Hydraulic characteristics of organomodified soils for use in sorptive zone applications

The sorption capabilities of subsoils for organic contaminants can be enhanced by modification of soil clays with cationic surfactants. The use of these organomodified soils to establish permeable sorptive zones has been suggested as a potential means for attenuating the migration of contaminant plumes. The hydraulic feasibility of sorptive zones was evaluated by measuring the hydraulic conductivities and porosities of both modified and unmodified soils at different effective stresses when permeated with water. Samples with 6, 12, 18, and 24% fines content were prepared and batch treated with hexadecyltrimethylammonium (HDTMA) to 80 % of their cation-exchange capacities. Under the first load (24 kPa), all treated soils showed higher conductivities and similar or higher porosities than untreated ones. Higher loads decreased the difference in porosity between treated and untreated soils while increasing the difference between their conductivities. At the highest load (766 kPa), treated samples were 5 to 124 times more conductive than untreated ones depending on their clay contents. Differences in conductivities were explained in terms of the role of treated and untreated clays in controlling initial effective pore size and its change during consolidation. Creation of organomodified sorptive zones by batch soil processing is shown to be hydraulically feasible as evidenced by a marked increase in the conductivities of all treated samples compared with untreated ones. In addition, an increase in the sorptive capacity of the zone could potentially be achieved, without experiencing a loss in conductivity, by increasing the clay content during modification