OPTIMIZATION OF PUMP-TREAT-INJECT (PTI) DESIGN FOR THE REMEDIATION OFA CONTAMINATED AQUIFER - MULTISTAGE DESIGN WITH CHANCE CONSTRAINTS

A large scale groundwater remediation project using pump-and-treat (PA T) or pump-treat-inject (PTI) cannot be designed as a single time-step operation, because of uncertainties associated with the system. The c hanges in concentrations in reality may differ significantly from pred icted ones. Instead, a multi-stage decision process is formulated and solved as a two-level hierarchical optimization model. Cost serves as the objective function, while contaminant concentration and total clea nup time are constraints. The entire cleanup time is divided into seve ral stages. The number of wells for both pumping and injection is trea ted as a decision variable in each design stage. At the basic level, w ell locations and pumping/injection rates are sought so as to maximize mass removal of contaminants. At the upper level, the number of wells for pumping and injection is optimized, so as to minimize the cost, t aking maximum contaminant level (MCL) as a constraint. Indices for the equivalent centroid and areal extent of a contaminant plume are propo sed and used to initiate well locations at each design stage. (C) 1998 Elsevier Science B.V.