Radon in a Phase I

A user or a lender asks whether the Phase I covers radon, or the history of the subject property includes material that gives off radon. The standard lists naturally occurring radon among its non-scope considerations (E1527-21, 13.1.5.13). Whether radon comes inside the assessment depends on three things: where the radon comes from, whether the concern is only the air inside a building, and what the user or the transaction asks for.

What the answer turns on

Where the radon comes from. The standard's appendixes are nonmandatory. The one on non-scope issues describes radon as a radioactive gas formed as uranium, radium and thorium break down naturally in soil, rock and groundwater (E1527-21, X6.2). The legal background appendix reports that radon and its decay products count as radionuclides, which the federal agency has designated hazardous substances under the cleanup law; that radon moving into a building would not normally be a release under that law where its source is naturally occurring; and that radon in a structure or on a property can count as a release of a hazardous substance where it comes from radioactive waste that was disposed of or spilled (E1527-21, X1.1.4.3(1), footnote 68). It also reports the federal agency's example of radium wastes disposed of in subsoil, with radon gathering in nearby homes, as able to bring liability under that law (E1527-21, X1.1.1.2(3)). The appendix on the recognized environmental condition (REC) definition says a release is not meant to cover most naturally occurring conditions (E1527-21, X4.1). The body of the standard names no use that involves radioactive material. Establish whether the history shows radioactive material disposed of or spilled on the subject property or near it.
Only the air inside a building, or a release. Indoor air quality unrelated to a release of hazardous substances or petroleum products into the environment is a separate non-scope consideration (E1527-21, 13.1.5.7). The REC definition asks whether hazardous substances or petroleum products are present or likely present at the subject property owing to a release or likely release to the environment, or present where conditions pose a material threat of one (E1527-21, 3.2.73). Migration covers movement in any form, with vapor in the subsurface among the standard's examples (E1527-21, 3.2.53); see vapor in a Phase I. The non-scope appendix ties radon's danger to gas building up in an interior space, and says building construction, ventilation systems and occupancy patterns affect actual exposure (E1527-21, X6.2, X6.2.3).
What the user or the transaction asks for. No assessment of a non-scope consideration is required for all appropriate inquiries as the practice defines them (E1527-21, 13.1.2). The practice includes no testing or sampling of air (E1527-21, 7.4). Work on naturally occurring radon is a service beyond the practice, which should be weighed against the property and the reasons for the assessment and agreed before the assessment begins (E1527-21, 1.4, 4.4). The non-scope appendix describes the federal agency's three radon zones, set by counties' predicted average indoor screening levels, and says the cost of investigating and reducing radon can matter in some transactions (E1527-21, X6.2.2, X6.2.4). For a multifamily loan the Federal Housing Administration insures, the Department of Housing and Urban Development's radon report is on radon on an FHA multifamily loan.

The records that bear on it

History of uses. The historical research is meant to show how likely it is that past uses led to RECs, and a specific use tells more than a general one (E1527-21, 8.3.1, 8.3.7).
Government records. The standard's tables of government records name no radon or radioactive material record (E1527-21, 8.2.2, Table 2, 8.2.4, Table 3). The inquiry rule says the review of records for the subject property should include public health records (40 CFR 312.26(b)(4)), and a state or local health agency is one of the kinds of agency the standard names for official interviews (E1527-21, 11.5.1.2). Pennsylvania's agency publishes radon test data by zip code, which the handbook's page treats as background and not as a building's result (Pennsylvania).

What the federal rule says

The inquiry rule (40 CFR part 312) does not mention radon. A party seeking the liability protections conducts the investigations it requires, the professional's inquiry among them,

to identify conditions indicative of releases or threatened releases, as defined in CERCLA section 101(22), of hazardous substances, as defined in CERCLA section 101(14).

40 CFR 312.1(c)(1), edition revised as of July 1, 2025

The legal background appendix notes that the rule points to the statute's definition of release, which carries exclusions, and does not say whether releases those exclusions cover have to be identified (E1527-21, X1.1.1.3). The appendix files the exclusion for naturally occurring substances, which it applies to radon, under the statute's limits on cost recovery (E1527-21, X1.1.4.3(1), footnote 67).

How it is written up

A use, a record or an observation that points to radioactive waste disposed of or spilled is a finding when the professional judges it may indicate hazardous substances present or likely present at the subject property, and the opinion gives the reasoning for or against each class the finding pertains to (E1527-21, 12.5, 12.6).

Where the professional concludes that radon or its source material is present or likely present at the subject property owing to a release of such waste into the environment, the opinion gives the grounds: the use, the disposal or spill, and the record or observation that shows it. Unless judged a de minimis condition or a historical REC, the REC is listed in the Conclusions, and the professional should give an opinion on additional investigation, if any (E1527-21, 3.2.20, 3.2.39, 12.7, 12.8).

Where the professional concludes the radon is naturally occurring, it stays a non-scope consideration (E1527-21, 13.1.2, 13.1.5.13). Radon work the user has engaged is reported only as the terms of engagement specify, and additions to the practice are listed (E1527-21, 12.10, 12.11). The suggested format in Appendix X5 places it in a non-scope services section, and lets business environmental risks that go with it be discussed in the Findings, Opinions and Conclusions (E1527-21, X5.7, X5.8, X5.9).

An interview with a staff member of a state or local agency, which the standard has the professional make a reasonable attempt to hold, may be what cannot be had (E1527-21, 11.5.1). Required information that good faith efforts could not obtain is a data gap, significant if it affects the ability to identify a REC: named in the Findings with the sources consulted, discussed in the Opinions and listed in the Conclusions (E1527-21, 3.2.19, 3.2.78, 12.5.1, 12.6.2, 12.7).

This page is general reference for environmental professionals. It does not classify any property. ASTM E1527-21 is the standard and is not reproduced here; the judgment of the environmental professional on the facts governs.