A rain gauge on the trailer is the traditional answer, and it fails the way all manual records fail: it is only as good as whoever remembered to read it. The permit asks for the rainfall that triggered each inspection, in the record, with the inspection.
The requirement
The EPA 2022 CGP covers the rain documentation tied to storm-triggered inspections at Part 4.2.2, and the three-year retention at Part 4.7.4. Read them in the primary source: EPA 2022 Construction General Permit (PDF). The Texas equivalent sits in TXR150000 Part III.F.8(c).
What a defensible rain record looks like
- The event window, not just a day. A storm that straddles midnight has one window.
- The amount in decimal inches, against the trigger your election uses.
- Where the number came from, so an inspector can check it rather than take your word.
- The inspection that answered it, and what the inspector found.
RainClock records all four per site from NOAA MRMS multi-sensor precipitation sampled at the site coordinates, and prints them in the binder as one document. When the feed is ambiguous we mark the event “possible, check your gauge” rather than assert a storm that may not have happened on your dirt.