Regional hydrostratigraphy and groundwater flow modeling in the arsenic-affected areas of the western Bengal basin, West Bengal, India
Regional hydrostratigraphy and groundwater flow modeling in the arsenic-affected areas of the western Bengal basin, West Bengal, India
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DOI：
10.1007/s10040-007-0208-7
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发表时间：
2007-11-01
影响因子：
2.8
通讯作者：
Howell, Paul D.
中科院分区：
文献类型：
--
作者：
Mukherjee, Abhijit;Fryar, Alan E.;Howell, Paul D.
第一次对区域尺度水文地层学和地下水流进行了有文件记录的解释，该解释涉及印度西孟加拉[Murshidabad、Nadia、北24 Parganas和南24 Parganas（包括加尔各答）]砷污染区面积约21，000 km（2）。水文地层模型表明，存在一个连续的，半封闭的砂含水层下面的厚粘土弱透水层。含水层向东和向南变厚。在南部，不连续的粘土层局部地将近地表含水层分成几个较深的、横向相连的承压含水层。根据观测到的地形、季节条件和推断的水文地层学，开发了8个22层的区域地下水流模型情景。该模型表明，在20世纪70年代开始广泛抽水之前，存在着季节性变化的区域性南北向水流。抽水严重地扭曲了水流模式，在宽的减压锥上产生了很高的垂直水力梯度。抽水还增加了总补给量（包括灌溉回流）、河流流入量和海水入侵量。因此，受砷污染的浅层地下水向下流动，由于机械混合和化学平衡的变化，似乎已导致以前安全的含水层受到污染。
The first documented interpretation of the regional-scale hydrostratigrahy and groundwater flow is presented for a similar to 21,000-km(2) area of the arsenic-affected districts of West Bengal [Murshidabad, Nadia, North 24 Parganas and South 24 Parganas (including Calcutta)], India. A hydrostratigraphic model demonstrates the presence of a continuous, semi-confined sand aquifer underlain by a thick clay aquitard. The aquifer thickens toward the east and south. In the south, discontinuous clay layers locally divide the near-surface aquifer into several deeper, laterally connected, confined aquifers. Eight 22-layer model scenarios of regional groundwater flow were developed based on the observed topography, seasonal conditions, and inferred hydrostratigraphy. The models suggest the existence of seasonally variable, regional, north-south flow across the basin prior to the onset of extensive pumping in the 1970s. Pumping has severely distorted the flow pattern, inducing high vertical hydraulic gradients across wide cones of depression. Pumping has also increased total recharge (including irrigational return flow), inflow from rivers, and sea water intrusion. Consequently, downward flow of arsenic contaminated shallow groundwater appears to have resulted in contamination of previously safe aquifers by a combination of mechanical mixing and changes in chemical equilibrium.