October 8, 2026
APT vs. field indicators: what each one tells a wetland reviewer
A delineation report lands on your desk. Table 1 cites an APT run for the site visit date, calling conditions "Normal." Table 2 lists wetland hydrology indicators observed at three sample points, two primary, one secondary. You're supposed to weigh these together, but it helps to be clear that they're not answering the same question.
What the APT checks
The Antecedent Precipitation Tool pulls precipitation records from the nearest reporting NOAA station and compares the 30-day and 90-day periods before the site visit against that station's WETS table normal range for the month. It buckets the result into Normal, Drier than normal, or Wetter than normal. That's it. It's a weather report for the weeks leading up to the visit, not a reading of the parcel itself. A consultant can run the APT correctly and still never set foot on the property that day.
What field indicators record
Hydric soil, hydrophytic vegetation, wetland hydrology indicators, these come from a soil pit dug at the sample point and a vegetation plot read around it. Oxidized rhizospheres along root channels, a drainage pattern cut into the duff layer, a dominance test on the plant community. This is physical evidence of what the ground and the plants have been doing, independent of what the sky did that month or the month before.
Where the two are supposed to meet
Under the 1987 Manual, a determination only holds under "normal circumstances." If the precipitation record ahead of a visit was atypical, drought-dry or unusually saturated, the delineator is supposed to flag it and either adjust the hydrology call or come back during a more representative window. That's the whole job of the APT in this workflow: it's documentation telling you how much weight to put on a hydrology indicator that didn't show up on a dry year, or one that showed up everywhere during a wet one. It doesn't replace the indicators and it doesn't grade them. A report that runs the APT and gets "Normal" but skips a proper hydrology read at the sample points hasn't satisfied the three-parameter approach. It's checked one footnote of it.
This is also where reviewers get tripped up on atypical situations under Part IV of the Manual. An APT reading of "Wetter than normal" doesn't automatically mean the site qualifies for atypical-situation procedures, and it doesn't excuse a thin vegetation plot or a soil description that doesn't match the mapped series. It's a flag that tells you to look harder at how the delineator handled the mismatch, not a substitute finding.
The gap neither tool closes
Both of these are built to answer a question about a single visit, a single season. A consultant can run the APT correctly for this year's visit date, read the indicators correctly at this year's sample points, and the report can still miss that the wetland boundary on that parcel has crept thirty feet inland, or pulled back from the ditch line, since the permit was issued three cycles ago. Neither the APT nor a day of indicator reading was built to answer "has this changed since last time," because neither one looks past the day it was run.
For a parcel under an active permit or a mitigation bank in its monitoring years, that's a separate question worth checking before the file even gets to a field visit. Pulling an annual wetland type map for the permit area ahead of the field season flags where the boundary looks like it's shrunk against last year's record, so you know which sample points need a revisit and which ones are just confirming what the imagery already showed.
None of this changes what belongs in the delineation report, only what a reviewer checks first. Pull that annual layer before the first boots hit the mud this season, and you'll know exactly where to send the crew.