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I sort of wish I'd left the stump a little longer and bought a winch, but the thought of the chain whizzing past my head or damaging the anchor tree did not turn me on. So I decided to go the digging out root (ha-ha). This is looking like a 10+ hour job including the shed hole, only two hours invested so far. Although I'm nowhere near exposing enough of the stump to get under the tree. It's been insert shovel, use grub-axe to break roots, remove half a shovel of dirt. I have to remove about 3 cubic yards for the shed hole and I've only move about .5 yards so far. The stump is now too short to winch it out, but some pressure might help me expose the roots to help with the excavation?
Trees are two spruce trees about 8" in diameter, but I suspect they share a common root. Site is not accessible by vehicle, dynamite is not an option, waiting is not an option. The stump is about 16" above ground and must be excavated to 10" below grade. Possible anchor tree is a Mountain Ash about 12" in diameter.