I've not seen any mounds lately, but some years ago when they were more common I would pour a gallon or two of boiling water on the mound, with a spoon of dish soap mixed in. The mound would collapse immediately, then the water would penetrate deeply into the tunnels underneath. They may regroup in a couple days, but with a much reduced colony, or the queen may get cooked in the first try. No expense, no regrets. (depending on the location, vis-a-vis nearby plants.