SUBSURFACE STORMFLOW MODELING WITH SENSITIVITY ANALYSIS USING A LATIN-HYPERCUBE SAMPLING TECHNIQUE

During storm events, the shallow disposal facilities at Oak Ridge Nati onal Laboratory become inundated, and subsurface stormflow may intermi ttently extract radionuclides from the surrounding soils and the waste s themselves, It is estimated that 90% of the rain water infiltrating the soil horizons becomes subsurface stormflow, yet stormflow is a poo rly understood process, The objectives of this research are to model s tormflow: (1) to identify important parameters for waste site monitori ng 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, an d a Latin-hypercube simulation technique was used to study the uncerta inty of model parameters, Sensitivity analyses of model parameters sug gested 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, ther efore, may not be used as the only reference for subsurface flow monit oring and engineering designs. Neither of two engineering designs, cap ping and French drains, was found to be effective in hydrologically Is olating downslope waste trenches. However, combinations of both design s may prove more effective than either one alone.