66964 Federal Register / Vol. 73, No. 219 / Wednesday, November 12, 2008 / Rules and Regulations 

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. 

SUMMARY: Based on its review of the air 

quality criteria and national ambient air 

quality standards (NAAQS) for lead 

(Pb), EPA is making revisions to the 

primary and secondary NAAQS for Pb 

to provide requisite protection of public 

health and welfare, respectively. With 

regard to the primary standard, EPA is 

revising the level to 0.15 μg/m3. EPA is 

retaining the current indicator of Pb in 

total suspended particles (Pb-TSP). EPA 

is revising the averaging time to a 

rolling 3-month period with a maximum 

(not-to-be-exceeded) form, evaluated 

over a 3-year period. EPA is revising the 

secondary standard to be identical in all 

respects to the revised primary 

standard. 

EPA is also revising data handling 

procedures, including allowance for the 

use of Pb-PM10 data in certain 

circumstances, and the treatment of 

exceptional events, and ambient air 

monitoring and reporting requirements 

for Pb, including those related to 

sampling and analysis methods, 

network design, sampling schedule, and 

data reporting. Finally, EPA is revising 

emissions inventory reporting 

requirements and providing guidance 

on its approach for implementing the 

revised primary and secondary 

standards for Pb. 

DATES: This final rule is effective on 

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; email: 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 PbPM10

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 PbPM10 Data 

3. Conclusions on Use of Pb-TSP and PbPM10 Data 

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Federal Register / Vol. 73, No. 219 / Wednesday, November 12, 2008 / Rules and Regulations 66965 

1The 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). 

F. Data Reporting and Rounding 

1. Proposed Provisions 

2. Comments on Data Reporting and 

Rounding 

3. Conclusions on Data Reporting and 

Rounding 

G. Other Aspects of Data Interpretation 

V. Ambient Monitoring Related to Revised 

Lead Standards 

A. Sampling and Analysis Methods 

1. Pb-TSP Method 

a. Proposed Changes 

b. Comments on Pb-TSP Method 

c. Decisions on Pb-TSP Method 

2. Pb-PM10 Method 

a. Proposed FRM for Pb-PM10 Monitoring 

b. Comments on Proposed Pb-PM10 FRM 

c. Decisions on Pb-PM10 FRM 

3. FEM Requirements 

a. Proposed FEM Requirements 

b. Comments 

c. Decisions on FEM Requirements 

4. Quality Assurance Requirements 

a. Proposed Changes 

b. Comments 

c. Decisions on Quality Assurance 

Requirements 

B. Network Design 

1. Proposed Changes 

2. Comments on Network Design 

a. Source-oriented monitoring 

b. Non-source-oriented monitoring 

c. Roadway Monitoring 

d. Use of Pb-PM10 Monitors 

e. Required timeline for monitor 

installation and operation 

3. Decisions on Network Design 

Requirements 

C. Sampling Frequency 

D. Monitoring for the Secondary Standard 

E. Other Monitoring Regulation Changes 

1. Reporting of Average Pressure and 

Temperature 

2. Special Purpose Monitoring 

3. Reporting of Pb-TSP Concentrations 

VI. Implementation Considerations 

A. Designations for the Lead NAAQS 

1. Proposal 

2. Comments and Responses 

3. Final 

B. Lead Nonattainment Area Boundaries 

1. Proposal 

2. Comments and Responses 

3. Final 

C. Classifications 

1. Proposal 

2. Comments and Responses 

3. Final 

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

Infrastructure Requirements 

1. Proposal 

2. Final 

E. Attainment Dates 

1. Proposal 

2. Comments and Responses 

3. Final 

F. Attainment Planning Requirements 

1. RACM/RACT for Lead Nonattainment 

Areas 

a. Proposal 

b. Comments and Responses 

c. Final 

2. Demonstration of Attainment for Lead 

Nonattainment Areas 

a. Proposal 

b. Final 

3. Reasonable Further Progress (RFP) 

a. Proposal 

b. Comments and Responses 

c. Final 

4. Contingency Measures 

a. Proposal 

b. Comments and Responses 

c. Final 

5. Nonattainment New Source Review 

(NSR) and Prevention of Significant 

Deterioration (PSD) Requirements 

a. Proposal 

b. Comments and Responses 

c. Final 

6. Emissions Inventories 

a. Proposal 

b. Comments and Responses 

c. Final 

7. Modeling 

a. Proposal 

b. Comments and Responses 

c. Final 

G. General Conformity 

1. Proposal 

2. Final 

H. Transition From the Current NAAQS to 

a Revised NAAQS for Lead 

1. Proposal 

2. Final 

VII. Exceptional Events Information 

Submission Schedule for Lead NAAQS 

A. Proposal 

B. Comments and Responses 

C. Final 

VIII. Statutory and Executive Order Reviews 

A. Executive Order 12866: Regulatory 

Planning and Review 

B. Paperwork Reduction Act 

C. Regulatory Flexibility Act 

D. Unfunded Mandates Reform Act 

E. Executive Order 13132: Federalism 

F. Executive Order 13175: Consultation 

and Coordination With Indian Tribal 

Governments 

G. Executive Order 13045: Protection of 

Children From Environmental Health & 

Safety Risks 

H. Executive Order 13211: Actions That 

Significantly Affect Energy Supply, 

Distribution or Use 

I. National Technology Transfer and 

Advancement Act 

J. Executive Order 12898: Federal Actions 

to Address Environmental Justice in 

Minority Populations and Low-Income 

Populations 

K. Congressional Review Act 

References 

I. Summary and Background 

A. Summary of Revisions to the Lead 

NAAQS 

Based on its review of the air quality 

criteria and national ambient air quality 

standards (NAAQS) for lead (Pb), EPA is 

making revisions to the primary and 

secondary NAAQS for Pb to provide 

requisite protection of public health and 

welfare, respectively. With regard to the 

primary standard, EPA is revising 

various elements of the standard to 

provide increased protection for 

children and other at-risk populations 

against an array of adverse health 

effects, most notably including 

neurological effects in children, 

including neurocognitive and 

neurobehavioral effects. EPA is revising 

the level to 0.15 μg/m3. EPA is retaining 

the current indicator of Pb in total 

suspended particles (Pb-TSP). EPA is 

revising the averaging time to a rolling 

3-month period with a maximum (notto-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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66966 Federal Register / Vol. 73, No. 219 / Wednesday, November 12, 2008 / Rules and Regulations 

2Welfare 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, 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.’’ 

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. 

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

The requirement that primary 

standards include an adequate margin of 

safety was intended to address 

uncertainties associated with 

inconclusive scientific and technical 

information available at the time of 

standard setting. It was also intended to 

provide a reasonable degree of 

protection against hazards that research 

has not yet identified. Lead Industries 

Association v. EPA, 647 F.2d 1130, 1154 

(D.C. Cir 1980), cert. denied, 449 U.S. 

1042 (1980); American Petroleum 

Institute v. Costle, 665 F.2d 1176, 1186 

(D.C. Cir. 1981), cert. denied, 455 U.S. 

1034 (1982). Both kinds of uncertainties 

are components of the risk associated 

with pollution at levels below those at 

which human health effects can be said 

to occur with reasonable scientific 

certainty. Thus, in selecting primary 

standards that include an adequate 

margin of safety, the Administrator is 

seeking not only to prevent pollutant 

levels that have been demonstrated to be 

harmful but also to prevent lower 

pollutant levels that may pose an 

unacceptable risk of harm, even if the 

risk is not precisely identified as to 

nature or degree. The CAA does not 

require the Administrator to establish a 

primary NAAQS at a zero-risk level or 

at background concentration levels, see 

Lead Industries Association v. EPA, 647 

F.2d at 1156 n. 51, but rather at a level 

that reduces risk sufficiently so as to 

protect public health with an adequate 

margin of safety. 

The selection of any particular 

approach to providing an adequate 

margin of safety is a policy choice left 

specifically to the Administrator’s 

judgment. Lead Industries Association 

v. EPA, 647 F.2d at 1161–62. In 

addressing the requirement for an 

adequate margin of safety, EPA 

considers such factors as the nature and 

severity of the health effects involved, 

the size of the population(s) at risk, and 

the kind and degree of the uncertainties 

that must be addressed. In setting 

standards that are ‘‘requisite’’ to protect 

public health and welfare, as provided 

in section 109(b), EPA’s task is to 

establish standards that are neither more 

nor less stringent than necessary for 

these purposes. Whitman v. American 

Trucking Associations, 531 U.S. 457, 

473. Further the Supreme Court ruled 

that ‘‘[t]he text of § 109(b), interpreted in 

its statutory and historical context and 

with appreciation for its importance to 

the CAA as a whole, unambiguously 

bars cost considerations from the 

NAAQS-setting process * * *’’ Id. at 

472.3

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 fiveyear intervals thereafter, the committee 

referred to in subparagraph (A) shall 

complete a review of the criteria 

published under section 108 and the 

national primary and secondary ambient 

air quality standards promulgated under 

this section and shall recommend to the 

Administrator any new national 

ambient air quality standards and 

revisions of existing criteria and 

standards as may be appropriate under 

section 108 and subsection (b) of this 

section.’’ Since the early 1980’s, this 

independent review function has been 

performed by the Clean Air Scientific 

Advisory Committee (CASAC) of EPA’s 

Science Advisory Board. 

C. Review of Air Quality Criteria and 

Standards for Lead 

On October 5, 1978, EPA promulgated 

primary and secondary NAAQS for Pb 

under section 109 of the Act (43 FR 

46246). Both primary and secondary 

standards were set at a level of 1.5 

micrograms per cubic meter (μg/m3), 

measured as Pb in total suspended 

particulate matter (Pb-TSP), not to be 

exceeded by the maximum arithmetic 

mean concentration averaged over a 

calendar quarter. This standard was 

based on the 1977 Air Quality Criteria 

for Lead (USEPA, 1977). 

A review of the Pb standards was 

initiated in the mid-1980s. The 

scientific assessment for that review is 

described in the 1986 Air Quality 

Criteria for Lead (USEPA, 1986a), the 

associated Addendum (USEPA, 1986b) 

and the 1990 Supplement (USEPA, 

1990a). As part of the review, the 

Agency designed and performed human 

exposure and health risk analyses 

(USEPA, 1989), the results of which 

were presented in a 1990 Staff Paper 

(USEPA, 1990b). Based on the scientific 

assessment and the human exposure 

and health risk analyses, the 1990 Staff 

Paper presented options for the Pb 

NAAQS level in the range of 0.5 to 1.5 

μg/m3, and suggested the second highest 

monthly average in three years for the 

form and averaging time of the standard 

(USEPA, 1990b). After consideration of 

the documents developed during the 

review and the significantly changed 

circumstances since Pb was listed in 

1976, the Agency did not propose any 

revisions to the 1978 Pb NAAQS. In a 

parallel effort, the Agency developed 

the broad, multi-program, multimedia, 

integrated U.S. Strategy for Reducing 

Lead Exposure (USEPA, 1991). As part 

of implementing this strategy, the 

Agency focused efforts primarily on 

regulatory and remedial clean-up 

actions aimed at reducing Pb exposures 

from a variety of nonair sources judged 

to pose more extensive public health 

risks to U.S. populations, as well as on 

actions to reduce Pb emissions to air, 

such as bringing more areas into 

compliance with the existing Pb 

NAAQS (USEPA, 1991). 

EPA initiated the current review of 

the air quality criteria for Pb on 

November 9, 2004 with a general call for 

information (69 FR 64926). A project 

work plan (USEPA, 2005a) for the 

preparation of the Criteria Document 

was released in January 2005 for CASAC 

and public review. EPA held a series of 

workshops in August 2005, inviting 

recognized scientific experts to discuss 

initial draft materials that dealt with 

various lead-related issues being 

addressed in the Pb air quality criteria 

document. In February 2006, EPA 

released the Plan for Review of the 

National Ambient Air Quality 

Standards for Lead (USEPA 2006c) that 

described Agency plans and a timeline 

for reviewing the air quality criteria, 

developing human exposure and risk 

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Federal Register / Vol. 73, No. 219 / Wednesday, November 12, 2008 / Rules and Regulations 66967 

4The ‘‘indicator’’ of a standard defines the 

chemical species or mixture that is to be measured 

in determining whether an area attains the 

standard. 

5The ‘‘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. 

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. 

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 

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66968 Federal Register / Vol. 73, No. 219 / Wednesday, November 12, 2008 / Rules and Regulations 

6As 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). 

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 

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7Co-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. 

8See, e.g., ‘‘Implementation of the MercuryContaining 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. 

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. 

Federal abatement programs provide 

for the reduction in human exposures 

and environmental releases from inplace materials containing Pb (e.g., Pbbased 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 leadbased 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 leadbased 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 leadbased 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/). 

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 

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9The 5th percentile, geometric mean, and 95th 

percentile values for the 2003–2004 NHANES are 

0.7, 1.8 and 5.1 μg/dL, respectively (Axelrad, 

2008a,b). 

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 μg/dL and a level of 3.9 μg/dL for 

the 90th percentile child in the 2003– 

2004 National Health and Nutrition 

Examination Survey (NHANES) as 

compared to median and 90th percentile 

levels in 1988–1991 of 3.5 μg/dL and 9.4 

μg/dL, respectively (http:// 

www.epa.gov/envirohealth/children/ 

body_burdens/b1-table.htm). These 

levels (median and 90th percentile) for 

the general population of young 

children 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. 

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 μg/m3 to 0.30 μg/m3, in 

conjunction with retaining the current 

indicator of Pb in total suspended 

particles (Pb-TSP) but with allowance 

for the use of Pb-PM10 data. With regard 

to the averaging time and form, the 

Administrator proposed two options: to 

retain the current averaging time of a 

calendar quarter and the current not-tobe-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 

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10 In general, air-related pathways include those 

pathways where Pb passes through ambient air on 

its path from a source to human exposure. 

11Weathering of outdoor Pb paint may also 

contribute to soil Pb levels adjacent to the house. 

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. 

(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). 

(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 airrelated 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, 

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12The 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). 

13Additionally, 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). 

14As described by the Advisory Committee on 

Childhood Lead Poisoning Prevention, ‘‘In 1991, 

CDC defined the blood lead level (BLL) that should 

prompt public health actions as 10 μg/dL. 

Concurrently, CDC also recognized that a BLL of 10 

μg/dL did not define a threshold for the harmful 

effects of lead. Research conducted since 1991 has 

strengthened the evidence that children’s physical 

and mental development can be affected at BLLS 

<10 μg/dL’’ (ACCLPP, 2007). 

15With 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 μg/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 

μg/dL, CDC has not changed its level of concern, 

which remains at levels >10 μg/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 

μg/dL would be based on an arbitrary decision. In 

addition, the feasibility and effectiveness of 

individual interventions to further reduce BLLs 

below 10 μg/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 

μg/ dL and >10 μg/dL, so preventive lead hazard 

control measures need not be deferred pending 

further research findings or consensus.’’ [CDC, 

2005a, p. 2] CDC’s Advisory Committee on 

Childhood Lead Poisoning Prevention recently 

provided recommendations regarding interpreting 

and managing blood Pb levels below 10 μg/dL in 

children and reducing childhood exposures to Pb 

(ACCLPP, 2007). 

16This information documents a variation in 

mean blood Pb levels across the various age groups 

monitored. For example, mean blood Pb levels in 

2001–2002 for ages 1–5, 6–11, 12–19 and greater 

than or equal to 20 years of age, are 1.70, 1.25, 0.94, 

and 1.56 μg/dL, respectively (CD, p. 4–22). 

do not usually distinguish between airrelated and other sources of Pb or 

between air-related Pb associated with 

historical emissions and that from 

recent emissions.12

(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). 

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 

μg/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

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 Pbcontaining 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 

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17Ratios are presented in the form of 1:x, with the 

1 representing air Pb (in μg/m3) and x representing 

blood Pb (in μg/dL). Description of ratios as higher 

or lower refers to the values for x (i.e., the change 

in blood Pb per unit of air Pb). Slopes are presented 

as simply the value of x. 

18We 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. 

19Brunekreef 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). 

20This study considered changes in ambient air 

Pb levels and associated blood Pb levels over a fiveyear 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). 

Criteria Document summarizes related 

information as follows (CD, p. E–6). 

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 bloodPb levels in children aged 1 to 5 years from 

a geometric mean of ∼15 μg/dL in 1976–1980 

to ∼1–2 μg/dL in the 2000–2004 period. 

While blood Pb levels in the U.S. 

general population, including geometric 

mean levels in children aged 1–5, have 

declined significantly, levels have been 

found to vary among children of 

different socioeconomic status (SES) 

and other demographic characteristics 

(CD, p. 4–21), and racial/ethnic and 

income disparities in blood Pb levels in 

children persist. For example, as 

described in the proposal, blood Pb 

levels for lower income and African 

American children are higher than those 

for the general population. The recently 

released RRP rule (discussed above in 

section I.C) is expected to contribute to 

further reductions in blood Pb levels for 

children living in houses with Pb paint. 

(iii) Air-to-Blood Relationships 

As described in section II.A.1 above 

and discussed in section II.A of the 

proposal, Pb in ambient air contributes 

to Pb in blood by multiple pathways, 

with the pertinent exposure routes 

including both inhalation and ingestion 

(CD, sections 3.1.3.2, 4.2 and 4.4; Hilts, 

2003). The quantitative relationship 

between ambient air Pb and blood Pb 

(discussed in section II.B.1.c of the 

proposal), which is often termed a slope 

or ratio, describes the increase in blood 

Pb (in μg/dL) estimated to be associated 

with each unit increase of air Pb (in 

μg/m3).17

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. 

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). 

Additionally, the 1986 Criteria 

Document noted that ratios derived 

from studies involving higher blood and 

air Pb levels are generally smaller than 

ratios from studies involving lower 

blood and air Pb levels (USEPA, 1986a. 

p. 11–99). In consideration of this factor, 

the proposal observed that the range of 

1:3 to 1:5 in air-to-blood ratios for 

children noted in the 1986 Criteria 

Document generally reflected study 

populations with blood Pb levels in the 

range of approximately 10–30 μg/dL 

(USEPA 1986a, pp. 11–100; Brunekreef, 

1984), much higher than those common 

in today’s population. This observation 

suggests that air-to-blood ratios relevant 

for today’s population of children 

would likely extend higher than the 1:3 

to 1:5 range identified in the 1986 

Criteria Document. 

More recently, a study of changes in 

children’s blood Pb levels associated 

with reduced Pb emissions and 

associated air concentrations near a Pb 

smelter in Canada (for children through 

age six in age) reports a ratio of 1:6, and 

additional analysis of the data by EPA 

for the initial time period of the study 

resulted in a ratio of 1:7 (CD, pp. 3–23 

to 3–24; Hilts, 2003).20 Ambient air and 

blood Pb levels associated with the Hilts 

(2003) study range from 1.1 to 0.03 

μg/m3, and associated population mean 

blood Pb levels range from 11.5 to 4.7 

μg/dL, which are lower than levels 

associated with the older studies cited 

in the 1986 Criteria Document (USEPA, 

1986). 

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21 In the publication, the author acknowledges 

that remedial programs (e.g., community and homebased 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). 

22EPA 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. 

23As 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. 

24The CASAC Panel stated ‘‘The Schwartz and 

Pitcher analysis showed that in 1978, the midpoint 

of the National Health and Nutrition Examination 

Survey (NHANES) II, gasoline Pb was responsible 

for 9.1 μg/dL of blood Pb in children. Their estimate 

is based on their coefficient of 2.14 μg/dL per 100 

metric tons (MT) per day of gasoline use, and usage 

of 426 MT/day in 1976. Between 1976 and when 

the phase-out of Pb from gasoline was completed, 

air Pb concentrations in U.S. cities fell a little less 

than 1 μg/m3 (24). These two facts imply a ratio of 

9–10 μg/dL per μg/m3 reduction in air Pb, taking 

all pathways into account.’’ (Henderson, 2007a, pp. 

D–2 to D–3). 

25Air-to-blood ratios for the full study area of the 

primary Pb smelter range from 1:3 to 1:7 across the 

range of alternative standard levels from 1.5 down 

to 0.02 μg/m3 (USEPA, 2007b). 

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 airto-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

In addition to the study by Hilts 

(2003), we are aware of two other 

studies published since the 1986 

Criteria Document that report air-toblood 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-toblood ratio of approximately 1:3.6 for an 

analysis of children aged six through ten 

in India. The ambient air and blood Pb 

levels in this study (geometric mean 

blood Pb levels generally ranged from 

10 to 15 μg/dL) are similar to levels 

reported in older studies reviewed in 

the 1986 Criteria Document and are 

much higher than current conditions in 

the U.S. The study by Hayes et al. (1994) 

compared patterns of ambient air Pb 

reductions and blood Pb reductions for 

large numbers of children in Chicago 

between 1971 and 1988, a period when 

significant reductions occurred in both 

measures. The study reports an air-toblood ratio of 1:5.6 associated with 

ambient air Pb levels near 1 μg/m3 and 

a ratio of 1:16 for ambient air Pb levels 

in the range of 0.25 μg/m3, indicating a 

pattern of higher ratios with lower 

ambient air Pb and blood Pb levels 

consistent with conclusions in the 1986 

Criteria Document.23

In their advice to the Agency prior to 

the proposal, CASAC identified air-toblood 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

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, airto-blood ratios ranged from 1:2 to 1:9 

across the alternative standard levels 

assessed, which ranged from the current 

standard of 1.5 μg/m3 down to a level 

of 0.02 μg/m3. This pattern of modelderived 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-toblood 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-toblood ratios. 

For the primary Pb smelter (subarea) 

case study, air-to-blood ratios ranged 

from 1:10 to 1:19 across the same range 

of alternative standard levels, from 1.5 

down to 0.02 μg/m3.25 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 evidencebased observation discussed above that 

consideration of more of the exposure 

pathways relating ambient air Pb to 

blood Pb, may result in higher air-toblood 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 

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26Lead 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). 

27At mean blood Pb levels, in children, on the 

order of 10 μg/dL, and somewhat lower, 

associations have been found with effects to the 

immune system, including altered macrophage 

activation, increased IgE levels and associated 

increased risk for autoimmunity and asthma (CD, 

Sections 5.9, 6.8, and 8.4.6). 

28With 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 μg/dL (most clearly 

in the 5 to 10 μg/dL range, but, less definitively, 

possibly lower).’’ (p. 6–269) 29Epidemiological 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 μg/dL) is 

associated with ∼1.0 mm Hg increase in systolic 

blood pressure and ∼0.6 mm Hg increase in 

diastolic pressure (CD, p. E–10). 

30This level has variously been called an 

advisory level or level of concern (http:// 

www.atsdr.cdc.gov/csem/lead/pb_standards2.html). 

In addressing children’s blood Pb levels, CDC has 

stated ‘‘Specific strategies that target screening to 

high-risk children are essential to identify children 

with BLLs ≥ 10 μg/dL.’’ (CDC, 2005, p.1) 

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 

μg/dL, or possibly lower (although the possibility of 

a threshold for such neurotoxic effects cannot be 

ruled out at lower blood-Pb concentrations)’’ (CD, 

p. 8–38). 

of the degree of dust Pb reduction 

associated with a specified degree of 

ambient air Pb reduction, which in turn 

could produce air-to-blood Pb ratios that 

are biased high. 

In summary, EPA’s view in the 

proposal was that the current evidence 

in conjunction with the results and 

observations drawn from the exposure 

assessment, including related 

uncertainties, supports consideration of 

a range of air-to-blood ratios for children 

ranging from 1:3 to 1:7, reflecting 

multiple air-related pathways beyond 

simply inhalation and the lower air and 

blood Pb levels pertinent to this review. 

EPA invited comment on this range as 

well as the appropriate weight to place 

on specific ratios within this range. 

Advice from CASAC and comments 

from the public on this issue are 

discussed below in section II.C.3. 

b. Array of Health Effects and At-Risk 

Subpopulations 

Lead has been demonstrated to exert 

‘‘a broad array of deleterious effects on 

multiple organ systems via widely 

diverse mechanisms of action’’ (CD, p. 

8–24 and section 8.4.1). This array of 

health effects includes effects on heme 

biosynthesis and related functions; 

neurological development and function; 

reproduction and physical 

development; kidney function; 

cardiovascular function; and immune 

function. The weight of evidence varies 

across this array of effects and is 

comprehensively described in the 

Criteria Document. There is also some 

evidence of Pb carcinogenicity, 

primarily from animal studies, together 

with limited human evidence of 

suggestive associations (CD, sections 

5.6.2, 6.7, and 8.4.10).26

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 

μg/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 μg/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 μg/dL in 

children and/or adults’’ (CD, p. 8–25). 

Some health effects associated with 

individual blood Pb levels extend below 

5 μg/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 μg/dL’’ (CD, p. E–9). 

We note that many studies over the 

past decade, in investigating effects at 

lower blood Pb levels, have utilized the 

CDC advisory level or level of concern 

for individual children (10 μg/dL) 30 as 

a benchmark for assessment, and this is 

reflected in the numerous references in 

the Criteria Document to 10 μg/dL. 

Individual study conclusions stated 

with regard to effects observed below 10 

μg/dL are usually referring to individual 

blood Pb levels. In fact, many such 

study groups have been restricted to 

individual blood Pb levels below 10 

μg/dL or below levels lower than 10 

μg/dL. We note that the mean blood Pb 

level for these groups will necessarily be 

lower than the blood Pb level they are 

restricted below. 

Threshold levels, in terms of blood Pb 

levels in individual children, for 

neurological effects cannot be discerned 

from the currently available studies (CD, 

pp. 8–60 to 8–63). The Criteria 

Document states ‘‘There is no level of Pb 

exposure that can yet be identified, with 

confidence, as clearly not being 

associated with some risk of deleterious 

health effects’’ (CD, p. 8–63). As 

discussed in the Criteria Document, ‘‘a 

threshold for Pb neurotoxic effects may 

exist at levels distinctly lower than the 

lowest exposures examined in these 

epidemiologic studies’’ (CD, p. 8–67).31

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 

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32Further, 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). 

33As 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). 

34For 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). 

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 

d-aminolevulinic acid dehydratase-2 

[ALAD-2] allele) have increased 

sensitivity to Pb toxicity, which may be 

due to increased susceptibility to the 

same internal dose and/or to increased 

internal dose associated with same 

exposure (CD, p. 8–71, sections 6.3.5, 

6.4.7.3 and 6.3.6). 

• Some children may have blood Pb 

levels higher than those otherwise 

associated with a given Pb exposure 

(CD, section 8.5.3) as a result of 

nutritional status (e.g., iron deficiency, 

calcium intake), as well as genetic and 

other factors (CD, chapter 4 and sections 

3.4, 5.3.7 and 8.5.3). 

• Situations of elevated exposure, 

such as residing near sources of ambient 

Pb, as well as socioeconomic factors, 

such as reduced access to health care or 

low socioeconomic status (SES) 

(USEPA, 2003, 2005c) can also 

contribute to increased blood Pb levels 

and increased risk of associated health 

effects from air-related Pb. 

• As described in the proposal 

(sections II.B.1.b and II.B.3), children in 

poverty and black, non-Hispanic 

children have notably higher blood Pb 

levels than do economically well-off 

children and white children, in general. 

c. Neurological Effects in Children 

Among the wide variety of health 

endpoints associated with Pb exposures, 

there is general consensus that the 

developing nervous system in children 

is among the, if not the, most sensitive. 

While blood Pb levels in U.S. children 

have decreased notably since the late 

1970s, newer studies have investigated 

and reported associations of effects on 

the neurodevelopment of children with 

these more recent blood Pb levels (CD, 

chapter 6). Functional manifestations of 

Pb neurotoxicity during childhood 

include sensory, motor, cognitive and 

behavioral impacts. Numerous 

epidemiological studies have reported 

neurocognitive, neurobehavioral, 

sensory, and motor function effects in 

children with blood Pb levels below 10 

μg/dL (CD, sections 6.2 and 8.4).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). 

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 abovenoted studies were significant even after 

adjusting for IQ, suggesting that Pbsensitive 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). 

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 μg/dL (CD, 

section 6.2.5 and pp. 8–30 to 8–31). The 

evidence for the role of Pb in this suite 

of effects includes experimental animal 

findings (discussed in CD, section 

8.4.2.1; p. 8–31), which provide strong 

biological plausibility of Pb effects on 

learning ability, memory and attention 

(CD, section 5.3.5), as well as associated 

mechanistic findings. 

The persistence of such Pb-induced 

effects is described in the proposal and 

the Criteria Document (e.g., CD, sections 

5.3.5, 6.2.11, and 8.5.2). The persistence 

or irreversibility of such effects can be 

the result of damage occurring without 

adequate repair offsets or of the 

persistence of Pb in the body (CD, 

section 8.5.2). It is additionally 

important to note that there may be 

long-term consequences of such deficits 

over a lifetime. Poor academic skills and 

achievement can have ‘‘enduring and 

important effects on objective 

parameters of success in real life’’, as 

well as increased risk of antisocial and 

delinquent behavior (CD, section 

6.2.16). 

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 μg/dL, and some analyses 

indicate Pb effects on intellectual 

attainment of children for which 

population mean blood Pb levels in the 

analysis ranged from 2 to 8 μg/dL (CD, 

sections 6.2, 8.4.2 and 8.4.2.6). Thus, 

while blood Pb levels in U.S. children 

have decreased notably since the late 

1970s, newer studies have investigated 

and reported associations of effects on 

the neurodevelopment of children with 

blood Pb levels similar to the more 

recent, lower blood Pb levels (CD, 

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35The median of the concurrent blood Pb levels 

modeled was 9.7 μg/dL; the 5th and 95th percentile 

values were 2.5 and 33.2 μg/dL, respectively 

(Lanphear et al., 2005). 

36The 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 (AlSaleh 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. 

38One 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 μg/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 μg/ 

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 leadbased 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 

μg/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 

Continued 

chapter 6; and as discussed in section 

II.B.2.b of the proposal). 

The current evidence reviewed in the 

Criteria Document with regard to the 

quantitative relationship between 

neurocognitive decrement, such as IQ, 

and blood Pb levels indicates that the 

slope for Pb effects on IQ is nonlinear 

and is steeper at lower blood Pb levels, 

such that each μg/dL increase in blood 

Pb may have a greater effect on IQ at 

lower blood Pb levels (e.g., below 10 μg/ 

dL) than at higher levels (CD, section 

6.2.13; pp. 8–63 to 8–64; Figure 8–7). As 

stated in the CD, ‘‘the most compelling 

evidence for effects at blood Pb levels 

<10 μg/dL, as well as a nonlinear 

relationship between blood Pb levels 

and IQ, comes from the international 

pooled analysis of seven prospective 

cohort studies (n=1,333) by Lanphear et 

al. (2005)’’ (CD, pp. 6–67 and 8–37 and 

section 6.2.3.1.11). Using the full pooled 

dataset with concurrent blood Pb level 

as the exposure metric and IQ as the 

response from the pooled dataset of 

seven international studies, Lanphear 

and others (2005) employed 

mathematical models of various forms, 

including linear, cubic spline, loglinear, 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 concentrationresponse 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). 

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 bloodPb levels greater than 10 μg/dL. 

The current evidence includes 

multiple studies that have examined the 

quantitative relationship between IQ 

and blood Pb level in analyses of 

children with individual blood Pb 

concentrations below 10 μg/dL. In 

comparing across the individual 

epidemiological studies and the 

international pooled analysis, the 

Criteria Document observed that at 

higher blood Pb levels (e.g., above 10 

μg/dL), the slopes (for change in IQ with 

blood Pb) derived for log-linear and 

linear models are almost identical, and 

for studies with lower blood Pb levels, 

the slopes appear to be steeper than 

those observed in studies involving 

higher blood Pb levels (CD, p. 8–78, 

Figure 8–7). In making these 

observations, the Criteria Document 

focused on the curves from the models 

from the 10th percentile to the 90th 

percentile saying that the ‘‘curves are 

restricted to that range because loglinear curves become very steep at the 

lower end of the blood Pb levels, and 

this may be an artifact of the model 

chosen’’. 

The quantitative relationship between 

IQ and blood Pb level has been 

examined in the Criteria Document 

using studies where all or the majority 

of study subjects had blood Pb levels 

below 10 μg/dL and also where an 

analysis was performed on a subset of 

children whose blood Pb levels have 

never exceeded 10 μg/dL (CD, Table 6– 

1).36 The datasets for three of these 

studies included concurrent blood Pb 

levels above 10 μg/dL; the 

concentration-response (C–R) 

relationship reported for one of the 

three was linear while it was log-linear 

for the other two. For the one study 

among these three that reported a linear 

C-R relationship, the highest blood Pb 

level was just below 12 μg/dL and the 

population mean was 7.9 μg/dL (Kordas 

et al., 2006). Of the two studies with loglinear functions, one reported 69% of 

the children with blood Pb levels below 

10 μg/dL and a population mean blood 

Pb level of 7.44 μg/dL (Al-Saleh et al., 

2001), and the second reported a 

population median blood Pb level of 9.7 

μg/dL and a 95th percentile of 33.2 μg/ 

dL (Lanphear et al., 2005). In order to 

compare slopes across all of these 

studies (linear and log-linear) in the 

Criteria Document, EPA estimated, for 

each, the average slope of change in IQ 

with change in blood Pb between the 

10th percentile 37 blood Pb level and 10 

μg/dL (CD, Table 6–1). The resultant 

group of reported and estimated average 

linear slopes for IQ change with blood 

Pb levels up to 10 μg/dL range from -0.4 

to -1.8 IQ points per μg/dL blood Pb 

(CD, Tables 6–1 and 8–7), with a median 

of -0.9 IQ points per μg/dL blood Pb 

(CD, p. 8–80).38 These slopes from 

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used the piece-wise model with node at 10 μg/dL, 

for which the steeper of the two slopes is less steep 

than it is for the model with node at 7.5 μg/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 μg/dL rather than at 7.5 μg/dL, 

is a small protection against applying an incorrectly 

rapid change (steep slope with increasingly smaller 

effect as concentrations lower) to the calculation’’ 

(USEPA, 2008). We note here that the slope for the 

less-than-10-μg/dL portion of the model used in the 

RRP analysis (-0.88) is similar to the median for the 

slopes included in the Criteria Document analysis 

of quantitative relationships for studies in which 

the majority of blood Pb levels were below 10 μg/ 

dL. 

39This 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 μg/dL (population mean blood Pb 

of 6.9 μg/dL; n=101) was ¥0.94 points per μg/dL 

blood Pb but was not statistically significant, with 

a p value of 0.12. The difference in the slope 

between the <5 μg/dL and the 5–10 μg/dL groups 

was not statistically significant (Tellez-Rojo et al., 

2006; Tellez-Rojo, 2008). 

41The 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). 

Tables 6–1 and 8–7 of the Criteria 

Document are presented in the second 

set of slopes in Table 1 below (adapted 

from Table 1 of the proposal). In this 

second set are studies (included in the 

Criteria Document Table 6–1) that 

examined the quantitative relationships 

of IQ and blood Pb in study populations 

for which most blood Pb levels were 

below 10 μg/dL and for which a linear 

slope restricted to blood Pb levels below 

about 10 μg/dL could be estimated. 

Among this group of quantitative IQblood Pb relationships examined in the 

Criteria Document (CD, Tables 6–1 and 

8–7), the steepest slopes for change in 

IQ with change in blood Pb level are 

those derived for the subsets of children 

in the Rochester and Boston cohorts for 

which peak blood Pb levels were <10 

μg/dL; these slopes, in terms of IQ 

points per μg/dL blood Pb, are ¥1.8 (for 

concurrent blood Pb influence on IQ) 

and ¥1.6 (for 24-month blood Pb 

influence on IQ), respectively. The 

mean blood Pb levels for children in 

these subsets of the Rochester and 

Boston cohorts are 3.32 (Canfield, 2008) 

and 3.8 μg/dL (Bellinger, 2008), 

respectively, which are the lowest 

population mean levels among the 

datasets included in the table. Other 

studies with analyses involving 

similarly low blood Pb levels (e.g., mean 

levels below 4 μg/dL) also had slopes 

steeper than ¥1.5 points per μg/dL 

blood Pb. These include the slope of 

¥1.71 points per μg/dL blood Pb 39 for 

the subset of 24-month old children in 

the Mexico City cohort with blood Pb 

levels less than 5 μg/dL (n=193), for 

which the mean concurrent blood Pb 

level was 2.9 μg/dL (Tellez-Rojo et al. 

2006, 2008),40 and the slope of ¥2.94 

points per μg/dL blood Pb for the subset 

of 6–10 year old children whose peak 

blood Pb levels never exceeded 7.5 μg/ 

dL (n=112), and for which the mean 

concurrent blood Pb level was 3.24 μg/ 

dL (Lanphear et al. 2005; Hornung 

2008a). Thus, from these subset 

analyses, the slopes range from ¥1.71 to 

¥2.94 IQ points per μg/dL of concurrent 

blood Pb, as shown in the first set of 

slopes in Table 1. In this first set are 

studies that included quantitative 

relationships for IQ and blood Pb that 

focused on lower individual blood Pb 

levels (below 7.5 μg/dL). We also note 

that for blood Pb levels up to 

approximately 3.7 μg/dL, the slope of 

the nonlinear C–R function in which 

greatest confidence is placed in 

estimating IQ loss in the quantitative 

risk assessment (the LLL function) 41

falls intermediate between these two 

values. 

TABLE 1—SUMMARY OF QUANTITATIVE RELATIONSHIPS OF IQ AND BLOOD Pb FOR TWO SETS OF STUDIES DISCUSSED

ABOVE

Study/analysis Study cohort Analysis dataset N Range BLL A

(μg/dL) 

Geometric 

mean BLL A

(μg/dL) 

Form of 

model from 

which 

average 

slope 

derived 

Average linear 

slope B (points 

per μg/dL) 

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

Tellez-Rojo <5 subgroup.Mexico City, age 24 

mo.

Children—BLL<5 μg/ 

dL.

193 0.8–4.9 ......... 2.9 ................ Linear ........... ¥1 .71 

based on Lanphear 

et al 2005 C, Loglinear with low-exposure 

linearization (LLL).

Dataset from which the log-linear function is derived is the pooled International dataset 

of 1333 children, age 6–10 yr, having median blood Pb of 9.7 μg/dL and 5th–95th 

percentile of 2.5–33.2 μg/dL. 

LLL D: ¥2.29 at 2 μg/dL 

¥1.89 at 3 μg/dL 

Lanphear et al. 

2005 C, <7.5 peak 

subgroup.

Pooled International, 

age 6–10 yr.

Children—peak BLL 

<7.5 μg/dL.

103 0.9–7.4 ......... 3.24 .............. Linear ........... ¥2 .94 

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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). 

TABLE 1—SUMMARY OF QUANTITATIVE RELATIONSHIPS OF IQ AND BLOOD Pb FOR TWO SETS OF STUDIES DISCUSSED

ABOVE—Continued 

Study/analysis Study cohort Analysis dataset N Range BLL A

(μg/dL) 

Geometric 

mean BLL A

(μg/dL) 

Form of 

model from 

which 

average 

slope 

derived 

Average linear 

slope B (points 

per μg/dL) 

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

Canfield et al 

2003 C, <10 peak 

subgroup.

Rochester, age 5 yr Children—peak BLL 

<10 μg/dL.

71 0.5–8.4 ......... 3.32 .............. Linear ........... ¥1 .79 

Bellinger and 

Needleman 2003 C.

Boston B F ................ Children—peak BLL 

<10 μg/dL.

48 1–9.3 F .......... F 3.8 .............. Linear ........... ¥1 .56 

Tellez-Rojo et al. 

2006.

Mexico City, age 24 

mo.

Full dataset ............. 294 0.8–9.8 ......... 4.28 .............. Linear ........... ¥1 .04 

Tellez-Rojo et al. 

2006 full— 

loglinear.

Mexico City, age 24 

mo.

Full dataset ............. 294 0.8–9.8 ......... 4.28 .............. Log-linear ..... G¥0 .94 

Lanphear et al. 

2005 C, <10 

peak C subgroup.

Pooled International, 

age 6–10 yr.

Children—peak BLL 

<10 μg/dL.

244 0.1–9.8 ......... 4.30 .............. Linear ........... ¥0 .80 

Al-Saleh et al 2001 

full—loglinear.

Saudi Arabia, age 

6–12 yr.

Full dataset ............. 533 2.3–27.36 H .. 7.44 .............. Log-linear ..... G¥0 .76 

Kordas et al 2006, 

<12 subgroup.

Torreon, Mexico, 

age 7 yr.

Children—BLL <12 

μg/dL.

377 2.3–<12 ........ 7.9 ................ Linear ........... ¥0 .40 

Lanphear et al 

2005 C full— 

loglinear.

Pooled International, 

age 6–10 yr.

Full dataset ............. 1333 0.1–71.7 ....... 9.7 (median) Log-linear ..... G¥0 .41 

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 μg/dL. In estimating IQ loss with this function in the risk assessment (section II.A.3) the nonlinear form of the model with varying 

slope was used for all BLL above 1 μg/dL. The slopes shown are the average slopes (IQ points per μg/dL blood Pb) associated with application 

of the LLL functions from zero to the blood Pb levels identified (2 and 3 μg/dL). E These studies and quantitative relationships are discussed in the Criteria Document (CD, sections 6.2, 6.2.1.3 and 8.6.2). 

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

G For nonlinear models, this is the estimated average slope for change in IQ with change in blood Pb over the range from the 10th percentile 

blood Pb value in study to 10 μg/dL (CD, p. 6–65). The shape of these models is such that the average slopes from the 10th percentiles to a 

value lower than 10 μg/dL are larger negative values than those shown here (e.g., the slopes to 5 μg/dL are 50% larger negative values). H 69% of children in Al-Saleh et al. (2001) study had BLL<10 μg/dL. 

3. Overview of Human Exposure and 

Health Risk Assessments 

To put judgments about risk 

associated with exposure to air-related 

Pb in a broader public health context, 

EPA developed and applied models to 

estimate human exposures to air-related 

Pb and associated health risk for various 

air quality scenarios and alternative 

standards. The design and 

implementation of the risk assessment 

needed to address significant limitations 

and complexity that go far beyond the 

situation for similar assessments 

typically performed for other criteria 

pollutants. The multimedia and 

persistent nature of Pb and the role of 

multiple exposure pathways add 

significant complexity as compared 

with other criteria pollutants that focus 

only on the inhalation exposure. Not 

only was the risk assessment 

constrained by the timeframe allowed 

for this review in the context of the 

breadth of information to address, it was 

also constrained by significant 

limitations in data and modeling tools 

for the assessment, as described in 

section II.C.2.h of the proposal. 

The scope and methodology for this 

assessment were developed over the last 

few years with considerable input from 

the CASAC Pb Panel and the public, as 

described in the proposal (section 

II.C.2.a).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). 

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 

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43CASAC advice on the design of the risk 

assessment is summarized in section II.C.2.a of the 

proposal. 

44A 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. 

45As 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. 

46The 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. 

47Current conditions for the three locationspecific urban case studies in terms of maximum 

quarterly average air Pb concentrations were 0.09, 

0.14 and 0.36 μg/m3 for the study areas in Los 

Angeles, Chicago and Cleveland, respectively. 

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

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. 

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 airrelated exposures are most impacted by 

emissions associated with the Pb 

smelter from which air Pb 

concentrations were estimated. 

The three location-specific urban case 

studies focus on specific residential 

areas within Cleveland, Chicago, and 

Los Angeles to provide representations 

of urban populations with a broader 

range of air-related exposures due to 

spatial gradients in both ambient air Pb 

levels and population density. For 

example, the highest air concentrations 

in these case studies (i.e., those closest 

to the standard being assessed) are 

found in very small parts of the study 

areas, while a large majority of the case 

study populations reside in areas with 

much lower air concentrations. 

Based on the nature of the population 

exposures represented by the two 

categories of case study, the first 

category (the general urban and primary 

Pb smelter case studies) relates more 

closely to the air-related IQ loss 

evidence-based framework described in 

the proposal (sections II.D.2.a.ii and 

II.E.3.a) with regard to estimates of airrelated 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 μg/m3, with a 

form of maximum monthly average, as 

well as a level of 0.20 μg/m3, with a 

form of maximum quarterly average. 

Details of the assessment scenarios, 

including the Pb concentrations for 

other media are presented in Sections 

2.3 and 5.1.1 of the Risk Assessment 

Report (USEPA, 2007b). 

Exposure and associated blood Pb 

levels were simulated using the IEUBK 

model, as more fully described and 

presented in the Risk Assessment 

Report (USEPA, 2007b). Because of the 

nonlinear response of blood Pb to 

exposure and also the nonlinearity 

reflected in the C–R functions for 

estimation of IQ loss, this assessment 

first estimated total blood Pb and risk 

(air- and nonair-related), and then 

separated out those estimates of blood 

Pb and associated risk associated with 

the pathways of interest in this review. 

We separated out the estimates of total 

(all-pathway) blood Pb and IQ loss into 

a background category and two airrelated 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 airrelated 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 

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48Similarly, 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. 

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

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 Pbrelated 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 airrelated 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 airrelated risk estimates. 

• Interindividual Variability in Blood 

Pb Levels: Uncertainty related to 

population variability in blood Pb levels 

and limitations in modeling of this 

introduces significant uncertainty into 

blood Pb and IQ loss estimates for the 

95th percentile of the population. 

• Pathway Apportionment for Higher 

Percentile Blood Pb and IQ Loss: 

Limitations in data, modeling tools and 

assessment design introduce uncertainty 

into estimates of air-related blood Pb 

and IQ loss for the upper ends of 

population distribution. 

• IQ Loss Concentration-Response 

Functions: Specification of the 

quantitative relationship between blood 

Pb level and IQ loss is subject to 

significant uncertainty at lower blood 

Pb levels (e.g., below 5 μg/dL concurrent 

blood Pb). 

b. Summary of Blood Pb Estimates 

Key observations regarding the blood 

Pb estimates from this analysis are 

noted here: 

• As shown in Table 2 of the proposal 

(73 FR 29215), median blood Pb levels 

for the current conditions air quality 

scenario in the urban case studies 

ranged from 1.7–1.8 μg/dL for the 

location-specific case studies up to 1.9 

μg/dL for the general urban case study. 

These values are slightly larger than the 

median value from NHANES for 

children aged 1–5 years old in 2003– 

2004 of 1.6 μg/dL (http://www.epa.gov/ 

envirohealth/children/body_burdens/ 

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50The 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. 

51For 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. 52As 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. 53Because 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. 

54As 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. 

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). 

• 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. 

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

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: 

• 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

• Alternate standards provide 

substantial reduction in estimates of airrelated risk across the full set of 

alternative NAAQS considered, 

particularly for the lower bound of airrelated risk which includes only the 

pathways that were varied with changes 

in air concentrations (as shown in Table 

2). 

• In the general urban case study, the 

estimated population median air-related 

risk falls between 1.9 and 3.6 points IQ 

loss for an alternative NAAQS of 0.50 

μg/m3, maximum monthly average, 

between 1.2 and 3.2 points IQ loss for 

an alternative NAAQS of 0.20 μg/m3

and between 0.5 and 2.8 points IQ loss 

for an alternate NAAQS of 0.05 μg/m3, 

maximum monthly average, (as shown 

in Table 2). Higher risk estimates are 

associated with a maximum quarterly 

averaging time (USEPA, 2007b). 

• At each NAAQS level assessed, the 

upper bound of population median airrelated 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 locationspecific case studies is smaller because 

of the broader range of air-related 

exposures and the population 

distribution. For example, the majority 

of the populations in each of the 

location-specific case studies resides in 

areas with ambient air Pb levels well 

below each standard level assessed, 

particularly for standard levels above 

0.05 μg/m3, maximum monthly average. 

Consequently, risk estimates for these 

case studies indicate little response to 

alternative standard levels above 0.05 

μg/m3 maximum monthly average (as 

shown in Table 2). 

TABLE 2—SUMMARY OF RISK ATTRIBUTABLE TO AIR-RELATED Pb EXPOSURE

NAAQS level simulated 

(μg/m3 max monthly, except as noted below) 

Median air-related IQ loss A

General urban 

case study 

Primary Pb 

smelter (subarea) case 

study B C

Location-specific urban case studies 

Cleveland 

(0.56 μg/m3) 

Chicago 

(0.31 μg/m3) 

Los Angeles 

(0.17 μg/m3) 

1.5 max quarterly D .............................................................. 3.5–4.8 

(1.5–7.7) 

<6 

<(3.2–9.4) 

2.8–3.9 E

(0.6–4.6) 

3.4–4.7 E

(1.4–7.4) 

2.7–4.2 E

(1.1–6.2) 

0.5 ........................................................................................ 1.9–3.6 

(0.7–4.8) 

<4.5 

<(2.1–7.7) 

0.6–2.9 

(0.2–3.9) 

(F) (F) 

0.2 ........................................................................................ 1.2–3.2 

(0.4–4.0) 

<3.7 

<(1.2–5.1) 

0.6–2.8 

(0.1–3.2) 

0.6–2.9 

(0.3–3.6) 

0.7–2.9 G

(0.2–3.5) 

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TABLE 2—SUMMARY OF RISK ATTRIBUTABLE TO AIR-RELATED Pb EXPOSURE—Continued 

NAAQS level simulated 

(μg/m3 max monthly, except as noted below) 

Median air-related IQ loss A

General urban 

case study 

Primary Pb 

smelter (subarea) case 

study B C

Location-specific urban case studies 

Cleveland 

(0.56 μg/m3) 

Chicago 

(0.31 μg/m3) 

Los Angeles 

(0.17 μg/m3) 

0.05 ...................................................................................... 0.5–2.8 

(0.2–3.3) 

<2.8 

<(0.9–3.4) 

0.1–2.6 

(<0.1–3.1) 

0.2–2.6 

(0.1–3.2) 

0.3–2.7 

(0.1–3.2) 

0.02 ...................................................................................... 0.3–2.6 

(0.1–3.1) 

<2.9 

<(0.9–3.3) 

<0.1–2.6 

(<0.1–3.0) 

0.1–2.6 

(<0.1–3.1) 

0.1–2.6 

(<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. 

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

C—Median air-related IQ loss estimates for the primary Pb smelter (full study area) range from <1.7 to <2.9 points, with no consistent pattern 

across simulated NAAQS levels. This lack of a pattern reflects inclusion of a large fraction of the study population with relatively low ambient air 

impacts such that there is lower variation (at the population median) across standard levels (see section 4.2 of the Risk Assessment, Volume 1). D—This corresponds to roughly 0.7–1.0 μg/m3 maximum monthly mean, across the urban case studies. E—A ‘‘roll-up’’ was performed so that the highest monitor in the study area is increased to just meet this level. 

F—A ‘‘roll-up’’ to this level was not performed. 

G—A ‘‘roll-up’’ to this level was not performed; these estimates are based on current conditions in this area. 

B. Need for Revision of the Current 

Primary Standard 

The initial issue to be addressed in 

the current review of the primary Pb 

standard is whether, in view of the 

advances in scientific knowledge 

reflected in the Criteria Document and 

Staff Paper, the existing standard should 

be revised. In evaluating whether it is 

appropriate to revise the current 

standard, the Administrator builds on 

the general approach used in the initial 

setting of the standard, as well as that 

used in the last review, and reflects the 

broader body of evidence and 

information now available. The 

approach used is based on an 

integration of information on health 

effects associated with exposure to 

ambient Pb; expert judgment on the 

adversity of such effects on individuals; 

and policy judgments as to when the 

standard is requisite to protect public 

health with an adequate margin of 

safety, which are informed by air quality 

and related analyses, quantitative 

exposure and risk assessments when 

possible, and qualitative assessment of 

impacts that could not be quantified. 

The Administrator has taken into 

account both evidence-based and 

quantitative exposure- and risk-based 

considerations in developing 

conclusions on the adequacy of the 

current primary Pb standard. 

The Administrator’s proposed 

conclusions on the adequacy of the 

current primary standard are 

summarized below in the Introduction 

(section II.B.1), followed by 

consideration of comments received on 

the proposal (section II.B.2) and the 

Administrator’s final decision with 

regard to the need for revision of the 

current primary standard (II.B.3). 

1. Introduction 

As described in section II.D.1.a of the 

proposal, the current standard was set 

in 1978 to provide protection to the 

public, especially children as the 

particularly sensitive population 

subgroup, against Pb-induced adverse 

health effects (43 FR 46246). The 

standard was set to provide protection 

against anemia (as well as effects 

associated with higher exposures), with 

consideration of impacts on the heme 

synthesis pathway leading to anemia (43 

FR 46252–46253). In setting the 

standard, EPA determined that ‘‘the 

maximum safe level of blood lead for an 

individual child’’ should be no higher 

than 30 μg/dL, and described 15 μg/dL 

Pb as ‘‘the maximum safe blood lead 

level (geometric mean) for a population 

of young children’’ (43 FR 46247, 

46253). The basis for the level, 

averaging time, form and indicator are 

described in section II.D.1.a of the 

proposal. 

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 Pbexposure levels (indexed by blood-Pb 

levels extending to as low as 10 to 15 

μg/dL or, possibly, below) as being 

associated with slowed physical and 

neurobehavioral development, lower IQ, 

impaired learning, and/or other 

indicators of adverse neurological 

impacts; and (b) other 

pathophysiological effects of Pb on 

cardiovascular function, immune 

system components, calcium and 

vitamin D metabolism and other 

selected health endpoints’’ (CD, pp. 8– 

24 to 8–25). This evidence is discussed 

fully in the Criteria Document. 

In the proposal, EPA explained its 

evidence-based considerations regarding 

the adequacy of the current standard. 

With regard to the sensitive population, 

while the sensitivity of the elderly and 

other particular subgroups is 

recognized, as at the time the current 

standard was set, young children 

continue to be recognized as a key 

sensitive population for Pb exposures. 

With regard to the exposure levels at 

which adverse health effects occur, the 

proposal noted that the current evidence 

demonstrates the occurrence of adverse 

health effects at appreciably lower blood 

Pb levels than those demonstrated by 

the evidence at the time the standard 

was set. This evidence is reflected in 

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55The 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. 

56For 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). 

57This is based on the calculation in which 1.5 

μg/m3 is multiplied by a ratio of 3 μg blood Pb per 

1 μg/m3 air Pb to yield an air-related blood Pb 

estimates of 4.5 μg/dL; using a 1:5 ratio yields an 

estimate of 7.5 μg/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. 

changes over the intervening years in 

the CDC’s identification and description 

of their advisory level for Pb in 

individual children’s blood (as 

described above in section II.A.2.a). The 

current evidence indicates the 

occurrence of a variety of health effects, 

including neurological effects in 

children, associated with blood Pb 

levels extending well below 10 μg/dL 

(CD, sections 6.2, 8.4 and 8.5). For 

example, as noted in the Criteria 

Document with regard to the 

neurocognitive effects in children, the 

‘‘weight of overall evidence strongly 

substantiates likely occurrence of [this] 

type of effect in association with bloodPb concentrations in range of 5–10 μg/ 

dL, or possibly lower * * * Although 

no evident threshold has yet been 

clearly established for those effects, the 

existence of such effects at still lower 

blood-Pb levels cannot be ruled out 

based on available data.’’ (CD, p. 8–61). 

The Criteria Document further notes 

that any such threshold may exist ‘‘at 

levels distinctly lower than the lowest 

exposures examined in these 

epidemiological studies’’ (CD, p. 8–67). 

In considering the adequacy of the 

current standard, the Staff Paper 

considered the evidence in the context 

of the framework used to determine the 

standard in 1978, as adapted to reflect 

the current evidence. In so doing, the 

Staff Paper recognized that the health 

effects evidence with regard to 

characterization of a threshold for 

adverse effects has changed since the 

standard was set in 1978, as have the 

Agency’s views on the characterization 

of a safe blood Pb level. As summarized 

in the proposal (73 FR 29237–38) and 

described in the Staff Paper (section 

5.4.1), parameters for this framework 

include estimates for average nonair 

blood Pb level, and air-to-blood ratio, as 

well as a maximum safe individual and/ 

or geometric mean blood Pb level. For 

this last parameter, the Staff Paper for 

the purposes of this evaluation 

considered the lowest population mean 

blood Pb levels with which some 

neurocognitive effects have been 

associated in the evidence. 

Based on the current evidence, the 

Staff Paper first concluded that young 

children remain the sensitive 

population of primary focus in this 

review and that ‘‘there is now no 

recognized safe level of Pb in children’s 

blood and studies appear to show 

adverse effects at population mean 

concurrent blood Pb levels as low as 

approximately 2 μg/dL (CD, pp. 6–31 to 

6–32; Lanphear et al., 2000)’’ (USEPA, 

2007c). The Staff Paper further stated 

that ‘‘while the nonair contribution to 

blood Pb has declined, perhaps to a 

range of 1.0–1.4 μg/dL, the air-to-blood 

ratio appears to be higher at today’s 

lower blood Pb levels than the estimates 

at the time the standard was set, with 

current estimates on the order of 1:3 to 

1:5 and perhaps up to 1:10’’ (USEPA, 

2007c). Adapting the framework 

employed in setting the standard in 

1978, the Staff Paper concluded that 

‘‘the more recently available evidence 

suggests a level for the standard that is 

lower by an order of magnitude or 

more’’ (USEPA, 2007c, p. 5–17). 

Since completion of the Staff Paper 

and ANPR, the Agency further 

considered the evidence with regard to 

adequacy of the current standard using 

an approach other than the adapted 

1978 framework considered in the Staff 

Paper. This alternative evidencebased 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. 

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. 

In the proposal, while we noted the 

evidence of steeper slope for the C–R 

relationship for blood Pb concentration 

and IQ loss at lower blood Pb levels 

(described above in sections II.A.2.c), 

we stated that for purposes of 

consideration of the adequacy of the 

current standard we were concerned 

with the C–R relationship for blood Pb 

levels that would be associated with 

exposure to air-related Pb at the level of 

the current standard. For this purpose, 

we focused on a median linear estimate 

of the slope of the C–R function from 

study populations for which most blood 

Pb levels were below 10 μg/dL and for 

which a linear slope restricted to blood 

Pb levels below about 10 μg/dL could be 

estimated (described in CD, pp. 6–65 to 

6–66 and summarized in section II.B.2.b 

of the proposal). The median slope 

estimate is ¥0.9 IQ points per μg/dL 

blood Pb (CD, p. 8–80). Applying 

estimates of air-to-blood ratios ranging 

from 1:3 to 1:5, drawing from the 

discussion of air-to-blood ratios in 

section II.B.1.c of the proposal, to a 

population of children exposed at the 

current level of the standard is 

estimated to result in an average airrelated blood Pb level above 4 μg/dL.57

Multiplying these blood Pb levels by the 

slope estimate, identified above, for 

blood Pb levels extending up to 10 μg/ 

dL (¥0.9 IQ points per μg/dL), would 

imply an average air-related IQ loss for 

such a group of children on the order of 

4 or more IQ points. 

In the proposal, EPA also explained 

its exposure- and risk-based 

considerations regarding the adequacy 

of the current standard. EPA estimated 

exposures and health risks associated 

with air quality that just meets the 

current standard (as described in the 

Risk Assessment Report) to help inform 

judgments about whether or not the 

current standard provides adequate 

protection of public health, taking into 

account key uncertainties associated 

with the estimated exposures and risks 

(summarized above in section II.C of the 

proposal and more fully in the Risk 

Assessment Report). In considering the 

adequacy of the standard, the Staff 

Paper considered exposure and risk 

estimates from the quantitative risk 

assessment, taking into account 

associated uncertainties. The Staff Paper 

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58As 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. 

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 (publichealth based) Lead NAAQS, to an upper 

bound of no higher than 0.2 μg/m3 with 

a monthly averaging time’’ (Henderson, 

2008a, p. 1). The Panel additionally 

advised that the current Pb NAAQS ‘‘are 

totally inadequate for assuring the 

necessary decreases of lead exposures in 

sensitive U.S. populations below those 

current health hazard markers identified 

by a wealth of new epidemiological, 

experimental and mechanistic studies’’, 

and that ‘‘it is the CASAC Lead Review 

Panel’s considered judgment that the 

NAAQS for Lead must be decreased to 

fully-protect both the health of children 

and adult populations’’ (Henderson, 

2007a, p. 5). CASAC drew support for 

their recommendation from the current 

evidence, described in the Criteria 

Document, of health effects occurring at 

dramatically lower blood Pb levels than 

those indicated by the evidence 

available when the standard was set and 

of a recognition of effects that extend 

beyond children to adults. 

At the time of proposal, in 

considering whether the current 

primary standard should be revised, the 

Administrator carefully considered the 

conclusions contained in the Criteria 

Document, the information, exposure/ 

risk assessments, conclusions and 

recommendations presented in the Staff 

Paper, the advice and recommendations 

from CASAC, and public comments 

received on the ANPR and other 

documents to date. In so doing, the 

Administrator noted the following: (1) A 

substantially expanded body of 

available evidence, described briefly in 

section II.A above and more fully in 

section II.B of the proposal and 

discussed in the Criteria Document, 

from that available when the current 

standard was set three decades ago; (2) 

evidence of the occurrence of health 

effects at appreciably lower blood Pb 

levels than those demonstrated by the 

evidence at the time the standard was 

set in 1978; (3) the currently available 

robust evidence of neurotoxic effects of 

Pb exposure in children, both with 

regard to epidemiological and 

toxicological studies; (4) associations of 

effects on the neurodevelopment of 

children with blood Pb levels notably 

decreased from those in the late 

1970s; 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. 

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 

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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 PaiuteShoshone 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, NonFerrous 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 

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that the health risk associated with airrelated 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-toblood 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 evidencebased 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 evidencebased 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 

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59The 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). 

60For simplicity, the discussion in this notice 

speaks as if PM10 samplers have a sharp size cutoff. 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. 

61 ‘‘Low-volume PM10 sampling’’ refers to 

sampling using any of a number of monitor models 

that draw 16.67 liters/minute (1 m3/hour) of air 

through the filter, in contrast to ‘‘high-volume’’ 

sampling of either TSP or PM10 in which the 

monitor draws 1500 liters/minute (90 m3/hour). 

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. 

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 μm 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. 

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 highvolume 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 PbTSP 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 TSPbased standard in certain situations, 

such as where sufficient data are 

available to adequately demonstrate a 

relationship between Pb-TSP and PbPM10 or, in combination with more 

limited Pb-TSP monitoring, in areas 

where Pb-TSP data indicate Pb levels 

well below the NAAQS level. 

The ANPR further identified issues 

and options associated with 

consideration of the potential use of PbPM10 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 PbTSP and Pb-PM10, and use of Pb-PM10

data, with adjustment, as a surrogate for 

Pb-TSP data. The ANPR broadly 

solicited comment in these areas. 

As noted in the proposal, the Agency 

in setting the standard and CASAC in 

providing their advice (described below) 

both recognized that ingestion pathways 

are important to air-related Pb 

exposures and that Pb particles 

contributing to these pathways include 

ultra-coarse particles. Thus, as noted in 

the proposal, choosing the appropriate 

indicator requires consideration of the 

impact of the indicator on the protection 

provided from exposure to air-related Pb 

of all particle sizes, including ultracoarse 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, 

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63Low-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. 

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’’. 

especially in areas near sources of ultracoarse 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 lowvolume 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 PbTSP measurements. The larger scale of 

representation for Pb-PM10 would mean 

that reported measurements of this 

indicator, and hence designation 

outcomes, would be less sensitive to 

exact monitor siting than with Pb-TSP 

as the indicator. 

As discussed in the proposal, 

however, there is a different source of 

error associated with the use of Pb-PM10

as the indicator, in that larger Pb 

particles not captured by PM10 samplers 

would not be measured. As noted above, 

these particles contribute to the health 

risks posed by air-related Pb, especially 

in areas influenced by sources of ultracoarse 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., sourceoriented, 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 PbTSP sampling data 64 (Henderson, 

2007a, 2007b, 2008a). 

For reasons discussed in the proposal 

and recognized above, and taking into 

account information and assessments 

presented in the Criteria Document, 

Staff Paper, and ANPR, the advice and 

recommendations of CASAC and of 

members of the CASAC AAMM 

Subcommittee, and public comments 

received prior to proposal, the 

Administrator proposed to retain the 

current indicator of Pb-TSP, measured 

by the current FRM, a current FEM, or 

an FEM approved under the proposed 

revisions to 40 CFR part 53. The 

Administrator also proposed an 

expansion of the measurements 

accepted for determining attainment or 

nonattainment of the Pb NAAQS to 

provide an allowance for use of Pb-PM10

data, measured by the new low-volume 

Pb-PM10 FRM specified in the proposed 

appendix Q to 40 CFR part 50 or by a 

FEM approved under the proposed 

revisions to 40 CFR part 53, with sitespecific 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 Staffmstockstill on PROD1PC66 with RULES2

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65 Data from collocated TSP and PM2.5 monitors 

are generally presented in the Staff Paper (section 

2.3.5). 

recommended range (with an TSP 

indicator) of between 0.1 to 0.2 μg/m3 as 

an upper bound and 0.02 to 0.05 μg/m3

as a lower bound (with the added 

consideration that the selection be made 

somewhat ‘conservatively’ within this 

range to accommodate the potential loss 

of ultra-coarse lead with a PM10 Pb 

indicator)’’ (emphasis in original) 

(Henderson, 2008b). They additionally 

noted that ‘‘at most population-oriented 

monitoring sites, levels of PM10 Pb are 

essentially the same as TSP Pb, but at 

source-oriented monitoring sites with 

high coarse mode particulate lead 

emissions, TSP Pb was roughly twice as 

high as PM10 Pb’’ and that this ‘‘factorof-two difference * * * could be readily 

accommodated by considering a slightly 

more conservative upper bound of 0.1 

μg/m3 rather than 0.2 μg/m3 ’’ 

(Henderson, 2008b). The CASAC panel 

concluded that ‘‘a transition to a PM10

indicator would be preferable, but only 

at a level conservatively below an upper 

bound of 0.2 μg/m3 or lower’’ 

(Henderson, 2008b). EPA interprets this 

advice on the whole to be supportive of 

Pb-TSP as the indicator for any standard 

level greater than 0.10 μg/m3, 

particularly when the level has been 

selected with recognition of the 

inclusion of ultra-coarse particles in PbTSP measurements. 

The EPA received many public 

comments on issues related to the 

indicator for Pb. The large majority of 

public comments were in support of 

EPA’s proposal to retain Pb-TSP as the 

indicator for Pb. Represented in this 

group were many state agencies, as well 

as some Tribes and tribal environmental 

agencies, and local environmental 

agencies. Many commenters supported 

Pb-TSP as the indicator regardless of a 

level for the standard, variously citing 

evidence also cited by EPA in the 

proposal notice, such as the relevance of 

all sizes of Pb particles to exposures, 

blood Pb levels and effects and the 

omission of ultra-coarse particles with 

PM10 samples. In support of Pb-TSP as 

the indicator, a few commenters also 

stated that air-to-blood ratios used in the 

evidence-based framework for 

considering a level for the standard are 

generally based on Pb-TSP data. Some 

comments, similar to CASAC, supported 

Pb-TSP as the indicator for levels above 

the lower end of the proposed range 

(i.e., above 0.10 μg/m3), including a 

level of 0.15 μg/m3. One commenter 

(NESCAUM) specifically recommended 

an indicator of Pb-TSP for a NAAQS 

with a level of 0.15 μg/m3, 

recommending a revision to Pb-PM10

only if some other, much lower, level 

(0.05 μg/m3) was selected. 

EPA generally agrees with CASAC 

and the large number of public 

commenters with regard to the 

appropriateness of a Pb-TSP indicator 

for the level of the standard identified 

for the revised standard in section II.C.3 

below. This conclusion is supported by 

the current scientific evidence, 

discussed above in section II.C.1.a, 

recognizing the range of particle sizes 

inclusive of ultra-coarse particles which 

contribute to Pb exposures, evidence of 

the presence of ultra-coarse particles in 

some areas, particularly near sources, 

and variation in the relationship 

between Pb-TSP and Pb-PM10 at such 

sites, which together contribute to 

uncertainty about the sufficiency of 

public health protection associated with 

a Pb-PM10 standard at the level of 0.15 

μg/m3. 

A few commenters (including the 

National Association of Clean Air 

Agencies) recommended transition to a 

Pb-PM10 indicator for the standard at 

levels below 0.2 μg/m3. These 

commenters stated that low-volume 

PM10 samplers measure Pb much more 

accurately than high-volume TSP 

samplers, referring to EPA’s discussion 

in the proposal that recognized the 

variability of Pb-TSP measurements 

associated with wind speed and 

direction, and also referred to support 

among CASAC AAMM members and 

the July 2008 comments from CASAC 

on indicator. These commenters, 

however, did not provide rationales as 

to why a Pb-PM10 indicator might be 

justified in light of the health 

considerations identified by EPA in the 

proposal. Further, as noted above, EPA 

interprets CASAC’s July 2008 comments 

on the whole to be supportive of Pb-TSP 

as the indicator for any standard level 

greater than 0.10 μg/m3. 

A few commenters, including both 

state and industry commenters, 

recommended transition to Pb-PM10

without reference to a particular level. 

Some of these commenters, like CASAC, 

noted concerns with the high-volume 

TSP sampling methodology and 

advantages of the PM10 monitoring 

method in reduced variability of the 

measurements. Two industry 

commenters additionally suggested 

consideration of an indicator based on 

Pb-PM2.5, stating as their rationale that 

almost all airborne Pb in air is in ‘‘the 

small size fraction’’, ambient sampling 

for PM10 and PM2.5 size fractions is 

already required, and precision which 

might be greater with PM10 monitors is 

needed for ‘‘lower’’ standards. None of 

this group of commenters provided a 

rationale as to why a Pb-PM10 indicator 

might be justified in light of the health 

considerations identified by EPA in the 

proposal. 

EPA disagrees with this group of 

commenters, noting the potential 

presence at some sites of particles that 

would not be captured by PM10 or PM2.5

samplers yet would contribute to human 

exposure to Pb and associated health 

effects. As discussed below, EPA 

believes that, in light of the evidence of 

all particle sizes of Pb contributing to 

blood Pb and health effects by both 

ingestion and inhalation pathways, the 

available data on relationships between 

Pb-TSP and Pb-PM10 (discussed in 

section II.E.1 of the proposal and in 

section IV.C below) are inadequate to 

support development of a Pb-PM10- 

based NAAQS that would provide 

sufficient but not more than necessary 

protection of public health, with an 

adequate margin of safety, across the 

wide variety of ambient Pb 

circumstances affecting this 

relationship, and at the level selected by 

the Administrator. Although, EPA did 

not consider relationships between PbTSP 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

A number of comments were received 

regarding the potential use of sitespecific 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 sitespecific 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 

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66As 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. 

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 ultracoarse 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 ultracoarse Pb particles, which, as noted 

above, may have a greater presence in 

areas near sources where Pb 

concentrations are highest. In light of 

these considerations, the Administrator 

concludes that it is appropriate to retain 

Pb-TSP as the indicator to protect 

against health risks from ultra coarse 

particulate Pb emitted to ambient air. 

With regard to the use of scaling 

factors to relate Pb-PM10 data to a PbTSP 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 PbPM10 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 PbPM10 measurements at sites not 

influenced by sources of ultra-coarse Pb 

and where Pb concentrations are well 

below the standard would take 

advantage of the increased precision of 

these measurements and decreased 

spatial variation of Pb-PM10

concentrations, without raising the same 

concerns over a lack of protection 

against health risks from all particulate 

Pb emitted to the ambient air that 

support retention of Pb-TSP as the 

indicator. Accordingly, the 

Administrator is expanding the types of 

measurements which may be considered 

with regard to implementation of the Pb 

NAAQS. This expansion, as discussed 

more fully in sections IV and V below, 

provides a role for Pb-PM10 data under 

certain limited circumstances and with 

certain conditions. The circumstances 

and conditions under which such data 

are allowed, as described in sections IV 

and V below, are those in which the Pb 

concentrations are expected to be 

substantially below the standard and 

ultra-coarse particles are not expected to 

be present. 

2. Averaging Time and Form 

a. Basis for Proposed Decision 

The averaging time and form of the 

current standard is a not-to-be-exceeded 

or maximum value, averaged over a 

calendar quarter. The basis for this 

averaging time and form reflects 

consideration of the evidence available 

when the Pb NAAQS were promulgated 

in 1978. At that time, the Agency had 

concluded that the level of the standard, 

1.5 μg/m3, would be a ‘‘safe ceiling for 

indefinite exposure of young children’’ 

(43 FR 46250), and that the slightly 

greater possibility of elevated air Pb 

levels for shorter periods within the 

quarterly averaging period, as contrasted 

to the monthly averaging period 

proposed in 1977 (43 FR 63076), was 

not significant for health. These 

conclusions were based in part on the 

Agency’s interpretation of the health 

effects evidence as indicating that 30 μg/ 

dL was the maximum safe level of blood 

Pb for an individual child, and the 

Agency’s views that the distribution of 

air concentrations made it unlikely 

there could be sustained periods greatly 

above the average value and that the 

multipathway nature of Pb exposure 

lessened the impact of short-term 

changes in air concentrations of Pb. 

In the 1990 Staff Paper, this issue was 

again considered in light of the evidence 

available at that time. The 1990 Staff 

Paper concluded that ‘‘[a] monthly 

averaging period would better capture 

short-term increases in lead exposure 

and would more fully protect children’s 

health than the current quarterly 

average’’ (USEPA, 1990b). The 1990 

Staff Paper further concluded that ‘‘[t]he 

most appropriate form of the standard 

appears to be the second highest 

monthly average in a 3-year span. This 

form would be nearly as stringent as a 

form that does not permit any 

exceedances and allows for discounting 

of one ‘bad’ month in 3 years which 

may be caused, for example, by unusual 

meteorology.’’ In their review of the 

1990 Staff Paper, the CASAC Pb Panel 

concurred with the staff 

recommendation to express the lead 

NAAQS as a monthly standard not to be 

exceeded more than once in three years. 

As summarized in section II.A above 

and discussed in detail in the Criteria 

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67The differing evidence and associated strength 

of the evidence for these different effects is 

described in the Criteria Document. 

68For 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). 

69Lead 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). 

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

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. 

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 airrelated 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-tobe exceeded (maximum) form and also 

combined a monthly averaging time 

with a second maximum form, so as to 

provide an appropriate degree of yearto-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 

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70The 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 Pbexposure 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) 

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. 

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 

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66994 Federal Register / Vol. 73, No. 219 / Wednesday, November 12, 2008 / Rules and Regulations 

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 timerelated 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 airrelated exposures of children today. 

Accordingly, the relatively greater focus 

today (than at the time of leaded 

gasoline usage) on deposition-related 

pathways of exposure to air-related Pb 

such as indoor dust ingestion would 

tend to support consideration of an 

averaging time longer than a month. We 

additionally note results from dust Pb 

modeling analyses performed as part of 

the quantitative risk assessment. These 

results provide an estimate of 

approximately four months as the time 

over which an increase in air Pb will 

reach 90% of the final steady-state 

change in dust Pb (USEPA, 2007b, 

section G.3.2.2). Additionally, we note 

that multiple studies have observed 

blood Pb levels to exhibit seasonal 

patterns, perhaps related to seasonality 

in exposure variables (e.g., Rabinowitz 

et al., 1985). 

Some commenters who supported a 

monthly averaging time cited concern 

for the potential for the occurrence of 

single month average air Pb 

concentration, within a quarter that met 

the standard, to be substantially above 

the level of the standard. For example, 

one commenter suggested that a 

monthly averaging time would be more 

likely to capture exceedances related to 

periodic activities (such as industrial 

activity, construction or demolition). 

Another commenter submitted 

examples of such temporal variability in 

ambient air concentrations at specific 

monitoring sites, one of which indicated 

a quarter in which the current standard 

of 1.5 μg/m3 was met, while a single 

month within that quarter was some 

30% percent higher (2.07 μg/m3). In 

considering this example, we consider 

the likelihood of differing blood Pb 

responses between children in two 

different situations: one in which the 3- 

month average Pb concentration just 

met the level of the standard but a single 

month within the quarter was 30% 

higher than that level (with the other 

two months below the standard level), 

and the other in which each of three 

consecutive monthly average Pb 

concentrations just met the level of the 

standard. The current evidence is 

limited with regard to the consideration 

of this issue. Given the range of airrelated 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 monthto-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 

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71These analyses incorporate the revised 

averaging method identified above and discussed 

more fully in section IV below. 

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’ threemonth (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 ‘secondhighest 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-beexceeded 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

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, multipathway situation for Pb, it is necessary 

to consider all of the relevant factors, 

both those pertaining to the human 

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72Among 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). 

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 notto-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 μg/dL of blood Pb at the 

lower levels of blood Pb in the exposed 

population (CD, section 6.2.13). In this 

context EPA notes that the health effects 

evidence most useful in determining the 

appropriate level of the NAAQS is the 

large body of epidemiological studies 

discussed in the Criteria Document. The 

discussion in the proposal and below 

therefore focuses on the epidemiological 

studies, recognizing and taking into 

consideration the complexity and 

resulting uncertainty in using this body 

of evidence to determine the 

appropriate level for the NAAQS. 

The Administrator’s proposed 

conclusions on range of levels for the 

primary standard are summarized below 

in the Introduction (section II.C.3.a), 

followed by consideration of comments 

received on the proposal (section 

II.C.3.b) and the Administrator’s final 

decision with regard to level for the 

current primary standard (II.C.3.c). 

a. Basis for Proposed Range 

For the reasons discussed in the 

proposal and summarized below, and 

taking into account information and 

assessments presented in the Criteria 

Document, Staff Paper, and ANPR, the 

advice and recommendations of 

CASAC, and the public comments 

received prior to proposal, the 

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73As described in section II.E.3.a.ii of the 

proposal, the first set focused on C–R functions 

from analyses involving population mean 

concurrent blood Pb levels of approximately 3 μg/ 

dL (closer to current mean blood Pb levels in U.S. 

children). The second set (CD, pp. 8–78 to 8–80) 

considered functions descriptive of the C–R 

relationship from a larger set of studies that include 

population mean blood Pb levels ranging from a 

mean of 3.3 up to a median of 9.7 μg/dL (see 

Table 1). 

74 In considering alternative levels for the 

standard within the air-related IQ loss framework, 

the Agency focused on estimates using an air-toContinued 

Administrator proposed to revise the 

existing primary Pb standard. 

Specifically, the Administrator 

proposed to revise the level of the 

primary Pb standard, defined in terms of 

the current Pb-TSP indicator, to within 

the range of 0.10 to 0.30 μg/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 

μg/m 3 up to 0.50 μg/m 3 and below 0.10 

μg/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 atrisk 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 airrelated 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 airrelated 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 airrelated 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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blood ratio of 1:5 and also provided IQ loss 

estimates using higher and lower estimates (i.e., 1:3 

and 1:7). 

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 airrelated exposures including many well below the 

standard level being evaluated. 

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 airrelated Pb to the proposed range of 

protection. 

Taking these considerations into 

account, and based on the full range of 

information presented in Table 7 of the 

proposal on estimates of air-related IQ 

loss in children over a broad range of 

alternative standard levels, the 

Administrator concluded that it was 

appropriate to propose a range of 

standard levels, and that a range of 

levels from 0.10 to 0.30 μg/m3 would be 

consistent with the target for protection 

from air-related IQ loss in children 

identified in the proposal. In 

recognition of the uncertainties in the 

key parameters of air-to-blood ratio and 

C–R functions, the Administrator stated 

that the selection of a standard level 

from within this range was conditional 

on judgments as to the most appropriate 

parameter values to use in the context 

of this evidence-based framework. He 

noted that placing more weight on the 

use of a C–R function with a relatively 

steeper slope would tend to support a 

standard level in the lower part of the 

proposed range, while placing more 

weight on a C–R function with a 

shallower slope would tend to support 

a level in the upper part of the proposed 

range. Similarly, placing more weight 

on a higher air-to-blood ratio would 

tend to support a standard level in the 

lower part of the proposed range, 

whereas placing more weight on a lower 

ratio would tend to support a level in 

the upper part of the range. In soliciting 

comment on a standard level within this 

proposed range, the Administrator 

specifically solicited comment on the 

appropriate values to use for these key 

parameters in the context of this 

evidence-based framework. 

The Administrator also considered 

the results of the exposure and risk 

assessments conducted for this review 

to provide some further perspective on 

the potential magnitude of air-related IQ 

loss.75 The Administrator found these 

quantitative assessments to provide a 

useful perspective on the risk from airrelated 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 airrelated IQ loss estimates discussed in 

section II.E.3.b of the proposal, lending 

support to the proposed range based on 

this evidence-based framework. 

In the proposal, the Administrator 

noted his view that the above 

considerations, taken together, provided 

no evidence- or risk-based bright line 

that indicates a single appropriate level. 

Instead, he noted, there is a collection 

of scientific evidence and judgments 

and other information, including 

information about the uncertainties 

inherent in many relevant factors, 

which needs to be considered together 

in making this public health policy 

judgment and in selecting a standard 

level from a range of reasonable values. 

Based on consideration of the entire 

body of evidence and information 

available at the time of proposal, as well 

as the recommendations of CASAC and 

public comments, the Administrator 

proposed that a standard level within 

the range of 0.10 to 0.30 μg/m3 would 

be requisite to protect public health, 

including the health of sensitive groups, 

with an adequate margin of safety. He 

also recognized that selection of a level 

from within this range was conditional 

on judgments as to what C–R function 

and what air-to-blood ratio are most 

appropriate to use within the context of 

the air-related IQ loss framework. The 

Administrator noted that this proposed 

range encompasses the specific level of 

0.20 μg/m3, the upper end of the range 

recommended by CASAC and by many 

public commenters on the ANPR. The 

Administrator provisionally concluded 

that a standard level selected from 

within this range would reduce the risk 

of a variety of health effects associated 

with exposure to Pb, including effects 

indicated in the epidemiological studies 

at low blood Pb levels, particularly 

including neurological effects in 

children, and cardiovascular and renal 

effects in adults. 

The proposal noted that there is no 

bright line clearly directing the choice 

of level within this reasonable range, 

and therefore the choice of what is 

appropriate, considering the strengths 

and limitations of the evidence, and the 

appropriate inferences to be drawn from 

the evidence and the exposure and risk 

assessments, is a public health policy 

judgment. To further inform this 

judgment, the Administrator solicited 

comment on the air-related IQ loss 

evidence-based framework considered 

by the Agency and on appropriate 

parameter values to be considered in the 

application of this framework. More 

specifically, we solicited comment on 

the appropriate C–R function and air-toblood 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 

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76Similarly, 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). 

77Some 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. 

proposal, indicated that for standard 

levels above 0.30 μg/m3 up to 0.50 μg/ 

m3, the estimated degree of impact on 

population mean IQ loss from airrelated 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-toblood ratios considered, and would 

extend from somewhere within the 

proposed range of 1 to 2 points IQ loss 

to above that range when using the 

second set of C–R functions and the full 

range of air-to-blood ratios considered. 

The Administrator proposed to 

conclude in light of his consideration of 

the evidence in the framework 

discussed above that the magnitude of 

air-related Pb effects at the higher blood 

Pb levels that would be allowed by 

standards above 0.30 up to 0.50 μg/m3

would be greater than what is requisite 

to protect public health with an 

adequate margin of safety. 

In addition, the Administrator noted 

that for standard levels below 0.10 μg/ 

m3, the estimated degree of impact on 

population mean IQ loss from airrelated Pb would generally be somewhat 

to well below the proposed range of 1 

to 2 points air-related population mean 

IQ loss regardless of which set of C–R 

functions or which air-to-blood ratio 

within the range of ratios considered are 

used. The Administrator proposed to 

conclude that the degree of public 

health protection that standards below 

0.10 μg/m3 would likely afford would be 

greater than what is requisite to protect 

public health with an adequate margin 

of safety. 

Having reached these proposed 

decisions based on the interpretation of 

the evidence, the evidence-based 

frameworks, the exposure/risk 

assessment, and the public health policy 

judgments described above, the 

Administrator recognized that other 

interpretations, frameworks, 

assessments, and judgments are 

possible. There are also potential 

alternative views as to the range of 

values for relevant parameters (e.g., C– 

R function, air-to-blood ratio) in the 

evidence-based framework that might be 

considered supportable and the relative 

weight that might appropriately be 

placed on any specific value for these 

parameters within such ranges. In 

addition, the Administrator recognized 

that there may be other views as to the 

appropriate degree of public health 

protection that should be afforded in 

terms of air-related population mean IQ 

loss in children that would provide 

support for alternative standard levels 

different from the proposed range. 

Further, there may be other views as to 

the appropriate weight and 

interpretation to give to the exposure/ 

risk assessment conducted for this 

review. Consistent with the goal of 

soliciting comment on a wide array of 

issues, the Administrator solicited 

comment on these and other issues. 

In the proposal, the Administrator 

also recognized that Pb can be 

considered a non-threshold pollutant 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. 

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 evidencebased framework and inputs to the 

framework, and comments related to the 

risk assessment. More detailed 

responses to some of the public 

comments on level described below, as 

well as responses to other comments 

related to level not discussed here, are 

provided in the Response to Comments 

document. 

(i) General Comments on Range of 

Levels 

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 μg/m3’’ 

(emphasis in originals). 

The vast majority of public comments 

that addressed a level for the standard 

recommended standard levels below, or 

no higher than 0.2 μg/m3. Many of these 

commenters noted the advice of CASAC 

and recommended that EPA follow this 

advice. Specific rationales provided by 

this large group of commenters included 

various considerations, such as 

recognition that the current evidence 

indicates Pb effects at much lower 

exposure levels than when the current 

standard was set and in multiple 

systems (e.g., neurological effects in 

children, cardiovascular and renal 

effects in adults), and does not indicate 

a threshold; impacts associated with 

some neurological effects can persist 

into adulthood; and there is now 

evidence of a greater air-to-blood ratio 

than was considered when the standard 

was set. Many of these commenters 

recommended a specific level or range 

of levels for the standard that was equal 

to or below 0.2 μg/m3. In recommending 

levels below 0.2 μg/m3, some of these 

stated that CASAC’s recommendation 

for an upper bound of 0.2 μg/m3 should 

not be read to imply that CASAC 

supported a standard level of 0.2 μg/m3

if that level did not account for 

CASAC’s other specific 

recommendations on the framework and 

its inputs. Some commenters’ specific 

recommendations for level (including a 

standard level of 0.15 μg/m3) were based 

on consideration of the air-related IQ 

loss evidence-based framework and 

their application of it using their 

recommended parameter inputs and 

public health policy goal. The specific 

recommendations on application of the 

framework are discussed separately 

below. Some commenters (including 

EPA’s Children’s Health Protection 

Advisory Committee, NESCAUM, 

several States and Tribes, and several 

environmental or public health 

organizations) specified levels below 0.2 

μg/m3 as necessary to protect public 

health with an adequate margin of 

safety, with some of these additionally 

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stating that in assuring this level of 

protection, EPA must take into account 

susceptible or vulnerable subgroups. In 

discussing these subgroups, some 

commenters noted factors such as 

nutritional deficiencies as contributing 

to susceptibility and identified minority 

and low-income children as a sensitive 

subpopulation for Pb exposures. Some 

of these commenters recommended 

much lower levels, such as 0.02 μg/m3, 

based on their views as to the level 

needed to protect public health with an 

adequate margin of safety in light of 

their interpretation of the advice of 

CASAC and EPA Staff and the evidence, 

including the lack of identifiable 

threshold. Some of these commenters 

recommending much lower levels 

expressed the view that the standard 

should be as protective as possible. 

A second, much smaller, group of 

comments (including some industry 

comments and some state agency 

comments), recommended levels for the 

standard that are higher than 0.2 μg/m3. 

Among this group, some commenters 

provide little or no health-based 

rationale for their comment. Other 

commenters, in recommending various 

levels above 0.2 μg/m3, generally state 

that there is no benefit to be gained by 

setting a lower level for the standard. In 

support of this general conclusion, the 

commenters variously stated that there 

is substantial uncertainty associated 

with the slope of the blood Pb-IQ loss 

concentration-response function at 

lower blood Pb levels, such that EPA 

should not rely on estimates that 

indicate a steeper slope at lower blood 

Pb levels; that the risk assessment 

results for total risk at alternative 

standard levels indicate no benefit to be 

achieved from a standard level below 

0.5 μg/m3; that levels derived from the 

evidence-based framework need upward 

adjustment for use with an averaging 

time less than a year and that IQ loss 

estimates derived from the evidencebased framework presented in the 

proposal for levels from 0.10 to 0.50 μg/ 

m3 do not differ much (e.g., from 2 to 

4.1 points IQ loss [steeper slopes] and 

from 1.1 to 2.2 points IQ loss [shallower 

slope] for the two sets of C–R functions). 

For the range of reasons summarized 

in section II.C.3.a above, and the reasons 

described more fully in section II.C.3.c 

below, EPA does not believe that a level 

for the standard above 0.2 μg/m3 would 

protect public health with an adequate 

margin of safety. Rather, EPA concludes 

that such a level for the standard would 

not be protective of public health with 

an adequate margin of safety. Further, 

EPA disagrees with the industry 

comment that levels identified using the 

evidence-based framework should be 

adjusted upward; this and other specific 

aspects of comments summarized above 

are discussed further in the Response to 

Comments document. 

(ii) Use of Air-related IQ Loss Evidencebased 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 airrelated 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 

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78EPA 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). 

79A ratio of 1:5 was recommended by one of 

these commenters (Doe Run Resources Corp.). 

80See previous footnote regarding Hayes et al. 

(1994). 

than at an upper percentile. This 

commenter also stated the view that 

there is likely little difference in airrelated 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-toblood ratio estimates from the exposure/ 

risk assessment. 

EPA agrees with CASAC and these 

commenters that an upper end air-toblood 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. 

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-toblood 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

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 airto-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 

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67002 Federal Register / Vol. 73, No. 219 / Wednesday, November 12, 2008 / Rules and Regulations 

81Using the ratio of 1:7 identified above as central 

within the reasonable range of air-to-blood ratios, 

the estimate of air-related blood Pb associated with 

a standard level of 0.15 μg/m3 would be 

approximately 1 μg/dL. Adding this to the mean 

total blood Pb level for the U.S. population would 

yield a mean total blood Pb estimate of 2.8 μg/dL. 

82As noted above, we also recognize that blood 

Pb levels are expected to further decline in response 

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 evidencebased 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 μg/ 

dL, also includes studies with mean or 

median blood Pb levels ranging up to 

9.7 μg/dL. Further, they emphasize that 

we are concerned ‘‘with current blood 

Pb levels in the setting of a healthprotective NAAQS, not with blood Pb 

levels of the past’’ (emphasis in 

original). In conclusion, they state that 

‘‘the selection of C–R function should be 

based on determining which studies 

indicate slopes that best reflect the 

current, lower blood Pb levels for 

children in the U.S.—which, in this 

instance, are those studies from which 

steeper slopes are drawn’’ (emphasis in 

original) (Henderson, 2008a). 

A number of commenters (including 

EPA’s Children’s Health Protection 

Advisory Committee, NESCAUM and 

some state agencies) made 

recommendations with regard to C–R 

functions that were similar to those of 

CASAC. These commenters 

recommended consideration of C–R 

functions with slopes appreciably 

steeper than the median value 

representing the second set of functions 

in the proposal, giving greater weight to 

steeper slopes drawn from analyses 

involving children with lower blood Pb 

levels, closer to those of children in the 

U.S. today. Some of these commenters 

(e.g., NESCAUM) additionally suggested 

alternate approaches to identify a slope 

estimate relevant to today’s blood Pb 

levels, considering lower blood Pb level 

studies across both sets of functions 

presented in the proposal, and to avoid 

placing inappropriate weight on a single 

highest value. 

Based on the evidence described in 

detail in the Criteria Document and 

briefly summarized in section II.A.2.c 

above, EPA agrees with CASAC and 

these commenters that, given the 

nonlinearity of the blood Pb-IQ loss 

relationship (steeper slope at lower 

blood Pb levels), the C–R functions 

appropriate to use with the air-related 

IQ loss framework are those drawn from 

analyses of children with blood Pb 

levels closest to those of children in the 

U.S. today. As a result of this nonlinear 

relationship, a given increase in blood 

lead levels (e.g., 1 μg/dl of Pb) is 

expected to cause a greater incremental 

increase in adverse neurocognitive 

effects for a population of children with 

lower blood Pb levels than would be 

expected to occur in a population of 

children with higher blood Pb levels. 

Thus, estimates of C–R functions drawn 

from analyses of children with blood Pb 

levels that are more comparable to blood 

Pb levels in today’s U.S. children are 

likely to better represent the 

relationship between health effects and 

blood Pb levels that would apply for 

children in the U.S. now and in the 

future, as compared to estimates derived 

from analyses of children with higher 

blood lead levels. As discussed in 

section II.A.2.a.ii above, blood Pb levels 

in U.S. children have declined 

dramatically over the past thirty years. 

The geometric mean blood Pb level for 

U.S. children aged five years and below, 

reported for NHANES in 2003–04 (the 

most recent years for which such an 

estimate is available), is 1.8 μg/dL and 

the 5th and 95th percentiles are 0.7 μg/ 

dL and 5.1 μg/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 airrelated 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 airrelated 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

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to this and other public health protection actions, 

including those described above in section I.D. 

Among the analyses presented in the 

proposal (Table 1), we note that six 

study groups from four different studies 

have blood Pb levels appreciably closer 

to the mean blood Pb levels in today’s 

young children. Mean blood Pb levels 

for these study groups range from 2.9 to 

4.3 μg/dL, while mean blood Pb levels 

for the other three study groups 

considered in the proposal range from 

7.4 up to 9.7 μg/dL. Further, among the 

six slopes from analyses with blood Pb 

levels closest to today’s blood Pb levels, 

four come from two studies, with these 

two studies each providing two analyses 

of differing blood Pb levels. Focusing on 

the single analysis from each of the four 

studies that has a mean blood Pb level 

closest to today’s mean for U.S. children 

yields four slopes ranging from ¥1.56 to 

¥2.94, with a median of ¥1.75 IQ 

points per μg/dL (Table 3). Consistent 

with the evidence for nonlinearity in the 

C–R relationship, the slopes for the C– 

R functions from these four analyses are 

steeper than the slopes for the other 

higher blood Pb level analyses. In 

considering the C–R functions from 

these four analyses with the air-related 

IQ loss framework in section II.C.3.c 

below, we have placed greater weight on 

the median of the group, giving less 

weight to the minimum or maximum 

values, recognizing the uncertainty in 

determining the C–R relationship. 

TABLE 3—SUMMARY OF QUANTITATIVE RELATIONSHIPS OF IQ AND BLOOD Pb FOR ANALYSES WITH BLOOD Pb LEVELS

CLOSEST TO THOSE OF CHILDREN IN THE U.S. TODAY

Blood Pb levels 

(μg/dL) 

Study/analysis 

Average linear 

slope A

(IQ points per 

Geometric mean μg/dL) Range 

(min–max) 

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

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

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

3.8 .................................................... 1–9.3 Bellinger and Needleman 2003 B, <10 peak subgroup ............................. ¥1.56 

Median value ............................ ........................ .................................................................................................................... ¥1.75 

A Average linear slope estimates here are for relationship between IQ and concurrent blood Pb levels except for Bellinger & Needleman for 

which study reports relationship 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 IQblood 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 

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67004 Federal Register / Vol. 73, No. 219 / Wednesday, November 12, 2008 / Rules and Regulations 

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-toblood 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 airrelated 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 airrelated pathways and the ratios 

expected at today’s air and blood Pb 

levels. The Administrator also 

concludes that it is appropriate to focus 

on 1:7 as a generally central value 

within this range. 

With regard to C–R functions, the 

Administrator has further considered 

the evidence regarding quantitative 

relationships between IQ loss and blood 

Pb levels described in section II.A.2.c 

above, in light of advice from CASAC 

and comments from the public as 

described in section II.C.3.b above. He 

recognizes the evidence of nonlinearity 

and of steeper slopes at lower blood Pb 

levels (summarized in section II.A.2.c 

above), and as a result, he believes it is 

appropriate to focus on those analyses 

that are based on blood Pb levels that 

most closely reflect today’s population 

of children in the U.S., recognizing that 

the evidence does not include analyses 

involving mean blood Pb levels as low 

as the mean blood Pb level for today’s 

children. He notes that, as described in 

section II.C.3.b above, a review of the 

evidence with this focus in mind has 

identified four analyses that have a 

mean blood Pb level closest to today’s 

mean for U.S. children and that yield 

four slopes ranging from ¥1.56 to 

¥2.94, with a median of ¥1.75 IQ 

points per μg/dL (Table 3). The 

Administrator concludes that it is 

appropriate to consider this set of C–R 

functions for use in the air-related IQ 

loss evidence based framework, as this 

set of C–R functions best represents the 

evidence pertinent to children in the 

U.S. today. In addition, the 

Administrator determines that it is 

appropriate to give more weight to the 

central estimate for this set of functions, 

which is the median of the set of 

functions, and not to rely on any one 

function. 

As noted in the proposal, in 

considering this evidence-based 

framework, the Administrator 

recognizes that there are currently no 

commonly accepted guidelines or 

criteria within the public health 

community that would provide a clear 

basis for reaching a judgment as to the 

appropriate degree of public health 

protection that should be afforded to 

protect against risk of neurocognitive 

effects in sensitive populations, such as 

IQ loss in children. With regard to 

making a public health policy judgment 

as to the appropriate protection against 

risk of air-related IQ loss and related 

effects, the Administrator believes that 

ideally air-related (as well as other) 

exposures to environmental Pb would 

be reduced to the point that no IQ 

impact in children would occur. The 

Administrator recognizes, however, that 

in the case of setting a NAAQS, he is 

required to make a judgment as to what 

degree of protection is requisite to 

protect public health with an adequate 

margin of safety. 

The Administrator generally agrees 

with CASAC and the commenters who 

emphasize that the NAAQS should 

prevent air-related IQ loss of a 

significant magnitude in all but a small 

percentile of the population. However, 

as discussed above in section II.C.3.b, it 

is important to note that in selecting a 

target degree of public health protection 

that should be afforded to at-risk 

populations of children in terms of airrelated 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. 

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83Further, 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 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 airrelated IQ loss for a high, albeit 

unquantifiable, percentage of the entire 

population of U.S. children.83

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 airrelated IQ loss to focus on in applying 

the framework should not be seen as a 

decision that a specific level of airrelated 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 airrelated 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 airrelated IQ loss of 2 points should be 

used in conjunction with the evidencebased 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 airrelated IQ loss of that magnitude. 

With this specific air-related IQ loss 

in mind, the Administrator considered 

the application of this framework to a 

broad range of standard levels, using 

estimates for the two key parameters— 

air-to-blood ratio and C–R function— 

that are appropriate for use within the 

framework, as shown in Table 4 below. 

In so doing, the Administrator 

recognized that, relying on the median 

of the four C–R functions from analyses 

with blood Pb levels closest to those of 

today’s children, a standard level in the 

lower half of the proposed range (0.10– 

0.20 μg/m3) would limit the estimated 

mean IQ loss from air-related Pb to 

below 2 points, depending on the choice 

of air-to-blood ratio within the range 

from 1:5 to 1:10. 

As noted above, however, the 

Administrator does not believe it is 

appropriate to consider only a single airto-blood ratio. Using the air-to-blood 

ratio of 1:7, a generally central estimate 

within the well supported range of 

estimates, the estimates of air-related IQ 

loss are below a 2-point IQ loss for 

standard levels of 0.15 μg/m3 and lower. 

At a level of 0.15 μg/m3, the 

Administrator recognizes that use of a 

1:10 ratio produces an estimate greater 

than 2 IQ points and use of a 1:5 ratio 

produces a lower IQ loss estimate. 

Given the uncertainties and limitations 

in the air-related IQ loss framework, the 

Administrator views it as appropriate to 

place primary weight on the results 

from this central estimate rather than 

estimates derived using air-to-bloodratios either higher or lower than this 

ratio. 

TABLE 4—ESTIMATES OF AIR-RELATED MEAN IQ LOSS FOR THE SUBPOPULATION OF CHILDREN EXPOSED AT THE LEVEL

OF THE STANDARD

Potential level for standard 

(μg/m3) 

Air-related mean IQ loss (points) for the subpopulation of children exposed at level of the standard 

IQ loss estimate is based on median slope of 4 C–R functions with blood Pb levels closer to those of today’s U.S. children (range shown for estimates based on lowest and highest of 4 slopes) 

Air-to-blood ratio 

1:10 1:7 1:5 

0.50 >5 * >5 * 4.4 (3.9–7.4) 

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84For example, in considering a standard level of 

0.2 μg/m3, we note that the risk assessment 

provides estimates falling within the range of 1.2 to 

3.2 points IQ loss for the general urban case study 

and <3.7 for the primary Pb smelter subarea. These 

estimates are inclusive of the range of estimates for 

the 0.20 standard level presented in Table 4 based 

on the median C–R slope applied in the air-related 

IQ loss framework. As noted in section II.A.3.a 

above, these case studies, based on the nature of the 

population exposures represented by them, relate 

more closely to the air-related IQ loss evidencebased framework than other case studies assessed. 

TABLE 4—ESTIMATES OF AIR-RELATED MEAN IQ LOSS FOR THE SUBPOPULATION OF CHILDREN EXPOSED AT THE LEVEL

OF THE STANDARD—Continued 

Potential level for standard 

(μg/m3) 

Air-related mean IQ loss (points) for the subpopulation of children exposed at level of the standard 

IQ loss estimate is based on median slope of 4 C–R functions with blood Pb levels closer to those of today’s U.S. children (range shown for estimates based on lowest and highest of 4 slopes) 

Air-to-blood ratio 

1:10 1:7 1:5 

0.40 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 airrelated 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 evidencebased 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

In the Administrator’s view, the above 

considerations, taken together, provide 

no evidence-or risk-based bright line 

that indicates a single appropriate level. 

Instead, there is a collection of scientific 

evidence and other information, 

including information about the 

uncertainties inherent in many relevant 

factors, which needs to be considered 

together in making the public health 

policy judgment to select the 

appropriate standard level from a range 

of reasonable values. In addition, the 

results of the evidence-based framework 

are seen as a useful guide in 

determining whether the risks to public 

health from exposure to ambient levels 

of Pb in the air, in the context of a 

specified averaging time and form, 

provide a degree of protection from risk 

with an adequate margin of safety that 

is sufficient but not more than 

necessary. 

Based on consideration of the entire 

body of evidence and information 

available at this time, as well as the 

recommendations of CASAC and public 

comments, the Administrator has 

decided that a level for the primary Pb 

standard of 0.15 μg/m3, in combination 

with the specified choice of indicator, 

averaging time, and form, is requisite to 

protect public health, including the 

health of sensitive groups, with an 

adequate margin of safety. The 

Administrator notes that this level is 

within the range recommended by 

CASAC, the Staff Paper, and by the vast 

majority of commenters. The 

Administrator concludes that a standard 

with a level of 0.15 μg/m3 will reduce 

the risk of a variety of health effects 

associated with exposure to Pb, 

including effects indicated in the 

epidemiological studies at low blood Pb 

levels, particularly including 

neurological effects in children, and the 

potential for cardiovascular and renal 

effects in adults. 

The Administrator notes that the 

evidence-based framework indicates 

that for standard levels above 0.15 μg/ 

m3, the estimated mean air-related IQ 

loss in the subpopulation of children 

exposed at the level of the standard 

would range in almost all cases from 

above 2 points to 5 points or more with 

the range of air-to-blood ratios 

considered. He concludes, in light of his 

consideration of all of the evidence, 

including the framework discussed 

above, that the protection from airrelated Pb effects at the higher blood Pb 

levels that would be allowed by 

standards above 0.15 μg/m3 would not 

be sufficient to protect public health 

with an adequate margin of safety. 

In addition, the Administrator notes 

that for standard levels below 0.15 μg/ 

m3, the estimated mean IQ loss from airrelated 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 evidencebased framework, that the degree of 

public health protection that standards 

below 0.15 μg/m3 would likely afford 

would be greater than what is necessary 

to protect public health with an 

adequate margin of safety. 

The Administrator also recognizes 

that several commenters expressed 

concern that the proposal did not 

adequately address the need for the 

standard to be set with an adequate 

margin of safety. As noted above, in 

section I, the requirement that primary 

standards include an adequate margin of 

safety was intended to address 

uncertainties associated with 

inconclusive scientific and technical 

information available at the time of 

standard setting. It was also intended to 

provide a reasonable degree of 

protection against hazards that research 

has not yet identified. Both kinds of 

uncertainties are components of the risk 

associated with pollution at levels 

below those at which human health 

effects can be said to occur with 

reasonable scientific certainty. Thus, in 

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selecting a primary standard that 

includes an adequate margin of safety, 

the Administrator is seeking not only to 

prevent pollutant levels that have been 

demonstrated to be harmful but also to 

prevent lower pollutant levels that may 

pose an unacceptable risk of harm, even 

if the risk is not precisely identified as 

to nature or degree. 

Nothing in the Clean Air Act, 

however, requires the Administrator to 

identify a primary standard that would 

be protective against demonstrated 

harms, and then identify an additional 

‘‘margin of safety’’ which results in 

further lowering of the standard. Rather, 

the Administrator’s past practice has 

been to take margin of safety 

considerations into account in making 

decisions about setting the primary 

standard, including in determining its 

level, averaging time, form and 

indicator, recognizing that protection 

with an adequate margin of safety needs 

to be sufficient but not more than 

necessary. 

Consistent with past practice, the 

Administrator has taken the need to 

provide for an adequate margin of safety 

into account as an integral part of his 

decision-making on the appropriate 

level, averaging time, form, and 

indicator of the standard. As discussed 

above, the consideration of health 

effects caused by different ambient air 

concentrations of Pb is extremely 

complex and necessarily involves 

judgments about uncertainties with 

regard to the relationships between air 

concentrations, exposures, and health 

effects. In light of these uncertainties, 

the Administrator has taken into 

account the need for an adequate margin 

of safety in making decisions on each of 

the elements of the standards. 

Consideration of the need for an 

adequate margin of safety is reflected in 

the following elements: selection of TSP 

as the indicator and the rejection of the 

use of PM10 scaling factors; selection of 

a maximum, not to be exceeded form, in 

conjunction with a 3-month averaging 

time that employs a rolling average, 

with the requirement that each month in 

the 3-month period be weighted equally 

(rather than being averaged by 

individual data) and that a 3-year span 

be used for comparison to the standard; 

and, the use of a range of inputs for the 

evidence-based framework, that 

includes a focus on higher air-to-blood 

ratios than the lowest ratio considered 

to be supportable, and steeper rather 

than shallower C-R functions, and the 

consideration of these inputs in 

selection of 0.15 μg/m3 as the level of 

the standard. The Administrator 

concludes based on his review of all of 

the evidence (including the evidencebased framework) that when taken as a 

whole the standard selected today, 

including the indicator, averaging time, 

form, and level, will be sufficient but 

not more than necessary to protect 

public health, including the health of 

sensitive subpopulations, with an 

adequate margin of safety. 

Thus, after carefully taking the above 

comments and considerations into 

account, and fully considering the 

scientific and policy views of the 

CASAC, the Administrator has decided 

to revise the level of the primary Pb 

standard to 0.15 μg/m3. In the 

Administrator’s judgment, based on the 

currently available evidence, a standard 

set at this level and using the specified 

indicator, averaging time, and form 

would be requisite to protect public 

health with an adequate margin of 

safety. The Administrator judges that 

such a standard would protect, with an 

adequate margin of safety, the health of 

children and other at-risk populations 

against an array of adverse health 

effects, most notably including 

neurological effects, particularly 

neurobehavioral and neurocognitive 

effects, in children. A standard set at 

this level provides a very significant 

increase in protection compared to the 

current standard. The Administrator 

believes that a standard set at 0.15 μg/ 

m3 would be sufficient to protect public 

health with an adequate margin of 

safety, and believes that a lower 

standard would be more than what is 

necessary to provide this degree of 

protection. This judgment by the 

Administrator appropriately considers 

the requirement for a standard that is 

neither more nor less stringent than 

necessary for this purpose and 

recognizes that the CAA does not 

require that primary standards be set at 

a zero-risk level, but rather at a level 

that reduces risk sufficiently so as to 

protect public health with an adequate 

margin of safety. 

D. Final Decision on the Primary Lead 

Standard 

For the reasons discussed above, and 

taking into account information and 

assessments presented in the Criteria 

Document and Staff Paper, the advice 

and recommendations of CASAC, and 

the public comments, the Administrator 

is revising the various elements of the 

standard to provide increased protection 

for children and other at-risk 

populations against an array of adverse 

health effects, most notably including 

neurological effects in children, 

including neurocognitive and 

neurobehavioral effects. Specifically, 

the Administrator has decided to revise 

the level of the primary standard to a 

level of 0.15 μg/m3, in conjunction with 

retaining the current indicator of PbTSP. 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. 

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67008 Federal Register / Vol. 73, No. 219 / Wednesday, November 12, 2008 / Rules and Regulations 

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 gasolinederived 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 

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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 

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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 μg Pb/m3, as a maximum arithmetic 

mean averaged over a calendar quarter), 

the basis for which is summarized in 

section II.C.1. At the time the standard 

was set, the Agency concluded that the 

primary air quality standard would 

adequately protect against known and 

anticipated adverse effects on public 

welfare, as the Agency stated that it did 

not have evidence that a more restrictive 

secondary standard was justified. In the 

rationale for this conclusion, the Agency 

stated that the available evidence cited 

in the 1977 Criteria Document indicated 

that ‘‘animals do not appear to be more 

susceptible to adverse effects from lead 

than man, nor do adverse effects in 

animals occur at lower levels of 

exposure than comparable effects in 

humans’’ (43 FR 46256). The Agency 

recognized that Pb may be deposited on 

the leaves of plants and present a hazard 

to grazing animals. With regard to 

plants, the Agency stated that Pb is 

absorbed but not accumulated to any 

great extent by plants from soil, and that 

although some plants may be 

susceptible to Pb, it is generally in a 

form that is largely unavailable to them. 

Further the Agency stated that there was 

no evidence indicating that ambient 

levels of Pb result in significant damage 

to manmade materials and Pb effects on 

visibility and climate are minimal. 

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 μg/m3. 

Given the full body of current 

evidence, despite wide variations in Pb 

concentrations in soils throughout the 

country, Pb concentrations are in excess 

of concentrations expected from 

geologic or other non-anthropogenic 

forces. There are several difficulties in 

quantifying the role of recent air 

emissions of Pb in the environment: 

Some Pb deposited before the standard 

was enacted is still present in soils and 

sediments; historic Pb from gasoline 

continues to move slowly through 

systems as does current Pb derived from 

both air and nonair sources. 

Additionally, the evidence of adversity 

in natural systems is limited due in no 

small part to the difficulty in 

determining the effects of confounding 

factors such as multiple metals or 

factors influencing bioavailability in 

field studies. 

The evidence summarized above, in 

the Proposed Rule, in section 4.2 of the 

Staff Paper, and described in detail in 

the Criteria Document, informs our 

understanding of Pb in the environment 

today and evidence of environmental Pb 

exposures of potential concern. For 

areas influenced by point sources of air 

Pb that meet the current standard, 

concentrations of Pb in soil may exceed 

by many orders of magnitude the 

concentrations which are considered 

harmful to laboratory organisms (CD, 

sections 3.2 and AX7.1.2.3). In addition, 

conditions exist in which Pb associated 

adverse effects to aquatic organisms and 

thereby ecosystems may be anticipated 

given experimental results. While the 

evidence does not indicate that 

dissolved Pb in surface water 

constitutes a threat to those ecosystems 

that are not directly influenced by point 

sources, the evidence regarding Pb in 

sediment is less clear (CD, sections 

AX7.2.2.2.2 and AX7.2.4). It is likely 

that some areas with long term 

historical deposition of Pb to sediment 

from a variety of sources as well as areas 

influenced by point sources have the 

potential for adverse effects to aquatic 

communities. The Staff Paper 

concluded, based on laboratory studies 

and current media concentrations in a 

wide range of areas, that it seems likely 

that adverse effects are occurring, 

particularly near point sources, under 

the current standard. The long residence 

time of Pb in sediment and its ability to 

be resuspended by turbulence make Pb 

contamination likely to be a factor for 

the foreseeable future. Based on this 

information, the Staff Paper concluded 

that the evidence suggests that the 

environmental levels of Pb occurring 

under the current standard, set nearly 

thirty years ago, may pose risk of 

adverse environmental effect. 

In addition to the evidence-based 

considerations described in the previous 

section, the screening level ecological 

risk assessment is informative, taking 

into account key limitations and 

uncertainties associated with the 

analyses. As discussed in the previous 

section, as a result of its persistence, Pb 

emitted in the past remains today in 

aquatic and terrestrial ecosystems of the 

United States. Consideration of the 

environmental risks associated with the 

current standard is complicated by the 

environmental burden associated with 

air Pb concentrations that exceeded the 

current standard, predominantly in the 

past. Concentrations of Pb in soil and 

sediments associated with the case 

studies exceeded screening values for 

those media, indicating potential for 

adverse effect in terrestrial organisms 

(plants, birds, and mammals) and in 

sediment dwelling organisms. While the 

contribution to these Pb concentrations 

from air as compared to 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 

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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 

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85As 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. 

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 PbTSP data and all valid FRM/FEM PbPM10 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. 

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 readjustment to local conditions, unless 

the monitoring agency voluntarily resubmitted 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., nonscheduled samples that are not eligible 

to be considered make-up samples 

because they either were taken too long 

after the missed sample or another nonscheduled 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. 

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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. 

87The scheduled sampling days, in contrast, are 

expected to be uncorrelated with Pb concentration, 

since they do not emphasize any particular day of 

the week. 

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 nonoverlapping 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

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. 

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 

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67014 Federal Register / Vol. 73, No. 219 / Wednesday, November 12, 2008 / Rules and Regulations 

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. 

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-insix 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-insix 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. 

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. 

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Federal Register / Vol. 73, No. 219 / Wednesday, November 12, 2008 / Rules and Regulations 67015 

89No public comment was received on this 

provision. 

90Comments regarding whether Pb-TSP or PbPM10 should be the indicator for the NAAQS and 

EPA’s response to them are discussed in section 

II.C.1. 

91Scaling Factor: PM10 versus TSP, Neptune and 

Company, Inc., Final Report, September 30, 2008. 

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 highconcentration 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

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 PbPM10 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 PbTSP NAAQS. Comments on the specific 

subject of scaling factors to relate PbPM10 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. 

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 sitespecific 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 PbTSP in hopes of obtaining the option of 

indefinitely monitoring only for PbPM10 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 highvolume 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 

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67016 Federal Register / Vol. 73, No. 219 / Wednesday, November 12, 2008 / Rules and Regulations 

92The 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 sitespecific 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. 

93The 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. 

94Of 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 

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 monthto-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-sourceoriented 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 sitespecific scaling factors under the criteria 

of the proposed rule. 

The alternative approach of 

establishing default scaling factors was 

also opposed by virtually all 

commenters who addressed it, and no 

commenter supported any specific 

default factor or set of default factors. 

Many commenters asserted that no 

reliable default factor or factors could be 

developed and that all Pb measurements 

for comparison to the NAAQS should be 

Pb-TSP measurements because of the 

possible presence of ultra-coarse 

particles containing significant amounts 

of Pb. One commenter did not oppose 

the concept of default scaling factors but 

even that commenter said that EPA 

should conduct more testing before 

developing such factors. A number of 

commenters said that if scaling factors 

are used, they should be conservative, 

health protective factors to ensure that 

the use of Pb-PM10 monitors does not 

result in increased lead exposures; some 

of these commenters pointed to the case 

of a particular Pb monitoring site that 

was reported in the preamble to the 

proposed rule to have a scaling factor of 

2.0. Other commenters argued that the 

data set from the site (in East Helena, 

MT) suggesting such a high ratio of PbTSP 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 PbPM10 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 PbPM10 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-sourceoriented 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 

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ratios of average concentrations of Pb-TSP to PbPM10 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. 95M. Schmidt and P. Lorang (October 15, 2008). 

Memo to Lead NAAQS Docket, Analysis of 

Expected Range of Pb-TSP Concentrations at NonSource Oriented Monitoring Sites in CBSAs with 

Population Over 500,000. 96Based 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. 

97When 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. 

98 If three years of Pb-TSP monitoring results in 

no 3-month average Pb concentration equal to or 

greater than 0.10 μg/m3, as might occur after the 

source improves its control of Pb emissions, the site 

would again be eligible for Pb-PM10 monitoring. 

ultra-coarse Pb fraction is zero to 0.3. 

Also, a new EPA staff analysis, 

completed since proposal, of recent PbTSP concentrations at existing 

monitoring sites that appear to be nonsource-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 precondition that the available Pb-TSP 

monitoring data at the site during the 

previous three years, if any are 

available, do not show any 3-month 

average concentrations equal to or 

greater than 0.10 μg/m3, which is 67 

percent of the final NAAQS level.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 PbPM10, increasing the concern over the 

protectiveness of this approach, here the 

use of Pb-PM10 data does not raise 

similar concerns. To guard against the 

possibility that any of these required 

sites may be different in a way that 

contradicts the previous experience at 

such sites and against the possibility 

that source conditions around one or 

more of these monitoring sites may 

change over time, the final rule also 

provides that if any 3-month average 

concentration of Pb-PM10 is ever 

observed to be equal to or greater than 

0.10 μg/m3, a Pb-TSP monitor must be 

installed.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-sourceoriented sites. If the 3-month average 

Pb-PM10 concentration at a site was 

below 0.10 μg/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. 

EPA has also considered whether any 

of the required source-oriented sites 

should be allowed to be monitored for 

Pb-PM10 rather than Pb-TSP, also with 

the Pb-PM10 concentrations compared 

directly to the Pb-TSP NAAQS. As 

explained in Section V, the final 

requirements for monitoring near 

sources of Pb are based on the quantity 

of Pb emitted being above an emissions 

threshold. We are extending the 

allowance for the use of Pb-PM10

monitors to allow Pb-PM10 monitors 

without the use of scaling factors for 

source-oriented monitors where Pb 

concentrations are expected to be less 

than 0.10 μg/m3 (based on modeling or 

historic data) and where the ultra-course 

Pb fraction is expected to be low. We are 

also requiring, as for non-sourceoriented sites, that a Pb-TSP monitor be 

required at a source-oriented site if at 

some point in the future the Pb-PM10

monitor shows that Pb-PM10

concentrations are equal to or greater 

than 0.10 μg/m3.98 A state may also 

operate non-required Pb monitors at any 

other locations of its choosing, and 

these may be of any type. 

3. Conclusions on Scaling Factors 

The final version of Appendix R 

eliminates all reference to scaling 

factors. As explained in detail in section 

V, the final rule allows Pb-PM10

monitoring as a surrogate for Pb-TSP 

monitoring under certain specified 

conditions, with continuation of such 

monitoring being contingent on 

measured 3-month average Pb-PM10

concentrations remaining without 

application of any scaling factor staying 

less than 0.10 μg/m3. Section IV.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) PbPM10 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. PbTSP 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 PbPM10 data could be used to show both 

compliance and violation of the 

NAAQS. 

2. Comments on Use of Pb-TSP and PbPM10 Data 

No comments were received 

specifically on the proposed provisions 

of Appendix R addressing the 

precedence between Pb-TSP and PbPM10 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 

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99Such 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. 

100Only 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. 

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 PbTSP 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 PbPM10 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 PbPM10 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 PbPM10 monitoring in place of Pb-TSP 

monitoring only at required non-sourceoriented 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 PbPM10 data may include data from sites 

with non-zero ultra-coarse fractions and 

may include data from sites with high 

or unknown ultra-coarse factions, EPA 

believes it would undermine the 

protectiveness of the NAAQS to always 

allow any Pb-PM10 data from any 

monitoring site to demonstrate 

compliance with the NAAQS. Some site 

applicability restriction and/or 

compliance margin when using Pb-PM10

data to show compliance would be 

needed to avoid undermining the 

protectiveness of the NAAQS. The 

technical issues to be overcome in 

designing site applicability restrictions 

and/or compliance margins would be 

the same as the issues that arise when 

considering default scaling factors, 

described above. 

EPA is also mindful that the 

distinction between a finding of 

compliance with the NAAQS and not 

making a finding of violation is much 

more theoretical than practical. The 

distinction is not important to the initial 

stages of the implementation process for 

a revised NAAQS, because (1) by the 

time of the initial designations very few 

Pb-PM10 monitoring sites will have 

three years of data so a finding of 

compliance would not be possible 

anyway 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 PbTSP or Pb-PM10, since Pb-TSP 

monitoring must begin at any site where 

Pb-PM10 concentrations have exceeded 

even 50 percent of the NAAQS. This 

makes it moot whether Pb-PM10 data 

alone can be used to redesignate a 

nonattainment area to attainment after 

emission controls are implemented. In 

light of the technical issues and the lack 

of any substantive consequences, the 

final version of Appendix R does not 

allow Pb-PM10 data to be used to show 

affirmative compliance with the 

NAAQS. 

The above discussion addresses the 

compliance versus violation 

consequences of comparing Pb-PM10

and Pb-TSP data to the Pb-TSP NAAQS. 

EPA has also considered the issue of 

how design values should be 

determined when there is only Pb-PM10

data or there is a mixture of Pb-PM10

data and Pb-TSP data for a single 

monitoring site over a given period. In 

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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. 

102A 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. 

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. 

3. Conclusions on Use of Pb-TSP and 

Pb-PM10 Data 

The final version of Appendix R 

specifies that the NAAQS is violated 

whenever Pb-PM10 data or Pb-TSP data 

result in a 3-month average 

concentration above the NAAQS level, 

but that compliance with the NAAQS 

can only be demonstrated using Pb-TSP 

data. Pb-PM10 data will be used in the 

calculation of a design value only when 

doing so results in a higher design value 

than using only Pb-TSP data and that 

design value is above the level of the 

NAAQS. 

F. Data Reporting and Rounding 

1. Proposed Provisions 

EPA proposed that individual daily 

concentrations of Pb be reported to the 

nearest thousandth μg/m3 (0.xxx) with 

additional digits truncated, and that 

monthly averages calculated from the 

daily averages would be rounded to the 

nearest hundredth μg/m3 (0.xx). 

Decimals 0.xx5 and greater would be 

rounded up, and any decimal lower 

than 0.xx5 would be rounded down. 

E.g., a monthly average of 0.104925 

would round to 0.10 and a monthly 

average of 0.10500 would round to 0.11. 

Because the proposed NAAQS level 

would be stated to two decimal places, 

no additional rounding beyond what is 

specified for monthly averages would be 

required before a design value selected 

from among rounded monthly averages 

would be compared to the level of the 

NAAQS. 

2. Comments on Data Reporting and 

Rounding 

No comments were received on this 

aspect of the proposal. 

3. Conclusions on Data Reporting and 

Rounding 

The final version of Appendix R 

differs from that proposed because the 

proposed version addressed a single 

month as the averaging time for the 

NAAQS and the final NAAQS is based 

on a 3-month average concentration. In 

the preamble to the proposal, EPA did 

not specifically address whether and 

how, in the case of the NAAQS being 

based on a 3-month averaging time, 

calculated monthly averages would be 

rounded before being used to calculate 

the 3-month average. The final version 

of Appendix R specifies that all digits of 

the monthly average shall be retained 

for the purpose of calculating the 3- 

month average, with the 3-month 

average then rounded to the nearest 

hundredth μg/m3, i.e., 3-month average 

decimals 0.xx5 and greater would be 

rounded up and any decimal lower than 

0.xx5 would be rounded down. Because 

individual monthly averages are never 

compared to the level of the NAAQS 

there is no need to specify a rounding 

convention for them, and retaining all 

digits until the final comparison of the 

3-month average to the NAAQS allows 

a more precise determination of 

compliance compared to rounding at 

both the monthly and 3-month levels. 

G. Other Aspects of Data Interpretation 

One implication of the selection of a 

rolling 3-month period as the averaging 

time of the NAAQS is that there will be 

two 3-month periods that span each pair 

of adjacent calendar years: NovemberJanuary and December-February. EPA 

has considered whether, for any threecalendar-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-peryear 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 

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103The 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. 

104The 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. 

105For a list of currently approved FRM/FEMs for 

Pb-TSP refer to: http://www.epa.gov/ttn/amtic/ 

criteria.html. 

106The 21 distinct approved FEMs represent less 

than 21 fundamentally different analysis methods, 

as some differ only in minor aspects. 

situation, Appendix R provides that a 

finding of compliance will be made if 

all 34 available 3-month average 

concentrations of Pb-TSP are at or below 

the level of the NAAQS. 

As discussed in Section V on 

monitoring requirements, EPA proposed 

and is finalizing a change to the Pb 

monitoring requirements to no longer 

allow monitoring agencies to combine 

several daily Pb-TSP filters for chemical 

analysis, at required Pb monitoring 

sites.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. 

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 highvolume 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 highvolume TSP samplers and a variety of 

approved equivalent analysis 

methods.106

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 highvolume 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 lowvolume 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 PbPM10 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, 

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107Sampling 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. 

108Proper 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 ultracoarse PM in a wind-tunnel setting. 

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 μg/m3 or above, 

then the high-volume Pb-TSP sampler 

should be used. Some public 

commenters also stated similar concerns 

with the performance of the Pb-TSP 

sampler. 

A large number of other commenters 

stated that the high-volume TSP 

sampler should continue to be the 

sampler for determining compliance 

with the Pb NAAQS. They expressed 

concerns that PM10 samplers would not 

capture ultra-coarse particles (i.e., 

particulate matter with an aerodynamic 

diameter greater than 10 μm), and could 

greatly underestimate Pb concentrations 

in the ambient air, especially near Pb 

sources. 

Despite some limitations with 

sampler performance and consistent 

with CASAC advice for methods at the 

level of the NAAQS we have chosen, we 

believe the high-volume sampler is the 

most appropriate currently available 

sampler for the measurement of Pb-TSP 

in ambient air. Ultra-coarse particulate 

matter (larger than PM10) can contribute 

to a significant portion of the total Pb 

concentration in ambient air, especially 

near Pb sources (Schmidt, 2008) where 

Pb-TSP concentrations may be as much 

as twice as high as Pb-PM10. 

Furthermore, we believe the precision 

and bias of the high-volume TSP 

sampler are acceptable and similar to 

those for other PM samplers (Camalier 

and Rice, 2007). 

We received several comments 

supporting the need for the 

development of a low-volume Pb-TSP 

sampler. However, in our consultation 

with CASAC’s AAMM Subcommittee, 

we were cautioned against finalizing a 

new low-volume Pb-TSP FRM without 

an adequate characterization of the 

sampler’s performance over a wide 

range of particle sizes.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. 

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 PbTSP) 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 PbPM10 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 lowvolume 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 

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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 ICPMS 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 lowvolume sampling to be 0.001 μg/m3 and 

0.00006 μg/m3, respectively. No 

commenters disagreed with these 

estimates. 

Several states requested approval for 

alternative analysis methods because 

their laboratories are already equipped 

to perform those analysis methods. Our 

decision to use XRF as the FRM analysis 

method does not prevent monitoring 

agencies from using alternative analysis 

methods. However, before these 

alternative analysis methods can be 

used they must be approved as FEMs for 

the measurement of Pb-PM10. 

Monitoring agencies can seek FEM 

approval for alternative analysis 

methods by following the FEM 

requirements (40 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 thinfilm 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 μg/m3. 

Calibration materials for XRF are not 

destroyed during analysis; therefore, the 

SRM should be stable over time and can 

be reused multiple times if properly 

handled and protected. 

The AAMM Subcommittee raised 

concerns regarding lot-specific 

laboratory blanks, field blanks, and 

possible contamination of filters. The 

commenters suggested that the 

laboratory blanks (the results of Pb 

analysis of ‘‘clean’’ filters that have not 

been used in a sampler) that are used for 

XRF background measurement and 

correction be lot-specific. The addition 

of lot-specific laboratory blanks will 

help minimize contamination that may 

be due to new filter lots and the 

analytical system. A few commenters 

suggested the addition of field blanks in 

order to minimize the Pb contamination 

of filters in the field. Field blanks are 

filter blanks that are sent to the field and 

are placed into the sampler for the 

sampling duration without ambient air 

flow. We agree with the suggestions to 

make laboratory blanks lot-specific and 

to add the collection of field blanks. A 

comment to add annual MDL 

determinations and filter-lot specific 

MDL determinations was received. We 

agree that the addition of annual MDL 

estimates and lot-specific MDL 

determinations is an improvement to 

the proposed FRM text. In addition, 

several editorial comments were 

received that related to modifying 

existing statements to add clarity and 

help to ensure consistency across 

laboratories. We are making changes to 

the XRF analysis method to address 

these editorial comments. 

We received one comment related to 

the need for data quality objectives 

(DQOs). We agree with the commenter 

on the need for DQOs for the Pb-PM10

FRM. Since the time of proposal, we 

have completed the DQO analysis to 

evaluate the acceptable measurement 

uncertainty for precision and bias. The 

DQO report is in the docket. As part of 

that process, the recommended goals for 

precision were defined as an upper 90 

percent confidence limit for the 

coefficient of variation of 20 percent and 

the goals for bias were defined as an 

upper 95 percent confidence limit for 

the absolute bias of 15 percent. We have 

reflected this in our final regulation. 

c. Decision on Pb-PM10 FRM 

We are finalizing the FRM for PbPM10 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 lotspecific MDL determinations. Several 

minor changes were made to address 

editorial comments received that related 

to modifying existing statements to add 

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clarity and help to ensure consistency 

across laboratories. Examples of these 

changes include the addition of other 

commercial XRF instrumentation 

vendors; clarification of the maximum 

filter loading for Pb analysis which is 

based on the maximum mass loading 

(200 μg/m3) for a PM10C sampler; 

inclusion of additional references for 

spectral processing methods; and 

clarification that the FRM applies 

specifically to Pb. A reference was 

included for additional guidance if 

multi-elemental analysis is performed. 

To ensure consistency in reporting 

uncertainties for Pb by XRF across 

laboratories, an equation to calculate 

uncertainties was added and follows the 

same procedure used for XRF in the 

PM2.5 speciation program. Based on the 

DQO process, the FRM precision and 

bias requirements were modified to 

reflect the measurement uncertainty 

goals of 20 percent and 15 percent, 

respectively. 

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 μg/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 μg/m3. In 

addition, the Agency proposed to lower 

the Pb NAAQS level to between 0.10 

and 0.30 μg/m3. Consistent with this 

proposed revision, we also proposed to 

revise the Pb concentration 

requirements for candidate FEM testing 

to a range of 30 percent of the revised 

level to 250 percent of the revised level 

in μg/m3. The requirements were 

changed from actual concentration 

values to percentages of the NAAQS 

level to allow the FEM requirements to 

remain appropriate if subsequent 

changes to NAAQS levels occur during 

future NAAQS reviews. 

The current FEM does not have a 

requirement for a maximum MDL. In 

order to ensure that candidate analytical 

methods have adequate sensitivity or 

MDLs, we proposed adding a 

requirement for testing of a candidate 

FEM. The applicant must demonstrate 

that the MDL of the method is less than 

1 percent of the level of Pb NAAQS. 

We proposed to modify the FEM 

requirements for audit samples. Audit 

samples are the known concentration or 

reference samples provided by EPA and 

used to verify the accuracy with which 

a laboratory conducts the FRM 

analytical procedure before it may be 

compared to the candidate FEM. The 

current requirements are that audit 

samples be analyzed at levels that are 

equal to 100, 300, and 750 μg per spiked 

filter strip (equivalent to 0.5, 1.5, and 

3.75 μg/m3 of sampled air). We 

proposed to revise the levels of the audit 

concentrations to percentages (30 

percent, 100 percent and 250 percent) of 

the level of the Pb NAAQS to provide 

for reduced audit concentrations that 

are more appropriate for a reduced level 

of the revised NAAQS. 

The existing FEM requirements are 

based on the high-volume TSP sampler, 

and as such, refer to 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 

μg/m3), the maximum LOQ would still 

be less than one half of the NAAQS (i.e., 

0.075 μg/m3). We believe this is 

adequate for the purposes of 

determination of compliance with the 

NAAQS. The three most commonly 

used Pb-PM10 analysis methods (XRF, 

ICP-MS, and GFAA) all have estimated 

method detection limits below 5 percent 

of the revised Pb NAAQS. We note, 

however, that for areas where 

concentrations may frequently be well 

below the NAAQS such as at nonsource-oriented sites it may be desirable 

to use a FEM with a more sensitive 

analysis method (such as ICP-MS) to 

assure fewer non-detect measurements 

and to provide better accuracy at 

concentrations well below the NAAQS. 

We received two comments 

supporting the development and 

consideration of the use of continuous 

Pb monitors. We agree that the FEM 

testing requirements should include 

language regarding FEM testing and 

approval of continuous or semicontinuous 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 

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67024 Federal Register / Vol. 73, No. 219 / Wednesday, November 12, 2008 / Rules and Regulations 

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 lowvolume 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 highvolume TSP sampler, and we proposed 

edits to account for the proposed PbPM10 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 μg/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. 

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109For the complete definition of CBSA refer to: 

http://www.census.gov/population/www/estimates/ 

aboutmetro.html. 

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 sourceoriented monitors, data from these nonsource-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-sourceoriented 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.) 

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 

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67026 Federal Register / Vol. 73, No. 219 / Wednesday, November 12, 2008 / Rules and Regulations 

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 

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Federal Register / Vol. 73, No. 219 / Wednesday, November 12, 2008 / Rules and Regulations 67027 

110Required PM2.5 sites have additional criteria 

where monitoring sites are to represent communitywide 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. 

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 sourceoriented 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, longestablished 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. 

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-sourceoriented 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 reentrained 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-sourceoriented 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 nonsource 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 nonsource-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 

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67028 Federal Register / Vol. 73, No. 219 / Wednesday, November 12, 2008 / Rules and Regulations 

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 PbPM10 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 ultracoarse 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 PbPM10 monitor with a Pb-TSP monitor. 

We support this suggested approach, 

noting that it allows for the use of PbPM10 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 PbPM10 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 PbPM10 in lieu of Pb-TSP where the 

maximum 3-month arithmetic mean Pb 

concentration is expected to be less than 

0.10 μg/m3 (i.e., two thirds of the 

NAAQS) and where sources are not 

expected to emit ultra-coarse Pb. By 

limiting the use of Pb-PM10 monitoring 

to locations where the Pb concentrations 

are less than 0.10 μg/m3 on a 3-month 

arithmetic mean and where ultra-coarse 

Pb is expected to be low, we believe that 

the Pb-TSP concentrations will also be 

less than 100% of the NAAQS. 

Examples of locations where Pb-PM10

monitoring may be more representative 

of Pb-TSP levels than others are urban 

areas away from Pb sources (i.e., nonsource-oriented monitoring locations), 

near airports, combustion sources, and 

other Pb sources which are expected to 

only emit Pb in the fine PM size 

fraction. Locations where it would not 

be appropriate to monitor using Pb-PM10

samplers include near smelters, 

roadways, and sources with significant 

fugitive dust emissions. 

We are revising the proposed 

allowance for the use of Pb-PM10

monitors to allow Pb-PM10 monitors 

without the use of scaling factors for 

non-source-oriented monitors (unless 

existing data indicates maximum 3- 

month arithmetic mean Pb 

concentration has exceeded 0.10 μg/m3

in the last three years) and for sourceoriented monitors where maximum 3- 

month arithmetic mean Pb 

concentration is expected to be less than 

0.10 μg/m3 (based on modeling or 

historic data) and where ultra-coarse Pb 

is expected to be low. We are also 

requiring that a Pb-TSP monitor be 

required at the site if at some point in 

the future the Pb-PM10 monitor shows 

that the maximum 3-month arithmetic 

mean Pb-PM10 concentration was equal 

to or greater than 0.10 μg/m3. Section 

IV.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 

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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 sourceoriented 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 sourceoriented 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-sourceoriented 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 reentrained 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-sourceoriented monitoring requirements tied 

to CBSA population provided that 

historical monitoring does not indicate 

Pb-TSP or Pb-PM10 concentrations 

greater than an arithmetic 3-month 

mean of 0.10 μg/m3, and to meet the 

source-oriented monitoring 

requirements where Pb concentrations 

are expected (based on historic data, 

monitoring data, or other means) to be 

less than 0.10 μg/m3 on an arithmetic 3- 

month mean, and ultra-coarse Pb is 

expected to be low. However, 

monitoring agencies are required to 

begin monitoring for Pb-TSP within six 

months of a measured Pb-PM10

arithmetic 3-month mean concentration 

of 0.10 μg/m3 or more. For example, if 

a Pb-PM10 monitoring site measures an 

arithmetic 3-month mean concentration 

of 0.10 μg/m3 or more for the period 

March–May 2011, the responsible 

monitoring agency would be required to 

install and begin operation of a Pb-TSP 

monitor at the site no later than 

December 1, 2011. 

We are allowing monitoring agencies 

to stagger installation of any newly 

required monitors over a two-year 

period. Each monitoring agency is 

required to install and operate the 

required source-oriented monitors by 

January 1, 2010. The non-sourceoriented 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 PbPM2.5 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 PbPM2.5 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 

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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 μg/m3

have occurred in locations with active 

industrial sources of lead emissions. 

Accordingly, we anticipate that many 

areas may be able to attain the revised 

NAAQS by implementing air pollution 

control measures on lead emitting 

industrial sources only. These controls 

could include measures such as 

particulate matter fabric filter control 

devices and industrial fugitive dust 

control measures applied in plant 

buildings and on plant grounds. 

However, it may become necessary in 

some areas to also implement controls 

on non-industrial, or former industrial, 

type sources. Based on these 

considerations, EPA believes that the 

regulations and guidance currently 

being used to implement the preexisting 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 preexisting 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 

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111American Petroleum Institute v. Costle, 609 

F.2d 20 (D.C. Cir. 1979). 

112Under 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 

Continued 

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. 

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 

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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. 

anticipates that state and Tribal officials 

will be able to base their 

recommendations on existing 

monitoring data, and can therefore 

identify an area as ‘‘attainment’’ or 

‘‘nonattainment.’’ EPA also anticipates 

that there will be other areas where state 

and Tribal officials will not have 

sufficient information to make such a 

determination. State and Tribal officials 

are advised to identify such areas as 

‘‘unclassifiable.’’ For these areas EPA 

may wait until sufficient ambient air 

quality data from the newly deployed 

Pb monitoring network are available to 

take final action on the state and Tribal 

recommendations. 

Several commenters stated that EPA 

should promulgate designations for the 

revised Pb NAAQS within the 2 year 

period provided in the CAA. 

Commenters further stated that they do 

not understand why EPA needs to take 

an additional year beyond the two years 

provided under the CAA to do the 

designations. In addition, the 

commenters stated that they believe 

EPA does not have the authority to take 

the additional year (i.e., the 3rd year 

provided under section 107(d)(1)(B)(i) of 

the CAA) to do designations for the Pb 

NAAQS because sufficient monitoring 

data is available to do the designations 

within 2 years of promulgation of the 

NAAQS. 

Other commenters stated that they 

agree with EPA that, given that the 

current monitoring network for the Pb 

NAAQS is insufficient to base 

designations on for the new NAAQS, 

EPA should not promulgate 

designations until there is sufficient 

data from the new monitoring network. 

Section 107(d)(1)(B)(i) provides that 

the Administrator shall promulgate the 

designations of all areas as 

expeditiously as practicable, but in no 

case later than 2 years from the date of 

promulgation of the new or revised 

national ambient air quality standard. 

Such period may be extended by up to 

one year in the event the Administrator 

has insufficient information to 

promulgate the designations. 

After considering the comments, and 

recognizing that in some locations there 

may be monitoring data sufficient to 

determine whether or not the area is 

attaining the standard, EPA now 

believes that the benefits of identifying 

nonattainment areas as soon as possible, 

in some areas as discussed shortly 

below, outweigh the potential 

administrative benefits of designating 

all areas at the same time. 

At the same time, EPA continues to 

believe that the current monitoring 

network is inadequate for making 

designations in many, if not most, areas 

of the country, and agrees with those 

commenters who stated that it would be 

preferable to wait until additional 

monitoring data was available for those 

areas than to proceed to designate areas 

based only on data from the current 

insufficient monitoring network. The 

EPA notes that any delay in 

designations beyond two years would be 

based on the lack of monitoring data 

(and the expectation that additional 

monitoring data would be available if 

designations were delayed) and would 

not be based on staffing and other nondata 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 

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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. 

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67034 Federal Register / Vol. 73, No. 219 / Wednesday, November 12, 2008 / Rules and Regulations 

113Two 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. 

This presumption was also EPA’s 

recommendation for defining the 

nonattainment boundaries for the preexisting 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 areaspecific 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: 

• 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 

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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 

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67036 Federal Register / Vol. 73, No. 219 / Wednesday, November 12, 2008 / Rules and Regulations 

114EPA 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. 

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. 

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 

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115See 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. 

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. 

Given the proposal to promulgate a 

revised Pb NAAQS that is significantly 

lower than the current level of 1.5 μg/ 

m3, EPA requested comment on the 

appropriate threshold for the minimum 

starting point for future Pb RACT 

analyses for stationary lead sources in 

nonattainment areas. In the proposed 

rule, EPA requested comment on the 

emissions level associated with the 

minimum network source monitoring 

requirements. These source levels range 

from 200 kg/yr to 600 kg/yr. The EPA 

also stated that one possible approach 

for RACT is to recommend that RACT 

analyses for Pb sources be consistent 

with sources that are required to 

monitor such that all stationary sources 

above 200 kg/yr to 600 kg/yr should 

undergo a RACT review. EPA also 

requested comment on source 

monitoring for stationary sources that 

emit lead emissions in amounts that 

have potential to cause ambient levels at 

least one-half the selected NAAQS level. 

This suggests another potential 

recommendation for the starting point 

for the RACT analysis. The EPA sought 

comment on these ideas as well as any 

information which commenters could 

provide that would help inform EPA’s 

recommendation on an appropriate 

emissions threshold for initiating RACT 

analyses. 

b. Comments and Responses 

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 μg/m3 and the 

existing threshold for RACT analysis is 

5 tpy. Since the standard is being 

reduced by a factor of ten, from 1.5 μg/ 

m3 to 0.15 μg/m3, it is appropriate to 

also reduce the threshold for RACT 

analysis by a factor of 10, from 5 tpy to 

0.5 tpy. Furthermore, the monitor siting 

criteria include a requirement for 

monitoring agencies to conduct 

monitoring taking into account sources 

that are expected to exceed the NAAQS, 

and require monitoring for sources 

which emit Pb at a rate of one ton per 

year. Although EPA expects that sources 

emitting less than one tpy may also 

contribute to violations of the revised Pb 

NAAQS, EPA believes that the one tpy 

requirement in the monitor siting 

criteria provides a benchmark that is 

more likely to clearly identify sources 

that would contribute to exceedances of 

the NAAQS. Accordingly, using 50% of 

that figure (0.5 tpy) as the threshold for 

RACT analysis is generally consistent 

with EPA’s consideration in the 

proposal of setting the RACT threshold 

to include those stationary sources that 

emit lead emissions in amounts that 

have the potential to cause ambient 

levels at least one-half the selected 

NAAQS. 

EPA believes that setting the RACT 

threshold higher (e.g., at 1 tpy) would 

not be appropriate because it is likely 

that in a nonattainment area sources 

emitting less than one tpy are 

contributing to the nonattainment of the 

NAAQS. EPA also does not believe a 

lower threshold is warranted as a 

general matter, but EPA agrees with 

commenters that the state’s control 

technology analysis should also include, 

as appropriate, sources which actually 

emit less than the threshold level of 0.5 

tpy of lead or lead compounds in the 

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67038 Federal Register / Vol. 73, No. 219 / Wednesday, November 12, 2008 / Rules and Regulations 

116As 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). 

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 technologyintensive 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 technologyintensive control measures, such as 

those involving the installation of new 

hardware. Finally, failure to implement 

the SIP provisions required to meet 

annual incremental reductions in 

emissions (i.e., RFP) in a particular area 

could result in the application of 

sanctions as described in section 179(b) 

of the CAA (pursuant to a finding under 

section 179(a)(4)), and the 

implementation of contingency 

measures required by section 172(c)(9) 

of the CAA. 

b. Comments and Responses 

Several commenters stated that EPA’s 

proposal related to RFP would allow 

states to avoid the need to demonstrate 

linear progress towards attainment, 

departing from the typical method used, 

and statutorily required in some cases, 

for other criteria pollutants. These 

commenters further state that the 

recognition that some nonattainment 

urban areas have numerous sources 

contributing to excessive ambient levels 

of lead which undermines the reasoning 

employed to justify a non-linear 

approach in the context of single source 

nonattainment areas. If areas with large 

sources install key controls early on in 

the attainment process, and thus 

achieve attainment ahead of schedule, 

that would advance the goals and 

requirements of the CAA. 

Historically, for some pollutants, RFP 

has been met by showing annual 

incremental emission reductions 

generally sufficient to maintain linear 

progress toward attainment by the 

applicable attainment date. As EPA has 

previously noted, we expect that some 

nonattainment designations will be 

attributable to a single stationary source, 

and others may be attributable to a 

number of smaller sources. Where a 

single source is the cause of 

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Federal Register / Vol. 73, No. 219 / Wednesday, November 12, 2008 / Rules and Regulations 67039 

nonattainment, EPA would not expect 

linear progress towards attainment. 

Rather, there may be relatively less 

progress while the source adopts nontechnological 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 technologyintensive control measures (e.g., work 

practices to control fugitive dust 

emissions at the stationary sources) 

while phasing in the more technologyintensive 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 

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67040 Federal Register / Vol. 73, No. 219 / Wednesday, November 12, 2008 / Rules and Regulations 

117The 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. 

118 In addition, the PSD program applies to noncriteria pollutants subject to regulation under the 

Act, except those pollutants regulated under section 

112 and pollutants subject to regulation only under 

section 211(o). 

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: 

• 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. 

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 

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Federal Register / Vol. 73, No. 219 / Wednesday, November 12, 2008 / Rules and Regulations 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 

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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 

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119Criteria pollutants are those pollutants for 

which EPA has established a NAAQS under section 

109 of the CAA. 

120Transportation 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. 

121The 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) 

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

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

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 

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summarizes and responds to all 

comments received regarding 

exceptional events data submission. 

Section C provides the final preamble 

text considering comments received and 

incorporating final revisions to the 

proposal. 

A. Proposal 

The EPA proposed Pb-specific 

changes to the deadlines, in 40 CFR 

50.14, by which States must flag 

ambient air data that they believe has 

been affected by exceptional events and 

submit initial descriptions of those 

events, and the deadlines by which 

States must submit detailed 

justifications to support the exclusion of 

that data from EPA determinations of 

attainment or nonattainment with the 

NAAQS. The deadlines in 40 CFR 50.14 

are generic, and are not always 

appropriate for Pb given the anticipated 

schedule for the designations of areas 

under the proposed Pb NAAQS. 

For the specific case of Pb, EPA 

anticipates that designations under the 

revised NAAQS may be made in 

September 2011 based on 2008–2010 

data, (or possibly in September 2010 

based on 2007–2009 data if sufficient 

data are available), and thus will 

depend in part on air quality data 

collected as late as December 2010 (or 

December 2009). (Section IV.C of the 

proposed preamble had a more detailed 

discussion of the designation schedule 

and what data EPA intends to use.) 

There is no way for a State to flag and 

submit documentation regarding events 

that happen in October, November, and 

December 2010 (or 2009) by one year 

before designation decisions that are 

made in September 2011 (or 2010). 

The proposed revisions to 40 CFR 

50.14 involved only changes in 

submission dates for information 

regarding claimed exceptional events 

affecting Pb data. The proposed rule text 

showed only the changes that would 

apply if designations are made three 

years after promulgation; where a 

deadline would be different if 

designations were made at the two-year 

point, the difference in deadline was 

noted in the proposed preamble. We 

proposed to extend the generic deadline 

for flagging data (and providing a brief 

initial description of the event) of July 

1 of the year following the data 

collection, to July 1, 2009 for data 

collected in 2006–2007. The proposed 

extension included 2006 and 2007 data 

because Governors’ designation 

recommendations will consider 2006– 

2008 data, and possibly EPA will 

consider 2006–2008 or 2007–2009 data 

if complete data for 2008–2010 are not 

available at the time of final 

designations. EPA noted that it does not 

intend to use data prior to 2006 in 

making Pb designation decisions. The 

generic event flagging deadline in the 

Exceptional Events Rule would 

continue to apply to 2008 and later 

years following the promulgation of the 

revised Pb NAAQS. The Governor of a 

State would be required to submit 

designation recommendations to EPA a 

year after promulgation of the revised 

NAAQS (i.e., in Fall 2009). States would 

therefore have enough time to flag data 

and submit their demonstrations and 

know what 2008 data need to be 

excluded due to exceptional events 

when formulating their 

recommendations to EPA. 

For data collected in 2010 (or 2009), 

we proposed to move up the generic 

deadline of July 1 for data flagging to 

May 1, 2011 (or May 1, 2010) (which is 

also the applicable deadline for 

certifying data in AQS as being 

complete and accurate to the best 

knowledge of the responsible 

monitoring agency head). This would 

give a State less time, but EPA believes 

still sufficient time, to decide what 2010 

(or 2009) data to flag, and would allow 

EPA to have access to the flags in time 

for EPA to develop its own proposed 

and final plans for designations. 

Finally, EPA proposed to make the 

deadline for submission of detailed 

justifications for exclusion of data 

collected in 2006 through 2008 be 

September 15, 2010 for the three year 

designation schedule, or September 15, 

2009 under the two year designation 

schedule. EPA generally does not 

anticipate data from 2006 and 2007 

being used in final Pb designations. 

Under the three year designation 

schedule, for data collected in 2010, 

EPA proposed to make the deadline for 

submission of justifications be May 1, 

2011. This is less than a year before the 

designation decisions would be made, 

but we believe it is a good compromise 

between giving a State a reasonable 

period to prepare the justifications and 

EPA a reasonable period to consider the 

information submitted by the State. 

Similarly, under the two year 

designation schedule, for data collected 

in 2009, EPA proposed to make the 

deadline for submission of justifications 

be May 1, 2010. Table 5 summarizes the 

three year designation deadlines in the 

proposal and discussed in this section, 

and Table 6 summarizes the two year 

designation deadlines. 

TABLE 5—PROPOSED SCHEDULE FOR EXCEPTIONAL EVENT FLAGGING AND DOCUMENTATION SUBMISSION IF

DESIGNATIONS PROMULGATED IN THREE YEARS

Air quality data collected for 

calendar year Event flagging deadline 

Detailed 

documentation 

submission deadline 

2006 ...................................................................................... July 1, 2009 * ....................................................................... September 15, 2010. * 

2007 ...................................................................................... July 1, 2009 * ....................................................................... September 15, 2010. 

2008 ...................................................................................... July 1, 2009 ......................................................................... September 15, 2010. * 

2009 ...................................................................................... 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 

calendar year Event flagging deadline 

Detailed 

documentation 

submission deadline 

2006 ...................................................................................... July 1, 2009 * ....................................................................... September 15, 2009. 

2007 ...................................................................................... July 1, 2009 * ....................................................................... September 15, 2009. * 

2008 ...................................................................................... July 1, 2009 ......................................................................... September 15, 2009. * 

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TABLE 6—PROPOSED SCHEDULE FOR EXCEPTIONAL EVENT FLAGGING AND DOCUMENTATION SUBMISSION IF

DESIGNATIONS PROMULGATED IN TWO YEARS—Continued 

Air quality data collected for 

calendar year Event flagging deadline 

Detailed 

documentation 

submission deadline 

2009 ...................................................................................... May 1, 2010 * ....................................................................... May 1, 2010. * 

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

EPA invited comment on these 

proposed changes in the exceptional 

event flagging and documentation 

submission deadlines. 

B. Comments and Responses 

EPA received only one comment on 

the proposed revision to the schedule 

for flagging and documenting 

exceptional event data which could 

affect Pb designation decisions. The 

comment from the North Carolina 

Department of Environment and Natural 

Resources’ (NCDENR) Division of Air 

Quality (DAQ) stated that: ‘‘NCDAQ 

believes states need proper time to 

provide exceptional events 

documentation before designations are 

made.’’ 

EPA believes that the final schedule 

provides states with adequate time for 

flagging exceptional values and 

providing documentation to support 

exceptional event claims. Also, NCDAQ 

did not specifically state either that the 

proposed deadlines were inadequate or 

ask for more time; nor did it provide any 

alternative schedules for the Agency’s 

consideration. 

C. Final 

EPA’s final schedule for flagging and 

documenting exceptional event data 

claims is shown in the tables that 

follow. Table 7 summarizes the final 

deadlines for areas where final 

designations occur no later than October 

15, 2011 (i.e., no later than three years 

after promulgation of a new NAAQS). 

Table 8 summarizes the final dealines 

for areas where final desiginations occur 

no later than October 15, 2010 (i.e., no 

later than two years after promulgation 

of a new NAAQS). 

TABLE 7—FINAL SCHEDULE FOR EXCEPTIONAL EVENT FLAGGING AND DOCUMENTATION SUBMISSION IF DESIGNATIONS

PROMULGATED WITHIN THREE YEARS

Air quality data collected for 

calendar year Event flagging deadline 

Detailed documentation submission 

deadline 

2006 ...................................................................................... July 1, 2009 * ....................................................................... October 15 2010. * 

2007 ...................................................................................... July 1, 2009 * ....................................................................... October 15, 2010. 

2008 ...................................................................................... July 1, 2009 ......................................................................... October 15, 2010. * 

2009 ...................................................................................... 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 

calendar year Event flagging deadline 

Detailed 

documentation 

submission deadline 

2006 ...................................................................................... July 1, 2009 * ....................................................................... October 15, 2009. 

2007 ...................................................................................... July 1, 2009 * ....................................................................... October 15, 2009. * 

2008 ...................................................................................... July 1, 2009 ......................................................................... October 15, 2009. * 

2009 ...................................................................................... May 1, 2010 * ....................................................................... May 1, 2010. * 

* Indicates change from generic schedule in 40 CFR 50.14. 

VII. Statutory and Executive Order 

Reviews 

A. Executive Order 12866: Regulatory 

Planning and Review 

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 μg/m3, 

0.40 μg/m3, 0.30 μg/m3, 0.20 μg/m3, 0.15 

μg/m3 and 0.10 μg/m3. The RIA contains 

illustrative analyses that consider a 

limited number of emissions control 

scenarios that States and Regional 

Planning Organizations might 

implement to achieve these alternative 

Pb NAAQS. However, the CAA and 

judicial decisions make clear that the 

economic and technical feasibility of 

attaining ambient standards are not to 

be considered in setting or revising 

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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 

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indicated previously, in setting a 

NAAQS EPA cannot consider the 

economic or technological feasibility of 

attaining ambient air quality standards. 

Because the Clean Air Act prohibits 

EPA from considering the types of 

estimates and assessments described in 

section 202 when setting the NAAQS, 

the UMRA does not require EPA to 

prepare a written statement under 

section 202 for the revisions to the Pb 

NAAQS. 

With regard to implementation 

guidance, the CAA imposes the 

obligation for States to submit SIPs to 

implement the Pb NAAQS. In this final 

rule, EPA is merely providing an 

interpretation of those requirements. 

However, even if this rule did establish 

an independent obligation for States to 

submit SIPs, it is questionable whether 

an obligation to submit a SIP revision 

would constitute a Federal mandate in 

any case. The obligation for a State to 

submit a SIP that arises out of section 

110 and section 191 of the CAA is not 

legally enforceable by a court of law, 

and at most is a condition for continued 

receipt of highway funds. Therefore, it 

is possible to view an action requiring 

such a submittal as not creating any 

enforceable duty within the meaning of 

2 U.S.C. 658 for purposes of the UMRA. 

Even if it did, the duty could be viewed 

as falling within the exception for a 

condition of Federal assistance under 2 

U.S.C. 658. 

EPA has determined that this final 

rule contains no regulatory 

requirements that might significantly or 

uniquely affect small governments 

because it imposes no enforceable duty 

on any small governments. Therefore, 

this rule is not subject to the 

requirements of section 203 of the 

UMRA. 

E. Executive Order 13132: Federalism 

Executive Order 13132, entitled 

‘‘Federalism’’ (64 FR 43255, August 10, 

1999), requires EPA to develop an 

accountable process to ensure 

‘‘meaningful and timely input by State 

and local officials in the development of 

regulatory policies that have federalism 

implications.’’ ‘‘Policies that have 

federalism implications’’ is defined in 

the Executive Order to include 

regulations that have ‘‘substantial direct 

effects on the States, on the relationship 

between the national government and 

the States, or on the distribution of 

power and responsibilities among the 

various levels of government.’’ 

This final rule does not have 

federalism implications. It will not have 

substantial direct effects on the States, 

on the relationship between the national 

government and the States, or on the 

distribution of power and 

responsibilities among the various 

levels of government, as specified in 

Executive Order 13132. The rule does 

not alter the relationship between the 

Federal government and the States 

regarding the establishment and 

implementation of air quality 

improvement programs as codified in 

the CAA. Under section 109 of the CAA, 

EPA is mandated to establish NAAQS; 

however, CAA section 116 preserves the 

rights of States to establish more 

stringent requirements if deemed 

necessary by a State. Furthermore, 

under CAA section 107, the States have 

primary responsibility for 

implementation of the NAAQS. Finally, 

as noted in section E (above) on UMRA, 

this rule does not impose significant 

costs on State, local, or tribal 

governments or the private sector. Thus, 

Executive Order 13132 does not apply 

to this rule. 

F. Executive Order 13175: Consultation 

and Coordination With Indian Tribal 

Governments 

This action does not have tribal 

implications, as specified in Executive 

Order 13175 (65 FR 67249, November 9, 

2000). It does not have a substantial 

direct effect on one or more Indian 

Tribes, since Tribes are not obligated to 

adopt or implement any NAAQS or 

monitoring requirements for NAAQS. 

Thus, Executive Order 13175 does not 

apply to this action. 

Although Executive Order 13175 does 

not apply to this action, EPA contacted 

tribal environmental professionals 

during the development of this rule. 

EPA staff participated in the regularly 

scheduled Tribal Air Call sponsored by 

the National Tribal Air Association 

during the spring of 2008 as the 

proposal was under development, and 

also offered several informational 

briefings on the proposal to Tribal 

environmental professionals in Summer 

2008 during the public comment period 

on the proposed rule. EPA sent 

individual letters to all federally 

recognized Tribes within the lower 48 

states and Alaska to give Tribal leaders 

the opportunity for consultation, and 

EPA staff also participated in Tribal 

public meetings, such as the National 

Tribal Forum meeting in June 2008, 

where Tribes discussed their concerns 

regarding the proposed rule. EPA 

received comments from a number of 

Tribes on the proposed rule; these 

comments are addressed in the relevant 

sections of the preamble and Response 

to Comments for this rulemaking. 

G. Executive Order 13045: Protection of 

Children from Environmental Health & 

Safety Risks 

This action is subject to EO 13045 (62 

FR 19885, April 23, 1997) because it is 

an economically significant regulatory 

action as defined by EO 12866, and we 

believe that the environmental health 

risk addressed by this action has a 

disproportionate effect on children. The 

final rule establishes uniform national 

ambient air quality standards for Pb; 

these standards are designed to protect 

public health with an adequate margin 

of safety, as required by CAA section 

109. However, the protection offered by 

these standards may be especially 

important for children because 

neurological effects in children are 

among if not the most sensitive health 

endpoints for Pb exposure. Because 

children are considered a sensitive 

population, we have carefully evaluated 

the environmental health effects of 

exposure to Pb pollution among 

children. These effects and the size of 

the population affected are summarized 

in chapters 6 and 8 of the Criteria 

Document and sections 3.3 and 3.4 of 

the Staff Paper, and the results of our 

evaluation of the effects of Pb pollution 

on children are discussed in sections 

II.B and II.C of the notice of proposed 

rulemaking, and section II.A of this 

preamble. 

H. Executive Order 13211: Actions That 

Significantly Affect Energy Supply, 

Distribution or Use 

This rule is not a ‘‘significant energy 

action’’ as defined in Executive Order 

13211, ‘‘Actions Concerning Regulations 

That Significantly Affect Energy Supply, 

Distribution, or Use’’ (66 FR 28355 (May 

22, 2001)) because it is not likely to 

have a significant adverse effect on the 

supply, distribution, or use of energy. 

The purpose of this rule is to establish 

revised NAAQS for Pb. The rule does 

not prescribe specific control strategies 

by which these ambient standards will 

be met. Such strategies will be 

developed by States on a case-by-case 

basis, and EPA cannot predict whether 

the control options selected by States 

will include regulations on energy 

suppliers, distributors, or users. Thus, 

EPA concludes that this rule is not 

likely to have any adverse energy 

effects. 

I. National Technology Transfer and 

Advancement Act 

Section 12(d) of the National 

Technology Transfer and Advancement 

Act of 1995 (NTTAA), Public Law No. 

104–113, § 12(d) (15 U.S.C. 272 note) 

directs EPA to use voluntary consensus 

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67048 Federal Register / Vol. 73, No. 219 / Wednesday, November 12, 2008 / Rules and Regulations 

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 lowvolume 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 sociodemographic 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 lowincome 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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lead. January 22, 2008. 

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Henderson, Chair, Clean Air Scientific 

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Stephen L. Johnson. Re: Clean Air 

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Sci. Total Environ. 303: 51–58. 

Hornung, R. 2008a. E-mail message to JeeYoung Kim, U.S. EPA. February 11, 2008. 

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Hornung, R. 2008b. E-mail message to JeeYoung Kim, U.S. EPA. August 19, 2008. 

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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. 

■ For the reasons stated in the preamble, 

title 40, chapter I of the code of Federal 

regulations is amended as follows: 

PART 50—NATIONAL PRIMARY AND 

SECONDARY AMBIENT AIR QUALITY 

STANDARDS 

■ 1. The authority citation for part 50 

continues to read as follows: 

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

■ 2. Section 50.3 is revised to read as 

follows: 

§ 50.3 Reference conditions. 

All measurements of air quality that 

are expressed as mass per unit volume 

(e.g., micrograms per cubic meter) other 

than for particulate matter (PM2.5) 

standards contained in §§ 50.7 and 

50.13 and lead standards contained in 

§ 50.16 shall be corrected to a reference 

temperature of 25 (deg) C and a 

reference pressure of 760 millimeters of 

mercury (1,013.2 millibars). 

Measurements of PM2.5 for purposes of 

comparison to the standards contained 

in §§ 50.7 and 50.13 and of lead for 

purposes of comparison to the standards 

contained in § 50.16 shall be reported 

based on actual ambient air volume 

measured at the actual ambient 

temperature and pressure at the 

monitoring site during the measurement 

period. 

■ 3. Section 50.12 is amended by 

designating the existing text as 

paragraph (a) and adding paragraph (b) 

to read as follows: 

§ 50.12 National primary and secondary 

ambient air quality standards for lead. 

* * * * * 

(b) The standards set forth in this 

section will remain applicable to all 

areas notwithstanding the promulgation 

of lead national ambient air quality 

standards (NAAQS) in § 50.16. The lead 

NAAQS set forth in this section will no 

longer apply to an area one year after 

the effective date of the designation of 

that area, pursuant to section 107 of the 

Clean Air Act, for the lead NAAQS set 

forth in § 50.16; except that for areas 

designated nonattainment for the lead 

NAAQS set forth in this section as of the 

effective date of § 50.16, the lead 

NAAQS set forth in this section will 

apply until that area submits, pursuant 

to section 191 of the Clean Air Act, and 

EPA approves, an implementation plan 

providing for attainment and/or 

maintenance of the lead NAAQS set 

forth in § 50.16. 

■ 4. Section 50.14 is amended by: 

■ a. Revising paragraph (a)(2); 

■ b. Revising paragraph (c)(2)(iii); 

■ c. Redesignating paragraph (c)(2)(v) as 

paragraph (c)(2)(vi) and adding a new 

paragraph (c)(2)(v); and 

■ d. Redesignating existing paragraphs 

(c)(3)(iii) and (c)(3)(iv) as paragraphs 

(c)(3)(iv) and (c)(3)(v), respectively, and 

adding a new paragraph (c)(3)(iii). 

The additions and revisions read as 

follows: 

§ 50.14 Treatment of air quality monitoring 

data influenced by exceptional events. 

(a) * * * 

(2) Demonstration to justify data 

exclusion may include any reliable and 

accurate data, but must demonstrate a 

clear causal relationship between the 

measured exceedance or violation of 

such standard and the event in 

accordance with paragraph (c)(3)(iv) of 

this section. 

* * * * * 

(c) * * * 

(2) * * * 

(iii) Flags placed on data as being due 

to an exceptional event together with an 

initial description of the event shall be 

submitted to EPA not later than July 1st 

of the calendar year following the year 

in which the flagged measurement 

occurred, except as allowed under 

paragraph (c)(2)(iv) or (c)(2)(v) of this 

section. 

* * * * * 

(v) For lead (Pb) data collected during 

calendar years 2006–2008, that the State 

identifies as resulting from an 

exceptional event, the State must notify 

EPA of the flag and submit an initial 

description of the event no later than 

July 1, 2009. For Pb data collected 

during calendar year 2009, that the State 

identifies as resulting from an 

exceptional event, the State must notify 

EPA of the flag and submit an initial 

description of the event no later than 

July 1, 2010. For Pb data collected 

during calendar year 2010, that the State 

identifies as resulting from an 

exceptional event, the State must notify 

EPA of the flag and submit an initial 

description of the event no later than 

May 1, 2011. 

* * * * * 

(3) * * * 

(iii) A State that flags Pb data 

collected during calendar years 2006– 

2009, pursuant to paragraph (c)(2)(v) of 

this section shall, after notice and 

opportunity for public comment, submit 

to EPA a demonstration to justify 

exclusion of the data not later than 

October 15, 2010. A State that flags Pb 

data collected during calendar 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. 

* * * * * 

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67052 Federal Register / Vol. 73, No. 219 / Wednesday, November 12, 2008 / Rules and Regulations 

■ 5. Section 50.16 is added to read as 

follows: 

§ 50.16 National primary and secondary 

ambient air quality standards for lead. 

(a) The national primary and 

secondary ambient air quality standards 

for lead (Pb) and its compounds are 0.15 

micrograms per cubic meter, arithmetic 

mean concentration over a 3-month 

period, measured in the ambient air as 

Pb either by: 

(1) A reference method based on 

Appendix G of this part and designated 

in accordance with part 53 of this 

chapter or; 

(2) An equivalent method designated 

in accordance with part 53 of this 

chapter. 

(b) The national primary and 

secondary ambient air quality standards 

for Pb are met when the maximum 

arithmetic 3-month mean concentration 

for a 3-year period, as determined in 

accordance with Appendix R of this 

part, is less than or equal to 0.15 

micrograms per cubic meter. 

■ 6. Appendix G is amended as follows: 

■ a. In section 10.2 the definition of the 

term ‘‘VSTP’’ in the equation is revised, 

■ b. In section 14 reference 10 is added 

and reference 15 is revised: 

Appendix G to Part 50—Reference 

Method for the Determination of Lead 

in Suspended Particulate Matter 

Collected From Ambient Air 

* * * * * 

10.2 * * * 

VSTP = Air volume from section 10.1. 

* * * * * 

14. * * * 

10. Intersociety Committee (1972). 

Methods of Air Sampling and Analysis. 1015 

Eighteenth Street, N.W. Washington, D.C.: 

American Public Health Association. 365– 

372. * * * 

15. Sharon J. Long, et al., ‘‘Lead Analysis 

of Ambient Air Particulates: Interlaboratory 

Evaluation of EPA Lead Reference Method’’ 

APCA Journal, 29, 28–31 (1979). 

* * * * * 

■ 7. Appendix Q is added to read as 

follows: 

Appendix Q to Part 50—Reference 

Method for the Determination of Lead 

in Particulate Matter as PM10 Collected 

From Ambient Air 

This Federal Reference Method (FRM) 

draws heavily from the specific analytical 

protocols used by the U.S. EPA. 

1. Applicability and Principle 

1.1 This method provides for the 

measurement of the lead (Pb) concentration 

in particulate matter that is 10 micrometers 

or less (PM10) in ambient air. PM10 is 

collected on an acceptable (see section 6.1.2) 

46.2 mm diameter polytetrafluoroethylene 

(PTFE) filter for 24 hours using active 

sampling at local conditions with a lowvolume air sampler. The low-volume sampler 

has an average flow rate of 16.7 liters per 

minute (Lpm) and total sampled volume of 

24 cubic meters (m3) of air. The analysis of 

Pb in PM10 is performed on each individual 

24-hour sample. Gravimetric mass analysis of 

PM10c filters is not required for Pb analysis. 

For the purpose of this method, PM10 is 

defined as particulate matter having an 

aerodynamic diameter in the nominal range 

of 10 micrometers (10 μm) or less. 

1.2 For this reference method, PM10 shall 

be collected with the PM10c federal reference 

method (FRM) sampler as described in 

Appendix O to Part 50 using the same sample 

period, measurement procedures, and 

requirements specified in Appendix L of Part 

50. The PM10c sampler is also being used for 

measurement of PM10¥2.5 mass by difference 

and as such, the PM10c sampler must also 

meet all of the performance requirements 

specified for PM2.5 in Appendix L. The 

concentration of Pb in the atmosphere is 

determined in the total volume of air 

sampled and expressed in micrograms per 

cubic meter (μg/m3) at local temperature and 

pressure conditions. 

1.3 The FRM will serve as the basis for 

approving Federal Equivalent Methods 

(FEMs) as specified in 40 CFR Part 53 

(Reference and Equivalent Methods). This 

FRM specifically applies to the analysis of Pb 

in PM10 filters collected with the PM10c

sampler. If these filters are analyzed for 

elements other than Pb, then refer to the 

guidance provided in the EPA Inorganic 

Compendium Method IO–3.3 (Reference 1 of 

section 8) for multi-element analysis. 

1.4 The PM10c air sampler draws ambient 

air at a constant volumetric flow rate into a 

specially shaped inlet and through an inertial 

particle size separator, where the suspended 

particulate matter in the PM10 size range is 

separated for collection on a PTFE filter over 

the specified sampling period. The Pb 

content of the PM10 sample is analyzed by 

energy-dispersive X-ray fluorescence 

spectrometry (EDXRF). Energy-dispersive Xray 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 Xrays produced at a given energy provides a 

measure of the amount of the element present 

by comparisons with calibration standards. 

The X-rays are detected and the spectral 

signals are acquired and processed with a 

personal computer. EDXRF is commonly 

used as a non-destructive method for 

quantifying trace elements in PM. A detailed 

explanation of quantitative X-ray 

spectrometry is described in references 2, 3 

and 4. 

1.5 Quality assurance (QA) procedures 

for the collection of monitoring data are 

contained in Part 58, Appendix A. 

2. PM10 Pb Measurement Range and 

Detection Limit. The values given below in 

section 2.1 and 2.2 are typical of the method 

capabilities. Absolute values will vary for 

individual situations depending on the 

instrument, detector age, and operating 

conditions used. Data are typically reported 

in ng/m3 for ambient air samples; however, 

for this reference method, data will be 

reported in μg/m3 at local temperature and 

pressure conditions. 

2.1 EDXRF Pb Measurement Range. The 

typical ambient air measurement range is 

0.001 to 30 μg Pb/m3, assuming an upper 

range calibration standard of about 60 μg Pb 

per square centimeter (cm2), a filter deposit 

area of 11.86 cm2, and an air volume of 24 

m3. The top range of the EDXRF instrument 

is much greater than what is stated here. The 

top measurement range of quantification is 

defined by the level of the high concentration 

calibration standard used and can be 

increased to expand the measurement range 

as needed. 

2.2 Detection Limit (DL). A typical 

estimate of the one-sigma detection limit (DL) 

is about 2 ng Pb/cm2 or 0.001 μg Pb/m3, 

assuming a filter size of 46.2 mm (filter 

deposit area of 11.86 cm2) and a sample air 

volume of 24 m3. The DL is an estimate of 

the lowest amount of Pb that can be reliably 

distinguished from a blank filter. The onesigma detection limit for Pb is calculated as 

the average overall uncertainty or propagated 

error for Pb, determined from measurements 

on a series of blank filters from the filter 

lot(s) in use. Detection limits must be 

determined for each filter lot in use. If a new 

filter lot is used, then a new DL must be 

determined. The sources of random error 

which are considered are calibration 

uncertainty; system stability; peak and 

background counting statistics; uncertainty 

in attenuation corrections; and uncertainty in 

peak overlap corrections, but the dominating 

source by far is peak and background 

counting statistics. At a minimum, 

laboratories are to determine annual 

estimates of the DL using the guidance 

provided in Reference 5. 

3. Factors Affecting Bias and Precision of 

Lead Determination by EDXRF 

3.1 Filter Deposit. X-ray spectra are 

subject to distortion if unusually heavy 

deposits are analyzed. This is the result of 

internal absorption of both primary and 

secondary X-rays within the sample; 

however, this is not an issue for Pb due to 

the energetic X-rays used to fluoresce Pb and 

the energetic characteristic X-rays emitted by 

Pb. The optimum mass filter loading for 

multi-elemental EDXRF analyis is about 100 

μg/cm2 or 1.2 mg/filter for a 46.2-mm filter. 

Too little deposit material can also be 

problematic due to low counting statistics 

and signal noise. The particle mass deposit 

should minimally be 15 μg/cm2. The 

maximum PM10 filter loading or upper 

concentration limit of mass expected to be 

collected by the PM10c sampler is 200 μg/m3

(Appendix O to Part 50, Section 3.2). This 

equates to a mass loading of about 400 μg/ 

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 nonmstockstill on PROD1PC66 with RULES2

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1These 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. 

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 Lα line exclusively to quantify the Pb 

concentration. This is because the Pb Lα line 

and the As Kα lines severely overlap. The use 

of multiple Pb lines, including the Lβ and/or 

the Lγ lines for quantification must be used 

to reduce the uncertainty in the Pb 

determination in the presence of As. There 

can be instances when lines partially overlap 

the Pb spectral lines, but with the energy 

resolution of most detectors these overlaps 

are typically de-convoluted using standard 

spectral de-convolution software provided by 

the instrument vendor. An EDXRF protocol 

for Pb must define which Pb lines are used 

for quantification and where spectral 

overlaps occur. A de-convolution protocol 

must be used to separate all the lines which 

overlap with Pb. 

3.3 Particle Size Effects and Attenuation 

Correction Factors. X-ray attenuation is 

dependent on the X-ray energy, mass sample 

loading, composition, and particle size. In 

some cases, the excitation and fluorescent Xrays 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. 

6.2.2 Thin film standards. Thin film 

standards are used for calibration because 

they most closely resemble the layer of 

particles on a filter. Thin films standards are 

typically deposited on Nuclepore substrates. 

The preparation of thin film standards is 

discussed in reference 8, and 10. The NIST 

SRM 2783 (Air Particulate on Filter Media) 

is currently available on polycarbonate filters 

and contains a certified concentration for Pb. 

Thin film standards at 15 and 50 μg/cm2 are 

commercially available from MicroMatter 

Inc. (Arlington, WA). 

6.2.3 Filter Preparation. Filters used for 

sample collection are 46.2-mm PTFE filters 

with a pore size of 2 microns and filter 

deposit area 11.86 cm2. Cold storage is not a 

requirement for filters analyzed for Pb; 

however, if filters scheduled for XRF analysis 

were stored cold, they must be allowed to 

reach room temperature prior to analysis. All 

filter samples received for analysis are 

checked for any holes, tears, or a nonuniform deposit which would prevent 

quantitative analysis. Samples with physical 

deformities are not quantitatively analyzable. 

The filters are carefully removed with 

tweezers from the Petri dish and securely 

placed into the instrument-specific sampler 

holder for analysis. Care must be taken to 

protect filters from contamination prior to 

analysis. Filters must be kept covered when 

not being analyzed. No other preparation of 

filter samples is required. 

6.2.4 Calibration. In general, calibration 

determines each element’s sensitivity, i.e., its 

response in x-ray counts/sec to each μg/cm2

of a standard and an interference coefficient 

for each element that causes interference 

with another one (See section 3.2 above). The 

sensitivity can be determined by a linear plot 

of count rate versus concentration (μg/cm2) in 

which the slope is the instrument’s 

sensitivity for that element. A more precise 

way, which requires fewer standards, is to fit 

sensitivity versus atomic number. Calibration 

is a complex task in the operation of an XRF 

system. Two major functions accomplished 

by calibration are the production of reference 

spectra which are used for fitting and the 

determination of the elemental sensitivities. 

Included in the reference spectra (referred to 

as ‘‘shapes’’) are background-subtracted peak 

shapes of the elements to be analyzed (as 

well as interfering elements) and spectral 

backgrounds. Pure element thin film 

standards are used for the element peak 

shapes and clean filter blanks from the same 

lot as routine filter samples are used for the 

background. The analysis of Pb in PM filter 

deposits is based on the assumption that the 

thickness of the deposit is small with respect 

to the characteristic Pb X-ray transmission 

thickness. Therefore, the concentration of Pb 

in a sample is determined by first calibrating 

the spectrometer with thin film standards to 

determine the sensitivity factor for Pb and 

then analyzing the unknown samples under 

identical excitation conditions as used to 

determine the calibration. Calibration shall 

be performed annually or when significant 

repairs or changes occur (e.g., a change in 

fluorescers, X-ray tubes, or detector). 

Calibration establishes the elemental 

sensitivity factors and the magnitude of 

interference or overlap coefficients. See 

reference 7 for more detailed discussion of 

calibration and analysis of shapes standards 

for background correction, coarse particle 

absorption corrections, and spectral overlap. 

6.2.4.1 Spectral Peak Fitting. The EPA 

uses a library of pure element peak shapes 

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67054 Federal Register / Vol. 73, No. 219 / Wednesday, November 12, 2008 / Rules and Regulations 

(shape standards) to extract the elemental 

background-free peak areas from an unknown 

spectrum. It is also possible to fit spectra 

using peak stripping or analytically defined 

functions such as modified Gaussian 

functions. The EPA shape standards are 

generated from pure, mono-elemental thin 

film standards. The shape standards are 

acquired for sufficiently long times to 

provide a large number of counts in the peaks 

of interest. It is not necessary for the 

concentration of the standard to be known. 

A slight contaminant in the region of interest 

in a shape standard can have a significant 

and serious effect on the ability of the least 

squares fitting algorithm to fit the shapes to 

the unknown spectrum. It is these elemental 

peak shapes that are fitted to the peaks in an 

unknown sample during spectral processing 

by the analyzer. In addition to this library of 

elemental shapes there is also a background 

shape spectrum for the filter type used as 

discussed below in section 6.2.4.2 of this 

section. 

6.2.4.2 Background Measurement and 

Correction. A background spectrum 

generated by the filter itself must be 

subtracted from the X-ray spectrum prior to 

extracting peak areas. Background spectra 

must be obtained for each filter lot used for 

sample collection. The background shape 

standards which are used for background 

fitting are created at the time of calibration. 

If a new lot of filters is used, new background 

spectra must be obtained. A minimum of 20 

clean blank filters from each filter lot are kept 

in a sealed container and are used 

exclusively for background measurement and 

correction. The spectra acquired on 

individual blank filters are added together to 

produce a single spectrum for each of the 

secondary targets or fluorescers used in the 

analysis of lead. Individual blank filter 

spectra which show atypical contamination 

are excluded from the summed spectra. The 

summed spectra are fitted to the appropriate 

background during spectral processing. 

Background correction is automatically 

included during spectral processing of each 

sample. 

7. Calculation. 

7.1 PM10 Pb concentrations. The PM10 Pb 

concentration in the atmosphere (μg/m3) is 

calculated using the following equation: 

M C A

V Pb

Pb

LC

= ×

Where, 

MPb is the mass per unit volume for lead in 

μg/m3; 

CPb is the mass per unit area for lead in μg/ 

cm2 as measured by XRF; 

A is the filter deposit area in cm2; 

VLC is the total volume of air sampled by the 

PM10c sampler in actual volume units 

measured at local conditions of 

temperature and pressure, as provided 

by the sampler in m3. 

7.2 PM10 Pb Uncertainty Calculations. 

The principal contributors to total 

uncertainty of XRF values include: field 

sampling; filter deposit area; XRF calibration; 

attenuation or loss of the x-ray signals due to 

the other components of the particulate 

sample; and determination of the Pb X-ray 

emission peak area by curve fitting. See 

reference 12 for a detailed discussion of how 

uncertainties are similarly calculated for the 

PM2.5 Chemical Speciation program. 

The model for calculating total uncertainty 

is: 

δtot = (δf

2 + δa2 + δc2 + δv2) 1/2

Where, 

δf = fitting uncertainty (XRF-specific, from 2 

to 100+%) 

δa = attenuation uncertainty (XRF-specific, 

insignificant for Pb) 

δc = calibration uncertainty (combined lab 

uncertainty, assumed as 5%) 

δv = volume/deposition size uncertainty 

(combined field uncertainty, assumed as 

5%) 

8. References 

1. Inorganic Compendium Method IO–3.3; 

Determination of Metals in Ambient 

Particulate Matter Using X-Ray Fluorescence 

(XRF) Spectroscopy; U.S. Environmental 

Protection Agency, Cincinnati, OH 45268. 

EPA/625/R–96/010a. June 1999. 

2. Jenkins, R., Gould, R.W., and Gedcke, D. 

Quantitative X-ray Spectrometry: Second 

Edition. Marcel Dekker, Inc., New York, NY. 

1995. 

3. Jenkins, R. X-Ray Fluorescence 

Spectrometry: Second Edition in Chemical 

Analysis, a Series of Monographs on 

Analytical Chemistry and Its Applications, 

Volume 152. Editor J.D.Winefordner; John 

Wiley & Sons, Inc., New York, NY. 1999. 

4. Dzubay, T.G. X-ray Fluorescence 

Analysis of Environmental Samples, Ann 

Arbor Science Publishers Inc., 1977. 

5. Code of Federal Regulations (CFR) 40, 

Part 136, Appendix B; Definition and 

Procedure for the Determination of the 

Method Detection Limit—Revision 1.1. 

6. Drane, E.A, Rickel, D.G., and Courtney, 

W.J., ‘‘Computer Code for Analysis X-Ray 

Fluorescence Spectra of Airborne Particulate 

Matter,’’ in Advances in X-Ray Analysis, J.R. 

Rhodes, Ed., Plenum Publishing Corporation, 

New York, NY, p. 23 (1980). 

7. Analysis of Energy-Dispersive X-ray 

Spectra of Ambient Aerosols with Shapes 

Optimization, Guidance Document; TR– 

WDE–06–02; prepared under contract EP–D– 

05–065 for the U.S. Environmental Protection 

Agency, National Exposure Research 

Laboratory. March 2006. 

8. Billiet, J., Dams, R., and Hoste, J. (1980) 

Multielement Thin Film Standards for XRF 

Analysis, X-Ray Spectrometry, 9(4): 206–211. 

9. Bonner, N.A.; Bazan, F.; and Camp, D.C. 

(1973). Elemental analysis of air filter 

samples using x-ray fluorescence. Report No. 

UCRL–51388. Prepared for U.S. Atomic 

Energy Commission, by Univ. of Calif., 

Lawrence Livermore Laboratory, Livermore, 

CA. 

10. Dzubay, T.G.; Lamothe, P.J.; and 

Yoshuda, H. (1977). Polymer films as 

calibration standards for X-ray fluorescence 

analysis. Adv. X-Ray Anal., 20:411. 

11. Giauque, R.D.; Garrett, R.B.; and Goda, 

L.Y. (1977). Calibration of energy-dispersive 

X-ray spectrometers for analysis of thin 

environmental samples. In X-Ray 

Fluorescence Analysis of Environmental 

Samples, T.G. Dzubay, Ed., Ann Arbor 

Science Publishers, Ann Arbor, MI, pp. 153– 

181. 

12. Harmonization of Interlaboratory X-ray 

Fluorescence Measurement Uncertainties, 

Detailed Discussion Paper; August 4, 2006; 

prepared for the Office of Air Quality 

Planning and Standards under EPA contract 

68–D–03–038. http://www.epa.gov/ttn/amtic/ 

files/ambient/pm25/spec/xrfdet.pdf. 

■ 8. Appendix R is added to read as 

follows: 

Appendix R to Part 50—Interpretation of the 

National Ambient Air Quality Standards for 

Lead 

1. General. 

(a) This appendix explains the data 

handling conventions and computations 

necessary for determining when the primary 

and secondary national ambient air quality 

standards (NAAQS) for lead (Pb) specified in 

§ 50.16 are met. The NAAQS indicator for Pb 

is defined as: lead and its compounds, 

measured as elemental lead in total 

suspended particulate (Pb-TSP), sampled and 

analyzed by a Federal reference method 

(FRM) based on appendix G to this part or 

by a Federal equivalent method (FEM) 

designated in accordance with part 53 of this 

chapter. Although Pb-TSP is the lead NAAQS 

indicator, surrogate Pb-TSP concentrations 

shall also be used for NAAQS comparisons; 

specifically, valid surrogate Pb-TSP data are 

concentration data for lead and its 

compounds, measured as elemental lead, in 

particles with an aerodynamic size of 10 

microns or less (Pb-PM10), sampled and 

analyzed by an FRM based on appendix Q to 

this part or by an FEM designated in 

accordance with part 53 of this chapter. 

Surrogate Pb-TSP data (i.e., Pb-PM10 data), 

however, can only be used to show that the 

Pb NAAQS were violated (i.e., not met); they 

can not be used to demonstrate that the Pb 

NAAQS were met. Pb-PM10 data used as 

surrogate Pb-TSP data shall be processed at 

face value; that is, without any 

transformation or scaling. Data handling and 

computation procedures to be used in 

making comparisons between reported and/ 

or surrogate Pb-TSP concentrations and the 

level of the Pb NAAQS are specified in the 

following sections. 

(b) Whether to exclude, retain, or make 

adjustments to the data affected by 

exceptional events, including natural events, 

is determined by the requirements and 

process deadlines specified in §§ 50.1, 50.14, 

and 51.930 of this chapter. 

(c) The terms used in this appendix are 

defined as follows: 

Annual monitoring network plan refers to 

the plan required by section 58.10 of this 

chapter. 

Creditable samples are samples that are 

given credit for data completeness. They 

include valid samples collected on required 

sampling days and valid ‘‘make-up’’ samples 

taken for missed or invalidated samples on 

required sampling days. 

Daily values for Pb refer to the 24-hour 

mean concentrations of Pb (Pb-TSP or PbPM10), measured from midnight to midnight 

(local standard time), that are used in 

NAAQS computations. 


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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 monthspanning 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 siteparameter-year-month). 

Parameter refers either to Pb-TSP or to PbPM10. 

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-OctoberNovember 3-month mean, (2) the OctoberNovember-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 PbTSP 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 nonrequired 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 sitelevel 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 nonviolating 3-month Pb-PM10 mean exists). 

(b) As noted in section 1(a) of this 

appendix, FRM/FEM Pb-PM10 data will be 

processed at face value (i.e., at reported 

concentrations) without adjustment when 

computing means and making NAAQS 

comparisons. 

3. Requirements for Data Used for 

Comparisons With the Pb NAAQS and Data 

Reporting Considerations. 

(a) All valid FRM/FEM Pb-TSP data and all 

valid FRM/FEM Pb-PM10 data submitted to 

EPA’s Air Quality System (AQS), or 

otherwise available to EPA, meeting the 

requirements of part 58 of this chapter 

including appendices A, C, and E shall be 

used in design value calculations. Pb-TSP 

and Pb-PM10 data representing sample 

collection periods prior to January 1, 2009 

(i.e., ‘‘pre-rule’’ data) will also be considered 

valid for NAAQS comparisons and related 

attainment/nonattainment determinations if 

the sampling and analysis methods that were 

utilized to collect that data were consistent 

with previous or newly designated FRMs or 

FEMs and with either the provisions of part 

58 of this chapter including appendices A, C, 

and E that were in effect at the time of 

original sampling or that are in effect at the 

time of the attainment/nonattainment 

determination, and if such data are submitted 

to AQS prior to September 1, 2009. 

(b) Pb-TSP and Pb-PM10 measurement data 

are reported to AQS in units of micrograms 

per cubic meter (μg/m3) at local conditions 

(local temperature and pressure, LC) to three 

decimal places; any additional digits to the 

right of the third decimal place are truncated. 

Pre-rule Pb-TSP and Pb-PM10 concentration 

data that were reported in standard 

conditions (standard temperature and 

standard pressure, STP) will not require a 

conversion to local conditions but rather, 

after truncating to three decimal places and 

processing as stated in this appendix, shall 

be compared ‘‘as is’’ to the NAAQS (i.e., the 

LC to STP conversion factor will be assumed 

to be one). However, if the monitoring agency 

has retroactively resubmitted Pb-TSP or PbPM10 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), PbTSP 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 siteparameter data record (i.e., that siteparameter’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 siteparameter-daily basis, will constitute the sitemstockstill on PROD1PC66 with RULES2

67056 Federal Register / Vol. 73, No. 219 / Wednesday, November 12, 2008 / Rules and Regulations 

parameter data record. Where pre-rule PbTSP data (or subsequent non-required PbTSP 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 PbTSP 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 siteparameter data record (i.e., that siteparameter’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 siteparameter record are used in monthly mean 

calculations. However, not all daily values 

are given credit towards data completeness 

requirements. Only ‘‘creditable’’ samples are 

given credit for data completeness. Creditable 

samples include valid samples on scheduled 

sampling days and valid make-up samples. 

All other types of daily values are referred to 

as ‘‘extra’’ samples. Make-up samples taken 

in the (first week of the) month after the one 

in which the miss/void occurred will be 

credited for data capture in the month of the 

miss/void but will be included in the month 

actually taken when computing monthly 

means. For example, if a make-up sample 

was taken in February to replace a missed 

sample scheduled for January, the make-up 

concentration would be included in the 

February monthly mean but the sample 

credited in the January data capture rate. 

4. Comparisons With the Pb NAAQS. 

(a) The Pb NAAQS is met at a monitoring 

site when the identified design value is valid 

and less than or equal to 0.15 micrograms per 

cubic meter (μg/m3). A Pb design value that 

meets the NAAQS (i.e., 0.15 μg/m3 or less), 

is considered valid if it encompasses 36 

consecutive valid 3-month site means 

(specifically for a 3-year calendar period and 

the two previous months). For sites that 

begin monitoring Pb after this rule is effective 

but before January 15, 2010 (or January 15, 

2011), a 2010–2012 (or 2011–2013) Pb design 

value that meets the NAAQS will be 

considered valid if it encompasses at least 34 

consecutive valid 3-month means 

(specifically encompassing only the 3-year 

calendar period). See 4(c) of this appendix 

for the description of a valid 3-month mean 

and section 6(d) for the definition of the 

design value. 

(b) The Pb NAAQS is violated at a 

monitoring site when the identified design 

value is valid and is greater than 0.15 μg/m3, 

no matter whether determined from Pb-TSP 

or Pb-PM10 data. A Pb design value greater 

than 0.15 μg/m3 is valid no matter how many 

valid 3-month means in the 3-year period it 

encompasses; that is, a violating design value 

is valid even if it (i.e., the highest 3-month 

mean) is the only valid 3-month mean in the 

3-year timeframe. Further, a site does not 

have to monitor for three full calendar years 

in order to have a valid violating design 

value; a site could monitor just three months 

and still produce a valid (violating) design 

value. 

(c)(i) A 3-month parameter mean is 

considered valid (i.e., meets data 

completeness requirements) if the average of 

the data capture rate of the three constituent 

monthly means (i.e., the 3-month data 

capture rate) is greater than or equal to 75 

percent. Monthly data capture rates 

(expressed as a percentage) are specifically 

calculated as the number of creditable 

samples for the month (including any makeup 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 PbTSP 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 NAAQSlevel 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 yearmonths. Data substitution may only use data 

of the same parameter type. 

(A) The ‘‘above NAAQS level’’ test is as 

follows: Data substitution will be done in 

each month of the 3-month period that has 

less than 75 percent data capture; monthly 

capture rates are temporarily rounded to 

integers (zero decimals) for this evaluation. If 

by substituting the lowest reported daily 

value for that month (year non-specific; e.g., 

for January) over the 38-month design value 

period in question for missing scheduled 

data in the deficient months (substituting 

only enough to meet the 75 percent data 

capture minimum), the computation yields a 

recalculated test 3-month parameter mean 

concentration above the level of the standard, 

then the 3-month period is deemed to have 

passed the diagnostic test and the level of the 

standard is deemed to have been exceeded in 

that 3-month period. As noted in section 

4(c)(ii), in such a case, the 3-month 

parameter mean of the data actually reported, 

not the recalculated (‘‘test’’) result including 

the low values, shall be used to determine 

the design value. 

(B) The ‘‘below NAAQS level’’ test is as 

follows: Data substitution will be performed 

for each month of the 3-month period that 

has less than 75 percent but at least 50 

percent data capture; if any month has less 

than 50% data capture then the 3-month 

mean can not utilize this substitution test. 

Also, incomplete 3-month Pb-PM10 means 

can not utilize this test. A 3-month Pb-TSP 

mean with less than 75% data capture shall 

still be considered valid (and complete) if, by 

substituting the highest reported daily value, 

month-specific, over the 3-year design value 

period in question, for all missing scheduled 

data in the deficient months (i.e., bringing 

the data capture rate up to 100%), the 

computation yields a recalculated 3-month 

parameter mean concentration equal or less 

than the level of the standard (0.15 μg/m3), 

then the 3-month mean is deemed to have 

passed the diagnostic test and the level of the 

standard is deemed not to have been 

exceeded in that 3-month period (for that 

parameter). As noted in section 4(c)(ii), in 

such a case, the 3-month parameter mean of 

the data actually reported, not the 

recalculated (‘‘test’’) result including the high 

values, shall be used to determine the design 

value. 

(d) Months that do not meet the 

completeness criteria stated in 4(c)(i) or 

4(c)(ii), and design values that do not meet 

the completeness criteria stated in 4(a) or 

4(b), may also be considered valid (and 

complete) with the approval of, or at the 

initiative of, the Administrator, who may 

consider factors such as monitoring site 

closures/moves, monitoring diligence, the 

consistency and levels of the valid 

concentration measurements that are 

available, and nearby concentrations in 

determining whether to use such data. 

(e) The site-level design value for a 38- 

month period (three calendar years plus two 

previous months) is identified from the 

available (between one and 36) valid 3-month 

site means. In a situation where there are 

valid 3-month means for both parameters 

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(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 PbTSP and Pb-PM10 data. 

(f) The procedures for calculating monthly 

means and 3-month means, and identifying 

Pb design values are given in section 6 of this 

appendix. 

5. Rounding Conventions. 

(a) Monthly means and monthly data 

capture rates are not rounded. 

(b) Three-month means shall be rounded to 

the nearest hundredth μg/m3 (0.xx). Decimals 

0.xx5 and greater are rounded up, and any 

decimal lower than 0.xx5 is rounded down. 

E.g., a 3-month mean of 0.104925 rounds to 

0.10 and a 3-month mean of .10500 rounds 

to 0.11. Three-month data capture rates, 

expressed as a percent, are round to zero 

decimal places. 

(c) Because a Pb design value is simply a 

(highest) 3-month mean and because the 

NAAQS level is stated to two decimal places, 

no additional rounding beyond what is 

specified for 3-month means is required 

before a design value is compared to the 

NAAQS. 

6. Procedures and Equations for the Pb 

NAAQS. 

(a)(i) A monthly mean value for Pb-TSP (or 

Pb-PM10) is determined by averaging the 

daily values of a calendar month using 

equation 1 of this appendix, unless the 

Administrator chooses to exercise his 

discretion to use the alternate approach 

described in 6(a)(ii). 

 Equation 1

X

n m,y,s X

m

i,m,y,s

i=

nm

= ∑1

1

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. 

 Equation 2

X ; n m ,m ,m s X

m

m,y:z,s

i=

nm

123

1

= ∑1

Where: 

X ̄ m1, m2, m3; s = the 3-month parameter mean 

for months m1, m2, and m3 for site s; 

and 

nm = the number of monthly means available 

to be averaged (typically 3, sometimes 1 

or 2 if one or two months have no valid 

daily values); and 

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 

■ 9. The authority citation for part 51 

continues to read as follows: 

Authority: 23 U.S.C. 101; 42 U.S.C. 7401– 

7671q. 

■ 10. Section 51.117 is amended by 

revising paragraph (e)(1) to read as 

follows: 

§ 51.117 Additional provisions for lead. 

* * * * * 

(e) * * * 

(1) The point source inventory on 

which the summary of the baseline for 

lead emissions inventory is based must 

contain all sources that emit 0.5 or more 

tons of lead per year. 

* * * * * 

PART 53—AMBIENT AIR MONITORING 

REFERENCE AND EQUIVALENT 

METHODS 

■ 11. The authority citation for part 53 

continues to read as follows: 

Authority: Sec. 301(a) of the Clean Air Act 

(42 U.S.C. sec. 1857g(a)), as amended by sec. 

15(c)(2) of Pub. L. 91–604, 84 Stat. 1713, 

unless otherwise noted. 

Subpart C—[Amended] 

■ 12. Section 53.33 is revised to read as 

follows: 

§ 53.33 Test Procedure for Methods for 

Lead (Pb). 

(a) General. The reference method for 

Pb in TSP includes two parts, the 

reference method for high-volume 

sampling of TSP as specified in 40 CFR 

50, Appendix B and the analysis 

method for Pb in TSP as specified in 40 

CFR 50, Appendix G. Correspondingly, 

the reference method for Pb in PM10

includes the reference method for lowvolume 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 highvolume 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: 


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(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 semicontinuous sampling) method that uses 

the same sampling inlet and flow rate as 

the FRM and the same or different 

analytical procedure may be tested. The 

direct measurements are then aggregated 

to 24-hour equivalent concentrations for 

comparison with the FRM. For 

determining precision in section (k), 

two collocated direct reading devices 

must be used. 

(f) Audit samples. Three audit 

samples must be obtained from the 

address given in § 53.4(a). For Pb in TSP 

collected by the high-volume sampling 

method, the audit samples are 3⁄4 x 8- 

inch glass fiber strips containing known 

amounts of Pb in micrograms per strip 

(μg/strip) equivalent to the following 

nominal percentages of the National 

Ambient Air Quality Standard 

(NAAQS): 30%, 100%, and 250%. For 

Pb in PM10 collected by the low-volume 

sampling method, the audit samples are 

46.2-mm polytetrafluorethylene (PTFE) 

filters containing known amounts of Pb 

in micrograms per filter (μg/filter) 

equivalent to the same percentages of 

the NAAQS: 30%, 100%, and 250%. 

The true amount of Pb (Tqi), in total μg/ 

strip (for TSP) or total μg/filter (for 

PM10), will be provided for each audit 

sample. 

(g) Filter analysis. 

(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 

(μg/m3) for each analysis of each filter. 

Calculate the indicated total Pb amount 

for the audit samples in μg/strip for each 

analysis of each strip or μg/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 μg/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: 

 1 Equation

R

RRR iave

iA iB iC = ( ) + +

3

Where, i is the filter number. 

(i) Analytical Bias. 

(1) For the audit samples, calculate 

the average Pb concentration for each 

strip or filter analyzed by the reference 

method by averaging the concentrations 

calculated from the three analyses as 

described in (g)(1) using equation 2 of 

this section: 

 Equation 2

Q QQQ iave

iA iB iC = ( ) + +

3

Where, i is audit sample number. 

(2) Calculate the percent difference 

(Dq) between the average Pb 

concentration for each audit sample and 

the true Pb concentration (Tq) using 

equation 3 of this section: 

 Equation 3

D Q T

T qi

iave qi

qi

= − × 100

(3) If any difference value (Dqi) 

exceeds ±5 percent, the bias of the 

reference method analytical procedure 

is out-of-control. Corrective action must 

be taken to determine the source of the 

error(s) (e.g., calibration standard 

discrepancies, extraction problems, etc.) 

and the reference method and audit 

sample determinations must be repeated 

according to paragraph (g) of this 

section, or the entire test procedure 

(starting with paragraph (e) of this 

section) must be repeated. 

(j) Acceptable filter pairs. Disregard 

all filter pairs for which the Pb 

concentration, as determined in 

paragraph (h) of this section by the 

average of the three reference method 

determinations, falls outside the range 

of 30% to 250% of the Pb NAAQS level 

in μg/m3 for Pb in both TSP and PM10. 

All remaining filter pairs must be 

subjected to the tests for precision and 

comparability in paragraphs (k) and (l) 

of this section. At least five filter pairs 


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must be within the specified 

concentration range for the tests to be 

valid. 

(k) Test for precision. 

(1) Calculate the precision (P) of the 

analysis (in percent) for each filter and 

for each method, as the maximum 

minus the minimum divided by the 

average of the three concentration 

values, using equation 4 or equation 5 

of this section: 

 Equation 4

 

P

R R

R Ri

i i 

iave

= − × max min 100

or

 Equation 5

P C C

C Ci

i i 

iave

= − × max min 100

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: 

 6 Equation

D

C R

R in

ij jk

jk

= − × 100

Where, i is the filter number, and n numbers 

from 1 to 9 for the nine possible 

difference combinations for the three 

determinations for each method (j = A, 

B, C, candidate; k = A, B, C, reference). 

(2) If none of the percent differences 

(D) exceeds ±20 percent, the candidate 

method passes the test for 

comparability. 

(3) If one or more of the percent 

differences (D) exceed ±20 percent, the 

candidate method fails the test for 

comparability. 

(4) The candidate method must pass 

both the precision test (paragraph (k) of 

this section) and the comparability test 

(paragraph (l) of this section) to qualify 

for designation as an equivalent method. 

(m) Method Detection Limit (MDL). 

Calculate the estimated MDL using the 

guidance provided in 40 CFR, Part 136 

Appendix B. It is essential that all 

sample processing steps of the 

analytical method be included in the 

determination of the method detection 

limit. Take a minimum of seven blank 

filters from each lot to be used and 

calculate the detection limit by 

processing each through the entire 

candidate analytical method. Make all 

computations according to the defined 

method with the final results in μg/m3. 

The MDL of the candidate method must 

be equal to, or less than 5% of the level 

of the Pb NAAQS. 

■ 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 percentage of NAAQS in 

μg/m3.

30% to 

250% 

Minimum number of 24-hr 

measurements.

5 

Maximum reference method analytical bias, Dq.±5% 

Maximum precision, PR or PC .. ≤15% 

Maximum difference (D) ........... ±20% 

Estimated Method Detection 

Limit (MDL), μg/m3.

5% of 

NAAQS 

level. 

PART 58—AMBIENT AIR QUALITY 

SURVEILLANCE 

■ 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] 

■ 15. Section 58.10, is amended by 

added paragraph subsections (a)(4) and 

adding paragraph (b)(9) to read as 

follows: 

§ 58.10 Annual monitoring network plan 

and periodic network assessment. 

* * * * * 

(a) * * * 

(4) A plan for establishing Pb 

monitoring sites in accordance with the 

requirements of appendix D to this part 

shall be submitted to the EPA Regional 

Administrator no later than July 1, 2009 

as part of the annual network plan 

required in paragraph (a)(1) of this 

section. The plan shall provide for the 

required source-oriented Pb monitoring 

sites to be operational by January 1, 

2010, and for all required non-sourceoriented Pb monitoring sites to be 

operational by January 1, 2011. Specific 

site locations for the sites to be 

operational by January 1, 2011 are not 

required as part of the July 1, 2009 

annual network plan, but shall be 

included in the annual network plan 

due to be submitted to the EPA Regional 

Administrator on July 1, 2010. 

* * * * * 

(b) * * * 

(9) The designation of any Pb 

monitors as either source-oriented or 

non-source-oriented according to 

Appendix D to 40 CFR part 58. 

(10) Any source-oriented monitors for 

which a waiver has been requested or 

granted by the EPA Regional 

Administrator as allowed for under 

paragraph 4.5(a)(ii) of Appendix D to 40 

CFR part 58. 

(11) Any source-oriented or nonsource-oriented site for which a waiver 

has been requested or granted by the 

EPA Regional Administrator for the use 

of Pb-PM10 monitoring in lieu of Pb-TSP 

monitoring as allowed for under 

paragraph 2.10 of Appendix C to 40 CFR 

part 58. 

* * * * * 

■ 16. Section 58.13 is amended by 

revising paragraph (b) to read as follows: 

§ 58.13 Monitoring network completion. 

* * * * * 

(b) Not withstanding specific dates 

included in this part, beginning January 

1, 2008, when existing networks are not 

in conformance with the minimum 

number of required monitors specified 

in this part, additional required 

monitors must be identified in the next 

applicable annual monitoring network 

plan, with monitoring operation 

beginning by January 1 of the following 

year. To allow sufficient time to prepare 

and comment on Annual Monitoring 

Network Plans, only monitoring 

requirements effective 120 days prior to 

the required submission date of the plan 

(i.e., 120 days prior to July 1 of each 

year) shall be included in that year’s 

annual monitoring network plan. 

■ 17. Section 58.16 is amended by 

revising paragraph (a) to read as follows: 

§ 58.16 Data submittal and archiving 

requirements. 

(a) The State, or where appropriate, 

local agency, shall report to the 

Administrator, via AQS all ambient air 

quality data and associated quality 

assurance data for SO2; CO; O3; NO2; 


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NO; NOY; NOX; Pb-TSP mass 

concentration; Pb-PM10 mass 

concentration; PM10 mass concentration; 

PM2.5 mass concentration; for filterbased 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] 

■ 18. Section 58.20 is amended by 

revising paragraph (e) to read as follows: 

§ 58.20 Special purpose monitors (SPM). 

* * * * * 

(e) If an SPM using an FRM, FEM, or 

ARM is discontinued within 24 months 

of start-up, the Administrator will not 

designate an area as nonattainment for 

the CO, SO2, NO2, or 24-hour PM10

NAAQS solely on the basis of data from 

the SPM. Such data are eligible for use 

in determinations of whether a 

nonattainment area has attained one of 

these NAAQS. 

* * * * * 

■ 19. Appendix A to Part 58 is amended 

to read as follows: 

■ a. Revising paragraph 1, 

■ b. Adding paragraph 2.3.1.4, 

■ c. Revising paragraph 3.3.4, 

■ d. Revising paragraph 4c, 

■ e. Revising paragraph 4.4, 

■ f. Removing paragraph 4.5 and 

■ g. Revising Table A–2. 

Appendix A to Part 58—Quality 

Assurance Requirements for SLAMS, 

SPMs and PSD Air Monitoring 

* * * * * 

1. General Information. 

This appendix specifies the minimum 

quality system requirements applicable to 

SLAMS air monitoring data and PSD data for 

the pollutants SO2, NO2, O3, CO, Pb, PM2.5, 

PM10 and PM10–2.5 submitted to EPA. This 

appendix also applies to all SPM stations 

using FRM, FEM, or ARM methods which 

also meet the requirements of Appendix E of 

this part. Monitoring organizations are 

encouraged to develop and maintain quality 

systems more extensive than the required 

minimums. The permit-granting authority for 

PSD may require more frequent or more 

stringent requirements. Monitoring 

organizations may, based on their quality 

objectives, develop and maintain quality 

systems beyond the required minimum. 

Additional guidance for the requirements 

reflected in this appendix can be found in the 

‘‘Quality Assurance Handbook for Air 

Pollution Measurement Systems’’, volume II, 

part 1 (see reference 10 of this appendix) and 

at a national level in references 1, 2, and 3 

of this appendix. 

* * * * * 

2.3.1.4 Measurement Uncertainty for Pb 

Methods. The goal for acceptable 

measurement uncertainty is defined for 

precision as an upper 90 percent confidence 

limit for the coefficient variation (CV) of 20 

percent and for bias as an upper 95 percent 

confidence limit for the absolute bias of 15 

percent. 

* * * * * 

3.3.4 Pb Methods. 

3.3.4.1 Flow Rates. For the Pb Reference 

Methods (40 CFR Part 50, appendix G and 

appendix Q) and associated FEMs, the flow 

rates of the Pb samplers shall be verified and 

audited using the same procedures described 

in sections 3.3.2 and 3.3.3 of this appendix. 

3.3.4.2 Pb Analysis Audits. Each calendar 

quarter or sampling quarter (PSD), audit the 

Pb Reference Method analytical procedure 

using filters containing a known quantity of 

Pb. These audit filters are prepared by 

depositing a Pb solution on unexposed filters 

and allowing them to dry thoroughly. The 

audit samples must be prepared using 

batches of reagents different from those used 

to calibrate the Pb analytical equipment 

being audited. Prepare audit samples in the 

following concentration ranges: 

Range Equivalent ambient Pb 

concentration, μg/m3

1 ........ 30–100% of Pb 

NAAQS. 

2 ........ 200–300% of Pb 

NAAQS. 

(a) Audit samples must be extracted using 

the same extraction procedure used for 

exposed filters. 

(b) Analyze three audit samples in each of 

the two ranges each quarter samples are 

analyzed. The audit sample analyses shall be 

distributed as much as possible over the 

entire calendar quarter. 

(c) Report the audit concentrations (in μg 

Pb/filter or strip) and the corresponding 

measured concentrations (in μg Pb/filter or 

strip) using AQS unit code 077. The percent 

differences between the concentrations are 

used to calculate analytical accuracy as 

described in section 4.1.3 of this appendix. 

(d) The audits of an equivalent Pb method 

are conducted and assessed in the same 

manner as for the reference method. The flow 

auditing device and Pb analysis audit 

samples must be compatible with the specific 

requirements of the equivalent method. 

3.3.4.3 Collocated Sampling. The 

collocated sampling requirements for Pb-TSP 

and Pb-PM10 shall be determined using the 

same procedures described in sections 3.3.1 

of this appendix with the exception that the 

first collocated Pb site selected must be the 

site measuring the highest Pb concentrations 

in the network. If the site is impractical, 

alternative sites, approved by the EPA 

Regional Administrator, may be selected. If 

additional collocated sites are necessary, 

collocated sites may be chosen that reflect 

average ambient air Pb concentrations in the 

network. 

3.3.4.4 Pb Performance Evaluation 

Program (PEP) Procedures. Each year, one 

performance evaluation audit, as described in 

section 3.2.7 of this appendix, must be 

performed at one Pb site in each primary 

quality assurance organization that has less 

than or equal to 5 sites and two audits at 

primary quality assurance organizations with 

greater than 5 sites. In addition, each year, 

four collocated samples from primary quality 

assurance organizations with less than or 

equal to 5 sites and six collocated samples at 

primary quality assurance organizations with 

greater than 5 sites must be sent to an 

independent laboratory, the same laboratory 

as the performance evaluation audit, for 

analysis. 

* * * * * 

4. Calculations for Data Quality 

Assessment. 

* * * * * 

(c) At low concentrations, agreement 

between the measurements of collocated 

samplers, expressed as relative percent 

difference or percent difference, may be 

relatively poor. For this reason, collocated 

measurement pairs are selected for use in the 

precision and bias calculations only when 

both measurements are equal to or above the 

following limits: 

(1) TSP: 20 μg/m3. 

(2) Pb: 0.02 μg/m3. 

(3) PM10 (Hi-Vol): 15 μg/m3. 

(4) PM10 (Lo-Vol): 3 μg/m3. 

(5) PM10–2.5 and PM2.5: 3 μg/m3. 

* * * * * 

4.4 Statistics for the Assessment of Pb. 

4.4.1 Precision Estimate. Follow the same 

procedures as described for PM10 in section 

4.2.1 of this appendix using the data from the 

collocated instruments. The data pair would 

only be considered valid if both 

concentrations are greater than the minimum 

values specified in section 4(c) of this 

appendix. 

4.4.2 Bias Estimate. For the Pb analysis 

audits described in section 3.3.4.2 and the Pb 

Performance Evaluation Program described 

in section 3.3.4.4, follow the same procedure 

as described in section 4.1.3 for the bias 

estimate. 

4.4.3 Flow rate calculations. For the one 

point flow rate verifications, follow the same 

procedures as described for PM10 in section 

4.2.2; for the flow rate audits, follow the 

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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

Method Assessment method Coverage Minimum 

frequency 

Parameters 

reported 

Automated Methods 

1-Point QC for SO2, NO2, 

O3, CO.

Response check at concentration 0.01–0.1 ppm 

SO2, NO2, O3, and 1–10 

ppm CO.

Each analyzer ................... Once per 2 weeks ............. Audit concentration 1 and 

measured concentration 2. 

Annual performance evaluation for SO2, NO2, O3, 

CO.

See section 3.2.2 of this 

appendix.

Each analyzer ................... Once per year ................... Audit concentration 1 and 

measured concentration 2 for each level. 

Flow rate verification PM10,

PM2.5, PM10–2.5.

Check of sampler flow rate Each sampler .................... Once every month ............ Audit flow rate and measured flow rate indicated 

by the sampler. 

Semi-annual flow rate audit 

PM10, PM2.5, PM10–2.5.

Check of sampler flow rate 

using independent 

standard.

Each sampler .................... Once every 6 months ....... Audit flow rate and measured flow rate indicated 

by the sampler. 

Collocated sampling PM2.5,

PM10–2.5.

Collocated samplers ......... 15% ................................... Every 12 days ................... Primary sampler concentration and duplicate 

sampler concentration. 

Performance evaluation 

program PM2.5, PM10–2.5.

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

sites.

2. 8 valid audits for primary QA orgs, with >5 

sites.

3. All samplers in 6 years

Over all 4 quarters ............ Primary sampler concentration and performance evaluation sampler 

concentration. 

Manual Methods 

Collocated sampling PM10,

TSP, PM10–2.5, PM2.5, PbTSP, Pb-PM10.

Collocated samplers ......... 15% ................................... Every 12 days PSD— 

every 6 days.

Primary sampler concentration and duplicate 

sampler concentration. 

Flow rate verification PM10

(low Vol), PM10–2.5,

PM2.5, Pb-PM10.

Check of sampler flow rate Each sampler .................... Once every month ............ Audit flow rate and measured flow rate indicated 

by the sampler. 

Flow rate verification PM10

(High-Vol), TSP, Pb-TSP.

Check of sampler flow rate Each sampler .................... Once every quarter ........... Audit flow rate and measured flow rate indicated 

by the sampler. 

Semi-annual flow rate audit 

PM10, TSP, PM10–2.5,

PM2.5, Pb-TSP, Pb-PM10.

Check of sampler flow rate 

using independent 

standard.

Each sampler, all locations Once every 6 months ....... Audit flow rate and measured flow rate indicated 

by the sampler. 

Pb audit strips Pb-TSP, 

Pb-PM10.

Check of analytical system 

with Pb audit strips.

Analytical ........................... Each quarter ..................... Actual concentration and 

audit concentration. 

Performance evaluation 

program PM2.5, PM10–2.5.

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

sites.

2. 8 valid audits for primary QA orgs, with >5 

sites.

3. All samplers in 6 years

Over all 4 quarters ............ Primary sampler concentration and performance evaluation sampler 

concentration. 

Performance evaluation 

program Pb-TSP, PbPM10.

Collocated samplers ......... 1. 1 valid audit and 4 collocated samples for primary QA orgs, with >5 

sites.

2. 2 valid audits and 6 collocated samples for primary QA orgs, with >5 

sites.

Over all 4 quarters ............ Primary sampler concentration and performance evaluation sampler 

concentration. Primary 

sampler concentration 

and duplicate sampler 

concentration. 

1Effective concentration for open path analyzers. 

2 Corrected concentration, if applicable, for open path analyzers. 

■ 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 

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Appendix D to part 58 if there is no existing 

monitoring data indicating that the maximum 

arithmetic 3-month mean Pb concentration 

(either Pb-TSP or Pb-PM10) at the site was 

equal to or greater than 0.10 micrograms per 

cubic meter during the previous 3 years. 

2.10.1.2 Pb-PM10 samplers can be 

approved for use at source-oriented sites 

required under paragraph 4.5(a) if the 

monitoring agency can demonstrate (through 

modeling or historic monitoring data from 

the last 3 years) that Pb concentrations (either 

Pb-TSP or Pb-PM10) will not equal or exceed 

0.10 micrograms per cubic meter on an 

arithmetic 3-month mean and the source is 

expected to emit a substantial majority of its 

Pb in the fraction of PM with an aerodynamic 

diameter of less than or equal to 10 

micrometers. 

2.10.2 The approval of a Pb-PM10 sampler 

in lieu of a Pb-TSP sampler as allowed for 

in paragraph 2.10.1 above will be revoked if 

measured Pb-PM10 concentrations equal or 

exceed 0.10 micrograms per cubic meter on 

an arithmetic 3-month mean. Monitoring 

agencies will have up to 6 months from the 

end of the 3-month period in which the 

arithmetic 3-month Pb-PM10 mean 

concentration equaled or exceeded 0.10 

micrograms per cubic meter to install and 

begin operation of a Pb-TSP sampler at the 

site. 

■ 22. Appendix D to Part 58 is amended 

by revising paragraph 4.5 to read as 

follows: 

Appendix D to Part 58—Network 

Design Criteria for Ambient Air Quality 

Monitoring 

* * * * * 

4.5 Lead (Pb) Design Criteria. (a) State 

and, where appropriate, local agencies are 

required to conduct ambient air Pb 

monitoring taking into account Pb sources 

which are expected to or have been shown 

to contribute to a maximum Pb concentration 

in ambient air in excess of the NAAQS, the 

potential for population exposure, and 

logistics. At a minimum, there must be one 

source-oriented SLAMS site located to 

measure the maximum Pb concentration in 

ambient air resulting from each Pb source 

which emits 1.0 or more tons per year based 

on either the most recent National Emission 

Inventory (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 reentrained 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-sourceoriented 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 

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