Would it be quicker and equally effective to use normal purging and filter the samples if you’re only concerned with metals contamination?

Would it be quicker and equally effective to use normal purging and filter the samples if you’re only concerned with metals contamination?

Metals are our biggest concern when it comes to filtering the sample.  We see the greatest bias or effect on the sample results when the samples are filtered. When we generate turbidity through, for example, high rate purging or bailing, we’re generating a distribution of particle sizes. Some of them are very small, many of them as small as a 10th of a micron in size and yet, they’re expandable and may be mobile with the groundwater.  If we use a typical 0.45 micron filter, some of those small particles are going to actually pass right through.  So, if we took a highly turbid sample and filtered it and compared that with a low turbidity sample from the same well, we’d see a difference in concentration and now, unfortunately, the chemistry doesn’t match. This is because filters do several things. They allow small particles to pass through and they actually will pull some particles out of the sample through sorption onto the filter membrane.  Also, in the process of handling the sample, we see some changes in chemistry.  So unfortunately, no, filters do not provide an effective means of giving us a good indication of what is the true mobile contaminant load.