DRAFT
Revised Policy
On Exclusions from "Ambient Air"
I nileil Suites Environmcnl;il Protection Agency
\o\ember 2018
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I. INTRODUCTION
The Environmental Protection Agency (EPA) defines "ambient air" as "that portion of
the atmosphere, external to buildings, to which the general public has access" 40 CFR § 50.1(e)
(emphasis added). The regulatory definition plainly excludes areas that are inside buildings, and
such areas are not specifically addressed in this document. However, the EPA has long
recognized that some areas that are external to buildings are also not covered by the regulatory
definition of ambient air. In 1980, Administrator Douglas Coslle wrote a letter to Senator
Jennings Randolph saying that the EPA was retaining the policy that "the exemption from
ambient air is available only for the atmosphere over land o\\ ned or controlled by the source and
to which public access is precluded by a fence or other physical barriers" (emphases added).1
Stakeholders have identified situations arising in specific air quality analyses (e.g., in the
Prevention of Significant Deterioration (PSD) permitting process), that the EPA may not have
considered when it issued the 1980 letter. These stakeholders have argued that the application of
the ambient air policy is overly restrictive and that, given the advances in surveillance and
monitoring capabilities and the variety of ambient air situations that have arisen since 1980, the
restrictive language from the 1980 letter that solely focuses on the use of "a fence or other
physical barriers" to preclude public access should he updated to provide for consideration of
additional types of measures that are effecti\ e in deterring or precluding access to the land by the
general public, and that can he implemented consistent with the regulatory definition of ambient
air.
As stakeholders ha\ e noted, the ability of a regulated entity, such as a PSD permit
applicant, to exclude a particular area of land from a specific air quality analysis has generally
depended on the source showing that the public does not have access to that area. Historically, a
source has been expected to demonstrate that (1) the area, although external to buildings, is
owned or controlled In the source, and (2) access to the area by the public is precluded by means
of a fence or other physical barriers. Tor example, a PSD permit applicant generally has been
able to exclude lYom its air quality analysis the site of the proposed source where that site is
owned by the source and the site is fenced so as not to allow access by the general public.
As articulated by Administrator Costle, the EPA's policy has been that an area's
exclusion from ambient air is a\ ailahle only if both conditions described above are met. At the
same time, Administrator Costle said that the "EPA will continue to review individual situations
on a case-by-case basis to ensure the public is adequately protected."2 Considering the wording
of that policy, the EPA has often expressed in individual cases that both conditions, i.e., (1)
ownership or control and (2) preclusion of public access by physical barriers, should be satisfied
in justifying the exclusion of an area from ambient air. However, notwithstanding that historic
1	Letter from EPA Administrator Douglas Costle to Senator Jennings Randolph, Chairman, Committee on
Environment and Public Works, December 19, 1980 (1980 letter).
2	The Administrator also said that the EPA would seek to ensure "that there is no attempt by sources to circumvent
the requirement of section 123 of the Clean Air Act." Section 123 of the CAA states that the emissions limitations
required under state implementation plans (SIPs) shall not be affected by the use of air pollutant dispersion
techniques.
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approach, the EPA has never codified either of these two conditions in the regulatory definition
of ambient air or elsewhere in regulations.
The policy articulated by Administrator Costle has over time resulted in concerns, such as
those expressed by parties seeking to obtain permits under the PSD program, especially after the
promulgation of increasingly stringent National Ambient Air Quality Standards (NAAQS) (such
as the 1-hour 2010 nitrogen oxide and sulfur dioxide standards ) The EPA has received
numerous stakeholder requests to clarify what areas may he excluded from ambient air in
required air quality analyses, consistent with applicable regulations. Additionally, in accordance
with the President's initiative to promote regulatory reform, including the streamlining of the
federal permitting processes,3 stakeholders have identified the ambient air policy as a topic that
they would like the EPA to address.
In response, the EPA has evaluated its ambient air policy and identified an element of the
policy that warrants revision.
II. BACKGROUND
As discussed above, the EPA's longstanding policy has been that the general public
should not be deemed to have access to land occupied by a stationary source (or that would be
occupied by a proposed stationary source or modification) when the land meets both of the
following two conditions (I) the land is "ow ned or controlled" by the owner or operator of the
stationary source; and (2) the land is surrounded by a fence or other physical barriers that
preclude general public access to it Although not expressly stated by Administrator Costle in
1980, it is clear that these conditions of the policy have been fundamentally grounded on an
interpretation of the regulatory phrase "to which the general public has access." In a 2007 memo,
the EPA explained that it uses "controlled" in the context of the first condition of the policy to
mean that the owner or operator of the source has the legal right to use the land, and that its land-
use right includes "the power to control public access" and "the power to exclude the general
public."4 The EPA has also explained that the second condition calls for a source to actually take
steps to preclude the general public from accessing the property "by relying on some type of
physical barrier (such as a fence, wall, or natural obstructions)"5 Thus, the first condition
establishes that the general public does not have access in a legal sense (is not permitted to enter)
while the second establishes that the general public does not have access in a practical or
physical sense (is not able to enter). The EPA has also recognized that some persons that have
both legal and practical access to the property are not necessarily considered members of the
general public, such as employees of the owner or operator who work at the site, or "business
invitees," such as contractors or delivery persons.6
3	Executive Order 13777, 82 FR 17793 (April 13, 2017).
4	Memorandum from Stephen D. Page, EPA OAQPS, to EPA Regional Air Division Directors, "Interpretation of
'Ambient Air' in Situations Involving Leased Land Under the Regulations for Prevention of Significant
Deterioration (PSD)," attachment at 2-3, June 22, 2007.
5	Id., attachment at 2.
6	Id., attachment at 5-6.
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Over the years, the EPA has provided clarifying guidance to explain how the definition of
ambient air, and the associated ambient air policy, should be applied under specific
circumstances for air quality analyses, such as analyses used to demonstrate compliance with the
NAAQS and PSD increments within the PSD permitting process. For example, in the
aforementioned 2007 memo, we explained how the EPA intended to apply the definitions of
"ambient air" and "building, structure, facility, or installation" to arrangements where a source
locates on land that it leases from another entity. The I -PA has pi o\ ided its views in other cases,
on a case-by-case basis, concerning the adequacy of certain types of fencing or other physical
barriers (e.g., a steep cliff or rugged terrain) based on the I.IWs understanding of the core
concept of "access" to an area of land by the public, as this term is used in the regulatory
definition of ambient air.
In addition to seeking assistance from the EPA in case-specific permitting situations,
stakeholders have requested that the EPA reconsider aspects of the ambient air policy that they
consider to be inflexible or outdated, such as the need to demonstrate NAAQS attainment just
beyond the property boundary in areas where few or 110 members of the general public are
expected to be present. As relevant here, stakeholders have specifically argued that the EPA's
historic focus on a fence or other physical barriers is outdated in that it does not address or allow
consideration of the additional ways by which a facility can deter or preclude public access (e.g.,
routine security patrols, remote surveillance cameras, drones). They point out that fences or
physical barriers arc not mandated by the regulatory definition of ambient air and, therefore, the
EPA's ambient air policy should not consider them to be the only allowable means of preventing
access by the general public
I11 its re\ ieu of indi\ idual situations 011 a case-by-case basis, the EPA in a few instances
has agreed that an area may qualify for exclusion from ambient air notwithstanding the fact that
the specific property or facility at issue, or a certain portion of the property or facility, was not
completely surrounded by a fence or other physical barriers.7 In one instance, the EPA granted
an exclusion based on a means of preventing or deterring practical access by the general public
other than a fence or other physical barriers. The United States Court of Appeals for the Ninth
Circuit reviewed and upheld the exclusion, finding that although fencing or other physical
barriers were not used, other methods were used to effectively preclude public access, and "[t]he
essence of the EPA's regulatory definition links ambient air to public access."8'9 Although that
case involved permitting of a source located over water, where installation of a fence or other
physical barriers was not feasible, the language of the regulatory definition of ambient air does
not preclude extending this reasoning to other factual situations. For example, there are situations
over land where it may also be impractical or unduly burdensome to require a source to install a
fence or other physical barriers when other means of precluding or deterring access by the
general public may be equally effective. Indeed, as discussed above, the EPA has on occasion
already supported excluding some areas of land from ambient air by recognizing that access by
7	See, e.g., 50 FR 7056, 7057 (Feb. 20, 1985) (allowing ambient air exclusion based on cumulative effect of
company's extensive property holdings, installation of fences, posts, and no-trespassing signs, security patrolling,
and the rugged mountainous terrain).
8	See REDOIL v. EPA, 716 F.3d 1155, 1164-65 (9th Cir. 2012) (A proposed offshore drill ship in the Arctic Ocean
seeking a PSD permit was allowed to exempt from ambient air a "safety zone" surrounding the ship that was
established by the U.S. Coast Guard and effectively precluded public access).
9	See Arco Alaska Permit Application for Beaufort Sea Exploratory Drill Project, March 1, 1993.
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the general public may be effectively precluded or deterred by means other than a fence or other
physical barriers and still be consistent with the regulatory definition of ambient air.
III. CORE ELEMENTS OF REGULATORY DEFINITION OF "AMBIENT AIR"
In response to stakeholders' concerns, the EPA has evaluated the terms in the regulatory
definition of ambient air and identified three core conceptual elements: "access," "general
public," and "external to buildings." The EPA has then assessed how it has been applying each
of these terms or phrases under the existing ambient air policy and whether additional flexibility
may be appropriate within the context of the regulatory definition of ambient air. The EPA
concludes that it is reasonable and appropriate to adopt and apply a revised policy addressing
how public access to land may be precluded in order to facilitate greater flexibility while at the
same time ensuring that the public health protection afforded In current Clean Air Act programs
is not eroded.
Consistent with the EPA's past practice and the discussion aho\ e. the access element of
the ambient air policy encompasses two concepts physical or practical access, and legal access.
First, the physical or practical aspect addresses ^ hether the general public has the physical or
practical ability to enter a particular parcel of land As discussed above, the EPA previously
stated in the 1980 letter that for an area to be excluded from ambient air, public access should be
precluded by means of a fence or other physical barriers \otw ithstanding this earlier policy
statement, however, in some situations the I-PA has subsequently found that a natural barrier,
such as a steep cliff or rugged terrain, may he an adequate substitute, in lieu of a fence, to
prevent public access.
The EPA's revised ambient air policy replaces "a fence or other physical barriers" with
"measures, which may include physical barriers, that are effective in deterring or precluding
access to the land by the general public "" The EPA expects that this change in its ambient air
policy will pro\ ide greater flexibility in determining where to place modeling receptors for air
quality analyses, while maintaining public health protection.
Willi ad\ ances in technology and greater experience in a variety of ambient air scenarios
since the 19N<) letter, the EPA believes there are various measures other than fencing or other
physical barriers that a facility can employ to serve as an effective deterrent to public access.
These measures may include traditional fencing, but may also include video surveillance and
monitoring, clear signage, routine security patrols, drones, and other potential future
technologies. In many cases, such measures are already being used as effective means to deter or
preclude public access to private property, even if not specifically for purposes of an ambient air
exclusion.
Air agencies should evaluate the effectiveness of a "measure" in precluding public access
based on the relevant, specific circumstances. This evaluation should address relevant factors,
such as the nature of the measure used (e.g., physical or non-physical), facility location (e.g.,
rural or urban), type and size of facility and property to be excluded, surrounding area (including
the proximity, nature, and size of the population in the area), and other factors affecting the
extent to which persons would be likely or able to trespass upon or otherwise have access to the
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facility's land. Air agencies should consider any information provided by the regulated entity, or
otherwise available to the air agencies, regarding the effectiveness of the measures to prevent
public access. For instance, the use of clearly visible, well-spaced "No Trespassing" signs, either
with or without fencing, may be effective in certain areas. Another example of an effective
measure may involve atypical public access such as swamps and large tracts of undeveloped
private land. In other cases, where there is a greater incentive for persons to access or trespass
over the property (e.g., to shorten the walking distance to a destination), it may be necessary to
use a combination of measures, and not solely signage, to adequately preclude public access.
It is not the intent of this revised policy to prescribe the specific types of measures
(physical barriers or otherwise) that should be used but, instead, to provide guidance to air
agencies when assessing whether measures to prevent public access are sufficient under the
circumstances to exclude an area from ambient air. The goal of such an assessment is to ensure
that the measures in question are effective in preventing or deterring public access. Air agencies
are expected to apply a rule of reason in assessing the effectiveness of proposed measures. Even
under the prior policy, it was always possible for some fences to be scaled and other types of
barriers to be breached. It is generally recognized that a fence is an effecli\ e means of precluding
or deterring public access, even if it might not in all concei\ able cases pre\ enl site access.
Similarly, under this revised policy, measures may lx- considered to be acceptable even if they
are not 100 percent effective in pre\ enling public access Instead, measures should provide
reasonable assurance that the general public w ill not ha\ e access
The second aspect of the access element concerns whether the public is legally precluded
from entering onto Ihe property l\\ its owner. The l-IWs historic policy states that an exclusion
from ambient air is a\ ailable only lor areas owned or controlled by the source, which generally
means that the source has legal authority to preclude access by the public to the area of land it
owns. This revised policy makes no change in this regard.
As pre\ iously stated, determinations concerning the adequacy of such measures can only
be made In air agencies on a case-by-case basis after consideration of the relevant administrative
record in each case. Where air agencies seek EPA's assistance in making such determinations,
the EPA will address these requests via the Ambient Air Review Team (AART). The AART is
responsible for e\ aluating ambient air issues, in conjunction with the appropriate EPA regional
office, to ensure nationally consistent implementation of the ambient air policy.
IV. CONCI.l SION
In setting forth this revised ambient air policy, the EPA is making a limited change to the
way it applies the regulatory definition of ambient air, while maintaining public health
protection. This change replaces the specific concept of a fence or other physical barriers with
the more general concept of measures, which may include physical barriers, that are effective in
deterring or precluding access by the general public. Accordingly, the EPA's revised ambient air
policy, consistent with its discretion available under the regulatory definition of ambient air, is
that it is appropriate to exclude the atmosphere over land owned or controlled by the stationary
source, where the owner or operator of the source employs measures, which may include
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physical barriers, that are effective in deterring or precluding access to the land by the general
public.
This revised policy should be implemented by EPA Regional offices and delegated state
and local air agencies, e.g., for the issuance of federal PSD permits. The EPA expects each air
agency with a State Implementation Plan-approved program to ensure that its ambient air policy
is applied consistent with the definition of ambient air contained in its approved program.
This revised policy is neither a regulation subject to notice-and-comment rulemaking
requirements nor a final agency action and does not creak- or change any legal requirements on
the EPA, on state, local, and tribal agencies, or on the public This document does not provide
any final determination that any particular area may be excluded from ambient air on the basis of
particular measures taken to deter or preclude access, since determinations concerning the
adequacy of such measures can only be made by air agencies 011 a case-by-case basis after
consideration of the relevant administrative record in each case.
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