sure fire way to get rid of them from nest in the ground
Multnomah County Oregon yellow jackets
You are dealing with a yellow jacket wasp nest. Yellow jackets nest in the ground, usually in old animal burrows but any underground void can be used. Yellow jacket colonies are annual and will be dying out shortly if not already. Here is a fact sheet on these insects.: http://bspm.agsci.colostate.edu/files/2013/03/Yellowjackets.pdf
This is good information that includes eradication methods, the yellow plastic baited trap is one that I personally have found useful. There are methods for inground eradication that include the use of various toxic spray applications with clear instructions on the container that is best applied after dark when they have returned to the nest.