title: Using a passive multilayer sampler for measuring detailed profiles of gas-phase VOCs in the unsaturated zone.
abstract: 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 (VOCs) 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 at the saturated-unsaturated interface region of a VOC-contaminated area using the MLS shows steep TCE concentration gradients (1119 microg TCE/L-air/cm) in the gas phase of the unsaturated zone just above the water table.
authors.affiliation: Institute of Soil, Water and Environmental Sciences, The Volcani Center, Agricultural Research Organization, P.O.B 6, Bet-Dagan, Israel 50250. laor@volcani.agri.gov.il
authors.forename: Yael
authors.initials: Y
authors.lastname: Laor
authors.forename: Daniel
authors.initials: D
authors.lastname: Ronen
authors.forename: Ellen R
authors.initials: ER
authors.lastname: Graber
mesh_terms: D004784:Environmental Monitoring / Q000379:methods*; D005740:Gases; D019015:Geologic Sediments / Q000737:chemistry*; D009930:Organic Chemicals / Q000032:analysis; D013048:Specimen Handling; D014835:Volatilization; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D005740:Gases; D009930:Organic Chemicals; D014874:Water Pollutants, Chemical