The 7-digit numbers are identifiers for survey points - either benchmarks, radius points, elevation markers or other registered landmarks used for reference later.
Based on the type of pencil the guy is using, he's in the engineering field. But based on his tool belt and its contents, they are likely surveyors. This is further evidenced by the hand-written comment asking them to find a "current survey for this area".
Based on the notes in red, it appears that these gentlemen have been tasked with taking a survey of the area inside the red lines. The note-writer (who is an architect or engineer, based on their hand writing and the way they draw their arrow heads) is saving them some time by letting them know there was a survey done within the last year for the "food cart" area.
The +/-10' comment is telling them to make note of anything in that general area.
What are they ultimately doing? Absolutely no way to tell from these photos (or from the papers they have). All we can tell is that they've been given the task of surveying that area. They'll take their findings back to the designers, who will then use it for the mystery project.
EDIT: Awesome photos, btw. If we only had more ninja spies like you at our disposal, there would be NO secrets!
