What purging/sampling procedure would you recommend for low-yielding wells that have limited volume in the screened interval?

Use a passive or no purge sampling approach. If you have a well that produces so little water and has so little water stored in it that you can’t pump it then the water standing in the well is going to be the best representation of the formation – it is not perfect, and has to be considered as such. If you need a lot of sample volume or you are looking for analytes beyond VOCs you can use a hydrosleeve or a snap sampler. If you are looking at just VOCs that is when passive devises can come into play.