Bangladesh: DPHE/BGS National Hydrochemical Survey

The aims of the survey were to:

make maps showing the regional distribution of arsenic and other elements in Bangladesh groundwaters
provide estimates of the percentage of wells exceeding various limits for arsenic and other elements

The survey was carried out in two phases: the first phase (1998) covered what were then believed to be the worst-affected southern and eastern districts of Bangladesh, while the second phase (1999) completed the remainder of Bangladesh apart from the three districts of the Chittagong Hill Tracts.

Most of the samples were analysed for arsenic by hydride generation-atomic fluorescence spectrometry (HG-AFS) in the UK but some of the early samples collected in the Phase I survey were analysed by hydride generation-ICP-AES. Additional elements in the survey samples were measured by ICP-AES and in a few cases by ICP-MS. All analyses were carried out in the BGS laboratories.

Point-source and smoothed maps

The data are presented here as point-source maps, a threshold map, and in a few cases as smoothed maps. The point-source data used to prepare these maps are also available for downloading.

Where appropriate, the class intervals have been chosen to be at the rounded quartiles, i.e. approximately the same number of samples in each of the four classes. The percentage of all samples in each class is often shown by a small histogram inset. The size of the bars going from left to right corresponds with the percentage of values in the lowest class interval, the next lowest class interval, and so on. In the case of the maps with '(health)' in their title, the chosen class limits include recognised health limits. Health thresholds refer to WHO guideline values at the time of mapping (2001).

The smoothed maps were derived by disjunctive kriging and are based on a 5 km grid. In the arsenic threshold maps, tubewells with less than or equal to the indicated arsenic concentration are displayed in blue, those with a greater concentration are displayed in red.

The maps are in Adobe Acrobat PDF format, each file is less than 500 KB unless marked otherwise.