How to finish a stump removal project.

[dakkon]

I cut down several crate murtal's and had the stumps ground. However, on a couple of the stumps the guy couldn't get all the way down to the tap root.

One of these stumps is an issue. I am building a retaining wall, and i need a rail road tie to be right where the stump is at!!, the stump is just inside my property line..


Here are a couple photos, you can see the remaining part of the stump, as well as the tie that i need to move by about 10-12"

I have a rotary hammer drill, that i tried with a chisel bit... It did not work out well for me...
3-in-1 1" SDS Rotary Hammer
this is the drill i was using, while i like this hammer drill the hammer action did not have enough travel, i think all of the impacts were absorbed by the wood.

I was thinking about trying a jack hammer?
Either rent one, or buy one from Harbor freight, there is a full size jack hammer on sale until the 12/31.

Another option that would be a possibility, would be to use an auger bit to cut through the rest of the stump with a boxer that i am going to rent. This is a photo of the machine that i am going to rent with an auger bit on it.

i am going to be renting the Boxer on Sunday, so i need to figure this out pretty soon.

Thanks for any and all help!