River Bank Filtration Process Using Groundwater Flow Modeling and Particle Tracking Approach in a Saline Coastal Aquifer

River bank filtration (RBF), as one of the sustainable natural treatment techniques, can provide risk-free drinking water supply to rural villages where piped water supply through conventional treatment schemes is very expensive. The main purpose of this paper is to report the results of a RBF production well implemented in a complex hydrogeological setting under the ephemeral Varaha river influenced by the saline coastal aquifer in the Visakhapatnam district of Andhra Pradesh (India) for the supply of drinking water to the nearby rural habitats that have no organized water supply. To understand and identify the hydraulics of the river–aquifer exchanged water, particle tracking analysis to determine the travel times of river water path lines, capture zones, the proportion of bank filtrate and river water, and groundwater into RBF production well consequent to pumping were carried out using modular finite difference groundwater flow model (MODFLOW) in conjunction with a particle-tracking model for MODFLOW (MODPATH). The river–aquifer and well field interaction were studied by developing a two-dimensional two-layer groundwater flow model with a partially penetrating well in an unconfined aquifer. The flow modeling simulation results together with MODPATH particle tracking analyses revealed that the installed RBF production well could yield about 61% river water through bank filtration and the remainder from the groundwater. The flow model was also used to optimize the pumping duration from the RBF production well without compromising the water quality of the bank filtrate water. The optimum pumping duration was estimated to be 5 h a day at the rate of $31.2{\mathrm{m}}^3/\mathrm{h}$ from continuous pumping during the monsoon period. The performance and quality of the bank filtrate from the well demonstrated that the RBF technique could also be a potential and viable approach for the supply of safe drinking water from an ephemeral river-induced bank filtrate influenced by the saline coastal aquifer.

River bank filtration (RBF), a process to extract river water and groundwater through RBF wells, is one of the sustainable natural treatment techniques successfully providing risk-free drinking water supply in many urban, periurban, and rural areas in different countries. In India, it is gaining popularity, particularly in rural clusters where piped water supply through conventional treatment schemes has a remote chance of being effective. RBF wells are very effective in removing suspended particles, pathogenic compounds, and microorganisms present in the source water. The quantity of RBF water depends on the user requirements; for a town with a series of RBF wells or a small village using a single RBF well, RBF techniques can be employed. For establishing RBF wells in coastal regions, extra care would be required to fix the pumping rate and its duration to avoid mixing of saline with fresh water. The present study demonstrates the successful implementation of a RBF well on an ephemeral river (Varaha river in Andhra Pradesh State, India) in a saline coastal aquifer. The RBF technique can be employed to any other river reach or waterbody in the region where there is a need for potable water supply with minimum water treatment cost.