Also a (mainly) civils and highways planner here
I would tend to set this up so that each area is a summary task, with individual tasks within it- see enclosed pic . this will allow you to set start and end dates for each section of work within an area- I have also added volumes(number column 1) and resources, as this is info that may well be required (for us it would be, but not necessarily for you).
This allows you to add more excavation items as you go through, as the summary is the indicator of the area. I suspect this is what you are looking at, if you need to keep records of what.when/where, although it may be easier ot ignore project and just record this info in an excel sheet, although obviously it depends on how it needs to be produced, but that would be simpler and probably more useful.