A 3-D SEMIANALYTIC MODEL DESCRIBING THE FATE AND TRANSPORT OF MULTICOMPONENT DEGRADING CONTAMINANTS IN THE PRESENCE OF UNCERTAINTY

摘要

A Monte Carlo based, three-dimensional, semi-analytical model is presented for the simulation of the transport and degradation of organic contaminants in groundwater. The model takes into account the formation of degradation-related daughter products from a suite of organic contaminant inputs at a source, either along straight or branching decay chains. The stoichiometry of the reaction pathways and the biodegradation rate parameters can be represented as uncertain stochastic processes. In addition to accounting for uncertainty in the factors controlling the biodegradation of the multiple organic species being transported, the model also allows the source concentrations, the groundwater velocity and the sorption of each species to be uncertain. The Monte Carlo stochastic approach is used to quantify the probabilistic likelihood that the concentration of either the parent compounds, or any of their daughter products, exceed regulatory or risk levels at a compliance boundary or at specified sampling locations within the migrating contaminant plumes. In essence, the model is used to estimate probability-of-exceedence plumes, with these plumes representing the likelihood of a given contaminant to exceed a specified threshold concentration at any point in three-dimensional space as a function of time. A case study is presented, with examples from a chlorinated-solvents plume being treated by an in situ permeable reaction wall installed at the NAS Fort Worth JRB, Texas.