UNITED STATES ENVIRONMENTAL PROTECTION AGENCY Office of Air Quality Planning and Standards Research Triangle Park, North Carolina 27711 January 21, 1986 MEMORANDUM SUBJECT: Receptor Locations In Ambient Air FROM: Joseph A. Tikvart, Chief /s/ Source Receptor Analysis Branch (MD-14) TO: Regional Modeling Contacts, Regions I-X As the attachments indicate, OAQPS has reinforced the position that the ambient air policy has been clearly defined and does not require review. The Regional Meteorologists' memorandum (dated 5/16/85) harmonizes modeling procedures with this long-standing policy. In future Model Clearinghouse actions we will use that memorandum to ensure consistent Regional implementation of that policy and to resolve questions about pollutant concentrations at receptor locations where the public has access. Attachments cc: R. Campbell T. Helms R. Rhoads D. Tyler D. Wilson (Attachments Following) Attachment UNITED STATES ENVIRONMENTAL PROTECTION AGENCY Office of Air Quality Planning and Standards Research Triangle Park, North Carolina 27711 January 22, 1986 William F. O'Keefe, Vice President American Petroleum Institute 1220 L Street Northwest Washington, D. C. 20005 Dear Mr. O'Keefe: Mr. Elkins has asked me to respond to your letter of December 18, 1985, in which you perceive a change in our policy with regard to the location of receptors for air quality dispersion modeling. Let me assure you there is no change in our long-standing national policy with regard to the definition of ambient air. That policy is based on 40 CFR Part 50.1 (e) which defines ambient air as ". . . that portion of the atmosphere, external to buildings, to which the general public has access." A letter dated December 19, 1980, from Douglas Costle to Senator Jennings Randolph, reaffirmed and clarified this definition by stating 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. A copy of Mr. Costle's letter is enclosed. The codified definition plus the 1980 clarification essentially constitute the national policy on ambient air. The Regional Meteorologists' memorandum to which you refer does not imply any change in this national policy and simply harmonizes modeling procedures with our long-standing policy. It is intended to ensure con- sistent Regional implementation of that policy and to dispel any questions about pollutant concentrations at locations where the general public has access. Thus, since the Regional Meteorologists' memorandum does not imply any change in our policy, I do not believe there is any need for policy review at this time. Sincerely, /s/ Gerald A. Emison Director Office of Air Quality Planning and Standards Enclosure cc: W. Quanstrom E. Elkins Attachment December 19, 1980 Honorable Jennings Randolph Chairman, Committee on Environment and Public Works United States Senate Washington, D.C. 20510 Dear Mr. Chairman: Thank you for your letter of October 23, 1980 expressing your continued interest in the Agency's definition of "ambient air." During the time since David Hawkins, my Assistant Administrator for Air, Noise, and Radiation, met with you last February, the definition has been extensively reviewed and debated. After reviewing the issues and alternatives, I have determined that no change from the existing policy is necessary. We are retaining the policy 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. EPA will continue to review individual situations on a case-by-case basis to ensure that the public is adequately protected and that there is no attempt by sources to circumvent the requirement of Section 123 of the Clean Air Act. I hope that this has been responsive to your needs. Sincerely yours, /s/ Douglas M. Costle Douglas M. Costle Attachment UNITED STATES ENVIRONMENTAL PROTECTION AGENCY Region V DATE: May 16, 1985 SUBJECT: Ambient Air FROM: Regional Meteorologists, Regions I-X TO: Joseph Tikvart, Chief (MD-14) Source Receptor Analysis Branch At the recent Regional Meteorologists' meeting in Dallas, we identified inconsistencies among the Regional Offices on what areas are to be considered as ambient air for regulatory purposes. The existing incon- sistency on ambient air is due to both the lack of clear National guidance and the allowed Regional Office discretion. A standardized approach is necessary both to satisfy the consistency requirements of Section 301 of the Clean Air Act and in order for those responsible for Regional modeling activities to provide effective and efficient review of and guidance on modeling analysis. Accordingly, the Regional Meteor- ologists have decided to address the problem at the working level through the use of a consistent modeling approach. 40 CRF Part 50.1(e) defines ambient air as ". . . that portion of the atmosphere, external to buildings, to which the general public has access." A letter dated December 19, 1980, from Douglas Costle to Senator Jennings Randolph, clarified this definition by stating 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." The codified definition plus the 1980 clarification essentially constitute the National policy on ambient air. The Regional Meteorologists propose that for modeling purposes the air everywhere outside of contiguous plant property to which public access is precluded by a fence or other effective physical barrier should be considered in locating receptors. Specifically, for stationary source modeling, receptors should be placed anywhere outside inaccessible plant property. For example, receptors should be included over bodies of water, over unfenced plant property, on buildings, over roadways, and over property owned by other sources. For mobile source modeling (i.e., CO modeling), receptors should continue to be sited in accordance with Volume 9 of the "Guidelines for Air Quality Maintenance Planning". Unless you disagree with our position, we will require new actions with modeling analyses submitted to EPA after January 1, 1986, to conform to this modeling policy. Please note that all 10 Regional Meteorologists have reviewed and concur with this memo. cc: Regional Meteorologist, Regions I-X