Journal of Hydrology, 76 {1985) 85--106 85 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands [2] HYDRAULIC GRADIENT CONTROL FOR GROUNDWATER CONTAMINANT REMOVAL DOROTHY FISHER ATWOOD and STEVEN M. GORELICK U.S. Geological Survey, Menlo Park, CA 94025 (U.S.A.) (Received April 24, 1984; accepted for publication June 13, 1984) ABSTRACT Fisher Atwood, D. and Gorelick, S.M., 1985. Hydraulic gradient control for groundwater contaminant removal. J. Hydrol., 76: 85--106. The Rocky Mountain Arsenal near Denver, Colorado, U.S.A., is used as a realistic setting for a hypothetical test of a procedure that plans the hydraulic stabilization and removal of a groundwater contaminant plume. A two-stage planning procedure success- fully selects the best wells and their optimal pumping/recharge schedules to contain the plume while a well or system of wells within the plume removes the contaminated water. In stage I, a combined groundwater flow and solute transport model is used to simulate contaminant removal under an assumed velocity field. The result is the approximated plume boundary location as a function of time. In stage II, a linear program, which in- cludes a groundwater flow model as part of the set of constraints, determines the optimal well selection and their optimal pumping/recharge schedules by minimizing total pumping and recharge. The simulation--management model eliminates wells far from the plume perimeter and activates wells near the perimeter as the plume decreases in size. This successfully stablizes the hydraulic gradient during aquifer cleanup. 1. INTRODUCTION In recent years the increase in the number of incidents of groundwater pollution has lead to a greater interest in the best way to manage and restore contaminated areas. Accompanying this interest has been the development of aquifer management tools which integrate groundwater flow and solute transport simulation with optimization methods. As demonstrated here, such methods can aid the hydrologist in evaluating and planning schemes for aquifer restoration. In particular, we present a design methodology for hydraulic gradient control aimed at containing and removing groundwater contaminants. Although many works have combined aquifer simulation with optimi- zation techniques such as linear and quadratic programming, few studies have considered the problem of contaminant plume containment. Molz and Bell (1977) considered the problem of hydraulic screening to keep a zone of