Technical Note Multiobjective Groundwater Remediation Design Using a Coupled MFree Point Collocation Method and Particle Swarm Optimization Meenal Mategaonkar 1 and T. I. Eldho 2 Abstract: Pump and treat (PAT) is one of the commonly used techniques for groundwater remediation in which the contaminated ground- water is pumped, treated, and put back to the aquifer system or other sources. For an effective PAT system design, simulation-optimization (S/O) models are very useful; the simulation model helps in predicting the spatial and temporal variation of the contamination plume, and optimization models are used to minimize the cost of pumping. For large-scale groundwater flow and transport simulation, grid-based or mesh-based models such as the finite difference method (FDM) and the FEM have been found to be cumbersome and time consuming. Meshfree (MFree)-based numerical models that use a set of nodes scattered within the problem domain and on the boundaries of the domain regardless of the connectivity information between them are found to be very effective for large-scale field problems. In this study, the MFree point collocation method (PCM) is used for the groundwater flow and transport simulation, and an evolutionary algorithm based on particle swarm optimization (PSO) is proposed for optimization. The S/O model based on PCM and PSO with multiobjective(PCM-PSO-PAT-MO) strategies are developed and applied for remediation of an unconfined aquifer polluted by total dissolved solids (TDS) using PAT. The PCM- PSO–based models are found to be simple and effective in groundwater remediation design using PAT. DOI: 10.1061/(ASCE)HE.1943-5584 .0000899. © 2014 American Society of Civil Engineers. Author keywords: Groundwater remediation; Pump and treat; Point collocation method; Particle swarm optimization; Simulation- optimization model. Introduction For the optimal design of large-scale groundwater remediation projects using pump and treat (PAT), it is required to know the movement of the contaminant plume by using the simulation model, and optimization models are used to achieve the maximum contaminant mass removal with minimum cost and time by consid- ering all uncertainties. For groundwater flow and transport simu- lation, grid-based or mesh-based methods like finite difference method (FDM) or FEM are commonly used. However, these meth- ods are cumbersome due to gridding/meshing for most of the field problems. The meshfree (MFree) methods are being developed which do not require any mesh/grid but require a set of nodes scat- tered within the problem domain and on the boundaries. As there is no grid/mesh, it leads to substantial saving in computational time and cost (Liu 2003; Liu and Gu 2005). Many researchers applied different types of MFree methods for groundwater study (Liu 2003; Liu and Gu 2005; Mategaonkar and Eldho 2012a, b). For many engineering problems including groundwater management problems, an evolutionary algorithm–based technique of particle swarm optimization (PSO) has been found to be very effective (Kennedy and Eberhart 2001). Further coupled simulation- optimization (S/O) models give the complete solution for the com- plex groundwater management and remediation problems (Mondal et al. 2010; Gaur et al. 2011; Mategaonkar and Eldho 2012a). In this paper, an S/O model is presented using MFree point collocation method (PCM) for the simulation of coupled ground- water flow and transport and the PSO technique for multiobjective (MO) optimization of PAT remediation. The remediation cost, time of remediation, and number of pumping wells are considered in the optimization as objective functions, with appropriate con- straints. The developed model is applied to the optimal ground- water remediation using PATof an unconfined aquifer in Belgaum, Karnataka, India, polluted by total dissolved solids (TDS). PCM-Based Simulation Model Here, PCM with standard MQ-RBF (multiquadrics radial basis function) is used to develop the groundwater flow and contaminant transport model by solving the governing equations describing the flow and contaminant transport in an unconfined aquifer in two dimensions as given by Bear (1979). The formulation for the groundwater flow and transport equation (PCM-flow and transport) as given in Mategaonkar and Eldho (2012a, b) is used in this study to obtain the hydraulic head, velocity, and concentration distribu- tion in the domain considered. Because details of the PCM-based flow and transport model [PCM-groundwater flow transport model-2 dimensions (GFTM-2D)] are given in Mategaonkar and Eldho (2012a, b), they are not repeated here. The developed flow and transport models are verified with the available analytical and numerical solutions (Mategaonkar and Eldho 2012b) and found to be satisfactory. For the simulation of coupled flow and transport, the PCM-GFTM model (Mategaonkar and Eldho 2012b) 1 Research Scholar, Dept. of Civil Engineering, Indian Institute of Technology Bombay, Mumbai 400076, India. E-mail: meenal@.iitb.ac .in; meenal.mategaonkar@gmail.com 2 Professor, Dept. of Civil Engineering, Indian Institute of Technology Bombay, Mumbai 400076, India (corresponding author). E-mail: eldho@ civil.iitb.ac.in Note. This manuscript was submitted on January 18, 2012; approved on August 30, 2013; published online on February 8, 2014. Discussion period open until November 1, 2014; separate discussions must be submitted for individual papers. This technical note is part of the Journal of Hydrologic Engineering, Vol. 19, No. 6, June 1, 2014. © ASCE, ISSN 1084-0699/ 2014/6-1259-1263/$25.00. JOURNAL OF HYDROLOGIC ENGINEERING © ASCE / JUNE 2014 / 1259 J. Hydrol. Eng. 2014.19:1259-1263. Downloaded from ascelibrary.org by Shri Vile Parle Kelavani Mandal’s on 07/11/14. Copyright ASCE. For personal use only; all rights reserved.