The gravel ideally should go all the way to the top-soil, but if necessary for aesthetics you can put a few inches of top-soil.The drain needs to either empty downhill (Obviously) or drain into some kind of underground detention system... or a correctly-installed dry-well system (Most dry-wells are not correctly installed).

Hi,I am building new construction on one of my multifamily and I need soil reports.

They burrow into the soil and make their home there.How does this effect investing? 

Quote from @Sandy G.: My response is the same as @Theresa Harris.1.

The seller is removing underground oil tank and remediating the soil contamination.

@Sandy Sawyer You are completely right.

I heard that the cities near Houston have high flooding and hurricane risks and houses tend to settle due to their soil - though I really don't know enough about TX in general.

They will be coming in from the beach, wet and sandy. 

In addition to a simple zoning, there are things like IPES Scores, Coverage %, compact soil presence, stream zoning.So, my questions is what information I need to gather before I make an offer and what contingencies do I need to think about. thanks.Lenny

For pool @Steve S, you are working to break concrete and using heavy vehicles to do so and also bringing lots of soil as well.