TY - JOUR
T1 - Vapor-phase transport of trichloroethene in an intermediate-scale vadose-zone system
T2 - Retention processes and tracer-based prediction
AU - Costanza-Robinson, Molly S.
AU - Carlson, Tyson D.
AU - Brusseau, Mark L.
N1 - Funding Information:
This research was supported by grants provided by the National Institute of Environmental Health Sciences Superfund Basic Research Program ( ES 04940 ) and by the U.S. Department of Energy . The authors wish to thank Dr. Glenn Thompson and Mr. John Oliver of Tracer Research Corporation (Tucson, AZ) for their generous donation of time and analytical resources. We also thank the reviewers for their constructive comments.
PY - 2013
Y1 - 2013
N2 - Gas-phase transport experiments were conducted using a large weighing lysimeter to evaluate retention processes for volatile organic compounds (VOCs) in water-unsaturated (vadose-zone) systems, and to test the utility of gas-phase tracers for predicting VOC retardation. Trichloroethene (TCE) served as a model VOC, while trichlorofluoromethane (CFM) and heptane were used as partitioning tracers to independently characterize retention by water and the air-water interface, respectively. Retardation factors for TCE ranged between 1.9 and 3.5, depending on water content. The results indicate that dissolution into the bulk water was the primary retention mechanism for TCE under all conditions studied, contributing approximately two-thirds of the total measured retention. Accumulation at the air-water interface comprised a significant fraction of the observed retention for all experiments, with an average contribution of approximately 24%. Sorption to the solid phase contributed approximately 10% to retention. Water contents and air-water interfacial areas estimated based on the CFM and heptane tracer data, respectively, were similar to independently measured values. Retardation factors for TCE predicted using the partitioning-tracer data were in reasonable agreement with the measured values. These results suggest that gas-phase tracer tests hold promise for characterizing the retention and transport of VOCs in the vadose-zone.
AB - Gas-phase transport experiments were conducted using a large weighing lysimeter to evaluate retention processes for volatile organic compounds (VOCs) in water-unsaturated (vadose-zone) systems, and to test the utility of gas-phase tracers for predicting VOC retardation. Trichloroethene (TCE) served as a model VOC, while trichlorofluoromethane (CFM) and heptane were used as partitioning tracers to independently characterize retention by water and the air-water interface, respectively. Retardation factors for TCE ranged between 1.9 and 3.5, depending on water content. The results indicate that dissolution into the bulk water was the primary retention mechanism for TCE under all conditions studied, contributing approximately two-thirds of the total measured retention. Accumulation at the air-water interface comprised a significant fraction of the observed retention for all experiments, with an average contribution of approximately 24%. Sorption to the solid phase contributed approximately 10% to retention. Water contents and air-water interfacial areas estimated based on the CFM and heptane tracer data, respectively, were similar to independently measured values. Retardation factors for TCE predicted using the partitioning-tracer data were in reasonable agreement with the measured values. These results suggest that gas-phase tracer tests hold promise for characterizing the retention and transport of VOCs in the vadose-zone.
KW - Air-water interface
KW - Gas-transport
KW - Tracers
KW - VOCs
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U2 - 10.1016/j.jconhyd.2012.12.004
DO - 10.1016/j.jconhyd.2012.12.004
M3 - Article
C2 - 23333418
AN - SCOPUS:84872416791
VL - 145
SP - 82
EP - 89
JO - Journal of Contaminant Hydrology
JF - Journal of Contaminant Hydrology
SN - 0169-7722
ER -