What is a data gap?

A data gap is information the Phase I standard requires that is missing or could not be obtained, even though the environmental professional made good faith efforts to get it (E1527-21, 3.2.19). It is a significant data gap only when it affects the environmental professional's ability to identify a recognized environmental condition (E1527-21, 3.2.78). The report must deal with each significant data gap in its Findings, Opinions and Conclusions (E1527-21, 12.5.1, 12.6.2, 12.7).

The AAI rule defines a data gap in nearly the same terms, but there the good faith efforts may be those of the environmental professional "or persons identified under § 312.1(b), as appropriate" (40 CFR 312.10). Those are the persons the rule applies to: anyone seeking a landowner liability protection, and anyone assessing a site with a CERCLA section 104(k)(2)(B) grant (40 CFR 312.1).

What makes it a data gap

A data gap can arise in any required activity, among them the site reconnaissance, as when the site visit cannot be made, and the interviews, as when the key site manager or regulatory officials cannot be interviewed (E1527-21, 3.2.19).

The limits on what the practice requires therefore bear on it:

Records. Only records reasonably ascertainable from standard sources must be reviewed (E1527-21, 8.1.4). Information counts as obtainable within reasonable time and cost when the source provides it within 20 calendar days after receiving a request, for no more than a nominal charge to retrieve and copy it; where a record can only be read at the source, the test is whether the source allows a visit within 20 calendar days of the request (E1527-21, 8.1.5).
The site visit. The visit need not find hidden conditions, such as what lies behind walls, below floors or above ceilings, or what is on rooftops (E1527-21, 9.2.4.2). Physical limits on what could be seen, such as paving or snow, are noted and documented (E1527-21, 9.2.6).
Interviews. When someone other than the user does not answer, the interviews are not for that reason incomplete, if a record was kept of who was asked and any answers, and there was at least one reasonable follow-up (E1527-21, 10.7.2). For government officials, unanswered or partly answered questions do not leave the section incomplete, so long as they were put, or an attempt was made to put them, face to face or by phone, and a written record names the person asked and gives any answers (E1527-21, 11.8).

When a data gap is significant

The standard says a data gap is not significant in itself (E1527-21, 12.5.1). It is significant only where other information or professional experience gives reasonable grounds for concern about how the gap limits the environmental professional's ability to form an opinion on whether there are conditions pointing to RECs or controlled RECs (E1527-21, 12.5.1). The standard gives two examples (E1527-21, 12.5.1):

Data failure leaves the history short of 1940, but the earliest source found shows the subject property undeveloped. That gap alone might not be significant.
A building cannot be entered at the site visit, and the environmental professional's experience says buildings put to that use often involve activity that leads to a REC. Not being able to inspect it is a significant data gap: it goes in the Findings and is discussed in the Opinions.

What the report must say

Findings. Each significant data gap, and the resources or sources consulted to try to fill it (E1527-21, 12.5.1).
Opinions. A comment on how the missing information affects the environmental professional's ability to give an opinion on whether the inquiry found signs of releases or threatened releases. The environmental professional should also discuss whether more information would likely help decide whether a REC or controlled REC exists; this does not require any recommendation (E1527-21, 12.6.2).
Conclusions. Every significant data gap, listed with the RECs and controlled RECs (E1527-21, 12.7).

The rule's minimum for the written report includes the data gaps that bear on spotting signs of releases or threatened releases, with comments on their significance (40 CFR 312.21). It adds: "If there are data gaps such that the environmental professional cannot reach an opinion regarding the identification of conditions indicative of releases and threatened releases, such data gaps must be noted in the environmental professional's opinion in paragraph (c)(1) of this section" (40 CFR 312.21). The rule also says "Sampling and analysis may be conducted to develop information to address data gaps" (40 CFR 312.20). E1527-21 itself includes no sampling or testing (E1527-21, 7.4).

Data failure in the historical research

The standard counts data failure as a kind of data gap (E1527-21, 3.2.18). The historical research ends when its objective is met or when data failure is reached: every standard historical source that can reasonably be had and is likely to help has been checked, and the objective is still not met (E1527-21, 8.3.1, 8.3.6). The standard notes that this is not uncommon when uses are sought about every five years, as far back as 1940 or first use if earlier (E1527-21, 8.3.5, 8.3.6).

The report shall document the data failure and give the reason any standard historical resource was left out; if the failure amounts to a significant data gap, the report must say how it affects identifying RECs (E1527-21, 8.3.6). It shall also explain gaps in the history of use, and say why any of aerial photographs, fire insurance maps, local street directories or historical topographic maps was not reviewed (E1527-21, 8.3.8).

When the site visit cannot be made

The rule excuses the visual on-site inspection only in an unusual circumstance, where physical limits, a remote and inaccessible location or another inability to get access prevent it after good faith efforts (40 CFR 312.27). "The mere refusal of a voluntary seller to provide access to the subject property does not constitute an unusual circumstance" (40 CFR 312.27). The inquiry must then look at the property another way, such as by aerial imagery or from the nearest point that can be reached, document the efforts to get access and why they failed, and document the other sources consulted; that documentation should comment on how much the missed inspection matters (40 CFR 312.27(c)).

This page is general reference. It does not assess any property. ASTM E1527-21 is the standard and is not reproduced here.