Municipal Biosolids Capillary Barrier Covers for Reactive Mine Tailings

This project investigated the use of municipal biosolids as a low-cost, low-permeability material in capillary barrier covers (CBC) for reactive mine tailings. The biosolids exhibited low saturated hydraulic conductivities (k = 4.21 x 10 -7 cm/s @ e = 4.01) and an air-entry value of approximately 400 kPa. During laboratory column testing, biosolids layers within the CBCs remained highly saturated, acting as a barrier to oxygen diffusion and water flux. Pore water samples in the tailings of the monolayer cover show elevated concentrations of nitrate, potassium, and sodium relative to CBC columns. No significant change in pH was observed in any of the columns. Numerical models showed reduction in water flux at the tailings surface by 98% and a reduction in oxygen diffusion by up to three orders of magnitude when using biosolids CBCs relative to uncovered tailings. Cover function was not significantly impacted by the characteristics of the underlying tailings.