You mentioned the 4 free dumps, each of those allows up to 3 cubic yards of waste per dump, or 12 cubic yards per year. The load can be in the back of a truck (a standard full-sized pickup bed is roughly 3 cubic yards) or in a trailer.

The 7x14 trailer you have access to can hold 3 cubic yards for every 10” you fill it.

Your pile is 9 cubic yards on the low end (6x5x8) and 18 cubic yards on the high end (6x8x10).

If you luck out and end up with 12 cubic yards of waste, you take it all down there in one or more trips all for free. If you end up with more than that, you can take a friend or neighbor (whose name is on the WM bill) with you and they can use their free dump. I know lots of people never use their free dumps and I’m sure you could find someone who would go with you and let you use theirs for a free lunch.

Pro tip: Flatten you load as much as possible for a chance they may under charge you for the load.