Change is in the Air — Ambient Air, that is.

Change is in the Air — Ambient Air, that is.

The EPA has extended the comment period for a draft policy revision regarding the definition of “ambient air” until January 11, 2019. For some facilities that own property well beyond their fence-line or can demonstrate that there is additional buffer or space around the facility, the draft policy revision may provide an opportunity to obtain substantial relief in demonstrating compliance with the recent, much stricter, short-term ambient air quality standards. Such facilities should take the opportunity to comment on the proposed revisions.

Ambient air is defined in the Clean Air Act (code 40 CFR 50.1[e]) as: “that portion of the atmosphere, external to buildings, to which the general public has access.” This seems a relatively straightforward definition — if anyone can get to an outdoor location, it represents ambient air, even if it is unrestricted private property. However, what is of most interest to facility owners having sources of air emissions is what is excluded from ambient air and therefore not required to be included in an ambient air quality compliance demonstration.

Existing policy, reinforced by EPA Administrator Douglas Costle in his 1980 letter to Senator Jennings Randolph, is that “the 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.” That has been the guidance followed by regulatory agencies and imposed on sources of air emissions since then.

Whenever a source of air emissions is required to demonstrate compliance with a national ambient air quality standard or other potential impact from its permitted operations, it must assume that the public has access everywhere, including property owned by the source, unless there is a physical barrier keeping anyone unauthorized from entering that space. Whether the source chooses to use an ambient air monitor to demonstrate compliance or is required to apply an air dispersion model to assess potential impacts, it must do so at the physical barrier or fence line establishing the ambient air boundary and beyond.

Over the years, sources have sought relief from the hard and fast policy of establishing a physical barrier or fence around a facility, especially in remote areas where public access is unlikely, or where existing natural barriers physically make public access unlikely or impossible (e.g. water bodies, cliffs, swamps, etc.). EPA has considered these requests on a case-by-case basis and in a few cases has determined that the general public is effectively precluded access or deterred by means other than a man-made physical barrier or fence.

The draft revised policy issued by EPA in November 2018 recognizes recent technological advances and the availability of measures other than fences and physical barriers, such as video surveillance and monitoring, drones, or security patrols that can be used as effective means to deter or prevent access to certain areas.

The proposed update would replace “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.” This change is expected to provide greater flexibility for sources to request and for regulatory agencies to consider, where appropriate, which cost-effective and practical measures, other than a fence, can be used to establish the “ambient air” boundary for the facility.

The draft policy revision provides guidance on factors to consider in evaluating potential public access restriction measures based on the circumstances of a case-by-case assessment. EPA acknowledges that it may be appropriate to include certain measures for establishing the “ambient air” boundary of a facility even if they are not 100 percent effective in preventing public access.

For those facilities that own property well beyond their fence-line or can demonstrate that there is additional buffer or space that can be excluded from ambient air designation, the draft policy revision may provide an opportunity to obtain substantial relief in demonstrating compliance with the recent, much stricter, short-term ambient air quality standards. These include the 1-hour average sulfur dioxide and nitrogen dioxide standards and the 24-hour fine particulate standard. Facilities with large tracts of property contemplating expansion, modification or construction of new air emission sources that require an ambient air compliance demonstration would be well served to consider this policy change. It may mean the difference between having to consider costly higher-efficiency emission controls, accepting unnecessarily restrictive permit terms, or even scaling back a proposed project. 

Our engineers and air-quality permitting and compliance staff can assist in evaluating the potential benefits of the ambient air draft policy change from a federal perspective as well as how it may apply to specific state or local permitting agencies. We can also help to identify and evaluate potential alternative measures and resulting ambient air boundaries, and assess the potential air quality impacts at the new boundary via dispersion modeling sensitivity analyses. We welcome the opportunity to discuss the proposed policy change and assist with any permitting or compliance challenges you may face.

Author

National Practice Leader
Air Services

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