Hanford Site Composite Analysis: Aggregation of Continuing Source Term Simulation Results for Fate and Transport Predictions - 21179

The Hanford Site composite analysis (CA) estimates the possible future dose to receptors due to waste operations at the site. The calculation requires an estimate of future groundwater concentrations of contaminants in the uppermost aquifer at the Hanford Site over a 10,052 year time frame. As part of the full composite analysis, the groundwater flow and fate and transport of contaminants in the saturated zone of the aquifer were simulated using MODFLOW and MT3DMS, respectively. The extent of the groundwater model used for simulating the saturated zone includes the footprint of 26 vadose zone models, developed for the CA, and completed performance assessments at the Hanford Site. The simulated output from the simulations were combined as an estimate of the magnitude, timing, and location of contaminant activity entering the saturated zone of the aquifer. Combining all the simulated sources of contaminant to one simulation provides an estimate of the cumulative effects of vadose zone sources on the predicted concentrations over time. Sensitivity analysis on the predicted concentrations were carried out to evaluate uncertainty in the predicted concentrations. (authors)