Potential use of calcareous mudstones in low hydraulic conductivity earthen barriers for environmental applications

Abstract

Earthen layers play a significant role in isolating contaminants in subsurface, controlling the migration of contaminant plumes, and as landfill liners and covers. Physical, chemical and mineralogical properties of three calcareous mudstones from the Jagüel and Roca formations in Northpatagonia, Argentine, are evaluated to determine their potential for the construction of liners. These mudstones were deposited in a marine environment in the Upper Cretaceous Paleocene. Tested specimens are mainly composed by silt and clay size particles and their mineralogy is dominated by a smectite/illite mixed layer (70-90% Sm) and calcite in less proportion. Powdered mudstone samples have little viscosity and swelling potential when suspended in water. The hydraulic conductivity of compacted mudstones and sand-mudstone mixtures is very low (around 1 - 3 x 10-10 m/s) and in good agreement with the expected hydraulic behavior of compacted earthen layers. This behavior can be attributed to the high amount of fine particles, high specific surface and the close packing of particles as confirmed by means of Scanning Electron Microscope analysis. In addition, tested materials also show a high cation exchange capacity (50 - 70 cmol/kg), indicating a high contaminant retardation capability. The calcareous mudstones show satisfactory mineralogical and chemical properties as well as an adequate hydraulic behavior, demonstrating the potential use of these materials for the construction of compacted liners for the containment of leachate or as covers in landfills. These findings confirm the potential usage of marine calcareous mudstones as a low cost geomaterial in environmental engineering projects.