Saline water removal from a soil column composed of Andisol by porewater flow due to rainwater infiltration

Abstract Sodium chloride, calcium chloride, etc. accumulate in soils near roads where road salt has been applied during winter, and have the potential to degrade water quality and ecosystems. It is important to understand how much saline water is retained in a soil, and how fast it is leached from the soil by rainwater infiltration for environmental management in cold climate regions. This study, therefore, investigated saturated/unsaturated flow driven by infiltrating rainwater in a soil column composed of Andisol and the removal of saline water due to previous road salt application from the soil by experiments and simulations. The Andisol is the result of volcanic activities, and is often seen in Japan. The Andisol used in the experiments consisted of clay (7.0%), silt (17%), fine sand (51%), medium sand (15%) and coarse sand (10%). The X – ray fluorescence results showed that the Andisol was composed mainly of oxygen (50.5%), carbon (18.9%), silicon (13.1%), aluminum (8.28%), and iron (4.52%). Experimental NaCl concentrations in the effluent from the bottom of the soil column increased with time, became largest at 2000–3000 s after freshwater was begun to be supply from the top of the soil column, then decreased, and finally, approached zero. Despite the soil – water retention curve for Andisol was obtained, and incorporated, the model had difficulties in describing neither the experimental time variation of NaCl concentrations in the effluent nor salt mass left in the soil column. This suggests that chemical processes have a significant effect on salt mass transport in the soil. Experimental results revealed that about 0.71–1.25 pore volumes of freshwater are needed to reduce salt mass left in the soil column to 1% of initial value of total salt mass in the pore volume of the soil.