I once had an unpleasant surprise when digging footings for a concrete slab foundation.
The composition of the soil wouldn’t offer sufficient support for the foundation.
Because the site was in a subdivision where I had already built several houses without a problem, I made the reasonable assumption that we could just start digging as usual.
The problem was corrected by bringing in fill dirt and building a compacted pad.
But the point is that I wasted time and money by not being certain in advance of what I was digging into.
Particularly for you, the one-time house builder, I recommend soil testing before starting foundation work, or even before you close the sale of the land.
Compaction Test
You should be able to find a local environmental engineering company to perform a “compaction test”.
The test will determine soil density ─ is it sufficiently compacted to support your foundation, or is additional work required?
Different soils have different load-bearing capacities. Don’t start your foundation until a compaction test gives you a positive result.
If you know in advance that you are having an excavation contractor do site preparation anyway, the test can wait until after he has finished.
He should know in advance that his site preparation is not considered complete until acceptable compaction is achieved.
Soil testing is meant as a precaution. The chances are very small that your lot will need additional work to make it foundation acceptable, especially if you’re building in an established subdivision. I’ve only had to do additional work one time in twenty years of building.