In this study, we formulate a contaminant source characterization problem as a nonlinear optimization model, in which contaminant source locations and release histories are defined as explicit unknown variables. The optimization model selected is the standard model, in which the residuals between the simulated and measured contaminant concentrations at observation sites are minimized. In the proposed formulation, simulated concentrations at the observation locations are implicitly embedded into the optimization model through the solution of ground-water flow and contaminant fate and transport simulation models. It is well known that repeated solutions of these models, which is a necessary component of the optimization process, dominate the computational cost and adversely affect the efficiency of this approach. To simplify this computationally intensive process, a new combinatorial approach, identified as the progressive genetic algorithm, is proposed for the solution of the nonlinear optimization model. Numerical experiments show that the proposed approach provides a robust tool for the solution of ground-water contaminant source identification problems.

In this paper, the authors propose a new approach, the simulation–optimization method, to solve a nonlinear contaminant-source and release-history identification problem for a complex water distribution system. This approach is based on optimization analysis, using the EPANET water distribution system model as a simulator. In this approach, EPANET is used to generate concentrations at arbitrarily selected monitoring locations by specifying release histories of potential contaminant sources that are arbitrarily located within the water distribution system. This information is used in a continuous optimal predictor–corrector algorithm to identify the sources and their release histories. Throughout the simulation sequence, the water distribution system being studied is assumed to operate under known hydraulic operational patterns. The optimization model that is used as a corrector to estimate the release histories of the contaminant sources is designed to identify the similarity between the simulation respon...

Analytical solutions to advection-dispersion equations are of continuous interest because they present benchmark solutions to problems in hydrogeology, chemical engineering, and fluid mechanics. In this paper, we examine solutions to two-dimensional advection-dispersion equation with time-dependent dispersion coefficients. The time- and space-dependent nature of the dispersion coefficient in subsurface contaminant transport problems has been demonstrated in the literature in both field and laboratory scale studies. Analytical solutions given in this paper could be used to model the transport of solute in hydrogeologic systems characterized by dispersion coefficients that may vary as a function of travel time from the input source. In particular, in this paper we develop instantaneous and continuous point-source solutions for constant, linear, asymptotic, and exponentially varying dispersion coefficients. The relationship between the proposed general solution and the particular solutions given in the relev...