Indus alluvial system, Pakistan

The Indus alluvial plain of Punjab and Sindh provinces in Pakistan is of Quaternary age and is similar to the Ganges alluvial system of India and Bangladesh. The sediments of the plain have their provenance in the western Himalayas and are brought down by the River Indus and its tributaries. The alluvial deposits are widespread and thick (Smedley, 2005) and mostly form unconfined aquifers. However, in contrast to the Bengal basin, the aquifers are relatively oxic (Mahmood et al., 1998 Tasneem, 1999). The area also differs in having a more arid climate and greater proportion of Pleistocene deposits with greater apparent connectivity between the river systems and the aquifers (Smedley, 2005). 

Results from Sindh province, down the Indus valley (to the south) from Punjab, indicate additional arsenic hotspots in groundwater (Appendix D). In 2001, the provincial Public Health Engineering Department found arsenic contamination in five of nine surveyed districts with 16 % of samples exceeding 50 pgL-1 (Haque, 2005). In follow-up sampling conducted between 2002 and 2004, almost 15000 (22%) of field tests yielded arsenic concentrations of 10pgL-1 and 4317 (6%) were 50pgL-1 (Haque, 2005). The worst-affected district was Dadu with 29% of samples 10 pgL-1 and 10% 50pg L-1 (Haque, 2005). 

Because of the generally oxic conditions in the Indus alluvial aquifers, the mechanisms of arsenic mobilization may differ from those observed in the Ganges basin. Elevated arsenic concentrations in the shallow Quaternary aquifers of the urban Thai Doab area (Muzaffargarh district, Punjab) are thought 

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