What is your opinion of passive sampling?

Passive sampling has its place, just like no-purge sampling, minimum purge sampling, low-flow purging and sampling, and multilevel sampling systems all have their uses. Low-flow purging and sampling can be used across a wide range of applications, whereas passive and no-purge sampling may be more selective. Passive and no-purge sampling seem to be the most effective methodologies in extremely well yield wells where you can't really purge the well.  Passive sampling is an excellent methodology when you need to sample the water that’s in the bore without creating any disturbance and without actually changing the head inside the bore. There are some conditions, however, where passive sampling isn’t the best method to use. That’s when there is significant redistribution in contaminant mass through the ambient vertical flow.