Model testing using Chernobyl data .1. Wash-off of Sr-90 and Cs-137 from two 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 placed on chemical speciation and on the geochemical and geophysical processes affecting transfer of contaminants from soil to water. The scenario gives descriptions of two experimental plots near the Chernobyl power plant, one using heavy rain and one using snow melt, together with characteristics of the initial aerial deposition of the radionuclides and data on topography, soil type and characteristics, and time-varying precipitation. Predictions are requested for (1) the vertical distribution of concentrations of exchangeable and nonexchangeable forms of Cs-137 and Sr-90 in the soil of the experimental plots, (2) concentrations of Cs-137 and Sr-90 in runoff water from the experimental plots, and (3) total amounts of Cs-137 and Sr-90 removed by runoff from the experimental plots. Test data (field measurements) are available for all endpoints.