Chloride Movement in Undisturbed Swelling Clay Soil

Relatively large, continuous soil pores were important pathways of downward Cl‐movement in saturated, swelling clay soils. Using water‐soluble fluorescein as a tracer for downward water and Cl‐movement in field basins, distinct small areas of the soil contained fluorescein, whereas nearby areas contained no visible fluorescein after Cl‐and fluorescein was ponded at the surface for 1.5 days. Chloride contents in the areas containing fluorescein were considerably higher than in nearby areas. Breakthrough curves of a large saturated core of undisturbed swelling clay soil indicated that Cl‐was moving quite rapidly through large connected pores. In the undisturbed swelling clay soil, the volume of soil water not containing Cl‐was about 60%; when the disturbed soil was repacked to the same density this value decreased to 40%. More of the original soil solution was eluted from long undisturbed cores than from short undisturbed cores of the same diameter before Cl‐appeared in the effluent. Apparently the longer core wall blocked more connected flow paths which were not vertical.