First, use a little care.
Yellowjackets start with one queen at the beginning of the year, the
rest die during the winter. By the end of August the colony is
generally about 1500. The fatal dose (assuming no allergies) is
between 500 and 1000 for the average human. So, do the math!
Living in Virginia, I usually find one nest a year while mowing the
lawn. I think they start in a mole tunnel then dig it out.
I kill them with soapy water. I set a couple five gallon pails of
water and laundry soap near the hole, wait until dark, and pour it
in. No risk like with gasoline or pesticides. I've never had this
method fail, though I've sometimes had to do it a couple of times. It
took a little nerve the first time, I thought they might wake and come
flying out the hole, but that's never happened.