Effect of Electrical Conductivity on the Saturated Hydraulic Conductivity of Some Lining Materials.

The disposal of saline wastes produced by inland desalination in evaporation ponds has lower cost of operation compared with the deep-well injection. Increase in concentration of salts by evaporation reduces the resistance of clay-based lining material to liquid flow due to change in the thickness of the diffuse double layer. The objectives of this research were to 1) determine the effect of electrical conductivity (EC), bulk density and time on the saturated hydraulic conductivity (K_s) of the soil and some liner materials and 2) identify a lining material of low K_s that could be used to immobilize and prevent the leaking of saline wastes from evaporation ponds into the groundwater. The soil columns were repacked with a surrogate soil, Tularosa soil and different lining materials (sodium silicate, calcium hydroxide and magnesium hydroxide). The columns were saturated with solutions of different electrical conductivities (2, 5, 10, 20, and 30 dS/m). The K_s was determined by the constant head method separately for each solution. In general, K_s was lower in columns packed with a layer of lining material than the homogeneous columns. The K_s of the Tularosa soil and lining material decreased with increasing EC but the K_s of the surrogate soil remained constant. The K_s of the lining materials decreased with time. Based on the reduction in K_s values, the layers of calcium hydroxide and magnesium hydroxide were found to work better than the layer of sodium silicate. More experiments are underway to determine the effect of the compaction of lining material and porous media on further reductions in the K_s of the system. These results are important to determining effective lining materials for evaporation ponds.