Finding soil that is 99.9% safe can only be confirmed with soil testing for heavy metals.  

These tests can be expensive and must be performed  by a private company.  Though typically you won't have an issue with soil being sold as topsoil.  Where do you live in the county? 

I would suggest getting only 66 cubic feet of top soil (then getting the 44 cubic feet of organic compost).  Blending it yourself ensures you have some control of the process and know the source.  Orange.  County sells 'Brooks OMRI Listed compost' available in bulk or bag (I think for $40 per yard).

Some places 'try to pass off topsoil'.  They blend fill dirt with compost and claim it is topsoil.  (Not the same) They usually sell it as a 50/50 or 75/25 blend.  

Usually topsoil has organic matter in it and you can see it is not blended with things like pine bark and compost to break it up. (seeing a blend someone is selling as topsoil is a red flag for me.) 

You will need approximately 4 cubic yards. (3.7 Cubic yards equals 100 cubic feet).  

Understand 1 cubic yard of soil weighs about 2,000 pounds.  A standard pickup truck can only haul about 1,000 pounds without overloading it.  

A pallet of bagged soil (3' x 3' x 3') is a cubic yard to put size into prospective. 

Compost weighs about 1,000 pounds a cubic yard. (So you can carry 1 cubic yard of compost in the bed of a pick up truck without overloading it.)