SHORT-TERM PLUME CONTAINMENT - MULTIOBJECTIVE COMPARISON

Multiobjective strategies and models for optimizing the short-term containment of a 2-D ground-water contaminant plume are compared. These are designed for cases in which an appropriate means of treating the contaminated water is unavailable or unauthorized, and the management goal is to prevent plume movement, without pumping contaminated water and without importing or exporting water. Because optimal unsteady strategies are usually more efficient than optimal steady strategies at achieving goals at a prespecified time, the models optimize the needed time-varying rates of extracting and injecting water. The objective function can use coefficients to consider, one at a time, the objectives of minimizing final hydraulic gradients between observation wells and the plume source, minimizing the cost of pumping, or minimizing the volume of pumping. Alternatively, the model can simultaneously consider the gradient objective and one of the other two objectives in developing a compromise strategy. If the plume must be contained only for the period of optimal unsteady pumping, either the minimizing cost or the minimizing pumping volume objective is most appropriate. For short periods, a minimum pumping strategy, which is the easiest to use, is almost the same as a least-cost strategy. If the plume must be contained for a longer period, the hydraulic objective becomes increasingly important because it causes a more horizontal potentiometric surface, and less additional pumping is needed to maintain that surface after the end of unsteady pumping.