Groundwater arsenic and safe water supply in Bangladesh

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1).It is considered that arsenic may be mainly released into groundwater from As-rich Fe oxyhydroxide in the ground under the condition of reduction in Samta village from the following new finding.(1)Arsenic was highly included at peat bed in upper muddy layer.(2)The distribution of upper muddy layer was in accordance with that of arsenic contamination of groundwater.(3)Arsenic concentration was higher at the zone where the trivalent arsenic was detected more compared with the pentavalent arsenic, low arsenic concentration in the pentavalent srsenic zone.(4)It was characteristic that HCO_3 and Fe^<2+> contents of groundwater were high and their distribution was in accordance with that of arsenic contamination.(5)The high arsenic-contaminated zone of groundwater agrees well with the drifting zone of groundwater where the aquifer is more in the state of reduction in the zone.2).Arsenic free water has been successfully obtained from Pond Sand Filter(PSF) as follows.(1)The major cause of arsenic contamination of ponds was considered as inflow of surface drainage from arsenic-contaminated shallow tube wells and co-precipitation of arsenic with sediment grains in suspension in the pond water.(2)It was observed that gravel filter tank, an altemative pre-treatment system, for sand filter tank, had the ability to decrease the turbidity and the number of bacteria of raw water efficiently.(3)The PSF installed in Samta is working very well. PSF No.2, constructed February 2000 in a adjacent village, is now supplying good treated water, too.3).Further research(1)Numerical analyses for the advection and diffusion of arsenic in the groundwater.(2)Application of PSF to removal of arsenic from tube well water.