ABSTRACT
Reasons for sampling pore-liquids in the vadose zone include determining contaminant concentration/mass trends in time and depth, detection of contaminants, and tracing contaminant flow paths (Starr et al., 1991). Pore-liquid samples can be obtained either by direct, in situ methods (e.g., tile lines, pan lysimeters, and wells, for saturated regions, and suction samplers for unsaturated regions), or by indirect methods, e.g., soil core samples. A major difference between these two approaches is that core sampling methods are destructive, i.e., repetitive samples cannot be obtained from the same location. More importantly, as pointed out by Dorrance et al. (1991), the two techniques do not sample the same types of liquid. In situ samplers generally sample pore-liquids held under tensions below about 60 kilopascals (kPa) *** (Everett and McMillion, 1985). In contrast, pore-liquids extracted from soil cores include liquids held at tensions far in excess of 60 kPa. Extraction under several bars of (equivalent) tension may strip off cations preferentially sorbed in electrical double layers, sorbed organic compounds, and native soil components. These ions may or may not be present in the same concentrations in samples obtained by in situ pore-liquid samplers. Thus, Zabowski and Ugolini (1990) found solute concentrations in liquids obtained by centrifuging core samples were 478frequently higher than those from suction samplers. They concluded that solutions from suction samplers are more representative of solute movement than core derived samples.
