You actually saved the day for once. One way to fix an enemy stuck under the ground is to use A Napalmer. I have a ported heavy napalmer from a enclave hellfire troop.

I brought it across Taffington Boathouse location & put an end to the underground & stuck bloodbug beside the picnic table and camp tent. The land mines I had planted for several hours did not show success. Thanks Enclave. RIP squad.