HISTORY MATCHING OF ENVIRONMENTAL DATA AT HANFORD USING THE SYSTEM ASSESSMENT CAPABILITY (SAC) MODEL

The System Assessment Capability (SAC) model was developed to facilitate the understanding of the effects of waste disposal at Hanford and to aid in decision making for environmental cleanup. The SAC consists of a linked set of models that stochastically simulate the inventory, release, environmental transport and impacts of Hanford contaminants, and their associated environmental data. In order to have confidence in these models, it is necessary to compare historical data to the SAC model results. For SAC Rev. 1, historical data were matched to model results for contaminant transport in the atmosphere and the groundwater.

For the purposes of the history matching exercise, the SAC Rev.1 model was used to simulate the release, migration and fate of contaminants for the years 1944 to 2020. Comparisons were conducted for contaminants and time periods for which historical data were available. SAC is notable for modeling both past and future releases and migration (rather than adopting an initial condition), so that history matching can be used to demonstrate the veracity of the simulator.

Release of Krypton-85 from various source areas to the atmosphere during the years 1983-1987 was simulated using the SAC Rev. 1 component model RATCHET2. Model results were compared to monitoring data for various sites.

Transport of contaminants in the groundwater was simulated using the SAC Rev. 1 component model CFEST. Geostatistical methods were used to generate groundwater contaminant distributions for tritium, technetium-99, iodine-129, uranium, and hexavalent chromate based on historical data for comparison to model results. Mass in the aquifer, center of mass of the plume, and total area for which contaminant concentrations are above the drinking water standard were used as comparison metrics.