Phosphates used to do the trick too, now they are banned. Any old laundry soap used to thin out the shells so they were much easier to kill.
They are not very deep just dig out the effected area3"-4" deep and go 8"-10" beyond the obvious effected area. that should take a big chunk of the population out. Hopefully you just have a few small spots.
Try Arbico if any one would have a biological control they would. Try this link