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EPA Finalizes Revised "Ambient Air" Guidelines

On December 2, 2019, EPA Administrator Andrew Wheeler issued the "Revised Policy on Exclusions from 'Ambient Air'" to update its "policy on the exclusion of certain areas from the scope of 'ambient air'" under the Clean Air Act's NSR programs. EPA's new policy guidance is that "the atmosphere over land owned or controlled by the stationary source may be excluded from ambient air where the source employs measures, which may include physical barriers, that are effective in precluding access to the land by the general public."


The EPA's revised policy begins by tracing the history of the ambient air definition and exclusion. Administrator Wheeler stated that EPA's current policy took shape in 1980, when Administrator Costle issued a letter stating that "exemption from ambient air is available only for the atmosphere over land owned or controlled by the source and to which public access is precluded by a fence or other physical barriers." This policy was criticized by the GAO, but EPA left it in place for 40 years.

In issuing the revised policy, Administrator Wheeler states that EPA had received requests from industry representatives to allow regulatory authorities to consider additional types of measures, besides fences or other physical barriers, to preclude public access. A draft revision was released and 37 comments received. Based upon review of those comments, EPA determined that it would proceed with a revision of the policy to allow more measures.

In the revised policy memo, Administrator Wheeler states that the exclusion of areas from "ambient air" rests upon the regulatory phrase "to which the general public has access" and that the EPA has always required two steps for sources seeking to exclude an area from coverage by the NAAQS (and increments): (1) the source must show a legal right to control entry to land; and (2) the source must take practical steps to preclude access. Based on this understanding, Administrator Wheeler noted that the EPA historically had provided guidance addressing situations where a source locates on the property of another source, whether a steep cliff or rugged terrain may be an adequate physical barrier, noting that in 1985, the EPA had allowed an ambient air exclusion "based on the cumulative effect of a company's extensive property holdings, installation of fences, posting of 'No Trespassing' signs, security patrolling and the rugged mountainous terrain." Similarly, EPA had recently allowed a source located in water to use a regulatory exclusion zone and patrols to define the ambient air boundary, which the Ninth Circuit had upheld in REDOIL v. EPA, 716 F.3d 1155 (9th Cir. 2012).

In responding to comments on the draft revision, Administrator Wheeler stated that those advocating for "legal access" as the only criterion were reading it too narrowly. As he observed, "an alternative reading of 'general public' that excludes all persons on any private property to which access is restricted (e.g., private homeowners with fenced yards) would expand the exclusion beyond reason and deny the protection of the NAAQS to large numbers of people." Policy, at 6. Instead, only the source owner/operator and its employees or business invitees are not "general public."

The EPA revised policy memo next discusses the "practical preclusion" aspect of its policy. Here, Administrator Wheeler found that there are other forms of precluding access effective at this time, such as patrols and signage, and other measures, such as drones and advanced video surveillance, that might become effective in the future. Accordingly, Administrator Wheeler stated:

Rather, this revised policy calls for staff at the EPA (and other air agencies as well) to carefully assess measures proposed by a source to preclude public access under specific factual circumstances. The goal of such an assessment is to be satisfied that the measures (whether physical or not) proposed by a source are effective in precluding public access under the circumstances presented. Thus, under this revised policy, measures may be considered effective, under a given set of circumstances, even if there is not 100 percent certainty that they will prevent public access.

Policy, at 8.

In the closing part of the revised policy, Administrator Wheeler addressed comments by some that the means of preclusion should be assured by permit conditions. Administrator Wheeler determined that this is not always necessary, and stated that EPA and permitting authorities should consider whether the measures precluding access might require a permit condition on a case-by-case basis.

In closing, Administrator Wheeler stated that the EPA's new "ambient air policy" would is as follows:

Thus, the EPA 's revised ambient air policy, consistent with its discretion available under the regulatory definition of ambient air, is that the atmosphere over land owned or controlled by the stationary source may be excluded from ambient air where the source employs measures, which may include physical barriers, that are effective in precluding access to the land by the general public.


The EPA's revised ambient air policy issued by Administrator Wheeler is a fairly narrow revision of the existing policy. It rejected requests to broaden the exclusion by focusing on "legal" access solely, rather than practical access, thus leaving in place protections for the general public in areas where they routinely congregate even if on private land. It also rejected a broader reading of "precluded" from access, to limit the area of preclusion to only the area controlled by the source owner/operator. On the other hand, it broadened the scope of "measures" that a source can take to preclude practical access in line with advancments in technology since the 1970s and 1980s. In so doing, the EPA has hewed a carefully balanced line between protecting public health while reforming a policy that, over time, has proven rigid and and threatens to become increasingly costly in its former insistence on "physical barriers" only.

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