Origin of Groundwater Arsenic in a Rural Pleistocene Aquifer in Bangladesh Depressurized by Distal Municipal Pumping
Origin of Groundwater Arsenic in a Rural Pleistocene Aquifer in Bangladesh Depressurized by Distal Municipal Pumping
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DOI：
10.1029/2020wr027178
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发表时间：
2020-07-01
影响因子：
5.4
通讯作者：
van Geen, A.
中科院分区：
文献类型：
--
作者：
Mozumder, M. R. H.;Michael, H. A.;van Geen, A.
在整个南亚，数百万村民通过改用低砷威尔斯井来减少对高砷地下水的暴露。同位素示踪剂和流动模拟在这项研究中使用的更新世（>10 kyr）年龄在孟加拉国的半承压含水层的地下水流系统，一般是低的，但已被扰动的大规模抽水约25公里的距离为达卡的市政供水。在3 km（2）的研究区域内，10- 15 m厚的粘土弱透水层覆盖了大部分中间含水层（深度>40- 90 m），其中一些被较年轻的河道砂沉积物中断，表明河流冲刷。粘土覆盖区以下的中间含水层中的水头比粘土层以上的高As浅层含水层中的水头低1-2 m。相比之下，在缺少粘土层的浅层和中层含水层中观察到类似的水头。水头分布表明，通过弱透水层中的中断和从桑迪地区到含水层承压部分的横向平流，存在向下流动的模式。解释的流动系统与（3）H-He-3年龄，稳定同位素数据和地下水流动模型一致。侧流可以解释一个关联的升高的作为与高甲烷浓度的灰色砂层下面的某些粘土覆盖的部分更新世含水层。从粘土层本身的溶解有机碳的流入，导致最初的橙子砂减少也可能有助于上升的As。
Across South Asia, millions of villagers have reduced their exposure to high-arsenic (As) groundwater by switching to low-As wells. Isotopic tracers and flow modeling are used in this study to understand the groundwater flow system of a semi-confined aquifer of Pleistocene (>10 kyr) age in Bangladesh that is generally low in As but has been perturbed by massive pumping at a distance of about 25 km for the municipal water supply of Dhaka. A 10- to 15-m-thick clay aquitard caps much of the intermediate aquifer (>40- to 90-m depth) in the 3-km(2)study area, with some interruptions by younger channel sand deposits indicative of river scouring. Hydraulic heads in the intermediate aquifer below the clay-capped areas are 1-2 m lower than in the high-As shallow aquifer above the clay layer. In contrast, similar heads in the shallow and intermediate aquifer are observed where the clay layer is missing. The head distribution suggests a pattern of downward flow through interruptions in the aquitard and lateral advection from the sandy areas to the confined portion of the aquifer. The interpreted flow system is consistent with(3)H-He-3 ages, stable isotope data, and groundwater flow modeling. Lateral flow could explain an association of elevated As with high methane concentrations within layers of gray sand below certain clay-capped portions of the Pleistocene aquifer. An influx of dissolved organic carbon from the clay layer itself leading to a reduction of initially orange sands has also likely contributed to the rise of As.