We obtained a building permit which required a soils compaction report with 95% compaction density.

You'll also likely need to do a Phase I Environmental (again in the $2500 range) which pulls up the history of chemical spills, soil contamination, water quality, etc. 

You could remove one board...cut around it with a utility knife first to remove caulk...and see what is underneath.

Mostly and specifically you want all vegetation and soil below the bas line of slab foundation.  

It was a single family home built in 1881, 912 square ft on one level with a utility room underneath a hatch in the kitchen.

It is important I think to mentally separate the property and the dirt underneath it.

I have done cost plus contracts for a bridge where volume of embankments are undefined and test pile and pile lengths are undetermined, soils report are unreliable.

Even after mitigating or removing lead-based paint hazards, if the building is a certain age (pre-1978), give tenants a lead-based paint hazards disclosure at the start of tenancy and the EPA booklet:"Protect Your Family From Lead In Your Home".Also, be aware of other lead hazards that may exist, such as in old plumbing and lead in soil.

I ended up putting a new 3.5 ton heat pump in, and added flexible ducting underneath to add 3 floor registers to the addition.  

We have recently replaced the roof and got a 3-ft ice sheet underneath.