Experimental evaluation of surface water sampling variability for environmental monitoring in iron ore operations

Environmental self-monitoring is a government requirement for Swedish process industries. This includes sampling and analysis of recipient water that might be adversely affected by emissions. The requirements for accredited analytical methods are strict, with well-defined measurement uncertainties, but estimations of the attendant sampling variability are seldom required, presented, or evaluated in environmental surface water sampling. The goal of this study was to perform an initial evaluation of the measurement variability for surface water sampling within the self-monitoring program for a large mining company in northern Sweden. The results indicate that the method for evaluation of sampling and measurement variability itself affects the results obtained. Therefore, the evaluation scope must be clearly defined in advance, so that the most appropriate approach, resulting in a realistic quantification of total variability, can be selected. This study shows that duplicate sampling experiments result in significantly larger sampling variability estimates when accounting for ambiguities in the sampling protocol than similar experiments under repeatability conditions. This is due to large temporal variations in stream flux and analyte concentrations in the evaluated sampling targets. The ambiguities in different sampling protocols must be fully described and considered when designing empirical evaluation experiments to allow valid evaluation of the total sampling and measurement system variability. An automated sampler using volume-proportional sampling to collect increments for composite samples is recommended to reduce unnecessary sampling variability and address significant temporal changes in stream flux and analyte concentrations appropriately.