Document ID: EPA-HQ-OAR-2006-0735-5909
Agency: epa
Document Type: Rule
Title: National Ambient Air Quality Standards for Lead
Posted Date: 2008-11-12T05:00Z

[Federal Register: November 12, 2008 (Volume 73, Number 219)]
[Rules and Regulations]               
[Page 66963-67062]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr12no08-21]                         

[[Page 66963]]

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Part II

Environmental Protection Agency

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40 CFR Parts 50, 51, 53, and 58

National Ambient Air Quality Standards for Lead; Final Rule

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 50, 51, 53 and 58

[EPA-HQ-OAR-2006-0735; FRL-8732-9]
RIN 2060-AN83

 
National Ambient Air Quality Standards for Lead

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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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 
[mu]g/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 January 12, 2009.

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 
www.regulations.gov Web site. 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 
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; e-mail: 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; e-mail: 
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; e-mail: 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; e-mail: 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; e-mail: 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

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    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 [mu]g/
m\3\. 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.'' \1\ A secondary standard, as 
defined in section 109(b)(2), must ``specify a level of air quality the 
attainment and

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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.'' \2\
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    \1\ 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).
    \2\ 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.''
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    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 Sec.  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.\3\
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    \3\ 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.
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    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 ([mu]g/m\3\), 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 
[mu]g/m\3\, 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

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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,\4\ averaging time, form,\5\ 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.
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    \4\ The ``indicator'' of a standard defines the chemical species 
or mixture that is to be measured in determining whether an area 
attains the standard.
    \5\ 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.
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    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 (http:/
/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 
(http://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

[[Page 66968]]

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).\6\ 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

[[Page 66969]]

increased awareness that children face disproportionate risks from 
environmental health and safety hazards (62 FR 19885).\7\ 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.
---------------------------------------------------------------------------

    \6\ 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).
    \7\ 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.
---------------------------------------------------------------------------

    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.\8\ Similarly, Federal programs provide for the 
reduction in environmental releases of hazardous substances such as Pb 
in the management of wastewater (http://www.epa.gov/owm/).
---------------------------------------------------------------------------

    \8\ 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.
---------------------------------------------------------------------------

    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

[[Page 66970]]

conservation of energy and materials. These include the Resource 
Conservation Challenge (http://www.epa.gov/epaoswer/osw/conserve/
index.htm), the National Waste Minimization Program (http://
www.epa.gov/epaoswer/hazwaste/minimize/leadtire.htm), ``Plug in to 
eCycling'' (a partnership between EPA and consumer electronics 
manufacturers and retailers; http://www.epa.gov/epaoswer/hazwaste/
recycle/electron/crt.htm#crts), and activities to reduce the practice 
of backyard trash burning (http://www.epa.gov/msw/backyard/pubs.htm).
    As a result of coordinated, intensive efforts at the national, 
state and local levels, including those programs described above, blood 
Pb levels in all segments of the population have dropped significantly 
from levels observed around 1990. In particular, blood Pb levels for 
the general population of children 1 to 5 years of age have dropped to 
a median level of 1.6 [mu]g/dL and a level of 3.9 [mu]g/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 [mu]g/dL and 9.4 [mu]g/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 \9\ 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.
---------------------------------------------------------------------------

    \9\ The 5th percentile, geometric mean, and 95th percentile 
values for the 2003-2004 NHANES are 0.7, 1.8 and 5.1 [mu]g/dL, 
respectively (Axelrad, 2008a,b).
---------------------------------------------------------------------------

    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 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 [mu]g/m\3\ 
to 0.30 [mu]g/m\3\, 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

[[Page 66971]]

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.\10\ 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.
---------------------------------------------------------------------------

    \10\ In general, air-related pathways include those pathways 
where Pb passes through ambient air on its path from a source to 
human exposure.
---------------------------------------------------------------------------

    (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,\11\ 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).
---------------------------------------------------------------------------

    \11\ Weathering of outdoor Pb paint may also contribute to soil 
Pb levels adjacent to the house.
---------------------------------------------------------------------------

    (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,

[[Page 66972]]

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.\12\
---------------------------------------------------------------------------

    \12\ 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).
---------------------------------------------------------------------------

    (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.\13\ 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).
---------------------------------------------------------------------------

    \13\ 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).
---------------------------------------------------------------------------

    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
    Blood Pb levels are extensively used as an index or biomarker of 
exposure by national and international health agencies, as well as in 
epidemiological (CD, sections 4.3.1.3 and 8.3.2) and toxicological 
studies of Pb health effects and dose-response relationships (CD, 
chapter 5). The U.S. Centers for Disease Control and Prevention (CDC), 
and its predecessor agencies, have for many years used blood Pb level 
as a metric for identifying children at risk of adverse health effects 
and for specifying particular public health recommendations (CDC, 1991; 
CDC, 2005a). Most recently, in 2005, with consideration of a review of 
the evidence by their advisory committee, CDC revised their statement 
on Preventing Lead Poisoning in Young Children, specifically 
recognizing the evidence of adverse health effects in children with 
blood Pb levels below 10 [mu]g/dL \14\ 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).\15\
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    \14\ 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 [mu]g/dL. 
Concurrently, CDC also recognized that a BLL of 10 [mu]g/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 [mu]g/
dL'' (ACCLPP, 2007).
    \15\ With the 2005 statement, CDC did not lower the 1991 level 
of concern and identified a variety of reasons, reflecting both 
scientific and practical considerations, for not doing so, including 
a lack of effective clinical or public health interventions to 
reliably and consistently reduce blood Pb levels that are below 10 
[mu]g/dL, the lack of a demonstrated threshold for adverse effects, 
and concerns for deflecting resources from children with higher 
blood Pb levels (CDC, 2005a, pp. 2-3). The preface for the CDC 
statement included the following: ``Although there is evidence of 
adverse health effects in children with blood lead levels below 10 
[mu]g/dL, CDC has not changed its level of concern, which remains at 
levels >10 [mu]g/dL. We believe it critical to focus available 
resources where the potential adverse effects remain the greatest. 
If no threshold level exists for adverse health effects, setting a 
new BLL of concern somewhere below 10 [mu]g/dL would be based on an 
arbitrary decision. In addition, the feasibility and effectiveness 
of individual interventions to further reduce BLLs below 10 [mu]g/dL 
has not been demonstrated.'' [CDC, 2005a, p. ix] CDC further stated 
``Nonetheless, the sources of lead exposure and the population-based 
interventions that can be expected to reduce lead exposure are 
similar in children with BLLs <10 [mu]g/ dL and >10 [mu]g/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 [mu]g/dL in children and reducing childhood 
exposures to Pb (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).\16\ 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

[[Page 66973]]

Criteria Document summarizes related information as follows (CD, p. E-
6).
---------------------------------------------------------------------------

    \16\ 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 
[mu]g/dL, respectively (CD, p. 4-22).

    In the United States, decreases in mobile sources of Pb, 
resulting from the phasedown of Pb additives created a 98% decline 
in emissions from 1970 to 2003. NHANES data show a consequent 
parallel decline in blood-Pb levels in children aged 1 to 5 years 
from a geometric mean of ~15 [mu]g/dL in 1976-1980 to ~1-2 [mu]g/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 [mu]g/
dL) estimated to be associated with each unit increase of air Pb (in 
[mu]g/m\3\).\17\
---------------------------------------------------------------------------

    \17\ Ratios are presented in the form of 1:x, with the 1 
representing air Pb (in [mu]g/m\3\) and x representing blood Pb (in 
[mu]g/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.
---------------------------------------------------------------------------

    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,\18\ 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.
---------------------------------------------------------------------------

    \18\ 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.
---------------------------------------------------------------------------

    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 \19\ 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).
---------------------------------------------------------------------------

    \19\ 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).
---------------------------------------------------------------------------

    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 [mu]g/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).\20\ Ambient air and blood Pb levels 
associated with the Hilts (2003) study range from 1.1 to 0.03 [mu]g/
m\3\, and associated population mean blood Pb levels range from 11.5 to 
4.7 [mu]g/dL, which are lower than levels associated with the older 
studies cited in the 1986 Criteria Document (USEPA, 1986).
---------------------------------------------------------------------------

    \20\ 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).

---------------------------------------------------------------------------

[[Page 66974]]

    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. \21\
---------------------------------------------------------------------------

    \21\ 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).
---------------------------------------------------------------------------

    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.\22\ 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 [mu]g/
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 [mu]g/m\3\ and a 
ratio of 1:16 for ambient air Pb levels in the range of 0.25 [mu]g/
m\3\, indicating a pattern of higher ratios with lower ambient air Pb 
and blood Pb levels consistent with conclusions in the 1986 Criteria 
Document.\23\
---------------------------------------------------------------------------

    \22\ 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.
    \23\ 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.
---------------------------------------------------------------------------

    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).\24\
---------------------------------------------------------------------------

    \24\ 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 [mu]g/dL of blood Pb in children. Their estimate 
is based on their coefficient of 2.14 [mu]g/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 [mu]g/m\3\ (24). These two facts imply a ratio of 9-10 [mu]g/
dL per [mu]g/m\3\ reduction in air Pb, taking all pathways into 
account.'' (Henderson, 2007a, pp. D-2 to D-3).
---------------------------------------------------------------------------

    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 [mu]g/m\3\ down to a level of 
0.02 [mu]g/m\3\. 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 [mu]g/m\3\.\25\ 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

[[Page 66975]]

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.
---------------------------------------------------------------------------

    \25\ 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 [mu]g/m\3\ (USEPA, 2007b).
---------------------------------------------------------------------------

    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).\26\
---------------------------------------------------------------------------

    \26\ 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 (http://www.epa.gov/
iris/subst/0277.htm; CD, p. 6-195).
---------------------------------------------------------------------------

    This review is focused on those effects most pertinent to ambient 
exposures, which, given the reductions in ambient Pb levels over the 
past 30 years, are generally those associated with individual blood Pb 
levels in children and adults in the range of 10 [mu]g/dL and lower. 
These key effects include neurological, hematological and immune \27\ 
effects for children, and hematological, cardiovascular and renal 
effects for adults (CD, Tables 8-5 and 8-6, pp. 8-60 to 8-62). As 
evident from the discussions in chapters 5, 6 and 8 of the Criteria 
Document, ``neurotoxic effects in children and cardiovascular effects 
in adults are among those best substantiated as occurring at blood Pb 
concentrations as low as 5 to 10 [mu]g/dL (or possibly lower); and 
these categories are currently clearly of greatest public health 
concern'' (CD, p. 8-60).28 29 The toxicological and 
epidemiological information available since the time of the last review 
``includes assessment of new evidence substantiating risks of 
deleterious effects on certain health endpoints being induced by 
distinctly lower than previously demonstrated Pb exposures indexed by 
blood Pb levels extending well below 10 [mu]g/dL in children and/or 
adults'' (CD, p. 8-25). Some health effects associated with individual 
blood Pb levels extend below 5 [mu]g/dL, and some studies have observed 
these effects at the lowest blood levels considered. With regard to 
population mean levels, the Criteria Document points to studies 
reporting ``Pb effects on the intellectual attainment of preschool and 
school age children at population mean concurrent blood-Pb levels 
ranging down to as low as 2 to 8 [mu]g/dL'' (CD, p. E-9).
---------------------------------------------------------------------------

    \27\ At mean blood Pb levels, in children, on the order of 10 
[mu]g/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).
    \28\ With regard to blood Pb levels in individual children 
associated with particular neurological effects, the Criteria 
Document states ``Collectively, the prospective cohort and cross-
sectional studies offer evidence that exposure to Pb affects the 
intellectual attainment of preschool and school age children at 
blood Pb levels <10 [mu]g/dL (most clearly in the 5 to 10 [mu]g/dL 
range, but, less definitively, possibly lower).'' (p. 6-269)
    \29\ Epidemiological studies have consistently demonstrated 
associations between Pb exposure and enhanced risk of deleterious 
cardiovascular outcomes, including increased blood pressure and 
incidence of hypertension. A meta-analysis of numerous studies 
estimates that a doubling of blood-Pb level (e.g., from 5 to 10 
[mu]g/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).
---------------------------------------------------------------------------

    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 [mu]g/dL) \30\ as a 
benchmark for assessment, and this is reflected in the numerous 
references in the Criteria Document to 10 [mu]g/dL. Individual study 
conclusions stated with regard to effects observed below 10 [mu]g/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 [mu]g/dL or below levels lower than 10 [mu]g/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.
---------------------------------------------------------------------------

    \30\ 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 [mu]g/
dL.'' (CDC, 2005, p.1)
---------------------------------------------------------------------------

    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).\31\
---------------------------------------------------------------------------

    \31\ 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 [mu]g/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).
---------------------------------------------------------------------------

    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

[[Page 66976]]

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.
     Children with particular genetic polymorphisms (e.g., 
presence of the [delta]-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 [mu]g/dL (CD, sections 6.2 and 
8.4).\32\ 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).
---------------------------------------------------------------------------

    \32\ 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).
---------------------------------------------------------------------------

    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).\33\ 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).\34\ 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).
---------------------------------------------------------------------------

    \33\ 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).
    \34\ 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).
---------------------------------------------------------------------------

    Other cognitive effects observed in studies of children have 
included effects on attention, executive functions, language, memory, 
learning and visuospatial processing (CD, sections 5.3.5, 6.2.5 and 
8.4.2.1), with attention and executive function effects associated with 
Pb exposures indexed by blood Pb levels below 10 [mu]g/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).
    Multiple epidemiologic studies of Pb and child development have 
demonstrated inverse associations between blood Pb concentrations and 
children's IQ and other cognitive-related outcomes at successively 
lower Pb exposure levels over the past 30 years (as discussed in the 
CD, section 6.2.13). For example, the overall weight of the available 
evidence, described in the Criteria Document, provides clear 
substantiation of neurocognitive decrements being associated in 
children with mean blood Pb levels in the range of 5 to 10 [mu]g/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 [mu]g/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,

[[Page 66977]]

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 
[mu]g/dL increase in blood Pb may have a greater effect on IQ at lower 
blood Pb levels (e.g., below 10 [mu]g/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 
[mu]g/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 \35\ 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).
---------------------------------------------------------------------------

    \35\ The median of the concurrent blood Pb levels modeled was 
9.7 [mu]g/dL; the 5th and 95th percentile values were 2.5 and 33.2 
[mu]g/dL, respectively (Lanphear et al., 2005).
---------------------------------------------------------------------------

    As noted in the Criteria Document, a number of examples of non- or 
supralinear dose-response relationships exist in toxicology (CD, pp. 6-
76 and 8-38 to 8-39). With regard to the effects of Pb on 
neurodevelopmental outcome such as IQ, the Criteria Document suggests 
that initial neurodevelopmental effects at lower Pb levels may be 
disrupting very different biological mechanisms (e.g., early 
developmental processes in the central nervous system) than more severe 
effects of high exposures that result in symptomatic Pb poisoning and 
frank mental retardation (CD, p. 6-76). The Criteria Document describes 
this issue in detail with regard to Pb (summarized in CD at p. 8-39). 
Various findings within the toxicological evidence, presented in the 
Criteria Document (described in the proposal), provide biologic 
plausibility for a steeper IQ loss at low blood levels, with a 
potential explanation being that the predominant mechanism at very low 
blood-Pb levels is rapidly saturated and that a different, less-
rapidly-saturated process, becomes predominant at blood-Pb levels 
greater than 10 [mu]g/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 [mu]g/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 [mu]g/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 [mu]g/dL and 
also where an analysis was performed on a subset of children whose 
blood Pb levels have never exceeded 10 [mu]g/dL (CD, Table 6-1).\36\ 
The datasets for three of these studies included concurrent blood Pb 
levels above 10 [mu]g/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 
[mu]g/dL and the population mean was 7.9 [mu]g/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 [mu]g/dL and a population 
mean blood Pb level of 7.44 [mu]g/dL (Al-Saleh et al., 2001), and the 
second reported a population median blood Pb level of 9.7 [mu]g/dL and 
a 95th percentile of 33.2 [mu]g/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 \37\ 
blood Pb level and 10 [mu]g/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 [mu]g/dL range from -0.4 to -1.8 IQ points per 
[mu]g/dL blood Pb (CD, Tables 6-1 and 8-7), with a median of -0.9 IQ 
points per [mu]g/dL blood Pb (CD, p. 8-80).\38\ These slopes from

[[Page 66978]]

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 [mu]g/dL 
and for which a linear slope restricted to blood Pb levels below about 
10 [mu]g/dL could be estimated.
---------------------------------------------------------------------------

    \36\ 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.
    \37\ 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.
    \38\ One of these slopes (CD, Table 6-1) is for the IQ-blood Pb 
(concurrent) relationship for children whose peak blood Pb levels 
are below 10 [mu]g/dL in the international pooled dataset studied by 
Lanphear and others (2005); these authors reported this slope along 
with the companion slope, from the same (piece-wise) model, for the 
remaining children whose peak blood Pb level equals or is above 10 
[mu]g/dL (Lanphear et al., 2005). In the economic analysis for EPA's 
recent Lead Renovation, Repair and Painting (RRP) Program rule 
(described above in section I.C) for children living in houses with 
lead-based paint, changes in IQ were estimated as a function of 
changes in lifetime average blood Pb level using the corresponding 
piece-wise model for lifetime average blood Pb derived from the 
pooled dataset (USEPA, 2008; USEPA, 2007d). The piecewise models 
that gave greater weight to impacts in this blood Pb range were 
chosen because peak blood Pb levels are likely to be less than 10 
[mu]g/dL for the vast majority of children exposed to Pb during 
renovation activities. Further, while Lanphear et al. (2005) used 
peak blood Pb concentrations to determine which segment of a model 
to apply, for the hypothetical children to whom the approach is 
discussed in the RRP Program rule, only lifetime averages were used 
(in the RRP analysis). To counter the impact of assigning additional 
hypothetical RRP children to the steeper of the two slopes than 
would have been the case if they could be assigned based on peak 
blood Pb levels (as a child's lifetime average blood Pb is lower 
than peak blood Pb), the RRP analysis used the piece-wise model with 
node at 10 [mu]g/dL, for which the steeper of the two slopes is less 
steep than it is for the model with node at 7.5 [mu]g/dL. As stated 
in the RRP economic analysis document, ``[s]electing a model with a 
node, or changing one segment to the other, at a lifetime average 
blood Pb concentration of 10 [mu]g/dL rather than at 7.5 [mu]g/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-[mu]g/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 [mu]g/dL.
---------------------------------------------------------------------------

    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 [mu]g/dL; these slopes, in terms of IQ 
points per [mu]g/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 
[mu]g/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 [mu]g/dL) also had slopes steeper than -1.5 points 
per [mu]g/dL blood Pb. These include the slope of -1.71 points per 
[mu]g/dL blood Pb \39\ for the subset of 24-month old children in the 
Mexico City cohort with blood Pb levels less than 5 [mu]g/dL (n=193), 
for which the mean concurrent blood Pb level was 2.9 [mu]g/dL (Tellez-
Rojo et al. 2006, 2008),\40\ and the slope of -2.94 points per [mu]g/dL 
blood Pb for the subset of 6-10 year old children whose peak blood Pb 
levels never exceeded 7.5 [mu]g/dL (n=112), and for which the mean 
concurrent blood Pb level was 3.24 [mu]g/dL (Lanphear et al. 2005; 
Hornung 2008a). Thus, from these subset analyses, the slopes range from 
-1.71 to -2.94 IQ points per [mu]g/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 [mu]g/dL). We 
also note that for blood Pb levels up to approximately 3.7 [mu]g/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) \41\ falls intermediate between these two values.
---------------------------------------------------------------------------

    \39\ 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''.
    \40\ In this study, the slope for blood Pb levels between 5 and 
10 [mu]g/dL (population mean blood Pb of 6.9 [mu]g/dL; n=101) was -
0.94 points per [mu]g/dL blood Pb but was not statistically 
significant, with a p value of 0.12. The difference in the slope 
between the <5 [mu]g/dL and the 5-10 [mu]g/dL groups was not 
statistically significant (Tellez-Rojo et al., 2006; Tellez-Rojo, 
2008).
    \41\ The LLL function is the loglinear function from Lampshear 
et al. (2005), with linearization at low exposures (as described in 
sections 2.1.5 and 4.1.1.2 ofthe Risk Assessment Report).

                        Table 1--Summary of Quantitative Relationships of IQ and Blood Pb for Two Sets of Studies Discussed Above
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                                         Form of model    Average linear
                                                                                  Range BLL \A\    Geometric mean BLL      from which        slope \B\
        Study/analysis             Study cohort     Analysis dataset     N         ([mu]g/dL)        \A\ ([mu]g/dL)      average slope      (points per
                                                                                                                            derived          [mu]g/dL)
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                           Set of studies from which steeper slopes are drawn in the proposal
--------------------------------------------------------------------------------------------------------------------------------------------------------
Tellez-Rojo <5 subgroup.......  Mexico City, age   Children--BLL<5        193  0.8-4.9...........  2.9...............  Linear...........           -1.71
                                 24 mo.             [mu]g/dL.
--------------------------------------------------------------------------------------------------------------------------------------------------------
based on Lanphear et al 2005      Dataset from which the log-linear function is derived is the pooled International
 \C\, Log-linear with low-         dataset of 1333 children, age 6-10 yr, having median blood Pb of 9.7 [mu]g/dL and
 exposure linearization (LLL).                         5th-95th percentile of 2.5-33.2 [mu]g/dL.
                                    LLL \D\: -2.29 at 2 [mu]g/dL
                                         -1.89 at 3 [mu]g/dL
--------------------------------------------------------------------------------------------------------------------------------------------------------
Lanphear et al. 2005 \C\, <7.5  Pooled             Children--peak         103  0.9-7.4...........  3.24..............  Linear...........           -2.94
 peak subgroup.                  International,     BLL <7.5 [mu]g/
                                 age 6-10 yr.       dL.
--------------------------------------------------------------------------------------------------------------------------------------------------------

[[Page 66979]]

                            Set of studies with shallower slopes (Criteria Document Table 6-1) presented in the proposal \E\
--------------------------------------------------------------------------------------------------------------------------------------------------------
Canfield et al 2003 \C\, <10    Rochester, age 5   Children--peak          71  0.5-8.4...........  3.32..............  Linear...........           -1.79
 peak subgroup.                  yr.                BLL <10 [mu]g/dL.
Bellinger and Needleman 2003    Boston \B\ \F\...  Children--peak          48  1-9.3 \F\.........  \F\ 3.8...........  Linear...........           -1.56
 \C\.                                               BLL <10 [mu]g/dL.
Tellez-Rojo et al. 2006.......  Mexico City, age   Full dataset.....      294  0.8-9.8...........  4.28..............  Linear...........           -1.04
                                 24 mo.
Tellez-Rojo et al. 2006 full--  Mexico City, age   Full dataset.....      294  0.8-9.8...........  4.28..............  Log-linear.......       \G\ -0.94
 loglinear.                      24 mo.
Lanphear et al. 2005 \C\, <10   Pooled             Children--peak         244  0.1-9.8...........  4.30..............  Linear...........           -0.80
 peak \C\ subgroup.              International,     BLL <10 [mu]g/dL.
                                 age 6-10 yr.
Al-Saleh et al 2001 full--      Saudi Arabia, age  Full dataset.....      533  2.3-27.36 \H\.....  7.44..............  Log-linear.......       \G\ -0.76
 loglinear.                      6-12 yr.
Kordas et al 2006, <12          Torreon, Mexico,   Children--BLL <12      377  2.3-<12...........  7.9...............  Linear...........           -0.40
 subgroup.                       age 7 yr.          [mu]g/dL.
Lanphear et al 2005 \C\ full--  Pooled             Full dataset.....     1333  0.1-71.7..........  9.7 (median)......  Log-linear.......       \G\ -0.41
 loglinear.                      International,
                                 age 6-10 yr.
--------------------------------------------------------------------------------------------------------------------------------------------------------
    Median value........................................................................................................................       \D\ -0.9
--------------------------------------------------------------------------------------------------------------------------------------------------------
\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).
\B\ Average 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.
\D\ The 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 [mu]g/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 [mu]g/dL. The slopes shown are the average slopes (IQ points per [mu]g/dL blood Pb) associated with application of the
  LLL functions from zero to the blood Pb levels identified (2 and 3 [mu]g/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 [mu]g/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 [mu]g/dL are larger negative values than those shown here (e.g., the slopes to 5 [mu]g/dL are 50% larger negative values).
\H\ 69% of children in Al-Saleh et al. (2001) study had BLL<10 [mu]g/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).\42\ 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).
---------------------------------------------------------------------------

    \42\ 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).
---------------------------------------------------------------------------

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

[[Page 66980]]

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).\43\
---------------------------------------------------------------------------

    \43\ CASAC advice on the design of the risk assessment is 
summarized in section II.C.2.a of the proposal.
---------------------------------------------------------------------------

    The brief summary provided here focuses on blood Pb and risk 
estimates for five case studies \44\ 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.
---------------------------------------------------------------------------

    \44\ 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.
---------------------------------------------------------------------------

    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.\45\ 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.
---------------------------------------------------------------------------

    \45\ 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 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); \46\ (b) current conditions for the 
location-specific \47\ 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 [mu]g/m\3\, with a form of maximum monthly 
average, as well as a level of 0.20 [mu]g/m\3\, 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).
---------------------------------------------------------------------------

    \46\ 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.
    \47\ 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 [mu]g/m\3\ for the study 
areas in Los Angeles, Chicago and Cleveland, respectively.
---------------------------------------------------------------------------

    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

[[Page 66981]]

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).\48\ These exposures were held constant 
across all air quality scenarios.\49\
---------------------------------------------------------------------------

    \48\ 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.
    \49\ 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.
---------------------------------------------------------------------------

    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 [mu]g/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 [mu]g/dL for the location-
specific case studies up to 1.9 [mu]g/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 [mu]g/dL 
(http://www.epa.gov/envirohealth/children/body_burdens/

[[Page 66982]]

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.\50\ 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).
---------------------------------------------------------------------------

    \50\ 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.
---------------------------------------------------------------------------

     Air-to-blood ratios estimated for the primary Pb smelter 
subarea ranged from 1:10 and higher.\51\ 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.
---------------------------------------------------------------------------

    \51\ 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.
---------------------------------------------------------------------------

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.\52\
---------------------------------------------------------------------------

    \52\ 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.
---------------------------------------------------------------------------

    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 \53\ of air-related risk for the current NAAQS and 
alternative standards include:
---------------------------------------------------------------------------

    \53\ 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 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.\54\
---------------------------------------------------------------------------

    \54\ 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.
---------------------------------------------------------------------------

     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 [mu]g/m\3\, maximum monthly average, between 
1.2 and 3.2 points IQ loss for an alternative NAAQS of 0.20 [mu]g/m\3\ 
and between 0.5 and 2.8 points IQ loss for an alternate NAAQS of 0.05 
[mu]g/m\3\, 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 [mu]g/m\3\, maximum monthly average. Consequently, risk 
estimates for these case studies indicate little response to 
alternative standard levels above 0.05 [mu]g/m\3\ maximum monthly 
average (as shown in Table 2).

                        Table 2--Summary of Risk Attributable to Air-related Pb Exposure
----------------------------------------------------------------------------------------------------------------
                                                          Median air-related IQ loss \A\
                                 -------------------------------------------------------------------------------
 NAAQS level simulated  ([mu]g/                                        Location-specific urban case studies
   m\3\ max monthly, except as                      Primary Pb   -----------------------------------------------
          noted below)             General urban      smelter        Cleveland                      Los Angeles
                                    case study    (subarea) case   (0.56 [mu]g/   Chicago  (0.31   (0.17 [mu]g/
                                                    study \B C\        m\3\)        [mu]g/m\3\)        m\3\)
----------------------------------------------------------------------------------------------------------------
1.5 max quarterly \D\...........         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)

[[Page 66983]]

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 [mu]g/m\3\ 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 [mu]g/
dL, and described 15 [mu]g/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.
    As noted in the proposal, the body of available evidence today, 
summarized above in section II.A.2 and in section II.B of the proposal, 
and discussed in the Criteria Document, is substantially expanded from 
that available when the current standard was set three decades ago. The 
Criteria Document presents 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. Further, subsequent to the 
setting of the standard, the Pb NAAQS criteria review during the 1980s 
and the current review have provided ``(a) increasingly stronger 
evidence that substantiatied still lower fetal and/or postnatal Pb-
exposure levels (indexed by blood-Pb levels extending to as low as 10 
to 15 [mu]g/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

[[Page 66984]]

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 [mu]g/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 [mu]g/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 
[mu]g/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 
[mu]g/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 \55\ 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.
---------------------------------------------------------------------------

    \55\ 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.
---------------------------------------------------------------------------

    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.\56\ 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.
---------------------------------------------------------------------------

    \56\ 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).
---------------------------------------------------------------------------

    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 [mu]g/dL and for which a 
linear slope restricted to blood Pb levels below about 10 [mu]g/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 [mu]g/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 
[mu]g/dL.\57\ Multiplying these blood Pb levels by the slope estimate, 
identified above, for blood Pb levels extending up to 10 [mu]g/dL (-0.9 
IQ points per [mu]g/dL), would imply an average air-related IQ loss for 
such a group of children on the order of 4 or more IQ points.
---------------------------------------------------------------------------

    \57\ This is based on the calculation in which 1.5 [mu]g/m\3\ is 
multiplied by a ratio of 3 [mu]g blood Pb per 1 [mu]g/m\3\ air Pb to 
yield an air-related blood Pb estimates of 4.5 [mu]g/dL; using a 1:5 
ratio yields an estimate of 7.5 [mu]g/dL. As with the 1978 framework 
considered in 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.
---------------------------------------------------------------------------

    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

[[Page 66985]]

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 [mu]g/m\3\ 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; \58\ (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.
---------------------------------------------------------------------------

    \58\ 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.
---------------------------------------------------------------------------

    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

[[Page 66986]]

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

[[Page 66987]]

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

[[Page 66988]]

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.\59\ 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 [mu]m in diameter (Pb-PM10) \60\ 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.
---------------------------------------------------------------------------

    \59\ 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 CFR 
50.12, Appendix G).
    \60\ 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.
---------------------------------------------------------------------------

    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) \61\ 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.
---------------------------------------------------------------------------

    \61\ ``Low-volume PM10 sampling'' refers to sampling 
using any of a number of monitor models that draw 16.67 liters/
minute (1 m\3\/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 m\3\/hour).
---------------------------------------------------------------------------

    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) \62\, 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.
---------------------------------------------------------------------------

    \62\ 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.
---------------------------------------------------------------------------

    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,

[[Page 66989]]

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 \63\ 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.
---------------------------------------------------------------------------

    \63\ 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.
---------------------------------------------------------------------------

    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 \64\ (Henderson, 2007a, 2007b, 
2008a).
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    \64\ 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 PM10 Pb/TSP Pb `equivalency ratio' could be 
determined on a regional or site-specific basis''.
---------------------------------------------------------------------------

    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-

[[Page 66990]]

recommended range (with an TSP indicator) of between 0.1 to 0.2 [mu]g/
m\3\ as an upper bound and 0.02 to 0.05 [mu]g/m\3\ 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 [mu]g/m\3\ rather than 
0.2 [mu]g/m\3\ '' (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 [mu]g/m\3\ 
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 [mu]g/m\3\, 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 [mu]g/m\3\), including a level 
of 0.15 [mu]g/m\3\. One commenter (NESCAUM) specifically recommended an 
indicator of Pb-TSP for a NAAQS with a level of 0.15 [mu]g/m\3\, 
recommending a revision to Pb-PM10 only if some other, much 
lower, level (0.05 [mu]g/m\3\) 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 [mu]g/m\3\.
    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 [mu]g/m\3\. 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 [mu]g/m\3\.
    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.\65\
---------------------------------------------------------------------------

    \65\ Data from collocated TSP and PM2.5 monitors are 
generally presented in the Staff Paper (section 2.3.5).
---------------------------------------------------------------------------

    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

[[Page 66991]]

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,\66\ 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.
---------------------------------------------------------------------------

    \66\ 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.
---------------------------------------------------------------------------

    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 [mu]g/
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 [mu]g/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

[[Page 66992]]

Document, the currently available health effects evidence \67\ 
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.\68\
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    \67\ The differing evidence and associated strength of the 
evidence for these different effects is described in the Criteria 
Document.
    \68\ 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).
---------------------------------------------------------------------------

    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 
\69\ provides an additional complication in the case of Pb.
---------------------------------------------------------------------------

    \69\ 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).
---------------------------------------------------------------------------

    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

[[Page 66993]]

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.\70\ 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.
---------------------------------------------------------------------------

    \70\ 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)
---------------------------------------------------------------------------

    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

[[Page 66994]]

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 [mu]g/m3 was 
met, while a single month within that quarter was some 30% percent 
higher (2.07 [mu]g/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

[[Page 66995]]

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).\71\
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    \71\ These analyses incorporate the revised averaging method 
identified above and discussed more fully in section IV below.
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    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

[[Page 66996]]

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.\72\ 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 [mu]g/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.
---------------------------------------------------------------------------

    \72\ 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).
---------------------------------------------------------------------------

    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

[[Page 66997]]

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 [mu]g/m \3\, 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 [mu]g/m \3\ up to 0.50 [mu]g/m \3\ and below 
0.10 [mu]g/m \3\. 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.\73\ 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.\74\
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    \73\ 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 [mu]g/
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 [mu]g/dL (see Table 1).
    \74\ 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).

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[[Page 66998]]

    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 [mu]g/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.\75\ 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.
---------------------------------------------------------------------------

    \75\ 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.
---------------------------------------------------------------------------

    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 [mu]g/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 [mu]g/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

[[Page 66999]]

proposal, indicated that for standard levels above 0.30 [mu]g/
m3 up to 0.50 [mu]g/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 [mu]g/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 [mu]g/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 [mu]g/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 \76\ 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.
---------------------------------------------------------------------------

    \76\ 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).
---------------------------------------------------------------------------

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,\77\ 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.
---------------------------------------------------------------------------

    \77\ 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.
---------------------------------------------------------------------------

(i) General Comments on Range of Levels
    In considering comments received on the proposal related to the 
standard level, EPA first notes the general advice provided by CASAC 
concerning the proposal in a July 2008 letter to the Administrator 
(Henderson, 2008b). In that letter, CASAC emphasized their unanimous 
recommendation (initially stated in their March 2007 letter) regarding 
``the need to substantially lower the level'' of the primary Pb 
standard such that the upper bound should be ``no higher than 0.2 
[mu]g/m\3\'' (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 
[mu]g/m\3\. 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 [mu]g/m\3\. In recommending 
levels below 0.2 [mu]g/m\3\, some of these stated that CASAC's 
recommendation for an upper bound of 0.2 [mu]g/m\3\ should not be read 
to imply that CASAC supported a standard level of 0.2 [mu]g/m\3\ 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 [mu]g/
m\3\) 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 [mu]g/m\3\ as necessary to protect public health with an 
adequate margin of safety, with some of these additionally

[[Page 67000]]

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 
[mu]g/m\3\, 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 [mu]g/m\3\. Among this group, some 
commenters provide little or no health-based rationale for their 
comment. Other commenters, in recommending various levels above 0.2 
[mu]g/m\3\, 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 [mu]g/m\3\; 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 [mu]g/m\3\ 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 [mu]g/m\3\ 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

[[Page 67001]]

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) \78\ 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.
---------------------------------------------------------------------------

    \78\ 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).
---------------------------------------------------------------------------

    Alternatively, two industry commenters supported the range 
presented in the proposal of 1:3 to 1:7.\79\ 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).\80\
---------------------------------------------------------------------------

    \79\ A ratio of 1:5 was recommended by one of these commenters 
(Doe Run Resources Corp.).
    \80\ See previous footnote regarding Hayes et al. (1994).
---------------------------------------------------------------------------

    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

[[Page 67002]]

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 [mu]g/dL, also 
includes studies with mean or median blood Pb levels ranging up to 9.7 
[mu]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 [mu]g/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 [mu]g/dL and the 5th and 95th 
percentiles are 0.7 [mu]g/dL and 5.1 [mu]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.\81\ 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.\82\
---------------------------------------------------------------------------

    \81\ 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 [mu]g/m\3\ 
would be approximately 1 [mu]g/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 [mu]g/dL.
    \82\ 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.

---------------------------------------------------------------------------

[[Page 67003]]

    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 [mu]g/dL, while mean blood Pb levels for the other three study 
groups considered in the proposal range from 7.4 up to 9.7 [mu]g/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 [mu]g/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 ([mu]g/dL)                                                      Average linear
---------------------------------------------------------------                                    slope \A\ (IQ
                                                  Range (min-            Study/analysis             points per
                Geometric mean                       max)                                            [mu]g/dL)
----------------------------------------------------------------------------------------------------------------
2.9...........................................         0.8-4.9  Tellez-Rojo et al. 2006, <5                -1.71
                                                                 subgroup.
3.24..........................................         0.9-7.4  Lanphear et al. 2005 \B\, <7.5             -2.94
                                                                 peak subgroup.
3.32..........................................         0.5-8.4  Canfield et al. 2003 \B\, <10              -1.79
                                                                 peak subgroup.
3.8...........................................           1-9.3  Bellinger and Needleman 2003               -1.56
                                                                 \B\, <10 peak subgroup.
                                               -----------------------------------------------------------------
    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 for 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

[[Page 67004]]

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 [mu]g/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.

[[Page 67005]]

    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.\83\
---------------------------------------------------------------------------

    \83\ 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.
---------------------------------------------------------------------------

    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 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 
[mu]g/m\3\) 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 [mu]g/m\3\ and 
lower. At a level of 0.15 [mu]g/m\3\, 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
------------------------------------------------------------------------
                         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
 Potential level     functions with blood Pb levels closer to those of
   for standard       today's U.S. children (range shown for estimates
   ([mu]g/m\3\)           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)

[[Page 67006]]

           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.\84\
---------------------------------------------------------------------------

    \84\ For example, in considering a standard level of 0.2 [mu]g/
m\3\, 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.
---------------------------------------------------------------------------

    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 [mu]g/m\3\, 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 [mu]g/m\3\ 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 [mu]g/m\3\, 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 [mu]g/m\3\ 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 [mu]g/m\3\, 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 [mu]g/m\3\ 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

[[Page 67007]]

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 [mu]g/m\3\ 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 [mu]g/m\3\. 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 [mu]g/m\3\ 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 
[mu]g/m\3\, 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.

[[Page 67008]]

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

[[Page 67009]]

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 nonair 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

[[Page 67010]]

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
    The current standard was set in 1978 to be identical to the primary 
standard (1.5 [mu]g Pb/m\3\, 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.
    The secondary standard was subsequently considered during the 1980s 
in development of the 1986 Criteria Document (USEPA, 1986a) and the 
1990 Staff Paper (USEPA, 1990b). In summarizing OAQPS staff conclusions 
and recommendations at that time, the 1990 Staff Paper stated that a 
qualitative assessment of available field studies and animal 
toxicological data suggested that ``domestic animals and wildlife are 
as susceptible to the effects of lead as laboratory animals used to 
investigate human lead toxicity risks.'' Further, the 1990 Staff Paper 
highlighted concerns over potential ecosystem effects of Pb due to its 
persistence, but concluded that pending development of a stronger 
database that more accurately quantifies ecological effects of 
different Pb concentrations, consideration should be given to retaining 
a secondary standard at or below the level of the then-current 
secondary standard of 1.5 [mu]g/m\3\.
    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 nonair 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 nonair 
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

[[Page 67011]]

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

[[Page 67012]]

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.\85\ 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.
---------------------------------------------------------------------------

    \85\ 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.
---------------------------------------------------------------------------

    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 to 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.
    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. 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.

[[Page 67013]]

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.\86\
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    \86\ 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 test 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 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.C, 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.\87\ 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.
---------------------------------------------------------------------------

    \87\ 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.
---------------------------------------------------------------------------

    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

[[Page 67014]]

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.\88\ 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.
---------------------------------------------------------------------------

    \88\ 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.
---------------------------------------------------------------------------

    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.

[[Page 67015]]

    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.\89\
---------------------------------------------------------------------------

    \89\ No public comment was received on this provision.
---------------------------------------------------------------------------

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 \90\, 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.E.
---------------------------------------------------------------------------

    \90\ 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.
---------------------------------------------------------------------------

    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.\91\ 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

[[Page 67016]]

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.\92\ 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.\93\ For the non-source-oriented sites and years of data for 
which all the proposed criteria were met, the scaling factors 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.
---------------------------------------------------------------------------

    \91\ Scaling Factor: PM10 versus TSP, Neptune and 
Company, Inc., Final Report, September 30, 2008.
    \92\ 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.
    \93\ 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.
---------------------------------------------------------------------------

    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 monitoring (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.\94\ The corresponding range of

[[Page 67017]]

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.\95\ 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 [mu]g/m3, which is 67 percent of the final NAAQS 
level.\96\ 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 [mu]g/m3, a Pb-
TSP monitor must be installed.\97\ 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 
[mu]g/m3 and 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.
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    \94\ 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.
    \95\ 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.
    \96\ 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.
    \97\ 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.
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    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 [mu]g/m\3\ (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 [mu]g/m\3\.\98\ A state may also 
operate non-required Pb monitors at any other locations of its 
choosing, and these may be of any type.
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    \98\ If three years of Pb-TSP monitoring results in no 3-month 
average Pb concentration equal to or greater than 0.10 [mu]g/m\3\, 
as might occur after the source improves its control of Pb 
emissions, the site would again be eligible for Pb-PM10 
monitoring.
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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 [mu]g/m\3\. Section IV.E 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

[[Page 67018]]

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.\99\ 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.
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    \99\ 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.
---------------------------------------------------------------------------

    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 \100\, 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.
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    \100\ 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.
---------------------------------------------------------------------------

    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

[[Page 67019]]

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.\101\ 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.
---------------------------------------------------------------------------

    \101\ 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.
---------------------------------------------------------------------------

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 [mu]g/m\3\ (0.xxx) with additional digits 
truncated, and that monthly averages calculated from the daily averages 
would be rounded to the nearest hundredth [mu]g/m\3\ (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 [mu]g/
m\3\, 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,\102\ 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

[[Page 67020]]

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.
---------------------------------------------------------------------------

    \102\ 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.
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    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.\103\ 
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,\104\ but they will not be combined because that might give double 
weight to some days.
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    \103\ 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.
    \104\ 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.
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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.\105\ All 21 FEMs are based 
on the use of high-volume TSP samplers and a variety of approved 
equivalent analysis methods.\106\
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    \105\ For a list of currently approved FRM/FEMs for Pb-TSP refer 
to: http://www.epa.gov/ttn/amtic/criteria.html.
    \106\ The 21 distinct approved FEMs represent less than 21 
fundamentally different analysis methods, as some differ only in 
minor aspects.
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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,

[[Page 67021]]

or other ways to supplement Pb-TSP monitoring data with Pb-
PM10 data, and those comments are addressed in Section IV.D, 
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.\107\ 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 
[mu]g/m\3\ 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.
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    \107\ 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.
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    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 [mu]m), 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.\108\ 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.
---------------------------------------------------------------------------

    \108\ 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.
---------------------------------------------------------------------------

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

[[Page 67022]]

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 cannot 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 [mu]g/m\3\ and 0.00006 [mu]g/m\3\, 
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 CFR 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 is a polycarbonate filter that contains a 
certified concentration for Pb equivalent to 0.013  0.002 
[mu]g/m\3\. 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

[[Page 67023]]

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 [mu]g/
m\3\) 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.
 3. 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.
a. 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 [mu]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 [mu]g/m3. In addition, 
the Agency proposed to lower the Pb NAAQS level to between 0.10 and 
0.30 [mu]g/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 [mu]g/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 [mu]g per spiked filter 
strip (equivalent to 0.5, 1.5, and 3.75 [mu]g/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 \3/4\-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 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 [mu]g/
m3), the maximum LOQ would still be less than one half of 
the NAAQS (i.e., 0.075 [mu]g/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 non-source-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 certain language including 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

[[Page 67024]]

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 [mu]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) has been 
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, has been removed and 
sections 4.2.2 and 4.2.3 have been used to assess flow rate information 
and section 4.1.3 has been 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.

[[Page 67025]]

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 reasonably 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 \109\) 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 http://www.census.gov/popest/
metro/index.html for the latest census estimates.)
---------------------------------------------------------------------------

    \109\ For the complete definition of CBSA refer to: http://
www.census.gov/population/www/estimates/aboutmetro.html.
---------------------------------------------------------------------------

    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 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 non-source-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

[[Page 67026]]

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 without 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 source's 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

[[Page 67027]]

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.'' The commenter argued 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.\110\ 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.
---------------------------------------------------------------------------

    \110\ 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.
---------------------------------------------------------------------------

    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 based on the latest available census 
figures. 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 Bureau).
    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 meet the quality assurance requirements 
that are collected from non-required FRM or FEM monitors will also be 
used to determine compliance with the Pb NAAQS. Additionally, as

[[Page 67028]]

described previously, source-oriented monitoring would be required in 
rural and small communities if a Pb source emitting 1 ton per year or 
more is 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 exceedance 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 non-source-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. These commenters also 
suggested that if at some point in the future the monitor were to show 
that Pb-PM10 concentrations exceeded 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 only in 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 altogether 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 [mu]g/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 
[mu]g/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., non-
source-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 non-source-oriented monitors (unless 
existing data indicates maximum 3-month arithmetic mean Pb 
concentration has exceeded 0.10 [mu]g/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 
[mu]g/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 
[mu]g/m3. Section IV.E 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

[[Page 67029]]

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 non-source-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 
non-source-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 [mu]g/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 [mu]g/
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 [mu]g/
m3 or more. For example, if a Pb-PM10 monitoring 
site measures an arithmetic 3-month mean concentration of 0.10 [mu]g/
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 non-source-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 exceedances 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 provide 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

[[Page 67030]]

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 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 [mu]g/m\3\ 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

[[Page 67031]]

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.\111\ 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.
---------------------------------------------------------------------------

    \111\ American Petroleum Institute v. Costle, 609 F.2d 20 (D.C. 
Cir. 1979).
---------------------------------------------------------------------------

    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.\112\ In some areas, EPA

[[Page 67032]]

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.
---------------------------------------------------------------------------

    \112\ 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.
---------------------------------------------------------------------------

    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

[[Page 67033]]

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.

[[Page 67034]]

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 
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 
demonstrate 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.\113\ 
The list of section 110(a)(2) NAAQS implementation requirements are the 
following:
---------------------------------------------------------------------------

    \113\ 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.
---------------------------------------------------------------------------

     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

[[Page 67035]]

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

[[Page 67036]]

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,\114\ 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 timeframes.
---------------------------------------------------------------------------

    \114\ 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.
---------------------------------------------------------------------------

    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

[[Page 67037]]

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.\115\ 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.
---------------------------------------------------------------------------

    \115\ 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.
---------------------------------------------------------------------------

    Given the proposal to promulgate a revised Pb NAAQS that is 
significantly lower than the current level of 1.5 [mu]g/m\3\, 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
    Several commenters stated that given the proposed level of the lead 
NAAQS that EPA should set the threshold for RACT analysis for 
stationary sources at a threshold level similar to the level being 
considered for the source monitoring requirements, which is between 200 
kg/yr-600 kg/yr. Several commenters suggested a lower threshold (such 
as 45 kg/year) or stated that depending on the attainment needs for the 
affected area, it may be necessary to evaluate control technology that 
is reasonably available for sources with actual emissions that are 
lower than the recommended RACM/RACT threshold to take into 
consideration the actual attainment needs for the affected area. One 
commenter suggested the threshold should be set only at a level at 
which an exceedance of the NAAQS is expected, while another suggested 
it should be set no higher than that level.
    The EPA believes that it is appropriate to set the recommended 
threshold for the RACT analysis for the new standard at 0.5 tpy. The 
existing Pb NAAQS is set at 1.5 [mu]g/m\3\ and the existing threshold 
for RACT analysis is 5 tpy. Since the standard is being reduced by a 
factor of ten, from 1.5 [mu]g/m\3\ to 0.15 [mu]g/m\3\, 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

[[Page 67038]]

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 states' 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.\116\ 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.
---------------------------------------------------------------------------

    \116\ 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).
---------------------------------------------------------------------------

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

[[Page 67039]]

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

[[Page 67040]]

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 CFR 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.\117\ The NSR program is 
composed of three different permit programs:
---------------------------------------------------------------------------

    \117\ 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.
---------------------------------------------------------------------------

     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.\118\ 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.
---------------------------------------------------------------------------

    \118\ 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).
---------------------------------------------------------------------------

    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 the 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

[[Page 67041]]

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 statewide 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 
preexisting 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

[[Page 67042]]

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

[[Page 67043]]

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: \119\ 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.\120\
---------------------------------------------------------------------------

    \119\ Criteria pollutants are those pollutants for which EPA has 
established a NAAQS under section 109 of the CAA.
    \120\ 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.
---------------------------------------------------------------------------

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.\121\
---------------------------------------------------------------------------

    \121\ 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)
---------------------------------------------------------------------------

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

[[Page 67044]]

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                                         Detailed  documentation  submission
             calendar year                   Event flagging deadline                     deadline
----------------------------------------------------------------------------------------------------------------
2006...................................  July 1, 2009 *.................  September 15, 2010. *
2007...................................  July 1, 2009 *.................  September 15, 2010.
2008...................................  July 1, 2009...................  September 15, 2010. *
2009...................................  July 1, 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                                         Detailed  documentation  submission
             calendar year                   Event flagging deadline                     deadline
----------------------------------------------------------------------------------------------------------------
2006...................................  July 1, 2009 *.................  September 15, 2009.
2007...................................  July 1, 2009 *.................  September 15, 2009. *
2008...................................  July 1, 2009...................  September 15, 2009. *

[[Page 67045]]

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                                          Detailed documentation submission
             calendar year                   Event flagging deadline                     deadline
----------------------------------------------------------------------------------------------------------------
2006...................................  July 1, 2009 *.................  October 15 2010. *
2007...................................  July 1, 2009 *.................  October 15, 2010.
2008...................................  July 1, 2009...................  October 15, 2010. *
2009...................................  July 1, 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                                         Detailed  documentation  submission
             calendar year                   Event flagging deadline                     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

    Under section 3(f)(1) of Executive Order (EO) 12866 (58 FR 51735, 
October 4, 1993), this action is an ``economically significant 
regulatory action'' because it is likely to have an annual effect on 
the economy of $100 million or more. Accordingly, EPA submitted this 
action to the Office of Management and Budget (OMB) for review under EO 
12866 and any changes made in response to OMB recommendations have been 
documented in the docket for this action (EPA-HQ-OAR-2006-0735). In 
addition, EPA prepared a Regulatory Impact Analysis (RIA) of the 
potential costs and benefits associated with this action. A copy of the 
analysis is available in the RIA docket (EPA-HQ-OAR-2008-0253) and the 
analysis is briefly summarized here. The RIA estimates the costs and 
monetized human health and welfare benefits of attaining four 
alternative Pb NAAQS nationwide. Specifically, the RIA examines the 
alternatives of 0.50 [mu]g/m3, 0.40 [mu]g/m3, 
0.30 [mu]g/m3, 0.20 [mu]g/m3, 0.15 [mu]g/
m3 and 0.10 [mu]g/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

[[Page 67046]]

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

[[Page 67047]]

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, Sec.  12(d) (15 U.S.C. 272 
note) directs EPA to use voluntary consensus

[[Page 67048]]

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 EO 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 January 12, 2009.

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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: October 15, 2008.
Stephen L. Johnson,
Administrator.

0
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

0
1. The authority citation for part 50 continues to read as follows:

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

0
2. Section 50.3 is revised to read as follows:

Sec.  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 Sec. Sec.  50.7 and 
50.13 and lead standards contained in Sec.  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 Sec. Sec.  50.7 and 50.13 and of lead for purposes of comparison to 
the standards contained in Sec.  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.

0
3. Section 50.12 is amended by designating the existing text as 
paragraph (a) and adding paragraph (b) to read as follows:

Sec.  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 Sec.  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 Sec.  50.16; 
except that for areas designated nonattainment for the lead NAAQS set 
forth in this section as of the effective date of Sec.  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 Sec.  50.16.

0
4. Section 50.14 is amended by:
0
a. Revising paragraph (a)(2);
0
b. Revising paragraph (c)(2)(iii);
0
c. Redesignating paragraph (c)(2)(v) as paragraph (c)(2)(vi) and adding 
a new paragraph (c)(2)(v); and
0
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:

Sec.  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 year 
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.
* * * * *

[[Page 67052]]

0
5. Section 50.16 is added to read as follows:

Sec.  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.

0
6. Appendix G is amended as follows:
0
a. In section 10.2 the definition of the term ``VSTP'' in 
the equation is revised,
0
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).
* * * * *

0
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 [mu]m) 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 ([mu]g/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 [mu]g/m3 at local temperature and pressure 
conditions.
    2.1 EDXRF Pb Measurement Range. The typical ambient air 
measurement range is 0.001 to 30 [mu]g Pb/m3, assuming an 
upper range calibration standard of about 60 [mu]g 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 [mu]g 
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 [mu]g/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 [mu]g/cm2. 
The maximum PM10 filter loading or upper concentration 
limit of mass expected to be collected by the PM10c 
sampler is 200 [mu]g/m3 (Appendix O to Part 50, Section 
3.2). This equates to a mass loading of about 400 [mu]g/
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-

[[Page 67053]]

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.
    3.2 Spectral Interferences and Spectral Overlap. Spectral 
interference occurs when the entirety of the analyte spectral lines 
of two species are nearly 100% overlapped. The presence of arsenic 
(As) is a problematic interference for EDXRF systems which use the 
Pb L[alpha] line exclusively to quantify the Pb concentration. This 
is because the Pb L[alpha] line and the As K[alpha] lines severely 
overlap. The use of multiple Pb lines, including the L[beta] and/or 
the L[gamma] 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 
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 (http://www.spectro.com), Xenemetrix (http://
www.xenemetrix.com) and PANalytical (http://www.panalytical.com).\1\ 
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.
---------------------------------------------------------------------------

    \1\ 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.
---------------------------------------------------------------------------

    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 [mu]g/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 [mu]g/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 ([mu]g/
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

[[Page 67054]]

(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 ([mu]g/m3) is calculated using the 
following equation:
[GRAPHIC] [TIFF OMITTED] TR12NO08.000

Where,

MPb is the mass per unit volume for lead in [mu]g/m3;
CPb is the mass per unit area for lead in [mu]g/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:

[delta]tot = ([delta]f2 + [delta]a2 + [delta]c2 + [delta]v2) 1/2

Where,

[delta]f = fitting uncertainty (XRF-specific, from 2 to 
100+%)
[delta]a = attenuation uncertainty (XRF-specific, 
insignificant for Pb)
[delta]c = calibration uncertainty (combined lab 
uncertainty, assumed as 5%)
[delta]v = 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.

0
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 Sec.  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 
Sec. Sec.  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.

[[Page 67055]]

    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-month mean 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 ([mu]g/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-

[[Page 67056]]

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 ([mu]g/m3). A Pb design value that meets the 
NAAQS (i.e., 0.15 [mu]g/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 [mu]g/
m3, no matter whether determined from Pb-TSP or Pb-
PM10 data. A Pb design value greater than 0.15 [mu]g/
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 [mu]g/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

[[Page 67057]]

(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 
[mu]g/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).
[GRAPHIC] [TIFF OMITTED] TR12NO08.001

Where:

Xm,y,s = the mean for month m of the year y for sites; 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.
[GRAPHIC] [TIFF OMITTED] TR12NO08.002

Where:

Xm1, 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
Xm, 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

0
9. The authority citation for part 51 continues to read as follows:

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

0
10. Section 51.117 is amended by revising paragraph (e)(1) to read as 
follows:

Sec.  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

0
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]

0
12. Section 53.33 is revised to read as follows:

Sec.  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:

[[Page 67058]]

    (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 
part 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 part 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 Sec.  53.4(a). For Pb in TSP collected by the high-
volume sampling method, the audit samples are \3/4\ x 8-inch glass 
fiber strips containing known amounts of Pb in micrograms per strip 
([mu]g/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 ([mu]g/filter) 
equivalent to the same percentages of the NAAQS: 30%, 100%, and 250%. 
The true amount of Pb (Tqi), in total [mu]g/strip (for TSP) or total 
[mu]g/filter (for PM10), will be provided for each audit 
sample.
    (g) Filter analysis.
    (1) For both the reference method samples (e) and the audit samples 
(f), analyze each filter or filter extract three times in accordance 
with the reference method analytical procedure. This applies to both 
the Pb in TSP and Pb in PM10 methods. The analysis of 
replicates should not be performed sequentially, i.e., a single sample 
should not be analyzed three times in sequence. Calculate the indicated 
Pb concentrations for the reference method samples in micrograms per 
cubic meter ([mu]g/m\3\) for each analysis of each filter. Calculate 
the indicated total Pb amount for the audit samples in [mu]g/strip for 
each analysis of each strip or [mu]g/filter for each analysis of each 
audit filter. Label these test results as R1A, 
R1B, R1C, R2A, R2B, etc., 
Q1A, Q1B, Q1C, etc., where R denotes 
results from the reference method samples; Q denotes results from the 
audit samples; 1, 2, 3 indicate the filter number, and A, B, C indicate 
the first, second, and third analysis of each filter, respectively.
    (2) For the candidate method samples, analyze each sample filter or 
filter extract three times and calculate, in accordance with the 
candidate method, the indicated Pb concentration in [mu]g/m 
3 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:
[GRAPHIC] [TIFF OMITTED] TR12NO08.003

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:
[GRAPHIC] [TIFF OMITTED] TR12NO08.004

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:
[GRAPHIC] [TIFF OMITTED] TR12NO08.005

    (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 [mu]g/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

[[Page 67059]]

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:
[GRAPHIC] [TIFF OMITTED] TR12NO08.006

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:
[GRAPHIC] [TIFF OMITTED] TR12NO08.007

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 [mu]g/m3. The MDL of the 
candidate method must be equal to, or less than 5% of the level of the 
Pb NAAQS.

0
13. Table C-3 to Subpart C of Part 53 is revised to read as follows:

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

------------------------------------------------------------------------
Concentration range equivalent to           30% to 250%
 percentage of NAAQS in [mu]g/m\3\.
Minimum number of 24-hr measurements......  5
Maximum reference method analytical bias,   5%
 Dq.
Maximum precision, PR or PC...............  <=15%
Maximum difference (D)....................  20%
Estimated Method Detection Limit (MDL),     5% of NAAQS level.
 [mu]g/m\3\.
------------------------------------------------------------------------

PART 58--AMBIENT AIR QUALITY SURVEILLANCE

0
14. 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]

0
15. Section 58.10, is amended by added paragraph subsections (a)(4) and 
adding paragraph (b)(9) to read as follows:

Sec.  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 non-source-
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 non-source-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.
* * * * *

0
16. Section 58.13 is amended by revising paragraph (b) to read as 
follows:

Sec.  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.
0
17. Section 58.16 is amended by revising paragraph (a) to read as 
follows:

Sec.  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;

[[Page 67060]]

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 onsite 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]

0
18. Section 58.20 is amended by revising paragraph (e) to read as 
follows:

Sec.  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.
* * * * *

0
19. Appendix A to Part 58 is amended to read as follows:
0
a. Revising paragraph 1,
0
b. Adding paragraph 2.3.1.4,
0
c. Revising paragraph 3.3.4,
0
d. Revising paragraph 4c,
0
e. Revising paragraph 4.4,
0
f. Removing paragraph 4.5 and
0
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, [mu]g/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 [mu]g Pb/filter or 
strip) and the corresponding measured concentrations (in [mu]g 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 [mu]g/m3.
    (2) Pb: 0.02 [mu]g/m3.
    (3) PM10 (Hi-Vol): 15 [mu]g/m3.
    (4) PM10 (Lo-Vol): 3 [mu]g/m3.
    (5) PM10-2.5 and PM2.5: 3 [mu]g/
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

[[Page 67061]]

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
----------------------------------------------------------------------------------------------------------------
                                                                                                  Parameters
             Method                Assessment method       Coverage       Minimum  frequency       reported
----------------------------------------------------------------------------------------------------------------
                                                Automated Methods
----------------------------------------------------------------------------------------------------------------
1-Point QC for SO2, NO2, O3, CO.  Response check at   Each analyzer.....  Once per 2 weeks..  Audit
                                   concentration                                               concentration \1\
                                   0.01-0.1 ppm SO2,                                           and measured
                                   NO2, O3, and 1-10                                           concentration
                                   ppm CO.                                                     \2\.
Annual performance evaluation     See section 3.2.2   Each analyzer.....  Once per year.....  Audit
 for SO2, NO2, O3, CO.             of this appendix.                                           concentration \1\
                                                                                               and measured
                                                                                               concentration \2\
                                                                                               for each level.
Flow rate verification PM10,      Check of sampler    Each sampler......  Once every month..  Audit flow rate
 PM2.5, PM10	2.5.                  flow rate.                                                  and measured flow
                                                                                               rate indicated by
                                                                                               the sampler.
Semi-annual flow rate audit       Check of sampler    Each sampler......  Once every 6        Audit flow rate
 PM10, PM2.5, PM10	2.5.            flow rate using                         months.             and measured flow
                                   independent                                                 rate indicated by
                                   standard.                                                   the sampler.
Collocated sampling PM2.5,        Collocated          15%...............  Every 12 days.....  Primary sampler
 PM10	2.5.                         samplers.                                                   concentration and
                                                                                               duplicate sampler
                                                                                               concentration.
Performance evaluation program    Collocated          1. 5 valid audits   Over all 4          Primary sampler
 PM2.5, PM10	2.5.                  samplers.           for primary QA      quarters.           concentration and
                                                       orgs, with <=5                          performance
                                                       sites.                                  evaluation
                                                      2. 8 valid audits                        sampler
                                                       for primary QA                          concentration.
                                                       orgs, with >5
                                                       sites.
                                                      3. All samplers in
                                                       6 years.
----------------------------------------------------------------------------------------------------------------
                                                 Manual Methods
----------------------------------------------------------------------------------------------------------------
Collocated sampling PM10, TSP,    Collocated          15%...............  Every 12 days PSD-- Primary sampler
 PM10	2.5, PM2.5, Pb-TSP, Pb-      samplers.                               every 6 days.       concentration and
 PM10.                                                                                         duplicate sampler
                                                                                               concentration.
Flow rate verification PM10 (low  Check of sampler    Each sampler......  Once every month..  Audit flow rate
 Vol), PM10	2.5, PM2.5, Pb-PM10.   flow rate.                                                  and measured flow
                                                                                               rate indicated by
                                                                                               the sampler.
Flow rate verification PM10       Check of sampler    Each sampler......  Once every quarter  Audit flow rate
 (High-Vol), TSP, Pb-TSP.          flow rate.                                                  and measured flow
                                                                                               rate indicated by
                                                                                               the sampler.
Semi-annual flow rate audit       Check of sampler    Each sampler, all   Once every 6        Audit flow rate
 PM10, TSP, PM10	2.5, PM2.5, Pb-   flow rate using     locations.          months.             and measured flow
 TSP, Pb-PM10.                     independent                                                 rate indicated by
                                   standard.                                                   the sampler.
Pb audit strips Pb-TSP, Pb-PM10.  Check of            Analytical........  Each quarter......  Actual
                                   analytical system                                           concentration and
                                   with Pb audit                                               audit
                                   strips.                                                     concentration.
Performance evaluation program    Collocated          1. 5 valid audits   Over all 4          Primary sampler
 PM2.5, PM10	2.5.                  samplers.           for primary QA      quarters.           concentration and
                                                       orgs, with <=5                          performance
                                                       sites.                                  evaluation
                                                      2. 8 valid audits                        sampler
                                                       for primary QA                          concentration.
                                                       orgs, with >5
                                                       sites.
                                                      3. All samplers in
                                                       6 years.
Performance evaluation program    Collocated          1. 1 valid audit    Over all 4          Primary sampler
 Pb-TSP, Pb-PM10.                  samplers.           and 4 collocated    quarters.           concentration and
                                                       samples for                             performance
                                                       primary QA orgs,                        evaluation
                                                       with >5 sites.                          sampler
                                                      2. 2 valid audits                        concentration.
                                                       and 6 collocated                        Primary sampler
                                                       samples for                             concentration and
                                                       primary QA orgs,                        duplicate sampler
                                                       with >5 sites.                          concentration.
----------------------------------------------------------------------------------------------------------------
\1\ Effective concentration for open path analyzers.
\2\ Corrected concentration, if applicable, for open path analyzers.

0
20. Appendix C to Part 58 is amended by adding paragraph 2.10 to read 
as follows:
* * * * *

    2.10 Use of Pb-PM10 at 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 non-source-oriented sites required under paragraph 4.5(b) of

[[Page 67062]]

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.

0
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 (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 non-source-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, or 
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 
non-source-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.
* * * * *

[FR Doc. E8-25654 Filed 11-10-08; 8:45 am]

BILLING CODE 6560-50-P