Model validation lessons learned: A case study at Oak Ridge National Laboratory

Abstract

A groundwater flow and contaminant transport model validation study was performed to determine the applicability of typical groundwater flow models for performance assessment of proposed waste disposal facilities at Oak Ridge, Tennessee. Standard practice site interpretation and groundwater modeling resulted in inaccurate predictions of contaminant transport at a proposed waste disposal site. The site's complex and heterogeneous geology, the presence of flow dominated by fractured and weathered zones, and the strongly transient character of shallow aquifer recharge and discharge combined to render assumptions of steady-state, homogeneous groundwater flow invalid. The study involved iterative phases of site field investigation and modeling. Prior to initial modeling, which involved conventional applications of a porous medium code, the site geology and geohydrology were intensively characterized and a groundwater dye tracer test was performed to obtain data against which model results could be compared to test accuracy. The initial site groundwater model incorporated the assumptions of horizontally layered, homogeneous but anisotropic aquifer materials. Simulations using this approach failed to accurately simulate the dye tracer behavior because of poor resolution of the heterogeneous site conditions. 7 figs.