MODEL TESTING USING CHERNOBYL DATA .1. WASH-OFF OF SR-90 AND CS-137 FROM 2 EXPERIMENTAL PLOTS ESTABLISHED LN THE VICINITY OF THE CHERNOBYL REACTOR

The ''Wash-off' scenario is designed to test models concerned with the movement of trace contaminants from terrestrial sources to bodies of water, specifically the contamination of surface water by wash-off of radionuclides initially deposited onto soils. Particular emphasis is p laced on chemical speciation and on the geochemical and geophysical pr ocesses affecting transfer of contaminants from soil to water. The sce nario gives descriptions of two experimental plots near the Chernobyl power plant, one using heavy rain and one using snow melt, together wi th characteristics of the initial aerial deposition of the radionuclid es and data on topography, soil type and characteristics, and time-var ying precipitation. Predictions are requested for (1) the vertical dis tribution of concentrations of exchangeable and nonexchangeable forms of Cs-137 and Sr-90 in the soil of the experimental plots, (2) concent rations of Cs-137 and Sr-90 in runoff water from the experimental plot s, and (3) total amounts of Cs-137 and Sr-90 removed by runoff from th e experimental plots. Test data (field measurements) are available for all endpoints.