Subsurface stormflow modeling with sensitivity analysis using a Latin-hypercube sampling technique

During storm events, the shallow disposal facilities at Oak Ridge National Laboratory become inundated, and subsurface stormflow may intermittently extract radionuclides from the surrounding soils and the wastes themselves. It is estimated that 90% of the rain water infiltrating the soil horizons becomes subsurface stormflow, yet stormflow is a poorly understood process. The objectives of this research are to model stormflow: (1) to identify important parameters for waste site monitoring and data collections; (2) to evaluate remediation designs; and (3) to investigate the effect of local heterogeneities on stormflow paths. Numerical models of a proposed waste disposal site were developed, and a Latin-hypercube simulation technique was used to study the uncertainty of model parameters. Sensitivity analyses of model parameters suggested that hydraulic conductivity was the most influential parameter. However, local heterogeneities may alter flow patterns and result in complex recharge and discharge processes. Hydraulic conductivity, therefore, may not be used as the only reference for subsurface flow monitoring and engineering designs. Neither of two engineering designs, capping and French drains, was found to be effective in hydrologically isolating downslope waste trenches. However, combinations of both designs may prove more effective than either one alone