(predominantly of Pleistocene age) are not as thick as those in the other districts, and form mainly one aquifer 10– 25 min depth. The other districts have sediment layers from both the Pleistocene and Holocene ages, with the latter being partly derived from postglacial marine transgressions (Trafford et al., 1996). Of the 2–3 present aquifers, the first (10–30 m) and the second (30–70 m) are exploited for drinking water. Due to frequent riverbed migrations, theaquifers are not fully separated and are in some locations connected through sand lenses. Even without the pumping of groundwater, recharge in the upper two (Quaternary) aquifers can partly originate from Red River bank filtration. However, Hanoi's high demand of water is causing a significant drawdown of the groundwater table.This is particularly severe in districts Band Dwhere cones of depression reach 30 m deep. Under these conditions, bank filtrates from the Red River must be of major importance and strongly influence the groundwater recharge in the Hanoi area. More detailed information can be found in Berg et al. (2001) and references therein
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