Data gap or significant data gap

Something the standard requires could not be had: part of the subject property could not be seen, the key site manager could not be interviewed, the sources for the early history ran out. That is a data gap only if the information was required and good faith efforts were made to get it. It is a significant data gap only if it affects the ability to identify a recognized environmental condition (REC). The answer depends on three things: whether the information was required, what was done to get it, and what the rest of the assessment says about the hole.

What the answer turns on

Whether the information was required. A data gap is a lack of, or an inability to obtain, information the practice requires; its own examples are a site visit that could not be made and an interview that could not be held (E1527-21, 3.2.19). Records are required only where reasonably ascertainable: publicly available, obtainable within 20 calendar days of a request for no more than a nominal charge, and practically reviewable (E1527-21, 8.1.4, 8.1.5). A listing without the address information to be located is not generally practically reviewable (E1527-21, 3.2.65). Historical research that reviews every standard resource that can reasonably be had and is likely to help, and still falls short of its objective, is a data failure, one type of data gap (E1527-21, 3.2.18, 8.3.6).
What was done to get it. The definition counts only what could not be had though the environmental professional made good faith efforts (E1527-21, 3.2.19). Where neither standard nor alternative sources can reasonably supply a record, the professional attempts to get the information by the practice's other means, such as questions to the owner or occupants (E1527-21, 8.1.7). An interview section is not incomplete merely because a person other than the user gave no answer or a partial one, if a record was kept and a follow-up was made (E1527-21, 10.7.2).
What the rest of the assessment says. A data gap is not significant by itself. It is significant when it affects the professional's ability to identify a REC (E1527-21, 3.2.78): when other information or experience raises reasonable concerns about what the gap does to the ability to give an opinion on whether conditions indicative of RECs or controlled RECs exist (E1527-21, 12.5.1). The standard gives an example each way. A history not traced to 1940 for want of sources, where the earliest source shows the subject property undeveloped, might not be significant by itself. A building that could not be entered on the site visit, where the professional's experience is that such a building's use is often tied to activity that ends in a REC, would be (E1527-21, 12.5.1).

The records that bear on it

Records. Each source checked is documented, even one that revealed no findings (E1527-21, 8.1.9). A reduced search distance and a file not reviewed each need a stated reason (E1527-21, 8.1.2.1, 8.2.3.1).
History. The report documents a data failure, says why any standard historical resource was left out, and explains gaps in the history of use (E1527-21, 8.3.6, 8.3.8).
Site visit. Limits on what could be seen are noted on the visit and documented in the report (E1527-21, 9.2.6).
The user. The report notes whether the user reported the user's own information; if not, the professional should consider what that absence means (E1527-21, 6.1, 7.3.2).

What the federal rule says

The rule defines the term and says what to do about one. A data gap is

a lack of or inability to obtain information required by the standards and practices listed in subpart C of this part despite good faith efforts by the environmental professional

40 CFR 312.10

The definition goes on to count the efforts of the persons the rule applies to, as appropriate. Where gaps bear on what the inquiry can find, the rule says

such persons should identify such data gaps, identify the sources of information consulted to address such data gaps, and comment upon the significance of such data gaps

40 CFR 312.20(g)

The rule has no separate term for a significant data gap. It permits sampling and analysis as a way to fill a gap, and where gaps leave the professional unable to reach an opinion, it requires that to be noted in the opinion itself (40 CFR 312.20(g), 312.21(c)(2)).

How it is written up

Where the information was not required, or was had from another source, no data gap arises; the sources checked are still documented (E1527-21, 3.2.19, 8.1.9).

Where a data gap exists and the professional judges it not significant, the standard names no place for it; the documentation duties above still apply. The standard asks for significant data gaps in the Findings and the Conclusions (E1527-21, 12.5.1, 12.7).

Observation of part of the subject property on the site visit may be what cannot be had. 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).

For a significant data gap, the Opinions say what the missing information does to the professional's ability to judge whether the inquiry found signs of a release or threatened release, and should discuss whether more information would likely help. That is not a requirement to make recommendations (E1527-21, 12.6.2). The closing statement of the Conclusions either says no RECs, controlled RECs or significant data gaps were revealed, or lists those that were (E1527-21, 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.