T54 Arsenic: Fate and Transport in Natural Waters and Aquifers from Basin to Pore-Space Scale II

Sunday, 4 November 2012
1:30 PM - 5:30 PM
213D

MODEL TO ASSESS GROUNDWATER FLOW IN THE MULTI-LAYERED AQUIFER SYSTEM OF ARSENIC AFFECTED SOUTHERN BANGLADESH

Paper number: T54-12
Program: Technical Sessions
Time: 4:15 PM – 4:30 PM

Authors

Abstract

Use of deep groundwater is becoming an important issue in Bangladesh due to water quality problems at shallow depths in many areas. In the southeastern Bangladesh, multi-layered aquifer conditions exist, with arsenic contamination at shallow depth and high iron and brackish groundwater occurring mainly in the deeper layers. Still >50% of cultivable land in the study area has the potential for future irrigation. Development of deep aquifers needs to assess the trend of groundwater flow. Three-dimensional model was used for this study to simulate groundwater flow in southeastern portion of the Delta. The model was used to study the impacts of geologic formations and different development stresses on groundwater flowpaths and travel time infiltrated through arsenic contaminated layers. Simulation results depict that flowpaths and travel time of groundwater are primarily controlled by hydrogeologic characteristics of sediments. Aquifers are recharged by vertical percolation as well as water from long distance travel from highly elevated eastern hilly areas mainly to deeper aquifers. Under current trend of groundwater development, the average travel time for the upper and the lower parts of the 1st and the 2nd and the upper part of the 3rd aquifers at different geologic conditions are estimated between 37 and 234, 133 and 317, 832 and 2485, 1009 and 3027 and 1065 and 3543 years respectively. Excessive irrigation abstraction in future from the shallow aquifer may decrease vertical percolation of recharge water to deeper aquifers. The water from the shallow i.e. the 1st arsenic-contaminated aquifer generally has a higher head than water in the main i.e. the 2nd aquifer during irrigation abstraction. 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. 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 water. Maintaining current trend of abstraction, if only domestic wells are shifted to the main aquifer from the shallow aquifer, would provide better results and lower part of the main aquifer and the deep aquifer will remain safe for a longer period of time.