SEDIMENT COLOUR BASED TUBEWELL INSTALLATION PROCESS IN BIHAR, INDIA

Bihar along with many other states in India is facing a widespread occurrence of geogenic arsenic in groundwater. Due to the occurrences of high concentrations of arsenic (As) and iron (Fe) in the alluvial shallow aquifers safe sources of drinking water are becoming scarce. This situation is leading to serious health threats for the millions of people of Bihar. A sediment colour concept based study is being considered in Bangladesh for providing safe water. Based on this concept the study aimed to investigate the sediment color of soil in Bihar at various depths and safe sources of drinking water without higher concentrations of As and Fe. It was found from the local masons that deeper tubewells are being preferred at present in Bihar than the earlier days due to lesser concentrations of As and Fe at deeper depths. After thorough discussions and information by the local drillers, 10 shallow and deep aquifers were selected to test water samples. Initially, the water samples were tested using field test kit for four parameters: As, Fe, Fluoride, and Manganese (Mn). Later, all the water samples were retested using atomic absorption spectroscopy (AAS) technique in the lab and was found consistent with the field kit results. The black color sediments are not used for drinking water and usually had higher As and Fe concentrations. According to the test results, the range of As concentration was found from less than 1 µL^-1 to a maximum of 300 µL^-1. However, in the deeper tubewells (>230 feet depth) Mn was present while the concentration of As, Fe, and Fluoride was found within the WHO permissible limit of 10 µL^-1_. While drilling tubewells, local masons identified five different types of sediment colours: black; white; off-white (buff); brown; and red. Now a days, brown, off-white or red sediment layers are targeted to install tubewells instead of using white and off-white sediments, which was the case in the past. In order to test the applicability of the sediment colour concept in Bihar, three tubewell (2 shallow tubewells and 1 deep tubewell) installation process by local masons was observed and sediments from different depths (40 feet; 80 feet; 110-120 feet; 140 feet; 150 feet; 200 feet; 230 feet and 250 feet) were collected for comparison with that of the Bangladesh sediment colours. Based on the perception of the local drillers from both Bangladesh and Bihar it can be concluded that sediment colour concept can also be applied in Bihar to target safe water depth despite having differences in terms of soil characteristics.