Laor, Y., Present address: Newe Ya’ar Research Center, P.O.B. 1021 Ramat Yishay 30095, Israel
Ronen, D., Israel Hydrological Service and Ben-Gurion University of the Negev
Graber, E.R., Inst. of Soil/Water/Environ. Sci., Volcani Center, Agricultural Research Organization, P.O.B. 6, Bet-Dagan 50250, Israel

The purpose of this study was to test in the laboratory the performance of a passive multilayer sampler (MLS) for obtaining detailed profiles of gas-phase volatile organic compounds (V0Cs) in unsaturated sediments. The MLS is essentially a chain of isolated, cylindrical stainless steel dialysis cells filled with distilled water and closed with membranes at both ends. The sampling principle is based on passive equilibration of the unsaturated zone gas phase with water in the cells. Using trichloroethene (TCE) as a model VOC, and after testing the required equilibration time in the laboratory (about 50 h), results of a large container (210 L) experiment show that TCE concentrations obtained by the MLS deployed inside a well screen corresponded very well to the profile obtained by dialysis cells buried in the sediment. A field profile taken atthe saturated-unsaturated interface region of a VOC-contaminated area using the MLS shows steep TCE concentration gradients (1119 μg TCE/L-air/cm) in the gas phase of the unsaturated zone just above the water table.