Since 1980, the U.S. Environmental Protection Agency (EPA) has defined “ambient air” at 40 CFR §50.1(e) as “that portion of the atmosphere, external to buildings, to which the general public has access.” In applying this definition, many sites and studies conducting ambient monitoring or dispersion modeling have been required to include fence lines, right-of-ways, company-owned but not fenced properties, open areas, waterways, and other public access limited areas. “Physical barriers” or “fences” were generally considered to be necessary to fulfill this requirement, and exclusions were rare for other company-owned or other areas limited by accessibility. In a memorandum from Andrew R. Wheeler (Director, U.S. EPA) to all Regional Administrators on December 2, 2019, the EPA updated the policy on the exclusion of certain areas from the scope of “ambient air,” without changing the definition of ambient air.

In 1980, the EPA Administrator, Douglas Costle, wrote a letter to Senator Jennings Randolph that included a policy to exclude the “atmosphere over land owned or controlled by the [stationary] source to which public access is precluded by a [fence or other physical barriers].” The 2019 update to the policy addresses the underlined section.

Discussion topics included in the December 2 memorandum are:

  • “Legal” vs. “physical” aspects of trespassing
  • General public definition, in terms of private owners, employees, owners and invitees
  • Determination of whether the general public can actually enter a parcel of land, or whether physical restraints would prevent such entry (dense vegetation, waterbodies, steep cliffs or other rugged terrain)

Thus, EPA recognized that electronic security measures have advanced much since 1980 and that future technologies may potentially be used to preclude public access. So, EPA's revision recognizes that a fence or other physical barrier is not the only type of measure that may be used to establish that the general public does not have access to land that is owned or controlled by the source. Thus, a source may employ measures, perhaps including physical barriers, that are effective in preventing access to the land by the general public. As stated by the attachment to the December 2 memorandum, some of these additional measures may include video surveillance, monitoring, clear and exclusionary signage, routine security patrols, and even the possible use of drone technology to monitor property boundaries.

One topic to be aware of in the December 2 memorandum, is whether or not enforceable permit conditions would be required as part of an air permit to make non-physical barriers count as precluding access. One air agency commented that a physical fence could be viewed as being permanent for the life of the facility, but a non-physical measure may warrant consideration on a permit term basis. EPA seems to put this issue aside, just saying that the appropriateness of permit conditions should be reviewed on a case-by-case basis, and that a rule of reason will be applied in evaluating the effectiveness of any measures proposed by a source. Under this revised policy, measures may be considered effective, under some circumstances, even if they do not provide 100 percent certainty of preventing public access.

Earlier consideration by the EPA in the draft ambient air policy (regarding exclusion of lakes, rivers, and other waterbodies as well as roadways and trainlines due to short exposure periods) was no longer considered in this final ambient air memorandum.

This revision to the interpretation of precluding the public from access via fences or other physical barriers is welcome relief to facilities where fences are not always possible. The way this may be interpreted will depend on your EPA Region and state. We are glad to provide more details on how it can be rolled into current and future permitting specific for state and facility, please contact Trinity at (972) 661-8100.