MODELLING OF ARSENIC TRANSPORT GROUNDWATER USING MODFLOW

Abstract

Arsenic contamination in the groundwater is increasing at an alarming level with time and more areas are becoming contaminated. At least 28 million people currently drink water containing more than 50 μ g/l of arsenic and many more consume water with > 10 μ g/l of arsenic. Evidence of chronic arsenic toxicity is accumulating and includes melanosis , hyperkeratosis of palm and sole, gangrene and skin cancer. A MODFLOW based three-dimensional model has been simulated to understand the movement of water and arsenic in the study area situated in the Yamuna Sub-basin, West Bengal. Microbial reduction of iron oxyhydroxide (FeOOH) and release of its sorbed arsenic load to solution is an important mechanism by which arsenic enters groundwater. Arsenic pollution does not arise from oxidation of sedimentary sulphides nor from ionexchange with phosphorus derived from fertilizer (or other sources). MODFLOW was run for the study area and the movement of water in the study area was simulated. It was seen that the variation of hydraulic heads was more in clay than in sand layer. Arsenic was assumed to be injected continously at a well 12005m away from both the western and northern side of the Yamuna Sub-basin in the block of Chakdah, Nadia district at a depth of 25m from the ground level. Simulation was performed for the movement of arsenic for every 1 year for a stretch of 20 years. The spatial and temporal distribution of arsenic was studied through contours maps for 1, 5, 10, 15, and 20 years. The concentration of arsenic vs time graph was also drawn. It was seen that arsenic was spreading more in the sand layer than in the clay layer, affecting more and more places near the study area.