15 U.S. Code § 2663 - EPA citizen’s guide
In order to make continuous progress toward the long-term goal established in section 2661 of this title, the Administrator of the Environmental Protection Agency shall, not later than June 1, 1989, publish and make available to the public an updated version of its document titled “A Citizen’s Guide to Radon”. The Administrator shall revise and republish the guide as necessary thereafter.
(b) Information included
(1) Action levels
The updated citizen’s guide published as provided in subsection (a) of this section shall include a description of a series of action levels indicating the health risk associated with different levels of radon exposure.
(2) Other information
The updated citizen’s guide shall also include information with respect to each of the following:
(A) The increased health risk associated with the exposure of potentially sensitive populations to different levels of radon.
(B) The increased health risk associated with the exposure to radon of persons engaged in potentially risk-increasing behavior.
(C) The cost and technological feasibility of reducing radon concentrations within existing and new buildings.
(D) The relationship between short-term and long-term testing techniques and the relationship between
(ii) the actions  levels set forth as provided in paragraph (1).
 So in original. Probably should be “action”.