Hydraulic conductivities of cationic surfactant modified soil mixtures

Surfactant-enhanced sorbent zones have potential utility for contaminant pl ume management in the subsurface. Changes in the hydraulic properties assoc iated with the formation of such zones were studied by measuring hydraulic conductivities of sandy-loam soil mixtures with different fine contents (6, 12, 18, and 24%) that were either untreated, or treated in batch systems w ith hexadecyltrimethylammonium (HDTMA). Experimental conditions included tr eatment to 0.1, 0.7, 1.0, and 2.3 times the cation exchange capacities (CEC ), and effective stresses from 0 to 766 kPa. Achieved treatment levels and the kinetics of HDTMA adsorption were evaluated using C-14-labeled HDTMA. S oil suspension turbidity was used to infer the degree of clay dispersion or flocculation; clays were dispersed in O, 0.1, and 2.3 CEC treated soils an d flocculated in 0.7 and 1.0 CEC treated soils. Consistent with their flocc ulated clay structures, the 0.7 and 1.0 CEC treated soils showed equal or h igher conductivities compared to 0, 0.1, and 2.3 CEC treated soils. The 0.7 , 1.0, and 2.3 CEC treated soils also showed higher compressibility. HDTMA adsorption occurred rapidly at levels up to 1.0 CEC but was kinetically lim ited at the high treatment level (2.3 CEC). Creation of sorbent zones by ex situ batch treatment with cationic surfactants was deemed hydraulically fe asible as evidenced by equal or higher conductivity of HDTMA-treated soils to 0.7 and 1.0 CEC treatment levels, as compared to untreated soil, under a ll loads.