[Federal Register Volume 62, Number 214 (Wednesday, November 5, 1997)]
[Rules and Regulations]
[Pages 59813-59818]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-29294]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 58

[AD-FRL-5903-5]
RIN 2060-AF71


Ambient Air Quality Surveillance for Lead

AGENCY: Environmental Protection Agency (EPA).

ACTION: Direct final rule.

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

SUMMARY: Lead air pollution levels measured near the Nation's roadways 
have decreased 97 percent between 1976 and 1995 with the elimination of 
lead in gasoline used by on-road mobile sources. Because of this 
historic decrease, EPA is shifting its ambient air monitoring focus 
from measuring lead air pollutant concentrations emanating from mobile 
source emissions toward a focus on stationary point sources of lead

[[Page 59814]]

air pollution. Today's action revises the part 58 lead air monitoring 
regulations to allow many lead monitoring stations to be discontinued 
while maintaining a core lead monitoring network in urban areas to 
track continued compliance with the lead National Ambient Air Quality 
Standard (NAAQS). This action also requires lead ambient air monitoring 
around lead stationary sources. This action is being taken at the 
direct request of numerous State and local agencies whose on-road 
mobile source-oriented lead monitors have been reporting peak lead air 
pollution values that are many times less than the quarterly lead NAAQS 
of 1.5 <greek-m>g/m\3\ for many years. Approximately 70 of the National 
Air Monitoring Stations (NAMS) and a number of the State and Local Air 
Monitoring Stations (SLAMS) could be discontinued with this action, 
thus making more resources available to those State and local agencies 
to deploy lead air quality monitors around heretofore unmonitored lead 
stationary sources.

DATES: The effective date of this rule is December 22, 1997 unless 
adverse or critical comments are received by December 5, 1997. If 
adverse or critical comments are received by December 5, 1997, and the 
effective date is delayed, timely notice will be published in the 
Federal Register.

ADDRESSES: Comments should be submitted (in duplicate, if possible) to: 
Air Docket (LE-131), US Environmental Protection Agency, Attn: Docket 
No. A-91-22, 401 M Street, SW, Washington, DC 20460.

FOR FURTHER INFORMATION CONTACT: Brenda Millar, Emissions, Monitoring, 
and Analysis Division (MD-14), Office of Air Quality Planning and 
Standards, U.S. Environmental Protection Agency, Research Triangle 
Park, North Carolina 27711, Telephone: (919) 541-4036, e-mail: millar, 
<a href="/cdn-cgi/l/email-protection#f59787909b9194b59098949c99db908594db929a83"><span class="__cf_email__" data-cfemail="3654445358525776535b575f5a1853465718515940">[email protected]</span></a>.

SUPPLEMENTARY INFORMATION:

I. Authority

    Sections 110, 301(a), and 319 of the Clean Air Act as amended 42 
U.S.C. 7410, 7601(a), 7619.

II. Background

    The current ambient air monitoring regulations that pertain to lead 
air sampling were written in the 1970's when lead emissions from on-
road mobile sources (e.g., automobiles, trucks) were the predominant 
lead air emission source affecting our communities. As such, the 
current lead monitoring requirements focus primarily upon the idea of 
determining the air quality impacts from major roadways and urban 
traffic arterial highways. Since the 1970's, lead has been removed from 
gasoline sources for on-road vehicles (on-road vehicles now account for 
less than 1 percent of total lead emissions), and a 97 percent decrease 
in lead air pollution levels measured in our neighborhoods and near 
roadways has occurred nationwide. Because of this historic decrease, 
EPA is reducing its requirements for measuring lead air pollutant 
concentrations near major highways, and is focusing on stationary point 
sources and their impacts on neighboring populations.
    The current lead air monitoring regulations require that each 
urbanized area with a population of 500,000 or more operate at least 
two lead NAMS, one of which must be a roadway-oriented site and the 
second must be a neighborhood site with nearby traffic arteries or 
other major roadways. There are approximately 85 NAMS in operation and 
reporting data for 1996. This action would reduce this NAMS requirement 
to include one NAMS site in one of the two largest Metropolitan 
Statistical Areas (MSA/CMSA) within each of the ten EPA Regions, and 
one NAMS population-oriented site in each populated area (either a MSA/
CMSA, town, or county) where lead violations have been measured over 
the most recent 8 calendar quarters. This latter requirement is 
designed to provide information to citizens living in areas that have 
one or more lead stationary sources that are causing recent air quality 
violations.
    At present, the MSA/CMSAs, cities, or counties that have one or 
more quarterly Pb NAAQS violations that would be subject to this 
requirement include:

 Table 1.--CMSA/MSA's or Counties With One or More Lead NAAQS Violations
                               in 1995-96                               
------------------------------------------------------------------------
            CMSA/MSA or county               Contributing lead source(s)
------------------------------------------------------------------------
Philadelphia-Wilmington-Atlantic City CMSA  Franklin Smelter in         
                                             Philadelphia County, PA.   
Tampa-St. Petersburg-Clearwater MSA.......  Gulf Coast Lead in          
                                             Hillsborough County, FL.   
Memphis MSA...............................  Refined Metals in Shelby    
                                             County, TN.                
Nashville MSA.............................  General Smelting in         
                                             Williamson County, TN.     
St. Louis MSA.............................  Chemetco in Madison County, 
                                             IL, and Doe Run in         
                                             Jefferson County, MO.      
Cleveland-Akron CMSA......................  Master Metals in Cuyahoga   
                                             County, OH.                
Iron County, MO...........................  ASARCO in/near Hogan, MO.   
Omaha MSA.................................  ASARCO in Douglas County,   
                                             NE.                        
Lewis and Clark County, MT................  ASARCO in/near East Helena, 
                                             MT.                        
------------------------------------------------------------------------

    Data from these NAMS will be used to assess national trends in lead 
ambient air pollution. Figure 1 demonstrates the effect that these 
monitoring reductions will have on our national lead air pollutant 
trends.

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    For other monitoring within the SLAMS network, EPA is requiring 
State and local agencies to focus their efforts toward establishing air 
monitoring networks around lead stationary sources which are causing or 
have a potential to cause exceedances of the quarterly lead NAAQS. Many 
of these sources have been identified through EPA's ongoing Lead NAAQS 
Attainment Strategy, and monitoring has already been established. In 
general, stationary sources emitting five or more tons per year are 
considered to be candidates for additional lead monitoring, although 
smaller stationary sources may also be problematic depending upon the 
facility's size and proximity to neighborhoods. EPA recommends a 
minimum of two sites per source, one located for stack emission impacts 
and the other for fugitive emission impacts. Variations of this two-
site network are expected as source type, topography, locations of 
neighboring populations, and other factors play a role in how to most 
appropriately design such a network. EPA guidance for lead monitoring 
around point sources has been developed and is available through a 
variety of sources including the National Technical Information Service 
(703-487-4650), and electronic forms accessible through EPA's Office of 
Air Quality Planning & Standards Technology Transfer Network, Ambient 
Monitoring Technology Information Center (AMTIC) bulletin board system 
at http://ttnwww.rtpnc.epa.gov.
    In addition to the changes to the lead monitoring requirements, EPA 
is making several minor changes to update and correct regulatory 
provisions to current practices. Specifically this affects sections 
58.31, 58.34, 58.41, Appendix B, Appendix D sections 3.2 and 3.3, and 
Appendix G, sections 1 and 2b.

III. Administrative Requirements Section

A. Executive Order 12866

    Under Executive Order 12866 (58 FR 51735, October 4, 1993), the 
Agency must determine whether the regulatory action is ``significant'' 
and therefore subject to Office of Management and Budget (OMB) review 
and to the requirements of the Executive Order. The Order defines 
``significant regulatory action'' as one that is likely to result in a 
rule that may:
    (1) Have an annual effect on the economy of $100 million or more or 
adversely affect in a material way the economy, a sector of the 
economy, productivity, competition, jobs, the environment, public 
health or safety, or State, local, or governments or communities;
    (2) Create a serious inconsistency or otherwise interfere with an 
action taken or planned by another Agency;
    (3) Materially alter the budgetary impact of entitlements, grants, 
user fees, or loan programs or the rights and obligations or recipients 
thereof; or
    (4) Raise novel legal or policy issues arising out of legal 
mandates, the President's priorities, or the principles set forth in 
the Executive Order.
    It has been determined that this action is not a ``significant 
regulatory action'' under the terms of the Executive Order 12866 and is 
therefore not subject to formal OMB review.

B. Paperwork Reduction Act

    Today's action does not impose any new information collection 
burden. This action revises the part 58 air monitoring regulations for 
lead to allow many monitoring sites to be discontinued. The Office of 
Management and Budget (OMB) has previously approved the information 
collection requirements in the part 58 regulation under the provisions 
of the Paperwork Reduction Act, 44 U.S.C. 3501 et seq. and has assigned 
OMB control number 2060-0084 (EPA ICR No. 0940.13 and revised by 
0940.14).

C. Impact on Small Entities

    The Regulatory Flexibility Act (RFA) generally requires an agency 
to conduct a regulatory flexibility analysis of any rule subject to 
notice and comment rulemaking requirements unless the agency certifies 
that the rule will not have a significant economic impact on a 
substantial number of small entitites. Small entities include small 
businesses, small not-for-profit enterprises, and small governmental 
jurisdictions whose jurisdictions are less than 50,000 people. This 
final rule will not have a significant impact on a substantial number 
of small entities because it does not impact small entities whose

[[Page 59816]]

jurisdictions cover less than 50,000 people. Pursuant to the provision 
of 5 U.S.C. 605(b), I certify that this action will not have a 
significant economic impact on a substantial number of small entities.
    Since this modification is classified as minor, no additional 
reviews are required.

D. Unfunded Mandates Reform Act of 1995

    Under section 202 of the Unfunded Mandates Reform Act of 1995 
(``Unfunded Mandates Act''), signed into law on March 22, 1995, EPA 
must prepare a budgetary impact statement to accompany any proposed or 
final standards that include a Federal mandate that may result in 
estimated costs to State, local, or tribal governments, or to the 
private sector, of, in the aggregate, $100 million or more. Under 
section 205, the EPA must select the most cost-effective and least 
burdensome alternative that achieves the objectives of the standard and 
is consistent with statutory requirements. Section 203 requires EPA to 
establish a plan for informing and advising any small governments that 
may be significantly or uniquely impacted by the standards. The EPA has 
determined that this action does not include a Federal mandate that may 
result in estimated costs of $100 million or more to either State, 
local, or tribal governments. Therefore, the requirements of the 
Unfunded Mandates Act of 1995 do not apply to this action.

E. Submission to Congress and the General Accounting Office

    Under 5 U.S.C. 801(a)(1)(A) as added by the Small Business 
Regulatory Enforcement Fairness Act of 1996, 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 
General Accounting Office prior to publication of the rule in today's 
Federal Register. This rule is not a ``major rule'' as defined by 5 
U.S.C. 804(2).

List of Subjects in 40 CFR Part 58

    Environmental protection, Air pollution control, Intergovernmental 
relations, Reporting and recordkeeping requirements, Quality assurance 
requirements.

    Dated: October 30, 1997.
Carol W. Browner,
Administrator.
    For the reasons set forth in the preamble, title 40, chapter I, 
part 58 of the Code of Federal Regulations is amended as follows:

PART 58--[AMENDED]

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

    Authority: 42 U.S.C. 7410, 7601(a), 7613, 7619.

    2. Section 58.31(a) is revised to read as follows:


Sec. 58.31  NAMS network description.

* * * * *
    (a) The AIRS site identification number for existing stations.
* * * * *
    3. Section 58.34(a) is revised to read as follows:


Sec. 58.34  NAMS network completion.

* * * * *
    (a) Each NAMS must be in operation, be sited in accordance with the 
criteria in Appendix E to this part, and be located as described in the 
AIRS database; and
* * * * *
    4. Section 58.41(b) is revised to read as follows:


Sec. 58.41  PAMS network description.

* * * * *
    (b) The AIRS site identification number for existing stations.
* * * * *
    5. Appendix D is amended by revising the first sentence of 
paragraph 3 of section 1, revising section 2.7, revising the fifth 
paragraph of section 3, revising the last sentence of the first 
paragraph of section 3.2, revising the last sentence of the first 
paragraph of section 3.3, revising section 3.6, and revising references 
6, 7, 10 of section 6 and adding reference 19 to section 6 to read as 
follows:

Appendix D--Network Design for State and Local Air Monitoring 
Stations (SLAMS), National Air Monitoring Stations (NAMS), and 
Photochemical Assessment Monitoring Stations (PAMS)

* * * * *
    1. SLAMS Monitoring Objectives and Spatial Scales
* * * * *
    It should be noted that this appendix contains no criteria for 
determining the total number of stations in SLAMS networks. * * *
* * * * *
    2.7 Lead (Pb) Design Criteria for SLAMS. Presently, less than 1 
percent of the Nation's Pb air pollution emissions originate from 
on-road mobile source exhaust. The majority of Pb emissions come 
from stationary point sources, such as metals processing facilities, 
waste disposal and recycling, and fuel combustion (reference 19 of 
this appendix). The SLAMS networks are used to assess the air 
quality impacts of stationary Pb sources, and to determine the broad 
population exposure from any Pb source. The most important spatial 
scales to effectively characterize the emissions from both mobile 
and stationary sources are the micro, middle, and neighborhood 
scales. For purposes of establishing monitoring stations to 
represent large homogeneous areas other than the above scales of 
representativeness, urban or regional scale stations may also be 
needed.
    Microscale--This scale would typify areas in close proximity to 
stationary lead sources or downtown street canyons and traffic 
corridors where the general public would be exposed to maximum 
concentrations from mobile sources. Because of the very steep 
ambient Pb gradients resulting from Pb emissions from mobile sources 
(reference 7 of this appendix), the dimensions of the microscale for 
Pb generally would not extend beyond 15 meters from the roadway. 
Emissions from stationary 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. Data collected at microscale stations 
provide information for evaluating and developing ``hot-spot'' 
control measures.
    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 stationary sources. Pb 
monitors in such areas are desirable because of the higher 
sensitivity of children to exposures of elevated Pb concentrations 
(reference 7 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.
    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. Stations 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.
    Urban Scale--Such stations would be used to present ambient Pb 
concentrations over an entire metropolitan area with dimensions in 
the 4 to 50 kilometer range. An urban scale station would be useful 
for assessing trends in citywide air quality and the effectiveness 
of larger scale air pollution control strategies.
    Regional Scale--Measurements from these stations would 
characterize air quality levels

[[Page 59817]]

over areas having dimensions of 50 to hundreds of kilometers. This 
large scale of representativeness, rarely used in Pb monitoring, 
would be most applicable to sparsely populated areas and could 
provide information on background air quality and inter-regional 
pollutant transport.
    Monitoring for ambient Pb levels is required for all major 
urbanized areas where Pb levels have been shown or are expected to 
be of significant concern due to the proximity of stationary Pb 
emissions sources. Sources emitting five tons per year or more of 
actual point and fugitive Pb emissions would generally be candidates 
for lead ambient air monitoring. Smaller sources could also pose a 
potential air quality problem in certain cases, e.g., if the 
facility is geographically compact and located very close to 
neighborhoods. Modeling may be needed to determine if a source has 
the potential to exceed the quarterly lead National Ambient Air 
Quality Standard (NAAQS). The total number and type of stations for 
SLAMS are not prescribed but must be determined on a case-by-case 
basis. As a minimum, there must be two stations in any area where Pb 
concentrations currently exceed or have exceeded 1.5 <greek-m>g/m\3\ 
quarterly arithmetic mean measured during any one quarter of the 
most recent eight quarters. Where the Pb air quality violations are 
widespread or the emissions density, topography, or population 
locations are complex and varied, there may be a need to establish 
more than two Pb ambient air monitoring stations. The EPA Regional 
Administrator may specify more than two monitoring stations if it is 
found that two stations are insufficient to adequately determine if 
the Pb standard is being attained and maintained. The Regional 
Administrator may also specify that stations be located in areas 
outside the boundaries of the urbanized areas.
    Concerning the previously discussed required minimum of two 
stations, at least one of the stations must be a category (a) type 
station and the second may be either category (a) or (b) depending 
upon the extent of the stationary source's impact and the existence 
of residential neighborhoods surrounding the source. When the source 
is located in an area that is subject to NAMS requirements as in 
Section 3 of this Appendix, it is preferred that the NAMS site be 
used to describe the population's exposure and the second SLAMS site 
be used as a category (a) site. Both of these categories of stations 
are defined in section 3.
    To locate monitoring stations, it will be necessary to obtain 
background information such as stationary and mobile source 
emissions inventories, climatological summaries, and local 
geographical characteristics. Such information should be used to 
identify areas that are most suitable to the particular monitoring 
objective and spatial scale of representativeness desired. 
References 9 & 10 of this appendix provide additional guidance on 
locating sites to meet specific urban area monitoring objectives and 
should be used in locating new stations or evaluating the adequacy 
of existing stations.
    After locating each Pb station and, to the extent practicable, 
taking into consideration the collective impact of all Pb sources 
and surrounding physical characteristics of the siting area, a 
spatial scale of representativeness must be assigned to each 
station.
* * * * *
    3. Network Design for National Air Monitoring Stations (NAMS).
* * * * *
    For each urban area where NAMS are required, both categories of 
monitoring stations must be established. In the case of Pb and 
SO<INF>2</INF> if only one NAMS is needed, then category (a) must be 
used. The analysis and interpretation of data from NAMS should 
consider the distinction between these types of stations as 
appropriate.
* * * * *
    3.2  Sulfur Dioxide Design Criteria for NAMS *  *  *
    The actual number and location of the NAMS must be determined by 
EPA Regional Offices and the State Agency, subject to the approval 
of EPA Headquarters, Office of Air Quality Planning and Standards 
(OAQPS).
* * * * *
    3.3  Carbon Monoxide (CO) Design Criteria for NAMS *  *  *
    At the national level, EPA will not routinely require data from 
as many stations as are required for PM-10, and perhaps 
SO<INF>2</INF>, since CO trend stations are principally needed to 
assess the overall air quality progress resulting from the emission 
controls required by the Federal motor vehicle control program 
(FMVCP) and other local controls.
* * * * *
    3.6  Lead (Pb) Design Criteria for NAMS. In order to achieve the 
national monitoring objective, one NAMS site must be located in one 
of the two cities with the greatest population in the following ten 
regions of the country (the choice of which of the two metropolitan 
areas should have the lead NAMS requirement is made by the 
Administrator or the Administrator's designee using the 
recommendation of the Regional Administrators or the Regional 
Administrators' designee):

  EPA Regions & Two Current Largest MSA/CMSAs (Using 1995 Census Data)  
------------------------------------------------------------------------
            Region (States)                   Two largest MSA/CMSAs     
------------------------------------------------------------------------
I (Connecticut, Massachusetts, Maine,    Boston-Worcester-Lawrence CMSA,
 New Hampshire, Rhode Island, Vermont).   Hartford, CT MSA              
II (New Jersey, New York, Puerto Rico,   New York-Northern New Jersey-  
 U.S. Virgin Islands).                    Long Island, CMSA, San Juan-  
                                          Caguas-Arecibo, PR CMSA.      
III (Delaware, Maryland, Pennsylvania,   Washington-Baltimore CMSA,     
 Virginia, West Virginia, Washington,     Philadelphia-Wilmington-      
 D.C.).                                   Atlantic City CMSA.           
IV (Alabama, Florida, Georgia,           Miami-Fort Lauderdale CMSA,    
 Kentucky, Mississippi, North Carolina,   Atlanta, GA MSA.              
 South Carolina, Tennessee).                                            
V (Illinois, Indiana, Michigan,          Chicago-Gary-Kenosha CMSA,     
 Minnesota, Ohio, Wisconsin).             Detroit-Ann Arbor-Flint CMSA. 
VI (Arkansas, Louisiana, New Mexico,     Dallas-Fort Worth CMSA, Houston-
 Oklahoma, Texas).                        Galveston-Brazoria CMSA.      
VII (Iowa, Kansas, Missouri, Nebraska).  St. Louis MSA, Kansas City MSA 
VIII (Colorado, Montana, North Dakota,   Denver-Boulder-Greeley CMSA,   
 South Dakota, Utah, Wyoming).            Salt Lake City-Ogden MSA.     
IX (American Samoa, Arizona,             Los Angeles-Riverside-Orange   
 California, Guam, Hawaii, Nevada).       County CMSA, San Francisco-   
                                          Oakland-San Jose CMSA.        
X (Alaska, Idaho, Oregon, Washington)..  Seattle-Tacoma-Bremerton CMSA, 
                                          Portland-Salem CMSA.          
------------------------------------------------------------------------

    In addition, one NAMS site must be located in each of the MSA/
CMSAs where one or more violations of the quarterly Pb NAAQS have 
been recorded over the previous eight quarters. If a violation of 
the quarterly Pb NAAQS is measured at a monitoring site outside of a 
MSA/CMSA, one NAMS site must be located within the county in a 
populated area, apart from the Pb source, to assess area wide Pb air 
pollution levels. These NAMS sites should represent the maximum Pb 
concentrations measured within the MSA/CMSA, city, or county that is 
not directly impacted from a single stationary Pb source. This site 
may be a microscale or middle scale category (a) station, located 
adjacent to a major roadway (e.g., >30,000 ADT), or a neighborhood 
scale category (b) station that is located in a highly populated 
residential section of the MSA/CMSA or county where the traffic 
density is high. Data from these sites will be used to assess 
general conditions for large MSA/CMSAs and other populated areas as 
a marker for national trends, and to confirm continued attainment of 
the Pb NAAQS. In some cases, the MSA/CMSA subject to the latter lead 
NAMS requirement due to a violating stationary source will be the 
same MSA/CMSA subject to the lead NAMS requirement based upon its 
population. For

[[Page 59818]]

these situations, the total minimum number of required lead NAMS is 
one.
* * * * *
    6. References.
* * * * *
    6. Lead Guideline Document, U.S. Environmental Protection 
Agency, Research Triangle Park, NC. EPA-452/R-93-009.
    7. Air Quality Criteria for Lead. Office of Research and 
Development, U.S. Environmental Protection Agency, Washington, DC. 
EPA-600/8-83-028 aF--dF, 1986, and supplements EPA-600/8-89/049F, 
August 1990. (NTIS document numbers PB87-142378 and PB91-138420.)
* * * * *
    10. ``Guidance for Conducting Ambient Air Monitoring for Lead 
Around Point Sources,'' Office of Air Quality Planning and 
Standards, U.S. Environmental Protection Agency, Research Triangle 
Park, NC EPA-454/R-92-009, May 1997.
* * * * *
    19. National Air Pollutant Emissions Trends, 1900-1995, Office 
of Air Quality Planning and Standards, U.S. Environmental Protection 
Agency, Research Triangle Park, NC. EPA-454/R96-007, October 1996, 
updated annually.
* * * * *
    6. Appendix E is amended by revising the first paragraph of 
section 7.1, adding a sentence at the beginning of section 7.3, 
revising section 7.4, and revising reference 18 in section 13 to 
read as follows:

Appendix E--Probe and Monitoring Path Siting Criteria for Ambient Air 
Quality Monitoring

* * * * *
    7.1  Vertical Placement. Optimal placement of the sampler inlet 
for Pb monitoring should be at breathing height level. However, 
practical factors such as prevention of vandalism, security, and 
safety precautions must also be considered when siting a Pb monitor. 
Given these considerations, the sampler inlet for microscale Pb 
monitors must be 2-7 meters above ground level. The lower limit was 
based on a compromise between ease of servicing the sampler and the 
desire to avoid unrepresentative conditions due to re-entrainment 
from dusty surfaces. The upper limit represents a compromise between 
the desire to have measurements which are most representative of 
population exposures and a consideration of the practical factors 
noted above.
* * * * *
    7.3.  Spacing from Roadways. This criteria applies only to those 
Pb sites designed to assess lead concentrations from mobile sources. 
Numerous studies have shown that ambient Pb levels near mobile 
sources are a function of the traffic volume and are most pronounced 
at ADT >30,000 within the first 15 meters on the downwind side of 
the roadways. *  *  *
    7.4.  Spacing from trees and other considerations. Trees can 
provide surfaces for deposition or adsorption of Pb particles and 
obstruct normal wind flow patterns. For microscale and middle scale 
category (a) sites there must not be any tree(s) between the source 
of the Pb and the sampler. For neighborhood scale category (b) 
sites, the sampler should be at least 20 meters from the drip line 
of trees. The sampler must, however, be placed at least 10 meters 
from the drip line of trees which could be classified as an 
obstruction, i.e., the distance between the tree(s) and the sampler 
is less than the height that the tree protrudes above the sampler.
* * * * *
    13. References.
* * * * *
    18. Air Quality Criteria for Lead. Office of Research and 
Development, U.S. Environmental Protection Agency, Washington, DC 
EPA-600/8-83-028 aF-dF, 1986, and supplements EPA-600/8-89/049F, 
August 1990. (NTIS document numbers PB87-142378 and PB91-138420.)
* * * * *
    7. Section 1 and section 2b of Appendix G are revised to read as 
follows:

Appendix G--Uniform Air Quality Index and Daily Reporting

* * * * *
    1. General. This appendix describes the uniform air quality index 
to be used by States in reporting the daily air quality index required 
by Sec. 58.50.
    2. Definitions.
* * * * *
    b. Reporting Agency means the applicable State agency or a local 
air pollution control agency designated by the State, that will carry 
out the provisions of Sec. 58.50.
* * * * *
[FR Doc. 97-29294 Filed 11-4-97; 8:45 am]
BILLING CODE 6560-50-P


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