When pH temperature and conductivity are being documented, how important is DO in determining accuracy in a sampling well?

DO is very important. However, if you are measuring conductivity, you are most likely measuring the inverse of your DO. As we get toward water in the sampling zone that’s under formation which has generally lower DO than the water standing in the well, we see the commensurate increase in electrical conductivity. So DO is important, but is it critical in order to get a sample? If you are only required to monitor the three parameters that you just indicated, as long as you are measuring specific conductance or electrical conductivity, you should be able to get representative sample without a DO measurement. The pH isn’t going to help you much but you can still get a field reading there too. If you can add DO though, you’ve got the added benefit of knowing exactly what's going on in the well. We've been in situations where we’ve had a consistent pattern in DO during purging and then it changed over time. Sometimes it changed due to changing water levels, sometimes changing geochemical conditions. But in a couple of instances, we had some indication that there were problems with rapidly changing DO during purging that were actually related to a broken fitting or air line in a pump. Now, you probably would see some change in the connectivity but you may not see the spikes that you would see with the DO meter. So in summary, I would say if you are measuring pH and EC, you are probably in good shape. But if you can add DO, it’s a great parameter to have – it helps tell the complete story.