1 Geological and hydrogeological controls of arsenic in groundwater and other aquatic systems

A total of 6 nests of 37 monitoring wells (5-91 m) (Table 1) were installed in 25 km2 of study area to capture the wide spectrum of arsenic distribution.

At all sites except site B, shallow Holocene aquifer composed mostly of gray sand, are separated from the deep Pleistocene aquifer composed of orange/light brown sand aquifer by at least one fine sediment layer of clay or silty clay. The thickness of each section varies considerably from site to site (Dhar et al., 2008).