Comparison and modeling of leachate transportation dominated by the field permeability with an anisotropic characteristic based on a large-scale field trial study

Abstract

Permeability significantly affects leachate transportation. Yet, there often exists a gap for its measurements between laboratory and the field. To predict the fate and transport of heavy metals from IBA leaching, a large-scale field trial study was performed using a big column (d × h = 3 m × 5.5 m) packed with 1-m thickness of IBA (approx. 10.6 tons) overlaid by 4-m sand layer. The determined field permeability (k_F) was compared with that achieved from the laboratory, demonstrating a large disparity as much as 4 orders of magnitude likely due to IBA self-compaction. Indeed, back calculation using Blake-Kozeny's equation unveiled that, the "effective" diameters were significantly reduced by 21-46%. k_F also demonstrated an anisotropic characteristic associated with fingered flows, trapped bubbles and heterogeneous consolidation/cementation efficiencies. To quantify the effects by k_F, we ran a mechanistic model to simulate the transport of 11 heavy metals under advection (d_h/d_x = 0.05 m/m), indicating dramatically prolonged breakthrough time from days to centuries. Interestingly, breakthrough time was comparable among various metal ions (0-16.6% of RSD), suggesting their synchronous movements. Metal flux under k_F was predicted in the end to address its toxicity potential, demonstrating limited environmental impacts in presence of the USEPA criterion.

Keywords: Anisotropic; Field permeability; Heavy metals; IBA leachate; Transportation.