Simulation of coupled flow and contaminant transport in an unconfined aquifer using the local radial point interpolation meshless method

Groundwater can be contaminated by natural or manmade activities. The quality of groundwater is affected by increased levels of contaminants in effluents from industries, pesticides from agriculture, septic systems, landfills, leakage from fuel tanks, toxic chemical spills, etc. There are various methods available for numerical modeling of contaminant transport, which include the finite difference method, finite element method, boundary element method, etc. Meshless methods are a new class of techniques that are gaining popularity because they have certain benefits over conventional approaches. Based on the formulation approach, meshless methods may be divided into two types: strong and weak. In this study, the local radial point interpolation method (LRPIM), a meshless weak form formulation, is developed to simulate the flow and contaminant movement in groundwater. LRPIM uses the multiquadric radial basis function (MQ-RBF) for shape function evaluation. Here, a LRPIM-based coupled flow and transport (CFT) model is developed. The model is applied to verify test problems and a field case study. For the test problem, the results obtained are checked against the available analytical solutions and found to give good accuracy. The model is then applied to a real aquifer with chloride contamination from industry. Two different cases, of (1) initial concentration with continuous release of contaminant, and (2) initial concentration with no further release of contaminant, were considered. The LRPIM model predictions are satisfactory and comparable to the results of standard MODFLOW/MT3DMS models. As shown in the study, the LRPIM-CFT model can be effectively used for large-scale field-level aquifer problems.