| Autor: |
Mozumder, M. R. H., Michael, H. A., Mihajlov, I., Khan, M. R., Knappett, P. S. K., Bostick, B. C., Mailloux, B. J., Ahmed, K. M., Choudhury, I., Koffman, T., Ellis, T., Whaley‐Martin, K., San Pedro, R., Slater, G., Stute, M., Schlosser, P., Geen, A. |
| Předmět: |
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| Zdroj: |
Water Resources Research; Jul2020, Vol. 56 Issue 7, p1-26, 26p |
| Abstrakt: |
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 acquitard caps much of the intermediate aquifer (>40‐ to 90‐m depth) in the 3‐km2 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 acquitard and lateral advection from the sandy areas to the confined portion of the aquifer. The interpreted flow system is consistent with 3H‐3He 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. Key Points: A clay‐capped Pleistocene aquifer under the influence of municipal pumping is contaminated with arsenic (As)After pumping started, breaks in the clay aquitard became conduits for accelerated transport of tritium, As, and carbon from the shallow aquiferPumping induced transport of reactive carbon or arsenic emanating from the clay aquitard itself could lead to local release of As [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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