In situ colloid generation and transport in 30-year-old mine soil profiles receiving biosolids

Colloid mobility has been tied to contaminant transport in many agricultural soils, and may be a factor in reclaimed mine soils as well. Before contaminant transport can be predicted, the actual patterns in colloid generation and transport following disturbance needs to be elucidated. A site in the Appalachian region of southwest Virginia was chosen to observe colloid transport within natural forest soils (F), reclaimed soils (R) and reclaimed soils underlain by spoil material (RS). A fourth treatment included the application of lime-stabilised biosolids to separate RS monoliths (RSB). These intact soil monoliths were leached with de-ionised water at a rate of 1.0 cm/h for at least 2 pore volumes. Total eluted colloid loads were greatest within natural forest (F) soil monoliths (2205 mg), followed by R (1460 mg) and RS (76 mg) monoliths. The addition of biosolids (RSB) induced greater colloid transport (871 mg) compared to RS monoliths not receiving biosolids. This was likely due to an increase in pH and EC from the applied biosolids. The results suggested that colloid and potentially contaminant transport should indeed be a concern in soils disturbed by mining activities, but predicting the magnitude and patterns of colloid behaviour may be difficult due to variations in physical and chemical properties of the reclaimed soils.