US EPA Region 4 Guidance on Ambient Air Monitor Siting Criteria Waivers
September 26, 2018
pose
This document is intended to serve as guidance for air monitoring agencies that are considering
requesting a waiver of one or more ambient air monitor siting criteria requirements.
Additionally, this document clarifies the regulatory requirements that must be met for a waiver
to be approved and provides examples and instructions on what information should be
submitted with a waiver request. This document intends to promote consistency in how these
waiver requests are developed by monitoring agencies and evaluated by EPA Region 4. It is
meant only to provide clarification of existing requirements and does not create new
requirements or supersede existing requirements.
Monitoring agencies should endeavor to ensure that siting criteria requirements are met,
especially at long-term monitoring sites, and siting criteria waiver requests should be rare. To
ensure that siting criteria requirements are met and reduce the need for waiver requests,
monitoring agencies should conduct siting evaluations of all monitoring sites annually, and
provide the results of these evaluations in their annual ambient air monitoring network plans.
As stated in 40 CFR Part 58, Appendix E, Section 10, new sites should generally be able to meet
siting criteria and existing sites may be granted exceptions if provisions in the CFR can be met
and it is adequately demonstrated that the need or purpose for monitoring is still relevant if
siting criteria are not met.
Alternatives to requesting a waiver of siting requirements include:
• site reconfiguration such as addressing obstructions or tree dripline issues or moving the
probe inlet to meet siting requirements;
• moving the monitor(s) to another location that accomplishes the same monitoring
objective and that is representative of the same spatial scale and air shed ;
• redefining the monitoring objective and operating the monitor(s) as special purpose
monitor(s) that do not meet siting criteria (Note: Such monitors will not count toward
minimum regulatory monitoring requirements but may serve another purpose such as
monitoring in a unique or important area. If such monitors would not be comparable to
the NAAQS, then a NAAQS exclusion flag can also be requested.); or
• discontinue the site, if appropriate and not required by regulation.
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Before developing a siting criteria waiver request, agencies should consult with the appropriate
air monitoring state contact at EPA Region 4. The Region will work to provide advice on what
options may be appropriate for each site. Typically, EPA Region 4 does not grant siting
requirement waivers for monitors with larger spatial scales (e.g. neighborhood or larger scales). In
most cases, waivers have been previously granted for source-oriented monitors or for unique
circumstances. EPA can provide examples of previously-approved submittals upon request.
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The regulatory requirements for waivers of ambient air monitoring siting criteria requirements
are found in 40 CFR Part 58, Appendix E, Section 10:
10. WAIVER PROVISIONS
Most sampling probes or monitors can be located so that they meet the requirements of
this appendix. New sites with rare exceptions, can be located within the limits of this
appendix.
However, some existing sites may not meet these requirements and still produce useful
data for some purposes. The EPA will consider a written request from the State agency to
waive one or more siting criteria for some monitoring sites providing that the State can
adequately demonstrate the need (purpose) for monitoring or establishing a monitoring
site at that location.
10.1 For establishing a new site, a waiver may be granted only if
both of the following criteria are met:
10.1.1 The site can be demonstrated to be as representative of the
monitoring area as it would be if the siting criteria were being met.
10.1.2 The monitor or probe cannot reasonably be located to meet the
siting criteria because of physical constraints (e.g., inability to locate the
required type of site the necessary distance from roadways orobstructions).
10.2 However, for an existing site, a waiver may be granted if
either of the criteria in sections 10.1.1 and 10.1.2 of this appendix are
met.
10.3 Cost benefits, historical trends, and other factors may be used to
add support to the criteria in sections 10.1.1 and 10.1.2 of this appendix,
however, they in themselves, will not be acceptable reasons for granting a
waiver. Written requests for waivers must be submitted tothe Regional
Administrator.
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Example Information Needed to .Support a Waiver
EPA Region 4 requests that each siting criteria waiver request be included in the annual air
monitoring network plan and be renewed every five years in the 5-year air monitoring
network assessment. Monitoring agencies should review existing waivers that have been
previously approved by EPA to determine if they are still necessary, or if actions can be taken
to bring those sites into compliance with the siting criteria. A waiver request should include:
• The specific siting criteria requirement(s) in 40 CFR Part 58, Appendix E, including the
appropriate citation(s), for which a waiver is being requested.
• A narrative explaining why a waiver is being requested.
• Measurements or other information documenting why the site does not currently or
will not meet siting criteria requirements (e.g., distance measurements to nearby trees,
obstructions, or roadways, wind rose(s), photos from the cardinal directions, specific AQS
reports, etc.).
• Evidence that either criterion in section 10.1.1 or 10.1.2, for an existing site, or the
criteria in both sections for a new site, are met. Examples of evidence for each of these
requirementsare provided in the next section.
Examples of Information to Provide
I. Demonstrate that a site is as representative of the monitoring area as it would be if the
siting criteria were being met.
To demonstrate that this requirement is met, provide data or other analyses to demonstrate
that the proposed site is representative of the monitoring area, and quantify any effect(s) on the
data from the siting criteria issues. General examples of appropriate data or analyses include:
• Comparison of concurrent monitoring data (hourly, or the finest time resolution
of data available) collected at the site for which a waiver is requested and a
nearby site that does meet siting criteria. Appropriateness of a nearby
comparison site can be determined on a case-by-case basis considering factors
such as monitoring objective, distance, spatial scale, pollutant, nearby sources,
terrain, meteorology, and the nature of the siting criteria issues.
• Comparison of concurrent air sensor data comparing the site for which a waiver is
requested with nearby site(s) that do meet sitingcriteria.
o Additional guidance on air sensors, and results of EPA sensor evaluations is
available at EPA's Air Sensor Toolbox1.
1 Air sensor performance testing conducted by EPA has indicated that sensor performance and data quality depends
on several factors. Some ozone and PM sensors have demonstrated good correlation with regulatory monitors. Your
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The analysis provided should cover a complete calendar year of data to account for seasonal
variability, or at a minimum should cover the season of expected highest concentration for
the pollutant/area.
Prior to beginning the process of developing information to support a siting criteria waiver
request, please consult with the appropriate air monitoring EPA Region 4 state contact. Since
each site, pollutant, and circumstance can be different, EPA Region 4 would like the
opportunity to provide input early in the process on a proposed analysis. Example analyses
that may be appropriate include scatter plot/correlation analyses, summary statistics
(maximum, minimum, median, variance), and boxplots.
In limited cases, a narrative and descriptive discussion may be a sufficient demonstration. For
example, at a source-oriented site, an obstruction might not interfere with measuring air from
a target source due to the orientation of the source, orientation of the monitor, and typical
wind patterns.
II. Demonstrate that the monitor or probe cannot reasonably be located to meet the siting
criteria because of physical constraints.
To demonstrate that this requirement is met, provide a list or table, and a map of other
candidate sites that were considered. The list should demonstrate that no sites are available in
the area suitable for the intended monitoring objective that meet siting criteria requirements
and describe the other sites that were considered and why they were not selected.
When identifying a candidate site's suitability, statements like "Site does not meet X siting
criterion," or "Site meets all siting criteria, but property owner is not agreeable to housing the
monitoring site" are acceptable. This requirement may be easier to demonstrate for source-
oriented sites that are intended to characterize the maximum concentration near a source, since
the number of areas expected to experience maximum concentration may be limited. More
alternative sites can be considered for sites that are representative of a larger spatial scale. For
sites with larger spatial scales (e.g., neighborhood or larger scale ozone or PM2.5 sites), suitable
sites can usually be found that both meet the intended monitoring objective and meet siting
criteria requirements.
Please consult with the appropriate air monitoring EPA Region 4 contact when considering an
analysis or discussion to demonstrate that the proposed site cannot be reasonably located to
meet siting criteria. Each site, pollutant, and circumstance can be different. The Region would
like the opportunity to provide input on a proposed analysis or rationale as early in the
process as possible.
EPA state air monitoring contact can assist in developing an appropriate sensor study for your application. While air
sensors may present a lower-cost alternative to operating concurrent monitors, data from air sensors that have not
been designated by EPA as Federal Reference Methods or Federal Equivalent Methods cannot be used for regulatory
decisions related to the national ambient air quality standards. EPA's Air Sensor Toolbox is available at: epa.gov/air-
sensor-toolbox.
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