GROUNDWATER ARSENIC CONTAMINATION AND LAND SUBSIDENCE IN HANOI CITY, VIETNAM

Groundwater Arsenic (As) contamination in three groundwater tables (Holocene (qh), Pleistocene (qp(2-3)), and Pleistocene (qp(1))) was examined by using 300, 423, and 204 samples in qh, qp(2-3), and qp(1), respectively, in Hanoi City in 2000-2003. Land subsidence was derived from JERS-1 images in 1995-1998, and Envisat-ASAR from Jan to April in 2004. Results show that Arsenic was lower in surface water and wastewater than groundwater. Also, Arsenic in groundwater was lower near surface (qh) than far from surface (qp(2-3) and qp(1)). Land subsidence was significant in downtown areas where large and medium groundwater supply stations are located. Spatial correlation between Arsenic in qh, qp(2-3), and qp(1) and land subsidence indicates more subsidence was observed in regions with higher Arsenic contamination. Such findings support the hypothesis that increasing groundwater abstraction results in enhancing oxygenation to boost redox reaction to release Arsenic from ore into groundwater.