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 contamina nts from near-surface groundwater. Automatic control systems in auxili ary 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 ine rt substrate below the water table and recirculated to provide uniform groundwater concentrations. Continuous monitoring was undertaken of w ater imports/exports, the vertical distribution of soil water potentia l and soil temperature, and climatological variables. Regular measurem ents 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 19 91 show a strong contrast in climatic conditions between the 2 yr. Rad iochemical data are presented in an accompanying paper.