60-24 Arsenic at the Fringe: Well Lifespan and Water Quality in Dhaka’s Expanding Cone of Depression

Session: 2YC and 4YCU Geoscience Student Research Poster Showcase

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Abstract:

Despite 25 years of study and interventions, groundwater arsenic contamination remains a serious public health issue in Bangladesh. In this study we analyze exposure patterns over time in a densely populated peri-urban area 25 km east of Dhaka which has been intensively studied by Columbia University’s Arsenic Superfund Project (SRP) since 2000. Numerous studies have documented the expansion of Dhaka's cone of depression from deep (>150 m) municipal pumping, which now extends more than 30 km eastward and profoundly influences groundwater flow. Our study examines whether this drawdown cone is impacting well construction and arsenic exposure in the Araihazar sub-district. Using data collected by the SRP (2000, 2012) and from the Bangladesh Arsenic Mitigation Water Supply Project (BAMWSP) (2022), we analyzed well age and arsenic concentrations across seven west-east longitudinal sections. Wells were grouped by depth: 10–50 meters (above the clay layer, higher in arsenic but relatively geochemically stable) and 51–90 meters (below the clay, lower arsenic but susceptible to depressurization). The hypothesis was that sections nearer Dhaka (1–3) would contain shallower, younger wells with increasing arsenic concentrations from 2000 to 2012 due to intensified pumping. In the 51–90 m interval, median well age in 2012 was lowest in Section 1 (3 years) and highest in Section 3 (5 years), supporting the idea that newer wells are replacing older ones where drawdown is most intense. Shallow wells in Sections 1 and 5 had the highest arsenic concentrations in both 2000 and 2012, with median values exceeding 100 µg/L. Deeper wells remained below 50 µg/L except for a few outliers. Section 5 showed high shallow arsenic and older wells, indicating localized geochemical influence. In eastern Araihazar, the exhaustive 2012 survey revealed much higher arsenic concentrations at 51–90 m compared to 2000, which had limited sampling there. The 2022 BAMWSP dataset was reviewed but could not be confidently aligned with earlier years because well locations did not correspond to known villages. These results suggest that depressurization near Dhaka may be shortening well lifespans and indirectly increasing arsenic risk in new, shallow wells. Meanwhile, deeper aquifers remain safer but are seeing increased use in the suburban fringe.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-11202

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