Stochastic analysis of contaminant transport: One-dimensional non-reactive and reactive cases

Abstract

A reliability approach for probabilistic modeling of one-dimensional non-reactive and reactive transport in porous media provides two important quantitative results: (1) an estimate of the probability that dimensionless concentration equals or exceeds some specified level and, (2) the sensitivity of the probabilistic outcome to likely changes in each uncertain variable. The reliability approach is particularly attractive because it can incorporate various marginal probability density functions (PDF) for any of the uncertain variables. In this work uncertain variables include: groundwater flow velocity, diffusion coefficient, dispersivity, distribution coefficient, porosity and bulk density. The primary objective is to examine how the probabilistic outcome is influenced by choice of marginal PDF, correlation and magnitude of uncertainty for the variables. Because little information exists concerning the statistical characteristics of these uncertain variables, the investigation assumes a wide range of PDF types and statistical values in order to identify and isolate the most critical issues for further study. Results indicate that, even for very slow mean velocity, the probability estimate for non-reactive transport is most sensitive to uncertain flow velocity. For practical analysis, it appears acceptable to treat dispersivity as a deterministic constant. For non-reactive transport, correlation between flow velocity and diffusion coefficient has a slightmore » impact, but correlation among other combinations of uncertain variables is not important. 34 refs., 10 tabs.« less