In very low-yield wells when several samples need to be taken, what is the best method?
In very low-yield wells that may have only a liter or so of liquid present but several samples need to be taken, what would be the best method?
If you have a very low-yield well and very little water column present, you are going to be best off using a passive or no-purge approach. A no-purge device that collects water right from the water column would be the best possible means of getting a representative sample from the water you have to work with, but it’s a bit of a problematic thing. It’s essentially the “lesser of two evils” approach because, unfortunately, the water sample that’s standing in that water column is not necessarily a great representation of the surrounding formation chemistry. But, because of the limitations of a very low-yield formation, it's the best you can get with that well.
If you need a significant sample volume that exceeds what you have in the well, you need to sit down with your laboratory and ask what the absolute minimum volume is that they can work with. Many laboratories are becoming more cognizant of the need to reduce sample volumes. For example, we have always provided 125-250 mL of water when looking at metals. When in reality, 20 mL of water would be sufficient to run the metals sample, as well as the QC samples that are necessary.
If you have a very low-yield well and very little water column present, you are going to be best off using a passive or no-purge approach. A no-purge device that collects water right from the water column would be the best possible means of getting a representative sample from the water you have to work with, but it’s a bit of a problematic thing. It’s essentially the “lesser of two evils” approach because, unfortunately, the water sample that’s standing in that water column is not necessarily a great representation of the surrounding formation chemistry. But, because of the limitations of a very low-yield formation, it's the best you can get with that well.
If you need a significant sample volume that exceeds what you have in the well, you need to sit down with your laboratory and ask what the absolute minimum volume is that they can work with. Many laboratories are becoming more cognizant of the need to reduce sample volumes. For example, we have always provided 125-250 mL of water when looking at metals. When in reality, 20 mL of water would be sufficient to run the metals sample, as well as the QC samples that are necessary.