"The lowest amount of an analyte in a sample that can be quantitatively determined with stated, acceptable precision and accuracy under stated analytical conditions (i.e. the lower limit of quantitation). Therefore, analyses are calibrated to the MRL, or lower. To take into account day-to-day fluctuations in instrument sensitivity, analyst performance, and other factors, the MRL is established at three times the MDL (or greater)."
[Edit 2] In my town's overall distribution system there are multiple samples above the allowable Reference Concentration. The highest were:
Are you in Wisconsin, a region with large amounts of fracking, or near a nuclear disposal site, by any chance? Such a large molybdenum concentration is exceptionally rare as far as I know.
Chromium, strontium, and vanadium can enter groundwater from many different sources including water seeping through concentrated deposits and industrial pollution. It's the molybdenum concentration that caught my eye because it is unusually rare due to mineral insolubility. It's only when high pressure fracing chemicals oxidize molybdenum does it become readily soluble in untapped deposits, causing it to seep down.
"The lowest amount of an analyte in a sample that can be quantitatively determined with stated, acceptable precision and accuracy under stated analytical conditions (i.e. the lower limit of quantitation). Therefore, analyses are calibrated to the MRL, or lower. To take into account day-to-day fluctuations in instrument sensitivity, analyst performance, and other factors, the MRL is established at three times the MDL (or greater)."
[Edit 2] In my town's overall distribution system there are multiple samples above the allowable Reference Concentration. The highest were: