How do I get rid of ground wasps?

OK this might sound absolutely ridiculous, but my dad set up a shop vac, it was the first thing he thought of, knowing that my cousin was allergic and would be there soon. He had it somehow secured the hose to the side of the house so when they would fly back to their nest they would get sucked up. He had that thing running all day waiting for the exterminator to come and by the time he came they were all dead. I would call someone to come take care of the situation, though, personally. You don't want to get stung.

If they are going in and out of the holes individually they are probably laying eggs in the holes. A lawn insecticide granule formula that you water into the soil, especially one labeled for grubs and larvae, should keep them from coming back and will help chase away the ones there this year. If lots are flying in and out of the same hole, it's a nest best taken care of by a professional.