ABSTRACT
The objective of this study is to present an approach to determine the optimum location for groundwater production wells. Several factors like the intrinsic aquifer vulnerability to contamination, the prevention of seawater intrusion and cost of well installation and pumping are considered in the well site selection process. The optimization problem is formulated as the maximization of the pumped groundwater from new wells that are added to already existing wells. Pumping rates of existing wells that are prone to seawater intrusion are optimized to prevent groundwater flux from the shoreline towards these wells. Also, the purpose of the optimization is to find new well locations that are relatively less susceptible to groundwater contamination and that are in suitable areas for new groundwater exploration with respect to land use.
A regional-scale groundwater flow model is coupled with an optimization procedure to determine the optimum location and pumping rates of new wells. The solution of the presented well site selection optimization problem is obtained by the Differential Evolution algorithm, which belongs to the class of heuristic optimization methods. The objective of the optimization is to find locations of new wells, where groundwater is the least vulnerable (i.e. more likely to obtain clean groundwater), the pumping rate is maximum and the cost of well installation and pumping are minimum for a prescribed set of constraints. The optimization problem is formulated using two objective functions; the first objective function defines the pumping rate maximization. The second objective function minimizes the cost of well installation and pumping operation. To obtain optimum well locations with respect to the groundwater vulnerability index, both objective functions include terms in the form of a penalty function, which penalizes the objective function, if the differential evolution algorithm determines well locations that happen to be in areas with a high groundwater vulnerability index (i.e. more vulnerable to contamination).
The proposed optimization process is demonstrated on an existing groundwater flow model for the Tahtali watershed in Izmir-Turkey. The process identifies locations for up to three new production wells, where the total costs decrease with increasing number of new wells. The pumping rate per production well decreases when the total number of wells increases, thereby reduces the total pumping costs significantly. Furthermore, all well locations in the optimized solution coincide with areas of relatively low groundwater vulnerability. Vulnerability indices for new wells vary between 29.64 and 46.66 (on a scale of 0 to 100, where 100 indicates high vulnerability), depending on the total number of wells found in the solution.
