (Henderson,
2008b).  Comments from a state environmental agency also recommended use
of a 3-month rolling average, rather than the current block calendar
quarter average.

EPA agrees with CASAC as to the stronger basis for a “rolling”
3-month average as compared to a block calendar quarter.  A 3-month
average not constrained to calendar quarters would consider each of the
twelve 3-month periods associated with a given year, not just the four
calendar years within that year.  We agree with CASAC that the averaging
time of calendar quarter inappropriately separates air concentrations
occurring in months such as March and April that span two calendar
quarters.  For example, under the calendar quarter approach, two
consecutive “high” months that occur in different calendar quarters
(e.g., March and April) may be mitigated by “low” months in those
calendar quarters (i.e., January and February for March, May and June
for April).  Thus, the same air quality data could cause an exceedance
of the calendar quarter standard if it occurred in February and March
but could meet the calendar quarter standard if it occurred in March and
April.  EPA believes there is no evidence-based justification for this
potential disparity in outcomes.  By contrast, with a rolling 3-month
averaging time, each month contributes to three separate 3-month
periods, through separate combinations with three different pairs of
months (e.g. January-March, February-April, and March-June), thus
providing a more complete consideration of air quality during that month
and the periods in which it falls.  EPA also notes that analyses of air
quality data for 2005-2007 indicate a greater degree of protection is
afforded by a rolling 3-month average as compared to a block calendar
quarter average (Schmidt, 2008). 

CASAC also provided advice on a form for a monthly average standard,
noting that a “monthly or ‘rolling’ 30-day averaging time with a
‘not to be exceeded’ form would be more protective against adverse
short-term effects than a form (such as a ‘second-highest month in
three years’) that periodically allows a month of exposures to much
higher concentrations” (Henderson, 2008b).  Public comments also
included recommendations for a not-to-be-exceeded maximum form for a
monthly average (e.g., NACAA), as well as some recommendations for a
second maximum monthly average (e.g., NESCAUM).  While these comments
are instructive on the relative merits of a maximum and a second maximum
form for a monthly averaging time, given the Administrator’s selection
of a 3-month averaging time (as described in section II.C.2.c below),
and his reasons for this selection, including his consideration of the
issue of short-term changes in ambient air concentrations over the
3-month averaging time, EPA believes it is unnecessary to address
comments on the appropriate form for a monthly averaging time further
here.  

EPA notes, however, that a maximum rolling 3-month average would be
expected to provide greater protection from deposition-related pathways
in an area of highly variable air concentrations than the proposed
second maximum monthly average because the former does not allow for the
“discounting” or omitting of airborne Pb in any month.  While the
averaging time for a maximum rolling 3-month average is longer than the
monthly averaging time recommended by CASAC and several commenters, the
combination of a rolling 3-month averaging time with a maximum form
would be expected to offer greater protection from deposition-related
exposure pathways than the proposed option of a second maximum monthly
average, because each month contributes to three 3-month averages and no
month is omitted from the calculation of averages for comparison to the
standard.  Results of analyses of air quality data for 2005-2007 are
consistent with this view, in that a greater percentage of monitors
meeting data completeness criteria are not likely to meet the revised
standard based on a maximum rolling 3-month average as compared to a
second maximum monthly average (Schmidt, 2008).

More detailed responses to some of the public comments described above,
as well as responses to other comments related to averaging time and
form not considered here, are provided in the Response to Comments
document.  

c.	Conclusions on Averaging Time and Form

Having carefully considered CASAC’s advice and the public comments on
the appropriate averaging time and form for the standard, the
Administrator concludes that the fundamental scientific conclusions
pertaining to averaging time described in the Criteria Document and
Staff Paper, briefly summarized above in section II.C.2.a and discussed
more fully in section II.E.2 of the proposal remain valid.  In light of
all of the evidence, the Administrator concludes that the appropriate
averaging time for the standard is no longer than a 3-month period.  

In considering the option of a monthly averaging time, the Administrator
recognizes the complexity inherent in considering the averaging time and
form for the primary Pb standard, which is greater than in the case of
the other criteria pollutants, due to the multimedia nature of Pb and
its multiple pathways of human exposure.  Accordingly, while the
Administrator recognizes there are some factors that might support a
period as short as a month for the averaging time, other factors support
use of a longer averaging time, as discussed in section II.C.2.b above. 
The Administrator believes that in the complex multimedia, multi-pathway
situation for Pb, it is necessary to consider all of the relevant
factors, both those pertaining to the human physiological response to
changes in Pb exposures and those pertaining to the response of
air-related Pb exposure pathways to changes in airborne Pb, in an
integrated manner.

The Administrator recognizes that the evidence as well as the results of
the quantitative risk assessment for this review indicate a greater role
for ingestion pathways than inhalation pathways in contributing to
children’s air-related exposure.  He further recognizes that ingestion
pathways are influenced by more factors than inhalation pathways, and
those factors are considered likely to lessen the impact of
month-to-month variations in airborne Pb concentrations on levels of
air-related Pb in children’s blood.  Accordingly, while the evidence
is limited as to our ability to characterize these impacts, this
evidence suggests that the multiple factors affecting ingestion
pathways, such as ingestion of indoor dust, are likely to lead to
response times (e.g., for the response of blood to air Pb via these
pathways) extending longer than a month.  In addition, there remains
uncertainty over the period of time needed for air Pb concentrations to
lead to the health effects most at issue in this review.  

Further, it is important to note, as discussed above, that a rolling
3-month averaging time is likely to be somewhat more protective from a
broad national perspective than a calendar quarter averaging time.  Over
a 3-year time frame, the rolling 3-month averaging time is also likely
to be more protective with regard to air-related Pb exposures than would
be a form that allows one month in three years to be greater than the
level of the standard (i.e., a monthly averaging time with a second
maximum form).  In combination with the additional changes in form
discussed below, this means that a rolling 3-month average can be
expected to provide a high degree of control over all of the months of a
three-year period, with few individual months exceeding the level of the
standard.  This expectation appears to be generally supported by
analyses of air quality data for 2005-2007 comparing percentages of
monitors not likely to meet a revised standard with different averaging
times and forms (Schmidt, 2008).  

The Administrator further notes that, as discussed in section II.C.2.b
above, the rolling three-month average eliminates the possibility for
two consecutive “high” months falling in two separate calendar
quarters to be considered independently (perhaps being mitigated by
“low” months falling in each of the same calendar quarters). 
Rather, the same month, in the rolling three-month approach, would
contribute to three different 3-month periods through separate
combinations with three different pairs of months, thus providing a more
complete consideration of air quality during that month and the 3-month
periods in which it falls.  Taking these considerations into account,
the Administrator concludes that a rolling 3-month averaging time is
appropriate.  This conclusion to revise from a block calendar quarter
average to a rolling 3-month average is consistent with the views of
CASAC and some commenters on this issue.

In recognition of the uncertainty in the information on which the
decision to select a 3-month averaging time is based, the Administrator
further concludes that the month-to-month variability allowed by the
current method by which the 3-month average metric is derived is not
sufficiently protective of public health.  Accordingly, he concludes it
is appropriate to modify the method by which the 3-month average metric
is derived, as described in section IV below, to be the average of three
monthly average concentrations, as compared to the current practice by
which the average is derived across the full dataset for a quarter,
without equally weighting each month within the quarter.  Thus, in
consideration of the uncertainty associated with the evidence pertinent
to averaging time discussed above, the Administrator notes that the two
changes in form for the standard (to a rolling 3-month average and to
providing equal weighting to each month in deriving the 3-month average)
both afford greater weight to each individual month than does the
current form, tending to control both the likelihood that any month will
exceed the level of the standard and the magnitude of any such
exceedance.  

Based on the evidence and air quality considerations discussed above,
EPA concludes that a monthly averaging time is not warranted. 
Furthermore, the Administrator concludes that the appropriate averaging
time and form for the revised primary Pb standard is a
not-to-be-exceeded (maximum) 3-month rolling average evaluated over a
3-year span, derived in accordance with calculation methods described
below in section IV. 

3.	Level 

As noted in the proposal, EPA recognizes that in the case of Pb there
are several aspects to the body of epidemiological evidence that add
complexity to the selection of an appropriate level for the primary
standard.  As summarized above and discussed in greater depth in the
Criteria Document (CD, sections 4.3 and 6.1.3), the epidemiological
evidence that associates Pb exposures with health effects generally
focuses on blood Pb for the dose metric.  In addition, exposure to Pb
comes from various media, only some of which are air-related, and
through both inhalation and ingestion pathways.  These complexities are
in contrast to the issues faced in the reviews for other air pollutants,
such as particulate matter and ozone, which involve only inhalation
exposures.  Further, for the health effects receiving greatest emphasis
in this review (neurological effects, particularly neurocognitive and
neurobehavioral effects, in children), no threshold levels can be
discerned from the evidence.  As was recognized at the time of the last
review, estimating a threshold for toxic effects of Pb on the central
nervous system entails a number of difficulties (CD, pp. 6-10 to 6-11). 
The task is made still more complex by support in the evidence for a
nonlinear rather than linear relationship between blood Pb and
neurocognitive decrement, with greater risk of decrement-associated
changes per µg/dL of blood Pb at the lower levels of blood Pb in the
exposed population (CD, section 6.2.13).  In this context EPA notes that
the health effects evidence most useful in determining the appropriate
level of the NAAQS is the large body of epidemiological studies
discussed in the Criteria Document.  The discussion in the proposal and
below therefore focuses on the epidemiological studies, recognizing and
taking into consideration the complexity and resulting uncertainty in
using this body of evidence to determine the appropriate level for the
NAAQS.

The Administrator’s proposed conclusions on range of levels for the
primary standard are summarized below in the Introduction (section
II.C.3.a), followed by consideration of comments received on the
proposal (section II.C.3.b) and the Administrator’s final decision
with regard to level for the current primary standard (II.C.3.c).

a.	Basis for Proposed Range

For the reasons discussed in the proposal and summarized below, and
taking into account information and assessments presented in the
Criteria Document, Staff Paper, and ANPR, the advice and recommendations
of CASAC, and the public comments received prior to proposal, the
Administrator proposed to revise the existing primary Pb standard. 
Specifically, the Administrator proposed to revise the level of the
primary Pb standard, defined in terms of the current Pb-TSP indicator,
to within the range of 0.10 to 0.30 µg/m3, conditional on judgments as
to the appropriate values of key parameters to use in the context of the
air-related IQ loss evidence-based framework summarized below (and
discussed in section II.E.3.a.ii of the proposal).  Further, in
recognition of alternative views of the science, the exposure and risk
assessments, the uncertainties inherent in the science and these
assessments, and the appropriate public health policy responses based on
the currently available information, the Administrator solicited
comments on alternative levels of a primary Pb-TSP standard within
ranges from above 0.30 µg/m3 up to 0.50 µg/m3 and below 0.10 µg/m3. 
In addition, the Administrator solicited comments on when, if ever, it
would be appropriate to set a NAAQS for Pb at a level of zero.

The Administrator’s consideration of alternative levels of the primary
Pb-TSP standard built on his proposed conclusion, discussed above in
section II.B.1, that the overall body of evidence indicates that the
current Pb standard is not requisite to protect public health with an
adequate margin of safety and that the standard should be revised to
provide increased public health protection, especially for members of
at-risk groups, notably including children, against an array of adverse
health effects.  These effects include IQ loss, decrements in other
neurocognitive functions, other neurological effects and immune system
effects, as well as cardiovascular and renal effects in adults, with IQ
loss the health outcome quantified in the risk assessment.  In reaching
a proposed decision about the level of the Pb primary standard, the
Administrator considered:  the evidence-based considerations from the
Criteria Document, Staff Paper, and ANPR, and those based on the
air-related IQ loss evidence-based framework discussed in the proposal;
the results of the exposure and risk assessments summarized in section
II.A.3 above and in the Staff Paper, giving weight to the exposure and
risk assessments as judged appropriate; CASAC advice and
recommendations, as reflected in discussions of the Criteria Document,
Staff Paper, and ANPR at public meetings, in separate written comments,
and in CASAC’s letters to the Administrator; EPA staff
recommendations; and public comments received during the development of
these documents, either in connection with CASAC meetings or separately.
 In considering what standard is requisite to protect public health with
an adequate margin of safety, the Administrator noted at the time of
proposal that he was mindful that this choice requires judgment based on
an interpretation of the evidence and other information that neither
overstates nor understates the strength and limitations of the evidence
and information nor the appropriate inferences to be drawn. 

In reaching a proposed decision on a range of levels for a revised
standard, as in reaching a proposed decision on the adequacy of the
current standard, the Administrator primarily considered the evidence in
the context of the air-related IQ loss evidence-based framework as
described in the proposal (section II.E.3.a.ii).  The air-related IQ
loss evidence-based framework considered by the Administrator in the
proposal focuses on the contribution of air-related Pb to the
neurocognitive effect of IQ loss in children, with a public health goal
of identifying the appropriate ambient air level of Pb to protect
exposed children from health effects that are considered adverse, and
are associated with their exposure to air-related Pb.  In this
air-related IQ loss evidence-based framework, the Agency drew from the
entire body of evidence as a basis for concluding that there are causal
associations between air-related Pb exposures and IQ loss in children. 
Building on recommendations from CASAC to consider the body of evidence
in a more quantitative manner, the framework additionally draws more
quantitatively from the evidence by combining air-to-blood ratios with
evidence-based C-R functions from the epidemiological studies to
quantify the association between air Pb concentrations and air-related
population mean IQ loss in exposed children.  This framework was also
premised on a public health goal of selecting a proposed standard level
that would prevent air-related IQ loss (and related effects) of a
magnitude judged by the Administrator to be of concern in populations of
children exposed to the level of the standard.  The framework explicitly
links a public health goal regarding IQ loss with two key parameters --
a C-R function for population IQ response associated with blood Pb level
and an air-to-blood ratio.  

As a general matter, in considering this evidence-based framework, the
Administrator recognized that in the case of Pb there are several
aspects to the body of epidemiological evidence that add complexity to
the selection of an appropriate level for the primary standard.  As
discussed above, these complexities include evidence based on blood Pb
as the dose metric, multimedia exposure pathways for both air-related
and nonair-related Pb, and the absence of any discernible threshold
levels in the health effects evidence.  Further, the Administrator
recognized that there are a number of important uncertainties and
limitations inherent in the available health effects evidence and
related information, including uncertainties in the evidence of
associations between total blood Pb and neurocognitive effects in
children, especially at the lowest blood Pb levels evaluated in such
studies, as well as uncertainties in key parameters used in the
evidence-based framework, including C-R functions and air-to-blood
ratios.  In addition, the Administrator recognized 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 neurocognitive effects in sensitive populations,
such as IQ loss in children.  

Based on the discussion of the key parameters used in the framework, as
discussed in the proposal, the Administrator concluded that, in
considering alternative standard levels below the level of the current
standard, it was appropriate to take into account two sets of C-R
functions (described in section II.E.3.a.ii of the proposal),
recognizing uncertainties in the related evidence.  In the proposal, the
first set of C-R functions was described as reflecting the evidence
indicative of steeper slopes in relationships between blood Pb and IQ in
children, and the second set of C-R functions as reflecting
relationships with shallower slopes between blood Pb and IQ in children.
 In addition, the Administrator concluded that it was appropriate to
consider various air-to-blood ratios within a range of values considered
to be generally supported by the available evidence, again recognizing
the uncertainties in the relevant evidence.

With regard to making a public health policy judgment as to the
appropriate level of protection against air-related IQ loss and related
effects, the Administrator first noted 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
recognized, 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 NAAQS must
be sufficient but not more stringent than necessary to achieve that
result, and does not require a zero-risk standard.  Considering the
advice of CASAC and public comments on this issue, notably including the
comments of the American Academy of Pediatrics (AAP, 2008), the
Administrator proposed to conclude that an air-related population mean
IQ loss within the range of 1 to 2 points could be significant from a
public health perspective, and that a standard level should be selected
to provide protection from air-related population mean IQ loss in excess
of this range.  

In reaching his proposed decision, the Administrator considered the
application of this air-related IQ loss framework with this target
degree of protection in mind, drawing from the information presented in
Table 7 of the proposal (section II.E.3.a.ii) which addresses a broad
range of standard levels.  In so doing, the Administrator considered
estimates associated with both sets of C-R functions and the range of
air-to-blood ratios identified in the proposal, and noted those that
would limit the estimated degree of impact on population mean IQ loss
from air-related Pb to the proposed range of protection.

Taking these considerations into account, and based on the full range of
information presented in Table 7 of the proposal on estimates of
air-related IQ loss in children over a broad range of alternative
standard levels, the Administrator concluded that it was appropriate to
propose a range of standard levels, and that a range of levels from 0.10
to 0.30 µg/m3 would be consistent with the target for protection from
air-related IQ loss in children identified in the proposal.  In
recognition of the uncertainties in the key parameters of air-to-blood
ratio and C-R functions, the Administrator stated that the selection of
a standard level from within this range was conditional on judgments as
to the most appropriate parameter values to use in the context of this
evidence-based framework.  He noted that placing more weight on the use
of a C-R function with a relatively steeper slope would tend to support
a standard level in the lower part of the proposed range, while placing
more weight on a C-R function with a shallower slope would tend to
support a level in the upper part of the proposed range.  Similarly,
placing more weight on a higher air-to-blood ratio would tend to support
a standard level in the lower part of the proposed range, whereas
placing more weight on a lower ratio would tend to support a level in
the upper part of the range.  In soliciting comment on a standard level
within this proposed range, the Administrator specifically solicited
comment on the appropriate values to use for these key parameters in the
context of this evidence-based framework.

The Administrator also considered the results of the exposure and risk
assessments conducted for this review to provide some further
perspective on the potential magnitude of air-related IQ loss.  The
Administrator found these quantitative assessments to 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 discussed in sections II.A.3 above and section II.E.3.b
of the proposal, for purposes of evaluating potential new standards, the
Administrator placed less weight on the risk estimates than on the
evidence-based assessments.  Nonetheless, the Administrator found the
risk estimates to be roughly consistent with and generally supportive of
the evidence-based air-related IQ loss estimates discussed in section
II.E.3.b of the proposal, lending support to the proposed range based on
this evidence-based framework.

In the proposal, the Administrator noted his view that the above
considerations, taken together, provided no evidence- or risk-based
bright line that indicates a single appropriate level.  Instead, he
noted, there is a collection of scientific evidence and judgments and
other information, including information about the uncertainties
inherent in many relevant factors, which needs to be considered together
in making this public health policy judgment and in selecting a standard
level from a range of reasonable values.  Based on consideration of the
entire body of evidence and information available at the time of
proposal, as well as the recommendations of CASAC and public comments,
the Administrator proposed that a standard level within the range of
0.10 to 0.30 µg/m3 would be requisite to protect public health,
including the health of sensitive groups, with an adequate margin of
safety.  He also recognized that selection of a level from within this
range was conditional on judgments as to what C-R function and what
air-to-blood ratio are most appropriate to use within the context of the
air-related IQ loss framework.  The Administrator noted that this
proposed range encompasses the specific level of 0.20 µg/m3, the upper
end of the range recommended by CASAC and by many public commenters on
the ANPR.  The Administrator provisionally concluded that a standard
level selected from within this range would 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
cardiovascular and renal effects in adults.

The proposal noted that there is no bright line clearly directing the
choice of level within this reasonable range, and therefore the choice
of what is appropriate, considering the strengths and limitations of the
evidence, and the appropriate inferences to be drawn from the evidence
and the exposure and risk assessments, is a public health policy
judgment.  To further inform this judgment, the Administrator solicited
comment on the air-related IQ loss evidence-based framework considered
by the Agency and on appropriate parameter values to be considered in
the application of this framework.  More specifically, we solicited
comment on the appropriate C-R function and air-to-blood ratio to be
used in the context of the air-related IQ loss framework.  The
Administrator also solicited comment on the degree of impact of
air-related Pb on IQ loss and other related neurocognitive effects in
children considered to be significant from a public health perspective,
and on the use of this framework as a basis for selecting a standard
level.

The Administrator further noted that the evidence-based framework, with
the inputs illustrated at the time of proposal, indicated that for
standard levels above 0.30 µg/m3 up to 0.50 µg/m3, the estimated
degree of impact on population mean IQ loss from air-related Pb would
range from approximately 2 points to 5 points or more with the use of
the first set of C-R functions and the full range of air-to-blood ratios
considered, and would extend from somewhere within the proposed range of
1 to 2 points IQ loss to above that range when using the second set of
C-R functions and the full range of air-to-blood ratios considered.  The
Administrator proposed to conclude in light of his consideration of the
evidence in the framework discussed above that the magnitude of
air-related Pb effects at the higher blood Pb levels that would be
allowed by standards above 0.30 up to 0.50 µg/m3 would be greater than
what is requisite to protect public health with an adequate margin of
safety.

In addition, the Administrator noted that for standard levels below 0.10
µg/m3, the estimated degree of impact on population mean IQ loss from
air-related Pb would generally be somewhat to well below the proposed
range of 1 to 2 points air-related population mean IQ loss regardless of
which set of C-R functions or which air-to-blood ratio within the range
of ratios considered are used.  The Administrator proposed to conclude
that the degree of public health protection that standards below 0.10
µg/m3 would likely afford would be greater than what is requisite to
protect public health with an adequate margin of safety.

Having reached these proposed decisions based on the interpretation of
the evidence, the evidence-based frameworks, the exposure/risk
assessment, and the public health policy judgments described above, the
Administrator recognized that other interpretations, frameworks,
assessments, and judgments are possible.  There are also potential
alternative views as to the range of values for relevant parameters
(e.g., C-R function, air-to-blood ratio) in the evidence-based framework
that might be considered supportable and the relative weight that might
appropriately be placed on any specific value for these parameters
within such ranges.  In addition, the Administrator recognized that
there may be other views as to the appropriate degree of public health
protection that should be afforded in terms of air-related population
mean IQ loss in children that would provide support for alternative
standard levels different from the proposed range.  Further, there may
be other views as to the appropriate weight and interpretation to give
to the exposure/risk assessment conducted for this review.  Consistent
with the goal of soliciting comment on a wide array of issues, the
Administrator solicited comment on these and other issues.

In the proposal, the Administrator also recognized that Pb can be
considered a non-threshold pollutant and that, as discussed in section
I.B above, the CAA does not require that NAAQS be established 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.  However,
expecting that, as time goes on, future scientific studies will continue
to enhance our understanding of Pb, and that such studies might lead to
a situation where there is very little if any remaining uncertainty
about human health impacts from even extremely low levels of Pb in the
ambient air, the Administrator recognized that there is the potential in
the future for fundamental questions to arise as to how the Agency could
continue to reconcile such evidence with the statutory provision calling
for the NAAQS to be set at a level that is requisite to protect public
health with an adequate margin of safety.  In light of such
considerations, EPA solicited comment on when, if ever, it would be
appropriate to set a NAAQS for Pb at a level of zero.

b.	Comments on Level

In this section we discuss advice and recommendations received from
CASAC and the public on the proposed range of levels for the primary Pb
standard with a Pb-TSP indicator, including comments on specific levels
and ranges appropriate for the standard, comments pertaining to the use
of the evidence-based framework and inputs to the framework, and
comments related to the risk assessment.  More detailed responses to
some of the public comments on level described below, as well as
responses to other comments related to level not discussed here, are
provided in the Response to Comments document.  

(i) General Comments on Range of Levels

no higher than 0.2 μg/m3” (emphasis in originals).  

The vast majority of public comments that addressed a level for the
standard recommended standard levels below, or no higher than 0.2
µg/m3.  Many of these commenters noted the advice of CASAC and
recommended that EPA follow this advice.  Specific rationales provided
by this large group of commenters included various considerations, such
as recognition that the current evidence indicates Pb effects at much
lower exposure levels than when the current standard was set and in
multiple systems (e.g., neurological effects in children, cardiovascular
and renal effects in adults), and does not indicate a threshold; impacts
associated with some neurological effects can persist into adulthood;
and there is now evidence of a greater air-to-blood ratio than was
considered when the standard was set.  Many of these commenters
recommended a specific level or range of levels for the standard that
was equal to or below 0.2 µg/m3.  In recommending levels below 0.2
µg/m3, some of these stated that CASAC’s recommendation for an upper
bound of 0.2 µg/m3 should not be read to imply that CASAC supported a
standard level of 0.2 µg/m3 if that level did not account for CASAC’s
other specific recommendations on the framework and its inputs.  Some
commenters’ specific recommendations for level (including a standard
level of 0.15 µg/m3) were based on consideration of the air-related IQ
loss evidence-based framework and their application of it using their
recommended parameter inputs and public health policy goal.  The
specific recommendations on application of the framework are discussed
separately below.  Some commenters (including EPA’s Children’s
Health Protection Advisory Committee, NESCAUM, several States and
Tribes, and several environmental or public health organizations)
specified levels below 0.2 µg/m3 as necessary to protect public health
with an adequate margin of safety, with some of these additionally
stating that in assuring this level of protection, EPA must take into
account susceptible or vulnerable subgroups.  In discussing these
subgroups, some commenters noted factors such as nutritional
deficiencies as contributing to susceptibility and identified minority
and low-income children as a sensitive subpopulation for Pb exposures. 
Some of these commenters recommended much lower levels, such as 0.02
µg/m3, based on their views as to the level needed to protect public
health with an adequate margin of safety in light of their
interpretation of the advice of CASAC and EPA Staff and the evidence,
including the lack of identifiable threshold.  Some of these commenters
recommending much lower levels expressed the view that the standard
should be as protective as possible.

A second, much smaller, group of comments (including some industry
comments and some  state agency comments), recommended levels for the
standard that are higher than 0.2 µg/m3.  Among this group, some
commenters provide little or no health-based rationale for their
comment.  Other commenters, in recommending various levels above 0.2
µg/m3, generally state that there is no benefit to be gained by setting
a lower level for the standard.  In support of this general conclusion,
the commenters variously stated that there is substantial uncertainty
associated with the slope of the blood Pb-IQ loss concentration-response
function at lower blood Pb levels, such that EPA should not rely on
estimates that indicate a steeper slope at lower blood Pb levels; that
the risk assessment results for total risk at alternative standard
levels indicate no benefit to be achieved from a standard level below
0.5 µg/m3; that levels derived from the evidence-based framework need
upward adjustment for use with an averaging time less than a year and
that IQ loss estimates derived from the evidence-based framework
presented in the proposal for levels from 0.10 to 0.50 µg/m3 do not
differ much (e.g., from 2 to 4.1 points IQ loss [steeper slopes] and
from 1.1 to 2.2 points IQ loss [shallower slope] for the two sets of C-R
functions).  

For the range of reasons summarized in section II.C.3.a above, and the
reasons described more fully in section II.C.3.c below, EPA does not
believe that a level for the standard above 0.2 µg/m3 would protect
public health with an adequate margin of safety.  Rather, EPA concludes
that such a level for the standard would not be protective of public
health with an adequate margin of safety.  Further, EPA disagrees with
the industry comment that levels identified using the evidence-based
framework should be adjusted upward; this and other specific aspects of
comments summarized above are discussed further in the Response to
Comments document. 

(ii) Use of Air-related IQ Loss Evidence-based Framework

As noted above, EPA received advice and recommendations from CASAC and
comments from the public with regard to application of the air-related
IQ loss evidence-based framework in the selection of a level for the
primary standard.  In the discussion that follows, we first describe
CASAC advice and public comments on the appropriate degree of public
health protection that should be afforded to at-risk populations in
terms of IQ loss in children as estimated by this framework,  We then
describe CASAC advice and public comments on the specific parameters of
C-R function and air-to-blood ratio.

In their July 2008 advice to the Agency on the proposal notice, CASAC
characterized the target degree of protection proposed for use with the
air-related IQ loss framework to be inadequate (Henderson, 2008a).  As
basis for this characterization, they repeat the advice they conveyed
with their March 2007 letter, that they considered that “a population
loss of 1-2 IQ points is highly significant from a public health
perspective” and that “ the primary lead standard should be set so
as to protect 99.5% of the population from exceeding that IQ loss”
(emphasis in original).  They further emphasized their view that an IQ
loss of 1-2 points should be “prevented in all but a small percentile
of the population – and certainly not accepted as a reasonable change
in mean IQ scores across the entire population” (emphasis in
original).

Recommendations from several commenters, including the American Academy
of Pediatrics, and state health agencies that commented on this issue,
are in general agreement with the view emphasized by CASAC that
air-related IQ loss of a specific magnitude, such as on the order of 1
or 2 points, should be prevented in a very high percentage (e.g., 99.5%)
of the population.

EPA generally agrees with CASAC and the commenters that emphasize that
the NAAQS should prevent air-related IQ loss of a significant magnitude
in all but a small percentile of the population.  However, it is
important to note that in selecting a target degree of public health
protection from air-related IQ loss in children for the purposes of this
review, EPA is addressing this issue more specifically in the context of
this evidence-based framework.  In so doing, EPA is not determining a
specific quantitative public health policy goal in terms of an
air-related IQ loss that is acceptable or unacceptable in the U.S.
population per se, but instead is determining what magnitude of
estimated air-related IQ loss should be used in conjunction with the
specific air-related IQ loss evidence-based framework being applied in
this review, recognizing the uncertainties and limitations in this
framework.  As discussed later, the estimated air-related IQ loss
resulting from the application of this evidence-based framework should
not be viewed as a bright line estimate of expected IQ loss in the
population that would or would not occur.  Nonetheless, these results
provide a useful guide for the Administrator to use in making the
basically qualitative public health policy judgment about the risk to
public health that could reasonably be expected to result from exposure
to the ambient air quality patterns that would be allowed by varying
levels of the standard, in light of the averaging time, form, and
indicator specified above.  

In that context, it is important to recognize that the air-related IQ
loss framework provides estimates for the mean of a subset of the
population.  It is an estimate for a subset of children that are assumed
to be exposed to the level of the standard.  The framework in effect
focuses on the sensitive subpopulation that is the group of children
living near sources and more likely to be exposed at the level of the
standard.  The evidence-based framework estimates a mean air-related IQ
loss for this subpopulation of children; it does not estimate a mean for
all U.S. children.

EPA is unable to quantify the percentile of the U.S. population of
children that corresponds to the mean of this sensitive subpopulation. 
Nor is EPA confident in its ability to develop quantified estimates of
air-related IQ loss for higher percentiles than the mean of 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, EPA 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.  

One industry association commenter noted agreement with EPA’s focus on
population mean (or median) for the framework, and the statement of
greater confidence in estimates for air-related (as contrasted with
total Pb-related) IQ loss at a central point in the distribution than at
an upper percentile.  This commenter also stated the view that there is
likely little difference in air-related IQ loss between the mean and the
upper percentiles of the exposed population, based on their
interpretation of EPA risk estimates for the location-specific urban
case studies.  While EPA disagrees with the commenter’s view and
interpretation of the risk estimates from these case studies (as seen by
differences in median and 95th percentile estimates presented in section
5.3.2 of the Risk Assessment Report), EPA agrees that there is a much
higher level of confidence in estimates of air-related IQ loss for the
mean as compared to that for an upper percentile, consistent with the
Agency’s recognition of such limitations in the blood Pb estimates
from the risk assessment, due to limitations in the available data (as
noted in section II.C.h of the proposal).  

(iii)  Air-to-blood Ratio

Regarding the air-to-blood ratio, CASAC, in their July 2008 advice to
the Agency on the proposal, objected to constraining the range of ratios
used with the framework to the range from 1:3 to 1:7 (Henderson, 2008a).
 In so doing, they noted that the Staff Paper concluded that while
“there is uncertainty and variability in the absolute value of an
air-to-blood relationship, the current evidence indicates a notably
greater ratio [than the value of 1:2 used in 1978] … e.g., on the
order of 1:3 to 1:10” (USEPA, 2007, p. 5-17).  With regard to the
range of 1:3 to 1:7 emphasized in the proposal, CASAC stated that the
lower end of the range (1:3) “reflects the much higher air and blood
levels encountered decades ago” while “the upper end of the range
(1:7) fails to account for the higher ratios expected at lower current
and future air and blood Pb levels, especially when multiple air-related
lead exposure pathways are considered.”  With particular recognition
of the analysis of declining blood Pb levels documented by NHANES that
reflected declines in air Pb levels associated with declining use of
leaded gasoline over the same period and from which CASAC notes a ratio
on the order of 1:10 (Schwartz and Pitcher, 1989, as cited in Henderson,
2007a), CASAC recommended that EPA consider an air-to-blood ratio
“closer to 1:9 to 1:10 as being most reflective of current
conditions” (Henderson, 2008b).

Similar to the advice from CASAC, many commenters, including EPA’s
Children’s Health Protection Advisory Committee, NESCAUM and Michigan
Department of Environmental Quality recommended that EPA consider ratios
higher than the upper end of the range used in the proposal (1:7), such
as values on the order of 1:9 or 1:10 or somewhat higher and rejected
the lower ratios used in the proposal as being inappropriate for
application to today’s children.  In support of this recommendation,
commenters cite ratios resulting from the study noted by CASAC (Schwartz
and Pitcher, 1989), as well as others by Hayes et al. (1994) and
Brunekreef et al. (1983), and also air-to-blood ratio estimates from the
exposure/risk assessment. 

EPA agrees with CASAC and these commenters that an upper end
air-to-blood ratio of 1:7 does not give appropriate weight to the
air-to-blood ratios derived from or reported by the studies by Schwartz
and Pitcher (1989) and Brunekreef et al. (1983) and on ratios derived
from the risk assessment results, which extend higher than the range
identified in the proposal for consideration with the framework. 
Accordingly, EPA agrees that the range of air-to-blood estimates
appropriate for consideration in using the air-related IQ loss
evidence-based framework should extend up to ratios greater than the 1:7
ratio presented as an upper end in the proposal, such that the
evidence-based framework should also consider values on the order of
1:10.  

Alternatively, two industry commenters supported the range presented in
the proposal of 1:3 to 1:7.  These two and another industry commenter
asserted that higher air-to-blood ratios are not supported by the
evidence.  Specifically, one commenter disagrees with CASAC’s
interpretation of the Schwartz and Pitcher (1989) study with regard to
air-to-blood ratio, stating that the study indicates a potential ratio
of 1:7.8, rather than 1:9 or 1:10 as stated by CASAC, and that there is
a weak association between air Pb associated with leaded gasoline usage
and blood Pb, making the Schwartz and Pitcher study inappropriate to
consider.  EPA considers both the CASAC approach and the alternate
approach presented by the commenter to generally represent conceptually
sound strategies for translating the relationship between gasoline usage
and blood Pb (provided in the Schwartz and Pitcher, 1989 study) to
air-to-blood Pb ratios.  In addition, EPA notes that these approaches
support both the commenters ratio of approximately 1:8 and the CASAC
recommendation for EPA to use an estimate “closer to 1:9 to 1:10”. 
Further, EPA disagrees with the commenter’s view that the association
between gasoline-related air Pb and blood Pb is weak.  On the contrary,
the body of evidence regarding this relationship is robust (e.g., USEPA,
1986a, sections 11.3.6 and 11.6).  As stated in the 1986 Criteria
Document, “there is strong evidence that changes in gasoline lead
produce large changes in blood lead” (USEPA, 1986a, p. 11-187). 
Further, EPA notes that the analysis by Hayes et al. (1994), cited by
the commenter as basis for their view regarding leaded gasoline,
recognizes the role of leaded gasoline combustion in affecting blood Pb
levels through pathways other than the inhalation pathway (e.g., via
dust, soil and food pathways).

Additionally, two commenters stated that the “higher ratios” have
been generated inappropriately, citing ratios reported by Brunekreef
(1984) or those derived from NHANES data (e.g., Schwartz and Pitcher,
1989 or Hayes et al., 1994) as inappropriately including blood Pb not
associated with air Pb concentrations in the derivation of the
air-to-blood ratio.  Last, two of the three industry commenters
suggested that some of the air-to-blood ratios derived from the risk
assessment are overstated as a result of the methodology employed.

EPA generally disagrees with these commenters’ assertions that nonair
sources of blood Pb are a source of bias in studies indicating ratios
above 1:7 that were identified in the proposal, and emphasized by CASAC
and by other commenters, as described above.  For example, in section
II.B.1.c of the proposal, the proposal noted ratios of 1:8.5 (Brunekreef
et al., 1983; Brunekreef, 1984), as well as a ratio of approximately
1:10 (presented by CASAC in consideration of Schwartz and Pitcher,
1989).  In reporting these ratios, authors of these studies described
how consideration was given or what adjustments were made for other
sources of blood Pb, providing strength to their conclusion that the
reported air-to-blood ratio reflects air Pb contributions, with little
contribution from nonair sources.  In addition, the study by Hilts
(2003) includes an analysis that provides control for potential
confounders, including alternate sources of Pb exposure, through study
design (i.e., by following a similar group of children located within
the same study area over a period of time).  As discussed in section
II.A.2.a above, the study authors report a ratio of 1:6 from this study
and additional analysis of the data by EPA for the initial time period
of the study resulted in a ratio of 1:7.

With regard to air-to-blood ratios derived from the risk assessment,
while EPA recognizes uncertainties in these estimates, particularly
those extending substantially above 1:10 (as described in the Risk
Assessment Report and section II.C of the proposal), EPA disagrees with
commenters’ conclusions that they do not provide support for estimates
on the order of 1:10.  

In summary, while EPA agrees with the industry commenters that a ratio
of 1:5 or 1:7.8 is supportable for use in the evidence-based framework,
as noted above, EPA interprets the current evidence as providing support
for use of a higher range than that described in the proposal that is
inclusive at the upper end of estimates on the order of 1:10 and at the
lower end on the order of 1:5.  Further, EPA agrees with CASAC that the
lower end of the range in the proposal, an air-to-blood ratio of 1:3, is
not supported by the evidence for application to the current population
of U.S. children, in light of the multiple air-related exposure pathways
by which children are exposed, in addition to inhalation of ambient air,
and of today’s much lower air and blood Pb levels.  Taking these
factors into consideration, we conclude that the air-related IQ loss
evidence-based framework should consider air-to-blood ratios of 1:10 at
the upper end and 1:5 at the lower end.

(iv) Concentration-response Functions

Regarding the appropriate C-R functions to consider with the
evidence-based framework, CASAC, in their July 2008 advice to the Agency
on the proposal notice (Henderson, 2008a), objected to EPA’s
consideration of C-R functions based on analyses of populations
“exhibiting much higher blood Pb levels than is appropriate for
current U.S. populations” (emphasis in original).  They note that the
second set of C-R functions, while including some drawn from analyses of
U.S. children with mean blood Pb levels below 4 (g/dL, also includes
studies with mean or median blood Pb levels ranging up to 9.7 (g/dL. 
Further, they emphasize that we are concerned “with current blood Pb
levels in the setting of a health-protective NAAQS, not with blood Pb
levels of the past” (emphasis in original).  In conclusion, they state
that “the selection of C-R function should be based on determining
which studies indicate slopes that best reflect the current, lower blood
Pb levels for children in the U.S. – which, in this instance, are
those studies from which steeper slopes are drawn” (emphasis in
original) (Henderson, 2008a). 

A number of commenters (including EPA’s Children’s Health Protection
Advisory Committee, NESCAUM and some state agencies) made
recommendations with regard to C-R functions that were similar to those
of CASAC.  These commenters recommended consideration of C-R functions
with slopes appreciably steeper than the median value representing the
second set of functions in the proposal, giving greater weight to
steeper slopes drawn from analyses involving children with lower blood
Pb levels, closer to those of children in the U.S. today.  Some of these
commenters (e.g., NESCAUM) additionally suggested alternate approaches
to identify a slope estimate relevant to today’s blood Pb levels,
considering lower blood Pb level studies across both sets of functions
presented in the proposal, and to avoid placing inappropriate weight on
a single highest value. 

Based on the evidence described in detail in the Criteria Document and
briefly summarized in section II.A.2.c above, EPA agrees with CASAC and
these commenters that, given the nonlinearity of the blood Pb-IQ loss
relationship (steeper slope at lower blood Pb levels), the C-R functions
appropriate to use with the air-related IQ loss framework are those
drawn from analyses of children with blood Pb levels closest to those of
children in the U.S. today.  As a result of this nonlinear relationship,
a given increase in blood lead levels (e.g., 1 µg/dl of Pb) is expected
to cause a greater incremental increase in adverse neurocognitive
effects for a population of children with lower blood Pb levels than
would be expected to occur in a population of children with higher blood
Pb levels.  Thus, estimates of C-R functions drawn from analyses of
children with blood Pb levels that are more comparable to blood Pb
levels in today’s U.S. children are likely to better represent the
relationship between health effects and blood Pb levels that would apply
for children in the U.S. now and in the future, as compared to estimates
derived from analyses of children with higher blood lead levels.  As
discussed in section II.A.2.a.ii above, blood Pb levels in U.S. children
have declined dramatically over the past thirty years.  The geometric
mean blood Pb level for U.S. children aged five years and below,
reported for NHANES in 2003-04 (the most recent years for which such an
estimate is available), is 1.8 (g/dL and the 5th and 95th percentiles
are 0.7 (g/dL and 5.1 (g/dL, respectively (Axelrad, 2008a, 2008b).  The
mean blood Pb levels in all of the analyses from which C-R functions
were drawn and described in the proposal (presented in Table 1 of
section II.A.2.c above) are higher than this U.S. mean and some are
substantially higher.

In consideration of the advice from CASAC and comments from the public,
we have further considered the analyses presented in Table 1 of section
II.A.2.c above from which quantitative relationships between IQ loss and
blood Pb levels are described in the proposal (section II.B.2.b) for the
purpose of focusing on those analyses that are based on blood Pb levels
that best reflect today’s population of children in the U.S.  Given
the evidence of nonlinearity and of steeper slopes at lower blood Pb
levels (summarized in section II.A.2.c above), a focus on 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.  More specifically, in applying the
evidence-based framework, we are focused on a subpopulation of U.S.
children, those living near air sources and more likely to be exposed at
the level of the standard.  While the air-related Pb in the blood of
this subpopulation is expected to be greater than that for the general
population given their greater air-related Pb exposure, we do not have
information on the mean total blood Pb level (or, more specifically, the
nonair component) for this subpopulation.  However, even if we were to
assume, as an extreme hypothetical example, that the mean for the
general population of U.S. children included zero contribution from
air-related sources, and added that to our estimate of air-related Pb
for this subpopulation, the result would still be below the lowest mean
blood Pb level among the set of quantitative C-R analyses.  Thus, our
goal in considering these quantitative analyses was to identify C-R
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 AX7.1.4.2).

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 AX7.1.4.2 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 7.1.4.2).  

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 7.1.4.1). 

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 7.1.3.1 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 7.1.3.3 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
X7.2.1.2 and AX7.2.1.3).

• 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 AX7.2.1.4; 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 AX7.1.2.3). 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
AX7.2.2.2.2 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
FRM network, and that are seeing growing use in the PM10 and PM10-2.5
networks.  Finally, the use of a low-volume sampler is consistent with
the comments and recommendations from CASAC and members of CASAC's AAMM
Subcommittee (Henderson 2007a, Henderson 2008a, Russell 2008b).

We proposed XRF as the FRM analysis method because we believe that it
has several advantages which make it a desirable analysis method.  XRF
does not require sample preparation or extraction with acids prior to
analysis.  It is a non-destructive method; therefore, the sample is not
destroyed during analysis and can be archived for future re-analysis if
needed.  XRF analysis is a cost-effective approach that could be used to
simultaneously analyze for many additional metals (e.g., arsenic,
antimony, and iron) which may be useful in source apportionment.  XRF is
also the method used for the urban PM2.5 Chemical Speciation Network
(required under Appendix D to 40 CFR part 58) and for the Interagency
Monitoring of Protected Visual Environments (IMPROVE) rural visibility
monitoring program in Class I visibility areas, and is being considered
by EPA for a role in PM10-2.5 coarse speciation monitoring.  Based on
data from the PM2.5 speciation monitoring program, the XRF analysis
method when coupled with the low-volume PM10c sampler, is expected to
have an adequate method detection limit (MDL, the lowest quantity of a
substance that can be distinguished from the absence of that substance)
and meet the measurement uncertainty goals for precision and bias as
determined through the data quality objective (DQO) analysis (Papp,
2008), as explained later in this preamble. 

b.	Comments on the proposed Pb-PM10 FRM

	We received a number of comments on the proposed FRM for Pb-PM10.  In
addition, the CASAC AAMM Subcommittee provided a peer review of the
proposed Pb-PM10 FRM.  The following paragraphs describe the comments
received and our responses.

The CASAC AAMM Subcommittee agreed with our proposed use of the PM10C
sampler. Other comments on our proposed use of the low-volume PM10C
sampler for the Pb-PM10 FRM were in support of the PM10C as an
appropriate sampler for the FRM.  We are promulgating the Pb-PM10 FRM
based on the use of the low-volume PM10C sampler.

We also received comments on our proposed use of XRF as the analysis
method for the Pb-PM10 FRM, including comments from CASAC’s AAMM
Subcommittee during the peer review of the proposed FRM.  Several
commenters agreed with our proposed use of XRF as the analysis method,
citing several of the advantages we identified in the preamble to the
proposed rule.  However, several other commenters suggested that
Inductively-Coupled Plasma-Mass Spectrometry (ICP-MS) would be a more
appropriate analysis method for the FRM.  

The AAMM Subcommittee and other commenters raised concerns with the
potential for measurement bias due to non-uniform filter loadings.  They
noted that the analysis beam of the XRF analyzer does not cover the
entire filter collection area; therefore, it is possible for the
measurement to be biased if the Pb particles deposit more (or less) on
the edge of the filter as compared to the center of the filter.  To
address these concerns, EPA’s Office of Research and Development (ORD)
conducted qualitative and quantitative tests of filter deposits
generated in the laboratory under controlled conditions.  Although test
results confirmed prior reports of formation of a deposition band at the
circumference of the PM10C filters, this band comprises only 5 percent
of the filter’s deposition area.  Quantitative analysis of collected
calibration aerosols in the 0.035 micrometer to 12.5 micrometer size
range revealed that use of either a centrally located 10 mm or 20 mm
spot size can accurately represent the filter’s mean mass
concentration within approximately 2 percent.  Similar results were
obtained using a PM2.5 FRM sampler and a “total particulate sampler”
(a PM2.5 sampler with the internal separator removed).  Based on these
results, it can be concluded that any non-uniformity of particle
deposition on PM10C filters will represent a small fraction of the
overall uncertainty in ambient Pb concentration measurement.  As such,
we believe the concerns associated with non-uniform filter loading are
sufficiently addressed to allow XRF as an appropriate analysis method
for the FRM. 

The AAMM Subcommittee and other commenters suggested ICP-MS as an
alternative to the XRF analysis method.  Advantages identified with
ICP-MS included the analysis of the entire filter deposit and a higher
sensitivity (i.e., lower MDL.)  We agree that the ICP-MS analysis method
is also an appropriate method for the analysis of Pb.  However, ICP-MS
(and other analysis methods requiring the extraction of Pb prior to
analysis) also has potential bias due to uncertainty in the percentage
of total Pb that is extracted.  While this bias can be minimized by use
of very strong acids (i.e., hydrogen fluoride), many laboratories wish
to avoid these strong acids due to the damage they can do to the
analyzer and due to safety concerns.  In addition, ICP-MS is a
destructive method and samples can not be saved for further analysis. 
We agree that the ICP-MS method is more sensitive than the XRF method. 
However, the XRF method detection limit provides sufficient sensitivity
for use in determining compliance with the Pb NAAQS being promulgated
today.  As pointed out in our preamble to the proposed rule, we
estimated the method detection limit for XRF and ICP-MS coupled with
low-volume sampling to be 0.001 (g/m3 and 0.00006 (g/m3, respectively. 
No commenters disagreed with these estimates. 

	Several states requested approval for alternative analysis methods
because their laboratories are already equipped to perform those
analysis methods.  Our decision to use XRF as the FRM analysis method
does not prevent monitoring agencies from using alternative analysis
methods.  However, before these alternative analysis methods can be used
they must be approved as FEMs for the measurement of Pb-PM10. 
Monitoring agencies can seek FEM approval for alternative analysis
methods by following the FEM requirements (40 CRF Part 53.33).  In
addition, we plan to approve (after conducting the necessary testing and
developing the necessary applications ourselves) FEMs for ICP-MS and
Graphite Furnace Atomic Absorption (GFAA) to support monitoring agencies
that prefer to use these analysis methods.

We also received comments on the specific details of the proposed XRF
analysis method. The AAMM Subcommittee and one other commenter raised
concerns about the lack of a thin-film XRF National Institute of
Standards and Technology (NIST)-traceable Pb standard.  NIST currently
offers Standard Reference Material (SRM) 2783, “Air Particulate on
Filter Media”, that are a polycarbonate filter that contain a
certified concentration for Pb equivalent to 0.013 ± 0.002 µg/m3. 
Calibration materials for XRF are not destroyed during analysis;
therefore, the SRM should be stable over time and can be reused multiple
times if properly handled and protected.  

The AAMM Subcommittee raised concerns regarding lot-specific laboratory
blanks, field blanks, and possible contamination of filters.  The
commenters suggested that the laboratory blanks (the results of Pb
analysis of “clean” filters that have not been used in a sampler)
that are used for XRF background measurement and correction be
lot-specific. The addition of lot-specific laboratory blanks will help
minimize contamination that may be due to new filter lots and the
analytical system. A few commenters suggested the addition of field
blanks in order to minimize the Pb contamination of filters in the
field.  Field blanks are filter blanks that are sent to the field and
are placed into the sampler for the sampling duration without ambient
air flow. We agree with the suggestions to make laboratory blanks
lot-specific and to add the collection of field blanks.  A comment to
add annual MDL determinations and filter-lot specific MDL determinations
was received.  We agree that the addition of annual MDL estimates and
lot-specific MDL determinations is an improvement to the proposed FRM
text.  In addition, several editorial comments were received that
related to modifying existing statements to add clarity and help to
ensure consistency across laboratories. We are making changes to the XRF
analysis method to address these editorial comments. 

We received one comment related to the need for data quality objectives
(DQOs).   We agree with the commenter on the need for DQOs for the
Pb-PM10 FRM.  Since the time of proposal, we have completed the DQO
analysis to evaluate the acceptable measurement uncertainty for
precision and bias.  The DQO report is in the docket.  As part of that
process, the recommended goals for precision were defined as an upper 90
percent confidence limit for the coefficient of variation of 20 percent
and the goals for bias were defined as an upper 95 percent confidence
limit for the absolute bias of 15 percent.  We have reflected this in
our final regulation.

c.  Decision on Pb-PM10 FRM

We are finalizing the FRM for Pb-PM10 as proposed with the exception of
the following amendments and additions.  Changes to the XRF analysis
method are being made to address comments received during the public
comment period and peer review of the proposed Pb-PM10 FRM.  These
changes include a revision to the Pb-PM10 FRM text to include reference
to the SRM 2783 NIST-traceable calibration standard.  The FRM text was
modified to add a section that requires the collection of field blanks,
and clarify that the laboratory blanks used for background measurement
and correction shall be lot-specific.  We added the requirements for
annual MDL estimates and lot-specific MDL determinations.  Several minor
changes were made to address editorial comments received that related to
modifying existing statements to add clarity and help to ensure
consistency across laboratories.  Examples of these changes include the
addition of other commercial XRF instrumentation vendors; clarification
of the maximum filter loading for Pb analysis which is based on the
maximum mass loading (200 µg/m3) for a PM10C sampler; inclusion of
additional references for spectral processing methods; and clarification
that the FRM applies specifically to Pb.  A reference was included for
additional guidance if multi-elemental analysis is performed.  To ensure
consistency in reporting uncertainties for Pb by XRF across
laboratories, an equation to calculate uncertainties was added and
follows the same procedure used for XRF in the PM2.5 speciation program.
 Based on the DQO process, the FRM precision and bias requirements were
modified to reflect the measurement uncertainty goals of 20 percent and
15 percent, respectively.

FEM Requirements

We are finalizing changes to the FEM requirements for Pb.  These
requirements will apply for both Pb-TSP and Pb-PM10 methods.  This
section discusses the proposed changes to the FEM requirements, comments
received on the proposed changes, and the final FEM requirements being
promulgated with this action.

Proposed FEM Requirements

The current FEM requirements state that the ambient Pb concentration
range at which the FEM comparability testing must be conducted to be
valid is 0.5 to 4.0 (g/m3.  Currently there are few locations in the
United States where FEM testing can be conducted with assurance that the
ambient concentrations during the time of the testing would exceed 0.5
(g/m3.  In addition, the Agency proposed to lower the Pb NAAQS level to
between 0.10 and 0.30 µg/m3.  Consistent with this proposed revision,
we also proposed to revise the Pb concentration requirements for
candidate FEM testing to a range of 30 percent of the revised level to
250 percent of the revised level in µg/m3.  The requirements were
changed from actual concentration values to percentages of the NAAQS
level to allow the FEM requirements to remain appropriate if subsequent
changes to NAAQS levels occur during future NAAQS reviews.

The current FEM does not have a requirement for a maximum MDL.  In order
to ensure that candidate analytical methods have adequate sensitivity or
MDLs, we proposed adding a requirement for testing of a candidate FEM. 
The applicant must demonstrate that the MDL of the method is less than 1
percent of the level of Pb NAAQS. 

We proposed to modify the FEM requirements for audit samples.  Audit
samples are the known concentration or reference samples provided by EPA
and used to verify the accuracy with which a laboratory conducts the FRM
analytical procedure before it may be compared to the candidate FEM. 
The current requirements are that audit samples be analyzed at levels
that are equal to 100, 300, and 750 µg per spiked filter strip
(equivalent to 0.5, 1.5, and 3.75 µg/m3 of sampled air).  We proposed
to revise the levels of the audit concentrations to percentages (30
percent, 100 percent and 250 percent) of the level of the Pb NAAQS to
provide for reduced audit concentrations that are more appropriate for a
reduced level of the revised NAAQS. 

The existing FEM requirements are based on the high-volume TSP sampler,
and as such, refer to ¾-inch x 8-inch glass fiber strips.  In order to
also accommodate the use of low-volume sample filters, we proposed to
add references to 46.2 mm filters where appropriate.  For FEM candidates
that differ only from the FRM with respect to the analysis method for
Pb, pairs of these filters will be collected by a pair of FRM samplers.

b.  Comments

We received few comments on the proposed amendments to the FEM
requirements for Pb.  One commenter suggested that the proposed MDL
requirement, 1 percent of the NAAQS, was overly stringent, and that an
MDL of 5 percent would be sufficient. Another commenter suggested that
an MDL at 10 percent would be more achievable.  After reviewing these
comments, we have reconsidered the requirement for the MDL to be 1
percent of the NAAQS or less and now believe that the requirement may be
unduly restrictive.  The MDL represents an estimate of the lowest Pb
concentration that can be reliably distinguished from a blank.  The
concept of the “limit of quantitation” (LOQ), the level at which the
we can reasonably tell the difference between two different values, is
often used to determine the concentration at which we have confidence in
the accuracy of the measurement.  The LOQ is usually estimated at 5 to
10 times the MDL.  At a MDL of 5 percent (i.e., 0.0075 µg/m3), the
maximum LOQ would still be less than one half of the NAAQS (i.e., 0.075
µg/m3).  We believe this is adequate for the purposes of determination
of compliance with the NAAQS.  The three most commonly used Pb-PM10
analysis methods (XRF, ICP-MS, and GFAA) all have estimated method
detection limits below 5 percent of the revised Pb NAAQS.  We note
however, that for areas where concentrations may frequently be well
below the NAAQS such as at nonsource-oriented sites it may be desirable
to use a FEM with a more sensitive analysis method (such as ICP-MS) to
assure fewer non-detect measurements and to provide better accuracy at
concentrations well below the NAAQS.

We received two comments supporting the development and consideration of
the use of continuous Pb monitors. We agree that the FEM testing
requirements should include language regarding FEM testing and approval
of continuous or semi-continuous monitors. 

c.  Decisions on FEM Requirements

We are finalizing the FEM requirements for Pb as proposed except for the
addition of language to include FEM testing and approval of continuous
or semi-continuous monitors.

4.  Quality Assurance Requirements

	We are finalizing changes to the quality assurance (QA) requirements
for Pb.  These requirements will apply for both Pb-TSP and Pb-PM10
measurements.  This section discusses the proposed changes to the QA
requirements, comments received on the proposed changes, and the final
QA requirements being promulgated with this action.

a.  Proposed Changes

We proposed modifications to the quality assurance (QA) requirements for
Pb in 40 CFR part 58 Appendix A paragraph 3.3.4 in order to accommodate
Pb-PM10 monitoring.  In addition, we proposed to consolidate several
existing requirements for PM samplers (TSP and PM10 samplers) into
paragraph 3.3.4 to clarify that these requirements also apply to Pb-TSP
and Pb-PM10 samplers.  The following paragraphs detail the QA
requirements we proposed to amend.

The collocation requirement for all TSP samplers (15 percent of a
primary quality assurance originations sites at a 1 in 12 day sampling
frequency, paragraph 3.3.1) applies to TSP samplers used for Pb-TSP
monitoring.  These requirements are the same for PM10 (paragraph 3.3.1);
thus, no changes are needed to accommodate low-volume Pb-PM10 samplers. 
However, to clarify that this requirement applies to Pb-PM10 monitoring,
in addition to mass measurements for PM10, we proposed to add a
reference to this requirement in paragraph 3.3.4.  The current
requirement for selecting the collocated site requires that the site be
selected from the sites having annual mean concentrations among the
highest 25 percent of the annual mean concentration for all sites in the
network.

 The sampler flow rate verifications requirement (paragraph 3.3.2) for
low-volume PM10 and for TSP are at different intervals.  To clarify that
this requirement also applies to Pb monitoring (in addition to sample
collection for TSP and PM10 mass measurements) we proposed to add a
reference to this requirement in paragraph 3.3.4.

Paragraph 3.3.4.1 has an error in the text that suggests an annual flow
rate audit for Pb, but then includes reference in the text to
semi-annual audits.  The correct flow rate audit frequency is
semi-annual.  We proposed to correct this error.  We also proposed to
change the references to the Pb FRM to include the proposed Pb-PM10 FRM.

Paragraph 3.3.4.2 discusses the audit procedures for the Pb analysis
method.  This section assumes the use of a high-volume TSP sampler, and
we proposed edits to account for the proposed Pb-PM10 FRM.

We proposed to require one audit at one site within each primary quality
assurance organization (PQAO) once per year.  We also proposed that, for
each quarter, one filter of a collocated sample filter pair from one
site within each PQAO be sent to an independent laboratory for analysis,
for a total of 5 audits per year.  The independent measurement on one
filter from each pair would be compared to the monitoring agency’s
routine laboratory’s measurement on the other filter of the pair, to
allow estimation of any bias in the routine laboratory’s measurements.
 

b. Comments

	We received one comment on the proposed QA requirements specifically
addressing the overall sampling and analysis bias.  The commenter was
concerned that the proposal to implement one independent performance
evaluation audit (similar to the PM2.5 Performance Evaluation Program
(PEP)) and then augment that sample with four samples from collocated
precision site would be inadequate.  The commenter suggested that in
order for the audit program to be successful it would require the same
independent laboratory be used by all monitoring agencies across the
country.  

We believe it is important to have a measurement of the bias of the
overall method for Pb (including both sampling and analysis aspects).  
We proposed five audits per PQAO per year (one independent audit and
four collocated samples all analyzed at an independent lab).  This
proposal was based on data evaluations of PM2.5 bias information, and
the assumption that no PQAO would have more than 5 Pb sites.  However,
we now recognize that some PQAO are likely to have more than 5 sites,
and as part of our consideration of this comment, we are revising the
audit requirements to require 1 additional audit per PQAO and an
additional 2 collocated sample filters for PQAO’s with more than 5
sites.  This sampling frequency would parallel the PM2.5 performance
evaluation.  Based on our review of PM2.5 bias information, five audits
per year for PQAOs with five or fewer monitoring sites provide an
adequate assessment of bias over a 3-year period.  We believe we can
provide an adequate three-year estimate of bias with this approach since
it will yield the same number of audit results as the PM2.5 PEP program.
 In addition, the statistic used to assess bias for PM10-2.5 and the
gaseous pollutants (section 4.1.3) will be used for the Pb bias
assessment and will be referenced in section 4.4.2.  This will eliminate
the need to assess bias by combining data from the flow rate audits and
Pb audit strips as discussed in sections 4.4.2 through 4.4.5, so this
assessment will be removed. The use of the flow rate audits and Pb audit
strips  will be able to be assessed separately using statistics already
available in Appendix A. Sections 4.2.2 and 4.2.3 for flow rate
information  and section 4.1.3 will be used for the Pb strip assessment.

Like the PM2.5 PEP program, we are planning to implement an audit
program for monitoring agencies requesting federal implementation of the
audits, but allow monitoring agencies to implement their own audit
program.  We plan to utilize one laboratory for the analysis of the Pb
audit samples for those monitoring organization requesting federal
implementation of these audits.  However, we expect some states will
elect to implement their own audits.  Independent laboratory services
will be offered to monitoring organizations that are self-implementing
this performance evaluation program, however, they may use other
independent labs.  Based on the current PM2.5 PEP program, we expect the
majority of monitoring agencies will elect to make use of the federally
implemented audit program.

	We also received comments on our proposed precision and bias goals from
individual members of the CASAC AAMM Subcommittee as part of the
consultation on March 25, 2008.  The AAMM Subcommittee members indicated
that we should base the precision and bias goals on the findings of the
ongoing DQO analysis identified in our proposal.  We have completed the
DQO analysis as described in the proposed rule, and a copy of the report
is in the docket for this rule.  Based on the findings from the DQO
analysis, we are finalizing a goal for precision and bias of 20 percent
and 15 percent, respectively.  These values allow for slightly higher
uncertainty than the proposed values and reflect the finding that the
existing high-volume samplers may not routinely be capable of meeting
the proposed precision and bias goals.

c. Decisions on Quality Assurance Requirements

We are finalizing amendments to the QA requirements for Pb measurements
as proposed with the following differences.  Based on the DQO analysis,
the goal for acceptable measurement uncertainty will be defined for
precision as an upper 90 percent confidence limit for the coefficient of
variation (CV) of 20 percent and as an upper 95 percent confidence limit
for the absolute bias of 15 percent.  The evaluation of precision will
also be limited to those data greater than or equal to 0.02 (g/m3. 
These goals are included in section 2.3.1 of 40 CFR Part 58 Appendix A. 
We are requiring 1 PEP audit per year per PQAO with 5 or fewer sites,
and 2 PEP audits per year per PQAO with more than 5 sites.  Due to the
addition of the Pb performance evaluation, a reference to the
statistical  assessment of bias used for PM10-2.5 and the gaseous
pollutants (section 4.1.3) will be included in section 4.4.2 and the
requirement for the bias calculation using the Pb strips in combination
with the flow rate audits, as discussed in sections 4.4.2 through 4.4.5,
will be removed and  sections 4.2.2 and 4.2.3 will be used to assess
flow rate information  and section 4.1.3 will be used for the Pb strip
laboratory bias assessment.

B.  Network Design

As a result of this Pb NAAQS review and the tightening of the standards,
EPA recognizes that the current network design requirements are
inadequate to assess compliance with the revised NAAQS.  Accordingly, we
are promulgating new network design requirements for the Pb NAAQS
surveillance network.  The following sections provide background,
rationale, and details for the final changes to the Pb network design
requirements.

1.  Proposed changes

We proposed to modify the existing network design requirements for the
Pb surveillance monitoring network to achieve better understanding of
ambient Pb air concentrations near Pb emission sources and to provide
better information on exposure to Pb in large urban areas.  We proposed
that monitoring be presumptively required at sites near sources that
have Pb emissions (as identified in the latest National Emissions
Inventory (NEI) or by other scientifically justifiable methods and data)
that exceed a Pb “emission threshold”.  This monitoring requirement
would apply not only to existing industrial sources of Pb, but also to
fugitive sources of Pb (e.g., mine tailing piles, closed industrial
facilities) and airports where leaded aviation gasoline is used.  In
this context, the “emission threshold” was intended to be the lowest
amount of Pb emissions per year for a source that may reasonable be
expected to result in ambient air concentrations at a nearby monitoring
site in excess of the proposed Pb NAAQS (as discussed later, based on
reasonable worst case scenarios).  We conducted an analysis to estimate
the appropriate emission threshold (Cavender 2008a) which is available
in the docket for this rulemaking.  Using the results from this
analysis, we proposed that the emission threshold be set in the range of
200 kg-600 kg per year total Pb emissions (including point, area, and
fugitive emissions and including Pb in all sizes of PM), corresponding
to the proposed range of levels for the Pb NAAQS, with the final
selection of the threshold to be dependent on the final level for the
NAAQS. 

We recognized that a number of factors influence the actual impact a
source of Pb has on ambient Pb concentrations (e.g., local meteorology,
emission release characteristics, and terrain).  Accordingly, we also
proposed to allow monitoring agencies to petition the EPA Regional
Administrator to waive the requirement to monitor near a source that
emits less than 1000 kilograms per year where it can be shown that
ambient air concentrations at that site are not expected to exceed 50
percent of the NAAQS during a three year period (through modeling,
historical monitoring data, or other means).  We proposed that for
facilities identified as emitting more than 1000 kilograms per year in
the NEI, a waiver would only be provided for those sites at which it
could be demonstrated that actual emissions are less than the emission
threshold. 

We proposed that source-oriented monitors be located at locations of
maximum impact classified primarily as microscale monitors
representative of small hot-spot areas adjacent or nearly adjacent to
facility fence-lines.  We also indicated that source-oriented monitors
may be located at locations of maximum impact but which are
representative of larger areas and classified as middle scale. 
Additionally we sought comments on the appropriateness of requiring
monitors near Pb sources.  

We also proposed a small network of non-source oriented monitors in
urban areas in addition to the source-oriented monitors discussed above,
in order to gather additional information on the general population
exposure to Pb in ambient air.  While it is expected that these
non-source oriented monitors will show lower concentrations than source
oriented monitors, data from these non-source oriented monitors will be
helpful in better characterizing population exposures to ambient
air-related Pb and may assist in determining nonattainment boundaries. 
We proposed to require one non-source oriented monitor in each Core
Based Statistical Area (CBSA, as defined by the Office of Management and
Budget) with a population of 1,000,000 people or more as determined in
the most recent census estimates.  Based on the most current census
estimates, 52 CBSAs would be required to have non-source oriented
population monitors (see   HYPERLINK
"http://www.census.gov/popest/metro/index.html" 
http://www.census.gov/popest/metro/index.html  for the latest census
estimates.) 

We noted in our proposal that monitoring agencies would need to install
new Pb monitoring sites as a result of the proposed revisions to the Pb
monitoring requirements.  We estimated that the size of the required Pb
network would range from between approximately 160 and 500 sites,
depending on the level of the final standard.  If the size of the final
network is on the order of 500 sites, we proposed to allow monitoring
agencies to stagger the installation of newly required sites over two
years, with at least half the newly required Pb monitoring sites being
installed and operating by January 1, 2010 and the remaining newly
required monitoring sites installed and operating by January 1, 2011. 
As proposed, monitors near the highest Pb emitting sources would need to
be installed in the first year, with monitors near the lower Pb emitting
sources and nonsource-oriented monitors being installed in the second
year.  We also proposed to allow monitoring agencies one year following
the release of updates to the NEI or an update to the census to add new
monitors if these updates would trigger new monitoring requirements. 

We also proposed to allow States to use Pb-PM10 monitors to meet the
network design requirements if our proposed use of scaled Pb-PM10 data
was adopted in the final rule.

2.  Comments on Network Design

We received several comments on the proposed network design
requirements.  These comments and our responses are broken down into the
following categories: source-oriented monitoring, non-source oriented
monitoring, roadway monitoring, the use of Pb-PM10 samplers, and the
required timeline for installing newly required monitors.

a.  Source-oriented monitoring

We received several comments supporting the need for monitoring near Pb
sources.  Alternatively, one commenter suggested that near source
monitoring is not necessary because “the EPA and the State already
know where and what the problems are” and “EPA should … develop
control standards to deal with the problem …”   We note individual
sources do not violate a NAAQS but that under the CAA a primary method
to achieve control of emissions at sources contributing to an exceedence
of the NAAQS is the State Implementation Plan (SIP).  We expect the
highest concentrations of Pb to be near sources of Pb due to its
dispersion characteristic.  Monitoring data are important evidence used
to designate areas as non-attainment of the NAAQS.  Thus, monitoring
near Pb sources is needed to properly designate areas that violate or
contribute to air quality in a nearby area that does not meet the Pb
NAAQS.

We received a comment that the methods used in developing the emission
thresholds estimated ambient impacts over different averaging periods,
and that the emission thresholds should be recalculated for all methods
using the final averaging period.  We recognized this issue in our
memorandum documenting the analysis (Cavender, 2008a), and we have
recalculated the estimate of the lowest Pb emission rate that under
reasonable worst-case conditions could lead to Pb concentrations
exceeding the NAAQS, based on the final level and form of the standard
(Cavender, 2008b).

We also received comments on the approach used in developing the
proposed emission thresholds that would trigger consideration of the
placement of a monitoring site near a Pb source.  Commenters expressed
concerns that the approach overestimated the potential impact of Pb
sources, and would result in either unnecessary burden on monitoring
agencies or worse yet, monitoring agencies would install and operate
monitors at sources that had little to no potential to exceed the NAAQS.
 Several commenters suggested various alternative levels, including a
threshold of 1 ton or higher, basing their recommendations on concerns
such as the reliability of data in the NEI.  Other commenters suggested
that EPA was in the best position to determine which sources had the
potential to exceed the NAAQS.  

We note that the approach used in developing the emission threshold in
the proposal was intended to represent a reasonable worst case scenario.
 As such, we recognize that many Pb sources which emit at or above the
proposed emission threshold will have Pb impacts that are below the Pb
NAAQS.  To account for this, we proposed to allow monitoring agencies to
request monitoring waivers if they could demonstrate that facilities
would not contribute to a Pb impact of greater than 50 percent of the
NAAQS.  However, upon further consideration, we agree that by basing the
threshold on these worse case condtions we will be placing an
unnecessary burden on monitoring agencies to evaluate or monitor around
sources that may not have a significant potential to exceed the NAAQS. 
As a result, we are finalizing changes to our approach for requiring
source-oriented monitors.  We are including a requirement that
monitoring agencies conduct monitoring taking into account sources that
are expected to exceed or shown to have contributed to a maximum
concentration that exceeded the NAAQS, the potential for population
exposure, and logistics.  In addition, specifically we are requiring
monitoring agencies to conduct monitoring at sources which emit Pb at a
rate of 1.0 or more tons per year.  This emissions rate corresponds to
two times the estimate of the lowest Pb emission rate that under
reasonable worst-case conditions could lead to Pb concentrations
exceeding the NAAQS.  This recognizes the thresholds used in the
proposal represented reasonable worst case scenarios, and that a more
appropriate approach to balance the factors important in designing a
network is to use a higher threshold that is more likely to clearly
identify sources that would contribute to exceedences of the NAAQS.   In
addition, the State, and the Agency working together will identify what
additional sources should be taken into account because they are
expected to or have been shown to contribute to maximum concentrations
that contribute to exceedences.  

To account for the other sources that may contribute to a maximum Pb
concentration in ambient air in excess of the NAAQS, we are retaining
the authority granted to the EPA Regional Administrator in the existing
monitoring requirements to require monitoring “where the likelihood of
Pb air quality violations is significant or where the emissions density,
topography, or population locations are complex and varied.”  We
believe that these final monitoring requirements are adequate to ensure
that monitoring will be conducted respecting facilities that have the
potential to exceed the NAAQS with out placing undue burden on
monitoring agencies.  

We received several comments supporting the need for monitoring waivers,
and one comment that did not support waivers.  Those in favor of the
waivers pointed out that, as discussed above, many Pb sources will
result in much lower Pb impacts than the “worst case” Pb source. 
They argued that the states need flexibility in meeting the
source-oriented monitoring requirements, and agreed that it is
appropriate to focus on sites near those Pb sources with the greater
potential to result in Pb concentrations that exceed the Pb NAAQS.   The
commenter who cautioned against the allowance of monitoring waivers
expressed concerns that modeling results are not exact and this
uncertainty could result in waivers being granted when actual Pb
concentrations could exceed the NAAQS.  We took the uncertainty of
modeled results into account when proposing to limit waivers to
situations where the modeled data indicated maximum concentrations would
be 50 percent of the NAAQS, rather than at 100 percent of the NAAQS, and
we believe this provides a sufficiently protective approach to account
for uncertainty in modeling and other assessments estimating a Pb
sources expected impacts.  

We received comments questioning the need to restrict the provision of
waivers to sites near sources emitting less than 1000 kg/yr.  We agree
it is possible for sources greater than 1000 kg/yr to have an impact
less than 50 percent of the NAAQS under certain conditions.  We also
acknowledge the need for flexibility in implementing the Pb NAAQS
monitoring network.  As such, we have reconsidered our proposed
restriction limiting waivers to those for sources emitting less than
1000 kg/yr, and we are not finalizing a restriction on the size of
sources near sites eligible for a waiver from the source-oriented
monitoring requirement.

We received comments on relying on the National Emission Inventory (NEI)
to identify Pb sources with emissions greater than the emission
threshold.  In general, several commenters said better data should be
used to identify Pb sources emitting above the proposed emission
threshold.  Several commenters expressed concerns with the accuracy of
the NEI, and recommended allowing states to use “the best available
information” on emissions from Pb sources. Some commenters pointed to
differences in Pb emissions data reported in the Toxics Release
Inventory and the NEI as evidence that the NEI was inaccurate.  One
commenter said current practices to reduce toxic emissions are not
reflected in the NEI and wanted the opportunity to update the
information. Commenters said EPA should correct the errors in the NEI or
allow states to submit revised local data that more accurately reflect
Pb emissions before emissions inventory data are used to determine which
sources exceed the threshold.  

We agree that the most current Pb emissions information should be used
when making final decisions about which sources exceed the emission
threshold.  This may include datasets that could include sources not
contained in the NEI.  We acknowledge that many of the NEI emission
estimates likely would be improved with more site specific data (e.g.,
emissions test data).  We have added the phrase “or other
scientifically justifiable methods and data” to the monitoring
requirements to clarify that NEI emissions estimates are not the only
emission estimates that can be used to estimate emissions. 

We received comments that the proposed source-oriented monitoring
requirements did not address situations where multiple sources
contribute to Pb concentrations at one location.  Our proposed waiver
requirements do take into account the impacts from multiple sources. 
The proposed language stated that waivers could only be granted for
source-oriented sites that did not “contribute to a maximum Pb
concentration in ambient air in excess of 50 percent of the NAAQS”. 
We recognize that exceedances of the standard may be caused by emissions
from a number of smaller sources none of which would cause a violation
in isolation, but we expect it is unlikely that violations would occur
when all of the sources in an area are below the emissions threshold due
to the rapid decrease in Pb concentrations with distance from a Pb
source.  However, the purposes of the monitoring network would be
undermined if multiple sources in a single area were able to receive
waivers, with the result that no monitor was required even though Pb
concentrations in the area were in excess of 50 percent of the standard.
 Accordingly, EPA expects that Regional Administrators, in deciding
whether to grant waivers, will take into account whether other waivers
have been granted or sought for sources in the same area, and whether
the cumulative emissions of the sources in the area warrant at least one
monitor being sited.  

Several monitoring agencies expressed concern about the need for
flexibility in implementing the source-oriented monitoring requirements.
 We believe that the proposed rule provides significant flexibility to
monitoring agencies for the implementation of the monitoring
requirements.  One area where we believe it is appropriate to provide
additional flexibility is for situations where multiple sources above
the emission threshold contribute to a single maximum impact.  A strict
reading of the proposed source-oriented monitoring requirement could be
that monitoring agencies would be required to monitor each Pb source
separately.  This was not intended, and our existing monitoring guidance
is clear that a single monitor can be used to monitor multiple sources
where the maximum impact is influenced by multiple sources. 
Nonetheless, we believe it is appropriate to clarify this point in the
rule language.  As such, we are adding a clause to the source-oriented
monitoring requirement that specifies that a single monitor can be used
to monitor multiple Pb sources where they contribute to a single maximum
impact.

We received two comments that source-oriented monitors should be located
at the location of maximum estimated Pb concentration without
consideration for the potential for population exposure, and six
comments that source-oriented monitors should be located in an area
where population exposure occurs.  In their comments on the proposed
rule, one commenter argued that monitors “should be located in or
around only those Pb point sources with a nearby population base”
because “air Pb concentrations have regulatory importance largely in
those areas where significant groups of children are exposed for
considerable time periods.”  They argue that as an example “a rural
road going by a lead mining facility is an unlikely place that children
will spend considerable amounts of time” and as such “placing a
monitoring site on such a road would have de minimis, if any, value.” 
Another commenter suggested that “monitors should be located near
playgrounds, sports fields, long-established highways, and the like.” 

Siting of required monitors at the expected maximum concentration in
ambient air is consistent with how all NAAQS pollutants are monitored. 
In considering the siting criteria for the required Pb source-oriented
monitors, we recognize that Pb is a persistent, multimedia pollutant,
such that deposited Pb from current emissions can contribute to human
exposures over extended amounts of time.  Also, Pb deposited in one area
can be transported to another area by “tracking” from vehicle and
foot traffic.  In addition, unlike the case for other criteria
pollutants, ingestion of deposited Pb is a major Pb exposure pathway. 
Given these complexities, it is appropriate to allow siting agencies to
also consider the potential for population exposure in siting monitors
near sources.  

In our proposed rule, we recognized that there are reasons for not
requiring monitoring at the location of expected maximum concentration
such as logistical limitations (i.e., the location of expected maximum
concentration occurs in the middle of a lake).  In consideration of
public comments on this issue and due to the complexities of Pb, we
believe it is appropriate, in the final rule, to also allow states to
consider the potential for population exposure as a factor (in addition
to other factors such as logistical considerations) when siting required
source-oriented monitors.  Thus, we are including the potential for
population exposure as a factor that monitoring agencies can consider
when siting a maximum concentration source-oriented monitoring site
required under part 58.

b.  Non-source oriented monitoring 

We received a number of comments on our proposed non-source oriented
monitoring requirement.  One state and several tribes commented that the
proposed population limit would result in no required non-source
oriented monitors in low population states and tribal lands.  One
commenter expressed concerns that the population limit was too high, and
would result in environmental justice concerns since many poor
communities would not be monitored.

As stated in the proposed rule, it is unlikely that exceedences of the
Pb NAAQS will occur at sites distant from Pb sources.  As such, our
non-source-oriented monitoring requirements satisfy monitoring
objectives in addition to ensuring compliance with the Pb NAAQS.  For
the most part, these monitoring sites should be sited to represent
neighborhood scale exposures.  We are requiring non-source oriented Pb
monitors to provide additional information that will be useful in better
characterizing air-related Pb exposures in neighborhoods.  Sources
affecting neighborhoods may include re-entrained dust from roadways,
closed industrial sources which previously were significant sources of
Pb, hazardous waste sites, construction and demolition projects, or
other fugitive sources of Pb.  Non-source sites will also support the
next Pb NAAQS review by providing additional information on the spatial
variations in Pb concentrations between areas that are affected by
sources to a significant degree and those that are not.  

We believe it is most appropriate to focus the non-source monitoring
requirements in large urban areas since high population locations are
most used in health and epidemiological studies.  We proposed to require
one non-source oriented monitor in each CBSA with a population of
1,000,000 or more as determined in the most recent census.  That
proposed requirement would have resulted in approximately 50 CBSAs
required to have non-source Pb monitors.  EPA notes the comments that
the proposed population limit of 1,000,000 was too high, and may result
in the lack of non-source oriented monitors in smaller urban
communities.  Accordingly, we have decreased the population limit for
requiring non-source monitors to CBSAs with a population of 500,000
people or more, thereby increasing the number of required non-source Pb
monitors from approximately 50 to approximately 100 (based on 2007
population estimates from the Census Buearu).

We also note that these requirements are minimum monitoring
requirements, and that state and tribal monitoring agencies may operate
additional non-source oriented monitors beyond the minimum number of
required monitors.  Data that meets the quality assurance requirements
that is collected from non-required FRM or FEM monitors will also be
used to determine compliance with the Pb NAAQS, assuming that the data
meets.  Additionally, as described previously, source-oriented
monitoring would be required in rural and small communities if a Pb
source emitting 1 ton per year or more are present. 

c.  Roadway Monitoring

The majority of commenters agreed with our finding that the available
data on Pb concentrations near roadways do not indicate the potential
for exceedances of the proposed range of Pb NAAQS levels and
requirements for monitors near roadways were not needed to ensure
compliance with the NAAQS.  However, one commenter argued that our
finding that activity on roadways would not likely contribute to air Pb
concentrations in exceedence of the proposed levels for the standard was
based on data from monitors that did not represent the maximum impact
from roadways. 

While some of the monitors used in our analysis of air Pb impacts from
activity on roadways may not represent the site of maximum impact, we
believe they are representative of locations where roadway monitoring
might be conducted.  As we indicated in our proposal, these monitors
indicate that Pb concentrations are slightly elevated near roadways, but
do not occur at levels approaching the Pb NAAQS being finalized today. 
Nonetheless, we agree that more information on Pb concentrations near
roadways would be valuable, and we encourage monitoring agencies to
consider placing Pb monitors near population centers heavily impacted by
roadways in some of the CBSAs required to install and operate
nonsource-oriented monitors to provide information for use in future
NAAQS reviews.  In addition, the EPA has research initiatives
investigating Pb concentrations near roadways that will provide
additional information that can be used in future NAAQS reviews.

d. 	Use of Pb-PM10 monitors

Comments were received on the use of Pb-PM10 monitoring in lieu of
required Pb-TSP under certain circumstances.  Several commenters
suggested an approach for the use of Pb-PM10 monitors as an alternative
to the proposed use of scaling factors.  Commenters suggested that
Pb-PM10 monitoring would only be allowed in certain instances. 
Specifically, Pb-PM10 monitoring would be allowed where estimated Pb
concentrations were predicted to be less than 50 percent of the NAAQS
and where Pb in ultra-coarse particulate was expected to be low.  That
commenter also suggested that if at some point in the future the monitor
were to show that Pb-PM10 concentrations exceeded an arithmetic 50
percent of the NAAQS, the monitoring agency would be required to replace
the Pb-PM10 monitor with a Pb-TSP monitor.  

We support this suggested approach, noting that it allows for the use of
Pb-PM10 in areas where we do not expect Pb concentrations to exceed the
Pb NAAQS without the burden and uncertainty associated with the
development and use of site-specific scaling factors.  As noted in
section II.C.1, use of Pb-PM10 monitors in these locations offers the
advantages of increased monitor precision and decreased spatial
variation of Pb-PM10 concentrations, without raising the same concerns
over a lack of protection against health risks from all particulate Pb
emitted to the ambient air that support retention of Pb-TSP as the
indicator.  

However, we feel the combined requirements for allowing use of Pb-PM10
monitors to areas where the concentration is expected to be less than
50% of the NAAQS and where Pb in ultra-coarse particles is expected to
be low  may be too restrictive, especially in light of the fact that a
monitoring agency may request a waiver from monitoring all together if
the expected concentration is less than 50% of the NAAQS.  We believe it
is appropriate to allow Pb-PM10 in lieu of Pb-TSP where the maximum
3-month arithmetic mean Pb concentration is expected to be less than
0.10 µg/m3 (i.e., two thirds of the NAAQS) and where sources are not
expected to emit ultra-coarse Pb.  By limiting the use of Pb-PM10
monitoring to locations where the Pb concentrations are less than 0.10
µg/m3 on a 3-month arithmetic mean and where ultra-coarse Pb is
expected to be low, we believe  that the Pb-TSP concentrations will also
be less than 100% of the NAAQS.  Examples of locations where Pb-PM10
monitoring may be more representative of Pb-TSP levels than others are
urban areas away from Pb sources (i.e., nonsource-oriented monitoring
locations), near airports, combustion sources, and other Pb sources
which are expected to only emit Pb in the fine PM size fraction. 
Locations where it would not be appropriate to monitor using Pb-PM10
samplers include near smelters, roadways, and sources with significant
fugitive dust emissions.  

We are revising the proposed allowance for the use of Pb-PM10 monitors
to allow Pb-PM10 monitors without the use of scaling factors for
nonsource-oriented monitors (unless existing data indicates maximum
3-month arithmetic mean Pb concentration have exceeded 0.10 µg/m3 in
the last three years) and for source-oriented monitors where maximum
3-month arithmetic mean Pb concentration is expected to be less than
0.10 µg/m3 (based on modeling or historic data) and where ultra-coarse
Pb is expected to be low.  We are also requiring that a Pb-TSP monitor
be required at the site if at some point in the future the Pb-PM10
monitor shows that the maximum 3-month arithmetic mean Pb-PM10
concentration was equal to or greater than 0.10 µg/m3.  Section IV.C of
this preamble discusses how data from Pb-PM10 monitors will be used in
comparison to the Pb NAAQS.

e.	Required timeline for monitor installation and operation

We received several comments from monitoring agencies regarding the
proposed timeline for monitor installation.  Commenters supported the
need for a staggered network deployment, especially if a large number of
new monitors would be required.  Two commenters argued that even the
proposed two-year deployment would not provide enough time for
monitoring agencies to site and install the number of monitors needed.

Based on the network design requirements being finalized with this
action, we estimate that approximately 135 facilities emit Pb at levels
over the “emissions threshold” of 1 ton per year and would result in
required monitoring.  We are also requiring urban areas with populations
over 500,000 to site non-source oriented monitors, thus another 101
monitors are required.  Together the required source oriented and
non-source oriented monitors are expected to total 236 monitors.  Some
of the existing 133 lead monitoring stations will be useful to support
the required network, but other stations may need to move.  We are
estimating that approximately 90 of the existing stations are in
locations that are of benefit to other monitoring objectives, even when
well below the NAAQS (e.g., long-term trends or for use in a health
study) and are not part of the minimum network requirements being
finalized in today’s action.  Once the network is fully operational
the 236 required stations plus an additional 90 stations in existing
locations that are not required results in an expected network of 326
lead monitoring stations to adequately support characterization of lead
across the country.  

We believe it would be unrealistic to require monitoring agencies to
site and install the required 240 new monitoring stations within one
year, even if some of these are already in the right locations. 
However, we do believe it is reasonable to require monitoring agencies
to site and install half of these stations in one year with the
remaining stations deployed in the following year.  Accordingly, and as
discussed further below, we are finalizing a two-year monitor deployment
schedule for required monitoring.

3.  Decisions on Network Design Requirements

We are finalizing new network design requirements for the Pb NAAQS
monitoring network that differ from those proposed in the following
aspects. The differences from the proposal reflect our consideration of
the comments on the proposed network design requirements and
consideration of the level, form, and averaging time for the final NAAQS
being promulgated today.  

We are adding a requirement that monitoring agencies conduct ambient air
Pb monitoring taking into account Pb sources which are expected to or
have been shown to contribute to a maximum Pb concentration in ambient
air in excess of the NAAQS, the potential for population exposure, and
logistics. At a minimum, there must be one source-oriented SLAMS site
located to measure the maximum Pb concentration in ambient air resulting
from each Pb source which emits 1.0 or more tons per year based on
either the most recent NEI or other scientifically justifiable methods
and data (such as improved emissions factors or site-specific data).  We
are maintaining the existing authority for the EPA Regional
Administrator to require additional monitoring where the likelihood of
Pb air quality violations is significant or where the emissions density,
topography, or population locations are complex and varied.  In
addition, we are adding a clause to the source-oriented monitoring
requirement to clarify that a single monitor may be used to monitor
multiple Pb sources when the sources contribute to a single maximum Pb
concentration.

In addition, monitoring agencies may consider the potential for
population exposure when siting source-oriented monitors.  While this
change does not restrict monitoring agencies from monitoring at any
location meeting the definition of ambient air, this provision allows
monitoring agencies to consider the potential for population exposure
when siting the required source-oriented monitors at the maximum Pb
concentration.

We are removing the proposed restriction that waivers may only be
granted for sites near sources emitting less than 1000 kg/yr.  The EPA
Regional Administrator may approve waivers for the source-oriented
monitoring requirement for any site where the monitoring agency
demonstrates that the emissions from the source will not contribute to a
Pb-TSP concentration greater than 50 percent of the final NAAQS (based
on historic data, monitoring data, or other means).

We are requiring one nonsource oriented monitor in every CBSA with a
population of 500,000 people or more.  In addition, we are requiring
these monitors be placed in neighborhoods within urban areas impacted by
re-entrained dust from roadways, closed industrial sources which
previously were significant sources of Pb, hazardous waste sites,
construction and demolition projects, or other fugitive dust sources of
Pb.

Monitoring agencies may use Pb-PM10 monitors to meet the
nonsource-oriented monitoring requirements tied to CBSA population
provided that historical monitoring does not indicate Pb-TSP or Pb-PM10
concentrations greater than an arithmetic 3-month mean of 0.10 µg/m3,
and to meet the source-oriented monitoring requirements where Pb
concentrations are expected (based on historic data, monitoring data, or
other means) to be less than 0.10 µg/m3 on an arithmetic 3-month mean,
and ultra-coarse Pb is expected to be low.  However, monitoring agencies
are required to begin monitoring for Pb-TSP within six months of a
measured Pb-PM10 arithmetic 3-month mean concentration of 0.10 µg/m3 or
more.  For example, if a Pb-PM10 monitoring site measures an arithmetic
3-month mean concentration of 0.10 µg/m3 or more for the period March
– May 2011, the responsible monitoring agency would be required to
install and begin operation of a Pb-TSP monitor at the site no later
than December 1, 2011.

We are allowing monitoring agencies to stagger installation of any newly
required monitors over a two-year period.  Each monitoring agency is
required to install and operate the required source-oriented monitors by
January 1, 2010.  The nonsource-oriented monitors are required to be
installed and operated by January 1, 2011.  The annual monitoring plan
due July 1, 2009 must describe the planned monitoring that will begin by
January 1, 2010, and the plan due July 1, 2010 must describe the planned
monitoring that will begin by January 1, 2011.

C.  Sampling Frequency

	We proposed to maintain the 1-in-6 day sampling frequency if the final
averaging time for the NAAQS standard was based on a quarterly average. 
We did not receive any comments on our proposed sampling frequency for a
NAAQS based on a quarterly average.  While the final NAAQS is based on a
moving 3-month average rather than a quarterly average, the statistical
and practical monitoring considerations are the same.  As such, we are
maintaining the current 1-in-6 day minimum sampling frequency as
proposed (i.e., monitoring agencies will be required to collect at least
one 24-hour Pb sample every six days.)

D.  Monitoring for the Secondary Standard

We did not propose any specific additional monitoring requirements for
the secondary standard because based on the available data, we do not
expect exceedences of either the primary or the secondary NAAQS away
from the point sources that will be addressed by the monitoring
requirements already described.  We also noted that the Pb-PM2.5 data
collected as part of the Interagency Monitoring of Protected Visual
Environments (IMPROVE) program provides useful information on Pb
concentrations in rural areas that can be used to track trends in
ambient air Pb concentrations in rural areas including important
ecosystems.  We received one comment supporting our proposed reliance on
the IMPROVE network Pb-PM2.5 data.  We did not receive any other
comments on additional monitoring needs to support the secondary Pb
NAAQS.  Thus, we are not finalizing any additional requirements for Pb
monitoring specifically for the secondary Pb NAAQS.

E.  Other Monitoring Regulation Changes

We are finalizing two other proposed changes to the monitoring
requirements for Pb, and making one editorial revision for ease of
reference.  We are changing the reporting requirements to require the
reporting of average pressure and temperature for each Pb sample
collected.  We are also removing Pb from the list of criteria pollutants
where data from special purpose monitors can be excluded from
consideration for designations.  The proposed changes, comments
received, and final amendments are described in the following
paragraphs.

1.  Reporting of Average Pressure and Temperature

We proposed revisions to 40 CFR 58.16(a) to add a requirement that the
monitoring agency report the average pressure and temperature during the
time of sampling for both Pb-TSP monitoring and Pb-PM10 monitoring.  We
did not receive any comments on this proposed requirement.  As such, we
are finalizing this requirement as proposed.  Monitoring agencies may
use site specific meteorological measurements generated by on-site
equipment (meteorological instruments, or sampler generated), a
representative nearby monitoring station, or measurements from the
nearest airport reporting ambient pressure and temperature.

2.  Special Purpose Monitoring

We proposed to revise 40 CFR Section 58.20(e) by removing the specific
reference to Pb in the rule language.  We proposed to make this change
because the form of the proposed Pb NAAQS would allow a non-attainment
finding to be based on as little as 3-months of data which would have to
be considered during mandatory designations.  We did not receive any
comments on this proposed revision to the special purpose monitoring
requirements.  As such, we are finalizing the revision to 40 CFR Section
58.20(e) as proposed.

VI.	Implementation Considerations

This section of the final rule discusses the specific CAA requirements
related to implementation of the revised Pb NAAQS based on the structure
outlined in the CAA, existing rules, existing guidance, and in some
cases revised guidance.  

The CAA assigns important roles to EPA, states, and tribal governments
in implementing NAAQS.  States have the primary responsibility for
developing and implementing State Implementation Plans (SIPs) that
contain state measures necessary to achieve the air quality standards in
each area.  EPA provides assistance to states and tribes by providing
technical tools, assistance, and guidance, including information on the
potential control measures. 

A SIP is the compilation of regulations and control programs that a
state uses to carry out its responsibilities under the CAA, including
the attainment, maintenance, and enforcement of the NAAQS.  States use
the SIP development process to identify the emissions sources that
contribute to the nonattainment problem in a particular area, and to
select the emissions reduction measures most appropriate for the
particular area in question.  Under the CAA, SIPs must ensure that areas
reach attainment as expeditiously as practicable, but by no later than
the statutory attainment date that is set for the area.  

	The EPA’s analysis of the available Pb monitoring data suggests that
a large percentage of recent Pb ambient air concentrations in excess of
0.15 µg/m3 have occurred in locations with active industrial sources of
lead emissions.  Accordingly, we anticipate that many areas may be able
to attain the revised NAAQS by implementing air pollution control
measures on lead emitting industrial sources only.  These controls could
include measures such as particulate matter fabric filter control
devices and industrial fugitive dust control measures applied in plant
buildings and on plant grounds.  However, it may become necessary in
some areas to also implement controls on non-industrial, or former
industrial, type sources. Based on these considerations, EPA believes
that the regulations and guidance currently being used to implement the
pre-existing Pb NAAQS are still appropriate to implement the revised Pb
NAAQS with modifications in some cases.  

The regulations and guidance which address the implementation of the
pre-existing NAAQS for Pb are mainly provided in the following
documents: (1) “State Implementation Plans; General Preamble for the
Implementation of Title I of the Clean Air Act Amendments of 1990”, 57
FR 13549, April 16, 1992, (2) “State Implementation Plans for Lead
Nonattainment Areas; Addendum to the General Preamble for the
Implementation of Title I of the Clean Air Act Amendments of 1990”, 58
FR 67748, December 22, 1993, and (3) regulations listed at 40 CFR
51.117.  These documents address requirements such as designating areas,
setting nonattainment area boundaries, promulgating area
classifications, nonattainment area SIP requirements such as Reasonably
Available Control Measures (RACM), Reasonably Available Control
Technology (RACT), New Source Review (NSR), Prevention of Significant
Deterioration (PSD), and emissions inventory requirements.  The EPA
believes that the existing guidance and regulations are sufficient to
implement the revised Pb NAAQS at this time.  As discussed below, EPA is
finalizing some changes to the existing guidance and regulations, and
EPA will, as appropriate, review, and revise or update these policies,
guidance, and regulations to ensure effective implementation of the Pb
NAAQS.   

Several commenters submitted comments stating that the usual agency
practice for revising the NAAQS has been to first promulgate a rule
setting the health and welfare based standards, and then to promulgate a
rule that addresses the numerous implementation issues relating to the
NAAQS.  These commenters stated that the lead NAAQS proposal, however,
combines these two rulemakings into one compressed rule.  Commenters
stated that they theoretically believe that this two-in-one rule
approach could benefit states and localities by preventing the types of
delays that have been encountered with the implementation of other
pollutants.  The commenters, however, stated that they believe that the
lead NAAQS implementation provisions in the proposed rule are
insufficient to give state and local agencies adequate guidance to
implement the revised standard.  Commenters further stated that they
believe that EPA should particularly update lead control strategy and
emissions inventory guidance documents to account for the change to the
level of the standard. 

As stated in the proposed rule, EPA believes that the regulations and
guidance currently being used to implement the pre-existing Pb NAAQS are
generally still appropriate to address the issues required to begin
implementing the revised Pb NAAQS. As discussed in the proposal, EPA is
revising the emission inventory requirements of 40 CFR 51.117(e)(1).  In
some areas, as discussed below, EPA is providing additional guidance in
response to comments.  The EPA believes that these policies, guidance
and regulations should be used by states, local, and Tribal governments
as a basis for implementing the revised Pb NAAQS.  Also, as stated in
the proposed rule, EPA will as appropriate, further review and revise or
update these policies, guidance, and regulations in the future to ensure
that states, local, and Tribal governments have the appropriate
information necessary to fully implement the revised Pb NAAQS in a
timely manner.	

As discussed below, the EPA is generally finalizing the guidance
concerning the implementation of the revised Pb NAAQS consistent with
the proposed rule.  

A.	Designations for the Lead NAAQS

1.	Proposal

As discussed in the proposed rule, after EPA establishes or revises a
primary and/or secondary NAAQS, the CAA requires EPA and the states to
begin taking steps to ensure that the new or revised NAAQS are met.  The
first step is to identify areas of the country that do not meet the new
or revised NAAQS.  The CAA defines EPA’s authority to designate areas
that do not meet a new or revised NAAQS.  Section 107(d)(1) provides
that “By such date as the Administrator may reasonably require, but
not later than 1 year after promulgation of a new or revised NAAQS for
any pollutant under section 109, the Governor of each state shall
…..submit to the Administrator a list of all areas (or portions
thereof) in the state” that designates those areas as nonattainment,
attainment, or unclassifiable.  Section 107(d)(1)(B)(i) further
provides, “Upon promulgation or revision of a NAAQS, the Administrator
shall promulgate the designations of all areas (or portions thereof)
….as expeditiously as practicable, but in no case later than 2 years
from the date of promulgation.  Such period may be extended by up to one
year in the event the Administrator has insufficient information to
promulgate the designations.”  The term “promulgation” has been
interpreted by the courts to mean the signature and dissemination of a
rule.   By no later than 120 days prior to promulgating final
designations, EPA is required to notify states or Tribes of any intended
modifications to their boundaries as EPA may deem necessary.  States and
Tribes then have an opportunity to comment on EPA’s tentative
decision.  It should be noted that, whether or not a state or a Tribe
provides a recommendation, EPA must promulgate the designation that it
deems appropriate.

In the proposal, EPA indicated that Governors and tribal leaders would
be required to submit their initial designation recommendations to EPA
no later than September 2009, and the initial designation of areas for
the new Pb NAAQS would occur no later than September 2010, although that
date may be extended by up to one year under the CAA (or no later than
September 2011) if EPA has insufficient information to promulgate the
designations.  These dates were based on the court-ordered schedule in
effect at the time of proposal, which required a final rule to be signed
no later than September 15, 2008.  The court-ordered schedule was
subsequently amended to require a notice of final rulemaking to be
signed no later than October 15, 2008.  

In the proposed rule, EPA also discussed issues related to possible
schedules for designations, and EPA took comment on issues related to
the anticipated designation schedule.  The proposal identified two
“key considerations” in establishing a schedule for designations:
“(1) The advantages of promulgating all designations at the same time;
and (2) the availability of a monitoring network and sufficient
monitoring data to identify areas that may be violating the NAAQS” (73
FR 29267).  The EPA then stated its view that “there are important
advantages to promulgating designations for all areas at the same
time” and expressed its intention to do so.

The proposal also discussed EPA’s belief that the existing Pb
monitoring network is not adequate to evaluate attainment of the revised
Pb NAAQS at locations consistent with EPA’s proposed new monitoring
network siting criteria and data collection requirements.  These new
requirements would result in a more strategically targeted network that
would begin operation by January 1, 2010.   The proposal pointed out
that taking the additional year provided under section 107(d)(1)(B)(i)
of the CAA (which would allow up to 3 years to promulgate initial
designations following the promulgation of a new or revised NAAQS) would
allow the first year of data from the new monitoring network to be
available. The proposal also stated that, due to the updated monitoring
network design requirements, this additional data would be of
significant benefit for designating areas for the new NAAQS.  

Accordingly, the proposal identified an initial designation schedule
under which states (and Tribes) would be required to submit designation
recommendations to EPA no later than one year following promulgation of
the new NAAQS.  States would be able to consider ambient data collected
with the existing network FRM and FEM samplers through the end of
calendar year 2008 when formulating their recommendations.  The proposal
further indicated that if, as EPA anticipated, EPA needed an additional
year to make designations due to insufficient information, EPA would
have access to Pb air quality monitoring data from calendar year 2010,
which state monitoring officials have certified as being complete and
accurate, since the deadline for such certification is May 1, 2011. 
Under this schedule, EPA would be able to consider data from calendar
years 2008-2010 in formulating its proposed revisions, if any, to the
designations recommended by states and Tribes.  States and Tribes would
then have an opportunity to comment on EPA’s proposed modifications,
if any, prior to the promulgation of designations by Fall 2011. The EPA
solicited comment on whether EPA has the authority to determine in this
final rule that three years would be necessary to make designations. 
The EPA also solicited comment on making designations within two years
from promulgation of a revised NAAQS.

2.	Comments and Responses 

	Several commenters suggested that EPA should require that states with
current nonattainment or maintenance areas submit designation
recommendations for those counties or Metropolitan Statistical Areas
(MSAs) with nonattainment or maintenance areas within 120 days of
promulgation of the rule.

	Section 107(d)(1)(A) provides that States shall submit recommendations
for areas to be designated attainment, nonattainment, and unclassifiable
“[b]y such date as the Administrator may reasonably require, but not
later than 1 year after promulgation of a  new or revised  national
ambient  air quality standard for  any pollutant under section 109.”  
EPA’s consistent practice in revising NAAQS has been to allow states a
year to prepare their lists of designations, and the proposal likewise
indicated EPA’s intent to allow a year for states to prepare their
recommendations.  It is often true that when a standard is made more
stringent there will be existing nonattainment and maintenance areas
that may be expected to be nonattainment for the new standard as well. 
Furthermore, EPA notes that the most recent three years of available
monitoring data for East Helena , MT, one of the two current
nonattainment areas, showed no violations of the current standard,
although the monitors were shut down in December 2001 following the
shutdown of the large stationary source of lead emissions there.  The
EPA also notes that preparing designation recommendations is a complex
task, and the magnitude of the reduction in the Pb NAAQS, and the long
interval since the last revision to the standard is likely to add to the
difficulty for states.  

Thus, while EPA considers the increased stringency of the standard to be
relevant to the question of when states should submit designation
recommendations, EPA does not believe that under the current
circumstances it would be reasonable to require states to submit a list
of areas to be designated attainment, nonattainment, or unclassifiable
sooner than one year following promulgation year.

Therefore, pursuant to section 107(d)(1)(A), states shall, and Tribes
may, provide area designation recommendations to EPA no later than
October 15, 2009.  In some areas, EPA anticipates that state and Tribal
officials will be able to base their recommendations on existing
monitoring data, and can therefore identify an area as “attainment”
or “nonattainment.”  EPA also anticipates that there will be other
areas where state and Tribal officials will not have sufficient
information to make such a determination.  State and Tribal officials
are advised to identify such areas as “unclassifiable.”  For these
areas EPA may wait until sufficient ambient air quality data from the
newly deployed Pb monitoring network are available to take final action
on the state and Tribal recommendations.

	Several commenters stated that EPA should promulgate designations for
the

revised Pb NAAQS within the 2 year period provided in the CAA. 
Commenters further stated that they do not understand why EPA needs to
take an additional year beyond the two years provided under the CAA to
do the designations.  In addition, the commenters stated that they
believe EPA does not have the authority to take the additional year
(i.e., the 3rd year provided under section 107(d)(1)(B)(i) of the CAA)
to do designations for the Pb NAAQS because sufficient monitoring data
is available to do the designations within 2 years of promulgation of
the NAAQS. 

	Other commenters stated that they agree with EPA that, given that the
current monitoring network for the Pb NAAQS is insufficient to base
designations on for the new NAAQS, EPA should not promulgate
designations until there is sufficient data from the new monitoring
network. 

	Section 107(d)(1)(B)(i) provides that the Administrator shall
promulgate the designations of  all areas as expeditiously as
practicable,  but in no case later than  2 years from the date of
promulgation of  the  new  or  revised  national  ambient  air  quality
standard.  Such period may be extended by up to one year in the event
the   Administrator has insufficient information to promulgate the
designations.

	After considering the comments, and recognizing that in some locations
there may be monitoring data sufficient to determine whether or not the
area is attaining the standard, EPA now believes that the benefits of
identifying nonattainment areas as soon as possible, in some areas as
discussed shortly below, outweigh the potential administrative benefits
of designating all areas at the same time.

	At the same time, EPA continues to believe that the current monitoring
network is inadequate for making designations in many, if not most,
areas of the country, and agrees with those commenters who stated that
it would be preferable to wait until additional monitoring data was
available for those areas than to proceed to designate areas based only
on data from the current insufficient monitoring network.  The EPA notes
that any delay in designations beyond two years would be based on the
lack of monitoring data (and the expectation that additional monitoring
data would be available if designations were delayed) and would not be
based on staffing and other non-data resource issues.  

	Accordingly, EPA believes that the most appropriate approach to
designations for the Pb NAAQS is for EPA to complete final designations
as expeditiously as possible, and to recognize that “as expeditiously
as possible” may result in making nonattainment designations at
different times for different areas.  In some areas, EPA expects that it
will be possible to do designations within two years based on currently
available monitoring data.  In other areas, EPA expects that taking the
additional year will prove necessary in order to collect the necessary
monitoring data before making designations.

3.	Final

	After considering the comments and for the reasons discussed above, EPA
no longer plans to make all designations, and particularly all
nonattainment designations, at the same time.  The EPA intends to make
designations as expeditiously as possible in areas where monitoring data
is currently sufficient, or will be sufficient in the immediate future,
to accurately characterize the areas as either not attaining or
attaining the new Pb NAAQS.  In some cases this will be possible  as
expeditiously as practicable, but no later than two years following
promulgation of the final rule. In other cases this will not be possible
until additional data are collected from the newly deployed monitoring
network, and may take up to three years.

B.	Lead Nonattainment Area Boundaries 

1.	Proposal

The process for initially designating areas following the promulgation
of a new or revised NAAQS is prescribed in section 107(d)(1) of the CAA.
 This section of the CAA provides each state Governor an opportunity to
recommend initial designations of attainment, nonattainment, or
unclassifiable for each area in the state.  Section 107(d)(1) of the CAA
also directs the state to provide the appropriate boundaries to EPA for
each area of the state, and provides that EPA may make modifications to
the boundaries submitted by the state as it deems necessary. A lead
nonattainment area must consist of that area that does not meet (or
contributes to ambient air quality in a nearby area that does not meet)
the Pb NAAQS.  Thus, a key factor in setting boundaries for
nonattainment areas is determining the geographic extent of nearby
source areas contributing to the nonattainment problem.  For each
monitor or group of monitors that exceed a standard, nonattainment
boundaries must be set that include a sufficiently large enough area to
include both the area judged to be violating the standard as well as the
source areas that are determined to be contributing to these violations.

Historically, Pb NAAQS violations have been the result of lead emissions
from large stationary sources and mobile sources that burn lead-based
fuels.  In some locations, a limited number of area sources have also
been determined to have contributed to violations.  Since lead has been
successfully phased out of motor vehicle gasoline, these sources are no
longer a significant source of ambient lead concentrations. At the
revised standard level, EPA expects stationary sources to be the primary
contributor to violations of the NAAQS.  However, it is possible that
fugitive dust emissions from area sources containing deposited lead will
also contribute to violations of the revised Pb NAAQS.  The location and
dispersion characteristics of these sources of ambient lead
concentrations are important factors in determining nonattainment area
boundaries.  

In the proposed rule, EPA proposed to presumptively define the boundary
for designating a nonattainment area as the perimeter of the county
associated with the air quality monitor(s) which records a violation of
the standard.  This presumption was also EPA’s recommendation for
defining the nonattainment boundaries for the 1978 Pb NAAQS, and is
described in the 1992 General Preamble (57 FR 13549).  In the proposed
rule, EPA also requested comment on an option to presumptively define
the nonattainment boundary using the OMB-defined Metropolitan
Statistical Area (MSA) associated with the violating monitor(s).  This
presumption was used historically, by the CAA requirement, for the 1-hr
ozone and CO NAAQS nonattainment boundaries, and was also recommended by
EPA as the appropriate presumption for the 1997 8-hour ozone and PM2.5
NAAQS nonattainment boundaries.  In the proposed rule we stated that
under either option, the state and EPA may conduct additional
area-specific analyses that could lead EPA to depart from the
presumptive boundary. The factors relevant to such an analysis are
described below.

For the proposed Pb NAAQS, EPA recommended that nonattainment area
boundaries that deviate from presumptive county boundaries should be
supported by an assessment of several factors, which are discussed
below. The factors for determining nonattainment area boundaries for the
Pb NAAQS under this recommendation closely resemble the factors
identified in recent EPA guidance for the 1997 8-hour ozone NAAQS, the
1997 PM2.5 NAAQS, and the 2006 PM2.5 NAAQS nonattainment area
boundaries.  For this particular option of the proposal, EPA would
consider the following factors in assessing whether to exclude portions
of a county and whether to include additional nearby areas outside the
county as part of the designated nonattainment area:

(	Emissions in areas potentially included versus excluded from the
nonattainment area

(	Air quality in potentially included versus excluded areas

(	Population density and degree of urbanization including commercial
development in included versus excluded areas

(	Expected growth (including extent, pattern and rate of growth)

(	Meteorology (weather/transport patterns)

(	Geography/topography (mountain ranges or other air basin boundaries)

(	Jurisdictional boundaries (e.g., counties, air districts,
Reservations, etc.)

(	Level of control of emission sources

The proposal indicated that analyses of these factors may suggest
nonattainment area boundaries that are either larger or smaller than the
county boundary.  A demonstration supporting the designation of
boundaries that are less than the full county would be required to show
both that violation(s) are not occurring in the excluded portions of the
county and that the excluded portions are not source areas that
contribute to the observed violations.  Recommendations to designate a
nonattainment area larger than the county should also be based on an
analysis of these factors.  The proposal stated that EPA would consider
these factors as well in evaluating state and Tribal recommendations and
assessing whether any modifications are appropriate.  

Under previous Pb implementation guidance, EPA advised that Governors
could choose to recommend lead nonattainment boundaries by using any
one, or a combination of the following techniques, the results of which
EPA would consider when making a decision as to whether and how to
modify the Governors’ recommendations: (1) qualitative analysis, (2)
spatial interpolation of air quality monitoring data, or (3) air quality
simulation by dispersion modeling.  These techniques are more fully
described in “Procedures for Estimating Probability of Nonattainment
of a PM10 NAAQS Using Total Suspended Particulate or  PM10 Data,”
December 1986 (see 57 FR 13549).  In the proposed rule,  EPA solicited
comments on the use of these factors and modeling techniques, and other
approaches, for adjusting county boundaries in designating nonattainment
areas. 

2.	Comments and Responses

Several commenters submitted comments stating that the nonattainment
boundaries should be limited to the smallest political boundary that
possesses an ambient monitor-based design value above the standard,
unless subsequent analyses demonstrate that the boundaries should be
larger or smaller.  Commenters also stated that because lead does not
transport over long distances, monitoring data from upwind and downwind
sites illustrate that violations of the lead NAAQS are most commonly
isolated within a specific geographic area in close proximity to a major
source.

The EPA agrees with the commenter that lead emissions do not generally
transport over long distances (as compared, e.g., to fine particulate
matter).  In the proposed rule, EPA proposed to presumptively define the
boundary for designating a nonattainment area as the perimeter of the
county associated with the air quality monitor(s) which records a
violation of the standard.  In the proposed rule, EPA also stated that,
at the revised level of the standard, EPA expects stationary sources to
be the primary contributor to violations of the NAAQS, although we also
believe that nearby area sources may also contribute to concentrations
of lead emissions that may affect a violating monitor.  In light of the
possibility that a number of smaller sources may collectively contribute
to concentrations in excess of the NAAQS, EPA believes that adopting the
county boundary as the presumptive boundaries for lead nonattainment
areas is appropriate.  However, as stated in the proposed rule, a state,
Tribe, or EPA may conduct additional area-specific analyses that could
lead to the boundary for an area either being increased or decreased
from the presumptive county boundary.  In situations where a single
source, rather than multiple sources, is causing a NAAQS violation, the
EPA believes that a state may well be able to use area-specific analyses
to identify whether a nonattainment area that is smaller than the county
boundary is appropriate.

	Several commenters stated that EPA should use the MSA as the
presumptive boundary for designating areas for the Pb NAAQS in order for
a broader range of source emissions to be taken into consideration when
the state develops its SIP for the nonattainment area. 

As stated previously, at the revised level of the standard, EPA expects
stationary sources to be the primary contributor to violations of the Pb
NAAQS, although we also expect that in some areas a number of smaller
sources may collectively contribute to concentrations in excess of the
NAAQS.  MSAs are frequently composed of several  counties.  Recognizing
that lead emissions, particularly ultracoarse particles, deposit
relatively short distances from the proximity of their initial source,
EPA believes that adopting the county boundary surrounding a violating
monitor as the presumptive boundary for any given lead nonattainment
area is more appropriate than presuming the larger MSA boundary.
Furthermore, as stated in the proposed rule (and the previous response),
a state, Tribe, or EPA may conduct additional area-specific analyses
that could lead to the boundary for an area either being increased or
decreased from the presumptive boundary.  Thus, where it appears that
emissions from one or more sources are contributing to nonattainment
throughout an MSA, the site-specific analysis may result in the
boundaries of the nonattainment area overlapping with those of the MSA.

3.	Final

The EPA is finalizing the option to presumptively define the boundary
for designating a nonattainment area as the perimeter of the county
associated with the air quality monitor(s) which records a violation of
the standard as proposed.  This presumption was also EPA’s
recommendation for defining the nonattainment boundaries for the
pre-existing Pb NAAQS, and is described in the 1992 General Preamble (57
FR 13549).  As a part of the county boundary presumption for
nonattainment areas, the state and/or EPA may conduct additional
area-specific analyses that could lead EPA to depart from the
presumptive county boundary. The EPA is also finalizing the factors
relevant to such an analysis as described in the proposed rule because
we believe that they will allow for both the State as well as EPA in
some cases to define better the appropriate boundaries for an area.  The
state may, in addition to submitting recommendations for boundaries
based on the factor analysis, also choose to recommend lead
nonattainment boundaries using any one, or a combination of the
following techniques, the results of which EPA would consider when
making a decision as to whether and how to modify the Governors’
recommendations: (1) qualitative analysis, (2) spatial interpolation of
air quality monitoring data, or (3) air quality simulation by dispersion
modeling,  as described more fully in “Procedures for Estimating
Probability of Nonattainment of a  PM10 NAAQS Using Total Suspended
Particulate or  PM10 Data,” December 1986 (see 57 FR 13549).

C.	Classifications

1.	Proposal  

Section 172(a)(1)(A) of the CAA authorizes EPA to classify areas
designated as nonattainment for the purpose of applying an attainment
date pursuant to section 172(a)(2), or for other reasons.  In
determining the appropriate classification, EPA may consider such
factors as the severity of the nonattainment problem and the
availability and feasibility of pollution control measures (see section
172(a)(1)(A) of the CAA).  The EPA may classify lead nonattainment
areas, but is not required to do so.  

While section 172(a)(1)(A) provides a mechanism to classify
nonattainment areas, section 172(a)(2)(D) provides that the attainment
date extensions described in section 172(a)(2)(A) do not apply to
nonattainment areas having specific attainment dates that are addressed
under other provisions of the part D of the CAA.  Section 192(a), of
part D, specifically provides an attainment date for areas designated as
nonattainment for the Pb NAAQS.  Therefore, EPA has legal authority to
classify lead nonattainment areas, but the 5 year attainment date under
section 192(a) cannot be extended pursuant to section 172(a)(2)(D). 
Based on this limitation, EPA proposed not to establish classifications
within the 5 year interval for attaining any new or revised NAAQS.  This
approach is consistent with EPA’s previous classification decision for
Pb in the 1992 General Preamble (See 57 FR 13549, April 16, 1992).

2.	Comments and Responses: 

Several commenters stated that they disagreed with EPA’s proposal not
to classify lead nonattainment areas under CAA section 172(a)(1)(A). 
The commenters stated that existing nonattainment areas, meaning areas
that have not yet achieved the pre-existing Pb NAAQS, would benefit from
more rigorous SIP requirements associated with classifications.  The
commenters stated that such classifications are appropriate not only for
deadline extensions (not applicable in this case, as EPA notes), but
“for other purposes”.   The commenters state that such purposes
should include lower emissions thresholds for defining major stationary
sources, higher offset ratios, and a more ambitious definition of
reasonable further progress. 

EPA stated in the proposed rule, that while section 172(a)(1)(A)
provides a mechanism to classify nonattainment areas, section
172(a)(2)(D) provides that the attainment date extensions described in
section 172(a)(2)(A) do not apply to nonattainment areas having specific
attainment dates that are addressed under other provisions of the part D
of the CAA.  Based on this limitation, EPA proposed not to establish
classifications within the 5 year interval for attaining any new or
revised NAAQS.  This approach is consistent with EPA’s previous
classification decision for Pb in the 1992 General Preamble (See 57 FR
13549, April 16, 1992) notes that subpart 2 of part D of the CAA
specifies mandatory control measures required for areas with different
classifications for the ozone standard, including such items as higher
offset ratios and specific percentage requirements for reasonable
further progress.  Areas with higher classifications are subject to more
stringent controls, but also receive additional time to attain the
standard.  Subpart 5 of part D contains no such provisions, but instead
requires submittal of a SIP within 18 months of designation of an area
as nonattainment, and requires attainment for all areas as expeditiously
as practicable, but no later than 5 years following designation.  
Although EPA does have authority to establish classifications for Pb,
EPA continues to believe, taking into consideration these differing
statutory schemes (and particularly the requirement to attain as
expeditiously as practicable, but no later than 5 years from
designation) that it is not appropriate or necessary to establish
classifications for the revised Pb NAAQS.

3.	Final

The EPA is finalizing the guidance for classifications as provided in
the proposed rule.  Therefore, there will be no classifications under
the revised Pb NAAQS.

D.	Section 110(a)(2) Lead NAAQS Infrastructure Requirements 

1.	Proposal

	Under section 110(a)(1) and (2) of the CAA, all states are required to
submit plans to provide for the implementation, maintenance, and
enforcement of any new or revised NAAQS.  Section 110(a)(1) and (2)
require states to address basic program elements, including requirements
for emissions inventories, monitoring, and modeling, among other things.
 States are required to submit SIPs to EPA which demonstrates that these
basic program elements have been addressed within 3 years of the
promulgation of any new or revised NAAQS.  Subsections (A) through (M)
of section 110(a)(2) listed below, set forth the elements that a
state’s program must contain in the SIP.  The list of section
110(a)(2) NAAQS implementation requirements are the following: 

Ambient air quality monitoring/data system:  Section 110(a)(2)(B)
requires SIPs to provide for setting up and operating ambient air
quality monitors, collecting and analyzing data and making these data
available to EPA upon request.

Program for enforcement of control measures:  Section 110(a)(2)(C)
requires SIPs to include a program providing for enforcement of measures
and regulation and permitting of new/modified sources.

Interstate transport:  Section 110(a)(2)(D) requires SIPs to include
provisions prohibiting any source or other type of emissions activity in
the state from contributing significantly to nonattainment in another
state or from interfering with measures required to prevent significant
deterioration of air quality or to protect visibility. 

Adequate resources:  Section 110(a)(2)(E) requires states to provide
assurances of adequate funding, personnel and legal authority for
implementation of their SIPs.

Stationary source monitoring system:  Section 110(a)(2)(F) requires
states to establish a system to monitor emissions from stationary
sources and to submit periodic emissions reports to EPA.

Emergency power:  Section 110(a)(2)(G) requires states to include
contingency plans, and adequate authority to implement them, for
emergency episodes in their SIPs.  

Provisions for SIP revision due to NAAQS changes or findings of
inadequacies:  Section 110(a)(2)(H) requires states to provide for
revisions of their SIPs in response to changes in the NAAQS,
availability of improved methods for attaining the NAAQS, or in response
to an EPA finding that the SIP is inadequate.

Section 121 consultation with local and Federal government officials: 
Section 110(a)(2)(J) requires states to meet applicable local and
Federal government consultation requirements of section 121.

Section 127 public notification of NAAQS exceedances:  Section
110(a)(2)(J) requires states to meet applicable requirements of section
127 relating to public notification of violating NAAQS.

PSD and visibility protection:  Section 110(a)(2)(J) also requires
states to meet applicable requirements of title I part C related to
prevention of significant deterioration and visibility protection.

Air quality modeling/data:  Section 110(a)(2)(K) requires that SIPs
provide for performing air quality modeling for predicting effects on
air quality of emissions of any NAAQS pollutant and submission of data
to EPA upon request.

Permitting fees:  Section 110(a)(2)(L) requires the SIP to include
requirements for each major stationary source to pay permitting fees to
cover the cost of reviewing, approving, implementing and enforcing a
permit.

Consultation/participation by affected local government:  Section
110(a)(2)(M) requires states to provide for consultation and
participation by local political subdivisions affected by the SIP.

2.	Final

	The EPA is finalizing the guidance related to the submittal of SIPs to
address the infrastructure requirements of section 110(a)(1) and (2) as
stated in the proposed rule.

E. 	Attainment Dates

1.	Proposal

	As discussed in the proposal, the maximum deadline date by which an
area is required to attain the Pb NAAQS is determined by the effective
date of the nonattainment designation for the area.  For areas
designated nonattainment for the revised Pb NAAQS, SIPs must provide for
attainment of the NAAQS as expeditiously as practicable, but no later
than 5 years from the date of the nonattainment designation for the area
(see section 192(a) of the CAA).  In the proposed rule, EPA stated it
would determine whether an area had demonstrated attainment of the Pb
NAAQS by evaluating air quality monitoring data from the one, two, or
three previous years as available.

2. 	Comments and Responses

A commenter stated that the attainment deadline for the current
nonattainment and maintenance areas should be three years.

Under the CAA, states are required to attain as expeditiously as
practicable (but in no case later than five years).  If it is
practicable for a nonattainment area to attain the standard within three
years, then the SIP must provide for attainment within three years.  If,
however, attainment within three years is not practicable, then EPA has
no authority to require attainment by that deadline.

2.	Final

	The EPA is generally finalizing the guidance related to attainment
dates as provided in the proposed rule.  States with nonattainment areas
will be required to attain the standard as expeditiously as practicable,
but in no event later than five years from the effective date of the
nonattainment designation.  EPA wishes to clarify that it will be
considering air quality monitoring data from the three previous years,
as available, in determining whether areas have demonstrated attainment
(i.e., EPA would only consider data for less than the three previous
years in situations where the data for all three years was unavailable).

F.  	Attainment Planning Requirements 

	Any state containing an area designated as nonattainment with respect
to the Pb NAAQS must develop for submission, a SIP meeting the
requirements of part D, Title I, of the CAA, providing for attainment by
the applicable deadline (see sections 191(a) and 192(a) of the CAA).  As
indicated in section 191(a) all components of the lead part D SIP must
be submitted within 18 months of the effective date of an area’s
designation as nonattainment.  Additional specific plan requirements for
lead nonattainment areas are outlined in 40 CFR 51.117. 

The general part D nonattainment plan requirements are set forth in
section 172 of the CAA. Section 172(c) specifies that SIPs submitted to
meet the part D requirements must, among other things, include
Reasonably Available Control Measures (RACM) (which includes Reasonably
Available Control Technology (RACT)), provide for Reasonable Further
Progress (RFP), include an emissions inventory, require permits for the
construction and operation of major new or modified stationary sources
(see also CAA section 173), contain contingency measures, and meet the
applicable provisions of section 110(a)(2) of the CAA related to the
general implementation of a new or revised NAAQS.  It is important to
note that lead nonattainment SIPs must meet all of the requirements
related to part D of the CAA, including those specified in section
172(c), even if EPA does not provide separate specific guidance for each
provision. 

1.	RACM/RACT for Lead Nonattainment Areas

	a.	Proposal

Lead nonattainment area SIPs must contain RACM (including RACT) that
address sources of ambient lead concentrations.  In general, EPA
believes that lead NAAQS violation issues will usually be attributed to
emissions from stationary sources. In EPA’s 2002 National Emissions
Inventory (NEI), there were 12 stationary sources in the country with
lead emissions over 5 tons per year, and 124 sources over 1 ton of lead
emissions per year. 

Some emissions that contribute to violations of the Pb NAAQS may also be
attributed to smaller area sources.  At primary lead smelters, the
process of reducing concentrated ore to lead involves a series of steps,
some of which are completed outside of buildings, or inside of buildings
that are not totally enclosed.  Over a period of time, emissions from
these sources have been deposited in neighboring communities (e.g., on
roadways, parking lots, yards, and off-plant property).  This
historically deposited lead, when disturbed, may be re-entrained into
the ambient air and may contribute to violations of the Pb NAAQS in
affected areas.   

The first step in addressing RACM for lead is identifying potential
control measures for sources of lead in the nonattainment area.  A
suggested starting point for specifying RACM in lead nonattainment area
SIPs is outlined in appendix 1 of the guidance entitled “State
Implementation Plans for Lead Nonattainment Areas; Addendum to the
General Preamble for the Implementation of Title I of the Clean Air Act
Amendments of 1990”, 58 FR 67752, December 22, 1993.  If a state is
aware of facts, or receives substantive public comments, that
demonstrate through appropriate documentation, that additional control
measures may be reasonably available in a specific area, the measures
should be added to the list of available measures for consideration in
that particular area.  

While EPA does not presume that these control measures are reasonably
available in all areas, a reasoned justification for rejection of any
available control measure should be prepared.  If it can be shown that
measures, considered both individually as well as in a group, are
unreasonable because emissions from the affected sources are
insignificant, then the measures may be excluded from further
consideration as they would not be representative of RACM for the
affected area. The resulting control measures should then be evaluated
for reasonableness, considering their technological feasibility and the
cost of control in the area for which the SIP applies.  In the case of
public sector sources and control measures, this evaluation should
consider the impact and reasonableness of the measures on the municipal,
or other governmental entity that must assume the responsibility for
their implementation.  It is important to note that a state should
consider the feasibility of implementing measures in part when full
implementation would be infeasible.  A reasoned justification for
partial or full rejection of any available control measure, including
those considered or presented during the state’s public hearing
process, should be prepared.  The justification should contain a
detailed explanation, with appropriate documentation, as to why each
rejected control measure is deemed infeasible or otherwise unreasonable
for implementation. 

	Economic feasibility considers the cost of reducing emissions and the
difference between the cost of the emissions reduction approach at the
particular source in question and the costs of emissions reduction
approaches that have been implemented at other similar sources.  Absent
other indications, EPA as a general matter expects that it is reasonable
for similar sources to bear similar costs of emissions reduction. 
Economic feasibility for RACT purposes is largely determined by evidence
that other sources in a particular source category have in fact applied
the control technology or process change in question.  The EPA also
encourages the development of innovative measures not previously
employed which may also be technically and economically feasible.

	The capital costs, annualized costs, and cost effectiveness of an
emissions reduction technology should be considered in determining
whether a potential control measure is reasonable for an area or state. 
One available reference for calculating costs is the EPA Air Pollution
Control Cost Manual, which describes the procedures EPA uses for
determining these costs for stationary sources. The above costs should
be determined for all technologically feasible emission reduction
options.  States may give substantial weight to cost effectiveness in
evaluating the economic feasibility of an emission reduction technology.
 The cost effectiveness of a technology is its annualized cost ($/year)
divided by the emissions reduced (i.e., tons/year) which yields a cost
per amount of emission reduction ($/ton).  Cost effectiveness provides a
value for each emission reduction option that is comparable with other
options and other facilities.  With respect to a given pollutant, a
measure is likely to be reasonable if it has a cost per ton similar to
other measures previously employed for that pollutant.  In addition, a
measure is likely to be reasonable from a cost effectiveness standpoint
if it has a cost per ton similar to that of other measures needed to
achieve expeditious attainment in the area within the CAA’s time
frames.   

The fact that a measure has been adopted or is in the process of being
adopted by other states is also an indicator (though not a definitive
one) that the measure may be technically and economically feasible for
another state.  We anticipate that states may decide upon RACT and RACM
controls that differ from state to state, based on the state’s
determination of the most effective strategies given the relevant
mixture of sources and potential controls in the relevant nonattainment
areas, and differences in difficulty of attaining expeditiously. 
Nevertheless, states should consider and address RACT and RACM measures
developed for other areas, as part of a well reasoned RACT and RACM
analysis.  The EPA’s own evaluation of SIPs for compliance with the
RACT and RACM requirements will include comparison of measures
considered or adopted by other states.

	In considering what level of control is reasonable, EPA is not adopting
a specific dollar per ton cost threshold for RACT. Areas with more
serious air quality problems typically will need to obtain greater
levels of emissions reductions from local sources than areas with less
serious problems, and it would be expected that their residents could
realize greater public health benefits from attaining the standard as
expeditiously as practicable.  For these reasons, we believe that it
will be reasonable and appropriate for areas with more serious air
quality problems and higher design values to impose emission reduction
requirements with generally higher costs per ton of reduced emissions
than the cost of emissions reductions in areas with lower design values.
 In addition, where essential reductions are more difficult to achieve
(e.g., because many sources are already controlled), the cost per ton of
control may necessarily be higher.  

The EPA believes that in determining appropriate emission control
levels, the state should consider the collective public health benefits
that can be realized in the area due to projected improvements in air
quality.  Because EPA believes that RACT requirements will be met where
the state demonstrates timely attainment, and areas with more severe air
quality problems typically will need to adopt more stringent controls,
RACT level controls in such areas will require controls at higher cost
effectiveness levels ($/ton) than areas with less severe air quality
problems.

In identifying the range of costs per ton that are reasonable,
information on benefits per ton of emission reduction can be useful as
one factor to consider. It should be noted that such benefits estimates
are subject to significant uncertainty and that benefits per ton vary in
different areas.  Nonetheless this information could be used in a way
that recognizes these uncertainties.  If a per ton cost of implementing
a measure is significantly less than the anticipated benefits per ton,
this would be an indicator that the cost per ton is reasonable. If a
source contends that a source-specific RACT level should be established
because it cannot afford the technology that appears to be RACT for
other sources in its source category, then the source should support its
claim by providing detailed and verified information regarding the
impact of imposing RACT on:

fixed and variable production costs ($/unit),

product supply and demand elasticity,

product prices (cost absorption vs. cost pass-through),

expected costs incurred by competitors,

company profits, and

employment costs.

The technical guidance entitled “Fugitive Dust Background Document and
Technical Information Document for Best Available Control Measures”
(EPA-450/2-92-004, September 1992) provides an example for states on how
to analyze control costs for a given area. 

Once the process of determining RACM for an area is completed, the
individual measures should then be converted into a legally enforceable
vehicle (e.g., a regulation or permit program) (see section 172(c)(6)
and section 110(a)(2)(A) of the CAA).  The regulations or other measures
submitted should meet EPA’s criteria regarding the enforceability of
SIPs and SIP revisions. These criteria were stated in a September 23,
1987 memorandum (with attachments) from J. Craig Potter, Assistant
Administrator for Air and Radiation; Thomas L. Adams, Jr. Assistant
Administrator for Enforcement and Compliance Monitoring; and S. Blake,
General Counsel, Office of the General Counsel; entitled “Review of
State Implementation Plans and Revisions of Enforceability and Legal
Sufficiency.” As stated in this memorandum, SIPs and SIP revisions
that fail to satisfy the enforceability criteria should not be forwarded
for approval.  If they are submitted, they will be disapproved if, in
EPA’s judgment, they fail to satisfy applicable statutory and
regulatory requirements. 

The EPA’s historic definition of RACT is the lowest emissions
limitation that a particular source is capable of meeting by the
application of control technology that is reasonably available
considering technological and economic feasibility.  RACT applies to the
“existing sources” of lead in an area including stack emissions, 
industrial process fugitive emissions, and industrial fugitive dust
emissions (e.g., on-site haul roads, unpaved staging areas at the
facility, etc) (see section 172(c)(1)).  The EPA’s previous guidance
for implementing the pre-existing Pb NAAQS recommends that stationary
sources which emit a total of 5 tpy of lead or lead compounds, measured
as elemental lead, be the minimum starting point for RACT analysis (see
58 FR 67750, December 22, 1993).  Further, EPA’s existing guidance
recommends that available control technology be applied to those
existing sources in the nonattainment area that are reasonable to
control in light of the attainment needs of the area and the feasibility
of such controls.  Thus, under existing guidance, a state’s control
technology analysis may need to include sources which actually emit less
than 5 tpy of  lead or lead compounds in the area, or other sources in
the area that are reasonable to control, in light of the attainment
needs and feasibility of control for the area.

 significantly lower than the current level of 1.5 μg/m3, EPA requested
comment on the appropriate threshold for the minimum starting point for
future Pb RACT analyses for stationary lead sources in nonattainment
areas.  In the proposed rule, EPA requested comment on the emissions
level associated with the minimum network source monitoring
requirements. These source levels range from 200 kg/yr to 600 kg/yr. 
The EPA also stated that one possible approach for RACT is to recommend
that RACT analyses for Pb sources be consistent with sources that are
required to monitor such that all stationary sources above 200 kg/yr to
600 kg/yr should undergo a RACT review.  EPA also requested comment on
source monitoring for stationary sources that emit lead emissions in
amounts that have potential to cause ambient levels at least one-half
the selected NAAQS level.  This suggests another potential
recommendation for the starting point for the RACT analysis.  The EPA
sought comment on these ideas as well as any information which
commenters could provide that would help inform EPA’s recommendation
on an appropriate emissions threshold for initiating RACT analyses. 

b.	Comments and Responses 

μg/m3 and the existing threshold for RACT analysis is 5 tpy.  Since the
standard is being reduced by a factor of ten, from 1.5  μg/m3 to 0.15 
μg/m3, it is appropriate to also reduce the threshold for RACT analysis
by a factor of 10, from 5 tpy to 0.5 tpy.  Furthermore, the monitor
siting criteria include a requirement for monitoring agencies to conduct
monitoring taking into account sources that are expected to exceed the
NAAQS, and require monitoring for sources which emit Pb at a rate of one
ton per year.  Although EPA expects that sources emitting less than one
tpy may also contribute to violations of the revised Pb NAAQS, EPA
believes that the one tpy requirement in the monitor siting criteria
provides a benchmark that is more likely to clearly identify sources
that would contribute to exceedances of the NAAQS.  Accordingly, using
50% of that figure (0.5 tpy) as the threshold for RACT analysis is
generally consistent with EPA’s consideration in the proposal of
setting the RACT threshold to include those stationary sources that emit
lead emissions in amounts that have the potential to cause ambient
levels at least one-half the selected NAAQS.  

EPA believes that setting the RACT threshold higher (e.g., at 1 tpy)
would not be appropriate because it is likely that in a nonattainment
area sources emitting less than one tpy are contributing to the
nonattainment of the NAAQS.  EPA also does not believe a lower threshold
is warranted as a general matter, but EPA agrees with commenters that
the state’s control technology analysis should also include, as
appropriate, sources which actually emit less than the threshold level
of 0.5 tpy of lead or lead compounds in the area, or other sources in
the area that are reasonable to control, in light of the attainment
needs and feasibility of controls for the affected area. 

Several commenters stated that in the proposed rule EPA suggests that
the 1993 guidance document, which lists control measures as a starting
point for state’s consideration, puts the burden on the public to
demonstrate through appropriate documentation that additional control
measures may be reasonably available in a particular circumstance for an
area. The commenters further stated that in light of an anticipated
substantial reduction in the Pb NAAQS, as well as the failure of the
remaining two existing nonattainment areas to achieve attainment of the
pre-existing (1978) NAAQS under the 1993 guidance, that both EPA and the
states should bear the principal responsibility for developing an
updated roster of successful control measures.

As stated in the proposed rule, EPA believes that the regulations,
policies, and guidance currently in place for the implementation of the
pre-existing Pb NAAQS are still appropriate to address the issues
required to implement the revised Pb NAAQS.  The EPA believes that these
guidance, policies, and regulations should be used by states, local, and
Tribal governments as a starting point to begin implementation of the
revised Pb NAAQS.  The EPA expects that as states gain additional
experience with implementing the revised NAAQS, additional information
on successful control measures will become available to states, EPA, and
the public.  The EPA will, as appropriate, review, and revise or update
policies, guidance, and regulations to provide for effective
implementation of the Pb NAAQS. 

c.	Final 

The EPA is finalizing the guidance related to RACM (including RACT) for
lead nonattainment areas consistent with the proposed rule.  Based upon
the above considerations regarding the scale of the reduction in the
standard, the final monitor siting criteria, and the public comments
received related to the starting point for a RACT analysis, EPA is
recommending a threshold for RACT analysis such that at least all
stationary sources emitting 0.5 tpy or more should undergo a RACT
review.

2.  	Demonstration of Attainment for Lead Nonattainment Areas

a.	Proposal

The SIPs for lead nonattainment areas should provide for the
implementation of control measures for point and area sources of lead
emissions which demonstrate attainment of the Pb NAAQS as expeditiously
as practicable, but no later than the applicable statutory attainment
date for the area (see also 40 CFR 51.117(a) for additional control
strategy requirements).  Therefore, if a state adopts less than all
available measures in an area but demonstrates, adequately, that
reasonable further progress (RFP), and attainment of the Pb NAAQS are
assured, and the application of all such available measures would not
result in attainment any faster, then a plan which requires
implementation of less than all technologically and economically
available measures may be approved (see 44 FR 20375 (April 4, 1979) and
56 FR 5460 (February 11, 1991)).  The EPA believes that it would be
unreasonable to require that a plan which demonstrates attainment
include all technologically and economically available control measures
even though such measures would not expedite attainment.  Thus, for some
sources in areas which demonstrate attainment, it is possible that some
available control measures may not be “reasonably” available because
their implementation would not expedite attainment for the affected
area. 

b.	Final

The EPA is finalizing the guidance related to demonstration of
attainment for lead nonattainment areas as stated in the proposed rule. 
Further discussion of modeling for attainment and other topics is
presented below.

3.  	Reasonable Further Progress (RFP)

a.	Proposal

	Part D SIPs must provide for RFP (see section 172(c)(2) of the CAA). 
Section 171 of the CAA defines RFP as “such annual incremental
reductions in emissions of the relevant air pollution as are required by
part D, or may reasonably be required by the Administrator for the
purpose of ensuring attainment of the applicable NAAQS by the applicable
attainment date.”  Historically, for some pollutants, RFP has been met
by showing annual incremental emission reductions generally sufficient
to maintain linear progress toward attainment by the applicable
attainment date. The EPA believes that RFP for lead nonattainment areas
should be met by “adherence to an ambitious compliance schedule”
which is expected to periodically yield significant emission reductions,
and as appropriate, linear progress.  The EPA recommends that SIPs for
lead nonattainment areas provide a detailed schedule for compliance of
RACM (including RACT) in the affected areas and accurately indicate the
corresponding annual emission reductions to be achieved.  In reviewing
the SIP, EPA believes that it is appropriate to expect early
implementation of less technology-intensive control measures (e.g.,
controlling fugitive dust emissions at the stationary source, as well as
required controls on area sources) while phasing in the more
technology-intensive control measures, such as those involving the
installation of new hardware.  Finally, failure to implement the SIP
provisions required to meet annual incremental reductions in emissions
(i.e., RFP) in a particular area could result in the application of
sanctions as described in section 179(b) of the CAA (pursuant to a
finding under section 179(a)(4)), and the implementation of contingency
measures required by section 172(c)(9) of the CAA. 

b.	Comments and Responses

Several commenters stated that EPA’s proposal related to RFP would
allow states to avoid the need to demonstrate linear progress towards
attainment, departing from the typical method used, and statutorily
required in some cases, for other criteria pollutants.  These commenters
further state that the recognition that some nonattainment urban areas
have numerous sources contributing to excessive ambient levels of lead
which undermines the reasoning employed to justify a non-linear approach
in the context of single source nonattainment areas.  If areas with
large sources install key controls early on in the attainment process,
and thus achieve attainment ahead of schedule, that would advance the
goals and requirements of the CAA.

Historically, for some pollutants, RFP has been met by showing annual
incremental emission reductions generally sufficient to maintain linear
progress toward attainment by the applicable attainment date. As EPA has
previously noted, we expect that some nonattainment designations will be
attributable to a single stationary source, and others may be
attributable to a number of smaller sources.  Where a single source is
the cause of nonattainment, EPA would not expect linear progress towards
attainment.  Rather, there may be relatively less progress while the
source adopts non-technological control measures and begins to install
necessary technological controls, and then significant progress towards
attainment in a short period of time once all the controls are
operational.  EPA expects that, since states are required to attain the
standard as expeditiously as practicable, the SIP will require large
sources to install “key controls” as expeditiously as practicable. 
At the same time, where a number of sources are contributing to
nonattainment, it is more reasonable to expect that controls (both
technological and non-technological) may be adopted at different times,
making linear progress a more reasonable expectation.  To accommodate
both of these possible situations, EPA concludes it is appropriate that
RFP for lead nonattainment areas should be met by the strict adherence
to an ambitious compliance schedule which is expected to periodically
yield significant emission reductions, and, to the extent appropriate,
linear progress.  

c.	Final

The EPA is finalizing the guidance related to reasonable further
progress (RFP) consistent with the proposed rule.  The EPA believes that
RFP for lead nonattainment areas should be met by the strict adherence
to an ambitious compliance schedule which is expected to periodically
yield significant emission reductions, and to the extent appropriate,
linear progress.  The EPA recommends that SIPs for lead nonattainment
areas provide a detailed schedule for compliance of RACM (including
RACT) and accurately indicate the corresponding annual emission
reductions to be achieved.  In reviewing the SIP, EPA believes that it
is appropriate to expect early implementation of less
technology-intensive control measures (e.g., work practices to control
fugitive dust emissions at the stationary sources) while phasing in the
more technology-intensive control measures, such as those involving the
installation of new hardware.  The EPA believes that the expeditious
implementation of RACM/RACT at affected sources within the nonattainment
area is an appropriate approach to assure attainment of the Pb NAAQS in
an expeditious manner.

4.   	Contingency Measures 

a.	Proposal

Section 172(c)(9) of the CAA defines contingency measures as measures in
a SIP that are to be implemented if an area fails to achieve and
maintain RFP, or fails to attain the NAAQS by the applicable attainment
date.  Contingency measures must be designed to become effective without
further action by the state or the Administrator, upon determination by
EPA that the area has failed to achieve, or maintain reasonable further
progress (RFP), or attain the Pb NAAQS by the applicable statutory
attainment date.  Contingency measures should consist of available
control measures that are not already included in the primary control
strategy for the affected area.

Contingency measures are important for lead nonattainment areas, which
may violate the NAAQS generally due to emissions from stationary
sources, for several reasons.  First, process and fugitive emissions
from these stationary sources, and the possible re-entrainment of
historically deposited emissions, have historically been difficult to
quantify.  Therefore, the analytical tools for determining the
relationship between reductions in emissions, and resulting air quality
improvements, can be subject to some uncertainties.  Second, emission
estimates and attainment analysis can be influenced by overly-optimistic
assumptions about fugitive emission control efficiency.

Examples of contingency measures for controlling area source fugitive
emissions may include measures such as stabilizing additional storage
piles.  Examples of contingency measures for process-related fugitive
emissions include increasing the enclosure of buildings, increasing air
flow in hoods, modifying operation and maintenance procedures, etc.
Examples of contingency measures for stack sources include reducing
hours of operation, changing the feed material to lower lead content,
and reducing the occurrence of malfunctions by modifying operation and
maintenance procedures, etc.

	Section 172(c)(9) provides that contingency measures should be included
in the state SIP for a lead nonattainment area and shall “take effect
without further action by the state or the Administrator.” The EPA
interprets this requirement to mean that no further rulemaking actions
by the state, or EPA, would be needed to implement the contingency
measures (see generally 57 FR 12512 and 13543-13544).  The EPA
recognizes that certain actions, such as the notification of sources,
modification of permits, etc., may be needed before a measure could be
implemented.  However, states must show that their contingency measures
can be implemented with only minimal further action on their part and
with no additional rulemaking actions such as public hearings or
legislative review.  After EPA determines that a lead nonattainment area
has failed to maintain RFP or timely attain the Pb NAAQS, EPA generally
expects all actions needed to affect full implementation of the measures
to occur within 60 days after EPA notifies the state of such failure. 
The state should ensure that the measures are fully implemented as
expeditiously as practicable after the requirement takes effect. 

b.	Comments and Responses 

Several commenters stated that EPA noted in the proposed rulemaking that
“contingency measures are important for lead nonattainment areas”
and that the CAA requires that contingency measures must “take effect
without further action” by the state or the Administrator.” However,
the commenters stated that EPA then interprets the “take effect
without further action” requirement too broadly, indicating that it is
satisfied if the contingency measure can take effect without further
rulemaking.  The EPA would allow contingency measures that require a
state to undertake a permit modification before the contingency measures
would go into effect. 

As stated in the proposed rule, section 172(c)(9) of the CAA defines
contingency measures as measures in a SIP that are to be implemented if
an area fails to achieve and maintain RFP, or fails to attain the NAAQS
by the applicable attainment date.  Contingency measures must be
designed to become effective without further action by the state or the
Administrator, upon determination by EPA that the area has failed to
achieve, or maintain reasonable further progress, or attain the Pb NAAQS
by the applicable statutory attainment date.  As stated in the proposed
rule, the EPA believes that this requirement means that no further
rulemaking actions by the state, or EPA, would be needed to implement
the contingency measures (see generally 57 FR 12512 and 13543-13544). 
The EPA recognizes that in some circumstances minimal actions, such as
the notification of sources, modification of permits, etc., may be
needed before a measure could be implemented.  However, as also stated
in the proposed rule, states must show that their contingency measures
can be implemented with only minimal further action on their part and
that no additional rulemaking actions will be required, such as public
hearings or legislative review, which will delay the expeditious
implementation of the contingency measures in the affected area.  To the
extent that modifications in title V operating permits would be required
to implement contingency measures, the SIP should provide that those
permits will be issued or modified prior to the time such contingency
measures may be needed to include alternative operating scenarios
providing for implementation of the contingency measures if necessary. 
See 40 C.F.R. 70.6(a)(9).  The EPA generally expects that all actions,
including those actions related to modification of permits, that are
needed to affect full implementation of the contingency measures, must
occur within 60 days following EPA’s notification to the state of such
failure.

c.	Final

	The EPA is finalizing the guidance related to contingency measures for
lead nonattainment areas as stated in the proposed rule.  The key
requirements associated with contingency measures are: (1)  Contingency
measures must be fully adopted rules or control measures that are ready
to be implemented as expeditiously as practicable upon a determination
by EPA that the area has failed to achieve, or maintain reasonable
further progress, or attain the Pb NAAQS by the applicable statutory
attainment date; (2)  The SIP should contain trigger mechanisms for the
contingency measures and specify a schedule for implementation; and (3)
The SIP must indicate that the measures will be implemented without
further action (or only minimal action) by the state or by the
Administrator.   The contingency measures should also consist of control
measures for the area that are not already included in the control
strategy for the attainment demonstration of the SIP.  The EPA believes
that the measures should provide for emission reductions that are at
least equivalent to one year’s worth of reductions needed for the area
to meet the requirements of RFP, based on linear progress towards
achieving the overall level of reductions needed to demonstrate
attainment.

5. 	Nonattainment New Source Review (NSR) and Prevention of Significant
Deterioration (PSD) Requirements

a.  Proposal

The PSD and nonattainment NSR programs contained in parts C and D of
Title I of the CAA govern preconstruction review and permitting programs
for any new or modified major stationary sources of air pollutants
regulated under the CAA as well as any precursors to the formation of
that pollutant when identified for regulation by the Administrator.  The
EPA rules addressing these regulations can be found at 40 CFR 51.165,
51.166, 52.21, 52.24, and part 51, appendix S.

States containing areas designated as nonattainment for the Pb NAAQS
must submit SIPs that address the requirements of nonattainment NSR. 
Specifically, section 172(c)(5) of the CAA requires that states which
have areas designated as nonattainment for the Pb NAAQS must submit, as
a part of the nonattainment area SIP, provisions requiring permits for
the construction and operation of new or modified stationary sources
anywhere in the nonattainment area, in accordance with the permit
requirements pursuant to section 173 of the CAA.  Likewise, areas
designated attainment must submit infrastructure SIPs that address the
requirements of PSD pursuant to section 110(a)(2)(C). 

Stationary sources that emit lead are currently subject to regulation
under existing requirements for the preconstruction review and approval
of new and modified stationary sources.  The existing requirements,
referred to collectively as the New Source Review (NSR) program, require
all major and certain minor stationary sources of any air pollutant for
which there is a NAAQS to undergo review and approval prior to the
commencement of construction.  The NSR program is composed of three
different permit programs:

Prevention of Significant Deterioration (PSD)

Nonattainment NSR (NA NSR)

Minor NSR.

The PSD program and nonattainment NSR programs, contained in parts C and
D, respectively, of Title I of the CAA, are often referred to as the
major NSR program because these programs regulate only major sources. 

	The PSD program applies when a major source, that is located in an area
that is designated as attainment or unclassifiable for any criteria
pollutant, is constructed, or undergoes a major modification.  The
nonattainment NSR program applies when a major source of a criteria
pollutant that is located in an area that is designated as nonattainment
for that pollutant is constructed or undergoes a major modification. 
The minor NSR program addresses both major and minor sources that
undergoes construction or modification activities that do not qualify as
major, and it applies regardless of the designation of the area in which
a source is located.

	The national regulations that apply to each of these programs are
located in the CFR as shown below:

	Applications

PSD	40 CFR 52.21, 40 CFR 51.166, 

40 CFR 51.165(b)

NA NSR	40 CFR 52.24, 40 CFR 51.165, 40 CFR part 51, Appendix S

Minor NSR	40 CFR 51.160-164

	The PSD requirements include but are not limited to the following:

installation of Best Available Control Technology (BACT);

air quality monitoring and modeling analyses to ensure that a
project’s emissions will not cause or contribute to a violation of any
NAAQS or maximum allowable pollutant increase (PSD increment);

notification of Federal Land Manager of nearby Class I areas; and

public comment on permit.

Nonattainment NSR requirements include but are not limited to:

installation of Lowest Achievable Emissions Rate (LAER) control
technology;

offsetting new emissions with creditable emissions reductions;

a certification that all major sources owned and operated in the state
by the same owner are in compliance with all applicable requirements
under the CAA;

an alternative siting analysis demonstrating that the benefits of
proposed source significantly outweigh the environmental and social
costs imposed as a result of its location, construction, or
modification; and

public comment on the permit.

Minor NSR programs must meet the statutory requirements in section
110(a)(2)(C) of the CAA which requires “…regulation of the
modification and construction of any stationary source …as necessary
to assure that the [NAAQS] are achieved.”

Areas which are newly designated as nonattainment for the Pb NAAQS as a
result of any changes made to the NAAQS will be required to adopt a
nonattainment NSR program to address major sources of lead where the
program does not currently exist for the Pb NAAQS.  Prior to adoption of
the SIP revision addressing NSR for lead nonattainment areas, the
requirements of 40 CFR part 51, appendix S will apply.

b.	Comments and Responses

Several commenters stated that given the significant changes being
proposed for the revised Pb NAAQS, EPA must promptly undertake
rulemaking action in order to satisfy the PSD requirements related to
the revised Pb NAAQS.  The commenters further stated that EPA should
revise the current regulations related to the establishment of maximum
allowable increases or increments for lead under 40 CFR 51.166(a), and a
substantial reduction in the significant/de minimis emissions levels for
lead set forth in 40 CFR 51.166(b)(23)(i) and 40 CFR 52.21(b)(23)(i).  

As stated previously, the EPA believes that generally, there is
sufficient guidance and regulations already in place to fully implement
the revised Pb NAAQS.  The EPA notes that, under section 110(a)(2)(D),
every minor source NSR program must be sufficiently complete and
stringent “to assure that the [NAAQS] are achieved.”  The EPA will
as appropriate review and revise and update policies, guidance, and
regulations for implementing the revised Pb NAAQS following the
promulgation of the NAAQS.  

c.	Final

The EPA is finalizing the guidance related to nonattainment NSR and PSD
requirements for lead nonattainment areas as provided in the proposed
rule.

6.   	Emissions Inventories

a.	Proposal

States must develop and periodically update a comprehensive, accurate,
current inventory of actual emissions affecting ambient lead
concentrations.  The emissions inventory is used by states and EPA to
determine the nature and extent of the specific control strategy
necessary to help bring an area into attainment of the NAAQS.  Emissions
inventories should be based on measured emissions or documented
emissions factors.  Generally, the more comprehensive and accurate the
inventory, the more effective the evaluation of possible control
measures can be for the affected area (see section 172(c)(3) of the
CAA).  

Pursuant to its authority under section 110 of Title I of the CAA, EPA
has long required states to submit emission inventories containing
information regarding the emissions of criteria pollutants as well as
their precursors.  The EPA codified these requirements in 40 CFR part
51, subpart Q in 1979 and amended them in 1987.  The 1990 Clean Air Act
Amendments (CAAA) revised many of the provisions of the CAA related to
attainment of the NAAQS.  These revisions established new emission
inventory requirements applicable to certain areas that were designated
as nonattainment for certain pollutants.  

In June 2002, EPA promulgated the Consolidated Emissions Reporting Rule
(CERR)(67 FR 39602, June 10, 2002). The CERR consolidates the various
emissions reporting requirements that already exist into one place in
the Code of  Federal Regulations (CFR), and establishes new requirements
for the state wide reporting of area (non-point) source and mobile
source emissions.  The CERR establishes two types of required emissions
inventories: (1) Annual inventories, and (2) 3-year cycle inventories. 
The annual inventory requirement is limited to reporting statewide
emissions data from the larger point sources.  For the 3-year cycle
inventory, states will need to report data from all of their point
sources plus all of the area (non-point) and mobile sources on a
statewide basis.  

By merging emissions information from relevant point sources, area
sources, and mobile sources into a comprehensive emission inventory, the
CERR allows state, local and tribal agencies to do the following:

set a baseline for SIP development.  

measure their progress in reducing emissions.  

answer the public(s request for information.

	The EPA uses the data submitted by the states to develop the National
Emission Inventory (NEI). The NEI is used by EPA to show national
emission trends, as modeling input for analysis of potential
regulations, and other purposes.

Most importantly, states need these inventories to help in the
development of control strategies and demonstrations to attain the Pb
NAAQS. While the CERR sets forth requirements for data elements, EPA
guidance complements these requirements and indicates how the data
should be prepared for SIP submissions.  Our current regulations at 40
CFR 51.117(e) require states to include in the SIP inventory all point
sources that emit 5 or more tons of lead emissions per year.  As stated
previously, in the proposed rulemaking EPA took comment on whether the
recommended threshold for RACT analysis should be less than the current
5 tons/yr (see section VI.F.1), and proposed that if EPA lowered the
recommended threshold for RACT in the final rulemaking, we would also
revise, to be consistent, the emissions threshold for including sources
in the inventory pursuant to 40 CFR 51.117(e).  In the proposed rule, we
solicited comment on the appropriate threshold for Pb point source
inventory reporting requirements.

The SIP inventory must be approved by EPA as a SIP element and is
subject to public hearing requirements, whereas the CERR inventory is
not.  Because of the regulatory significance of the SIP inventory, EPA
will need more documentation on how the SIP inventory was developed by
the state as opposed to the documentation required for the CERR
inventory.  In addition, the geographic area encompassed by some aspects
of the SIP submission inventory will be different from the statewide
area covered by the CERR emissions inventory. 

	The EPA has proposed the Air Emissions Reporting Rule (AERR) at 71 FR
69 (Jan. 3, 2006).  When finalized, the AERR will update, consolidate,
and harmonize new emissions reporting requirements with pre-existing
sets of reporting requirements under the CERR and the NOx SIP Call.  The
AERR is expected to be a means by which the Agency will implement
additional data reporting requirements for the Pb NAAQS SIP emission
inventories. 

b.	Comments and Responses 

	One commenter stated that states currently work with regional offices
in developing nonattainment area inventories and that this approach
should be encouraged.  The commenter further indicated that states
should be allowed to start with the National Emissions Inventory (NEI)
and customize their nonattainment area inventories to analyze
nonattainment problems.

	The EPA encourages the states to continue to work closely with the EPA
Regional Offices in developing their nonattainment area emissions
inventories as well as any enhancements that need to be made to the NEI.
The EPA encourages the use of the NEI as a tool to assist states in
developing their nonattainment area SIP emissions inventory.  States,
however, are reminded that the nonattainment area SIP emissions
inventory is required pursuant to 40 CFR 51.117(e) and must be approved
by EPA pursuant to the CAA, and is subject to the public hearing
requirements pursuant to section 110(a)(2).  

	One commenter stated that EPA should develop additional guidance on
emission inventories related to the nonattainment area SIP submittal
because the requirements under the CERR and the AERR may not be enough
to adequately address the emissions inventory requirements related to
the attainment demonstration for the SIP.  

	The EPA will review the need for additional guidance concerning the
emissions inventories related to the nonattainment area SIP submittal on
an ongoing basis.  As stated previously, EPA believes that the current
guidance, policies, and regulations provide a sufficient basis for
states to implement the revised Pb NAAQS at this time.  The EPA, as
appropriate, will review and revise or update these policies, guidance,
and regulations to provide for effective implementation of the Pb NAAQS.
  

	Several commenters stated that EPA should revise 40 CFR 51.117(e)(1),
relating to the emissions reporting threshold level for lead
nonattainment area SIPs.  The current threshold level as stated in
51.117(e)(1), requires that the point source inventory on which the
summary of the baseline lead emissions inventory is based must contain
all sources that emit 5 or more tpy of lead.

	The EPA agrees with the commenters that the requirement for the
emissions inventory reporting threshold for lead nonattainment SIPs, as
stated in 40 CFR 51.117(e)(1), should be revised to reflect the
stringency of the revised Pb NAAQS.  In the proposed rule, EPA proposed
to revise the current threshold level for emissions inventory reporting
from 5 tpy to be consistent with the threshold for the analysis of
RACM/RACT control measures.  As discussed above, EPA is setting the
threshold for RACT analysis at 0.5 tpy.  EPA concludes it is also
appropriate to set the threshold level of the emissions inventory
reporting requirement at 0.5 tpy.

c.  Final

	The EPA is finalizing the guidance contained related to the emissions
inventories requirements for the Pb NAAQS as provided in the proposed
rule.  The EPA is updating the emissions reporting requirements for lead
nonattainment area SIPs stated in 40 CFR 51.117(e)(1) by revising the
source emission inventory reporting threshold from 5 tpy to 0.5 tpy.

7. 	Modeling 

a.	Proposal

	The lead SIP regulations found at 40 CFR 51.117 require states to
employ atmospheric dispersion modeling for the demonstration of
attainment for areas in the vicinity of point sources listed in 40 CFR
51.117(a)(1).  To complete the necessary dispersion modeling,
meteorological, and other data are necessary.  Dispersion modeling
should follow the procedures outlined in EPA’s latest guidance
document entitled “Guideline on Air Quality Models”.  This guideline
indicates the types and historical records for data necessary for
modeling demonstrations (e.g., on-site meteorological stations, 12
months of meteorological data are required in order to demonstrate
attainment for the affected area).

b.	Comments and Responses

One commenter stated that the SIPs for lead nonattainment areas should
provide for the implementation of control measures for point and area
sources of lead emissions which demonstrate attainment of the lead NAAQS
as expeditiously as practicable, but no later than the applicable
statutory attainment date for the area.  The commenter further stated
that they believe that the requirements currently stated under 40 CFR
51.117(a)(1),  related to additional control strategy requirements,
should be revised to reflect the stringency of  the revised lead NAAQS. 
The commenter stated that specifically, the threshold level of 25 tpy as
stated in 40 CFR 51.117(a)(1), related to modeling for point source
emissions, should be revised to reflect the stringency of the revised
NAAQS.

The EPA agrees with the commenter that lead nonattainment area SIPs must
provide for the implementation of control measures for point and area
source emissions of lead in order to demonstrate attainment of the Pb
NAAQS as expeditiously as practicable, but no later than the attainment
date for the affected area. EPA notes that  40 CFR 51.117(a) provides
that states must include, as a part of their attainment modeling
demonstration, an analysis showing that the SIP will attain and maintain
the standard in areas in the vicinity of certain point sources that are
emitting at the level of 25 tpy, and also in “any other area that has
lead air concentrations in excess of the national ambient air quality
standard concentration.”  EPA does not believe it is necessary to
amend the 25 tpy threshold in 40 CFR § 51.117(a)(1) because the
provisions of 40 CFR § 51.117(a)(2) are sufficient to ensure an
adequate attainment demonstration. Accordingly, EPA believes that the
current requirements concerning control strategy demonstration as stated
in 40 CFR 51.117(a) are adequate for states to develop SIPs which
address attainment of the revised Pb NAAQS.  In doing the analysis,
required under 40 CFR 51.117(a)(2), EPA expects the state will take into
consideration all sources of lead emissions within the nonattainment
area that may be required to be controlled, taking into consideration
the attainment needs of the area. 

c.	Final

	The EPA is finalizing the guidance related to modeling attainment
demonstrations for lead nonattainment area SIPs as proposed.  The EPA
will continue to review whether  any additional changes related to
modeling demonstrations or applicable modeling guidance are appropriate.

G. 	General Conformity

1.	Proposal

	Section 176(c) of the CAA, as amended (42 U.S.C. 7401 et seq.),
requires that all Federal actions conform to an applicable
implementation plan developed pursuant to section 110 and part D of the
CAA.  Section 176(c) of the CAA requires EPA to promulgate criteria and
procedures for demonstrating and assuring conformity of Federal actions
to a SIP.  For the purpose of summarizing the general conformity rule,
it can be viewed as containing three major parts: applicability,
procedure, and analysis. These are briefly described below.

The general conformity rule covers direct and indirect emissions of
criteria pollutants, or their precursors, that are caused by a Federal
action, are reasonably foreseeable, and can practicably be controlled by
the Federal agency through its continuing program responsibility.  The
general conformity rule generally applies to Federal actions except; (1)
Actions covered by the transportation conformity rule; (2) Actions with
respect to associated emissions below specified de minimis levels; and
(3) Certain other actions that are exempt or presumed to conform.  

	The general conformity rule also establishes procedural requirements. 
Federal agencies must make their conformity determinations available for
public review.  Notice of draft and final general conformity
determinations must be provided directly to air quality regulatory
agencies and to the public by publication in a local newspaper.

	The general conformity determination examines the impacts of direct and
indirect emissions related to Federal actions.  The general conformity
rule provides several options to satisfy air quality criteria, such as
modeling or offsets, and requires the Federal action to also meet any
applicable SIP requirements and emissions milestones. Each Federal
agency must determine that any actions covered by the general conformity
rule conform to the applicable SIP before the action is taken.  The
criteria and procedures for conformity apply only in nonattainment and
maintenance areas with respect to the criteria pollutants under the CAA:
 carbon monoxide (CO), lead (Pb), nitrogen dioxide (NO2), ozone (O3),
particulate matter (PM2.5 and  PM10),  and sulfur dioxide (SO2).  The
general conformity rule establishes procedural requirements for Federal
agencies for actions related to all NAAQS pollutants, both nonattainment
and maintenance areas and will apply one year following the promulgation
of designations for any new or revised Pb NAAQS. 

2.         Final

	The EPA is finalizing the guidance related to general conformity as
provided in the proposed rule.

H. 	Transition from the Current NAAQS to a Revised NAAQS for Lead 

1.	Proposal

As discussed in the proposal, EPA believes that Congress’s intent, as
evidenced by section 110(l), 193, and section 172(e) of the CAA, was to
ensure that continuous progress, in terms of public health protection,
takes place in transitioning from a current NAAQS for a pollutant to a
new or revised NAAQS.  Therefore, EPA proposed that the existing NAAQS
be revoked one year following the promulgation of designations for any
new NAAQS, except that the existing NAAQS will not be revoked for any
current nonattainment area until the affected area submits, and EPA
approves, an attainment demonstration which addresses the attainment of
the new Pb NAAQS.

The CAA contains a number of provisions that indicate Congress’s
intent to not allow states to alter or remove provisions from
implementation plans if the plan revision would jeopardize the air
quality protection being provided by the plan.  For example, section
110(l) provides that EPA may not approve a SIP revision if it interferes
with any applicable requirement concerning attainment and RFP, or any
other applicable requirement under the CAA.  In addition section 193 of
the CAA prohibits the modification of a control, or a control
requirement, in effect or required to be adopted as of November 15, 1990
(i.e., prior to the promulgation of the Clean Air Act Amendments (CAAA)
of 1990), unless such a modification would ensure equivalent or greater
emissions reductions. One other provision of the CAA provides additional
insight into Congress’s intent related to the need to continue
progress towards meeting air quality standards during periods of
transition from one standard to another.  Section 172(e) of the CAA,
related to future modifications of a standard, applies when EPA
promulgates a new or revised NAAQS and makes it less stringent than the
previous NAAQS.  This provision of the CAA specifies that in such
circumstances, states may not relax control obligations that apply in
nonattainment area SIPs, or avoid adopting those controls that have not
yet been adopted as required.  

The EPA believes that Congress generally did not intend to permit states
to relax levels of pollution control when EPA revises a standard until
the new or revised standard is implemented. Therefore, we believe that
controls that are required under the current Pb NAAQS, or that are
currently in place under the current Pb NAAQS, should generally remain
in place until new designations are established and, for current
nonattainment areas, new attainment SIPs are approved for any new or
revised standard.  As a result, EPA proposed that the current Pb NAAQS
should stay in place for one year following the effective date of
designations for any new or revised NAAQS before being revoked, except
in current nonattainment areas, where the existing NAAQS will not be
revoked until the affected area submits, and EPA approves, an attainment
demonstration for the revised Pb NAAQS.  Accordingly, the CAA
mechanisms, including sanctions, that help ensure continued progress
toward timely attainment would remain in effect for the existing Pb
NAAQS, and would apply to existing Pb nonattainment areas.

Pursuant to CAA section 110(l), any proposed SIP revision being
considered by EPA after the effective date of the revised Pb NAAQS would
be evaluated for its potential to interfere with attainment or
maintenance of the new standard.  The EPA believes that any area
attaining the revised Pb NAAQS would also attain the existing Pb NAAQS,
and thus reviewing proposed SIP revisions for interference with the new
standard will be sufficient to prevent backsliding.  Consequently, in
light of the nature of the proposed revision of the Pb NAAQS, the lack
of classifications (and mandatory controls associated with such
classifications pursuant to the CAA), and the small number of
nonattainment areas, EPA believes that retaining the current standard
for a limited period of time until SIPs are approved for the new
standard in current nonattainment areas, or one year after designations
in other areas, will adequately serve the anti-backsliding goals of the
CAA. 

2.  Final

The EPA is finalizing the guidance related to transition from the
current NAAQS to the new Pb NAAQS generally consistent with the proposal
that the existing standard be retained until one year following the
effective date of designations, except that for current nonattainment
areas the standard would remain in effect until approval of a SIP for
the new standard.  EPA notes that the most recent three years of
available monitoring data from the East Helena nonattainment area showed
no violations of the current standard, although the monitors were shut
down in December, 2001 following the shutdown of the large stationary
source of lead emissions there.  Accordingly, it is unclear whether East
Helena will be designated nonattainment for the new standard, or whether
it could possibly receive another designation.  In the event East Helena
is designated unclassifiable or attainment for the new standard, EPA
believes it is still appropriate to retain the existing standard until
the state submits, and EPA approves, a maintenance SIP for the new
standard.  Accordingly EPA has amended the proposed text of 40 CFR 50.12
to reflect the possibility that in this specific set of circumstances,
the old standard could be revoked upon EPA’s approval of a maintenance
SIP for the new standard.

 VII. Exceptional Events Information Submission Schedule for Lead NAAQS

EPA proposed changes to the original dates for submitting and
documenting exceptional event data claims and the Agency is adopting the
proposed changes with some minor revisions and they are described below.

Section A presents the information stated in the proposal.  Section B
summarizes and responds to all comments received regarding exceptional
events data submission.  Section C provides the final preamble text
considering comments received and incorporating final revisions to the
proposal.

A.  Proposal  

The EPA proposed Pb-specific changes to the deadlines, in 40 CFR 50.14,
by which States must flag ambient air data that they believe has been
affected by exceptional events and submit initial descriptions of those
events, and the deadlines by which States must submit detailed
justifications to support the exclusion of that data from EPA
determinations of attainment or nonattainment with the NAAQS.  The
deadlines in 40 CFR 50.14 are generic, and are not always appropriate
for Pb given the anticipated schedule for the designations of areas
under the proposed Pb NAAQS.  

For the specific case of Pb, EPA anticipates that designations under the
revised NAAQS may be made in September 2011 based on 2008-2010 data, (or
possibly in September 2010 based on 2007-2009 data if sufficient data
are available), and thus will depend in part on air quality data
collected as late as December 2010 (or December 2009).  (Section IV.C of
the proposed preamble had a more detailed discussion of the designation
schedule and what data EPA intends to use.)  There is no way for a State
to flag and submit documentation regarding events that happen in
October, November, and December 2010 (or 2009) by one year before
designation decisions that are made in September 2011 (or 2010).

The proposed revisions to 40 CFR 50.14 involved only changes in
submission dates for information regarding claimed exceptional events
affecting Pb data.  The proposed rule text showed only the changes that
would apply if designations are made three years after promulgation;
where a deadline would be different if designations were made at the
two-year point, the difference in deadline was noted in the proposed
preamble.  We proposed to extend the generic deadline for flagging data
(and providing a brief initial description of the event) of July 1 of
the year following the data collection, to July 1, 2009 for data
collected in 2006-2007.  The proposed extension included 2006 and 2007
data because Governors’ designation recommendations will consider
2006-2008 data, and possibly EPA will consider 2006-2008 or 2007-2009
data if complete data for 2008-2010 are not available at the time of
final designations.  EPA noted that it does not intend to use data prior
to 2006 in making Pb designation decisions. The generic event flagging
deadline in the Exceptional Events Rule would continue to apply to 2008
and later years following the promulgation of the revised Pb NAAQS.  The
Governor of a State would be required to submit designation
recommendations to EPA a year after promulgation of the revised NAAQS
(i.e. in Fall 2009).  States would therefore have enough time to flag
data and submit their demonstrations and know what 2008 data need to be
excluded due to exceptional events when formulating their
recommendations to EPA.

For data collected in 2010 (or 2009), we proposed to move up the generic
deadline of July 1 for data flagging to May 1, 2011 (or May 1, 2010)
(which is also the applicable deadline for certifying data in AQS as
being complete and accurate to the best knowledge of the responsible
monitoring agency head).  This would give a State less time, but EPA
believes still sufficient time, to decide what 2010 (or 2009) data to
flag, and would allow EPA to have access to the flags in time for EPA to
develop its own proposed and final plans for designations.

Finally, EPA proposed to make the deadline for submission of detailed
justifications for exclusion of data collected in 2006 through 2008 be
September 15, 2010 for the three year designation schedule, or September
15, 2009 under the two year designation schedule.  EPA generally does
not anticipate data from 2006 and 2007 being used in final Pb
designations.  Under the three year designation schedule, for data
collected in 2010, EPA proposed to make the deadline for submission of
justifications be  May 1, 2011.  This is less than a year before the
designation decisions would be made, but we believe it is a good
compromise between giving a State a reasonable period to prepare the
justifications and EPA a reasonable period to consider the information
submitted by the State.  Similarly, under the two year designation
schedule, for data collected in 2009, EPA proposed to make the deadline
for submission of justifications be  May 1, 2010.  Table 5 summarizes
the three year designation deadlines in the proposal and discussed in
this section, and Table 6 summarizes the two year designation deadlines.

Table 5.  Proposed Schedule for Exceptional Event Flagging and
Documentation Submission if Designations Promulgated in Three Years.

Air Quality Data Collected for Calendar Year	Event Flagging Deadline
Detailed Documentation Submission Deadline

2006	July 1, 2009*	September 15 2010*

2007	July 1, 2009*	September 15, 2010

2008	July 1, 2009	September 15, 2010*

2009	July1, 2010	September 15, 2010 *

2010	May 1, 2011*	May 1, 2011*

* Indicates proposed change from generic schedule in 40 CFR 50.14.

Table 6.  Proposed Schedule for Exceptional Event Flagging and
Documentation Submission if Designations Promulgated in Two Years.

Air Quality Data Collected for Calendar Year	Event Flagging Deadline
Detailed Documentation Submission Deadline

2006	July 1, 2009*	September 15, 2009

2007	July 1, 2009*	September 15, 2009*

2008	July 1, 2009	September 15, 2009*

2009	May 1, 2010*	May 1, 2010*

* Indicates proposed change from generic schedule in 40 CFR 50.14.

	EPA invited comment on these proposed changes in the exceptional event
flagging and documentation submission deadlines.

B.  Comments and Responses

EPA received only one comment on the proposed revision to the schedule
for flagging and documenting exceptional event data which could affect
Pb designation decisions.  The comment from the North Carolina
Department of Environment and Natural Resources’ (NCDENR) Division of
Air Quality (DAQ) stated that:  “NCDAQ believes states need proper
time to provide exceptional events documentation before designations are
made.”

EPA believes that the final schedule provides states with adequate time
for flagging exceptional values and providing documentation to support
exceptional event claims. Also, NCDAQ did not specifically state either
that the proposed deadlines were inadequate or ask for more time; nor
did it provide any alternative schedules for the Agency’s
consideration.

C.  Final

EPA’s final schedule for flagging and documenting exceptional event
data claims is shown in the tables that follow.   Table 7 summarizes the
final deadlines for areas where final designations occur no later than
October 15, 2011 (i.e., no later than three years after promulgation of
a new NAAQS).  Table 8 summarizes the final dealines for areas where
final desiginations occur no later than October 15, 2010 (i.e., no later
than two years after promulgation of a new NAAQS.

Table 7.  Final Schedule for Exceptional Event Flagging and
Documentation Submission if Designations Promulgated within Three Years.

Air Quality Data Collected for Calendar Year	Event Flagging Deadline
Detailed Documentation Submission Deadline

2006	July 1, 2009*	October 15 2010*

2007	July 1, 2009*	October 15, 2010

2008	July 1, 2009	October 15, 2010*

2009	July1, 2010	October 15, 2010 *

2010	May 1, 2011*	May 1, 2011*

* Indicates change from generic schedule in 40 CFR 50.14.

Table 8.  Final Schedule for Exceptional Event Flagging and
Documentation Submission if Designations Promulgated within Two Years. 

Air Quality Data Collected for Calendar Year	Event Flagging Deadline
Detailed Documentation Submission Deadline

2006	July 1, 2009*	October 15, 2009

2007	July 1, 2009*	October 15, 2009*

2008	July 1, 2009	October 15, 2009*

2009	May 1, 2010*	May 1, 2010*

* Indicates change from generic schedule in 40 CFR 50.14.

VII.	Statutory and Executive Order Reviews

A.	Executive Order 12866: Regulatory Planning and Review

0.50 μg/m3, 0.40 μg/m3, 0.30 μg/m3, 0.20 μg/m3, 0.15 μg/m3 and 0.10
μg/m3.  The RIA contains illustrative analyses that consider a limited
number of emissions control scenarios that States and Regional Planning
Organizations might implement to achieve these alternative Pb NAAQS. 
However, the CAA and judicial decisions make clear that the economic and
technical feasibility of attaining ambient standards are not to be
considered in setting or revising NAAQS, although such factors may be
considered in the development of State plans to implement the standards.
 Accordingly, although an RIA has been prepared, the results of the RIA
have not been considered in issuing this final rule.

B.	Paperwork Reduction Act

The information collection requirements in this final rule will be
submitted for approval to the Office of Management and Budget (OMB)
under the Paperwork Reduction Act, 44 U.S.C. 3501 et seq.  The
information collection requirements are not enforceable until OMB
approves them.

The information collected under 40 CFR part 53 (e.g., test results,
monitoring records, instruction manual, and other associated
information) is needed to determine whether a candidate method intended
for use in determining attainment of the National Ambient Air Quality
Standards (NAAQS) in 40 CFR part 50 will meet the design, performance,
and/or comparability requirements for designation as a Federal reference
method (FRM) or Federal equivalent method (FEM).  While this final rule
amends the requirements for Pb FRM and FEM determinations, they merely
provide additional flexibility in meeting the FRM/FEM determination
requirements.  Furthermore, we do not expect the number of FRM or FEM
determinations to increase over the number that is currently used to
estimate burden associated with Pb FRM/FEM determinations provided in
the current ICR for 40 CFR part 53 (EPA ICR numbers  0559.12).  As such,
no change in the burden estimate for 40 CFR part 53 has been made as
part of this rulemaking. 

The information collected and reported under 40 CFR part 58 is needed to
determine compliance with the NAAQS, to characterize air quality and
associated health and ecosystem impacts, to develop emissions control
strategies, and to measure progress for the air pollution program.  The
proposed amendments would revise the technical requirements for Pb
monitoring sites, require the siting and operation of additional Pb
ambient air monitors, and the reporting of the collected ambient Pb
monitoring data to EPA’s Air Quality System (AQS).  We have estimated
the burden based on the final monitoring requirements of this rule. 
Based on these requirements, the annual average reporting burden for the
collection under 40 CFR part 58 (averaged over the first 3 years of this
ICR) for 150 respondents is estimated to increase by a total of 22,376
labor hours per year with an increase of $1,910,059 per year.  Burden is
defined at 5 CFR 1320.3(b).

An agency may not conduct or sponsor, and a person is not required to
respond to, a collection of information unless it displays a currently
valid OMB control number.  The OMB control numbers for EPA's regulations
in 40 CFR are listed in 40 CFR part 9.  When this ICR is approved by
OMB, the Agency will publish a technical amendment to 40 CFR part 9 in
the Federal Register to display the OMB control number for the approved
information collection requirements contained in this final rule.  

C.	Regulatory Flexibility Act

The Regulatory Flexibility Act (RFA) generally requires an agency to
prepare a regulatory flexibility analysis of any rule subject to notice
and comment rulemaking requirements under the Administrative Procedure
Act or any other statute unless the agency certifies that the rule will
not have a significant economic impact on a substantial number of small
entities.  Small entities include small businesses, small organizations,
and small governmental jurisdictions.

For purposes of assessing the impacts of this rule on small entities,
small entity is defined as:  (1) a small business that is a small
industrial entity as defined by the Small Business Administration’s
(SBA) regulations at 13 CFR 121.201;  (2) a small governmental
jurisdiction that is a government of a city, county, town, school
district or special district with a population of less than 50,000; and
(3) a small organization that is any not-for-profit enterprise which is
independently owned and operated and is not dominant in its field.

After considering the economic impacts of this final rule on small
entities, I certify that this action will not have a significant
economic impact on a substantial number of small entities.  This final
rule will not impose any requirements on small entities.  Rather, this
rule establishes national standards for allowable concentrations of Pb
in ambient air as required by section 109 of the CAA.  American Trucking
Ass’ns v. EPA, 175 F. 3d 1027, 1044-45 (D.C. cir. 1999) (NAAQS do not
have significant impacts upon small entities because NAAQS themselves
impose no regulations upon small entities). Similarly, the amendments to
40 CFR part 58 address the requirements for States to collect
information and report compliance with the NAAQS and will not impose any
requirements on small entities.

D.	Unfunded Mandates Reform Act

Title II of the Unfunded Mandates Reform Act of 1995 (UMRA), Public Law
104-4, establishes requirements for Federal agencies to assess the
effects of their regulatory actions on State, local, and tribal
governments and the private sector.  Unless otherwise prohibited by law,
under section 202 of the UMRA, EPA generally must prepare a written
statement, including a cost-benefit analysis, for proposed and final
rules with “Federal mandates” that may result in expenditures to
State, local, and tribal governments, in the aggregate, or to the
private sector, of $100 million or more in any one year.  Before
promulgating an EPA rule for which a written statement is required under
section 202, section 205 of the UMRA generally requires EPA to identify
and consider a reasonable number of regulatory alternatives and to adopt
the least costly, most cost-effective or least burdensome alternative
that achieves the objectives of the rule.  The provisions of section 205
do not apply when they are inconsistent with applicable law.  Moreover,
section 205 allows EPA to adopt an alternative other than the least
costly, most cost-effective or least burdensome alternative if the
Administrator publishes with the final rule an explanation why that
alternative was not adopted.  Before EPA establishes any regulatory
requirements that may significantly or uniquely affect small
governments, including tribal governments, it must have developed under
section 203 of the UMRA a small government agency plan.  The plan must
provide for notifying potentially affected small governments, enabling
officials of affected small governments to have meaningful and timely
input in the development of EPA regulatory proposals with significant
Federal intergovernmental mandates, and informing, educating, and
advising small governments on compliance with the regulatory
requirements. 

This action is not subject to the requirements of sections 202 and 205
of the UMRA.  EPA has determined that this final rule does not contain a
Federal mandate that may result in expenditures of $100 million or more
for State, local, and tribal governments, in the aggregate, or the
private sector in any one year.  The revisions to the Pb NAAQS impose no
enforceable duty on any State, local or Tribal governments or the
private sector.  The expected costs associated with the increased
monitoring requirements are described in EPA’s ICR document, but those
costs are not expected to exceed $100 million in the aggregate for any
year.  Furthermore, as indicated previously, in setting a NAAQS EPA
cannot consider the economic or technological feasibility of attaining
ambient air quality standards.  Because the Clean Air Act prohibits EPA
from considering the types of estimates and assessments described in
section 202 when setting the NAAQS, the UMRA does not require EPA to
prepare a written statement under section 202 for the revisions to the
Pb NAAQS. 

With regard to implementation guidance, the CAA imposes the obligation
for States to submit SIPs to implement the Pb NAAQS. In this final rule,
EPA is merely providing an interpretation of those requirements.
However, even if this rule did establish an independent obligation for
States to submit SIPs, it is questionable whether an obligation to
submit a SIP revision would constitute a Federal mandate in any case.
The obligation for a State to submit a SIP that arises out of section
110 and section 191 of the CAA is not legally enforceable by a court of
law, and at most is a condition for continued receipt of highway funds.
Therefore, it is possible to view an action requiring such a submittal
as not creating any enforceable duty within the meaning of 2 U.S.C. 658
for purposes of the UMRA. Even if it did, the duty could be viewed as
falling within the exception for a condition of Federal assistance under
2 U.S.C. 658.

EPA has determined that this final rule contains no regulatory
requirements that might significantly or uniquely affect small
governments because it imposes no enforceable duty on any small
governments.  Therefore, this rule is not subject to the requirements of
section 203 of the UMRA.

E.	Executive Order 13132: Federalism

Executive Order 13132, entitled “Federalism” (64 FR 43255, August
10, 1999), requires EPA to develop an accountable process to ensure
“meaningful and timely input by State and local officials in the
development of regulatory policies that have federalism implications.”
 “Policies that have federalism implications” is defined in the
Executive Order to include regulations that have “substantial direct
effects on the States, on the relationship between the national
government and the States, or on the distribution of power and
responsibilities among the various levels of government.”  

This final rule does not have federalism implications.  It will not have
substantial direct effects on the States, on the relationship between
the national government and the States, or on the distribution of power
and responsibilities among the various levels of government, as
specified in Executive Order 13132.  The rule does not alter the
relationship between the Federal government and the States regarding the
establishment and implementation of air quality improvement programs as
codified in the CAA.  Under section 109 of the CAA, EPA is mandated to
establish NAAQS; however, CAA section 116 preserves the rights of States
to establish more stringent requirements if deemed necessary by a State.
 Furthermore, under CAA section 107, the States have primary
responsibility for implementation of the NAAQS.  Finally, as noted in
section E (above) on UMRA, this rule does not impose significant costs
on State, local, or tribal governments or the private sector.  Thus,
Executive Order 13132 does not apply to this rule.

F.	Executive Order 13175: Consultation and Coordination with Indian
Tribal Governments

	This action does not have tribal implications, as specified in
Executive Order 13175 (65 FR 67249, November 9, 2000).  It does not have
a substantial direct effect on one or more Indian Tribes, since Tribes
are not obligated to adopt or implement any NAAQS or monitoring
requirements for NAAQS.  Thus, Executive Order 13175 does not apply to
this action.  

	Although Executive Order 13175 does not apply to this action, EPA
contacted tribal environmental professionals during the development of
this rule.  EPA staff participated in the regularly scheduled Tribal Air
call sponsored by the National Tribal Air Association during the spring
of 2008 as the proposal was under development, and also offered several
informational briefings on the proposal to Tribal environmental
professionals in Summer 2008 during the public comment period on the
proposed rule.  EPA sent individual letters to all federally recognized
Tribes within the lower 48 states and Alaska to give Tribal leaders the
opportunity for consultation, and EPA staff also participated in Tribal
public meetings, such as the National Tribal Forum meeting in June 2008,
where Tribes discussed their concerns regarding the proposed rule.  EPA
received comments from a number of Tribes on the proposed rule; these
comments are addressed in the relevant sections of the preamble and
Response to Comments for this rulemaking.

G.	Executive Order 13045: Protection of Children from Environmental
Health & Safety Risks

This action is subject to EO 13045 (62 FR 19885, April 23, 1997) because
it is an economically significant regulatory action as defined by EO
12866, and we believe that the environmental health risk addressed by
this action has a disproportionate effect on children. The final rule
establishes uniform national ambient air quality standards for Pb; these
standards are designed to protect public health with an adequate margin
of safety, as required by CAA section 109.  However, the protection
offered by these standards may be especially important for children
because neurological effects in children are among if not the most
sensitive health endpoints for Pb exposure.  Because children are
considered a sensitive population, we have carefully evaluated the
environmental health effects of exposure to Pb pollution among children.
 These effects and the size of the population affected are summarized in
chapters 6 and 8 of the Criteria Document and sections 3.3 and 3.4 of
the Staff Paper, and the results of our evaluation of the effects of Pb
pollution on children are discussed in sections II.B and II.C of the
notice of proposed rulemaking, and section II.A of this preamble.

H.	Executive Order 13211: Actions that Significantly Affect Energy
Supply, Distribution or Use

This rule is not a “significant energy action” as defined in
Executive Order 13211, “Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution, or Use” (66 FR 28355
(May 22, 2001)) because it is not likely to have a significant adverse
effect on the supply, distribution, or use of energy.  The purpose of
this rule is to establish revised NAAQS for Pb.  The rule does not
prescribe specific control strategies by which these ambient standards
will be met.  Such strategies will be developed by States on a
case-by-case basis, and EPA cannot predict whether the control options
selected by States will include regulations on energy suppliers,
distributors, or users.  Thus, EPA concludes that this rule is not
likely to have any adverse energy effects.

 I.	National Technology Transfer and Advancement Act

Section 12(d) of the National Technology Transfer and Advancement Act of
1995 (NTTAA), Public Law No. 104-113, §12(d) (15 U.S.C. 272 note)
directs EPA to use voluntary consensus standards in its regulatory
activities unless to do so would be inconsistent with applicable law or
otherwise impractical.  Voluntary consensus standards are technical
standards (e.g., materials specifications, test methods, sampling
procedures, and business practices) that are developed or adopted by
voluntary consensus standards bodies.  The NTTAA directs EPA to provide
Congress, through OMB, explanations when the Agency decides not to use
available and applicable voluntary consensus standards.

This final rule involves technical standards.  EPA has established
low-volume PM10 samplers coupled with XRF analysis as the FRM for
Pb-PM10 measurement.  While EPA identified the ISO standard
“Determination of the particulate lead content of aerosols collected
on filters” (ISO 9855: 1993) as being potentially applicable, the
final rule does not permit its use.  EPA determined that the use of this
voluntary consensus standard would be impractical because the analysis
method does not provide for the method detection limits necessary to
adequately characterize ambient Pb concentrations for the purpose of
determining compliance with the revisions to the Pb NAAQS.  

J.	Executive Order 12898: Federal Actions to Address Environmental
Justice in Minority Populations and Low-Income Populations

Executive Order 12898 (59 FR 7629; Feb. 16, 1994) establishes federal
executive policy on environmental justice.  Its main provision directs
federal agencies, to the greatest extent practicable and permitted by
law, to make environmental justice part of their mission by identifying
and addressing, as appropriate, disproportionately high and adverse
human health or environmental effects of their programs, policies, and
activities on minority populations and low-income populations in the
United States.  

EPA has determined that this final rule will not have disproportionately
high and adverse human health or environmental effects on minority or
low-income populations because it increases the level of environmental
protection for all affected populations without having any
disproportionately high and adverse human health or environmental
effects on any population, including any minority or low-income
population.  The final rule establishes uniform national standards for
Pb in ambient air.   In the Administrator’s judgment, the revised Pb
NAAQS protect public health, including the health of sensitive groups,
with an adequate margin of safety.  As discussed earlier in this
preamble (see section II) and in the Response to Comments, the
Administrator expressly considered the available information regarding
health effects among vulnerable and susceptible populations in making
the determination about which standards are requisite.  

Some commenters expressed concerns that EPA had failed to adequately
assess the environmental justice implications of its proposed decision. 
These commenters asserted specifically that low-income and minority
populations constitute susceptible subpopulations and that the proposed
revisions to the primary Pb standards would be insufficient to protect
these subpopulations with an adequate margin of safety.  In addition,
some commenters stated that EPA had failed to adequately evaluate or
address the disproportionate adverse impact of Pb exposure on poor and
minority populations as required by E.O. 12898.  These commenters assert
that in spite of significant scientific evidence indicating that the
burden of lead exposure is higher in poor communities and communities of
color, EPA has not taken the differing impacts of lead exposure into
account in revising the Pb NAAQS.    

At the time of proposal, EPA prepared a technical memo to assess the
socio-demographic characteristics of populations living near ambient air
Pb monitors and stationary sources of Pb emissions (Pekar et al., 2008).
 Due to limitations in the available data, most significantly
limitations on information regarding whether current ambient air
concentrations of Pb (as measured by fixed-site monitors or proximity to
stationary sources of Pb) are associated with elevated exposure or
increased risk for any socio-demographic group, EPA was not able to draw
conclusions regarding the impact of Pb air pollution on minority and
low- income populations in this analysis [or “memo”].  However, EPA
believes that the newly strengthened Pb standards and the new
requirements for ambient air monitoring for Pb will have the greatest
benefit in reducing health risks associated with exposure to ambient air
Pb in those areas where ambient air concentrations are currently the
highest.  Thus, to the extent that any population groups, including
minorities or low-income populations, are currently experiencing
disproportionate exposure to ambient air-related Pb, those groups can be
expected to experience relatively greater air quality improvements under
the revised standards.  Nationwide, these revised, more stringent
standards will not have adverse health impacts on any population,
including any minority or low-income population.

K.  Congressional Review Act

	The Congressional Review Act, 5 U.S.C. 801 et seq., as added by the
Small Business Regulatory Enforcement Fairness Act of 1996, generally
provides that before a rule may take effect, the agency promulgating the
rule must submit a rule report, which includes a copy of the rule, to
each House of the Congress and to the Comptroller General of the United
States.  EPA submitted a report containing this rule and other required
information to the U.S. Senate, the U.S. House of Representatives, and
the Comptroller General of the United States prior to publication of the
rule in the Federal Register.  A major rule cannot take effect until 60
days after it is published in the Federal Register.  This action is a
“major rule” as defined by 5 U.S.C. 804(2).  This rule will be
effective [insert date 60 days after publication in the Federal
Register].

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Occup. Environ. Health 42: 231-239. List of Subjects 

40 CFR Part 50

Environmental protection, Air pollution control, Carbon monoxide, Lead,
Nitrogen dioxide, Ozone, Particulate matter, Sulfur oxides.

40 CFR Part 51

Environmental protection, Administrative practice and procedure, Air
pollution control, Carbon monoxide, Intergovernmental relations, Lead,
Nitrogen dioxide, Ozone, Particulate matter, Reporting and recordkeeping
requirements.	

40 CFR Part 53

Environmental protection, Administrative practice and procedure, Air
pollution control, Intergovernmental relations, Reporting and
recordkeeping requirements

40 CFR Part 58

Environmental protection, Administrative practice and procedure, Air
pollution control, Intergovernmental relations, Reporting and
recordkeeping requirements

	

Dated:	 

Stephen L. Johnson, 

Administrator.For the reasons stated in the preamble, title 40, chapter
I of the code of Federal regulations is amended as follows:

PART 50-NATIONAL PRIMARY AND SECONDARY AMBIENT AIR QUALITY STANDARDS

1. The authority citation for part 50 continues to read as follows:

Authority: 42 U.S.C.7401 et seq.

2. Section 50.3 is revised to read as follows:  

§50.3	Reference conditions. 

All measurements of air quality that are expressed as mass per unit
volume (e.g., micrograms per cubic meter) other than for particulate
matter (PM2.5) standards contained in §§50.7 and 50.13 and lead
standards contained in §50.16 shall be corrected to a reference
temperature of 25 (deg) C and a reference pressure of 760 millimeters of
mercury (1,013.2 millibars).  Measurements of PM2.5 for purposes of
comparison to the standards contained in §§50.7 and 50.13 and of lead
for purposes of comparison to the standards contained in §50.16 shall
be reported based on actual ambient air volume measured at the actual
ambient temperature and pressure at the monitoring site during the
measurement period.

3. Section 50.12 is amended by designating the existing text as
paragraph (a) and adding paragraph (b) to read as follows:

§50.12	National primary and secondary ambient air quality standards for
lead.

* * * * *

(b) The standards set forth in this section will remain applicable to
all areas notwithstanding the promulgation of lead national ambient air
quality standards (NAAQS) in §50.16.  The lead NAAQS set forth in this
section will no longer apply to an area one year after the effective
date of the designation of that area, pursuant to section 107 of the
Clean Air Act, for the lead NAAQS set forth in §50.16;  except that for
areas designated nonattainment for the lead NAAQS set forth in this
section as of the effective date of §50.16, the lead NAAQS set forth in
this section will apply until that area submits, pursuant to section 191
of the Clean Air Act, and EPA approves, an implementation plan providing
for attainment and/or maintenance of the lead NAAQS set forth in
§50.16.

4. Section 50.14 is amended by:

a.	Revising paragraph (a)(2);

b.	Revising paragraph (c)(2)(iii);

c.	Redesignating paragraph (c)(2)(v) as paragraph (c)(2)(vi) and adding
a new 	paragraph (c)(2)(v); and

d.	Redesignating existing paragraphs (c)(3)(iii) and (c)(3)(iv) as
paragraphs 	(c)(3)(iv) and (c)(3)(v), respectively, and adding a new
paragraph (c)(3)(iii)

The additions and revisions read as follows:

§50.14 Treatment of air quality monitoring data influenced by
exceptional events.

(a) *** 

(2)  Demonstration to justify data exclusion may include any reliable
and accurate data, but must demonstrate a clear causal relationship
between the measured exceedance or violation of such standard and the
event in accordance with paragraph (c)(3)(iv) of this section. 

(c) ***

(2) *** 

 (iii) Flags placed on data as being due to an exceptional event
together with an initial description of the event shall be submitted to
EPA not later than July 1st of the calendar year following the year in
which the flagged measurement occurred, except as allowed under
paragraph (c)(2)(iv) or (c)(2)(v) of this section.

*****

 (v) For lead (Pb) data collected during calendar years 2006-2008, that
the State identifies as resulting from an exceptional event, the State
must notify EPA of the flag and submit an initial description of the
event no later than July 1, 2009. For Pb data collected during calendar
year 2009, that the State identifies as resulting from an exceptional
event, the State must notify EPA of the flag and submit an initial
description of the event no later than July 1, 2010.  For Pb data
collected during calendar year 2010, that the State identifies as
resulting from an exceptional event, the State must notify EPA of the
flag and submit an initial description of the event no later than May 1,
2011.

*****

(3) ***

 (iii) A State that flags Pb data collected during calendar years
2006-2009, pursuant to paragraph (c)(2)(v) of this section shall, after
notice and opportunity for public comment, submit to EPA a demonstration
to justify exclusion of the data not later than October 15, 2010.  A
State that flags Pb data collected during calendar years 2010 shall,
after notice and opportunity for public comment, submit to EPA a
demonstration to justify the exclusion of the data not later than May 1,
2011.  A state must submit the public comments it received along with
its demonstration to EPA.

*****

5. Section 50.16 is added to read as follows:

§50.16	National primary and secondary ambient air quality standards for
lead.

 (a) The national primary and secondary ambient air quality standards
for lead (Pb) and its compounds are 0.15 micrograms per cubic meter,
arithmetic mean concentration over a 3-month period, measured in the
ambient air as Pb either by: 

(1) A reference method based on Appendix G of this part and designated
in accordance with part 53 of this chapter or; 

(2) An equivalent method designated in accordance with part 53 of this
chapter. 

(b)  The national primary and secondary ambient air quality standards
for Pb are met when the maximum arithmetic 3-month mean concentration
for a 3-year period, as determined in accordance with Appendix R of this
part, is less than or equal to 0.15 micrograms per cubic meter.

6.  Appendix G is amended as follows; a. in section 10.2 the definition
of the term “VSTP” in the equation is revised, b. in section 14
reference 10 is added and reference 15 is revised:

Appendix G to Part 50 - Reference Method for the Determination of Lead
in Suspended Particulate Matter Collected From Ambient Air

* * * * * 

10.2   * * * 

VSTP= Air volume from section 10.1.

* * * * *

14. * * *

10.  Intersociety Committee (1972). Methods of Air Sampling and
Analysis. 1015 Eighteenth Street, N.W. Washington, D.C.: American Public
Health Association. 365-372.

* * * 

15.  Sharon J. Long, et. al., "Lead Analysis of Ambient Air
Particulates: Interlaboratory Evaluation of EPA Lead Reference Method"
APCA Journal, 29, 28-31 (1979).

* * * * *

7. Appendix Q is added to read as follows:

Appendix Q to Part 50 – Reference Method for the Determination of Lead
in Particulate Matter as PM10 Collected From Ambient Air

This Federal Reference Method (FRM) draws heavily from the specific
analytical protocols used by the U.S. EPA. 

1. Applicability and Principle 

1.1 This method provides for the measurement of the lead (Pb)
concentration in particulate matter that is 10 micrometers or less
(PM10) in ambient air. PM10 is collected on an acceptable (see section
6.1.2) 46.2 mm diameter polytetrafluoroethylene (PTFE) filter for 24
hours using active sampling at local conditions with a low-volume air
sampler. The low-volume sampler has an average flow rate of 16.7 liters
per minute (Lpm) and total sampled volume of 24 cubic meters (m3) of
air. The analysis of Pb in PM10 is performed on each individual 24-hour
sample. Gravimetric mass analysis of PM10c filters is not required for
Pb analysis. For the purpose of this method, PM10 is defined as
particulate matter having an aerodynamic diameter in the nominal range
of 10 micrometers (10 µm) or less.  

1.2 For this reference method, PM10 shall be collected with the PM10c
federal reference method (FRM) sampler as described in Appendix O to
Part 50 using the same sample period, measurement procedures, and
requirements specified in Appendix L of Part 50. The PM10c sampler is
also being used for measurement of PM10-2.5 mass by difference and as
such, the PM10c sampler must also meet all of the performance
requirements specified for PM2.5 in Appendix L. The concentration of Pb
in the atmosphere is determined in the total volume of air sampled and
expressed in micrograms per cubic meter (µg/m3) at local temperature
and pressure conditions. 

1.3 The FRM will serve as the basis for approving Federal Equivalent
Methods (FEMs) as specified in 40 CFR Part 53 (Reference and Equivalent
Methods).  This FRM specifically applies to the analysis of Pb in PM10
filters collected with the PM10c sampler. If these filters are analyzed
for elements other than Pb, then refer to the guidance provided in the
EPA Inorganic Compendium Method IO-3.3 (Reference 1 of section 8) for
multi-element analysis.

1.4 The PM10c air sampler draws ambient air at a constant volumetric
flow rate into a specially shaped inlet and through an inertial particle
size separator, where the suspended particulate matter in the PM10 size
range is separated for collection on a PTFE filter over the specified
sampling period. The Pb content of the PM10 sample is analyzed by
energy-dispersive X-ray fluorescence spectrometry (EDXRF).
Energy-dispersive X-ray fluorescence spectrometry provides a means for
identification of an element by measurement of its characteristic X-ray
emission energy. The method allows for quantification of the element by
measuring the intensity of X-rays emitted at the characteristic photon
energy and then relating this intensity to the elemental concentration.
The number or intensity of X-rays produced at a given energy provides a
measure of the amount of the element present by comparisons with
calibration standards. The X-rays are detected and the spectral signals
are acquired and processed with a personal computer. EDXRF is commonly
used as a non-destructive method for quantifying trace elements in PM. A
detailed explanation of quantitative X-ray spectrometry is described in
references 2, 3 and 4.

1.5 Quality assurance (QA) procedures for the collection of monitoring
data are contained in Part 58, Appendix A.

2. PM10 Pb Measurement Range and Detection Limit. The values given below
in section 2.1 and 2.2 are typical of the method capabilities. Absolute
values will vary for individual situations depending on the instrument,
detector age, and operating conditions used. Data are typically reported
in ng/m3 for ambient air samples; however, for this reference method,
data will be reported in µg/m3 at local temperature and pressure
conditions.

2.1 EDXRF Pb Measurement Range. The typical ambient air measurement
range is 0.001 to 30 µg Pb/m3, assuming an upper range calibration
standard of about 60 µg Pb per square centimeter (cm2), a filter
deposit area of 11.86 cm2, and an air volume of 24 m3. The top range of
the EDXRF instrument is much greater than what is stated here. The top
measurement range of quantification is defined by the level of the high
concentration calibration standard used and can be increased to expand
the measurement range as needed. 

2.2  Detection Limit (DL). A typical estimate of the one-sigma detection
limit (DL) is about 2 ng Pb/cm2 or 0.001 µg Pb/m3, assuming a filter
size of 46.2 mm (filter deposit area of 11.86 cm2) and a sample air
volume of 24 m3. The DL is an estimate of the lowest amount of Pb that
can be reliably distinguished from a blank filter. The one-sigma
detection limit for Pb is calculated as the average overall uncertainty
or propagated error for Pb, determined from measurements on a series of
blank filters from the filter lot(s) in use. Detection limits must be
determined for each filter lot in use. If a new filter lot is used, then
a new DL must be determined. The sources of random error which are
considered are calibration uncertainty; system stability; peak and
background counting statistics; uncertainty in attenuation corrections;
and uncertainty in peak overlap corrections, but the dominating source
by far is peak and background counting statistics. At a minimum,
laboratories are to determine annual estimates of the DL using the
guidance provided in Reference 5. 

3. Factors Affecting Bias and Precision of Lead Determination by EDXRF

3.1 Filter Deposit. X-ray spectra are subject to distortion if unusually
heavy deposits are analyzed. This is the result of internal absorption
of both primary and secondary X-rays within the sample; however, this is
not an issue for Pb due to the energetic X-rays used to fluoresce Pb and
the energetic characteristic X-rays emitted by Pb. The optimum mass
filter loading for multi-elemental EDXRF analyis is about 100 µg/cm2 or
1.2 mg/filter for a 46.2-mm filter. Too little deposit material can also
be problematic due to low counting statistics and signal noise. The
particle mass deposit should minimally be 15 µg/cm2. The maximum PM10
filter loading or upper concentration limit of mass expected to be
collected by the PM10c sampler is 200 µg/m3 (Appendix O to Part 50,
Section 3.2). This equates to a mass loading of about 400µg/cm2 and is
the maximum expected loading for PM10c filters. This maximum loading is
acceptable for the analysis of Pb and other high-Z elements with very
energetic characteristic X-rays. A properly collected sample will have a
uniform deposit over the entire collection area. Samples with physical
deformities (including a visually non-uniform deposit area) should not
be quantitatively analyzed. Tests on the uniformity of particle
deposition on PM10C filters showed that the non-uniformity of the filter
deposit represents a small fraction of the overall uncertainty in
ambient Pb concentration measurement. The analysis beam of the XRF
analyzer does not cover the entire filter collection area. The minimum
allowable beam size is 10 mm.

α line exclusively to quantify the Pb concentration. This is because
the Pb Lα line and the As Kα lines severely overlap. The use of
multiple Pb lines, including the Lβ and/or the Lγ lines for
quantification must be used to reduce the uncertainty in the Pb
determination in the presence of As. There can be instances when lines
partially overlap the Pb spectral lines, but with the energy resolution
of most detectors these overlaps are typically de-convoluted using
standard spectral de-convolution software provided by the instrument
vendor.  An EDXRF protocol for Pb must define which Pb lines are used
for quantification and where spectral overlaps occur.  A de-convolution
protocol must be used to separate all the lines which overlap with Pb.

3.3 Particle Size Effects and Attenuation Correction Factors. X-ray
attenuation is dependent on the X-ray energy, mass sample loading,
composition, and particle size. In some cases, the excitation and
fluorescent X-rays are attenuated as they pass through the sample. In
order to relate the measured intensity of the X-rays to the thin-film
calibration standards used, the magnitude of the any attenuation present
must be corrected for. See references 6, 7, and 8 for more discussion on
this issue. Essentially no attenuation corrections are necessary for Pb
in PM10: both the incoming excitation X-rays used for analyzing lead and
the fluoresced Pb X-rays are sufficiently energetic that for particles
in this size range and for normal filter loadings, the Pb X-ray yield is
not significantly impacted by attenuation. 

4. Precision 

4.1 Measurement system precision is assessed according to the procedures
set forth in Appendix A to part 58. Measurement method precision is
assessed from collocated sampling and analysis. The goal for acceptable
measurement uncertainty, as precision, is defined as an upper 90 percent
confidence limit for the coefficient of variation (CV) of 20 percent.

5. Bias

5.1 Measurement system bias for monitoring data is assessed according to
the procedures set forth in Appendix A of part 58. The bias is assessed
through an audit using spiked filters. The goal for measurement bias is
defined as an upper 95 percent confidence limit for the absolute bias of
15 percent. 

6. Measurement of PTFE Filters by EDXRF 

6.1 Sampling 

6.1.1 Low-Volume PM10c Sampler. The low-volume PM10c sampler shall be
used for PM10 sample collection and operated in accordance with the
performance specifications described in Part 50, Appendix L.

6.1.2 PTFE Filters and Filter Acceptance Testing. The PTFE filters used
for PM10c sample collection shall meet the specifications provided in
Part 50, Appendix L. The following requirements are similar to those
currently specified for the acceptance of PM2.5 filters that are tested
for trace elements by EDXRF. For large filter lots (greater than 500
filters) randomly select 20 filters from a given lot. For small lots
(less than 500 filters) a lesser number of filters may be taken. Analyze
each blank filter separately and calculate the average lead
concentration in ng/cm2. Ninety percent, or 18 of the 20 filters, must
have an average lead concentration that is less than 4.8 ng Pb/cm2. 

6.1.2.1 Filter Blanks. Field blank filters shall be collected along with
routine samples. Field blank filters will be collected that are
transported to the sampling site and placed in the sampler for the
duration of sampling without sampling.  Laboratory blank filters from
each filter lot used shall be analyzed with each batch of routine sample
filters analyzed. Laboratory blank filters are used in background
subtraction as discussed below in Section 6.2.4.

6.2 Analysis. The four main categories of random and systematic error
encountered in X-ray fluorescence analysis include errors from sample
collection, the X-ray source, the counting process, and inter-element
effects. These errors are addressed through the calibration process and
mathematical corrections in the instrument software. Spectral processing
methods are well established and most commercial analyzers have software
that can implement the most common approaches (references 9-11) to
background subtraction, peak overlap correction, counting and deadtime
corrections. 

6.2.1 EDXRF Analysis Instrument. An energy-dispersive XRF system is
used. Energy-dispersive XRF systems are available from a number of
commercial vendors. Examples include Thermo (www.thermo.com), Spectro ( 
HYPERLINK "http://www.spectro.com"  www.spectro.com ), Xenemetrix ( 
HYPERLINK "http://www.xenemetrix.com"  www.xenemetrix.com ) and
PANalytical (www.panalytical.com). The analysis is performed at room
temperature in either vacuum or in a helium atmosphere. The specific
details of the corrections and calibration algorithms are typically
included in commercial analytical instrument software routines for
automated spectral acquisition and processing and vary by manufacturer.
It is important for the analyst to understand the correction procedures
and algorithms of the particular system used, to ensure that the
necessary corrections are applied. 

6.2.2 Thin film standards. Thin film standards are used for calibration
because they most closely resemble the layer of particles on a filter.
Thin films standards are typically deposited on Nuclepore substrates.
The preparation of thin film standards is discussed in reference 8, and
10. The NIST SRM 2783 (Air Particulate on Filter Media) is currently
available on polycarbonate filters and contains a certified
concentration for Pb. Thin film standards at 15 and 50 µg/cm2 are
commercially available from MicroMatter Inc. (Arlington, WA).

6.2.3 Filter Preparation. Filters used for sample collection are 46.2-mm
PTFE filters with a pore size of 2 microns and filter deposit area 11.86
cm2. Cold storage is not a requirement for filters analyzed for Pb;
however, if filters scheduled for XRF analysis were stored cold, they
must be allowed to reach room temperature prior to analysis. All filter
samples received for analysis are checked for any holes, tears, or a
non-uniform deposit which would prevent quantitative analysis. Samples
with physical deformities are not quantitatively analyzable. The filters
are carefully removed with tweezers from the Petri dish and securely
placed into the instrument-specific sampler holder for analysis. Care
must be taken to protect filters from contamination prior to analysis.
Filters must be kept covered when not being analyzed. No other
preparation of filter samples is required. 

6.2.4 Calibration. In general, calibration determines each element’s
sensitivity, i.e., its response in x-ray counts/sec to each µg/cm2 of a
standard and an interference coefficient for each element that causes
interference with another one (See section 3.2 above).  The sensitivity
can be determined by a linear plot of count rate versus concentration
(µg/cm2) in which the slope is the instrument’s sensitivity for that
element. A more precise way, which requires fewer standards, is to fit
sensitivity versus atomic number. Calibration is a complex task in the
operation of an XRF system. Two major functions accomplished by
calibration are the production of reference spectra which are used for
fitting and the determination of the elemental sensitivities. Included
in the reference spectra (referred to as “shapes”) are
background-subtracted peak shapes of the elements to be analyzed (as
well as interfering elements) and spectral backgrounds. Pure element
thin film standards are used for the element peak shapes and clean
filter blanks from the same lot as routine filter samples are used for
the background. The analysis of Pb in PM filter deposits is based on the
assumption that the thickness of the deposit is small with respect to
the characteristic Pb X-ray transmission thickness. Therefore, the
concentration of Pb in a sample is determined by first calibrating the
spectrometer with thin film standards to determine the sensitivity
factor for Pb and then analyzing the unknown samples under identical
excitation conditions as used to determine the calibration. Calibration
shall be performed annually or when significant repairs or changes occur
(e.g., a change in fluorescers, X-ray tubes, or detector). Calibration
establishes the elemental sensitivity factors and the magnitude of
interference or overlap coefficients. See reference 7 for more detailed
discussion of calibration and analysis of shapes standards for
background correction, coarse particle absorption corrections, and
spectral overlap. 

6.2.4.1 Spectral Peak Fitting. The EPA uses a library of pure element
peak shapes (shape standards) to extract the elemental background-free
peak areas from an unknown spectrum. It is also possible to fit spectra
using peak stripping or analytically defined functions such as modified
Gaussian functions. The EPA shape standards are generated from pure,
mono-elemental thin film standards. The shape standards are acquired for
sufficiently long times to provide a large number of counts in the peaks
of interest. It is not necessary for the concentration of the standard
to be known. A slight contaminant in the region of interest in a shape
standard can have a significant and serious effect on the ability of the
least squares fitting algorithm to fit the shapes to the unknown
spectrum. It is these elemental peak shapes that are fitted to the peaks
in an unknown sample during spectral processing by the analyzer. In
addition to this library of elemental shapes there is also a background
shape spectrum for the filter type used as discussed below in section
6.2.4.2 of this section. 

6.2.4.2 Background Measurement and Correction.  A background spectrum
generated by the filter itself must be subtracted from the X-ray
spectrum prior to extracting peak areas. Background spectra must be
obtained for each filter lot used for sample collection. The background
shape standards which are used for background fitting are created at the
time of calibration. If a new lot of filters is used, new background
spectra must be obtained. A minimum of 20 clean blank filters from each
filter lot are kept in a sealed container and are used exclusively for
background measurement and correction. The spectra acquired on
individual blank filters are added together to produce a single spectrum
for each of the secondary targets or fluorescers used in the analysis of
lead. Individual blank filter spectra which show atypical contamination
are excluded from the summed spectra. The summed spectra are fitted to
the appropriate background during spectral processing. Background
correction is automatically included during spectral processing of each
sample. 

7. Calculation.  

7.1 PM10 Pb concentrations. The PM10 Pb concentration in the atmosphere
(µg/m3) is calculated using the following equation:

  		

where,

		MPb is the mass per unit volume for lead in µg/m3;

	CPb is the mass per unit area for lead in µg/cm2 as measured by XRF;

		A is the filter deposit area in cm2;

	VLC is the total volume of air sampled by the PM10c sampler in actual
volume units measured at local conditions of temperature and pressure,
as provided by the sampler in m3. 

7.2 PM10 Pb Uncertainty Calculations.    

The principal contributors to total uncertainty of XRF values include:
field sampling; filter deposit area; XRF calibration; attenuation or
loss of the x-ray signals due to the other components of the particulate
sample; and determination of the Pb X-ray emission peak area by curve
fitting. See reference 12 for a detailed discussion of how uncertainties
are similarly calculated for the PM2.5 Chemical Speciation program. 

The model for calculating total uncertainty is:

δtot = (δf 2 + δa 2 + δc 2 + δv 2) ½

Where,

δf = fitting uncertainty (XRF-specific, from ~2 to 100+%)

δa = attenuation uncertainty (XRF-specific, insignificant for Pb) 

δc = calibration uncertainty (combined lab uncertainty, assumed as 5%)

δv = volume/deposition size uncertainty (combined field uncertainty,
assumed as 5%)

8. References 

1. Inorganic Compendium Method IO-3.3; Determination of Metals in
Ambient Particulate Matter Using X-Ray Fluorescence (XRF) Spectroscopy;
U.S. Environmental Protection Agency, Cincinnati, OH 45268.
EPA/625/R-96/010a. June 1999.

2. Jenkins, R., Gould, R.W., and Gedcke, D. Quantitative X-ray
Spectrometry: Second Edition. Marcel Dekker, Inc., New York, NY. 1995. 

3. Jenkins, R. X-Ray Fluorescence Spectrometry: Second Edition in
Chemical Analysis, a Series of Monographs on Analytical Chemistry and
Its Applications, Volume 152. Editor J.D.Winefordner; John Wiley & Sons,
Inc. New York, NY. 1999. 

4. Dzubay, T.G. X-ray Fluorescence Analysis of Environmental Samples,
Ann Arbor Science Publishers Inc., 1977.

5. Code of Federal Regulations (CFR) 40, Part 136, Appendix B;
Definition and Procedure for the Determination of the Method Detection
Limit – Revision 1.1.

6. Drane, E.A, Rickel, D.G., and Courtney, W.J., “Computer Code for
Analysis X-Ray Fluorescence Spectra of Airborne Particulate Matter,”
in Advances in X-Ray Analysis, J.R. Rhodes, Ed., Plenum Publishing
Corporation, New York, NY, p. 23 (1980).

7. Analysis of Energy-Dispersive X-ray Spectra of ambient Aerosols with
Shapes Optimization, Guidance Document; TR-WDE-06-02; prepared under
contract EP-D-05-065 for the U.S. Environmental Protection Agency,
National Exposure Research Laboratory. March 2006.

8. Billiet, J., Dams, R., and Hoste, J. (1980) Multielement Thin Film
Standards for XRF Analysis, X-Ray Spectrometry, 9(4): 206-211.

9. Bonner, N.A.; Bazan, F.; and Camp, D.C. (1973). Elemental analysis of
air filter samples using x-ray fluorescence. Report No. UCRL-51388.
Prepared for U.S. Atomic Energy Commission, by Univ. of Calif., Lawrence
Livermore Laboratory, Livermore, CA.

10. Dzubay, T.G.; Lamothe, P.J.; and Yoshuda, H. (1977). Polymer films
as calibration standards for X-ray fluorescence analysis. Adv. X-Ray
Anal., 20:411.

11. Giauque, R.D.; Garrett, R.B.; and Goda, L.Y. (1977). Calibration of
energy-dispersive X-ray spectrometers for analysis of thin environmental
samples. In X-Ray Fluorescence Analysis of Environmental Samples, T.G.
Dzubay, Ed. Ann Arbor Science Publishers, Ann Arbor, MI, pp. 153-181.

12. Harmonization of Interlaboratory X-ray Fluorescence Measurement
Uncertainties, Detailed Discussion Paper; August 4, 2006; prepared for
the Office of Air Quality Planning and Standards under EPA contract
68-D-03-038.
http://www.epa.gov/ttn/amtic/files/ambient/pm25/spec/xrfdet.pdf

8. Appendix R is added to read as follows:

Appendix R to Part 50 — Interpretation of the National Ambient Air
Quality Standards for Lead

1. General.

(a) This appendix explains the data handling conventions and
computations necessary for determining when the primary and secondary
national ambient air quality standards (NAAQS) for lead (Pb) specified
in §50.16 are met.  The NAAQS indicator for Pb is defined as: lead and
its compounds, measured as elemental lead in total suspended particulate
(Pb-TSP), sampled and analyzed by a Federal reference method (FRM) based
on appendix G to this part or by a Federal equivalent method (FEM)
designated in accordance with part 53 of this chapter.  Although Pb-TSP
is the lead NAAQS indicator, surrogate Pb-TSP concentrations shall also
be used for NAAQS comparisons; specifically, valid surrogate Pb-TSP data
are concentration data for lead and its compounds, measured as elemental
lead, in particles with an aerodynamic size of 10 microns or less
(Pb-PM10), sampled and analyzed by an FRM based on appendix Q to this
part or by an FEM designated in accordance with part 53 of this chapter.
Surrogate Pb-TSP data (i.e., Pb-PM10 data), however, can only be used to
show that the Pb NAAQS were violated (i.e., not met); they can not be
used to demonstrate that the Pb NAAQS were met.  Pb-PM10 data used as
surrogate Pb-TSP data shall be processed at face value, that is, without
any transformation or scaling. Data handling and computation procedures
to be used in making comparisons between reported and/or surrogate
Pb-TSP concentrations and the level of the Pb NAAQS are specified in the
following sections. 

(b) Whether to exclude, retain, or make adjustments to the data affected
by exceptional events, including natural events, is determined by the
requirements and process deadlines specified in §§50.1, 50.14, and
51.930 of this chapter.

(c) The terms used in this appendix are defined as follows:

Annual monitoring network plan refers to the plan required by section
58.10 of this chapter.

Creditable samples are samples that are given credit for data
completeness. They include valid samples collected on required sampling
days and valid “make-up” samples taken for missed or invalidated
samples on required sampling days.

Daily values for Pb refer to the 24-hour mean concentrations of Pb
(Pb-TSP or Pb-PM10), measured from midnight to midnight (local standard
time), that are used in NAAQS computations.

Design value is the site-level metric (i.e., statistic) that is compared
to the NAAQS level to determine compliance; the design value for the Pb
NAAQS is selected according to the procedures in this appendix from
among the valid three-month Pb-TSP and surrogate Pb-TSP (Pb-PM10)
arithmetic mean concentration for the 38-month period consisting of the
most recent 3-year calendar period plus two previous months (i.e., 36
3-month periods) using the last month of each 3-month period as the
period of report.

Extra samples are non-creditable samples. They are daily values that do
not occur on scheduled sampling days and that can not be used as
“make-up samples” for missed or invalidated scheduled samples. Extra
samples are used in mean calculations.   For purposes of determining
whether a sample must be treated as a make-up sample or an extra sample,
Pb-TSP and Pb-PM10 data collected before January 1, 2009 will be treated
with an assumed scheduled sampling frequency of every sixth day.

Make-up samples are samples taken to replace missed or invalidated
required scheduled samples. Make-ups can be made by either the primary
or collocated (same size fraction) instruments; to be considered a valid
make-up, the sampling must be conducted with equipment and procedures
that meet the requirements for scheduled sampling. Make-up samples are
either taken before the next required sampling day or exactly one week
after the missed (or voided) sampling day.  Make-up samples can not span
years; that is, if a scheduled sample for December is missed (or
voided), it can not be made up in January.  Make-up samples, however,
may span months, for example a missed sample on January 31 may be made
up on February 1, 2, 3, 4, 5, or 7 (with an assumed sampling frequency
of every sixth day).  Section 3(e) explains how such month-spanning
make-up samples are to be treated for purposes of data completeness and
mean calculations.  Only two make-up samples are permitted each calendar
month; these are counted according to the month in which the miss and
not the makeup occurred.  For purposes of determining whether a sample
must be treated as a make-up sample or an extra sample, Pb-TSP and
Pb-PM10 data collected before January 1, 2009 will be treated with an
assumed scheduled sampling frequency of every sixth day.

Monthly mean refers to an arithmetic mean, calculated as specified in
section 6(a) of this appendix.  Monthly means are computed at each
monitoring site separately for Pb-TSP and Pb-PM10 (i.e., by
site-parameter-year-month. 

Parameter refers either to Pb-TSP or to Pb-PM10.

Pollutant Occurrence Code (POC) refers to a numerical code (1, 2, 3,
etc.) used to distinguish the data from two or more monitors for the
same parameter at a single monitoring site.

Scheduled sampling day means a day on which sampling is scheduled based
on the required sampling frequency for the monitoring site, as provided
in section 58.12 of this chapter.

Three-month means are arithmetic averages of three consecutive monthly
means. Three-month means are computed on a rolling, overlapping basis. 
Each distinct monthly mean will be included in three different 3-month
means; for example, in a given year, a November mean would be included
in: (1) the September-October-November 3-month mean, (2) the
October-November-December 3-month mean, and (3) the
November-December-January(of the following year) 3-month mean.
Three-month means are computed separately for each parameter per section
6(a) (and are referred to as 3-month parameter means and are validated
according to the criteria specified in section 4(c).  The
parameter-specific 3-month means are then prioritized according to
section 2(a) to determine a single 3-month site mean. 

Year refers to a calendar year.

2.  Use of Pb-PM10 Data as Surrogate Pb-TSP Data.

(a)  As stipulated in section 2.10 of Appendix C to 40 CFR part 58, at
some mandatory Pb monitoring locations, monitoring agencies are required
to sample for Pb as Pb-TSP, and at other mandatory Pb monitoring sites,
monitoring agencies are permitted to monitor for Pb-PM10 in lieu of
Pb-TSP.  In either situation, valid collocated Pb data for the other
parameter may be produced.  Additionally, there may be non-required
monitoring locations that also produce valid Pb-TSP and/or valid Pb-PM10
data.   Pb-TSP data and Pb-PM10 data are always processed separately
when computing monthly and 3-month parameter means; monthly and 3-month
parameter means are validated according to the criteria stated in
section 4 of this appendix.  Three-month “site” means, which are the
final valid 3-months means from which a design value is identified, are
determined from the one or two available valid 3-month parameter means
according to the following prioritization which applies to all Pb
monitoring locations.

(i)  Whenever a valid 3-month Pb-PM10 mean shows a violation and either
is greater than a corresponding (collocated) 3-month Pb-TSP mean or
there is no corresponding valid 3-month Pb-TSP mean present, then that
3-month Pb-PM10 mean will be the site-level mean for that (site’s)
3-month period.

(ii) Otherwise (i.e., there is no valid violating 3-month Pb-PM10 that
exceeds a corresponding 3-month Pb-TSP mean),

(A) if a valid 3-month Pb-TSP mean exists, then it will be the
site-level mean for that (site’s) 3-month period, or

(B) if a valid 3-month Pb-TSP mean does not exist, then there is no
valid 3-month site mean for that period (even if a valid non-violating
3-month Pb-PM10 mean exists). 

 (b) As noted in section 1(a) of this appendix, FRM/FEM Pb-PM10 data
will be processed at face value (i.e., at reported concentrations)
without adjustment when computing means and making NAAQS comparisons.

3.  Requirements for Data Used for Comparisons with the Pb NAAQS and
Data Reporting Considerations.

(a) 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 the requirements of part 58 of this chapter including
appendices A, C, and E shall be used in design value calculations. 
Pb-TSP and Pb-PM10 data representing sample collection periods prior to
January 1, 2009 (i.e., “pre-rule” data) will also be considered
valid for NAAQS comparisons and related attainment/nonattainment
determinations if the sampling and analysis methods that were utilized
to collect that data were consistent with previous or newly designated
FRMs or FEMs and with either the provisions of part 58 of this chapter
including appendices A, C, and E 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.

(b) Pb-TSP and Pb-PM10 measurement data are reported to AQS in units of
micrograms per cubic meter (µg/m3) at local conditions (local
temperature and pressure, LC) to three decimal places; any additional
digits to the right of the third decimal place are truncated.  Pre-rule
Pb-TSP and Pb-PM10 concentration data that were reported in standard
conditions (standard temperature and standard pressure, STP) will not
require a conversion to local conditions but rather, after truncating to
three decimal places and processing as stated in this appendix, shall be
compared “as is” to the NAAQS (i.e., the LC to STP conversion factor
will be assumed to be one).  However, if the monitoring agency has
retroactively resubmitted Pb-TSP or Pb-PM10 pre-rule data converted from
STP to LC based on suitable meteorological data, only the LC data will
be used. 

(c) At each monitoring location (site), Pb-TSP and Pb-PM10 data are to
be processed separately when selecting daily data by day (as specified
in section 3(d) of this appendix),  when aggregating daily data by month
(per section 6(a)), and when forming 3-month means (per section 6(b)). 
However, when deriving (i.e., identifying) the design value for the
38-month period, 3-month means for the two data types may be considered
together; see sections 2(a) and 4(e) of this appendix for details.  

(d) Daily values for sites will be selected for a site on a size cut
(Pb-TSP or Pb-PM10, i.e., “parameter”) basis; Pb-TSP concentrations
and Pb-PM10 concentrations shall not be commingled in these
determinations.  Site level, parameter-specific daily values will be
selected as follows:

(i) The starting dataset for a site-parameter shall consist of the
measured daily concentrations recorded from the designated primary
FRM/FEM monitor for that parameter. The primary monitor for each
parameter shall be designated in the appropriate state or local agency
annual Monitoring Network Plan. If no primary monitor is designated, the
Administrator will select which monitor to treat as primary.  All daily
values produced by the primary sampler are considered part of the
site-parameter data record (i.e., that site-parameter’s set of daily
values); this includes all creditable samples and all extra samples. 
For pre-rule Pb-TSP and Pb-PM10 data, valid data records present in AQS
for the monitor with the lowest occurring Pollutant Occurrence Code
(POC), as selected on a site-parameter-daily basis, will constitute the
site-parameter data record.  Where pre-rule Pb-TSP data (or subsequent
non-required Pb-TSP or Pb-PM10 data) are reported in “composite”
form (i.e., multiple filters for a month of sampling that are analyzed
together), the composite concentration will be used as the
site-parameter monthly mean concentration if there are no valid daily
Pb-TSP data reported for that month with a lower POC. 

(ii) Data for the primary monitor for each parameter shall be augmented
as much as possible with data from collocated (same parameter) FRM/FEM
monitors. If a valid 24-hour measurement is not produced from the
primary monitor for a particular day (scheduled or otherwise), but a
valid sample is generated by a collocated (same parameter) FRM/FEM
instrument, then that collocated value shall be considered part of the
site-parameter data record (i.e., that site-parameter’s monthly set of
daily values). If more than one valid collocated FRM/FEM value is
available, the mean of those valid collocated values shall be used as
the daily value.  Note that this step will not be necessary for pre-rule
data given the daily identification presumption for the primary monitor.

(e) All daily values in the composite site-parameter record are used in
monthly mean calculations. However, not all daily values are given
credit towards data completeness requirements. Only “creditable”
samples are given credit for data completeness. Creditable samples
include valid samples on scheduled sampling days and valid make-up
samples. All other types of daily values are referred to as “extra”
samples.  Make-up samples taken in the (first week of the) month after
the one in which the miss/void occurred will be credited for data
capture in the month of the miss/void but will be included in the month
actually taken when computing monthly means.  For example, if a make-up
sample was taken in February to replace a missed sample scheduled for
January, the make-up concentration would be included in the February
monthly mean but the sample credited in the January data capture rate. 

4.  Comparisons with the Pb NAAQS.

(a) The Pb NAAQS is met at a monitoring site when the identified design
value is valid and less than or equal to 0.15 micrograms per cubic meter
(µg/m3).  A Pb design value that meets the NAAQS (i.e., 0.15 µg/m3 or
less), is considered valid if it encompasses 36 consecutive valid
3-month site means (specifically for a 3-year calendar period and the
two previous months)   For sites that begin monitoring Pb after this
rule is effective but before January 15, 2010 (or January 15, 2011), a
2010-2012 (or 2011-2013) Pb design value that meets the NAAQS will be
considered valid if it encompasses at least 34 consecutive valid 3-month
means (specifically encompassing only the 3-year calendar period).  See
4(c) of this appendix for the description of a valid 3-month mean and
section 6(d) for the definition of the design value.   

(b) The Pb NAAQS is violated at a monitoring site when the identified
design value is valid and is greater than 0.15 µg/m3, no matter whether
determined from Pb-TSP or Pb-PM10 data. A Pb design value greater than
0.15 µg/m3 is valid no matter how many valid 3-month means in the
3-year period it encompasses; that is, a violating design value is valid
even if it (i.e., the highest 3-month mean) is the only valid 3-month
mean in the 3-year timeframe.  Further, a site does not have to monitor
for three full calendar years in order to have a valid violating design
value; a site could monitor just three months and still produce a valid
(violating) design value.

(c) (i) A 3-month parameter mean is considered valid (i.e., meets data
completeness requirements) if the average of the data capture rate of
the three constituent monthly means (i.e., the 3-month data capture
rate) is greater than or equal to 75 percent. Monthly data capture rates
(expressed as a percentage) are specifically calculated as the number of
creditable samples for the month (including any make-up samples taken
the subsequent month for missed samples in the month in question, and
excluding any make-up samples taken in the month in question for missed
samples in the previous month) divided by the number of scheduled
samples for the month, the result then multiplied by 100 but not
rounded.  The 3-month data capture rate is the sum of the three
corresponding unrounded monthly data capture rates divided by three and
the result rounded to the nearest integer (zero decimal places).  As
noted in section 3(c), Pb-TSP and Pb-PM10 daily values are processed
separately when calculating monthly means and data capture rates; a
Pb-TSP value cannot be used as a make-up for a missing Pb-PM10 value or
vice versa.  For purposes of assessing data capture, Pb-TSP and Pb-PM10
data collected before January 1, 2009 will be treated with an assumed
scheduled sampling frequency of every sixth day.  

(ii) A 3-month parameter mean that does not have at least 75 percent
data capture and thus is not considered valid under 4(c)(i) shall be
considered valid (and complete) if it passes either of the two following
“data substitution” tests, one such test for validating an above
NAAQS-level (i.e., violating) 3-month Pb-TSP or Pb-PM10 mean (using
actual “low” reported values from the same site at about the same
time of the year (i.e.,  in the same month) looking across three or four
years), and the second test for validating a below-NAAQS level 3-month
Pb-TSP mean (using actual “high” values reported for the same site
at about the same time of the year (i.e., in the same month) looking
across three or four years). Note that both tests are merely diagnostic
in nature intending to confirm that there is a very high likelihood if
not certainty that the original mean (the one with less than 75% data
capture) reflects the true over / under NAAQS-level status for that
3-month period; the result of one of these data substitution tests
(i.e., a “test mean”, as defined in section 4(c)(ii)(A) or
4(c)(ii)(B)) is not considered the actual 3-month parameter mean and
shall not be used in the determination of design values.  For both types
of data substitution, substitution is permitted only if there are
available data points from which to identify the high or low 3-year
month-specific values, specifically if there are at least 10 data points
total from at least two of the three (or four for November and December)
possible year-months. Data substitution may only use data of the same
parameter type.   

(A) The “above NAAQS level” test is as follows: Data substitution
will be done in  each month of the 3-month period that has less than 75
percent data capture; monthly capture rates are temporarily rounded to
integers (zero decimals) for this evaluation.  If by substituting the
lowest reported daily value for that month (year non-specific; e.g., for
January) over the 38-month design value period in question for missing
scheduled data in the deficient months (substituting only enough to meet
the 75 percent data capture minimum), the computation yields a
recalculated test 3-month parameter mean concentration above the level
of the standard, then the 3-month period is deemed to have passed the
diagnostic test and the level of the standard is deemed to have been
exceeded in that 3-month period.  As noted in section 4(c)(ii), in such
a case, the 3-month parameter mean of the data actually reported, not
the recalculated (“test”) result including the low values, shall be
used to determine the design value.  

(B) The “below NAAQS level” test is as follows: Data substitution
will be performed for each month of the 3-month period that has less
than 75 percent but at least 50 percent data capture; if any month has
less than 50% data capture then the 3-month mean can not utilize this
substitution test.  Also, incomplete 3-month Pb-PM10 means can not
utilize this test.  A 3-month Pb-TSP mean with less than 75% data
capture shall still be considered valid (and complete) if, by
substituting the highest reported daily value, month-specific, over the
3-year design value period in question, for all missing scheduled data
in the deficient months (i.e., bringing the data capture rate up to
100%), the computation yields a recalculated 3-month parameter mean
concentration equal or less than the level of the standard (0.15
µg/m3), then the 3-month mean is deemed to have passed the diagnostic
test and the level of the standard is deemed not to have been exceeded
in that 3-month period (for that parameter).  As noted in section
4(c)(ii), in such a case, the 3-month parameter mean of the data
actually reported, not the recalculated (“test”) result including
the high values, shall be used to determine the design value.

(d)  Months that do not meet the completeness criteria stated in 4(c)(i)
or 4(c)(ii), and design values that do not meet the completeness
criteria stated in 4(a) or 4(b), may also be considered valid (and
complete) with the approval of, or at the initiative of, the
Administrator, who may consider factors such as monitoring site
closures/moves, monitoring diligence, the consistency and levels of the
valid concentration measurements that are available, and nearby
concentrations in determining whether to use such data.  

(e) The site-level design value for a 38-month period (three calendar
years plus two previous months) is identified from the available
(between one and 36) valid 3-month site means.  In a situation where
there are valid 3-month means for both parameters (Pb-TSP and Pb-PM10),
the mean originating from the reported Pb-TSP data will be the one
deemed the site-level monthly mean and used in design value
identifications unless the Pb-PM10 mean shows a violation of the NAAQS
and exceeds the Pb-TSP mean; see section 2(a) for details.  A monitoring
site will have only one site-level 3-month mean per 3-month period;
however, the set of site-level 3-month means considered for design value
identification (i.e., one to 36 site-level 3-month means) can be a
combination of Pb-TSP and Pb-PM10 data.

(f) The procedures for calculating monthly means and 3-month means, and
identifying Pb design values are given in section 6 of this appendix.

5. Rounding Conventions.

(a) Monthly means and monthly data capture rates are not rounded.

(b) Three-month means shall be rounded to the nearest hundredth µg/m3
(0.xx). Decimals 0.xx5 and greater are rounded up, and any decimal lower
than 0.xx5 is rounded down.  E.g., a 3-month mean of 0.104925 rounds to
0.10 and a 3-month mean of .10500 rounds to 0.11.   Three-month data
capture rates, expressed as a percent, are round to zero decimal places.

(c) Because a Pb design value is simply a (highest) 3-month mean and
because the NAAQS level is stated to two decimal places, no additional
rounding beyond what is specified for 3-month means is required before a
design value is compared to the NAAQS.  

6.   Procedures and Equations for the Pb NAAQS.

(a)(i) A monthly mean value for Pb-TSP (or Pb-PM10) is determined by
averaging the daily values of a calendar month using equation 1 of this
appendix, unless the Administrator chooses to exercise his discretion to
use the alternate approach described in 6(a)(ii).  

Equation 1

Where:

 Xm,y,s	=	the mean for month m of the year y for site s; and

nm	=	the number of daily values in the month (creditable plus extra
samples); and

Xi,m,y,s	=	The ith value in month m for year y for site s.

(a)(ii) The Administrator may at his discretion use the following
alternate approach to calculating the monthly mean concentration if the
number of extra sampling days during a month is greater than the number
of successfully completed scheduled and make-up sample days in that
month.  In exercising his discretion, the Administrator will consider
whether the approach specified in 6(a)(i) might in the Administrator’s
judgment result in an unrepresentative value for the monthly mean
concentration.  This provision is to protect the integrity of the
monthly and 3-month mean concentration values in situations in which, by
intention or otherwise, extra sampling days are concentrated in a period
during which ambient concentrations are particularly high or low.  The
alternate approach is to average all extra and make-up samples (in the
given month) taken after each scheduled sampling day (“Day X”) and
before the next scheduled sampling day (e.g., “Day X+6”, in the case
of one-in-six sampling) with the sample taken on Day X (assuming valid
data was obtained on the scheduled sampling day), and then averaging
these averages to calculate the monthly mean.  This approach has the
effect of giving approximately equal weight to periods during a month
that have equal number of days, regardless of how many samples were
actually obtained during the periods, thus mitigating the potential for
the monthly mean to be distorted.  The first day of scheduled sampling
typically will not fall on the first day of the calendar month, and
there may be make-up and/or extra samples (in that same calendar month)
preceding the first scheduled day of the month.  These samples will not
be shifted into the previous month’s mean concentration, but rather
will stay associated with their actual calendar month as follows.  Any
extra and make-up samples taken in a month before the first scheduled
sampling day of the month will be associated with and averaged with the
last scheduled sampling day of that same month.

(b) Three-month parameter means are determined by averaging three
consecutive monthly means of the same parameter using Equation 2 of this
appendix.

Equation 2

Where:

  EQ X\d\ba8()\s\up8(–)  m1, m2, m3; s	=	the 3-month parameter mean
for months m1, m2, and m3 for site s; and

nm	=	the number of monthly means available to be averaged (typically 3,
sometimes 1 or 2 if one or two months have no valid daily values); and

X m, y:z, s	=	The mean for month m of the year y (or z) for site s.

(c) Three-month site means are determined from available 3-month
parameter means according to the hierarchy established in 2(a) of this
appendix. 

(d) The site-level Pb design value is the highest valid 3-month
site-level mean over the most recent 38-month period (i.e., the most
recent 3-year calendar period plus two previous months).  Section 4(a)
of this appendix explains when the identified design value is itself
considered valid for purposes of determining that the NAAQS is met or
violated at a site.

PART 51-REQUIREMENTS FOR PREPARATION, ADOPTION, AND, SUBMITTAL OF
IMPLEMENTATION PLANS

9  The authority citation for part 51 continues to read as follows:

Authority:  23 U.S.C. 101; 42 U.S.C. 7401-7671q

10.  Section 51.117 is amended by revising paragraph (e)(1) to read as
follows:

§ 51.117 Additional provisions for lead.

*****

(e) *****

(1) The point source inventory on which the summary of the baseline for
lead emissions inventory is based must contain all sources that emit 0.5
or more tons of lead per year.

*****

PART 53--AMBIENT AIR MONITORING REFERENCE AND EQUIVALENT METHODS

11.  The authority citation for part 53 continues to read as follows:

Authority:   Sec. 301(a) of the Clean Air Act (42 U.S.C. sec. 1857g(a)),
as amended by sec. 15(c)(2) of Pub. L. 91–604, 84 Stat. 1713, unless
otherwise noted.

Subpart C-[AMENDED]

12.  Section 53.33 is revised to read as follows:	

§53.33  Test Procedure for Methods for Lead (Pb).

(a) General. The reference method for Pb in TSP includes two parts, the
reference method for high-volume sampling of TSP as specified in 40 CFR
50, Appendix B and the analysis method for Pb in TSP as specified in 40
CFR 50, Appendix G. Correspondingly, the reference method for Pb in PM10
includes the reference method for low-volume sampling of PM10 in 40 CFR
50, Appendix O and the analysis method of Pb in PM10 as specified in 40
CFR 50, Appendix Q. This section explains the procedures for
demonstrating the equivalence of either a candidate method for Pb in TSP
to the high-volume reference methods, or a candidate method for Pb in
PM10 to the low-volume reference methods. 

(1) Pb in TSP- A candidate method for Pb in TSP specifies reporting of
Pb concentrations in terms of standard temperature and pressure.
Comparisons of candidate methods to the reference method in 40 CFR 50,
Appendix G must be made in a consistent manner with regard to
temperature and pressure.

(2) Pb in PM10 -  A candidate method for Pb in PM10 must specify
reporting of Pb concentrations in terms of local conditions of
temperature and pressure, which will be compared to similarly reported
concentrations from the reference method in 40 CFR 50 Appendix Q.  

(b) Comparability. Comparability is shown for Pb methods when the
differences between:

(1) Measurements made by a candidate method, and 

(2) Measurements made by the reference method on simultaneously
collected Pb samples (or the same sample, if applicable), are less than
or equal to the values specified in table C–3 of this subpart.

(c) Test measurements. Test measurements may be made at any number of
test sites.  Augmentation of pollutant concentrations is not permitted,
hence an appropriate test site or sites must be selected to provide Pb
concentrations in the specified range.

(d) Collocated samplers. The ambient air intake points of all the
candidate and reference method collocated samplers shall be positioned
at the same height above the ground level, and between 2 meters (1 meter
for samplers with flow rates less than 200 liters per minute (L/min))
and 4 meters apart. The samplers shall be oriented in a manner that will
minimize spatial and wind directional effects on sample collection. 

 	(e) Sample collection. Collect simultaneous 24-hour samples of Pb at
the test site or sites with both the reference and candidate methods
until at least 10 sample pairs have been obtained. 

(1) A candidate method for Pb in TSP which employs a sampler and sample
collection procedure that are identical to the sampler and sample
collection procedure specified in the reference method in 40 CFR 50,
Appendix B, but uses a different analytical procedure than specified in
40 CFR Appendix G, may be tested by analyzing pairs of filter strips
taken from a single TSP reference sampler operated according to the
procedures specified by that reference method.  

(2) A candidate method for Pb in PM10 which employs a sampler and sample
collection procedure that are identical to the sampler and sample
collection procedure specified in the reference method in 40 CFR 50,
Appendix O, but uses a different analytical procedure than specified in
40 CFR Appendix Q, requires the use of two PM10 reference samplers
because a single 46.2-mm filter from a reference sampler may not be
divided prior to analysis. It is possible to analyze a 46.2-mm filter
first with the non-destructive X-ray Fluorescence (XRF) FRM and
subsequently extract the filter for other analytical techniques. If the
filter is subject to XRF with subsequent extraction for other analyses,
then a single PM10 reference sampler may be used for sample collection. 

(3) A candidate method for Pb in TSP or Pb in PM10 which employs a
direct reading (e.g., continuous or semi-continuous sampling) method
that uses the same sampling inlet and flow rate as the FRM and the same
or different analytical procedure may be tested.  The direct
measurements are then aggregated to 24-hour equivalent concentrations
for comparison with the FRM. For determining precision in section (k),
two collocated direct reading devices must be used.  

(f) Audit samples.  Three audit samples must be obtained from the
address given in § 53.4(a). For Pb in TSP collected by the high-volume
sampling method, the audit samples are ¾ x 8-inch glass fiber strips
containing known amounts of Pb in micrograms per strip (μg/strip)
equivalent to the following nominal percentages of the National Ambient
Air Quality Standard (NAAQS): 30%, 100 %, and 250%. For Pb in PM10
collected by the low-volume sampling method, the audit samples are
46.2-mm polytetrafluorethylene (PTFE) filters containing known amounts
of Pb in micrograms per filter (µg/filter) equivalent to the same
percentages of the NAAQS: 30%, 100%, and 250%. The true amount of Pb
(Tqi), in total µg/strip (for TSP) or total µg/filter (for PM10), will
be provided for each audit sample.

(g) Filter analysis.  

μg/m3 for each analysis of each filter. The analysis of replicates
should not be performed sequentially. Label these test results as C1A,
C1B, C2C, etc., where C denotes results from the candidate method. For
candidate methods which provide a direct reading or measurement of Pb
concentrations without a separable procedure, C1A=C1B=C1C, C2A=C2B=C2C,
etc. 

(h) Average Pb concentration. For the reference method, calculate the
average Pb concentration for each filter by averaging the concentrations
calculated from the three analyses as described in (g)(1) using equation
1 of this section:

Equation 1

 

Where, i is the filter number.

(i) Analytical Bias. 

(1) For the audit samples, calculate the average Pb concentration for
each strip or filter analyzed by the reference method by averaging the
concentrations calculated from the three analyses as described in (g)(1)
using equation 2 of this section:

	Equation 2

 

Where, i is audit sample number.

(2) Calculate the percent difference (Dq) between the average Pb
concentration for each audit sample and the true Pb concentration (Tq)
using equation 3 of this section:

Equation 3

 

(3) If any difference value (Dqi) exceeds ±5 percent, the bias of the
reference method analytical procedure is out-of-control. Corrective
action must be taken to determine the source of the error(s) (e.g.,
calibration standard discrepancies, extraction problems, etc.) and the
reference method and audit sample determinations must be repeated
according to paragraph (g) of this section, or the entire test procedure
(starting with paragraph (e) of this section) must be repeated.

(j) Acceptable filter pairs. Disregard all filter pairs for which the Pb
concentration, as determined in paragraph (h) of this section by the
average of the three reference method determinations, falls outside the
range of 30% to 250% of the Pb NAAQS level in µg/m3 for Pb in both TSP
and PM10. All remaining filter pairs must be subjected to the tests for
precision and comparability in paragraphs (k) and (l) of this section.
At least five filter pairs must be within the specified concentration
range for the tests to be valid.

(k) Test for precision. 

(1) Calculate the precision (P) of the analysis (in percent) for each
filter and for each method, as the maximum minus the minimum divided by
the average of the three concentration values, using equation 4 or
equation 5 of this section:

Equation 4

 

or 

	Equation 5

 

where, i indicates the filter number.

(2) If a direct reading candidate method is tested, the precision is
determined from collocated devices using equation 5 above.

 (3) If any reference method precision value (PRi) exceeds 15 percent,
the precision of the reference method analytical procedure is
out-of-control. Corrective action must be taken to determine the
source(s) of imprecision, and the reference method determinations must
be repeated according to paragraph (g) of this section, or the entire
test procedure (starting with paragraph (e) of this section) must be
repeated.

(4) If any candidate method precision value (PCi) exceeds 15 percent,
the candidate method fails the precision test.

(5) The candidate method passes this test if all precision values (i.e.,
all PRi's and all PCi's) are less than 15 percent.

(l) Test for comparability. 

(1) For each filter or analytical sample pair, calculate all nine
possible percent differences (D) between the reference and candidate
methods, using all nine possible combinations of the three
determinations (A, B, and C) for each method using equation 6 of this
section:

Equation 6

 

where, i is the filter number, and n numbers from 1 to 9 for the nine
possible difference combinations for the three determinations for each
method (j = A, B, C, candidate; k = A, B, C, reference).

(2) If none of the percent differences (D) exceeds ±20 percent, the
candidate method passes the test for comparability.

(3) If one or more of the percent differences (D) exceed ±20 percent,
the candidate method fails the test for comparability.

(4) The candidate method must pass both the precision test (paragraph
(k) of this section) and the comparability test (paragraph (l) of this
section) to qualify for designation as an equivalent method.

(m) Method Detection Limit (MDL). Calculate the estimated MDL using the
guidance provided in 40 CFR, Part 136 Appendix B. It is essential that
all sample processing steps of the analytical method be included in the
determination of the method detection limit. Take a minimum of seven
blank filters from each lot to be used and calculate the detection limit
by processing each through the entire candidate analytical method. Make
all computations according to the defined method with the final results
in µg/m3. The MDL of the candidate method must be equal to, or less
than 5% of the level of the Pb NAAQS. 

Table C–3 to Subpart C of Part 53—Test Specifications for Pb in TSP
and Pb in PM10 Methods

≤15%

Maximum difference (D) 	±20 %

Estimated Method Detection Limit (MDL), µg/m3	5 % of NAAQS level

PART 58--AMBIENT AIR QUALITY SURVEILLANCE

13.  The authority citation for part 58 continues to read as follows:

Authority:   42 U.S.C. 7403, 7410, 7601(a), 7611, and 7619.

Subpart B-[AMENDED]

14.  Section 58.10, is amended by revising paragraph subsections (a)(4)
and adding paragraph (b)(9) to read as follows:

§ 58.10   Annual monitoring network plan and periodic network
assessment.

* * * * *

	(a) * * * 

(4)  A plan for establishing Pb monitoring sites in accordance with the
requirements of appendix D to this part shall be submitted to the EPA
Regional Administrator no later than July 1, 2009 as part of the annual
network plan required in paragraph (a)(1) of this section.  The plan
shall provide for the required source-oriented Pb monitoring sites to be
operational by January 1, 2010, and for all required nonsource-oriented
Pb monitoring sites to be operational by January 1, 2011.  Specific site
locations for the sites to be operational by January 1, 2011 are not
required as part of the July 1, 2009 annual network plan, but shall be
included in the annual network plan due to be submitted to the EPA
Regional Administrator on July 1, 2010.

* * * * *

(b) * * *

(9)  The designation of any Pb monitors as either source-oriented or
non-source oriented according to Appendix D to 40 CFR part 58. 

(10)  Any source-oriented monitors for which a waiver has been requested
or granted by the EPA Regional Administrator as allowed for under
paragraph 4.5(a)(ii) of Appendix D to 40 CFR part 58.

(11)  Any source-oriented or nonsource-oriented site for which a waiver
has been requested or granted by the EPA Regional Administrator for the
use of Pb-PM10 monitoring in lieu of Pb-TSP monitoring as allowed for
under paragraph 2.10 of Appendix C to 40 CFR part 58.

* * * * * 

17.  Section 58.13 is amended by revising paragraph (b) to read as
follows:

§ 58.13   Monitoring network completion.

* * * * *

(b) Not withstanding specific dates included in this part, beginning
January 1, 2008, when existing networks are not in conformance with the
minimum number of required monitors specified in this part, additional
required monitors must be identified in the next applicable annual
monitoring network plan, with monitoring operation beginning by January
1 of the following year.  To allow sufficient time to prepare and
comment on Annual Monitoring Network Plans, only monitoring requirements
effective 120 days prior to the required submission date of the plan
(i.e., 120 days prior to July 1 of each year) shall be included in that
year’s annual monitoring network plan.

18.  Section 58.16 is amended by revising paragraph (a) to read as
follows:

§ 58.16   Data submittal and archiving requirements.

(a) The State, or where appropriate, local agency, shall report to the
Administrator, via AQS all ambient air quality data and associated
quality assurance data for SO2; CO; O3; NO2; NO; NOY; NOX; Pb-TSP mass
concentration; Pb-PM10 mass concentration; PM10 mass concentration;
PM2.5 mass concentration; for filter-based PM2.5 FRM/FEM the field blank
mass, sampler-generated average daily temperature, and sampler-generated
average daily pressure; chemically speciated PM2.5 mass concentration
data; PM10–2.5 mass concentration; chemically speciated PM10–2.5
mass concentration data; meteorological data from NCore and PAMS sites;
average daily temperature and average daily pressure for Pb sites if not
already reported from sampler generated records; and metadata records
and information specified by the AQS Data Coding Manual
(http://www.epa.gov/ttn/airs/airsaqs/manuals/manuals.htm ).  The State,
or where appropriate, local agency, may report site specific
meteorological measurements generated by on site equipment
(meteorological instruments, or sampler generated) or measurements from
the nearest airport reporting ambient pressure and temperature.  Such
air quality data and information must be submitted directly to the AQS
via electronic transmission on the specified quarterly schedule
described in paragraph (b) of this section.

* * * * *

SUBPART D--[AMENDED]

19.  Section 58.20 is amended by revising paragraph (e) to read as
follows:

§ 58.20   Special purpose monitors (SPM).

* * * * *

(e) If an SPM using an FRM, FEM, or ARM is discontinued within 24 months
of start-up, the Administrator will not designate an area as
nonattainment for the CO, SO2, NO2, or 24-hour PM10 NAAQS solely on the
basis of data from the SPM. Such data are eligible for use in
determinations of whether a nonattainment area has attained one of these
NAAQS.

* * * * *

20.  Appendix A to Part 58 is amended to read as follows; (a) revising
paragraph 1, (b) inserting paragraph 2.3.1.4, (c) revising paragraph
3.3.4, (d) revising paragraph 4c,  (e) revising paragraph 4.4, (f)
eliminating paragraph 4.5 and (g) revising Table A-2.

Appendix A to Part 58—Quality Assurance Requirements for SLAMS, SPMs
and PSD Air Monitoring

* * * * *

1. General Information

This appendix specifies the minimum quality system requirements
applicable to SLAMS air monitoring data and PSD data for the pollutants
SO2, NO2, O3, CO, Pb, PM2.5, PM10 and PM10-2.5 submitted to EPA.  This
appendix also applies to all SPM stations using FRM, FEM, or ARM methods
which also meet the requirements of Appendix E of this part. Monitoring
organizations are encouraged to develop and maintain quality systems
more extensive than the required minimums. The permit-granting authority
for PSD may require more frequent or more stringent requirements.
Monitoring organizations may, based on their quality objectives, develop
and maintain quality systems beyond the required minimum. Additional
guidance for the requirements reflected in this appendix can be found in
the “Quality Assurance Handbook for Air Pollution Measurement
Systems”, volume II, part 1 (see reference 10 of this appendix) and at
a national level in references 1, 2, and 3 of this appendix.

* * * * *

2.3.1.4 Measurement Uncertainty for Pb Methods. The goal for acceptable
measurement uncertainty is defined for precision as an upper 90 percent
confidence limit for the coefficient variation (CV) of 20 percent and
for bias as an upper 95 percent confidence limit for the absolute bias
of 15 percent.

* * * * *

3.3.4  Pb Methods.

3.3.4.1   Flow Rates. For the Pb Reference Methods (40 CFR Part 50,
appendix G and appendix Q) and associated FEMs, the flow rates of the Pb
samplers shall be verified and audited using the same procedures
described in sections 3.3.2 and 3.3.3 of this appendix.

3.3.4.2  Pb Analysis Audits. Each calendar quarter or sampling quarter
(PSD), audit the Pb Reference Method analytical procedure using filters
containing a known quantity of Pb. These audit filters are prepared by
depositing a Pb solution on unexposed filters and allowing them to dry
thoroughly. The audit samples must be prepared using batches of reagents
different from those used to calibrate the Pb analytical equipment being
audited. Prepare audit samples in the following concentration ranges:

Range	Equivalent ambient Pb 

concentration, µg/m3

1	30-100% of Pb NAAQS

2	200-300% of Pb NAAQS

(a) Audit samples must be extracted using the same extraction procedure
used for exposed filters.

(b) Analyze three audit samples in each of the two ranges each quarter
samples are analyzed. The audit sample analyses shall be distributed as
much as possible over the entire calendar quarter.

(c) Report the audit concentrations (in µg Pb/filter or strip) and the
corresponding measured concentrations (in µg Pb/filter or strip) using
AQS unit code 077. The percent differences between the concentrations
are used to calculate analytical accuracy as described in section 4.1.3
of this appendix.

(d) The audits of an equivalent Pb method are conducted and assessed in
the same manner as for the reference method. The flow auditing device
and Pb analysis audit samples must be compatible with the specific
requirements of the equivalent method.

3.3.4.3  Collocated Sampling.  The collocated sampling requirements for
Pb-TSP and Pb-PM10 shall be determined using the same procedures
described in sections 3.3.1 of this appendix with the exception that the
first collocated Pb site selected must be the site measuring the highest
Pb concentrations in the network. If the site is impractical,
alternative sites, approved by the EPA Regional Administrator, may be
selected. If additional collocated sites are necessary, collocated sites
may be chosen that reflect average ambient air Pb concentrations in the
network.

3.3.4.4   Pb Performance Evaluation Program (PEP) Procedures. Each
year, one performance evaluation audit, as described in section 3.2.7 of
this appendix, must be performed at one Pb site in each primary quality
assurance organization that has less than or equal to 5 sites and two
audits at primary quality assurance organizations with greater than 5
sites.  In addition, each year, four collocated samples from  primary
quality assurance organizations with less than or equal to 5 sites and
six collocated samples at primary quality assurance organizations with
greater than 5 sites must be sent to an independent laboratory, the same
laboratory as the performance evaluation audit, for analysis.

* * * * *

4.  Calculations for Data Quality Assessment

* * *

(c) At low concentrations, agreement between the measurements of
collocated samplers, expressed as relative percent difference or percent
difference, may be relatively poor. For this reason, collocated
measurement pairs are selected for use in the precision and bias
calculations only when both measurements are equal to or above the
following limits:

(1) TSP: 20 µg/m3.

(2) Pb: 0.02 µg/m3.

(3) PM10 (Hi-Vol): 15 µg/m3.

(4) PM10 (Lo-Vol): 3 µg/m3.

(5) PM10-2.5 and PM2.5: 3 µg/m3.

* * * * *

4.4 Statistics for the Assessment of Pb.

4.4.1  Precision Estimate. Follow the same procedures as described for
PM10 in section 4.2.1 of this appendix using the data from the
collocated instruments. The data pair would only be considered valid if
both concentrations are greater than the minimum values specified in
section 4(c) of this appendix.

4.4.2  Bias Estimate. For the Pb analysis audits described in section
3.3.4.2 and the Pb Performance Evaluation Program described in section
3.3.4.4, follow the same procedure as described in section 4.1.3 for the
bias estimate.

4.4.3  Flow rate calculations. For the one point flow rate
verifications, follow the same procedures as described for PM10 in
section 4.2.2; for the flow rate audits, follow the same procedures as
described in section 4.2.3.

* * * * *

Table A–2 of Appendix A to Part 58. Minimum Data Assessment
Requirements for SLAMS Sites

1. 5 valid audits for primary QA orgs, with ≤ 5 sites

2. 8 valid audits for primary QA orgs, with > 5 sites

3. All samplers in 6 years	Over all 4 quarters	Primary sampler
concentration and performance evaluation sampler concentration.

Manual Methods

Collocated sampling PM10, TSP, PM10–2.5, PM2.5, Pb-TSP, Pb-PM10
Collocated samplers	15%	Every 12 days PSD—every 6 days	Primary sampler
concentration and duplicate sampler concentration.

Flow rate verification PM10(low Vol), PM10–2.5, PM2.5, Pb-PM10	Check
of sampler flow rate	Each sampler	Once every month	Audit flow rate and
measured flow rate indicated by the sampler.

Flow rate verification PM10(High-Vol), TSP, Pb-TSP	Check of sampler flow
rate	Each sampler	Once every quarter	Audit flow rate and measured flow
rate indicated by the sampler.

Semi-annual flow rate audit PM10, TSP, PM10–2.5, PM2.5, Pb-TSP,
Pb-PM10 	Check of sampler flow rate using independent standard	Each
sampler, all locations	Once every 6 months	Audit flow rate and measured
flow rate indicated by the sampler.

Pb audit strips Pb-TSP, Pb-PM10 	Check of analytical system with Pb
audit strips	Analytical	Each quarter	Actual concentration and audit
concentration.

Performance evaluation program PM2.5, PM10–2.5	Collocated samplers	1.
5 valid audits for primary QA orgs, with ≤ 5 sites

2. 8 valid audits for primary QA orgs, with ≥ 5 sites

3. All samplers in 6 years	Over all 4 quarters	Primary sampler
concentration and performance evaluation sampler concentration.

Performance evaluation program Pb-TSP, Pb-PM10 	Collocated samplers	1. 1
valid audits and 4 collocated samples for primary QA orgs, with ≤ 5
sites

2. 2 valid audits and 6 collocated  samples for primary QA orgs, with >
5 sites

	Over all 4 quarters	Primary sampler concentration and performance
evaluation sampler concentration. Primary sampler concentration and
duplicate sampler concentration

1Effective concentration for open path analyzers.

2Corrected concentration, if applicable, for open path analyzers.

21.  Appendix C to Part 58 is amended by adding paragraph 2.10 to read
as follows:

* * * * *

2.10 Use of Pb-PM10 at a SLAMS Sites.  

2.10.1 The EPA Regional Administrator may approve the use of a Pb-PM10
FRM or Pb-PM10 FEM sampler in lieu of a Pb-TSP sampler as part of the
network plan required under part 58.10(a)(4) in the following cases.

2.10.1.1 Pb-PM10 samplers can be approved for use at the
nonsource-oriented sites required under paragraph 4.5(b) of Appendix D
to part 58 if there is no existing monitoring data indicating that the
maximum arithmetic 3-month mean Pb concentration (either Pb-TSP or
Pb-PM10) at the site was equal to or greater than 0.10 micrograms per
cubic meter during the previous 3 years.  

2.10.1.2 Pb-PM10 samplers can be approved for use at source-oriented
sites required under paragraph 4.5(a) if the monitoring agency can
demonstrate (through modeling or historic monitoring data from the last
3 years) that Pb concentrations (either Pb-TSP or Pb-PM10) will not
equal or exceed 0.10 micrograms per cubic meter on an arithmetic 3-month
mean and the source is expected to emit a substantial majority of its Pb
in the fraction of PM with an aerodynamic diameter of less than or equal
to 10 micrometers.

2.10.2 The approval of a Pb-PM10 sampler in lieu of a Pb-TSP sampler as
allowed for in paragraph 2.10.1 above will be revoked if measured
Pb-PM10 concentrations equal or exceed 0.10 micrograms per cubic meter
on an arithmetic 3-month mean.  Monitoring agencies will have up to 6
months from the end of the 3-month period in which the arithmetic
3-month Pb-PM10 mean concentration equaled or exceeded 0.10 micrograms
per cubic meter to install and begin operation of a Pb-TSP sampler at
the site.

22.  Appendix D to Part 58 is amended by revising paragraph 4.5 to read
as follows:

Appendix D to Part 58—Network Design Criteria for Ambient Air Quality
Monitoring

* * * * *

4.5  Lead (Pb) Design Criteria. (a) State and, where appropriate,
local agencies are required to conduct ambient air Pb monitoring taking
into account Pb sources which are expected to or have been shown to
contribute to a maximum Pb concentration in ambient air in excess of the
NAAQS, the potential for population exposure, and logistics.  At a
minimum, there must be one source-oriented SLAMS site located to measure
the maximum Pb concentration in ambient air resulting from each Pb
source which emits 1.0 or more tons per year based on either the most
recent National Emission Inventory (  HYPERLINK
"http://www.epa.gov/ttn/chief/eiinformation.html" 
http://www.epa.gov/ttn/chief/eiinformation.html ) or other
scientifically justifiable methods and data (such as improved emissions
factors or site-specific data)  taking into account logistics and the
potential for population exposure. 

(i)  One monitor may be used to meet the requirement in paragraph 4.5(a)
for all sources involved when the location of the maximum Pb
concentration due to one Pb source is expected to also be impacted by Pb
emissions from a nearby source (or multiple sources).  This monitor must
be sited, taking into account logistics and the potential for population
exposure, where the Pb concentration from all sources combined is
expected to be at its maximum.

(ii)  The Regional Administrator may waive the requirement in paragraph
4.5(a) for monitoring near Pb sources if the State or, where
appropriate, local agency can demonstrate the Pb source will not
contribute to a maximum Pb concentration in ambient air in excess of 50%
of the NAAQS (based on historical monitoring data, modeling, or other
means).  The waiver must be renewed once every 5 years as part of the
network assessment required under 58.10(d).

 (b) State and, where appropriate, local agencies are required to
conduct Pb monitoring in each CBSA with a population equal to or greater
than 500,000 people as determined by  the latest available census
figures.  At a minimum, there must be one nonsource-oriented SLAMS site
located to measure neighborhood scale Pb concentrations in urban areas
impacted by re-entrained dust from roadways, closed industrial sources
which previously were significant sources of Pb, hazardous waste sites,
construction and demolition projects, and other fugitive dust sources of
Pb.  

(c)  The EPA Regional Administrator may require additional monitoring
beyond the minimum monitoring requirements contained in 4.5(a) and
4.5(b) where the likelihood of Pb air quality violations is significant
or where the emissions density, topography, or population locations are
complex and varied.

(d) The most important spatial scales for source-oriented sites to
effectively characterize the emissions from point sources are microscale
and middle scale.  The most important spatial scale for
nonsource-oriented sites to characterize typical lead concentrations in
urban areas is the neighborhood scale.  Monitor siting should be
conducted in accordance with 4.5(a)(i) with respect to source-oriented
sites.

(1) Microscale —This scale would typify areas in close proximity to
lead point sources. Emissions from point sources such as primary and
secondary lead smelters, and primary copper smelters may under
fumigation conditions likewise result in high ground level
concentrations at the microscale. In the latter case, the microscale
would represent an area impacted by the plume with dimensions extending
up to approximately 100 meters.  Pb monitors in areas where the public
has access, and particularly children have access, are desirable because
of the higher sensitivity of children to exposures of elevated Pb
concentrations.

(2) Middle scale —This scale generally represents Pb air quality
levels in areas up to several city blocks in size with dimensions on the
order of approximately 100 meters to 500 meters. The middle scale may
for example, include schools and playgrounds in center city areas which
are close to major Pb point sources. Pb monitors in such areas are
desirable because of the higher sensitivity of children to exposures of
elevated Pb concentrations (reference 3 of this appendix). Emissions
from point sources frequently impact on areas at which single sites may
be located to measure concentrations representing middle spatial scales.

(3) Neighborhood scale —The neighborhood scale would characterize air
quality conditions throughout some relatively uniform land use areas
with dimensions in the 0.5 to 4.0 kilometer range. Sites of this scale
would provide monitoring data in areas representing conditions where
children live and play. Monitoring in such areas is important since this
segment of the population is more susceptible to the effects of Pb.
Where a neighborhood site is located away from immediate Pb sources, the
site may be very useful in representing typical air quality values for a
larger residential area, and therefore suitable for population exposure
and trends analyses.

(d) Technical guidance is found in references 4 and 5 of this appendix.
These documents provide additional guidance on locating sites to meet
specific urban area monitoring objectives and should be used in locating
new sites or evaluating the adequacy of existing sites.

* * * * *

 The legislative history of section 109 indicates that a primary
standard is to be set at “the maximum permissible ambient air level .
. . which will protect the health of any [sensitive] group of the
population,” and that for this purpose “reference should be made to
a representative sample of persons comprising the sensitive group rather
than to a single person in such a group.” S. Rep. No. 91-1196, 91st
Cong., 2d Sess. 10 (1970)

 Welfare effects as defined in section 302(h) (42 U.S.C. 7602(h))
include, but are not limited to, “effects on soils, water, crops,
vegetation, man-made 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.”

    In considering whether the CAA allowed for economic considerations
to play a role in the promulgation of the NAAQS, the Supreme Court
rejected arguments that because many more factors than air pollution
might affect public health, EPA should consider compliance costs that
produce health losses in setting the NAAQS.  Whitman v. American
Trucking Associations, 531 U.S. at 466.  Thus, EPA may not take into
account possible public health impacts from the economic cost of
implementation.  Id.

 The “indicator” of a standard defines the chemical species or
mixture that is to be measured in determining whether an area attains
the standard.

 The “form” of a standard defines the air quality statistic that is
to be compared to the level of the standard in determining whether an
area attains the standard.

 As described in section II.A.2.a below the CDC stated in 2005 that no
“safe” threshold for blood Pb levels in young children has been
identified (CDC, 2005a).

 Co-chaired by the Secretary of the HHS and the Administrator of the
EPA, the Task Force consisted of representatives from 16 Federal
departments and agencies.

 See, e.g., “Implementation of the Mercury-Containing and Rechargeable
Battery Management Act”
http://www.epa.gov/epaoswer/hazwaste/recycle/battery.pdf and
“Municipal Solid Waste Generation, Recycling, and Disposal in the
United States: Facts and Figures for 2005”
http://www.epa.gov/epaoswer/osw/conserve/resources/msw-2005.pdf.

 The 5th percentile, geometric mean, and 95th percentile values for the
2003-2004 NHANES are 0.7, 1.8 and 5.1 μg/dL, respectively (Axelrad,
2008a,b).  

 In general, air-related pathways include those pathways where Pb passes
through ambient air on its path from a source to human exposure.

 Weathering of outdoor Pb paint may also contribute to soil Pb levels
adjacent to the house.

 The exposure assessment for children performed for this review employed
available data and methods to develop estimates intended to inform a
characterization of these pathways (as described in the proposal and the
final Risk Assessment Report).

 Additionally, Pb freely crosses the placenta resulting in continued
fetal exposure throughout pregnancy, with that exposure increasing
during the latter half of pregnancy (CD, section 6.6.2).

 As described by the Advisory Committee on Childhood Lead Poisoning
Prevention, “In 1991, CDC defined the blood lead level (BLL) that
should prompt public health actions as 10 μg/dL.  Concurrently, CDC
also recognized that a BLL of 10 μg/dL did not define a threshold for
the harmful effects of lead.  Research conducted since 1991 has
strengthened the evidence that children’s physical and mental
development can be affected at BLLS <10 μg/dL” (ACCLPP, 2007).

in children with BLLs <10 μg/ dL and >10 μg/dL, so preventive lead
hazard control measures need not be deferred pending further research
findings or consensus.” [CDC, 2005a, p. 2]  CDC’s Advisory Committee
on Childhood Lead Poisoning Prevention recently provided recommendations
regarding interpreting and managing blood Pb levels below 10 μg/dL in
children and reducing childhood exposures to Pb (ACCLPP, 2007).

 This information documents a variation in mean blood Pb levels across
the various age groups monitored.  For example, mean blood Pb levels in
2001-2002 for ages 1-5, 6-11, 12-19 and greater than or equal to 20
years of age, are 1.70, 1.25, 0.94, and 1.56 µg/dL, respectively (CD,
p. 4-22).

 Ratios are presented in the form of 1:x, with the 1 representing air Pb
(in µg/m3) and x representing blood Pb (in µg/dL).  Description of
ratios as higher or lower refers to the values for x (i.e., the change
in blood Pb per unit of air Pb).  Slopes are presented as simply the
value of x.

 We note that the 2006 Criteria Document did not include a discussion of
more recent studies relating to air-to-blood ratios; more recent studies
were discussed in the Staff Paper, including discussion by CASAC in
their review of those documents.

 Brunekreef et al. (1984) discusses potential confounders to the
relationship between air Pb and blood Pb, recognizing that ideally all
possible confounders should be taken into account in deriving an
adjusted air-to-blood relationship from a community study.  The studies
cited here adjusted for parental education (Zielhuis et al., 1979), age
and race (Billick et al., 1979, 1980) and additionally measuring height
of air Pb (Billick et al., 1983); Brunekreef et al. (1984) used multiple
regression to control for several confounders.  The authors conclude
that “presentation of both unadjusted and (stepwise) adjusted
relationships is advisable, to allow insight in the range of possible
values for the relationship” (p. 83).  Unadjusted ratios were
presented for two of these studies, including ratios of 4.0 (Zielhuis et
al., 1979) and 18.5 (Brunekreef et al., 1983). The proposal noted that
the Brunekreef et al, 1983 study is subject to a number of sources of
uncertainty that could result in air-to-blood Pb ratios that are biased
high, including the potential for underestimating ambient air Pb levels
due to the use of low volume British Smoke air monitors and the
potential for higher historical ambient air Pb levels to have influenced
blood Pb levels (see Section V.B.1 of the 1989 Pb Staff Report for the
Pb NAAQS review, EPA, 1989).  In addition, the 1989 Staff Report notes
that the higher air-to-blood ratios obtained from this study could
reflect the relatively lower blood Pb levels seen across the study
population (compared with blood Pb levels reported in other studies from
that period).

 This study considered changes in ambient air Pb levels and associated
blood Pb levels over a five-year period which included closure of an
older Pb smelter and subsequent opening of a newer facility in 1997 and
a temporary (3 month) shutdown of all smelting activity in the summer of
2001. The author observed that the air-to-blood ratio for children in
the area over the full period was approximately 1:6. The author noted
limitations in the dataset associated with exposures in the second time
period, after the temporary shutdown of the facility in 2001, including
sampling of a different age group at that time and a shorter time period
(3 months) at these lower ambient air Pb levels prior to collection of
blood Pb levels. Consequently, EPA calculated an alternate air-to-blood
Pb ratio based on consideration for ambient air Pb and blood Pb
reductions in the first time period (after opening of the new facility
in 1997).   

 In the publication, the author acknowledges that remedial programs
(e.g., community and home-based dust control and education) may have
been responsible for some of the blood Pb reduction seen during the
study period (1997 to 2001). However, the author points out that these
programs were in place in 1992 and he suggests that it is unlikely that
they contributed to the sudden drop in blood Pb levels occurring after
1997. In addition, the author describes a number of aspects of the
analysis which could have implications for air-to-blood ratios including
a tendency over time for children with lower blood Pb levels to not
return for testing, and inclusion of children aged 6 to 36 months in Pb
screening in 2001 (in contrast to the wider age range up to 60 months as
was done in previous years). 

 EPA is not basing its decisions on these two studies, but notes that
these estimates are consistent with other studies that were included in
the 1986 and 2006 Criteria Documents and considered by CASAC and the
public.

 As with all studies, we note that there are strengths and limitations
for these two studies which may affect the specific magnitudes of the
reported ratios, but that the studies’ findings and trends are
generally consistent with the conclusions from the 1986 Criteria
Document.

 The CASAC Panel stated "The Schwartz and Pitcher analysis showed that
in 1978, the midpoint of the National Health and Nutrition Examination
Survey (NHANES) II, gasoline Pb was responsible for 9.1 μg/dL of blood
Pb in children. Their estimate is based on their coefficient of 2.14
μg/dL per 100 metric tons (MT) per day of gasoline use, and usage of
426 MT/day in 1976.  Between 1976 and when the phase-out of Pb from
gasoline was completed, air Pb concentrations in U.S. cities fell a
little less than 1 μg/m3 (24).  These two facts imply a ratio of 9-10
μg/dL per μg/m3 reduction in air Pb, taking all pathways into
account." (Henderson, 2007a, pp. D-2 to D-3).

 Air-to-blood ratios for the full study area of the primary Pb smelter
range from 1:3 to 1:7 across the range of alternative standard levels
from 1.5 down to 0.02 µg/m3 (USEPA, 2007b).

 Lead has been classified as a probable human carcinogen by the
International Agency for Research on Cancer (inorganic lead compounds),
based mainly on sufficient animal evidence, and as reasonably
anticipated to be a human carcinogen by the U.S. National Toxicology
Program (lead and lead compounds) (CD, Section 6.7.2).  U.S. EPA
considers Pb a probable carcinogen (  HYPERLINK
"http://www.epa.gov/iris/subst/0277.htm" 
http://www.epa.gov/iris/subst/0277.htm ; CD, p. 6-195).

 At mean blood Pb levels, in children, on the order of 10 μg/dL, and
somewhat lower, associations have been found with effects to the immune
system, including altered macrophage activation, increased IgE levels
and associated increased risk for autoimmunity and asthma (CD, Sections
5.9, 6.8, and 8.4.6).

ss-sectional studies offer evidence that exposure to Pb affects the
intellectual attainment of preschool and school age children at blood Pb
levels <10 μg/dL (most clearly in the 5 to 10 μg/dL range, but, less
definitively, possibly lower).” (p. 6-269)

s that a doubling of blood-Pb level (e.g., from 5 to 10 μg/dL) is
associated with ~1.0 mm Hg increase in systolic blood pressure and ~0.6
mm Hg increase in diastolic pressure (CD, p. E-10).  

 This level has variously been called an advisory level or level of
concern (http://www.atsdr.cdc.gov/csem/lead/pb_standards2.html).  In
addressing children’s blood Pb levels, CDC has stated “Specific
strategies that target screening to high-risk children are essential to
identify children with BLLs > 10 µg/dL.” (CDC, 2005, p.1)

 In consideration of the evidence from experimental animal studies with
regard to the issue of threshold for neurotoxic effects, the CD notes
that there is little evidence that allows for clear delineation of a
threshold, and that “blood-Pb levels associated with neurobehavioral
effects appear to be reasonably parallel between humans and animals at
reasonably comparable blood-Pb concentrations; and such effects appear
likely to occur in humans ranging down at least to 5-10 µg/dL, or
possibly lower (although the possibility of a threshold for such
neurotoxic effects cannot be ruled out at lower blood-Pb
concentrations)” (CD, p. 8-38).

 Further, neurological effects in general include behavioral effects,
such as delinquent behavior (CD, sections 6.2.6 and 8.4.2.2), sensory
effects, such as those related to hearing and vision (CD, sections 6.2.7
and 8.4.2.3), and deficits in neuromotor function (CD, p. 8-36).

 As an example, the Criteria Document states “although an increase of
a few mmHg in blood pressure might not be of concern for an
individual’s well-being, the same increase in the population mean
might be associated with substantial increases in the percentages of
individuals with values that are sufficiently extreme that they exceed
the criteria used to diagnose hypertension” (CD, p. 8-77).

 For example, for a population mean IQ of 100 (and standard deviation of
15), 2.3% of the population would score above 130, but a shift of the
population to a mean of 95 results in only 0.99% of the population
scoring above 130 (CD, pp. 8-81 to 8-82).

 The median of the concurrent blood Pb levels modeled was 9.7 µg/dL;
the 5th and 95th percentile values were 2.5 and 33.2 µg/dL,
respectively (Lanphear et al., 2005).

 The tests for cognitive function in these studies include
age-appropriate Wechsler intelligence tests (Lanphear et al., 2005;
Bellinger and Needleman, 2003), the Stanford-Binet intelligence test
(Canfield et al., 2003), the Test of Non-Verbal Intelligence (Al-Saleh
et al., 2001), an abbreviated form of the Wechsler tests (Kordas et al.,
2006) and the Bayley Scales of Infant Development (Tellez-Rojo et al.,
2006).  The Wechsler and Stanford-Binet tests are widely used to assess
neurocognitive function in children and adults, however, these tests are
not appropriate for children under age three.  For such children,
studies generally use the age-appropriate Bayley Scales of Infant
Development as a measure of cognitive development.  

 In the Criteria Document analysis, the 10th percentile was chosen as a
common point of comparison for the loglinear (and linear) models at a
point prior to the lowest end of the blood Pb levels.

b concentration of 10 μg/dL rather than at 7.5 μg/dL, is a small
protection against applying an incorrectly rapid change (steep slope
with increasingly smaller effect as concentrations lower) to the
calculation" (USEPA, 2008).  We note here that the slope for the
less-than-10-µg/dL portion of the model used in the RRP analysis
(-0.88) is similar to the median for the slopes included in the Criteria
Document analysis of quantitative relationships for studies in which the
majority of blood Pb levels were below 10 µg/dL.

 This slope reflects effects on cognitive development in this cohort of
24-month old children based on the age-appropriate test described
earlier, and is similar in magnitude to slopes for the cohorts of older
children described here.  The strengths and limitations of this
age-appropriate test, the Mental Development Index (MDI) of the Bayley
Scales of Infant Development (BSID), were discussed in a letter to the
editor by Black and Baqui (2005).  The letter states that "the MDI is a
well-standardized, psychometrically strong measure of infant mental
development."  The MDI represents a complex integration of
empirically-derived cognitive skills, for example, sensory/perceptual
acuities, discriminations, and response; acquisition of object
constancy; memory learning and problem solving; vocalization and
beginning of verbal communication; and basis of abstract thinking. Black
and Baqui additionally state that although the MDI is one of the most
well-standardized, widely used assessment of infant mental development,
evidence indicates low predictive validity of the MDI for infants
younger than 24 months to subsequent measures of intelligence.  They
explain that the lack of continuity may be partially explained by "the
multidimensional and rapidly changing aspects of infant mental
development and by variations in performance during infancy, variations
in tasks used to measure intellectual functioning throughout childhood,
and variations in environmental challenges and opportunities that may
influence development."  Martin and Volkmar (2007) also noted that
correlations between BSID performance and subsequent IQ assessments were
variable, but they also reported high test-retest reliability and
validity, as indicated by the correlation coefficients of 0.83 to 0.91,
as well as high interrater reliability, correlation coefficient of 0.96,
for the MDI.  Therefore, the BSID has been found to be a reliable
indicator of current development and cognitive functioning of the
infant.  Martin and Volkmar (2007) further note that “for the most
part, performance on the BSID does not consistently predict later
cognitive measures, particularly when socioeconomic status and level of
functioning are controlled”.

 In this study, the slope for blood Pb levels between 5 and 10 μg/dL
(population mean blood Pb of 6.9 μg/dL; n=101) was -0.94 points per
μg/dL blood Pb but was not statistically significant, with a p value of
0.12.  The difference in the slope between the <5 µg/dL and the 5-10
µg/dL groups was not statistically significant (Tellez-Rojo et al.,
2006; Tellez-Rojo, 2008).

 The LLL function is the loglinear function from Lanphear et al. (2005),
with linearization at low exposures (as described in sections 2.1.5 and
4.1.1.2 of the Risk Assessment Report).

 In their review of the final risk assessment, CASAC expressed strong
support, stating that “[t]he Final Risk Assessment report captures the
breadth of issues related to assessing the potential public health risk
associated with lead exposures; it competently documents the universe of
knowledge and interpretations of the literature on lead toxicity,
exposures, blood lead modeling and approaches for conducting risk
assessments for lead” (Henderson, 2008a, p. 4).

 CASAC advice on the design of the risk assessment is summarized in
section II.C.2.a of the proposal.

 A sixth case study (the secondary Pb smelter case study) is also
described in the Risk Assessment Report.  However, as discussed in
Section 4.3.1 of that document (USEPA, 2007a), significant limitations
in the approaches have contributed to large uncertainties in the
corresponding estimates. 

 As the blood Pb model used in the risk assessment was limited in that
it did not accept inputs of a temporal time step shorter than annual
average, ratios of relationships in the available air monitoring data
between different statistical forms being considered for the standard
and an annual average were employed for the urban case studies (that did
not rely on dispersion modeling) as a method of simulating the temporal
variability in air Pb concentrations that occurs as a result of
meteorology, source and emissions characteristics.

 The current NAAQS scenario for the urban case studies assumes ambient
air Pb concentrations higher than those currently occurring in nearly
all urban areas nationally.  While it is extremely unlikely that Pb
concentrations in urban areas would rise to meet the current NAAQS and
there are limitations and uncertainties associated with the roll-up
procedure used for the location-specific urban case studies (as
described in Section II.C.2.h of the proposal), this scenario was
included for those case studies to provide perspective on potential
risks associated with raising levels to the point that the highest level
across the study area just meets the current NAAQS.  This scenario was
simulated for the location-specific urban case studies using a
proportional roll-up procedure.  For the general urban case study, the
maximum quarterly average ambient air concentration was set equal to the
current NAAQS.

 Current conditions for the three location-specific urban case studies
in terms of maximum quarterly average air Pb concentrations were 0.09,
0.14 and 0.36 µg/m3 for the study areas in Los Angeles, Chicago and
Cleveland, respectively.

 Similarly, since dietary Pb was included within “background”,
reductions in dietary Pb, e.g., as a result of reduced deposition to
crops, were also not simulated.

 In comparing total risk estimates between alternate NAAQS scenarios,
this aspect of the analysis will tend to underestimate the reductions in
risk associated with alternative NAAQS.  However, this does not mean
that overall risk has been underestimated.  The net effect of all
sources of uncertainty or bias in the analysis, which may also tend to
under- or overestimate risk, could not be quantified.

 The ratios increase as the level of the alternate standard decreases. 
This reflects the nonlinearity in the Pb response, which is greater on a
per-unit basis for lower ambient air Pb levels.

 For the primary Pb smelter (full study area), for which limitations are
noted in section II.C.2.c of the proposal, the air-to-blood ratio
estimates, presented in section 5.2.5.2 of the Risk Assessment Report
(USEPA, 2007b), ranged from 1:3 to 1:7. As in the other case studies,
ratios are higher at lower ambient air Pb levels.  It is noted that the
underlying changes in both ambient air Pb and blood Pb across standard
levels are extremely small, introducing uncertainty into ratios derived
using these data.

 As shown in the presentation in the Staff Paper (section 4.4), risk
estimates for the LLL function are generally bounded by estimates based
on the other three C-R functions included in the assessment.

Because of greater uncertainty in characterizing high-end population
risk, and specifically related to pathway apportionment of IQ loss
estimates for high-end percentiles, results discussed here focus on
those for the population median.

 As noted in Table 2 below and sections II.C.2.d and II.C.2.h of the
proposal, with regard to associated limitations and uncertainties, a
proportional roll-up procedure was used to estimate air Pb
concentrations in this scenario for the location-specific case studies.

 The term “evidence-based” as used here refers to the drawing of
information directly from published studies, with specific attention to
those reviewed and described in the Criteria Document, and is distinct
from considerations that draw from the results of the quantitative
exposure and risk assessment.

 For example, as stated in the Criteria Document, “Fortunately, there
exists a large database of high quality studies on which to base
inferences regarding the relationship between Pb exposure and
neurodevelopment.  In addition, Pb has been extensively studied in
animal models at doses that closely approximate the human situation. 
Experimental animal studies are not compromised by the possibility of
confounding by such factors as social class and correlated environmental
factors.  The enormous experimental animal literature that proves that
Pb at low levels causes neurobehavioral deficits and provides insights
into mechanisms must be considered when drawing causal inferences
(Bellinger, 2004; Davis et al., 1990; U.S. Environmental Protection
Agency, 1986a, 1990).” (CD, p. 6-75)

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᠀ the Staff Paper, the context for use of the air-to-blood ratio here
is a population being exposed at the level of the standard.

 As noted in the proposal (73 FR 29228), while blood Pb levels in U.S.
children have decreased notably since the late 1970s, newer studies have
investigated and reported associations of effects on the
neurodevelopment of children with these more recent blood Pb levels.

The current standard specifies the measurement of airborne Pb with a
high-volume TSP federal reference method (FRM) sampler with atomic
absorption spectrometry of a nitric acid extract from the filter for Pb,
or with an approved equivalent method (40 C.F.R §50.12, Appendix G).

 For simplicity, the discussion in this notice speaks as if PM10
samplers have a sharp size cut-off.  In reality, they have a size
selection behavior in which 50% of particles 10 microns in size are
captured, with a progressively higher capture rate for smaller particles
and a progressively lower capture rate for larger particles.  The ideal
capture efficiency curve for PM10 samplers specifies that particles
above 15 microns not be captured at all, although real samplers may
capture a very small percentage of particles above 15 microns.  TSP
samplers have 50% capture points in the range of 25 to 50 microns
(Wedding et al., 1977), which is broad enough to include virtually all
sizes of particles capable of being transported any significant distance
from their source except under extreme wind events. 

 “Low-volume PM10 sampling” refers to sampling using any of a number
of monitor models that draw 16.67 liters/minute (1 m3 /hour) of air
through the filter, in contrast to “high-volume” sampling of either
TSP or PM10 in which the monitor draws 1500 liters/minute (90 m3 /hour).

 In this notice, we use “ultra-coarse” to refer to particles
collected by a TSP sampler but not by a PM10 sampler.  We note that
CASAC has variously also referred to these particles as “very
coarse” or “larger coarse-mode” particles.  This terminology is
consistent with the traditional usage of “fine” to refer to
particles collected by a PM2.5 sampler, and “coarse” to refer to
particles collected by a PM10 sampler but not by a PM2.5 sampler,
recognizing that there will be some overlap in the particle sizes in the
three types of collected material.

 Low-volume PM10 samplers are equipped with an omni-directional
(cylindrical) inlet, which reduces the effect of wind direction, and a
sharp particle separator which excludes most of the particles greater
than 10-15 microns in diameter whose collection efficiency is most
sensitive to wind speed.  Also, in low-volume samplers, the filter is
protected from post-sampling contamination.

 In their advice, CASAC recognized the potential for site-to-site
variability in the relationship between Pb-TSP and Pb-PM10 (Henderson,
2007a, 2007b).  They also stated in their September 2007 letter, “The
Panel urges that PM10 monitors, with appropriate adjustments, be used to
supplement the data.  …  A single quantitative adjustment factor could
be developed from a short period of collocated sampling at multiple
sites; or a PM10 Pb/TSP Pb ‘equivalency ratio’ could be determined
on a regional or site-specific basis”.

 Data from collocated TSP and PM2.5 monitors are generally presented in
the Staff Paper (section 2.3.5).

 As described in the proposal (73 FR29233), collocated data from
source-oriented sites were available from just three locations near
three different types of sources and include data from as long ago as
1988 (Schmidt and Cavender, 2008).  A limited amount of additional data
has been provided in comments on the proposal.

 The differing evidence and associated strength of the evidence for
these different effects is described in detail in the Criteria Document.

 For example, EPA recognizes today that “there is no level of Pb
exposure that can yet be identified, with confidence, as clearly not
being associated with some risk of deleterious health effects” (CD, p.
8-63).  

 Lead accumulates in the body and is only slowly removed, with bone Pb
serving as a blood Pb source for years after exposure and as a source of
fetal Pb exposure during pregnancy (CD, sections 4.3.1.4 and 4.3.1.5).

 The health evidence with regard to the susceptibility of the developing
fetus and infants is well documented in the evidence as described in the
1986 Criteria Document, the 1990 Supplement (e.g., chapter III) and the
2006 Criteria Document.  For example, “[n]eurobehavioral effects of
Pb-exposure early in development (during fetal, neonatal, and later
postnatal periods) in young infants and children (< 7 years old) have
been observed with remarkable consistency across numerous studies
involving varying study designs, different developmental assessment
protocols, and diverse populations.” (CD, p. E-9)

 These analyses incorporate the revised averaging method identified
above and discussed more fully in section IV below.

 Among the studies of Pb health effects, in which blood Pb level is
generally used as an index of exposure, the sources of exposure vary and
are inclusive of air-related sources of Pb such as smelters (e.g., CD,
chapter 6).   

 As described in section II.E.3.a.ii of the proposal, the first set
focused on C-R functions from analyses involving population mean
concurrent blood Pb levels of approximately 3 µg/dL (closer to current
mean blood Pb levels in U.S. children).  The second set (CD, pp. 8-78 to
8-80) considered functions descriptive of the C-R relationship from a
larger set of studies that include population mean blood Pb levels
ranging from a mean of 3.3 up to a median of 9.7 µg/dL (see Table 1).

 In considering alternative levels for the standard within the
air-related IQ loss framework, the Agency focused on estimates using an
air-to-blood ratio of 1:5 and also provided IQ loss estimates using
higher and lower estimates (i.e., 1:3 and 1:7). 

 In considering the risk estimates in light of IQ loss estimates based
on the air-related IQ loss evidence-based framework in the proposal, the
Agency focused on risk estimates for the general urban and primary Pb
smelter subarea case studies as these case studies generally represent
population exposures for more highly air-pathway exposed children
residing in small neighborhoods or localized residential areas with air
concentrations nearer the standard level being evaluated, as compared
to, the location-specific case studies in which populations have a
broader range of air-related exposures including many well below the
standard level being evaluated.

 Similarly, in the most recent reviews of the NAAQS for ozone and PM,
EPA recognized that the available epidemiological evidence neither
supports nor refutes the existence of thresholds at the population
level, while noting uncertainties and limitations in studies that make
discerning thresholds in populations difficult (e.g., 73 FR 16444, March
27, 2008; 71 FR 61158, October 17, 2006).

 Some commenters provided recommendations with regard to a level for a
Pb-PM10–based standard.  While these comments are instructive on that
issue, the Administrator has decided to retain the current indicator of
Pb-TSP, and therefore they do not need to be addressed here.

 EPA agrees that the study by Hayes et al. (1994), cited by CASAC and
commenters, presents an air-to-blood ratio greater 1:10, but notes that
we are not relying on this study in our decision as it has not been
reviewed as part of the Criteria Document or Staff Paper (as described
in Section I.C). 

 A ratio of 1:5 was recommended by one of these commenters (Doe Run
Resources Corp.). 

  See previous footnote regarding Hayes et al. (1994).

 Using the ratio of 1:7 identified above as central within the
reasonable range of air-to-blood ratios, the estimate of air-related
blood Pb associated with a standard level of 0.15 µg/m3 would be
approximately 1 µg/dL.  Adding this to the mean total blood Pb level
for the U.S. population would yield a mean total blood Pb estimate of
2.8 µg/dL.

 As noted above, we also recognize that blood Pb levels are expected to
further decline in response to this and other public health protection
actions, including those described above in section I.D.

 Further, in determining what level of estimated IQ loss should be used
for evaluating the results obtained from this specific evidence-based
framework, the Administrator is not determining that such an IQ loss is
appropriate for use in other contexts.

 For example, in considering a standard level of 0.2 µg/m3, we note
that the risk assessment provides estimates falling within the range of
1.2 to 3.2 points IQ loss for the general urban case study and <3.7 for
the primary Pb smelter subarea.  These estimates are inclusive of the
range of estimates for the 0.20 standard level presented in Table 4
based on the median C-R slope applied in the air-related IQ loss
framework.  As noted in section II.A.3.a above, these case studies,
based on the nature of the population exposures represented by them,
relate more closely to the air-related IQ loss evidence-based framework
than other case studies assessed. 

 As explained below, under the proposal sufficiently complete Pb-TSP
data would take precedence over Pb-PM10 data, so not all Pb-PM10 data
would necessarily be actually used in the design value calculations.

In the final Appendix R, there is a provision to calculate a
“3-month” average based on only one (or two) months of data if two
(or one) of the months in the 3-month period have no valid reported data
at all.  In this case, the sum of the available monthly averages is
divided by the number of months contributing data.  Because a lack of
data for an entire month (or two) would mean that the completeness over
a 3-month period cannot be higher than 67 percent (or 33 percent), which
is less than the normal requirement for 75 percent completeness, a
situation like this could result in a valid 3-month average
concentration only via application of the “above NAAQS” diagnostic
data substitution tests described in section IV.C.  With that test, if
substituting historically low data for the month (or two months) of
missing data still results in a 3-month average above the level of the
NAAQS, then the 3-month mean computed from only two (or one) months of
data is deemed valid and complete.

 The scheduled sampling days, in contrast, are expected to be
uncorrelated with Pb concentration, since they do not emphasize any
particular day of the week.

 Incomplete data for one month of a 3-year period would not necessarily
prevent a finding of a NAAQS violation, because a single 3-month average
concentration above the NAAQS level in any period not affected by that
month’s incompleteness would constitute a violation.

 No public comment was received on this provision.

 Comments regarding whether Pb-TSP or Pb-PM10 should be the indicator
for the NAAQS and EPA’s response to them are discussed in section
II.C.1.  

 Scaling Factor: PM10 versus TSP,  Neptune and Company, Inc., Final
Report, September 30, 2008.

 The issues include but are not limited to the following: the available
paired data sets with enough pairs of data to apply the criteria are all
from sites where Pb-TSP concentrations were well below the final level
of the revised NAAQS so there is uncertainty about how well they
represent sites for which the accuracy of the scaling factor is critical
to compliance with or violation of the NAAQS; many of the available data
sets were not able to meet the proposed criteria for the correlation
between parameters and for consistency of the ratio between parameter
averages from month to month, meaning that no valid scaling factors
could be derived following the terms of the proposed Appendix R; the
proposed methods are sensitive to how measurements below the method
detection limit are reported and it is not clear how this reporting was
done in the available sets of paired data, and EPA did not propose any
particular reporting conventions for public comment; the site-specific
scaling factors in some cases varied from year to year in those few
cases where more than one year had enough pairs of data; and there are
indications that a linear relationship between the two parameters with a
non-zero intercept may be a better representation than a scaling factor
which inherently presumes a zero intercept.

 The consultant’s report does not characterize the orientation of the
monitoring sites, but based on other information it appears that sites
060250005, 260770905, and 261390009 are non-source oriented.

 Of 20 sites with paired data which EPA believed at the time of the
proposal to not be influenced by nearby industrial sources, only 3 had
ratios of average concentrations of Pb-TSP to Pb-PM10 greater than 1.4. 
One of these sites had only 13 data pairs.  The other two sites had very
low concentrations of both parameters, such that the ratio may reflect
the influence of data rounding/truncation or censoring of data below the
method detection limit more than actual atmospheric concentration
ratios. Also, these paired data were from 2001 or earlier. (Development
of Pb-PM10 to Pb-TSP Scaling Factors, Mark Schmidt, 4/22/08.)  Also, as
noted above, the data from these sites are not adequate for the
development of site-specific scaling factors if the proposed criteria
for such data are applied to them.

 M. Schmidt and P. Lorang (October 15, 2008). Memo to Lead NAAQS Docket,
Analysis of Expected Range of Pb-TSP Concentrations at Non-Source
Oriented Monitoring Sites in CBSAs with Population Over 500,000.

 Based on the analysis described in the memo referenced in the previous
footnote, EPA estimates that this provision might have the effect of
prohibiting the use of Pb-PM10 monitoring for at most only a few
existing Pb monitoring sites which otherwise might be eligible for
Pb-PM10 monitoring instead of Pb-TSP monitoring.

 When the Pb-TSP monitor is installed, the monitoring agency would have
the option of discontinuing the Pb-PM10 monitor, and we expect that most
agencies would do so for cost reasons.  

 If three years of Pb-TSP monitoring results in no 3-month average Pb
concentration equal to or greater than 0.10 µg/m3, as might occur after
the source improves its control of Pb emissions, the site would again be
eligible for Pb-PM10 monitoring.

 Such a comparison based on actual Pb-TSP data would of course be able
to support a compliance conclusion, because Pb-TSP is the actual
indicator for the NAAQS.  

 Only a handful of low-volume Pb-PM10 monitoring sites are now
operational none of which indicate NAAQS violations. In addition, any
sites which begin operation in response to the final monitoring
requirements cannot collect three years of data by the time designations
must be completed.

 It is also possible for a period of less than three years to have a
valid design value, but only if the procedures in Appendix R when
applied to that shorter period result in a design value greater than the
level of the NAAQS.  It is possible to establish a violation of the
NAAQS on a monitoring period as short as three months but three years
are needed to establish compliance with the NAAQS.

 A violation will exist as soon as any 3-month average exceeds the level
of the NAAQS.  It is not required that three years of data collection be
completed before a site can be found in violation.  This is consistent
with the proposal.

 The FRM specification in the new Appendix Q for Pb-PM10 monitoring
excludes the possibility of composite sampling for Pb-PM10, so this in
an issue that applies only to Pb-TSP.

 The pollutant occurrence code is a numerical code (1, 2, 3, etc.) used
to distinguish the data from two or more monitors for the same parameter
at a single monitoring site.  For example, if a monitoring agency has
been using both composite analysis for filters from one sampler and
individual sample analysis for filters from a collocated sampler, data
from these would be distinguished using this code.  Choosing which set
of data to use based on which has the lower code value is an approach
chosen for its simplicity, to avoid specifying what would have to be a
complicated set of procedures to determine which set of data or
combination of the two sets actually is the more robust for determining
whether the NAAQS is met.

 For a list of currently approved FRM/FEMs for Pb-TSP refer to:
www.epa.gov/ttn/amtic/criteria.html

 The 21 distinct approved FEMs represent less than 21 fundamentally
different analysis methods, as some differ only in minor aspects.

 Sampling efficiency refers to the percentage of total Pb (or PM) that
is collected by the sampler.  For the TSP sampler, research shows that
the sampling efficiency varies for particulates greater than PM10 as a
function of wind speed and wind direction.

 Proper characterization of a new Pb-TSP FRM sampler would require
extensive wind-tunnel testing and field testing.  Wind tunnel testing
would be complicated by the difficulty in quantifiably generating and
delivering precise amounts of ultra-coarse PM in a wind-tunnel setting.

 For the complete definition of CBSA refer to:
ww.census.gov/population/www/estimates/aboutmetro.html

 Required PM2.5 sites have additional criteria where monitoring sites
are to represent community-wide air quality [40 CFR part 58, appendix D
paragraph 4.7.1(b)] with at least one required site in a
population-oriented area of expected maximum concentration.  

 American Petroleum Institute v. Costle, 609 F.2d 20 (D.C. Cir. 1979)

 Under the CAA and the Tribal Authority Rule (TAR), eligible Indian
Tribes may develop and submit Tribal Implementation Plans (TIPs) for EPA
approval, to administer requirements under the CAA on their reservations
and in nonreservation areas under their jurisdiction.  However, Tribes
are not required to develop TIPs or otherwise implement relevant
programs under the CAA.  In cases where a Tribal air quality agency has
implemented an air quality monitoring network which is affected by Pb
emissions, the criteria and procedures identified in this rule may be
applied for regulatory purposes.  Certain Tribes may implement all
relevant components of an air quality program for purposes of meeting
the various requirements of this rule.  

  Two elements identified in section 110(a)(2) are not listed below
because, as EPA interprets the CAA,  SIPs incorporating any necessary
local nonattainment area controls would not be due within 3 years, but
rather are due at the time the nonattainment area planning requirements
are due.  These elements are: (1) Emission limits and other control
measures, section 110(a)(2)(A), and (2) Provisions for meeting part D,
section 110(a)(2)(I), which requires areas designated as nonattainment
to meet the applicable nonattainment planning requirements of part D,
title I of the CAA.  

 EPA Air Pollution Control Cost Manual - Sixth Edition (EPA
452/B-02-001), EPA Office of Air Quality Planning and Standards,
Research Triangle Park, NC, Jan 2002.

  See for example, 44 FR 53762 (September 17, 1979) and footnote 3 of
that notice.  Note that EPA’s emissions trading policy statement has
clarified that the RACT requirement may be satisfied by achieving
“RACT equivalent” emission reductions in the aggregate from the full
set of existing stationary sources in the area. See also EPA’s
economic incentive proposal which reflects the Agency’s policy
guidance with respect to emissions trading, 58 FR 11110, February 23,
1993. 

 As previously stated in the proposed rule, EPA believes that most lead
nonattainment problems will most likely be due to emissions from
stationary sources of lead.  For this reason EPA believes that the RFP
for Pb should parallel the RFP policy for SO2 (see General Preamble, 57
FR 13545, April 16, 1992).

 The terms “major” and “minor” define the size of a stationary
source, for applicability purposes, in terms of an annual emissions rate
(tons per year, tpy) for a pollutant.  Generally, a minor source is any
source that is not “major.”  “Major” is defined by the
applicable regulations—PSD or nonattainment NSR.

 In addition, the PSD program applies to non-criteria pollutants subject
to regulation under the Act, except those pollutants regulated under
section 112 and pollutants subject to regulation only under section
211(o).

.

 Criteria pollutants are those pollutants for which EPA has established
a NAAQS under section 109 of the CAA.

 Transportation conformity is required under CAA section 176(c) (42
U.S.C. 7506(c) to ensure that federally supported highway and transit
project activities are consistent with (“conform to”) the purpose of
the SIP.  Transportation conformity applies to areas that are designated
nonattainment, and those areas redesignated to attainment after 1990
(“maintenance areas” with plans developed under CAA section 175A)
for transportation-related criteria pollutants.  In light of the
elimination of Pb additives from gasoline, transportation conformity
does not apply to the Pb NAAQS.

 The areas that are currently nonattainment for the pre-existing Pb
NAAQS are East Helena, Montana and Jefferson County (part)/Herculaneum,
Missouri. ( See http://www.epa.gov/oar/oaqps/greenbk/lnc.html)

  These are examples of available systems and is not an all inclusive
list. The mention of commercial products does not imply endorsement by
the U.S. Environmental Protection Agency.

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