Elemental analyses of goundwater: demonstrated advantage of low-flow sampling and trace-metal clean techniques over standard techniques

The combined use of both (1) low-flow purging and sampling and (2) trace-me tal clean techniques provides more representative measurements of trace-ele ment concentrations in groundwater than results derived with standard techn iques. The use of low-flow purging and sampling provides relatively undistu rbed groundwater samples that are more representative of in situ conditions , and the use of trace-element clean techniques limits the inadvertent intr oduction of contaminants during sampling, storage, and analysis. When these techniques are applied, resultant trace-element concentrations are likely to be markedly lower than results based on standard sampling techniques. In a comparison of data derived from contaminated and control groundwater wel ls at a site in California, USA, trace-element concentrations from this stu dy were 2-1000 times lower than those determined by the conventional techni ques used in sampling of the same wells prior to (5 months) and subsequent to (1 month) the collections for this study. Specifically, the cadmium and chromium concentrations derived using standard sampling techniques exceed t he California Maximum Contaminant Levels (MCL), whereas in this investigati on concentrations of both of those elements are substantially below their M CLs. Consequently, the combined use of low-flow and trace-metal clean techn iques may preclude erroneous reports of trace-element contamination in grou ndwater.