POTENTIAL USE OF WEATHERED SANDSTONES TO CONSTRUCT A LOW PERMEABILITY BARRIER TO ISOLATE PROBLEMATIC COAL MINE SPOILS 1

Specific conductance and selenium (Se) are two water quality parameters of emerging concern in the Appalachian coalfields. Isolation of high specific conductance and Se producing spoils from environmental water flows using a low permeability barrier is one method of minimizing the leaching of these constituents from coal mine spoils. Ideally, the material used to form the barrier should be readily accessible, have low levels of specific conductance and Se, and be capable of achieving a low permeability with the proper moisture adjustment. Brown and gray weathered sandstones are often readily available at mine sites in the Appalachian coalfields. Spoil samples and water quality samples from the University of Kentucky Bent Mountain Research Complex near Pikeville, Kentucky indicated that these spoil types hold promise in meeting the criteria of being a low specific conductance producing material. However, these sandstones tend to have higher sand contents than those typically used in compacted barriers or liners in landfills. The objective of this study was to assess the potential of using brown and/or gray weathered sandstones to create a low permeability barrier. To meet the objective of the study, a total of four spoil samples (identified as M1-M4) were collected in 2012. Each spoil sample was obtained from a different mine in eastern Kentucky. Samples M1 and M2 consisted of brown sandstone; sample M3 was gray sandstone; and sample M4 was a mixture of brown and gray sandstones. Each spoil sample was screened and analyzed for soil texture. Spoil moisture content-density relationships and spoil saturated hydraulic conductivity-moisture content relationships were developed for each sample using double ring permeameters. Maximum saturated hydraulic conductivity values ranged between a low of 5.9 x 10 -8 cm s -1 to a high of 3.1 x 10 -7 cm s -1 in the laboratory for the <2mm fraction. These saturated hydraulic conductivity values were comparable to soils used to construct liners in landfills, particularly in instances where the percentage of fines in the spoils were about 50% or greater. When in the field, however, it is expected that these saturated hydraulic conductivity values will typically be 1-3 orders of magnitude higher due to rock fragments. These results demonstrate that brown sandstone, with its higher fines content, is likely a more suitable media than gray sandstone for constructing a low permeability barrier to isolate high specific conductance producing and/or Se generating spoils. Based on these laboratory results, field assessments of brown weathered sandstones for this application are recommended.