Engineered Fill vs Gravel

I emailed Eric at Farmington City to ask for a definition of "engineered fill", and he said it's anything that comes from a gravel pit that has a Proctor number. I stopped at Lakeview Rock Products on the way home tonight to find out what a Proctor number is and to see if I could get enough answers to decide between using engineered fill and just using gravel. Turns out a Proctor number is a rating of compactibility.

The least expensive compactible material is 4" bank run, which is $5.35 per ton. The cheapest gravel, which doesn't have to be compacted, is $9.30 per ton. I figured out the volume we'll need for the first round of fill, and calculated it would cost about $1000 more for gravel. However, the other fill would have to be compacted every eight inches, and would have to have compaction tested every eight inches, which would be slow and cost a lot in labor, likely eating away any savings. Since gravel is preferable for drainage and for placement time, and doesn't appear to be significantly more expensive, I think we'll go that way.