THREE-DIMENSIONAL MODELING OF HYDROGEOLOGICAL PROPERTIES IN THE RINGOLD FORMATION, HANFORD SITE, SOUTHEAST WASHINGTON

Reactive transport modeling of carbon tetrachloride movement at the Hanford Site requires detailed numerical models of hydrogeological properties in three dimensions. We are generating those models using a combination of lithofacies modeling and geostatistical simulation of the hydraulic properties. Lithofacies modeling is being performed within a stratigraphic framework for the fluvial gravel deposits of the Ringold Formation. Data incorporated in the lithofacies modeling include core and sample descriptions, and borehole logs from the study area. Models of the horizontal continuity of the stratigraphic units are being developed using terrestrial LiDAR (light detection and ranging) imagery of a nearby outcrop of the Ringold gravel. Transition probability modeling is being used to generate multiple realizations of the lithofacies. This approach accounts for the vertical and horizontal continuity of the lithofacies as well as transition probabilities between the lithofacies. Porosity and hydraulic conductivity vary within each of these lithofacies. We simulate this variability using sequential Gaussian methods within the previously defined lithofacies simulations. Values for porosity and hydraulic conductivity used to condition these simulations are estimated from grain size data using a fractional packing model, where grain size data are available. The resulting model will be extended in the near future to incorporate lithofacies controls on geochemical properties critical to reactive transport of carbon tetrachloride in the aquifer.