RADIONUCLIDE TRANSPORT ABOVE A NEAR-SURFACE WATER-TABLE .1. AN AUTOMATED LYSIMETER FACILITY FOR NEAR-SURFACE CONTAMINANT TRANSPORT STUDIES

The design and operation is described of a held lysimeter experimental facility to investigate the migration in vegetated soils of contaminants from near-surface groundwater. Automatic control systems in auxiliary buffer tanks were used to maintain fixed water table depths of 35 and 65 cm, respectively. A cocktail of radionuclides, consisting of Cs-137, Cd-109, Co-60, Na-22, Cl-36, and Tc-99, was introduced to an inert substrate below the water table and recirculated to provide uniform groundwater concentrations. Continuous monitoring was undertaken of water imports/exports, the vertical distribution of soil water potential and soil temperature, and climatological variables. Regular measurements were made of soil moisture content, crop root distribution, crop height and leaf area index, as well as radiochemical concentrations in groundwater and the control system. Intensive radiochemical analyses were made on soil cores and crop. Hydrological results for 1990 and 1991 show a strong contrast in climatic conditions between the 2 yr. Radiochemical data are presented in an accompanying paper.