Concerning sample collection methods that compared the DMLS Geoprobe blow flowing and the bailer, what constituent was the study measuring? Based on these results, is that reasonable to assume that grab sampling may produce reasonably reliable results?

The parameter being measured in that study was chrome and it was total chrome not hex chrome, so chrome 3 not chrome 6.  In that particular study, they found that the grab samples taken using a bailer were not representative of what they saw as an average concentration of wells using either a passive diffusion device or using a low flow pump including the ones they compared to the actual Geoprobe Samples taken adjacent to the well screen.  It’s not recommended to use the grab sampling approach – it's not reasonable to assume that it would produce reliable results.  And it showed very specifically in that case that it didn’t.  Now, if you had a parameter that was less sensitive, you could arguably use a bailer for that approach.  The problem with a bailer is you are still going to achieve some water column mixing and you are almost always going to affect turbidity with them.