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The highest concentrations of arsenic in groundwater are found in the Nebraska Panhandle, southwestern Nebraska, and the Republican River valley. Data from 33 public water supply wells indicate that significant variability in arsenic concentrations did not occur over a one-year study. The general absence of temporal variability in arsenic concentrations suggests that the collection of one sample per year from most wells will adequately characterize the arsenic concentrations to which the population drinking this water will be exposed. The collection of additional samples is strongly recommended if the reported arsenic concentrations are at, or slightly above, 10 μg/L in order to verify that the average arsenic concentration is above the maximum contaminant level. Short-term (4 to 24 hours) sampling experiments indicate that arsenic concentrations may increase, decrease, or remain relatively constant during the first 30 to 60 minutes after a well is turned on. The potential for these changes need to be considered when collecting samples for regulatory purposes. It is recommended that the sampling scheme be designed around the operational history of the individual wells within a system. This will provide a more realistic assessment of the arsenic concentration to which the consumers of the water are exposed.