Spatial variation of selenium in Appalachian coal seams

Selenium (Se) is a trace element that can cause human physical deformations due to selenosis, and mutagenic changes on a range of sensitive macro-organisms. Previous studies indicated that Se enrichment is significantly greater in coal than in other rock units, suggesting a correlation between Se and coal bed proximity. Since coal extraction can cause a release of Se, some regulatory authorities have responded by requiring sampling of coal seams and adjacent rock for Se prior to issuing coal mining permits. This sampling is done under the assumption that Se in a small number of samples will be correlated to the Se concentrations throughout the strata they represent. For example, in one case a single continuous deep rock core was sampled for Se to estimate the concentrations of Se across a 2.52 km² proposed surface coal mine. This project examined the adequacy of such an approach using univariate statistics and variograms to determine the spatial variability and correlation of Se concentrations collected from six Appalachian coal seams. The results from all analyses showed no significant spatial correlation of Se within any coal seam examined. Given this lack of measured Se spatial correlation in Appalachian coal seams for scales as small as 0.10 km, it is unlikely that a Se spatial correlation exists in adjacent rock units at similar scales either, which is currently the assumption being made for sampling to minimize Se pollution from surface coal mining.