Simulation of flowpaths and travel time of groundwater through arsenic-contaminated zone in the multi-layered aquifer system of Bengal Basin

Use of deep groundwater is becoming an important issue in Bengal Basin due to water quality problems in upper aquifers in many areas. Still >50 % of cultivable land in the model area has the potential for future irrigation. Prior to development of deep aquifers it is important to know the trend of flowpaths from recharge zone and travel time of stored water in field geologic conditions and development stresses, which is the principal objective of this study. A three-dimensional model was used for this study to simulate groundwater flow. Model simulation results depict that flowpaths and travel time of groundwater are primarily controlled by hydrogeologic characteristics. However, the recharge zone for different aquifer units is about the same in different conditions with variation of travel time. Continued irrigation abstraction from the shallow aquifer may decrease vertical percolation of recharge water to deeper aquifers. The water of the shallow, i.e., the 1st aquifer, generally has a higher head than water in the main, i.e., the 2nd aquifer. Water from the shallow aquifer may move downward into the deeper units through aquitard windows. The water level of the deep, i.e., the 3rd aquifer, is higher than that of the main aquifer. The arsenic or chloride-rich groundwater in the upper aquifers is not likely to be drawn into the deep aquifer under conditions of moderate use of the deep aquifer.