Identifying Potential Preferential Paths for Subsurface Transport Using Simulated Annealing
نویسندگان
چکیده
Connected zones of high hydraulic conductivity in subsurface environments can constitute preferential pathways for contaminant transport and fluid flow. The identification of such pathways is important for well head protection, groundwater monitoring and capture system design for groundwater remediation. Since it is not practical to exhaustively sample the subsurface, the existence and probable extent and location of such paths must be inferred from available data. Drill or bore hole logs are the primary source of subsurface data considered. A stochastic simulator is used to generate realizations of subsurface soil attributes on a lattice. Measures of connectivity between any two locations in the aquifer are introduced. These measures consider travel time between lattice locations under an assumption of unit hydraulic gradient along each candidate connected path. A preferential pathway between any two points in the aquifer is then one with the highest degree of connectivity (lowest travel time). A simulated annealing algorithm is then used to identify potential preferential pathways between any two prescribed points in the aquifer for each realization. This algorithm seeks superior solutions to global optimization problems which have a large solution space. Simulated annealing proceeds by generating a sequence of random connected paths between the two points of interest. The objective function (connectivity) is evaluated for each candidate path. A threshold probability is defined for accepting or rejecting alternate solutions that may have higher objective function values than
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