What is a data gap?

A data gap arises when a piece of information the standard calls for simply cannot be gotten, even after the environmental professional has genuinely tried: an inaccessible building area, an owner who will not respond to interview requests, historical sources that do not exist for the parcel, an agency file that did not arrive in time. ASTM E1527-21 requires the report to identify significant data gaps and the sources consulted in trying to close them.

The important distinction is between a data gap and a significant one. A gap matters when it affects the professional's ability to identify recognized environmental conditions. No fire insurance map coverage of a parcel that aerials show as farmland until 1985 is a gap without consequence. No historical coverage of the decades when the corner lot may have held a filling station goes to the heart of the inquiry, and the report should say what it means for the conclusions.

For a report reader, data gaps are a quality signal in both directions. A report with zero acknowledged gaps on a hundred-year-old urban property is claiming better information than usually exists. A report that lists gaps but never says whether they are significant, or uses them to hedge every conclusion, is passing its uncertainty to you unpriced. The professional's job is not gap-free research. It is stating plainly what is unknown and whether it matters.