It took 10 days of cutting and digging but I finally got it out. I had cut down to dirt around the wood the cast is in and it still wouldn't budge. I noticed the last piece was a roughly vertical root a few inches in diameter running into the bottom of the colony. It was out of reach and would have required many more days of work to get down to where I could cut it. So instead, I chained it to the truck and broke the root enough and tilted the wood chunk enough for me to cut it with the chainsaw and remove the cast.
▶️ 3Speak