U.S EPA recently issued a draft guidance document titled Revised Policy on Exclusions from “Ambient Air” (Draft Guidance) in which the Agency revises its 1980 policy on the exclusion of certain areas from the scope of “ambient air” under the Clean Air Act. Under the National Ambient Air Quality Standards (NAAQS) program, “ambient air” is defined as “that portion of the atmosphere, external to buildings, to which the general public has access.” 40 CFR 50.1(e). Longstanding EPA policy provides that the regulatory definition of “ambient air” excludes the atmosphere “over land owned or controlled by the source and to which public access is precluded by a fence or other physical barriers.” The Agency’s policy is based on three core conceptual elements in the regulatory definition of ambient air: (1) access, (2) general public, and (3) external to buildings.

Most EPA determinations regarding the applicability of the exclusion have focused on the access element. Notably, EPA has explained that the access element of the ambient air policy encompasses two concepts – physical or practical access, and legal access. In response to stakeholder requests that EPA consider revising the policy to provide for more flexibility, and after considering past case-specific decisions, the Agency determined that physical barriers are not the only means of satisfying the access element of the exclusion from ambient air.

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 The Draft Guidance instructs air agencies to evaluate the effectiveness of a “measure” in precluding public access based on the relevant, specific circumstances, and notes that video surveillance, monitoring, clear signage (with or without fencing), routine security patrols, drones, swamps or large tracts of undeveloped land surrounding a facility may adequately preclude public access.

EPA is accepting comments on the Draft Guidance through December 21, 2018.