Arsenic mitigation: water quality of dug wells and tubewells

Arsenic concentration in very shallow and deep aquifers is comparatively lower than shallow aquifers in arsenic contaminated areas. As a result, dug wells and deep tubewells have emerged as two major water supply options for populations exposed to high levels of arsenic through drinking contaminated shallow tubewell water in Bangladesh and West Bengal (India). The concentrations of other impurities of health concern also vary with depth and other characteristics of the aquifer. Hence, shifting from one source to another may be the cause of exposure to health risk of a different nature. This paper presents an assessment of water quality of dug wells (DW) and deep tubewells (DTW) as compared to shallow tubewells (STW) for water supply. The results show that a shift from STW to DW reduces median arsenic ingestion from 151 μg/L (Mean 172μg/L) to 0.74 μg/L(mean 7.92μg/L), while DTW further reduces median arsenic ingestion to 0.41μg/L (mean 1.05μg/L). On the other hand, microbial contamination indicated by median value of Thermotolerant Coliform (TTC) count was found to be 48 cfu/100ml for DW water as compared to 0 cfu/100ml for both STW and DTW waters.